Substrate with a self-cleaning coating

SUBSTRATE WITH SELF-CLEANING COATING

0002The invention relates to different types of material that can be found in buildings, vehicles, street furniture or even in household appliances, namely, in particular:

0003- transparent glass or polymer substrates intended to serve as glazing, display screen for example,

0004- ceramic or glass-ceramic substrates which can be used, for example, in household appliances,

0005- architectural materials such as tiles, tiles, stone, cementitious compositions, metal surfaces - fibrous mineral materials, such as glass wool insulation or glass fiber yarn, which can be used as filtration material, to make false ceilings, quartz fibers, silica ...

0006Recent studies have been made to try to improve the comfort of use of these materials, in particular to facilitate their maintenance. In particular, functional coatings with photocatalytic properties have been developed. These include coatings comprising TiO₂ at least partially crystallized, in particular in anatase form and which are in particular described in patents WO 97/10185, WO 97/10186, WO 99/44954 and WO 01/66271. This type of semiconductor material based on metal oxide, possibly doped (there are also other oxides capable of being photocatalytic, such as ZnO, etc.) is suitable under the effect of radiation of length of adequate wave to initiate radical reactions causing the oxidation of organic compounds: this type of coating, if it is sufficiently exposed to ad hoc radiation (generally ultraviolet, possibly the visible range), is therefore very effective in degrading organic soiling. Furthermore, it has been discovered that, in particular when it comes to titanium oxide coatings, these also exhibit a certain hydrophilic character if they are exposed to this radiation for long enough. This coating is therefore very efficient, in the sense that it is capable of degrading organic dirt, and of removing mineral dirt by its hydrophilicity. However, its activity is linked to its exposure (for a sufficient period) to (sufficiently intense) radiation of ad hoc wavelength. This type of coating therefore has a behavior which strongly depends on the surrounding climatic conditions in the event of outdoor exposure, in particular the conditions of sunshine, rainfall. Similarly, it tends to have less nocturnal activity than its daytime activity, in the absence of appropriate lighting. The object of the invention is therefore to further improve the functionality conferred by this type of “self-cleaning” or “fouling retardant” coatings. It aims in particular to obtain coatings which can have an increased efficiency, which can be more “versatile” in different ways: first with respect to the conditions of exposure to radiation, then with respect to the constraints mechanical (resistance to abrasion ...), finally with regard to the association of other functionalities. It is more particularly aimed at obtaining coatings which can, even in poor sunshine conditions, even at night, or indoors in particular under the action of the residual ultraviolet radiation of conventional lighting lamps or of ultra-violet radiation. purple passing through a window, show some anti-fouling activity. It also targets products with which a UV lamp is associated, in particular self-cleaning filters.

0007The invention firstly relates to a substrate which can be essentially transparent, in particular based on glass or polymer (s), or which can be in ceramic or in vitro-ceramic, or which can also be in architectural material (of the type coated with a facade, concrete slab or paving stone, architectural concrete, tile, material with a cement composition, terracotta, slate, stone, or which may still be a fibrous substrate, glass-based mineral wool insulation type or reinforcing glass son, or a product comprising quartz or silica fibers). This substrate is characterized by the fact that it is provided on at least part of its surface with a coating whose mesoporous structure has photocatalytic properties and comprises titanium oxide at least partially crystallized, in particular in anatase form and / or rutile. The term "mesoporous" refers to pores with diameters between 2 and 50 nm. The mesoporous structure, obtained in the manner which will be described below, is in particular based on at least one compound of at least one of the elements Si, W, Sb, Ti, Zr, Ta, V, B, Pb , Mg, Al, Mn, Co, Ni, Sn, Zn, In, Fe and Mo, optionally in covalent bond with elements such as O, S, N, C or the like. The at least partially crystallized titanium oxide is for example incorporated into the mesoporous structure in the form of perfectly discernible particles. The whole of the mesoporous structure incorporating the titanium oxide is essentially solid, capable of cohesion, mechanical strength and excellent abrasion resistance. The mesoporous structure is likely to be exclusively composed of titanium or of a titanium compound such as oxide, in particular crystallized in anatase, rutile form ... It has been found that the titanium oxide thus incorporated exerts its activity photocatalytic to an exceptionally high degree. Residual ultraviolet radiation after passing through single, double glazing, etc., or residual ultraviolet radiation from indoor electric lighting is enough for the substrate of the invention to degrade a residue organic, and so that it is then entrained in a relatively uniform liquid film which is formed if necessary on the substrate rendered hydrophilic by radiation. The coating of the invention combines the functionality of degradation of organic residues - by photocatalysis - and evacuation of organic and mineral residues - hydrophilic / oleophilic character - under the effect of any liquid, such as condensation. The high performance provided by the invention may be attributable at least in part to the interconnection of the pore network, allowing good accessibility of pollution towards the particles of titanium oxide, as well as good diffusion in the coating. photogenerated species on the surface of these particles.

0008On the other hand, the abrasion resistance and the durability of the photocatalytic activity to such a high degree are excellent (see examples below). The invention therefore also makes it possible to retain the porosity after abrasion, whereas it could rather be expected that abrasion would result in densification of the surface layer and therefore ultimately, a loss of anti-fouling properties.

0009In addition, the mesoporous nature of the substrate makes it possible to envisage an impregnation thereof after the formation of the mesoporous structure with deodorizing, antibacterial or all other functional agents.

0010Advantageously, the substrate according to the invention is essentially transparent, flat or curved, of the glazing type, because it is in this type of application that the accumulation of dirt preventing visibility is the most troublesome, and that the washes are the no longer necessary to guarantee their transparency. It may be glazing having macroscopic relief, for example pyramid patterns in depths of the order of a few millimeters - printed glass - or glazing having much smaller surface irregularities such as resulting from a chemical attack with hydrofluoric acid - sandblasted, matt glass-.

0011Preferably, the coating of the invention is formed with the interposition of a sublayer based on an at least partially oxidized derivative of silicon chosen from silicon dioxide, substoichiometric silicon oxides, oxycarbide, oxynitride or silicon oxycarbonitride. The undercoat proves useful when the underlying surface is made of glass, since the migration of alkaline ions (sodium) from the glass into the coating of the invention can, under certain conditions, alter its photocatalytic properties; however, the undercoat acts as a barrier to alkalis. The sub-layer can be of the type described in patent WO 01/32578 cited above. It advantageously has a refractive index of between 1.45 and 1.80, in particular between 1.50 and 1.75, for example between 1.55 and 1.68. Such a relatively low index makes it possible, on a transparent substrate of the glass type, to avoid a reflective effect which can be considered unsightly. This sublayer therefore advantageously comprises Si, O, optionally carbon and nitrogen. However, it can also include minority materials compared to silicon, for example metals such as Al, Zn or Zr. The sublayer can be deposited by sol-gel or by pyrolysis, in particular by gas phase pyrolysis (CVD). This last technique makes it possible to obtain coatings in SiO_xVS_y or in SiO₂ fairly easily, in particular by depositing directly on the float glass ribbon in the case of glass substrates. However, deposition can also be carried out by a vacuum technique, for example by sputtering from an Si target (optionally doped) or a target made of silicon sub-oxide (in a reactive oxidizing and / or nitriding atmosphere). for example).

0012This sublayer preferably has a thickness of at least 5 nm, in particular a thickness between 10 and 200 nm, for example between 80 and 120 nm. According to other advantageous characteristics of the substrate of the invention:

0013the coating with a mesoporous structure is deposited by the sol-gel route;

0014- Its thickness is between 30 and 800 nm;

0015the titanium oxide incorporated into the mesoporous structure is optionally doped as explained in applications WO 97/10185 and WO 97/10186 incorporated here for reference, and comprises nanoparticles with diameters between 0.5 and 100 nm, in particular between 1 and 80 nm, themselves made up of clusters of elementary grains or crystallites with diameters between 0.5 and 10 nm. The term "diameter" is to be taken here in the broad sense, it is more an evaluation of the size of the nanoparticle or of the crystallite. The shape of this one can approach a sphere, or an elongated shape in grain of rice or a completely random shape.

0016Another object of the invention resides in a process for manufacturing a substrate as described above, successively comprising: - the preparation of a liquid composition comprising at least one precursor of the material constituting the mesoporous structure of the coating and at less an organic structuring agent,

0017- the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor, - the addition in the liquid composition of nanoparticles or crystallites - according to the definition above - of possibly doped titanium oxide, diameters between 0.5 and 100 nm,

0018- applying the composition to the surface to be coated,

0019the elimination of the organic structuring agent, the elementary grains or crystallites of titanium oxide being incorporated into the mesoporous structure while essentially preserving their integrity there, several of them being able to be aggregated therein in clusters. During such manufacture of the substrate, it is not excluded that grains or crystallites of titanium oxide aggregate with each other and / or grow, in particular the smallest of them, according to the operating conditions (content, pH, temperature ...). For the manufacture of the substrate of the invention, the preparation of the liquid composition advantageously comprises:

0020- the preparation of an oxide precursor sol (in particular of silica), - the maturing of the sol, then

0021- mixing with the structuring agent.

0022Indeed, the maturing of the soil allows a preliminary condensation of the oxide precursor which promotes the structuring of the coating of condensed oxide on the support surface in large domains. Advantageous curing conditions include maintaining the soil at a temperature of 40 to 60 ° C for a period of 30 min to 24 hours, the curing time being shorter the higher the temperature.

0023In this case, the oxide precursor is advantageously a hydrolyzable compound, such as a halide or an alkoxide, the structuring agent is advantageously chosen from cationic surfactants, preferably of the quaternary ammonium type such as cetyltrimethylammonium bromide, or not. ionic, including di-block or tri-block copolymers based_^ for example, ethylene or propylene oxide.

0024The subject of the invention is also the application of the substrates according to the invention, in particular those which are essentially transparent, to the manufacture of “self-cleaning” glazings, which can be at the same time anti-fouling, anti-fogging and anti -condensation. It can be glazing for the building of the double-glazing type, glazing for vehicle of the windshield, rear window, auto roof, side windows type. It can also be glazing for trains, planes, boats. It can also be useful glazing such as aquarium glass, glass for showcases, greenhouse, or glazing used in interior furnishings, in urban furniture, mirrors. It can also be glazing used as display screens of the television, computer, telephone screen type. This type of coating can also be applied to electro-controllable glazing, such as heated glazing or coated glazing, electrochromic glazing, glazing with liquid crystal film, electroluminescent glazing, photovoltaic glazing.

0025In the application of the substrate of the invention as glazing (based on transparent plastic or glass), one or more thin layers other than the above-mentioned sublayer based on an at least partially oxidized derivative of silicon, may be interposed between the support surface and the coating with a mesoporous structure. They can be, in particular, layers with an antistatic, thermal (heating by providing it with current leads, low-emissivity, anti-solar, etc.), optical (reducing light reflection and / or making more neutral) function. the color in reflection of the substrate ...), of a stack of anti-reflection layers ... With regard to such functional layers applied in a known manner to the glazing, possibly in the form of stacks, the applications WO 97/10186 already cited and WO 02/02472 are incorporated here by reference.

0026The substrate according to the invention, in addition to its application as glazing, can be of any architectural material which can be used to manufacture partitions, facades, roofs, floors, indoors or outdoors (metal, wood, stone, cement, concrete, terracotta , ceramic, facade coating ...) The substrate, if it is rather based on mineral wool insulation, and textile based on reinforcing glass fibers, can be used as a filtration material, or even used to make false ceilings, whose cleaning is awkward.

0027The invention also relates to the application of a woven, nonwoven substrate (needle mat, felt, wool ...), knitted, braided, block of sintered fibers (known as rigid silica) based on fibers with diameters between 1 and 20 μm of fused silica, washed glass (more than 90% of silica), of alumina and mullite according to claim 1, in the manufacture of anti-odor filters, of depollution of industrial effluents, anti-bacteria, indoor pollution control, purification of domestic air, purification of the interior of transport vehicles (cars, railways, aeronautics, water), purification of cigarette smoke, purification of household appliances (refrigerator, etc.).

0028The invention will be described below using nonlimiting examples.

EXAMPLE 1

0030Is deposited on the glass in the form of a ribbon of float glass, a sublayer based on silicon oxycarbide noted by SiOC convenience (without prejudging the real rate of oxygen and carbon in the coating) - the glass is a clear silica-soda-lime glass 4 mm thick, as marketed by Saint-Gobain Glass France under the name Planilux-. This sublayer is deposited by CVD from Si precursors, in particular from a mixture of SiH₄ and ethylene diluted in nitrogen, using a nozzle arranged above and transversely to the float glass ribbon of a flat glass production line, in the float enclosure, when the glass is still at a temperature of about 550 to 600 ° C. The coating obtained has a thickness of approximately 50 nm and a refractive index of approximately 1.55. 10 cm x 10 cm samples are cut from the float glass provided with its alkali barrier SiOC undercoat thus obtained; these samples are washed, rinsed, dried and subjected to a UV ozone treatment for 45 min.

0031A coating with a mesoporous structure is formed on the sub-layer.

0032The liquid treatment composition is obtained by mixing in a first step 22.3 ml of tetraethoxysilane, 22.1 ml of absolute ethanol, 9 ml of HCl in demineralized water (pH 1.25) until the solution becomes clear, then placing the flask in a water bath at 60 ° C for 1 hour.

0033In a second step, a solution of cetyltrimethylammonium bromide (CTAB) is added to the soil obtained above, on the one hand, and a solution of a polyoxyethylene-polyoxypropylene block copolymer sold by the company BASF under the registered trademark Pluronic PE6800 (molar mass 8000) on the other hand, in proportions such that the CTAB / Si molar ratios = 0.1, respectively PE6800 / Si = 0.01. This is obtained by mixing: - 0.686 g of CTAB, 20 ml of ethanol, and 10 ml of the sol;

0034- 3.78 g of PE6800, 50 ml of ethanol and 25 ml of the soil.

0035The nanoparticles of T1O2 crystallized anatase and of size approximately 50 nm are added in various proportions to one or the other of the two liquid compositions thus obtained, just before deposition on the sample. The deposit is made by spin coating in a starting quantity of 3 ml per sample. (Other equivalent deposition techniques are dip coating, spraying, laminar coating, roll coating, flow coating ...)

0036The samples are then subjected to the following annealing treatment:

0037- 30 min 100 ° C level 2 h; - 15 min 150 ° C level 2 h;

0038- 15 min 175 ° C level 2 h;

0039- 10 min 200 ° C no step;

0040- 3 h 20 min 300 ° C level 1 h; - 2 h 30 min 450 ° C level 1 h.

0041The pores of the coating thus formed have a size of 2-3 nm when the cationic surfactant CTAB is used as a structuring agent, this size being of 4-5 nm when the copolymer PE6800 is used as a structuring agent. It is verified by SIMS analysis of the coating with a mesoporous structure that the Ti / Si atomic ratio is exactly identical to that of the starting liquid composition. SIMS analysis also makes it possible to verify that the nanoparticles are homogeneously distributed in the three dimensions of the coating. Various characteristics of the coatings are formed in the table below when they form and after 500 cycles of the Opel abrasion test - in the latter case, the values ​​are given in brackets. The Opel test (Building Standard In 1096-2 of January 2001) consists in applying to a part of the coated surface of 9.4 cm in length - this part is called track -, a felt of 14 mm in diameter, 10 mm thick and 0.52 g / cm² density, under a load of 400 g / cm², the felt being subjected to a translation (50 round trips over the entire length of the track per minute) combined with a rotation of 6 revolutions / min (1 cycle = 1 round trip).

0042The thickness E of the coatings in nm is measured from SIMS profiles and SEM images.

0043The amount of TiO₂ in μg / cm² is evaluated by X-ray fluorescence. The photocatalytic activity is measured as follows:

00441- test carried out on approximately 15 cm² coating;

00452- weighing of the sample and measurement of the thickness of the substrate, of the light transmission TL and of the blur Td (both in%);

00463- deposition by spray of a palmitic acid solution (8 grams of acid for 1 l of chloroform), with a glass / spray distance of 20 cm, on a vertical substrate, and 3 to 4 successive passages;

00474- weighing of the sample after deposition of palmitic acid to evaluate the thickness of palmitic acid deposited in nanometers;

00485- measurement of the light transmission T and the blur Td after deposition;

00496- measurement of the variation of the blur as a function of the irradiation time under UVA of intensity approximately 50W / m² ; 7- graphical determination of the time after which the blur has decreased by 50%: time called T₁ 2 (disappearance); 8- evaluation of the photocatalytic activity of the coating at the rate of disappearance of palmitic acid v (in nm / h), which is defined as follows: v (nm / h) = (thickness of palmitic acid (nm )) / (2 x T y₂ (disappearance (h))

0050The value of the photocatalytic activity reduced to the amount of TiO is also recorded in the table below.₂ in the coating. Finally, the optical properties of light reflection RI and of blur Td (in%) are indicated. The test numbers are defined as follows: - 1 and 2: CTAB as structuring agent, Ti / Si = 0.1, respectively 0.25; - 3 to 7: PE6800 as structuring agent, Ti / Si = 0.1, respectively 0.25, respectively 0.5, respectively 1, respectively 2.

0051<img file="WO03087002A1_D0001.tif" /> The thicknesses of the layers vary from 200 to 500 nm depending on the quantity of TiO nanoparticles₂ incorporated. After 500 Opel cycles, only the thickest coatings (450 and 500 nm) settle down more than half their initial thickness. The photoactivity of these coatings was nevertheless tested.

0052The coatings have photoactivities of 43 nm / h for the structured coating with the cationic surfactant and the least concentrated in

0053TiO₂ (2.2 μg / cm²) at 684 nm / h for the structured coating with the copolymer and the most concentrated in TiO₂ (66 μg / cm²). The v / TiO ratio₂ is always at least 9.

0054Partial or total maintenance of functionality is observed after 500 Opel cycles, which moreover only alters the optical properties for the thickest layers and the most concentrated in Ti0₂ (Ti / Si = 1 and 2) -for the others, the values ​​of RI and Td remain below 11.4 and 1.2% respectively- Tests 3 to 7 are reproduced (tests 3 'to 7') with l 1.5 W / m weak UVA irradiation² a conventional lighting lamp; the values ​​of v (nm / h) and v / TiO₂ recorded for tests N °:

0055- 3 ': 0 and 0;

0056- 4 ': 0 and 0; - 5 ': 13 and 0.75;

0057- 6 ': 19 and 0.57; and

0058- 7 ': 28 and 0.42.

0059The coated substrate of the invention is therefore also photoactive under weak UVA irradiation for the degradation of palmitic acid.

EXAMPLE 2

0061In addition, discs 47 mm in diameter, 8 mm thick and 1000 g / m2 of surface mass are impregnated with needle-punched felts of silica fibers, sold by the company Saint-Gobain Quartz under the name needled-punched Quartzel. mat (fibers between 7 and 16 μm) by immersion in the composition of test No. 6 above, then heat treatment described above. The increase in mass of the discs thus obtained is 10%. The capacity of these discs is tested to decompose a concentration of 350 ppm by volume of methanol in nitrogen gas, by filtration with a flow rate of 62.5 ml / mm, under UV illumination (190-350 nm).

0062At an illumination power of 48 m W / cm2, the efficiency, that is to say the proportion of decomposed methanol, is 100%. At a power of 25.6 m W / cm2, it is around 96%, and again around 58% under illumination as low as 8.22 m W / cm2.

0063Thus, the invention provides it with a substrate capable of providing the optical quality of transparency required in glazing applications, and a self-cleaning functionality which is durable under the conditions of erosion and bad weather of the external atmosphere. The remarkably high degree of photocatalytic functionality also makes it possible to envisage night or indoor use by taking advantage of low intensity radiation such as produced by conventional lighting or the passage of solar radiation through the glazing, as well as effluent or atmospheric depollution applications, filtration ...