The present invention relates to a blank for a high- stacking strength box made of foldable sheet material, and to a part- erected and erected box made from said blank.

Background of the invention

In the field of packaging, transport and storage, one of the most important aspects is the capability to stack packaging boxes one on top of the other in order to eliminate the need for shelves and similar structures and to allow the same storage space to be used by different -size packaging boxes. Therefore, a key issue to consider in stacking is an adequate vertical strength of the packaging boxes because it

determines the number of boxes that can be stacked on top of each other without the lower-lying boxes being crushed or damaged. This is even more important if the contents of the packaging box are delicate items because the box must ensure that no forces acting upon it due to stacking are transmitted onto the delicate items.

Hitherto, solutions to increasing the vertical strength of packaging boxes generally included either using a

particularly heavy grade of cardboard, or to use various reinforcing structures applied to a standard foldable box. For example, WO 2010/079124 Al describes such a standard foldable box with a reinforcing lining on the inside of the box. The lining is made from a separate blank and is fixed to the blank of the external box before the box is erected.

Producing the box in an automated manner thus requires the use of two blanks and two different cutting and folding machines, together with a device for fixing the lining to the outer box. This approach also requires a lot of raw material and additional manufacturing time so that, ultimately, such a reinforced box is rather costly. A different approach is used in US 2,594,156, in which a single blank is folded to obtain a box with triple thickness sidewalls. In this case, although a single blank is used, a large amount of cardboard material has to go into the blank in order to produce, ultimately, a relatively small box. A similar approach is described in WO 2006/075935 Al . This document relates to an open box container with short sides that include an inner and outer part folded onto each other to provide a double layer sidewall to the open box. Again, additional material is required to obtain a box having increased vertical stacking strength, together with

additional requirements at the manufacturing line. Also, this box is open-topped and cannot provide flaps that form a top closure .

Finally, it is known from EP 1 657 169 Bl to avoid stacking strength problems in boxes which contain pre-cut weakening lines or rupture lines in their sidewalls. To that end, the blank ends are overlapped in the middle of a vertical side panel of the box rather than at the corner so that a double material layer is formed at the overlap which gives added strength to compensate for the mentioned weakening or rupture lines in the box. However, the double material layer merely compensates for the weakening caused by the lines of rupture.

Further, the mentioned state-of-the art blanks largely have complex shapes that render them difficult to transport, either in empty form from manufacturing or in a flat form to be erected just before filling.

Summary of the invention

In order to address the above problems, it is an object of the present invention to increase the vertical compression strength of the box without having to use additional

material, either by having to resort to larger blanks or to a heavier grade of cardboard. Further, it is an object to provide a blank for a high-stacking strength box which allows to meet similar performance targets as currently known boxes of high-stacking strength, but with a lower grade of

cardboard, leading to a reduction of the total amount of fibers, and less material consumption. This object is achieved by means of a blank for a high- stacking strength box as defined in claim 1, and a box as defined in claim 14.

Preferred and optional embodiments are defined in the

dependent claims.

According to the invention, there is provided a blank for a high-stacking strength box made of foldable sheet material, comprising first sidewalls, each having at least a bottom or top closure flap hingedly connected thereto along a first flap fold line, and second sidewalls alternately arranged with the first sidewalls and each being hingedly connected along wall fold lines to the first sidewalls, wherein the second sidewalls each have at least one second-side flap hingedly connected thereto along a second flap fold line, characterized in that the at least one second- side flap of each second sidewall comprises at least two flap portions separated from each other by a cut starting at the second flap fold line, and being hingedly connected to the second sidewall substantially along a part or all of the length of the second flap fold line so as to be individually foldable towards and/or onto the second sidewall. Correspondingly, three flap portions will be separated from each other by two cuts, and so on. It is to be understood that the cuts are not restricted either in shape, length or number as long as they separate the second-side flap into flap portions so as to be foldable towards and/or onto the second sidewall. In this sense, the expression "the cut starting at the second flap fold line" does not exclude one or more further cuts to be present on the second-side flap. The further cut(s) may also start at the same point as said cut but extend in other directions than said cut. Also, the cut that starts at the second fold line may, but does not have to, extend to some extent along the second fold line.

In the case the box is an "open" box, i.e. it is not

envisioned to provide top closure flaps, the second sidewalls may each have only one second-side flap (on the same side of the sidewalls) hingedly connected thereto along a second flap fold line and forming, together with e.g. the bottom closure flaps, the base of the box, whereas for closable boxes that are provided with top closure flaps in addition to the bottom ones, the second sidewalls will each be provided with two second-side flaps, one corresponding to the top and one to the bottom of the box.

By the above-described configuration, one of the flap

portions can be folded in such manner onto the second

sidewall that the box, in its erected configuration, will be vertically reinforced at both second sidewalls without additional material outlay. Moreover, while one flap portion of a second-side flap will serve to reinforce the second sidewall, the other flap portion is still available for support of the bottom and top closure flaps of the first sidewalls, thus allowing the box to be conventionally handled and closed. In other words, the box compression strength is increased by moving (through folding) parts of sheet material from the second- side flaps onto the side panels or walls. As a result, the side panels obtain an extra board thickness which gives increased compression strength. It is to be understood that said other flap portion might either lie below or above the closure flaps, i.e. be arranged inside or outside the box, respectively.

The foldable sheet material may be any type of paper or fibre based material, for example corrugated (flute type) liners, solid board and the like. Also, foldable sheet materials based on plastics such as plasticised laminates, correx or the like are considered. For convenience of description, the sidewalls may be

described as being oriented vertically in the finished box, and the closure flaps as being top and bottom closure flaps. Of course, it is to be understood that such orientation of the box is only an example, and that other orientations are equally possible as the box may be turned or laid on its side. However, the orientation of the box will always be such that the load applied to the box by stacking is directed substantially in a direction of folding the flap portions onto the sidewalls, i.e. mostly perpendicular to the second fold line.

Preferably, one flap portion is folded and fixed onto the second sidewall, and is most preferably folded and glued onto the second sidewall. By fixing and preferably gluing the flap portion onto the second sidewall additional rigidity is provided to the box, thereby additionally increasing vertical stacking strength, because now the flap portion and the second sidewall can no longer move with respect to each other, which otherwise might have caused kinks and,

therefore, reduced the stacking strength. It is to be

understood that other types of fixing are equally envisioned, such as by stapling or, if allowed by the sheet material, by welding. The flap portions can be folded and fixed (glued} to the inside or to the outside of the second side wall, according to requirements.

In a preferred embodiment, at least one flap portion is defined by at least one substantially U- or V-shaped cut which starts and ends at the second flap fold line. In other words, the cut separating the at least two flap portions starts at the second flap fold line, runs in the mentioned shape and ends again at the second flap fold line. This configuration allows on the one hand to obtain the

individually foldable flap portion that creates, when the box is erected, an additional reinforcing layer at the second sidewalls. On the other hand, it allows to maintain at least another flap portion for the usual closure function because it extends interruptedly from one side of the second-side flap to the other and can thus provide an abutment surface for the top and bottom closure flaps that extends right to the first sidewalls when the box is erected.

In an alternative embodiment, the at least one second-side flap of each sidewall comprises two lateral flap portions and a middle flap portion. In such case, there are two cuts starting at the second flap fold line and running to the opposite edge of the flap to separate the two lateral flap portions from the middle flap portion. This configuration has the advantage that it requires only minimum modification on the process line of the blank, but allows to obtain a high vertical compression strength because the whole length (from the fold line to the opposite free edge) of the middle flap portion is available for reinforcement. Further, it is possible to choose between folding and fixing (both) the lateral flap portions onto the second sidewalls to further increase vertical stacking strength, and folding and fixing the middle flap portion that still provides increased

vertical stacking strength and, in addition, allows a large abutment surface for the closure flaps formed by the two lateral flap portions.

In a further embodiment, the one or more cuts define

substantially rectangular flap portions. Again, this way of subdividing and separating the flap portions can be

implemented on existing blank production lines.

Alternatively, it may also be preferred to have the one or more cuts define substantially triangular lateral flap portions. In this embodiment, the substantial triangular lateral flap portions allow to specifically reinforce the edge and corner portions of the second sidewalls while maintaining a large middle flap portion of substantially trapezoidal shape for closure purposes.

In another alternate embodiment, the blank has two cuts that are substant ally L-shaped and mirror-inverted with respect to each other, with the cuts starting at the second flap fold line and ending at the respective lateral edge of the second- side flap. In this manner, the lateral flap portions may be folded onto the second sidewall to serve as reinforcement, while the middle flap portion of substantially T-shape is used as closure flap, for example. This configuration is particularly preferred for flap portions formed on the long sidewalls (also called main panels) of the blank/box. It is noted that the term "lateral edge" as used herein refers to the edge of the flap or flap portion that is connected at one end to the sidewall the flap or flap portion belongs to. In contrast, the term "free edge" as used herein is the edge opposite to the fold line of the flap or flap portion.

In a particularly preferred embodiment, the at least one second-side flap has two cuts that are substantially L-shaped and mirror- inverted with respect to each other, and which separate three flap portions, with the cuts starting at the second flap fold line, running initially along the second flap fold line and ending at the free edge of the second-side flap, and wherein the lateral flap portions each comprise a third flap fold line which runs from the respective cut's starting point on the second flap fold line to the free edge of the respective lateral flap portion. This advantageous configuration allows to fold the part of the lateral flap portions adjacent to the middle flap portion along the third flap fold line onto the "outer" part of the lateral flap portions, that is the part of the lateral flap portion that is adjacent or closest to the corner of the erected box.

These "doubled-up" lateral flap portions are then foldable, as before, onto the second sidewall to provide three layers of sheet material in correspondence with the corners of the box, thereby further increasing the vertical compression strength at the critical load points of stacked boxes. It is also observed that in this context, applicable also to the preceding embodiment, the term "mirror-inverted" is to be understood as "substantially mirror-symmetric" in the sense that the cut on one side and the cut on the opposed side of the second-side flap create substantially equally or

similarly-shaped flap portions.

In certain embodiments it is preferred that the length of the flap portions measured from the second flap fold line is about half the length of the second sidewalls measured between the second flap fold lines. In providing flap

portions measuring half the length on both (top and bottom) second-side flaps of each second sidewall it is possible to obtain a reinforcement along the whole length of the second sidewall because the flap portions folded onto the second sidewall from top and bottom will meet in the middle of the second sidewall and be able to abut each other thereby providing reinforcement along the entire length of the second sidewall .

In an alternate embodiment, the length of the flap portions measured from the second flap fold line is about the length of the second sidewalls measured between the second flap fold lines. This embodiment particularly applies to blanks in which only one second-side flap on each second sidewall is subdivided in flap portions, and provides thus a flap portion foldable onto the second sidewall that covers the entire length of the second sidewall on its own and thus provides an uninterrupted reinforcement at the given second sidewall.

In a particularly preferred embodiment, the free opposed edges of the first and second sidewalls are fixed to each other in an overlapping manner so as to form a tubular body when the blank is partially erected. The advantage of fixing the first and second sidewalls in such overlapping manner, for example by providing on one of the opposed edges a narrow flap for gluing, is that the tubular body (pre™ folded and glued) can be provided to the customer in its still collapsed flat form which is very quickly erected (no more gluing required) and filled at the packaging- site of the customer. Moreover, in its collapsed form, the tubular body comprises in general two regions in which three layers of sheet material are present, i.e. the second sidewall, the folded flap portion and the overlying sidewall, thus giving stacking strength also to stacked piles of collapsed part-erected blanks (tubular bodies) .

Finally, in some embodiments it is preferred that the first sidewalls are wider than the second sidewalls, measured between the wall fold lines. In other words, this allows for the foldable flap portions to be situated at the short second sidewalls where they can provide a larger increase in vertical stacking strength of the wall.

In the above summary of the invention, the at least one flap portion is foldable or folded onto the second sidewall. As mentioned, this includes both folding towards the outside and the inside of the second sidewall, although it is preferred to fold towards the inside to provide a smooth outer box surface. Also, carrying holes may be provided on either first or second sidewalls of the blanks. To that end, if a carrying hole in the finished box coincides at the sidewall with a reinforcement flap portion, said flap portion might have a partial cut to provide in a known manner a foldable handle flap.

Further, in the present invention defined above, the terms "lateral" and "width" refer to a direction on the blank running from one flap to the adjacent flap, or from one

(first or second) sidewall to the adjacent (second or first) sidewall, whereas ^xx length" is to be measured in a direction from flap to associated sidewall, i.e. substantially perpendicular to the "lateral" direction. These relations apply correspondingly to the raised box.

Brief description of the drawings

In the following, preferred embodiments of the invention are described, in exemplary form, by referring to the enclosed drawings, in which:

Figure 1 shows a perspective view of a blank according to a first embodiment of the invention, with Figure la) showing the cut blank, Figure lb) showing the cut blank with flap portions folded and glued to the second sidewalls, and Figure lc) showing the tubular body (pre-folded and glued blank) based on the blank of Figures la) and b) , in its collapsed state

Figure 2 shows a perspective view of a part -erected tubular body made from the blank of Figure 1,

Figure 3 shows a perspective view from the inside of a finished box made from the blank of Figure la) ,

Figure 4 shows a perspective view from the inside of an alternative box made from the blank of Figure la) ,

Figure 5 shows a perspective view from the inside of yet another alternative box made from a variant similar to the blank of Figure la) ,

Figure 6 shows an alternative embodiment of a blank of the present invention,

Figure 7 shows a perspective view of a box erected from the blank of Figure 6, Figure 8 shows a perspective view from the inside of the box of Figure 7,

Figure 9 shows a perspective view from the inside of a box based on an alternative embodiment to the blank of Figure 6,

Figure 10 shows a further alternative embodiment of a blank of the invention,

Figure 11 shows a perspective view of the box made form the blank of Figure 10,

Figure 12 shows a further embodiment of the blank of the invention,

Figure 13 shows a perspective view of an open (Figure 13a) and closed (Figure 13b) box made from the blank of Figure 12,

Figure 14 shows a yet further embodiment of the blank of the invention,

Figure 15 shows a perspective view of an open box made from the blank of Figure 14, that has gone through the phases of Figures 16a to 16e and was erected from the flat tubular body of Figure 16e, and

Figures 16a to 16e show perspective views of the blank of Figure 14, with Figure 16a showing the cut blank, Figure 16b showing the cut blank with the inner flap sub-portions folded over and glued to the outer flap sub-portion, Figure 16c showing the next phase in which the "doubled-up" flap

portions are folded onto the second sidewalls, Figure 16d showing the "doubled-up" flap portions glued to the second sidewalls, and Figure 16e) showing the finished tubular body (pre-folded and glued blank) based on the blank of Figure 14.

Detailed description of preferred embodiments Figure la shows a perspective view of a cut blank of a first embodiment of the present invention. The blank 1, which is obtained by cutting a rectangular board of corrugated

cardboard, for example, comprises a pair of first sidewalls 2, 4 alternately arranged with second sidewalls 3, 5. The first sidewalls 2, 4 each have a bottom and top closure flap 6, 8 that are connected to the first sidewalls 2, 4 along first flap fold lines 10, 12. The second sidewalls 3, 5 are connected to the first sidewalls 2, 4 along wall fold lines 14, and the free edge (opposite to the edge with the wall fold line) of one of the first sidewalls 4 comprises a narrow flap 16 for gluing the opposed edges of the blank 1 together. The second sidewalls 3, 5 also each have two second-side flaps 7, 9 that are connected to the second sidewalls 3, 5 along second flap fold lines 11, 13. The second-side flaps 7, 9 comprise two lateral flap portions 71, 91, and a middle flap portion 7m, 9m, with the flap portions 71, 7m, 91, 9m being separated from each other by a cut 15 that starts at the second flap fold line 11, 13 and runs to the free edge of the second-side flap 7, 9 opposite to the second flap fold line 11, 13. The flap portions remain hingedly connected to the second sidewall 3,5 substantially along the length of the second flap fold line 11, 13 and one of them, the middle flap portions 7m, 9m can thus be folded towards and onto the second sidewall 3,5, as indicated by the arrows in Figure la) .

In a typical manufacturing process of the blank of Figure 1, which employs basically the same production line and material area as used for standard RSC (Regular Slotted Container) FEFCO 0201 boxes, the blank is first produced by

appropriately cutting the uncut rectangular blank (for example made of cardboard) so as to obtain the blank as shown in Figure la) . Subsequently, as shown in Figure lb) , the middle flap portions 7m, 9m are folded over onto the second sidewalls 3,5 and glued to it so as to form a permanent reinforcement of the second sidewall in a vertical direction (see circles in Figure lb) . In the next processing step, the results of which are illustrated in Figure lc) , the blank 1 is formed into a yet collapsed tubular body 1' by gluing the narrow connecting flap 16 at one of the first sidewalls 4 to the opposite edge of the blank at the second sidewall 3. It is noted that the process to fold and glue the flaps and panels of the box may be performed both inline and on a separated folder/gluer station. It is also thinkable to glue the second-side flaps only at the customer site before filling the cartons.

The erected tubular body 1' ' is shown in Figure 2. As can be observed, the tubular body 1' ' is reinforced where the middle flap portions 7m, 9m have been folded over and glued onto the second sidewalls 3, 5. Figure 3 shows a perspective view from the inside of the finished box, obtained by closing the top and bottom flaps 6, 8 and abutting/overlying them onto the lateral flap portions 71, 91. It can be seen from the figure that the middle flap portions 7m, 9m of both second-side flaps 7, 9 are folded towards and onto the second sidewall 3 and glued therewith (indicated by the letter "F" for

"fixed"). The remaining two lateral flap portions 71, 91 serve as standard side flaps on which the top and bottom closure flaps 6, 8 of the first sidewalls 2,4 come to rest and may, preferably, be glued for closure.

Figure 4 shows a second embodiment of a box made from the blank 1 of Figure la) . Here, not the middle flap portion 7m, 9m is folded over and glued onto the second sidewall, but the two lateral flap portions 71, 91 of each flap 7, 9 are folded over onto the second sidewalls 3,5 and glued thereto. This is particularly advantageous if the edge or corner regions are to be reinforced, too.

Figure 5 shows yet another embodiment of the box. This box is made from a blank that is similar to blank 1 as shown in figure la) . In this case, the cuts 15 are not perpendicular to the second flap fold lines 11, 13 but run from a point on the fold line towards the near lateral edge of the second- side flaps 7, 9. Thus, the lateral flap portions 71, 91 become triangular, and the middle flap portions 7m, 9m become trapezoidal . This configuration reinforces the box only at the corners, but due to having the trapezoidal middle flap portions 7, 9m leaves a large abutment surface for the top and bottom closure flaps 6, 8.

Figure 6 shows a blank 100 according to a further preferred embodiment of the present invention. Here, the blank 100 has substantially the same outline as the blank 1 of Figure 1 (although the narrow flap 16 is now at the free edge of the second sidewall 3), but the second-side flaps 7, 9 of each second sidewall 3, 5 now comprise two flap portions 7i, 7o; 9i, 9o only, in which one flap portion 7i, 9i is separated from the other 7o, 9o by one substantially U-shaped cut 115, both ends of which cut start at the second flap fold line 11, 13. Thus, a large or outer flap portion 7o, 9o is created at each second-side flap 7, 9, which flap portions 7o, 9o are foldable towards and onto the second sidewall 3, 5. The result is shown in Figure 7. As can be seen, the length of the large flap portions 7o, 9o, measured from the second flap fold lines 11, 13 to the opposite edge, is about half the length of the second sidewall 3, 5 (measured between second flap fold lines 11, 13 so that, when the large flap portions 7o, 9o of each second-side flap 7, 9 are folded and glued onto the second sidewall 3, 5, they substantially abut each other along their free edge, thus creating an almost complete reinforcing layer on the second sidewall. The small or inner flap portions 7i, 9i remaining in the middle at the second flap fold line 11, 13 merely serve as abutment surface when closing the top and bottom closure flaps 6, 8 to avoid the top and bottom closure flaps from bending through to the inside of the box. An alternative embodiment of the blank or the box of Figures 6 and 7 is shown in Figure 8, which is a perspective view from the inside of such a box. Again, the each second-side flap 7, 9 comprises a large and small flap portion 7o, 9o; 7i, 9i obtained by a square U-shaped cut. Here, the large flap 7o, 9o is conventionally used as abutment closure flap for the top and bottom closure flaps 6, 8 of the first sidewalls 2, 4. The small flap portion 7i, 9i cut out in the middle of the second-side flap 7, 9 is, in contrast to Figure 7, folded towards and glued onto the second sidewall 3, 5 to reinforce it in the center area. A still further embodiment thereof is shown in Figure 9, in which the cut is still substantially U- or V-shaped, now in the form of a chevron.

Another alternative embodiment of the blank of the invention is shown in Figures 10 and 11. Figure 10 shows a top view of the blank 200 in which each second-side flap is separated into three flap portions by two substantially L-shaped cuts 215 which each start at the second flap fold line 11, 13 and end at the lateral edge of the second-side flap 7, 9. This creates two lateral flap portions 71, 91 that, in the shown embodiment, have a length about equal to half the length of the second sidewall 3, 5. When folded over (see arrows in Figure 10) , the lateral flap portions 71 from the upper second- side flap 7 abut the lateral flap portion 91 from the lower second- side flap 9, and being fixed (preferably glued) to the second sidewalls 3, 5, provide superior vertical stacking strength to the finished box (Figure 11a) . The substantially T-shaped middle flap portions 7m, 9m serve as abutment surface for the closure of the top and bottom closure flaps 6, 8, and their length, measured from the second flap fold line 11, 13, is about half the width, measured between wall fold lines 14, of the first sidewall 2, 4. Thus, when closing the box, the corresponding middle flap portions 7m, 9m of opposite second sidewalls will abut each other along their free end. In this instance, the

substantially T-shaped middle flap portions 7m, 9m abut the closure flaps 6, 8 so as to lie on the outside of the box, as is seen in figure lib) . In this configuration, the T-shape of the middle flap portions 7m, 9m and their abutment along their free edge allow the application of packaging tape along the abutment line of the two Ts, thereby conventionally closing and securing the box. Here, it is preferred that the lateral flap portions 71, 91 and the T-shaped middle flap portion 7m, 9m are formed on second sidewalls 3, 5 that are wider than the first sidewalls 2, 4.

Figures 12 and 13 show yet another embodiment of a blank according to the present invention. In this blank 300, the second sidewalls 3, 5 are again wider than the first

sidewalls 2, 4, and three flap portions are formed by two substantially U-shaped (rectangular U-shaped) cuts 315 both ends of which start at the second flap fold line 11, 13. The two U-shaped cuts 315 are arranged symmetrical with respect to the center and lateral sides of the flap 7, 9. In this case, there are two formed flap portions 7i, 9i on either side of each second sidewall 3, 5, which are again folded over and glued onto the second sidewall 3, 5, with the substantially square M-shaped other flap portion 7o, 9o serving as abutment surface for the top and bottom closure flaps 6, 8 of the first sidewalls 2, 4 (see figures 13a} and b) ) .

Figures 14 and 15 respectively show a further, particularly preferred embodiment of the blank of invention and the box made from it, while figures 16a to 16e show the sequence of steps from the cut blank to the glued and folded, but not yet fully erected tubular body which is in a form ready to be shipped to the customer. As can be seen from Figure 14, the second- side flaps 7 and 9 comprise each two lateral flap portions 71, 91, and a middle flap portion 7m, 9m. The two cuts defining the flap portions are, like in the embodiment of Figures 10 and 11, L~shaped and performed so as to be mirror-symmetric to each other. But in contrast to the embodiment of Figures 10 and 11 the cuts 415 that define the flap portions start at the second flap fold line 11, 13 and initially run along it, before turning 90° and running toward the free edge of the second-side flaps 7, 9, where the cuts 415 end. By this arrangement, the lateral flap portions 71, 91 remain hingedly connected to the second side wall 3, 5 only along a length of the second flap fold line 11, 13 that is shorter than the width (from lateral edge to lateral edge) of the lateral flap portion 71, 91, by the same length of the cut portion that runs along the second flap fold line 11, 13, or a little shorter still.

Starting at where the cut 415 begins on the second flap fold line 11, 13, there is a further fold line 425 on the lateral flap portions 71, 91, which directly runs towards the free edge of the lateral flap portion and sub-divides the lateral flap portion 71, 91 into two flap sub-portions 71' and 71'', 91' and 91'', with the laterally outer flap sub-portions 71', 91' connected via the hinge line 11, 13, and the laterally inner flap sub-portions 71'', 91'' not being directly

connected to the second-side wall 3, 5 but only indirectly via the further flap fold line 425 and the laterally outer flap sub-portion 71', 91'. Thus, the laterally inner flap sub-portions 71'', 91'' are foldable onto the laterally outer flap sub-portions 71', 91' so as to "double them up".

In the method of folding the blank to generate a flat tubular structure (erect the box) , the laterally inner flap sub- portions 71'', 91'' are thus first folded (Fig. 16a) onto the laterally outer flap sub-portions 71', 91' along the further fold line 425, and glued thereto. Here, as in the embodiments above, any type of glue suitable for the sheet material may be used, for example hot -melt glue or polyvinyl acetate glue. By thus folding and gluing, the lateral flap portions 71, 91 now have a double-layer thickness and strength {Fig. 16b) . In the next step, the doubled-up lateral flap portions 71, 91 are folded towards and onto the second sidewalls 3, 5 of the blank 400 (Fig. 16c) , and are glued to them like in the preceding embodiments. In this manner, a triple-layer

thickness is generated at the corners and edges of the second sidewalls 3, 5 (Fig. 16d) . In the step of making the tubular structure, the second sidewall 3 is connected to the first sidewall 4 by gluing the narrow connecting flap 16 thereto, thus forming the tubular structure 400' {Fig. 16e) . The triple layer thickness of the sheet material is indicated by the hatched area 17 next to the edges of the second sidewall 3.

The flat tubular structure 400' shown in Figure 16e, which due to its flatness can itself be stacked in a space-saving manner, is now ready to be shipped to the customer who, in turn, erects it to give the box shown in Figure 15. By the triple layer thickness of sheet material, a very strong reinforcement to the box is provided at the crucial corner regions where the lateral edges of the sidewalls meet, thereby greatly increasing crushing strength as compared to prior art boxes .

To assess the increase in vertical stacking strength of the boxes made from the blanks described above, the so-called box compression test (BCT) has been employed. To that end, finished boxes were produced from the above-described blanks and conditioned, without content, according to ISO 187, i.e. first for at least 24 hours at 30% relative humidity and then for at least 24 hours at 50% relative humidity, both at a constant temperature of 23 °C. The BCT itself is measured according to ISO 12048, that means the sample is compressed between 2 parallel plates, oversized with respect to the box, at a rate of 10 mm/min. The BCT value is the maximum force at collapse/break .

The box compression test (BCT) performed on the boxes

employed a standard load-registering cell MTS 4 L and

resulted in BCT values for the box that were larger by up to 30% compared to the BCT performed on a comparative example of an RSC 0201 box.

In summary, all of the above described embodiments manage to provide a blank for a high- stacking strength box made of foldable sheet material, as well as the box made therefrom, which achieves a superior vertical stacking strength as evidenced by the box compression test results shown in precedence. In particular, these excellent BCT results are obtained starting from a standard RSC0201 blank that is configured according to the blank of the present invention. No additional material in terms of size and paper grade is required, and blanks, part-raised tubular bodies and boxes based thereupon can be obtained with minimal intervention at the manufacturing lines, thereby permitting delivery of blanks or partially erected boxes of high stacking strength to customers at very little additional costs.