Substrates with self-cleaning coatings, e.g. for filter, windows, electronic components, have mesoporous structure with photocatalytic properties and comprises titanium oxide at least partially crystallized

Holder (s):

© Agent (s): SAINT GOBAIN RECHERCHE.

FR 2 838 734 - A1 ® SELF-CLEANING COATING SUBSTRATE.

@) The invention relates to a transparent substrate based on glass or polymer (s) or ceramic or glass-ceramic substrate or in architectural material such as facade coating, concrete slabs or paving stones, architectural concrete, tile, cementitious material, terracotta, slate, stone, metal surface, or glass-based fibrous substrate such as mineral wool for insulation or glass strands for reinforcement. This substrate is distinguished in that it is provided on at least part of its surface with a coating, the mesoporous structure of which has photocatalytic properties and comprises at least partially crystallized titanium oxide.

A method of manufacturing this substrate, its application in glazing, an architectural material or an insulating mineral wool.

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SELF-CLEANING COATING SUBSTRATE

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

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

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

- architectural materials such as tiles, tiles, stone, cementitious compositions, metal surfaces

- fibrous mineral materials, such as insulating glass wool or textile glass threads, which can be used as filtration material, to make false ceilings ...

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

In particular, functional coatings exhibiting photocatalytic properties have been developed. They are in particular coatings comprising at least partially crystallized TiCh, in particular in the anatase form and which are described in particular in patents WO 97 / T01 £ 5, WO 97/10186, WO 99/44954 and WO 01/66271. This type of material will be conductive based on metal oxide, possibly doped (there are also other oxides capable of being photocatalytic, such as ZnO ...) is suitable under the effect of radiation of wavelength suitable for initiating radical reactions causing the oxidation of organic compounds: this type of coating, if it is sufficiently exposed to ad hoc radiation (generally ultraviolet rays, possibly the visible range), is therefore very effective in degrading organic soiling. In addition, it has been discovered that, in particular when it comes to coatings based on titanium oxide, these also exhibit a certain hydrophilic character if they are exposed for a sufficiently long time to said radiation. This coating is therefore very efficient, in that it is capable of degrading organic soiling, and of removing mineral soiling through its hydrophilicity. However, its activity is linked to its exposure (for a sufficient duration) to radiation (sufficiently intense) 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 and rainfall. Likewise, 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 increased efficiency, which can be more "versatile" in various ways: first with respect to the conditions of exposure to radiation, then with respect to the constraints. mechanical (abrasion resistance, etc.), and finally with respect to the combination of other functions. It aims more particularly to obtain coatings which can, even under poor sunlight conditions, even at night, or indoors, in particular under the action of residual ultraviolet radiation from conventional lighting lamps or ultra-violet radiation. purple passing through a glazing, exhibit some anti-fouling activity.

The subject of the invention is first of all a substrate which can be essentially transparent, in particular based on glass or on polymer (s), or which can be made of ceramic or glass-ceramic, or which can also be made of architectural material. (of the facade plaster, concrete slab or paver, architectural concrete, tile, cementitious material, terracotta, slate, stone, or which may also be a fibrous substrate, glass-based type insulation mineral wool or reinforcing glass yarns). This substrate is characterized in 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 covalently bonded 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 entire mesoporous structure incorporating titanium oxide is essentially solid, capable of excellent cohesion, mechanical strength and abrasion resistance. It has been found that the titanium oxide thus incorporated exerts its photocatalytic activity to an exceptionally high degree. Thus, a residual ultraviolet radiation after passing through a window or a residual ultraviolet radiation originating from an electrical interior lighting is sufficient for the substrate of the invention for it to degrade an organic residue, and for the latter to degrade an organic residue. ci is then entrained in a relatively uniform liquid film which forms, where appropriate, on the substrate made hydrophilic by the radiation. The coating of the invention combines the functionality of degrading organic residues - by photocatalysis - and of removing organic and inorganic 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 network of pores, allowing good accessibility of pollution to the titanium oxide particles, as well as good diffusion in the coating. species photogenerated on the surface of these particles.

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

In addition, the mesoporous nature of the substrate makes it possible to envisage impregnation thereof subsequent to the formation of the mesoporous structure with functional deodorants, antibacterial agents or of any other nature.

Advantageously, 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 washing is the most difficult. more necessary to ensure their transparency. It may be glazing having a 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 chemical attack with hydrofluoric acid - sandblasted glass, mattified.

Preferably, the coating of the invention is formed with the interposition of an underlayer based on an at least partially oxidized derivative of silicon chosen from silicon dioxide, substoichiometric silicon oxides, oxycarbide, oxynitride or silicon oxycarbonitride. The undercoat is useful when the underlying surface is glass, because the migration of alkali ions (sodium) from the glass in the coating of the invention can, under certain conditions, alter its photocatalytic properties; however, the undercoat acts as a barrier to alkalis. The underlayer may be of the type of that described in the aforementioned patent WO 01/32578. 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 reflecting effect which may be judged to be unsightly.

This sublayer therefore advantageously comprises Si, O, optionally carbon and nitrogen. But it can also include materials in a minority with respect 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 SiO coatings_xVS_y or in SiO₂ quite easily, in particular by depositing directly on the float glass ribbon in the case of glass substrates. However, the deposition can also be carried out by a vacuum technique, for example by cathodic sputtering from an Si target (possibly doped) or from a silicon suboxide target (in a reactive oxidizing and / or nitriding atmosphere. for example).

This sublayer preferably has a thickness of at least 5 nm, in particular a thickness of between 10 and 200 nm, for example between 80 and 120 nm.

According to other advantageous characteristics of the substrate of the invention:

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

- its thickness is between 30 and 800 nm;

- the titanium oxide incorporated into the mesoporous structure is optionally doped as explained in applications WO 97/10185 and WO 97/10186 incorporated here by way of 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 of between 0.5 and 10 nm. The term “diameter” is to be taken here in the broad sense, it is more of an evaluation of the size of the nanoparticle or of the crystallite. The shape of the latter can be closer to a sphere, or else to an elongated shape like a grain of rice or to a completely random shape.

Another object of the invention resides in a method of manufacturing a substrate as described above, comprising successively:

- the preparation of a liquid composition comprising at least one precursor of the material constituting the mesoporous structure of the coating and at least one organic structuring agent,

- the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor,

- the addition to the liquid composition of nanoparticles or crystallites - according to the definition above - of optionally doped titanium oxide, with diameters between 0.5 and 100 nm,

- the application of the composition to the surface to be coated,

the 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 therein, several of them possibly being aggregated therein in clusters. During such manufacture of the substrate, it is not excluded that the grains or crystallites of titanium oxide aggregate with each other and / or grow, in particular the smallest of them, depending on the conditions. operating conditions (content, pH, temperature, etc.).

For the manufacture of the substrate of the invention, the preparation of the liquid composition advantageously comprises:

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

- the ripening of the soil, then

- mixing with the structuring agent.

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

In 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, on ethylene or propylene oxide.

A 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” glazing, which can be both anti-fouling, anti-fog and anti-fog. -condensation. It may be glazing for buildings of the double glazing type, glazing for vehicles of the windshield, rear window, car roof, side windows. It can also be glazing for trains, planes, boats. It can also be utility glazing such as aquarium glass, glass for display cases, greenhouse, or even glazing used in interior furnishings, in street furniture, mirrors. It can also be glazing used as display screens of the television, computer or telephone screen type. This type of coating can also be applied to electro-controllable glazing, such as heated wire or coated glazing, electrochromic glazing, liquid crystal film glazing, electroluminescent glazing, photovoltaic glazing.

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

The substrate according to the invention, in addition to its application as glazing, can be in any architectural material that can be used to manufacture partitions, facades, roofs, floors, indoors or outdoors (metal, wood, stone, cement, concrete, terracotta , ceramic, facade plaster ...)

The substrate, if it is rather based on mineral fibrous material (glass, rock, silica, etc.), can be used as filtration material, or even used to make false ceilings, the cleaning of which is inconvenient.

The invention will be described below with the aid of non-limiting examples; the substrate is a clear silico-soda-lime glass 4 mm thick (type of glass marketed by Saint-Gobain Glass France under the name Planilux).

EXAMPLES

Is deposited on the glass in the form of a float glass ribbon, an underlayer based on silicon oxycarbide denoted SiOC for convenience (without prejudging the real level of oxygen and carbon in the coating). 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 550-600 ° C. The resulting coating has a thickness of about 50 nm and a refractive index of about 1.55. Samples of 10 cm × 10 cm are cut from the float glass provided with its alkali barrier SiOC sublayer thus obtained; these samples are washed, rinsed, dried and subjected to a UV ozone treatment for 45 min.

A coating with a mesoporous structure is formed on the sublayer.

The 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 by placing the flask in a water bath at 60 ° C for 1 hour.

In a second step, one adds to the sol obtained previously a solution of cetyltrimethylammonium bromide (CTAB) on the one hand, and a solution of a polyoxyethylene-polyoxypropylene block copolymer marketed by the company BASF under the registered trademark Pluronic PE6800 (molar mass 8000) on the other hand, in proportions such that the molar ratios CTAB / Si = 0.1, respectively PE6800 / Si = 0.01. This is achieved by mixing:

- 0.686 g of CTAB, 20 ml of ethanol, and 10 ml of soil;

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

The 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 the deposition on the sample. The deposit is made by spin coating in a starting amount of 3 ml per sample. (Other equivalent deposition techniques are dip coating, spraying, laminar coating, roll coating, flow coating ...)

The samples are then subjected to the following annealing treatment:

- 30 min 100 ° C level 2 h;

- 15 min 150 ° C level 2 h;

- 15 min 175 ° C, level 2 h;

- 10 min 200 ° C no plateau;

- 3 h 20 min 300 ° C level 1 h;

- 2 h 30 min 450 ° C level 1 h.

The 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 4-5 nm when the PE6800 copolymer is used as a structuring agent.

It is verified by SIMS analysis of the coating with a mesoporous structure that the atomic ratio Ti / Si is exactly identical to that of the starting liquid composition. The SIMS analysis also makes it possible to verify that the nanoparticles are distributed homogeneously in the three dimensions of the coating.

The table below shows various characteristics of the coatings on their formation and after 500 cycles of the Opel abrasion test in the latter case, indication of the values ​​in brackets. The Opel test (Building Standard En 1096-2 of January 2001) consists of applying to a part of the coated surface 9.4 cm in length -this part is called track-, a felt 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).

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

The amount of TiO₂ in pg / cm² is evaluated by X-ray fluorescence.

The photocatalytic activity is measured as follows:

1- test carried out on approximately 15 cm² coating;

2- weighing the sample and measuring the thickness of the substrate, the light transmission Tl and the haze Td (both in%);

3- spray deposition of a solution of palmitic acid (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;

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

5 — measurement of the light transmission T1 and of the blur Td after deposition;

6- measurement of the variation of the haze as a function of the irradiation time under U VA of intensity about 50W / m² ;

7- graphical determination of the time after which the blur has decreased by 50%: time called Tv₂ (disappearance) ;

8- evaluation of the photocatalytic activity of the coating at the speed of disappearance of palmitic acid v (in nm / h), which is defined as follows:

v (nm / h) = (palmitic acid thickness (nm)) / (2 x T% (disappearance (h))

Also recorded in the table below is the value of the photocatalytic activity reduced to the amount of Τ1Ό2 in the coating. Finally, the optical properties of light reflection RI and blur Td (in%) are indicated.

The test numbers are defined as follows:

- 1 and 2: CTAB as structuring agent, Ti / Si = 0.1, 0.25 respectively;

- 3 to 7: PE6800 as structuring agent, Ti / Si = 0.1, respectively 0.25, respectively 0.5, respectively 1, respectively 2.

<td>Test No.</td><td>E nm</td><td>TiO₂pg / cm²</td><td>V nm / h</td><td>V / T1O2</td><td>RI %</td><td>Td %</td>

<td> 1</td><td> 214 (220)</td><td> 2,2 (1,9)</td><td> 43 (21)</td><td> 20 (11)</td><td> 6,5 (10,2)</td><td> 0,8 (0,5)</td>

<td> 2</td><td> 208 (247)</td><td> 7,5 (5,7)</td><td> 117 (114)</td><td> 16 (20)</td><td> 8,7 (7,9)</td><td> 1,1 (1,2)</td>

<td> 3</td><td> 274 (209)</td><td> 4,7 (3,4)</td><td> 47 (31)</td><td> 10 (9)</td><td> 10,2 (7,8)</td><td> 0,2 (0,4)</td>

<td> 4</td><td> 308 (299)</td><td> 8,0 (10,2)</td><td> 209 (123)</td><td> 26 (12)</td><td> 12,8 (10,2)</td><td> 0,2 (0,3)</td>

<td> 5</td><td> 336 (294)</td><td> 17,3 (14,8)</td><td> 349 (181)</td><td> 20 (12)</td><td> 9,7 (11,4)</td><td> 0,4 (0,4)</td>

<td> 6</td><td> 454 (184-320)</td><td> 33,3 (28,7)</td><td> 620 (354)</td><td> 18 (12)</td><td> 9,7 (14,3)</td><td> 0,3 (0,8)</td>

<td> 7</td><td> 515 (209-268)</td><td> 66,0 (46,7)</td><td> 684 (...)</td><td>10 U)</td><td> 9,4 (17,7)</td><td> 0,8 (1,1)</td>

<td>The shoulders</td><td colspan="3">diaper isseurs vary from 20</td><td colspan="3">0 to 500 nm depending on the amount of</td>

incorporated TiCh nanoparticles. After 500 Opel cycles, only the thickest coatings (450 and 500 nm) experience a settlement greater than half of their initial thickness. The photoactivity of these coatings has nevertheless been tested.

The coatings exhibit photoactivities of 43 nm / h for the structured coating with the cationic surfactant and the least concentrated in TiO₂ (2.2 pg / cm²) at 684 nm / h for the structured coating with the copolymer and the most concentrated in TiO₂ (66 pg / cm²). The V / T1O2 ratio is always at least equal to 9.

A partial or total maintenance of the functionality is observed after 500 Opel cycles, which moreover alters the optical properties only for the thickest layers and the most concentrated in TiO₂ (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 (tests 3 'to 7') are reproduced with irradiation 1.5 W / m low UVA² a conventional lighting lamp; the values ​​of v (nm / h) and v / TiO₂ readings are for tests N °:

-3 ': 0and0;

- 4 ': 0 and 0;

- 5 ': 13 and 0.75;

-6 ': 19 and 0.57; and

- 7 ': 28 and 0.42.

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

Thus, the invention provides a substrate capable of providing the optical quality of transparency required in glazing applications, and a lasting self-cleaning functionality under the conditions of erosion and bad weather in the external atmosphere. The remarkably high degree of photocatalytic functionality also makes it possible to envisage use at night or indoors by making use of low-intensity radiation such as produced by conventional lighting or the passage of solar radiation through the glazing.