LIQUID-CRYSTAL MEDIA AND LIGHT MODULATION ELEMENT

Abstract

The present invention relates to liquid crystalline (LC) medium, to a method of its production and to the use of such LC media in polymer network liquid crystalline (PNLC) light modulation elements operated in the reverse mode. Furthermore, the present invention relates to such light modulation elements, as such, to the use of such light modulation elements as light shutters for transparent OLED displays, and to a method of production of such light modulation elements according to the present invention.

Claims

1. A liquid-crystalline medium having a negative dielectric anisotropy comprising one or more compounds of formula I,
P.sup.a-(Sp.sup.a).sub.s1-(A.sup.1-Z.sup.1).sub.n1-A.sup.2-Q.sup.1-A.sup.3-(Z.sup.4-A.sup.4).sub.n2-(Sp.sup.b).sub.s2-P.sup.b  I in which the individual radicals have the following meanings: P.sup.a denotes a polymerizable group, P.sup.b denotes a polymerizable group, H or F, Sp.sup.a, Sp.sup.b each, independently of one another, denote a spacer group, s1, s2 each, independently of one another, denote 0 or 1, n1, n2 each, independently of one another, denote 0 or 1, Q.sup.1 denotes —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2, —(CO)O—, —O(CO)—, —(CH.sub.2).sub.4—, —CH.sub.2CH.sub.2—, —CF.sub.2—CF.sub.2—, —CF.sub.2—CH.sub.2—, —CH.sub.2—CF.sub.2—, —CH═CH—, —CF═CF—, —CF═CH—, —(CH.sub.2).sub.3O—, —O(CH.sub.2).sub.3—, —CH═CF—, —C≡C—, —O—, —CH.sub.2—, —(CH.sub.2).sub.3—, or —CF.sub.2—, Z.sup.1, Z.sup.4 denote a single bond, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —(CO)O—, —O(CO)—, —(CH.sub.2).sub.4—, —CH.sub.2CH.sub.2—, —CF.sub.2—CF.sub.2—, —CF.sub.2—CH.sub.2—, —CH.sub.2—CF.sub.2—, —CH═CH—, —CF═CF—, —CF═CH—, —(CH.sub.2).sub.3O—, —O(CH.sub.2).sub.3—, —CH═CF—, —C≡C—, —O—, —CH.sub.2—, —(CH.sub.2).sub.3—, or —CF.sub.2—, where Z.sup.1 and Q.sup.1 or Z.sup.2 and Q.sup.1 do not simultaneously denote a group selected from —CF.sub.2O— and —OCF.sub.2—, A.sup.1, A.sup.2, A.sup.3, A.sup.4 each, independently of one another, denotes a radical selected from the following groups: a) the group consisting of 1,4-phenylene and 1,3-phenylene, in which, in addition, one or two CH groups may each be replaced by N and in which, in addition, one or more H atoms may each be replaced by L, b) the group consisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene and 1,4′-bicyclohexylene, in which, in addition, one or more non-adjacent CH.sub.2 groups may each be replaced by —O— and/or —S— and in which, in addition, one or more H atoms may each be replaced by F or Cl, c) the group consisting of tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl and selenophene-2,5-diyl, each of which may, in addition, be mono- or polysubstituted by L, and d) the group consisting of saturated, partially unsaturated or fully unsaturated, and optionally substituted, polycyclic radicals having 5 to 20 cyclic C atoms, one or more of which may also be replaced by heteroatoms, L denotes on each occurrence, identically or differently, F, Cl, CN, SCN, SF.sub.5 or straight-chain or branched, in each case optionally fluorinated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms,

2. A liquid-crystalline medium according to claim 1, wherein Q.sup.1 in formula I denotes a group —CF.sub.2O—.

3. A liquid-crystalline medium according to claim 1, wherein A.sup.2 and A.sup.3 in formula I denotes independently of one another, denote 1,4-phenylene or 1,3-phenylene, in which, in addition, one or more H atoms may each be replaced by L, and wherein L denotes on each occurrence, identically or differently, F, Cl, CN, SCN, SF.sub.5 or straight-chain or branched, in each case optionally fluorinated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms.

4. A liquid-crystalline medium according to claim 1, wherein said medium contains one or more compounds of following formula ##STR00098## in which P.sup.a, P.sup.b, Sp.sup.a, Sp.sup.b, s1, s2 are as defined in claim 1, and L.sup.3 and L.sup.4, independently of one another, denote H or F.

5. A liquid-crystalline medium according to claim 1, wherein said medium additionally comprises one or more other polymerizable compounds and/or one or more unpolymerizable liquid-crystalline compounds.

6. A liquid-crystalline medium according to claim 1, wherein said medium comprises one or more compounds of formulae II and/or III, ##STR00099## in which A denotes 1,4-phenylene or trans-1,4-cyclohexylene, a is 0 or 1, R.sup.3 denotes alkenyl having 2 to 9 C atoms, and R.sup.4 denotes 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—, —CH═CH—, ##STR00100##  —O—, —CO—O—, or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, preferably alkyl having 1 to 12 C atoms or alkenyl having 2 to 9 C atoms.

7. A liquid-crystalline medium according to claim 1, wherein said medium comprises one or more compounds of formula N, ##STR00101## in which 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—, ##STR00102##  —O—, —CO—O—, or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, 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, trans-1,4-cyclohexylene, in which, in addition, one or two CH.sub.2 groups may each be replaced by —O—, or 1,4-cyclohexenylene, Z.sup.N1 and Z.sup.N2 each, independently of one another, denote a single bond, —CH.sub.2CH.sub.2—, —COO—, —OCO—, —C≡C—, —CH.sub.2O—, —OCH.sub.2—, —CF.sub.2O—, —OCF.sub.2— or —CH═CH—, and n denotes 0, 1 or 2.

8. A liquid-crystalline medium according to claim 1, wherein said medium comprises one or more compounds selected from the group of the compounds of formulae Y-1, Y-2, Y-3 and Y-4, ##STR00103## in which R.sup.2A denotes H, 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—, —CH═CH—, ##STR00104##  —O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, L.sup.1 and L.sup.2 each, independently of one another, denote F, Cl, CF.sub.3 or CHF.sub.2, preferably each denote F, Z.sup.2 and Z.sup.2′ each, independently of one another, denote a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —CF═CF— or —CH═CHCH.sub.2O—, p denotes 0, 1 or 2, q denotes 0 or 1, (O)C.sub.vH.sub.2v+1 denotes OC.sub.vH.sub.2v+1 or C.sub.vH.sub.2v+1, and v denotes 1 to 6.

9. A liquid-crystalline medium according claim 1, wherein said medium comprises one or more dichroic dyes.

10. A process for the preparation of an medium according to claim 1, said process comprising mixing one or more liquid-crystalline compounds or a liquid-crystal medium with one or more compounds of the formula I.

11. Use of a medium according to claim 1 in a light modulation element.

12. A light modulation element containing an medium according to claim 1.

13. A light modulation element according to claim 12, wherein said element is a polymer network liquid crystalline (PNLC) light modulation element operated in the reverse mode.

14. A light modulation element according to claim 12, wherein said element comprises an LC cell having two substrates and two electrodes, where at least one substrate is transparent to light and at least one substrate has one or two electrodes, and a layer, located between the substrates, of an LC medium comprising a polymerized component and a low-molecular-weight component, where the polymerized component is obtainable by polymerization of one or more polymerizable compounds between the substrates of the LC cell in the LC medium, wherein at least one of the polymerizable compounds is a compound of the formula I.

15. A process for production of a light modulation element according to claim 12, said process comprising: cutting and cleaning of the substrates, providing electrode structures on each of the substrates, optionally coating of a dielectric layer on the electrode structure, optionally providing an alignment layer on the electrode structure, assembling the cell using an adhesive (UV or heat curable) with spacer, filling the cell with the LC medium, and exposing the LC medium to actinic radiation that induces photopolymerization of the polymerizable compounds.

16. A light modulation element according to claim 12, wherein said element is a light shutter for a transparent OLED display.

Description

DETAILED DESCRIPTION

[0110] In a preferred embodiment of the invention, P.sup.a and/or P.sup.b in formula I denote a radical containing two or more polymerizable groups (multifunctional polymerizable radicals). Suitable radicals of this type and polymerizable compounds containing them and the preparation thereof are described, for example, in U.S. Pat. No. 7,060,200 B1 or US 2006/0172090 A1. Particular preference is given to multifunctional polymerizable radicals selected from the following formulae:

—X-alkyl-CHP.sup.1—CH.sub.2—CH.sub.2P.sup.2  I*a

—X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)—CH.sub.2P.sup.3  I*b

—X-alkyl-CHP.sup.1CHP.sup.2—CH.sub.2P.sup.3  I*c

—X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)—C.sub.aaH.sub.2aa+1  I*d

—X-alkyl-CHP.sup.1—CH.sub.2P.sup.2  I*e

—X-alkyl-CHP.sup.1P.sup.2  I*f

—X-alkyl-CP.sup.1P.sup.2—C.sub.aaH.sub.2aa+1  I*g

—X-alkyl-C(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)—CH.sub.2OCH.sub.2—C(CH.sub.2P.sup.3)(CH.sub.2P.sup.4)CH.sub.2P.sup.5  I*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.2—C.sub.aaH.sub.2aa+1  I*k

—X-alkyl-C(CH.sub.3)(CH.sub.2P.sup.1)(CH.sub.2P.sup.2)  I*m

in which [0111] 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.0)═C(R.sup.00)—, —C≡C—, —N(R.sup.00)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, or —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 each be replaced by F, Cl or CN, where R.sup.0 and R.sup.00 have the meanings indicated above, [0112] aa and bb each, independently of one another, denote 0, 1, 2, 3, 4, 5 or 6, [0113] X has one of the meanings indicated for X′, and [0114] P.sup.1-5 each, independently of one another, have one of the meanings indicated for P.sup.a. [0115] A.sup.1, A.sup.2, A.sup.3 and A.sup.4 in formula I preferably each, independently of one another, denote a radical as given above, particularly preferably selected from the group consisting of the following formulae:

##STR00008## ##STR00009##

in which the individual rings may also additionally be mono- or polysubstituted by L as described above and below.

[0116] A.sup.1, A.sup.2, A.sup.3 and A.sup.4 in formula I particularly preferably each, independently of one another, denote a radical selected from the group consisting of the following formulae:

##STR00010##

[0117] A.sup.1, A.sup.2, A.sup.3 and A.sup.4 in formula I furthermore preferably each, independently of one another, denote a radical selected from the group consisting of the following formulae:

##STR00011##

[0118] Further particularly preferred compounds of the formula I and sub-formulae thereof indicated above and below are those in which [0119] Q.sup.1 denotes a group —CF.sub.2O—, [0120] Q.sup.1 denotes a group —OCF.sub.2—, [0121] s1 and s2 each denote 1, [0122] n1 and n2 each denote 0, [0123] n1 denotes 1 and n2 denotes 0 or n1 denotes 0 and n2 denotes 1, [0124] A.sup.3 denotes a group of the formula

##STR00012## [0125] A.sup.2 denotes a group of the formula

##STR00013##

particularly preferably

##STR00014## [0126] A.sup.2 and Q.sup.1 together denote a group of the formula

##STR00015## [0127] in which L.sup.1 and L.sup.2 independently denote H, Cl or F, preferably L.sup.1=F and L.sup.2 denotes H or F, and particularly preferably L.sup.1 and L.sup.2 both denote F.

[0128] The compounds of the formula I are therefore particularly preferably compounds of the formula

##STR00016##

in which P.sup.a, P.sup.b, Sp.sup.a, Sp.sup.b, s1, s2 are as defined for formula I, and L.sup.3 and L.sup.4, independently of one another, denote H or F.

[0129] A high degree of fluorination in the rings A.sup.2 and A.sup.3 makes the polymerizable compounds very readily combinable with mixtures of compounds containing polyfluorinated aromatic rings.

[0130] Particularly preferred compounds of the formula I are selected from the group consisting of the following formulae:

##STR00017## ##STR00018## ##STR00019## ##STR00020## ##STR00021##

in which L on each occurrence, identically or differently, has one of the meanings indicated above and below, r denotes 0, 1, 2, 3 or 4, s denotes 0, 1, 2 or 3, and n denotes an integer between 1 and 20 preferably between 1 and 12, very particularly preferably between 2 and 8, and in which, if a radical at the end of a single or double bond is not named, it is a terminal CH.sub.3 or CH.sub.2 group. r is preferably 0, 1 or 2, and particularly preferably 1 or 2. Of these, very particular preference is given to the compounds of the formulae I1, I2, I3 and I4 and very particularly the compounds of the formulae I1 and I2, especially the compounds of the formulae I2.

[0131] In the formulae I1-I28,

##STR00022##

preferably denotes a group selected from the group consisting of the following formulae:

##STR00023##

particularly preferably

##STR00024##

[0132] Of the compounds of the formula I, preference is given to those containing two ring systems (n1, n2=0), in particular compounds selected from the compounds of the formulae Ia to Iq:

##STR00025## ##STR00026## ##STR00027##

in which P.sup.a, P.sup.b, Sp.sup.a, Sp.sup.b, s1 and s2 are as defined for formula I. Sp.sup.a/b here preferably denote an alkylene group —(CH.sub.2).sub.n—, where n=3, 4, 5, 6 or 7, and P.sup.a/b preferably denote a methacrylate or acrylate group or H, in particular a methacrylate or acrylate group. Of these, particular preference is given to the compounds of the formulae Ia, Ib, Ic, Id, Ie, If, Ig and Ih and very particularly of the formula Ia.

[0133] Of the compounds of the formula I, particular preference is given to those in which [0134] the radicals P.sup.a and P.sup.b are selected from the group consisting of vinyloxy, acrylate, methacrylate, fluoroacrylate, chloroacrylate, oxetane and epoxide groups, particularly preferably acrylate or methacrylate groups, [0135] the radicals Sp.sup.a and Sp.sup.b are selected from the group consisting of —(CH.sub.2).sub.p1—, —(CH.sub.2).sub.p1—O—, —(CH.sub.2).sub.p1—O—CO— and —(CH.sub.2).sub.p1—O—CO—O— and mirror images thereof, in which p1 denotes an integer from 1 to 12, preferably from 1 to 6, particularly preferably 1, 2 or 3, where these radicals are linked to P.sup.a or P.sup.b in such a way that O atoms are not directly adjacent.

[0136] The compounds 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.

[0137] Particularly suitable and preferred processes for the preparation of compounds of the formula I and sub-formulae thereof are described, for example in EP 2714844 A1.

[0138] The polymerizable compounds of formula I can be polymerized individually, but it is also possible to polymerize mixtures which comprise two or more polymerizable compounds according to the invention, or mixtures comprising one or more polymerizable compounds according to the invention and one or more further polymerizable compounds (co-monomers), which are preferably mesogenic or liquid-crystalline. In the case of polymerization of such mixtures, copolymers form. Preference is given to the use of a mixture comprising two or more compounds according to the invention or a mixture comprising one or more compounds according to the invention with one or more further polymerizable compounds. The invention furthermore relates to the polymerizable mixtures mentioned above and below. The further polymerizable compounds and co-monomers are mesogenic or non-mesogenic, preferably mesogenic or liquid-crystalline.

[0139] Suitable and preferred comonomers for use in displays according to the invention are selected, for example, from the following formulae:

##STR00028## ##STR00029## ##STR00030## ##STR00031## ##STR00032##

in which the individual radicals have the following meanings: [0140] P.sup.1 and P.sup.2 each, independently of one another, denote a polymerizable group, preferably having one of the meanings indicated above and below for P.sup.a, particularly preferably an acrylate, methacrylate, fluoroacrylate, oxetane, vinyloxy or epoxide group, [0141] Sp.sup.1 and Sp.sup.2 each, independently of one another, denote a single bond or a spacer group, preferably having one of the meanings indicated above and below for Sp.sup.a, particularly preferably —(CH.sub.2).sub.p1—, —(CH.sub.2).sub.p1—O—, —(CH.sub.2).sub.p1—CO—O— or —(CH.sub.2).sub.p1—O—CO—O—, in which p1 is an integer from 1 to 12, where the linking to the adjacent ring in the last-mentioned groups takes place via the O atom, [0142] where, in addition, one or more of the radicals P.sup.1-Sp.sup.1- and P.sup.2-Sp.sup.2- may denote a radical R.sup.aa, with the proviso that at least one of the radicals P.sup.1-Sp.sup.1- and P.sup.2-Sp.sup.2- present does not denote R.sup.aa, [0143] 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 [0144] C(R.sup.0)═C(R.sup.00)—, —C≡C—, —N(R.sup.0)—, —O—, —S—, —CO—, —CO—O—, —O—CO—, or —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 each 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 or alkylcarbonyloxy 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), [0145] R.sup.0, R.sup.00 each, independently of one another and on each occurrence identically or differently, denote H or alkyl having 1 to 12 C atoms, [0146] Z.sup.1 denotes —O—, —CO—, —C(R.sup.yR.sup.z)— or —CF.sub.2CF.sub.2—, [0147] R.sup.y and R.sup.z each, independently of one another, denote H, F, CH.sub.3 or CF.sub.3, [0148] 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, [0149] L on each occurrence, identically or differently, denotes F, Cl, CN, SCN, SF.sub.5 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, [0150] L′ and L″ each, independently of one another, denote H, F or Cl, [0151] r denotes 0, 1, 2, 3 or 4, [0152] s denotes 0, 1, 2 or 3, [0153] t denotes 0, 1 or 2, [0154] x denotes 0 or 1.

[0155] Particular preference is given to an LC medium, a light modulation element, a process or the use as described above and below in which the LC medium or the polymerizable or polymerized component present therein does not comprise any compounds of the following formula:

##STR00033##

in which P.sup.a, P.sup.b, Sp.sup.a, Sp.sup.b, s1, s2 and L have the meanings indicated above and below, r denotes 0, 1, 2, 3 or 4, and Z.sup.2 and Z.sup.3 each, independently of one another, denote —(CO)O— or —O(CO)—.

[0156] Suitable and preferred comonomers for the LC medium according to the invention are selected, for example, from monoreactive compounds, preferably in an amount of 1 to 9%, particularly preferably 4 to 7%. Preferred monoreactive compounds are those of the formulae M1 to M29 in which one or more of the radicals P.sup.1-Sp.sup.1- and P.sup.2-Sp.sup.2- denote a radical R.sup.aa, meaning that only one reactive group is present.

[0157] The compounds of the formula M1 to M29 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.

[0158] For the production of light modulation elements according to the invention, the polymerizable compounds are polymerized or crosslinked (if one compound contains two or more polymerizable groups) by in-situ polymerization in the LC medium between the substrates of the LC light modulation element with application of a voltage. The polymerization can be carried out in one step. It is also possible firstly to carry out the polymerization with application of a voltage in a first step in order to generate a pretilt angle, and subsequently, in a second polymerization step without an applied voltage, to polymerize or crosslink the compounds, which have not reacted in the first step (“end curing”).

[0159] Suitable and preferred polymerization methods are, for example, thermal or photopolymerization, preferably photopolymerization, in particular UV photopolymerization. One or more initiators can optionally also be added here. Suitable conditions for the polymerization and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Suitable for free-radical polymerization are, for example, the commercially available photoinitiators from the Irgacure® series (Ciba AG), such as Irgacure651®, Irgacure184®, Irgacure907®, Irgacure369® or Darocure 1173® (Ciba AG). If an initiator is employed, its proportion is preferably 0.001 to 5% by weight, particularly preferably 0.001 to 1% by weight.

[0160] The polymerizable compounds of formula I are also suitable for polymerization without an initiator, which is accompanied by considerable advantages, such as, for example, lower material costs and in particular less contamination of the LC medium by possible residual amounts of the initiator or degradation products thereof. The polymerization can thus also be carried out without the addition of an initiator. In a preferred embodiment, the LC medium thus comprises no polymerization initiator.

[0161] Particularly preferred LC media for use in light modulation elements according to the present invention are described below and preferably comprise: [0162] >5%, preferably >7%, more preferably >9, especially 15%, but not more than 30% of the polymerizable compounds, [0163] >5%, preferably >7%, more preferably >9, especially 15%, but not more than 30% of the polymerizable compounds of the formula I mentioned above or sub-formulae thereof, [0164] one, two or three polymerizable compounds of the formula I or sub-formulae thereof according to the invention, [0165] a polymerizable component which comprises exclusively polymerizable compounds of the formula I or sub-formulae thereof according to the invention, [0166] a polymerizable and/or liquid-crystalline component which comprises exclusively achiral compounds, [0167] a polymerizable component which comprises one or more polymerizable compounds containing one polymerizable group (monoreactive) and one or more polymerizable compounds according to the invention containing two or more, preferably two, polymerizable groups (di- or multireactive), preferably selected from compounds of the formula I or sub-formulae thereof, and optionally from the above-mentioned comonomers selected from the list comprising the formulae M1-M29, [0168] a polymerizable component which comprises exclusively polymerizable compounds according to the invention containing two polymerizable groups (direactive), preferably selected from compounds of the formula I or sub-formulae thereof, and optionally additionally from the above-mentioned co-monomers from the list comprising the formulae M1-M29, [0169] 1 to 5, preferably 1, 2 or 3, polymerizable compounds, preferably selected from polymerizable compounds according to the invention, in particular of the formula I or sub-formulae thereof.

[0170] In a preferred embodiment, the LC media according to the present invention comprises beside the polymerizable component additionally one or more unpolymerizable LC compounds, which form the liquid crystalline component of the LC medium that has preferably a nematic liquid-crystal phase.

[0171] The liquid-crystalline component according to the present invention consists of several compounds, preferably of 2 to 30, more preferably of 3 to 20 and most preferably of 4 to 16 compounds. These compounds are mixed in conventional way.

[0172] Preferably, the liquid crystalline component comprises one or more unpolymerizable LC compounds selected from compounds indicated below: [0173] the medium comprises one or more dielectrically neutral compounds of the formulae II and/or III,

##STR00034## [0174] in which [0175] A denotes 1,4-phenylene or trans-1,4-cyclohexylene, [0176] a is 0 or 1, [0177] R.sup.3 denotes alkenyl having 2 to 9 C atoms, and [0178] R.sup.4 denotes 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—, —CH═CH—,

##STR00035##

—O—, —CO—O—, or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, preferably alkyl having 1 to 12 C atoms or alkenyl having 2 to 9 C atoms. [0179] The compounds of the formula II are preferably selected from the following formulae:

##STR00036## [0180] in which R.sup.3a and R.sup.4a each, independently of one another, denotes H, CH.sub.3, C.sub.2H.sub.5 or C.sub.3H.sub.7, and “alkyl” denotes a straight-chain alkyl group having 1 to 8 C atoms. Particular preference is given to compounds of the formulae IIa and IIf, in particular, in which R.sup.3a denotes H or CH.sub.3, and compounds of the formula IIc, in particular in which R.sup.3a and R.sup.4a denote H, CH.sub.3 or C.sub.2H.sub.5.

[0181] Preference is furthermore given to compounds of the formula II which have a non-terminal double bond in the alkenyl side chain:

##STR00037## [0182] Very particularly preferred compounds of the formula II are the compounds of the formulae

##STR00038## ##STR00039## [0183] Of the compounds of the formulae IIa-1 to IIa-19, particular preference is given, in particular, to the compounds of the formulae IIa-1, IIa-2, IIa-3 and IIa-5. [0184] Besides one or more compounds of the formula I, the liquid-crystalline component according to the invention particularly preferably comprise 5-70% by weight, in particular 10-50% by weight and very particularly preferably 15-40% by weight, of compounds of the formula

##STR00040## [0185] The compounds of the formula III are preferably selected from the following formulae:

##STR00041## [0186] in which “alkyl” and R.sup.3a have the meanings indicated above, and R.sup.3a preferably denotes H or CH.sub.3. Particular preference is given to compounds of the formula IIIb; [0187] Very particular preference is given to the compound of the formula IIIb-1,

##STR00042## [0188] in which “alkyl” has the meaning indicated above and preferably denotes CH.sub.3, furthermore C.sub.2H.sub.5 or n-C.sub.3H.sub.7. [0189] Preferred mixtures comprise at least one compound from the group S-1, S-2, S-3 and S-4,

##STR00043## [0190] in which [0191] R.sup.0 denotes H, F or straight-chain or branched alkyl having 1 to 12 C atoms, in which, in addition, one or more H atoms may each be replaced by F, alkyl denotes a straight-chain alkyl radical having 1 to 9 C atoms, preferably 2 to 6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms, since these compounds help, inter alia, to suppress the smectic phases of the mixtures. [0192] The liquid-crystalline component preferably comprises one or more neutral compounds of the general formula N,

##STR00044## [0193] in which [0194] 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—, —CH═CH—, —CF.sub.2O—,

##STR00045##

—O—, —CO—O—, or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, [0195] 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, trans-1,4-cyclohexylene, in which, in addition, one or two CH.sub.2 groups may each be replaced by —O—, or 1,4-cyclohexenylene, [0196] Z.sup.N1 and Z.sup.N2 each, independently of one another, denote a single bond, —CH.sub.2CH.sub.2—, —COO—, —OCO—, —C≡C—, —CH.sub.2O—, —OCH.sub.2—, —CF.sub.2O—, —OCF.sub.2— or —CH═CH—, [0197] n denotes 0, 1 or 2. [0198] Preferred compounds of the formula N are shown below:

##STR00046## ##STR00047## ##STR00048## ##STR00049## [0199] in which [0200] 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. [0201] Of the compounds of the formula N, particular preference is given to the compounds of the formulae N-1, N-2, N-3, N-4, N-8, N-9, N-14, N-15, N-17, N-18, N-19, N-20, N-21, N-22, N-23, N-24, N-25, N-31, N-33 and N-36. [0202] The liquid-crystalline component preferably comprises one or more compounds selected from the group of the compounds of the formulae Y-1, Y-2, Y-3 and Y-4,

##STR00050## [0203] in which [0204] R.sup.2A denotes H, 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—, —CH═CH—,

##STR00051##

—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and in which, in addition, one or more H atoms may each be replaced by halogen, [0205] L.sup.1 and L.sup.2 each, independently of one another, denote F, Cl, CF.sub.3 or CHF.sub.2, preferably each denote F, [0206] Z.sup.2 and Z.sup.2′ each, independently of one another, denote a single bond, —CH.sub.2CH.sub.2—, —CH═CH—, —CF.sub.2O—, —OCF.sub.2—, —CH.sub.2O—, —OCH.sub.2—, —COO—, —OCO—, —C.sub.2F.sub.4—, —CF═CF— or —CH═CHCH.sub.2O—, [0207] p denotes 0, 1 or 2, [0208] q denotes 0 or 1, [0209] (O)C.sub.vH.sub.2v+1 denotes OC.sub.vH.sub.2v+1 or C.sub.vH.sub.2v+1, and [0210] v denotes 1 to 9, preferably 1 to 6. [0211] Particularly preferred compounds of the formulae Y-1 to Y-4 are shown below:

##STR00052## ##STR00053## ##STR00054## ##STR00055## [0212] in which [0213] 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 and (O) denotes —O— or a single bond. [0214] Of the said compounds, particular preference is given to the compounds of the formulae Y-1a, Y-1c, Y-1e, Y-1g, Y-1j, Y-1r, Y-1t, Y-2b, Y-2h, Y-2j and Y-3a.

[0215] The compounds of the formulae II, III, N and Y-1 to Y-4 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.

[0216] Other mesogenic compounds which are not mentioned explicitly above can also optionally and advantageously be used in the LC media in accordance with the present invention. Such compounds are known to the person skilled in the art.

[0217] In a preferred embodiment, the liquid-crystalline component according to the invention having negative dielectric anisotropy are characterized by optical anisotropy values as high as possible. The birefringence values are preferably in the range from 0.065 or more to 0.300 or less, more preferably in the range from 0.090 or more to 0.250 or less, especially in the range from 0.095 or more to 0.200 or less, in particular in the range from 0.100 or more to 0.175 or less.

[0218] Preferably, the liquid-crystalline component according to the invention having negative dielectric anisotropy are characterized by relatively high values of the modulus of the dielectric anisotropy (|Δ∈|), preferably as high as possible. In a preferred embodiment, values of the modulus of the dielectric anisotropy (|Δ∈|) are preferably in the range from 1.0 or more to 10 or less, preferably from 2 or more to 8 or less, particularly preferably from 3 or more to 7 or less and very particularly preferably from 4 or more to 6 or less.

[0219] The nematic phase of the liquid-crystalline component 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.

[0220] Preferably, the liquid-crystalline component according to the present invention are characterized by relatively high values for the elastic constant K11, preferably as high as possible. In a preferred embodiment, the elastic constant K11 is approximately 10 pN or more, more preferably approximately 12 pN or more.

[0221] The liquid-crystalline component according to the present invention preferably have an elastic constant K33 of approximately 30 pN or less, more preferably of approximately 20 pN or less.

[0222] The rotational viscosity of the liquid-crystalline component is preferably as low as possible. Typically, the media according to the present invention, exhibit a rotational viscosity of approximately 400 mPas or less, preferably of approximately 300 mPas or less.

[0223] The optimum mixing ratio of the compounds of the above-mentioned formulae 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.

[0224] The total amount of compounds of the above-mentioned formulae in the liquid-crystalline component according to the invention is not crucial. The liquid-crystalline component may therefore comprise one or more further components for the purposes of optimization of various properties. Preferred compounds which, besides one, two or more compounds of the formula I, can be employed in a liquid-crystalline medium according to the invention having negative dielectric anisotropy are indicated below: [0225] the medium preferably comprises one or more compounds of the formula II, preferably selected from the group of the compounds of the formulae CC-n-V and CC-n-Vm, preferably CC-3-V, CC-3-V1, CC-4-V and CC-5-V, particularly preferably selected from the group of the compounds CC-3-V, CC-3-V1 and CC-4-V, very particularly preferably the compound CC-3-V, and optionally additionally the compound CC-4-V and/or CC-3-V1, [0226] the medium preferably comprises the compound PP-1-2V1, [0227] the medium preferably comprises one or more compounds of the formula Y-1, preferably of the formula Y-1c, selected from the group of the compounds of the formulae CY-3-O2, CY-3-O4, CY-5-O2 and CY-5-O4, [0228] the medium preferably comprises one or more compounds of the formula Y-1, preferably selected from the group of the compounds of the formulae Y-1e and Y-1d, preferably of the formula CCY-n-Om, preferably selected from the group of the compounds of the formulae CCY-3-O2, CCY-2-O2, CCY-3-O1, CCY-3-O3, CCY-4-O2, CCY-3-O2 and CCY-5-O2, [0229] the medium preferably comprises one or more compounds of the formula Y-2, preferably of the formula Y-2b, preferably selected from the group of the compounds of the formulae CPY-2-O2, CPY-3-O2, CPY-4-O2 and CPY-5-O2, [0230] the medium preferably comprises one or more compounds of the formula Y-2h, preferably selected from the group of the compounds of the formulae PY-3-O2, PY-1-O4 and PY-4-O2, [0231] the medium preferably comprises one or more compounds of the formula Y-3, preferably selected from the group of the compounds of the formulae PYP-2-3 and PYP-2-4, [0232] the medium preferably optionally comprises one or more compounds of the formula Y-4, preferably of the formula CLY-n-Om, preferably selected from the group of the compounds of the formulae CLY-2-O4, CLY-3-O2 and CLY-3-O3, [0233] the medium preferably comprises compounds of the formulae Y-1 to Y-4 in an amount of 20 to 99% by weight in the mixture as a whole, [0234] the medium preferably comprises 1% by weight or more to 60% by weight or less, preferably 3% by weight or more to 50% by weight or less, particularly preferably 5% by weight or more to 45% by weight or less, of compounds of the formulae II and/or III, [0235] the medium preferably comprises 45% by weight or more to 80% by weight or less of compounds of the formulae Y-1 to Y-4, [0236] the medium preferably comprises 10% by weight or more to 40% by weight or less of compounds of the formula Y-1, [0237] the medium preferably comprises 10% by weight or more to 40% by weight or less of compounds of the formula Y-2, [0238] the medium preferably comprises 10% by weight or more to 40% by weight or less of compounds of the formula Y-3, [0239] the medium preferably comprises 0% by weight or more to 40% by weight or less of compounds of the formula Y-4.

[0240] Furthermore, it is possible to add to the LC media, for example, 0 to 15% by weight of pleochroic dyes, furthermore nanoparticles, conductive salts, preferably ethyldimethyldodecylammonium 4-hexoxybenzoate, tetrabutyl-ammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. 24, 249-258 (1973)), for improving the conductivity, or substances for modifying the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.

[0241] The LC media according to the present invention preferably also comprise one or more stabilizers in order to prevent undesired spontaneous polymerization of the RMs, for example during storage or transport. Suitable types and amounts of stabilizers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the commercially available stabilizers from the Irganox® series (Ciba AG), such as, for example, Irganox® 1076. If stabilizers are employed, their proportion, based on the total amount of RMs or the polymerizable component, is preferably 10-10,000 ppm, particularly preferably 50-500 ppm.

[0242] The LC media according to the present invention preferably also comprise one or more dyes, preferably one or more dichroic dyes.

[0243] Preferably, the dichroic dyes are selected from the group of perylene dyes, anthrachinone dyes, and/or azo dyes.

[0244] More preferably, the dichroic dyes are selected from the group of compounds of formula D,

##STR00056## [0245] wherein,

##STR00057## [0246] are at each occurrence, identically or differently, selected from

##STR00058## [0247] and, in case i is 2 or more, the terminal one of group

##STR00059## [0248] may also be

##STR00060## [0249] and, in case j is 2 or more, the terminal one of group

##STR00061## [0250] may also be

##STR00062## [0251] Z.sup.11 and Z.sup.12 are, independently of each other, —N═N—, —OCO— or —COO—, [0252] R.sup.11 and R.sup.12 are, independently of each other, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy, alkenyl, alkenyloxy, alkoxyalkyl or fluorinated alkenyl, alkylaminyl, dialkylaminyl, alkylcarbonyl, alkyloxycarbonyl, alkylcarbonyloxy, alkyloxycarbonyloxy or alkylcyclohexylalkyl, and [0253] i and j are independently of each other 1, 2, 3 or 4.

[0254] In a preferred embodiment of the present invention, the liquid crystalline medium comprises one or more dichroic dyes preferably selected from the group of compounds of formulae D-1 to D-7,

##STR00063##

wherein the parameters have the respective meanings given under formula I above.

[0255] In a preferred embodiment of the present invention, the liquid crystalline medium comprises one or more dichroic dyes preferably selected from the group of compounds of formulae D′-1 to D′-7

##STR00064##

wherein the parameters have the respective meanings given under formula I above.

[0256] Further preferred compounds of formula I are represented by the following formulae

##STR00065##

[0257] Preferably the concentration of the dichroic dyes in the medium is in the range from 0.1% to 5%, more preferably from 0.2% to 4%, even more preferably from 0.3% to 3%, most preferably from 0.5% to 2% and in particular about 1%.

[0258] In a preferred embodiment, the medium comprises a mixture of two or more, preferably of three or more dichroic dyes. Most preferably three dichroic dyes are at present. Preferably, the dichroic dyes have mutually complementing absorption spectra to each other, i. e. complementary absorption colors and are preferably mixed in a ratio relative to each other which results in a neutral color of the combined absorption of the mixture, i. e. in a black appearance. This means that the absorption is almost constant over the visible spectral range.

[0259] For example, the spectral characteristic of a preferred combination of three compounds D′-1a, D′-4a and D′-5a are given in the following table:

TABLE-US-00001 D′-1a D′-4a D′-5a Absorption Spectrum in CH.sub.2Cl.sub.2 (1/100,000) λ.sub.max /nm 621 536 426 Δλ.sub.max /nm ±2 ±2 ±2 OD* 0.620 0.785 0.520 ΔOD* ±0.020 ±0.020 ±0.020 Color Blue Red Yellow (Orange) Dichroic Properties Host LC.sup.§ No. ZLI- 2903 2452 DR** 16.2 13.7 13.0 S*** 0.83 0.81 0.80 *Optical Density: OD ≡ log.sub.10 (I.sub.i/I.sub.t), Ii = Intensity of incident light, It = Intensity of transmitted light, .sup.§ZLI-mixtures available from Merck KGaA, Germany, **Dichroic Ratio of Dye in Host LC and ***Order Parameter of Dye in Host LC.

[0260] The LC media according to the invention may also comprise further additives known to the person skilled in the art like for example further stabilizers, inhibitors, chain-transfer agents, isotropic 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, colorants, further dyes, pigments or nanoparticles in usual concentrations. Polymerizable additives are accordingly ascribed to the polymerizable component. Unpolymerizable additives are accordingly ascribed to the liquid-crystalline component.

[0261] In general, the total concentration of all compounds in the media according to this application is 100%.

[0262] It goes without saying to the person skilled in the art that the LC media according to the invention may also comprise compounds in which, for example, H, N, O, Cl, F have been replaced by the corresponding iso-topes.

[0263] The 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 compounds with one or more polymerizable 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. The invention furthermore relates to the process for the preparation of the LC media according to the invention.

[0264] In a preferred embodiment, the liquid-crystal media according to the invention having negative dielectric anisotropy are characterized by optical anisotropy values in the moderate to low region. The birefringence values are preferably in the range from 0.065 or more to 0.250 or less, particularly preferably in the range from 0.090 or more to 0.200 or less and very particularly preferably in the range from 0.095 or more to 0.175 or less.

[0265] Preferably, the liquid-crystal media according, which consists preferably of the polymerizable component and the liquid-crystalline component, have relatively high values of the modulus of the dielectric anisotropy (|Δ∈|), which are preferably in the range from 1.0 or more to 10 or less, preferably from 2 or more to 8 or less, particularly preferably from 3 or more to 7 or less and very particularly preferably from 4 or more to 6 or less.

[0266] The nematic phase of the media 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.

[0267] The invention furthermore relates to a light modulation element comprising a LC cell having two substrates and two electrodes, where at least one substrate is transparent to light and at least one substrate has one or two electrodes, and a layer, located between the substrates, of an LC medium comprising a polymerized component and a low-molecular-weight component, where the polymerized component is obtainable by polymerization of one or more polymerizable compounds between the substrates of the LC cell in the LC medium, preferably with application of an electrical voltage to the electrodes, characterized in that at least one of the polymerizable compounds is selected from formula I.

[0268] The invention furthermore relates to a process for the production of an light modulation element as described above and below in which an LC medium comprising one or more low-molecular-weight liquid-crystalline compounds or a LC host mixture as described above and below and one or more polymerizable compounds, at least one of which is selected from formula I, is introduced into an LC cell having two substrates and two electrodes as described above and below, and the polymerizable compounds are polymerized, preferably with application of an electrical voltage to the electrodes.

[0269] The light modulation elements according to the invention have two electrodes, preferably in the form of transparent layers, which are applied to one or both of the substrates which form the LC cell. Either in each case one electrode is applied to each of the two substrates, or both electrodes are applied to only one of the two substrates, while the other substrate has no electrode.

[0270] The structure of the light modulation element according to the invention, with electrode substrates and surface-treated electrode layers, corresponds to the conventional structure for displays, which is known to the person skilled in the art.

[0271] 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 polymerization.

[0272] 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®.

[0273] In a preferred embodiment, the substrates are arranged with a separation in the range from approximately 1 μm to approximately 50 μm from one another, preferably in the range from approximately 2 μm to approximately 20 μm from one another, and more preferably in the range from approximately 3 μm to approximately 10 μm from one another. The layer of the liquid-crystalline medium is thereby located in the interspace.

[0274] 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, etc.

[0275] In a further preferred embodiment of the invention, the layer of the liquid-crystalline medium is located between two flexible layers, for example flexible polymer films. The device 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 polarizers. 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. Furthermore, electrodes and further electrical components and connections may be present in the device according to the invention in order to facilitate electrical switching of the device, comparable to the switching of an LC display. Preferably, the utilized electrode structure is capable to induce an electric field, which is perpendicular with respect to the substrate's main plane.

[0276] Thin films of ITO are commonly deposited on substrates by physical vapor deposition, electron beam evaporation, or sputter deposition techniques.

[0277] Depending on the utilized electrode structure, preferably both substrates carry patterns or layers of opposing electrodes on their facing surfaces with the intervening liquid crystal medium there between. Other, suitable electrode structures are commonly known to the expert.

[0278] Suitable electrode materials are commonly known to the expert, as for example electrodes made of metal or metal oxides, such as, for example transparent indium tin oxide (ITO), which is preferred according to the present invention.

[0279] Preferably, thin films of ITO are commonly deposited on substrates by physical vapor deposition, electron beam evaporation, or sputter deposition techniques.

[0280] Preferably, the electrodes of the light modulation element are associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD).

[0281] In a preferred embodiment, the light modulation element comprises at least one dielectric layer, which is preferably on the electrode structure.

[0282] Typical dielectric layer materials are commonly known to the expert, such as, for example, SiOx, SiNx, Cytop, Teflon, and PMMA.

[0283] 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.

[0284] In a further preferred embodiment, the light modulation element comprises at least one alignment layer, which is preferably provided on the electrode layer.

[0285] The light modulation element may have further alignment layers, which are in direct contact with the layer of the liquid-crystalline medium.

[0286] Preferably, the alignment layer(s) induce(s) homeotropic alignment, preferably throughout the entire liquid-crystalline medium.

[0287] However, as commonly known to the expert, by choosing a substrate with a corresponding surface energy, it is likewise possible to induce homeotropic alignment to the liquid-crystalline medium without utilizing a special alignment layer.

[0288] The alignment layers may also serve as substrate layers, so that substrate layers are not necessary in the 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. Typical alignment layer materials are commonly known to the expert. Suitable methods to achieve homeotropic alignment are described, for example, in J. Cognard, Mol. Cryst. Liq. Cryst. 78, Supplement 1, 1-77 (1981).

[0289] It is likewise possible that a homeotropically alignment can be achieved by adding to the liquid-crystalline medium one or more so called “self-alignment agents”. Suitable self-alignment agents are, for example, described by Shie-Chang Jeng et al. Optics Letters (2009), 34, 455-457 or Shug-June Hwang et al. J. Phys D. Appl. Phys 2009, 42, 025102 or the self-alignment agents disclosed in US 2008/0198301, JP 2010-170090 A, EP 2 593 529 A1 or EP 2 606 101 A1.

[0290] 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 vapor 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.

[0291] It is likewise possible in accordance with the present invention and advantageous under certain conditions for the light modulation element to comprise no alignment layers adjacent to the layer of the liquid-crystalline medium.

[0292] The device 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.

[0293] The functional principle of the 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.

[0294] The light transmission of the device according to the invention is dependent on the applied electric field. In a preferred embodiment, the light transmission of the device is high in the initial state when no electric field is applied and preferably, gradually decreases when an electric field is applied.

[0295] In a preferred embodiment, the device according to the invention has a boundary state A and a boundary state B.

[0296] The 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.

[0297] The light modulation element preferably has another boundary state B when an electric field is applied, the so called “on state” or opaque state, in which the liquid crystal medium is increasingly distorted away from the vertical, whereby

T.sub.A>T.sub.B.

[0298] In a preferred embodiment, a large proportion of the liquid-crystalline compounds are aligned vertically to the substrate surface (homeotropic alignment). With increasing electric field, the director of LC medium is changed.

[0299] The required applied electric field strength is mainly dependent on the electrode gap and the modulus of Δ∈ 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 are in the range from 4V/μm.sup.−1 to 20V/μm.sup.−1.

[0300] Preferably, the applied driving voltage in order to switch the 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.

[0301] A typical process of preparing a liquid crystal light modulation element according to the present invention comprises at least the steps of [0302] cutting and cleaning of the substrates, [0303] providing electrode structure on each of the substrates, [0304] optionally coating of a dielectric layer on the electrode structure, [0305] optionally providing an alignment layer on the electrode structure, [0306] assembling the cell using an adhesive (UV or heat curable) with spacer, [0307] filling the cell with the LC medium, and [0308] exposing the LC medium to actinic radiation that induces photopolymerization of the polymerizable compounds.

[0309] In the first step the LC medium, as described above and below, is provided as a layer between two substrates forming a cell. Typically, the liquid crystal medium is filled into the cell. Conventional filling methods can be used which are known to the skilled person, like for example the so-called “one-drop filling” (ODF). Likewise also other commonly known methods can be utilized, such as, for example, vacuum injection method or inkjet printing method (IJP)

[0310] In the irradiation step, the light modulation element is exposed to actinic radiation that causes photopolymerization of the polymerizable functional groups of the polymerizable compounds contained in the cholesteric liquid crystal medium. Polymerization is achieved for example by exposing the polymerizable material to heat or 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. Preferably, polymerization 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.

[0311] Because of the irradiation the polymerizable compounds are substantially polymerized or crosslinked (in case of compounds with two or more polymerizable groups) in situ within the liquid crystal medium between the substrates forming the light modulation element.

[0312] The 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. On the other hand, the wavelength of the photo radiation should not be too high, to allow quick and complete UV photopolymerization of the RMs, and should be not higher than, preferably the same as or lower than the UV absorption maximum of the polymerizable component.

[0313] Suitable wavelengths are preferably selected from 300 to 400 nm, for example 340 nm or more, preferably 350 nm or more, more preferably 360 nm or more.

[0314] The irradiation or exposure time should be selected such that polymerization is as complete as possible, but still not be too high to allow a smooth production process. Also, the radiation intensity should be high enough to allow quick and complete polymerization as possible, but should not be too high to avoid damage to the cholesteric liquid crystal medium.

[0315] The curing time depends, inter alia, on the reactivity of the polymerizable material, the thickness of the coated layer, the type of polymerization initiator and the power of the UV lamp. The curing time is preferably ≦10 minutes, very preferably ≦5 minutes, most preferably ≦3 minutes. In general, for mass production shorter curing times are preferred, such as approximately 200 seconds to 10 seconds.

[0316] A suitable UV radiation power is preferably in the range from 5 to 250 mWcm.sup.−2′ more preferably in the range from 6 to 200 mWcm.sup.−2, especially in the range from 7 to 200 mWcm.sup.−2, and in particular 10 to 200 mWcm.sup.−2.

[0317] In connection with the applied UV radiation and as a function of time, a suitable UV dose is preferably in the range from 500 to 7200 mJcm.sup.−2 more preferably in the range from 1000 to 5000 mJcm.sup.−2 and most preferably in the range from 1250 to 2500 mJcm.sup.−2.

[0318] The light modulation element of the present invention can be used in various types of optical and electro-optical devices.

[0319] 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 and Smart Windows, preferably as light shutters for see through OLED displays.

[0320] 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.

[0321] 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.

[0322] 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).

[0323] 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.

[0324] 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.

[0325] 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.

[0326] All groups C.sub.nH.sub.2n+1, C.sub.mH.sub.2m+1, and C.sub.IH2.sub.I+1 are preferably straight chain alkyl groups with n, m and I C-atoms, respectively, all groups C.sub.nH.sub.2n, C.sub.mH.sub.2m and C.sub.IH.sub.2I are preferably (CH.sub.2).sub.n, (CH.sub.2).sub.m and (CH.sub.2).sub.I, respectively and —CH═CH— preferably is trans- respectively E vinylene.

TABLE-US-00002 TABLE A Ring Elements C [00066] P [00067] D [00068] DI [00069] A [00070] AI [00071] G [00072] GI [00073] U [00074] UI [00075] Y [00076] M [00077] MI [00078] N [00079] NI [00080] np [00081] n3f [00082] n3fl [00083] th [00084] thl [00085] th2f [00086] th2fl [00087] o2f [00088] o2fl [00089] dh [00090] K [00091] KI [00092] L [00093] LI [00094] F [00095] FI [00096]

TABLE-US-00003 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-00004 TABLE C End Groups Left hand side, used alone or Right hand side, used alone or in combination with others in 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 Right hand side, used in combination 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—
wherein n and m each are integers and three points “ . . . ” indicate a space for other symbols of this table.

EXAMPLES

LC Component

[0327] The following mixture M−1 is prepared.

TABLE-US-00005 CY-3-O4 25.00% T(N, I) [° C.]: 81.0 CY-5-O2 9.00% Δn [589 nm, 20° C.] 0.153 CCY-3-O2 7.00% Δε [kHz, 20° C.]: −5.0 CCY-3-O3 4.50% γ.sub.1 [mPa .Math. s, 20° C.]: 298 CPY-2-O2 10.00% K.sub.1 [20° C.]: 13.1 CPY-3-O2 10.00% K.sub.3 [20° C.]: 15.9 PYP-2-3 14.00% V.sub.0 [V]: 1.89 PYP-2-4 10.00% CCP-V-1 3.00% CPP-3-2 2.00% PP-1-2V1 3.50% PGP-2-3 2.00%

Polymerizable Compounds

[0328] ##STR00097##

Test Cell

[0329] On an ITO coated glass substrates, a 50 nm VA-polyimide (AL60702, JSR) layer is spin coated. After drying, the test cell is assembled, while two of the above described substrates are oriented parallel to each other with a cell gap of 10 μm. The test cell is filled with the corresponding mixture as described in the following examples. The polymerizable component is then cured with in the test cell with the corresponding curing parameters as given in the following examples. A corresponding electric field as given in the following examples is applied to the test cell in order to switch from the “off state” to the opaque “on state”.

Methods

[0330] The haze performance is measured depending on the applied voltage (Haze vs. Voltage) with a corresponding commonly used haze meter. V.sub.op is thereby the operating voltage to achieve maximum haze level.

Example 1

[0331] 89.7% of mixture M1, 10.0% of RM-3, and 0.3% of Irgacure®651 (from CIBA) are mixed and filled in the test cell as given above. The cell is then exposed to UV light with Mirho UV CURE 850 (Mercuri UV lamp) with 365 band pass filter and with 200 mW for 10 s.

[0332] An electric field (35 V to 100V, 60 Hz) is applied to the test cell in order to switch from the “off state” to the opaque “on state”.

[0333] The V.sub.op is about 35 V (10 um cell gap) and haze level is 78%.

Example 2

[0334] 89.7% of mixture M1, 10.0% of RM-3, and 0.3% of Irgacure®651 (from CIBA) are mixed and filled in the test cell as given above. The cell is then exposed to UV light (Mirho UV CURE 850 (Mercuri UV lamp) with 365 band pass filter with 7.5 mW for 180 s.

[0335] An electric field of 25V and 60 Hz is applied to the test cell in order to switch from the “off state” to the opaque “on state”.

[0336] The V.sub.op is about 25V (10 um cell gap) and haze level is 83%

Comparative Example 1

[0337] 90.0% of mixture M1, 10.0% and RM-1 are mixed and filled in the test cell as given above. The cell is then exposed to UV light (Mirho UV CURE 850 (Mercuri UV lamp) with 365 band pass filter, 200 mW for 10 s).

[0338] An electric field (35 V to 100V, 60 Hz) is applied to the test cell in order to switch from the “off state” to the opaque “on state”.

[0339] The V.sub.op is about 50 V (10 um cell gap) and haze level is 84%.

Comparative Example 2

[0340] 89.55% of mixture M1, 4.975% of RM-1, 4.975% of RM-2, and Irgacure®907 (from CIBA) are mixed and filled in the test cell as given above. The cell is then exposed to UV light (Mirho UV CURE 850 (Mercuri UV lamp) with 365 band pass filter, 200 mW for 10 s).

[0341] An electric field (35 V to 100V, 60 Hz) is applied to the test cell in order to switch from the “off state” to the opaque “on state”.

[0342] The V.sub.op is about 80 V (10 um cell gap) and haze level is 85%.

[0343] The entire disclosures of all applications, patents and publications, cited herein and of corresponding application No. EP 16158122.8, filed Mar. 1, 2017, are incorporated by reference herein.

[0344] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0345] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.