Substrates, e.g. for windows, filter, electronic components, have hydrophilic coating based on oxidized silicon derivative covered by photocatalytic coating of at least partially crystallized titanium oxide

SELF-CLEANING COATING SUBSTRATE

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

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

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

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

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

Recent studies have been made to try to improve the comfort of use of these materials, in particular to facilitate their maintenance, and two main ways have been studied to give these materials such functionality.

According to a first approach, functional coatings having the particular feature of being highly hydrophilic have been studied and developed. This is the case, in particular, with coatings based on silicon oxide or oxycarbide which can be deposited on glazing in accordance with the teaching of patent WO.01 / 32578. This type of coating has a marked anti-fouling effect with respect to dust, especially with respect to mineral dust: a simple runoff of water on the surface of such a coating, which is very "wetting. », Allows dust to be carried away. This runoff can be natural (rain) if the substrate is used outdoors and exposed appropriately. It can also be caused: it becomes washing, but very easy, since there is no need to rub the substrate, and there is no need to resort to detergents. The substrates thus treated become dirty less, and less quickly. We can thus space out the more conventional washes, with detergents (especially when it comes to glazing). However, this hydrophilic coating has a less marked effect with regard to organic dust (which is for example residues of exhaust gases from motor vehicles, various residues of hydrocarbons in airport environments, or more simply, fingerprints). These organic soils tend to accumulate on the surface of the coating, gradually reducing, at least locally, its hydrophilic character. Its function of delaying fouling is therefore real, but capable of improvement depending on the type of soiling encountered, depending on the type of pollution to which the substrate is exposed.

According to a second route, functional coatings having photocatalytic properties have been developed. These are in particular coatings comprising at least partially crystallized partiellement1Ό2, in particular in anatase form and which are described in particular in patents WO.97 / 10185, WO.97 / 10186, WO.99 / 44954 and WO.01 / 66271 . This type of semiconductor material based on metal oxide, possibly doped (there are also other oxides capable of being photocatalytic, such as ZnO, etc.) is suitable under the effect of radiation of length of adequate wave to initiate radical reactions causing the oxidation of organic compounds: this type of coating, if it is sufficiently exposed to ad hoc radiation (generally ultraviolet rays, possibly the visible range), is therefore very effective in degrading organic soiling. In addition, it has been discovered that, in particular when it comes to coatings based on titanium oxide, these also exhibit a certain hydrophilic character if they are exposed for a sufficiently long time to said radiation. This coating is therefore very efficient, in that it is capable of degrading organic soiling, and of removing mineral soiling through its hydrophilicity. However, its activity is linked to its exposure (for a sufficient duration) to radiation (sufficiently intense) of ad hoc wavelength. This type of coating therefore has a behavior which strongly depends on the surrounding climatic conditions in the event of outdoor exposure, in particular the conditions of sunshine and rainfall. Likewise, it tends to have less nocturnal activity than its daytime activity, in the absence of appropriate lighting.

The aim of the invention is therefore to further improve the functionality conferred by these different types of “self-cleaning” or “fouling retardant” coatings. It aims in particular to obtain coatings which can have increased efficiency, which can be more "versatile" in various ways: first with respect to soiling of various chemical natures, then with respect to various climatic conditions in particular. use of the substrate outdoors. It aims more particularly to obtain coatings which can, even in poor sunlight conditions, even at night, exhibit a certain anti-fouling activity.

The subject of the invention is first of all a substrate which can be essentially transparent, in particular based on glass or on polymer®, or which can be made of ceramic or glass-ceramic, or which can also be made of architectural material (from facade plaster type, concrete slab or paver, architectural concrete, tile, cementitious material, terracotta, slate, stone, or which may also be a fibrous substrate, glass-based type insulation mineral wool or reinforcing glass yarns). This substrate is characterized in that it is provided on at least part of its surface with a first coating comprising one or more stacked layers preferably based on an at least partially oxidized derivative of silicon chosen from silicon dioxide. , substoichiometric silicon oxides, silicon oxycarbon, oxynitride or oxycarbonitride. This first coating is chosen so as to have a hydrophilic character, and it is surmounted by a second coating chosen so as to have photocatalytic properties. This second coating preferably comprises at least partially crystallized titanium oxide, in particular in the anatase form. This second coating has a discontinuous / permeable structure. By these terms is meant that the second coating is sufficiently porous, that it is sufficiently “non-covering” to leave accessible a certain part of the exterior surface of the underlying first coating. The distribution of the second coating (photocatalytic) on the first coating (hydrophilic) is advantageously chosen which is “regular”, or as regular as possible, in the sense that at the scale of mm² or cm² of substrate, there is approximately the same amount and / or the same thickness of second coating, and preferably distributed approximately in the same way on this scale. We will come back in more detail later on how the second coating is distributed over the first, how the structure of the second coating thus allows contact with the external atmosphere of the underlying coating, but two cumulative or alternative cases. are possible in particular: the second coating can be chosen so thin that it is in fact in the form of islands distributed more or less randomly on the surface of the first underlying coating. It can also have a porous structure, with at least partially open porosity, which allows water from the ambient atmosphere to reach the first coating. Preferably, both for the first and for the second coating, one remains in the range of interference thicknesses, for example of the order of at most one hundred nanometers for the first coating. Particularly in the case of coatings suitable for transparent substrates of the glazing type, these very small thicknesses guarantee that, even if the second coating is only in fact a collection of more or less disjointed islands, there is no inhomogeneity of the optical properties linked to the discontinuity of the second coating, no iridescence in particular.

The invention has therefore discovered a very interesting synergy between two coatings with complementary properties: the first coating, which is hydrophilic, is effective against soiling which is more of a mineral type, regardless of the sunshine conditions. It is able to be active under the effect of rain, or by splashing water. The second coating, for its part, is effective against organic soiling and even against mineral soiling when it has a certain hydrophilicity, its efficiency being dependent on the conditions of exposure to appropriate radiation (ultraviolet and / or in the visible most of the time). It is further designed to leave the first underlying coating with its anti-fouling property (at least in part), allowing water to pass through it (and dust to be entrained with). In addition, the hydrophilicity at least in part retained of the first coating retains its anti-fog and anti-condensation effects, which are also very appreciated.

This double coating is therefore very versatile: in the event of sunshine, the effectiveness of the fouling retardation is very high, by exploiting the complementary properties of the two coatings. And even in the event of weak sunshine (or at night), it retains a certain effectiveness, at least with respect to mineral soiling, either thanks to natural rainfall, or by simple water projection. The underlying first (hydrophilic) coating thus makes it possible to easily remove mineral soiling which is harmful because it is unsightly, but also because its accumulation could end up deactivating / passivating the photocatalytic properties of the second photocatalytic coating. So there is really a combination of effects which gives excellent results, whereas one would have expected that the second photocatalytic coating, because of its discontinuous / porous character, adds nothing or almost nothing. in terms of the anti-fouling properties of the underlying hydrophilic coating, or, worse, that it removes from the underlying hydrophilic coating its anti-fouling, anti-fog and anti-condensation properties.

Advantageously, the substrate according to the invention is essentially transparent, flat or curved, of the glazing type, printed or not, because it is in this type of application that the accumulation of dirt preventing visibility is the most troublesome, and that the washes are the most necessary to guarantee their transparency.

Preferably, the first coating of hydrophilic nature may be of the type of that described in the aforementioned patent WO.01 / 32578. It advantageously has a refractive index of between 1.45 and 1.80, in particular between 1.50 and 1.75, for example between 1.55 and 1.68. Such a relatively low index makes it possible, on a transparent substrate of the glass type, to avoid a reflecting effect which may be judged to be unsightly.

This coating therefore advantageously comprises Si, O, optionally carbon and nitrogen. But it can also include materials in a minority with respect to silicon, for example metals such as Al, Zn or Zr. This coating can be deposited by sol-gel or by pyrolysis, in particular by gas phase pyrolysis (CVD). This last technique makes it possible to obtain SiO coatings_xVS_y or in S1O2 quite easily, in particular by depositing directly on the float glass ribbon in the case of glass substrates. However, such a coating can also be deposited by a vacuum technique, for example by cathodic sputtering from an Si target (possibly doped) or from a silicon suboxide target (in an oxidizing and / or reactive atmosphere. nitriding for example).

This first coating preferably has a thickness of at least 5 nm, in particular a thickness of between 10 and 200 nm, for example between 30 and 120 nm.

To exacerbate its hydrophilicity, it has been shown that it is advantageous for this coating to have a certain roughness. It can in particular take the form of protuberances and / or hollows of nanometric size. It can more particularly be protuberances of which at least a part are not contiguous: it is thus possible to have a coating whose outer face has a relatively smooth profile from which protuberances emerge which can overlap, be joined, but whose at least some are disjoint. Such a surface structuring is achieved very particularly with coatings obtained by pyrolysis. It is also generally by this type of technique that it is possible to obtain coatings which are quite dense and strongly adherent to the substrate-carrier, therefore quite durable, which is of course of interest to the invention.

These protuberances / hollows have variable sizes, for example with a diameter distribution of between 5 and 300 nm, in particular between 50 and 100 nm. The term “diameter” is understood here in the broad sense, by assimilating these protuberances, hollow to full half-spheres (protuberances) or empty (hollow). It goes without saying that this is an average size, and that we include protrusions / hollows of more random shape, more elongated for example.

These protuberances and / or hollows may also have a height (for the protuberances) or a depth (for the hollows) of between 5 and 100 nm, in particular between 10 and 50 nm. This is an indication of the maximum value for each protrusion / hollow whose size we want to assess.

One way to measure these dimensions is to make the measurements based on photos taken by scanning microscopy (abbreviated as SEM).

These photos also make it possible to evaluate the distribution of these hollows / protuberances per unit area of ​​the substrate. It is thus possible to have a number of protuberances / hollows for this first coating evaluated between 5 and 300 per μm.² of substrate covered, in particular between 20 and 200 per μm².

One way to measure those protrusions / valleys that exacerbate hydrophilicity is to take rms roughness measurements expressed in nm. It is thus possible to have a roughness rms for this first coating of between 4 and 12 nm, in particular between 5 and 10 nm, more particularly between 6 and 9 nm.

The second coating, that with photocatalytic properties, is preferably thin, that is to say with a thickness of at most 10 nm, in particular at most 8 or 5 or 3 nm in thickness in the areas where it covers actually the first coating. In fact, it can be so thin that it tends to reach the detection limits of the apparatuses usually used to evaluate the thicknesses of interference layers. As mentioned above, the term coating is to be taken in its broadest sense insofar as this coating can be discontinuous, in the form of at least partly separate islands, or so porous that it can be considered as discontinuous. It is precisely this point which is surprising in the invention, that such a coating provides, despite its very “thin” character, a certain functionality.

One can, perhaps more precisely, quantify its presence not so much by a value of thickness as by a value of quantity of material deposited per unit surface area of ​​substrate (the possible discontinuity of the coating is thus taken into account). In this case, this quantity can advantageously be calculated at a value of at most 10 micrograms per cm.², especially not more than 5 or 3 micrograms per cm². We are preferably in a range of around 0.5 to 3 micrograms per cm², that is to say very low quantities (to be compared to the quantity of material per cm² provided for example by a first hydrophilic coating based on SiOC of about fifty nanometers, which is already about 10 micrograms per cm² substrate for an SiOC material that is less dense than solid Τ1Ό2.).

Advantageously, this second coating will therefore be capable of letting the first coating “breathe”, of leaving it at least part of the anti-fouling activity linked to its hydrophilic character that it would have in its absence.

The second coating is preferably deposited by sol-gel, pyrolysis of the CVD type or by a vacuum technique of the sputtering type.

Industrially, the most advantageous manufacture of this double coating consists in depositing the first then the second coating by pyrolysis in the gas phase, on a ribbon of float glass for example, continuously, when we are interested in glass substrates.

Advantageously, the second coating is essentially based on optionally doped titanium oxide, comprising grains or crystallites with a diameter of between 0.5 and 100 nm, in particular between 2 and 20 nm. Here again, “diameter” is to be taken in the broad sense, it is more of an evaluation of the size of the crystallite. The shape of the grain can be similar to a sphere or an elongated shape like a grain of rice or a completely random shape. These grains / crystallites can be at least partially contiguous. They can also exhibit cohesion by means of the amorphous oxide which incorporates / binds these crystalline grains.

Preferably, the ratio of the diameter of the protuberances of the outer surface of the first coating (hydrophilic) to that of the grains or crystallites of the second coating (photocatalytic) is at least 2, in particular at least 4.5 or even of at least 10.

Advantageously, the second coating will “follow” the roughness of the first, if there is roughness and even sometimes exacerbate it. Thus the surface roughness rms in nm of the substrate coated with the first hydrophilic coating and the second photocatalytic coating will be between 4 and 15 nm, in particular between 5 and 12 nm, more particularly between 7 and 10 nm.

Returning to an embodiment described above where the outer surface of the first coating is provided with hollows / protuberances and where the second coating comprises grains / crystallites, these grains / crystallites can be placed between these hollows / protuberances, and optionally cover, at least in part, these hollows / protrusions.

Advantageously, the transparent substrate, in particular made of glass of the glazing type, which is provided with the double coating according to the invention, has a light reflection R_L coating side of at most 12%, in particular at most 11% depending on the illuminant Dôs. We are thus dealing with a very poorly reflecting coating, which therefore does not penalize the substrate optically, which remains quite “neutral” optically. Its colorimeter in reflection can be very little intense, and in neutral colors, little (almost not) perceptible to the eye and preferably in blue-green. This colorimetry can for example be quantified by values ​​of a * and b * in the colorimeter system (L, a *, b *): preferably, b * is the negative sign. Preferably b * and a * are negative. In absolute values, a * and b * are preferably less than 5 or 4 or 3.

Advantageously, all of the first and second coatings exhibit photocatalytic activity characterized by a degradation rate of palmitic acid of at least 5 nm / h, in particular of at least 10 nm / h under exposure to appropriate radiation, in particular to ultraviolet. The conditions of the test measuring this degradation rate will be detailed in the subsequent description of the examples.

Again advantageously, the set of two coatings exhibits a hydrophilicity characterized by a contact angle with water of at most 10 or 5 °, with or without exposure to ultraviolet or visible radiation.

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

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

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

The invention will be described below with the aid of non-limiting examples and FIGS. 1 to 3. All of the figures are SEM images of the examples. In all the examples, the substrate 1 is a clear silico-soda-lime glass 4 mm thick (type of glass marketed by Saint-Gobain Glass France under the name SGG Planilux).

Example 1

This example relates to the deposition, on glass 1 in the form of a float glass ribbon, of a first coating 2 based on silicon oxycarbide, denoted for convenience SiOC (without prejudging the real rate of oxygen and carbon in the coating). This coating 2 is deposited by CVD from Si precursors in particular from a mixture of SiH₄ and ethylene diluted in nitrogen, using a nozzle arranged above and transversely to the float glass ribbon 1 of a flat glass production line, in the float chamber, when the glass is still at a temperature of about 600-700 ° C. The coating obtained has a thickness of about 50 nm and a refractive index of about 1.55. Still on the float line in the float chamber and at the same glass temperature, one deposits, using a second nozzle, the coating 3 based on titanium oxide, from titanium isopropoxide diluted in nitrogen. This coating is very thin, probably "non-covering" vis-à-vis the underlying coating. Its thickness is evaluated at less than 5 nm, corresponding to a quantity of Τ1Ό2 of the order of 1 microgram per cm² of substrate. The photos in figures 1a, 1b and 1c relate to this example 1, once the ribbon of glass has been cut off the float line: we see at two different scales, in top view and obliquely for figure 1c, the coating 2 which is sown with pseudo-circular protuberances 4 according to the section plane, and with a diameter of about 30 to 70 nm. We also see traces of the coating 3, in the form of grains 5 of size much smaller than the protuberances 4. These grains are arranged between the protuberances 4 and perhaps also at least also on these protuberances, but this is difficult to confirm in view of these photographs alone. These grains have a size of the order of 2 to 10 nm.

Glass 1 was then subjected to two series of tests, one in natural aging, the other in accelerated aging:

- Natural aging:

Glass 1 with the double coating was exposed outdoors for 6 months at Charles de Gaulle airport in the Paris region, on an incline and in direct contact with rain and sun. The environment of an airport is indeed a good test environment, because it is a highly polluted atmosphere, with notably higher levels of hydrocarbons in the air than elsewhere. It was found that after 6 months, the glass remained of a clean and wetting appearance: the glass treated according to the invention therefore has real “self-cleaning” capacities, even in climatic conditions that are not very. sunny nor very rainy that we meet in the Paris region. It is therefore capable of getting rid of organic soiling, even with a very thin or even discontinuous photocatalytic coating 3. And in addition, it remains hydrophilic. By comparison, uncoated glass, of the untreated SGGPlanilux type, subjected to exactly the same climatic conditions, loses its wetting character after 15 days of exposure, with visible traces of droplets and dust.

- Accelerated aging :

The photocatalytic activity of the glass treated according to Example 1 is first of all measured with the test known as the palmitic acid test. This test consists of depositing on 15 cm² from the surface of the treated glass, by spraying, a solution of palmitic acid (8 grams of acid for 1 l of chloroform), with a glass / spray distance of 20 cm, on a vertical substrate, and 3 to 4 successive passages. Next, the glass is weighed to evaluate the thickness of palmitic acid deposited in nanometers (having weighed the glass sample before depositing the palmitic acid). The glass is then exposed to UVA of around 30W / m². The photocatalytic activity is then calculated as the speed of disappearance of palmitic acid v (in nm / h), which is defined as follows:

V (nm / h) = (palmitic acid thickness (nm)) / (2 x T¹Λ (disappearance (h))

The v value for the treated area of ​​the treated glass is initially about 10 nm / h. Its contact angle with water is 5: this surface is therefore very strongly hydrophilic and also photocatalytic.

• Test in variable climate

This test is carried out according to the NF P 78 451 standard. It involves subjecting the glass to 4 cycles per 24 hours, with stages of 2 hours at 55 ° C in 95% relative humidity, then 1 hour at -15 ° C, with transitions of 1 hour 30 minutes. The contact angle with water is measured every 10 days as follows: the glass is subjected to a 20-minute UV exposure then the glass is stored at black for 72 hours. The measurement is then made, which is an average of three measurements on three different drops.

After 10 days of testing, the contact angle with water, which was 5 ° initially, increases to 10 °. Then, at 20 days, the contact angle with water drops back to 5 °. This value of 5 ° then remains more or less constant up to 55 days. These measurements therefore clearly prove that the hydrophilicity of the treated glass is well preserved over time, hydrophilicity which is probably the conjunction of the hydrophilicity of the first and of the second coating.

• High humidity test

This test is carried out according to standard EN 1096-2. This involves subjecting the glass to a temperature of 40 ° C in an enclosure saturated with humidity, with a relative humidity greater than 95%, with water streaming with a conductivity less than 30 yS and a pH greater than 5 on the treated side of the glass. The treated glass which has undergone this test for 10 and 20 days is then exposed to UV light, then it is stored for 72 hours in the dark as in the previous test. The water contact angle measurement is also an average of three measurements. After 10 days, the contact angle with water is 10 °, and after 20 days it has dropped back to 5 °.

• Neutral salt spray test

This test is carried out according to standard EN 1036. It involves placing the glass in an enclosure at 35 ° C, with a fine spray of hot brine at 35 ° C and neutral (5% NaCl in water), the treated surface being exposed to this fog. The contact angle with water of the treated surface is again measured under the same conditions as the two previous tests. The contact angle remains at 5 ° for 55 days.

Example 2

This example is similar to Example 1, but the coating 3 is "thicker", by spraying a greater quantity of titanium oxide precursor: in the case of Example 2, the quantity of Τ1Ό2 deposited on coating 2 is approximately 2.3 micrograms per cm² of substrate. The SEM photos of FIGS. 2a, 2b and 2c show the treated surface in top view and obliquely at two different scales: there is a structure similar to that of example 1. The initial photocatalytic activity of the treated surface is of 20 nm / h, and its initial contact angle with water is 5 °. After 15 days of variable climate test, the contact angle with water is 10 °. It is still 18 ° after 15 days of testing in high humidity (same conditions as in the example). Everything happens as if the presence of a larger quantity of photocatalytic Τ1Ό2 increased the photocatalytic activity of the coating by a factor of 2, but would be a reason (not yet explained) why the hydrophilicity would decrease a little after accelerated climatic aging. It should be noted however that ton is still in the presence of a hydrophilic coating in the common sense of the term with a contact angle with water of at most 20 °, after the tests undergone.

By way of comparison, FIG. 3 shows an SEM photo in top view of a glass coated only with the SiOC coating 2: the protuberances can still be seen, but the grains of Τ1Ό2 placed between these protuberances can no longer be seen.