BARRIER MEMBRANES E.G. FOR USE IN BUILDING

Abstract: A barrier, particularly to methane and radon, employs a barrier layer (10) (preferably aluminium) encapsulated in protective layers (14, 16) which are bonded to all of its surfaces and extend beyond its main edges where they are mutually bonded. The protective layers (14, 16) include at least one plastics layer. Typically there is a strengthening layer (14) e.g. of polyester coextrusive with the aluminium (10), the aluminium and polyester being encapsulated by a layer (16) of polyolefin on one face and another layer (16) of polyolefin and/or bitumen at the other face.

Description: BARRIER MEMBRANES E.G. FOR USE IN BUILDING Technical Field The present invention relates to barrier membranes suitable for incorporation in foundations; to a method of producing such membranes; to foundations incorporating such membranes; and to a method of constructing foundations. It is particularly concerned with barriers to gases, notably methane and radon. Background Art There is growing awareness that methane may be generated in the ground beneath a building or other construction (particularly by decomposition of vegetable matter) , and tend to seep up through the foundations. Accumulations, e.g. in cellars, can pose hazards. Furthermore, particularly in some areas of the country, radon may be a serious health risk. A conventional foundation comprises a porous bottom layer, e.g. of aggregate; an intermediate layer which may be of bitumen or of synthetic resin e.g. polythene (through which gases may be able to permeate); and a top layer of concrete, which may intrinsically have good barrier properties, but these are generally spoiled by the effects of cracks and joints. Thus the present invention seeks to provide a gas barrier membrane which may be incorporated between the intermediate layer and the concrete (though it is not restricted to this position, nor to use in this type of foundation). Generally it will be arranged to allow gas to pass to the atmosphere, externally of the building interior. Membranes impermeable to liquids are well known, e.g. for damp-proof courses. One such membrane is polyethylene film with a layer of bitumen on one face. However, such liquid-proof barriers do not provide sufficient resistance to gases. Disclosure of Invention In one aspect the invention provides a barrier membrane for incorporation in a building foundation comprising a gas barrier layer, preferably comprising aluminium encapsulated in protective material comprising plastics, the encapsulating material being bonded to substantially the entire surface of the barrier layer. NB The term "layer" encompasses coatings and deposits as well as preformed layers. Aluminium has excellent barrier properties, even in the form of thin films, provided it is not so thin as to have an unacceptable incidence of pinholes. For example, acceptable film of 18μm thickness can be reliably produced with less than 10 holes/m^ though 25μm film is more realistic from the point of view of mass production. Gauges down to 12μm can be produced with not more than 50 holes 2 (for 95% of samples), whereas the corresponding figure for 9μm foil is typically about 500 holes/m 2 . But aluminium foil is prone to corrosion by both acidic and alkaline reagents (and concrete has a high pH, e.g. pH 13) . Furthermore, thin layers are mechanically weak. We have found that merely coating an aluminium foil on both faces with plastics material may not be sufficient, since it may still be open to attack at the edges. Therefore complete encapsulation is desirable, the plastics extending beyond the metal, at least at the major edges, suitably by at least 5mm and preferably by about lOmm. In a preferred form, the aluminium is supported by a strengthening layer (e.g. of a polyester) on one or both faces, and the whole is encapsulated in a surrounding jacket, e.g. of a polyolefin, suitably by extrusion. Suitable polyolefins include polyethylene (including linear low or medium density polyethylene), polypropylene and polybutylene. The latter two are better gas barriers than polyethylene and tend to be stronger. If the encapsulating layers are strong enough, an internal strengthening layer may be unnecessary. Polyesters also have gas barrier properties. However they are vulnerable to strongly alkaline conditions, so that it may be desirable for a polyester layer to have some protective coat. Polyvinylidene chloride ("PVdC"), e.g. Saranex (trademark), is an example of another material with barrier properties that may supplement, or in some circumstances even replace, aluminium. Rather heavy coatings, e.g. up to 20glm~ , preferably about 12g/m 2 , may be used. They would generally be formed by application of a plurality of coating layers. Material with a 3gm/m 2 layer of PVdC is available, and this can be given one or more further coatings, eg giving a total of 15g/m 2 . However there is a risk that a multilayer PVdC coating will suffer some delami ' nation. Thus to ensure reliable maintenance of barrier properties, encapsulation is required, as for aluminium. Another possible gas barrier is a thick (eg lOOμm) layer of ethylene - vinyl alcohol ("EVOH" ). However, EVOH is prone to absorb water, with serious degradation of its properties. Thus, again, encapsulation is required to produce a material that can withstand the rigours of the treatment it is likely to face during and prior to installation, and still give good barrier protection for many years. A barrier layer may comprise aluminium deposited (eg by vapour deposition) on a strengthening layer. The strengthening layer, eg of polyethylene terephthalate ("PET") may also have gas barrier properties, thus permitting use of relatively thin aluminium. Barrier properties may also be enhanced by one or more further coatings of barrier materials, eg PVdC or EVOH. Alternative materials for the outer layer(s) include lightweight PVC ( referably at least 20μm thick) . When aluminium is used in conjunction with one or more strengthening layers, the or each strengthening layer may be bonded to the aluminium using an adhesive, which may comprise a polyolefin extrusion. The adhesive layer or layers may extend beyond the aluminium at the sides. The resulting sandwich may then be encapsulated by extrusion coating a polyolefin layer on each face, the layers extending beyond the aluminium and bonding to the projecting adhesive layer. Extruded films tend to be thicker at the sides. It can thus be arranged that the thickened marginal portions of the extruded layers have, together, an additional thickness approximating to the thickness of the aluminium layer. Thus the membrane is of substantially uniform thickness throughout its width, since the lateral regions where there is no aluminium have instead the thicker encapsulating layers. A simpler form of membrane has a strengthening layer at only one face. It is bonded to the aluminium by an extruded adhesive layer which extends beyond the aluminium. A further resin (e.g. polyolefin) layer is extruded on to the other face of the aluminium so as to extend beyond it, and to bond to the adhesive layer. Membranes can also be produced by adhesive lamination. A membrane may have a pair of strengthening layers at respective faces of the aluminium, each extending beyond it so that the strengthening layers can be adhered together. A membrane embodying the invention may be provided on a reel, with any desired length. For convenience the width is quite small (e.g. 1 metre). Strips of membrane may be coated with bitumen, preferably at least 1mm thick. To provide a barrier in a foundation, bitumen-coated strips may be laid, bitumen side down, over the bottom layer of the foundation. Adjacent strips are overlapped and secured together with adhesive tape. Preferred tape comprises a strip of barrier membrane generally as described, having a layer of adhesive optionally protected by a release paper. In a typical embodiment, an aluminium layer is bonded to a (or a respective) coextensive strengthening layer of polyester on one or both of its faces, and the aluminium/polyester composite is encapsulated between polyolefin (eg polyethylene) films, or a polyolefin film on one side and bitumen on the other. The encapsulating films extend laterally beyond the composite. They are bonded to the composite over substantially all of its surface area, and to each other at the projecting margins. Polyethylene is easily extendible while aluminium is not. Thus if it were not for the strengthening material, there would be a risk of damage. Encapsulation with bonding over the whole surface is much safer than merely seaming the encapsulating films together at their edges. Some embodiments of the invention will now be described in greater detail with reference to the accompanying drawings. Brief Description of Drawings Fig. 1 is a schematic section through a first embodiment of a membrane; Fig. 2 is a like view of a second embodiment; and Fig. 3 is a like view of a third embodiment which is adhesive tape. Modes for Carrying out the Invention The membrane shown in Fig. 1 is in the form of an elongate strip of width 1 metre, shown in transverse section. An aluminium foil 10 (e.g. of thickness 19μm) bears on each face an extruded layer 12 of polyethylene serving as adhesive, which projects laterally beyond the aluminium 10. These secure respective strengthening layers 14 of polyester (e.g. P.E.T., polyethylene terephthalate) suitably of thickness 12-24μm. These are of lesser lateral extent than the adhesive layers 12, which are thus exposed at the edges. The strengthening layers have some gas barrier properties, and thus allow the use of relatively thin aluminium, since more pinholes can be tolerated. Finally, there are extruded layers of polyolefin 16 which project laterally at least as much as the adhesive layers 12, and are bonded to them. Suitable polyolefin materials are based on polyethylene, polypropylene, or copolymers. Fig. 2 shows a membrane produced by adhesive lamination. When using this technique rather than extrusion lamination, it is not practicable to extend the adhesive laterally beyond the substrate. Thus for example a 2-part curing adhesive 12' (e.g. polyurethane-base ) is applied to one or both faces of the aluminium 10, and a strengthening, layer 14' of the same width as the aluminium 10 is applied to the or each coated face. At least one face is then adhesively adhered by a further layer of adhesive 12' to a web 16 of polyolefin, e.g. polyethylene, which extends laterally beyond the aluminium etc. If there is polyethylene on each face, the lateral portions of the two polyethylene webs are mutually adhered to achieve encapsulation. If there is polyethylene at only one face, encapsulation may rely on the application of bitumen to the other face. In a related embodiment, the aluminium layer is adhered (by a two-part polyurethane adhesive) on one face to polyethylene and on the other face to polyester, the two polymer layers being wider than the aluminium, their projecting margins being adhered to one another. Subsequently the exposed face of the polyester is coated with bitumen. Fig. 3 shows an adhesive tape 30 which is a strip of barrier membrane having many similarities to those just described, though of course it is generally produced in smaller widths. The tape 30 has a barrier layer 32 of metal foil encapsulated with plastics layers 34, 36, 38, 40 which extend beyond each lateral side of the foil 32 by at least 5mm and preferably at least 7mm and are bonded together so that the foil is fully protected (except at the ends, where the tape is likely to be cut). At one face there is a layer of adhesive 42, protected by a release paper 44. Details of suitable layers are given below Layer Thickness Material _m 32 18 Aluminium 34 23 Film(e.g.Polyester, suitably Melinex 800) 36 25 Resin(e.g.Polyethylene 30gsm) 38 25 Resin(e.g.Polyethylene 30gsm) 40 50 Film (e.g. Polyethylene) 42 20 Adhesive 44 Release paper Layer 40 is optional and could be replaced by an ethylene copolymer or omitted. Such a tape may be made by extrusion lamination. The process may be as follows: 1st pass: the Melinex 800 is key coated (in line) and extrusion laminated with strips of aluminium foil, using molten resin (layer 36). Generally a sheet of material is produced, with a multiplicity of aluminium strips spaced 10-20mm apart. 2nd pass: a preformed sheet to constitute the thick layer film (40) is extrusion laminated over the foil strips using molten resin (layer 38). 3rd pass: adhesive (42) and release paper (44) are applied. 4th pass: the sheet is slit into strips each containing a single encapsulated aluminium strip. The sheet strips are reeled. Polyethylene is heat extendible to a marked degree. Thus if the polyester layer 34 were replaced by another polyethylene, the product would crease and crinkle seriously on cooling. Indeed, the second and subsequent passes might be impossible. This could be avoided by employing adhesive lamination instead of extrusion lamination. However, the step of applying spaced aluminium strips to an adhesive-coated preceding layer 36 would tend to be messy owing to the gaps where adhesive would remain exposed. Strips of membrane e.g. as shown in Figs 1 and 2 can be connected by means of tape as shown in Fig. 3 to produce a composite membrane with excellent barrier properties and resistance to corrosion.

Claims: CLAIMS : 1. A barrier membrance for incorporation in a building foundation comprising a gas barrier layer (10;32) encapsulated in protective material ( 12, 14, 16; 12' ,14' , 16' ;34,36,38,40) comprising plastics, the protective material covering the barrier layer (10;32) on both faces and at least a substantial part of the periphery; the protective material bonded to substantially the entire surface of the barrier layer. 2. A barrier membrane according to claim 1 having encapsulating layers (12,16;12' ,16;36,38) of polyolefin or polyvinyl chloride. 3. A barrier membrane according to claim 1 or claim 2 wherein the protective material (12,16;12' ,16;34-40) from the two faces extends beyond the barrier layer (10;32) by at least 5mm and at least a substantial part of the periphery, the material (12,12';36) from one face being connected to material (12;12;38) from the other face. 4. A barrier membrane according to any preceding claim wherein the barrier layer (10;32) comprises aluminium. 5. A barrier membrane according to claim 4 wherein the aluminium (10) is at least 12μm thick. 6. A barrier membrane according to claim 4 or 5 wherein the aluminium (10;32) is supported by a strengthening layer (14;14';34) on one or both faces. 7. A barrier membrane according to claim 6 wherein the or a said strengthening layer (14;14'34) is of a polyester material . 8. A barrier membrane according to claim 6 or 7 wherein the aluminium (10) and strengthening layer(s) are encapslated in a surrounding (16;12*16). 9. A barrier membrane according to claim 8 having encapsulating layers (12,16;12' 16) of polyolefin or polyvinyl chloride which encapsulate both the barrier layer (10) and the strengthening layer or layers (14;14'). 10. A barrier membrane according to claim 9 wherein the or each strengtheing layer (14) is bonded to the aluminium (10) using an adhesive (12) comprising a polyolefin extrusion, and wherein the adhesive layer or layers (12) extends beyond the aluminium at the sides, and the resulting sandwich is encapsulated by extrusion coating a polyolefin layer (16) on each face, the layers extending beyond the aluminium and bonding to the projecting adhesive layer or layers. 11. A barrier membrane according to any preceding claim having an external layer of bitumen. 12. A barrier membrane according to any preceding claim in the form of an enlongate strip, the encapsulating material covering the lateral edges of the aluminium layer (10). 13. A barrier membrane according to claim 12 in the form of adhesive tape (30), having a layer of adhesive 42) optionally protected by a release paper (44). 14. A foundation comprising an upper concrete layer, a lower layer, and a barrier comprising a barrier membrane according to any preceding claim interposed between them. 15. A foundation according to claim 4 wherein the barrier comprises a plurality of discrete portions of membrane according to any of claims 1-12 adjacent portions being connected with adhesive tape according to claim 13.

Inventors: FREEMAN MICHAEL ASHLEY, FREEMAN, MICHAEL, ASHLEY
Applicants: DRG UK LTD, DRG (UK) LIMITED
Application year: 1989
Main classification: B32B15
IPC codes: B32B3, B32B7, B32B15, B32B27, E02D31