Method for manufacturing folded foam structure

Abstract

Provided is a method of continuously manufacturing a folded foam structure, comprising the steps of: a) continuously providing a foamed sheet having a top surface and a bottom surface, wherein the foamed sheet has been made by a foamed extrusion process of a thermoplastic polymer composition; b) providing a plurality of slits in the foamed sheet, wherein: - a first set of slits extends from the top surface over only a part of the thickness towards the bottom surface, thereby providing first living hinges between the first set of slits and the bottom surface; - a second set of slits extends from the bottom surface over only a part of the thickness towards the top surface, thereby providing second living hinges between the second set of slits and the top surface; - wherein, in the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged; c) heating the foamed sheet to obtain a foldable foamed sheet; d) folding the foldable foamed sheet over the first living hinges and the second living hinges, wherein: - adjacent parts of the bottom surface that are on opposite sides relative to a respective first living hinge are folded together; - adjacent parts of the top surface that are on opposite sides relative to a respective second living hinge are folded together; and e) providing a thermal bond between the parts that have been folded together, to thereby form the folded foam structure wherein the direction of extrusion of the foamed sheet extends in the thickness direction.

Description

24POLY0033-WO-ORD 1METHOD FOR MANUFACTURING FOLDED FOAM STRUCTUREThe present invention relates to a method for manufacturing a folded foam structure.It is known to use a multilayer composite comprising two face sheets and one core layer as insulation panels, roof panels, wall panels and floor panels. These panels are used in various industries such as transportation and building & construction. Examples of the articles using these panels include walls for trucks, insulated rooftops of houses and constructions for housing of electronics.The face sheets are visible on the outside of the multilayer composite and the core layers is in between the face sheets. Sometimes in-between layers are used, like for instance adhesive layers.Examples of face sheets are plywood, MDF (medium-density fiberboard) or fiberglass reinforced layers. The core layer is often a foam, for instance Polystyrene foam (PS), Polyurethane foam (PUR) or Polyester foam (PET). In some cases, a wooden construction is further applied to the face sheet to strengthen the construction.Traditional floor sandwich panels that are used in mobile homes are produced manually. The production starts with a wooden construction that is put together via screws and glue. The gaps in between the wooden construction are filled with a PS foam core layer. This core layer is covered by multiplex layers, which are connected to the core layer via screws and nails.An important property for floor sandwich panels and their core layers is its compression strength in its thickness direction. WO2023118202A1 discloses a method of manufacturing a foamed assembly having a high compression strength. A foamed sheet is made from a polypropylene composition by a foamed extrusion process. The foamed sheet is cut in the direction parallel to its cross section, i.e. perpendicular to its top surface and perpendicular to the extrusion direction to obtain elongated foamed elements. These elongated foamed elements are turned sideways such that their cross sections face upwards and downwards and their top surfaces face sideways. The elongated foamed elements are bonded to each other to form a foamed assembly which has a compression strength in the thickness direction which corresponds to the compression strength in the extrusion direction of the elongated foamed elements.24POLYOQ33-WO-ORD 2WO2023118202A1 further discloses a multilayer composite comprising cover layers and a core layer between the cover layers wherein the core layer comprises the foamed assembly so obtained.It is an objective of the invention to provide an efficient method for manufacturing a folded foam structure having a high compression strength in its thickness direction.Accordingly, the present invention provides a method of continuously manufacturing a folded foam structure, comprising the steps of: a) continuously providing a foamed sheet having a top surface and a bottom surface, wherein the foamed sheet has been made by a foamed extrusion process of a thermoplastic polymer composition; b) providing a plurality of slits in the foamed sheet, wherein: o a first set of slits extends from the top surface over only a part of the thickness towards the bottom surface, thereby providing first living hinges between the first set of slits and the bottom surface; o a second set of slits extends from the bottom surface over only a part of the thickness towards the top surface, thereby providing second living hinges between the second set of slits and the top surface; o wherein, in the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged; c) heating the foamed sheet to obtain a foldable foamed sheet; d) folding the foldable foamed sheet over the first living hinges and the second living hinges, wherein: o adjacent parts of the bottom surface that are on opposite sides relative to a respective first living hinge are folded together; o adjacent parts of the top surface that are on opposite sides relative to a respective second living hinge are folded together; and e) providing a thermal bond between the parts that have been folded together, to thereby form the folded foam structure wherein the direction of extrusion of the foamed sheet extends in the thickness direction.The method according to the invention continuously provides a folded foam structure having the same level of compression strength as the assembly of the prior art with a higher production efficiency. The formation of the alternative living hinges allows folding of the foamed sheet with less manual intervention. The heating of the foamed sheet24POLYOQ33-WO-ORD 3 allows in the subsequent step an efficient provision of bonding between the parts that have been folded together.The foamed sheet is a foamed sheet having a length (L), that is defined by a longitudinal direction that extends in the direction of extrusion, a width (W), and a thickness (T), and wherein opposite sides of the foamed sheet define a first surface (top surface) and a second surface (bottom surface).A sheet as defined herein is a shape which has a longer length than width, and a larger width than thickness. The thickness of the sheet may for example be > 5pm and < 100 cm, more typically from 0.1 mm to 10 cm. Preferably, the sheet has a thickness of 1.0 mm to 10 cm or 5.0 mm to 10 cm.Particularly, the invention provides a method of continuously manufacturing a folded foam structure, comprising the steps of: a) continuously providing a foamed sheet having a top surface and a bottom surface, wherein the foamed sheet has been made by a foamed extrusion process of a thermoplastic polymer composition comprising polypropylene; b) providing a plurality of slits in the foamed sheet, wherein: o a first set of slits extends from the top surface over only a part of the thickness towards the bottom surface, thereby providing first living hinges between the first set of slits and the bottom surface; o a second set of slits extends from the bottom surface over only a part of the thickness towards the top surface, thereby providing second living hinges between the second set of slits and the top surface; o wherein, in the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged; c) heating the foamed sheet to a temperature of 155 to 165 °C; d) folding the foamed sheet obtained by step c) over the first living hinges and the second living hinges, wherein: o adjacent parts of the bottom surface that are on opposite sides relative to a respective first living hinge are folded together; o adjacent parts of the top surface that are on opposite sides relative to a respective second living hinge are folded together; and e) providing a thermal bond between the parts that have been folded together, to thereby form the folded foam structure wherein the direction of extrusion of the foamed sheet extends in the thickness direction.24POLYOQ33-WO-ORD 4The method according to the invention comprises a) continuously providing a foamed sheet which has been made by a foamed extrusion process of a polymer composition. Such foamed sheet may have skin layers without open cells on its surfaces, which skin layers may be formed during the foamed extrusion process.Step a) involves continuously providing a foamed sheet at a constant speed Vfeed. Step a) may involve continuous foamed extruding of a polymer composition. In this case, the foamed sheet is extruded from an extruder at a constant speed Vfeed. This is particularly suitable when the blowing agent to produce the foamed sheet is not flammable, e.g. carbon dioxide. Alternatively, step a) may involve uncoiling of a coil of a foamed sheet which has been made by a foamed extrusion process. In this case, the foamed sheet is uncoiled at a constant speed Vfeed. This is particularly suitable when the blowing agent to produce the foamed sheet is flammable, e.g. isobutane.of foamed sheetThe foamed sheet has been made by a foamed extrusion process of a thermoplastic polymer composition.Preferably, the amount of the thermoplastic polymer composition with respect to the foamed sheet is at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%.In some embodiments, the thermoplastic polymer composition comprises a polymer selected from polycarbonate, polyvinyl chloride, polystyrene and polyethylene terephthalate. These polymers generally have a glass transition point which can be determined by differential scanning calorimetry according to IS011357-2.Preferably, the thermoplastic polymer composition comprises a polyolefin. Polyolefins generally have a melting point which can be determined by differential scanning calorimetry according to IS011357-3. More preferably, the thermoplastic polymer composition comprises polypropylene and / or polyethylene.Most preferably, the thermoplastic polymer composition comprises polypropylene. The use of polypropylene advantageously leads to the formation of living hinges that are mechanically strong for the folding.24POLY0033-WO-ORD 5Preferably, the amount of polyolefin with respect to the total amount of polymers in the polymer composition is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%.Preferably, the amount of polypropylene with respect to the total amount of polymers in the polymer composition is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%.Hiqh melt strenqth polypropylenePreferably, the polymer composition comprises a high melt strength polypropylene. A high melt strength polypropylene is branched and, thus, differs from a linear polypropylene in that the polypropylene backbone covers side chains whereas a nonbranched polypropylene, i.e. a linear polypropylene, does not cover side chains. The side chains have significant impact on the rheology of the polypropylene. Accordingly linear polypropylenes and high melt strength polypropylenes can be clearly distinguished by their flow behaviour under stress.The folded foam structure according to the invention made using high melt strength polypropylene shows an increased overall bending and compression stiffness. This means that the high melt strength polypropylene in the folded foam structure allows for I) the production of foams that have an increased bending stiffness (same thickness) and II) for the production of foams using less raw material, while still achieving the same bending stiffness (lower thickness and / or lower foam density). The use of less raw material (down-gauging is advantageous from an environmental point of view in terms of carbon footprint (less material and less transport costs and energy) as well as from an economical (cost) perspective.Branching can be generally achieved by using specific catalysts, i.e. specific single-site catalysts, or by chemical modification. Concerning the preparation of a branched polypropylene obtained by the use of a specific catalyst reference is made to EP 1 892 264. With regard to a branched polypropylene obtained by chemical modification it is referred to EP 0 879 830 A1 . In such a case the branched polypropylene is also called high melt strength polypropylene.Preferably, the high melt strength polypropylene has a branching index g’ of less than 1 .00, more preferably less than 0.90, more preferably less than 0.80, more preferably less than 0.75.24POLYOQ33-WO-ORD 6The branching index g' is explained e.g. in EP1847555A1. The branching index g' defines the degree of branching and correlates with the amount of branches of a polymer. The branching index g' is defined as g'=[IV] br / [IV]iin in which g' is the branching index, [I br] is the intrinsic viscosity of the branched polypropylene and [IV]iin is the intrinsic viscosity of the linear polypropylene having the same weight average molecular weight (within a range of ±10 %) as the branched polypropylene. Thereby, a low g'-value is an indicator for a high branched polymer. In other words, if the g'-value decreases, the branching of the polypropylene increases. Reference is made in this context to B.H. Zimm and W.H. Stockmeyer, J. Chem. Phys. 17,1301 (1949). This document is herewith included by reference. The intrinsic viscosity needed for determining the branching index g' is measured according to DIN ISO 1628 / 1 , October 1999 (in Decalin at 135 °C).Preferably, the high melt strength polypropylene has a melt strength of > 30 cN. The melt strength of the high melt strength polypropylene is herein determined in accordance with ISO 16790:2005 at a temperature of 200°C, using a cylindrical capillary having a length of 20mm and a width of 2mm, a starting velocity vO of 7.5mm / s and an acceleration of 12mm / s2.High melt strength polypropylene having a melt strength > 30 cN, preferably > 45 cN, can for example be obtained by the process as disclosed in W02009 / 003930A1 . W02009 / 003930A1 discloses an irradiated polymer composition comprising at least one polyolefin resin and at least one non-phenolic stabilizer, wherein the irradiated polymer composition is produced by a process comprising mixing the polyolefin resin with the non-phenolic stabilizer and irradiating this mixture in a reduced oxygen environment. In addition, a high melt strength polypropylene having a melt strength > 45 cN is available from SABIC as SABIC® PP UMS 561 P as of 18 February 2021 .Preferably, the high melt strength polypropylene is prepared by a) irradiation of a mixture comprising a polypropylene and a stabilizer, wherein the irradiation is performed with > 2.0 and < 20 Megarad electron-beam radiation in a reduced oxygen environment, wherein the amount of active oxygen is < 15% by volume with respect to the total volume of the reduced oxygen environment for a time sufficient for obtaining a long chain branched polypropylene and b) deactivation of the free radicals in the long chain branched polypropylene to form the high melt strength polypropylene.24POLY0033-WO-ORD 7How to deactivate the free radicals is known in the art, for example by heating as described in W02009003930A1 .In some preferred embodiments, the stabilizer is or comprises a non-phenolic stabilizer. Preferably, the non-phenolic stabilizer is chosen from the group of hindered amines.Examples of non-phenolic stabilizers are known in the art and are for example disclosed on pages 37 - 60 of W02009 / 003930A1 , hereby incorporated by reference. Preferably, the non-phenolic stabiizer is chosen from the group of hindered amines. More preferably, the non-phenolic stabilizer comprises at least one hindered amine selected from the group of Chimassorb® 944, Tinuvin® 622, Chimassorb® 2020, Chimassorb® 119, Tinuvin® 770, and mixtures thereof, separate or in combination with at least one hydroxylamine, nitrone, amine oxide, or benzofuranone selected from N.M- dehydrogenated tallow)amine (Irgastab® FS-042), an N,N- di(alkyl)hydroxylamine produced by a direct oxidation of N,N-di(hydrogenated tallow)amine (Irgastab® FS- 042), N-octadecyl-a-heptadecylnitrone, Genox™ EP, a di(C16 -C18 )alkyl methyl amine oxide, 3-(3,4-dimethylphenyl)-5,7-di-tert-butyl-benzofuran-2-one, Irganox® HP- 136 (BFI), and mixtures thereof, and separate or in combination with at least one organic phosphite or phosphonite selected from tris(2,4-di-tert-butylphenyl) phosphite (Irgafos® 168). Even more preferably, the non-phenolic stabilizers of the present subject matter can include those described in U.S. Patents 6,664,317 and 6,872,764, both of which are incorporated herein by reference in their entirety.In some preferred embodiments, the stabilizer is or comprises a phenolic stabilizer. In particularly preferred embodiments, the stabilizer is or comprises vitamin E. The use of vitamin E was surprisingly found to allow obtaining a good surface quality of the foamed article within a particularly large temperature processing window. In particular, the use of vitamin E allows using low temperature for foaming during foaming process such as foam extrusion process.The stabilizer may comprise a non-phenolic stabilizer and a phenolic stabilizer, for example a non-phenolic stabilizer and vitamin E.Preferably, the melt strength of the high melt strength polypropylene is > 37 cN, preferably > 40 cN, preferably > 45 cN, > more preferably 50 cN, more preferably >24POLY0033-WO-ORD 855 cN, even more preferably > 60 cN, most preferably > 65 cN and / or preferably the melt strength of the high melt strength polypropylene is <100 cN, for example < 95 cN, for example < 90 cN, for example < 87cN.With polypropylene as used herein is meant propylene homopolymer, a copolymer of propylene with an a-olefin or a heterophasic propylene copolymer.Preferably, the high melt strength polypropylene is polypropylene chosen from the group of propylene homopolymers and propylene copolymers comprising moieties derived from propylene and one or more comonomers chosen from the group of ethylene and alpha-olefins with > 4 and < 12 carbon atoms.Preferably, the propylene copolymer comprises moieties derived from one or more comonomers chosen from the group of ethylene and alpha-olefins with > 4 and < 12 carbon atoms in an amount of < 10wt%, for example in an amount of > 1.0 and < 7.0wt% based on the propylene copolymer, wherein the wt% is determined using13C NMR. For example, the propylene copolymer comprises moieties derived from one or more comonomer chosen from the group of ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1 -pentene, 1-heptene, 1-octene, 1-decene and 1-dodecene, preferably moieties derived from ethylene.Polypropylenes and the processes for the synthesis of polypropylenes are known. A propylene homopolymer is obtained by polymerizing propylene under suitable polymerization conditions. A propylene copolymer is obtained by copolymerizing propylene and one or more other comonomers, for example ethylene, under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is for example described in Moore, E. P. (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.Propylene homopolymers, propylene copolymers and heterophasic propylene copolymers can be made by any known polymerization technique as well as with any known polymerization catalyst system. Regarding the techniques, reference can be given to slurry, solution or gas phase polymerizations; regarding the catalyst system reference can be given to Ziegler-Natta, metallocene or single-site catalyst systems. All are, in themselves, known in the art.24POLYOQ33-WO-ORD 9In some embodiments, the polypropylene in the polymer composition is a high melt strength polypropylene described in WO2017021292, p.2, 1.26 to p.15, 1.32, incorporated herein by reference. Suitable examples of commercially available products include Daploy™ WB140HMS from Borealis.In some embodiments, the polypropylene in the polymer composition is a polypropylene commercially available as Achieve™ Advanced PP6302E1 from Exxon Mobil.In one embodiment, the polymer composition further comprises a further polypropylene which is not a high melt strength polypropylene. Preferably the amount of such further polypropylene is > 10 wt% and < 40 wt% based on the polymer composition. The further polypropylene can be a propylene homopolymer, a propylene copolymer, for example a copolymer of propylene with an a-olefin as described herein or a heterophasic propylene copolymer.Preferably, the (high melt strength) polypropylene (the polypropylene in the polymer composition or the high melt strength polypropylene in the polymer composition) has a VOC value as determined in accordance with VDA278 (2011-10) < 250 pg / g, preferably a VOC value < 50 pg / g and / or an FOG value as determined in accordance with VDA278 (2011-10) < 500 pg / g, preferably an FOG-value < 100 pg / g.Preferably, the (high melt strength) polypropylene has a melt flow rate > 0.50 and < 8.0 g / 1 Omin, more preferably > 0.70 and < 5.0 g / 1 Omin, most preferably > 1.0 and < 4.0 g / 1 Omin as determined in accordance with ASTM D1238 (2013) at a temperature of 230°C under a load of 2.16 kg.Preferably, the (high melt strength) polypropylene is present in an amount > 10wt% based on the polymer composition, preferably wherein the (high melt strength) polypropylene is present in an amount > 10wt% based on the polymer composition, more preferably in an amount < 99.5 wt% based on the polymer composition. For example, the amount of (high melt strength) strength polypropylene based on the polymer composition is > 15wt%, > 20wt%, > 25wt%, preferably > 30wt% and / or < 99.5wt%, < 99 wt%, < 98.5wt%, < 98.0wt%, < 97.0wt%, < 96.0wt%, < 95.0wt%.The polypropylene composition may comprise the (high melt strength) polypropylene in an amount of > 95wt%, more preferably > 96wt%, even more preferably > 97wt%, even24POLY0033-WO-ORD 10 more preferably > 98wt%, for example > 99wt%, for example > 99.6wt%, for example > 99.8wt%, for example > 99.9 wt% based on the polymer composition.The polymer composition may further comprise additives, such as for example flame retardants, pigments, lubricants, slip agents flow promoters, antistatic agents, processing stabilizers, long term stabilisers and / or UV stabilizers. The additives may be present in any desired amount to be determined by the man skilled in the art, but are preferably present > 0.001 wt% and < 5.0 wt%, more preferably > 0.01 wt% and < 4.0 wt%, even more preferably > 0.01 wt% and < 3.0 wt%, even more preferably > 0.01 wt% and < 2.0 wt% based on the polymer composition.The polymer composition may further comprise a nucleating agent. A nucleating agent may be desired to increase the cell density and to modify the dynamics of bubble formation and growth. (Gendron, Thermoplastic foam Processing, 2005, page 209).The amount of nucleating agent may for example be > 0.010 wt% and < 5.0 wt%, for example > 0.030 wt% and < 4.0 wt%, for example > 0.050 wt% and < 3.0 wt%, preferably > 0.10 wt% and < 2.5 wt%, more preferably > 0.30 wt% and < 1.5 wt% based on the polymer composition, most preferably > 0.50 wt% and < 1 ,2wt% based on the polymer composition.Suitable nucleating agents include but are not limited to talc, silica and a mixture of sodium bicarbonate and citric acid. Other suitable nucleating agents include amides, for example azo dicarbonamide, amines and / or esters of a saturated or unsaturated aliphatic (C10-C34) carboxylic acid. Examples of suitable amides include fatty acid (bis)amides such as for example stearamide, caproamide, caprylamide, undecylamide, lauramide, myristamide, palmitamide, behenamide and arachidamide, hydroxystearamides and alkylenediyl-bis-alkanamides, preferably (C2-C32) alkylenediyl- bis-(C2-C32) alkanamides, such as for example ethylene bistearamide (EBS), butylene bistearamide, hexamethylene bistearamide, ethylene bisbehenamide and mixtures thereof. Suitable amines include or instance (C2-C18) alkylene diamines such as for example ethylene biscaproamine and hexamethylene biscaproamine. Preferred esters of a saturated or unsaturated aliphatic (C10-C34) carboxylic acid are the esters of an aliphatic (C16-C24) carboxylic acid. Preferably, the nucleating agent is chosen from the group of talc, sodium bicarbonate, citric acid, azodicarbonamide and mixtures thereof, more preferably, the nucleating agent is talc.24POLY0033-WO-ORD 11For the preparation of the foamed sheet, it may be desired to use a cell stabilizer. Cell stabilizers are permeability modifiers which retard the diffusion of for example hydrocarbons such as isobutane to create dimensionally stable foams. (Gendron, Thermoplastic foam Processing, 2005, pages 31 and 149) Preferred cell stabilizers include but are not limited to glycerol monostearate (GMS), glycerol monopalmitate (GMP), palmitides and / or amides. Suitable amides are for example stearyl stearamide, palmitide and / or stearamide. Suitable mixtures include for example a mixture comprising GMS and GMP or a mixture comprising stearamide and palmitamide. Preferably, in case a cell stabilizer is used, the cell stabilizer is glycerol monostearate or stearamide.The amount of cell stabilizer to be added depends on desired cell size and the polymer composition used for the preparation of the foamed sheet. Generally, the cell stabiliser may be added in an amount > 0.10 and < 3.0 wt % relative to the polymer composition. Preferably, the polymer composition is present in the foamed sheet in an amount > 95 wt% based on the foamed sheet. For example, the polymer composition is present in the foamed sheet in an amount > 96 wt%, > 97 wt%, > 98 wt%, > 99 wt%, > 99.5 wt% based on the foamed sheet. The foamed sheet may also consist of the polymer composition.Preferably, the density of the foamed sheet is < 650 kg / m3and > 20kg / m3preferably < 500 kg / m3and > 30kg / m3, wherein the density is determined according to ISO 845 (2006).Preferably, the foamed sheet has an open cell content of < 15.0 % , preferably < 12.0%, more preferably < 10.0%, even more preferably < 7.0%, even more preferably < 5.0%, even more preferably < 4.0%, even more preferably < 3.0%, even more preferably < 2.0%, wherein the open cell content is determined according to ASTM D6226-10.Processes for the preparation of polypropylene foams and foamed sheets are within the knowledge of the person skilled in the art. In such a process, a melt of a composition of the high melt strength polypropylene mixed with a gaseous or liquid blowing agent is suddenly expanded through a pressure drop. Continuous foaming processes as well as discontinuous processes may be applied. In a continuous foaming process, the polymer composition is melted and laden with gas in an extruder24POLY0033-WO-ORD 12 under pressures typically above 20 bar before being extruded through a die where the pressure drop causes the formation of a foam. The mechanism of foaming polypropylene in such foam extrusion process is explained, for example, in H. E. Naguib, C. B. Park, N. Reichelt, Fundamental foaming mechanisms governing the volume expansion of extruded polypropylene foams, Journal of Applied Polymer Science, 91 , 2661-2668 (2004 ). Processes for foaming are outlined in S. T. Lee, Foam Extrusion, Technomic Publishing (2000 ). In a discontinuous foaming process, the polypropylene composition (micro-)pellets are laden with foaming agent under pressure and heated below melting temperature before the pressure in the autoclave is suddenly relaxed. The dissolved foaming agent forms bubbles and creates a foam structure.During the extrusion, parameters such as the die opening size and the pulling speed may be adjusted such that sufficient shear stress is applied to result in anisotropic properties, e.g. higher stiffness in the extrusion direction than the thickness direction, of the foamed sheet obtained.Preferably, the foamed sheet is prepared by a process comprising the sequential steps of: i) providing the polymer composition and ii) adding a blowing agent to the polymer composition, for example wherein the blowing agent is added in an amount > 0.10 wt% and < 20 wt% based on the polymer composition and iii) subjecting the mixture of the polymer composition and the blowing agent to a foam extrusion process to form the foamed sheet.The amount of blowing agent for example depends on the desired density and the polymer composition used. For example, the blowing agent may be used in an amount > 0.10 wt% and < 20 wt% based on the polymer composition.Examples of suitable physical blowing agents include, but are not limited to isobutane, CO2, pentane, butane, nitrogen and / or a fluorohydrocarbon. Preferably, the physical blowing agent is isobutane and / or CO2, most preferably isobutane.Examples of suitable chemical blowing agents include, but are not limited to citric acid or a citric acid-based material (e.g. mixtures of citric acid and sodium bicarbonate) and azo dicarbonamide. Such chemical blowing agents are for example commercially available from Clariant Corporation under for example the name Hydrocerol ™ CF-24POLYOQ33-WO-ORD 1340E™ or Hydrocerol™ CF-05E™.The foamed sheets thus prepared may be stretched monoaxially or biaxially using a manner known per se. This further enhances the anisotropy of the compression strength of the foamed sheet.Therefore, the foamed sheet may be prepared by a process comprising the sequential steps of: i) providing the thermoplastic polymer composition of the invention and ii) adding a blowing agent to the polymer composition, for example wherein the blowing agent is added in an amount > 0.10 wt% and < 20 wt% based on the polymer composition and iii) subjecting the mixture of the thermoplastic polymer composition and the blowing agent to a foam extrusion process to form the foamed sheet and iv) stretching the foamed sheet in at least one direction.The foamed sheet may be a foamed sheet which has been stretched in at least one direction, for example wherein the foamed sheet has been monoaxially stretched (for example in the machine direction) or for example the foamed sheet has been biaxially stretched, for example in both the machine direction (MD) and in the transverse direction (TD). As is known to the person skilled in the art, the stretching in MD and TD may be carried out simultaneously, or in consecutive steps.The draw ratio in MD may for example be > 1.1 and < 7.0, for example > 1.1 and < 3.0. The draw ratio in transverse direction may for example be > 1.1 and < 7.0, for example > 1.1 and < 3.0.The method according to the invention comprises b) providing a plurality of slits in the foamed sheet. This can be performed e.g. using a knife or blade, by means of thermoforming or by crushing. A first set of slits extends from the top surface over only a part of the thickness towards the bottom surface, thereby providing first living hinges between the first set of slits and the bottom surface. A second set of slits extends from the bottom surface over only a part of the thickness towards the top surface, thereby providing second living hinges between the second set of slits and the top surface. In the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged.24POLYOQ33-WO-ORD 14Preferably, the distance between adjacent slits of the first set of slits is substantially equal to twice the thickness of the foamed sheet.Preferably, the distance between adjacent slits of the second set of slits is substantially equal to twice the thickness of the foamed sheet.The method according to the invention comprises c) heating the foamed sheet to obtain a foldable foamed sheet. Thus, the foamed sheet is heated to a temperature which allows folding of the foamed sheet over the first living hinges and the second living hinges in step d). The heating can be done e.g. by means of hot air, infrared heating or contacting the foamed sheet with a hot surface.The temperature to which the foamed sheet is heated is close to the melting point or a glass transition point of the thermoplastic polymer in the thermoplastic polymer composition. When the thermoplastic polymer composition comprises a semicrystalline polymer, the foamed sheet is heated to close to the melting point of the semicrystalline polymer. When the thermoplastic polymer composition comprises an amorphous polymer, the foamed sheet is heated to close to the glass transition point of the amorphous polymer.In some embodiments, the thermoplastic polymer composition comprises a polymer selected from polycarbonate, polyvinyl chloride, polystyrene and polyethylene terephthalate and step c) comprises heating the foamed sheet to a temperature within a range between Tg (°C)-20 °C and Tg (°C)+10 °C, wherein Tg is a glass transition point of the thermoplastic polymer composition determined by differential scanning calorimetry according to ISO11357-2.Tg is a glass transition point of the polymer composition determined by differential scanning calorimetry according to ISO11357-2, e.g. using a first heating step at a heating rate of 10 per minute up to 200°C, a dynamic cooling at a cooling rate of 10°C per minute down to 25°C and a second heating step at a heating rate of 10°C per minute up to 200°C.In some embodiments, the thermoplastic polymer composition comprises polycarbonate preferably in an amount of at least 90 wt%, at least 95 wt%, at least 9824POLYOQ33-WO-ORD 15 wt%, at least 99 wt% or 100 wt% with respect to the total amount of polymers in the polymer composition and the heating temperature of step c) is 145 to 155 °C.In some embodiments, the thermoplastic polymer composition comprises polyvinyl chloride preferably in an amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% with respect to the total amount of polymers in the polymer composition and the heating temperature of step c) is 75 to 85 °C.In some embodiments, the thermoplastic polymer composition comprises polystyrene preferably in an amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% with respect to the total amount of polymers in the polymer composition and the heating temperature of step c) is 95 to 105 °C.In some embodiments, the thermoplastic polymer composition comprises polyethylene terephthalate preferably in an amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% with respect to the total amount of polymers in the polymer composition and the heating temperature of step c) is 75 to 85 °C.Preferably, the thermoplastic polymer composition comprises a polyolefin and step c) comprises heating the foamed sheet to a temperature within a range between Tm (°C)- 20 °C and Tm (°C)+10 °C, wherein Tm is a melting point of the polymer composition determined by differential scanning calorimetry according to IS011357-3.Tm is a melting point of the polymer composition determined by differential scanning calorimetry according to ISO11357-3, e.g. using a first heating step at a heating rate of 10 per minute up to 200°C, a dynamic crystallization at a cooling rate of 10°C per minute down to 25°C and a second heating step at a heating rate of 10°C per minute up to 200°C.In some embodiments, the thermoplastic polymer composition comprises polyethylene preferably in an amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% with respect to the total amount of polymers in the polymer composition and the heating temperature of step c) is 110 to 120 °C.In particularly preferred embodiments, the thermoplastic polymer composition comprises polypropylene preferably in an amount of at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% with respect to the total amount of24POLY0033-WO-ORD 16 polymers in the polymer composition and the heating temperature of step c) is 155 to 165 °C.The method according to the invention comprises d) folding the foldable foamed sheet obtained by step c) over the first living hinges and the second living hinges. In this step, adjacent parts of the bottom surface that are on opposite sides relative to a respective first living hinge are folded together and adjacent parts of the top surface that are on opposite sides relative to a respective second living hinge are folded together.The step of folding the foamed sheet can comprise the step of providing the heated foamed sheet of step c) at speed Vfeed on a surface moving at a constant line speed Vfold, wherein Vfold < Vfeed, to promote natural folding.Step d) may be performed in a manner similar to those described e.g. in EP1824667B1 , FIG. 5 and

[0018] -

[0022] , which describes making a folded honeycomb planar structure. In the present invention, the heated foamed sheet with slits can be folded in a similar manner using a similar folding equipment.Preferably pairs of rollers are used to push the foamed sheet in machine direction direction. Rotating tools, oscillating translating tools or guiding profiles can be used to help or ensure the folding up of the foamed sheet. The foamed sheet is preferably drawn by a profiled roll with the aid of vacuum. Inter-engaging profiles on the rolls running against each other can also be used.The step of folding the foamed sheet can comprise the step of feeding the heated foamed sheet of step c) through a first pair of rollers running at a first roller speed V1 and a second, downstream pair of rollers running at a second roller speed V2, wherein V2 < V1. In an example, the foamed sheet runs at a speed of 2.696 in arbitrary speed units; the reduces to 2.5 within the first set of rollers and then further to 1 in the second rollers. The final speed is that of the throughput of the folded foam structure.The folding unit contain a pair of feeding rollers, e.g. rubber coated feeding rollers, with grooves within the surfaces are placed upstream of a guiding grid to keep the folded sheet in-plane during folding and a second set of rollers, e.g. rubber coated pushing rollers with similar grooves to apply a counter pressure, which ensures a sufficient inplane compression force to enable the folding. A gating and / or braking mechanism24POLY0033-WO-ORD 17 initially retards or stops the foamed sheet. It opens at a force that is generated only by the folded foam structure in the fully folded stage. It continues to apply a friction force in its open state as the folded foam structure is formed.The method according to the invention comprises e) providing a thermal bond between the parts that have been folded together, to thereby form the folded foam structure wherein the direction of extrusion of the foamed sheet extends in the thickness direction.Due to the previous heating of the surface, good adhesion can be reached between the parts that have been folded together by thermal bonding.Folded foam structureThe folded foam structure has a first main surface and a second main surface opposite the first main surface. The folded foam structure is a sheet having a thickness between the first main surface (top surface of the folded foam structure) and the second main surface (bottom surface of the folded foam structure).Preferably, the folded foam structure according to the invention has a compression stress at yield in the thickness direction of at least 100 kPa, more preferably at least 300 kPa, more preferably at least 500 kPa, as determined by ISO 844 (2014).For the avoidance of doubt, “the compression strength in the thickness direction” (sometimes referred as compression strength in H or compression strength in PD) is understood as the as the stress that is observed in a compression test in the PD direction; “the compression strength in the extrusion direction” (sometimes referred as compression strength in MD) is understood as the as the stress that is observed in a compression test in the MD direction; and “the compression strength in the transverse direction” (sometimes referred as compression strength in TD) is understood as the as the stress that is observed in a compression test in the TD direction.In particular, the compression strength may refer to the compression stress at yield observed at a compression of typically between 0.1% and 15%, where the slope of the stress-compression curve changes strongly from high to low as illustrated in figure 2. In Example 1 illustrated in figure 2, the compression stress at yield (oyield) is the compression stress at the peak of the stress-compression curve. In Example 224POLYOQ33-WO-ORD 18 illustrated in figure 2, the compression stress at yield (oyield) is the compression stress at a point where the the slope of the stress-compression curve becomes close to zero.The method according to the invention may further comprise: f) bonding a first cover layer on a first main surface of the folded foam structure and optionally bonding a second cover layer on a second main surface of the folded foam structure opposite the first main surface.After step f), a multilayer composite is thus obtained comprising a core layer and a first cover layer provided on the core layer and optionally a second cover layer provided on the core layer wherein the core layer is provided between the first cover layer and the second cover layer, wherein the core layer comprises the folded foam structure according to the invention.The bonding of the first cover layer to the first main surface may be performed with or without an adhesive layer between the first cover layer and the first main surface. Preferably, the first cover layer is directly bonded to the first main surface, i.e. without an adhesive layer between the first cover layer and the first main surface. Such direct bonding may be achieved e.g. by thermal bonding.Similarly, the bonding of the second cover layer to the second main surface may be performed with or without an adhesive layer between the second cover layer and the second main surface. Preferably, the second cover layer is directly bonded to the second main surface, i.e. without an adhesive layer between the second cover layer and the second main surface. Such direct bonding may be achieved e.g. by thermal bonding.Step f) may be performed e.g. by double belt press.Preferably, step f) is performed directly after step e), i.e. the invention provides a method of continuously manufacturing a multilayer composite comprising steps a)-e) and f) bonding a first cover layer on a first main surface of the folded foam structure obtained by step e) and optionally bonding a second cover layer on a second main surface of the folded foam structure opposite the first main surface to obtain a multilayer composite.24POLYOQ33-WO-ORD 19Preferably, the first cover layer comprises a first composition comprising a polymer which is preferably polypropylene and optionally reinforcement fibers and the second cover layer comprises a second composition comprising a polymer which is preferably polypropylene and optionally reinforcement fibers. Although polypropylene is preferred as the polymer in the first composition and the polymer in the second composition, in some embodiments, the polymer in the first composition and the polymer in the second composition are not polypropylene, e.g. polyethylene or PET.The use of the folded foam structure of the invention with cover layers that comprise compositions comprising polypropylene has an advantage that no adhesive layer is needed for bonding to the cover layers. As the multilayer composite is made of one type of polymer, this is highly advantageous from a recycling point of view. In some preferred embodiments, the first composition and the second composition do not comprise reinforcement fibers, in which case the recyclability is even more improved.In the context of the invention, with ‘foamed’ or ‘foam’ is meant that the material has a lower density due to the presence of gas bubbles (such as air) as compared to the density of the same material without gas bubbles.The use of polypropylene in the core layer, the first cover layer and the optional second cover layer is advantageous in that it is thermoplastic and recyclable and produces less toxic chemicals after combustion, compared e.g. to polystyrene. Further, polypropylene has a lower glass transition temperature than e.g. polystyrene and polyethylene terephthalate, which makes the folded foam structure and the multilayer composite according to the invention more durable at room temperature.Preferably, the multilayer composite according to the invention has a compression stress at yield in the thickness direction at least 100 kPa, more preferably at least 300 kPa, more preferably at least 500 kPa, as determined by ISO 844 (2014).First and second cover layersThe first cover layer and / or the second cover layer may have a thickness of e.g. 0.1 to 4.0 mm, for example 0.3 to 2.0 mm.The first cover layer comprises a first composition and the second cover layer comprises a second composition. The first composition and the second composition may be the same or different from each other.24POLY0033-WO-ORD 20Preferably, the first composition and / or the second composition is a non-foamed composition, more preferably the first composition is a non-foamed composition and the second composition is a non-foamed composition.Preferably, the first composition and / or the second composition has a density of at least 0.903 g / cm3, more preferably 0.904 g / cm3, more preferably 0.905 g / cm3.Preferably, the first composition and / or the second composition comprises polypropylene and optionally reinforcement fibers.Preferably, the amount of polypropylene with respect to the total amount of polymers in the first composition is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%. Preferably, the amount of polypropylene with respect to the total amount of polymers in the second composition is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt%.In some embodiments, the reinforcement fibers may be glass fibers. In other embodiments, the reinforcement fibers may be selected from basalt fibers, carbon fibers, aramid fibers and natural fibers such as hemp, flax and bamboo fibers.In some cases, the first composition and the second composition are free from reinforcement fibers. This is advantageous in view of recyclability.Glass fibersThe glass fibers, as added to the composition, can comprise long and / or short glass fibers.Compositions filled with short glass fibers can be made by mixing chopped strands of pre-determined length with a thermoplastic polymer in an extruder, during which the glass fibers are dispersed in the molten thermoplastic. Compositions filled with long glass fibers can be made by a cable-wiring process, a co-mingling process or by a pultrusion process. The length of the added glass fibers can decrease during processing and as such the final length of the glass fibers in the composition and, in particular after compounding, can be less than that of the added glass fibers. Long glass fibers can have an average fiber length, before compounding, of 1 mm or more. Preferably, the long glass fibers can have an average fiber length, before24POLY0033-WO-ORD 21 compounding, of 1-50 mm, more preferably 1 -20 mm, and even more preferably 5-15 mm. Short glass fibers can have an average fiber length, before compounding, of 1 -10 mm, preferably 2-8 mm, more preferably 3-7 mm. The diameter of the glass fibers, before compounding, can be 5-50 pm , preferably 8-30 pm , more preferably 10-20 pm.The aspect ratio of the fibers can for example be in the range of 200-2000, preferably in the range of 200-1000, such as in the range of 250-750. The aspect ratio refers to the ratio between the average fiber length and the average fiber diameter. Generally, the length of glass fibers in a polymer composition decreases during a melt processing step like injection moulding. The average length of the glass fibers in a moulded article made from the composition according to the invention, i.e. after compounding, is therefore typically significantly shorter. Typically, after compounding, the glass fibers have an average fiber length of 1 mm or less. Preferably, the average fiber length in a moulded article (after compounding) can be from 0.05-0.9 mm, more preferably 0.1 - 0.6 mm, even more preferably 0.1 -0.4 mm. Since the average glass fiber diameter does not substantially change upon compounding, the average glass fiber diameter in a moulded article made from the composition according to the invention, i.e. after compounding, can be in the range of 5-50 pm, preferably 8-30 pm, such as 10-20 pm.Suitably, the glass fibers can be coated in order to improve the interaction with the polypropylene. Such coated glass fibers are also known in the art as sized glass fibers. Such coatings typically include amino-silane or silane coatings. Amino-silane and silane coated glass fibers are commercially available. Some examples include ECS03- 480H (from NEG), 03T480 (from NEG), HP3270 (from PPG Industries), HP3299 (from PPG Industries), ECS 305H (from CPIC), ECS 305K (from CPIC), DS2100-13P (from Binani 3B fiberglass), DS2200-10P (from Binani 3B fiberglass), DS2200-13P (from Binani 3B fiberglass), OwensCorning SE4805 SE4850, SE4849 Type 30.The glass fibers may be treated with a coupling agent so as to improve the interaction between the glass fibers and the polypropylene. Such coupling agents facilitate adhesion of the polypropylene to the polar glass fiber surface. Suitable coupling agents include functional organo-silanes, transition metal coupling agents, amino-containing Werner coupling agents and mixtures thereof. Examples of functional organo-silane coupling agents include 3-aminopropyldimethylethoxysilane, y-aminopropyltriethoxysilane, y-aminopropyltrimethoxysilane, P-aminoethyltriethoxysilane, N-p-aminoethylamino-propyltrimethoxysilane,24POLYOQ33-WO-ORD 22Y-isocyanatopropyltriethoxysilane, vinyl-trimethoxysilane, vinyl-triethoxysilane, allyltrimethoxysilane, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, glycidoxypropyltriethoxysilane, glycidoxypropyltrimethoxysilane, 4.5-epoxycyclohexyl- ethyltrimethoxysilane, ureidopropyltrimethoxysilane, ureidopropyltriethoxysilane, chloropropyltrimethoxysilane, and chloropropyltriethoxysilane. Examples of transition metal coupling agents include chrome, titanium and zirconium coupling agents.Examples of amino-containing Werner type coupling agents include complex compounds in which a trivalent nuclear atom such as chromium is coordinated with an organic acid having amino functionality. Such treated glass fibers are known in the art. The amount of glass fibers in the thermoplastic composition can vary depending on the specific application and needs. For example, the amount of glass fibers in the thermoplastic composition may be 10-40 wt%, for example 20-30 wt% or 20-25 % based on the total composition.The glass fiber can be prepared from continuous lengths of fibers by, for example, a sheathing or wire-coating process, by crosshead extrusion, or by a pultrusion technique. Using these technologies, fibers strands impregnated or coated with a polymer are formed. The fiber can then be cut into a desired length and can optionally be formed into pellets or granules. The fibers can be further processed, e.g., by injection moulding or extrusion processes, into a composition.In some preferred embodiments, the first cover layer and / or the second cover layer may be or may comprise a continuous glass fiber reinforced tape, e.g. described in W02021053180A1 , hereby incorporated by reference.Preferably, in case a continuous glass fiber reinforced tape is used, at least two (for example 2, 3, 4, 5, 6, 7, 8, 9 or 10) tape layers are applied in the first cover layer and / or the second cover layer. The stacking of the tape layers is preferably done such that the tapes are in a quasi isotropic lay-up (for example a +0 90°stacking).Examples of glass fiber reinforced tapes include but are not limited to UDMAX™ tapes and Polystrand™ tapes as commercially available . Furthermore, such tapes are also disclosed in WO2016 / 142786A1 , hereby incorporated by reference, WO2016 / 142781A1 , hereby incorporated by reference, WO2016 / 142784A1 , hereby incorporated by reference.24POLY0033-WO-ORD 23Thus, the continuous glass fiber reinforced tape may be a fiber-reinforced composite comprising: a matrix material including polypropylene; and a non-woven fibrous region comprising a plurality of continuous glass fibers dispersed in the matrix material; wherein the width and the length of the non-woven fibrous region are substantially equal to the width and the length, respectively, of the fiber-reinforced composite; wherein the non-woven fibrous region has a mean relative fiber area coverage (RFAC) (%) of from 65 to 90 and a coefficient of variance (COV) (%) of from 3 to 20; and wherein each of the plurality of continuous fibers is substantially aligned with the length of the fiber-reinforced composite.Another example of a continuous glass fiber reinforced tape is for example described in WO2019122317A1 , hereby incorporated by reference and in WO2019122318A1 , hereby incorporated by reference.In some preferred embodiments, the first cover layer and / or the second cover layer may be or may comprise a monoaxially drawn polypropylene multilayer film or tape e.g. as described in W00308190. The film or tape may be of the AB or ABA type, having a stretch ratio of more than 12, having an E-modulus of at least 10 GPa, substantially consisting of a central layer (B) of polypropylene, and one or two other layers (A) of polypropylene, the DSC melting point of the material of the said other layers (A) being lower than the DSC melting point of the material of the said central layer (B), wherein the central layer (B) is between 50 and 99 wt.% of the material and the other layers (A) between 1 and 50 wt.%. It is of advantage to use a monoaxially drawn polypropylene multilayer film or tape as it makes the use of fibers redundant, thereby improving the recyclability.Typically, the thickness of the first cover layer and / or the second cover layer is smaller than the thickness of the folded foam structure according to the invention, for example the thickness of the first cover layer and / or the second cover layer is at most 90%, at most 70%, at most 50%, at most 30%, at most 10% or at most 5% of the thickness of the folded foam structure according to the invention.Core layer24POLYOQ33-WO-ORD 24The core layer comprises the folded foam structure according to the invention. The folded foam structure according to the invention may be present in the core layer at an amount of 50 to 100 wt% of the core layer.In some embodiments, the core layer consists of the folded foam structure according to the invention.In other embodiments, the core layer comprises a part consisting of the folded foam structure according to the invention and further one or more parts consisting of a third composition having a higher density than that of the folded foam structure according to the invention. Such parts consisting of the third composition may be present e.g. at the peripheral part of the core layer and / or multiple such parts may be distributed over the core layer. In some embodiments, the core layer consist of a central part consisting of the folded foam structure according to the invention and a peripheral part at least partly surrounding the circumference of the central part, wherein the peripheral part consists of a third composition. In some embodiments, the peripheral part completely surrounds the circumference of the central part.The parts consisting of the third composition may function as a reinforcement of the core layer, e.g. for ensuring the attachment of the core layer to the first and the second cover layers. This is particularly useful for a multilayer composite wherein the first cover layer, the second cover layer and the core layer are screwed together. By using a third composition having a higher density than that of the folded foam structure according to the invention for the peripheral part of the core layer, a more secure attachment by screw can be achieved.Preferably, the third composition comprises polypropylene and optionally glass fibers.Preferably, the third composition is a non-foamed composition.Preferably, the third composition has a density of at least 0.903 g / cm3, preferably at least 0.904 g / cm3, more preferably at least 0.905 g / cm3.Suitable components for the third composition are those described for the first composition and the second composition. The third composition may be the same or different from the first composition and / or the second composition.24POLYOQ33-WO-ORD 25The multilayer composite may further comprise a surface layer provided over the first cover layer and / or the second cover layer. The surface layer may for example be a decorative layer and may comprise e.g. PVC, wood.ArticlesThe folded foam structure according to the invention can suitably be used in applications such as building and construction, automotive applications, household applications, such as food packaging and protective packaging; and consumer applications.In another aspect therefore, the invention relates to an article comprising the folded foam structure of the invention. In yet another aspect, the invention relates to use of the folded foam structure of the invention in an applications such as building and construction, automotive applications, household applications, such as food packaging and protective packaging; and consumer applications.In another aspect, the invention relates to an article comprising the multilayer composite of the invention. In yet another aspect, the invention relates to use of the multilayer composite of the invention in the preparation of an article. In preferred embodiments, the article is a panel (in particular a sandwich panel) for a building or a transportation or recreation vehicle, in particular a panel selected from the group consisting of a floor panel, a wall panel, a roof panel, an insulation panel, for example an inner wall or front wall panel for a truck, a roof panel of a house, a floor panel for a caravan.It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the compositions according to the invention; all combinations of features relating to the processes according to the invention and all combinations of features relating to the compositions according to the invention and features relating to the processes according to the invention are described herein.It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a24POLYOQ33-WO-ORD 26 product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.The invention is now elucidated referring to the drawings in which:Figures 1 (a)- 1(c) illustrate one embodiment of a method of manufacturing the folded foam structure according to the inventionFigure 2 illustrates graphs for determining the Young’s modulus (E) and compression stress at yield (compression strength, oyield) of a sample according to the invention.Figure 1 (a) illustrates a side view of an example of a foamed sheet provided by steps a)-c) of the method of the invention.The foamed sheet is provided in the machine direction MD at a constant speed Vfeed (step a)). The foamed sheet has a length (L) in the machine direction MD, a width (W), and a thickness (Tsheet). The foamed sheet has a top surface and the bottom surface and the thickness is the distance between the top surface and the bottom surface.A plurality of slits is provided in the foamed sheet (step b)). A first set of slits extends from the top surface over depth d, i.e. only a part of the thickness towards the bottom surface. First living hinges are thereby provided between the first set of slits and the bottom surface. Similarly, a second set of slits extends from the bottom surface over depth d, i.e. only a part of the thickness towards the top surface. Second living hinges are thereby provided between the first set of slits and the second surface. In the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged. The distance between a first slit and a neighboring second slit is constant and defines the thickness of the folded foam structure tpanei.In this embodiment, the foamed sheet has been made from a thermoplastic polymer composition comprising polypropylene and the foamed sheet is heated to a temperature of 155 to 165 °C (step c)).24POLY0033-WO-ORD 27Figure 1 (b) illustrates a sideview of the foamed sheet being folded over the first living hinges and the second living hinges (step d)). The folding can be performed in a manner similar to that described in EP1824667B1 , FIG. 5 and

[0018] -

[0022] ,Figure 1 (c) illustrates a sideview of the folded foam structure obtained by step e). Thermal bond has been provided between the parts that have been folded together. The folded foam structure having a thickness panel is obtained wherein the direction of extrusion of the foamed sheet extends in the thickness direction.Figure 2 illustrates graphs for determining the Young’s modulus (E) and compression stress at yield (compression strength, oyield) of a sample according to the invention.Young’s modulus (E) (compressive modulus of elasticity in MPa) and compression stress at yield (compressive strength, oyield in MPa) in the thickness direction (H), the extrusion direction (MD) and the transverse direction (TD) are determined with the use of a ZwickRoell tensile testing machine using ISO844:2014. Samples of 20x20x20mm were taken. 1 N pre-load was applied before measurement. During the measurement, the applied compression speed is 5 mm / min until a compression of 80% is reached. The compression stress during compression is recorded. Young’s modulus (E) is determined as the initial slope in the elastic region of the stress-strain response of the sample. The compression stress at yield (oyield) is determined after the end of the elastic region. Depending on the different compression behavior of the samples the compression stress at yield is determined as shown in graphs of Figure 2.The compression strength may refer to the compression stress at yield observed at a compression of typically between 0.1% and 15%, where the slope of the stresscompression curve changes strongly from high to low as illustrated in figure 2(a). In Example 1 illustrated in figure 2, the compression stress at yield (oyield) is the compression stress at the peak of the stress-compression curve. In Example 2 illustrated in figure 2(b), the compression stress at yield (oyield) is the compression stress at a point where the the slope of the stress-compression curve becomes close to zero.

Claims

24POLYOQ33-WO-ORD 28CLAIMS1 . A method of continuously manufacturing a folded foam structure, comprising the steps of: a) continuously providing a foamed sheet having a top surface and a bottom surface, wherein the foamed sheet has been made by a foamed extrusion process of a thermoplastic polymer composition; b) providing a plurality of slits in the foamed sheet, wherein: o a first set of slits extends from the top surface over only a part of the thickness towards the bottom surface, thereby providing first living hinges between the first set of slits and the bottom surface; o a second set of slits extends from the bottom surface over only a part of the thickness towards the top surface, thereby providing second living hinges between the second set of slits and the top surface; o wherein, in the longitudinal direction of the foamed sheet, the slits of the first set of slits and the slits of the second set of slits are alternatingly arranged; c) heating the foamed sheet to obtain a foldable foamed sheet; d) folding the foldable foamed sheet over the first living hinges and the second living hinges, wherein: o adjacent parts of the bottom surface that are on opposite sides relative to a respective first living hinge are folded together; o adjacent parts of the top surface that are on opposite sides relative to a respective second living hinge are folded together; and e) providing a thermal bond between the parts that have been folded together, to thereby form the folded foam structure wherein the direction of extrusion of the foamed sheet extends in the thickness direction.

2. The method according to claim 1 , wherein the thermoplastic polymer composition comprises a polyolefin and step c) comprises heating the foamed sheet to a temperature within a range between Tm (°C)-20 °C and Tm (°C)+10 °C, wherein Tm is a melting point of the polymer composition determined by differential scanning calorimetry according to ISO11357-3.

3. The method according to any one of the preceding claims, wherein the polymer composition comprises polypropylene and / or polyethylene.24POLYOQ33-WO-ORD 294. The method according to any one of the preceding claims, wherein the polymer composition comprises polypropylene, preferably a high melt strength polypropylene.

5. The method according to any one of the preceding claims, wherein the heating temperature of step c) is 155 to 165 °C.

6. The method according to claim 1 , wherein the thermoplastic polymer composition comprises a polymer selected from polycarbonate, polyvinyl chloride, polystyrene and polyethylene terephthalate and step c) comprises heating the foamed sheet to a temperature within a range between Tg (°C)-20 °C and Tg (°C)+10 °C, wherein Tg is a glass transition point of the thermoplastic polymer composition determined by differential scanning calorimetry according to ISO11357-2.

7. The method according to any one of the preceding claims, wherein the distance between adjacent slits of the first set of slits is substantially equal to twice the thickness of the foamed sheet and / or the distance between adjacent slits of the second set of slits is substantially equal to twice the thickness of the foamed sheet.

8. The method according to any one of the preceding claims, wherein step d) comprises the step of feeding the heated foamed sheet of step c) through a first pair of rollers running at a first roller speed V1 and a second, downstream pair of rollers running at a second roller speed V2, wherein V2 < V1 .

9. The method according to any one of the preceding claims, wherein the foamed sheet has been prepared by a process comprising the sequential steps of: i) providing the polymer composition, ii) adding a blowing agent to the thermoplastic polymer composition, for example wherein the blowing agent is added in an amount > 0.10 wt% and < 20 wt% based on the polymer composition, iii) subjecting the mixture of the polymer composition and the blowing agent to a foam extrusion process to form the foamed sheet and optionally iv) stretching the foamed sheet in at least one direction.

10. The method according to any one of claims 1 to 9, wherein step a) comprises continuous foamed extruding of the polymer composition.24POLYOQ33-WO-ORD 3011. The method according to any one of claims 1 to 9, wherein step a) comprises continuous uncoiling of a coil of the foamed sheet which has been made by a foamed extrusion process.

12. The method according to any one of the preceding claims, further comprising the step of: f) bonding a first cover layer on a first main surface of the folded foam structure and optionally bonding a second cover layer on a second main surface of the folded foam structure opposite the first main surface to obtain a multilayer composite, preferably wherein the first cover layer comprises a first composition having a density of at least 0.903 g / cm3and comprising polypropylene and optionally reinforcement fibers such as glass fibers and the optional second cover layer comprises a second composition having a density of at least 903 g / cm3and comprising polypropylene and optionally reinforcement fibers such as glass fibers.

13. The method according to claim 12, wherein step f) comprises thermal bonding of the first cover layer and the first main surface and optionally thermal bonding of the second cover layer and the second main surface.

14. The method according to claim 12, wherein step f) comprises bonding the first cover layer and the first main surface with an adhesive layer between the first cover layer and the first main surface and optionally bonding the second cover layer on the second main surface with an adhesive layer between the second cover layer and the second main surface.

15. The folded foam structure obtained by or obtainable by the method according to any one of claims 1 to 11 or the multilayer composite obtained by or obtainable by the method according to 12 to 14.

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