Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
2002-08-21
2004-11-16
Stein, Stephen (Department: 1775)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S428000, C428S447000, C428S448000, C428S336000, C428S698000
Reexamination Certificate
active
06818309
ABSTRACT:
The invention relates to the deposition of thin layers, especially those having an interferential thickness, on transparent substrates so as to confer a particular functionality on them.
The transparent substrates may be made of an organic polymer, of a glass ceramic or, preferably, of a glass, in various applications, detailed below, of the glazing, screen or mirror type.
A recurrent problem with transparent substrates of the glass type (or with semi-transparent substrates) is that of they gradually become fouled, requiring tedious periodic cleaning. Another problem is the phenomenon of condensation, when it causes undesirable misting in contact with water vapour and, beyond simple misting, a build-up of water droplets preventing vision.
At least partial solutions have already been proposed: thus, coatings are known which are based on a fluoropolymer whose highly hydrophobic surface allows water to be rejected and less dirt to be attached. Coatings having photocatalytic properties are also known, for example those comprising anatase-crystallized titanium oxide, which are effective for degrading at least organic dirt by oxidation.
These various types of coating are effective but relatively complex. Furthermore, none of them solves all the above mentioned problems optimally. Thus, hydrophobic coatings do not prevent the condensation phenomenon and, in contrast, photocatalytic coatings are only truly effective when exposed to ultraviolet radiation and can therefore be used more outside a dwelling than inside it.
The invention therefore aims to find coatings which are simple to use and are capable of facilitating the cleaning of glass-type or similar substrates and/or of lessening the phenomenon of water vapour condensation on their surface or at the very least of preventing the condensation from resulting in the appearance of misting or of a multitude of droplets.
The subject of the invention is a transparent substrate, especially made of glass, provided on at least one of its faces with a layer based on an at least partially oxidized silicon derivative chosen from silicon dioxide, silicon oxycarbide or silicon oxynitride, and having a hydrophilic character.
Within the context of the invention, the silicon derivative may comprise only the elements Si and O in the case of SiO
2
, the elements Si, O and N in the case of an oxynitride and the elements Si, O and C in the case of an oxycarbide. However, the silicon derivative according to the invention also includes materials furthermore containing, in minor amounts (by weight) compared with silicon, at least one metal such as aluminium, zinc or zirconium. The addition of a metal may have three advantages. By reactive sputtering, this addition amounts to “doping” the Si target in order to make it more conducting, thereby speeding up/facilitating the deposition. Furthermore, whatever the method of deposition (for example by pyrolysis), the addition of a metal of the aluminium type can increase the durability of the material, most particularly if it contains little or no carbon
itrogen. Finally, the addition of a controlled amount of this type of metal into the layer makes it possible to vary its refractive index, especially to increase it (aluminium oxide has in an index of about 1.65, while zinc and zirconium oxides have an index of about 2).
Within the context of the invention, the silicon derivative also includes silicon oxides which are substoichiometric in terms of oxygen, of formula SiO
x
, where x is less than 2.
The invention has thus revealed a novel characteristic of this type of material, namely a certain hydrophilicity giving it unexpected properties: it was noticed that the substrate, preferably glass, provided with this type of layer cleans much more easily than a bare glass (less friction force for cleaning the glass with a cloth, most of the dirt being removed without any effort by spraying water). Furthermore, the rate of fouling was observed to be less, making it possible to reduce the frequency of the cleaning operations, this effect being more marked if the glass is on the outside and exposed periodically to rain: by running down the glass, rain naturally carries away the dirt. The third unexpected effect is that any water condensation phenomenon on the surface of the glass coated in this way does not reduce visibility through the glazing or reduces it very little: it seems that the water appears in the form of an invisible, transparent and homogeneous liquid film, and no longer in the form of droplets.
The same improvements are observed when comparing a glass provided with a multilayer film surmounted by the layer according to the invention with a glass provided only with the multilayer film (for example a film having a solar-control or low-emissivity function or an optical function, terminating in a layer which is chemically different from that of the invention, for example a layer of a metal oxide or metal nitride).
These advantageous effects may be adjusted/increased by varying the chemical composition, the surface appearance and the method of deposition chosen.
Thus, the layer may have a refractive index of about 1.45 (pure SiO
2
) or greater than 1.45 in the case of a silicon suboxide or if the derivative contains carbon or nitrogen. Advantageously, in the latter cases, the refractive index is adjusted to be between 1.45 and 1.80, especially between 1.50 and 1.75 or between 1.55 and 1.68. The term “refractive index” should be understood to mean within the context of the invention either its refractive index within the usual meaning of the term when the layer is homogeneous with regard to composition and with regard to index through its thickness, or its apparent average index when the layer has a composition or an index which varies through its thickness. One advantageous embodiment of the invention relates in fact to layers whose refractive index decreases from the carrier substrate to the external surface of the layer.
There are two advantages in choosing a low refractive index:
on the one hand, the index is close to that of the glass when this is the substrate, thus preventing the glass from having a reflective appearance;
on the other hand, the more the refractive index tends to higher values, and the more the C or N content increases to the detriment of oxygen, and it turns out that the hydrophilicity of the layer is enhanced by increasing its oxygen content.
Another parameter that can influence the hydrophilicity of the layer is its surface roughness which, in certain embodiments of invention, is much higher than that of a standard bare glass.
The layer according to the invention may be deposited by any type of process capable of depositing thin layers of this type: the process may be a vacuum process such as sputtering, especially magnetic-field-enhanced sputtering (for example starting with a silicon target, optionally doped with boron or with aluminium). In order to favour the formation on the surface of Si—OH groups favourable to high hydrophilicity, it is possible to use a reactive atmosphere containing, for example, in addition to a purely oxidising compound of the O
2
type, a compound containing hydrogen and/or to use a compound containing both hydrogen and oxygen. The reactive atmosphere may thus contain an O
2
/H
2
, O
2
/H
2
O or H
2
O
2
mixture when a silicon oxide is manufactured. When a silicon oxynitride is to be deposited, it is possible to use reactive atmospheres comprising, as nitrogen and/or hydrogen compounds for example, an amine, an imine, hydrazine or ammonia. The SiO
2
(optionally doped with a small amount of a metal or with boron)—based layers deposited by reactive sputtering may have quite variable refractive indices. Depending on the deposition parameters chosen, especially the pressure when sputtering the target, the refractive index (averaged between 380 and 780 nm) of the layers may thus be in the region of 1.4-1.5, resulting in quite dense layers. It may also have a lower value of about 1.25-1.40, especially 1.28-1.35, for example, around 1.30 (to within ±0.05)
Azzopardi Marie-Jose
Durandeau Anne
Simonet Michel
Talpaert Xavier
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobian Glass France
Stein Stephen
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