Substrate with a self-cleaning coating

Description of the invention

The invention relates to a method of producing a substrate, including a substantially transparent substrate, in particular based on glass or one or more polymers, or a ceramic substrate or a glass-ceramic substrate, or a substrate in the form of an architectural material of the type including a plastered wall, concrete slab or concrete mass, architectural concrete, tile, cement composition material, terracotta, roof slate, stone, a metallic surface or a fibrous substrate, based on glass of the insulating mineral wool type or glass fibers to strengthen a substantially transparent substrate, or a ceramic substrate or a glass-ceramic substrate, or a substrate in the form of an architectural material or a fibrous substrate based on glass of the insulating mineral wool or glass wool type fibers for reinforcement. In general, the invention discloses various types of materials that can be found in buildings, vehicles, street furnishings or household appliances, in particular:

- transparent glass or polymer substrates intended for use e.g. as glazing, display, etc.,

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

- architectural materials such as roof tiles,

- tile cladding, stone, cement compositions, metallic surfaces,

- fibrous mineral materials such as glass wool for insulation or glass fiber, which can be used as filter material, for the preparation of suspended ceilings, quartz fibers, silica, etc.

Recent studies have been carried out to try to improve the comfort of use of these materials, especially in order to facilitate their maintenance.

In particular, functional coatings with photocatalytic properties have been developed. These are in particular coatings containing TiO2, at least partially crystalline, especially in the form of anatase, and which are described more particularly in WO 97/10185, WO 97/10186, WO 99/44954 and WO 01/66271. This type of semiconducting material based on a possibly doped metal oxide (there are also other oxides with photocatalytic properties, such as ZnO, etc.) is capable, when exposed to radiation of an adequate wavelength, to initiate radical reactions causing oxidation of organic compounds: this type of coating, if sufficiently exposed to appropriate radiation (generally ultraviolet, possibly the visible range) is therefore very effective in degrading organic pollutants. Moreover, it has been found that, when they are especially titanium oxide based coatings, they also exhibit certain hydrophilic properties if they are exposed to the radiation mentioned long enough. This coating is therefore very effective in that it is able to degrade organic contaminants and remove inorganic contaminants due to its hydrophilicity. However, its activity is related to exposing it (for a sufficient period of time) to radiation (sufficiently intense) of an appropriate wavelength. This type of coating thus exhibits a behavior that is strongly dependent on the climatic conditions of the environment in the event of outdoor exposure, especially sunlight and rainfall conditions. In addition, it tends to be less active at night than during the day, in the absence of adequate lighting.

The invention therefore aims to further improve the function conferred by this type of "self-cleaning" or "soil retarder" coatings. It is particularly concerned with obtaining coatings that may have increased effectiveness, which could be more "universal" in various respects: first in terms of radiation exposure conditions, then in terms of mechanical stresses (abrasion resistance, etc.), and finally in terms of combination with others. functions. More particularly, it aims to obtain coatings which, even in conditions of moderate sunlight, and even at night or indoors, especially under the action of the residual ultraviolet radiation of conventional lighting lamps or ultraviolet radiation passing through the glazing, can exhibit some anti-fouling activity. Products related to UV lamps, especially self-cleaning filters, are also disclosed.

The subject of the invention is a method for producing a substantially transparent substrate, in particular based on glass or one or more polymers, or a ceramic substrate or a glass-ceramic substrate, or a substrate in the form of an architectural material of the type including a plastered wall, concrete slab or concrete mass, architectural concrete, roof tile. ,

A cement composition material, terracotta, roofing slate, stone, metallic surface or a fibrous substrate based on glass of the insulating mineral wool type or glass fibers for reinforcement, said substrate being provided with a coating on at least part of its surface, the mesoporous structure of which exhibits photocatalytic characteristics and comprises at least partially crystalline titanium oxide, wherein said method comprises:

- producing a liquid composition comprising at least one mesoporous structure forming material precursor of a coating and at least one organic structure forming agent, the preparation of the liquid composition further comprising:

- preparation of an oxide precursor sol (especially silica), wherein the oxide precursor is a hydrolysable compound such as a halide or an alkoxide;

- maturation of the sol, the maturation conditions being that the sol is kept at a temperature of 40-60 ° C for between 30 minutes and 24 hours,

mixing with a structure-forming agent, the structure-forming agent being selected from cationic surfactants, preferably of the quaternary ammonium type, such as cetyltrimethylammonium bromide, or nonionic surfactants including diblock or triblock copolymers based on, for example, ethylene oxide or propylene oxide,

- precipitation of the precursor around the organic structure-forming factor and growth of precursor-derived molecules,

- adding nanoparticles or elementary crystallites to the liquid composition of optionally doped titanium oxide with diameters between 0.5 and 100 nm,

- applying the composition to the surface to be coated, removing the organic structure-forming agent, the titanium oxide crystallites are incorporated into the mesoporous structure, while substantially maintaining their integrity there, it is also possible that some of them aggregate into nanoparticles there.

Preferably the substrate is substantially transparent, flat or curved, of the glazing type.

Preferably the coating is formed with the insertion of a sublayer based on an at least partially oxidized silicon derivative selected from silicon dioxide, substoichiometric silicon oxides, or silicon oxynitride, oxynitride or silicon oxynitride.

Preferably, the sublayer has a thickness of at least 5 nm, in particular between 10 and 200 nm, preferably between 30 and 120 nm.

Preferably the coating has a thickness between 30 and 800 nm.

Preferably, the titanium oxide is optionally doped and comprises nanoparticles with diameters between 0.5 and 100 nm, in particular between 1 and 80 nm, formed by aggregates of grains or elementary crystallites with diameters between 0.5 and 10 nm.

Preferably the substantially transparent substrate is a glazing based on glass or clear plastic, and wherein an anti-reflective multi-layer system is interposed between the bearing surface and the mesoporous coating.

The substrate may be substantially transparent, especially with a matrix of glass or polymer (s), or may be made of a ceramic or glass-ceramic material, or it may also be an architectural material (such as a plastered wall, concrete slab or concrete massif, architectural concrete, roof tiles, cement composition material, terracotta, roof slate [ang. slate], stone, or it can also be a glass-based fibrous substrate of the type of insulating mineral wool or glass fibers for reinforcement, or a product containing quartz or silica fibers). This substrate is provided, at least partially on its surface, with a coating, the mesoporous structure of which exhibits photocatalytic characteristics and contains titanium oxide at least partially crystalline, in particular in the form of anatase and / or rutile. The term "mesoporous" refers to pores having a size of 2-50 nm. The mesoporous structure is obtained as will be described below, especially on the basis of 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, where appropriate covalently bonded to elements such as O, S, N, C or the like. The at least partially crystalline titanium oxide is e.g. incorporated into the mesoporous structure in the form of clearly recognizable particles. The entire mesoporous structure with incorporated titanium oxide is essentially stable, cohesive, with excellent mechanical resistance and abrasion resistance. The mesoporous structure can be composed only of titanium or a titanium compound such as an oxide, especially crystalline in the form of anatase, rutile

Etc. It turns out that the titanium oxide thus introduced shows an extremely high photocatalytic activity. So the residual ultraviolet radiation after passing through single glazing, double glazing, etc. or the residual ultraviolet radiation from electric lighting in the interior is sufficient for the disclosed substrate to degrade the organic residues and to then stretch them into a relatively homogeneous liquid film that is formed on the substrate, if any, which the radiation has rendered hydrophilic. The disclosed coating combines the function of degrading organic residues - by photocatalysis - and removing organic and inorganic residues - hydrophilic / oleophilic nature - under the influence of any liquid, such as condensation. The high efficiency provided by the invention can be at least partly attributed to the combination of the pore lattice allowing good access of contaminants to the titanium oxide particles as well as good diffusion into the coating of light-formed substances on the surface of these particles.

The coatings, on the other hand, have excellent abrasion resistance and durability of photocatalytic activity to such a high degree (see examples below). The invention thus also allows the porosity to be retained after abrasion, whereas one would rather expect the abrasion to result in a thickening of the surface layer and thus eventually a loss of self-cleaning properties.

Moreover, the mesoporous nature of the substrate makes it possible to take into account subsequent impregnation with agents having a deodorizing, antibacterial or any other nature after the formation of the mesoporous structure.

The substrate is substantially transparent, flat or curved, of the glazing type, since it is in this application that the accumulation of contaminants obstructs visibility and is most detrimental, and washing is most needed to ensure its transparency. It can be glazing with macroscopic relief, e.g. with a pyramid pattern with a depth of a few millimeters - patterned glass - or glazing showing much smaller surface irregularities, such as due to the chemical action of hydrofluoric acid - sandblasted, frosted glass.

The coating is formed with the intermediate insertion of a backsheet based on an at least partially oxidized silicon derivative selected from silicon dioxide, substoichiometric silicon oxides, oxynitride, silicon oxynitride, silicon oxynitride. The backsheet proves to be useful when the underlying surface is glass, since migration of alkali metal (sodium) ions from the glass into the coating can under certain conditions degrade the photocatalytic properties; thus the backsheet is a barrier to alkali metals. The backsheet may be of the type described in the above-cited WO 01/32578. It preferably has a refractive index of 1.45-1.80, especially 1.50-1.75, e.g. 1.55-1.68. Such a not too high factor allows, in the case of a transparent substrate of the glass type, to avoid the reflection effect, which may be assessed as unsightly.

This backsheet therefore preferably comprises Si, O, optionally carbon and nitrogen. But it can also contain lesser amounts of materials than silicon, for example metals such as Al, Zn or Zr. The backsheet may be applied by a sol-gel method or by pyrolysis, especially gas phase pyrolysis (CVD). The latter method allows the preparation of SiOxCy or SiO2 coatings quite conveniently, in particular by direct deposition onto a float glass ribbon in the case of glass substrates. It is also possible to carry out the deposition by a vacuum method, e.g. by sputtering a Si target (optionally doped) or a silicon oxide target (e.g. in an oxidizing and / or nitriding reaction atmosphere).

This backsheet preferably has a thickness of at least 5 nm, in particular 10-200 nm, e.g. 80-120 nm.

According to the other advantageous properties of the disclosed substrate:

- the coating with a mesoporous structure is applied by the sol-gel method;

- its thickness is 30-800 nm;

- the titanium oxide incorporated into the mesoporous structure is optionally doped, as explained in WO 97/10185 and WO 97/10186, incorporated herein by reference, and contains nanoparticles with diameters of 0.5-100 nm, especially 1-80 nm, formed by clusters elementary grains or crystallites with diameters of 0.5-10 nm. The term "diameter" is used herein in a broad sense, it is more like a nanoparticle or crystallite size estimate. Its form may be close to a sphere or elongated in shape of a grain of rice, or completely random.

The invention relates to a method for producing a substrate as described above, comprising, in turn:

- producing a liquid composition comprising at least one mesoporous structure forming material precursor of the coating and at least one organic structure forming agent,

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- precipitation of the precursor around the organic structure-forming factor and growth of precursor-derived molecules,

- adding nanoparticles or crystallites to the liquid composition - as defined above - titanium oxide, optionally doped, with a diameter of 0.5-100 nm,

- applying the composition to the surface to be coated,

- removing the organic structure-forming agent, the elementary titanium oxide grains or crystallites being incorporated into the mesoporous structure, substantially maintaining their integrity, and some of them may accumulate into clusters. During such preparation of the substrate, it is possible that the titanium oxide grains or crystallites aggregate and / or grow, especially the smallest of them, depending on the operational conditions (content, pH, temperature, etc.).

In order to produce the substrate, the preparation of the liquid composition preferably comprises:

- preparation of an oxide precursor sol (especially silica),

- sol maturation,

- followed by mixing with a structure-forming agent.

Indeed, the maturation of the sol allows for the initial condensation of the oxide precursor, which favors the cross-linking of the oxide coating on the support surface in large domains. Preferred maturation conditions include keeping the sol at a temperature of 40-60 ° C for 30 minutes - 24 hours, the maturing time being the shorter the higher the temperature.

In this case, the oxide precursor is preferably a hydrolyzable compound such as a halide or an alkoxide, the structure-forming agent is preferably selected from cationic surfactants, preferably of the quaternary ammonium type, such as cetyltrimethylammonium bromide, or non-ionic, such as diblock or triblock copolymers based on e.g. ethylene or propylene oxide.

The invention also discloses the use of substrates, especially those that are substantially transparent, for the production of "self-cleaning" glazing which can simultaneously protect against dirt deposit, against fogging and against condensation. These are glazing for buildings such as double glazing, glazing for vehicles such as windshield, rear window, sunroof, side windows. They can also be glazing in trains, airplanes, ships. It can also be utility glazing, such as aquarium glass, glass for display windows, for greenhouses or in interior furnishings, for street furnishings, for mirrors. They may also be glazings used as displays of the television, computer and telephone screen type. This type of coating can also be used for electrically operated glazing, such as heated or laminated glazing, electrochromic glazing, liquid crystal glazing, electroluminescent glazing, photoelectric glazing.

When the substrate is used as a glazing (based on transparent plastic or glass), one or more thin layers other than the aforementioned backsheet based at least partially on silicon oxide can be inserted between the surface of the carrier and the mesoporous coating. These can be, in particular, electrostatic, thermal (heating with electricity, low-emission, solar protection, etc.), optical (reducing light reflection and / or making the color of the substrate more neutral during reflection, etc.) or a system of anti-reflective layers, etc. of such functional layers used in a known manner for glazing, possibly in the form of a stack, the already cited applications WO 97/10186 and WO 02/02472 are hereby incorporated by reference.

The substrate, apart from its use as glazing, can be made of any architectural material that can be used for the production of partition walls, facades, roofs, floors, indoors or outdoors (metal, wood, stone, cement, concrete, terracotta, ceramic materials, plastered walls, etc.).

The substrate, if it is rather based on mineral insulating wool and fibrous on the matrix of reinforcing glass fibers, can serve as a filter material or serve as a false ceiling, the cleaning of which is inconvenient.

The invention also discloses the use of a woven, non-woven (needle mat, felt, wool, etc.), knitted, braided, block of sintered fibers (known as rigid silica) on a matrix of 1-20 mm diameter fused silica fibers, washed glass. (over 90% of silica), alumina and mullite, for the production of filters for deodorizing, disinfecting industrial wastewater, antibacterial, for disinfecting indoors, cleaning domestic air,

Cleaning the cabins of transport vehicles (car, railroad, airline, floating), cleaning of cigarette smoke, cleaning household appliances (refrigerators, etc.).

The invention is further described by way of non-limiting examples.

Example 1

On the glass in the form of a float glass ribbon, a backing layer was applied on a matrix of silicon oxocarbide marked for the convenience of SiOC (without prior confirmation of the actual oxygen and carbon ratio in the coating) - the glass is a 4mm clear silicon soda-lime glass, sold by Saint Gobain Glass France under the name Planilux. This backing layer is CVD deposited from Si precursors, in particular from a mixture of SiH4 and ethylene, diluted with nitrogen, with a nozzle positioned above and transverse to the float ribbon from a flat glass production line, in a float chamber while the glass is still in a temperature of about 550 to 600 ° C. The resulting coating is approximately 50 nm thick and has a refractive index of approximately 1.55. 10 cm x 10 cm samples were cut from the float glass thus obtained provided with an alkali metal barrier SiOC; these samples were washed, rinsed, dried and subjected to UV treatment with ozone for 45 minutes.

A coating with a mesoporous structure was formed on the bottom layer.

The treatment liquid composition was prepared by stirring in the first step 22.3 ml of tetraethoxysilane, 22.1 ml of absolute alcohol, 9 ml of HCl in deionized water (pH 1.25) until the solution turned clear, then placing the flask in a water bath at a temperature of 60 ° C for 1 hour.

In the second step, the previously prepared cetyltrimethylammonium bromide (CTAB) solution was added to the sol, on the one hand, and the polyoxyethylene-polyoxypropylene block copolymer solution sold by BASF under the registered brand Pluronic PE6800 (molar mass 8000), on the other hand, in such proportions that the molar ratios were equal to CTAB / Si = 0.1, correspondingly PE6800 / Si = 0.01. They were obtained by mixing:

- 0.86 g of CTAB and 10 ml of sol;

- 3.78 g of PE6800, 50 ml of ethanol and 25 ml of sol.

TiO2 nanoparticles, crystallized in the form of anatase with a size of about 50 nm, were added in varying proportions to one or the other of the liquid compositions thus obtained, just before being deposited on the sample. The deposition was performed by the spin coating method in an initial amount of 3 ml per sample. (Other equivalent deposition methods are dip coating, spray coating, laminar coating, roller coating, curtain coating, etc.).

The samples were then subjected to the following annealing treatment:

- 30 minutes at 100 ° C, 2 hours of sleep;

- 15 minutes at a temperature of 150 ° C, 2 hours of sleep;

- 15 minutes at 175 ° C, 2 hours sleep;

- 10 minutes at 200 ° C without rest;

- 3 hours 20 minutes at the temperature of 300 ° C, 1 hour sleep;

- 2 hours 30 minutes at the temperature of 450 ° C, 1 hour of sleep.

The pores of the thus obtained coating were 2-3 nm in size when the CTAB cationic surfactant was used as structure forming agent, however this size was 4-5 nm when PE6800 copolymer was used as structure forming agent.

By SIMS analysis of the mesoporous coating, it was confirmed that the Ti / Si atomic ratio was exactly the same as the composition of the starting liquid composition. The SIMS analysis also confirmed that the nanoparticles were homogeneously distributed in the three dimensions of the coating.

The table below shows the different properties of the coatings during their formation and after 500 cycles of Opel abrasion tests - in the latter case, the marking of the values ​​is in parentheses. The Opel test (Building Standard EN 1096-2 of January 2001) consists of applying 9.4 cm in length to a part of the covered surface - this part is called the track - felt 14 mm in diameter, 10 mm thick and with a density of 22

0.53 g / cm², under a load of 400 g / cm²wherein the felt is moved (50 back and forth movements over the entire path length per minute) combined with a rotation of 6 rpm (1 cycle = 1 back and forth movement).

The thickness E of the coatings in nm was measured from the SIMS profiles and from MEB plates.

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The amount of TiO₂ in g / cm was assessed by X-fluorescence.

The photocatalytic activity was measured as follows:

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1. the test was carried out at about 15 cm² coatings;

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2. the sample was weighed and the substrate thickness was measured by transmission of light TL and haze Td (both in%);

3. deposited by spraying a palmitic acid solution (8 grams of acid per 1 liter of chloroform) at a glass / spray distance of 20 cm onto the vertical substrate for another 3-4 passes;

4. the sample was weighed after deposition of palmitic acid to evaluate the thickness of the deposited palmitic acid in nanometers;

5. light transmission TL and haze Td after deposition were measured;

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6. the changes in haze were measured with the duration of UVA irradiation at an intensity of about 50 W / m²;

7. the time at which haze decreased by 50% was graphically determined;

8. the photocatalytic activity of the coating was assessed on the basis of the rate of palmitic acid decay v (in nm / hour), which was determined as follows:

v (nm / hour) = (palmitic acid thickness (nm)) / (2 x T1 / 2 decay (hours)).

The value of the photocatalytic activity related to the amount of TiO2 in the coating is also given in the table below. Finally, the optical characteristics are given, namely RL light reflection and Td haze (in%).

Sample numbers are given as follows:

- 1 and 2: CTAB as structure forming factor, Ti / Si = 0.1, respectively 0.25;

- 3-7: PE68000 structure-forming factor, Ti / Si = 0.1, suitably 0.25, suitably 0.5, suitably 1, suitably 2.

<td>Attempt no</td><td>E nm</td><td>TiO2 ug / cm²</td><td>v nm / h</td><td>v / TiO2</td><td>Rl%</td><td>Td%</td>

<td> 1</td><td> 214</td><td> 2,2</td><td> 43</td><td> 20</td><td> 6,5</td><td> 0,8</td>

<td></td><td> (220)</td><td> (1,9)</td><td> (21)</td><td> (11)</td><td> (10,2)</td><td> (0,5)</td>

<td> 2</td><td> 208</td><td> 7,5</td><td> 117</td><td> 16</td><td> 8,7</td><td> 1,1</td>

<td></td><td> (247)</td><td> (5,7)</td><td> (114)</td><td> (20)</td><td> (7,9)</td><td> (1,2)</td>

<td> 3</td><td> 274</td><td> 4,7</td><td> 47</td><td> 10</td><td> 10,2</td><td> 0,2</td>

<td></td><td> (209)</td><td> (3,4)</td><td> (31)</td><td> (9)</td><td> (7,8)</td><td> (0,4)</td>

<td> 4</td><td> 308</td><td> 8,0</td><td> 209</td><td> 26</td><td> 12,8</td><td> 0,2</td>

<td></td><td> (299)</td><td> (10,2)</td><td> (123)</td><td> (12)</td><td> (10,2)</td><td> (0,3)</td>

<td> 5</td><td> 336</td><td> 17,3</td><td> 349</td><td> 20</td><td> 9,7</td><td> 0,4</td>

<td></td><td> (294)</td><td> (14,8)</td><td> (181)</td><td> (12)</td><td> (11,4)</td><td> (0,4)</td>

<td> 6</td><td> 454</td><td> 33,3</td><td> 620</td><td> 18</td><td> 9,7</td><td> 0,3</td>

<td></td><td> (184-320)</td><td> (28,7)</td><td> (354)</td><td> (12)</td><td> (14,3)</td><td> (0,8)</td>

<td> 7</td><td> 515</td><td> 66,0</td><td> 684</td><td> 10</td><td> 9,4</td><td> 0,8</td>

<td></td><td> (209-268)</td><td> (46,7)</td><td> (...)</td><td> (...)</td><td> (17,7)</td><td> (1,1)</td>

The thickness of the layers is in the range of 200-500 nm depending on the number of nanoparticles incorporated

TiO₂. After 500 Opel cycles, only the thickest coatings (450 and 500 nm) are compacted more than half their original thickness. Nevertheless, the photoactivity of these coatings has been tested.

The coatings show photoactivity from 43 nm / hour for a coating built with a cationic medium₂ with a surfactant and the lowest concentration of TiO₂ (2.2 μg / cm) to 684 nm / hour for the coating built with the copolymer and the lowest concentration of TiO₂ (66 g / cm²). V / TiO ratio₂ is still at least 9.

It is noted that partial or complete functionality is maintained after 500 Opel cycles, which, moreover, deteriorate the optical properties only of the thickest layers and with the highest concentration of TiO2 (Ti / Si = 1 and 2) - for other values ​​RL and Td remain lower than 11.4 and 1, respectively 2%.

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Trials 3-7 (trials 3'-7 ') were repeated with low UVA irradiation of 1.5 W / m² classic lighting lamp; the respective values ​​of v (nm / hour) and TiO2 are for test No:

- 3 ': 0 and 0;

- 4 ': 0 and 0;

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- 5 ': 13 and 0.75;

- 6 ': 19 and 0.57;

- and 7 ': 28 and 0.42.

The coating substrate is therefore also photoactive under low UVA irradiation to degrade palmitic acid.

Example 2

In addition, discs with a diameter of 47 mm, a thickness of 8 mm and a surface density were impregnated ₂

1000 g / m², from silica fiber needle felts sold by Saint-Gobain Quartz under the name needled-punched Quatrzel mat (7-16 µm fibers) by dipping into the composition of Test No. 6 above, followed by the heat treatment described previously. The weight increase of the thus obtained discs was 10%.

The ability of these discs to decompose methanol in nitrogen gas at a concentration of 350 ppm (v / v) was tested by filtration at a flow rate of 62.5 ml / mm under UV irradiation (190-350 nm).

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With a lighting power of 48 W / cm²the effectiveness, i.e. the amount of methanol broken down, was ₂

100%. At a power of 25 W / cm², was about 96% and still about 58% in as low light as

8.22 W / cm².

Thus, the invention provides a substrate capable of providing the optical transparency properties required for glazing applications and a self-cleaning function that will last under various weather and erosion conditions. The remarkably high degree of photocatalytic function allows also to anticipate the use at night and indoors by using low-intensity radiation, such as that produced by classical lighting or solar transmitted through glazing, as well as applications for decontamination of wastewater or atmosphere, filtration, etc.