Devices for adjusting light transmission

Abstract

The present invention relates to a device for regulating light transmission, in particular to a switchable window. The present invention particularly relates to a window element comprising a switchable optical cell having a homeotropically aligned liquid crystal layer, wherein the pretilt angle is set in the range of 77° to 88°.

Description

Technical Field

[0001] The present invention relates to a device for regulating light transmission, in particular to a switchable window. The present invention particularly relates to a window element comprising a switchable optical cell having a homeotropically aligned liquid crystal layer, wherein the pretilt angle is set in the range of 77° to 88°. Background Art

[0002] Devices for controlling or modulating the transmission of light are commonly used in display applications, but they can also be used, for example, in so-called smart window applications. R. Baetens et al., "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, review various dynamic smart windows. As described therein, smart windows can utilize several technologies for modulating the transmittance of light, such as electrochromic devices, liquid crystal devices, and electrophoretic or suspended particle devices.

[0003] Shutters and light intensity modulators, particularly those based on liquid crystals, are used in switchable windows for architectural, automotive, railway, aeronautical, and marine applications.

[0004] In such devices, the transmission of light can be reversibly altered, where the intensity of incident light can be attenuated, dimmed, or colored. Thus, these devices can operate in and switch between bright and dark states—that is, between a state of relatively high light transmittance and a state of relatively low light transmittance.

[0005] While switching between different optical states in liquid crystal-based devices can also be thermally controlled, in many cases it is advantageous and reasonably preferred that the device employ different optical states using electrical switching, where the application of a voltage controls the switching. Such liquid crystal-based devices, in principle, operate by applying an electric field to change the orientation of liquid crystal (LC) molecules between two conductive electrodes, which results in a change in transmittance.

[0006] In principle, several modes or configurations can be used to provide this reversible transmission change. For twisted nematic (TN), super twisted nematic (STN) and vertical alignment (VA) liquid crystal cells, polarizers are typically used to control the transmission of light. Guest-host liquid crystal cells based on liquid crystal hosts doped with dichroic dye molecules can also be used. These guest-host systems can be used to change light transmittance without any polarizers. However, in some embodiments and applications, guest-host liquid crystal cells are also used in combination with at least one polarizer.

[0007] WO 2015 / 090506 A1 describes the use of dichroic dye-doped liquid-crystalline media having negative dielectric anisotropy in devices for regulating the passage of light.

[0008] WO 2017 / 118465 A1 describes a device for regulating the entry of light into a room comprising a switchable layer containing a dichroic dye-doped liquid crystal medium and having a twisted configuration in one of the switching states.

[0009] There remains a need in the art for devices for regulating the passage of light, particularly switchable windows, which provide reliable and efficient switching performance. Summary of the Invention

[0010] It is therefore an object of the present invention to provide an improved device for regulating the passage of light, in particular a window element comprising an optical cartridge, which exhibits robust and reliable switching while providing performance benefits in particular in terms of switching speed and appearance of the switched state. Other objects of the present invention will be immediately apparent to a person skilled in the art from the following detailed description.

[0011] This object is solved by the subject matter defined in the independent claims, while preferred embodiments are set forth in the respective dependent claims and are described further below.

[0012] The present invention particularly provides the following including main aspects, preferred embodiments and specific features, which individually or in combination contribute to solving the above objects and ultimately provide additional advantages.

[0013] A first aspect of the present invention provides a window element comprising a switchable optical box having a layer structure comprising, in this order:

[0014] - a first substrate,

[0015] - a first electrode layer,

[0016] - a first alignment layer,

[0017] - Switchable layers

[0018] - a second alignment layer,

[0019] - a second electrode layer, and

[0020] - a second substrate,

[0021] wherein the switchable layer is a homeotropically aligned liquid crystal layer comprising a liquid crystal medium, and

[0022] At least one of the first alignment layer and the second alignment layer sets a pretilt angle in a range of 77° to 88°.

[0023] Preferably and advantageously, the switchable optical cartridge is operable in a light state and a dark state and is electrically switchable between them.

[0024] In the present invention, it has been recognized that it would be advantageous to provide a switchable window element based on a liquid crystal cell using homeotropic alignment (also known as vertical alignment (VA)), in particular in combination with electrical switching. This configuration can provide benefits in terms of achievable contrast between optical states and dark state performance, while allowing for suitable viewing angle dependence and response time. It also offers the possibility of using dichroic dyes in these configurations to improve the performance of guest-host systems.

[0025] However, it has further been recognized that for these VA configurations under certain conditions, a non-uniform state may initially be obtained instead of the desired uniform optical state. This may be the case in particular when applying an electric field to switch between the optical states, and in particular when using a so-called overdrive voltage, i.e. a drive voltage exceeding the saturation voltage. It has further been found that for cell area and cell gap thicknesses that are typical of window elements and are generally larger than those of conventional liquid crystal displays, this undesirable effect may be more pronounced both in appearance and duration. In particular, after switching, an undesirable state may initially be obtained that has a grainy appearance that may last for several seconds or even minutes, only after which the desired uniform appearance appears. Without wishing to be bound by any particular theory, it is believed that this phenomenon is due to undesirable backflow dynamics that may initially lead to inhomogeneities, disclinations and visible domains that may be perceived as a grainy state. Subsequently, the actual desired uniform state may form or emerge from this temporary intermediate state.

[0026] In the present invention, it was recognized that it is desirable to quickly (immediately or at least reasonably quickly) obtain a given state with a uniform appearance when switching, thereby providing advantageous switching properties, in particular a fast switching speed. Surprisingly, it was found that by purposefully controlling the alignment of the liquid crystal medium in the switchable layer, in particular by specifically setting the pretilt angle in the range of 77° to 88° in at least one of the alignment layers, preferably in both alignment layers, the detrimental effects associated with intermediate inhomogeneities and temporal domain modes can be significantly mitigated or even avoided, thereby providing substantial benefits in terms of speed and reliability of switching.

[0027] In order to orient or align the liquid crystal molecules on the cell wall, i.e., the substrate surface, an alignment layer, also called an orientation layer, may be used to provide an interface that specifically causes or induces a predetermined or desired molecular orientation. In many cases, the liquid crystal molecules at or near the interface are tilted on average even and especially when no voltage is applied. In this regard, the average tilt angle of the liquid crystal molecules measured from the substrate surface plane or the interface plane is called the pretilt angle. For homeotropic or vertical alignment, a pretilt angle of between 88° and 89° is typically observed, i.e., an angle very close to perpendicular to the surface plane. However, it has been found that for these conventional VA configurations, the above-mentioned inhomogeneities and granular domain structures, in particular the effects attributable to field-induced reflow or countercurrent LC dynamics, may occur in certain circumstances or under certain conditions.

[0028] According to the present invention, alignment layers are used, wherein the pretilt angle is set in the range of 77° to 88°, particularly preferably in the range of 84° to 86°, at and near the interface of at least one alignment layer, and preferably at the interface of two alignment layers. This targeted provision and observation of the pretilt angle within a given specific range can significantly contribute to shortening and / or reducing the occurrence of undesirable inhomogeneities, or even to avoiding such occurrences, thereby leading to a rapid switching to the desired defect-free, uniform optical state. Furthermore, it was surprisingly found that, in particular with regard to maintaining the desired transmittance in the bright state as well as in the dark state, suitably effective and advantageous electro-optical properties can still be achieved, thereby providing the possibility of providing a sufficiently high contrast between the switching states.

[0029] Based on the advantageous optical and electro-optical properties of the switchable optical cartridge, the device of the present invention can be advantageously used in several different window and shutter applications.

[0030] In another aspect, the window element according to the invention is used in a window of a building or a vehicle. Vehicles may include, for example, road vehicles such as cars, buses and trucks, as well as trains, boats, ships and airplanes.

[0031] Without limiting the invention thereby, the invention is hereinafter illustrated by a detailed description of aspects, embodiments and specific features, and specific embodiments are described in more detail.

[0032] According to the invention, a switchable layer is arranged between two substrates in order to provide an optical cartridge operable in different optical states, which optical cartridge is preferably and advantageously electrically switchable.

[0033] The window element preferably comprises an optical box that can be switched between a light state and a dark state. In this respect, the light state has a greater degree of light transmittance than the dark state.

[0034] In the clear state, the window element according to the invention preferably has a degree of visible light transmission determined according to DIN EN 410 of more than 45%, more preferably more than 55%, even more preferably more than 65%.

[0035] In the dark state, the window element according to the invention preferably has a visible light transmission of less than 40%, more preferably less than 30%, even more preferably less than 20%, measured in accordance with DIN EN 410. In a preferred embodiment, in the dark state, the window element has a visible light transmission in the range of 1% to 35%, and more preferably in the range of 5% to 30%, measured in accordance with DIN EN 410.

[0036] According to the invention, in one of the optical states, in particular in the absence of an electric field, the liquid-crystalline medium in the switchable layer is homeotropically aligned.

[0037] The first substrate and the second substrate may comprise, 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.

[0038] Electrical switching according to the present invention is achieved by providing a substrate (e.g., a glass substrate or a plastic substrate) with first and second electrodes. Preferably, a conductive layer is provided on the substrate, wherein the conductive layer comprises or is formed from a transparent conductive material, such as a transparent conductive oxide, preferably indium tin oxide (ITO), SnO2:F, or doped zinc oxide, in particular ITO, or a conductive polymer, such as poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), or poly(4,4-dioctylcyclopentadithiophene), or a thin transparent metal and / or metal oxide layer, such as silver. The transparent conductive material is preferably a transparent conductive oxide, more preferably indium tin oxide. The transparent electrode is preferably applied to the substrate by a coating process. For example, ITO can be sputtered to typically obtain a layer thickness in the range of 5 nm to 250 nm or a sheet resistance in the range of 5 Ω / □ to 500 Ω / □.

[0039] The conductive layer is preferably provided with an electrical connection, in particular a busbar. The voltage is preferably provided by a battery, a rechargeable battery, a supercapacitor or an external current source, more preferably provided by an external current source. In this regard, the terminal can be combined with the busbar by soldering, welding or using a conductive adhesive or conductive film. In particular, an anisotropic conductive film can be used to combine a flat cable as a terminal wire to the corresponding busbar. The terminal can be used to provide a connection to a controller or a driver that generates a drive signal for controlling the state of a switchable medium located inside the electro-optical box. The terminal can, for example, be configured as a terminal wire or a connector (for attaching a wire).

[0040] Preferably, the two substrates of the switchable optical device are arranged such that each substrate has at least one region that does not overlap with the other substrate. These non-overlapping regions can therefore provide access to the corresponding transparent electrodes, and the busbars can be conveniently placed in these non-overlapping regions. The non-overlapping region is preferably an offset between the first and second substrates in the range of 1 mm to 20 mm, preferably in the range of 2 mm to 10 mm, for example about 4 mm.

[0041] The liquid crystal medium can be included in the electro-optical cell in a suitable manner, such as using vacuum fill or drop fill. Typically, a frame sealant or edge sealant is provided to close the cell or contain the medium. Examples of suitable materials for sealing the cell include epoxy-based sealants, polyurethanes, hot melt sealants, and acrylates.

[0042] In a window element, in particular in a switchable optical cell, the thickness of the switchable layer is preferably at least 5 μm, more preferably at least 7 μm, even more preferably at least 10 μm, still more preferably at least 15 μm, and particularly preferably at least 20 μm. In an embodiment, the thickness of the switchable layer comprising the liquid-crystalline medium is from 5 μm to 100 μm, more preferably from 10 μm to 50 μm, in particular from 15 μm to 25 μm.

[0043] In order to maintain an appropriate thickness of the switching layer, spacers may be included within the cell gap of the switching layer. Typically, the spacers have a spherical shape with a diameter within the cell gap. For example, a spherical non-conductive spacer made of a polymer or glass with a predetermined diameter may be used. In some embodiments, it may be useful to provide a sticky spacer, i.e., a spacer having some inherent adhesive properties to better adhere to the surface. It may also be useful to use a black spacer, for example to avoid or minimize unwanted light leakage. The use of a black and sticky spacer may be particularly beneficial. Alternatively, the cell thickness may be set or maintained by other suitable means, for example by using columnar spacers. The columnar spacers may also be formed to provide compartments, thereby optionally allowing a freely cuttable structure.

[0044] In this context, the terms film and layer include rigid or flexible, self-supporting or independent films or layers with more or less pronounced mechanical stability, as well as coatings or layers on a supporting substrate or between two substrates.

[0045] A passivation layer or barrier layer may also be provided on the substrate, for example a passivation layer comprising, preferably consisting of, silicon oxide or silicon nitride. In this case, the passivation layer is arranged on the substrate such that the alignment layer is uppermost, i.e. in contact with the LC medium.

[0046] Preferably, the transparent conductive electrode layer is respectively embedded between two transparent dielectric layers. Thus, according to a particularly preferred embodiment of the optical device, a liquid crystal medium is provided in the switchable layer, wherein the switchable layer is sandwiched between a first alignment layer and a second alignment layer and is in direct contact therewith, and wherein the electrodes are respectively arranged on the passivation layer and are particularly embedded between the two transparent dielectric layers.

[0047] Preferably, the liquid-crystalline medium comprises one or more dichroic dyes.

[0048] As used herein, dichroic dyes are considered to refer to light-absorbing compounds in which the absorption properties depend on the compound's orientation relative to the polarization direction of light. Dichroic dye compounds according to the present invention typically have an elongated shape, meaning that the compound is significantly longer in one spatial direction (i.e., along the longitudinal axis) than in the other two spatial directions. Dichroic dyes absorb or preferentially absorb light in one direction, thereby enabling the transmission of light to be adjusted by varying the dichroic dye's orientation.

[0049] Thus, guest-host liquid crystal cells based on liquid crystal hosts doped with dichroic dye molecules can be used, wherein these guest-host systems can be used without any polarizers to vary the light transmittance.

[0050] Each of the one or more dichroic dyes is preferably present in the liquid-crystalline medium in a proportion of 0.005 to 12.5% by weight, more preferably 0.01 to 10% by weight, even more preferably 0.025 to 7.5% by weight, still even more preferably 0.05 to 5% by weight, yet even more preferably 0.1 to 2.5% by weight and particularly preferably 0.25 to 1% by weight, based on the total weight of the entire medium.

[0051] Preferably, the one or more dichroic dyes are present in the liquid-crystalline medium in a total concentration of 0.01% to 30% by weight, more preferably 0.025% to 25% by weight, even more preferably 0.05% to 15% by weight, yet even more preferably 0.1% to 10% by weight and particularly preferably 0.5% to 5% by weight.

[0052] The concentration of the dye(s) is preferably chosen to ensure suitable properties of the resulting modulated material, in particular with respect to the desired colour and / or dimming effect.

[0053] The dichroic dye can be preferably selected from, for example, azo dyes, anthraquinones, thiophenol anthraquinones, methine compounds, azomethine compounds, merocyanidin compounds, naphthoquinones, tetrazines, pyrromethene dyes, malononitrile dyes, nickeldithiolenes, (metal)phthalocyanines, (metal)naphthalocyanines and (metal)porphyrins, rylenes (especially perylene and terylene), thiadiazole dyes, thienothiadiazole dyes, benzothiadiazoles, thiadiazolequinoxalines and diketopyrrolopyrroles. Particularly preferred are azo compounds; anthraquinones; thiophenol anthraquinones, benzothiadiazoles, as described in particular in WO 2014 / 187529; diketopyrrolopyrroles, as described in particular in WO 2015 / 090497; thiadiazoquinoxalines, as described in particular in WO 2016 / 177449, and rylene, as described in particular in WO 2014 / 090373.

[0054] The liquid-crystalline medium preferably comprises one, two, three, four, five, six, seven, eight, nine or ten different dichroic dyes, particularly preferably two or three dichroic dyes.

[0055] In an embodiment, the absorption spectra of the dichroic dyes optionally contained in the medium or the switchable layer are preferably complementary to one another in such a way that the eye appears black. Preferably, two or more, more preferably three or more, dichroic dyes are used in the liquid-crystalline medium to preferably cover a large part of the visible spectrum. The precise manner in which mixtures of dyes that appear black or grey to the eye can be prepared is known to those skilled in the art and is described, for example, in M. Richter, Einführung in die Farbmetrik [Introduction to Colorimetry], 2nd edition, 1981, ISBN 3-11-008209-8, Walter de Gruyter & Co.

[0056] In another embodiment, for example, different color settings are implemented, such as red, green or blue.

[0057] The color position of a dye mixture is described in the colorimetry area. For this purpose, the spectra of the individual dyes are calculated according to the Lambert-Beer law to obtain a total spectrum and converted into corresponding color positions and brightness values according to the rules of colorimetry under the relevant illumination, for example, daylight illuminant D65. The position of the white point is fixed by the individual illuminants (e.g., D65) and is given in tables, for example, in the references above. Different color positions can be set by varying the ratios of the different dyes.

[0058] In a preferred embodiment, three or more different dichroic dyes are contained in the liquid-crystalline medium.

[0059] According to a preferred embodiment, the medium and the switchable layer comprise one or more dichroic dyes which absorb light in the red and NIR region, i.e. at wavelengths in the range of 600 nm to 2000 nm, preferably in the range of 600 nm to 1800 nm, particularly preferably in the range of 650 nm to 1300 nm.

[0060] In an embodiment, the dichroic dyes that may be provided in the medium and the switchable layer are preferably selected from the classes of dyes indicated in B. Bahadur, Liquid Crystals—Applications and Uses, Vol. 3, 1992, World Scientific Publishing, chapter 11.2.1, and are particularly preferably selected from the explicit compounds given in the tables presented herein.

[0061] Said dyes belong to the class of dichroic dyes known to the person skilled in the art and have already been described in the literature. For example, anthraquinone dyes are described in EP 34832, EP 44893, EP 48583, EP 54217, EP 56492, EP 59036, GB 2065158, GB 2065695, GB 2081736, GB 2082196, GB 2094822, GB 2094825, JP-A 55-123673, DE 3017877, DE 3040102, DE 3115147, DE 3115762, DE 3150803 and DE 3201120, naphthoquinone dyes in DE 3126108 and DE 3202761, azo dyes in EP 43904, DE 3123519, WO 200001 82 / 2054, GB 2079770, JP-A 56-57850, JP-A 56-104984, US 4308161, US 4308162, US 4340973, T. Uchida, C. Shishido, H. Seki and M. Wada: Mol. Cryst. Liq. Cryst. 39, 39-52 (1977) and H. Seki, C. Shishido, S. Yasui and T. Uchida: Jpn. J. Appl. Phys. 21, 191-192 (1982), and perylene is described in EP 60895, EP 68427 and WO 82 / 1191. Rylene dyes are described, for example, in EP 2166040, US 2011 / 0042651, EP 68427, EP 47027, EP 60895, DE 3110960 and EP 698649.

[0062] The switchable optical device may include other functional layers, for example, UV blocking layers and / or color filters.

[0063] The optical cell and the window element are preferably characterized in that they do not contain a polymer-based polarizer, particularly preferably do not contain a polarizer in the solid material phase, and very particularly preferably do not contain a polarizer at all. Therefore, in a particularly preferred embodiment, the device, in particular the window element, does not contain a polarizer.

[0064] However, according to alternative embodiments, the device may further include one or more polarizers. Thus, in embodiments, at least one polarizing layer and optionally at least one retardation layer are provided in the optical device. In this case, the polarizer is preferably a linear polarizer. Both absorbing and reflective polarizers may optionally be used. Preferably, the polarizer is in the form of an optical film.

[0065] Thus, in addition to or as an alternative to providing one or more dichroic dyes in the liquid crystal medium, a window element may be provided, wherein the switchable optical cell further comprises one or more polarizer layers and optionally one or more optical retarder layers.

[0066] In a specific alternative, it is preferred that the device comprises only one polarizer. If exactly one polarizer is present, a Heilmeier-type guest-host arrangement is preferably used. In another alternative, a liquid crystal cell having two polarizers, preferably in the absence of any dichroic dye in the liquid crystal medium, is used to control the transmission of light.

[0067] According to the invention, in the optical cell, first and second alignment layers are provided in direct contact with the liquid-crystalline medium.

[0068] It has been found that even when a pretilt angle in the range of 77° to 88° is set in only one of the first and second alignment layers, undesirable non-uniformity during electrical switching can be significantly reduced. However, preferably, both the first and second alignment layers have a pretilt angle in the range of 77° to 88°. In this way, a greater reduction in the effect can be achieved.

[0069] According to the present invention, the pretilt angle is controlled by at least one alignment layer, and preferably by two alignment layers, and is set within a range of 77° to 88°, more preferably within a range of 79° to 87.5°, even more preferably within a range of 81° to 87°, and particularly within a range of 84° to 86°. Surprisingly, it has been found that the control of the defined pretilt angle can reduce and shorten the occurrence of non-uniformity while also providing sufficient contrast and suitable transmittance in the optical state.

[0070] As used herein, the term "pretilt angle" is understood to refer to the tilted alignment of the liquid crystal molecules of the liquid crystal medium relative to the surface of the optical cell. In particular, the pretilt angle here denotes the average angle (<90°) between the longitudinal molecular axis of the LC molecules (LC director) and the surfaces of the plane-parallel outer plates forming the cell. A suitable method for measuring the pretilt angle is based on the Mueller matrix polarimetry and is given in the examples. Unless otherwise stated, the pretilt angle values disclosed above and below relate to this measurement method.

[0071] In principle, the first alignment layer and the second alignment layer can be formed based on conventional materials and methods, wherein the alignment layers are provided to achieve homeotropic edge alignment.

[0072] Preferably, the first alignment layer and the second alignment layer comprise an organic material, more preferably consist of an organic material, wherein in particular the organic material is rubbed, in particular mechanically rubbed, or phototreated, in particular photo-aligned. For example, organic materials such as lecithin and in particular polyimide can be used.

[0073] Preferably, the first and second alignment layers are polyimide-based layers. Thus, in a preferred embodiment, the alignment layer comprises, and more preferably consists of, a polyimide. Chemically modified or reinforced polyimides, such as azobenzene-containing polyimides, may also be used or included. The alignment layer, preferably comprising polyimide, may also be rubbed or prepared by photoalignment.

[0074] The alignment layers, preferably polyimide layers, are arranged such that they provide a homeotropic orientation of the molecules of the liquid-crystalline medium, in particular at the interface, in particular setting a pretilt angle as defined herein. In a particularly preferred embodiment, rubbed polyimide layers are used on both substrates.

[0075] Polyimide layers produced by photoalignment (orientational ordering of the surface using light-induced alignment) can also be used. This can be achieved by photolysis, photodimerization or photoisomerization with the aid of polarized light.

[0076] The switchable layer is a homeotropic or vertically aligned liquid crystal layer. The molecules of the liquid crystal medium, with a predetermined pretilt angle, are aligned nearly perpendicular to the substrate surface. Therefore, the liquid crystal medium preferably has a negative dielectric anisotropy Δε, meaning it is perpendicular to the electric field. Thus, by applying an electric field perpendicular to the plane, the medium can be switched to an orientation parallel to the plane of the layer structure.

[0077] Examples of suitable liquid crystal media with negative dielectric anisotropy are given in EP1378558A1. For example, the liquid crystal mixture ZLI-2806 from Merck can be used. The liquid crystal medium may include additives. In particular, the liquid crystal medium preferably contains an antioxidant or stabilizer in a concentration of at least 5 ppm.

[0078] In this context, Δn represents the optical anisotropy, where Δn=n e -n o , and wherein the optical anisotropy Δn is preferably determined at 20° C. and a wavelength of 589.3 nm. The optical anisotropy Δn of the liquid-crystalline medium is preferably from 0.03 to 0.30, more preferably from 0.04 to 0.27, even more preferably from 0.06 to 0.21, in particular from 0.09 to 0.16.

[0079] In this context, Δε represents dielectric anisotropy, where Δε = ε|| - ε ⊥The dielectric anisotropy Δε is preferably determined at 20° C. and 1 kHz. The dielectric anisotropy Δε of the liquid-crystalline medium is preferably in the range from −0.5 to −20, preferably from −1.5 to −10, in particular from −3 to −6.

[0080] All physical properties and physicochemical or electro-optical parameters were determined by generally known methods, in particular according to “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status Nov. 1997, Merck KGaA, Germany, and are given for a temperature of 20° C., unless expressly stated otherwise.

[0081] In this document, all concentrations are given as percentages by weight and relate to the respective complete mixture, unless expressly stated otherwise.

[0082] The transmission and scattering of light preferably refers to the transmission and scattering of electromagnetic radiation in the spectral range from 380 nm to 780 nm.

[0083] The liquid crystal medium of the switchable layer preferably has a nematic phase at the operating temperature of the switchable window element. Particularly preferably, the nematic liquid crystal is in a range of + / -20°C above and below the operating temperature of the window element, very particularly preferably in a range of + / -30°C. The operating temperature of the switchable window element is preferably between -20°C and 70°C.

[0084] The liquid-crystalline medium preferably has a clearing point of at least 70° C., preferably above 80° C., more preferably above 100° C., particularly preferably above 105° C., very particularly preferably above 110° C., most preferably above 115° C., preferably the phase transition from the nematic liquid-crystalline state to the isotropic state. In an embodiment, the liquid-crystalline medium used in the present invention preferably has a clearing point in the temperature range of 70° C. to 170° C., more preferably 80° C. to 160° C., even more preferably 90° C. to 150° C., in particular 100° C. to 140° C.

[0085] The clearing point marks the temperature at which the phase transition from the nematic liquid crystal state to the isotropic state occurs. The clearing point, in particular the phase transition temperature between the nematic phase and the isotropic phase, can be measured and determined by known methods, for example using a Mettler oven or a hot stage under a polarizing microscope, and is preferably determined herein using a Mettler oven.

[0086] Furthermore, the liquid-crystalline media preferably exhibit advantageous low-temperature stability without visible crystallization or decomposition, in particular a long shelf life of more than 200 hours measured in bulk at -40°C.

[0087] Preferably, the liquid-crystalline medium comprises one or more compounds selected from the group consisting of compounds of the formulae CY, PY and AC.

[0088]

[0089] in

[0090] a means 1 or 2,

[0091] b represents 0 or 1,

[0092] c represents 0, 1 or 2,

[0093] d represents 0 or 1,

[0094] express

[0095]

[0096] and

[0097] express

[0098]

[0099] express

[0100]

[0101] R 1 ,R 2 ,R AC1 and R AC2 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein in addition one or two non-adjacent CH2 groups may be

[0102] -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly connected to one another, preferably alkyl or alkoxy having 1 to 6 C atoms,

[0103] Z x , Z y and Z AC each independently of one another represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, preferably a single bond, and

[0104] L 1-4Each independently of one another represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2, preferably F.

[0105] Preferably, L 1 and L 2 Both mean F or L 1 and L 2 One of them represents F and the other represents Cl, and L 3 and L 4 Both mean F or L 3 and L 4 One represents F and the other represents Cl.

[0106] In an embodiment, the group R 1 , R 2 , R AC1 and R AC2 One or more of represents a cycloalkyl group, in particular selected from cyclopropyl, cyclobutyl and cyclopentyl.

[0107] Here

[0108]

[0109] represents trans-1,4-cyclohexylene.

[0110] Particularly preferably, the liquid-crystalline media used according to the invention contain one or more compounds selected from the compounds of the formulae CY, PY and AC in an amount of at least 5% by weight, more preferably at least 10% by weight, even more preferably at least 15% by weight, still more preferably at least 25% by weight, yet more preferably at least 35% by weight and particularly preferably at least 50% by weight, based on the total content of the medium.

[0111] The compound of formula CY is preferably selected from the compounds of the following formulae:

[0112]

[0113]

[0114]

[0115]

[0116]

[0117] wherein a represents 1 or 2, alkyl and alkyl* each independently represent a straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl represents a straight-chain alkenyl radical having 2 to 6 C atoms, and (O) represents an oxygen atom or a single bond. Alkenyl preferably represents 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-.

[0118] In another embodiment, the compound of formula CY is additionally or alternatively selected from compounds of the formula:

[0119]

[0120] wherein alkyl* each independently represents a straight-chain alkyl group having 1 to 6 C atoms, and (O) represents an oxygen atom or a single bond.

[0121] In a specific embodiment, the medium includes compound CY-a-1, wherein compound CY-a-1 corresponds to a compound of formula CY-a wherein (O)alkyl* is ethoxy.

[0122] The compound of formula PY is preferably selected from the compounds of the following formulae:

[0123]

[0124]

[0125]

[0126] wherein alkyl and alkyl* each independently represent a straight-chain alkyl radical having 1 to 6 C atoms, and alkenyl represents a straight-chain alkenyl radical having 2 to 6 C atoms, and (O) represents an oxygen atom or a single bond. Alkenyl preferably represents 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-.

[0127] The compound of formula AC is preferably selected from the compounds of the following formulae:

[0128]

[0129]

[0130] Where R3 and R4 have R as described above AC1 and R AC2 meaning.

[0131] The mesogenic compounds described above and below are known or can be prepared by methods known per se, as described in the literature (e.g., in standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), specifically under reaction conditions known and suitable for the described reactions. Variants known per se but not mentioned in greater detail here can also be used. The media according to the invention are prepared in a conventional manner per se. In general, the components are preferably dissolved in one another at elevated temperatures. Suitable additives or substances can be added to modify the dielectric anisotropy, viscosity, and / or orientation of the liquid-crystalline phase.

[0132] The term "alkyl" according to the present invention preferably encompasses 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.

[0133] The alkoxy group may be linear or branched, and it is preferably linear and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms, and is therefore preferably methoxy, ethoxy, propoxy, butoxy, pentyloxy, hexyloxy or heptyloxy.

[0134] The term "alkenyl" according to the present invention preferably includes straight and branched alkenyl groups having 2 to 7 carbon atoms, particularly 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, particularly 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 up to 5 carbon atoms are generally preferred.

[0135] Fluorinated alkyl or alkoxy groups preferably include CF3, OCF3, CFH2, OCFH2, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CH2CF3, CH2CF2H, CH2CFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCH2CF3, OCH2CF2H, OCH2CFH2, OCCF 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, with OCF3 or OCF2H being particularly preferred. Fluoroalkyl groups in preferred embodiments include linear groups having terminal fluorine, i.e., fluoromethyl, 2-fluoroethyl, 3-fluoropropyl, 4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl. However, other positions of fluorine are not excluded.

[0136] Oxaalkyl groups preferably include those of formula C n H 2n+1 -O-(CH2) m wherein n and m are each independently 1 to 6. Preferably, n=1 and m is 1 to 6.

[0137] Oxaalkyl is preferably a 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.

[0138] Halogen is preferably F or Cl, in particular F.

[0139] If one of the abovementioned radicals is an alkyl radical in which one CH2 group has been replaced by -CH=CH-, it may be straight-chain or branched. It is preferably straight-chain and has 2 to 10 carbon atoms. Thus, it is especially 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.

[0140] If one of the above groups is an alkyl group in which one CH2 group has been replaced by -O- and one by -CO-, they are preferably adjacent. Thus, they contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. They are preferably straight-chain and have 2 to 6 carbon atoms.

[0141] Thus, they are in particular acetoxy, propionyloxy, butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl, propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl, 2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl, 3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl, propoxycarbonylmethyl, butoxycarbonylmethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0142] If one of the above radicals is an alkyl radical in which one CH2 group has been replaced by an unsubstituted or substituted -CH=CH- radical and the adjacent CH2 group has been replaced by CO, CO-O or O-CO, it may be straight-chain or branched. It is preferably straight-chain and has 4 to 13 carbon atoms. Thus, it is particularly 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.

[0143] If one of the above groups is an alkyl or alkenyl group which is monosubstituted by CN or CF3, this group is preferably straight-chain. The CN or CF3 substitution can be at any position.

[0144] If one of the above groups is an alkyl or alkenyl group which is at least monosubstituted by halogen, the group is preferably straight-chain, 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 perfluorinated groups. In the case of monosubstitution, the fluorine or chlorine substituent can be in any desired position, but is preferably in the ω-position.

[0145] Compounds containing branched groups may occasionally be important due to improved solubility in some conventional liquid-crystalline base materials. However, if they are optically active, they are particularly suitable as chiral dopants.

[0146] Branched groups of this type usually contain no more than one 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-ethylhexyloxy, 1-methylhexyloxy or 1-methylheptyloxy.

[0147] If one of the above radicals is an alkyl radical in which two or more CH2 groups have been replaced by -O- and / or -CO-O-, it may be straight-chain or branched. It is preferably branched and has 3 to 12 carbon atoms. Thus, it is in particular a dicarboxymethyl, 2,2-dicarboxyethyl, 3,3-dicarboxypropyl, 4,4-dicarboxybutyl, 5,5-dicarboxypentyl, 6,6-dicarboxyhexyl, 7,7-dicarboxyheptyl, 8,8-dicarboxyoctyl, 9,9-dicarboxynonyl, 10,10-dicarboxydecyl, 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.

[0148] In addition to a suitably high optical anisotropy, the liquid-crystalline medium comprised in the switchable layer may advantageously also exhibit a good high voltage holding ratio (VHR), together with good light stability and a suitably high clearing point.

[0149] In some embodiments, preferably, in one of the optical states, in particular in the presence of an electric field, the switchable layer has a twisted or super-twisted configuration. Surprisingly, it has been found that this provision, in addition to setting the pre-tilt angle as defined herein, can further contribute to reducing and / or shortening the detrimental occurrence of inhomogeneities as described above.

[0150] Thus, the liquid-crystalline medium optionally further comprises one or more chiral compounds, in particular one or more chiral dopants.

[0151] Chiral compounds, in particular chiral dopants, and their concentrations can be provided such that the cholesteric pitch of the liquid crystal medium can be appropriately set or adjusted. The pitch here refers to the pitch p of the cholesteric helix, wherein the pitch p is the distance over which the orientation axis (director) of the cholesteric liquid crystal undergoes a 2π rotation. In a preferred embodiment, the cholesteric medium is prepared by doping a nematic liquid crystal medium with a chiral dopant having a high helical twisting power (HTP). It is also possible to use two or more chiral dopants, for example, to compensate for the temperature dependence of the HTP of the individual dopants and thus achieve a low temperature dependence of the pitch.

[0152] Therefore, the liquid crystal medium in the switching layer preferably contains one or more chiral compounds, in particular chiral dopants. Chiral dopants preferably have moderately high to high absolute HTP values, can generally be added to the mesogenic base mixture at relatively low concentrations, and have good solubility in the achiral component. If two or more chiral compounds are used, they can have the same or opposite directions of rotation and the same or opposite temperature dependence of the twisting.

[0153] Preferably, the absolute value of the helical twisting force of the one or more chiral compounds optionally contained in the liquid crystal medium is 5 μm -1 or larger, more preferably 10 μm -1 or larger, even more preferably 15 μm -1 or larger, preferably in the commercially available liquid crystal mixture MLC 6828 from Merck KGaA. Particular preference is given to liquid crystals having a density of 20 μm -1 or larger, more preferably 40 μm -1 or larger, even more preferably 60 μm -1 or larger, most preferably in the range of 80 μm -1 or larger up to 260μm -1 Chiral compounds with an absolute value of the helical twisting force of 100 Å or less are preferably found in the commercially available liquid crystal mixture MLC 6828 from Merck KGaA.

[0154] Preferably, the content of the one or more chiral compounds in the liquid-crystalline medium is 2% by weight or less, more preferably 1% by weight or less, based on the total content of the medium.

[0155] Suitable chiral dopants are known in the art and some are commercially available, such as cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011, R / S-3011, R / S-4011, R / S-5011, B(OC)2C*HC-3 or CB15 (all Merck KGaA, Darmstadt, Germany).

[0156] Particularly suitable chiral dopants are compounds containing one or more chiral groups and one or more mesogenic groups, or one or more aromatic or alicyclic groups which form mesogenic groups with chiral groups. In a particularly preferred embodiment of the present invention, the liquid crystal medium comprises one or more compounds selected from the group consisting of the compounds shown in Table F below.

[0157] In some embodiments, the layer thickness d of the switchable layer is purposefully set relative to the pitch p of the medium, wherein the ratio d / p is preferably in the range of 0-1 and is particularly preferably 0.25 or approximately 0.25. In some cases, a ratio d / p of 0.66 or approximately 0.66 is particularly preferred.

[0158] In a preferred embodiment, the optical state in the presence of an electric field has a twisted nematic (TN) geometry with a twist of 90°. In another preferred embodiment, a super-twisted (STN) configuration, for example with a twist of 240°, can be provided, wherein in this case preferably only a single optical cell is used in the window element.

[0159] In certain embodiments, the switchable layer is polymer-stabilized.It has surprisingly been found that polymer stabilization can advantageously help to obtain and maintain an optical state having a desired alignment and configuration over time.

[0160] In this respect, it is preferred to provide one or more polymerizable, curable or hardenable compounds, preferably one or more photocurable monomers, in the liquid-crystalline medium as precursors of the polymer component for polymer stabilization and subsequently polymerize these reactive compounds in situ.

[0161] Thus, in embodiments, one or more polymerizable compounds are included in the liquid crystal medium as precursors to polymers for polymer stabilization. Preferably, the one or more polymerizable compounds are selected so that they have suitable and sufficient solubility in the LC medium. In embodiments, polymerizable mesogens or liquid crystal compounds, also known as reactive mesogens (RMs) or mesogenic monomers, are used. These compounds contain a mesogenic group and one or more polymerizable groups, i.e., functional groups suitable for polymerization. The RMs may be monoreactive, direactive, or polyreactive. In another embodiment, non-mesogenic polymerizable compounds, i.e., compounds that do not contain mesogenic groups, are used.

[0162] It is particularly preferred that the one or more polymerisable compounds comprise only one or more reactive mesogens, ie all reactive monomers are mesogens. Alternatively, the RM may be provided in combination with one or more non-mesogenic polymerisable compounds.

[0163] The polymerizable or reactive groups are preferably selected from vinyl, acrylate, methacrylate, fluoroacrylate, oxetane or epoxy groups, particularly preferably acrylate or methacrylate groups. Preferably, the one or more polymerizable compounds are selected from acrylates, methacrylates, fluoroacrylates and vinyl acetate, wherein the medium more preferably further comprises one or more di- and / or tri-reactive polymerizable compounds, preferably selected from diacrylates, dimethacrylates, triacrylates and trimethacrylates.

[0164] Suitable and conventionally used thermal initiators or photoinitiators may be added to promote the polymerization reaction, such as azo compounds or organic peroxides, for example Luperox type initiators. In addition, suitable conditions for polymerization and suitable types and amounts of initiators are known in the art and described in the literature. In the case where a polymerization initiator is included in the medium, a photoinitiator is preferably used.

[0165] For example, when polymerizing by ultraviolet light, a photoinitiator can be used that decomposes upon exposure to ultraviolet radiation to produce free radicals or ions that initiate polymerization. For polymerizing acrylate or methacrylate groups, a free radical photoinitiator is preferably used. For polymerizing vinyl, epoxy, or oxetane groups, a cationic photoinitiator is preferably used. Thermal polymerization initiators can also be used that decompose upon heating to produce free radicals or ions that initiate polymerization.

[0166] In a preferred embodiment, the polymerization is carried out by photoirradiation, ie with light, preferably ultraviolet light.

[0167] According to a particularly preferred embodiment, no polymerization initiator is used, in particular no photoinitiator. In some cases, this can improve the VHR and reduce the tendency of ion generation in the switchable layer. This can help to obtain and maintain a modulation material with good reliability and stability. Therefore, according to a preferred embodiment, no polymerization initiator is added to the liquid crystal medium.

[0168] In order to maintain and achieve a good VHR, impurities in the polymerization stabilization reaction product are preferably kept to a minimum or substantially avoided. In particular, residual reactive species and charged contaminants are suitably and preferably kept to a minimum. For example, when UV polymerization is performed, in a preferred embodiment, light having a relatively long wavelength approaching or even extending into the visible spectrum is used, advantageously preferably UV light and light in the range of 340 nm to 410 nm, more preferably UV light in the range of 340 nm to 380 nm, and even more preferably UV light in the range of 360 nm to 380 nm. In this way, undesirable photodegradation or decomposition of components of the LC medium, in particular the optionally provided one or more dichroic dyes, can be avoided or at least minimized. When a photoinitiator is used, the irradiation wavelength and the photoinitiator can be appropriately matched or adjusted.

[0169] In the preferred case where no photoinitiator is used, the wavelength range of the light can be set so that at least some of the polymerizable compounds can undergo a photoreaction and itself initiate a polymerization reaction, while also avoiding or at least minimizing degradation or decomposition of non-polymerizable components of the LC medium, in particular one or more optionally provided dichroic dyes. Achieving and setting the desired wavelength range can be achieved by conventional methods known in the art, for example by using optical filters, in particular edge filters.

[0170] Preferably and advantageously, the polymer structure used for stabilization is prepared in situ. By appropriately selecting one or more polymerizable compounds, particularly polymerizable mesogenic compounds, optionally together with one or more dichroic dyes, and by setting and adjusting the wavelength of the light used in the photopolymerization, particularly with respect to the absorption characteristics of the dichroic dye, an efficient and robust method can be provided that provides the desired polymeric and polymeric components in the switchable layer while also preserving the non-polymerizable components, including the dichroic dye, and their properties. In embodiments, the wavelength or wavelength spectrum of the irradiating light is selected to minimize overlap with the absorption band of the dichroic dye.

[0171] Preferably, the content of one or more polymerizable compounds optionally provided in the liquid-crystalline medium for polymer stabilization is from 0 to 5% by weight, based on the total content of the medium, more preferably from 0.1 to 2.5% by weight, particularly preferably in the range from 0.3 to 1% by weight.

[0172] Particularly suitable polymerizable compounds are listed in Table G below.

[0173] The optical box and window element can have various shapes, for example, square, rectangular, triangular, or polygonal. The window element can, for example, be housed or arranged in a double-glazed or triple-glazed unit, and in particular, in an insulating glazing unit. The window element can be suitably and advantageously used in buildings or vehicles.

[0174] In addition to being used on the exterior surfaces of buildings, i.e., as part of facades, window elements can also be used in interior building applications. For example, window elements can be used as partitions or room dividers, or in partition walls, particularly to provide a privacy feature when required. For this privacy feature, a very good dark state is required to effectively prevent viewing.

[0175] Preferably, the switchable optical box comprises only a single switching layer.In an embodiment of the invention, the window element comprises exactly one switchable optical box.

[0176] However, in an alternative and particularly preferred embodiment, the window element comprises an additional switchable optical cell. In the latter case, the two switching layers are provided separately or individually in the optical cell and then combined and configured as a so-called double cell, in particular by using, for example, lamination or adhesive bonding. In a particularly preferred embodiment, the window element comprises a double cell using a liquid crystal medium doped with a dichroic dye.

[0177] In cases where a very good dark state is desired, for example in indoor applications intended to provide a switchable privacy mode, embodiments in which the window element comprises a double cell using a liquid-crystalline medium doped with dichroic dyes are particularly preferred.

[0178] Hence, the window element preferably comprises a further switchable optical cartridge in addition to the switchable optical cartridge described above and below, wherein more preferably the further switchable optical cartridge conforms to said first switchable optical cartridge.

[0179] The window element preferably has a width of at least 100 cm 2 , more preferably at least 1600 cm 2 , even more preferably at least 10,000 cm 2 Additionally, preferably, the switchable layer is undivided, or in the alternative case where the switchable layer is divided into compartments, said compartments each have an area of at least 1 cm 2 , more preferably at least 10 cm 2 , even more preferably at least 50 cm 2 In contrast to conventional liquid crystal displays, which display a large number of microscopically small pixels, the window element typically comprises an extended, continuous area of LC material and an equally extended, uniform electrode area. Consequently, typical contributions from pixel boundaries and possible crosstalk between adjacent pixels are less pronounced in the case of a window configuration.

[0180] In the present invention and in particular in the following examples, the structures of the mesogenic compounds are indicated by means of abbreviations (also called acronyms). In these acronyms, the chemical formulae are abbreviated as follows using Tables A to C below. All groups C 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-1Each represents a straight-chain alkyl or alkenyl group, preferably a 1-E-alkenyl group, each having n, m, and 1 carbon atoms, respectively. Table A lists the codes for the ring elements of the compound core structure, while Table B shows the linking groups. Table C gives the meaning of the codes for the left-hand or right-hand terminal groups. Acronyms are composed of the code for the ring element with the optional linking group, followed by a first hyphen and the code for the left-hand terminal group, and a second hyphen and the code for the right-hand terminal group. Table D shows illustrative structures of the compounds and their corresponding abbreviations.

[0181] Table A: Ring elements

[0182]

[0183]

[0184]

[0185] Table B: Linking Groups

[0186]

[0187] Table C: End Groups

[0188] Left-hand side Right-hand side

[0189] Use alone

[0190]

[0191] Use with each other and with others

[0192]

[0193] where n and m each represent an integer, and the triple dots "..." are placeholders for other abbreviations from this table.

[0194] The following table shows illustrative structures and their respective abbreviations. These are shown to illustrate the meaning of the abbreviation rules. In addition, they represent compounds that can be preferably used.

[0195] Table D: Illustrative Structure

[0196]

[0197]

[0198]

[0199]

[0200]

[0201]

[0202]

[0203]

[0204]

[0205]

[0206] wherein n, m and l preferably represent 1 to 7 independently of one another.

[0207] The following table shows illustrative compounds that can be used as stabilizers in the media according to the present invention.

[0208] Table E

[0209] Table E shows possible stabilizers which can be added to the LC media according to the invention, wherein n represents an integer from 1 to 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8.

[0210]

[0211]

[0212]

[0213]

[0214]

[0215]

[0216] 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.

[0217] Table F below shows illustrative compounds that may be preferably used as chiral dopants in the mesogenic media of the present invention.

[0218] Table F

[0219]

[0220]

[0221]

[0222] In a preferred embodiment of the present invention, the mesogenic medium comprises one or more compounds selected from the compounds shown in Table F.

[0223] The mesogenic medium according to the present invention preferably comprises two or more, preferably four or more, compounds selected from the compounds shown in Tables D to F above.

[0224] In one embodiment, the LC media according to the present invention preferably comprise three or more, more preferably five or more, compounds shown in Table D.

[0225] Table G

[0226] Table G lists exemplary compounds that can be used in the LC media according to the invention, preferably as reactive mesogenic compounds. Preferably, one initiator or a mixture of two or more initiators is added for the polymerization. The initiator or initiator mixture is preferably added in an amount of 0.001% to 2% by weight, based on the mixture. Suitable initiators are, for example, 651 (from BASF).

[0227]

[0228]

[0229]

[0230]

[0231]

[0232]

[0233]

[0234]

[0235]

[0236]

[0237]

[0238]

[0239]

[0240]

[0241]

[0242]

[0243]

[0244] In a preferred embodiment of the present invention, the mesogenic medium comprises one or more compounds selected from the group of compounds from Table G.

[0245] The liquid-crystalline medium according to the present invention preferably comprises four or more, more preferably six or more, even more preferably seven or more, and particularly preferably eight or more compounds selected from the group of compounds of Table D, preferably three or more compounds of different formulae selected from the group of formulae of Table D. The medium particularly preferably additionally contains one, two or more compounds selected from the group of formulae of Table E. Even more preferably, the medium further contains one, two or more compounds selected from the group of formulae of Table G.

[0246] The following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention in any way. In view of this disclosure, the examples and their modifications or other equivalents will become apparent to those skilled in the art.

[0247] However, the physical properties and compositions presented below illustrate which properties can be achieved and to what extent they can be modified. In particular, combinations of different properties that can be preferably achieved are therefore fully defined. DETAILED DESCRIPTION

[0248] Example

[0249] In an embodiment,

[0250] V o represents the threshold voltage at 20°C, capacitive [V],

[0251] n e represents the extraordinary refractive index at 20°C and 589 nm,

[0252] n o represents the ordinary refractive index at 20°C and 589 nm,

[0253] Δn represents the optical anisotropy at 20°C and 589 nm,

[0254] ε|| represents the dielectric constant parallel to the director at 20°C and 1kHz,

[0255] ε ⊥ represents the dielectric constant perpendicular to the director at 20°C and 1kHz,

[0256] Δε represents the dielectric anisotropy at 20°C and 1 kHz,

[0257] cl.p.,T(N,I) represents the clearing point [℃],

[0258] γ1 represents the rotational viscosity [mPa·s] measured at 20°C, determined by a rotation method in a magnetic field.

[0259] K1 represents the elastic constant, the “bending” deformation at 20°C [pN],

[0260] K2 represents the elastic constant, "torsion" deformation at 20°C [pN],

[0261] K3 represents the elastic constant, the “bending” deformation at 20°C [pN],

[0262] Unless otherwise explicitly stated, the term "threshold voltage" of the present invention relates to the capacitive threshold (V0). In an embodiment, as usual, the optical threshold may also be for a 10% relative contrast ratio (V 10 ) pointed out.

[0263] Reference Example 1

[0264] Liquid crystal host mixture H-1 was prepared and characterized with respect to its general physical properties. Its composition and properties are shown in the following table.

[0265]

[0266]

[0267] Mixture M-1 was prepared by mixing 99.01% of mixture H-1, 0.05% of compound

[0268]

[0269] 0.16% of compound

[0270]

[0271] 0.35% of compound

[0272] and

[0273] 0.43% of compound

[0274]

[0275] Reference Example 2

[0276] Liquid crystal base mixture B-2 was prepared and characterized with respect to its general physical properties. Its composition and properties are shown in the following table.

[0277]

[0278] Mixture M-2 was prepared analogously to mixture M-1 described above in Reference Example 1, using mixture B-2 instead of mixture H-1.

[0279] Reference Example 3

[0280] Liquid crystal base mixture B-3 was prepared and characterized with respect to its general physical properties. Its composition and properties are shown in the following table.

[0281]

[0282] Mixture M-3 was prepared by mixing 99.638% of mixture B-3, 0.332% of the compound of formula S-811 described in Table F above, and 0.030% of the compound of formula

[0283]

[0284] Reference Example 4

[0285] Liquid crystal base mixture B-4 was prepared and characterized with respect to its general physical properties. Its composition and properties are shown in the following table.

[0286]

[0287] Mixture M-4 was prepared by mixing 99.51% of mixture B-4 and 0.49% of the compound of formula S-811 as described in Table F above.

[0288] Reference Example 5

[0289] Liquid crystal mixture B-5 was prepared and characterized with respect to its general physical properties. Its composition and properties are shown in the following table.

[0290]

[0291] Reference Example 6

[0292] Liquid crystal mixture M-6 was prepared and characterized with respect to its general physical properties, wherein compound CY-a-1 is as defined above.

[0293]

[0294] Comparative Example 1

[0295] Two optical boxes were assembled using two glass plates (20 mm x 26 mm, 1.1 mm thick), each coated with an indium tin oxide (ITO) layer (50 nm thick, 100 Ω / □ resistance).

[0296] For each glass plate, a polyimide layer (50 nm, JSR, JALS-2096-R1) was applied on top of the ITO layer by spin coating.The polyimide layer was rubbed antiparallel with a velvet cloth (Yoshikawa YA-20R) on a metal roller.

[0297] The pretilt angle caused by rubbing was 88.5°, wherein the pretilt angle was measured using a Mueller matrix polarimeter "AxoScan" from Axometrics.

[0298] Two glass plates, each with a polyimide layer, facing inwards and facing each other, including a 25 μm diameter plastic spacer, were assembled to form a box in which a 3 mm offset of the short edges was used to provide wiring opportunities. The box edges were also sealed except for the filling port.

[0299] The dye-doped liquid crystal mixture M-1 as described above in Reference Example 1 was filled into the cell by capillary forces and the filling port was sealed. Cables were soldered to the offset contact areas of the cell.

[0300] Use double-sided tape to stack two boxes near the edge to form a double box with one box rotated 90° relative to the other.

[0301] Using a 30 Vrms square wave voltage, the dual cell switched to a dark state with a grainy and irregular appearance, with small bright spots and irregular narrow bright lines visible. These defects gradually disappeared over time. Only after 120 seconds after switching did a dark state with a uniform dark appearance be achieved.

[0302] Comparative Example 2

[0303] Similar to Comparative Example 1 above, a switchable cell was assembled, but where instead the cell thickness was set to 15 μm and the pretilt angle was set to 89°.

[0304] Using a 20 Vrms square wave voltage for switching, the grainy defects in the initial dark state disappeared after 60 seconds, resulting in a uniform dark appearance.

[0305] Example 1

[0306] Two optical boxes were assembled using two glass plates (20 mm x 26 mm, 1.1 mm thick), each coated with an indium tin oxide (ITO) layer (50 nm thick, 100 Ω / □ resistance).

[0307] For each glass plate, a polyimide layer (50 nm) was coated on top of the ITO layer by spin coating. The polyimide layer was rubbed with a velvet cloth (Yoshikawa YA-20R) on a metal roller at a rotation speed of 200 rpm, a moving speed of 25 mm / s and a rubbing depth of 0.3 mm.

[0308] The pretilt angle caused by rubbing was 86°, wherein the pretilt angle was measured using a Mueller matrix polarimeter "AxoScan" from Axometrics.

[0309] Two glass plates, each with a polyimide layer, facing inward and facing each other, including a 25 μm diameter plastic spacer, were assembled to form a box in which a 3 mm offset on the short edge was used to provide wiring opportunities. The box edges were also sealed except for the filling port.

[0310] The dye-doped liquid crystal mixture M-1 as described above in Reference Example 1 was filled into the cell by capillary forces and the filling port was sealed. Cables were soldered to the offset contact areas of the cell.

[0311] Use double-sided tape to stack two boxes near the edge to form a double box with one box rotated 90° relative to the other.

[0312] Using a 30 Vrms square wave voltage, the dual cell switched to a dark state with a grainy and irregular appearance, with small bright spots and irregular narrow bright lines visible. These defects quickly disappeared, and after 10 seconds after switching, a dark state with a uniform dark appearance was obtained.

[0313] Example 2

[0314] Similar to Example 1 above, a switchable cell was assembled, however, where instead the cell thickness was set to 15 μm and the pretilt angle was set to 85°.

[0315] Using a 20 Vrms square wave voltage for switching, the granular defects in the initial dark state disappear after 10 seconds, resulting in a uniform dark state.

[0316] Example 3

[0317] Similar to Example 1 above, a switchable dual cell was assembled, however, wherein the pretilt angle was set to 86° in one polyimide layer and 89° in the other polyimide layer in each cell having a thickness of 25 μm.

[0318] Using a 20Vrms square wave voltage for switching, the granular defects in the initial dark state disappear after 15 seconds, resulting in a uniform dark appearance.

[0319] Example 4

[0320] Similar to Example 1 above, a switchable cell was assembled using a cell thickness of 25 μm and setting the pretilt angle to 85°, which, at an applied voltage of 20 V, provided a twisted TN configuration with a twist angle of 90°.

[0321] Using a 20 Vrms square wave voltage for switching, the grainy defects in the initial dark state disappeared in less than 10 seconds, resulting in a uniform dark appearance.

Claims

1. A window element comprising a switchable optical box having a layer structure comprising, in this order: - a first substrate, - a first electrode layer, - a first alignment layer, - switchable layers, - a second alignment layer, - a second electrode layer, and - a second substrate, wherein the switchable layer is a homeotropically aligned liquid crystal layer comprising a liquid crystal medium, and in, The pretilt angle is set in the range of 84° to 86° by at least one of the first alignment layer and the second alignment layer, wherein the liquid crystal medium comprises one or more dichroic dyes and one or more compounds selected from the group consisting of compounds of the formulae CY, PY and AC, in a means 1 or 2, b represents 0 or 1, c represents 0, 1 or 2, d represents 0 or 1, express express express R 1 , R 2 , R AC1 and R AC2 each independently of one another represents an alkyl radical having 1 to 12 C atoms, wherein in addition one or two non-adjacent CH2 groups may be -O-, -CH=CH-, -CO-, -OCO- or -COO- are replaced in such a way that the O atoms are not directly connected to one another, Z x , Z y and Z AC each independently of one another represents -CH2CH2-, -CH=CH-, -CF2O-, -OCF2-, -CH2O-, -OCH2-, -CO-O-, -O-CO-, -C2F4-, -CF=CF-, -CH=CH-CH2O- or a single bond, and L 1-4 each independently of one another represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2, wherein the window element does not include a polarizer, Wherein, the window element has a width of at least 100 cm 2 and wherein the switchable layer is undivided or divided into layers each having an area of at least 1 cm 2 The area of the compartment, wherein the switchable optical cell is operable in a light state and a dark state and is electrically switchable between the light state and the dark state, and wherein, in the absence of an electric field, the switchable layer is homeotropically aligned, wherein, in the bright state, the window element has a visible light transmission degree of more than 55%, measured according to DIN EN 410, The window element is used in a window of a building or a vehicle.

2. The window element according to claim 1, wherein R 1 , R 2 , R AC1 and R AC2 Each independently of one another represents an alkyl or alkoxy radical having 1 to 6 C atoms.

3. The window element according to claim 1, wherein Z x , Z y and Z AC Indicates a single bond.

4. The window element according to claim 1, wherein L 1-4 Indicates F.

5. The window element according to claim 1, wherein The switchable layer has a thickness of at least 5 μm.

6. The window element according to claim 5, wherein The switchable layer has a thickness of at least 10 μm.

7. The window element according to any one of claims 1 to 6, wherein The liquid-crystalline medium has a negative dielectric anisotropy Δε, an optical anisotropy Δn in the range from 0.03 to 0.30, and a clearing point of at least 70°C.

8. The window element according to any one of claims 1 to 6, wherein the switchable layer is polymer-stabilized.

9. The window element according to any one of claims 1 to 6, wherein The pretilt angle is set in the range of 84° to 86° by the first alignment layer and the second alignment layer.

10. The window element according to any one of claims 1 to 6, wherein The first alignment layer and the second alignment layer include an organic material that has been rubbed or phototreated.

11. The window element according to any one of claims 1 to 6, wherein The first alignment layer and the second alignment layer are polyimide-based layers.

12. The window element according to any one of claims 1 to 6, wherein The window element further comprises a further switchable optical box.

13. The window element according to claim 12, wherein The further switchable optical box corresponds to a switchable optical box comprised in a window element as claimed in any one of the preceding claims.

14. The window element according to any one of claims 1 to 6, wherein In the presence of an electric field, the switchable layer adopts a twisted or super-twisted configuration.

15. Use of a window element according to any one of claims 1 to 14 in a window of a building or a vehicle.

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