Method for thin layer deposition

[0001] The invention relates to the field of thin inorganic layers, in particular when applied to glass substrates. It relates in particular to a method for at least partial crystallization of said thin layers and certain products obtained by this method.

[0002] Numerous thin layers are applied to a substrate, in particular flat or slightly convex glass, in order to give the obtained materials special properties: optical properties, e.g. reflection or absorption, radiation in the given wavelength range, special electrical conductivity properties or properties related to easy cleaning or the possibility of self-cleaning material.

[0003] These thin layers are most often based on inorganic compounds: oxides, nitrides or metals. Their thickness is generally from a few nanometers to several hundred nanometers, hence they are referred to as "thin".

[0004] In particular, thin layers based on titanium oxide can be mentioned, which have the property of being self-cleaning, facilitating the degradation of organic compounds under the action of ultraviolet radiation and the removal of mineral impurities (dust) under the action of flowing water.

[0005] These layers have a special feature that some of their properties can be improved when they are in at least partially crystallized state. In general, efforts are underway to maximize the degree of crystallization of these layers (weight or volume ratio of crystallized material) and the size of crystallites (or the size of coherent diffraction ranges measured by X-ray diffraction methods), and even in some cases to support a particular crystallographic form.

[0006] In the case of titanium oxide, it is known that titanium oxide crystallized in the form of anatase is much more effective in the understanding of the degradation of organic compounds from the titanium oxide amorphous or crystallized in the form of rutile or cobalt.

[0007] The method commonly used on an industrial scale for applying thin layers, in particular to glass substrates, is a method of cathodic sputtering assisted by a magnetic field, called the "magnetron" method. In this method, the plasma is generated in a vacuum supplied near the target containing the chemical elements to be applied. Active types of plasma, by bombarding the shield, pull out the elements mentioned above, which settle on the substrate, forming the desired thin layer. This method is called the "reactive" method when the layer consists of a material that is the result of a chemical reaction between elements removed from the shield and the gas contained in the plasma. It is therefore known that titanium oxide layers are applied by means of a magnetron reactive method using a metallic titanium disk or a TiOx ceramic disk (where x <2) and oxygen-based plasmogenic gas. The big advantage of this method is the possibility of applying on the same line very complex systems of layers by moving the substrate successively under different discs, usually in one and the same device.

[0008] During the industrial use of the magnetron method, the substrate maintains the ambient temperature or its temperature increases moderately (below 80 ° C), especially when the substrate's speed is high (which is generally desirable for economic reasons). What may seem to be an advantage, however, is a disadvantage in the case of the above layers, since the implied low temperatures generally do not allow sufficient crystal growth. This is particularly the case for thin layers of very small thickness and / or layers made of materials whose melting point is very high. The layers obtained according to this method are therefore mostly or even completely amorphous or nanocrystalline (the average size of the crystallite is less than a few nanometers), and thermal treatment appears necessary to obtain the desired degree of crystallization or the desired size of the crystallites.

[0009] US 2003/003304 describes a glass substrate coated with a titanium oxide-based layer and an anti-reflection layer.

[0010] Possible heat treatment consists in heating the substrate either during application or after application at the output of the magnetron line. Usually, temperatures of at least 200 ° C or 300 ° C are necessary.

[0011] The overwhelming of the substrate on industrial magnetron lines (during application), however, proves to be difficult to implement, in particular because heat transfer in a vacuum, necessarily of a radiation nature, is difficult to control and entails high costs for a large-sized substrate, a few meters wide. For a thin glass substrate, this type of treatment often implies a high risk of breakage.

[0012] Heating the coated substrate after application, for example by placing the substrate in an oven or dryer, or by subjecting the substrate to infrared radiation from a conventional heating device such as infrared lamps, also has drawbacks because these different methods contribute to heating both the substrate and a thin layer. Heating the substrate to a temperature higher than 150 ° C may generate bruises in the case of a large substrate (several meters wide) because it is not possible to provide the same temperature over the entire width of the substrate. Heating the substrate also slows down the whole way because you have to wait for it to cool completely before cutting or storing it, which is usually done by stacking the layers of the substrate on you. Very controlled cooling is also necessary in order to avoid stress generation in the glass, and thus possible breakage. Because such very controlled cooling is very expensive, annealing is generally not sufficiently controlled to eliminate thermal stress in the glass, which generates more breakage on the line. Annealing also has the disadvantage that cutting glass becomes more difficult, with cracks showing a weaker tendency for linear propagation.

[0013] The heating of the substrate occurs when the glass is convex and / or toughened because the glass is heated to a temperature above its softening point (generally over 600 ° C and even 700 ° C for several minutes). Hardening or bending therefore allows the desired crystallization result of thin layers to be obtained. However, it would be costly to treat all glass panes in this manner merely to improve the crystallization of the layers. In addition, toughened glass can no longer be cut, and some thin film systems cannot withstand the high temperatures they have been subjected to when toughening glass.

[0014] In order to solve these problems, the applicant has developed a method of treating at least one thin layer based on titanium oxide, continuous and applied to a first surface of a substrate, characterized in that each point of said at least one thin layer is heated to a temperature of at least 300 ° C maintaining a temperature lower or equal to 150 ° C at each point of the surface of said substrate opposite to said first surface, to increase the crystallinity of said thin layer while maintaining its continuity without the melting step of said thin layer. [0015] Among the possible methods are in particular heating by infrared radiation, a plasma torch or flame.

[0016] The inventors have now shown that it is still possible to improve the crystallization properties of titanium oxide-based layers by improving this method.

[0017] Accordingly, the object of the invention is a method for obtaining a material comprising a substrate and at least one thin layer based on titanium oxide at least partially crystallized applied to the first surface of said substrate, said method comprising the following steps:

• the said at least one thin layer based on titanium oxide is applied, • the said at least one thin layer based on titanium oxide is treated by crystallization bringing in energy, which can raise the temperature of each point of said at least one thin layer based on titanium oxide to a temperature of at least 300 ° C while maintaining a temperature lower or equal to 150 ° C in particular 50 ° C at any point of the surface of said substrate opposite said first surface. In the process of the invention, the crystallization treatment is preceded by the step of applying, above and / or below said thin layer based on titanium oxide, an energy supply layer that can absorb energy provided during said treatment by crystallization more effectively than said at least one layer based on titanium oxide and / or generate additional energy during said treatment by crystallization, and transfer at least a portion of said energy of said at least one thin layer based on titanium oxide during said crystallization treatment.

[0018] The improvement brought to the method previously developed by the applicant consists therefore in the presence of an additional layer and / or sublayer (preferably an additional layer) which will support crystallization of titanium oxide due to phenomena of absorption or production of energy, and transfer of energy absorbed or generated into the titanium oxide layer . The final energy supplied to the titanium oxide layer is therefore greater than the energy brought only by the crystallization treatment. The method according to the invention therefore allows, in the case of the same energy supplied during the crystallization treatment, to improve the crystallization properties, or, alternatively, to obtain equivalent crystallization properties of the crystallization treatment consuming less energy.

[0019] By "layer point", is meant a zone of a layer that has been processed at a given moment. According to the invention, the entire layer (and hence each point) is heated to a temperature of at least 300 ° C, but not every point of the layer must be processed simultaneously. The layer can be processed all at the same time, with each point of the layer being simultaneously heated to a temperature of at least 300 ° C. The layer can be successively treated in such a way that the various points of the layer or group of points are successively heated to a temperature of at least 300 ° C, the latter example being more often used in the case of continuous use on an industrial scale.

[0020] By "applied to the first surface of said substrate" it is not necessarily meant that the layer is applied directly to the substrate. This may be the case, but one or more sub-layers may be sandwiched between the substrate and the titanium oxide-based layer, as follows.

[0021] The energy supply layer is preferably applied over a thin layer based on titanium oxide. This is an additional layer.

[0022] The method according to the invention makes it possible to provide a large amount of energy which promotes the crystallization of the thin layer, via a mechanism of crystal growth around the embryos already present in the layer, remaining in the solid phase.

[0023] The method of the invention has the advantage that only a thin layer (or thin layers in the case of a layer system) is heated, without significantly heating the entire substrate. It is therefore no longer necessary to cool the substrate slowly and controlled before cutting or storing glass. This method also allows connecting the heating device to existing continuous production lines, in particular in the space between the outlet of the vacuum deposition chamber of the magnetron line and the glass storage device by stacking. It is also possible in some cases to carry out the treatment according to the invention in the vacuum deposition chamber itself.

[0024] In the case of an industrial application connected to a magnetron line, the method is generally continuous in that the substrate is shifted and thus experiences a linear movement in the X direction. Each point of the thin layer is then preferably machined according to one of the following embodiments : the heating means are stationary and all points forming the flat calcium line can be processed simultaneously.

along the Y direction perpendicular to the X direction, or the heating means are movable along the Y direction and each point is machined in turn. The method according to the invention can be applied to a surface placed both horizontally and vertically. It can also be applied to a substrate having thin layers on both of its surfaces, wherein at least one layer of one of the surfaces or each of the surfaces is treated according to the invention. If the thin layers applied to both surfaces of the substrate are treated according to the invention, it is possible to treat said thin layers of each surface simultaneously or sequentially by means of identical or different methods, in particular depending on whether the type of processed layers is identical or different. The case where the treatment according to the invention is carried out simultaneously on both surfaces of the substrate therefore falls within the scope of the invention.

[0025] It is not physically possible to heat the layer without heating the substrate, since an increase in temperature in the layer inevitably entails, due to thermal conduction mechanisms, the heating of the substrate zone of the nearest layer; and therefore a high thermal gradient in the thickness of the substrate. These high thermal gradients, sometimes called heat shocks, are known to generate regular bruises in the case of silicon-sodium glass commonly used in the glass industry. These bruises, which are caused by the difference in thermal expansion of different glass zones subjected to different temperatures, are more easily formed in the case of sodium silicon glass - calcium because its expansion coefficient is quite high. They are also easier to form for substrates with large widths of at least 1 m, 2 or even 3 m wide because it is more difficult to ensure high temperature uniformity for large substrates.

[0026] The inventors have shown, however, that heat treatment only with moderate and controlled heating of a limited substrate zone allows to get rid of this cracking problem, hitherto considered inevitable. It is therefore necessary when applying the present invention that the surface temperature of the substrate opposite to the surface on which the thin treated layer is not higher than

150 ° C. This property is obtained by choosing a heating method specially adapted to heat the thin layer rather than the substrate and controlling the time and intensity of heating and / or other parameters depending on the heating method used, as described in more detail later in the text.

[0027] A common characteristic of all heating methods suitable for use according to the invention is that they allow the generation of very high power per unit area, which, however, cannot be quantified in absolute terms because it depends on many factors, including type and thickness of thin layer. This high power per unit area allows extremely fast achievement of the desired temperature at the layer level (usually in less than or equal to 1 second) and therefore shortens the same processing time, while the heat generated does not have time to penetrate the substrate . Each point of the thin layer is treated according to the invention (i.e. heated to a temperature higher or equal to 300 ° C) in a time generally shorter than or equal to 1 second, or even 0.5 second. Conversely, because the classic infrared lamps do not allow these very high powers per unit area to be achieved, the processing time must be longer to achieve the desired temperatures (often several seconds), and the substrate is then inevitably heated to a high temperature by heat dissipation.

[0028] In order to minimize the number of tables per student for the largest substrates (for example 6 m in length by 3 m in width), the temperature is preferably maintained throughout the entire treatment period lower than or equal to 100 ° C, in particular 50 ° C , at any point of the substrate surface opposite to the surface on which the thin layer is applied.

[0029] Another advantage of the invention is that the method allows a treatment equivalent to quenching a thin layer or thin layer system. It happens that in some systems of thin layers, their optical properties (colorimetric coordinates, light transmission or energy transmission) change when the glass is toughened. The method according to the invention thus allows obtaining non-toughened glass (and thus having no stress profile specific to toughened glass, which makes it suitable for cutting) but having essentially the same optical properties as if it were toughened glass.

[0030] The crystallinity index obtained by the method of the invention is preferably higher than or equal to 10%, and even 20% or 50%, in particular 70% and even 90%. This crystallinity index, defined as the mass of crystallized material in relation to the total mass of the material, can be assessed by X-ray diffraction using the Rietveld method. Due to the crystallization mechanism by the growth of crystallites from embryos or nuclei, an increase in the crystallinity index is generally accompanied by an increase in the size of the crystallites or coherent diffraction domains measured by X-ray diffraction.

[0031] The substrate is preferably transparent, made of glass, in particular silicon soda-lime. The substrate may be colorless or colored, for example blue, green, brown or gray. It may also be of plastic, such as polycarbonate or polymethyl methacrylate. It preferably has at least a dimension greater than or equal to 1 m, or even 2 m or 3 m. The thickness of the substrate is generally from 0.5 mm to 19 mm, the method of the invention being particularly advantageous for the thinnest substrates whose thickness is less than or equal to 4 mm or even 2 mm.

[0032] The surface of the substrate opposite the surface to which the titanium oxide-based layer is applied may be bare, or be covered with one or more thin layers. It may in particular be a layer based on titanium oxide, or layers with a thermal function (layers or layers of solar control or low emissivity layers, in particular of a type containing at least one silver layer) or optical (e.g. layers or layers of layers with anti-reflective layers).

[0033] The titanium oxide layer is preferably a titanium oxide layer (optionally with the addition of a metal ion, for example a transition metal ion, or for example nitrogen, carbon, fluorine ...).

[0034] The entire surface of this layer preferably contacts the outside in such a way that titanium oxide can fully perform its self-cleaning function. However, it may be advantageous to coat the titanium oxide layer with a very thin hydrophilic layer, in particular based on silica. One of the advantages of the process according to the invention is that this very thin layer can be formed from the energy supply layer after treatment by crystallization, as is described in detail in the following text.

[0035] In order to further improve the crystallization of these layers, it is possible to place a sublayer directly under the titanium oxide layer, which promotes the growth of titanium oxide crystals, in particular in the form of anatase. It may in particular be a ZrO2 sublayer such as that described in patent application WO 02/40417, or a sublayer supporting titanium oxide hetero-epitaxial growth in the form of anatase, such as for example described in patent application WO2005 / 040058, in particular the layer BaTiO3 or SrTiO3. [0036] Other sub-layers may be sandwiched between the substrate and the titanium oxide-based layer. For example, it may be barrier layers for alkali metal migration, in particular layers based on SiO2, SiOC, Al2O3 alumina, Si3N4 silicon nitride. It may also be layers or layers of layers with a thermal function (layers or layers of layers controlling solar or low emissivity, in particular of a type containing at least one silver layer) or optical (e.g. layers or layers of layers with anti-reflective layer).

[0037] A thin layer based on titanium oxide or an energy supply layer can be obtained by any type of method, in particular methods generating layers mostly amorphous or nanocrystalline, such as the magnetron method, plasma-assisted vapor phase chemical deposition method (PECVD ), vacuum evaporation method, or sol-gel method. It is, however, preferably a "dry" layer, containing no aqueous or organic solvent, in contrast to the "wet" layer, for example obtained by the sol-gel method.

[0038] A thin layer based on titanium oxide and an energy supply layer are preferably applied by cathodic sputtering, in particular aided by a magnetic field (magnetron method).

[0039] In the case of a layer obtained by the sol-gel method, the precursors in solution (sol) are applied to the substrate, the layer obtained must then be dried and annealed to remove any traces of solvent. In this case, the energy supplied by heating then mainly serves to remove this solvent, without inevitably affecting the crystallization properties of the layer, and it is therefore more difficult to improve said properties in a short time so as not to heat the substrate as well.

[0040] The energy supply layer is preferably applied in direct contact with the titanium oxide based layer, preferably on this layer. Accordingly, the energy transfer from the energy supply layer to the titanium oxide based layer is optimized.

[0041] The energy supply layer preferably has an absorption in the wavelength range from 300 to 3000 nm, preferably from 600 to 1100 nm, in particular from 800 to 1100 nm. It is therefore possible to use radial methods located in this range, such as YAG lasers, laser diodes or infrared lamps connected to these focusing devices. The energy supply layer absorbs this radiation, and transfers part of the energy through the conductivity to the titanium oxide layer. In the absence of an energy supplying layer, this type of radiation would have little effect on titanium oxide because it has no specific absorption energy in this wavelength range.

[0042] The energy supply layer may, alternatively or additionally, emit energy through an exothermic reaction, in particular combustion or oxidation. The energy supply layer can therefore burn under the effect of crystallization treatment, emitting near the titanium oxide layer, and transfer a large amount of energy to the titanium oxide layer, which contributes to the improvement of crystallization.

[0043] The energy supply layer may evaporate at least partially or even completely during the treatment by crystallization. In this case, the combustion or oxidation reaction can transform the layer at least partially into gas.

[0044] The energy supply layer may still oxidize at least partially or even completely during processing by crystallization and become at least partially transparent in the visible light range.

[0045] Those energy supply layers that evaporate or oxidize can be referred to as sacrificial layers, in the sense that after playing their role as energy supplier to titanium oxide, they are no longer as such (in their original form) part of the material final.

[0046] Alternatively, the energy supply layer, or the result of its reaction during treatment by crystallization, may remain on the surface of the material after treatment. In this case, it may be necessary to remove them, for example by chemical treatment or cleaning.

[0047] One or more of these beneficial properties may occur in different types of layers.

[0048] The energy supply layer may be, for example, a metallic titanium layer. Metallic titanium absorbs in the wavelength range of visible and near infrared light, in which range its oxide is transparent. In addition, some of the metallic titanium will evaporate during heat treatment and the remainder will oxidize to become titanium oxide. The metallic titanium layer therefore disappears during the crystallization treatment and the final product obtained no longer contains an absorbing additional titanium layer. The titanium layer is preferably applied by means of sputtering supported by a magnetic field (magnetron method) using a titanium target in an argon atmosphere.

[0049] The energy supply layer may also be a carbon layer, in particular of the graphite and / or diamond type. Carbon absorbs infrared radiation, and under the action of crystallization treatment, in particular when using a flame or plasma torch, carbon will experience a combustion reaction. The energy released in this exothermic reaction will contribute to the crystallization of titanium oxide. The graphite layer is preferably applied by cathodic sputtering assisted by a magnetic field (magnetron method) using a graphite disk in an argon atmosphere. Other possible methods include application through an ion source, plasma-assisted gas phase chemical application (PECVD).

[0050] The energy supply layer may also be a silicon layer, optionally doped with aluminum. Silicon exhibits strong absorption in the wavelength range from visible to near infrared light. Under the action of crystallization treatment, in particular with the use of an infrared laser, the silicon will also be oxidized to form a layer of silica, possibly containing aluminum. This oxidation is exothermic and thus will cause the release of energy, some of which will be used to support the crystallization of titanium oxide. The obtained silica layer is hydrophilic and can contribute, if its thickness is small (less than 5 nm and even less than 2 nm), to improve the light-induced hydrophilicity of titanium oxide, and therefore its self-cleaning and anti-fouling properties. The silicon may be doped with aluminum, in particular with a content of 5 to 10% by weight. The presence of aluminum improves the chemical durability of the layer.

In addition, cathodic sputtering is facilitated because aluminum contributes to the electronic conductivity of silicon disks.

[0051] The energy supply layer may also be a layer of titanium carbide or silicon carbide. These layers show strong absorption in the visible and near infrared range, in which range the titanium oxide is transparent. Under the action of crystallization treatment, these layers will oxidize to titanium oxide (and thus be combined with the underside of titanium oxide to form a thickening), or to silicon oxide, which has the above-mentioned advantages.

[0052] The energy supply layer has a thickness of preferably from 1 to 100 nm, in particular from 1 to 20 nm. [0053] For greater simplicity, the crystallization treatment preferably takes place in air and / or at atmospheric pressure. However, some treatments are compatible with vacuum, and it may be advantageous to perform the crystallization treatment in the vacuum deposition chamber itself.

[0054] Various heating means allow the use of crystallization treatment, enabling the generation of very high power per unit area. Heating parameters such as the power of heating means or heating time should in any case be adjusted by a skilled person depending on various parameters such as the type of heating method, layer thickness, size and thickness of the substrate to be treated.

[0055] The crystallization treatment can be carried out by means of infrared radiation. In order to limit the heat input to the substrate as much as possible, the wavelength of the selected radiation is preferably not included in the infrared radiation part absorbed by the substrate. For the aforementioned reasons, radiation should be characterized by high power per unit area. For this reason, the heating of the thin layer is preferably carried out by means of an infrared laser. Systems of infrared lamps connected to a focusing device (e.g. a cylindrical lens) enabling high power per unit area are also usable. [0056] A laser emitting radiation whose wavelength is from 5 to 15 micrometers can be used, for example a CO2 laser emitting a radiation whose wavelength is 10.6 micrometers. The advantage is that titanium oxide absorbs in this wavelength range.

[0057] However, it is preferred to use a laser emitting radiation whose wavelength is between 0.5 and 3 micrometers. Preferably, the energy supply layer is chosen that has a high absorption in this wavelength range, such as titanium, carbon in the form of graphite, silicon optionally with the addition of aluminum, or silicon or titanium carbide. YAG laser (Y2Al15O2 yarn-aluminum grenade) with an admixture of neodymium, emitting, in a continuous or pulsed mode, radiation with a wavelength of about 1 micrometer, proved to be particularly suitable, especially when the substrate does not absorb in this wavelength range, as is the case in the case of transparent glass in which the iron oxide content is 0,1% or less than 0,1%. It is also possible to use diode lasers with an emission wavelength of 800 nm.

[0058] The use of excimer lasers that emit ultraviolet light is also possible for layers absorbing such radiation.

[0059] To facilitate the wider application, the lasers used in the context of the invention may be fiber lasers, which means that the laser radiation is transmitted to the fiber optic then released at the surface to be treated by the focusing head. The laser can also be fiber in the sense that the zoom environment is the optical fiber itself.

[0060] Because lasers can only illuminate a very small area (typically in the order of a fraction of mm)² up to several hundred mm²), in order to treat the entire surface, it is necessary to have a laser beam displacement system in the ground plane or a laser beam forming system in the line that simultaneously illuminates the entire width of the substrate under which the latter shifts.

[0061] The crystallization treatment can also be carried out by means of thermal spraying methods, in particular the method of spraying with a plasma spray (plasma spray).

[0062] Pl azma is an ionized gas generally obtained by subjecting a gas called "plasmogenic" excitation to such a strong constant or alternating electric field (for example an electric arc). Under the action of this excitation, the electrons are pulled out of the gas atoms and the charges formed in this way migrate to the opposite charge electrodes. These charges then excite other gas atoms through the collision, producing a uniform or microfibrous discharge or an arc due to the avalanche effect. The plasma can be "hot" (the gas was then completely ionized and the plasma temperature is about 10)⁶° C), or "thermal" (the gas has almost completely ionized and the plasma temperature is about 10)⁴° C, as is the case with electric arcs, for example). Plasma contains many active particles, i.e. they can interact with the material, including ions, electrons or free radicals. In the case of a plasma torch, the gas is blown through an electric arc, and the resulting thermal plasma is blown into the substrate to be treated. Plasma torch is commonly used to apply thin layers to various substrates by adding powder precursors to the plasma.

[0063] In the context of the invention, the plasma torch is preferably connected to an automatic displacement system arranged perpendicular to the direction of travel of the coated substrate enabling the entire surface to be treated by successive back and forth passes above the substrate.

[0064] The blown gas is preferably nitrogen, air or argon, preferably with a volume of hydrogen from 5 to 50%, in particular from 15 to 30%.

[0065] The crystallization treatment can also be carried out by subjecting the thin layer to at least one flame.

[0066] This flame treatment is preferably carried out in a flame treatment station positioned perpendicular to the direction of travel of the substrate. The length of the flame device is preferably at least equal to the width of the coated substrate, which allows easy movement during movement without requiring a displacement system. The gas used may be a mixture of an oxidizing gas, in particular air, oxygen or mixtures thereof, and a combustible gas, in particular natural gas, propane, butane, and even acetylene or hydrogen, or a mixture thereof. Oxygen is preferred as an oxidizing gas, in particular in combination with natural gas (methane) or propane, on the one hand because it allows higher temperatures and therefore shortens the treatment and avoids heating the substrate, and on the other hand because it avoids the formation of oxides nitrogen NOx. In order to achieve the desired temperatures at the level of the thin layer, the coated substrate is generally placed in a visible flame, in particular at the level of the hottest flame zone, with part of the visible flame then being around the treated zone.

[0067] Flame treatment is used to treat surfaces to improve their wetting properties by the common polymer method in order to facilitate their treatment and combustion, without coating with a paint coating. In the case of use that is made of it, the rule is to subject the surface, which has the action of radicals created by heating this surface to a high temperature. Patent application US 2006/128563 describes the use of this method for activating the surface of titanium oxide layers to improve their hydrophilic properties. The treatments described, quite similar to those practiced on polymeric substrates, consist of moving the substrate at or slightly below the level (a few centimeters) of the visible flame end. This type of treatment, which aims to form hydroxyl groups on the surface of titanium oxide, is not suitable, however, for heating a thin layer of titanium oxide to a temperature higher than 200 ° C and for increasing the crystallinity index of titanium oxide, because the temperature at the visible flame level is insufficient.

[0068] Flame treatment is preferred when you do not want to use a mechanical device to move above the ground. However, infrared radiation treatment can be used in a vacuum coating device for a magnetron line. It is also beneficial when you don't want to use a lot of gas.

[0069] All possible combinations of different types of energy supply layers and different crystallization methods are allowed. According to one preferred embodiment of the invention, the energy supply layer is a titanium layer and the crystallization treatment is carried out by means of infrared radiation, in particular by means of a laser emitting radiation of 0.5 to 3 micrometers, for example a YAG laser or a laser diode. According to another preferred embodiment, the energy supply layer is a graphite layer and the crystallization treatment is carried out by flame treatment.

[0070] The method of the invention is particularly advantageous when the alkaline ion-containing substrate (e.g. silicon-sodium-calcium glass) is heated to a high temperature, said ions tend to disperse in the titanium oxide layer significantly reducing and even abolishing , its photocatalytic properties. For this reason, it is customary to place a barrier layer for alkali metal migration between the thin titanium oxide layer and the substrate, as described in patent application EP-A-0 850 204, or the thickness of the titanium oxide layer is increased so that at least the end surface of the layer does not become impure, as described in patent application EP-A-0 966 409. In the case of the method according to the invention, the substrate is almost unheated and the migration of alkali metals is therefore practically zero. The method according to the invention thus makes it possible to obtain silico-soda-lime glass substrates coated directly with a thin layer of titanium oxide (e.g. on the order of 10 nanometers thick), however, having very high photocatalytic activity. [0071] The invention is presented by means of non-limiting embodiments, which are presented below.

[0072] Silica-soda-lime glass substrate obtained by means of the float process is then cut in such a way that its size is 3 m wide by 6 m long, it is coated in a known manner by a magnetron method with a 20 nm thick layer of silica then a thin layer 10 nm thick titanium oxide.

[0073] Comparative example C1 does not include an energy supply layer. The examples according to the invention are instead coated with an additional layer of Ti with a thickness of 5 nm. The titanium layer is preferably applied by means of magnetic field-assisted sputtering (magnetron process) using a titanium target in an argon atmosphere.

[0074] Between the outlet of the magnetron line and the storage device is placed a device containing a diode laser emitting radiation at a wavelength of 808 nm focused on the additional layer Ti along a line corresponding to the width of the substrate.

[0075] All examples except Example C2 undergo this treatment by crystallization. The temperature of the glass substrate during processing does not exceed 50 ° C, measured by pyrometry at the surface level of the substrate opposite to the surface containing the thin film coating.

[0076] In table 1, the photocatalytic activity of the layers before and after treatment is given below. Each test is characterized by the thickness of the additional titanium layer and the speed of processing. The processing speed, directly related to the heating of the layer, is expressed in meters per minute: it corresponds to the speed of the glass in the length direction. [0077] Photocatalytic activity corresponds to a measurement of stearic acid degradation rate.

[0078] The measurement of photocatalytic activity is carried out as follows:

• cutting samples 5x5 cm², • cleaning samples for 45 minutes under UV irradiation and in the oxygen stream, infrared spectrum measurement using FTIR for a number of waves from 4000 to 400cm^-1, in order to create the reference spectrum, stearic acid application: 60 microliters of the stearic acid solution dissolved in 5g / l in ethanol is applied to the sample by spin-coating, infrared spectrum measurement by FTIR, surface measurement of elongation bands of CH2-CH3 bonds from 3000 to 2700cm^-1, UVA type exposure: power received by the sample, about 35 W / m² to simulate outdoor exposure, it is controlled by a photoelectric cell in the 315400nm wavelength range, monitoring photodegradation of the stearic acid layer after subsequent exposures for 30 minutes, then 30 minutes, and then 1 hour by measuring the surface area of ​​the elongation bands of CH2-CH3 bonds from 3000 to 2700cm^-1.

photocatalytic activity is determined by the slope, expressed in cm^-1.min^-1, a straight line representing the surface area of ​​the elrogant bands of CH2-CH3 bonds from 3000 to 2700cm^-1, between 0 and 2 hours.

through time

Table 1

<td></td><td>Ep (nm)</td><td>speed (m / min)</td><td>Activity (x10 ⁴cm ¹.min ¹)</td>

<td>C1</td><td> 0</td><td> 5</td><td> 3</td>

<td>C2</td><td> 5</td><td> 0</td><td> -</td>

<td> 1</td><td> 5</td><td> 10</td><td> 6</td>

<td> 2</td><td> 5</td><td> 8</td><td> 12</td>

<td> 3</td><td> 5</td><td> 6</td><td> 10</td>

<td> 4</td><td> 5</td><td> 4</td><td> 22</td>

[0079] Comparative example C1 does not include an energy supply layer. Photocatalytic activity is weak but not zero, which probably indicates low crystallization during processing. Crystallization is small because titanium oxide is transparent at the wavelength used and therefore does not absorb energy. Comparative example C2 has been covered with a layer of titanium has been titanium by very weakens photocatalytic activity that is not measurable. Examples 1 to 4 according to the invention show that the use of an energy supply layer allows a significant improvement in photocatalytic activity. This result is due to the fact that titanium absorbs laser radiation and transfers this energy to titanium oxide, which can then transform and crystallize. In addition, titanium turns into steam and / or oxidizes in large part because the light transmission after treatment is almost as high as before applying the additional layer. Lower speeds under the laser lead to greater metallic, crystallization but not the presence of surface treated photocatalytic activity, therefore the layer heating is more intense.

the fact that