Self-cleaning lighting device

CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 1 SELF-CLEANING LIGHTING DEVICE The present invention relates to a lighting device of the type subjected to atmospheric pollution, mainly organic.

Document EP 0 887 104 B1 describes the general principle of a TiO 2 coating on the translucent protective cover of a lighting device;

TiO 2, in particular in crystallized anatase form, exhibits photocatalytic activity, that is to say an ability to catalyze radical oxidations under UV radiation.

Oil residues from automobile exhaust gases, for example, can be broken down in this way into smaller, less sticky and less fatty particles than the starting oil.

TiO 2 also has a hydrophilic character: on TiO 2, water is deposited in the form of a film capable of guaranteeing the best distribution, dissolution and then elimination by hydrodynamic effect of the aforementioned degradation products.

There is therefore, in a manner known from EP 850 204 B1 in particular, synergy between the catalysis of radical oxidation and the fi ~ drophilicity of Ti02, for the production of a self-cleaning efFet, very decisive when the coated substrate is a glazing , since the best optical quality of transparency is thus preserved over the long term.

EP 887 104 B1 cites major families of processes for the preparation of TiO 2; in more detail is cited the heat treatment at 650800 ° C for 30 s. at 5 min - conventional tempering treatment of a glass sheet with a solution of titanium alkoxide.

Such a process aims to produce TiO2 mainly in anatase crystallized form, with a view to application to translucent protective covers for tunnel lamps.

The inventors have also studied this field of application, and realized that the effectiveness of a self-cleaning coating on tunnel lamps depends in particular on the position in the tunnel (distance from the ends of the tunnel) and CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 2 of the nature of the light source, in particular because this source has or does not have a UVA component (wavelength of 315-400 nm).

Indeed, it is essentially these wavelengths which are capable of activating TiO2 crystallized anatase.

Near one end of the tunnel, the amount of residual UVA may be sufficient for the photocatalytic activation of TiO2. On the other hand, the illumination source of the lamp itself may have a UVA component, a part of which sufficient to activate Ti02 is transmissible through the translucent cover, up to its surface in contact with the atmosphere of the tunnel. ; this is the case with fluorescent type lamps.

On the other hand, when the distance at the two ends of the tunnel is great and the light emitted by the lamp has little or no UVA component, which is the case with sodium lamps for example, the aforementioned TiO2 preparation process does not make it possible to obtain a product with sufficiently high photocatalytic activity for the desired and usable self-cleaning effect to be observed, unless specific and undisclosed operating conditions apply. this method of preparation does not allow it.

To solve this problem, the subject of the invention is a lighting device comprising a light source and a wall allowing at least part of the radiation emitted by said source to pass, said wall being coated on at least part of one at least. less than its two faces, of a photocatalytically active layer, characterized in that under the conditions of lower illumination, the photocatalytic activity of said layer is high enough to degrade and reduce organic soiling into easily removable particles which do not adhere to said layer, and / or to give said layer a hydrophilic character.

The weaker illumination conditions here refer to the fact that the photocatalytically active layer receives UVA neither from the atmosphere external to the lighting device, nor from the lighting source which has little or no UVA component.

The inventors thus provide lamps provided, on their surface in contact with the ambient atmosphere in particular, with a layer with such high photocatalytic activity that, even under low illumination at lengths CA 02552567 2006-07-05 WO 2005 / 070540 PCT / FR2005 / 050009 3 waves other than UVA, such as visible light, UVB, they have the property of breaking down fatty and sticky hydrocarbon vapors into fine particles, non-adherent dust, removable by aerodynamic effect (very low air current) or hydrodynamic effect (spraying of liquid).

This very high photocatalytic activity is also manifested by a marked hydrophilic character: this property also called wettability, observed in the context of the invention, also reflects the fact that the soiling that may be present is less greasy, and is products of radical degradation of soiling present on a lamp which has not been coated with the active layer.

The wall of the lighting system takes the usual shapes that are substantially flat, more or less curved or even with sharp angles, depending on what the materials and the manufacturing processes used allow.

According to a criterion of minimal photocatalytic activity, much greater than that exhibited by most of the known photocatalytic TiO2 layers, the layer according to the invention preferably comprises TiO2, and its photocatalytic activity under radiation of wavelengths centered on 365 nm and power 50 W / m2, induces a speed of disappearance of palmitic acid deposited on said layer, determined by measuring the haze and related to the amount of TiO ~; ~ of at least 10 nm.h- ~ .Ng ~ .cm2.

In a first main variant of the invention, the coated wall of the lighting device consists essentially of glass, in particular tempered so that a surface of 50 x 50 mm breaks into at least 40 pieces (standard R 43 for automotive tempered glass), including more than 50 pieces.

This choice guarantees maximum transmission of the light emitted, as well as the safety of the public in the event of breakage.

This security would be affected by breaking into a small number of pieces, then going hand in hand in a known manner, with a sharper shape of the edges thereof.

In this first variant, the problem of migration of alkalis from the glass (in particular Na) to its surface, which may occur in the event of heating - for example due to the lighting source, must be taken into consideration.

As discussed in EP 850 204 B1, alkalis affect the photocatalytic activity of a TiC ~ a coating.

A first means CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 4 to remedy this, according to the invention, consists in that at least in a zone of its surface oriented towards said photocatalytically active layer, said glass wall does not contain alkali and alkaline earth oxides in a total proportion exceeding 15% by weight, nor sodium oxide in a proportion exceeding 10% by weight.

Soda-lime glass thus dealkalized is obtained by treatments using various techniques, in particular electrical such as corona discharge, as described in documents WO 94/07806 A1 and WO 94/07807-A1.

In the second main variant of the invention, said wall is essentially made of a transparent plastic material or of several in combination.

Such suitable plastics are, for example, polycarbonate, polymethyl methacrylate, polypropylene, polyurethane, polyvinylbutyral, poly (ethylene terephthalate), poly (butylene terephthalate), resin ionomer such as ethylene / neutralized (meth) acrylic acid copolymer by a polyamine, cycloolefinic copolymer such as ethylene / norbormene or ethylene / cyclopentadiene, polycarbonate / polyester copolymer, ethylene / vinyl acetate copolymer and the like, alone or in mixtures.

Of course, the preparation temperatures ~ y of the photocatalytic layer of the order of 650 ° C or more are incompatible with deposition on these plastics.

The highly active layer in accordance with the invention can on the contrary be prepared at a more moderate temperature, not exceeding 250 ° C. for example, or even at room temperature, it is therefore possible to coat the plastics with it without affecting them in any way.

In each of the two main variants mentioned above, a layer in particular based on silicon is advantageously interposed between said wall and said photocatalytically active layer; it is ~ when the wall is made of glass, a barrier layer to the diffusion of alkalis from the glass, constituting a second solution to the above-mentioned problem: interlayer of silica and derivatives such as oxycarbide or silicon oxynitride, SiOX with x <2 prepared by thermal CVD on a float glass ribbon supported by the bath of molten tin, by vacuum technique such as magnetron, by sol-gel route, etc;

CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 ~ when the wall is made of plastic, an anti-scratch layer essential in this case: SiOCH (N) interlayer by plasma-assisted chemical vapor dep8t (PE CVD), electron beam evaporation, magnetic field assisted sputtering (magnetron), ion assisted CVD, ion source CVD, etc.

The antifouling effect being correlated, in a known manner, with the thickness of the active layer for a fixed photocatalytically active composition, this thickness is advantageously between 100 and 1000 nm, and the surface density of the TiO 2 layer between 1 and 100 ; preferably 2 and 65 Ng / cm2.

To make the most of the synergy between the ability to catalyze radical oxidations and the hydrophilic nature, the lighting device of the invention advantageously comprises a means of spraying liquid on the active layer, which is moreover already provided on the headlights of certain motor vehicles, for example, in the absence of a photocatalytic layer.

Preferably, the translucent wall of the lighting device is coated, at least on its face opposite to said light source, with the photocatalytically active layer. It is in fact the problem of pollution of the exterior surfaces of the lighting device which is' i'é more important (atmospheric pollution) and which it is intended to resolve in a privileged manner within the framework of the invention.

However, insofar as the light source is protected in an enclosure which may not be waterproof, the face of said wall oriented towards this light source may be accessible to some organic pollution. It is therefore not excluded to coat this face with a photocatalytically active layer.

In this case, the proportion of the radiation from the light source capable of activating the layer is much greater than for a layer on the opposite face, a greater or lesser proportion of the radiation not being transmitted through the wall.

Excellent results are obtained in particular with an active layer comprising Ti02 doped with Fe, Nb, Ta, Pt, Rh, Ag, Pd, Sn, Cd, W, Ce, Zr, Cu, Ru, Mo, Al, Bi, V , Co and / or Ni, optionally their oxides and / or salts, CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 6 in particular in particulate form of smaller dimensions than those of the Ti ~ 2 particles and in an intimate mixture or alloy therewith.

Doping amplifies the photocatalytic phenomenon due to titanium oxide, by increasing its absorption band and / or by increasing the number of charge carriers and / or by increasing the yield and the kinetics of the photocatalytic reactions.

The doping element can consist of small particles interposed between the titanium oxide crystallites aggregated into nanoparticles, that is to say integrated into them, or of small particles distributed on the outer surface of the TiO 2 nanoparticles, or even in a thin layer covering the photocatalytically active layer.

The subject of the invention is also a method of manufacturing the lighting device described above, in which said photocatalytically active layer is formed by sol-gel, by thermal chemical vapor deposition (CVD) or assisted by plasma at atmospheric pressure. (APPECVD), or under vacuum or at reduced pressure, in particular by cathodic sputtering assisted by a magnetic field (magnetron).

The sol-gel processes are particularly well suited to deposits on walls of complex shapes.

According to a preferred method of preparing the layer with high photocatalytic activity, the latter is formed into a mesoporous structure by the solgel route comprising ~ the preparation of a liquid composition comprising at least one precursor of the essentially mineral material constituting the mesoporous structure of said layer and at least one organic structuring agent, ~ the precipitation of the precursor around the organic structuring agent and the growth of molecules derived from the precursor, ~ the addition to the liquid composition of nanoparticles or elementary crystallites of optionally doped titanium oxide, of diameters between 0.5 and 100 nm, ~ the application of the composition to the surface to be coated, CA 02552567 2006- 07-05 WO 2005/070540 PCT / FR2005 / 050009 7 the elimination of the organic structuring agent, the titanium oxide crystallites being incorporated into the mesoporous structure while essentially preserving their integrity therein, several of them can be aggregated into nanoparticles.

Preferably, the temperature does not exceed 250 ° C. in the implementation of this process, so as to preserve a conventional toughening of glass.

Thus, the step of removing the structuring agent can consist of heating at 250 ° C. for 2 hours, or else irradiation with UVA at ambient temperature.

Other objects of the invention are - a glass or plastic-based wall intended for the lighting device described above, and - the application of the above lighting device to the lighting of a tunnel , public lighting, airport runways, or headlights or signaling lights of land, water or air transport vehicles, in particular of motor vehicles, as well as interior lighting.

The invention is illustrated by the example below.

EXAMPLE A sublayer based on silicon oxycarbide, denoted SiOC for convenience, is deposited on the glass, again in the form of a ribbon of float glass (without prejudging the actual level of oxygen and carbon in the coating).

This sublayer is deposited by CVD from Si precursors, in particular a mixture of SiH4 and ethylene diluted in nitrogen, using a nozzle placed above and transversely to the glass ribbon. float of a flat glass production line, in the float enclosure, when the glass is still at a temperature of about 550 to 600 ° C.

The resulting coating has a thickness of about 50 nm and a refractive index of about 1.55.

Samples of float glass provided with its alkali barrier SiOC sublayer thus obtained are cut to the dimensions of a tunnel lamp cover; these samples are washed, rinsed, dried and subjected to a UV ozone treatment for 45 min.

When the glass is subjected to bending / tempering, an alternative to the SiOC underlayer by CVD in the float is an Si02 layer by sol-gel in CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 8 recovery, on bent-tempered glass, practically cold or at a temperature not exceeding 250 ° C, allowing the benefit of the toughening to be retained.

This layer is in fact equivalent to SiOC by CVD in the alkali diffusion barrier function.

A coating with a mesoporous structure is formed on the sublayer.

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

In a second step, a solution of a polyoxyethylene-polyoxypropylene block copolymer marketed by the company BASF under the registered trademark Pluronic PE6800 (molar mass 8000) is added to the sol obtained previously, in proportions such that the molar ratio PE6800 / Si = 0 , 01.

This is obtained by mixing 3.78 g of PE6800, 50 ml of ethanol and 25 ml of the soil.

The crystallized anatase TiO 2 nanoparticles of approximately 50 nm size are added to the liquid composition thus obtained, just before the deposition on the sample.

The deposit is made by spin coating in a starting amount of 3 ml per sample. (Other equivalent deposition techniques are dip coating, spraying, laminar coating, roll coating, flow coating, etc.) The samples are then heated at 250 ° C. for 2 hours.

The pores of the coating thus formed have a size of 4-5 nm.

It is verified by SIMS analysis of the coating with a mesoporous structure that the atomic ratio Ti / Si is exactly identical to that of the starting liquid composition. The SIMS analysis also makes it possible to verify that the nanoparticles are distributed homogeneously in the three dimensions of the coating.

The thickness E of the coatings in nm is measured from SIMS profiles and SEM images.

The amount of Ti02 in ~, glcm2 is evaluated by X-ray fluorescence.

The photocatalytic activity is measured as follows: 1. - test carried out on approximately 15 cm 2 of coating;

2. - Weighing of the sample and measurement of the thickness of the substrate, of the light transmission T ~ and of the blur Td (both in%);

CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 9 3. - spray deposition of a solution of palmitic acid (8 grams of acid for 1 L of chloroform), with a verrelspray distance of 20 cm, on vertical substrate, and 3 to 4 successive passages;

4. - Weighing of the sample after deposition of palmitic acid to evaluate the thickness of palmitic acid deposited in nanometers;

5. - Measurement of the light transmission T ~ and of the blur Td after deposition;

6. - measurement of the variation of the haze as a function of the irradiation time under UVA with an intensity of approximately 50W1m2;

7. - graphic determination of the time after which the blur has decreased by 50% time called T ~, 2 (disappearance);

8. - evaluation of the photocatalytic activity of the coating in speed of disappearance of palmitic acid v (in nm / h), which is defined as follows v (nm / h) _ (thickness of palmitic acid (nm)) / (2 x T ~~ Z (disappearance (h)) The value of the photocatalytic activity reduced to the amount of TiO2 in the coating is also measured.

Finally, the optical properties of light reflection RI and blur Td (in%) are indicated.

The Ti / Si ratio is equal to 1.

We obtain: -w "= ~ '~ E = 454 nm Ti02 = 33.3 Ng / cm2 V = 620 nm / h V / Ti02 = 18 nm.h' '. Ng ~ .cm2 Ri = 9.7% Td = 0.3 Two sodium tunnel lamps, radiating hardly any UVA, and two of the fluorescent type, are equipped with a glass cover treated according to the example.

Two lamps of each of the above types are fitted with an untreated float glass cover.

A lamp of each type with a treated glass cover, and one with an untreated glass cover, is placed separately for 84 days in the CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 tunnel entrance area. on the one hand, in the central tunnel zone receiving almost no or very little UVA from the outside atmosphere.

When dismantling, care is taken to ensure that the treated glasses are not exposed to UVA rays not present in the tunnel.

5 The lights are not switched on all the time, as the tunnel is rarely 100% lit, but on average 9:30 a.m. per day.

The treated glasses are perfectly wetting on installation.

The lids are examined as follows: visual observations of pollution;

10 ~ noted on a cloth the dust deposited on a surface of 5 cm2: revealing of the state of soiling, and allows to understand the ease of cleaning ("easy to clean" function);

~ evaluation of hydrophilicity by depositing a few drops of deionized water on the surface of the glass.

The results are recorded in the tables below. Input zone Fluorescent lamp Sodium lamp Treated Untreated Treated Untreated Observations Little Presence of Little Presence of visuals ~~~ '' dust dust dusts which generate a haze haze Rag test Lightly soiled Dirty Lightly soiled Dirty Hydrophilicity Wetting Non-wetting Wetting Wetting Table 1: Expertise in the entrance area for the 2 types of lamps CA 02552567 2006-07-05 WO 2005/070540 PCT / FR2005 / 050009 11 Central zone Fluorescent lamp Sodium lamp Line Untreated Line Untreated Observations Presence Presence of presence of visual dust dust dusts generate a haze which generate a No very clear difference a haze + between the 2 glasses important only on treated glasses Test with a cloth Very dirty, Very dirty, Very dirty but in both cases but impression No difference in very clear oily dust between the 2 easy-to-peel glasses Hydrophilicity Wetting Non-wetting Wetting Non-wetting Table 2: Expertise in the central zone for the 2 types of lamps The difference in behavior in the entrance zone can be explained by ~ the presence of UVA which enter the tunnel, and allow the Ti02 layer of the hearth to perform better ~ pollution less confined than in the central zone In the central part, there is pollution of the glasses, even treated, and a hydrophilic character maintained for the treated glasses.

On the other hand, for treated luminaires containing fluorescent lamps (UVA emission and therefore activation of the layer), the pollution is in the form of dry dust which is very easily detached from the surface.

Strong adhesion is observed on untreated glasses with the presence of fatty pollution.

Thus, the inventors provide lamps that are permanently clean and / or easy to clean under the weakest illumination conditions and the strongest pollution.