WO2014068203A1

WO2014068203A1 - Variable light diffusion system comprising a pdlc layer

Info

Publication number: WO2014068203A1
Application number: PCT/FR2013/051764
Authority: WO
Inventors: Nicolas LE HOUX; Vincent Rachet; Stéphanie MORLENS; Jingwei Zhang
Original assignee: Saint-Gobain Glass France
Priority date: 2012-10-31
Filing date: 2013-07-22
Publication date: 2014-05-08
Also published as: FR2997517A1; DE202013006516U1; EP2915004A1; JP2015532982A; FR2997517B1; KR20150081274A; CN103792717A

Abstract

The invention concerns a variable light diffusion system switching between a transparent state and a translucent state comprising a PDLC layer located between two electrodes. The PDLC layer comprises a mixture of liquid crystals forming micro-droplets dispersed in a polymer matrix obtained from a photopolymerisable composition comprising vinyl compounds. The invention also concerns the use of a variable light diffusion system switching between a transparent state and a translucent state operating with a switching voltage lower than 30 Vrms.

Description

VARIABLE LUMINOUS DIFFUSION SYSTEM COMPRISING

A PDLC LAYER

The invention relates to the field of electrically controllable glazings with variable optical properties and more particularly to a variable light scattering system comprising a PDLC layer located between two electrodes carried by supports.

Glazes are known whose characteristics can be modified under the effect of a suitable power supply, especially the transmission, absorption, reflection in certain wavelengths of electromagnetic radiation, especially in the visible and / or in the infrared, or the light diffusion.

The switchable glazings between a transparent state and a currently available diffusing state comprise a functional film consisting of two electrode-carrying supports in the form of plastic sheets enclosing a layer incorporating liquid-crystal droplets, all laminated via spacers or glued on a glass substrate or between two glass substrates. Liquid crystals, when the film is switched on (ON state), are oriented along a preferred axis, which allows vision through the functional film. Off (OFF state), in the absence of alignment in the liquid crystal droplets, the film becomes diffusive and prevents vision.

The applicant has developed new switchable windows comprising liquid crystals not using functional film technology. These switchable glazings comprise a layer comprising a multitude of liquid crystal droplets without preferential orientations dispersed in a polymer matrix (hereinafter PDLC layer, "Polymer-Dispersed Liquid Crystal"). The PDLC layer is directly encapsulated between two glass substrates. The assembly consisting of the substrates and the PDLC layer is sealed via a sealing gasket or peripheral adhesive bead. Patent applications WO 2012/028823 and WO 2012/045973 describe such glazings. The use of this technique makes it possible to manufacture less expensive glazings by saving on the materials used and more efficient from an electro-optical point of view.

The switchable glazings comprising a layer based on liquid crystals incorporated in a functional film or directly encapsulated between two glass substrates have the disadvantage of not requiring significant tensions of use. The effective values of the sinusoidal operating voltages are typically greater than 50 Vrms (rms: "root mean square"). Indeed, in addition to the interest related to the reduction of the electrical consumption and / or the limitation of electrical failures (reduction of the risk of short circuit), the lowering of the operating voltages makes it possible to envisage the use of such systems. for applications requiring greater security such as bathroom applications.

According to the invention, the following terms mean:

- switching voltage, the rms voltage of a sinusoidal signal from which fuzziness values measured in accordance with ASTM D 1003 below 5% are obtained,

- operating voltage, the effective voltage of a sinusoidal signal recommended by the functional film suppliers to obtain the transparent state without specification of the obtained fuzziness values.

The switching voltage corresponds to a minimum operating voltage to have a low blur. Blur (haze) is the amount of transmitted light that is scattered at angles of more than 2.5 °. Liquid crystals are all the better ordered (so less blurred) than the applied voltage is high. When the applied voltage is insufficient, the PDLC layer remains diffusing and can generate a white haze. This white veil is the main cause of non-transparency printing.

The lowering of the switching voltages must therefore not be to the detriment of the optical properties and performances of the systems with variable light diffusion, which are in particular the absence of blur in the transparent state, a good transmission of the light in the state transparent, a transmission of the correct light in the diffusing state and a good hiding power regardless of the angle of view in the diffusing state. The hiding power of a glazing in the diffusing state corresponds to its ability not to allow vision through.

Therefore, in order to improve the optical properties of the variable light scattering systems while lowering the switching voltages, the applicant is interested in the mechanisms governing these complex systems.

The diffusing systems comprising diffusers dispersed in a matrix diffuse the light differently according to the size and density of the diffusers they contain. The variable light scattering systems of the invention, in the diffusing state, correspond to diffusing layers comprising as diffusers droplets of liquid crystals dispersed in a volume. These diffusers must have dimensions and a density such that the light passing through the medium constituted by the diffusing layer undergoes Mie diffusion. To observe this phenomenon, the size of the diffusers must be larger than the wavelengths of the visible, typically one or a few micrometers.

When this type of scattering layer is illuminated at normal incidence, the spatial distribution of the light scattered in transmission is not isotropic and strongly depends on the shape of the diffusers (sphere, cylinder, plate, etc.), their size. and their density.

It is possible for a given scattering layer to determine its transmission diffusion indicator. This consists in illuminating the diffusing layer at normal incidence and measuring in transmission the intensity of the scattered rays as a function of the angle with respect to the initial direction of illumination. This diffusion indicator can be measured using a device measuring the bidirectional transmission distribution function (BTDF) such as the REFLET bench of the STIL company. This indicator obtained by measuring the light transmitted over a 90 ° -90 ° arc in the hemisphere opposite that of the incident light, constitutes a peak-shaped curve. The information that can be extracted from these scattering indicia results from the height of the peak apex, the shape and width of the peak base. The vertex of the peak centered on 0 ° corresponds to the normal angle of incidence, to which the light that has not been diffused comes out.

Among the scattering layers whose diffusion is explained by the diffusion of Mie, a distinction must be made. Depending on the size and density of the diffusers as well as on the thickness of the PDLC layer, the diffusion indicatrices have a variable shape.

When the diffusing layer comprises large diffusers or a low density of diffusers, the diffusion indicatrices have a shape close to a quasi-triangular peak. The half-width of the base of the triangle corresponds to the limit angle (in absolute value) beyond which almost no ray is diffused. It is then considered that the transmission diffusion indicator is very pointed forward.

In contrast, when the scattering layer comprises smaller particles. The diffusion indicator can be divided into two main parts. A peak is obtained superimposed on a curve that is called "the bottom" having a bell shape. In this case, rays can be scattered at large angles. It is considered that the transmission diffusion indicator is less pointed forward.

The transmission scattering indicator analysis makes it possible to demonstrate that when the diffusing layer comprises particles of dimension and density such that the diffusion profile is pointed towards the front, almost no ray is scattered at angles. above a limit value. In this case, the weakness of the average angular deviation of the rays that passes through the scattering layer relative to their initial direction results in a low hiding power. On the other hand, when the scattering layer has a diffusion profile that is not pointed forwardly, the greatest average angular deviation of the rays which passes through the scattering layer relative to their initial direction seems to allow a better hiding power to be obtained.

Obtaining good hiding power in the diffusing state requires optimization of the size and density of the liquid crystal droplets as well as the thickness of the scattering layer.

In the case of systems with variable light diffusion, obtaining a satisfactory transparent state with low operating voltages must not be to the detriment of the improvement of the hiding power in the diffusing state. However, the variable light scattering systems comprising a PDLC layer are complex systems, each characteristic of which is capable of influencing the decrease or increase of the switching voltages. A number of features affecting hiding power and switching voltages are common. Among the characteristics influencing the switching voltage are:

the size, the density and the morphology of droplets of the liquid crystals,

the quality of the droplets of liquid crystals and of the polymer matrix, in particular the absence of the components of one in the other,

the presence of residual impurities resulting from the process for preparing the PDLC layer, such as ionic species,

the thickness of the PDLC layer,

- the nature of the liquid crystals.

Of these characteristics, some depend on the method of preparing the PDLC layer, the choice of starting materials, or both.

The processes for preparing the PDLC layers comprise a phase separation step for forming the liquid crystal droplets dispersed in the polymer matrix. The nature, the concentration of the components in the composition precursor of the PDLC layer, the temperature and the operating conditions, in particular the kinetics of polymerization, influence the morphology of the microdroplets obtained and in particular determines their size, their shape, their purity and possibly their interconnection (open or closed porosity).

Therefore, the lowering of switching voltages of the variable light scattering systems comprising a PDLC layer depends not only on the starting components but also on the method of preparing said PDLC layer. It is not possible to correlate in a simple manner the parameters of the preparation process and / or the characteristics of the PDLC layer with the decrease of the switching voltage and the improvement of the hiding power.

There is therefore a need to develop new systems with variable light diffusion having improved optical properties including good hiding power regardless of the angle of view and better quality in normal vision in the transparent state and at lower cost and with switching voltages lowered.

The invention thus relates to a variable light scattering system switching between a transparent state and a translucent state comprising a PDLC layer located between two electrodes, the PDLC layer comprising a mixture of liquid crystals forming microdroplets dispersed in a polymer matrix and satisfying the criteria. following:

the polymer matrix is obtained from a photopolymerizable composition comprising vinyl compounds,

the proportions by weight of the liquid crystal mixture with respect to the total mass of the liquid crystal and photopolymerizable composition mixture are between 40 and 70%,

the PDLC layer has a thickness of between 5 and 25 μηη,

the average diameter of the droplets of liquid crystals dispersed in the polymer matrix is between 0.25 μηη and 2.00 μηη.

Surprisingly, the variable light scattering system of the invention combining the claimed characteristics contributes to obtaining the desired properties and in particular exhibits excellent transparency for low applied effective stresses, especially of less than 30 Vrms, and even less than 20 Vrms. or 15 Vrms, and good hiding power in the diffusing state. These advantageous properties are in particular obtained with PDLC layers of approximately 15 μηη of thickness. The PDLC layer has, in order of increasing thickness of 10 to 20 μηι or 12 to 17 μηι.

The invention also relates to the use of such a system operating with a switching voltage of less than 30 Vrms.

The choice of a PDLC layer obtained by phase separation induced by polymerization from a radically photopolymerizable composition makes it possible to reduce the ionic pollution in the final product and therefore to limit the screening of the electric field at the level of the droplets of liquid crystal. The presence of ionic impurities in a PDLC layer requires the application of a larger voltage to switch to the transparent state because these impurities tend to decrease the effective field at each liquid crystal droplet. Radical polymerization does not require as starting compounds ionic species. This type of polymerization does not generate ionic species either. Therefore, in the case of radical polymerization no ionic species is likely to dissolve in the liquid crystal and participate in the screening of the electric field.

The density of the droplets in the PDLC layer can be estimated indirectly by the average droplet size and the relative mass proportions of the liquid crystal mixture relative to the photopolymerizable composition (assuming very little liquid crystal is dissolved in the matrix). polymer). The average size of the droplets and their homogeneity in terms of size and distribution in the PDLC layer strongly depend on the polymerization conditions.

The ratio of size, droplet density, type of porosity (closed, open or semi-open) of the PDLC layer and the switching voltage is complex.

The switching voltage for closed porosity spherical droplets is expected to decrease as the size of the droplets increases.

However, the increase in droplet size is to the detriment of obtaining a good hiding state diffusing state.

Increasing droplet density improves hiding power.

However, increasing the density of the droplets also increases the risk of interconnection between said droplets (open or semi open porosity). Experience seems to show that open porosity leads to an increase in switching voltages. This seems to be explained by the fact that a closed porosity gives a surface ratio of matrix polymer / crystal mixture interface significantly lower volume of the PDLC layer than in the case of open porosity. However, the liquid crystals precisely located at this interface are to a certain extent "locked" by the polymer matrix and switch less easily.

The choice of a particular morphology for the PDLC layers used according to the invention resulting from the choice of the size of the liquid crystal droplets and the proportion ratio between the mixture of liquid crystals and the photopolymerizable composition contributes to the lowering of the voltages of switching and improving optical properties. The morphology of the PDLC layer used according to the invention can be defined by an excellent individualization or non-coalescence of the liquid crystal droplets with each other. These liquid crystal droplets have substantially closed porosity and comprise a lower proportion of liquid crystal at the interface between the liquid crystal mixture and the polymer matrix that can be blocked. The choice of this particular morphology is an excellent compromise to lower the switching voltage without impairing optical properties such as obtaining a good hiding power.

The particular choice of vinyl compounds as monomers, oligomers or prepolymers constituting the polymer matrix among the various compounds that can be envisaged makes it possible to obtain excellent phase separation during crosslinking for the densities of liquid crystal droplets targeted. This leads to a PDLC layer having droplets whose dimensions are uniform even for small dimensions in particular of the order of a micrometer and whose density is high. The liquid crystals are well distributed in the droplets and not dispersed alone in the polymer matrix.

There is thus little liquid crystal diluted in the polymer matrix and little monomer or prepolymer in the liquid crystal droplets. This prevents the presence of residual monomers or prepolymers within the liquid crystal droplets capable of reducing the dielectric anisotropy of the liquid crystals and therefore of involving the use of a higher voltage to order the liquid crystals. This also prevents the presence of liquid crystals dissolved in the polymer matrix that do not belong to droplets that can not switch during power up.

The combination of the choice of a preparation method for the PDLC layer comprising radical polymerization, nature and particular proportions Starting compounds and polymerization conditions result in a PDLC layer having optimum thickness, droplet density and morphology to lower the switching voltage without impairing the optical properties and performance of the system.

The variable light diffusion systems of the invention advantageously have a light transmission that varies little between the transparent state and the diffusing state. Preferably, the variable light scattering system has:

a variation in light transmission between the transparent state TL _on and the translucent state TL ₀ ff defined by (TL _on -TL ₀ ff) less than 35%, preferably less than 30% and better still less than 25%, and /or

a variation of the fuzziness between the transparent state H _on and the translucent state H _off defined by (H ₀ H ₀ - H _on ) greater than 90%, preferably greater than 95% and better still greater than 97%, and / or

- in the transparent state the light transmission TL _it is at least 75%, preferably at least 80% measured according to ASTM D1003 and the blur in the transmission _is H is at most 5%, preferably not more than 3% as measured by ASTM D1003, and / or

in the state diffusing the light transmission TL ₀ ff is at least 50%, preferably at least 60% measured according to the ASTM D1003 standard and the Hoff transmission blur of at least 95%, preferably at least 88% measured by hazemeter HazeGard plus BYK, and / or

in the diffusing state and in the transparent state, the luminous reflection RL measured according to the ISO 9050: 2003 standard (illuminant D65, 2 ° observer) is strictly less than 30%, preferably less than 25% and better still less than 20% ,

a variation of light reflection RL between the transparent state RL _on and the translucent state RL ₀ ff defined by (RL _on -RL ₀ ff) less than 15%, preferably less than 10% and better still less than 5%.

The blur and transmission values (H and TL) in%, are measured by hazemeter Hazegard plus BYK. The RL light reflection is measured according to the ISO 9050: 2003 standard (illuminant D65, 2 ° observer). The light transmission, light reflection and blur values given above in the transparent state, ie in the ON state, are preferably obtained for an applied voltage of 30 Vrms, preferably 20 Vrms. and better than 15 Vrms.

In the diffusing state most of the incident light is diffusely transmitted and only a very small portion of the incident light is reflected or backscattered by the liquid crystal droplets.

A PDLC layer comprising liquid crystals can be obtained by preparing a precursor composition of the PDLC layer comprising a mixture of liquid crystals and a photopolymerizable composition, followed by crosslinking or polymerization of said composition. The photopolymerizable composition comprises monomers, oligomers and / or prepolymers and a polymerization initiator. This precursor composition of the PDLC layer is deposited on a support coated with an electrode in the form of a "layer". A second electrode carried by a support sandwiches said layer. During curing by irradiation with UV light, a polymer matrix is formed in which the liquid crystals are incorporated as microdroplets. The PDLC layer is thus obtained by a phase separation step induced by radical photopolymerization.

The liquid crystals used according to the invention are preferably nematic at room temperature and with positive dielectric anisotropy. Examples of liquid crystals and liquid crystal mixtures suitable according to the invention are described in particular in patents EP 0 564 869 and EP 0 598 086.

As liquid crystal mixture that is particularly suitable according to the invention, it is possible to use the product marketed by Merck under the reference MDA-00-3506 comprising a mixture of 4 - ((4-ethyl-2,6- difluorophenyl) ethinyl) -4'-propylbiphenyl and 2-fluoro-4,4'-bis (trans-4-propylcyclohexyl) biphenyl.

Nematic liquid crystals are birefringent materials. The birefringence Δη of the liquid crystal or mixture of liquid crystals corresponds to the variation between the two main indices of the material, the ordinary index n ₀ and the extraordinary index n _e (Δη = n _e -n ₀ ).

The liquid crystals are randomly oriented in the droplets. In the absence of an applied field, it is therefore possible to calculate the average refractive index of the liquid crystal droplets defined by the following relationship: n _m ² = 1/3 (n _e ² + 2n ₀ ² ).

The polymer matrix also has a refractive index n _p .

Preferably, the PDLC layer satisfies the following conditions:

the difference between the ordinary and extraordinary refractive indices of the liquid crystals is between 0.2 and 0.3,

the liquid crystals or the mixture of liquid crystals and the polymer matrix respectively have an ordinary refractive index and a refractive index that are substantially equal, the difference between the ordinary refractive index of the liquid crystal mixture and the refractive index of the polymer matrix is less than 0.050, better still less than 0.010,

the difference between the average refractive index of the liquid crystal mixture and the refractive index of the polymer matrix is greater than 0.100, better still greater than 0.125.

According to the invention, the following terms mean:

"Substantially equal refractive indices", when the absolute value of the difference between the refractive indices at a wavelength of 550 nm is less than or equal to 0.050, preferably less than 0.015 and better still less than 0.010,

"Different refractive indices", when the absolute value of the difference between their refractive indices at a wavelength of 550 nm is strictly greater than 0.050, preferably greater than or equal to 0.100 and better still greater than 0.125.

The droplets of liquid crystals have, in order of increasing preference, a mean diameter of between 0.25 and 1.80 μηη, between 0.60 and 1, 30 μηη or between 0.70 and 1.00 μηη (limits included). .

The proportions by weight of the liquid crystal mixture relative to the total mass of the liquid crystal and photopolymerizable composition mixture are advantageously between 50 and 65%.

The photopolymerizable composition corresponds to the precursor composition of the polymer matrix of the PDLC layer. This composition comprises compounds capable of polymerizing or cross-linking by radical means under the action of radiation preferably UV.

For the purposes of the present invention, the term "vinyl compound" is intended to mean a monomer, an oligomer, a prepolymer or a polymer comprising at least one vinyl function (CH ₂ = CR) which, when it is subjected to the conditions of photopolymerization, gives a polymer network with a solid structure. According to the invention, the term vinyl compound includes acrylic and methacrylic compounds comprising at least one function (CH ₂ = CH-CO-O-) or (CH ₂ = C (CH ₃ ) -CO-O-).

As vinyl compounds or compounds comprising vinyl groups, mention may be made of monomers, oligomers, prepolymers and polymers comprising acryloyl or methacryloyl, allyl or vinylbenzene groups. These compounds comprising vinyl groups may be monofunctional or multifunctional. Mention may be made in particular of monoacrylates, diacrylates, N-substituted acrylamides, N-vinylpyrrolidone, styrene and its derivatives, polyester acrylates, epoxy acrylates, polyurethane acrylates and polyether acrylates.

According to the present invention, various compounds comprising photocurable vinyl groups may be used. However, it is preferable to use compounds comprising (meth) acrylate groups, since they allow an excellent phase separation between the polymer matrix and the liquid crystals by irradiation with in particular a high rate of hardening and thus obtaining a stable and homogeneous product.

Vinyl compounds that are suitable according to the present invention are for example described in patent EP 0272 585, in particular acrylate oligomers. The vinyl compounds are preferably acrylate compounds or methacrylate or (meth) acrylate compounds. By (meth) acrylate is meant an acrylate or a methacrylate.

The photopolymerizable composition according to the invention preferably comprises acrylate and / or methacrylate compounds (hereinafter (meth) acrylate). The (meth) acrylate compounds used according to the invention may be chosen from monofunctional and polyfunctional (meth) acrylates such as mono-, di-, tri-, polyfunctional (meth) acrylates. Examples of such monomers are:

monofunctional (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, n- or tert-butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, benzyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, phenyloxyethyl (meth) acrylate, hydroxyethylacrylate, hydroxypropyl (meth) acrylate, vinyl (meth) acrylate caprolactone acrylate, isobornyl methacrylate, lauryl methacrylate, polypropylene glycol monomethacrylate,

difunctional (meth) acrylates such as 1,4-butanediol di (meth) acrylate, ethylene dimethacrylate, 1,6-hexandiol di (meth) acrylate, bisphenol A di (meth) acrylate, trimethylolpropane diacrylate, pentaerythritol triacrylate, triethylene glycol diacrylate, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate,

trifunctional (meth) acrylates such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tripropylene glycol triacrylate,

the (meth) acrylate of higher functionality such as pentaerythritol tetra (meth) acrylate, ditrimethylpropane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate or hexa (meth) acrylate.

Preferably, the photopolymerizable composition comprises at least one monofunctional vinyl compound, preferably an acrylate monomer, at least one difunctional vinyl compound, preferably a diacrylate monomer, and at least one mono-, di- or polyfunctional vinyl oligomer, of preferably an acrylate oligomer.

The photopolymerizable composition comprises in mass relative to the total mass of the photopolymerizable composition:

30 to 95%, preferably 35 to 60% and better still 40 to 55% of monofunctional vinyl compound,

1 to 35%, preferably 10 to 25% and better still 5 to 25% of difunctional vinyl compound,

1 to 50%, preferably 20 to 40% and more preferably 25 to 35% vinyl mono-, di- or polyfunctional oligomer.

- 0 to 15%, preferably 5 to 10% of at least one mercaptan compound.

According to one embodiment, the photopolymerizable composition comprises, by weight relative to the total weight of the photopolymerizable composition, in order of increasing preference, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% of vinyl compounds.

Insofar as no solvent is used, the polymer matrix once crosslinked will therefore comprise at least 50% of polymer obtained by polymerization of vinyl compounds. Preferably, the polymer matrix comprises, in order of increasing preference, in mass relative to the total mass of the polymer matrix, at least 60%, at least 70%, at least 80%, at least 90%, at least 92% at least 95% of polymers obtained by polymerization of the vinyl compounds.

According to an advantageous embodiment, the photopolymerizable composition comprising vinyl compounds comprises, by weight relative to the total mass of the photopolymerizable composition, in order of increasing preference, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95% of acrylate compounds and / or methacrylate compounds.

The photopolymerizable composition may further comprise 0.01 to 5% of a photoinitiator by mass relative to the total weight of the photopolymerizable composition. Suitable photoinitiators according to the invention include 2,2-dimethoxy-1,2-diphenylethanone. The polymerizable composition may comprise other polymerizable comonomers.

An example of a photopolymerizable composition is a composition obtained from the product MXM 035 sold by Nematel. This product includes:

a mixture of two acrylate monomers, ethylhexylacrylate and hexanediol diacrylate and acrylate oligomers,

- a mercaptan,

a photoinitiator for its UV polymerization.

Other examples of acrylate and mercaptan compositions are described in US Patents 4,891, 152, EP 0564869 and EP 0 598 086.

The PDLC layer may further comprise spacers. The spacers may be glass such as glass beads or hard plastics for example polymethyl methacrylate (PMMA) or divinylbenzene polymer. These spacers are preferably transparent and preferably have an optical index substantially equal to the refractive index of the polymer matrix. The spacers are of non-conductive material.

The electrodes are each carried by a support preferably chosen from glass substrates. The supports are attached to each other at their edge by a seal.

The electrode-carrying supports are fixed on the edge by a sealing joint. Preferably, the seal is chosen from a material of the same nature as the polymer matrix forming the PDLC layer, that is to say based on a vinyl compound, preferably (meth) acrylate.

The invention also relates to an electrically controllable glazing comprising a variable light diffusion system switching between a transparent state and a translucent state comprising a PDLC layer comprising liquid crystals forming microdroplets dispersed in a polymer matrix located between two electrodes each carried by a support. Said supports may be sheets of glass, preferably of mineral glass, maintained at their edges on the side of the electrodes by a sealing gasket, preferably based on crosslinked polymer.

Finally, the invention relates to the use of a variable light scattering system switching between a transparent state and a translucent state as defined above, characterized in that a lower switching voltage is applied to 30 Vrms, preferably less than 20 Vrms and better still less than 15 Vrms.

The PDLC layer is framed by two electrodes, the electrodes being in contact with the diffusing layer. The electrodes each comprise at least one electroconductive layer. The electroconductive layer may comprise transparent conductive oxides (TCO), that is, materials that are both good conductors and transparent in the visible, such as indium oxide doped with tin. (ITO), antimony or fluorine doped tin oxide (SnO ₂ : F) or aluminum doped zinc oxide (ZnO: Al). An electroconductive layer based on ITO has a surface resistance of 50 to 200 ohms per square.

These electroconductive layers based on oxides are preferably deposited on thicknesses of the order of 50 to 100 nm, directly on a substrate or on an intermediate layer, by a large number of known techniques such as cathodic sputtering assisted by Magnetic field, evaporation, sol-gel technique, as well as vapor deposition techniques (CVD).

The electroconductive layer may also be a metal layer, preferably a thin layer or a stack of thin layers, called TCC (for "transparent conductive coating" in English) for example Ag, Al, Pd, Cu, Pd, Pt In, Mo, Au and typically of thickness between 2 and 50 nm.

The electrodes comprising an electrically conductive layer are connected to a power supply.

The electrodes comprise for example a transparent electrically conductive layer with a thickness of about 20 to 400 nm made of indium tin oxide (ITO) for example. ITO layers have a surface electrical resistance of between 5 Ω / Ώ and 300 Ω / Ώ. Instead of the layers made of ITO, it is also possible to use for the same purpose for the first and / or the second electrode other layers of electrically conductive oxide or silver stacks whose surface resistance is comparable.

The electroconductive layers of the electrodes can then be deposited directly on a face of a substrate and thus form the electrode-carrying substrates. The substrates may be glass substrates, for example flat float glass sheets. When the electrode support is a glass substrate, it may be chosen from among the glass substrates sold by Saint-Gobain Glass in the DIAMANT® or Planilux® range. The glass substrates preferably have a thickness of between 0.4 and 12 mm, preferably 0.7 and 6 mm. The invention also relates to an electrically controllable glazing comprising a variable light diffusion system according to the invention and two supports each carrying an electrode of the variable light scattering system.

The electrically controllable liquid crystal glazing can be used everywhere, both in the construction sector and in the automotive sector, whenever the view through the glazing must be prevented at given times and in particular:

- as an internal partition (between two rooms or in a space) in a building, in a means of locomotion terrestrial, aerial, aquatic (between two compartments or in a taxi),

- as glazed door, window, ceiling, tiling (floor, ceiling),

- as lateral glazing or roof of a means of locomotion terrestrial, aerial, aquatic,

- as a projection screen,

- as a shop facade, showcase including a counter.

The glazing according to the invention can form all or part of a partition and other window (transom type).

The installation of electrically controllable glazings generally requires:

- the installation of glazing in a frame and

- the installation of a specific power supply to the glazing.

These facilities are traditionally made separately by authorized persons for each area, a glazier and an electrician.

The electrically controllable glazings comprising a variable light diffusion system according to the invention have low switching voltages while keeping good optical properties. The power consumption is then low enough to allow the use of a less bulky power supply. The electrically controllable glazing according to the invention can thus be integrated into "ready-to-use" devices. The installation of said glazings is simplified and costs are reduced.

The invention therefore also relates to a device comprising a glazing unit as defined above, a frame and a power supply. The power supply is included in the frame.

The power supply corresponds to the system which transfers the electric current of an electrical network to supply it, under the appropriate parameters (power, voltage), in a stable and constant manner to the variable light scattering system. Due to its small size, the power supply can be placed inside the frame, for example in an amount. In a first variant, the power supply is connected to a power cord comprising an electrical outlet that can be connected to the electrical network. The device is ready to use in that it can be easily installed and switched on with only the connection of the electrical outlet to the mains.

Power supplies can be small enough to fit inside the frame and run on batteries rather than being connected to a power supply. Having battery power allows direct use after installation.

In a second variant, the power supply is a battery powered. The device further comprises a compartment for receiving the batteries. The compartment is located on the frame and may for example include a flap openable and closable, accessible on the amount of the frame. The valve allows access to the battery compartment and change them when necessary.

During installation, it is no longer necessary to call an electrician since the power supply is already included in the device. Advantageously, the integration of the power supply in the device makes it more robust for handling during installation as well as for transport. Finally, in case of failure, the device can easily be removed and replaced to examine the causes, regardless of whether the fault is due to power or electrically controllable glazing.

The device may further comprise a switch mounted on the frame. The switch can be connected to the socket and the power supply. The power supply The switch can be a push button or an infrared receiver that can be remotely controlled.

Structures of large dimensions can be realized by putting side by side several devices. When each device comprises an infrared receiver, the same remote control can individually control these infrared receivers either by ordering them at once, or in a rhythmic program over time.

The choice of frame is based on the use of glazing, as a glass door, window or partition for example.

FIG. 4 illustrates a device according to the invention integrated in a glazed door or window element 6. The device comprises an electrically controllable glazing unit 1, a frame 2, a power supply 3, a switch 4 fixed on a frame post 2 and a power cord comprising a power outlet 5 located side to which the door or window opens.

FIG. 5 illustrates a device according to the invention integrated in a glazed door or window element 6. The device comprises an electrically controllable glazing unit 1, a frame 2, a power supply 3, a switch 4 fixed on a frame upright 2 and a compartment to hold the batteries 7.

Example

I. Materials used

The transparent substrates used are Planilux® glasses marketed by Saint-Gobain.

These substrates have a thickness of 3.85 mm. The electrodes consist of a layer of ITO (tin doped indium oxide) with a surface resistance of about 50 to 200 ohms per square.

The liquid crystal mixture used corresponds to the product marketed by Merck under the reference MDA-00-3506 comprising:

4 - ((4-ethyl-2,6-difluorophenyl) ethinyl) -4'-propylbiphenyl and

2-Fluoro-4,4'-bis (trans-4-propylcyclohexyl) biphenyl.

This liquid crystal mixture has the following properties:

- ordinary refractive indices: 1, 5164,

- extraordinary refractive indices: 1, 7738,

- birefringence: 0.2574.

The photopolymerizable composition is obtained from the product MXM 035 sold by Nematel. This two-part product A and B includes:

a mixture of two acrylate monomers, ethylhexylacrylate and hexanediol diacrylate and acrylate oligomers (part B),

a mercaptan (part A),

a photoinitiator for its UV polymerization (part A).

The polymer matrix resulting from the crosslinking of such a photopolymerizable composition has a refractive index of 1.482 (without liquid crystal droplets).

The spacers are beads marketed under the name Sekisui Micropearl of 15 μηη average diameter.

The seal is composed of a photo-crosslinkable acrylate glue. II. Preparation of systems with variable light scattering

Preparation of the precursor composition of the PDLC layer:

the photopolymerizable composition is prepared from product MXM35 by mixing 13.5% by weight of Part A with 86.5% by weight of Part B relative to the total weight of Parts A and B,

47.5% by mass of photopolymerizable composition and 52.5% by weight of the liquid crystal mixture MDA 00-3506 are mixed with respect to the total mass of the liquid crystal and photopolymerizable composition mixture,

0.3% by weight of Sekisui micropearl spacers are added relative to the total mass of the liquid crystal mixture and photopolymerizable composition.

Preparation of the supports coated with an electrode: a layer of ITO is deposited by magnetron process on Planilux® glass.

Preparation of systems with variable light scattering:

the acrylate adhesive used as a seal is applied at the edge of the support,

the precursor composition of the PDLC layer is deposited on an electrode carried by a support,

a second support coated with an electrode is deposited on the first with the two conductive layers facing each other separated by the precursor composition layer of the PDLC layer,

- the two glasses are pressed together,

- the whole is insolated with UV rays.

For more details on the encapsulation of the precursor layer between the electrode-carrying glass substrates, reference can be made to the patent applications WO 2012/028823 and WO 2012/045973 describing precisely these preparation method. III. Characterization of systems with variable light scattering

* In the ON state, the measurements were performed with an applied voltage of 30 Vrms.

In order to vary the mean dimensions of the droplets and the density of the droplets, the insolation conditions, ie the insolation power and the duration of the UV exposure, are varied.

FIG. 1 shows the three images A, B and C taken under the scanning electron microscope of the SDLV1, SDLV2 and SDLV3 variable light scattering systems.

Figures 2 and 3 are graphs showing the evolution of the blur (in%) for the variable light scattering systems SDLV1, SDLV2 and SDLV3 as a function of the applied voltage (in Vrms).

The optimal variable light scattering system is SDLV1 with spherical droplets and a switching voltage of 15 Vrms. SDLV3 has smaller droplet sizes which results in some increase in switching voltage. This may be due to the increase in the interface area / volume ratio.

IV. Ready-to-use devices

Electrically controllable glazing comprising a variable luminous diffusion system of SDLV1 type laminated with 4 mm glass weighs 35 kg / m ² . The electrical consumption per m ² of glazing at 30 Vrms is 1 W / m ² . The power consumption per m ² of glazing at 12 Vrms is 0.16 W / m ² . A glazing of square form of dimensions 20x20 cm ² below glazing pane has the following characteristics: - weight 1, 4 kg,

- power consumption: 6.4 mW, ie a current of 0.53 mA.

Therefore, a device comprising a glazing pane powered by an AA type battery power supply (capacity of the order of 1 A) with a current of 0.53 mA at 12 Vrms has a range of more than 78 days 24h / 24h (1000 mAh / 0.53 mA = 1875 h).

Under the same conditions, a device comprising a battery power supply and an active glazing tile of 1 m ² has an autonomy of 3 days.

Claims

A variable light scattering system switching between a transparent state and a translucent state comprising a PDLC layer located between two electrodes, the PDLC layer comprising a liquid crystal mixture forming microdroplets dispersed in a polymer matrix and satisfying the following criteria:

the PDLC layer has a thickness of between 5 and 25 μηη,

2. Variable light scattering system according to claim 1 characterized in that the PDLC layer has a thickness between 10 and 20 μηη.

3. Variable light scattering system according to any one of the preceding claims, characterized in that the liquid crystal mixture comprises a mixture of 4 - ((4-ethyl-2,6-difluorophenyl) -ethinyl) -4'-propylbiphenyl and 2-fluoro-4,4'-bis (trans-4-propylcyclohexyl) biphenyl.

4. variable light scattering system according to any one of the preceding claims characterized in that the difference between the ordinary refractive index of the liquid crystal mixture and the refractive index of the polymer matrix is less than 0.050.

5. Variable light scattering system according to any one of the preceding claims characterized in that the difference between the average refractive index of the liquid crystal mixture and the refractive index of the polymer matrix is greater than 0.100.

6. Variable light scattering system according to any one of the preceding claims characterized in that the average diameter of the liquid crystal droplets is between 0.70 and 1.00 μηη.

7. variable light scattering system according to any one of the preceding claims characterized in that the mass proportions of the liquid crystal mixture relative to the total mass of the liquid crystal mixture and photopolymerizable composition are between 50 and 65% .

8. Variable light scattering system according to any one of the preceding claims characterized in that the vinyl compounds are acrylate compounds or methacrylate compounds.

9. Variable light scattering system according to any one of the preceding claims characterized in that the photopolymerizable composition comprises:

at least one monofunctional vinyl compound, preferably an acrylate monomer,

at least one difunctional vinyl compound, preferably a diacrylate monomer,

at least one vinyl mono-, di- or polyfunctional oligomer, preferably an acrylate oligomer.

10. Variable light scattering system according to any one of the preceding claims characterized in that the photopolymerizable composition comprises in mass relative to the total mass of the photopolymerizable composition:

30 to 95% of monofunctional vinyl compound,

1 to 35% of difunctional vinyl compound,

1 to 50% of mono-, di- or polyfunctional vinyl oligomer,

0 to 15% of at least one mercaptan compound.

1 1. Variable light scattering system according to any one of the preceding claims characterized in that the photopolymerizable composition comprising vinyl compounds comprises, by weight relative to the total weight of the photopolymerizable composition, at least 50% of acrylate compounds and / or methacrylate compounds.

12. variable light scattering system according to any one of the preceding claims characterized in that the PDLC layer further comprises spacers.

13. Variable light scattering system according to any one of the preceding claims characterized in that the electrodes are each carried by a support selected from glass substrates.

14. Variable light scattering system according to claim 13 characterized in that the supports are fixed to each other at their edge by a seal.

15. Variable light scattering system according to any one of the preceding claims, characterized in that the light transmission variation between the transparent state TL _on and the translucent state TL ₀ ff defined by (TL _on -TL ₀ ff) is less than 35%.

16. Variable light scattering system according to any one of the preceding claims, characterized in that the variation of the blur between the transparent state H _on and the translucent state H defined by (H ₀ ff - H _on ) is greater than 90 %.

17. Variable light scattering system according to any one of the preceding claims, characterized in that it has:

in the transparent state a light transmission TL _on of at least 75% and a blur in transmission H _on of not more than 5% measured according to the standard ASTM D1003, and / or

in the state diffusing a TL _off light transmission of at least 50% measured according to the ASTM D1003 standard and a blur in H _off transmission of at least 95% measured at the hazemeter Hazegard more than BYK, and / or

in the diffusing state and in the transparent state, a luminous reflection RL measured according to ISO 9050: 2003 strictly less than 30%.

18. Use of a variable light scattering system switching between a transparent state and a translucent state according to any one of claims 1 to 17, characterized in that a switching voltage of less than 30 Vrms is applied.

19. Electrically controllable glazing comprising a variable light scattering system according to any one of claims 1 to 17 and two supports each carrying an electrode of the variable light scattering system.

20. Device comprising an electrically controllable glazing according to claim 19, a frame and a power supply included in the frame.

21. Device according to claim 20 characterized in that the power supply is connected to a power cord comprising an electrical outlet.

22. Device according to claim 20 characterized in that the power supply is a battery powered.

23. Device according to claim 22 characterized in that it further comprises a compartment for receiving the batteries.

24. Device according to any one of claims 20 to 23 characterized in that it further comprises a switch mounted on the frame.