New photo-catalytic coatings based on titanium di:oxide in a mineral or organic dispersion

- 1 PHOTO-CATALYTIC COATING SUBSTRATE

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

More and more, attempts are made to functionalize glazing by depositing thin layers on their surface intended to give them a particular property depending on 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 function, or a heating function of the anti-frost type, it is also possible to provide thin electrically conductive layers, for example based on metal or on doped metal oxide. For a thermal, low-emissivity or anti-solar function for example, one can turn to thin metal layers of the silver type or based on nitride or metal oxide. To obtain an “anti-rain” effect, layers of a hydrophobic nature can be provided, for example based on fluorinated organo-silane.

However, there is still a need for a substrate, in particular a glazing which could be qualified as “anti-fouling”, that is to say aimed at the permanence over time of the appearance and surface properties, and in particular making it possible to space out the cleaning operations and / or to improve visibility, succeeding in gradually eliminating the dirt gradually settling 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 mist-type dirt.

- 2 Now we know that there are certain semiconductor materials, based on metal oxide, which are able, under the effect of radiation of adequate wavelength, to initiate radical reactions causing oxidation organic products: we generally speak of “photo-catalytic” or “photo-reactive” materials.

The aim of the invention is therefore to develop photocatalytic coatings on a substrate, which exhibit a marked “anti-fouling” effect with respect to the substrate and which can be manufactured in an industrial manner.

The subject of the invention is a glass-based, ceramic or glass-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 oxide of at least partially crystallized titanium, incorporated into said coating in the form of particles, in particular with a size of between 5 and 70 nm, essentially crystallized in the anatase or anatase / rutile form. The incorporation is preferably carried out with a binder.

Titanium oxide is in fact part of the semiconductors which, under the action of light in the visible range or of ultraviolet rays, degrade organic products which are deposited on their surface. Choosing titanium oxide to manufacture glazing with an “anti-fouling” effect is therefore particularly recommended, especially since this oxide has good mechanical and chemical resistance: to be effective for a long time, it is obviously important for the coating to retain its integrity, even though it is directly exposed to numerous attacks, in particular during the assembly of the glazing on site (building) or on a 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 (windscreen wiper, abrasive cloth) and contact with aggressive chemicals (atmospheric pollutants such as SO₂, cleaning product, ...,.

The choice fell, 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.

- 3 or in the form of a mixture of anatase and rutile, with a degree of crystallization of at least 25%, in particular of about 30 to 80%. (The crystallization rate is understood to mean the amount by weight of TiO₂ crystallized relative to the total amount by weight of TiO₂ in the coating).

It has also been observed, in particular in the case of crystallization in anatase form, that the orientation of the cristaux02 crystals growing on the substrate had an influence on the photo-catalytic performance of the oxide: there is a preferred orientation ( 1,1,0) which clearly favors photocatalysis.

Advantageously, the production of the coating is carried out so that the crystalline titanium oxide that it contains is in the form of “crystallites”, that is to say of single crystals, having an average size of between 0, 5 and 60 nm, preferably 1 to 50 nm, especially 10 to 40 nm. It is in fact in this size range that titanium oxide appears to have an optimum photocatalytic effect, probably because crystallites of this size develop a large active surface.

As will be seen in more detail later by the description of the various methods of obtaining the coating, the titanium oxide particles can in fact be incorporated into the coating in multiple ways. These particles are in fact generally agglomerates of crystallites and in particular have an average size of the order of 5 to 70 nm.

The binder which can be used to incorporate the particles into the coating can be inorganic, in particular in the form of an amorphous or partially crystallized oxide (or mixture of oxides), for example in oxide of silicon, titanium, tin, zirconium or d. 'aluminum. It can be confined to its role of matrix vis-à-vis the active particles of titanium oxide, which is the case for example with silicon oxide. But it can also participate in the photocatalytic effect of the particles, by itself exhibiting a certain photocatalytic effect, even weak compared to that of the particles, which is the case with amorphous or partially crystallized titanium oxide.

The binder can also be chosen partially or essentially organic, in particular in the form of a polymeric matrix. It may be a polymer which may have properties complementary to those of the particles.

- 4 titanium oxide, and in particular hydrophobic and / or oieophobic properties and which can be deposited by a sol-gel type technique. As an example of such matrices, reference may be made to patent application FR-94/03689 of March 29, 1994, which describes such a matrix sometimes referred to as a hybrid and obtained from a solution comprising an epoxidized alkoxysilane, a silane. non-epoxidized hydrolyzable, colloidal silica, a catalyst and at least one hydrolyzable fluorinated alkylsilane. The fluorinated alkylsilane is of general formula;

CF₃- (CF₂)_not- (CH₂)_m-Six₃, with n from 0 to 12, m from 2 to 5, X a hydrolyzable function. The epoxidized alkylsilane has the formula:

CH₂-CM-CH₂-O- (CH₂-CH₂-O)_r- (CH₂)_s-If {OM ')₃.p \ *

O Mp in which p is O or Δ, r is 0.1 or 2, s is an integer between 1 and 6, M = H or an alkyl comprising 1 to 4 carbon atoms, M 'and M are alkyls comprising 1 to 3 carbon atoms. The unepoxidized silane has the general formula:

NOT'

I

Q-Si-Q '

I

N in which N and N 'are organic groups linked to the silicon atom by an Si-C bond and which do not contain a group capable of reacting with the hydrolyzed silanes present in the composition, and where Q and Q' are hydrolyzable functions.

It is also possible to choose to superimpose on the coating according to the invention an oleophobic and / or hydrophobic layer grafted, for example based on the fluorinated organosilane described in the patents US-5,368,892 and US-5,389,427, as well as on base of perfluoroalkylsilane described in patent application FR94 / 08734 of July 13, 1994, in particular of formula:

CF₃- (CF₂)_not- {CH₂)_m-Six₃ wherein n is 0 to 12, m is 2 to 5 and X is a hydrolyzable group.

To amplify the photo-catalytic effect of the titanium oxide particles of the coating according to the invention, suitable additives can be incorporated therein.

The absorption band of the coating can first of all be increased by incorporating into the coating other particles, in particular metallic particles and based on cadmium, tin, tungsten, zinc, cerium or zirconium.

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

This doping can also be done by surface doping only of the titanium oxide particles, surface doping carried out by covering at least part of said particles with a layer of oxides or of metal salts, the metal being chosen from the following group: iron, copper, ruthenium, cerium, molybdenum, vanadium and bismuth.

Finally, the photocatalytic phenomenon can be amplified by increasing the yield and / or kinetics of the photocatalytic reactions, by covering at least part of the particles with a noble metal in the form of a thin layer of the platinum, rhodium or silver type.

Quite surprisingly, the coating in fact exhibits not one property but two, as soon as it is exposed to an adequate radiation such as visible light and / or ultraviolet: by the presence of titanium oxide photo-catalytic, as already seen, it promotes the gradual disappearance, as they accumulate, of soiling of organic origin, causing their degradation by a radical oxidation process.

However, the coating of the invention also preferably has an outer surface with a pronounced hydrophilic and / or oleophilic nature, in particular in the case where the binder is mineral, which brings two not insignificant advantages: a hydrophilic nature allows perfect wetting of the water. water which can be deposited on the coating. Instead of a deposit of water droplets in the form of mist obstructing visibility, there is in fact a continuous thin film of water which forms on the surface of the coating and which is quite transparent. This “anti-fog” effect is demonstrated in particular by measuring a contact angle with water of less than 5 ° after exposure to light.

Together with a hydrophilic character, it can also have an oleophilic character, allowing the “wetting” of organic soiling which,

- 6as for water, then tend to be deposited on the coating in the form of a continuous film less visible than well localized "spots". An “organic anti-fouling” effect is thus obtained which takes place in two stages: as soon as it is deposited on the coating, the dirt is already barely visible. Then, gradually, it disappears by radical degradation initiated by photocatalysis.

The thickness of the coating according to the invention is variable, it is preferably between 5 nm and 1 micron, in particular between 5 and 100 nm, in particular between 10 and 80 nm, or between 20 and 50 nm. In fact, the choice of the thickness can depend on various parameters, in particular on the envisaged application of the substrate of the glazing type, or also on the size of the TiO crystallites.₂ in the coating. The coating can also be chosen to have a more or less smooth surface: a low surface roughness can in fact be advantageous, if it makes it possible to develop a larger active photocatalytic surface. However, too pronounced, it can be penalizing by promoting encrustation, the accumulation of dirt. In the event that the coating is based on TiO particles₂ coated in a binder, it is possible to choose the deposition method and the thickness of the coating so that the particles or crystallites of which they are made “emerge” at the surface of this binder.

Between the substrate and the coating according to the invention, one or more other thin layers with a function different or complementary to that of the coating can be placed. They may be, in particular, layers with an antistatic, thermal, optical function or layers forming a barrier to the migration of certain elements coming from the substrate, in particular forming a barrier to alkalis and more particularly to sodium ions when the substrate is made of glass. It 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 for the coating to have a relatively low refractive index, which is the case when it consists, in particular, of a mineral matrix of the silicon oxide type in which particles of silicon are embedded. titanium oxide, or a mixed oxide of titanium and silicon.

- 7 The layer with an anti-static and or thermal function (heating by providing it with current supplies, low-emissivity, anti-solar, etc.) can in particular be chosen based on a conductive material of the metal type, such as silver, or of the doped metal oxide type such as indium oxide doped with tin ITO, tin oxide doped with a halogen of the fluorine SnO type₂: F, or zinc oxide doped with indium ZnOdn, fluorine ZnO: F, aluminum ZnO: A or tin ZnO: Sn.

The anti-static layer preferably has a square resistance value of 20 to 1000 ohms / square. Provision can be made to provide it with current inputs in order to polarize it (supply voltages for example between 5 and 100V). This controlled polarization makes it possible in particular to fight against the deposition of dust of the order of a millimeter liable to deposit on the coating, in particular dry dust adhering only by electro-static effect: by suddenly reversing the polarization of the layer, we "Ejects" this dust.

The thin layer with an optical function can be chosen in order to reduce the light reflection and / or to make the color in reflection of the substrate more neutral. In this case, it preferably has an index of refraction intermediate between that of the coating and that of the substrate and an appropriate optical thickness, and may consist of an oxide or of a mixture of oxides of the aluminum oxide type. HAVE₂O₃, tin oxide SnO₂, indium oxide ln₂O₃, oxycarbide or silicon oxynitride. To obtain maximum attenuation of the color in reflection, it is preferable that this thin layer has a refractive index close to the square root of the product of the squares of the refractive indices of the two materials which surround it, that is to say say the substrate and the coating according to the invention. At 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, in particular about 500 to 550 nm.

The thin layer with the function of an alkali barrier can in particular be chosen based on silicon oxide, nitride, oxynitride or oxycarbide, aluminum oxide containing fluorine Al₂O₃: F, or in nitride

- 8 aluminum. In fact, it has proved to be useful when the substrate is made of glass, since the migration of sodium ions in the coating according to the invention can, under certain conditions, alter its photocatalytic properties.

All these optional thin layers can, in a known manner, be deposited by vacuum techniques of the cathode sputtering type or by other techniques of the thermal decomposition type such as pyrolysis in the solid, liquid or gas phase. Each of the aforementioned layers can combine several functions, but they can also be superimposed.

A subject of the invention is also “anti-fouling” and / or “anti-fog” glazing, whether monolithic, multiple insulators of the double-glazing or laminated type, and which incorporate the coated substrates described above.

The invention therefore relates to the manufacture of glass, ceramic or glass-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 "on the outside" and / or "on the inside", that is to say on face 1 and / or opposite. 4). This is particularly advantageous for glazing that is not easily accessible for cleaning and / or which needs to be cleaned very frequently, such as roof glazing, airport glazing, etc. It can also be glazing. for vehicles where maintaining visibility is an essential safety criterion. This coating can thus be placed on the windshields, side panels or rear windows of a car, in particular on the face of the glazing facing the interior of the passenger compartment. This coating can then prevent the formation of fogging, and / or remove traces of soiling of the type fingerprints, nicotine or organic material of the volatile plasticizer type released by the plastic lining the interior of the passenger compartment, in particular that of the control panel. edge (release sometimes known under the English term of "fogging"). Other vehicles such as airplanes or trains may also find it advantageous to use glazing provided with the coating of the invention.

Many other applications are possible, including aquarium glasses, shop windows, greenhouses, conservatories, used glasses

- 9 in interior furnishings or street furniture, but also mirrors, television screens, ...

Another advantageous application of the coating according to the invention consists in combining 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, viologen glazing, etc. Since all these glazing units generally consist of a plurality of transparent substrates between which the “active” elements are placed, the coating can then advantageously be placed on the outer face of at least one of these substrates.

Particularly in the case of an electrochromic glazing, when the latter is in the colored state, its absorption leads to a certain heating at the surface, which, in fact, is liable to accelerate the photocatalytic decomposition of the carbonaceous substances depositing on it. the coating according to the invention. For more details on the structure of an electrochromic glazing, reference will advantageously 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.

The subject of the invention is also the various processes for obtaining the coating according to the invention. It is possible to have recourse to a deposition technique of the pyrolysis type, which is advantageous because it allows in particular the deposition of the continuous coating, directly on the float glass ribbon, when a glass substrate is used.

The pyrolysis can be carried out in the liquid phase, from a solution comprising the particles of titanium oxide and at least one organometallic precursor, in particular of titanium of the titanium chelate and / or titanium alcoholate type. 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.

The coating can also be deposited by other techniques, in particular by the so-called “sol-gel” technique. Different deposition methods are possible, such as “dipping” also called “dip-coating” or deposition using a cell called “cell-coating”, the latter technique being

- 10described in detail in patent application FR-95/05978 filed May 19, 1995. It can also be a deposition method by "spray-coating" or by laminar coating, the latter technique being detailed in the patent application WO-94/01598. All 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 the substrate with the solution on one of its faces, or on both of its faces. faces.

These deposition techniques set out above, which use a solution, therefore incorporate into the solution of metal precursors a powder or a colloidal dispersion of particles of titanium oxide already formed and crystallized, in particular in the anatase or anatase / rutile form. These particles, mentioned above, are highly active on the photocatalytic level and can also promote the crystallization of TiO₂ formed by thermal decomposition from the precursors, probably playing the role of seeds of crystallization. In the final coating, we thus have titanium oxide "made" in two different ways. Advantageously, it is possible to choose a rate of introduction of titanium oxide particles into the solution so as to use from 0.1 to 0.6 grams of these particles per gram of titanium oxide effectively deposited on the substrate. Preferably, the titanium oxide particles have a particle size distribution such that at least 80% of them have the same average diameter, in particular around 20 or 40 nm. The dispersion of TiO 2 particles advantageously has specific characteristics, in particular it comprises particles of titanium dioxide at least partially crystallized and “monodisperse”.

By monodisperse is meant particles having a dispersion index of at most 0.5, preferably at most 0.3, the dispersion index being given by the following formula: I = (084-0,₆) / 2. 0_5O in which :

0₈₄ is the particle diameter for which 84% of the particles have a diameter less than 0₈₄,

0₁₆ is the particle diameter for which 16% of the particles have a diameter less than 0₁₆.

- 11 It may be advantageous, moreover, to deposit the coating, regardless of the deposition technique envisaged, not all at once, but by at least two successive stages, which appears to promote crystallization of the oxide. titanium over the entire thickness of the coating when chosen relatively thick.

Likewise, it is advantageous to subject the coating with photo-catalytic property, after deposition, to a heat treatment of the annealing type. A heat treatment is essential for a technique of the sol-gel or laminar coating type in order to decompose the organometallic precursor (s) into oxide, once the substrate has been coated, which is not necessary. this is the case when a pyrolysis technique is used 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 TiO₂ formed, improves its crystallization rate. The treatment temperature chosen can also make it possible to better control the rate of crystallization and the crystalline nature, anatase and / or rutile, of the oxide.

Other details and advantageous characteristics of the invention emerge from the following description of non-limiting exemplary embodiments, with the aid of the following figures:

• figure 1: a cross section of a glass substrate provided with the coating according to the invention, • figure 2: a diagram of a sol-gel deposition technique, called “by dipping” or by “dip-coating” of the coating , • figure 3: a diagram of a so-called "cell-coating" deposition technique, • figure 4: a diagram of a so-called "spray-coating" deposition technique, • figure 5: a diagram of a deposition by laminar coating.

As shown extremely schematically in FIG. 1, all the following examples relate to the deposition of a so-called “antifouling” coating 3 essentially based on titanium oxide on a transparent substrate 1.

Substrate 1 is made of clear soda-lime glass 6 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.

- 12 Between 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 alkali diffusion and / or a layer attenuating light reflection, or to fluorine-doped tin oxide base SnO₂: F with a view to constituting an anti-static and / or low-emissivity layer, even with a low-emissive effect which is not very accentuated, and / or attenuating the color, in particular in reflection.

EXAMPLES 1 TO 3

Examples 1 to 4 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 ribbon of float glass, leaving the enclosure of the float bath proper. Here, we proceeded discontinuously, using a static nozzle placed facing 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 a suitable solution.

EXAMPLE 1

In this example, there is no optional layer 2. The coating 3 is deposited using a solution comprising two organometallic precursors of titanium, titanium di-iso-propoxy di-acetylacetonate and tetraoctylene glycolate. of titanium dissolved in a mixture of two solvents, which are ethyl acetate and isopropanof and a colloidal suspension of titanium oxide particles, in a proportion of 5 grams of TiO₂ per liter of solution. The particles consist of agglomerated crystallites of anatase, crystallites with an average size of about 5 nm. The particles having a size distributed in a range going from 5 to 45 nm, are suspended in ethylene glycol in a mass concentration of 5 to 20%. TiO₂ can be doped with bismuth or niobium.

To know a preferred method of preparation of these particles, reference will advantageously be made to patent application EP-A-0 335 773.

It can be noted that other precursors of the same type can also be used quite well, in particular other titanium chelates of the type.

- 13 titanium acetylacetonate, titanium methylacetoacetate, titanium ethylacetoacetate or else titanium tri-ethanol amine or titanium di-ethanol amine.

As soon as the substrate 1 has reached the desired temperature in the oven, namely around 500 ° C., the latter passes in front of the nozzle, projecting the indicated mixture at room temperature using compressed air.

We then obtain a layer of TiO₂ approximately 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 the anatase form.

The substrate 1 provided with this coating is then subjected to annealing in an oven at a temperature of approximately 500 to 550 ° C. for a period of time which may range from 1 minute to 3 hours.

After deposition and annealing, a coating 3 of titanium oxide is obtained which is more crystallized than in the case of Example 1, in the anatase form. This coating thus contains both TiO₂ from the decomposition of organometallics and TiO₂ from TiO particles₂ in colloidal suspension, the first playing in a way the role of mineral binder with respect to the second.

EXAMPLE 2

It renews example 1, but by interposing between the substrate 1 and coating 3 a layer 2 in SnO₂: F 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-0 648 196. In the vapor phase, a mixture of monobutyl can in particular be used. tin trichloride and a fluorinated precursor optionally combined with a "mild" type H oxidant₂O.

The index of the layer obtained is approximately 1.9. Its square resistance is about 50 ohms / square.

In example 1 above, the coated substrate 1, mounted in double glazing so that the coating is on face 1 (with another substrate 1 'uncoated but of the same nature and dimensions as the substrate 1 by means of 'an air gap of 12 mm) has a purity value

- 14 of color in reflection of 26% and a value of color purity in transmission of 6.8%.

In this example 3, the color purity in reflection (in golds) is only 3.6%, and it is 1.1% in transmission.

Thus, the SnO underlay₂: F allows the substrate to be given anti-static properties due to its electrical conductivity, it also has a favorable influence on the colorimetry of the substrate, by making its coloration clearly 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 power supply, to limit the deposition of dust of relatively large size of the order of a millimeter.

EXAMPLE 3

He repeated Example 2, but this time inserting 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, a layer that the can be obtained by CVD from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in patent application EP-A-0 518 755. This layer is particularly effective in preventing the tendency to diffusion of alkalis (Na⁺, K⁺) and alkaline earth (Ca ^{+ +}) from substrate 1 to coating 3. Having, as SnO₂: F, a refractive index 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 both in reflection than in transmission and globally reduce the value of light reflection R_THE of said substrate.

EXAMPLE 4

This example uses the so-called sol-gel technique using a “dip-coating” deposition method also called “dip-coating”, the principle of which emerges from FIG. 2: this involves immersing the substrate 1 in the liquid solution 4 containing the appropriate precursor (s) of the coating 3, then extracting the substrate 1 at a controlled rate 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,

- 15 after heat treatment of the latter to both evaporate the solvent and decompose the precursor or precursors into oxide.

A solution 4 comprising either titanium tetrabutoxide Ti (0-Bu) is used to deposit the coating 3₄ stabilized with DEA ​​diethanol amine in a 1: 1 molar proportion in an ethanol-type solvent containing 0.2 moles of tetrabutoxide per liter of ethanol, ie the mixture of precursors and solvents described in Example 1. {Can also be used another precursor such as titanium dibutoxy-diethanolamine), solution supplemented with 5 grams / liter of TiO solution₂ in the form of anatase particles in a 10% colloidal solution in ethylene glycol, so as to use approximately 0.24 grams of these particles per gram of TiO₂ actually filed.

After extraction of each of the solutions 4, the substrates 1 are heated for 1 hour at 100 ° C. then approximately 3 hours at 550 ° C. with a gradual rise in temperature.

A coating 3 is obtained on each side, in both cases in TiO₂ well crystallized in the anatase form.

EXAMPLE 5

This example uses the technique called “cell-coating”, the principle of which is recalled in FIG. 3 and the detailed description of which is given in the aforementioned patent application FR-95/05978 of May 19, 1995. This involves forming a narrow cavity delimited by two substantially parallel faces 6, 7 and two joints 8, 9, at least one of these faces 6, 7 being formed by the face of the substrate 1 to be treated. Then the cavity is filled with the solution 4 of the precursor (s) of the coating, and the solution 4 is withdrawn in a controlled manner, so as to form a wetting meniscus using a peristaltic pump for example, leaving a film of solution 4 on the face of substrate 1 as the solution is withdrawn.

The cavity 5 is then maintained for at least the time necessary for drying, hardening by heat treatment of the film on the substrate. The advantage of this technique over "dip-coating" is in particular that it is possible to treat only one of the two faces of the substrate 1, and not both systematically, unless a masking system is used. .

This example uses solution 4 described in example 5. The same heat treatments are then carried out to obtain the coating 3 of TiO.₂.

In both cases, the coatings 3 exhibit good mechanical durability, the coatings according to Example 9 having had recourse to the colloidal suspension of TiO.₂ are well crystallized: the particles should facilitate the anatase crystallization of the TiO "binder"₂ originating from the organometallic precursor (s) which is rather amorphous before the post-deposition heat treatments.

These same types of 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 mode, or by laminar coating as shown in Figure 5. In the latter case, the substrate 1, maintained by suction under vacuum, is passed against a support 11 made of stainless steel and Teflon above a reservoir 12 containing the solution, the solution in which a split cylinder 14 is partially immersed. then moves the assembly of the reservoir 12 and of the cylinder 14 over the entire length of the substrate 1, the mask 13 preventing too rapid evaporation of the solvent from the solution 4. For more details on this latter technique, reference will be made to the aforementioned patent application WO94 / 01598.

Tests were carried out on the substrates obtained according to the preceding examples in order to characterize the coatings deposited and to evaluate their “anti-fog” and “anti-fouling” performance.

□ Test 1: this is the test for fog patterns. 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 and therefore anti-fog. A quantitative assessment can also be made by suddenly heating the coated substrate initially stored in the cold or simply by blowing on the substrate, measuring whether any fogging appears.

- 17 and if so, at what time, then by measuring the time required for said mist to disappear.

□ Test 2: this involves evaluating the hydrophilicity and oleophilicity at the surface of 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 (dioctyl phthalate) on their surfaces, after leaving the substrates for one week in the ambient atmosphere under natural lighting, in the dark and then having subjected them to UVA radiation for 20 minutes.

□ Test 3: this is a test for the quantitative evaluation of photocatalysis by depositing a known and well “calibrated” soiling. A carbonaceous mono-layer from octadecyltrichlorosilane (OTS) is grafted by dipping onto the coatings of the invention:

- operating conditions: OTS at 0.3% in decane, grafting at 0 ° C under anhydrous atmosphere on a clean substrate

- layer obtained: 2 to 3 nm thick.

The substrates thus grafted are irradiated under UVA at approximately 25 mW / cm².

The disappearance of the organic layer is characterized by periodic water contact angle measurements. Initially, we have about 100 °. When the angle drops to approximately 15 °, it is considered that the organic “dirt” deposited is completely destroyed: there is then also a marked anti-fog effect.

The monolayer disappearance time is given below for various examples of the patent.

All the preceding examples pass test 1, that is to say that when the substrates coated with the coating are blown, they remain perfectly transparent, while a clearly visible layer of mist is deposited on uncoated substrates.

Examples 2, 3 and 4 were subjected to test 2: the coated substrates, after exposure to UVA radiation, exhibit 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 °.

- 18 Examples 4 and 5 were subjected to test 3: in the two examples, in the case where the solution uses titanium tetrabutoxide, the duration of disappearance of the monolayer obtained from OTS is approximately 6 time. In the case where the solution uses the mixture of titanium di-iso-propoxy-diacetylacetonate and tetra-octylene phthalate precursors, the disappearance time is reduced to 20 minutes.