Devices that control light transmission

Abstract

To provide a device for the regulation of light transmission.SOLUTION: The present invention relates to a device for the regulation of light transmission, in particular a switchable window. The present invention in particular relates to a window element comprising a switchable optical cell having a homeotropically aligned liquid crystal layer wherein a pretilt angle in the range of from 77° to 88°is set.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Devices that control or modulate 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, Vol. 94 (2010) pp. 87-105 (Non-Patent Document 1) provides an overview of various dynamic smart windows. As described there, smart windows may use several technologies for modulating the transmission of light, such as devices based on electrochromism, liquid crystal devices and electrophoretic or suspended particle devices.

[0003] Light shutters and light intensity modulators, especially liquid crystal based light modulators, can be used in switchable windows for architectural, automotive, railway, aviation and marine applications.

[0004] In such devices the light transmission can be reversibly changed to attenuate, dim or color the intensity of the incident light, and thus these devices can operate and switch between bright and dark states, i.e., states of relatively high and relatively low light transmission.

[0005] While the switching between different optical states of liquid crystal based devices can also be thermally controlled, it is often advantageous and suitably preferred to adopt the different optical states using an electrical switch, where the switch is controlled by the application of a voltage. Such liquid crystal based devices principally use a change in the orientation of liquid crystal (LC) molecules between two conducting electrodes by the application of an electric field, resulting in a change in transmission.

[0006] In principle, several modes or configurations can be employed to provide such a reversible transmission change. Polarizers are commonly used in twisted nematic (TN), super-twisted nematic (STN) and vertical alignment (VA) liquid crystal cells 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 systems can be used without any polarizers to modify the light transmission. 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 describes the use of dichroic dye-doped liquid crystal media with negative dielectric anisotropy in devices for controlling the passage of light.

[0008] WO 2017 / 118465 (Patent Document 2) describes a device for controlling the ingress of light into a room, comprising a switchable layer that contains a dichroic dye-doped liquid crystal medium and has a twisted configuration in one of the switch states.

[0009] There remains a need in the art for devices that control the passage of light, and in particular for switchable windows that have reliable and efficient switching performance. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2015 / 090506 [Patent Document 2] International Publication No. 2017 / 118465 [Non-patent literature]

[0011] [Non-Patent Document 1] 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, Vol. 94 (2010), pp. 87-105 Summary of the Invention [Problem to be solved by the invention]

[0012] It is therefore an object of the present invention to provide an improved device for controlling the passage of light, including an optical cell, and in particular a window element, which exhibits robust and reliable switching whilst offering performance advantages, particularly in terms of switch state appearance and switching speed. Further objects of the present invention will become readily apparent to those skilled in the art from the following detailed description. [Means for solving the problem]

[0013] The object is solved by the subject matter defined in the independent claims, while preferred embodiments are set out in the respective dependent claims and are further described below.

[0014] The present invention provides the following items including in particular main aspects, preferred embodiments and specific features, each of which alone and in combination contributes to solving the above objects and ultimately provides additional advantages. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The first aspect of the present invention is A first substrate; A first electrode layer; A first alignment layer, A switchable layer; A second alignment layer; a second electrode layer, and The second board and A switchable optical cell having a layer structure comprising, in this order: wherein the switchable layer is a homeotropically aligned liquid crystal layer comprising a liquid crystal medium; and However, the window element is provided such that the pretilt angle in at least one of the first alignment layer and the second alignment layer is set within the range of 77° to 88°.

[0016] Preferably and advantageously the switchable optical cell is operable between a bright state and a dark state and is electrically switchable.

[0017] It has been recognized that in the present invention, especially in combination with an electrical switch, it may be advantageous to provide a switchable window element based on a liquid crystal cell using homeotropic alignment, also known as vertical alignment (VA). This configuration may offer particular advantages, especially in terms of the resulting contrast between optical states and the performance of the dark state, while allowing suitable viewing angle dependence and response times. This configuration also offers the possibility of using dichroic dyes in these configurations to provide guest-host systems with improved performance.

[0018] However, it has further been recognized that in these VA configurations, under certain conditions, an initially non-uniform state may be obtained instead of the desired uniform optical state. This may be the case when applying an electric field to switch between optical states, and especially when using so-called overdrive voltages, i.e. driving voltages above the saturation voltage. Furthermore, it has been found that such undesirable effects become more pronounced, both in terms of appearance and duration, with cell areas and cell gap thicknesses that are typically larger than those typical of window elements and common liquid crystal displays. In particular, after the initial switch, an undesirable state with a granular appearance may be obtained, which may last for several seconds or even minutes, and only after that the desired uniform appearance occurs. Without being bound to a particular theory, it is believed that this phenomenon is due to undesirable countercurrent dynamics that may initially lead to visible areas that may be recognized as non-uniformities, disclinations and granular states. The actually desired uniform state may then form or emerge from this temporary intermediate state.

[0019] It has been recognised that it is desirable to switch in the present invention either quickly, immediately or at least reasonably quickly to a specified state with a uniform appearance, thus providing favourable switching performance and particularly fast switching speed.Surprisingly, it has been found that by deliberately 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°-88° in at least one alignment layer, preferably both alignment layers, the deleterious effects of intermediate non-uniformity and temporary domain patterns can be significantly reduced or even avoided, thus providing substantial advantages in terms of switching speed and reliability.

[0020] To align or orient the liquid crystal molecules at the cell walls, i.e., substrate surfaces, it is possible to use alignment layers, also known as alignment layers, to provide interfaces that specifically produce or induce a predefined or desired molecular alignment. In many cases, the liquid crystal molecules at or near the interfaces are tilted on average, even in the absence of any applied voltage. In this regard, the average tilt angle of the liquid crystal molecules measured from the plane of the substrate surface or the plane of the respective interface is called the pretilt angle. For homeotropic or vertical alignment, typically pretilt angles between 88° and 89° are observed, i.e. angles very close to perpendicular to the plane of the surface. However, it has been found that in these conventional VA configurations, non-uniformities and granular domain structures, effects due to the electric field induced counter-current or counter-current LC dynamics mentioned above, may occur in certain cases or under certain conditions.

[0021] According to the present invention, alignment layers are used, and a pretilt angle is set at and near the interface of at least one alignment layer, preferably at the interface of both alignment layers, in the range of 77°-88°, particularly preferably in the range of 84°-86°. By deliberately setting and observing the pretilt angle within this given specific range, it can significantly contribute to shortening and / or reducing the occurrence of undesirable non-uniformities, and even avoid such occurrence, thus leading to a fast switch to the desired defect-free uniform optical state. In addition, it has been surprisingly found that a suitably efficient and advantageous electro-optical performance can still be obtained, especially in terms of maintaining the desired transmission in the bright and dark states, thus giving the possibility of providing a sufficiently high contrast between the switching states.

[0022] Based on the favorable optical and electro-optical performance of the switchable optical cell, the device of the present invention may be advantageously used in a number of different window and shutter applications.

[0023] In a further embodiment the window element according to the invention is used in windows in buildings or vehicles, including for example road vehicles such as cars, buses and trucks as well as trains, boats, ships and aircraft.

[0024] Without thereby limiting the invention, the invention is hereinafter illustrated by a detailed description of aspects, embodiments and specific features, and specific embodiments are described in more detail.

[0025] According to the invention a switchable layer is disposed between two substrates so as to provide an optical cell which is operable in different optical states and which is preferably and advantageously electrically switchable.

[0026] The window element preferably comprises an optical cell switchable between a bright state and a dark state, in which the bright state has a greater degree of light transmission as compared to the dark state.

[0027] In the light state the window element according to the invention preferably has a visible light transmission, determined in accordance with DIN EN 410, of higher than 45%, more preferably higher than 55%, even more preferably higher than 65%.

[0028] In the dark state the window element according to the invention preferably has a visible light transmission, determined according to DIN EN 410, of less than 40%, more preferably less than 30%, even more preferably less than 20%. In a preferred embodiment in the dark state the window element has a visible light transmission, determined according to DIN EN 410, in the range of 1% to 35%, more preferably in the range of 5% to 30%.

[0029] According to the invention in one of the optical states, particularly in the absence of an electric field, the liquid crystal medium in the switchable layer is homeotropically aligned.

[0030] The first and second substrates may comprise, and preferably consist of, glass or a 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.

[0031] The electrical switch according to the invention is achieved by providing a first and a second electrode on a substrate, for example a glass substrate or a plastic substrate. A conductive layer is preferably provided on the substrate, the conductive layer comprising or formed of a transparent conductive material, for example 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) polystyrenesulfonate (PEDOT:PSS) or poly(4,4-dioctylcyclopentadithiophene), or a thin transparent metal and / or metal oxide layer, for example silver. The transparent conductive material is preferably a transparent conductive oxide, more preferably indium tin oxide. The transparent electrodes are preferably applied to the substrate by a coating process. For example ITO may be sputtered to obtain a layer thickness typically in the range of 5 nm to 250 nm or a sheet resistance in the range of 5 Ω / □ to 500 Ω / □.

[0032] The conductive layer is preferably provided with an electrical connection, in particular a busbar. The voltage is preferably supplied by a battery, a secondary battery, a supercapacitor or an external current source, more preferably by an external current source. The joining of the terminals to the busbars in this respect can be achieved by soldering, welding, the use of conductive adhesives or conductive films. Anisotropic conductive film bonding may in particular be used to join flat cables as terminal wires to the respective busbars. The terminals may be used to provide a connection to a controller or driver that generates a drive signal for controlling the state of the switchable medium arranged inside the electro-optical cell. The terminals may for example be configured as connectors for attaching terminal wires or electrical wires.

[0033] The two substrates of the switchable optical device are preferably arranged such that each substrate has at least one region where it does not overlap the other substrate. These non-overlapping regions thus provide access to the respective transparent electrodes and bus bars can be conveniently located in these non-overlapping regions. The non-overlapping regions are preferably offset between the first and second substrates in the range of 1 mm to 20 mm, preferably 2 mm to 10 mm, for example about 4 mm.

[0034] The liquid crystal medium can be contained in the electro-optical cell in any suitable manner, for example using vacuum filling or drop filling. Typically a frame sealant or respective edge sealant is provided to close the cell or to contain the respective medium. Examples of materials suitable for sealing the cell include epoxy-based sealants, polyurethanes, hot melt sealants and acrylates.

[0035] In the window element, in particular in the switchable optical cell, the switchable layer preferably has a thickness of at least 5 μm, more preferably at least 7 μm, even more preferably at least 10 μm, even more preferably at least 15 μm, particularly preferably at least 20 μm. In one embodiment the switchable layer comprising a liquid crystal medium has a thickness in the range of 5 μm to 100 μm, more preferably 10 μm to 50 μm, in particular 15 μm to 25 μm.

[0036] Spacers may be included in the cell gap of the switch layer to maintain the appropriate thickness of the switch layer. Typically the spacers have a spherical shape with a diameter within the range of the cell gap. Non-conductive spacers may be used, for example made of polymer or glass, having a spherical shape with a predetermined diameter. In some embodiments it may be useful to provide sticky spacers, i.e. spacers with some inherent adhesive properties to better adhere to the surface. It may also be useful to use black spacers, for example to avoid or minimize undesirable light leakage. It may be particularly beneficial to use black sticky spacers. Other suitable means may also be used to set or maintain the cell thickness, for example column spacers. The column spacers may also be formed to provide compartments, thus allowing for arbitrary freely cuttable structures.

[0037] As used herein, the terms films and layers include free-standing or free-standing films or layers, either rigid or flexible, with more or less pronounced mechanical stability, as well as coatings or layers on a supporting substrate or between two substrates.

[0038] It is also possible to provide a passivation or barrier layer on the substrate, for example a passivation layer comprising silicon oxide or silicon nitride, preferably consisting of silicon oxide or silicon nitride, which is then arranged on the substrate in such a way that the alignment layer is uppermost, i.e. in contact with the LC medium.

[0039] Preferably, the transparent conductive electrode layer is also respectively embedded between two transparent dielectric layers.Accordingly, according to a particularly preferred embodiment, in the optical device, the liquid crystal medium is provided in a switchable layer, which is sandwiched between and in direct contact with a first and a second alignment layer, and the electrodes are respectively arranged on a passivation layer, in particular embedded between two transparent dielectric layers.

[0040] Preferably the liquid crystal medium contains one or more dichroic dyes.

[0041] By dichroic dye herein is meant a light absorbing compound whose absorption properties depend on the orientation of the compound relative to the polarization direction of light. The dichroic dye compounds according to the present invention typically have an elongated shape, i.e. the compound is significantly longer along one spatial direction, i.e. the long axis direction, than along the other two spatial directions. Since dichroic dyes absorb light in one direction or preferentially absorb each, the light transmission can be adjusted by changing the orientation of the dichroic dye.

[0042] It is thus possible to use guest-host liquid crystal cells based on a liquid crystal host doped with dichroic dye molecules, and these guest-host systems can be used without any polarizers to alter the light transmission.

[0043] Each of the one or more dichroic dyes is present in the liquid crystal medium in a proportion of preferably 0.005% by weight to 12.5% ​​by weight, more preferably 0.01% by weight to 10% by weight, even more preferably 0.025% by weight to 7.5% by weight, even more preferably 0.05% by weight to 5% by weight, even 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.

[0044] The one or more dichroic dyes are present in the entire liquid crystal medium at a total concentration within the range of preferably 0.01% by weight to 30% by weight, more preferably 0.025% by weight to 25% by weight, even more preferably 0.05% by weight to 15% by weight, even more preferably 0.1% by weight to 10% by weight, and particularly preferably 0.5% by weight to 5% by weight.

[0045] The concentration of the dye(s) is preferably selected to ensure proper performance of the resulting modulating material, in particular the desired color and / or photochromic effect.

[0046] The dichroic dyes may preferably be selected from, for example, azo dyes, anthraquinones, thiophenolanthranoquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, pyrromethene dyes, malononitrile dyes, nickel dithiolenes, (metal)phthalocyanines, (metal)naphthalocyanines and (metal)porphyrins, rylenes, in particular perylenes and terrylenes, thiadiazole dyes, thienothiadiazole dyes, benzothiadiazoles, thiadiazoloquinoxalines, and diketopyrrolopyrroles. Particular preference is given to azo compounds, anthraquinones, thiophenolanthranoquinones, benzothiadiazoles, especially as described in WO 2014 / 187529, diketopyrrolopyrroles, especially as described in WO 2015 / 090497, thiadiazoloquinoxalines, especially as described in WO 2016 / 177449, and rylenes, especially as described in WO 2014 / 090373.

[0047] The liquid crystal medium preferably comprises 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 different dichroic dyes, particularly preferably 2 or 3 different dichroic dyes.

[0048] The absorption spectra of the dichroic dyes optionally contained in the medium or in the switchable layer, respectively, in one embodiment are preferably complementary to each other so as to produce the impression of black to the eye. Preferably, two or more, more preferably three or more, dichroic dyes are used in the liquid crystal medium, preferably to cover a large part of the visible spectrum. The exact methods for preparing mixtures of dyes that appear black or grey to the eye are known in the art and are described, for example, in M. Richter, Einfuhrung in die Farbmetrik [Introduction to Colorimetry], 2nd edition, 1981, ISBN 3 11-008209-8, Walter de Gruyter & Co.

[0049] In another embodiment, different color settings are provided, for example red, green, and blue.

[0050] The determination of the color position of a mixture of dyes is described in the field of colorimetry. For this purpose, the spectra of the individual dyes are calculated taking into account the Beer-Lambert law, giving an overall spectrum which is then converted according to the rules of colorimetry into the corresponding color positions and luminance values ​​under an integrated illuminant, e.g. illuminant D65 for daylight. The position of the white point is fixed for the respective illuminant, e.g. D65, and is referenced, for example, in the tables in the abovementioned documents. By varying the proportions of the various dyes, different color positions can be determined.

[0051] In a preferred embodiment, three or more different dichroic dyes are contained in the liquid crystal medium.

[0052] According to a preferred embodiment, the medium and the switchable layer contain one or more dichroic dyes absorbing light in the red and NIR region, i.e. at wavelengths between 600 nm and 2000 nm, preferably in the range of 600 nm to 1800 nm, particularly preferably in the range of 650 nm to 1300 nm.

[0053] In one embodiment, the dichroic dyes which may be provided in the medium and switchable layer are 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 particularly preferably from the explicit compounds given in the tables present therein.

[0054] Said dyes belong to the class of dichroic dyes known to those skilled in the art and described many times in the literature.Thus, 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, The naphthoquinone dyes are described in German Patent No. 3126108 and German Patent No. 3202761. The azo dyes are described in European Patent No. 43904, German Patent No. 3123519, International Publication No. 82 / 2054, British Patent No. 2079770, Japanese Patent Application Laid-Open No. 56-57850, Japanese Patent Application Laid-Open No. 56-104984, U.S. Pat. No. 4308161, U.S. Pat. No. 4308162, U.S. Pat. No. 4340973, 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), and perylenes are 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.

[0055] The switchable optical device may further comprise functional layers, such as, for example, a UV blocking layer and / or a color filter.

[0056] The optical cell and the window element are preferably characterized in that they do not comprise a polymer-based polarizer, particularly preferably they do not comprise a polarizer in a solid material phase, very particularly preferably they do not comprise a polarizer at all. In a particularly preferred embodiment, the device, in particular the window element, therefore does not comprise a polarizer.

[0057] However, according to alternative embodiments, the device may also include one or more polarizers. Thus, in some embodiments, at least one polarizing layer and, optionally, at least one retardation layer are provided in the optical device. The polarizer in this case is preferably a linear polarizer. Both absorptive and reflective polarizers may optionally be employed. The use of polarizers in the form of thin optical films is particularly preferred.

[0058] Thus, in addition to or instead of providing one or more dichroic dyes in the liquid crystal medium, it is possible to provide a window element in which the switchable optical cell further comprises one or more polarizer layers and optionally one or more optical retarder layers.

[0059] In a particular alternative, it is preferred that the device contains only one polarizer. When exactly one polarizer is present, a Heilmeyer type guest-host configuration is preferably used. In another alternative, a liquid crystal cell with two polarizers is used to control the light transmission, preferably when no dichroic dye is present in the liquid crystal medium.

[0060] According to the present invention in the optical cell there are provided first and second alignment layers in direct contact with the liquid crystal medium.

[0061] It has been found that even if a pretilt angle in the range of 77°-88° is set only in one of the first and second alignment layers, the undesired non-uniformity during electrical switching can already be significantly reduced. However, preferably, a pretilt angle in the range of 77°-88° is set in both the first and second alignment layers. In this way, an even stronger reduction in the effect can be achieved.

[0062] According to the present invention the pretilt angle is controlled and set by at least one alignment layer, preferably by both alignment layers, in the range of 77°-88°, more preferably in the range of 79°-87.5°, even more preferably in the range of 81°-87°, especially in the range of 84°-86°. Surprisingly it has been found that controlling the pretilt angle as defined can reduce and shorten the occurrence of non-uniformities while still providing sufficient contrast and adequate transmission in the optical state.

[0063] Pretilt angle as used herein is understood to mean the tilt orientation of the LC molecules of the LC medium with respect to the surface of the optical cell. In particular, pretilt angle herein 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 Mueller matrix polarimetry and is given in the examples. Unless otherwise indicated, the pretilt angle values ​​disclosed above and below refer to this measurement method.

[0064] In principle the first and second alignment layers may be formed according to conventional materials and methods, the alignment layers being provided to have an effect on homeotropic edge alignment.

[0065] Preferably the first and second alignment layers comprise, more preferably consist of, an organic material, in particular an organic material that is rubbed, in particular mechanically rubbed, or phototreated, in particular photoaligned. For example organic materials such as lecithin, in particular polyimides, may be used.

[0066] Preferably, the first and second alignment layers are polyimide-based layers. Thus, in a preferred embodiment, the alignment layers comprise polyimide, more preferably consist of polyimide. It is also possible to use or include chemically modified or reinforced polyimides, such as azobenzene-containing polyimides. Also, preferably, the alignment layers comprising polyimide may be rubbed or prepared by photoalignment methods.

[0067] The alignment layers, preferably polyimide layers, are arranged so as to provide homeotropic alignment of the molecules of the liquid crystal medium, especially at the interface, and in particular setting the pretilt angle as defined herein. In a particularly preferred embodiment non-rubbed polyimide layers are used on both substrates.

[0068] It is also possible to use polyimide layers prepared by photoalignment, taking advantage of the photoinduced orientational order of the alignment surface, which can be achieved through photolysis, photodimerization, or photoisomerization with polarized light.

[0069] The switchable layer is a homeotropic or vertically aligned liquid crystal layer. With a given pretilt angle the molecules of the liquid crystal medium are aligned close to perpendicular to the substrate surface. The liquid crystal medium therefore preferably has a negative dielectric anisotropy Δε, i.e. perpendicular to the electric field. The medium can therefore be switched to an alignment parallel to the plane of the layer structure by applying an electric field perpendicular to the plane.

[0070] Examples of suitable liquid crystal media with negative dielectric anisotropy are described in EP 1 378 558 A1. For example, the liquid crystal mixture ZLI-2806 from Merck may be used. The liquid crystal medium may contain additives. In particular, the liquid crystal medium preferably contains antioxidants or stabilizers in a concentration of at least 5 ppm.

[0071] Above and below, Δn represents the optical anisotropy,

number

[0072] Above and below, Δε represents the dielectric anisotropy,

number

[0073] All physical properties and physicochemical or electro-optical parameters are determined according to generally known methods, in particular according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", November 1997, Merck, Germany, and are given at a temperature of 20° C., unless expressly stated otherwise.

[0074] Unless expressly stated otherwise herein, all concentrations are given in weight percent and relate to the respective complete mixtures.

[0075] Light transmission and scattering preferably refers to the transmission and scattering of electromagnetic radiation in the spectral range of 380 nm to 780 nm.

[0076] The liquid crystal medium of the switchable layer preferably has a nematic phase at the operating temperature of the switchable window element. It is particularly preferably nematic within a range of + / - 20°C above and below the operating temperature of the window element, very particularly preferably within a range of + / - 30°C. The operating temperature of the switchable window element is preferably between -20°C and 70°C.

[0077] The liquid crystal medium preferably has a clearing point, preferably a phase transition from a nematic liquid crystal state to an isotropic state, 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. and most preferably above 115° C. In one embodiment the liquid crystal medium as used in the present invention preferably has a clearing point within a temperature range of 70° C. to 170° C., more preferably 80° C. to 160° C., even more preferably 90° C. to 150° C. and in particular 100° C. to 140° C.

[0078] The clearing point indicates 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 and isotropic phases, can be measured and determined by commonly known methods, such as using a Mettler oven or a hot stage under a polarizing microscope, and is preferably determined herein using a Mettler oven.

[0079] In addition the liquid crystal medium preferably exhibits good low temperature stability without visible crystallization or decomposition, in particular a long term storage stability of more than 200 hours in bulk measurement at -40°C.

[0080] Preferably the liquid crystal medium comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC.

[0081] [ka]

[0082] During the ceremony, a represents 1 or 2; b represents 0 or 1; c represents 0, 1 or 2; d represents 0 or 1; [ka] [ka] [ka] R 1 , R 2 , R AC1 and R AC2 are each independently an alkyl group having 1 to 12 C atoms (provided that in addition, one or two non-adjacent CH2 groups are independently connected to each other such that the O atoms are not directly linked to each other), [ka] -O-, -CH=CH-, -CO-, -OCO- or -COO-), preferably represents alkyl or alkoxy having 1 to 6 C atoms, Z x , Z y and Z AC each independently represents -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, and L 1~4 each independently represents F, Cl, CN, OCF3, CF3, CH3, CH2F or CHF2, preferably F.

[0083] Preferably, L 1 and L 2 Both represent F, or L 1 and L 2 One of the groups represents F and the other represents Cl, or L 3 and L 4 Both represent F, or L 3 and L 4 One of these represents F and the other represents Cl.

[0084] In some embodiments, one or more groups R 1 , R 2 , R AC1 and R AC2 represents cyclic alkyl selected in particular from cyclopropyl, cyclobutyl and cyclopentyl.

[0085] In this specification, [ka] represents trans-1,4-cyclohexylene.

[0086] It is particularly preferred that the liquid crystal medium used according to the present invention comprises 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, even more preferably at least 25% by weight, even more preferably at least 35% by weight and particularly preferably at least 50% by weight, based on the total content of the medium.

[0087] The compound of formula CY is preferably selected from the group of compounds of the following formulae:

[0088] [ka]

[0089] [ka]

[0090] [ka]

[0091] [ka]

[0092] [ka]

[0093] In the formula, a represents 1 or 2; alkyl and alkyl *each independently represents a linear alkyl group having 1 to 6 C atoms, alkenyl represents a linear alkenyl group 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-.

[0094] In another embodiment the compound of formula CY is additionally or alternatively selected from the group of compounds of the following formulae:

[0095] [ka]

[0096] alkyl in the formula * each independently represents a linear alkyl group having 1 to 6 C atoms, and (O) represents an oxygen atom or a single bond.

[0097] In a particular embodiment, the compound CY-a-1 is included in the medium, and the compound CY-a-1 is an (O)alkyl * corresponds to the compound of formula CY-a, where

[0098] The compound of formula PY is preferably selected from the group of compounds of the following formulae:

[0099] [ka]

[0100] [ka]

[0101] [ka]

[0102] In the formula, alkyl and alkyl * each independently represents a linear alkyl group having 1 to 6 C atoms, alkenyl represents a linear alkenyl group 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-.

[0103] The compound of formula AC is preferably selected from the group of compounds of the following formulae:

[0104] [ka]

[0105] R in the formula 3 and R 4 is R as above. AC1 and R AC2 It has the meaning:

[0106] Many of the mesogenic compounds or mixtures thereof mentioned above and below are commercially available. These compounds are known or can be prepared by methods known per se under known and appropriate reaction conditions for the reactions described above, as described in the literature (e.g. standard works, e.g. Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart). Variants known per se can also be used here, but are not mentioned in more detail here. The media according to the invention are prepared in a manner conventional per se. In general, the components are dissolved in each other, preferably at high temperature. The dielectric anisotropy, viscosity and / or alignment of the liquid crystal phase can be modified by adding suitable additives or substances.

[0107] The term "alkyl" according to the present invention preferably includes straight-chain and branched-chain 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.

[0108] Alkoxy can be straight or branched chain, preferably straight chain and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms, and is therefore preferably methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy.

[0109] The term "alkenyl" according to the present invention preferably encompasses 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, 4E-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl and 6-heptenyl. Groups having 5 or fewer carbon atoms are generally preferred.

[0110] The alkyl or alkoxy fluoride is preferably CF3, OCF3, CFH2, OCFH2, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CH2CF3, CH2CF2H, CH2CFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCH2CF3, OCH2CF2H, OCH2CFH2, OCF 2CF2H, 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 positions of fluorine are not excluded.

[0111] The oxaalkyl is preferably of the formula C n H 2n+1 -O-(CH2) m (wherein n and m are each independently an integer of 1 to 6). Preferably, n=1, and m is an integer of 1 to 6.

[0112] 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.

[0113] Halogen is preferably F or Cl, in particular F.

[0114] If one of the above mentioned groups is an alkyl group in which one CH2 group is replaced by -CH=CH-, it can 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.

[0115] If one of the above mentioned groups is an alkyl group in which one CH2 group is replaced by -O- and one by -CO-, then they are preferably adjacent. Thus, they contain an acyloxy group -CO-O- or an oxycarbonyl group -O-CO-. They are preferably linear and have 2 to 6 carbon atoms.

[0116] 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-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl, 3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

[0117] If one of the above mentioned groups is an alkyl group in which one CH2 group is replaced by an unsubstituted or substituted -CH=CH- and the adjacent CH2 groups are replaced by CO, CO-O or O-CO, it can 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.

[0118] When one of the above mentioned groups is an alkyl or alkenyl group monosubstituted by CN or CF3, this group is preferably linear. The substitution by CN or CF3 can be in any position.

[0119] When one of the above mentioned groups is an alkyl or alkenyl group at least monosubstituted by a halogen, this group is preferably linear and the halogen is preferably F or Cl, more preferably F. In case of polysubstitution, the halogen is preferably F. The resulting groups also include perfluorinated groups. In case of monosubstitution, the fluoro or chloro substituent can be in any desired position, but is preferably in the ω position.

[0120] Compounds containing branched groups may be important for better solubility in some conventional liquid crystal-based materials, but when they are optically active they are particularly suitable as chiral dopants.

[0121] Branched groups of this type generally contain not more than 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.

[0122] If one of the above mentioned radicals is an alkyl radical in which two or more CH2 groups are replaced by -O- and / or -CO-O-, it can be linear or branched. It is preferably branched and has 3 to 12 carbon atoms. It is therefore particularly preferred for use as 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.

[0123] In addition to an appropriately high optical anisotropy the liquid-crystalline media contained in the switchable layer can advantageously exhibit a preferably high voltage holding ratio (VHR) in combination with good light stability and an appropriately high clearing point.

[0124] In some embodiments, it is preferred that in one of the optical states, particularly in the presence of an electric field, the switchable layer has a twisted or supertwisted configuration, which has surprisingly been found to contribute further to mitigating and / or reducing the occurrence of deleterious non-uniformities as described above, in addition to setting the pretilt angle as defined herein.

[0125] The liquid crystal medium may therefore further comprise one or more chiral compounds, in particular one or more chiral dopants.

[0126] Chiral compounds and especially chiral dopants and their concentrations can be provided so that the cholesteric pitch of the liquid crystal medium can be appropriately set or adjusted. By pitch in this specification is meant the pitch p of the cholesteric helix, which is the distance for the 2π rotation of the director of the cholesteric liquid crystal. 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 reduce the temperature dependence of the helical pitch.

[0127] The liquid crystal medium in the switch layer therefore preferably comprises one or more chiral compounds, in particular chiral dopants. The chiral dopants preferably have a moderately high to high absolute value of HTP, can generally be added to the mesogenic base mixture in relatively low concentrations and have good solubility in the achiral component. If two or more chiral compounds are employed, they may have the same or opposite sense of rotation and the same or opposite temperature dependence of twist.

[0128] Preferably, the one or more chiral compounds which may be contained in the liquid crystal medium are preferably those having a 5 μm -1 More preferably, 10 μm -1 More preferably, 15 μm or more -1 Preferably, the absolute value of the helical twisting power is 20 μm or more in the commercially available liquid crystal mixture MLC6828 manufactured by Merck. -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 the helical twisting power within the following ranges:

[0129] Preferably, the one or more chiral compounds are contained in the liquid-crystalline medium in an amount of less than or equal to 2% by weight, more preferably less than or equal to 1% by weight, relative to the total content of the medium.

[0130] Suitable chiral dopants are known in the art, e.g., 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, Darmstadt).

[0131] Particularly suitable chiral dopants are compounds which contain one or more chiral groups and one or more mesogenic groups or one or more aromatic or alicyclic groups which together with the chiral groups form a mesogenic group. In a particularly preferred embodiment of the invention the liquid crystal medium comprises one or more compounds selected from the compounds shown in Table F below.

[0132] In some embodiments, the layer thickness d of the switchable layer is set expediently in relation to the pitch p of the medium, with the ratio d / p preferably being in the range of 0 to 1, particularly preferably being 0.25 or approximately 0.25. In some cases, a ratio d / p of 0.66 or approximately 0.66 is particularly preferred.

[0133] In a preferred case the optical state in the presence of an electric field has a twisted nematic (TN) configuration with a twist of 90°. In another preferred case a supertwisted nematic (STN) configuration with a twist of e.g. 240° may be set up, in which case preferably only a single optical cell is used for the window element.

[0134] In certain embodiments, the switchable layer is polymer stabilized. Surprisingly, it has been found that polymer stabilization advantageously contributes to obtaining and maintaining over time an optical state having a desired alignment and configuration.

[0135] In this respect preferably one or more polymerizable, curable or hardenable compounds, preferably one or more photocurable monomers, are provided in the liquid crystal medium as precursors of the polymer components used for polymer stabilization, and these reactive compounds are subsequently polymerized in situ.

[0136] In one embodiment, one or more polymerizable compounds are therefore included in the liquid crystal medium as polymer precursors used for polymer stabilization. Preferably, the one or more polymerizable compounds are selected to have an appropriate and sufficient solubility in the liquid crystal medium. In one embodiment, polymerizable mesogenic or liquid crystal compounds, also known as reactive mesogens (RM) 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 mono- or di- or polyreactive. In another embodiment, non-mesogenic polymerizable compounds, i.e. compounds without mesogenic groups, are used.

[0137] It is particularly preferred that the polymerisable compound(s) only comprise reactive mesogen(s), i.e. all reactive monomers are mesogenic. The RM may also be provided in combination with one or more non-mesogenic polymerisable compounds.

[0138] 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 acetates, more preferably the medium further comprises one or more di- and / or tri-reactive polymerizable compounds, preferably selected from diacrylates, dimethacrylates, triacrylates and trimethacrylates.

[0139] Suitable thermal or photoinitiators conventionally used to promote polymerization reactions can be added, for example organic peroxides such as azo compounds or Luperox-type initiators. Further suitable polymerization conditions, types and amounts of suitable 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.

[0140] For example, when polymerizing using UV light, photoinitiators can be used that decompose upon UV irradiation to generate free radicals and ions to start the polymerization reaction. Radical photoinitiators are preferably used for the polymerization of acrylate and methacrylate groups. Cationic photoinitiators are preferably used for the polymerization of vinyl, epoxide, and oxetane groups. It is also possible to use thermal polymerization initiators that decompose upon heating to generate free radicals and ions that start the polymerization.

[0141] In a preferred embodiment the polymerization is carried out by photoirradiation, ie by light, preferably UV light.

[0142] According to a particularly preferred embodiment, no polymerization initiator, especially no photoinitiator, is used. In certain cases, this can improve the VHR and reduce the tendency to generate ions in the switchable layer. This can contribute to obtaining and maintaining a modulation material with good reliability and stability. Therefore, according to a preferred embodiment, no polymerization initiator is added in the liquid crystal medium.

[0143] In order to maintain and achieve a good VHR, impurities in the reaction product of the polymerization stabilization are preferably minimized or substantially avoided. In particular, residual reactive species and charged contaminants are preferably kept to a minimum. For example, when carrying out UV polymerization, in a preferred embodiment, light with a relatively long wavelength approaching or extending into the visible spectrum is used, preferably UV light and light in the range of 340 nm to 410 nm, more preferably UV light of 340 nm to 380 nm, even more preferably light of 360 nm to 380 nm is advantageously used. In this way, undesired photolysis or decomposition of the components of the LC medium, in particular one or more dichroic dyes optionally provided, can be avoided or at least minimized. When using a photoinitiator, the irradiation wavelength and the photopolymerization initiator can be appropriately matched or adjusted.

[0144] In the preferred case where no photoinitiator is used, the wavelength range of light can be set so that at least a portion of the polymerizable compounds can photoreact and initiate the polymerization reaction themselves, while still avoiding or at least minimizing degradation or decomposition of the non-polymerizable components of the LC medium, in particular the optionally provided one or more dichroic dyes. Obtaining and setting the desired wavelength range can be achieved by conventional methods known in the art, for example using optical filters, in particular edge filters.

[0145] Preferably and advantageously, the polymeric structure for stabilization is prepared in situ. By appropriately selecting one or more polymerizable compounds, particularly polymerizable mesogenic compounds, together with one or more dichroic dyes, which are optionally provided preferably, and setting and adjusting the wavelength of the light used for photopolymerization, particularly with respect to the absorption characteristics of the dichroic dye, an efficient and robust method can be provided, which can obtain the desired polymerization and polymer components in the switchable layer, and further maintain the non-polymerizable components and their performance, including the dichroic dye. In some embodiments, the wavelength or each wavelength spectrum of the irradiating light is selected to minimize overlap with the absorption band of the dichroic dye.

[0146] Preferably, one or more polymerizable compounds optionally provided in the liquid crystal medium for polymer stabilization are contained in an amount in the range of 0 to 5% by weight, more preferably in the range of 0.1% by weight to 2.5% by weight, particularly preferably in the range of 0.3% by weight to 1% by weight, based on the total content of the medium.

[0147] Particularly suitable polymerizable compounds are listed in Table G below.

[0148] The optical cells and window elements have various shapes, for example square, rectangular, triangular or polygonal. The window elements may, for example, be housed or arranged in double or triple glazing units, in particular insulating glazing units. The window panes can be suitably used in buildings and automobiles.

[0149] In addition to being used as part of the exterior wall or facade of a building, window elements can also be used for interior applications in buildings. For example, window elements may serve as partitions or room dividers or in separating walls, particularly to provide a privacy mode when desired, where very good darkness is desired to effectively block visual contact.

[0150] Preferably, a switchable optical cell comprises only a single switchable layer.In one embodiment of the present invention, the window element comprises exactly one switchable optical cell.

[0151] In another particularly preferred embodiment, however, the window element comprises an additional switchable optical cell. In this latter case, two switch layers are provided separately or individually in the optical cell, which are then joined together, for example by lamination and bonding with an adhesive, to form a so-called double cell. In a particularly preferred embodiment, the window element comprises a double cell which uses a liquid-crystalline medium doped with a dichroic dye.

[0152] This is particularly preferred in interior applications where a very good dark state is desired, for example in embodiments where the window element comprises a double cell with a dichroic dye-doped liquid crystal medium, and where it is intended to provide a switchable privacy mode.

[0153] Thus, in addition to the switchable optical cells described above and below, the window element preferably comprises a further switchable optical cell, more preferably the further switchable optical cell is matched to said first switchable optical cell.

[0154] The window element is preferably at least 100 cm 2 , more preferably at least 1600 cm 2 , more preferably at least 10000 cm 2 Further, the switchable layer may be unsegmented, or alternatively, in the case where the switchable layer is segmented into segments, each of said segments may have an area of ​​at least 1 cm 2 , more preferably at least 10 cm 2 , more preferably at least 50 cm 2 In contrast to conventional liquid crystal displays, which have a large number of tiny pixels, the window elements typically include a continuous area of ​​liquid crystal material and an equally uniform area of ​​electrodes, so that typical effects due to pixel boundaries and possible cross effects between adjacent pixels are not important in the case of window configurations.

[0155] The structures of the mesogenic compounds according to the present invention and in particular in the following examples are shown using abbreviations, also called acronyms. In these acronyms, the chemical formulae are abbreviated as follows, using the following tables A to 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-1denotes linear alkyl or alkenyl, preferably 1-E-alkenyl, 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, while Table B indicates the linking groups. Table C gives the meaning of the codes for the left- or right-hand end groups. The acronyms consist of the code for the ring element with any linking group, followed by the first hyphen and the code for the left-hand end group and the code for the second hyphen and the code for the right-hand end group. Table D shows exemplary structures of the compounds with the respective abbreviations.

[0156] <Table A: Ring elements> [Table 1]

[0157] [Table 2]

[0158] [Table 3]

[0159] <Table B: Linking group> [Table 4]

[0160] <Table C: Terminal group> [Table 5]

[0161] where n and m each represent an integer and the three dots "..." are places for other abbreviations from this table.

[0162] The following table shows exemplary structures, each with their abbreviation. These are presented to illustrate the meaning of the abbreviation rules. They further represent compounds which may be preferably used.

[0163] <Table D: Example structure>

Table 6

[0164]

Table 7

[0165]

Table 8

[0166]

Table 9

[0167]

Table 10

[0168]

Table 11

[0169]

Table 12

[0170]

Table 13

[0171]

Table 14

[0172]

Table 15

[0173] [Table 16]

[0174] [Table 17]

[0175] [Table 18]

[0176] [Table 19]

[0177] In the formula, n, m and l preferably each independently represent 1 to 7.

[0178] The following table shows exemplary compounds which can be used as stabilizers in the media according to the invention.

[0179] Table E shows possible stabilizers which can be added to the LC media according to the invention, where n denotes an integer between 1 and 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8. [Table 20]

[0180] [Table 21]

[0181] [Table 22]

[0182] [Table 23]

[0183] [Table 24]

[0184] [Table 25]

[0185] [Table 26]

[0186] 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 stabilizers.

[0187] Table F below shows exemplary compounds which can be preferably used as chiral dopants in the mesogenic media according to the present invention.

[0188]

[0189] [Table 27]

[0190] [Table 28]

[0191] [Table 29]

[0192] [Table 30]

[0193] In a preferred embodiment of the invention the mesogenic medium comprises one or more compounds selected from the compounds shown in Table F.

[0194] 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.

[0195] In one embodiment the LC medium according to the invention preferably comprises 3 or more, more preferably 5 or more compounds as shown in Table D.

[0196] Table G collates exemplary compounds which can be preferably used as reactive mesogenic compounds in the LC media according to the invention. Preferably for the polymerization, an initiator or a mixture of two or more initiators is added. The initiator or initiator mixture is preferably added in an amount of 0.001% to 2% by weight, based on the mixture. A suitable initiator is for example Irgacure® 651 (BASF).

[0197] [Table 31]

[0198] [Table 32]

[0199] [Table 33]

[0200] [Table 34]

[0201] [Table 35]

[0202] [Table 36]

[0203]

Table 37

[0204]

Table 38

[0205]

Table 39

[0206]

Table 40

[0207]

Table 41

[0208]

Table 42

[0209]

Table 43

[0210]

Table 44

[0211]

Table 45

[0212]

Table 46

[0213]

Table 47

[0214] [Table 48]

[0215] [Table 49]

[0216] [Table 50]

[0217] In a preferred embodiment of the invention the mesogenic medium comprises one or more compounds selected from the group of compounds in Table G.

[0218] 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 3 or more compounds of different formulae selected from the group of compounds 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. More preferably, the medium further comprises one, two or more compounds selected from the group of formulae of table G.

[0219] The following examples are merely illustrative of the present invention, and they should not be construed as limiting the scope of the present invention in any manner. The examples and modifications or other equivalents thereof will be apparent to those of skill in the art in light of this disclosure.

[0220] However, the exemplary physical properties and compositions given below show what properties can be achieved and to what extent they can be varied, so that the various property combinations which can be particularly preferably achieved are well defined. EXAMPLES

[0221] In the example, V0 represents the capacitance threshold voltage [V] at 20°C. n e represents the extraordinary refractive index at 20°C and 589 nm, n0 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) stands for clearing point [℃], γ1 is the rotational viscosity at 20°C [mPa s], determined by the rotation method in a magnetic field, K1 represents the elastic constant for "splay" deformation at 20°C [pN], K2 represents the elastic constant [pN] for the "twist" deformation at 20°C, K3 represents the elastic constant [pN] for "bend" deformation at 20°C.

[0222] The term "threshold voltage" in the present invention, unless otherwise specified, refers to the capacitance threshold (V0). Also, as is generally customary in the examples, the 10% relative contrast (V 10 ) may also be given.

[0223] <Reference Example 1> A liquid crystal host mixture H-1 having the composition and properties as shown in the table below is prepared and characterized with respect to its general physical properties.

[0224] [Table 51]

[0225] Mixture M-1 is 99.01% mixture H-1, 0.05% of the lower compound, [ka] 0.16% of lower compound, [ka] 0.35% of the lower compound; [ka] and 0.43% of the lower compound [ka] It is prepared by mixing the following:

[0226] <Reference Example 2> A liquid crystal base mixture B-2 having the composition and properties as shown in the table below is prepared and characterized with respect to its general physical properties.

[0227] [Table 52]

[0228] Mixture M-2 is prepared similarly to mixture M-1 described in Reference Example 1 above, except that mixture B-2 is used instead of mixture H-1.

[0229] <Reference Example 3> A liquid crystal base mixture B-3 having the composition and properties as shown in the table below is prepared and characterized with respect to its general physical properties.

[0230] [Table 53]

[0231] Mixture M-3 is prepared by mixing 99.638% of Mixture B-3, 0.332% of a compound of formula S-811 as set forth in Table F above, and 0.030% of a compound of the formula: [ka]

[0232] <Reference Example 4> A liquid crystal base mixture B-4 having the composition and properties as shown in the table below is prepared and characterized with respect to its general physical properties.

[0233] [Table 54]

[0234] Mixture M-4 is prepared by mixing 99.51% of Mixture B-4 and 0.49% of the compound of formula S-811 as set forth in Table F above.

[0235] <Reference Example 5> A liquid crystal mixture B-5 having the composition and properties as shown in the table below is prepared and characterized with respect to its general physical properties.

[0236] [Table 55]

[0237] <Reference Example 6> The liquid crystal mixture M-6 was prepared and characterized with respect to its general physical properties, where compound CY-a-1 is defined as specified above.

[0238] [Table 56]

[0239] <Comparative Example 1> Two optical cells were assembled using two glass plates (20 mm × 26 mm, 1.1 mm thick), each coated with an indium tin oxide (ITO) layer (50 nm thick, 100 Ω / □ resistance). A layer of polyimide (50 nm, JSR, JALS-2096-R1) was spin-coated on top of the ITO layer for each glass plate. The polyimide layer was rubbed antiparallel with a velvet cloth (Yoshikawa Kako Co., Ltd. YA-20R) on a metal roller.

[0240] Rubbing induces a pretilt angle of 88.5°, which is determined using an Axometrics Mueller Matrix Polarimeter “AxoScan.”

[0241] Combine two glass plates together, each with the polyimide layer facing inwards, including a plastic spacer with a diameter of 25 µm, to form a cell, using a 3 mm offset on the short side to provide wiring access. Seal the edges of the cell, except for the filling port.

[0242] The dye-doped liquid crystal mixture M-1 as described in Reference Example 1 above is filled into the cell by capillary forces and the filling port is sealed. Electrical cables are soldered to the offset contact areas of the cell.

[0243] The two cells are laminated together using double-sided tape near the edges, forming a double cell with one cell rotated 90° relative to the other.

[0244] Switching the dual cell with a 30Vrms square wave voltage results in a dark state with a granular and irregular appearance, with small bright spots and irregular thin bright lines. These defects gradually disappear over time. Only 120 seconds after switching, a dark state with a uniform dark appearance is obtained.

[0245] <Comparative Example 2> A switchable cell is assembled similar to Comparative Example 1 above, except instead the cell thickness is set to 15 μm and the pretilt angle is set to 89°.

[0246] Using a square wave voltage of 20 Vrms for the switch, the granular defects of the initial dark state disappear after 60 seconds, resulting in a uniform dark appearance.

[0247] <Example 1> Two optical cells were assembled using two glass plates (20 mm × 26 mm, 1.1 mm thick), each coated with an indium tin oxide (ITO) layer (50 nm thick, 100 Ω / □ resistance). A layer of polyimide (50 nm) was spin-coated on top of the ITO layer for each glass plate. The polyimide layer was rubbed with a velvet cloth (Yoshikawa Kako Co., Ltd. YA-20R) on a metal roller using a rotation speed of 200 rpm, a travel speed of 25 mm / s, and a rubbing depth of 0.3 mm.

[0248] A pretilt angle of 86° was induced by rubbing, and the pretilt angle was determined using an Axometrics Mueller Matrix Polarimeter "AxoScan."

[0249] Combine two glass plates together, each with the polyimide layer facing inwards, including a plastic spacer with a diameter of 25 µm, to form a cell, using a 3 mm offset on the short side to provide wiring access. Seal the edges of the cell, except for the filling port.

[0250] The dye-doped liquid crystal mixture M-1 as described in Reference Example 1 above is filled into the cell by capillary forces and the filling port is sealed. Electrical cables are soldered to the offset contact areas of the cell.

[0251] The two cells are laminated together using double-sided tape near the edges, forming a double cell with one cell rotated 90° relative to the other.

[0252] Switching the dual cell with a 30Vrms square wave voltage results in a dark state with a granular, irregular appearance with small bright spots and irregular thin bright lines. These defects disappear quickly and a uniform dark appearance is obtained 10 seconds after switching.

[0253] <Example 2> A switchable cell is constructed similar to Example 1 above, except instead the cell thickness is set to 15 μm and the pretilt angle is set to 85°.

[0254] Using a square wave voltage of 20 Vrms for the switch, the granular defects of the initial dark state disappear after 10 seconds, resulting in a uniform dark appearance.

[0255] <Example 3> Switchable cells are fabricated similarly to Example 1 above, except that a pretilt angle of 86° is set in one polyimide layer and a pretilt angle of 89° is set in the other polyimide layer in each of the cells having a thickness of 25 μm.

[0256] Using a square wave voltage of 20 Vrms for the switch, the granular defects of the initial dark state disappear after 10 seconds, resulting in a uniform dark appearance.

[0257] <Example 4> A switchable cell was assembled similar to Example 1 above using a cell thickness of 25 μm and setting the pretilt angle at 85°, but applying a voltage of 20 V to provide a twisted TN configuration with a twist angle of 90°.

[0258] Using a square wave voltage of 20 Vrms for the switch, the granular defects of the initial dark state disappear after 10 seconds, resulting in a uniform dark appearance.

Claims

1. A first substrate; A first electrode layer; a first alignment layer; A switchable layer; a second alignment layer; a second electrode layer, and A second substrate A switchable optical cell having a layer structure comprising, in this order: wherein the switchable layer is a homeotropically aligned liquid crystal layer comprising a liquid crystal medium; and However, the pretilt angle in at least one of the first alignment layer and the second alignment layer is set within a range of 84° to 86°, However, the liquid crystal medium contains one or more dichroic dyes, However, the window element does not include a polarizer. provided that the window element has an area of ​​at least 100 cm 2 ; A window element, with the proviso that the switchable layer is either undivided or divided into sections each having an area of ​​at least 1 cm 2 .

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

3. the switchable optical cell is operable between a bright state and a dark state and is electrically switchable; 3. A window element according to claim 1 or 2, wherein the switchable layer is homeotropically aligned in the absence of an electric field.

4. Window element according to any one of the preceding claims, 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.

5. Window element according to any one of claims 1 to 4, wherein the switchable layer is polymer stabilized.

6. 6. A window element according to any one of the preceding claims, wherein the first and second alignment layers set a pretilt angle in the range of 84° to 86°.

7. Window element according to any one of claims 1 to 6, wherein the first and second alignment layers comprise rubbed or photo-treated organic materials.

8. Window element according to any one of claims 1 to 7, wherein the first and second alignment layers are polyimide-based layers.

9. A window element according to any one of claims 1 to 8, wherein in addition to the switchable optical cell the window element comprises a further switchable optical cell, the further switchable optical cell corresponding to the switchable optical cell as defined in any one of claims 1 to 8.

10. Window element according to any one of the preceding claims, wherein in the presence of an electric field the switchable layer has a twisted or supertwisted configuration.

11. Window element according to any one of the preceding claims, wherein the liquid crystal medium comprises one or more compounds selected from the group of compounds of the formulae CY, PY and AC. 【Chemistry 1】 (In the formula, a represents 1 or 2; b represents 0 or 1; c represents 0, 1 or 2; d represents 0 or 1; 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 R １ , R ２ , R ＡＣ１ and R ＡＣ２ each independently represents an alkyl group having 1 to 12 carbon atoms (but in addition has 1 or 2 non-adjacent CH ２ The groups are independently selected such that the O atoms are not directly linked to each other. 【Chemistry 5】 may be replaced by -O-, -CH=CH-, -CO-, -OCO- or -COO-; Z ｘ , Z ｙ and Z ＡＣ are each independently -CH ２ CH ２ -, -CH=CH-, -CF ２ O-, -OCF ２ --, --CH ２ O-, -OCH ２ -, -CO-O-, -O-CO-, -C ２ F ４ -, -CF=CF-, -CH=CH-CH ２ represents O- or a single bond, and L １～４ are each independently F, Cl, CN, OCF ３ , C.F. ３ , C.H. ３ , C.H. ２ F or CHF2.) 12. A window element according to any one of claims 1 to 11, wherein the window element has an area of ​​at least 10,000 cm 2 .

13. Use of a window element according to any one of claims 1 to 12 in a building or vehicle window.

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