FIELD OF THE INVENTION

This invention relates to structural elements made from profiled sheet material - typically from cellulosic or other fibrous materials such as paper.

BACKGROUND TO THE INVENTION

In order to provide sufficient strength in the relevant loading directions and/or flexibility in certain directions, sheet materials such as paper is often formed and/or combined together.

One type of such formed sheet material is corrugated fibreboard, which is a paper- based material consisting of a fluted corrugated sheet and two flat linerboards, although it is often made with multiple layers of liners and fluted corrugated sheets. Corrugated fibreboard is relatively strong for its weight in the sense that it resists compression and bending in most directions.

Another type of formed sheet material is an expandable honeycomb structure comprising multiple sheets that are attached together (typically with adhesive) and that can expand to form an array of cells, each surrounded by paper. These structures are often used for cores or in-f ills (e.g. in doors) and they are relatively resistant to compression in the planar directions of the paper, but they offer practically no resistance to being compressed (returned) to their un-expanded form. The present invention seeks to provide structures made of sheet material that are cost-effective, versatile and strong.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a structural element comprising:

at least one support sheet, said support sheet being a composite sheet which includes at least a first liner and a second liner and at least one corrugated element extending between said first and second liners; and

at least one face sheet, said face sheet being a composite sheet which includes at least a first liner and a second liner and at least one corrugated element extending between said first and second liners, said face sheet being

adhesively attached to the support sheet;

characterised in that said support sheet is folded to form a plurality of generally parallel ribs and each rib of the support sheet comprises at least two generally parallel folds along which the support sheet is folded in the same direction, with an apex extending between the two folds of each of said ribs, said face sheet being adhesively attached to the apexes of at least some of the ribs of the support sheet.

The face sheet may also be folded to form a plurality of generally parallel ribs and each rib of the face sheet may comprise at least two generally parallel folds along which the face sheet is folded in the same direction, with an apex extending between the two folds of each of said ribs of the face sheet, said face sheet being adhesively attached to the support sheet, between the apexes of at least some of the ribs of the face sheet and the apexes of at least some of the ribs of the support sheet. The apexes of the ribs of the face sheet may extend generally perpendicular to the apexes of the ribs of the support sheet.

Each of the ribs may have a longitudinal apex and each apex may include at least two generally parallel folds of the composite sheet - the composite sheet being folded in the same direction along both said folds. At least some of the ribs may have an angular trapezoidal fluted profile and the angular trapezoidal fluted profile may have an isosceles trapezoidal shape, e.g. an "IBR" profile.

Instead, webs of the ribs of the support element may but against one another and may be adhesively attached to one another, to form a wafer structure.

The flutes of the corrugated elements in the composite sheets in the form of the support sheets and/or the face sheets, may intersect folds forming the ribs, generally at right angles.

The structural element may include two face sheets with at least one support sheet disposed between the two face sheets, with each of the face sheets being adhesively attached to the apexes of one or more ribs of the support sheet.

The structural element may include one or more intermediary sheets that are disposed between adjacent support sheets, each intermediary sheet being adhesively attached to the apexes of one or more ribs of the adjacent support sheets.

The apexes of the ribs of adjacent composite sheets may be attached together with adhesive with a predetermined degree of misalignment between them and/or the adhesive may protrude from contact surfaces between the adjacent apexes, e.g. the adhesive may form a bead.

One or more of the support sheets may be compressed from opposing sides of the support sheet, along each of the generally parallel folds that form the ribs of the support sheet, i.e. the apex of each rib of the support sheet may be formed by compressing the support sheet from one side along each of the two fold lines and from the opposite side of the support sheet along the same two fold lines.

The first and second liner and the corrugated elements, may be made of cellulosic material, e.g. paper.

According to another aspect of the present invention, there is provided a method of making a structural element, said method comprising adhesively attaching a support sheet comprising a composite sheet which includes at least a first liner and a second liner and at least one corrugated element extending between said first and second liners, to a face sheet comprising a composite sheet which includes at least a first liner and a second liner and at least one corrugated element extending between said first and second liners; wherein said method includes folding said support sheet to form a plurality of generally parallel ribs.

The method may include folding said support sheet between two ribbing elements, the surfaces of the ribbing elements facing each other being complementally shaped to form the ribs in the support sheet between said ribbing elements. The ribbing elements may include at least one roller with a ribbed surface.

The method may include applying a settable liquid to the structural element and may include drawing said liquid at least partly into the flutes of one or more of the corrugated elements, under vacuum.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how it may be carried into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 is a three-dimensional diagrammatic view of a first embodiment of a support sheet according to the present invention;

Figure 2 is a profile view of a second embodiment of a support sheet according to the present invention;

Figure 3 is a three-dimensional diagrammatic view of a first embodiment of a

structural element according to the present invention;

Figure 4 is a side view of the structural element of Figure 3, in use;

Figure 5 is a diagrammatic profile view of the formation of a support sheet according to Figures 1 or 2;

Figure 6 is a three-dimensional view of a second embodiment of a structural element according to the present invention;

Figure 7 is a profile view of third embodiment of a structural element according to the present invention;

Figure 8 is a profile view of a fourth embodiment of a structural element according to the present invention;

Figure 9 is a profile view of fifth embodiment of a structural element according to the present invention;

Figure 10 is a profile view of sixth embodiment of a structural element according to the present invention;

Figure 1 1 is three-dimensional diagrammatic view of a third embodiment of a support sheet according to the present invention;

Figure 12 is a profile view of seventh embodiment of a structural element according to the present invention; and

Figure 13 is a diagrammatic profile view of the formation of the support sheet of

Figure 1 1 .

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, a structural element according to the present invention is generally identified by reference number 10 and a support sheet that is intended to form part of a structural element 10, is generally identified by reference number 1 1 , with suffices referring to the embodiment of the structural element or support sheet, where applicable. However, it should be borne in mind that some of the

embodiments of structural elements are made up of a number of support sheets 1 1 and/or other embodiments of structural elements. Features that are common between different embodiments of the invention are identified by the same reference numbers.

The present invention can be used for various sheet materials, but in the illustrated examples, cellulosic sheet material in the form of paper has been used. Other suitable sheet materials include various polymeric substances.

Referring to Figures 1 and 2, the support sheets 1 1 .1 and 1 1.2 are made from composite sheets in the form of corrugated fibreboard sheets 12 and each sheet of corrugated fibreboard includes two liners 14 of flat paper sheets and a corrugated paper element 16 extending between them. The corrugated paper element 16 is folded in an undulating pattern to form many parallel flutes 18 and apexes 20 between the flutes, and the apexes 20 are attached to the liners 14 (as shown in Figure 2). Strictly speaking, terms such as "rib", "apex", "flute" and "trough" should be interpreted in relation to a particular side of the fibreboard. E.g.: the apex of a rib, when viewed from one side, forms the trough of a flute, when viewed from the other side. However, for the sake of brevity in this specification, these terms are not used as strictly. In particular, downwardly protruding parts that are attached to parts below them, are often referred to as "ribs" and "apexes", as they would be when viewed from below, even though they are shown from above in the drawings.

In each of the support sheets 1 1 .1 and 1 1 .2, the corrugated fibreboard 12 has been folded to form a plurality of parallel ribs 22 with flutes 24 between them. The ribs 22 and flutes 24 can have other profiles, but have been found to provide exceptional strength (load/span characteristics) and versatility for the weight of the fibreboard 12 used, if each rib and flute has a angular trapezoidal profile, e.g. a profile known as "IBR", which is an abbreviation for Inverted Box Rib. In preferred embodiments, the profile of each of the ribs 22 and flutes 24 has an isosceles trapezoidal shape. Which also holds the advantage of high resistance to compression in a direction

perpendicular to the general plane of the support sheet (i.e. along a vertical axis, as illustrated), because the mirrored angular orientations of the webs 34 hold the profile of the rib 22 or flute 24 in balance and prevents it from collapsing in parallelogram- fashion.

Each rib 22 has a longitudinal apex 26 and each apex extends between two parallel apex folds 28 and similarly, each flute 24 has a trough 30 extending between two parallel flute folds 32, with the webs 34 extending between each adjacent apex fold and flute fold. In the embodiments shown in Figures 1 and 2, the sizes of each apex 26, trough 30 and web 34 are about equal, but they need not be. If more stiffness is required, the widths of the apexes 22 and/or troughs can be increased relative to the webs 34. Further, the webs 34 are shown in the illustrated examples at slightly obtuse angles relative to the apexes 36 and troughs 30, but they may be placed at right angles if more stiffness is required - which would forego the benefits of the isosceles trapezoidal profile mentioned above. The dimensions of the ribs 22 and flutes 24 will need to be selected according to the intended purpose of the support sheet 1 1 .

The difference between support sheet 1 1 .1 shown in Figure 1 and support sheet 1 1 .2 shown in Figure 2, is that the flutes 18 of the fibreboard 12 extends

perpendicular to the ribs 22 and flutes 24 in Figure 1 , as shown with short lines on the outside of the fibreboard 12, whereas the flutes 18 of the fibreboard 12 extend parallel to the ribs 22 and flutes 24 in Figure 2. The selection of either of these two embodiments of the present invention will depend on the intended purpose of the support sheet 1 1 . The longitudinal/parallel orientation of flutes 18 in relation to the ribs 22 as shown in Figure 2 allows easier formation of the folds 28,32, better penetration of resins into the flutes 18 (see below) and easier bending of the support sheet 1 1 .2 in a direction parallel to the ribs 22. On the other hand, transverse orientation of the flutes 18 in relation to the ribs 22 as shown in Figure 1 provides better resistance against compression of the ribs 22 in a direction perpendicular to the general plane of the support sheet 1 1 .1 .

The support sheets 1 1 .1 and 1 1 .2 are remarkably resistant to bending in directions perpendicular to the ribs 22, yet are reasonably flexible in directions parallel to the ribs 22, because of flexibility of the folds 28,32.

Referring to Figure 7, a structural element 10.3 is formed by applying a face sheet 48 to a support sheet 1 1 , by attaching the face sheet to the apexes 26 of the ribs 22 of the support sheet, with adhesive. The face sheet 48 is preferably also a sheet of corrugated fibreboard - with similar construction to the sheet 12 shown in Figure 2, with a corrugated element 16 between two liners 14, to form longitudinal flutes 18. In the structural element 10.3, the flutes 18 in the face sheet 48 extend parallel to the ribs 22 of the support sheet 1 1 and the flutes of the support sheet 1 1 extend perpendicular to the ribs, but the flutes in the support sheet and/or the face sheet may be oriented in any direction, depending on the loading conditions the structural element 10.3 is intended to resist. Referring to Figure 8, a structural element 10.4 is shown that is identical to the structural element shown in Figure 7, with an isosceles trapezoid IBR profiled support sheet 1 1 and a face sheet 48.1 attached to the apexes 26 of the ribs 22. However, the structural element 10.4 also includes another face sheet 48.2 that is attached to the downward facing apexes 26 of the support sheet 1 1 .

Referring to Figure 9, a structural element 10.5 is shown that includes two support sheets 1 1 disposed between two face sheets 48, with an intermediary sheet 50 between the two support sheets. The attachment of each of the face sheets 48 and the intermediary sheet 50 to the support sheets 1 1 is by adhesive attachment between the upwardly and downwardly facing apexes 26, and the face sheets 48 and intermediary sheets 50, respectively. In other embodiments of the invention, structural elements can be provided with any number of support sheets 1 1 attached to face sheets 48 and/or intermediary sheets 50.

In the embodiment shown in Figure 9, the ribs 22.1 of the upper support sheet 1 1 .1 have a smaller profile than the ribs 22.2 of the lower support sheet 1 1 .2 and the ribs of the two support sheets are parallel to one another. However, in other

embodiments of the invention, the rib profiles and sizes in different support sheets 1 1 may be similar and/or may be oriented perpendicular to one another. The

intermediary layer 50 assists in transferring loads between the support sheets 1 1 .

The purpose of the use of multiple support sheets 1 1 in a structural element 10.5, is to allow different loads to be borne by the respective support sheets - i.e. for the support sheets to contribute in different ways to the overall strength of the structural element. As an example, if the structural element 10.5 is intended as a load deck (e.g. of a pallet), an upper support sheet 1 1 .1 can be provided with the ribs 22 spaced closely together, to support the upper face sheet 48.1 more evenly (e.g. to bear concentrated loads that may be imparted on the upper face sheet), whereas the lower support sheet 1 1 .2 can have larger ribs with deeper profiles, to support the upper support sheet and particularly resist bending (deflection) - bearing in mind that the concentrated load imparted on the upper support sheet will be transferred to the lower support sheet as a more evenly distributed load.

Referring to Figure 10, a structural element 10.6 is shown that is similar to the structural element shown in Figure 7, with a single, profiled support sheet 1 1 and a single face sheet 48 adhesively attached to the apexes 26 of the support sheet's ribs 22. However, instead of an IBR profile, each rib 22 and each 24 is formed with its webs 34 in abutment and adhesively attached together, so that the webs 34 form a continuous wafer structure 52. Referring to Figures 3 and 4, a composite structural element 10.1 has been formed by attaching a support sheet 1 1 and face sheet 48 together, but the face sheet 48 has been profiled in the same way as the support sheet 1 1 , with ribs 22 and flutes 24. In the illustrated embodiment, the face sheet 48 and support sheet 1 1 have different orientations of their flutes 18 relative to their ribs 22, but this need not be the case, depending on the intended purpose of the structural element 10.1 . The face sheet 48 and support sheet 1 1 are attached together by applying adhesive to their apexes 26 and brining them into firm contact, with their ribs 22 extending generally perpendicular to each other and in the illustrated example, this would mean that the flutes 18 inside the corrugated sheets 12 extend in the same direction. Only one face sheet 48 and one support sheet 1 1 are shown in Figures 3 and 4, but if required, another face sheet and any number of further support sheets can be included in the structural element - with intermediary sheets, if desired.

The structural element 10.1 has remarkably high resistance to bending in any direction and can be used in a very wide variety of applications, e.g. as floors in temporary shelters (preferably with the addition of an abrasion resistant cover) load decks for transport and storage items such as pallets and bins, and many more.

In applications where the structural element 10.1 of Figure 3 needs to curve cylindrically, e.g. if it is required to make a part cylindrical roof for a temporary shelter, the face sheet 48 can easily flex parallel to its ribs 22 to form a part cylindrical element, but the support sheet 1 1 would normally resist such bending. However, if spaced cuts 36 are made in the ribs 22 of the support sheet 1 1 , it's ribs can kink at the cuts, to provide the required cylindrical flexion, while still retaining adequate stiffness in the rib. Instead of cuts 36, the ribs 22 may be prepared in other ways to allow the required degree of kinking, e.g. they may be scored, bent, and/or may be slightly weakened locally in other ways.

The support sheets 1 1 .1 and 1 1 .2 shown in Figures 1 and 2 can be formed from corrugated fibreboard 12 in any suitable manner, but the most commonly used method for forming three-dimensional objects from fibreboard, is to score the board (i.e. compress it) along lines where folds are required and then to fold the fibreboard along the score lines. The scoring and folding method can be used to form the support sheets 1 1 .1 and 1 1.2 and if so, the fibreboard would be expected to pivot fairly easily about the score lines along folds 28 and 32. However, instead of scoring and folding, the support sheets 1 1 .1 and 1 1 .2 can be formed according to the present invention by feeding corrugated fibreboard 12 (preferably from a roll) through a set of ribbing elements in the form of contra-rotating rollers 38, as shown in Figure 5. Each roller 38 has a ribbed surface and the rollers are complementally shaped and timed, in that the ribs 40 of each roller fit into the troughs 42 of the other roller, as the rollers rotate. As the fibreboard 12 passes through the rollers 38, it is folded by the meshing ribs 40 and troughs 42 to form its ribs 22.

Referring to Figure 6, an IBR-profiled face sheet 48 and any number of IBR-profiled support sheets 1 1 (three support sheets are shown in Figure 6) can be attached together with their ribs extending parallel and with the apexes of each fibreboard 12 attached adhesively to the apex of the adjacent fibreboard, to form a structural element 10.2. The structural element 10.2 defines a plurality of longitudinal apertures 44, each formed of the combined troughs 30 that face each other, between adjacent fibreboards 12 and each aperture has a near regular hexagonal cross-sectional profile - depending on the angles between the apexes 26, webs 34 and troughs 30. However, if the fibreboard 12 can pivot or flex easily at the folds 28,32, then the shapes of the apertures 44 can easily be changed and the whole structural element 10.2 can be expanded or compressed, vertically.

Practical experimentation has revealed that the vertical compressibility of the structural element 10.2 can vary greatly. In some instances, there is practically no resistance to deformation and in other instances, the structural element 10.2 offers significant resistance to compression. These two variations of the structural element 10.2 can be applied advantageously to suit different intended uses.

For example, in cases where the structural element 10.2 need not withstand significant compression in a direction perpendicular to the sheets of fibreboard 12 (i.e. in the vertical direction as shown in Figure 6), embodiments of the structural element may be used where the fibreboard pivots freely about the folds 28,32. In these cases, the structural element 10.2 will act much the same as a conventional "honeycomb" structure - apart from being substantially more resistant to

compression in the longitudinal direction (i.e. in the direction of the apertures 44 and folds 28,32). In other cases, where it is desirable for the structural element 10.2 to offer a degree of resistance to compression, it can be made such and it can be used to as a compressible protector (e.g. against impact), as a compressible support (e.g. to support objects in transit), or many other applications.

The techniques used to alter the vertical compressibility of the structural element 10.2 can include any one of more of a number of techniques. The first technique is the use of different methods in forming the ribs 22 in the fibreboard 12. If the fibreboard 12 is folded, material on the outside of the fold is necessarily under tension and the material on the inside of the fold is compressed and crushed to form a zone 46 of crushed material, as shown in Figure 2. If the corrugated fibreboard 12 is scored deeply, material on opposing sides of the score is crushed and in the centre of the score only a thin compressed sheet of material remains, that can flex easily, so that a fold 28,32 can easily form along the score and the fold can easily be undone. By contrast, if the corrugated fibreboard 12 is folded as shown in Figure 5, no distinct line of thin, compressed material is formed along the fold line (as in the case of scoring), but instead, the material is crushed in the crush zone 46 as the fibreboard is folded and the crushing action crumples the corrugated element 16 and liner 14 of the fibreboard. If a load is applied to unfold the fibreboard 12, some resistance to this unfolding is provided by the crumpled material in the crush zone 46 - at least more resistance than when the folding action was preceded by scoring. Accordingly, the structural element 10.2 can be made more resistant to vertical compression by forming the ribs 22 without scoring the fibreboard.

Another technique that affects vertical compressibility of the structural element 10.2 is the application of adhesive to the apexes 26 to attach them together. The adhesive is applied in a manner that sets the fibreboard 12 along the folds 28,32 so that the folds are more resistant to unfolding, e.g. the adhesive can protrude from the apexes 26 and into the apertures 44, where it can form beads or other

protuberances that can interfere with unfolding, or the adhesive can penetrate the fibreboard 12 in the crush zone 46 and further set the crumpled material in the crush zone, to resist unfolding. Yet a further technique that affects vertical compressibility of the structural element 10.2 is alignment of the ribs 22. If the ribs 22 of adjacent fibreboards 12 are perfectly aligned, the apertures 44 would be symmetrical about the plane intersecting the attachment of the apexes (i.e. the horizontal plane that intersects the centre of each aperture 44) and as the structural element 10.4 is compressed vertically, the folds 28,32 would open (unfold) until the webs 34 and trough 30 above the aperture are aligned and at the same time the webs and trough below the aperture are aligned - i.e. the two fibreboards have been "flattened". By contrast, if the apexes 26 of the ribs 22 that are adhesively attached together, are not perfectly aligned, the apertures 44 would not be symmetrical about the horizontal plane intersecting the attachment of the apexes and they would not collapse as described above. Instead, the webs 34 and trough 30 either above or below the aperture 44 would be straightened out completely before the webs and trough on the opposite side of the aperture have been completely straightened and any attempts to straighten such webs and trough would be resisted by tension in the straightened webs and trough.

If the structural element 10.2 is intended to resist vertical compression minimally, it can be manufactured by deep scoring the corrugated fibreboard 12, applying adhesive to the unfolded fibreboard and forming the ribs 22 only after the adhesive has set. This technique provides easily pivoting compressed material at the score lines, assists alignment of the apexes 26 together (assuming that they are of the same size and are parallel) and prevents the adhesive from setting the folded material or forming beads, because while the fibreboard is unfolded, there are no apertures 44 into which the adhesive can protrude to form beads).

If the structural element 10.2 is intended to offer substantial resistance to vertical compression, it is manufactured by first folding the corrugated fibreboard 12 to form the ribs 22 between rollers 38 and only then is adhesive applied to the apexes 26 and are they attached together. This technique allows the adhesive to set the folds 28,32 (whether by forming a bead or penetrating the material), does not form a thin flexible sheet as is the case with deep scoring and allows for misalignment of the ribs 22 to any desired extent.

These manufacturing techniques can be combined and/or can be applied to different degrees, to form a structural element 10.2 with a desired degree of vertical compressibility. Referring to all the drawings, if required, the support sheets 1 1 and/or face sheets 48 can be enhanced by impregnating them with settable liquids such as resins, e.g. thermosetting resins such as polyester resin. The resins can serve the purposes of improving the strength of the sheets 1 1 ,48 and/or protecting them against the elements. In some cases, the resin would only be applied on the outside of the fibreboard 12 and could penetrate the liners 14 partially or completely, or could penetrate the fibreboard further up to complete penetration. However, in cases where extensive penetration of resin in the fibreboard 12 is required, this is better achieved by drawing the resin into the flutes 18 from the exposed ends of the flutes at the edges of the fibreboard 12, preferably under vacuum.

The structural elements 10 are extremely versatile and some of their practical applications include: load decks for pallets; walls, roofs or cladding for temporary shelters; supporting material in packaging; and many more. Depending on the intended purpose of the structural element 10 (and thus the expected load conditions and other requirements such as insulation and appearance), different variations and permutations of the structural elements described herein, can be used - each including at least one profiled support sheet 1 1 and at least one face sheet 48 - which could be flat or profiled. In structural elements 10 where straight portions of the face sheets 48 span across the flutes 24 and are adhesively attached to the apexes 26 on opposing sides of the flutes, the face sheets add structural strength to the support sheets 1 1 by retaining the shapes of the flutes and ribs 22 of the support sheet. The face sheets 48 thus act synergistically with the support sheets 1 1 to provide strong structural elements 10.

Referring to Figures 1 1 to 13, in cases where a support sheet 1 1 is to be formed from a sheet 52 that is too thick to form the apex folds 28 and flute folds 32, the sheet 52 is compressed from opposing sides along these fold lines. Examples of sheets 52 that would require this folding technique include sheets that are more than 7 mm thick, sheets comprising multiple layers of corrugated fibreboard and/or sheets made up of corrugated fibreboard wafers. Figure 13 shows a pair of opposing rollers 56, each including a number of

circumferential ridges 58 that are aligned between the two rollers. The sheet 54 is passed through the gap 60 between the rollers 56, with the rollers counter-rotating and rolling along the opposing surfaces of the sheet and at the same time, the ridges 58 compress the sheet to form parallel fold lines for the apex folds 28 and flute folds 32.

Figure 12 shows a structural element 10.7 which includes two thick face sheets 48 that could each be made of a wafer of corrugated fibreboard, or multi-layered corrugated fibreboard. The support sheet 1 1 is folded along the fold lines 28,32 and is attached to the apexes 26 of the face sheet 48 and the webs 34 of the ribs 22 so formed, act as supports between the face sheets 48. In the illustrated example, the apexes 26 are relatively small, compared to the webs 34, because the webs are intended to perform the structural tasks of spacing the face sheets 48 apart, whereas the primary purpose of the apexes is to provide a surface for adhesive attachment between the support sheet 1 1 and face sheets 48. The structural element 10.7 is structurally very strong, yet light and it can be used for load bearing layers, e.g. a floor in a temporary structure, for roofs of temporary structures, or the like. If the fibreboard is adequately treated, e.g. by impregnation with a suitable resin, the structural element 10.7 can be used in permanent structures.