Liquid Crystal Optical System

Abstract

The present invention proposes an optical system (1000), which consists of an electrically controllable variable polarizer (100) using liquid crystals and dichroic dyes.

Description

[Technical field]

[0001] The present invention relates to a liquid crystal optical system having liquid crystal electrically controllable devices. [Background technology]

[0002] The liquid crystal system comprises first and second electroactive liquid crystal cells arranged opposite each other and capable of either transmitting light or blocking it. Summary of the Invention [Problem to be solved by the invention]

[0003] One of the aims of the present invention is to develop liquid crystal systems which alternately have alternating electro-optical properties or even provide new functionalities. [Means for solving the problem]

[0004] To this end, the invention proposes a liquid crystal optical system comprising an electrically switchable device with a variable polarization (in transmission), called a variable polarizer, which comprises: a first transparent electrode, which has an electric field E2 between it and the second electrode, in particular in the form of an electrically conductive layer on a common carrier element (coplanar arrangement), the first and second electrodes (preferably layered) being coplanar (preferably not self-supporting but on a common carrier element) and forming alternating first and second electrically conductive strips (for example metal) with different electric potentials, in particular elongated strips (straight, preferably bounded by straight lines) in the direction r0. an electroactive layer, which is sub-millimeter thick, even up to 100 μm, and at least 50 nm, in particular between 50 nm and 50 μm, even between 100 nm and 20 μm, more preferably at least 1 μm or 5 μm thick, which is made of a thermotropic material, which (preferably) comprises (or consists of): - a liquid crystal (preferably thermotropic), which is nematic, curved or not, preferably twisted (by the action of an anchor layer), powerless in the off state, and / or cholesteric - (preferably the major component by weight of the material (preferably at least 50, 70, 80, 85 weight percent of said liquid crystal), in particular the liquid crystal comprises mesogens, for example without polymer chains, or comprises mesogenic groups incorporated in the main or side chains of a polymer (class called "LCP"), in particular the liquid crystal has a size of up to 50 nm, 20 nm or 10 nm (and less than Ep2), in particular a mixture of several liquid crystals (in the case of pure, non-LCP), and therefore several mesogens. - dichroic dyes (especially in solution, especially in liquid crystals), for example up to 30 weight percent, 20 weight percent, 10 weight percent, 5 weight percent of dichroic dye (single or multiple dichroic dyes), the dichroic dyes being in particular up to 50 nm, 20 nm or 10 nm in size (and less than Ep2); in particular the liquid crystal and the dichroic dye are of comparable size, for example less than 20 nm or less than 10 nm, respectively. - optionally a polymer (preferably non-crosslinked) or a precursor of a polymer, preferably up to 20 weight percent, 15 weight percent, 10 weight percent, 5 weight percent or 1 weight percent of a polymer (or a precursor of a polymer), e.g. the electroactive layer is not of that type (PDLC or PSLC); - preferably spacers, in particular of height (and even of relatively large dimensions) less than or equal to Ep2, located at the periphery (dielectric, transparent or, optionally, not masked by a frame, for example made of mylar) and / or dispersed in the electroactive layer (dielectric, transparent, in particular plastic, glass, silica, preferably sub-centimeter, in particular beads); - optionally other additives (other than dichroic dyes), such as coloring particles, such as metal nanoparticles (gold, silver, alloys of both, etc.) or metal oxide nanoparticles (tungsten oxide, tin oxide, etc.), or even any other non-dichroic dyes, or any other light absorbing molecules, preferably with a height of Ep2 or less (or even with relatively large dimensions of Ep2 or less).

[0005] Preferably the electrically switchable electroactive layer is sealed at its periphery (at the edges of the main faces in contact with the material (or separated by a peripheral spacer)) by a dielectric seal, in particular a polymeric one.

[0006] Designed in this way, the variable polarizer can transmit polarized light having a polarization P1 (predominant) in a first functional state, the off state, and can transmit polarized light having a second polarization P2 (preferably dominant) different from P1 in a second functional state, the on state.

[0007] The invention finds application in various fields, especially in buildings (windows, partitions, glazing floors), especially in urban spaces, or in road, sea, rail or air vehicles (windshields, side roofs, sunroofs, etc.).

[0008] When incorporated within the glazing of a building or vehicle, the other devices may be oriented either outwardly or inwardly.

[0009] The variable polarizer itself operates without the need for one or more polarizers, such as crossed polarizers and an analyzer. In particular, the variable polarizer may not have a static polarizing film.

[0010] The switching time of the variable polarizer can be less than a few seconds. The switching state of the optical system is reversible and (to some extent) instantaneous.

[0011] A variable polarizer does not require multiple layers of liquid crystals, but only one layer of liquid crystal (single cell system) to form a variable polarizer.

[0012] The optical properties of the optical system may be adjustable by: - by switching off or applying an electric field E2 (preferably an alternating electric field) and by selecting a voltage level U2; - by selecting the orientation of the (dominant) output polarization, called P1, relative to a characteristic direction b of another polarization-sensitive device, which will be described in more detail below, in particular by selecting an orientation such that P1 is substantially parallel or substantially perpendicular to b.

[0013] For the variable polarizer, the dichroic dye plays an important role in providing the variable polarization function according to the liquid crystal, preferably twisted in the off state. The variable polarizer with variable polarization is preferably transparent and has a haze of at most 10%, or at most 1%, or at most 0.5% in both the off and on states.

[0014] U2 may be less than 120V, or even less than 80V.

[0015] It may be possible to apply U2 (and even select the level of U2) as a function of the set point, thus providing a means for controlling the variable polarizer.

[0016] The optical system may have a thickness of up to 1 cm, or up to 5 mm, or up to 1 mm.

[0017] The variable polarizer may have a thickness of up to 5mm, or up to 1mm, or up to 0.5mm.

[0018] The first and second electrodes (preferably laminar) are coplanar and provide planar switching.

[0019] The parameters influencing the optical properties are in particular: - selection of liquid crystals, in particular mixtures of mesogens (in particular with regard to the operating temperature range and the reduction in the voltage level in the on-state) and their dielectric anisotropy; - the level of transparency of the least absorbing electrodes (and their substrates, if any) possible and, in the case of strip-shaped electrodes, the density of the strips (this allows a smaller spacing between the strips, thereby lowering the electrical voltage and thus reducing the zones without switching the liquid crystals, thus increasing the off / on contrast); - selecting the dichroic dye (dichroic ratio, etc.) so as to have the highest and most constant absorption spectrum, especially in the visible range; - The thickness of the electroactive layer.

[0020] Optical characterization of the optical system according to the invention can be performed on either side.

[0021] However, light exiting the side with the strip electrodes (along r0) will be polarized relatively more according to P1 (perpendicular to r0, preferably with the unidirectional anchor layer along r1 parallel to r0 on the strip electrodes) and relatively more according to P2 when exiting the side without the strip electrodes. This could be a plastic (stretched) film with a dichroic dye.

[0022] The first (respectively second) electrode may comprise (or even consist of) an electrically conductive layer (single or multilayer, in particular one or more deposits), in particular an inorganic, in particular an electrically conductive layer up to 200 nm thick (an electrically conductive layer on the carrier element, preferably between the carrier element and the anchor layer), in particular having current supply means (strips - busbars - in particular made of metal, copper, silver, etc.) at the edges.

[0023] Preferably, the density of the electrically conductive strips is as great as possible (the width of the strips is as small as possible and the spacing between the strips is as small as possible).

[0024] In this way, a potential difference is applied between two "terminals" which lie in the same plane and are electrically isolated from each other.

[0025] E2 lies mostly in a plane (parallel to the first and second electrodes).

[0026] While maintaining electrical conductivity, the strips are required to be as thin as possible to improve the "polarizer" power in the ON mode, and the width between the strips (in other words the non-conductive insulating strips) is required to be as small as possible, thereby reducing the applied potential difference.

[0027] For example, the electrically conductive strips and / or the width between the strips (insulating strips) is at most 50 μm or at most 30 μm or at most 10 μm.

[0028] For example, the insulating strips may form a serpentine arrangement, with a first zone of the electrically conductive layer being insulated from a second zone of the layer by a first portion of a first insulating strip of the coil and a final portion of a final insulating strip of the coil.

[0029] Such an arrangement of insulating strips can be provided by removing the electrically conductive layer, in particular by a laser beam. The limit for the thickness of the strips is given by the size of the laser beam. The limit for the distance between the strips is determined by the motion of the laser beam.

[0030] Advantageously, the electric field E2 is an alternating electric field and preferably the voltage U2 applied between the first and second electrodes is at most 120V.

[0031] E2 is an alternating electric field, preferably with a frequency of 50 Hz or more, for example 100 Hz, 1 kHz or 2 kHz. Voltage is intended to mean the peak voltage (Vpeak).

[0032] The selection of U2 may be controlled and in particular adjusted (by controlling the power supply source) based on data (temperature, brightness, etc.) collected by sensors in communication with the device.

[0033] Preferably, in a functional state which is the off state, the variable polarizer can transmit as output (particularly to the first and second electrodes) light having polarization P1 (preferably dominant), and in a functional state which is the on state (second functional state described in more detail below) can transmit as output light having a second polarization P2 (preferably dominant), which is perpendicular to P1.

[0034] More broadly, a variable polarizer can have first and second functional states as follows: In a first functional state, being the OFF state (no voltage), from incident light (in particular on the side opposite the first and second electrodes), the variable polarizer is able to transmit (polarized) output light having a first component of a (polarization) electric field P1 along a first axis and a second component of a (polarization) electric field P2 along a second axis perpendicular to the first axis (in particular towards the first and second electrodes) with a first polarization ratio defined by:

[0035]

number

[0036] rp1 is at least 70%, more preferably at least 90% or even at least 95%, T1 is the total transmittance along a first axis at wavelengths from 380 to 800 nm, or even averaged from at least 400 to 600 nm or even from 380 to 640 nm, and T2 is the total transmittance along a second axis (for a first voltage being zero between the first and second electrodes) at wavelengths from 380 to 800 nm, or even averaged from at least 400 to 600 nm or even from 380 to 640 nm.

[0037] - In the second functional state, which is on (powered): From unpolarized incident light (particularly towards the side opposite the first and second electrodes), the variable polarizer can transmit output light (particularly towards the first and second electrodes) with a second polarization ratio defined by:

[0038]

number

[0039] rp2 is at least 30%, or even at least 50% or 60%.

[0040] T'1 is the total transmittance along a first axis at wavelengths from 380 to 800 nm, or even at least averaged from 400 to 600 nm and even at least averaged from 380 to 640 nm, and T'2 is the total transmittance along a second axis (for a second non-zero voltage between the first and second electrodes) at wavelengths from 380 to 800 nm, or even at least averaged from 400 to 600 nm and even at least averaged from 380 to 640 nm.

[0041] And, of course, the variable polarizer has multiple functional states in the on-state: in particular, there is a threshold voltage at which the anchoring force of the liquid crystal is overcome for a portion of the liquid crystal, and the more the voltage is increased, the more the liquid crystal reorients, up to a saturation voltage, which is preferably up to 80V.

[0042] And it is possible to have a polarization ratio that varies according to the applied voltage U2.

[0043] The dielectric anisotropy of the electroactive layer may be non-zero, negative or positive.

[0044] In one advantageous configuration, the variable polarizer includes: - a unidirectional planar anchor layer on (in contact with) a main face of the electroactive layer and on (in contact with) the first and second electrodes, in a direction r1, in particular P1 perpendicular to r1 and P2 parallel to r1, - and another unidirectional planar anchor layer on (in contact with) a major surface of the electroactive layer, in a direction r2, preferably in a direction r2 spaced apart from r1.

[0045] In particular, r1 forms an angle with r2 of 90°±15°, more preferably 90°±5° (and the nematic liquid crystal has a strong twist in the off state): - r0 forms an angle with r1 of at most 15°, or even at most 5°, and the liquid crystal has positive dielectric anisotropy; or r0 forms an angle with r1 of 90°±15°, or even up to 90°±5°, and the second liquid crystal has negative dielectric anisotropy.

[0046] The optical system may comprise a static polarizer facing the variable polarizer, the static polarizer being defined by a polarization axis, in particular a polarization axis arranged to absorb P1 (polarization axis perpendicular to P1) or a polarization axis arranged to absorb P2 (polarization axis perpendicular to P2).

[0047] Static polarizers may include those made of plastic films with dichroic dyes stretched in a direction that forms a polarization axis (perpendicular to the direction of light absorption). In particular, static polarizers may be designed to block light of a given polarization.

[0048] There are several possible cases: - The light at the output of the variable polarizer is along P1 (off state) and the polarizer essentially blocks P1, thereby obscuring / darkening the optical system in the off state. - The light at the output of the variable polarizer is entirely along P2 (on state) and the polarizer substantially blocks P1, so that the optical system in the on state remains along P2 and does not obscure. - The light at the output of the variable polarizer is along P1 (off state) and the polarizer essentially blocks P2, so that the optical system in the off state remains along P1 and does not obscure. - The light at the output of the variable polarizer is entirely along P2 (on state) and the polarizer essentially blocks P2, thereby obscuring / darkening the optical system in the on state.

[0049] The static polarizer is preferably of a similar shape to the variable polarizer and may extend over all or part of the variable polarizer depending on requirements.

[0050] The optical system may not have an optical element capable of depolarizing light between a variable polarizer and a static polarizer.

[0051] The optical system can be of any size; since polarizers can be easily fabricated on surfaces of at least 1 m length.

[0052] It may be desirable to avoid placing the diffuser between polarizers.

[0053] Of course, any opaque elements that obscure or reflect between the variable and static polarizers may be avoided.

[0054] When a device is added, particularly an electrically switchable device, in particular a unidirectional anchor layer with a characteristic direction b (along b for a PSLC liquid crystal device with focal conic domains), the following transitions (relative to the device's off state) may be selected: (a) From the unmasked off state to the masked on state when P1 is perpendicular to b (the effect of the mask increases as a function of U2). (b) Or, if P1 is parallel to b, from a masked OFF state to an unmasked ON state (the effect of the mask decreases as a function of U2).

[0055] The device, in particular the polarization-sensitive and electrically switchable device, is preferably of similar shape to the variable polarizer and may extend over all or part of the variable polarizer depending on the requirements.

[0056] The optical system may have no optical elements between the variable polarizer and the polarization sensitive device that are capable of depolarizing light.

[0057] The optical systems can be of any size; since these devices can be easily fabricated on surfaces of at least 1 m in length.

[0058] It may be desirable to avoid placing a diffuser between the variable polarizer and the polarization sensitive device.

[0059] Of course, one might avoid having opaque elements that obscure or reflect between the variable polarizer and the polarization sensitive device.

[0060] In one embodiment, the variable polarizer and the static polarizer (preferably a plastic film with a dichroic dye) and / or the electrically controllable polarization-sensitive device are separated and connected by a transparent bonding layer, in particular an optical adhesive, or a thermoplastic layer, in particular a lamination interlayer, or the variable polarizer comprises an element carrying the first and second electrodes that form said variable polarizer.

[0061] The transparent bonding layer may be colorless or may be colored.

[0062] The transparent bonding layer may have a thickness of up to 0.5 mm, or even 0.1 mm.

[0063] The optical system can be flat or curved, flexible to accommodate curvatures, such as glazing (monolithic or laminated), and curved on the monolithic glazing or, for example, within said laminated glazing.

[0064] An optical system according to the invention may comprise an (electrically controllable) polarization-sensitive device, in particular one having an optical response that depends on the polarization state of the light incident on said device, in particular a variably scattering electrically controllable device using nematic liquid crystals, preferably comprising focal conic domains, in particular one as described in WO 2020 / 065038, which is incorporated by reference, facing a variable polarizer.

[0065] Defect line domains are preferred because they have significant haze (scattering power). Focal conic domains of the smectic (meso)phase are preferred, as described in WO 2020 / 065038, which is incorporated by reference.

[0066] The defect domains are generally focal conic domains, each having two defect lines, arranged in pairs, specifically one elliptical with different eccentricities and the other hyperbolic, hence giving them the name "elliptic-hyperbolic focal conic domains" or EHFCDs.

[0067] Preferably, it is nematic and the domains are focal conic domains, in particular of a smectic mesophase (mesophase P'), in particular having two defect lines, which are preferably one elliptical and the other hyperbolic (EHFCD).

[0068] The focal conic domains, in particular the EHFCD, preferably form a linear network parallel to the direction b.

[0069] The liquid crystals of this polarization-sensitive device are preferably more or less organized globally in a given direction b on the FA1 or FA2 surface (referred to as planar alignment surfaces), with their director n- or long axis- generally aligned along this first direction b, which is in particular the (rubbish) axis of the unidirectional planar anchor layer in contact with this planar alignment surface (generating the interaction between the liquid crystals and this solid layer).

[0070] The above electrically controllable device with variable scattering by liquid crystals has an electroactive layer with liquid crystals (nematic and preferably containing focal conic domains), and the direction b forms an angle of 0°±15° or 0°±5° with the polarization P1 of the output light in the off state of the variable polarizer (first and second electrodes), or an angle of 0°±15° or 0°±5° with r1 perpendicular to P1, or an angle of 90°±15° or 90°±5° with the polarization P1 (or an angle of 90°±15° with r1).

[0071] Thus, according to the invention, the combination of the electrically controllable device with polarization-sensitive variable scattering with the variable polarizer makes it possible to have a wide range of available optical properties, in particular a wide range of haze and light transmission.

[0072] When incorporated within the glazing of a building or vehicle, the polarization sensitive device may be either exterior-facing or interior-facing.

[0073] The polarization sensitive device is preferably of similar shape to the variable polarizer and may extend over all or part of the variable polarizer depending on requirements.

[0074] The optical system may not have an optical element capable of depolarizing light between the polarization sensitive device and the variable polarizer.

[0075] It may be desirable to avoid placing a diffuser between the polarization sensitive device and the variable polarizer.

[0076] Of course, one may avoid any opaque elements that obscure or reflect between the polarization sensitive device and the variable polarizer.

[0077] The optical system of the polarization sensitive device plus the variable polarizer may have a maximum thickness of 1 cm or 5 mm or 1 mm.

[0078] The polarization sensitive device may have a thickness of up to 5 mm or 1 mm or 0.5 mm.

[0079] Parameters influencing the optical properties of a polarization-sensitive device are, in particular: - selecting liquid crystals, in particular mixtures of mesogens (in particular for the operating temperature range and the voltage level U1 for "unanchoring" in the on-state) and their dielectric anisotropy, - the thickness of the electroactive layer, - Anchor layer selection.

[0080] In particular, the haze value when no electric field is applied (or for a given voltage) can vary based on the size or type of two-dimensional defects, their density, the thickness of the electroactive material, the choice of liquid crystal, the polymer network (degree of cross-linking, polymerization conditions), the monomer, and the differences in the refractive indices of the polymer and liquid crystal.

[0081] In particular, the haze value in the absence of an applied electric field (or for a given voltage) will vary based on the orientation of the liquid crystals, specifically the angle between the long (molecular) axis of the first liquid crystal and the polarization axis of light polarized along a plane parallel to the surface of the first electroactive layer.

[0082] The haze H is preferably defined as the ratio between the integrated light transmittances associated with the diffuse transmittances DT and LT.

[0083] Advantageously, the electric field E1 of the polarization sensitive device is an alternating electric field, preferably the applied voltage U1 is at most 120 V. Preferably, the electrodes are in separate planes and the liquid crystal has a positive dielectric anisotropy (independent of the frequency of the electric field E1).

[0084] E2 and / or E1 are alternating electric fields, preferably with a frequency of 50 Hz or higher, for example 100 Hz, 1 kHz or 2 kHz. Voltage is intended to mean peak voltage (Vpeak).

[0085] An electrically controllable device with variable scattering has an optical response that depends on the polarization of the incident light. This differentiated response to the polarization of light is induced by: - the form factor, internal structure of two-dimensional topological defects, in particular defect lines, in particular non-toric focal conic domains, (non-"TFCD"), of smectic mesophases, and / or the arrangement of different domains (in particular focal conic domains of smectic mesophases containing "TFCD"), in particular their shape, their orientation, their degree of symmetry, distributed randomly, irregularly, for example, the distribution being dictated by anchoring conditions (two-dimensional anchor layers, e.g. multidirectional anchors, which can be adjusted as required);

[0086] Examples of various structures of polarization-sensitive smectic focal cone domains (in other words, focal cone domains) are shown in the publication by Ling Ma et al., "Smectic Layer Origami Preprogrammed Photoalignment," Advances Materials 2017 1606671, pages 1-7.

[0087] In a preferred embodiment, the variable polarizer is capable of transmitting light having polarization P1 in a first functional state, which is an off state, the polarization sensitive device has a directional anchor layer on a surface thereof in a first direction b, and the variable polarizer is positioned such that P1 forms an angle with b of 0°±20°, or more preferably 0°±5° (in particular, r2 forms an angle with b of 0°±20°, or more preferably 0°±5°).

[0088] In one embodiment, the variable polarizer can transmit light having polarization P1 in a first functional state, which is an off state, and the polarization sensitive device has a directional anchor layer on a surface thereof in a first direction b, and the variable polarizer is positioned such that P1 forms an angle with b of 90°±20° or more preferably ±5° (in particular, such that r1 forms an angle with b of 90°±20° or preferably ±5°).

[0089] As unidirectional planar anchors, fluoropolymers such as polytetrafluoroethylene, PTFE, or Teflon (where the polymer chains are aligned along the displacement direction of the Teflon bar during deposition) can be used.

[0090] The unidirectional planar anchor fixes the zenithal and azimuthal orientation of the director n of the liquid crystal, for example by texturing, polishing (also called rubbing) the planar anchor layer, for example by including nano- or micro-grooves.

[0091] The polishing may be made of velvet fabric.

[0092] For vertical anchoring, the most commonly used layers are based on octyltrichlorosilane (OTS) and N,N-dimethyl-N-octadecyl-3-aminopropyltrimethoxysilane chloride (DMOAP), or polyimides, etc.

[0093] Layers based on sodium dodecyl sulfate (SDS) or even mixtures of alkanethiols may also produce perpendicular anchoring.

[0094] The one or more anchor layers are deposited, for example, by liquid pathway.

[0095] One anchor layer, for example, is as follows: - preferably dielectric materials (especially amorphous, polymeric and / or inorganic, glass) with surface functionalization; in particular layers based on polyimides, polyvinyl alcohol (PVA), for example for planar anchoring.

[0096] The dichroic dyes may be anisotropic organic molecules, which have optical anisotropy and are elongated, in particular rod-like, which are dissolved in the material, in particular in the liquid crystal. The percentage of the (each) dichroic dye is adjusted so as not to exceed the solubility limit. In particular, the dichroic dye(s) is / are selected to be chemically compatible with the liquid crystal.

[0097] In particular, the (elongated, rod-like) dichroic dye(s) may have a long molecular axis, with absorption varying along either the long or short axis.

[0098] The dichroic dye is controlled by the orientation of the liquid crystal in the electroactive layer; the movement (rotation) of the liquid crystal under the influence of an applied electric field (E2) tends to align with the electric field, resulting in a movement (rotation) of the dichroic dye, whose long axis also tends to align with the electric field.

[0099] In this way, the absorption of a dichroic dye changes based on its orientation relative to the polarization of the incident light. Conversely, non-dichroic dyes, which do not exhibit absorption anisotropy, will be insensitive or less sensitive to electric fields and will not change absorption. Such dyes can be added to tune the desired color shade.

[0100] There are several classes of dichroic dyes, which are described in particular in the publication by Mark T Sims "dies as guests in ordered systems: current understanding and future directions" Liquid Crystals, 2016, Vol 43, NOS. 13-15, pages 2363-2374.

[0101] The dichroic dye according to the invention can be an azo dye, in particular a rod-shaped dye, having the structure AZO(-N=N). It is possible to induce chemical changes in the azo dye, for example to incorporate an ester group (see page 2366 of the above publication).

[0102] Other dyes are anthraquinones, which are generally fused rings or made rod-like by adding substituents. Examples of dichroic dyes (chromophores) are given in Table 1 of this above mentioned publication.

[0103] Examples of dichroic dyes suitable for the present invention are further described in the book "Electrooptic effect in Liquid Crystal Materials" by LMBlinov et al., published by Springer in 1994, in particular in chapter 2.3 entitled "Optical Anisotropy and Dichroism", and on pages 66-68, including Table 2.2.

[0104] For example, in the case of a blue dye, 630 nm±10 nm may be selected as the maximum absorption wavelength, and 430 nm±50 nm or ±10 nm may be selected as the wavelength outside the absorption band. For example, the dye M412 sold by Mitsui Chemicals may be mentioned.

[0105] For example, in the case of a red dye, 500 nm±10 nm may be selected as the maximum absorption wavelength, and 650 nm±50 nm or ±10 nm as the wavelength outside the absorption band. For example, the dye SI-426 sold by Mitsui Chemicals may be mentioned.

[0106] For example, in the case of a yellow dye, 400 nm±10 nm may be selected as the maximum absorption wavelength, and 600 nm±50 nm or ±10 nm as the wavelength outside the absorption band. For example, the dye SI-486 sold by Mitsui Chemicals may be mentioned.

[0107] For example, in the case of a black dye, mention may be made of the dye SI-428, sold by Mitsui Chemicals. The variable polarizer may include: a first transparent dielectric element carrying first and second electrodes made of strips (coplanar configuration), and also an anchor layer, preferably unidirectional according to r1, said first element being chosen from a glass sheet or a transparent polymeric sheet, different from or corresponding to said dielectric support. a second transparent dielectric element, carrying at least one anchor layer, preferably unidirectional, according to r2, the second element being chosen from a glass sheet (with an optional external anti-scratch layer) or a transparent polymeric sheet.

[0108] The optical system can be flat or curved, e.g. flexible to accommodate the curvature of the glazing (monolithic or laminated), which may be curved on a monolithic glazing unit or e.g. within said laminated glazing.

[0109] The present invention also relates to an optionally curved laminated glazing comprising: - a first glass sheet, preferably with a thickness of 0.7 mm to 4 mm - a laminating interlayer, of thermoplastic, in particular EVA or PVB, a second additional glass sheet, in particular with a thickness of 0.7 mm to 4 mm, or even less than 0.7 mm, or else a plastic sheet, such as polycarbonate or PMMA (in particular with a PU laminated interlayer).

[0110] The main inner faces, designated F2 and F3, of the first and second additional glass sheets face each other and the aforementioned optical system is preferably between faces F2 and F3, preferably within a laminate interlayer; preferably the first element carrying the first and second electrodes is polymeric and also the second element (on the anchor layer side of r2) is polymeric.

[0111] Preferably, the thermoplastic laminate interlayer surrounds the edges of the optical system (such as a variable polarizer).

[0112] The edge surface of the optical system may be recessed relative to the outermost edge surface of the laminate interlayer (or first sheet).

[0113] Preferably, the optional layer-bearing sheets (substrate, support, first and second elements) are preferably at most 0.7 mm, or even at most 0.3 or 0.2 mm thick. For the glass sheets, thin glass (less than 1 mm) or even ultra-thin glass (UTG) may be chosen.

[0114] One of the additional glass sheets may be tinted and the other may be clear or ultra-clear. The thermoplastic lamination interlayer may be untinted (clear, ultra-clear) or tinted.

[0115] For the carrier element, or else for the additional glass sheets or glazing of the laminated and / or double glazing, clear or extra clear glass may be selected. Clear glass typically contains iron oxide in an amount of about 0.05 to 0.2 weight percent, while extra clear glass generally contains about 0.005 to 0.03% iron oxide.

[0116] The additional glass sheets or glazing of the laminated and / or multi-glazing may nevertheless be tinted, for example blue, green, grey or bronze.

[0117] The tinted additional glass sheets or tinted glazing of the laminated glazing and / or the double glazing preferably have a light transmittance T L may have.

[0118] The glass is preferably of the soda-lime-silica type, but it can also be of the borosilicate or aluminoborosilicate glass type. The thickness of the glass is generally in the range of 0.5 mm to 19 mm, preferably 0.7 mm to 9 mm, in particular 2 mm to 8 mm, or even 4 mm to 6 mm.

[0119] The thermoplastic lamination interlayer provides the connection to the rigid or flexible element and can be in particular a layer based on polyvinyl butyral (PVB), ethylene vinyl acetate (EVA), polyethylene (PE), polyvinyl chloride (PVC), thermoplastic urethane, polyurethane (PU), ionomer, polyolefin adhesive, thermoplastic silicone or a multi- or single-component resin, a thermally crosslinkable (epoxy, PU) resin or a UV-crosslinkable (epoxy, acrylic) resin.

[0120] The PVB interlayer may be wedge-shaped, i.e. have a cross section that decreases in a wedge shape from the top to the bottom of the laminated glazing, in the case of a head-up display (HUD), especially a windscreen, thereby avoiding double images. The PVB interlayer is optionally soundproof and / or colored. The soundproof PVB interlayer comprises at least one "middle" layer made of a viscoelastic plastic with vibration-sound damping properties, especially based on polyvinyl butyral (PVB) and a plasticizer, and further comprises two outer layers made of standard PVB, the middle layer being between the two outer layers.

[0121] Optionally, one or both outer layers have a cross section that decreases in the shape of a wedge from the top to the bottom of the laminated glazing, and the layer made of a viscoelastic plastic with vibration-acoustic damping properties has a cross section that does not change from the top to the bottom of the laminated glazing. As an example of an acoustic sheet, EP 0 844 075 can be mentioned.

[0122] The first and / or second glazing of the laminated glazing may be (depending on the aesthetic expression or the desired optical effect) clear glass (4 mm thick with a light transmission of T L 90% or more), for example glass of standard soda lime composition, such as Planilux™ from Saint-Gobain Glass, or ultra-clear glass (4 mm thick with a light transmittance of T L91.5% or more), for example soda-lime-silica glasses containing less than 0.05% FeIII or Fe2O3, such as the glass Diamant® from Saint-Gobain Glass, or the glass Optiwhite® from Pilkington, or the glass B270® from Schott, or glasses of other compositions as described in WO 2004 / 025334. Planiclear® glasses from Saint-Gobain Glass may also be chosen.

[0123] The glasses of the first and / or second glazing may be neutral (untinted) or (slightly) tinted, in particular grey or green, such as the TSA glasses of Saint-Gobain Glass. The glasses of the first and / or second glazing may have undergone a chemical or heat treatment of hardening or annealing type, or toughening (in particular to obtain better mechanical strength) or may be semi-toughened.

[0124] Light transmittance T L is the total transmittance (in particular integrated over the visible range and weighted by the sensitivity curve of the human eye) taking into account both direct and possible diffuse transmission, which may be measured in accordance with the ISO 9050:2003 standard using an illuminance of D65, the measurement being carried out, for example, using a spectrophotometer equipped with an integrating sphere, the measured value at a given thickness then being converted, if necessary, to a reference thickness of 4 mm in accordance with the ISO 9050:2003 standard.

[0125] The optical system according to the invention may be integrated into a glazing, in particular a monolithic one (flat and / or curved), the optical system forming a strip, in particular a peripheral strip, over a portion of the main surface of the glazing.

[0126] The optical system according to the invention as defined above may be used in a vehicle or in a building.

[0127] It can be used specifically as follows: - as interior partitions in buildings (between two rooms or within one space), in road, rail, ship or aircraft vehicles (between two compartments, in taxis, buses, trains, etc.), especially as glazing shower or bath walls, - Glass doors (front doors or service doors), windows (single, double or triple glazed), ceilings, tiles (floor or ceiling), toilet doors, glazing parts of residential or street furniture, - Glazing for motor vehicles (cars, trucks, buses, coaches etc.) and therefore road, rail and marine (boat) vehicles, windscreens, side glazing, roof glazing etc. - projection or back projection screens, - Shop windows, especially booth windows.

[0128] Of course, it may form all or part of the glazing (such as transom-type partitions and windows).

[0129] Thus, the glazing of the building may comprise optical systems as described above, in particular monolithic, double or triple glazing (with or without laminated glazing) partitions, windows etc.

[0130] Thus, a vehicle glazing unit, in particular a glazing unit for a road vehicle, may comprise the aforementioned optical system, in particular a windshield (wherein the optical system forms one or more peripheral bands), a sunroof, a (monolithic or laminated) side glazing, in particular a quarter glass.

[0131] The laminated glazing according to the invention, in particular for cars (windshields etc.) or trucks, may be curved (bent) in one or more directions, in particular for the first sheet, the second sheet and with a radius of curvature between 10 cm and 40 cm. In the case of buses, trains and tractors, it may be flattened.

[0132] The optical system according to the invention may be incorporated into a stacked, in particular curved, glazing, between a first and a second glazing, called the outer and inner glazing respectively, forming a peripheral strip over the upper part of the glazing, the edge faces referred to as the outer faces of the stack being masked from the outside by a first opaque peripheral layer, in particular enamel over the outer glazing (preferably on face F2), and / or the edge faces referred to as the inner faces of the stack being masked from the inside by an opaque peripheral layer, in particular enamel over the inner glazing (for example on face F4, or even on face F3).

[0133] The curved laminated glazing according to the invention, in particular the windscreen or side glazing, preferably has at least 70%, or even at least 75%, or even at least 80% -T in clear glass panes. L may have.

[0134] The curved laminated glazing according to the invention, in particular the sunroof, has a light transmission T of up to 10%, even 1% to 6%. L may have.

[0135] For car roofs, at least one or all of the following criteria are preferred: - Energy transmission T up to 10%, even 4-6% E , - Energy reflectance R of at most 10%, preferably 4-5% E (Preferably on the surface F1 side), - total transmittance of solar energy TTS less than 30%, even less than 26%, or even 20-23%.

[0136] The bending of the first and second glazing (particularly the windshield) may be in one or more directions, for example as described in WO 2010 / 136702.

[0137] At least one of the glazings (preferably the exterior glass) is tinted in order to reduce heating in the passenger compartment or to reduce the use of air conditioning, and the laminated glazing may also have a layer that reflects or absorbs solar radiation, preferably on face F4 or on faces F2 or F3, in particular a transparent electrically conductive oxide layer known as a "TCO layer" (on face F4), or even a stack of thin layers comprising at least one TCO layer, or a stack of thin layers comprising at least one silver layer (on F2 or F3), the or each silver layer being arranged between dielectric layers.

[0138] The optical system according to the invention can be used in combination with other electrically controllable devices, such as those with electroluminescent systems (sets of inorganic point sources LEDs, organic diodes or OLEDs, TFELs (with thin films)). Both can be opposite or adjacent in a laminated glazing (laminated interlayer).

[0139] The optical system according to the invention can be used in particular in laminated glazing, in combination with other electrically controllable devices, for example electroluminescent electrically controllable devices, in particular LEDs, OLEDs, TFELs, etc. Other details and features of the invention will become apparent from the following detailed description given in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0140] [Figure 1] FIG. 1 shows a schematic cross-sectional view of an optical system 1000 having an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in conjunction with a static polarizer 10 in a first embodiment of the present invention.

[0141] [Figure 1] FIG. 2 is a front view of electrodes used in the variable polarizer of FIG. 1, which are in the form of strips and are powered in pairs.

[0142] [Diagram 2]FIG. 3 shows a schematic cross-sectional view of an optical system 1000' consisting of an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in association with a static polarizer 10' in a second embodiment of the present invention.

[0143] [Diagram 3] FIG. 4 shows a schematic cross-sectional view of an optical system 1001 consisting of an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in association with a polarization-sensitive electrically controllable device 20 in a third embodiment of the present invention.

[0144] [Figure 4] FIG. 5 is a perspective schematic partial view of the variable polarizer of FIG. 1 in a first functional state, which is an off state.

[0145] [Diagram 5] FIG. 6 is a perspective schematic partial view of the variable polarizer of FIG. 1 in a second state, which is the on-state, at a given voltage U2.

[0146] [Figure 6] FIG. 7 is a perspective schematic partial view of a system 1002 including a variable polarizer and an AC static polarizer having a similar structure to the variable polarizer but without electrodes, in a first functional state of the variable polarizer, which is an off state.

[0147] [Figure 7] FIG. 8 is a perspective schematic partial view of the variable polarizer and the alternating current static polarizer of FIG. 7 in a second functional state of the variable polarizer, which is an on state.

[0148] [Figure 8] 9 is a perspective schematic partial view of the variable polarizer of FIG. 1 with a variable polarizer in a first functional state of the variable polarizer, which is an off state, in a variant of FIG. 7 in which the alternating current static polarizer is rotated by 90°, and an alternating current static polarizer having a structure similar to the variable polarizer but without electrodes.

[0149] [Figure 9] FIG. 10 is a perspective schematic partial view of the variable polarizer and the alternating current static polarizer of FIG. 9 in a second functional state, which is an on state.

[0150] [Figure 10] FIG. 11 shows a set of five curves corresponding to the total transmittance TT as a function of wavelength λ from 380 to 630 nm for a variable polarizer illuminated with light polarized along (parallel to) r2.

[0151] [Figure 11] FIG. 12 shows a set of five curves corresponding to the total transmittance TT as a function of wavelength λ from 380 to 630 nm for a variable polarizer illuminated with light polarized perpendicular to r2.

[0152] [Figure 12] FIG. 13 shows a schematic cross-sectional view of a glazing comprising an optical system 2000 according to the invention.

[0153] [Figure 13] FIG. 14 shows a schematic cross-sectional view of a laminated glazing comprising an optical system 3000 according to the invention.

[0154] [Figure 14] FIG. 15 is a schematic cross-sectional view of a laminated glazing comprising an optical system 3000 according to the invention, which in a variant of FIG. 14 adds a polarization-sensitive electrically controllable device 20 in addition to the variable polarizer 100 and the static polarizer 10 .

[0155] [Figure 15] FIG. 16 shows a front view of laminated glazing comprising an optical system 4000 according to the invention.

[0156] [Figure 16] FIG. 17 shows a schematic cross-sectional view of a laminated glazing comprising an optical system 4000 according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0157] Elements illustrated in the drawings are not to scale.

[0158] Figure 1 shows a schematic cross-sectional view of an optical system 1000 having an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in conjunction with a static polarizer 10 (a stretched plastic film containing dichroic dyes) in a first embodiment of the present invention. Figure 2 shows a front view of the electrodes used in the variable polarizer 100 of Figure 1, which are in the form of strips and are powered in pairs.

[0159] Define a Cartesian coordinate system X, Y, Z.

[0160] The electrically controllable polarizer 100 in this case is characterized by a first direction r1 anchoring the surface of the liquid crystal on the output side (on the side of its coplanar electrodes 21, 22) (OFF state) and further characterized by a second direction r2 anchoring the surface of the liquid crystal on the opposite side of the output.

[0161] The variable polarizer 100 has first and second functional states: In a first functional state, in this case the OFF state, from unpolarized incident light (on its side of the coplanar electrodes 21, 22) (schematically represented by vertical components Pa and Pb of equal intensity, where k is the propagation vector of the light along Z), the variable polarizer can deliver polarized output light having a first component P1 of the polarizing electric field along the axis X (perpendicular to r1) and a second component P2 of the polarizing electric field along the axis Y perpendicular to Y, with a first polarization ratio, which is defined by:

[0162]

number

[0163] rp1 is preferably at least 70% or 90%, or even at least 95%. T1 is the total transmittance along X from 380 nm to 800 nm, and T2 is the total transmittance along Y from 380 nm to 800 nm (so P1 is super-dominant over P2).

[0164] In the second functional state, which is the on-state, at voltage U2 (between two electrodes in a coplanar strip): From unpolarized input light, the variable polarizer can deliver polarized output light with a second polarization ratio, which is defined by:

[0165]

number

[0166] rp2 is at least 30%, or even at least 50% or 60%. T'1 is the total transmittance along the first axis at wavelengths between 380 and 800 nm and T'2 is the total transmittance along the second axis at wavelengths between 380 and 800 nm for a voltage U2b between the third and fourth electrodes.

[0167] P2 is preferably dominant over P1.

[0168] The polarization of the output light of the variable polarizer can be elliptical.

[0169] And, of course, the variable polarizer has multiple functional states in the on state: in particular, there is a threshold voltage at which the anchoring force of the liquid crystal is overcome for a portion of the liquid crystal, and the more the voltage is increased the more the liquid crystal realigns, up to a saturation voltage, which is preferably up to 80V.

[0170] We can then have the following polarization ratio r(U2), which varies as a function of the applied voltage U2:

[0171]

number

[0172] Optionally, depending on requirements, a static polarizer 10 is added, so that in the off state there is no more light (or almost no light) - (represented by the cross in Figure 1) - and in the on state there remains a little light along the P2 axis (at U2).

[0173] More specifically, variable polarizer 100 includes a stack of (physical, solid) layers in this order: a first transparent dielectric element 1' having main faces 11' and 12', in this case made of glass - or in an alternative form plastic, such as PET - with a thickness of 1.1 mm, - first and second transparent electrodes in separate strips 2, including a first strip 21 and a second / first strip 22 between insulating strips 23; - a layer of indium tin oxide ITO with a sheet resistance of 100 Ω / sq., more generally 5-300 Ω / sq.; a first unidirectional planar anchor layer 4', transparent in the direction r1 along Y, on the first transparent dielectric element 1' (face 11') and on the strips 21, 22; a colored dielectric electroactive layer 3, in contact with the first anchor layer 4′, having a main surface called face FA3 on the side of the other surface and a main surface called opposite face FA4, in this case having a thickness Ep1 (less than 20 μm) and made of a material comprising: - LCD, - one or more dichroic dyes (in solution), - spacers, in this case glass beads, which are dispersed in the material; a layer 3, which is sealed at the periphery by a polymeric seal 5, for example made of an epoxy acrylate, in this case a cyanoacrylate; a second transparent anchor layer 4, in this case unidirectionally anchored in a direction r2 perpendicular to a direction r1 parallel to X, - a second transparent dielectric element 1 (of layer 4) having main faces 11 and 12, in this case glass - or in an alternative form plastic, such as PET - with a thickness of 1.1 mm.

[0174] For power supply via a power source, conductive tapes (not shown), in particular metallic conductive tapes, for example made of copper, are fixed by adhesive bonding along and on the peripheral edge and in contact with the electrodes 21, 22 (one tape per electrode, the tape preferably on the opposite edge). These tapes are then connected to the power supply. The edge faces of the electrodes 21, 22 and the edges of the electroactive layers are preferably set back relative to the edges of the rectangular (square) or other shaped elements 1, 1'. The thickness of the (glass) elements 1, 1' may be, for example, 0.7 mm to 4 mm. They may be preferably more than 100 μm, up to 300 μm thick, for a relatively good mechanical strength of the assembly and / or ease of use and handling, but may go down to, for example, 50 μm, if a relatively high flexibility is desired.

[0175] In the following the preparation process is described more precisely.

[0176] The first anchor layer 4' is therefore a layer which induces (without an electric field) a unidirectional planar anchoring in the direction r1 of the liquid crystal at the surface in contact with this layer 4.

[0177] A first anchor layer 4' is deposited on the ITO strips 21 and 22 and between the strips 23 by spin-coating an approximately 500 nm thick solution of polyvinyl alcohol (PVA; Sigma-Aldrich; molecular weight 27 kDa) on the first element 1'.

[0178] The first anchor layer 4' is then rubbed in a direction r1 parallel to the strips extending in a direction r0 which is parallel to the direction r1.

[0179] The second anchor layer 4' is therefore a layer which induces (without an electric field) unidirectional planar anchoring of the second liquid crystal in the direction r2 at the surface in contact with this layer 4'.

[0180] The second anchor 4 is deposited on the second element 1 by spin-coating a solution of polyvinyl alcohol (PVA; Sigma-Aldrich; molecular weight 27 kDa) with a thickness of about 300 nm. The second anchor layer 4 is then rubbed in a direction r2 perpendicular to r1.

[0181] The electroactive layer of the liquid crystal 3 consists of nematic liquid crystal (98% by weight) together with a black dichroic dye (2% by weight) called S428 sold by Mitsui Chemicals. The thickness of the electroactive layer is 10 μm.

[0182] As shown in FIG. 2, for example, the insulating strips 23 form a serpentine arrangement, with a first zone of the electrically conductive layer being separated (insulated) from a second zone of the layer by a first portion 23a of a first insulating strip of the coil and by a last portion 23b of the last insulating strip of the coil.

[0183] Conductive strips 21 and 22 are parallel to r0 and r1.

[0184] Such an arrangement of insulating strips may be provided by removing the electrically conductive layer, in particular by means of a femtosecond laser beam, for example with a diameter of 30 μm and strips of 15 μm. The limit of the thickness of the strips is determined by the size of the laser beam. The limit of the distance between the strips is determined by the motion of the laser beam.

[0185] The liquid crystal in this case exhibits positive dielectric anisotropy.

[0186] FIG. 3 shows a schematic cross-sectional view of an optical system 1000′ consisting of an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in association with a static polarizer 10′ (a stretched plastic film containing a dichroic dye) in a second embodiment of the present invention, which differs from the first embodiment in that the static polarizer 10′ is rotated by 90° and therefore cuts the polarized light along P2.

[0187] FIG. 4 shows a schematic cross-sectional view of an optical system 1001 consisting of an electrically controllable variable polarizer 100 using liquid crystals and dichroic dyes in association with a polarization-sensitive electrically controllable device 20 in a third embodiment of the present invention.

[0188] The apparatus 100 is similar to that described in FIG.

[0189] Apparatus 20 may have a similar layer stack as apparatus 10, with the following modifications: - directional anchor layer along b, - Planar anchor layer, - planar electrodes (on either side of the electroactive layer), hence a vertical electric field (along Z), - nematic liquid crystals with focal conic domains, in particular EFHCD, - An optionally coloured electroactive layer, of the PSCL type (comprising a cross-linked polymer).

[0190] FIG. 5 is a perspective schematic partial view of the variable polarizer of FIG. 1 in a first functional state, which is an off state.

[0191] At the surface of the anchor layer 4, the liquid crystal 312 (defined by the director n2) and the dichroic dye 322 are (generally) parallel to r2.

[0192] At the surface of the opposing anchor layer 4', the liquid crystal 310 (defined by the director n1) and the dichroic dye 320 are (generally) parallel to r1.

[0193] This antagonistic action forces the nematic liquid crystal to undergo a twist deformation, and the dichroic dye is controlled by the nematic.

[0194] In the thickness of the electroactive layer 3, the liquid crystal 311 (defined by the director n3) and the dichroic dye 321 form an angle (approximately) with r1 and r2.

[0195] FIG. 6 is a perspective schematic partial view of the variable polarizer of FIG. 1 in a second state, which is the on-state, at a given voltage U2.

[0196] At the surface of the anchor layer 4, the liquid crystal 312 (defined by the director n2) and the dichroic dye 322 remain (generally) parallel to r2.

[0197] In the thickness of the electro-active layer 3, the liquid crystals 311 (defined by the director n3) and the dichroic dye 321 tend to align generally along r2.

[0198] At the output, the polarization P1 perpendicular to r1 is reduced and may be quasi-off.

[0199] The first polarization ratio is defined for polarization P1 (perpendicular to r1) as follows:

[0200]

number

[0201] The second polarization ratio is defined for polarization P2 (parallel to r1 and perpendicular to P1) as follows:

number

[0202] T1 is the average total transmittance from 380 to 640 nm along the axis of P1, and T2 is the average total transmittance from 380 to 640 nm along the axis of P2. A Perkin Elmer Lambda 900 type spectrometer was used.

[0203] The relative evaluation of the ratio of r1 to r2 as a function of the applied voltage U2 is given in Table 1.

[0204] [Table 1]

[0205] At zero voltage, the polarization along P1 is nearly perfect.

[0206] As the voltage increases, the component P2 increases.

[0207] FIG. 7 is a perspective schematic partial view of a system 1002 including a variable polarizer and an AC static polarizer having a similar structure to the variable polarizer but without electrodes, in a first functional state of the variable polarizer, which is the off state (described in FIG. 5).

[0208] The AC static polarizer 3' has the same unidirectional anchor layers 40, 40' with r4 and r5 that reproduce r1 and r2, and has twisted nematic liquid crystals between the surface 40 (nematic 315 and dye 325) and the core of the passive liquid crystal layer 3' (nematic 314 and dye 324) and the surface 40' (nematic 313 and dye 323).

[0209] FIG. 8 is a perspective schematic partial view of the variable polarizer and the alternating current static polarizer of FIG. 7 in a second functional state of the variable polarizer, which is the on state (illustrated in FIG. 6).

[0210] FIG. 9 is a perspective schematic partial view of a system 1002 having the variable polarizer of FIG. 1 in a first functional state of the variable polarizer, which is the off state, in a variant of FIG. 7 in which the alternating current static polarizer 3'' is rotated 90 degrees, and an alternating current static polarizer 3' having a structure similar to the variable polarizer but without electrodes.

[0211] FIG. 10 is a perspective schematic partial view of the variable polarizer and the alternating current static polarizer 3'' of FIG. 9 in a second functional state, which is the on state.

[0212] FIG. 11 shows a set of five curves corresponding to the total transmittance TT as a function of wavelength λ from 380 to 630 nm for a variable polarizer illuminated with light polarized along (parallel to) r2. Curve 1 is the on mode (voltage U2 equal to 80V). Curve 2 is the on mode (voltage U2 equal to 60V). Curve 3 is the on mode (voltage U2 equal to 40V). Curve 4 is the on mode (voltage U2 equal to 20V). Curve 5 is the off mode (voltage U2 equals 0V). The total transmission TT is approximately zero in the off state of the variable polarizer and increases as a voltage is applied.

[0213] FIG. 12 shows a set of five curves corresponding to the total transmittance TT as a function of wavelength λ from 380 to 630 nm for a variable polarizer illuminated with light polarized perpendicular to r2. Curve 1 is the off mode (voltage U2 equal to 0V). Curve 2 is the on mode (voltage U2 equal to 20V). Curve 3 is the on mode (voltage U2 equal to 40V). Curve 4 is the on mode (voltage U2 equal to 60V). Curve 5 is the on mode (voltage U2 equal to 80V). The total transmittance TT increases with applied voltage.

[0214] Assembly Example

[0215] FIG. 13 shows a schematic cross-sectional view of a glazing assembly 2000 including a transparent sheet 7 (of any possible thickness) comprising an optical system 1000 according to the invention.

[0216] Static polarizer 10 is bonded to a transparent glass or plastic (eg rigid) sheet 7 by optical adhesive 60 and is also bonded to variable polarizer 100 by optical adhesive 61 .

[0217] For example, this is a divider (vertical position).

[0218] The assembly may form part of a multiple glazing (double or triple glazing). In the case of double glazing, the system 1000 may be on face F1 (conventionally on the outside), F2, F3; F4 (conventionally on the inside). In the case of triple glazing, the stack may be on face F1 (on the outside), F2, F3; F4 (on the outside). The sheet 7 may be of the same dimensions as the system 1000 or may be larger.

[0219] The glazing assembly 2000 can be: a shower wall, preferably on the outer face of the shower wall or element 7; - preferably curved vehicle glazing, in particular in a car: roof, side glazing, windscreen, rear window or curved glazing on the inner surface (surface "F4") of element 7.

[0220] In particular, the glazing assembly 2000 can function as a projection screen.

[0221] FIG. 14 is a schematic cross-sectional view of a laminated glazing 3000 comprising an optical system 1000 according to the present invention, including a static polarizer 10 coupled to a variable polarizer 100 by an optical adhesive 60 .

[0222] The laminated glazing 3000 has: - a first additional glass sheet 8, which is transparent; a lamination interlayer 70 of thermoplastic, in particular EVA or PVB, - a second additional glass sheet 8' or a transparent plastic sheet, The major inner surfaces of the first and second additional sheets, designated F2 and F3, face each other, and the optical system 1000 is between surfaces F2 and F3, within a sub-millimeter stack interlayer, or up to 2 mm.

[0223] In manufacture, three interlayer sheets may be used: two complete sheets 72, 73 against the inner faces of sheets 8, 8', and a central sheet 71 with an opening to accommodate the system 1000. After lamination, the interlayer between the sheets (indicated by dots) is not necessarily discernible. The opening is preferably closed on one side rather than completely open. Thus, the entire edge of the system 1000 is surrounded by the laminated interlayer 70. Of course, for the power supply, connections may exit the system 1000 and even protrude beyond one or more side edges of the glazing.

[0224] Alternatively, two intermediate layer sheets could be used and if the system 1000 is sufficiently thin, for example at most 0.2 mm thick, the central sheet with the hole would not be necessary.

[0225] One of the sheets 8 or 8' may be colorless or colored (grey, green, bronze, etc.) and the glazing of the other may be clear or ultra-clear 8' or 8. One of the first interlayer sheets may be colored (grey, green, bronze, etc.) and the other(s) may be clear or ultra-clear. One of the sheets 8 or 8' may be replaced by a plastic sheet such as polycarbonate or PMMA (especially with a PU laminated interlayer).

[0226] The edges of the laminate interlayer 70 may be recessed (eg, by up to 5 mm) from the edges of the sheets 8, 8'.

[0227] The system 1000, for example, covers substantially the entire major surface of the sheet 8, and in this case is even centrally located. On either side of the system 1000 there is a PVB of the same width.

[0228] The glazing 8, 8' may be flat or curved, and the system 1000 may accommodate the curvature(s) of the glass sheets 8, 8', which in this case are curved.

[0229] The optical system 1000 can be a partition or a roof of a vehicle. For example, for a roof of a vehicle: - Sheet 8 is the outermost, curved, optionally coloured and for example 3 mm. - Sheet 8' is the innermost, curved and preferably clear or ultra clear, for example less than 3 mm. The laminated interlayer 70 is made of PVB and may be acoustically effective, in particular two- or three-ply (sheets 71 or 72 or 73).

[0230] Thus, the roof may also be of a color that can be changed with voltage U1 or U2, for example from dark blue to light blue.

[0231] Figure 15 is a schematic cross-sectional view of a laminated glazing comprising an optical system 3000 according to the present invention, in which, in a variant of Figure 14, a polarization-sensitive electrically controllable device 20 is added in addition to the variable polarizer 100 and the static polarizer 10, and the electrically controllable device is adhered to the static polarizer 10 by an optical adhesive 60'.

[0232] In one variant, the static polarizer 10 is eliminated.

[0233] 16 and 17 show respectively a front view and a schematic cross-sectional view of a laminated glazing comprising an optical system 4000 according to the invention.

[0234] The laminated glazing 4000 differs from that of FIG. 14 in that the optical system 1000 covers a surface portion of the sheet 8, in particular a peripheral strip, for example along the upper longitudinal edge H over substantially the entire length of the laminated glazing.

[0235] This is for example the windshield of a car.

[0236] This optical system 1000 is in the marginal zone, where the LT criterion and the absence of haze criterion are more liberal than in the central zone ZB.

[0237] Thus, the optical system 1000 may be of a voltage-variable color, for example from dark blue to light blue.

[0238] As shown in FIG. 17 (cross-sectional view), the width 7a of the central intermediate layer 73 between the optical system 1000 and the lower longitudinal edge B is greater than the width 7b of the central intermediate layer 73 between the optical system 1000 and the upper longitudinal edge H.

[0239] Alternatively, or in addition, it may be present along the entire length or part of the length of the lower longitudinal edge B of the windscreen.

[0240] As shown in FIG. 16 (front view of the interior side of the vehicle), the windscreen has a first opaque frame, e.g. made of enamel (black, etc.) 91'-94', on the short and long edges of the free surface (F4) 82' of the inner sheet 8', and a second opaque frame, e.g. made of enamel (black, etc.) 91-94, on the short and long edges of the free surface (F1) 82 of the outer sheet 8.

[0241] The edge faces of the optical system 1000 at the lower longitudinal edge and also at the lateral edges may be between (face) the layers 92, 92', 93, 93', 94, 94' of the enamel frame. For example, the connections and other current supply strips (for U1 and U2) may also be masked by these layers 92, 92', 93, 93', 94, 94'.

[0242] In one variant, it is the roof of a car, for example having a tinted outer glass 8 and / or a tinted PVB 71 and an optical system 1000 covering substantially the entire main surface of the glass 8, 8'.

Claims

1. A liquid crystal optical system (1000, 1000', 1001, 1002, 1003) comprising a variable polarization electrically switchable device called a variable polarizer (100, 100', 101, 102), said variable polarizer comprising: first and second transparent electrodes (21, 22) having an electric field E2 between them, said first and second electrodes being coplanar and forming alternating first and second electrically conductive strips (21, 22) of different potentials, in particular elongated in the direction r0; an electroactive layer (3) made of a material containing nematic liquid crystals and dichroic dyes; A liquid crystal optical system (1000, 1000', 1001, 1002, 1003) comprising:

2. 10. The liquid crystal optical system (1000, 1000', 1001, 1002, 1003) of claim 1, wherein the liquid crystal is twisted nematic in the off-state of the variable polarizer.

3. 3. The liquid crystal optical system (1000, 1000', 1001, 1002, 1003) of claim 1 or 2, wherein the variable polarizer does not have a static polarizing film.

4. 3. A liquid crystal optical system (1000, 1000', 1001, 1002, 1003) according to claim 1 or 2, wherein the electric field E2 is an alternating electric field.

5. the variable polarizer having first and second functional states: In the first functional state, which is an off state, from unpolarized incident light, the variable polarizer can transmit output light having a first component of an electric field P1 along a first axis and a second component of an electric field P2 along a second axis perpendicular to the first axis, with a first polarization ratio defined by: [Equation 1] rp1 is at least 70%, or even at least 90%, t1 is the total transmittance along said first axis at wavelengths from 380 to 800 nm, and T2 is the total transmittance along said second axis at wavelengths from 380 to 800 nm; in said second functional state being the on state: From the unpolarized input light, the variable polarizer can deliver output light with a second polarization ratio defined by: [Equation 2] rp2 is at least 30%, or even at least 50%, T'1 is the total transmittance along the first axis at wavelengths between 380 and 800 nm, and T'2 is the total transmittance along the second axis at wavelengths between 380 and 800 nm for a non-zero voltage between the first and second electrodes; A liquid crystal optical system (1000, 1000', 1001, 1002, 1003) according to claim 1 or claim 2.

6. the first and second electrically conductive strips are elongated in a direction r0; The variable polarizer comprises: - a unidirectional planar anchor layer (4') on the main face of the electroactive layer and on the first and second electrodes, in particular in a direction r1, where P1 is perpendicular to r1 and P2 is perpendicular to r1; - and another unidirectional planar anchor layer in a direction r2, preferably separate from r1, on another major surface of said electroactive layer (3); 3. The liquid crystal optical system according to claim 1 or claim 2, comprising:

7. r1 forms an angle with r2 of 90°±15°, more preferably 90°±5°; r0 forms an angle with r1 of at most 15°, or even at most 5°, and said liquid crystal has a positive dielectric anisotropy; or r0 forms an angle with r1 of 90°±15°, or even at most 90°±5°, and said liquid crystal has negative dielectric anisotropy; 7. The liquid crystal optical system according to claim 6.

8. 3. The liquid crystal optical system according to claim 1, further comprising a static polarizer opposite the variable polarizer.

9. A liquid crystal optical system (2000, 3000, 4000) as described in claim 1 or claim 2, wherein the variable polarizer and the static polarizer or electrically controlled polarization-sensitive device are separated or connected by a transparent bonding layer, in particular an optical adhesive, or a thermoplastic layer, in particular a lamination interlayer, or the variable polarizer has an element carrying the first and second electrodes, which forms the static polarizer.

10. 3. The liquid crystal optical system of claim 1, further comprising an electrically controllable polarization-sensitive device facing the variable polarizer, in particular the electrically controllable polarization-sensitive device being a variable scattering electrically controllable device using nematic liquid crystals, preferably including focal conic domains.

11. 11. The liquid crystal optical system of claim 10, wherein the domain is a focal conic domain, in particular having two defect lines, in particular one elliptical and the other hyperbolic, and preferably the focal conic domain forms a linear network parallel to direction b, in particular for anchoring the liquid crystal on the surface.

12. 12. The liquid crystal optical system of claim 11 , wherein the variably scattering, electrically controllable device using liquid crystals comprises an electro-active layer, the electro-active layer comprising the liquid crystals and having the direction b forming an angle of 0°±15° or 90°±15° with the polarization P1 of the output light in the off state of the variable polarizer.

13. A laminated glazing unit (3000, 4000) comprising: a first additional glass sheet (8), which is transparent; a laminating interlayer of thermoplastic, in particular EVA or PVB, a second additional glass sheet (8'), or a transparent plastic sheet, wherein the main inner surfaces, designated F2 and F3, of the first and second additional glass sheets face each other, and the optical system described in claim 1 or claim 2 is preferably between the surfaces F2 and F3, and preferably within the lamination interlayer.

14. Vehicle glazing (3000, 4000) comprising an optical system as described in claim 1 or claim 2.

15. Glazing for buildings (2000) comprising an optical system as described in claim 1 or claim 2.

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