Substrate with a self-cleaning coating

(54) Title: SUBSTRATE MANUFACTURING PROCESS, SUBSTRATE, AND SUBSTRATE APPLICATION.

(30) Unionist Priority: 17/04/2002 fr 02/04775 (73) Holder (s): Saint-Gobain Glass France (72) Inventor (s): Clarisse Durand, Jean-Pierre Boilot, Lethicia Gueneau, Mauricette Rondet, Sophie Besson, Thierry Gacoin “SUBSTRATE MANUFACTURING PROCESS, SUBSTRATE, AND SUBSTRATE APPLICATION”

The invention refers to different types of materials that can be found in buildings, vehicles, urban moving parts or even in household appliances, namely, notably:

- transparent substrates in glass or polymer intended to serve, for example, as glazing, viewing screen;

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

- architectural materials such as tiles, tiles, stone, cement compositions and metallic surfaces,

- fibrous mineral materials, such as insulating glass wool or textile glass threads, which can be used as a filtration material, to make false lining, quartz, silica fibers, etc.

Recent studies have been done to improve the comfort of using these materials, notably to facilitate their maintenance,

In particular, functional coatings have been developed that have photocatalytic properties. These are notably coatings that comprise TiO₂ at least partially crystallized, notably in anatase form and which are notably described in patent documents WO97 / 10185, WO97 / 10186, WO99 / ​​44954 and WOOl / 66271. This type of semiconductor material based on metal oxide, possibly doped (there are also other oxides that may be photocatalytic, such as ZnO), is able under the effect of radiation of a wavelength suitable to initiate radical reactions that cause the oxidation of compounds organic. This type of coating, if it is sufficiently exposed to adequate radiation (usually ultraviolet, possibly in the visible domain), is then quite effective in degrading organic dirt. In addition, it was found that, especially when it comes to coatings based on titanium oxide, they also had a certain hydrophilic character if they were exposed to radiation for a sufficiently long time. This coating is therefore very effective in the sense that it is able to degrade organic dirt, and evacuate mineral dirt by its hydrophilicity. However, its activity is linked to its exposure (for a sufficient duration) to radiation (sufficiently intense) of adequate wavelength. This type of coating therefore has a behavior that depends heavily on the ambient climatic conditions in case of exposure to the outside, notably, the conditions of insolation and pluviometry. Likewise, he tends to have less nocturnal activity than his daytime activity, in the absence of appropriate light.

The invention then aims to further improve the functionality conferred by this type of "self-cleaning" or "grease retardant" coating. The invention aims notably at obtaining coatings that can have an increased efficiency, that can be more "versatile" in different aspects; first in the face of conditions of exposure to radiation, then in the face of mechanical stresses (abrasion resistance), finally in the face of the association of other features. The invention aims more partially to obtain coatings that can, even in mediocre sunshine conditions, even at night, or inside environments notably under the action of the residual ultraviolet radiation from classic lighting lamps or the ultraviolet radiation that passes through a pane of glass, present a certain anti-dirt activity. It also targets products with which a UV lamp is associated, notably self-cleaning filters.

The invention is primarily concerned with a substrate which can be essentially transparent, notably based on glass or polymer (s), or which can be ceramic or glass-ceramic, or which can also be made of architectural material (of the type plaster facade, concrete slab or pavement, architectural concrete, tile, material with cement composition, terracotta, slate, stone, which can also be a fibrous substrate, based on insulating mineral wool or reinforcing glass yarns, or a product comprising quartz or silica fibers). This substrate is characterized by the fact that it is provided on at least part of its surface with a coating whose mesoporous structure has photocatalytic properties and comprises at least partially crystallized titanium oxide, notably in anatase and / or rutile form. The term "mesoporous" refers to pores with diameters between 2 and 50 nm. The mesoporous structure, obtained in the manner that will be described below, is notably 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, if applicable in covalent bond with elements such as O, S, N, C or similar. Titanium oxide at least partially crystallized is, for example, incorporated into the mesoporous structure in the form of perfectly discernible particles. The mesoporous structure that incorporates titanium oxide is essentially solid, susceptible to excellent cohesion, mechanical strength and abrasion resistance. The mesoporous structure is likely to be exclusively composed of titanium or a titanium compound such as oxide, notably r

crystallized in anatase or rutile form. It is shown that the titanium oxide thus incorporated exerts its photocatalytic activity to an exceptionally high degree. Thus, a residual ultraviolet radiation after passing through a single or double glazing, or a residual ultraviolet radiation from electric lighting from the inside is enough for the substrate of the invention to degrade an organic residue, and for the latter to be dragged in a relatively uniform liquid film that forms, if applicable, on the substrate taken hydrophilic by radiation. The coating of the invention combines the functionality of degradation of organic residues - by photocatalysis - and of evacuation of organic and mineral residues - hydrophilic / oleophilic character - under the effect of any liquid, such as condensation. The high performances obtained by the invention are perhaps attributable, at least in part, to the intercommunication of the pore network that allows good accessibility of pollutions to titanium oxide particles, as well as a good diffusion in the coating of the photo-generated species on the surfaces of these particles .

On the other hand, the abrasion resistance and the durability of the photocatalytic activity to such a high degree are excellent (see examples above). The invention therefore also makes it possible to conserve porosity after abrasion, however one could preferentially expect an abrasion to result in a densification of the surface layer and then finally, a loss of anti-dirt properties.

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

Advantageously, the substrate according to the invention is essentially transparent, flat or curved, of the glazing type, as it is in this type of application that the accumulation of dirt that prevents visibility is the most uncomfortable, and that the washes are the most necessary for ensure its transparency. It may be a pane that has a macroscopic relief, for example, pyramid motifs in depths of the order of a few millimeters - printed glass -, or a pane that has much smaller surface irregularities such as those resulting from a chemical attack with hydrofluoric acid - sanded glass, or opacified.

Preferably, the coating of the invention is formed by interposing a sub-layer based on at least partially oxidized silicon derivative chosen from silicon dioxide, substoichiometric silicon oxides, oxycarbonide, oxynitride or silicon oxycarbonitride. The sub-layer is useful when the underlying surface is glass, since the migration of alkaline ions (sodium) from the glass in the coating of the invention can, under certain conditions, alter the photocatalytic properties; or the sub-layer is a barrier to alkali. The sub-layer can be of the type described in the previously mentioned patent document WOO1 / 32578. The sub-layer advantageously has a refractive index between 1.45 and 1.80, notably between 1.50 and 1.75, for example, between 1.55 and 1.68. Such a relatively low index allows, in a transparent glass-type substrate, to avoid a reflection effect that can be judged to be unsightly.

This sub-layer then advantageously comprises Si, O, possibly carbon and nitrogen. But it can also comprise minority materials, in reaction to silicon, for example, metals like Al, Zn or Zr. The sub-layer can be deposited by sol-gel or by pyrolysis, notably by gas phase pyrolysis (CVD). This last technique allows to obtain coatings and, SiO_xCy or SiO₂ very easily, notably, by depositing directly on the float glass strip in the case of glassy substrates. But the deposit can also be carried out by a vacuum technique, for example, by sputtering from a Si target (possibly doped) or a silicon suboxide target (in an oxidizing and / or nitriding reactive atmosphere) , for example).

This sub-layer preferably has a thickness of at least 5 nm, notably a thickness comprised 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 mesoporous structure is placed via sol-gel;

- its thickness is between 30 and 800 nm;

- the titanium oxide incorporated in the mesoporous structure is eventually doped as explained in the patent documents WO97 / 10185 and WO97 / 10186 incorporated here for reference, and comprises nanoparticles with diameters between 0.5 and 100 nm, notably between 1 and 80 nm, in turn made up of groups of grains or elementary crystallites with diameters between 0.5 and 10 nm. The term "diameter" should be taken here in the broad sense, it is more an assessment of the size of the nanoparticle or the crystallite. The shape of the latter can approach a sphere or an elongated rice-grain shape or a completely random shape.

Another object of the invention resides in a process of manufacturing a substrate as described above which successively comprises:

- the preparation of a liquid composition comprising at least one precursor to the material that constitutes 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 of nanoparticles or crystallites to the liquid composition - according to the above definition - possibly doped titanium oxide, with diameters between 0.5 and 100 nm,

- applying the composition to the surface to be coated,

- the elimination of the organic structuring agent, the elemental grains or crystallites of titanium oxide being incorporated in the mesoporous structure while preserving its integrity essentially, several of them can be aggregated here in groups. Throughout such a substrate manufacture, it is not excluded that grains or crystallites of titanium oxide aggregate with each other and / or grow, notably, the smallest among them, according to the operating conditions (content, pH, temperature).

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

- the preparation of an oxide precursor sol (notably silicon),

- the maturation of the sun, and then

- mixing with the structuring agent.

In fact, the maturation of the sun allows for a preliminary condensation of the oxide precursor, which favors the structuring of the condensed oxide coating on the support surface in large domains. Advantageous maturation conditions include keeping the sun at a temperature of 40 to 60 ° C for a period of 30 min to 24 hours, the maturation time being, however, 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 non-ionic, including bi-block or tri-block copolymers based on, for example, ethylene oxide or propylene.

The invention also has the object of applying the substrates according to the invention, notably those that are essentially transparent, for the manufacture of "self-cleaning" glazing that can be both anti-dirt, anti-fog and anti-condensation. This may be double-glazed windows, vehicle windshields, rear windshields, sunroofs and side windows. It can also be windows for trains, planes and boats. It can also be utilitarian glazing such as aquarium glass, window glass, greenhouse, or even glass used in interior furniture, and urban furniture. It can also be glazing used as television, computer and telephone display screens. This type of coating can also be applied on electrocommandable glazing, such as heated glazing with wire or layer, electrochromic glazing, glazing with liquid crystal film, electroluminescent glazing and photovoltaic glazing.

In this application of the substrate of the invention as glazing (based on transparent plastic material or glass), one or more thin layers, in addition to the sub-layer precited on the basis of at least partially oxidized silicon derivative, can be interposed between the support surface and the coating with mesoporous structure. It may be, notably, layers with antistatic, thermal function (heater providing it with current inputs, low-emission, anti-solar), optical (reducing the luminous reflection and / or making the color in reflection more neutral) substrate) from a stack of anti-reflective layers. With regard to such functional layers applied in a known manner on the panes, possibly in the form of stacks, the patent documents WO97 / 10186 already cited and W002 / 02472 are hereby incorporated by reference.

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

The substrate, preferably based on mineral insulating wool and textile based on reinforcing glass fibers, can serve as a filtration material, or even serve to make false ceilings, whose cleaning is uncomfortable.

The invention also has the object of applying a woven, non-woven substrate (needle punctured mat, felt, wool), knitted, braided, sintered fiber block (known under the name of rigid silica) based on fibers of diameters comprised between 1 and 20 pm of fused silica, washed glass (more than 90% silica), alumina and mullite, for the manufacture of anti-odor filters, for the removal of industrial effluents, antibacterials, for interior depollution, for domestic air purification, for the purification of passenger compartments for transport vehicles (automotive, rail, aeronautical, water), for the purification of cigarette smoke, for the purification of the home appliance system (refrigerator).

The invention will be described below with the help of non-limiting examples.

EXAMPLE 1

Placed on the glass in the form of a float glass tape, a sub-layer based on silicon oxycarbonate denoted by SiOC convenience (without prejudging the actual oxygen and carbon rate in the coating), the glass is a glass clear 4 mm thick silico-sodo-calcium, as marketed by Saint-Gobain Glass France under the name Planilux. This sub-layer is placed by CVD from Si precursors, in particular, a mixture of S1H4 and ethylene diluted in nitrogen, with the help of a nozzle arranged above and across the float glass strip of a glass production line. flat, in the float enclosure, when the glass is still at a temperature of about 550 to 600 ° C. The coating obtained has a thickness of about 50 nm and a refractive index of about 1.5. Cut the 10 cm x 10 cm samples of the float glass with its alkaline barrier SiOC sub-layer 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 sub-layer.

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

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

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

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

TiO nanoparticles₂ crystallized anatase and about 50 nm in size are added in different proportions to the two liquid compositions thus obtained, immediately before depositing on the sample. The deposit is made by spin coating in a starting quantity of 3 ml per sample. Other equivalent deposition techniques are dip coating, spraying, laminar coating, roll coating (roll coatinf), flow coating (⁴y7cw coatinff).

The samples are then subjected to the following cooking treatment:

- 30 min 100 ° C plateau 2 h;

-15 min 150 ° C plateau 2 h;

-15 min 175 ° C plateau 2 h;

-10 min 200 ° C without landing;

- 3h 20min 300 ° C plateau 1h;

- 2h 30 min 450 ° C plateau 1 h.

The pores of the coating thus formed have a size of 2-3 nm when the CTAB cationic surfactant 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 mesoporous structure that the Ti / Si ratio is exactly identical to that of the liquid starting composition. SIMS analysis also makes it possible to verify that the nanoparticles are evenly distributed in the three dimensions of the coating.

The table below gives different characteristics of the coatings with their formation and after 500 cycles of the Opel abrasion test - in the latter case, indication of the values ​​in parentheses. The Opel test (Construction Standard En 1096-2 of January 2001) consists of applying a 14 mm diameter, 10 mm thick felt on a 9.4 cm long coated surface (this part is called a track). and 0.52 g / cm of density, under a load of 400 g / cm², the felt being subjected to a translation (50 rounds over the entire length of the track per minute) combined with a rotation of 6 rpm (1 cycle = 1 round trip).

The thickness E of the coatings in nm is measured from SIMS profiles and MEV micrographs.

The amount of TiO₂ in pg / cm² is assessed by fluorescence X.

Photocatalytic activity is measured as follows:

1- test performed on approximately 15 cm of coating;

2- weighing the sample and measuring the thickness of the substrate, the light transmission T_L and the Td fog (all two in%);

3- spray deposit of a solution of palmitic acid (8 groups of acid to 1 1 of chloroform), with a glass / spray distance of 20 cm, on the vertical substrate, and 3 to 4 successive passes;

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

5- measurement of TL light transmission and fog spun Td after deposit;

6- measurement of the variation of the fog as a function of the radiation time under UVA of intensity of about 50 W / m;

7- graphic determination of the final time in which the fog spun decreases by 50%: time called T * / 2 (disappearance);

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

v (nm / h) = (thickness of palmitic acid (nm) / (2 xTYz (disappearance (h)).

r

And still given in the table below the value of the photocatalytic activity related to the amount of TiO₂ in the coating. Finally, the optical properties of light reflection RL and fog Td (in%) are indicated.

The test numbers are defined as follows:

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

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

<td>Test No.</td><td>AND nm</td><td>Uncle₂pg / cm²</td><td>V nm / h</td><td>V / TiO₂</td><td>RL %</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 (.·.)</td><td> 9,4 (17,7)</td><td> 0,8 (1,1)</td>

The thickness of the layers varies from 200 to 500 nm according to the amount of TiO nanoparticles₂ incorporated. After 500 Opel cycles, only the thickest coatings (450 and 500 nm) suffer a compaction higher than the average of their initial thickness. The photoactivity of these coatings, however, was tested.

The coatings have 43 nm / h photoactivities for the structured coating with the cationic surfactant and the least concentrated in TiO₂ (2.2 pg / cm) at 684 nm / h for the structured coating with the copolymer and the most concentrated in TiO₂ (66 pg / cm). The v / TiO ratio₂ is always at least equal to 9.

Partial or total maintenance of functionality is observed after 500 Opel cycles, which, in addition, changes only the optical properties of the thicker layers and those more concentrated in TiO₂ (Ti / Si = 1 and 2) - for the others, the values ​​of RL and Td remain below 11.4 and 1.2%, respectively.

Test 3 to 7 (tests 3 'to 7') is reproduced with low UVA radiation of 1.5 W / m² of a classic light bulb, the values ​​of v (nm / h) and v / TiO₂ high are for tests N °:

-3 ': 0e0,

-4 ': 0e0,

-5 ': 13 and 0.75,

-6 ': 19e0.57, and

-7 ': 28e0.42.

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

EXAMPLE 2

In addition, discs of 47 mm in diameter, 8 mm in thickness and 1000 g / m² by surface mass, felts punctured with a silica fiber needle, marketed by the company Saint-Gobain Quartz under the name needled-punched Quartzel mat (fibers between 7 and 16 pm) by immersion in the composition of test No. 6 above, and then heat treatment described above. The increase in mass of the discs thus obtained is 10%.

The ability of these discs to decompose a concentration of 350 ppm by volume of methanol in nitrogen gas is tested by filtering an amount of 62.5 ml / mm, under UV illumination (190-350 nm).

With a lighting power of 48 m W / cm, the efficiency, that is, the proportion of decomposed methanol, is 100%. With a power of 25.6 mW / cm², it is about 96%, and still about 58% under lighting as low as 8.22 mW / cm.

Thus, the invention makes available a substrate capable of obtaining the optical quality of transparency in glazing applications, and a durable self-cleaning functionality in the conditions of erosion and bad weather in the external atmosphere. The considerably high degree of photocatalytic functionality also makes it possible to consider use at night or indoors by taking advantage of low intensity radiation such as products for classic lighting or passing solar radiation through the panes, as well as applications for effluent or atmospheric clean-up, filtration.