Liquid crystal medium and liquid crystal display

Abstract

The invention relates to a dielectric positive liquid crystal medium comprising one or more compounds of formulae S1 and S2, # imgabs0 # and one or more compounds selected from the group consisting of compounds of formulae II and III and / or IV and / or VIII # imgabs1 # wherein the parameters have the respective meanings indicated in the description, and optionally one or more other dielectrically positive compounds and optionally one or more other dielectrically neutral compounds, and to liquid crystal displays, in particular active matrix displays, in particular TN, IPS and FFS displays, comprising these media.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of August 27, 2019, an application number of 201910793105.X, and an invention title of "Liquid Crystal Medium and Liquid Crystal Display". Technical Field

[0002] The present invention relates to liquid crystal media and to liquid crystal displays containing these media, in particular to displays addressed by active matrix, and especially to displays of the twisted nematic (TN), in-plane switching (IPS) or fringe field switching (FFS) type. Background Art

[0003] Prior Art and Problems to be Solved

[0004] Liquid crystal displays (LCDs) are used for information display in many fields. LCDs are used for both direct-view displays and for projection displays. Electro-optical modes used are, for example, the 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 of these modes employ an electric field substantially perpendicular to the substrate or the liquid crystal layer. In addition to these modes, there are 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 edge, 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 intended for television and multimedia applications. Liquid crystals according to the present invention are preferably used in this type of display. Generally, a dielectrically positive liquid crystal medium having a relatively low dielectric anisotropy value is used in FFS displays, but in some cases, a liquid crystal medium having a dielectric anisotropy of only about 3 or even lower is also used in IPS displays.

[0005] For these displays, novel liquid crystal dielectrics with improved properties are required. For many types of applications, it is particularly necessary to improve the addressing time. Therefore, liquid crystal dielectrics with a low viscosity (η), in particular with a low rotational viscosity (γ1), are needed. Especially for monitor applications, the rotational viscosity should be 80 mPa·s or lower, preferably 60 mPa·s or lower, especially 55 mPa·s or lower. In addition to these viscosity parameters, the dielectric must have a nematic phase range of suitable width and position and a suitable birefringence (Δn). Furthermore, the dielectric anisotropy (Δε) should be high enough to allow a fairly low operating voltage. Δε should preferably be greater than 2, more preferably greater than 3, but preferably not greater than 20, especially not greater than 17, as this can prevent at least a fairly high resistivity.

[0006] For applications as displays in laptop computers or other mobile applications, the rotational viscosity should preferably be 120 mPa·s or lower, particularly preferably 100 mPa·s or lower. Here, the dielectric anisotropy (Δε) should preferably be greater than 8, particularly preferably greater than 12.

[0007] 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 (TFT). However, the liquid crystals according to the invention can also be advantageously used in displays with other known addressing methods.

[0008] There are many different display modes that use composite systems of low molecular weight liquid crystal materials and polymer materials. These are, for example, polymer dispersed liquid crystals (PDLC), nematic curvilinear aligned phases (NCAP), and polymer network (PN) systems, such as those disclosed in WO 91 / 05 029, or axially symmetric microdomain (ASM) systems, etc. In contrast to these, the display mode particularly preferred according to the invention uses the liquid crystal dielectric itself, which is oriented on the surface. These surfaces are usually pretreated to achieve a uniform alignment of the liquid crystal material. The display mode according to the invention preferably uses an electric field that is substantially parallel to the composite layer.

[0009] Liquid crystal compositions suitable for LCDs and especially suitable 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 compositions have serious drawbacks. Among other deficiencies, most of them result in unfavorably long addressing times, have insufficient resistivity values, and / or require too high an operating voltage. In addition, improvement of the low-temperature behavior of LCDs is needed. Improvements are necessary herein in terms of both operating performance and shelf life, especially stability against visible and ultraviolet radiation, and stability against heat, especially the combination of heat and light and / or ultraviolet radiation.

[0010] This concerns not only the normal life cycle of the display, but also the individual steps in the production of the display, where, in some cases, these displays are subjected to extreme loads compared to normal operation. Thus, for example, in the production of the bonding of the frame, a method is often employed that results in a very high thermal load on the display already containing liquid crystal. To enable the liquid crystal to survive this strong thermal load without damage, it is advantageous to add one or more thermal stabilizers to the liquid crystal formulation accordingly. In the subsequent daily operation of the display, loads caused by the light of the backlight and by ambient light (usually daylight) and temperature loads from the environment may subsequently occur as important load factors. This means that, in particular, the combination of various load amounts may be of particular importance in practice.

[0011] This combination of various loads can occur in sequential chronological order or can occur in parallel in time. Thus, for example, depending on the installation location, a display used as an electronic billboard can be simultaneously subjected to strong heating and sunlight during operation and in the stationary state.

[0012] EP 3 246 374 etc. disclose a dielectrically positive LC mixture containing the following

[0013]

[0014] EP 3 112 441 also discloses a dielectrically positive LC mixture containing the following

[0015]

[0016] which preferably contains simultaneously

[0017]

[0018] or

[0019]

[0020] Many liquid crystal media, especially those with large polarity or high dielectric anisotropy, do not meet the high stability requirements needed for practical applications.

[0021] Therefore, there is a considerable need for liquid crystal media having properties suitable for practical applications, such as a broad nematic range, a suitable optical anisotropy Δn corresponding to the type of display used, a high Δε, and a particularly low viscosity for particularly short response times. SUMMARY OF THE INVENTION

[0022] Surprisingly, it has been found that liquid crystal media with a suitably high Δε, a suitable phase range, and a suitable Δn can be achieved which do not exhibit the disadvantages of the materials of the prior art, or at least exhibit said disadvantages only to a significantly lesser extent.

[0023] Surprisingly, it has been found here that, as shown below, compounds of the formulas S1 and S2 lead to a considerable, in most cases sufficient, stability of the liquid crystal mixture.

[0024] The present invention relates to a liquid crystal medium having a nematic phase and a positive dielectric anisotropy, comprising:

[0025] a) one or more compounds of formula S1 and one or more compounds of formula S2, preferably in concentration ranges each of 1 ppm to 5,000 ppm, more preferably in concentration ranges each of 100 ppm to 2,000 ppm.

[0026]

[0027]

[0028] wherein each group, independently of one another and in each occurrence, is the same or different and has the following meanings:

[0029] represents

[0030] R a-d is a straight-chain or branched alkyl having 1 to 10 C atoms, preferably having 1 to 6 C atoms, very preferably having 1 to 4 C atoms, most preferably methyl.

[0031] X is H, CH3, OH or O ● preferably H.

[0032] A is a straight-chain, branched or cyclic alkylene having 1 to 20 C atoms, which is optionally substituted, preferably -(CH2)8-, and

[0033] n is an integer from 1 to 6, preferably 3.

[0034] and

[0035] b) one or more compounds selected from the compounds of formula II and III

[0036]

[0037] wherein

[0038] R 2 and R 3 , independently of one another, represent alkyl, alkoxy, fluoroalkyl or fluoroalkoxy having 1 to 7 C atoms, alkenyl, alkenoxy, alkoxyalkyl or fluoroalkenyl having 2 to 7 C atoms, and preferably R 2 and R 3 represent alkyl or alkenyl,

[0039]

[0040] each occurrence, independently of one another, represents

[0041]

[0042] preferably

[0043]

[0044] L 21 L 22 L 31 and L 32 , independently of one another, represent H or F,

[0045] preferably

[0046] L 21 and / or L 31 represents F,

[0047] X 2 and X 3 , independently of one another, represent halogen, haloalkyl or alkoxy having 1 - 3 C atoms or haloalkenyl or alkenoxy having 2 or 3 C atoms, preferably F, Cl, -OCF3 or -O-CH=CF2, -CF3, especially F, -OCF3 or -O-CH=CF2,

[0048] Z 3 represents -CH2CH2-, -CF2CF2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O- or a single bond, preferably -CH2CH2-, -COO-, trans-CH=CH- or a single bond and very preferably -COO-, trans-CH=CH- or a single bond, and

[0049] m and n, independently of one another, represent 0, 1, 2 or 3,

[0050] m preferably represents 1, 2 or 3, and

[0051] n preferably represents 0, 1 or 2 and particularly preferably 1 or 2,

[0052] and / or

[0053] c) one or more compounds of formula IV

[0054]

[0055] wherein

[0056] R 41 and R 42 , independently of one another, have the meanings shown above for R 2 under formula II, preferably R 41 represents alkyl and R 42 represents alkyl or alkoxy or R 41 represents alkenyl and R 42 represents alkyl,

[0057]

[0058] independently of one another, and, if occur twice, these also independently of one another represent

[0059]

[0060] preferably

[0061] one or more of represent

[0062] Z 41 and Z 42 , independently of one another and, if Z 41 occurs twice, these also independently of one another represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O-, -C≡C- or a single bond, preferably one or more of them represent a single bond, and

[0063] p represents 0, 1 or 2, preferably 0 or 1,

[0064] and / or

[0065] d) one or more compounds of formula VIII

[0066]

[0067] Among them

[0068] R 81 and R 82 , each independently has the meaning shown above for R under formula II, and 2 and

[0069] means

[0070] preferably

[0071]

[0072]

[0073] means

[0074]

[0075] Z 81 and Z 82 , each independently represents -CH2CH2-, -C≡C-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, preferably one or more of them represent a single bond and very preferably both represent a single bond,

[0076] L 81 and L 82 , each independently represents C-F or N, preferably one of L 81 and L 82 represents or both represent C-F and very preferably both represent C-F, and

[0077] s represents 0 or 1 and

[0078] L 81 and L 82 , each independently represents C-F or N, preferably one of L 81 and L 82 represents or both represent C-F and very preferably both represent C-F, and

[0079] In the case of

[0080]

[0081] means one of L

[0082] L 81 and L 82 alternatively may represent C-H.

[0083] The present invention also relates to an LC medium as described above in the context, which further comprises one or more polymerizable compounds.

[0084] In the present application, elements include all their respective isotopes. In particular, one or more H in a compound can be replaced by D, and this is also particularly preferred in certain embodiments. The corresponding highly deuterated corresponding compounds enable, for example, the detection and identification of compounds. This is very useful in certain cases, especially in the case of compounds of formulas S1 and S2.

[0085] In the present application,

[0086] Alkyl particularly preferably denotes a straight-chain alkyl, especially CH3-, C2H5-, n-C3H7-, n-C4H9- or n-C5H 11 -, and

[0087] Alkenyl particularly preferably denotes CH2=CH-, E-CH3-CH=CH-, CH2=CH-CH2-CH2-, E-CH3-CH=CH-CH2-CH2- or E-(n-C3H7)-CH=CH-.

[0088] The liquid crystal medium according to the present application preferably comprises in total from 1 ppm to 25,000 ppm, preferably from 50 ppm to 20,000 ppm, even more preferably from 100 to 15,000 ppm, preferably at most 10,000 ppm, very particularly preferably from 200 ppm to 10,000 ppm of compounds of formulas S1 and S2. In another preferred embodiment, the liquid crystal medium according to the present application comprises in total from 1 ppm to 2,000 ppm, preferably from 10 ppm to 1,000 ppm, even more preferably from 20 to 600 ppm, preferably at most 500 ppm, and very particularly preferably from 50 ppm to 400 ppm of compounds of formulas S1 and S2.

[0089] Compounds of formulas S1 and S2 are very suitable as stabilizers in liquid crystal mixtures. In particular, they provide very effective thermal stability for such mixtures. In contrast to these compounds, hitherto known compounds providing good thermal stability lead to a more or less significant reduction in the "voltage holding ratio" (VHR or simply HR for short) upon UV exposure. In contrast, compounds of formulas S1 and S2 show a significant improvement. Although the HR of the mixture often still decreases after UV exposure, this reduction in HR upon UV exposure is significantly less compared to what occurs in the case of hitherto known materials.

[0090] Preferred compounds of formula S1 are selected from the following sub-formulas

[0091]

[0092]

[0093] Most preferably, it is a compound of formula S1a.

[0094] The preferred compounds of formula S2 are selected from the following sub-formulas

[0095]

[0096] Most preferably, it is a compound of formula S2a.

[0097] In a preferred embodiment of the present invention, the medium according to the present invention comprises one or more compounds of formulas S1 and S2, preferably selected from their respective preferred sub-formulas,

[0098] and

[0099] one or more compounds of formula II, preferably selected from their preferred sub-formulas,

[0100] and / or

[0101] one or more compounds of formula III, preferably selected from their preferred sub-formulas,

[0102] and / or

[0103] one or more compounds of formula IV, preferably selected from their preferred sub-formulas,

[0104] and / or

[0105] one or more compounds of formula VIII, preferably selected from their preferred sub-formulas.

[0106] In addition to the compounds of formulas S1 and S2 or their preferred sub-formulas, the medium according to the present invention preferably comprises one or more dielectrically neutral compounds of formula Iv, with a total concentration of 5% or higher to 90% or lower, preferably 10% or higher to 80% or lower, and particularly preferably 20% or higher to 70% or lower.

[0107] The compounds of formulas II and III are preferably dielectrically positive compounds, preferably having a dielectric anisotropy greater than 3.

[0108] The compounds of formula IV are preferably dielectrically neutral compounds, preferably having a dielectric anisotropy of -1.5 to 3.

[0109] The compounds of formulas S1 and S2 are very suitable as stabilizers in liquid crystal mixtures. In particular, they provide very effective thermal stability of the mixture. Materials that have provided good thermal stability to date have led to a more or less significant reduction in HR upon UV exposure. In contrast, the compounds of formulas S1 and S2 show an improvement, i.e., a reduction in the decrease of HR upon UV exposure.

[0110] The use concentration of each compound of formula II and / or III is 1-20%, preferably 1-15%. In particular, if two or more homologues of the same formula, i.e., compounds of the same formula, are used in each case, these limitations apply. If only a single substance of a compound of the formula is used, i.e., only one homologue, its concentration can be 2 to 20%, preferably 3 to 14%.

[0111] In addition to the compounds of formula S1 and S2 or their preferred sub-formulae, the medium according to the invention preferably contains one or more dielectrically positive compounds with a dielectric anisotropy greater than 3, selected from the compounds of formula II and III.

[0112] In a preferred embodiment of the invention, the medium according to the invention contains one or more compounds selected from the following: compounds of formula II-1 to II-4, preferably formula II-1 and / or II-2,

[0113]

[0114]

[0115] wherein the parameters have their respective meanings as shown above under formula II, and L 23 and L 24 , independently of each other, represent H or F, preferably L 23 represents F, and

[0116] has one of the meanings given for

[0117] and, in the case of formula II-1 and II-4, X 2 preferably represents F or OCF3, particularly preferably F, and, in the case of formula II-3,

[0118] , independently of each other, preferably represent

[0119]

[0120] and / or compounds selected from formula III-1 and III-2:

[0121]

[0122] wherein the parameters have the meanings given under formula III.

[0123] In a preferred embodiment, the medium according to the invention contains one or more compounds of formula III-3 in addition to or in place of the compounds of formula III-1 and / or III-2

[0124]

[0125] wherein the parameters have their respective meanings as indicated above, and the parameter L 31 and L 32 , independently of each other and independently of the other parameters, represent H or F.

[0126] The medium according to the invention preferably comprises one or more compounds selected from the compounds of formulae II-1 to II-4, wherein L 21 and L 22 and / or L 23 and L 24 both represent F.

[0127] In a preferred embodiment, the medium comprises one or more compounds selected from the compounds of formulae II-2 and II-4, wherein L 21 , L 22 , L 23 and L 24 all represent F.

[0128] The medium preferably comprises one or more compounds of formula II-1. The compounds of formula II-1 are preferably selected from the compounds of formulae II-1a to II-1f:

[0129]

[0130] wherein the parameters have their respective meanings as indicated above, and L 23 to L 25 , independently of each other and independently of the other parameters, represent H or F, and

[0131] preferably

[0132] in formulae II-1a and II-1b

[0133] L 21 and L 22 both represent F,

[0134] in formulae II-1c and II-1d

[0135] L 21 and L 22 both represent F and / or L 23 and L 24 both represent F, and

[0136] in formula II-1e

[0137] L 21 , L 22 and L 25 represent F, and in each case, the other parameters have their respective meanings given above.

[0138] Particularly preferred compounds of formula II-1 are

[0139]

[0140]

[0141] wherein R 2 has the above meanings, in particular the compounds of formula II-1a-2.

[0142] The medium preferably contains one or more compounds of formula II-2, which are preferably selected from the compounds of formula II-2a to II-2k

[0143]

[0144]

[0145]

[0146] wherein the parameters have their respective meanings as indicated above, and L 25 to L 28 , independently of one another, represent H or F, preferably L 27 and L 28 both represent H, particularly preferably L 26 represents H and the other parameters have their respective meanings as above.

[0147] The medium according to the invention preferably contains one or more compounds selected from the compounds of formula II-2a to II-2k, wherein L 21 and L 22 both represent F and / or L 23 and L 24 both represent F, and the other parameters have their respective meanings as above.

[0148] In a preferred embodiment, the medium according to the invention contains one or more compounds selected from the compounds of formula II-2a to II-2k, wherein L 21 , L 22 , L 23 and L 24 all represent F, and the other parameters have their respective meanings as above.

[0149] Particularly preferred compounds of formula II-2 are the compounds of the following formula:

[0150]

[0151]

[0152]

[0153] wherein R 2 and X 2 have the meanings given above, and X 2 preferably represents F, and particularly preferably compounds of formula II-2a-1 and / or II-2h-1 and / or II-2j-1 and / or II-2k-1.

[0154] The medium according to the invention preferably comprises one or more compounds of formula II-3, which are preferably selected from the compounds of formulae II-3a to II-3c

[0155]

[0156] wherein the parameters have their respective meanings as indicated above, and L 21 and L 22 both preferably represent F.

[0157] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula II-4, preferably a compound of formula II-4a,

[0158] wherein the parameters have the meanings given above, and X 2 preferably represents F or OCF3, and particularly preferably F.

[0159] The medium according to the invention preferably comprises one or more compounds of formula III-1, which are preferably selected from the compounds of formulae III-1a and III-1b

[0160]

[0161] wherein the parameters have their respective meanings as indicated above, and the parameter L 33 and L 34 , independently of each other and independently of the other parameters, represent H or F.

[0162] The medium according to the invention preferably comprises one or more compounds of formula III-1a, which are preferably selected from the compounds of formulae III-1a-1 to III-1a-6:

[0163]

[0164]

[0165] wherein R 3 has the meaning indicated above.

[0166] The medium according to the invention preferably comprises one or more compounds of formula III-1b, which are preferably selected from the compounds of formulae III-1b-1 to III-1b-4, preferably a compound of formula III-1b-4:

[0167]

[0168]

[0169] wherein R 3 has the meaning indicated above.

[0170] The medium according to the invention preferably comprises one or more compounds of formula III-2, which are preferably selected from the compounds of formulae III-2a to III-2k:

[0171]

[0172]

[0173]

[0174] wherein the parameters have the meanings given above and preferably wherein the parameters have their respective meanings indicated above, and the parameter L 33 , L 34 , L 35 and L 36 , independently of one another and independently of the other parameters, represent H or F.

[0175] The medium according to the invention preferably comprises one or more compounds of formula III-2a, which are preferably selected from the compounds of formulae III-2a-1 to III-2a-5

[0176]

[0177] wherein R 3 has the meaning as defined above.

[0178] The medium according to the invention preferably comprises one or more compounds of formula III-2b, which are preferably selected from the compounds of formulae III-2b-1 to III-2b-2, preferably the compound of formula III-2b-2

[0179]

[0180] wherein R 3 has the meaning as defined above.

[0181] The medium according to the invention preferably comprises one or more compounds of formula III-2c, which are preferably selected from the compounds of formulae III-2c-1 to III-2c-6:

[0182]

[0183]

[0184] wherein R 3 has the above meanings, and compounds of formula III-2c-1 and / or III-2c-2 and / or III-2c-4 are particularly preferred.

[0185] The medium according to the invention preferably comprises one or more compounds selected from the compounds of formula III-2d and III-2e, preferably selected from the compounds of formula III-2d-1 and III-2e-1

[0186]

[0187] wherein R 3 has the above meanings.

[0188] The medium according to the invention preferably comprises one or more compounds of formula III-2f, preferably selected from the compounds of formula III-2f-1 to III-2f-5

[0189]

[0190]

[0191] wherein R 3 has the above meanings.

[0192] The medium according to the invention preferably comprises one or more compounds of formula III-2g, preferably selected from the compounds of formula III-2g-1 to III-2g-5

[0193]

[0194]

[0195] wherein R 3 has the above meanings.

[0196] The medium according to the invention preferably comprises one or more compounds of formula III-2h, preferably selected from formula III-2h-1 to III-2h-3, preferably the compound of formula III-2h-3

[0197]

[0198] wherein the parameters have the meanings given above, and X 3 preferably represents F.

[0199] The medium according to the invention preferably comprises one or more compounds of formula III-2i, preferably selected from formula III-2i-1 and III-2i-2, particularly preferably the compound of formula III-2i-2

[0200]

[0201] wherein the parameters have the meanings given above, and X 3 preferably represents F or OCF3.

[0202] The medium according to the invention preferably comprises one or more compounds of formula III-2j, which are preferably selected from formulae III-2j-1 to III-2j-2, particularly preferably the compound of formula III-2j-1

[0203]

[0204] wherein the parameters have the meanings given above.

[0205] The medium according to the invention preferably comprises one or more compounds of formula III-2k, which are preferably the compound of formula III-2k-1:

[0206]

[0207] wherein the parameters have the meanings given above and X 3 preferably represents F.

[0208] Instead of or in addition to the compounds of formula III-1 and / or III-2, the medium according to the invention may comprise one or more compounds of formula III-3

[0209]

[0210] wherein the parameters have the respective meanings shown above under formula III.

[0211] These compounds are preferably selected from formulae III-3a and III-3b

[0212]

[0213] wherein R 3 has the meaning given above.

[0214] The liquid crystal medium according to the invention preferably comprises a dielectrically neutral component, component C. This component has a dielectric anisotropy in the range from -1.5 to 3. It preferably comprises a dielectrically neutral compound having a dielectric anisotropy in the range from -1.5 to 3, more preferably consists mainly of it, even more preferably consists essentially of it and particularly preferably consists entirely of it. Such a component preferably comprises one or more dielectrically neutral compounds, more preferably consists mainly of dielectrically neutral compounds of formula IV having a dielectric anisotropy in the range from -1.5 to 3, even more preferably consists essentially of it and very preferably consists entirely of it.

[0215] The dielectrically neutral component, component C, preferably comprises one or more compounds selected from the compounds of formulae IV-1 to IV-8:

[0216]

[0217] wherein R 41 and R 42 have their respective meanings as indicated above under formula IV, and in formulae IV-1, IV-6 and IV-7, R 41 preferably represents alkyl or alkenyl, preferably alkenyl, and R 42 preferably represents alkyl or alkenyl, preferably alkyl, and in formula IV-2, R 41 and R 42 preferably represent alkyl, and in formula IV-5, R 41 preferably represents alkyl or alkenyl, more preferably alkyl, and R 42 preferably represents alkyl, alkenyl or alkoxy, more preferably alkenyl or alkoxy, and in formulae IV-4 and IV-8, R 41 preferably represents alkyl and R 42 preferably represents alkyl or alkoxy, more preferably alkoxy.

[0218] The dielectrically neutral component, component C, preferably comprises one or more compounds selected from the compounds of formulae IV-1, IV-5, IV-6 and IV-7, preferably one or more compounds of formula IV-1 and one or more compounds selected from formulae IV-5 and IV-6, more preferably one or more compounds of each of formulae IV-1, IV-5 and IV-6, and very preferably one or more compounds of each of formulae IV-1, IV-5, IV-6 and IV-7.

[0219] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula IV-4, more preferably each of the respective sub-formulae selected from formulae CP-V-n and / or CP-nV-m and / or CP-Vn-m, more preferably formulae CP-V-n and / or CP-V2-n, very preferably selected from formulae CP-V-1 and CP-V2-1. The definitions of these abbreviations (acronyms) are shown in Table D below, or are obvious from Tables A to C.

[0220] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula IV-5, more preferably one or more compounds of each of the respective sub-formulae selected from formulae CCP-V-n and / or CCP-nV-m and / or CCP-Vn-m, said sub-formulae more preferably formulae CCP-V-n and / or CCP-V2-n and very preferably selected from CCP-V-1 and CCP-V2-1. The definitions of these abbreviations (acronyms) are indicated below in Table D, or are obvious from Tables A to C.

[0221] In an equally preferred embodiment, the medium according to the invention comprises one or more compounds of formula IV-1, more preferably selected from its individual sub-formulae, which are of the formula CC-n-m, CC-n-V, CC-n-Vm, CC-V-V, CC-V-Vn and / or CC-nV-Vm, more preferably of the formula CC-n-V and / or CC-n-Vm, and very preferably selected from the formulae CC-3-V, CC-4-V, CC-5-V, CC-3-V1, CC-4-V1, CC-5-V1, CC-3-V2 and CC-V-V1. The definitions of these abbreviations (acronyms) are likewise indicated in Table D below, or are obvious from Tables A to C.

[0222] In another preferred embodiment of the invention, which may be the same as or different from the previous one, the liquid crystal mixture according to the invention comprises component C, which component C comprises a compound of formula IV, preferably consists mainly of it and very preferably consists entirely of it, said compound of formula IV being selected from the compounds of formulae IV-1 to IV-8 as shown above and optionally the compounds of formulae IV-9 to IV-15:

[0223]

[0224]

[0225] where

[0226] R 41 and R 42 , independently of one another, represent an alkyl, alkoxy, fluoroalkyl or fluoroalkoxy group having 1 to 7 C atoms, an alkenyl, alkenoxy, alkoxyalkyl or fluoroalkenyl group having 2 to 7 C atoms, and

[0227] L 4 represents H or F.

[0228] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula IV-10, more preferably one or more compounds selected from its individual sub-formulae, which are of the formula CPP-3-2, CPP-5-2 and CGP-3-2, more preferably of the formula CPP-3-2 and / or CGP-3-2 and very particularly preferably of the formula CPP-3-2. The definitions of these abbreviations (acronyms) are indicated below in Table D, or are obvious from Tables A to C.

[0229] The liquid crystal medium according to the invention preferably comprises one or more compounds of formula V

[0230]

[0231] where

[0232] R 51 and R 52 , each independently has the meaning as indicated above for R under formula II, preferably R 2 represents alkyl and R 51 represents alkyl or alkenyl, 52 If it appears twice, in each case independently of one another at each occurrence, it represents

[0233] If it appears twice, in each case independently of one another at each occurrence, it represents

[0234]

[0235] Preferably

[0236] one or more of represents

[0237] Z 51 and Z 52 , each independently, and if Z 51 appears twice, then these also each independently represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, preferably one or more of them represents a single bond, and

[0238] r represents 0, 1 or 2, preferably 0 or 1, particularly preferably 1.

[0239] The compound of formula V is preferably a dielectrically neutral compound having a dielectric anisotropy in the range of -1.5 to 3.

[0240] The medium according to the invention preferably comprises one or more compounds selected from the compounds of formula V-1 and V-2

[0241]

[0242] wherein R 51 and R 52 have their respective meanings as indicated above under formula V, and R 51 preferably represents alkyl, and in formula V-1, R 52 preferably represents alkenyl, preferably -(CH2)2-CH=CH-CH3, and in formula V-2, R 52 preferably represents alkyl or alkenyl, preferably -CH=CH2, -(CH2)2-CH=CH2 or -(CH2)2-CH=CH-CH3.

[0243] The medium according to the invention preferably comprises one or more compounds selected from the compounds of formula V-1 and V-2, wherein R51 preferably represents a normal alkyl group, and in formula V-1, R 52 preferably represents an alkenyl group, and in formula V-2, R 52 preferably represents a normal alkyl group.

[0244] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula V-1, more preferably its sub-formula PP-n-2Vm compounds, and even more preferably the compound of formula PP-1-2V1. The definitions of these abbreviations (acronyms) are indicated in Table D below, or are obvious from Tables A to C.

[0245] In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula V-2, more preferably its sub-formulas PGP-n-m, PGP-n-V, PGP-n-2Vm, PGP-n-2V and PGP-n-2Vm compounds, and even more preferably its sub-formulas PGP-3-m, PGP-n-2V and PGP-n-V1 compounds, and very preferably compounds selected from the formulas PGP-3-2, PGP-3-3, PGP-3-4, PGP-3-5, PGP-1-2V, PGP-2-2V and PGP-3-2V. The definitions of these abbreviations (acronyms) are likewise indicated in Table D below, or are obvious from Tables A to C.

[0246] Alternative or in addition to the compounds of formula II and / or III, the medium according to the invention may further comprise one or more dielectrically positive compounds of formula VI

[0247]

[0248] wherein

[0249] R 6 represents an alkyl, alkoxy, fluoroalkyl or fluoroalkoxy group having 1 to 7 C atoms, an alkenyl, alkenyloxy, alkoxyalkyl or fluoroalkenyl group having 2 to 7 C atoms, and preferably an alkyl or alkenyl group

[0250] independently of one another represent

[0251]

[0252] L 61 and L 62 , independently of one another represent H or F, preferably L 61 represents F,

[0253] X 6denotes a halogen, a haloalkyl or alkoxy group having 1 - 3 C atoms or a haloalkenyl or alkenoxy group having 2 or 3 C atoms, preferably F, Cl, -OCF3 or -CF3, very preferably F, Cl or -OCF3,

[0254] Z 6 denotes -CH2CH2-, -CF2CF2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O- or -CF2O-, preferably -CH2CH2-, -COO- or trans-CH=CH- and very preferably -COO- or trans-CH=CH-, and

[0255] q denotes 0 or 1.

[0256] The medium according to the invention preferably comprises one or more compounds of formula VI, which are preferably selected from the compounds of formula VI-1 and VI-2

[0257]

[0258] wherein the parameters have the respective meanings indicated above, and the parameter L 63 and L 64 , independently of each other and independently of the other parameters, denote H or F, and Z 6 preferably denotes -CH2-CH2-.

[0259] The compounds of formula VI-1 are preferably selected from the compounds of formula VI-1a and VI-1b

[0260]

[0261] wherein R 6 has the above meaning.

[0262] The compounds of formula VI-2 are preferably selected from the compounds of formula VI-2a to VI-2d

[0263]

[0264] wherein R 6 has the above meaning.

[0265] Additionally, the liquid crystal medium according to the invention may comprise one or more compounds of formula VII

[0266]

[0267] wherein

[0268] R 7 has the meaning indicated above for R 2 under formula II,

[0269] the ring present

[0270] One of the representations

[0271]

[0272] Preferably

[0273]

[0274] Preferably

[0275]

[0276] Represents Has the same meaning as other groups or independently of each other represents

[0277]

[0278] Preferably

[0279]

[0280] Z 71 And Z 72 , independently of each other, represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, preferably one or more of them represent a single bond and very preferably both represent a single bond,

[0281] t represents 0, 1 or 2, preferably 0 or 1, more preferably 1, and

[0282] X 7 Has the meaning as indicated above for X under formula II 2 , or alternatively, independently of R 7 , may have one of the meanings indicated for R 7 .

[0283] The compound of formula VII is preferably a dielectrically positive compound.

[0284] In addition, the liquid crystal medium according to the present invention may contain one or more compounds of formula VIII

[0285]

[0286] Wherein

[0287] R 81 And R 82 , independently of each other, have the meanings as shown above for R under formula II 2 , and

[0288] represent

[0289] preferably

[0290]

[0291]

[0292] represent

[0293]

[0294] Z 81 and Z 82 , independently of one another, represent -CH2CH2-, -C≡C-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, preferably one or more of them represent a single bond and very preferably both represent a single bond,

[0295] s represents 0 or 1 and

[0296] L 81 and L 82 , independently of one another, represent C-F or N, preferably L 81 and L 82 one or both of them represent C-F and very preferably both represent C-F, and

[0297] in

[0298]

[0299] represent case,

[0300] L 81 and L 82 one or both of them alternatively may represent C-H.

[0301] The compound of formula VIII is preferably a dielectrically negative compound. Preferably, the compound of formula VIII is selected from the compounds of the following sub-formulas of formula VIII

[0302]

[0303]

[0304] wherein each group, independently of one another and each time it appears, the same or different, has the following meanings:

[0305] represent

[0306] representation

[0307]

[0308] wherein at least one ring F is cyclohexenylene,

[0309] R 1 and R 2 is an alkyl group having 1 to 12 C atoms, wherein in addition, one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO- in such a way that the O atoms are not directly connected to each other, preferably an alkyl group or an alkoxy group having 1 to 6 C atoms,

[0310] Z x and Z y is -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond,

[0311] L 1-4 is F, Cl, OCF3, CF3, CH3, CH2F, CHF2,

[0312] a is 1 or 2,

[0313] b is 0 or 1, and

[0314] f is 1 or 2.

[0315] The liquid crystal medium according to the invention preferably comprises one or more compounds selected from the compounds of formulae I to VIII, preferably the compounds of formulae I to VII and more preferably the compounds of formulae I and II and / or III and / or IV and / or VI. They are particularly preferably mainly composed of these compounds, even more preferably substantially composed of these compounds and very preferably completely composed of these compounds.

[0316] In the present application, "comprising" in relation to a composition means that the entity under discussion, i.e. the medium or the component, comprises the one or more components or one or more compounds indicated, preferably with a total concentration of 10% or higher, and very preferably 20% or higher.

[0317] In this regard, "consisting essentially of" means that the entity under discussion comprises 55% or higher, preferably 60% or higher and very preferably 70% or higher of the one or more components or one or more compounds indicated.

[0318] In this regard, "consisting essentially of" means that the entity in question contains 80% or more, preferably 90% or more and very preferably 95% or more of the indicated one or more components or one or more compounds.

[0319] In this regard, "consisting almost entirely of" or "consisting entirely of" means that the entity in question contains 98% or more, preferably 99% or more and very preferably 100% of the indicated one or more components or one or more compounds.

[0320] It is also possible and advantageous to use other mesogenic compounds not specifically mentioned above in the medium according to the invention. Such compounds are known to those skilled in the art.

[0321] The liquid crystal medium according to the invention preferably has a clearing point of 70 °C or greater, more preferably 75 °C or greater, particularly preferably 80 °C or greater and very particularly preferably 85 °C or greater.

[0322] The nematic phase of the medium according to the invention preferably extends at least from 0 °C or less to 70 °C or greater, more preferably at least from -20 °C or less to 75 °C or greater, very preferably at least from -30 °C or less to 75 °C or greater and especially at least from -40 °C or less to 80 °C or greater.

[0323] At 1 kHz and 20 °C, the Δε of the liquid crystal medium according to the invention is preferably 2 or greater, more preferably 3 or greater, even more preferably 4 or greater and very preferably 6 or greater. Δε is preferably 30 or less, and Δε is particularly preferably 20 or less.

[0324] At 589 nm (Na D ) and 20 °C, the Δn of the liquid crystal medium according to the invention preferably ranges from 0.060 or greater to 0.300 or less, preferably ranges from 0.070 or greater to 0.150 or less, more preferably ranges from 0.080 or greater to 0.140 or less, even more preferably ranges from 0.090 or greater to 0.135 or less and very particularly preferably ranges from 0.100 or greater to 0.130 or less.

[0325] In the first preferred embodiment of the present application, the Δn of the liquid crystal medium according to the invention is preferably from 0.080 or greater to 0.120 or less, more preferably ranges from 0.090 or greater to 0.110 or less and very particularly preferably ranges from 0.095 or greater to 0.105 or less, while the Δε preferably ranges from 6 or greater to 11 or less, preferably ranges from 7 or greater to 10 or less and particularly preferably ranges from 8 or greater to 9 or less.

[0326] In this embodiment, the nematic phase of the medium according to the invention preferably extends from at least -20 °C or less to 70 °C or more, more preferably from at least -20 °C or less to 70 °C or more, very preferably from at least -30 °C or less to 70 °C or more and especially from at least -40 °C or less to 70 °C or more.

[0327] In a second preferred embodiment of the present application, Δn of the liquid crystal medium according to the invention is preferably 0.060 or more to 0.300 or less, preferably in the range of 0.100 or more to 0.140 or less, more preferably in the range of 0.110 or more to 0.130 or less and very particularly preferably in the range of 0.115 or more to 0.125 or less, while Δε is preferably in the range of 7 or more to 13 or less, preferably in the range of 9 or more to 20 or less and particularly preferably in the range of 10 or more to 17 or less.

[0328] In this embodiment, the nematic phase of the medium according to the invention preferably extends from at least -20 °C or less to 80 °C or more, more preferably from at least -20 °C or less to 85 °C or more, very preferably from at least -30 °C or less to 80 °C or more and especially from at least -40 °C or less to 85 °C or more.

[0329] According to the invention, the compounds of formula S1 and S2 together are preferably used in the medium at a total concentration of 1 ppm to 5,000 ppm, more preferably 10 ppm to 3,000 ppm, more preferably 100 ppm to 2,000 ppm, more preferably 200 ppm to 1,500 ppm, very preferably 250 ppm to 1,000 ppm of the overall mixture.

[0330] The compounds selected from formula II and III are preferably used at a total concentration of 2% to 60%, more preferably 3% to 35%, even more preferably 4% to 20%, very preferably 5% to 15% of the overall mixture.

[0331] The compound of formula IV is preferably used at a total concentration of 5% to 70%, more preferably 20% to 65%, even more preferably 30% to 60%, very preferably 40% to 55% of the overall mixture.

[0332] The compound of formula V is preferably used at a total concentration of 0% to 30%, more preferably 0% to 15%, very preferably 1% to 10% of the overall mixture.

[0333] The compound of formula VI is preferably used at a total concentration of 0% to 50%, more preferably 1% to 40%, even more preferably 5% to 30%, very preferably 10% to 20% of the overall mixture.

[0334] The medium according to the invention may optionally contain other liquid crystal compounds to adjust the physical properties. Such compounds are known to those skilled in the art. Their concentration in the medium according to the invention is preferably from 0% to 30%, more preferably from 0.1% to 20%, very preferably from 1% to 15%.

[0335] In a preferred embodiment, the concentration of the compound of formula CC-3-V in the medium according to the invention can be from 50% to 65%, particularly preferably from 55% to 60%.

[0336] The liquid crystal medium preferably contains in total from 50% to 100%, more preferably from 70% to 100%, very preferably from 80% to 100%, in particular from 90% to 100% of the compounds of formulae I to VII, preferably selected from the compounds of formulae I-1, I-2 and II to VI, particularly preferably the compounds of formulae I to V, in particular the compounds of formulae I-1, I-2, II, III, IV, V and VII and very particularly preferably the compounds of formulae I-1, I-2, II, III, IV and V. They preferably consist mainly of these compounds and very preferably consist almost entirely of these compounds. In a preferred embodiment, the liquid crystal medium contains in each case one or more compounds of each of these formulae.

[0337] In the present application, the expression "dielectrically positive" describes compounds or components in which Δε > 3.0, "dielectrically neutral" describes those in which -1.5 ≤ Δε ≤ 3.0, and "dielectrically negative" describes those in which Δε < -1.5. Δε is determined at a frequency of 1 kHz and at 20 °C. The dielectric anisotropy of the individual compounds is determined from the results of a 10% solution of the individual compounds in a nematic host mixture. If the solubility of the individual compound in the host mixture is less than 10%, the concentration is reduced to 5%. The capacitance of the test mixture is measured in both a liquid crystal cell with homeotropic alignment and a liquid crystal cell with planar alignment. The cell thickness of both types of liquid crystal cells is about 20 μm. The applied voltage is a rectangular wave having a frequency of 1 kHz and typically an rms value of 0.5 V to 1.0 V, but it is always chosen to be below the capacitance threshold of the individual test mixture.

[0338] Δε is defined as (ε || - ε ⊥ ), while ε 平均 is (ε || + 2ε ⊥ ) / 3.

[0339] The host mixture for dielectrically positive compounds was mixture ZLI-4792, and the host mixture for dielectrically neutral and dielectrically negative compounds was mixture ZLI-3086, both from Merck KGaA, Germany. The absolute values of the dielectric constants of the compounds were determined from the changes in the corresponding values of the host mixtures when the compound of interest was added. The values were extrapolated to a concentration of 100% of the compound of interest.

[0340] Components having a nematic phase at a measurement temperature of 20° C. were measured as such, and all other substances were treated as compounds.

[0341] In the present application, in both cases, unless explicitly stated otherwise, the expression "threshold voltage" relates to the optical threshold and is quoted as 10% relative contrast (V 10 ), and the expression "saturation voltage" relates to optical saturation and is quoted as 90% relative contrast (V 90 ). Capacitor threshold voltage (V0), also known as Freedericks threshold (V Fr ) are only used if explicitly mentioned.

[0342] The parameter ranges indicated in this application all include the limit values, unless explicitly stated otherwise.

[0343] The different upper and lower value limits indicated for the various ranges of properties in combination with one another give rise to additional preferred ranges.

[0344] Throughout this application, the following conditions and definitions apply, unless expressly stated otherwise. All concentrations are indicated as weight percent and relate to the respective mixture as a whole, all temperatures are quoted in degrees Celsius, and all temperature differences are quoted in differential degrees. All physical properties are measured according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", November 1997 Status, Merck KGaA, Germany, and are quoted for a temperature of 20°C, unless expressly stated otherwise. The optical anisotropy (Δn) is measured at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is measured at a frequency of 1 kHz. The threshold voltage, as well as all other electro-optical properties, are measured using a test box produced at Merck KGaA, Germany. The test box used to measure Δε has a box thickness of about 20 μm. The electrode is a 1.13 cm 2 The alignment layer, for the homeotropic orientation (ε||), was SE-1211 from Nissan Chemicals, Japan, and for the axial orientation (ε||), was⊥ ) and is polyimide AL - 1054 obtained from Japan Synthetic Rubber, Japan. Capacitance is measured using a Solatron 1260 frequency response analyzer, which uses a sine wave at 0.3V rms voltage. The light used in the electro - optical measurement is white light. The device used in this article is a DMS instrument commercially available from Autronic - Melchers, Germany. The characteristic voltage is measured under vertical observation. The threshold voltage (V 10 ), medium - gray voltage (V 50 ) and saturation voltage (V 90 ) are measured for 10%, 50% and 90% relative contrast ratios respectively.

[0345] The liquid - crystal medium according to the invention can contain additional additives and chiral dopants in a conventional concentration. The total concentration of these additional components is in the range of 0% to 10%, preferably 0.1% to 6% based on the overall mixture. The concentration of each compound used is preferably in the range of 0.1% to 3% respectively. When the values and concentration ranges of the liquid - crystal components and compounds of the liquid - crystal medium are cited in this application, the concentrations of these and similar additives are not taken into account.

[0346] The liquid - crystal medium according to the invention consists of a plurality of compounds, preferably consisting of 3 to 30, more preferably 4 to 20, and very preferably 4 to 16 compounds. These compounds are mixed in a conventional manner. Generally, the desired amount of the compound used in a smaller amount is dissolved in the compound used in a larger amount. If the temperature is higher than the clearing point of the compound used in a higher concentration, the completion of the dissolution process can be particularly easily observed. However, the medium can also be prepared in other conventional ways, for example, using a so - called premix, which can be, for example, a homologous or eutectic mixture of compounds, or using a so - called "multi - bottle" system, the components of which are ready - to - use mixtures themselves.

[0347] By adding suitable additives, the liquid - crystal medium according to the invention can be improved in such a way that they can be used in all known types of liquid - crystal displays, which either use the liquid - crystal medium as it is, such as TN, TN - AMD, ECB - AMD, VAN - AMD, IPS - AMD, FFS - AMD LCDs, or in composite systems, such as PDLC, NCAP, PN LCDs and especially in ASM - PA LCDs.

[0348] All temperatures, for example, the melting point T(C,N) or T(C,S) of the liquid crystal, the transition point T(S,N) from the smectic (S) phase to the nematic (N) phase, and the clearing point T(N,I), are cited in degrees Celsius. All temperature differences are cited in differential degrees.

[0349] In the present invention and in particular in the following examples, the structure of the mesogenic compounds is indicated by means of abbreviations which are also known as acronyms. In these acronyms, the chemical formulae are abbreviated as described below using Tables A to C. All groups C n H 2n+1 、C m H 2m+1 and C l H 2l+1 or C n H 2n-1 、C m H 2m-1 and C l H 2l-1 refer to straight-chain alkyl or alkenyl groups, preferably 1E-alkenyl groups, each having n, m and l carbon atoms respectively. Table A lists the codes for the ring elements of the core structure of the compounds, while Table B shows the linking groups. Table C gives the meaning of the codes for the left- or right-hand end groups. The acronyms consist of the code for the ring element with an optional linking group, followed by a first hyphen and the code for the left-hand end group, and a second hyphen and the code for the right-hand end group. Table D shows exemplary structures of the compounds and their respective abbreviations.

[0350] Table A: Ring Elements

[0351]

[0352]

[0353]

[0354] Table B: Linking Groups

[0355]

[0356] Table C: End Groups

[0357]

[0358] Used in combination with each other and with others

[0359]

[0360]

[0361] wherein n and m each represent an integer, and the three dots "..." are placeholders for other abbreviations obtained from the table.

[0362] The following table shows exemplary structures and their respective abbreviations. These are shown to illustrate the meaning of the rules for said abbreviations. They further represent compounds that are preferably used.

[0363] Table D: Exemplary Structures

[0364]

[0365]

[0366]

[0367]

[0368]

[0369]

[0370]

[0371]

[0372]

[0373]

[0374]

[0375]

[0376]

[0377]

[0378]

[0379]

[0380]

[0381]

[0382]

[0383]

[0384]

[0385]

[0386]

[0387]

[0388]

[0389]

[0390]

[0391] wherein n, m and l preferably each independently represent from 1 to 7.

[0392] The following table (Table E) shows exemplary compounds that can be used as additional stabilizers in the mesogenic media according to the invention.

[0393] Table E

[0394]

[0395]

[0396]

[0397] In a preferred embodiment of the invention, the mesogenic medium comprises one or more compounds selected from the compounds obtained from Table E.

[0398] The following table F shows exemplary compounds that can preferably be used as chiral dopants in the mesogenic media according to the invention.

[0399] Table F

[0400]

[0401]

[0402]

[0403] In a preferred embodiment of the invention, the mesogenic medium comprises one or more compounds selected from the compounds obtained from Table F.

[0404] The mesogenic medium according to the present application preferably comprises two or more, preferably four or more compounds selected from the compounds from the above table.

[0405] The liquid crystal medium according to the invention preferably comprises

[0406] - seven or more, preferably eight or more individual compounds (preferably three or more, particularly preferably four or more different formulas), selected from the compounds obtained from Table D. Detailed Description

[0407] Example

[0408] The following examples illustrate the present invention by way of example and not in any way limit the present invention.

[0409] However, the physical properties show to those skilled in the art what kind of performance can be achieved and within what ranges they can be improved. In particular, for those skilled in the art, the combinations of the various properties that can preferably be achieved are thus well defined.

[0410] Prepare and study a liquid crystal mixture having the composition and properties shown in the following table.

[0411] Example 1

[0412] Prepare an LC mixture (M-1.0) having a positive dielectric anisotropy as follows.

[0413]

[0414]

[0415] Divide the above mixture (M1-0) into four parts. Study the first part as it is. Add 300 ppm, 500 ppm or 1,000 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 (mixtures M-11 to M-1-3) to each of the other three parts.

[0416]

[0417] Use the example

[0418] Fill the LC media M1-1 to M-1-3 prepared as in Example 1 into the VHR test cells as described above.

[0419] Subject the test cells to thermal stress (100 °C). Measure the VHR as described above at different time intervals (t 热 ) After that. For comparison purposes, repeat the measurement with the reference LC medium M1-0 (which is prepared as in Example 1). The VHR values are shown in Table 1 below.

[0420] Table 1: VHR after Thermal Loading

[0421]

[0422]

[0423] Another set of filled test cells is exposed by the backlight unit of the LCD. Measure the VHR as described above at various time intervals (T 光 ) After that. The VHR values are shown in Table 2 below.

[0424] Table 2: VHR after Backlight Loading

[0425]

[0426] It can be seen that, compared with the LC medium M-1 which does not contain any compounds of formula S1 and S2, the LC media M1-1 to M-1-3 containing both stabilizers S1a and S2a1 show a significantly lower reduction in VHR after long-term heat exposure.

[0427] The absence of the additive results in a significant decrease in the HR of the mixture after heating and after the backlight test.

[0428] Example 2

[0429] An LC mixture (M-2.0) with positive dielectric anisotropy was formulated as follows.

[0430]

[0431]

[0432] 1,000 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 were added to the above mixture. The resulting mixture showed excellent stability against both heat load and backlight load.

[0433] Example 3

[0434] An LC mixture (M-3.0) with positive dielectric anisotropy was formulated as follows.

[0435]

[0436]

[0437] 500 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 were added to the above mixture. The resulting mixture showed excellent stability against both heat load and backlight load.

[0438] Example 4

[0439] An LC mixture (M-4.0) with positive dielectric anisotropy was formulated as follows.

[0440]

[0441] To each part of the above mixture, 500 ppm of stabilizer S2a1 was added, and 100 ppm, 500 ppm, 1,000 ppm or 1,500 ppm of stabilizer S1a was added. The resulting mixture showed excellent stability against both heat load and backlight load.

[0442] Example 5

[0443] An LC mixture (M-5.0) having positive dielectric anisotropy was formulated as follows.

[0444]

[0445] 300 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 were added to the above mixture. The resulting mixture showed excellent stability against both heat load and backlight load.

[0446] Example 6

[0447] An LC mixture (M-6.0) having positive dielectric anisotropy was formulated as follows.

[0448]

[0449]

[0450] 300 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 were added to the above mixture. The resulting mixture showed excellent stability against both heat load and backlight load.

[0451] Example 7

[0452] An LC mixture (M-7.0) having positive dielectric anisotropy was formulated as follows.

[0453]

[0454]

[0455] 300 ppm of stabilizer S1a and 200 ppm, 500 ppm or 800 ppm of stabilizer S2a1 respectively were added to each part of the above mixture. The resulting mixture showed excellent stability against both heat load and backlight load.

[0456] Example 8

[0457] An LC mixture (M-8.0) having positive dielectric anisotropy was formulated as follows.

[0458]

[0459] To each part of the above mixture, 600 ppm of stabilizer S2a1 and 300 ppm or 500 ppm of stabilizer S1a, respectively. The resulting mixture shows excellent stability to both heat load and backlight load.

[0460] Example 9

[0461] An LC mixture (M - 9.0) having positive dielectric anisotropy was formulated as follows.

[0462]

[0463] To the above mixture, 500 ppm of stabilizer S1a and 500 ppm of stabilizer S2a1 were added. The resulting mixture shows excellent stability to both heat load and backlight load.

Claims

1. A liquid crystal medium having positive dielectric anisotropy, characterized in that It comprises a) one or more compounds of formulae S1 and S2, wherein each group, independently of one another and each time it occurs, is the same or different and has the following meanings: Indicate R a to R d is a straight-chain or branched alkyl group having 1 to 10 C atoms, preferably having 1 to 6 C atoms, very preferably having 1 to 4 C atoms, and most preferably methyl X is H, CH3, OH or O ● , preferably H, A is a straight-chain, branched or cyclic alkylene having 1 to 20 C atoms, which is optionally substituted, preferably -(CH2)8-, and n is an integer from 1 to 6, and b) one or more compounds selected from the compounds of formulae II and III wherein R 2 and R 3 , independently of one another, represent an alkyl, alkoxy, fluoroalkyl or fluoroalkoxy group having 1 to 7 C atoms, an alkenyl, alkenoxy, alkoxyalkyl or fluoroalkenyl group having 2 to 7 C atoms, to each time it occurs, independently of one another, represents L 21 ,L 22 ,L 31 and L 32 each independently represents H or F, X 2 and X 3 , independently of one another, represent halogen, haloalkyl or alkoxy having 1 to 3 C atoms or haloalkenyl or alkenyloxy having 2 or 3 C atoms, Z 3 represents -CH2CH2-, -CF2CF2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O- or a single bond, and m and n, independently of one another, represent 0, 1, 2 or 3, and / or c) one or more compounds of formula IV wherein R 41 and R 42 , each independently has the meaning as defined above for R under formula II 2 as shown Independently of one another, and if appears twice, then these also represent independently of one another Z 41 and Z 42 , independently of each other and if Z 41 appears twice, these also independently of each other represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O-, -C≡C- or a single bond, and p represents 0, 1 or 2, and / or d) one or more compounds of formula VIII wherein R 81 and R 82 , each independently has the meaning shown for R 2 , and indicate Indicate Z 81 and Z 82 , independently of one another, represent -CH2CH2-, -C≡C-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, s represents 0 or 1, and L 81 and L 82 , independently of each other, represent C-F or N, and in Indicates in the case of L 81 and L 82 Alternatively, one or both of them may represent C-H.

2. The medium according to claim 1, characterized in that it comprises - one or more compounds selected from the compounds of formulae II and III wherein R 2 and R 3 , independently of one another, represent an alkyl, alkoxy, fluoroalkyl or fluoroalkoxy group having 1 to 7 C atoms, an alkenyl, alkenyloxy, alkoxyalkyl or fluoroalkenyl group having 2 to 7 C atoms, to each time it occurs, independently of one another, represents L 21 , L 22 , L 31 and L 32 , independently represent H or F, X 2 and X 3 , independently of one another, represent halogen, haloalkyl or alkoxy having 1 to 3 C atoms or haloalkenyl or alkenyloxy having 2 or 3 C atoms, Z 3 represents -CH2CH2-, -CF2CF2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O- or a single bond, and m and n, independently of one another, represent 0, 1, 2 or 3.

3. The medium according to claim 2, wherein It comprises a compound of formula II-2j wherein the parameters have their respective meanings indicated in claim 2, and L 25 to L 28 independently of one another represent H or F.

4. The medium according to claim 2, wherein It comprises at least one compound of formula II-2j-1 wherein R 2 and X 2 have their respective meanings as set forth in claim 2.

5. The medium according to claim 2, characterized in that It comprises at least one compound of formula PGUQU-n-F PGUQU-n-F where n represents from 1 to 7.

6. The medium according to claim 5, wherein It comprises at least one compound of formula PGUQU-n-F, where n represents 5.

7. The medium according to claim 5, wherein It comprises at least two compounds of formula PGUQU-n-F, where n represents 3 and 5, respectively.

8. The medium according to claim 1 or 2, characterized in that It comprises - one or more compounds of formula IV wherein R 41 and R 42 , each independently has the meaning as shown above for R under formula II in claim 2 2 as defined independently of one another, and if occurring twice, these also independently of one another represent Z 41 and Z 42 , independently of each other and, if Z 41 occurs twice, these also independently of each other represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O-, -C≡C- or a single bond, and p represents 0, 1 or 2.

9. The medium according to claim 1 or 2, characterized in that The total concentration of the compounds of formulae S1 and S2 in the medium is 1 ppm - 5,000 ppm.

10. The medium according to claim 1 or 2, characterized in that The compounds of formulae S1 and S2 are compounds selected from their sub-formulae S1a and S1b and S2a and S2b, respectively, wherein n represents an integer from 1 to 6.

11. The medium according to claim 1 or 2, characterized in that It comprises one or more compounds of formula II as claimed in claim 2.

12. The medium according to claim 1 or 2, wherein It comprises one or more compounds of formula III as claimed in claim 2.

13. The medium according to claim 1 or 2, characterized in that It comprises one or more dielectrically neutral compounds of formula V, wherein R 51 and R 52 , each independently has the meaning as shown for R under formula II in claim 2 2 as defined Each occurrence, independently of one another, represents Z 51 and Z 52 , independently of one another, and if Z 51 occurs twice, these also independently of one another represent -CH2CH2-, -COO-, trans-CH=CH-, trans-CF=CF-, -CH2O-, -CF2O- or a single bond, and r represents 0, 1 or 2.

14. The medium according to claim 1 or 2, characterized in that It comprises one or more compounds selected from the compounds of the following formula: where n and m independently of one another represent from 1 to 7.

15. Liquid crystal display, characterized in that It contains a medium according to any one of claims 1 to 14.

16. The display according to claim 15, characterized in that It is addressed by an active matrix.

17. Use of a medium according to any one of claims 1 to 14 in a liquid crystal display.

18. A method for preparing a medium according to any one of claims 1 to 14, characterized in that Mix one or more compounds of formulae S1 and S2 as given in claim 1 with one or more compounds mentioned in any one of claims 2 and 3, and / or one or more other mesogenic compounds and / or one or more additives.

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