Paper based sheet

Abstract

A paper based sheet having an area comprising a plurality of displaced regions, each being either elevated or depressed relative to the median plane of the sheet thus defining a network of elevated an

Description

Technical Field

[0001] The present disclosure relates to a paper-based sheet. Aspects of the invention relate to a paper-based sheet, an item comprising the paper-based sheet, and a method of forming a paper-based sheet. Background

[0002] In the field of logistics and packaging, the use of paper-based materials for shipping bags and mailers has been a longstanding practice due to their costeffectiveness and relative strength. These shipping bags are typically constructed from corrugated material, which comprises several layers of paper including a fluted layer that is key to the structural integrity of the packaging. The flutes within the corrugated material serve critical functions: they act as a cushion for the contents and impart rigidity to prevent crushing. Additionally, the layers of linerboard on either side of the flutes offer a smooth surface for printing and further structural support.

[0003] Despite these advantageous properties, the traditional paper-based shipping bags and mailers have shortcomings that have become increasingly evident with the rise in e-commerce and the need to transport a wide variety of item shapes and sizes. The rigidity of the fluted structure, while protective, does not allow for the accommodation of irregularly shaped objects without significant compromise to the space efficiency and security of the packaging.

[0004] As a result, businesses and consumers can choose to use oversized packaging to accommodate these items, which is economically and environmentally inefficient and can increase the carbon footprint due to the extra weight and volume during transport. Further, items that do not conform to the standard shapes for which these mailers are designed may shift during transit, leading to potential damage from impact and pressure. The industry standard has been to fill these voids with additional dunnage materials like air pillows or paper fill, which increases waste and does not always provide adequate protection.

[0005] It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. Summary of Invention

[0006] Aspects and embodiments of the invention provide a paper-based sheet, an item comprising the paper-based sheet and a method of forming a paper based sheet as claimed in the appended claims

[0007] According to an aspect of the present invention, there is provided a paper-based sheet. The paper-based sheet has an area comprising a plurality of displaced regions. Each displaced region is either elevated or depressed relative to a median plane of the sheet, thus defining a network of elevated and / or depressed regions over the area. The paper-based sheet is thereby rendered conformable under applied stress.

[0008] Accordingly, the invention results in a material where the displaced regions have different material properties to transitions or connections located between the displaced regions. Specifically, the displaced regions are more rigid and less flexible than the transitions between the displaced regions. This is because vertices are created in the surface of the sheet at the transitions between the displaced regions where the surface changes direction. These regions of reduced radii cause a localised increase in stress intensity at the transitions between the displaced regions which act as natural flex points where the sheet can bend more easily. Since the sheet can flex at these points, additional degrees of freedom are introduced into the sheet, allowing the displaced regions to move more independently of each other. The more flexible transition regions also redistribute stress across the whole sheet, thus avoiding stress build-up in only a part of the sheet.

[0009] Crucially, the displacement of regions of material away from the median plane according to the invention creates this network of varying materials properties without creasing the sheet. Creasing herein is defined as a process which results in permanent deformation of a material by a localised folding along a specific line or axis, thereby reducing thickness along the axis and creating a distinct, linear indentation or ridge where the sheet's fibres, grains, or structural elements have been rearranged or compacted.

[0010] When a material undergoes bending along a specific line, as with creasing, the outer side of this bend stretches, while the inner side compresses. At the crease line, the sheet is subjected to a force acting perpendicular (normal) to its surface which compresses the sheet, causing the fibres or structural elements to compact and form a permanent indentation. Since the force is applied perpendicular to the surface at a specific line, the force is inherently localised. Accordingly, the deformation is concentrated along a very narrow region along the fold line, creating a sharp transition between the deformed and undeformed areas.

[0011] In paper-based materials, which are composed of a network of cellulose fibres, the extreme deformation at the crease line has a drastic impact on structural integrity. In particular, the creasing process causes the fibres to buckle and break apart in the compressed area. The intense pressure exerted on the crease line forces the fibres closer together, disrupting their original alignment and reducing the space between them. This compaction effectively weakens the bonds between the fibres, diminishing the sheet's ability to distribute stress. The extreme compression can also cause microfractures and fibre rupturing, particularly in thicker or more rigid paper materials like cardboard. This damage is not always visible to the naked eye but significantly affects the sheet's mechanical properties. The creased area becomes a point of weakness, making it more susceptible to further tearing or breaking under stress.

[0012] The drastic reduction in thickness at the crease line also inherently introduces weakness into the sheet. This is because the strength of a material in resisting bending or compression is partly determined by its cross-sectional area. When the thickness at the crease line is reduced, the cross-sectional area through which the sheet can distribute stress is also diminished. This reduced area means that the sheet can bear less force before failing and is also more susceptible to fatigue.

[0013] In contrast to this, the material according to an embodiment of the invention is formed in such a way that no force is applied perpendicular to the surface of the sheet. Instead, force is applied parallel to the surface of the sheet (ie. the sheet is sheared) to displace regions from the median plane. This has the effect of essentially stretching or elongating the sheet at the transitions between the displaced regions, rather than crushing it. Consequently, the force which is applied during the deformation is distributed over a larger volume of the sheet compared to the concentrated stress of a perpendicular force at a crease line.

[0014] It has been observed that the structural integrity of the sheet at the transition is maintained remarkably well. In particular, fracturing or "bursting" of the sheet is not seen. It is believed that the stretching of the sheet causes the sheet's fibres to be pulled apart from each other, but that the distribution of this pulling force is more uniform across the area where the force is applied, leading to less extreme deformation than with creasing. The sheet according to an embodiment of the invention also avoids the sharp transitions in thickness seen with creasing, thus preserving strength at the flex points and improving the overall resistance to fatigue.

[0015] Each displaced region may be either elevated or depressed relative to an adjacent displaced region, thus defining a network of elevated and / or depressed regions over the area.

[0016] The displacement of regions of material away from neighbouring regions creates this network of varying materials properties without creasing the sheet. Some regions are elevated relative to the median plane and some regions are depressed relative to the median plane. By applying force parallel to the surface of the sheet to displace neighbouring regions in opposite directions, the stretching of the sheet is further emphasised.

[0017] A transition region may be defined at a transition or connection between adjacent displaced regions. The transition region may comprise material which is stretched relative to a material at the displaced regions.

[0018] As the material at the transition region is stretched rather than crushed, its integrity is maintained.

[0019] The sheet may have a first surface and a second surface. At a transition or connection between adjacent displaced regions, a cross-section of the sheet may be defined by a plane connecting the first surface with the second surface along a shortest distance. Further, a surface normal of the first surface along this cross-section may be parallel to and displaced from a surface normal of the second surface along this crosssection.

[0020] The displacement of regions of material away from neighbouring regions under shear force according to the invention creates a structure in which the surface normals of the opposing surfaces at the vertices where those surfaces change direction are displaced or are not collinear. This is in contrast to a creased structure where the surface normals at each surface along the crease line are aligned or collinear. This is important because the perpendicular distance relative to the surface normal aligns with the direction in which the sheet experiences the most significant change in stress. According to bending mechanics, when a material is bent, one surface of the sheet will be placed in tension, while the opposing surface will be placed in compression. Between these surfaces, stress will typically vary linearly along the surface normal. In a creased arrangement, the sharp radius at the crease defines an area where compressive forces will concentrate when the sheet is bent along the crease. The surface normal on the inside of the crease (i.e., the surface in compression) therefore determines the direction along which the variation in stress will be greatest and hence the region which will experience maximum tension.

[0021] However, in the current arrangement, the displacement of the material and the associated non-coIlinear alignment of surface normals at the transition regions means that, when the sheet is subjected to a bending force, the stress distribution is altered compared to a creased structure. Like with the creased structure, the sharp radius at the transition regions defines the area where compressive force will concentrate under bending, however, the surface normal at this region of maximum compression no longer runs in a through-thickness direction but is instead at an oblique angle. This implies that the regions of maximum compressive stress and maximum tension are separated over a wider volume than with the creased structure, and hence that the bending stress is distributed over a wider volume of material, reducing the likelihood of material failure at a single, concentrated point, as is often the case in sharply creased structures.

[0022] Accordingly, the structure of the sheet of the invention achieves a balance between using stress concentration to create functional bending points, while also altering the pattern of stress distribution to mitigate the risk of material failure. While the displaced regions create points of sharp radius in the surface where stress is intentionally concentrated to create bending points, the non-coIlinear alignment of surface normals at the transition regions changes how the stress emanating from these points is spread through the material. Instead of a sharp, linear distribution of stress (as in a crease), the stress radiates more broadly, reducing the intensity of concentration at any single point.

[0023] The paper-based sheet may be corrugated paperboard comprising a plurality of elongated flutes extending across the paper-based sheet.

[0024] The invention is particularly advantageous for corrugated / fluted materials. In such materials, the fluting provides rigidity and strength as well as cushioning properties. This is because the arch-like structure allows for uniform stress distribution. When a compressive load is applied, this stress is evenly distributed throughout the structure, allowing the flute to maintain its shape and resist compression and buckling.

[0025] Once crushed, this uniformity is disrupted. Stress becomes concentrated at certain points, particularly where the flute is bent or creased. These stress concentrations are more likely to fail under load.

[0026] Since the invention involves a controlled stretching of material at the transitions between the displaced regions, as opposed to compression of material along a line, the fluting remains relatively intact and is not crushed. Although the fluting may be stretched such that, for instance, the curvature of the flutes may be reduced, the arched structure of the flutes is maintained. This allows the material to retain its beneficial properties in resisting compression and buckling.

[0027] In addition, the act of creasing a fluted material can lead to delamination between the fluted layer and the liners. In contrast, the inventors have observed that delamination does not occur in the sheet of the invention. Delamination further diminishes the structural integrity and load-bearing capacity of the sheet.

[0028] A transition region may be defined at a transition between adjacent displaced regions. An arched shape of the flutes may be maintained within the transition region.

[0029] Optionally, the fluted structure being maintained may refer to flutes in the transition region maintaining an arched shape. Optionally, the fluted structure being maintained may refer to flutes in the transition region being substantially uncrushed. That is, the flutes may maintain at least 60% of a height of the flutes in a flat sheet precursor from which the paper-based sheet is formed. Optionally, the flutes may maintain at least 70%, at least 80%, at least 90% or at least 98% of a height of the flutes in a flat sheet precursor from which the paper-based sheet is formed. Optionally, the height of the flutes may be substantially unchanged from a height of the flutes in a flat sheet precursor from which the paper-based sheet is formed. The height of the flutes may refer to a height of an arched cross-section defined by the flutes, as measured.

[0030] The network of displaced regions may form a tessellated pattern.

[0031] A tessellated pattern refers to a network of interconnected elements arranged in a geometric patter. The network is characterised by the alignment of these elements, forming a continuous and non-overlapping mosaic. The interconnectedness of the elements means that the transition regions between the displaced regions (where stress concentrates) can more effectively distribute stress across the whole network, thus acting to avoid stress concentrations when the sheet is deformed.

[0032] Tessellated patterns also allow for more predictable and controlled folding paths. This predictability comes from the geometric properties of the tessellated shapes, where the angles and lengths of the sides are consistent, leading to a more uniform transformation of the flat sheet into a 3D shape. Further, in tessellation, the angles around a vertex sum to 360 degrees, allowing the sheet to fold smoothly without excess material bunching up or creating voids. This property is important for adapting to irregular shapes, as it allows the sheet to 'mould' itself around the object.

[0033] In some embodiments, the tessellated pattern may be a polygonal tessellated pattern in which the elements making up the pattern are polygonal in shape, such as triangles, squares, hexagons, or other multi-sided figures. The polygons can be regular, where all sides and angles are equal, or irregular, with varying side lengths and angles.

[0034] Alternatively, the tessellated pattern may comprise elements that are not strictly polygonal. These may include curved shapes, irregular forms, or a mix of polygonal and non-polygonal elements.

[0035] The tessellated pattern may also be either periodic or aperiodic. In the periodic pattern the tessellation is repeated along the surface at regular intervals. In contrast, in embodiments comprising an aperiodic tessellated pattern, the tessellation does not follow a regular, repeating pattern. Instead, it may display a quasi-periodic or entirely random arrangement of elements.

[0036] The tessellated pattern may also be either heterogeneous or homogeneous. Heterogeneous tessellated patterns are characterised by a mix of different types of polygons or elements within the same tessellation. The polygons may vary in size, shape, or orientation. In contrast, homogeneous tessellated patterns involve tessellations where all elements are identical in shape and size, leading to a highly uniform structure.

[0037] One or more of the displaced regions may have a triangular shape.

[0038] In other embodiments, one or more of the displaced regions may have other shapes, for example the regions may be circular, arcuate, hexagonal, octagonal, square or rectangular.

[0039] Any of these shapes may be used to form a tessellated pattern. For instance, in some embodiments, the network of elevated and depressed regions may form a pattern of tessellated triangles. In other embodiments, the network of elevated and depressed regions may form a pattern of tessellated hexagons, squares or octagons. Where the network of elevated and depressed regions form a tessellated pattern, the displaced regions defining the tessellations may all have the same shape. For instance, all of the displaced regions may be one of triangular, hexagonal, square or octagonal). Alternatively, the sheet can comprise displaced regions having different shapes which are combined to form a tessellated pattern. For instance, there could be a combination of hexagonal, square and triangular displaced regions which are arranged to form a tessellated pattern.

[0040] The network of displaced regions may comprise a network of alternating elevated and depressed regions.

[0041] In a further aspect of the invention, an item is provided comprising the paperbased sheet of the previous aspect. The item may be a package, optionally a shipping bag or mailer. Alternatively, the item may be a point-of-sale item such as a display column or shelf-ready packaging.

[0042] Advantageously, the plurality of displaced regions may allow at least a portion of the package to conform to items at least partially enclosed by the package.

[0043] The package may have first and second panels formed from the paper-based sheet. The network of displaced regions may extend over a majority of both the front and rear panels.

[0044] In a further aspect of the invention a method of forming a paper-based sheet is provided. The method comprises the steps of providing a die comprising first and second parts, the first part comprising an array of raised elements and the second part comprising an array of recessed elements, wherein the raised elements of the first part are aligned with and configured to intermesh with the recessed elements of the second part when the first and second parts of the die are brought together, providing a paper substrate having first and second surface, arranging the paper substrate between the first and second parts of the die and bringing the first part of the die towards the second part of the die so that the first part of the die contacts the first surface of the paper substrate and the second part of the die contacts the second surface of the paper substrate, applying a force to the die to form a plurality of displaced regions in the substrate, each displaced region being either elevated or depressed relative to a median plane of the paper substrate, thus defining the paper sheet having a network of displaced regions over the sheet.

[0045] Each of the first and second parts of the die may comprise an array of raised elements separated by recessed elements. The raised elements of one part may be configured to intermesh with the recessed elements of the other part when the first and second parts of the die are brought together. When the force is applied to the die to form a plurality of displaced regions in the substrate, each displaced region may be either elevated or depressed relative to an adjacent displaced region, thus defining the paper sheet having a network of elevated and depressed regions over the sheet.

[0046] The step of applying force to the die to form the network of displaced regions over the substrate may causes the substrate to shear between adjacent intermeshing raised elements.

[0047] The step of applying force to the die to form the network of displaced regions over the substrate may cause the substrate to stretch between adjacent intermeshing raised elements.

[0048] The step of applying force to the die to form the network of displaced regions over the substrate may cause substantially no compression of the substrate between adjacent intermeshing raised elements.

[0049] The paper substrate may be corrugated paperboard comprising a plurality of elongated flutes extending across the substrate.

[0050] A transition region may be defined at a transition between adjacent displaced regions. Following the step of applying pressure to the die to form a network of displaced regions over the substrate, an arched shape of the flutes may be maintained in the transition region.

[0051] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. Brief Description of Drawings

[0052] One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0053] Figure 1 is a perspective view of a paper-based sheet according to the invention;

[0054] Figure 2 is an exploded perspective view of an arrangement of a tool plate, a die, a substrate and a platen during a first step in a method of forming a paper-based sheet according to the invention;

[0055] Figure 3 is an exploded perspective view of the arrangement during a second, subsequent step in the method;

[0056] Figure 4 is a cross-sectional view of the arrangement during the first step;

[0057] Figure 5 is an enlarged cross-sectional view of the circled portion A in figure 3; and

[0058] Figures 6 to 8 are enlarged cross-sectional views of the circled portion A of figure 3 at later stages during the method;

[0059] Figure 9 is a schematic cross-sectional view of the paper sheet of Figure 1; and

[0060] Figure 10 is a schematic cross-sectional view of a paper sheet not within the scope of the invention. Detailed Description

[0061] With reference to Figure 1, a paperboard sheet according to an embodiment of the present invention is indicated generally at 10. In this embodiment, the sheet 10 is formed from corrugated paperboard and includes a first surface 12 and an opposing second surface 14. In this embodiment, the first surface 12 is an upper surface and the second surface 14 is a lower surface. An area is defined having a plurality of displaced regions 16. A displaced region 16 is where material is displaced along a direction perpendicular to a median plane MP of the sheet. In Figure 1, the left side of the sheet 10 does not have any displaced regions 16 and so is an indication of the median plane MP. Each displaced region 16 is either elevated or depressed relative to the median plane MP. In this embodiment, each displaced region is either elevated or depressed relative to an adjacent displaced region 16. It will be appreciated, though, that in some embodiments, only elevated displaced regions could be provided, or only depressed regions. In some embodiments, the number of elevated displaced regions could be higher or lower than the number of depressed displaced regions.

[0062] In this embodiment, the displaced regions 16 alternate in being either elevated or depressed relative to the median plane of the sheet MP. In this embodiment, the displaced regions 16 are shaped as triangles, specifically equilateral triangles. The displaced regions 16 are congruent and are arranged to form a homogeneous tessellated pattern over the sheet 10. It will be appreciated, however, that the displaced regions 16 could be of any suitable shape. For example, the displaced regions 16 could be another type of polygon, or a more irregular shape such as a company logo.

[0063] Transition regions 18 are defined between adjacent displaced regions 16. The transition regions 18 define a change in direction in the first and second surfaces 12, 14 define an edge with a low radius of curvature. These regions of reduced radii cause a localised increase in stress intensity between the displaced regions 16 which act as natural flex points where the sheet 10 can bend more easily. Since the sheet 10 can flex at these points, additional degrees of freedom are introduced into the sheet 10, allowing the displaced regions 16 to move more independently of each other. In this way, a network of interconnected regions is created that move relative to each other. Unlike a solid sheet, this network can deform locally, allowing the sheet 10 to conform to complex surfaces; each shape in the pattern can move, rotate, or tilt relative to its neighbours. When a force is applied to this patterned sheet 10, the stress is distributed across the network of shapes. This distribution allows the sheet 10 to deform in a way that a solid, unpatterned sheet cannot, as the deformation can be localised to specific areas of the pattern.

[0064] In this embodiment, the arrangement of the displaced regions 16 as a tessellated pattern is particularly advantageous as the interconnectedness of the displaced regions 16 means that the transition regions 18 between the displaced regions 16 (where stress concentrates) can more effectively distribute stress across the whole network, thus acting to avoid stress concentrations when the sheet 10 is deformed.

[0065] Tessellated patterns also allow for more predictable and controlled folding paths. This predictability comes from the geometric properties of the tessellated shapes, where the angles and lengths of the sides are consistent, leading to a more uniform transformation of the sheet 10 into a 3D shape. Further, in tessellation, the angles around a vertex sum to 360 degrees, allowing the sheet to fold smoothly without excess material bunching up or creating voids.

[0066] The sheet 10 according to an embodiment of the invention is particularly useful to form an item that requires a certain level of flexibility or curvature. It is useful for these items to conform in some way, for example by being curveable. The item may be a package. In this application, the term package refers to a container that at least partially encloses or holds something within it. Such a package can be a container that fully encloses the contents such as a shipping bag, pouch, mailer, box or any other container suitable for enclosing and protecting items for transport or storage. Alternatively, the item may be a point-of-sale item such as a display column or shelf-ready packaging. Such an item may have no contents, such as the display column. Alternatively, such an item could at least partially enclose goods, such as a shelf-ready package or a carrier bag. When used to form the item, the conformable nature of the paperboard sheet is particularly advantageous for packaging a 3D object by adapting and conforming to the 3D shape of the object without damaging the sheet material.

[0067] Referring to figures 2 and 3, a method of forming the paperboard sheet 10 of figure 1 according to an embodiment of the invention will now be described. A flat sheet of corrugated paperboard including elongated flutes is used as a substrate 22. The substrate 22 is formed into the paperboard sheet 10 of Figure 1 with a stamping arrangement including a tool plate 24, a platen 26 and a die having a first part and a second part. In this embodiment, the first part is a stamp die part 28 and the second part is a webbing die part 30 aligned along a die axis D-D. The webbing die part 30 and the stamp die part 28 include an alternating array of congruent equilateral triangular elements 32, which define the raised surfaces of the die parts 28, 30, and triangular recesses 34. Together, the elements 32 and the recesses 34 form a tessellated pattern over the surface of the die parts 28, 30.

[0068] In this embodiment, the two die parts 28, 30 are configured as exact complements of each other, where each triangular element 32 on one die part matches precisely with a recess 34 on the other. Specifically, the webbing die part 30 and the stamp die part 28 are respectively affixed to the tool plate 24 and the platen 26 in such a way that, when the tool plate 24 and platen 26 are aligned along the die axis D-D, the recesses 34 on one die part align precisely with the raised triangular elements 32 on its counterpart. This matching ensures that, when the die parts 28, 30 are brought together, they interlock or fit together, with every feature on one die part filling or fitting into the space provided by the other, causing the substrate to conform to the shape of the recesses, as illustrated in figure 3. In other embodiments, it will be appreciated that only raised elements may be provided, if it is desired to form a paper sheet that only has elevated displaced regions 16 or only has depressed displaced regions 16, rather than a combination of both.

[0069] In this embodiment, the precise matching between the two die parts 28, 30 is achieved by cutting the die parts 28, 30 from the same sheet of material. The process begins with programming a cutting machine with a digital design of the tessellated pattern, where each triangular element 32 and its corresponding recess 34 are mapped out. Optionally, a high precision cutting technique can be used such as CNC (Computer Numerical Control) milling, laser cutting or waterjet cutting, which allow for extremely accurate and clean cuts. However, any suitable cutting technology may be used, for instance, manual milling.

[0070] The cutting process involves slicing through the sheet material following the designed pattern. Since the two die parts 28, 30 are exact complements of each other, the machine cuts along the borders of the triangular elements 32 and their recesses 34 simultaneously. This means that when one part of the die is being formed as a triangular element 32, the complementary part is created as a recess 34, and vice versa. The precision of the cutting technology ensures that the tolerance between the die halves is virtually zero, meaning that the fit between the two parts is tight and precise.

[0071] To form the material, the substrate 22 is arranged between the stamp die part 28 and the webbing die part 30 and force is applied to the tool plate 24 along the die axis D-D. When the die closes, the raised triangular elements 32 on one die part exert pressure onto the substrate 22, precisely driving the material into the corresponding recesses 34 on the other die part.

[0072] Figures 4 to 8 illustrate the change in the surface structure as the die surface is pressed into the substrate 22. Figure 5 illustrates the moment prior to the application of force along the die axis D-D. It can be seen that there is direct contact at the boundaries between the edges of the raised triangular elements 32 and the empty recesses 34. The geometry of the tessellated pattern means that there is no material directly opposing the raised triangular elements 32. Instead, they meet the edges of the empty recesses 34. To maintain equilibrium, the normal forces at the boundaries, which press the raised protrusions against the edges of the recesses 34, create resultant forces. These resultant forces, which arise from the contact between the features, are oriented parallel to the surface of the substrate 22. As a result, substrate material which is interposed between regions of the die parts at the interface between the triangular elements 32 and the recesses 34 is subject to a shear force. During the initial contact, these shear forces induce a torque or rotational force on the flutes which respond by bending and twisting elastically.

[0073] As the die continues to close and applies increasing pressure, this material reaches its yield point, where it begins to undergo plastic deformation and conform more permanently to the edges of the die's raised and recessed areas. At this point the cellulose fibres may begin to slide over each other, and the bonds between the fibres break to allow the fibres to realign. Once the die is fully closed, the material has been shaped to the die's profile. When the die opens, the material retains the imprinted shape due to the plastic deformation it has undergone, as illustrated by figure 8.

[0074] Figures 9 and 10 are schematic views of fluted paperboard sheet material. Each include first and second layers 12, 14 sandwiching a fluted layer 13.

[0075] Figure 9 shows a fluted paperboard sheet according to an embodiment of the invention. The sheet has adjacent displaced regions 16, divided by the transition region 18. As can be seen, the integrity of the fluted layer 13 is maintained in the transition region 18, which contributes to the overall strength of the sheet being maintained.

[0076] In contrast, Figure 10 shows a fluted paperboard sheet not within the scope of the current invention. A creased region 19 is shown. As can be seen, in the creased region 19, the fluted layer 13 is crushed and its integrity is not maintained, resulting in a weakened region.

[0077] Where the word ’or’ appears this is to be construed to mean ’and / or’. This is such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.

[0078] The invention has been described above with reference to one or more specific embodiments. However, it will be appreciated that various changes and modifications can be made without departing from the scope of the invention as defined in the claims.

[0079] For example, although the method is described in relation to forming a sheet of fluted paperboard, in other embodiments, another paper-based sheet material could be formed, for example a non-fluted sheet material. Further, as mentioned, the sheet material may have only depressed displaced regions or elevated displaced regions rather than a combination of both. The paper sheet may be used to form a package that conforms to a 3D object but may also be used to form a package that does not conform to a 3D object, such as a box or similar.

[0080] The appended claims set out particular combinations of features described above. However, the scope of the present disclosure is not limited to these particular combinations claimed. Instead, the scope of the present disclosure extends to encompass any combination of features herein disclosed.

Claims

1. A paper-based sheet having an area comprising a plurality of displaced regions, each displaced region being either elevated or depressed relative to a median plane of the sheet, thus defining a network of elevated and / or depressed regions over the area and thereby rendering the paper-based sheet conformable under applied stress.

2. The paper-based sheet according to claim 1, wherein each displaced region is either elevated or depressed relative to an adjacent displaced region, thus defining a network of elevated and / or depressed regions over the area.

3. The paper-based sheet according to claim 1 or claim 2, wherein a transition region is defined at a transition or connection between adjacent displaced regions, wherein the transition region comprises material which is stretched relative to a material at the displaced regions.

4. The paper-based sheet according to any previous claim, wherein the sheet has a first surface and a second surface and wherein, at a transition or connection between adjacent displaced regions, a cross-section of the sheet is defined by a plane connecting the first surface with the second surface along a shortest distance, further wherein a surface normal of the first surface along this cross-section is parallel to and displaced from a surface normal of the second surface along this cross-section.

5. The paper-based sheet according to any preceding claim, wherein the paper-based sheet is corrugated paperboard comprising a plurality of elongated flutes extending across the paper-based sheet.

6. The paper-based sheet according to claim 5, further wherein a transition region is defined at a transition between adjacent displaced regions, further wherein an arched shape of the flutes is maintained within the transition region.

7. The paper-based sheet according to any preceding claim, wherein the network of displaced regions forms a tessellated pattern.

8. The paper-based sheet according to any preceding claim, wherein one or more of the displaced regions have a triangular shape.

9. The paper-based sheet according to any preceding claim, wherein the network of displaced regions comprises a network of alternating elevated and depressed regions.

10. An item comprising the paper-based sheet of any preceding claim.11.The item according to claim 10, wherein the item is a package.12.The item according to claim 11, wherein the package has first and second panels formed from the paper-based sheet, wherein the network of displaced regions extends over a majority of both the front and rear panels.

13. A method of forming a paper-based sheet, the method comprising the steps of:providing a die comprising first and second parts, the first part comprising an array of raised elements and the second part comprising an array of recessed elements, wherein the raised elements of the first part are aligned with and configured to intermesh with the recessed elements of the second part when the first and second parts of the die are brought together;providing a paper substrate having first and second surfaces;arranging the paper substrate between the first and second parts of the die and bringing the first part of the die towards the second part of the die so that the first part of the die contacts the first surface of the paper substrate and the second part of the die contacts the second surface of the paper substrate;applying a force to the die to form a plurality of displaced regions in the substrate, each displaced region being either elevated or depressed relative to a median plane of the paper substrate, thus defining the paper sheet having a network of displaced regions over the sheet.14.The method of forming a paper-based sheet according to claim 13, wherein each of the first and second parts of the die comprise an array of raised elements separated by recessed elements, wherein the raised elements of one part are configured to intermesh with the recessed elements of the other part when the first and second parts of the die are brought together, such that when the force is applied to the die to form a plurality of displaced regions in the substrate, each displaced region is either elevated or depressed relative to an adjacent displaced region, thus defining the paper sheet having a network of elevated and depressed regions over the sheet.15.The method according to claim 13 or claim 14, wherein the step of applying force to the die to form the network of displaced regions over the substrate causes the substrate to shear between adjacent intermeshing raised elements.16.The method according to claim 13 or claim 14, wherein the step of applying force to the die to form the network of displaced regions over the substrate causes the substrate to stretch between adjacent intermeshing raised elements.17.The method according to claim 13 or claim 14, wherein the step of applying force to the die to form the network of displaced regions over the substrate causes substantially no compression of the substrate between adjacent intermeshing raised elements.18.The method according to any of claims 13 to 17, wherein the paper substrate is corrugated paperboard comprising a plurality of elongated flutes extending across the substrate.19.The method according to claim 18, further wherein a transition region is defined at a transition between adjacent displaced regions, further wherein, following the step of applying pressure to the die to form a network of displaced regions over the substrate, an arched shape of the flutes is maintained in the transition region.

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