JOYCE, David, N (Holscot Fluoroplastics Limited, Alma Park RoadAlma Park Ind Estate, Grantham Lincolnshire NG31 9SE, GB)
| CLAIMS 1. An architectural glazed panel comprising a rigid frame with a pre- stretched fluoroplastic film shrunk on to the frame so as to be stretched across the opposed open faces of the frame. 2. A panel according to Claim 1 , wherein the fluoroplastic film is fluohnated ethylene propylene (FEP) or ethylene tetrafluoroethylene (EFTE). 3. A panel according to Claim 1 or 2, wherein the thickness of the film is 100 to 150 microns. 4. A panel according to Claim 3, wherein the thickness of the film is 125 microns. 5. An architectural glazing structure, comprising two or more panels according to any preceding claim, stacked one upon the other and secured together at the periphery thereof. 6. A structure according to Claim 5, including a spacer located be- tween the or each adjacent pair of panels. 7. A structure according to Claim 5 or 6, wherein the edges of the panels are sealed together into channel members. 8. A method of making an architectural glazing panel, comprising forming a rigid frame of a desired shape, forming a fluoroplastic cover member for enclosing the frame, said cover member having at least two closed sides and being initially dimensioned so that the circumferential distance of the member between the two closed sides is smaller than the corresponding circumferential dimension of the frame, heating the film and stretching the cover member in at least the direction between the said two sides until the said circumferential dimension of the member is greater than that of the frame, cooling the member while stretched, inserting the frame into the cover member and heating the cover member to shrink the member on to the frame whereby to stretch the member between the said two sides, and then sealing the or each other side of the cover member to enclose the frame. 9. A method according to Claim 8, wherein the cover member is formed as a tube. 10. A method according to Claim 9, comprising extruding the tube. 11. A method according to Claim 8, 9 or 10, wherein the fluoroplastic film is fluorinated ethylene propylene (FEP) or ethylene tetrafluoroethylene (EFTE). 12. A method according to any of Claims 8 to 11 , wherein the thick- ness of the film is 100 to 150 microns. 13. A method according to Claim 12, wherein the thickness of the film is 125 microns. 14. A method according to any of Claims 8 to 13, further comprising stacking two or more panels together and fastening the panels together at the edges thereof. 15. A method according to Claim 14, comprising inserting a spacer between adjacent panels in the stack. |
[0001] This invention relates to plastics film glazed panels for architectural use, and to a method of making such frames. Background to the Invention
[0002] While glass has been used to glaze greenhouses and like structures for many years, there are disadvantages to its use. Firstly, glass only allows passage of the visible part of the photosynthetically active radiation ("PAR") spectrum. This can cause plants such as tomatoes, cucumbers or flowers to grow in an anaemic condition. In addition, glass is heavy, and so almost all commercial greenhouses are glazed with only a single thickness of glass. In Northern latitudes this means that greenhouses have to be heated over a significant part of the year, and heat loss through the single layer of glass is costly.
[0003] Thin fluoroplastic films, such as ETFE (ethylene tetrafluoroethylene) and FEP (fluorinated ethylene propylene), offer some advantages for replacement of glass in large greenhouse structures. They are substantially lighter than glass, and allow the passage of a much greater range of the spectrum which can be beneficial to plant growth. By providing two or more spaced layers of the film, greatly enhanced thermal insulation can be achieved. Some of these properties have been exploited in structures such as the Eden Centre in Cornwall and in the Water Sports Cube at the 2008 Olympics, but the structures rely on air-inflated panels which need to be constantly supplied with air under pressure to keep them inflated and so maintain the integrity of the structure. If the panels were to deflate in windy conditions, for example, there would be a risk of structural failure. In addition, the need to keep the panels inflated adds to the complexity of the structure and the cost of its maintenance.
[0004] An inflated building structure of this general type is disclosed in US2007/0277451A1 , but here the inflated space is supplied with humidified air to promote the formation of a layer of condensation in the structure to act as a shade curtain within the building, requiring an even more complex control system to maintain the functionality. The panels are formed by trapping the edges of the film sheets in two-part clamping formations around the edges of the frame, making the structure complicated and expensive to manufacture.
[0005] There is a need for a panel which offers the advantages of fluoroplas- tic films with the simplicity of conventional glazed structures. Summary of the Invention
[0006] According to the invention, there is provided an architectural glazed panel comprising a rigid frame with a pre-stretched fluoroplastic film shrunk on to the frame so as to be stretched across the opposed open faces of the frame.
[0007] The invention also provides a method of making an architectural glaz- ing panel, comprising forming a rigid frame of a desired shape, forming a fluoroplastic cover member for enclosing the frame, said cover member having at least two closed sides and being initially dimensioned so that the circumferential distance of the member between the two closed sides is smaller than the corresponding circumferential dimension of the frame, heating the film and stretching the cover member in at least the direction between the said two sides until the said circumferential dimension of the member is greater than that of the frame, cooling the member while stretched, inserting the frame into the cover member and heating the cover member to shrink the member on to the frame whereby to stretch the member between the said two sides, and then sealing the or each other side of the cover member to enclose the frame.
[0008] The cover member is suitably formed as a tube, which may be extruded, although it is possible to fabricate the cover member, for example to accommodate non-rectangular shapes of frame.
[0009] The fluoroplastic film is suitably FEP or ETFE, but other melt proc- essable fluoroplastic films can be used, such as EFEP resin (a copolymer of ethylene, tetrafluoroethylene and hexafluoropropylene), PFA (perfluoroalkoxy resin) and other modified fluoropolymers, including crosslinked polymers for enhanced properties. The thickness is typically 100-150 microns, preferably 125 microns. The panels can be made in any desired shape, and the film is conven- iently produced in tubular form by extrusion, although larger sizes, for example having a circumference in excess of about 2m, are more readily formed by welding sheets together.
[0010] The manufacture of heat-shhnkable fluoroplastic tubular film is well- known. For example, a suitable length of tube (conveniently more than suffi- cient to fit the frame) is cut, and the open ends are temporarily sealed by inserting aluminium plugs and fixing a circular strap or clamp over the tube and around the plug. Hot air, or preferably steam, at around 100 0 C is introduced to expand the film so that the width is approximately 2% greater than the frame dimension, and the stretched tube or bag is then cooled in the stretched form by the introduction of cool compressed air to displace the steam.
[0011] The frame is then introduced into the stretched tube and the assembly heated to a lower temperature than originally, for example 70 0 C to 80°C, to enable the elastic memory of the film to try to restore it to its original dimension, resulting in its becoming stretched over the frame and held under tension thereby.
[0012] The open ends of the tube may be tensioned and then folded over the respective sides of the frame, to be bonded or clamped thereto.
[0013] Two or more of the panels may be stacked one on top of the other to provide composite panels providing an even higher degree of thermal insulation without significantly affecting the transmission of light through the panels.
[0014] The panels of the invention may be used to replace glass in existing structures such as greenhouses, affording an economical way of upgrading the light transmission and heat retention of such structures. Because of their light weight, there are no problems with the loading of the supporting structure, such as might arise from using conventional double-glazed glass panels.
[0015] Additional advantages arise from the use of fluoroplastic films. The films are very durable and show no significant changes in strength or optical properties after long exposure to the atmosphere. The refractive index of the materials is such that, even at low angles of incidence, most light will be trans- mitted through the films. FEP and ETFE will not support combustion, and so - A -
are safer in use, requiring the provision of fewer fire exits than might be the case with other plastics construction materials. FEP, and to a lesser extent ETFE, exhibit very low coefficients of friction, which means that dirt finds it difficult to adhere to the panels; they are thus self-cleaning. FEP and ETFE have been shown to be completely resistant to mildew growth, by testing in humidity chambers inoculated with a spore suspension, and in soil burial tests. At the thicknesses used in the panels of the invention, FEP and ETFE transmit a high percentage of ultra violet and visible light, and FEP is much more transparent in the infra red region of the spectrum than glass. As a result, plant growth under such panels can be enhanced as compared to those grown under glass.
Brief Description of the Drawings
[0016] In the drawings, which illustrate exemplary embodiments of the invention:
[0017] Figure 1 is a diagrammatic perspective view of an architectural glaz- ing panel manufactured according to a method according to the invention;
[0018] Figure 2 is a sectional view on line A-A in Figure 1 ;
[0019] Figure 3 is a sectional view of a composite panel according to another embodiment of the invention; and
[0020] Figure 4 is a perspective view illustrating an alternative method of making the frame in accordance with the invention.
Detailed Description of the Invention
[0021] Referring to Figures 1 and 2, a frame 1 is formed from extruded aluminium jointed together with suitable corner pieces. While the illustrated frame is rectangular, it will be appreciated that any shape of frame may be employed, for example triangular to fit into the ends of structures having pitched roofs. Aluminium, or an alloy thereof, is a suitable material for the manufacture of the frames, being light and strong, but other materials may be suitable, such as fibre-reinforced plastics. For frames up to 1 m x 3m, a 30mm x 30mm box- section aluminium extrusion with a 2mm wall thickness has been found to be satisfactory. Thinner wall thicknesses may be possible using a more complex cross-section.
[0022] The fluoroplastic film 2 is suitably of 0.125mm thickness, and may be formed from such materials as FEP, ETFE, and PFA. For panels having a cir- cumference greater than about 2m, fabricating a tube by welding two sheets together is preferred, while extrusion of a tube is convenient for the smaller sizes. The circumference of the tube is smaller by a few percent than the circumference of the frame cross-section for the smallest dimension of the frame, e.g. width. The length is selected to be in excess of that required to cover the frame.
[0023] The tube is then heated using hot air or steam to approximately 100 0 C and stretched using internal air pressure (with the ends sealed) or mechanical means to increase the size until it is about 2% greater than the circumference of the frame cross-section. The total stretch is therefore approximately 3% to 5% from the original welded or extruded size of the tube. When the tube has cooled, it has been given an elastic memory by which it will try to return to its previous un-stretched dimensions, if subjected to temperatures significantly above ambient.
[0024] The stretched fluoroplastic tube is pulled over the frame at ambient temperature, and the frame and tube are placed in a low temperature oven, heated to approximately 70 0 C to 80°C, which is sufficient for memory effect of the stretched fluoroplastic material to cause it to shrink back to the un-stretched dimensions. However, before it can fully achieve this state, the material engages the frame, and as a result is held under tension as a flat film on and around the frame, forming a fluoroplastic glazed panel. The ends of the frame are covered by tensioning the fluoroplastic film in a biaxial orientation and folding it over the ends of the frame. The folded film is clamped or bonded. No attempt is made to vacuum seal or encapsulate the panels with an air-tight method. In this way, the air pressure within the panel will always be the same as the outside atmospheric pressure. The tension of the film, its residual elastic mennory, and, to a minor extent, the elasticity of the frame maintain the tautness of the film on the frame.
[0025] The applicants' experience with fluoroplastic materials shows that they can operate at very elevated temperatures (up to 200 0 C), and that the elastic memory is retained for years. The panels, which operate only at ambient temperatures, are therefore expected to have a long useful lifespan. The panels are light in weight and can be erected on to a load-bearing framework to produce large structures which require no energy consumption to maintain in position. The panels allow a much greater range of the light spectrum to pass through than glass does, and offer a high degree of thermal insulation.
[0026] However, if an even greater degree of thermal insulation is required, two or more panels can be stacked, as shown in Figure 3. In this embodiment, the panels 30 are conveniently formed from solid aluminium strip, to permit the thickness of each panel to be kept to a minimum, for example around 6mm. It will be appreciated, however, that hollow section of suitable configuration could be employed. Three panels are employed, the two outer ones having the fluoroplastic film covering as hereinbefore described, and the inner one being constituted simply by the frame as a spacer. The stack of three panels is located in aluminium channel members 31 , using a silicone sealant 32 in the channel members and with fixing screws 33 passed through the channel members and into the inner frame. Such a configuration has been found to offer the highest insulation value achieved by a glazing panel, while still allowing a high proportion of ambient radiation to pass through it.
[0027] Referring now to Figure 4, an alternative method of making the pan- els involves forming a fluoroplastics film tube, typically by extrusion, stretching the tube laterally under the influence of hot air or steam, locating the stretched tub 40 over a frame 41 , and passing the assembly through a hot air stream from one or more hot air nozzles 42 and either rotating the frame around its longitudinal axis 43 to ensure uniform heating on both sides or directing heated air flow upwardly at the same time on to the underside. The hot air causes the film tube to revert to its pre-stretched dimensions, stretching it across the frame 41. The ends of the tube are then folded over and sealed, for example by adhesive tape or welding, or they may be secured by pushing them into a groove extending across the respective end of the frame, and then inserting a capping strip into the groove to trap the material firmly therein.
[0028] While the frames have been described herein as suitably formed from aluminium extrusions, it will be appreciated that the invention may be applied to frames made of other materials, such as plastics or wood, which may offer advantages in having reduced thermal conductivity.
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