Polymerisable mixtures and the use thereof in liquid crystal displays

Abstract

The present invention relates to polymerizable mixtures and to the use thereof for optical, electro-optical and electronic purposes, in particular in liquid-crystal (LC) media and LC displays, especially in LC displays of the PS (polymer sustained) or PSA (polymer sustained alignment) type.

Claims

1. Polymerisable mixture comprising at least one first polymerisable compound and at least one second polymerisable compound, where the first polymerisable compound initiates and/or accelerates the polymerisation of the second polymerisable compound, wherein the first polymerisable compound is selected from the group consisting of the following formulae: ##STR00207## wherein L on each occurrence, identically or differently, denotes F, Cl, CN, or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, r denotes 0, 1, 2, 3 or 4, s denotes 0, 1, 2 or 3, t denotes 0, 1 or 2, P on each occurrence, identically or differently, denotes a polymerisable radical selected from the group consisting of:
CH.sub.2CW.sup.1COO,
CH.sub.2CHO,
(CH.sub.2CH).sub.2CHOCO,
(CH.sub.2CH).sub.2CHO, ##STR00208## in which W.sup.1 denotes H, F, Cl, CN, CF.sub.3, phenyl or alkyl having 1 to 5 C atoms, W.sup.2 denotes H or alkyl having 1 to 5 C atoms, and k1 denotes 0 or 1, Sp on each occurrence, identically or differently, denotes a spacer group or a single bond, R, R.sup.a each denote P-Sp; and wherein the second polymerisable compound contains a ring system which is different from the first polymerisable compound, containing one or more carbo- or heterocyclic radicals and two or more than two polymerisable radicals, which are connected to the ring system directly or via a spacer group and wherein the polymerisable radicals are selected from the group consisting of:
CH.sub.2CW.sup.1COO,
CH.sub.2CHO,
(CH.sub.2CH).sub.2CHOCO,
(CH.sub.2CH).sub.2CHO, ##STR00209## in which W.sup.1 denotes H, F, Cl, CN, CF.sub.3, phenyl or alkyl having 1 to 5 C atoms, W.sup.2 denotes H or alkyl having 1 to 5 C atoms, and k1 denotes 0 or 1.

2. Polymerisable mixture according to claim 1, characterised in that the second polymerisable compound is selected from the group consisting of the following formulae: ##STR00210## in which P, Sp, R, L and r have the meanings indicated in claim 1, Z.sup.1 denotes O, CO, COO, OCO, C(R.sup.yR.sup.z) or CF.sub.2CF.sub.2, R.sup.y and R.sup.z each, independently of one another, denote H, F, CH.sub.3 or CF.sub.3, Z.sup.2 and Z.sup.3 each, independently of one another, denote COO, OCO, CH.sub.2O, OCH.sub.2, CF.sub.2O, OCF.sub.2, or (CH.sub.2).sub.n, where n is 2, 3 or 4, L and L each, independently of one another, denote H, F or Cl, and x denotes 0 or 1.

3. A LC medium comprising a polymerisable mixture according to claim 1.

4. A LC medium, comprising a polymerisable component A) comprising the polymerisable mixture according to claim 1, and a liquid-crystalline component B) comprising one or more low-molecular-weight compounds.

5. A LC medium comprising a polymer which is obtainable by polymerisation of a polymerisable mixture according to claim 1, and one or more additional compounds other than the first polymerisable compound and second polymerisable compound of said polymerisable mixture according to claim 1.

6. A LC medium comprising a polymerisable mixture comprising at least one first polymerisable compound and at least one second polymerisable compound, where the first polymerisable compound initiates and/or accelerates the polymerisation of the second polymerisable compound, wherein the first polymerisable compound contains a ring system containing a divalent radical and two or more than two polymerisable radicals, which are connected to the ring system directly or via a spacer group, and the second polymerisable compound contains a ring system which is different from the first polymerisable compound, containing one or more carbo- or heterocyclic radicals and two or more than two polymerisable radicals, which are connected to the ring system directly or via a spacer group and wherein the polymerisable radicals are selected from the group consisting of:
CH.sub.2CW.sup.1COO,
CH.sub.2CHO,
(CH.sub.2CH).sub.2CHOCO,
(CH.sub.2CH).sub.2CHO, ##STR00211## in which W.sup.1 denotes H, F, Cl, CN, CF.sub.3, phenyl or alkyl having 1 to 5 C atoms, W.sup.2 denotes H or alkyl having 1 to 5 C atoms, and k1 denotes 0 or 1 and wherein the first polymerisable compound contains a divalent radical selected from the group consisting of the formulae A, B, C and D: ##STR00212## in which the individual radicals have the following meanings: L on each occurrence, identically or differently, denotes F, Cl, CN, or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, r denotes 0, 1, 2, 3 or 4, s denotes 0, 1, 2 or 3, and t denotes 0, 1 or 2, which additionally comprises one or more compounds of the formulae CY and/or PY: ##STR00213## in which the individual radicals have the following meanings: a denotes 1 or 2, b denotes 0 or 1, ##STR00214## 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.

7. A LC medium according to claim 3, characterised in that it additionally comprises one or more compounds of the following formula: ##STR00215## in which the individual radicals have the following meanings: ##STR00216## 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.

8. A LC display of the PS or PSA type comprising a polymerisable mixture comprising at least one first polymerisable compound and at least one second polymerisable compound, where the first polymerisable compound initiates and/or accelerates the polymerisation of the second polymerisable compound, wherein the first polymerisable compound contains a ring system containing a divalent radical and two or more than two polymerisable radicals, which are connected to the ring system directly or via a spacer group, and the second polymerisable compound contains a ring system which is different from the first polymerisable compound, containing one or more carbo- or heterocyclic radicals and two or more than two polymerisable radicals, which are connected to the ring system directly or via a spacer group and wherein the polymerisable radicals are selected from the group consisting of:
CH.sub.2CW.sup.1COO,
CH.sub.2CHO,
(CH.sub.2CH).sub.2CHOCO,
(CH.sub.2CH).sub.2CHO, ##STR00217## in which W.sup.1 denotes H, F, Cl, CN, CF.sub.3, phenyl or alkyl having 1 to 5 C atoms, W.sup.2 denotes H or alkyl having 1 to 5 C atoms, and k1 denotes 0 or 1 and wherein the first polymerisable compound contains a divalent radical selected from the group consisting of the formulae A, B, C and D: ##STR00218## in which the individual radicals have the following meanings: L on each occurrence, identically or differently, denotes F, Cl, CN, or straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, r denotes 0, 1, 2, 3 or 4, s denotes 0, 1, 2 or 3, and t denotes 0, 1 or 2.

9. A LC display containing an LC medium according to claim 5.

10. A LC display according to claim 8, characterised in that the LC display comprises an LC cell having two substrates and two electrodes, where at least one substrate is transparent to light and at least one substrate has one or two electrodes, and a layer, located between the substrates, of said LC medium as defined in claim 8 where the polymer obtainable by polymerisation of the polymerisable mixture is obtained between the substrates of the LC cell in the LC medium.

11. A LC display according to claim 8, characterised in that it is a PSA-VA, PSA-OCB, PSA-positive-VA, PSA-IPS, PSA-FFS or PSA-TN display.

12. A process for the production of an LC display of the PS or PSA type in which an LC medium according to claim 8 is introduced into an LC cell having two substrates and two electrodes, where at least one substrate is transparent to light and at least one substrate has one or two electrodes, and the polymerisable mixture is polymerised.

13. Polymerisable mixture according to claim 1, wherein P is a vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane-O or epoxide group.

14. Polymerisable mixture according to claim 1, wherein Sp, when being different from a single bond, denotes (CH.sub.2).sub.P1, (CH.sub.2).sub.P1O, (CH.sub.2).sub.P1OCO or (CH.sub.2).sub.P1OCOO, in which P1 denotes an integer from 1 to 12, where these groups are linked to P in such a way that O atoms are not directly adjacent.

15. Polymerisable mixture according to claim 14 wherein P1 denotes an integer from 1 to 6.

16. Polymerisable mixture according to claim 14 wherein P1 denotes an integer which is 1, 2 or 3.

17. A LC display containing an LC medium according to claim 6.

Description

EXAMPLE 1

(1) The nematic LC mixture N1 is formulated as follows:

(2) TABLE-US-00005 CCH-501 9.00% Cl.p. +70.0 CCH-35 14.00% n 0.0825 PCH-53 8.00% 3.5 CY-3-O4 14.00% .sub. 3.5 CY-5-O4 13.00% K.sub.3/K.sub.1 1.00 CCY-3-O2 8.00% 141 CCY-5-O2 8.00% V.sub.0 2.06 CCY-2-1 9.00% CCY-3-1 9.00% CPY-2-O2 8.00%

(3) The following polymerisable compounds are tested:

(4) ##STR00206##

(5) Polymerisable monomeric compounds of the formulae shown above are added to LC mixture N1 in the amounts and combinations indicated in each case, and the resultant mixtures are introduced into VA e/o test cells (alkali-free glass, rubbed antiparallel, VA-polyimide alignment layer, layer thickness d4 m). The cells are irradiated with UV light having an intensity of 100 mW/cm.sup.2 for the stated time with application of a voltage of 24 V (alternating current), causing polymerisation of the monomeric compound. The tilt angle is determined by crystal rotation experiment (Autronic-Melchers TBA-105) before and after the UV irradiation.

(6) The comparative tilt-angle results are shown in Table 1.

(7) TABLE-US-00006 TABLE 1 (t = exposure time) 0.25% M2A1 + 0.25% M2A1 + 0.25% M2A1 + 0.3% M2A1 0.05% M1A1 0.05% M1B1 0.05% M1C1 t/s Tilt angle/ 0 88.3 88.3 88.2 88.2 120 83.4 77.7 78.9 80.2 240 76.3 71.0 72.6 75.8 360 74.8 70.3 72.2 75.1

(8) In order to determine the polymerisation rate, the residual content of unpolymerised RM (in % by weight) in the test cells is measured by the HPLC method after various exposure times. To this end, each mixture is polymerised in the test cell under the conditions indicated. The mixture is then rinsed out of the test cell using MEK (methyl ethyl ketone) and measured.

(9) The RM concentrations after various exposure times are shown in Table 2.

(10) TABLE-US-00007 TABLE 2 (t = exposure time) 0.25% M2A1 + 0.25% M2A1 + 0.25% M2A1 + 0.3% M2A1 0.05% M1A1 0.05% M1B1 0.05% M1C1 t/s RM concentration/% 0 0.300 0.300 0.300 0.300 120 0.251 0.180 0.175 0.154 240 0.140 0.078 0.108 0.108 360 0.080 0.054 0.051 0.051

(11) The VHR value is measured as follows: one or more polymerisable monomeric compounds are added to LC host mixture N1 in the amounts respectively indicated, and the resultant mixture is introduced into VHR test cells (VA-polyimide alignment layer, homeotropic alignment). The VHR value is determined after a waiting time of 5 min at 100 C. before and after corresponding exposure at 1 V, 60 Hz, 64 s pulse (measuring instrument: Autronic-Melchers VHRM-105). For comparative purposes, a measurement is carried out with the pure LC mixture N1 (i.e. without addition of monomers).

(12) The respective VHR values are shown in Table 3.

(13) TABLE-US-00008 TABLE 3 N1 without 0.3% M2A1 0.3% M1A1 0.3% M1B1 monomers in N1 in N1 in N1 Condition VHR/% initial 98.5 98.2 98.6 98.2 2 h suntest 97.8 97.9 97.7 97.2 2 min UVA 98.4 97.9 97.5 96.7 15 min UVA 97.4 97.6 97.3 96.2 2 min 96.5 97.7 97.7 97.0 UVA + 2 h suntest 15 min 95.7 97.6 97.5 95.1 UVA + 2 h suntest 0.25% 0.25% 0.25% 0.3% M2A1 + M2A1 + M2A1 + M1C1 0.05% M1A1 0.05% M1B1 0.05% M1C1 in N1 in N1 in N1 in N1 Condition VHR/% initial 98.0 98.6 98.4 98.3 2 h suntest 93.5 97.8 98.1 97.6 2 min UVA 92.3 98.0 97.9 97.6 15 min UVA 89.6 97.2 97.8 97.3 2 min 94.7 97.7 97.8 97.7 UVA + 2 h suntest 15 min 90.7 97.6 97.7 97.4 UVA + 2 h suntest

(14) The experiments described above are carried out analogously for the polymerisable monomeric compound M1C2 of the formula 1C2 shown above. Differences from the experimental conditions described above are indicated in the respective table.

(15) The comparative tilt-angle results are shown in Table 4.

(16) TABLE-US-00009 TABLE 4 (t = exposure time), intensity 50 mW/cm.sup.2 0.25% M2A1 + 0.3% M2A1 0.05% M1C2 t/s Tilt angle/ 0 89.2 89.6 30 89.1 88.5 60 88.4 85.7 120 83.9 81.5 240 76.5 77.9 360 75.3

(17) The RM concentrations after various exposure times are shown in Table 5.

(18) TABLE-US-00010 TABLE 5 (t = exposure time), intensity 50 mW/cm.sup.2, test cells made from soda-lime glass 0.25% M2A1 + 0.3% M2A1 0.05% M1C2 t/s RM concentration/% 0 0.300 0.300 120 0.268 0.181 240 0.226 0.134 360 0.176 0.116

(19) The respective VHR values are shown in Table 6.

(20) TABLE-US-00011 TABLE 6 Test cells with TN polyimide, planar alignment 0.25% M2A1 + N1 without 0.3% M2A1 0.3% M1C2 0.05% M1C2 monomers in N1 in N1 in N1 Condition VHR/% initial 93.8 91.6 91.8 92.9 2 h suntest 89.3 92.2 86.9 92.0

(21) It can be seen from Tables 1, 2, 4 and 5 that the commencement of polymerisation and the tilt-angle generation are accelerated by addition of a first polymerisable compound (M1A1-M1C1) to the second polymerisable compound (M2A1). This behaviour of the first polymerisable compound corresponds to that of a typical photoinitiator. The resultant advantages are faster establishment of the desired tilt angle and faster polymerisation, i.e. a lower residual RM content, in the later display.

(22) In addition, it can be seen from Tables 3 and 6 that, in addition, very good VHR values can be achieved, even after very long UV exposures, on use of a combination of a first polymerisable compound (M1A1-M1C1) and a second polymerisable compound (M2A1). This is not possible on use of a respective single polymerisable compound If fast polymerisation is desired. The polymerisable compounds 1C1 and 1C2 each exhibit, for example, a relatively low VHR after UV exposure. The combination of this polymerisable compound with a second polymerisable compound M2A1 results, however, in a very good VHR after UV exposure.

(23) The polymerisation and tilt-angle generation thus proceed more quickly in an LC mixture comprising a combination of two polymerisable compounds than in an LC mixture which comprises only the polymerisable compound M2A1. In addition, a very good VHR value can also be achieved in addition to a faster reaction rate.