Liquid crystal medium

Abstract

The invention relates to a liquid-crystalline medium comprising at least one compound of formula (I), # imgabs0 # and one or more compounds selected from the group consisting of formulae (IIA), (IIB) and (IIC), # imgabs1 # in which the groups and parameters present have the meanings indicated in claim 1, and to the use thereof for active matrix displays, in particular for active matrix displays based on VA, PSA, PA-VA, SS-VA, SA-VA, PS-VA, PALC, IPS, PS-IPS, UB-FFS, U-IPS, FFS or PS-FFS effects.

Description

[0001] This application is a divisional application of patent application number 201880078751.1.

[0002] The present invention relates to liquid-crystalline media comprising one or more compounds of the formula I:

[0003]

[0004] in,

[0005] R 11 and R 12 , each independently of one another represents H, alkyl or alkoxy having 1 to 15 C atoms, wherein, in addition, one or more of these radicals CH 2 The groups can be independently -C≡C-, -CF 2 O-、-OCF 2 -、-CH=CH-、 -O-, -CO-O-, -O-CO- are substituted in such a way that the O atoms are not directly connected to one another, and wherein, in addition, one or more H atoms may be replaced by halogen,

[0006] A 1 Each occurrence represents independently of the other

[0007] a) 1,4-cyclohexenyl or 1,4-cyclohexylene, one or two non-adjacent CH 2 The group can be replaced by -O- or -S-,

[0008] b) 1,4-phenylene, in which one or both CH groups may be replaced by N,

[0009] c) is selected from piperidine-1,4-diyl, 1,4-bicyclo[2.2.2]-octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl,

[0010] wherein the groups a), b) and c) may be mono- or poly-substituted by halogen atoms,

[0011] Z 1 Each occurrence represents independently of each other -CO-O-, -O-CO-, -CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2 -、-CH 2 -、-CH 2 CH 2 -、-(CH 2 )4 -、-CH=CH-CH 2 O-、-C 2 F 4 -、-CH 2 CF 2 -、-CF 2 CH 2 -, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond, and

[0012] L 11 and L 12 Each independently represents F, Cl, CF 3 or CHF 2 , preferably H or F, more preferably F,

[0013] and

[0014] one or more compounds selected from the group consisting of compounds of formula IIA, IIB and IIC,

[0015]

[0016] in,

[0017] R 2A , R 2B and R 2C Independently of each other, H, unsubstituted, replaced by CN or CF 3 Alkyl or alkenyl having up to 15 C atoms, monosubstituted or at least monosubstituted by halogen, wherein, in addition, one or more of these radicals CH 2 The group can be -O-, -S-, -C≡C-, -CF 2 O-、-OCF 2 -, -OC-O- or -O-CO- are substituted in such a way that the O atoms are not directly connected to each other,

[0018] L 1 To L 4 Each independently represents F, Cl, CF 3 or CHF 2 ,

[0019] Z 2 and Z 2’ Each independently represents a single bond, -CH 2 CH 2 -、-CH=CH-、-CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2-、-COO-、-OCO-、-C 2 F 4 -, -CF=CF-, -CH=CHCH 2 O-,

[0020] p means 0, 1 or 2

[0021] q represents 0 or 1, and

[0022] v means 1-6.

[0023] Media of this type can be used in particular in electro-optical displays with active-matrix addressing based on the ECB effect, and in IPS (in-plane switching) or FFS (fringe field switching) displays.

[0024] In 1971, the principle of electric field controlled birefringence, namely ECB effect or DAP (deformation of arranged phase) effect was first proposed (MF Schieckel and K. Fahrenschon, "Deformation of nematic liquid crystals with vertical orientation in electrical fields", Appl. Phys. Lett. 19 (1971), 3912). Later, JF Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869) published papers.

[0025] Papers published by J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) show that liquid crystal phases must have a high elastic constant K 3 / K 1 The negative dielectric liquid crystal medium has a ratio of 1:1 to 1:1, a high optical anisotropy Δn value and a dielectric anisotropy Δε≤-0.5, so that it is suitable for high-information display elements based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic edge alignment (VA technology = vertical alignment). Negative dielectric liquid crystal media can also be used for displays with the so-called IPS or FFS effect.

[0026] Displays using the ECB effect, such as so-called VAN (vertically aligned nematic) displays, for example in MVA (multi-domain vertical alignment, for example: Yoshide, H. et al., paper 3.1: "MVA LCD for Notebook or Mobile PCs...", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 6-9, and Liu, CT et al., paper 15.1: "A46-inch TFT-LCD HDTV Technology...", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 750 -753), PVA (patterned vertical alignment, for example: Kim, Sang Soo, paper 15.4: "Super PVA Sets New State-of-the-Art for LCD-TV", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book II, pp. 750 -753) and in LCDs. II, pp.760-763), ASV (super viewing angle, for example: Shigeta, Mitzuhiro and Fukuoka, Hirofumi, paper 15.2: "Development of High Quality LCDTV", SID 2004InternationalSymposium, Digest of Technical Papers, XXXV, Book II, pp.754-757) modes, in addition to IPS (in-plane switching) displays (for example: Yeo, SD, paper 15.3: "An LC Display for the TVApplication", SID 2004InternationalSymposium, Digest of Technical Papers, XXXV, Book II, pp.758&759) and the long-known TN (twisted nematic) displays, have all developed themselves into one of the three most important new types of liquid crystal displays, especially for use in televisions.For example, the above techniques are compared in a conventional form in Souk, Jun, SID Seminar 2004, seminar M-6: "Recent Advances in LCD Technology", Seminar Lecture Notes, M-6 / 1 to M-6 / 26, and Miller, Ian, SID Seminar 2004, seminar M-7: "LCD-Television", Seminar Lecture Notes, M-7 / 1 to M-7 / 32. Although the response time of modern ECB displays has been significantly improved by using overdrive addressing methods, for example; Kim, Hyeon Kyeong et al., paper 9.1: "A 57-in. Wide UXGA TFT-LCD for HDTV Application", SID 2004 International Symposium, Digest of Technical Papers, XXXV, Book I, pp. 106-109, the progress of image-compatible response time, especially in gray shade switching, is still a problem that has not been satisfactorily solved.

[0027] Industrial use of this effect in electro-optical display elements requires LC phases which have to meet a diversity of requirements. Of particular importance is the chemical resistance to moisture, air and physical influences such as heat, infrared, visible and ultraviolet light and direct and alternating electric fields.

[0028] Furthermore, industrially usable LC phases are required to have a liquid crystal mesophase in a suitable temperature range and a low viscosity.

[0029] None of the series of compounds disclosed to date which have a liquid-crystalline mesophase contains a single compound which meets all of these requirements. Mixtures of 2 to 25, preferably 3 to 18, compounds are therefore usually prepared in order to obtain a substance which can be used as an LC phase. However, it is not possible to easily prepare the most suitable phase in this way, since no liquid-crystalline materials having a significantly negative dielectric anisotropy and a sufficiently long-term stability have been available to date.

[0030] Matrix liquid crystal displays (MLC displays) are known. Non-linear elements that can be used to switch individual pixels individually are, for example, active elements (such as transistors). In the following, the term "active matrix" is used, where a distinction is made between two types:

[0031] 1. MOS (metal oxide semiconductor) transistors on a silicon wafer as a substrate

[0032] 2. Thin-film transistors (TFTs) on a glass plate as a substrate.

[0033] In the case of type 1, the electro-optical effect used is generally dynamic scattering or the guest-host effect. The use of single-crystal silicon as substrate material limits the display size, as does the modular integration of the different display parts, which also leads to problems at the connections.

[0034] In the case of the preferred more promising type 2, the electro-optical effect used is generally the TN effect.

[0035] A distinction is made between two technologies: TFTs containing compound semiconductors such as CdSe or TFTs based on polycrystalline or amorphous silicon. The latter technology is being intensively researched worldwide.

[0036] The TFT matrix is ​​applied to the inside of one glass plate of the display, while the other glass plate carries the transparent counter electrode. Compared with the size of the pixel electrode, the TFT is very small and has almost no adverse effect in the image. The technology can also be extended to full-color capable displays, where mosaics of red, green and blue filters are arranged in such a way that the filter elements are opposite to each switchable pixel.

[0037] Here, the term MLC display includes any matrix display with integrated non-linear elements, ie displays which, in addition to the active matrix, also have passive elements, such as varistors or diodes (MIM=metal-insulator-metal).

[0038] Such MLC displays are particularly suitable for TV applications (e.g. pocket TVs) or for high-information displays in automobile or aircraft structures. In addition to the problems with the angular dependence of the contrast and response time, problems also arise in MLC displays due to the insufficient specific resistance of the liquid crystal mixture [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E., SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Euro-display 84, Sept. 1984: A210-288 Matrix LCD Controlled by Double Stage Diode Rings, p. 141ff., Paris; STROMER, M., Proc. Eurodisplay 84, Sept. 1984: Design of Thin Film Transistors for Matrix Addressing of Television Liquid Crystal Displays, p. 145ff., Paris]. As the resistance decreases, the contrast of the MLC display deteriorates. Since the specific resistance of the liquid crystal mixture generally decreases over the lifetime of an MLC display due to interaction with the inner surfaces of the display, a high (initial) resistance is very important for the display to have acceptable resistance values ​​after long-term operation.

[0039] Therefore, there is still a great need for MLC displays having very high resistivity while having a large operating temperature range, short response time and low threshold voltage, with the aid of which a wide range of grey scales can be produced.

[0040] Disadvantages of the frequently used MLC-TN displays are their comparatively low contrast, the relatively high viewing angle dependence and the difficulty in producing grey scales in these displays.

[0041] The market for VA, PS-VA, IPS, FFS and UB-FFS applications is looking for LC blends with fast response times and very high reliability. One approach to achieving fast response times is to identify highly polar LC materials with low rotational viscosity, whose use in LC blends contributes to the desired effect. However, the use of this type of highly polar LC material has an adverse effect on reliability parameters, especially after exposure to light.

[0042] The object of the present invention is to provide LC mixtures based on the ECB, UB-FFS, IPS or FFS effect, in particular for monitor and TV applications, which do not have the above-mentioned disadvantages, or have them only to a small extent. In particular, for monitors and TVs it must be ensured that they also operate at very high and very low temperatures and at the same time have very short response times and at the same time have improved reliability behavior, in particular exhibit no or significantly reduced image sticking after long operating times.

[0043] Compounds of the general formula

[0044]

[0045] In European patent application No. EP 17161352.4 it is mentioned as a component of a liquid crystal medium. Also disclosed is a compound of the formula

[0046]

[0047] However, only a single compound is used in the medium of this document

[0048]

[0049] Where n is 2 and m is 5.

[0050] The present invention therefore relates to liquid-crystalline media comprising at least one compound of the formula I and one or more compounds selected from the group consisting of compounds of the formulae IIA, IIB and IIC. These media are particularly suitable for obtaining liquid-crystalline displays having fast response times and good voltage holding ratios at low temperatures and excellent storage stability. This is sufficient for many applications.

[0051] The mixture according to the invention preferably exhibits a very broad nematic phase range, a clearing point of ≥70° C., preferably ≥75° C., in particular ≥80° C., very favorable values ​​of the capacitance threshold, relatively high retention values ​​and at the same time very good low-temperature stability at temperatures of −20° C. and −30° C., as well as very low rotational viscosity values ​​and short response times. The mixture according to the invention is further characterized in that, in addition to improving the rotational viscosity γ 1 , we can also observe a relatively high value of the elastic constant K 33 To improve the response time. The compounds of formula I are used in LC mixtures preferably having negative dielectric anisotropy, the rotational viscosity γ 1 and elastic constant K i The ratio decreases.

[0052] Some preferred embodiments of the mixture according to the invention are set out below.

[0053] In the compound of formula I, R 11and R 12 Preferably each independently of one another represents a straight-chain alkyl group, in particular CH 3 、nC 2 H 5 、nC 3 H 7 、nC 4 H 9 、nC 5 H 11 、nC 6 H 13 - or nC 7 H 15 , straight chain alkoxy, especially CH 3 -O、nC 2 H 5 -O、nC 3 H 7 -O、nC 4 H 9 -O、nC 5 H 11 -O or nC 6 H 13 -O, and alkenyl, especially CH 3 =CH, CH 3 CH=CH、CH 3 CH=CHCH 2 or CH 3 CH 2 CH=CH, branched alkoxy, in particular, (CH 3 ) 2 CH(CH 2 ) 3 O, and alkenyloxy, especially CH 2 =CHO, CH 2 =CH 2 CHO, CH 3 CH 2 =CHCHO or OCH 2 CH 2 CH=CHCH 2 O.

[0054] R 11 Particularly preferably, it represents a straight-chain alkyl radical having 1 to 7 C atoms. 12 Particularly preferably it denotes straight-chain alkoxy having 1 to 6 C atoms, in particular methoxy, ethoxy, propoxy, butoxy, pentyloxy or hexyloxy.

[0055] In the compound of formula I, L 11 and L 12 Preferably, they all represent F.

[0056] Preferred compounds of formula I present in the medium are compounds of formulae I-1 to I-3, preferably formula I-2,

[0057]

[0058]

[0059] in,

[0060] The parameters have the meanings given above, R 11 represents a straight chain alkyl group, R 12 Preferably represents an alkoxy group, L 11 and L 12 Preferably, they all represent F.

[0061] In a preferred embodiment, the medium comprises one or more compounds of formula I selected from the group consisting of compounds of formulae IO-1 to IO-3, preferably compounds of formula IO-2,

[0062]

[0063] where the parameters have the meanings given above,

[0064] In another preferred embodiment, the medium comprises one or more compounds of formula I selected from the group consisting of compounds of formulae IS-1 to IS-3, preferably formula IS-2,

[0065]

[0066]

[0067] where the parameters have the meanings given above.

[0068] In a preferred embodiment of the invention, the medium comprises one or more compounds selected from the group consisting of formulae IO-1 to IO-3 and one or more compounds selected from the group consisting of formulae IS-1 to IS-3.

[0069] Compounds of formula I can be prepared, for example, as described in US 2005 / 0258399 or WO 02 / 055463 A1.

[0070] The medium according to the invention preferably comprises one, two, three, four or more, preferably one, two or three, compounds of the formula I.

[0071] The amount of the compound of the formula I in the liquid-crystalline medium is preferably ≥1% by weight, preferably ≥3% by weight, based on the entire mixture. Particular preference is given to liquid-crystalline media which comprise 1 to 40% by weight, very particularly preferably 2 to 30% by weight, of one or more compounds of the formula I.

[0072] Preferred embodiments of the liquid-crystalline media according to the invention are as follows:

[0073] a) a liquid-crystalline medium which additionally comprises one or more compounds selected from the group consisting of compounds of the formulae IIA, IIB and IIC,

[0074] In the compounds of Formula IIA and IIB, Z 2 can have the same or different meanings. In the compounds of formula IIB, Z 2 and Z 2 ' can have the same or different meanings.

[0075] In the compounds of Formula IIA, IIB and IIC, R 2A , R 2B and R 2C each preferably represents an alkyl radical having 1 to 6 C atoms, in particular, CH 3 , C 2 H 5 、nC 3 H 7 、nC 4 H 9 、nC 5 H 11 .

[0076] In the compounds of Formula IIA and IIB, L 1 , L 2 , L 3 and L 4 Preferred expression L 1 =L 2 = F and L 3 =L 4 =F, and L 1 = F and L 2 =Cl,L 1 =Cl and L 2 =F,L 3 = F and L 4 =Cl,L 3 =Cl and L 4 =F. Z in Formula IIA and IIB 2 and Z 2 ' preferably each independently represents a single bond, and also represents C 2 H 4 -bridge.

[0077] If in Formula IIB, Z 2 =-C 2 H 4 -or-CH 2 O-, Z 2’ is preferably a single bond, or if Z 2 '=-C2 H 4 -or-CH 2 O-, Z 2 Preferably, it is a single bond. In the compounds of formula IIA and IIB, (O)C v H 2v+1 Preferred means OC v H 2v+1 , also means C v H 2v+1 In the compound of formula IIC, (O)C v H 2v+1 Preferred expression C v H 2v+1 In the compound of formula IIC, L 3 and L 4 Preferably each represents F.

[0078] Preferred compounds of formula IIA, IIB and IIC are shown below:

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088] in,

[0089] alkyl and alkyl * each independently of one another represents a straight-chain alkyl group having 1 to 6 C atoms, and

[0090] alkenyl and alkenyl * each independently of one another represents a straight-chain alkenyl group having 2 to 6 C atoms.

[0091] Particularly preferred mixtures according to the invention comprise one or more compounds of the formulae IIA-2, IIA-8, IIA-14, IIA-26, II-28, IIA-33, IIA-39, IIA-45, IIA-46, IIA-47, IIA-50, IIB-2, IIB-11, IIB-16 and IIC-1.

[0092] The proportion of compounds of the formula IIA and / or IIB in the mixture as a whole is preferably at least 20% by weight.

[0093] Particularly preferred media according to the invention comprise at least one compound of the formula IIC-1,

[0094]

[0095] Among them, alkyl and alkyl * Having the meanings given above, preferably amounts are >3% by weight, in particular >5% by weight and particularly preferably from 5 to 25% by weight.

[0096] b) a liquid-crystalline medium additionally comprising one or more compounds of the formula III,

[0097]

[0098] in,

[0099] R 31 and R 32 each independently of one another represents straight-chain alkyl, alkoxy, alkenyl, alkoxyalkyl or alkoxy having up to 12 C atoms, and

[0100] d means en means o

[0101]

[0102] Z 3 Represents a single bond, -CH 2 CH 2 -、-CH=CH-、-CF 2 O-、-OCF 2 -、-CH 2 O-、-OCH 2 -、-COO-、-OCO-、-C 2 F 4 -、-C 4 H 8 -, -CF=CF-.

[0103] Preferred compounds of formula III are shown below:

[0104]

[0105] in,

[0106] alkyl and alkyl * Each independently of one another represents a straight-chain alkyl radical having 1 to 6 C atoms.

[0107] The medium according to the invention preferably comprises at least one compound of the formula IIIa and / or IIIb.

[0108] The proportion of the compound of the formula III in the mixture as a whole is preferably at least 5% by weight.

[0109] c) a liquid-crystalline medium further comprising a compound of the formula

[0110] and / or

[0111] and / or

[0112]

[0113] Preferably the total amount is ≥5% by weight, in particular ≥10% by weight.

[0114] It is further preferred that the mixture according to the invention comprises the following compounds

[0115] (Abbreviation: CC-3-V1),

[0116]

[0117] The preferred amount is 2-15% by weight.

[0118] Preferred mixtures contain 5 to 60% by weight, preferably 10 to 55% by weight, in particular 20 to 50% by weight of a compound of the formula (abbreviation: CC-3-V):

[0119]

[0120] Further preferred is a compound comprising the following formula (abbreviation: CC-3-V)

[0121]

[0122] and the following compound (abbreviation: CC-3-V1)

[0123]

[0124] A mixture of

[0125] The preferred amount is 10-60% by weight.

[0126] d) a liquid-crystalline medium additionally comprising one or more tetracyclic compounds of the formula

[0127]

[0128]

[0129] in,

[0130] R 7-10 Each independently has the following characteristics for R in claim 5 2A One of the meanings, and w and x each independently represent 1-6.

[0131] Particularly preferred are mixtures comprising at least one compound of the formula V-9.

[0132] e) a liquid-crystalline medium further comprising one or more compounds of the formulae Y-1 to Y-6

[0133]

[0134]

[0135] Where R 14 -R 19 Each independently represents an alkyl group or an alkoxy group having 1 to 6 C atoms; z and m each independently represent 1 to 6; and x represents 0, 1, 2 or 3.

[0136] The medium according to the invention particularly preferably comprises one or more compounds of the formulae Y-1 to Y-6, preferably in an amount of ≥5% by weight.

[0137] f) Liquid-crystalline medium, additionally comprising one or more fluorinated terphenyls of the formulae T-1 to T-21

[0138]

[0139]

[0140]

[0141] in,

[0142] R represents straight-chain alkyl or alkoxy having 1-6 C atoms, and m=0, 1, 2, 3, 4, 5 or 6 and n represents 0, 1, 2, 3 or 4.

[0143] R preferably represents methyl, ethyl, propyl, butyl, pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy or pentyloxy.

[0144] The medium according to the invention preferably comprises the terphenyls of the formulae T-1 to T-21 in an amount of 2 to 30% by weight, in particular 5 to 20% by weight.

[0145] Particularly preferred are compounds of formula T-1, T-2, T-4, T-20 and T-21. In these compounds, R preferably represents alkyl and alkoxy, each having 1 to 5 C atoms. In the compound of formula T-20, R preferably represents alkyl or alkenyl, in particular alkyl. In the compound of formula T-21, R preferably represents alkyl.

[0146] Terphenyls are preferably used in the mixtures according to the invention if the Δn value of the mixture is ≥ 0.1. Preferred mixtures comprise 2 to 20% by weight of one or more terphenyl compounds selected from the group consisting of compounds T-1 to T-21.

[0147] g) a liquid-crystalline medium additionally comprising one or more biphenyls of the formulae B-1 to B-3,

[0148]

[0149] in,

[0150] alkyl and alkyl * each independently of one another represents a straight-chain alkyl group having 1 to 6 C atoms, and

[0151] alkenyl and alkenyl * each independently of one another represents a straight-chain alkenyl group having 2 to 6 C atoms.

[0152] The proportion of biphenyls of the formulae B1 to B3 in the mixture as a whole is preferably at least 3% by weight, in particular ≥5% by weight.

[0153] Among the compounds of formulae B1 to B3, the compound of formula B-2 is particularly preferred.

[0154] Particularly preferred biphenyls are

[0155]

[0156]

[0157] Among them, alkyl * denotes an alkyl radical having 1 to 6 C atoms. The medium according to the invention particularly preferably comprises one or more compounds of the formula B-1a and / or B-2c.

[0158] h) a liquid-crystalline medium comprising at least one compound of the formulae Z-1 to Z-7,

[0159]

[0160] Herein, R and alkyl have the meanings shown above.

[0161] i) the liquid-crystalline medium additionally comprises at least one compound of the formulae O-1 to O-18,

[0162]

[0163]

[0164] Among them, R 1 and R 2 With respect to R 2A The meaning of R 1 and R 2 Preferably each independently of one another represents a straight-chain alkyl or alkenyl group.

[0165] Preferred media comprise one or more compounds of formula O-1, O-3, O-4, O-6, O-7, O-10, O-11, O-12, O-14, O-15, O-16 and / or O-17.

[0166] Particularly preferred are compounds comprising one or more selected from the group consisting of formula O-17,

[0167] The mixtures according to the invention very particularly preferably comprise compounds of the formulae O-10, O-12, O-16 and / or O-17, in particular in an amount of 5 to 30%.

[0168] Preferred compounds of formula O-10 and O-17 are shown below:

[0169]

[0170] The medium according to the invention particularly preferably contains tricyclic compounds of the formula O-10a and / or O-10b and one or more bicyclic compounds of the formulae O-17a to O-17d. The total proportion of compounds of the formulae O-10a and / or O-10b and one or more compounds selected from the bicyclic compounds of the formulae O-17a to O-17d is 5-40%, very particularly preferably 15-35%.

[0171] Very particularly preferred mixtures comprise the compounds O-10a and O-17a:

[0172]

[0173]

[0174] The compounds O-10a and O-17a are preferably present in the mixture in a concentration of 15 to 35%, particularly preferably 15 to 25% and especially preferably 18 to 22%, based on the entire mixture.

[0175] Very particularly preferred mixtures comprise the compounds O-10b and O-17a:

[0176]

[0177] The compounds O-10b and O-17a are preferably present in the mixture in a concentration of 15 to 35%, particularly preferably 15 to 25% and especially preferably 18 to 22%, based on the entire mixture.

[0178] Very particularly preferred mixtures comprise the following three compounds:

[0179]

[0180] The compounds O-10a, O-10b and O-17a are preferably present in the mixture in a concentration of 15 to 35%, particularly preferably 15 to 25% and especially preferably 18 to 22%, based on the entire mixture.

[0181] Preferred mixtures contain at least one compound selected from the group consisting of

[0182]

[0183]

[0184] Where R 1 and R 2 Preferably, in compounds O-6, O-7 and O-17, R 1 represents an alkyl or alkenyl group having 1 to 6 or 2 to 6 C atoms and R 2 represents an alkenyl group having 2 to 6 C atoms.

[0185] Preferred mixtures contain at least one compound of formula O-6a, O-6b, O-7a, O-7b, O-17e, O-17f, O-17g and O-17h:

[0186]

[0187]

[0188] Here, alkyl represents an alkyl group having 1 to 6 C atoms.

[0189] The compounds of the formulae O-6, O-7 and O-17e-h are preferably present in the mixture according to the invention in an amount of 1 to 40% by weight, preferably 2 to 35% by weight and very particularly preferably 2 to 30% by weight.

[0190] j) Preferred liquid-crystalline media according to the invention comprise one or more substances containing tetralinyl or naphthyl units, for example compounds of the formulae N-1 to N-5,

[0191]

[0192]

[0193] Where R 1N and R 2N Each independently has a 2A The meanings shown in the table preferably represent straight-chain alkyl, straight-chain alkoxy or straight-chain alkenyl, and

[0194] Z 1 and Z 2 Each independently represents -C 2 H 4 -, -CH=CH-, -(CH 2 ) 4 -、-(CH 2 ) 3 O-、-O(CH 2 ) 3 -、-CH=CHCH 2 CH 2 -、-CH 2 CH 2 CH=CH-、-CH 2 O-、-OCH 2 -、-COO-、-OCO-、-C 2 F 4 -, -CF=CF-, -CF=CH-, -CH=CF-, -CF 2 O-、-OCF 2 -、-CH 2 - or single key.

[0195] k) preferably a mixture comprising one or more compounds selected from the group consisting of difluorodibenzochromane compounds of formula BC, chromanes of formula CR, fluorophenanthrene compounds of formula PH-1 and PH-2, fluorodibenzofuran compounds of formula BF-1 and BF-2,

[0196]

[0197]

[0198] Among them, R B1 , R B2 , R CR1 , R CR2 , R 1 , R 2 Each independently has R2A c is 0, 1 or 2 and d is 1 or 2. 1 and R 2 Preferably, independently of one another, they represent alkyl or alkoxy radicals having 1 to 6 C atoms. The compounds of the formulae BF-1 and BF-2 should not be identical to one or more compounds of the formula I.

[0199] The mixture according to the invention preferably comprises the compounds of the formulae BC, CR, PH-1, PH-2 and / or BF in an amount of 3 to 20% by weight, in particular in an amount of 3 to 15% by weight.

[0200] Particularly preferred compounds of formula BC and CR are compounds BC-1 to BC-7 and CR-1 to CR-5,

[0201]

[0202]

[0203]

[0204] in,

[0205] alkyl and alkyl * each independently of one another represents a straight-chain alkyl group having 1 to 6 C atoms, and

[0206] alkenyl and alkenyl * each independently of one another represents a straight-chain alkenyl group having 2 to 6 C atoms.

[0207] Very particular preference is given to mixtures comprising one, two or three compounds of the formulae BC-2, BF-1 and / or BF-2.

[0208] 1) Preferred mixtures contain one or more indane compounds of the formula In,

[0209]

[0210] in

[0211] R 11 , R 12 , R 13 each independently of one another represents a straight-chain alkyl, alkoxy, alkoxyalkyl or alkenyl radical having 1 to 6 C atoms,

[0212] R 12 and R 13 Additionally represents halogen, preferably F,

[0213] express

[0214]

[0215] i represents 0, 1 or 2.

[0216] Preferred compounds of formula In are compounds shown in the following formulae In-1 to In-16:

[0217]

[0218]

[0219]

[0220] Particularly preferred are compounds of the formulae In-1, In-2, In-3 and In-4.

[0221] The compounds of the formula In and subformulae In-1 to In-16 are preferably used in the mixtures according to the invention in a concentration of ≥5% by weight, in particular 5 to 30% by weight and very particularly preferably 5 to 25% by weight.

[0222] m) Preferred mixtures additionally comprise one or more compounds of the formulae L-1 to L-11,

[0223]

[0224]

[0225] in,

[0226] R, R 1 and R 2 Each independently has the following characteristics for R in claim 5 2A alkyl represents an alkyl group having 1 to 6 C atoms. s represents 1 or 2.

[0227] Particularly preferred are compounds of formulae L-1 and L-4, especially L-4.

[0228] The compounds of the formulae L-1 to L-11 are preferably used in a concentration of 5 to 50% by weight, in particular 5 to 40% by weight and very particularly preferably 10 to 40% by weight.

[0229] Particularly preferred mixture concepts are explained below: (the abbreviations used are explained in Table A. Here n and m each independently of one another represent 1 to 15, preferably 1 to 6).

[0230] The mixture according to the invention preferably comprises,

[0231] - one or more compounds of formula I, wherein L 11 =L 12 = F and R 1 = alkyl, R1* = alkoxy; and / or

[0232] CPY-n-Om, in particular CPY-2-O2, CPY-3-O2 and / or CPY-5-O2, preferably in a concentration of >5%, in particular 10 to 30%, based on the entire mixture,

[0233] and / or

[0234] -CY-n-Om, preferably CY-3-O2, CY-3-O4, CY-5-O2 and / or CY-5-O4, preferably in a concentration of >5%, in particular 15 to 50%, based on the entire mixture,

[0235] and / or

[0236] - CCY-n-Om, preferably CCY-4-O2, CCY-3-O2, CCY-3-O3, CCY-3-O1 and / or CCY-5-O2, preferably in a concentration of >5%, in particular 10-30%, based on the entire mixture,

[0237] and / or

[0238] - CLY-n-Om, preferably CLY-2-O4, CLY-3-O2 and / or CLY-3-O3, preferably in a concentration of >5%, in particular 10-30%, based on the entire mixture,

[0239] Further preferred are mixtures according to the invention which comprise:

[0240] (n and m each independently represent 1 to 6.)

[0241] The compounds of formula I, preferably formula I-1 to I-3, i.e., compounds of formula IO-1 to IO-3 and / or IS-1 to IS-3, especially LB-3-O4 and / or LB(S)-4-O3, are present in a concentration of 1 to 20% by weight, more preferably 2 to 15% by weight, particularly preferably 3 to 12% by weight, and very particularly preferably 4 to 11% by weight.

[0242] - CPY-n-Om and CY-n-Om, preferably in a concentration of 10-80% based on the entire mixture, and / or

[0243] - CPY-n-Om and CK-nF, preferably in a concentration of 10-70% based on the entire mixture and / or

[0244] - CPY-n-Om and PY-n-Om, preferably CPY-2-O2 and / or CPY-3-O2 and PY-3-O2, preferably in a concentration of 10 to 45%, based on the entire mixture,

[0245] and / or

[0246] - CPY-n-Om and CLY-n-Om, preferably in a concentration of 10-80% based on the entire mixture, and / or

[0247] - CCVC-nV, preferably CCVC-3-V, preferably in a concentration of 2 to 10%, based on the entire mixture,

[0248] and / or

[0249] - CCC-nV, preferably CCC-2-V and / or CCC-3-V, preferably in a concentration of 2 to 10%, based on the entire mixture,

[0250] and / or

[0251] -CC-VV, preferably in a concentration of 5 to 50%, based on the entire mixture.

[0252] In a particularly preferred embodiment of the invention, the medium comprises the compound B-2O-O5 in a concentration of 2-8%, the compound CC-3-V in a concentration of 25-35% and the compound CC-3-V1 in a concentration of 8-12%.

[0253] The invention further relates to an electro-optical display with active-matrix addressing based on the ECB, VA, PS-VA, PA-VA, IPS, PS-IPS, FFS or PS-FFS effect, characterised in that it contains a liquid-crystalline medium according to one or more of claims 1 to 11 as dielectric.

[0254] The liquid-crystalline media according to the invention preferably have a nematic phase at ≤-20° C. to ≥70° C., particularly preferably ≤-30° C. to ≥80° C. and very particularly preferably ≤-40° C. to ≥90° C.

[0255] The expression "having a nematic phase" here means on the one hand that at low temperatures no smectic phase and no crystallization is observed at the corresponding temperature and on the other hand that no clearing occurs on heating from the nematic phase. The low temperature investigations are carried out in a flow viscometer at the corresponding temperature and checked by storage in test cells with a layer thickness corresponding to at least 100 hours of electro-optical use. If the storage stability in the corresponding test cells at a temperature of -20°C is 1000 hours or more, the medium is said to be stable at this temperature. At temperatures of -30°C and -40°C, the corresponding times are 500 hours and 250 hours, respectively. At high temperatures, the clearing point is measured by conventional methods in a capillary.

[0256] The liquid crystal mixture preferably has a nematic phase range of at least 60 K and a maximum of 30 mm at 20° C. 2 ·s -1 The flow viscosity ν 20.

[0257] The birefringence Δn in the liquid crystal mixture is generally in the range of 0.07 to 0.16, preferably 0.08 to 0.13.

[0258] The liquid crystal mixtures according to the invention have a Δε of -0.5 to -8.0, in particular -2.5 to -6.0, where Δε denotes the dielectric anisotropy. Rotational viscosity γ at 20°C 1 Preferably it is ≤150 mPa·s, in particular ≤120 mPa·s.

[0259] The liquid-crystal media according to the invention have relatively low threshold voltage values ​​(V 0 ). The preferred range is 1.7 V to 3.0 V, particularly preferably ≤2.5 V and very particularly preferably ≤2.3 V.

[0260] For the present invention, unless otherwise expressly stated, the term "threshold voltage" refers to the capacitance threshold (V 0 ), also known as the Freedericks threshold.

[0261] Furthermore, the liquid-crystalline media according to the invention have high voltage holding ratio values ​​in liquid-crystal cells.

[0262] Typically, liquid-crystal media having a low addressing voltage or threshold voltage exhibit lower voltage holding ratios than those having a higher addressing voltage or threshold voltage, and vice versa.

[0263] For the purposes of the present invention, the term "positive dielectric compound" denotes compounds having Δε>1.5, the term "neutral dielectric compound" denotes those having -1.5≤Δε≤1.5 and the term "negative dielectric compound" denotes those having Δε<-1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% of the compound in a liquid-crystal host in at least one test cell, the test cell having in each case a layer thickness of 20 μm and having a homeotropic and planar surface alignment at 1 kHz. The measuring voltage is generally between 0.5 V and 1.0 V, but is always below the capacitance threshold of the respective liquid-crystal mixture under investigation.

[0264] All temperature values ​​described in the present invention are expressed in °C.

[0265] The mixtures according to the invention are suitable for all VA-TFT applications, for example, VAN, MVA, (S)-PVA, ASV, PSA (polymer-stabilized VA) and PS-VA (polymer-stabilized VA). They are also suitable for IPS (in-plane switching) and FFS (fringe field switching) applications with negative Δε.

[0266] The nematic liquid-crystal mixtures in the displays according to the invention generally comprise two components A and B which consist of one or more individual compounds.

[0267] Component A has a significantly negative dielectric anisotropy and gives the nematic phase a dielectric anisotropy of ≤-0.5. In addition to one or more compounds of the formula I, it preferably comprises compounds of the formulae IIA, IIB and / or IIC and also one or more compounds of the formula O-17.

[0268] The proportion of component A is preferably 45-100%, in particular 60-100%.

[0269] For component A, preference is given to selecting one (or more) individual compounds having a value of Δε≤−0.8. The smaller the proportion of A in the overall mixture, the more negative this value must be.

[0270] Component B has significant nematogeneity and a diameter of no more than 30 mm at 20°C. 2 ·s -1 , preferably no more than 25mm 2 ·s -1 The flow viscosity.

[0271] A person skilled in the art will know a variety of suitable substances from the literature. Particularly preferred are compounds of formula O-17.

[0272] Particularly preferred individual compounds in component B are very low viscosity nematic liquid crystals having a viscosity of not more than 18 mm at 20° C. 2 ·s -1 The flow viscosity is preferably not more than 12 mm 2 ·s -1 The flow viscosity.

[0273] Component B is a unidirectionally transitioning or interconverting nematic phase, does not have a smectic phase and is able to prevent the appearance of a smectic phase when dropped to very low temperatures in the liquid crystal mixture. For example, if a variety of highly nematic materials are added to a smectic liquid crystal mixture, the nematicity of these materials can be compared by the degree of suppression of the smectic phase achieved.

[0274] The mixture may also optionally comprise a component C comprising compounds having a dielectric anisotropy of Δε≥1.5. These so-called positive compounds are usually present in negative dielectric anisotropic mixtures in an amount of ≤20% by weight, based on the overall mixture.

[0275] In addition to one or more compounds of the formula I, the phase preferably comprises 4 to 15, in particular 5 to 12, particularly preferably <10 compounds of the formulae IIA, IIB and / or IIC and optionally one or more compounds of the formula O-17.

[0276] Besides the compounds of the formula I and the compounds of the formulae IIA, IIB and / or IIC and optionally O-17, further components may also be added beforehand, for example in amounts of up to 45%, but preferably up to 35%, in particular up to 10%, of the total mixture.

[0277] The further components are preferably selected from nematic or nematic substances, in particular known substances from the group consisting of azobenzene oxide, benzylidene aniline, biphenyl, terphenyl, phenylbenzoate or cyclohexylbenzoate, phenylcyclohexane carboxylate or cyclohexylcyclohexane carboxylate, phenylcyclohexane, cyclohexylbiphenyl, cyclohexylcyclohexane, cyclohexylnaphthalene, 1,4-dicyclohexylbiphenyl or cyclohexylpyrimidine, phenyldi ... cyclohexyl alkanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamates.

[0278] The most important compounds suitable as constituents of this type of liquid crystal phase can be characterized by the formula IV

[0279] R 20 -LGER 21 IV

[0280] wherein L and E each represent a system selected from 1,4-disubstituted benzene and cyclohexane rings, 4,4'-disubstituted biphenyls, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidines and 1,3-disubstituted pyrimidines. carbocyclic or heterocyclic ring systems of alkane rings, 2,6-disubstituted naphthalenes, di- and tetrahydronaphthalenes, quinazoline and tetrahydroquinazoline,

[0281] G represents -CH=CH--N(O)=N-

[0282] -CH=CQ--CH=N(O)-

[0283] -C≡C--CH 2 -CH 2 -

[0284] -CO-O--CH 2 -O-

[0285] -CO-S--CH 2 -S-

[0286] -CH=N--COO-Phe-COO-

[0287] -CF 2 O--CF=CF-

[0288] -OCF 2 --OCH 2 -

[0289] -(CH 2 ) 4 --(CH 2 ) 3 O-

[0290] or a CC single bond; Q represents a halogen, preferably chlorine, or -CN, and R 20 and R 21 each represents an alkyl, alkenyl, alkoxy, alkoxyalkyl or alkoxycarbonyloxy radical having up to 18, preferably up to 8, carbon atoms, or one of these radicals alternatively represents CN, NC, NO 2 、NCS、CF 3 , SF 5 、OCF 3 , F, Cl or Br.

[0291] In the vast majority of these compounds, R 20 and R 21 Different from each other, one of these groups is usually an alkyl or alkoxy group. Other variations of the proposed substituents are also conventional. Many such substances or mixtures thereof are commercially available. All of these substances can be prepared by methods known in the literature.

[0292] It is self-evident to the person skilled in the art that the VA, IPS or FFS mixtures according to the invention may also comprise compounds in which, for example, H, N, O, Cl and F have been replaced by the corresponding isotopes.

[0293] Polymerizable compounds, so-called reactive mesogens (RMs), such as disclosed in US Pat. No. 6,861,107, can further be added to the mixtures according to the invention in a concentration of preferably 0.01-5% by weight, particularly preferably 0.2-2% by weight, based on the mixture. These mixtures may also optionally contain initiators, such as described in US Pat. No. 6,781,665. Initiators, such as Irganox-1076 from BASF, are preferably added in an amount of 0-1% to the mixture comprising the polymerizable compounds. Mixtures of this type can be used in the so-called polymer-stabilized VA mode (PS-VA) or PSA (polymer-stabilized VA), in which polymerization of the reactive mesogens is intended to take place in the liquid-crystalline mixture. A prerequisite for this is that the liquid-crystalline compounds of the LC host do not react under the polymerization conditions of the reactive mesogens, i.e. generally on exposure to UV in the wavelength range of 320-360 nm. Liquid-crystalline compounds containing alkenyl side chains, such as CC-3-V, do not react under the polymerization conditions of the RMs (UV polymerization).

[0294] The mixture according to the invention may further comprise conventional additives, such as stabilizers, antioxidants, UV absorbers, nanoparticles, microparticles and the like.

[0295] The structure of the liquid crystal display according to the invention conforms to the customary geometry as described, for example, in EP-A 0 240 379.

[0296] The following examples are intended to illustrate the invention without limiting it. Above and below, percentage data indicate percentages by weight; all temperatures are expressed in degrees Celsius.

[0297] Throughout this application, 1,4-cyclohexylene rings and 1,4-phenylene rings are depicted as follows:

[0298]

[0299] Unless otherwise specified, a cyclohexylene ring is a trans-1,4-cyclohexylene ring.

[0300] Throughout this application and the working examples, the structures of the liquid crystal compounds are expressed by abbreviations. Unless otherwise indicated, they are converted into chemical formulas according to Tables 1-3. All groups C n H 2n+1 , C m H 2m+1 and C m‘ H 2m‘+1 or C n H 2n and C m H 2m is a straight-chain alkyl or alkylene group, each occurrence having n, m, m' or z C atoms. n, m, m', z each independently represent 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, preferably 1, 2, 3, 4, 5 or 6. Table 1 encodes the ring elements of each compound, Table 2 lists the bridge members and Table 3 illustrates the meaning of the symbols of the left-hand side chain or right-hand side chain of the compound.

[0301] Table 1: Ring elements

[0302]

[0303]

[0304]

[0305] Table 2: Bridge members

[0306]

[0307] Table 3: Sidechains

[0308]

[0309] Besides one or more compounds of the formula I, the mixtures according to the invention preferably comprise one or more compounds mentioned in Table A below.

[0310] Table A

[0311] The following abbreviations are used:

[0312] (n, m, m', z: in each case, independently of one another, are 1, 2, 3, 4, 5 or 6; (O) C m H 2m+1 Meaning OC m H 2m+1 or C m H 2m+1 )

[0313]

[0314]

[0315]

[0316]

[0317]

[0318]

[0319]

[0320]

[0321]

[0322]

[0323]

[0324]

[0325]

[0326]

[0327]

[0328]

[0329]

[0330]

[0331]

[0332]

[0333]

[0334]

[0335] The liquid crystal mixtures used according to the invention are prepared in a manner conventional per se. Usually, the required amount of the component used in smaller amounts is dissolved in the components constituting the main component, advantageously at elevated temperature. It is also possible to mix the solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent after thorough mixing, for example by distillation.

[0336] By means of suitable additives, the liquid-crystalline phases according to the invention can be modified so that they can be used in any type of ECB, VAN, IPS, GH or ASM-VA LCD displays which have been disclosed to date.

[0337] The dielectric may also contain other additives known to those skilled in the art and described in the literature, such as UV absorbers, antioxidants, nanoparticles and free radical scavengers. For example, 0-15% of pleochroic dyes, stabilizers such as phenols, HALS (hindered amine light stabilizers) or chiral dopants may be added. Suitable stabilizers for the mixtures according to the invention are in particular those listed in Table C.

[0338] For example, 0-15% of pleochroic dyes can be added, as well as conductive salts, preferably ethyldimethyldodecylammonium 4-hexyloxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (see, for example, Haller et al., Mol. Cryst. Liq. Cryst., Vol. 24, pp. 249-258 (1973)), to improve the conductivity or substances can be added to change the dielectric anisotropy, viscosity and / or the alignment of the nematic phase. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.

[0339] Table B

[0340] Table B shows possible dopants which are usually added to the mixtures according to the invention. If the mixtures comprise dopants, they are used in amounts of 0.01 to 4% by weight, preferably 0.01 to 3% by weight.

[0341]

[0342]

[0343] The mixture according to the invention comprises at least one stabilizer from Table C below.

[0344] Table C

[0345] For example, stabilizers which can be added to the mixture according to the invention in an amount of 0-10% by weight, preferably 0.001-5% by weight, in particular 0.001-1% by weight are as follows:

[0346]

[0347]

[0348]

[0349]

[0350]

[0351]

[0352]

[0353] Working Example:

[0354] The following examples are intended to illustrate the present invention but not to limit it. In the examples, mp represents the melting point, C represents the clearing point of the liquid crystal material, expressed in degrees Celsius; the boiling temperature is expressed in mp. Also: C represents the crystalline solid state, S represents the smectic phase (the index represents the phase type), N represents the nematic state, Ch represents the cholesteric phase, I represents the isotropic phase, T represents the crystalline solid state, and C represents the crystalline solid state. g Indicates the glass transition temperature. The number between the two symbols indicates the switching temperature in degrees Celsius.

[0355] The host mixture used to determine the optical anisotropy Δn of the compounds of formula I was the commercial mixture ZLI-4792 (Merck KGaA). The dielectric anisotropy Δε was determined using the commercial mixture ZLI-2857. The physical data for the compounds to be investigated were obtained from the change in the dielectric constant of the host mixture after the addition of the compound to be investigated and extrapolated to 100% of the compound used. Typically, 10% of the compound to be investigated was dissolved in the host mixture, depending on the solubility.

[0356] Unless stated otherwise, parts or percentages are parts or percentages by weight.

[0357] In context,

[0358] V o Indicates the threshold voltage, capacitance at 20°C [V]

[0359] n e represents the extraordinary refractive index at 20°C and 589nm,

[0360] n o represents the ordinary refractive index at 20°C and 589nm,

[0361] Δn represents the optical anisotropy measured at 20 °C and 589 nm

[0362] ε ⊥ represents the dielectric constant perpendicular to the director at 20°C and 1kHz,

[0363] ε || represents the dielectric constant parallel to the director at 20°C and 1kHz,

[0364] Δε represents the dielectric anisotropy at 20°C and 1kHz

[0365] cl.p.,T(N,I) represents the clearing point [℃]

[0366] γ 1 Indicates the rotational viscosity at 20°C [mPa·s], measured by the rotation method in a magnetic field

[0367] K 1 represents the elastic constant, the “unfolded” deformation at 20°C [pN]

[0368] K 2 represents the elastic constant, the "twist" deformation at 20°C [pN],

[0369] K 3 represents the elastic constant, the "bending" deformation at 20°C [pN],

[0370] and

[0371] LTS stands for low temperature stability (nematic phase) determined in test cells or bulk samples as described.

[0372] Unless expressly stated otherwise, all temperature values ​​indicated in this application, such as melting point T(C,N), transition from smectic (S) phase to nematic (N) phase T(S,N) and clearing point T(N,I) or cl.p., are expressed in degrees Celsius (°C). Mp denotes melting point. Also, Tg = glassy state, C = crystalline state, N = nematic phase, S = smectic phase and I = isotropic phase. The data between these symbols denote transition temperatures.

[0373] For the purposes of this invention, the term "threshold voltage" refers to the capacitive threshold (V0 ), also referred to as the Freedericksz threshold, unless otherwise expressly stated. In the embodiments, as is generally the case, the optical threshold (V 10 ).

[0374] The display used to measure the capacitive threshold voltage consisted of two plane-parallel glass outer plates separated by 20 μm, each of which had an electrode layer on the inside and an unrubbed polyimide alignment layer on top, which resulted in homeotropic edge alignment of the liquid crystal molecules.

[0375] The display or test cell for measuring the tilt angle consists of two plane-parallel glass outer plates separated by 4 μm, each of which has an electrode layer on the inside and a polyimide alignment layer on top, wherein the two polyimide layers are rubbed antiparallel to each other and result in homeotropic edge alignment of the liquid crystal molecules.

[0376] Unless otherwise specified, VHR is at 20°C (VHR 20 ) and in an oven at 100°C (VHR 100 ) after 5 minutes in a commercially available instrument Model 6254 from TOYO Corporation, Japan. Unless indicated more precisely, the voltages used have a frequency in the range from 1 Hz to 60 Hz.

[0377] The accuracy of the VHR measurement depends on the corresponding value of VHR. The accuracy decreases with decreasing values. The deviations usually observed in the case of values ​​within various value ranges are written in the table below in their order of magnitude.

[0378]

[0379]

[0380] The stability to UV radiation was investigated in the commercial instrument "Suntest CPS" from Heraeus, Germany. Unless expressly stated otherwise, the sealed test boxes were irradiated for 30 minutes to 2.0 hours without additional heating. The irradiation power in the wavelength range 300 nm-800 nm was 765 W / m 2 V. A UV "cut-off" filter with an edge wavelength of 310 nm was used to simulate the so-called window glass mode. In each series of experiments, at least four test boxes were investigated for each condition and the respective results are expressed as the mean of the respective individual measurements.

[0381] The reduction in voltage holding ratio (ΔVHR) typically caused by light exposure, such as UV irradiation or LCD backlight, is determined according to the following equation (1):

[0382] ΔVHR(t)=VHR(t)-VHR(t=0) (1)

[0383] To study the low temperature stability, also called "LTS", i.e. the stability of the LC mixture in the bulk against spontaneous crystallization of the individual components or, as the case may be, the appearance of a smectic phase at low temperatures, several sealed vials, each containing about 1 g of material, are stored at one or more given temperatures, typically -10°C, -20°C, -30°C and / or -40°C, and visually inspected at regular time intervals whether a phase change is observed. As soon as the first sample at a given temperature shows a change, the time is recorded. The time for which no change is observed until the last inspection is recorded as the corresponding LTS.

[0384] The ion density for calculating resistivity was measured using a commercially available LC material characteristics measurement system model 6254 from Toyo Corporation, Japan, using a VHR test cell of AL16301 polyimide (JSR Corp., Japan) with a cell gap of 3.2 μm. The measurements were performed after storage in an oven at 60° C. or 100° C. for 5 minutes.

[0385] By "HTP" is meant the helical twisting power (in μm) of an optically active or chiral substance in an LC medium. Unless otherwise indicated, HTP is measured at a temperature of 20°C in a commercially available nematic LC host mixture MLD-6260 (Merck KGaA).

[0386] Unless otherwise expressly stated, all concentrations in the present application are expressed as weight percent and relate to the corresponding entire mixture, which contains all solid or liquid crystal components and does not contain solvent. Unless otherwise expressly stated, all physical properties are 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.

[0387] The following mixture examples with negative dielectric anisotropy are particularly suitable for liquid-crystal displays having at least one planar alignment layer, such as IPS and FFS displays, in particular UB-FFS (=Ultra Bright FFS), and VA displays.

[0388] Mixture Examples and Comparative Examples

[0389] Prepare as follows Comparative mixture C1

[0390]

[0391]

[0392] This mixture has a rather poor response time but good VHR values.

[0393] Prepare as follows Comparative mixture C2 :

[0394]

[0395] This mixture shows an improved response time compared to the mixture of Comparative Example 1, mainly due to its reduced gamma 1 , but lower VHR results.

[0396] Prepare as follows Mixture M1 :

[0397]

[0398] Prepare as follows Mixture M2

[0399]

[0400] Storage tests at low temperatures were carried out with the above mixtures in test boxes of appropriate thickness.

[0401] The good VHR, and the simultaneously improved response time, are mainly due to its good (γ 1 / K 1 ) values, as shown in the following table.

[0402] Table 1: VHR values

[0403]

[0404] (Note: *All VHR values ​​are measured at 1V, 1Hz and 60°C).

Claims

1. A liquid crystal medium, characterized in that It comprises one or more compounds of formula I, in, R 11 and R 12 , each independently of one another represents H, an alkyl or alkoxy radical having 1 to 15 C atoms, wherein in addition, one or more CH2 groups in these radicals can each independently of one another be replaced by -C≡C-, -CF2O-, -OCF2-, -CH=CH-, -O-, -CO-O-, -O-CO- are substituted in such a way that the O atoms are not directly connected to one another, and wherein in addition one or more H atoms may be replaced by halogen, A 11 Each occurrence represents independently of the other a) 1,4-cyclohexenyl or 1,4-cyclohexylene, in which one or two non-adjacent CH2 groups may be replaced by -O- or -S-, b) 1,4-phenylene, in which one or both CH groups may be replaced by N, c) is selected from piperidine-1,4-diyl, 1,4-bicyclo[2.2.2]-octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl, wherein the groups a), b) and c) may be mono- or poly-substituted by halogen atoms, Z 11 represents, independently of one another at each occurrence, -CO-O-, -O-CO-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CH2CH2-, -(CH2)4-, -CH=CH-CH2O-, -C2F4-, -CH2CF2-, -CF2CH2-, -CF=CF-, -CH=CF-, -CF=CH-, -CH=CH-, -C≡C- or a single bond, and L 11 and L 12 each independently represents F, Cl, CF3 or CHF2, X 1 represents O or S, and a represents 1 or 2, preferably 1, and one or more compounds selected from the group consisting of compounds of formula IIA, IIB and IIC, in, R 2A , R 2B and R 2C each independently of one another represents H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF3 or at least monosubstituted by halogen, wherein in addition one or more CH2 groups in these radicals may be replaced by -O-, -S-, -C≡C-, -CF2O-, -OCF2-, -OC-O- or -O-CO- are substituted in such a way that the O atoms are not directly connected to each other, L 1 To L 4 each independently represents F or Cl, Z 2 and Z 2’ each independently represents a single bond, -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -COO-, -OCO-, -C2F4-, -CF=CF-, -CH=CHCH2O-, p means 0, 1 or 2 q represents 0 or 1, and v means 1-6.

2. The liquid crystal medium according to claim 1, characterized in that The medium comprises one or more compounds selected from the group consisting of compounds of formulae I-1 to I-3, The parameters have the meanings given in claim 1.

3. The liquid crystal medium according to claim 1 or 2, characterized in that It comprises one or more compounds selected from formulae IO-1 to IO-3, The parameters have the meanings given in claim 1.

4. Liquid-crystalline medium according to one or more of claims 1 to 3, characterized in that It comprises one or more compounds selected from the compounds of formulae IS-1 to I-SO-3, The parameters have the meanings given in claim 1.

5. Liquid-crystalline medium according to one or more of claims 1 to 4, characterized in that It comprises one or more compounds of formula IIA, The parameters have the meanings given in claim 1.

6. Liquid-crystalline medium according to one or more of claims 1 to 5, characterized in that It also comprises one or more compounds of formula IIB, The parameters have the meanings given in claim 1.

7. Liquid-crystalline medium according to one or more of claims 1 to 6, characterized in that The medium comprises one or more compounds of formula IIC, The parameters have the meanings given in claim 1.

8. Liquid-crystalline medium according to one or more of claims 1 to 7, characterized in that The medium further comprises one or more compounds selected from the group consisting of compounds of formulae O-1 to O-18, in, R 1 and R 2 Each independently has the following characteristics for R in claim 6 2A The meaning stated.

9. Liquid-crystalline medium according to one or more of claims 1 to 8, characterized in that The medium further comprises one or more compounds selected from the group consisting of compounds of formulae T-1 to T-21, in, R represents a straight-chain alkyl or alkoxy group having 1-6 C atoms, and m=0, 1, 2, 3, 4, 5 or 6, and n represents 0, 1, 2, 3 or 4.

10. Liquid-crystalline medium according to one or more of claims 1 to 9, characterized in that The proportion of the compound of the formula I in the mixture as a whole is from 1 to 40% by weight.

11. Liquid-crystalline medium according to one or more of claims 1 to 10, characterized in that The proportion of the compounds of the formulae IIA to IIC in the total medium is 10% to 70%.

12. Process for producing a liquid-crystalline medium according to one or more of claims 1 to 11, characterized in that One or more compounds of formula I are mixed with one or more compounds selected from the group consisting of compounds of formulae IIA to IIC and one or more compounds of formulae.

13. Use of a liquid-crystalline medium according to one or more of claims 1 to 11 in electro-optical displays.

14. An electro-optical display with active matrix addressing, characterized in that It comprises a liquid-crystalline medium according to one or more of claims 1 to 11 as dielectric.

15. The electro-optic display of claim 15, wherein the electro-optic display is a VA, PSA, PA-VA, SS-VA, SA-VA, PS-VA, PALC, IPS, PS-IPS, FFS, UB-FFS, U-IPS, or PS-FFS display.

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