Substrate with a photocatalytic coating

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428428, 428432, 427164, 427165, 427166, 427167, 427255, B32B 1800, B05D 506

Patent

active

061033634

DESCRIPTION:

BRIEF SUMMARY
The invention relates to glass-, ceramic- or vitroceramic-based substrates, more particularly made of glass, in particular transparent substrates, which are furnished with coatings with photocatalytic properties, for the purpose of manufacturing glazing for various applications, such as utilitarian glazing or glazing for vehicles or for buildings.
There is an increasing search to functionalize glazing by depositing at the surface thereof thin layers intended to confer thereon a specific property according to the targeted application. Thus, there exist layers with an optical function, such as so-called anti-glare layers composed of a stack of layers alternatively with high or low refractive indices. For an anti-static function or a heating function of the anti-icer type, it is also possible to provide electrically conducting thin layers, for example based on metal or doped metal oxide. For an anti-solar or low-emissivity thermal function for example, thin layers made of metal of the silver type or based on metal oxide or nitride may be used. To obtain a "rain-repellent" effect, it is possible to provide layers with a hydrophobic nature, for example based on fluorinated organosilane and the like.
However, there still exists a need for a substrate, particularly a glazing, which could be described as "dirt-repellent", that is to say targeted at the permanence over time of the appearance and surface properties, and which makes it possible in particular to render cleaning less frequent and/or to improve the visibility, by succeeding in removing, as they are formed, the dirty marks which are gradually deposited at the surface of a substrate, in particular dirty marks of organic origin, such as finger marks or volatile organic products present in the atmosphere, or even dirty marks of condensation type.
In point of fact, it is known that there exist certain semiconductive materials based on metal oxides which are capable, under the effect of radiation of appropriate wavelength, of initiating radical reactions which cause the oxidation of organic products; they are generally referred to as "photocatalytic" or alternatively "photoreactive" materials.
The aim of the invention is then to develop photocatalytic coatings on a substrate which exhibit a marked "dirt-repellent" effect with respect to the substrate and which can be manufactured industrially.
The object of the invention is a glass-, ceramic- or vitroceramic-based substrate, in particular made of glass and transparent, provided on at least part of at least one of its faces with a coating with a photocatalytic property containing at least partially crystalline titanium oxide. The titanium oxide is preferably crystallized "in situ" during the formation of the coating on the substrate.
Titanium oxide is in fact one of the semiconductors which, under the effect of light in the visible or ultraviolet range, degrade organic products which are deposited at their surface. The choice of titanium oxide to manufacture a glazing with a "dirtrepellent" effect is thus particularly indicated, all the more so since this oxide exhibits good mechanical strength and good chemical resistance: for long-term effectiveness, it is obviously important for the coating to retain its integrity, even if it is directly exposed to numerous attacks, in particular during the fitting of the glazing on a building site (building) or on a production line (vehicle) which involves repeated handlings by mechanical or pneumatic prehension means, and also once the glazing is in place, with risks of abrasion (windscreen wipers, abrasive rag) and of contact with aggressive chemicals (atmospheric pollutants of SO.sub.2 type, cleaning product, and the like).
The choice has fallen, in addition, on a titanium oxide which is at least partially crystalline because it has been shown that it had a much better performance in terms of photocatalytic property than amorphous titanium oxide. It is preferably crystallized in the anatase form, in the rutile form or in the form of a mixture of anatase and rutile, with

REFERENCES:
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patent: 5618579 (1997-04-01), Boire et al.
patent: 5854169 (1998-12-01), Heller et al.
Journal of Materials Science, vol. 24, No. 1 M. Takahashi et al. "pt-tio2 thin films on glass substrates as efficient photocataylsts", Jan. 1989.
Chemical Abstracts, vol. 116, No. 10, abstract No. 89812a, p. 396, Sep. 1992.

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