Substrate with photocatalytic coating

7§) Holder (s):

© Agent (s): SAINT GOBAIN RECHERCHE.

FR 2 775 696 - A1 © SUBSTRATE WITH PHOTOCATALYTIC COATING.

©) The invention relates to a process for obtaining a substrate (1) provided on at least part of its surface with a coating (3) with photocatalytic properties, crystallized particles (4) of an oxide of a metal A with photocatalytic property being incorporated into said coating using an inorganic binder (5) comprising an oxide of a metal B also exhibiting photocatalytic properties in the crystallized state. According to the process, the coating (3) is deposited from liquid phase dispersions containing:

- on the one hand said crystallized particles (4) of oxide of metal A,

- on the other hand at least one organo-metallic compound precursor of the oxide of metal B of the binder (5), in a relative proportion A / B by weight reduced to the weight of the metals entering respectively in the composition of the oxide A and of the precursor (s) of the oxide B of between 60/40 and 40/60.

The invention also relates to the substrate thus coated and its various applications.

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PHOTOCATALYTIC COATING SUBSTRATE

The present invention relates to substrates provided with a photocatalytic coating, the process for obtaining such a coating and its various applications.

It relates more particularly to coatings comprising semiconductor materials based on metal oxide, in particular on titanium oxide, which are capable, under the effect of radiation of adequate wavelength, of initiating radical reactions. causing oxidation of organic products.

The coatings thus make it possible to confer new functionalities on the materials they cover, in particular anti-fouling, fungicidal, bactericidal properties, possibly combined with hydrophilic, anti-fog, optical properties, etc.

A wide variety of substrates can be envisaged, in particular those used in the field of vehicles or buildings, such as glazing, facade materials, cladding, roofing such as tiles, and any material used in construction. These materials can thus be glass, metal, glass-ceramic, ceramic, cement, bricks, wood, stone or material reconstituted from these natural materials, plastic material, fibrous material of the mineral wool type, in particular. for filtration processes, etc ...

Coatings containing TiO are already known from international patent applications WO97 / 10186 and WO97 / 10185.₂ crystallized anatase with photocatalytic properties, coatings obtained from the thermal decomposition of suitable organometallic precursors and / or from TiO particles₂ “Pre-crystallized” and coated in an inorganic or organic binder.

The object of the invention is therefore to improve these types of coating so that their photocatalytic performance is prolonged over time, in the face of aging conditions which may be encountered in the various applications envisaged.

The aim of the invention is thus to improve these types of coatings, in particular by retaining or increasing their photocatalytic properties while increasing their durability, in particular mechanical or chemical.

The subject of the invention is first of all a process for obtaining a substrate provided on at least part of its surface with a photocatalytic coating, crystallized particles of an oxide of a metal A with photocatalytic properties being incorporated into said coating using an inorganic binder comprising an oxide of a metal B also exhibiting photocatalytic properties in the crystalline state. This process consists in depositing the coating from dispersion (s) in liquid phase containing: Φ on the one hand said crystallized particles of metal oxide A, on the other hand, at least one organometallic compound precursor of oxide of the metal B of the inorganic binder, and this in a relative proportion defined by an A / B ratio of between 60/40 and 40/60. This ratio corresponds to that of the weights of metals A and B entering respectively in the composition of oxide A in the form of particles and in that of the precursor (s) of oxide B.

Advantageously, the conditions for depositing / treating the coating are chosen such that the inorganic binder, and most particularly the oxide of B which forms part of it, is at least partially crystallized in the final coating.

Preferably, the oxides of metals A and B are chosen from at least one of the following oxides: titanium oxide, zinc oxide, tin oxide, tungsten oxide. A particularly preferred embodiment consists in choosing the oxides of A and B both in the form of titanium oxide, the anatase crystalline form of which is highly photocatalytic.

The authors of the present invention succeeded by this process in reconciling two constraints which had hitherto been difficult to reconcile, namely photocatalytic performance and durability, and more precisely they succeeded in prolonging the photocatalytic properties of the coating over time. Indeed, it turned out that the catalytic effect of the coating is probably mainly obtained by the particles which are incorporated therein which are already crystallized, already active on the catalytic level at the start. The temptation is then to increase the quantity in the coating as much as possible. But surprisingly, both excessively high and excessively low amounts of particles have not proved to be appropriate for the desired aim, the adjustment to the ratio discovered by the invention being all the less easy to make than the rate and type of particles of the oxide of A probably influence the morphology of the binder comprising the oxide of B, the evolution of the more or less pronounced photocatalytic character and its maintenance over time of the coating not being linear as a function of a particular parameter.

The process according to the invention has therefore discovered that it is possible to select an A / B ratio within a range which manages to make the optimum photocatalytic activity coincide and to maintain a high level of photocatalytic activity over time. The reasons are not fully explained, at least for the photocatalytic performance of the coating. It can be argued that the inorganic binder also contributes to the activity of the coating. It should also be noted that the coatings obtained tend to have excellent optical properties, in particular a high light transmission and a very low level of blur.

Advantageously, the method according to the invention uses crystallized particles of the oxide of A (in particular TiO₂ predominantly crystallized in the anatase form) in the form of agglomerates of crystallites, preferably with agglomerates of average size of about 5 to 80 nm and of crystallites of average size of about 5 to 20 nm (especially 5 to 10 nm). These sizes correspond to the "diameters" of the agglomerates and crystallites in question, assimilating their shapes to spheres (even if this is not necessarily the case, and that in particular, the agglomerates in question can also be approximately lenticular or in shape. stick shape). As a first approximation, we can consider that we find in the final coating the same agglomerates, having undergone little or no structural or dimensional modification. A detailed description of these particles will be found, for example, in the aforementioned application WO / FR97 / 10185 or in the application WO / FR97 / 02068 of November 18, 1997.

Preferably, the organometallic compound (s) precursor (s) of the oxide of B are chosen from the family of tetraalcoholates of form M (OR)₄, with M the metal in question and R a carbon-based radical of the linear or branched alkyl type, all identical or different, having in particular from 1 to 6 C. Mention may thus be made of titanium tetrabutoxide or tetraisopropylate. They can also be chosen from among the trialcoolates of the MR '(OR) type₃, with R and R 'radicals identical or different of the type from those of the tetraalcoholates mentioned above, or from halides, in particular titanium chlorides. These precursors being highly hydrolyzable and reactive, it is preferred to put them in solution with at least one chelating / stabilizing agent, for example of the β-diketone type such as acetylacetone (2,4-pentanedione), benzoylacetone (1-phenyl- 1,3 butanedione), di-isopropylacetylacetone, or else acetic acid, diethanolamine or compounds of the glycol family such as ethylene glycol or tetraoctylene glycol. The precursor concentration in the solution is then adjusted (at a given dry extract level, for example) by carrying out the appropriate dilutions using organic solvent (s).

The simplest embodiment of the process according to the invention consists in depositing the coating from a dispersion containing the precursor (s) and from a dispersion containing the particles, which is premixed into a dispersion. single before projection onto the substrate or immersion of the latter therein.

A first type of deposition technique is called "hot" deposition, that is to say that during the dispersion / substrate contact, the latter is at a temperature high enough to allow thermal decomposition of the precursor (s): this is the technique of the liquid phase pyrolysis type.

A second type of technique is called "cold" deposition, that is to say that during the dispersion / substrate contact, the latter is at room temperature or at least at a temperature too low to cause the decomposition of the substrate. (Des) precursor (s): these are the techniques of the sol-gel type, with a deposition method of the “soaked”, “cell-coating”, laminar coating or “spraycoating” type.

A heat treatment subsequent to the phase of placing the dispersion / substrate in contact is necessary in the case of “cold” deposits, to harden the coating and ensure complete decomposition of the precursors. But it also proves to be advantageous in the case of “hot” deposits, since it can improve the cohesion of the coating and promote at least partial crystallization of the binder resulting from the decomposition of the precursor (s). This treatment is carried out in particular at more than 500 ° C, in particular around 500 to 550 ° C; more particularly when the substrate is able to withstand this type of treatment, which is the case with substrates with a glass, ceramic or glass-ceramic matrix.

A subject of the invention is also a substrate provided on at least part of its surface with a photocatalytic coating incorporating crystallized particles of an oxide of a metal A with photocatalytic properties using at least one inorganic binder. partially crystallized comprising an oxide of a metal B also exhibiting photocatalytic properties in the crystallized state, in particular a substrate obtained according to the method described above. It is characterized by a high porosity, in particular greater than 40% and preferably between 45 and 65%. This porosity could be calculated indirectly, by measuring the index of the layer, in comparison with what it should be if the material were totally dense. This indirect method is fairly representative of the porosity and of the surface morphology of the layer, since the index measurement also takes into account, at least in part, the level of surface roughness of the layer.

(Other indirect methods also exist, in particular those consisting in measuring the weight of the coating deposited per unit area of ​​the substrate, reduced to a given coating thickness).

In fact, this high porosity has many advantages. First of all, it makes it possible to drop the refractive index of the material, to modulate its optical appearance. In the case of a TiO-based coating₂ (i.e. with crystallized TiO particles₂ mainly anatase and a TiO-based binder₂), dropping its index to values ​​of at most 2, in particular of the order of 1.4 to 1.8, makes it possible to very strongly attenuate its well-known reflecting aspect.

Furthermore, the porosity of the coating is linked to a high surface roughness, hence a high developed surface area of ​​the coating promoting its photocatalytic activity.

Finally, this roughness, which is probably in two different orders as described in the aforementioned patent WO / FR97 / 02068, gives the coating a reinforced and durable hydrophilic character, which gives it marked anti-rain and anti-fog properties (by spreading of water drops in an invisible film), and promotes the elimination of mineral soiling by rainwater entrainment. Surprisingly, this high porosity did not lead to excessive mechanical embrittlement of the coating.

A subject of the invention is also a substrate provided on at least part of its surface with a coating with photocatalytic properties incorporating crystallized particles of an oxide of a metal A with photocatalytic properties using a binder at less partially crystallized, comprising an oxide of a metal B also exhibiting photocatalytic properties in the crystallized state, in particular obtained according to the method described above, and which is characterized by a relative proportion A / B between 60/40 and 40/60, by weight reduced to the weight of the metals entering respectively in the composition of the particles of the oxide of A and in the composition of the oxide of B mineral binder.

The coating according to the invention, whether it is obtained by the process described above, and / or whether it complies with the coatings whose intrinsic characteristics have been described above, advantageously has the following structure (very particularly in the case of where the oxides of A and B are both based on TiO₂): crystallized particles with dimensions between 5 and 80 nm made up of agglomerates of crystallites with dimensions between 5 and 20 nm (with the conventions described above), and an inorganic binder at least partially in the form of grains which come to be placed around crystallized particles, in the inter-particle interstices, and which have an average size of between 5 and 25 nm, preferably 10 to 20 nm. These “grains” of approximately spherical shape are not totally crystallized, however probably partially crystallized on a very small scale which is difficult to measure and thus “coat” the particles and bind them together.

The substrates provided with such coatings can comprise a transparent material of the glass type, plastic material, in particular to form part of glazing fitted to buildings or vehicles, or of screens of apparatuses of the television or computer type, of touch screens for example.

It is thus advantageous to incorporate a transparent substrate provided with the coating of the invention in a structure of insulating multiple glazing, either so that the coating either on an internal face of the glazing, or on an external face of the glazing. It may be conventional insulating glazing with one or more interleaving gas sheets, for example of the type marketed by Saint-Gobain Vitrage under the name BIVER or CLIMALIT D, CONTRATHERM, CONTRASONOR, CONTRARISC, or those so-called “under vacuum” where the intermediate gas blade is replaced by vacuum, as described for example in patent EP-645,516. In the latter case, in particular, it is particularly advantageous to have the coating on the outer face, on the face of the insulating glazing facing outward, to prevent the formation of fogging thanks to its hydrophilic character.

The coating of the invention is also advantageous for glass walls of freezers / refrigerators. In fact, many materials can serve as substrates for the coating according to the invention, for example materials made of metal, ceramic, plastic, cement and all the materials mentioned above used in architecture, for applications as facade material, cladding, roofing such as tiles.

The coating can also be deposited on fibrous materials of the thermal and / or acoustic insulating mineral wool type, or else fibers of the reinforcing textile yarn type, these fibrous materials can find application in filtration processes for example: it is possible to thus exploiting the anti-fouling, bactericidal, fungicidal and anti-fog properties of the coating of the invention as required.

Other details and advantageous characteristics of the invention emerge from the following description of non-limiting embodiments, with the aid of the following figures:

□ FIG. 1: a very schematic representation of the structure of a photocatalytic coating according to the invention, □ FIG. 2: an image obtained by scanning electron microscopy (SEM) of the surface of a photocatalytic coating according to the invention.

All the following examples relate to the deposition of a so-called “anti-fouling” coating 3 essentially based on titanium oxide on a transparent substrate 1.

Substrate 1 is 15 x 40 cm clear soda-silicate flat glass² and 4 mm thick. It goes without saying that the invention is not limited to this specific type of glass. The glass may also not be flat, but curved.

Between the coating 3 and the substrate 1, there is an (optional) thin layer 2 based on silicon oxycarbide denoted SiOC in order to constitute an alkali diffusion barrier which is detrimental to the photocatalytic property of the coating, and / or a layer with an optical function deposited for example in a known manner by a vapor phase pyrolysis (CVD) technique and with a thickness of approximately 50 nm.

Two different “cold” deposition processes were used, namely deposition by soaking in “cell-coating” with a bath emptying speed of the order of 5 to 30 cm / minute, and deposition by “spray”. -coating ”, that is to say by cold liquid spraying. These well-known techniques are detailed in the patent applications referenced above, to which reference may be made.

The deposits are made from a dispersion mixing two initial solutions / dispersions 1 and 2:

solution 1: it is the solution containing the organometallic precursor of the mineral binder based on TiO₂. It is titanium isopropylate Ti (O CH (CH₃)₂) 4, stabilized with acetylacetonate CH₃-CO-CH₂-CO-CH₃, in solution in ethanol, dispersion 2: this is the liquid phase in ethylene glycol containing the crystallized photocatalytic particles, with the following characteristics:

* -► specific particle surface: 350 m²/ g particle sizes: 45 nm sizes of the crystallites which constitute the particles: 7 nm crystal phase: more than 80% anatase

The composition of the dispersion resulting from the mixture of solution 1 and dispersion 2 is adjusted to obtain the ratio Ti₍₂₎/ Ti₍₁₎ desired, i.e. the ratio of the weight of titanium (2) from the particles of dispersion 2 to the weight of titanium (1) from the precursors of solution 1. (By convention, the ratio can also be that of the weight of titanium oxide originating from the particles on the weight of titanium oxide originating from the metallic precursor, assuming that 100% of the precursor is converted into oxide: this amounts to the same).

Examples 1 to 7 relate to a deposition by soaking in cell-coating, under comparable deposition conditions, that is to say with the same rate of emptying of the bath, and the same titanium concentration (namely 3% of dry extract, converted to weight of oxide) from the precursor in solution 1.

At the end of the deposition, the substrates are subjected to a heat treatment at around 450-500 ° C. for at least 30 minutes.

Table 1 below groups together for each of them:

the Ti report₍₂₎/ Ti₍₁₎ explained above, without unit, the thickness (e) of the coating (3) in nm, the light transmission value T_L in%, measured according to illuminant D₆₅, the “blur” value in%, measured by the ratio of the diffuse transmission to the integrated light transmission over the entire visible range.

TABLE 1

<td></td><td>Ti₍₂₎/ Ti₍₁₎</td><td>e (nm)</td><td>T_L (%)</td><td>blurry (%)</td>

<td>EXAMPLE 1</td><td> 0/100</td><td> 20</td><td> 88,5</td><td> 0,88</td>

<td>EXAMPLE 2</td><td> 20/80</td><td>20 to 30</td><td> 89,6</td><td> 0,27</td>

<td>EXAMPLE 3</td><td> 40/60</td><td>40 to 50</td><td> 89,5</td><td> 0,76</td>

<td>EXAMPLE 4</td><td> 50/50</td><td>40 to 60</td><td> 90,2</td><td> 0,50</td>

<td>EXAMPLE 5</td><td> 60/40</td><td> 60</td><td> 90,5</td><td> 0,61</td>

<td>EXAMPLE 6</td><td> 80/20</td><td>30 to 40</td><td> 89,7</td><td> 0,44</td>

<td>EXAMPLE 7</td><td> 100/0</td><td>30 to 40</td><td> 90,3</td><td> 1</td>

Example 8 was produced from the dispersion in accordance with that used for Example 4, but deposited on the substrate by cold spraying, by a so-called “airless” spray nozzle at a pressure of 0.7 bar (0 , 7.10⁵Pa). The layer obtained, after heat treatment at around 450-500 ° C for at least 30 minutes, has a thickness of about 35 to 60 nm, with a value of T_L of 88.6% and blur of 0.6% with the same conventions as in Table 1.

Examples 1 to 8 above were evaluated in terms of photocatalytic activity, before and then after a treatment aimed at simulating accelerated aging of the coating.

The photocatalytic activity is measured as follows:

O - test carried out on about 15 cm² coating, ^ * © - weighing the sample and measuring the thickness of the substrate, the T_Land blur.

- spray deposit of a solution of palmitic acid (8g of acid for 11 of chloroform) glass / spray distance 20 cm, vertical substrate, 3 to 4 successive passages,> - *> © - weighing of the sample after deposition of palmitic acid to evaluate the thickness of acid deposited in nanometers, © - measurement of haze and T_L after deposition, © - measurement of the variation of the haze as a function of the irradiation time under UVA ("2.5W / m²),

- graphical determination of the time after which the blur has decreased by 50%: time called T_1/2 (disappearance), © - evaluation of the photocatalytic activity of the coating at rate of disappearance v (in nm / h) defined by:

v (nm / h) = [thickness of palmitic acid (nm)] / [2 xt_1/2 (disappearance) (h)]

The aging of the coatings consists of subjecting them to mechanical abrasion as follows:

sample size 7 cm x 15 cm applied load: 600 grams surface of the abrasion felt: 1.5 cm²n cycles (1 cycle = 1 round trip of the felt carrying arm and load), with n = 200 and 500.

Table 2 below groups together for each of the examples:

the speed of disappearance v1 before abrasion, the speed of disappearance v2 after 200 cycles, ** the speed of disappearance v3 after 500 cycles

TABLE 2

<td></td><td>V1 (0 cycle)</td><td>V2 (200 cycles)</td><td>V3 (500 cycles)</td>

<td>EXAMPLE 1</td><td> 20</td><td> 10</td><td> 0</td>

<td>EXAMPLE 2</td><td> 40</td><td> 5-10</td><td> 0</td>

<td>EXAMPLE 3</td><td> 35</td><td> -</td><td> « 10</td>

<td>EXAMPLE 4</td><td> 70</td><td> 10-20</td><td> « 10</td>

<td>EXAMPLE 5</td><td> 35</td><td> -</td><td> «5</td>

<td>EXAMPLE 6</td><td> 20</td><td> 1-2</td><td> 0</td>

<td>EXAMPLE 7</td><td> 20</td><td> 0</td><td> 0</td>

<td>EXAMPLE 8</td><td> 40</td><td> -</td><td> 7</td>

Moreover, the analyzes showed that the coatings of Examples 3, 4 and 5 exhibited a structure probably close to that, very simplified, represented in FIG. 1 representing the glass substrate 1, the SiOC layer 2 and the coating 3. This coating comprises the particles, aggregates of crystallites 5 between which grains 4 of TiO come to agglomerate₂amorphous or slightly crystallized which form the mineral binder of the coating.

FIG. 2, relating more precisely to Example 4 is a photograph obtained by scanning electron microscopy giving an indication of the surface appearance of Example 4: a fairly rough surface, allowing the coating to provide a surface significant development.

Note that Example 4 has a refractive index of about 1.65. As a first approximation, we can therefore consider, knowing that the refractive index of TiO₂ "Solid" is 2.4, that the porosity of the coating is about (2.4-1.65) / (2.4-1), that is, about 54%. The coating according to Example 4 also exhibits a strong hydrophilicity: exposed to UVA rays for 20 minutes to activate it, it is placed in the dark and the contact angle with water φ is measured regularly: this angle of contact remains below 10 ° for at least 20 days in the dark.

From these data can be drawn the following conclusions: these are examples 3, 4, 5 and 8 and, in particular example 5 where the ratio Ti₍₂₎/ Ti₍₁₎ is 50/50 which combines all the desired properties, namely:

** a high T_L, a low blur, a refractive index less than 2, giving the coating a very favorable optical appearance, an optimal photocatalytic activity, which is always present even after mechanical attack, which proves the durability of the coatings, and which makes it possible to use these coatings in real conditions, for example on exterior glazing, while having an acceptable “lifespan”. These are in fact the only examples produced which still exhibit a photocatalytic activity, even moderate, after 500 abrasion cycles.

It goes without saying that the invention is not limited to these precise examples. It is in particular within the framework of the invention to further improve the photocatalytic activity of the particles 5 by doping them, by introducing the dopants into the crystal lattice or by covering the particles with said dopants, of the Fe, Cu, Ru, Mo type. , Bi, Ta, Nb, Co, Ni, Va, ... as described in the aforementioned patent WO97 / 10185.

In the context of the invention, it is also possible, within the framework of the invention, to add to the mineral binder other oxides which are not or not very photocatalytic in the crystallized state, for example by adding to the dispersion of the precursors of other oxides of the SiO type.₂, such as TEOS tetraethoxysilane.