LIQUID-CRYSTAL MEDIUM COMPRISING POLYMERIZABLE COMPOUNDS

Abstract

The present invention relates to a liquid-crystal (LC) medium comprising polymerizable compounds, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in LC displays of the PSA (polymer sustained alignment) or SA (self-aligning) mode, to an LC display of the PSA or SA mode comprising the LC medium, and to a process of manufacturing the LC display.

Claims

1. An LC medium having negative dielectric anisotropy and comprising one or more polymerizable compounds, one or more compounds of formula IA, and one or more compounds of formula IB ##STR00546## in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: R.sup.1, R.sup.2 straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CH.sub.2-groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, CR.sup.0═CR.sup.00—, —C≡C—, ##STR00547##  in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl, preferably alkyl or alkoxy having 1 to 6 C atoms, R.sup.0, R.sup.00 H or alkyl having 1 to 12 C atoms, L.sup.1, L.sup.2 F or Cl, preferably F.

2. The LC medium according to claim 1, wherein compounds of formula IA are selected from formulae IA-1 to IA-10: ##STR00548## ##STR00549## in which R.sup.12 denotes alkyl having 1 to 7 C-atoms, preferably ethyl, n-propyl or n-butyl, or alternatively cyclopropylmethyl, cyclobutylmethyl or cyclopentylmethyl.

3. The LC medium according to claim 1, wherein compounds of formula IB are selected from the following subformulae: ##STR00550## in which alkyl and alkyl* independently of each other denote a straight-chain alkyl radical having 1-6 C atoms and (O) denotes an oxygen atom or a single bond.

4. The LC medium according to claim 1, wherein the total proportion of the compounds of formula IB in the LC medium is from 0.5 to 5% by weight.

5. The LC medium according to claim 1, further comprising one or more compounds of formula II ##STR00551## wherein the individual radicals, independently of each other and on each occurrence identically or differently, have the following meanings R.sup.1 and R.sup.2 straight chain, branched or cyclic alkyl having 1 to 25 C atoms, wherein one or more non-adjacent CH.sub.2-groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—, CR.sup.0═CR.sup.00—, —C≡C—, ##STR00552##  in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl, preferably alkyl or alkoxy having 1 to 6 C atoms, R.sup.0, R.sup.00 H or alkyl having 1 to 12 C atoms, A.sup.1 and A.sup.2 a group selected from the following formulae ##STR00553## ##STR00554## Z.sup.1 and Z.sup.2 —CH.sub.2CH.sub.2—, —CH═CH—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —CO—O—, —O—CO—, —C.sub.2F.sub.4—, —CF═CF—, —CH═CH—CH.sub.2O— or a single bond, preferably a single bond, L.sup.1, L.sup.2, L.sup.3 and L.sup.4 F, Cl, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2F or CHF.sub.2, preferably F or Cl, very preferably F, Y H, F, Cl, CF.sub.3, CHF.sub.2 or CH.sub.3, preferably H or CH.sub.3, very preferably H, L.sup.C CH.sub.3 or OCH.sub.3, preferably CH.sub.3, a1 1 or 2, a2 0 or 1.

6. The LC medium according to claim 5, wherein compounds of formula II are selected from compounds of formulae IIA, IIB, IIC and IID ##STR00555## in which R.sup.2A and R.sup.2B each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF.sub.3 or at least monosubstituted by halogen, where, in addition, one or more CH.sub.2 groups in these radicals may be replaced by —O—, —S—, ##STR00556## —C≡C—, —CF.sub.2O—, —OCF.sub.2—, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another, L.sup.1 to L.sup.4 each, independently of one another, denote F, Cl, CF.sub.3 or CHF.sub.2, Y denotes H, F, Cl, CF.sub.3, CHF.sub.2 or CH.sub.3, preferably H or CH.sub.3, particularly preferably H, Z.sup.2, Z.sup.2B, Z.sup.2D each, independently of one another, denote a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —CF═CF—, —CH═CHCH.sub.2O—, p denotes 0, 1 or 2, and q on each occurrence, identically or differently, denotes 0 or 1.

7. The LC medium according to claim 1, further comprising one or more compounds of formula III ##STR00557## in which R.sup.11 and R.sup.12 each, independently of one another, denote H, an alkyl or alkoxy radical having 1 to 15 C atoms, where one or more CH.sub.2 groups in these radicals may each be replaced, independently of one another, by ##STR00558## —C≡C—, —CF.sub.2O—, —OCF.sub.2—, —CH═CH—, by —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by halogen, A.sup.3 on each occurrence, independently of one another, denotes a) 1,4-cyclohexenylene or 1,4-cyclohexylene radical, in which one or two non-adjacent CH.sub.2 groups may be replaced by —O— or —S—, b) a 1,4-phenylene radical, in which one or two CH groups may be replaced by N, or c) a radical selected from the group consisting of spiro[3.3]heptane-2,6-diyl, 1,4-bicyclo[2.2.2]octylene, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, 1,2,3,4-tetrahydronaphthalene-2,6-diyl, phenanthrene-2,7-diyl and fluorene-2,7-diyl, wherein the radicals a), b) and c) may be mono- or polysubstituted by halogen atoms, n denotes 0, 1 or 2, preferably 0 or 1, Z.sup.1 on each occurrence independently of one another denotes —CO—O—, —O—CO—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —CH.sub.2—, —CH.sub.2CH.sub.2—, —(CH.sub.2).sub.4—, —CH═CH—CH.sub.2O—, —C.sub.2F.sub.4—, —CH.sub.2CF.sub.2—, —CF.sub.2CH.sub.2—, —CF═CF—, —CH═CF—, —CF═CH—, —CH═CH—, —C≡C— or a single bond, L.sup.11 and L.sup.12 each, independently of one another, denote F, Cl, CF.sub.3 or CHF.sub.2, preferably H or F, most preferably F, and W denotes O or S.

8. The LC medium according to claim 1, further comprising one or more compounds of formula IV ##STR00559## in which R.sup.41 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably an n-alkyl radical, particularly preferably having 2, 3, 4 or 5 C atoms, and R.sup.42 denotes an unsubstituted alkyl radical having 1 to 7 C atoms or an unsubstituted alkoxy radical having 1 to 6 C atoms, both preferably having 2 to 5 C atoms, an unsubstituted alkenyl radical having 2 to 7 C atoms, preferably having 2, 3 or 4 C atoms, more preferably a vinyl radical or a 1-propenyl radical and in particular a vinyl radical.

9. The LC medium according to claim 1, further comprising one or more compounds of formula V ##STR00560## in which R.sup.51 and R.sup.52 independently of one another, have one of the meanings given for R.sup.41 and R.sup.42 and preferably denote alkyl having 1 to 7 C atoms, preferably n-alkyl, particularly preferably n-alkyl having 1 to 5 C atoms, alkoxy having 1 to 7 C atoms, preferably n-alkoxy, particularly preferably n-alkoxy having 2 to 5 C atoms, alkoxyalkyl, alkenyl or alkenyloxy having 2 to 7 C atoms, preferably having 2 to 4 C atoms, preferably alkenyloxy, ##STR00561## identically or differently, denote ##STR00562## in which ##STR00563## preferably denotes ##STR00564## Z.sup.51, Z.sup.52 each, independently of one another, denote —CH.sub.2—CH.sub.2—, —CH.sub.2—O—, —CH═CH—, —C≡C—, —COO— or a single bond, preferably —CH.sub.2—CH.sub.2—, —CH.sub.2—O— or a single bond and particularly preferably a single bond, and n is 1 or 2.

10. The LC medium according to claim 1, further comprising one or more additives selected from the group consisting of stabilizers, chiral dopants, polymerization initiators, and self alignment additives.

11. The LC medium according to claim 1, wherein the one or more polymerizable compounds are selected from formula M
R.sup.a—B.sup.1—(Z.sup.b—B.sup.2).sub.m—R.sup.b  M in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: R.sup.a and R.sup.b P, P-Sp-, H, F, Cl, Br, I, —CN, —NO.sub.2, —NCO, —NCS, —OCN, —SCN, SF.sub.5 or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH.sub.2 groups may each be replaced, independently of one another, by —C(R.sup.0)═C(R.sup.00)—, —C≡C—, —N(R.sup.00)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, Br, I, CN, P or P-Sp-, where, if B.sup.1 and/or B.sup.2 contain a saturated C atom, R.sup.a and/or R.sup.b may also denote a radical which is spiro-linked to this saturated C atom, wherein at least one of the radicals R.sup.a and R.sup.b denotes or contains a group P or P-Sp-, P a polymerizable group, Sp a spacer group or a single bond, B.sup.1 and B.sup.2 an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having 4 to 25 ring atoms, which may also contain fused rings, and which is unsubstituted, or mono- or polysubstituted by L, Z.sup.b —O—, —S—, —CO—, —CO—O—, —OCO—, —O—CO—O—, —OCH.sub.2—, —CH.sub.2O—, —SCH.sub.2—, —CH.sub.2S—, —CF.sub.2O—, —OCF.sub.2—, —CF.sub.2S—, —SCF.sub.2—, —(CH.sub.2).sub.n1—, —CF.sub.2CH.sub.2—, —CH.sub.2CF.sub.2—, —(CF.sub.2).sub.n1—, —CH═CH—, —CF═CF—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH—, CR.sup.0R.sup.00 or a single bond, R.sup.0 and R.sup.00 H or alkyl having 1 to 12 C atoms, m 0, 1, 2, 3 or 4, n1 1, 2, 3 or 4, L P, P-Sp-, OH, CH.sub.2OH, F, Cl, Br, I, —CN, —NO.sub.2, —NCO, —NCS, —OCN, —SCN, —C(═O)N(R.sup.x).sub.2, —C(═O)Y.sup.1, —C(═O)R.sup.x, —N(R.sup.x).sub.2, optionally substituted silyl, optionally substituted aryl having 6 to 20 C atoms, or straight-chain or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which, in addition, one or more H atoms may be replaced by F, Cl, P or P-Sp-, Y.sup.1 halogen, R.sup.x P, P-Sp-, H, halogen, straight-chain, branched or cyclic alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH.sub.2 groups may be replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, P or P-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 C atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 C atoms.

12. The LC medium according to claim 1, wherein the one or more polymerizable compounds are selected from the following formulae: ##STR00565## ##STR00566## ##STR00567## ##STR00568## ##STR00569## in which the individual radicals, on each occurrence identically or differently, and each, independently of one another, have the following meaning: P.sup.1, P.sup.2, P.sup.3 a vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane or epoxy group, Sp.sup.1, Sp.sup.2, Sp.sup.3 a single bond or a spacer group where, in addition, one or more of the radicals P.sup.1-Sp.sup.1-, P.sup.2-Sp.sup.2- and P.sup.3-Sp.sup.3- may also denote R.sup.aa, with the proviso that at least one of the radicals P.sup.1-Sp.sup.1-, P.sup.2-Sp.sup.2 and P.sup.3-Sp.sup.3- present is different from R.sup.aa, R.sup.aa H, F, Cl, CN or straight-chain or branched alkyl having 1 to 25 C atoms, in which, in addition, one or more non-adjacent CH.sub.2 groups may each be replaced, independently of one another, by —C(R.sup.0)═C(R.sup.00)—, —C≡C—, —N(R.sup.0)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that O and/or S atoms are not linked directly to one another, and in which, in addition, one or more H atoms may be replaced by F, Cl, CN or P.sup.1-Sp.sup.1-, particularly preferably straight-chain or branched, optionally mono- or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, where the alkenyl and alkynyl radicals have at least two C atoms and the branched radicals have at least three C atoms, R.sup.0, R.sup.00 H or alkyl having 1 to 12 C atoms, R.sup.y and R.sup.z H, F, CH.sub.3 or CF.sub.3, X.sup.1, X.sup.2, X.sup.3 —CO—O—, —O—CO— or a single bond, Z.sup.1 —O—, —CO—, —C(R.sup.yR.sup.z)— or —CF.sub.2CF.sub.2—, Z.sup.2, Z.sup.3 —CO—O—, —O—CO—, —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 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, L′, L″ H, F or Cl, r 0, 1, 2, 3 or 4, s 0, 1, 2 or 3, t 0, 1 or 2, x 0 or 1.

13. The LC medium according to claim 1, wherein the polymerizable compounds are present in polymerized form.

14. A process of preparing an LC medium according to claim 1, comprising the steps of mixing one or more one or more compounds of formula IA, and one or more one or more compounds of formula IB, with one or more polymerizable compounds and optionally with one or more further liquid-crystalline compounds and/or additives, and optionally polymerizing the polymerizable compounds.

15. An LC display comprising an LC medium as defined claim 1.

16. The LC display of claim 17, wherein the display is a PS-VA, PS-IPS, PS-FFS or SA-VA display.

17. The LC display of claim 15, wherein said display further comprises two substrates, at least one of which is transparent to light, an electrode provided on each substrate or two electrodes provided on only one of the substrates, and located between the substrates a layer of the LC medium, wherein the polymerizable compounds are polymerized between the substrates of the display by UV photopolymerization.

18. A process for the production of an LC display according to claim 17, comprising: providing the LC medium between the substrates of the display, and polymerizing the polymerizable compounds by irradiation with UV light, preferably while a voltage is applied to the electrodes of the display.

19. (canceled)

20. The LC medium according to claim 5, wherein groups A.sup.1 and A.sup.2 are each selected from formulae A1, A2, A3, A4, A5, A6, A9 and A10.

21. The LC medium according to claim 5, wherein groups A.sup.1 and A.sup.2 are each selected from formulae A1, A2, A3, A4, A5, A9 and A10.

Description

EXAMPLES

[0484] The following examples explain the present invention without restricting it. However, they show the person skilled in the art preferred mixture concepts with compounds preferably to be employed and the respective concentrations thereof and combinations thereof with one another. In addition, the examples illustrate which properties and property combinations are accessible.

[0485] In addition, the following abbreviations and symbols are used: [0486] V.sub.0 threshold voltage, capacitive [V] at 20° C., [0487] n.sub.e extraordinary refractive index at 20° C. and 589 nm, [0488] n.sub.o ordinary refractive index at 20° C. and 589 nm, [0489] Δn optical anisotropy at 20° C. and 589 nm, [0490] ε.sub.⊥ dielectric permittivity perpendicular to the director at 20° C. and 1 kHz, [0491] ε∥ dielectric permittivity parallel to the director at 20° C. and 1 kHz, [0492] Δε dielectric anisotropy at 20° C. and 1 kHz, [0493] cl.p., T(N,I) clearing point [° C.], [0494] γ.sub.1 rotational viscosity at 20° C. [mPa.Math.s], [0495] K.sub.1 elastic constant, “splay” deformation at 20° C. [pN], [0496] K.sub.2 elastic constant, “twist” deformation at 20° C. [pN], [0497] K.sub.3 elastic constant, “bend” deformation at 20° C. [pN].

[0498] Unless explicitly noted otherwise, all concentrations in the present application are quoted in percent by weight and relate to the corresponding mixture as a whole, comprising all solid or liquid-crystalline components, without solvents.

[0499] Unless explicitly noted otherwise, all temperature values indicated in the present application, such as, for example, for the melting point T(C,N), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,I), are quoted in degrees Celsius (° C.). M.p. denotes melting point, cl.p.=clearing point. Furthermore, C=crystalline state, N=nematic phase, S=smectic phase and I=isotropic phase. The data between these symbols represent the transition temperatures.

[0500] All physical properties are and have been determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., and Δn is determined at 589 nm and Δε at 1 kHz, unless explicitly indicated otherwise in each case.

[0501] The term “threshold voltage” for the present invention relates to the capacitive threshold (V.sub.0), also known as the Fredericks threshold, unless explicitly indicated otherwise. In the examples, the optical threshold may also, as generally usual, be quoted for 10% relative contrast (V.sub.10).

[0502] Unless stated otherwise, the process of polymerizing the polymerizable compounds in the PSA displays as described above and below is carried out at a temperature where the LC medium exhibits a liquid crystal phase, preferably a nematic phase, and most preferably is carried out at room temperature.

[0503] 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.

[0504] The display used for measurement of the capacitive threshold voltage consists of two plane-parallel glass outer plates at a separation of 25 μm, 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.

[0505] The PSVA display or PSVA test cell used for measurement of the tilt angles consists of two plane-parallel glass outer plates at a separation of 4 μm unless stated otherwise, each of which has on the inside an electrode layer and a polyimide alignment layer on top, where the two polyimide layers are rubbed antiparallel to one another and effect a homeotropic edge alignment of the liquid-crystal molecules. The SAVA display or test cell has the same structure but wherein one or both polyimide layers are omitted.

[0506] The polymerizable compounds are polymerized in the display or test cell by irradiation with UV light of defined intensity for a prespecified time, with a voltage simultaneously being applied to the display (usually 10 V to 30 V alternating current, 1 kHz). In the examples, unless indicated otherwise, a metal halide lamp and an intensity of 100 mW/cm.sup.2 is used for polymerization. The intensity is measured using a standard meter (Hoenle UV-meter high end with UV sensor).

[0507] The tilt angle is determined using the Mueller Matrix Polarimeter “AxoScan” from Axometrics. A low value (i.e. a large deviation from the 90° angle) corresponds to a large tilt here.

[0508] Unless stated otherwise, the term “tilt angle” means the angle between the LC director and the substrate, and “LC director” means in a layer of LC molecules with uniform orientation the preferred orientation direction of the optical main axis of the LC molecules, which corresponds, in case of calamitic, uniaxially positive birefringent LC molecules, to their molecular long axis.

Comparison Example 1

[0509] The nematic LC host mixture C1 is formulated as follows

TABLE-US-00006 B(S)-2O-O4 4.00% cl.p. 74.6° C. B(S)-2O-O5 5.00% Δn 0.1052 CCP-3-1 8.50% Δε −3.4 CCY-3-O2 8.00% ε.sub.|| 3.6 CLY-3-O2 1.00% γ.sub.1 98 mPa .Math. s CPY-3-O2 6.00% K.sub.1 15.9 CC-3-V1 8.00% K.sub.3 16.2 CC-4-V1 16.00% K.sub.3/K.sub.1 1.02 CCH-34 8.00% V.sub.0 2.30 V CCH-35 7.50% CY-3-O2 6.50% PCH-302 5.00% PY-1-O2 8.00% PY-2-O2 8.50%

[0510] The mixture contains 1% of compound CLY-3-O2 of formula IB, but does not contain a compound of formula IA.

Comparison Example 2

[0511] The nematic LC host mixture C2 is formulated as follows

TABLE-US-00007 COB(S)-2-O4 9.00% cl.p. 74.5° C. CCP-3-1 4.00% Δn 0.1056 CCY-3-O2 11.00% Δε −3.4 CPY-3-O2 4.50% ε.sub.|| 3.6 CC-3-V1 8.00% γ.sub.1 103 mPa .Math. s CC-4-V1 16.00% K.sub.1 15.2 CCH-34 6.50% K.sub.3 15.8 CCH-35 9.00% K.sub.3/K.sub.1 1.05 CY-3-O2 4.50% V.sub.0 2.26 V PCH-302 7.50% PY-1-O2 11.00% PY-2-O2 9.00%

[0512] The mixture contains 9% of compound COB(S)-2-O4 of formula IA but does not contain a compound of formula IB.

Example 1

[0513] The nematic LC host mixture N1 is formulated as follows

TABLE-US-00008 B(S)-2O-O4 4.00% cl.p. 75.0° C. COB(S)-2-O4 5.00% Δn 0.1057 CCP-3-1 8.00% Δε −3.4 CCY-3-O2 10.50% ε.sub.|| 3.6 CLY-3-O2 1.00% γ.sub.1 99 mPa .Math. s CPY-3-O2 2.00% K.sub.1 15.7 CC-3-V1 8.00% K.sub.3 16.2 CC-4-V1 16.00% K.sub.3/K.sub.1 1.03 CCH-34 7.00% V.sub.0 2.30 V CCH-35 9.00% CY-3-O2 4.00% PCH-302 4.50% PY-1-O2 11.00% PY-2-O2 10.00%

[0514] The mixture contains 5% of compound COB(S)-2-O4 of formula IA and 1% of compound CLY-3-O2 of formula IB.

Example 2

[0515] The nematic LC host mixture N2 is formulated as follows

TABLE-US-00009 B(S)-2O-O5 4.00% cl.p. 74.6° C. COB(S)-2-O4 5.00% Δn 0.1058 CCP-3-1 7.00% Δε −3.4 CCY-3-O2 10.50% ε.sub.|| 3.6 CLY-3-O2 1.00% γ.sub.1 100 mPa .Math. s CPY-3-O2 3.00% K.sub.1 15.6 CC-3-V1 8.00% K.sub.3 15.9 CC-4-V1 16.00% K.sub.3/K.sub.1 1.02 CCH-34 7.00% V.sub.0 2.27 V CCH-35 9.00% CY-3-O2 4.00% PCH-302 4.50% PY-1-O2 11.00% PY-2-O2 10.00%

[0516] The mixture contains 5% of compound COB(S)-2-O4 of formula IA and 1% of compound CLY-3-O2 of formula IB.

Example 3

[0517] The nematic LC host mixture N3 is formulated as follows

TABLE-US-00010 B(S)-2O-O6 4.00% cl.p. 74.1° C. COB(S)-2-O4 5.00% Δn 0.1061 CCP-3-1 7.00% Δε −3.4 CCY-3-O2 10.50% ε.sub.|| 3.6 CLY-3-O2 1.00% γ.sub.1 99 mPa .Math. s CPY-3-O2 3.00% K.sub.1 15.7 CC-3-V1 8.00% K.sub.3 16.0 CC-4-V1 16.00% K.sub.3/K.sub.1 1.02 CCH-34 7.00% V.sub.0 2.28 V CCH-35 9.00% CY-3-O2 4.00% PCH-302 4.50% PY-1-O2 11.00% PY-2-O2 10.00%

[0518] The mixture contains 5% of compound COB(S)-2-O4 of formula IA and 1% of compound CLY-3-O2 of formula IB.

Example 4

[0519] The nematic LC host mixture N4 is formulated as follows

TABLE-US-00011 COB(S)-2-O4 9.00% cl.p. 74.5° C. CCP-3-1 5.00% Δn 0.1059 CCY-3-O2 11.00% Δε −3.4 CLY-3-O2 1.00% ε.sub.|| 3.6 CPY-3-O2 3.00% γ.sub.1 101 mPa .Math. s CC-3-V1 8.00% K.sub.1 15.2 CC-4-V1 16.00% K.sub.3 15.9 CCH-34 5.50% K.sub.3/K.sub.1 1.05 CCH-35 9.00% V.sub.0 2.26 V CY-3-O2 4.00% PCH-302 7.50% PY-1-O2 11.00% PY-2-O2 10.00%

[0520] The mixture contains 9% of compound COB(S)-2-O4 of formula IA and 1% of compound CLY-3-O2 of formula IB.

[0521] Polymerizable Mixtures

[0522] Polymerizable comparison mixtures PC1 and PC2 are prepared by adding 0.3% of the polymerizable compound M1 and 0.015% of the stabiliser S1 to the nematic LC host mixture C1 or C2, respectively.

[0523] Polymerizable mixtures P1 to P4 according to the invention are prepared by adding 0.3% of the polymerizable compound M1 and 0.015% of the stabiliser S1 to the nematic LC host mixtures N1 to N4, respectively.

##STR00545##

[0524] VHR

[0525] The VHR of the polymerizable mixtures was measured with a TOYO 6254 equipment at 60° C. in VA-VHR test cells before and after UV exposure for 40, 80 and 120 min at RT using a fluorescent UV lamp type C. The measurement cells had a thickness of approximately 3 μm and two substrates with unrubbed polyimide layers JSR AL64101.

[0526] Light stress usually causes the decrease of VHR in LC mixtures, therefore the smaller the absolute decrease of VHR value after stress, the better performance for display applications. The results are shown in Table 1.

TABLE-US-00012 TABLE 1 VHR VHR (%) VHR (%) VHR (%) VHR (%) 40 min UV 80 min UV 120 min Mixture Initial load load UV load PC1 99.4 96.5 94.4 89.7 PC2 99.5 94.7 84.1 72.9 P1 99.4 96.9 95.0 91.3 P2 99.4 96.9 95.0 91.2 P3 99.4 97.0 95.1 91.3 P4 99.4 97.4 95.9 93.2

[0527] From Table 1 it can be seen that the VHR values of the polymerizable mixtures P1 to P4 according to the invention are significantly higher compared to the polymerizable reference mixtures PC1 and PC2, which contain only one of the compounds of formula IA and formula IB.

[0528] Tilt Angle

[0529] The UV photopolymerization was carried out at RT by UV exposure of 6J with 50 mW/cm2 at RT using a high pressure Hg lamp in VA-tilt test cells having a cell thickness of approximately 4 m and two substrates with anti-parallel rubbed polyimide layers (JALS-2096-R1).

[0530] The test cells were given at least 12 hours to relax before the final tilt angle was measured and calculated with an Axometrics AxoScan®. The results are shown in Table 2.

TABLE-US-00013 TABLE 2 Tilt angle Mixture PC1 PC2 P1 P2 P3 P4 Tilt Angle/° 87.4 86.7 87.3 87.5 87.5 87.4

[0531] It can be seen that the tilt angles generated in the polymerizable mixtures P1 to P4 according to the invention are as good as in the polymerizable reference mixtures PC1 and PC2.

[0532] Residual RM

[0533] The residual content of unpolymerized RM (in % by weight) in the mixture was determined after UV photopolymerization. The smaller the residual RM content after a given time interval, the faster the polymerization. For this purpose the polymerizable mixtures were filled in test cells and polymerized by UV exposure for 80 min at RT using a fluorescent UV lamp type C. After photopolymerization the test cells were opened, and the mixture was dissolved and rinsed out of the test cell with methyl ethyl ketone and analyzed by Ultra Performance Liquid Chromatography (UPLC).

[0534] The results are shown in Table 3.

TABLE-US-00014 TABLE 3 Residual RM Mixture PC1 PC2 P1 P2 P3 P4 RM % Initial 0.3000 0.3000 0.3000 0.3000 0.3000 0.3000 RM % 80 min 0.0046 0.0037 0.0043 0.0045 0.0054 0.0067

[0535] It can be seen that the residual RM content after polymerization in the polymerizable mixtures P1 to P4 according to the invention is as good as in the polymerizable reference mixtures PC1 and PC2.

[0536] In conclusion, the polymerizable mixtures P1 to P4 according to the invention which contain a compound of formula IA and IB enable a significant increase of the VHR after UV exposure and the reliability, without showing an adverse effect on other properties like tilt generation or completeness of polymerization. This can be achieved even when using only a small amount of 1% of the compound of formula IB. These mixtures are therefore especially suitable for use in PS-VA-displays.

[0537] 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.

[0538] 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.