Switching layers used in switching elements

Abstract

The present invention relates to an assembly of switchable layers that attenuate and scatter light, and to a window element that includes said switchable layer assembly.

Description

[Technical field]

[0001] The present invention relates to an assembly of switchable layers that attenuate and scatter light, and to a window element comprising said switchable layer assembly.

[0002] Devices that control or modulate the transmission of light are widely used in display applications, but may also be used, for example, in so-called smart window applications. R. Baetens et al. discuss various dynamic smart windows 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), pp. 87-105. As described there, smart windows can utilize several technologies that modulate the transmission of light, such as devices based on electrochromism, liquid crystal devices, and electrophoretic or suspended particle devices.

[0003] It is also commonly known that light shutters and optical intensity modulators can be based on liquid crystals (LC). LC-based light modulators are sometimes used in switchable windows in architectural, automotive, aviation, and marine applications.

[0004] Switching between different optical states may for example be thermally controlled, however in many cases it may be preferable and advantageous to use electrical switching.

[0005] LC-based light modulation or conditioning devices may essentially rely on light absorption or light scattering.

[0006] Some devices can reversibly change light transmission and can attenuate, dim, or color the intensity of incident light, but exhibit little or no scattering or haze in different operating states.Such devices thus operate in and can be switched between bright and dark states, i.e., states of relatively high light transmission and relatively low light transmission, and neither state is substantially hazy.

[0007] Several modes or configurations can be used to provide such a reversible change in transmittance. In twisted nematic (TN), super twisted nematic (STN), and vertically aligned (VA) liquid crystal cells, polarizers are used to control the light transmission. It is also possible to use guest-host liquid crystal cells based on a liquid crystal host doped with dichroic dye molecules. These guest-host devices can be used without a polarizer to alter the light transmission. However, in some embodiments and applications, the guest-host liquid crystal cells are used in combination with at least one polarizer.

[0008] LC-based light modulators that use light scattering include so-called polymer dispersed liquid crystals (PDLCs) or encapsulated or nematic curved phase liquid crystals (NCAPs), polymer network liquid crystals (PNLCs), cholesteric liquid crystals (CLCs), polymer stabilized cholesterically textured liquid crystals (PSCTs), and dynamic scattering liquid crystal devices. These scattering devices can be switched between a transparent state, i.e., optically clear or non-cloudy, and a light scattering state, i.e., translucent or cloudy.

[0009] When such a scattering device is switched from a non-scattering state to a scattering state, the light transmission changes, producing a translucent or opaque appearance, which may be perceived as cloudy, hazy, diffuse, or hazy.

[0010] A device operating in a scattering mode can be used in particular as a privacy window, where the privacy mode can be provided by switching the device, particularly the window element, from a clear state allowing visual contact to a scattering state to provide a visual barrier as desired.

[0011] US 2014 / 0226096 describes an optically variable device for adjusting ambient light, particularly for use in see-through near-eye display devices. The device is described as being capable of both absorbing and scattering light management. The device is further described as being capable of transitioning between three different optical states under different electric field conditions, namely a low haze low colored state, a low haze high colored state, and a high haze high colored state. The device uses a single switching layer, in which an LC material is mixed with a dichroic dye to provide absorption and with an ionic dopant to provide so-called dynamic scattering.

[0012] J.-W. Huh et al., “Double-layered light shutter using long-pitch cholesteric liquid crystal cells”, Applied Optics, 54 (2015), pp. 3792-3795, propose a double-layered light shutter device using two cholesteric liquid crystal cells, which includes a light-scattering layer using long-pitch cholesteric LC and a light-absorbing layer using dye-doped cholesteric LC.

[0013] WO 2016 / 173693 describes a switching layer for use in a switching element that has forward scattering properties in one of its switching states, for the purpose of adjusting solar glare and, if desired, providing privacy. The switching layer facilitates switching from a transparent state to a translucent or opaque state. In one embodiment, scattering is achieved by nematic liquid crystals with a polymer component. In another embodiment, cholesteric liquid crystals are used instead. It is further described that in some embodiments, one or more additional switching layers can be used to provide scattering or control of light intensity or transmission.

[0014] Nevertheless, there is a need in the art for improved control and management of natural light transmission, especially under specific conditions and in specific situations, such as in direct sunlight or varying amounts of sunlight.

[0015] It is therefore an object of the present invention to provide a multi-layer assembly and a window element, particularly for use in architectural, automotive, aviation and maritime applications as a switchable or smart window, capable of providing advantageous control of ambient light and providing light conditions or respective lighting conditions that minimize discomfort, e.g., associated with glare and glare, in naturally lit spaces. In addition to providing comfortable and pleasant ambient conditions, it is desirable for the switchable device to provide efficiency in terms of energy and cost. A further object of the present invention is to provide a multi-layer assembly and a window element, which has good stability, e.g., against dielectric breakdown, advantageously has a low operating voltage or low energy consumption, and also exhibits fast, suitably efficient and sufficiently uniform switching. Further objects of the present invention will be readily apparent to those skilled in the art from the following detailed description.

[0016] These objects are solved by the subject matter defined in the independent claims, preferred embodiments of which are indicated in the respective dependent claims and are also described below.

[0017] The present invention specifically provides the following articles, including main aspects, preferred embodiments, and specific features, each of which alone or in combination contributes to solving the above-mentioned objects and thus provides additional advantages:

[0018] A first aspect of the present invention provides a multi-layer assembly for modulating the passage of light, the multi-layer assembly comprising: - a first switching layer which is switchable between an optically clear state and a light scattering state and which comprises a material comprising a liquid crystal medium comprising one or more mesogenic compounds and one or more chiral compounds and a polymeric component, the polymeric component being present in the material in an amount of 5% by weight or less relative to the total amount of the material; a switching element including a second switching layer, the switching element being switchable between a light state and a dark state, the second switching layer being a liquid crystal layer; and Includes.

[0019] In the present invention, advantageous multi-layer assemblies are constructed which may be advantageously used in switchable windows in architectural, automotive, aviation, and marine applications. The multi-layer assemblies are particularly useful and efficient in providing anti-glare effects as desired or required by providing switchability, particularly electrical switchability, between an optically clear and bright state and a light scattering and dark state.

[0020] The present invention recognizes that the source of glare can not only come from the high luminance of a bright light source, but also from a large luminance contrast. Although the human eye can basically adapt to different light intensities, it has a limited ability to accommodate a certain luminance range at a given moment or in a given adaptation state.

[0021] It has further been recognized that reducing the overall luminous flux, in combination with reducing the contrast between source luminance and background luminance, can be particularly effective in reducing discomfort from glare, especially in situations where the sun is perceived to be too bright and / or in a relatively inconvenient position relative to observers such as building occupants.

[0022] Surprisingly, it has been found that by including a first switching layer, as described above and below, which can provide scattering and diffuse light as required, in combination with a switching element, which includes a second switching layer, as described above and below, which can provide dimming and reduce luminous flux or overall light transmission as required, a multi-layer assembly that performs effective and efficient anti-glare can be obtained. Thereby, the amount of light can be advantageously limited and also advantageously distributed, thereby significantly reducing perceived glare, especially solar glare. Thus, the multi-layer assembly of the present invention can prevent or minimize glare, excessive solar heating, and illuminated areas with high intensity contrast.

[0023] In addition, the multilayer assembly exhibits advantageous appearance: in particular, an advantageous clear state with uniform low haze, and a scattering state with increased and uniform scattering efficiency can be obtained, along with a homogenous, achromatic appearance, advantageously avoiding or minimizing undesirable color effects.

[0024] Furthermore, the multi-layer assembly of the present invention can provide fast switching while still allowing a significant amount of natural light to pass through even in a dark and scattered state. Given this benefit of still allowing natural light to pass through, the use of artificial lighting can be limited, thus saving costs and energy. Additionally, the multi-layer assembly can be positioned and controlled such that even in a dark and scattered state, one can still see, at least to some extent, the outside surroundings.

[0025] In contrast, traditional mechanical solutions such as closing blinds or curtains are slow and often impede or limit the penetration of natural light, thus necessitating artificial lighting and obstructing the view. In addition, mechanical sunscreens require maintenance and need to take into account stresses such as wind loads.

[0026] Thus, the multi-layer assemblies of the present invention can provide improved comfort as well as energy and cost savings.

[0027] The multilayer assemblies of the present invention can provide further benefits such as favorable reliability, durability and stability, for example stability against dielectric breakdown and light stability, especially UV light stability, as well as advantageously low switching voltages and low energy consumption.In this respect, the present invention can conveniently and advantageously use liquid crystal media with improved chemical, physical and electro-optical properties, which in particular can have a broad liquid crystal phase with a favorably high clearing point, an advantageously high voltage holding ratio (VHR), good low temperature stability and favorable storage stability.

[0028] Another aspect of the invention relates to the use of the multi-layer assembly of the invention in an insulating glazing unit.

[0029] In another aspect of the invention, a window element is provided, the window element comprising the layer assembly of the invention and being electrically switchable between an optically clear and bright state and a light scattering and dark state.

[0030] The window elements of the present invention are useful for adjusting or modulating the passage of light, particularly for controlling the passage of sunlight. The window elements are particularly effective in reducing the overall light intensity to a comfortable level and reducing the contrast or intensity difference between a bright light source and its surroundings by providing a relatively smooth angular distribution of transmitted light with reduced intensity. As a result of the limited luminance range and reduced contrast difference, user comfort may be improved by avoiding or minimizing glare or dazzle.

[0031] The window elements are capable of reversible optical transitions, and such switching is rapid, typically taking less than a second, and the devices can be conveniently switched between states by application of a voltage.

[0032] Furthermore, the window element may offer significant advantages over, for example, conventional shades or blinds, since it may be installed with minimal space requirements. The window element of the present invention may be advantageously used in windows for the exterior facades of buildings, but may also be used in automobiles, commercial vehicles, trains, airplanes, ships, etc.

[0033] Window elements can significantly reduce glare while still allowing natural light to pass through and a view of the outside surroundings, which also allows the use of artificial light sources to be minimized.

[0034] Therefore, another aspect of the present invention relates to the advantageous use of the layer assembly or window element according to the invention for reducing glare due to solar radiation.

[0035] Without intending to limit the invention thereby, the invention will now be illustrated by detailed descriptions of aspects, embodiments and specific features, and specific embodiments will be described in more detail.

[0036] In this specification, the term "liquid crystal (LC)" preferably relates to materials or media that have a liquid crystal mesophase in a certain temperature range (thermotropic LC). These contain mesogenic compounds.

[0037] The terms "mesogenic compound" and "liquid crystal compound" mean compounds that contain one or more rod-shaped (rod or board / lath shaped) or discotic (disc shaped) mesogenic groups, i.e. groups capable of inducing liquid crystal phase or mesophase behavior.

[0038] LC compounds or materials containing mesogenic groups and mesogenic compounds or materials do not necessarily exhibit liquid crystal phases themselves. They may exhibit liquid crystal phase behavior only in mixtures with other compounds. This includes low molecular weight non-reactive liquid crystal compounds, reactive or polymerizable liquid crystal compounds, and liquid crystal polymers.

[0039] Rod-shaped mesogenic compounds typically comprise a mesogenic nucleus consisting of one or more aromatic or non-aromatic cyclic groups connected to each other directly or via linking groups, optionally comprising terminal groups attached to the ends of the mesogenic nucleus, and optionally comprising one or more side groups attached to the long sides of the mesogenic nucleus, the terminal and side groups typically being selected from, for example, carbyl or hydrocarbyl groups, polar groups such as halogen, nitro, hydroxy, etc., or polymerizable groups.

[0040] For simplicity, the terms "liquid crystal" or "liquid-crystalline" material or medium are used for both liquid crystal materials or media and mesogenic materials or media, and vice versa, and the term "mesogen" is used for the mesogenic groups of the material.

[0041] The term "non-mesogenic compound or material" means a compound or material which does not contain a mesogenic group as defined above.

[0042] As used herein, the term "polymer" is understood to mean a molecule that includes a backbone of one or more different types of repeating units (the smallest building blocks of the molecule), including such commonly known terms as "oligomer," "copolymer," "homopolymer," and the like. Furthermore, the term polymer is understood to include the polymer itself as well as the residues of polymerization initiators, catalysts, and other elements involved in the synthesis of such polymers, even if such residues are not covalently incorporated into the polymer. Moreover, such residues and other elements are usually removed during post-polymerization purification processes, but are typically mixed or intermingled with the polymer and therefore often remain when the polymer is transferred from container to container, or from solvent to solvent, or from dispersion medium to dispersion medium.

[0043] The term "polymerization" refers to a chemical process of forming a polymer by bonding together multiple polymerizable groups or polymer precursors (polymerizable compounds) containing such polymerizable groups.

[0044] Polymerizable compounds with one polymerizable group are also called "monoreactive" compounds, compounds with two polymerizable groups are also called "direactive" compounds, and compounds with three or more polymerizable groups are also called "multireactive" compounds. Compounds with no polymerizable groups are also called "nonreactive" or "nonpolymerizable" compounds.

[0045] The term "chiral" is generally used to describe an object that is not superimposable on its mirror image. In contrast, an "achiral" (non-chiral) object is an object that is identical to its mirror image. Some of the media used in the present invention exhibit chirality. This can be achieved by providing cholesteric liquid crystals, also known as chiral nematic liquid crystals. In this specification, the terms chiral nematic and cholesteric are used synonymously unless otherwise specified.

[0046] In this specification, [ka] represents trans-1,4-cyclohexylene.

[0047] In this specification, all concentrations are stated in weight percent and relate to the respective complete mixtures, unless otherwise stated.

[0048] All temperatures are stated in degrees Celsius (°C) and all temperature differences are also stated in degrees Celsius. All physical properties and physicochemical or electro-optical parameters are determined and stated at a temperature of 20°C unless otherwise stated.

[0049] For the purposes of the present invention, the term energy is intended to mean energy from electromagnetic radiation, in particular from the UV-A, VIS and NIR regions. In particular, it is intended to mean energy from radiation that is not absorbed or is only negligibly absorbed by materials commonly used for windows, such as glass. In this specification, the UV-A region means the wavelength range from 320 to 380 nm, the VIS region means the wavelength range from 380 nm to 780 nm, and the NIR region means the wavelength range from 780 nm to 2000 nm. Correspondingly, the term light is intended to mean electromagnetic radiation having a wavelength of 320 to 2000 nm in general, in particular 380 nm to 780 nm.

[0050] Light transmission and scattering preferably refers to the transmission and scattering of electromagnetic radiation in the spectral range of 380 nm to 780 nm.

[0051] As used herein, dichroic dye refers to a compound that absorbs light, and its absorption characteristics depend on its relative orientation with respect to the polarization direction of the light.The dichroic dye compounds of the present invention typically have an elongated shape, i.e., they are significantly longer in one spatial direction, i.e., along their longitudinal axis, than in the other two spatial directions.

[0052] The terms "film" and "layer" include self-supporting or free-standing films or layers, either rigid or flexible, with some appreciable mechanical stability, as well as coatings or layers on a supporting substrate or between two substrates.

[0053] The switching layer may be disposed on a substrate or between two substrates so as to provide a switching element operable in different optical states, and preferably electrically switchable.

[0054] The switching of the present invention preferably means electrical switching. Electrical switching can typically be achieved by providing electrodes on a substrate, for example a glass substrate or a plastic substrate. In an embodiment, the substrate is provided with a conductive layer, which comprises or is formed of a transparent conductive material, for example a transparent conductive oxide, preferably indium tin oxide (ITO) or SnO2:F, in particular ITO, or a conductive polymer, or a transparent thin layer of a metal and / or metal oxide, for example silver. The conductive layer is preferably provided with electrical connections. The voltage is preferably provided by a battery, a rechargeable battery, a supercapacitor, or an external current source, more preferably by an external current source.

[0055] In an embodiment, the substrate is provided with an orientation layer, for example made of polyimide (PI). It is particularly preferred that both the conductive layer and the orientation layer are provided on the substrate. In this case, the orientation layer or alignment layer is provided on the conductive layer so that it can be in contact with the LC medium. The orientation layer, preferably a polyimide layer, can be arranged to provide a parallel or planar orientation or a homeotropic orientation of the molecules of the liquid crystal medium, especially at the interface. In a particular embodiment, a rubbed polyimide is used on two substrates with a 90° difference in orientation as used in the so-called twisted nematic (TN) geometry. In some embodiments, a so-called pretilt angle can be set and obtained.

[0056] Alternatively, and in another preferred embodiment, a substrate without an alignment layer is used. Surprisingly, it has been found that in some embodiments, the provision of an additional alignment layer, e.g. a polyimide layer, can be beneficially avoided and still provide effective and efficient switching behavior.

[0057] Instead of, but in addition to, the alignment layer, the substrate can also be provided with a passivation or barrier layer, for example a passivation layer comprising, preferably consisting of, silicon oxide or silicon nitride. If the substrate is provided with both a passivation layer and an alignment layer, the alignment layer is arranged to be on top, i.e. in contact with the LC medium.

[0058] Thus, the first and second switching layers of the present invention are preferably each placed between two transparent substrates, each supporting an electrode arranged as a transparent conductive layer, preferably each embedded between two transparent dielectric layers, such as silicon oxide or silicon nitride layers, and optionally further provided with an alignment layer in direct contact with the switching layer.

[0059] Switching of a given switching layer preferably refers to switching between two states.

[0060] In the present invention, the first switching layer described above and below is switchable between an optically clear state and a light scattering state, the optically clear state being a non-scattering or substantially non-scattering state and appearing substantially transparent or clear to the human eye, and the light scattering state being a scattering or having diffuse transmission and appearing translucent or opaque to the human eye.

[0061] In an optically clear state, the first switchable layer of the present invention preferably provides a haze of less than 20%, more preferably less than 15%, even more preferably less than 10%, especially less than 5%, as determined according to ASTM D 1003.

[0062] In the scattering state, the first switchable layer of the present invention preferably provides a haze greater than 75%, more preferably greater than 85%, and even more preferably greater than 90%, as determined according to ASTM D 1003. In the scattering state, it is particularly preferred that the first switchable layer of the present invention provides a haze of 95% or greater, as determined according to ASTM D 1003.

[0063] To measure the haze, a BYK-Gardner transmittance meter may be used, in particular a BYK-Gardner haze-gard i. It is also possible to use a spectrophotometer, for example a Perkin Elmer Lambda 1050 spectrophotometer and a 150 mm integrating sphere.

[0064] In the present invention, a switching element including a second switching layer is switchable between a bright state and a dark state, where the bright state has a greater degree of light transmission than the dark state.

[0065] In the bright state, a switching element comprising the second switching layer of the present invention preferably has a visible light transmittance, determined according to DIN EN410, of more preferably more than 45%, more preferably more than 55%, even more preferably more than 65%.

[0066] In the dark state, a switching element comprising the second switching layer of the present invention preferably has a visible light transmission of less than 40%, more preferably less than 30%, even more preferably less than 20%, as determined according to DIN EN 410. In a preferred embodiment, in the dark state, a switching element comprising the second switching layer has a visible light transmission of in the range of 14% to 40%, more preferably in the range of 25% to 36%, as determined according to DIN EN 410.

[0067] The multilayer assemblies and in particular the window elements of the present invention are switchable, conveniently and preferably electrically switchable, between an optically clear and bright state and a light scattering and dark state.

[0068] In a preferred embodiment, the window element is switchable to an optically clear and bright state by application of an AC voltage V1, and to an optically scattering and dark state by application of an AC voltage V2, where V1>V2.

[0069] In addition, the multilayer assemblies and in particular the window elements of the present invention are preferably further operable in optically clear and dark and light scattering and bright states and are electrically switchable between these states.

[0070] However, it is also possible that the switching layer, the multilayer assembly and the window element further have further switching states, in particular intermediate states.

[0071] In the present invention, the first switching layer comprises a material including a liquid crystal medium containing one or more mesogenic compounds and one or more chiral compounds, and a polymer component, the polymer component being contained in the material in an amount of 5% by weight or less based on the total amount of the material.

[0072] Preferably, the polymer component is contained in the material in an amount of 2.5% by weight or less, particularly 1% by weight or less, based on the total amount of the material. In a preferred embodiment, the polymer component is contained in the material in an amount in the range of 0.5 to 1.5% by weight, based on the total amount of the material.

[0073] In a preferred embodiment, the polymeric component comprised in the first switching layer comprises one or more polymeric structures obtained by or obtainable from the polymerization of one or more polymerizable mesogenic compounds.

[0074] It is preferred that the polymeric component results from the polymerization of only one or more polymerizable mesogenic compounds, i.e. that the polymeric component consists of one or more polymeric structures that are based exclusively on or are derived exclusively from, respectively, one or more polymerizable mesogenic compounds as precursors.

[0075] It is particularly preferred that the polymeric component is prepared in situ, in particular within the switching layer, by polymerization of one, two or three polymerizable mesogenic compounds, more preferably one or two polymerizable mesogenic compounds.

[0076] The polymerizable mesogenic compounds of the present invention contain a mesogenic group and one or more polymerizable groups, i.e. functional groups suitable for polymerization. These compounds are also known as reactive mesogens (RM) or mesogenic monomers. The RMs can be monoreactive and / or di- or multireactive.

[0077] Although it is preferred that the polymerizable compounds used in the present invention comprise only reactive mesogens, i.e. all reactive monomers are mesogenic, in alternative embodiments it is also possible to use one or more RMs in combination with one or more non-mesogenic polymerizable compounds.

[0078] The polymerisable and mesogenic compounds can be chosen with a view to matching the refractive index of the resulting polymeric components in the modulation material and the LC medium, which can favourably contribute to improved clarity.

[0079] Preferably, the liquid crystal medium contained in the first switching layer has a clearing point of 80° C. or more, more preferably 90° C. or more, even more preferably 100° C. or more, in particular 115° C. or more. It is preferred that the medium has a clearing point in the range of 80° C. to 170° C., more preferably 100° C. to 150° C.

[0080] All physical properties and physicochemical or electro-optical parameters are determined by commonly known methods, in particular according to “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status Nov. 1997, Merck KGaA, Germany.

[0081] The clearing point, specifically the phase transition temperature between the nematic phase or the chiral nematic phase or the cholesteric phase, respectively, and the isotropic phase, can be measured and determined by common known methods, for example, using a Mettler oven, a hot stage of a polarizing microscope, or differential scanning calorimetry (DSC) analysis. In the present invention, the clearing point is preferably determined using a Mettler oven.

[0082] Preferably, the liquid crystal medium contained in the first switchable layer exhibits, in the scattering state, a pitch of 0.55 μm or more.

[0083] The cholesteric or chiral nematic media provided herein preferably have a relatively long pitch, in particular a pitch that preferably provides Bragg-type reflection above 780 nm, in which case the planar texture may also provide favorable transmission of the entire visible light spectrum.

[0084] By pitch is meant herein the pitch p of the cholesteric helix, which is the distance over which the director of the CLC makes a 2π rotation. In particularly preferred embodiments, the medium exhibits a pitch of 0.75 μm or more, more preferably 1.00 μm or more, especially 1.50 μm or more.

[0085] Preferably, the concentration of the one or more chiral dopants is set so that the resulting chiral pitch is in the range of 0.55 μm to 10 μm.

[0086] In the present invention, the pitch is, in particular, at 20° C., the selective reflection maximum λ max The pitch p is determined from NIR spectroscopy at wavelengths of λ max From the measured values ​​of , the equation λ max =n(λ max ) * p[where n(λ max ) is λ max The refractive index is determined using the refractive index of

[0087] It is also possible to measure the helical twisting power HTP using the wedge cell method known in the art, particularly at 20° C., and to confirm the determined pitch.

[0088] It has been recognized herein that when the material in the first switching layer comprises a chiral nematic or cholesteric liquid crystal medium having a relatively long pitch and an advantageously high clearing point in combination with a polymeric component as defined herein, and in particular when a so-called polymer stabilized cholesteric texture (PSCT) is provided, certain additional benefits can be obtained, for example in terms of scattering efficiency or uniformity and appearance of the scattering effect.

[0089] Surprisingly, the first switchable layer of the present invention can provide an efficient and sufficiently strongly scattering scattering state with a uniform appearance over a large area, which is particularly desirable for larger windows. This uniform appearance advantageously includes a neutral appearance, which means that undesirable color effects or respective color artifacts can be minimized or even avoided.

[0090] It has been recognized that in layers containing cholesteric materials, the inherent chiral periodicity can produce color effects, for example, different colors can be transmitted at different angles when the material is illuminated with non-diffuse light. In such cases, the transmitted light is colored when viewed off-axis, and the window elements and windows may appear colored when viewed off-axis, with the observed color depending on the angle of observation. This effect can give the appearance of an iridescence. It has further been recognized that in many applications, such color effects are undesirable.

[0091] It is believed that the materials provided in the first switching layer of the present invention can provide sufficient scattering with the desired haze, for example due to scattering from domains of the material, in particular boundaries, scratches or random structures, and that on the other hand diffraction of incident light caused by periodic structures can be substantially suppressed or avoided by sufficiently disrupting or disrupting the periodicity on the relevant length scales, in particular by the introduction of polymeric components, which can be surprisingly effective in this respect even when present in small amounts.

[0092] In a preferred embodiment, the liquid crystal medium contained in the first switchable layer according to the invention has a positive dielectric anisotropy. In this case, liquid crystal mixtures having a dielectric anisotropy Δε in the range from 3 to 45, more preferably in the range from 5 to 30, are preferred.

[0093] Δε represents the dielectric anisotropy, and Δε=ε || -ε ⊥ The dielectric anisotropy Δε is determined at 20° C. and 1 kHz.

[0094] In an alternative embodiment, it is however also possible to provide an LC medium with negative dielectric anisotropy, in which case liquid crystal mixtures with a dielectric anisotropy Δε in the range from −6 to −3 are preferred.

[0095] The liquid-crystalline medium contained in the first switchable layer according to the invention comprises at least 15% by weight, based on the total amount of the medium, of one or more compounds of formula I [ka] [In the formula, R 1 and R 2represent, independently of one another, a radical selected from F, Cl, CF3, OCF3, and unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms, or straight-chain or branched alkenyl having 2 to 15 carbon atoms, in which one or more CH2 groups are each independently selected from -O-, -S-, -CO-, -COO-, -OCO-, -OCOO-, -C≡C-, [ka] provided that the oxygen atoms are not directly linked to each other, A 11 teeth, [ka] represents n represents 0 or 1; A 21 , A 31 , and A 41 are independent of each other, [ka] represents L, at each occurrence, is the same or different and is a halogen selected from F, Cl, and Br. It is particularly preferable that the mesogenic compound contains the following formula:

[0096] In one embodiment, the liquid crystal medium comprises one or more compounds of formula I as shown above and below in an amount of at least 20% by weight, preferably at least 25% by weight, more preferably at least 30% by weight and in particular at least 35% by weight, based on the total amount of the medium.

[0097] In one embodiment, the one or more compounds of formula I are present in the medium in an amount ranging from 15% to 75% by weight, more preferably from 20% to 65% by weight, even more preferably from 20% to 55% by weight, and particularly preferably from 25% to 50% by weight, based on the total weight of the medium.

[0098] Thus, the medium in the first switching layer preferably comprises at least one compound of formula I. However, in many cases it may be beneficial or preferred for two, three or more compounds of formula I to be included in the medium.

[0099] Preferably, the group A defined in formula I 11 teeth, [ka] Represents.

[0100] In another embodiment, n as defined in formula I represents 0.

[0101] In a preferred embodiment, one or more compounds of formula I are represented by formulae Ia, Ib, and Ic [ka]

[0102] [ka] [In the formula, R 1 and R 2 represent, independently of one another, a radical selected from F, Cl, CF3, OCF3 and a straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms, which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, or a straight-chain or branched alkenyl having 2 to 15 carbon atoms, in which one or more CH2 groups may each time be replaced, independently of one another, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, with the proviso that the oxygen atoms are not directly linked to one another and preferably represent a radical selected from F, CF3, OCF3, a straight-chain alkyl or alkoxy having 1 to 9 carbon atoms or an alkenyl having 2 to 9 carbon atoms, L, at each occurrence, is the same or different and is H or a halogen selected from F, Cl, and Br, preferably a halogen selected from F and Cl, and more preferably, at each occurrence, is the same or different and is H or F. and more preferably selected from compounds of formula Ia and Ib.

[0103] When the phenylene ring of the compound of formula I is substituted, the substituent is F and further the terminal group R 1 and R 2 It is particularly preferred that does not contain Cl.

[0104] In a preferred embodiment, the amount of Cl-containing compounds contained in the medium is limited, preferably to 55% by weight or less, more preferably to 40% by weight or less, even more preferably to 25% by weight or less, based on the total amount of the medium. In a particularly preferred embodiment, the liquid crystal medium is free of Cl-containing compounds.

[0105] It is therefore also preferred to limit the amount of Cl-containing compounds in the components of the LC media consisting of compounds of formula I as shown above and below, preferably to 55% by weight or less, more preferably to 40% by weight or less, even more preferably to 25% by weight or less, based on the total amount of compounds of formula I contained in the medium. In a particularly preferred embodiment, the one or more compounds of formula I are selected from Cl-free compounds.

[0106] Ring A of Formula I 21 , A 31 , and A 41 It is further particularly preferred that at least one of the rings A of formula I has at least one F substituent. 21 , A 31 , and A 41 It is even more particularly preferred that in total there are at least two F substituents.

[0107] In the medium, the use of CN-containing compounds is preferably and advantageously limited to less than 75% by weight, more preferably less than 50% by weight, even more preferably less than 25% by weight, especially less than 15% by weight, and in a particularly preferred embodiment is avoided completely.

[0108] In addition to one or more compounds of formula I, the liquid crystal medium in the first switchable layer preferably comprises one or more further mesogenic compounds.These additional compounds are also preferably added in view of contributing to or maintaining favorable properties of the medium, such as good VHR and favorable stability.

[0109] Preferably, the liquid crystal medium contained in the first switchable layer according to the invention has the formulae II and III [ka] [In the formula, R 3 , R 4 , R 5 , and R 6 represent, independently of one another, a radical selected from F, CF3, OCF3, CN, and unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, straight-chain or branched alkyl or alkoxy having 1 to 15 carbon atoms, or straight-chain or branched alkenyl having 2 to 15 carbon atoms, in which one or more CH2 groups are each independently selected from -O-, -S-, -CO-, -COO-, -OCO-, -OCOO-, -C≡C-, [ka] provided that the oxygen atoms are not directly linked to each other, L 1 , L 2 , L 3 , L 4 , and L 5 represent, independently of each other, H or F. The compound further comprises one or more mesogenic compounds selected from the group consisting of:

[0110] In an embodiment the liquid crystal medium comprises one or more mesogenic compounds of formula II.

[0111] In another embodiment the liquid crystal medium comprises one or more mesogenic compounds of formula III.

[0112] It is preferred that the medium comprises at least 15% by weight, relative to the total amount of the medium, of one or more mesogenic compounds of formula I, optionally one or more photoinitiators and one or more mesogenic compounds selected from the group of compounds of formulae II and III.

[0113] It is particularly preferred that the medium comprises one or more compounds of formula I, one or more compounds of formula II, and one or more compounds of formula III as described above.

[0114] Preferably, the liquid crystal medium in the first switchable layer has one or more compounds of formula IV [ka] [In the formula, R 7 represents a group selected from linear or branched alkyl or alkoxy having 1 to 15 carbon atoms, preferably having 1 to 7 carbon atoms, which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, or linear or branched alkenyl having 2 to 15 carbon atoms, in which one or more CH2 groups may be replaced, in each case independently of one another, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, with the proviso that the oxygen atoms are not directly linked to one another, I is 0, 1, or 2; L 6 and L 7 are, independently of each other, H or F; X 1 stands for F, CF3, OCF3, or CN. The compound further includes the compound of the formula:

[0115] The compound of formula II is preferably used in a total concentration of 1% to 45% by weight, more preferably 5% to 25% by weight, in the medium.

[0116] The compound of formula III is preferably used in a total concentration in the medium of from 1% to 45% by weight, more preferably from 5% to 25% by weight.

[0117] The compound of formula IV is preferably used in a total concentration in the medium of from 1% to 45% by weight, more preferably from 5% to 25% by weight.

[0118] It is particularly preferred that the medium comprises one or more compounds of formula I, one or more compounds of formula II, one or more compounds of formula III, and one or more compounds of formula IV as shown above and below.

[0119] In particularly preferred embodiments, one or more of the compounds of formula I are of formulae I-1 and I-2 [ka] [In the formula, R 1 and R 2 is as defined in formula Ia above, L, in each occurrence, is the same or different and is H or F. The compound is selected from the group consisting of

[0120] Optionally, the medium may contain additional liquid crystal compounds to adjust the physical properties. Such compounds are known in the art. The concentration of these optional liquid crystal compounds further contained in the medium is preferably 0% to 30% by weight, more preferably 0.1% to 20% by weight, and most preferably 1% to 15% by weight.

[0121] In an embodiment, a medium is provided, the medium comprising: - PGP-nm, PGP-n-mV, PGU-nF, PGIGI-nF, GGP-nF, GGP-n-Cl, in particular GGP-5-Cl, CPGP-nm, CPGP-n-OT, CPGU-n-OT, DPGU-nF, and / or - CPP-nm, CPG-nF, CGU-nF, BCH.nFFF, in particular BCH.7.FFF, and / or - CP-nm, CP-nN, and / or - a compound of formula R-5011 or S-5011, and / or - one or more reactive polymerizable compounds, and / or - one or more polymerization initiators and The meaning and structure of each abbreviation or acronym is explained and illustrated in the table below.

[0122] The liquid crystal media used in the present invention may contain further additives in their usual concentrations. The total concentration of these further constituents ranges from 0% to 10%, preferably from 0.1% to 6%, based on the total mixture. The concentrations of the individual compounds used are each preferably in the range from 0.1% to 3%. The concentrations of these and similar additives are not taken into account herein in the values ​​and ranges of the concentrations of the liquid crystal components and compounds of the liquid crystal media. The same applies to the concentrations of dichroic dyes optionally used in the mixtures, unless otherwise stated, and dichroic dyes are not included when the concentrations of the compounds or components of the host mixture are specified. The concentrations of the respective additives are always stated relative to the doped final mixture.

[0123] All concentrations herein are stated as weight percent unless otherwise specified.

[0124] The liquid crystal media used in the present invention consist of several compounds, preferably 3-30, more preferably 4-20, most preferably 4-16. These compounds are mixed in a conventional manner. As a rule, the compound used in the smaller required amount is dissolved in the compound used in the larger amount. The completion of the dissolution process is particularly easy to observe at temperatures above the clearing point of the compound used in the higher concentration. However, it is of course also possible to prepare the medium in other conventional ways, for example using so-called premixes, which can be mixtures of, for example, homologous or eutectic compounds, or so-called multi-bottle systems, the components of which are themselves ready-to-use mixtures.

[0125] Many of the mesogenic compounds or mixtures thereof described above and below are commercially available. These compounds are known or can be prepared by known methods, as described in the literature (e.g. classic works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), precisely under known reaction conditions and suitable for said reaction. Known variants may also be used here, which will not be discussed in more detail here. The medium of the invention is prepared essentially in a conventional manner. In general, the components are dissolved in each other, preferably at high temperature. Suitable additives or substances can be added to modify the dielectric anisotropy, viscosity and / or alignment of the liquid crystal phase.

[0126] The medium may further include common additives such as stabilizers, antioxidants, free radical scavengers, chain transfer agents, e.g., thioethers, and / or plasticizers.

[0127] It is further preferred that the medium comprises one or more compounds selected from the compounds designated PCH-n shown in Table D, in particular selected from PCH-3, PCH-5 and PCH-7.

[0128] In the present invention, the term "alkyl" preferably embraces straight-chain and branched alkyl groups having 1 to 7 carbon atoms, in particular the straight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having 2 to 5 carbon atoms are generally preferred.

[0129] Alkoxy may be straight chain or branched, but is preferably straight chain and has 1, 2, 3, 4, 5, 6, or 7 carbon atoms, and thus is preferably methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, or heptoxy.

[0130] In the present invention, the term "alkenyl" preferably includes straight-chain and branched alkenyl groups having 2 to 7 carbon atoms, in particular straight-chain groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E-alkenyl, C5-C7-4E-alkenyl, C6-C7-5E-alkenyl and C7-6E-alkenyl, in particular C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4E-alkenyl. Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, and 6-heptenyl. Groups having 5 or fewer carbon atoms are generally preferred.

[0131] The fluorinated alkyl or alkoxy is preferably CF3, OCF3, CFH2, OCFH2, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CH2CF3, CH2CF2H, CH2CFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCH2CF3, OCH2CF2H, OCH2CFH2, OC F2CF2H, OCF2CFH2, C3F7, or OC3F7, in particular CF3, OCF3, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCF2CF2H, OCF2CFH2, C3F7, or OC3F7, particularly preferably OCF3 or OCF2H. In a preferred embodiment, fluoroalkyl includes linear groups with terminal fluorine, i.e., fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl, and 7-fluoroheptyl. However, other fluorine positions are not excluded.

[0132] The oxaalkyl is preferably of the formula C n H 2n+1 -O-(CH2) m wherein n and m are each, independently of one another, an integer from 1 to 6. Preferably, n=1 and m is an integer from 1 to 6.

[0133] Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3- or 4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0134] Halogen is preferably F or Cl, in particular F.

[0135] If one of the above mentioned groups is an alkyl group in which one CH2 group is replaced by -CH=CH-, it may be linear or branched. It is preferably linear and has 2 to 10 carbon atoms. It is thus in particular vinyl, prop-1- or prop-2-enyl, but-1-, -2- or but-3-enyl, pent-1-, -2-, -3- or pent-4-enyl, hex-1-, -2-, -3-, -4- or hex-5-enyl, hept-1-, -2-, -3-, -4-, -5- or hept-6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or oct-7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or non-8-enyl, dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or dec-9-enyl.

[0136] If one of the above groups is an alkyl group, in which one CH2 group is replaced by -O- and one CH2 group is replaced by -CO-, then these are preferably adjacent. Thus, they include acyloxy groups -CO-O-, or oxycarbonyl groups -O-CO-. These are preferably linear and have 2 to 6 carbon atoms.

[0137] They are therefore in particular acetyloxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetyloxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetyloxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetyloxypropyl, 3-propionyloxypropyl, 4-acetyloxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(meta-oxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0138] If one of the above groups is an alkyl group in which one CH2 group is replaced by unsubstituted or substituted -CH=CH- and the adjacent CH2 groups are replaced by CO, CO-O or O-CO, it may be linear or branched, it is preferably linear and has 4 to 13 carbon atoms. It is therefore in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

[0139] When one of the above mentioned groups is an alkyl or alkenyl group monosubstituted with CN or CF3, this group is preferably straight-chained. The substitution with CN or CF3 may be in any position.

[0140] When one of the above mentioned groups is an alkyl or alkenyl group which is at least mono-substituted with a halogen, this group is preferably linear and the halogen is preferably F or Cl, more preferably F. In the case of polysubstitution, the halogen is preferably F. The resulting groups also include perfluoro groups. In the case of monosubstitution, the fluoro or chloro substituent may be in any desired position, but is preferably in the ω-position.

[0141] Compounds containing branched groups can sometimes be of interest because they are more soluble in some conventional liquid crystal base materials, but when they are optically active they are particularly suitable as chiral dopants.

[0142] Branched groups of this type generally contain at most one chain branch. Preferred branched groups are isopropyl, 2-butyl (=1-methylpropyl), isobutyl (=2-methylpropyl), 2-methylbutyl, isopentyl (=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl, 2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexoxy, 1-methylhexoxy, or 1-methylheptoxy.

[0143] If one of the abovementioned groups is an alkyl group, in which two or more CH2 groups are replaced by -O- and / or -CO-O-, this may be linear or branched. It is preferably branched and has 3 to 12 carbon atoms. It is therefore particularly represented by biscarboxymethyl, 2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl, 5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl, 8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl, bis(methoxycarbonyl)methyl, 2,2-bis(methoxycarbonyl)ethyl, 3,3-bis(methoxycarbonyl) propyl, 4,4-bis(methoxycarbonyl)butyl, 5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl, 7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl, bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl, or 5,5-bis(ethoxycarbonyl)pentyl.

[0144] Advantageously, the liquid-crystalline medium in the first switchable layer may have a suitably high optical anisotropy Δn, also known as birefringence. In a preferred embodiment, the liquid-crystalline medium contained in the first switchable layer exhibits an optical anisotropy Δn of 0.13 or more, more preferably 0.16 or more, even more preferably 0.20 or more, measured at 20° C. and 589 nm.

[0145] Above and below, Δn denotes the optical anisotropy, where Δn=n e -n o and the optical anisotropy Δn is determined at 20° C. and at a wavelength of 589.3 nm.

[0146] In addition to a suitably high optical anisotropy, the liquid crystal media contained in the first switchable layer according to the invention can advantageously exhibit a suitably high voltage holding ratio (VHR) in combination with good light stability and a suitably high clearing point.

[0147] The use of reactive mesogens in low amounts as specifically stated, and preferably chiral dopants with high HTPs which can be used in low concentrations, can advantageously contribute to maintaining a high clear point.

[0148] The liquid crystal medium in the first switchable layer is a cholesteric or chiral nematic medium. Cholesteric liquid crystals (CLC) typically include media that, for example, initially have a planar structure that reflects light with a particular wavelength, and that can be switched to a focal conic light scattering structure upon application of an alternating voltage pulse, and vice versa. Upon application of a stronger voltage, in particular a stronger voltage pulse, the CLC medium can be switched to a homeotropic transparent state, from which it relaxes to the planar state when the voltage is switched off quickly, or to the focal conic state when the voltage is switched off slowly.

[0149] In the planar texture, Bragg reflection occurs, and the reflected light has the same rotation as the cholesteric helix.

[0150] In the focal conic state, the helical axes are randomly aligned and the tissue exhibits light scattering due to discontinuous spatial disparities in refractive index at the domain boundaries.

[0151] In the absence of an external electric field, both the planar and focal conic configurations are typically stable. The electric field-driven texture transition effect between the planar and focal conic states is the basis for the operation of CLC displays; when the texture of CLCs switches from the planar to focal conic texture, the Bragg reflection disappears and the CLCs scatter the incident light due to the random distribution of the helical axes.

[0152] However, switching between these states is typically achieved exclusively via the homeotropic state, in which the cholesteric helix is ​​completely unwound by dielectric coupling of LC molecules with positive dielectric anisotropy (Δε>0) with a perpendicular electric field.

[0153] In some embodiments of the present invention, the scattering state of the switchable layer may be the focal conic state described above.

[0154] In the present invention, or in a preferred embodiment, the scattering state is formed by a polydomain structure, which is preferably capable of generating sufficiently strong scattering, while at the same time Bragg-type reflection behavior is still observable, at least to some extent. In this phase, which comprises, and preferably consists of, polydomains, the orientation of the helical axis typically varies from domain to domain, and domain boundaries typically occur. However, macroscopically, the phase may appear homogeneously, in particular homogeneously opaque or cloudy to the human eye, and without visible defects, over the entire area of ​​the layer.

[0155] Polydomain structures can be obtained using conventional alignment layers, for example aligned as planar or homeotropic, and advantageously, switching to the polydomain state can be achieved at relatively low voltages, but polydomain structures can also be obtained in the absence of alignment layers.

[0156] In addition, the presence of a polymeric component in the first switching layer can favorably influence and stabilize the scattering performance.

[0157] In a preferred embodiment, a non-scattering or clear state may be formed by the homeotropic state described above. The use of this clear state may be advantageous, for example, when large area devices are used. In this regard, the advantageously high VHR obtained herein may be beneficial in stabilizing the device in this state against self-discharge behavior, thus allowing this state to persist even at a much lower refresh rate and / or with lower power consumption.

[0158] Alternatively, a non-scattering or clear state may be formed by the planar texture described above.

[0159] The use of chiral nematic or cholesteric media can have the advantage that they can provide relatively stable states, even bistable, so that devices containing them can have lower energy consumption, in particular by retaining the respective states for at least a significant time after the electric field is switched off, and by reducing the number of addressing or refreshing voltages required.

[0160] In a preferred embodiment, the first switching layer is switchable to an optically transparent state by application of an AC voltage Vi and switchable to a scattering state by application of an AC voltage Vii, where Vi>Vii.

[0161] In one embodiment, the switched clear state of the first switching layer, particularly the state having homeotropic alignment, is maintained by applying a voltage in the range of 15V to 100V, more preferably 20V to 80V, especially 25V to 50V, although the switched scattering state of the first switching layer may be stable even at 0V, at least for some time.

[0162] Preferably, the switching of the first switching layer does not use dual frequency addressing, thus simplifying the electronics required.

[0163] As mentioned above, the liquid crystal medium preferably exhibits selective reflection for wavelengths above 780 nm. The medium therefore preferably reflects in the near infrared (NIR) spectral region.

[0164] The chiral compounds and in particular the chiral dopants, as well as their concentrations, can be provided such that the cholesteric pitch of the liquid crystal medium is suitably set or adjusted. A CLC medium can be prepared, for example, by doping a nematic LC medium with a chiral dopant having a high twisting power. The pitch p of the induced cholesteric helix is ​​then determined by the concentration c and the helix-inducing power HTP of the chiral dopant according to equation (1): p=(HTP c) -1 (1) and calculate it.

[0165] It is also possible to use more than one dopant, for example, to compensate for the temperature dependence of the HTP of the individual dopants, thereby reducing the temperature dependence of the helical pitch and reflection wavelength of the CLC medium. HTP total =Σ i c i HTP i (2) [In the formula, c i is the concentration of each dopant, and HTP i is the helical induction power of each dopant] Total HTP (HTP total ) is estimated.

[0166] The liquid crystal medium in the first switching layer comprises one or more chiral compounds, in particular chiral dopants. The chiral dopants preferably have high HTP absolute value, can generally be added to the mesogenic base mixture in relatively low concentration, and have good solubility in the achiral component. When two or more chiral compounds are used, their rotation directions can be the same or opposite, and the temperature dependence of the twist can be the same or opposite.

[0167] Preferably, the one or more chiral compounds contained in the liquid crystal medium contained in the first switchable layer have a 5 μm chromaticity, preferably in the liquid crystal mixture MLC-6828 available from Merck KGaA. -1 More preferably, 10 μm -1 More preferably, 15 μm -1 Preferably, in the liquid crystal mixture MLC-6828 available from Merck KGaA, the absolute value of the helical twisting power is 20 μm or more. -1 More preferably, 40 μm -1 More preferably, 60 μm or more -1 More than 80 μm, most preferably -1 More than 260μm -1 Particularly preferred are chiral compounds having absolute values ​​of helix twisting power (HTP) in the following ranges:

[0168] Preferably, the one or more chiral compounds are contained in the liquid-crystalline medium in an amount of at most 2% by weight, more preferably at most 1% by weight, based on the total amount of the medium.

[0169] In a preferred embodiment of the present invention, the chiral component consists of two or more chiral compounds, all of which have the same sign of HTP. The temperature dependence of the HTP of the individual compounds may be high or low. The temperature dependence of the pitch of the medium can be compensated by mixing compounds with different HTP temperature dependences in the corresponding ratios.

[0170] Suitable chiral dopants are known in the art, for example, cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011, R / S-3011, R / S-4011, B(OC)2C * Some are commercially available, such as HC-3, or CB15 (all from Merck KGaA, Darmstadt, Germany).

[0171] Particularly suitable chiral dopants are compounds which contain one or more chiral radicals and one or more mesogenic groups or one or more aromatic or alicyclic groups which together with the chiral radical form a mesogenic group.

[0172] Suitable chiral radicals are, for example, monovalent or polyvalent chiral radicals selected from the group consisting of chiral branched hydrocarbon radicals, chiral ethanediols, binaphthols or dioxalanes, as well as sugar derivatives, sugar alcohols, sugar acids, lactic acids, chiral substituted glycols, steroid derivatives, terpene derivatives, amino acids or a string of a small number of amino acids, preferably 1 to 5.

[0173] Preferred chiral radicals are sugar derivatives such as glucose, mannose, galactose, fructose, arabinose, and dextrose; sugar alcohols such as sorbitol, mannitol, iditol, galactitol, or their anhydrous derivatives, in particular dianhydrohexitols such as dianhydrosorbide (1,4:3,6-dianhydro-D-sorbide, isosorbide), dianhydromannitol (isosorbitol), or dianhydroiditol (isoiditol); sugar acids such as gluconic acid, gulonic acid, and ketogulonic acid; mono- or oligoethylene glycols such as ethylene glycols, ... chiral substituted glycol radicals (where one or more CH groups are replaced by alkyl or alkoxy), such as propylene glycol; amino acids, such as alanine, valine, phenylglycine, or phenylalanine, or strings of 2-5 of these amino acids; steroid derivatives, such as cholesteryl or cholic acid radicals; terpene derivatives, such as menthyl, neomenthyl, campheyl, pineyl, terpineyl, isolongifolyl, fenchyl, careyl, myrtenyl, nopyr, geraniyl, linaloyl, neryl, citronellyl, or dihydrocitronellyl.

[0174] Suitable chiral radicals and mesogenic chiral compounds are described, for example, in DE-A-3425503, DE-A-3534777, DE-A-3534778, DE-A-3534779 and DE-A-3534780, DE-A-4342280, EP-A-01038941 and DE-A-19541820.

[0175] Preferred chiral compounds for use in the present invention are selected from the following group of compounds:

[0176] In one embodiment, the compounds of formulae AI to A-III are shown below: [ka] [In the formula, R a11 and R a12 are each independently an alkyl, oxaalkyl, or alkenyl having 2 to 9, preferably up to 7, carbon atoms; R a11 are alternatively methyl or alkoxy having 1 to 9 carbon atoms, preferably both are alkyl, preferably n-alkyl; R a21 and R a22 are each independently an alkyl or alkoxy having 1 to 9, preferably up to 7, carbon atoms, an oxaalkyl, alkenyl, or alkenyloxy having 2 to 9, preferably up to 7, carbon atoms, preferably both alkyl, preferably n-alkyl; R a31 and R a32 are each independently an alkyl, oxaalkyl, or alkenyl having 2 to 9, preferably up to 7, carbon atoms; R a11 are alternatively methyl or alkoxy having 1 to 9 carbon atoms, preferably both are alkyl, preferably n-alkyl. Preferably, the dopant is selected from the group consisting of the compounds:

[0177] The following formula: [ka] Particularly preferred are chiral dopants selected from the group consisting of the compounds:

[0178] More preferred dopants are those of formula A-IV: [ka] isosorbide, isomannitol, or isoiditol derivatives of the formula: basis [ka] teeth, [ka] Preferably dianhydrosorbitol, and chiral ethanediols, such as diphenylethanediol (hydrobenzoin), in particular those of the formula AV [ka] including the (R,S), (S,R), (R,R), and (S,S) enantiomers, not shown; During the ceremony, [ka] are each independently 1,4-phenylene optionally mono-, di- or tri-substituted by L, or 1,4-cyclohexylene; L is H, F, Cl, CN, or an optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, or alkoxycarbonyloxy having 1 to 7 carbon atoms; c is 0 or 1; Z 0 is -COO-, -OCO-, -CH2CH2-, or a single bond, R0 is an alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms.

[0179] Compounds of formula A-IV are described in WO 98 / 00428. Compounds of formula AV are described in GB 2,328,207.

[0180] In another embodiment, particularly preferred chiral dopants are chiral binaphthyl derivatives as described in WO 02 / 94805, chiral binaphthol acetal derivatives as described in WO 02 / 34739, chiral TADDOL derivatives as described in WO 02 / 06265, and chiral dopants having at least one fluorinated bridging group and a terminal or central chiral group as described in WO 02 / 06196 and WO 02 / 06195.

[0181] Formula A-VI [ka] [In the formula, X 1 , X 2 , Y 1 , and Y 2 are each independently selected from the group consisting of F, Cl, Br, I, CN, SCN, SF, linear or branched alkyl having 1 to 25 carbon atoms (F, Cl, Br, I, or CN, and in addition, one or more non-adjacent CH groups are each independently selected from the group consisting of -O-, -S-, -NH-, NR 0 -, -CO-, -COO-, -OCO-, -OCOO-, -S-CO-, -CO-S-, -CH=CH-, or -C≡C-, with the proviso that the O and / or S atoms are not directly bonded to each other), a polymerizable group, or a cycloalkyl or aryl having up to 20 carbon atoms, which may optionally be mono- or polysubstituted with halogen, preferably F, or a polymerizable group, x 1 and x 2 are each, independently of one another, 0, 1, or 2; y 1 and y 2 are each, independently of one another, 0, 1, 2, 3, or 4; B 1 and B. 2 are each, independently of one another, an aromatic or partially or fully saturated aliphatic 6-membered ring in which one or more CH groups may be optionally replaced by an N atom and one or more non-adjacent CH groups may be optionally replaced by O and / or S; W 1 and W 2 are each, independently of the other, -Z 1 -A 1 -(Z 2 -A 2 ) m -R, one of the two is or R 1 Or A 3 But they cannot both be H at the same time, or [ka] U 1 and U 2 are each, independently of one another, CH2, O, S, CO, or CS; V 1 and V 2 are, independently of each other, (CH2) n wherein 1 to 4 non-adjacent CH groups may be replaced by O and / or S; 1 and V 2 One of them is also [ka] Both are single bonds, Z 1 and Z 2 are each independently -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR 0 -, -NR 0-CO-, -O-CH2-, -CH2-O-, -S-CH2-, -CH2-S-, -CF2-O-, -O-CF2-, -CF2-S-, -S-CF2-, -CH2-CH2-, -CF2-CH2-, -CH2-CF2-, -CF2-CF2-, -CH=N-, -N=CH-, -N=N-, -CH=CH-, -CF=CH-, -CH=CF-, -CF=CF-, -C≡C-, a combination of two of these groups, in which the two O and / or S and / or N atoms are not directly bonded to each other, preferably -CH=CH-COO-, or -COO-CH=CH-, or a single bond, A 1 , A 2 , and A 3 are each, independently of one another, 1,4-phenylene in which one or two non-adjacent CH groups may be replaced by N, 1,4-cyclohexylene in which one or two non-adjacent CH groups may be replaced by O and / or S, 1,3-dioxalane-4,5-diyl, 1,4-cyclohexenylene, 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, each of which may be mono- or polysubstituted by L, and in addition A 1 is a single bond, L is a halogen atom, preferably F, CN, NO2, alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, or alkoxycarbonyloxy having 1 to 7 carbon atoms, in which one or more H atoms may be substituted with F or Cl; m is independently, each occurrence, 0, 1, 2, or 3; R and R 1 are each independently H, F, Cl, Br, I, CN, SCN, SF5, a straight-chain or branched alkyl having 1 or 3 to 25 carbon atoms, optionally mono- or polysubstituted with F, Cl, Br, I, or CN, and one or more non-adjacent CH2 groups are -O-, -S-, -NH-, -NR 0-, -CO-, -COO-, -OCO-, -O-COO-, -S-CO-, -CO-S-, -CH=CH-, or -C≡C-, where the two O and / or S atoms are not directly bonded to each other or are polymerizable groups. Particularly preferred are chiral compounds of the formula:

[0182] Formula A-VI-1 [ka] Particularly preferred are chiral binaphthyl derivatives of the formulae A-VI-1a to A-VI-1c: [ka] [Wherein, B and Z 0 is as defined in formula A-IV; Z 0 is more preferably -OCO- or a single bond, R 0 is as defined in formula A-IV, or H, or alkyl having 1 to 4 carbon atoms; b is 0, 1, or 2] It is preferred that the compound is selected from the group consisting of:

[0183] Furthermore, the formula A-VI-2 [ka] Particularly preferred are chiral binaphthyl derivatives of the formulae A-VI-2a to A-VI-2f: [ka]

[0184] [ka] [In the formula, R 0 is as defined in formula A-VI, and X is H, F, Cl, CN, or R 0 , preferably F. It is preferred that the compound is selected from the group consisting of:

[0185] In particularly preferred embodiments, the chiral medium included in the first switching layer comprises one or more compounds of formula R-5011 and S-5011 as shown in Table F below. In one embodiment, the medium comprises R-5011. In another embodiment, the medium comprises S-5011.

[0186] The LC medium contained in the first switching layer preferably and advantageously exhibits high reliability and high electrical resistivity. The LC medium contained in the first switching layer also preferably and advantageously exhibits a high voltage holding ratio (VHR). See S. Matsumoto et al., Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); T. Jacob and U. Finkenzeller in “Merck Liquid Crystals - Physical Properties of Liquid Crystals”, 1997. The VHR of the LC medium according to the invention is preferably ≧85%, more preferably ≧90%, even more preferably ≧95%, particularly preferably ≧98%. Unless otherwise stated, the measurement of the VHR is carried out as described by T. Jacob, U. Finkenzeller in “Merck Liquid Crystals - Physical Properties of Liquid Crystals”, 1997.

[0187] Preferably, the polymeric component comprised in the first switching layer comprises one or more polymeric structures obtained or respectively obtainable from the polymerization of one or more polymerizable mesogenic compounds, wherein preferably one or more of the one or more polymerizable mesogenic compounds comprises one, two or more acrylate and / or methacrylate groups.

[0188] Preferably, one or more polymerizable, curable or solidifiable compounds, preferably one or more photocurable monomers, are provided as precursors of the polymeric components in the first switchable layer of the liquid crystal medium and are subsequently polymerized in situ.

[0189] Preferably, reactive mesogens (RM) or mesogenic monomers are used which contain a mesogenic group and one or more polymerisable groups, ie functional groups suitable for polymerisation.

[0190] It is preferred that the polymerizable compounds used contain only reactive mesogens, i.e. all reactive monomers are mesogenic. Alternatively, the RM can be provided in combination with one or more non-mesogenic polymerizable compounds. The RM can be monoreactive and / or di- or multireactive.

[0191] One or more of the one or more polymerizable mesogenic compounds has the formula M R Ma -A M1 -(Z M1 -A M2 ) m1 -R Mb M Particularly preferably, the compounds are selected from the following compounds, where the definitions of the individual radicals are as follows: R Ma and R Mb are each independently P, P-Sp-, H, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, SF5, or a straight chain or branched alkyl having 1 to 25 carbon atoms, wherein the alkyl is a straight chain or branched alkyl having one or more non-adjacent CH2 groups each independently selected from -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 00 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, provided that the oxygen and / or sulfur atoms are not directly bonded to each other and one or more hydrogen atoms may be replaced by F, Cl, Br, I, CN, P, or P-Sp-, where preferably R Ma and RMb at least one of the radicals is or contains a P or P-Sp- group, Preferably, R Ma and R Mb are each independently P, P-Sp-, H, halogen, SF, NO, an alkyl, alkenyl, or alkynyl group, preferably R Ma and R Mb at least one of the radicals is or contains a P or P-Sp- group, P is a polymerizable group, Sp is a spacer group or a single bond; A M1 and A M2 are each independently an aromatic, heteroaromatic, alicyclic, or heterocyclic group, preferably having 4 to 25 ring atoms, preferably carbon atoms, which may or may not contain fused rings, and which may be optionally mono- or polysubstituted with L; L is P, P-Sp-, OH, CH2OH, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R x )2, -C(=O)Y 1 , -C(=O)R x , -N(R x )2, optionally substituted silyl, optionally substituted aryl having 6 to 20 carbon atoms, or linear or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy, or alkoxycarbonyloxy having 1 to 25 carbon atoms, or alkenyl or alkynyl having 2 to 25 carbon atoms, in which one or more hydrogen atoms may be replaced by F, Cl, P, or P-Sp-, preferably P, P-Sp-, H, OH, CH2OH, halogen, SF5, NO2, alkyl, alkenyl, or alkynyl groups, Y 1 is a halogen, preferably F, Z M1-O-, -S-, -CO-, -CO-O-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-, -SCH2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH2) n1 -, -CF2CH2-, -CH2CF2-, -(CF2) n1 -, -CH=CH-, -CF=CF-, -C≡C-, -CH=CH-, -COO-, -OCO-CH=CH-, CR 0 R 00 , or a single bond, R 0 and R 00 are each independently H or alkyl having 1 to 12 carbon atoms; R x is P, P-Sp-, H, halogen, a linear, branched or cyclic alkyl having 1 to 25 carbon atoms (wherein one or more non-adjacent CH groups may be replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, and provided that the oxygen and / or sulfur atoms are not directly bonded to each other and one or more hydrogen atoms may be replaced by F, Cl, P, or P-Sp-), an optionally substituted aryl or aryloxy group having 6 to 40 carbon atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 carbon atoms; m1 is 0, 1, 2, 3, or 4; n1 is 1, 2, 3, or 4; R Ma , R Mb and of the group of substituents L present, at least one substituent, preferably one, two or three substituents, more preferably one or two substituents, is a P or P-Sp- group or contains at least one P or P-Sp- group.

[0192] R ma and R mb Particularly preferred are compounds of formula M, wherein one or both of are P or P-Sp-.

[0193] Suitable and preferred RM for use in the liquid crystal media are, for example, those of the following formula: [ka]

[0194] [ka]

[0195] [ka]

[0196] [ka]

[0197] [ka] wherein the definitions of each radical are as follows: P 1 From P 3 are each independently a polymerizable group, preferably having one of the definitions for P specified above and below, more preferably an acrylate, methacrylate, fluoroacrylate, oxetane, vinyloxy, or epoxy group; Sp 1 From Sp 3 are each independently a single bond or a spacer group, preferably having one of the definitions for Sp specified above and below, more preferably -(CH2) p1 -, -(CH2) p1 -O-, -(CH2) p1 -CO-O-, or -(CH2) p1 -O-CO-O-, p1 is an integer from 1 to 12, and in the latter group, the bond to the adjacent ring is via an oxygen atom, P 1 -Sp 1 -, P 2 -Sp 2 - and P 3 -Sp3 -One of the radicals is R aa may be R aa is H, F, Cl, CN, or a straight or branched alkyl having 1 to 25 carbon atoms, wherein the alkyl is such that one or more non-adjacent CH groups are each independently selected from C(R 0 )=C(R 00 )-, -C≡C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, provided that the oxygen and / or sulfur atoms are not directly bonded to each other and one or more hydrogen atoms are replaced by F, Cl, CN, or P 1 -Sp 1 -, more preferably a linear or branched alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms, optionally mono- or polyfluorinated, with alkenyl and alkynyl radicals having at least 2 and branched radicals having at least 3 carbon atoms; R 0 and R 00 may be the same or different in each instance and are each independently H or alkyl having 1 to 12 carbon atoms; R y and R z are each independently H, F, CH3, or CF3; Z 1 -O-, -CO-, -C(R y R z )-, or -CF2CF2-, Z 2 and Z 3 are each independently -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CF2O-, -OCF2-, or -(CH2) n where n is 2, 3, or 4; L is, in each case, the same or different, and has the meaning given in formula M above, preferably F, Cl, CN, or linear or branched, optionally monofluorinated or polyfluorinated, alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms, preferably F; L' and L'' are each independently H, F, or Cl; X 1 From X 3 are independently -CO-O-, -O-CO- or a single bond, r is 0, 1, 2, 3, or 4; s is 0, 1, 2, or 3; t is 0, 1, or 2; x is 0 or 1.

[0198] Suitable polymerizable compounds are listed, for example, in Table G. Particularly preferred reactive mesogens are the compounds of formula RM-A and RM-B and RM-C, as shown in Comparative Examples 3 and 2, respectively.

[0199] The polymerizable compound has at least one polymerizable group. The polymerizable group is preferably CH2=CW 1 -COO-, [ka] , CH2=CW 2 -(O) k1 -, CH3-CH=CH-O-, (CH2=CH)2CH-OCO-, (CH2=CH-CH2)2CH-OCO-, (CH2=CH)2CH-O-, (CH2=CH-CH2)2N-, HO-CW 2 W 3 -, HS-CW 2 W 3 -, H.W. 2 N-, HO-CW 2 W 3 -NH-, CH2=CW 1 -CO-NH-, CH2=CH-(COO)k1 -Phe-(O) k2 -, Phe-CH=CH-, HOOC-, and OCN-; W 1 is H, Cl, CN, phenyl or alkyl having 1 to 5 C atoms, in particular H, Cl or CH3, W 2 and W 3 are, independently of one another, H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, Phe is 1,4-phenylene and k1 and k2 are, independently of one another, 0 or 1. The polymerizable or reactive groups are preferably selected from vinyl, acrylate, methacrylate, fluoroacrylate, oxetane or epoxy groups, particularly preferably from acrylate or methacrylate groups.

[0200] In an embodiment, in addition to one or more RMs, non-mesogenic monomers are included in the medium. Preferably, the one or more polymerizable compounds, either the non-mesogenic monomers or the RMs, or both, are selected from acrylates, methacrylates, fluoroacrylates, and vinyl acetates, where the composition more preferably further comprises one or more di- and / or tri-reactive polymerizable compounds, which are preferably selected from diacrylates, dimethacrylates, triacrylates, and trimethacrylates.

[0201] In a particular embodiment, one or more non-mesogenic monoacrylates are provided, particularly preferably one or more compounds selected from methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, nonyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxy-butyl acrylate and isobornyl acrylate.

[0202] Additionally or alternatively, one or more non-mesogenic monomethacrylates may be provided, particularly preferably one or more compounds selected from methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, nonyl methacrylate, dodecyl methacrylate, 2-ethyl-hexyl methacrylate, 2-hydroxy-ethyl methacrylate, 2-hydroxy-butyl methacrylate, isobornyl methacrylate and 1-adamantyl methacrylate.

[0203] It is particularly preferred that at least one crosslinker is added to the polymerizable composition, ie a polymerizable compound comprising two or more polymerizable groups, where preferably a di- or polyreactive RM is used.

[0204] In this regard, the di- and multi-reactive compounds may serve to form their own polymer networks and / or to cross-link polymer chains formed substantially from the polymerizing monoreactive compounds.

[0205] Alternatively or additionally, conventional crosslinkers known in the art can be used. It is particularly preferred to provide additional di- or multi-reactive acrylates and / or methacrylates. Particularly preferred compounds are selected from ethylene diacrylate, propylene diacrylate, butylene diacrylate, pentylene diacrylate, hexylene diacrylate, glycol diacrylate, glycerol diacrylate, pentaerythritol tetraacrylate, ethylene dimethacrylate also known as ethylene glycol dimethacrylate, propylene diamethcrylate, butylene dimethacrylate, pentylene dimethacrylate, hexylene dimethacrylate, tripropylene glycol diacrylate, glycol dimethacrylate, glycerol dimethacrylate, trimethylpropane trimethacrylate, and pentaerythritol triacrylate.

[0206] The ratio of monoreactive monomers to di- or multireactive monomers can be conveniently set and adjusted to affect the properties of the polymeric component formed.

[0207] A suitable and conventionally used thermal or photoinitiator can be added to promote the polymerization reaction, such as an azo compound or an organic peroxide, such as a Luperox type initiator. Furthermore, suitable conditions for polymerization, as well as suitable types and amounts of polymerization initiators, are known in the art and described in the literature. When the medium contains a polymerization initiator, the use of a photoinitiator is preferred.

[0208] For example, in the case of polymerization by UV light, photoinitiators can be used which decompose under UV irradiation to generate free radicals or ions, thus initiating the polymerization reaction. For the polymerization of acrylate or methacrylate groups, preferably radical photoinitiators are used. For the polymerization of vinyl, epoxide or oxetane groups, preferably cationic photoinitiators are used. It is also possible to use thermal initiators, which decompose when heated to generate free radicals or ions, thus initiating the polymerization. Typical radical photoinitiators are, for example, commercially available Irgacure®, such as Irgacure 651 (available from BASF, containing 2,2-dimethoxy-1,2-diphenylethan-1-one), or Darocure® (Ciba Geigy AG, Basel, Switzerland). Typical cationic photoinitiators are, for example, UVI 6974 (Union Carbide). Further useful photoinitiators include alpha-aminoketones such as Irgacure 907, coumarins, phosphine oxides such as Irgacure 2100, acylphosphines such as Irgacure 819.

[0209] In a particular embodiment, the added polymerization initiator, preferably a photoinitiator, comprises, preferably consists of, one or more mesogenic polymerization initiators, preferably one or more mesogenic photoinitiators, i.e. one or more reactive compounds capable of initiating polymerization and which themselves have anisotropic and mesogenic properties.

[0210] However, in particularly preferred embodiments, no polymerization initiator, particularly no photoinitiator, is used, which in some cases may improve the VHR and reduce the tendency for ions to be generated in the switchable layer.

[0211] In order to maintain and achieve good VHR, impurities in the reaction product of polymerization are preferably minimized or substantially avoided. In particular, residual reactive species and charged contaminants are preferably and preferably minimized. For example, when performing UV polymerization, in a preferred embodiment, a relatively long wavelength light close to the visible spectrum is used, preferably UV light in the range of 340 nm to 380 nm, more preferably 360 nm to 380 nm is advantageously used. In this way, undesirable photodegradation or decomposition of the components of the LC medium can be avoided or at least minimized. When a photopolymerization initiator is used, the irradiation wavelength and the photopolymerization initiator can be suitably matched or adjusted.

[0212] In the alternative case of not using a photoinitiator, which is preferred in some embodiments, the range of irradiation wavelengths may be set so that at least some of the polymerizable compounds can initiate the polymerization reaction themselves via photoreaction, and further degradation or decomposition of non-reactive components of the LC medium is avoided or at least minimized. Obtaining and setting the desired wavelength range can be achieved by conventional methods known in the art, for example by using optical filters, especially edge filters.

[0213] Surprisingly, it has been found that polymeric structures can be advantageously generated in situ by providing in a medium one or more polymerizable compounds, in particular polymerizable mesogenic compounds, as indicated above and below, and polymerizing them.

[0214] The polymerizable compounds in the medium can be selected to obtain a stable system after polymerization, for example the stable system can be stable during further processing steps, such as a heating step, where good VHR can be maintained.

[0215] Furthermore, the polymerizable compound is used in a relatively small amount to form the polymeric components, especially the polymer network, in the first switching layer, which may favorably affect stability and minimization of undesirable degradation.

[0216] The provision of a polymeric component may be useful for stabilising one or more states or phases of the LC medium.

[0217] The polymeric component may contribute advantageous properties to the resulting material in the first switching layer, for example, it may contribute to a much more stable scattering state, especially a polydomain state, which may be maintained for a longer period of time, especially up to several days, without refreshing or reapplication of voltage.

[0218] Furthermore, the polymeric components provided in the materials comprising the CLC media of the present invention can favorably affect the scattering efficiency and appearance, for example in terms of uniformity and viewing angle dependence, and thus color effects that may occur under oblique viewing angles can be significantly reduced.

[0219] In a preferred embodiment, the modulation material in the first switching layer comprises a liquid crystal medium and a polymeric component, the polymeric component comprising a polymer network obtained by polymerization of a reactive mesogen, the reactive mesogen preferably comprising at least one group selected from acrylate groups, particularly preferably from mono-, di- or triacrylate groups, vinyl ether groups and epoxide groups. Compounds comprising acrylate groups as used herein include acrylic monomers, methacrylic monomers and mixtures of such monomers.

[0220] Polymerization can be carried out using conventional methods. Polymerization can be carried out in one or more steps. Specifically, polymerization of polymerizable compounds is preferably achieved by exposure to heat or actinic radiation, where exposure to actinic radiation means irradiation with light such as UV light, visible light or IR light, irradiation with X-rays or gamma rays, or irradiation with high energy particles such as ions or electrons. In a preferred embodiment, free radical polymerization is carried out.

[0221] The polymerization can be carried out at any suitable temperature. In some embodiments, the polymerization is carried out at a temperature below the clearing point of the mesogenic mixture. However, in alternative embodiments, it is also possible to carry out the polymerization at or above the clearing point.

[0222] In an embodiment, polymerization is carried out by photoirradiation, i.e. by light, preferably UV light. For example, a UV lamp or a set of UV lamps can be used as the actinic radiation source. If a powerful lamp is used, the curing time can be shortened. Another possible photoirradiation source is a laser, such as a UV laser, a visible laser, or an IR laser.

[0223] In one embodiment, polymerization is carried out by adding one or more polymerizable compounds, preferably including a direactive compound, and optionally a suitable photoinitiator, to the chiral liquid crystal host mixture and exposing the polymerizable compounds to UV radiation to polymerize.

[0224] Preferably, the polymerization is carried out in an electro-optical cell of the chiral liquid crystal host mixture maintained in a predetermined state. In a preferred embodiment, the polymerization, preferably with UV light, is carried out when the medium is in the homeotropic state, typically and preferably with an applied electric field.

[0225] In a preferred embodiment, the liquid-crystalline medium comprising one or more polymerizable compounds, in particular polymerizable mesogenic compounds, is provided as a layer between two facing transparent substrates, each provided with an electrode, preferably arranged as a conductive layer on the inner surface of each substrate, more preferably wherein each conductive layer is covered with a passivation layer and optionally further provided with an alignment layer in direct contact with the liquid-crystalline medium.

[0226] The one or more polymerizable compounds are then polymerized, in particular in the presence of an electric field applied to the layer.

[0227] Preferably, the polymerization is carried out by photopolymerization, preferably with UV light. In a particularly preferred embodiment, during the polymerization, an electric field is applied at least temporarily to induce alignment, preferably homeotropic alignment, of the medium.

[0228] Applying a voltage to induce a predetermined orientation during polymerization can favorably affect the product properties of the switching layer and window element, for example inducing homeotropic orientation during polymerization can contribute to achieving a uniform low haze clear state, and furthermore a uniform and suitably strong haze can be obtained in the scattering state.

[0229] During photopolymerization, the temperature can be controlled, for example, in the range of 20° C. to 100° C., preferably below the clearing point.

[0230] In some embodiments, the reactive mesogens are self-initiated, while in other embodiments a photoinitiator is used to cause polymerization.

[0231] Photopolymerization of the material in the switching layer preferably uses exposure times of 30 seconds to 240 minutes, more preferably 1 minute to 120 minutes, and preferably uses a light intensity of 0.01 mW / cm 2 ~100mW / cm 2 , more preferably 0.1 mW / cm 2 ~50mW / cm 2 , especially 1 mW / cm 2 ~20mW / cm 2 Irradiation intensities in the range of

[0232] For the polymerization, several parameters, such as the irradiation dose, the applied voltage, the frequency of the AC voltage, and the amount of chiral dopant in the medium, can be suitably set or changed.

[0233] Further processing can be carried out following the polymerization, particularly the photopolymerization step. Preferably, after the polymerization step, a heat treatment is carried out in the presence or absence of an electric field. Heat treatment, i.e. exposure to a relatively elevated temperature with respect to the previous polymerization step, can result in further curing, or further conversion or completion of the polymerization.

[0234] The substrates used can also be subjected to pretreatment steps, for example surface treatment methods such as UV-ozone or plasma treatment, which can improve the alignment and wetting behavior over large areas and can also contribute to improved homogeneity and advantageous reduction of undesirable haze in the clear state.

[0235] The methods described herein are advantageously useful for producing convenient and durable window elements, where the first switching layer can exhibit achromaticity, a low haze clear state, and an efficient and uniform scattering state.

[0236] The liquid crystal medium in the first switching layer may contain additional compounds, for example one or more pleochroic dyes, in particular one or more dichroic dyes, and / or other common and suitable additives such as stabilizers, preferably in an amount of 0.001% to 25% by weight, more preferably 0.1% to 5% by weight.

[0237] Preferably however the first switching layer does not contain any dye and therefore can provide a higher transmission in the clear state and a colourless or respectively white appearance.

[0238] The multilayer assembly for regulating the passage of light of the present invention further comprises a switching element comprising, in addition to the first switching layer, a second switching layer, which is switchable between a bright state and a dark state, and the second switching layer is a liquid crystal layer.

[0239] This additional switching element, which may comprise a liquid crystal based switching layer, or in each of some embodiments two liquid crystal based switching layers, is provided to generate an overall reduction in light intensity as desired or required, i.e. to provide light attenuation or dimming switching capability.

[0240] In a preferred embodiment, the switching element is based on one or two guest-host liquid crystal switching layers, which means that in that embodiment the second switching layer is a liquid crystal layer containing one or more dichroic dyes. The switching element may comprise one switching layer, i.e. the second switching layer. Alternatively, the switching element may comprise an additional switching layer. In the latter case, the two switching layers may be provided separately or individually as so-called cells, which are then combined, in particular for example by lamination or bonding with an adhesive, and configured as a so-called double cell.

[0241] Therefore, the second switching layer, and any optional further switching layers, provided in the switching element preferably comprise at least one dichroic dye.

[0242] In the second switchable layer, and optionally in further switchable layers, a dye-doped nematic liquid crystal medium may be used.

[0243] Alternatively, in addition to at least one dichroic dye, the second switching layer, and optionally also the additional switching layers, may comprise one or more chiral compounds, preferably selected from those described for the first switching layer.

[0244] Although such dye-doped cholesteric liquid crystal media can advantageously contribute to light scattering or diffusion, at least to some extent, these media are provided primarily for obtaining dimming or light attenuation. In preferred embodiments, the haze of the switching element, especially in the bright state, is minimized.

[0245] The switching elements can be in a variety of arrangements and configurations, particularly in terms of electrode configuration, placement of optional alignment layers and their types, and liquid crystal materials, but the switching elements are provided to provide switchable dimming capability and overall change in transmittance in the multi-layer assembly.

[0246] Preferred configurations, especially for cells containing a second switching layer, include the twisted nematic (TN), antiparallel, supertwisted nematic (STN) and vertically aligned supertwisted nematic (VA-STN) configurations.

[0247] In TN configurations, the twist angle is typically at or around 90°. In STN configurations, the twist angle is greater than 90°, typically greater than 90°, up to 270°. However, the STN configurations herein may also exhibit twist angles greater than 270°.

[0248] To further improve the switching contrast of the switching element of the multi-layer assembly, it is possible to provide two switching layers, in particular arranged as a double cell as described above. In this embodiment, two layers are preferably provided so as to provide an overall optimized, or at least increased, efficiency of attenuating both the parallel and the perpendicular polarization components of light.

[0249] The two switchable layers of the double cell preferably contain the same dye-doped liquid crystal medium, which may optionally contain one or more chiral compounds.

[0250] In another embodiment, the switching element comprises a polarizing layer, where preferably exactly one polarizer and a second switching layer as the only switching layer are arranged in a so-called Heilmeyer configuration, which is also suitable for further improving the switching contrast of the switching element by providing an efficient attenuation of both the parallel and perpendicular polarization components of light.

[0251] Alternatively, the switching element can be provided with more than one polarizing layer, in particular with two polarizing layers. In this case, the liquid crystal medium provided in the switching layer preferably does not contain any dichroic dye. In this alternative form in which two polarizers are used, the element is preferably arranged in a TN configuration, an STN configuration, a vertical alignment (VA) configuration, an in-plane switching (IPS) configuration or a fringe field switching (FFS) configuration. In this alternative embodiment, one or more retardation layers or compensation layers can be optionally further included.

[0252] Typical polarizers, particularly absorptive or reflective linear polarizers, such as thin film polarizers or wire grid polarizers, as well as typical retarders and compensators, such as uniaxial and biaxial plastic retardation films, are known in the art.

[0253] In the multilayer assembly, especially when the second switching layer contains one or more chiral dopants, it is preferred that the first switching layer is closer to the light source, i.e., the switching element is placed behind the first switching layer relative to the light source. Thus, the first switching layer is preferably placed in front of the switching element relative to the outer surface facing the light source. Surprisingly, it has been found that if the first switching layer faces the light source, especially the sun, and in this relationship the switching element is on the side away from the sun, further beneficial advantages can be obtained in terms of device performance, such as further improved achromaticity, favorable appearance, and better stability.

[0254] The liquid crystal medium used in the switching element, in particular the LC host medium of the guest-host mixture, may be the same as or different from the liquid crystal medium used in the first switching layer, in particular a nematic host mixture.

[0255] Basically, suitable host mixtures for use in the switching elements are any dielectrically negative or positive LC mixtures which are suitable for use in conventional VA, TN, STN, IPS or FFS displays.

[0256] Suitable LC mixtures are known in the art and described in the literature: LC media for VA displays having negative dielectric anisotropy are described, for example, in EP-A-1 378 557.

[0257] Suitable LC mixtures with positive dielectric anisotropy which are suitable for LCDs and in particular IPS displays are known, for example, from JP 07-181439 A, EP 0 667 555 A, EP 0 673 986 A, DE 195 09 410 A, DE 195 28 106 A, DE 195 28 107 A4, WO 96 / 23851 A, WO 96 / 28521 A and WO 2012 / 079676 A1.

[0258] Preferred embodiments of the liquid crystal medium according to the present invention having negative or positive dielectric anisotropy are given below.

[0259] In a preferred embodiment of the invention, the LC medium used in the switching layer of the switching element comprises an LC host mixture having negative dielectric anisotropy. Thus, in a preferred embodiment, the mesogenic medium comprises a LC host mixture having a negative dielectric anisotropy, a) Formulas CY, PY, and AC: [ka]

[0260] [ka] [In the formula, a represents 1 or 2; b represents 0 or 1; c is 0, 1, or 2; d is 0 or 1; [ka]

[0261] [ka] R 1 and R 2 R AC1 and R AC2 each independently of one another represents an alkyl having 1 to 12 C atoms, in which in addition one or two non-adjacent CH groups may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO-, with the proviso that the O atoms are not directly linked to one another, preferably an alkyl or alkoxy having 1 to 6 C atoms, Z x and Z yeach independently of one another is -CHCH-, -CH=CH-, -CFO-, -OCF-, -CHO-, -OCH-, -CO-O-, -O-CO-, -CF-, -CF=CF-, -CH=CH-CHO- or a single bond, preferably a single bond; L 1~4 each independently represents F, Cl, CN, OCF3, CF3, CH3, CH2F, or CHF2, where the individual radicals are each independently of the other represents an alkyl having 1 to 12 C atoms, in which in addition one or two non-adjacent CH2 groups may be replaced by -O-, -CH=CH-, -CO-, -O-CO- or -CO-O-, with the proviso that the O atoms are not directly linked to one another, Z AC represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CHO- or a single bond, preferably a single bond; Preferably, L 1 and L 2 Both represent F, or L 1 and L 2 One of them represents F and the other represents Cl, or L 3 and L 4 Both represent F, or L 3 and L 4 One of them represents F and the other represents Cl. A mesogenic medium comprising one or more compounds selected from the group consisting of The composition includes a component selected from the group consisting of

[0262] The compounds of formula CY preferably have the following sub-formula: [ka]

[0263] [ka]

[0264] [ka]

[0265] [ka]

[0266] [ka] [In the formula, a represents 1 or 2, and alkyl and alkyl * each independently of the other denotes a linear alkyl radical having 1 to 6 C atoms, alkenyl denotes a linear alkenyl radical having 2 to 6 C atoms, (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-] is selected from the group consisting of:

[0267] The compounds of formula PY preferably have the following sub-formula: [ka]

[0268] [ka]

[0269] [ka]

[0270] [ka] [Wherein, alkyl and alkyl* each independently of the other denotes a linear alkyl radical having 1 to 6 C atoms, alkenyl denotes a linear alkenyl radical having 2 to 6 C atoms, (O) denotes an oxygen atom or a single bond. Alkenyl preferably denotes CH2=CH-, CH2=CHCH2CH2-, CH3-CH=CH-, CH3-CH2-CH=CH-, CH3-(CH2)2-CH=CH-, CH3-(CH2)3-CH=CH- or CH3-CH=CH-(CH2)2-] is selected from the group consisting of:

[0271] The compounds of formula AC preferably have the following sub-formula: [ka] [In the formula, R3 and R4 are the same as R AC1 and R AC2 has the meaning The compound is selected from the group consisting of:

[0272] In another preferred embodiment of the present invention the LC medium used in the switching layer of the switching element comprises an LC host mixture with positive dielectric anisotropy. Thus, in a further preferred embodiment the inventive mesogenic medium comprises a component selected from the following items b) and c):

[0273] b) Formulas IIA to VIII as shown below [ka] [In the formula, R 20 each, identically or differently, represents a halogenated or unsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, where in addition one or more CH2 groups of these radicals can each independently be -C≡C-, -CF2O-, -CH=CH-, [ka] , -O-, -CO-O-, or -O-CO-, provided that the O atoms are not directly linked to each other; X 20 each independently represents, identically or differently, F, Cl, CN, SF5, SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl radical, a halogenated alkoxy radical or a halogenated alkenyloxy radical, each having up to 6 C atoms, Y 20~24 are the same or different and each represents H or F; [ka] are each, independently of the other, [ka] represents] mesogenic medium comprising one or more compounds selected from the group of compounds of formula IIA and IIIA, in particular from the group of compounds of formula IIA and IIIA

[0274] The compound of formula IIA preferably has the following formula: [ka]

[0275] [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0276] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably denotes F. Particularly preferred are compounds of the formulae IIAa and IIAb, in particular those in which X denotes F.

[0277] The compound of formula IIIA preferably has the following formula: [ka]

[0278] [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0279] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably denotes F. Particularly preferred are compounds of the formulae IIIAa and IIIAe, in particular compounds of the formula IIIAa.

[0280] c) The formula: [ka] [In the formula, R 20 , X 20 , and Y 20~23 has the meaning given above, Z 20 represents -C2H4-, -(CH2)4-, -CH=CH-, -CF=CF-, -C2F4-, -CH2CF2-, -CF2CH2-, -CHO-, -OCH2-, -COO-, or -OCF2-, and in formulas V and VI also represents a single bond, and in formulas V and VIII also represents -CF2O-, r represents 0 or 1; s represents 0 or 1. The mesogenic medium may alternatively or additionally comprise one or more compounds selected from:

[0281] The compound of formula IVA preferably has the following formula: [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0282] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably represents F, CN or OCF3, furthermore OCF=CF2 or Cl.

[0283] The compound of formula V preferably has the following formula: [ka]

[0284] [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0285] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably represents F and OCF3, and furthermore OCHF2, CF3, OCF=CF2, and OCH=CF2.

[0286] The compound of formula VI preferably has the following formula: [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0287] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably represents F, and furthermore OCF3, CF3, CF=CF2, OCHF2, and OCH=CF2.

[0288] The compound of formula VII preferably has the following formula: [ka] [In the formula, R 20 and X 20 have the meaning given above] is selected from.

[0289] R 20 preferably represents alkyl having 1 to 6 C atoms. 20 preferably represents F, and furthermore OCF3, OCHF2, and OCH=CF2.

[0290] When the medium used in the switching element has negative dielectric anisotropy, the dielectric anisotropy value (Δε) is preferably in the range of −2.0 to −8.0, more preferably in the range of −3.0 to −6.0, and particularly preferably in the range of −3.5 to −5.0.

[0291] When the medium used in the switching element has positive dielectric anisotropy, the dielectric anisotropy value (Δε) is preferably in the range of 3.0 to 60.0, more preferably in the range of 5.0 to 30.0, and particularly preferably in the range of 8.0 to 15.0.

[0292] The liquid crystal medium used in the switching element preferably has a clearing point of 70° C. or higher, more preferably 80° C. or higher, even more preferably 90° C. or higher, still more preferably 105° C. or higher, particularly preferably 110° C. or higher. In one embodiment, the liquid crystal medium used in the switching element has a clearing point in the range of 70° C. to 170° C.

[0293] A defined high clearing point can be beneficial in terms of the performance and reliability of the multilayer assembly and the devices containing the multilayer assembly. In particular, the medium can maintain its functional properties over a favorable wide temperature range and even at high temperatures. This can be particularly advantageous for use in window elements that regulate the passage of solar light, especially when the window elements are exposed to direct or prolonged irradiation with solar light. A high clearing point can also contribute to a favorable high degree of order of the liquid crystal host molecules, and thus of the dichroic dye guest molecules, at typical operating temperatures, and thus a high contrast can be obtained between the switching states.

[0294] In a preferred embodiment, the birefringence (Δn) of the liquid crystal medium used in the switching element is in the range of 0.040 to 0.080, more preferably in the range of 0.045 to 0.070, and most preferably in the range of 0.050 to 0.060. In this embodiment, the dielectric anisotropy is positive or negative, preferably negative.

[0295] In another preferred embodiment, the Δn of the liquid crystal medium used in the switching element is in the range from 0.075 to 0.130, more preferably from 0.090 to 0.125, and most preferably from 0.095 to 0.120.

[0296] In yet another preferred embodiment, the Δn of the liquid crystal medium used in the switching element is in the range of 0.100 to 0.200, more preferably 0.110 to 0.180, most preferably 0.120 to 0.160.

[0297] In a preferred embodiment, the second switching layer and the optional additional switching layer of the switching element comprise one or more pleochroic dyes, in particular one or more dichroic dyes. Preferably, the medium comprises 2, 3, 4, 5, 6, 7 or 8 dichroic dyes. It is particularly preferred that the medium comprises at least 3 dichroic dyes.

[0298] Preferably, the dichroic compound is present in the liquid crystal medium in a dissolved state.

[0299] Each of the one or more dichroic dyes is preferably present in the liquid crystal medium in a ratio of 0.01% by weight to 10% by weight, more preferably 0.025% by weight to 7.5% by weight, even more preferably 0.05% by weight to 5% by weight, still more preferably 0.1% by weight to 2.5% by weight, and particularly preferably 0.25% by weight to 1% by weight, based on the total weight of the entire medium.

[0300] Preferably, the one or more dichroic compounds are present in a total concentration in the range of 0.05% to 15% by weight, more preferably 0.1% to 10% by weight, and even more preferably 0.5% to 5% by weight in the total liquid crystal medium.

[0301] The dichroic compounds preferably exhibit a high dichroic ratio, favourable colour purity, and a high extinction coefficient, especially in the VIS and / or NIR region of light, and in addition suitable light fastness and solubility in suitable liquid-crystalline media.

[0302] The dichroic compounds, and the amounts of each compound, are conveniently selected and mixed to obtain the color effect desired or required for a given application.

[0303] In some embodiments, the dichroic compounds contained in the LC medium have red, green and blue colors, respectively. In a preferred embodiment, the dichroic compounds in the LC medium have absorbances covering the entire visible spectrum in total. In this way, achromatic or black appearance can be obtained. Such achromatic appearance can be advantageous in applications where color artifacts or residual colors should be minimized or avoided, for example, certain smart window applications.

[0304] It has further been found that it may be advantageous to include one or more near infrared dyes in the composition, the provision of which can advantageously contribute to minimizing or avoiding residual fluorescence in the visible spectrum, so that undesirable color artifacts, such as red glow, can be avoided or at least substantially reduced.

[0305] In a particularly preferred embodiment, the LC medium of the switching element comprises at least one violet dye, at least one blue dye, at least one yellow dye, at least one red dye and at least one near infrared dye.

[0306] It is particularly preferred that the absorption spectrum of the dichroic dye in the LC medium in the switching layer is complementary to each other so that the color black is perceived as the color black.The dye of the liquid crystal medium preferably covers most of the visible spectrum, more preferably the entire spectrum, and most preferably also covers the NIR spectrum.The exact method of preparing the dye mixture that produces the color black or gray is known in the art and described, for example, in M. Richter, Einfuehrung in die Farbmetrik [Introduction to Colorimetry], 2nd Edition, 1981, ISBN 3-11-008209-8, Walter de Gruyter & Co.

[0307] The determination of the color configuration of a dye mixture is described in the field of colorimetry. To do so, the spectra of the individual dyes are calculated to obtain an overall spectrum, taking into account the Beer-Lambert law, which is then converted according to the rules of colorimetry into the corresponding color configuration and luminance values ​​under the relevant illumination, e.g. under illuminant D65 in the case of natural light. The position of the white point is fixed by the respective illuminant, e.g. D65, and is cited, for example, in the tables of the above referenced works. By varying the ratios of the various dyes, different color configurations can be determined.

[0308] The dichroic compound is preferably a positive dichroic dye, ie a dye having a positive anisotropy R.

[0309] The magnitude of the anisotropy R of a dye-containing LC mixture is determined from the values ​​of the extinction coefficients of the molecules aligned relatively parallel and perpendicular to the polarization direction of the light.

[0310] In the present invention, the magnitude of the anisotropy R is preferably greater than 0.4, more preferably greater than 0.6, even more preferably greater than 0.7, and particularly preferably greater than 0.8.

[0311] The absorption is preferably maximized when the polarization direction of the light is parallel to the longest molecular extension of the dichroic compound, and is preferably minimized when the polarization direction of the light is perpendicular to the longest molecular extension of the dichroic compound.

[0312] In one embodiment, the dichroic dye is preferably selected from the dye classes set out in B. Bahadur, Liquid Crystals - Applications and Uses, Vol. 3, 1992, World Scientific Publishing, Section 11.2.1, and is particularly preferably selected from the compounds specified within that table.

[0313] Dichroic dyes can generally belong to the classification of dichroic dyes known in the art and described in the literature.Thus, for example, anthraquinone dyes can be used in the following applications: EP 34832, EP 44893, EP 48583, EP 54217, EP 56492, EP 59036, GB 2065158, GB 2065695, JP 2081736, JP 2082196, JP 2094822, JP 2094825, JP 55-123673, DE 3017877, DE 3040102, DE 3115147, DE 311 Naphthoquinone dyes are described in German Patent Publication Nos. 3,126,108 and 3,202,761, azo dyes are described in European Patent Publication No. 43,904, German Patent Publication No. 3,123,519, WO 82 / 2054, British Patent Publication No. 2,079,770, JP-A-56-57850, JP-A-56-104,984, U.S. Pat. Nos. 4,308,161, 4,308,161, 4,340,973, T. Uchida, C. Shishido, H. Seki and M. Wada: Mol. Cryst. Lig. Cryst. 39, 39-52 (1977), and H. Seki, C. Shishido, S. Yasui and T. Uchida: Jpn. J. Appl. Phys. 21, 191-192 (1982), perylenes are described in EP 60895, EP 68427, and WO 82 / 1191, and rylene dyes are described, for example, in EP 2166040, U.S. 2011 / 0042651, EP 68427, EP 47027, EP 60895, DE 3110960, and EP 698649.

[0314] The dichroic dyes may preferably be selected from, for example, azo dyes, anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, pyrromethene dyes, malononitrile dyes, rylenes, in particular perylenes, and terylenes, thiadiazole dyes, thienothiadiazole dyes, benzothiadiazoles, thiadiazoloquinoxalines, pyrromethenes, and diketopyrrolopyrroles. Particularly preferred are azo compounds, anthraquinones, benzothiadiazoles, in particular those described in WO 2014 / 187529, diketopyrrolopyrroles, in particular those described in WO 2015 / 090497, rylenes, in particular those described in WO 2014 / 090373, and thiadiazoloquinoxaline derivatives, in particular those described in WO 2016 / 177449. It is particularly preferred that the dichroic dye is selected from azo dyes, benzothiadiazoles, and / or thiadiazoloquinoxalines.

[0315] Examples of preferred dichroic dyes which may be present in the LC medium in the switching element of the multilayer assembly are given below.

[0316] [ka]

[0317] [ka]

[0318] [ka]

[0319] [ka]

[0320] [ka]

[0321] [ka]

[0322] [ka]

[0323] [ka]

[0324] [ka]

[0325] The liquid-crystalline media may additionally comprise suitable additives and auxiliary substances, such as stabilizers and quenchers.

[0326] It is preferred that the liquid crystal media used for the second switching layer and for the optional further switching layers in the switching element of the multi-layer assembly do not contain polymerisable compounds, in particular polymerisable mesogenic compounds.

[0327] The LC media of the present invention are prepared essentially in a conventional manner. In general, the components are dissolved in each other, preferably at elevated temperature. Mixing is preferably carried out under an inert gas, such as nitrogen or argon. Optional dyes are then added, preferably at elevated temperature, more preferably above 40°C, particularly preferably above 50°C. In general, the component that is used in the smaller desired amount is dissolved in the component that will be the main constituent. It is also possible to mix solutions of the components in organic solvents, such as acetone, toluene, chloroform or methanol, and remove the solvent again after mixing, for example by distillation.

[0328] In one aspect of the invention, the layer assembly is included in a window element that is electrically switchable between an optically clear and bright state and a light scattering and dark state.

[0329] Preferably, the window element is further operable in, and electrically switchable between, optically clear and dark and optically scattering and bright states.

[0330] The window elements are preferably 0.5 mm 2 Greater than 1m, preferably 2 Greater than 3m, preferably 2 In one embodiment, the window element has a size greater than 0.10 mm. 2 ~10m 2 More preferably, 0.5 m 2 ~10m 2 It has an area in the range of

[0331] The window element of the present invention allows light to pass through and can be advantageously used and included in windows, glazing units, including insulating glazing units, facade elements, partitions, dividing walls and the like and can be used therein as an element providing different switching states on demand and thus anti-glare control on demand.

[0332] Window elements as switchable devices may be used to regulate or modulate the passage of light from an exterior space to an interior space, for example inside a building such as a residence, an office building or a commercial building, or a vehicle. Window elements may also be used to regulate or modulate the passage of light from one interior space to another, especially in structural elements separating different functional areas or rooms.

[0333] The window element, and also the window as a whole comprising the window element, preferably does not contain any light source, so that all light transmitted through the window originates from an external light source, such as the sun or a lighting device in the dwelling, in particular the sun.

[0334] In the present invention, the state of the switching layer and window element is controlled by means of an electric field applied by an electrode, preferably a transparent electrode, disposed on the substrate as a coating, the coating typically being applied to the side or surface of the substrate facing the switching layer.

[0335] Preferably, the electrodes are not patterned and / or structured in a contiguous fashion. Thus, the entire switchable region is simultaneously addressed and switched by application of an electric field. In alternative embodiments, the electrodes may be patterned to form individually addressable regions, which can be switched independently of other regions by application of an electric field. In this case, the electrodes are preferably patterned such that there are between 2 and 10 independently addressable regions.

[0336] Preferably, the switching voltages for switching the switching elements having the first switching layer and the second switching layer can be matched for ease of operation. Advantageously, a relatively low switching voltage can be useful and effective, and preferably a switching voltage of 48V or less is used.

[0337] In one embodiment, the window element is switchable to an optically clear and bright state by application of an AC voltage V1, and switchable to an optically scattering and dark state by application of an AC voltage V2, where V1>V2.

[0338] In a window element, preferably a window comprising a window element which controls and adjusts the passage of light, the first switching layer providing the scattering mode and the switching element providing switchable dimming comprising the second switching layer may be suitably positioned and joined, for example by lamination or with an adhesive, but may also be separated, for example, by one or more intermediate substrates or sheets, plates or panels, optionally with the plates further separated by a vacuum or gas filled space.

[0339] In an embodiment, the first switching layer and the second switching layer contained in the switching element are assembled as a thermal insulating glazing unit, where the two layers are in particular separated by a vacuum or gas-filled space and, optionally, the substrate or support plate, in particular one or more of the one or more glazing sheets, has a low-e coating. In this case, it is preferred that the first switching layer is arranged on the outside of the window element, i.e. facing the side facing the light source, in particular the sun, and that the switching element with the second switching layer faces inwards, i.e. the switching element is on the side remote from said light source.

[0340] The switching layer of the present invention preferably has a thickness in the range of 1 μm to 100 μm, more preferably 2 μm to 50 μm, even more preferably 4 μm to 40 μm, and particularly preferably 10 μm to 25 μm.

[0341] Spacers may be included in the cell gap of the switching layer to maintain a suitable thickness of the switching layer. Typically, the spacers have a spherical shape with a diameter within the range of the cell gap. For example, non-conductive spacers with a spherical shape of a given diameter made of polymer or glass may be used. In some embodiments, it may be useful to provide sticky spacers, i.e. spacers with some adhesive characteristics, so that they tend to stick to surfaces. It may also be useful to use black spacers, for example to avoid or minimize undesired light leakage. In some embodiments, it may be particularly beneficial to use black and sticky spacers. Alternatively, other suitable means may be used, for example column spacers, to set or maintain the cell thickness. The column spacers may be formed to allow compartments, thus allowing a structure that can be cut freely at will. In some embodiments, the switching layer may thus include compartments that are separated, for example using a rectangular or honeycomb structure, each of which contains a liquid crystal medium.

[0342] The switching layer of the present invention may be disposed between two substrates, in particular two transparent substrates. The substrates may comprise, and preferably consist of, glass or polymer, in particular glass, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), polycarbonate (PC), polyimide (PI), COP (cyclic olefin polymer), or TAC (triacetyl cellulose). In a particularly preferred embodiment, a glass substrate is used. In an alternative embodiment, a plastic substrate is used.

[0343] The device of the present invention preferably uses an alignment layer, which can be any desired layer known to those skilled in the art for this purpose. A polyimide layer is preferred, and a layer comprising rubbed polyimide is particularly preferred. In some embodiments, a planar alignment is provided, more preferably a small pretilt angle is set. In alternative embodiments, a homeotropic alignment is provided, more preferably a large pretilt angle is set.

[0344] In a preferred embodiment, the device of the invention is a component of a window, more preferably a window component comprising at least one glass surface, especially preferred a component of an insulating glazing unit.

[0345] The window element may be suitably integrated as a window, for example by lamination or bonding, preferably by lamination, to a sheet or a glazing unit.

[0346] As used herein, a window specifically refers to a structure in a building, automobile, commercial vehicle, ship, train, airplane, etc., that comprises a frame and at least one substrate or pane, such as a plastic substrate or pane, enclosed by the frame. In a preferred embodiment, particularly for architectural applications, the window preferably comprises an insulating frame and two or more panes of glass, i.e., double insulating glazing.

[0347] In a preferred embodiment, the device of the invention is attached directly to the glass surface of a window, for example by lamination, particularly preferably in the space between two glass panes of insulating double glazing.

[0348] The window element of the present invention, or the window into which it may be integrated, for example arranged as a switchable glazing unit, in particular as a thermal insulating glazing unit, preferably comprises one or more layers that block UV light. In particular, the window element preferably comprises one or more layers that do not pass or only pass very little light having a wavelength of less than 350 nm, preferably even less than 360 nm, particularly preferably even less than 380 nm. In addition, one or more of the sheets may preferably be provided with a low-e coating.

[0349] The window may be part of a building, a container, a vehicle, or another substantially closed space. The use of the window element for interior spaces exposed to strong and / or highly variable solar radiation from the outside is particularly preferred.

[0350] Advantageously, the window elements can be operated in a dark and scattering state such that a significant amount of natural light, both direct and diffuse, can still be transmitted, meaning that the use of artificial lighting can be limited or avoided entirely since sufficient natural light can pass through, resulting in cost and energy savings.

[0351] Preferably, in the light scattering and dark state the window element of the invention exhibits a transmittance, preferably a direct transmittance, of visible light, preferably light having a wavelength of 550 nm, of less than 40%, preferably less than 36%, more preferably less than 30%, in particular less than 20%. In one embodiment the transmittance of the window element of the invention in the light scattering and dark state is in the range of 14% to 36%.

[0352] Providing dimming and scattering together in a switchable device, as configured herein, allows sunlight to be more evenly distributed in an interior space, e.g., inside a building, where scattering preferably occurs over a wide range of angles, resulting in a more homogenous light distribution at all angles. This form of light modulation can advantageously result in an effective reduction in glare due to solar radiation, and comfortable lighting conditions.

[0353] This favorable transmission behavior of the multilayer assembly and window element can be determined using the bidirectional transmission distribution function (BTDF).

[0354] Preferably, for a parallel beam of light incident at right angles from a white light source, in light scattering and dark conditions, the window element of the invention has a ratio of the average light intensity transmitted into radiation angles between -3° and +3° to the average light intensity transmitted into radiation angles between -60° and +60° of less than 15, more preferably less than 10, even more preferably less than 5, more preferably less than 3.5, in particular less than 2. Preferably, the field angle dependence measurements, in particular the BTDF measurements, are carried out using a white light source and a normal incidence of light with a field angle photometer based on Fourier optics, in particular an EZLite 120R instrument from Eldim, to determine the angle dependence of the luminance of the transmitted light and the ratio of the average light intensity transmitted into different radiation angle ranges or cones.

[0355] In the present invention, and in particular in the following examples, the structures of the mesogenic compounds are shown by abbreviations, including acronyms, where the chemical formulae are abbreviated as in Tables A to C below. n H 2n+1 , C m H 2m+1 and C l H 2l+1 , or C n H 2n-1 , C m H 2m-1 and C l H 2l-1all represent straight chain alkyl or alkenyl, preferably 1-E-alkenyl, each with n, m, and l C atoms, respectively. Table A lists the codes used for the ring elements of the core structure of the compounds, and Table B shows the linking groups. Table C shows the meaning of the codes for the left-hand or right-hand end groups. The acronyms consist of the codes for the ring elements and the optional linking group, followed by a first hyphen and the code for the left-hand end group, and then a second hyphen and the code for the right-hand end group. Table D shows the structural formulae of exemplary compounds and their respective abbreviations.

[0356] [Table 1-1]

[0357] [Table 1-2]

[0358] [Table 1-3]

[0359] [Table 2]

[0360] [Table 3-1]

[0361] [Table 3-2] [wherein n and m each represent an integer, and the three dots "..." are placeholders for other abbreviations in this table.]

[0362] The following table shows exemplary structural formulas and their respective abbreviations, which are provided to illustrate the meaning of the abbreviation rules, and which further represent compounds which may be preferably used.

[0363]

Table 4-1

[0364]

Table 4-2

[0365]

Table 4-3

[0366]

Table 4-4

[0367]

Table 4-5

[0368]

Table 4-6

[0369]

Table 4-7

[0370]

Table 4-8

[0371]

Table 4-9

[0372]

Table 4-10

[0373] [Table 4-11]

[0374] [Table 4-12]

[0375] [Table 4-13]

[0376] [Table 4-14]

[0377] [Table 4-15]

[0378] [Table 4-16]

[0379] [Table 4-17]

[0380] [Table 4-18]

[0381] [Table 4-19] [In the formula, n, m, and l preferably each independently represent 1 to 7.]

[0382] The following table shows exemplary compounds which may be used as stabilizers in the medium of the present invention.

[0383] Table E Table E shows possible stabilizers, where n represents an integer from 1 to 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8, which may be added to the LC media according to the invention.

[0384] [Table 5-1]

[0385] [Table 5-2]

[0386] [Table 5-3]

[0387] [Table 5-4]

[0388] [Table 5-5]

[0389] [Table 5-6]

[0390] The LC medium preferably comprises 0 to 10% by weight, in particular 1 ppm to 5% by weight, particularly preferably 1 ppm to 1% by weight, of stabilizer.

[0391] Table F below shows exemplary compounds which may be preferably used as chiral dopants in the mesogenic media of the present invention.

[0392] [Table 6-1]

[0393] [Table 6-2]

[0394] [Table 6-3]

[0395] In a preferred embodiment of the invention, the mesogenic medium comprises one or more compounds selected from the compounds shown in Table F.

[0396] The mesogenic medium of the present invention preferably comprises two or more, preferably four or more compounds selected from the compounds shown in Tables D to F above.

[0397] In one embodiment the LC medium of the present invention preferably comprises three or more, more preferably five or more, compounds as shown in Table D.

[0398] Table G Table G collates examples of compounds which can preferably be used as reactive mesogenic compounds in the LC media of the present invention. Preferably, a polymerization initiator or a mixture of two or more polymerization initiators is added for the polymerization. The polymerization initiator or the polymerization initiator mixture is preferably added in an amount of 0.001% to 2% by weight of the mixture. A suitable polymerization initiator is, for example, Irgacure® 651 (BASF).

[0399] [Table 7-1]

[0400] [Table 7-2]

[0401] [Table 7-3]

[0402]

Table 7-4

[0403]

Table 7-5

[0404]

Table 7-6

[0405]

Table 7-7

[0406]

Table 7-8

[0407]

Table 7-9

[0408]

Table 7-10

[0409]

Table 7-11

[0410]

Table 7-12

[0411]

Table 7-13

[0412] [Table 7-14]

[0413] [Table 7-15]

[0414] [Table 7-16]

[0415] [Table 7-17]

[0416] [Table 7-18]

[0417] [Table 7-19]

[0418] In a preferred embodiment of the invention the mesogenic medium comprises one or more compounds selected from the group of compounds in Table G.

[0419] The liquid crystal medium according to the invention preferably comprises 4 or more, more preferably 6 or more, even more preferably 7 or more, particularly preferably 8 or more compounds selected from the group of compounds of table D, preferably compounds of 3 or more different formulae selected from the group of formulae of table D. It is particularly preferred that the medium additionally comprises one, two or more compounds selected from the group of formulae of table E. Further preferably, the medium further comprises one, two or more compounds selected from the group of formulae of table G.

[0420] The following examples are merely illustrative of the present invention and are not to be considered as limiting the scope of the present invention in any way. The examples and modifications or other equivalents thereof will be apparent to those of ordinary skill in the art in view of this disclosure.

[0421] However, the physical properties and compositions given below are illustrative of what properties can be realized and to what extent they can be varied, so that in particular the various property combinations that can be preferably realized are well defined.

[0422] Working Example In the embodiment, V o represents the threshold voltage at 20°C, electrostatic [V], n e represents the extraordinary refractive index at 20°C and 589 nm, n o represents the ordinary refractive index at 20°C and 589 nm, Δn represents the optical anisotropy at 20° C. and 589 nm, ε || represents the dielectric constant parallel to the director at 20°C and 1 kHz, ε ⊥ represents the dielectric constant perpendicular to the director at 20°C and 1 kHz, Δε represents the dielectric anisotropy at 20° C. and 1 kHz, cl.p., T(N,I) represents the clearing point [℃], γ1 represents the rotational viscosity [mPa·s] measured at 20 °C, determined by the rotation method in a magnetic field; K1 represents the elastic constant of the "spread" deformation at 20°C [pN], K2 represents the elastic constant [pN] of the "torsion" deformation at 20°C, K3 represents the elastic constant [pN] of the "bending" deformation at 20°C.

[0423] The term "threshold voltage" in the present invention relates to the electrostatic threshold (V0) unless otherwise specified. In the examples, as is customary, the 10% relative contrast (V 10 ) may also be indicated.

[0424] Liquid crystal mixtures and composite systems are realized with the compositions and properties described below. Their properties and optical performances are investigated.

[0425] Reference Example 1 A liquid crystal base mixture B-1 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0426] [Table 8]

[0427] Reference Example 2 A liquid crystal base mixture B-2 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0428] [Table 9]

[0429] Reference Example 3 A liquid crystal base mixture B-3 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0430] [Table 10]

[0431] 99.97% of mixture B-3 and 0.03% of formula [ka] (hereinafter referred to as ST-1) to prepare a host mixture H-3.

[0432] Reference Example 4 A liquid crystal base mixture B-4 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0433] [Table 11]

[0434] Host mixture H-4 is prepared by mixing 99.97% of mixture B-4 with 0.03% of compound ST-1 shown in Reference Example 3 above.

[0435] Reference Example 5 A liquid crystal base mixture B-5 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0436] [Table 12]

[0437] Reference Example 6 A liquid crystal base mixture B-6 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0438] [Table 13]

[0439] Reference Example 7 A liquid crystal base mixture B-7 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0440] [Table 14]

[0441] Reference Example 8 A liquid crystal base mixture B-8 is prepared and characterized having the composition and properties as shown in the table below for general physical properties.

[0442] [Table 15]

[0443] Comparative Example 1 98.877% of mixture B-1 as described in Reference Example 1 is available from Merck KGaA, Darmstadt, Germany, and is also shown in Table F above. [ka] Compounds of 0.244% formula DD-2 [ka] and 0.280% formula DD-3 [ka] A mixture M-1 is prepared by mixing the compound of the formula:

[0444] Mixture M-1 is filled into a cell having a glass substrate with an ITO electrode and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0445] The resulting cell has a clear state with 3% haze and 64.5% transmission at 48 V. Additionally, the cell has a dark privacy state with 83% haze and 22% transmission at 5 V.

[0446] When viewed from the side, undesirable off-axis color effects are observed.

[0447] Bidirectional transmission distribution function (BTDF) measurements are performed on an Eldim EZLite 120R instrument using a white light source and normal incidence of light.

[0448] The ratio of the average intensity of light transmitted at a radiation angle between -3° and +3° to the average intensity of light transmitted at a radiation angle between -60° and +60°, -3°<θ<3° > / -60°<θ<60° > is 15.7.

[0449] Although the cells effectively attenuate the overall light intensity, the light is not diffused sufficiently, and the cells do not sufficiently reduce the contrast of bright light sources, so they do not reliably prevent glare from sunlight, for example.

[0450] Comparative Example 2 Mixture M-2 is prepared by mixing 98.72% of mixture H-3 described in Reference Example 3 with 0.05% of chiral dopant S-811 available from Merck KGaA, Darmstadt, Germany and also shown in Table F above, 0.24% of compound of formula DD-1 shown in Comparative Example 1 above, 0.46% of compound of formula DD-2 shown in Comparative Example 1 above, and 0.53% of compound of formula DD-3 shown in Comparative Example 1 above.

[0451] Mixture M-2 is filled into a cell having a glass substrate with an ITO electrode and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0452] The resulting cell has a clear state with a transmittance of 49% at 12 V. In addition, the cell has a dark state with a transmittance of 22% at 0 V.

[0453] Bidirectional transmission distribution function (BTDF) measurements are performed on an Eldim EZLite 120R instrument using a white light source and normal incidence of light.

[0454] The ratio of the average intensity of light transmitted at a radiation angle between -3° and +3° to the average intensity of light transmitted at a radiation angle between -60° and +60°, -3°<θ<3° > / <I​​​-60°<θ<60° > is 18.7.

[0455] Although the cells effectively attenuate the overall light intensity, the light is not diffused sufficiently, and the cells do not sufficiently reduce the contrast of bright light sources, so they do not reliably prevent glare from sunlight, for example.

[0456] Comparative Example 3 98.61% of mixture B-2 as described in Reference Example 2 is available from Merck KGaA, Darmstadt, Germany, and is also shown in Table F above, and 0.64% of chiral dopant R-5011, and 0.75% of a compound of the formula RM-A [ka] The cholesteric mixture C-1 is prepared by mixing with the compound:

[0457] Mixture C-1 is filled into a cell having a glass substrate with an ITO electrode and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0458] The cell was then exposed to UV light (UVA and UVB, light intensity 3.5 mW / cm 2 ) to carry out polymerization, and simultaneously apply a square wave voltage (50 V, 60 Hz) for 30 min.

[0459] The resulting cell after polymerization has a clear state with 6.6% haze and 88% transmission at 60 V. In addition, the cell has a privacy (scattering) state with 99% haze and 72% transmission at 0 V.

[0460] The transmittance of the privacy state is still too high to reliably eliminate the solar glare experienced by the user.

[0461] Example 1 The cell prepared in Comparative Example 3 is combined with the cell prepared in Comparative Example 1 to form a cell stack.

[0462] The assembly combining the cells has a transparent state with 7.7% haze and 57% transmittance at 63 V. In addition, the cell assembly has an anti-glare state with 100% haze and 12% transmittance at 5 V. Moreover, in the privacy state where the scattering cell of Comparative Example 3 operates at 5 V and the dye-doped cell of Comparative Example 1 operates at 63 V, the assembly has 99% haze and 46% transmittance.

[0463] Bidirectional transmission distribution function (BTDF) measurements of the antiglare state of the combined cells are performed with an Eldim EZLite 120R instrument using a white light source and normal incidence of light.

[0464] In the anti-glare state, the ratio of the average light intensity transmitted to a radiation angle of -3° to +3° to the average light intensity transmitted to a radiation angle of -60° to +60°, -3°<θ<3° > / -60°<θ<60° > is 3.0.

[0465] This cell combination effectively reduces the overall light transmission and distributes the transmitted light more evenly over a wider angle. This cell combination provides excellent anti-glare performance, especially against sunlight.

[0466] In addition, no undesirable off-axis color effects are observed.

[0467] Example 2 98.640% of the mixture B-1 described in Reference Example 1 was mixed with 0.423% of chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany, 0.450% of [ka] Compounds of Formula RM-C of 0.450% [ka]​​ and 0.037% photoinitiator Irgacure® 651, hereafter abbreviated as IRG-651, available from Ciba, Switzerland [ka] Cholesteric mixture C-2 is prepared by mixing with

[0468] Mixture C-2 is filled into a cell having a glass substrate with an ITO electrode and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0469] The cell was then exposed to UV light (UVA and UVB, light intensity 3.5 mW / cm 2 ) and simultaneously apply a square wave voltage (50 V, 60 Hz).

[0470] The resulting cell was stacked together with the cell prepared in Comparative Example 2.

[0471] The assembly of the combined cells has a transparent state with 17.6% haze and 46.3% transmittance at 48V. Moreover, the cell assembly has an anti-glare state with 100% haze and 18% transmittance at 0V. Moreover, in the privacy state where the scattering cell prepared herein operates at 0V and the dye-doped cell of Comparative Example 2 operates at 12V, the assembly has 100% haze and 26% transmittance, and in the solar intensity control state where the scattering cell prepared herein operates at 48V and the dye-doped cell of Comparative Example 2 operates at 0V, the assembly has 24% haze and 22% transmittance. Grayscale switching is also possible by changing the voltage of the dye-doped cell.

[0472] Bidirectional transmission distribution function (BTDF) measurements of the antiglare state of the combined cells are performed with an Eldim EZLite 120R instrument using a white light source and normal incidence of light.

[0473] In the anti-glare state, the ratio of the average light intensity transmitted to a radiation angle of -3° to +3° to the average light intensity transmitted to a radiation angle of -60° to +60°, -3°<θ<3° > / -60°<θ<60° > is 1.6.

[0474] This cell combination effectively reduces the overall light transmission and distributes the transmitted light more evenly over a wider angle. This cell combination provides excellent anti-glare performance, especially against sunlight.

[0475] In addition, no undesirable off-axis color effects are observed.

[0476] Example 3 Cholesteric mixture C-3 is prepared by mixing 98.764% of mixture B-2 described in Reference Example 2 with 0.486% of chiral dopant R-5011, available from Merck KGaA, Darmstadt, Germany, and also shown in Table F above, and 0.750% of the compound of formula RM-A shown in Comparative Example 3.

[0477] Mixture C-3 is filled into a cell having a glass substrate with an ITO electrode and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0478] The cell was then exposed to UV light (UVA and UVB, light intensity 3.5 mW / cm 2 ) and simultaneously apply a square wave voltage (50 V, 60 Hz).

[0479] ​​Mixture M-3 is prepared by mixing 99.559% of mixture H-3 described in Reference Example 3 with 0.050% of chiral dopant S-811 available from Merck KGaA, Darmstadt, Germany and also shown in Table F above, 0.077% of the compound of formula DD-1 shown in Comparative Example 1 above, 0.146% of the compound of formula DD-2 shown in Comparative Example 1 above, and 0.168% of the compound of formula DD-3 shown in Comparative Example 1 above.

[0480] Mixture M-3 is filled into two cells each having a glass substrate with ITO electrodes and a polyimide alignment layer (AL-1054, made by Japan Synthetic Rubber, Planar, TN) by vacuum filling, where the cell gap of each cell is 25 μm, and the filling port is sealed. The two dye-doped cells are made into a double cell, where the first dye-doped cell is oriented such that its main axis of absorption is perpendicular to that of the second dye-doped cell. Electrical wiring is provided to each cell by soldering.

[0481] The polymer-stabilized cholesteric scattering cell is combined with a dye-doped double cell assembly into a cell stack.

[0482] The assembly of the combined cells has a transparent state of 9.5% haze and 46% transmission, with the scattering cell operating at 48 V and the two dye-doped cells operating at 12 V. Additionally, the cell assembly has an anti-glare state of 99% haze and 8.5% transmission at 0 V. Moreover, in a privacy state where the scattering cell operates at 0 V and the dye-doped cell operates at 12 V, the assembly has 99% haze and 38.5% transmission, and in a solar intensity control state where the scattering cell operates at 48 V and the dye-doped cell operates at 0 V, the assembly has 11% haze and 10% transmission.

[0483] This cell combination provides excellent anti-glare performance, especially against sunlight, and in addition, no undesirable off-axis color effects are observed.

[0484] Example 4 Mixture M-3 as shown in Example 3 above is filled into an electrically switchable cell having a Heilmeyer configuration with an ITOS XP-40HT polarizer, an anti-parallel polyimide planar alignment layer, and a 12 μm thick switching layer.

[0485] Cholesteric mixture C-4 is prepared by mixing 98.89% of mixture B-2 described in Reference Example 2 with 0.33% of chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany and also shown in Table F above, 0.75% of the compound of formula RM-A shown in Comparative Example 3, and 0.03% of the compound of formula ST-1 shown in Reference Example 3.

[0486] Mixture C-4 is filled into a cell having a glass substrate with ITO electrodes but no alignment layer by vacuum filling, where the cell gap is 25 μm, and the filling port is sealed. Electrical wiring is provided to the cell by soldering.

[0487] The cell was then exposed to UV light (UVA and UVB, light intensity 3.5 mW / cm 2 ) and simultaneously apply a square wave voltage (50 V, 60 Hz).

[0488] Both cells are combined into a stack. This combination provides excellent anti-glare performance, especially against sunlight. In addition, no undesirable off-axis color effects are observed.

[0489] Example 5 The procedure described in Example 4 was repeated, but instead of mixture C-4, 98.78% of mixture B-2 as described in Reference Example 2, 0.44% of chiral dopant R-5011 available from Merck KGaA, Darmstadt, Germany and also shown in Table F above, 0.75% of the compound of formula RM-A as shown in Comparative Example 3, and 0.03% of the compound of formula ST-1 as shown in Reference Example 3. Mixture C-5 having the following composition is prepared and used:

[0490] Example 6 The procedure described in Example 4 is repeated, but instead of mixture M-3, 97.77% of the mixture H-3 described in Reference Example 3, 0.34% of the compound of formula DD-1 shown in Comparative Example 1 above, 0.72% of the compound of formula DD-2 shown in Comparative Example 1 above, 0.87% of the compound of formula DD-3 shown in Comparative Example 1 above, 0.15% of the compound of formula ST-1 shown in Reference Example 3, and 0.15% of the compound of formula ST-2 [ka] Compound A mixture M-6 having the following composition is prepared and used:

[0491] Example 7 The procedure described in Example 4 is repeated, but instead of mixture M-3, 95.55% of the mixture H-3 described in Reference Example 3, 1.20% of formula DD-4 [ka] Compounds of 0.35% formula DD-5 [ka] Compounds of 0.50% Formula DD-6 [ka] Compounds of 1.20% formula DD-7 [ka] and 1.20% formula DD-8 [ka] Compound A mixture M-7 having the following composition is prepared and used:

[0492] Example 8 Mixture M-8 is prepared by mixing 99.95% of mixture H-4 described in Reference Example 4 with 0.05% of chiral dopant S-811 available from Merck KGaA, Darmstadt, Germany, and also shown in Table F above.

[0493] Two VA cells, VA-1 and VA-2, were prepared using glass substrates with ITO electrodes and a rubbed polyimide homeotropic alignment layer with a pretilt of 3°, where the cell gap is 25 μm, with a thin film polarizer on the first substrate of each cell and a thin film polarizer with a retarder for optical compensation to improve the viewing angle dependence on the other substrate of each cell (both from Polatechno). In VA-1, the two polarizers are arranged at 0° relative to each other, and in VA-2, the two polarizers are arranged at 90° relative to each other.

[0494] Mixture M-8 is charged into cells VA-1 and VA-2, respectively.

[0495] Scattering cells SC are prepared using mixture C-3 and conditions described in Example 3 above.

[0496] Combining VA-1 with SC and VA-2 with SC respectively results in two stacks. Using the following operating voltages, various useful optical modes of the stacks can be obtained:

[0497] [Table 16]

[0498] Examples 9 to 11 The procedure described in Example 3 is repeated, but instead of using the dye-doped mixture M-3, mixtures M-9, M-10, and M-11 are prepared and used, respectively, having the following compositions:

[0499] [Table 17]

[0500] Example 12 The procedure described in Example 1 is repeated, but instead of mixture B-1, the basic mixture B-6 shown in Reference Example 6 is used to prepare mixture M-12, and a dye-doped cell based on this mixture M-12 is prepared.

[0501] Examples 13 and 14 The procedure described in Example 1 is repeated to prepare the cell of Comparative Example 2, but instead of using mixture H-3, basic mixture B-7 described in Reference Example 7 and basic mixture B-8 described in Reference Example 8 are used to prepare mixtures M-13 and M-14, respectively.

Claims

1. A multi-layer assembly for modulating the passage of light, comprising: a first switching layer which is switchable between an optically clear state and a light scattering state and which comprises a material comprising a liquid crystal medium comprising one or more mesogenic compounds and one or more chiral compounds and a polymeric component, said polymeric component being present in said material in an amount of not more than 5% by weight relative to the total amount of said material, and said liquid crystal medium contained in said first switching layer having a clearing point of not less than 80° C., a switching element comprising a second switching layer, said switching element being switchable between a light state and a dark state, said second switching layer being a liquid crystal layer, said second switching layer comprising one or more dichroic dyes and one or more chiral compounds; Including, A multi-layer assembly, wherein the first switching layer is positioned in front of the switching element, relative to an exterior surface facing a light source.

2. 2. The multilayer assembly of claim 1, wherein the first switching layer and the second switching layer are each disposed between two transparent substrates, each of the substrates supporting an electrode disposed as a transparent conductive layer.

3. 3. A multi-layer assembly according to claim 1 or 2, wherein the switching element comprises a further switching layer, the further switching layer being a liquid crystal layer and comprising at least one dichroic dye.

4. The multi-layer assembly according to claim 1 , wherein the switching element further comprises at least one polarizing layer.

5. 5. A multilayer assembly according to claim 1 , wherein the liquid crystal medium contained in the first switching layer exhibits a pitch of 0.55 μm or more in the scattering state, and the polymeric component contained in the first switching layer comprises one or more polymeric structures obtained by or obtainable from the polymerization of one or more polymerizable mesogenic compounds.

6. The liquid crystal medium contained in the first switchable layer comprises at least 15% by weight, based on the total amount of the medium, of one or more compounds of formula I 【Chemistry 1】 [In the formula, R １ and R ２ are each independently F, Cl, CF ３ , O.C.F. ３ and unsubstituted CN or CF ３ represents a group selected from linear or branched alkyl or alkoxy having 1 to 15 carbon atoms, or linear or branched alkenyl having 2 to 15 carbon atoms, each of which is mono- or poly-substituted with halogen, and which has one or more CH ２ The radicals are each independently selected from the group consisting of -O-, -S-, -CO-, -COO-, -OCO-, -OCOO-, -C≡C-, 【Chemistry 2】 provided that the oxygen atoms are not directly linked to each other, A １１ teeth, 【Chemistry 3】 represents n represents 0 or 1; A ２１ , A ３１ , and A ４１ are independent of each other, 【Chemistry 4】 represents L, at each occurrence, is the same or different and is a halogen selected from F, Cl, and Br.

6. A multi-layer assembly according to claim 1, comprising a mesogenic compound of formula:

7. The liquid crystal medium contained in the first switchable layer has the formula II and III 【Chemistry 5】 [In the formula, R ３ , R ４ , R ５ , and R ６ are, independently of each other, F, CF ３ , O.C.F. ３ , CN, and unsubstituted CN or CF ３ represents a group selected from linear or branched alkyl or alkoxy having 1 to 15 carbon atoms, or linear or branched alkenyl having 2 to 15 carbon atoms, each of which is mono- or poly-substituted with halogen, and which has one or more CH ２ The radicals are each independently selected from the group consisting of -O-, -S-, -CO-, -COO-, -OCO-, -OCOO-, -C≡C-, 【Chemistry 6】 provided that the oxygen atoms are not directly linked to each other, L １ , L ２ , L ３ , L ４ , and L ５ are each independently H or F.

7. The multilayer assembly according to claim 1, further comprising one or more mesogenic compounds selected from the group of compounds:

8. 8. A multi-layer assembly according to claim 1, wherein the liquid-crystalline medium contained in the first switchable layer has an optical anisotropy Δn of ≧0.13, measured at 20° C. and 589 nm.

9. 10. Use of a multi-layer assembly according to any one of claims 1 to 8 in a thermal insulating glazing unit.

10. 9. A window element comprising a multilayer assembly according to any one of claims 1 to 8 and electrically switchable between an optically clear and bright state and a light scattering and dark state.

11. 11. The window element of claim 10, further operable in and electrically switchable between optically clear and dark and optically scattering and bright states.

12. In the light scattering and dark state, - Visible light transmission less than 40%; and / or - In the case of parallel light rays incident at right angles from a white light source, the ratio of the average intensity of light transmitted at radiation angles of -3° to +3° to the average intensity of light transmitted at radiation angles of -60° to +60° is less than or equal to 5.

12. The window element according to claim 10 or 11, wherein

13. 13. Use of a multi-layer assembly according to any one of claims 1 to 8 or a window element according to any one of claims 10 to 12 for reducing glare due to solar radiation.

Images