Photocatalytic coating substrate

SUBSTRATE WITH PHOTOCATALYTIC COATING

0002The invention relates to glass-based, ceramic or vitro-ceramic substrates, more particularly glass, in particular transparent, which are provided with coatings with photo-catalytic properties, in order to produce glazing of various applications, such as utility glazing glazing for vehicles or for buildings.

0003Increasingly, it is sought to functionalize the glazing by depositing on its surface thin layers intended to give them a particular property according to the intended application. Thus, there are layers with an optical function, such as the so-called anti-reflection layers composed of a stack of layers alternately with high and low refractive indices. For an anti-static or heating function of the anti-frost type, it is also possible provide thin electrically conductive layers, for example based on metal or doped metal oxide. For a thermal, low-emissivity or anti-solar function for example, one can turn to thin layers of metal of the silver type or based on nitride or metal oxide. To obtain an “anti-rain” effect, hydrophobic layers can be provided, for example based on fluorinated organosilane ... However, there is still a need for a substrate, in particular a glazing which could be described as “anti-fouling”, that is to say targeting the permanence over time of the appearance and surface properties, and making it possible in particular to space cleaning times and / or to improve visibility, by succeeding in eliminating progressively the dirt deposits progressively deposited on the surface of the substrate, in particular dirt of organic origin such as fingerprints or volatile organic products present in the atmosphere, or even soiling of the fogging type.

0004SUBSTITUTE SHEET (RULE 26) Now we know that there are certain semiconductor materials, based on metal oxide, which are capable, under the effect of radiation of adequate wavelength, to initiate reactions radicals causing the oxidation of organic products: we generally speak of “photo-catalytic” or even “photo-reactive” materials.

0005The object of the invention is therefore to develop photocatalytic coatings on the substrate, which have a marked “anti-fouling” effect on the substrate and which can be manufactured industrially.

0006The subject of the invention is a glass-based, ceramic or vitro-ceramic substrate, in particular made of glass and transparent, provided on at least part of at least one of its faces with a coating with photo-catalytic property comprising titanium oxide at least partially crystallized. Titanium oxide is preferably crystallized "in situ" during the formation of the coating on the substrate.

0007Titanium oxide is in fact part of the semiconductors which, under the action of light in the visible range or ultraviolet, degrade organic products which deposit on their surface. Choosing titanium oxide to manufacture glazing with an “anti-fouling” effect is therefore particularly recommended, and all the more so since this oxide has good mechanical and chemical resistance: to be effective for a long time, it is obviously important that the coating retains its integrity, even when it is directly exposed to numerous attacks, in particular when mounting the glazing on site (building) or on production line (vehicle), which involves repeated handling by mechanical or pneumatic gripping means, and also once the glazing is in place, with risks of abrasion (wiper, abrasive cloth) and contact with aggressive chemicals (air pollutants type S0₂, cleaning product, ...).

0008The choice was made, moreover, on a titanium oxide which is at least partially crystallized because it has been shown to be much more efficient in terms of photo-catalytic property than amorphous titanium oxide. Preferably, it is crystallized in anatase form, in rutile form or in the form of a mixture of anatase and rutile, with a crystallization rate of at least 25%, in particular around 30 to 80%, in particular near of the surface, (the property being rather a surface property). (We understand by crystallization rate the amount by weight of Ti0₂ crystallized with respect to the total amount by weight of Ti0₂ in the coating).

0009It has also been observed, in particular in the case of crystallization in anatase form, that the orientation of the Ti0 crystals₂ growing on the substrate had an influence on the photo-catalytic performances of the oxide: there is a preferred orientation (1, 1, 0) which clearly favors photocatalysis.

0010Advantageously, the manufacturing of the coating is carried out in such a way that the crystallized titanium oxide which it contains is in the form of "crystallites", at least near the surface, that is to say of single crystals, having an average size of between 0.5 and 1 00 nm, preferably 1 to 50 nm, in particular 1 0 to 40 nm, more particularly between 20 and 30 nm. It is indeed in this range of dimensions that titanium oxide appears to have an optimal photo-catalytic effect, probably because the crystallites of this size develop a large active surface.

0011As will be seen in more detail later, the titanium oxide coating can be obtained in many ways:

0012D by decomposition of titanium precursors (pyrolysis techniques: liquid pyrolysis, powder pyrolysis, pyrolysis in value phase called CVD (Chemical Vapor Deposition), techniques associated with sol-gel: quenched or dipping, cell-coating, ...) ,

0013O by a vacuum technique (reactive sputtering or not).

0014The coating may also comprise, in addition to crystallized titanium oxide, at least one other type of mineral material, in particular in the form of an amorphous or partially crystallized oxide, for example a silicon oxide (or mixture of oxides), titanium, tin, zirconium or aluminum. This mineral material can also participate in the photocatalytic effect of crystallized titanium oxide, by itself presenting a certain photocatalytic effect, even weak compared to that of Ti0₂ crystallized, which is the case of tin oxide or amorphous titanium oxide. A “mixed” oxide layer thus combining at least partially crystallized titanium oxide with at least one other oxide may be advantageous from the optical point of view, especially if the other or the other oxides are chosen with a lower index. to that of Tι0₂ 'by lowering the "overall" refractive index of the coating, we can play on the light reflection of the substrate provided with the coating, in particular lower this reflection This is the case if, for example, we choose a Tι0 layer₂/ Al₂0₃, one method of obtaining is described in patent EP-0 465 309, or in Tι0₂/ Sι0₂. It is necessary, of course, that the coating does contain a content of

0015Tι0₂ sufficient to maintain a notable photocatalytic activity It is therefore considered that it is preferable that the coating contains at least

001640% by weight, in particular at least 50% by weight of Tι0₂ based on the total weight of oxide (s) in the coating

0017One can also choose to superimpose on the coating according to the invention an oleophobic and / or hydrophobic grafted layer which is stable or resistant to photocatalysis, for example based on the fluorinated organosilane described in patents US Pat. No. 5,368,892 and US Pat. 5,389,427, as well as perfluoroalkylsilane described in patent application FR-94/08734 of July 3, 1,994 published under the number FR-2,722,493 and corresponding to European patent EP-0 692 463, in particular of formula.

0018CF₃- (CF₂)_not- (CH₂)_m-SX₃ in which n is from 0 to 1 2, m is from 2 to 5 and X is a hydrolyzable group

0019To amplify the photocatalytic effect of titanium oxide of the coating according to the invention, it is first possible to increase the absorption band of the coating, by incorporating into the coating other particles, in particular metallic and based on cadmium, tin, tungsten, zinc, cerium, or zirconium

0020It is also possible to increase the number of charge carriers by doping the crystal lattice of the titanium oxide, by inserting therein at least one of the following metallic elements niobium, tantalum, iron, bismuth, cobalt, nickel, copper, ruthenium, cerium, molybdenum.

0021This doping can also be done by surface doping only of titanium oxide or of the entire coating, surface doping produced by covering at least part of the coating with a layer of oxides or metal salts, the metal being chosen from iron, copper, ruthenium, cerium, molybdenum, vanadium and bismuth.

0022Finally, the photocatalytic phenomenon can be amplified by increasing the yield and / or the kinetics of the photocatalytic reactions, by covering the titanium oxide, or at least part of the coating which incorporates it, with a noble metal in the form of a thin layer. platinum, rhodium, silver, palladium type.

0023Such a catalyst, for example deposited by a vacuum technique, makes it possible in fact to increase the number and / or the lifetime of the radical entities created by the titanium oxide, and thus to favor the chain reactions leading to the degradation of organic products.

0024Surprisingly, the coating does not actually have one property but two, as soon as it is exposed to adequate radiation such as in the visible and / or ultraviolet range, such as solar radiation: by the presence of photocatalytic titanium oxide, as already seen, it promotes the gradual disappearance, as and when they accumulate, of dirt of organic origin, by causing their degradation by a process of radical oxidation. Mineral soils are not degraded by this process: they therefore remain on the surface, and, apart from certain crystallizations, they are partly easily removed since they no longer have reason to adhere to the surface, the sticky organic agents being degraded by photocatalysis.

0025However, the coating of the invention, which is permanently self-cleaning, also preferably has an outer surface with a pronounced hydrophilic and / or oleophilic character, which induces three very advantageous effects:

0026O a hydrophilic nature allows perfect wetting of the water which can be deposited on the coating. When a phenomenon of water condensation occurs, instead of a deposit of water droplets in the form of a mist impeding visibility, there is in fact a thin continuous film of water which forms on the surface of the coating. and which is completely transparent. This “anti-fog” effect is notably demonstrated by the measurement of a contact angle with water of less than 5 ° after exposure to light, and, D after water runoff, in particular from rain, on a surface that is not treated with a photocatalytic layer, numerous drops of rain water remain attached to the surface and leave, once evaporated, unsightly and annoying traces, mainly of mineral origin. a surface exposed to ambient air quickly becomes covered with a layer of dirt which limits its wetting by water. These soils are added to the other soils, in particular mineral soils (crystallizations, etc.) provided by the atmosphere in which the glazing bathes. In the case of a photoreactive surface, these mineral soils are not directly degraded by photocatalysis. In fact, they are largely eliminated thanks to the hydrophilic nature induced by the photocatalytic activity. This hydrophilic nature in fact causes perfect spreading of the raindrops. The traces of evaporation are therefore no longer present. In addition, the other mineral soils present on the surface are washed, or redissolved in the case of crystallization, by the film of water and therefore largely removed.

0027We obtain a "mineral anti-fouling" effect, in particular induced by rain,

0028O together with a hydrophilic character, the coating can also have an oleophilic character, allowing the "wetting" of organic dirt which, as for water, then tends to be deposited on the coating in the form of a continuous film less visible than well localized "spots". There is thus obtained an “organic anti-fouling” effect which takes place in two stages: as soon as it is deposited on the coating, the soiling is already hardly visible. Then, gradually, it disappears by radical degradation initiated by photo-catalysis.

0029The coating can be chosen to have a more or less smooth surface. A certain roughness can indeed be advantageous. ^•

0030D it makes it possible to develop a larger active photocatalytic surface and therefore it induces a greater photocatalytic activity,

0031O it has a direct influence on the anchorage. The roughness indeed enhances the wetting properties. A smooth hydrophilic surface will be even more hydrophilic when roughened. It is understood by “roughness”, HERE, as well the surface roughness, as the roughness induced by a porosity of the layer in at least part of its thickness. The preceding effects will be all the more marked when the coating is porous and rough. , hence a superhydrophilic effect of rough photoreactive surfaces. However, too pronounced, the roughness can be penalizing by favoring the incrustation, the accumulation of dirt and / or by making appear a level of blurring optically unacceptable.

0032It has thus proved advantageous to adapt the method of deposition of Ti0-based coatings₂ so that they have a roughness of about 2 to 20 nm, preferably 5 to 15 nm, this roughness being evaluated by atomic force microscopy, by measuring the value of the mean square deviation (called "Root Mean Square or RMS in English) on a surface of 1 micrometer square. With such roughness, the coatings have a hydrophilic character resulting in a contact angle with water which can be less than 1 °. It has also been found that it is advantageous to promote a certain porosity in the thickness of the coating. Thus, if the coating consists only of Ti0₂, it preferably has a porosity of the order of 65 to 99%, in particular from 70 to 90%, the porosity being defined here indirectly by the percentage of the theoretical density of Ti0₂, which is about 3.8. To promote such porosity, one means consists, for example, of depositing the coating by a technique of the sol-gel type, involving the decomposition of materials of organo-metallic type: it is then possible to introduce into the solution, in addition to the precursor (s) (s) organo¬ metallic ^), an organic polymer of the polyethylene glycol PEG type: by hardening the layer by heating, the PEG is burned, which generates or amplifies a certain porosity in the thickness of the layer.

0033The thickness of the coating according to the invention is variable, it is preferably between 5 nm and 1 micron, in particular between 5 and 1 00 nm, in particular between 10 and 80 nm, or between 20 and 50 nm. In fact, the choice of thickness may depend on different parameters, in particular on the envisaged application of the glazing type substrate, or even on the size of the Ti0 crystallites.₂ in the coating or the presence of alkalies in high proportion in the substrate.

0034Between the substrate and the coating according to the invention, one or more other thin layers can be arranged with a function different or complementary to that of the coating. It may be, in particular, layers with an anti-static, thermal, optical function, or promoting the crystal growth of Tι0₂ in anatase or rutile form, or in layers making barrier to the migration of certain elements coming from the substrate, in particular making barrier with alkalies and very particularly with sodium ions when the substrate is out of glass.

0035It is also possible to envisage a stack of “anti-reflection” layers alternating thin layers with high and low indices, the coating according to the invention constituting the last layer of the stack. In this case, it is preferable that the coating be relatively low refractive index, which is the case when it consists of a mixed oxide of titanium and silicon.

0036The layer with an anti-static and or thermal function (heating by providing it with current leads, low-emissivity, anti-sun, etc.) can in particular be chosen based on a conductive material of the metal type, such as silver. , or of the metal oxide type doped such as indium oxide doped with tin ITO, tin oxide doped with a halogen of the fluorine type Sn0₂: F, or with antimony Sn0₂: Sb, or zinc oxide doped with indium ZnO: ln, fluorine ZnO: F, aluminum ZnO.AI or tin ZnO: Sn. They can also be metallic oxides substoichiometric in oxygen, such as Sn0_{2 x} or Zn0_2x with x <2.

0037The anti-static function layer preferably has a square resistance value of 20 to 1000 ohms / square. Provision may be made to provide it with current leads in order to polarize it (supply voltages for example between 5 and 100V). This controlled polarization makes it possible in particular to combat the deposition of dust of size on the order of a millimeter capable of being deposited on the coating, in particular dry adherent dust only by electro-static effect: by brutally reversing the polarization of the layer, "Ejects" this dust.

0038The thin layer with an optical function can be chosen in order to reduce the light reflection and / or make the color in reflection of the substrate more neutral. In this case, it preferably has an intermediate refractive index between that of the coating and that of the substrate and an appropriate optical thickness, and may consist of an oxide or a mixture of oxides of the aluminum oxide type. Al₂0₃, tin oxide Sn0₂, indium oxide ln₂0₃, oxycarbide or oxynitride of silicon. To obtain maximum attenuation of the color in reflection, it is preferable that this thin layer has an index of refraction close to the square root of the product of the squares of the indices of refraction of the two materials which surround it, that is to say say the substrate and the coating according to the invention.

0039At the same time, it is advantageous to choose its optical thickness (that is to say the product of its geometric thickness and its refractive index) close to lambda / 4, lambda being approximately the average wavelength in the visible range, especially around 500 to 550 nm.

0040The thin layer with an alkali barrier function can in particular be chosen based on silicon oxide, nitride, oxynitride or oxycarbide, in aluminum oxide containing fluorine AI₂0₃: F, or in aluminum nitride. In fact, it has been found to be useful when the substrate is made of glass, since the migration of sodium ions into the coating according to the invention can, under certain conditions, alter its photocatalytic properties.

0041The nature of the substrate or of the sub-layer also has an additional advantage; it can promote the crystallization of the photocatalytic layer which is deposited, in particular in the case of CVD deposition.

0042So when filing by CVD of Tι0₂, a sub-layer of Sn0₂: F crystallized promotes the growth of Tι0₂ in mainly rutile form, in particular for deposition temperatures of the order of 400 ° to 500 ° C., while the surface of a soda-lime glass or a sublayer of silicon oxycarbide rather induces growth anatase, in particular for deposition temperatures of the order of 400 ° to 600 ° C.

0043All these optional thin layers can, in known manner, be deposited by vacuum techniques of the sputtering type or by other techniques of the thermal decomposition type such as pyrolysis in solid, liquid or gas phase. Each of the pre-mentioned layers can combine several functions, but they can also be superimposed. The invention also relates to “anti-fouling” glazing

0044(organic and / or mineral soiling) and / or "anti-fogging", whether they are monolithic, multiple insulators of the double-glazing or laminated type, and which incorporate the coated substrates previously described.

0045The invention therefore relates to the manufacture of glass, ceramic or vitro-ceramic products, and more particularly the manufacture of "self-cleaning" glazing. These can advantageously be building glazing, such as double glazing (it is then possible to have the coating “outside side” and / or “inside side”, that is to say on face 1 and / or on face 4). This is particularly advantageous for glazing that is difficult to access for cleaning and / or that needs to be cleaned very frequently, such as roof glazing, airport glazing, etc. It may also be glazing for vehicles where maintaining visibility is an essential safety criterion. This coating can thus be placed on windshields, lateral or rear windows of the car, in particular on the face of the windows facing the interior of the passenger compartment. This coating can then prevent the formation of fogging, and / or remove the traces of soiling of the fingerprint type, nicotine or organic material of the volatile plasticizer type released by the plastic covering the interior of the passenger compartment, in particular that of the switchboard. edge (salting known sometimes under the English term of "fogging"). Other vehicles such as planes or trains may also find advantage in using glazing provided with the coating of the invention.

0046Many other applications are possible, in particular for aquarium glasses, shop windows, greenhouses, verandas, glasses used in interior or street furniture, but also mirrors, television screens, the field of eyewear or any architectural material such as facade material, cladding, roofing such as tiles, ...

0047The invention thus makes it possible to functionalize these known products, by giving them anti-ultraviolet, anti-fouling, bactericidal, anti-reflection, anti-static, anti-microorganism, ... properties.

0048Another interesting application of the coating according to the invention consists in associating it with an electrically controlled variable absorption glazing of the electrochromic glazing type, liquid crystal glazing optionally with dichroic dye, glazing with suspended particle system, viologene glazing ... All these glazings being generally made up of a plurality of transparent substrates between which the “active” elements are arranged, it is then advantageously possible to have the coating on the external face of at least one of these substrates.

0049In particular in the case of electrochromic glazing, when the latter is in the colored state, its absorption leads to a certain heating on the surface, which, in fact, is capable of accelerating the photocatalytic decomposition of the carbonaceous substances depositing on the coating according to the invention. For more details on the structure of an electrochromic glazing, advantageously reference will be made to patent application EP-A-0 575 207 describing an electrochromic laminated double glazing, the coating according to the invention preferably being able to be arranged in side 1.

0050The invention also relates to the various methods of obtaining the coating according to the invention. A deposition technique of the pyrolysis type can be used, which is advantageous because it allows the coating to be deposited continuously, directly on the float glass ribbon, when a glass substrate is used.

0051Pyrolysis can be carried out in the solid phase, using powder (s) of precursor (s) of the organo-metallic type (s).

0052Pyrolysis can be carried out in the liquid phase, starting from a solution comprising an organometallic titanium precursor of the titanium chelate and / or titanium alcoholate type. Such precursors are mixed with at least one other organometallic precursor. For more details on the nature of the titanium precursor or on the deposition conditions, reference will be made, for example, to patents FR-2 310 977 and EP-0 465 309.

0053Pyrolysis can also be carried out in the vapor phase, a technique which is also known by the term CVD (Chemical Vapor Deposition), from at least one halide-type titanium precursor such as TiCl₄ or titanium alcoholate of the tetraisopropylate type of Ti, Ti (OiPr)₄. The crystallization of the layer can also be controlled by the type of sub-layer, as mentioned above. The coating can also be deposited by other techniques, in particular by the techniques associated with “sol-gel”. Different modes of deposition are possible, such as "quenching" also called "dip-coating" or deposition using a cell called "cell-coating". It can also be a method of deposition by “spray-coating” or by laminar coating, the latter technique being detailed in patent application WO-94/01 598. All of these deposition methods generally use a solution comprising at least one organometallic precursor, in particular of titanium of the alcoholate type which is thermally decomposed after coating of the substrate with the solution on one of its faces, or on its two faces.

0054It may also be advantageous to deposit the coating, whatever the deposition technique envisaged, not at once, but by at least two successive stages, which appears to favor the crystallization of titanium oxide on the entire thickness of the coating when chosen relatively thick.

0055Similarly, it is advantageous to subject the coating with photo-catalytic property, after deposition, to a heat treatment of the annealed type. A heat treatment is essential for a sol-gel or laminar coating technique in order to decompose the organo¬ metallic precursor (s) into oxide, once the substrate has been coated and improve resistance to abrasion, which is not the case when using a pyrolysis technique where the precursor decomposes as soon as it comes into contact with the substrate. In the first case as in the second, however, a post-deposition heat treatment, once the Ti0₂ formed, improves its crystallization rate. The treatment temperature chosen can also allow better control of the crystallization rate and the crystalline, anatase and / or rutile nature of the oxide.

0056However, in the case of a soda-lime glass substrate, multiple and prolonged annealing can favor an attenuation of the photocatalytic activity because of too great migration of the alkalis from the substrate to the photoreactive layer. The use of a barrier layer between the substrate, if it is standard glass, and the coating, or the choice of a glass substrate of suitable composition, or the choice of a soda-lime glass whose surface is dealkalized, eliminating this risk.

0057Other details and advantageous characteristics of the invention emerge from the description below of nonlimiting exemplary embodiments, with the aid of the following figures:

0058FIG. 1: a cross section of a glass substrate provided with the coating according to the invention,

0059FIG. 2: a diagram of a sol-gel deposition technique, known as “by dipping” or by “dip-coating” of the coating,

0060FIG. 3: a diagram of a so-called "cell-coating" deposition technique,

0061FIG. 4: a diagram of a so-called “spray-coating” deposition technique,

0062FIG. 5: a diagram of a deposition technique by laminar coating.

0063As shown diagrammatically in FIG. 1, all of the following examples relate to the deposition of a coating 3 known as “anti-fouling” essentially based on titanium oxide on a transparent substrate 1.

0064The substrate 1 is made of clear soda-lime-silica glass 4 mm thick and 50 cm long and wide. It goes without saying that the invention is not limited to this specific type of glass. The glass may also not be flat, but curved.

0065Between the coating 3 and substrate 1, there is an optional thin layer 2 either based on silicon oxycarbide denoted SiOC in order to constitute a barrier to diffusion to alkalis and / or a layer attenuating light reflection, or based on tin oxide doped with fluorine Sn0₂: F in order to constitute an anti-static and / or low-emissive layer, even with a low-emissive effect that is not very accentuated, and / or attenuating the color, in particular in reflection.

EXAMPLES 1 TO 3

0067Examples 1 to 3 relate to a coating 3 deposited using a liquid phase pyrolysis technique. It is possible to proceed continuously, using a suitable dispensing nozzle arranged transversely and above the float glass ribbon, out of the enclosure of the float bath itself. Here, we proceeded discontinuously, using a movable nozzle arranged opposite the substrate 1 already cut to the dimensions indicated, substrate which is first heated in an oven at a temperature of 400 to 650 ° C before running at constant speed in front of the nozzle projecting an appropriate solution.

EXAMPLE 1

0069In this example, there is no optional layer 2. The coating 3 is deposited using a solution comprising two organometallic titanium precursors, titanium di-iso-propoxy di-acetylacetonate and titanium tetra-octylene glycolate dissolved in a mixture of two solvents, which are ethyl acetate and isopropanol.

0070It may be noted that other precursors of the same type are also quite usable, in particular other titanium chelates of the titanium acetylacetonate, titanium methylacetoacetate, titanium ethylacetoacetate or else the titanium tri-ethanol amine or the titanium di-ethanol amine.

0071As soon as the substrate 1 has reached the desired temperature in the oven, in particular around 500 ° C., the latter passes past the nozzle, projecting the indicated mixture at ambient temperature using compressed air.

0072We then obtain a layer of Ti0₂ about 90 nm thick, the thickness being able to be controlled by the speed of travel of the substrate 1 in front of the nozzle and / or the temperature of said substrate. The layer is partially crystallized in anatase form.

0073This layer has excellent mechanical strength. Its resistance to abrasion tests is comparable to that obtained for the surface of bare glass.

0074It is bendable and hardenable. There is no haze: the diffuse light transmission of the coated substrate is less than 0.6% (measured according to the illuminant D₆₅ at 560 nm). EXAMPLE 2

0075II repeats Example 1, but by inserting between layer 1 and coating 3 a layer 2 of Sn0₂: 73 nm thick. This layer is obtained by pyrolysis of powder from dibutyltin difluoride DBTF. It can also be obtained, in a known manner, by pyrolysis in the liquid or vapor phase, as is for example described in patent application EP-A-0 648 1 96. In the vapor phase, a mixture of monobutyl tin trichloride and a fluorinated precursor possibly combined with a “mild” oxidant of type H₂0.

0076The index of the layer obtained is approximately 1.9. Its square resistance is around 50 ohms.

0077In Example 1 above, the coated substrate 1, mounted in double glazing so that the coating is on face 1 (with another substrate 1 'not coated but of the same nature and dimensions as the substrate 1 by the (1 2 mm air gap) has a color purity value in reflection of 26% and a color purity value in transmission of 6.8%.

0078In this example 2, the color purity in reflection (in gold) is no more than 3.6%, and it is 1.1% in transmission.

0079So the underlay in Sn0₂: F makes it possible to impart anti-static properties to the substrate due to its electrical conductivity, it also has a favorable influence on the colorimetry of the substrate, by making its coloration much more "neutral", both in transmission and in reflection, coloration caused by the presence of the titanium oxide coating 3 having a relatively high refractive index. It can be polarized by providing it with a suitable electrical supply, in order to limit the deposition of dust of relatively large size of the order of a millimeter.

0080In addition, this sublayer reduces the diffusion of alkalis in the photocatalytic layer of Ti0₂. The photocatalytic activity is therefore improved. EXAMPLE 3

0081It repeats Example 2, but this time intercalating between substrate 1 and coating 3 a layer 2 based on silicon oxycarbide, with an index of about 1.75 and a thickness of about 50 nm, which layer is can be obtained by CVD from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in patent application EP-A-0 51 8 755. This layer is particularly effective in preventing the tendency to diffusion of alkalis (Na ⁺ , K ⁺ ) and alkaline earth (Ca^{+ +} ) from the substrate 1 to the coating 3 and therefore the photocatalytic activity is significantly improved. Having, like Sn0₂: F, an index of refraction intermediate between that of the substrate (1, 52) and of the coating 3 (approximately 2.30 to 2.35), it also makes it possible to attenuate the intensity of the coloring of the substrate as well in reflection than in transmission and overall reduction of the light reflection value R_L of said substrate.

0082The following examples 4 to 7 relate to CVD deposits.

EXAMPLE 4 TO 7 EXAMPLE 4

0084This example relates to the CVD deposition of the coating 3 directly on the substrate 1, using a standard nozzle such as that shown in the abovementioned patent application EP-A-0 51 8 755. As precursors, either an organometallic or a metallic halide is used. Here, the titanium tetra-isopropylate is chosen as the organometallic, which is interesting for its high volatility and its wide range of temperatures of use, from 300 to 650 ° C. The deposition is carried out in this example at approximately 425 ° C., the thickness of Ti0₂ is 15 nm.

0085Tetraethoxy titanium Ti (0-Et)₄ may also be suitable, and as halide, mention may be made of TiCI₄. EXAMPLE 5

0086It is carried out similarly to Example 4, except that here the 15 nm layer of Ti0 is deposited₂ not directly on the glass, but on a 50 nm SiOC undercoat deposited as in Example 3. EXAMPLE 6

0087It is carried out as in Example 4, except that here the thickness of the layer of Ti0₂ is 65 nm. EXAMPLE 7

0088It is carried out as in Example 5, except that here the thickness of the layer of Ti0₂ is 60 nm.

0089From these examples 4 to 7, it can be seen that the substrates thus coated have good mechanical resistance to the abrasion tests. In particular, no delamination of the Ti0 layer is observed₂. EXAMPLE 8

0090This example uses a technique associated with sol-gel using a “hardened” deposition method also called “dip-coating”, the principle of which emerges from FIG. 2: it involves immersing the substrate 1 in the liquid solution 4 containing the appropriate precursor (s) of the coating 3, then extracting the substrate 1 therefrom at a controlled speed using a motor means 5, the choice of the extraction speed making it possible to adjust the thickness of solution remaining on the surface of the two faces of the substrate and, in fact, the thickness of the coatings deposited, after heat treatment of the latter to both evaporate the solvent and decompose the precursor (s) into oxide.

0091A solution 4 comprising either titanium tetrabutoxide Ti (0-Bu) is used to deposit the coating 3₄ stabilized with DEA ​​diethanol amine in molar ratio 1: 1 in an ethanol type solvent with 0.2 mole of tetrabutoxide per liter of ethanol, ie the mixture of precursors and solvents described in Example 1. (Can also be used another precursor like titanium dibutoxy-diethanolamine).

0092The substrates 1 may include SiOC sublayers.

0093After extraction of each of the solutions 4, the substrates 1 are heated for 1 hour at 1 00 ° C and then about 3 hours at 550 ° C with a gradual rise in temperature.

0094A coating 3 is obtained on each of the faces, in both cases of Ti0₂ well crystallized in anatase form. EXAMPLE 9

0095This example uses the technique called “cell-coating”, the principle of which is recalled in FIG. 3. It involves forming a narrow cavity delimited by two substantially parallel faces 6, 7 and two seals 8, 9, at least one of these faces 6, 7 being constituted by the face of the substrate 1 to be treated. Then the cavity is filled with the solution 4 of precursor (s) of the coating, and the solution 4 is removed in a controlled manner, so as to form a wetting meniscus using a peristaltic pump 1 0 for example, leaving a film of the solution 4 on the face of the substrate 1 as the solution is withdrawn.

0096The cavity 5 is then maintained at least the time necessary for drying. The hardening of the film is carried out by heat treatment. The advantage of this technique compared to “dip-coating” is in particular that only one of the two faces of the substrate 1 can be treated, and not both systematically, unless a masking system is used. .

0097The substrates 1 include thin layers 2 based on silicon oxycarbide SiOC.

0098Example 6 uses the solutions 4 described in Example 8 respectively. The same heat treatments are then carried out to obtain the coating 3 of Ti0₂.

0099The coating 3 has good mechanical durability. A field effect appears in SEM (scanning electron microscope) in the form of “grains” of single crystals with a diameter of about 30 nm. The roughness of this coating induces enhanced wetting properties compared to a non-rough coating.

0100These same solutions 4 can also be used to deposit coatings by “spray-coating”, as shown in FIG. 4, where the solution 4 is sprayed in the form of a cloud against the substrate 1 in static, or by laminar coating. as shown in figure 5. In the latter case, the substrate 1 is passed, maintained by vacuum suction, against a support 1 1 made of stainless steel and Teflon over a tank 1 2 containing the solution, solution in which a cylinder 1 4 is partially immersed. split, the whole of the reservoir 1 2 and of the cylinder 14 is then moved over the entire length of the substrate 1, the mask 13 avoiding too rapid evaporation of the solvent from the solution 4. For more details on this latter technique, advantageously refer to the patent application WO-94/01 598 cited above.

0101Tests were carried out on the substrates obtained according to the preceding examples in order to characterize the coatings deposited and assess their "anti-fog" and "anti-fouling" performances.

0102Q Test 1: this is the fogging pattern test. It consists in observing the consequences of photo-catalysis and of the structure of the coating (rate of hydroxyl groups, porosity, roughness) on the wetting. If the surface is photo-reactive, the carbonaceous micro-pollution which is deposited on the coating is permanently destroyed, and the surface is hydrophilic therefore anti-fog. You can also make a quantitative assessment by suddenly reheating the initially coated substrate, stored in the cold or simply by blowing on the substrate, measuring if it appears fog and if so, when, then measuring the time. necessary for the disappearance of said mist.

0103Q Test 2: this involves evaluating the hydrophilicity and oleophilicity on the surface of the coating 3, in comparison with those of the surface of a bare glass, by measuring the contact angles of a drop of water and a drop of DOP (di-octyl-phthalate) on their surfaces, after having left the substrates for one week in the ambient atmosphere under natural light, in the dark and then having subjected them for 20 minutes to UVA radiation .

0104G Test 3: it consists of depositing on the substrate to be evaluated a layer of an organosilane and irradiating it with UVA so as to degrade it by photocatalysis. As the organosilane modifies the wetting properties, the measurements of the contact angle with water of the substrate during irradiation indicate the state of degradation of the grafted layer. The rate of disappearance of this layer is related to the photocatalytic activity of the substrate.

0105The grafted organosilane is a trichlorosilane: octadecyltrichlorosilane

0106(OTS). The grafting is carried out by soaking.

0107The test device consists of a carousel rotating around 1 to 6 low pressure UVA lamps. The test pieces to be evaluated are placed in the carousel, the side to be assessed on the UVA side. Depending on their position and the number of lamps lit, each test piece receives irradiation.

0108UVA varying from 0.5 W / m² at 50 W / m². For examples 1, 2, 3, 8 and 9, the irradiation power is chosen from 1.8 W / m², and for examples 4 to 7 of

01090.6 W / m².

0110The time between each contact angle measurement varies between 20 min and

01113 h, depending on the photocatalytic activity of the specimen considered. The measurements are carried out using a goniometer.

0112Before irradiation, the lenses have an angle of approximately 1,00 °. It is considered that the layer is destroyed after irradiation when the angle is less than 20 °.

0113Each test piece tested is characterized by the average speed of disappearance of the layer, given in nanometers per hour, that is to say the thickness of the layer of organosilane deposited divided by the duration of irradiation making it possible to reach a final level less than 20 ° (time of disappearance of the organosilane layer).

0114All the previous examples pass test 1, that is to say that when blowing on the substrates coated with the coating, they remain perfectly transparent, while a layer of very visible mist is deposited on the uncoated substrates.

0115The examples underwent test 2: the coated substrates, after exposure to UVA radiation, have a contact angle with water and with DOP of at most 5 °. On the contrary, a bare glass under the same conditions has a contact angle with water of 40 ° and a contact angle with DOP of 20 °

0116The table below groups together the results of the coated substrates according to the examples preceding in test 3.

0117<img file="WO9710186A1_D0001.tif" />

0118From the table, it can be seen that the presence of sublayers, in particular of SiOC, promotes the photocatalytic activity of the coating containing Ti0₂, by its barrier effect to alkaline and alkaline earth metals which can migrate from glass (comparison of examples 4 and 5 or 6 and 7).

0119We also observe that the thickness of the coating containing Ti0₂ also plays a role (comparison of examples 1 and 3): for a Ti0 coating thickness₂ larger than the average size of the monocrystals or “crystallites”, a better photocatalytic effect is obtained.

0120In fact, it has been observed that these are the Ti0 coatings₂ obtained by CVD which exhibit the most advanced crystallization, with crystallite sizes of the order of 20 to 30 nm. It can be seen that the photocatalytic activity of Example 6 (65 nm of Ti0₂) is clearly greater than that of Example 4 (1 5 nm of Ti0₂ only). It is therefore advantageous to provide a coating thickness of Ti0₂ at least twice the average diameter of the crystallites it contains. Alternatively, as in Example 5, a thin thickness of Ti0 coating can be kept₂ but then choose to use an underlay of the appropriate type and thickness to best promote the crystal growth of Ti0₂ from the "first" layer of crystallites.

0121It has been observed that the crystallization of Ti0₂ was slightly less advanced for coatings deposited by a technique other than CVD. Here again, however, everything is a matter of compromise: less advanced crystallization and a priori lower photocatalytic activity can be “compensated” by the use of a less expensive or less complex deposition process, for example. In addition, the use of an appropriate sublayer or doping of Ti0₂ can improve photocatalytic performance if necessary.

0122It is also verified from the comparison of examples 2 and 3 that the nature of the underlayer influences the mode of crystallization and, in fact, the photocatalytic activity of the coating.