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Title:
SETTABLE SHEET MATERIAL
Document Type and Number:
WIPO Patent Application WO/2023/007160
Kind Code:
A1
Abstract:
A sheet material (100) that is transformable between an unset state and a set state. The sheet material comprises: a first layer (102); a second layer (104); and a core (106). The core (106) comprises a core material (106a) extending between the first and second layers (102, 104). The core material (106a) defines a plurality of discrete cavities (108) formed by a plurality of holes (110) in the core material (106a), the holes (110) each extending though the core material (106a) between the first and second layers (102, 104). The sheet material (100) further comprises a settable material (112), the settable material (112) having an unset state and a set state and being capable of transitioning from the unset state to the set state, or between the set and unset states, the transition being activated by at least one activator. The plurality of cavities (108) are at least partly filled with the settable material (112). The first and second layers (102, 104) are arranged to control passage of the settable material (112) therethrough and/or at least partly retain the settable material (112) within the cavities (108). At least one or both of the first and second layers (102, 104) are arranged to allow passage or transmission of the activator into the plurality of cavities (108) to cause the settable material (112) to transition from the unset state to the set state, or between the set and unset states, in order to cause a corresponding transformation in the state of the sheet material (100). Also disclosed is an article (200) comprising the sheet material (100), a method (300) of manufacturing the sheet material (100) and a method (400) of manufacturing an inflatable article that incorporates the sheet material (100).

More Like This:
WO/2017/067605LAMINATES
WO/2022/176810PANEL STRUCTURE
Inventors:
STRANGE BENJAMIN ALEX (GB)
Application Number:
PCT/GB2022/051977
Publication Date:
February 02, 2023
Filing Date:
July 27, 2022
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
STRANGE BENJAMIN ALEX (GB)
International Classes:
B32B3/26; B32B3/10; B32B3/12; B32B3/20; B32B5/14; B32B5/18; B32B13/00
Domestic Patent References:
WO2018096333A12018-05-31
WO1993020300A11993-10-14
Foreign References:
US4495235A1985-01-22
EP0008960A21980-03-19
US8287982B22012-10-16
US4196251A1980-04-01
US5543188A1996-08-06
US5188879A1993-02-23
US20110089183A12011-04-21
Attorney, Agent or Firm:
BARKER BRETTELL LLP (GB)
Download PDF:
Claims:
CLAIMS

1. A sheet material that is transformable between an unset state and a set state, the sheet material comprising: a first layer; a second layer; a core comprising a core material extending between the first and second layers, the core material defining a plurality of discrete cavities formed by a plurality of holes in the core material, the holes each extending though the core material between the first and second layers; and a settable material, the settable material having an unset state and a set state and being capable of transitioning from the unset state to the set state, or between the set and unset states, the transition being activated by at least one activator, wherein: the plurality of cavities are at least partly filled with the settable material, the first and second layers are arranged to control passage of the settable material therethrough and/or at least partly retain the settable material within the cavities, and at least one or both of the first and second layers are arranged to allow passage or transmission of the activator into the plurality of cavities to cause the settable material to transition from the unset state to the set state, or between the set and unset states, in order to cause a corresponding transformation in the state of the sheet material.

2. A sheet material according to claim 1, wherein the settable material in each cavity forms an area of settable material which is arranged to control the shape of the sheet material in a region within and extending away from the boundary of the respective cavity when the settable material is in the set state.

3. A sheet material according to claim 1 or claim 2, wherein the settable material forms between 25% and 75% of the core by volume, and optionally forms between

55% and 65% of the core by volume, and preferably forms 60% of the core by volume.

4. A sheet material according to any preceding claim, wherein: a fold axis is defined as an axis extending across the region of the sheet material having the plurality of cavities; and the cavities are arranged such that fold axes in all possible orientations and positions with respect to the cavities are intersected by at least part of at least one of the plurality of cavities containing the settable material along the respective fold axis length.

5. A sheet material according to any preceding claim, wherein the cavities have an interlocking shape whereby each cavity is arranged to at least partly interlock or overlap with an adjacent cavity.

6. A sheet material according to claim 5, wherein the interlocking cavities each have a plurality of indented portions and a plurality of protruding portions, wherein the protruding portions of one cavity are each received in a respective indented portion of an adjacent cavity.

7. A sheet material according to any preceding claim, wherein the settable material comprises a material capable of transitioning from or between: an unset state in which it is relatively flexible, unsolidified or uncured; to/and a set state in which it is rigid or semi-rigid, solidified or cured.

8. A sheet material according to claim 7, wherein the settable material comprises a material that is a powder in the unset state and is a rigid or semi-rigid solid in the set state, and the activator is a liquid.

9. A sheet material according to claim 8, wherein the settable material comprises plaster, and the activator is water.

10. A sheet material according to claim 9, wherein the settable material comprises plaster of Paris.

11. A sheet material according to any preceding claim, wherein the core material comprises a flexible foam material.

12. A sheet material according to claim 11, wherein the flexible foam material is an open celled foam.

13. A sheet material according to any preceding claim, wherein the cavities are defined by interior walls formed by the core material.

14. A sheet material according to claim 13, wherein the interior walls have an at least partly curved cross-sectional profile in the plane of the sheet material.

15. A sheet material according to claim 13 or claim 14, wherein the interior walls of the cavities comprise a keying surface formed on the surface of the core material, the keying surface arranged to provide a keying engagement between the core material and the settable material in the set state.

16. A sheet material according to any preceding claim, wherein a cross sectional size of all or at least some of the cavities is less than or equal to 6 cm, and more preferably is in the range between 2 to 4 cm.

17. A sheet material according to any preceding claim, wherein one or both of the first and second layers is gas impermeable.

18. An article comprising the sheet material of any preceding claim.

19. An article according to claim 18, when also dependent on claim 17, wherein the article is an inflatable article, wherein the layer of the sheet material that is arranged to allow passage or transmission of the activator forms at least part of an outer surface of the article.

20. A method of manufacturing the article of claim 19, wherein the first layer of the sheet material is arranged to allow passage or transmission of an activator and the second layer of the sheet material is gas impermeable, the method comprising the steps of: forming the plurality of holes in the core material; attaching the core material to an outer surface, or a part thereof, of an inflatable component to form the second layer of the sheet material; at least partly filling the plurality of holes formed in the core with the settable material; and attaching or applying the material forming the first layer of the sheet material to an outer surface of the core material.

21. A method of manufacturing the sheet material of any of claims 1 to 17, the method comprising the steps of: forming the plurality of holes in the core material; forming one of the first and second layers by applying or attaching the material forming the one of the first and second layers to one face of the core material; at least partly filling the plurality of holes formed in the core material with the settable material; and forming the other of the first and second layers by applying or attaching the material forming the other of the first and second layers to the opposite face of the core material.

Description:
SETTABLE SHEET MATERIAL

Technical field The present application relates to a sheet material that is transformable between an unset state and a set state. The sheet material may be an initially flexible sheet material that can be transformed from the unset to the set state (i.e. it is settable). In some embodiments it may also be transformable from the set state to the unset state, and so may be provided in either state. The sheet material may be suitable for use as an arts and craft material. The present application also relates to an article made at least partly from the sheet material. The article may be an inflatable article. The present application also relates to a method of manufacturing the sheet material and a method of manufacturing the inflatable article. Background

Settable or hardenable materials are used in a number of different applications to allow a flexible sheet of material to be moulded or formed into a desired shape before being set to form a rigid structure.

An example of such a material is disclosed in US8287982B2, which discloses a knitted fabric having a tightly knitted bottom layer, a more loosely knitted upper layer and pile yarns extending across the space between the lower and upper faces. Settable material is introduced into the space between the upper and lower faces and can be caused to set by the addition of a liquid. Until set, the fabric is flexible and can be shaped but after the settable material has set, the fabric is rigid and can be used as a structural element in a wide range of situations.

US4196251 discloses a flexible open-celled foam core with fibrous sheets defining a foam core sandwich. The foam core sandwich is impregnated with a settable resin containing a curing agent. The foam core sandwich is then moulded into a desired shape and while maintaining this shape the resin is allowed to cure. This forms rigidized resinous foam core sandwich structure. Another example of a material for use in construction is disclosed in US5543188. A flexible, protective and waterproofing membrane for application onto a body to conform to a surface of the body and to be bonded thereto is disclosed. The membrane includes a flexible polymeric sheet which has an open-textured surface on each of its opposite faces. The textured surfaces are impregnated with a dry, cementitious material and define interconnected internal voids open to the atmosphere. The dry cementitious material includes a water-hardenable cement which is substantially non- hydrated. We are also aware of US5188879, which relates to polyimide foam filled structures, and US2011/0089183, which discloses a composite panel comprising a paper honeycomb core.

In these known examples a setting material such as a resin or cementitious material is dispersed throughout a substrate material so that a homogeneous, rigid composite material is formed when it is hardened. These materials may not be suitable for all applications as they do not exhibit sufficient flexibility before setting such that they can be easily formed into a desired shape, and once set are too brittle and shatter easily.

A general problem to be addressed therefore is how to provide a settable highly flexible material having desirable properties when set.

Summary

In a first aspect, the present application provides a sheet material that is transformable between an unset state and a set state, the sheet material comprising any one or more of the following features: a first layer; a second layer; a core comprising a core material extending between the first and second layers, the core material defining a plurality of discrete cavities formed by a plurality of holes in the core material, the holes each extending though the core material between the first and second layers; and a settable material, the settable material having an unset state and a set state and being capable of transitioning from the unset state to the set state, or between the set and unset states, the transition being activated by at least one activator, wherein: the plurality of cavities are at least partly filled with the settable material, the first and second layers are arranged to control passage of the settable material therethrough and/or at least partly retain the settable material within the cavities, and at least one or both of the first and second layers are arranged to allow passage or transmission of the activator into the plurality of cavities to cause the settable material to transition from the unset state to the set state, or between the set and unset states, in order to cause a corresponding transformation in the state of the sheet material.

By using discrete cavities extending through the thickness of the core material between the first and second layers a plurality of discrete solid masses or rigid/semi rigid regions of the set settable material are formed which are separated by the core material. The settable material is not therefore dispersed throughout the body of the sheet material, but rather separate regions of only the settable material and only the material of the core are formed. This provides the sheet material with improved properties when it is set. The discrete cavities of settable material may act to control the shape of the sheet material in within the cavity and in a region surrounding a respective cavity when the settable material is in the set state. The settable material in the cavities, once set, acts as a ‘keystone’ i.e. a strategically located rigid or semi rigid area of material that can control the shape of the more flexible core material.

For example, the set sheet material may exhibit a degree of deformation (which may be elastic deformation, depending on the properties of the core material) under application of an applied load before the material cracks or shatters upon failure of the settable material within the cavities. If the sheet material is stressed to such a degree that the settable material cracks or fails, the first and second layers may then act to hold the sheet material together rather than it failing entirely. The properties of the first and second layers can be adapted to achieve a certain degree of structural integrity if the settable material is cracked. The sheet material, once set, may therefore exhibit a primary stage of bending behaviour based on the flexibility of the core material and the degree to which it is uncontrolled or its bending is not resisted by the effect of the settable material. A secondary stage of bending behaviour may then occur at increased loads whereby the core material’s bending path is interrupted by the settable material and so loading is transferred to the settable material. A tertiary stage of behaviour may then occur in which failure within the regions of settable material occurs. This gives an article made from the sheet material a capacity, when in the set state, to absorb and recover from lower levels of stress without fracturing.

Before setting, the core material and cavities filled with the unset settable material may provide a high degree of flexibility to allow the shape of the sheet material to be manipulated.

The sheet material may be flexible in the unset state and rigid or at least partly rigid in the set state e.g. the sheet material may be relatively more rigid in the set state compared to the unset state. In the set state the sheet material is capable of holding its shape. When in the unset state the sheet material may be shaped or moulded into a desired shape.

The settable material in each cavity is arranged to control the shape of the sheet material in a region within the respective cavity and extending away from the boundary of the respective cavity (e.g. a region of the core material extending outwards from and surrounding the cavity, that region not being limited to the immediate periphery of the cavity) when the settable material is in the set state.

The settable material may form between 25% and 75% of the core by volume. Optionally, the settable material may form between 55% and 65% of the core by volume, and preferably may form 60% of the core by volume. In other embodiments, the cavities may be more sparsely distributed. In such embodiments, the settable material may form at least 10% of the core by volume.

A fold axis may be defined as an axis (i.e. straight line) extending across the region of the sheet material having the plurality of cavities from one edge (of that region) to another. The cavities may be arranged such that fold axes in all possible orientations and positions with respect to the cavities are intersected by at least part of at least one of the plurality of cavities along the respective fold axis length. In other words, the cavities are arranged such there is no straight line path, in any position or orientation across the sheet material or relevant part thereof, which does not intersect at least part of at least one cavity (e.g. no straight line path of only core material along the entirety of its length). This helps to reduce the susceptibility of the sheet material to folding even when in the set state along regions of continuous core material.

The shape, size and/or distribution of the cavities may provide the intersection of all possible fold axes. This may be achieved by providing a relative overlap between rows in which the cavities are arranged, and a relative overlap between columns in which the cavities are arranged. For example each row may overlap an adjacent row, and each column may overlap and adjacent column.

The maximum uninterrupted length of a part a fold axes (i.e. all possible orientations of fold axes across the relevant region of settable material) may be less than or equal to the cavity cross sectional size (e.g. the cross section of at least one of the cavities at the ends of a respective un-interrupted axis section if the cavity size varies). In other words, the maximum length a fold axis can extend without interruption, regardless of its orientation and position relative to the array of cavities, may be less than or equal to the associated cavity cross sectional size (defined below).

The settable material may be capable of transitioning from the unset to the set state and not back again, e.g. is suitable for single use of the sheet material. Alternatively, the settable material may be capable of transitioning between the set and unset states i.e. from the unset to the set state and from the set state to the unset state. The transition may be repeated e.g. the sheet material is reusable, with the settable material starting in either state.

The settable material may comprise a material capable of transitioning from or between: a) an unset state in which it is relatively flexible, unsolidified or uncured; to/and b) a set state in which it is rigid or semi-rigid, solidified or cured.

The settable material may comprise a material that is a powder in the unset state and is a rigid or semi-rigid solid mass in the set state, and the activator may be a liquid.

The settable material may comprise plaster, and the activator may be water. The settable material may comprise plaster of Paris (i.e. Gypsum plaster or calcium sulphate hemihydrate). This may make the settable material particularly suited for use as a craft material. Other settable materials may however be used for a craft material implementation.

The core material may be, or comprise, a flexible foam material. This may provide a light weight and highly flexible core material. The flexible foam material may be, or comprise, an open celled foam. The open cells of the foam may provide improved engagement with the settable material once it is hardened.

The cavities may be defined by interior walls formed by the core material. The cavities may form a non-interconnected array of individual cavities separated by the core material.

The interior walls may have an at least partly curved cross-sectional profile in the plane of the sheet material. This may allow stress to be distributed more evenly to avoid cracking of the material once set.

The interior walls of the cavities may comprise a keying surface formed on the surface of the core material. The keying surface may be arranged to provide a keying engagement between the core material and the settable material in the set state. The keying surface may be formed by using an open celled foam to form the core material.

The keying surface may be formed by a rough surface texture of the interior walls of the cavities.

The cavities may have an interlocking or overlapping shape. Each cavity may be arranged to at least partly interlock or overlap with an adjacent cavity. The footprint or outline of one cavity may therefore interlock with the footprint or outline of an adjacent cavity. This may reduce or disrupt otherwise continuous regions of the core material that would present regions of structural weakness. By overlapping/interlocking the cavities, extended regions of the sheet material in which the core material is not controlled by the settable material are avoided. An overlap length by which at least one or each of the cavities overlaps or interlocks with an adjacent cavity may be 10 mm ± 25% (e.g. in a range between 7.5 mm and 12.5 mm). The overlap length may be defined as the length by which part of a cavity overlaps the outline of an adjacent cavity such that they interlock.

The cavities may each have a plurality of indented portions and a plurality of protruding portions. The protruding portions of one cavity may be each received in a respective indented portion of an adjacent cavity such that they interlock.

The cavities may have a central region surrounded by radially extending arms or lobes. The arms of one cavity may each extend into a space between the arms of an adjacent cavity. The arms may have a distal bulbous region and a proximal neck region. The arms may narrow at the neck region. This may help to keep a powdered settable material from moving around the cavities.

A cross sectional size of the cavities may be less than or equal to 6 cm. This may reduce the amount of space for the settable material to move around the cavity and become unevenly distributed. A cross sectional size of the cavities may be in the range between 2 to 4 cm. This may provide a balance of the cavities holding enough settable material to provide strength once set, but not being so large as to increase the risk of the settable material becoming unevenly distributed within the cavity. More preferably, the cross sectional size may be about 3.5 cm. The overlap length may be expressed as a proportion of the cross sectional size of the cavities. The overlap length may be in a range between approximately 20% and 35% of the cross sectional size of the associated cavities (e.g. the cavity cross sectional size of all of the cavities if they are the same, or either of the overlapping cavities for which the overlap length is being measured, may be in this range).

The thickness of the core material may be 1 cm or less. The thickness of the core material may be in the range between 0.1 and 1 cm. This may provide a balance of strength in the set state, while still allowing the activator to reach the settable material. The overall thickness of the sheet material may be about 2 mm. In other embodiments, it may be in a range between 1 mm and 11 mm.

A cavity separation distance between each cavity and a respective adjacent cavity (or between at least some of the cavities) may be in a range between 3 mm and 7 mm, and more preferably may be 5 mm. The cavity separation distance may be defined as the closest separation distance between respective adjacent cavities.

The size of the cavities may also be expressed as an area. For example, each (or at least one or more) of the cavities may have an area of approximately 790 mm 2 ± 25%. The area of core material surrounding each cavity may be approximately 570 mm 2 ± 25%. The cavity “area” referred to in this paragraph may be the size of the area bounded by the wall of a cavity in the plane of the sheet material as defined elsewhere herein.

The cavity area given in the preceding paragraph will be understood as being dependent on the shape of the cavities. The area ranges and cross sectional sizes given above, and elsewhere herein, are therefore to be understood as being capable of being provided separately from each other in some embodiments. For example, the skilled person will understand that a suitable shape of cavity can be chosen so that one or both the cross sectional size and area fall within the respective ranges given herein. Some shapes of cavity having a cross sectional size falling within one of the ranges above may not therefore fall within one of the area ranges herein, and vice versa, in some embodiments. Preferably, the cavities may fall within both the area and cross sectional size ranges defined anywhere herein.

The cavities may form a non-uniform array. The distance between cavities (e.g. amount of core material) between the cavities may vary. This may allow the strength/flexibility/shape of the sheet material to be tailored by strategically placing the cavities of set material at certain points in an article formed from the material.

One or both of the first and second layers may be gas impermeable. This may allow an inflatable article to be formed from the sheet material. The sheet material may be intended to be single use. It may therefore be a sheet material that is transformable from the unset state to the set state (but not back again). In this case, the settable material is capable of transitioning from unset state to the set state and not back again. The sheet material may therefore be provided in the unset state as a flexible sheet material for activation by the user to transform it into the set state .

The sheet material may be reusable. The settable material may be capable of transforming from the set state to the unset state and back again (i.e. between the two states). The settable material may be capable of setting upon activation by the first activator. The settable material may further be capable of un-setting upon activation by a second activator (different from the first). At least one or both of the first and second layers may be further arranged to allow passage or transmission of the second activator into the cavities to cause the settable material to un-set in order to transform the sheet material from the set to the unset state. The sheet material may be transformed from the set state to the unset state and from the unset state to the set state by application of the same activator. The sheet material may be transformed from the set state to the unset state by an activator (e.g. heat) and from the unset state to the set state without an activator (e.g. by cooling).

A second aspect provides an article comprising the sheet material of the first aspect.

In a third aspect, the article of the second aspect may be an inflatable article. The layer of the sheet material that is arranged to allow passage or transmission of the activator may form at least part of an outer surface of the article. The gas impermeable layer may form an inner layer of the article.

A fourth aspect provides a method of manufacturing the sheet material of the first aspect, the method comprising any one or more of the following steps: forming the plurality of holes in the core material; forming one of the first and second layers by applying or attaching the material forming the one of the first and second layers to one face of the core material; at least partly filling the plurality of holes formed in the core material with the settable material; and forming the other of the first and second layers by applying or attaching the material forming the other of the first and second layers to the opposite face of the core material.

A fifth aspect provides a method of making the inflatable article of the third aspect. The first layer of the sheet material may be arranged to allow passage or transmission of an activator (and form an outer layer) and the second layer of the sheet material may be gas impermeable (and form an inner layer). The method comprises any one or more of the following steps: forming the plurality of holes in the core material; attaching the core material to an outer surface of an inflatable component to form the second layer of the sheet material; at least partly filling the plurality of holes formed in the core with the settable material; and attaching or applying the material forming the first layer of the sheet material to an outer surface of the core material.

The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied to any other aspect. As used herein, a range “from value X to value Y” or “between value X and value Y”, or the like, denotes an inclusive range; including the bounding values of X and Y.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a cross section view through a sheet material according to an embodiment;

Figure 2 shows a cross section view of the sheet material shown in Figure 1 through the plane marked AA;

Figures 3A to 3G show cross section views of various embodiments of the sheet material illustrating the disruption of fold lines and their associated fold regions; Figure 4 shows a cross section view corresponding to that of Figure 2 according to another embodiment of the sheet material;

Figure 5 shows a cross section view corresponding to that of Figure 2 according to yet another embodiment of the sheet material;

Figure 6 shows a larger scale illustration of some of the cavities provided in the sheet material shown in Figure 4;

Figures 7a and 7b show a change in shape of two embodiments of the sheet material having different number densities of cavities filled with settable material;

Figure 8 shows a cross section view through an inflatable article formed from the sheet material illustrated in Figure 1, the inflatable article being in an un-inflated state;

Figure 9 shows a cross section view of the inflatable article shown in Figure 8 once inflated;

Figure 10 shows the application of an activator to the inflatable article shown in Figure 8;

Figure 11 illustrates a method of manufacturing the sheet material illustrated in Figure 1; and

Figure 12 illustrates a method of manufacturing the inflatable article illustrated in Figures 8 to 10.

Detailed Description

A sheet material 100 is shown in Figures 1 and 2. Figure 1 shows a cross section through the thickness of the sheet material 100, while Figure 2 shows a cross section through a plane of the material parallel to its outer face (the cross section through the line marked AA in Figure 1, referred to as the plane of the sheet material). Figures 1 and 2 show only part of a larger section of material.

The sheet material 100 is transformable between an unset and a set state upon application of an activator. In the unset state the sheet material is flexible and can be conformed or moulded into a desired shape. This can be done by inflating an article made from the sheet material 100, by placing it in/on a mould, or contorting/manipulating the material by hand or using a tool. In the set state, the sheet material 100 is generally rigid or semi-rigid and is able to hold its shape. In the presently described embodiment, the sheet material is suitable for use as an arts and craft material or for use in children’s toys. For example, the material can be shaped (e.g. inflated) or moulded into a desirable shape before being painted or decorated (after the settable material is set). This allows it to be used as a modelling material to create shapes and objects to be decorated in a similar manner to Papier- mache. The sheet material of the present application is not however limited to only this use, and has a number of different applications as will be described later.

The sheet material 100 generally comprises a first layer 102; a second layer 104; and a core 106. Each of the first and second layers 102, 104 and the core 106 is formed from a respective sheet material component or element that are each flexible. When these separate components are combined the overall sheet material 100 is therefore flexible and can be formed into a desired shape before being set. The sheets forming the first layer, core and second layer are bonded together using any suitable method such as an adhesive or using thermal welding. In other embodiments, any of the first and second layers may be formed by applying a film of material (e.g. as a fluid) to the core 106 so, the fluid being hardened once applied to form a bonded layer.

The core 106 comprises a flexible core material 106a that extends between the first 102 and second 104 layers and is arranged to space them apart so that the core extends between (e.g. is sandwiched between) the first and second layers. The first and second layers may be bonded/applied to the faces of the core material 106a. The core material is deformable or flexible to such an extent that the shape of the sheet material can be manipulated as desired when it is in the unset state (e.g. in some embodiments it may still have some degree of stiffness or resistance to deformation when the sheet material is in the unset state such that it can be moulded into a desired shape).

The core material 106a defines a plurality of discrete cavities 108. The cavities 108 are formed by a plurality of holes 110 that extend through the core material 106a between the first and second layers 102, 104. Each of the cavities 108 are therefore defined by the interior surface of the walls of a respective hole 110 in the body of the core material 106a, and the interior surfaces of the first and second layers 102, 104. The material forming the core therefore forms a boundary between the cavities 108. The cavities 108 are separate, individual cavities that are not interconnected to each other as can be seen in Figures 1 and 2. Only one cavity is labelled in Figure 2 to aid clarity.

The holes 110 forming the cavities 108 have interior walls that extend perpendicularly to the plane of the first and second layers 102, 104 (e.g. plane AA) as can be seen in Figure 1. In other embodiments, they may be other shapes, and may, for example, be angled away from perpendicular, or may be curved or rounded.

The plurality of cavities 108 are filled with a settable material 112. The settable material is capable of setting upon activation by an activator. The settable material 112 is a material that is capable of setting into a rigid or semi-rigid solid upon interaction with or addition of a suitable activator. In its unset state, the settable material may be pliable or malleable so that the sheet material 100 can be shaped. By setting the settable material 112 the sheet material 100 is transformed from its unset to set state. In the unset state of the settable material 112 the sheet material 100 is in its unset state. In the set state the settable material forms a rigid or semi-rigid solid mass (i.e. it is solidified) so that the sheet material 100 is also set into a rigid or semi-rigid state. The settable material may not be set immediately upon interaction with the activator. The setting time may vary depending on the type of settable material and activator used. In some embodiments, a delay time between application of the activator to the sheet material may be provided so that the shape of the sheet material can manipulated after the activator is applied.

The type of transformation of the settable material between states may vary according to the type of settable material being used is described in more detail later. The settable material may be, or comprise, a material which is capable of transitioning from or between: a set state in which it is rigid or semi-rigid, solidified or cured; to/and an unset state in which it is relatively flexible, unsolidified or uncured. In the set state of the settable material the sheet material is relatively rigid or semi-rigid (e.g. such that it can hold its shape once moulded and can resist deformation under an applied load). Although being more rigid in the set state compared to the unset state, the sheet material overall may exhibit a degree of deformation in the set state because of the combination of core material and settable material (e.g. it may not be completely rigid). In the unset state of the settable material, the sheet material is relatively flexible (e.g. such that it can be moulded or shaped as desired before setting).

In the presently described embodiment, each of the cavities 108 is completely filled by the settable material 112 as shown by the shading in Figure 1. In other embodiments, the cavities 108 may each be only partly filled with the settable material 112. In the described embodiment, all of the cavities are filled equally, whereas in other embodiments they may be filled to differing degrees, or some of them may be unfilled.

The first and second layers 102, 104 are both arranged to retain the settable material 112 within the cavities 108 (e.g. before and after the settable material is set). The first and second layers are arranged to control movement of substances (e.g. the settable material and the activator) into and/or out of the cavities. The first and second layers 102, 104 may form a barrier that prevents, or restricts the amount of, the settable material 112 that can pass through them and escape from the cavities.

The properties of the material used to form the first and second layers 102, 104 may be chosen according to the settable material, and amount of settable material, that is desired to be allowed to pass through it. The first and second layers may not, therefore, form a completely impenetrable barrier to the settable material, or components of the settable material or other substances, within each cavity 108. For example, in one embodiment, the cavities 108 may be overfilled with settable material 112 during manufacture so that part of the fill is allowed to escape after the cavities are closed by the first and second layers 102, 104. In some embodiment, the settable material 112 may be arranged to expand upon activation by the activator. In such an embodiment, some of the settable material may be allowed to pass through the first and/or second layers 102, 104 to relieve pressure within the cavity or create a desired surface texture. In yet other embodiments, a component of the settable material such as a coloured dye may be allowed to pass through the first and/or second 102, 104 layers upon application of the activator to colour the outer surface of the sheet material 100. The first and second layers may be made of the same or different material, such that anything described herein in connection with the first layer may apply to the second layer, and vice versa. In some embodiments, the first and second layers may allow passage of the settable material (and other materials) across them to differing degrees. For example, the second layer may not allow passage of the settable material, whereas the first may to some degree.

In the presently described embodiment, only the first layer 102 is arranged to allow passage or transmission of the activator. The activator can therefore be applied to the first layer 102 and reach the cavities 108 to set the settable material 112.

In the presently described embodiment the second layer 104 is formed from a gas impermeable material such that the sheet material 100 can be used to make an inflatable article as will be described in more detail later. The second layer may not therefore allow the activator to pass through it. In this embodiment, the first layer 102, second layer 104 and core 106 are all made from materials that can expand when an article formed from the sheet material is inflated.

In other embodiments, both of the first and second layers 102, 104 may allow passage or transmission of the activator to into the cavities 108. The first and second layers 102, 104 may therefore be formed from the same material in some embodiments. In some embodiments, one or both of the first and second layers 102, 104 may be made from the same material as the core material 106a.

The use of discrete cavities 108 in which the settable material 112 is contained and set provides an advantageous result compared to known materials that have a settable material uniformly distributed throughout a fabric or similar material. Before being set the sheet material is highly flexible and can be easily conform to a desired shape. When the sheet material 100 is it the set state it is made up of individual solid masses of the set settable material 112 bound and separated by the core material 106a. As described in further detail later on, the discrete cavities of settable material control the shape of the sheet material in a region surrounding a respective cavity when the settable material is in the set state. The settable material in the cavities, once set, act as a ‘keystone’ i.e. strategically located rigid or semi-rigid areas of material that can control the shape of the more flexible core material in a region extending away from it (and the shape of the sheet material within the respective cavity itself). Rather than impregnating a fabric material or the like with a settable material as is known in the prior art, the sheet material of the present application instead relies on discrete cells of solid rigid or semi-rigid cells of settable material. The combination of core material and settable material in discrete cavities provides improved structural properties of the sheet material 100 when it is in the set state. For example, in the set state the sheet material 100 can exhibit a degree of elasticity provided by the core material 106a, with structural strength provided by the solid masses of settable material 112. The overall elasticity of the sheet material in the unset set is dependent on the properties of the core material. In some embodiments, the sheet material may not be elastically or resiliently deformable, but may be merely flexible or deformable.

The sheet material, once set, may exhibit a primary stage of bending based on the flexibility of the core material and the degree to which it is uncontrolled or its bending is not resisted by the effect of the settable material, and then a secondary stage of bending whereby the core material’ s bending path is interrupted by the settable material and so loading is transferred to the settable material, and a tertiary stage in which failure within the regions of settable material occurs. This gives an article made from the sheet material 100 a capacity, when it the set state, to absorb and recover from lower levels of stress without fracturing. This is particularly useful if being used for children’s craft or toy applications. In the tertiary stage of the behaviour of the sheet material, i.e. when the settable material cracks or otherwise fails in some way, the structural integrity of the overall sheet material 100 is retained by the first and second outer layers 102, 104 still holding the settable material together. In the present embodiment, the settable material 112 comprises Gypsum plaster/powder (i.e. plaster of Paris). The activator used in this embodiment is water. By using plaster of Paris the sheet material 100 may be suited for use in craft or children’s toy applications. In the present embodiment, the settable material 112 consists only of Gypsum plaster/powder. In other embodiments, it may include further components, such as any suitable additives. For example, in any of the embodiments described herein the settable material may comprise a coloured additive (e.g. a coloured dye) that may pass out of the cavities 108 when the settable material is set to colour the outside of the set sheet material. In other embodiments, other suitable settable materials 112 and corresponding activators may be used. In some embodiments, the settable material 112 may be any other form of plaster, and may for example be clay plaster, lime plaster, or cement plaster. Other types of settable material can be used as will be described later.

In the presently described embodiment, the sheet material is intended to be single use. It is therefore provided in the unset state as a flexible sheet material for activation by the user into the set state. In some embodiments, it may be possible to return the settable material back to an unset state from the set state. Moreover, the material may begin in the set state, and be transformed into the unset state to be moulded, before being reset (it may therefore be provided in either state in some embodiments). The transformation from the set state to the unset state may be caused by the application of a different activator (or possibly reactivation by the same activator). This may allow the sheet material to be re-shaped after it is set so that it can be reused. In such an embodiment, the settable material is therefore further capable of un-setting upon activation by a second activator. At least one or both of the first and second layers may be further arranged to allow passage or transmission of the second activator into the cavities to cause the settable material to unset in order to transform the sheet material from the set to the unset state. In yet other embodiments, an activator may be required to transition the settable material from one state to the other, but not vice versa e.g. an activator may be required to transition from the set state to the unset state (e.g. by using heat as the activator) while no activator is required for it to later transition back to the set state over a period of time (e.g. by being allowed to cool).

Referring again to Figure 1, the first layer 102 is formed from a material having a pore size that is smaller than the particles of powder forming the settable material (or the pore size is small enough in comparison to the size of the powder particles such that the majority, or a sufficient amount, of the settable material is retained in the cavities), but which are large enough to allow transmission of the activator (e.g. liquid such as water). The first layer 102 therefore may form a filter layer. This allows water sprayed on the outer surface of the first layer 102 to reach the settable material 112 within the cavities 108. Alternatively the sheet material 100 may be submerged in water to activate the settable material. The sheet material 100 may be soaked in water so that the water soaks through the first layer 112 to reach the settable material. As discussed above, the pores of the first layer may in some embodiments be arranged to allow a small amount of the settable material to pass through or certain components of the settable material or other material in the cavities. The relative pore size applies to embodiments such as those where the settable material is a powder or the like. In other embodiments, e.g. which are activated by UV light or similar, the first layer would be made from a material through which the UV light can penetrate - this may not therefore necessarily require pores to allow the activator to pass through.

In the presently described embodiment, the first layer 102 comprises or is formed from a spun-bond material. In yet other embodiments, it comprises or is formed from a paper mesh 102, e.g. it may be a filter paper. In yet other embodiments, it may be formed from or comprise a polymeric material such as polypropylene. The skilled person will understand that the material of the first layer is chosen according to the type of settable material 112 being used, and the corresponding activator required to cause that material to set, and the degree to which movement of the settable material out of the cavity is to be controlled.

In the presently described embodiment, the first layer 102 is formed from a single material. In other embodiments, it may be formed from a mix of different materials forming different sub layers so long as overall it allows the desired degree of retaining of the settable material 112 and transmission of the activator. As discussed elsewhere herein, the second layer 104 may be formed from the same material as the first layer 102 such that the activator can pass through both layers.

In the presently described embodiment, the core material 106a comprises or is formed from a foam material. This provides a flexible, light weight material that can easily be formed into a desired shape while the sheet material 100 is in its unset state. In other embodiments, other materials may be used for the core material.

In some embodiments, the core material 106a may comprise a keying surface formed on the interior surface of the walls of some or all of the cavities 108. The keying surface is adapted to engage with the settable material 112 once it is set so that a strong bond is formed between them. The keying surface may be formed by a rough surface texture provided on the surface of the cavity walls formed by the core material 106a. In some embodiments, the foam is, or comprises, an open-celled foam. The open cells of the foam material in such an embodiment may provide the keying surface of the cavity walls. This may allow a small amount of the settable material to impregnate the surface of the foam and improve the binding effect between them. In other embodiments, a closed-celled foam can be used. Despite the foam being open celled, the settable material 112 is not distributed throughout its volume, but may mix with the foam in a shallow surface layer of the interior walls of the cavities.

In the present embodiment, the second layer 104 is, or comprises, a gas-impermeable material, more specifically an air-impermeable material. In this embodiment, the second layer 104 is formed from a gas-impermeable material. In the present embodiment, the second layer comprises a polyester film. The polyester film may be a metalized polyester film. This allows an article formed from the sheet material to have a long inflation time. In other embodiments, other materials may be used, such as rubber, latex, synthetic rubbers (e.g. polychloroprene), plastic (polymeric) films, nylon fabric or metallic sheets. In some embodiments the material is not gas- impermeable.

In the described embodiment, the second layer 104 is formed from a single layer of gas impermeable material. In other embodiments, it may comprise a gas impermeable layer along with other materials or layers. By “gas impermeable” we mean a material that is impermeable to gas to a degree that it is able to contain pressurised gas such that it can be inflated. The gas impermeable material may not be completely impermeable to leakage of a gas over of long periods of time. In some embodiments, both the first and second layers may be gas impermeable where the activator is of a type that may still pass through the materials (e.g. light).

Referring to Figure 2, a cross section through the material 100 along line AA in Figure 1 is shown in order to illustrate the cross sectional shape of the cavities 108 (only one cavity is labelled in Figure 2). As can be seen in Figure 2, the cavities 108 are formed by cut-outs or holes 110 in the core material 106a. The cavities 108 are thus defined by the walls of the holes formed by in core material 106a. The inventor has found that the shape, size and distribution of the cavities 108 in the core 106 has an important effect on the properties of the sheet material 100 once it is transformed into its set state.

The inventor has found that resistance of the sheet material to bending or folding once in the set state is at least partly dependent on the shape of the cavities and how they are distributed or positioned relative to each other.

An extended region of sheet material which contains no settable material may form a region in which the shape of the set sheet material is not sufficiently controlled, and is thus susceptible to bending or folding. This effect is illustrated in Figure 3 A, which shows an embodiment of the sheet material having a uniform array of cavities 108 equally spaced apart and arranged in rows and columns. In this example a continuous region of uninterrupted core material (shown shaded in Figure 3A) is formed extending across the sheet material, centred on a fold axis FI. This represents a line or axis, and associated region, along which the settable sheet material would be susceptible to folding, despite the set material in the cavities being set. The fold region is the area of the sheet material that would bend if it were folded along the associated fold axis. By fold axis or fold line we mean a straight line path in the plane of the sheet material extending between two edges of the sheet material (or a relevant part of the sheet material).

A similar fold axis F2 is also shown in Figure 3 A, which is perpendicular to FI. Along these fold axes and associated fold regions the shape of the sheet material is not controlled by the settable material sufficiently to dictate its shape. A fold axis F3 that does not extend between the rows and columns of cavities would however be disrupted or intersected by the cavities (and therefore the set settable material in them). Folding along such a fold axis and associated fold region would therefore be resisted. In this example the cavities are square in cross section, but a similar effect would be found for other shapes in which fold lines are not intersected by the cavities.

In order to reduce this susceptibility to folding the arrangement of the cavities can be chosen according to the desired properties of the sheet material. In some embodiments, the cavities are arranged to disrupt or intersect a fold axis (and associated fold region) that would otherwise extend un-interrupted across the settable sheet material. The cavities may have a shape and distribution in order to provide this disruption. An example of this disruption effect is illustrated in Figure 3B. In this example, one of the columns of cavities has been offset with respect to the others such that the fold axis FI is intersected, and its associated shaded fold region at least partly disrupted. This reduces the susceptibility of the sheet material to fold along that axis compared to the equivalent axis shown in Figure 3A.

In order to further reduce the susceptibility to folding further, in some embodiments, the cavities are offset with respect to each other such that no uninterrupted fold lines are present in a direction perpendicular to the offset. This is illustrated in Figure 3C. In this example, alternate columns of cavities are offset with respect to those in between such that no uninterrupted fold lines extending perpendicularly (in the plane of the sheet material) to the columns are present. In other words, the cavities in one column are staggered or offset to an extent such that the otherwise undisrupted regions of core material spanning that region of the settable material are completely intersected. This corresponds to an offset equal to at least the degree of spacing between cavities in each column. This causes the row height R1 of one row to overlap the row height R2 of an adjacent row as shown in Figure 3C. This blocks the path of any fold axes that extend parallel to the rows. As can be seen in Figure 3C, wherever a fold axes running perpendicularly to the columns is located it will be intersected at some point along its length by the cavities - there is no clear path from one edge to the other along which such a fold axis could be located to avoid the cavities. In this example, all of alternate columns are offset. In other embodiments, only some of them may be offset so as to still provide disruption of the fold lines.

In the embodiments shown in Figures 3A, 3B and 3C the susceptibility of the sheet material in the set state to folding in at least one direction is reduced (e.g. along fold axes from left to right in the figures). It would however still be susceptible to folding along fold axes in other directions with a certain position within the array of cavities, specifically perpendicular to FI and extending between the columns of cavities - i.e. along fold line F2.

Further advantageously therefore, in some embodiments, the arrangement of cavities (e.g. their shape, orientation and relative position) may be configured such that no undisrupted fold lines or associated fold regions are possible e.g. there is no orientation and position of a fold axis extending across the sheet material (or an associated region of the sheet material) that would not be intersected at least partly by the cavities filled with settable material. This may be achieved using a number of different arrangements of cavities, provided that any fold axis (i.e. straight line) in the plane of the relevant part (or all) of the sheet material from one edge to another would cross over at least one cavity.

In some embodiments, where the cavities are arranged in rows and columns, the rows and columns may be offset and/or overlapped to disrupt or intersect fold lines in all orientations and positions across the sheet material. An example of this is shown in Figure 3D. In this embodiment, column width Cl overlaps adjacent column widths, such that the columns overlap. All fold axes parallel to the columns would therefore insect at least one cavity. Row height R1 similarly overlaps adjacent row widths, such that all parallel fold axes would also be intersected. In this embodiment, the cavities comprise an array of regular tessellating shapes (regular hexagons in this embodiment). Similar overlapping columns and rows may be provided using other shapes (e.g. generally or approximately tessellating, or non-tessellating). However a fold axis is positioned in Figure 3D, at all possible alignments with respect to the cavities, it will therefore be intersected as there is no straight clear path between cavities.

The inventor has found that an arrangement of regular tessellated hexagons (or similar tessellated shapes, either regular or un-regular) may not provide adequate disruption of possible fold lines in order to sufficiently resist bending in some directions. An example of this is shown in Figure 3E, where a fold axis F4 is shown. As can be seen in the Figure, there is still a significant amount of undisrupted or non-intersected length of the fold axis F4 because it is oriented to extend along the gaps between cavities.

The inventor has found that the disruption of potential fold lines and associated fold regions can be further improved by using cavity shapes which provide a degree of interlocking between them.

An example of the disruption of a fold axis F5 using interlocking cavities is shown in Figure 3F. By ‘interlocking’ it is meant that a part of one cavity fits within or extends into a part of an adjacent cavity (e.g. such that they cavities overlap). In order to interlock, the cavities therefore may have at least one protruding region of the cavity wall which may extend into a corresponding indented region of the wall of an adjacent cavity as shown in Figure 3F and described in more detail below. As can be seen in Figure 3F, the arrangement of interlocking cavities provides further disruption to a fold line F5 extending through the region of interlocking to further improve resistance to folding.

The inventor has found that another factor which may have an effect on the resistance of the sheet material to folding when set is the maximum possible length of an undisrupted fold axis. This is illustrated in Figure 3G. In this example, spacing between the cavities is such that an uninterrupted part of fold axis F6 (and associated fold region) of length P is present. If the length of un-interrupted core material is too great the sheet material may still be susceptible to folding, despite all fold axes still being interrupted along at least another part of their respective length. In some embodiments, the cavities may be arranged so that the maximum undisrupted length P of all possible fold axes with any orientation is equal to or less than the respective cavity cross section (as defined later). Where the cavities are not of equal cross section, the maximum un-interrupted length P may be less than or equal to the cross section of at least one of the cavities at either end of the un-interrupted path length (i.e. cavities 108b and 108c in Figure 3G).

Any reference above to a fold line being intersected by a cavity is intended to mean a cavity at least partly filled with settable material.

Figure 4 illustrates a cross section (e.g. alone line AA) of the sheet material according to another embodiment. The same reference numbers have been used for corresponding components to aid explanation. In the embodiment shown in Figure 4, the walls of the cavities 108 have a curved cross-sectional profile (i.e. they are curved in the plane of the sheet material 100). The use of a curved profile helps to resist and distribute spread stress through the cavity wall and reduces the risk of the sheet material 100 cracking once it is set. In the present embodiment, the cross sectional profile is continuously curved around the perimeter of the each cavity 100 in order to ensure stress is distributed. In other embodiments, the cavities have only an at least partly curved interior wall profile. In the embodiment illustrated in Figure 4, the cavities 108 each have an interlocking shape such that each cavity is arranged to (at least partly) interlock or overlap with an adjacent cavity which surrounds it. The cavities 108 thus form an interlocking or overlapping array. This has been found to help break-up or disrupt regions of the sheet material that would otherwise have no settable material as described above. For example, where the cavities are spaced apart to an extent such that no interlocking or overlapping occurs, extended regions or paths across the sheet material made up of core material only will be present. In these regions the shape of the sheet material is not controlled by the settable material sufficiently to dictate its shape. The interlocking or overlap of the cavities may therefore prevent folding of the sheet material along un-controlled fold lines extending across the sheet material through regions where there are no cavities. This effect can be modified by the degree of interlocking or overlap. For example, the closer the cavities are together and the greater the extent of the overlap, the more the overall properties of the sheet material tend towards those of the set settable material ( and vice versa).

Referring now to the inset of Figure 4, a close up of one of the cavities 108 is illustrated. Each of the cavities 108 comprise three protruding portions 114a, 114b, 114c and three indented portions 116a, 116b, 116c. The protruding portions 116a,

116b, 116c are arranged between the indented portions 114a, 114b, 114c around the perimeter of the respective cavity 108. The interior wall of each cavity 108 has a concave curved shape within the protruding portions as can be seen in Figure 4. Between the protruding portions, the wall of each cavity extends inwards towards the centre of that cavity, and forms a curved convex interior surface region. The protruding portions 114a, 114b, 114c form lobes or arms that are shaped so that each of them is received within a corresponding indented portion of an adjacent cavity. This allows the cavities 108 to form an interlocking array. As can be seen in Figure 4, the cavities therefore have a central region from which the arms extend radially. Each arm comprises a bulbous distal region and a proximal neck region (closer to the central region) at which each arm narrows relative to the bulbous region. The neck region allows the foot print of a cavity (e.g. dotted lines in the inset of Figure 4 marking out the greatest extent of the cavity shape) to interlock with the footprint of an adjacent cavity. The neck region also helps to keep the settable material in the bulbous region (for example where the settable material is a powder).

Although the cavities in Figure 4 are shown as having three protruding portions and three indented portions (e.g. three arms), in other embodiments there may be greater than three (e.g. three or more). An example of an array of cavities in which each cavity has four protruding portions and 114a, 114b, 114c, 114d and four indented portions 116a, 116b, 116c, 116d to form four arms is shown in Figure 5.

The degree of interlock between the cavities, separation between adjacent cavities and size of the cavities can be quantified as illustrated in Figure 6. Figure 6 shows a larger scale view of some of the cavities of the sheet material shown in Figure 4. All of the distances and lengths shown in Figure 6 are measured in the plane of the sheet material.

The numerical parameters given in connection with Figure 6, and elsewhere herein, may be preferred for an embodiment in which the cavities are filled with plaster of Paris and the sheet material is used as a craft material. This is however only one exemplary embodiment. The skilled person will understand that the physical parameters of the sheet material defined herein can be modified accordingly to provide suitable properties for any specific implementation.

A cavity separation distance D as shown in Figure 6 may be defined as the distance between a wall of one cavity and the wall of an adjacent cavity. It therefore corresponds to the thickness of core material 106a between those cavities. In the embodiment shown in Figure 6, the separation distance is approximately the same at all points around the perimeter of a respective cavity. This however may not be the case for all cavity shapes. The cavity separation distance may therefore be defined as the closest separation distance between adjacent cavities. In the presently described embodiment, the cavity separation distance is approximately 5 mm. In other embodiments, in may be in a range between 3 mm and 7 mm. In the present embodiment, the separation between all of the cavities is the same. This may not however be the case for all embodiments if the cavities are unevenly distributed. A cavity overlap length L as shown in Figure 6 may be defined as the length by which part of a cavity overlaps the outline of an adjacent cavity such that they interlock as described above. As can be seen in Figure 6, the footprint or outline 108a of a cavity corresponds to an outer perimeter of the wall of the cavity without the presence of the indented or recessed portions 116a, 116b, 116c. The overlap or interlock length L is defined as the length of part of an adjacent cavity which overlaps the outline 108a. In the embodiment shown in Figure 6, the overlap length is approximately 9.5 mm. More generally it may be 10 mm ± 25% (e.g. in a range between 7.5 mm and 12.5mm), while still providing the desired properties. In the present embodiment, the cavity overlap length between all of the cavities is the same. This may not however be the case for all embodiments if the cavities are unevenly distributed.

A cavity cross sectional size C as shown in Figure 6 may be defined as a distance across a cavity. The cavity cross sectional size C may correspond to the largest cross sectional size of a cavity e.g. the largest size that can be measured between two points on the wall of the cavity. In the embodiment shown in Figure 6, the cavity cross sectional size is approximately 35 mm. In other embodiments, the cross sectional size of each cavity 108 may be less than or equal to 60 mm. If the cavities are too large, the settable material has been found to move around within the cavity and may leave gaps when set. More specifically, the cavities may have a cross sectional size in a range between 20 mm to 40 mm. This has been found to provide a suitable degree of strength to the sheet material 100 once it is set, while the cavities are not so large as to mean the settable material has too much space to move around. The cavity cross section may be the same for all cavities, but in other embodiments the cavities may vary in size throughout the sheet material.

The values of the cavity overlap length L given in the paragraph above may be suitable for cavities having the cross sectional sizes given in the previous paragraph. The cavity overlap length may be expressed more generally as a proportion of the cavity cross sectional size which may be applicable to any cavity size. In some embodiments, the cavity overlap length may be in the range between 20% and 35% of the cavity cross sectional size C (e.g. either the cross sectional size of all of the cavities if they are the same, or the cross sectional size of at least one of the overlapping cavities for which the cavity overlap length is being measured). The thickness of the core material (e.g. the thickness of the core) may be less than or equal to 1 cm thick (e.g. thickness Y marked on Figure 1). This may also help to reduce the risk of the settable material becoming unevenly distributed in the cavities. More specifically, the thickness of the core material (which may correspond to the depth of the cavities) may be in the range of 0.1 cm to 1 cm. This range has also been found to provide a suitable balance of strength and containment of the settable material. The overall thickness of the sheet material 100 may, in some embodiments, be about 2 mm. In other embodiments, the overall thickness may be in a range between 1 mm and 11 mm.

The size of the cavities may also be expressed as an area of the cavities measures in the plane of the sheet material 100 (e.g. as shown shaded with cross hatching in Figure 6). For example, the cavities of the embodiment shown in Figure 6 have an area of approximately 790 mm 2 . The area of core material surrounding each cavity is approximately 570 mm 2 . In other embodiments, the cavities may have an area of approximately 790 mm 2 ± 25% (e.g. in a range between 590 mm 2 and 990 mm 2 ). The area of core material surrounding each cavity may be approximately 570 mm 2 ± 25% (e.g. in a range between 430 mm 2 and 720 mm 2 ). Where the settable material is a powder material (e.g. plaster of Paris) the cavity dimensions in this paragraph may allow the use of a binder material (e.g. fibres) to ensure even distribution to be avoided. This may simplify the material, and aid manufacture.

In other embodiments, other sizes and areas of cavities may be used for different implementations of the sheet material, and for different settable materials. The cavity shape shown in the figures is to be understood as only one example only. The present application is not limited to any specific shape and arrangement of cavity. For example, cavity shapes different from those shown in Figures 4, 5 and 6 may be used to provide an interlocking array of cavities. In yet other embodiments, the cavities may not be interlocking, or only some of them may interlock. Although the cavities are shown having curved profiled interior walls, in other embodiments they have be straight sided, or at least partly straight sided.

In the embodiment shown in the Figures, a relatively thin wall thickness of the core material separates each cavity from adjacent cavities. This provides a dense array of cavities, and may allow them to interlock (e.g. overlap) if shaped accordingly as shown in the described example. In other embodiments, a greater separation of the cavities may be provided. The sheet material once set may be formed from an equal or greater amount of core material compared to the settable material (or the volume of the cavities). Spacing the cavities further apart in this way retains the flexibility of the core material once the sheet material is set. It may also allow the properties of the sheet material to be tailored to the desired use, or reduce its overall weight by using less settable material. In other embodiments, where greater strength is required, the material may comprise more settable material than core material.

In any of the embodiments described herein, the cavities 108 of the sheet material 100 that are filled with settable material 112 are each arranged to control the shape of the sheet material 100 in a region within, extending away from, and surrounding a respective cavity 108 when the settable material 112 is in the set state. Once set, the settable material 112 within each cavity 108 forms a region of the sheet material which resists the surrounding region of the sheet material (e.g. the otherwise flexible core material) from returning to its original pre-moulded shape. The number of cavities of a given size provided per unit area of the sheet material affects the complexity of the shape in which the sheet material can be moulded. An example of this is illustrated in Figures 7a and 7b, which illustrate two different examples of the sheet material 100, 100' being moulded into a desired shape before being transformed into the set state. In parts (i) of each of Figures 7a and 7b the sheet material is in a flat, unmoulded state. Parts (ii) and (iii) show the sheet material being moulded into a desired shape.

In the embodiment in Figure 7a, the cavities 108 have a lower number density compared to those of the embodiment shown in Figure 7b (e.g. there are fewer cavities per unit area). As can be seen in Figure 7a, the complexity of the shape in which the cavities 108 of settable material 112 are able to retain the sheet material 100 is less than for the embodiment in Figure 7b because of the lower cavity number density. As can be seen in part (iii) of Figure 7b, the greater number density of cavities 108 filled with settable material 112 allows the sheet material 100' to be moulded and set into a more complex shape. In other words, the modelling “dexterity” or “resolution” of the moulding ability of the sheet material is affected by the number density or frequency at which the cavities are provided. The greater the number density, the greater the level of modelling dexterity or resolution provided. The effect of the number density of the cavities described in the previous paragraphs may be reflected in the ratio of the amount of settable material compared to the amount of core material making up each region of the sheet material. Where a high degree of moulding complexity is desired in a region of the sheet material, a higher ratio of settable material to core material may be provided (e.g. more settable material) so that the shape of the sheet material can be manipulated as desired. The converse may be the case where a low degree of moulding complexity is needed e.g. the relevant region sheet material may be made up from a greater amount of core material compared to settable material.

In the embodiment shown in Figure 6, and others described elsewhere herein, the settable material may make up 60% of the overall volume of a respective region of the core of the sheet material (that region being large enough to span multiple cavities and surrounding core material). In other embodiments, the settable material may make by between 55% and 65% of the core by volume. The remaining volume may be made up of the core material, and any other components that may be present in the core. More generally, the settable material may make up between 60% ± 25% of the overall volume of the core (e.g. it may be in a range between 25% and 75%). The values of the amount of settable material in this paragraph may be advantageous for embodiments in which the settable material is plaster of Paris, and the sheet material is to be used as a craft material. This is however only one example, and other ratios of settable material and core material may be used as appropriate for other implementations. In other embodiments, for example, the cavities may be more sparely distributed. In such embodiments, the settable material may form at least 10% of the volume of the core.

In some embodiments, there may be a varying distance between each or some of the cavities (i.e. some are closer together than others). The density of the cavities (e.g. number per unit area), and the ratio of settable material to core material, may therefore vary over the area of the sheet material. This may apply to cavities that are at least partly filled with settable material, rather than those left empty. This may allow the settable material to be located at strategic points within the material to influence its shape when set using a reduced amount of the settable material, rather than using an evenly distributed array of cavities throughout the material. By altering the spacing of the cavities from each other the amount of stress that can be absorbed by the core material before being transferred to the settable material can be adapted.

By using discrete cells of settable material, compared to a settable material distributed throughout the body of the material, the settable material may be more strategically placed within the material. This allows it to be placed at points where it is required to maintain the shape of the material once set (e.g. points on an article in which there is greater degree of change in shape of the sheet material). For example, a strategically positioned cavity of set settable material may control the shape of the surrounding core material without needing to distribute cavities throughout that entire region of the sheet material. This may allow the material to maintain its shape once set, but also be lightweight. A similar effect may be achieved by leaving some of the cavities empty of settable material. Similarly, the size of the cavities vary across the sheet material. For example, larger cavities (and therefore more settable material) may be provided at points where greater strength is required.

In the described embodiments, the plurality of cavities 108 each have the same size and shape (apart from at the boundary of the material, which is not shown in the Figures). This may provide an approximately or generally uniform strength over the whole of the material when it is in the set state, and provide a uniform degree of complexity to which the shape of the material can be moulded as described above. In other embodiments, the cavities may not be equal/uniform in size and/or shape and/or distribution. Each of these factors may be adjusted to achieve the desired level of modelling “dexterity” or “resolution” of the moulding ability of the sheet material as described above.

Figures 8 to 10 illustrate an article made from the sheet material 100. In this embodiment, the sheet material 100 has a gas-impermeable second layer, and is used to form an inflatable article 200.

As can be seen in Figure 8, the second layer 104 of the sheet material 100 forms a sealed cavity that may be inflated via a valve 204. Over part of the sealed cavity the core 106 and first layer 102 of the sheet material 100 are bonded or applied. The first layer 102 is arranged to form the outer surface of the inflatable article 200 so that the activator can be applied to it and reach the settable material 112 within the cavities. In this embodiment, the sheet material 100 forms only part of the inflatable article 200 (only part of it has the first, and second layers and the core). In other embodiments, it may form all, or substantially all, of the inflatable article.

The inflatable article 200 may be formed into any desired shape. It may, for example, be shaped such that, when inflated, it has the appearance of a decorative object or animal or the like that can then be painted or decorated similarly to a Papier-mache model. In one example, the inflatable article is shaped to have the appearance of a unicorn and is intended for decoration by children once inflated and the settable material set.

Use of the sheet material 100 is illustrated in the sequence of Figures 8, 9 and 10. In Figure 8, the article 200 is in a deflated state. The article 200 is inflated via the valve 204 so that it expands as can be seen in Figure 9. Once it is sufficiently inflated to the desired shape, the activator is applied to transform the sheet material into its set state. In the presently described embodiment, the activator is water and is sprayed onto the outer surface of the article 200 as illustrated by the arrows in Figure 10. The water may alternatively be applied by soaking the article in water. This may help all of the settable material to be reached by the water. The settable material is thus transformed into the set state in which it is rigid (or at least semi-rigid). The inflatable article then remains in this shape, and can be painted or otherwise decorated. In other embodiments, the activator may be applied before the sheet material is shaped by moulding or inflating. Where the activator does not have an immediate effect of setting the settable material, the activator may be applied before shaping the sheet material. The sheet material is then allowed to set after it has been shaped or moulded as desired. This may be the case for plaster of Paris and water being used as the settable material and activator for example, where the material 100 may be soaked in water before being shaped and then allowed to set. The activator can therefore be applied either before or after the sheet material has been shaped into the desired shape. At which stage the activator is applied or introduced may depend on the type of settable material and activator being used.

The settable material may be used for a range of different purposes other than as an arts and craft material as already described. In other embodiments, the sheet material may be used in other applications such as in medicine instead of bandages and plaster to make a plaster cast to heal broken bones. In yet other embodiments, the sheet material may be used as a manufacturing, building or construction material. The sheet material can be used in construction in place of poured concrete to more easily create concrete structures in complex shapes. Where the material is inflatable, it may be used to form pre-fabricated structures or shelters than can be inflated and then set to shape using the activator. In manufacturing applications, the sheet material can be used in a similar way to prepreg carbon or glass fibre sheets.

The present application is not limited to settable materials that comprise plaster. Any suitable substance that can be transformed from a state which does not too greatly inhibit the flexibility of the sheet material to a set state in which the sheet material is rigid or semi-rigid can also be used. The material used to form settable material may be chosen according to the application for which the sheet material is to be used.

In some embodiments, the settable material 112 may be another form of powder material. In such embodiments, the settable material comprises a material which is a powder in the unset state and a rigid or semi-rigid solid mass in the set state. The settable material may comprise cement. It may, for example, comprise a cement-based dry concrete mix. In this embodiment, the sheet material 100 may be more suitable for use in construction as a building material.

The settable material 112 may comprise any suitable plasticisers and other additives in additional to any powdered settable material in order to provide suitable properties when set depending on the use of the sheet material 100. Where the settable material is a powder, it may comprise a binder material to help ensure a more even distribution through the cavities. The binder material may be a fabric or fibres or the like.

In some embodiments, the settable material may be a UV settable material. The settable material may, for example, be a UV settable resin or adhesive. In this embodiment, the activator is UV light, and at least one of the first and second layers are arranged to transmit UV light. In this embodiment, the settable material may comprise a photopolymer or light activated resin e.g. a methacrylate polymer. The skilled person will understand that any other UV setting material known in the art may be used.

In other embodiments, the settable material may be one component of a multipart curable resin that cures when two or more component parts are mixed together, e.g. an epoxy resin system. In this embodiment, one or more component parts of the curable resin may form the settable material, with the activator being formed by the other component part or parts required to result in curing. In such an embodiment, the settable material may be any suitable multi-component adhesive known in the art.

In yet other embodiments, the settable material may comprise a material that is set upon application of heat (the activator in this embodiment is heat being transmitted by one or more of the first and second layers), e.g. a thermosetting material. In such an embodiment, the settable material may comprise a thermosetting adhesive such as epoxy, polyurethane, cyanoacrylate and acrylic polymers. The settable material may be a thermosetting polymer, resin or plastic material.

Where the settable material is an adhesive or settable resin or the like the settable material is un-cured in the unset set and cured in the set state.

In other embodiments, the settable material may be a wax arranged to soften on exposure to heat, and harden at room temperature. This may be particularly suitable for embodiments in which the settable material can be repeatedly transitioned from the set state to the unset state and back again to the set state. In embodiments such as these, the settable material may be flexible in the unset set, and relatively rigid or semi-rigid in the set state.

In yet other embodiments, the settable material may comprise a material that is set by application of an electric current (the activator in this embodiment is electrical current being transmitted by one or more of the first and second layers). In such an embodiment, the settable material comprises an electroactive polymer (EAP) or electro -active adhesive. In yet other embodiments, the settable material may be an electro-active or magneto active material that is set by the application of an electric or magnetic field. For example, the settable material may be a magnetorheological fluid (MR fluid, or MRF) that, when subject to a magnetic field increases its apparent viscosity to the point of becoming a viscoelastic solid.

Other settable materials that are activated by humidity, change in pH, solvent or tension/compression may be used.

Although various embodiments of the sheet material disclosed herein use a first and second layer to retain the settable material and through which the activator passes, one or both of these layers may be absent in other embodiments. For example, some of the types of settable material described above may not require one or both of the layers to be present to hold it in place.

Figure 11 illustrates a method 300 of manufacturing the sheet material 100. The method 300 comprises a step 302 of forming the plurality of holes 110 in the core material 106a. This may be done by cutting or stamping holes through the thickness of the core material 106a. The skilled person will understand that a variety of cutting techniques can be used.

The method then proceeds with the step 304 of forming one of the first and second layers 102, 104 by applying or attaching the material forming that layer to one face of the core material 106a. Either of the first and second layers 102, 104 may be formed first. The material forming the first or second layer may be bonded to the core material using a suitable adhesive, or using other methods such as thermal welding. In one embodiment, an adhesive is applied to the core material in advance of assembly of the components of the sheet material. The adhesive is retained by a cover layer such as a silicone paper, which is removed to expose the adhesive and allow the core material to be bonded to the first and second layers.

Once the first layer is formed, the method comprises a step 306 of at least partly filling the plurality of holes of the core with the settable material. Where the settable material is a powdered material (or similar), this may comprise distributing the settable material over the surface of the core material 106a such that it settles into the holes. This step may comprise vibrating or shaking the core material 106a and first layer 102 so that the settable material is distributed between the holes and fills them to the desired amount. In some embodiments, the cavities are ‘overfilled’ with settable material which is then compressed within the cavities. The cavities may, for example, be overfilled by about 1/3 of their volume with uncompressed settable material. This may avoid shrinkage of the settable material away from the cavity walls when it is set, which may occur in some settable materials such as plaster of Paris. The settable material may be sieved before being added so that it can be distributed evenly.

Once the holes have been filed, the method 300 proceeds with the step 308 of forming the other of the first and second layers. This again comprises applying or attaching the material forming the layer being formed to the opposite face of the core material. This layer may be formed by applying the material from which it is formed as a fluid and allowing it to set. The other of the first and second layers may be applied in a similar way to the first.

Once manufactured in this way, the sheet material 100 may be used in sheet form, or may be cut and shaped into an article in a similar way as a fabric.

Figure 12 illustrates a method 400 of manufacturing an inflatable article that incorporates the sheet material. The inflatable article may, for example, be the inflatable article illustrated in Figures 8 to 10.

The method 400 comprises the step 402 of forming the plurality of holes in the core material 106a. This may be done in the same way as for step 302 of method 300.

The method 400 then comprises the step 404 of attaching the material forming the core 106 to an outer surface of an inflatable component that forms the second layer 104 of the sheet material. The inflatable component in this example is a balloon or other suitable inflatable article that can be filled with air or other gas to achieve the desired resulting shape of the inflatable article.

The method 400 then comprises the step 406 of at least partly filling the plurality of holes 110 of the core 106 with the settable material. This may be done in a similar way as for step 306 in the method 300 of Figure 11. The method further comprises the step 408 of attaching or applying the material forming the first layer 102 of the sheet material to an outer surface of the core material 106a. This may be done in a similar way as for step 308 in the method 400 of first 7. Once the first layer is formed, the settable material is retained in the cavities 108, and can be set upon application of the activator.

Various modifications will be apparent to the skilled person without departing form the scope of the claims. The embodiments described above should be understood as exemplary only. Any feature of any of the aspects or embodiments of the disclosure may be employed separately or in combination with any other feature of the same or different aspect or embodiment of the disclosure and the disclosure includes any feature or combination of features disclosed herein. Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom. For the sake of completeness, it is also stated that the term "comprising" does not exclude other elements or steps, the term "a" or "an" does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and any reference signs in the claims shall not be construed as limiting the scope of the claims.