Multilayered system with high reflective capability in the infrared spectrum and high transmissivity in the visible light range.

p0001The invention relates to a multi-layer system of high reflectivity in the infrared spectral region and of high transmissivity imsichtbaren spectral region, having a carrier substrate and two metal layers, which are embedded fine metal oxide layers between the two, an intermediate dielectric layer and a dielectric layer and arranged by a dielectric spacer layer at a distance from each other ,

p0002Such a multilayer system is known from US-PS 4,799,745 and is used as transparent in the visible region but in the infrared reflecting film which can be used in particular in the production of windshields for motor vehicles. The layer construction of the known multi-layer system is a Fabry-Perot interference filter, which is formed by sputtering silver layers with an intermediate spacer layer and the optional barrier layers on a transparent support substrate. The spacer layer and the optional barrier layers consist of metal oxides.

p0003In EP-PS 303 586 and 303 587 kind 5-layer systems are described in which the metal layers are flowed through heating by an electric current.

p0004Proceeding from the above-described prior art, the invention aims to provide a multi-layer system of a laminate, which is characterized by a particularly high transmission in the visible spectral region with a broadband antireflection coating and high corrosion stability.

p0005This object is achieved in that at least contains the dielectric coating layer as a main component niobium oxide.

p0006In a preferred embodiment, all the dielectric layers contain 40 to 100 percent Nioboxidanteil. The refractive index of the niobium oxide layer will depend on the specific production parameters and ranges from n = 2.4 and n = 2.7.

p0007The niobium oxide layers may be produced by sputtering, chemical vapor deposition or plasma enhanced chemical vapor deposition.

p0008The metal layers consist in known manner of a metal of the group silver, gold, copper, aluminum or an alloy containing at least one of these metals. They have a thickness which lies between 5 and 50 nanometers, preferably between 5 and 30 nanometers.

p0009As the carrier substrate can be used with a thickness of 12-200 microns in a conventional manner, a transparent plastic film, in particular a polyester film, a polycarbonate film or a polymethyl methacrylate.

p0010It is also possible to apply containing the niobium oxide dielectric layers having multi-layer system on a transparent glass plate as the support substrate.

p0011The multilayer system on film substrate can be processed by two-sided application of hot melt adhesive films to a plastic laminate which is suitable for the manufacture of windscreens with an extremely high transparency in the visible and a good reflectivity for unwanted heat radiation.

p0012An exemplary embodiment of the invention will be described with reference to the single figure showing a cross section of the multilayer system according to the invention in perspective view.

p0013In the not scale drawing can be seen a Fabry-Perot interference filter containing the multilayer system 100 in cross-section, the support substrate 31 as a glass sheet or a plastic film such as polyester film, polycarbonate sheet or polymethyl methacrylate having. If the support substrate 31 is a glass sheet, this has a sufficient mechanical stability for the layer thickness. If the support substrate 31 is a plastic film, it has a thickness of 12-200 micrometers. The support substrate 31 made of glass or plastic transparent to visible light and has an areal extent which depends on the subsequent use of the multilayer system. The transmittance of the plastic film used as a carrier substrate for example, is 88 percent.

p0014In the embodiment shown in the drawing, a dielectric interlayer 32 on the support substrate 31 is first provided. The desired properties of the multilayer system 100 are particularly advantageous when all dielectric layers 32, 34, 44 have as a main component niobium oxides.

p0015The interlayer dielectric layer 32 has a thickness of 20 to 50 nanometers and is partially or entirely of niobium oxide (Nb₂O₅) having a refractive index n which is 2.4 to 2.7.

p0016The interlayer dielectric layer 32 preferably contains 40 to 100 percent of niobium oxide. If the interlayer dielectric layer 32 adjacent niobium oxide contains other substances, these are preferably made of metal oxides or metal nitrides. If the dielectrics 32, 34, 44 each consist of more than 95 percent of niobium oxide, the thickness of the intermediate layer is from 32 28 nanometers. If the spacer layer 34, however, is composed of tin oxide, the thickness of the intermediate layer is from 32 21 nanometers.

p0017The next layer in the layer structure of the multilayer system shown in the drawing a first metal layer 33 is provided. The first metal layer 33 is comprised of a silver layer having a thickness between 5 and 50 nanometers, preferably 5 to 30 nanometers. The electrical sheet resistance of the first metal layer 33 of silver is between 3 and 8 ohms / square.

p0018Instead of a first metal layer 33 made of pure silver and a first metal layer 33 may be provided which contains gold, copper or aluminum. These metals can be present in pure form or as an alloy with other metals mentioned.

p0019The first metal layer 33 is covered with a further dielectric layer, namely, a dielectric spacer layer 34, which forms an antireflection layer on the basis of the Fabry-Perot interferometer in the visible region together with the first metal layer 33 and a second metal layer 43 similarly formed. The dielectric spacer layer 34 is constructed chemically according to the interlayer dielectric layer 32, but it is about twice as thick. It consists also entirely or essentially of niobium oxide and has a thickness between 40 and 100 nanometers, particularly 59 nanometers at a Nioboxidanteil of more than 95 percent.

p0020In a modified embodiment of the invention, the spacer layer 34 made of a metal or metal alloy oxide having a refractive index of more than 1.8, mainly made of tin oxide, indium oxide, zinc oxide or titanium oxide. The preferred thickness of a spacer layer 34 of tin oxide is 89 nanometers.

p0021After application of the second metal layer 43, whose thickness 33 is like that of the first metal layer between 5 and 50 nanometers, preferably 5 to 30 nanometers, a dielectric covering layer 44 is applied to the second metal layer 43, which in their chemical composition of the interlayer dielectric layer 32 corresponds. The thickness of the dielectric covering layer 44 is from 20 to 50 nanometers, and thus is approximately half the thickness of the spacer layer 34. The layers 32 and 44 containing as a main component from 40 to 100 percent of niobium oxide. In a niobium oxide content of 95 percent or more of the thickness of the cover layer 44 is preferably 30 nanometers. As secondary constituents preferably metal oxides.

p0022The interlayer dielectric 32, dielectric top layer 44 of pure niobium oxide or niobium oxide and other metal oxides are characterized not only by the favorable optical properties, but also by the fact that niobium is corrosion resistant and provides excellent protection for the enclosed metal layers. This has the advantage of a higher life in the application. Another advantage of the niobium oxide is that no measures have to be taken to 33 and 43 prevent the application of the dielectric spacer layer 34 and the dielectric top layer 44, a damage of the metal layers made of silver.

p0023In a preferred embodiment, the intermediate layer 32 to 100 percent of niobium oxide with a layer thickness of 28 nanometers, wherein the spacer layer 34 and the covering layer 44 made of niobium oxide. The thickness of the intermediate layer 32 is preferably 21 nanometers, when the spacer layer 34 is made of tin. The thickness of the spacer layer 34 is preferably 59 nanometers, when the spacer layer 34 of niobium oxide and 89 nanometers, when the spacer layer 34 is made of tin.

p0024The application of the dielectric interlayer 32, the first metal layer 33, the dielectric spacer layer 34, the second metal layer 43 and the dielectric top layer 44 to the support substrate 31 made of glass or plastic can be carried out by various methods. In particular, the method of the cathode sputtering, chemical vapor deposition and plasma enhanced chemical vapor deposition can be used to generate the layers used.

p0025A preferred method for deposition of the layers containing niobium oxide, the magnetron cathode in the form of a DC-powered reactive process (reactive sputtering of NbO_x). Here, working with metallic targets and the discharge gas - preferably argon - as a reactive gas oxygen mixed. In order to produce absorption-free layers in an industrial scale controlled in this way, a preferred embodiment of the method is to mix the discharge gas a proportion of 5 to 30 percent hydrogen.

p0026The multilayer system 100 illustrated in the drawing may be the starting material for a plastic laminate, each of the two sides of the multilayer system with a film of polyvinyl butyral, polyurethane or another melt adhesive film is laminated. The thickness of the adhesive films amounts to 0.2 to 0.4 millimeters. The plastic laminate formed in this way can be embedded between two glass plates, with which it forms a laminated safety glass pane, the 100 large transmission is distinguished by a high reflectivity in the infrared region due to the characteristic property of the multilayer system in the visible range.

p0027Of particular interest for use as laminated glass safety panel is that the use of niobium oxide for the intermediate layer 32, the spacer layer 34 and the covering layer 44, the reflection in the wavelength range of 400 to 660 nanometers can be used to below 0.5 percent.

p0028Instead of the above-mentioned embedding a plastic laminate between two glass plates, it is a multi-layer system is also possible to provide a resin having a carrier substrate 31 and to apply this multilayer system with its outer layer 44 using an adhesive film on a glass pane.

p0029The metal layers 33, 43 in addition to their optical mission the task of a heating layer, for example, at a front window of a car, meet when they are connected to a correspondingly designed heater circuit.

p0030Another possible application of the multilayer system described above is to arrange this stretched freely between two sheets of glass to form in this way a sunscreen and heat insulation for windows. It is particularly advantageous is that a desiccant cartridge is not needed in such an insulated glass window.