FR2738812A1 - New photo-catalytic coatings based on titanium di:oxide in a mineral or organic dispersion - Google Patents

Abstract

A substrate (1) provided on one face with a coating(3) having photo-catalytic properties and based on TiO2 in a partially crystallised state and incorporated into the coating as particles mainly in the anatase form. Also claimed, are the uses of the treated substrates, the procedure for producing the coatings, and the organic dispersions providing the carrier for the particles.

Description

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

Increasingly, 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 to 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 may 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 allowing in particular to space cleaning and / or to improve visibility, by succeeding in eliminating progressively the stains gradually depositing on the surface of the substrate, in particular stains of organic origin such as fingerprints or products volatile organic substances present in the atmosphere, or even soiling of the fogging type.

 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 radical reactions causing the oxidation of products. organic: we generally speak of photo-catalytic or photo-reactive materials.

 The 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.

 The subject of the invention is a glass-based, ceramic or glass-ceramic substrate, in particular 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 of size between 5 and 70 nm, essentially crystallized in anatase or anatase / rutile form.

The incorporation is preferably done with a binder.

 Titanium 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 implies repeated handling by mechanical gripping means or tires, and also once the glazing is in place, with the risk of abrasion (windscreen wiper, abrasive cloth) and contact with aggressive chemicals (atmospheric pollutants such as SO2, cleaning product, etc.).

 The 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%. (The amount by weight of TiO2 crystallized relative to the total amount by weight of TiO2 in the coating is understood by degree of crystallization.

 It has also been observed, in particular in the case of crystallization in anatase form, that the orientation of the growing TiO2 crystals on the substrate had an influence on the photo-catalytic performances of the oxide: there is a preferred orientation ( 1,1,0) which clearly promotes photocatalysis.

 Advantageously, the coating is produced in such a way that the crystallized titanium oxide which it contains is in the form of crystallites, that is to say 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 indeed in this dimension range that titanium oxide appears to have an optimal photo-catalytic effect, probably because the crystallites of this size develop a large active surface.

 As will be seen in more detail later on 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 in general 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 may be mineral, in particular in the form of an amorphous or partially crystallized oxide (or mixture of oxides), for example made of silicon, titanium, tin, zirconium or d oxide. 'aluminum. It can be confined to its role as a matrix with respect to the active particles of titanium oxide, which is the case for example of silicon oxide. But it can also participate in the photocatalytic effect of the particles, by itself presenting a certain photocatalytic effect, even weak compared to that of the particles, which is the case of amorphous or partially crystallized titanium oxide.

dans laquelle p est O ou A, r est 0,1 ou 2, s est un nombre entier entre 1 et 6,
M = H ou un alkyle comprenant 1 à 4 atomes de carbone, M' et M " sont des alkyles comprenant 1 à 3 atomes de carbone. Le silane non époxydé est de formule générale

dans laquelle N et N' sont des groupements organiques liés à l'atome de silicium par une liaison Si-C et qui ne comportent pas de groupement susceptible de réagir avec les silanes hydrolysés présents dans la compositions, et où Q et Q' sont des fonctions hydrolysables.The binder can also be chosen partially or essentially organic, in particular in the form of a polymer matrix. It can be a polymer which can have properties complementary to those of titanium oxide particles, and in particular hydrophobic and / or oleophobic properties and which can be deposited by a technique of the sol-gel type. 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 qualified as hybrid and obtained from a solution comprising an epoxidized alkoxysilane, a silane hydrolysable non-epoxidized, colloidal silica, a catalyst and at least one hydrolyzable fluorinated alkylsilane. The fluorinated alkylsilane has the general formula: CF, - (CF,), - (CH2), - SiX3, with n from 0 to 12, m from 2 to 5, X a hydrolysable function. The epoxidized alkylsilane has the formula

where p is O or A, 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 non-epoxidized silane has the general formula

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

 One can also 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 patents US-5,368,892 and US-5,389,427, as well as base of perfluoroalkylsilane described in patent application FR94 / 08734 of July 13, 1994, in particular of formula CF3 ~ (CF2) n ~ (CH2) m ~ Six3 in which n is from 0 to 12, m is from 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.

 We can first of all 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.

 It is also possible to increase the number of charge carriers by doping the crystal lattice of the titanium oxide constituting the particles, by inserting therein at least one of the following metallic elements: niobium, tantalum, iron, bismuth, cobalt, nickel, copper, 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 metal salts, the metal being chosen from among 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, silver type.

 Surprisingly, the coating actually has not one property but two, as soon as it is exposed to adequate radiation such as visible light and / or ultraviolet light: by the presence of photo titanium oxide -catalytic, as already seen, it promotes the progressive disappearance, as and when they accumulate, of dirt of organic origin, by causing their degradation by a process of radical oxidation.

 However, the coating of the invention also preferably has an outer surface with a pronounced hydrophilic and / or oleophilic character, in particular in the case where the binder is mineral, which brings two significant advantages: a hydrophilic character allows perfect wetting of the water that can settle on the coating. Instead of depositing water droplets in the form of a mist which impairs 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 demonstrated in particular by measuring a contact angle with water less than 50 after exposure to light.

 In conjunction with a hydrophilic character, it 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. . An organic anti-fouling effect is thus obtained 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 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 thickness may depend on various parameters, in particular on the envisaged application of the glazing type substrate, or even on the size of the TiO2 crystallites in the coating. The coating can also be chosen to have a more or less smooth surface: a low surface roughness can indeed be advantageous, if it makes it possible to develop a larger active photocatalytic surface. However, too pronounced, it can be penalizing by favoring the incrustation, the accumulation of dirt. In the case where the coating is based on TiO2 particles coated in a binder, the mode of deposition and the thickness of the coating can be chosen so that the particles or the crystallites from which they are formed emerge on the surface of this binder .

 Between 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. They can be, in particular, layers with an antistatic, thermal, optical function or layers making a barrier to the migration of certain elements coming from the substrate, in particular making a barrier to alkalis and very particularly to sodium ions when the substrate is made of glass. One can also 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 is made up, in particular, of a mineral matrix of the silicon oxide type in which particles of titanium oxide, or a mixed oxide of titanium and silicon.

The 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 like indium oxide doped with tin ITO, Tin oxide doped with a halogen of fluorine type
SnO2: F, or zinc oxide doped with indium ZnO: ln, fluorine ZnO: F, aluminum ZnO: A or tin ZnO: Sn.

 The anti-static function layer preferably has a square resistance value of 20 to 1000 ohms / square. Provision can be made for supplying current 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 adherent dry dust only by electro-static effect: by brutally reversing the polarization of the layer, ejects this dust.

 The 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 a refractive index intermediate 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. Al2O3, tin oxide SnO2, indium oxide Ion203, oxycarbide or silicon oxynitride. 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.

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 range, especially around 500 to 550 nm.

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

 All 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 aforementioned layers can combine several functions, but they can also be superimposed.

 The 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 previously described.

 The invention therefore relates to the manufacture of glass, ceramic or vitro-ceramic products, and in particular the manufacture of self-cleaning glazing. These can advantageously be building glazing, such as double glazing (the coating can then be placed on the outside and / or on the inside, 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 arranged on windshields, lateral or rear windows of the car, in particular on the face of the glazing turned towards 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 it advantageous to use glazing provided with the coating of the invention.

Many 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,
Another 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, viologen 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 arrange the coating on the external face of at least one of these substrates.

 In particular in the case of an 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-AO 575 207 describing an electrochromic laminated double glazing, the coating according to the invention preferably being able to be placed opposite 1 .

 The invention also relates to the various methods of obtaining the coating according to the invention. It is possible to use a deposition technique of the pyrolysis type, which is advantageous because it allows the coating to be deposited continuously, directly on the ribbon of float glass, 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 type and / or titanium alcoholate. 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-O 465 309.

 The coating can also be deposited by other techniques, in particular by the so-called sol-gel technique. Different deposition modes are possible, such as quenching also called dip-coating or deposition using a cell called cell-coating, the latter technique being described in detail in patent application FR-95/05978 filed on May 19, 1995. It can also be a mode of deposition by spray-coating or by laminar coating, the latter technique being detailed in patent application WO-94/01598. All of these deposition methods generally use a solution comprising at least one organometallic precursor, in particular titanium of the alcoholate type which is thermally decomposed after coating of the substrate with the solution on one of its faces, or on both. faces.

 These previously stated deposition techniques, which use a solution, therefore incorporate into the solution of metallic precursors a colloidal powder or dispersion of titanium oxide particles 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 further promote the crystallization of the TiO2 formed by thermal decomposition from the precursors, probably playing the role of seeds of crystallization. In the final coating, titanium oxide is thus produced in two different ways. Advantageously, one can choose a rate of introduction of titanium oxide particles into the solution so as to use from 0.1 to 0.6 gram 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 mean diameter, in particular around 20 or 40 nm. The dispersion of TiO2 particles advantageously has specific characteristics, in particular it comprises at least partially crystallized and monodisperse titanium dioxide particles.

The term “monodisperses” is understood to mean 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 = (84-16) / 2 .50 in which 84 is the particle diameter for which 84% of the particles have a diameter less than 84 16 is the particle diameter for which 16% of the particles have a diameter less than 16
It 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.

 Likewise, 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 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 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 is formed, improves its crystallization rate The chosen treatment temperature can also allow better control of the crystallization rate and the crystalline, anatase and / or rutile nature of the oxide.

Other details and advantageous characteristics of the invention emerge from the description below of nonlimiting exemplary embodiments, with the aid of the following figures e 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 soaking
or by dip-coating the coating,
FIG. 3: a diagram of a so-called cell-coating deposition technique,
FIG. 4: a diagram of a spray-coating deposition technique,
FIG. 5: a diagram of a deposition technique by laminar coating.

 As shown very diagrammatically in FIG. 1, all of the following examples relate to the deposition of a coating 3 known as antifouling essentially based on titanium oxide on a transparent substrate 1.

 The substrate 1 is made of clear soda-lime-silica 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.

 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 diffusion to alkalis and / or a layer attenuating light reflection, or based on tin oxide doped with fluorine SnO2: F in order to constitute an anti-static and / or low-emissive layer, even with a weakly accentuating effect, 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. One can 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 static 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 6500C before running at constant speed in front of the nozzle projecting an appropriate solution.

EXAMPLE 1
In 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 tetraoctylene glycolate titanium dissolved in a mixture of two solvents, which are ethyl acetate and isopropanol 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 of average size of approximately 5 nm. The particles having a size distributed in a range 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 find out a preferred method of preparation of these particles, reference is advantageously made to patent application EP-A-0 335 773.

 It 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.

 As soon as the substrate 1 has reached the desired temperature in the oven, in particular about 5000C, the latter passes in front of the nozzle projecting the indicated mixture at ambient temperature using compressed air.

We then obtain a TiO2 layer about 90 nm thick,
The thickness being able to be controlled by the running speed of the substrate 1 in front of the nozzle and / or the temperature of said substrate. The layer is partially crystallized in anatase form.

 The substrate 1 provided with this coating is then subjected to annealing in an oven at a temperature of approximately 500 to 5500C for a period of time which can range from 1 minute to 3 hours.

 After deposition and annealing, a coating 3 of more crystallized titanium oxide is obtained than in the case of Example 1, in anatase form. This coating thus contains both TiO2 from the breakdown of organometallics and TiO2 from TiO2 particles in colloidal suspension, the former in a way playing the role of mineral binder compared to the latter.

EXAMPLE 2
He repeats Example 1, but by inserting between the substrate 1 and coating 3 a layer 2 of SnO2: F 73 nm thick. This layer is obtained by powder pyrolysis from dibutyltin difluoride DBTF.

It can also be obtained, in known manner, by pyrolysis in the liquid or vapor phase, as is for example described in patent application EP-AO 648 196. In the vapor phase, it is in particular possible to use a mixture of monobutyl trichloride d tin and a fluorinated precursor possibly associated with a mild oxidant of the H2O type.

 The index of the layer obtained is approximately 1.9. Its square resistance is around 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 'not coated but of the same nature and dimensions as the substrate 1 via (12 mm air gap) has a color purity value in reflection of 26% and a color purity value in transmission of 6.8%.

 In this example 3, the color purity in reflection (in gold) is no more than 3.6%, and it is 1.1% in transmission.

 Thus, the SnO2: F sublayer 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 that in reflection, coloring caused by the presence of the coating 3 of titanium oxide 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.

EXAMPLE 3
It 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-AO 518 755. This layer is particularly effective in preventing the tendency to diffusion alkalis (Na +, K +) and alkaline earths (Ca ++) from substrate 1 to coating 3. Having, as SnO2: F, a refractive index intermediate between that of the substrate (1.52) and 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 and in transmission and to globally reduce the light reflection value RL of said substrate.

EXAMPLE 4
This example uses the so-called sol-gel technique using a dip coating 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 adequate precursor (s) of the coating 3, then extract 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 in order both to evaporate the solvent and to decompose the precursor (s) into oxide.

 Is used to deposit the coating 3 a solution 4 comprising either titanium tetrabutoxide Ti (O-Bu) 4 stabilized with diethanol amine DEA in molar ratio 1: 1 in an ethanol solvent at 0.2 mole of tetrabutoxide per liter ethanol, i.e. the mixture of precursors and solvents described in Example 1. (Another precursor such as titanium dibutoxy-diethanolamine) can also be used, solution containing 5 grams / liter of TiO2 solution in the form of anatase particles in colloidal solution at 10% in ethylene glycol, so as to use approximately 0.24 gram of these particles per gram of TiO2 actually deposited.

 After extraction of each of the solutions 4, the substrates 1 are heated for 1 hour at 1000C and then about 3 hours at 5500C with a gradual rise in temperature.

A coating 3 is obtained on each of the faces, in both cases in
TiO2 well crystallized in 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 above-mentioned 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 seals 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 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 10 for example, leaving a film of the solution 4 on the face of the substrate 1 as the solution is withdrawn.

 The cavity 5 is then maintained for at least the time necessary for drying, curing by heat treatment of the film on the substrate.

The advantage of this technique compared to 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 recourse is had to a masking system.

 This example uses the solution 4 described in example 5. The same heat treatments are then carried out to obtain the coating 3 of TiO2.

 In both cases, the coatings 3 have good mechanical durability, the coatings according to Example 9 having used the colloidal suspension of TiO2 are well crystallized: the particles should facilitate the anatase crystallization of the binder TiO2 coming from the precursor (s) (s) organo-metallic (s) which is rather amorphous before 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 form, or by laminar coating. as shown in Figure 5. In the latter case, the substrate 1 is passed, maintained by suction under vacuum, against a support 1 1 made of stainless steel and Teflon over a tank 12 containing the solution, solution in which is partially submerged a split cylinder 14, the entire reservoir 12 and the cylinder 14 are 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 WO94 / 01598 cited above.

 Tests 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 performance.

O Test 1: this is the fogging pattern test. It consists in observing the
consequences of photo-catalysis and the structure of the coating (rate
hydroxyl groups, porosity, roughness) on wetting. If the surface is
photo-reactive, carbonaceous micro-pollution that is deposited on the
coating are permanently destroyed, and the surface is hydrophilic therefore
antifog. We can also make a quantitative evaluation by warming up
suddenly the coated substrate initially stored cold or
simply by blowing on the substrate, measuring if it appears fogging
and if so, when and then measuring the time required
when said mist disappears.

O 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 the
measurement of contact angles of a drop of water and a drop of DOP (di
octyl-phthalate) on their surfaces, after leaving the substrates for a week
in the ambient atmosphere under natural light, in the dark then have them
subjected to UVA radiation for 20 minutes.

O Test 3: this is a quantitative evaluation test of photocatalysis by
deposit of known and well calibrated soiling. We graft by soaking a
carbon monolayer from octadecyltrichlorosilane (OTS) on
coatings of the invention - operating conditions: 0.3% OTS in decane, grafting with OOC under anhydrous atmosphere on clean substrate - layer obtained: 2 to 3 nm thick.

2
The substrates thus grafted are irradiated under UVA at approximately 25 mW / cm 2.

 The disappearance of the organic layer is characterized by measurements of the angle of contact with water periodically. Initially, we have around 1000.

When the angle drops to approximately 150, it is considered that the organic dirt deposited is completely destroyed: there is then a marked anti-fogging effect.

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

 All the preceding 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 fogging is clearly visible on uncoated substrates.

 Examples 2, 3 and 4 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 400 and a contact angle with DOP of 200.

 Examples 4 and 5 underwent 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 hours. In the case where the solution uses the mixture of di-iso-propoxy-diacetylacetonate and titanium tetra-octylene phthalate precursors, the disappearance time is reduced to 20 minutes.

Claims (22)

 1. Substrate (1) based on glass, ceramic or vitro-ceramic, provided on at least part of at least one of its faces with a coating (3) with photocatalyst property, characterized in that it comprises titanium oxide at least partially crystallized and incorporated into said coating (3) in the form of particles, in particular of size between 5 and 70 nm, essentially crystallized in anatase form or anatase / rutile mixture.  2. Substrate (1) according to claim 1, characterized in that the particles are incorporated into the coating using a binder.  3. Substrate (1) according to claim 2, characterized in that the binder is mineral, in particular in the form of an oxide or a mixture of oxides, amorphous or partially crystallized of the silicon oxide, titanium oxide type, tin oxide, zirconium oxide, aluminum oxide.  4. Substrate (1) according to claim 2, characterized in that the binder is essentially organic, in particular in the form of a polymer matrix with oleophobic and / or hydrophobic property.  5. Substrate (1) according to one of the preceding claims, characterized in that the coating comprises additives capable of amplifying the photocatalytic phenomenon of the titanium oxide particles, in particular by increasing the absorption band of the coating in the form of additive particles, and / or by increasing the number of charge carriers by doping the crystal lattice of the oxide constituting the particles or by doping the surface of the particles and / or by increasing the yield and kinetics of the photocatalytic reactions, by covering the particles with catalyst.  6. Substrate (1) according to claim 5, characterized in that the doping of the crystal lattice of the particles is carried out by insertion of at least one of the metallic elements of the group comprising niobium, tantalum, iron and bismuth.  7. Substrate (1) according to claim 5, characterized in that the titanium oxide is coated with a catalyst, in particular in the form of a thin layer of noble metal of the platinum, rhodium, silver type.  8. Substrate (1) according to claim 5, characterized in that the surface doping of the titanium oxide particles is carried out by covering at least part of said particles with a layer of oxides or metal salts, the metal being chosen from iron, copper, ruthenium, cerium, molybdenum, bismuth, vanadium.  9. Substrate (1) according to claim 5, characterized in that the additive particles are based on cadmium, tin, tungsten, zinc, cerium or zirconium.  10. Substrate (1) according to claim 3, characterized in that the surface of the coating (3) is hydrophilic, with in particular a contact angle with water less than 50 after exposure to light radiation, and / or oleophilic.  11. Substrate (1) according to one of the preceding claims, characterized in that the thickness of the coating (3) is between 5 nm and 1 micron, in particular between 5 nm and 100 nm, preferably 10 to 80, in particular 20 to 50 nanometers.  12. Substrate (1) according to one of the preceding claims, characterized in that at least one thin layer (2) with anti-static, thermal, optical function is disposed under the coating (3) with photocatalyst property. or forming a barrier to the migration of alkalis from the substrate (1).  13. Substrate (1) according to claim 11, characterized in that the thin layer (2) with anti-static function, optionally with controlled polarization, and / or thermal and / or optical is based on conductive material of the metal type or of the doped metal oxide type such as ITO, SnO2: F, ZnO: ln, ZnO: F, ZnO: Al, ZnO: Sn.  14. Substrate (1) according to claim 12, characterized in that the thin layer (2) with optical function is based on an oxide or a mixture of oxides whose refractive index is intermediate between that of coating and that of the substrate, in particular chosen from the following oxides: Al2O3, SnO2, In203, oxycarbide or silicon oxynitride.  1 5. Substrate (1) according to claim 12, characterized in that the thin layer (2) with an alkali barrier function is based on silicon oxide, nitride, oxynitride or oxycarbide, A1203: F or aluminum nitride.  16. Substrate (1) according to claim 12, characterized in that the coating (3) constitutes the last layer of a stack of anti-reflective layers.  17. Anti-fouling and / or anti-fog glazing, monolithic, multiple of the double-glazing or laminated type incorporating the substrate (1) according to one of the preceding claims.  18. Application of the substrate (1) according to one of claims 1 to 16 to the manufacture of self-cleaning, anti-fog and / or anti-fouling glazing, in particular glazing for the building of the double-glazing type, glazing for vehicles such as windshields, rear or side windows of automobiles, trains, planes, or utility glazing such as aquarium glasses, display cases, greenhouses, interior furnishings, street furniture, or mirrors, screens television, electrically controlled variable absorption glazing.  19. Method for obtaining the substrate (1) according to one of claims 1 to 16, characterized in that the coating (3) with photocatalytic property is deposited by pyrolysis in the liquid phase, in particular from a solution comprising at least one organometallic titanium precursor of the titanium chelate and / or titanium alcoholate type as well as a colloidal powder or dispersion of titanium oxide particles crystallized in anatase or anatase / rutile form, in particular in such a proportion with respect to the precursor (s) which are used approximately 0.1 to 0.6 gram of these particles per gram of TiO2 actually deposited.  20. Method for obtaining the substrate (1) according to one of claims 1 to 16, characterized in that the coating (3) with photocatalytic property is deposited by a sol-gel technique, with a method of depositing the quenched or dip-coating, cell-coating, spray-coating or laminar coating type, from a solution comprising at least one organometallic titanium precursor of the titanium alcoholate type as well as a colloidal powder or dispersion of particles of titanium oxide crystallized in anatase or anatase / rutile form, in particular in a proportion such as relative to the precursor (s) that about 0.1 to 0.6 grams of these particles are used per gram of TiO2 actually deposited.  21. Method according to one of claims 19 or 20, characterized in that the titanium oxide particles have a particle size distribution such that at least 80% of them have the same mean diameter in particular of about 20 or 40 nm.  22. Method according to one of claims 19 to 21, characterized in that the coating (3) with photocatalyst property is deposited in at least two successive stages.  23. Method according to one of claims 19 to 22, characterized in that the coating (3) with photo-catalytic property is subjected, after deposition, to at least one heat treatment of the annealed type.