Substrate with photocatalytic coating and process for preparing thereof

Technical field

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

In particular, the present invention relates to coatings consisting of semiconductor materials based on metal oxide, in particular titanium dioxide, which are capable of initiating radical reactions causing oxidation of organic products under the influence of radiation at a suitable wavelength.

BACKGROUND OF THE INVENTION

Coatings of this kind make it possible to impart new functional properties to the materials they cover, in particular stain resistance, fungicidal and bactericidal properties, where these are optionally combined with hydrophilic, fogging, optical properties, etc.

In this context, a very wide range of substrates can be envisaged, particularly those used in the automotive or construction industry, such as glazing products, masonry, wall and floor coverings, such as tiles, tiles, slabs and tiles , and in particular any material used in construction. Thus, these materials may be made of glass, metal, glass ceramics, ceramics, cement bricks, wood, stone or materials reconstituted from these natural materials, plastics or mineral wool type fibrous materials, particularly useful for filtration processes, etc.

These materials may also be classified as transparent materials, particularly used for glazing, such as glass substrates or substrates made of flexible or rigid plastics, for example substrates made of polyester or acrylate, for example polymethyl methacrylate (PMMA). The substrates may also be classified in the category of non-porous or slightly porous materials (glass) or in the category of (relatively) porous materials such as tiles and ceramics.

Substrates may also be considered as single-species materials, such as glass substrates, or as comprising an assembly or layers of materials, such as masonry, which is coated with a plaster type.

Coatings containing crystalline TiC2 with photocatalytic properties are already known from published international patent applications WO 97/10186 and WO 97/10185, where these coatings are obtained by thermal decomposition of suitable organometallic precursors and / or from pre-crystallized T1O2 particles embedded in mineral or organic binder.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to improve these types of coatings so that their photocatalytic efficiency is prolonged by exposure to aging conditions such as may be encountered in a variety of intended uses.

It is therefore an object of the invention to improve these types of coatings, in particular by maintaining or enhancing their photocatalytic properties while increasing their durability, in particular their mechanical or chemical durability.

In particular, the present invention provides a method of obtaining a substrate provided with at least a portion of its surface with a photocatalytic coating of crystallized metal oxide particles A having photocatalytic properties and incorporated into said coating by means of a mineral binder comprising at least one metal oxide B which also has a crystalline state photocatalytic properties. Optionally, the binder may also comprise at least one metal oxide M which does not have photocatalytic properties and / or at least one silicon dioxide of the SiO2 type. The method comprises depositing a coating from a single liquid phase dispersion or from multiple such dispersions comprising:

on the one hand, said crystallized metal oxide particles A;

on the one hand, at least one metal oxide precursor compound B of a mineral binder and optionally a metal oxide precursor compound M and / or a Si compound in relative proportions defined by the ratio A / (B + M + Si) between 60/40 and 40/60. This ratio corresponds, on the one hand, to the weight ratios of metal A and, on the other hand, to the weight of metal B and optionally metal M and silicon Si optionally contained in the particulate oxide composition A and in the precursor composition (s).

The coating / treatment conditions are preferably selected such that the mineral binder, and in particular the oxide B, which is part of it, is at least partially crystallized in the final coating.

The metal oxides A and B are preferably selected from at least one of the following oxides: titanium dioxide, zinc oxide, tin oxide and tungsten oxide. One particularly preferred embodiment consists in selecting both oxides A and B in the form of titanium dioxide, whose crystalline anatase form is highly photocatalytic.

Type M oxides devoid of intrinsic photocatalytic properties are, for example, aluminum oxide and zirconium oxide.

According to the present invention, a compromise of two hitherto difficult to reconcile barriers, namely photocatalytic performance and durability of this factor, has been successfully compromised, and in particular, success in the time extension of the photocatalytic properties of the coating has been achieved. These results have been achieved because it has been shown that the catalytic effect of the coating is likely to be predominantly due to the particles introduced into it, when these particles have crystallized and are active from a catalytic point of view from the outset. Therefore, efforts have been made to maximize the amount of particles in the coating. Surprisingly, however, it has been shown that both excessively high and excessively small amounts of particles are unsuitable for the purposes of achieving both of the aforementioned desired objectives (namely photocatalytic properties and sufficient persistence of this factor), and adjusting the ratio in cases where the amount and type of oxide A particles are likely to affect the morphology of the B-containing binder, and when the change in the relatively pronounced photocatalytic nature of the coating and its temporal retention are: · · · ···················· Are not linear functions or do not represent a parameter of these properties.

The process of the invention has therefore shown that it is possible to select an A / (B + M + Si) ratio within a range that allows the best compromise between a satisfactory level of photocatalytic activity and maintaining this high level of photocatalytic activity over time. The reasons for this behavior are not fully explained, at least as to the photocatalytic performance of the coating. It may be appreciated that the mineral binder also contributes to the activity of the coating. Furthermore, it should be noted that the coatings obtained tend to have excellent optical properties, in particular high light transmission and very low haze levels.

The precursors for oxide B mentioned above and optionally the precursors for oxide or oxides M are preferably organometallic compounds which are capable of decomposing to oxide by a suitable treatment, in particular a heat treatment. With regard to the precursors for the Si compound, in particular the SiCl 2 precursor, a compound from the group of silicon alkoxides (silanes) can be used.

The process according to the invention advantageously uses crystalline particles of oxide A (especially T10O crystallized predominantly in the form of anatase) in the form of crystallite agglomerates, preferably agglomerates with an average size of about 5 to 80 nm, and crystallites with an average size of about 5 to 20 nm (especially 1 to 10 nm) ) in a liquid phase dispersion, in particular a colloidal suspension in an aqueous medium or in a dispersion in at least one organic solvent. These sizes correspond to the diameters of the agglomerates and crystallites that approximate their shapes to the beads (although this is not necessarily the case, since the agglomerates in question are not necessarily the same; they may also be lenticular or rod-shaped). Rather than talking about crystallite agglomerates, the correct terminology may actually be used, namely that agglomerates are particles and crystallites are what can be termed the crystalline coherence domain. In the first approximation, the same agglomerates are found in the final coating where they have undergone little or no structural or dimensional change. In fact, it has been observed that in the case where the process for obtaining the photocatalytic coating comprises a heat treatment (explained in detail below), this treatment results in structurally altered particles with a considerably increased crystallite size. For example, in cases where TiO2 crystallites initially have a size of about 5 to 10 nm, they generally have about 10 to 20 nm in the final coating; their size has increased approximately twice (by a factor of 1.5 to 2.5). A detailed description of these particles can be found, for example, in the above-mentioned published international patent application WO 97/10185, or in published international patent application WO / FR97 / 02068 of November 18, 1987, published under WO 98/23549, or in FR- 2,681,534.

The organometallic compound (s) as a precursor of oxide B and optionally oxide M is preferably selected from the group of tetraalkoxides of formula M (OR) 2, where M is the metal concerned and R is a linear or branched alkyl group-containing carbon group which are all the same or different and in particular have 1 to 6 carbon atoms. Titanium tetrabutoxide or titanium tetraisopropoxide may be mentioned in this context. It is also possible to select these precursors from the group of trialcoxides of the type MR (OR), where R and R 'are residues which are identical or different from the above-mentioned tetraalkoxides or with the abovementioned tetraalkoxides.

» · · 1

Halides, especially titanium chlorides. Since these precursors are readily hydrolyzable and highly reactive, it is preferable to dissolve them with at least one chelating and / or stabilizing agent, for example of the β-diketone type, such as acetylacetone (2,4-pentanedione), benzoylacetone (1-phenyl-1). (3-butanedione) and diisopropylacetylacetone, or further acetic acid, diethanolamine, or glycol compounds such as ethylene glycol or tetraoctylene glycol. The concentration of the precursor in solution (e.g., for a given solids content) is adjusted by appropriate dilution with one or more organic solvents.

According to a first variant of the process according to the invention, the mineral binder of the coating contains only the metal oxide B, so that the aforementioned A / (B + M + Si) ratio is simplified to the A / B ratio.

According to a second variant of the process according to the invention, the mineral binder comprises a metal oxide B of the TiCl 2 type and a silicon compound of the SiO 2 type so that the ratio A / (B + M + Si) is changed to the ratio A / (B + Si).

The simplest method of carrying out the process of the invention is to apply a coating of the dispersion containing the precursor (s) and the dispersion containing particles that have been premixed to a single dispersion prior to spraying onto the substrate, or before the substrate is immersed in the single dispersion. a plurality of separate dispersions, in particular two dispersions, without premixing.

The first type of deposition technology is called hot deposition, which means that during contact of the dispersion with the substrate, the substrate is at a temperature sufficiently high to allow thermal decomposition of the precursor (s), which method represents liquid phase pyrolysis technology.

The second kind of deposition technology is called cold deposition, which means that during contact of the dispersion with the substrate, the substrate has a room temperature or at least a temperature that is too low to cause decomposition of the precursor (s); these methods are referred to as sol-gel technologies and are used by dipping, electrolytic, laminar, or spray deposition methods.

In the case of the application of the cold deposition technique, after the phase of contact of the dispersion with the substrate, a heat treatment is necessary in order to cure the coating and to ensure complete distribution of the precursors. However, this also proves advantageous in the case of hot deposition technology, since it can improve the cohesiveness 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 at a temperature of at least 400 ° C, for example above 450 ° C, in particular in the temperature range of 550 ° C to 500 ° C, especially where the substrate is able to withstand this treatment, which is the case with substrates. with glass, ceramic or glass ceramic matrix.

The invention also provides a substrate provided with at least a portion of its surface with a photocatalytic coating containing crystalline metal oxide particles

And with photocatalytic properties obtained using at least partially crystalline mineral binder,

<img file="CZ20003244A3_D0001.tif" />

containing a metal oxide B which also has photocatalytic properties in the crystalline state, in particular a substrate obtained as described above. This substrate is characterized by a high porosity, particularly higher than 40% and preferably between 45 and 65%. This porosity can be determined indirectly by measuring the refractive index of the layer and comparing this index to that of a completely dense material. This indirect method represents a completely representative method for determining the porosity and morphology of the layer surface, since the refractive index measurement also takes into account at least partially the degree of unevenness of the layer surface.

(There are also other indirect methods, in particular methods of measuring the weight of the coating applied per unit area of ​​substrate relative to a given coating thickness.)

This high porosity actually has many advantages. First, it allows to reduce the refractive index of the material and change its optical appearance. In the case of a T1O2-based coating (i.e., T1O2 particles crystallized mainly as anatase and a T1O2-based binder, optionally combined with S1O2), a reduction in the refractive index to a value of at most 2, in particular to about 1.4 to 1.8 and preferably to about 1 7 to 1.8 allows to greatly reduce its well-known appearance in reflection.

In addition, the porosity of the coating is associated with a high surface roughness, i.e. a highly structured surface area of ​​the coating, which increases its photocatalytic activity.

Finally, this roughness, which is probably of two different types, as described in the above-mentioned published international patent application WO 98/23459, imparts a coating to the coating.

It has an increased and lasting hydrophilic character, thus contributing to its distinctive anti-rain and anti-fog properties (water droplets leak into an invisible film) and support the removal of mineral impurities by carrying them with rainwater. Surprisingly, this high porosity does not lead to excessively high thinning of the coating from a mechanical point of view.

The present invention also provides a substrate having at least a portion of its surface coated with photocatalytic properties comprising crystallized metal oxide particles A having photocatalytic properties using at least partially crystallized binder comprising at least one metal oxide B which also has photocatalytic properties in a crystallized state, and optionally at least one photocatalytic-free metal oxide M and / or a silica-type silicon compound, in particular one obtained as described above. This substrate is characterized by a relative weight ratio of A / (B + M + Si) of between 60/40 and 40/60, calculated on the weight of the metals (and optionally Si), optionally contained in the oxide particle composition A and in the mineral binder oxide composition B , and optionally an M oxide and a Si compound.

In this context, it should be noted that the substrate of the present invention may have a certain porosity, for example when it is a tile or fibrous appearance (for example, insulating mineral wool). In the context of the present invention, where it is stated that a substrate is provided with a photocatalytic coating, it is understood that the coating is deposited on its surface, but it can also be impregnated to a certain depth when the substrate is porous or fibrous. This is why the amount of fc · fcfc fcfcfc fcfc fcfc fc fcfc fc fcfc fcfcfc The exposed coating may express its thickness on the substrate if it is non-porous, for example if it is a glass substrate, or by the amount of material per unit area, usually when the substrate has a certain porosity.

The coating according to the invention, obtained either by the process described above and / or corresponding to coatings whose intrinsic characteristics have been described above, preferably has the following structure (especially when oxides A and B are both based on TiCl 2): crystalline particles between 5 and 80 nm in size with crystalline coherence domains between 5 and 20 nm (according to the convention described above) and a mineral binder at least partially in the form of grains surrounding the crystalline particles in the particle gaps and having a mean particle size of between 5 and 80 nm and 25 nm, preferably between 10 and 20 nm. These grains of approximately spherical shape are not fully crystallized, although they are probably partially crystallized in a very small size, which are difficult to measure and thus encapsulate the particles and join them together.

According to a preferred embodiment, the substrate according to the invention is provided with a photocatalytic coating according to the invention which comprises T102 particles substantially in the form of anatase and a mineral binder comprising a combination of partially crystallized T102 and SiCl2. The coating preferably has a refractive index of at most 2, in particular between 1.5 and 1.9 or between 1.6 and 1.9 or between 1.6 and 1.8.

According to one embodiment of the invention, at least one layer is inserted between the substrate and the photocatalytic coating, or layers that may have different functions (optical function, barrier function to substances capable of migrating from the substrate, for example alkali metals) are inserted.

<img file="CZ20003244A3_D0002.tif" />

antistatic function, adhesive layer function, etc.)

In this context, the layers may be based on Si compounds such as Si, SiO 2, SiON, SiOC and Si 3 N 4, or optionally doped metal oxides (F: SnO 2, SbcSnCl 2, etc.).

Substrates provided with such coatings have already been mentioned in the introduction to this description. They may include transparent materials of the glass or plastic type, in particular for forming part of the glazing provided with buildings or vehicles, or screens for televisions or computers, for example screens of touch or any laminated or monolithic glazing (ie containing only a single glass pane or a single plastic plate) . It is also advantageous in the context of the present invention to incorporate a transparent substrate coated with the present invention into the multiple insulating glazing structure either so that the coating is situated on the inside of the glazing or on the outside of the glazing. In this case, it may be a conventional insulating glazing having one or more gas interlayers, for example of the type supplied by Saint Gobain Vitrage under the names BIVER or CLIMALIT D, CONTRATHERM, CONTRASONOR, CONTRARISC, or vacuum glazing types with gas the intermediate layer replaced by vacuum, as described, for example, in European patent EP-645 516. In the latter case in particular, it is advantageous to place the coating on the outside, that is to say the side of the insulating glazing which faces outwards, in order to prevent the formation of fog by its hydrophilic nature.

The coating according to the invention is also advantageous for glazed walls of freezers. Indeed, many materials, such as metal, ceramics, plastics or cementitious materials, and all of the above-mentioned materials used in architecture as masonry, cladding or roofing materials such as tiles and tiles can be used for the coatings of the invention. They may also be materials provided with interior and exterior floors or walls of apartments, such as slabs or tiles.

It is also possible to apply mineral wool-like fibrous materials for thermal and / or acoustic insulation or to fibers of the type of textile yarns used as reinforcement, where these fibrous materials can be used, for example, in filtration: thus, non-soiling, bactericidal , the fungicidal and antiseptic properties of the coatings according to the invention.

The present invention also relates to a liquid phase dispersion which has been particularly described above and which can be used for the production of the photocatalytic coating according to the invention. In particular, said dispersion comprises a solvent selected from the group consisting of water, ethylene glycol, ethanol, propylene glycol, and mixtures thereof.

The nature of the crystalline phase of the titanium dioxide particles in the dispersion is preferably predominantly a crystalline form of anatase. It predominantly means that the content of anatase titanium dioxide particles in the coating is greater than 50% by weight. The coating particles preferably have an anatase content of greater than 80%. The extent of crystallization and the nature of the crystalline phase are measured by X-ray diffraction.

The dispersions according to the invention are usually obtained by mixing a dispersion of titanium dioxide particles with precursor solutions.

4 4

4 4 •4 4444

444 4*4

44

4 4

4 4

44 and / or silicone compounds. Depending on the nature of the compounds used, it is also possible to add additives such as cosolvents, surfactants or stabilizers during this mixing. Stirring can also be aided by ultrasonic mixing of the dispersion.

DETAILED DESCRIPTION OF THE INVENTION

Further details and advantageous features of the present invention will become apparent from the following description and examples, which, however, are not intended to limit the scope of the present invention in any way, with reference to the accompanying drawings.

Description of attached pictures

Figures 1 and 2 show a photocatalytic coated substrate according to the present invention, showing in each figure:

Figure 1: a simplified schematic representation of the structure of the photocatalytic coating according to the invention;

Figure 2: scanning electron microscopy (SEM) photograph of the surface of the photocatalytic coating according to the invention.

A first set of examples relates to the deposition of a so-called non-dirty coating 3 based essentially on titanium dioxide on a transparent substrate 1.

The substrate 1 is made of clear flat silica

About soda-lime glass with an area of ​​15 x 40 cm and thickness of 4 mm. It goes without saying that the invention is not limited to this specific species

<img file="CZ20003244A3_D0003.tif" />

<img file="CZ20003244A3_D0004.tif" />

«• to to • to. &lt;

• To Glass To Glass To Glass To Glass To Glass To Glass. In addition, the glass need not be flat, but may be curved.

Optionally, between the coating 3 and the substrate 1 there may be a silicon oxycarbide thin film 2 of the formula SiOC to form an alkali metal diffusion barrier that is deleterious to the photocatalytic properties of the coating, and / or an optical-functional layer, e.g. vapor deposition (CVD), about 50 nm thick.

Examples 1 to 7

In this context, two different cold deposition methods have been used, namely dip coating in a cuvette at a bath runoff rate of about 5 to 30 cm / minute and spraying, i.e., spraying a cold liquid. These well known technologies are explained in detail in the patent applications cited above.

The coatings are deposited from the dispersion obtained by mixing two starting solutions / dispersions 1 and 2:

solution 1: a solution containing an organometallic precursor of a mineral binder based on TiCl 2. It is titanium isopropylate Ti (OCH (CH3) 2) 4, stabilized with CH3-CO-CH2-CO-CH3 acetylacetonate in ethanol;

- dispersion 2: the liquid phase of ethylene glycol containing photocatalytic crystalline particles having the following characteristics:

· · · ·

<img file="CZ20003244A3_D0005.tif" />

O

-> specific particle surface area: 350 m / g

-> particle size

-> size of the crystallites that form particles nm nm

-> crystalline phase: more than 80% of anatase

The dispersion composition obtained by mixing solution 1 with dispersion 2 is adjusted to obtain the desired ratio

Ti

<img file="CZ20003244A3_D0006.tif" />

originating from the particles in dispersion 2 to the weight of titanium (1) originating from the precursor in solution 1 (usually this ratio may also be the ratio of the weight of particulate titanium dioxide to the weight of titanium dioxide originating from the metal precursor, provided 100% of the precursor is converted to oxide, which leads to the same result).

Examples 1 to 7 relate to deposition in cuvettes under comparable deposition conditions, i.e. at the same bath runoff rate (6 cm / min) and at the same titanium concentration (namely, a solids content of 3% by weight of the oxide) originating from the precursor in solution 1.

After application, the substrates are heat treated at about 450-500 ° C for at least 30 minutes.

Table 1 below gives for each example:

- the Ti / Ti (2) ratio explained above is a dimensionless value;

• · • »

- the thickness (e) of the coating (3) in nm;

- the light transmittance value T v in%, measured by the light source D55;

- a haze value in%, expressed as the ratio of diffuse transmittance to light transmittance integrated overall in the visible area.

TABLE 1

<td>Example</td><td>^Ti(l) /^Ti(2)</td><td>e (nm)</td><td>T_L (%)</td><td>Turbidity (%)</td>

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

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

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

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

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

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

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

Example 8

The sample of Example 8 was made from a dispersion as in Example 4, but applied to the substrate by cold spraying using a so-called airless spray nozzle with a pressure of 0.07 bar (0.7 MPa). The obtained layer after heat treatment at a temperature of about 450-500 ° C for at least 30 minutes had a thickness of about 35-60 nm, a T value of 88.6% and a haze value of 0.6% under the same conditions as in Table 1.

The above examples 1 to 8 were evaluated for photocatalytic activity before and after treatment, aimed at simulating accelerated coating aging.

Photocatalytic activity was measured as follows:

O

-> 1. the test was carried out on approximately 15 cm of coating; -> 2. the sample was weighed and the substrate thickness was measured,

Τγ and turbidity;

-> 3. a solution of palmitic acid (8 grams of acid per liter of chloroform) was sprayed at a nozzle-to-glass distance of 20 centimeters at a vertical position of the substrate in 3 to 4 successive procedures;

> 4. after palmitic acid deposition, the sample was weighed to determine the deposition of the acid in nm;

Turbidity and T ^ were measured after application;

-> 6. Measurement of haze change as a function of UV irradiation time (= 30 V / m ^);

-> 7. graphical determination of the time after which the turbidity decreased by 50%: this time is denoted T ^ / 2 (disappearance);

-> 8. evaluation of the photocatalytic activity of the coating as the rate of disappearance of this activity in (nm / h), defined as follows:

v (nm / h) = [palmitic acid thickness (nm)] / [2 xt ^ / 2 (disappearance) (h)].

The aging of the coating was carried out by subjecting it to mechanical abrasion as follows:

that the coating

- sample size: 7 cm x 15 cm;

- applied load: 600 g;

- felt abrading area: 1.5 cm;

- n cycles (1 cycle = 1 forward and backward movement of the felt support arm and load) at n = 200 and 500.

• ·

9

<img file="CZ20003244A3_D0007.tif" />

<img file="CZ20003244A3_D0008.tif" />

Table 2 below shows for each example:

- disappearance rate vl before abrasion;

- disappearance rate at 2 after 200 cycles;

- clearance rate in 3 after 500 cycles.

TABLE 2

<td>Example</td><td>pr.n. (0 cycles)</td><td>v2 (200 cycles)</td><td>v3 (500 cycles)</td>

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

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

<td> 3</td><td> 35</td><td> -</td><td> =10</td>

<td> 4</td><td> 70</td><td> 10-20</td><td> =10</td>

<td> 5</td><td> 35</td><td> -</td><td> =5</td>

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

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

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

However, analyzes have shown that the coatings in Examples 3, 4 and 5 have a structure likely to be close to that shown in a very simplified manner in Figure 1, which is a glass substrate 1, a SiOC 2 layer and a coating 3. This coating comprises particles or aggregates of crystallites 5 among which are agglomerates of amorphous or weakly crystallized TiO2 grains which form the mineral binder of the coating.

Figure 2, more precisely corresponding to Example 4, is a photograph obtained by scanning electron microscopy and gives information about the surface appearance of Example 4: considerably

44 · 4 4

4 4 · · 4 4

4 4 4

4 4 4 • 4 4

4444 a rough surface allowing the coating to provide a highly structured surface area.

It should be noted that the sample of Example 4 has a refractive index of about 1.65. Knowing the refractive index of the basic TiO2 2.4, it can be assumed in the first approximation that the porosity of the coating is approximately (2.4 - 1.65) / (2.4 - 1), ie approximately 54%. The coating of Example 4 also exhibits strong hydrophilicity. After exposure to UV radiation for 20 minutes to activate, the sample is stored in the dark and the contact angle Φ relative to water is measured periodically: this contact angle remains below 10 ° for at least 20 days in the dark.

The following conclusions can be drawn from these data: in examples 3, 4, 6 and 8, and in particular in example 5, in which the ratio is Ti (2)^:Ti (-Q 50/50) combines all required properties, namely:

high TJ, low haze and refractive index less than 2 give the coating a very favorable optical appearance;

- satisfactory photocatalytic activity, which remains even after mechanical stress, which proves the durability of the coating and allows the use of these coatings under real conditions, for example for external glazing, since they have an acceptable durability. It is in fact the only example produced that still exhibits photocatalytic activity after 500 cycles of abrasion, albeit moderately.

Examples 9 to 13

The second series of examples relates to the same type of coating based on the same solution 1 and the same dispersion 2. The deposition conditions are the same as above for Examples 1 to 7, with the same

The difference is that the drip rate of the bath is now higher and is equal to 24 cm / minute. Another difference relates to the substrate: in these examples, it is the same glass but is pre-coated with a first 50 nm SiOC layer coated with CVD and then a second 450 nm layer of fluorine F: SnCl 2 doped tin oxide, applied by a known method of powder pyrolysis. Further, in this set of examples, the amount Q of the photocatalytic coating is not measured by measuring its thickness, but by measuring the amount of material per unit area of ​​the substrate, expressed in pg / cm.

The photocatalytic activity of the examples is measured prior to the abrasion test, i.e. the value of ll explained above. The durability of a coating is assessed qualitatively simply by wiping with a cloth: ++ means that the coating is very strong, + means that it is still suitably resistant and means that the coating is (almost) removed by wiping with a cloth.

Table 3 below lists the Ti (i): Ti (2) ratio for Examples 9-13. ^se with the same meaning as in Table 1, the Q value, the vl value and the rag wipe test rating:

TABLE 3

<td>Example</td><td>^Ti(2)/^Ti(l)</td><td>Q (pg / cm²)</td><td>ll (nm / h)</td><td>Evaluation wiping</td>

<td> 9</td><td> 0/100</td><td> 22</td><td> 18</td><td> ++</td>

<td> 10</td><td> 20/80</td><td> 24</td><td> 128</td><td> +</td>

<td> 11</td><td> 40/60</td><td> 23</td><td> 159</td><td> +</td>

<td> 12</td><td> 50/50</td><td> 25</td><td> 231</td><td> +</td>

<td> 13</td><td> 100/0</td><td> 23</td><td> 222</td><td> -</td>

···· » · ···· • · « · 4 · * · ·«· • · · · · ··· ·· · · » · · · ♦ · ···· ··· ··· ·· ·♦

This table shows the same tendency as in the first series of experiments related to the same or almost the same amount of coating applied. Optimum occurs in Examples 11 and 12 with Ti / TI (g) ratios of 40/60 and 50/50. Only Example 12 exhibits photocatalytic activity above 200 and proper durability.

Examples 14 to 16

A third series of examples relates to coatings with TiO2 particles in dispersion used in all the previous examples, but with a hybrid binder with a combination of T1O2 and S1O2.

In a solution containing binder precursors:

as solvent: ethanol and ethylene glycol in a weight ratio of 75/25;

as stabilizer: acetylacetonate;

as a precursor TiCl 4: titanium tetrabutoxide (TBT);

- as a precursor SiCl2: tetraethyl orthosilicate (TEOS).

The relative proportion of TBT and TEOS is adjusted so that the solution has a Ti2O / SiO2 mass ratio of 15/85 (assuming all TBT has been converted to T1O2 and all TEOS to S1O2).

Then this solution was added to the particle dispersion used in the previous examples in such proportions as to obtain the desired ratio r Ti (particles) / (Ti_precursor + Si_precursor). (The solids content of this solution is 3%.)

The deposition and substrate conditions are identical

44 44 4 · 4 4

4 4 4 4 4 with the conditions in Examples 9 to 13.

Table 4 below shows the values ​​of the ratio r explained above, the values ​​of the above explained velocity vl, the light reflection on the coated substrate R ^ (%) and the changes ΐγ (delta ΐγ) achieved after the 500 abrasion test cycles described in the first series of examples. as well as a ratio r, which expresses the ratio of the amount of Ti to the amount of Si as the weight of the oxide.

^rl = ^Ti02^particle/(^Ti02pojivo ^{+ Si0}2 binder)

The table also shows the amount of total TiC ^ in the coating (particles and TiC ^ from the titanium precursor) in μg / cm and the calculated amount of coating as total weight ζγ also in μg / cm².

TABLE 4

<td>Example</td><td>r</td><td>^rl</td><td>pr.n.</td><td>^rl</td><td>delta Tj ^</td><td>^Qand</td><td>q₂</td>

<td> 14</td><td> 45,1/54,9</td><td> 40/60</td><td> 8</td><td> 12,5</td><td> 0</td><td> 8,8</td><td> 18,2</td>

<td> 15</td><td> 55,3/44,7</td><td> 50/50</td><td> 40</td><td> 10</td><td> 1</td><td> 9,3</td><td> 16,3</td>

<td> 16</td><td> 65/35</td><td> 60/40</td><td> 45</td><td> 14</td><td> 4</td><td> 10,1</td><td> 15,4</td>

The deposition was repeated to adjust the solids content of the solution and the drip rate, with the ratio r being determined to be 55.3 / 44.7 and the amount of coating applied was varied.

Table 5 below shows, for these additional experiments to Test 6, the amount Q in µg / cm, corresponding to the thickness in nm, if measured, in l. (in nm / h), the value and the delta ΐγ value explained above:

TABLE 5

<td>Example</td><td>Q</td><td>E</td><td>pr.n.</td><td>^rl</td><td>delta Tj ^</td>

<td>15a</td><td> 17</td><td> 110</td><td> 42</td><td> 8,5</td><td> 1,5</td>

<td>15b</td><td> 33</td><td> -</td><td> 88</td><td> 12,1</td><td> 2,5</td>

<td>15c</td><td> 49</td><td> 460</td><td> 130</td><td> 11</td><td> 0,8</td>

From this third series of experiments it is apparent that it is advantageous to add the material S1O2 to the binder, which does not participate in photocatalysis, but allows a more homogeneous coating and leads to an increase in its durability. It is also apparent that, although the ratio r is key, other parameters may also act, in particular a value of Q, which is preferably between 15 and 45 µg / cm 2 to take into account the cost of the coating and the impact of its thickness on the optical appearance.

Of course, the invention is not limited to these specific examples. In particular, it is within the scope of the invention to further improve the photocatalytic activity of particles 5 by doping them by introducing a dopant into the crystal lattice, or by coating the particles with said dopant from the group comprising Fe, Cu, Ru, Mo, Bi, Ta, Nb, Co, Ni, etc. as described in the aforementioned International Published Patent Application WO 97/10185.

It is also within the scope of the invention to add a mineral binder containing oxides that are not photocatalytic or only slightly photocatalytic in the crystalline state, for example by adding precursors of other S102 type oxides, such as tetraethoxysilane, to the dispersion.

The aforementioned A / (B + M + Si) ratio, which is optimal in the range of 40/60 to 60/40, may range from 35/65 to 40/60 and 65/35 to 60/40 in the lower claims.

AND⁷ l &amp; W