WO2012055473A1 - Liquid-crystal medium and process for preparing a liquid-crystal device - Google Patents

Abstract

The present invention relates to a liquid-crystal (LC) medium comprising a photosensitive compound and a compound having an alkenyl group, to a process of preparing an LC display of the PS (polymer stabilised) or PSA (polymer sustained alignment) type, and to PS or PSA type LC displays obtained by such a process and containing such an LC medium.

Description

Liquid-crystal medium and process for preparing a liquid-crystal device

The present invention relates to a liquid-crystal (LC) medium comprising a photosensitive compound and a compound having an alkenyl group, to a process of preparing an LC display of the PS (polymer stabilised) or PSA (polymer sustained alignment) type, and to PS or PSA type LC displays obtained by such a process and containing such an LC medium. Background of the Invention

The LC displays used at present are mostly those of the TN (twisted nematic) type. However, these have the disadvantage of a strong viewing- angle dependence of the contrast.

In addition, so-called VA (vertical alignment) displays are known which have a broader viewing angle. The LC cell of a VA display contains a layer of an LC medium between two transparent electrodes, where the LC medium usually has a negative value of the dielectric anisotropy. In the switched-off state, the molecules of the LC layer are aligned perpendicular to the electrode surfaces (homeotropically) or have a tilted homeotropic alignment. On application of an electrical voltage to the electrodes, a realignment of the LC molecules parallel to the electrode surfaces takes place. Furthermore, OCB (optically compensated bend) displays are known which are based on a birefringence effect and have an LC layer with a so- called "bend" alignment and usually positive dielectric anisotropy. On application of an electrical voltage, a realignment of the LC molecules perpendicular to the electrode surfaces takes place. In addition, OCB displays normally contain one or more birefringent optical retardation films in order to prevent undesired transparency to light of the bend cell in the dark state. OCB displays have a broader viewing angle and shorter response times compared with TN displays. Also known are IPS (in-plane switching) displays, which contain an LC layer between two substrates, but wherein the two electrodes are located only on one of the substrates, usually with comb-shaped, interdigital structures. When applying a voltage to the electrodes, an electric field which has a significant component parallel to the LC layer is thereby generated. This causes realignment of the LC molecules in the layer plane.

Furthermore, so-called FFS (fringe field switching) displays have been proposed (see, inter alia, S.H. Jung et al., Jpn. J. Appl. Phys., Volume 43, No. 3, 2004, 1028), which likewise contain two electrodes on the same substrate, but, in contrast to IPS displays, only one of these is in the form of a structured (comb-shaped) electrode, and the other electrode is unstructured. A strong, so-called "fringe field" is thereby generated, i.e. a strong electric field close to the edge of the electrodes, and, throughout the cell, an electric field which has both a strong vertical component and a strong horizontal component. Both IPS displays and also FFS displays have a low viewing-angle dependence of the contrast.

In VA displays of the more recent type, uniform alignment of the LC molecules is restricted to a plurality of relatively small domains within the LC cell. Disclinations can exist between these domains, also known as tilt domains. VA displays having tilt domains have, compared with conventional VA displays, a greater viewing-angle independence of the contrast and the grey shades. In addition, displays of this type are simpler to produce since additional treatment of the electrode surface for uniform align- ment of the molecules in the switched-on state, such as, for example, by rubbing, is no longer necessary. Instead, the preferential direction of the tilt or pretilt angle is controlled by a special design of the electrodes.

In so-called MVA (multidomain vertical alignment) displays, this is usually achieved by the electrodes having protrusions which cause a local pretilt. As a consequence, the LC molecules are aligned parallel to the electrode surfaces in different directions in different, defined regions of the cell on application of a voltage. "Controlled" switching is thereby achieved, and the formation of interfering disclination lines is prevented. Although this arrangement improves the viewing angle of the display, it results, however, in a reduction in its transparency to light. A further development of MVA uses protrusions on only one electrode side, while the opposite electrode has slits, which improves the

transparency to light. The slitted electrodes generate an inhomogeneous electric field in the LC cell on application of a voltage, meaning that controlled switching is still achieved. For further improvement of the transparency to light, the separations between the slits and protrusions can be increased, but this in turn results in a lengthening of the response times. In the so-called PVA (patterned VA), protrusions are rendered completely superfluous in that both electrodes are structured by means of slits on the opposite sides, which results in increased contrast and improved transparency to light, but is technologically difficult and makes the display more sensitive to mechanical influences (tapping, etc.). For many applications, such as, for example, monitors and especially TV screens, however, a shortening of the response times and an improvement in the contrast and luminance (transmission) of the display are desired.

A further development are the so-called PS (polymer sustained) or PSA (polymer sustained alignment) displays, also known as "polymer stabilised" displays. In these, a small amount (for example 0.3% by weight, typically < 1% by weight) of a polymerisable compound is added to the LC medium and, after introduction into the LC cell, is polymerised or crosslinked in situ, usually by UV photopolymerisation, optionally with an electrical voltage applied between the electrodes. The addition of polymerisable mesogenic or liquid-crystalline compounds, also known as "reactive mesogens" (RMs), to the LC mixture has proven particularly suitable. In the meantime, the PS or PSA principle is being used in diverse classical LC displays. Thus, for example, PSA-VA, PSA-OCB, PS-IPS and PSTN displays are known. In PSA-VA and PSA-OCB displays polymerisation is usually carried out while a voltage is applied to the electrodes, whereas in PSA-IPS displays polymerisation it is carried out with or without, preferably without application of a voltage. As can be demonstrated in test cells, the PSA method results in a pretilt in the cell. In the case of PSA- OCB displays, it is therefore possible for the bend structure to be stabilised so that an offset voltage is unnecessary or can be reduced. In the case of PSA-VA displays, this pretilt has a positive effect on response times. For PSA-VA displays, a standard MVA or PVA pixel and electrode layout can be used. In addition, however, it is possible, for example, to manage with only one structured electrode side and no protrusions, which significantly simplifies production and at the same time results in very good contrast at the same time as very good transparency to light. Furthermore, the so-called posi-VA displays ("positive VA") have proven to be a particularly suitable mode. Like in classical VA displays, the initial orientation of the LC molecules in posi-VA displays is homeotropic, i.e. substantially perpendicular to the substrates, in the initial state when no voltage is applied. However, in contrast to classical VA displays, in posi- VA displays LC media with positive dielectric anisotropy are used. Like in the usually used IPS displays, the two electrodes in posi-VA displays are arranged on only one of the two substrates, and preferably exhibit intermeshed and comb-shaped (interdigital) structures. By application of a voltage to the interdigital electrodes, which create an electrical field that is substantially parallel to the layer of the LC medium, the LC molecules are transferred into an orientation that is substantially parallel to the

substrates. In posi-VA displays, too, it a polymer stabilisation (PSA) has proven to be advantageous, i.e. the addition of RMs to the LC medium, which are polymerised in the cell, whereby a significant reduction of the switching times could be realised.

PSA-VA displays are described, for example, in JP 10-036847 A,

EP 1 170 626 A2, US 6,861 ,107, US 7,169,449, US 2004/0191428 A1 , US 2006/0066793 A1 and US 2006/0103804 A1. PSA-OCB displays are described, for example, in T.-J- Chen et al., Jpn. J. Appl. Phys. 45, 2006, 2702-2704 and S. H. Kim, L.-C- Chien, Jpn. J. Appl. Phys. 43, 2004, 7643-7647. PSA-IPS displays are described, for example, in

US 6,177,972 and Appl. Phys. Lett. 1999, 75(21), 3264. PSA-TN displays are described, for example, in Optics Express 2004, 12(7), 1221. PSA displays, like the conventional displays described above, can be operated either as active matrix or passive matrix displays. In active matrix type displays the individual pixels are usually addressed by integrated, non-linear active elements like for example thin film transistors (TFT), in passive matrix type displays by multiplexing, with both methods being well-known from prior art.

In particular for monitor and especially TV applications, optimisation of the response times, but also of the contrast and luminance (i.e. also transmission) of the LC display, is still demanded. The PSA process still appears to provide crucial advantages here. In particular in the case of PSA-VA, a shortening of the response times, which correlate with a measurable pretilt in test cells, can be achieved without a significant adverse effects on other parameters.

In the prior art, use is made, for example, of polymerisable compounds of the following formula:

in which P denotes a polymerisable group, usually an acrylate or methacryl- ate group, as described, for example, in US 7,169,449.

However, it has been found that the LC mixtures and RMs known from the prior art still have some disadvantages on use in PSA displays. Thus, not every desired soluble RM is also suitable for PSA displays, and it is often difficult to find more suitable selection criteria than the direct PSA

experiment with pretilt measurements. The choice becomes even smaller if polymerisation by means of UV light without the addition of photoinitiators is desired, which may be advantageous for certain applications.

In addition, the selected material system of LC mixture (also referred to as "LC host mixture") and polymerisable component should have the best possible electrical properties, in particular a high "voltage holding ratio" (HR or VHR). A high HR after irradiation with UV light is especially important for use in a PSA display, because UV irradiation is an indis- pensible part of the display manufacturing process, although it can also occur as "normal" stress in the finished display. However, the problem arises that not every combination of LC mixture and polymerisable component is suitable for use in PSA displays, since, for example, an inadequate tilt or no tilt at all is established or since, for example, the HR is inadequate for TFT display applications. In particular it is desired to have available novel and improved materials for PSA displays which enable the generation of a small pretilt. Especially desired are materials which will, during polymerisation, either generate a smaller pretilt after the same UV irradiation time as used for prior art materials, and/or generate the same pretilt as the prior art materials already after shorter exposure time. This allows to reduce the

manufacturing time (tact time) and the manufacturing costs for the display.

Another problem when manufacturing PSA displays ist the presence and removal of unreacted RMs after the polymerisation step used for tilt angle generation. Such unreacted RMs can negatively affect the display properties and performance, for example by uncontrolled polymerisation in the display during its operation.

Thus, PSA displays of prior art often show the undesired "image sticking" or "image burn" effect, wherein the image generated in the display by addressing selected pixels remains visible, even when the voltage for this pixel has been switched off, or when other pixels have been addressed.

Image sticking can occur for example when using LC host mixtures with a low HR, wherein the UV component of ambient light or emitted by the display backlight can induce undesired cleavage reactions in the LC molecules. This can lead to ionic impurities which are enriched at the electrodes or alignment layers, where they cause a reduction of the effective voltage applied to the display. This effect is also known for conventional displays not containing a polymeric component. ln PSA displays an additional image sticking effect can be observed which is caused by the presence of residual unpolymerised RMs. In such displays the UV component of ambient light or emitted by the backlight causes undesired spontaneous polymerisation of the unreacted RMs. In the addressed pixels this can change the tilt angle after several addressing cycles, thereby causing a change of the transmission, whereas in the unaddressed pixels the tilt angle and transmission remain unaffected.

It is therefore desirable that the polymerisation reaction when

manufacturing the PSA display is as complete as possible, and that the amount of residual unpolymerised RMs in the PSA display after its manufacture is as low as possible.

For these purposes RMs and LC host mixtures are desired which enable a complete and effective polymerisation reaction. In addition it is desired to achieve a controlled polymerisation of any residual amounts of unreacted RMs that are still present in the display. Also, RMs and LC host mixtures are desired that enable a faster and more effective polymerisation than the materials currently known.

Another problem is that LC media known in prior art for use in LC displays, including but not limited to those of the PSA type, do often exhibit high viscosities and, as a consequence, high switching times. In order to reduce the viscosity and switching time of the LC medium, it has been suggested in prior art to add LC compounds with an alkenyl group. However, it was observed that LC media containing alkenyl compounds often show a decrease of the reliability and stability, and a decrease of the VHR especially after exposure to UV radiation.

The VHR drop was observed in LC media with alkenyl-containing compounds even after UV exposure at higher wavelengths of 300nm or more. This is a considerable disadvantage when using LC media with alkenyl-containing compounds in PSA displays, because the photo- polymerisation of the RMs in the PSA display is usually carried out by exposure to UV radiation with a wavelength around 300nm, which will then cause a VHR drop in the LC medium.

The VHR drop in alkenyl-containing LC media at high UV wavelengths cannot simply be explained by a higher UV absorption of the alkenyl groups compared to e.g. alkyl groups, because the alkenyl groups do not show significant UV absorption at wavelengths around 300nm, which are normally used for photopolymerisation of the RMs. Instead, the alkenyl groups contained in conventional LC compounds do usually show signifcant UV absorption only at very short wavelengths below 200nm. This is, however, far below the wavelength of UV lamps that are commonly used for photopolymerisation in a standard PSA display production process. It is therefore desirable to have improved materials and material combinations, especially RMs and LC host mixtures, for use in PS or PSA displays, which are suitable to solve the above-mentioned problems. It is also desirable to have an improved process for manufacturing PSA displays, which does not show the drawbacks of the processes known from prior art.

It was an aim of the present invention to provide novel PSA displays and novel materials for use in PSA displays, in particular LC host mixtures and RMs, and novel processes for the manufacture of PSA displays, which are suitable for solving the above-mentioned problems, do not have the disadvantages described above, or only do so to a smaller extent, and provide one or more of the improvements and advantages discussed above and below. In particular, the improved LC media for use in PSA displays should have a high specific resistance, a large working-temperature range, short response times even at low temperatures, and a low threshold voltage, which enable a large number of grey shades, high contrast and a wide viewing angle, and have high values for the HR after UV exposure. In PSA displays for mobile applications, the LC media should show low threshold voltage and high birefringence. Also, the LC media should have high reliability and do not cause unwanted image sticking. They should enable the fast generation of a hight pretilt and allow quick and complete polymerisation of the RMs, with low amounts, or preferably no amounts at all, of unpolymerised RM remaining in the LC medium. The improved processes for manufacturing PSA displays should enable to avoid the above-mentioned negative effects of the alignment layer material on the LC medium, should also enable fast and complete polymerisation of the RMs contained in the LC medium by photopolymerisation inside the display cell, and should also avoid a decrease of the reliability, stability and VHR of the LC medium in the display.

Surprisingly, it has now been found that these aims can be achieved by using LC media and processes according to the present invention as described hereinafter in PSA displays.

In particular, the inventors of the present invention have found that it is possible to provide a process for preparing a PSA display from a polymerisable LC medium containing LC compounds with an alkenyl group, which allows to avoid a decrease of the reliability and VHR of the LC medium during UV photopolymerisation of the polymerisable

component. This is achieved by carrying out the photopolymerisation of the polymerisable component using higher UV wavelengths, preferably in the range from 340 to 400nm. Surprisingly it was found that an LC medium for PSA use, which contains alkenyl compounds, does not show a significant decrease of the VHR after exposure to UV wavelengths at the upper end of the range from 300 to 400nm, e.g. from 360 to 400nm, whereas, after exposure to UV wavelengths at the lower end of the range from 300 to 400nm, e.g. from 300 to 340nm, the LC medium shows a significant decrease of the VHR. As mentioned above, this effect cannot be explained merely by a possible higher UV absorption between 300 and 340nm than between 360 and 400nm, because the alkenyl groups show significant UV absorption only at much lower wavelengths (below 200nm). Without wishing to be bound to a specific theory, it is believed that a possible explanation could be that the alignment layers used in

conventional PSA displays could negatively affect the reliability and VHR of an LC medium that contains compounds with alkenyl groups. PSA displays do usually contain alignment layers provided on the surfaces of the electrodes contacting the LC layer, in order to create the initial vertical alignment of the LC molecules. The alignment layers usually consist of polyimide which is prepared from commercially available precursor materials that are coated on the electrodes and e.g. thermally cured.

However, the commonly used polyimide materials often show significant absorption of UV light in the range from 300 to 340nm. Therefore, during photopolymerisation of the RMs in the LC medium when manufacturing the PSA display, the polyimide can absorb UV light that generates undesired radicals, which can interact especially with the alkenyl compounds in the LC medium and cause decomposition reactions that lead to a decrease of the reliability and VHR.

The inventors have found that, by using UV radiation of higher

wavelengths for the polymerisation of the RMs during display

manufacture, especially UV radiation with wavelengths above 340nm, a decrease of the reliability and VHR of the LC medium can be suppressed or even completely avoided.

However, the RMs that have been suggested in prior art for use in PSA displays do often show maximum UV absorption at short wavelengths, for example around 300nm. Using such an RM in the process of the present invention, which employs higher UV wavelengths, would lead to slow and incomplete polymerisation and high amounts of residual unreacted RM. In the process of the present invention this drawback is overcome by using RMs which show sufficient absorption at the higher UV wavelengths applied in the photopolymerisation step, in particular in the range between 340nm and 400nm. The use of these RMs enables quick and complete photopolymerisation and reduces the amount of unreacted RMs. Also, since the UV lamps conventionally used for the photopolymerisation step in PSA display manufacture do usually not emit a single wavelength but a broader UV waveband, the inventors have found an effective way of selecting RMs that are suitable for the process of the present invention. This is achieved by selecting the RMs according to their total absorption over a broader UV waveband. Accordingly, for the purposes of this invention the UV absorption of a given RM is defined by its integral of the molar extinction coefficient over a desired wavelength range. Thus, by using higher UV wavelengths for photopolymerisation of the

RMs, and by using RMs which show significant total UV absorption above 340nm, it is possible to avoid a decrease of the reliability and VHR in the LC medium, and at the same time to enable fast and complete

polymerisation and the generation of a high pretilt in the LC medium. As a further consequence, this enables to use LC media containing LC compounds with alkenyl groups, thereby achieving faster switching times, while avoiding the disadvantages that have previously been observed when using alkenyl compounds in PSA displays. Summary of the Invention

The invention relates to a liquid crystal (LC) medium, characterized in that said LC medium comprises one or more mesogenic compounds or liquid crystal compounds that contain an alkenyl group, and in that said LC medium further comprises one or more photosensitive compounds which are polymerisable by photopolymerisation and which have an integral molar extinction coefficient E^_CM_OO≥ 1000 L nm cm^'1 mol^"1 in the wavelength range from 340nm to 400nm. The invention further relates to the use of an LC medium

as described above and below in LC displays, very preferably in PS (polymer sustained) or PSA (polymer sustained alignment) displays.

Especially preferred is an LC medium comprising

- a polymerisable component A), comprising one or more photosensitive compounds as described above and below, and - an LC component B), preferably having a nematic phase, comprising one or more mesogenic or LC compounds containing an alkenyl group.

The invention further relates to a method of preparing an LC medium as described above and below, by mixing one or more photosensitive compound with one or more mesogenic or LC compounds and optionally with one or more further liquid-crystalline compounds and/or additives.

The invention further relates to an LC display comprising an LC medium as described above and below, which is preferably a PS or PSA display.

Especially preferred PS and PSA displays are PSA-VA, PSA-OCB, PSA- IPS, PS-FFS, PSA-posi-VA or PSA-TN displays, very preferred PSA-VA and PSA-IPS displays.

The invention further relates to an LC medium, its use in PS and PSA displays, and to PS and PSA displays comprising it as described above and below, wherein the photosensitive compounds, or the polymerisable component, respectively, are polymerised.

The invention further relates to the use of an LC medium comprising a polymerisable component and an LC component as described above and below, for the generation of a pretilt angle in a layer of said LC medium when being provided in a display comprising two substrates and two electrodes, by in situ polymerisation of the polymerisable component while applying a voltage to the electrodes.

The invention further relates to a process of manufacturing a PS or PSA display as described above and below, comprising the steps of

a) providing an LC medium as described above and below between two substrates, wherein at least one substrate comprises one or two electrodes provided thereon, and

b) exposing the LC medium to UV radiation with a wavelength > 340nm, preferably > 340nm, wherein preferably a voltage is applied to the

electrodes at least part-time during said exposure to UV radiation in step b). The invention further relates to a PS or PSA display obtained by a process as described above and below.

Preferably the PS or PSA display comprises two substrates and two electrodes, wherein at least one substrate comprises one or two

electrodes provided thereon, and a layer of an LC medium comprising a polymerised component and an unpolymerised LC component provided between the two substrates,

wherein the unpolymerised LC component comprises one or more mesogenic or LC compounds that contain an alkenyl group, and

wherein the polymerised component is obtained by photopolymerisation of a polymerisable component in the LC medium between the substrates, and

wherein said polymerisable component comprises one or more

photosensitive compounds which are polymerisable by

photopolymerisation and which have an integral molar extinction coefficient E340-400≥ 1000 L nm cm^'1 mol^"1 in the wavelength range from 340nm to 400nm, and

wherein photopolymerisation of said polymerisable component is carried out by exposing it to UV radiation with a wavelength > 340nm, preferably > 340nm,

preferably while applying a voltage to the electrodes at least part-time during said exposure to UV radiation.

The PS and PSA displays of the present invention preferably comprise two electrodes, preferably in form of transparent layers, which are applied onto one or both of the two substrates which form the display. In one preferred emdoiment only one electrode is provided on each of the two substrates, as for example in PSA-VA, PSA-OCB or PSA-TN displays. In another preferred embodiment two electrodes are provided on one of the two substrates and no electrode is provided on the other substrate, as for example in PSA-posi-VA, PSA-IPS or PSA-FFS displays. In the PS or PSA display of the present invention, preferably at least one substrate, very preferably both substrates, are transparent to visible light.

Definition of Terms

Unless stated otherwise, the term "PSA" is used above and below for both PS and PSA displays.

The terms"tilt" and "tilt angle" refer to a tilted or inclined orientation of the LC molecules in an LC mixture or LC medium relative to the surface of the cell walls in an LC display. The tilt angle herein means the average angle (<90°) between the molecular long axes of the LC molecules (LC director) and the surface of the plane parallel substrates forming the LC cell. A low value of the tilt angle (i.e. a large deviation from the 90° angle) herein corresponds to a large tilt. A suitable method for measuring the tilt angle is described in the example section. Unless stated otherwise, the tilt angle values as given above and below refer to this measurement method.

The term "photosensitive compound" means a compound that contains one or more functional groups that undergo a polymerisation reaction when exposed to photoradiation, for example UV radiation. Preferably the photosensitive compounds are selected from reactive mesogens which are photopolymerisable (i.e. polymerisable by photopolymerisation, i.e. by polymerisation caused by exposure to photoradiation).

The term "reactive mesogen" or "RM" denotes a compound containing a mesogenic group and one or more functional polymerisable groups.

The UV absorption of a photosensitive polymerisable compound as used in an LC medium or a process according to the present invention is defined by the integral of the molar absorption (extinction) coefficient of the compound within a given wavelength range (in L nm cm^'1 mol^" ).

Unless stated otherwise, this refers to the absorption spectrum of a solution of the compound in dichloromethane (DCM), which is measured using a UV/VIS/NIR-spectrometer Varian Cary 500 (from Varian Inc.). Generally, the molar extinction coefficient of a chemical compound, which is also known as "molar absorption coefficient" or "molar absorptivity", is known to the skilled person as an intrinsic compound property, and is a measure of the absorption of the compound at a given wavelength. It is defined by equation (1)

E

ε = [L cm^"1 mol^"1] or [m² mol]

c x d (1) wherein ε is the molar decadic extinction coefficient, E is the extinction (or absorption) at the given wavelength of the compound sample (as used in the measurement of the absorption spectrum), c is the concentration of the compound in the sample (which is usually a solution), and d is the distance the light travels through the sample, i.e. the path length of the light, which is given by the layer thickness of the sample.

The integral molar extinction coefficient Ε_λι_-λ2 as used in the present invention is given by equation (2)

as the integral of the molar extinction coefficient ε in the range from wavelength λ1 to wavelength λ2 (in L nm cm^"1 mol^"1).

For example, the integral molar extinction coefficient E₃₂o-4oo refers to the wavelength range from 320nm to 400nm, and the integral molar extinction coefficient E340-400 refers to the wavelength range from 340nm to 400nm.

An LC mixture or LC component B) as described above and below, which contains mesogenic or LC compounds with an alkenyl group and optionally further LC or mesogenic compounds, but does not contain the polymerisable or polymerised photosensitive compounds, is hereinafter also referred to as "(LC) host mixture or "(LC) low-molecular-weight component". The terms "low-molecular-weight" and "unpolymerisable" denote

compounds, usually monomeric, which do not contain any functional group which is suitable for polymerisation under the usual conditions known to the person skilled in the art, especially under the conditions applied during polymerisation of the polymerisable compounds and RMs as used in the LC media of the present invention.

The LC compounds containing an alkenyl group comprised in the LC media of the present invention do not photopolymerise, at least not to a significant extent, under the conditions used for the UV photopolymerisa- tion of the photosensitive compounds. "Significant extent" as used herein means that more than 5 mol% of the compounds will polymerise. The term "alkenyl group" means an optionally substituted hydrocarbyl group containing a C=C double bond. Preferably the term "alkenyl group" means a straight-chain, branched or cyclic alkyl group that is optionally substituted, preferably comprises at least 2 C atoms (in case of branched groups at least 3 C atoms, in case of cyclic groups at least 4 C atoms) and up to 30 C atoms, and comprises at least one CH=CH moiety, wherein one or more H atoms in the alkyl group and/or in the CH=CH moiety may also be replaced by F.

The terms "nematic component" and "nematic LC mixture" as used hereinafter mean an LC mixture which has a nematic LC phase, but may in addition have other LC phases (like e.g. a smectic phase), but very preferably means an an LC mixture that has only a nematic LC phase and no other LC phases. The term "mesogenic group" is known to the person skilled in the art and is described in the literature, and denotes a group which, due to the ani- sotropy of its attracting and repelling interactions, essentially contributes to causing a liquid-crystal (LC) phase in low-molecular-weight or polymeric substances. Compounds containing mesogenic groups ("mesogenic com- pounds") do not necessarily have to have an LC phase themselves. It is also possible for mesogenic compounds to exhibit LC phase behaviour only after mixing with other compounds and/or after polymerisation. 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 Appl. Chem. 73(5), 888 (2001) and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368.

The term "spacer group", also referred to as "Sp", is known to the person skilled in the art and is described in the literature, see, for example, Pure Appl. Chem. 73(5), 888 (2001) and C. Tschierske, G. Pelzl, S. Diele, Angew. Chem. 2004, 116, 6340-6368. Unless indicated otherwise, the terms "spacer group" or "spacer" above and below denotes a flexible group which connects the mesogenic group and the polymerisable group(s) to one another in a polymerisable mesogenic compound or RM. The term "conjugated" means a compound or moiety containing mainly C atoms with sp²-hybridisation (or optionally also sp-hybridisation), which may also be replaced by hetero atoms, or hetero atoms with lone pairs (of electrons). In the simplest case this is for example a compound with alternating C-C single and double (or triple) bonds, but does also include compounds with aromatic units like 1 ,4-phenylene, or compounds with lone paris like N, O or S.

"Containing mainly C atoms with sp²-hybridisation" means in this connection that a compound with naturally (spontaneously) occurring defects, which may lead to interruption of the conjugation, is still regarded as a conjugated compound, and that the compound or moiety may in addition also contain C atoms with sp³-hybridisation that do not interrupt the conjugation, e.g. in side chains or substitutents attached to the conjugated C atoms or hetero atoms.

Detailed Description of the Invention

The LC medium for use in the PSA displays according to the present invention contains one or more photosensitive compounds which are polymerisable by exposure to UV radiation. In addition, the LC medium contains an LC host mixture comprising one or more compounds selected from mesogenic or LC compounds, preferably selected from nematic or nematogenic compounds, wherein one or more of these compounds contain at least one alkenyl group that does not polymerise or otherwise react under the condition used for UV photopolymerisation of the

photosensitive compounds. The LC host mixture preferably consists only of low-molecular-weight (i.e. monomeric or unpolymerised) compounds, which are stable or unreactive to a polymerisation reaction under the conditions used for the UV photopolymerisation of the photosensitive compounds. In addition to the above-mentioned components, the LC medium may contain further additives like for example polymerisation initiators, inhibitors, surfactants, wetting agents, defoamers etc.

In the process of the present invention, the step of UV exposure as described above and below leads to photopolymerisation of the

photosensitive compounds. The LC compounds containing an alkenyl group preferably do not photopolymerise, at least not to a significant extent, under the conditions used for the UV photopolymerisation of the photosensitive compounds.

The combination of a process and an LC medium as described above and below enables the manufacture of PSA displays by using longer UV wavelengths, thereby reducing or even avoiding hazardous and damaging effects of short UV light components, and still achieves fast and complete polymerisation of the polymerisable component in the LC medium.

In particular, the process for the preparation of PSA displays and the LC media according to the present invention provide one or more of the following advantages:

- PSA displays can be manufactured by using longer UV wavelengths of

340nm or higher, preferably of 350nm or higher, very preferably of

360nm or higher, most preferably of 375nm or higher,

- better protection against negative influence of the UV irradiation used for photopolymerisation of the RMs is provided,

- the negative influence of alignment layer materials, like polyimide, on the reliability of the LC medium is reduced or even suppressed, - the overall UV stability of the LC medium and the LC display are improved,

- the VHR of the LC medium can be increased, so that it can even show a similar VHR level as an LC medium that does not contain a

compound with an alkenyl group,

- the use of LC media containing compounds with alkenyl groups is enabled, which allows faster switching times, while avoiding drawbacks like reduced VHR,

- the decrease of VHR and reliability during UV photopolymerisation can be reduced or even avoided,

- advantages like low viscosity and fast response time of the LC medium can be combined with the fast generation of a high pretilt and high VHR values,

- the polymerisation of the RMs can be carried out fast and effectively, and the extent of polymerisation of the RMs can be increased, thereby also reducing the amount of residual unpolymerised RMs in the display,

- the same small tilt angles as in displays using materials of prior art can be generated faster, and/or smaller tilt angles can be generated than in PSA displays using materials of prior art,

- the image sticking in the PSA display can be reduced.

In addition, the LC media and LC mixtures of the present invention have high specific resistance values and a good low temperature stability (LTS) against undesired spontaneous crystallization, and when used in PSA displays, exhibit adequate tilt angles, even without the use of a

photoinitiator.

The invention also relates to a process of manufacturing a PS or PSA display as described above and below, which comprises the steps of providing an LC medium, which comprises one or more photosensitive compounds and one or more mesogenic or LC compounds that contain an alkenyl group as described above and below, in a display or display cell comprising two substrates and two electrodes, wherein at least one substrate is transparent to light and at least one substrate has one or two electrodes provided thereon, and polymerising the photosensitive compounds by exposing them to UV radiation, preferably with a wavelength > 340nm, further preferably while applying a voltage to the electrodes.

The polymerisable compounds are polymerised or crosslinked (if a com- pound contains two or more polymerisable groups) by in-situ UV

photopolymerisation in the LC medium between the substrates of the LC cell. The polymerisation reaction is started by exposure of the

photosensitive compounds to UV radiation, preferably while a voltage is applied to the electrodes that are provided on the substrates.

In the polymerisation process of the present invention, the conditions are selected such that all photosensitive compounds present in the LC medium are polymerised as completely as possible. The wavelength of the UV radiation used for photopolymerisation can be controlled for example by using a conventional UV lamp together with one or more optical filters that do only transmit the desired wavelengths, for example conventional interference or absorption filters, which are known to the skilled person and are commercially available.

For example, it is possible to use a longpass (LP) optical filter, which attenuates (e.g. absorbs) shorter wavelengths and transmits (passes) longer wavelengths over the desired spectrum (e.g. including the UV, and optionally also the visible and infrared range). In contrast thereto, a shortpass (SP) filter attenuates (e.g. absorbs) longer wavelengths and transmits (passes) shorter wavelengths over the desired spectrum (e.g. including the UV and short UV range).

It is also possible to use a bandpass (BP) filter, which is e.g. a

combination of a LP and SP filter, and absorbs all wavelengths outside the desired wavelength band.

LP and SP filters (also known as edgepass or cut-off filters) can be characterized by their cut-off wavelength (also known as cut-on or center wavelength), which corresponds to the wavelength at 50% of their peak (i.e. maximum) transmission. For example, a 340nm LP filter has a cut-off wavelength of 340nm, below which it transmits < 50% of the maximum transmission.

Suitable LP, SP and BP filters for use in the process according to the present invention are known to the skilled person, like for example the optical filters from the Schott WG® or Schott GG® series, which are commercially available from Schott AG

For example, when photopolymerisation by irradiation with UV light of wavelengths from 300 to 400nm is desired, this can be achieved by using a UV lamp emitting in this range and and a BP filter being substantially transmissive for wavelengths between 300nm and 400nm. Alternatively it is possible to use a LP filter that transmits UV light above 300nm wavelength and also visible light, since the latter will usually not negatively affect the polymerisation reaction.

As mentioned above, the cut-off wavelength is the wavelength above which the LP filter (or below which an SP filter) transmits 50% or more of its maximum transmission. Therefore, if it is desired to completely exclude a certain part of wavelengths, the filter has to be chosen accordingly.

Preferably filters with a steep slope of the wavelength/transmission curve are used, so that the total transmission of light below the cut-off wavelength (in case of LP filters) or outside the desired waveband (in case of BP filters) is as small as possible.

This is illustrated by Figure 1, which shows the transmission spectra of several longpass filters of the Schott WG® or Schott GG® series, which are suitable for use in a process according to the present invention. The individual graphs show (a) a WG320 filter, (b) a WG335 filter, (c) a

WG345 filter, and (d) a GG375 filter (the numbers indicating the cut-off wavelength). Graph (e) shows a calculated combination of a WG335 and WG345 filter, having a cut-off wavelength of ca. 340nm. It can be seen that for example the 320nm LP filter has at least 50% transmission at wavelengths above 320nm, but no substantial transmission at wavelengths below 300nm. Likewise, the 340nm LP filter has no substantial transmission at wavelengths below 320nm, and the 375nm LP filter has no substantial transmission at wavelengths below 355 nm and even below 360nm. "No substantial transmission" as used herein means less than 5%, preferably less than 1% of the maximum

transmission within the transmitted spectrum.

Thus, for example irradiation with UV light having a wavelength λ > 320nm and excluding UV light having a wavelength < 320nm is preferably achieved by using a 340nm LP filter. Likewise, irradiation with UV light having a wavelength λ > 340nm and excluding UV light having a

wavelength < 340nm is preferably achieved by using a 360nm LP filter, and irradiation with UV light having a wavelength λ > 360nm and excluding UV light having a wavelength < 360nm is preferably achieved by using a 360nm or 375nm LP filter. Depending on the cut-off wavelength and the slope of the transmission curve of the filter, the skilled person can select further suitable filters for achieving the desired wavelengths.

In the process according to the present invention, the photosensitive polymerisable compounds are polymerised by exposure to UV radiation having a wavelength of 340nm or higher than 340nm, preferably 350nm or higher than 350nm, very preferably 360nm or higher than 360nm, most preferably 375nm or higher than 375nm. "Exposure to UV radiation having a wavelength of XXX nm or higher" as used herein means that the UV radiation spectrum, to which the

compounds are exposed, does not contain radiation of substantial intensity at a wavelength below XXX nm. "Substantial intensity" at a given wavelength as used herein means at least 5% of the maximum intensity observed within the entire radiation spectrum to which the compound is exposed.

Preferably the UV radiation used in the process according to the present invention does not contain radiation of substantial intensity at wavelengths < 340nm, preferably < 340nm. The photopolymerisation of the photosensitive compounds is carried out in-situ in the LC medium, which is confined between the two substrates of the display or display cell. The display further comprises two electrodes, wherein only one electrode is provided on each of the two substrates, or both electrodes are provided on only one of the substrates. Preferably a voltage is applied to the electrodes during UV exposure of the LC medium containing the photosensitive compound(s), to cause a reorientation of the LC molecules. The voltage can be applied during the entire UV exposure step, or for a given time period that may be shorter or longer than the time period of UV exposure.

As mentioned above, the UV absorption of a photosensitive compound at a given wavelength is usually defined by its molar extinction coefficient or molar absorptivity, which is an intrinsic material property and can be determined by measurement and calculation methods known to the skilled person and described in the "Definitions" section.

However, the UV lamps conventionally used for photopolymerisation of the polymerisable compounds in the PSA display manufacturing process, and also as preferably used in the process of the present invention, do not emit a single wavelength but a wavelength band. Also, different

photosensitive polymerisable compounds usually have a different shape of their absorption spectrum over a broad waveband. Therefore, for the purposes of the present invention the effective UV absorption of a photosensitive compound is defined by its integral of the extinction coefficient over a given UV wavelength range. This was found to be a better way for evaluating the total UV absorption of the

photosensitive compound when being photopolymerised in the PSA display manufacturing process, and thus a better way for selecting photosensitive compounds that are best suitable for this process.

Generally, if the integral molar extinction coefficient (from 340 to 400nm) of the compound is < 1000 L nm cm^"1 mol^"1, it was observed that the polymerisation is slow and incomplete, and the compound is not suitable for the PSA display process. If the integral molar extinction coefficient of the compound is in the range from 1000 to 10000 L nm cm^'1 mol^"1, it was observed that the speed and completeness of the polymerisation are already acceptable. If the integral molar extinction coefficient of the compound is > 10000 L nm cm^'1 mol^"1, it was observed that the speed and completeness of the polymerisation are especially good, and these compounds are especially preferred for use in an LC medium and a process according to the present invention.

Also, the photosensitive compounds are selected such that they are especially adopted to the longer wavelengths used for photopolymerisation in the process according to the present invention.

Preferably the photosensitive compounds used in the LC medium and the process according to the present invention have an integral molar extinction coefficient E340- ₀₀≥ 1000 L nm cm^"1 mol^"1 in the range from 340nm to 400nm, wherein E340-400 '^{s as} defined above. Very preferably the

photosensitive compounds have a value of E340-₄₀₀≥ 2000 L nm cm^"1 mol^"1, most preferably a value of E340-₄₀₀≥ 3000 L nm cm^'1 mol^"1.

In another preferred embodiment of the present invention, the

photosensitive compounds are selected such that they have an integral molar extinction coefficient E₃₂o oo^≥ 5000 L nm cm^"1 mol^"1 in the range from 320nm to 400nm, wherein E_{32C OO} is the as defined above. Very preferably the photosensitive compounds of this preferred embodiment have a value of E320-4₀₀≥ 10000 L nm cm^"1 mol^"1.

In another preferred embodiment of the present invention, the

photosensitive compounds are selected such that they have an integral molar extinction coefficient E₃₀o- oo≥ 20000 L nm cm^'1 mol^'1 in the range from 300nm to 400nm, wherein E300-₄₀₀ is the as defined above. Very preferably the photosensitive compounds of this preferred embodiment have a value of E₃₀o-4oo≥ 30000 L nm cm^'1 mol^"1.

In yet another preferred embodiment of the present invention, the photosensitive compounds are selected such that they have an E340-₄₀₀≥ 1000 L nm cm^"1 mol^"1, very preferably an E_{3 0-}4oo≥ 3000 L nm cm^"1 mol^"1, and at the same time have an E320- 00≥ 5000 L nm cm^"1 mol^"1, very preferably an E₃₂o-4oo≥ 10000 L nm cm^"1 mol^'1.

In yet another preferred embodiment of the present invention, the photosensitive compounds are selected such that they have an E₃4o-4oo≥ 1000 L nm cm^"1 mol^"1, very preferably an E34o- oo≥ 3000 L nm cm^'1 mol^"1, and at the same time have an E320-400≥ 5000 L nm cm^"1 mol^"1, very preferably an E₃₂o-4oo^≥ 10000 L nm cm^"1 mol^"1, and at the same time have an E₃oo-4oo^≥ 20000 L nm cm^"1 mol^"1, very preferably an E₃₀o- oo≥ 20000 L nm cm^"1 mol^"1.

In a preferred embodiment of the present invention, the photosensitive compounds are selected from compounds containing a conjugated moiety and one or more photopolymerisable functional groups, which are attached to the conjugated moiety either directly or via spacer groups.

In a very preferred embodiment, said conjugated moiety contains five or more than five, preferably more than six electron pairs that are

delocalized, preferably selected from of pi electron pairs (like for example in a C-C double or triple bond or a double or triple bond between a C atom and a hetero atom) and lone (electron) pairs in a heteratom (like for example N, P, O, S or Se). The conjugated moiety is preferably a ring system comprising one or more aromatic or partially unsaturated rings. If the conjugated system comprises two or more rings, these rings can be linked directly to each other via single or double bonds, or can be linked to each other via linear or branched conjugated groups, or can be fused with each other. Typical and preferred examples for this type of compounds are those of formula A, B, C, F and G, and those of formula D wherein W¹ and/or W² is CY=CY, like those of formula D2, D3, D5 and D7, as shown below.

In another very preferred embodiment, said conjugated moiety contains six or more than six, preferably six, electron pairs that are delocalized (as defined above), and wherein the conjugated moiety is a ring system comprising two or more rings, wherein each ring is linked to at least one adjacent ring via at least two ring atoms such that conjugation is maintained and such that the entire ring system has a planar structure. For example, two adjacent rings are linked to each other at a first position via a first carbon or hydrocarbon bridging group that is saturated or unsaturated, and at a second position via a single bond or via a second carbon or hydrocarbon bridging group that is saturated or unsaturated. As a result, free rotation of the rings around around the bond(s) connecting them to adjacent rings (like e.g. in case of biphenyl) is no longer possible, and the entire ring system has a planar structure. Suitable and preferred bridging groups are for example saturated alkylene or alkyleneoxy groups. Typical and preferred examples for this type of compounds are those of formula D, wherein preferably at least one of W and W² is different from CY=CY, and those of formula E, like those of formula D1 , D4, D6, E1 , E2 and E3, as shown below. Preferably the photosensitive compounds are selected from the group consisting of the following formulae:

wherein the individual radicals have the following meanings is a photopolymerisable group,

Sp is, on each occurrence identically or differently, a spacer group or a single bond, denote, independently of each other, Ρ-Sp-, H, F, CI, Br, I, - CN, -NO2, -NCO, -NCS, -OCN, -SCN, SF₅, straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH2 groups may be replaced by - C(R°)=C(R⁰⁰)-, -C≡C-, -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 H atoms may be replaced by F, CI or P-Sp-, or aryl or heteroaryl having 4 to 30 ring atoms which may also contain one or more fused rings and which is optionally substituted by one or more groups L, wherein in formula D, E, F, G and H at least one of R^a and R^b is P-Sp-, denote, independently of each other, H or straight-chain or branched alkyl having from 1 to 12 C atoms, denote, independently of each other, -CY2CY2-, -CY=CY-, - CY2-O-, -O-CY2-, -C(O)-O-, -O-C(O)-, -C(R^cR^d)-, -O-, -S-, - CO-, or -NR^C-, is -CY2CY2-, -CY2-O-, -O-CY2-, -C(O)-O-, -O-C(O)-, -C(R^cR^d)- , -O-, -S-, -CO-, or -NR^C-, is, on each occurrence identically or differently H or F, denote, independently of each other, H or straight-chain or branched alkyl having from 1 to 12 C atoms, denote, independently of each other, 1 ,4-phenylene, naphthalene-1 ,4-diyl or naphthalene-2,6-diyl wherein, 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 CH₂ 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, octahydro- 4,7-methanoindane-2,5-diyl, anthracene-2,7-diyl, fluorene- 2,7-diyl or phenanthrene-2,7-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L, is, on each occurrence identically or differently, P, P-Sp-, OH, CH₂OH, F, CI, Br, I, -CN, -NO₂, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R^x)₂₎ -C(=O)Y¹, -C(=O)R^x, -N(R^X)₂, optionally substituted silyl, optionally substituted aryl or heteroaryl having 4 to 30 ring atoms, straight-chain or branched alkyl or alkoxy having 1 to 25 C atoms, or straight-chain or branched alkenyl, alkinyl, alkylcarbonyl, alkoxycarbonyl,

alkylcarbonyloxy or alkoxycarbonyloxy having 2 to 25 C atoms, wherein in all of these groups, in addition, one or more H atoms may be replaced by F, CI or P-Sp-, is halogen, is P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH₂ groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, CI or P-Sp-, independently of each other -O-, -S-, -CO-, -CO-O-, -OCO-, - O-CO-O-, -OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF₂- -(CH₂)_n-, -CF₂CH₂-, -CH₂CF₂-, -(CF₂)_n-, - CH=CH-, -CF=CF-, -CH=CF-, -CF=CH-, -C≡C-, -CH=CH- COO-, -OCO-CH=CH-, -CH₂-CH₂-COO-, -OCO-CH₂-CH₂-, - C(R°R⁰⁰)-, -C(R^yR²)-, or a single bond, denote, independently of each other, H, F, CH₃ or CF₃, is 1 , 2, 3 or 4, are, independently of each other, 0, 1 , 2 or 3, is 0, 1 , 2, 3 or 4, is 0, 1 , 2 or 3, is 0, 1 or 2, is 0, 1 or 2.

The compounds of formula A-F are preferably selected from the group consisting of the following subformulae:

-32-

-35-

wherein P, Sp, L, R^a, R^b, R^c, R^d, A¹, A², Z¹, Z², p, q, r, s and t have the meanings given in formula A-G, R^e has one of the meanings of R^a as given in formula A that is different from P-Sp-, s+t > 1 , s+r > 1 , in formulae H3 and H4 at least one s is > 1 , r1 is 0, 1 or 2, r2 is 0, 1 or 2, with r1+r2 > 1 , and r3 is 1 or 2.

Further preferred are compounds of subformulae A1 to H4 above, wherein L denotes, F, CI, straight-chain or branched alkyl or alkoxy having 1 to 12 C atoms, or straight-chain or branched alkenyl, alkinyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 2 to 12 C atoms, wherein in all of these groups, in addition, one or more H atoms may be replaced by F or CI, very preferably F, CI, or alkyl, alkoxy or carbonyl with 1 to 4 C atoms that is optionally fluorinated.

Further preferred are compounds of formulae A1 , A3, B1 , B3, B5, B7, B9, C1 , C3, H1 and H3 wherein both groups Sp are a single bond.

Further preferred are compounds of formulae A1 , A3, B1 , B3, B5, B7, B9, C1 , C3, H1 and H3 wherein one of the two groups Sp is a single bond and the other of the two groups Sp is not a single bond.

Further preferred are compounds of formulae D1-D7, formulae E1-E3, formulae F1-F4 and formulae G1-G4 wherein R^a denotes P-Sp-.

Further preferred are compounds of formulae D1-D7, formulae E1-E3, formulae F1-F4 and formulae G1-G4 wherein R^a is different from P-Sp-.

Further preferred are compounds of formulae D1-D7 and formulae E1-E3 wherein p and q are 0. Further preferred are compounds of formulae D1- D7 and formulae E1-E3 wherein p and q are 1. Further preferred are compounds of formulae D1-D7 and formulae E1-E3 wherein one of p and q is 0 and the other is 1. Very preferred are compounds of formulae D1- D7 and formulae E1-E3 wherein p and/or q is 1 , and wherein A¹-Z¹ and Z²-A² denote 1 ,4-phenylene that is optionally substituted with one or more groups L as defined above. Further preferred photosensitive compounds of formulae A-G and their subformulae are selected from the following list of preferred embodiments, including any combination thereof:

the compounds contain two groups P-Sp, wherein of the two groups Sp one is a single bond and the other of the two groups Sp is not a single bond,

the compounds contain two groups P-Sp, wherein both groups Sp are a single bond,

the group R^a, R^b, R^c, R^d or R^e that is different from P-Sp- denotes an unpolymerisable group selected from straight-chain or branched alkyl having from 1 to 25 C atoms, in which one or more non-adjacent CH₂ groups may be replaced by -C(R°)=C(R⁰⁰)-, -C≡C-, -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 one or more H atoms may be replaced by F or CI,

the group R^a, R^b, R^c, R^d or R^e that is different from P-Sp- denotes alkyl or alkoxy having from 1 to 12 C atoms wherein one or more H atoms are optionally replaced by F,

P is acrylate, methacrylate or oxetane, preferably acrylate or methacrylate,

the groups Sp that are not a single bond denote -(CH₂)_p1-, -(CH₂)_pi- O-, -(CH₂)_Pi-O-CO-, -(CH₂)_pi-O-CO-O-, very preferably -(CH₂)_p1- or -

(CH₂)_pi-O-, wherein p1 is an integer from 1 to 12, preferably from 1 to 5, very preferably , 2 or 3,

A¹ and A² denote 1 ,4-phenylene that it optionally substituted by one or more groups L,

L does not denote or contain a group P-Sp-,

L is selected from F, CI, -CN, straight-chain or branched alkyl having from 1 to 25 C atoms, preferably from 1 to 12 C atoms, in which one or more non-adjacent CH₂ groups may be replaced by - C(R°)=C(R⁰⁰)-, -C≡C-, -N(R⁰)-, -O-, -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 one or more H atoms may be replaced by F or CI,

L denotes, F, CI, straight-chain or branched alkyl or alkoxy having 1 to 12 C atoms, or straight-chain or branched alkenyl, alkinyl, alkyl- carbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 2 to 12 C atoms, wherein in all of these groups, in addition, one or more H atoms may be replaced by F or CI,

Z¹ and Z² independently of each other, and on each occurrence identically or differently, are selected from -0-, -CO-0-, -OCO-, - OCH₂-, -CH₂O-, -CF₂O-, -OCF₂-, -CH₂CH₂-, -CH=CH-, -CF=CF-, - CH=CF-, -CF=CH-, -C≡C-, or a single bond,

Z¹ and Z² are a single bond,

p=0 and q=0,

p=1 and q=1 ,

p=0 and q=1 , or p=1 und q=0,

R^a-(A¹-Z¹)_p- and -(Z²-A²)_q-R^b are not halogen.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula A and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula B and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula C and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula D and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula E and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula F and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula G and its preferred subformulae.

Another preferred embodiment of the present invention relates to a process and an LC medium as described above and below, wherein the photosensitive compounds are selected from formula H and its preferred subformulae.

Above and below, "carbyl group" denotes a mono- or polyvalent organic group containing at least one carbon atom which either contains no further atoms (such as, for example, -C≡C-) or optionally contains one or more further atoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). "Hydrocarbyl group" denotes a carbyl group which additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge. "Halogen" denotes F, CI, Br or I.

A carbyl or hydrocarbyl group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. A carbyl or hydrocarbyl group having more than 3 C atoms can be straight- chain, branched and/or cyclic and may also contain spiro links or condensed rings.

Above and below, 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" in

accordance with the above definition containing one or more heteroatoms.

Preferred carbyl and hydrocarbyl groups are optionally substituted alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 25, particularly preferably 1 to 18 C atoms, optionally substituted aryl or aryloxy having 6 to 40, preferably 6 to 25 C atoms, or optionally substituted alkylaryl, arylalkyi, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 6 to 40, preferably 6 to 25 C atoms.

Further preferred carbyl and hydrocarbyl groups are C1-C40 alkyl, C2-C40 alkenyl, C2-C40 alkynyl, C3-C40 allyl, C4-C40 alkyldienyl, C4-C40 polyenyl, C&- C40 aryl, C6-C40 alkylaryl, C₆-C₄o arylalkyi, C₆-C₄o alkylaryloxy, C6-C40 aryl- alkyloxy, C2-C40 heteroaryl, C4-C40 cycloalkyl, C4-C40 cycloalkenyl, etc. Particular preference is given to C1-C22 alkyl, C2-C22 alkenyl, C2-C22 alkynyl, C3-C22 allyl, C4-C22 alkyldienyl, C₆-Ci2 aryl, C6-C20 arylalkyi and C2-C20 heteroaryl. Further preferred carbyl and hydrocarbyl groups are straight-chain, branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25 C atoms, which are unsubstituted or mono- or polysubstituted by F, CI, Br, I or CN and in which one or more non-adjacent CH₂ groups may each be replaced, independently of one another, by -C(R^X)=C(R^X)-, -C≡C-, -N(R^X)-, -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.

R^x preferably denotes H, halogen, 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 H atoms may be replaced by fluo- rine, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 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, cyclo- pentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoro- methyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluoro- hexyl, 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-heptyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, n-dodecyloxy, 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 have one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently linked (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 2 to 25 C atoms, which optionally contain fused rings and are optionally substitu- ted. 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,

[l

naphthyl, anthracene, binaphthyl, phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzo- pyrene, 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, ,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, iso- indole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphth- imidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxa- linimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxa- zole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quino- line, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenan- throline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazothiophene, or combinations of these groups. The heteroaryl groups 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 which contain 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, O, 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 poly- cyclic, i.e. contain a plurality of rings (such as, for example, decahydro- naphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 3 to 25 C 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, pyrrolidine, 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. The aryl, heteroaryl, carbyl and hydrocarbyl radicals optionally have one or more substituents, which are preferably selected from the group comprising silyl, sulfo, sulfonyl, formyl, amine, imine, nitrile, mercapto, nitro, halogen, Ci-12 alkyl, Ce-12 aryl, C_{1- 2} alkoxy, hydroxyl, or combinations of these groups.

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, also referred to as "L" below, are, for example, F, CI, Br, I, OH, -CN, -NO₂, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R^x)₂,

-C(=O)Y¹, -C(=O)R^x, -C(=O)OR^x, -N(R^X)₂, in which R^x has the above- mentioned meaning, and Y¹ denotes halogen, optionally substituted silyl, optionally substituted aryl or heteroaryl having 4 to 40, preferably 4 to 20 ring atoms, and straight-chain or branched alkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which one or more H atoms may optionally be replaced by F or CI.

"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, in which R° has the above-mentioned meaning.

Particularly preferred substituents L are, for example, F, CI, CN, NO₂, CH₃, C₂H₅, OCH₃, OC₂H5, COCH3, COC₂H5, COOCH₃, COOC₂H₅, CF₃, OCF₃, OCHF₂₎ OC₂F₅, furthermore phenyl.

I e ring

in which L has, on each ocurrence identically or differently, one of the meanings given abvoe and below, and is preferably F, CI, CN, NO₂, CH₃, C₂H₅, C(CH₃)₃, CH(CH₃)₂, CH₂CH(CH₃)C₂H₅, OCH₃₎ OC₂H₅, COCH₃, COC₂H₅, COOCH3, COOC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅ or P-Sp-, very preferably F, CI, CN, CH₃, C₂H₅, OCH₃, COCH₃, OCF₃ or P-Sp-, most preferably F, CI, CH₃, OCH₃, COCH₃ or OCF₃.

The photopolymerisable group P is preferably selected from groups containing a C=C double bond or C≡C triple bond, and groups which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxide groups. ery preferably the photopolymerisable group P is selected from the

CW¹=CH-CO-(0)_k3-, CW¹=CH-CO-NH-, CH₂=CW¹-CO-NH-, CH₃-CH=CH- 0-, (CH₂=CH)₂CH-OCO-, (CH₂=CH-CH₂)₂CH-OCO-, (CH₂=CH)₂CH-0-, (CH₂=CH-CH₂)₂N-, (CH₂=CH-CH₂)₂N-CO-, CH₂=CW¹-CO-NH-, CH₂=CH- (COO)_ki-Phe-(O)_k2-, CH₂=CH-(CO)_k1-Phe-(O)_k2-, Phe-CH=CH-, in which W¹ denotes H, F, CI, CN, CF₃, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, CI or CH₃, W² denotes H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W³ and W⁴ each, independently of one another, denote H, CI or alkyl having 1 to 5 C atoms, Phe denotes 1 ,4-phenylene, which is optionally substituted by one or more radicals L as being defined above but being different from P-Sp, and ki, k₂ and k₃ each, independently of one another, denote 0 or 1 , k₃ preferably denotes 1 , and k4 is an integer from 1 to 10.

Particularly preferred groups P are CH₂=CH-COO-, CH₂=C(CH₃)-COO-,

CH₂=CF-COO-, CH₂=CH-, CH₂=CH-0-, (CH₂=CH)₂CH-OCO-,

O

A

(CH₂=CH)₂CH-0-, W²HC— -CH - and W² -^ (^{C H}2)_kr°- , _in particular vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably acrylate or methacrylate.

In a further preferred embodiment of the invention, the polymerisable compounds of the formulae and II^* and sub-formulae thereof contain, instead of one or more radicals Ρ-Sp-, one or more branched radicals containing two or more polymerisable groups P (multifunctional

polymerisable radicals). Suitable radicals of this type, and polymerisable compounds containing them, are described, for example, in US 7,060,200 B1 or US 2006/0172090 A1. Particular preference is given to multifunctional polymerisable radicals selected from the following formulae:

-X-alkyl-CHP¹-CH₂-CH₂P² l^*a

-X-alkyl-C(CH₂P )(CH₂P²)-CH₂P³ l^*b

-X-alkyl-CHP¹CHP²-CH₂P³ l^*c

-X-alkyl-C(CH₂P )(CH₂P²)-C_aaH₂aa₊i l^*d

-X-alkyl-CHP¹-CH₂P² l^*e

-X-alkyl-CHP P² l^*f

-X-alkyl-CP¹P²-CaaH_2aa+i l^*g

-X-alkyl-C(CH₂P¹)(CH₂P²)-CH₂OCH₂-C(CH₂P³)(CH₂P⁴)CH₂P⁵ l^*h

-X-alkyl-CH((CH₂)_aaP¹)((CH₂)_bbP²) l^*i

-X-alkyl-CHP¹CHP²-C_aaH₂aa₊i l^*k in which alkyl denotes a single bond or straight-chain or branched alkylene having 1 to 12 C atoms, in which one or more non-adjacent CH₂ groups may each be replaced, independently of one another, by -C(R^X)=C(R^X)-, -C≡C-, -N(R^X)-, -0-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, CI or CN, where R^x has the above- mentioned meaning and preferably denotes R° as defined above, aa and bb each, independently of one another, denote 0, 1 , 2, 3, 4, 5 or 6, X has one of the meanings indicated for X', and

P^1"5 each, independently of one another, have one of the meanings indicated above for P.

Preferred spacer groups Sp are selected from the formula Sp'-X', so that the radical "P-Sp-" conforms to the formula "P-Sp'-X'-", where Sp' denotes alkylene having 1 to 20, preferably 1 to 12 C atoms, which is optionally mono- or polysubstituted by F, CI, Br, I or CN and in which, in addition, one or more non-adjacent CH₂ groups may each be replaced, independently of one another, by -O-, -S-, -NH-, -NR⁰-, -SiR°R⁰⁰-, -CO-, -COO-, -OCO-, -OCO-O-, -S-CO-, -CO-S-,

-NR°-CO-O-, -O-CO-NR⁰-, -NR°-CO-NR⁰-, -CH=CH- or -C≡C- in such a way that O and/or S atoms are not linked directly to one another,

X' denotes -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR⁰-,

-NR°-CO-, -NR°-CO-NR⁰-, -OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF₂-, -CF₂CH₂-, -CH₂CF₂-, -CF₂CF₂-, -CH=N-, -N=CH-, -N=N-, -CH=CR⁰-, -CY²=CY³-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH- or a single bond,

R° and R⁰⁰ each, independently of one another, denote H or alkyl having 1 to 12 C atoms, and

Y² and Y³ each, independently of one another, denote H, F, CI or CN.

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

Typical spacer groups Sp' are, for example, -(CH₂)_pi-, -(CH₂CH₂O)_qi- CH₂CH₂-, -CH₂CH₂-S-CH₂CH₂-, -CH₂CH₂-NH-CH₂CH₂- or -(SiR°R⁰⁰-O)_pi-, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R° and R⁰⁰ have the above-mentioned meanings. Particularly preferred groups -X'-Sp - are -(CH₂)_pi-, -0-(CH₂)_pi-, -OCO- (CH₂)_pi-, -OCOO-(CH₂)_p1-.

Particularly preferred groups Sp' are, for example, in each case straight- chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethyl- ene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.

The polymerisable compounds are prepared analogously to processes known to the person skilled in the art and described in standard works of organic chemistry, such as, for example, in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Thieme-Verlag, Stuttgart. The synthesis of polymerisable acrylates and methacrylates of the formula I can be carried out analogously to the methods described in US 5,723,066. Further, particularly preferred methods are given in the examples. In the simplest case, the synthesis is carried out by esterification or etheri- fication of commercially available diols of the general formula HO-A¹-(Z¹- A²)mi-OH, in which A¹, A², Z¹ and ml have the above-mentioned

meanings, such as, for example, 2,6-dihydroxynaphthalene (naphthalene- 2,6-diol), or 1-(4-hydroxyphenyl)phenyl-4-ol, using corresponding acids, acid derivatives, or halogenated compounds containing a group P, such as, for example, methacryloyi chloride or methacrylic acid, in the presence of a dehydrating reagent, such as, for example, DCC

(dicyclohexylcarbodiimide). As shown above, the photosensitive compounds are preferably selected from compounds that contain only one photopolymerisable group and compounds that contain only two photopolymerisable groups. It is, however, also possible to use photosensitive compounds that contain more than two, for example three, four, five or six, photopolymerisable groups. In another preferred embodiment of the present invention, the

polymerisable component of the LC medium comprises one or more polymerisable compounds containing only one polymerisable group

(monoreactive) and one or more polymerisable compounds containing two or more, preferably only two, polymerisable groups (di- or multireactive).

In another preferred embodiment of the present invention, the

polymerisable component of the LC medium consists of polymerisable compounds containing only two polymerisable groups (direactive).

The proportion of the photosensitive, polymerisable compounds in the LC medium is preferably >0 and < 5%, especially >0 and < 1%, very

preferably >0 and < 0.5%, most preferably from 0.01 to 0.5%. The LC medium preferably contains one, two or three, most preferably only one, photosensitive compound(s).

The proportion of the LC host mixture in the LC medium is preferably > 95%, very preferably > 99%.

Preferably the LC medium according to the present invention does essentially consist of one or more photosensitive compounds and an LC host mixture as described above and below. However, the LC medium or LC host mixture may additionally comprise one or more further components or additives, preferably selected from the list including but not limited to chiral dopants, polymerisation 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.

For example, it is also possible to add one or more photoinitiators may also be added to the LC medium. Suitable conditions for the polymerisation, and suitable types and amounts of initiators, are known to the person skilled in the art and are described in the literature. Suitable photoinitiators for free-radical polymerisation are, for example, the commercially available photoinitiators Irgacure651^®, Irgacure184^®, Irgacure907®, Irgacure369^® or Darocurel 173^® (Ciba AG). If an initiator is employed, its proportion in the mixture as a whole is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight. However, it is also possible to carry out polymerisation without addition of a conventional photoinitiator. Thus, in a further preferred embodiment, the LC medium does not comprise a polymerisation initiator. The polymerisable component or the LC medium may also comprise one or more stabilisers in order to prevent undesired spontaneous polymerisation 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 of the Irganox^® series (Ciba AG). If stabilisers are employed, their proportion, based on the total amount of RMs or polymerisable component A), is preferably 10 - 5000ppm, particularly preferably 50 - 500ppm. The polymerisable compounds according to the invention are also suitable for polymerisation without initiator, which is associated with considerable advantages, such as, 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 polymerisable compounds according to the invention can be added individually to the LC media, but it is also possible to use mixtures comprising two or more polymerisable compounds. On polymerisation of mixtures of this type, copolymers are formed. The invention furthermore relates to the polymerisable mixtures mentioned above and below.

In addition to the photosensitive polymerisable compounds described above, the LC medium according to the invention comprises a low- molecular-weight component. The low-molecular-weight component is preferably an LC mixture ("LC host mixture") comprising one or more, preferably two or more, low-molecular-weight (i.e. monomeric or unpolymerised) compounds, where at least one of these compounds is a mesogenic or liquid-crystalline compound containing one or more alkenyl groups ("alkenyl compound"), where these alkenyl groups are stable to a polymerisation reaction under the conditions used for the polymerisation of the methacrylate groups.

The LC host mixture is preferably a nematic LC mixture.

The alkenyl groups are preferably straight-chain, branched or cyclic alkenyl, in particular having 2 to 25 C atoms, particularly preferably having 2 to 12 C atoms, in which, in addition, one or more non-adjacent CH₂ groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F and/or CI.

Preferred alkenyl groups are straight-chain alkenyl having 2 to 7 C atoms and cyclohexenyl, in particular ethenyl, propenyl, butenyl, pentenyl, hex- enyl, heptenyl, 1 ,4-cyclohexen-1-yl and 1 ,4-cyclohexen-3-yl. The concentration of compounds containing an alkenyl group in the LC host mixture (i.e. without any polymerisable compounds) is preferably from 5% to 100%, very preferably from 20% to 60%.

Especially preferred are LC mixtures containing 1 to 5, preferably 1 , 2 or 3 compounds having an alkenyl group.

The compounds containing an alkenyl group are preferably selected from the following formulae:

in which the individual radicals, on each occurrence identically or differently, each, independently of one another, have the following meaning:

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^d, 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-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

-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, each, independently of one another, H, F, CI, OCF₃, CF₃, CH₃, CH₂F or CHF₂H, preferably H, F or CI, X 1 or 2, z 0 or 1. R²² is preferably straight-chain alkyl or alkoxy having 1 to 8 C atoms or straight-chain alkenyl having 2 to 7 C atoms.

The LC medium preferably comprises no compounds containing a terminal vinyloxy group (-0-CH=CH₂), in particular no compounds of the for- mula A or B in which R ¹ or R¹² denotes or contains a terminal vinyloxy group (-0-CH=CH₂).

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

The compounds of the formula AN are preferably selected from the following sub-formulae:

alkenyl- H V-→C H V- O — alkyl AN6

alkenyl— ( H — ( O )— o — alkyl

The compounds of the formula AY are preferably selected from the following sub-formulae:

in which alkyi denotes a straight-chain alkyi 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 particularly preferred compounds of the formula A are selected from the following sub-formulae:

A1a

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

F F

AY 14a

//-Λ ⁰ ^°-^Cm^H2m₊₁ in which m and n each, independently of one another, denote 1 , 2, 3, 4, 5 or 6, i denotes 0, 1 , 2 or 3, R^b1 denotes H, CH₃ or C₂H₅, and alkenyl denotes CH₂=CH-, CH^CHChbChb-, CH₃-CH=CH-, CH₃-CH₂-CH=CH-, CH₃-(CH₂)2-CH=CH-, CH₃-(CH₂)₃-CH=CH- or CH₃-CH=CH-(CH₂)₂-.

Further preferred LC media and LC host mixtures are indicated below: a) LC host mixture comprising one or more compounds selected from the following formulae:

wherein the individual radicals have the following meanings 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, in which, in addition, one or two non-adjacent CH₂ 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 from 1 to 6 C atoms, Z^x and Z^y each, independently of one another, denote -CH₂CH₂-, -CH=CH-, -CF₂O-, -OCF₂-, -CH₂0-, -OCH₂-, -CO-O-, -O-CO-, -C₂F₄-, -CF=CF-, -CH=CH-CH₂O-, or a single bond, preferably a single bond,

L ^"4 each, independently of one another, denote F, CI, OCF₃,

CF₃, CH₃, CH₂F, CHF₂ , preferably F or CI.

Especially preferably both L¹ and L² denote F, or one of L¹ and L² denote F and the other denotes CI. Further preferably both L³ and L denote F, or one of L³ and L⁴ denote F and the other denotes CI.

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

CY1

alkyl— < H >— CF₂O— ( O )— (O)alkyl^{* CY25}

F F alkyl CH=CHCH₂0— ( O )— (O)alkyl^{* CY26}

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 (O) denotes an O atom or a single bond.

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

in which alkyi and alkyi* each, independently of one another, denote a straight-chain alkyi radical having 1-6 C atoms, and (O) denotes an O atom or a single bond. LC host mixture which comprises one or more compounds of the following formula:

in which the individual radicals have the following meanings:

denotes — H — or — (

o

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-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

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

-OCH₂-, -COO-, -OCO-, -C₂F₄-, -CF=CF-, -CH=CHCH₂O- or a single bond, preferably a single bond.

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

alkyl— ( H >— < O >— alkyl ZK5

alkyl— H — ( O Vo-alkyl* ZK6

alkyl— ( H alkyl* ZK7

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

LC host mixture which additionally comprises one or more compounds of the following formula:

in which the individual radicals have on each occurrence, identically or differently, the following meanings: R⁵ and R⁶ each, independently of one another, have one of the meanings indicated above for R¹,



in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms. LC host mixture which additionally comprises one or more

compounds of the following formula:

which the individual radicals have the following meanings

f denotes 0 or 1 ,

R¹ and R² 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 -O-, -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-, -COO-, -OCO-, -C₂F₄-, -CF=CF-, -CH=CHCH₂O- or a single bond, preferably a single bond,

L⁵ and L⁶ each, independently of one another, denote F, CI, OCF₃,

CF₃, CH₃, CH₂F, CHF₂.

Preferably, both radicals L⁵ and L⁶ denote F or one of the radicals L⁵ and L⁶ denotes F and the other denotes CI.

The compounds of the formula TY are preferably selected from the following sub-formulae:

in which R¹ has the above-mentioned meaning, (O) denotes an O atom or a single bond, alkyl denotes a straight-chain alkyl radical having 1-6 C atoms, and v denotes an integer from 1 to 6. R¹ preferably denotes straight-chain alkyl having 1-6 C atoms. The LC medium according to the invention preferably comprises one or more compounds of the above-mentioned formulae in amounts of > 0 to < 10% by weight. LC host mixture which additionally comprises one or more

compounds selected from the following formulae:

G

F F L^x

G2 alkyl→ ₀ )— ( O >— < O >— X

alkyl— o >— < O >— < O hX G3

alkyl— < o O )—( O X G4

in which alkyl denotes d-6-alkyl, L^x denotes H or F, and X denotes F, CI, OCF₃, OCHF₂ or OCH=CF₂. Particular preference is given to compounds of the formula G1 in which X denotes F.

LC host mixture which additionally comprises one or more

compounds selected from the following formulae:

(0)_d-alkyl Y15

F F

R⁵- H -CH₂CH2 O >— (0)_d-alkyl Y16

in which R⁵ has one of the meanings indicated above for R¹, alkyl denotes

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 > 0 to < 10% by weight. LC host mixture which additionally comprises one or more biphenyl compounds of the following formula:

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

The proportion of the biphenyls of formula BP in the LC mixture is preferably at least 3% by weight, in particular > 5% by weight.

The compounds of the formula BP are preferably selected from the following sub-formula:

B1a in which alkyl* denotes an alkyl radical having 1-6 C atoms.

LC host mixture which additionally comprises one or more compounds of the following formulae:

in which R and R² have the above-mentioned meanings and preferably each, independently of one another, denote straight-chain alkyl or alkenyl.

Preferred mixtures comprise one or more compounds selected from the formulae O1 , 03 and 04. LC host mixture which additionally comprises one or more compounds of the following formula:

R⁹ denotes H, CH₃, C₂H₅ or n-C₃H₇, (F) denotes an optional fluoro substituent, 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 Fl are selected from the following sub-formulae:

in which R⁷ preferably denotes straight-chain alkyl having 1-6 C atoms, and R⁹ denotes CH_3l C2H5 or n-C3H₇. Particular preference given to the compounds of the formulae FI1 , FI2 and FI3.

LC host mixture which additionally comprises one or more compounds of the following formulae:

F F

VK3

R° H O O H alkyl

F F F F

VK4

R" H alkyl in which R⁸ has the meaning indicated for R¹, and alkyl denotes a straight-chain alkyl radical having 1-6 C atoms.

LC host mixture which additionally comprises one or more compounds which contain a tetrahydronaphthyl or naphthyl unit, such as, for example, the compounds selected from the following formulae:

in which R¹⁰ and R¹ each, independently of one another, have one of the meanings indicated for R¹, preferably denote straight-chain alkyl or straight-chain alkoxy having 1-6 C atoms or straight-chain alkenyl having 2-6 C atoms, and Z¹ and Z² each, independently of one another, denote -C₂H₄-, -CH=CH-, -(CH₂)₄-, -(CH₂)₃O-, -O(CH₂)₃- , -CH=CHCH₂CH₂-, -CH₂CH₂CH=CH-, -CH₂O-, -OCH₂-, -COO-, -OCO-, -C₂F₄-, -CF=CF-, -CF=CH-, -CH=CF-, -CH₂- or a single bond.

LC host mixture which additionally comprises one or more difluoro- dibenzochromans and/or chromans of the following formulae:

in which R¹¹ and R¹² each, independently of one another, have the above-mentioned meaning, and c denotes 0 or 1 , 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 and CR are selected from the following sub-formulae:

CR5 alkenyl- H alkyl^*

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-.

Very particular preference is given to mixtures comprising one, two or three compounds of the formula BC-2.

LC host mixture which additionally comprises one or more fluorinated phenanthrenes or dibenzofurans of the following formulae:

in which R¹¹ and R¹² each, independently of one another, have the above-mentioned meanings, 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 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.

LC host mixture which comprises one or more, preferably from 3 to 20 compounds of the formulae CY, PY and/or TY. The proportion of these compounds in the host mixture as a whole is preferably from 10 to 80 % very preferably from 20 to 70 %. The content of these individual compounds is preferably in each case from 2 to 25 % by weight.

LC host mixture or nematic component wherein the compounds of formulae CY, PY and TY are selected from the group consisting of formulae CY1 , CY2, CY9, CY10, PY1 , PY2, PY9 and PY10.

LC host mixture which comprises one or more, preferably from 3 to 20 compounds of the formulae ZK and DK. The proportion of these compounds in the host mixture as a whole is preferably from 5 to 50% very preferably from 10 to 40%. The content of these individual compounds is preferably in each case from 2 to 20 % by weight.

LC host mixture or nematic component wherein the compounds of formulae ZK and DK are selected from the group consisting of formulae ZK1 , ZK2, ZK5, ZK6, DK1 and DK2.

LC medium which, apart from the polymerisable compounds as described above and below, contains no compounds which contain a terminal vinyl or vinyloxy group (-CH=CH₂, -0-CH=CH₂).

LC medium which comprises 1 to 5, preferably 1 , 2 or 3 polymerisable compounds.

LC medium in which the proportion of polymerisable compounds in the medium as a whole is 0.05 to 5 %, preferably 0.1 to 1 %.

LC medium which comprises in addition one or more, preferably low- molecular-weight and/or unpolymerisable, chiral dopants, very preferably selected from Table B, preferably in the concentration ranges given for Table B.

The combination of compounds of the preferred embodiments mentioned above with the polymerised compounds described above and below effects low threshold voltages and very good low-temperature stabilities with maintenance of high clearing points and high HR values in the LC media according to the invention and allows a pretilt angle to be set in PSA displays. In particular, the LC media exhibit significantly shortened response times, in particular also the grey-shade response times, in PSA displays compared with the media from the prior art.

The LC host mixture preferably has a nematic phase range of at least 80 K, particularly preferably at least 100 K, and a rotational viscosity of not greater than 450 mPa-s, preferably not greater than 350 mPa-s, at 20°C. The LC host mixture preferably has a negative dielectric anisotropy Δε, preferably of about -0.5 to -7.5, in particular of about -2.5 to -6.0, at 20°C and 1 kHz. The LC host mixture preferably has a birefringence Δη > 0.06, very preferably > 0.09, most preferably > 0.12, and preferably has a

birefringence Δη < 0.20, very preferably < 0.18, most preferably < 0.16.

The LC media may also comprise further additives known to the person skilled in the art and described in the literature, like for example chiral dopants, polymerisation 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 or nanoparticles. These additives can be polymerisable or unpolymerisable. Accordingly, polymerisable additives will belong to the polymerisable component, and unpolymerisable additives will belong to the nematic component of the LC media. The LC media can for example contain one or more chiral dopants, which are preferably selected from the group consisting of compounds from Table B below.

For example, 0 to 15% by weight of pleochroic dyes may be added.

Furthermore nanoparticles, conductive salts, preferably ethyldimethyldo- decylammonium 4-hexoxybenzoate, tetrabutylammonium tetraphenyl- borate or complex salts of crown ethers (see e.g. Haller et al., Mol. Cryst.

Liq. Cryst. 24, 249-258 (1973)), may be added to improve the conductivity.

Also, substances may be added to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 27, 22 40 864,

23 21 632, 23 38 281 , 24 50 088, 26 37 430 and 28 53 728.

The individual components of the preferred embodiments of the LC media according to the invention are either known or the ways in which they are prepared can readily be derived from the prior art by the person skilled in the relevant art since they are based on standard methods described in the literature. Corresponding compounds of the formula CY are described, for example, in EP-A-0 364 538. Corresponding compounds of the formula ZK are described, for example, in DE-A-26 36 684 and

DE-A-33 21 373.

Preference is furthermore given to LC media comprising one, two or three polymerisable compounds as described above and below. Preference is furthermore given to achiral polymerisable compounds and LC media comprising, preferably consisting exclusively of, achiral compounds.

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 polymerisable compounds as defined above and optionally with further liquid-crystalline compounds and/or additives. In general, the desired amount of the components 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, CI, F have been replaced by the corresponding isotopes.

The construction of the LC displays according to the invention corresponds to the conventional geometry for PSA displays, as described in the prior art cited at the outset. Geometries without protrusions are preferred, in particular those in which, in addition, the electrode on the colour filter side is unstructured and only the electrode on the TFT side has slits. Par- ticularly suitable and preferred electrode structures for PSA-VA displays are described, for example, in US 2006/0066793 A1.

Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example

"comprising" and "comprises", mean "including but not limited to", and are not intended to (and do not) exclude other components.

It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).

The following examples explain the present invention without limiting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addi- tion, the examples illustrate which properties and property combinations are accessible.

In the tables below the following abbreviations are used:

(n, m, z: each, independently of one another, 1 , 2, 3, 4, 5 or 6) Table A

CCH-nm CCH-nOm

CC-n-V CC-n-V1

CC-n-mV PP-n-m

CVC-n-m CVY-V-m

CEY-V-m PY-n-(0)m

CCY-n-m CCY-n-Om

CCY-V-m CCY-Vn-m

CCY-V-Om CCY-n-OmV

CPY-n-(0)m CPY-V-Om

CQY-n-(0)m CQIY-n-(0)m

CLY-n-(0)m

LYLI-n-m LY-n-(0)m

PGIGI-n-F PGP-n-m

PYP-n-(0)m PYP-n-mV

YPY-n-m YPY-n-mV

BCH-nm BCH-nmF

CNa -n-Om CCNap-n-Om

CETNap-n-Om

DFDBC-n(0)-(0)m C-DFDBF-n-(0)m ⁰ ^C_mH_2m-^

PGU-n-F PPGU-n-F

In a preferred embodiment of the present invention, the LC media according to the invention comprise one or more compounds selected from the group consisting of compounds from Table A.

Table B

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

C 15 CB 15

CM 21 R/S-811

CM 44 CM 45

R/S-4011 R/S-5011

R/S-1011

The LC media preferably comprise 0 to 10% by weight, in particular 0.01 to 5% by weight and 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 indicates possible stabilisers which can be added to the LC media according to the invention (n here denotes an integer from 1 to 12, terminal methyl groups ar not shown)

35 -98-



The LC media preferably comprise 0 to 10% by weight, in particular 1 ppm to 5% by weight and particularly preferably 1ppm to 3% 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:

V₀ denotes threshold voltage, capacitive [V] at 20°C,

Vpp denotes applied voltage peak-to-peak,

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

Δη denotes optical anisotropy at 20°C and 589 nm,

ε± denotes the dielectric permittivity perpendicular to the

director at 20°C and 1 kHz,

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

Δε denotes dielectric anisotropy at 20°C and 1 kHz,

cl.p., T(N,I) denotes clearing point [°C],

γ-, denotes rotational viscosity at 20°C [mPa-s],

Ki denotes elastic constant, "splay" deformation at 20°C [pN],

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

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

LTS denotes low-temperature stability, determined in test cells, HR / VHR denotes voltage holding ratio at 100°C [%].

Unless explicitly noted otherwise, all concentrations in the present application are indicated in per cent by weight and relate to the corresponding mixture or mixture component, unless explicitly indicated otherwise.

Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, 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 indicated in degrees Celsius (°C).

Unless explicitly noted otherwise, all measurements described above and below are carried out at room temperature.

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 Δη is determined at 589 nm and Δε is determined at 1 kHz, unless explicitly indicated otherwise in each case.

For the present invention, the term "threshold voltage" relates to the capa- citive threshold (V₀), also known as the Freedericksz threshold, unless explicitly indicated otherwise. In the examples, as is generally usual, the optical threshold for 10% relative contrast (Vi₀) may also be indicated.

The display test cells used for the measurements described in the examples contain two plane-parallel outer plates at a separation of 4 μΐτι and electrode layers with overlying alignment layers of rubbed polyimide on the insides of the outer plates, which cause a homeotropic edge alignment of the liquid-crystal molecules. The polymerisable compounds are polymerised in test cells by UV irradiation for a pre-determined time, with a voltage simultaneously being applied to the display, usually 10 to 40 Vpp (pp = peak-to-peak) alternating current with 1 kHz. In the examples, unless indicated otherwise, polymerisation was carried out at 40°C using a 100 mW/cm² metal halide lamp, the intensity was measured using a standard UV meter (model Ushio UNI meter). In this case the lamp intensity itself was measured, not UV after specific filters.

The tilt angle is determined by a rotational crystal experiment (Autronic- Melchers TBA-105). A small value (i.e. a large deviation from a 90° angle) corresponds to a large tilt here.

The VHR is measured as follows: To the LC host mixture a defined amount (e.g. 0.3%) of the RM are added, and the resulting mixture is filed into VA-VHR test cells (no rubbing, alignment layer VA polyimide, cell gap 6 pm). The test cells are exposed to UV radiation using a 100 mW/cm² metal halide lamp at 40°C, and the VHR value is measured after certain time intervals at 1V, 60Hz, 64ps pulse, 100°C (Autronic-Melchers VHRM- 105). The UV absorption of the photosensitive compounds is determined as follows: The compound is dissolved in a solvent, unless stated otherwise in dichloromethane (DCM). The UV/VIS spectrum of the sample is then measured using a UV/VIS/NIR-spectrometer Varian Cary 500 with the following parameters:

Wavelength range 200-800 nm

Spectral slit width 2

Integration time 0.1 s

Interval 0.5 nm

Base line DCM

Layer thickness 1 cm

Ordinate (y-axis) extinction

Temperature Room Temperature

The integral of the extinction (y-axis of the spectrum) over a given wavelength range (x-axis of the spectrum) is calculated for each compound and multiplied with its mass and divided by its concentration in the measurement sample and by the sample thickness, in accordance with equations (1) and (2) above, to give the integral molar extinction coefficient Ε_λι_-λ2 for the wavelength range from λ1 to λ2.

Due to its definition (see equations 1 and 2 above), the value of Ε_λι_-λ2 for a given compound, just like its value of ε, is in theory independent from the concentration, sample thickness and molar mass, and is an intrinsic compound property. Nevertheless, in order to reduce measurement errors, it is preferable to prepare multiple samples with similar and/or varying concentration, and to use the average of the Ε_λι_-λ2 values obtained from individual measurements. In addition the same solvent should be used (e.g. DCM) if different samples are compared due to the fact that the molar extinction coefficient depend on the solvent used for the experiments.

Unless explicitly noted otherwise, the extinction values described above and below are given for a temperature of 20°C. Unless stated otherwise, the process of polymerizing the photosensitive compounds in the PSA displays as described above and below is carried out at a temperature where the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably is carried out at room temperature.

Determination of E^n- nn

The UV/VIS absorption spectra of various photosensitive polymerisable compounds were measured in DCM as described above, and the integral extinction coefficient was calculated. Table 1 shows for each compound the chemical structure, the wavelength X_max of the absorption maximum, the molar extinction coefficient ε at the maximum wavelength X_max, and the integral molar extinction coefficient Ε^_ΟΜΟΟ in the range from 340 to 400nm.

Table 1

From Table 1 it can be seen that compounds RM1-RM6 have a value of E340-400≥ 1000 in the desired wavelength range, and therefore represent photosensitive compounds in the sense of the present invention, whereas compound RM7 has a value of E_{3 0-}4oo < 1000 and does not represent a photosensitive compound in the sense of the present invention. It can also be seen that, when comparing different photosensitive compounds, a high value of the wavelength at the absorption maximum λ[Π3χ, and/or a high value of the extinction coefficient ε at

does not necessarily mean that the compound also has a high value of Ε340-400· in the desired wavelength range from 340-400nm. For example, RM5 and RM6 have an absorption maximum at a lower wavelength than RM7, but do still have a higher overall extinction at higher wavelengths, as indicated by their higher values of E₃4_0-4oo- R 2 has a lower value of the extinction coefficient ε at _max than RM1 , but does still have a higher overall extinction at higher wavelengths, as indicated by its value of £340-400· RM4 and RM5 have similar values of

and ε at X_max, nevertheless RM5 has a significantly higher value of E340-400 than RM4.

This shows that the value of Ε34θ οο is a better indicator for the total UV absorption of a photosensitive compound in the desired wavelength range from 340-400nm than the value of X_max or the value of ε at X_max.

Comparison Example 1

The following nematic LC host mixture C1 is formulated:

CY-3-O2 15.00 % Cl.p. +75.5

CCY-3-03 8.50 % Δη 0.1018

CCY-4-02 10.00 % Δε - 3.0

CPY-2-02 5.00 % ^ειι 3.4

CPY-3-02 10.00 % Υι 1 12

CCH-34 10.00 %

CCH-23 22.00 %

PYP-2-3 11.50 %

PCH-301 8.00 %

The mixture C1 does not contain a compound with an alkenyl group. Example 1

The following nematic LC host mixture M1 is formulated: CY-3-02 18.00 % Cl.p +74.5

CCY-3-02 9.00 % Δη 0.1021

CCY-4-O2 4.00 % Δε - 3.1

CPY-2-02 10.00 % ^ειι 3.5

CPY-3-O2 10.00 % Υι 86

CC-3-V 40.00 %

PYP-2-3 9.00 %

The mixture M1 contains 40% of a compound with an alkenyl group selected of formula A1 , and shows a significantly reduced viscosity compared to LC host mixture C1.

Comparison Example A

The polymerisable LC media PC1-PC3 are prepared by adding 0.4% of one of RM1 , RM2 and RM3, respectively, to the alkenyl-free host mixture C1 of Comparison Example 1.

The polymerisable LC media PC4 and PC5 are prepared by adding 0.3% of RM7 (see Table 1) to the alkenyl-containing host mixture M1 of Example 1 , and to the alkenyl-free host mixture C1 of Comparison Example 1 , respectively. Use Example A

The polymerisable LC media PM1-PM3 are prepared by adding 0.4% of one of RM1 , RM2 and RM3 (see Table 1), respectively, to the alkenyl- containing host mixture M1 of Example 1.

The compositions of the individual mixtures are shown in Table 2 below.

Table 2

No. PM1 PM2 PM3 PC1 PC2 PC3 PC4 PC5

RM 1 2 3 1 2 3 7 7 Host M1 M1 M1 C1 C1 C1 C1 M1

PM1-PM3 represent polymerisable LC media according to the invention, whereas PC1-PC5 do not represent polymerisable LC media according to the invention.

The VHR is measured for mixtures M1 , C1 , PC4 and PC5 by the general method as described above, after exposure to UV light for different time periods using a UV lamp and a 320nm cut-off filter. As shown in Figure 1, this results in exposure to UV light that does not contain radiation of substantial intensity below 300nm. The results are shown in Table 3.

Table 3

From Table 3 it can be seen that the alkenyl-free host mixture C1 shows a decrease of the VHR after UV exposure. After addition of RM7, the resulting polymerisable mixture PC4 does only show a slight decrease of the VHR, so that by addition of RM7 the VHR drop is suppressed. The alkenyl-containing host mixture M1 shows a stronger decrease of the VHR than the alkenyl-free host mixture C1. After addition of the RM7 to M1 , the VHR decrease in the resulting polymerisable mixture PC5 is even stronger.

Thus, compared to the alkenyl-free host C1 , the VHR drop after UV exposure in the alkenyl-containing host M1 is much stronger, and is not suppressed, but to the contrary even enhanced, by addition of RM 7. This shows that the alkenyl-containing host mixture M1 has drawbacks when being used in a standard PSA display production process, because photopolymerisation of the RM at wavelengths around 300nm will lead to a decrease of the VHR. This decrease cannot be avoided even when using RM7 in the alkenyl-containing host.

The VHR is measured for the polymerisable LC media PM1-PM3 and PC1-PC3 by the general method as described above, after exposure for different time periods to UV radiation having either a shorter wavelength or a longer wavelength, by using a UV lamp with a 340nm cut-off filter or a 375nm cut-off filter, respectively.

As shown in Figure 1 , the use of a 340nm cut-off filter results in exposure to UV light that does not contain radiation of substantial intensity below 320nm, and the use of a 375nm cut-off filter results in exposure to UV light that does not contain radiation of substantial intensity below 340nm.

The results are shown in Table 4 for the polymerisable LC media PC1 (alkenyl-free host & RM1) and PM1 (alkenyl-containing host & RM1).

Table 4

^* exposure time was 3 minutes From Table 4 it can be seen that, after exposure to shorter UV

wavelength, the polymerisable mixture PM1 with the alkenyl-containing host and RM1 shows a larger drop of the VHR than the polymerisable mixture PC1 with the alkenyl-free host and RM1 , wherein almost no drop of the VHR is observed. However, after exposure to higher UV

wavelength, polymerisable mixture PM1 with the alkenyl-containing host shows almost no drop of the VHR, just like polymerisable mixture PC1 with the alkenyl-free host. The same result is obtained for the

polymerisable mixture PM2 with the alkenyl-containing host and RM2.

Thus, by chosing larger UV wavelengths it is possible to avoid a VHR drop in the alkenyl-containing mixture. The VHR is measured for polymerisable mixture PM1 by the general method as described above, but wherein the mixture is either exposed to two different UV wavelengths in two steps, either first to UV light having a shorter wavelength and then to UV light having a longer wavelength, or vice versa, by using either a 340nm or 375nm cut-off filter as described above. The results are shown in Table 5.

For comparison purposes the VHR values after exposure to either a longer or a shorter wavelength in a single step are also shown.

Table 5

Cut-off filter (nm) & UV exp. time (min) VHR in PM1 (%)

340nm & 10 min 90.67

1^st 340nm & 3min, 2^πα 375nm & 25min 90.82

1^st 375nm & 4min, 2^na 340nm & 9min 88.81

1^SI 375nm & 9min, 2^na 340nm & 7min 89.98

1^st 375nm & 15min, 2^na 340nm & 6min 90.05

375nm & 25min 97.10 From Table 5 it can be seen that the exposure to a shorter UV

wavelength, either in a single step or as a first or second step in a two- step process, leads to a significant decrease of the VHR of the LC medium to values < 90%. Contrary thereto, after exposure to only a longer UV wavelength the VHR is still high even after a long exposure time.

This confirms that by avoiding exposure to shorter UV wavelenghts it is possible to maintain a high VHR in the LC medium, and that the LC medium has a high reliability and high VHR when being exposed to longer UV wavelengths even for a long time.

The polymerisable LC media PM1 and PM2 are filled into a test cell and the RM is polymerised while applying a voltage to the cell, following the general method as described above, wherein the test cells are exposed to UV radiation of shorter or longer wavelength by using a 340nm or 375nm cut-off filter as described above.

The pretilt angle generated in an individual mixture after polymerisation of the RM is determined by the general method as described above. The results are shown in Table 6.

Table 6

Mixture => PM1 PM2

Filter => 375nm 375nm

Voltage => 40V_Pp 30V_Pp

UV exp.time / min JJ

0 89 89

2 85.55 73.03

5 80.05 73.12*

10 77.35 72.49

15 75.91

20 76.28 25 75.99

^*exposure time was 4 minutes

From Table 6 it can be seen that in the LC media PM1 and PM2, which contain an alkenyl compound and RM1 or RM2 with a high value of E340- 400, a high pretilt can be generated already after a short exposure time of 5 minutes even when using long UV wavelengths.

The amount of unpolymerised RM in a test cell is measured for mixtures PM1-PM3 and PC5 after different time periods of UV exposure. For this purpose each mixture is polymerised in the test cell following the general method as described above, wherein the test cells are exposed to UV radiation of shorter or longer wavelength by using a 340nm or 375nm cutoff filter as described above.

After polymerisation the mixture is washed out of the test cell with MEK and the amount of unpolymerized reactive mesogen is measured by HPLC. The results are shown in Table 7.

Table 7

ND = not detectable

* exposure time was 15 min From Table 7 it can be seen that in the LC media PM1 , PM2 and PM3, which contain an alkenyl compound and RM1 , RM2 or RM3 with a high value of £340-400, a high extent of polymerisation and a low amount of residual unpolymerised RM is achieved both after exposure to shorter and to longer UV wavelengths. In contrast thereto, in the LC medium PC5, which contains an alkenyl compound and RM7 with a low value of E340-400, a high extent of polymerisation is achieved only after exposure to shorter UV wavelength, but not after exposure to longer UV wavelength.

Claims

Patent Claims

Liquid crystal (LC) medium, characterized in that it comprises one or more mesogenic compounds or liquid crystal compounds that contain an alkenyl group, and further comprises one or more photosensitive compounds which are polymerisable by

photopolymerisation and which have an integral molar extinction coefficient E340-400≥ 000 L nm cm^"1 ΪΤΙΟΓ¹ in the wavelength range from 340nm to 400nm.

LC medium according to claim 1 , characterized in that the

compounds containing an alkenyl group do not photopolymerise under the conditions used for the polymerisation of the

photosensitive compounds.

LC medium according to claim 1 or 2, characterized in that the photosensitive compounds are selected from the group consisting of the following formulae

wherein the individual radicals have the following meanings P is a photopolymerisable group,

Sp is, on each occurrence identically or differently, a spacer group or a single bond, R^a, R^b denote, independently of each other, P-Sp-, H, F, CI, Br, I, - CN, -NO₂, -NCO, -NCS, -OCN, -SCN, SF₅, straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent Chfe groups may be replaced by - C(R°)=C(R⁰⁰)-, -C≡C-, -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 H atoms may be replaced by F, CI or P-Sp-, or aryl or heteroaryl having 4 to 30 ring atoms which may also contain one or more fused rings and which is optionally substituted by one or more groups L, wherein in formula D, E, F and G at least one of R^a and R^b is P-Sp-,

R°, R⁰⁰ denote, independently of each other, H or straight-chain or branched alkyl having from 1 to 12 C atoms,

W¹, W² denote, independently of each other, -CY₂CY₂-, -CY=CY-, - CY2-O-, -O-CY2-, -C(O)-O-, -O-C(O)-, -C(R^cR^d)-, -O-, -S-, - CO-, or -NR^C-,

W³ is -CY2CY2-, -CY2-O-, -O-CY2-, -C(O)-O-, -O-C(O)-, -C(R^cR^d)- , -O-, -S-, -CO-, or -NR^C-,

Y is, on each occurrence identically or differently H or F,

R^c, R^d denote, independently of each other, H or straight-chain or branched alkyl having from 1 to 12 C atoms,

A¹, A² denote, independently of each other, 1 ,4-phenylene,

naphthalene-1 ,4-diyl or naphthalene-2,6-diyl wherein, 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 CH₂ groups may be replaced by O and/or S, ,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, octahydro- 4,7-methanoindane-2,5-diyl, anthracene-2,7-diyl, fluorene- 2,7-diyl or phenanthrene-2,7-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L, is, on each occurrence identically or differently, P, P-Sp-, OH, CH₂OH, F, CI, Br, I, -CN, -NO₂₎ -NCO, -NCS, -OCN, -SCN, -C(=O)N(R^x)_2> -C(=O)Y¹, -C(=O)R^x, -N(R^X)₂₎ optionally substituted silyl, optionally substituted aryl or heteroaryl having 4 to 30 ring atoms, straight-chain or branched alkyl or alkoxy having 1 to 25 C atoms, or straight-chain or branched alkenyl, alkinyl, alkylcarbonyl, alkoxycarbonyl,

alkylcarbonyloxy or alkoxycarbonyloxy having 2 to 25 C atoms, wherein in all of these groups, in addition, one or more H atoms may be replaced by F, CI or P-Sp-, is halogen, is P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH₂ groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, CI or P-Sp-,

Z¹, Z² independently of each other -O-, -S-, -CO-, -CO-O-, -OCO-, - O-CO-O-, -OCH₂-, -CH₂O-, -SCH₂-, -CH₂S-, -CF₂O-, -OCF₂-, -CF₂S-, -SCF₂- -(CH₂)_n-, -CF₂CH₂-, -CH₂CF₂-, -(CF₂)_n-, - CH=CH-, -CF=CF-, -CH=CF-, -CF=CH-, -C≡C-, -CH=CH-

COO-, -OCO-CH=CH-, -CH₂-CH₂-COO-, -OCO-CH₂-CH₂-, - C(R°R⁰⁰)-, -C(R^yR^z)-, or a single bond,

R^y, R^z denote, independently of each other, H, F, CH₃ or CF₃, n is 1 , 2, 3 or 4, p, q are, independently of each other, 0, 1 , 2 or 3, r is 0, 1 , 2, 3 or 4, s is 0, 1 , 2 or 3, t is 0, 1 or 2, c is 0, 1 or 2.

LC medium according to one or more of claims 1 to 3, characterized in that the photosensitive compounds are selected from the group consisting of the following subformulae:

 - 121 -

- 123-

wherein P, Sp, L, R^a, R^b, R^c, R^d, A¹, A², Z Z², p, q, r, s and t have the meanings given in claim 3, R^e has one of the meanings of R^a as given in claim 3 that is different from P-Sp-, s+t > 1 , s+r > 1 , in formulae H3 and H4 at least obe s is > 1 , r1 is 0, 1 or 2, r2 is 0, 1 or 2, with r1+r2 > 1 , and r3 is 1 or 2.

5. LC medium according to one or more of claims 1 to 4, characterized in that the compounds containing an alkenyl group are selected from the group consisting of the following formulae:

in which the individual radicals, on each occurrence identically or differently, each, independently of one another, have the following meaning:

R¹¹ 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^d,

R²² 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-, -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-CH₂O-, or a single bond, preferably a single bond,

L^1" each, independently of one another, H, F, CI, OCF₃, CF₃, CH₃, CH₂F or CHF₂H, preferably H, F or CI, x 1 or 2, z 0 or 1.

6. LC medium according to one or more of claims 1 to 5, characterized in that the compounds containing an alkenyl group are selected from the group consisting of the following sub-formulae:

alkenyl— { H — { H >— OOF-— ( O )— O-alkyl* ^AY25

F F alkenyl— ⁽ H >—CF₂0— O >— (O)alkyl^* AY26

in which alkyl denotes 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, and 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-.

7. LC medium according to one or more of claims 1 to 6, characterized in that the compounds containing an alkenyl group are selected from the group consisting of the following sub-formulae:

35 AY14a

in which m and n each, independently of one another, denote 1 , 2, 3, 4, 5 or 6, i denotes 0, 1 , 2 or 3, R^b1 denotes H, CH₃ or C₂H₅, 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-.

8. LC medium according to one or more of claims 1 to 4, characterized in that it additionally comprises one or more compounds selected from the group consisting of the following formulae:

wherein the individual radicals have the following meanings: denotes 1 or 2, denotes 0 or 1 ,

R and R² each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adja- cent CH₂ groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having from 1 to 6 C atoms, each, independently of one another, denote -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,

1-4 each, independently of one another, denote F, CI, OCF₃,

CF₃, CH₃, CH₂F, CHF₂ , preferably F or CI.

LC medium according to one or more of claims 1 to 8, characterized that it comprises one or more compounds selected from the group consisting of the following formulae:

in which the individual radicals have the following meanings:

R and R 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 -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that O atoms are not linked directly to one another,

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

-OCH₂-, -COO-, -OCO-, -C₂F₄-, -CF=CF-, -CH=CHCH₂O- or a single bond, preferably a single bond. each, independently of one another, have one of the meanings indicated above for R¹, and denotes 1 or 2.

10. Use of an LC medium according to one or more of claims 1 to 9 in

PS (polymer sustained) or PSA (polymer sustained alignment) LC displays.

11. LC display comprising an LC medium according to one or more of

claims 1 to 9.

12. LC display according to claim 11 , characterized in that it is a PSA-VA, PSA-OCB, PSA-IPS, PSA-FFS, PSA-posi-VA or PSA-TN display.

13. LC medium, use or display according to one or more of claims 1 to 12, wherein the photosensitive compounds are polymerised.

14. Process of manufacturing a PS or PSA display, comprising the steps of a) providing an LC medium according to one or more of claims 1 to 9 between two substrates, wherein at least one of the substrates comprises one or two electrodes provided thereon, and

b) exposing the LC medium to UV radiation with a wavelength >

340nm,

and wherein preferably a voltage is applied to the electrodes at least part-time during said exposure to UV radiation in step b).

PS or PSA display obtained by a process according to claim 14.

PS or PSA display, characterized in that it comprises two substrates, wherein at least one substrate comprises one or two electrodes provided thereon, and a layer of an LC medium comprising a

polymerised component and an unpolymerised LC component provided between the two substrates,

wherein the unpolymerised LC component comprises one or more mesogenic or LC compounds that contain an alkenyl group, and wherein the polymerised component is obtained by photopolymerisation of a polymerisable component in the LC medium between the substrates, and

wherein said polymerisable component comprises one or more photosensitive compounds which are polymerisable by

photopolymerisation and have an integral molar extinction coefficient E340-400≥ 1000 L nm cm^'1 mol^"1 in the wavelength range from 340nm to 400nm, and

wherein photopolymerisation of said polymerisable component is carried out by exposing it to UV radiation with a wavelength > 340nm, preferably while applying a voltage to the electrodes at least part-time during said exposure to UV radiation.