Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2002-02-22
2004-01-20
LaVilla, Michael (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S336000, C428S450000, C428S469000, C428S432000, C428S632000, C428S687000, C428S428000, C428S496000, C428S523000, C428S208000, C428S208000
Reexamination Certificate
active
06680135
ABSTRACT:
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 “dirt-repellent” 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
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 a degree of crystallization of at least 25%, in particular of approximately 30 to 80%, in particular close to the surface (the property being rather a surface property). (Degree of crystallization is understood to mean the amount by weight of crystalline TiO
2
with respect to the total amount by weight of TiO
2
in the coating).
It has also been possible to observe, in particular in the case of crystallization in anatase form, that the orientation of the TiO
2
crystals growing on the substrate had an effect on the photocatalytic behaviour of the oxide: there exists a favoured orientation (1, 1, 0) which markedly promotes photocatalysis.
The coating is advantageously manufactured so that the crystalline titanium oxide which it contains is in the form of “crystallites”, at least close to the surface, that is to say of monocrystals, having an average size of between 0.5 and 100 nm, preferably 1 to 50 nm, in particular 10 to 40 nm, more particularly between 20 and 30 nm. It is in fact in this size range that titanium oxide appears to have an optimum photocatalytic effect, probably because the crystallites of this size develop a high active surface area.
As will be seen in more detail subsequently, it is possible to obtain the coating based on titanium oxide in many of ways:
by decomposition of titanium precursors (pyrolysis techniques: liquid pyrolysis, powder pyrolysis, pyrolysis in the vapour phase, known as CVD (Chemical Vapour Deposition), or techniques associated with the sol-gel: dipping, cell coating, and the like),
by a vacuum technique (reactive or non-reactive cathodic sputtering).
The coating can also contain, in addition to the crystalline titanium oxide, at least one other type of inorganic material, in particular in the form of an amorphous or partially crystalline oxide, for example a silicon oxide (or mixture of oxides), titanium oxide, tin oxide, zirconium oxide or aluminium oxide. This inorganic material can also participate in the photocatalytic effect of the crystalline titanium oxide, by itself exhibiting to a certain extent a photocatalytic effect, even a weak effect compared with that of crystalline TiO
2
, which is the case with tin oxide or amorphous titanium oxide.
A layer of “mixed” oxide thus combining at least partially crystalline titanium oxide with at least one other oxide can be advantageous from an optical viewpoint, very particularly if the other oxide or oxides are chosen with a lower index than that of TiO
2
: by lowering the “overall” refractive index of the coating, it is possible to vary the light reflection of the substrate provided with the coating, in particular to lower this reflection. This is the case if, for example, a layer made of TiO
2
/Al
2
O
3
, a method for the preparation of which is described in Patent EP-0,465,309, or made of TiO
2
/SiO
2
is chosen. It is necessary, of course, for the coating to contain however a TiO
2
content which is sufficient to maintain a significant photocatalytic activity. It is thus considered that it is preferable for the coating to contain at least 40% by weight, in particular at least 50% by weight, of TiO
2
with respect to the total weight of oxide(s) in the coating.
It is also possible to choose to superimpose, with the coating according to the invention, a grafted oleophobic and/or hydrophobic layer which is stable or resistant to photocatalysis, for example based on the fluorinated organosilane described in Patents U.S. Pat. No. 5,368,892 and U.S. Pat. No. 5,389,427 and on the perfluoroalkylsilane described in Patent Application FR-94/08734 of Jul. 13, 1994, published under the number FR-2,722,493 and corresponding to European Patent EP-0,692,463, in particular of formula:
CF
3
−(
CF
2
)
n
−(
CH
2)
m
−SiX3
in which n is from 0 to 12, m is from 2 to 5 and X is a hydrolysable group.
To amplify the photocatalytic effect of the titanium oxide of the coating according to the invention, it is possible first of all to increase the absorption band of the coating, by incor
Boire Philippe
Talpaert Xavier
LaVilla Michael
Saint-Gobain Glass France
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