Coating processes – Optical element produced – Transparent base
Reexamination Certificate
2000-05-04
2003-01-07
Chen, Bret (Department: 1762)
Coating processes
Optical element produced
Transparent base
C427S255394
Reexamination Certificate
active
06503557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transparent substrate which is provided with at least one thin layer that is based on silicon nitride or silicon oxynitride. One application of the invention is the manufacture of so-called functional glazing assemblies used in buildings, vehicles, or as a plasma television screen. Another application which may be envisaged is the surface treatment of glass bottle containers. The invention also relates to a process for depositing these layers using a pyrolysis reaction.
2. Discussion of the Background
Within the context of the invention, the term functional glazing assembly should be understood to mean a glazing assembly in which at least one of its constituent transparent substrates is covered with a stack of thin layers so as to give it particular properties, especially thermal, optical, electrical or mechanical properties, such as scratch-resistance.
As an example, so-called low-emissivity thin layers are typically composed of a doped metal oxide, for example fluorine-doped tin oxide (F:SnO
2
) or tin-doped indium oxide (ITO), which may be deposited on glass using pyrolysis techniques. Once coated with a low-emissivity layer, the substrate mounted in a glazing assembly, in particular in a building, makes it possible to reduce emission, in the far infrared, to the outside of the room or vehicle interior through the said glazing assembly. By reducing the energy losses due in part to this radiation leakage, the thermal comfort is greatly improved, and particularly in the winter.
Alternatively, the substrate thus covered may be mounted in a double-glazing assembly; the low-emissivity layer being turned towards the gas-filled cavity separating the two substrates, for example, as the 3 face (the faces of a multiple-glazing assembly are conventionally numbered starting from the outermost face with respect to the room or the vehicle interior). The double-glazing assembly thus formed has enhanced thermal insulation, with a low heat-exchange coefficient, K, while maintaining the benefit of solar energy influx, with a high solar factor (i.e. the ratio of the total energy entering the room to the incident solar energy). On this subject, the reader may refer, in particular, to patent applications, EP-0,544,577, FR-2,704,543 and EP-0,500,445.
The low-emissivity layers are generally made of good electrical conductors. This allows the glazing assemblies, by providing suitable current leads, to be used as heating/de-icing glazing assemblies in motor vehicles, which application is described, for example, in EP-0,353,140.
Thin filtering layers, also called selective or anti-solar layers, are known which, when deposited on substrates mounted in a glazing assembly, make it possible to reduce the heat influx from solar radiation through the glazing assembly into the room or vehicle interior, by absorption/reflection. The layers may, for example, be layers of titanium nitride TiN (or titanium oxynitride), such as those obtained using a gas-phase pyrolysis technique and described in patent applications EP-0,638,527 and EP-0,650,938. The layer may also be a thin (less than or equal to 30 nm) reflective layer of aluminum, obtained by condensation of a metal vapor, CVD or the technique described in international patent application PCT/FR-96/00362 filed on Mar. 7, 1996, in the name of Saint-Gobain Vitrage.
The invention also relates to the techniques for depositing these various layers, and more particularly to those involving a pyrolysis reaction. These techniques consist in spraying “precursors”, for example of an organometallic nature, which are either in the form of a gas, or in the form of a powder, or are liquids by themselves or else in solution in a liquid, onto the surface of the substrate which is heated to a high temperature. On coming into contact with the substrate, the said precursors decompose thereon, leaving, for example, a layer of metal, oxide, oxynitride or nitride. The advantage of pyrolysis resides in the fact that it allows direct deposition of the layer onto the glass ribbon in a line for manufacturing flat glass of the float type, continuously, and also in the fact that the pyrolysed layers have (in general) very good adhesion to the substrate.
The low-emissivity or filtering layers mentioned above frequently form part of a stack of layers and are, at least on one of their faces, in contact with another layer, generally a dielectric material having an optical and/or protective role.
Thus, in the aforementioned patent applications EP-0,544,577 and FR-2,704,543, the low-emissivity layer, for example made of F:SnO
2
, is surrounded by two layers of dielectric of the SiO
2
, SiOC or metal-oxide type, which layers have a refractive index and a thickness which are selected so as to adjust the optical appearance of the substrate, in particular in reflection, for example its color.
In patent application EP-0,500,445, also previously mentioned, the low-emissivity layer of ITO lies under a layer of aluminum oxide so as to protect it from oxidation and also, under certain conditions, to avoid having to subject it to a reducing annealing operation and/or to allow the coated substrate to be bent or toughened without adversely affecting its properties.
The TiO
2
layer or the TiO
2
/SiOC double layer which covers the TiN filtering layer in the aforementioned patent application EP-0,650,938 also protects the TiN from oxidation and improves its durability in general.
However, the integrity of the stacks of thin layers is important. Thus, it is necessary for them to display:
the ability to withstand chemical attack. It frequently happens that the transparent substrate, once coated with layers, is stored for quite a long period before being mounted in a glazing assembly. If the coated substrate is not carefully packaged in a sealed, and therefore expensive manner, the layers with which it is coated may be directly exposed to a contaminated atmosphere or may be subjected to cleaning by detergents which are not well suited to removing dust therefrom, even if the substrates are subsequently joined together in a double-glazing assembly or in a laminated glazing assembly with the deposited thin layers as the 2 or 3 face, and therefore protected. Moreover, apart from the storage problem, there is a disincentive to use the substrates as “monolithic glazing assemblies” or to arrange the layers as the 1 or 4 face in the case of multiple glazing assemblies, i.e., configurations in which the layers are exposed all year long to the ambient atmosphere if the stacks are susceptible to chemical corrosion;
the ability to resist mechanical damage. For example, the transparent substrate, once coated with layers, may be used in configurations in which it is readily exposed to scratching damage. Consequently, on the one hand, the substrate no longer has a “correct” aesthetic appearance, since it is partially scratched, and, on the other hand, the durability of both the stack and the substrate is greatly diminished, because scratching may introduce possible sites of mechanical weakness, depending on the case.
There is therefore a continual search for a stack of layers having improved chemical and/or mechanical durability. However, these improvements must not adversely affect the optical properties of the assembly formed by the substrate and the stack of thin layers.
As mentioned previously, overlayers of dielectric material already exist which protect the underlying layers in the stack. In order to maintain integrity of an assembly that is exposed to intense or lengthy chemical corrosion, and/or to protect the possibly “weaker” underlying layers completely, patent application EP-0,712,815 describes a thin layer based on an oxide comprising silicon and a third element, for example a halogen of the fluorine F type, which facilitates the formation of a mixed silicon/aluminum structure.
The layer described above is particularly suitable for use as the final layer in stacks in which the functional layer is of the filtering or low-e
Chen Bret
Saint-Gobain Vitrage
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