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

Translation of description of equivalent WO 9710185 A1

PHOTOCATALYTIC COATING SUBSTRATE

BASED ON TITANIUM DIOXIDE

AND ORGANIC DISPERSIONS BASED ON TITANIUM DIOXIDE

p0004The present invention relates to substrates provided with a photocatalytic coating based on titanium dioxide, said titanium dioxide being incorporated partly in the form of particles. It also relates to a process for preparing these substrates and of novel organic dispersions based on monodisperse titanium dioxide particles used in this process.

p0005It is known to functionalize the materials of various applications, such as materials for vehicles or buildings (glass, metals, ceramics, facing materials, cladding, roofing such as tiles, ...) by conferring upon them properties such as in particular UV stabilizers, anti-fouling, bactericidal, anti-glare, anti-static, anti-microorganism, ....

p0006This is particularly true in the case of glazing, such as windshield glass for transportation, which it is desired to functionalize by depositing on the surface thereof thin layers intended to confer thereon a specific property according to the intended application . Thus, there exist layers with an optical function, such as so-called anti-glare layers composed of a stack of layers alternatively with high and low refractive indices. For anti-static function, or heating the antifreeze type that may well provide conductive thin electrically, for example based on metal or doped metal oxide. For thermal function, low-emissivity or anti-solar, for example, one can turn to the metal thin film type or silver nitride or metal oxide. To produce a "Rain" can be provided of hydrophobic layers, for example based on fluorinated organosilane ...

p0007Today another desired property is to get the permanence in time of appearance and surface properties, which promote render cleaning and / or improve visibility, managing to eliminate as and gradually able dirt being deposited on the surface of the substrate, including dirt of organic origin, such as fingerprints or volatile organic products present in the atmosphere, or even mist type of dirt.

p0008A solution to these problems consists of soiling, for example, to drop on the substrates a coating ensuring degradation of these surface contaminations by photocatalysis. Under the effect of a suitable wavelength of radiation, the components of the coating initiate radical reactions which cause oxidation of organic products.

p0009This degradation can be induced by any compound that generates radicals under the action of light (photocatalytic effect). This may be in particular titanium dioxide, which is already used for the treatment of architectural substrates and especially glass substrates.

p0010Thus, it is known to use titanium compounds of solutions or colloidal dispersions of titanium dioxide to create photocatalytic properties on the substrates. However, it was found that the specific characteristics of said colloidal titanium compounds of solutions or dispersions of titanium dioxide used for treating the substrate influence the quality of the photocatalytic coating. According to these specifications, the quality of coating adhesion on the substrate can also vary widely. Finally, it happens, in the case where the substrate is glass, the coating induces a lack of transparency and a fuzziness on the glass.

p0011An object of the present invention is thus to provide novel substrates having a titanium dioxide based coating exhibiting good photocatalytic properties, the said coatings being durable, transparent and capable of being prepared industrially.

p0012For this purpose, the invention relates to a substrate provided on at least a portion of one of its faces with a photocatalytic coating based on titanium dioxide at least partially crystalline and incorporated into said coating partially in the form of particles predominantly crystalline anatase form.

p0013The invention also relates to methods of producing the substrate consists in depositing the coating by liquid phase pyrolysis or by a technique called sol-gel from a suspension comprising at least one organometallic compound and a dispersion of particles of titanium dioxide, said particles having the characteristics of the particles incorporated in the final coating.

p0014Finally, the invention relates to an organic dispersion comprising:

p0015- Size of titanium dioxide particles of between 5 and 70 nm, monodisperse and predominantly in the anatase crystalline form, - and at least one organic solvent, preferably exhibiting a latent heat of vaporization less than that of water. This dispersion is used for the preparation of the substrate according to the invention. Other advantages of the invention appear more clearly on reading the following description, examples and figures:

p0016. Figure 1: Cross-section of a substrate provided with the coating according to the invention. Figure 2: Diagram of a technique of sol-gel deposition, known as "dip" or "dip-coating" the coating,

p0017. Figure 3: Diagram of a deposition technique known as "cell coating". Figure 4: Diagram of a deposition technique known as "spray-coating". Figure 5: diagram of a deposition technique by laminar coating.

p0018The invention therefore firstly relates to a substrate provided on at least a portion of one of its faces with a photocatalytic coating based on titanium dioxide at least partially crystalline and incorporated into said coating partially in the form of particles predominantly crystallized in the anatase form.

p0019Overall, coating titanium dioxide in the form of particles or otherwise, is partially crystallized in the anatase crystal form, rutile form or a mixture of anatase and rutile with a degree of crystallization preferably of at least 25 %, in particular approximately 30 to 80%. The degree of crystallization represents the amount by weight of TiO₂ crystallized with respect to the total amount by weight of T1O2 in the coating. For coating titanium dioxide particles, the nature of the crystalline phase is, preferably, predominantly the anatase crystalline form. "Predominantly" means that the level of anatase coating titanium dioxide particles is greater than 50 mass%. Preferably, the coating of the particles exhibit a level of anatase of greater than 80%. The degree of crystallization and the nature of the crystalline phase are measured by X ray diffraction.

p0020The crystalline titanium dioxide particles incorporated in the coating exhibit a mean size between 5 to 80 nm, preferably between 5 and 70 nm, even more preferably between 10 and 50 nm. The diameters are measured by transmission electron microscopy (TEM).

p0021titanium dioxide the particles are preferably incorporated in the coating using a binder.

p0022In a first variant, the binder incorporating the particles in the coating can be inorganic. It may especially be in the form of an oxide (or mixture of oxides) amorphous or partially crystallized, for example silicon oxide, titanium, tin, zirconium or aluminum. It can be confined to its role vis-à-vis the titanium dioxide particle matrix, which is the case of silicon oxide. But it can also participate in the photocatalytic effect of the particles, presenting himself even a photocatalytic effect, even low relative to that of the particles, which is the case of the amorphous titanium dioxide or partially crystallized.

p0023In a second variant, the binder can also be at least partly organic, particularly in the form of a polymeric matrix. It can be a polymer which can have complementary properties to the titanium dioxide particles, including hydrophobic and / or oleophobic.

p0024As example of such matrices, reference may be made to the patent application

p0025EP-A-675 087, which describes a matrix described as hybrid and obtained from a solution comprising an epoxidized alkoxysilane, a non-hydrolyzable epoxidized silane, colloidal silica, a catalyst and at least one hydrolysable fluorinated alkylsilane.

p0026The fluorinated alkylsilane is of the general formula:

p0027CF₃- (CF₂)_not- (CH₂)_m-Six₃With n from 0 to 12, m from 2 to 5, X is a hydrolysable function. The alkylsilane epoxide has the formula: CH₂-CM-CH2-0- (CH₂CH₂-0)_f- (CH₂)_sSi (OM ') 3._p

p0028\ / I

p0029O M "_p wherein 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 having 1 to 3 carbon atoms.

p0030The non-epoxidized silane of general formula:

NOT'

p0032Q - If - Q '

p0033N wherein N and N 'are organic groups bonded to the silicon atom by an Si-C bond and do not contain a group capable of reacting with the hydrolyzed silanes present in the composition, and wherein Q and Q' are hydrolyzable functions.

p0034One can also choose to superimpose the coating according to the invention an oleophobic layer and / or hydrophobic grafted, for example based on the fluorinated organosilane described in US-A-5 368 892 and patents US-A-5,389,427, as well as basic perfluoroalkylsilane described in patent application EP-A-692 463, in particular of formula:

p0035CF₃- (CF₂)_not- (CH₂)_m-Six₃With n from 0 to 12, m from 2 to 5, X is a hydrolysable function.

p0036With titanium dioxide particles incorporated in the coating, it may have a refractive index ranging between 1, 40 and 2.35, preferably between 1 and 6 2.3 This is due to the fact that titanium dioxide particles are porous and thus exhibit a lower refractive index than the bulk titanium dioxide. The coating obtained thus has a low refractive index compared to the refractive indices of coatings based on bulk titanium dioxide Optical advantage related to obtaining low indices is very important in the case of glass substrates based on a layer high index of bulk titanium dioxide leads to increase the light reflection of the carrier glass, so as to reduce its light transmission. However, for certain applications, especially in the field of glazings equipping vehicles, it is essential to have high levels of light transmission (for a lens BNSE, a minimum light transmission of 75% is necessary)

p0037To amplify the photocatalytic effect of the coating titanium dioxide particles according to the invention, the said particles can comprise catalysts and additives for better UV filter, or to shift the absorption band towards the visible, or even metal to dope the titanium dioxide in particular to increase the number of electronic carriers. Several variants can amplify this effect

p0038In a first variant, at least a portion of the coating titanium dioxide particles can include 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 with respect to the mass of titanium dioxide particles is generally between 0.01 and 10% in a second variant, at least some of the particles titanium dioxide can be coated at least partly with a layer of metal oxides or salts, the metal being selected 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 with respect to the mass of titanium dioxide particles is generally between 0.01 and 20%

p0039In a third variant, at least a portion of the titanium dioxide particles can be covered at least in part of a layer of metal selected from platinum, silver or rhodium The ratio of the mass of these metals with respect to the mass of titanium dioxide particles can be between 0.01 and 5%.

p0040In a fourth variant, the coating according to the invention comprises, in addition to the titanium dioxide particles and additive particles based on metal compounds chosen from cadmium, tin, tungsten, zinc, cerium or zirconium. These particles are of colloidal size generally of between 5 and 100 nm. The ratio of the mass of these particles with respect to the mass of titanium dioxide particles is generally between 0.01 and 20%.

p0041These additive particles can be composed of metal oxides or sulfides, such as Ce0₂, Sn0₂, W0₃, ZnO, Zr0₂ or CdSe_xS_there with x and y between 0 and 1, and x + y = 1.

p0042The 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 various parameters. It may depend on the intended application of the substrate, or alternatively the size of the titanium dioxide particles in the coating. The coating can also be chosen more or less smooth surface: a certain roughness can indeed be advantageous if it can develop a greater active photocatalytic surface. However, too pronounced, it can be penalizing by promoting incrustation of dirt. In case the coating is based on titanium dioxide particles incorporated in a binder, one can choose the method of deposition and the thickness of coating such that the particles or crystallites which they are made "emerge" in surface of the binder.

p0043The substrate of the invention may be varied in nature: any type of architectural material can be used (metals, concrete, ...), and substrates based glass, ceramic or glass-ceramic. Between the substrate and the coating according to the invention, one can deposit one or more thin layers to different or complementary functions to that of based on titanium dioxide coating. This may be, in particular, layers with an anti-static function, thermal, optical, or barrier layers to the migration of certain elements originating from the substrate, for example forming a barrier to alkali metals and very particularly to sodium ions when the substrate is glass. One can envisage a stack of layers "anti-glare" alternating thin layers with high and low indices, the coating of the invention constituting the final layer of the stack. In this case, it is preferable that the coating be relatively faiblel O refractive index, which is the case when it is constituted of an inorganic matrix of silicon oxide embedded therein titanium dioxide particles , or a mixed oxide of titanium and silicon.

p0044The layer with an anti-static and / or heat (heating by providing it with current leads, low-emissive, anti-solar, ...) can be chosen in particular to based on a metal-type conductive material, such as silver, or doped metal oxide type, such as indium oxide doped with tin ITO, tin oxide doped with fluorine type halogen Sn0₂: F or zinc oxide doped with indium ZnO: In, with fluorine ZnO: F, with aluminum ZnO: Al or with tin ZnO: Sn. Such a layer can be obtained by powder pyrolysis from dibutyltin difluoride DBTF tin, or by pyrolysis in the liquid or vapor phase, as described in patent application EP-A-648 196. In the vapor phase, there may in particular use a mixture of monobutyltin chloride and of a fluorinated precursor optionally in combination with an oxidizing "soft" type H₂O. The layer with anti-static function preferably has a sheet resistance value of 20 to 1000 ohms / square. We can provide the providing of current leads to polarize (supply voltages for example between 5 and 100 V). This controlled polarization helps fight against the deposit of the order of size of dust millimeter capable of being deposited on the coating, in particular dry dust which adheres by electrostatic effect: by suddenly reversing the polarization layer, "eject" the dust.

p0045The thin film optical function can be chosen to reduce the light reflection and / or make it more neutral color in reflection of the substrate. It has in this case, preferably, a refractive index intermediate between that of the coating and that of the substrate and an appropriate optical thickness and can be made of an oxide or a mixture of oxides of the type AI₂O₃, SnO₂ln₂0₃Or oxycarbide or silicon oxynitride.

p0046To obtain maximum attenuation of the color in reflection, it is preferable for this thin layer has a refractive index close to the square root of the squares of the refractive indices of the two materials which frame it, that is, say the substrate and coating. Meanwhile, it is advantageous to choose its optical thickness (ie the product of its geometric thickness and of its refractive index) close to λ / 4, λ being approximately the average wavelength in the visible, in particular from about 500 to 550 nm. Preferably, the titanium dioxide based coating constitutes the final layer of a stack of antireflection layers.

p0047The thin layer to alkali-barrier function can be chosen based on silicon oxide, nitride, oxynitride or oxycarbide, aluminum oxide containing fluorine AI₂0₃: F, or aluminum nitride. It has proven useful when the substrate is glass, because the migration of sodium ions into the titanium dioxide based coating may, under certain conditions, detrimentally affect the photocatalytic properties. All these optional thin layers can, as is known, be deposited by vacuum techniques of the sputtering type or by other techniques of the thermal decomposition type, such as pyrolysis into solid, liquid or gaseous. Each of the abovementioned layers can combine several functions, but can also overlay. Such a layer can be obtained by CVD ( "Chemical Vapour Deposition") from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in patent application EP-A-518 755.

p0048So quite surprisingly, the substrate according to the present invention in fact not one property but two, as soon as it is exposed to appropriate radiation such as visible light and / or ultraviolet: the presence of titanium dioxide photocatalytic, it promotes the gradual disappearance of dirty marks of organic origin, causing their degradation by a radical oxidation process.

p0049The substrate according to the invention may also have an outer surface with hydrophilic and / or oleophilic pronounced, especially if the binder is mineral, which brings two significant advantages. First, the hydrophilic nature makes possible complete wetting of the coating by water: instead of a deposition of droplets in the form of condensation which hampers visibility, there is in fact a thin continuous film of water to all made transparent which is formed on the substrate surface. This anti-fogging effect can be controlled by measuring a contact angle with water less than 5 ° after exposure to light.

p0050Along with the hydrophilic nature, the substrate of the invention may also exhibit oleophilicity allowing the wetting of organic dirt, which like water, then tend to be deposited on the substrate as a continuous film less visible than of "tasks" well located. There is thus obtained an effect "organic antifouling" which operates in two stages: as soon as it is deposited on the substrate, dirt is already not very visible because it spreads; and then it gradually disappears by radical degradation initiated by photocatalysis.

p0051The invention particularly relates glazing "antifouling" and / or "anti-fog", whether monolithic, multiple double-glazing or laminated type, flat or curved, incorporating the previously described substrates.

p0052These glazings have applications in the building, for example for the preparation of double glazing (it is possible to have the outer covering and / or inner side, ie on face 1 and / or on face 4). This is especially interesting for glazing very accessible to cleaning and / or which need to be cleaned very frequently, such as roofing glazing, airport glazing, ... It may also be of glass for vehicles where maintaining visibility refinements essential safety. This coating can then be deposited on the windshield, side or rear windows of cars, especially on the face of the windows turned towards the inside of the cabin. This coating can then prevent fogging and / or remove traces of dirt on the type fingerprints, nicotine or organic material of the volatile plasticizer-type released by the plastic lining the interior of the cabin, especially that of table edge (release sometimes known under the term "fogging").

p0053Many other applications are possible, especially for aquarium glass, window, greenhouses, interior furniture, urban furniture or mirrors, television screens, variable absorption glazing electrically controlled. Another interesting application of the coating according to the invention is to associate it with a variable absorption glazing electrically controllable electrochromic glazing type, liquid crystal glazing, optionally with dichroic dye, glazing system of suspended particles, viologen glazing, ... as all these glazing types are generally composed of a plurality of transparent substrates between which are arranged the "active" components, it is then possible advantageously to arrange the coating on the outer face of at least one of these substrates.

p0054Particularly in the case of an electrochromic glazing, when the latter is in the colored state, its absorption results in a degree of surface heating which, in fact, is capable of accelerating the photocatalytic decomposition of the carbonaceous substances which are deposited on the coating based on titanium dioxide. For details on the structure of an electrochromic glazing, reference will advantageously be made to Patent Application EP-A-575 207 describes an electrochromic laminated double glazing, titanium dioxide based coating may, preferably, be disposed 1 opposite.

p0055The invention also relates to various methods of preparing the above-described substrates.

p0056In a first embodiment, the substrate of the method of obtaining consists in depositing the coating by liquid phase pyrolysis, from a dispersion comprising at least one organometallic compound and titanium dioxide particles, said particles having the characteristics of particles incorporated in the final coating described above.

p0057The technique of deposition by pyrolysis is interesting because it allows the continuous deposition of the coating directly on the ribbon of float glass, when a glass substrate. In a second embodiment, the substrate of the method of obtaining consists in depositing the coating by a technique of the sol-gel, with a deposit method tempered 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 described above.

p0058The principle of the so-called sol-gel technique using a method of deposition by "hardened" spring of Figure 2: it is immersing the substrate (1) in the liquid dispersion (4) containing the (s) component (s) suitable (s) of the coating (3), then extracting the substrate (1) at a controlled rate using a motor means (5). The choice of the extraction rate is used to adjust the thickness of solution remaining at ia area of ​​both faces of the substrate and, in fact, the thickness of the coating deposited after heat treatment thereof. This treatment aims both to evaporate the solvent, decomposing the compound (s) organometallic (s) oxide (s) and decomposing the mechanical strength of the coating.

p0059The cell coating technique spring of Figure 3. This is to form 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 composed of the face of the substrate (1) to be treated. the dispersion is filled cavity comprising the compound (s) (s) organometallic (s) and the particles, and removing the solution 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 surface of the substrate (1) by progressively withdrawing the solution. The cavity (5) is subsequently maintained at least the time required for drying and hardening by heat treatment the film on the substrate. The advantage of this technique compared to "dip-coating" is such that we can process one of the two faces of the substrate (1), and not systematically both, unless you use a system masking.

p0060The technique of "spray coating" is detailed in Figure 4. It consists in spraying the dispersion (4) comprising the compound (s) (s) organometallic (s) and particles in the form of a cloud against the substrate (1 ) static.

p0061The laminar-coating technique is illustrated in Figure 5. It consists in passing the substrate (1), held by vacuum suction against a support (11) in stainless steel and Teflon, over a tank (12) containing the dispersion comprising (s) compound (s) organometallic (s) and the particles, which solution is partially immersed a cylinder (14) split. then moves the entire tank (12) and the cylinder (14) over the entire length of the substrate (1), the mask (13) preventing excessively rapid evaporation of the solvent of the solution (4). For more details on this technique, one can refer to the teaching of patent application WO 94/01598. According to this second mode, the compound (s) (s) organometallic (s) is decomposed thermally after coating the substrate with the solution on one or both of these faces. The two modes described above employ basic compound in a dispersion (s) organometallic (s) and titanium dioxide particles already formed and crystallized.

p0062The organometallic compounds are compounds with the metal atom M may be selected from titanium, silicon, tin, zirconium, aluminum ...

p0063It may be organometallic compounds of the general formula M (OR)₄ wherein M represents the metal selected, for example, titanium, silicon, tin, zirconium or aluminum, and R is an alkyl, cycloalkyl, aryl, alkylaryl or arylalkyl, alkenyl or alkynyl, radical acetylacetonate or a derivative thereof (methylacetoacetate, ethylacetoacetate, titanium acetylacetonate ...), an amino radical or one of its derivatives (titanium triethanolamine, titanium diethanolamine, ...), glycolate (tetra-octylene glycolate titanium), ...

p0064Preferred compounds of titanate or silicate types.

p0065Tetraisopropoxytitanium organometallic compound particularly suitable as organometallic compound. Organometallic compounds of titanium are preferred titanium chelate and / or titanium alkoxide, they can be of the type described in patent applications FR-A-2310977 and EP-A-465 309. Thus, organometallic titanium compounds can be selected from the compounds of formula R_notTi (OR ')_p with: - p between 1 and 4,

p0066- N = 4 - p,

p0067- R alkyl radical C₁ -C ₁₈,

p0068- R "alkyl radical C-_! - C₄ methyl guy, ethyl or isobutyl.

p0069Preferred organometallic compounds of silicon may be selected from the compounds of formula R_notSi (OR ')_p with:

p0070- P between 1 and 4, - n = 4 - p,

p0071- R radical alkyl Ci to C ₁₈,

p0072- R 'alkyl radical C_λ - C₄ methyl guy, ethyl or isobutyl. The preferred compounds are tetramethyl orthosilicate (TMOS), ie, tetraethylorthosilicate (TEOS) and (CH₃)₂Si (OC₂H₅)₂.

p0073It is of course possible to use mixtures of these compounds.

p0074The particles exhibit, themselves, the characteristics mentioned above in size, degree of crystallinity and optionally doping by metal compounds. The dispersion generally comprises 5 to 90% by weight of organometallic compounds expressed as metal oxides (MO_x) Relative to the weight of TiO₂ contributed by the particles and of organometallic compounds, expressed as oxides metal (MO_x), Preferably 15 to 80%, even more preferably from 20 to 75%.

p0075After deposition and heat treatment, the coating can contain, both of titanium dioxide originating from the decomposition of the organometallic compounds, if they are based on titanium, and the particles of the dispersion of titanium dioxide, the first playing somehow, the role of inorganic binder to the second.

p0076The particles are highly reactive on the photocatalytic plane and can also promote the crystallization of the titanium dioxide formed by thermal decomposition from organometallic compounds based on titanium, presumably acting as crystallization seeds. In the final coating and were titanium dioxide of two different origins.

p0077It is preferable to use titanium dioxide particles monodisperse in order to obtain transparent coatings. Monodisperse is understood to mean particles exhibiting a dispersion index of at most 0.5, preferably at most 0.3, the dispersion index being given by the following formula:

p0078084-016

p00792050

p0080in which :

p0081- 0_Q4 is the particle diameter for which 84% of particles have a diameter less than 0 ^ - 016 ^{is the} particle diameter for which 16% of particles have a diameter less than 0 ^,

p0082- 0_5O is the mean particle diameter.

p0083It can be advantageous, moreover, to deposit the coating, whatever the deposition technique envisaged, not in a single step but via at least two successive stages, which appears to promote the crystallization of the titanium dioxide throughout the coating thickness where selected relatively thick.

p0084Similarly, it may be advantageous to subject the coating, after depositing it, at least one heat treatment of the annealing type. This heat treatment of the annealing type is especially essential if the coating was deposited by a technique of the sol-gel or laminar coating type, according to the second mode described above, to decompose the compound (s) (s) organometallic (s) dioxide, once the coating of the substrate performed. By cons, this heat treatment of the annealing type is not essential in the case where coating is deposited by a pyrolysis technique, according to the first embodiment described above, where the organometallic compound decomposes as soon as it is in contact with the substrate. However, for the first as the second mode, a post-deposition heat treatment, once formed titanium dioxide, improves the rate of crystallization and the adhesion. The chosen treatment temperature can also help in controlling the rate of crystallization and the crystalline nature.

p0085This annealing is generally to introducing the substrate in an oven at a temperature of about 500 to 550 ° C for a period of time ranging from 1 minute to 3 hours.

p0086For both modes, an alkali-barrier layer may be useful between the substrate and the coating, particularly if the coating must undergo a relatively long heat treatment and / or high temperature, because the migration of alkali metals from the glass under the effect of heat in the coating, in excessive amounts, can be detrimental to the photocatalytic activity. This is also the case if the coating is selected to be relatively thin, particularly when a thickness of less than 20 nm.

p0087Any type of titanium dioxide dispersion in which the particles exhibit the characteristics desired for the substrate, including size and crystallinity, is used, the liquid phase is aqueous or organic. However, an organic phase is preferred.

p0088Finally, rinvention relates to an organic dispersion comprising:

p0089- Particle size of titanium dioxide between 5 and 70 nm, monodisperse and predominantly in the anatase crystalline form,

p0090- And at least one organic solvent, preferably exhibiting a latent heat of vaporization less than that of water.

p0091The notion of monodispersity is the same as defined above.

p0092The titanium dioxide particles exhibit the same characteristics of size and crystallinity than the substrate coating of particles of the invention described above.

p0093Thus, the particles of the dispersion of titanium dioxide exhibit a size of between 5 and 80 nm in general, preferably between 5 and 70 nm, even more preferably between 10 and 50 nm. The size is measured by TEM. In addition, the nature of the crystalline phase of these titanium dioxide particles is preferably predominantly the anatase crystalline form. "Predominantly" means that the level of anatase particles of the dispersion of titanium dioxide by the invention is greater than 50 mass%. Preferably, the particles of the dispersions used exhibit a level of anatase of greater than 80%.

p0094For the liquid phase, preferably, the organic solvent exhibits a latent heat of vaporization less than that of water. Means latent heat of vaporization of 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 temperature is 540 cal / g (Handbook of Chemistry and Physics, 75th ed.). Such an organic solvent may be chosen from alcohols (ethanol, isopropanol, ...) and in particular glycols (ethylene glycol), esters such as ethyl acetate, ...

p0095The rate of the dispersion of titanium dioxide according to the invention may be between 1 g / l and 300 g / l.

p0096These organic dispersions may include depending on the process used to prepare a water content of at most 10% by weight, preferably at most 5% and even more preferably at most 1%.

p0097The monodisperse particles of the dispersion are, in general, derived from a process called solution or wet (thermolysis, thermal hydrolysis or precipitation of a se! Titanium) versus oxidation processes or high pyrolysis temperature of a titanium salt. This may be for example titanium dioxide particles obtained by the method described in EP-A-0335773.

p0098It may in particular be the preparation process which consists in hydrolysing at least one titanium compound A in the presence of at least one compound B chosen from: (i) the acids which exhibit:

p0099- Either a carboxyl group and at least two hydroxyl and / or amino,

p0100- Either at least two carboxyl groups and at least one hydroxyl and / or amine groups, (ii) organic phosphoric acids of following formulas:

HO O R2 O OH

p0102\ II I II /

p0103P - (C)_not _ P / I \

HO OH R1 OH HO O O OH

p0105\ II I II /

p0106_ P C - P

p0107/ I \ HO OH R3

p0108O OH He / O HO CH₂ _ _ P OH \ ll /

p0109P - CH₂ - [N - (CH₂)_m]_p- N / I \

p0110HO CH₂ CH₂ - P - OH

p0111I II \ O = P - O OH OH

I OH

p0113in which n and m are integers between 1 and 6, p is an integer between 0 and 5, R1, R2, R3, identical or different, representing a hydroxyl, amino, aralkyl, aryl or alkyl or hydrogen,

p0114(Iii) the compounds capable of releasing acidic sulphate ions,

p0115(Iv) salts of the acids described above, and in the presence of seeds of anatase titanium dioxide having a size of at most 5 nm and in a weight ratio expressed as Ti0₂ present in the seeds / titanium present before introduction of the seeds in the hydrolysis medium, expressed as TiO₂ between 0.01% and 3%.

p0116This particulate preparation process thus comprises several stages and, firstly, a starting solution preparation step comprising a titanium compound A, a compound B as defined above and titanium dioxide seeds.

p0117This starting solution, intended to be hydrolysed, is preferably completely aqueous; can optionally be added another solvent, for example an alcohol, provided that the titanium compound A and the compound B used are then substantially soluble in this mixture.

p0118As regards the titanium compound A, use is generally made a compound chosen from halides, oxyhalides, alkoxides of titanium, sulphates and more particularly synthetic sulphates.

p0119Synthetic sulphates is understood to mean titanyl sulphate solutions produced by ion exchange from titanium chloride solutions or by very pure reaction of sulfuric acid with a titanium alkoxide.

p0120Preferably, one operates with compounds of the titanium halide or titanium oxyhalide. Titanium halides or oxyhalides which are more particularly used in the present invention are the fluorides, chlorides, bromides and iodides (respectively oxyfluorides, oxychlorides, oxybromides and oxyiodides).

p0121According to a particularly preferred embodiment, the titanium compound is titanium oxychloride TiOCI₂.

p0122The amount of titanium compound A present in the solution to be hydrolysed is not critical.

p0123The initial solution additionally contains at least one compound B as defined above. As non-limiting examples of compounds B coming within the scope of the present invention, there may be mentioned:

p0124- Hydroxypolycarboxylic acids and more particularly hydroxydi- or hydroxytricarboxylic acids such as citric acid, maleic acid and tartaric acid.

p0125- Acids (polyhydroxy) moπocarboxyliques such as glucoheptonic acid and gluconic acid,

p0126- Poly (hydroxycarboxylic) acids, such as tartaric acid,

p0127- Dicarboxylic monobasic acids and their corresponding amides, such as aspartic acid, asparagine and glutamic acid,

p0128- Monocarboxylic aminoacids, hydroxylated or not, as for example, lysine, serine and threonine,

p0129- The aminotriphosphonate methylene, the methylene ethylenediaminotetraphosphonate, methylene triethylenetetraaminohexaphosphonate, methylene tétraéthylènepentaaminoheptaphosphonate, methylene pentaéthylènehexaaminooctaphosphonate, - methylene diphosphonate; of 1, 1 'ethylene; 1, 2-ethylene; of 1, 1 propylene; 1, 3 propylene; of 1, 6 hexamethylene diisocyanate; 2,4 dihydroxypentaméthylène - 2,4-diphosphonate; dihydroxyhexaméthylène 2,5 - 2,5 diphosphonate; 2,3 dihydroxybutylène - 2,3-diphosphonate; hydroxybenzyl 1 - 1, 1-diphosphonate; aminoethylene 1 1 -1^* diphosphonate; the hydroxymethylene diphosphonate; 1 hydroxyethylene 1, 1-diphosphonate; 1 hydroxypropylene-1,1'-diphosphonate; 1-hydroxybutylene 1 -1 "diphosphonate; 1 hydroxyhexamethylene - 1, 1-diphosphonate.

p0130As already indicated, it is also possible to use, as compound B, all the salts of the abovementioned acids. In particular, these salts are either alkali metal salts, more particularly sodium salts, or ammonium salts.

p0131These compounds may also be chosen from sulfuric acid and ammonium sulphate, potassium, ... Preferably, the B compounds as defined above are hydrocarbon compounds of aliphatic type. In this case, the length of the main hydrocarbon chain preferably does not exceed 15 carbon atoms, more preferably 10 carbon atoms. The amount of compound B is not critical. In general, the molar concentration of compound B with respect to that of the titanium compound is between 0.2 and 10% and preferably between 1 and 5%.

p0132Finally, the starting solution comprises titanium dioxide seeds used in a specific way. Thus, the titanium dioxide seeds used in the present invention must first of all exhibit a size of less than 8 nm, measured by X-ray diffraction is preferably used titanium dioxide seeds exhibiting a size of between 3 and 5 nm.

p0133Then, the weight of titanium dioxide present in the seeds to the titanium present in the hydrolysis medium before introduction of the seeds - that is to say contributed by the titanium compound A - and expressed as Ti0₂ is between 0.01 and 3%. This report can be preferably between 0.05 and 1, 5%. The meeting of these two conditions on the seeds (size and weight ratio) associated with the process as described above allows control prev isément the final size of the titanium dioxide particles by combining a germ rate particle size. One can thus obtain particles ranging in size from 5 to 100 nm.

p0134Are used titanium dioxide seeds in the anatase form so as to induce precipitation of the titanium dioxide in the anatase form. Generally, due to their small size, these seeds instead exist in the form of poorly crystallized anatase. The seeds are generally provided in the form of an aqueous suspension composed of titanium dioxide. They can generally be obtained in known manner by a process of neutralization of a titanium salt by a base.

p0135The next step is to carry out the hydrolysis of this starting solution by any means known in the art and generally by heating. In the latter case, the hydrolysis can preferably be carried out at a temperature greater than or equal to 70 ° C. It can also work in a first time to a temperature below the boiling temperature of the medium and maintain level hydrolysis medium at the boiling temperature.

p0136Upon completion of hydrolysis, 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 titanium dioxide dispersion. This liquid medium can be acidic or basic. It is preferably an acidic solution, for example an aqueous solution of nitric acid or hydrochloric acid. Then obtain an organic dispersion of these titanium dioxide particles, any method known for performing the titanium dioxide particle suspension in an organic phase from an aqueous dispersion of titanium dioxide can be used. The dispersion can thus be obtained by contacting an aqueous dispersion of titanium dioxide particles with the desired organic solvent and then heating to remove the water by distillation. Such a process can be implemented only in the case where the organic solvent chosen exhibits a boiling temperature greater than that of water and is soluble in water. This is the case for example of ethylene glycol.

p0137The dispersion can also be obtained by grafting a hydrophobic chain to the surface of titanium dioxide particles in suspension in water and then mixed with an immiscible organic solvent with water so as to migrate dioxide particles titanium in the organic phase. It was observed that the titanium dioxide particles resulting from a process called solution or wet, and in particular from the process described above with hydrolysis at a temperature of about 100 ° C, exhibit, by their porosity, a lower refractive index than the titanium dioxide particles resulting from other processes. As indicated above, this property is of great interest when these particles are used for preparing a coating on a substrate, particularly a glass-based substrate, because the coating obtained also exhibits a low refractive index as stated above.

p0138Advantageously, the liquid phase of the dispersion according to the invention comprises at least one organometallic compound based on a metal M selected from titanium, silicon, tin, zirconium or aluminum. Preferred compounds correspond to the organometallic compounds described above.

p0139When 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 titanium dioxide particles. Can, depending on the nature of the organometallic compound employed, add also when this mixture of additives such as co-solvents, surfactants or stabilizers. The mixture may also be improved by stirring the dispersion by ultrasonic. The solution of organometallic compound added to the organic dispersions based on titanium dioxide particles is generally a solution in organic phase, said organic phase can be chosen from: ethanol, isopropanol, ethyl acetate. .. It is also possible to add the organometallic compounds to the titanium dioxide dispersions in the pure form.

p0140These organometallic compounds can advantageously be stabilized by products such as diethanolamine (DEA), acetylacetone derivatives, such as ethyl acetoacetate, glycols, ...

p0141The dispersion generally comprises 5 to 90% by weight of organometallic compounds expressed as metal oxides (MO_x) Based on the weight of Ti0₂ contributed by the particles and of organometallic compounds expressed as metal oxides (MO_x), Preferably 15 to 80% or from 20 to 75%. As indicated above, in order to exacerbate the photocatalytic effect of the coating based on titanium dioxide, it is possible to add titanium dioxide, as indicated above, catalysts, additives to better absorb UV, or to shift the absorption band towards the visible, as well as metals to dope the titanium dioxide in order among other things to increase the number of electron carriers.

p0142According to a first variant, at least some of the particles dispersions of titanium dioxide include 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 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 the metal ions during the preparation of titanium dioxide particles. Thus, if the titanium dioxide particles are obtained by thermal hydrolysis of a titanium compound as it is described in application EP-A-0335773, it is possible to add in the middle of the metal ions thermohydrolysis so as to introduce the ions into the crystal lattice of titanium dioxide.

p0143In a second variant, at least a portion of the dispersion of titanium dioxide particles are coated at least partly with a layer of metal salts or oxides, the metal being selected 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 with respect to the mass of titanium dioxide can be between 0.01 and 20%. Such dispersion may be obtained by precipitating metal salts on the titanium dioxide particles before placing in organic medium. Thus, when titanium dioxide particles are still in aqueous medium following a wet preparation process is introduced into the aqueous phase and the metal salts are precipitated so as to cover at least partly the titanium dioxide particles. In a third variant, at least a portion of the dispersion of titanium dioxide particles are coated at least in part of a layer of metal selected from platinum, silver or rhodium. The ratio of the mass of these metals with respect 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 organic medium. For example, when titanium dioxide particles are still in aqueous medium following a wet preparation process is introduced into the aqueous phase and the metal salts are reduced so as to cover at least partly of the titanium dioxide particles.

p0144In a fourth variant, the dispersions comprise, in addition to titanium dioxide particles, additives in the form of particles based on metal compounds chosen from cerium, cadmium, tin, tungsten, zinc or zirconium. These particles are colloidal in size, generally between 5 and 100 nm. Their rate in the dispersion can be between 0.1 and 20% by weight. As indicated above, the metal compounds may be oxides or metal sulfides, such as Ce0₂, Sn0₂, W0₃, ZnO, Zr0₂ or CdSe_xS_there with x and y 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 after a wet then transfer all particles from the aqueous phase into organic phase.

p0145The dispersions according to the invention can have the characteristics of the four variants separately or simultaneously.

p0146Finally, the invention relates to the use of an organic dispersion as described above in a substrate preparation method of the invention.

p0147Other details and advantageous features of the invention emerge from the following description of examples of non-limiting embodiments.

p0148As shown extremely schematically in Figure 1, all the following examples relate to the deposition of a coating (3) called "antifouling" essentially based on titanium dioxide on a substrate (1). EXAMPLES

p0149Example 1 Preparation of a dispersion of titanium orαaniαue dioxvde particles

p0150An aqueous dispersion of titanium dioxide particles according to patent application teaching EP-A-0335773, in the presence of germs.

p0151Hydrolysis

p0152are successively added to 394.7 g of a titanium oxychloride solution containing 1, 9 mol / kg:

p0153- 42.02 g of 36% hydrochloric acid - 4.73 g citric acid,

p0154- 547.1 g of purified water,

p0155- 1 1 36 g (0.2% by weight relative to the Ti0₂) Of anatase seeds exhibiting a size of between 5 and 6 nm.

p0156The mixture is heated to boiling and held there for 3 hours.

p0157Retrieving particles and Redispersing

p0158The solution is then filtered and the obtained particles are washed with water until complete elimination of chloride. They are subsequently redispersed at pH 1, 5 (controlled by the addition of HN0₃) With a solids content of 20% by weight.

p0159An aqueous dispersion comprising particles of diameter 45 nm, measured by TEM. The X ray diffraction analysis shows that the particles are based on titanium dioxide solely in the anatase form at 80% by weight. The obtained particles are porous.

p0160Getting dipersion in organic medium

p0161Mixing 100 parts by mass of this dispersion to 100 parts of ethylene glycol. The mixture is then heated to 80 ° C to remove the water formed by distillation under reduced pressure (100 mbar) and then at 120 ° C to remove the bound water. A dispersion of titanium dioxide particles in ethylene glycol. The solids content is 20 wt%. The particle size measured in ethylene glycol by TEM, is 45 nm. The residual water content is 0.7% by weight relative to titanium dioxide. Example 2 Preparation of an organic dispersion of niobium doped titanium particles dioxvde

p0162Example 1 is repeated except that we add NBCI₅ in the hydrolysis medium in an amount such that the molar ratio of Nb / Ti0₂ is 0.1%.

p0163Examples 3 to 7: deposit of the dispersions of Examples 1 and 2 by pvrolvse

p0164The substrate (1) is clear silico-sodo-calcic 6 mm thick and 50 cm long and wide.

p0165Between the coating (3) and the substrate (1), is an optional thin layer (2).

p0166Examples 3 to 7 relate to a coating (3) deposited by a pyrolysis technique in liquid phase. This can be done continuously, using a suitable distribution nozzle arranged transversely and above the float glass ribbon, to leave the enclosure of the float bath itself. Here, we conducted batchwise: the substrate (1), already cut to the dimensions shown, is first heated in an oven at a temperature of 400 to 650 ° C, before progressing a constant speed past a movable nozzle projecting an appropriate solution.

p0167- Example 3

p0168In this example, there is no optional layer (2). The coating (3) is deposited using an organic dispersion A comprising: - a formulation comprising two organometallic titanium compounds and two solvents according to the following proportions:

p0169. 20% by weight of di-iso-propoxy-di acetylacetonate titanium. 20% by weight of titanium tetraoctylene glycolate. 40% by weight of ethyl acetate,. 20% by weight of isopropanol,

p0170- The organic dispersion of titanium dioxide particles according to Example 1 and diluted with the following characteristics:

p0171. particle mass content: 10%. particle size: 45 nm, measured by TEM. crystallite size: 5 nm,

p0172. crystalline phase: anatase greater than 80%. liquid phase: ethylene glycol. The formulation and the organic dispersion are in relative proportions such that the titanium dioxide particle content in the dispersion A is adjusted so as to obtain a content of 25% by weight of titanium dioxide from the particles in the coating once deposited (mass of Ti0₂ from the particles / total mass of the oxides in the coating assuming that the decomposition of the organometallic compounds of the dispersion A to oxides is total).

p0173As soon as the substrate (1) has reached the desired temperature in the furnace is about 500 ° C, the latter moves past the nozzle spraying at room temperature the mixture indicated with the aid of compressed air. then obtain a titanium dioxide layer of about 90 nm thick, the latter being controlled by the substrate tape speed (1) to the nozzle and / or the temperature of said substrate. The layer is partially crystallized in the anatase form.

p0174This coating contains both titanium dioxide originating from the decomposition of the organometallic and particles of the dispersion of titanium dioxide, the first acting, as it were, the role of the inorganic binder relative to the second. The layer has excellent mechanical strength.

p0175The refractive index is 2.3.

p0176- Example 4

p0177Example 3 is repeated, except that the substrate (1) comprises a thin layer (2) fluorine-doped tin oxide Sn0₂F in order to form a static layer and / or low-emissivity and / or attenuating the color in particular in reflection.

p0178This layer is obtained by powder pyrolysis from dibutyltin difluoride DBTF. It may also obtain a known way by chemical liquid or vapor phase, as described for example in the EP-patent application 0648 196. vapor that may especially use a mixture of monobutyltin trichloride tin and a fluorinated precursor optionally associated with oxidative "soft" H-type₂0. This thin layer has a thickness of 73 nm, an index of 1, 9 and a sheet resistance of 50 ohms / square.

p0179This substrate treated in the same manner as in Example 3 and mounted in double glazing so that the coating (3) is on face 1 (with another non-coated but of the same nature and dimensions substrate as the substrate (1)) via an air gap of 12 mm, has a color purity value in reflection (in the golden) of 3.6%, and 1, 1% transmission.

p0180The substrate of Example 3, mounted in the same way, exhibits a color purity value in reflection (in the golden) 26% and 6.8% in transmission. The underlay Sn0₂F has a favorable influence on colorimetry of the substrate, making it significantly more "neutral" its color, both in transmission and in reflection, coloring caused by the presence of the coating (3) of titanium dioxide having an index of relatively high refractive. In addition, this sublayer decreases the diffusion of alkali metals into the photocatalytic layer of Ti0₂. The photocatalytic activity is improved. Despite the presence of a high amount of particles in the coating, the blur is much less than 1%. blur is defined by the Hours of Operation of the diffracted light transmission to the total light transmission at 560 nm substrate.

p0181- Example 5

p0182Example 3 is repeated, except that the substrate (1) comprises a thin layer (2) oxycarbide based silicon to constitute a barrier to the diffusion of alkali metals and / or a layer which attenuates light reflection. This layer is obtained by CVD from a mixture of SiH₄ and ethylene diluted in nitrogen, as described in the patent application EP-A-0 518 755. This layer is particularly effective to avoid the tendency of alkali metals (Na⁺, K *) and alkaline earth (Ca²⁺) From the substrate (1) towards the coating (3). This thin layer has a thickness of 50 nm, an index of 1.75.

p0183Having as Sn0₂: F, a refractive index intermediate between that of the base substrate (1) (1, 52) and the coating (3) (2.3), it also helps to mitigate the intensity of the coloration of the substrate, both transmitted and reflected, and generally reduce the value of the light reflection R_L said substrate. In addition, the undercoat silicon oxycarbide base is an effective barrier to the diffusion of alkali, and thus the photocatalytic activity of the coating is significantly improved.

p0184- Example 6 Example 3 is repeated, except that the coating (3) is deposited using a dispersion B comprising:

p0185- A formulation based on silicon tetraethoxide Si (OEt)₄ diluted in ethanol in an amount 0.1 mole per liter of ethanol,

p0186- The organic dispersion of titanium dioxide particles of Example 1. The formulation and the organic dispersion are in relative proportions such that the titanium dioxide particle content in the dispersion B is adjusted so as to obtain a content of 80 % by weight of titanium dioxide in the coating, once deposited (mass of Ti0₂ from the particles / mass of Ti0₂ particle + mass of Si0₂ obtained by decomposition of Si (OEt)₄ assuming that the decomposition is complete).

p0187As soon as the substrate (1) has reached the desired temperature in the furnace is about 200 ° C, it passes in front of the nozzle which projects the dispersion at room temperature B with the aid of compressed air.

p0188One then obtains a composite layer of particles of Ti0₂ from the dispersion, bonded together and to the substrate through the Si0₂ from the decomposition of the organometallic. The coating has a thickness of about 50 nm, it is crystallized to 65% in anatase form.

p0189The layer has high photocatalytic activity due to the high surface area developed by the particles of Ti0₂ (> 250 m²/ G). In addition, the binder Si0₂ acts as a barrier to alkali particularly efficient at the substrate interface / particle. Finally, the refractive index is much lower than a layer of Ti0₂ massive, thanks to the presence of Si0₂ and to its high porosity. This index is less than 1, 6. The value of the light reflection R_L the substrate is thus decreased.

p0190- Example 7 Example 6 is repeated, except that the dispersion B contains titanium dioxide particles doped niobium 0.1% according to Example 2.

p0191The layer exhibits an even higher photocatalytic activity.

p0192Example 8: depositing the dispersion of Example 1 by dip coating

p0193This example uses the so-called sol-gel technique using a method of deposition by "hardened" or "dip-coating", the principle of spring Figure 2: it is immersing the substrate (1) in the liquid solution ( 4) containing the dispersion and then in extracting the substrate (1) at a controlled rate using a motor means (5), the choice of the extraction rate making it possible to adjust the thickness of the dispersion remaining on the surface of both faces of the substrate and, in fact, the thickness of the coatings deposited, after heat treatment of the latter for both to evaporate the solvent and decompose the precursors of the metal oxides.

p0194The coating (3) is deposited using a dispersion A or B as defined in Examples 3, 6 or 7. Use is also an organic dispersion C comprising: - A titanium tetrabutoxide formulation based on Ti (0-Bu)₄ stabilized with di-ethanol amine OF A in a molar proportion 1: 1 and diluted in ethanol at a rate of 0.2 mol of tetrabutoxide per liter of ethanol,

p0195- A dispersion of titanium dioxide particles according to Example 1 having the following characteristics:

p0196. particle mass content: 10%. particle size of 45 nm, measured by TEM. crystallite size: 5 nm. crystalline phase: anatase greater than 80%. liquid phase: ethylene glycol.

p0197The formulation and the organic dispersion are in relative proportions such that the titanium dioxide particle content in the dispersion C is adjusted so as to obtain a content of 80% by weight of titanium dioxide from the particles in the coating once deposited (mass of Ti0₂ from the particles / total mass of the oxides in the coating assuming that the decomposition of the organometallic compounds in the dispersion C to oxides is total).

p0198After quenched substrates (1) containing thin layers (2) based on silicon oxycarbide in the dispersions A, B or C, the substrates (1) are heated for 3 hours at 550 ° C with a progressive increase in temperature.

p0199Is obtained in all three cases, on each side a coating (3) titanium dioxide well crystallized in the anatase form. anatase crystallization rates are comparable to examples utilisatn technqiue a deposition by pyrolysis, but the crystallite size is greater due to prolonged heat treatment. The result is a better photocatalytic activity.

p0200The coating has a refractive index of at most 1: 8.

p0201Example 9: deposition of the dispersion of Example 1 by "cell coating"

p0202This example uses the technique known as "cell coating" whose principle spring of Figure 3: this is to form 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 composed of the face of the substrate (1) to be treated. Then, filling the dispersion chamber (4) in a controlled manner so as to form a wetting meniscus by means of a pump (10) by peristaltic example, leaving a film of the dispersion (4) the face of the substrate (1) by progressively withdrawing the solution. The cavity is subsequently maintained at least the time required for drying. Curing the film on the substrate is provided by heat treatment as in the previous examples.

p0203The coating (3) is deposited using solutions A, B or C described in Examples 3, 6 and 8.

p0204After the tempered 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 made.

p0205Is obtained in the three cases, a coating (3) similar to the coatings of Example 8, but here only one face of each substrate is processed.

p0206Example 10: Control properties of substrates obtained

p0207Test 1 of wetting: It consists in depositing on the substrate to evaluate a layer of an organosilane and in irradiating it with UVA radiation so as to degrade by photocatalysis. The organosilane modifying the wetting properties, the water contact angle measurements of the substrate during the 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. The grafted organosilane is a trichlorosilane: octadecyltrichlorosilane (OTS). The grafting is carried out by dipping.

p0208The test device is composed of a turntable rotating around from 1 to 6 Low pressure UVA lamps. The specimens to be evaluated are placed in the carousel, the side to assess the UVA radiation side Depending on their position and the number of lighted lamps, each specimen receives a UVA irradiation varying from 0.5 W / m² 50 W / m².

p0209The time between each measurement of the contact angle varies between 20 min and 3 h, depending on the photocatalytic activity of the test specimen under consideration. The measurements are performed using a goniometer. Before irradiation, the lenses have an angle of about 100 °. It is considered that the layer is destroyed after irradiation when the angle is less than 20 °.

p0210Each specimen tested is characterized by the average velocity of the layer of disappearance, given in nanometers per hour, ie the thickness of the organosilane layer deposited divided by the irradiation time to reach a lower final level at 20 ° ( time for disappearance of the organosilane layer).

p0211Test 2 of isobutane It consists in controlling the degradation of isobutane gas brought into contact with a glass treated according to the invention.

p0212Are introduced into a reactor the glass to be tested and an amount of isobutane equal to 20% of the total reactor volume. The test apparatus consists of a rotary carousel of around 1 to 6 Light

p0213UVA low pressure having an emission maximum between 300 and 400 nm. The reactors containing glasses to be evaluated are placed in the carousel, the face of the glass to assess the UVA radiation side Depending on their position and the number of lights on each glass receives UVA irradiation up to 30 W / m². The irradiation lasts 8 to 22 hours.

p0214then assayed using a gas chromatograph advancing the photodecomposition of the isobutane by monitoring the amount of 0₂. this progress is translated using the constant disappearance rate of 0₂ mol / h / cm².

p0215Test 3 of palmitic acid

p0216It consists of depositing on the substrate to evaluate a palmitic acid layer and irradiating it with UVA radiation so as to degrade by photocatalysis.

p0217Is sprayed onto the glass to be tested a palmitic acid chloroform solution containing 8 g / l. The amount of palmitic acid deposited by 30 cm² glass is 1, 5 mg. Then, the lenses are introduced into a sealed reactor surrounded by six UV lamps exhibiting an emission maximum between 300 and 400 nm. The glasses testing irradiated Aunsi receive a power of 10 W / m². The irradiation lasts 40 hours.

p0218The lenses are then removed from the reactor. For assaying the palmitic acid remaining on the lenses, they are washed with a chloroformic acid solution; the solution obtained is then assayed by liquid chromatography in order to assay the remaining palmitic acid.

p0219thus is given the time to complete degradation of 1, 5 mg of palmitic acid, expressed in minutes.

p0220The degradation of palmitic acid can also be visually observed by the decrease of the blur of the glass induced by the palmitic acid layer.

p0221Test 4 of the anti-fogging;

p0222It consists in observing the consequences of the photocatalysis and the coating structure (hydroxyl group content, porosity, roughness) on the wetting. If the surface is photoreactive, the carbonaceous micropollutants which are deposited on the coating are continually destroyed and the surface thus anti-fogging is hydrophilic. One can also make a quantitative evaluation by suddenly reheating the initially coated substrate stored cold or simply by blowing on the substrate, watching if condensation appears and, if so, at what time and then measuring the time required to the disappearance of that fog

p0223Test 5 contact angles

p0224This is to evaluate the hydrophilicity and the oleophilicity at the surface of the coating (3), in comparison with those of the surface of a bare glass, by measuring contact angles of a drop of water and of a drop of DOP (dioctyl phthalate) at their surfaces. The measurement is performed after leaving ies substrates one week to the surrounding atmosphere under natural light in the dark and then having subjected to 20 min UVA radiation.

p0225Dhotocatalytioues results of tests.

p0226<img id="imgf000031_0001" he="78" wi="158" file="imgf000031_0001.tif" img-format="tif" img-content="table" orientation="portrait" inline="no" />

p0227Test results 4. for all the substrates of Examples 3 to 9, there appears no fogging.

p02285 test results. for all substrates of Examples 3-9, the water contact angle and the DOP is less than 5 ° after 20 min of exposure to UVA.