LIQUID-CRYSTAL MEDIA AND PNLC LIGHT MODULATION ELEMENT
20220348827 · 2022-11-03
Assignee
Inventors
Cpc classification
G02F1/133365
PHYSICS
C09K19/322
CHEMISTRY; METALLURGY
C09K19/20
CHEMISTRY; METALLURGY
C09K19/32
CHEMISTRY; METALLURGY
C09K2019/0448
CHEMISTRY; METALLURGY
International classification
C09K19/20
CHEMISTRY; METALLURGY
Abstract
The present invention relates to a cholesteric liquid crystalline (LC) medium for a Polymer-Network Liquid Crystalline (PNLC) light modulation element, to a method of its production and to the use of such cholesteric LC media in PNLC light modulation elements. Furthermore, the present invention relates to PNLC light modulation elements, as such, to a method of their production, to the use of such light modulation elements in optic or electro optic devices, in particular in LC displays, and to optic or electro optic devices comprising such light modulation elements according to the present invention.
Claims
1. Cholesteric LC Medium for a PNLC light modulation element comprising A) one or more polymerisable compounds in an amount of ≥2% to ≤10% by weight, whereby at least one of which is a compound of formula I,
P.sup.11-Sp.sup.11-Ar-Sp.sup.12-P.sup.12 I wherein Ar is a group selected from the following formulae ##STR00108## which is optionally substituted by one or more groups L, L is on each occurrence identically or differently F, Cl, CN, P-Sp-, or 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—C—, —O—CO—, —O—CO—C— in such a manner that C- 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, P.sup.11 and P.sup.12 denote each and independently from another a polymerisable group, Sp.sup.11 and Sp.sup.12 denote each and independently from another a spacer group that is optionally substituted by one or more groups P.sup.11 or P.sup.12, or a single bond, and B) one or more non-polymerisable mesogenic or liquid-crystalline compounds, and C) one or more chiral compounds.
2. Cholesteric LC medium according to claim 1, wherein one or more chiral compounds having each alone or in combination with each other an absolute value of the helical twisting power (|HTP.sub.total|) of 5 μm.sup.−1 or more.
3. Cholesteric LC medium according to claim 1, comprising one or more chiral compounds in an amount from ≥0.1 to ≥0.9% by weight.
4. Cholesteric LC medium according to claim 1, wherein one or more non-polymerisable mesogenic or liquid-crystalline compounds are selected from compounds of formula A and/or B, ##STR00109## in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings: ##STR00110## each, independently of one another, and on each occurrence, identically or differently ##STR00111## R.sup.21, R.sup.31 each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, X.sup.0 F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms, Z.sup.31 —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, L.sup.21, L.sup.22, L.sup.31 and L.sup.32 each, independently of one another, H or F, g 0, 1, 2 or 3.
5. Process for the production of a cholesteric LC medium according to claim 1 comprising at least the step of mixing the non-polymerisable compounds and the chiral compounds with ≥2% to ≤10% of the polymerisable LC compounds.
6. A PNLC light modulation element comprising the cholesteric LC medium according to claim 1.
7. PNLC light modulation element comprising a pair of opposing substrates, an in-plane electrode structure and a cholesteric LC medium located in the interspace of said substrates, characterized in that the light modulation element comprises a polymer network obtainable from the cholesteric LC medium according to claim 1 by exposing said Cholesteric LC Medium to actinic radiation that induces photopolymerisation of the polymerisable compounds in the cholesteric LC medium.
8. PNLC light modulation element according to claim 7, comprising an electrode structure, corresponding to an IPS or FFS electrode structure.
9. PNLC light modulation element according to claim 7, wherein the interspace between the two opposing substrates is in the range from 1 to 20 μm.
10. Process for the production of a PNLC light modulation element according to claim 7 comprising at least the steps of cutting and cleaning of the substrates, providing an in plane electrode structure on one of the substrates, optionally providing an alignment layer on the electrode structure, assembling the cell, filling the cell with the cholesteric LC medium, and exposing said cholesteric LC medium to actinic radiation that induces photopolymerisation of the polymerisable compounds in the cholesteric LC medium.
11. Process according to claim 10, wherein photopolymerisation step is performed with light having a wavelength in the range from 250 to 450 nm.
12. Process according to claim 10, wherein photopolymerisation step is performed with an irradiation intensity in the range from 5 to 150 mW/cm.sup.2.
13. (canceled)
14. Optical or electro-optical device comprising the PNLC light modulation element according to claim 7.
Description
DETAILED DESCRIPTION
[0134] Preferably in the compounds of formula I and its subformulae as described above and below all polymerisable groups P that are present in the compound have the same meaning, and more preferably denote acrylate or methacrylate, most preferably methacrylate.
[0135] Further preferred are compounds of formula I and its subformulae wherein the group Ar is selected from formulae Ar5, Ar 6 and Ar7, and the groups P present in the compound are identical or different.
[0136] In the compounds of formula I and its subformulae as described above and below, Ar is preferably selected from formulae Ar1, Ar2 and Ar5.
[0137] Preferred compounds of formula I are selected from the following subformulae
##STR00012##
[0138] wherein P, Sp, and L have one of the meanings given in formula I,
[0139] r1, r3, r7 are independently of each other 0, 1, 2 or 3,
[0140] r2 is 0, 1, 2, 3 or 4,
[0141] r4, r5, r6 are independently of each other 0, 1 or 2.
[0142] Very preferred are compounds of formula I1, I2 and I5.
[0143] Further preferred compounds of formula I are selected from the following subformulae
##STR00013##
[0144] wherein P, Sp, L, r1-r7 have the meanings given in formula I or one of the preferred meanings as given above and below.
[0145] Very preferred compounds of formula I are selected from the following subformulae:
##STR00014## ##STR00015## ##STR00016## ##STR00017##
[0146] wherein P, Sp, have the meanings given above or below, and La and L.sup.b have each and independently from another one of the meanings given for L above or below.
[0147] Very preferred compounds of subformulae I1-1-1 to I2-1-18 are those wherein all groups P are identical and denote either an acrylate or methacrylate group, furthermore those wherein Sp is, —(CH.sub.2).sub.p1—, —(CH.sub.2).sub.p1—O—, —(CH.sub.2).sub.p1—O—CO— or —(CH.sub.2).sub.p1—CO—O—, in which p1 is an integer from 1 to 12, preferably 1 to 6, and the O— or CO-group is connected to the benzene ring, furthermore those wherein L.sup.a and L.sup.b denotes F, CH.sub.3, CH.sub.2CH.sub.3, OCH.sub.3, OC.sub.2H.sub.5, O(CH.sub.2).sub.2CH.sub.3, OC(CH.sub.3).sub.3 or OCF.sub.3.
[0148] Further preferred compounds of formula I and its subformulae are selected from the following preferred embodiments, including any combination thereof: [0149] All groups P in the compound have the same meaning, [0150] Ar is selected from formulae Ar1, Ar2, Ar3 and Ar4, and all groups P present in the compound have the same meaning, [0151] Ar is selected from formulae Ar1, Ar2, Ar3, Ar4 and Ar5, and all groups P present in the compound have the same meaning, [0152] Ar is selected from formulae Ar1, Ar2, Ar3, Ar4 and Ar6, and all groups P present in the compound have the same meaning, [0153] Ar is selected from formulae Ar1, Ar2, Ar3, Ar4 and Ar7, and all groups P present in the compound have the same meaning, [0154] Ar is selected from formulae Ar1, Ar2, Ar3, Ar4, A5 and Ar7, and all groups P present in the compound have the same meaning, [0155] Ar is selected from formulae Ar1, Ar2, Ar3, Ar4, A6 and Ar7, and all groups P present in the compound have the same meaning, [0156] Ar is selected of formula Ar5, and the groups P present in the compound can have the same or different meanings, [0157] Ar is selected of formula Ar6, and the groups P present in the compound can have the same or different meanings, [0158] Ar is selected of formula Ar7, and the groups P present in the compound can have the same or different meanings, [0159] the compounds contain exactly two polymerisable groups (represented by the groups P), [0160] P is selected from the group consisting of acrylate, methacrylate and oxetane, [0161] Sp, when being different from a single bond, is —(CH.sub.2).sub.p2—, —(CH.sub.2).sub.p2—O—, —(CH.sub.2).sub.p2—CO—O—, —(CH.sub.2).sub.p2—O—CO—, wherein p2 is 2, 3, 4, 5 or 6, and the O-atom or the CO-group, respectively, is connected to the benzene ring, [0162] L.sup.b, when being different from L.sup.a, denotes F, Cl or CN, [0163] L.sup.a is F, CH.sub.3, CH.sub.2CH.sub.3, OCH.sub.3, OC.sub.2H.sub.5, O(CH.sub.2).sub.2CH.sub.3, OC(CH.sub.3).sub.3 or OCF.sub.3. [0164] r1, r2 and r3 denote 0 or 1, [0165] r1, r2, r3, r4, r5 and r6 denote 0 or 1, [0166] one of r1 and r7 is 0 and the other is 1, [0167] r1 is 1, and r2 and r3 are 0, [0168] r3 is 1 and r1 and r2 are 0, [0169] one of r4 and r5 is 0 and the other is 1, [0170] r4 and r6 are 0 and r5 is 1, [0171] r1 and r4 are 0 and r3 is 1, [0172] r1 and r3 are 0 and r4 is 1, [0173] r3 and r4 are 0 and r1 is 1.
[0174] Further preferred compounds of formula I and its subformulae are selected from compounds of formula I1-1-1, I1-1-3, I1-2-2 and I2-1-1 to I2-1-6 wherein P is selected from the group consisting of acrylate, methacrylate and oxetane, L.sup.a and L.sup.b is each and independently from another F, CH.sub.3, CH.sub.2CH.sub.3, OCH.sub.3, OC.sub.2H.sub.5, O(CH.sub.2).sub.2CH.sub.3, OC(CH.sub.3).sub.3 or OCF.sub.3.
[0175] The compounds and intermediates of the formula I and sub-formulae thereof can be prepared analogously to processes known to the person skilled in the art and described in standard works of organic chemistry, such as, for example, in Houben-Weyl, Methoden der organischen Chemie [Methods of Organic Chemistry], Thieme-Verlag, Stuttgart.
[0176] For example, acrylic or methacrylic esters can be prepared by esterification of the corresponding alcohols with acid derivatives like, for example, (meth)acryloyl chloride or (meth)acrylic anhydride in the presence of a base like pyridine or triethyl amine, and 4-(N,N-dimethylamino)pyridine (DMAP). Alternatively the esters can be prepared by esterification of the alcohols with (meth)acrylic acid in the presence of a dehydrating reagent, for example according to Steglich with dicyclohexylcarbodiimide (DCC), N-(3-dimethylaminopropyl)-N′ ethylcarbodiimide (EDC) or N-(3-dimethylaminopropyl)-N′ ethylcarbodiimide hydrochloride and DMAP.
[0177] Particular preference is given to cholesteric LC media in which the polymerisable component A) comprises one, two or three polymerisable compounds of formula I.
[0178] Preference is furthermore given to cholesteric LC media in which the polymerisable component A) comprises exclusively polymerisable compounds of formula I.
[0179] Optionally one or more polymerisation initiators can be added to the cholesteric LC medium. Suitable conditions for the polymerisation and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature.
[0180] Suitable for free-radical polymerisation are, for example, the commercially available photoinitiators Irgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure1173® (Ciba AG). If a polymerisation initiator is employed, its proportion is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.
[0181] The polymerisable compounds according to the invention are also suitable for polymerisation without an initiator, which is accompanied by considerable advantages, such, for example, lower material costs and in particular less contamination of the cholesteric LC medium by possible residual amounts of the initiator or degradation products thereof. The polymerisation can thus also be carried out without the addition of an initiator. In a preferred embodiment, the cholesteric LC medium does not contain a polymerisation initiator.
[0182] The cholesteric LC medium may also comprise one or more stabilisers in order to prevent undesired spontaneous polymerisation of the RMs, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature.
[0183] Particularly suitable are, for example, the commercially available stabilisers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076. If stabilisers are employed, their proportion, based on the total amount of RMs or the polymerisable component (component A), is preferably 10-500,000 ppm, particularly preferably 50-50,000 ppm.
[0184] Preferably, the cholesteric LC medium according to the present invention does essentially consist of a polymerisable component A), or one or more polymerisable compounds of formula I, a LC component B), or LC host mixture, and a chiral component C) comprising one or more chiral compounds as described above and below.
[0185] However, the cholesteric LC medium may additionally comprise one or more further components or additives, preferably selected from the list including but not limited to inhibitors, further stabilizers, wetting agents, lubricating agents, dispersing agents, hydrophobing agents, adhesive agents, flow improvers, defoaming agents, deaerators, diluents, reactive diluents, auxiliaries, colourants, dyes, pigments and nanoparticles.
[0186] In another preferred embodiment the polymerisable component A) comprises, in addition to the compounds of formula I, one or more further polymerisable compounds (“co-monomers”), preferably selected from RMs.
[0187] Suitable and preferred mesogenic co-monomers are selected from the following formulae:
##STR00018## ##STR00019## ##STR00020## ##STR00021##
[0188] in which the individual radicals have the following meanings: [0189] P.sup.1, P.sup.2 and P.sup.3 each, independently of one another, denote an acrylate or methacrylate group, [0190] Sp.sup.1, Sp.sup.2 and Sp.sup.3 each, independently of one another, denote a single bond or a spacer group having one of the meanings indicated above and below for Sp, and particularly preferably denote —(CH.sub.2).sub.p1—, [0191] —(CH.sub.2).sub.p1—O—, —(CH.sub.2).sub.p1—CO—O—, —(CH.sub.2).sub.p1—O—CO— or —(CH.sub.2).sub.p1—O—CO—O—, in which p1 is an integer from 1 to 12, where, in addition, one or more of the radicals P.sup.1-Sp.sup.1-, P.sup.1-Sp.sup.2- and P.sup.3-Sp.sup.3- may denote R.sup.aa, with the proviso that at least one of the radicals [0192] 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, [0193] R.sup.aa denotes 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 [0194] 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), [0195] R.sup.0, R.sup.00 each, independently of one another and identically or differently on each occurrence, denote H or alkyl having 1 to 12 C atoms, [0196] R.sup.y and R.sup.z each, independently of one another, denote H, F, CH.sub.3 or CF.sub.3, [0197] X.sup.1, X.sup.2 and X.sup.3 each, independently of one another, denote —CO—O—, —O—CO— or a single bond, [0198] Z.sup.1 denotes —O—, —CO—, —C(R.sup.yR.sup.z)— or —CF.sub.2CF.sub.2—, [0199] Z.sup.2 and Z.sup.3 each, independently of one another, denote —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, [0200] 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, preferably F, [0201] L′ and L″ each, independently of one another, denote H, F or Cl, [0202] r denotes 0, 1, 2, 3 or 4, [0203] s denotes 0, 1, 2 or 3, [0204] t denotes 0, 1 or 2, [0205] x denotes 0 or 1.
[0206] Especially preferred are compounds of formulae M2, M13, M17, M22, M23, M24 and M30.
[0207] Further preferred are trireactive compounds M15 to M30, in particular M17, M18, M19, M22, M23, M24, M25, M26, M30 and M31.
[0208] In the compounds of formulae M1 to M31 the group
##STR00022##
is preferably
##STR00023##
[0209] wherein L on each occurrence, identically or differently, has one of the meanings given above or below, and is preferably F, Cl, CN, 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, CN, CH.sub.3, C.sub.2H.sub.5, OCH.sub.3, COCH.sub.3, OCF.sub.3 or P-Sp-, more preferably F, Cl, CH.sub.3, OCH.sub.3, COCH.sub.3 or OCF.sub.3, especially F or CH.sub.3.
[0210] Besides the polymerisable compounds described above, the LC media for use in the LC displays according to the invention comprise an liquid-crystalline component B) or LC host mixture exhibiting dielectrically positive anisotropy, which preferably comprises one or more, more preferably two or more LC compounds, which are selected from low-molecular-weight compounds that are unpolymerisable.
[0211] These LC compounds are selected such that they stable and/or unreactive to a polymerisation reaction under the conditions applied to the polymerisation of the polymerisable compounds.
[0212] Preferred LC compounds, which can be employed in the liquid-crystalline component B) according to the invention, are indicated below:
##STR00024##
[0213] in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings:
##STR00025##
each, independently of one another, and on each occurrence, identically or differently
##STR00026## [0214] R.sup.21, R.sup.31 each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, [0215] X.sup.0 F, Cl, CN, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms, [0216] Z.sup.31 —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, preferably —CH.sub.2CH.sub.2—, [0217] —COO—, trans-CH═CH— or a single bond, particularly preferably —COO—, trans-CH═CH— or a single bond, [0218] L.sup.21, L.sup.22, L.sup.31, L.sup.32 each, independently of one another, H or F, [0219] g 0, 1, 2 or 3.
[0220] In the compounds of formula A and B, X.sup.0 is preferably F, Cl, CF.sub.3, CHF.sub.2, OCF.sub.3, OCHF.sub.2, OCFHCF.sub.3, OCFHCHF.sub.2, OCFHCHF.sub.2, OCF.sub.2CH.sub.3, OCF.sub.2CHF.sub.2, OCF.sub.2CHF.sub.2, OCF.sub.2CF.sub.2CHF.sub.2, OCF.sub.2CF.sub.2CHF.sub.2, OCFHCF.sub.2CF.sub.3, OCFHCF.sub.2CHF.sub.2, OCF.sub.2CF.sub.2CF.sub.3, OCF.sub.2CF.sub.2CClF.sub.2, OCClFCF.sub.2CF.sub.3 or CH═CF.sub.2, very preferably F or OCF.sub.3, most preferably F.
[0221] In the compounds of formula A and B, R.sup.21 and R.sup.31 are preferably selected from straight-chain alkyl or alkoxy with 1, 2, 3, 4, 5 or 6 C atoms, and straight-chain alkenyl with 2, 3, 4, 5, 6 or 7 C atoms.
[0222] In the compounds of formula A and B, g is preferably 1 or 2.
[0223] In the compounds of formula B, Z.sup.31 is preferably COO, trans-CH═CH or a single bond, very preferably COO or a single bond.
[0224] Preferably, component B) of the Cholesteric LC medium comprises one or more compounds of formula A selected from the group consisting of the following formulae:
##STR00027##
[0225] in which A.sup.21, R.sup.21, X.sup.0, L.sup.21 and L.sup.22 have the meanings given in formula A, L.sup.23 and L.sup.24 each, independently of one another, are H or F, and X.sup.0 is preferably F. Particularly preferred are compounds of formulae A1 and A2.
[0226] Particularly preferred compounds of formula A1 are selected from the group consisting of the following subformulae:
##STR00028##
[0227] in which R.sup.21, X.sup.0, L.sup.21 and L.sup.22 have the meaning given in formula A1, L.sup.23, L.sup.24, L.sup.25 and L.sup.26 are each, independently of one another, H or F, and X.sup.0 is preferably F.
[0228] Very particularly preferred compounds of formula A1 are selected from the group consisting of the following subformulae:
##STR00029##
[0229] In which R.sup.21 is as defined in formula A1.
[0230] Particularly preferred compounds of formula A2 are selected from the group consisting of the following subformulae:
##STR00030## ##STR00031##
[0231] in which R.sup.21, X.sup.0, L.sup.21 and L.sup.22 have the meaning given in formula A2, L.sup.23, L.sup.24, L.sup.25 and L.sup.26 each, independently of one another, are H or F, and X.sup.0 is preferably F.
[0232] Very particularly preferred compounds of formula A2 are selected from the group consisting of the following subformulae:
##STR00032## ##STR00033##
[0233] in which R.sup.21 and X.sup.0 are as defined in formula A2.
[0234] Particularly preferred compounds of formula A3 are selected from the group consisting of the following subformulae:
##STR00034##
[0235] in which R.sup.21, X.sup.0, L.sup.21 and L.sup.22 have the meaning given in formula A3, and X.sup.0 is preferably F.
[0236] Particularly preferred compounds of formula A4 are selected from the group consisting of the following subformulae:
##STR00035##
[0237] in which R.sup.21 is as defined in formula A4.
[0238] Preferably, component B) of the Cholesteric LC medium comprises one or more compounds of formula B selected from the group consisting of the following formulae:
##STR00036##
[0239] in which g, A.sup.31, A.sup.32, R.sup.31, X.sup.0, L.sup.31 and L.sup.32 have the meanings given in formula B, and X.sup.0 is preferably F or CN. Particularly preferred are compounds of formulae B1 and B2.
[0240] Particularly preferred compounds of formula B1 are selected from the group consisting of the following subformulae:
##STR00037##
[0241] in which R.sup.31, X.sup.0, L.sup.31 and L.sup.32 have the meaning given in formula B1, and X.sup.0 is preferably F.
[0242] Very particularly preferred compounds of formula B1a are selected from the group consisting of the following subformulae:
##STR00038##
[0243] in which R.sup.31 is as defined in formula B1.
[0244] Very particularly preferred compounds of formula B1 b are selected from the group consisting of the following subformulae:
##STR00039##
[0245] in which R.sup.31 is as defined in formula B1.
[0246] Particularly preferred compounds of formula B2 are selected from the group consisting of the following subformulae:
##STR00040## ##STR00041##
[0247] in which R.sup.31, X.sup.0, L.sup.31 and L.sup.32 have the meaning given in formula B2, L.sup.33, L.sup.34, L.sup.35 and L.sup.36 are each, independently of one another, H or F, and X.sup.0 is preferably F or CN.
[0248] Very particularly preferred compounds of formula B2 are selected from the group consisting of the following subformulae:
##STR00042##
[0249] in which R.sup.31 is as defined in formula B2.
[0250] Very particularly preferred compounds of formula B2b are selected from the group consisting of the following subformulae
##STR00043##
[0251] in which R.sup.31 is as defined in formula B2.
[0252] Very particularly preferred compounds of formula B2c are selected from the group consisting of the following subformulae:
##STR00044##
[0253] in which R.sup.31 is as defined in formula B2.
[0254] Very particularly preferred compounds of formula B2d and B2e are selected from the group consisting of the following subformulae:
##STR00045##
[0255] in which R.sup.31 is as defined in formula B2.
[0256] Very particularly preferred compounds of formula B2f are selected from the group consisting of the following subformulae:
##STR00046##
[0257] in which R.sup.31 is as defined in formula B2.
[0258] Very particularly preferred compounds of formula B2g are selected from the group consisting of the following subformulae:
##STR00047##
[0259] in which R.sup.31 is as defined in formula B2.
[0260] Very particularly preferred compounds of formula B2h are selected from the group consisting of the following subformulae:
##STR00048##
[0261] in which R.sup.31 is as defined in formula B2.
[0262] Very particularly preferred compounds of formula B2i are selected from the group consisting of the following subformulae:
##STR00049##
[0263] in which R.sup.31 is as defined in formula B2.
[0264] Very particularly preferred compounds of formula B2k are selected from the group consisting of the following subformulae:
##STR00050##
[0265] in which R.sup.31 is as defined in formula B2.
[0266] Very particularly preferred compounds of formula B2l are selected from the group consisting of the following subformulae:
##STR00051##
[0267] in which R.sup.31 is as defined in formula B2.
[0268] Alternatively to, or in addition to, the compounds of formula B1 and/or B2 component B) of the Cholesteric LC medium may also comprise one or more compounds of formula B3 as defined above.
[0269] Particularly preferred compounds of formula B3 are selected from the group consisting of the following subformulae:
##STR00052##
[0270] in which R.sup.31 is as defined in formula B3.
[0271] Preferably, component B) of the Cholesteric LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula C
##STR00053##
[0272] in which the individual radicals have the following meanings:
##STR00054##
each, independently of one another, and on each occurrence, identically or differently
##STR00055## [0273] R.sup.41, R.sup.42 each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, [0274] Z.sup.41, Z.sup.42 each, independently of one another, —CH.sub.2CH.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O—, —CF.sub.2O—, —C≡C— or a single bond, preferably a single bond, [0275] h 0, 1, 2 or 3.
[0276] In the compounds of formula C, R.sup.41 and R.sup.42 are preferably selected from straight-chain alkyl or alkoxy with 1, 2, 3, 4, 5 or 6 C atoms, and straight-chain alkenyl with 2, 3, 4, 5, 6 or 7 C atoms.
[0277] In the compounds of formula C, h is preferably 0, 1 or 2.
[0278] In the compounds of formula C, Z.sup.41 and Z.sup.42 are preferably selected from COO, trans-CH═CH and a single bond, very preferably from COO and a single bond.
[0279] Preferred compounds of formula C are selected from the group consisting of the following subformulae:
##STR00056## ##STR00057##
[0280] wherein R.sup.41 and R.sup.42 have the meanings given in formula C, and preferably denote each, independently of one another, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 7 C atoms, or alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl with 2 to 7 C atoms.
[0281] Preferably, the component B) of the Cholesteric LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula D
##STR00058##
[0282] in which A.sup.41, A.sup.42, Z.sup.41, Z.sup.42, R.sup.41, R.sup.42 and h have the meanings given in formula C or one of the preferred meanings given above.
[0283] Preferred compounds of formula D are selected from the group consisting of the following subformulae:
##STR00059##
[0284] in which R.sup.41 and R.sup.42 have the meanings given in formula D and R.sup.41 preferably denotes alkyl, and in formula D1 R.sup.42 preferably denotes alkenyl, particularly preferably —(CH.sub.2).sub.2—CH═CH—CH.sub.3, and in formula D2 R.sup.42 preferably denotes alkyl, —(CH.sub.2).sub.2—CH═CH.sub.2 or —(CH.sub.2).sub.2—CH═CH—CH.sub.3.
[0285] Preferably, the component B) of the Cholesteric LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula E containing an alkenyl group
##STR00060##
[0286] in which the individual radicals, on each occurrence identically or differently, each, independently of one another, have the following meaning:
##STR00061## [0287] R.sup.A1 alkenyl having 2 to 9 C atoms or, if at least one of the rings X, Y and Z denotes cyclohexenyl, also one of the meanings of R.sup.A2, [0288] R.sup.A2 alkyl having 1 to 12 C atoms, in which, in addition, one or two non-adjacent CH.sub.2 groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, [0289] x 1 or 2.
[0290] R.sup.A2 is preferably straight-chain alkyl or alkoxy having 1 to 8 C atoms or straight-chain alkenyl having 2 to 7 C atoms.
[0291] Preferred compounds of formula E are selected from the following sub-formulae:
##STR00062##
[0292] in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-7 C atoms. Alkenyl and alkenyl* preferably denote CH.sub.2═CH—, CH.sub.2═CHCH.sub.2CH.sub.2—, CH.sub.3—CH═CH—, CH.sub.3—CH.sub.2—CH═CH—, CH.sub.3—(CH.sub.2).sub.2—CH═CH—, CH.sub.3—(CH.sub.2).sub.3—CH═CH— or CH.sub.3—CH═CH—(CH.sub.2).sub.2—.
[0293] Very preferred compounds of the formula E are selected from the following sub-formulae:
##STR00063##
in which m denotes 1, 2, 3, 4, 5 or 6, i denotes 0, 1, 2 or 3, and R.sup.b1 denotes H, CH.sub.3 or C.sub.2H.sub.5.
[0294] Very particularly preferred compounds of the formula E are selected from the following sub-formulae:
##STR00064##
[0295] Most preferred are compounds of formula E1a2, E1a5, E3a1 and E6a1.
[0296] Preferably, the component B) of the Cholesteric LC medium comprises, in addition to the compounds of formula A and/or B, one or more compounds of formula F
##STR00065##
[0297] in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings:
##STR00066##
denote
##STR00067## [0298] R.sup.21, R.sup.31 each, independently of one another, alkyl, alkoxy, oxaalkyl or alkoxyalkyl having 1 to 9 C atoms or alkenyl or alkenyloxy having 2 to 9 C atoms, all of which are optionally fluorinated, [0299] X.sup.0 F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms, [0300] Z.sup.21 —CH.sub.2CH.sub.2—, —CF.sub.2CF.sub.2—, —COO—, trans-CH═CH—, trans-CF═CF—, —CH.sub.2O— or a single bond, preferably —CH.sub.2CH.sub.2—, [0301] —COO—, trans-CH═CH— or a single bond, particularly preferably —COO—, trans-CH═CH— or a single bond, [0302] L.sup.21, L.sup.22, L.sup.23, L.sup.24 each, independently of one another, H or F, [0303] g 0, 1, 2 or 3.
[0304] Particularly preferred compounds of formula F are selected from the group consisting of the following formulae:
##STR00068##
[0305] in which R.sup.21, X.sup.0, L.sup.21 and L.sup.22 have the meaning given in formula F, L.sup.25 and L.sup.26 are each, independently of one another, H or F, and X.sup.0 is preferably F.
[0306] Very particularly preferred compounds of formula F1-F3 are selected from the group consisting of the following subformulae:
##STR00069##
[0307] In which R.sup.21 is as defined in formula F1.
[0308] The medium preferably comprises one or more neutral compounds of the general formula N,
##STR00070##
[0309] in which
[0310] R.sup.N1 and R.sup.N2 each, independently of one another, denote an alkyl or alkoxy radical having 1 to 15 C atoms, where, in addition, one or more CH.sub.2 groups in these radicals may each be replaced, independently of one another, by —C≡C—, —CF.sub.2O—,
##STR00071##
[0311] —CO—O—, —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,
[0312] rings A.sup.N1, A.sup.N2 and A.sup.N3 each, independently of one another, denote 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene, 3,5-difluoro-1,4-phenylene trans-1,4-cyclohexylene, in which, in addition, one or two CH.sub.2 groups may be replaced by —O—, or 1,4-cyclohexenylene,
[0313] Z.sup.N1 and Z.sup.N2 each, independently of one another, denote a single bond or —C≡C—, whereby at least one of Z.sup.N1 and Z.sup.N2 denotes —C≡C—,
[0314] n denotes 0, 1 or 2.
[0315] Preferred compounds of the formula N are shown below:
##STR00072##
[0316] in which
[0317] alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1 to 9 C atoms, preferably 2 to 6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms.
[0318] The concentration of the compounds of formula A and B in the LC host mixture is preferably from 2 to 60%, very preferably from 3 to 55%, most preferably from 4 to 50%.
[0319] The concentration of the compounds of formula C and D in the LC host mixture is preferably from 5 to 75%, very preferably from 10 to 70%, most preferably from 15 to 60%.
[0320] The concentration of the compounds of formula E in the LC host mixture is preferably from 5 to 30%, very preferably from 10 to 25%.
[0321] The concentration of the compounds of formula F in the LC host mixture is preferably from 2 to 30%, very preferably from 5 to 20%.
[0322] Further preferred embodiments of the present invention are listed below, including any combination thereof. [0323] 2a) The LC host mixture comprises one or more compounds of formula A and/or B with high positive dielectric anisotropy, preferably with Δε>15. [0324] 2b) The LC host mixture comprises one or more compounds selected from the group consisting of formulae A1a2, A1 b1, A1d1, A1f1, A2a1, A2h1, A2l2, A2k1, B2g3, and/or B2F. The proportion of these compounds in the LC host mixture is preferably from 5 to 50. [0325] 2c) The LC host mixture comprises one or more compounds selected from the group consisting of formulae C3, C4, C5, C9 and D2. The proportion of these compounds in the LC host mixture is preferably from 8 to 75%, very preferably from 10 to 70%. [0326] 2d) The LC host mixture comprises one or more compounds selected from the group consisting of formulae E1, E3 and E6, preferably E1a, E3a and E6a, very preferably E1a2, E1a5, E3a1 and E6a1. The proportion of these compounds in the LC host mixture is preferably from 5 to 40%, very preferably from 10 to 25%.
[0327] The optimum mixing ratio of the compounds of the above-mentioned formulae in the liquid-crystalline component B) depends substantially on the desired properties, on the choice of the components of the above-mentioned formulae and on the choice of any further components that may be present. Preferred physical properties are given in the following.
[0328] In a preferred embodiment, the liquid-crystalline component B) according to the invention are characterised by optical anisotropy values as high as possible. Preferably, the liquid-crystalline component B) exhibits an optical anisotropy (Δn) in the range from 0.05 or more to 0.500 or less, more preferably in the range from 0.100 or more to 0.300 or less, especially in the range from 0.150 or more to 0.250 or less.
[0329] Preferably, the liquid-crystalline component B) according to the invention is characterised by relatively high positive values of the dielectric anisotropy (Δε), preferably as high as possible. In a preferred embodiment, the liquid-crystalline component B) exhibits a dielectrically positive anisotropy in the range from 3 to 50, preferably from 4 or more to 25 or less, particularly preferably from 5 or more to 20 or less.
[0330] The nematic phase of the liquid-crystalline component B) according to the invention preferably extends at least from 0° C. or below to 70° C. or above, more preferably at least from −20° C. or below to 75° C. or above, very preferably at least from −30° C. or below to 75° C. or above and in particular at least from −40° C. or below to 80° C. or above.
[0331] The clearing point of the liquid-crystalline component B) according to the invention is preferably in the range from 10° C. to 120° C., particularly preferably in the range from 40° C. to 110° C. and very particularly preferably in the range from 60° C. to 100° C.
[0332] The rotational viscosity of the liquid-crystalline component B) is preferably as low as possible. Preferably, the liquid-crystalline component B) exhibits a rotational viscosity of approximately 500 mPas or less, preferably in the range from 1 mPas or more to 500 mPas or less, more preferably in the range from 10 mPas or more to 300 mPas or less, especially in the range from 50 mPas to 200 mPas.
[0333] The cholesteric medium in accordance with the present invention comprises one or more chiral dopants or a chiral component C).
[0334] Preferably, the cholesteric LC Medium according to the present invention comprises one or more chiral compounds having each alone or in combination with each other an absolute value of the helical twisting power (|HTP.sub.total|) of 5 μm.sup.−1 or more, preferably 10 μm.sup.−1 or more, more preferably 15 μm.sup.−1 or more.
[0335] Preferred are chiral dopants with the higher helical twisting power (HTP), in particular those disclosed in WO 98/00428.
[0336] Typically, used chiral dopants are e.g. the commercially available R/S-5011, CD-1, R/S-811 and CB-15 (from Merck KGaA, Darmstadt, Germany).
[0337] In another preferred embodiment, the chiral dopants are preferably selected from formula Ch I,
##STR00073##
[0338] and/or formula Ch II,
##STR00074##
[0339] including the respective (S,S) enantiomer,
[0340] wherein E and F are each independently 1,4-phenylene or trans-1,4-cyclohexylene, v is 0 or 1, Z.sup.0 is —COO—, —OCO—, —CH.sub.2CH.sub.2— or a single bond and R is alkyl, alkoxy or alkanoyl with 1 to 12 C atoms.
[0341] The compounds of formula Ch I and their synthesis are described in WO 98/00428. The compounds of formula Ch II and their synthesis are described in GB 2,328,207.
[0342] The above-mentioned chiral dopants R/S-5011 and the compounds of formula Ch I and Ch II exhibit a very high helical twisting power (HTP) and are therefore particularly useful for the purpose of the present invention.
[0343] The liquid crystalline medium preferably comprises preferably 1 to 5, in particular 1 to 3, very preferably 1 or 2 chiral dopants, preferably selected from the above formula Ch I, and/or formula Ch II and/or R-5011 or S-5011, very preferably, the chiral compound is R-5011, S-5011.
[0344] Typically the amount of chiral compounds having an absolute value of the helical twisting power (|HTP.sub.total|) of 5 μm.sup.−1 or more as a whole in the cholesteric liquid crystalline medium is preferably from ≥0.1 to ≥0.9% by weight of the total mixture.
[0345] The cholesteric LC media should in addition be of such a nature that different reflection wavelengths, in particular in the infrared region, can be achieved by simple and targeted variation. Preferably the cholesteric pitch of the cholesteric LC Medium is selected such, that their wavelength of reflection is in the in the range in the infrared range of the electromagnetic spectrum i.e. in the range from of 800 nm to 5000 nm, more preferably form 1000 to 4000 nm. In particular, the reflection wavelength of the liquid crystalline medium is in the range of 2000 nm to 3500 nm.
[0346] The cholesteric LC media according to the present invention are prepared in a manner conventional per se, for example by mixing one or more of the above-mentioned polymerisable compounds with one or more non-polymerisable compounds and one or more chiral compounds, both as defined above, and optionally with further liquid-crystalline compounds and/or additives.
[0347] 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. Accordingly, the invention also relates to the process for the preparation of the cholesteric LC media according to the invention.
[0348] The cholesteric LC media according to the present invention are very suitable for the use in different types of PNLC light modulation elements. Therefore, the present invention also relates to the use of an cholesteric LC medium as described and below in a PNLC light modulation element.
[0349] Accordingly, the present invention also relates to the PNLC light modulation element comprising a pair of opposing substrates, an electrode structure, preferably an in-plane electrode structure, a cholesteric LC medium located in the interspace of said substrates, characterized in that the PNLC light modulation element comprises a polymer network obtainable from the Cholesteric LC medium according as described above by exposing said Cholesteric LC medium to actinic radiation that induces photopolymerisation of the polymerisable compounds in the Cholesteric LC medium.
[0350] The invention furthermore relates to a process for the production of a PNLC light modulation element comprising at least the steps of [0351] cutting and cleaning of the substrates, [0352] providing the electrode structure on one or both substrates, [0353] optionally providing an alignment layer on the electrode structure, [0354] assembling the cell, [0355] filling the cell with the cholesteric LC medium according to the present invention, and [0356] exposing said cholesteric LC medium to actinic radiation that induces photopolymerisation of the polymerisable compounds in the LC medium.
[0357] In one embodiment of the present invention, the cholesteric LC medium is injected between the first and second substrates or is filled into the assembled cell by capillary force or vacuum filing after combining the first and second substrates.
[0358] However, it is likewise preferable that the liquid crystal composition may be interposed between the first and second substrates by combining the second substrate to the first substrate after loading the liquid crystal composition on the first substrate. In a preferred embodiment, the liquid crystal is dispensed dropwise onto a first substrate in a process known as “one drop filling” (ODF) process, as disclosed in for example JPS63-179323 and JPH10-239694, or using the Ink Jet Printing (IJP) method
[0359] In the irradiation step, the cell is exposed to actinic radiation that causes photopolymerisation of the polymerisable functional groups of the polymerisable compounds contained in the cholesteric liquid crystal medium.
[0360] Polymerisation is achieved for example by exposing the polymerisable material to heat or preferably actinic radiation. Actinic radiation means irradiation with light, like UV light, IR light or visible light, irradiation with X-rays or gamma rays or irradiation with high-energy particles, such as ions or electrons.
[0361] Preferably, polymerisation is carried out by UV irradiation. As a source for actinic radiation, for example a single UV lamp or a set of UV lamps can be used. Another possible source for actinic radiation is a laser, like for example a UV, IR or visible laser.
[0362] Because of the irradiation, the polymerisable compounds are substantially crosslinked in situ within the liquid crystal medium between the substrates forming the PNLC light modulation element whereby the polymer network is formed which preferably extends through the whole switching layer.
[0363] As a consequence, the formed polymer network reduces the effective cell gap to something much smaller than the typical cell gaps normally considered for LC cells. This allows for much faster switching and relaxation of the focal conic texture back to the aligned helical twist. Instead of switch times in the order of 10 seconds or more, the switching time can be reduced to the order of (sub-)milliseconds.
[0364] The utilized wavelength of the actinic radiation should not be too low, in order to avoid damage to the LC molecules of the medium, and should preferably be different from, very preferably higher than, the UV absorption maximum of the LC host mixture.
[0365] On the other hand, the wavelength of the photo radiation should not be too high, to allow quick and complete UV photopolymerisation of the polymerisable compounds, and should be not higher than, preferably the same as or lower than the UV absorption maximum of the polymerisable component.
[0366] Suitable wavelengths are preferably selected from wavelengths in the range from 250 to 450 nm, for example 400 nm or less, preferably 350 nm or less, more preferably 300 nm or less.
[0367] The irradiation or exposure time should be selected such that polymerisation is as complete as possible, but still not be too high to allow a smooth production process. In addition, the radiation intensity should be high enough to allow quick and complete polymerisation as possible, but should not be too high to avoid damage to the cholesteric liquid crystal medium.
[0368] The curing time depends, inter alia, on the reactivity of the polymerisable material, the thickness of the coated layer, the type of polymerisation initiator and the power of the UV lamp. The curing time is preferably 10 minute, very preferably 5 minutes, and most preferably 1 minutes. In general, for mass production shorter curing times are preferred, such as approximately 60 seconds to 1 second.
[0369] A suitable UV radiation power is preferably in the range from 5 to 150 mWcm.sup.−2, more preferably in the range from 10 to 75 mWcm.sup.−2, especially in the range from 25 to 60 mWcm.sup.−2, and in particular 45 to 55 mWcm.sup.−2.
[0370] Polymerisation is preferably performed under an inert gas atmosphere, preferably in under a nitrogen atmosphere, but also polymerisation in air is possible.
[0371] Polymerisation is preferably performed at a temperature in the range from −10° C. to +70° C., more preferably 0° C. to +50° C., even more preferably +15° C. to +40° C.
[0372] In an preferred embodiment, the PNLC light modulation element can additionally be annealed after the polymerisation, preferably at a temperature above 20° C. and below 140° C., more preferably above 40° C. and below 130° C. and most preferably above 70° C. and below 120° C., in order to reach full conversion of the monomers and in order to achieve an optimum stability
[0373] Typically, the structure of the PNLC light modulation element according to the invention corresponds to the conventional structure for displays, which is known to the person skilled in the art.
[0374] As substrate, for example, glass or quartz sheets or plastic films can be used. When using two substrates in case of curing by actinic radiation, at least one substrate has to be transmissive for the actinic radiation used for the polymerisation.
[0375] 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 plastic films can be used. PET films are commercially available for example from DuPont Teijin Films under the trade name Melinex®.
[0376] In a preferred embodiment, the substrates are arranged with a separation in the range from approximately 1 μm to approximately 20 μm from one another, preferably in the range from approximately 3 μm to approximately 10 μm from one another, and more preferably in the range from approximately 3 μm to approximately 6 μm from one another. The layer of the cholesteric LC medium is thereby located in the interspace.
[0377] The substrate layers can be kept at a defined separation from one another, for example, by spacers, or projecting structures in the layer. Typical spacer materials are commonly known to the expert, as for example spacers made of plastic, silica, epoxy resins, or the like.
[0378] In a further preferred embodiment of the invention, the layer of the cholesteric LC medium is located between two flexible layers, for example flexible polymer films. The corresponding PNLC light modulation element according to the invention is consequently flexible and bendable and can be rolled up, for example. The flexible layers can represent the substrate layer, the alignment layer, and/or polarisers. Further layers, which are preferable flexible, may also, be present. For a more detailed disclosure of the preferred embodiments, in which the layer of the liquid-crystalline medium is located between flexible layers, reference is given to the application US 2010/0045924 A1.
[0379] Furthermore, an electrode arrangement and optionally further electrical components and connections are be present in the PNLC light modulation element according to the invention in order to facilitate electrical switching of the PNLC light modulation element, comparable to the switching of an LC display.
[0380] Preferably, the PNLC light modulation element comprises an electrode arrangement, which is capable to allow the application of an electric field, which is substantially in parallel to the substrate main plane or the cholesteric liquid-crystalline medium layer. Suitable electrode arrangements or in-plane electrode structures fulfilling this requirement are commonly known to the expert.
[0381] For example, the first substrate includes a pixel electrode and a common electrode for generating an electric field substantially parallel to the surface of the first substrate in the pixel region. Various kinds of displays having at least two electrodes on one substrate are known to the skilled person wherein the most significant difference is that either both the pixel electrode and the common electrode are structured, as it is typical for IPS displays, or only the pixel electrode is structured and the common electrode is unstructured, which is the case for FFS displays.
[0382] It has to be understood that the present invention refers to any kind of electrode configurations suitable for generating an electric field substantially parallel to a surface of the first substrate in the pixel region; mentioned above, i.e. IPS as well as FFS displays.
[0383] Suitable electrode materials are commonly known to the expert, as for example electrode structures made of metal or metal oxides, such as, for example indium tin oxide (ITO), which is preferred according to the present invention.
[0384] Thin films of ITO, for example, are preferably deposited on substrates by physical vapour deposition, electron beam evaporation, or sputter deposition techniques.
[0385] Preferably, the electrodes of the PNLC light modulation element are associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD).
[0386] In a preferred embodiment, the PNLC light modulation element may comprise at least one dielectric layer. Typical dielectric layer materials are commonly known to the expert, such as, for example, SiOx, SiNx, Cytop, Teflon, and PMMA.
[0387] The dielectric layer materials can be applied onto the substrate or electrode layer by conventional coating techniques like spin coating, roll coating, blade coating, or vacuum deposition such as PVD or CVD. It can also be applied to the substrate or electrode layer by conventional printing techniques, which are known to the expert, like for example screen printing, offset printing, reel-to-reel printing, letterpress 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.
[0388] In a further preferred embodiment, the PNLC light modulation element comprises at least one alignment layer, which is preferably provided adjacent to the cholesteric LC medium. The PNLC light modulation element may have further alignment layers, which are in direct contact with the layer of the liquid-crystalline medium.
[0389] The alignment layers may also serve as substrate layers, so that substrate layers are not necessary in the PNLC light modulation element. If substrate layers are additionally present, the alignment layers are in each case arranged between the substrate layer and the layer of the liquid-crystalline medium.
[0390] Preferably, the alignment layer(s) induce(s) planar alignment, preferably throughout the entire liquid-crystalline medium.
[0391] Suitable planar alignment layer materials are commonly known to the expert, such as, for example, AL-3046 or AL-1254 both commercially available from JSR.
[0392] The alignment layer materials can be applied onto the substrate array or electrode structure by conventional coating techniques like spin coating, roll coating, dip coating or blade coating. It can also be applied by vapour deposition or conventional printing techniques, which are known to the expert, like for example screen printing, offset printing, reel-to-reel printing, letterpress 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.
[0393] In a preferred embodiment, the planar alignment layer is processed by rubbing or photo-alignment techniques known to the skilled person, preferably by rubbing techniques. Accordingly, a uniform preferred direction of the director can be achieved without any physical treatment of the cell like shearing of the cell (mechanical treatment in one direction), etc. The rubbing direction is uncritical and mainly influences only the orientation in which the polarizers have to be applied. However, preferred are antiparallel rubbed planar alignment layers. Typically the rubbing direction is in the range of +/−45°, more preferably in the range of +/−20°, even more preferably, in the range of +/−10, and in particular, in the range of the direction +/−5° with respect to the substrates largest extension.
[0394] In a further preferred embodiment of the invention, the PNLC light modulation element optionally comprises two or more polarisers, at least one of which is arranged on one side of the layer of the liquid-crystalline medium and at least one of which is arranged on the opposite side of the layer of the liquid-crystalline medium. The layer of the liquid-crystalline medium and the polarisers here are preferably arranged parallel to one another.
[0395] The polarisers can be linear polarisers. Preferably, precisely two polarisers are present in the PNLC light modulation element. In this case, it is furthermore preferred for the polarisers either both to be linear polarisers. If two linear polarisers are present in the PNLC light modulation element, it is preferred in accordance with the invention for the polarisation directions of the two polarisers to be crossed.
[0396] It is furthermore preferred in the case where two circular polarisers are present in the PNLC light modulation element for these to have the same polarisation direction, i.e. either both are right-hand circular-polarised or both are left-hand circular-polarised.
[0397] The polarisers can be reflective or absorptive polarisers. A reflective polariser in the sense of the present application reflects light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light. Correspondingly, an absorptive polariser absorbs light having one polarisation direction or one type of circular-polarised light, while being transparent to light having the other polarisation direction or the other type of circular-polarised light. The reflection or absorption is usually not quantitative; meaning that complete polarisation of the light passing through the polariser does not take place.
[0398] For the purposes of the present invention, both absorptive and reflective polarisers can be employed. Preference is given to the use of polarisers, which are in the form of thin optical films. Examples of reflective polarisers which can be used in the PNLC light modulation element according to the invention are DRPF (diffusive reflective polariser film, 3M), DBEF (dual brightness enhanced film, 3M), DBR (layered-polymer distributed Bragg reflectors, as described in U.S. Pat. Nos. 7,038,745 and 6,099,758) and APF (advanced polariser film, 3M).
[0399] Examples of absorptive polarisers, which can be employed in the PNLC light modulation elements according to the invention, are the Itos XP38 polariser film and the Nitto Denko GU-1220DUN polariser film. An example of a circular polariser, which can be used in accordance with the invention, is the APNCP37-035-STD polariser (American Polarizers). A further example is the CP42 polariser (ITOS). The PNLC light modulation element may furthermore comprise filters which block light of certain wavelengths, for example, UV filters. In accordance with the invention, further functional layers, such as, for example, protective films, heat-insulation films or metal-oxide layers, may also be present.
[0400] The functional principle of the PNLC light modulation element according to the invention will be explained in detail below. It is noted that no restriction of the scope of the claimed invention, which is not present in the claims, is to be derived from the comments on the assumed way of functioning.
[0401] In a first preferred embodiment, the retardation or phase change of the PNLC light modulation element according to the invention is dependent on the applied electric field. Preferably, the retardation gradually increases while applying an electric field with gradually increasing voltage.
[0402] In this preferred embodiment, the components A and B are selected dependently from one another in that way that birefringence of the polymerisable component A matches the birefringence of the component B. Preferably, the difference between values for the birefringence is below 10%, more preferably below 5% and more preferably below 3%.
[0403] The required applied electric field strength is mainly dependent on the electrode gap and the modulus of Δε of the LC mixture. The applied electric field strengths are typically lower than approximately 50 V/μm.sup.−1, preferably lower than approximately 30 V/μm.sup.−1 and more preferably lower than approximately 25 V/μm.sup.−1. In particular, the applied electric field strengths is in the range from 1 V/μm.sup.−1 to 20V/μm.sup.−1.
[0404] Preferably, the applied driving voltage in order to switch the PNLC light modulation element should be as low as possible. Typically, the applied driving voltage is in the range from 2 V to approximately 20 V, more preferably in the range from approximately 5 V to approximately 10 V.
[0405] In this first preferred embodiment, the retardation change or phase change (Γ) is given in accordance with the following equation
[0406] wherein d is the layer thickness of the applied liquid crystalline medium, λ is the wavelength of the incident light and n.sub.eff is the effective birefringence induced by the reorientation of the LC in the applied field.
[0407] In a second preferred embodiment, the PNLC light modulation element according to the invention has a boundary state A and a boundary state B.
[0408] The PNLC light modulation element preferably has the boundary state A with a transmission T.sub.A when no electrical field is applied, the so called “off state” or transparent state.
[0409] The PNLC light modulation element preferably has another boundary state B when an electric field is applied, the so called “on state” or opaque state, whereby
T.sub.A>T.sub.B.
[0410] In this second preferred embodiment, the components A and B are selected dependently from one another in that way that birefringence of the polymerisable component A differs from the birefringence of the component B. Preferably, the difference between values for the birefringence is more than 3%, more preferably more than 5% and more preferably more than 10%.
[0411] The required applied electric field strength is mainly dependent on the electrode gap and the modulus of Δε of the LC mixture. The applied electric field strengths are typically lower than approximately 50 V/μm.sup.−1, preferably lower than approximately 30 V/μm.sup.−1 and more preferably lower than approximately 25 V/μm.sup.−1. In particular, the applied electric field strengths is in the range from 1 V/μm.sup.−1 to 20V/μm.sup.−1.
[0412] Preferably, the applied driving voltage in order to switch the PNLC light modulation element should be as low as possible. Typically, the applied driving voltage is in the range from 2 V to approximately 200 V, more preferably in the range from approximately 3 V to approximately 100 V, and even more preferably in the range from approximately 5 V to approximately 50 V.
[0413] The transmission change is governed by the strength of the applied field. With more field applied to the system, the degree of scatter increases, which causes a reduction in the intensity of forward propagating light, and an increase in light emitted in other directions. Hence for side-illuminated devices, the amount of light visible orthogonal to the illumination direction increases with increasing applied field strength.
[0414] As described above, the PNLC light modulation element of the present invention can be used in various types of optical and electro-optical devices. Accordingly, the present invention is also directed to the use of the PNLC light modulation element as described above in an optical or electro-optical device and to an optical or electro-optical device comprising the PNLC light modulation element according to the present invention.
[0415] Said optical and electro optical devices include, without limitation electro-optical displays, liquid crystal displays (LCDs), non-linear optic (NLO) devices, optical information storage devices, light shutters, Smart Windows, privacy windows, lenses, virtual reality devices and augmented reality devices.
[0416] It will be appreciated that many of the features described above, particularly of the preferred embodiments, are inventive in their own right and not just as part of an embodiment of the present invention. Independent protection may be sought for these features in addition to, or alternative to any invention presently claimed.
[0417] 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. Alternative features serving the same, equivalent or similar purpose may replace each feature disclosed in this specification, unless stated otherwise. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
[0418] 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).
[0419] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.
[0420] The parameter ranges indicated in this application all include the limit values including the maximum permissible errors as known by the expert. The different upper and lower limit values indicated for various ranges of properties in combination with one another give rise to additional preferred ranges.
[0421] In the present application and especially in the following examples, the structures of the liquid crystal compounds are represented by abbreviations, which are also called “acronyms”. The transformation of the abbreviations into the corresponding structures is straightforward according to the following three tables A to C. Table A lists the symbols used for the ring elements, table B those for the linking groups and table C those for the symbols for the left hand and the right hand end groups of the molecules.
[0422] All groups C.sub.nH.sub.2n+1, C.sub.mH.sub.2m+1, and C.sub.lH2.sub.l+1 are preferably straight chain alkyl groups with n, m and l C-atoms, respectively, all groups C.sub.nH.sub.2n, C.sub.mH.sub.2m and C.sub.lH.sub.2l are preferably (CH.sub.2).sub.n, (CH.sub.2).sub.m and (CH.sub.2).sub.l, respectively and —CH═CH— preferably is trans-respectively E vinylene.
TABLE-US-00001 TABLE A Ring Elements C
TABLE-US-00002 TABLE B Linking Groups E —CH.sub.2—CH.sub.2— V —CH═CH— T —C≡C— W —CF.sub.2—CF.sub.2— B —CF═CF— Z —CO—O— ZI —O—CO— X —CF═CH— XI —CH═CF— O —CH.sub.2—O— OI —O—CH.sub.2— Q —CF.sub.2—O— QI —O—CF.sub.2—
TABLE-US-00003 TABLE C End Groups Left hand side, used alone or in Right hand side, used alone or in combination with others combination with others -n- C.sub.nH.sub.2n+1— -n —C.sub.nH.sub.2n+1 -nO- C.sub.nH.sub.2n+1—O— -nO —O—C.sub.nH.sub.2n+1 -V- CH.sub.2═CH— -V —CH═CH.sub.2 -nV- C.sub.nH.sub.2n+1—CH═CH— -nV —C.sub.nH.sub.2n—CH═CH.sub.2 -Vn- CH.sub.2═CH—C.sub.nH.sub.2n— -Vn —CH═CH—C.sub.nH.sub.2n+1 -nVm- C.sub.nH.sub.2n+1—CH═CH—C.sub.mH.sub.2m— -nVm —C.sub.nH.sub.2n—CH═CH—C.sub.mH.sub.2m+1 -N- N≡C— -N —C═N -S- S═C═N— -S —N═C═S -F- F— -F —F -CL- Cl— -CL —Cl -M- CFH.sub.2— -M —CFH.sub.2 -D- CF.sub.2H— -D —CF.sub.2H -T- CF.sub.3— -T —CF.sub.3 -MO- CFH.sub.2O— -OM —OCFH.sub.2 -DO- CF.sub.2HO— -OD —OCF.sub.2H -TO- CF.sub.3O— -OT —OCF.sub.3 -A- H—C≡C— -A —C≡C—H -nA- C.sub.nH.sub.2n+1—C≡C— -An —C≡C—C.sub.nH.sub.2n+1 -NA- N≡C—C≡C— -AN —C≡C—C≡N Left hand side, used in combination Right hand side, used in with others only combination with others only - . . . n . . . - —C.sub.nH.sub.2n— - . . . n . . . —C.sub.nH.sub.2n— - . . . M . . . - —CFH— - . . . M . . . —CFH— - . . . D . . . - —CF.sub.2— - . . . D . . . —CF.sub.2— - . . . V . . . - —CH═CH— - . . . V . . . —CH═CH— - . . . Z . . . - —CO—O— - . . . Z . . . —CO—O— - . . . ZI . . . - —O—CO— - . . . ZI . . . —O—CO— - . . . K . . . - —CO— - . . . K . . . —CO— - . . . W . . . - —CF═CF— - . . . W . . . —CF═CF—
[0423] wherein n und m each are integers and three points “ . . . ” indicate a space for other symbols of this table.
EXAMPLES
[0424] Compounds
[0425] Utilized Polymerisable Liquid Crystalline Compounds—Component A)
##STR00106##
[0426] Utilized Host Mixtures—Component B)
TABLE-US-00004 Mixture N-!: Composition [%-w/w] Physical properties PGP-3-2V 5.0 cl.p. [° C.]: 71 PGUQU-3-F 6.0 n.sub.e [589 nm, 20° C.]: 1.7142 PGUQU-4-F 6.0 n.sub.o [589 nm, 20° C.]: 1.5145 PGUQU-5-F 6.0 Δn [589 nm, 20° C.]: 0.1997 CP-3-O1 6.0 ε.sub.∥ [1 kHz, 20° C.]: 23.7 PGP-1-2V 6.0 ε.sub.⊥ [1 kHz, 20° C.]: 4.4 PGP-2-2V 7.0 Δε [1 kHz, 20° C.]: 19.4 CC-3-V 8.0 K.sub.1 [pN, 20° C.]: 16.6 CPU-3-F 10.0 K.sub.3 [pN, 20° C.]: 21.2 PGU-2-F 10.0 PGU-3-F 10.0 γ.sub.1 [mPa s, 20° C.]: 161 PP-1-2V1 10.0 PP-2-N 10.0 Σ 100.0
[0427] Utilized Chiral Compounds—Component C)
##STR00107##
[0428] Test Cells
[0429] Test cell 1: VHR AL16301 Type [0430] Cell gap=6 μm, no spacer [0431] Cell type=Antiparallel planar alignment type PI [0432] Electrode structure=ITO=200A, 1 cm×1 cm square pattern.
[0433] Test cell 2: VHR AL6301 Type [0434] Cell gap=6 μm, no spacer [0435] Cell type=Antiparallel planar alignment type PI [0436] Electrode structure=ITO=200A, 1 cm×1 cm square pattern.
[0437] Methods
[0438] Switching Speed Measurement:
[0439] Switching times are recorded either using a microscope or with a HeNe laser operating at 632.8 nm, with the sample placed between crossed polarizers in both cases. Transmitted light is received by a photodiode, which is connected to an oscilloscope in the microscope case, or connected to a data acquisition board in the laser case. The switching times are acquired from the oscilloscope or from analyzing the data acquired from the data acquisition board.
[0440] Haze
[0441] The haze level is determined in accordance to the ASTM D1003 standard definition of haze.
[0442] Four different transmission measurements (T1 to T4) are performed, which are commonly known by the skilled person:
[0443] T1: Transmission without sample and white reflection standard
[0444] T2: Transmission with sample and white reflection standard
[0445] T3: Transmission without sample with light trap
[0446] T4: Transmission with sample and with light trap
[0447] As commonly known by the skilled person, the total transmittance (T2) is thereby defined as the sum of the parallel transmittance and the diffusion transmittance (T4).
[0448] The Haze is thereby defined as follows: Haze=[(T4/T2)−(T3/T1)]×100%
[0449] The haze data is taken from the active area of the cell only. The glue is masked off from the measurement system to avoid inconsistencies
WORKING EXAMPLES
[0450] Experiment 1
[0451] Cholesteric LC mixtures are prepared as given in the following table. The corresponding mixtures are capillary filled in test cells 1 using capillary action at room temp, annealed for 1 h at 100° C. and then irradiated at the same temperature with linearly polarised UV light (35 mW/cm.sup.2) for the given time. The cells are then cooled to room temperature.
[0452] V.sub.op, t.sub.on and t.sub.off were measured using Speedy electrooptic microscope set up.
[0453] % Haze was measured in transmission mode in Shimadzu 3600 UV-Vis with a single wavelength of 550 nm. V.sub.op was determined to be when the maximum % haze was achieved. T.sub.on and T.sub.off were taken to be the time when switching between 10% and 90% switched. The results are summarized in the following table:
TABLE-US-00005 R-5011 RM-1 V.sub.op t.sub.on t.sub.off Haze Exp. LC Host [%- W/w] [%- w/w] [V] [ms] [ms] [%] 1.1* N-1 0 6 16 0.62 1.16 29.77 1.2* 0.5 0 9 6.74 51100 42.00 1.3 0.5 6 16 1.02 0.83 54.76 1.4 0.6 6 16 1.18 0.8 63.28 1.5 0.7 6 16 1.23 0.72 55.09 1.6 0.8 6 16 1.44 0.71 58.8 1.7 0.9 6 16 1.68 0.69 57.79 1.8 1 6 23 0.81 0.58 32.05
[0454] As seen above, with a chiral system a good level of haze can be achieved compared to without a chiral system (c.f Exp. 1.1). Crucially in the polymer network chiral systems, the t.sub.off times are dramatically smaller than systems without a polymer network (c.f Exp. 1.2) showing good relaxation to the well-ordered state.
[0455] Experiment 2
[0456] The cholesteric LC mixtures are prepared as given in the following table. The corresponding mixtures are capillary filled in test cells 2 using capillary action at room temp, annealed for 1 h at 100° C. and then irradiated at the same temperature with linearly polarised UV light (35 mW/cm.sup.2) for the given time. The cells are then cooled to room temperature.
[0457] V.sub.op, t.sub.on and t.sub.off were measured using Speedy electrooptic microscope set up.
[0458] % Haze was measured in transmission mode in Shimadzu 3600 UV-Vis with a single wavelength of 550 nm. V.sub.op was determined to be when the maximum % haze was achieved. T.sub.on and T.sub.off were taken to be the time when switching between 10% and 90% switched. The results are summarized in the following table:
TABLE-US-00006 R-5011 RM-1 V.sub.op t.sub.on t.sub.off Haze Exp. LC Host [%- W/w] [%- w/w] [V] [ms] [ms] [%] 2.1* N-1 0 0 8 2.9 5.6 19.39 2.2 0.5 6 12 2.4 1.2 51.75 2.3 0.6 6 12 1.95 0.75 52.05 2.4 0.7 6 12 1.99 0.95 51.48 2.5 0.8 6 12 2.05 1.15 59.31 2.6 0.9 6 12 2.38 1.07 54.01 2.7 1 6 12 2.7 0.72 49.03
[0459] As seen above, a reduced cell thickness has the effect of reducing V.sub.op compared to a thicker cell as given in experiment 1. This also slightly reduces the maximum % haze achieved.