Titanium dioxide-based photocatalytic coating substrate, and titanium dioxide-based organic dispersions

0001The present invention relates to substrates provided with a coating with a photocatalytic property based on titanium dioxide, said titanium dioxide being incorporated in part in the form of particles. It also relates to a process for the preparation of these substrates and to new organic dispersions based on monodisperse titanium dioxide particles which can be used in this process.

0002It is known to functionalize materials of various applications, such as materials for vehicles or for buildings (glasses, metals, ceramics, facade materials, cladding, roofing such as tiles, ...) by giving them properties. such as in particular anti-UV, anti-fouling, bactericidal, anti-reflection, anti-static, anti-micro-organism properties, etc.

0003This is particularly true in the case of glazing, such as windshield glazing for means of transport, which one seeks to functionalize by depositing on their surface thin layers intended to give them a particular property according to the intended application. .

0004Thus, 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 thus 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, etc.

0005Today, another sought-after property is to obtain the permanence over time of the appearance and surface properties, making it possible in particular to space cleaning times and / or to improve visibility, by succeeding in eliminating as and when measures soiling gradually settling on the surface of the substrate, in particular soiling of organic origin, such as fingerprints or volatile organic products present in the atmosphere, or even soiling of the fogging type.

0006A solution to these soil problems consists, for example, in depositing on the substrates a coating ensuring degradation of these soils by photocatalysis. Under the effect of radiation of adequate wavelength, the coating components initiate radical reactions causing the oxidation of organic products.

0007This degradation can be induced by any compound generating radicals under the action of light (photocatalytic effect). It may in particular be titanium dioxide which is already used for the treatment of architectural substrates and especially glass substrates.

0008Thus, it is known to use solutions of titanium compounds or colloidal dispersions of titanium dioxide to create photocatalytic properties on the substrates (see for example EP-A-581216). However, it has been found that the specific characteristics of said solutions of titanium compounds or colloidal dispersions of titanium dioxide used to treat the substrate influence the quality of the photocatalytic coating. According to these specific characteristics, the quality of the adhesion of the coating to the substrate can also be very variable. Finally, it happens, in the case where the substrate is glass, that the coating induces a lack of transparency and blurring on the glass.

0009An object of the present invention is therefore to propose new substrates having a coating based on titanium dioxide having good photocatalytic properties, said coatings being durable, transparent and capable of being prepared industrially.

0010To this end, the invention relates to a substrate provided on at least part of one of its faces with a coating with photocatalytic property based on titanium dioxide at least partially crystallized and incorporated in said coating partly in the form of particles mainly crystallized in anatase form.

0011The invention also relates to methods for obtaining this substrate which consists in depositing the coating by pyrolysis in the liquid phase or by a so-called sol-gel technique from a suspension comprising at least one organometallic compound and a dispersion of particles. titanium dioxide, said particles having the characteristics of the particles incorporated in the final coating.

0012Finally, the invention relates to an organic dispersion comprising:<ul id="ul0001" list-style="dash" compact="compact"><li>titanium dioxide particles of size between 5 and 70 nm, monodispersed and predominantly in crystalline anatase form,</li><li>and at least one organic solvent, preferably having a latent heat of vaporization lower than that of water. This dispersion is used for the preparation of the substrate according to the invention.</li></ul>

0013Other advantages of the invention will appear more clearly on reading the following description, examples and figures:<ul id="ul0002" list-style="none" compact="compact"><li>. FIG. 1: cross section of a substrate provided with the coating according to the invention,</li><li>. FIG. 2: diagram of a sol-gel deposition technique, called "by dipping" or by "dip-coating" of the coating,</li><li>. FIG. 3: diagram of a "cell-coating" deposition technique,</li><li>. FIG. 4: diagram of a so-called "spray-coating" deposition technique,</li><li>. Figure 5: diagram of a laminar coating deposition technique.</li></ul>

0014The invention therefore relates first of all to a substrate provided on at least part of one of its faces with a coating with photocatalytic property based on titanium dioxide at least partially crystallized and incorporated in said coating partly in the form of particles. mostly crystallized in anatase form.

0015Overall, the titanium dioxide in the coating, in the form of particles or not, is partially crystallized in crystalline form anatase, rutile or in the form of a mixture of anatase and rutile with a degree of crystallization preferably of at least 25 %, especially around 30 to 80%. The crystallization rate represents the quantity by weight of TiO₂ crystallized with respect to the total amount by weight of TiO₂ in the coating.

0016For the titanium dioxide particles in the coating, the nature of the crystalline phase is preferably mainly the anatase crystalline form. "Mostly" means that the level of anatase in the titanium dioxide particles in the coating is greater than 50% by mass. Preferably, the coating particles have an anatase level greater than 80%.

0017The crystallization rate and the nature of the crystalline phase are measured by X-ray diffraction.

0018The particles of crystallized titanium dioxide incorporated in the coating have an average size between 5 to 80 nm, preferably between 5 and 70 nm, even more preferably between 10 and 50 nm. Diameters are measured by transmission electron microscopy (TEM).

0019The titanium dioxide particles are preferably incorporated into the coating using a binder.

0020According to a first variant, the binder incorporating the particles in the coating can be mineral. It may in particular be in the form of an amorphous or partially crystallized oxide (or mixture of oxides), for example of silicon, titanium, tin, zirconium or aluminum oxide. It can be confined to its role as a matrix with respect to particles of titanium dioxide, which is the case with silicon oxide. However, it can also participate in the photocatalytic effect of the particles, by itself having a certain photocatalytic effect, even weak compared to that of the particles, which is the case of amorphous or partially crystallized titanium dioxide.

0021According to a second variant, the binder can also be at least partially organic, in particular in the form of a polymer matrix. It may be a polymer which may have properties complementary to those of the titanium dioxide particles, and in particular hydrophobic and / or oleophobic properties.

0022As an example of such matrices, reference may be made to patent application EP-A-675 087, which describes a matrix qualified as hybrid and obtained from a solution comprising an epoxidized alkoxysilane, a hydrolysable non-epoxidized silane, colloidal silica, a catalyst and at least one hydrolyzable fluorinated alkylsilane. The fluorinated alkylsilane has the general formula:         CF₃- (CF₂)_not- (CH₂)_m-Six₃,    with n from 0 to 12, m from 2 to 5, X is a hydrolyzable function. The epoxidized alkylsilane has the formula:<chemistry id="chem0001" num="0001"><img file="EP0850203B1_D0001.tif" /></chemistry>    in which p is 0 or 1, r is 0, 1 or 2, s is an integer between 1 and 6, M is a hydrogen atom or an alkyl radical comprising 1 to 4 carbon atoms, M 'and M " are alkyl radicals comprising 1 to 3 carbon atoms.

0023The non-epoxidized silane has the general formula:<chemistry id="chem0002" num="0002"><img file="EP0850203B1_D0002.tif" /></chemistry>    in which N and N 'are organic groups linked to the silicon atom by an Si-C bond and do not comprise a group capable of reacting with the hydrolyzed silanes present in the composition, and where Q and Q' are functions hydrolyzable.

0024It is also possible to choose to superimpose on the coating according to the invention an grafted oleophobic and / or hydrophobic layer, for example based on the fluorinated organosilane described in patents US-A-5,368,892 and US-A-5,389,427, as well as based on perfluoroalkylsilane described in patent application EP-A-692 463, in particular of formula:         CF₃- (CF₂)_not- (CH₂)_m-Six₃,    with n from 0 to 12, m from 2 to 5, X is a hydrolyzable function.

0025Thanks to the particles of titanium dioxide incorporated into the coating, the latter can have a refractive index of between 1.40 and 2.35, preferably between 1.6 and 2.3. This is due to the fact that the titanium dioxide particles are porous and thus have a lower refractive index than solid titanium dioxide. The coating obtained therefore has a low refractive index compared to the refractive indices of coatings based on solid titanium dioxide.

0026The optical advantage linked to obtaining low indices is very important in the case of glass-based substrates: a high index layer of solid titanium dioxide leads to increasing the light reflection of the carrier glass, therefore to reducing its transmission. bright. However, for certain applications, in particular in the field of glazing fitted to vehicles, it is essential to have high light transmission levels (for a windshield, a minimum light transmission of 75% is necessary).

0027To amplify the photocatalytic effect of the titanium dioxide particles of the coating according to the invention, said particles can comprise catalysts and additives making it possible to better filter UV rays, or to shift the absorption band towards the visible, or even metals which make it possible to boost titanium dioxide, in particular to increase the number of electronic carriers. Several variants can amplify this effect.

0028According to a first variant, at least a portion of the titanium dioxide particles of the coating can comprise in their crystal lattice metal ions chosen from iron, copper, ruthenium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium. The ratio of the mass of these ions to the mass of the particles of titanium dioxide is, in general, between 0.01 and 10%.

0029According to a second variant, at least part of the particles of titanium dioxide can be covered at least in part with a layer of oxides or metal salts, the metal being chosen from iron, copper, ruthenium, cerium , molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium, tungsten, tin, zirconium, cadmium, zinc. The ratio of the mass of these metals to the mass of the titanium dioxide particles is generally between 0.01 and 20%.

0030According to a third variant, at least part of the particles of titanium dioxide can be covered at least in part with a layer of metal chosen from platinum, silver or rhodium. The ratio of the mass of these metals to the mass of the titanium dioxide particles can be between 0.01 and 5%.

0031According to a fourth variant, the coating according to the invention comprises, in addition to the particles of titanium dioxide, additive particles based on metallic compounds chosen from cadmium, tin, tungsten, zinc, cerium or zirconium . These particles are of colloidal size, in general, between 5 and 100 nm. The ratio of the mass of these particles to the mass of the titanium dioxide particles is generally between 0.01 and 20%.

0032These additive particles can be composed of metal oxides or sulfides, such as CeO₂, SnO₂, WO₃, ZnO, ZrO₂ or CdSe_xS_y with x and including between 0 and 1, and x + y = 1.

0033The thickness of the coating of the substrate according to the invention is variable. It is generally between 5 nm and 1 micron, preferably between 5 nm and 100 nm, even more preferably between 5 and 80 nm, or even between 10 and 80 nm; it can for example be between 20 and 50 nm. In fact, the thickness can depend on different parameters. It can depend on the envisaged application of the substrate, or even on the size of the titanium dioxide particles in the coating. The coating can also be chosen to have a more or less smooth surface: a certain 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 favoring the incrustation of dirt. In the case where the coating is based on particles of titanium dioxide incorporated in a binder, one can choose the mode of deposition and the thickness of coating so that the particles or the crystallites from which they are made "emerge" in surface of this binder.

0034The substrate according to the invention can be of various natures: any type of architectural material can be used (metals, concretes, etc.), as well as glass-based, ceramic or vitro-ceramic substrates.

0035Between the substrate and the coating according to the invention, one or more other thin layers can be deposited with functions different or complementary to that of the coating based on titanium dioxide. They may be, in particular, layers with an anti-static, thermal, optical function, or layers forming a barrier to the migration of certain elements coming from the substrate, for example forming a barrier to alkalis and very particularly to sodium ions when the substrate is made of glass. It is possible to envisage a stack of “anti-reflection” layers alternating thin layers with high and low indices, the coating of the invention constituting the last layer of the stack. In this case, it is preferable that the coating has a relatively low refractive index 10, which is the case when it consists of a mineral matrix of the silicon oxide type in which particles of titanium dioxide are embedded. , or 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 fluorine type SnO₂: F, or zinc oxide doped with indium ZnO: ln, fluorine ZnO: F, aluminum ZnO: Al or tin ZnO: Sn.

0037Such a layer can be obtained by pyrolysis of powder from dibutyl tin difluoride DBTF, or by pyrolysis in the liquid or vapor phase, as described in patent application EP-A-648 196. In the vapor phase, it is possible to in particular use a mixture of monobutyl tin chloride and a fluorinated precursor possibly associated with a "mild" oxidant of type H₂O.

0038The anti-static function layer preferably has a square resistance value of 20 to 1000 ohms / square. Provision may be made for supplying current to polarize it (supply voltages for example between 5 and 100 V). This controlled polarization makes it possible to combat the deposit of dust of size on the order of a millimeter capable of depositing on the coating, in particular dry dust adhering by electrostatic effect: by brutally reversing the polarization of the layer, these "ejects" dust.

0039The 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 type Al₂O₃, SnO₂, In₂O₃, or of oxycarbide or oxynitride of silicon.

0040To 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 its coating. At the same time, it is advantageous to choose its optical thickness (ie the product of its geometric thickness and its refractive index) close to λ / 4, λ being approximately the average wavelength in the visible range, in particular approximately 500 to 550 nm.

0041Preferably, the coating based on titanium dioxide constitutes the last layer of a stack of anti-reflection layers.

0042The alkaline barrier thin layer can be chosen based on silicon oxide, nitride, oxynitride or oxycarbide, aluminum oxide containing fluorine Al₂O₃: F, or aluminum nitride. It has been found to be useful when the substrate is made of glass, since the migration of sodium ions into the coating based on titanium dioxide can, under certain conditions, alter its photocatalytic properties.

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 above-mentioned layers can combine several functions, but they can also be superimposed. Such a layer can be obtained by CVD ("Chemical Vapor Deposition") from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in patent application EP-A-518,755.

0044Surprisingly, the substrate according to the invention has in fact 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 carbon dioxide titanium photocatalytic, it promotes the gradual disappearance of dirt of organic origin, causing their degradation by a radical oxidation process.

0045The substrate according to the invention may also have an outer surface with a pronounced hydrophilic and / or oleophilic nature, in particular in the case where the binder is mineral, which brings two significant advantages. First of all, the hydrophilic nature allows perfect wetting of the coating by water: instead of a deposit of droplets in the form of a mist which impairs visibility, there is, in fact, a thin continuous film of water at all made transparent which forms on the surface of the substrate. This anti-fog effect can be controlled by measuring a contact angle with water of less than 5 ° after exposure to light.

0046In conjunction with the hydrophilic nature, the substrate according to the invention may also have an oleophilic character allowing the wetting of organic dirt, which as for water, then tends to be deposited on the substrate in the form of a continuous film less visible than well located "tasks". An “organic anti-fouling” effect is thus obtained which operates in two stages: as soon as it is deposited on the substrate, the soiling is already not very visible because it spreads; and then gradually it disappears through radical degradation initiated by photocatalysis.

0047The invention relates particularly to "anti-fouling" and / or "anti-fog" glazing, whether monolithic, multiple of the double-glazing or laminated type, flat or curved, incorporating the substrates previously described.

0048These glazings find applications in the building, for example for the preparation of double glazing (the coating can be placed on the outside and / or on the inside, ie 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 can also be glazing for vehicles where maintaining visibility is an essential safety criterion. This coating can thus be deposited 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 traces of soiling such as fingerprints, nicotine or organic materials of the volatile plasticizer type released by the plastic coating the interior of the passenger compartment, especially that of the painting. edge (salting out sometimes known under the English term of "fogging").

0049A number of other applications are possible, in particular for aquarium glasses, display cases, greenhouses, interior furnishings, street furniture, or mirrors, television screens, electrically controlled variable absorption glazing.

0050Another 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, etc. 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.

0051In 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 likely to accelerate the photocatalytic decomposition of the carbonaceous substances depositing on the coating based on titanium dioxide. For more details on the structure of an electrochromic glazing, advantageously reference will be made to patent application EP-A-575 207 describing an electrochromic laminated double glazing, the coating based on titanium dioxide possibly being able to be arranged. opposite 1.

0052The subject of the invention is also the various methods of preparing the substrates previously described.

0053According to a first embodiment, the process for obtaining the substrate consists in depositing the coating, by pyrolysis in the liquid phase, from a dispersion comprising at least one organometallic compound and particles of titanium dioxide, said particles having the characteristics of particles incorporated in the final coating previously described.

0054The pyrolysis deposition technique is interesting because it allows the coating to be deposited continuously, directly on the float glass ribbon, when a glass substrate is used.

0055According to a second mode, the process for obtaining the substrate consists in depositing the coating by a sol-gel technique, with a deposition type of the quenched type (or "dip-coating"), "cell-coating", laminar coating. or "spray-coating", from a dispersion comprising at least one organometallic compound and particles of titanium dioxide, said particles having the characteristics of the particles incorporated in the final coating previously described.

0056The principle of the so-called sol-gel technique, using a “soaking” deposition mode, emerges from FIG. 2: it involves immersing the substrate (1) in the liquid dispersion (4) containing the (s) suitable component (s) of the coating (3), then extract the substrate (1) at a controlled speed therefrom using a motor means (5). The choice of extraction speed makes 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 coating deposited after heat treatment of the latter. This treatment aims both to evaporate the solvent, to decompose the organometallic compound (s) into oxide (s) and to ensure the mechanical strength of the coating.

0057The cell-coating technique is shown in FIG. 3. It involves forming a narrow cavity delimited by two substantially parallel faces (6) and (7), and two seals (8) and (9), at least one of these faces (6), (7), being constituted by the face of the substrate (1) to be treated. The cavity is filled with the dispersion comprising the organometallic compound (s) and the particles, and the solution is withdrawn in a controlled manner, so as to form a wetting meniscus using a pump ( 10) peristaltic for example, leaving a film of the solution on the face of the substrate (1) as the solution is withdrawn. The cavity (5) is then maintained at least the time necessary for drying and curing by heat treatment of the film on the substrate. 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 system is used. masking.

0058The “spray coating” technique is detailed in FIG. 4. It consists in spraying the dispersion (4) comprising the organometallic compound (s) and particles in the form of a cloud against the substrate (1 ) in static.

0059The laminar coating technique is illustrated in FIG. 5. It consists in passing the substrate (1), maintained by vacuum suction, against a support (11) made of stainless steel and Teflon over a tank (12) containing the dispersion comprising of organometallic compound (s) and the particles, solution in which a split cylinder (14) is partially immersed. Then moving the entire reservoir (12) and the cylinder (14) 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 technique, reference can be made to the teaching of patent application WO 94/01598.

0060According to this second mode, the organometallic compound (s) is thermally decomposed after coating the substrate with the solution on one or two of these faces.

0061The two modes previously described use a dispersion based on organometallic compound (s) and on titanium dioxide particles already formed and crystallized.

0062Organometallic compounds are compounds whose metallic atom M can be chosen from titanium, silicon, tin, zirconium, aluminum, etc.

0063They may be organometallic compounds of general formula M (OR)₄ in which M represents the metal chosen from, for example, titanium, silicon, tin, zirconium or aluminum, and R an alkyl, cycloalkyl, aryl, alkylaryl or arylakyl, alkenyl or alkynyl radical, an acetylacetonate radical or one of its derivatives (methylacetoacetate, ethylacetoacetate, titanium acetylacetonate ...), an amino radical or one of its derivatives (titanium tri-ethanolamine, titanium di-ethanolamine, ...), a glycolate (tetra-octylene glycolate of titanium), ...

0064Compounds of the titanate or silicate type are preferred.

0065The tetraisopropoxytitanium organometallic compound is particularly suitable as an organometallic compound. The preferred organometallic titanium compounds are of the titanium chelate and / or titanium alcoholate type, they may be of the type described in patent applications FR-A-2 310 977 and EP-A-465 309. Thus, the organometallic titanium compounds can be chosen from the compounds of formula R_notTi (OR ')_p with:<ul id="ul0003" list-style="dash" compact="compact"><li>p between 1 and 4,</li><li>n = 4 - p,</li><li>R C alkyl radical₁ at C ₁₈,</li><li>R 'C alkyl radical₁ - VS₄ of the methyl, ethyl or isobutyl type.</li></ul>

0066The preferred organometallic silicon compounds can be chosen from the compounds of formula R_notIf (OR ')_p with:<ul id="ul0004" list-style="dash" compact="compact"><li>p between 1 and 4,</li><li>n = 4 - p,</li><li>R C alkyl radical₁ at C ₁₈,</li><li>R 'C alkyl radical₁ - VS₄ of the methyl, ethyl or isobutyl type.</li></ul>

0067The preferred compounds are tetramethylorthosilicate (TMOS), ie tetraethylorthosilicate (TEOS) and (CH₃)₂If (OC₂H₅)₂.

0068It is of course possible to use mixtures of these compounds.

0069The particles have, themselves, the characteristics mentioned above in size, crystallinity rate and possibly doping with metallic compounds.

0070The dispersion generally comprises 5 to 90% by weight of organometallic compounds expressed as metal oxides (MO_x) relative to the weight of TiO₂ brought by particles and organometallic compounds expressed as metallic oxides (MO_x), preferably 15 to 80%, even more preferably 20 to 75%.

0071After deposition and heat treatment, the coating may contain both titanium dioxide from the decomposition of organometallic compounds, if they are based on titanium, and particles of titanium dioxide from the dispersion, the first playing , in a way, the role of mineral binder compared to the second.

0072The particles are highly photocatalytically reactive and can also promote the crystallization of titanium dioxide formed by thermal decomposition from organometallic compounds based on titanium, probably playing the role of seeds of crystallization. In the final coating, there is thus titanium dioxide from two different origins.

0073It is preferable to use monodisperse titanium dioxide particles in order to obtain transparent coatings. The term “monodisperses” means particles having a dispersion index of at most 0.5, preferably at most 0.3, the dispersion index being given by the following formula:<maths id="math0001"><math display="block"><mrow><mtext>I = </mtext><mfrac><mrow><msub><mrow><mtext>⌀</mtext></mrow><mrow><mtext>84</mtext></mrow></msub><msub><mrow><mtext> - ⌀</mtext></mrow><mrow><mtext>16</mtext></mrow></msub><mtext></mtext></mrow><mrow><msub><mrow><mtext>2⌀</mtext></mrow><mrow><mtext>50</mtext></mrow></msub></mrow></mfrac></mrow></math><img file="EP0850203B1_D0003.tif" /></maths>    in which :<ul id="ul0005" list-style="dash" compact="compact"><li>⌀₈₄ is the particle diameter for which 84% of the particles have a diameter less than ⌀₈₄,</li><li>⌀₁₆ is the particle diameter for which 16% of the particles have a diameter less than ⌀₁₆,</li><li>⌀₅₀ is the average particle diameter.</li></ul>

0074It 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 dioxide over the entire surface. coating thickness when chosen relatively thick.

0075Similarly, it may be advantageous to subject the coating, after having deposited it, at least one heat treatment of the annealed type.

0076This heat treatment of the annealed type is in particular essential if the coating has been deposited by a technique of the sol-gel or laminar coating type, according to the second mode described above, in order to decompose the organometallic compound (s) into dioxide, once the substrate has been coated.

0077On the other hand, this heat treatment of the annealed type is not essential in the case where the coating is deposited by a pyrolysis technique, according to the first mode described above, where the organometallic compound decomposes as soon as it is in contact with the substrate. However, for both the first and the second mode, a post-deposition heat treatment, once the titanium dioxide has formed, improves the rate of crystallization and adhesion. The treatment temperature chosen can also allow better control of the crystallization rate and the crystalline nature.

0078This annealing generally consists in introducing the substrate into an oven at a temperature of around 500 to 550 ° C. for a period of time which can range from 1 minute to 3 hours.

0079For both modes, an alkali barrier layer can be useful between the substrate and the coating, especially if the coating has to undergo a relatively long heat treatment and / or at high temperature, because the migration of alkalis from the glass under the effect of the heat in the coating, in too large a quantity, can be detrimental to the photocatalytic activity. This is also the case if the coating is chosen to be relatively thin, in particular when it has a thickness of less than 20 nm.

0080Any type of titanium dioxide dispersion whose particles have the desired characteristics for the substrate, in particular in size and crystallinity, can be used, whether the liquid phase is aqueous or organic. However, an organic phase is preferred.

0081Finally, the invention relates to an organic dispersion comprising:<ul id="ul0006" list-style="dash" compact="compact"><li>titanium dioxide particles of size between 5 and 70 nm, monodispersed and predominantly in crystalline anatase form,</li><li>and at least one organic solvent, preferably having a latent heat of vaporization lower than that of water.</li></ul>

0082The concept of monodispersity is the same as that defined above.

0083The titanium dioxide particles have the same size and crystallinity characteristics as the particles of the coating of the substrate according to the invention described above.

0084Thus, the particles of titanium dioxide in the dispersion have a size of between 5 and 80 nm in general, preferably between 5 and 70 nm, even more preferably between 10 and 50 nm. Size is measured by MET.

0085In addition, the nature of the crystalline phase of these titanium dioxide particles is preferably predominantly in anatase crystalline form. "Mostly" means that the anatase level of the titanium dioxide particles in the dispersion according to the invention is greater than 50% by mass. Preferably, the particles of the dispersions used have an anatase level greater than 80%.

0086For the liquid phase, preferably, the organic solvent has a latent heat of vaporization lower than that of water. By latent heat of vaporization is meant the number of calories necessary to vaporize 1 g of liquid at the boiling temperature of said liquid. The latent heat of vaporization of water at its boiling point is 540 cal / g (Handbook of Chemistry and Physics, 75th ed.). Such an organic solvent can be chosen from alcohols (ethanol, isopropanol, etc.) and in particular glycols (ethylene glycol), esters such as ethyl acetate, etc.

0087The level of titanium dioxide in the dispersion according to the invention can be between 1 g / l and 300 g / l.

0088These organic dispersions can comprise, according to the type of process used to prepare it, a water content of at most 10% by weight, preferably at most 5% and even more preferably at most 1%.

0089The monodisperse particles in the dispersion generally come from a so-called solution or wet preparation process (thermolysis, thermohydrolysis or precipitation of a titanium residue) as opposed to oxidation or high pyrolysis processes temperature of a titanium salt. They may, for example, be particles of titanium dioxide obtained by the process described in application EP-A-0 335 773.

0090It may especially be the preparation process which consists in hydrolyzing at least one titanium compound A in the presence of at least one compound B chosen from:<ul id="ul0007" list-style="none" compact="compact"><li>(i) acids which have:<ul id="ul0008" list-style="dash" compact="compact"><li>either a carboxyl group and at least two hydroxyl and / or amine groups,</li><li>either at least two carboxyl groups and at least one hydroxyl and / or amine group,</li></ul></li><li>(ii) organic phosphoric acids of the following formulas:<chemistry id="chem0003" num="0003"><img file="EP0850203B1_D0004.tif" /></chemistry><chemistry id="chem0004" num="0004"><img file="EP0850203B1_D0005.tif" /></chemistry><chemistry id="chem0005" num="0005"><img file="EP0850203B1_D0006.tif" /></chemistry> in which, n and m are whole numbers between 1 and 6, p is an integer between 0 and 5, R1, R2, R3 identical or different representing a hydroxyl group, amino, aralkyl, aryl, alkyl or the hydrogen,</li><li>(iii) compounds capable of releasing sulphate ions in an acid medium,</li><li>(iv) the salts of the acids described above,</li></ul>    and in the presence of anatase titanium dioxide seeds having a size of at most 5 nm and in a weight ratio expressed as TiO₂ present in the seeds / titanium present before introduction of the seeds in the hydrolysis medium, expressed as TiO₂ between 0.01% and 3%.

0091This process for preparing the particles therefore comprises several stages and, first of all, a stage for preparing the starting solution comprising a titanium compound A, a compound B as defined above and seeds of titanium dioxide.

0092This starting solution, intended to be hydrolyzed, is preferably completely aqueous; optionally another solvent, for example an alcohol, can be added, provided that the titanium compound A and the compound B used are then substantially soluble in this mixture.

0093As regards the titanium compound A, a compound chosen from halides, oxyhalides, titanium alkoxides, sulfates and more particularly synthetic sulfates is generally used.

0094The term “synthetic sulfates” is understood to mean solutions of titanyl sulfates produced by ion exchange from very pure titanium chloride solutions or by reaction of sulfuric acid with a titanium alkoxide.

0095Preferably, the operation is carried out with titanium compounds of the halide or titanium oxyhalide type. The titanium halides or oxyhalides more particularly used in the present invention are fluorides, chlorides, bromides and iodides (respectively oxyfluorides, oxychlorides, oxybromides and oxyiodides) of titanium.

0096According to a particularly preferred embodiment, the titanium compound is titanium oxychloride TiOCl₂.

0097The amount of titanium compound A present in the solution to be hydrolyzed is not critical.

0098The initial solution also contains at least one compound B as defined above. By way of nonlimiting examples of compounds B falling within the scope of the present invention, there may be mentioned in particular:<ul id="ul0009" list-style="dash" compact="compact"><li>hydroxypolycarboxylic acids, and more particularly hydroxydi- or hydroxytricarboxylic acids such as citric acid, maleic acid and tartaric acid.</li><li>(polyhydroxy) monocarboxylic acids, such as for example glucoheptonic acid and gluconic acid,</li><li>poly (hydroxycarboxylic) acids, such as for example tartaric acid,</li><li>dicarboxylic monoacids and their corresponding amides, such as for example aspartic acid, asparagine and glutamic acid,</li><li>monocarboxylic amino acids, hydroxylated or not, such as for example lysine, serine and threonine,</li><li>methylene aminotriphosphonate, methylene diaminotetraphosphonate, methylene triethylenetetraaminohexaphosphonate, methylene tetraethylene pentaaminoheptaphosphonate, methylene pentaethylenehexaaminooctaphosphonate,</li><li>methylene diphosphonate; 1.1 'ethylene; 1.2 ethylene; 1.1 'propylene; 1.3 propylene; 1.6 hexamethylene; 2,4 dihydroxypentamethylene - 2,4 diphosphonate; 2.5 dihydroxyhexamethylene - 2.5 disphosphonate; 2,3 dihydroxybutylene - 2,3 diphosphonate; 1 hydroxybenzyl - 1,1 'diphosphonate; 1 aminoethylene 1-1 'diphosphonate; hydroxymethylene diphosphonate; 1 hydroxyethylene 1,1 'diphosphonate; 1 hydroxypropylene 1-1 'diphosphonate; 1 hydroxybutylene 1-1 'diphosphonate; 1 hydroxyhexamethylene - 1,1 'diphosphonate.</li></ul>

0099As already indicated, it is also possible to use, as compound B, all the salts of the abovementioned acids. In particular, these salts are either alkaline salts, and more particularly sodium salts, or ammonium salts.

0100These compounds can also be chosen from sulfuric acid and ammonium and potassium sulfates, etc.

0101Preferably, the compounds B as defined above are hydrocarbon compounds of the aliphatic type. In this case, the length of the main hydrocarbon chain preferably does not exceed 15 carbon atoms, and more preferably 10 carbon atoms.

0102The amount of compound B is not critical. In general, the molar concentration of compound B relative to that of the titanium compound A is between 0.2 and 10% and preferably between 1 and 5%.

0103Finally, the starting solution comprises titanium dioxide seeds used in a specific way.

0104Thus, the seeds of titanium dioxide used in the present invention must first have a size less than 8 nm, measured by X-ray diffraction. Preferably, seeds of titanium dioxide having a size of between 3 and 5 are used. nm.

0105Next, the weight ratio of titanium dioxide present in the seeds to the titanium present in the hydrolysis medium before introduction of the seeds - that is to say provided by the titanium compound A - and expressed as TiO₂ is between 0.01 and 3%. This ratio can preferably be between 0.05 and 1.5%. The combination of these two conditions on seeds (size and weight ratio) associated with the process as described above makes it possible to precisely control the final size of the titanium dioxide particles by associating a particle size with a rate of seeds. It is thus possible to obtain particles whose size varies between 5 and 100 nm.

0106Titanium dioxide seeds are used in anatase form so as to induce the precipitation of titanium dioxide in anatase form. Generally, because of their small size, these germs are rather in the form of poorly crystallized anatase. The germs usually come in the form of an aqueous suspension made of titanium dioxide. They can generally be obtained in a known manner by a process for neutralizing a titanium salt with a base.

0107The next step consists in carrying out the hydrolysis of this starting solution by any means known to those skilled in the art and in general by heating. In the latter case, the hydrolysis may preferably be carried out at a temperature greater than or equal to 70 ° C. It is also possible to work initially at a temperature below the boiling temperature of the medium and then to maintain the hydrolysis medium in level with the boiling temperature.

0108Once the hydrolysis has been carried out, the titanium dioxide particles obtained are recovered by separation of the precipitated solid from the mother liquors before being redispersed in an aqueous liquid medium so as to obtain a dispersion of titanium dioxide. This liquid medium can be acidic or basic. It is preferably an acid solution, for example an aqueous solution of nitric or hydrochloric acid.

0109To then obtain an organic dispersion of these titanium dioxide particles, any known method making it possible to carry out the suspension of titanium dioxide particles in an organic phase from an aqueous dispersion of titanium dioxide can be used.

0110The dispersion can thus be obtained by bringing an aqueous dispersion of titanium dioxide particles into contact with the desired organic solvent and then heating so as to remove the water by distillation. Such a process can only be implemented in the case where the organic solvent chosen has a boiling point higher than that of water and is soluble in water. This is the case, for example, with ethylene glycol.

0111The dispersion can also be obtained by grafting a hydrophobic chain on the surface of particles of titanium dioxide suspended in water then mixing with an organic solvent immiscible with water so as to migrate the particles of dioxide titanium in the organic phase.

0112It has been observed that the particles of titanium dioxide resulting from a process of preparation known as in solution or by wet way, and in particular resulting from the process described above with hydrolysis at temperature of approximately 100 ° C, present, by their porosity, a lower refractive index than the titanium dioxide particles from other processes. As indicated above, this property is of great interest when these particles are used to prepare a coating on a substrate, in particular a glass-based substrate, since the coating obtained also has a low refractive index as indicated above.

0113Advantageously, the liquid phase of the dispersion according to the invention comprises at least one organometallic compound based on a metal M chosen from titanium, silicon, tin, zirconium or aluminum. The preferred compounds correspond to the organometallic compounds previously described.

0114When the liquid phase of the dispersion according to the invention also comprises an organometallic compound, said compound is generally added by mixing a solution of the organometallic compound and a dispersion in organic phase of the particles of titanium dioxide. Depending on the nature of the organometallic compound used, additives such as co-solvents, surfactants or stabilizers can also be added during this mixing. The mixing can also be improved by agitation of the dispersion by ultrasound.

0115The solution of organometallic compound added to the organic dispersions based on titanium dioxide particles is generally a solution in organic phase, said organic phase being able to be chosen from: ethanol, isopropanol, ethyl acetate. ..

0116It is also possible to add the organometallic compounds to the dispersions of titanium dioxide in pure form.

0117These organometallic compounds can be advantageously stabilized by products such as diethanolamine (DEA), acetylacetone derivatives such as ethylacetoacetate, glycols, etc.

0118The dispersion generally comprises 5 to 90% by weight of organometallic compounds expressed as metal oxides (MO_x) relative to the weight of TiO₂ brought by particles and organometallic compounds expressed as metallic oxides (MO_x), preferably 15 to 80%, or even 20 to 75%.

0119As indicated above, in order to exacerbate the photocatalytic effect of the coating based on titanium dioxide, it is possible to add to the titanium dioxide, as indicated previously, catalysts, additives making it possible to better absorb UV, or to shift the absorption band towards the visible, or alternatively metals making it possible to boost titanium dioxide in order, inter alia, to increase the number of electronic carriers.

0120According to a first variant, at least part of the particles of titanium dioxide of the dispersions comprise in their crystal lattice metal ions chosen from iron, copper, ruthenium, molybdenum, bismuth, tantalum, niobium, cobalt , nickel, vanadium. The mass ratio of these metal ions with respect to the mass of titanium dioxide can be between 0.01 and 10%. These dispersions can be obtained by introducing salts of metal ions during the preparation of the titanium dioxide particles. Thus, if the particles of titanium dioxide are obtained by thermohydrolysis of a titanium compound as it is described in the application EP-A-0 335 773, it is possible to add to the thermohydrolysis medium the metal ions so as to introduce the ions into the crystal lattice of titanium dioxide.

0121According to a second variant, at least part of the particles of titanium dioxide in the dispersions are covered at least in part with a layer of metal salts or oxides, the metal being chosen from iron, copper, ruthenium, cerium, molybdenum, bismuth, tantalum, niobium, cobalt, nickel, vanadium, tungsten, tin, zirconium, cadmium, zinc. The ratio of the mass of these metals to the mass of titanium dioxide can be between 0.01 and 20%. These dispersions can be obtained by precipitation of metal salts on the titanium dioxide particles before placing in an organic medium. Thus, when the titanium dioxide particles are still in an aqueous medium following a wet preparation process, metal salts are introduced into the aqueous phase and they are precipitated so as to at least partially cover the titanium dioxide particles.

0122According to a third variant, at least part of the particles of titanium dioxide in the dispersions are covered at least in part with a layer of metal chosen from platinum, silver or rhodium. The ratio of the mass of these metals to the mass of titanium dioxide can be between 0.01 and 5%. These dispersions can be obtained by reduction of metal salts on the titanium dioxide particles before placing in an organic medium. For example, when the titanium dioxide particles are still in an aqueous medium following a wet preparation process, metal salts are introduced into the aqueous phase and they are reduced so as to at least partially cover the titanium dioxide particles.

0123According to a fourth variant, the dispersions comprise, in addition to the particles of titanium dioxide, additives in the form of particles based on metallic compounds chosen from cerium, cadmium, tin, tungsten, zinc or zirconium. These particles are colloidal in size, generally between 5 and 100 nm. Their level in the dispersion can be between 0.1 and 20% by weight. As indicated previously, the metal compounds can be metal oxides or sulphides, such as CeO₂, SnO₂, WO₃, ZnO, ZrO₂ or CdSe_xS_y with x and including between 0 and 1, and x + y = 1. The latter particles can be introduced into the dispersions by simple mixing with an aqueous dispersion of titanium dioxide particles from a wet process then transfer of all the particles of the aqueous phase in organic phase.

0124The dispersions according to the invention can have the characteristics of the four variants separately or simultaneously.

0125Finally, the invention relates to the use of an organic dispersion as described above in a process for preparing the substrate according to the invention.

0126Other details and advantageous characteristics of the invention appear from the following description of nonlimiting exemplary embodiments.

0127As shown diagrammatically in FIG. 1, all of the following examples relate to the deposition of a coating (3) called "anti-fouling" essentially based on titanium dioxide on a substrate (1).

EXAMPLES

<u>EXAMPLE 1 Preparation of an Organic Dispersion of Titanium Dioxide Particles</u>

0128An aqueous dispersion of titanium dioxide particles is prepared according to the teaching of patent application EP-A-0 335 773, in the presence of germs.

Hydrolysis

0129Was successively added to 394.7 g of a titanium oxychloride solution at 1.9 mol / kg:<ul id="ul0010" list-style="dash" compact="compact"><li>42.02 g of 36% hydrochloric acid,</li><li>4.73 g of citric acid,</li><li>547.1 g of purified water,</li><li>11.36 g (0.2% by weight relative to TiO₂) of anatase germs having a size of between 5 and 6 nm.</li></ul>

0130The mixture is brought to a boil and kept there for 3 h.

Particle recovery and re-dispersion

0131The solution is then filtered and the particles obtained are washed with water until complete elimination of the chlorides. They are then redispersed at pH 1.5 (controlled by the addition of HNO₃) with a dry extract is 20% by weight.

0132An aqueous dispersion is obtained comprising particles with a diameter of 45 nm measured by TEM. X-ray diffraction analysis indicates that the particles are based on titanium dioxide only in anatase form at 80% by weight. The particles obtained are porous.

Dipersion in organic medium

0133100 parts by mass of this dispersion are mixed with 100 parts of ethylene glycol. The mixture is then heated to 80 ° C so as to remove the water by gentle distillation under reduced pressure (100 mbar), then to 120 ° C to remove the bound water.

0134A dispersion of particles of titanium dioxide in ethylene glycol is obtained. The dry extract is 20% by weight. The particle size measured in ethylene glycol by TEM is 45 nm. The residual water content is 0.7% by weight relative to the titanium dioxide.

<u>EXAMPLE 2 Preparation of an Organic Dispersion of Niobium-doped Titanium Dioxide Particles</u>

0135We repeat example 1 except that we add NbCl₅ in the hydrolysis medium in an amount such as the Nb / TiO molar ratio₂ is 0.1%.

<u>Examples 3 to 7: deposition of the dispersions of Examples 1 and 2 by pyrolysis</u>

0136The substrate (1) is made of clear soda-lime-silica glass 6 mm thick and 50 cm long and wide.

0137Between the coating (3) and the substrate (1) is an optional thin layer (2).

0138The following examples 3 to 7 relate to a coating (3) deposited by 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: the substrate (1), already cut to the dimensions indicated, is first heated in an oven at a temperature of 400 to 650 ° C, before running at a constant speed in front of a movable nozzle planning an appropriate solution.

- Example 3

0139In this example, there is no optional layer (2). The coating (3) is deposited using an organic dispersion A comprising:<ul id="ul0011" list-style="dash" compact="compact"><li>a formulation comprising two organometallic titanium compounds and two solvents in the following proportions:<ul id="ul0012" list-style="none" compact="compact"><li>. 20% by weight of titanium di-iso-propoxy di-acetylacetonate,</li><li>. 20% by weight of titanium tetraoctylene glycolate,</li><li>. 40% by weight of ethyl acetate,</li><li>. 20% by weight of isopropanol,</li></ul></li><li>the organic dispersion of titanium dioxide particles according to Example 1 diluted and having the following characteristics:<ul id="ul0013" list-style="none" compact="compact"><li>. mass content of particles: 10%,</li><li>. particle size: 45 nm, measured at TEM,</li><li>. size of the crystallites: 5 nm,</li><li>. crystalline phase: anatase greater than 80%</li><li>. liquid phase: ethylene glycol.</li></ul></li></ul>

0140The formulation and the organic dispersion are in relative proportions such that the content of particles of titanium dioxide in dispersion A is adjusted so as to obtain a content of 25% by weight of titanium dioxide coming from the particles in the coating once deposited. (TiO mass₂ from particles / total mass of oxides in the coating assuming that the decomposition of the organometallic compounds of dispersion A into oxides is total).

0141As soon as the substrate (1) has reached the desired temperature in the oven, that is to say around 500 ° C., the latter passes before the nozzle, projecting the indicated mixture at ambient temperature using compressed air.

0142A layer of titanium dioxide approximately 90 nm thick is then obtained, the latter being 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.

0143This coating contains both titanium dioxide from the decomposition of organometallic and titanium dioxide particles in the dispersion, the former playing, so to speak, the role of mineral binder compared to the latter. The layer has excellent mechanical strength.

0144The refractive index is 2.3.

- Example 4

0145Example 3 is repeated, except that the substrate (1) comprises a thin layer (2) of tin oxide doped with SnO fluorine.₂: F in order to constitute a static and / or low-emissive layer and / or attenuating the color in particular in reflection.

0146This layer is obtained by powder pyrolysis 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, 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 type H₂O.

0147This thin layer has a thickness of 73 nm, an index of 1.9 and a square resistance of 50 ohms / square.

0148This substrate, treated in the same way as in Example 3 and mounted in double glazing so that the coating (3) is on face 1 (with another substrate not coated but of the same nature and dimensions as the substrate (1)) through a 12 mm air gap, has a color purity value in reflection (in gold) of 3.6%, and 1.1% in transmission.

0149The substrate of Example 3, mounted in the same way, has a color purity value in reflection (in gold) of 26%, and 6.8% in transmission.

0150The SnO underlay₂: F has a favorable influence on the colorimetry of the substrate, making its coloration much more "neutral", both in transmission and in reflection, coloration caused by the presence of the coating (3) of titanium dioxide, having an index of relatively high refraction. In addition, this sublayer reduces the diffusion of alkalis in the photocatalytic layer of TiO₂. The photocatalytic activity is therefore improved. Despite the presence of a high amount of particles in the coating, the haze is much less than 1%. The blurring is defined by the ratio of the diffracted light transmission to the total light transmission of the substrate at 560 nm.

- Example 5

0151Example 3 is repeated, except that the substrate (1) comprises a thin layer (2) based on silicon oxycarbide in order to constitute a barrier to the diffusion of alkalis and / or a layer attenuating the light reflection.

0152This layer is 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 for diffusion of alkalis (Na⁺, K⁺) and alkaline earth (Ca²⁺) from the substrate (1) to the coating (3).

0153This thin layer has a thickness of 50 nm, an index of 1.75.

0154Having, like SnO₂: F, an intermediate refractive index between that of the base substrate (1) (1.52) and of the coating (3) (2.3), it also makes it possible to attenuate the intensity of the coloring of the substrate as well in transmission than in reflection, and overall decrease the value of the light reflection R_L of said substrate.

0155In addition, the sublayer based on silicon oxycarbide constitutes an effective barrier to the diffusion of alkalis, and therefore the photocatalytic activity of the coating is significantly improved.

- Example 6

0156Example 3 is repeated, except that the coating (3) is deposited using a dispersion B comprising:<ul id="ul0014" list-style="dash" compact="compact"><li>a formulation based on silicon tetraethoxide Si (OEt)₄ diluted in ethanol at a rate of 0.1 mol per liter of ethanol,</li><li>the organic dispersion of titanium dioxide particles from Example 1.</li></ul>

0157The formulation and the organic dispersion are in relative proportions such that the content of particles of titanium dioxide in dispersion B is adjusted so as to obtain a content of 80% by weight of titanium dioxide in the coating once deposited (mass of TiO₂ from TiO particles / mass₂ particles + mass of SiO₂ obtained by decomposition of Si (OEt)₄ assuming the decomposition is complete).

0158As soon as the substrate (1) has reached the desired temperature in the oven, that is to say around 200 ° C., the latter passes past the nozzle which projects the dispersion B at ambient temperature using compressed air.

0159A mixed layer of TiO particles is then obtained₂ coming from the dispersion, linked together and to the substrate by SiO₂ from the breakdown of organometallic. The coating has a thickness of approximately 50 nm, it is crystallized at 65% in anatase form.

0160The layer has a high photocatalytic activity thanks to the high specific surface developed by the TiO particles₂(> 250 m²/ g). In addition, the binder SiO₂ plays the role of a particularly effective alkali barrier at the substrate / particle interface.

0161Finally, the refractive index is much lower than a layer of TiO₂ massive, thanks to the presence of SiO₂ and its high porosity. This index is less than 1.6. The value of light reflection R_L of the substrate is therefore reduced.

- Example 7

0162Example 6 is repeated, except that dispersion B contains particles of titanium dioxide doped with niobium at 0.1% according to example 2.

0163The layer has an even higher photocatalytic activity.

<u>Example 8: deposition of the dispersion of example 1 by dip-coating</u>

0164This example uses the so-called sol-gel technique using a “hardened” or “dip-coating” deposition method, the principle of which emerges from FIG. 2: it involves immersing the substrate (1) in the liquid solution (4) containing the dispersion, then extracting the substrate (1) at a controlled speed using a driving means (5), the choice of the extraction speed making it possible to adjust the thickness of the dispersion 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 so as to both evaporate the solvent and decompose the precursors of metal oxides.

0165The coating (3) is deposited using a dispersion A or B, as defined in Examples 3, 6 or 7. An organic dispersion C is also used comprising:<ul id="ul0015" list-style="dash" compact="compact"><li>a formulation based on titanium tetrabutoxide Ti (O-Bu)₄ stabilized with di-ethanol amine DEA in a molar ratio 1: 1, and diluted in ethanol at a rate of 0.2 mole of tetrabutoxide per liter of ethanol,</li><li>a dispersion of titanium dioxide particles according to Example 1 having the following characteristics:<ul id="ul0016" list-style="none" compact="compact"><li>. mass content of particles: 10%,</li><li>. particles of 45 nm size, measured at TEM,</li><li>. size of the crystallites: 5 nm,</li><li>. crystalline phase: anatase greater than 80%,</li><li>. liquid phase: ethylene glycol.</li></ul></li></ul>

0166The formulation and the organic dispersion are in relative proportions such that the content of particles of titanium dioxide in dispersion C is adjusted so as to obtain a content of 80% by weight of titanium dioxide coming from the particles in the coating once deposited. (TiO mass₂ from particles / total mass of oxides in the coating assuming that the decomposition of the organometallic compounds of dispersion C into oxides is total).

0167After soaking substrates (1) comprising thin layers (2) based on silicon oxycarbide in dispersions A, B or C, the substrates (1) are heated for 3 hours at 550 ° C. with a gradual rise in temperature.

0168In all three cases, a coating (3) of titanium dioxide well crystallized in anatase form is obtained on each of the faces. The anatase crystallization rates are comparable to the examples using a pyrolysis deposition technique, but the size of the crystallites is greater thanks to the prolonged heat treatment. This results in better photocatalytic activity.

0169The coating has a refractive index of at most 1.8.

<u>Example 9: deposition of the dispersion of Example 1 by "cell-coating"</u>

0170This example uses the technique called "cell-coating", the principle of which emerges from 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 of the dispersion (4) is filled in a controlled manner, so as to form a wetting meniscus using a peristaltic pump (10) for example, leaving a film of the dispersion (4) on the face of the substrate (1) as the solution is withdrawn.

0171The cavity is then maintained for at least the time necessary for drying. The hardening of the film on the substrate is ensured by heat treatment as in the previous examples.

0172The coating (3) is deposited using solutions A, B or C described in Examples 3, 6 and 8.

0173After quenching of the substrate (1) comprising thin layers (2) based on silicon oxycarbide in the dispersions A, B or C, the same heat treatments as in Example 8 are carried out.

0174In all three cases, a coating (3) is obtained comparable to the coatings of Example 8, but here only one side of each substrate is treated.

<u>Example 10: Control of the Properties of the Substrates Obtained</u>

Wetting test 1:

0175It consists in depositing on the substrate to be evaluated a layer of an organosilane and in irradiating it with UVA so as to degrade it by photocatalysis. As the organosilane modifies the wetting properties, the measurements of the contact angle of the substrate with water 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.

0176The grafted organosilane is a trichlorosilane: octadecyltrichlorosilane (OTS). The grafting is carried out by soaking.

0177The test device consists of a carousel rotating around 1 to 6 low pressure UVA lamps. The test tubes to be evaluated are placed in the carousel, the side to be evaluated on the UVA radiation side. Depending on their position and the number of lamps lit, each test tube receives a UVA irradiation varying from 0.5 W / m² at 50 W / m².

0178The time between each measurement of the contact angle varies between 20 min and 3 h, depending on the photocatalytic activity of the test specimen considered. The measurements are made using a goniometer.

0179Before irradiation, the glasses have an angle of approximately 100 °. It is considered that the layer is destroyed after irradiation when the angle is less than 20 °.

0180Each test piece tested is characterized by the average speed of disappearance of the layer, given in nanometers per hour, ie the thickness of the layer of organosilane deposited, divided by the irradiation time making it possible to reach a final plateau of less than 20 ° ( time of disappearance of the organosilane layer).

Isobutane test 2

0181It consists in controlling the degradation of the isobutane gas brought into contact with a glass treated according to the invention.

0182The glass to be tested and an amount of isobutane equal to 20% of the total volume of the reactor are introduced into a reactor.

0183The test device consists of a carousel rotating around 1 to 6 low pressure UVA lamps with a maximum emission between 300 and 400 nm. The reactors containing the glasses to be evaluated are placed in the carousel, the face of the glass to be evaluated on the side of the UVA radiation. Depending on their position and the number of lamps lit, each glass receives UVA irradiation of up to 30 W / m².

0184The irradiation lasts 8 to 22 h.

0185The progress of the photodecomposition of isobutane is then assayed using a gas chromatograph by monitoring the amount of O₂. We translate this advancement using the rate of disappearance of the O₂ in mole / h / cm².

Palmitic acid test 3

0186It consists in depositing on the substrate to be evaluated a layer of palmitic acid and in irradiating it with UVA so as to degrade it by photocatalysis.

0187A chloroformic palmitic acid solution at 8 g / l is sprayed onto the test glasses. The amount of palmitic acid deposited per 30 cm² of glass is 1.5 mg. Then, the glasses are introduced into a sealed reactor surrounded by six UV lamps having a maximum emission between 300 and 400 nm. The irradiated test glasses receive a power of 10 W / m². The irradiation lasts a maximum of 40 h.

0188The glasses are then removed from the reactor. To measure the palmitic acid remaining on the glasses, the latter are washed with a chloroformic acid solution; the solution obtained is then assayed by liquid chromatography in order to assay the remaining palmitic acid.

0189This gives the time for the total degradation of 1.5 mg of palmitic acid expressed in minutes.

0190The degradation of palmitic acid can also be observed visually by the reduction in the blurring of the glass induced by the palmitic acid layer.

Anti-fog test 4:

0191It consists in observing the consequences of photocatalysis and of the structure of the coating (rate of hydroxyl groups, porosity, roughness) on the wetting. If the surface is photoreactive, the carbonaceous micropollutions which deposit on the coating are permanently destroyed, and the surface is hydrophilic therefore anti-fog. A quantitative evaluation can also be made by suddenly reheating the coated substrate initially stored in the cold or simply by blowing on the substrate, looking for fogging and if so, when, then measuring the time required. when said mist disappears.

Contact angles test 5:

0192It is a question of evaluating the hydrophilicity and the 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 (dioctylphthalate) on their surfaces. The measurement is carried out 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 min to UVA radiation.

Photocatalytic test results:

0193<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="5" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col2" align="center">Substrate</entry><entry namest="col3" nameend="col3" align="center">1.8 W / m wetting test² UVA (in nm / h)</entry><entry namest="col4" nameend="col4" align="center">Isobutane test 30 W / m² UVA (in mole O₂/ h / cm²)</entry><entry namest="col5" nameend="col5" align="center">Palmitic acid test 10 W / m² UVA (in min)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col2" align="center">Example 3</entry><entry namest="col3" nameend="col3" align="center">0,1</entry><entry namest="col4" nameend="col4" align="center">10^-8</entry><entry namest="col5" nameend="col5" align="center">> 1000</entry></row><row><entry namest="col1" nameend="col2" align="center">Example 4</entry><entry namest="col3" nameend="col3" align="center">0,3</entry><entry namest="col4" nameend="col4" align="center">2.10^-8</entry><entry namest="col5" nameend="col5" align="center">> 1000</entry></row><row><entry namest="col1" nameend="col2" align="center">Example 5</entry><entry namest="col3" nameend="col3" align="center">3</entry><entry namest="col4" nameend="col4" align="center">10^-7</entry><entry namest="col5" nameend="col5" align="center">800</entry></row><row><entry namest="col1" nameend="col2" align="center">Example 6</entry><entry namest="col3" nameend="col3" align="center">4</entry><entry namest="col4" nameend="col4" align="center">10^-7</entry><entry namest="col5" nameend="col5" align="center">730</entry></row><row><entry namest="col1" nameend="col2" align="center">Example 7</entry><entry namest="col3" nameend="col3" align="center">6</entry><entry namest="col4" nameend="col4" align="center">10^-7</entry><entry namest="col5" nameend="col5" align="center">620</entry></row><row><entry namest="col1" nameend="col1" morerows="2" align="center">Examples 8 and 9</entry><entry namest="col2" nameend="col2" align="center">dispersion A</entry><entry namest="col3" nameend="col3" align="center">5</entry><entry namest="col4" nameend="col4" align="center">10^-7</entry><entry namest="col5" nameend="col5" align="center">660</entry></row><row><entry namest="col2" nameend="col2" align="center">dispersion B</entry><entry namest="col3" nameend="col3" align="center">10</entry><entry namest="col4" nameend="col4" align="center">2.10^-7</entry><entry namest="col5" nameend="col5" align="center">390</entry></row><row rowsep="1"><entry namest="col2" nameend="col2" align="center">dispersion C</entry><entry namest="col3" nameend="col3" align="center">20</entry><entry namest="col4" nameend="col4" align="center">5.10^-7</entry><entry namest="col5" nameend="col5" align="center">250</entry></row></tbody></tgroup></table></tables>

0194Test results 4: for all the substrates of examples 3 to 9, no fogging appears.

0195Test results 5: for all the substrates of examples 3 to 9, the contact angle with water and with DOP is less than 5 ° after 20 min of exposure to UVA.