AU2012258413A1 - Cellular structured product - Google Patents

Abstract

The present invention provides a substantially planar structure comprising a plurality of gas-retaining cells, one or more of the gas-retaining cells comprising means for allowing egress of a gas, wherein in use egress of the gas occurs in response to a force applied to the cell. The structure is useful as thermal insulation sheeting in the housing construction industry.

Description

CELLULAR PRODUCT 2 FIELD OF THE INVENTION The present invention relates to sheeting and panels having a cellular structure, having 5 utility in packaging, building construction and thermal insulation. BACKGROUND TO THE INVENTION Insulation against environmental conditions such as heat, cold, noise, vibration, shock and 10 the like are important in fieldsdiverse as building construction and packaging. Encapsulated gases possess significant insulation properties, and are often incorporated in sheeting and panels in the form of air-filled cellular structures. Existing examples of such structures include BUBLBVRAPEh (used in packaging) and ASTFaFIL h (as applied in 15 building construction). A problem with existing cellular products is that they are not easily deformable and can therefore be difficult or even impossible to use or install in certain circumstances. In addition, where the product is deformable, the cellular structures can rupture leading to a !0 decrease of insulation properties. A further problem relates to dislodgement of cellular structures after fixation. As an example, building panels composed of cellular structures can pull away from a substrate (such as a batten) to which they have been affixed. 25 Another problem is that cellular structures are not amenable to interposition between two objects such as roof sheeting and an underlying frame member. The cells prevent the dose juxtaposition of the two objects, leading to the potential for separation of the sheeting and member. 30 The use of products having cells of limited depth may overcome these problems in some circumstances, however this approach comprises insulation properties of the product. 1 It is an aspect of the present invention to overcome or ameliorate a problem in the prior art 15 to provide cellular products having improved characteristics. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base 10 or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. SUM M ARY OF THE INVENTION In a first aspect the present invention provides a substantially planar structure comprising a 15 plurality of gas-retaining cells, one or more of the gas-retaining cells comprising means for allowing egress of a gas, wherein in use egress of the gas occurs in response to a force applied to the cell. In one embodiment, the structure comprises means for allowing ingress of a gas to one or ;0 more of the gas-retaining cells, wherein ingress of the gas occurs in response to release of the force applied to the one or more cells. In another embodiment, the ingress of gas into the one or more cells is effected or assisted by the presence of a resilient material within or about the structure. In a further embodiment, upon release of the force the floor-to-ceiling distance of the one or more cells returns to at least about 90% of the pre-compression 55 distance. The means for egress and ingress of the gas may be the same means. In one embodiment the means for allowing the egress (and optionally ingress) of a gas is a gas-permeable material, such as a woven material, which may be a woven polymeric material such as a 60 woven polyolefin or a woven foil. The structure may comprise or consist of three layers: a central layer defining a wall and ceiling of the one or more cells, the central layer bonded to an upper layer, the central layer 2 bonded to a lower layer defining the floor of the one or more cells. The structure may have 15 no more than three layers. In one embodiment of the structure, the upper layer and/or the lower layer and/or the central layer is/are a gas-permeable material. The central layer may be a substantially gas impermeable material, and the upper layer or the lower layer may be a substantially gas '0 impermeable material such as a woven material, which may be a woven polymeric material such as a woven polyolefin or a woven foil. In one embodiment, the structure comprises a thermal barrier. The first and/or second layer may be athermal barrier. preferably the thermal barrier is also means for allowing '5 egress (and optionally ingress) of a gas In one embodiment the one or more cells are substantially circular, and may be substantially-disk shaped. In one embodiment the one or more cells have a width or diameter of between about 5 and 50mm. In another embodiment the one or more cells have a width or diameter of between about 25 and 35 mm. Afurther embodiment provides 10 that the one or more cells have a depth of between about 5 and 20 mm, or a depth of between about 10 and 14 mm. In another embodiment the one or more cells have a width of less than about 15 mm or more than about 25 mm. In a further embodiment the one or more cells have a depth of 85 less than about 6 mm or more than about 10 mm. The structure may be adapted or configured to function as a building product, such as a sarking product. 90 In another aspect the present invention provides a method for fabricating a substantially planar cellular structure, the method comprising the steps of: providing a pre-extruded sheet material, contacting the sheet material with a mould under conditions allowing the sheet material to conform to the mould to form a moulded sheet, providing an upper layer 3 material and a lower layer material, contacting the moulded sheet to the upper and lower )5 layers, and bonding the moulded sheet to the upper and lower layers. In one embodiment of the method, the conditions for allowing the sheet material to conform to the mould to form a moulded sheet comprise heating the sheet material to a temperature where it is sufficiently flexible to conform to the shape of the mould. The )0 conditionsfor allowing the sheet material to conform to the mould to form a moulded sheet may comprise the application of a vacuum about the sheet and mould such that the sheet conforms closely to the shape of the mould. The bonding may comprise a thermo lamination process. )5 Yet a further aspect of the present invention provides a product produced by a method described herein. In one embodiment, the product is or comprises a structure as described herein. BRIEF DESCRIPTION OF THE DRAW INGS 0 Figure 1 is a perspective view of a tripartite structure of the present invention showing upper and lower layersforming the ceiling and floor of the cells, and a central layer defining the walls of the cells. The cells are in a non-collapsed state. Figure 2A is a cross-sectional view of the structure shown in Figure 1, the structure in a non 15 collapsed state. Figure 2B is a cross-sectional view of the structure shown in Figure 1, the structure in a collapsed state. 20 D ETAILED D ESCRIPTION OF TH E INVEN TION After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative applications. 25 However, although various embodiments of the present invention will be described herein, 4 it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects apply to specific exemplary embodiments, and 10 not necessarily to all embodiments covered by the aims. Unless the contrary intention is expressed, the features presented as preferred or alternative forms of the invention can be present in any of the inventions disposed as alone or in any combination with each other. 15 Throughout the description and the aims of this specification the word "comprise" and variations of the word, such as "comprising" and "comprises" is not intended to exude other additives, components, integers or steps. [0 As used herein, the term "wall" in intended to include any bounding structure of a cell. Elsewhere in this specification, the terms "ceiling" and "floor" are used and it will be appreciated that these terms are used as subsidiaries to the broader term of "wall". Where the terms "wall", "ceiling" and "floor" are used to describe a single cell, the term "wall" is used to refer to the bounding structure that joins the floor to the ceiling [5 The present invention is predicated at least in part on the finding that problems with sheeting products and panels having air-filled cells are overcome or ameliorated by the incorporation of cells that are collapsible under a compressive force such as that resulting from handling, deformation or fastening. 50 Accordingly, in a first aspect the present invention provides a substantially planar structure comprising a plurality of gas-retaining oells, one or more of the gas-retaining cells comprising means for allowing egress of a gas, wherein in use egress of the gas occurs in response to aforce applied to the cell. 55 Applicant has discovered that an advantageous or alternative product is achieved by providing a planar structure comprised of substantially airtight cells that are capable of 5 collapsing when compressed. The present structures are a significant departure from prior art products such as BUBBLE WRAP (used for packaging) and ASTROFOILm (as used in i0 building construction) which contain substantially gas-impermeable cells The gas impermeable cells of prior art products are not designed to collapse, and indeed aim to prevent any leakage of gas from the one or more cells. Applicant proposes that this inability to collapse is a reason for the inferior performance of oell-based structures of the prior art in certain applications '5 Thus, the gas (typically air) is substantially retained within the cell before compression, and is therefore able to provide insulation against sound, heat, cold and vibration. However, upon compression, cells of the present structures collapse under the force, the collapse due to egress of gas from the cell. 'O It will be appreciated that the present structures provide that a proportion of cells in the structure may be selectively collapsed as required, while the majority of cells remain turgid thereby retaining their insulation properties. '5 The ability to selectively collapse cells may be advantageous in one or more circumstances. As an example, prior art building panels comprising cellular structures are often affixed to a substrate using a fastener such as a nail or a staple. The sealed cells about the fastener are typically compressed in the course of inserting the fastener through the panel and into the substrate. The pressure of gas inside the compressed cells increases, leading to the exertion 80 of a counteracting force against the cell wall. This counteracting force may push against the fastener and/or substrate leading to dislodgement of the panel. Because the one or more cells of the present structures are able to deflate under a compressive force, the air pressure within does not substantially increase and there is therefore no counteracting force to urge the fastener or panel away from the substrate. Importantly, the one or more 85 cells surrounding the fastener are not compressed (and therefore do not deflate) hence retaining their normal insulation properties. Generally, only a small number of cells will be deflated during installation meaning that the overall insulation properties of the panel are not greatly compromised. 6 )0 This problem of dislodgement is particularly problematic in panels having oells that are deep (for example, greater than 5 mm). Deeper cells provide for improved insulation properties, however compression of the longer column of air can result in very high internal pressures. The present structures may at least ameliorate that problem by essentially dissipating these high internal pressures. )5 Both shallow and deep cells of prior art panels cause a further problem where a cellular building panel is interposed between two structures, and the two structures are intended to be juxtaposed as dosely as possible. For example, where a cellular building panel is to be placed between a roofing rafter and external sheeting the action of fastening the external )0 sheeting to the underlying rafter compresses the interposed panel. The counteracting forces exerted by the cellular structures limits the extent to which the external sheeting can be dosely secured to the underlying rafter. By contrast, panels fabricated from cellular structures of the present invention deflate as the external sheeting is screwed into position, securely abutting the rafter. The one or more cells to each side of the rafter remain )5 unaffected, and retain their normal insulation properties. It will be understood that the pressure of gas within the cell before compression may be any pressure suitable for a required application. Generally, the gas within in the gas retaining cell is at approximately atmospheric pressure (i.e. 14.7 psi). However, other exemplary 0 pressures are between about 10.5 psi and about 18.5 psi, more preferably between about 11.5 to about 17.5 psi, more preferably from about 12.5 to about 16.5 psi, more preferably from about 13.5 psi to about 15.5 psi, more preferably from about 14.5 psi to about 15 psi. The means for allowing egress of the gas may be any means, and indudes any physical 15 disruption to a wall that is otherwise gas impermeable, induding a hole, perforation, aperture, slit, or tear. In some embodiments of the structure, the meansfor allowing egress of the gas is not a tear. The means may be present before a compressive force is applied to the cell, or may be created in response to a compressive force. 7 !0 In some embodiments, the meansfor allowing egress is inherent in the structure of the cell wall and may rely on the molecular structure of the wall, or the microscopic structure, or the macroscopic structure. The means for allowing egress of a gas may be an area of weakness or frangibility in the cell !5 wall, the area engineered, designed, adapted or configured to stretch, deform or rupture upon application of a compressive force such that it becomes permeable to gas. The means for allowing egress of a gas may be a join between two parts of a cell wall, or a join between a wall and ceiling or a wall and floor, the join engineered, designed, adapted 10 or configured to stretch, deform or rupture upon application of a compressive force such that it becomes permeable to gas. The means for allowing egress of a gas may be a general structural weakness in the wall material per se, the material engineered, designed, adapted or configured such that any 15 part of the wall ruptures upon application of a compressive force. It will be appreciated that the means for allowing egress of a gas may be distinct from any cellular structure existing at the filing date of this application. It is known that cells in products such as BUBBLEWRAPm can be compressed to the point of rupture, leading to the [0 egress of gas from the cell. These prior art cells do not contain a means for allowing egress of a gas, and simply rupture due to excessive stress. Typically, the compressive force required to rupture a cell of the prior art is high, and the force required to rupture a wall of a cell of the present structures may be lower that than required to rupture any prior art cell. 45 In any event, the means for egress may be selected depended upon the expected force required to cause collapse of the cell. For example, where it isdesired that the cell collapses under relatively minor compressive forces, the means might allow egress more easily (for example as provided by the incorporation of more perforations in the cell wall, larger perforations, a more open molecular structure, use of a weaker wall material, or use of a 50 more loosely woven material. Where it is desired that the cell collapses only in response to a relatively high compressive force, the means might allow egress less easily (for example as 8 provided the by the incorporation of less perforations in the cell wall, smaller perforations, a more dosed molecular structure, use of a stronger wall material, or use of a more closely woven material). The rate of egress of the gas is not critical, but for convenience it should be such that the cell deflates within about 5, 4, 3, 2 or 1 seconds from the time of application of the compressive force. The time will depend on the pressure applied, with shorter periods being preferred. i0 The gas is typically expelled to the environment, and is not retained within or about the structure. In preferred embodiments of the structure, the structure is capable of returning or partially ;5 returning to the shape and/or size prior to application of the compressive force. This capability may rely of the one or more cells allowing the ingress of air into the cell. Accordingly, in certain embodiments, the structure comprises means for allowing ingress of a gas to the one or more cells, wherein ingress of the gas occurs in response to release of the force applied to the one or more cells. 'O During installation, application or other usage of the structure, some cells may become unnecessarily compressed, leading to egress of the gas within. The ability for a cell to at least partially return to the size or shape before compression provides an advantage additional to those aforementioned. In particular, the insulation characteristics of the cell 75 concerned (and therefore the structure as a whole) is improved. It iswell understood that thermal insulation characteristics are generally proportional to the distance between the floor and ceiling of a gas containing cell. Accordingly, a cell which has collapsed will demonstrate significantly reduced thermal insulation properties. A cell which 80 is capable of admitting a gas will (upon release of the compressive force) provides for an increased floor-to-ceiling distance leading to an at least partial return to the insulation properties of the structure pre-compression. In certain embodiments of the structure, the floor-to-ceiling distance returns to at least about 5% 10%, 15/q 20% 25/q 30/0 35%, 40/q 9 45/4 50 0 % 55/4 60% 65% 70% 75/q 80/ 85% 90% or 95% of the pre-compression 15 distance. preferably, the floor-to-ceiling distance returns to at least about 90%of the pre compression distance. In certain embodiments of the structure, the cell volume returns to at least about 50/ 1OA 15% 200% 2504 300% 3504 40% 4504 504 550% 60% 650/ 704 7504 80% 8504 90% or )0 95% of the volume pre-compression. preferably, the cell volume returns to at least about 90%of the cell volume pre-compression. In certain embodiments of the structure, the thermal insulation properties return to at least about 5% 10% 15% 20/ 250/ 30% 3504 4 0 4 4504 50% 5504 600/ 650/ 7004 75/4 80%, )5 850/ 90%or 95% of these properties pre-compression. Preferably, the thermal insulation properties return to at least about 90%of the pre-compression distance. The thermal insulation properties of a structure according to the present invention may be assessed by any method known to the skilled person. For example, thermal resistance (and 10 the inverse measurement of thermal conductivity) are relevant means of assessing the structures of the present invention. The prior art provides are a number of means for measuring thermal resistance. One method that is used particularly in the assessment of building materials provides an Rvalue 05 (or the inverse, being the U-value). Under uniform conditions the R-value is the ratio of the temperature difference across an insulating material and the heat flux (heat transfer per unit area, Q A) through it, as defined by the equationR A T/ Q A. 10 This value is applicable for a unit amount of any particular material. For the thermal resistance of an entire section of material, instead of the unit resistance, the unit thermal resistance is divided by the area of the material. For example, where the unit thermal resistance of a wall is provided, this unit is divided by the cross-sectional area of the depth 15 of the wall to compute the thermal resistance. The unit thermal conductance of a material is 10 denoted as C and is the reciprocal of the unit thermal resistance. This can also be called the unit surface conductance and denoted by h. The higher the number, the higher the level of thermal insulation. !0 In one embodiment, the structure has an R-value of at least about 0.5, 0.6. 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0. Standard foils used in building materials (such as sarking products) have an Rvalue of about 0.5. The cellular structures of the present invention can provide !5 significantly higher Rvalues than standard thermal insulation products by the inclusion of collapsible gas cells As discussed elsewhere herein, the ability of the cells to collapse (and optionally, to at least partially rebound) allows for the infusion of relatively deep cells The increased depth may translate to higher thermal insulation capabilities, and therefore higher Rvalues. 10 The Applicant has fabricated a sarking product comprising a cellular structure as described herein having an Rvalue of around 3.1. This product has a cell diameter of 30mm and a depth of 12mm (when uncompressed). The gas permeable layer is fabricated from woven aluminium (as further described infra), with the walls of the cells fabricated from a 5 polyolefin. The product readily collapses and is therefore able to be easily accommodated between a roof sheeting material and an underlying rafter. Cells which have been compressed during installation but are not subject to the compressive force of the rafter when installed are able to return to a depth similar to that pre-compression. 40 The present structures provide a significant advantage over prior art building products Existing products are necessarily a trade-off between profile (depth) and Rvalue, with the present cellular structures providing for a lesser consideration of profile and a greater consideration of R-value in designing thermal insulating building products. 45 The combination of the thermal insulation properties of the gas-filled cells of the cellular structures couple with the ability of the cells to collapse provides for a structure that has superior insulation. The ability of the cells to collapse allowsfor cells of significant height to 11 be incorporated into building materials, such as sarking. The greater height of the cells means that a greater volume of air may be trapped, thereby providing superior thermal 50 insulation properties. Of course, any cells which are collapsed and forcibly retained in that collapsed state (by a nail or staple, for example) will be unable to resume the uncompressed structure. This may in some circumstances compromise the insulation properties of the whole cellular structure, 5 however any compromise is minimized where as many cells as possible are allowed to return to a pre-compression size and/or shape. In some embodiments of the structure, the ingress of gas into the cell may be effected or assisted by the presence of a resilient material within or about the structure. Referably the i0 resilient material is a wall of the cell, or form a part of a wall of the cell. In operation, compression of the cell leads to egress of the contained gas and also to deformation of a wall of the cell. Upon release of the compressive force, the resilient wall returns at least in part to the size and/or shape pre-compression. 5 The skilled person is familiar with many types of material having the requisite characteristics for embodiments of the invention that are intended to return toward a pre-compression morphology. Resilient polymeric materials are particularly suitable and include: Low Density Fblyethylene (LDPE, such as Roduct Code XF-143, Qenos Pty Ltd, Australia), Linear Low Density Pblyethylene (LLDPE, such as Roduct (bde LL425, Qenos Ry Ltd, Australia), High 70 Density Polyethylene (HDPE, such as Roduct (bde HD1090, Qenos Ry Ltd, Australia) , White Masterbatch (such as Roduct Code T016-02, Martogg & Co, Australia), Metalocene and derivatives thereof. The polymeric material may include a filler such as calcium carbonate. 75 It is contemplated that the mean for egress and ingress may be the same means, or different means Referably they are the same means. Preferably the same means is a gas permeable material 12 Gas permeable materials that allow for the egress (and optionally ingress) of a gas (or a io mixture of gases such as air) are known to the skilled artisan. The skilled person is capable of selecting a suitable material based on a number of factors relevant to a given application. One factor may be the pressure of gas that is retained in the cell. For example, where it is desired to retain gas at a relatively high pressure within the cell the gas permeability will typically be low. Another factor may be the compressive force necessary to cause egress of 5 the gas from the cell. Where it is intended that gas egress is caused by the application of a relatively high compressive force the gas permeability will be typically low. Where it is intended that the gas egress is relatively rapid, the gas permeability will be typically high. It will be apparent that for a given application a balance will be generally achievable whereby a material of a certain permeability is able to address the various factors under )0 consideration. By a process of routine experimentation, the skilled person will be capable of selecting a material with suitable permeability. In some embodiments, the gas permeable material is also resilient. )5 In a preferred embodiment, the gas permeable material is the wall of a cell, or forms part of the wall of a cell. In one embodiment of the structure the gas permeable material is a woven material. Sich materials can be fabricated to be closely woven (and therefore providing for relatively low gas permeability) or loosely woven (to provide for relatively high levels of gas permeability). High density polyethylene weave materials are particularly 00 suitable. In a highly preferred form of the invention the high density polyethylene weave is coated with a low density polyethylene sheet. In certain embodiments the low density coating acts as a bonding layer between the HPEweave and the polyethylene bubble core. In a preferred embodiment of the structure the woven material is a woven polymeric 05 material, and may be a woven polyolefin. Typically, the polyolefin is a thermoplastic polyolefin. Thermoplastic materials are particularly suitable for the extrusion processes used in the fabrication of the structures, including the processes described elsewhere herein. 10 13 The thermoplastic polyolefin may be of any type, but is preferably selected from the group consisting of a polyethylene, a polypropylene, a polymet hylpentene, and polybutene-1. In a highly preferred embodiment, the thermoplastic polyolefin is a polypropylene. 5 In a more highly preferred embodiment of the structure, the woven material is a woven foil. A particularly suitable product has the following specifications: 7 micron aluminium foil / Dry bond / 7 x 8 high density weave / 30 micron Low density polyethylene coating. In certain embodiments, the woven foil has an anti-glare surface or coating. !0 The substantially planar structure may be flexible, partially flexible or substantially rigid depending on the application. Rexible forms will be applicable where the structure must form around another object. Rgdity can be conferred on the structure by any means, including the use of higher pressures in the one or more cells or the dose spacing of the one or more cells. Rgidity may also be provided by the use of deformation-resistant materials !5 within or about the structure. Preferably the structure comprises or consists of three layers: a central layer defining a wall and ceiling of the one or more cells, the central layer bonded to an upper layer, the central layer bonded to a lower layer defining the floor of the one or more cells. 10 More preferably, the structure has no more than three layers. This minimal number of layers provides for greater ease in collapsibility of the one or more cells. Increasing the number of layers leads to greater difficulty in compressing the cells thereby overcoming a central advantage of the invention. 35 Preferably, the upper layer and/or the lower layer is a gas-permeable material, optionally of any type as discussed elsewhere herein. In some embodiments the upper and/or lower layer is a substantially gas-impermeable 40 material such as a non-woven polymeric material. Preferably the non-woven polymeric material is a polyolefin such as a thermoplastic polyolefin. The thermoplastic polyolefin is preferably selected form the group consisting of a polyethylene, a polypropylene, a 14 polymethylpentene, and polybutene-1. Preferably, the thermoplastic polyolefin is a polyethylene. [5 The upper and/or lower layer may have a relatively high level of thermal reflectivity, to provide the structure as a whole with a relatively high R-value. In one embodiment the upper and/or lower layer is, or functions as, a radiant barrier. Radiant barriers (also known as reflective barriers) inhibit heat transfer by thermal radiation. i0 Radiant barriers rely on the fact that all materials emit thermal radiation as a result of their temperature. The amount of energy radiated depends on the surface temperature and a property called the emissivity (also called the "emittance"). Emissivity is expressed as a number between zero (0) and one (1) at a given wavelength. The higher the emissivity, the greater the emitted radiation at that wavelength. A related material property is the 5 reflectivity (also called the "reflectance"). This is a measure of how much energy is reflected by a material at a given wavelength. The reflectivity is also expressed as a number between 0 and 1 (or a percentage between 0 and 100%). At a given wavelength and angle of incidence the emissivity and reflectivity values sum to 1. ladiant barrier materials typically have low emissivity (usually 0.1 or less) at the io wavelengths at which they are expected to function. For typical building materials, the wavelengths are in the mid- and long- infrared spectrum, in the range of 3- 15 micrometres. lbdiant barriers may or may not exhibit high visual reflectivity. This is because while reflectivity and emissivity must sum to unity at a given wavelength, reflectivity at one set of wavelengths (visible) and emissivity at a different set of wavelengths (thermal) do not 65 necessarily sum to unity. In one embodiment, the upper and/or lower layer is afoil, such as an aluminium foil. Cellular structures having an upper and/or lower layer may have a relatively high level of thermal reflectivity have particular applications in building construction. S)lar energy is absorbed by a roof, heating the roof sheathing and causing the underside of 70 the sheathing and the roof framing to radiate heat downward and into the living areas. 15 When a radiant barrier is placed directly underneath the roofing material incorporating an air gap, much of the heat radiated from the hot roof is reflected back toward the roof and the low emissivity of the underside of the radiant barrier means very little radiant heat is emitted downwards. This makes the top surface of the insulation cooler than it would have '5 been without a radiant barrier and thus reduces the amount of heat that moves through the insulation into the rooms below the ceiling. Radiant barriers can also reduce indoor heat losses through the ceiling in the winter. On residential homes radiant barrier is typically installed one of two ways- radiant barrier decking or radiant barrier foil, and the present structures may be incorporated into these 10 types of building product. lRdiant Barrier Decking is typically used in new home construction. This product is made by laminating a highly reflective piece of aluminium foil to one side of OSB board or plywood. The foil side will face the attic which creates the required air space. It is important to note that if the structure is located in a humid area, the radiant barrier should be perforated to 5 ensure proper passage of moisture. Generally pre-laminated radiant barrier sheathing will have vapour barrier properties because the lamination adhesive fills in the perforations. It is typically preferred to use a perforated, reflective radiant barrier and staple it to the roof decking before installing it on the rafters. Radiant Barrier Foil is installed inside the roof space of existing buildings. This product is a 90 tarp-type material with a layer of aluminium foil laminated on both sides to create a double sided radiant barrier. The radiant barrier foil material can be either stapled to the bottom of the roof rafters or laid out over the existing insulation. Embodiments of the cellular structure having the combination of gas filled cells that are capable of collapsing and having a radiant barrier provides significant advantages over the 95 prior art. The ability to have cells of significant depth that are capable of providing high levels of thermal insulation in conjunction with a radiate barrier to confer higher control of thermal radiation is a dear advance in the art. 16 Yet further advantage is provided where the means for allowing the egress (and optionally ingress) of gas is also the radiant barrier, or is part of the radiant barrier. Fbr example, the )0 upper and/or lower layer of the structure may be a woven foil which allows passage of gas and also reflects thermal radiation. The incorporation of these two features into a single layer providesfor a less complex and/or thinner and/or less expensive structure, compared with the situation whereby the gas permeability and radiant barrier functions are provided by separate layers )5 The one or more gas-filled cells of the present structure may be any shape capable of being moulded in the production process including circular, ovoid, square, rectangular, pentagonal, hexagonal, heptagonal, or octagonal. Preferably the one or more cells are substantially circular when considered in plan view. Taking depth into consideration, the one or more cells are generally substantially-disk shaped. 0 In certain embodiments the one or more cells have a width or diameter of between about 5 and 50mm. Preferably the one or more cells have a width or diameter of between about 25 and 35 mm. In some embodiments the one or more cells have a depth of between about 5 and 20 mm. Preferably the one or more cells have a depth of between about 10 and 14 mm. 5 In other embodimentsthe one or more cells have awidth of lessthan about 15 mm or more than about 25 mm. Further embodiments of the structure provide for the one or more cells having a depth of less than about 6 mm or more than about 10 mm. As will be understood, the present structures may find use in any field where insulation is 20 required. However, in a preferred form of the invention the structure is adapted or configured to function as a building product. Thus, the structure may be fabricated so as to have a minimum strength, to be waterproof, to be dust proof, to be resistant to fire, to be resistant to mould or pests, to be paintable, to have minimum R-value, to be light weight, to be non-toxic, or to be thermally reflective. 17 !5 Sme embodiments provide that the building product is a sarking product. 8rking is a layer of flexible insulation typically installed under roof tiles in building construction. Preferably the sarking product complies with the requirements of the Building Cbde of Australia (BCA), specifically relating to pliable building membranes (AS'NZ 4200.1), and/or have a flammability index not greater than 5. 10 In another aspect the present invention provides a method for fabricating a substantially planar cellular structure, the method comprising the steps of: providing a pre-extruded sheet material, contacting the sheet material with a mould under conditions allowing the sheet material to conform to the mould to form a moulded sheet, providing an upper layer material and a lower layer material, contacting the moulded sheet to the upper and lower 15 layers, and bonding the moulded sheet to the upper and lower layers. This method is particularly suitable for fabricating the cellular structures described elsewhere herein, and is distinguished from prior art methods. Methods of the prior art require the central "bubble film" layer being formed during the extrusion process. The present methods are distinguished from existing methods which do [0 not allow for a single layer of bubble film to be formed and sandwiched between upper and lower layers, and also require the lamination of separate laminates on both sides. It will be appreciated that the requirement for laminates on both sides of the structure results in a structure having five layers. This contrasts to the structures of the present invention that in some embodiments consist of only three layers, and may therefore not be capable of 45 fabrication with prior art methods. The pre-extruded sheet material may be any sheet material discussed herein, including any preferable materials. Generally, the sheet material is a substantially gas impermeable material such as a polyethylene. At least one of the upper or lower layers may be a sheet material, such as polyethylene. Where it is required that layer be capable of gas egress (and 50 optionally ingress), the moulded sheet and/or the upper layer and/or the lower layer comprises means for allowing egress (and optionally ingress) of a gas Any of the means referred to elsewhere herein are contemplated to be capable of incorporation into the present methods, however preferably the means is a woven material. 18 The conditions for allowing the sheet material to conform to the mould to form a moulded 5 sheet may depend on a number of parameters such as the type of sheet material, the size of the mould et cetera. In one embodiment of the method, the conditions comprise heating the sheet material to a temperature where it is suffiidently flexible to conform to the shape of the mould. In another embodiment the conditions comprise the application of a vacuum about the sheet and mould such that the sheet conforms closely to the shape of the mould. iO The bonding step may be accomplished by any means known to the skilled artisan including the use of adhesives. In a preferred form of the method the bonding step comprises a thermo-lamination process. Yet a further aspect of the present invention provides a product produced according to a method disclosed herein. Preferably the product is or comprises a cellular structure as 5 described herein. The present invention will now be further described by reference to a preferred embodiment. In particular reference is made to Figures 1, and 2 herein which show a three layered cellular structure 2 having an upper layer 4 composed of a nonwoven polymer and a lower layer 6 composed of a woven foil. The walls 8 of the cells are formed by the central 'O layer 10 which is bonded to the upper layer 4 and lower layer 6 to form a gas-filled cell 12. It will be noted that within the central layer 10 forms the ceiling and walls of the cell 12, while the lower layer 6 forms the floor of the cell. The lower layer 6 is a woven foil, which also functions as a thermal barrier. Figure 2A shows a structure prior to the application of a compressive force, while Figure 2B 75 shows the result of application of a compressive force 14. The compressive force 14 applied to the upper layer 4 leads to a decrease in volume of an affected cell (and also possibly adjacent cells, not shown). This compression in turn leads to an increase in air pressure within the cell, resulting in egress of air through the woven foil lower layer 6. Upon removal of the compressive force the upper layer 4 and/or lower layer 6 and/or wall 8 rebound 80 toward their original position, as shown in Figure 2A 19

Claims (34)

1. A substantially planar structure comprising a plurality of the gas-retaining cells, one 15 or more of gas-retaining cells comprising means for allowing egress of a gas, wherein in use egress of the gas occurs in response to a force applied to the cell.

2. A structure according to daim 1 comprising means for allowing ingress of a gas to one or more of the gas- retaining cells, wherein ingress of the gas occurs in response to release of the force applied to the one or more cells. )0

3. Astructure according to daim 2 wherein the ingress of gas into the one or more cells is effected or assisted by the presence of a resilient material within or about the structure.

4. A structure according to any one of aims 1 to 3 wherein upon release of the force the floor-to-oeiling distance of the one or more cells returns to at least about 90%of the pre-compression distance.

)5 5. A structure according to any one of aims 2 to 4 wherein the means for egress and ingress of the gas are the same means.

6. A structure according to any one of daims ito 5 wherein the means for allowing the egress (and optionally ingress) of a gas is a gas-permeable material

7. A structure according to daim 6 wherein the gas permeable material is a woven )0 material.

8. A structure according to daim7 wherein the woven material is a woven polymeric material.

9. A structure according to daim 8 wherein the woven polymeric material is a woven polyolefin. 05

10. A structure according to any one of aims 1 to 9 comprising or consisting of three layers- a central layer defining a wall and ceiling of the one or more cells, the central layer bonded to an upper layer, the central layer bonded to a lower layer defining the floor of the one or more cells.

11. A structure according to daim 10 having no more than three layers 10

12. A structure according to daim 10 or claim 11 wherein the upper layer and/or the lower layer and/or the central layer is/are a gas-permeable material. 20

13. A structure according to any one of daims 10 to 12 wherein (i) the central layer is a substantially gas-impermeable material and (ii) the upper layer or the lower layer is a substantially gas-impermeable material. 5

14. A structure according to daim 12 or daim 13 wherein the substantially gas impermeable material is a non-woven polymeric material.

15. A structure according to daim 14 wherein the non-woven polymeric material is a polyolefin.

16. A structure according to any one of daims ito 15 wherein the one or more cells are !0 substantially circular.

17. A structure according to any one of aims 1 to 16 wherein the one or more cells are substantially-disk shaped.

18. A structure according to any one of aims 1 to 17 wherein the one or more cells have a width or diameter of between about 5 and 50mm. !5

19. Astructure according to daim 18 wherein the one or more cells have a width or diameter of between about 25 and 35 mm.

20. A structure according to any one of aims 1 to 19 wherein the one or more cells have a depth of between about 5 and 20 mm.

21. A structure according to daim 20 wherein the one or more cells have a depth of 10 between about 10 and 14 mm

22. A structure according to any one of aims 1 to 21 wherein the one or more cells have a width of less than about 15 mm or more than about 25 mm.

23. A structure according to any one of aims 1 to 22 wherein the one or more cells have a depth of less than about 6 mm or more than about 10 mm. 35

24. A structure according to any one of aims 1 to 23 comprising a thermal barrier.

25. A structure according to any one of aims 1 to 24 wherein the first and/or second layer is a thermal barrier.

26. A structure according to daim 24 or 25 wherein the thermal barrier is also means for allowing egress (and optionally ingress) of a gas. 40

27. A structure according to any one of daims 1 to 26 that is adapted or configured to function as a building product.

28. A structure according to daim 27 wherein the building product is a sarking product. 21

29. A method for fabricating a substantially planar cellular structure, the method comprising the steps of: providing a pre-extruded sheet material, contacting the sheet 5 material with a mould under conditions allowing the sheet material to conform to the mould to form a moulded sheet, providing an upper layer material and a lower layer material, contacting the moulded sheet to the upper and lower layers, and bonding the moulded sheet to the upper and lower layers

30. A method according to daim 29 wherein the conditionsfor allowing the sheet 0 material to conform to the mould to form a moulded sheet comprise heating the sheet material to a temperature where it is suffiidently flexible to conform to the shape of the mould.

31. A method according to daim 29 or daim 30 wherein the conditionsfor allowing the sheet material to conform to the mould to form a moulded sheet comprise the application 5 of a vacuum about the sheet and mould such that the sheet conforms dosely to the shape of the mould.

32. A method according to any one of daims29 to 31 wherein the bonding step comprises a thermo-lamination process.

33. A product produced by a method according to any one of daims29 to 32. 0o

34. A product according to daim 33 that is or comprises a structure according to any one of aims 1 to 25. 22