NL2035600B1

NL2035600B1 - Panel and a method for manufacturing a panel

Info

Publication number: NL2035600B1
Application number: NL2035600A
Authority: NL
Inventors: Luc Martine Baert Thomas; Van Poyer Tom; Boon Sven
Original assignee: Cfl Holding Ltd
Priority date: 2023-08-11
Filing date: 2023-08-11
Publication date: 2025-02-25
Also published as: WO2025036845A1; CN119459091A

Abstract

The present invention relates to a panel, comprising a core layer, comprising a multicellular substrate and a support structure and a decorative layer attached to at 5 least one core layer. The panel is typically made via extrusion, in particular co- extrusion.

Description

Panel and a method for manufacturing a panel

The present invention relates to a panel. The invention also related to a method for manufacturing a panel. The invention further relates to a system for performing the method according to the invention.

Construction and/or decorative panels generally used for the purpose of serving as panel in furniture, shelving, flooring, doors and building panels are typically wood- based, with chipboard, HDF, MDF, OSB, plywood and the like forming the core layer of the panel. However, these wood-based panels have several disadvantages. As these panels generally comprise a melamine uraa- formaldshyde- (MUF) and/or phenol-based resin as a binder, this raises concerns on volatile organic compounds (VOCs) and indoor air quality. As they are wood- based, they are susceptible to moisture fluctuations and water, which may cause warping and delamination. The sealing of the panel's edges with a decorative foil requires the use of an adhesive, which adhesive might leak and be visible on the seams. Wood-based panels are generally anisotropic, with the material having distinct physical properties according to the axis it is measured, for example rigidity, expansion and/or swelling, which could provide disadvantageous when fastening means are provided. Wood-based panels may have local deficiencies, such as cracks or knots, that may impact its strength topically.

Hence, a goal of the invention is to provide an improved panel for the purpose of serving as panel in furniture, shelving, flooring, doors and building panels which overcomes at least part of the abovementioned drawbacks or least find an alternative to the known panels.

The invention provides thereto a panel, comprising at least one core layer, in particular comprising at least one multicellular substrate, and optionally at least one support structure, and at least one decorative layer attached to at least one core layer, wherein at least one core layer comprises a front surface and a back surface located on opposite sides, wherein the thickness of at least one core layer is defined by the distance between the front surface and the back surface, and wherein preferably at least part of at least one support structure extends over the thickness of at least one core layer.

The panel according to the present invention benefits of at least one core laying comprising at least one multicellular substrate and at least one support structure.

The combination of a multicellular substrate and at least one support structure according to the present invention results in a relatively strong core layer. The core layer benefits of at least part of at least one support structure extending over the thickness of at least one core layer, such that a strong and effective geometry is obtained. At least one support structure can thereby form a backbone construction of the panel. The support structure could also be referred to as backbone structure.

Due to the use of at least one support structure which extends over the thickness of at least one core layer a relatively thin multicellular substrate can be used. The orientation of at least part of the support structure provides rigidity to the multicellular substrate. The core layer benefits thus from both the multicellular material and the support structure. The panel according to the present invention in particular benefits of a good rigidity and strength.

Within the context of the present invention, the panel can be any panel suitable for decoration and/or construction. Hence, the panel can be a decorative panel and/or a structural panel. The panel according to the present invention can for example be configured for and/or suitable for use in furniture, shelving, doors but could also be decorative and non-decorative building panels, flooring, wall and/or ceiling panels.

The panel can for example be a floor, wall or ceiling panel. When it is referred to a multicellular substrate also a substrate comprising multicellular material can be meant. A non-limiting example of a multicellular material is for example foamed material. The panel according to the present invention could thus comprise at least one at least partially foamed core layer. It is for example imaginable that the panel comprises a foamed thermoplastic core layer, for example foamed PVC, foamed

PET, foamed PP, and/or foamed WPC, a foamed thermoset core layer, for example foamed TPU and/or PU foams, and/or a foamed inorganic core layer, for example comprising MgO, MgSO4, MgCi2, fiber cement and/or aluminosilicate. it is also imaginable that the panel comprises an organic core layer, for example comprising cork, mycelium or the like. The core layer is preferably a waterproof core layer. The panel is preferably a waterproof panel.

It is imaginable that at least part of the front surface and the back surface of the core layer is formed by the support structure. It is also imaginable that at least part of at least one support structure extends over the entire thickness of the multicellular substrate of at least one core layer. The panel and substrate can have several possible shapes. It is for example possible that the panel and/or the substrate are substantially plate-shaped. It is imaginable that the thickness of the core layer is substantially consistent over the entire core layer, and/or over the length of the core layer. In this case, it is beneficial if the height of at least part of the support structure substantially equals the thickness of the core layer. It is also imaginable that at least part of at least one support structure extends over at least the smallest thickness of at least one core layer. The core layer can have a variable thickness. It is for example imaginable that at least part of at least one support structure forms a connection or connecting bridge between the front surface of the core layer and the back surface of the core layer. It is imaginable that at least part of at least one support structure is positioned under an angle with respect to a plane defined by the front surface and/or back surface of the core layer. An embodiment is conceivable wherein at least part of at least one support structure is substantially perpendicular to a plane defined by the front surface and/or the back surface of at least one core layer. When it is referred to a front surface and a back surface, this could also be a first (side) and a second (side) surface. lt is in particular referred to opposing sides of the panel. The panel according to the present invention can be applied in several orientations. Hence, the term front and back should not be interpreted as limiting. Instead of the wording front and back for example also upper and lower, first and second, primary and secondary could be used. The upper and lower side, or front and back side, are typically two opposite faces with largest surface area which serve as main decorative faces. The panel is for example substantially rectangular. However, the panel according to the present invention can have any convenient shape. It is for example imaginable that the panel is a cuboid or a hexahedron in particular comprising multiple faces.

The at least one core layer preferably may have a thickness of at least 3 mm. lt is for example conceivable that at least one core layer has a thickness between 3 mm and 20 mm or between 5 and 16 mm, preferably between 6 mm and 8 mm or between 14 mm and 16 mm. Beneficial embodiments comprise a core layer having a thickness in the range of 2.5 to 4 mm or in the range of 3.5 to 5 mm. In case the panel comprises multiple core layers, it is also conceivable that said core layers vary in thickness. It is for example conceivable that the combination of core layers has a thickness between 3 and 12 mm. lt is conceivable that the panel has multiple core layers, wherein at least one core layer has a thickness in the range of 0.5 to 1 mm and at least one further core layer has a thickness in the range of 1 to 3 mm. lt is possible that a panel comprises at least three core layers adjacent to each other, wherein a central core layer is enclosed between an upper core layer and a lower core layer. It may be preferred that the upper core layer and/or the lower core layer have a larger thickness than the central core layer, or vice versa. At least support structure can for example have a thickness which is substantially equal to the thickness of the core layer.

In a preferred embodiment, at least one support structure or at least one backbone structure comprises a plurality of ribs. In a further preferred embodiment, at least one rib, and preferably at least two ribs, or more preferably each rib, extends over the thickness of at least one core layer. In this way, at least one rib or the plurality of ribs can form a reinforcing configuration within the core layer, and in particular within the multicellular substrate. It is also imaginable that at least one support structure comprises a plurality of struts. When it is referred to a rib also a strut could be meant, or vice versa. In a preferred embodiment, at least one rib, preferably at least two ribs, and more preferably each rib, of at least one support structure extends over the entire thickness of the multicellular substrate of at least one core layer. At least two ribs are preferably substantially parallel to each other.

In this embodiment, a good strength can be achieved by the applied ribs. The parallel orientation of the ribs can contribute to a decent rigidity of the core layer, and of the panel as such. It is possible that at least two ribs, or the plurality of ribs extend substantially parallel throughout the entire multicellular substrate. It is for example imaginable that at least two ribs are oriented substantially parallel to each other in a direction substantially perpendicular to a length direction of the panel. In case the panel is an extruded panel, it is imaginable that at least two ribs are oriented substantially parallel to each other in a direction substantially angled with respect to the extrusion direction. It is for example possible that at least two ribs are oriented substantially parallel to each other in a direction substantially perpendicular to the extrusion direction. Alternatively and/or additionally, at least two ribs could define a triangle shape, for example wherein the legs of the triangle extend from the front surface to the back surface of the core layer, or vice versa. it is also imaginable that least two ribs are oriented substantially parallel to each other in a direction which equals length direction of the panel.

In a possible embodiment, at least two ribs of at least one support structure can be 5 interconnected. Hence, it is imaginable that at least one support structure is formed by a plurality of substantially adjacent and/or parallel-oriented ribs which are interconnected. The ribs could form an interconnected network, thereby defining a support structure. It is also conceivable that at least two ribs are substantially isolated from each other. Hence, it is imaginable that at least one support structure is formed by a plurality of separate ribs. It is for example possible that a plurality of individual ribs together form a support structure. It is also imaginable that the core layer comprises a plurality of support structures. The orientation and/or positioning of at least one support structure, and/or at least one rib and preferably the plurality of ribs, can contribute to the rigid characteristics of the core layer.

Advantageously, the strength of the panel is markedly increased by the presence of the support structure in the core layer. Several aspects of the panel can be measured. The American Society for Testing and Materials provides a standard test method, ASTM D 1037-96, for evaluating properties of wood-based fiber and particle panel materials. The tests included therein are the bending modulus of elasticity (MOE) and the modulus of rupture (MOR). Other useful tests included in

ASTM D 1037-96 include the direct screw withdrawal test, the hardness test, the hardness modulus test, shear strength in the plane of the board, glue-line shear test, falling ball impact test. In the case if the panel is used as a part of a furniture product, test ANSI/KCMA A161.1 Kitchen Cabinet Furniture Testing may be useful.

When testing three multicellular polyethylene terephthalate (PET) core layers having an average density of 250 kg/m? and including a support structure, there are notable differences between the Modulus of Rupture (MOR) and the Modulus of

Elasticity (MOE) when the direction of extension of the support structure is taken into account. The MOE and MOR were tested according to ASTM D 1037-96. The three panels are multicellular panels consisting of polyethylene terephthalate (PET) comprising cells or voids. The volume of the cells of the support structures in each panel is on average smaller than the volume of the cells of the surrounding multicellular substrate. The support structure of each panel is in this test thus formed by PET having a relatively high density as compared to the average density of the panel.

The support structures are ribs extending linearly and parallel throughout the core layer, and as such divide the multicellular substrate into two parts, wherein these parts are located on opposite sides of the ribs. The ribs themselves have a beam or plate-like shape. In the first core layer, the MOE is tested in a direction from the front surface and a back surface located on opposite sides of the core layer, and a single rib (the support structure) extends throughout the core layer parallel to both this front and back surface. A force is thus applied in a direction perpendicular to the directions of the plane wherein the rib extends. The MOE of this first core layer was 82.3 MPa and a MOR of 3.5 MPa.

In the second multicellular PET core layer, a similar rib extends throughout the core layer perpendicular to both the front and the back surface of the core layer.

Compared to the support structure of the first multicellular PET core layer, the support structure of the second multicellular PET core layer is rotated by 90 degrees. Forces applied to measure the MOE and the MOR thus had a direction that is the same as the direction of extension of the rib. The measured MOE and

MOR were almost doubled to 176 MPa and 5.7 MPa respectively.

In the third multicellular PET core layer, the rib had the same direction of extension as in the second multicellular PET core layer, but was offset to a side of core layer.

The measured MOE and MOR values were 191 MPa and 5.7 MPa, respectively.

These results were very similar to the results obtained for the second multicellular

PET core layer. As such, the orientation of the support structure in the core layer appears to have a significant effect on the overall strength of the core layer.

The average strength of multicellular PET including an (integrated) support structure appear to range between 170 and 200 MPa, while the average strength of foamed PET without any support structure appears to range between 70 and 90

Mpa for core layers having an average density of 250 kg/m3. Integrated as described herein is defined as being a part of the core layer, and in this case being constituted of the same compounds as the multicellular substrate itself.

If the core layer is made of a Wood Plastic Composite (WPC), the average MOE would range between 400 and 800 MPa, in particular between 500 and 700 MPa, such as 600 MPa if no support structure would be present. In case a support structure was present, having the same shape and orientation as the support structure in either the second or the third multicellular PET core layer, the average

MOE would range between 1200 and 1800 MPa, in particular between 1350 and 1650 MPa, such as 1500 MPa.

Another option is to provide a support structure made of aluminium in a WPC multicellular substrate. If a thickness of the support structure, having a shape and orientation as described hereinabove for either the second or the third multicellular

PET core layer and a thickness ranging between 0.3 and 2 mm, the average MOE would range between 4000 and 600 MPa, in particular between 4500 and 5500

MPa, such as 5000 MPa.

In a possible embodiment of a panel according to the present invention, the panel comprises at least two core layers. lt is for example possible that the panel comprises at least two core layers, wherein each core layer comprises at least one multicellular substrate and at least one support structure. It is then imaginable that a first support structure of a first core layer is arranged at an angle with respect to a second support structure of a second core layer. Each core layer can be any of the described embodiments of a core layer according to the present invention. The panel can for example comprise at least two stacked or coupled core layers, wherein said at least two layers comprise a plurality of ribs, in particular parallel ribs, wherein at least part of the ribs of a first core layer are arranged at an angle, and preferably substantially perpendicular, with respect to at least part of the ribs of a second core layer.

Preferably, at least part of the support structure is substantially rigid. In a further preferred embodiment, the support structure is a rigid support layer. It is also imaginable that the parts defining the support structure are not rigid as such, but that the orientation and/or positioning thereof results in the support structure having rigid characteristics. It is conceivable that at least part of the support structure forms a lattice structure.

In a possible embodiment of the panel according to the present invention, at least part of at least one support structure is embedded in at least one multicellular substrate. Hence, at least part of at least one support structure, and preferably the entire support structure is embedded within the multicellular material forming the multicellular substrate. In this way, at least one support structure can form part of the core layer in an effective and controlled manner. At least part of the support structure being embedded in at least one multicellular substrate enhances the co- action between the support structure and the multicellular substrate. It is for example imaginable that at least part of at least one support structure is attached to atleast part of at least one multicellular substrate by means of an adhesive. It is also possible that at least part of at least one support structure is connected to at least part of at least one multicellular substrate via lamination, in particular thermolamination. In this embodiment, the support structure is typically made of a different material than the material forming the multicellular substrate. It is conceivable that the support structure and the substrate are made of the same material.

It is also imaginable that at least part of at least one support structure forms integral part of at least one multicellular substrate. In this way, the core layer can benefit of an integrally formed support structure which will provide strength and rigidity from the nucleus of the core layer, and in particular of the multicellular substrate. An integrally formed support structure is less likely to be prone to weakened spots at the joints and/or connections. The support structure can for example be an integrated support structure, wherein in particular the support structure is integrated in the multicellular material of the multicellular substrate. For this embodiment, the support structure is preferably made of the same material as the multicellular substrate. The support structure can be formed during the formation of the core layer.

Itis imaginable that at least part of at least one support structure defines a honeycomb structure, a bubble guard sheet, a corrugated sheet, a corflute construction and/or a twinwall structure. At least part of at least one support structure defining any of said structures can further benefit to the strength and/or rigidity of the panel. It is for example imaginable that the walls defining the honeycomb structure, a bubble guard sheet, a corrugated sheet, a corflute construction and/or twinwall structure extend over the thickness of the core layer. It is also imaginable that the walls defining the honeycomb structure, a bubble guard sheet, a corrugated sheet, a corflute construction and/or twinwall structure extend under an angle, and in particular substantially perpendicular with respect to a plane defined by the front surface and/or back surface of the panel, and in particular the core layer. The honeycomb structure can for example be an aluminium honeycomb structure and/or a thermoplastic honeycomb structure. Yet a further embodiment is conceivable wherein the panel comprises at least one additional support structure or secondary support structure. At least one secondary support structure can be a separate layer additional to at least one core layer. It is also imaginable that at least one secondary support structure forms part of at least one core layer. At least one secondary support structure can be defined as any of the described embodiments of the support structure according to the present invention. A further embodiment is conceivable, wherein at least part of at least one support structure defines a grid.

The support structure preferably extends over the entire core layer of the panel.

Hence, it is imaginable that the support structure defining a grid extends over the entire core layer. At least part of the support structure can be filled with at least one multicellular material.

Atleast one support structure when provided on the front and/or back surface of the panel can improve rigidity of the panel, as such the support structure is preferably substantially rigid. The use of at least one support structure according to the present invention can further improve the screw pullout strength which allows for stronger fastening means between panels to be provided.

In a preferred embodiment, at least one core layer is an extruded core layer. In a preferred embodiment, at least one multicellular substrate is an extruded substrate.

In some embodiments, the extruded substrate comprises at least two materials that are extruded simultaneously. The panel according to the present invention can also be an extruded panel. Extrusion is a preferred production method as it is relatively cost competitive and enables continuous bulk production. The panel according to the present invention can for example be produced via the method according to the present invention. It is conceivable that the core layer of the panel is made via co- extruded layers which form a plurality of individually extruded layers that are then cut to form a block or slice comprising a plurality of mutually bonded co-extruded core layers, with the reinforcing layers formed by said adjacent skin layers, or crust layers, forming reinforcing struts or ribs throughout the volume of the at least one core layer. Possibility at least one support structure has a ribbed structure reaching into the core, for example formed by a specifically formed extrusion die.

Conceivable that this is then co-extruded with top and/or bottom layers, or front and/or back layers, both having ribbed structure reaching into the core, with a multicellular material shaping into the grooves formed by this ribbed structure.

The core layer, or the multicellular substrate, can also be obtained via multi- extrusion. lt is imaginable that the core layer, or the multicellular substrate comprises multiple materials. For example, at least one core layer or at least one multicellular substrate can comprise an alternating sequence of materials. At least one core layer, or multicellular substrate can for example comprise an alternating sequence of a first polymer material and a second polymer material, for example in a (-SPC-WPC-)*n configuration with n being an integer 2 1.

In a possible embodiment, the panel according to the invention comprises at least two decorative layers. It is imaginable that a first decorative layer is attached to the front surface of the core layer and/or that a second decorative layer is attached to the back surface of the core layer. It is also imaginable that a further layer is present between at least one core layer and at least one decorative layer. A first decorative layer can be substantially identical to a second decorative layer.

However, it is also conceivable that a first decorative layer differs from a second decorative layer. Any of the embodiments described for the decorative layer according to the present invention could be applied for the first and/or second decorative layer, if applied.

At least one core layer could comprise at least one side edge, and at least one decorative layer can be attached to at least one side edge. In such embodiment, the panel could for example be used for decorative purposes, and/or for furniture and/or the formation of a door. Typically, in a panel according to the present invention, the surface area defined by the front surface and/or the surface area defined by the back surface is larger than the surface area defined by at least one side edge. It is imaginable that at least one decorative layer completely surrounds core layer. lt is possible at all side edges, including the front surface and back surface of the panel are provided with a decorative layer. A (rectangular) block shaped panel can for example have six sides provided with a decorative layer.

The panel according to the present invention, and in particular the core layer thereof could comprise sealed edges. Hence, it is conceivable that the multicellular material forming the multicellular substrate is substantially sealed at all edges. The panel could for example comprise sealing strips or sealing layers, preferably applied via thermolamination. The sealing layer may be thermolaminated to the outer edges of the core layer. This has the added benefit that the porous structure of the multicellular substrate, and optionally the porous structure of parts of the support structure is sealed. This prevents the collection of dirt or the uptake of moisture from the surroundings into the core layer. A separate sealing strip may be used. Such embodiment could provide for sealing of the multicellular substrate through heat, allowing for stronger structural integrity at the edges, and for screws, fastening means, a click system and/or interlocking mechanism to be provided.

In a preferred embodiment, the panel comprising complementary coupling elements and/or coupling parts. It is for example imaginable that at least two side edges of the panel comprise complementary coupling elements. The coupling elements and/or coupling parts can for example be configured to provide a snap connection and/or click connection. The coupling parts of the panel may for example be interlocking coupling parts, which are preferably configured for providing both horizontal and vertical locking. Interlocking coupling parts are coupling parts that require elastic deformation, a click or a movement in multiple directions to couple or decouple the parts with or from each other. Any suitable interlocking coupling parts as known in the art could be applied. A non-limiting example is an embodiment wherein a first edge of said first pair of opposing edges comprises a first coupling part, and wherein a second edge of said first pair of opposing edges comprises a complementary second coupling part, said coupling parts allowing a plurality of panels to be mutually coupled; wherein the first coupling part comprises a sideward tongue extending in a direction substantially parallel to a plane defined by the panel, and wherein the second coupling part comprises a groove configured for accommodating at least a part of the sideward tongue of another panel, said groove being defined by an upper lip and a lower lip. It is imaginable that the coupling parts, or the click-assembly is thermoformed and/or milled.

A compression strength of the support structure may be higher than a compression strength of the multicellular substrate, measured according to ASTM-D1037 in a direction from the front surface to the back surface of the core layer.

Advantageously, the support structure as such increases the overall compression strength of the core layer and the panel as a whole. This results in a sturdier, more rigid panel, that is less likely to break under compressive forces.

Preferably, the at least one support structure and the multicellular substrate comprise the same compounds and the density of the support structure is higher than the density of the multicellular substrate. This allows the support structure and the multicellular substrate to be bonded together without any adhesive, for example by thermolamination. The same compounds are herein defined as molecules being substantially the same. For example, both the support structure and the multicellular substrate could be made of polyvinyl chloride. The density of the multicellular substrate may nevertheless be lower than the density of the support structure because the multicellular substrate may contain more cells and/or cell having a larger volume (i.e. having a larger cell size). Due to the increased density of the support structure relative to the multicellular substrate, the support structure is stronger than the multicellular substrate, enabling the support structure to support the entire core layer. In line therewith, an average cell volume of the multicellular substrate is preferably larger than an average cell volume of the support structure. Optionally, the support structure may be substantially free of cells.

The multicellular substrate and/or the support structure may comprise a thermoplastic polymer or a thermoset polymer. A thermoplastic polymer is preferred, as this enables heating of the thermoplastic polymer prior to extrusion, enabling a better control over the viscosity of the extruded material. A thermoset polymer is however also a possibility.

The multicellular substrate and/or the support structure may comprise at least one polymer selected from polyvinyl chloride (PVC), polystyrene (PS), polyethylene

(PE), high-density polyethylene (HDPE), low-density polyethylene (LDPE), cross- linked polyethylene (XPE), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polypropylene (PP), Polyethylene terephthalate (PET), thermoplastic starch (TPS), cross-linked polystyrene (XPS), styrene acrylonitrile (SAN), polyphenylene oxide (PPO), polylactic acid (PLA), phenolic resin, melamine resin, formaldehyde resin, or any combination thereof. Preferably, the multicellular substrate and/or the support structure is at least partially biodegradable. Therefore preferred polymers are biodegradable. It is imaginable that the multicellular substrate comprises at least one bioplastic. It is also imaginable that the multicellular substrate and/or the support structure is made of bioplastics.

The polymer described above may also be a thermoplastic binder. The core layer preferably comprises at least one such thermoplastic binder. However, it is also conceivable that the core layer comprises additionally or alternatively at least one thermosetting binder. The use of at least one thermoplastic or thermosetting material in the core layer is conceived to impart flexibility characteristics to the panel when deemed necessary, for example when flexibility is required to achieve engagement of a locking mechanism.

The multicellular substrate and/or the support structure may comprise starch-based plastic, soybean-based plastic, cellulose-based plastic, lignin-based plastic, and/or natural fibers. The biodegradability of these plastics results in an environmentally friendly panel, as the panel can be biodegraded after its lifetime.

The core layer, and in particular the multicelluar substrate may comprise at least one filler. The filler material can comprise organic or inorganic materials which includes but is not limited to cellulose materials, fibrous materials, kraft paper, saw dusts, wood dusts, wood fibers, long wood fibers, short wood fibers, sand, lime, volcanic ash, plants-based fibers such as mushroom fibers, cotton fibers, bamboo fibers, abaca fibers, pineapple fibers, magnesium compounds, magnesium oxide, magnesium carbonate, limestone, polymeric fibers, glass fibers, carbon-based fibers, polymeric pellets, or hollow microspheres or particles having size ranging from 1 to 1000 micrometers made of but is not limited to ceramics, glass, polymers, composites, or metals. Preferably, the core layer includes at least one filler selected from the group consisting of: minerals, preferably calcium carbonate; and pigments,

modifiers, fibers, such as: glass fiber, wood, straw and/or hemp. The fibers can be loose fibers and/or interconnected fibers to form a woven or nonwoven layer.

Preferably the core layer further includes at least one additional filler selected from the group consisting of steel, glass, polypropylene, wood, acrylic, alumina, curaua, carbon, cellulose, coconut, kevlar, Nylon, perlon, polyethylene, PVA, rock wool, viburnum and fique. This can further increase the strength of the panel itself and/or the water resistance and/or fire resistance of the panel. The core layer can be a wood plastic composite core layer.

A density of the multicellular substrate may be lowest at a position most remote from the support structure, and a density of the multicellular substrate may be highest at another position adjacent to the support structure. The multicellular substrate may be formed by multiple multicellular plates formed by expansion of an extruded mixture that includes a thermoplastic polymer and laminated together. As such, the laminated outer edges of the multicellular plates form the support structure. As the outer edges cool rapidly, expansion at these outer edges is minimal. The center of each multicellular plate remains at elevated temperature for a longer period of time as compared to the outer edges, and as such, expansion in these centers is more profound, resulting in a lowest density at these centers.

Advantageously, this results in the support structure having the highest density of the core layer. In line therewith, the density of the multicellular substrate may be a gradient. Hence, at least one multicellular substrate, and in particular the multicellular material of the multicellular substrate can have a density gradient. It is imaginable that the density of part of multicellular substrate is higher at at least one edge, or at least two edges compared to a central part of the substrate. A density gradient can be beneficial for providing support for screwing, for example when provided in a plane perpendicular to the panel. The density gradient can for example be a density gradient over the thickness or height of the core layer. It is also imaginable that the density gradient extends over a direction substantially perpendicular to the thickness of the panel. It is for example imaginable that the density near the front surface and/or the density near the back surface is higher than the density of a central region of the core layer which is situated between said front surface and back surface. The density over at least part of the central region of the core layer is preferably substantially constant or homogeneous. lt is for example conceivable that the density near the front surface and/or the density near the back surface of the at least one core layer is at least 5% higher, and preferably at least 10% higher than the average density of the core layer. The density near the front surface and/or the density near the back surface is preferably higher than the density of the bulk of the core layer. When the density near the front surface or near the back surface is mentioned, an upper region or bottom region of the core layer could be meant. Basically, an embodiment is imaginable wherein the core layer, or the multicellular substrate, comprises an upper skin layer and/or a bottom skin layer. Each skin layer can have a density which is at least 5% higher, and preferably at least 10% higher than the average density of the core layer. Such skin layer is an internal skin layer which forms integrally part of the core layer. The skin layer could also be referred to as crust layer. The skin layer basically forms an integral protective layer for the core layer. In a further preferred embodiment, the density (of the core layer) near the front surface is higher than the density (of the core layer) near the back surface. lt is for example also imaginable that at least one core layer has a density in the range of 70 to 90%, and preferably in the range of 75 to 85%, of the gravimetric density of the composite material (forming the core layer) in a non-foamed state.

A density of the multicellular substrate may range between 80 and 1000 kg/m?, preferably between 100 and 1000 kg/m3, more preferably between 300 and 1000 kg/m3, such as approximately 600 kg/m3. The density of the multicellular substrate may be relatively homogenous when the multicellular substrate and the support structure are formed from different compounds. The density of the multicellular substrate may also vary from a location most remote from the support structure to a location adjacent to the support structure. A low density at a location remote from the support structure is advantageous, as the overall weight of the core layer will be significantly reduced, while the strength is increased by the relatively high density of the support structure.

Preferably, the core layer has a discrete density gradient. It is preferred that the multicellular substrate has a density that is relatively low compared to the average density of the core layer and also relatively homogenous. Preferably, the density of the support structure is relatively high compared to the average density of the core layer and also relatively homogenous. In particular, in the case where the multicellular substrate and the support structure comprise the same compounds,

and only differ by the volume and amount of cells present, the gradient in density between the multicellular substrate and the support structure is discrete. This ensures that the multicellular substrate is very light, while the support structure is heavy and bears the vast majority of the load applied on the panel.

At least one core layer of the panel according to the invention is preferably at least partly foamed. Different degrees of foaming are conceivable within the scope of the present invention. lt is preferred that the panel, and in particular at least one core layer, has an expansion percentage in the range of 5% to 50%. Non-limiting examples are an expansion percentage in the range of 15% to 35%, in particular in the range of 20% to 30%. However, it is also conceivable that the panel, and in particular at least one core layer, has an expansion percentage of at least 10%, in particular at least 20%, more in particular at least 30% and even more in particular at least 40%. The expansion percentage is in particular a measure for the rate of change of the volume of the panel, and in particular the core layer.

At least one core layer may comprise at least one mineral filler preferably chosen from the group of: calcium carbonate (CaCO3), chalk, clay, calcium silicate (Si-

Cal), dolomite, talc, magnesium oxide (MgO), magnesium chloride (MgCl or MOC cement), magnesium oxysulfate (MOS cement) and/or limestone. The use of at least one mineral material in the core layer is conceived to impart a sufficient rigidity thereby ensuring dimensional stability of the panel. It is for example conceivable that the mineral material comprises a magnesium-based mineral, such as but not limited to magnesium oxide (MgO), magnesium chloride (MgC! or MOC cement), magnesium oxysulfate (otherwise known as MOS cement). In case limestone is applied as mineral filler, it is beneficial if the mesh of limestone used is 325 mesh or 400 mesh. The core layer can for example comprise a composite material having a weight ratio of mineral filler to thermoplastic binder which is at least 3:1. It is also conceivable that the composite material has a weight ratio of mineral filler to thermoplastic binder which is greater than 3.5:1 or in the range of 3:1 to 4:1. However, alternatively, it is also conceivable that the core layer comprises at least 30 wit% of at least one mineral filler, preferably at least 50% by weight, more preferably at least 60% by weight. The composite material could for example comprise at most 40% of said at least one thermoplastic binder, preferably at most 30% by weight, more preferably at most 25% by weight. It is conceivable that the ratio is smaller, such as 1:1, 1.5:1 or 2:1. The core layer can have a Vicat softening temperature of at least 80 degrees Celsius, preferably at least 85 degrees

Celsius and/or and wherein the front surface of the panel and/or the back surface of the panel can have a Shore D hardness of at least 85. The use of at least one mineral material in the core layer is conceived to impart a sufficient rigidity, advantageously higher than 4000Mpa MOE and 22 Mpa MOR thereby ensuring dimensional stability and toughness of the panel. The use of at least one polymer in the core layer is conceived to impart flexibility characteristics to the panel when deemed necessary, or for example when flexibility is required to achieve engagement of a locking mechanism, if applied, advantageously lower than 9000Mpa and 36Nm MOR. The core layer according to the present invention is in particular configured and suitable for use in a thermo bonding process. The composite material of the core layer may for example comprise at least one additive configured to increase the Vicat softening temperature. At least one additive could for example comprise acrylonitrile styrene acrylate (ASA), acrylonitrile butadiene styrene (ABS), a thermoset system and/or an epoxy system.

At least one additive can also be a Vicat modifier or referred to as Vicat modifier. In an alternative embodiment, it is possible that at least one polymer of the composite material is a thermosetting polymer.

In an embodiment, the multicellular substrate and/or the support structure comprises a wood plastic composite (WPC). These wood plastic composites are aesthetically pleasing and as such, a decorative layer can be omitted.

The support structure may comprise a stone plastic composite (SPC) and/or a metal, such as aluminium. Like WPC, SPC is aesthetically pleasing as will, allowing the decorative layer to be omitted. Metals, such as aluminium provide extra stability to the support structure, while being relatively light weight, resulting in a strong but lightweight panel.

Advantageously, the core layer and/or the panel is substantially free of adhesive. In particular if the support structure and the multicellular substrate comprise the same compound, there is no need to provide an adhesive layer between the multicellular substrate and the support structure. In addition, in this case extruded multicellular plates can be adhered together via thermolamination soon after extrusion, instead of providing an adhesive. Adhesives often release harmful volatile organic compounds. As such, the lack of adhesives is a major advantage. In particular, panels may be connected via complementary coupling means, such as a tongue and groove, omitting use of adhesives even when panels are installed together to cover a surface larger than an individual panel.

The core layer comprises at least one bio-based plasticizer, such as palm oil, epoxidized soybean oil, castor oil, succinic acid, citrates or any combination thereof. This allows the panel to be somewhat flexible, aiding in installing panels. In particular if the panels have complementary coupling means, the coupling means can be more flexible, resulting in facilitated coupling of the panels.

At least one decorative layer as applied in panel according to the present invention can for example comprise at least one support layer, for example at least one (highly) filled thermoplastic support layer thermolaminated with a thermoplastic décor layer, an optional wear layer and optionally finished with a UV coating. At least one decorative layer, and in particular at least one support layer, can comprise or consist of SPC, LVT, extruded, calendered or injection moulded thermoplastic.

At least one decorative layer, if applied, preferably comprises at least one support layer, at least one décor layer and/or at least one protective layer. lt is conceivable that at least one décor layer is attached to said the core layer, if applied. It is also conceivable that the décor layer is a print layer. lt is also conceivable that at least one decorative layer is a print layer, in particular a digital print layer. The décor layer may also form integral part of a support layer. In a beneficial embodiment of the panel, at least part of the upper surface of the support layer is provided with at least one decorative pattern or decorative image. It is for example possible that such decorative image or pattern is provided via printing, for example via digital and/or inkjet printing. It is also possible that at least one decorative pattern is formed by relief provided in the upper surface of the support layer or panel. lt is also conceivable that the décor layer or decorative layer is a separate layer, for example a high-pressure laminate (HPL), a veneer layer, a directly laminated paper layer, and/or a ceramic tile. In a preferred embodiment, at least one decorative layer comprises a thermoplastic film or a ply of cellulose. It is for example possible that the décor layer comprises a plurality of impregnated layers containing lignocellulose but also a wood veneer, a thermoplastic layer, a stone veneer, a veneer layer or the like and/or a combination of said materials. The veneer layer is preferably selected from the group comprising of wood veneer, cork veneer, bamboo veneer, and the like. Other materials such as ceramic tiles or porcelain, a real stone veneer, a rubber veneer, a decorative plastic or vinyl, linoleum, and laminated decorative thermoplastic material in the form of foil or film. It is imaginable that the support layer of at least one decorative layer is connected to the support structure of at least one core layer.

At least one decorative layer can comprise at least one thermoplastic material. For example, at least one support layer of at least one decorative layer can comprise at least one thermoplastic material. The thermoplastic material can be PP, PET,

RPET, PVC, PLA, PE, HDPE, LDPE, XPE, or a bioplastic such as thermoplastic starch (TPS) and the like. The design of the decorative layer can for example be chosen from a design database which includes digitally processed designs, traditional patterns, pictures or image files, customized digital artworks, randomized image pattern, abstract art, wood-patterned images, ceramic or concrete style images, or user-defined patterns. The designs can be printed or reproduced using laser printers, inkjet printers, or any other digital printing means including the conventional printing methods. Various types of inks can also be used to suit the design needs of the décor layer. Preferably, the ink used during the printing method comprises properties such as but is not limited to waterproofness, lightfastness, acid-free, metallic, glossy, sheen, shimmering, or deep black, among others. It is desirable that the decorative layer is visually exposed by the coating layer being a substantially transparent coating layer. The décor layer may comprise a pattern, wherein the pattern is printed via digital printing, inkjet printing, rotogravure printing machine, electronic line shaft (ELS) rotogravure printing machine, automatic plastic printing machine, offset printing, flexography, or rotary printing press. The thickness of the decorative layer is preferably in the range of 0.05 mm and 0.10 mm, for example substantially 0.07 mm. In a preferred embodiment, the decorative layer comprises at least one décor layer and/or at least one wear layer. The wear layer could for example be scratch resistant layer. The decorative layer could possibly comprise a wear layer or finishing layer, for example with a thermosetting varnish or lacquer such as polyurethane, PUR, or a melamine based resin. In a preferred embodiment, the decorative layer comprises at least one substantially transparent wear layer or finishing layer. The wear layer may comprise one or more transparent layers of a thermoplastic or thermosetting resin. Non-limiting examples of thermoplastic or thermosetting materials which could be used are polyvinyl chloride (PVC), polystyrene (PS), polyethylene (PE), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polypropylene (PP), Polyethylene terephthalate (PET), phenolic and/or melamine or formaldehyde resins. Said wear layer may also be in a liquid or paste-like form made of a thermosetting resin such as but not limited to phenolic and/or melamine or formaldehyde resins. The wear layer may comprise or may be substantially composed of an inherently scratch-resistant thermosetting resin impregnating a carrier layer such as paper or lignocellulose. An advantage of this latter embodiment is that the urea-formaldehyde also acts a relatively scratch- resistant wear layer. Typically, a preferred thickness of the wear layer structure in the panel of the invention is in the range of 0.1 to 2.0 mm, more preferably between 0.15 mm to 1mm and most preferably between 0.2 mm to 0.8 mm. At least one support layer can have a thickness in the range of 0.2-2mm, preferably 0.5-1.5mm.

Such embodiment will provide sufficient body to the panel surface for screw strength and/or the screw pullout strength. At least one support layer of at least one decorative layer is preferably substantially rigid. A rigid support layer can provide rigidity and strength to the panel. The rigidity, or MOE, of at least one support layer can for example be larger than 2000 Mpa, preferably larger than 4000Mpa, more preferably larger than 6000 Mpa according to EN 310 or a mandrel test >100mm according to ISO 24344.

The decorative top layer, and in particular the support layer thereof, could optionally comprise at least one filler. The filler material of the decorative layer, or the support layer thereof can comprise organic or inorganic materials which includes but is not limited to cellulose materials, fibrous materials, kraft paper, saw dusts, wood dusts, wood fibers, long wood fibers, short wood fibers, sand, lime, volcanic ash, plants- based fibers such as mushroom fibers, cotton fibers, bamboo fibers, abaca fibers, pineapple fibers, magnesium compounds, magnesium oxide, magnesium carbonate, limestone, polymeric fibers, glass fibers, carbon-based fibers, polymeric pellets, or hollow microspheres or particles having size ranging from 1 to 1000 micrometers made of but is not limited to ceramics, glass, polymers, composites, or metals. Preferably, the decorative layer, or the support layer, includes at least one filler selected from the group consisting of: minerals, preferably calcium carbonate; and pigments, modifiers, fibers, such as: glass fiber, wood, straw and/or hemp. The fibers can be loose fibers and/or interconnected fibers to form a woven or nonwoven layer. Preferably the decorative layer further includes at least one additional filler selected from the group consisting of steel, glass, polypropylene, wood, acrylic, alumina, curaua, carbon, cellulose, coconut, kevlar, Nylon, perlon, polyethylene, PVA, rock wool, viburnum and fique. This can further increase the strength of the panel itself and/or the water resistance and/or fire resistance of the panel.

In a preferred embodiment, the wear layer or finishing layer can comprise at least one coating layer. For example, the at least one coating layer may comprise a protective coating layer that is at least partially transparent or translucent. In a preferred embodiment, the at least one coating layer can for example be a polyurethane coating, an acrylic coating, and/or an epoxy polyol coating. Such coating can for example be an ultraviolet (UV) or electron beam (EB) curable coating. It is further conceivable that the coating layer comprises a thermoset resin and a photoinitiator cross-linked by a UV, excimer or electron beam curing process. ltis further conceivable that at least one decorative layer includes a tactile texture, preferably of at least 0.1 mm depth, most preferably at least 0.3mm depth. Such tactile texture may provide an enhanced visual effect. The enhanced visual effect could also be referred to as embossing. In a possible embodiment of the invention, a texture or embossing can be provided during the production process by means of rotary or plate imprinting. It is possible that at least one wear layer, if applied, is embossed with a surface texture design. The texture design can be any design desired, such as the natural texture found in wood, stone and the like. The tactile structure, if applied, may for example have an irregular tactile texture. It is also conceivable that only part of at least one decorative layer is provided with a tactile texture. In another possible embodiment, both the upper surface of the decorative layer and the surface of a chamfer, which may be applied, can include a tactile texture, preferably of at least 0.1 mm dept. Especially when the decorative layer is produced via a lamination process, a single press machine can be used which makes it cost efficient to use a press plate with matching embossing for each decorative pattern in order to obtain a relief pattern on the top surface of the panel that matches the decorative pattern.

At least one decorative layer may further comprise at least one resin impregnated ply of paper comprising at least one antibacterial agent, preferably zinc oxide (ZnO) and/or silver nanoparticles or the like. It is also conceivable that the resin composition with which at least one ply of paper is impregnated comprises at least one antibacterial agent, preferably metal oxides such as titanium dioxide (TiO2), zinc oxide (ZnO), or isothiazolinone, zinc pyrithione, thiabendazole, and/or silver nanoparticles. The presence of at least one antibacterial agent can be beneficial in case it desired to apply the floor panel or floor covering made of such panel for business, industries or areas where a high hygiene standard is present. In case a wear layer or overlay is applied, it is also conceivable that the antibacterial agent is present in the wear layer or overlay. The antibacterial agent may form integral part of the decorative layer. A panel comprising a decorative layer which comprises at least one antibacterial agent typically provide a much better protection against bacteria, fungus, parasites and/or viruses compared to panels which are covered with an antibacterial agent. lt is beneficial if at least one decorative layer and at least one core layer are bonded via the provision of heat and/or pressure. At least one decorative layer and at least one core layer can for example be bonded via thermo bonding and/or thermolamination. It is beneficial to apply thermo bonding as for the use of an intermediate adhesive layer between the decorative layer and the core layer can be omitted. The use of the core layer and decorative layer according to the present invention allow the application of a thermo bonding process.

In an alternative embodiment, the invention also relates to a panel, comprising at least one core layer, comprising at least one multicellular substrate, and at least one support structure, and optionally at least one decorative layer attached to at least one core layer, wherein at least one core layer comprises a front surface and a back surface located on opposite sides, wherein at least part of at least one support structure is substantially parallel to the front surface and/or back surface and/or wherein at least one support structure extends over the entire width and/or length of at least one core layer. The support structure is preferably an integrated support structure. Any of the described embodiment in this application could apply to this alternative embodiment too.

In another aspect, the present invention relates to a method for manufacturing a panel, in particular a panel as outlined above, comprising the following steps: a) extruding at least one mixture comprising at least one expandable thermoplastic material, such that at least two multicellular plates are formed; b) optionally, providing an intermediate layer; ¢) adhering the at least two multicellular plates to each other, optionally via the intermediate layer, to provide a stack of multicellular plates which are connected via at least one joint; and d) cutting the stack of multicellular plates in a direction from one of the multicellular plates to another one of the multicellular plates to provide at least one core layer comprising at least one multicellular substrate and at least one support structure, wherein at least one multicellular substrate is formed of at least two multicellular plates parts and wherein at least part of at least one support structure is formed by at least part of at least one joint connecting said multicellular plate parts; and e) adhering at least one decorative layer to at least one core layer to obtain a panel. The method is particularly advantageous, as the at least two multicellular plates are extruded that are adhered to each other, either with or without an intermediate layer. The joint between both plates acts as a support structure after the stack of multicellular plates are cut. As such, the joint may form a rib-like structure that is formed by a part cut from joint. The obtained panel is typically a flat plate cut from either side of the stack of multicellular plates. In the case that the multicellular plates themselves have a flat-plate shape as well, the obtained core layer comprises ribs that are also partly plate-like. Two opposite outer edges of these ribs are in this case directed towards the front surface and back surface of the core layer, while the largest surfaces of these ribs may be adjacent to the multicellular substrate.

Multicellular is herein defined with reference to either a substrate or a plate. The multicellular substrate or multicellular plate is composed of a material comprising a plurality of cells. The cells are voids in the material surrounding the cells and the cells can have a varying volume. Typically, the material surrounding the cells is a polymer. In general, the expandable thermoplastic material is a material that is capable of expanding by the formation of cells. The cells may be filled with any type of gas, either created by the thermoplastic material itself as a by-product of an expansion reaction, or as a separate component in the mixture. A thermoplastic material is a polymer material that becomes pliable at elevated temperatures, and solidifies when cooled. A process of cooling and heating the thermoplastic material to change the thermoplastic material from a solid to a moldable or pliable state and the other way around, can be repeated almost indefinitely.

The formed core layer, and/or the mixture, could further comprise at least one additive. It is for example conceivable that the core layer and/or the mixture comprises at least one expansion agent, such as a foaming agent. Other additives could be a catalyst and/or at least one further filler. At least one (secondary) filler can for example be selected from the group consisting of: minerals, preferably calcium carbonate, and pigments, modifiers, fibers, such as: glass fiber, wood, straw and/or hemp. The fibers, if applied, can be loose fibers and/or interconnected fibers which form a woven or nonwoven layer. It is also conceivable that the core layer and/or the mixture comprises at least one additional filler selected from the group consisting of steel, glass, polypropylene, wood, acrylic, alumina, curaua, carbon, cellulose, coconut, kevlar, Nylon, perlon, polyethylene, PVA, rock wool, viburnum and fique. The use of any of said components can further increase the strength of the core layer and as such the panel and/or the water resistance and/or the fire resistance thereof.

An embodiment of a panel is conceivable which comprises multiple core layers. In case multiple core layers are applied, preferably at least one core layer, and more preferably each core layer is an extruded core layer. It is further beneficial if at least one core layer and in particular each core layer is at least partially foamed, and as such a multicellular core layer. The panel could for example comprise at least two core layers. The core layers may be directly attached to another, for example without the interference of an adhesive layer. It is conceivable that that the core layers vary in thickness. It is also conceivable that the core layers have a different material composition. It is for example imaginable that an upper core layer has a lower density than a bottom core layer, or vice versa. Each core layer can be a core layer according to any of the embodiments described for the present invention. . It is for example conceivable that each core layer comprises at least one skin layer. A skin layer is also referred to as a crust layer. A skin layer is formed by cooling the outsides of an expanding multicellular substrate. Cooling, actively or non-actively, ensures that expansion of the multicellular substrate on the outer surfaces thereof is somewhat inhibited, resulting in a skin or crust. Hence, it is conceivable that two adjacent core layers are attached such that said adjacent skin layers are merged together forming an integral support structure within the core layer. In a preferred embodiment, at least one core layer is a co-extruded core layer. This can be for example 2 or 3-layer co-extrusion. In a preferred embodiment, at least one core layer is a co-extruded core layer. This can be for example 2 or 3-layer co-extrusion.

It is conceivable that substantially total decomposition of an expansion component present in the mixture occurs. A decomposition temperature of this expansion component typically depends on the type of expansion component which is used.

This temperature can for example be in the range of 170 to 190 degrees Celsius.

The temperatures applied in practice depend on the specific material compositions applied and the preferred extrusion conditions.

The mixture or melt can be subjected to multiple subsequent (axially) temperature zones from the screw of an extruder to the die nip of the extruder. A first temperature zone can be in the range of 170 to 190 degrees Celsius and/or a second temperature zone is in the range of 190 to 210 degrees Celsius and/or a third temperature cone can be in the range of 160 to 190 degrees Celsius. The surface temperature of at least one surface of the melt close to die nip can for example be in a range of 170 to 190 degrees Celsius, in particular 175 to 185 degrees Celsius, in particular to enable formation of a protective skin or crust on at least one surface of the extruded multicellular plate. The temperature difference between the screw and the die of the extruder and in particular the die nip of the extruder is for example at least 20 degrees Celsius, preferably at least 30 degrees

Celsius.

By means of temperature control and/or pressure control in the die of the extruder a foamed composition can be formed in a desired plate-shape. The pressure within the extruder may also be controlled. It is for example conceivable that pressure is controlled by adapting the volumetric profile of the internal channels of the extrusion die, in particular the height and/or volume of the internal channels.

The adhering of step e) may comprise laminating at least one decorative top layer onto an upper core surface of the core layer. The lamination of at least one decorative top layer onto the core layer can for example be done by merging said layers. A conventional lamination module or lamination unit can be applied in order to perform the lamination. By applying lamination, the use of an adhesive layer can be omitted. It is for example conceivable that at least one core layer and at least one decorative top layer are at least partially fused together.

A joint is a connection between two materials. When an intermediate layer is provided in step b), the joint may be composed by the intermediate layer on its own, or by a combination of an outer surface of both multicellular plates directly adjacent to the intermediate layer and the intermediate layer. In the case where an intermediate layer is not provided, the joint may be composed of two adjacent outer surfaces of two multicellular plates. In both cases, a thickness of the joint may vary.

Usually a thickness of the joint is in the order of magnitude of several millimeters.

Preferably a direction of cutting during step d) is substantially perpendicular to a direction of extruding in step a). This provides the advantage that the joints formed in the stack of multicellular plates, may form the support structure of the core layer.

Depending on the position where the stack of multicellular plates is cut, the tis conceivable that the co-extruded multicellular plates form a plurality of individually extruded plates, referred to as a stack of multicellular plates, that are then cut to form a block or slice comprising a plurality of mutually bonded co- extruded multicellular plate parts, with the support structure formed by adjacent skin layers or crusts. The support structures as such may be formed from reinforcing struts or ribs throughout the entire volume of the core layer.

In an embodiment, the adhering in step c) and/or step e) comprises thermolaminating. This circumvents the need for any adhesives. As such, the method is more environmentally friendly, due to the lack of harmful volatile organic compounds released by adhesives.

The at least two multicellular plates may be cooled prior to step ¢). This provides the advantage that the formation of cells and the volume of each cell in outer surfaces of the multicellular plates is reduced due to cooling. As a result, the density of these outer surfaces is relatively high as compared to the density of the multicellular plates in a center thereof. As the outer surfaces of each multicellular plate may together form the support structure, the support structure itself will have a relatively high density. The high density of the support structure advantageously increases the strength of the support structure, enabling the resulting panel to bear a higher load.

At least part of the upper surface of the multicellular plate and/or at least part of the lower surface of the multicellular plate can be cooled before and/or after the multicellular plate has left the die nip of the extruder, preferably substantially directly after the (formed) multicellular plate has left the die nip of the extruder. This step can in particularly be applied such that a (discrete) density gradient is created within the multicellular plate. It is for example possible to apply a cooling step of at least part of the upper surface of the multicellular plate and/or at least part of the lower surface of the multicellular plate which causes that the density near the upper surface and/or near the lower surface to be higher than the average density of the multicellular plate. Said cooling can in particular cause the formation of a skin layer which forms integral part of the multicellular plate.

It is conceivable that cooling at least part of the melt in the die of the extruder is performed such that the temperature of the melt is decreased with at least 10 degrees Celsius, preferably at least 20 degrees Celsius, more preferably at least 25 degrees Celsius. It is also conceivable that the melt in the die nip of the extruder is performed such that the temperature of the melt is decreased with at least 5 degrees Celsius, preferably at least 10 degrees Celsius. It is conceivable that the temperature of the melt at its top and bottom surfaces is reduced to substantially equal or less than the decomposition temperature of the expansion component. It is conceivable that the temperature within the melt which is not directly exposed to the cooling step, substantially within the inner part of the multicellular plate, is higher than the decomposition temperature of the expansion component, allowing further expansion of the core. This can create a beneficial density gradient where at least one surface of the multicellular plate has a higher density than the rest of the

The method may further comprise the step of cooling at least part of the upper core surface and/or at least part of the bottom core surface of the core layer before and/or after the core layer has left the die nip of the extruder, preferably substantially directly after the (formed) core layer has left the die nip of the extruder. This step can in particularly be applied such that a density gradient is created within the core layer. It is for example possible to apply a cooling step of at least part of the upper core surface and/or at least part of the bottom core surface of the core layer which causes that the density near the upper core surface and/or near the bottom core surface is higher than the average density of the core layer.

Said cooling step can in particular cause the formation of a skin layer which forms integral part of the core layer. it is conceivable that cooling at least part of the melt in the die of the extruder is performed such that the temperature of the melt is decreased with at least 10 degrees Celsius, preferably at least 20 degrees Celsius, more preferably at least 25 degrees Celsius. It is also conceivable that the melt in the die nip of the extruder is performed such that the temperature of the melt is decreased with at least 5 degrees Celsius, preferably at least 10 degrees Celsius. It is conceivable that the temperature of the melt at its top and bottom surfaces is reduced to substantially equal or less than the decomposition temperature of the blowing agent composition. It is conceivable that the temperature within the melt which is not directly exposed to the cooling step, substantially within the inner part of the core, is higher than the decomposition temperature of the blowing agent composition, allowing further expansion of the core. This can create a beneficial density gradient where at least one surface of the core has a higher density than the rest of the multicellular plate.

Preferably, the at least two multicellular plates may be extruded simultaneously.

This has the added benefit that the multicellular plates are automatically stacked on top of each other during production. In addition, when the multicellular plates exit the extruder, the multicellular plates have a relatively high temperature. As such, the multicellular plates may adhere to each other, automatically forming joints, without the need of introducing additional heat or pressure.

In an embodiment, the at least two multicellular plates may be at least 10 multicellular plates, more preferably at least 15 multicellular plates, even more preferably at least 20 multicellular plates, most preferably 30 to 50 multicellular plates. A larger amount of multicellular plates result in a panel having a larger surface area. lt is in particular advantageous if the multicellular plates are extruded simultaneously, as the lamination of the multicellular plates can occur as a part of this process, instead of during a separate thermolamination process.

Additionally or alternatively, the method may comprise prior to the step e) of adhering, a step of adhering at least two core layers to each other, wherein a direction of extension of the support structure of at least one core layer of the at least two core layers is arranged at an angle to a direction of extension of the support structure of at least one other core layer of the at least two core layers.

This is in particular advantageous if ribs, or ribs having a plate-like shape have been formed in a core layer. A first core layer with a support structure comprising or consisting of such ribs can be rotated approximately 90 degrees with reference to another such a core layer. Adhering both core layers together results in a combined core layer having a total support structure that has a grid like structure when viewed from a front surface of the combined core layer to a back surface of the combined core layer. The core layers can also be rotated at an angle other than 90 degrees. A combination of multiple core layers, such as three, is also possible. In the case of combining three core layers, the angle of rotation of each core layer with respect to the core layer directly above or below can be 60 degrees. When viewed from above, a grid containing triangular shaped multicellular substrate parts is formed.

The mixture may comprise an expansion agent or expansion component, such as supercritical CO2. This expansion agent aids in the formation of cells in the resulting multicellular plate. The expansion agent can be added separately, as a part of the mixture, or can be generated in a chemical reaction initiated by the mixture after extrusion.

In a preferred embodiment, at least one expansion component comprises azodicarbonamide (C2HsN4O2) and/or sodium bicarbonate (NaHCO). It was experimentally found that said chemical compounds are suitable to use as expansion agents. The foaming agent can be added to the mixture at a total weight percentage of the mixture of at most 1%, more preferably at most 0.8 wt%. In particular for sodium bicarbonate it is required that said compound is applied in an appropriate quantity as too much of it would cause the cells of the multicellular plates to collapse resulting in a denser multicellular structure. It was experimentally found that the multicellular plate density decreases almost linearly with an increase of sodium bicarbonate. In a preferred embodiment, the expansion agent is added in the range of 0.3 to 0.5 wi%, based on total weight of the mixture.

Alternatively, or additionally, it is for example also possible that at least one expansion agent comprises N,N'-dinitroso-N,N'-dimethy! terephthalamide, N- aminophthalimide 4,4'-oxybis (benzenesulphonylhydrazide), N,N'- dinitrosopentamethylenetetramine, Azoisobutyric dinitrile, Diazoaminobenzene,

Dinitropentamethylene tetramine, Benzenesulfohydrazide, Terephthalyl bis (N- nitrosomethylamide), Toluene-2,4-bis (sulfonyl hydrazide) p-tertiary butylbenzazide), p-carbomethoxy benzazide, Diarylpentaazadiene and/or 3 methyl, 1 ,5-diphenylpentaazadiene. At least one expansion agent can be an exothermic expansion agent or an endothermic foaming agent. The expansion agent can also be referred to as blowing agent

It is beneficial if at least one expansion catalyst is added to the mixture. Non- limiting examples of foaming catalyst which can be added to the mixture are CaO,

Carbamide, Zinc 2-ethylhexanoate, Zinc benzenesulfinate, Zinc carbonate, Zinc ditolyl sulfinate, Zinc oxide, Zinc stearate, Ca/Zn esters, Ba/Zn esters, K/Zn esters,

Dibutyltin bis{iso-octylmaleate) and/or Dialkyltin bis(alkylthioglycollates).

In an embodiment, prior to step e) a sealing strip may be thermolaminated to at least a part of at least one core layer. The sealing layer may be thermolamitated to the outer edges of the core layer. As such, the sealing strip has an edge sealing function. This has the added benefit that the porous structure of the multicellular substrate, and optionally the porous structure of parts of the support structure is sealed. This prevents the collection of dirt or the uptake of moisture from the surroundings into the core layer. A separate sealing strip may be used. This sealing strip may be composed from the same or a different material than the core layer itself. Advantageously, the sealing strip does not comprise or consist of a multicellular material. It is also imaginable that the at least part of at least one core layer is heated, such that an outer crust substantially free from cells, and having a relatively high density, is formed. The thermolamination has again the added benefit that separate adhesives are not required. In addition, screws may be inserted in the sealing strip or a formed outer crust, as this part of the core layer has a relatively high density, and as such is very suitable to hold screws. The sealing strip or crust may also be processed such that they form a click system.

In yet another aspect, the present invention relates to a system for performing the method as outlined above, comprising: at least one extruder for extruding an expandable thermoplastic material, comprising a plurality of extrusion dies; and a conveyor for conveying extruded thermoplastic material; wherein the plurality of dies and/or die nips are arranged parallel to each other, and wherein an extrusion direction of each die is substantially the same. This system allows to create multicellular plates simultaneously that can be thermolaminated to each other. The system has all the advantages as described hereinabove.

Preferably, the system comprises a cooler for cooling the extruded thermoplastic material. In particular, by adjusting the amount of cooling on the outside of the extruded thermoplastic material, a thickness of the outer surface of the resulting multicellular plate can be adjusted as desired. When the stack of multicellular plates has been formed, the resulting joints, and as such the support structure in the core layer, can be adapted according to the required strength and/or weight of the support structure.

The plurality of dies and/or die nips may be stacked upon each other. As such, the multicellular plates are advantageously automatically stacked upon each other.

When the stack of multicellular plates requires cutting, the system may comprise a cutting element for cutting a stack of multicellular plates. As such, the cutting is performed by the system itself, in line, and there is no need for a separate cutting device. The position of cutting can be adjusted according to the desired thickness of the core layer.

The invention will now be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures. Herein shows:

- Figure 1 a first possible embodiment of a panel according to the present invention; - Figures 2a, 2b, 2c and 2d a possible method of producing a panel according to the present invention; - Figure 3 a third possible embodiment of a panel according to the present invention; - Figures 4a, 4b, 4c and 4d schematic representations of side views of possible embodiments of panels according to the present invention; - Figures 5a and 5b further possible embodiments of panels according to the present invention; and - Figure 6a and 6b show yet further possible embodiments of panels according to the present invention.

Within these figures, the same reference number refer to similar or equivalent technical features or elements.

Figure 1 shows a first possible embodiment of panel 100 according to the present invention. The panel 100 is in particular a decorative and/or structural panel 100.

The embodiment as shown comprises a core layer 101 and a decorative layer 102.

The decorative layer 102 is attached to the core layer 101, in particular to a front surface of the core layer 101. In the figure, only part of the decorative layer 102 is shown in order to visualize the core layer 101 in more detail. The core layer 101 comprises a multicellular substrate 103 and support structure 104. The core layer 101 comprises a front surface and a back surface located on opposite sides, wherein the thickness T of the core layer is defined by the distance between the front surface and the back surface. The figure shows that part of the support structure 104 extends over the thickness T of the core layer 101. In the shown embodiment, the support structure 104 comprises a plurality of ribs 104a which extends over the thickness T of the core layer 101. The ribs 104a are positioned substantially parallel to each other and define a substantially rectangular angle with respect to the front surface and back surface of the core layer. In the shown embodiment, the ribs 104a are positioned at a distance from each other. In fact, the ribs 104a of the shown embodiment are isolated ribs 104a which are embedded in the multicellular substrate 103. Optionally, the panel could comprise coupling elements and/or further layer attached to the decorative layer 102 and/or the core layer 101.

Figures 2a to 2d show a possible embodiment of a production process or method of producing a panel 200 according to the present invention. Figure 2a shows an intermediate product produced via an extrusion process. The arrow indicates the direction of extrusion E. Figure 2a shows that a plurality of interconnected multicellular plates 250 are produced, thus via an extrusion process. In the shown embodiment, a plurality of plates 250 is obtained via extruding at least one mixture comprising at least one expandable thermoplastic material, thereby creating a plurality of multicellular plates 250. The multicellular plates 250 are adhered to each other, optionally via an intermediate layer, to provide a stack of multicellular plates 250 as shown in figure 2a. The multicellular plates 250 are connected via joints 251. The stack of multicellular plates 250 is subsequently to be cut such that a core layer 201 according to the invention can be formed, which is shown in figure 2b.

Figure 2a shows the cut lines C, which are in a direction from one of the multicellular plates 250 to another one of the multicellular plates 250. As can be seen the direction of cutting is substantially perpendicular to the direction of extrusion. By this cutting step, a core layer 201 is formed comprising a multicellular substrate 203 and a support structure 204, wherein the multicellular substrate 203 is formed of at least two multicellular plates parts 250a and at least part of the support structure 204 is formed by at least part of at least one joint 251a connecting said multicellular plate parts 250a. Step 2c shows the provision of a plurality of decorative layers 202. In the shown embodiment two decorative layers 202 are adhered to the core layer 201. Figure 2d shown the panel 200 according to the present invention, which is provided with complementary coupling parts 230a, 230b. Figure 2d shows a side view of the panel.

Figure 3 shows a picture of a panel 300 according to the present invention. The panel 300 comprises a core layer layer 301 comprising a multicellular substrate 303 and a support structure 304. The multicellular substrate 303 is an extruded PET substrate 301 and support structure 304 forms integral part of the multicellular substrate 303. Hence, the core layer 301 is formed via extrusion. The support structure 304 is defined by a plurality of ribs 304a which are integrally formed within the multicellular substrate 303.

Figures 4a, 4b, 4c and 4d show schematic representations of side views of possible embodiments of panels 400a, 400b, 400c, 400d according to the present invention.

The panels could optionally be provided with coupling parts.

Figure 4a shows a panel 400a comprising a core layer 401 comprising a multicellular substrate 403 and a support structure 404. The embodiment as shows comprises two decorative layers 402a, 402b attached to opposing sides of the core layer 401. The support structure 404 extends over the thickness T of the core layer 401. In the shown embodiment, the support structure 404 has a triangular shaped configuration. Adjacent ribs 404a of the support structure 404 defines triangles. The legs of each triangle extend from the front surface to the back surface of the core layer 401. In the shown embodiments, the ribs 404a are interconnected. However, it is also conceivable that a triangular shaped support structure would have ribs which are positioned at a distance from each other.

Figure 4b shows an embodiment of a panel 400b comprising two core layers 401a, 401b. The upper core layer 401a comprising a multicellular substrate 403 and a support structure 404. The lower core layer 401b comprises a multicellular substrate 403b. The lower core layer 401b is free of reinforcing structures. The panel 400b further comprises three decorative layers 402a, 402b, 402c which enclose at least part of the core layers 401a, 401b. The density of the upper core layer 401a is lower than the density of the lower core layer 401b. The front surface of the upper core layer 401a and the side edges of the core layer combination 401a, 401b are provided with decorative layers 402a, 402b, 402c.

Figure 4c shows a panel 400c comprising a core layer 401 and a decorative layer 402 attached to a front surface of the core layer 401. The core layer 401 comprises a multicellular substrate 403 and a support structure 404. The multicellular material of the multicellular substrate 403 is provided inside the support structure 404. The support structure 404 provides support for the multicellular substrate 403 and for the panel 400c as such.

Figure 4d shows panel 400d comprising a core layer 401 and a decorative layer 402a attached to a front surface of the core layer 401 and a decorative layer 402b attached to a back surface of the core layer 401. The core layer 401 further comprises a support structure 404. The support structure 404 is integrally formed in the multicellular substrate 403. It can be seen that the density of the multicellular material of the multicellular substrate 403 is lower than the density of the multicellular material of the support structure 404. The support structure 404 is formed by crust layers forming part of the multicellular material of the multicellular substrate 403. It is imaginable that there is a density gradient between the support structure 404, and in particular the ribs thereof, and the substrate 403.

Figures 5a and 5b show possible embodiment of panels 500a, 500b according to the present invention.

Figure 5a shows and exploded view and an assembled view of a panel 500a comprises a core layer 501, a secondary support structure 540 and a the decorative layer 502 formed by a decorative print. The decorative print is provided via printing, for example digital printing or inkjet printing. The printing device 580 and printing step is schematically shown in the upper part of the figure. The secondary support structure 540 is a separate layer additional to the core layer 501. The secondary support structure 540 defines a honeycomb structure and a twinwall structure. The plates 540a, 540b enclose the honeycomb structure 540c, thereby forming a twinwall structure. It is for example possible that the honeycomb structure 540c is made of a different material than the plates 540a, 540b enclosing the honeycomb structure 540c. The honeycomb structure 540c can for example be made of of a metal, in particular aluminium and the plates 540a, 540b can be made of a polymer. The core layer 501 comprising a multicellular substrate 503 and a support structure 504.

Figure 5b shows yet a further embodiment of a panel 500b according to the present invention. The panel 500b comprises a core layer 501 comprising a multicellular substrate 503 and a support structure 504 and two decorative layers 502a, 502b enclosing the core layer 501. The support structure 504 defines a honeycomb structure. The support structure 504 is filled with multicellular material forming a multicellular substrate 503.

Figures 6a and 6b show further possible embodiments of panels 600a, 600b according to the present invention. The figures show schematic representations,

where figure 6a shows both an exploded view and a perspective view. Figure 6b shows a partially exploded view.

The upper part of figure 6a shows a front view and exploded view of the panel 600a and the bottom part of the figure shows the panel in the final configuration, or a combined view. The panel 600a comprises a core layer 601 and a plurality of decorative layers 602 which are laminated to the core | Each decorative layer 602 comprises a support layer 602a, a decor layer 602b and a wear and/or protective layer 602c. The core layer 601 comprises a multicellular material. The core layer 601 in particular comprises a multicellular substrate 603. It can be seen that the material of the core layer 601 has different densities of the multicellular material.

Basically, a density gradient is shown over the core layer 601. The core layer 601 small bubbles near the surfaces to show the higher density and larger bubbles near the middle of the core layer 601 to show the lower density. Near the edges of the core layer 601, the bubbles are relatively small indicating that this side features a higher density which is caused by the thermolamination on those edges. The core layer 601 could optionally be provided with a support structure according to the present invention.

Figure 6b shows a further possible embodiment of a panel 600b according to the present invention. The panel 600b, and in particular the core layer 601 comprises a plurality of ribs 604a defining a support structure 604. The support structure 604 is embedded in the multicellular substrate 603. The panel 600b comprises decorative layers 602 on all six surfaces of the panel. In the shown embodiment, the decorative layers 602 comprise a wood design. Each decorative layer 602 can comprise a laminate of functional layers, for example at least one support layer, decor layer, wear layer and/or protective layer. it will be apparent that the invention is not limited to the working examples shown and described herein, but that numerous variants are possible within the scope of the attached claims that will be obvious to a person skilled in the art.

The verb “comprise” and conjugations thereof used in this patent publication are understood to mean not only “comprise”, but are also understood to mean the phrases “contain”, “substantially consist of”, “formed by” and conjugations thereof.

Claims

Conclusions

1. Panel comprising: — at least one core layer comprising: e at least one multicellular substrate, and e at least one support structure; and — at least one decorative layer attached to the at least one core layer; wherein at least one core layer comprises a front side and a back side located on opposite sides, wherein the thickness of at least one core layer is defined by the distance between the front side and the back side, and wherein at least a portion of the at least one support structure extends across the thickness of the at least one core layer.

2. The panel of claim 1, wherein at least a portion of at least one support structure extends over the entire thickness of the multicellular substrate of at least one core layer.

3. A panel according to any preceding claim, wherein at least a portion of at least one support structure is positioned at an angle relative to a plane defined by the front and/or the back of at least one core layer.

4. A panel according to any preceding claim, wherein at least one support structure comprises a plurality of ribs, at least one rib, and preferably each rib, extending across the thickness of at least one core layer.

5. A panel according to claim 4, wherein at least two ribs run substantially parallel to each other.

6. A panel as claimed in claim 4 or claim 5, wherein at least two ribs are interconnected.

7. A panel as claimed in any one of claims 4 to 6, wherein at least two ribs are insulated from each other.

8. A panel according to any preceding claim comprising at least two core layers, each core layer comprising at least one multicellular substrate and at least one support structure, a first support structure of a first core layer being disposed at an angle to a second support structure of a second core layer.

9. Panel according to any one of the preceding claims, wherein at least part of the supporting structure is rigid.

10. A panel according to any preceding claim, wherein at least a portion of at least one support structure is embedded in at least one multicellular substrate.

11. A panel according to any preceding claim, wherein at least a portion of at least one support structure forms an integral portion of at least one multicellular substrate.

12. Panel according to any one of the preceding claims, wherein at least a part of at least one supporting structure defines a honeycomb structure and/or a double-wall structure.

13. A panel according to any preceding claim, wherein at least a portion of at least one support structure defines a grid.

14. A panel according to any preceding claim, wherein at least one core layer is an extruded core layer.

15. A panel according to any preceding claim, wherein at least one multicellular substrate is an extruded multicellular substrate.

16. Panel according to any of the preceding claims, comprising at least two decorative layers.

17. A panel according to any preceding claim, wherein the core layer comprises at least one side edge, and wherein at least one decorative layer is attached to at least one side edge.

18. Panel according to any of the preceding claims, comprising complementary coupling parts.

19. A panel according to any preceding claim, wherein a compressive strength of the support structure is higher than the compressive strength of the multicellular substrate, measured according to ASTM-D1037 in a direction from the front to the back of the core layer.

20. A panel according to any preceding claim, wherein at least one support structure and the multicellular substrate comprise the same compounds and wherein the density of the support structure is higher than the density of the multicellular substrate.

21. A panel according to any preceding claim, wherein an average cell volume of the multicellular substrate is greater than an average cell volume of the support structure.

22. A panel according to any preceding claim, wherein at least one multicellular substrate and/or at least one support structure comprises a thermoplastic polymer or a thermosetting polymer.

23. A panel according to any preceding claim, wherein at least one multicellular substrate and/or at least one support structure comprises at least one polymer selected from polyvinyl chloride (PVC), polystyrene (PS), polyethylene (PE), high density polyethylene (HDPE), low density polyethylene (LDPE), crosslinked polyethylene (XPE), polyurethane (PU), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyethylene terephthalate (PET), thermoplastic starch (TPS), crosslinked polystyrene (XPS), styrene acrylonitrile (SAN), polyphenylene oxide (PPO), polylactic acid (PLA), phenothin, melamine resin, formaldehyde resin, or a combination thereof.

24. A panel according to any preceding claim, wherein at least one multicellular substrate and/or at least one support structure is biodegradable.

25. A panel according to any preceding claim, wherein at least one multicellular substrate and/or at least one support structure comprises starch-based plastic, soybean-based plastic, cellulose-based plastic, lignin-based plastic, and/or natural plastic.

26. A panel according to any preceding claim, wherein the density of at least one multicellular substrate is lowest at a position most remote from the support structure and wherein the density of said multicellular substrate is highest at another position adjacent to the support structure.

27. A panel according to any preceding claim, wherein the density of at least one multicellular substrate has a density gradient.

28. Panel according to any of the preceding claims, wherein a density of the core layer ranges between 80 and 1000 kg/m3, preferably between 100 and 1000 kg/m3, more preferably between 300 and 1000 kg/m3, such as approximately 600 kg/m3.

29. A panel according to any preceding claim, wherein at least one multicellular substrate and/or at least one support structure comprises a wood-plastic composite (WPC) and/or foamed thermoplastic.

30. A panel according to any preceding claim, wherein at least one supporting structure comprises a rigid thermoplastic composite, a rigid thermosetting composite, a stone-plastic composite (SPC) and/or a metal, such as aluminium.

31. A panel according to any preceding claim, wherein at least one core layer and/or the panel is substantially free of adhesive.

32. A panel according to any preceding claim, wherein at least one core layer comprises at least one bio-based plasticizer, such as palm oil,

epoxidized soybean oil, castor oil, succinic acid, citrates or a combination thereof.

33. Method for manufacturing a panel, in particular a panel according to any one of claims 1 to 32, comprising the following steps: a) extruding at least one mixture comprising at least one expandable thermoplastic material, so as to form at least two multicellular sheets; b) optionally, providing an intermediate layer; c) bonding the at least two multicellular sheets together, optionally via the intermediate layer, to provide a stack of multicellular sheets connected via at least one bond; and d) cutting the multicellular sheets in a direction from one of the multicellular sheets to another of the multicellular sheets to provide at least one core layer comprising at least one multicellular substrate and at least one support structure, wherein at least one multicellular substrate is formed by at least two multicellular sheet members and wherein at least a part of at least one support structure is formed by at least a part of at least one bond connecting said multicellular sheet members; and e) bonding at least one decorative layer to at least one core layer to obtain a panel.

34. A method according to claim 33, wherein a cutting direction during step d) is substantially perpendicular to an extrusion direction in step a).

35. A method according to claim 33 or claim 34, wherein the bonding in step c) and/or step e) comprises a thermolamination process.

36. A method according to any one of claims 33 to 35, wherein the at least two multicellular plates are cooled prior to step c).

37. A method according to any one of claims 33 to 36, wherein the at least two multicellular sheets are extruded simultaneously.

38. The method of any one of claims 33 to 37, wherein the at least two multicellular plates are at least 10 multicellular plates, more preferably at least 15 multicellular plates, even more preferably at least 20 multicellular plates, most preferably 30 to 50 multicellular plates.

39. A method according to any one of claims 33 to 38, comprising, prior to step e) of bonding, a step of bonding at least two core layers together, wherein an extension direction of the support structure of at least one core layer is arranged at an angle to an extension direction of the support structure of the at least one other core layer of the at least two core layers.

40. A method according to any one of claims 33 to 39, wherein the mixture comprises an expanding agent, such as supercritical CO2.

41. A method according to any one of claims 33 to 40, wherein prior to step e) a sealing strip is thermolaminated to at least a portion of at least one core layer.

42. A system for carrying out the method according to any one of claims 33 to 41, comprising: at least one extruder for extruding an expandable thermoplastic material, comprising a plurality of extrusion heads; and a conveyor for conveying extruded thermoplastic material; wherein the plurality of extrusion heads and/or extrusion nipples are arranged parallel to each other, and wherein an extrusion direction of each extrusion head is substantially the same.

43. The system of claim 42, comprising a cooler for cooling the extruded thermoplastic material.

44. A system as claimed in claim 42 or claim 43, wherein the plurality of extrusion heads and/or extrusion nipples are stacked on top of each other.

45. System according to any one of claims 42 to 44, comprising a cutting element for cutting a stack of multicellular plates.