Liquid-crystalline medium and electro-optical display

Abstract

The invention relates to a liquid-crystalline medium having a nematic phase and negative dielectric anisotropy which comprises a) one or more compounds of formula I ##STR00001## b) one or more compounds of formula II ##STR00002##
and c) one or more compounds selected from the compounds of formulae III-1 to III-4 ##STR00003##
in which the parameters have the meanings indicated herein, to the use thereof in an electro-optical display, particularly in an active-matrix display based on the VA, ECB, PALC, FFS or IPS effect, to displays of this type which contain a liquid-crystalline medium of this type, and to the use of the compounds of the formula I for the stabilisation of a liquid-crystalline medium which comprises one or more compounds of formula II and one or more compounds selected from the compounds of formulae III-1 to III-4.

Claims

1. A liquid-crystalline medium having a nematic phase and negative dielectric anisotropy which comprises a) one or more compounds of formula I or one or more compounds of formula I-1a ##STR00168## in which R.sup.11 to R.sup.14 each, independently of one another, denote alkyl having 1 to 4 C atoms, X.sup.1 denotes O.sup., Y.sup.1 and Y.sup.01 each, independently of one another, denote straight-chain or branched alkyl having 1 to 10 C atoms, also cycloalkyl, cycloalkylalkyl or alkylcycloalkyl, where one or more CH.sub.2 groups in each of these groups may each be replaced by O in such a way that no two O atoms in the molecule are connected directly to one another, and Z.sup.1 denotes O, (CO)O, O(CO), O(CO)O, NH, NY.sup.01 or NH(CO), and, in the case where Z.sup.1 denotes O(CO)O, Y.sup.1 may also denote ##STR00169## and b) one or more compounds of formula II ##STR00170## in which R.sup.21 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms, and R.sup.22 denotes an unsubstituted alkenyl radical having 2 to 7 C atoms, and c) one or more compounds selected from formulae III-1 to III-4 ##STR00171## in which R.sup.31 denotes an unsubstituted alkyl radical having 1 to 7 C atoms, R.sup.32 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, and m, n and o each, independently of one another, denote 0 or 1.

2. The medium according to claim 1, wherein said medium comprises one or more compounds of formula II, in which R.sup.22 denotes vinyl.

3. The medium according to claim 2, wherein said medium comprises a compound of formula II, in which R.sup.21 denotes n-propyl and R.sup.22 denotes vinyl.

4. The medium according to claim 3, wherein the total concentration of the compounds of the formula II, in the medium as a whole is 25% or more to 45% or less.

5. The medium according to claim 1, wherein said medium comprises one or more compounds of formula III-2-2 ##STR00172## in which R.sup.31 and R.sup.32 have the respective meanings given for formula III-2 in claim 1.

6. The medium according to claim 1, wherein said medium comprises one or more compounds of the formula III-3-2 ##STR00173## in which R.sup.31 and R.sup.32 have the respective meanings given for formula III-2 in claim 1.

7. The medium according to claim 1, wherein said medium comprises one or more compounds of the formula III-4.

8. The medium according to claim 1, wherein said medium comprises one or more chiral compounds.

9. An electro-optical display or electro-optical component, wherein said display or component contains a liquid-crystalline medium according to claim 1.

10. The display or component according to claim 9, wherein said display or component is based on the VA or ECB effect.

11. The display or component according to claim 9, wherein said display or component comprises an active-matrix addressing device.

12. A method of generating an electro-optical effect comprising applying a voltage to an electro-optical display or electro-optical component according to claim 9.

13. A process for the preparation of a liquid-crystalline medium according to claim 1, comprising mixing one or more compounds of formula I or formula I-1a with one or more compounds of formula II and one or more compounds selected from formulae III-1 to III-4.

14. A process for the stabilization of a liquid-crystalline medium which comprises one or more compounds of the formula II ##STR00174## in which R.sup.21 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms, and R22 denotes an unsubstituted alkenyl radical having 2 to 7 C atoms, and one or more compounds selected from formulae III-1 to III-4 ##STR00175## in which R.sup.31 denotes an unsubstituted alkyl radical having 1 to 7 C atoms, R.sup.32 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, and m, n and o each, independently of one another, denote 0 or 1, said method comprising adding to said medium one or more compounds of formula I or formula I-1a ##STR00176## in which R.sup.11 to R.sup.14 each, independently of one another, denote alkyl having 1 to 4 C atoms, X.sup.1 denotes O.sup., Y.sup.1 and Y.sup.01 each, independently of one another, denote straight-chain or branched alkyl having 1 to 10 C atoms, also cycloalkyl, cycloalkylalkyl or alkylcycloalkyl, where one or more CH.sub.2 groups in each of these groups may each be replaced by O in such a way that no two O atoms in the molecule are connected directly to one another, and Z.sup.1 denotes O, (CO)O, O(CO), O(CO)O, NH, NY.sup.01 or NH(CO), and, in the case where Z.sup.1 denotes O(CO)O, Y.sup.1 may also denote ##STR00177## and optionally one or more compounds selected from formulae OH-1 to OH-6, ##STR00178## are added to the medium.

15. The medium according to claim 1, wherein said medium contains one or more compounds of formula I-1a-2: ##STR00179##

16. The medium according to claim 1, wherein said medium contains one or more compounds of formula I.

17. The medium according to claim 1, wherein said medium contains one or more compounds of formula I selected the compounds of formulae I-1 to I-7: ##STR00180## wherein Y.sup.1, Y.sup.01, X.sup.1, and R.sup.11 R.sub.14 are as defined in claim 1.

18. The medium according to claim 1, wherein said medium contains one or more compounds of formula I selected the compounds of formulae I-1b to I-7b: ##STR00181## ##STR00182## wherein Y.sup.1, Y.sup.01, X.sup.1, and R.sup.11R.sup.14 are as defined in claim 1, and R and R each, independently of one another, denote straight-chain or branched alkyl having 1 to 10 C atoms, also cycloalkyl, cycloalkylalkyl or alkylcycloalkyl, where one or more CH.sub.2 groups in each of these groups may each be replaced by O in such a way that no two O atoms in the molecule are connected directly to one another.

19. The medium according to claim 1, wherein said medium contains one or more compounds of formula I selected the following compounds of formulae I-1b-2, I-1b-4, I-5a-2, and I-6a-2: ##STR00183##

20. The medium according to claim 1, wherein said medium contains one or more dielectrically negative compounds of formula II in a total concentration in the range from 5% to 90%, and contains one or more compounds selected from formulae III-1 to III-4 in a total concentration in the range from 10% to 80%.

Description

EXAMPLES

(1) The following examples explain the present invention without restricting it in any way. However, the physical properties make it clear to the person skilled in the art 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.

Substance Examples

(2) The following substances are preferred substances of the formula I in accordance with the present application.

(3) ##STR00161## ##STR00162##

(4) Liquid-crystal mixtures having the composition and properties as indicated in the following tables are prepared.

Example 1 and Comparative Examples 1.0 to 1.5

(5) The following mixture (M-1) is prepared and investigated.

(6) TABLE-US-00008 Mixture M-1 Composition Compound Concentration No. Abbreviation % by weight 1 CY-3-O4 10.0 2 CY-5-O4 10.0 3 CCY-2-O2 10.0 4 CCY-3-O2 10.0 5 CCY-5-O2 6.0 6 CCY-2-1 10.0 7 CCY-3-1 6.0 8 PCH-53 12.0 9 CCH-34 6.0 10 CC-3-V 20.0 100.0 Physical properties T(N, I) = 68 C. n(20 C., 589 nm) = 0.0757 (20, 1 kHz) = 2.8 .sub.1(20 C.) = n.d. mPa .Math. s k.sub.11(20 C.) = 12.4 pN k.sub.33(20 C.) = 13.3 pN V.sub.0(20 C.) = 2.31 V Note: n.d.: not determined

(7) 360 ppm of the compound of the formula I-1a-2 (TEMPOL) are added to mixture M-1. The resultant mixture (M-1-1) is, like mixture M-1 itself, investigated with respect to its stability to illumination by means of cold-cathode (CCFL) LCD backlighting in a test cell with an alignment material for homeotropic alignment and flat ITO electrodes. To this end, the test cells are exposed to the illumination for more than 1000 hours. The voltage holding ratio is determined in each case after fixed times after 5 minutes at a temperature of 100 C.

(8) The reproducibility of the voltage holding ratio values in various measurement series is in the range from about 3 to 4%.

(9) The decrease in the voltage holding ratio (VHR) usually caused by the load is determined in accordance with the following equation (1):
VHR(t)=VHR(t)VHR(t=0)(1).

(10) If the relative stability (S.sub.rel) of an LC mixture to LCD backlighting after a time t is determined in accordance with the following equation, equation (2):

(11) $\begin{array}{cc}{S}_{\mathrm{rel}}\left(t\right)=\frac{\mathrm{VHRref}\left(t=0\right)-\mathrm{VHRref}\left(t\right)}{\mathrm{VHR}\left(t=0\right)-\mathrm{VHR}\left(t\right)},& \left(2\right)\end{array}$
where ref stands for the corresponding unstabilised mixture (here M-1), a relative stabilisation of S.sub.rel (1000 h)=2.8 is obtained for this example (Example 1) compared with the reference mixture (Comparative Example 1.0). This result corresponds virtually to an effective doubling of the stability of the mixture investigated through the use of 360 ppm of TEMPOL.

Comparative Examples 1.1 to 1.5

(12) Alternatively, 600 ppm of TINUVIN770 (T770), 770 ppm of TINUVIN123 (T123), 820 ppm of TINUVIN622 LD (T622) or 580 ppm of Cyasorb UV-3853S(C3853) are added to mixture M-1. The resultant mixtures (CM-1-1 to CM-1-4) are investigated as described above.

(13) ##STR00163##

(14) Cyasorb UV-3853S(C3853 for short here) is a commercially available product from Cytec, West Paterson, USA, which is employed as light stabiliser, for example in formulations for plastic parts made from polypropylene for the automobile industry and for garden furniture. According to the manufacturer's data, it comprises 50% of a mixture of various HALS of the general formula

(15) ##STR00164##

(16) in an LDPE resin, where the alkyl radical R in Cyasorb UV-3853S essentially denotes C.sub.11 to C.sub.20 alkyl and predominantly denotes C.sub.16 to C.sub.18 alkyl. According to NA/867, Sep. 1, 2001, NICAS, Government of Australia, Cyasorb UV-3853S comprises 50% of polyethylene and the HALS component of Cyasorb UV-3853S comprises esters of the following acids:

(17) TABLE-US-00009 Proportion of the compound in the Ester of the acid R HALS (% by wt.) Stearic acid (CH.sub.2).sub.16CH.sub.3 40-65 Palmitic acid (CH.sub.2).sub.14CH.sub.3 31-49 Heptadecanoic (CH.sub.2).sub.15CH.sub.3 0.3-4.8 acid Myristic acid (CH.sub.2).sub.12CH.sub.3 0.1-3.0 Oleic acid (CH.sub.2).sub.7CHCH(CH.sub.2).sub.7CH.sub.3 0.2-4.0 Others C.sub.11 to C.sub.20 0.2-6.2

(18) TABLE-US-00010 TABLE 1 VHR No. Mixture Stabiliser c(stab.)/ppm (1000 h)/% S.sub.rel(1000 h) 1 M-1 none 0 70.7 1.0* 2 M-1-1 I-1a-2 360 89.2 2.8 3 CM-1-1 T770 600 79.6 1.5 4 CM-1-2 T123 770 73.3 1.1 5 CM-1-3 T622 820 79.9 1.1 6 CM-1-4 C3853 580 73.9 1.2 7 CM-1-5 LC-Stab 640 73.4 1.1 Note: *not applicable

Example 2

(19) The following mixture (M-2) is prepared and investigated.

(20) TABLE-US-00011 Mixture M-2 Composition Compound Concentration No. Abbreviation % by weight 1 CY-3-O4 20.0 2 CCY-3-O2 13.0 3 CCY-4-O2 5.0 4 CPY-2-O2 10.0 5 CPY-3-O2 10.0 6 CC-3-4 9.0 7 CC-3-5 4.0 8 CC-3-O1 9.0 9 CC-3-V 12.0 10 CP-3-O1 3.0 11 CCP-V-1 5.0 100.0 Physical properties T(N, I) = 80C. n(20 C., 589 nm) = 0.0913 (20, 1 kHz) = 3.4 .sub.1(20 C.) = 117 mPa .Math. s k.sub.11(20 C.) = 13.6 pN k.sub.33(20 C.) = 14.8 pN V.sub.0(20 C.) = 2.19 V

(21) Mixture M-2 is investigated as described in Example 1. To this end, 200 ppm of the compound of the formula I-1a-2 are added to this mixture. The resultant mixture (M-2-1) is, like mixture M-2 itself, investigated in a test cell with respect to its stability to illumination by means of LCD backlighting. To this end, the test cells are exposed to the illumination for 1000 hours. The voltage holding ratio is then determined after 5 minutes at a temperature of 100 C. The relative improvement in the voltage holding ratio here is S.sub.rel (1000 h)=1.8.

Example 3 and Comparative Examples 3.0 to 3.2

(22) 500 ppm of the compound of the formula I-1a-2 are added to mixture M-1 of Example 1. The resultant mixture (M-1-2) is, like mixture M-1 itself, investigated in a test cell with respect to its stability to illumination by means of LCD backlighting. To this end, the test cells are exposed to the illumination for 1000 hours. The voltage holding ratio is then determined after 5 minutes at a temperature of 100 C. The relative improvement in the voltage holding ratio here is S.sub.rel(1000 h)=2.8.

Examples 4.1 to 4.3

Example 4.1

(23) 500 ppm of the compound of the formula I-1a-2 are added to mixture M-1 of Example 1 (M-1-3), and the mixture is subjected to a temperature of 150 C. for 4 h in a sealed glass bottle. The VHR is subsequently determined and compared with the initial value of the mixture comprising 360 ppm of the compound of the formula I-1a-2 before heating. The VHR is 99% before heating and 98% after heating.

Example 4.2

(24) Both 360 ppm of the compound of the formula I-1a-2 and also 200 ppm of compound OH-1

(25) ##STR00165##
are then added to mixture M-1 (M-1-4). This mixture (M-1-4) was also subjected to a temperature of 150 C. for 4 h. In contrast to the mixture which comprises only 360 ppm of the compound of the formula I-1a-2, but no OH-1, the voltage holding ratio here is at the same level after the heating as before the heating test. The VHR is 96% before heating and 95% after heating.

(26) The two mixtures are investigated with respect to their stability to irradiation by means of LCD backlighting. The results are equally good for both mixtures. It is thus apparent that the addition of phenolic antioxidants is unnecessary on use of stabiliser I-1a-2.

Example 4.3

(27) 200 ppm of the compound of the formula I-1a-1 (4-hydroxy-2,2,6,6-tetramethylpiperidine) are added to mixture M-1 of Example 1 (M-1-5), and the mixture is subjected to a temperature of 150 C. for 4 h in a sealed glass bottle. The VHR is subsequently determined and compared with the initial value of the mixture comprising 200 ppm of 4-hydroxy-2,2,6,6-tetramethylpiperidine before the heating. The VHR is 98% before heating and 81% after heating. Here too, relatively favourable properties are obtained with respect to the stability. However, these are somewhat less favourable than in the case of the two preceding examples (Examples 4.1 and 4.2). For this reason, this embodiment is less preferred. However, better results can also be achieved here if a phenol compound is used as additional or supplementary thermal stabiliser in addition to the compound of the formula I-1a-1.

Example 5

(28) 200 ppm of the compound of the formula I-1b-2 are added to mixture M-1 of Example 1 (M-1-6), and the mixture is subjected to a temperature of 150 C. for 4 h in a sealed glass bottle. The VHR is subsequently determined and compared with the initial value of the mixture comprising 200 ppm of the compound of the formula I-1b-2 before the heating. The VHR is 98% before heating and 93% after heating.

(29) 500 ppm of the compound of the formula I-1b-2 are then added to mixture M-1 of Example 1. The resultant mixture (M-1-7) is, like mixture M-1 itself, investigated in a test cell with respect to its stability to illumination by means of LCD backlighting. To this end, the test cells are exposed to the illumination for 1000 hours. The voltage holding ratio is then determined after 5 minutes at a temperature of 100 C. The relative improvement in the voltage holding ratio here is S.sub.rel(1000 h)=2.4.

Example 6

(30) 200 ppm of the compound of the formula I-6a-2 are added to mixture M-1 of Example 1 (M-1-8), and the mixture is subjected to a temperature of 150 C. for 4 h in a sealed glass bottle. The VHR is subsequently determined and compared with the initial value of the mixture comprising 200 ppm of the compound of the formula I-6a-2 before the heating. The VHR is 98% before heating and 95% after heating.

(31) 200 ppm of the compound of the formula I-1b-2 are then added to mixture M-1 of Example 1. The resultant mixture (M-1-9) is, like mixture M-3 itself, investigated in a test cell with respect to its stability to illumination by means of LCD backlighting. To this end, the test cells are exposed to the illumination for 1000 hours. The voltage holding ratio is then determined after 5 minutes at a temperature of 100 C. The relative improvement in the voltage holding ratio here is S.sub.rel(1000 h)=2.2.

Example 6 and Comparative Examples 6.0 and 6.1

(32) The following mixture (M-3), which comprises 40% of compounds containing an alkenyl end group, is prepared and investigated.

(33) TABLE-US-00012 Mixture M-3 Composition Compound Concentration No. Abbreviation % by weight 1 CY-3-O2 10.0 2 PY-3-O2 10.0 3 CCY-3-O2 11.0 4 CPY-2-O2 8.5 5 CPY-3-O2 10.5 6 PYP-2-3 7.0 7 CC-3-V 33.5 8 CC-3-V1 6.5 9 CCP-3-1 3.0 100.0 Physical properties T(N, I) = 74.9 C. n.sub.e(20 C., 589 nm) = 1.5931 n(20 C., 589 nm) = 0.1081 .sub.(20, 1 kHz) = 6.5 (20, 1 kHz) = 3.0 .sub.1(20 C.) = n.d. mP .Math. s k.sub.11(20 C.) = 13.0 pN k.sub.33(20 C.) = 15.9 pN V.sub.0(20 C.) = 2.43 V

(34) Mixture M-3 is, as described in Example 1, divided into three parts and, as described therein, investigated as such or alternatively mixed with the compound of Substance Example 11

(35) ##STR00166##
or with TINUVIN770, and the corresponding mixtures are investigated in test cells with respect to their stability to illumination by means of LCD backlighting. For the mixture which comprises the compound of the formula shown, comparably favourable results are also achieved here as in Example 1. These are compiled in the following table (Table 2).

(36) TABLE-US-00013 TABLE 2 c(stab.)/ VHR(t)/% S.sub.rel(t) Ex. No. Mixture Stabiliser ppm t = 0 h t = 750 h t = 750 h C6.0 1 M-3 none 0 98.0 0.3 68 2 1 C6.1 2 CM-3-1 T770 250 96.6 0.4 79 2 1.7 B6 3 M-3-1 I* 50 97.2 0.2 79 2 1.6 Notes: I*: Compound of the formula (11) shown above T770 TINUVIN770

(37) In addition, the ion densities were determined for the three mixtures. The results are compiled in the following table (Table 3).

(38) TABLE-US-00014 TABLE 3 c(stab.)/ Ion density/ S.sub.rel(t) Ex. No. Mixture Stabiliser ppm pC t = 750 h C6.0 1 M-3 none 0 181 25 1.0 C6.1 2 CM-3-1 T770 250 1.031 58 1.7 B6 3 M-3-1 I* 50 223 32 1.6 Notes: I*: Compound of the formula (11) shown above T770: TINUVIN770

(39) It is readily evident here that the above-mentioned compound exhibits significantly stabilising properties even in relatively low concentrations. The voltage holding ratio is significantly superior to that of the starting mixture and is comparable with that of the comparative mixture. In addition, the ion density is virtually unchanged compared with the undoped reference. TINUVIN770, by contrast, exhibits an ion density which is four times as high. The behaviour of the above-mentioned compound overall thus appears significantly more favourable.

Example 7 and Comparative Examples 7.0 and 7.1

(40) Mixture M-3 of Example 6 is, as described therein, divided into three parts and, as described therein, investigated as such or alternatively mixed with the compound of Substance Example 12

(41) ##STR00167##
or with TINUVIN770, and the corresponding mixtures are investigated in test cells with respect to their stability to illumination by means of LCD backlighting. For the mixture which comprises the compound shown, comparably favourable results are also achieved here as in Example 6. These are compiled in the following tables (Tables 4 and 5).

(42) TABLE-US-00015 TABLE 4 c(stab.)/ VHR(t)/% S.sub.rel(t) Ex. No. Mixture Stabiliser ppm t = 0 h t = 750 h t = 750 h C7.0 1 M-3 none 0 98.0 0.3 68 2 1 C7.1 2 CM-3-1 T770 250 96.6 0.4 79 2 1.7 B7 3 M-3-2 I* 50 97.3 0.3 78 2 1.6 Notes: I*: Compound of the formula (12) shown above T770 TINUVIN770

(43) TABLE-US-00016 TABLE 5 c(stab.)/ Ion density/ S.sub.rel(t) Ex. No. Mixture Stabiliser ppm pC t = 750 h C7.0 1 M-3 none 0 181 25 1.0 C7.1 2 CM-3-1 T770 250 1.031 58 1.7 B7 3 M-3-2 I* 50 250 43 1.5 Notes: I*: Compound of the formula (12) shown above T770: TINUVIN770

(44) It is also evident here that the above-mentioned compound exhibits significantly stabilising properties even in relatively low concentrations. The voltage holding ratio is significantly superior to that of the starting mixture and is at least comparable to that of the comparative mixture. In addition, the ion density is virtually unchanged compared with the undoped reference. TINUVIN770, by contrast, exhibits an ion density which is four times as high. The behaviour of the above-mentioned compound in total thus also looks significantly more favourable.