Coatings with a silver layer

Details Coatings with a silver layer Coatings with a silver layer

2000-02-09

2003-06-03

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Light transmissive sheets, with gas space therebetween and...

C428S332000, C428S336000, C428S426000, C428S432000, C428S457000, C428S469000, C428S472000, C204S192100, C204S192120, C204S192150, C204S192260, C204S192290

Reexamination Certificate

active

06572940

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the production of a thin-layer system with a transparent silver layer by means of magnetron cathode sputtering, to a glass pane with transparent thin-layer system including a silver layer applied by magnetron cathode sputtering, and to a double glazing pane or unit (insulating unit) comprising such a pane.
2. Description of the Related Art
Glass panes with thin-layer systems for the purpose of influencing their transmission and reflection properties are being employed in increasing numbers for the glazing of buildings and vehicles. Here, in practice, in addition to pyrolytically applied layer systems based on semi-conductive metal oxides, primarily layer systems with at least one transparent silver layer are of significance. These layer systems typically possess the following structure: glass/lower antireflection layer/silver layer/outer antireflection layer. They are applied widely on a major industrial scale by means of magnetron cathode sputtering (U.S. Pat. No. 4,166,018).
In layer systems of this type, the silver layer serves mainly as an IR reflection layer, whilst the antireflection layers are employed specifically, through suitable selection of material and thickness, to influence the transmission and reflection properties in the visible region of the spectrum, according to application. It is generally endeavoured to provide the coated glass pane with a high light transmission factor, as well as maximum neutrality of colour in respect of transmission and external appearance.
A development of this layer system consists of employing more than one silver layer, where between the individual silver layers, additional transparent spacing layers are provided. The silver layers and the spacing layers then form a type of Fabry and Pŕot interference filter. These multiple-silver-layer systems allow the specialist further improved “fine tuning” of the optical data of glass panes coated in this way. Layer systems with two or more silver layers are employed primarily as solar control coatings, where especially high selectivity is involved. Selectivity denotes the ratio of light transmission factor to total energy transmission factor.
Thin-layer systems with only one silver layer are employed in practice primarily as large-area thermal insulation coatings which can be produced at relatively low cost, where importance is placed primarily on a high light transmission factor and a high reflection factor in the long-wave IR region, corresponding to low emissivity. From glass panes with such thin-layer systems it is possible, by combination with a normally uncoated second glass pane, to produce a thermal insulation glass which can be used primarily in the construction field, whose k value is 1.3 W/m
2
K or less.
As materials for the antireflection layers, in the case of common market products, primarily metal oxides such as SnO
2
, ZnO and Bi
2
O
3
are used; these can be applied especially cost-effectively by means of magnetron cathode sputtering. Numerous other materials have already been designated for this purpose. When selecting the materials for the individual component layers of the thin-layer system, the coating specialist must take account of a considerable number of conditions. Thus, for the properties of the thin-layer system, not only the refractive indices of the individual component layers and their thickness play a significant part in selective regulation of the optical properties in respect of interference. The component layers also possess different properties in respect of refractive index, crystalline structure, crystallite size, roughness, porosity, surface energy, etc., according to the process with which they are applied and which component layer had been applied beforehand. As is known, the properties of thin layers, which frequently consist of only a few atomic layers, are determined very pronouncedly by the conditions of epitaxy and on their boundary areas.
In the past, the specialist world has devoted special attention to improving the properties of silver layers. Silver layers are sensitive to a whole series of chemical and physical influences during the production of thin-layer systems, then during further processing and transportation of the coated glass panes, and finally during their use for the intended purpose. It is already known practice to protect the silver layer from the corrosive coating atmosphere during application of the outer antireflection layer of a Low-E thin-layer system by reactive cathode sputtering through application of thin metal or metal oxide layers (EP 0 104 870, EP 0 120 408). It is also known practice to protect silver layers from the influence of oxygen during heat treatment, for example during bending or tempering of glass panes by applying special auxiliary layers of greater thickness than that of the above-mentioned protective layers to the silver layer, which inhibit the diffusion of oxygen to the silver layer (EP 0 233 003). Both the first-mentioned protective layers and the last-mentioned auxiliary layers are preferably designed such that they are oxidised to the maximum extent in the finished product, so that they reduce the light transmission factor as little as possible and, as transparent dielectric layers, become component parts of the outer antireflection layers on the silver layers.
It is also known that the corrosion resistance of the silver layer can be improved by suitable selection of the materials for the lower antireflection layer. DE 39 41 027 A1, from which the invention is derived as generic state-of-the-art, teaches in this connection that the lower antireflection layer be configured as a sandwich coating, where the component layer contiguous to the silver layer will have an zinc oxide layer with a maximum thickness of 15 nm. The lower antireflection layer should according to this publication possess at least one further component layer, for which tin oxide, titanium oxide, aluminium oxide and bismuth oxide are named. Preferred, and dealt with exclusively in the embodiments, is a layer structure, where the lower antireflection layer possesses three component layers, that is to say, a first 2-14 nm thick layer of titanium oxide, a second 15-25 nm thick layer of tin oxide, and as third, the zinc oxide layer mentioned, with a maximum thickness of 15 nm. Onto the contiguous silver layer is applied, according to this publication, an outer antireflection layer, which consists of a metal layer of specially selected metals, permitting bending or tempering while being oxidized during the course of heat treatment, as well as of one or more additional metal oxide layer(s).
A similar structure is shown by EP 0 773 197, where the teaching is to be taken from this publication that to achieve a high level of light transmission and reduced emissivity, the zinc oxide layer contiguous to the silver layer is to be applied with a minimum thickness of 16 nm. As materials for at least one further layer of the lower antireflection layer, metal oxides, such as bismuth oxide, tin oxide or silicon nitride, are named. Both publications teach the application of the single layers required by means of conventional magnetron cathode sputtering, where metal targets are sputtered by application of a DC voltage (DC cathode sputtering).
SUMMARY OF THE INVENTION
The inventors have thoroughly investigated these and other previously known thin-layer systems and have found that they may be further improved in respect of the properties attainable. They have concerned themselves particularly with the problem that the transparent silver layers according to the state-of-the-art possess specific conductivity which is far below that which should be achievable for a defect-free silver layer of corresponding uniform thickness. This reduction in specific conductivity is especially apparent in the case of relatively thin silver layers. Thus, it was observed that in the case of thin-layer systems produced and constructed according to the state-of-the-art, me

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