Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-10-22
2001-04-03
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S216000, C428S332000, C428S336000, C428S432000, C428S433000, C428S446000, C428S697000, C428S699000, C428S701000, C428S702000, C359S580000, C359S585000
Reexamination Certificate
active
06210784
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a transparent substrate, in particular made of glass, provided with a thin-film stack including at least one metallic layer with infrared reflection properties, in particular a low-emissivity layer, arranged between two dielectric-based coatings.
The main application which the invention addresses is the use of such a substrate for the manufacture of thermal-insulation and/or solar-protection windows.
These are intended to be fitted both to buildings and to vehicles, in particular with a view to decreasing the air-conditioning workload and/or reducing excessive overheating entailed by the ever-increasing size of glazed areas in rooms and passenger compartments.
One type of thin-film stack well-known for giving a transparent substrate thermal properties, in particular low-emissivity properties, which is suited to the aforementioned required application consists of a metallic layer, in particular one made of silver, arranged between two dielectric-based coatings of the metal oxide type. This stack is, in the usual way, manufactured using a sequence of depositions carried out using a vacuum technique, for example sputtering, where appropriate assisted by a magnetic field.
A layer having a protective role for preventing degradation of the silver may also be provided in this stack.
In this type of stack, the silver layer essentially dictates the thermal, solar-protection and/or low-emissivity performance of the final window, whereas the dielectric layers primarily affect the optical appearance of the window obtained through interference. They furthermore have a function of protecting the silver layer against chemical and/or mechanical attack.
The improvements made to windows provided with stacks of the aforementioned type have so far allowed their field of application to be increased, while allowing them to keep a satisfactory level of thermal and optical performance.
Regarding the latter point, however, thermal performance is susceptible of yet further improvement, in particular with a lower insulation coefficient K being obtained.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a substrate provided with a thin-film stack of the aforementioned type, having improved thermal performance, but without this being to the detriment of its optical performance.
To that end, the invention relates to a transparent substrate, in particular made of glass, provided with a thin-film stack including at least one metallic layer with infrared reflection properties, in particular a low-emission layer, arranged between two dielectric-based coatings, the underlying coating having a wetting layer based on zinc oxide ZnO, optionally doped with aluminium ZnO:Al, directly in contact with the metallic layer.
According to the invention, each of the two coatings based on the dielectric material comprises at least one layer with high refractive index, preferably greater than or equal to 2.2.
It is to be noted that, in the context of the invention, a high refractive index means strictly greater than 2.
The combination according to the invention makes it possible to obtain a substrate both with very low emission and with very high optical transmission, these being performance features that are never achieved according to the prior art.
The calorimetric appearance of the substrate in reflection furthermore remains sufficiently neutral.
In order to achieve the solution according to the invention, the inventors firstly observed that, according to the prior art, it was necessary firstly to have a metallic layer thick enough to be able to achieve low enough an emissivity value, and that the presence of zinc oxide ZnO as a wetting layer directly in contact with the metallic layer precisely made it possible to limit the thickness of the aforementioned metallic layer to a value of the order of a few nanometers, typically of the order of 15 nanometers. They were then able to demonstrate that, in spite of the limitation of the thickness of the silver layer provided by the presence of the zinc oxide ZnO, it was not easy to obtain a low optical reflection value R
L
.
The inventors thought they had to resort to the insertion of a single high-index material, an effect which is known per se.
Surprisingly, they found that the insertion of this type of material on either side of the metallic layer not only optimized the desired anti-reflection effect. In addition, the fact that, according to the invention, the high-index layer of the upper dielectric coating is not in direct contact with the environment, such as air, this makes it possible to have a better colorimetric appearance of the substrate in reflection.
The functional metallic layer is advantageously based on silver. Its thickness may be selected between 7 et 20 nanometers, in particular between 9 and 15 nanometers, when it is desired to obtain windows with low emissivity and high optical transmission (in particular a T
L
. of at least 70 to 80%), particularly for those intended to be fitted to buildings in cold countries. When the desire is for reflective windows with a solar-protection function, which are intended rather to be fitted to buildings in hot countries, the silver layer may be thicker, for example between 20 and 25 nm (which clearly has the consequence of producing windows with much lower optical transmission, for example less than 60%).
Preferably, provision may be made for the stack according to the invention to have a protective metallic layer placed immediately above and in contact with the layer with infrared reflection properties.
The protective layer provided is advantageously based on a single metal selected from niobium Nb, titanium Ti, chromium Cr or nickel Ni or an alloy of at least two of these metals, in particular an alloy of nickel and chromium (Ni/Cr), and has a geometrical thickness of less than or equal to 2 nm. According to this variant, the metal or the alloy constituting the protective layer may be doped with palladium Pd. It fulfils its role as a “sacrificial” layer with the aim of protecting the functional layer in the case of depositing the next layer by reactive sputtering.
The wetting layer based on zinc oxide ZnO according to the invention preferably has a geometrical thickness of between 5 and 40 nm, in particular between 15 and 30 nm. With such thicknesses, further to its wetting function, it can contribute to adjusting the optical appearance of the stack in combination with the dielectric coating lying above the functional layer.
The wetting layer is advantageously based on at least partly crystallized zinc oxide. Such a layer makes it possible to avoid penalizing the stack from an optical point of view in the case when the carrier substrate if subjected to a heat treatment such as tempering or bending.
Each of the layers with high refractive index according to the invention can be arranged directly under the wetting layer if it is present, and may advantageously be based on a material selected from niobium oxide Nb
2
O
5
, manganese-doped bismuth oxide Bi
2
O
3
:Mn, a mixed oxide of zinc and titanium ZnTiO
x
, titanium oxide TiO
2
, a mixed oxide of tantalum and titanium TiTaO
x
, or a mixed oxide of zirconium and titanium ZrTiO
x
.
Of these materials, titanium oxide TiO
2
is particularly preferred, in particular because of its compatibility with the other layers in the stack according to the invention.
According to one variant of the invention, the dielectric coating above the reflective metallic layer has a superposed set of layers, including the layer with index greater than or equal to 2.2 and at least one layer whose refractive index is low, in particular less than or equal to 1.8, in particular less than or equal to 1.6. It may, for example, be a layer of SiO
2
, SiON or SiOAl.
According to another variant, the dielectric coating above the reflective metallic layer may also have, as an alternative or in addition to the first variant, a superposed set of layers, including the layer of index greater than or equal to 2.2 on top of which, in p
Didier Fabrice
Rondeau Veronique
Jones Deborah
McNeil Jennifer
Pennie & Edmonds LLP
Saint-Gobain Vitrage
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