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US-12619110-B2 - Device for the regulation of light transmission

US12619110B2US 12619110 B2US12619110 B2US 12619110B2US-12619110-B2

Abstract

A polymerizable LC material containing one or more reactive mesogenic compounds, one or more chiral compounds and one or more compounds of formula I, wherein the individual radicals have one of the meaning as defied herein, is suitable for use in in optical, electro-optical, decorative or security devices. Polymer films with improved thermal and UV stability are obtainable from the polymerizable LC material.

Inventors

  • Michael Junge
  • Andreas Beyer
  • Ewa Dominika PTAK

Assignees

  • MERCK PATENT GMBH

Dates

Publication Date
20260505
Application Date
20211209
Priority Date
20201211

Claims (17)

  1. 1 . A window element, comprising: a switchable optical cell which is arranged in a laminate, wherein the switchable optical cell is electrically switchable between at least two optical states, and the switchable optical cell 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, wherein the switchable layer comprises a liquid-crystalline medium having a clearing point in the temperature range of from 15° C. to 45° C., and wherein the working temperature range of the window element is between −5° C. to 55°C., and wherein the switchable optical cell can be switched both electrically and thermally.
  2. 2 . The window element according to claim 1 , wherein the absolute value of a dielectric anisotropy of the liquid-crystalline medium is 2.5 or more.
  3. 3 . The window element according to claim 1 , wherein the liquid-crystalline medium comprises one or more dichroic dyes.
  4. 4 . The window element according to claim 1 , wherein the liquid-crystalline medium comprises a chiral dopant.
  5. 5 . The window element according to claim 1 , wherein the liquid-crystalline medium has a negative dielectric anisotropy.
  6. 6 . 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.
  7. 7 . The window element according to claim 6 , wherein the first alignment layer and/or the second alignment layer is a homeotropic alignment layer.
  8. 8 . 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.
  9. 9 . The window element according to claim 1 , wherein the element is configured as an insulated glazing unit.
  10. 10 . 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 wherein a denotes 1 or 2, b denotes 0 or 1, c denotes 0, 1 or 2, d denotes 0 or 1, denotes denote denotes R 1 , R 2 , R AC1 and R AC2 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH 2 groups may each be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another, Z x , Z y and Z AC each, independently of one another, denote —CH 2 CH 2 —, —CH═CH—, —CF 2 O—, —OCF 2 —, —CH 2 O—, —OCH 2 —, —CO—O—, —O—CO—, —C 2 F 4 —, —CF═CF—, —CH═CH—CH 2 O—, or a single bond, and L 1-4 each, independently of one another, denote F, Cl, CN, OCF 3 , CF 3 , CH 3 , CH 2 F or CHF 2 .
  11. 11 . A building or vehicle comprising a window element according to claim 1 .
  12. 12 . The window element according to claim 1 , wherein the element is configured as an insulated double glazing or a triple glazing unit.
  13. 13 . The window element according to claim 9 , 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.
  14. 14 . The window element according to claim 10 , wherein R 1 , R 2 , R AC1 and R AC2 each, independently of one another, denote alkyl or alkoxy having 1 to 6 atoms, and Z x , Z y and Z AC each denote a single bond.
  15. 15 . The window element according to claim 1 , wherein the liquid-crystalline medium comprises one or more compounds selected from the group of compounds of formulae CY-a and AC-a wherein R 3 , R 4 , R 5 and R 6 each, independently of one another, denote alkyl having 1 to 12 C atoms, where, in addition, one or two non-adjacent CH 2 groups may be replaced by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O atoms are not linked directly to one another.
  16. 16 . The window element according to claim 15 , wherein R 3 , R 5 and R 6 each, independently of one another, denote alkyl having 1 to 6 C atoms and R 4 denotes alkoxy having 1 to 6 C atoms.
  17. 17 . A method of operating the window element according to claim 1 , comprising electrically switching the switchable layer when the liquid-crystalline medium is at a temperature at which a nematic phase and an isotropic phase co-exist.

Description

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. Devices for controlling or modulating the transmission of light are commonly used in display applications, but they may also be used e.g. in so-called smart windows applications. R. Baetens et al. in “Properties, requirements and possibilities of smart windows for dynamic daylight and solar energy control in buildings: A state-of-the-art review”, Solar Energy Materials & Solar Cells, 94 (2010) on pages 87-105 review different dynamic smart windows. As described therein, smart windows can make use of several technologies for modulating the transmittance of light such as devices based on electrochromism, liquid crystal devices and electrophoretic or suspended-particle devices. Light shutters and optical intensity modulators, in particular liquid crystal-based light modulators, may be used in switchable windows for architectural, automotive, railway, avionic and nautical applications. Light modulating or regulating devices may in principle rely on the absorption of light or the scattering of light or a combination of both. In some devices the transmission of light can be reversibly changed wherein the intensity of incident light can be attenuated, dimmed or tinted. Such devices may thus be operated in and switched between a bright state and a dark state, i.e. between a state of relatively higher light transmission and a state of relatively lower light transmission. In principle, several modes or configurations may be employed to provide such reversible transmission change. For twisted nematic (TN), super-twisted nematic (STN) and vertical alignment (VA) liquid crystal cells polarizers are commonly used to control the light transmission. It is also possible to use guest-host liquid crystal cells which are based on a liquid crystal host which is doped with dichroic dye molecules. These guest-host systems can be used without any polarizers to alter the light transmission. However, in some embodiments and applications guest-host liquid crystal cells are also used in combination with at least one polarizer. In other cases a scattering-type device may be used to change the transmission of light by switching between a transparent non-scattering state, i.e. an optically clear or non-hazy state, and a light scattering state, i.e. a translucent or hazy state, which may also be perceived or appear as cloudy, turbid, diffuse or opaque. A device operating in the scattering mode can in particular be used in a privacy window. In this case a privacy mode can be provided when desired by switching the device, in particular the window element, from a clear state with possible viewing contact to a scattering state giving a visual barrier. Based in principle on a change in phase and optical state by changing the temperature across a phase transition temperature, in particular the clearing point and especially the nematic-isotropic phase transition temperature, switching in liquid crystal-based devices between the different optical states may be thermally controlled, as described e.g. in WO 2011/134582 A1. In alternative designs liquid crystal-based devices may adopt the different optical states using electrical switching, where the application of voltage controls the switching. Such liquid crystal-based devices in principle employ a change in the orientation of liquid crystal (LC) molecules between two conductive electrodes by applying an electric field which results in a change of the transmittance, as described e.g. in WO 2015/090506 A1. In US 2019/0162989 A1 multi-layered filter assemblies for smart windows are described, wherein in the dynamic filters a nematic liquid crystal layer is thermally driven or alternatively is electrically driven. There is still a need in the art for devices for regulating the passage of light and in particular switchable windows which give effective and efficient switching performance. An object of the present invention is therefore to provide improved devices for regulating the passage of light and in particular window elements comprising optical cells which give reliable and uniform switching, especially at typical working temperatures, while furthermore giving benefits in terms of the ease of configuration as well as energy efficiency. It is a further object to provide liquid-crystalline media which are advantageously useful in these devices. Further objects of the present invention are immediately evident to the person skilled in the art from the following detailed description. The objects are solved by the subject-matt