Substrate with photocatalytic coating

The present invention relates to a method of sputtering a coating having photocatalytic properties, a substrate provided on at least one part of one of its sides with a coating having photocatalytic properties, and a glazing.

The invention relates to generally transparent or translucent substrates, in particular of glass, plastic, glass-ceramic, provided with a coating having photocatalytic properties to render them a dirt-repellent or more particularly self-cleaning function.

An important application of these substrates is for glazing that can have a wide variety of uses, from utility glazing to glazing used in electrical household appliances, from vehicle glazing to building glazing.

It is also used for reflective glazing of the mirror type (mirror for apartments or rear-view mirror for vehicles) and for non-transparent wall type glazing.

Likewise, the invention also applies to opaque substrates, such as ceramic substrates or any other substrate that can be used, especially as an architectural material (metal, tile cladding, etc.). It is preferably used, irrespective of the nature of the substrate, for more or less flat or slightly convex substrates.

Photocatalytic coatings, especially those based on titanium oxide crystallized in the form of anatase, have been studied for a long time. Their ability to break down organic soils or microorganisms under the influence of UV radiation is very interesting. They are also often hydrophilic in nature, which allows the removal of inorganic contaminants by spraying with water or, for exterior glazing, by rain.

This type of coating with anti-fouling, bactericidal and algaicidal properties has already been described in particular in WO 97/10186, which describes several methods of its preparation.

The invention therefore aims to improve the deposition methods of this type of coating, in particular to simplify them. At the same time, it also aims to improve the appearance of the coating, especially to improve the optical properties of the substrate on which it is deposited.

The present invention relates to a method of depositing a coating with photocatalytic properties, containing titanium oxide at least partially crystallized, especially in the form of anatase, on a transparent or translucent carrier substrate, such as glass, glass, ceramics, plastic, by sputtering, where the atomization is carried out under the deposition pressure P of at least 2 Pa, characterized in that the atomization is carried out at ambient temperature, after deposition of the coating, thermal treatment of the annealing type takes place.

Preferably, the deposition pressure P is at most 6.67 Pa, in particular at least 2.67 Pa.

Preferably, the coating has a refractive index greater than 2, in particular greater than 2.1, preferably between 2.15-2.35 or 2.35-2.50.

Preferably, the coating comprises titanium oxide crystallites with dimensions equal to or lower than 50 or 40 nm, preferably 15-30 nm or 20-40 nm.

Preferably, the coating has a RMS roughness of at least 2 nm, in particular at most 10 nm, preferably 2.5-7 nm or 2.8-5 nm.

Preferably, the coating has a geometrical thickness of less than 150 nm, in particular of 80-120 nm or 10-25 nm.

Preferably, sputtering is performed from a bombarded electrode, substantially metallic or non-reactive from a bombarded ceramic electrode. Preferably, a metal is added to the sputter bombardment electrode, in particular selected from Nb, Ta, Fe, Bi, Co, Ni, Cu, Ru, Ce, Mo, Al.

Preferably, the method is preceded and / or followed by the step of depositing at least one thin layer, in particular having an optical, antistatic, anticolor, antireflection, hydrophilic, protective, or to enhance the roughness of the coating with photocatalytic properties by cathode sputtering or by a method involving thermal decomposition such as pyrolysis or sol-gel methods. Preferably, the process is preceded by the deposition of at least one thin layer by pyrolysis, in particular by CVD, said thin layer having an RMS roughness of at least 5 nm, in particular at least 10 nm.

The subject of the invention is also a transparent or translucent substrate of the type of glass, glass, ceramics, plastic, provided on at least one part of one of its sides.

A photocatalytic coating comprising titanium oxide at least partially crystallized, in particular in the form of anatase, characterized in that a photocatalytic coating exhibiting a RMS roughness between 2.5 and 4.6 nm has been deposited by the method of invention.

Preferably, said coating has a high refractive index of at least 2, in particular at least 2.1 and at most 2.45 or 2.35, and in that it constitutes the last layer of a layer system of thin "anti-reflective" layers composed of alternating high and low layers. refractive index.

Preferably, the coating with photocatalytic properties has a refractive index equal to or higher than 2.30, in particular from 2.35-2.50 or equal to or lower than 2.30, in particular from 2.15-2.25.

Preferably, the photocatalytic coating has an optical thickness of 200-350 nm, in particular 210-310 nm.

Preferably, the coating with photocatalytic properties has an optical thickness of less than 50 nm, in particular of 25-45 nm.

Preferably the coating with photocatalytic properties has a geometric thickness of 80-120 nm, preferably 90-110 nm or 10-25 nm.

Preferably, the photocatalytic coating is sputter-deposited in the process of the invention.

Preferably, the coating with photocatalytic properties comprises titanium oxide crystallites with dimensions equal to or less than 50 or 40 nm, in particular 15-30 nm or 20-40 nm, or titanium oxide crystallites with dimensions of at least 30 nm, especially 30-50 nm.

Preferably, the anti-reflective layer system comprises at least three layers, successively a first high refractive index layer, a second low refractive index layer, and a photocatalytic coating that is attached or disconnected to at least one other high refractive index layer.

Preferably, the high index layer (s) has a factor of at least 1.9, in particular 1.9-2.3 or 1.9-2.2, e.g. on a matrix of tin oxide, zinc oxide, zirconium oxide, nitride. aluminum or silicon nitride or based on a mixture of at least two of these compounds.

Preferably, the first high-index layer has an optical thickness of 48-68 nm, especially 53-63 nm or 20-48 nm.

Preferably, the first high-index layer has a geometric thickness of 20-40 nm, or 25-35 nm or 10-20 nm.

Preferably, the low refractive index layer (s) has an index of 1.4-1.75, in particular 1.45-1.55, e.g. based on silica, alumina or a mixture of both.

Preferably, the low refractive index layer has an optical thickness of 20-79 nm.

Preferably, the low refractive index layer has a geometric thickness of 12-50 nm, especially 15-30 nm.

Preferably, the high index layer and the low index layer are replaced by a layer having an intermediate refractive index greater than 1.65 and less than 1.9, especially 1.75-1.85.

Preferably, the intermediate index layer is based on silicon and / or aluminum oxynitride or on a mixture of silicon oxide and at least one other oxide of tin oxide, zirconium oxide, titanium oxide, zinc oxide.

Preferably, the intermediate index layer has an optical thickness of 120-150 nm, in particular 125-135 nm, and preferably a geometric thickness of 65-80 nm, in particular 68-76 nm.

Preferably, a barrier layer for substances diffusible from a substrate, of the alkaline type, is interposed between said substrate and the anti-reflection layer.

Preferably, the barrier layer is based on a silicon oxide matrix, optionally containing Al, C or N, in particular with a thickness of at least 50 nm, e.g. from 60 or 80 nm to 200 nm. The invention also relates to glazing, in particular single glazing, thin-layer glazing, i.e. laminated, multi-layer glazing of the double-glazed type, characterized in that it comprises at least one substrate according to the invention.

Preferably, the glazing has a light reflection RL on the layer side of at most 20%, in particular at most 18%.

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Preferably the glazing shows light reflection on the side of the layers in blue or green with negative values ​​of a * and b * in the colorimetric system (L, a *, b *) and preferably less than 3 or 2.5 in absolute values.

Preferably, the glazing also comprises at least one other functional coating, in particular anti-pollution, solar control, low-E, heating, hydrophobic, hydrophilic, anti-reflective, antistatic or a second photocatalytic coating.

Preferably, the glazing on the first face comprises a photocatalytic coating containing at least partially crystallized titanium oxide, in particular in the form of anatase, and furthermore comprises one or more other functional coatings deposited by cathodic sputtering or pyrolysis or by the sol method at least on the second face. gel, especially anti-pollution, anti-sun, low-emission, heating, hydrophobic, hydrophilic coatings, anti-glare, anti-static or a second coating with photocatalytic properties.

Preferably, these other functional coatings, in particular solar control or low-E layer systems, consist of one or more layers of silver or of nickel / chromium or titanium nitride or zirconium nitride.

The present invention relates to a process for the cathodic sputtering of a photocatalytic coating containing titanium oxide at least partially crystallized in the form of anatase on a transparent or translucent carrier substrate. The method of spraying onto the substrate is carried out at a deposition pressure of at least 2 pascals. Preferably it is at most 6.67 Pa, in particular at least 2.67 Pa (i.e. at least 15 millitor, especially 20-50 millitor).

Indeed, as is known from the above-cited WO 97/10186, this type of coating can be deposited by sputtering. It is a method under reduced pressure, which allows, in particular, a very precise adjustment of the thickness and stoichiometry of the deposited layers. It is implemented in a magnetic field for greater efficiency. It can be reactive: it then starts from a bombarded electrode, essentially metallic, here on a titanium matrix (possibly fused with another metal or silicon) and the sputtering takes place in an oxidizing atmosphere, generally an Ar / O2 mixture. It may be non-reactive, then it starts from a bombarded electrode, called a ceramic electrode, which is already in the oxidized form of titanium (possibly in molten form).

However, the layers obtained by this type of method are generally amorphous, while the functionality of the coating according to the invention is directly related to the fact that it should be clearly crystalline. This is the reason why it was recommended in the above-cited patent the need to crystallize (i.e. increase the degree of crystallinity) of the coating by subjecting it to a thermal treatment, e.g. on the order of 30 minutes to several hours at a temperature of at least 400 ° C.

It was also shown that the increased pressure favored a specific crystallization of the layer, the level of density / roughness, which had a significant impact on the level of photocatalytic properties of the coating. In some cases, annealing may become optional. For the sake of clarity, the deposition pressure generally used for metallic oxides is usually in the range of 0.27-1.07 Pa (2-8 milliitor): in the process of the invention, therefore, a deposition pressure completely unusual in the field is selected. It has also been shown that it is possible to remove an optional post-coating treatment step or to make it at least optional (and / or to limit its length or temperature) by spraying the layer on a hot substrate, not at ambient temperature, especially at a temperature of at least 100 ° C. This heating during coating is alternative or combined with the application of the high pressures previously mentioned.

This heating has at least five advantages:

- energy profit during production,

- the possibility of using substrates which could not withstand the thermal treatment at 400-500 ° C, at least without degradation,

- in the case when the annealing requires the insertion of a barrier layer between the substrate and the photocatalytic coating, protecting against diffusion of the substrate elements (alkaline type, when it is glass), the possibility of using a very thin barrier layer, and even completely omitting the barrier layer, because thermal treatment is much less aggressive than annealing,

- the production cycle is much shorter (because the thermal treatment of the substrate is much shorter and at a much lower temperature),

- omission of the storage of "semi-finished" products for annealing.

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Nevertheless, the values ​​of photocatalytic activity for coatings are obtained quite similar to that of deposited and annealed coatings.

Now, this was not so obvious to predict, as it might have been expected that a prolonged annealing would be necessary to cause a gradual growth of nuclei in the amorphous oxide matrix. This was not the case: hot-coating promotes the direct deposition of the crystalline layer, at least partially.

It was also not obvious that the coating so deposited "hot" would crystallize preferably in the form of anatase rather than in the form of rutile (the form of anatase is much more photocatalytic than the form of rutile or titanium oxide cobite).

Depending on the type of spraying equipment available, it is possible to heat the substrate prior to deposition in a proper sense, outside the vacuum chamber. It is also possible to heat the substrate during coating while the coating chamber is equipped with heating means if necessary. The heating of the substrate can therefore be carried out before and / or during spraying of the coating. It can also be gradual during coating or act on only a part of the thickness of the deposited layer (e.g. the upper part).

The substrate is at a temperature of 150-350 ° C, preferably at least 200 ° C and more preferably 210-280 ° C when the layer is sprayed. Thus, sufficiently crystalline layers can be obtained without the substrate having to be heated to temperatures generally used for annealing, of at least 400-500 ° C.

Generally, when the coating is essentially a titanium oxide (TiO2) matrix and when deposited by sputtering ("hot" or at ambient temperature), it has a fairly high refractive index, greater than 2 or 2.1 or 2. 15, or 2.2. It is generally 2.15-2.35 or 2.35-2.50 (may be slightly below stoichiometric), especially 2.40-2.45. This is quite a specific property of this type of coating, because the coatings of this nature are deposited by other methods, e.g. by sol-gel, they are much more porous and have refractive indices much lower (below 2, and even below 1.8 or 1.7). The invention enables sputtering layers to be obtained which exhibit a porosity and / or roughness (especially RMS roughness) of 2.5-10 nm, increasing their photocatalytic properties. Therefore, they may have refractive indices of the order of 2.15 or 2.35 lower than those usually obtained by sputtering, which is a direct evidence of their porosity. This is optically advantageous as they appear less reflective at a given thickness when the refractive index is lowered.

The crystallographic structure of the coatings is influenced by the fact that they are cold deposited, then annealed or hot deposited. Surprisingly, the "hot" and / or high pressure deposited coatings generally have mean TiO2 crystallite dimensions generally equal to or less than 50 or 40 or 30 nm, and more preferably 15-30 nm or 20-40 nm. Coatings deposited in a standard manner, especially "cold", then annealed, tend to have larger size crystallites, at least 30 nm or 40 nm, generally 40-50 nm when standard deposition pressures are used.

Conversely, when the coating is deposited at ambient temperature but under high pressure and then an annealing operation is performed, the crystallites are smaller (20-40 nm) and comparable to the crystallite dimensions of the hot-deposited coatings, optionally under high or low pressure.

The photocatalytic activity of coatings deposited at ambient temperature under high pressure and then annealed is much better than that of coatings deposited at ambient temperature under low pressure and then annealed: for all other factors, it is clear that the coating pressure contributes to the good properties of the coating, especially everything in the case of "cold" deposition, and this significantly.

Heating simultaneously with the growth of the layer leads to the formation of a microstructure favoring roughness and / or porosity favorable to photocatalytic properties. This is almost the same case where high coating pressure is applied (eg with "cold" deposition followed by annealing).

By the method (by hot and / or pressurized coating), coatings showing RMS (Root Mean Square) roughness as measured by electron microscopy can be obtained by taking measurements on the same surface with steps of 2 micrometers:

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- at least 2 nm, in particular at least 2.5 nm, preferably 2.8-4.6 nm in the case of coating at ambient temperature under high pressure in the process according to the invention (2-5 Pa), followed by annealing,

- at least 4 nm, in particular 5 nm, preferably 5.5-6.0 nm in the case of hot-coating (about 250 ° C.) without annealing, optionally at high or low pressure.

For comparison, the roughness of coatings deposited at ambient temperature under standard pressure (especially 2.10-3 mbar, i.e. 0.2 Pa), then annealed, is only 2 nm at most: this confirms that the application of increased pressure allows to achieve The roughness is surprisingly high for the sputter-deposited layers, with the result that the photocatalytic properties of the coating are improved.

Preferably, the coating has a geometrical thickness of less than 150 nm, in particular of 80-120 nm or 10-25 nm. It appears that, although very thin, the coating can exhibit sufficient photocatalytic properties (at least for certain applications), further having the optical advantage of exhibiting low glare.

As noted above, the sputtering of the coating may be reactive or non-reactive. In both the first and second cases, a dopant can be added to the sputtering bombarded electrode, in particular of at least one metal. It may be one or more metals selected from the following list: Nb, Ta, Fe, Bi, Co, Ni, Cu, Ru, Ce, Mo, Al.

Before and / or after the coating process according to the invention, one or more steps of deposition of another thin layer or layers, in particular having an optical, antistatic, anticolor, antireflective, hydrophilic, protective, or to enhance the roughness of the coating with photocatalytic properties may be performed. Thus, it has been found that there may be the benefit of depositing one (at least) layer to be particularly roughened, e.g. by pyrolysis or by sol-gel method followed by photocatalytic coating; the coating then tends to "conform" to the roughness of the adjacent layer and, therefore, show considerable roughness, while the sputter-deposited layers tend to be less rough. It is also possible to make sandwich systems with a sublayer in this way (with RMS roughness, e.g. at least 5 or 10 nm), of the SiO2, SiOC or SiON type deposited by gas phase pyrolysis (CVD), then a photocatalytic layer by sputtering.

The invention thus covers any combination between the deposition of one or more layers by sputtering (at least one photocatalytic coating therein) and the deposition of another or other layers in a layered system by a method involving thermal decomposition, in particular pyrolysis (in the liquid, gas or powder phase) or by sol-gel.

As stated above, the photocatalytic TiO2 matrix coatings have a high refractive index. This means that they are reflective and that they give their carrier substrate a reflective appearance that is often considered to be unattractive. Moreover, the color of the reflection, due to its glossy nature, may be undesirable. Improving this reflective appearance is not simple as the photocatalytic functionality has limitations: the coating should generally be in contact with the outside atmosphere to come into contact with UV and break down external dirt. Therefore, a low-index layer cannot be applied to it (unless it is very thin and / or porous). The coating should also have a given minimum thickness in order to be sufficiently effective.

Another object of the present invention is therefore to improve the reflection appearance of the substrate without disturbing the photocatalytic activity of the coating, in particular by reducing its light reflection best and / or giving it a reflection color which is as neutral as possible.

The invention also relates to a transparent or translucent substrate as defined above and which is provided on at least one part of at least one of its sides with a photocatalytic coating containing titanium oxide at least partially crystallized as anatase, the coating having a high refractive index, at least 2 or 2.1 or 2.2. According to the invention, this coating is considered to be part of a layer system of thin anti-reflection layers, the coating being the last layer (i.e. the layer furthest from the carrier substrate). The antireflective layer system is composed of alternating high and low index layers and ends in the present case with a high photocatalytic index layer. The term "anti-glare" is used for convenience: it is generally used when seeking to obtain a reflection of light that is less than that of the substrate itself. In the context of the invention it is more a limitation of the increase in light reflection (and / or the modification or weakening of its color in reflection) caused by the use of a coating containing titanium oxide.

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For the purposes of the invention, by "layer" is meant a single layer or set of layers superimposed on each other. If it is a layer system, its total thickness is considered to be the sum of the thicknesses of each of the layers and that its total index is the average of all the refractive indices of said layers. This also applies to the photocatalytic coating. It can also be associated with another layer with a high index.

For the purposes of the invention and as mentioned above, by "anti-glare" is meant a function which allows to reduce the amount of light reflection from the coated substrate and / or to weaken its color in reflection, especially to make it the palest and most indifferent, as aesthetic as possible (says then it is also about the "anti-color" effect).

This is a fairly independent and unexpected adaptation of conventional anti-reflective layering systems. Indeed, as is known in the art, these layer systems alternate between high and low index layers and are terminated by low index layers (as close as possible to the refractive index of 1, air) and which are generally layers based on SiO2, MgF2, ... it ends with a high-index layer, which is rather paradoxical. However, when the characteristics of the various layers are conveniently selected, this particular anti-reflective layer system leads to a significant weakening of the intrinsic reflective character of the high index TiO and giving the substrate an acceptable color in reflection (neutral, in pale shades, avoiding reds and other warm colors considered not aesthetic enough, in favor of gray, blue or especially green).

The photocatalytic coating has a refractive index equal to or greater than 2.30, in particular of 2.35-2.50, or 2.40-2.45 (as stated previously, it can also be deposited to have only a factor of 2.10-2 ,thirty). It is preferably deposited by sputtering. Its optical thickness is selected, along with those of other layers of the layer system, to reduce light reflection from the substrate. It has been shown that the optimal optical thickness is about λ / 2 with λ about 580 nm. This corresponds to an optical thickness of 250-350 nm, in particular 270-310 nm; and a geometric thickness of 80-120 nm, in particular 90-110 nm. This range of geometric thickness turned out to be sufficient to obtain at the same time photocatalytic activity considered to be sufficient (photocatalytic activity depends in fact on many parameters, including thickness, but also surface roughness, crystal morphology of the layer, its porosity, ...). It is also possible to use much thinner layers, in particular having a geometric thickness of 10-25 nm.

Depending on whether the coating is sputter-deposited "hot" or at ambient temperature, cold and annealed, it contains crystallites with variable dimensions as stated above (generally below 30 nm "hot" and in the order of 30-50 nm or more at ambient temperature and standard pressure as demonstrated above).

According to the invention, the antireflection layer system in its simplest embodiment comprises three layers, successively a high index layer, a low index layer, then a high index photocatalytic coating.

The high index layer or layers of the layered system in addition to the photocatalytic coating generally has a factor of at least 1.9, in particular 1.9-2.3 or 1.9-2.2. It can be zinc oxide, tin oxide, zirconium oxide, aluminum nitride, or silicon nitride. It can also be a mixture of at least two of these compounds.

The optical thickness of these high-index layers is selected. Their optimum optical thickness is preferably in the region of λ / 10 with a λ of about 580 nm. This corresponds to an optical thickness of 48-68 nm, especially 53-63 nm, and a geometric thickness of 20-40 nm, especially 25-35 nm. It is also possible to choose a lower thickness, in particular from 20-48 nm.

The low index layer or layers generally has a factor of 1.4-1.75, especially 1.45-1.65. They can, for example, be based on silicon oxide, alumina or a mixture of both. The optical thickness of these low-index layers is chosen: their optimum optical thickness is preferably in the region of λ / 20 with a λ of about 580 nm. This corresponds to an optical thickness of 20-79 nm, especially 19-39 nm, especially 25-35 nm, and a geometric thickness of 12-50 nm, especially 15-30 nm, e.g. 20-28 nm.

According to another variant, in the three-layer sandwich system mentioned above, the sequence high index layer / low index layer may be replaced by a layer having an "intermediate" refractive index, i.e. preferably higher than 1.65 and lower than 1.9. The preferred range of the coefficients is 1.75-1.85. It may be based on silicon and / or aluminum oxynitride. It can also be based on an oxide mixture with a low index, such as SiO2 and at least 8

There is less one oxide with a higher index, such as SnO2, ZnO2, ZrO2, TiO2 (the ratio between the oxides allows the ratio to be adjusted).

This intermediate layer may also be used to replace the first sequence high index layer / low index layer in a layered system having, for example, not three, but five or seven layers.

The optical thickness of this layer with an intermediate factor is selected. The optimum optical thickness is about λ / 4 with a λ of about 580 nm. This corresponds to an optical thickness of 120-150 nm, in particular 125-135 nm, and a geometric thickness of 65-80 nm, especially 68-76 nm.

As mentioned above, these different choices of optical thickness take into account all aspects of the reflection from the substrate: an attempt is made not only to reduce the amount of light reflection RL, but also to give it a color which is currently considered aesthetic (i.e. in cold colors rather than towards yellow or red) and as low as possible. So you have to find the best compromise to make the rebound look better in this team. Depending on the application, it may be preferable to reduce the RL value, or rather to select a specific reflectance colorimetry (e.g. quantified by the a * and b * values ​​of the L, a *, b * colorimetric system or by the dominant wavelength associated with color purity).

Advantageously, the plurality of layers in the anti-reflective layer system can be sputter deposited one after the other on the same production line.

According to an optional variant of the invention, a barrier layer for substances capable of diffusing from the substrate may be inserted between the substrate and the anti-reflection layer. They are especially alkaline substances when the substrate is made of glass. It is, for example, a matrix of silicon oxide (or oxycarbide): SiO2 can be deposited by sputtering and SiOC, in a known manner by gas-phase pyrolysis (CVD). It is preferably at least 50 nm thick, e.g. of 80-200 nm. When selected from this type of material with a relatively small index (about 1.45-1.55), it is in fact generally broadly termed optically "neutral". The silicon oxide may contain a minority of elements, especially selected from Al, C, N.

The invention also relates to glazing, in particular plain glazing (rigid substrate), multi-layer glazing, multi-layer glazing of the double-glazed type, and which comprises at least one substrate coated according to the invention.

Due to the anti-glare effect, the aforementioned glazing preferably has a light reflection RL (on the layer side) of which at most 20%, in particular at most 18%, remains. Preferably, this light reflection has a pleasant tint in blue or green with negative a * and b * values ​​in the colorimetric system (L, a *, b *) and especially less than 3 or 2.5 in absolute values. The coloring is therefore a color that is both pleasing to the eye and pale, not very intense.

The glazing may also include one or more other functional coatings (deposited by sputtering or pyrolysis, or by sol-gel method), either on the same side of a substrate having a photocatalytic coating, or on the reverse side of that substrate, or on the side of another substrate bonded to the first. in glazing (double glazing or multi-layer glazing). It may also be a double glazing of the glass / gas layer / glass type with a photocatalytic coating on the outer side or sides of the glass and on the inner sides (facing the gas layer) in a layered arrangement of one or two silver layers. The same type of configuration applies to multi-layer glazing.

The other functional coating or coatings may be, in particular, anti-pollution, solar control, low-emission, heating, hydrophobic, hydrophilic, anti-reflective, antistatic, other photocatalytic coating etc. / chromium or titanium or zirconium nitride. In the case of layers based on metal nitride, the CVD method may be used.

The invention will now be described in more detail in non-limiting examples.

Examples 1 and 1, comparative, relate to the hot deposition of photocatalytic TiO2 layers by sputtering.

Example 1

On a transparent silico-soda-lime glass with a thickness of 4 mm, the first layer of SiOC by CVD was deposited, 80 mm thick, then a second layer of photocatalytic TiO2 with a thickness of

It is also possible to replace the SiOC layer with a SiO2: Al layer obtained by sputtering reactive sputtering from an Al-doped Si-bombarded electrode).

The TiO2 layer was deposited by sputtering in a magnetic field. It was reactive sputtering, in the presence of oxygen, from a titanium bombarded electrode. The glass was preheated to a temperature of about 220-250 ° C. This temperature was kept constant at about 5 ° C during the nebulization of the film by means of a heating device placed next to the bombarded electrode.

The obtained TiO2 layer had a refractive index of 2.44. It was crystallized in the form of anatase (it could also contain amorphous zones), with crystallite dimensions below 25 nm.

Its photocatalytic activity was quantified using the palmitic acid test: it consisted of depositing palmitic acid of a given thickness on the photocatalytic coating, exposing it to UV radiation, centered at 365 nm with a surface power of about 50 W / m² for the entire duration of the test, and then measuring the rate of disappearance of palmitic acid according to the following equation:

V (nm h^-1) = [thickness of palmitic acid (nm)] / [2 · t1 / 2 disappearance (h)]

For the layer obtained by the method according to the invention, this calculation resulted in a -1 -1 -1 photocatalytic activity of at least 10 nm · h^-1, especially at least 20 nm h^-1, especially 20-100 nm - h^-1depending on the choice of coating parameters, such as pressure, temperature.

The glass coated in this way with two layers had a light reflection RL of 23% at illuminant D65 and a * and b * reflectance values ​​according to the colorimetric system (L, a *, b *) of 17 and 28 respectively. The photocatalytic activity of the layer was therefore interesting, but its optical appearance still showed considerable reflection and a color too intense.

It should be noted that it is possible to increase the photocatalytic activity of the layer by subjecting it to conventional annealing after deposition (one or several hours at a temperature of at least 400 ° C).

Comparative example 1

Example 1 was repeated, but this time the TiO2 layer was deposited on an unheated substrate and then treated for four hours at a temperature of about 500-550 ° C. In addition, the SiO2 sublayer was thickened to 100 nm. The layer morphology differed little, with mean crystallite dimensions rather than 30 nm.

Its photocatalytic activity was similar to that of the Example 1 coating without annealing, but was lower when a lower SiO2 sublayer thickness was chosen.

Example 2 et seq. Relates to the inclusion of a high index photocatalytic TiO2 layer, especially deposited by sputtering, in anti-reflective layer systems to improve optical properties.

Example 2 (made)

The following system of layers was embedded on 4 mm thick silicon-soda-lime cast glass:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾ nm 22 nm 104 nm (geometric thicknesses)

Layer (1) of Si3N4 was deposited by sputtering reactive in the presence of nitrogen from an Al-doped Si-bombarded electrode.

The SiO2 layer (2) was deposited by sputtering reactive in the presence of oxygen from an Al doped Si-bombarded electrode.

The layer (3) TiO2 is photocatalytic and was hot deposited as described in example 1.

Optionally, an additional layer can be inserted between the glass and the Si3N4 layer, a SiO2 layer of about 100 nm obtained as the second SiO2 layer (2) described above. It has almost no effect on the optical properties of the substrate and can serve as a barrier layer against the alkaline substances of the glass. It is a choice, especially since the layers of anti-reflection coating under the photocatalytic layer, namely layers (1) and (2), are barrier layers themselves, quite sufficient, apart from their optical properties: these two layers already form a 100 nm barrier for substances capable of diffusion out of the glass.

The photocatalytic activity of the layer (3) was 80 nm · h^-1.

Alternatively, a cold-deposited, then annealed TiO2 layer can be used as described in Comparative Example 1.

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In the reflection from the side of the layers, the result for such a layered system was as follows:

RL (for the illuminant D65) = 17.3% a * (RL) = -2 b * (RL) = -2.8 λ_d (nm) = 494 nm (wavelength of dominant reflection of light) pe (%) = 2.5% (color purity in reflection)

Compared to example 1, a significant decrease in the RL value can be seen, the color obtained here was in shades of blue-green, rather pale. Overall, the reflective appearance was aesthetically pleasing and clearly improved.

Example 3

It was very similar to example 2, the only change was a slight change in the thickness of the TiO2 layer. Here are the data:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾ nm 22 nm 99 nm (geometric thicknesses)

The light reflection result was as follows (using the same conventions as for example 2):

RL = 17.9% a * = -0.8 b * = -0.7 λ_d (nm) = 494 nm pe (%) = 0.8%

So there was a little different compromise, with RL a little higher, but a * and b * lower in absolute terms.

Example 4 (modeling)

It was very similar to example 2, the only change was the thickness of the Si3N4 layer:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾ nm 22 nm 104 nm (geometric thicknesses)

The light reflection result was as follows (still using the same conventions):

RL = 15.8% a * = 0 b * = -9 λ_d (nm) = 475 nm pe (%) = 4.0%

There was a big drop in the RL value here, but the color in the reflection had a different shade.

Example 5 (modeling / comparative)

Compared to example 2, all thicknesses have been changed here. Here are the data:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾ nm 30 nm 75 nm (geometric thicknesses)

The light reflection result is as follows:

RL = 25.8% a * = -0.3 b * = -0.7 λ_d (nm) = 492 nm pe (%) = 0.5%

While the substrate showed a satisfactory color in reflection, it had an RL well above 20%, which is too much: the thicknesses selected were not optimal.

Example 6 (modeling / comparative)

Here, in the following layer system, the layer thicknesses recommended in the invention are even further removed:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ^<3) nm 20 nm 60 nm (geometric thicknesses)

The light reflection result was as follows:

RL = 30% a * = 2.3 b * = 7.2

Xd (nm) = 587 nm pe (%) = 14%

PL 200 159 B1

At the same time, it had a very high RL value, the color in reflection was not very sought after and very intense. So its appearance in reflection was not satisfactory.

Example 7 (made)

This time the layering was as follows:

Glass / SnO₂⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾ nm 27 nm 105 nm (geometric thicknesses)

So Si3N4 was replaced with SnO2 deposited by sputtering reactive in the presence of oxygen from a tin bombarded electrode.

The light reflection result was as follows:

RL = 17.4% a * = -2.8 b * = -2.7 λ_d (nm) = 496 nm pe (%) = 2.8%

The appearance in reflection was similar to that obtained in example 2.

Example 8 (modeled)

Here, the first two layers are replaced with one layer with a factor of 1.84 made of silicon oxynitride SiON. So here is the layering:

Glass / SiON / TiO2 nm 101 nm (geometric thicknesses)

The light reflection result was as follows:

RL = 17.4% a * = 0 b * = -1.08 λ_d (nm) = 480 nm pe (%) = 1%

The appearance in reflection was therefore satisfactory.

Example 9 (modeled)

Example 8 was repeated, but with a factor of 1.86 for the SiON layer.

The appearance in reflection turned out to be a little changed. The light reflection result was as follows:

RL = 17.8% a * = -1.1 b * = -1.5 λ_d (nm) = 494 nm pe (%) = 1.3%

Example 10 (made)

Here is a layered layout:

Glass / Si3N4 / SiO2 / Si3N4 / TiO2 ⁽³⁾ nm 17.5 nm 24 nm 92.5 nm

The last high-index "layer" was thus an overlapping of Si3N4 and TiO2 layers. The light reflection from the RL layers was 16.5-17.5%. The photocatalytic activity was about 80 nm · h^-1.

Example 11 (made)

The sandwich type of example 3 was taken again with different thicknesses. They were:

Glass / Si₃N₄⁽¹⁾ / SiO2 ⁽²⁾ / TiO2 ⁽³⁾

14.5 nm 43 nm 14.5 nm

The light reflection from the layers was 13-16%. Optical variations of the substrate covered in this way, if for each of the layers of the system the change was by 3%, were as follows:

ΔRL · = 0.8%

Δa * (Rl): = 0.3

Δ ^ (Rl): = 1.3

This example showed a photocatalytic activity of around 15-20 nm h^-1.

This example is interesting for several reasons: it was very insensitive to thickness variations, so it would be easy to produce industrially. It remained sufficiently photocatalytic, although the titanium oxide layer was very thin. It was satisfactory in terms of colorimetry.

PL 200 159 B1

In conclusion, the invention provides a new method of deposition under reduced pressure of layers containing photocatalytic TiO2. A new type of anti-reflection / anti-color layering system terminating in a high-index layer was developed, a layering system that is simple for industrial performance and greatly weakens the reflective appearance of TiO2 without destroying its photocatalytic properties. It allows to obtain glazing with a shade of blue or pale green in reflection, while maintaining fully logical thickness of the photocatalytic layer, in the order of tens of nanometers. It is also possible to choose a much thinner photocatalytic layer.

The invention is equally applicable to photocatalytic coatings which only contain TiO2.

The invention therefore proposes to deposit these coatings at ambient temperature, followed by an appropriate heat treatment, preferably with defined control of the coating pressure, to obtain layers deposited under reduced pressure having quite unusual properties, manifested by distinctive anti-soil deposition characteristics.