LC media

Abstract

The present invention relates to LC media and LC displays comprising these media, in particular to displays addressed by an active matrix, and in particular to displays in IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT mode.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of June 24, 2020, an application number of 202010587078.3, and an invention title of "LC Medium". Technical Field

[0002] The present invention relates to LC (Liquid Crystal) media and LC displays (LCDs) comprising these media, in particular to LCDs addressed by active matrix, and more particularly to LCDs in IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT modes. Background Art

[0003] LCDs are used for information display in many fields. LCDs are used for both direct-view displays and for projection displays. The electro-optical modes used are, for example, twisted nematic (TN), super-twisted nematic (STN), optically compensated bend (OCB) and electrically controlled birefringence (ECB) modes and various variants thereof, as well as other modes. All these modes employ an electric field substantially perpendicular to the substrate or the liquid crystal layer. In addition to these modes, there are also electro-optical modes that employ an electric field substantially parallel to the substrate or the liquid crystal layer, such as the in-plane switching (IPS) mode (such as those disclosed in DE 40 00 451 and EP 0 588 568) and the fringe field switching (FFS) mode, in which there is a strong "fringe field", i.e., a strong electric field close to the electrode edges, and an electric field having both a strong vertical component and a strong horizontal component throughout the liquid crystal cell. These latter two electro-optical modes are particularly used in LCDs in modern desktop monitors and in displays for televisions and multimedia applications. Liquid crystals according to the present invention are preferably used in this type of display. Generally, dielectric positive liquid crystal media with a rather low dielectric anisotropy value are used in FFS displays, but in some cases, liquid crystal media with a dielectric anisotropy of only about 3 or even lower are also used in IPS displays.

[0004] Another development is the so-called PS ("polymer stabilized") or PSA ("polymer stabilized alignment") type displays, for which the term "polymer stabilization" is also occasionally used. In these, a small amount (e.g., 0.3 wt%, typically <1 wt%) of one or more polymerizable compounds, preferably polymerizable monomer compounds, is added to the liquid crystal medium, and after the liquid crystal medium has been filled into the display, it is polymerized or crosslinked in situ (usually by UV photopolymerization), while optionally applying a voltage to the electrodes of the display. The polymerization is carried out at a temperature at which the liquid crystal medium exhibits a liquid crystal phase, usually at room temperature. Adding polymerizable mesogenic or liquid crystal compounds (also called reactive mesogens or "RMs") to the liquid crystal mixture has proven to be particularly suitable.

[0005] For these displays, new liquid crystal dielectrics with improved performance are needed. For many types of applications, it is particularly necessary to improve the addressing time. Therefore, a liquid crystal dielectric with a low viscosity (η), in particular a low rotational viscosity (γ 1 ) is required. In addition to these viscosity parameters, the dielectric must have a nematic range with a suitable width and position and a suitable birefringence (Δn), and the dielectric anisotropy (Δε) should be high enough to allow a reasonably low operating voltage.

[0006] The displays according to the invention are preferably addressed by active matrix (active matrix LCD, abbreviated as AMD), preferably by matrix addressing of thin film transistors (TFTs). However, the liquid crystals according to the invention can also be advantageously used in displays with other known addressing methods.

[0007] Liquid crystal dielectrics suitable for LCDs and especially for IPS displays are known, for example, from the following documents: JP07-181 439(A), EP 0 667 555, EP 0 673 986, DE 195 09 410, DE 195 28 106, DE 195 28107, WO 96 / 23 851, and WO 96 / 28 521. However, these liquid crystal dielectrics have certain disadvantages. Among other disadvantages, most of them result in unfavorably long addressing times, have insufficient resistivity values, and / or require too high an operating voltage. Improvements are necessary both in terms of operating performance and shelf life.

[0008] Especially in the case of using LC dielectrics in the growing public information display (PID) and automotive display markets, high reliability and a wide operating range are extremely important factors. Therefore, for these applications, an LC dielectric with a high clearing temperature (Tni), good LTS (low temperature stability), and high reliability is required. Summary of the Invention

[0009] The object of the present invention is to provide a dielectric, especially for this type of FFS, IPS, TN, or STN display, especially for active matrix displays, such as those of the TFT (thin film transistor) type, which does not show the disadvantages indicated above or shows them only to a lesser extent, and preferably exhibits one or more of the following: a wide operating range, a high clearing temperature, high reliability, a low threshold voltage, a high dielectric constant anisotropy, good low temperature stability (LTS), a low rotational viscosity, and a fast response time

[0010] This object is achieved by providing the LC dielectric as described and claimed below.

[0011] The present invention relates to an LC medium having positive dielectric anisotropy, characterized in that it comprises one or more compounds of formula I, in a concentration > 0 and ≤ 10%

[0012]

[0013] wherein R 1 and R 2 each independently represent an alkyl group having 1 to 6 carbon atoms.

[0014] Preferably, the LC medium has a birefringence < 0.15, more preferably from 0.08 to 0.15.

[0015] The present invention also relates to the use of the LC medium described above for electro-optical purposes, in particular for shutter glasses, for 3D applications, and in IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT displays.

[0016] The present invention also relates to an electro-optical LC display comprising the LC medium described above, in particular an IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT display.

[0017] The present invention also relates to a method for preparing the LC medium described above, which comprises the step of mixing one or more compounds of formula I with one or more other LC compounds and optionally one or more additives.

[0018] In the present application, all atoms also include their isotopes. In particular, one or more hydrogen atoms (H) may be replaced by deuterium (D), which is particularly preferred in some embodiments; highly deuterated compounds enable the analytical determination of compounds or simplify the analytical determination of compounds, especially at low concentrations.

[0019] If R 0 represents an alkyl group and / or an alkoxy group, it may be straight-chain or branched. It is preferably straight-chain and has 2, 3, 4, 5, 6 or 7 carbon atoms, and thus preferably represents ethyl, propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy or heptyloxy, as well as methyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, tridecyloxy or tetradecyloxy. R 0 preferably represents a straight-chain alkyl group having 2 - 6 carbon atoms.

[0020] The oxaalkyl group preferably represents a straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0021] If R 0 represents an alkyl group in which one of the CH 2 groups has been replaced by -CH=CH-, it can be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Thus, it particularly represents vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

[0022] If R 0 represents an alkyl or alkenyl group that is at least monosubstituted by a halogen, the group is preferably straight-chain, and the halogen is preferably F or Cl. In the case of polysubstitution, the halogen is preferably F. The resulting group also includes perfluoro groups. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the ω-position.

[0023] In the formulas of the context, X 0 is preferably F, Cl or a mono- or polyfluorinated alkyl or alkoxy group having 1, 2 or 3 carbon atoms or a mono- or polyfluorinated alkenyl group having 2 or 3 carbon atoms. X 0 is particularly preferably F, Cl, CF 3 , CHF 2 , OCF 3 , OCHF 2 , OCFHCF 3 , OCFHCHF 2 , OCFHCHF 2 , OCF 2 CH 3 , OCF 2 CHF 2 , OCF 2 CHF 2 , OCF2 CF 2 CHF 2 ,OCF 2 CF 2 CHF 2 ,OCFHCF 2 CF 3 ,OCFHCF 2 CHF 2 ,OCF 2 CF 2 CF 3 ,OCF 2 CF 2 CClF 2 ,OCClFCF 2 CF 3 ,OCH=CF 2 or CH=CF 2 ,very particularly preferably F or OCF 3 ,and CF 3 ,OCF=CF 2 ,OCHF 2 or OCH=CF 2 。

[0024] Particularly preferably those in which X 0 represents F or OCF 3 ,preferably compounds of F

[0025] In the compounds of formula I, R 1 and R 2 are preferably selected from ethyl, propyl, butyl and pentyl, all of which are straight-chain

[0026] The preferred compounds of formula I are selected from the following sub-formulas

[0027]

[0028] Very preferably the compound of formula I2

[0029] The concentration of the compounds of formula I and its sub-formulas in the LC medium is preferably 0.2 to 10%, more preferably 1.0 to 10%, very preferably 1.0 to 8%

[0030] Preferably, the LC medium contains 1, 2 or 3 compounds of formula I or its sub-formulas

[0031] The following shows other preferred embodiments of the LC medium according to the invention, including any combination thereof

[0032] - The medium further contains one or more compounds selected from the following formulas

[0033]

[0034] Each of the groups is independent of one another and, each time it appears, has the same or different meanings as follows

[0035] is is

[0036] R 0 is an unsubstituted or halogenated alkyl or alkoxy group having 1 to 15 C atoms, wherein, furthermore, in these groups one or more CH 2 groups may each independently of one another be replaced by -C≡C-, -CF 2 O-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, or represents

[0037] X 0 is F, Cl, CN, SF 5 , SCN, NCS, a halogenated alkyl group having at most 6 C atoms, a halogenated alkenyl group, a halogenated alkoxy group or a halogenated alkenyloxy group, and

[0038] Y 0 is H or CH 3 ,

[0039] Y 1-6 is H or F.

[0040] In the compounds of formulae II and III and their sub-formulae, R 0 preferably represents a straight-chain alkyl group having 1 to 6 carbon atoms, in particular methyl, ethyl or propyl, and an alkenyl group having 2 to 6 carbon atoms, in particular vinyl, 1E-propenyl, 1E-butenyl, 3-butenyl, 1E-pentenyl, 3E-pentenyl or 4-pentenyl.

[0041] -LC medium comprises one or more compounds of formula II in which Y 0 is H, preferably selected from the following sub-formulae

[0042]

[0043] wherein R 0 and X 0 have the meanings given above.

[0044] Preferred compounds are the compounds of formulae II1, II2 and II3, very preferably the compounds of formulae II1 and II2.

[0045] In the compounds of formulae II1 to II7, R 0Preferably represents an alkyl group having 1 to 6 C atoms, very preferably ethyl or propyl, and X 0 Preferably represents F or OCF 3 and very preferably F.

[0046] - The medium comprises one or more compounds of formula II in which Y 0 is CH 3 and is preferably selected from the following sub-formulae

[0047]

[0048]

[0049] wherein R 0 and X 0 have the meanings given above.

[0050] Preferred compounds are those of formulae IIA1, IIA2 and IIA3, and very preferably those of formulae IIA1 and IIA2.

[0051] In the compounds of formulae IIA1 to IIA7, R 0 Preferably represents an alkyl group having 1 to 6 C atoms, very preferably ethyl or propyl, and X 0 Preferably represents F or OCF 3 and very preferably F.

[0052] - The medium comprises one or more compounds of formula III in which Y 0 is H and is preferably selected from the following sub-formulae

[0053]

[0054]

[0055]

[0056]

[0057] wherein R 0 and X 0 have the meanings given above.

[0058] Preferred compounds are those of formulae III1, III4, III6, III16, III19 and III20.

[0059] In the compounds of formulae III1 to III21, R 0 Preferably represents an alkyl group having 1 to 6 C atoms, very preferably ethyl or propyl, X 0 Preferably represents F or OCF 3 and very preferably F, and Y2 Preferably represented by F.

[0060] - The medium comprises one or more compounds of formula III in which Y 0 is CH 3 and is preferably selected from the following sub-formulas

[0061]

[0062]

[0063]

[0064]

[0065] wherein R 0 and X 0 have the meanings given above.

[0066] Preferred compounds are those of formulae IIIA1, IIIA4, IIIA6, IIIA16, IIIA19 and IIIA20.

[0067] Among the compounds of formulae IIIA1 to IIIA21, R 0 is preferably an alkyl group having 1 to 6 C atoms, very preferably ethyl or propyl, X 0 is preferably F or OCF 3 and very preferably F, and Y 2 is preferably represented by F.

[0068] - The medium additionally comprises one or more compounds selected from the following formulae:

[0069]

[0070]

[0071] wherein

[0072] R 0 , X 0 and Y 1-4 have the meanings given above, and

[0073] Z 0 represents -C 2 H 4 -, -(CH 2 ) 4 -, -CH=CH-, -CF=CF-, -C 2 F 4 -, -CH 2 CF 2 -, -CF 2 CH2 -, -CH 2 O-, -OCH 2 -, -COO- or -OCF 2 -, which can also be a single bond in Formulas V and VI, and can also be -CF in Formulas V and VIII 2 O-,

[0074] r represents 0 or 1, and

[0075] s represents 0 or 1;

[0076] - The medium contains one or more compounds of Formula IV selected from the following sub-formulas:

[0077]

[0078]

[0079] wherein R 0 and X 0 have the above meanings.

[0080] R 0 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F or OCF 3 and, in addition, represents OCF=CF 2 or Cl;

[0081] - The medium contains one or more compounds of Formula IVa selected from the following sub-formulas:

[0082]

[0083] wherein R 0 has the above meanings and is preferably propyl or pentyl.

[0084] - The medium contains one or more compounds of Formula IVc selected from the following sub-formulas:

[0085]

[0086] wherein R 0 has the above meanings and is preferably propyl or pentyl.

[0087] - The medium contains one or more compounds of Formula V selected from the following sub-formulas:

[0088]

[0089]

[0090] wherein R 0 and X 0 have the above meanings.

[0091] R 0 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F and OCF 3 and additionally represents OCHF 2 CF 3 OCF═CF 2 and OCH═CF 2 ;

[0092] - The medium comprises one or more compounds of formula VI selected from the following sub-formulas:

[0093]

[0094] wherein R 0 and X 0 have the above meanings.

[0095] R 0 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F, and additionally represents OCF 3 CF 3 CF═CF 2 OCHF 2 and OCH═CF 2 ;

[0096] - The medium comprises one or more compounds of formula VII selected from the following sub-formulas:

[0097]

[0098]

[0099] wherein R 0 and X 0 have the above meanings.

[0100] R 0 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F, and additionally represents OCF 3 OCHF 2 and OCH═CF 2 .

[0101] - The medium additionally comprises one or more compounds selected from the following formula:

[0102]

[0103] wherein X 0 has the above meaning, and

[0104] "alkyl" represents C1-6 -alkyl

[0105] "alkenyl" represents C 2-6 -alkenyl,

[0106] L represents H or F,

[0107] R" represents C 1-6 -alkyl, C 1-6 -alkoxy or C 2-6 -alkenyl,

[0108] R a1 ,R b1 each independently represents CH 3 or C 2 H 5 ,

[0109] i and k each independently are 0, 1, 2 or 3,

[0110] - The medium comprises one or more compounds of formulae IX - XII selected from the following sub - formulae:

[0111]

[0112] wherein "alkyl" has the meaning given in formula IX.

[0113] In formulae IX, IXa and IXb, "alkyl" preferably represents C 2 H 5 , n - C 3 H 7 , n - C 4 H 9 or n - C 5 H 11 ,especially n - C 3 H 7 。

[0114] In formulae IXa and IXb, "alkyl" preferably represents CH 3 or C 2 H 5 ,especially CH 3 。

[0115] - The medium comprises one or more compounds of formulae IX - XII selected from the following sub - formulae;

[0116]

[0117]

[0118] Compounds of formulae IXa2, IXb1, XIa1 and XIa2 are very preferably used.

[0119] - The medium does not contain any compound of the following formula:

[0120]

[0121] wherein L 1 and L 2 each independently represent H or F, R' represents, each time it occurs, identically or differently, an alkyl or alkoxy group having 1 to 12 C atoms, R" represents, each time it occurs, identically or differently, an alkenyl group having 2 to 7 C atoms containing a terminal vinyl group, and R''' represents R' or R".

[0122] - The medium additionally contains one or more compounds selected from the following formulae:

[0123]

[0124] wherein R 3 and R 4 each independently of one another represent a n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl group each having at most 6 C atoms, and preferably each independently of one another represent an alkyl group having 1 to 6 C atoms or an alkenyl group having 2 to 6 C atoms.

[0125] - The medium contains one or more compounds of formula XV selected from the following sub-formulae:

[0126]

[0127] wherein "alkyl" has the above meaning, and preferably represents methyl, ethyl or propyl.

[0128] - The medium contains one or more compounds of formula XV selected from the following sub-formulae:

[0129]

[0130] Compounds of formula XVd1 and XVe1 are very preferably used.

[0131] - The medium contains one or more compounds of formula XVI,

[0132]

[0133] wherein L, R 3 and R 4 have the above meaning and preferably each independently of one another represent an alkyl group having 1 to 6 C atoms.

[0134] Particularly preferred compounds of formula XVI are those of the following sub-formulae

[0135]

[0136]

[0137] wherein

[0138] alkyl and alkyl* each independently of the other represent a straight-chain alkyl group having 1 to 6 carbon atoms, especially ethyl, propyl or pentyl,

[0139] alkenyl and alkenyl* each independently of the other represent a straight-chain alkenyl group having 2 to 6 C atoms, especially CH 2 =CHC 2 H 4 ,CH 3 CH=CHC 2 H 4 ,CH 2 =CH and CH 3 CH=CH.

[0140] Compounds of the formula XVIb, XVIc and XVIg are particularly preferred. Compounds of the following formula are very particularly preferred:

[0141]

[0142] Compounds of the formula XVIc2, XVIg1 and XVIg2 are very preferably;

[0143] - The medium comprises one or more compounds of the following formula;

[0144]

[0145] wherein R 3 and R 4 have the above meanings and preferably each independently of the other represent an alkyl group having 1 to 6 C atoms. L represents H or F;

[0146] - The medium additionally comprises one or more compounds selected from the following formula:

[0147]

[0148]

[0149] wherein R 0 and X 0 each independently of the other have one of the above meanings, and Y 1-4 each independently of the other represents H or F. X 0 is preferably F, Cl, CF 3 ,OCF 3 or OCHF 2 。R 0Preferably represents an alkyl group, an alkoxy group, an oxaalkyl group, a fluoroalkyl group or an alkenyl group, each having up to 6 C atoms.

[0150] Very preferably, the mixture according to the invention comprises one or more compounds of formula XXIa,

[0151]

[0152] wherein R 0 has the above meaning. R 0 Preferably represents a straight-chain alkyl group, especially ethyl, n-propyl, n-butyl and n-pentyl, very particularly preferably n-propyl. The compounds of formula XXI, especially of formula XXIa, are preferably used in the mixture according to the invention in an amount of 1-15% by weight, particularly preferably 2-10% by weight.

[0153] Further preferably, the mixture according to the invention comprises one or more compounds of formula XXIIIa,

[0154]

[0155] wherein R 0 has the above meaning. R 0 Preferably represents a straight-chain alkyl group, especially ethyl, n-propyl, n-butyl and n-pentyl, very particularly preferably n-propyl. The compounds of formula XXIII, especially of formula XXIIIa, are preferably used in the mixture according to the invention in an amount of 0.5-10% by weight, particularly preferably 0.5-5% by weight.

[0156] - The medium additionally comprises one or more compounds of formula XXIV,

[0157]

[0158] wherein R 0 , X 0 and Y 1-6 have the meanings shown in formula I, s represents 0 or 1, and

[0159] represents

[0160] In formula XXIV, X 0 can also represent an alkyl group having 1-6 carbon atoms or an alkoxy group having 1-6 carbon atoms. The alkyl or alkoxy group is preferably straight-chain.

[0161] R 0 Preferably represents an alkyl group having 1 to 6 C atoms. X 0 Preferably represents F;

[0162] - The compounds of formula XXIV are preferably selected from the following formulas:

[0163]

[0164]

[0165] wherein R 0 ,X 0 and Y 1 have the meanings given above. R 0 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F, and Y 1 is preferably F;

[0166] - is preferably f

[0167] -R 0 is a straight-chain alkyl or alkenyl group having 2 to 6 carbon atoms;

[0168] - The medium contains one or more compounds of the following formula;

[0169]

[0170] wherein R 3 and X 0 have the meanings given above. R 3 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F or Cl. In formula XXIV, X 0 very particularly preferably represents Cl.

[0171] - The medium contains one or more compounds of the following formula:

[0172]

[0173] wherein R 3 and X 0 have the meanings given above. R 3 preferably represents an alkyl group having 1 to 6 C atoms. X 0 preferably represents F. The medium according to the invention particularly preferably contains one or more compounds of formula XXIX, wherein X 0 preferably represents F. The compounds of formulas XXVI - XXIX are preferably used in the mixture according to the invention in an amount of 1 - 20% by weight, particularly preferably 1 - 15% by weight. A particularly preferred mixture contains at least one compound of formula XXIX.

[0174] Very preferably, the mixture according to the invention contains one or more compounds of formula XXIXa,

[0175]

[0176] wherein R 3 has the above meaning, and preferably represents a straight-chain alkyl group, in particular ethyl, n-propyl, n-butyl and n-pentyl, very particularly preferably n-propyl. The compounds of formula XXIXa are preferably used in the mixtures according to the invention in an amount of from 1 to 15% by weight, particularly preferably from 2 to 10% by weight.

[0177] - The medium comprises one or more compounds of the following formula

[0178]

[0179] wherein R 3 and R 4 have the above meaning, and preferably each independently represents an alkyl group having 1 to 6 C atoms, very preferably methyl, ethyl or n-propyl.

[0180] Preferred compounds of formula XXX are those of formula XXXa

[0181]

[0182] Further preferred LC media are selected from the following preferred embodiments, including any combination thereof;

[0183] - The medium comprises one or more compounds of formula II, preferably selected from formulae II1, II2 and II3, very preferably selected from formulae II1 and II2. The individual concentration of each of these compounds is preferably from 1 to 15% by weight. The total concentration of these compounds is preferably from 5 to 25% by weight.

[0184] - The medium comprises one or more compounds of formula III, which are preferably selected from formulae III1, III4, III6, III16, III19 and III20, very preferably selected from formulae III16 and III20. The individual concentration of each of these compounds is preferably from 1 to 15% by weight. The total concentration of these compounds is preferably from 2 to 25% by weight.

[0185] - The medium comprises one or more compounds of formula IV, which are preferably selected from formulae IVa or IVc, very preferably selected from formulae IVa1 or IVc1. The individual concentration of each of these compounds is preferably from 1 to 15% by weight. The total concentration of these compounds is preferably from 5 to 25% by weight.

[0186] - The medium comprises one or more compounds of formula IX, preferably selected from formulae IXa and IXb, very preferably selected from formulae IXa2 and Xb1. The individual concentration of each of these compounds is preferably from 1 to 15% by weight. The total concentration of these compounds is preferably from 5 to 25% by weight.

[0187] - The medium contains one or more compounds of formula XI, preferably selected from formulae XIa and XIb. The individual concentration of each of these compounds is preferably 1 to 20% by weight. The total concentration of these compounds is preferably 5 to 25% by weight.

[0188] - The medium contains one or more compounds of formula XII, preferably formula XIIa. The total concentration of these compounds is preferably 3 to 20% by weight.

[0189] - The medium contains one or more compounds of formula XV, preferably selected from formulae XVd and XVe, very preferably selected from formulae XVd1 and XVe1. The individual concentration of each of these compounds is preferably 1 to 10% by weight. The total concentration of these compounds is preferably 2 to 15% by weight.

[0190] - The medium contains one or more compounds of formula XVIc, preferably formula XVIc2. The concentration of these compounds is preferably 1 to 15% by weight.

[0191] - The medium contains one or more compounds of formula XVIg, preferably formula XVIg1 and / or XVIg2. The concentration of these compounds is preferably 5 to 25% by weight.

[0192] - The medium contains one or more compounds of formula XVIIa or XVIIb. The concentration of these compounds is preferably 0.5 - 5% by weight.

[0193] - The medium contains one or more compounds of formula XXI, preferably formula XXIa. The concentration of these compounds is preferably 0.5 to 8% by weight.

[0194] - The medium contains one or more compounds of formula XXIII, preferably formula XXIIIa. The concentration of these compounds is preferably 0.5 - 5% by weight.

[0195] - The medium contains one or more compounds of formula XXIX, preferably formula XXIXa. The concentration of these compounds is preferably 2 to 10% by weight.

[0196] - The medium contains one or more compounds of formula XXX, preferably formula XXXa. The concentration of these compounds is preferably 2 to 10% by weight.

[0197] - The medium contains one or more compounds of formula I and one or more compounds selected from formulae II, III, IV, IX, XI, XII, XV, XVI, XXI, XXIX and XXX.

[0198] - The medium contains one or more compounds of formula I and one or more compounds selected from formulae II1, II2, II3, III1, III4, III6, III16, III19, III20, IVa, IVc, IXa, IXb, XIa, XIb, XIIa, XVd, XVe, XVIc, XXIa, XXIXa and XXXa.

[0199] - In the entire mixture, the proportion of the compounds of formulae II, III, IV, IX, XI, XII, XV, XVI, XXI, XXIX and XXX is 90 - 99% by weight.

[0200] - In the entire mixture, the proportion of the compounds of formulae II1, II2, II3, III1, III4, III6, III16, III19, III20, IVa, IVc, IXa, IXb, XIa, XIb, XIIa, XVd, XVe, XVIc, XXIa, XXIXa and XXXa is 90 - 99% by weight.

[0201] The term "alkyl" or "alkyl*" in this application encompasses straight-chain and branched-chain alkyl groups having 1 to 6 carbon atoms, especially the straight-chain groups methyl, ethyl, propyl, butyl, pentyl and hexyl. Groups having 2 - 5 carbon atoms are generally preferred.

[0202] The term "alkenyl" or “alkenyl*” encompasses straight-chain and branched-chain alkenyl groups having 2 - 6 carbon atoms, especially straight-chain groups. Preferred alkenyl groups are C 2 -C 7 -1E-alkenyl, C 4 -C 6 -3E-alkenyl, especially C 2 -C 6 -1E-alkenyl. Examples of particularly preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl and 5-hexenyl. Groups having at most 5 carbon atoms are generally preferred, especially CH 2 =CH, CH 3 CH=CH.

[0203] The term "fluoroalkyl" preferably encompasses straight-chain groups having a terminal fluorine, i.e., fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of fluorine are not excluded.

[0204] The term "oxaalkyl" or "alkoxy" preferably encompasses the formula C n H2n+1 -O-(CH 2 ) m linear group, where n and m each independently of one another represent from 1 to 6. m can also represent 0. Preferably, n = 1 and m = 1 - 6 or m = 0 and n = 1 - 3.

[0205] By a suitable choice of the meanings of R 0 and X 0 the addressing time, the threshold voltage, the steepness of the transfer characteristic line etc. can be modified in a desired manner. For example, compared with alkyl and alkoxy groups, 1E - alkenyl, 3E - alkenyl, 2E - alkenyloxy etc. generally result in a shorter addressing time, an improved nematic phase tendency and a higher ratio of the elastic constant k 33 (bend) to k 11 (splay). Compared with alkyl and alkoxy groups, 4 - alkenyl, 3 - alkenyl etc. generally have a lower threshold voltage and a lower k 33 / k 11 value. The mixtures according to the invention are particularly characterized by a high Δε value and thus have a significantly faster response time than mixtures of the prior art.

[0206] The optimum mixing ratio of the compounds of the above formula essentially depends on the desired properties, the choice of the components of the above formula and the choice of any other components that may be present.

[0207] A suitable mixing ratio within the above range can be easily determined according to the circumstances.

[0208] The total amount of the compounds of the above formula in the liquid - crystal medium according to the invention is not critical. Thus, for the purpose of optimizing various properties, the mixture can contain one or more other components. However, the greater the observed effect on the desired improvement of the properties of the medium, the higher the total concentration of the compounds of the above formula.

[0209] In a particularly preferred embodiment, the liquid - crystal medium according to the invention contains compounds of formulae IV to VIII (preferably IV and V), where X 0 represents F, OCF 3 , OCHF 2 , OCH = CF 2 , OCF = CF 2 or OCF 2 -CF 2 H. The favorable synergistic effect with the compounds of formulae IA, IIA, IB and IIB results in particularly favorable properties. In particular, mixtures of compounds of formula IA or IIA and IB or IIB are characterized by their low threshold voltage.

[0210] Each of the compounds of the above formula and its sub-formulas that can be used in the liquid crystal medium according to the present invention is known or can be prepared by a method similar to that of known compounds.

[0211] In another preferred embodiment of the present invention, the liquid crystal medium further comprises one or more polymerizable compounds. The polymerizable compounds are preferably selected from formula M

[0212] R a -B 1 -(Z b -B 2 ) m -R b M

[0213] wherein each group, each time it appears, is the same or different, and each is independently of one another as follows:

[0214] R a and R b are P, P-Sp-, H, F, Cl, Br, I, -CN, -NO 2 , -NCO, -NCS, -OCN, -SCN, SF 5 or a straight-chain or branched-chain alkyl group having 1 to 25 C atoms, wherein in addition, one or more non-adjacent CH 2 groups may each independently of one another be replaced by -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 00 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly connected to each other, and wherein in addition, one or more H atoms may be replaced by F, Cl, Br, I, CN, P or P-Sp-, where, if B 1 and / or B 2 contains a saturated C atom, then R a and / or R b may also represent a group spiro-linked to the saturated C atom,

[0215] wherein at least one of the groups R a and R b represents or contains the group P or P-Sp-,

[0216] P is a polymerizable group,

[0217] Sp is a spacer group or a single bond,

[0218] B 1 and B 2is an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted or mono- or polysubstituted by L,

[0219] Z b is -O-, -S-, -CO-, -CO-O-, -OCO-, -O-CO-O-, -OCH 2 -, -CH 2 O-, -SCH 2 -, -CH 2 S-, -CF 2 O-, -OCF 2 -, -CF 2 S-, -SCF 2 -, -(CH 2 ) n1 -, -CF 2 CH 2 -, -CH 2 CF 2 -, -(CF 2 ) n1 -, -CH=CH-, -CF=CF-, -C≡C-, -CH=CH-COO-, -OCO-CH=CH-, CR 0 R 00 or a single bond,

[0220] R 0 and R 00 each independently of one another represent H or an alkyl group having 1 to 12 C atoms,

[0221] m represents 0, 1, 2, 3 or 4,

[0222] n1 represents 1, 2, 3 or 4,

[0223] L is P, P-Sp-, OH, CH 2 OH, F, Cl, Br, I, -CN, -NO 2 , -NCO, -NCS, -OCN, -SCN, -C(=O)N(R x ) 2 , -C(=O)Y 1 , -C(=O)R x , -N(R x ) 2 , an optionally substituted silyl group, an optionally substituted aryl group having 6 to 20 C atoms, or a straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group having 1 to 25 C atoms, where in addition one or more H atoms may be replaced by F, Cl, P or P-Sp-,

[0224] P and Sp have the meanings indicated above,

[0225] Y 1 represents a halogen,

[0226] R x represents P, P-Sp-, H, a halogen, a straight-chain, branched or cyclic alkyl group having 1 to 25 C atoms, where in addition, one or more non-adjacent CH 2 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 directly linked to one another, and where in addition, one or more H atoms may be replaced by F, Cl, P or P-Sp-, 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.

[0227] Particularly preferred compounds of formula I are those in which B 1 and B 2 each independently of one another represent 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl, naphthalene-2,6-diyl, phenanthrene-2,7-diyl, 9,10-dihydrophenanthrene-2,7-diyl, anthracene-2,7-diyl, fluorene-2,7-diyl, coumarin, flavone, where in addition, one or more CH groups in these groups may be replaced by N, cyclohexane-1,4-diyl, where in addition, one or more non-adjacent CH 2 groups may be replaced by O and / or S, 1,4-cyclohexenylene, bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, piperidine-1,4-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, indane-2,5-diyl or octahydro-4,7-methanoindane-2,5-diyl, where all these groups may be unsubstituted or mono- or polysubstituted by L as described above.

[0228] Particularly preferred compounds of formula M are those in which B 1 and B 2 each independently of one another represent 1,4-phenylene, 1,3-phenylene, naphthalene-1,4-diyl or naphthalene-2,6-diyl, and very particularly preferred compounds of formula M are selected from the following formulae:

[0229]

[0230]

[0231]

[0232]

[0233] Each of the groups, each time it appears, is the same or different and, independently of one another, has the following meanings:

[0234] P 1 、P 2 、P 3 is a polymerizable group, preferably selected from vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetanyl and epoxy groups,

[0235] Sp 1 、Sp 2 、Sp 3 is a single bond or a spacer group, wherein, furthermore, the group P 1 -Sp 1 -、P 1 -Sp 2 - and P 3 -Sp 3 - one or more of which may represent R aa , provided that at least one of the groups P 1 -Sp 1 -、P 2 -Sp 2 and P 3 -Sp 3 - is different from R aa , preferably -(CH 2 ) p1 -, -(CH 2 ) p1 -O-, -(CH 2 ) p1 -CO-O- or -(CH 2 ) p1 -O-CO-O-, where p1 is an integer from 1 to 12,

[0236] R aa is H, F, Cl, CN or a straight-chain or branched alkyl group having 1 to 25 C atoms, wherein, furthermore, one or more non-adjacent CH 2 groups may each independently of one another be replaced by -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that O and / or S atoms are not directly linked to one another, and wherein, furthermore, one or more H atoms may be replaced by F, Cl, CN or P 1 -Sp 1- alternatively, particularly preferably a straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group having 1 to 12 C atoms (wherein the alkenyl and alkynyl groups have at least two C atoms and the branched groups have at least three C atoms),

[0237] R 0 、R 00 is H or an alkyl group having 1 to 12 C atoms,

[0238] R y and R z are H, F, CH 3 or CF 3 ,

[0239] X 1 、X 2 、X 3 is -CO-O-, -O-CO- or a single bond,

[0240] Z M1 is -O-, -CO-, -C(R y R z )- or -CF 2 CF 2 -,

[0241] Z M2 ,Z M3 is -CO-O-, -O-CO-, -CH 2 O-, -OCH 2 -, -CF 2 O-, -OCF 2 -, or -(CH 2 ) n -, where n is 2, 3 or 4,

[0242] L is F, Cl, CN or a straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy group having 1 to 12 C atoms,

[0243] L', L" are H, F or Cl,

[0244] k is 0 or 1

[0245] r is 0, 1, 2, 3 or 4,

[0246] s is 0, 1, 2 or 3,

[0247] t is 0, 1 or 2,

[0248] x is 0 or 1.

[0249] Particularly preferred are the compounds of formulas M2 and M13.

[0250] Further preferred are the tri-reactive compounds M15 to M31, especially M17, M18, M19, M22, M23, M24, M25, M30, M31 and M32.

[0251] Among the compounds of formulas M1 to M32, the group

[0252] is preferably

[0253]

[0254] wherein L, each time it occurs, is the same or different and has one of the meanings given in the context, and preferably F, Cl, CN, NO 2 , CH 3 , C 2 H 5 , C(CH 3 ) 3 , CH(CH 3 ) 2 , CH 2 CH(CH 3 )C 2 H 5 , OCH 3 , OC 2 H 5 , COCH 3 , COC 2 H 5 , COOCH 3 , COOC 2 H 5 , CF 3 , OCF 3 , OCHF 2 , OC 2 F 5 or P-Sp-, very preferably F, Cl, CN, CH 3 , C 2 H 5 , OCH 3 , COCH 3 , OCF 3 or P-Sp-, more preferably F, Cl, CH 3 , OCH 3 , COCH 3 or OCF 3 , especially F or CH 3 .

[0255] Preferred compounds of formulas M1 to M32 are those in which P 1, P 2 and P 3 Those representing acrylate group, methacrylate group, oxetanyl group or epoxy group (acrylate group or methacrylate group are highly preferred).

[0256] Further preferred compounds of formulas M1 to M32 are those in which Sp 1 , Sp 2 and Sp 3 are single bonds.

[0257] Further preferred compounds of formulas M1 to M32 are those in which one of Sp 1 , Sp 2 and Sp 3 is a single bond and the other of Sp 1 , Sp 2 and Sp 3 is different from a single bond.

[0258] Further preferred compounds of formulas M1 to M32 are those in which the groups Sp different from single bonds 1 , Sp 2 and Sp 3 represent -(CH 2 ) s1 -X"- where s1 is an integer from 1 to 6, preferably 2, 3, 4 or 5, and X" is a linking group to the benzene ring and is -O-, -O-CO-, -CO-O-, -O-CO-O- or a single bond.

[0259] Further preferred polymerizable compounds of formulas M1 to M32 are those selected from Table D below.

[0260] Particularly preferred is a liquid crystal medium comprising one, two or three polymerizable compounds of formula M (preferably selected from formulas M1 to M32).

[0261] Preferably, the proportion of the polymerizable compounds (including those of formula M and its sub-formulas) in the liquid crystal medium is 0.01 to 5%, very preferably 0.05 to 1%, and most preferably 0.1 to 0.5%.

[0262] It has been observed that adding one or more polymerizable compounds of formula M to the liquid crystal medium results in favorable properties such as fast response time. Such a liquid crystal medium is particularly suitable for PSA displays, in which it shows low image sticking, fast and complete polymerization, rapid generation of a low pretilt angle (which is stable after UV exposure), high reliability, a high VHR value after UV exposure and a high birefringence. By appropriately selecting the polymerizable compounds, the absorption of the liquid crystal medium at longer UV wavelengths can be increased, so that such longer UV wavelengths can be used for polymerization, which is advantageous for the display manufacturing process.

[0263] The polymerizable group P is a group suitable for polymerization reactions (such as free radical or ionic chain polymerization, addition polymerization or condensation polymerization), or a group suitable for polymer-analogous reactions (such as addition or condensation on the polymer backbone). Groups particularly preferred for chain polymerization, especially those containing a C═C double bond or a —C≡C— triple bond, and groups suitable for ring-opening polymerization, such as oxetanyl or epoxy groups, are preferred.

[0264] Preferred groups P are selected from CH 2 ═CW 1 —CO—O—, CH 2 ═CW 1 —CO—, CH 2 ═CW 2 —(O) k3 —, CW 1 ═CH—CO—(O) k3 —, CW 1 ═CH—CO—NH—, CH 2 ═CW 1 —CO—NH—, CH 3 —CH═CH—O—, (CH 2 ═CH) 2 CH—OCO—, (CH 2 ═CH—CH 2 ) 2 CH—OCO—, (CH 2 ═CH) 2 CH—O—, (CH 2 ═CH—CH 2 ) 2 N—, (CH 2 ═CH—CH 2 ) 2 N—CO—, HO—CW 2 W 3 —, HS—CW 2 W 3 —, HW 2 N—, HO—CW 2 W 3 —NH—, CH 2 ═CW 1 —CO—NH—, CH 2 ═CH—(COO) k1 —Phe—(O) k2 —, CH 2 ═CH—(CO) k1 —Phe—(O) k2-, Phe-CH=CH-, HOOC-, OCN- and W 4 W 5 W 6 Si-, where W 1 represents H, F, Cl, CN, CF 3 , phenyl or an alkyl group having 1 to 5 C atoms, especially H, F, Cl or CH 3 , W 2 and W 3 each independently of one another represent H or an alkyl group having 1 to 5 C atoms, especially H, methyl, ethyl or n-propyl, W 4 , W 5 and W 6 each independently of one another represent Cl, an oxaalkyl group or an oxacarbonylalkyl group having 1 to 5 C atoms, W 7 and W 8 each independently of one another represent H, Cl or an alkyl group having 1 to 5 C atoms, Phe represents 1,4-phenylene, which is optionally substituted by one or more groups L different from P-SP- as defined above, k 1 , k 2 and k 3 each independently of one another represent 0 or 1, k 3 preferably represents 1, and k 4 represents an integer from 1 to 10.

[0265] The very preferred group P is selected from CH 2 =CW 1 -CO-O-, CH 2 =CW 1 -CO-, CH 2 =CW 2 -O-, CH 2 =CW 2 -, CW 1 =CH-CO-(O) k3 - CW 1 =CH-CO-NH-, CH 2 =CW 1 -CO-NH-, (CH 2 =CH) 2 CH-OCO-, (CH 2 =CH-CH 2 ) 2 CH-OCO-, (CH 2 =CH) 2 CH-O-, (CH 2 =CH-CH 2 ) 2 N-, (CH2 =CH-CH 2 ) 2 N-CO-, CH 2 =CW 1 -CO-NH-, CH 2 =CH-(COO) k1 -Phe-(O) k2 -, CH 2 =CH-(CO) k1 -Phe-(O) k2 -, Phe-CH=CH- and W 4 W 5 W 6 Si-, where W 1 represents H, F, Cl, CN, CF 3 , phenyl or an alkyl group having 1 to 5 C atoms, especially H, F, Cl or CH 3 , W 2 and W 3 each independently of one another represents H or an alkyl group having 1 to 5 C atoms, especially H, methyl, ethyl or n-propyl, W 4 , W 5 and W 6 each independently of one another represents Cl, an oxaalkyl group or an oxacarbonylalkyl group having 1 to 5 C atoms, W 7 and W 8 each independently of one another represents H, Cl or an alkyl group having 1 to 5 C atoms, Phe represents 1,4-phenylene, k 1 , k 2 and k 3 each independently of one another represents 0 or 1, k 3 preferably represents 1, and k 4 represents an integer from 1 to 10.

[0266] A very particularly preferred group P is selected from CH 2 =CW 1 -CO-O-, especially CH 2 =CH-CO-O-, CH 2 =C(CH 3 )-CO-O- and CH 2 =CF-CO-O-, furthermore represents CH 2 =CH-O-, (CH 2 =CH) 2 CH-O-CO-, (CH 2 =CH) 2 CH-O-,

[0267] More preferably, the polymerizable group P is selected from vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetanyl and epoxy group, and most preferably selected from acrylate and methacrylate groups.

[0268] If Sp is different from a single bond, it preferably has the formula Sp"-X", so that the corresponding group P-Sp- conforms to the formula P-Sp"-X"-, where

[0269] Sp" represents an alkylene group having 1 to 20, preferably 1 to 12 C atoms, which is optionally mono- or polysubstituted by F, Cl, Br, I or CN and in which furthermore, one or more non-adjacent CH 2 groups can each independently of one another be replaced by -O-, -S-, -NH-, -N(R 0 )-, -Si(R 0 R 00 )-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -S-CO-, -CO-S-, -N(R 00 )-CO-O-, -O-CO-N(R 0 )-, -N(R 0 )-CO-N(R 00 )-, -CH=CH- or -C≡C- in such a way that O and / or S atoms are not directly linked to one another,

[0270] X" represents -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, -CO-N(R 0 )-, -N(R 0 )-CO-, -N(R 0 )-CO-N(R 00 )-, -OCH 2 -, -CH 2 O-, -SCH 2 -, -CH 2 S-, -CF 2 O-, -OCF 2 -, -CF 2 S-, -SCF 2 -, -CF 2 CH 2 -, -CH 2 CF 2 -, -CF 2 CF 2 -, -CH=N-, -N=CH-, -N=N-, -CH=CR 0 -, -CY 2 =CY 3-, -C≡C-, -CH=CH-CO-O-, -O-CO-CH=CH- or a single bond,

[0271] R 0 and R 00 each independently represent H or an alkyl group having 1 to 20 C atoms, and

[0272] Y 2 and Y 3 each independently represent H, F, Cl or CN.

[0273] X" is preferably -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR 0 -, -NR 0 -, -NR 0 -CO-, -NR 00 - or a single bond.

[0274] Typical spacer groups Sp and -Sp"-X"- are for example -(CH 2 ) p1 -, -(CH 2 CH 2 O) q1 -CH 2 CH 2 -, -CH 2 CH 2 -S-CH 2 CH 2 -, -CH 2 CH 2 -NH-CH 2 CH 2 - or -(SiR 0 R 00 -O) p1 -, where p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R 0 and R 00 have the meanings indicated above.

[0275] Particularly preferred groups Sp and -Sp”-X”- are -(CH 2 ) p1 -, -(CH 2 ) p1 -O-, -(CH 2 ) p1 -O-CO-, -(CH 2 ) p1 -CO-O-, -(CH 2 ) p1 -O-CO-O-, where p1 and q1 have the meanings indicated above.

[0276] Particularly preferred groups Sp" are, in each case, straight-chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethyl-N-methylimino-ethylene, 1-methylalkylene, vinylidene, propenylene and butenylene.

[0277] For the production of PSA displays, the polymerizable compounds comprised in the liquid-crystalline medium are polymerized or crosslinked (if a compound comprises two or more polymerizable groups) by in-situ polymerization in the liquid-crystalline medium between the substrates of the LC display, optionally with the application of a voltage to the counter electrode.

[0278] The structure of the PSA displays according to the invention corresponds to the usual geometry of PSA displays as described in the prior art cited at the beginning. A geometry without protrusions is preferred, in particular those in which, furthermore, the electrode on the color filter side is unstructured and only the electrode on the TFT side has slots. A particularly suitable and preferred electrode structure for PS-VA displays is described, for example, in US 2006 / 0066793 A1.

[0279] The combination of the compounds of the above preferred embodiments with the above polymerized compounds results in a low threshold voltage, low rotational viscosity and very good low-temperature stability in the liquid-crystalline medium according to the invention, while maintaining a constantly high clearing point and high VHR value.

[0280] The use of a liquid-crystalline medium containing polymerizable compounds allows a particularly low pretilt angle to be established rapidly in PSA displays. In particular, the liquid-crystalline medium exhibits a significantly shortened response time, in particular also the gray-scale response time, in PSA displays compared with the media of the prior art.

[0281] Liquid-crystalline media which preferably have a nematic liquid-crystalline phase and preferably do not have a chiral liquid-crystalline phase are generally preferred.

[0282] The invention also relates to the use of a liquid-crystalline medium according to the invention as described in context for electro-optical purposes, in particular for shutter glasses, for 3D applications, in IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT displays, and to electro-optical displays, in particular electro-optical displays of the above type, containing a liquid-crystalline medium according to the invention as described in context, in particular IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT displays.

[0283] The invention also relates to electro-optical displays, such as STN or MLC displays, having two plane-parallel outer plates (which together with the frame form a cell), integrated non-linear elements for switching the individual pixels on the outer plates, and a nematic liquid crystal mixture having positive dielectric anisotropy and high specific resistance located in the cell, wherein the nematic liquid crystal mixture is a liquid crystal medium according to the invention as described in the context.

[0284] The liquid crystal medium according to the invention enables a significant expansion of the range of achievable parameters. The combination of achievable clearing points, viscosities at low temperatures, thermal and UV stabilities, and high optical anisotropy is much superior to the materials hitherto known in the prior art.

[0285] The liquid crystal medium according to the invention is suitable for mobile applications and TFT applications, such as mobile phones and PDAs. In addition, the liquid crystal medium according to the invention is particularly suitable for use in FFS and IPS displays.

[0286] The liquid crystal medium according to the invention preferably retains the nematic phase down to -20 °C, very preferably down to -30 °C, and most preferably down to -40 °C. The liquid crystal medium according to the invention preferably has a clearing point of ≥ 85 °C, very preferably ≥ 95 °C, and most preferably ≥ 105 °C.

[0287] The liquid crystal medium according to the invention preferably has a rotational viscosity γ of ≤ 130 mPa·s, very preferably ≤ 115 mPa·s 1 , whereby an excellent MLC display with a fast response time can be obtained. The rotational viscosity is measured at 20 °C.

[0288] In a preferred embodiment, the dielectric anisotropy Δε of the liquid crystal medium according to the invention at 20 °C is preferably ≥ +4, very preferably ≥ +6, and most preferably ≥ +8.

[0289] The liquid crystal medium according to the invention preferably has a birefringence Δn in the range from 0.080 to 0.150, more preferably from 0.090 to 0.140, and particularly preferably from 0.100 to 0.130 at 20 °C.

[0290] The nematic phase range of the liquid crystal medium according to the invention preferably has a width of at least 100 °, more preferably at least 110 °, and especially at least 130 °. This range preferably extends at least from -25 °C to +105 °C.

[0291] It goes without saying that by a suitable selection of the components of the liquid crystal medium according to the invention, a higher clearing point (e.g. above 100 °C) can also be achieved at a higher threshold voltage or a lower clearing point at a lower threshold voltage while retaining other advantageous properties. A liquid crystal medium with a higher Δε and thus a low threshold can also be obtained at a correspondingly only slightly increased viscosity. The MLC display according to the invention preferably operates at the first Gooch and Tarry transmission minimum [C.H. Gooch and H.A. Tarry, Electron. Lett. 10, 2 - 4, 1974; C.H. Gooch and H.A. Tarry, Appl. Phys., Vol. 8, 1575 - 1584, 1975], where, in addition to particularly advantageous electro-optical properties such as a high steepness of the characteristic line and a low angular dependence of the contrast (German Patent 30 22 818), a lower dielectric anisotropy is sufficient at the same threshold voltage as in a similar display at the second minimum. This enables a significantly higher resistivity value to be obtained with the mixtures according to the invention at the first minimum than in the case of liquid crystal media containing cyano compounds. By a suitable selection of the individual components and their weight ratios, the person skilled in the art can set the birefringence required for a predetermined layer thickness for the MLC display using simple conventional methods.

[0292] Measurement of the voltage holding ratio (HR) [S. Matsumoto et al., Liquid Crystals 5 , 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); G. Weber et al., Liquid Crystals 5 , 1381 (1989)] has shown that the liquid crystal media according to the invention containing compounds of formulae ST-1, ST-2, RV, IA and IB show a significantly smaller decrease in HR upon UV exposure compared to similar mixtures containing cyanophenylcyclohexanes of formula or esters of formula (but not compounds of formula I ST-1, ST-2, RV, IA and IB).

[0293] The liquid crystal media according to the invention have significantly better light stability and UV stability, i.e. they show a significantly smaller decrease in HR when exposed to light, heat or UV.

[0294] The structure of the MLC display according to the invention, which consists of a polarizer, an electrode substrate, and a surface-treated electrode, corresponds to the conventional design of such displays. The term "conventional design" is understood here in a broad sense and also includes all derivatives and variants of MLC displays, in particular matrix display elements based on polysilicon TFTs or MIMs.

[0295] However, a significant difference between the display according to the invention and the conventional displays based on twisted nematic cells to date lies in the selection of the liquid crystal parameters of the liquid crystal layer.

[0296] The liquid crystal medium that can be used according to the invention is prepared in a conventional manner per se, for example by mixing one or more compounds of claim 1 with one or more compounds of formula IV-XXX or with other liquid crystal compounds and / or additives. Generally, the desired amounts of the components to be used in smaller amounts are advantageously dissolved in the components constituting the main component at an elevated temperature. It is also possible to mix solutions of the components in an organic solvent, such as a solution in acetone, chloroform, or methanol, and then remove the solvent, for example by distillation, after thorough mixing.

[0297] The liquid crystal medium can also contain other additives known to those skilled in the art and described in the literature, such as polymerization initiators, inhibitors, surface-active substances, light stabilizers, antioxidants, such as BHT, TEMPOL, microparticles, radical scavengers, nanoparticles, etc. For example, 0-15% of a polychromatic dye or a chiral dopant or an initiator such as or Suitable stabilizers and dopants are mentioned in Tables C and D below.

[0298] In a preferred embodiment, the liquid crystal medium contains one or more chiral dopants, preferably in a concentration of 0.01 to 1% by weight, very preferably 0.05 to 0.5% by weight. The chiral dopants are preferably selected from the compounds of Table B below, very preferably from R- or S-1011, R- or S-2011, R- or S-3011, R- or S-4011, and R- or S-5011.

[0299] In another preferred embodiment, the liquid crystal medium contains a racemate of one or more chiral dopants, which are preferably selected from the chiral dopants mentioned in the previous paragraph.

[0300] In another preferred embodiment of the invention, the liquid crystal medium contains one or more other stabilizers, which are preferably selected from the following formula

[0301]

[0302] where each group, independently of one another and each time it occurs, is the same or different and has the following meanings

[0303] R a-d is a straight-chain or branched alkyl group having 1 to 10, preferably 1 to 6, very preferably 1 - 4 C atoms, most preferably methyl

[0304] X S is H, CH 3 , OH or O ● ,

[0305] A S is an optionally substituted straight-chain, branched-chain or cyclic alkylene group having 1 to 20 C atoms

[0306] n is an integer from 1 to 6, preferably 3.

[0307] Preferred stabilizers of formula S3 are selected from formula S3A

[0308]

[0309] wherein n2 is an integer from 1 to 12, and wherein one or more H atoms in the group (CH 2 ) n2 are optionally replaced by methyl, ethyl, propyl, butyl, pentyl or hexyl.

[0310] Very preferred stabilizers are selected from the following formula

[0311]

[0312]

[0313]

[0314] In a preferred embodiment, the liquid crystal medium comprises one or more stabilizers selected from formulas S1-1, S2-1, S3-1, S3-1 and S3-3.

[0315] In a preferred embodiment, the liquid crystal medium comprises one or more stabilizers selected from Table D.

[0316] Preferably, the proportion of the stabilizer (such as those of formulas S1 - S3) in the liquid crystal medium is 10 to 500 ppm, very preferably 20 to 100 ppm.

[0317] In another preferred embodiment, the LC medium according to the invention comprises a self-aligning (SA) additive, preferably at a concentration of 0.1 to 2.5%.

[0318] The preferred SA additive used in this preferred embodiment is selected from compounds comprising a mesogenic group and a straight-chain or branched alkyl side chain terminated by one or more polar anchoring groups selected from hydroxyl, carboxyl, amino or thiol groups.

[0319] Further preferred SA additives contain one or more polymerizable groups which may optionally be linked to the mesogenic group via a spacer group. These polymerizable SA additives can be polymerized in the LC medium under conditions similar to those applied for RM in the PSA method.

[0320] Suitable SA additives are disclosed, for example, in US 2013 / 0182202A1, US 2014 / 0838581 A1, US 2015 / 0166890 A1 and US 2015 / 0252265 A1.

[0321] In another preferred embodiment, the LC medium or polymer-stabilized display according to the invention contains one or more self-aligning additives selected from Table E below.

[0322] In a preferred embodiment, the display according to the invention does not contain an alignment layer.

[0323] In addition, the following substances can be added to the liquid crystal medium, for example 0 - 15% by weight of a dichroic dye, and also nanoparticles, conductive salts for improving conductivity, preferably complex salts of ethyl dimethyldodecylammonium 4 - hexyloxybenzoate, tetrabutylammonium tetraphenylborate or crown ethers (see, for example, Haller et al., Mol. Cryst. Liq. Cryst. 24 , 249 - 258 (1973)), or substances for changing the dielectric anisotropy, viscosity and / or nematic alignment. Such substances are described, for example, in DE - A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728. Detailed Description

[0324] In this application and the following examples, the structures of the liquid crystal compounds are represented by acronyms and converted into chemical formulas according to Table A below. All groups C n H 2n+1 and C m H 2m+1 are straight-chain alkyl groups having n and m C atoms, respectively; n, m and k are integers and preferably represent 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding in Table B is self-explanatory. In Table A, only the acronyms of the parent structures are indicated. In each case, the acronym of the parent structure is followed by the substituents R 1* , R 2* , L 1* and L 2* encoded as follows:

[0325]

[0326] Preferred mixture components are shown in Tables A and B.

[0327] Table A

[0328]

[0329]

[0330]

[0331] Table B

[0332] In the following formula, n and m each independently of one another represent 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, in particular 2, 3, 5, and furthermore 0, 4, 6.

[0333]

[0334]

[0335]

[0336]

[0337]

[0338]

[0339]

[0340]

[0341]

[0342] Particularly preferred is a liquid crystal medium which, in addition to the compound of formula I, further comprises at least one, two, three, four or more compounds from Table B.

[0343] Table C

[0344] Table C indicates possible dopants which are usually added to the liquid crystal medium according to the invention. The liquid crystal medium preferably comprises 0 - 10% by weight, in particular 0.01 - 5% by weight and particularly preferably 0.01 - 3% by weight of dopants.

[0345]

[0346]

[0347] Table D

[0348] Stabilizers that can be additionally added to the liquid crystal medium according to the invention in an amount of 0-10% by weight are mentioned below.

[0349]

[0350]

[0351]

[0352]

[0353]

[0354] Table E

[0355] Table E shows exemplary reactive mesogenic compounds (RM) that can be used in the liquid crystal medium according to the invention.

[0356]

[0357]

[0358]

[0359]

[0360]

[0361]

[0362]

[0363]

[0364]

[0365]

[0366]

[0367]

[0368]

[0369]

[0370]

[0371]

[0372]

[0373]

[0374]

[0375] In a preferred embodiment, the liquid crystal medium according to the invention comprises one or more polymerizable compounds, preferably selected from the polymerizable compounds of the formulas RM-1 to RM-143. Among these, the compounds RM-1, RM-4, RM-8, RM-17, RM-19, RM-35, RM-37, RM-39, RM-40, RM-41, RM-48, RM-52, RM-54, RM-57, RM-64, RM-74, RM-76, RM-88, RM-102, RM-103, RM-109, RM-117, RM-120, RM-121 and RM-122 are particularly preferred.

[0376] Table E

[0377] Table E shows self-aligning additives for vertical alignment, which can be used together with the polymerizable compounds of formula I in the LC medium according to the invention;

[0378]

[0379]

[0380]

[0381]

[0382]

[0383]

[0384]

[0385]

[0386]

[0387]

[0388]

[0389] In a preferred embodiment, the LC medium and the display according to the invention comprise one or more SA additives selected from the formulas SA-1 to SA-48, preferably from the formulas SA-14 to SA-48, very preferably from the formulas SA-20 to SA-34 and SA-48, preferably in combination with one or more RM of the formula M.

[0390] The following examples are intended to illustrate the invention and not to limit it.

[0391] In the foregoing and in the following, all percentage data represent percentages by weight and relate to the entire corresponding mixture, including all solid or liquid crystal components, and excluding solvents, unless otherwise expressly specified. In addition, unless otherwise expressly specified, all temperatures are given in degrees Celsius (°C). m.p. represents the melting point and cl.p. = the clearing point. Furthermore, C = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols represent transition temperatures.

[0392] Furthermore, the following abbreviations and symbols are used:

[0393] V 0 Threshold voltage at 20 °C, capacitive [V],

[0394] n e Extraordinary refractive index at 20 °C and 589 nm,

[0395] n o Ordinary refractive index at 20 °C and 589 nm,

[0396] △n Optical anisotropy at 20 °C and 589 nm,

[0397] ε ⊥ Dielectric constant perpendicular to the director at 20 °C and 1 kHz,

[0398] ε || Dielectric constant parallel to the director at 20 °C and 1 kHz,

[0399] △ε Dielectric anisotropy at 20 °C and 1 kHz,

[0400] cl.p., T ni Clearing point [°C],

[0401] γ 1 Rotational viscosity at 20 °C [mPa·s],

[0402] K 1 Elastic constant, "splay" deformation at 20 °C [pN],

[0403] K 2Elastic constant, "twist" deformation at 20 °C [pN],

[0404] K 3 Elastic constant, "bend" deformation at 20 °C [pN].

[0405] Unless otherwise explicitly specified in each case, all physical properties are determined according to and have been determined according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", Status, November 1997, Merck KGaA, Germany and apply to a temperature of 20 °C.

[0406] Unless otherwise explicitly specified, the term "threshold voltage" used in the present invention refers to the capacitive threshold (V 0 ), which is also referred to as the Freedericks threshold. In the examples, as usual, the optical threshold can also be indicated for a relative contrast of 10% (V 10 ).

[0407] Comparative Example 1

[0408] LC mixture C1 is formulated as follows:

[0409]

[0410] 0.05% of stabilizer S2-1 is added to 99.95% of mixture C1:

[0411]

[0412] 0.05% of stabilizer S2-1 and 0.1% of stabilizer S3-1 are added to 99.85% of the resulting LC mixture to obtain mixture C11.

[0413]

[0414] Example 1

[0415] LC mixture N1 is formulated as follows:

[0416]

[0417] The mixture contains 1.0% of the compound CPGP-5-2 of formula I.

[0418] 0.1% of stabilizer S3-1 is added to 99.9% of mixture N1 to obtain mixture N11.

[0419] Example 2

[0420] The LC mixture N2 is prepared as follows:

[0421]

[0422] The mixture contains 1.0% of the compound CPGP-5-2 of formula I.

[0423] 0.1% of the stabilizer S3-1 is added to 99.9% of the mixture N2 to obtain the mixture N22.

[0424] VHR value

[0425] Before and after exposure using an LED lamp, the VHR values of the mixtures C11, N11, and N22 are measured in a VHR test cell at 100°C, 3 Hz, and 1 V.

[0426] The results are shown in Table 1.

[0427] Table 1 - VHR values before and after BL load, 3Hz / 100 °C

[0428]

[0429]

[0430] As can be seen from Table 1, before and after backlight stress, both the mixtures N11 and N22 according to the invention containing the compound of formula I show significantly higher VHR values than the mixture C11.

[0431] Comparative Example 2

[0432] The LC mixture C2 is prepared as follows:

[0433]

[0434] This mixture does not show satisfactory LTS.

[0435] Example 3

[0436] The LC mixture N3 is prepared as follows:

[0437]

[0438]

[0439] The mixture contains 0.5% of the compound CPGP-5-2 of formula I.

[0440] Example 4

[0441] The LC mixture N4 is formulated as follows:

[0442]

[0443]

[0444] The mixture contains 1.0% of the compound CPGP-5-2 of formula I and shows good LTS at -20 °C.

[0445] Example 5

[0446] The LC mixture N5 is formulated as follows:

[0447]

[0448] The mixture contains 2.0% of the compound CPGP-5-2 of formula I and shows good LTS at -20 °C.

[0449] Example 6

[0450] The LC mixture N6 is formulated as follows:

[0451]

[0452] The mixture contains 4.0% of the compound CPGP-5-2 of formula I and shows good LTS at -20 °C and -30 °C.

[0453] Example 7

[0454] The LC mixture N7 is formulated as follows:

[0455]

[0456]

[0457] The mixture contains 6.0% of the compound CPGP-5-2 of formula I and shows good LTS at -20 °C, -30 °C and -40 °C.

[0458] VHR value

[0459] At 60 °C, 60 Hz / 3 Hz and 1 V, in a VHR test cell, the change in the VHR value of mixtures C2, N4, N5, N6 and N7 before and after varying exposure using an LED lamp was measured.

[0460] The results are shown in Tables 2 and 3.

[0461] Table 2 - VHR values before and after BL load, 60Hz / 60 °C

[0462]

[0463]

[0464] Table 3 - VHR values before and after BL load, 3Hz / 60 °C

[0465]

[0466] As can be seen from Tables 2 and 3, the mixture N4-N7 of the inclusion compound I according to the present invention shows a higher VHR value than the mixture C2 after backlight stress.

[0467] Example 8

[0468] 0.05% of stabilizer S1-1 was added to 99.95% of the LC mixture of Example 7.

[0469]

[0470] Example 9

[0471] 0.05% of stabilizer S1-1 and 0.3% of monomer RM-1 were added to 99.65% of the LC mixture of Example 7.

[0472]

[0473] Example 10

[0474] 0.3% of monomer RM-35 was added to 99.7% of the LC mixture of Example 7.

[0475]

[0476] Example 11

[0477] 0.05% of stabilizer S2-1 and 0.3% of monomer RM-64 were added to 99.65% of the LC mixture of Example 7.

[0478]

[0479] Example 12

[0480] 0.3% of monomer RM-120 was added to 99.7% of the LC mixture of Example 6.

[0481]

[0482] Example 13

[0483] Add 0.3% of monomer RM-19 and 0.001% of Irgacure to 99.699% of the LC mixture of Example 5.

[0484]

[0485] Example 14

[0486] Add 0.3% of monomer RM-121 to 99.7% of the LC mixture of Example 4.

[0487]

[0488] Example 15

[0489] Add 0.3% of monomer RM-122 to 99.7% of the LC mixture of Example 6.

[0490]

[0491] Example 16

[0492] Add 0.3% of monomer RM-91 to 99.7% of the LC mixture of Example 7.

[0493]

[0494] Example 17

[0495] Add 0.02% of stabilizer S1-1 to 99.98% of the LC mixture of Example 7.

[0496] Example 18

[0497] Add 0.01% of stabilizer S2-1 to 99.99% of the LC mixture of Example 7.

[0498]

[0499] Example 19

[0500] Add 0.02% of stabilizer S3-1 to 99.98% of the LC mixture of Example 3.

[0501]

[0502] Example 20

[0503] 0.05% of stabilizer S3-2 was added to 99.95% of the LC mixture of Example 6.

[0504]

[0505] Example 21

[0506] 0.02% of stabilizer S3-3 was added to 99.98% of the LC mixture of Example 7.

[0507]

[0508] Example 22

[0509] 0.3% of monomer RM-39 was added to 99.7% of the LC mixture of Example 4.

[0510]

Claims

1. An LC medium having positive dielectric anisotropy, characterized in that it contains one or more compounds of formula I, in a concentration > 0 and ≤ 10% wherein R 1 and R 2 each independently represent an alkyl group having 1 to 6 C atoms, and further contains one or more compounds selected from formulae III20, XV and XVI: wherein R 0 represents an unsubstituted or halogenated alkyl or alkoxy group having 1 to 15 C atoms, wherein, furthermore, one or more CH 2 groups may each independently of one another be replaced by -C≡C-, -CF 2 O-, -CH=CH-, -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, or represents X 0 represents F, Cl, CN, SF 5 , SCN, NCS, a haloalkyl group, a haloalkenyl group, a haloalkoxy group or a haloalkenyloxy group having at most 6 C atoms where R 3 and R 4 each independently of the other represents a n-alkyl, alkoxy, oxa-alkyl, fluoroalkyl or alkenyl group each having at most 6 C atoms, and preferably each independently of the other represents an alkyl group having 1 to 6 C atoms or an alkenyl group having 2 to 6 C atoms, and L represents H or F.

2. The LC medium according to claim 1, characterized in that it has a birefringence < 0.

15.

3. The LC medium according to claim 1 or 2, characterized in that it contains one or more compounds of formula I selected from the following sub-formulae 4. The LC medium according to one or more of claims 1 to 3, characterized in that the concentration of the compound of formula I or its sub-formulae in the LC medium is 1.0 to 10%.

5. The LC medium according to one or more of claims 1 to 4, characterized in that it further contains one or more compounds selected from the following formulae: wherein each group is independent of one another and, each time it appears, has the following meaning, the same or different is is R 0 is an unsubstituted or halogenated alkyl or alkoxy group having 1 to 15 C atoms, wherein furthermore one or more CH 2 groups may each independently of one another be replaced by -C≡C-, -CF 2 O-, -CH=CH- -O-, -CO-O- or -O-CO- in such a way that the O atoms are not directly linked to one another, or represents X 0 is F, Cl, CN, SF 5 , SCN, NCS, a haloalkyl group having at most 6 C atoms, a haloalkenyl group, a haloalkoxy group or a haloalkenyloxy group, and Y 0 is H or CH 3, Y 1-6 is H or F.

6. The LC medium according to one or more of claims 1 to 5, characterized in that it contains one or more compounds selected from the following sub-formulae wherein R 0 and X 0 have the meanings given in claim 5.

7. The LC medium according to one or more of claims 1 to 6, characterized in that it contains one or more compounds selected from the following sub-formulae wherein R 0 and X 0 have the meanings given in claim 5.

8. The LC medium according to one or more of claims 1 to 7, characterized in that it further contains one or more compounds selected from the following formulae wherein R 0 , X 0 and Y 1-4 have the meanings given in claim 5, Z 0 represents -C 2 H 4 -, -(CH 2 ) 4 -, -CH=CH-, -CF=CF-, -C 2 F 4 -, -CH 2 CF 2 -, -CF 2 CH 2 -,-CH 2 O-,-OCH 2 -,-COO- or -OCF 2 -,which can also be a single bond in Formulas V and VI, and can also be -CF 2 O-, r represents 0 or 1, and s represents 0 or 1.

9. The LC medium according to one or more of claims 1 to 8, characterized in that it contains one or more compounds selected from the following formulae wherein R 0 has the meaning given in claim 5.

10. The LC medium according to one or more of claims 1 to 9, characterized in that it further contains one or more compounds selected from the following formulae: where X 0 has the meaning given in claim 5, and "alkyl" means C 1-6 -alkyl, "alkenyl" means C 2-6 -alkenyl, L represents H or F, "R" represents C 1-6 -alkyl, C 1-6 -alkoxy or C 2-6 -alkenyl, R a1 , R b1 each independently represents CH 3 or C 2 H 5 , i, k are independently 0, 1, 2 or 3.

11. The LC medium according to one or more of claims 1 to 10, characterized in that it contains one or more compounds selected from the following sub-formulae: wherein "alkyl" has the meaning given in claim 10.

12. The LC medium according to one or more of claims 1 to 10, characterized in that it does not contain any compound of the following formula: wherein L 1 and L 2 each independently represent H or F, R' represents, each time it occurs, identically or differently, an alkyl or alkoxy group having from 1 to 12 C atoms, R" represents, each time it occurs, identically or differently, an alkenyl group having from 2 to 7 C atoms containing a terminal vinyl group, and R"' represents R' or R".

13. The LC medium according to one or more of claims 1 to 12, characterized in that it further contains one or more compounds selected from the following sub-formulae: wherein "alkyl" has the meaning given in claim 10.

14. The LC medium according to one or more of claims 1 to 13, characterized in that it contains a compound of formula XVIc2 15. The LC medium according to one or more of claims 1 to 14, characterized in that it contains one or more compounds of formula IA1 wherein R 0 is ethyl or propyl and X 0 is F.

16. The LC medium according to one or more of claims 1 to 15, characterized in that it contains one or more compounds selected from the following compounds of formula wherein R 0 , X 0 and Y 1-4 each independently has one of the meanings given in claim 5.

17. The LC medium according to one or more of claims 1 to 16, characterized in that it contains one or more compounds of formula XXIa wherein R 0 represents ethyl, n-propyl, n-butyl or n-pentyl.

18. The LC medium according to one or more of claims 1 to 17, characterized in that it comprises one or more compounds selected from the compounds of the following formula wherein R 3 has the meaning shown in claim 10, and X 0 has the meaning shown in claim 5.

19. The LC medium according to one or more of claims 1 to 18, characterized in that it comprises one or more compounds of formula XXIXa wherein R 3 represents ethyl, n-propyl, n-butyl or n-pentyl.

20. A method for preparing the LC medium according to one or more of claims 1 to 19, characterized in that one or more compounds of formula I or its sub-formulas as defined in claim 1 or 3 are mixed with one or more compounds according to one or more of claims 4 to 19 or with other LC compounds.

21. Use of the LC medium according to one or more of claims 1 to 19 for electro-optical purposes.

22. The use according to claim 21, wherein the use is in shutter glasses, for 3D applications or in an IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT display.

23. An LC display comprising the LC medium according to one or more of claims 1 to 19.

24. The LC display according to claim 23, characterized in that it is an IPS, PS-IPS, FFS, PS-FFS, HB-FFS, U-IPS, TN, PS-TN, STN or TN-TFT display.

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