LIQUID-CRYSTAL MEDIUM

Abstract

The invention relates to a liquid-crystalline medium, in particular based on a mixture of polar compounds, and to the use thereof for an active-matrix display, in particular based on the VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS effect.

Claims

1. A liquid crystal (LC) medium having negative dielectric anisotropy and comprising one or more compounds of formula LB ##STR00493## in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: R.sup.1 alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, L.sup.1, L.sup.2 F or Cl, X.sup.1 fluorinated alkyl or alkoxy with 1, 2 or 3 C atoms, Y.sup.1 O or S. R.sup.1, R.sup.2 alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, L.sup.1, L.sup.2 F or Cl.

2. The LC medium according to claim 1, wherein the compounds of formula LB are: ##STR00494##

3. The LC medium according to claim 1, wherein the compounds of formula LB are ##STR00495##

4. The LC medium according to claim 1, additionally comprising one or more compounds of formulae AN or AY ##STR00496## in which individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: ##STR00497## R.sup.A1 alkenyl having 2 to 9 C atoms or, if at least one of the rings X, Y and Z denotes cyclohexenyl, also one of the meanings of R.sup.A2, R.sup.A2 alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, Z.sup.x CH.sub.2CH.sub.2, CHCH, CF.sub.2O, OCF.sub.2, CH.sub.2O, OCH.sub.2, COO, OCO, C.sub.2F.sub.4, CFCF, CHCHCH.sub.2O, or a single bond, L.sup.1-4 H, F, Cl, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F or CHF.sub.2H, x 1 or 2, z 0 or 1.

5. The LC medium according to claim 1, additionally comprising one or more compounds of formulae CY or PY: ##STR00498## in which individual radicals have the following meanings: a denotes 1 or 2, b denotes 0 or 1, ##STR00499## R.sup.1 and R.sup.2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, Z.sup.x denotes CHCH, CH.sub.2O, OCH.sub.2, CF.sub.2O, OCF.sub.2, O, CH.sub.2, CH.sub.2CH.sub.2 or a single bond, L.sup.1-4 each, independently of one another, denote F, Cl, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F, CHF.sub.2.

6. The LC medium according to claim 1, additionally comprising one or more compounds of formulae ZK or DK: ##STR00500## in which individual radicals on each occurrence, identically or differently, have the following meanings: ##STR00501## and R.sup.3 and R.sup.4 each, independently of one another, denote alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, Z.sup.y denotes CH.sub.2CH.sub.2, CHCH, CF.sub.2O, OCF.sub.2, CH.sub.2O, OCH.sub.2, COO, OCO, C.sub.2F.sub.4, CFCF or a single bond, R.sup.5 and R.sup.6 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, e denotes 1 or 2.

7. The LC medium according to claim 1, additionally comprising one or more compounds of formulae: ##STR00502## in which R and R each, independently of one another, denote a straight-chain alkyl or alkoxy radical having 1-7 C atoms.

8. An LC display comprising an LC medium as defined in claim 1.

9. The LC display of claim 8, which is a VA, SA-VA, IPS, PS-IPS, FFS, PS-FFS, UB-FFS or PS-UB-FFS display.

10. A process of preparing an LC medium according to claim 1, comprising mixing one or more compounds of formula LB with one or more compounds selected from formulae AN, AY, CY and PY and optionally with further LC compounds and/or additives, ##STR00503## in which individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: ##STR00504## R.sup.A1 alkenyl having 2 to 9 C atoms or, if at least one of the rings X, Y and Z denotes cyclohexenyl, also one of the meanings of R.sup.A2, R.sup.A2 alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, Z.sup.x CH.sub.2CH.sub.2, CHCH, CF.sub.2O, OCF.sub.2, CH.sub.2O, OCH.sub.2, COO, OCO, C.sub.2F.sub.4, CFCF, CHCHCH.sub.2O, or a single bond, L.sup.1-4 H, F, Cl, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F or CHF.sub.2H, x 1 or 2, z 0 or 1, ##STR00505## in which individual radicals have the following meanings: a denotes 1 or 2, b denotes 0 or 1, ##STR00506## R.sup.1 and R.sup.2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by O, CHCH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, Z.sup.x denotes CHCH, CH.sub.2O, OCH.sub.2, CF.sub.2O, OCF.sub.2, O, CH.sub.2, CH.sub.2CH.sub.2 or a single bond, L.sup.1-4 each, independently of one another, denote F, Cl, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F, CHF.sub.2.

Description

EXAMPLES

[0344] Unless stated otherwise, methods of preparing test cells and measuring their electrooptical and other properties are carried out by the methods as described hereinafter or in analogy thereto.

[0345] The display used for measurement of the capacitive threshold voltage consists of two plane-parallel glass outer plates at a separation of 25 m, each of which has on the inside an electrode layer and an unrubbed polyimide alignment layer on top, which effect a homeotropic edge alignment of the liquid-crystal molecules.

[0346] The VHR value is measured as follows: The LC mixture is introduced into VA-VHR test cells which comprise an unrubbed VA-polyimide alignment layer. The LC-layer thickness d is approx. 3 m, unless stated otherwise. The VHR value is determined before and after light exposure at 1 V, 60 Hz, 64 s pulse (measuring instrument: Autronic-Melchers VHRM-105).

Comparison Example 1

[0347] The nematic LC host mixture C1 is formulated as follows.

TABLE-US-00009 CC-3-V 24.50% cl.p. 85.9 C. CC-3-V1 12.00% n 0.0933 CCP-V-1 13.50% 3.3 CPY-3-O2 1.00% .sub. 3.4 CCY-5-O2 3.00% .sub.1 101 mPa s CLY-3-O2 9.00% K.sub.1 15.6 CLY-4-O2 5.50% K.sub.3 18.0 CLY-5-O2 5.50% K.sub.3/K.sub.1 1.15 CY-3-O2 12.00% V.sub.0 2.46 V CY-3-O4 4.00% CY-5-O2 4.00% B(S)-2O-O4 4.00% B(S)-2O-O5 2.00%

Example 1

[0348] The LC mixture N1 is formulated by mixing 99.5% of the LC host mixture C1 and 0.5% of the compound LB(S)-3-OT of formula LB2-2.

##STR00491##

Example 2

[0349] The LC mixture N2 is formulated by mixing 99.0% of the LC host mixture C1 and 1.0% of the compound LB(S)-3-OT of formula LB2-2.

Example 3

[0350] The LC mixture N3 is formulated by mixing 97.0% of the LC host mixture C1 and 3.0% of the compound LB(S)-3-OT of formula LB2-2.

Example 4

[0351] The LC mixture N4 is formulated by mixing 99.5% of the LC host mixture C1 and 0.5% of the compound LB-3-T of formula LB1-1.

##STR00492##

Example 5

[0352] The LC mixture N5 is formulated by mixing 99.0% of the LC host mixture C1 and 1.0% of the compound LB-3-T of formula LB1-1.

Example 6

[0353] The LC mixture N6 is formulated by mixing 97.0% of the LC host mixture C1 and 3.0% of the compound LB-3-T of formula LB1-1.

[0354] VHR Values

[0355] The VHR values of mixtures C1 and N1 to N3 are measured at 60 C., 3 Hz in UB-FFS VHR test cells before and after light exposure for varying time using a LED lamp.

[0356] The results are shown in Table 1.

TABLE-US-00010 TABLE 1 VHR values C1 N1 N2 N3 VHR at 60 C. (%) VHR/% Initial 95.3 95.0 94.9 94.6 After 24 h Light stress 90.8 90.7 90.4 89.4 After 72 h Light stress 84.9 85.2 83.8 82.1 After 168 h Light stress 74.2 74.5 73.0 68.9 After 240 h Light stress 66.9 68.1 66.4 60.9

[0357] From Table 1 it can be seen that the mixtures N1 to N3 according to the present invention show VHR values which are comparable to those of reference mixture C1.

[0358] White Flicker

[0359] The white flicker values of mixtures C1 and N1 to N3 are measured at 25 C., 10 Hz with V100 voltage loading in UB-FFS test cells.

[0360] The results are shown in Table 2.

TABLE-US-00011 TABLE 2 White flicker at V 100, 10 Hz, 25 C. C1 N1 N2 N3 White flicker 1.9 1.3 1.4 1.3

[0361] From Table 2 it can be seen that the mixtures N1 to N3 according to the present invention show significantly reduced white flicker compared to reference mixture C1.

[0362] Easy Axis Shift by AC Loading

[0363] The easy axis shift of mixtures C1 and N1 to N3 are measured at 0 voltage, room temperature for 90 min after stress which 10 Vrms for 2 hrs at 30 Hz in UB-FFS test cell.

[0364] The results are shown in Table 3.

TABLE-US-00012 TABLE 3 by AC loading C1 N1 N2 N3 0 min 0.11 0.09 0.10 0.09 30 min 0.03 0.02 0.02 0.03 60 min 0.02 0.01 0.01 0.03 90 min 0.01 0.01 0.01 0.02

[0365] From Table 3 it can be seen that the mixtures N1 to N3 according to the present invention show lower easy axis shift compared to reference mixture C1.

[0366] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0367] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.