LIQUID CRYSTALLINE MEDIUM AND LIQUID CRYSTAL DISPLAY

Abstract

The present invention relates to a liquid crystalline medium which comprises one or more mesogenic compounds selected from the group of compounds of formulae I and II as set forth in claim 1, one or more chiral compounds and one or more polymerisable compounds, to a composite system obtained from or respectively obtainable from the medium by polymerising the one or more polymerisable compounds, and to liquid crystal displays comprising the composite system, in particular displays operating in reflective mode. The present invention further relates to a process for preparing the composite system comprising spatially selective polymerisation.

Claims

1. A liquid-crystalline medium, comprising one or more mesogenic compounds selected from the group of compounds of formulae I and II ##STR00297## wherein R.sup.1 and R.sup.2 are, independently of each other, alkyl, alkoxy, fluorinated alkyl or fluorinated alkoxy with 1 to 12 C atoms, alkenyl, alkenyloxy, alkoxyalkyl, fluorinated alkenyl or fluorinated alkenyloxy with 2 to 12 C atoms, L.sup.11, L.sup.12, L.sup.21 and L.sup.22 are, independently of each other, H or F, ##STR00298## are, independently of each other, ##STR00299## X.sup.1 is CN or NCS, X.sup.2 is halogen, halogenated alkyl or alkoxy with 1 to 3 C atoms or halogenated alkenyl or alkenyloxy with 2 or 3 C atoms, and i, 1 and m are, independently of each other, 0 or 1, one or more chiral compounds, and one or more polymerisable compounds, wherein the one or more polymerisable compounds are present in an amount, based on the overall contents of the medium, of 2.0% or more by weight.

2. The medium according to claim 1, wherein the one or more polymerisable compounds comprise at least one compound which contains a cycloalkyl group, preferably selected from unsubstituted or substituted bridged bicyclic rings and unsubstituted or substituted adamantyl, more preferably isobornyl or adamantyl.

3. The medium according to claim 1, wherein the one or more polymerisable compounds comprise one, two or more acrylate and/or methacrylate groups.

4. The medium according to claim 1, wherein the one or more chiral compounds have an absolute value of the helical twisting power of 20 m.sup.1 or more, and wherein preferably the one or more chiral compounds are present in a concentration such that the medium exhibits a selective reflection with a wavelength in the near UV or in the visible range of the electromagnetic spectrum.

5. A composite system, obtained from or respectively obtainable from the medium according to claim 1 by polymerising the one or more polymerisable compounds wherein the system comprises a low molecular weight component comprising the one or more mesogenic compounds selected from the group of compounds of formulae I and II, and the one or more chiral compounds, and a polymeric component comprising one or more polymeric structures obtained by or respectively obtainable from polymerising the one or more polymerisable compounds.

6. The composite system according to claim 5, wherein the one or more chiral compounds are present in a concentration such that the low molecular weight component exhibits a selective reflection with a wavelength in the near UV or in the visible range of the electromagnetic spectrum.

7. A light modulation element, comprising the composite system according to claim 5 and at least one substrate, wherein the components as set forth in claim 5 are supported by the at least one substrate and are separated such that the polymeric component comprising the one or more polymeric structures forms polymeric walls to contain the low molecular weight component in compartments.

8. The element according to claim 7, wherein the at least one substrate comprises electrodes to electrically address the low molecular weight component, and wherein the polymeric walls are based on the surface of the at least one substrate and are at least partially formed in electrically inactive regions.

9. A process for preparing a composite system or a light modulation element, comprising the following steps (a) providing the medium according to claim 1 as a layer, (b) carrying out spatially selective polymerisation of the one or more polymerisable compounds in defined regions of the layer to obtain polymeric structures in the defined regions.

10. The process according to claim 9, wherein in step (b) the defined regions of the layer are selectively exposed to actinic radiation.

11. The process according to claim 9, wherein the layer is supported on a substrate, wherein preferably the layer is sandwiched between two substrates, and wherein the polymeric structures are formed as polymeric walls, preferably by selectively exposing the defined regions to UV radiation, more preferably by using a photomask.

12. The process according to claim 9, wherein subsequent to step (b) the whole layer is exposed to actinic radiation, preferably UV radiation.

13. A composite system or a light modulation element obtained by or respectively obtainable from carrying out the process according claim 9.

14. A liquid crystal display, comprising the composite system according to claim 5 in a light modulation element, a liquid crystal mirror or an electro-optical device.

15. A liquid crystal display, comprising the light modulation element according to claim 7.

16. The liquid crystal display according to claim 15, which is a reflective display.

17. The liquid crystal display according to claim 16, which exhibits a selective reflection with a wavelength in the near UV or in the visible range of the electromagnetic spectrum.

Description

EXAMPLES

[0316] Liquid crystal mixtures and composite systems are realized with the compositions and properties as given in the following. Their properties and optical performance are investigated.

Example 1

[0317] A liquid-crystal mixture B-1 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00008 Base Mixture B-1 Compound No. Abbreviation Conc./% Physical Properties 1 APUQU-2-F 7.00 T(N, I) = 100.0 C. 2 APUQU-3-F 8.00 n.sub.e (20 C., 589.3 nm) = 1.618 3 CCGU-3-F 10.00 n (20 C., 589.3 nm) = 0.134 4 CDUQU-3-F 10.00 .sub.| | (20 C., 1 kHz) = 60.6 5 DGUQU-4-F 8.00 (20 C., 1 kHz) = 52.4 6 CCP-3-1 8.00 7 CCQU-3-F 15.00 8 CCQU-5-F 8.00 9 PZG-2-N 8.00 10 PZG-3-N 8.00 11 PZG-4-N 10.00 100.00

[0318] A cholesteric mixture C-1 is prepared by adding the chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany to the base mixture B-1, wherein C-1 contains 98.37% of the mixture B-1 and 1.63% of R-5011.

[0319] Then a mixture M-1 is prepared by adding 2-ethylhexyl acrylate, isobornyl methacrylate and the photoinitiator Irgacure 651 abbreviated as IRG-651)

##STR00295##

available from Ciba, Switzerland, to the mixture C-1, wherein M-1 contains 95.96% of the mixture C-1, 2.00% of 2-ethylhexyl acrylate, 2.00% of isobornyl methacrylate and 0.04% of IRG-651.

[0320] The mixture M-1 is filled into a test cell having alkali-free glass substrates with ITO electrodes as well as rubbed polyimide alignment layers with a thickness of 50 nm, wherein the cell gap is 6 m. Subsequently polymerisation by exposure to UV radiation through a photomask is carried out. The photomask (chromium coated on quartz) exhibits a structure of an array of opaque squares each with a side length of 0.98 mm, wherein each square is bounded on all sides by transparent strips each having a width of 20 m. Each opaque square is thus boxed by a transparent frame and separated from neighbouring squares.

[0321] Polymerisation is carried out by irradiating the test cell with UV light from a lamp (Mirho, high pressure mercury vapour lamp with a 365 nm band-pass filter, power=10 mW/cm.sup.2) for 2,000 s, wherein polymeric walls are formed in the regions left exposed by the frame-like transparent structures of the photomask.

[0322] Then the photomask is removed and in a subsequent step the whole test cell, i.e. without spatial discrimination, is irradiated with UV light (power=10 mW/cm.sup.2) for 1,000 s.

[0323] The test cell obtained after the polymerisation steps exhibits the desired polymer walls, while furthermore providing suitable switching behaviour and electro-optical performance in the active regions and favourable contrast with respect to the inactive areas, in which unwanted reflection is reduced.

Example 2

[0324] A liquid-crystal mixture B-2 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00009 Base Mixture B-2 Compound No. Abbreviation Conc./% Physical Properties 1 CPZG-3-N 10.00 T(N, I) = 132.0 C. 2 PZG-2-N 17.00 n.sub.e (20 C., 589.3 nm) = 1.820 3 PZG-3-N 5.00 n (20 C., 589.3 nm) = 0.303 4 PGUQU-3-F 3.00 .sub.| | (20 C., 1 kHz) = 39.7 5 PGUQU-5-F 3.00 (20 C., 1 kHz) = 34.1 6 PPTUI-3-2 29.00 7 PPTUI-3-4 30.00 8 PTP-1-02 3.00 100.00

[0325] A mixture M-2 is then prepared by adding the chiral dopant R-5011 and the reactive mesogens RM-A and RM-B

##STR00296##

[0326] to the base mixture B-2, wherein the obtained mixture M-2 contains 87.35% of the mixture B-2, 2.65% of R-5011, 5.00% of RM-A and 5.00% of RM-B.

[0327] The mixture M-2 is then divided into two parts, wherein to one part 0.04% of IRG-651 is added.

[0328] Both parts of the mixture, i.e. with and without photoinitiator, are respectively filled in a test cell as described in Example 1. Polymerisation is carried out by irradiating each test cell with UV light from a lamp as described in Example 1 (power=10 mW/cm.sup.2) for 2000 s, using a photomask analogous to the mask in Example 1, wherein however the transparent strips each have a width of 40 m.

[0329] Even without a subsequent further exposure of the whole cell to UV light, the test cells obtained exhibit the desired polymer walls, while furthermore providing suitable switching behaviour and electro-optical performance in the active regions and favourable contrast with respect to the inactive areas, in which unwanted reflection is reduced.

Example 3

[0330] A liquid-crystal mixture B-3 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00010 Base Mixture B-3 Compound No. Abbreviation Conc./% Physical Properties 1 PZG-5-N 10.00 T(N, I) = 94.5 C. 2 CCU-3-F 4.00 n.sub.e (20 C., 589.3 nm) = 1.709 3 PGU-2-F 5.00 n (20 C., 589.3 nm) = 0.200 4 PGU-3-F 10.00 .sub.| .sub.| (20 C., 1 kHz) = 30.2 5 CCGU-3-F 6.00 (20 C., 1 kHz) = 24.9 6 PUQU-3-F 16.00 7 PGUQU-3-F 8.00 8 CP-3-O1 8.00 9 PP-1-2V1 4.00 10 PGP-2-2V 15.00 11 CPTP-3-O1 4.00 12 CPGP-4-3 5.00 13 CPGP-5-2 5.00 100.00

[0331] A mixture M-3 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-3.

[0332] The spatially selective polymerisation and the subsequent UV treatment of the whole cell are then carried out as described in Example 1.

[0333] A cell having polymeric walls and favourable properties is obtained.

Example 4

[0334] A liquid-crystal mixture B-4 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00011 Base Mixture B-4 Compound No. Abbreviation Conc./% Physical Properties 1 PZG-3-N 7.00 T(N, I) = 83.0 C. 2 PZG-5-N 10.00 n.sub.e (20 C., 589.3 nm) = 1.752 3 PGU-3-F 12.00 n (20 C., 589.3 nm) = 0.235 4 PUQU-3-F 8.00 .sub.| | (20 C., 1 kHz) = 31.1 5 PGUQU-3-F 9.00 (20 C., 1 kHz) = 25.9 6 CP-3-O1 8.00 7 PP-1-2V1 4.00 8 PTP-1-O2 4.00 9 PTP-2-O1 4.00 10 PGP-2-2V 11.00 11 PPTUI-3-2 8.00 12 PPTUI-3-4 10.00 13 CPGP-4-3 5.00 100.00

[0335] A mixture M-4 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-4.

[0336] The spatially selective polymerisation is then carried out as described in Example 1. However, no subsequent UV treatment of the whole cell is performed.

[0337] A cell having polymeric walls and favourable properties is obtained.

Example 5

[0338] A liquid-crystal mixture B-5 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00012 Base Mixture B-5 Compound No. Abbreviation Conc./% Physical Properties 1 PZG-3-N 8.50 T(N, I) = 91.5 C. 2 PZG-5-N 11.00 n.sub.e (20 C., 589.3 nm) = 1.767 3 PGU-3-F 8.00 n (20 C., 589.3 nm) = 0.250 4 PUQU-3-F 6.00 .sub.| | (20 C., 1 kHz) = 31.4 5 PGUQU-3-F 9.00 (20 C., 1 kHz) = 26.1 6 CP-3-O1 6.00 7 PTP-1-O2 4.00 8 PTP-2-O1 5.00 9 PGP-2-5 6.00 10 PGP-2-2V 10.00 11 PPTUI-3-2 10.00 12 PPTUI-3-4 13.00 13 CPGP-4-3 3.50 100.00

[0339] A mixture M-5 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-5.

[0340] The spatially selective polymerisation and the subsequent UV treatment of the whole cell are then carried out as described in Example 1.

[0341] A cell having polymeric walls and favourable properties is obtained.

Example 6

[0342] A liquid-crystal mixture B-6 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00013 Base Mixture B-6 Compound No. Abbreviation Conc./1% Physical Properties 1 PZG-3-N 10.00 T(N, I) = 85.5 C. 2 PZG-5-N 10.00 n.sub.e (20 C., 589.3 nm) = 1.771 3 PGU-3-F 18.00 n (20 C., 589.3 nm) = 0.251 4 PGUQU-3-F 10.00 .sub.| | (20 C., 1 kHz) = 37.9 5 CP-3-O1 6.00 (20 C., 1 kHz) = 32.1 6 PTP-1-O2 3.00 7 PTP-2-O1 3.00 8 PGP-2-3 8.00 9 PGP-2-4 7.00 10 PPTUI-3-2 10.00 11 PPTUI-3-4 15.00 100.00

[0343] A mixture M-6 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-6.

[0344] The spatially selective polymerisation and the subsequent UV treatment of the whole cell are then carried out as described in Example 1.

[0345] A cell having polymeric walls and favourable properties is obtained.

Example 7

[0346] A liquid-crystal mixture B-7 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00014 Base Mixture B-7 Compound No. Abbreviation Conc./% Physical Properties 1 PZG-2-N 11.00 T(N, I) = 81.5 C. 2 PZG-3-N 9.00 n.sub.e (20 C., 589.3 nm) = 1.752 3 PZG-5-N 7.00 n (20 C., 589.3 nm) = 0.229 4 PGU-2-F 7.00 .sub.| | (20 C., 1 kHz) = 30.4 5 PGU-3-F 7.00 (20 C., 1 kHz) = 24.2 6 CP-3-O1 6.00 7 PTP-1-O2 5.00 8 PTP-2-O1 7.00 9 PTP-3-O1 5.00 10 PGP-2-3 7.00 11 PGP-2-4 7.00 12 PGP-2-5 7.00 13 CPTP-3-O1 5.00 14 CPTP-3-O2 5.00 15 CPTP-3-O3 5.00 100.00

[0347] A mixture M-7 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-7.

[0348] The spatially selective polymerisation and the subsequent UV treatment of the whole cell are then carried out as described in Example 1.

[0349] A cell having polymeric walls and favourable properties is obtained.

Example 8

[0350] A liquid-crystal mixture B-8 is prepared and characterized with respect to its general physical properties, having the composition and properties as indicated in the following table.

TABLE-US-00015 Base Mixture B-8 Compound No. Abbreviation Conc./% Physical Properties 1 CU-3-N 10.00 T(N, I) = 95.5 C. 2 PZG-2-N 9.00 n.sub.e (20 C., 589.3 nm) = 1.626 3 PZG-3-N 9.00 n (20 C., 589.3 nm) = 0.129 4 PZG-4-N 10.00 .sub.| | (20 C., 1 kHz) = 36.1 5 PZG-5-N 8.00 (20 C., 1 kHz) = 28.9 6 CCG-V-F 16.00 7 CC-5-V 6.00 8 CCP-V-1 11.00 9 CPTP-3-O1 2.00 10 CCZPC-3-3 5.00 11 CCZPC-3-4 5.00 12 CCZPC-3-5 5.00 13 CPPC-3-3 2.00 14 CGPC-3-3 2.00 100.00

[0351] A mixture M-8 is then prepared analogous to Example 1, wherein the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to the mixture B-8.

[0352] The spatially selective polymerisation and the subsequent UV treatment of the whole cell are then carried out as described in Example 1.

[0353] A cell having polymeric walls and favourable properties is obtained.

Examples 9 to 12

[0354] Liquid-crystal mixtures B-9, B-10, B-11 and B-12 are prepared and characterized with respect to their general physical properties, having the respective compositions and properties as indicated in the following table.

TABLE-US-00016 Mixture B-9 B-10 B-11 B-12 Composition Compound No. Abbreviation c/% 1 CP-3-N 3.50 2 PZG-2-N 6.50 4.50 9.00 3 PZG-3-N 10.00 5.00 10.00 10.00 4 PZG-4-N 14.00 16.00 5 PZG-5-N 14.00 13.50 6 CPZG-3-N 5.00 7 CPZG-4-N 3.00 8 PGU-3-F 18.00 18.00 9 PUQU-3-F 7.50 10 PGUQU-3-F 8.50 8.00 7.00 11 CP-3-O1 8.00 8.00 12 PTP-1-O2 5.00 4.00 2.00 13 PTP-2-O1 5.00 5.00 14 PTP-3-O1 4.00 7.00 15 PGP-2-5 4.50 16 PGP-2-2V 11.50 13.00 17 CPTP-3-O1 3.50 18 CPTP-3-O3 5.00 19 PPTUI-3-2 8.50 6.50 20.00 20.00 20 PPTUI-3-3 10.00 10.00 23.00 21.50 21 CPGP-4-3 4.00 100.00 100.00 100.00 100.00 Properties T(N, I)/ C. 86.5 88.5 95.5 89.0 n.sub.e (20 C., 589.3 nm) 1.770 1.773 1.772 1.768 n (20 C., 589.3 nm) 0.249 0.254 0.257 0.252 .sub.| | (20 C., 1 kHz) 28.8 19.6 50.8 59.1 (20 C., 1 kHz) 23.4 15.2 43.5 50.7

[0355] To each of these mixtures B-9, B-10, B-11 and B-12 the chiral dopant, the reactive monomers and the photoinitiator as described in Example 1 are added in the amounts as given in Example 1 to prepare the respective mixtures M-9, M-10, M-11 and M-12

[0356] Each mixture M-9, M-10, M-11 and M-12 is then respectively filled in a test cell, and the spatially selective polymerisation and the subsequent UV treatment of the whole cells are then carried out as described in Example 1.

[0357] Cells having polymeric walls and favourable properties are obtained.