Structure comprising a substrate, notably glass, carrying a photocatalytic layer coated with a thin protective film for use in household appliance, motor vehicle and building glazing

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SUBSTRATE, IN PARTICULAR GLASS SUBSTRATE, BEARING A LAYER WITH PHOTOCATALYTIC PROPERTY COATED WITH A THIN PROTECTIVE LAYER.

The present invention relates to substrates such as glass, glass-ceramic or plastic substrates which have been provided with a coating with photocatalytic property to give them a so - called anti -soiling or self-cleaning function.

An important application of these substrates relates to glazing, which can have very diverse applications, from utility glazing to glazing used in household appliances, from glazing for vehicles to glazing for buildings.

It also applies to reflective glazing of the mirror type (mirror for homes or vehicle rear-view mirror) and to opacified glazing of the spandrel type.

The invention also applies, similarly, to non-transparent substrates, such as ceramic substrates or any other substrate which can in particular be used as an architectural material (metal, tiles, etc.). It is preferably applied, whatever the nature of the substrate, to substantially planar or slightly curved substrates.

Photocatalytic coatings have already been studied, in particular those based on titanium oxide crystallized in the anatase form. Their ability to degrade soiling of organic origin or microorganisms under the effect of UV radiation is very interesting. They also often have a hydrophilic character, which allows the evacuation of mineral dirt by splashing water or, for exterior glazing, by rain.

This type of coating with antifouling, bactericidal and algicidal properties has already been described, in particular in patent WO 97/10186, which describes several methods of obtaining it.

If it is not protected, the layer with photocatalytic property undergoes, over time, a wear which manifests itself by a loss of its activity, a loss of the optical qualities of the structure (appearance of a blur, a coloration), or even by delamination of the layer.

If the thickness of the layer with photocalytic property is reduced, the coloration likely to appear during a partial deterioration of the latter will be less intense and the variation in color will be less over time. However, this decrease in thickness will be to the detriment of the performance of the layer.

It is therefore necessary to ensure mechanical and chemical protection of the layer, the thickness of the protective layer having to be thin so that the layer with photocalytic property fully retains its function.

We know from European patent application EPA-0 820 967 an anti-fog element comprising a transparent substrate, a transparent film of a photocatalyst formed on the transparent substrate, and a transparent porous mineral oxide film formed on the film of photocatalyst and having a surface exhibiting a hydrophilic property.

Also known from Japanese patent JP 2002 047 032 is a method of manufacturing a substrate coated with a photocatalytic membrane which comprises the steps of spreading nanoparticles of TiO₂ with anatase crystal structure and 5-10 nm using a spray gun, heating and sputtering a SiO membrane₂ covering the TiO particles₂.

Neither of these structures is satisfactory, the first due to the porous nature of the protective coating, which, due to the presence of pores, does not provide sufficient protection of the layer with catalytic properties, and the second due to an insufficient level of photocatalytic material, which does not form a continuous layer.

The present invention provides a solution to this problem.

In fact, it first of all relates to a structure comprising a substrate carrying, on at least part of its surface, a layer with photocatalytic property, antifouling, based on titanium dioxide (TiO₂), characterized in that said layer with photocatalytic property is coated with a thin layer containing silicon and oxygen, with covering power, non-porous, capable of ensuring mechanical and chemical protection of the underlying photocatalytic layer while maintaining the photocatalytic activity of TiO₂.

Preferably, said thin film containing silicon and oxygen is present in the form of a continuous film. In particular, said thin layer is advantageously in the form of a film matching the surface roughness of the layer with underlying photocatalytic property.

The thin layer containing silicon and oxygen is in particular a layer of at least one compound of silicon and oxygen chosen from SiO₂, SiOC, SiON, SiO_x with x <2, and SiOCH, SiO₂ being particularly preferred.

In accordance with an advantageous variant of the structure according to the present invention, the thin layer containing silicon and oxygen is a layer of at least one compound of silicon and oxygen with which is associated at least one compound chosen from among Al₂O₃ and ZrO₂, such a compound providing chemical inertness and reinforcing resistance to hydrolysis. We can highlight the role of Al₂O₃, famous inert oxide which increases the chemical resistance of the whole.

The atomic ratio (Al and / or Zr) / Si is generally not greater than 1, the Al / Si ratio advantageously being between 0.03 and 0.5, in particular between 0.05 and 0.1, and the Zr / Si ratio, between 0.05 and 0.4.

The thin layer containing silicon and oxygen may have a thickness of at most 15 nm, in particular at most 10 nm, in particular at most 8 nm, preferably being at most 5 nm or approximately 5 nm. nm, in particular 2 to 3 nm.

Said thin layer provides a lubricating effect and has a mechanical role. It improves resistance to scratches and abrasion.

This greater mechanical resistance and this better chemical resistance are not, however, obtained to the detriment of a drop in photocatalytic activity. Indeed, while one could expect that the photocatalytic activity finally obtained from the TiO-based layer₂ is reduced due to the masking of the latter by the SiO overlay₂, this photocatalytic activity is preserved and even improved; in fact, soiling, diluted in a uniform film of SiO₂ due to the hydrophilic nature of the latter, are more easily destroyed by TiO₂.

The titanium dioxide-based layer consists of TiO₂ alone or with TiO₂ doped with at least one dopant chosen in particular from N; pentavalent cations such as Nb, Ta, V; Fe; and Zr. This TiO-based layer₂ may have been deposited by a solgel process, or by a pyrolysis process, in particular in the gas phase, or by cathodic sputtering, at room temperature, under vacuum, if necessary assisted by a magnetic field and / or ion beam, with the use of '' a metallic target or TiO_x with x <2 and an oxidizing atmosphere, or with the use of a TiO target₂ and an inert atmosphere, TiO₂ produced by sputtering which may then have been subjected to a heat treatment in order to be present in the crystallized state in a photocatalytically active form.

The thin layer containing silicon and oxygen has in particular been deposited by cathodic sputtering, at room temperature, under vacuum, where appropriate assisted by a magnetic field and / or ion beam, using a doped Si target. Al (8 atomic%) in an Ar + O atmosphere₂ at a pressure of 0.2 Pa.

The structure according to the present invention may include, immediately below the TiO-based layer₂, a sub-layer having a crystallographic structure which has allowed crystallization assistance by heteroepitaxial growth in the anatase form of the upper layer based on TiO₂, in particular made up of ATiO₃, A denoting barium or strontium. The thickness of this sublayer is not critical; it can for example be between 10 nm and 100 nm.

The substrate consists for example of a plate, flat or with curved or curved faces, of monolithic or laminated glass, of glass-ceramic material or of a hard thermoplastic material, such as polycarbonate, or of glass fibers or of glass-ceramic , said plates or said fibers having, where appropriate, received at least one other functional layer, before the application of the TiO-based layer₂ or a layer for assisting crystallization by heteroepitaxial growth of the latter. (In the case of more than one layer, we can also speak of stacking or layers).

The applications of the plates have been discussed above. As for fibers, mention may be made of their application to the filtration of air or of water, as well as bactericidal applications.

The other functional layer (s) are chosen from layers with optical functionality, thermal control layers, conductive layers, as well as, in the case where the substrate is made of glass or of a glass-ceramic material, the layers forming a barrier to the migration of particles. alkalis of glass or ceramic glass material.

The layers with optical functionality are in particular anti-reflection, light radiation filtration, coloring, diffusing, etc. layers. Mention may be made of SiO layers.₂, Yes₃NOT₄, TiO₂, SnO₂, ZnO.

The thermal control layers are in particular the solar control layers, or the so-called basemissive layers.

The conductive layers are in particular the heating, antenna or anti-static layers, among these layers, one can count the networks of conductive wires.

In the case where the substrate is made of glass or glass-ceramic material, at least one functional layer forming a barrier to the migration of alkalis from the glass or from the glass-ceramic material can be placed below the layer with photocatalytic property or below the sub-layer. -layer assisting the crystallization thereof, if such a sub-layer is provided. The other functional layers (with optical functionality, thermal control, conductive layers) when present are located above the barrier layer (s).

Migration of alkalis is likely to result from the application of temperatures exceeding 600 ° C.

Such layers forming an alkali barrier during subsequent heat treatments are known, and mention may be made of the layers of SiO₂, SiOC, SiO_xNOT_y, S13N4, for example at least 5 or 10 nm thick, in many cases at least 50 nm, as described in PCT international application WO 02/24971.

By way of example, mention may be made of substrates made of glass or of glass-ceramic material, in particular of the plate type, having received a layer forming a barrier to the migration of alkalis from the glass or from the glass-ceramic material, then a mono-, two- or three-layer with optical functionality.

A subject of the present invention is also a method of manufacturing a structure as defined above, characterized in that one deposits on a substrate of glass or of glass-ceramic material or of hard plastic material of polycarbonate type, of plate type, or on glass or glass-ceramic fibers, a layer of TiO₂ possibly doped which is subjected to a heat treatment to give it a photocatalytic property in the case where this is not provided by the conditions used for its deposition, then which is deposited on said layer with photocatalytic property a thin film containing silicon and oxygen as defined above.

In particular, the deposition of a layer of TiO is carried out successively₂ and that of the thin film containing silicon and oxygen at room temperature, by vacuum cathode sputtering, where appropriate assisted by magnetic field and / or ion beam, in the same enclosure, the conditions being the following:

- for the deposition of the TiO-based layer₂, supply in direct current or alternating current mode under a pressure of 1-3 mbar, and under an atmosphere of oxygen + inert gas (argon), from a target of Ti or TiO_x, x = 1.5 to 2;

- for the deposition of the layer containing silicon and oxygen, a power supply in alternating current mode under a pressure of 0.1 to 1 Pa and an Ar + O atmosphere₂ from a target with a high silicon content, the deposition of the TiO layer₂ being optionally preceded by the deposition of a sublayer to assist crystallization by epitaxial growth in the anatase form of the TiO layer₂.

The conditions for depositing a layer with a silicon and oxygen content which is not porous are known to those skilled in the art, being in particular conditions of low pressure and high power (Thornton diagram).

In the case where the coating of a glass substrate or of a glass-ceramic material is carried out, it is possible to provide that before the application of the TiO layer₂ or of the sublayer associated with the latter, at least one layer forming a barrier to the migration of alkalis present in the glass or the vitroceramic material is deposited on the substrate, an annealing or a toughening then being able to be carried out after the deposition of the TiO layer₂ and the thin silicon-based layer which covers it at a temperature between 250 ° C and 550 ° C, preferably between 350 ° C and 500 ° C for annealing, and at a temperature of at least 600 ° C for quenching.

According to the invention, it is also possible to provide that after the possible application of at least one layer forming a barrier to the migration of alkalis and that before the application of the TiO layer₂ or of the sublayer associated with it, at least one functional layer chosen from layers with optical functionality, thermal control layers and conductive layers is deposited, said functional layers being advantageously deposited by sputtering, under vacuum, if necessary assisted by magnetic field and / or ion beam.

The present invention also relates to a single or multiple glazing, in particular for automobiles or buildings, comprising on at least one face, a structure according to the invention, as defined above, said face being in particular that oriented towards the front. 'exterior, but can also be the one facing the interior.

The faces of these glazings which do not have the structure of the present invention can comprise at least one other functional layer.

Such glazing finds its application as “self-cleaning” glazing, in particular anti-fog, anti-condensation and anti-dirt, in particular glazing for buildings of the double-glazing type, glazing for vehicles of the windshield, rear window, side windows. automobile, rear-view mirror, glazing for trains, planes, boats, utility glazing such as aquarium glass, showcase, greenhouse, interior furnishings, street furniture (bus shelters, advertising panels, etc.), mirror, computer type display system screen, television, telephone, electrically controllable glazing such as electrochromic, liquid crystal, electroluminescent glazing, photovoltaic glazing.

The following examples illustrate the present invention without, however, limiting its scope.

Examples la and lb (of the invention): Glass / SiO stack₂ : Al / TiC ^ / SiCh: Al

On a glass plate with a thickness of 4 mm, the following successive layers were deposited: a sub-layer of SiO₂ 150 nm thick Al doped;

ίο a layer of Ti0₂ 100 nm thick (Example 1a) or 20 nm thick (Example 1b); and an overcoat of SiO₂ 2 nm thick Al doped.

The SiO sublayer₂: Al is deposited from an Si: Al target (8 at% aluminum) with a power of 2000W, with the following gas flow rates: 15 sccm Ar and 15 sccm O₂ and under a pressure of 2 x IO '³ mbar.

The TiO layer₂ is deposited from a TiO target_x with a power of 2000W, with the following gas flow rates: 2 00 sccm Ar and 2 sccm (¾ and under a pressure of 23 x 10 '³ mbar.

The SiO overlayer₂: Al is deposited from an Si: Al target (8 at% Al) with a power of 1000W, with the following gas flow rates: 15 sccm Ar and 15 sccm O₂and under a pressure of 2 x 10 '³ mbar.

Examples 2a and 2b (comparative):

Glass / SiO stack_{2 ;}Al / TiO₂

The same stacks were made as in Examples 1a and 1b, except that the overcoat of SiO₂: Al was omitted.

Example 3 (comparative):

Glass / SiO2 stack: Al / TiO₂/ SÎ3 N ₄ : Al

The same stack was made as in Example 1a, except that instead of the SiO overlayer₂: Al, we deposited an overlayer of SÎ3N₄: Al with a thickness also of 2 nm from a target Si: Al (8 at% Al) with a power of 1000W, with the following gas flow rates: 18 sccm Ar and 12 sccm N₂ and under a pressure of 2 x 10 '³ mbar.

Example 4: Resistance to the Opel test

A strong improvement in the resistance to the Opel test (dry friction of the stack surface using a felt pad) was observed when going from the stack of Example 2a to stacking of Example 1a.

No change is observed when switching from the stack of Example 2a to the stack of Example 3.

Furthermore, before and after the above Opel test, the photocatalytic activity of the TiO layer was evaluated.₂ of each of the stacks of Examples 1a, 2a and 3, according to the stearic acid photodegradation test followed by infrared transmission, described in PCT international application WO 00/75087.

The results are collated in Table I. This table also shows the colorimetric variation in reflection on the layer side due to the Opel test (ΔΕ), the blurring induced by the Opel test, and the observation of the layer as to its delamination after the Opel test.

TABLE I

<td rowspan="2">Example</td><td colspan="2">TAS (cm '¹.min '¹)</td><td rowspan="2">Δε</td><td rowspan="2">Blurry (%)</td><td rowspan="2">Delami- nation</td>

<td>Before test Opel</td><td>After test Opel</td>

<td>the (invention)</td><td>59 x 10 '³</td><td>41 x 10³</td><td> 2,0</td><td> 0,5</td><td>no</td>

<td>2a (comparative)</td><td>54 x 10 '³</td><td>25 x IO '³</td><td> 9,3</td><td> 9,3</td><td>Yes</td>

<td>3 (comparative)</td><td>40 x 10 '³</td><td>15 x 10 '³</td><td> 10,0</td><td> 12</td><td>Yes</td>

EXAMPLE 5: Taber test

An improvement in the resistance to the Taber test was observed (resistance to abrasion = resistance to the passage of an abrasive wheel) when passing from the stack of Example 2b to the stack of Example lb .

The layer of Example 2b is delaminated after 500 turns in the Taber test. For the stack of Example lb, 0.8% haze is observed after 200 rounds in the Taber test and 2% haze after 500 rounds in the Taber test.

EXAMPLE 6: BSN test

An improvement in the resistance to the BSN (neutral salt spray) test was observed when switching from the stack of Example 2a to the stack of Example 1a.