Transparent element with diffuse reflection comprising a sol-gel layer

Abstract

A transparent layered element with diffuse reflection properties includes two outer layers made of dielectric materials having substantially the same refractive index and a central layer intercalated between the two outer layers, formed either from a single layer which is a dielectric layer with a refractive index different from that of the outer layers or a metallic layer, or from a stack of layers which includes at least one dielectric layer with a refractive index different from that of the outer layers or a metallic layer. The upper outer layer is a sol-gel layer including a silica-based organic/inorganic hybrid matrix.

Claims

1. A transparent layered element having two main smooth outer surfaces, the transparent layered element comprising: a lower outer layer and an upper outer layer, which each form one of the two main outer surfaces of the transparent layered element and which consist of dielectric materials having substantially the same refractive index, and a central layer intercalated between the lower outer and upper outer layers, the central layer being formed either (a) by a single layer which is a dielectric layer of refractive index different from that of the lower outer and upper outer layers or a metallic layer, or (b) by a stack of layers which comprises at least one dielectric layer with a refractive index different from that of the lower outer and upper outer layers or a metallic layer, wherein each contact surface between two adjacent layers of the transparent layered element, one of which is a dielectric layer and the other is a metallic layer or which are both dielectric layers with different refractive indices, is textured and parallel to other textured contact surfaces between two adjacent layers, one of which is a dielectric layer and the other is a metallic layer or which are both dielectric layers with different refractive indices, wherein the upper outer layer is a sol-gel layer comprising an organic/inorganic hybrid matrix based on silica, wherein a smooth surface has a roughness parameter corresponding to an arithmetic mean difference Ra of less than 0.10 μm and a textured surface has a roughness parameter corresponding to the arithmetic mean difference Ra of at least 0.5 μm, wherein the absolute value of the difference in refractive index at 589 nm between constituent dielectric materials of the lower outer and upper outer layers of the transparent layered element is less than or equal to 0.020, and wherein the transmission haze of the transparent layered element is less than 5% and the lightness of the transparent layered element is greater than 93%.

2. The transparent layered element as claimed in claim 1, wherein the absolute value of the difference in refractive index at 589 nm between the lower outer and upper outer layers and at least one dielectric layer of the central layer is greater than or equal to 0.3.

3. The transparent layered element as claimed in claim 1, wherein the sol-gel layer also comprises particles of at least one metal oxide or of at least one chalcogenide.

4. The transparent layered element as claimed in claim 1, wherein the silica-based organic/inorganic hybrid matrix also comprises at least one metal oxide.

5. The transparent layered element as claimed in claim 3, wherein the metal oxide comprises a metal chosen from titanium, zirconium, zinc, niobium, aluminum and molybdenum.

6. The transparent layered element as claimed in claim 1, wherein the sol-gel layer comprises an organic/inorganic hybrid matrix of silica and of zirconium oxide in which are dispersed titanium dioxide particles.

7. The transparent layered element as claimed in claim 1, wherein the sol-gel layer is obtained by curing a sol-gel solution and comprises the product resulting from the hydrolysis and condensation of at least one organosilane of general formula R.sub.nSiX.sub.(4-n) in which: n is equal to 1, 2, 3, the groups X, which are identical or different, represent hydrolyzable groups chosen from alkoxy, acyloxy or halide groups, and the groups R, which are identical or different, represent non-hydrolyzable organic groups bonded to silicon via a carbon atom.

8. The transparent layered element as claimed in claim 1, wherein the sol-gel layer is obtained by curing a sol-gel solution and comprises the product resulting from the hydrolysis and condensation of: i) at least one organosilane and ii) at least one precursor of a metal oxide or iii) particles of at least one metal oxide or of at least one chalcogenide, or both ii) at least one precursor of a metal oxide and iii) particles of at least one metal oxide or of at least one chalcogenide.

9. The transparent layered element as claimed in claim 1, further comprising at least one additional layer positioned above or below the upper and/or lower outer layers, chosen from: transparent substrates chosen from polymers, glasses and ceramics comprising two smooth main surfaces, curable materials that are initially in a viscous, liquid or pasty state suitable for forming operations, inserts made of thermoformable or pressure-sensitive plastic material.

10. The transparent layered element as claimed in claim 1, wherein the lower outer layer of the layered element is chosen from: transparent substrates, one of the main surfaces of which is textured and the other smooth, a layer of dielectric material chosen from the oxides, nitrides or halides of one or more transition metals, non-metals or alkaline-earth metals, a layer based on curable materials that are initially in a viscous, liquid or pasty state, suited to forming operations comprising: photocrosslinkable and/or photopolymerizable materials, layers deposited via a sol-gel process, inserts made of thermoformable or pressure-sensitive plastic material.

11. The transparent layered element as claimed in claim 1, wherein the single layer or the stack of layers of the central layer comprises: at least one thin layer consisting of a dielectric material chosen from the oxides, nitrides or halides of one or more transition metals, non-metals or alkaline-earth metals, at least one thin metallic layer, especially a thin layer of silver, gold, copper, titanium, niobium, silicon, aluminum, nickel-chromium (NiCr) alloy, stainless steel, or an alloy thereof.

12. A process for manufacturing a transparent layered element as defined according to claim 1, comprising: providing a transparent substrate, one of the main surfaces of which is textured and the other main surface is smooth, as lower outer layer; depositing a central layer on a main textured surface of the lower outer layer, said depositing comprising, (a) when the central layer is formed by a single layer, which is a dielectric layer with a refractive index different from that of the lower outer layer or a metallic layer, depositing the central layer in compliant manner onto said main textured surface, or (b) when the central layer is formed by a stack of layers comprising at least one dielectric layer with a refractive index different from that of the lower outer layer or a metallic layer, depositing the layers of the central layer successively in compliant manner onto said main textured surface, and forming the upper outer sol-gel layer on the main textured surface of the central layer opposite the lower outer layer, where the lower and upper outer layers consist of dielectric materials having substantially the same refractive index, by deposition via a sol-gel process.

13. A method comprising utilizing a layered element as claimed in claim 1, as all or part of glazing for a vehicle, for a building, for street furniture, for interior furniture, for a display screen or for a head-up display system.

14. The transparent layered element as claimed in claim 1, wherein the absolute value of the difference is less than or equal to 0.015.

15. The transparent layered element as claimed in claim 2, wherein the absolute value of the difference is greater than or equal to 0.5.

16. The transparent layered element as claimed in claim 7, wherein n is equal to 1 or 2.

17. The transparent layered element as claimed in claim 16, wherein n is equal to 1.

18. The transparent layered element as claimed in claim 7, wherein the groups X are alkoxy groups.

19. The transparent layered element as claimed in claim 10, wherein the transparent substrates are chosen from polymers, glasses and ceramics.

20. The transparent layered element as claimed in claim 10, wherein the thermoformable or pressure-sensitive plastic material are based on polymers chosen from polyvinyl butyrals (PVB), polyvinyl chlorides (PVC), polyurethanes (PU), polyethylene terephthalates (PET) or ethylene-vinyl acetate (EVA) copolymers.

21. The process according to claim 12, further comprising forming at least one upper and/or lower additional layer on the main outer smooth surface of the layered element.

Description

(1) The characteristics and advantages of the invention will emerge in the description that follows of several embodiments of layered element, given solely as an example and made with reference to the attached drawings in which:

(2) FIG. 1 is a schematic cross section of layered element according to the invention;

(3) FIG. 2 is a view on a larger scale of the detail I of FIG. 1 for a first variant of the layered element;

(4) FIG. 3 is a view on a larger scale of the detail I of FIG. 1 for a second variant of the layered element; and

(5) FIGS. 4 and 5 represent schemes showing the steps of a process for manufacturing the layered element according to the invention,

(6) FIG. 6 represents the change in refractive index as a function of the volume proportions of TiO.sub.2 in a sol-gel layer,

(7) FIG. 7 shows images taken with a scanning electron microscope of satin-finish substrates made of Satinovo® transparent rough glass onto which a sol-gel layer has been deposited via the sol-gel process,

(8) FIGS. 8 and 9 are graphs showing the change in haze (right-hand y-axis) and in lightness (left-hand y-axis) as a function of the refractive index of the sol-gel layer and of the variation in refractive index between a Satinovo® substrate used as lower outer layer and the sol-gel layer.

(9) For the clarity of the drawing, the relative thicknesses of the various layers in the figures have not been rigorously respected. Furthermore, the possible variation in thickness of the or each constituent layer of the central layer as a function of the slope of the texture has not been shown in the figures, given that this possible thickness variation has no impact on the parallelism of the textured contact surfaces. Specifically, for each given slope of the texture, the textured contact surfaces are parallel with each other.

(10) The layered element 1 illustrated in FIG. 1 comprises two outer layers 2 and 4, which consist of transparent dielectric materials having substantially the same refractive index n2, n4. Each outer layer 2 or 4 has a smooth main surface, 2A or 4A, respectively, directed toward the exterior of the layered element, and a textured main surface, 2B or 4B, respectively, directed toward the interior of the layered element.

(11) The smooth outer surfaces 2A and 4A of the layered element 1 allow specular transmission of radiation at each surface 2A and 4A, i.e. the entry of radiation into an outer layer or the exit of radiation from an outer layer without modification of the direction of the radiation.

(12) The textures of the inner surfaces 2B and 4B are complementary to each other. As is clearly visible in FIG. 1, the textured surfaces 2B and 4B are positioned facing each other, in a configuration in which their textures are strictly parallel to each other. The layered element 1 also comprises a central layer 3, intercalated in contact between the textured surfaces 2B and 4B.

(13) In the variant shown in FIG. 2, the central layer 3 is a monolayer and consists of a transparent material that is either metallic or dielectric with a refractive index n3 different from that of the outer layers 2 and 4.

(14) In the variant shown in FIG. 3, the central layer 3 is formed by a transparent stack of several layers 3.sub.1, 3.sub.2, . . . , 3.sub.k, in which at least one of the layers 3.sub.1 to 3.sub.k is either a metallic layer or a dielectric layer with a refractive index different from that of the outer layers 2 and 4. Preferably, at least each of the two layers 3.sub.1 and 3.sub.k located at the ends of the stack is a metallic layer or a dielectric layer with a refractive index n3.sub.1 or n3.sub.k different from that of the outer layers 2 and 4.

(15) In FIGS. 2 and 3, S.sub.0 denotes the contact surface between the outer layer 2 and the central layer 3, and S.sub.1 denotes the contact surface between the central layer 3 and the outer layer 4. Furthermore, in FIG. 3, S.sub.2 to S.sub.k successively denote the inner contact surfaces of the central layer 3, starting from the contact surface closest to the surface S.sub.0.

(16) In the variant of FIG. 2, due to the arrangement of the central layer 3 in contact between the textured surfaces 2B and 4B which are parallel to each other, the contact surface S.sub.0 between the outer layer 2 and the central layer 3 is textured and parallel to the contact surface S.sub.1 between the central layer 3 and the outer layer 4. In other words, the central layer 3 is a textured layer having over its entire area a uniform thickness e3, taken perpendicular to the contact surfaces S.sub.0 and S.sub.1.

(17) In the variant of FIG. 3, each contact surface S.sub.2, . . . , S.sub.k between two adjacent layers of the constituent stack of the central layer 3 is textured and strictly parallel to the contact surfaces S.sub.0 and S.sub.1 between the outer layers 2, 4 and the central layer 3. Thus, all the contact surfaces S.sub.0, S.sub.1, . . . , S.sub.k between adjacent layers of the element 1 which are either of different dielectric or metallic nature, or dielectric with different refractive indices, are textured and parallel to each other. In particular, each layer 3.sub.1, 3.sub.2, . . . , 3.sub.k of the constituent stack of the central layer 3 has a uniform thickness e3.sub.1, e3.sub.2, . . . , e3.sub.k, taken perpendicular to the contact surfaces S.sub.0, S.sub.1, . . . S.sub.k.

(18) As shown in FIG. 1, the texture of each contact surface S.sub.0, S.sub.1 or S.sub.0, S.sub.1, . . . , S.sub.k of the layered element 1 is formed by a plurality of designs that are hollowed or protruding relative to a general plane π of the contact surface. Preferably, the mean height of the designs of each textured contact surface S.sub.0, S.sub.1 or S.sub.0, S.sub.1, . . . , S.sub.k is between 1 micrometer and 100 μm. The mean height of the designs of each textured contact surface is defined as the arithmetic mean

(19) $\frac{1}{n}\underset{i=1}{\overset{n}{.Math.}}.Math.y_i.Math.,$
with y.sub.i being the distance taken between the peak and the plane π for each design of the surface, as shown schematically in FIG. 1.

(20) According to one aspect of the invention, the thickness e3 or e3.sub.1, e3.sub.2, . . . , e3.sub.k of the or each constituent layer of the central layer 3 is less than the mean height of the designs of each textured contact surface S.sub.0, S.sub.1 or S.sub.0, S.sub.1, . . . , S.sub.k of the layered element 1. This condition is important for increasing the probability that the inlet interface of radiation into the layer of the central layer 3 and the outlet interface of radiation out of this layer are parallel, and thus for increasing the percentage of specular transmission of the radiation through the layered element 1. For the sake of visibility of the various layers, this condition has not been strictly respected in the figures.

(21) Preferably, the thickness e3 or e3.sub.1, e3.sub.2, . . . , e3.sub.k of the or each constituent layer of the central layer 3 is less than ¼ of the mean height of the designs of each textured contact surface of the layered element. In practice, when the central layer 3 is a thin layer or a stack of thin layers, the thickness e3 or e3.sub.1, e3.sub.2, . . . , e3.sub.k of each layer of the central layer 3 is of the order of or less than 1/10 of the mean height of the designs of each textured contact surface of the layered element.

(22) FIG. 1 illustrates the path of radiation, which is incident on the layered element 1 on the side of the outer layer 2. The incident beams R.sub.i arrive on the outer layer 2 with a given incident angle θ. As shown in FIG. 1, the incident beams R.sub.i, when they reach the contact surface S.sub.0 between the outer layer 2 and the central layer 3, are reflected either by the metallic surface or by the difference in refractive index at this contact surface between, respectively, the outer layer 2 and the central layer 3 in the variant of FIG. 2 and between the outer layer 2 and the layer 3.sub.1 in the variant of FIG. 3. As the contact surface S.sub.0 is textured, reflection takes place in a plurality of directions R.sub.r. The reflection of the radiation by the layered element 1 is thus diffuse.

(23) Part of the incident radiation is also refracted in the central layer 3. In the variant of FIG. 2, the contact surfaces S.sub.0 and S.sub.1 are parallel to each other, which implies according to the Snell-Descartes law that n2.Math.sin(θ)=n4.Math.sin(θ′), where θ is the incident angle of the radiation on the central layer 3 from the outer layer 2 and θ′ is the refraction angle of the radiation in the outer layer 4 from the central layer 3. In the variant of FIG. 3, as the contact surfaces S.sub.0, S.sub.1, . . . , S.sub.k are all parallel to each other, the relationship n2.Math.sin(θ)=n4.Math.sin(θ′) derived from the Snell-Descartes law remains verified. Consequently, in the two variants, since the refractive indices n2 and n4 of the two outer layers are substantially equal to each other, the beams R.sub.t transmitted by the layered element are transmitted with a transmission angle θ′ equal to their incident angle θ on the layered element. The transmission of the radiation by the layered element 1 is thus specular.

(24) Similarly, in the two variants, incident radiation on the layered element 1 on the side of the outer layer 4 is reflected in a diffuse manner and transmitted in a specular manner by the layered element, for the same reasons as previously.

(25) Advantageously, the layered element 1 comprises an anti-reflection coating 6 on at least one of its smooth outer surfaces 2A and 4A. Preferably, an anti-reflection coating 6 is provided on each main outer surface of the layered element that is intended to receive radiation. In the example of FIG. 1, only the surface 2A of the outer layer 2 is equipped with an anti-reflection coating 6, since it is the surface of the layered element that is directed on the radiation incident side.

(26) As mentioned previously, the anti-reflection coating 6, provided on the smooth surface 2A and/or 4A of the outer layer 2 or 4 may be of any type that makes it possible to reduce the radiation reflection at the interface between the air and the outer layer. It may especially be a layer with a refractive index between the refractive index of air and the refractive index of the outer layer, a stack of thin layers acting as an interference filter, or a stack of thin layers having a gradient of refractive indices.

(27) An example of a process for manufacturing the glazing of the invention is described below in reference to FIG. 4. According to this process, the central layer 3 is deposited in a compliant manner on a textured surface 2B of a rigid or flexible transparent substrate, forming the outer layer 2 of the layered element 1. The main surface 2A of this substrate opposite the textured surface 2B is smooth. This substrate 2 may especially be a textured glass substrate of the type such as Satinovo®, Albarino® or Masterglass®. As a variant, the substrate 2 may be a substrate based on rigid or flexible polymer material, for example of the type such as polymethyl methacrylate or polycarbonate.

(28) The compliant deposition of the central layer 3, whether it is a monolayer or formed by a stack of several layers, is preferably especially prepared under vacuum, by magnetic field-assisted cathodic sputtering (known as “cathodic magnetron” sputtering). This technique makes it possible to deposit, on the textured surface 2B of the substrate 2, either the single layer in compliant manner, or the various layers of the stack successively in compliant manner. They may in particular be thin dielectric layers, especially layers of Si.sub.3N.sub.4, SnO.sub.2, ZnO, ZrO.sub.2, SnZnO.sub.x, AlN, NbO, NbN, TiO.sub.2, SiO.sub.2, Al.sub.2O.sub.3, MgF.sub.2, AlF.sub.3, or thin metallic layers, especially silver, gold, titanium, niobium, silicon, aluminum, nickel-chromium (NiCr) alloy layers, or layers of alloys or these metals.

(29) In the process of FIG. 4, the second outer layer 4 of the layered element 1 may be formed by covering the central layer 3 with a transparent sol-gel layer with a refractive index substantially equal to that of the substrate 2. This layer, in the viscous, liquid or pasty state, embraces the texture of the surface 3B of the central layer 3 opposite the substrate 2. Thus, it is ensured that, in the cured state of the layer 4, the contact surface S.sub.1 between the central layer 3 and the outer layer 4 is indeed textured and parallel to the contact surface S.sub.0 between the central layer 3 and the outer layer 2.

(30) The outer layer 4 of the layered element 1 of FIG. 4 is a sol-gel layer, deposited via a sol-gel process on the textured surface of the central layer 3.

(31) Finally, one or more additional layers 12 may be formed over the layered element. In this case, the additional layer(s) are preferably a flat glass substrate, a plastic insert or a superposition of an insert and of a flat glass substrate.

(32) According to one embodiment of the invention, it may be advantageous to form on the sol-gel layer forming the outer layer of the layered element an additional layer 12 by positioning a PVB or EVA lamination insert against the main smooth outer surface of the layered element. The additional layer 12 preferentially has in this case substantially the same refractive index as the outer layer of the layered element obtained from a sol-gel process.

(33) The additional layer may also be a transparent substrate, for example a flat glass. In this case, the additional layer is used as a counter-substrate. The sol-gel layer then ensures integral connection between the lower outer layer equipped with the central layer and the counter-substrate.

(34) The use of a transparent substrate as additional upper layer is particularly useful when the additional layer directly below said additional upper layer is formed by a polymeric lamination insert.

(35) A first additional layer 12 formed by a PVB or EVA lamination insert may be positioned against the outer upper surface of the layered element and a second additional layer 12 consisting of a flat glass substrate may be mounted on the insert.

(36) In this configuration, the additional layers are combined with the layered element, via a standard lamination process. In this process, the polymeric lamination insert and the substrate are successively positioned, starting from the main upper outer surface of the layered element, and compression and/or heating is then applied to the laminated structure thus formed, at least to the glass transition temperature of the polymeric lamination insert, for example in a press or an oven.

(37) During this lamination process, when the insert forms the additional upper layer located directly above the layered element whose upper layer is a sol-gel layer, it conforms both with the upper surface of the sol-gel layer and with the lower surface of the flat glass substrate.

(38) In the process illustrated in FIG. 5, the layered element 1 is a flexible film with a total thickness of about 200-300 μm. The layered element is formed by the superposition: of an additional lower layer 12 formed by a polymeric flexible film, of an outer layer 2 made of a material that is photocrosslinkable and/or photopolymerizable under the action of UV radiation, applied against one of the main smooth surfaces of the flexible film, of a central layer 3, of a sol-gel layer having a thickness from 50 nm to 50 μm so as to form the second outer layer 4 of the layered element 1.

(39) The flexible film forming the additional lower layer may be a film of polyethylene terephthalate (PET) with a thickness of 100 μm, and the outer layer 2 may be a layer of UV-curable resin of the type such as KZ6661 sold by the company JSR Corporation with a thickness of about 10 μm. The flexible film and the layer 2 both have substantially the same refractive index, of about 1.65 at 589 nm. In the cured state, the layer of resin shows good adhesion with PET.

(40) The layer of resin 2 is applied to the flexible film with a viscosity allowing the insertion of texturing onto its surface 2B opposite the film 12. As illustrated in FIG. 5, the texturing of the surface 2B may be performed using a roller 13 having on its surface texturing complementary to that to be formed on the layer 2. Once the texturing has been formed, the superposed flexible film and layer of resin 2 are irradiated with UV radiation, as shown by the arrow in FIG. 5, which allows solidification of the layer of resin 2 with its texturing and assembly between the flexible film and the layer of resin 2.

(41) The central layer 3 with a refractive index different from that of the outer layer 2 is then deposited in a compliant manner onto the textured surface 2B, by magnetron cathodic sputtering. This central layer may be a monolayer or formed by a stack of layers, as described previously. It may be, for example: a layer of TiO.sub.2 having a thickness of between 55 and 65 nm, i.e. about 60 nm and a refractive index of 2.45 at 550 nm, a stack of layers comprising at least one silver-based layer as described in patent applications WO 02/48065 and EP 0 847 965.

(42) The sol-gel layer is then deposited on the central layer 3 so as to form the second outer layer 4 of the layered element 1. This second outer layer 4 embraces the textured surface 3B of the central layer 3 opposite the outer layer 2.

(43) An adhesive layer 14, covered with a protective strip (liner) 15 intended to be removed for bonding, may be applied to the outer surface 4A of the layer 4 of the layered element 1. The layered element 1 is thus in the form of a flexible film ready to be applied by bonding onto a surface, such as a surface of a glazing, so as to give this surface diffuse reflection properties. In the example of FIG. 5, the adhesive layer 14 and the protective strip 15 are applied to the outer surface 4A of the layer 4. The outer surface 2A of the layer 2, which is intended to receive incident radiation, is itself equipped with an anti-reflection coating.

(44) In a particularly advantageous manner, as suggested in FIG. 5, the various steps of the process may be performed continuously on the same manufacturing line.

(45) The insertion of the anti-reflection coating(s) of the layered element 1 has not been shown in FIGS. 4 to 5. It should be noted that, in each of the processes illustrated in these figures, the anti-reflection coating(s) may be inserted on the smooth surfaces 2A and/or 4A of the outer layers before or after assembling the layered element, without preference.

(46) The invention is not limited to the examples described and represented. In particular, when the layered element is a flexible film as in the example of FIG. 5, the thickness of each outer layer formed based on a polymer film, for example based on a PET film, may be greater than 10 μm, especially from about 10 μm to 1 mm.

(47) Furthermore, the texturing of the first outer layer 2 in the example of FIG. 5 may be obtained without making use of a layer of curable resin deposited on the polymer film, but directly by hot embossing of a polymer film, especially by lamination using a textured roller or by pressing using a punch.

(48) Similar architectures may also be envisaged for plastic substrates instead of glass substrates.

(49) The glazing according to the invention may be used for all known applications of glazings, such as for vehicles, buildings, street furniture, interior furniture, lighting, display screens, etc. It may also be a flexible film based on polymer material, which is especially able to be applied to a surface so as to give it diffuse reflection properties while at the same time preserving its transmission properties.

(50) The layered element with strong diffuse reflection of the invention may be used in a head-up display (HUD) system. In a known manner, HUD systems, which are useful especially in aircraft cockpits and trains, but also nowadays in private motor vehicles (cars, trucks, etc.), make it possible to display information projected onto a glazing, in general the windshield of the vehicle, which is reflected to the conductor or the observer. These systems make it possible to inform the conductor of the vehicle without him having to move his regard from the front field of vision of the vehicle, which greatly enhance safety. The conductor sees a virtual image located a certain distance behind the glazing.

(51) According to one aspect of the invention, the layered element is integrated into an HUD system as glazing, onto which is projected information. According to another aspect of the invention, the layered element is a flexible film applied to a main surface of glazing of an HUD system, especially a windshield, the information being projected onto the glazing on the flexible film side. In both these cases, strong diffuse reflection takes place on the first textured contact surface encountered by the radiation in the layered element, which allows good visualization of the virtual image, whereas the specular transmission through the glazing is preserved, which ensures clear vision through the glazing.

(52) It is noted that, in the HUD systems of the prior art, the virtual image is obtained by projecting the information onto glazing (especially a windshield) having a laminated structure formed from two sheets of glass and a plastic insert. A drawback of these existing systems is that the conductor then sees a double image, a first image reflected by the surface of the glazing oriented toward the interior of the cockpit, and a second image by reflection of the outer surface of the glazing, these two images being slightly shifted relative to each other. This shift may disrupt the viewing of the information.

(53) The invention makes it possible to overcome this problem. Specifically, when the layered element is integrated into an HUD system, as glazing or as a flexible film applied to the main surface of the glazing which receives the radiation from the projection source, the diffuse reflection on the first textured contact surface encountered by the radiation in the layered element may be markedly higher than the reflection on the outer surfaces in contact with the air. Thus, the double reflection is limited by promoting the reflection on the first textured contact surface of the layered element.

EXAMPLES

I. Preparation of Sol-Gel Solutions and of Sol-Gel Layers Comprising an Adjustable Refractive Index

(54) The sol-gel layers prepared in the examples comprise an organic/inorganic hybrid matrix of silica and of zirconium oxide in which are dispersed titanium dioxide particles. The main compounds used in the sol-gel solutions are: 3-glycidoxypropyltrimethoxysilane (GLYMO), zirconium propoxide in the form of a solution at 70% by mass in propanol, TiO.sub.2, sold under the name Cristal Activ™, in the form of particles with a diameter of less than 50 nm in an aqueous dispersion with a solids content of 23% by mass.

(55) A first precursor composition of the matrix is prepared by mixing the organosilane, the solution of zirconium propoxide, acetic acid and optionally water. The constituents are mixed dropwise with vigorous stirring. The other compounds are then added to this first composition, i.e. the aqueous dispersion of titanium dioxide in the form of particles, the surfactant and optionally other dilution solvents such as ethanol. The sol-gel solution is thus obtained.

(56) Depending on the dispersion proportions of titanium dioxide added to the sol-gel solution, the matrix of the sol-gel layer once crosslinked will be more or less charged with TiO.sub.2 particles. The refractive index of the sol-gel layer depends on the volume fraction of titanium dioxide. It is thus possible to vary the refractive index of the resulting sol-gel layer between 1.490 and 1.670 with a high-precision adjustment of the order of 0.001. It is thus possible to obtain for all types of standard glass substrates used as lower outer layer an index harmony of less than 0.015.

(57) The solids content of the sol-gel layer has an influence on the maximum thickness that it is possible to deposit in one pass.

(58) In order to illustrate these results, various sol-gel solutions were prepared. These solutions were then applied by spraying onto a support and crosslinked for a time of 20 minutes to a few hours at a temperature of 150° C. or 200° C. so as to form sol-gel layers having refractive indices varying between 1.493 to 1.670.

II. Influence of the Volume Proportions of TiO2 on the Refractive Index of the Sol-Gel Layer

(59) The tables below summarize the compositions of the sol-gel solutions tested and also the compositions of the resulting sol-gel layers.

(60) As regards the sol-gel solution, the given proportions correspond to the mass proportions relative to the total mass of the sol-gel solution.

(61) TABLE-US-00001 Sol-gel solution A B C D E F G H I Main compounds: GLYMO 68.1 64.2 55.6 52.5 22.5 20.3 18.3 16.6 14.8 Zirconium propoxide 4.8 4.5 3.9 3.7 1.6 1.4 1.3 1.2 1.0 TiO.sub.2 0.0 2.8 4.2 6.5 3.5 5.1 6.6 7.8 9.1 Additives Acetic acid 4.3 4.0 3.5 3.3 1.4 1.3 1.1 1.0 0.9 3M-FC 4430 0.0 0.1 0.2 0.3 0.2 0.2 0.3 0.3 0.4 Solvents Propanol 2.0 1.9 1.7 1.6 0.7 0.6 0.5 0.5 0.4 Water 12.8 21.6 24.4 31.6 16.0 20.9 25.5 29.2 33.3 Ethanol 0.0 12.4 18.2 28.2 15.3 22.2 28.6 33.9 39.6 Total 100 100 100 100 100 100 100 100 100

(62) As regards the sol-gel layer, the volume proportions of TiO.sub.2 are defined relative to the total volume of the main components comprising the hybrid matrix of silica and of zirconium oxide and the TiO.sub.2 particles. The proportions of the main components correspond to the mass proportions of the main compounds of the sol-gel layer relative to the total mass of main compounds.

(63) TABLE-US-00002 Sol-gel layer A B C D E F G H I Main compounds*: Gly-SiO2 96 91 87 82 79 72 65 59 53 ZrO2 4 3 3 3 3 3 2 2 2 TiO2 0 6 9 14 18 26 33 39 46 Volume % of TiO2** 0 3 5 8 9.8 15 20.1 24.7 30 Measured index 1.493 1.517 1.529 1.557 1.567 1.600 1.623 1.651 1.674 Theoretical index 1.493 1.515 1.528 1.549 1.564 1.599 — — —

(64) Following the crosslinking of the organosilane and of the zirconium propoxide by hydrolysis reaction and condensation, a matrix is obtained in the sol-gel layer, this matrix being based on silicon oxide comprising a non-hydrolyzable organic group referred to hereinbelow as “Gly-SiO.sub.2” and of zirconium oxide in which are dispersed the TiO.sub.2 particles. These three compounds represent the main compounds of the sol-gel layer.

(65) The volume fraction of titanium dioxide has a linear influence on the refractive index of the sol-gel layer for volume proportions of TiO.sub.2 of less than 20%. For higher proportions, the refractive index continues to increase, but a fall in the slope of the curve is observed. However, once this curve has been determined, a person skilled in the art is capable of estimating, by approximation, the refractive index of a sol-gel layer comprising a volume fraction of TiO.sub.2 of greater than 20%.

(66) FIG. 6 shows the change in refractive index as a function of the volume proportions of TiO.sub.2 in the sol-gel layer. The linear change in refractive index as a function of the proportions of TiO.sub.2 is observed; it is linear for proportions of less than 20%.

(67) The precision on the refractive index is 7×10.sup.−4 for an error of 0.1% by volume on the amount of TiO.sub.2.

III. SEM Observation

(68) Observations by scanning electron microscopy were performed to ensure that the sol-gel layers make it possible to fill in thickness the roughness of the substrate and to obtain a flat upper surface. The images in FIG. 7 show satin-finish substrates of transparent rough glass Satinovo® from the company Saint-Gobain on which a sol-gel layer has been deposited via a sol-gel process. These substrates 4 mm thick comprise a main textured surface obtained by acid attack. These substrates are thus used as lower outer layer of the layered element. The mean height of the texturing designs of this lower outer layer, which corresponds to the roughness Ra of the textured surface of the glass Satinovo®, is between 1 and 5 μm. Its refractive index is 1.518 and its PV is between 12 and 17 μm.

(69) In the left image showing in cutaway view the substrate Satinovo® covered with the sol-gel layer, it is clearly seen that the texture is formed by a plurality of designs that are hollowed or protruding relative to the general plane of the contact surface. The thickness of the sol-gel layer is 14.3 μm.

(70) The right image shows a top view of the same substrate. The sol-gel layer has deliberately not been applied to the entire surface of the substrate Satinovo®. The sol-gel layer makes it possible to even out the roughness of the substrate.

IV. Evaluation of the Influence of the Index Harmony

(71) In order to measure the effect of the variation of index of the sol-gel layer, various sol-gel solutions were prepared and deposited onto satin-finish substrates of transparent rough glass Satinovo® defined above. The thicknesses of the sol-gel layers deposited after drying are about 15 μm.

(72) The aim of this test is to show the influence of the index harmony between the upper and lower outer layer on the optical properties of the glazing, such as: the light transmission values T.sub.L in the visible range as a percentage, measured according to standard ISO 9050:2003 (illuminant D65; 2° observer), the haze transmission values (Haze T) as percentages, measured with a hazemeter according to standard ASTM D 1003 for incident radiation on the layered element on the lower outer layer side, the percentage lightness with the Haze-Gard hazemeter from BYK.

(73) Furthermore, the quality “of vision” through the substrate thus coated was evaluated visually by 5 observers in a blind test, i.e. without the observers knowing the characteristics such as the refractive index or the index harmony of the sol-gel layers with the substrate. The observers attributed for each substrate coated with a sol-gel layer an assessment indicator chosen from: “−” not correct, “+” correct, “++” good, “+++” excellent.

(74) To simplify this test, the central layer was omitted. However, the absence of the central layer does not modify the observed tendency regarding the properties studied.

(75) The tables below summarize the compositions of the sol-gel solutions tested and the compositions of the resulting sol-gel layers.

(76) The results obtained are collated in the table above.

(77) TABLE-US-00003 Sol-gel Index Haze Lightness Visual observation layer 589 nm Δn TL (%) (%) (%) P1 P2 P3 P4 P5 G 1.623 −0.105 — — 20.7 − − − − − E 1.566 −0.048 — — 76.9 − − − − − D 1.557 −0.039 — — 87.4 − + ++ ++ ++ P 1.532 −0.014 89.8 0.3 94 + + + ++ ++ C 1.529 −0.010 — — 97.5 ++ ++ ++ ++ ++ O 1.524 −0.006 90.0 0.5 98 +++ +++ +++ +++ +++ B 1.517 0.002 — — 98 +++ +++ +++ +++ +++ N 1.514 0.000 89.8 0.5 100 +++ +++ +++ +++ +++ M 1.508 0.010 90.0 0.5 98 ++ ++ ++ ++ ++ L 1.504 0.014 89.6 0.4 96 ++ ++ ++ ++ ++ K 1.500 0.018 90.0 0.5 93 − + ++ ++ ++ A 1.493 0.025 89.9 1.1 90 − − − − − Q 1.484 0.030 89.5 1.6 78 − − − − − R 1.476 0.038 89.5 3.5 68 − − − − − S 1.468 0.046 89.5 2.9 60 − − − − − Δn represents the variation in index between the substrate Satinovo ® and the sol-gel layer.

(78) FIG. 8 is a graph showing the change in haze (right-hand y-axis) and in lightness (left-hand y-axis) as a function of the refractive index of the sol-gel layer. The vertical black line illustrates the index of the glass substrate Satinovo®.

(79) FIG. 9 is a graph showing the change in the haze (right-hand y-axis) and in the lightness (left-hand y-axis) as a function of the variation in refractive index between the substrate Satinovo® and the sol-gel layer.

(80) When the sol-gel layer has an index of between 1.500 and 1.530, haze values through the substrate thus coated of less than 0.5% are obtained. However, the haze values alone do not suffice to characterize the excellence of vision. This is why the lightness was also determined. It is found that, contrary to the haze values, which are virtually constant in the indicated index range, the lightness values reflect within this range a peak centered for refractive index values of the sol-gel layer about the index value of the substrate, i.e. 1.518. More particularly, good results are obtained for an index difference of less than 0.020 and excellent results are obtained for an index difference of less than 0.015, or even less than 0.005.

(81) In conclusion, the absolute value of the index difference between the lower outer layer of index n1 and the upper outer sol-gel layer of index n2 is preferably less than 0.020, better still less than 0.015 and even better still less than 0.013.

V. Influence of the Lamination

(82) In order to demonstrate that the lamination does not disrupt the optical performance qualities, comparative tests were performed between: S1: a substrate Satinovo® coated with a sol-gel layer O, S2: a substrate Satinovo® coated with a sol-gel layer O laminated with a flat glass by means of a PVB insert, S3: a substrate Satinovo® coated with a PVB insert.

(83) TABLE-US-00004 TL (%) Haze (%) Lightness (%) S1 90.1 1.88 92.5 S2 88.5 1.22 99.4 S3 — 4.5 58

(84) Although better results are obtained when the substrate is not laminated, the optical performance qualities are good in both cases. The lamination has the advantage of “flattening out” or effacing the imperfections of the main surface of the sol-gel layer. A completely flat outer surface is thus obtained, without any wavelet aspect and protected from dust.

(85) It is interesting to note that a direct lamination without a sol-gel layer leads to a haze of 4.5% and a lightness of 58%, these values being entirely outside the admissible limits.

VI. Influence of the Presence of the Magnetron Layer

(86) This test was performed with a transparent layered element comprising the following stack: lower outer layer: glass substrate Satinovo® of 4 mm or 6 mm, central layer: stack of layers comprising at least one silver-based layer deposited by magnetron sputtering, upper outer layer: sol-gel layer O, additional upper layer: PVB insert, additional upper layer: flat glass of 4 mm.

(87) The presence of the central layer deposited by magnetron gives the layered element an intrinsic haze effect arising from the reflections on the central layer. Even in the case of a perfect index harmony, haze is then obtained. The haze value depends on the properties of the central layer.

(88) The sol-gel layer is applied. Finally, the assembly is laminated by placing in contact a PVB insert 0.38 mm thick with the sol-gel layer and a flat glass Planilux®. The satin-finish flat glasses have a thickness of 4 mm for the first two examples with the SKN layers and 6 mm for the last two.

(89) The stack of layers of the central layer is described, for example, in patent applications WO 02/48065 and EP 0 847 965. The central layers, when they are deposited on a flat surface, have the characteristics given below.

(90) TABLE-US-00005 TL(%) Re % Ri % SKN165 60 16 17 SKN154 50 18 28 PB120 20 21 31 SS108 8 42 37

(91) In the table below, the haze and lightness values were measured for different elements in layers comprising as central layer stacks of silver-based layers deposited by magnetron. It is then observed that the haze is increased and may reach relatively high values, of a few percent. On the other hand, the lightness remains very high with values above 97%. This makes it possible to have glazings with a very good quality of vision in transmission.

(92) TABLE-US-00006 Elements with layers TL (%) Haze (%) Lightness (%) E1: SKN165 52.7 4.5 97.8 E2: SKN154 46.1 4.3 97.5 E3: PB120 26.2 2.9 98.5 E4: SS108 12.4 3.5 98.1