UV-reflective interference layer system

Details UV-reflective interference layer system UV-reflective interference layer system

2002-10-21

2004-04-13

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of quartz or glass

C428S428000, C428S697000, C428S699000, C428S701000, C428S702000, C359S580000, C359S582000, C359S586000, C359S588000, C359S589000

Reexamination Certificate

active

06720081

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention concerns a UV-reflective interference layer system for transparent substrates with broadband antireflection in the visible wavelength range, a method for coating a substrate with such a layer system, and the use of such coating systems in various fields of application.
2. Description of the Prior Art
Currently known glass antireflections for the visible spectral range, such as the MIROGARD or the AMIRAN antireflection of Schott-DESAG AG, Grünenplan, are interference filters of three layers, wherein a layer with an intermediate index of refraction is first deposited, followed by a layer with high index of refraction, usually TiO
2
, and then a layer with low index of refraction, usually SiO
2
or MgF
2
. As the layer with intermediate index of refraction, for example, a mixture of SiO
2
and TiO
2
, but also Al
2
O
3
is used. Such three-layer antireflections are deposited, for example, on eyeglass lenses, on monitors, on plate glass, such as display window panels, on treated lenses, etc.
In most instances, these filters have a blue-violet or green residual reflection. When light impinges perpendicularly, the reflection characteristic of glasses coated on both sides is characterized in that the reflection within the wavelength interval of around 400-700 nm is less than 1%, for example, but outside this range the reflection rises to values of up to around 30% (V or W-shaped characteristic), i.e., far above the 8% of uncoated glass.
The drawback to such systems is that, when viewing at an angle that increasingly deviates from the perpendicular, the characteristic shifts to ever shorter wavelengths, so that the long-wave reflection maximum ends up in the visible range, and produces an undesirable red component to the reflected light color.
One goal of the present invention is therefore to find an antireflection whose residual reflection is low in a much broader wavelength range, i.e., in the range from 400 to at least 800 nm with perpendicular incidence of light, and which furthermore also provides broadband antireflection at rather large viewing angles. In many applications, such as display window glazings or glazings for pictures, a neutral-color appearance is in fact desirable, especially for different viewing angles.
Especially for picture glazings, say, in museums, but also in the case of display window glazings, furthermore, it is desirable that an antireflecting glass—if possible, color-neutral—at the same time provides the function of protecting the colors of the picture or the natural or synthetic fibers, as well as the dyestuffs of the window displays, against ultraviolet light.
As is known, the UV component of sunlight or that of lamp light, especially in the case of metal halide or other gas discharge lamps, but also even with halogen bulbs, is sufficient to cause considerable damage over a lengthy period of time, such as discoloration or embrittlement of natural or synthetic fabrics. A UV protection would also be desirable for glazings in office or residential buildings, in order to greatly reduce the fading of wood surfaces, draperies, upholstered furniture, etc., under direct sunlight, and thus enable, for example, an improved passive utilization of solar energy. Present-day thermal protection glasses, which contain a thin silver layer, are not antireflective in the visible range, and furthermore also do not offer sufficient UV protection, since thin silver layers become transparent in the UV.
In the case of known antireflective soft glass, UV protection is achieved by the use of organic polymers as absorbers of UV light, for example, as compound glass, wherein two glass panes are laminated together with a PVB plastic foil adapted by its index of refraction to the glass, for example, 380 &mgr;m in thickness (the glass MIROGARD-PROTECT from Schott-DESAG). Such glasses are [used] under intense lamp light, for example, as front panels for lamps, but they are not temperature-stable and they are also degraded by intensive UV radiation. Also, their three-layer antireflection on one side has the above-mentioned limitations, and furthermore the production of compound glass is costly.
Another possibility is the use of UV-absorbing varnish layers, which are several micrometers thick and are transparent to visible light. Such varnish layers are likewise not stable to UV and temperature, and after being deposited on the glass they must further be made antireflective. Regarding the state of the art, refer also to the following publications:
D1: H. Schröder, “Oxide Layers Deposited from Organic Solutions”, in Physics of Thin Films, Academic Press, New York, London, Vol. 5 (1969), pp. 87-140
D2: H. Schröder, Optica Acta 9, 249 (1962)
D3: W. Geffeken, Glastech. Ber. 24, p. 143 (1951)
D4: H. Dislich, E. Hussmann, Thin Solid films 77 (1981), pp. 129-139
D5: N. Arfsten, R. Kaufmann, H. Dislich, Patent DE 3300589 C2
D6: N. Arfsten, B. Lintner, et al., Patent DE 4326947 C1
D7: A. Pein, European Patent 0 438 646 B1
D8: I. Brock, G. Frank, B. Vitt, European Patent 0 300 579 A2
D9: Kienel/Frey (ed.), “Dünnschicht-Technologie [Thin layer technology]”, VDI-Verlag, Düsseldorf (1987)
D10: R. A. Häfer, “Oberflächen- und Dünnschicht-Technologie [Surface and thin layer technology]”, Part I, “Coating of Surfaces”, Springer-Verlag (1987)
whose disclosure contents are fully incorporated in the present application.
SUMMARY OF THE INVENTION
The object of the invention is to specify a coating for a transparent substrate, especially glasses, with which the above-described disadvantages can be overcome.
In particular, one should achieve a UV filtering, on the one hand, without the use of UV or temperature-unstable polymer foils or varnish, and, on the other hand, the antireflection of visible light should be much more broadband and color neutral at the same time.
As regards the UV filtering, one should achieve approximately the same characteristics as for foil or varnish systems.
According to the invention, the object is solved by an interference layer system that comprises at least four individual layers, wherein the consecutive layers have different indices of refraction and the individual layers comprise UV and temperature-stable inorganic materials.
Especially preferred is an interference layer system of five layers with the structure: glass +M1/T1/M2/T2/S, wherein the high-refracting material T has an index of refraction in the range of 1.9-2.3 at a wavelength of 550 nm, the low-refracting material S has an index of refraction between 1.38 and 1.50, and the intermediate-refracting material M has an index of refraction in the range of 1.6-1.8, with layer thicknesses of the individual materials in the ranges of 70 to 100 nm (M1), 30 to 70 nm (T1), 20 to 40 nm (M2), 30 to 50 nm (T2), and 90 to 110 nm (S).
In one embodiment of the invention the highly refractive material is titanium dioxide, the low-refracting material is silicon dioxide, and the intermediate-refracting material is a mixture of these substances.
In an alternative embodiment, instead of titanium dioxide one can also use niobium oxide Nb
2
O
5
, tantalum oxide Ta
2
O
5
, cerium oxide CeO
2
, hafnium oxide HfO
2
, as well as mixtures thereof with titanium dioxide or with each other, as the high-refractive layers; instead of silicon dioxide one can also use magnesium fluoride MgF
2
as the low-refractive layer; and instead of Ti—Si oxide mixtures one can also use aluminum oxide Al
2
O
3
or zirconium oxide ZrO
2
as the intermediate-refractive layers.
As the transparent substrate, in a first embodiment, one can use soft glass in the form of float glass, including a low-iron form.
As an alternative to this, one can also use hard glasses as the substrate, especially aluminosilicate and borosilicate hard glasses or quartz glass.
Besides the interference layer system, the invention also provides a method for applying it onto a substrate.
In a first embodiment of the invention, the individual layers are deposited by means of the dip method or

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