Electrically controllable system having variable optical properties

0001The present invention relates to electrically controllable systems with variable optical properties, and more specifically to glazings whose luminous diffusion and / or light transmission can be modified under the effect of an appropriate power supply.

0002There is indeed an increased demand for so-called "smart" glazing which can be modulated some properties at will. Controlling, modifying the level of light diffusion of the glazing thus makes it possible to control the degree of vision through the glazing, in particular so that it is transparent or on the contrary diffusing, thus preventing the identification of persons / objects on the other side of the window. glazing. The applications of such glazings are varied: one can thus think of equipping the internal partitions between the rooms in a building, especially in offices, or between two zones / compartments of means of locomotion terrestrial, air or sea, or to equip showcases or any type of container. In general, they can also equip any building window or means of locomotion (train window, boat cabin windows or aircraft)

0003There are currently various families of electrically controllable light scattering / transmission functional systems (hereinafter referred to as "functional systems").

0004A first family of functional systems is known as liquid crystal glazing. It is based on the use of a film placed between two conductive layers and based on a polymer material, in which droplets of liquid crystals, in particular nematic with positive dielectric anisotropy, are dispersed. The liquid crystals, when the film is energized, are oriented along a preferred axis, which allows vision. When the crystals are not aligned, the film becomes diffused and prevents vision. Examples of such films are described in particular in European patents EP-0 238 164, and US-4,435,047, US-4,806,922, US-4,732,456. This type of film, once laminated and incorporated between two glass substrates, is marketed by the company SAINT-GOBAIN VITRAGE under the trade name "Priva-Lite". In fact, all liquid crystal devices known as "NCAP" (Nematic Curvilinearly Aligned Phase (s) or "PLDC" (Polymer Dispersed Liquid Crystal) can be used.

0005Another family is that commonly referred to as an optical valve: it is generally films comprising a polymer matrix, optionally crosslinked, in which are dispersed micro-droplets containing particles which have the property of being placed according to a privileged direction under the action of an electric or magnetic field. As a function in particular of the potential applied across the conductive layers placed on either side of these films and the concentration and nature of the orientable particles, the films have variable optical properties. It is known, for example, from patent WO-93/09460, an optical valve based on a film comprising a crosslinkable polyorganosiloxane matrix and orientable inorganic or organic particles, more particularly light-absorbing particles such as polyiodide particles. . When the film is switched on, the particles intercept much less light than when it is off: this system thus makes it possible to obtain glazings with variable light transmission, generally associated with an equally variable light diffusion.

0006Whether they are optical valves or liquid crystal systems, these systems are usually in the form of a polymer film. In order to ensure its power supply, it is usually available between two electroconductive layers, in particular transparent layers, for example doped metal oxide of tin-doped indium oxide (ITO) or fluorine-doped tin oxide (SnO) type.₂F). In addition, the film with its two conductive layers is usually provided on at least one of its faces, and each of them, a carrier / protective substrate. This one is usually transparent. It can be chosen rigid or semi-rigid, mineral or organic, for example be made of glass, acrylic polymer of the polymethyl methacrylate PMMA type. It can also be flexible, especially polyethylene terephthalate PET. It is thus possible to have a PET / ITO / functional film / ITO / PET type structure, which is in the form of an easily manipulable flexible sheet. This assembly (polymer + electroconductive layers + at least one carrier substrate) can then be laminated to at least one transparent rigid substrate of the glass type using at least one polyvinylbutyral PVB type organic polymer assembly layer, ethylenevinylacetate. EVA or some PU polyurethanes.

0007We have sought to add other features to liquid crystal glazing, in particular to play not only on their level of light diffusion but also on their level of light transmission, using dyes. EP-0 156 615 and EP-0 121 415 thus describe, for example, pleochroic-type dyes which are dissolved in the droplets of liquid crystals, which makes it possible to obtain both dark / colored glazings. and diffusers in the de-energized state, and both clear and non-diffusing in the energized state. It is thus possible to obtain a "shutter" effect making it more attractive to use these glazings for exterior applications, for example as building facade glazing or roof-car glazing.

0008However, these external applications require a lot of glazing, and it has been found that functional systems with additional dyes (such as liquid crystal glazings) or functional systems with polarizing particles themselves providing a coloring effect, in particular being The same type of dichroic type tended to have a much shorter life span than those which did not, and all the more clearly because they were used outdoors.

0009The object of the invention was therefore to remedy this drawback by proposing an improvement of the electrically controllable diffusion / light transmission functional systems, in particular those using dichroic dichroic coloring or polarizing particles, improvement intended in particular to increase their lifespan, to increase their durability.

0010The invention firstly relates to an electrically controllable system with variable light transmission / transmission which comprises a functional film provided with electroconductive layers. This film comprises so-called "active" elements either in the form of particulates including polarizing (optical valve system) or liquid crystal (liquid crystal system) associated with dichroic dyes, and suspended in a medium. It is intended according to the invention to provide the system with means (s) preventing / compensating for the photoreduction degradation of at least a portion of the active elements, in particular that of dichroic dyes (in the case of liquid crystal systems) or polarizing particles themselves (in the case of optical valve systems).

0011The invention has indeed discovered the mechanism that caused the premature aging of the systems, a photoreduction mechanism that tended to irreversibly degrade dichroic dyes and polarizing particles when the systems were subjected to intense ultraviolet radiation and / or prolonged. The solution then consisted in implementing means for combating this degradation, these means being aimed either at preventing this photoreduction, or, preferentially, at making it possible, in a way, to "regenerate" the dyes, put in reduced / degraded form in them. continuously reoxidizing, thus "offsetting" the photochemical reduction suffered by them.

0012According to a first variant, the means preventing the degradation by photoreduction comprises the use of at least one of the two electroconductive layers in the form of a multi-component layer comprising a doped metal oxide-based conductive layer physically isolated from the functional film. by at least one barrier layer of different chemical nature.

0013By "multi-component" layer is meant a superposition of at least two layers made of different materials which generally constitute the electroconductive "layer" within the meaning of the invention. The doped metal oxide in question may be doped tin oxide, especially with fluorine SnO₂ : F, indium oxide doped with tin ITO, doped zinc oxide, for example with aluminum, all these materials are well known.

0014The term "physically isolated" means that there is no direct contact between the functional film and the doped metal oxide layer. The inventors have indeed realized that it is this direct contact that appeared to be responsible for the premature degradation of the system, a hypothesis to explain it that the metal oxide would have sufficient photocatalytic properties to cause degradation of the film which is contiguous to it. The solution of the invention was therefore to use a barrier layer, to be able to continue to use electroconductive layers doped metal oxide without bearing the disadvantages (these layers are indeed very interesting elsewhere because it masters well the manufacture, in particular by pyrolysis of the CVD type or vacuum cathode sputtering, and that they make it possible to reconcile at the best level of electrical conductivity and transparency).

0015This barrier layer may be essentially metallic, especially nickel, chromium, nickel-chromium alloy. In this case, it is also electrically conductive, but it is preferred to choose relatively thin to prevent it optically modifies the appearance of the glazing, to keep the multi-component conductive layer its level of transparency.

0016The barrier layer may also be chosen from a material with little or no conductive material, such as silicon, or derivatives of silicon, in particular silicon dioxide. Here again, it is advantageous to choose as thin as possible, the thickness sufficient for the physical insulation mentioned above. It is also possible to use silicon nitride Si₃NOT₄, silicon oxynitride SiON or aluminum nitride A_IN. Silicon oxide is, without limitation, the preferred illustration of the family of dielectrics based on non-photocatalytic oxide.

0017The barrier layers, all of them therefore advantageously having no or almost no photocatalytic activity, are therefore generally chosen with a thickness of less than 10 nm and preferably less than 5 nm, for example between 0.5 and 3 nm. (We can also superimpose two barrier layers of different natures if desired). A more radical solution is to eliminate the use of the electroconductive layers based on doped metal oxide, at least on one side of the functional film, and replace it with a conductive material that is not based on oxide.

0018Embodiments of this variant may be a system (for example deposited between two flexible substrates, or a flexible and a rigid):<ul id="ul0001" list-style="none" compact="compact"><li>1) ITO</li><li>2) NiCr or SiO barrier layer₂</li><li>3) functional film</li><li>4) NiCr or SiO barrier layer₂</li><li>5) ITO</li></ul> with the identical "bi-layer" conductive layers on each side of the functional film.

0019One of the two bi-layers may be replaced by a metal monolayer, for example a gold-titanium alloy, or a metal multilayer, for example NiCr / Au / NiCr. It is also possible to combine the use of a multi-component layer on one side of the functional film with a standard doped metal oxide conductive layer: a single conductive layer according to the invention already gives the system a longer service life.

0020The two bi-layers can also be replaced by this monolayer or metal multilayer. The means preventing the degradation then comprises the selection of at least one essentially metallic electroconductive layer (while completely eliminating the use of a doped metal oxide material in at least one of the two conductive layers). It has indeed been found that replacing the usual electroconductive doped oxide layers with metal layers, or at least one of them, considerably increases the lifetime of the system, without the precise reasons being fully explained.

0021This variant has the advantage of simplicity of implementation: metal-type thin-layer deposition technologies available make it possible to control its parameters, in particular the chemical nature, the density, the thickness, in order to obtain the desired properties, especially here a sufficient level of electrical conductivity combined with a transparent character. More particularly, magnetic field assisted sputter deposition technology can be mentioned.

0022The metal layer may advantageously be based on silver or gold, generally a noble metal or alloy containing at least one of them. In this case, it is desirable for the layer to be provided on at least one of its faces (preferably on both sides) with a protective layer and / or with a thinner attachment function, in particular a steel-like metal, Ni alloy NiCr type, Inconel.

0023The metal layer may also be based on a gold-titanium alloy. This alloy is particularly advantageous because titanium seems to be able to stabilize the gold, which makes the protective layers mentioned above optional and even unnecessary.

0024According to a second variant, (alternative or cumulative with the first variant), the means preventing degradation comprises contacting the film provided with its electroconductive layers, on at least one of its faces, with a sheet based on permeable polymer material to oxygen. It turned out that you could also dramatically increase the life of the system in this way. In a simplified / pictorial way, everything happens as if this sheet served as an oxygen "reservoir" for the film or allowed oxygen to pass through from an oxygen source, which has an oxidizing effect that "compensates" "the reducing effect of ultraviolet rays on dyes.

0025Advantageously, the sheet based on polymeric material has an oxygen permeability of at least 10, in particular of at least 20 or 40 cm.³/ cm²/ mm / cmHg, evaluated according to ASTM-D1434. It may especially be polymer (s) belonging to the family of polycarbonates, which have a permeability of about 55 cm³/ cm²/ mm / cmHg (especially those of flexible / flexible type).

0026By way of comparison, the polyethylene terephthalate (PET) sheets usually used have a permeability of 0.3 cm³/ cm²/ Mm / cmHg.

0027The term "sheet" is to be taken broadly: it may be a carrier substrate of the functional film and / or protective sheet and / or sheet allowing its lamination with a rigid substrate and more generally its incorporation in glazing multiple glazing type and / or laminated glazing. In general, this sheet is flexible / flexible.

0028In fact, it is preferable that the electroconductive layer (s) disposed between the functional film and the oxygen-permeable sheet have a certain "porosity" allowing the transfer of oxygen. . Similarly, it can be expected to trap enough oxygen in the permeable sheet so that it can gradually release to the functional film. It is then desirable that this sheet is in at least partial contact with a renewed source of oxygen. If the assembly (functional film + electroconductive layers + foil (s) permeable to oxygen) is intended to be incorporated in a glazing unit so that the permeable sheet (s) are sandwiched between the film and, for example, a rigid substrate that is not permeable to oxygen (laminated glazing structure), it is conceivable to provide the permeable sheet with peripheral means of venting to ensure the renewal of oxygen in the sheet for example by means of capillaries.

0029If the aforementioned assembly is intended to be incorporated in a multiple glazing of the insulating double-glazing type, pariétodynamique glazing, one can arrange the permeable sheet so as to bring it into contact with the inter-air gas blade, air-blade type , preferably providing an air renewal system of the "breathable" glazing type.

0030A preferred embodiment of the invention is in the form of a laminated glazing unit comprising the sequence: rigid substrate / insert sheet / protective sheet / functional film with its electroconductive layers / protective sheet / interlayer sheet / rigid substrate.

0031As mentioned at the beginning of this text, the rigid substrate may be glass, acrylic type such as PMMA or rigid polycarbonate. The intermediate sheet is made of thermoplastic polymer of the PVB, EVA or PU type, and the protective film of the functional film may be flexible of the PET or flexible polycarbonate type (the electroconductive layers on either side of the functional film may be monolayers or stacks of at least two layers).

0032A second preferred embodiment of the invention is in the form of a multiple glazing of the double glazing type, comprising the sequence: rigid substrate / spacer sheet / protective sheet / electroconductive layer functional film / protective sheet / spacer gas strip / rigid substrate.

0033The invention also relates to a double glazing type glazing assembly of the system, wherein the functional film provided with the electroconductive layers, and preferably at least one protective sheet on each of its sides, is stretched in the blade of intermediate gas separating the two rigid substrates of the multiple glazing.

0034Fixing can be done in different ways, in particular by means of fastening and tensioning means, mechanical type positioning means such as shims, spacers, a frame arranged at the periphery of the glazing, in particular between the two substrates at their periphery. The multiple glazing may also be designed so that it can be opened, in particular by a mechanical hinged system for example, in order to make accessible the zone of intermediate gas where the system is located. The system can then be designed to be removable: there is thus a functionalized double glazing, where it is easy to change, clean, repair the functional system and possibly the rigid substrates of the glazing themselves if necessary.

0035It is also preferably provided with peripheral sealing means of the intermediate gas strip. If it is necessary to renew the gas (air) of the gas strip, provision may be made to periodically open the glazing if it is designed so as to be opening, or to provide the peripheral sealing means with type joints (with dessicator) of capillaries.

0036This multiple glazing structure is particularly suitable for implementing the second variant, by choosing as a "gas-blade-side" protective sheet a sheet highly permeable to oxygen, with intermediate gas in the form of air, preferably renewable in a montage of breathable glazing type.

0037Whether it is a laminated glazing unit or a multiple glazing unit, it is therefore possible, according to the invention, to select at least one of the so-called "protective" sheets in the form of an oxygen-permeable sheet of the polycarbonate type. or plexiglass (flexible) and / or select at least one of the electroconductive layers in a metal material of Ag or Au type.

0038These protective sheets also serve as flexible carrier substrates for the functional film.

0039The system according to the invention is preferably provided with an ultraviolet filter, to mitigate the detrimental effects on the active elements and in particular on the dichroic dyes. An ultraviolet filter embodiment consists of in the laminated / multiple glazing structures described above, flipping the glass (the rigid substrate) outside with an additional rigid substrate, via a sheet or a plurality of polymer sheets having ultraviolet filter properties, for example based on PU polyurethane, polyvinyl butyral PVB or ethylene vinyl acetate EVA suitably treated, and possibly flipping in this way the second glass also. Another embodiment, in particular in the case of a laminated structure, consists in using at least one polymer sheet with ultraviolet filter properties as interlayer film between at least one of the protective films of the functional film and a film. rigid substrates. Laminating at least one side of the multiple glazing can also provide the functionality of a shield.

0040The various components of the functional film proper are described below.

0041Preferably, the active elements of the liquid crystal type are in the form of droplets dispersed in the medium, with the dichroic dyes dissolved in said droplets. Indeed, these dyes being in fact molecules of the organic type, with anisotropic absorption coefficient, if one wants to obtain a variation of the light absorption of the glazing (thus a variation of light transmission) coupled with a variation of its electrically controlled light diffusion, it is necessary that the active elements vis-à-vis the light diffusion are closely associated with the dyes.

0042These dichroic dyes may be for example of the type of pleochroic dyes, chosen from the family of diazoquinone derivatives or anthraquinone derivatives.

0043Advantageously, it is possible to select the percentage by weight of dichroic dyes with respect to the active elements with respect to the light diffusion, (namely the polarizing particles or the liquid crystals) in a range between 0.1 and 3%, in particular between 0.5 and 2%. This proportion is judicious for various reasons, taking into account a certain number of parameters, including the solubility limit of the dyes in the droplets, the size of the droplets, the light transmission value referred to in the faded / transparent state of the system in question. depending on the type of active elements and the type of medium used, ...

0044As regards the liquid crystals, these may be of the "NCAP" type, in particular those used in the "Priva-Lite" or "PDLC" glazings, which have been mentioned above. As a rule, their birefringence is between 0.1 and 0.2, it is variable especially according to the medium used, of the order of 0.1 if the polymer of the medium is of the polyurethane (PU) type and the order of 0.2 if it is polyvinyl alcohol (PVA) type.

0045This medium is indeed preferably based on a polymer of the family of PU (latex) and / or PVA, generally prepared in aqueous phase in a proportion of polymers of 15 to 50% by weight relative to water .

0046It has been seen above that with regard to polarizing particle systems, these systems in fact combine an effect vis-à-vis the light diffusion and especially a dye effect on the light transmission.

0047The active elements vis-à-vis the light scattering are advantageously in the form of droplets of average diameter between 0.5 and 3 microns, especially between 1 and 2.5 microns, dispersed in the medium. The size of the droplets depends on a number of parameters, including the ease of emulsification of the active elements in the medium in question. Preferably, these droplets represent between 120 and 220% by weight of the medium, in particular between 150 and 200% by weight, apart from the generally aqueous solvent of said medium.

0048Particularly preferably, liquid crystals are chosen in the form of droplets with a diameter of about 2.5 μm when the medium is based on polyurethane latex, (birefringence of about 0.1) and a diameter. about 1 μm when the medium is rather based on polyvinyl alcohol (birefringence of about 0.2). The size of the droplets may be selected in particular during the preparation of the emulsion by the conditions chosen, in particular the duration and the extent of the agitation caused to make the emulsion, and / or the viscosity of the mixture, viscosity, which it is possible to regulate by the temperature conditions of the mixture to be emulsified and / or by the addition of additives of the surfactant type. Addition of the dyes also changes the equilibrium of the emulsion.

0049It may thus be advantageous to cool the preparation to be emulsified when the medium is made of polyurethane latex (for example at less than 15 ° C., especially between 5 and 10 ° C.).

0050Once the emulsion with the desired droplet diameter has been obtained, it is frozen under these conditions by adding suitable stabilizers.

0051The combination of active elements with respect to the light diffusion and those active with respect to the light transmission, namely the dichroic dyes associated with the liquid crystals or the polarizing coloring particles, makes it possible to obtain glazings which can be at will diffusing or not diffusing and clear or dark. These glazings can thus have a contrast of at least 3, or even at least 5 or 10 and more between their live state and their de-energized state. The contrast is defined by the ratio of the light transmissions of the glazing to the lightest / transparent state (state corresponding generally to the state under tension) and to the darkest / opaque state (state off).

0052These dual function systems have many applications already mentioned, especially for building exterior glazing, roof glazing, or automotive glazing type roof-car, their increased durability through the invention allowing outdoor applications, and well sure also for interior glazing, partitioning in particular. They can also be used to equip windows / portholes with any means of transport such as trains, planes and boats.

0053Another interesting application concerns all display devices, display screens.

0054The invention will be detailed hereinafter with the aid of non-limiting examples illustrated by the following figures:<ul id="ul0002" list-style="none" compact="compact"><li><img file="EP0964288A2_D0001.tif" /><b>figure 1</b>: a laminated glazing unit according to the invention,</li><li><img file="EP0964288A2_D0002.tif" /><b>Figure 2:</b> a double glazing according to the invention.</li><li><img file="EP0964288A2_D0003.tif" /><b>figure 3:</b> a second double glazing according to the invention</li></ul>

<u>EXAMPLE 1</u>

0055This refers to the laminated glazing shown schematically in Figure 1 (without respecting the scales between the various materials shown for ease of reading).

0056Its general structure is as follows: it comprises the functional film itself 1 provided on one of its faces with a transparent electroconductive layer 2 indium oxide doped with tin ITO and on the other of its faces a stack 3 of NiCr / Au / NiCr transparent conductive layers, with the two layers of NiCr 1 nm thick and the Au layer 6 nm thick.

0057This film with conductive layers 1, 2, 3 is provided with two sheets 4, 5 of PET of 175 microns thick, and laminated with two glasses 8, 9 (clear silicodio-calcium glasses of thickness 2 mm) on one side by an interlayer sheet 6 of 0.76 mm thick PVB, and on the other side by two sheets 7, 11 of anti-ultraviolet treated PVB (the electrical supply system is produced in a known manner and not shown / detailed right here).

0058The film 1 is 30 μm thick. It consists of a medium in the form of polyurethane (PU) at 40% by weight prepared in water. in which are dispersed micro-droplets of liquid crystals NCAP type of about 1.5 microns in average diameter and 0.1 birefringence, in a proportion by weight of 165% relative to the PU except the solvent. The micro-droplets contain 1% by weight of a dissolved pleochroic type dichroic dye, giving a dark hue, in the blacks in the off state. This film is obtained by making an emulsion under strong stirring between the liquid crystals in which the dyes and the medium have been dissolved, then forming the film by casting on the PET sheet previously provided with the ITO electroconductive layer. The film after drying to remove the solvent from the medium, is calendered with the second PET sheet provided with the metal layer.

0059This structure illustrates the first variant of the invention, namely the substitution of one of the conventional ITO conductive layers by a metal conductive layer.

0060When it is switched on, the glazing has a non-diffusing state, with a blur of at most 8%, and clear, with a light transmission value T_The according to the illuminant D₆₅ 40%. Off, it is diffusing, with a blur of at least 96%, and dark, with a T_The 10%. This results in a contrast C of about 4. (The blur is defined as the ratio of the diffuse transmission to the total transmission measured at 550 nm).

0061Note that the glazing is here provided with an ultraviolet filter, in this case formed by the two sheets of PVB treated anti-ultraviolet 7, 11, each thickness of 0.76 mm, replacing a sheet interlayer in standard PVB as the PVB sheet 6. The assembly is carried out so that the glass 9 is turned outward.

0062The glazing thus formed was subjected to an accelerated aging test according to the "day" cycle of SAE J 1885 (Society of Automotive Engineers), by exposure to continuous radiation at 0.55 W / nm / m.² wavelength 340 nm, at 90 ° C to the black panel. It withstood degradation for an exposure time of 240 hours (i.e., the difference ΔE * according to the colorimetric system (L *, a *, b *) between the state of the glazing at the moment t and its state at the initial moment t₀, when the glazing is off, remained below or equal to 5 during this period of time).

COMPARATIVE EXAMPLE 1

0063For comparison, the same test was undergone by a glazing identical in all respects to the glazing of Example 1, but instead of using the NiCr / Au / NiCr stack a second layer of lTO identical to the first : This comparative glazing only withstood 70 hours, which corresponds to a lifetime more than three times lower than for the glazing of Example 1 according to the invention.

<u>EXAMPLE 2</u>

0064This also relates to a laminated glazing according to the structure shown in Figure 1.

0065In this example, another type of functional film 1 was used, which makes it possible to obtain a higher contrast C: it is 30 μm thick and consists of a medium with a PU and PVA latex prepared in water at a temperature of 20% by weight, in which are dispersed liquid crystal droplets of NCAP type with a diameter of about 1 μm and a high birefringence, equal to 0.2, in a proportion by weight relative to the PU + PVA latex of about 165%. out of solvent.

0066In these droplets are dissolved 2% of the same dark dichroic dye as in Example 1.

0067This glazing has, in the energized state, a non-diffusing state with a blur of at most 15% and a T_The 30%. Off, it is diffusing with a blur of 100% and a T_The 2%. This achieves a contrast C of 15.

0068This glazing equipped with the ultraviolet filter has undergone the same accelerated aging test as Example 1: it has withstood degradation for 200 hours, according to the same criterion.

COMPARATIVE EXAMPLE 2

0069This Comparative Example 2 is identical to Example 2, except that it uses a second ITO conductive layer rather than a NiCr / Au / NiCr stack. It only withstood 60 hours of the aging test, which corresponds to a life three times lower than that of Example 2 according to the invention.

<u>EXAMPLE 3</u>

0070This example relates to double-glazing very schematically shown in Figure 2.

0071It comprises the functional film 21 provided on each of its faces with a layer 22, 23 of lTO (same functional film and same layers of lTO as in Example 1). This layered film 21, 22, 23 is provided on one of its faces with a sheet 24 of PET identical to the layer 4 of PET of Example 1 and on the other of its faces with a sheet 25 made of soft polycarbonate 175 μm thick. The layer 22 of OT in contact with the polycarbonate sheet 25 is deposited by sputtering so as to have sufficient porosity (vis-à-vis the oxygen).

0072On the side of the sheet 24 made of PET, there are then two sheets of PVB 26, 28 anti-ultraviolet (like the sheets 7, 11 of Figure 1), then a glass substrate 27.

0073On the side of the sheet 25 in polycarbonate, there is then a spacer air plate 31, then a glass 32 (identical to the other glasses of the glazing).

0074This glass 32 is also provided with an ultraviolet filter composed of two sheets of PVB treated anti-ultraviolet 29, 30 (identical to the sheets 26, 28) and laminated to a third glass 33 identical to the other two glasses.

0075For the sake of clarity, it has not shown the power supply system of the film 21, or the mounting system of the double-glazing.

0076This glazing thus illustrates the second variant of the invention, in which one of the PET sheets has been substituted with a sheet of polycarbonate highly permeable to oxygen and in permanent contact with the air gap of the double-glazing unit. (by preferably providing the glazing with openings allowing the renewal of the air of the air space).

<u>EXAMPLE 4</u>

0077This example relates to double-glazing very schematically shown in FIG.

0078It comprises a functional film 31 identical to that of the preceding example, provided with one side of a stack 32 of NiCr / Au / NiCr conductive layers (as in Example 1) and then a PET sheet 33 as as in the previous example, and on the other side of a stack of conductive layers comprising a barrier layer 34 on the NiCr film side of about 1 nm and then of an ITO layer 35, such as the layer 22 of the example 3. This stack is covered with another sheet 36 of PET identical to the sheet 33. This assembly is mounted in the interglass of a double glazing with the aid of peripheral hollow spacers 40, 41 and wedged by a polymer spacer 42, according to a mounting similar to that proposed in US Pat. -5 784 853 concerning a PET film provided with a thermal radiation reflection layer also stretched in the interglass of a double glazing. Reference is made to this patent concerning the choice of materials for these spacers and the planned peripheral sealing system. The gas strip (air or oxygen preferably) is thus separated into two zones 43, 44 on either side of the functional system of the invention.

0079The external rigid substrate consists of two glass substrates 45, 46 laminated with a sheet 47 of EVA with anti-UV properties. The inner rigid substrate 48 is a monolithic glass substrate. Alternatively, it can be laminated in a manner similar to the external rigid substrate.

0080Advantageously, the peripheral assembly of the double-glazing can be designed so as to make the interglass accessible to clean the internal faces of the rigid substrates and / or to renew the air in the zones 43, 44 and / or to replace the system functional if needed.

0081It has an ultraviolet filter on the outside. One can predict another interior side.

0082It has been found that such glazing has an approximate lifetime of at least three times longer than glazing in all respects identical but having a PET sheet in place of the PC sheet.

0083In this example, the NiCr barrier layer is optional: if it is removed, then on one side of the liquid crystal film there is a standard ITO conductive layer and on the other side a conductive layer according to the invention, this is already enough to significantly increase the life of the system.

0084In conclusion, the invention has made it possible to discover how to overcome the premature degradation of electrically controllable diffusion glasses and of dichroic dyes or polarizing particles by implementing various means for inhibiting / preventing / compensating for the phenomenon of photoreduction of dichroic dyes. polarizing particles themselves dichroic.

0085It goes without saying that the two variants of the invention can be cumulated, that is to say, it can be provided to provide the functional films of both metal conductive layers and sheets of polymer permeable to the oxygen. It is therefore possible to use either a conductive layer according to the invention while keeping the other standard layer, or two conductive layers according to the invention. The layer according to the invention may comprise a metal oxide material doped with a "barrier" at the interface with the liquid crystal film (based on material without photocatalytic properties preferably), or completely suppressing this type. of material, the discovery of the invention being the suppression of the direct contact between this material and the liquid crystal film. The other non-exclusive variant of the previous one consists in modifying the oxygen permeability level of at least one of the protective sheets of the system.

0086The invention makes it possible to widen the applications of such glazings, while also aiming at outdoor applications where the glazings are particularly exposed to solar ultraviolet radiations, even in particularly demanding configurations, that is to say in horizontal or oblique position. (roof-car, roof glazing, ...). The invention has proved effective even for high contrast glazing and / or when the dye level is relatively high.