Liquid crystal light valve

Abstract

A liquid crystal light valve is provided. The present invention relates to a method for preparing a light valve operable in optically transparent and opaque states and electrically switchable between them, in which one or more polymerizable mesogenic compounds provided in a layer comprising a liquid crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds, one or more dichroic dyes and one or more polymerizable mesogenic compounds are subjected to photopolymerization. The invention further relates to the liquid crystalline medium used in the method, to a light valve obtained or respectively obtainable by carrying out the method, and to the use of the light valve in a mobile device.

Description

[Technical field]

[0001] The present invention relates to a method for the preparation of a light valve operable in optically transparent and opaque states and electrically switchable between them, in which one or more polymerizable mesogenic compounds provided in a layer comprising a liquid crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds, one or more dichroic dyes and one or more polymerizable mesogenic compounds are subjected to photopolymerization. The invention further relates to the liquid crystalline medium used in the method and to a light valve obtained or respectively obtainable by carrying out the method and to the use of the light valve in a mobile device. [Background technology]

[0002] Devices that control or modulate the transmission of light are commonly used in display applications and may also be used in a variety of mobile devices such as eyewear, glasses, goggles and visors, and may find application in the context of augmented and virtual reality environments. Light intensity modulators such as light valves or light shutters can be based on liquid crystals (LC). In principle, such light valves or light shutters can rely on light absorption or light scattering.

[0003] Some devices can reversibly change light transmission, typically by an electrical switch, to attenuate, dim or color the intensity of incident light, but exhibit little scattering or haze in different operating states.Such devices thus operate in and can be switched between bright and dark states, i.e., states of relatively high and relatively low light transmission, and both states are substantially non-hazy.

[0004] Several modes and configurations can be employed to provide such a reversible transmittance change. In twisted nematic (TN), super-twisted nematic (STN) and vertical alignment (VA) liquid crystal cells, polarizers are used to control the light transmittance. 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 polarizer to change the light transmittance. However, in some embodiments and applications, the guest-host liquid crystal cells are used in combination with at least one polarizer.

[0005] Liquid crystal-based light modulators using light scattering include so-called polymer dispersed liquid crystals (PDLC) or encapsulated or nematic curvilinear aligned phase liquid crystals (NCAP), polymer network liquid crystals (PNLC), cholesteric liquid crystals (CLC), polymer stabilized cholesteric texture liquid crystals (PSCT) and dynamic scattering liquid crystal devices. These scattering type devices can be switched between a transparent state, i.e. optically clear or non-haze state, and a light scattering state, i.e. translucent or haze state.

[0006] When such a scattering type device is switched from a non-scattering, i.e. optically transparent, state to a scattering state, the light transmission changes to produce a translucent appearance, which may also be perceived as cloudy, turbid, diffuse or haze. Devices based on the scattering mode can be used in particular to provide temporary privacy or to conceal features or information when desired by switching, typically electrically, the device from an optically transparent state to a scattering state.

[0007] D.-K. Yang et al., "Cholesteric liquid crystal / polymer dispersion for haze-free light shutters," Applied Physics Letters, Vol. 60 (1992), pp. 3102-3104 (Non-Patent Document 1), describes the dispersion of low concentrations of polymers with cholesteric liquid crystals and the use of this material in light modulators that can be switched between an opaque, light-scattering state and a transparent state.

[0008] It is also possible to combine light modulation by absorption and scattering in a device. In this way, in addition to providing haze, an opaque state can be obtained that exhibits a reduction in overall light intensity. In certain implementations, dichroic dyes can be used for light attenuation, and in some instances, these dyes can also provide coloration.

[0009] WO 00 / 60407 describes an electro-optical glazing structure with opaque and transparent modes of operation.

[0010] B.-H. Yu et al., "Simultaneous control of haze and transmittance using a dye-doped cholesteric liquid crystal cell," Liquid Crystals, Vol. 42 (2015), pp. 1460-1464 (Non-Patent Document 2), proposes an optical shutter device using dye-doped cholesteric liquid crystals for use in see-through displays.

[0011] J. Heo et al., "Fast-switching initially-transparent liquid crystal light shutter with crossed patterned electrodes," AIP Advances, Vol. 5, No. 047118 (2015) (Non-Patent Document 3) describes a light shutter using polymer network liquid crystals and dichroic dyes with crossed patterned electrodes that can be switched between transparent and opaque states. In the opaque state, the device can block the background image and provide the color black. The proposed light shutter may have potential applications in see-through displays and smart windows.

[0012] B.-H. Yu et al., "Light shutter using dye-doped cholesteric liquid crystals with polymer network structure," Journal of Information Display, Vol. 18 (2017), pp. 13-17 (Non-Patent Document 4), proposes a light shutter using dye-doped cholesteric liquid crystals with a polymer network structure for use in see-through displays.

[0013] There is a need in the art for further light modulators, particularly light valves such as light shutters, with improved optical and electro-optical performance, and there is also a need in the art for suitable methods of manufacturing such switchable devices. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] WO 00 / 60407 [Non-patent literature]

[0015] [Non-Patent Document 1] D.-K. Yang et al., "Cholesteric liquid crystal / polymer dispersion for haze-free light shutters," Applied Physics Letters, Vol. 60 (1992), pp. 3102-3104 [Non-Patent Document 2] B.-H. Yu et al., "Simultaneous control of haze and transmittance using a dye-doped cholesteric liquid crystal cell," Liquid Crystals, Vol. 42 (2015), pp. 1460-1464 [Non-Patent Document 3] J. Heo et al., "Fast-switching initially-transparent liquid crystal light shutter with crossed patterned electrodes," AIP Advances, Vol. 5, No. 047118 (2015) [Non-Patent Document 4] B.-H. Yu et al., "Light shutter using dye-doped cholesteric liquid crystals with polymer network structure," Journal of Information Display, Vol. 18 (2017), pp. 13-17 Summary of the Invention [Problem to be solved by the invention]

[0016] It is therefore an object of the present invention to provide a simple, efficient and robust method for preparing a light valve that can be operated in optically transparent and opaque states and electrically switched between them, and that has improved optical and electro-optical performance.A further object of the present invention is to provide a light valve that has favorable performance and is particularly suitable for use in mobile and portable devices and in the context of augmented reality or respectively virtual reality.Another object is to provide a liquid crystal medium that is particularly suitable for use in the method according to the present invention, that results in a favorable modulation material in a light valve, and that has advantageous chemical, physical and electro-optical properties.Further objects of the present invention will be immediately apparent to those skilled in the art from the following detailed description.

[0017] While the object is solved by the subject matter defined in the independent claims, preferred embodiments are defined in the respective dependent claims and are further described below.

[0018] The present invention particularly provides the following items including main aspects, preferred embodiments and specific features, which each alone and in combination contribute to solving the above objects and ultimately provide additional advantages: [Means for solving the problem]

[0019] A first aspect of the invention provides a method for preparing a light valve operable in and electrically switchable between optically transparent and opaque states, comprising the steps of: (i) providing a liquid crystal medium containing one or more mesogenic compounds, one or more chiral compounds, one or more dichroic dyes and one or more polymerizable mesogenic compounds as a layer interposed between two opposing transparent substrates each provided with an electrode; However, the liquid crystal medium must have a clearing point of 70°C or higher. provided that one or more polymerizable mesogenic compounds are contained in the medium in an amount of 4% by weight or less based on the total content of the medium, and (ii) polymerizing one or more polymerizable mesogenic compounds in the layer using photopolymerization The present invention provides a method comprising:

[0020] By light valve in this specification is meant an element for modulating light, configured as a cell formed of two spaced apart walls, in particular two transparent substrates, provided with electrodes, the cell containing a light modulating material.

[0021] The optically clear state refers to a state of high transmission with low haze. The light valve preferably prepared in the optically clear state has a haze of less than 15% as determined according to ASTM D 1003 and a light transmission of preferably more than 45% as determined according to DIN EN410. The opaque state refers to a state of low transmission with high haze. The light valve preferably prepared in the opaque state has a haze of more than 65% as determined according to ASTM D 1003 and a light transmission of less than 35% as determined according to DIN EN410.

[0022] In the present invention, it has been recognized that for certain situations and applications, it is desirable to provide light valves that are particularly advantageous for use in mobile or portable devices. In this case, it is desirable to obtain a high switching as well as a low operating voltage and low power consumption, in addition to a lightweight structure. It has been surprisingly found that by using the method and combination of materials according to the invention, light valves are obtained that exhibit high switching and can be operated at a suitable low voltage and low energy consumption. In addition, the method provides light valves that have advantageous performance even at low temperatures, especially in terms of switching speed. This combination of properties offers great advantages when considering the use in mobile applications. In addition, it has been surprisingly found that, despite the fact that the method involves exposing the medium to photopolymerization, light valves can be prepared that exhibit good reliability, durability and stability, e.g. in terms of electrical breakdown and photostability.

[0023] Surprisingly, the method according to the present invention provides a simple and efficient way to prepare light valves that exhibit the advantageous properties as described herein.

[0024] Another aspect of the present invention relates to a light valve operable in optically transparent and opaque states and electrically switchable between them, the light valve being obtained or obtainable, respectively, by carrying out the method according to the present invention as described herein above and below.

[0025] In the present invention, it is recognized that favorable performance and appearance are desirable not only in the opaque state but also in the optically transparent state, and that in the latter state, it is desirable to avoid or minimize unwanted haze and to have relatively high transmission. A light valve as provided in accordance with the present invention can advantageously provide such a low haze transparent state, and further provide sufficiently efficient and sufficiently uniform scattering, together with the possibility to tailor and in particular minimize the overall light transmission in the opaque state. In addition, the device can advantageously provide further advantages such as low switching voltage and low energy consumption, high switching between states, and good reliability, durability and stability, e.g. electrical breakdown and light stability.

[0026] Furthermore, the materials and methods used in the present invention offer the possibility to use active matrix addressing of the switchable cells, thus splitting the light valve into a large number of pixels for the display of information or for use in augmented or virtual reality contexts.

[0027] In another aspect of the invention there is provided a light valve operable in and electrically switchable between optically transparent and opaque states, comprising: a liquid-crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds and one or more dichroic dyes, wherein the liquid-crystalline medium has a clearing point above 70° C., and a polymeric component comprising one or more polymeric structures obtained or respectively obtainable by polymerization of one or more polymerizable mesogenic compounds, the polymeric component being present in the material in an amount of not more than 4% by weight, based on the total content of the material, a switch layer comprising a material comprising However, light valves in the optically clear state preferably have a haze of less than 15% determined according to ASTM D 1003 and a light transmission of preferably more than 45% determined according to DIN EN 410, and in the opaque state preferably have a haze of more than 65% determined according to ASTM D 1003 and a light transmission of less than 35% determined according to DIN EN 410 are provided.

[0028] The present invention provides a device for managing light that can both absorb and scatter light. The device can thus transition between two different optical states, a low haze high transmittance state and a high haze low transmittance state. Light valves are useful for regulating the passage of light, particularly sunlight, but also light from artificial sources such as lamps, light emitting diodes, particularly organic light emitting diodes, luminaires, etc. In the opaque state, the light valve can create a visual barrier.

[0029] In a preferred embodiment, the liquid crystal medium contained in the material contained in the switch layer of the light valve exhibits a pitch of 0.55 μm or more in the opaque state.

[0030] Surprisingly, it has been found that an improved light valve can be obtained by providing a switch layer comprising a material comprising a liquid crystal medium and a polymer component as described above and below. In particular, the provision of a cholesteric or chiral nematic medium with a high clearing point and preferably long pitch as currently defined, in combination with a relatively small amount of a polymer component comprising a polymer structure resulting from the polymerization of at least one polymerizable mesogenic compound, can surprisingly provide a device with a preferred transparent state, i.e. an advantageously homogeneous low haze and optically transparent state, and a scattering state with enhanced scattering efficiency, which can be conveniently switched between states by applying a voltage.

[0031] In particular, the long pitch cholesteric medium, as described herein, can be advantageously combined with the presence of a polymer component to provide unexpectedly strong scattering with a suitable wide angular scattering distribution. This is beneficial in that already providing only a single switch layer in the element can provide suitable haze. In addition, the thickness of the switch layer can be relatively low, in particular substantially less than 50 μm, thereby reducing the operating voltage and power consumption as well as the use of materials.

[0032] Furthermore, by suitably providing one or more dichroic dyes in the liquid crystal medium, preferably in solution, the light transmission, in particular in the opaque state, can be advantageously adjusted and, if desired, minimized, while at the same time offering the possibility of providing a colored opaque state.

[0033] By designing and adjusting the material combinations as defined herein, light valves with good performance can be obtained.

[0034] Another aspect of the invention therefore relates to a liquid crystalline medium, in particular for use in a method according to the invention, which medium comprises one or more polymerizable mesogenic compounds in an amount of up to 4% by weight, based on the total content of the medium, one or more mesogenic compounds, one or more chiral compounds and one or more dichroic compounds.

[0035] It has been found that by providing the liquid crystal medium according to the invention, improved properties are obtained, in particular a medium with a preferably high clearing point and a preferably long pitch, which is surprisingly particularly useful for the preparation of modulation materials for switch layers and light valves according to the invention. In addition, the medium can provide further advantages such as a broad liquid crystal phase, a preferably high optical anisotropy, a preferably high voltage holding ratio (VHR), good low temperature stability and good light stability.

[0036] In a further aspect of the invention there is provided a modulation material, particularly for use in a light valve according to the invention, comprising: a liquid-crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds and one or more dichroic dyes, wherein the liquid-crystalline medium has a clearing point above 70° C., and a polymeric component comprising one or more polymeric structures obtained or respectively obtainable by polymerization of one or more polymerizable mesogenic compounds, the polymeric component being present in the material in an amount of not more than 4% by weight, based on the total content of the material, A modulating material is provided that includes:

[0037] The modulation material according to the invention can be advantageously used in switching elements, preferably variable light devices for modulating light, in particular light valves based on light scattering and dimming. The modulation material according to the invention is advantageous in devices for modulating the passage of electromagnetic radiation, preferably light, in particular sunlight, but also light from artificial sources.

[0038] The modulation material according to the invention is particularly preferably used in CLC scattering type devices. It is now recognized that certain advantages can be obtained, for example in terms of scattering effect or uniformity and appearance, when the material comprises a chiral nematic or cholesteric liquid crystal medium having an advantageously high clearing point and preferably a relatively long pitch in combination with a polymer component as currently defined, especially when providing the so-called polymer stabilized cholesteric texture (PSCT).

[0039] Surprisingly, the modulation material obtained by carrying out the process described herein can show good reliability and stability, especially light stability.By advantageously adjusting and combining the combination of materials provided and the process conditions described herein, it is possible to obtain a stable and efficient modulation material comprising one or more dichroic dyes, even though the initial medium is subjected to photopolymerization.

[0040] According to the present invention the liquid crystal media and modulation materials described herein can be advantageously arranged and used in a switch layer. Thus in a further embodiment there is provided a switch layer which comprises, preferably consists of, the medium or respectively material according to the present invention.

[0041] A switch layer may be disposed between the two substrates, such as to provide a switch element that is electrically switchable and operable in optically transparent and opaque states.

[0042] Polymeric stabilization improves scattering performance and efficiency in the scattered state while still achieving acceptable transparency in the clear state.

[0043] Another aspect of the invention relates to the use of a light valve in a mobile or respectively portable device.

[0044] The light valve may preferably provide high switching times, reduced temperature dependence, reliable switching at temperatures below 0° C., in addition to low voltage and low power consumption. The combined properties are particularly useful in mobile applications. The light valve may contribute temporarily, i.e. for certain periods and not for other periods, to achieving enhanced contrast or legibility of information desired in mobile applications, for example in transparent or normally see-through displays and under different lighting conditions, especially different ambient light conditions.

[0045] Without limiting the invention thereby, the invention is illustrated below by aspects, embodiments and specific features, and specific embodiments are described in more detail. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] The term "liquid crystal" (LC) preferably used herein relates to a material or medium which has a liquid crystal mesophase in some temperature range (thermotropic LC).

[0047] The terms "mesogenic compound" and "liquid crystal compound" mean compounds that contain one or more calamitic (rod-like or plate-like / lath-like) or discotic (disk-like) mesogenic groups, i.e. groups capable of inducing liquid crystal phase or mesophase behavior.

[0048] LC compounds or materials and mesogenic compounds or materials containing mesogenic groups do not necessarily exhibit liquid crystal phases by themselves. It is also possible that they exhibit liquid crystal phase behavior only in mixtures with other compounds. These include low molecular weight non-reactive liquid crystal compounds, reactive or polymerizable liquid crystal compounds and liquid crystal polymers.

[0049] Calamitic mesogenic compounds typically comprise a mesogenic core consisting of one or more aromatic or non-aromatic cyclic groups linked to each other directly or via linking groups, optionally consisting of terminal groups attached to the ends of the mesogenic core, and optionally consisting of one or more lateral groups attached to the long sides of the mesogenic core, where these terminal and lateral groups can typically be selected, for example, from carbyl or hydrocarbyl groups, polar groups such as halogen, nitro, hydroxy, or polymerizable groups.

[0050] For simplicity, the terms "liquid crystal" or "liquid-crystalline" material or medium are used for both liquid crystal and mesogenic materials or media, and vice versa, and the term "mesogen" is used for the mesogenic group of the material.

[0051] The term "non-mesogenic compound or material" means a compound or material that does not contain a mesogenic group as defined above.

[0052] The term "polymer" as used herein is understood to mean a molecule that includes a backbone of one or more different types of repeating units (the smallest building blocks of a molecule), and includes the commonly known terms "oligomer," "copolymer," "homopolymer," and the like. The term polymer is further understood to include, in addition to the polymer itself, residues from initiators, catalysts, and other elements incidental to the synthesis of such a polymer, such residues not being covalently attached thereto. While such residues and other elements are further usually removed in purification steps following polymerization, they are typically mixed or co-mixed with the polymer such that they generally remain with the polymer when transferred between containers, solvents, or dispersion media.

[0053] The term "polymerization" refers to the chemical process of forming a polymer by linking together multiple polymerizable groups or polymer precursors (polymerizable compounds) that contain such polymerizable groups.

[0054] Polymerizable compounds with one polymerizable group are also called "monoreactive" compounds, compounds with two polymerizable groups are called "direactive" compounds, and compounds with more than two polymerizable groups are called "multireactive" compounds. Compounds with no polymerizable groups are also called "nonreactive" or "nonpolymerizable" compounds.

[0055] The terms "film" and "layer" include rigid or flexible self-supporting or free-standing films or layers having any significant mechanical stability, as well as coatings or layers on a supporting substrate or between two substrates.

[0056] The term "chiral" is generally used to describe an object that is not superimposable on its mirror image. In contrast, "achiral" (non-chiral) objects are objects that are identical to their mirror image. The media according to the present invention exhibit chirality. This can be achieved by providing cholesteric liquid crystals, also known as chiral nematic liquid crystals. The terms chiral nematic and cholesteric are used interchangeably herein unless otherwise stated.

[0057] In this specification [ka] represents trans-1,4-cyclohexylene.

[0058] Unless otherwise stated, all concentrations herein are given in weight percent and refer to the respective complete mixtures.

[0059] All temperatures are given in degrees Celsius (Celsius, °C) and temperature differences are expressed in whole degrees Celsius. All physical properties and physicochemical or electro-optical parameters are determined and given for a temperature of 20°C unless otherwise stated.

[0060] Light transmission and scattering preferably means transmission and scattering of electromagnetic radiation in the spectral range from 380 nm to 780 nm.

[0061] By switch it is preferably meant a change between two states, preferably one state being non-scattering and appearing substantially transparent or clear to the human eye, and the other state being scattering or diffusely transparent and appearing translucent or opaque to the human eye, the opaque state may simultaneously impart the colour black or alternatively another colour not covering the entire visible spectrum.

[0062] However, it is also possible for the switch layer according to the invention to have further switch states, in particular intermediate states.

[0063] The present invention therefore preferably and advantageously provides a switch between a completely opaque state and a state with visibility through the device.

[0064] In the optically transparent state the light valve according to the invention preferably has a haze, preferably determined according to ASTM D 1003, of less than 15%, more preferably less than 10%, even more preferably less than 5%, in particular less than 2.5%, and a light transmission, preferably determined according to DIN EN 410, of more than 45%, more preferably more than 50%, even more preferably more than 55%, in particular more than 65%.

[0065] In the optically opaque state the light valve according to the invention preferably has a haze of more than 65%, more preferably more than 80%, even more preferably more than 90%, preferably determined according to ASTM D 1003, and a light transmission of less than 35%, more preferably less than 25%, even more preferably less than 10%, in particular less than 5%, preferably determined according to DIN EN 410. In the opaque state the light valve according to the invention preferably has a haze of 75% or more, determined according to ASTM D 1003.

[0066] The haze can be measured using a haze meter from BYK-Gardner, or it can be measured using a spectrophotometer, in particular a spectrophotometer and an Ulbricht sphere.

[0067] The switch according to the present invention preferably means an electrical switch. An electrical switch can typically be achieved by providing an electrode on a substrate, for example a glass substrate or a plastic substrate. In one embodiment, a conductive layer is provided on the substrate, the conductive layer being made of or formed from a transparent conductive material, for example a transparent conductive oxide, preferably indium tin oxide (ITO) or SnO2:F, in particular ITO, or a conductive polymer, or a thin transparent metal and / or metal oxide layer, for example silver. The conductive layer preferably comprises an electrical connection. The voltage is preferably provided by a battery, a rechargeable battery, a supercapacitor or an external current source, more preferably by an external current source.

[0068] In one embodiment, an orientation layer, for example made of polyimide (PI), is provided on the substrate. In particular, it is preferred that the conductive layer and the orientation layer are provided together on the substrate. In this case, the orientation layer or alignment layer is provided on the conductive layer, so that the orientation layer is in contact with the LC medium. The orientation layer, preferably a polyimide layer, may be arranged to provide a uniform or planar orientation of the molecules of the liquid crystal medium, or alternatively a homeotropic orientation, especially at the interface. In a particular embodiment, a rubbed polyimide is used on both substrates with an orientation difference of 90°, as used in the so-called twisted nematic (TN) geometry.

[0069] In certain embodiments, alignment layers with a pretilt angle are used, for example with a pretilt angle ranging from 0° to 20° for a TN geometry or 80° to 90° for a vertically aligned (VA) geometry.

[0070] Alternatively or according to other embodiments, a substrate without an alignment layer is also used. It has surprisingly been found that providing an alignment layer, e.g. a polyimide layer, as an additional layer can be advantageously avoided, while effective and efficient switching behavior can still be achieved.

[0071] Alternatively, but in addition to the alignment layer, it is also possible to provide a passivation or barrier layer on the substrate, for example a passivation layer comprising, preferably consisting of, silicon oxide or silicon nitride. If both a passivation layer and an alignment layer are provided on the substrate, they are arranged such that the alignment layer is uppermost, i.e. in contact with the LC medium.

[0072] The method according to the invention provides a switching element, in particular a light valve, operable in and electrically switchable between optically transparent and opaque states and comprising a switching layer. The switching layer obtainable by carrying out the method comprises a material comprising a liquid crystal medium comprising one or more mesogenic compounds, one or more dichroic dyes and one or more chiral compounds, and a polymer component comprising one or more polymer structures obtained or respectively obtainable by polymerization of one or more polymerizable mesogenic compounds.

[0073] According to the present invention, the polymer component is present in the material in an amount of 4% by weight or less, preferably 3% by weight or less, more preferably 2% by weight or less, in particular 1% by weight or less, based on the total content of the material. In a preferred embodiment, the polymer component is present in the material in an amount in the range of 0.5% to 1.5% by weight, based on the total content of the material.

[0074] The polymer component comprises one or more polymer structures which are obtained or which can be obtained respectively by polymerization of one or more polymerizable mesogenic compounds. It is preferred that the polymer component is obtained exclusively by polymerization of one or more polymerizable mesogenic compounds, i.e. that the polymer component is based exclusively on or consists of one or more polymer structures which are derived exclusively from one or more polymerizable mesogenic compounds as precursors.

[0075] According to this method the polymer component is preferably prepared in situ, in particular in the switchable layer, by polymerising one, two or three polymerisable mesogenic compounds, even more preferably one or two polymerisable mesogenic compounds.

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

[0077] The liquid crystal medium used in the present method preferably comprises at least one di- or multireactive polymerizable mesogenic compound.

[0078] While it is preferred that the polymerizable compound(s) used according to the present invention comprise only reactive mesogen(s), i.e. all reactive monomers are mesogenic, in alternative embodiments it is also possible to use one or more RMs in combination with one or more non-mesogenic polymerizable compounds.

[0079] The polymerisable and mesogenic compounds may be selected with a view to matching the refractive index of the resulting polymer component and the LC medium in the modulating material, which may advantageously contribute to an improved transparency state.

[0080] The liquid crystal medium according to the invention, in particular that used in the method and provided in the light valve, has a clearing point of at least 70° C., more preferably at least 80° C., even more preferably at least 90° C., still more preferably at least 98° C., still more preferably at least 102° C. and in particular at least 115° C. The medium preferably has a clearing point in the range from 90° C. to 160° C., more preferably from 100° C. to 150° C.

[0081] All physical properties and physicochemical or electro-optical parameters are determined according to commonly known methods, in particular according to "Merck Liquid Crystals, Physical Properties of Liquid Crystals", November 1997, Merck AG, Germany.

[0082] The clearing point, in particular the phase transition temperature between the chiral nematic or cholesteric phase and the isotropic phase, can be measured and determined using commonly known methods, such as a Mettler oven, a hot stage under a polarizing microscope, or differential scanning calorimetry (DSC) analysis. According to the present invention, the clearing point is preferably determined using a Mettler oven.

[0083] Furthermore, the liquid crystal medium used in the switching layer of the light valve according to the invention preferably exhibits a pitch of 0.55 μm or more in the scattering state.

[0084] The cholesteric or chiral nematic media as provided herein preferably have a relatively long pitch, particularly preferably a pitch that provides Bragg-type reflection above 780 nm. Again, the planar texture can provide favorable transmission across the visible light spectrum.

[0085] By pitch is meant herein the pitch p of the cholesteric helix, the pitch p being the distance for the director of the CLC to make a 2π rotation. In preferred embodiments the medium exhibits a pitch of 0.75 μm or more, even more preferably 1.00 μm or more, especially 1.50 μm or more.

[0086] Preferably, the concentration of the one or more chiral dopants is set so that the resulting chiral pitch is in the range of 0.55 μm to 10 μm.

[0087] According to the present invention, the pitch is set to be equal to or smaller than the wavelength λ of the selective reflection maximum at 20° C. max The pitch p is determined from NIR spectroscopy at λ max =n(λ max )×p using the formula λ max is determined from measurements of n(λ max ) is λ max is the refractive index at

[0088] It is also possible to measure the helical twisting power (HTP) using a wedge cell method known in the art, particularly at 20° C., to confirm the determined pitch.

[0089] Surprisingly, the light valve according to the invention can be switched and operated in an opaque state that provides efficient and sufficiently strong scattering, especially diffuse transmittance, to the eye, giving a homogeneous appearance, especially over large areas, which advantageously includes a color-neutral appearance, which means that unwanted color artifacts, such as a rainbow appearance, can be minimized or even avoided.

[0090] It is believed that materials such as those provided in the switch layer according to the present invention can provide sufficient scattering with the desired haze, for example by scattering from material domains, in particular boundaries, defects or random structures, while diffraction of incident light caused by periodic structures can be substantially suppressed or avoided by sufficiently disrupting or destroying the periodicity on the relevant length scales, in particular by the introduction of polymer components, which surprisingly can be effective in this regard even when included in small amounts.

[0091] Additionally, by using the method according to the invention, it is possible to obtain light valves that advantageously have an optically clear state with little or no discernible residual haze and a relatively large light transmission.

[0092] The light valve itself preferably does not include any light source. The light valve may be suitably incorporated into an electro-optical device such as a display, screen or glasses, for example by lamination, bonding or mounting.

[0093] Preferably, the light valve does not include a polarizer.

[0094] The light valve is, for example, 1 mm 2 From small sizes of about 1m 2 It may be realized in a range of different sizes up to the above sizes and it may have different shapes, for example square, rectangular, circular, oval, triangular, polygonal.

[0095] According to the invention the state of the switch layer and light valve is controlled using an electric field applied by an electrode, which is preferably a transparent electrode disposed on the substrate in the form of a coating, which is typically applied to the side or surface of the substrate facing the switch layer.

[0096] In some embodiments, the electrodes are not patterned and / or structured so that they are continuous, so that the entire switchable region is addressed and switched simultaneously by applying an electric field. In alternative embodiments, the electrodes may be patterned to form individually addressable regions or pixels that can be switched independently from other regions by applying an electric field. In this case, commonly used TFT technology may be used to actively and independently address the divided regions.

[0097] A liquid crystal medium as described herein is used in the present method to provide the resulting switch layer and light valve.

[0098] In a preferred embodiment the LC medium as used according to the invention has a positive dielectric anisotropy. In this case, liquid crystalline mixtures having a dielectric anisotropy Δε in the range from 3 to 45, more preferably in the range from 5 to 30, are preferred.

[0099] Δε represents the dielectric anisotropy, and Δε = ε ∥ -ε ⊥ The dielectric anisotropy Δε is determined at 20° C. and 1 kHz.

[0100] In an alternative embodiment, however, it is also possible to provide an LC medium with negative dielectric anisotropy, in which case liquid-crystalline mixtures with a dielectric anisotropy Δε in the range from −6 to −3 are preferred.

[0101] Preferably, the medium according to the invention may have a suitably high optical anisotropy Δn, also known as birefringence. The medium described herein and used in the switch layers and light valves according to the invention preferably exhibits an optical anisotropy Δn determined at 20° C. and 589 nm of 0.13 or more, more preferably 0.16 or more, even more preferably 0.20 or more.

[0102] Above and below, Δn indicates the optical anisotropy, and Δn=n e -n o and the optical anisotropy Δn is determined at 20° C. and a wavelength of 589.3 nm.

[0103] The medium used according to the invention preferably comprises one or more mesogenic compounds selected from the compounds of formulae I and II.

[0104] [ka]

[0105] During the ceremony, R 1 and R 2 represent, independently of one another, radicals selected from F, Cl, CF3, OCF3, and linear or branched alkyl or alkoxy having 1 to 15 carbon atoms or linear or branched alkenyl having 2 to 15 carbon atoms, which radicals are unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, with the proviso that one or more CH2 groups may be replaced, independently of one another in each case, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, such that the oxygen atoms are not directly linked to one another, A 11 teeth, [ka] represents n represents 0 or 1, and A 21 , A 31 and A 41are independent of each other, [ka] represents wherein L, at each occurrence, is the same or different, a halogen selected from F, Cl, and Br; and R 3 and R 4 represent, independently of one another, a radical selected from F, CF3, OCF3, CN and a linear or branched alkyl or alkoxy having 1 to 15 carbon atoms or a linear or branched alkenyl having 2 to 15 carbon atoms, which radicals are unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, with the proviso that one or more CH2 groups may be replaced, independently of one another in each case, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, in such a way that the oxygen atoms are not directly linked to one another, and L 1 , L 2 and L 3 represent independently H or F.

[0106] It is particularly preferred that the medium used according to the invention comprises at least 5% by weight, more preferably at least 10% by weight, even more preferably 15% by weight, of one or more mesogenic compounds selected from the compounds of formulae I and II, based on the total content of the medium.

[0107] In addition to a suitably high optical anisotropy the media according to the invention may advantageously exhibit a suitably high voltage holding ratio (VHR) in combination with good light stability and a suitably high clearing point.

[0108] The use of reactive mesogens in specifically defined low amounts, and preferably chiral dopants with high HTP which can be used in low concentrations, can advantageously contribute to maintaining a high clear point.

[0109] The medium can be a cholesteric or chiral nematic medium. Cholesteric liquid crystals (CLC) usually include media that initially have a planar structure, e.g. reflecting light of a certain wavelength, and can be switched to a focal conic light scattering structure or vice versa by application of an alternating voltage pulse. Upon application of a stronger voltage, especially a stronger voltage pulse, the CLC medium can switch to a homeotropic transparent state, from which it can relax to the planar state after a fast switch-off of the voltage, or to the focal conic state after a slow switch-off.

[0110] Bragg reflection occurs in the planar texture, and the reflected light has the same handedness as the cholesteric helix.

[0111] In the focal conic state, the helical axes are randomly arranged, and light scattering is observed in the texture due to discontinuous spatial changes in the refractive index at the domain boundaries.

[0112] Both the planar and focal conic configurations are generally stable in the absence of an external electric field. When the texture of a CLC switches from planar to focal conic, the Bragg reflection disappears and the incident light is scattered due to the random distribution of the helical axes.

[0113] However, switching between states is usually only achieved by a homeotropic state in which the cholesteric helix is ​​completely unwound by dielectric coupling between liquid crystal molecules with positive dielectric anisotropy (Δε>0) and a perpendicular electric field.

[0114] In embodiments according to the present invention, the haze opaque state of the switch layer may be the focal conic state described above.

[0115] Alternatively, in accordance with a preferred embodiment, in the present invention, the high haze state is formed by a polydomain structure. Preferably, this polydomain structure produces sufficiently strong scattering while the Bragg-type reflection behavior remains observable at least to some extent. In this phase, which includes or preferably consists of polydomains, the direction of the helical axis usually differs from domain to domain and domain boundaries usually occur. However, macroscopically, this phase appears homogeneous, in particular to the human eye homogeneously opaque or hazy, and may be free of visible defects throughout the entire layer area.

[0116] Polydomain structures can be obtained, for example, using conventional alignment layers that are planar or homeotropically aligned and may advantageously be switchable to the polydomain state at relatively low voltages, however polydomain structures can also be obtained in the absence of alignment layers.

[0117] Additionally, the presence of polymer components in the modulation material and switch layer can favorably influence and stabilize scattering performance.

[0118] In a preferred embodiment, the non-scattering or transparent state can be formed by the homeotropic state described above. In this regard, the advantageously high VHR now available helps to stabilize the device in this state against self-discharge behavior, so that the state can be maintained even with significantly lower refresh rates and / or lower power consumption.

[0119] Alternatively, a non-scattering or transparent state can be created by the planar texture described above.

[0120] The use of chiral nematic or cholesteric media has the advantage that devices made from this medium consume less energy since they can provide relatively stable states, or even bistability, and can retain their respective states for at least a significant amount of time, especially after the electric field is turned off, allowing for more frequent addressing or refreshing of the voltages.

[0121] In a preferred embodiment, the light valve is switchable to an optically transparent state by application of an AC voltage V1, and switchable to an opaque state by application of an AC voltage V2, where V1>V2.

[0122] In some embodiments, the switched transparent state, particularly the state with homeotropic alignment, is maintained by applying a voltage in the range of 15V to 100V, more preferably 20V to 80V, especially 25V to 50V, while the switched opaque state may be stable even at 0V, at least for some time.

[0123] Preferably, the light valve according to the present invention does not use dual frequency addressing, thus simplifying the required electronics.

[0124] As noted above, the medium preferably exhibits selective reflection at wavelengths greater than 780 nm, and thus the medium preferably reflects in the near infrared (NIR) spectral region.

[0125] Chiral dopants and their concentrations can be provided such that the cholesteric pitch of the medium can be appropriately set or adjusted. A CLC medium can be prepared, for example, by doping a nematic LC medium with a chiral dopant having a high twisting power. The pitch p of the induced cholesteric helix is ​​then given by the concentration c of the chiral dopant and the helical twisting power HTP according to equation (1).

[0126]

number

[0127] It is also possible to use, for example, two or more dopants to compensate for the temperature dependence of the HTP of each dopant and reduce the temperature dependence of the reflection wavelength of the helical pitch and CLC medium. total ), equation (2) holds approximately.

[0128]

number

[0129] c in the formula i are the concentrations of the individual dopants, and HTP i are the helical twisting powers of each individual dopant.

[0130] The liquid crystal medium comprises one or more chiral compounds, in particular one or more chiral dopants. The chiral dopants preferably have a 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 used, they may have the same or opposite rotation sense and the same or opposite temperature dependence of twist.

[0131] The one or more chiral compounds according to the invention are preferably 5 μm in the liquid crystal mixture MLC-6828 available from Merck. -1 More preferably, 10 μm -1 More preferably, 15 μm or more -1 Preferably, the helical twisting force has an absolute value of 20 μm or more in the liquid crystal mixture MLC-6828 available from Merck. -1 More preferably, 40 μm -1 More preferably, 60 μm or more -1 Above 80μm, most preferred -1 More than ~260μm -1 Particularly preferred are chiral compounds having an absolute value of helical twisting power (HTP) within the following ranges:

[0132] The one or more chiral compounds are preferably contained in the liquid crystal medium in an amount of at most 2% by weight, more preferably at most 1% by weight, even more preferably at most 0.5% by weight, based on the total content of the medium.

[0133] In a preferred embodiment of the invention, the chiral component consists of two or more chiral compounds, all with the same sign of HTP. The temperature dependence of the HTP of the individual compounds may be high or low. The temperature dependence of the pitch of the medium can be compensated by mixing compounds with different temperature dependence of HTP in the corresponding ratio.

[0134] Suitable chiral dopants are known in the art, for example, cholesteryl nonanoate, R / S-811, R / S-1011, R / S-2011, R / S-3011, R / S-4011, R / S-5011, especially R / S-5011, B(OC)2C * Some are commercially available, such as HC-3 or CB15 (all from Merck, Darmstadt, Germany).

[0135] Particularly suitable 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 a chiral group form a mesogenic group.

[0136] Suitable chiral groups are, for example, mono- or polychiral groups selected from the group consisting of chiral branched hydrocarbon groups, chiral ethanediols, binaphthols or dioxolanes, furthermore sugar derivatives, sugar alcohols, sugar acids, lactic acid, chiral substituted glycols, steroid derivatives, terpene derivatives, amino acids or a small number, preferably 1 to 5 amino acid sequences.

[0137] Preferred chiral groups are sugar derivatives such as glucose, mannose, galactose, fructose, arabinose and dextrose; sugar alcohols such as, for example, sorbitol, mannitol, iditol, galactitol or their anhydrous derivatives, in particular dianhydrohexitols such as dianhydrosorbide (1,4:3,6-dianhydro-D-sorbide, isosorbide), dianhydromannitol (isosorbitol) or dianhydroiditol (isoiditol); sugar acids such as, for example, gluconic acid, gulonic acid and ketogulonic acid; chiral substituted glycol groups, such as mono- or oligoethylene or propylene glycol substituted with alkyl or alkoxy; amino acids, such as alanine, valine, phenylglycine or phenylalanine, or a sequence of 1-5 of these amino acids; steroid derivatives, such as cholesteryl or cholic acid groups; terpene derivatives, such as menthyl, neomenthyl, campheyl, pineyl, terpinyl, isolongifolyl, fenchyl, careyl, myrtenyl, nopyr, geranyl, linaloyl, neryl, citronellyl or dihydrocitronellyl.

[0138] Suitable chiral groups and mesogenic chiral compounds are described, for example, in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779 and DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820.

[0139] Preferred chiral compounds for use according to the present invention are selected from the group of compounds:

[0140] In one embodiment, dopants selected from the group consisting of compounds of the following formulae A-1 to A-III are preferred.

[0141] [ka]

[0142] During the ceremony, R a11 and R a12 are each independently an alkyl, oxaalkyl or alkenyl having from 2 to 9, preferably up to 7, carbon atoms, or R a11 is methyl or alkoxy having 1 to 9 carbon atoms, preferably both are alkyl, preferably n-alkyl; R a21 and R a22 are each independently an alkyl or alkoxy having 1 to 9, preferably up to 7, carbon atoms, an oxaalkyl, alkenyl or alkenyloxy having 2 to 9, preferably up to 7, carbon atoms, preferably both being alkyl, preferably n-alkyl; R a31 and R a32 are each independently an alkyl, oxaalkyl or alkenyl having from 2 to 9, preferably up to 7, carbon atoms, or R a11 is methyl or alkoxy having 1 to 9 carbon atoms, preferably both are alkyl, preferably n-alkyl.

[0143] Particularly preferred are chiral dopants selected from the group consisting of compounds of the following formulae:

[0144] [ka]

[0145] Further preferred dopants are derivatives of isosorbide, isomannitol or isoiditol of formula A-IV below.

[0146] [ka]

[0147] During the ceremony, [ka]

[0148] Dianhydrosorbitol is preferred.

[0149] and chiral ethanediols such as, for example, diphenylethanediol (hydrobenzoin), in particular the mesogenic hydrobenzoin derivatives of formula AV below (not shown but including the (R,S), (S,R), (R,R) and (S,S) enantiomers).

[0150] [ka]

[0151] During the ceremony, [ka] each independently represents 1,4-phenylene, which may be mono-, di- or trisubstituted by L, or 1,4-cyclohexylene; L is H, F, Cl, CN, or an optionally halogenated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, or alkoxycarbonyloxy having 1 to 7 carbon atoms; c is 0 or 1; Z 0 is -COO-, -OCO-, -CH2CH2- or a single bond, and R 0 is alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, or alkylcarbonyloxy having 1 to 12 carbon atoms.

[0152] Compounds of formula A-IV are described in WO 98 / 00428. Compounds of formula AV are described in GB 2,328,207.

[0153] In other embodiments very particularly preferred dopants are chiral binaphthyl derivatives as described in WO 02 / 94805, chiral binaphthol acetal derivatives as described in WO 02 / 34739, chiral TADDOL derivatives as described in WO 02 / 06265, and chiral dopants having at least one fluorinated bridging group and a terminal or central chiral group as described in WO 02 / 06196 and WO 02 / 06195.

[0154] Particularly preferred are chiral compounds of formula A-VI.

[0155] [ka]

[0156] During the ceremony, X 1 , X 2 , Y 1 and Y 2 are each independently of one another F, Cl, Br, I, CN, SCN, SF5, linear or branched alkyl having 1 to 25 carbon atoms (which may be mono- or polysubstituted by F, Cl, Br, I or CN, with the proviso that in addition one or more non-adjacent CH2 groups are each independently of one another -O-, -S-, -NH-, -NR2-, -S-, -NH-, -NR1 ...NR3-, -NR4-, -NR5-, -NR6-, -NR7-, -NR8-, -NR9-, -NR10-, -NR11-, -NR12-, -NR13-, -NR14-, -NR15-, -NR16-, -NR17-, -NR18-, -NR19-, -NR21-, -NR22-, -NR23-, -NR24-, -NR25-, -NR26-, -NR27-, -NR28-, -NR39-, -NR40-, -NR41-, -NR42-, -NR43-, -NR44-, -NR55-, -NR56-, -NR57-, -NR58-, -NR59-, -NR60-, -NR61- 0 -, -CO-, -COO-, -OCO-, -OCOO-, -S-CO-, -CO-S-, -CH=CH- or -C≡C-), a polymerizable group or a cycloalkyl or aryl having up to 20 carbon atoms, which groups may be mono- or polysubstituted by halogen, preferably F, or mono- or polysubstituted by polymerizable groups, x 1 and x 2 are each independently 0, 1 or 2, y 1 and y 2are each independently 0, 1, 2, 3 or 4, B 1 and B. 2 are each independently an aromatic or fully or partially saturated aliphatic 6-membered ring (provided that one or more CH groups may be replaced by an N atom and one or more non-adjacent CH groups may be replaced by O and / or S), W 1 and W 2 are, independently of each other, -Z 1 -A 1 -(Z 2 -A 2 ) m -R, or one of the two is R 1 Or A 3 provided that they are not both H at the same time, or [ka] U 1 and U 2 are each independently CH2, O, S, CO or CS, V 1 and V 2 are each independently (CH2) n (wherein 1 to 4 non-adjacent CH groups may be replaced by O and / or S), and V 1 and V 2 is a single bond, [ka] Both are single bonds, Z 1 and Z 2 are each independently -O-, -S-, -CO-, -COO-, -OCO-, -O-COO-, -CO-NR 0 -, -NR 0-CO-, -O-CH2-, -CH2-O-, -S-CH2-, -CH2-S-, -CF2-O-, -O-CF2-, -CF2-S-, -S-CF2-, -CH2-CH2-, -CF2-CH2-, -CH2-CF2-, -CF2-CF2-, -CH=N-, -N=CH-, -N=N-, -CH=CH-, -CF=CH-, -CH=CF-, -CF=CF-, -C≡C-, a combination of two of these groups (with the proviso that two O and / or S and / or N atoms are not directly bonded to each other, preferably -CH=CH-COO- or -COO-CH=CH-), or a single bond, A 1 , A 2 and A 3 are each, independently of one another, 1,4-phenylene (with the proviso that one or two non-adjacent CH groups may be replaced by N), 1,4-cyclohexylene (with the proviso that one or two non-adjacent CH groups may be replaced by O and / or S), 1,3-dioxolane-4,5-diyl, 1,4-cyclohexenylene, 1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl or 1,2,3,4-tetrahydronaphthalene-2,6-diyl (with the proviso that each of these groups may be mono- or polysubstituted by L), and in addition A 1 is a single bond, L is a halogen atom, preferably F, CN, NO2, alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl or alkoxycarbonyloxy having 1 to 7 carbon atoms (wherein one or more H atoms may be replaced by F or Cl); m is independently in each occurrence 0, 1, 2, or 3; and R and R 1are each independently H, F, Cl, Br, I, CN, SCN, SF5, linear or branched alkyl having 1 or 3 to 25 carbon atoms (which may be mono- or polysubstituted by F, Cl, Br, I or CN, provided that one or more non-adjacent CH2 groups are not -O-, -S-, -NH-, -NR 0 -, -CO-, -COO-, -OCO-, -O-COO-, -S-CO-, -CO-S-, -CH=CH- or -C≡C-, provided that the two O and / or S atoms are not directly bonded to each other) or a polymerizable group.

[0157] Chiral naphthyl derivatives of formula A-VI-1 are particularly preferred.

[0158] [ka]

[0159] In particular, they are selected from the following formulae A-VI-1a to A-VI-1c:

[0160] [ka]

[0161] In the formula, rings B and Z 0 is as defined in formula A-IV, more preferably Z 0 is -OCO- or a single bond, R 0 is as defined in formula A-IV, H, or an alkyl having 1 to 4 carbon atoms, and b is 0, 1 or 2.

[0162] Furthermore, chiral binaphthyl derivatives of formula A-VI-2 are particularly preferred.

[0163] [ka]

[0164] In particular, they are selected from the following formulae A-VI-2a to A-VI-2f:

[0165] [ka]

[0166] [ka]

[0167] In the formula, R 0 is as defined in formula A-VI, and X is H, F, Cl, CN or R 0 , preferably F.

[0168] In a particularly preferred embodiment, the chiral medium according to the invention comprises one or more compounds of formula R-5011 and S-5011. In one embodiment, the medium comprises R-5011. In another embodiment, the medium comprises S-5011.

[0169] The LC media according to the invention preferably and advantageously exhibit high reliability and high electrical resistivity. The LC media according to the invention also preferably and advantageously exhibit a high voltage holding ratio (VHR). See S. Mats et al., Liquid Crystals, vol. 5, p. 1320 (1989); K. Niwa et al., Proc. SID Conference, San Francisco, June 1984, p. 304 (1984); T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals", 1997. The VHR of the LC media according to the invention is preferably 75% or more, more preferably 85% or more, even more preferably 95% or more, particularly preferably 98% or more. Unless otherwise stated, the measurement of VHR is carried out as described in T. Jacob and U. Finkenzeller, "Merck Liquid Crystals-Physical Properties of Liquid Crystals", 1997.

[0170] According to the invention there is provided a method in which a liquid crystalline medium comprises one or more polymerizable mesogenic compounds in an amount of up to 4% by weight, based on the total content of the medium.

[0171] The one or more polymerizable mesogenic compounds are preferably contained in the medium in an amount of 3% by weight or less, even more preferably 2% by weight or less, particularly preferably 1.25% by weight or less, based on the total content of the medium.

[0172] Preferably the one or more polymerizable mesogenic compounds contain one or more acrylate and / or methacrylate groups.

[0173] In the medium according to the invention, preferably one or more polymerisable, hardenable or curable compounds, preferably one or more photocurable monomers, are provided, which can advantageously act as precursors to the polymeric components in the modulation material and switch layer.

[0174] The reactive mesogens (RM) or mesogenic monomers used contain a mesogenic group and one or more polymerisable groups, ie functional groups suitable for polymerisation.

[0175] In a particularly preferred embodiment the polymerisable compound(s) used comprise only reactive mesogen(s), i.e. all reactive monomers are mesogenic. Alternatively the RM may be provided in combination with one or more non-mesogenic polymerisable compounds.

[0176] The RM may be monoreactive and / or bireactive or polyreactive. Preferably, the RM used is bireactive or polyreactive, especially bireactive. In some embodiments, one or more bireactive RMs are used in combination with at least one monoreactive RM.

[0177] In a preferred embodiment of the invention, the one or more polymerizable mesogenic compounds are selected from compounds of formula M

[0178] [ka]

[0179] wherein the individual groups are defined as follows: R Ma and R Mb are each independently P, P-Sp-, H, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, SF5, or a linear or branched alkyl having 1 to 25 carbon atoms, with the proviso that non-adjacent CH2 groups are each independently -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 00)-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, provided that one or more hydrogen atoms may also be replaced by F, Cl, Br, I, CN, P or P-Sp-, provided that preferably R Ma and R Mb at least one of the groups is or contains a P or P-Sp- group, Preferably R Ma and R Mb are each independently P, P-Sp-, H, halogen, SF, NO, an alkyl, alkenyl or alkynyl group, but preferably R Ma and R Mb at least one of the groups is or contains a P or P-Sp- group, P is a polymerizable group, Sp is a spacer group or a single bond; A M1 and A M2 are each independently an aromatic, heteroaromatic, alicyclic or heterocyclic group, preferably having from 4 to 25 ring atoms, preferably carbon atoms, which may also include or contain fused rings, which may be mono- or polysubstituted by L, L is P, P-Sp-, OH, CH2OH, F, Cl, Br, I, -CN, -NO2, -NCO, -NCS, -OCN, -SCN, -C(=O)N(R x )2, -C(=O)Y 1 , -C(=O)R x , -N(R x2) optionally substituted silyl, optionally substituted aryl having 6 to 20 carbon atoms, or linear or branched alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 carbon atoms, or alkenyl or alkynyl group having 2 to 25 carbon atoms, with the proviso that one or more hydrogen atoms may also be replaced by F, Cl, P or P-Sp-, preferably P, P-Sp-, H, OH, CH2OH, halogen, SF5, NO2, alkyl, alkenyl or alkynyl group, Y 1 is a halogen, preferably F; Z M1 -O-, -S-, -CO-, -CO-O-, -OCO-, -O-CO-O-, -OCH2-, -CH2O-, -SCH2-, -CH2S-, -CF2O-, -OCF2-, -CF2S-, -SCF2-, -(CH2) n1 -, -CF2CH2-, -CH2CF2-, -(CF2) n1 -, -CH=CH-, -CF=CF-, -C≡C-, -CH=CH-, -COO-, -OCO-CH=CH-, -CR 0 R 00 or a single bond, R 0 and R 00 are each independently H or alkyl having 1 to 12 carbon atoms; R x is P, P-Sp-, H, halogen, linear, branched or cyclic alkyl having 1 to 25 carbon atoms, with the proviso that one or more non-adjacent CH groups are optionally replaced by -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O- in such a way that the oxygen and / or sulfur atoms are not directly linked to each other, and with the proviso that one or more hydrogen atoms are optionally replaced by F, Cl, P or P-Sp-, an optionally substituted aryl or aryloxy group having 6 to 40 carbon atoms, or an optionally substituted heteroaryl or heteroaryloxy group having 2 to 40 carbon atoms, m1 is 0, 1, 2, 3 or 4, and n1 is 1, 2, 3 or 4; However, R Ma , R Mb and at least one substituent, preferably 1, 2 or 3 substituents, more preferably 1 or 2 substituents from the group of substituents L present is a P or P-Sp- group or contains at least one P or P-Sp- group.

[0180] R ma and R mb Particularly preferred are compounds of formula M, wherein one or both of are P or P-Sp-.

[0181] Suitable and preferred RM for use in the liquid crystal media according to the invention are, for example, selected from the following formulae:

[0182] [ka]

[0183] [ka]

[0184] [ka]

[0185] [ka]

[0186] [ka]

[0187] [ka]

[0188] wherein the individual groups are defined as follows: P 1 ~P 3 are each independently of the other a polymerizable group (preferably with the definition specified above and below for P), more preferably an acrylate, methacrylate, fluoroacrylate, oxetane, vinyl, vinyloxy or epoxy group, Sp 1 ~Sp 3 are each independently a single bond or a spacer group (preferably having one of the definitions of Sp given above and below), more preferably -(CH) p1 -, -(CH2) p1 -O-, -(CH2) p1 -CO-O- or -(CH2) p1 -O-CO-O-, where p1 is an integer from 1 to 12, provided that in the last-mentioned group the bond to the adjacent ring is via an oxygen atom, provided that P 1 -Sp 1 -, P 2 -Sp 2 - and P 3 -Sp 3 One of the - groups is R aa But often, R aa is H, F, Cl, CN, or a straight or branched alkyl group having 1 to 25 carbon atoms (provided that one or more non-adjacent CH groups are each independently connected to each other such that oxygen and / or sulfur atoms are not directly linked to each other) and -C(R 0 )=C(R 00 )-, -C≡C-, -N(R 0 )-, -O-, -S-, -CO-, -CO-O-, -O-CO-, -O-CO-O-, provided that one or more hydrogen atoms may be replaced by F, Cl, CN or P 1 -Sp 1-), more preferably linear or branched, optionally monofluorinated or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1 to 12 carbon atoms (with the proviso that alkenyl and alkynyl groups have at least 2 carbon atoms and branched groups have at least 3 carbon atoms); R 0 and R 00 are the same or different in each occurrence and each, independently of the others, is H or alkyl having 1 to 12 carbon atoms, R y and R z are each independently H, F, CH3 or CF3, Z 1 -O-, -CO-, -C(R y R z )- or -CF2CF2-, Z 2 and Z 3 are each independently -CO-O-, -O-CO-, -CH2O-, -OCH2-, -CF2O-, -OCF2- or -(CH2) n -, where n is 2, 3 or 4; L is in each case identical or different and has the meaning given in formula M above, preferably F, Cl, CN or linear or branched, optionally monofluorinated or polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl, alkoxycarbonyl or alkylcarbonyloxy having 1 to 12 carbon atoms, preferably F, L' and L" are each independently H, F or Cl; X 1 ~X 3 are independently -CO-O-, -O-CO- or a single bond, r is 0, 1, 2, 3 or 4; s is 0, 1, 2 or 3; t is 0, 1 or 2, and x is 0 or 1.

[0189] Suitable polymerizable compounds are, for example, listed in Table G. Particularly preferred reactive mesogens are compounds of formulae RM-A, RM-B and RM-C as shown in Examples 1 and 3, respectively.

[0190] The polymerizable compound has at least one polymerizable group. The polymerizable group is preferably CH2=CW 1 -COO-, [ka] CH2=CW 2 -(O) k1 -, CH3-CH=CH-O-, (CH2=CH)2CH-OCO-, (CH2=CH-CH2)2CH-OCO-, (CH2=CH)2CH-O-, (CH2=CH-CH2)2N-, HO-CW 2 W 3 -, HS-CW 2 W 3 -, H.W. 2 N-, HO-CW 2 W 3 -NH-, CH2=CW 1 -CO-NH-, CH2=CH-(COO) k1 -Phe-(O) k2 -, Phe-CH=CH-, HOOC-, OCN-, where W 1 is H, Cl, CN, phenyl or alkyl having 1 to 5 C atoms, in particular H, Cl or CH3, W 2 and W 3 are each independently of one another H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, Phe is 1,4-phenylene and k1 and k2 are each independently of one another 0 or 1. The polymerizable or reactive groups are preferably selected from vinyl, acrylate, methacrylate, fluoroacrylate, oxetane or epoxy groups, particularly preferably acrylate or methacrylate groups.

[0191] In one embodiment, in addition to one or more RMs, non-mesogenic monomers are included in the medium. Preferably, one or more polymerizable compounds, either the non-mesogenic monomers or the RMs, or both, are selected from acrylates, methacrylates, fluoroacrylates and vinyl acetates, although more preferably the composition further comprises one or more di- and / or tri-reactive polymerizable compounds, preferably selected from diacrylates, dimethacrylates, triacrylates and trimethacrylates.

[0192] In a preferred embodiment, the medium according to the invention comprises one or more non-mesogenic monoacrylates, particularly preferably one or more compounds selected from methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, nonyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxy-butyl acrylate and isobornyl acrylate.

[0193] Additionally or alternatively, the medium according to the invention preferably comprises one or more non-mesogenic monomethacrylates, particularly preferably one or more compounds selected from methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, nonyl methacrylate, dodecyl methacrylate, 2-ethyl-hexyl methacrylate, 2-hydroxy-ethyl methacrylate, 2-hydroxy-butyl methacrylate, isobornyl methacrylate and 1-adamantyl methacrylate.

[0194] It is particularly preferred to add at least one cross-linking agent, ie a polymerizable compound containing two or more polymerizable groups, to the medium, however preferably a di- or multi-reactive RM is used.

[0195] In this regard, the di- and multi-reactive compounds may serve to form polymer networks of their own and / or to crosslink polymer chains formed substantially from the polymerization of the monoreactive compounds.

[0196] Alternatively or additionally, conventional crosslinkers known in the art can be used. It is particularly preferred to provide additional di- or multi-reactive acrylates and / or methacrylates. Particularly preferred compounds are selected from ethylene diacrylate, propylene diacrylate, butylene diacrylate, pentylene diacrylate, hexylene diacrylate, pentaerythritol tetraacrylate, ethylene dimethacrylate, propylene dimethacrylate, butylene dimethacrylate, pentylene dimethacrylate, hexylene dimethacrylate, tripropylene glycol diacrylate, trimethylpropane trimethacrylate and pentaerythritol triacrylate.

[0197] The ratio of monoreactive monomers to direactive or multireactive monomers can be advantageously designed and adjusted to affect the properties of the polymer component formed.

[0198] Suitable and conventional initiators, especially photoinitiators, such as azo compounds or organic peroxides, such as Luperox-type initiators, can be added to the medium to promote the reaction. Furthermore, suitable conditions for polymerization and suitable types and amounts of initiators are known in the art and described in the literature. When a polymerization initiator is included in the medium, the use of a photoinitiator is preferred.

[0199] For example, when polymerizing by UV light, photoinitiators can be used which decompose under UV irradiation to produce free radicals or ions that start the polymerization reaction. For polymerizing acrylate or methacrylate groups, preferably radical photoinitiators are used. For polymerizing vinyl, epoxide or oxetane groups, preferably cationic photoinitiators are used. It is also possible to use thermal polymerization initiators which decompose on heating to produce free radicals or ions that start the polymerization. Typical radical photoinitiators are, for example, commercially available Irgacure®, such as Irgacure 651 (available from BASF, containing 2,2-dimethoxy-1,2-diphenylethan-1-one) or Darocure® (Ciba-Geigy, Basel, Switzerland). Typical cationic photoinitiators are, for example, UVI 6974 (Union Carbide). Further useful photoinitiators include α-aminoketones such as Irgacure 907, coumarins, phosphine oxides such as Irgacure 2100, acylphosphines such as Irgacure 819.

[0200] The polymerization initiator, preferably photoinitiator, added in a particular embodiment comprises, and preferably consists of, one or more mesogenic polymerization initiators, preferably one or more mesogenic photoinitiators, i.e. one or more reactive compounds capable of initiating polymerization and which themselves have anisotropic and mesogenic properties.

[0201] However, according to a particularly preferred embodiment, no polymerization initiator, especially no photoinitiator, is used. In some cases, this can improve VHR and reduce the tendency to generate ions in the switch layer. This can contribute to obtaining and maintaining modulation materials and light valves with good reliability and stability. Therefore, according to a preferred embodiment in the liquid crystal medium for use in the method according to the present invention, no polymerization initiator is added.

[0202] In order to maintain and achieve a good VHR, impurities in the reaction product of the polymerization are preferably kept to a minimum or substantially avoided. In particular residual reactive species and charged contaminants are appropriately and preferably kept to a minimum. For example, when UV polymerization is carried out, light with a relatively long wavelength approaching the visible spectrum is used in a preferred embodiment, preferably UV light in the range of 340 nm to 380 nm, even more preferably 360 nm to 380 nm is advantageously used. In this way, undesirable photodegradation or decomposition of the components of the LC medium, in particular one or more dichroic dyes, can be avoided or at least minimized. When a photopolymerization initiator is used, the irradiation wavelength and the photopolymerization initiator can be appropriately adapted or adjusted.

[0203] In the preferred case where no photoinitiator is used, the wavelength range of light can be set such that at least some of the polymerizable compounds can undergo photoreaction and initiate the polymerization reaction themselves, while still avoiding or at least minimizing degradation or decomposition of non-reactive components of the LC medium, in particular the dichroic dye(s). Obtaining and setting the desired wavelength range can be achieved by conventional methods known in the art, such as by using optical filters, in particular edge filters.

[0204] It has surprisingly been found that the medium according to the invention can be advantageously used to produce polymeric structures in situ by providing the medium with one or more polymerizable mesogenic compounds as defined above and below. Furthermore, by appropriately selecting one or more polymerizable mesogenic compounds together with one or more dichroic dyes and setting and adjusting the wavelength of the light used in the photopolymerization with respect to the absorption properties of the dichroic dyes, an efficient and robust method can be provided to obtain the desired polymerization and polymerization products in the material, while still preserving the dichroic dyes and their performance. In one embodiment, the wavelength or the respective wavelength spectrum of the irradiating light is selected to have a minimal overlap with the absorption band of the dichroic dye.

[0205] The polymerizable compounds in the medium can be selected to provide a stable system after polymerization, which is stable during further processing steps, such as thermal heating steps, and maintains good VHR.

[0206] Furthermore, according to the present invention, only relatively small amounts of polymerizable mesogenic compound(s) are used, which advantageously influences stability and minimizes undesirable degradation.

[0207] According to the invention, the medium is used to prepare a modulating material comprising a polymer component, in particular a polymer network, which is obtained by polymerizing or can be obtained from, respectively, a polymerizable compound (one or more) as described above and below.

[0208] The provision of a polymeric component may be beneficial in stabilising one or more states or phases of the LC medium.

[0209] The polymer component is contained in the medium in an amount preferably in the range of 0.1% by weight to 4% by weight, more preferably in the range of 0.5% by weight to 1.5% by weight, based on the total content of the medium.

[0210] The polymer component may contribute advantageous properties to the resulting material. For example, the polymer component may contribute a remarkably stable haze state, especially a polydomain state, such that this haze state can be maintained for longer periods, especially up to several days, without refreshing or reapplication of voltage. Also, fast switching times, especially excellent τ off It can also contribute to achieving switch times.

[0211] Furthermore, the polymer component as provided in the material comprising the CLC medium according to the invention can favorably affect the scattering efficiency and appearance, e.g., in terms of uniformity and viewing angle dependence, whereby color artifacts that may occur under oblique viewing angles can be significantly reduced.

[0212] In a preferred embodiment the modulating material comprises a liquid crystal medium and a polymer component, the polymer component comprising a polymer network obtained by polymerization of reactive mesogens, the reactive mesogens preferably comprising at least one group selected from acrylate groups, particularly preferably mono-, di- or triacrylate groups, vinyl ether groups and epoxide groups. Compounds comprising acrylate group(s) as used herein include acrylic monomers, methacrylic monomers and mixtures of such monomers.

[0213] The polymerization can be carried out by conventional methods. The polymerization can be carried out in one or more steps. In the method according to the invention, the polymerization of the polymerizable compound(s) is achieved by exposure to actinic radiation, where exposure to actinic radiation means light irradiation such as UV light, visible light or IR light, irradiation with X-rays or gamma rays, or irradiation with high energy particles such as ions or electrons. In a preferred embodiment, free radical polymerization is carried out.

[0214] For photopolymerization, UV light is preferably used. It is also possible to use UV light in combination with visible light, especially violet or blue light. For example, light in the spectral range of 340 nm to 420 nm, preferably 360 nm to 405 nm, can be used. In an alternative embodiment, it is also possible to use only visible light, especially light in the range of 380 nm to 415 nm, for example visible light from a laser source.

[0215] The polymerization can be carried out at any suitable temperature. In one embodiment, the polymerization is carried out below the clearing point of the mesogenic mixture. However, in alternative embodiments, it is also possible to carry out the polymerization above the clearing point.

[0216] In this method, polymerization is carried out by photoirradiation, i.e. by light, preferably UV light. As a light source for actinic radiation, for example, a single UV lamp or a set of UV lamps can be used. When using high lamp power, the curing time can be shortened. Another possible light source for photoirradiation is a laser, for example a UV laser, a visible laser or an IR laser.

[0217] In one embodiment, polymerization is carried out by adding one or more polymerizable compounds, preferably comprising a direactive compound and optionally a suitable photoinitiator, to the dye-doped chiral liquid crystal host mixture and polymerizing the polymerizable compounds by exposure to UV radiation.

[0218] Preferably, the polymerization is carried out in an electro-optical cell in which the chiral liquid crystal host mixture is maintained at a predetermined state. In a preferred embodiment, the polymerization, preferably using UV light, is carried out when the medium is in the homeotropic state, typically and preferably with the application of an electric field.

[0219] For photopolymerization of the material in the layer, preferably exposure times of 30 seconds to 300 minutes, more preferably 1 minute to 240 minutes, are used, preferably at 0.01 mW / cm 2 ~100mW / cm 2 , more preferably 0.1 mW / cm 2 ~100mW / cm 2 , and even more preferably 0.5 mW / cm 2 ~75mW / cm 2 In a particular embodiment, the preferred time period for photopolymerization and the particularly preferred UV exposure time are in the range of 1 min to 120 min, more preferably 5 min to 60 min, especially 10 min to 30 min, and the UV light intensity is preferably 1 mW / cm 2 ~50mW / cm 2 is within the range.

[0220] The photopolymerization may be carried out at room temperature, although in an alternative embodiment it is preferred to carry out the photopolymerization at an elevated temperature.

[0221] Thus, in some embodiments, a thermal preheating step is carried out before the photopolymerization, raising the temperature above ambient room temperature. In this case, it is preferable to set and maintain the temperature below the clearing point. In this way, the polymerization can be carried out at a higher temperature, but with the medium having a nematic or, respectively, chiral nematic phase.

[0222] According to the invention the medium comprises one or more pleochroic dyes, in particular one or more dichroic dyes, preferably in an amount of 0.05% to 5% by weight, more preferably 0.1% to 2.5% by weight.

[0223] The concentration of the dye(s) is preferably selected to allow the process, and in particular the photopolymerization, to be carried out effectively and efficiently while still ensuring proper performance of the resulting modulating material, in particular the desired color and photochromic effect.

[0224] The dichroic dyes can be preferably selected from, for example, azo dyes, anthraquinones, thiophenolanthranoquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, pyrromethene dyes, malononitrile dyes, rylenes, in particular perylenes and terylenes, thiadiazole dyes, thienothiadiazole dyes, benzothiadiazoles, thiadiazoloquinoxalines, Irgaphor Black X11 DC and diketopyrrolopyrroles. Particularly preferred are azo compounds, anthraquinones, thiophenolanthranoquinones, benzothiadiazoles, in particular diketopyrrolopyrroles, in particular as described in WO 2014 / 187529, diketopyrrolopyrroles, in particular as described in WO 2015 / 090497, and rylenes, in particular as described in WO 2014 / 090373.

[0225] The liquid crystal medium for use in the present method preferably comprises 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 different dichroic dyes, particularly preferably 2 or 3 dichroic dyes.

[0226] In one embodiment the liquid crystal medium comprises at least three different dichroic dyes, preferably in an amount of 3% by weight or less, more preferably 1.5% by weight or less, based on the total content of the medium.

[0227] In one embodiment, the absorption spectra of the dichroic dyes of the switch layer are preferably complementary to each other so that the impression of black color is produced by the eye. The two or more dichroic dyes of the liquid crystal medium according to the invention preferably cover a large part of the visible spectrum. The exact methods by which mixtures of dyes that appear black or gray to the eye can be prepared are known to those skilled 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, Verlag Walter de Gruyter & Co.

[0228] In another embodiment, different color settings are provided, for example red, green, and blue.

[0229] The determination of the color range of a dye mixture 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, an overall spectrum is obtained and converted into the corresponding color range and luminance values ​​according to the rules of colorimetry under a combined illumination, e.g. illumination D65 for daylight. For each light source, e.g. D65, the position of the white point is fixed and cited in tables (e.g. in the above mentioned literature). By varying the ratio of the various dyes, different color ranges can be determined.

[0230] According to a preferred embodiment, the medium and the switch layer comprise one or more dichroic dyes which absorb light in the red and NIR region, i.e. at wavelengths between 600 and 2000 nm, preferably in the range of 650 to 1800 nm, particularly preferably in the range of 650 to 1300 nm.

[0231] Preferred dichroic dyes are selected from azo dyes, anthraquinones, thiophenol anthraquinones, methine compounds, azomethine compounds, merocyanine compounds, naphthoquinones, tetrazines, perylenes, terylenes, quaterrylenes, higher rylenes, pyrromethenes, thiadiazoles, benzothiadiazoles, nickel dithiolenes, (metal)phthalocyanines, (metal)naphthalocyanines and (metal)porphyrins. Among these, azo dyes, thiophenol anthraquinones, thiadiazoles and benzothiadiazoles are particularly preferred.

[0232] In one embodiment, the dichroic dye provided in the medium or switch layer is preferably selected from the dye classes given in B. Bahadur, Liquid Crystals-Applications and Uses, Vol. 3, 1992, World Scientific Publishing, Chapter 11.2.1, and particularly preferably from the explicit compounds given in the tables present herein.

[0233] 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.

[0234] Examples of preferred dichroic dyes that may be present in the medium and switch layer of the light valve are given below.

[0235] [Table 1]

[0236] [Table 2]

[0237] [Table 3]

[0238] [Table 4]

[0239] [Table 5]

[0240] [Table 6]

[0241] [Table 7]

[0242] [Table 8]

[0243] The dye in the switch layer can provide a variation in overall transmittance, giving the opaque state a colored or black appearance, respectively.

[0244] In a preferred embodiment, the switch layer of the device according to the invention comprises one or more quencher compounds. This is particularly preferred when the device according to the invention comprises one or more fluorescent dyes in the switch layer. To achieve effective quenching, the quencher compound must be matched to the longest absorbing dye in each dye system, especially in the dye combination. The quencher compound, which is optionally added in a preferred embodiment of the switch layer according to the invention, is selected so that the fluorescence in the visible part of the spectrum is suppressed.

[0245] A light valve according to the present invention preferably comprises only one switch layer.

[0246] In alternative embodiments it is however also possible to provide more than one switch layer, in particular two switch layers.

[0247] Preferably, the medium used according to the invention contains at least 5% by weight, more preferably at least 10% by weight, even more preferably 15% by weight, of one or more mesogenic compounds selected from the compounds of formula I and II, based on the total content of the medium. In one embodiment, the medium contains one or more compounds of formula I, preferably in an amount ranging from 5% to 30% by weight, based on the total content of the medium. In some cases, it may be beneficial and preferable for two or more compounds of formula I to be contained in the medium.

[0248] Preferably, the group A as defined in formula I 11 teeth, [ka] Represents.

[0249] In one embodiment, n as defined in formula I represents 0.

[0250] In a preferred embodiment, the one or more compounds of formula I are selected from compounds of formulae Ia, Ib and Ic, more preferably from compounds of formulae Ia and Ib.

[0251] [ka]

[0252] During the ceremony, R 1 and R 2 are independently selected from F, Cl, CF3, OCF3 and linear or branched alkyl or alkoxy having 1 to 15 carbon atoms or linear or branched alkenyl having 2 to 15 carbon atoms, which radicals are unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, with the proviso that one or more CH2 groups may be replaced, in each case independently of one another, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, in such a way that the oxygen atoms are not directly linked to one another, preferably from F, CF3, OCF3, linear alkyl or alkoxy having 1 to 9 carbon atoms or alkenyl having 2 to 9 carbon atoms, L, at each occurrence, is the same or different and is a halogen selected from H or F, Cl and Br, preferably F and Cl, and more preferably, at each occurrence, is the same or different and is H or F.

[0253] When the phenylene ring of the compound of formula I is substituted, the substituent(s) are F and further include a terminal group R 1 and R 2 It is particularly preferred that does not contain Cl.

[0254] In a particularly preferred embodiment, the one or more compounds of formula I are selected from Cl-free compounds.

[0255] In a particularly preferred embodiment the liquid crystalline medium is free of Cl-containing compounds.

[0256] Ring A according to Formula I 21 , A 31 and A 41It is further particularly preferred that at least one of the rings A according to formula I has at least one F substituent. 21 , A 31 and A 41 It is further particularly preferred that together have at least two F substituents.

[0257] The use of CN-containing compounds in the medium according to the invention is preferably advantageously limited to less than 75% by weight, more preferably less than 50% by weight, even more preferably less than 25% by weight, in particular less than 15% by weight. In a particularly preferred embodiment, the use of CN-containing compounds is completely avoided.

[0258] The liquid crystal medium preferably comprises mesogenic compounds which are added with a view to contributing to or maintaining favourable properties of the medium, such as good VHR and favourable stability.

[0259] In one embodiment the liquid crystal medium according to the invention comprises one or more compounds of formula II, preferably in an amount ranging from 1% to 45% by weight, more preferably from 5% to 25% by weight, based on the total content of the medium. In some cases it may be advantageous and preferred for two or more compounds of formula I to be present in the medium.

[0260] In a further embodiment the liquid crystal medium according to the invention comprises one or more compounds of formula III

[0261] [ka]

[0262] In the formula, R 5 and R 6 is R 3 is defined as follows, and L 4 and L 5 is L in formula II 1 It is defined as follows.

[0263] The compounds of formula III are preferably used in the medium in a total concentration of from 1% to 45% by weight, more preferably from 5% to 25% by weight.

[0264] The medium preferably comprises one or more mesogenic compounds of formula I, optionally one or more photoinitiators and one or more mesogenic compounds selected from the group of the compounds of formulae II and III.

[0265] It is particularly preferred that the medium comprises one or more compounds of formula I, one or more compounds of formula II, and one or more compounds of formula III as described above.

[0266] Preferably the liquid crystal media according to the invention alternatively, preferably in addition, contain one or more compounds of the formula IV.

[0267] [ka]

[0268] During the ceremony, R 7 represents a linear or branched alkyl or alkoxy having 1 to 15 carbon atoms, preferably having 1 to 7 carbon atoms, or a linear or branched alkenyl having 2 to 15 carbon atoms, which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, with the proviso that one or more CH2 groups may be replaced, in each case independently of one another, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, in such a way that the oxygen atoms are not directly linked to one another, i is 0, 1 or 2; L 6 and L 7 are each independently H or F, and X 1 represents F, CF3, OCF3 or CN.

[0269] The compound of formula IV is preferably used in the medium in a total concentration of from 1% to 45% by weight, more preferably from 5% to 25% by weight.

[0270] It is particularly preferred that the medium comprises one or more compounds of formula I, one or more compounds of formula II, one or more compounds of formula III and one or more compounds of formula IV as described above and below.

[0271] In a further embodiment the liquid crystal medium according to the invention comprises one or more compounds of formula V, preferably in an amount in the range from 1% to 15% by weight, more preferably from 5% to 10% by weight, based on the total content of the medium.

[0272] [ka]

[0273] During the ceremony, R 8 represents a linear or branched alkyl or alkoxy having 1 to 15 carbon atoms, preferably having 1 to 7 carbon atoms, or a linear or branched alkenyl having 2 to 15 carbon atoms, which is unsubstituted, monosubstituted by CN or CF3 or mono- or polysubstituted by halogen, with the proviso that one or more CH2 groups may be replaced, in each case independently of one another, by -O-, -S-, -CO-, -COO-, -OCO-, -OCOO- or -C≡C-, in such a way that the oxygen atoms are not directly linked to one another, and X 2 represents F, CF3, OCF3 or CN, preferably CF3.

[0274] In a particularly preferred embodiment, the one or more compounds of formula I are selected from the compounds of formulae I-1 and I-2.

[0275] [ka]

[0276] During the ceremony, R 1 and R 2 is as defined in formula Ia above, L is the same or different and is H or F in each occurrence.

[0277] Optionally, the medium further comprises one or more compounds selected from compounds designated as CC-nV and CC-n-Vm as shown and described in Table D, where preferably n and m are each independently an integer from 1 to 7, particularly in the concentration range of 1% to 25% by weight.

[0278] Optionally, the medium according to the present invention may contain further liquid crystal compounds to adjust the physical properties. Such compounds are known in the art. The concentration of these optionally further liquid crystal compounds in the medium according to the present invention is preferably 0% to 30% by weight, more preferably 0.1% to 20% by weight, and most preferably 1% to 15% by weight.

[0279] Preferably, the medium according to the invention comprises a compound of formula R-5011 as shown in Table F below.

[0280] The liquid-crystalline media according to the invention may contain further additives in the usual concentrations. The total concentration of these further components is in the range of 0% to 5%, preferably 0.1% to 4%, based on the total mixture. The concentration of each individual compound used is preferably in the range of 0.01% to 3%. The values ​​and ranges of the concentrations of the liquid-crystalline components and compounds of the liquid-crystalline media herein do not take into account the concentrations of these and similar additives. In particular the media may further contain customary and suitable additives, such as stabilizers, antioxidants, free radical scavengers, chain transfer agents, e.g. thioethers, and / or plasticizers, preferably in amounts of 0.01% to 5% by weight. Stabilizers may be useful for further stabilizing the media and the modulation materials against degradation or oxidation, e.g. due to thermal or light stress.

[0281] Unless otherwise stated herein, all concentrations are given in weight percent.

[0282] The liquid crystal media according to the invention consist of a number of compounds, preferably 3 to 30, more preferably 4 to 20, most preferably 4 to 16. These compounds are mixed in a conventional manner. As a rule, the required amount of the compound used in the lesser amount is dissolved in the compound used in the greater amount. It is particularly easy to observe the completion of the dissolution process if the temperature is above the clearing point of the compound used in the higher concentration. However, it is also possible to prepare the media in other conventional ways, for example using so-called premixes, which are homologous or eutectic mixtures of compounds, or using so-called multi-bottle systems, in which the components themselves are ready-to-use mixtures.

[0283] Many of the mesogenic compounds described above and below or mixtures thereof are commercially available. These compounds are known or can be prepared by methods known per se, as described in the literature (e.g. standard works such as Houben-Weyl, Methoden der Organischen Chemie [Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), precisely under known and suitable reaction conditions for said reactions. Modifications can also be made here that are known per se 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. Suitable additives or substances can be added to modify the dielectric anisotropy, the viscosity and / or the alignment of the liquid crystal phase.

[0284] The term "alkyl" according to the invention preferably includes 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.

[0285] Alkoxy may be straight-chained or branched, it is preferably straight-chained and has 1, 2, 3, 4, 5, 6 or 7 carbon atoms and is therefore preferably methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy.

[0286] The term "alkenyl" according to the present invention preferably encompasses linear and branched alkenyl groups having 2 to 7 carbon atoms, in particular linear groups. Particularly preferred alkenyl groups are C2-C7-1E-alkenyl, C4-C7-3E-alkenyl, C5-C7-4-alkenyl, C6-C7-5E-alkenyl and C7-6E-alkenyl, in particular C2-C7-1E-alkenyl, C4-C7-3E-alkenyl and C5-C7-4E-alkenyl. Examples of preferred alkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl, etc. Groups having up to 5 carbon atoms are generally preferred.

[0287] The fluorinated alkyl or alkoxy group is preferably CF3, OCF3, CFH2, OCFH2, CF2H, OCF2H, C2F5, OC2F5, CFHCF3, CFHCF2H, CFHCFH2, CH2CF3, CH2CF2H, CH2CFH2, CF2CF2H, CF2CFH2, OCFHCF3, OCFHCF2H, OCFHCFH2, OCH2CF3, OCH2CF2H, OCH2CFH2, O CF2CF2H, 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 the fluorine are not excluded.

[0288] The oxaalkyl is preferably of the formula C n H 2n+1 -O-(CH2) m where n and m are each independently an integer from 1 to 6. Preferably, n is 1 and m is 1 to 6.

[0289] Oxaalkyl preferably denotes 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, 2-, 3-, 4-, 5-, 6-, 7-, 8- or 9-oxadecyl.

[0290] Halogen is preferably F or Cl, in particular F.

[0291] If one of the abovementioned radicals is an alkyl radical in which one CH2 group is replaced by -CH=CH-, this may be linear or branched. It is preferably linear and has 2 to 10 C atoms. It therefore especially denotes vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, dec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

[0292] If one of the above 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 comprise a carbonyloxy group -CO-O- or an oxycarbonyl group -O-CO-. They are preferably linear and have 2 to 6 carbon atoms.

[0293] 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.

[0294] If one of the above mentioned groups is an alkyl group in which one CH2 group is replaced by unsubstituted or substituted -CH=CH- and the adjacent CH2 groups are replaced by CO, CO-O or O-CO, it may be linear or branched. It is preferably linear and has 4 to 13 carbon atoms. It is therefore in particular acryloyloxymethyl, 2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl, 5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl, 8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl, methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl, 4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl, 7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl or 9-methacryloyloxynonyl.

[0295] When one of the abovementioned groups is an alkyl or alkenyl group monosubstituted by CN or CF3, this group is preferably linear. The substitution by CN or CF3 may be in any position.

[0296] When one of the above groups is an alkyl or alkenyl group at least monosubstituted with a halogen, this group is preferably linear and the halogen is preferably F or Cl, more preferably F. In the case of polysubstitution, the halogen is preferably F. The resulting group also includes perfluoro groups. In the case of monosubstitution, the fluorine or chlorine substituent may be in any desired position, but preferably in the ω-position.

[0297] Compounds with branched groups are often valued due to their good solubility in conventional liquid crystal matrices, but when they are optically active they are particularly suitable as chiral dopants.

[0298] Branched groups of this type generally do not contain 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-ethylhexyl, 1-methylhexyl or 1-methylheptoxy.

[0299] If one of the abovementioned radicals is an alkyl group in which two or more CH2 groups are replaced by -O- and / or -CO-O-, this may be linear or branched. It is preferably branched and has 3 to 12 carbon atoms. It is therefore particularly 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, bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl, 3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)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.

[0300] In another aspect of the invention, there is provided a switch layer comprising a mediator or modulating material according to the invention.

[0301] The switch layer according to the present invention preferably has a thickness in the range of 2 μm to 50 μm, even more preferably 4 μm to 40 μm, in particular 10 μm to 25 μm.

[0302] In a light valve the switch layer is disposed between two substrates, typically two transparent substrates.

[0303] The substrate 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).

[0304] In a particularly preferred embodiment, a glass substrate is used.

[0305] The final assembled light valve may further include one or more layers that block UV light.

[0306] Advantageously, the light valves can be manufactured by the simple and efficient processes described herein.

[0307] In the preparation process, a liquid crystalline medium comprising one or more polymerizable mesogenic compounds is provided as a layer between two opposing transparent substrates each provided with an electrode, preferably arranged as a conductive layer on the inner surface of each substrate, more preferably each conductive layer arranged on a passivation layer, even more preferably between passivation layers, optionally further provided with an alignment layer in direct contact with the liquid crystalline medium.

[0308] The one or more polymerizable mesogenic compounds are then polymerized, in particular by means of photopolymerization. Preferably, the photopolymerization of the one or more polymerizable mesogenic compounds is carried out in the presence of an electric field in the layer, preferably an alternating electric field, preferably the layer has a thickness in the range of 2 μm to 50 μm, more preferably 5 μm to 25 μm, and preferably the applied electric field induces homeotropic alignment in the layer comprising the liquid crystal medium.

[0309] In the method described herein, polymerization is carried out by photopolymerization, preferably with UV light. In a particularly preferred embodiment, an electric field is applied during polymerization to induce at least temporarily an orientation of the medium, preferably a homeotropic orientation. The application of a voltage to set a predetermined orientation during polymerization can advantageously affect the product properties of the switch layer and the light valve. For example, inducing homeotropic orientation during polymerization can contribute to achieving a homogeneous low haze transparent state, and can also obtain a homogeneous and appropriately strong haze in the opaque state.

[0310] The temperature during photopolymerization can be controlled, for example, within the range of 20° C. to 100° C., preferably below the clearing point.

[0311] In a preferred embodiment the reactive mesogens are self-initiating, in another embodiment a photoinitiator is used to induce polymerization.

[0312] For photopolymerization of the material in the switching layer, preferably exposure times of 30 seconds to 240 minutes, more preferably 1 minute to 120 minutes, are used, preferably at 0.01 mW / cm 2 ~100mW / cm 2 , more preferably 0.1 mW / cm 2 ~50mW / cm 2 , and even more preferably 1 mW / cm 2 ~50mW / cm 2 , especially 2mW / cm 2 ~20mW / cm 2 Illumination intensities in the range are used.

[0313] Several parameters for the polymerization can be appropriately set or varied, such as the radiation dose, the magnitude or the respective frequency of the optionally applied voltage, the electric field strength, and the amount of chiral dopant and dichroic dye in the medium.

[0314] Further processing can be carried out following the photopolymerization. Preferably, the polymerization step is followed by a heat treatment. Heat treatment, i.e. exposure to an elevated temperature compared to the previous polymerization step, can result in further curing or further conversion or completion of polymerization. This is beneficial in terms of product performance and stability, especially in terms of minimizing the amount of residual unreacted monomer in the product.

[0315] The optional heat treatment step following polymerization is preferably carried out for a time in the range of from 5 to 240 minutes, more preferably from 10 to 120 minutes, and especially from 20 to 60 minutes. The heat treatment preferably uses a temperature in the range of from 85°C to 200°C, more preferably from 110°C to 190°C, and especially from 140°C to 180°C.

[0316] It is also possible to subject the substrates used to a pretreatment step, e.g. surface treatment methods such as UV-ozone or plasma treatment, which can improve the alignment and wetting behavior over larger areas, contributing to an increased homogeneity as well as a favorable reduction in unwanted haze in the transparent state.

[0317] The methods described herein are advantageously useful for fabricating light valves that have favorable durability, a transparent state with low haze, and a scattering state that provides good opacity, even when only a single switch layer is used in the device.

[0318] The structures of the mesogenic compounds in the present invention and especially 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 with n, m and l C atoms, respectively, preferably 1E-alkenyl. Table A lists the codes to be used for the ring elements of the core structure of the compounds, while Table B shows the linking groups. Table C gives the meaning of the codes for the left and rightmost groups. The acronyms consist of the code for the ring element with the optional linking group, followed by a first hyphen and the code for the left end group, a second hyphen and the code for the right end group. Table D shows exemplary structures of the compounds with their respective abbreviations.

[0319] <Table A: Ring elements>

[0320] [Table 9]

[0321] [Table 10]

[0322] [Table 11]

[0323] <Table B: Linking group>

[0324] [Table 12]

[0325] <Table C: Terminal group>

[0326] [Table 13]

[0327] [Table 14]

[0328] where n and m each represent an integer and the three dots "..." are places for other abbreviations from the table.

[0329] The following table shows exemplary structures with their respective abbreviations, which are presented to illustrate the meaning of the abbreviation rules, and further shows the compounds which are preferably used.

[0330] <Table D: Exemplary Structures>

[0331] [Table 15]

[0332] [Table 16]

[0333] [Table 17]

[0334] [Table 18]

[0335] [Table 19]

[0336] [Table 20]

[0337] [Table 21]

[0338] [Table 22]

[0339]

Table 23

[0340]

Table 24

[0341]

Table 25

[0342]

Table 26

[0343]

Table 27

[0344]

Table 28

[0345]

Table 29

[0346]

Table 30

[0347]

Table 31

[0348]

Table 32

[0349] [Table 33]

[0350] [Table 34]

[0351] [Table 35]

[0352] [Table 36]

[0353] [Table 37]

[0354] In the formula, n, m and l preferably each independently represent 1 to 7.

[0355] The following table shows exemplary compounds which can be used as stabilizers in the media according to the invention.

[0356] Table E shows possible stabilizers which can be added to the LC media according to the invention, where n represents an integer from 1 to 12, preferably 1, 2, 3, 4, 5, 6, 7 or 8, and no terminal methyl group is shown.

[0357] [Table 38]

[0358] [Table 39]

[0359] [Table 40]

[0360] [Table 41]

[0361] [Table 42]

[0362] [Table 43]

[0363] [Table 44]

[0364] [Table 45]

[0365] 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.

[0366] Table F below shows exemplary compounds which can be preferably used as chiral dopants in the mesogenic media according to the present invention.

[0367]

[0368] [Table 46]

[0369] [Table 47]

[0370] [Table 48]

[0371] [Table 49]

[0372] In a preferred embodiment of the invention the mesogenic medium comprises one or more compounds selected from the compounds shown in Table F.

[0373] 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.

[0374] 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.

[0375]

[0376] Table G collates exemplary compounds which can be preferably used as reactive mesogenic compounds in the LC media according to the invention. Preferably, an 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. A suitable initiator is for example Irgacure® 651 (BASF).

[0377] [Table 50]

[0378] [Table 51]

[0379] [Table 52]

[0380]

Table 53

[0381]

Table 54

[0382]

Table 55

[0383]

Table 56

[0384]

Table 57

[0385]

Table 58

[0386]

Table 59

[0387]

Table 60

[0388]

Table 61

[0389]

Table 62

[0390]

Table 63

[0391] [Table 64]

[0392] [Table 65]

[0393] [Table 66]

[0394] [Table 67]

[0395] [Table 68]

[0396] [Table 69]

[0397] In a preferred embodiment of the invention the mesogenic medium comprises one or more compounds selected from the group of compounds in Table G.

[0398] The liquid crystalline medium according to the invention comprises compounds of table D, preferably 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 at least 3 different formulae selected from the group of formulae of table D. It is particularly preferred that the medium additionally comprises one or more compounds selected from the group of formulae of table E. Even more preferably, the medium further comprises one or more compounds selected from the group of formulae of table G.

[0399] 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 manner The examples and modifications or other equivalents thereof will be apparent to those of skill in the art in light of this disclosure.

[0400] However, the physical properties and compositions given in the following examples show what properties can be achieved and to what extent they can be modified. The combinations of various properties that can be particularly preferably achieved are thus well defined. EXAMPLES

[0401] 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 represents the rotational viscosity [mPa s] measured at 20°C and is 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.

[0402] For the present invention, the term "threshold voltage" refers to the capacitance threshold (V0) unless otherwise specified. Also, in the examples, and as is generally customary, the 10% relative contrast (V 10 ) may also be indicated.

[0403] Liquid crystal mixtures and composite systems are realized with the compositions and properties given below. Their properties and optical performances are discussed.

[0404] <Reference Example 1> A liquid crystal base mixture B-1 having the composition and properties shown in the table below is prepared and characterized with respect to its general physical properties.

[0405] [Table 70]

[0406] <Reference Example 2> A liquid crystal base mixture B-2 having the composition and properties shown in the table below is prepared and characterized with respect to its general physical properties.

[0407] [Table 71]

[0408] Cholesteric mixture C-2 is prepared by mixing 99.00% of mixture B-2 with 1.00% of chiral dopant R-5011 available from Merck, Darmstadt, Germany.

[0409] <Reference Example 3> A liquid crystal base mixture B-3 having the composition and properties shown in the table below is prepared and characterized with respect to its general physical properties.

[0410] [Table 72]

[0411] Cholesteric mixture C-3 is prepared by mixing 99.54% of mixture B-3 with 0.46% of chiral dopant R-5011 available from Merck, Darmstadt, Germany.

[0412] <Comparative Example 1> Cholesteric mixture CC-1 is prepared by mixing 91.125% of mixture B-1 as described in Reference Example 1 above with 6.493% of chiral dopant CB15 available from Merck, Darmstadt, Germany, 2.370% of ethylene glycol dimethacrylate, 0.010% of polydimethylsiloxane, and 0.002% of 2,6-di-tert-butyl-4-methylphenol.

[0413] Mixture CC-1 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (Japan Synthetic Rubber AL-1054, flat, TN rubbing) with a cell gap of 25 μm.

[0414] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0415] The resulting cell has a white appearance and an opaque state with a haze of 96%, where the haze is determined according to ASTM 1003-92 using a spectrophotometer (Lambda 1050, PerkinElmer) and a 150 mm Ulbricht bulb. The resulting cell has an optically clear state with a haze of 5.2% at 50 V and a τ of 99 ms at 20° C. on and a τ of 32 ms off At 0°C, the cell has a τ of 750 ms. on and a τ of 134 ms off has.

[0416] <Example 1> A dye-doped mixture M-1 is prepared by mixing 99.50% of the cholesteric mixture C-2 described in Reference Example 2 above with 0.50% of Irgaphor Black X11DC (BASF). 99.225% of the mixture M-1 is mixed with 0.75% of a compound of formula RM-A, [ka] 0.025% of a photoinitiator Irgacure® 651 (hereinafter abbreviated as IRG-651) is mixed to prepare a mixture M-1-1. [ka]

[0417] The mixture M-1-1 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (AL-1054, flat, TN rubbing, manufactured by Japan Synthetic Rubber Co., Ltd.) with a cell gap of 25 μm.

[0418] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0419] The resulting cell has an optically transparent state with a haze of 67% at opaque state. The resulting cell has an optically transparent state with a haze of 2.0% at 100 V and a τ of 65 ms at 20° C. on and a τ of 2.8 ms off At 0°C, the cell has a τ of 236 ms. on and a τ of 10.0 ms off has.

[0420] <Example 2> 0.118% of the compound of formula DD-1 in the cholesteric mixture C-2 described in Reference Example 2 above; [ka] 0.142% of a compound of formula DD-2; [ka] 0.242% of the compound of formula DD-3 is added to prepare dye-doped mixture M-2. [ka]

[0421] Mixture M-2-1 is prepared by mixing 99.225% of mixture M-2 with 0.750% of the compound of formula RM-A described in Example 1 above and 0.025% of IRG-651 described in Example 1 above.

[0422] The mixture M-2-1 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (AL-1054, flat, TN rubbing, manufactured by Japan Synthetic Rubber Co., Ltd.) with a cell gap of 25 μm.

[0423] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0424] The resulting cell has an opaque state with a black appearance and a haze of 84%. The resulting cell has an optically transparent state with a haze of 2.5% at 100 V and a τ of 101 ms at 20° C. on and a τ of 2.8 ms off At 0°C, the cell has a τ of 368 ms. on and a τ of 9.8 ms off has.

[0425] <Example 3> Mixture M-2 (98.713%) prepared in Example 2 above was mixed with 0.037% IRG-651, 0.625% compound of formula RM-B, [ka] Mixture M-3 is prepared by mixing with 0.625% of a compound of formula RM-C. [ka]

[0426] Mixture M-3 is processed and measured as described above for Mixture M-2 in Example 2. The resulting cell exhibits favorable electro-optical performance in both the opaque and optically transparent states.

[0427] <Example 4> To the cholesteric mixture C-3 described in Reference Example 3 above, 0.750% of the compound of formula RM-A described in Example 1 above, 0.025% of IRG-651, 0.109% of the compound of formula DD-1 described in Example 2 above, 0.132% of the compound of formula DD-2 described in Example 2 above, and 0.254% of the compound of formula DD-3 described in Example 2 above are added to prepare mixture M-4.

[0428] Mixture M-4 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (Japan Synthetic Rubber AL-1054, flat, TN rubbing) with a cell gap of 25 μm.

[0429] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0430] The resulting cell has an opaque state with a black appearance and a haze of 93%. The resulting cell has an optically transparent state with a haze of 5.0% at 50 V and a τ of 68 ms at 20° C. on and a τ of 2.8 ms off At 0°C, the cell has a τ of 126 ms. on and a τ of 9.0 ms off has.

[0431] <Example 5> 98.298% of mixture B-3 described in Reference Example 3 above is mixed with 0.458% of chiral dopant R-5011, 0.750% of the compound of formula RM-A described in Example 1 above, 0.109% of the compound of formula DD-1 described in Example 2 above, 0.132% of the compound of formula DD-2 described in Example 2 above, and 0.253% of the compound of formula DD-3 described in Example 2 above to prepare mixture M-5.

[0432] Mixture M-5 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (Japan Synthetic Rubber AL-1054, flat, TN rubbing) with a cell gap of 25 μm.

[0433] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0434] The resulting cell has an opaque state with a black appearance and a haze of 83%. The resulting cell has an optically transparent state with a haze of 1.5% at 50 V and a τ of 56 ms at 20° C. on and a τ of 7.7 ms off At 0°C, the cell has a τ of 116 ms. on and a τ of 25 ms off has.

[0435] <Example 6> Mixture B-3, as described in Reference Example 3 above, is added with 0.458% of chiral dopant R-5011, 0.750% of the compound of formula RM-A, as described in Example 1 above, 0.025% of IRG-651, 0.123% of the compound of formula DD-4, [ka] 0.337% of a mixture of compounds of formulae DD-5 and DD-6; [ka] 0.117% of a compound of formula DD-7; [ka] Mixture M-6 is prepared by adding 0.173% of the compound of formula DD-8. [ka]

[0436] Mixture M-6 is filled into an electro-optical cell having a glass substrate (0.7 mm alkali-free glass) with an ITO electrode and a polyimide alignment film (Japan Synthetic Rubber AL-1054, flat, TN rubbing) with a cell gap of 25 μm.

[0437] The cell is preheated to 40 °C. While continuing to apply voltage (100 Vrms), UV light (facial toner with cutoff intensity below 340 nm, light intensity 3 mW / cm 2 The polymerization is carried out at 40° C. by irradiation with UV light for 60 minutes.

[0438] The resulting cell has an opaque state with a black appearance and a haze of 94%. The resulting cell has an optically transparent state with a haze of 7.6% at 100 V and a τ of 15 ms at 20° C. on and τ of 3.3 ms off At 0°C the cell has a τ of 42 ms. on and a τ of 9.8 ms off has.

[0439] <Example 7> Mixture M-7 is prepared by adding 0.037% of IRG-651, 0.625% of the compound of formula RM-B described in Example 3 above, 0.625% of the compound of formula RM-C described in Example 3 above, 0.109% of the compound of formula DD-1 described in Example 2 above, 0.132% of the compound of formula DD-2 described in Example 2 above, and 0.254% of the compound of formula DD-3 described in Example 2 above to mixture C-3 described in Reference Example 3 above.

[0440] Mixture M-7 is processed and measured as described above for Mixture M-2-1 in Example 2. The resulting cell exhibits favorable electro-optical performance in both the opaque and optically transparent states.

Claims

1. 1. A method of preparing a light valve operable in and electrically switchable between optically transparent and opaque states for use in a mobile or portable device, comprising: (i) providing a liquid crystal medium containing, as a layer interposed between two opposing transparent substrates each provided with an electrode, one or more kinds of mesogenic compounds, one or more kinds of chiral compounds, at least three kinds of dichroic dyes and one or more kinds of polymerizable mesogenic compounds; However, the liquid crystal medium has a clearing point of 70° C. or higher, provided that the one or more polymerizable mesogenic compounds are present in the medium in an amount of 2% by weight or less, based on the total content of the medium; and (ii) using photopolymerization to polymerize one or more polymerizable mesogenic compounds in the layer; The method includes:

2. 2. The method of claim 1, wherein the photopolymerization of the one or more polymerizable mesogenic compounds is carried out in the presence of an electric field in a layer, the layer having a thickness in the range of 2 μm to 50 μm, and wherein the applied electric field induces homeotropic alignment in the layer comprising a liquid crystalline medium.

3. 3. The method according to claim 1 or 2, wherein the one or more polymerizable mesogenic compounds contain one or more acrylate and / or methacrylate groups.

4. Photopolymerization was performed at 0.1 mW / cm ２ ~100mW / cm ２ 4. The method of any one of claims 1 to 3, carried out using light having an intensity in the range of 0.5 to 100 nm for a period in the range of 1 minute to 240 minutes.

5. The method according to any one of claims 1 to 4, wherein the at least one dichroic dye is selected from the group consisting of the compounds of formulae DD-1 to DD-8. 【Chemistry 1】 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】 【Chemistry 7】

6. The method according to any one of claims 1 to 5, wherein the total concentration of the dichroic dyes is 3% by weight or less.

7. 1. A light valve for use in a mobile or portable device, actuable in and electrically switchable between optically transparent and opaque states, comprising: a liquid-crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds and at least three dichroic dyes, with the proviso that the liquid-crystalline medium has a clearing point above 70° C., and a polymer component comprising one or more polymer structures obtained by polymerization of one or more polymerizable mesogenic compounds, the polymer component being contained in the material in an amount of 2% by weight or less based on the total weight of the liquid crystal medium and the polymer component; a switch layer including However, the light valve in its optically clear state has a haze of less than 10% as determined in accordance with ASTM D 1003 and a light transmission of greater than 45% as determined in accordance with DIN EN 410, and in its opaque state has a haze of greater than 65% as determined in accordance with ASTM D 1003 and a light transmission of less than 35% as determined in accordance with DIN EN 410.

8. 8. A light valve according to claim 7, wherein the liquid crystal medium exhibits a pitch of 0.55 [mu]m or greater in the opaque state.

9. The light valve of claim 7 or 8, wherein the at least one dichroic dye is selected from the group consisting of the compounds of formulae DD-1 to DD-8. 【Chemistry 8】 【Chemistry 9】 【Chemistry 10】 【Chemistry 11】 【Chemistry 12】 【Chemistry 13】 【Chemistry 14】

10. The light valve according to any one of claims 7 to 9, wherein the total concentration of the dichroic dyes is 3% by weight or less.

11. 1. A modulating material for use in a light valve for use in a mobile or portable device, the modulating material being actuable in and electrically switchable between optically transparent and opaque states, the modulating material comprising: a liquid-crystalline medium comprising one or more mesogenic compounds, one or more chiral compounds and at least three dichroic dyes, with the proviso that the liquid-crystalline medium has a clearing point above 70° C., and a polymer component comprising one or more polymer structures obtained by polymerization of one or more polymerizable mesogenic compounds, the polymer component being contained in the material in an amount of 2% by weight or less based on the total weight of the liquid crystal medium and the polymer component; Including, wherein the light valve in its optically clear state has a haze of less than 10% as determined in accordance with ASTM D 1003 and a light transmission of greater than 45% as determined in accordance with DIN EN 410, and wherein the modulating material in its opaque state has a haze of greater than 65% as determined in accordance with ASTM D 1003 and a light transmission of less than 35% as determined in accordance with DIN EN 410.

12. 12. The modulating material of claim 11, wherein the at least one dichroic dye is selected from the group consisting of the compounds of formulas DD-1 to DD-8. 【Chemistry 15】 【Chemistry 16】 【Chemistry 17】 【Chemistry 18】 【Chemistry 19】 【Chemistry 20】 【Chemistry 21】

13. 13. The modulation material according to claim 11, wherein the total concentration of the dichroic dyes is 3% by weight or less.

Images