DEVICE FOR THE REGULATION OF LIGHT TRANSMISSION

Abstract

The present invention relates to devices for the regulation of light transmission and in particular to switchable windows. The present invention in particular relates to window elements which comprise electrically switchable optical cells with a switchable layer containing a liquid-crystalline medium having a clearing point which is within the working temperature of the window element. The present invention also relates to liquid-crystalline media for use in the window elements.

Claims

1. A window element, comprising a switchable optical cell which is electrically switchable between at least two optical states and which comprises a switchable layer interposed between two opposing transparent substrates, wherein each substrate is provided with an electrode structure or one of the substrates is provided with two electrode structures and the other substrate is not provided with an electrode, and wherein the switchable layer comprises a liquid-crystalline medium having a clearing point which is within the working temperature of the window element.

2. The window element according to claim 1, wherein the absolute value of the dielectric anisotropy of the liquid-crystalline medium is 2.5 or more.

3. The window element according to claim 1, wherein the liquid-crystalline medium has a clearing point in the temperature range of from 5? C. to 65? C.

4. The window element according to claim 1, wherein the liquid-crystalline medium comprises one or more dichroic dyes.

5. The window element according to claim 1, wherein the liquid-crystalline medium comprises a chiral dopant.

6. The window element according to claim 1, wherein the liquid-crystalline medium has a negative dielectric anisotropy.

7. The window element according to claim 1, wherein the switchable optical cell has a layer structure comprising in this order a first substrate, a first electrode layer, a first alignment layer, the switchable layer, a second alignment layer, a second electrode layer, and a second substrate.

8. The window element according to claim 7, wherein the first alignment layer and/or the second alignment layer is a homeotropic alignment layer.

9. The window element according to claim 1, wherein the switchable optical cell is switchable between a bright state and a dark state, and wherein below the clearing point and in the absence of an electric field the switchable layer is homeotropically aligned.

10. The window element according to claim 1, wherein the element is configured as an insulated glazing unit, preferably as a double glazing or a triple glazing.

11. The window element according to claim 1, wherein the switchable optical cell is arranged in a laminate, wherein preferably a lamination layer is provided which is UV blocking, and wherein preferably the laminate is facing the light source.

12. The window element according to claim 1, wherein the liquid-crystalline medium comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC ##STR00037## wherein a denotes 1 or 2, b denotes 0 or 1, c denotes 0, 1 or 2, d denotes 0 or 1, ##STR00038## denotes ##STR00039## denote ##STR00040## denotes ##STR00041## R.sup.1, R.sup.2, R.sup.AC1 and R.sup.AC2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may each be replaced by ##STR00042## O, CH?CH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, Z.sup.x, Z.sup.y and Z.sup.AC each, independently of one another, denote 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, CH?CHCH.sub.2O, or a single bond, preferably a single bond, and L.sup.1-4 each, independently of one another, denote F, Cl, CN, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2 F or CHF.sub.2, preferably F.

13. The window element according to claim 1, wherein the liquid-crystalline medium comprises one or more compounds selected from the group of compounds of the formulae CY-a and AC-a wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 each, independently of one another, denote alkyl having 1 to 12 C atom ##STR00043## O, CH?CH, CO, OCO or COO in such a way that O atoms are not linked directly to one and wherein preferably R.sup.3, R.sup.5 and R.sup.6 each, independently of one another, denote alkyl having 1 to ##STR00044## wherein R.sup.3, R.sup.4, R.sup.5 and R.sup.6 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may each be replaced by ##STR00045## O, CH?CH, CO, OCO or COO in such a way that O atoms are not linked directly to one another.

14. A building or vehicle comprising a window element according to claim 1.

15. A liquid-crystalline medium for use in a window element according to claim 1, wherein the liquid-crystalline medium has a clearing point in the temperature range of from 5? C. to 65? C. and comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC ##STR00046## wherein a denotes 1 or 2, b denotes 0 or 1, c denotes 0, 1 or 2, d denotes 0 or 1, ##STR00047## denotes ##STR00048## denote ##STR00049## denotes ##STR00050## R.sup.1, R.sup.2, R.sup.AC1 and R.sup.AC2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH.sub.2 groups may each be replaced by ##STR00051## O, CH?CH, CO, OCO or COO in such a way that O atoms are not linked directly to one another, preferably alkyl or alkoxy having 1 to 6 C atoms, Z.sup.x, Z.sup.y and Z.sup.AC each, independently of one another, denote 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, CH?CHCH.sub.2O, or a single bond, preferably a single bond, and L.sup.1-4 each, independently of one another, denote F, Cl, CN, OCF.sub.3, CF.sub.3, CH.sub.3, CH.sub.2 F or CHF.sub.2, preferably F.

16. The window element according to claim 1, wherein the liquid-crystalline medium has a clearing point in the temperature range of from 15? C. to 45? C.

17. The window element according to claim 1, wherein the element is configured as an insulated double glazing or a triple glazing unit.

18. The window element according to claim 10, wherein the switchable optical cell is arranged in a laminate further comprising a lamination layer which is UV blocking, and wherein the laminate is facing a light source.

19. The window element according to claim 13, wherein R.sup.3, R.sup.5 and R.sup.6 each, independently of one another, denote alkyl having 1 to 6 C atoms and R.sup.4 denotes alkoxy having 1 to 6 C atoms.

Description

EXAMPLES

[0185] The following liquid-crystalline mixtures are prepared and investigated.

Example 1

[0186] A mixture M-1 having the following composition is prepared.

##STR00028##

[0187] The mixture M-1 has a clearing point of 36.0? C.

Example 2

[0188] A mixture M-2 is prepared by mixing 99.70% of mixture M-1 with 0.30% of the compound of formula

##STR00029##

Example 3

[0189] A mixture M-3 is prepared by mixing 96.914% of mixture M-1, 0.544% of the compound of formula

##STR00030##

1.152% of the compound of formula

##STR00031##

and 1.390% of the compound of formula

##STR00032##

[0190] The mixture M-3 has a clearing point of 41.6? C.

[0191] The mixture M-3 is filled into an electro-optical cell having glass substrates with ITO electrodes as well as polyimide alignment layers giving homeotropic alignment, wherein the cell gap is 25 ?m.

[0192] The thermal and electrical switching performance is investigated using a heating plate and a spectrometer as well as a microscope hot-stage system.

[0193] In the absence of an electric field the liquid-crystalline medium in the electro-optical cell at room temperature has a nematic phase giving a uniform bright state appearance of the device. The clearing point is observed at 41.6? C. At this temperature the nematic phase starts to transition into a multiphase system where dark droplets of isotropic medium are embedded in bright nematic domains. This clearing temperature region in which nematic and isotropic domains coexist is present from 41.6? C. to 44? C., wherein a non-uniform visual appearance of the device is observed.

[0194] The cell is electrically switched (30 V) in this temperature region of 41.6? C. to 44? C. and the nematic domains quickly switch into a dark state such that the device overall is giving a uniform dark appearance.

[0195] To give an especially improved switching performance and an aesthetically favourable appearance electrical switching is performed at temperatures just below the clearing point, in particular between 40.5? C. and 41.5? C.

[0196] In addition, electrical switching at room temperature gives a quick transition between a bright state and a dark state with excellent contrast and uniformity.

[0197] Electro-optical cells filled with the mixture M-3 are included in window elements by lamination.

Example 4

[0198] A dye-doped mixture M-4 is prepared analogous to Example 3, wherein instead of mixture M-1 the mixture M-2 is used.

Example 5

[0199] A mixture M-5 having the following composition is prepared.

TABLE-US-00001 CP-5-3 10.00% CCN-47 36.00% CCN-55 36.00% CCN-33 18.00%

[0200] A mixture M-5-1 is prepared by mixing 99.70% of mixture M-5 with 0.03% of the compound of formula

##STR00033##

[0201] A mixture M-5-2 is prepared by mixing 99.51% of mixture M-5 and 0.49% of chiral dopant S-811 available from Merck KGaA, Darmstadt, Germany.

Example 6

[0202] A mixture M-6 is prepared by mixing 96.914% of mixture M-5, 0.544% of the compound of formula

##STR00034##

1.152% of the compound of formula

##STR00035##

and 1.390% of the compound of formula

##STR00036##

[0203] The mixture M-6 has a clearing point of 50.5? C.

[0204] The mixture M-6 is filled into an electro-optical cell having glass substrates with ITO electrodes as well as polyimide alignment layers giving homeotropic alignment, wherein the cell gap is 25 ?m.

[0205] The thermal and electrical switching performance is investigated using a heating plate and a spectrometer as well as a microscope hot-stage system.

[0206] In the absence of an electric field the liquid-crystalline medium in the electro-optical cell at room temperature has a nematic phase giving a uniform bright state appearance of the device. The clearing point is observed at 50.5? C. At this temperature the nematic phase starts to transition into a multiphase system where dark droplets of isotropic medium are embedded in bright nematic domains. The clearing temperature region in which nematic and isotropic domains coexist is present from 50.5? C. to 53? C., wherein a non-uniform visual appearance of the device is observed.

[0207] The cell is electrically switched (30 V) in this temperature region of 50.5? C. to 53? C. and the nematic domains quickly switch into a dark state such that the device overall is giving a uniform dark appearance.

[0208] To give an especially improved switching performance and an aesthetically favourable appearance electrical switching is performed at temperatures just below the clearing point, in particular between 49.4? C. and 50.4? C.

[0209] In addition, electrical switching at room temperature gives a quick transition between a bright state and a dark state with excellent contrast and uniformity.

[0210] Electro-optical cells filled with the mixture M-6 are included in window elements by lamination.

Examples 7 and 8

[0211] Dye-doped mixtures M-7 and M-8 are prepared analogous to Example 6, wherein instead of mixture M-5 the mixtures M-5-1 and M-5-2 are respectively used.