The invention relates to jigsaw puzzle accessories, especially to an accessory for displaying a jigsaw puzzle or a jigsaw puzzle display system.

In different countries, it is a known custom to display jigsaw puzzles after finishing them. For instance, puzzles can be glued together and/or framed.

In a known method, a finished puzzle can be glued onto a backing board or the like. Said puzzle can then be displayed unframed. However, said puzzle can then also be framed, for instance in order to provide it with a decorative edging. For example, after gluing the puzzle onto the backing board, it may be fitted in a conventional photo frame selected for having a size corresponding to the size of said jigsaw puzzle.

Further, special jigsaw puzzle frames are known. For example, a jigsaw puzzle frame has been proposed comprising a transparent front plate, e.g. of acryhc glass, and a special shallow drawer. The shallow drawer has a height corresponding with the thickness of the jigsaw puzzle. The puzzle can be placed on top of the bottom of the drawer and the transparent front plate can then be placed on top of the puzzle, before sliding the stapled drawer, puzzle, and front plate into the frame. Due to the very small height of the drawer, the puzzle can be kept in place between the transparent front plate and the drawer.

A disadvantage of such and/or other puzzle frames can be that they generally are relatively complex and that producing them may therefore be relatively difficult and/or expensive.

Besides, it is noted that not all puzzles have the same size.

Actually, even jigsaw puzzles comprising the same number or puzzle pieces, e.g. different puzzles each consisting of about 1000 puzzle pieces, often have different sizes due to the fact that different producers use different internal standards. Therefore, and since frames generally have upper and lower size limits for the puzzles to be fitted therein that are very close to one another, it can be hard to find a frame matching the size of a specific puzzle, especially without having to measure the finished puzzle in advance. When buying a puzzle it can thus be hard to buy a matching frame at the same time. Moreover, when one wants to buy a puzzle frame as a gift for someone else, it may be almost impossible to find a right sized frame.

A further problem of displaying a jigsaw puzzle may lie in the position of a lug or suspension eye provided on the rear side of a frame for hanging said frame. It is noted that said lug or eye is normally provided centrally, i.e. in the middle of the width of the frame, in order to facilitate straight hanging of the frame. However, for instance due to unevenly distributed glue, for example a left side of the puzzle glued together may be heavier than its right side or vice versa. As a result, it may be hard to hang the framed puzzle straight.

An object of the present is to provide an alternative jigsaw display system and/or to provide a method and/or kit of parts for framing and/or displaying a jigsaw puzzle. It is a further object of the present invention to alleviate or solve at least one of the problems and

disadvantages of one or more the known systems, frames and methods, especially of one of the ones mentioned above. In particular, the invention aims at providing a jigsaw display system, wherein at least one of the problems and disadvantages mentioned above is counteracted or advantages there above are obtained. More in particular, the invention aims at providing a jigsaw display system, which is suitable for displaying jigsaw puzzles of several different sizes, especially a system which can be compatible with jigsaw puzzles of different jigsaw producing companies. Additionally or alternatively, the invention aims at providing a jigsaw display system that facilitates to hang jigsaw puzzles straight on the wall, especially puzzles glued together having an unevenly distributed weight. In a first aspect, the present invention provides for a jigsaw display system comprising a plurality of frame elements for forming a substantially rectangular frame having four side edges, wherein at least two opposite side edges comprise multiple frame elements at least partly, at least two of said multiple frame elements are arranged for overlapping each other at least partly, wherein the length of each of said two side edges is adjustable by adjusting a mutual overlap between said at least two elements.

By arranging at least two of said multiple frame elements such that the length of an overlap between them can be adjusted, the length of a side edge of the frame can be adjusted. As a result, the system may provide for jigsaw puzzle frames having various edge lengths. It is noted that the length of a side edge being adjustable is to be understood at least as being adjustable during assembling the frame and/or during assembling the respective side edge.

Preferably, the multiple frame elements can be injection moulded elements and/or lightweight elements. Therefore, the frame can be a lightweight frame, which - in embodiments - can be adhered to a jigsaw puzzle glued together and which may d be supported by said puzzle, at least partly, during use. The frame can be a stick-on-frame. Additionally or alternatively, the frame can be considered a modular frame.

In embodiments, the mutually overlapping elements may be arranged to be attached to each other in a multiple number of

predetermined positions, thereby providing various, e.g. two, three, four or more than four, predetermined overlap lengths. As a result, the system may be arranged to assemble frames corresponding with certain predetermined jigsaw puzzle sizes. For instance, a system can provided for a frame for differently sized jigsaw puzzles of about a certain number of pieces, such as for example differently sized puzzles of about 100, 500, 1000, or 2000 puzzle pieces, e.g. produced by different puzzle producers. Alternatively, in preferred embodiments, the frame elements that are arranged for overlapping each other can be arranged such that a second of said elements, e.g. a so-called overlapping element, can be slit over a first of the elements, e.g. a so-called overlapped element, at least partly. As a result, the length of a side edge of a puzzle frame may be varied steplessly or substantially continuously, at least within a certain range. The mutually overlapping elements may be movable substantially telescopically at least substantially in a longitudinal direction of the respective frame edge.

In embodiments, the frame elements can comprise a multiple number of elongated elements, each for forming a part of a side edge of the frame, and four corner elements, each for forming a corner of the frame. The corner elements may be substantially L-shaped. The elongated frame elements may be formed substantially straight.

In embodiments, at least two of the corner elements can be provided with at least one cavity for receiving at least a part of one of the elongated elements, such that said at least two corner elements are each arranged for during use overlapping an adjacent elongated element at least partly. The cavity may extend substantially in the longitudinal direction of the respective frame side edge. In preferred embodiments, the corner piece can be provided with two cavities provided at an angle with respect to each other, especially provided substantially transverse to each other. Both of said two cavities can be arranged for receiving at least a part of a respective elongated frame member of the respective one of two intersecting side edges of the frame.

In embodiments, the elongated elements can be provided with cooperating connectors for interconnecting two elongated element adjacent during use. It is noted that in an aspect of the present invention, only two opposite frame edges each needs to be provided with minimal one frame element arranged for overlapping an adjacent frame element. In that case, at least one of the width and height of the puzzle frame can be adjusted, e.g. in order to adapt to the width and/or height of a finished jigsaw puzzle. Advantageously, each of four side edges are provided with minimal one frame element having a part overlapping an adjacent frame part of the respective frame edge at least partly. Hence, both the width and the height of the puzzle frame can be adjustable.

Advantageously, the elongated element having a cover surface, preferably extending in longitudinal direction of said element, arranged to cover a connector of an adjacent elongated element to which it is connected.

The connectors of the elongated frame elements may be designed as click elements. Advantageously, the click elements can be arranged such that two adjacent elongated elements are pulled towards each other in longitudinal direction when their respective click elements are clicked together. Thereto, at least one of said click elements may be provided with a wedge shaped part, which may be directed such as to facilitate contracting two adjacent frame elements when clicked together. As a result of such designs, cracks between two frame elements clicked together may be kept minute, which may contribute to a pleasing appearance of the frame.

The elongated frame element can be provided with an attachment edge arranged for adhering said element onto a top surface or so-called front side of at least one puzzle piece forming a part of a side edge of a puzzle glued together. As a result, the jigsaw puzzle frame can be a stick-on frame which may adhered to a jigsaw puzzle glued together. It is noted that the frame elements may be made of a light-weight material, for instance a plastic material. Hence, the weight of the frame can be relatively low, facilitating that the puzzle glued together can support the weight of the frame.

By providing the elongated element with at least one stop element for abutting a side surface of at least one puzzle piece forming a part of a side edge of a puzzle glued together, it can be facilitated that the frame part and/or a number of interconnected frame parts can be neatly adhered to an edge of the puzzle, e.g. substantially parallel with said edge.

By providing a suspension element arranged to be adhered to a rear surface of the puzzle and further arranged to be connected to a suspension device such as a suspension string, the framed puzzle can be hung substantially without loading frame elements and/or loading the frame. By providing a least two of such suspension elements, it can be counteracted that a puzzle hung can tilt and/or it may be facilitated to hang the framed puzzle straight. Preferably, the suspension element can be arranged to be attached to a relatively large surface area of the puzzle, e.g. an area overlapping more than one jigsaw puzzle piece. Hence, the load resulting from suspending the framed puzzle can be spread among multiple puzzle pieces, thereby counteracting that a puzzle piece is pulled loose from the puzzle glued together.

The invention also relates to a kit of parts for forming a frame of jigsaw puzzle display system. The kit comprises at least a plurahty of frame elements for forming a substantially rectangular frame having four side edges, wherein at least two opposite side edges comprise multiple frame elements at least partly, at least two of said multiple frame elements are arranged for overlapping each other at least partly, wherein the length of each of said two side edges is adjustable by adjusting a mutual overlap between said at least two elements. By providing a kit, puzzle enthusiast can create his own fitting puzzle frame relatively easily.

It is noted that the kit may additionally comprise one or more other components. For example, the kit may comprise double-sided adhesive stickers or tape for adhering frame elements to the puzzle glued together and/or for attaching an overlapping frame element to a respective other frame element.

Additionally or alternatively, the kit may comprise means for adhering or gluing together interconnected puzzle pieces of a jigsaw puzzle. Advantageously, said means can comprise glue, especially puzzle glue.

However, other means for adhering or gluing the pieces together may be provided, such as for instance a sheet of adhesive plastic. Further, said kit may comprise an applicator and/or glue distributor, such as a spatula, a brush or block, e.g. a foam block, for spreading out the glue and/or for applying the sheet of adhesive plastic.

In embodiments, the kit may include strings or threads for hanging the puzzle, instructions, and/or other components, such as a cover, e.g. a flexible plastic sheet or foil, for covering a table-top at least partly, on which cover the puzzle can be placed during gluing it together such that can be counteracted that glue intentionally spoils a table-top or the like.

The kit may also comprise a packaging, for instance a box, preferably a cardboard box, or a blister packaging.

Further, the invention relates to a method for framing a jig-saw puzzle. Said method comprises the steps of adhering at least one first frame element to a jigsaw puzzle glued together, and attaching a second frame element to the first frame element, wherein said second frame element overlaps the first frame element at least partly.

Preferably, double-sided adhesive stickers or double-sided adhesive tape or the like can be used for adhering the at least one first frame element to a front side of a jigsaw puzzle and/or for attaching the second frame element to the first frame element.

In embodiments, the at least one first frame element can be adhered to a front side of the jigsaw puzzle glued together. Then, the frame can be installed relatively easily, e.g. without turning a finished jigsaw puzzle upside down, i.e. with its front surface down, and/or without the need to lift parts of the jigsaw puzzle located at or near an edge part of said puzzle. Moreover, adhering the first frame element to the front side of the puzzle can counteract that the edge of a framed puzzle can be visible, thereby it can enable that it answers a desire to have a visual appearance corresponding with a conventional frame at least partly.

The method may comprise a step of interconnecting at least two first frame elements such that at least parts thereof are aligned to form at least a part of an elongated side edge of a jigsaw puzzle frame, preferably before adhering one or multiple of said first frame elements to the front side of the puzzle.

Advantageous embodiments of the invention are described below and in the appended claims.

By way of non-limiting examples only, embodiments of the invention will now be described with reference to the accompanying figures in which:

Figure 1 shows a schematic view of a jigsaw puzzle display system according to an aspect of the invention; and

Figure 2 shows schematic views of three frame elements of the jigsaw puzzle display system of Fig. 1 and also shows a suspension element.

The embodiments disclosed herein are shown as examples only and should by no means be understood as limiting the scope of the claimed invention in any way. In this description the same or similar elements have the same or similar reference signs.

Figure 1 shows a jigsaw puzzle display system 1 according to an aspect of the invention, wherein said system 1 is installed at a jigsaw puzzle 9 glued together. In Figure 2 three frame elements said jigsaw puzzle display system 1 are shown. As can be seen in Fig. 1, a plurality of frame elements 7, 8 comprised in the system 1 can form a substantially

rectangular frame 2 having four side edges 3-6, wherein at least two opposite side edges 3, 4 comprise multiple frame elements 7, 8 at least partly. At least two of said multiple frame elements 7, 8 are arranged for overlapping each other at least partly. The length L of each of said two side edges 3, 4 is adjustable by adjusting a mutual overlap 10 between said at least two elements 7, 8.

It is noted that in this disclosure a rectangle can include a rectangle with four sides of equal length, i.e. a square. The rectangular frame 2 may thus be a substantially square frame. Furthermore, a rectangle can be a non-square rectangle or a so-called oblong rectangle. The

rectangular frame 2 may thus be an oblong rectangular frame.

As is best seen in Fig. 2, the frame elements 7, 8 that are arranged for overlapping each other are arranged such that a second one 8 of said elements can be slit over a first one 7 of said elements at least partly. Thereto, the second element 8, which also can be called an overlapping element 8, may comprise a cavity 11 for receiving at least a part of a first element 7 or a so-called overlapped element 7.

Here, the frame elements 7, 8 comprise a multiple number of elongated elements 7, each for forming a part of a side edge 3-6 of the frame 2. The frame elements 7, 8 further comprise four corner elements 8, each for forming a corner of the substantially rectangular frame 2. It is noted that the corner elements 8 can during use form part of two intersecting side edges 3, 6; 6, 4; 4, 5; 5, 3 of the frame 2. For example, the corner element 8 can comprise two elongated parts 12, 13, preferably provided under at substantially right angles with respect to each other, which during use can form parts of two adjacent side edges 3, 6; 6, 4; 4, 5; 5, 3 of the frame 2.

Here, each of the four corner elements 8 is provided with two cavities 11 for receiving at least a part of one of the elongated elements 7, such it 8 is arranged for during use overlapping an adjacent elongated element 7a at least partly. However, it is noted that in alternative

embodiments, a corner element 8 may be arranged to only overlap one of the two adjacent elongated elements 7a or may even not at all be arranged to overlap any adjacent elongated element 7a. Additionally or alternatively, at least one of the elongated elements, preferably at least one elongated element per adjustable side edge 3, 4 of the frame 2, can be arranged to overlap an adjacent frame element 7, 8, which adjacent element may be an elongated element, but may in embodiments also be a corner element. In yet another embodiment, the one or both of the two elongated parts 12, 13 of the corner element 8 may be relatively long and the system 1 may be arranged such that said one or both elongated parts 12, 13 can overlap an adjacent elongated part 13, 12 of an adjacent corner element 8.

As a result, the system 1 can be arranged to provide for a puzzle frame 2 which is adjustable to multiple puzzle sizes in a substantially continuous manner, preferably by providing frame elements of which at least a number are arranged for engaging each other in a somewhat telescopic manner. In embodiments, the system 1 can be arranged such that the length L of at least two opposite side edges 3, 4; 5, 6 can be adjusted. However, in advantageous embodiments, the length of all four side edges 3-6 is adjustable, such that the puzzle frame 2 can be adapted to both the width and height of a puzzle 9.

Advantageously, as can be seen in Fig. 2, the corner element 8, and/or one or both elongated parts 12, 13 thereof, can have an inner surface 28 arranged to substantially fit an outer surface 29 of the elongated and/or overlapped frame element 7. For example, said surfaces 18, 29 can be of substantially similar shape, wherein said inner surface 28 can be

substantially offset with respect to said outer surface 29, preferably over a relatively small distance. It is noted that certain parts 28a, 29a of said surfaces 28, 29, e.g. horizontal ledge parts 28a, 29a thereof and/or other parts arranged and/or intended to be provided with an adhesive means such as a piece of double sided tape, can be offset with respect to each other over a larger offset distance then other parts of said surfaces 28, 29, such that between said certain parts a space for accommodating adhesive means can be provided. Hence, also when the corner element 8 is adhered to the elongated element 7, the corner element 8 may substantially closely match or fit the elongated element 7.

In embodiments, as can be seen in Fig. 2, the corner element 8, and/or one or both elongated parts 12, 13 thereof, can be designed as a relatively thin walled element or part, e.g. having an outer surface 30 being substantially offset with respect to its inner surface 28, 28a. As a result, the corner frame element 8 can be of such design that it - for instance in a direction substantially transverse to the plane of the puzzle 9 - protrudes barely with respect to a number of interconnected elongated elements 7 which can form a major part of a side edge 3, 4, 5, 6 of the frame 2.

In embodiments, frame elements, e.g. overlapping corner elements 8 can be provided with ornaments. By providing the corner elements 8 with ornaments, it may be disguised to some extent that corner elements 8 are protruding with respect to the elongated elements 7 with which said corner elements 8 are forming a side edge 3-6 of the frame 2.

Additionally, at least some of the frame elements 7, 8 can be arranged to interconnect two of them to each other in a manner, wherein the combined length of said two elements cannot be substantially adjusted. For instance, said elements can only be connected to each other in a single position.

In embodiments, the elongated elements 7 can be provided with cooperating connectors for interconnecting two elongated element adjacent during use, as can be seen in Fig. 1. Advantageously, the connectors 14, 15 are designed as click elements 14, 15 arranged such that two adjacent elongated elements 7b are pulled towards each other in longitudinal direction 16 when their respective click elements 14, 15 are clicked together, especially by providing at least one of said click elements 14, 15 with a wedge shaped part 17, 18. Said wedge shaped part can for instance taper in a direction substantially transverse to the longitudinal direction 16, e.g. in a direction transverse to the top surface 37 or so-called front side 37 of the puzzle 9, preferably such that said wedge shaped part has a width in the longitudinal direction 16 which width decreases in said in a direction away from the puzzle. As a result, a cracks or splits 19 between two frame elements clicked together may be kept minute, which may contribute to a pleasing appearance of the frame 2. Advantageously, the elongated element 7 can have a cover surface 20 which can cover at least one 15 of its connectors and/or at least one 14 of the connectors of an elongated element attached thereto, such that said one or both connectors 14, 15 can be hidden form view at least partly.

Further, as can be seen in the lower side of Fig. 2, where a bottom view of an elongated element 7 is shown, one or more of the frame elements, preferably one or more elongated elements 7 can be provided with an attachment edge 21 arranged for adhering said element onto a top surface 37 of a puzzle 9 and/or on top of at least one puzzle piece forming a part of a side edge of a puzzle 9 glued together. It is noted that the top surface 37 or so-called front side 37 of the puzzle 9 may at least be understood as meaning a side 37 in the plane of the puzzle, which side 37 can be provided with a print. In embodiments, the attachment edge 21 can be a ledge 21 and/or can be arranged for receiving adhering means such as double-sided adhesive tape or the like. For example, the attachment edge 21 may be formed at least partly by ribs 22, which may for instance extend substantially in the longitudinal direction 16.

Further, the elongated element 7 can be provided with at least one stop element 23, preferably at least two stop elements 23 spaced apart, for abutting a side surface of at least one puzzle piece forming a part of a side edge of a puzzle 9 glued together. Preferably, said stop elements 23 define an abutting surface extending substantially transverse to the attachment edge 21.

Advantageously, an outer edge 31 of the elongated element 7 can extend further in a direction 33 substantially transverse to the puzzle 9 during use than an inner edge 34 of said element 7, e.g. such that when said inner edge 34 is substantially located on top of the puzzle 9, said outer edge 31 is located substantially at the level of the rear surface of the puzzle 9 or even beyond said rear surface. For example, the height 36 between the level of the outer edge 31 and the inner edge 34 can be chosen such that said height 36 substantially corresponds to the thickness of a puzzle 9 or to the combined thickness of a puzzle 9 and an applied adhesive means such as a piece of double sided tape. Additionally or alternatively, an outer edge 33 of the corner element 8 can during use extend further in said direction 33 than an inner edge 35 of said element 8, e.g. such that when said inner edge 35 is substantially located on top of the puzzle 9, said outer edge 33 is located substantially at the level of the rear surface of the puzzle 9 or even beyond said rear surface.

It is noted that the system 1 can comprise at least one, preferably at least two suspension elements 24. In Fig. 2, an embodiment of such suspension element 24 is shown. The suspension element 24 can be arranged to be adhered to a rear surface of a jigsaw puzzle 9 glued together. For example, the suspension element 24 can be provided with a self adhesive surface area 25, which can be covered by a removable sheet 26 before it is applied to the rear surface of said puzzle 9. Advantageously, the self adhesive surface area 25 is sized such as to cover at least multiple adjacent puzzle pieces at least partly, such that suspension force can be split up over those multiple puzzle pieces. Additionally or alternatively, the suspension element 24 can be arranged to be connected to a suspension device such as a suspension string or a nail protruding from a wall, for example by means of providing the suspension element with a hook, lug or eye 27.

Referring to Fig. 1, the jigsaw puzzle display system 1 is shown in a position wherein the frame elements 7, 8 are attached to each other such as to form the substantially rectangular frame 2. Here, said frame 2 is adhered to a jigsaw puzzle 9 glued together. Some of the frame elements 7, 8, for instance adjacent elongated elements 7b, can be interconnected by means of their connectors 14, 15. Further, an overlapping frame element 8, e.g. a corner element 8, overlapping an adjacent overlapped frame element 7a, e.g. an elongated element 7a, can be attached to said adjacent element 7a, preferably by adhering it thereto, especially by a double-sided adhesive sticker or by double-sided adhesive tape. Alternatively or additionally, other means may be used for attaching said two frame elements 7a, 8 to each other, such as for instance glue or Velcro. As another example, the

overlapping element 8 can be clicked onto an underlying element 7a being overlapped by said overlapping element 8 at least partly, preferably in a manner which allows the elongated part 12, 13of the corner element 8 to slide with respect to the at least partly overlapped element 7a in

longitudinal direction of said part 12, 13. In case the overlapping element is a corner element 8 clicked onto two underlying elements 7a located under an angle with respect to each other, a first 7a'of said two underlying or so- called first elements 7a can counteract that the overlapping corner element 8 can be moved in the longitudinal direction of an elongated part 13 of said corner element 8, whereas the second 7a" of said two first elements 7a can counteract that the overlapping corner element 8 can be moved in the longitudinal direction of the elongated part 12 of said corner element 8.

It is noted that the invention also relates to a kit of parts for forming a frame 2 of jigsaw puzzle display system 1. Said kit may for instance comprise one or more of the above described components and parts. For example, the kit may comprise at least a plurality of frame elements 7, 8 for forming a substantially rectangular frame 2 having four side edges 3-6, wherein at least two opposite side edges 3, 4 comprise multiple frame elements at least partly, at least two of said multiple frame elements are arranged for overlapping each other at least partly, wherein the length L of each of said two side edges 3, 4 is adjustable by adjusting a mutual overlap between said at least two elements. Additionally, the kit may comprise other parts, for example one or more, preferably two suspension element 24.

Further, the kit may comprise double-sided adhesive stickers or tape for adhering frame elements to the puzzle glued together and/or for attaching an overlapping frame element to a respective other frame element.

The invention also relates to a method for framing a jig-saw puzzle 9. The method comprises a step of adhering at least one first frame element 7 to a jigsaw puzzle 9 glued together. It is noted that the method may also comprise a step of gluing said puzzle 9 together, wherein said step of gluing the puzzle together may precede said adhering of the at least one first frame element. Said step of gluing the puzzle together can comprise putting glue, preferably special puzzle glue, onto a surface, preferably a top surface or so-called front side, of the puzzle. By doing so, the glue may become distributed over the puzzle and portions of the glue can end up in cracks between interlocking puzzle pieces of the jigsaw puzzle, which portions can - after setting of the glue - enable that adjacent puzzle pieces are glued together and that therefore the jigsaw puzzle is glued together.

The method further comprises attaching a second frame element 8 to the first frame element 7, wherein said second frame element 8 overlaps the first frame element 7 at least partly. Said second element 8, e.g. a corner element, can be adhered to the first element 7, for instance by using double-sided adhesive stickers or tape.

Further, the method may comprise gluing the at least one first frame element 7 to a front side 37 of the jigsaw puzzle 9 glued together. Advantageously, the first or elongated elements 7 of a single frame edge 3-6 can be attached to each other before adhering them onto the top surface 37 of the puzzle 9. However, it also possible to adhere a first one of the first or elongated elements 7 onto the puzzle and subsequently attach a second first element 7 to the first first element 7 already adhered to the puzzle, wherein the second first element 7 can preferably be provided with an adhesive means such as double-sided tape before attaching it to the first first element, such that said second first element can be adhered to the puzzle substantially while being attached to said first first element.

The invention is not restricted to the embodiments described above. It will be understood that many variants are possible.

For example, a system, frame and/or a kit of parts may comprise a certain number of elements. For example a system, kit and/or frame can comprise four corners elements and/or at least four, preferably at least eight, for instance about twelve, fourteen, or sixteen elongated elements. Advantageously, all elongated elements can have the same length, such that they can be interchangeable.

As another example, the lengths of the elongated elements, the cavities in the corner elements, and/or the elongated parts of the corner elements can be chosen such that different frames can be made, preferably covering a continuous range of different widths and/or covering a continuous range of different heights of puzzles. For example, the length of an

elongated frame element can be between about 50 and 250 mm, preferably between 100 and 200 mm, more preferably about 130, 140, or 150 mm.

Additionally or alternatively, the length of a cavity and/or the length of an elongated part 12, 13 of a corner element 8 can be between about 30 and 150 mm, preferably between 50 and 120 mm, especially about 75, 85, or 100 mm.

These and other embodiments will be apparent to the person skilled in the art and are considered to lie within the scope of the invention as formulated in the following claims.