DE102011077878A1 - A polymeric substrate material for physical and chemical vapor deposition processes, comprising an adhesion-promoting polymeric layer, and the use thereof for the production of concentrators of solar radiation - Google Patents

Abstract

The invention relates to a composite molded body undung in solar reflectors with the background of ensuring the required reflection of solar radiation (total solar reflection) as sustainably as possible. In particular, the invention relates to a novel substrate material and its coating by means of e.g. a physical and / or chemical vapor deposition process (PVD / CVD process), as well as an adhesion-promoting polymer layer contained in the composite body. The adhesion-promoting layer ensures that the reflective coating can be coated with permanent adhesion and that the service life of the composite molding is extended.

Description

Field of the invention

The invention relates to a composite molding and its application for the concentration of solar radiation in solar reflectors under the background of sustainable as possible guarantee the required reflection of solar radiation (total solar reflection).

In particular, the invention relates to a novel substrate material and its coating by means of e.g. a physical and / or chemical vapor deposition process (PVD / CVD process), as well as a contained in the composite, adhesion-promoting polymeric layer. The adhesion-promoting layer ensures a permanently adherent reflective coating and an extension of the service life of the composite molding.

State of the art

Polymer composite moldings in prior art solar reflectors have disadvantages in terms of sufficient weatherability and degradation by ultraviolet (UV) radiation. In particular, for outdoor applications, however, there are high demands on such films in terms of resistance and resistance to UV radiation and other weather conditions. These claims are in particular with regard to dimensional stability, the degree of reflection in the visible or in the near infrared spectrum and the external appearance.

The wavelength range of the solar radiation relevant for "solar thermal energy" ranges from 300 nm to 2500 nm. However, the range below 400 nm, in particular below 375 nm should be filtered out in order to extend the service life of the polymeric composite moldings, so that the "effective wavelength range" of 375 nm or from 400 nm to 2500 nm remains.

The reflectance of the composite molded articles in use as a flexible mirror film is determined by the quality and the durability. Such a laminate can be produced, for example, by vacuum vapor deposition of a flexible polymer film (carrier film) with a thin silver layer. Due to the particularly high reflectivity in the relevant wavelength range compared to other metals, silver is the preferred metal for this application. In order to protect the polymeric carrier film and optionally the silver layer against external influences, it is additionally coated with a protective layer. The purpose of this protective layer, which is usually a cover film for surface treatment, is the protection against mechanical abrasion, weathering and degradation by UV radiation.

In US 4,307,150 Such a protection system for aluminum mirrors is described. As carrier film, a PET laminate is used, which is vapor-deposited with aluminum and protected by gluing a (meth) acrylate film against corrosion and weathering. An explicit UV protection is not considered.

A silver vaporization is much better suited to the construction of such mirrors than an aluminum layer due to the higher degree of reflection. The use of silver is in US 4,645,714 described. Silver, in principle, has two disadvantages. On the one hand, especially thin silver layers are particularly susceptible to corrosion. For this reason, protective layers or laminates must be particularly dense. Otherwise, small holes or insufficient tightness will be sufficient at the edge of the laminate to cause unwanted oxidation. On the other hand, both silver and aluminum have an absorption gap in the spectral range of ultraviolet light (300-400 nm), especially in the range around a wavelength of 320 nm, which is an important part of the sunlight. The permeability is given especially in very thin layers. This short-wave radiation is detrimental to the carrier film and the silver-metal mirror layer, in particular for mostly used polyester films or laminates or the adhesive used for the production of laminates, especially in the case of prolonged exposure, as is the case in the field of solar mirrors. It can lead to blistering and thus to deformation and to reduce the degree of reflection.

Anticorrosion inhibitors and UV absorption reagents can be incorporated into the protective film listed above for better protection. The most commonly used inhibitors, however, have the disadvantage of exhibiting only reduced weathering or even UV stability and leading to discoloration after some time. However, the latter reduce the reflection in other spectral ranges and thus the efficiency of the solar system.

In contrast, UV absorbers alone do not contribute to the corrosion protection of the silver coating, but only prevent a weather-related aging of the polyester laminate. In order to obtain optimized protection, both components - inhibitor and UV absorber - are separated from each other.

IN US 4,645,714 For this purpose, two separate (meth) acrylate-based coatings are applied. Polymethacrylates have a significantly higher UV resistance than polyesters. For this purpose, poly (meth) acrylates can not be coated directly by means of CVD or PVD methods due to the thermal instability and lability, for example due to process-induced short-wave UV rays. The outer contains the UV absorber, the inner contains the inhibitor. By this construction, the inner is protected by the outer layer and it occur to a much reduced extent discoloration. The inhibitor layer is applied directly to the silver vaporization. The second layer containing the UV absorber again via this first layer. The polyester laminate used is a two-layer coextruded PET film, one layer containing a lubricant to improve flexibility and the other silver vapor-deposited layer containing no lubricant to ensure the smoothest possible surface. The uncoated side of the polyester laminate, in turn, is coated with a PSA (pressure sensitive adhesive) based on an isooctyl acrylate-acrylamide copolymer. For example, this coating can be protected with a silicone-coated polyester film prior to using the mirror laminate.

In the US 4,645,714 and US 4,307,150 Both described (meth) acrylate coatings, however, have the disadvantage that they have a reduced weathering stability in an outdoor application and thus are generally poorly suited for outdoor solar applications. These coatings are very poor at watering, abrasion resistant, and have very limited resistance to atmospheric moisture. After erosion of the poly (meth) acrylate coating, it may then come to the described degradation of the polyester laminate. To work around this problem, in US 5,118,540 an abrasion-resistant and moisture-resistant film glued on the basis of fluorocarbon polymers. Both the UV absorption reagent and the corrosion inhibitor are part of the adhesive layer with which the film is bonded to the metal surface of the vapor-deposited polyester support film. The adhesive layer may again consist of two different layers, analogously to the above-described (meth) acrylate double coating, in order to separate corrosion inhibitor and UV absorption reagent from one another.

In WO 2007/076282 On the other hand, an alternative structure for better protection of the silver coating is listed. The PET carrier film is no longer vaporized on the surface, but on the side facing away from the light with silver. On the other side of the PET film, a poly (meth) acrylate protective film is attached, which is equipped with UV absorption reagents. For this purpose, an adhesive layer is required, which causes two further disadvantageous layer interfaces. Additional layer interfaces in turn cause a higher risk of delamination of the film composite, as well as a reduction in the precision of the concentration of solar radiation. Furthermore, the process with the steps of producing PET carrier film, vapor deposition, production of poly (meth) acrylate film and lamination is complicated and therefore makes little sense from an economic point of view. The reverse side of the silver vaporization can either be provided directly with a pressure-sensitive adhesive (PSA) or coated with an additional layer of copper to improve the corrosion resistance on the back and for better adhesion of the PSA.

Because of this, there is a great interest in PMMA-based support materials for composite molded bodies, which are permanently adherently adherently coated by means of CVD or PVD.

Due to the lability of the PMMA to high temperatures as well as very short-wave UV rays with wavelengths smaller than that of solar radiation, as e.g. In the case of sputtering processes, a permanently adhering direct coating is not possible when using PMMA carrier materials. Due to this thermal instability, degradation of the PMMA interface would occur, which in turn would result in the formation of liquid or gaseous degradation products within this interface, which is essential for the successful performance of an adherent coating. The required sustained optical quality of the composite molded articles would not be attainable for a solar mirror application due to liability deficits and delamination phenomena. The same applies to adhesion-promoting layers, which are e.g. be applied by CVD or PVD between the support layer and the reflective (mirror) layer.

There is an increasing demand for composite moldings which clearly exceed the existing requirements for the longevity or performance preservation of the established composite moldings.

task

The object was to provide a novel composite molded article for solar reflectors with improved or at least equivalent optical properties, the lowest possible number of layer interfaces and improved weathering resistance and optical performance, especially with regard to long-term use. Long-term use is in particular an application over a period of more than 10 years, in particular more than 15 years, particularly preferably understood more than 20 years under particularly strong sunlight.

Furthermore, the object was that the composite molding for solar reflectors under particularly strong sunlight, such as. occurs in the Sahara or the Southwest of the US, remains stable for a long time.

This applies in particular with regard to the intrinsic resistance and filter efficiency of the surface coating layer of these composite shaped bodies in relation to the UV wavelength spectrum between 300 nm and 400 nm.

It was also the object to provide a composite molding for solar reflectors available that is easy and cost-effective to manufacture and process. In particular, the object was to produce an easy to manufacture, as few layers exhibiting system based on PMMA.

In addition, the composite molding described should have the most moisture-stable, abrasion-resistant and dirt-repellent properties

solution

Against the background of the state of the art and the technical solutions described therein for long-term applications, it is possible in the present invention to provide a composite molded article transparent to the metal layer with improved weathering stability and over a long period of time, which is not easily foreseeable by the person skilled in the art provide stable good solar reflection, which also has over the prior art over a particularly small number of layers and associated few, potentially disturbing layer interfaces.

In particular, a composite molded article was surprisingly found, which can largely consist of PMMA on the one hand and thus has the great advantages of PMMA and, on the other hand, has at least one PVD-deposited layer, in particular several layers applied by means of PVD and possibly CVD. Surprisingly, it has been found that such a composite molded article, without having an adhesive layer, can be realized if there is a second layer between the PMMA layer and the PVD or CVD layers and optionally a third layer on the other side of the PMMA layer. As a result, it is surprisingly possible, in particular, to coat PMMA moldings in a strongly adhesive manner by means of PVD or CVD, and thus to realize a composite molding of high optical quality. In this way, efficient and sustainable use of PMMA in high-end applications, e.g. as a solar mirror for the concentration of solar radiation in the desert climate, allows.

PMMA has a particularly attractive property profile with regard to the intended applications. Thus, PMMA has excellent weathering resistance, excellent optical properties and a pronounced protective effect against a reflective coating. The production of films or plates at moderate production costs is possible.

• – eine erste Schicht, die zu mehr als 50 Gew% aus PMMA oder einer PMMA-haltigen Polymermischung besteht,
• – eine direkt ohne Zwischenschicht auf einer Seite der ersten Schicht aufgebrachte zweite Schicht aus Polycarbonat oder einem Polyester,
• – eine optionale dritte Schicht aus einem Fluorpolymer, Polycarbonat oder einem Polyester, die sich auf der anderen Seite der ersten Schicht befindet,
• – und einer reflektierenden Beschichtung, die direkt auf die der ersten Schicht gegenüberliegende Seite der zweiten Schicht aufgebracht ist und dabei mittels PVD oder CVD in den Verbundformkörper integriert wurde.

The object is achieved by providing a novel composite molding for concentrating solar radiation in solar reflectors. This composite molding consists of at least the following two or three layers:

• A first layer consisting of more than 50% by weight of PMMA or a PMMA-containing polymer mixture,
• A second layer of polycarbonate or a polyester applied directly without intermediate layer on one side of the first layer,
• An optional third layer of a fluoropolymer, polycarbonate or a polyester located on the other side of the first layer,
• - And a reflective coating which is applied directly to the first layer of the opposite side of the second layer and was integrated by means of PVD or CVD in the composite molding.

The individual layers of the composite molding according to the invention preferably have the following layer thicknesses: The first layer has a thickness of between 6 μm and 10 cm, preferably between 25 μm and 25 mm. Particularly preferably, there are two different embodiments. A composite molding in the form of a flexible film has a preferred layer thickness of the first layer between 6 μm and 500 μm. The second possible composite shaped article in the form of a plate has a preferred layer thickness of the first layer between 500 μm and 10 cm.

The second layer generally has a thickness between 0.4 μm and 2 cm, preferably between 0.5 and 500 μm, more preferably between 1 and 400 μm and particularly preferably between 10 and 250 μm. For the optional third layer, the same preferred ranges of possible layer thicknesses apply as for the second layer. In this case, the second and the third layer may be the same thickness or have different thicknesses.

For the preferred embodiment of the composite molding as a film show the second and the optional third layer thicknesses each between 0.5 and 500 microns. For the equally preferred embodiment as a plate in each case a thickness between 10 .mu.m and 2 cm.

Furthermore, in particular composite shaped bodies are preferred in which the first layer is thicker than the second and the optional third layer.

The composite molding according to the invention may have, in addition to the reflective coating, further coatings applied by means of PVD or CVD. These may be located directly on the reflective coating and / or on the third layer. Furthermore, each may be multiple layers with different functions. The further layers can be, for example, scratch-resistant coatings, UV reflection layers, conductive layers, antisoiling coatings and / or optically functional layers. In turn, the optically functional layers are preferably reflection-enhancing layers.

In addition, the layers applied by means of PVD or CVD can be provided with an additional protective layer. In addition to the layers applied by means of PVD or CVD, these protective layers can also be polymer-based, resin-based or sol / gel-based paints. The protective layers can be applied as a solution, reactive resin with subsequent curing, by lamination of a corresponding protective film or by extrusion coating.

Likewise to the composite moldings, the process for their preparation is part of the present invention. This process consists in particular of the following three to four process steps:

In a first method step, the first layer is produced by extrusion. The production takes place in particular by means of extrusion through a slot die as in the flat film extrusion, a blown film extrusion or by solution casting.

In a second method step, the first layer is provided with the second layer by means of extrusion coating. Preferably, both process steps are carried out simultaneously by means of coextrusion. Alternatively, the production of this two-layer composite can also be effected by means of adhesive-free lamination or later extrusion coating of the first layer with the second layer.

In a third optional method step, this two-layer composite is joined to the third layer. This can also be done simultaneously by coextrusion of all three layers or likewise by a subsequent extrusion coating or tack-free lamination. It is also a method feasible, in which only a composite of the first and third layer is prepared by coextrusion and this composite is then connected by means of extrusion coating or tack-free lamination with the second layer.

Finally, in a third or fourth method step, a reflective coating is applied to the second layer by means of a vapor deposition.

The vapor phase deposition is preferably a PVD (physical vapor deposition) or a CVD (chemical vapor deposition).

PVD is the generic term for various physical vapor deposition processes. All of these methods have in common that they are vacuum-based coating methods for realizing in particular thin layers, and that the starting material is converted by means of physical processes into a gas phase and then deposited on a substrate as a coating by condensation or resublimation. The guide to the substrate surface is usually balistic or along an electric field. Typical working pressures are usually between 10 ^-4 Pa and 10 Pa. A special surface quality of the coating is usually achieved by the still occurring at the substrate surface diffusion of the deposited particles. By means of PVD not only pure metals can be deposited, but also, for example by supplying oxygen, nitrogen or hydrocarbons, oxides nitrides or carbides realize. The conversion into the gas phase can be carried out purely thermally or by electron beam, laser beam or arc evaporation.

A second, particularly preferred group in addition to the evaporation process, is the so-called sputtering or Sputterdeposition. In sputtering or cathode sputtering, the starting material is transferred by means of ion bombardment in the gas phase. Variants of sputtering are the IBAD (ion beam assisted deposition or ion beam-assisted deposition), by means of which, in particular, order effects within the layer can be effected, magnetron sputtering and ion beam sputtering. Another particularly suitable PVD technique is the ionized cluster beam (ICB) technique.

Chemical vapor deposition (CVD) is in contrast to PVD a method in which the deposition of a solid takes place under layer formation by a chemical reaction in the gas phase or at the substrate surface. In general, the raw materials used for this chemical reaction have a significantly lower evaporation temperature than the substance formed in the chemical reaction. By carrying out at a very reduced pressure, such as between 1 and 1000 Pa, a reaction at the substrate surface is preferred to a reaction in the gas phase, which in turn would lead to undesired particle formation. The deposition direction can be performed balistically parallel to the PVD process or influenced by an electric or magnetic field. A variant of CVD which is particularly suitable according to the invention represents the PECVD (plasma enhanced CVD), which can be carried out at lower temperatures, and which is a direct plasma method. An even more gentle variant is the RPECD (remote plasma enhanced CVD) In this variant, plasma and substrate are spatially separated.

According to the invention, CVD plays a role in the deposition of further layers on the PVD-produced reflective coating and / or on the optional third layer. The deposition of these further layers can alternatively also be effected by means of PVD. According to the invention, several layers can also be partially produced by means of CVD and partly by means of PVD.

• – Vermeidung nachteiliger Schichtgrenzflächen aufgrund der Herstellung des Verbundformkörpers ohne Einbeziehung weiterer Schichten, wie z.B. Kleberschichten, zwischen dem PMMA-Trägermaterial und der reflektierenden Beschichtung
• – Darstellung eines Verbundformkörpers nachhaltig hoher optischer Qualität
• – Effizienter und zudem nachhaltiger Einsatz von PMMA in hochwertigen bzw. hochbeanspruchten Anwendungen, z.B. als Solarspiegel zur Konzentration solarer Strahlung im Wüstenklima

The inventive novel PMMA-based composite molding for solar reflectors has the following properties, in combination as an advantage over the prior art, especially with regard to optical properties, on:

• - Avoiding disadvantageous layer interfaces due to the production of the composite molding without the inclusion of further layers, such as adhesive layers, between the PMMA substrate and the reflective coating
• - Representation of a composite molding sustainably high optical quality
• - Efficient and sustainable use of PMMA in high-quality or highly stressed applications, eg as a solar mirror for concentrating solar radiation in the desert climate

The transparent portion of the composite molded article according to the invention is also particularly neutral in color and does not cloud when exposed to moisture. The composite molding also shows excellent weather resistance and, with optional equipment with a fluoropolymer surface and / or a scratch resistant equipment, a very good chemical resistance, for example, against all commercial cleaning agents. These aspects also contribute to maintaining solar reflection over a long period of time.

Likewise, the use of the composite moldings according to the invention for the concentration of solar radiation is part of the present invention. The long-life solar reflectors produced with the composite moldings are also part of the present invention. In particular, the composite molded body containing solar reflectors whose solar reflection within 10 years by a maximum of 8%, preferably by a maximum of 5% and more preferably by a maximum of 3% decreases. The material according to the invention can thus also have a very long period of at least 10 years, preferably even at least 15 years, more preferably at least 20 years in places with particularly many hours of sunshine and particularly intense solar radiation, such as. used in the southwestern United States or the Sahara in solar reflectors.

In addition, the composite molding according to the invention is particularly moisture-stable. Thus, this does not show the known susceptibility to delamination of a reflective coating from the PMMA layer under the influence of moisture. PMMA and the reflective coating have different coefficients of thermal and hygroscopic expansion, so that, in the presence of moisture, due to these very different coefficients of expansion, the adhesion between the reflective coating and PMMA is known to be reduced and thus performance-deleterious delamination phenomena would occur. This disadvantage has been eliminated by the inventive structure of the composite molding.

Detailed description of the layer structure of the composite molding according to the invention

The PMMA-containing first layer

The first layer according to the invention is at least 50% by weight, preferably at least 80% by weight, of a layer of PMMA or a PMMA-containing polymer mixture. However, with the formulation PMMA or PMMA-containing layer, the layer is not restricted to pure methyl methacrylate compositions or a single-layer structure. Rather, the PMMA in the first layer may contain comonomers, which need not necessarily be methacrylates. Also, this layer of blends of various plastics, which need not contain all methacrylates, be composed. This layer may for example additionally comprise elastomers, for example a polyacrylate elastomer, for impact modification. In addition, this layer can consist of more than two layers be composed. Not all of these layers necessarily contain methacrylates.

Polymethyl methacrylate plastics are generally obtained by free radical polymerization of mixtures containing methyl methacrylate. In general, these mixtures contain at least 40% by weight, preferably at least 60% by weight and more preferably at least 80% by weight, based on the weight of the monomers, of methyl methacrylate. In addition, these mixtures for the preparation of polymethyl methacrylates may contain further (meth) acrylates which are copolymerizable with methyl methacrylate. The term (meth) acrylates include methacrylates and acrylates as well as mixtures of both. These monomers are well known.

In addition to the (meth) acrylates set out above, the compositions to be polymerized may also contain other unsaturated monomers which are copolymerizable with methyl methacrylate and the abovementioned (meth) acrylates. These include, inter alia, 1-alkenes, such as hexene-1, acrylonitrile; Vinyl esters such as vinyl acetate; Styrene or α-methylstyrene. In general, these comonomers in an amount of 0 wt .-% to 60 wt .-%, preferably 0 wt .-% to 40 wt .-% and particularly preferably 0 wt .-% to 20 wt .-%, based on the weight of the monomers used, wherein the compounds can be used individually or as a mixture.

The PMMA-based first layer used according to the invention may, as already described, contain an impact modifier. A more detailed description of these impact modifiers can also be found in WO 2007/073952.

In a particular embodiment of the invention, instead of pure PMMA-containing layers, PMMA / PVDF blends or PMMA / PVDF two-layer systems may also be used as the first layer. PVDF (polyvinylidene fluoride) as a component of a polymer blend or as an additional layer has several advantages: PVDF has high chemical resistance, low surface energy and extremely good weathering resistance. Thus, PVDF is water-repellent and shows even with long-term use almost no algae growth, comparable to antibiocidal materials.

The ratio of poly (meth) acrylate to polyvinylidene fluoride ranges from 1: 0.1 to 1: 1 by weight.

The PVDF polymers used in the context of the invention are polyvinylidene fluorides, which are generally transparent, partially crystalline, thermoplastic fluoroplastics. Basic building block for the polyvinylidene fluoride is vinylidene fluoride, which is polymerized in highly pure water under controlled pressure and temperature conditions by means of a special catalyst to polyvinylidene fluoride. The vinylidene fluoride in turn is accessible, for example, from the base materials hydrogen fluoride and methyl chloroform, via the intermediate chlorodifluoroethane. In principle, all types of PVDF available on the market can be used with great success in the context of the invention. These include Kynar ^® grades the manufacturer Arkema, Dyneon ^® grades the manufacturer Dyneon and Solef ^® grades the manufacturer Solvay.

The stabilizer package (sunscreen)

Preferably, the first layer, and optionally the second and / or third layer contains a stabilizer package consisting of a mixture of UV absorbers and UV stabilizers, more preferably consisting of at least one triazine UV absorber and at least one HALS UV stabilizer. Furthermore, further UV absorbers, e.g. Benzotriazoles be included.

In general, light stabilizers are well known and are used, for example, in Hans Zweifel, Plastics Additives Handbook, Hanser Verlag, 5th Edition, 2001, p. 141 ff described in detail. Sunscreens are to be understood as UV absorbers, UV stabilizers and free-radical scavengers. For example, UV absorbers can be selected from the group of substituted benzophenones, salicylic acid esters, cinnamic acid esters, oxalanilides, benzoxazinones, hydroxyphenylbenzotriazoles, triazines or benzylidene malonate. The preferred representative of UV stabilizers / radical scavengers is the group of hindered amines (HALS).

Preferably, the first layer between 0 wt% and 10 wt%, preferably between 0 wt% and 6 wt% and more preferably between 0 wt% and 4 wt% of the UV absorber of the benzotriazole type, between 0.1 wt% and 10% by weight, preferably between 0.2% by weight and 5% by weight and particularly preferably between 0.5% by weight and 3% by weight of the triazine-type UV absorbers and between 0.1% by weight and 5% by weight, preferably between 0.5% by weight and 3% by weight and particularly preferably between 0.2% by weight and 2% by weight of the UV stabilizers, preferably UV stabilizers of the HALS type. This blend of UV absorbers and UV stabilizers provides stable, long-lasting UV protection over a wide wavelength spectrum of solar radiation.

As further costabilizers also disulfites, such as sodium disulfite, or sterically hindered phenols and phosphites are used.

The thermoplastic second layer

The thermoplastic second layer is located on one side of the first layer and has the reflective coating on the side opposite the first layer. In a preferred embodiment, the second layer is located in a solar reflector made therefrom on the side of the first layer facing away from the sun. In this case one speaks of a backside mirror. In a front mirror, the second layer is on the sun-facing side.

The second layer according to the invention must have two compelling properties. On the one hand, the second layer together with the PMMA-containing first layer without intermediate layer, such as e.g. an adhesive layer, a sustainable stable laminate to be produced. Furthermore, the second layer must be e.g. with inorganic materials, for the construction of the reflective coating by means of PVD or CVD, without an additional primer layer or surface treatment sustainable adherent coating. In addition, the layer must be highly transparent and heat-resistant and preferably have a high flexibility. The reflective coating should have no loss of adhesion over a long period of time.

According to the invention, it is necessary to have a high compatibility between PMMA on the one hand and the material selected for the second and the optional third layer on the other hand. Only such materials are suitable for carrying out the invention, from which a stable bond without loss of adhesion can be produced with PMMA.

Particularly suitable for meeting the conditions mentioned are thermoplastic layers of a polyester or polycarbonate.

The usable polyester layers are, in particular, coextruded polyethylene terephthalate (PET) layers.

The reflective coating

The reflective coating is a functional PVD and / or CVD functional multi-layer structure that includes a metal mirror layer, preferably of silver, a silver alloy, or aluminum.

On the side facing away from the solar radiation, the metal mirror layer is optional and preferably coated with a second metal layer, for example made of copper or a nickel-chromium alloy. This essentially serves as protection of the metal mirror layer against corrosion, as well as for better adhesion of an optional pressure-sensitive adhesive layer.

In the case of mirror layers made of aluminum, the comparatively "low" reflection of the aluminum mirror in the relevant wavelength range is increased by the application of so-called "enhancement stack" layers (by means of further "physical vapor deposition").

In addition, "enhancement stack" layers can also be used analogously in silver mirror layers for further reflection improvement. This enhancement stack layer structure additionally acts as an active protective layer or Mifgrationssperre against the silver, and can also act UV-reflective with appropriate design.

Furthermore, the metal mirror layer can additionally be equipped with a primer layer for improving the bond on the second layer. This is usually a metallic or metal oxide layer.

The optional thermoplastic third layer

The requirements for the optional third layer are in principle the same as those applied to the second layer. The third layer is preferably applied in the composite molding on the sun-facing side of the first layer. The purpose is above all to impart a surface coating with further, preferably inorganic coatings, which are not the metal mirror coating, by means of PVD or CVD. As already mentioned, these coatings are, for example, scratch-resistant coatings, UV-reflecting layers, conductive layers, antisoiling coatings and / or optically functional layers, for example antireflective or reflection-enhancing layers.

The third layer may be identical in material or thickness to or different from the second layer.

In addition to polyesters or polycarbonates, it is also possible to use fluoropolymers, in particular PVDF (polyvinylidene fluoride), for the third layer. PVDF has high chemical resistance and low surface energy. In addition, PVDF is water-repellent and shows even with long-term use almost no algae growth, comparable with antibiocidal materials and thus is very well suited for surface treatment of the composite molding according to the invention.

Very thin PVDF layers with a layer thickness between 1 .mu.m and 20 .mu.m, preferably between 1 .mu.m and 10 .mu.m, can also be realized with a high degree of transparency.

Furthermore, the same applies to the PVDF in the third layer, as was already carried out for the PVDF as a blend component of the first layer.

The other (inorganic) layers

The other PVD or CVD applied layers that can be directly on the reflective coating and / or on the third layer are, in particular, scratch-resistant coatings, UV reflection layers, conductive layers, antisoiling coatings and / or optical act functional layers.

The term scratch-resistant coating is understood in the context of this invention as collective term for coatings which are applied to reduce surface scratching and / or to improve the abrasion resistance. In particular, a high abrasion resistance is of great importance for the use according to the invention of the composite shaped bodies in solar reflectors. Another important feature of the scratch-resistant coating in the broadest sense is that this layer does not adversely affect the optical properties of the film composite. These scratch-resistant coatings are e.g. silicon oxide layers applied directly by PVD or CVD.

The conductive layers are metal oxide layers, e.g. made of indium tin oxide (usually abbreviated ITO). These have the purpose of preventing electrostatic charges. This has both in the operation of the solar reflectors, e.g. in terms of dusting, as well as in the processing of the composite molded body great advantages. In addition, ITO has the great advantage of being additionally reflective, especially for radiation in the infrared range.

In addition to ITO, it is also possible to use, for example, antimony-doped or fluorine-doped tin oxide and aluminum-doped zinc oxide.

In addition, the surface of the coversheet may be provided with an antisoiling coating, so-called anisoiling coating, to facilitate cleaning. This coating can also be applied by means of PVD or CVD.

The application of titanium dioxide causes, after appropriate stimulation by the UV component of solar radiation, a catalytic degradation of superficial spores and algae.

In turn, the optically functional layers are preferably reflection-enhancing dielectric layers. These are e.g. composed of silica dioxide and titanium dioxide alternating layers. However, it is also possible to use magnesium fluoride, aluminum oxide, zirconium oxide, zinc sulfide or praseodymium titanium oxide. These layers can also act as a scratch-resistant coating and / or UV-reflective depending on the structure.

Further (organic) layers

Optionally, further, usually organic, in particular polymeric protective layers can be applied to the layers applied by means of PVD by means of extrusion coating, lamination or coating.

For example, these layers applied as a lacquer can likewise be scratch-resistant coatings. Polysiloxanes, such as CRYSTALCOAT ^™ MP-100 from SDC Techologies Inc., AS 400-SHP 401 or UVHC3000K, both from Momentive Performance Materials, can be used as such in particular. These paint formulations are applied to the surface of the film composite or the cover film, for example by roll coating, Knifecoating or Flowcoating.

Detailed description of use

The composite shaped bodies according to the invention are preferably used, in particular in concentrators, in concentrators for concentrating solar radiation in solar thermal or photovoltaic systems.

The concentration of the solar radiation can be done on the 2-dimensional geometry of a photovoltaic cell, on a Stirling engine or a thermal receiver of a solar thermal system. Furthermore, the solar radiation can be concentrated on an absorber tube of a solar thermal collector.

For all embodiments, both flat plates, as well as preferred curved shapes can be produced and installed in solar thermal system. The molding can be carried out after the preparation of the concentrators and the subsequent cutting, for example under cold bending or thermoforming, wherein a cold bending process is preferred.

As an alternative to use in concentrators, the composite shaped bodies according to the invention can also be used for the application of a metal decoration design for decorative purposes. More concrete examples are an adherent metal (frame) application on PMMA semi-finished products, as they can be used for the production of (mobile phone) displays, or for decoration purposes in the field of automotive or electrical appliances.

Moreover, the composite shaped bodies according to the invention can be used otherwise as a reflecting surface, e.g. as a traffic mirror in the context of road traffic control systems.

Examples

measurement methods

• a) The TSR measurements were carried out in the initial state according to ASTM G 159
• b) The adhesive strength was measured in the initial state by the cross hatch test according to ISO 2409, using adhesive bond tape of 0.7 N / mm.
• c) The investigation of the adhesive strength of the reflective coating was carried out after 48 h humidity and temperature at 65 ° C in distilled water by means of the "180 ° Peeltest" according to ISO 11339.

Front-panel mirror

Example 1: Front Plate Mirror with "Standard" Reflective Coating

A 4 mm thick composite panel, consisting of 3.9 mm PMMA plexiglass 7 H and 0.1 mm polycarbonate Makrolon 2607, is produced by means of adapter coextrusion.

Thereafter, the application of the reflective coating by means of a plasma-assisted sputtering process to the polycarbonate side of the composite plate, consisting of, in this order, 200 nm Ni / Cr, 100 nm Ag and 5 nm ZAO _x (substoichiometric zinc-aluminum oxide).

The lamination of a 65 μm thick Plexiglas 0F038 surface-treatment film then takes place on the reflective coating. For this purpose, a marketable acrylate-based adhesive system is applied in a layer thickness of 25 microns before.

The result is a TSR of 93.4% and a cross-cut adhesion "GT 0", both measured in the initial state, as well as a continued complete adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C. ,

Example 2: Front side plate mirror with improved reflection coating

A 4 mm thick composite panel, consisting of 3.9 mm PMMA plexiglass 7 H and 0.1 mm polycarbonate Makrolon 2607, is produced by means of adapter coextrusion.

Then, the application of the reflective coating by means of a plasma-assisted sputtering process to the polycarbonate side of the composite plate, consisting of, in this order, 200 nm Ni / Cr, 100 nm Ag, 0.6 nm ZAO _x , 30 nm SiO ₂ and 20 nm TiO ₂ .

The lamination of a 65 μm thick Plexiglas 0F038 surface-treatment film then takes place on the reflective coating. For this purpose, a marketable acrylate-based adhesive system is applied in a layer thickness of 25 microns before.

The result is a TSR of 93.9% and a cross-cut adhesion "GT 0", both measured in the initial state, as well as a continued complete adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C. ,

Comparative Example 1: Front side plate mirror

Analogous to Example 1, however, the production of the 4 mm composite panel is completely made of PMMA Plexiglas 7H without polycarbonate layer.

The result is a TSR of 93.4% and a cross-cut adhesion "GT 0", both measured in the initial state, and a complete loss of adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C.

Backside sheet mirror

Example 3: Backside foil mirror with "standard" reflective coating

A 0.15 mm thick composite film, consisting of 0.125 mm PMMA Plexiglas 7 H, which contains 2% CGX 006 and 0.6% Chimasorb 119 for the purpose of UV addition, and Makrolon 2607 0.025 mm polycarbonate, is produced by means of adapter coextrusion.

Then, the application of the reflective coating by means of a plasma-assisted sputtering process to the polycarbonate side of the composite film, consisting of, in this order, 0.5 nm ZAO (zinc-aluminum oxide), 100 nm Ag and 50 nm Cu.

The result is a TSR of 94.3% and a cross-cut adhesion "GT 0", both measured in the initial state, as well as a continued complete adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C. ,

Example 4: Backside foil mirror with alternative "standard" reflective coating

A 0.15 mm thick composite film consisting of 0.125 mm PMMA Plexiglas 7 H, which contains 2% CGX 006 and 0.6% Chimasorb 119 for the purpose of UV addition, and Makrolon 2607 0.025 mm polycarbonate, is produced by means of adapter coextrusion.

Then the application of the reflective coating by means of a plasma-assisted sputtering process to the polycarbonate side of the composite film, consisting of, in this order, 2 nm TiO _x (stoichiometric titanium oxide), 140 nm Ag and 50 nm Cu.

The result is a TSR of 93.8% and a cross-cut adhesion "GT 0", both measured in the initial state, as well as a continued complete adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C. ,

Comparative Example 2: Backside Foil Mirror

Analogous to example 3, however, the production of the 4 mm composite panel is completely made of PMMA Plexiglas 7H without polycarbonate layer.

The result is a TSR of 94.3% and a cross-cut adhesion "GT 0", both measured in the initial state, and a complete loss of adhesion of the reflective coating in the "180 ° Peeltest" after 48 h storage in distilled water at 65 ° C.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4307150 [0006, 0011]
• US 4645714 [0007, 0010, 0011]
• US 5118540 [0011]
• WO 2007/076282 [0012]
• WO 2007/073952. [0049]

Cited non-patent literature

• Plastics Additives Handbook, Hanser Verlag, 5th Edition, 2001, p. 141 ff. [0054]

Claims (18)

Composite molding for use in solar reflectors for concentrating solar radiation, characterized in that the composite molding is a composite of at least two or three layers, wherein the first layer contains more than 50% by weight PMMA or a PMMA-containing polymer mixture in the second layer around a layer of polycarbonate or a polyester located on one side of the first layer, in the optional third layer, a layer of a fluoropolymer, polycarbonate or a polyester located on the other side of the first layer is, is, and that the second layer has a reflective coating, which is located on the opposite side of the first layer, and was applied by PVD or CVD on the composite molding. Composite molding according to claim 1, characterized in that the reflective coating contains a silver, silver alloy or aluminum layer. Composite molding according to claim 1 or 2, characterized in that there are further applied by means of PVD or CVD coatings on the reflective coating and / or the third layer. Composite molding according to one of claims 1 to 3, characterized in that the first layer has a thickness between 6 .mu.m and 10 cm, the second layer has a thickness between 0.5 .mu.m and 2 cm and the optional third layer has a thickness between 0.5 .mu.m and 2 cm, wherein the first layer is thicker than the second and the optional third layer. Composite molding according to one of claims 1 to 4, characterized in that the first layer contains a mixture of UV absorbers and UV stabilizers consisting of at least one triazine UV absorber and at least one HALS UV stabilizer. Composite molding according to one of claims 1 to 5, characterized in that the first layer of PMMA or a PMMA-containing polymer mixture and polyvinylidene fluoride composed and UV stabilizers and UV absorbers. Composite molded article according to claim 3, characterized in that the further layers are scratch-resistant coatings, weatherproof layers, conductive layers, antisoiling coatings and / or optically functional layers. Composite molding according to claim 7, characterized in that the optically functional layers are reflection-enhancing layers. Composite molding according to at least one of claims 1 to 8 in the form of a film, characterized in that the first layer has a thickness between 6 and 500 microns and the second and the optional third layer each having a thickness between 0.5 and 500 microns, wherein the first layer is thicker than the second or the optional third layer. Composite molding according to at least one of claims 1 to 8 in the form of a plate, characterized in that the first layer has a thickness between 500 microns and 10 cm and the second and the optional third layer each having a thickness between 10 .mu.m and 2 cm. Composite molding according to at least one of claims 1 to 10, characterized in that the applied by means of PVD or CVD layers are provided with an additional protective layer. A process for producing a composite molded article according to claim 1, characterized in that the first layer is produced by extrusion and bonded by coextrusion, adhesive-free lamination or extrusion coating to the second and optionally to the third layer, and then to the second layer by means of a reflective coating PVD or CVD is applied. A method according to claim 12, characterized in that one or more further layers are applied to the reflective coating by means of PVD or CVD. A method according to claim 12 or 13, characterized in that one or more further layers are applied to the third layer by means of PVD or CVD. Process according to at least one of Claims 12 to 14, characterized in that a protective layer is additionally applied to the layers applied by means of PVD or CVD by means of extrusion coating, lamination or lacquering. Use of a composite molding according to one of claims 1 to 11 for the concentration of solar radiation in solar reflectors. Use of a composite molding according to one of claims 1 to 11 for the application of a metal decorative design for decorative purposes, as reflecting surface in the automotive industry or in electrical appliances or as a traffic mirror in the context of road traffic control systems. Long-life solar reflector, comprising a composite molding according to one of claims 1 to 11, characterized in that the solar reflection within 10 years by a maximum of 8%, preferably by a maximum of 5% and more preferably by a maximum of 3% decreases.