MXPA99009920A - Transparent substrate provided with a stack of layers reflecting thermal radiation - Google Patents

Abstract

The invention concerns a stack of layers reflecting thermal radiation for transparent substrates comprising at least a silver functional layer and on the two faces thereof antiglare layers formed by one or several metallic compounds. The antiglare layers under the silver layer comprises a top partial layer of zinc oxide adjacent to the silver layer and a partial additional beneath the zinc oxide layer, formed by aluminium nitride, under internal tractive stresses. By means of the AlN layer under tractive stresses, the internal compressive stresses present in the ZnO layer can be compensated.

Description

TRANSPARENT SUBSTRATE WITH STACKING OF LAYERS THAT REFLECT THERMAL RADIATION DESCRIPTION OF THE INVENTION The invention relates to a stack of layers that reflect, at least in part, in the infrared range and reflect, in particular, thermal radiation for transparent substrates, comprising at least one "functional" layer and "anti-reflective" layers. which are placed on both sides of the silver layer. In the context of the invention, the term "functional layers" is meant to mean the layer or layers which, in the stack, have the properties of reflection in the infrared range and / or in the range of solar radiation, and which they are generally metallic, more particularly based on a noble metal such as Ag (if appropriate, which also contains constituents in the minority, for example, a small portion of another metal). By way of explanation, silver layers having high reflectivity in the infrared range and therefore sunscreen or low emission properties can be used in this way. In the scope of the invention, the term "antireflective layers" is intended to mean a layer, or an overlapping series of layers, having in particular the function of adjusting the optical appearance of the stack, with a view to reduce its reflection to the light, and generally based on dielectric substances such as metal compounds, for example metal oxides. The present invention therefore relates to stacks of the type (antireflective layer / functional layer / antireflective layer), a sequence which, if appropriate, can be repeated n times, where n = 1, 2, 3, .. . It should be noted that thin layers, generally of metal, which are designed to protect and / or promote adhesion of the functional layers, can also be provided at the interfaces between the anti-reflective layers and the functional layers. They are sometimes referred to by the term "sacrificial layers" when they are on the functional layer and then oxidized at least partially subsequent to the subsequent deposition of an oxide-based layer by reactive electrodeposition in the presence of oxygen. The present invention relates, in particular, to a variant of this type of stacking in which the antireflective layer placed below the silver-based functional layer comprises a top partial layer, formed by zinc oxide, immediately adjacent to the layer of silver. silver, and an additional partial layer placed below it. A stack of layers of this type is known from document DE-39 41 027 Al. In this stack, the partial layer which is placed under the layer of zinc oxide which is part of the "lower" anti-reflective layer consists of a metal oxide from the group consisting of tin oxide, titanium dioxide, aluminum oxide, bismuth oxide or a mixture of two or more of these oxides. The thickness of the zinc oxide layer can not be more than 15 nm. This layer of zinc oxide significantly improves the stability of the silver layer against corrosion. This is probably attributable to the fact that the silver layer grows on the ZnO layer in a particularly regular and defect-free manner. Stacks with a plurality of layers comprising silver as the functional layer and a layer of zinc oxide placed immediately below the silver layer are also known from EP-0 464 789 Bl and EP-0 698 585 Al In the layer stacks described by these publications, the lower anti-reflective layer consists either entirely of zinc oxide, or of a plurality of alternating partial layers of ZnO and Sn02. The layers of zinc oxide have, as the lower layers for the silver layers, a highly -advantageous about the silver layer and its properties. However, they have the drawback that appreciable compressive internal stresses occur in the ZnO layers under conventional deposition conditions. These internal compressive stresses in the ZnO layers can have an unfavorable effect on the stack of the layers. As explained in detail, in particular in EP-0 464 789 Bl, the zinc oxide layer can be delimited from the silver layer under the effect of internal compression stresses. Stacks of layers including internal stresses are particularly unfavorable even when applied to thin polymer-based support films or polymers, in particular of the organic variety, for example, to thin films of polyethylene terephthalate (PET). As a rule, these PET films have a thickness in the order of 30 to 50 μm. PET films coated in this way are increasingly used, for example, for the manufacture of laminated windows which have, in particular, heat reflection properties. The PET film is interposed between two glass sheets of the silica-lime-soda type with the aid of two adhesive films based on a thermoplastic polymer, for example of polyvinyl butyral (PVB). It has been found that these films such as PET which are coated with stacks of layers comprising a layer of ZnO under the silver layer, are wound up under the influence of the internal compressive stresses in the stack of layers, so that it becomes difficult to handle and process them. The object of the invention is to develop a stack of layers of the kind described above, comprising in particular a layer of ZnO immediately below the silver layer and, when deposited on polymer films of the PET type, they do not show the disadvantages mentioned above, that is, they do not tend to be rolled once coated with the layers. In particular, this involves fixing the internal tensions in the stack of layers to be reduced / reduced to a minimum or even to be completely eliminated. The preferred system of layers, according to the invention, is defined as follows: it is a stack of layers that reflect the thermal radiation for transparent substrates, comprising at least one functional layer formed by silver and antireflective layers which are placed on both sides of the silver layer and which are formed by one or more metal compounds, the antireflective layer is placed under the silver layer and comprises an upper partial layer formed by zinc oxide immediately adjacent to the silver layer , and an additional partial layer placed below it. This stacking of layers is distinguished by the fact that it has an additional partial layer which is placed under the layer of zinc oxide and which belongs to the "lower" anti-reflective layer which is a layer based on aluminum nitride which it is under internal voltage tensions. Preferably, the stacking is such that the amplitude of the internal compressive stresses of the aluminum nitride layer corresponds, by adjustment of the coating parameters, to approximately the amplitude of the internal compression stresses in the zinc oxide layer of so that the extension and compression tensions of the two adjacent partial layers are at least balanced for the greater part. Preferably, the stack is such that the zinc oxide layer has a thickness of less than 15 nm, and preferably less than 12 nm, and advantageously at least 5 to 8 nm. According to one embodiment of the stack according to the invention, it comprises two functional layers formed by silver, which are separated from each other by an additional anti-reflective layer, this additional anti-reflective layer also comprises two partial layers, specifically a layer which is immediately contiguous to the upper silver layer, which is formed by zinc oxide and which is under internal compression stresses, and a partial layer which is contiguous with the lower silver layer, which is formed of nitride and aluminum and is under stress internal extension An example of a stack according to the invention is characterized by the following structure: Substrate / AlN / ZnO / Ag Ti / TiO, Another example is characterized by the following structure: Substrate / AlN / ZnO / Ag / AIN or by the following structure: Substrate / AlN / ZnO / Ag / AlN / ZnO / Ag / AIN The invention also relates to the use of such a stack of layers for coating thin polymer films, in particular PET, in particular so that the coating parameters of the A1N-based layers formed by reactive deposition from a cathode of The metallic aluminum is chosen so that the coated film does not have, after formation of the stack, any substantial curvature induced by internal stresses to the stack. The invention takes advantage of the fact that during the deposition of the A1N layers, it is possible, by choosing the parameters of the deposition conditions, for example by modifying the Ar: N2 ratio in the working gas, to modify within wide limits the internal mechanical stresses in the A1N layer. For example, it is described in the article "Strees tuning in A1N thin films", Z. Vakuum in der Praxis (1991) No. 2, pages 142-147 that, based on the proportion of Ar: N2, which is modified in the interval from 1: 3 to 3: 1, both the relatively high compression internal stresses and the relatively high internal tension tensions can be obtained without significant differences in the proportion of "Ar: N observed in the A1N layer itself Instead, the internal stresses are explained only by the microstructure of the AlN layer, the internal stretching stresses are generated in the layer when deposition conditions are chosen which lead to a low stacking density of The optimum conditions for the preparation of the sequence of layers according to the invention can be determined empirically by tests in each particular case, for example, a layer of AlN and a layer of ZnO which they have in the The desired layer thickness can be deposited successively by deposition (preferably aided by magnetic field) on thin substrates, for example thin PET films. Depending on the sign of the internal stress resulting in this sequence of layers, the coated film will curl and roll in one or the other direction. The deposition conditions for the AlN layer are intentionally modified based on the observed result until the PET sheet no longer shows significant deformations after coating formation. The deposition conditions found in this way are then used as parameters for the preparation of the stack under manufacturing conditions. The structure of the layers according to the invention can be exploited and find their application for all substrates. However, it is a particular advantage for the coating of thin polymer films because it is possible in this way to prevent the coated films from being rolled up, so that their handling is easier when the invention is put into practice. PET films often have thermally stabilized intrinsic stresses which are imparted to them by manufacturing processes. Likewise, it is possible that the internal tensions present originally are modified, or that new internal stresses are induced during the deposition operation under the effect of temperature and / or plastic deformation of the films. It is clear in these cases that, when optimum deposition conditions are determined for an AlN layer, these inherent stresses of the film must also be taken into consideration so that it is not the stack itself which is free of resultant internal stresses, but the film coated in its entirety. More generally, the invention can also be defined in the following manner: the invention also relates to a transparent substrate, most particularly in the form of a flexible polymer film such as PET, which is provided with a thin film stack including at least one metallic functional layer with reflection properties in the infrared range, such as Ag, placed between two anti-reflective layers based on dielectric material, designed here to be considered with the meaning of "functional" layer and "antireflective" layer as specified above. The "lower" anti-reflective layer, placed between the functional layer and the substrate, is a monolayer based on modified AlN whose level of tension is balanced (or -relaxed), or is a superimposed sequence of layers comprising at least one layer of AlN on top of which there is a layer of metal oxide whose voltage levels are mutually compensated / canceled, at least in part. The variant described above is found, specifically, with an anti-reflective layer of the AlN / ZnO type in which the level of extension tension of the AlN layer will be largely compensated, if not completely, with the level of compression stress in the layer of ZnO. A variant is also provided in which the antireflective layer comprising only AlN, and in which this time, that layer must be substantially free of tensions of any kind in order to obtain the same result as in the two-layer variant. The "two-layer" variant has the advantage of retaining the oxide layer such as ZnO which is known to be favorable for a good wetting of the silver layer, the "monolayer" variant on its part has the advantage of a stacking which is simpler, requires less processing time and has fewer layers. The AlN-based layer used in the lower anti-reflective layer, in particular, may comprise other minor material, in particular zinc, for example, in a proportion from 0.1 to 10 atomic% in relation to aluminum. Preferably, the oxide layer such as ZnO of the lower anti-reflective layer is contiguous to the functional layer. It should also be provided to interpose, among them, a thin metallic layer, such as titanium, nickel alloy such as NiCr, niobium, etc. The stack can contain a single functional layer or n functional layers where n >; 2. In this configuration, "intermediate" antireflective layers must be provided between the two functional layers, where n = 2, or between two successive functional layers when n > 2. This "intermediate" antireflective layer or at least one of them may include, as the "lower" anti-reflective layer, a monolayer based on modified AlN so that its tension level is balanced (or relax), or a sequence layer superimposed comprising at least one AlN-based layer on top of which is a metal oxide layer such as ZnO whose stress levels cancel out / cancel each other, at least in part.

Advantageously, the functional layer (or at least one of them, if there are more thereof) has a thin metal sacrificial layer on top of it, such as Nb, Ti or NiCr, which, in particular, it is important if the deposition is to be carried out by -enzymes of dielectric layers made of oxide by deposition under oxidation conditions. Advantageously, the "intermediate" and / or "higher" antireflection layers ("upper" corresponds to the layers which "finish" the stack) contain metal oxide-based layers selected from at least one of the following oxides : Sn02, Ta205, Nb205, Zr02, Ti02 and / or nitride-based layers such as AlN and Si3N4. The invention also applies to multi-layer lower anti-reflective coatings in which ZnO is replaced by another oxide having a given level of tension (of extension or of compression) which, the combination with the layer based on AlN, will make it possible to balance, and compensate to a great extent (Si02, W03, etc.). The invention can be applied to any rigid transparent substrate such as glass, certain polycarbonates such as PMMA (polymethyl methacrylate) or, more specifically, to substrates in the form of flexible polymer films such as PET, certain polyesters, etc. The invention makes it possible that the flexible polymeric film of this type is essentially free of any "unintended" radius of curvature after the layers have been deposited. The invention also relates to the use of a coated film for the manufacture of laminated functional solar filter or low emission windows, and laminated windows obtained in this manner. The invention also relates to the process for the preparation of the coating on the substrate of the type of flexible polymer, by deposition, the concept of the invention is to vary the parameters for the deposition, by reactive electrodeposition, the layer or layers constituting the at least anti-reflective layer, so as to minimize or cancel its total tension level so that substantially no curvature is induced in the film due to internal stresses. To do this, two particular parameters can be adjusted in an appropriate manner, specifically the total pressure in the atmosphere in which the deposit or reservoirs are made, and the ratio between the amount of inert gas (Ar) and reactive gas (02). or N2) in the reactive atmosphere. Examples of stacks of layers according to the invention deposited on PET polymer films are described in greater detail in the following.

EXAMPLE 1 A stack of layers that reflect the heat radiation, comprises the successive sequence of layers: sustrat? / AlN / ZnO / Ag / Ti / Ti02 it is applied to a 50 μm thick PET film of Hoechst company using the process of reactive deposition followed by magnetic field. In order to determine the optimal deposition conditions for the lower anti-reflective layer formed by two partial layers of AlN / ZnO. The PET film samples of dimensions 30 x 30 cm are first coated in succession with two partial layers of AlN 30 nm and ZnO nm in a laboratory deposition system of Leybold company. The deposition is carried out by the DC flat deposition process. After the coating is formed, the deformation of the film is determined by taking the measurement of the radius of curvature which the film assumes after the formation of the coating as the way to quantitatively determine the internal stresses of the coated film. It is considered that the layer structure is good when the coated film does not curl further after it has been removed from the coating system, but retains its flat shape.

After several tests, it is found that optimum coating conditions are obtained when the AlN layer is applied by reactive deposition of a pure aluminum objective in an argon / nitrogen working gas mixture having an 'Ar: N2 ratio of 2.5: 1, while the ZnO layer is formed by reactive deposition of a metallic zinc target in a mixture of argon and oxygen gases having an Ar: 02 ratio of 1: 1. Under these conditions, the film samples coated with this double layer do not exhibit any deformation, that is, the internal stresses in the various layers of the coated film are canceled by addition. After the deposition conditions have been determined in this manner for the lower anti-reflection layer, a multilayer system having a backing layer structure and the thickness of the layer below is applied to the same coating system to a film of PET 50 μm thick, the thickness of the layer is indicated in nm: substrate-30 A1N-10 Ag-1 Ti-30 Ti02 The target of Al is again deposited in an Ar: N2 atmosphere that has an Ar: N2 ratio of 2.25: 1 using the DC flat deposition process and the Zn objective is deposited in an Ar: 02 atmosphere that has a of Ar: 02 from 1: 1, also using the DC flat deposition process. The following layers are also deposited by the DC flat deposition process, the working gas for the deposition of Ag and Ti is formed by pure argon, and the working gas for the reactive deposition of the Ti02 layer consists of a mixture of Ar: 02 which has a ratio of Ar: 02 of 1.4: 1. By using the coated film, a laminated window is made using two sheets of ponyl butyral with a thickness of 0.38 mm to assemble the PET sheet coated with two sheets of float glass, each with a thickness of 2.1 mm using heat and pressurization , in the known way. Even after conversion into a laminated window, the coated PET sheet does not show any defect such as tears or deformations on the surface and the laminated window also has an excellent appearance. ^ N The optical properties which are determined using a conventional measurement process correspond to the requirements in terms of optical transmission, optical reflection and color neutrality. The tests carried out to determine the corrosion resistance of the stacks of layers, specifically the humidity test according to the standard ANSI Z 26.1, test No. 3 as well as the salt spray test according to standard DIN 50021 am ié provides good results.

EXAMPLE 2 A stack of a plurality of layers having the following layer structure is deposited on a PET film having a thickness of 50 μm, the thickness of the various layers again indicating that nm: substrate-30 A1N-10 ZnO-10 Ag-82 A1N-10 ZnO-10 Ag-40 AlN The deposition conditions for the various layers, considering the working gases and the applied deposition processes, correspond to the conditions indicated in example 1. The application of a thin metallic layer of sacrifice to each of the two layers of silver it is not necessary because the working gas for each of the following AlN layers is completely free of oxygen. In order to evaluate the usefulness and the properties of layer stacking in laminated glass, the coated film is assembled again with two sheets of ponyl butyral, each 0.38 mm thick, and two sheets of float glass, each with a thickness 2.1 mm, when applying 'sufficient heat and pressure. The tests are carried out on the laminated window that is obtained. Judging by the optical condition of the window, this stack of layers has a very good appearance in the laminated window, that is, there are no tears or deformations that can be observed in the coated film. The optical properties of the coated window, which is determined using conventional measurement processes, correspond in terms of optical transmission and optical reflection in the range of visible spectrum, total energy transmission and shadow neutrality, with the current requirements for use of a laminated window like a windshield of a motor vehicle. 'The following tests were carried out in order to evaluate the corrosion resistance of the stacking of layers in the laminated window: - humidity test in accordance with standard ANSI Z 26. 1 (test No. 3): according to this test, the sample is exposed for a period of 14 days at a temperature of 40 ° C in an atmosphere with 100% relative humidity. No traces of corrosion or delamination are observed. According to the salt spray test corresponding to standard DIN 50021, the samples are exposed for 10 days to a spray mist. There are some small traces of corrosion in the contour of the samples, but without delamination.

Claims (21)

Ows CLAIMS

1. A transparent substrate, in particular in the form of a polymer film or flexible polymers, which is provided with a thin film stack that includes at least one metallic functional layer with reflection properties in the infrared range, such as Ag, placed between two "antireflection prior" layers based on dielectric material, characterized in that the "lower" antireflective layer, placed between the functional layer and the substrate, is a monolayer based on modified AlN whose level of tension is balanced, or is an overlapping sequence of layers which comprise at least one layer of AlN at the top_of which there is a metal oxide layer whose stress levels cancel out / cancel each other, at least in part.

2. The substrate as described in claim 1, characterized in that the "lower" antireflective layer comprises an AlN layer which also includes at least one other minor metal, in particular zinc, preferably in a proportion from 0.1 to 10 atomic% in relation to to aluminum.

3. The substrate as described in claim 1 or claim 2, characterized in that the antireflective layer comprises a layer sequence based on AlN / zinc oxide based layer, the first one has a tension stress level, and the second one has a level of effort to tension.

4. The substrate as described in one of the preceding claims, characterized in that the oxide layer, in particular based on ZnO, of the "Lower" anti-reflective layer is contiguous with the functional layer.

5. The substrate as described in one of claims 1 to 3, characterized in that the thin metallic layer, in particular such as titanium or Ni alloy, such as a NiCr alloy, or niobium is placed between the "lower" anti-reflective layer. and the functional layer.

6. The substrate as described in one of the preceding claims, characterized in that the stack comprises at least two functional layers such as an Ag layer, with an antireflective layer "intermediate" between the two functional layers or between two successive functional layers.

7. The substrate as described in claim 6, characterized in that the "intermediate" antireflective layer, or at least one thereof, includes a monolayer based on AlN modified so that its stress level is balanced, or is a superimposed sequence of layers comprising at least one AlN-based layer on top of which there is a metal oxide layer such as ZnO whose stress levels cancel each other, at least in part.

8. The substrate as described in one of the preceding claims, characterized in that the functional layer, or at least. one of them, has a protective thin metal layer on top of it, in particular such as Nb, Ti or NiCr.

9. The substrate as described in one of the preceding claims, characterized in that the "intermediate" and / or "top" antireflective layers contain layers based on metal oxide which is selected from: Sn02, Ta205, Nb205, ZnO, Ti02 or layers based on 'nitrides such as AlN and Si3N4.

10. A polymeric film such as PET, coated as described in one of the preceding claims, characterized in that it is essentially free of any unintentional radius of curvature.

11. The use of the film, as described in claim 10, for the production of laminated functional solar filter or low emission wind

12. A laminated window, characterized in that it incorporates the polymeric film as described in claim 10.

13. A process for preparing the substrate in the form of a flexible polymer film coated according to one of claims 1 to 10, characterized in that the spraying technique is used to deposit stacking layers, while the low conditions which are deposited are varied. the layer or layers of the "lower" antireflective layer so that it minimizes the residual stress level of the "lower" antireflective layer - such that it substantially does not induce curvature in the film due to internal stresses.

14. A stack of reflective layers of heat radiation for transparent substrates, comprising at least one functional layer formed by silver and antireflective layers which are placed on both sides of the silver layer and which are formed by one or more metal compounds, the antireflective layer is placed under the silver layer comprising an upper partial layer formed by zinc oxide immediately adjacent to the silver layer, and an additional partial layer placed below, characterized in that "the stack of layers is distinguished by the fact that the additional partial layer which is placed below the zinc oxide layer and which belongs to the "lower" antireflective layer is a layer based on aluminum nitride which is under internal tension voltages.

15. The layer stacking, as described in claim 14, characterized in that the amplitude of the internal stresses of the compression of the aluminum nitride layer corresponds, by adjusting the coating parameters, to approximately the amplitude of the internal stresses of the coating. compression in the zinc oxide layer so that the tension and compression stresses of the two adjacent partial layers swing at least for the greater part.

16. The stacking of layers, as described in claim 14 or 15, characterized in that the. The zinc oxide layer has a thickness of less than 15 nm and "preferably less than 12 nm.

17. The stacking of layers, as described in any of claims 14 to 16, characterized in that it comprises two functional layers formed by silver, which are separated from each other by an additional anti-reflective layer, this additional anti-reflective layer also comprises two partial layers, specifically a layer which is immediately adjacent to the upper layer of silver, which is formed by zinc oxide and which is under internal compression stresses, and a partial layer which is contiguous with the lower silver layer, which is formed by nitride of aluminum and is under internal voltage tension.

18. The stacking of layers, as described "in any of claims 14 to 17, characterized by the following structure: (Substrate) / A1N / Zn0 / Ag / Ti / Ti02

19. The layer stacking, as described in any of claims 14 to 16, characterized by the following structure: (Substrate) / A1N / Zn0 / Ag / A1N

20. The layer stacking, as described in claim 17, characterized by the following structure: (Substrate) / A1N / Zn0 / Ag / A1N / Zn0 / Ag / A1N

21. The use of a stack of layers, as described in any of claims 14 to 20, for coating thin polymer films, in particular PET, so that the "coating parameters of the AlN-based layers formed by reactive sputtering at Starting from a metallic aluminum cathode are chosen so that the coated film does not have, after the formation of the stack, any substantial curvature induced by internal stresses.