METHOD FOR THE MANUFACTURE OF A CURVED FACE LAMINATED REFLECTOR FOR REFLECTING RADIATION ENERGY AND IN PARTICULAR SOLAR ENERGY

Abstract: Method for the manufacture of a curved face laminated reflector (1 to 6) which reflects radiation energy and in particular solar energy. According to the method, a first adhesive layer (4) penetrable by radiation and hardened by heat, a combination film (5, 6) consisting of a flexible core layer (5) and of a reflecting thin metal layer (6) deposited onto the said core layer, and a second adhesive layer (3) penetrable by radiation and hardened by heat are sandwiched, one upon the other, between two support layers (1, 2) of the desired curved form so that the edges of the combination film (5, 6) extend at the maximum to the level of the edges of the adhesive layers (3, 4). The laminate (1 to 6) produced in this way is subjected to a compression and heat treatment so that, when the combination film (5, 6) shrinks to some extent, the adhesive layers (3, 4) melt together around the edges of the combination film (5, 6) and completely enclose the combination film (5, 6) in a hermetical manner, which, among other things, substantially improves the weather resistance of the reflector.

Description: Method for the manufacture of a curved face laminated reflector for reflecting ratiation energy and in particular solar energy The present invention concerns a method in accordance with the preamble of claim 1 for the manufacture of a reflector. Such a concentrating reflector can be used for reflecting solar or other radiation energy a desir- ed direction under conditions in which moisture, air currents, impurities assembled on the face of the appa¬ ratus, and radiation detrimental to certain materials, e.g. UV radiation, occur. By means of a reflector shaped as a paraboloid, e.g., the radiation energy of the sun can be directed at one point in order to pro¬ duce the desired concentration effect. Correspondingly, as is well known, by means of an oblong reflector o-f parabolical section, it is possible to concentrate the radiation reflected from the reflector onto a linear area. It should be stated that, e.g., in the U.S.A., about 1,000,000 square metres of reflectors of this type are sold annually. In the manufacture of concentrating collectors of solar radiation, the mirror reflector face can be manu- factured in several different ways. Frequently, a smooth-faced base construction of approximately para¬ bolical section is used, onto which a plastic film is attached by means of adhesive-faced materials, the said plastic film being provided with a thin metallic reflector face. Thereby, however, the reflector face is subject to effects of the weather, is oxidated in a relatively short time, and becomes dim. In order to avoid this detrimental phenomenon, many sorts of lacquer-like materials or coatings have been developed, whereby the-weather resistance of the reflector face coated by such materials is improved. Thereby, it is often difficult to provide a smooth application of OMPI appropriate thickness of the surface layer, for the surface layer has a detrimental effect on the reflec¬ ting capacity. The surface layer is also readily da¬ maged if the face is cleaned inappropriately. A method that has been known for a long time is the silver plating of a glass pane in order manufacture a reflector. It is, however, technically more compli¬ cated to manufacture a high-quality concave reflector than a plane reflector. It is possible to manufacture a concave reflector by using a metal sheet that has been provided with a mirror face by means of the vacuum evaporating technique, but the face often becomes dim in a short time if there is moisture. A protective coating, on the other hand, deteriorates the mirror reflecting properties. Drawbacks of present-day reflector construc¬ tions are their usually poor resistance to weather, difficulty of cleaning without damaging the face, high cost of coated reflector film materials and, conse¬ quently, the material and labour cost resulting from the renewal of the reflector face from time to time. The object of the present invention is to eliminate the drawbacks present in the prior-art methods of manufacture and structures and to provide a method of an entirely novel type for the manufac¬ ture of a laminated reflector. The invention is based on preparing a reflecting film by means of a technique known from the capacitor film technology as a separate combination film of uniform quality, which film is air-tightly enclosed by means of layers of adhesive material between two support layers by using a lamination technique known from the manufacture of windshields. More specifically, the method in accordance with the invention is mainly characterized in what is "__ΛJ £ stated in the characterizing part of claim 1. It can be considered the most important advantage of the method of the present invention that the durability of the reflector face and the per a- nence of the mirror reflecting capacity are increased essentially so that the reflector endures several years of operation and cleaning without any other operations. Moreover, by means of the structure, an excellent stability of form is achieved. In the following, the invention will be exam¬ ined in more detail with the aid of the exemplifying embodiments in accordance with the attached drawings. . Figure 1 is a partly sσhematical sectional view of the edge portion of a reflector to be manu- factured by means of the method of the invention -before the compression and heat treatment. . Figure 2 shows the edge portion of Fig. 1 after the compression and heat treatment. In the example case, between two at least substantially identical glass panes 1 , 2 of parabo¬ lical section, two layers 3, 4 of adhesive material penetrable by radiation and hardened by heat are fitted, the thickness of each ofthe said layers being about 0.3 mm. Appropriate adhesive materials are, e.g., polyvinyl- butyral (PVB) and polyvinylalcohol (PVA) . Moreover, between the layers 3, 4 of adhesive material, a com¬ bination film 5,6 is fitted, which consists of a flexible core layer 5 and of a reflecting thin metal layer 6 deposited onto the said core layer. The core layer 5, whose thickness is about 250 μm, is made of polyester film. The metal layer 6 is preferably made of aluminium which has been deposited onto the core layer in accordance with the capacitor film technique by means of vacuum evaporation. The thickness of this aluminium layer is about 40 nm. Out of the combination film prepared in this way, a piece is cut off which is dimensioned so that its edges extend at the maximum to the level of the edges of the layers 3, 4 of adhesive material. In the example case, shown in Fig. 1, the adhesive layers 3, 4 extend somewhat beyond the edge of the combination film 5, 6 so that a groove 11 is formed, whose bottom con¬ sists of the outer edge of the combination film 5, 6 and whose walls consist of the outermost parts of the adhe¬ sive layers 3, 4. The " depth of this groove 11 is appro¬ priately at least 200 um. The combination in this way produced is then brought into a compression treatment known from the windshield technology by subjecting the edge zone between the support layers 1 , 2 to a negative pressure so that the support layers 1 , 2 are pressed against each other for the removal of any excess air. Hereupon, the laminate structure is sub¬ jected to infrared heating taking place at a tempera¬ ture of 80 to 120°C, preferably about 100°C. Then, the laminate is transferred into a pressure autoclave whose processing temperature is 130 to 170 C, prefer¬ ably about 150 C, pressure 8 to 13 bars, preferably about 10.5 bars, and the time of treatment 35 to 55 min., preferably about 45 min. On being heated, the adhesive layers 3 and 4 melt partly, whereby their outer edges melt gradually together across the edges of the combination film 5,6, thereby completely enclosing the combination film 5,6 hermetically. Thus, thereby the groove 11 disappears completely and a structure in accordance with Fig. 2 is produced, wherein the adhesive layers 3 and 4 form a unified edge face 12 connecting the support layers 1 and 2 at their edges. Since the combination film 5, 6 shrinks to some extent during the heat treatment, a groove 11 * shown in Fig. 1 is in itself not necessarily needed/ but the combination film 5, 6 may extend substantially to the outer edgesof the adhesive layers 3, 4. Owing to the said shrinkage, a result in accordance with - -RE Fig. 2 is also obtained in this case. The shrinkage does, however, not deteriorate the reflecting quality of the reflecting metal layer 6 excessively. As the layers 3 and 4, it is highly advan- tageously possible to use polyvinylbutyral (PVB) , be¬ cause it is also used advantageously in other laminate structures, e.g., in the manufacture of windshields for automobiles. When a beam 7 of light meets the glass pane 1 at point 8 on the finished reflector, it penetrates through the glass pane 1 and the adhesive layer 3 to point 9, where it is reflected and passes again out through the layers 3 and 1. The face 10 of the glass pane 1 can be cleaned easily / e.g., by means of water, of any dust or dirt gathered on it. On the other hand, the metal coating 6 is well protected, and even the glass pane 1 alone efficiently attenuates the UV radiation, which is so detrimental to the coating 6. In the following, in a condensed form, the thicknesses of the different layers in a reflector manufactured by means of the method of the invention in the case of the exemplifying embodiment as well as (in brackets) typical limits of variation are given: Glass panes 1 and 2 2.2 mm (1...3 mm) Adhesive layers 3 and 4 0.3 mm (0.1...1.0 mm) Core layer 5 250 μm (10...500 μm) Coating layer 6 40 nm (20...60 n ) The importance of the core layer 5 lies therein that the coating layer 6 can be formed readily onto the core layer. It should be noticed that the method of the present invention can also be applied easily to struc¬ tures bent in two directions, for, if required, • the adhesive layers 3 and 4 as well as the core layer 5 with the coating 6 can be formed into faces of a perma¬ nently unchangeable section, e.g. paraboloid faces or similar faces. IJUREAT /

Claims: WHAT IS CLAIMED IS: 1.. Method for the manufacture of a curved face laminated reflector (1 to 6) for reflecting radiation energy and in particular solar energy, according to which method a reflecting layer (6), e.g. n,aluminium layer, is produced between two support layers (1, 2), e.g., glass layers, penetrable by radiation, and - the support layers (1, 2) are connected together so that the reflecting layer (6) remains between the support layers, c h a r a c t e r i z e d, in that - a first adhesive layer (4) penetrable by radiation and hardened by heat, a combination film (5, 6) consisting of a flexible core layer (5) and of a reflecting thin metal layer (6) deposited onto the said ' core layer, and a second adhesive layer (3) penetrable by radiation and hardened by heat are sand- wiched, one upon- the other, between the two support layers (1 , 2) of the desired curved form so that the edges of the combination film (5, 6) extend at the maximum to the level of the edges of the adhesive layers (3, 4), and - the laminate (1 to 6) produced in this way is subjected to a compression and heat treatment so that, when the combination film (5, 6) shrinks to some extent, the adhesive layers (3, 4) melt • together around the edges of the combination film (5, β) and completely enclose the combination film (5, 6) in a hermetical manner. 2. Method as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the compression treatment is performed by subjecting the edge zone between the sup- port layers (1, 2) to a negative . pressure so that the support layers (1, 2) are pressed against each other for the removal of any excess air. "BUREA OMPI 3. Method as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the heat treatment comprises an infrared heating taking plac at a temperature of 80 to 120°C, preferably about 100°C, and a subsequent autoclave heating taking place at a temperature of 130 to 170°C, preferably about 150°C. 4. Method as claimed in claim 3, c h r ¬ a c t e r i z e d in that the autoclave heating is performed at a pressure of 8 to 13 bars, preferably about 10.5 bars, and its duration is 35 to 55 min., preferably about 45 min. 5. Method as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the adhesive layers (3, 4) are made of polyvinylbutyral (PVB) or polyvinylal- cohol (PVA) . 6. Method as claimed in claim 1 , c h a r ¬ a c t e r i z e d in that the combination film (5, 6) is prepared by depositing onto the core layer ( 5 ) , in accordance with the capacitor film technique by means of vacuum evaporation, a thin metal layer (6) , e.g., an aluminium layer, whose thickness is 20 to 60 nm, preferably about 40 nm. 7. Method as claimed in claim 6, c h a r ¬ a c t e r i z e d in that, as the core layer (5) , a polyester film is used, whose thickness is 10 to 500 um, preferably about 250 μm. 8. Method as claimed in claim 1 , c h a r ¬ a c t e r i z e d in that the compression and heat treatment is carried out in a pressure autoclave known from the windshield technology. 9. Method as claimed in claim 1, c h a r ¬ a c t e r i z e d in that the combination film. (5, 6) is originally dimensioned so that, when it is sandwiched between the support layers (1, 2) before the compression - and heat treatment, the edges of the adhesive layer ( " 3, 4) go beyond the edges of the combination film (5, 6) at every point by at least 200 μm.

Inventors: HEIKKILAE HANNES, WREDE THOMAS, HEIKKILAE, HANNES, WREDE, THOMAS
Applicants: WREDE KY
Application year: 1984
Main classification: C03C27
IPC codes: B32B17, B32B27, F24J2