Liquid-crystal media and PNLC light modulation element

1 . A 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, wherein at least one of said one or more polymerisable compounds is a compound of formula I,

P 11 -Sp 11 -Ar-Sp 12 -P 12

wherein

Ar is one of the following groups

which is optionally substituted by one or more groups L,

L is on each occurrence identically or differently F, Cl, CN, P-Sp-, or a straight chain alkyl having 1 to 25 C atoms or a branched or cyclic alkyl having 3 to 25 C atoms, wherein one or more non-adjacent CH 2 -groups are optionally replaced by —O—, —S—, —CO—, —CO—O—, —O—CO—, or —O—CO—O— in such a manner that O- and/or S-atoms are not directly connected with each other, and wherein one or more H atoms are each optionally replaced by F or Cl,

P 11 and P 12 denote each and independently from another a polymerisable group,

Sp 11 and Sp 12 denote each and independently from another a spacer group that is optionally substituted by one or more groups P 11 or P 12 , or a single bond, and

B) one or more non-polymerisable mesogenic or liquid-crystalline compounds, and

C) one or more non-polymerisable chiral compounds in an amount of 0.1% to 0.9% by weight.

2 . The Cholesteric LC medium according to claim 1 , wherein one or more non-polymerisable chiral compounds having each alone or in combination with each other an absolute value of the helical twisting power (|HTP total |) of 5 μm −1 or more.

3 . The Cholesteric LC medium according to claim 1 , comprising one or more non-polymerisable chiral compounds in an amount of 0.5% to 0.9% by weight.

4 . The Cholesteric LC medium according to claim 1 , wherein the one or more non-polymerisable mesogenic or liquid-crystalline compounds are selected from compounds of formula A and/or B,

in which the individual radicals have, independently of each other and on each occurrence identically or differently, the following meanings:

 each, independently of one another, and on each occurrence, identically or differently, are one of the following groups

R 21 , R 31 each, independently of one another, are 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 0 is F, Cl, halogenated alkyl or alkoxy having 1 to 6 C atoms or halogenated alkenyl or alkenyloxy having 2 to 6 C atoms,

Z 31 is —CH 2 CH 2 —, —CF 2 CF 2 —, —COO—, trans-CH═CH—, trans-CF═CF—, —CH 2 O— or a single bond,

L 21 , L 22 ,

L 31 and L 32 each, independently of one another, are H or F, and

g is 0, 1, 2 or 3.

5 . A process for the production of a cholesteric LC medium according to claim 1 , comprising at least the step of mixing the one or more non-polymerisable mesogenic or liquid-crystalline compounds compounds and the one or more non-polymerisable 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 . A 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, wherein 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 . The PNLC light modulation element according to claim 7 , comprising an electrode structure, corresponding to an IPS or FFS electrode structure.

9 . The PNLC light modulation element according to claim 7 , wherein the interspace between the two opposing substrates is in the range of 1 to 20 μm.

10 . A 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 . The process according to claim 10 , wherein the photopolymerisation step is performed with light having a wavelength in the range of 250 to 450 nm.

12 . The process according to claim 10 , wherein the photopolymerisation step is performed with an irradiation intensity in the range of 5 to 150 mW/cm 2 .

13 . An optical or electro-optical device comprising the PNLC light modulation element according to claim 7 .

14 . The Cholesteric LC medium according to claim 1 , wherein one or more non-polymerisable chiral compounds include the following compound

15 . The Cholesteric LC medium according to claim 14 , comprising one or more non-polymerisable chiral compounds in an amount of 0.5% to 0.9% by weight.

16 . The Cholesteric LC medium according to claim 1 , comprising one or more non-polymerisable chiral compounds in an amount of 0.1% to 0.5% by weight.

17 . The Cholesteric LC medium according to claim 1 , comprising one or more non-polymerisable chiral compounds in an amount of 0.5% to 0.6% by weight.

18 . The Cholesteric LC medium according to claim 1 , comprising one or more non-polymerisable chiral compounds in an amount of 0.6% to 0.9% by weight.

19 . The Cholesteric LC medium according to claim 1 , wherein one or more non-polymerisable chiral compounds include one or more of the following compounds of:

formula Ch I,

formula Ch II,

including the respective (S,S) enantiomer,

wherein

E and F are each independently 1,4-phenylene or trans-1,4-cyclohexylene,

v is 0 or 1,

Z 0 is —COO—, —OCO—, —CH 2 CH 2 — or a single bond, and

R is alkyl, alkoxy or alkanoyl with 1 to 12 C atoms.

20 . The Cholesteric LC medium according to claim 1 , wherein one or more non-polymerisable chiral compounds include one or more of the following compounds of: R/S-5011, CD-1, R/S-811 and/or CB-15,

wherein

R-5011 and S-5011 are enantiomers of (13bR)-5,6-dihydro-5-(trans-4-propylcyclohexyl)-4H-dinaphtho[2,1-f:1′,2′-h][1,5]dioxonine,

CD1 is R-(−)-2,2′-bis(diphenoxyphosphinyl)-1,1′-binaphthyl,

S-811 is S-(+)-2-Octyl 4-(4-hexyloxybenzoyloxy)benzoate,

R-811 is (R)-2-Octyl 4-((4-(hexyloxy)benzoyl)oxy)benzoate, and

CB-15 is 4′-[(S)-2-methylbutyl]-[1,1′-biphenyl]-4-carbonitrile.