Method of preparing a birefringent polymer film
10100253 · 2018-10-16
Assignee
Inventors
- Iain Gardiner (Southampton, GB)
- Owain Llyr Parri (Ringwood, GB)
- Tara Perrett (Bournemouth, GB)
- Joseph SARGENT (Southampton, GB)
- Jack BRADFORD (Southampton, GB)
- Sarah Whitehouse (Southampton, GB)
Cpc classification
C09K19/54
CHEMISTRY; METALLURGY
C09K2019/3433
CHEMISTRY; METALLURGY
C09K2019/0448
CHEMISTRY; METALLURGY
C09K2219/03
CHEMISTRY; METALLURGY
International classification
C09K19/54
CHEMISTRY; METALLURGY
Abstract
The invention relates to a method of preparing a polymer film and to the use of such polymer film as in liquid crystal displays (LCDs) or other optical or electrooptical devices, for decorative or security applications, as alignment layer or optical retardation film.
Claims
1. A method of preparing a polymer film comprising the following steps: a) providing a layer of a polymerisable liquid-crystalline material comprising at least one dichroic photoinitiator onto a substrate, b) irradiating the liquid-crystalline material in its isotropic phase with linear polarised light, wherein a polymerized film is formed that has uniform alignment, wherein the uniform alignment is a result of only the irradiation and the resulting polymer film exhibits uniform alignment, and c) optionally removing the polymerised film from the substrate.
2. The method according to claim 1, wherein step b) is performed at a temperature of 1 to 5 C. higher than the clearing point of the liquid-crystalline material.
3. The method according to claim 1, wherein the polymerisable liquid-crystalline material comprises at least one mono-, di- or multireactive polymerisable mesogenic compound, and at least one dichroic photoinitiator.
4. The method according to claim 1, wherein the polymerisable liquid-crystalline material comprises at least one monoreactive polymerisable mesogenic compound, at least one di- or multireactive polymerisable mesogenic compound, and at least one dichroic photoinitiator.
5. The method according to claim 1, wherein the polymerisable liquid-crystalline material comprises at least one monoreactive chiral polymerisable mesogenic compound, at least one mono-, di- or multireactive achiral polymerisable mesogenic compound, and at least one dichroic photoinitiator.
6. The method according to claim 1, wherein the polymerisable liquid-crystalline material comprises at least one di- or multireactive chiral polymerisable mesogenic compound, at least one mono-, di- or multireactive achiral polymerisable mesogenic compound, and at least one dichroic photoinitiator.
7. The method according to claim 1, wherein the polymerisable liquid-crystalline material comprises at least one non-polymerisable chiral compound, at least one mono-, di- or multireactive achiral polymerisable mesogenic compound and at least one dichroic photoinitiator.
8. The method according to claim 1, wherein the dichroic photoinitiator is a compound of formula I, ##STR00017## wherein P is a polymerisable group, Sp is a spacer group or a single bond, A.sup.11 is, in case of multiple occurrence independently of one another, an aryl-, heteroaryl-, aliphatic or heterocyclic group optionally being substituted by one or more identical or different groups L, Z.sup.11 is, in each occurrence independently from each other, O, S, CO, COO, OCO, SCO, COS, OCOO, CONR.sup.10, NR.sup.01CO, NR.sup.01CONR.sup.02, NR.sup.01COO, OCONR.sup.01, 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.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CHN, NCH, NN, CHCR.sup.01, CY.sup.01CY.sup.02, CC, CHCHCOO, OCOCHCH, or a single bond, m is 0, 1, 2 or 3, r is 0, 1, 2, 3 or 4, L is, in case of multiple occurrence independently of one another, H, F, Cl, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 5 C atoms, R.sup.11-13 are, independently of each other, H, halogen, CN, NO.sub.2, NCS, SF.sub.5, P-Sp- or straight chain or branched alkyl with 1 to 20 C-atoms that is optionally mono- or polysubstituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH.sub.2 groups are optionally replaced, in each case independently from one another, by O, S, NR.sup.01, SiR.sup.01R.sup.02, CO, COO, OCO, OCOO, NR.sup.01CO, CONR.sup.01, NR.sup.01CONR.sup.02, SCO, COS, CY.sup.01CY.sup.02 or CC in such a manner that O and/or S atoms are not linked directly to one another, Y.sup.01 and Y.sup.02 each, independently of one another, denote H, F, Cl or CN, and R.sup.01 and R.sup.02 are, in dependently of each other, H, or straight chain or branched alkyl with 1 to 20 C-atoms.
9. The method according to claim 1, wherein the proportion of the dichroic photoinitiator in the liquid-crystalline material as a whole is in the range of 1 to 20% by weight.
10. The method according to claim 1, wherein the substrate is a TAC, PET, PVA, PE film or glass plate.
11. The method according to claim 1, wherein step b) is performed by exposing the polymerisable liquid-crystalline material to linear polarised UV radiation.
12. The method according to claim 1, wherein the n of the polymer film is in the range of 0.01 to 0.30.
13. The method according to claim 1, wherein the UV radiation power is in the range of 5 to 200 mW cm.sup.2.
14. The method according to claim 1, wherein the UV dose is in the range of 25 to 7200 mJ cm.sup.2.
15. The method according to claim 1, wherein the polymerisable liquid-crystalline material is aligned into planar orientation with regards to the substrate main plane.
16. The method according to claim 1, wherein the polymerisable liquid-crystalline material is aligned into tilted orientation (>0<90) with regards to the substrate main plane.
17. The method according to claim 1, wherein the irradiation in step b) is performed at an oblique angle (>0<90) with regards to the substrate main plane.
18. The method according to claim 1, wherein the thickness of the polymer film is in the range of 3 to 30 m.
19. The method according to claim 1, wherein the optical retardation of the polymer film is less than 200 nm.
20. The method according to claim 1, wherein the polymerised film is an A-plate or tilted O-plate.
21. A method of preparing a polymer film comprising the following steps: a) providing a layer of a polymerisable liquid-crystalline material comprising at least one dichroic photoinitiator onto a substrate, which substrate is not a rubbed plastic substrate and/or does not contain an alignment layer, b) irradiating the liquid-crystalline material in its isotropic phase with linear polarised light, wherein a polymerized film is formed that has uniform alignment, wherein the uniform alignment is a result of only the irradiation and the resulting polymer film exhibits uniform alignment, and c) optionally removing the polymerised film from the substrate.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
(5)
DETAILED DESCRIPTION
(6) A suitable polymerisable liquid-crystalline material used for the method according to the present invention comprises at least one mono-, di- or multireactive polymerisable mesogenic compound and at least one dichroic photoinitiator.
(7) All known dichroic photoinitiators are suitable for the method according to the present invention. Preferably dichroic photoinitiators comprising a -amino group as disclosed in EP-A-1 388 538 are used. Especially preferred are dichroic photoinitiators of formula I,
(8) ##STR00001##
wherein, P is a polymerisable group, Sp is a spacer group or a single bond, A.sup.11 is in case of multiple occurrence independently of one another an aryl-, heteroaryl-, aliphatic or heterocyclic group optionally being substituted by one or more identical or different groups L, preferably 1,4-cyclohexylene or 1,4-phenylene optionally being substituted by one or more identical or different groups L, Z.sup.11 is in each occurrence independently from each other, O, S, CO, COO, OCO, SCO, COS, OCOO, CONR.sup.01, NR.sup.01CO, NR.sup.01CONR.sup.02, NR.sup.01COO, OCONR.sup.01, 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.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CHN, NCH, NN, CHCR.sup.01, CY.sup.01CY.sup.02, CC, CHCHCOO, OCOCHCH, or a single bond, preferably COO, OCO or a single bond, Y.sup.01 and Y.sup.02 each, independently of one another, denote H, F, Cl or CN. m is 0, 1, 2 or 3, preferably 2 or 3, r is 0, 1, 2, 3 or 4, preferably 0, 1, or 2, L is, in case of multiple occurrence independently of one another, H, halogen, CN or optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 5 C atoms, preferably H, halogen or CN, alkyl or alkoxy with 1 to 5 C atoms, R.sup.11-13 are independently of each other H, halogen, CN, NO.sub.2, NCS, SF.sub.5, P-Sp- or straight chain or branched alkyl with 1 to 20 C-atoms that is optionally mono- or polysubstituted by F, Cl, Br, I or CN, and wherein one or more non-adjacent CH.sub.2 groups are optionally replaced, in each case independently from one another, by O, S, NR.sup.01, SiR.sup.01R.sup.02, CO, COO, OCO, OCOO, NR.sup.01CO, CONR.sup.01, NR.sup.01CONR.sup.02, SCO, COS, CY.sup.01CY.sup.02 or CC in such a manner that O and/or S atoms are not linked directly to one another, preferably alkyl or alkoxy with 1 to 12 C-atoms, and R.sup.01 and R.sup.02 are in dependently of each other H, or straight chain or branched alkyl with 1 to 20 C-atoms, preferably 1 to 6 C atoms.
(9) Above and below, carbyl group denotes a mono- or polyvalent organic group containing at least one carbon atom which either contains no further atoms (such as, for example, CC) or optionally contains one or more further atoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge (for example carbonyl, etc.). Hydrocarbyl group denotes a carbyl group, which additionally contains one or more H atoms and optionally one or more heteroatoms, such as, for example, N, O, S, P, Si, Se, As, Te or Ge. Halogen denotes F, Cl, Br or I.
(10) A carbyl or hydrocarbyl group can be a saturated or unsaturated group. Unsaturated groups are, for example, aryl, alkenyl or alkinyl groups. A carbyl or hydrocarbyl group having more than 3 C atoms can be straight-chain, branched and/or cyclic and may also contain spiro links or condensed rings.
(11) Above and below, the terms alkyl, aryl, heteroaryl, etc., also encompass polyvalent groups, for example alkylene, arylene, heteroarylene, etc. The term aryl denotes an aromatic carbon group or a group derived therefrom. The term heteroaryl denotes aryl in accordance with the above definition containing one or more heteroatoms.
(12) Preferred carbyl and hydrocarbyl groups are optionally substituted alkyl, alkenyl, alkinyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to 25, particularly preferably 1 to 18 C atoms, optionally substituted aryl or aryloxy having 6 to 40, preferably 6 to 25 C atoms, or optionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy, arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxy having 6 to 40, preferably 6 to 25 C atoms. Further preferred carbyl and hydrocarbyl groups are C.sub.1-C.sub.40 alkyl, C.sub.2-C.sub.40 alkenyl, C.sub.2-C.sub.40 alkinyl, C.sub.3-C.sub.40 allyl, C.sub.4-C.sub.40 alkyldienyl, C.sub.4-C.sub.40 polyenyl, C.sub.6-C.sub.40 aryl, C.sub.6-C.sub.40 alkylaryl, C.sub.6-C.sub.40 arylalkyl, C.sub.6-C.sub.40 alkylaryloxy, C.sub.6-C.sub.40 arylalkyloxy, C.sub.2-C.sub.40 heteroaryl, C.sub.4-C.sub.40 cycloalkyl, C.sub.4-C.sub.40 cycloalkenyl, etc. Particular preference is given to C.sub.1-C.sub.22 alkyl, C.sub.2-C.sub.22 alkenyl, C.sub.2-C.sub.22 alkinyl, C.sub.3-C.sub.22 allyl, C.sub.4-C.sub.22 alkyldienyl, C.sub.6-C.sub.12 aryl, C.sub.6-C.sub.20 arylalkyl and C.sub.2-C.sub.20 heteroaryl.
(13) Further preferred carbyl and hydrocarbyl groups are straight-chain, branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25 C atoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br, I or CN and in which one or more non-adjacent CH.sub.2 groups may each be replaced, independently of one another, by C(R.sup.x)C(R.sup.x), CC, N(R.sup.x), O, S, CO, COO, OCO, OCOO in such a way that O and/or S atoms are not linked directly to one another.
(14) R.sup.x preferably denotes H, halogen, a straight-chain, branched or cyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one or more non-adjacent C atoms may be replaced by O, S, CO, COO, OCO, OCOO, and in which one or more H atoms may be replaced by fluorine, 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.
(15) Preferred alkyl groups are, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl, s-pentyl, cyclo-pentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl, cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, dodecanyl, trifluoro-methyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl, perfluorooctyl, perfluorohexyl, etc.
(16) Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl, pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl, octenyl, cyclooctenyl, etc.
(17) Preferred alkinyl groups are, for example, ethynyl, propynyl, butynyl, pentynyl, hexynyl, octynyl, etc.
(18) Preferred alkoxy groups are, for example, methoxy, ethoxy, 2-methoxy-ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy, t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy, n-decoxy, n-undecoxy, n-dodecoxy, etc.
(19) Preferred amino groups are, for example, dimethylamino, methylamino, methylphenylamino, phenylamino, etc.
(20) Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. they can have one ring (such as, for example, phenyl) or two or more rings, which may also be fused (such as, for example, naphthyl) or covalently linked (such as, for example, biphenyl), or contain a combination of fused and linked rings. Heteroaryl groups contain one or more heteroatoms, preferably selected from O, N, S and Se.
(21) Particular preference is given to mono-, bi- or tricyclic aryl groups having 2 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groups having 6 to 25 C atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6- or 7-membered aryl and heteroaryl groups, in which, in addition, one or more CH groups may be replaced by N, S or O in such a way that O atoms and/or S atoms are not linked directly to one another.
(22) Preferred aryl groups are, for example, phenyl, biphenyl, terphenyl, [1,1:3,1]terphenyl-2-yl, naphthyl, anthracene, binaphthyl, phenanthrene, pyrene, dihydropyrene, chrysene, perylene, tetracene, pentacene, benzo-pyrene, fluorene, indene, indenofluorene, spirobifluorene, etc.
(23) Preferred heteroaryl groups are, for example, 5-membered rings, such as pyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole, furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole, 1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole, 1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole, 1,2,5-thiadiazole, 1,3,4-thiadiazole, 6-membered rings, such as pyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, 1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine, 1,2,3,5-tetrazine, or condensed groups, such as indole, iso-indole, indolizine, indazole, benzimidazole, benzotriazole, purine, naphth-imidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole, quinoxa-linimidazole, benzoxazole, naphthoxazole, anthroxazole, phenanthroxa-zole, isoxazole, benzothiazole, benzofuran, isobenzofuran, dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline, benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine, phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine, quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline, phenanthridine, phenan-throline, thieno[2,3b]thiophene, thieno[3,2b]thiophene, dithienothiophene, isobenzothiophene, dibenzothiophene, benzothiadiazothiophene, or combinations of these groups. The heteroaryl groups may also be substituted by alkyl, alkoxy, thioalkyl, fluorine, fluoroalkyl or further aryl or heteroaryl groups.
(24) The (non-aromatic) alicyclic and heterocyclic groups encompass both saturated rings, i.e. those which contain exclusively single bonds, and also partially unsaturated rings, i.e. those which may also contain multiple bonds. Heterocyclic rings contain one or more heteroatoms, preferably selected from Si, O, N, S and Se.
(25) The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic, i.e. contain only one ring (such as, for example, cyclohexane), or polycyclic, i.e. contain a plurality of rings (such as, for example, decahydronaphthalene or bicyclooctane). Particular preference is given to saturated groups. Preference is furthermore given to mono-, bi- or tricyclic groups having 3 to 25 C atoms, which optionally contain fused rings and are optionally substituted. Preference is furthermore given to 5-, 6-, 7- or 8-membered carbocyclic groups in which, in addition, one or more C atoms may be replaced by Si and/or one or more CH groups may be replaced by N and/or one or more non-adjacent CH.sub.2 groups may be replaced by O and/or S.
(26) Preferred alicyclic and heterocyclic groups are, for example, 5-membered groups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran, pyrrolidine, 6-membered groups, such as cyclohexane, silinane, cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1,3-dioxane, 1,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, and fused groups, such as tetrahydronaphthalene, decahydronaphthalene, indane, bicyclo[1.1.1]-pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.
(27) The aryl, heteroaryl, carbyl and hydrocarbyl radicals optionally have one or more substituents, which are preferably selected from the group comprising silyl, sulfo, sulfonyl, formyl, amine, imine, nitrile, mercapto, nitro, halogen, C.sub.1-12 alkyl, C.sub.6-12 aryl, C.sub.1-12 alkoxy, hydroxyl, or combinations of these groups.
(28) Preferred substituents are, for example, solubility-promoting groups, such as alkyl or alkoxy, electron-withdrawing groups, such as fluorine, nitro or nitrile, or substituents for increasing the glass transition temperature (Tg) in the polymer, in particular bulky groups, such as, for example, t-butyl or optionally substituted aryl groups.
(29) Preferred substituents, also referred to as L below, are, for example, F, Cl, Br, I, OH, ON, NO.sub.2, NCO, NOS, OCN, SCN, C(O)N(R.sup.x).sub.2, C(O)Y.sup.1, C(O)R.sup.x, C(O)OR.sup.x, N(R.sup.x).sub.2, in which R.sup.x has the above-mentioned meaning, and Y.sup.1 denotes halogen, optionally substituted silyl, optionally substituted aryl or heteroaryl having 4 to 40, preferably 4 to 20 ring atoms, and straight-chain or branched alkyl, alkenyl, alkinyl, alkoxy, alkyl carbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 C atoms, in which one or more H atoms may optionally be replaced by F or Cl.
(30) Substituted silyl or aryl preferably means substituted by halogen, CN, R.sup.0, OR.sup.0, COR.sup.0, COOR.sup.0, OCOR.sup.0 or OCOOR.sup.0, in which R.sup.0 has the above-mentioned meaning.
(31) Particularly preferred substituents L are, for example, F, Cl, ON, NO.sub.2, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2, OC.sub.2F.sub.5, furthermore phenyl.
(32) In the formula shown above and below, a substituted phenylene ring
(33) ##STR00002##
is preferably
(34) ##STR00003##
in which L has, on each occurrence identically or differently, one of the meanings given above and below, and is preferably F, Cl, ON, NO.sub.2, CH.sub.3, C.sub.2H.sub.5, C(CH.sub.3).sub.3, CH(CH.sub.3).sub.2, CH.sub.2CH(CH.sub.3)C.sub.2H.sub.5, OCH.sub.3, OC.sub.2H.sub.5, COCH.sub.3, COC.sub.2H.sub.5, COOCH.sub.3, COOC.sub.2H.sub.5, CF.sub.3, OCF.sub.3, OCHF.sub.2, OC.sub.2F.sub.5 or P-Sp-, very preferably F, Cl, ON, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3, OCF.sub.3 or P-Sp-, most preferably F, Cl, CH.sub.3, OCH.sub.3, COCH.sub.3 or OCF.sub.3.
(35) The polymerisable group P is preferably selected from groups containing a CC double bond or CC triple bond, and groups, which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxide groups.
(36) Very preferably, the polymerisable group P is selected from the group consisting of CH.sub.2CW.sup.1COO, CH.sub.2CW.sup.1CO,
(37) ##STR00004##
CH.sub.2CW.sup.2(O).sub.k3, CW.sup.1CHCO(O).sub.k3, CW.sup.1CHCONH, CH.sub.2CW.sup.1CONH, CH.sub.3CHCHO, (CH.sub.2CH).sub.2CHOCO, (CH.sub.2CHCH.sub.2).sub.2CHOCO, (CH.sub.2CH).sub.2CHO, (CH.sub.2CHCH.sub.2).sub.2N, (CH.sub.2CHCH.sub.2).sub.2NCO, CH.sub.2CW.sup.1CONH, CH.sub.2CH(COO).sub.k1-Phe-(O).sub.k2, CH.sub.2CH(CO).sub.k1-Phe-(O).sub.k2, Phe-CHCH, in which W.sup.1 denotes H, F, Cl, CN, CF.sub.3, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, C.sub.1 or CH.sub.3, W.sup.2 denotes H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W.sup.3 and W.sup.4 each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionally substituted by one or more radicals L as being defined above but being different from P-Sp, and k.sub.1, k.sub.2 and k.sub.3 each, independently of one another, denote 0 or 1, k.sub.3 preferably denotes 1, and k.sub.4 is an integer from 1 to 10.
(38) Particularly preferred groups P are CH.sub.2CHCOO, CH.sub.2C(CH.sub.3)COO, CH.sub.2CFCOO, CH.sub.2CH, CH.sub.2CHO, (CH.sub.2CH).sub.2CHOCO, (CH.sub.2CH).sub.2CHO,
(39) ##STR00005##
in particular vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide, most preferably acrylate or methacrylate.
(40) In a further preferred embodiment of the invention, all polymerisable compounds and corresponding sub-formulae thereof contain, instead of one or more radicals P-Sp-, one or more branched radicals containing two or more polymerisable groups P (multireactive polymerisable radicals). Suitable radicals of this type, and polymerisable compounds containing them, are described, for example, in U.S. Pat. No. 7,060,200 B1 or US 2006/0172090 A1. Particular preference is given to multireactive polymerisable radicals selected from the following formulae:
X-alkyl-CHP.sup.1CH.sub.2CH.sub.2P.sup.2I*a
X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)CH.sub.2P.sup.3I*b
X-alkyl-CHP.sup.1CHP.sup.2CH.sub.2P.sup.3I*c
X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)C.sub.aaH.sub.2aa+1I*d
X-alkyl-CHP.sup.1CH.sub.2P.sup.2I*e
X-alkyl-CHP.sup.1P.sup.2I*f
X-alkyl-CP.sup.1P.sup.2C.sub.aaH.sub.2aa+1I*g
X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)CH.sub.2OCH.sub.2C(CH.sub.2P.sup.3)(CH.sub.2P.sup.4)CH.sub.2P.sup.5I*h
X-alkyl-CH((CH.sub.2).sub.aaP.sup.1)((CH.sub.2).sub.bbP.sup.2)I*i
X-alkyl-CHP.sup.1CHP.sup.2C.sub.aaH.sub.2aa+1I*k in which alkyl denotes a single bond or straight-chain or branched alkylene having 1 to 12 C atoms, in which one or more non-adjacent CH.sub.2 groups may each be replaced, independently of one another, by C(R.sup.x)C(R.sup.x), CC, N(R.sup.x), O, S, CO, COO, OCO, OCOO 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 or CN, where R.sup.x has the above-mentioned meaning and preferably denotes R.sup.0 as defined above, aa and bb each, independently of one another, denote 0, 1, 2, 3, 4, 5 or 6, X has one of the meanings indicated for X, and P.sup.1-5 each, independently of one another, have one of the meanings indicated above for P.
(41) Preferred spacer groups Sp are selected from the formula Sp-X, so that the radical P-Sp- conforms to the formula P-Sp-X, where Sp denotes alkylene having 1 to 20, preferably 1 to 12 C atoms, which is optionally mono- or polysubstituted by F, Cl, Br, I or CN and in which, in addition, one or more non-adjacent CH.sub.2 groups may each be replaced, independently of one another, by O, S, NH, NR.sup.01, SiR.sup.01R.sup.02, CO, COO, OCO, OCOO, SCO, COS, NR.sup.01COO, OCONR.sup.01, NR.sup.01CONR.sup.01, CHCH or CC in such a way that O and/or S atoms are not linked directly to one another, X denotes O, S, CO, COO, OCO, OCOO, CONR.sup.01, NR.sup.01CO, NR.sup.01CONR.sup.01, OCH.sub.2, CH.sub.2O, SCH.sub.2, CH.sub.2S, CF.sub.2O, OCF.sub.2, CF.sub.2S, SCF.sub.2, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CHN, NCH, NN, CHCR.sup.01, CY.sup.01CY.sup.02, CC, CHCHCOO, OCOCHCH or a single bond, R.sup.01 and R.sup.02 each, independently of one another, denote H or alkyl having 1 to 12 C atoms, and Y.sup.01 and Y.sup.02 each, independently of one another, denote H, F, Cl or CN. X is preferably O, S, CO, COO, OCO, OCOO, CONR.sup.0, NR.sup.01CO, NR.sup.01CONR.sup.01 or a single bond.
(42) Typical spacer groups Sp are, for example, (CH.sub.2).sub.p1, (CH.sub.2CH.sub.2O).sub.q1CH.sub.2CH.sub.2, CH.sub.2CH.sub.2SCH.sub.2CH.sub.2, CH.sub.2CH.sub.2NHCH.sub.2CH.sub.2 or (SiR.sup.01R.sup.02O).sub.p1, in which p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R.sup.01 and R.sup.02 have the above-mentioned meanings.
(43) Particularly preferred groups X-Sp- are (CH.sub.2).sub.p1, O(CH.sub.2).sub.1p, OCO(CH.sub.2).sub.p1, OCOO(CH.sub.2).sub.p1.
(44) Particularly preferred groups Sp are, for example, in each case straight-chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethyl-ene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.
(45) Compounds of formula I, which preferably can be used for the method according to the present invention, are the following
(46) ##STR00006##
wherein L is H or F, R.sup.11 is alkyl or alkoxy with 1 to 12 C-atoms, R.sup.12 and R.sup.13 are selected from alkyl or alkoxy with 1 to 6 C-atoms, very preferably from methyl, ethyl or propyl.
(47) Most preferred dichroic photoinitiators used for the method according to the present invention are compounds of the formula I-2 wherein L is F, R.sup.11 is alkyl 1 to 12 C-atoms, R.sup.12 and R.sup.13 are selected from alkyl, very preferably from methyl, ethyl or propyl.
(48) The proportion of the dichroic photoinitiator in a preferred liquid-crystalline material used for the method according to the present invention is preferably in the range from 1 to 40% by weight, more preferably in the range from 1 to 30% by weight and even more preferably in the range from 1 to 20% by weight.
(49) Preferably, the polymerisable liquid-crystalline material used for the method according to the present invention is a mixture of two or more, for example 2 to 25 liquid-crystalline compounds.
(50) The method according to the present invention is not limited to specific liquid-crystalline materials, but can in principle be used for alignment of all RMs known from prior art. The RMs are preferably selected from calamitic or discotic compounds demonstrating thermotropic or lyotropic liquid crystallinity, very preferably calamitic compounds, or mixtures of one or more types of these compounds having liquid-crystalline mesophases in a certain temperature range. These materials typically have good optical properties, like reduced chromaticity, and can be easily and quickly aligned into the desired orientation, which is especially important for the industrial production of polymer films at large scale. The liquid crystals can be small molecules (i.e. monomeric compounds) or liquid-crystalline oligomers.
(51) Preferably, the polymerisable liquid-crystalline material used for the method according to the present invention comprise preferably at least one monoreactive polymerisable mesogenic compounds, at least one di- or multireactive polymerisable mesogenic compounds, and at least one dichroic photoinitiator.
(52) Suitable polymerisable liquid-crystalline material in accordance with the present invention comprise polymerisable mono-, di- or multireactive compounds selected of formula II
P-Sp-MG-R.sup.0II wherein P is a polymerisable group, preferably an acryl, methacryl, vinyl, vinyloxy, propenyl ether, epoxy, oxetane or styrene group, Sp is a spacer group or a single bond, MG is a rod-shaped mesogenic group, which is preferably selected of formula M, M is -(A.sup.21-Z.sup.21).sub.k-A.sup.22-(Z.sup.22-A.sup.23).sub.l-, A.sup.21 to A.sup.23 are in each occurrence independently of one another an aryl-, heteroaryl-, heterocyclic- or alicyclic group optionally being substituted by one or more identical or different groups L, preferably 1,4-cyclohexylene or 1,4-phenylene, 1,4 pyridine, 1,4-pyrimidine, 2,5-thiophene, 2,6-dithieno[3,2-b:2,3-d]thiophene, 2,7-fluorine, 2,6-naphtalene, 2,7-phenanthrene optionally being substituted by one or more identical or different groups L, Z.sup.21 and Z.sup.22 are in each occurrence independently from each other, O, S, CO, COO, OCO, SCO, COS, OCOO, CONR.sup.01, NR.sup.01CO, NR.sup.01CONR.sup.02, NR.sup.01COO, OCONR.sup.01, 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.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CHN, NCH, NN, CHCR.sup.01, CY.sup.01CY.sup.02, CC, CHCHCOO, OCOCHCH, or a single bond, preferably COO, OCO, COO, OCO, OCH.sub.2, CH.sub.2O, , CH.sub.2CH.sub.2, (CH.sub.2).sub.4, CF.sub.2CH.sub.2, CH.sub.2CF.sub.2, CF.sub.2CF.sub.2, CC, CHCHCOO, OCOCHCH, or a single bond, L has one of the meanings as defined above in formula I, R.sup.0 is H, alkyl, alkoxy, thioalkyl, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 20 C atoms more, preferably 1 to 15 C atoms which are optionally fluorinated, or is Y.sup.0 or P-Sp-, Y.sup.0 is F, Cl, CN, NO.sub.2, OCH.sub.3, OCN, SCN, optionally fluorinated alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy with 1 to 4 C atoms, or mono-oligo- or polyfluorinated alkyl or alkoxy with 1 to 4 C atoms, preferably F, Cl, CN, NO.sub.2, OCH.sub.3, or mono-oligo- or polyfluorinated alkyl or alkoxy with 1 to 4 C atoms Y.sup.01 and Y.sup.02 have each and independently the meaning as defined above in formula I, R.sup.01 and R.sup.02 have each and independently the meaning as defined above in formula I, and k and l are each and independently 0, 1, 2, 3 or 4, preferably 0, 1 or 2, most preferably 1.
(53) Suitable RMs are known to the skilled person and are disclosed for example in WO 93/22397, EP 0 261 712, DE 195 04 224, WO 95/22586, WO 97/00600, U.S. Pat. No. 5,518,652, U.S. Pat. No. 5,750,051, U.S. Pat. No. 5,770,107 and U.S. Pat. No. 6,514,578. Examples of suitable and preferred monoreactive, direactive or multireactive RMs, used in accordance with the present invention, are shown in the following list.
(54) ##STR00007## ##STR00008## ##STR00009## ##STR00010## wherein P.sup.0 is, in case of multiple occurrence independently of one another, a polymerisable group, preferably an acryl, methacryl, oxetane, epoxy, vinyl, vinyloxy, propenyl ether or styrene group, A.sup.0 is, in case of multiple occurrence independently of one another, 1,4-phenylene that is optionally substituted with 1, 2, 3 or 4 groups L, or trans-1,4-cyclohexylene, Z.sup.0 is, in case of multiple occurrence independently of one another, COO, OCO, CH.sub.2CH.sub.2, CC, CHCH, CHCHCOO, OCOCHCH or a single bond, r is 0, 1, 2, 3 or 4, preferably 0, 1 or 2, t is, in case of multiple occurrence independently of one another, 0, 1, 2 or 3, u and v are independently of each other 0, 1 or 2, w is 0 or 1, x and y are independently of each other 0 or identical or different integers from 1 to 12, z is 0 or 1, with z being 0 if the adjacent x or y is 0,
and wherein the benzene and naphthalene rings can additionally be substituted with one or more identical or different groups L.
(55) The parameter R.sup.0, Y.sup.0, R.sup.01, R.sup.02 and L have the same meanings as given above in formula II.
(56) In another preferred embodiment, a suitable polymerisable liquid-crystalline material comprises at least one monoreactive chiral polymerisable mesogenic compounds, at least one mono-, di- or multireactive achiral polymerisable mesogenic compounds, and at least one dichroic photoinitiator.
(57) In an especially preferred embodiment, a suitable polymerisable liquid-crystalline material used for the method of the present invention comprises at least one di- or multireactive chiral polymerisable mesogenic compounds, at least one mono-, di- or multireactive achiral polymerisable mesogenic compounds, and at least one dichroic photoinitiator.
(58) The mono-, di- or multireactive chiral polymerisable mesogenic compounds used according to the present invention, preferably comprise one or more ring elements, linked together by a direct bond or via a linking group and, where two of these ring elements optionally may be linked to each other, either directly or via a linking group, which may be identical to or different from the linking group mentioned. The ring elements are preferably selected from the group of four-, five-, six- or seven-, preferably of five- or six-, membered rings.
(59) Preferably used polymerisable chiral compounds according to the instant invention, preferably have, each alone or in combination with each other, an absolute value of the helical twisting power (IHTP.sub.totalI) of 20 m.sup.1 or more, preferably of 40 m.sup.1 or more, more preferably in the range of 60 m.sup.1 or more, most preferably in the range of 80 m.sup.1 or more to 260 m.sup.1 or less.
(60) Suitable polymerisable chiral compounds and their synthesis are e.g. described in U.S. Pat. No. 7,223,450 or commercially available like Paliocolor LC756 (BASF AG).
(61) Preferred mono-, di- or multireactive chiral polymerisable mesogenic compounds used according to the present invention the polymerisable are selected from the following formulae
(62) ##STR00011## ##STR00012## wherein P.sup.0 is, in case of multiple occurrence independently of one another, a polymerisable group, preferably an acryl, methacryl, oxetane, epoxy, vinyl, vinyloxy, propenyl ether or styrene group, A.sup.0 and B.sup.0 are, in case of multiple occurrence independently of one another, 1,4-phenylene that is optionally substituted with 1, 2, 3 or 4 groups L, or trans-1,4-cyclohexylene, X.sup.0 and Z.sup.0 is, in case of multiple occurrence independently of one another, COO, OCO, CH.sub.2CH.sub.2, CC, CHCH, CHCHCOO, OCOCHCH or a single bond, R* is a chiral alkyl or alkoxy group with 4 or more, preferably 4 to 12 C atoms, like 2-methylbutyl, 2-methyloctyl, 2-methylbutoxy or 2-methyloctoxy, Ch is a chiral group selected from cholesteryl, estradiol, or terpenoid radicals like menthyl or citronellyl, L has one of the meaning as defined above in formula I, r is 0, 1, 2, 3 or 4, preferably 0, 1 or 2, t is, in case of multiple occurrence independently of one another, 0, 1, 2 or 3, u and v are independently of each other 0, 1 or 2, w is 0 or 1, x are independently of each other 0 or identical or different integers from 1 to 12, z is 0 or 1, with z being 0 if the adjacent x or y is 0,
and wherein the benzene and naphthalene rings can additionally be substituted with one or more identical or different groups L.
(63) In a preferred embodiment, the proportion of the monoreactive polymerisable mesogenic compounds, preferably selected from formulae II-1, II-13 in a liquid-crystalline material used for the method according to the present invention as a whole, is preferably in the range from 20 to 90% by weight, more preferably in the range from 30 to 80% by weight and even more preferably in the range from by weight 40 to 70%.
(64) In another preferred embodiment, the proportion of the direactive polymerisable mesogenic compounds, preferably selected from formula II-27 in a liquid-crystalline material used for the method according to the present invention as a whole, is preferably in the range from 1 to 30% by weight, more preferably in the range from 1 to 20% by weight and even more preferably in the range from 1 to 10% by weight.
(65) In another preferred embodiment, the proportion of the multireactive polymerisable mesogenic compounds in a liquid-crystalline material used for the method according to the present invention as a whole, is preferably in the range from 0 to 30% by weight, more preferably in the range from 0 to 20% by weight and even more preferably in the range from 0 to 10% by weight.
(66) The proportion of chiral polymerisable mesogenic compounds, preferably selected from formula CR8 in a preferred liquid-crystalline material used for the method according to the present invention as a whole, is preferably in the range from 0 to 30% by weight, more preferably in the range from 0 to 20% by weight and even more preferably in the range from 0 to 10% by weight.
(67) In a particularly preferred embodiment a polymerisable liquid-crystalline material used in accordance with the present invention, comprises at least one non-polymerisable chiral compound, at least one mono-, di- or multireactive achiral polymerisable mesogenic compound and at least one dichroic photoinitiator.
(68) Especially preferred are non-polymerisable chiral compounds with a high helical twisting power (HTP), in particular those disclosed in WO 98/00428. Further typically used non-polymerisable chiral compounds are e.g. the commercially available R/S-5011, R-811 or CB-15 (from Merck KGaA, Darmstadt, Germany).
(69) The proportion of said chiral non-polymerisable mesogenic compounds in a preferred liquid-crystalline material used for the method according to the present invention as a whole, is preferably in the range from 0 to 30% by weight, more preferably in the range from 0 to 20% by weight and even more preferably in the range from 0 to 10% by weight.
(70) Suitable polymerisable liquid-crystalline materials used for the method according to the present invention, may also comprise one or more dyes having an absorption maximum adjusted to the wavelength of the radiation used for polymerisation, in particular UV dyes like e.g. 4,4-azoxy anisole or Tinuvin dyes (from Ciba AG).
(71) The polymerisable liquid-crystalline material used in accordance with the present invention, may also comprise one or more stabilizers or inhibitors to prevent undesired spontaneous polymerisation, preferably in an amount of 0 to 0.1%, very preferably 0 to 0.2%, for example selected from the commercially available Irganox series (Ciba AG), like Irganox 1076.
(72) In a preferred embodiment, the suitable polymerisable liquid-crystalline material used for the method according to the present invention comprises one or more monoreactive polymerisable non-mesogenic compounds, preferably in an amount of 0 to 50%, very preferably 0 to 20%. Typical examples are alkylacrylates or alkylmethacrylates, preferably isobornyl methacrylate.
(73) In another preferred embodiment the polymerisable liquid-crystalline material used for the method according to the present invention, optionally comprises one or more di- or multireactive polymerisable non-mesogenic compounds, preferably in an amount of 0 to 50%, very preferably 0 to 20%, alternatively or in addition to the di- or multireactive polymerisable mesogenic compounds. Typical examples of direactive monomers are alkyldiacrylates or alkyldimethacrylates with alkyl groups of 1 to 20 C atoms or hexanediol diacrylate. Typical examples of multireactive monomers are trimethylpropanetrimethacrylate, or pentaerythritoltetraacrylate.
(74) It is also possible to add one or more chain transfer agents to the polymerisable liquid-crystalline material in order to modify the physical properties of the polymer film. Especially preferred are thiol compounds, for example monoreactive thiols like dodecane thiol or multireactive thiols like trimethylpropane tri(3-mercaptopropionate). Very preferred are mesogenic or liquid-crystalline thiols as disclosed for example in WO 96/12209, WO 96/25470 or U.S. Pat. No. 6,420,001. By using chain transfer agents the length of the free polymer chains and/or the length of the polymer chains between two crosslinks in the polymer film can be controlled. When the amount of the chain transfer agent is increased, the polymer chain length in the polymer film decreases.
(75) The polymerisable liquid-crystalline material in accordance with the present invention may also comprise a polymeric binder or one or more monomers capable of forming a polymeric binder, and/or one or more dispersion auxiliaries. Suitable binders and dispersion auxiliaries are disclosed for example in WO 96/02597. Preferably, however, the polymerisable material does not contain a binder or dispersion auxiliary.
(76) Said polymerisable liquid-crystalline material can additionally comprise one or more additional components like for example catalysts, sensitizers, stabilizers, inhibitors, chain-transfer agents, co-reacting monomers, surface-active compounds, lubricating agents, wetting agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes or pigments.
(77) The polymerisable liquid-crystalline material used in accordance with the present invention is prepared in a manner conventional per se, for example by mixing one or more of the above-mentioned dichroic photoinitiator with one or more polymerisable compounds as defined above, and optionally with further liquid-crystalline compounds and/or additives. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.
(78) For the method of the present invention, an especially preferred polymerisable liquid-crystalline material comprises: a) one or more achiral mono-, di- or multireactive polymerisable mesogenic compounds, b) one or more dichroic photoinitiator, c) optionally one or more polymerisable chiral compounds, d) optionally one or more stabilizers. e) optionally one or more mono-, di- or multireactive polymerisable non-mesogenic compounds, f) optionally one or more non-polymerisable chiral compounds g) optionally one or more dyes showing an absorption maximum at the wavelength used to initiate photopolymerisation, h) optionally one or more chain transfer agents, i) optionally one or more stabilizers.
(79) The polymerisable liquid-crystalline material can be applied onto a substrate by conventional coating techniques like spin-coating or blade coating. It can also be applied to the substrate by conventional printing techniques which are known to the expert, like for example screen printing, offset printing, reel-to-reel printing, letter press printing, gravure printing, rotogravure printing, flexographic printing, intaglio printing, pad printing, heat-seal printing, ink-jet printing or printing by means of a stamp or printing plate.
(80) It is also possible to dissolve the polymerisable liquid-crystalline material in a suitable solvent. This solution is then coated or printed onto the substrate, for example by spin-coating or printing or other known techniques, and the solvent is evaporated off before polymerisation. In most cases it is suitable to heat the mixture in order to facilitate the evaporation of the solvent. As solvents for example standard organic solvents can be used. The solvents can be selected for example from ketones such as acetone, methyl ethyl ketone, methyl propyl ketone or cyclohexanone; acetates such as methyl, ethyl or butyl acetate or methyl acetoacetate; alcohols such as methanol, ethanol or isopropyl alcohol; aromatic solvents such as toluene or xylene; halogenated hydrocarbons such as di- or trichloromethane; glycols or their esters such as PGMEA (propyl glycol monomethyl ether acetate), -butyrolactone, and the like. It is also possible to use binary, ternary or higher mixtures of the above solvents.
(81) As a substrate for the method according to the present invention for example a glass or quartz plate or a plastic film or plate can be used. Suitable and preferred plastic substrates are for example films of polyester such as polyethyleneterephthalate (PET) or polyethylene-naphthalate (PEN), polyvinylalcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAC), very preferably PET or TAC films. As birefringent substrates for example uniaxially stretched plastics film can be used. PET films are commercially available for example from DuPont Teijin Films under the trade name Melinex. In particular preferred substrates are TAC, PET, PVA, PE films or glass plates.
(82) Preferably, the coated substrates in accordance with the present invention are plane, but also structured substrates like e.g. Fresnel lenses can be used.
(83) It is also possible to put a second substrate on top of the coated material prior to and/or during and/or after polymerisation. The substrates can be removed after polymerisation or not. When using two substrates, at least one substrate has to be transmissive for the actinic radiation used for the polymerisation. Isotropic or birefringent substrates can be used. In case the substrate is not removed from the polymer film after polymerisation, preferably isotropic substrates are used.
(84) The irradiation in step b) according to the present invention is preferably performed by exposing the polymerisable liquid-crystalline material to linear polarized actinic radiation. Actinic radiation means irradiation with light, preferably UV light, IR light. In the process according to this invention the radiation wavelength should be selected such that it causes dissociation of the dichroic photoinitiator and polymerisation of the polymerisable compounds. In this regard, step b) is most preferably performed by exposing the polymerisable liquid-crystalline material to linear polarised UV radiation.
(85) The radiation wavelength can be adjusted by UV band pass filters. The irradiation wavelength is preferably in the range from 250 nm to 450 nm, more preferably in the range from 320 nm to 390 nm. Especially preferred is an irradiation wavelength of about 365 nm.
(86) As a source for UV radiation for example a single UV lamp or a set of UV lamps can be used. When using a high lamp power the curing time can be reduced. Another possible source for UV radiation is a laser.
(87) The linear polarisation of the actinic radiation can be achieved by methods known to the expert. Preferably the linear polarisation is achieved by passing the radiation through a suitable linear polarizer (e.g. a commercially available dye-doped absorption polarizer).
(88) The irradiation in step b) according to the present invention is performed at a temperature where the polymerisable liquid-crystalline material is in the isotropic phase. In a preferred embodiment, the irradiation is preferably performed at a temperature of 1 to 10 C. higher than the clearing point, more preferably at a temperature of 1 to 5 C. higher than the clearing point and most preferably at a temperature of 1 to 3 C. higher than the clearing point.
(89) The irradiation in step b) according to the present invention is preferably performed under an inert gas atmosphere, preferably in a heated nitrogen atmosphere, but also irradiation in air is possible.
(90) As described above, the polymerisable liquid-crystalline material used in the present invention comprises a dichroic photoinitiator. As with the common photoinitiators, dichroic photoinitiators dissociate when exposed to the correct wavelength and the formed radicals will initiate polymerisation of monomers. The dichroic photoinitiator used in the polymerisable liquid-crystalline material of the present invention has the property that the light absorption is dependent on the molecular orientation of the molecule. Therefore, when illuminated with said linear polarised UV light, polymerisation-initiating free radicals are predominantly produced where the local director lies parallel to the direction of polarisation. The local free-radical production results in different local polymerisation rates of the polymerisable liquid-crystalline material in the isotropic phase. The polymerisation rate of the liquid-crystalline molecules orientated parallel to the electric field of the linear polarized light proceeds faster than the polymerisation of the liquid-crystalline molecules orientated perpendicular to the electric field of the linear polarized light. As a result, the differences in the polymerisation rate prioritise domain formation parallel to the linear polarized UV light and finally induce, due to complete polymerisation and uniform alignment of the liquid-crystalline material in the polymer film, birefringence into the polymer film.
(91) The curing time is dependent, inter alia, on the reactivity of the polymerisable liquid-crystalline material, the thickness of the coated layer, the type of polymerisation initiator and the power of the UV lamp. The curing time is preferably 5 minutes, very preferably 3 minutes, most preferably 1 minute. For mass production short curing times of 30 seconds are preferred.
(92) A suitable UV radiation power is preferably in the range from 5 to 200 mWcm.sup.2, more preferably in the range from 50 to 175 mWcm.sup.2 and most preferably in the range from 100 to 150 mWcm.sup.2.
(93) In connection with the applied UV radiation and as a function of time, a suitable UV dose is preferably in the range from 25 to 7200 mJcm.sup.2 more preferably in the range from 500 to 7200 mJcm.sup.2 and most preferably in the range from 3000 to 7200 mJcm.sup.2.
(94) In a preferred embodiment, the liquid-crystalline molecules in the polymer film are aligned into planar orientation with regards to the substrate main plane. This planar orientation of the liquid-crystalline molecules in the resulting polymer film can be achieved, if the radiant source in step b) is located at an angle perpendicular to the substrate main plane.
(95) In another preferred embodiment, the liquid-crystalline material in the polymer film is aligned into tilted orientation (>0<90) with regards to the substrate main plane which can be achieved if the radiant source is located at an oblique angle (>0<90) with regards to the substrate main plane. Preferably, the irradiation angle is >10<80, more preferable >20<70 or more or even more preferable >30<60.
(96) The present invention also relates to a polymer film obtained by the method described above and below.
(97) The oriented polymer films of the present invention can be used as retardation or compensation film for example in LCDs to improve the contrast and brightness at large viewing angles and reduce the chromaticity. They can be used outside the switchable liquid-crystalline cell in an LCD, or between the substrates, usually glass substrates, forming the switchable liquid-crystalline cell and containing the switchable liquid-crystalline medium (incell application).
(98) Various types of optical retarders are known. For example, an A film (or A-plate) is an optical retarder utilizing a layer of uniaxially birefringent material with its extraordinary axis oriented parallel to the plane of the layer. In this connection an O film (or O-plate) is an optical retarder utilizing a layer of uniaxially birefringent material with its extraordinary axis tilted at an angle to the plane of the layer.
(99) Depending on the irradiation angle described above, the polymer film obtainable by the method according to the present invention can either be used as an A-plate (planar orientation of the liquid-crystalline molecules of the polymer film), if the radiant source in step b) is located at an angle perpendicular to the substrate main plane, or as an O-plate (tilted orientation of the liquid-crystalline molecules in the polymer film) if the radiant source is located at an oblique angle (>0<90) with regards to the substrate main plane.
(100) The optical retardation (()) of a polymer film as a function of the wavelength of the incident beam () is given by the following equation (6):
()=(2n.Math.d)/(6)
wherein (n) is the birefringence of the film, (d) is the thickness of the film and is the wavelength of the incident beam.
(101) According to Snellius law, the birefringence as a function of the direction of the incident beam is defined as
n=sin /sin (7)
wherein sin is the incidence angle or the tilt angle of the optical axis in the film and sin is the corresponding reflection angle.
(102) Based on these laws, the birefringence and accordingly also optical retardation basically depends on the thickness of a film and the tilt angle of optical axis in the film (cf. Berek's compensator). Therefore, the skilled expert is aware that different optical retardations or different birefringence can be induced by adjusting the orientation of the liquid-crystalline molecules in the polymer film.
(103) The birefringence (n) of the polymer film according to the present invention is preferably in the range from 0.01 to 0.30, more preferable in the range from 0.01 to 0.25 and even more preferable in the range from 0.01 to 0.16.
(104) The thickness of the polymer film obtained by the method according to the present invention is preferably in the range from 3 to 30 m, more preferable in the range from 3 to 20 m and even more preferable in the range from 3 to 10 m.
(105) The optical retardation as a function of the tilt angle and the thickness of the polymer film obtained by the method according to the present invention is less than 200 nm, preferable less than 180 nm and even more preferable less than 150 nm.
(106) The invention further relates to a method of preparing a polymer film comprising at least two regions with different birefringence, or comprising a pattern of two or more regions having different birefringence. The variation of birefringence leads to a variation of retardation in the different areas of the film.
(107) Such a film can be prepared by the method as described above, wherein only selected parts of the polymerisable liquid-crystalline material are exposed to irradiation, e.g. by using a photomask, or wherein different parts of the polymerisable liquid-crystalline material are exposed to different intensities of irradiation, e.g. by using a shaded photomask with different areas having different transmission of irradiation or by using a radiation source with variable intensity.
(108) Especially preferred is a polymer film according to the present invention that comprises a pattern of one or more, preferably one, two or three different regions having different values of the retardation, each of said values being adjusted such that its efficiency of converting linearly polarised light into circularly polarised light is optimized for light of one of the primary colours red, green and blue (R, G, B). In particular, said values of retardation correspond to a quarter of the wavelength of the respective colour and are preferably as follows:
(109) For red light of a wavelength of 600 nm the retardation is from 140 to 190 nm, preferably 145 to 180 nm, very preferably 145 to 160 nm, most preferably 150 nm.
(110) For green light of a wavelength of 550 nm the retardation is from 122 to 152 nm, preferably 127 to 147 nm, very preferably 132 to 142 nm, most preferably 137 nm.
(111) For blue light of a wavelength of 450 nm the retardation is from 85 to 120 nm, preferably 90 to 115 nm, very preferably 100 to 115 nm, most preferably 112 nm.
(112) The retardation of the film can be varied e.g. by varying the intensity and/or the duration of the irradiation.
(113) The polymer film of the present invention can also be used as alignment film for other liquid-crystalline or RM materials. For example, they can be used in an LCD to induce or improve alignment of the switchable liquid-crystalline medium, or to align a subsequent layer of polymerisable liquid-crystalline material coated thereon. In this way, stacks of polymerised liquid-crystalline films can be prepared.
(114) The polymer films of the present invention can be used in various types of liquid-crystalline displays, for example displays with vertical alignment like the DAP (deformation of aligned phases), ECB (electrically controlled birefringence), CSH (colour super homeotropic), VA (vertically aligned), VAN or VAC (vertically aligned nematic or cholesteric), MVA (multi-domain vertically aligned) or PVA (patterned vertically aligned) mode; displays with bend or hybrid alignment like the OCB (optically compensated bend cell or optically compensated birefringence), R-OCB (reflective OCB), HAN (hybrid aligned nematic) or pi-cell (-cell) mode; displays with twisted alignment like the TN (twisted nematic), HTN (highly twisted nematic), STN (super twisted nematic), AMD-TN (active matrix driven TN) mode; displays of the IPS (in plane switching) mode, or displays with switching in an optically isotropic phase.
(115) The present invention is described above and below with particular reference to the preferred embodiments. It should be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.
(116) Many of the compounds or mixtures thereof mentioned above and below are commercially available. All of these compounds are either known or can be prepared by methods which are known per se, as described in the literature (for example in the standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to be precise under reaction conditions which are known and suitable for said reactions. Use may also be made here of variants which are known per se, but are not mentioned here. Unless the context clearly indicates otherwise, as used herein plural forms of the terms herein are to be construed as including the singular form and vice versa.
(117) Throughout this application, unless explicitly stated otherwise, all concentrations are given in weight percent and relate to the respective complete mixture, all temperatures are given in degrees centigrade (Celsius) and all differences of temperatures in degrees centigrade. All physical properties have been and are determined according to Merck Liquid Crystals, Physical Properties of Liquid Crystals, Status November 1997, Merck KGaA, Germany and are given for a temperature of 20 C., unless explicitly stated otherwise. The optical anisotropy (n) is determined at a wavelength of 589 nm.
(118) Throughout the description and claims of this specification, the words comprise and contain and variations of the words, for example comprising and comprises, mean including but not limited to, and are not intended to (and do not) exclude other components. On the other hand, the word comprise also encompasses the term consisting of but is not limited to it.
(119) It will be appreciated that variations to the foregoing embodiments of the invention can be made while still falling within the scope of the invention. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
(120) All of the features disclosed in this specification may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. In particular, the preferred features of the invention are applicable to all aspects of the invention and may be used in any combination. Likewise, features described in non-essential combinations may be used separately (not in combination).
(121) The invention will now be described in more detail by reference to the following examples, which are illustrative only and do not limit the scope of the invention.
EXAMPLES
Example 1
(122) The following polymerisable liquid-crystalline material is prepared
(123) TABLE-US-00001 Compound (1) 9.86% Compound (2) 56.39% Compound (3) 7.17% Compound (4) 2.00% Compound (5) (dichroic photoinitiator) 16.00% Compound (6) (chiral RM) 8.00% BDH1533 0.50% Irganox 1076 (stabilizer) 0.08%
Clearing point: 48.5 C.
(124) ##STR00013##
(125) The polymerisable liquid-crystalline material is spin coated onto raw glass at 1000 rpm for 30 seconds. After annealing at 51 C. for 30 seconds, the material is exposed to polarized UV light (365 nm bandpass filter), at 120 mWcm.sup.2 for 40 seconds under nitrogen atmosphere at 51 C. The resulting polymer film has the following characteristics.
(126) Film thickness=3.93 m
(127) n=0.0358
(128) The retardation profile of the polymer film is shown in
Example 2
(129) The following polymerisable liquid-crystalline material is prepared
(130) TABLE-US-00002 Compound (1) 11.1% Compound (2) 63.72% Compound (3) 8.00% Compound (4) 5.00% Compound (5) (dichroic photoinitiator) 4.00% Compound (6) (chiral RM) 8.00% TegoRad 2500 0.10% Irganox 1076 (stabilizer) 0.08%
Clearing point: 48.5 C.
(131) ##STR00014##
(132) The polymerisable liquid-crystalline material is spin coated onto raw glass at 1000 rpm for 30 seconds. After that, the material is exposed to polarized UV light (365 nm bandpass filter), at 120 mWcm.sup.2 for 40 seconds under nitrogen atmosphere at 53 C. The resulting polymer film has the following characteristics.
(133) Film thickness=3.03 m
(134) n=0.0253
(135) The retardation profile of the polymer film is shown in
Example 3
(136) The following polymerisable liquid-crystalline material is prepared
(137) TABLE-US-00003 Compound (1) 40.23% Compound (2) 40.23% Compound (3) 5.46% Compound (4) (dichroic photoinitiator) 4.00% Paliocolor LC 756 (chiral RM) 10.00% Irganox 1076 (stabilizer) 0.08%
Clearing point: 41.9 C.
(138) ##STR00015##
(139) The polymerisable liquid-crystalline material is spin coated onto raw glass at 600 rpm for 30 seconds. After that, the material is exposed to polarized UV light (365 nm bandpass filter), at 35 mWcm.sup.2 for 30 seconds under nitrogen atmosphere at 43 C.
(140) The retardation profile of the polymer film is shown in
Example 4
Angle Dependency of the Radiation Source
(141) TABLE-US-00004 Compound (1) 35.71% Compound (2) 35.71% Compound (3) 10.00% Compound (4) 2.00% Compound (5) (dichroic photoinitiator) 8.00% Compound (6) (chiral RM) 8.00% BDH1533 0.50% Irganox 1076 (stabilizer) 0.08%
Clearing point: 48.9 C.
(142) ##STR00016##
(143) The polymerisable liquid-crystalline materials are each spin coated onto raw glass at 1000 rpm for 30 seconds. After that, the materials are exposed to polarised UV light (365 nm bandpass filter) each at different oblique angles of the radiation source (40, 50, 60, 70 and 90) at 50 mWcm.sup.2 for 30 seconds under nitrogen atmosphere at 51 C. The resulting polymer films have the following characteristics.
(144) Film thickness=3.31 m
(145) n=0.0272.
(146) The retardation profiles of the polymer films are shown in