Substrate with photocatalytic coating

The invention relates generally to transparent or semitransparent substrates, especially glass, plastic and ceramic, which are provided with a coating having photocatalytic properties, to impart a stain-resistant, or more precisely self-cleaning function.

A significant use of these substrates relates to glazing, which can be used to entirely different purposes, glass panes, which are useful as glazing, which are used for household appliances, vehicles and buildings.

It is also directed to reflective glass type mirror (mirror in homes or as a rearview mirror in a vehicle) and to opacified glazing type supporting glass panes.

The invention further relates to similarly non-transparent substrates, such as ceramic or any other substrates which can be used in particular as architectural materials (eg, metal and tiles). It is preferably independent of the nature of the substrate plane in substantially or directed slightly curved substrates.

Photocatalytic coatings have been investigated, particularly those on the basis of a crystallized in the form of anatase titanium oxide. Your assets, reduce soil organic origin or microorganisms under the influence of UV radiation, is very interesting. They also often a hydrophilic character, which allows the removal of inorganic contaminants by spraying with water or even in exterior glazing, by rain.

This type of coating with antisoiling, bactericidal and algicidal properties has already been described, especially in patent <patcit><text>WO 97/10186</text></patcit>In which a number of ways have been described for its preparation.

The invention has for its object, the method for applying this type to improve a coating, in particular to simplify them. In parallel, it is still an object to improve the appearance of the coating and especially the optical properties of the substrate, which is provided with it.

The invention has especially a method for applying a coating having photocatalytic properties, which only includes at least partially crystalline titanium oxide in the anatase form, by sputtering onto a transparent or semi-transparent substrate to the object. A feature of the invention consists in carrying out the spraying at a coating pressure of at least 2 Pascal to the substrate. This is preferably at most 6.67 Pa and especially at least 2.67 Pa (ie at least 15 millitorr, and especially between 20 and 50 millitorr). The spraying is carried out at ambient temperature and on applying the coating is followed by a heat treatment of the type annealing to obtain the crystallization of the coating.

As from the patent mentioned above <patcit><text>WO 97/10186</text></patcit> known, this type can be applied a coating by sputtering. This is a vacuum process that allows in particular to adjust the thickness and stoichiometry of the deposited layers very fine. It is generally for reasons of higher efficiency performed magnetic supported. It may be reactive: It is then assumed to be essentially metallic target, here on the basis of titanium (optionally alloyed with another metal or silicon), wherein the sputtering in an oxidizing atmosphere, generally in an Ar / O₂Mixture, is performed. It may also be non-reactive, it is then assumed that a ceramic target that is already present in the oxidized form of (optionally alloyed) titanium.

However, the data obtained by this type of process layers are generally amorphous, while the functionality of the coating according to the invention is directly connected to the fact that they must be significantly crystallized. This is the reason that, as has already been proposed in the above patent, it is necessary to crystallize the coating (or to increase their degree of crystallization) by being subjected to heat treatment, for example, about 30 minutes to several hours at least 400 ° C.

According to the invention has been shown that a high pressure is also a special crystallization of the layer and a height of the tightness / roughness favors that have a significant impact on the level of photocatalytic properties of the coating. To give an idea of ​​be the coating pressures which are generally used for metal oxides, usually 2 to 8 mt (ie from 0.27 to 1.07 Pa), which is why the present invention coating pressures are selected that are entirely uncommon in this area.

&lt;?page 3?&gt;In general, the coating is substantially on the basis of titanium oxide if they (TiO₂) And it is deposited by sputtering, a rather high refractive index of about 2 or 2.1 or 2.15 or 2.2. It is generally from 2.15 to 2.35 or 2.35 to 2.50 (it may be slightly substoichiometric), especially from 2.40 to 2.45. This is quite a specific feature of this deposit type as coatings with the same character, which are applied by other methods, for example, a sol-gel process, tend to be much more porous and significantly less high refractive indices (below 2 and even below 1, 8 or 1.7 to have). The invention makes it possible to get by cathode layers has a porosity and / or a roughness (especially an RMS roughness of 2.5 to 10 nm) have to improve their photocatalytic properties / improve. Therefore, they may have refractive indices of about 2.15 or 2.35, as are conventionally obtained by sputtering lower, which is an indirect evidence of their porosity. This provides a visual perspective is an advantage, since they for a given thickness have a less reflective appearance with a lower refractive index.

It has been found that the crystallographic structure of the coatings is influenced by the fact that they are applied in the cold and then annealed. So, surprisingly, have the high pressure inventively applied coatings generally have an average TiO₂Crystallite size of generally less than or equal to 50 or 40 or 30 nm, and especially 15 to 30 nm or between 20 and 40 nm. The standard, especially "cold" applied and subsequently annealed coatings tend larger crystallites of a size of at least 30 nm or 40 nm, and generally contain from 40 to 50 nm when standard coating pressures.

In contrast, if according to the invention the coating is applied at ambient temperature, but at high pressure and then annealed, the crystallite size is smaller (20 to 40 nm) and comparable to the crystallite size of coatings in heat, whether at high or low pressure can be applied.

The photocatalytic activity of the applied at ambient temperature and high pressure, and then annealed coatings is significantly higher than that of the at low pressure and ambient temperature applied and subsequently annealed coatings, it being understood that, when all other things being equal, the coating pressure, the properties of the coating, especially in a "cold" coating, affected, and this. have noticeable

A the same time executive with the layer growth heating leads to the formation of a favorable structure for the surface roughness and / or an advantageous for the photocatalytic properties porosity. That is about the same as when a high pressure is coating (for example, in a "cold" coating and subsequent annealing) applied.

By the inventive method (coating at high pressure) coatings can be obtained which have a surface roughness RMS (Root Mean Square), measured by atomic force microscopy by on the same surface can be carried out with a distance of 2 microns measurements: <ul list-style="bullet"><li>- Of at least 2 nm, in particular at least 2.5 nm, preferably 2.8 to 4.6 nm in coatings at ambient temperature and high pressure according to the invention (2 to 5 Pa) and subsequent firings, and</li><li>- Of at least 4 nm, especially at least 5 nm, and preferably between 5.5 and 6.0 nm for coatings in the heat (about 250 ° C) without annealing, regardless of high or low pressure.</li></ul>

For comparison, the surface roughness of at ambient temperature and pressure (preferably 2 · 10^-3 Millibars, ie 0.2 Pa) applied coatings, which are then annealed, only at most 2 nm, which proves that the application of high pressures makes it possible to attain an astonishingly high roughness in layers that are deposited by sputtering, which is an improvement of has photocatalytic properties of the coating.

Advantageously, the geometrical thickness of the coating is less than 150 nm, especially 80 to 120 nm, or 10-25 nm. It has been shown that the coating, even if it is very thin, can have sufficient photocatalytic properties (at least at certain uses) with also the optical advantage that it is less reflective.

As was seen above, the sputtering of the coating may be reactive or non-reactive.

The coating method according to the invention may be preceded and / or followed by one or more steps for applying one or more other thin layers, in particular optical, antistatic, decolorizing, anti-reflective, hydrophilic and protective function or to &lt;?page 4?&gt;the roughness of the coating to enlarge with photocatalytic properties. So it has been observed that it may be advantageous to (at least) a layer applied such that it is particularly rough, for example, by pyrolysis or sol-gel method, and then applying the photocatalytic coating, which then tends the coating to the roughness of the underlying layer to "follow" and therefore also has a significant roughness, while the applied layers by sputtering rather have a tendency to be a little rough. It can so superstructures with a sub-layer (with an RMS roughness of for example at least 5 or 10 nm) of the type SiO₂, SiOC or SiON applied can be produced by gas phase deposition (CVD), and then the photocatalytic film by sputtering.

The invention therefore includes any combination between the application of one or more layers by sputtering (of which at least the photocatalytic coating), and the application of the or the other layers of the structure by a method in which a thermal decomposition, in particular a pyrolysis (from the liquid, gaseous or pulverulent phase) or a sol-gel method, is involved.

As was seen above, have the photocatalytic coatings on TiO₂-based High refractive index. This means that they are reflective and expressing their substrate a reflective appearance, which is often considered to be unattractive. In addition, the color can with reflection, apart from this brilliant character, be undesirable. It is not easy to improve this appearance in reflection, since the photocatalytic functionality has constraints: The coating must be in general with the external atmosphere in contact to receive UV light and reduce the external contaminants. It can not therefore be covered with a layer of low refractive index (at least it has to be very thin and / or porous). You must also have a given minimum thickness, to be sufficiently effective.

The invention also has as its object the glazing, in particular a simple glass plate (a rigid substrate), a laminated glazing and multiple glazing of the type of double glazing, comprising at least one coated in the manner described further above substrate.

The glazing may also include one or more other functional coatings include (deposited by sputtering, pyrolysis or sol-gel), either on the same side of the bearing the photocatalytic coating the substrate on the other side of the substrate or on one side of another substrate, the connected to the first in the glazing (double glazing or laminated glazing). You can also be a double-glazing type glass / gas filling / glass, being on (the) outside (s) of the glass panes, the photocatalytic coating and on the inside (the show for gas filling) is a building with one or two layers of silver. The same type of design can also be applied to laminated glass.

The other (s) functional (n) coating (s) can (can) in particular, for example, a dirt-repellent, be protective, niedrigemittierende, heated, hydrophobic, hydrophilic, non-glare and anti-static or another photocatalytic coating from sun. In particular, protecting or niedrigemittierende structures with one or more layers of silver, nickel chromium, titanium nitride or zirconium nitride may be mentioned from the sun. In the case of layers based on a metal nitride, a CVD method can be applied.

The invention will be further illustrated with reference to embodiments.

Example 1 and Comparative Example 1 relate to the deposition of photocatalytic TiO₂Layers by sputtering.

Example 1 (Invention)

On a 4 mm thick soda lime silicate clear gas, a 80 nm thick first layer of SiOC deposited by CVD, and then a 90 nm thick photocatalytic second layer of TiO₂ applied (the SiOC film can also be a SiO₂: Al-layer to be replaced, which is obtained by reactive cathodic sputtering from a doped Si target having Al).

The TiO₂Layer was deposited by magnetically enhanced sputtering. These were, starting from a titanium target by a reactive sputtering in the presence of oxygen. The glass was preheated to a temperature of about 220 to 250 ° C. This temperature was kept constant at ± 5 ° C during the spraying of the layer by means of a relative to the target arranged heated device.

The TiO obtained₂Layer had a refractive index of 2.44. She was in the anatase form (it may also contain amorphous zones) having an average crystallite size of less than 25 nm crystallized.

Their photocatalytic activity was quantified by means of an experiment, was used in which palmitic acid: It is a matter of applying a given thickness of palmitic acid on a photocatalytic coating, these having an ultraviolet radiation having a center wavelength of 365 nm and with an energy flux density of about 50 W / m² irradiate throughout the experimental period and then measuring the rate of disappearance of palmitic acid according to the following relationship: <maths><formula-text>V (nm · h^-1) = [Thickness of the palmitic acid (nm)] / [2 · t_1/2 Disappearance (h)].</formula-text></maths>

With the layer of the invention was determined by calculating a photocatalytic activity of at least 10 nm · h^-1, In particular of at least 20 nm · h^-1, Especially from 20 to 100 nm * h^-1 depending on the choice of the coating parameters of the type obtained pressure and temperature.

The glass thus provided with two layers had for a standard illuminant D65 light reflectance, R_L, Of 23%, with values ​​for a * and b * in accordance with the standard color chart (L, a *, b *) of about 17 or 28 at reflection.

The photocatalytic activity of the layer is therefore interesting, but their appearance is still clearly reflective with too intense color.

It should be noted that it is possible to increase the photocatalytic activity of the layer by a conventional annealing process is performed after the coating (one or more hours at at least 400 ° C).

Example 1

Example 1 was repeated, but this time was the TiO₂applied layer on a non-heated substrate, and then treated for four hours at about 500 to 550 ° C. In addition, the SiO₂Sublayer to 100 nm made thicker. The morphology of the film was a little different with an average crystallite size of more than 30 nm.

Their photocatalytic activity was similar to that of the layer of example 1 without annealing, but wherein it is lower when a smaller thickness of the SiO₂Sublayer is chosen.

In summary, the present invention is a new way of applying layers only photocatalytic TiO₂ include, developed under vacuum.