LIQUID-CRYSTALLINE MEDIUM

Abstract

Liquid-crystalline media comprising one or more compounds of formula D

##STR00001##

and one or more compounds selected from the group of compounds of formulae I, II and III,

##STR00002##

in which the occurring groups and parameters have the meanings defined in claim 1, and to high-frequency components comprising these media, especially microwave components for high-frequency devices, such as devices for shifting the phase of microwaves, tunable filters, tunable metamaterial structures, and electronic beam steering antennas (e.g. phased array antennas).

Claims

1. A liquid-crystal medium, which comprises a) one or more compounds of the formula D, ##STR00344## in which ##STR00345## denotes or ##STR00346## R.sup.1A denotes H, an alkyl, alkenyl or alkoxy radical having up to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00347## and in which one or more H atoms may be replaced by halogen, R.sup.2A denotes H, alkyl or alkenyl or alkoxy having up to 7 C atoms, in which one or more H atoms may be replaced by halogen, r is 0 or 1; and b) one or more compounds selected from the group of compounds of formulae I, II and III, ##STR00348## in which R.sup.1 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00349## n is 0, 1 or 2, ##STR00350## on each occurrence, independently of one another, denote ##STR00351## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms, and wherein ##STR00352## alternatively denotes ##STR00353## R.sup.2 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00354## Z.sup.21 denotes trans-CHCH, trans-CFCF or CC, ##STR00355## independently of one another, denote ##STR00356## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms; R.sup.3 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00357## one of Z.sup.31 and Z.sup.32, denotes trans-CHCH, trans-CFCF or CC and the other one, independently thereof, denotes CC, trans-CHCH, trans-CFCF or a single bond, and ##STR00358## independently of one another, denote ##STR00359## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms, and wherein ##STR00360## alternatively denotes ##STR00361##

2. A liquid-crystal medium according to claim 1, wherein the one or more compounds of formula D are selected from the group of compounds of formulae D-1 and D-2 ##STR00362## in which R.sup.1A denotes alkyl having 1 to 7 C atoms.

3. A liquid-crystal medium according to claim 1, wherein the total concentration of the compounds of the formula D in the medium is in the range of from 0.05% to 1% by weight.

4. A liquid-crystal medium according to claim 1, wherein the medium comprises one or more compounds selected from the group of compounds of formula I-1 to I-5 ##STR00363## in which L.sup.1, L.sup.2 and L.sup.3 on each occurrence, identically or differently, denote H or F, R.sup.1 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00364## on each occurrence, independently of one another, denote ##STR00365## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms.

5. A liquid-crystal medium according to claim 1, wherein the medium comprises one or more compounds selected from the group of compounds of the formulae II-1 to II-3 ##STR00366## in which R.sup.2 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00367## independently of one another, denote ##STR00368## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms.

6. A liquid-crystal medium according to claim 1, wherein the medium comprises one or more compounds selected from the group of compounds of the formulae III-1 to III-6 ##STR00369## in which R.sup.3 denotes H, unfluorinated alkyl or unfluorinated alkoxy having 1 to 17 C atoms, or unfluorinated alkenyl, unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to 15 C atoms, in which one or more CH.sub.2-groups may be replaced by ##STR00370## independently of one another, denote ##STR00371## in which R.sup.L, on each occurrence identically or differently, denotes H or alkyl having 1 to 6 C atoms, and wherein ##STR00372## alternatively denotes ##STR00373## Z.sup.31 and Z.sup.32 independently of one another, denote trans-CHCH or trans-CFCF, and in formula III-6 alternatively one of Z.sup.31 and Z.sup.32 may denote CC.

7. A liquid-crystal medium according to claim 1, wherein the medium additionally comprises one or more chiral compounds.

8. A component for high-frequency technology, characterised in that it comprises a liquid crystal medium according to claim 1.

9. A component according to claim 8, wherein the component is suitable for operation in the microwave range.

10. A component according to claim 8, wherein the component is a liquid-crystal based antenna element, a phase shifter, a tunable filter, a tunable metamaterial structure, a matching network or a varactor.

11. A microwave antenna array, characterised in that it comprises one or more components according to claim 8.

12. A method which comprises including a liquid-crystal medium according to claim 1 in a component for high-frequency technology.

13. A process for the preparation of a liquid-crystal medium according to claim 1, characterised in that one or more compounds of formula D are mixed with one or more compounds selected from the group of compounds of formulae I, II and III and optionally additional mesogenic compounds, and optionally a chiral compound are added.

Description

EXAMPLES

[0492] The following examples illustrate the present invention without limiting it in any way.

[0493] However, it is clear to the person skilled in the art from the physical properties what properties can be achieved and in what ranges they can be modified. In particular, the combination of the various properties which can preferably be achieved is thus well defined for the person skilled in the art.

[0494] The voltage holding ratio (VHR) is determined in test cells produced at Merck Japan. The test cells have alkali-free glass substrates and are provided with polyimide alignment layers with a layer thickness of 50 nm, which result in planar alignment of the liquid crystals. The layer gap is uniform (3.0 m). The surface area of the transparent ITO electrodes is 1 cm2.

[0495] Unless indicated otherwise, the VHR is determined at 20 C. (VHR20) and after 5 minutes in an oven at 100 C. (VHR100) in a commercially available instrument from Autronic Melchers, Germany. The voltage used has a frequency of 60 Hz, unless indicated otherwise.

[0496] The accuracy of the VHR measurement values depends on the respective value of the VHR. The accuracy decreases with decreasing values. The deviations generally observed in the case of values in the various magnitude ranges are compiled in their order of magnitude in the following table.

TABLE-US-00007 Deviation VHR range (relative) VHR values A.sub.GVHR/VHR/% from to Approx. 99.6% 100% +/0.1 99.0% 99.6% +/0.2 98% 99% +/0.3 95% 98% +/0.5 90% 95% +/1 80% 90% +/2 60% 80% +/4 40% 60% +/8 20% 40% +/10 10% 20% +/20

[0497] The stability to UV irradiation is investigated in a Suntest CPS, a commercial instrument from Heraeus, Germany. The sealed test cells are irradiated for between 30 min and 2.0 hours, unless explicitly indicated, without additional heating. The irradiation power in the wavelength range from 300 nm to 800 nm is 765 W/m.sup.2 V. A UV cut-off filter having an edge wavelength of 310 nm is used in order to simulate the so-called window glass mode. In each series of experiments, at least four test cells are investigated for each condition, and the respective results are indicated as averages of the corresponding individual measurements.

[0498] The decrease in the voltage holding ratio (VHR) usually caused by the exposure, for example by heat, by UV irradiation or by LCD backlighting, is determined in accordance with the following equation (1):

VHR(t)=VHR(t)VHR(t=0)(1).

Mixture Examples

[0499] Liquid-crystal mixtures N1 to N5 having the compositions and properties as indicated in the following tables are prepared and characterized with respect to their general physical properties and their applicability in microwave components at 19 GHz and 20 C. These data are given in the tables below the composition tables for the individual mixture examples.

Mixture N1

[0500]

TABLE-US-00008 PU-3-S 10.0% T.sub.(N, I). [ C.]: 123.5 PTU-3-S 10.0% (1 kHz, 20 C.): 22.3 PTU-5-S 10.0% .sub. (1 kHz, 20 C.): 26.9 PGU-3-S 16.0% .sub. (1 kHz, 20 C.): 4.7 PPTU-4-S 7.0% .sub.1 [mPa .Math. s], (20 C.): 287 PPTU-5-S 7.0% K.sub.1 [pN], (20 C.): 14.0 CPU-2-S 20.0% K.sub.3 [pN], (20 C.): 19.5 CPU-4-S 20.0% V.sub.0 [V] (20 C.) 0.84 100.0%

Mixture N2

[0501]

TABLE-US-00009 PTU-3-S 10.0% T.sub.(N, I). [ C.]: 149.5 PTU-5-S 8.0% (1 kHz, 20 C.): 23.3 PGU-3-S 18.0% .sub. (1 kHz, 20 C.): 27.8 PPTU-4-S 7.0% .sub. (1 kHz, 20 C.): 4.5 PPTU-5-S 9.0% .sub.1 [mPa .Math. s], (20 C.): 396 PGTU-4-S 6.0% K.sub.1 [pN], (20 C.): 16.9 CPU-2-S 22.0% K.sub.3 [pN], (20 C.): 20.8 CPU-4-S 22.0% LTS (bulk, 20 C.) [h] 1000 100.0% LTS (bulk, 30 C.) [h] 768

Mixture N3

[0502]

TABLE-US-00010 PTU-3-S 16.0% T.sub.(N,I). [ C.]: 151 PGU-3-S 14.0% (1 kHz, 20 C.): 22.7 PPTU-5-S 20.0% .sub. (1 kHz, 20 C.): 27.0 CPU-2-S 35.0% .sub. (1 kHz, 20 C.): 4.4 CPU-4-S 15.0% .sub.1 [mPa .Math. s], (20 C.): 384 100.0%

Mixture N4

[0503]

TABLE-US-00011 PU-3-S 20.0% T.sub.(N, I). [ C.]: 128 PGU-3-S 20.0% (1 kHz, 20 C.): 23.6 PGU-4-S 20.0% .sub. (1 kHz, 20 C.): 28.2 CPU-2-S 20.0% .sub. (1 kHz, 20 C.): 5.0 CPU-4-S 20.0% .sub.1 [mPa .Math. s], (20 C.): 318 100.0% K.sub.1 [pN], (20 C.): 13.7 K.sub.3 [pN], (20 C.): 18.6 V.sub.0 [V] (20 C.) 0.80

Mixture N5

[0504]

TABLE-US-00012 PTU-3-S 8.0% T.sub.(N, I). [ C.]: 151.5 PTU-5-S 8.0% (1 kHz, 20 C.): 22.9 PGU-3-S 10.0% .sub. (1 kHz, 20 C.): 27.4 PGU-4-S 6.0% .sub. (1 kHz, 20 C.): 4.5 PGU-5-S 4.0% .sub.1 [mPa .Math. s], (20 C.): 403 PPTU-4-S 4.0% K.sub.1 [pN], (20 C.): 17.3 PPTU-5-S 8.0% K.sub.3 [pN], (20 C.): 20.4 PGTU-4-S 5.0% V.sub.0 [V] (20 C.) 0.92 PGTU-5-S 5.0% LTS bulk [h, 30 C.]: 1000 CPU-2-S 22.0% LTS bulk [h, 40 C.]: 1000 CPU-4-S 20.0% [20 C., 19 GHz]: 0.307 100.0 .sub.r, [20 C., 19 GHz]: 3.5830 .sub.r, [20 C., 19 GHz]: 2.4838 tan .sub. r, [20 C., 19 GHz]: 0.0058 tan .sub. r, [20 C., 19 GHz]: 0.0113 [20 C., 19 GHz]: 27.2

[0505] The mixtures N1 to N5 are stabilised with the compound D-1c

##STR00341##

[0506] The stabilised mixtures S1 to S5 consist of 99.90% of mixtures N1 to N5, respectively, and 0.10% of the compound D-1c.

[0507] Comparative Mixture C1 comprises the alternative stabiliser ST-3a-1 from the state of the art:

##STR00342##

TABLE-US-00013 Mixture Host c(D-1c) [%] S1 N1 0.10 S2 N2 0.10 S3 N3 0.10 S4 N4 0.10 S5 N5 0.10 Mixture Host c(ST-3a-1) [%] C1 N1 0.10

[0508] The VHR of the mixtures N1 to N5, S1 to S5 and C1 is determined as described above (VHR100.sub.initial). Next, the mixtures are split into two parts and are each filled into sealed ampoules under nitrogen and stored in an oven for 24 h and 100 h, respectively. Afterwards the VHR is determined again (VHR.sub.heat load24 and VHR.sub.heat load100). The results are summarised in the Table 1.

TABLE-US-00014 TABLE 1 VHR after heat load: VHR100.sub.initial VHR.sub.heat load 24 VHR.sub.heat load 100 Mixture [%] [%] [%] N1 88 38 13 S1 86 78 65 C1 85 80 15 N2 85 60 17 S2 85 78 55 N3 S3 N4 78 80 20 S4 82 82 82 N5 S5

[0509] The stabilised mixtures S1 to S5 exhibit significantly improved VHR values after heat load compared to the unstabilised mixtures N1 to N5. Furthermore, the VHR values of comparative mixture C1 show that the stabiliser D-1c according to the invention is also effective after long term stress of 100 h, whereas the use of the stabiliser ST-3a-1 from the state of the art gives a very similar result as the unstabilised mixture N1.

[0510] The liquid-crystal mixtures S6 to S9 and Ch1 to Ch6 are prepared according to the following tables. S6 to S9 and Ch1 to Ch6 show equally high VHR values after heat load as the examples above.

Mixture S6

[0511]

TABLE-US-00015 PTU-3-S 14.98% T.sub.(N, I). [ C.]: 124.0 PTU-5-S 14.98% n [20 C., 589.3 nm] 0.3628 PGU-3-S 14.98% n.sub.e [20 C., 589.3 nm] 1.9034 PPTU-5-S 9.99% n.sub.o [20 C., 589.3 nm] 1.5406 CPU-2-S 27.97% (1 kHz, 20 C.): 22.1 CPU-4-S 16.98% (1 kHz, 20 C.): 26.7 D-1c 0.12% .sub. (1 kHz, 20 C.): 4.6 100.00% .sub.1 [mPa .Math. s], (20 C.): 307 K.sub.1 [pN], (20 C.): 14.5 K.sub.3 [pN], (20 C.): 18.01 LTS (bulk, 20 C.) [h] 1000 [19 GHz, 20 C.] 0.305 .sub.r, [19 GHz, 20 C.] 3.5338 .sub.r, [19 GHz, 20 C.] 2.4562 tan .sub. r, [19 GHz, 20 C.] 0.0064 tan .sub. r, [19 GHz, 20 C.] 0.0116 [19 GHz, 20 C.] 26.3

Mixture S7

[0512]

TABLE-US-00016 D-1c 0.12 Klrpunkt [ C.]: 151.5 PTU-3-S 7.99 n [589 nm, 20 C.]: 0.3790 PTU-5-S 7.99 n.sub.e [589 nm, 20 C.]: 1.9172 PGU-3-S 9.99 n.sub.o [589 nm, 20 C.]: 1.5382 PGU-4-S 5.99 [1 kHz, 20 C.]: 22.9 PGU-5-S 4.0 .sub. [1 kHz, 20 C.]: 27.4 PPTU-4-S 4.0 .sub. [1 kHz, 20 C.]: 4.5 PPTU-5-S 7.99 .sub.1 [mPa s, 20 C.]: 403 PGTU-4-S 4.99 K.sub.1 [pN, 20 C.]: 17.3 PGTU-5-S 4.99 K.sub.3 [pN, 20 C.]: 20.4 CPU-2-S 21.97 K.sub.3/K.sub.1 [pN, 20 C.]: 1.18 CPU-4-S 19.98 V.sub.0 [V, 20 C.]: 0.92 100.0 LTS bulk [h, 10 C.]: LTS bulk [h, 20 C.]: LTS bulk [h, 30 C.]: 1000 LTS bulk [h, 40 C.]: 1000 [20 C., 19 GHz]: 0.307 .sub.r, [20 C., 19 GHz]: 3.5830 .sub.r, [20 C., 19 GHz]: 2.4838 tan .sub. r, [20 C., 19 GHz]: 0.0058 tan .sub. r, [20 C., 19 GHz]: 0.0113 [20 C., 19 GHz]: 27.2

Mixture S8

[0513]

TABLE-US-00017 D-1c 0.12 Klrpunkt [ C.]: 153.5 PTU-3-S 7.99 n [589 nm, 20 C.]: 0.3754 PTU-5-S 7.99 n.sub.e [589 nm, 20 C.]: 1.9124 PGU-3-S 7.99 n.sub.o [589 nm, 20 C.]: 1.5370 PPTU-4-S 7.99 [1 kHz, 20 C.]: 21.1 PPTU-5-S 7.99 .sub. [1 kHz, 20 C.]: 25.3 PGTU-4-S 7.99 .sub. [1 kHz, 20 C.]: 4.2 CPU-2-S 27.97 .sub.1 [mPa s, 20 C.]: 353 CPU-4-S 23.97 K.sub.1 [pN, 20 C.]: 16.1 100.0 K.sub.3 [pN, 20 C.]: 19.9 K.sub.3/K.sub.1 [pN, 20 C.]: 1.24 V.sub.0 [V, 20 C.]: 0.92 LTS bulk [h, 10 C.]: LTS bulk [h, 20 C.]: 1000 LTS bulk [h, 30 C.]: 1000 LTS bulk [h, 40 C.]: 1000 [20 C., 19 GHz]: 0.313 .sub.r, [20 C., 19 GHz]: 3.5496 .sub.r, [20 C., 19 GHz]: 2.4374 tan .sub. r, [20 C., 19 GHz]: 0.0057 tan .sub. r, [20 C., 19 GHz]: 0.0106 [20 C., 19 GHz]: 29.5

Mixture S9

[0514]

TABLE-US-00018 D-1c 0.12 Klrpunkt [ C.]: 151 PTU-3-S 15.98 n [589 nm, 20 C.]: 0.3779 PGU-3-S 13.98 n.sub.e [589 nm, 20 C.]: 1.9169 PPTU-5-S 19.98 n.sub.o [589 nm, 20 C.]: 1.5390 CPU-2-S 34.96 [1 kHz, 20 C.]: 22.7 CPU-4-S 14.98 .sub. [1 kHz, 20 C.]: 27.0 100.0 .sub. [1 kHz, 20 C.]: 4.4 .sub.1 [mPa s, 20 C.]: 384 K.sub.1 [pN, 20 C.]: 16.8 K.sub.3 [pN, 20 C.]: 21.6 K.sub.3/K.sub.1 [pN, 20 C.]: 1.29 V.sub.0 [V, 20 C.]: 0.91 LTS bulk [h, 20 C.]: 1000 LTS bulk [h, 30 C.]: 216 LTS bulk [h, 40 C.]: 0 [20 C., 19 GHz]: 0.311 .sub.r, [20 C., 19 GHz]: 3.5851 .sub.r, [20 C., 19 GHz]: 2.4705 tan .sub. r, [20 C., 19 GHz]: 0.0059 tan .sub. r, [20 C., 19 GHz]: 0.0106 [20 C., 19 GHz]: 29.3

[0515] Preferred cholesteric mixtures are preferred using the chiral dopants A-II-1-1 or A-III-1-1 shown below.

##STR00343##

[0516] The cholesteric mixtures Ch1 to Ch6 have the following composition:

TABLE-US-00019 Mixture Host % Host Dopant % Dopant Ch1 S7 99.90 A-II-1-1 0.10 Ch2 S7 99.80 A-II-1-1 0.20 Ch3 S7 99.70 A-II-1-1 0.30 Ch4 S7 99.75 A-III-1-1 0.25 Ch5 S7 99.50 A-III-1-1 0.50 Ch6 S7 99.25 A-III-1-1 0.75

[0517] The mixtures Ch1 to Ch6 show faster switching than the host mixture S7 without chiral dopant.