DECORATIVE TILES, THE CORE LAYER, AND THE MANUFACTURING METHOD OF THESE TILES

Abstract

The invention proposes a decorative cladding, specifically a decorative floor cladding, a decorative ceiling cladding, or a decorative wall cladding, comprising: at least one core layer, a decorative upper structure attached directly or indirectly to the upper surface of the aforementioned core layer. The invention also proposes a core layer for use in the decorative cladding as described in the invention. The invention also proposes a method for the manufacture of the decorative cladding, specifically the decorative cladding as described in the invention.

Description

[0001] Decorative panel, core layer, and method for producing such a panel

[0002] The present invention relates to a decorative panel, in particular a decorative floor panel, decorative ceiling panel, or decorative wall panel, comprising: at least one core layer, a decorative top structure directly or indirectly affixed to a top surface said core layer. The invention also relates to a core layer intended for use in a decorative panel according to the invention. The invention further relates to a method for producing a decorative panel, in particular a decorative panel according to the invention.

[0003] In the last decades many improvements have been observed in the world of decorative panels, such as floor panels and wall panels. These improvements cover various aspects of the decorative panels, such as, for example, improving the aesthetical appearance of the panels, improving mechanical coupling profiles of the panels, improving the acoustic properties of the panels, improving the scratch resistance of the panel, and improving the core composition of the panels. With respect to this latter aspect, a trend is visible that traditional core layer materials, like medium density board (MDF) and high density board (HDF) are partially replaced by other materials, like PVC based compositions. Contrary to MDF and HDF, PVC is waterproof and therefore easy to maintain and moreover exhibits relatively attractive noise reducing properties. However, the use of PVC in core compositions of decorative panels is not undisputed. As this PVC is typically softened by using hazardous plasticizers, like phthalates, health risks may be involved. Moreover, during the production of PVC toxic chemicals are used and toxic by-products and waste are generated. Furthermore, in case of a fire, PVC based panels may generate carcinogens called dioxins and furans, which is less preferred from a health safety and environmental point of view. In addition to the above, the carbon footprint of PVC, also referred to as embodied carbon, is substantial, which also puts pressure on the use of PVC in core layers of decorative panels. As awareness is increasing regarding the health safety of materials as well as regarding the environment, a response is being demanded from the industry and its customers to also use alternative raw materials for manufacturing decorative panels. More in particular, there is a need to develop a core composition of the decorative panel, which is relatively health safe and which seriously reduces the carbon footprint to spare the environment as much as possible. It is therefore a first objective of the present invention to provide a decorative panel having a relatively low carbon footprint.

[0004] It is therefore a second objective of the present invention to provide a decorative panel having an improved core composition.

[0005] It is therefore a third objective of the present invention to provide a decorative panel having a more health safe and / or environmental friendly core composition.

[0006] It is therefore a fourth objective of the present invention to provide a PVC-free decorative panel.

[0007] At least one of these objectives can be achieved by providing a decorative panel according to the preamble, comprising:

[0008] • at least one core layer,

[0009] • a decorative top structure directly or indirectly affixed to a top surface said core layer; wherein said at least one core layer comprises at least one chain-extended condensation polymer, preferably at least one chain-extended polyester, more preferably at least one chain-extended polyethylene terephthalate (PET) at least partially composed of condensation polymer based molecules, preferably polyester based molecules, more preferably PET based molecules, each molecule comprising at least two polymer chains of recycled condensation polymer, preferably recycled polyester, more preferably recycled PET, mutually chemically bonded by at least one chain extender.

[0010] The decorative panel according to the invention has several advantages. First of all, since the material composition of the core layer is either based upon a recycled condensation polymer, preferably a recycled polyester, more preferably recycled PET, the carbon footprint of the core composition and hence of the decorative panel as such can be reduced significantly, in particular compared to virgin fossil based polymers (based upon non-renewable fossil fuel). Moreover, these recycled polymer(s) is / are relatively health safe compared to PVC, as these polymer(s) do / does not require hazardous plasticizers, such as phthalates, to make the polymer more flexible for the aimed application. Moreover, the production of condensation polymer, such as polyester, preferably PET, (contrary to PVC) does not lead to toxic by-products, and these condensation polymers (contrary to PVC) will not release extremely potent carcinogens called dioxins and furans in the case of a fire. Hence, (recycled) condensation polymer, preferably polyester, more preferably PET, have significant advantages over PVC, and the use of recycled material further reduces the embodied carbon (carbon footprint) of the core composition, and hence of the decorative panel as such. To keep the carbon footprint of the core composition, and hence of the decorative panel, as limited as possible, it may be preferred that said core layer is free of virgin fossil-based polymers. It may also be preferred that said core layer is free of polyvinyl chloride (PVC) and / or other polyvinyls. It may also be preferred that said core layer is free of polyamides (nylons) and / or fluoropolymers and / or polyurethane and / or acrylic polymers and / or silicones and / or polyetheretherketone (PEEK) and / or cellulose acetate and / or polycarbonate and / or phenolic resins and / or elastomers. It may also be preferred that said core layer is free of polyolefin(s), like e.g. polyolefins include polymers and copolymers of polyethylene, polypropylene, polybutylene, among others or combinations thereof. This absence of other polymer types in the core layer significantly improves the post-use recyclability of the core layer. Moreover, polyesters and polyolefins have different chemical structures, making them inherently incompatible. Polyesters are polar, while polyolefins (like polyethylene or polypropylene) are nonpolar. This incompatibility can lead to poor adhesion and phase separation, which negatively impacts the mechanical properties (such as strength, flexibility, and durability) of the final product. Even in case compatibilizers would be used to improve the interface between these materials, achieving optimal dispersion and adhesion between these two distinct types of polymers is very difficult, potentially compromising the overall quality of the core material. Moreover, the presence of the compatibilizer further affects the recyclability of the core layer. Furthermore, polyolefins typically have lower thermal stability compared to polyesters. In environments where decorative floor or wall coverings are exposed to heat (such as sunlight in a hot room or near radiators), the polyolefin component typically softens and / or degrades, leading to warping, loss of shape, or discoloration, which reduces the aesthetic and functional lifespan of the covering, especially in areas with temperature variations. Additionally, mixing polyesters and other polymers (non-polyesters) often leads to processing difficulties and complications due to different melting points and processing requirements. Polyolefins typically melt at lower temperatures, while polyesters require higher temperatures for processing. Ensuring that all components mix uniformly and form a stable composite during production might require complex, energy-intensive processes, which not only leads to higher production costs, but also increased difficulty in ensuring consistent product quality. Therefore, it is generally preferred that the core layer is free of other polymers (other than one or more polyesters), these other polymers also being referred to “non-polyester polymers”.

[0011] Compared to PVC, PET has the advantage to be more rigid and to be more temperature stable. In case decorative panels are exposed to sunlight, the panel temperature can easily exceed 50 degrees Celsius, which often leads to deformation of PVC based panels, wherein such a deformation can be prevented with the more heat resistant panel according to the invention. Moreover, the panel according to the invention is also relatively water and moisture resistant (contrary to MDF and HDF), which leads to an additional major benefit of the decorative panel according to the invention over traditional panels.

[0012] During thermomechanical processing, PET is subject to high temperature and shear stress conditions able to produce severe degradation to the PET in terms of molar mass and (co-related) viscosity. Virgin PET typically has a molar mass of between 20,000 and 30,000 g / mol, while recycled PET often has a molar mass of between 10,000 and 20,000 g / mol. The presence of water (and / or PVC (traces)) in the recycled PET material produces PET chain scission during normal extrusion. At processing temperature (270-290 degrees Celsius), hydrolysis reactions occur between water and PET, resulting in shorter chains with carboxyl and hydroxyl end groups. The thermal cleavage of the PET ester bond results in PET chains with carboxyl and vinyl ester end groups. The broken PET chains (PET having a reduced molar mass) is less ideal for use decorative panels. In order to increase the molar mass of PET and / or the viscosity of PET to a higher level for use in decorative panels, broken PET chains are chemically bonded (rejoined) by one or more chain extenders, which is preferably realized by reactive extrusion. These chain extenders are preferably di- or polyfunctional chain extenders because of their high reaction rate without generating (undesired) by-products (possibly apart from water). In this manner PET can be created with a higher (average) molar mass, and hence a higher viscosity, preferably at least 0.8 dl / g, to allow or to improve manufacturing of the core layer, and hence of the decorative panel as such. Recycled PET, before chain extension, used as raw material for composing the core composition preferably has a viscosity of 0.5-0.6 dl / g. This viscosity will increase during the chain extension process (normally during the reactive extrusion process) to values of at least 0.8 dl / g (and preferably less than 1 .0 dl / g). Preferably the core layer and / or the decorative panel is substantially free of PVC to reduce the carbon footprint of the decorative panel. It is imaginable, but not necessary, that the core layer and / or the decorative panel is substantially free of virgin PET to reduce the carbon footprint of the decorative panel. This viscosity is preferably measured by applying the Chinese standard: T / CCFA 00011-2021 requiring amongst others a testing temperature of 25 degrees Celsius.

[0013] It may be preferred that at least a fraction of said PET based molecules each comprises at least three or at least four polymer chains of recycled PET mutually chemically bonded by at least one chain extender. This can for example be realized by applying a tetrafunctional chain extender, such as for example pyromellitic dianhydride (PM DA). In this latter example, the PM DA chain extender forms the molecular centre to which (outer ends of) four chains of, preferably recycled, PET are chemically bonded. It is also imaginable that at least a fraction of said PET based molecules each comprises more than four polymer chains of recycled PET mutually chemically bonded by at least one chain extender. This may, for example, be realized by using a combination of different chain extenders. By increasing the number of rejoined PET chains, the molar mass, and consequently the viscosity of the chain-extended PET can be increased to obtain desired properties for manufacturing (and / or for use).

[0014] It is imaginable, but not necessary, that the core layer and / or the decorative panel is substantially free of virgin PET to reduce the carbon footprint of the decorative panel. However, it is also imaginable that the material composition of at least one core layer comprises virgin PET, preferably in addition to recycled PET. As this virgin PET has the same functional end groups compared to recycled PET, also the virgin PET may and likely will become part of the chain-extended PET based molecules. Hence, it is imaginable that the core layer comprises chain-extended PET at least partially composed of PET based molecules each comprising at least one polymer chain of recycled PET and at least one polymer chain of virgin PET mutually chemically bonded by at least one chain extender. In order to efficiently process a mixture of virgin PET and recycled PET, in particular by using an extruder, it is preferred that that both raw materials are chosen or selected such that their melting points are practically the same or come close to each other. Preferably the melting point difference of the chosen virgin PET and the chosen recycled PET is less than 10 degrees Celsius, more preferably less than 5 degrees Celsius, even more preferred less than 3 degrees Celsius.

[0015] Typically the length of the recycled PET chain, and consequently the molar mass, is (much) smaller than the length and molar mass of the virgin PET chain. The molar mass of the recycled PET is preferably at least 10,000 g / mol and normally smaller than 20,000 g / mol, while the molar mass of the virgin PET is typically between 20,000 and 30,000 g / mol. Dependent on the number of PET chains (re)joined in molecules of the chain-extended PET, the molar mass of these modified chain-extended PET molecules, preferably exceeds 20,000 g / mol and may even exceed 30,000 g / mol, 40,000 g / mol and / or 50,000 g / mol, but is preferably less than 100,000 g / mol to secure a sufficient low viscosity to allow proper extrusion of the chain-extended PET material. The rejoinder of the PET chains normally takes place within the extruder, and is considered as a chemical reaction between PET chains and at least one chain extender. Optionally, water molecules are produced during this reaction. Depending on the properties, in particular average chain length, of the recycled PET used as raw material, the type(s) and amount(s) of chain extender(s) can be chosen to arrive at a preferred molar mass and hence viscosity for proper processing of the modified chain- extended PET based material.

[0016] It is imaginable that not all raw materials initially present in a masterbatch to be extruded will react during the reactive extrusion. It is therefore imaginable that the core layer comprises unbonded recycled PET and / or unbonded virgin PET (if applied, and / or wherein the core layer comprises unbonded chain extender molecules.

[0017] As already indicated above, it may be imaginable and even preferred that the core layer comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least two different chain extenders. This may increase the number of chemically bonded PET chains in single molecules, which may increase the molar mass and viscosity of the core layer composition during extrusion.

[0018] At least one chain extender may be or may comprise at least one multifunctional epoxide oligomer including for example, epoxylated novolacs, and phenoxy resins.. This said multifunctional epoxide oligomer, prior to bonding to the PET chains, may be represented by the chemical structure: wherein:

[0019] R1-R5 are H, CH3, a higher alkyl group, or combinations of them;

[0020] R6 is an alkyl group, and x, y, and z are each between 1 and 20.

[0021] This solid multifunctional epoxide oligomer is also known as JONCRYL® ADR-4368 (from BASF), abbreviated as “ADR”.

[0022] ADR has at least a fourfold functionality is capable to quickly bond at least four PET chains, as depicted below:

[0023] Additionally or alternatively, at least one chain extender, prior to bonding to PET chains, may be or may comprise at least one dianhydride, preferably pyromellitic dianhydride (PMDA) and / or mellophanic dianhydride (MEDA). PMDA (1 H,3H- Benzo[1 ,2-c:4,5-c']difuran-1 ,3,5,7-tetrone) is represented by the following chemical structure:

[0024] MEDA (1 ,2:3,4-benzenetetracarboxylic anhydride) can be represented by the following chemical structure:

[0025] Both dianhydrides are tetrafunctional and are each capable to chemically bond four PET chains. Typically, this bonding process constitutes a two-stage reaction mechanism, wherein in a first fast reaction step two PET chains are chemically bonded to the dianhydride, for example PMDA, as shown below:

[0026] In a second slower reaction step two further PET chains are or can be chemically bonded to said dianhydride:

[0027] In this second reaction step water molecules are produced. This leads to a chain- extended PM DA-PET molecule with four PET arms. It is imaginable, and may even be preferred that the core layer comprises a mixture of (i) at least one (bonded) dianhydride, preferably (bonded) pyromellitic dianhydride (PMDA) and / or (bonded) mellophanic dianhydride (MEDA), and (ii) (bonded) JONYCRYL® ADR 4368 (from BASF; see above). Preferably, the mass ratio between dianhydride and JONYCRYL® ADR 4368 is between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4. The molar mass of ADR is approximately 6,800 g / mol, and the molar mass of PMDA is 218.12 g / mol. By applying this balanced ratio the molar mass of the chain-extended PET molecules is sufficiently high to achieve a desired viscosity for extrusion purposes, while at the same time being sufficiently low or limited in order to prevent that the viscosity will become too high for extrusion. By applying this mixture of chain extenders a more comprehensive molecule (molecular complex) can be realised as depicted in Figure 8, wherein each molecule may have at least eight PET chains. In this reaction, each PMDA molecule reacts with four PET chains (as explained above), followed by a chemical bonding of each four-arms PMDA-PET molecule with ADR, resulting in the ADR-(PMDA-PET)nmolecule, wherein n > 2, as shown e.g. in Figure 8. Other variants are conceivable. The presence of the ADR-(PMDA-PET)n molecule may go hand in hand with the presence of the ADR-PET molecule and / or the presence of the PMDA-PET molecule as described above. Hence, in more generic wording, it is imaginable that at least a fraction of the PET based molecules, each comprises: a plurality of clusters, wherein each cluster comprises of a plurality of polymer chains of recycled PET mutually chemically bonded by a dianhydride, preferably PMDA and / or MEDA, wherein said clusters are mutually chemically bonded by said multifunctional epoxide oligomer.

[0028] Additionally or alternatively, at least one chain extender comprises or is formed by bis-(2,4-di-t-butylphenol) pentaerythritol diphosphite (Irgafos® 126 obtainable via Ciba Specialty Chemicals). This chain extender may also act as secondary chain extender in addition to one or more primary chain extenders, such as one or more of the chain extenders addressed above. Irgafos® 126 can be represented by the following chemical formula:

[0029] During the chain extension reaction with PET, the Irgafos® 126 molecule will be cleaved into two Irgafos® 126 fragments, wherein each fragment is capable to be chemically bonded to three PET chains (PET molecules). The molar mass of the chain-extended PET molecules also here increases as a function of the concentration of the chain extenders, while crystallinity tends to lower values.

[0030] The application of one or more additional or alternative chain extenders is also imaginable. For example, the chain extender may be an epoxy based chain extender comprising at least one epoxide group, such as 2-methyl-, oxirane methyl ester. This epoxy based chain extender is typically suitable to undergo a ringopening polymerisation reaction with chains of (recycled) PET.

[0031] The amount of chain-extended polyethylene terephthalate (PET) in the core layer is preferably situated between 25 and 45, preferably between 30 and 35, percent by weight of the core layer. The amount of chain extender in the core layer is preferably situated between 0.25 and 4, preferably between 0.5 and 1 , percent by weight of the core layer. The remaining fraction of the core layer is typically formed by one or more fillers and / or one or more functional additives, as discussed below.

[0032] In an embodiment of the decorative panel according to the invention, the panel comprises a plurality of laminated core layers, wherein at least one core layer, preferably at least two core layers or even each core layer comprises PET, preferably recycled PET, more preferably chain-extended (recycled) PET. At least one of the core layer may be a reinforcement layer, such as a glass fibre layer. The recycled PET comprising core layers may have different compositions or may have the same compositions. The core layers may be manufactured by means of coextrusion, in particular reactive coextrusion, wherein the recycled PET chains are extended by using one or more chain extenders, preferably during this (co)extrusion process. In a preferred embodiment, the panel comprises at least three laminated core layers in an alternating configuration, wherein core layers of substantially identical composition enclose a core layer with a different composition. This alternating configuration may e.g. an A-B-A configuration, wherein the outer layers (A) have substantially the same composition, and wherein the inner layer (B) has a different composition. The outer layers (A) preferably have a lower viscosity than the inner layer (B). This has a two-fold advantage. A first advantage is that a lower viscosity leads to a relatively smooth surface of the outer layers (A), which facilitates an easy application of the decorative top structure, including e.g. a digitally printed decor layer, on top. Preferably, at least one of these outer layers

[0033] (A) is solid (unfoamed). A second advantage of providing the inner layer (B) a higher viscosity allows more filler(s), such as limestone, to be applied in said layer

[0034] (B), which reduces the cost price of the inner layer (B). Moreover, the inner layer (B) may be a foamed layer, which reduces the density and which commonly improves the sound dampening properties and / or the comfort properties of the decorative panel as such. Hence, at least one core layer may be unfoamed, and / or at least one core layer may be foamed. The thickness of each outer core layer (A) may be smaller than the thickness of the inner core layer (B), and may also lead to the situation wherein the overall thickness of the (sum of the) the outer core layers (A) is smaller than the thickness of the inner core layer (B). Alternative configuration are also imaginable. It is imaginable that only a single core layer is applied, which may be foamed or unfoamed. It is imaginable that at least one core layer, such as the inner core layer (B), comprises recycled PET, while another core layer, such as at least one outer core layer (A), comprises PETG (polyethylene terephthalate glycol) and / or while another core layer comprises virgin PET. This AB and / or ABA and / or (AB)n(wherein n>1) configuration can be realized by means of coextrusion, in particular due to the structural similarities between PET and PETG. It has been found that PETG, compared to PET, is more suitable to act as a support layer and / or to adhere to a decorative top structure and / or a UV cured layer, applied onto of said PETG layer. Due to the improved adhesion properties of PETG, the application of a separate adhesion layer on top of the PETG layer may no longer be needed to realize a reliable and durable connection between the core layer(s) and the decorative structure. A type of filler, like calcium carbonate, may be the same for each core layer, or, alternatively, may also differ between at least two core layers.

[0035] Preferably, the mutually bonded recycled PET chains which make part of the chained-extended PET molecules, and consequently the raw recycled PET material used to form the chain-extended PET molecules, each has an average molar mass smaller than 20,000, preferably smaller than 15,000, more preferably smaller than 12,000 g / mol. Preferably, this average molar mass is higher than 10,000 g / mol to secure a sufficiently high viscosity, preferably of at least 0.5 dl / g. The molar mass of the chain-extended PET based molecules is approximately a multiplexity of these preferred value(s), depending on the number of PET chains bonded by the at least one chain extender used (and depending on the molar mass of the chain extender(s) used).

[0036] The core layer preferably comprises at least one inorganic filler, such as limestone, and / or organic filler, such as wood particles. Typically, the chain-extended PET molecules form a polymer matrix, wherein one or more additives are dispersed. Other possibly inert and / or functional fillers are for example, chalk, calcined clay, glass particles, glass fibres, carbon particles, silicon particular, a(nother) mineral filler, rice, a(nother) natural filler, a(nother) (auxiliary) polymer, such as an elastomer and / or latex. These fillers are often used to either reduce the cost price of the core layer and / or to make the core layer either more flexible or more rigid (stiff). The amount of filler in the core layer is preferably at least 50 percent by weight of the core layer, preferably in an amount of between 60 and 70 percent by weight of the core layer. Preferably, the weight amount of filler in the core layer is at least 1 .5 times the weight amount of PET, preferably chain-extended PET, of said core layer. The presence of a relatively large fraction (> weight%) of filler in the core layer leads to a relatively large distance between recycled PET molecules initially present in the masterbatch (fed into an extruder for extrusion). In order to improve the chain extension process during reactive extrusion, an excess of chain extender, such as PM DA, is preferably added to the masterbatch. This will increase the reaction activity and hence yield of the chain extension process during processing of the masterbatch. It may be preferred that the core layer comprises at least one lubricant configured to withstand temperatures of at least 200 degrees Celsius, preferably at least 255 degrees Celsius (which approximately corresponds to the melting temperature of recycled PET), more preferably at least 280 degrees Celsius (which approximately corresponds to the extrusion temperature). The lubricant is preferably present in an amount of less than 1 percent by weight of the core layer. Typically extrusion takes place at these higher temperature (> 200 degrees Celsius). The lubricant’s primary role is to reduce friction, minimize wear and prevent overheating of parts during extrusion. Preferably, the core layer comprises at least one lubricant formed by silicone oil, preferably in an amount of less than 1 percent by weight of the core layer. Silicone oil, contrary to e.g. ordinary wax, is an example of a lubricant which is capable to withstand extrusion temperatures of at least 200 degrees Celsius.

[0037] The core layer preferably comprises at least one toughening agent, preferably in an amount of less than 10 percent by weight of the core layer, more preferably in an amount of between 3 and 8 percent by weight of the core layer. This toughening agent may e.g. be formed by a styrene-ethylene-butylene-styrene terpolymer functionalized with maleic anhydride (SEBS-g-MA) (such as (FG1901X obtained from KRATON Corporation). This toughening agent may reduce the melt flow index (MFI) of recycled PET based masterbatch during extrusion, for example to a value of approximately 50 g / 10 min, which is favourable to produce the core layer.

[0038] The decorative top structure preferably comprises a primer layer applied onto the top surface of the core layer, and at least one further layer applied onto said primer layer. The primer may for example comprise calcium carbonate and / or a hydrogenated castor oil and wherein preferably the adhesive primer is a two- component adhesive, for example based on a (polyether) polyol and a curing agent. The primer layer facilitates adhesion of another layer, such as a basecoat layer onto the core layer.

[0039] The decorative top structure may comprise at least one basecoat layer, directly or indirectly, applied onto the top surface of the core layer, and at least one further layer applied onto said basecoat layer. The basecoat layer is typically configured to provide a base for applying a decorative layer. At least one basecoat is preferably a white layer, which will improve the colour authenticity of a decor layer optionally digitally printed on top of said basecoat layer(s). This white basecoat layer may be an UV cured layer. This white basecoat layer may e.g. comprise unsaturated aliphatic polyurethane acrylate, and / or hydroxyethyl methacrylate, and / or titanium dioxide. The white basecoat layer may be covered by a further basecoat layer to balance to surface tension to prevent shrinkage of ink droplets optionally to be printed onto said basecoat layer. This additional basecoat layer may be an UV cured layer. This additional basecoat layer may e.g. comprise unsaturated aliphatic polyurethane acrylate, and / or hydroxyethyl methacrylate, and / or calcium carbonate, and / or silicon dioxide.

[0040] The decorative top structure typically comprises at least one decorative layer, directly or indirectly, applied onto the top surface of the core layer, and preferably at least one further layer, such as a wear layer and / or anti-scratch layer, applied onto said decorative layer. The decorative layer is preferably a digitally printed decorative layer, but may also be formed by a veneer layer (wood layer, stone layer, polymer layer, other synthetic or natural layer), or by a decorative, preferably, polymer based, film, such as a PET comprising film, in particular a recycled PET comprising film, and / or a PETG comprising film. The wear layer(s) and the antiscratch layer (preferably acting as top coating), are preferably UV cured layers which are at least partially transparent and / or translucent. Additionally or alternative, at least one wear layer and / or at least one anti-scratch layer comprises PET, which may have a thickness ranging from 10 to 100 pm. The PET comprising wear layer(s) and / or anti-scratch layer(s) may be a PET comprising film. This film hay have a superior transparency, heat resistance, durability, and chemical resistance. Hence, the decorative top structure and / or at least one layer of the decorative top structure may at least partially be composed of at least one polyester, preferably polyethylene terephthalate (PET), more preferably chain- extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender. Examples of suitable PET formulations can be found throughout this document. Preferably, the PET composition used in the core layer is the same as the PET composition used in the decorative top structure. This will improve the recyclability of the decorative panel as such. The top surface of the decorative top structure is provided with a relief pattern, also referred to as embossing structure, wherein said relief pattern is preferably aligned with a decorative image of the decorative layer. The relief pattern may initially be provided in one of the wear layers or another intermediate layer, and may be covered by a top coating, such that the relief of the relief pattern remains visible and / or feelable at least partially at the top surface of the decorative top structure.

[0041] It is imaginable that the decorative top structure comprises and / or is formed by a single embossed, preferably PET and / or PETG comprising, wear layer provided with a decorative print on its lower side (facing the core layer(s)). The decorative print may simply be a decorative ink layer or may be a separate decorative film. The embossing applied in or on the wear layer is preferably aligned with said decorative print. In this manner a relatively compact, simple, and hence efficient decorative panel configuration can be realized.

[0042] The panel may comprise a backing layer attached, such as glued, directly or indirectly, to a bottom surface of the core layer, wherein the backing layer is preferably at least composed of PET. The backing layer may be foamed or unfoamed. The backing layer may contribute to the sound dampening properties and / or comfort properties of the decorative panels. The backing layer preferably comprises PET, more preferably recycled PET. It is imaginable that the backing layer, like the core layer, comprises at least one chain-extended condensation polymer, preferably at least one chain-extended polyester, more preferably at least one chain-extended PET at least partially composed of condensation polymer based molecules, preferably polyester based molecules, more preferably PET based molecules, each molecule comprising at least two polymer chains of recycled condensation polymer, preferably recycled polyester, more preferably recycled PET, mutually chemically bonded by at least one chain extender.

[0043] It is imaginable that the panel comprises at at least one pair of opposing side edges complementary coupling profiles allowing intercoupling of adjacent decorative panels. This allows decorative panels according to the invention for example to realize a so-called floating (unglued) floor covering or wall covering. Each side edge of the panel may be provided with a coupling profile. Each coupling profile may comprise one or more tongues and / or one or more grooves. The coupling profiles may be formed substantially out of the core layer material (by removal of core layer material at the side edges).

[0044] The panel may be an oblong panel. The panel may be rectangular or may have an alternative polygon shape, such as e.g. a triangular shape, a hexagonal shape, and a parallelogrammatic shape. The thickness of the core layer may vary, but is often situated between 4 and 10 mm, preferably between 4.5 and 8 mm.

[0045] The invention also relates to a core layer for use in a decorative panel according to the invention, wherein the core layer comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0046] The invention further relates to a method for producing a decorative panel, in particular a decorative panel according to the invention, comprising the steps of: a) mixing recycled PET material with at least one chain extender, said recycled PET material preferably having an intrinsic viscosity of between 0.50 dl / g and 0.80 dl / g, preferably between 0.50 and 0.60 dl / g, and / or having a molar mass of between 10,000 and 20,000 g / mol; b) loading said mixture in an extruder, preferably a twin screw extruder; c) extruding said mixture by said extruder, preferably at a temperature between 250 and 300 degrees Celsius, more preferably between 256 and 285 degrees Celsius, wherein at least a fraction of the PET material reacts with at least a fraction of the chain extender resulting in chain-extended polyethylene terephthalate (PET) wherein at least two polymer chains of recycled PET mutually are chemically bonded by said chain extender, wherein optionally water is generated, and wherein a core layer of the decorative panel is generated; d) cooling, preferably actively cooling, said extruded core layer to a temperature below 100 degrees Celsius, e) applying a decorative top structure on top of said core layer thereby forming the decorative panel. Preferably, the mass ratio of recycled PET and chain extender mixed during step a) is between 100: 1 and 100:2 (50: 1 ). This leads to sufficient chain extender to join sufficient PET chains. Preferably, during step a) at least two chain extenders are mixed, wherein a first chain extender is formed by at least one dianhydride, preferably pyromellitic dianhydride (PM DA) and / or mellophanic dianhydride (MEDA), and a second chain extender is formed by ADR, preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4. By applying this mixture of chain extenders, preferably in said preferred mass ratio, a desired and / or controller molar mass, and hence desired viscosity (preferably at least 0.8 dl / g), of the chain-extended PET can be obtained during the reactive extrusion process according to step c). Further advantages and embodiments have been described in the above and will be described below in a comprehensive manner.

[0047] Further embodiments of the invention are presented in the following non-limitative first set of clauses:

[0048] 1. Decorative panel (1 ), in particular a decorative floor panel, decorative ceiling panel, or decorative wall panel, comprising:

[0049] • at least one core layer (2),

[0050] • a decorative top structure (6) directly or indirectly affixed to a top surface said core layer (2); wherein said at least one core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0051] 2. Decorative panel (1) according to clause 1 , wherein at least a fraction of said PET based molecules each comprises at least four polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0052] 3. Decorative panel (1) according to clause 2, wherein at least a fraction of said PET based molecules each comprises more than four polymer chains of recycled PET mutually chemically bonded by at least one chain extender. 4. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least one polymer chain of recycled PET and at least one polymer chain of virgin PET mutually chemically bonded by at least one chain extender.

[0053] 5. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises unbonded recycled PET and / or unbonded virgin PET.

[0054] 6. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises unbonded chain extender molecules.

[0055] 7. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least two different chain extenders.

[0056] 8. Decorative panel (1) according to any of the preceding clauses, wherein at least one chain extender comprises a multifunctional epoxide oligomer.

[0057] 9. Decorative panel (1) according to clause 8, wherein said multifunctional epoxide oligomer (ADR), prior to bonding to the PET chains, is represented by the chemical structure: wherein:

[0058] R1-R5 are H, CH3, a higher alkyl group, or combinations of them;

[0059] R6 is an alkyl group, and x, y, and z are each between 1 and 20. 10. Decorative panel (1) according to any of the preceding clauses, wherein at least one chain extender, prior to bonding to PET chains, comprises at least one dianhydride, preferably pyromellitic dianhydride (PM DA) and / or mellophanic dianhydride (MEDA).

[0060] 11 . Decorative panel (1) according to clause 9 and 10, wherein the core layer comprises a mixture of (i) at least one dianhydride, preferably pyromellitic dianhydride (PMDA) and / or mellophanic dianhydride (MEDA), and (ii) ADR, preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4.

[0061] 12. Decorative panel (1) according to clauses 8 or 9 and clause 10 or 11 , wherein at least a fraction of the PET based molecules, each molecule comprising: a plurality of clusters, wherein each cluster comprises of a plurality of polymer chains of recycled PET mutually chemically bonded by a dianhydride, preferably PMDA and / or MEDA, wherein said clusters are mutually chemically bonded by said multifunctional epoxide oligomer.

[0062] 13. Decorative panel (1) according to any of the preceding clauses, wherein the amount of chain-extended polyethylene terephthalate (PET) in the core layer is situated between 25 and 45, preferably between 30 and 35, percent by weight of the core layer.

[0063] 14. Decorative panel (1) according to any of the preceding clauses, wherein the amount of chain extender in the core layer is situated between 0.25 and 4, preferably between 0.5 and 1 , percent by weight of the core layer.

[0064] 15. Decorative panel (1) according to any of the preceding clauses, wherein the panel comprises a plurality of laminated core layers, wherein at least one core layer, preferably each core layer comprises PET, more preferably chain-extended PET. 16. Decorative panel (1) according to clause 15, wherein the panel comprises three laminated core layers in an A-B-A configuration, wherein the outer layers (A) have the same composition, and wherein the inner layer (B) has a different composition.

[0065] 17. Decorative panel (1) according to any of the preceding clauses, wherein at least one core layer is unfoamed, and wherein at least one core layer is foamed.

[0066] 18. Decorative panel (1) according to any of the preceding clauses, wherein the mutually bonded recycled PET chains each has an average molar mass smaller than 20,000, preferably smaller than 15,000, more preferably smaller than 12,000 g / mol.

[0067] 19. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one inorganic filler, such as limestone, and / or organic filler, such as wood particles.

[0068] 20. Decorative panel (1) according to clause 19, wherein the amount of filler in the core layer is at least 50 percent by weight of the core layer, preferably in an amount of between 60 and 70 percent by weight of the core layer.

[0069] 21 . Decorative panel (1 ) according to clause 19 or 20, wherein the amount of filler in the core layer is at least 1 .5 times the amount of PET, preferably chain- extended PET, of said core layer.

[0070] 22. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one lubricant configured to withstand temperatures of at least 200 degrees Celsius, preferably in an amount of less than 1 percent by weight of the core layer.

[0071] 23. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one lubricant formed by silicone oil, preferably in an amount of less than 1 percent by weight of the core layer. 24. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one toughening agent, preferably in an amount of less than 10 percent by weight of the core layer, more preferably in an amount of between 3 and 8 percent by weight of the core layer.

[0072] 25. Decorative panel (1) according to any of the preceding clauses, wherein the decorative top structure comprises a primer layer applied onto the top surface of the core layer, and at least one further layer applied onto said primer layer.

[0073] 26. Decorative panel (1) according to any of the preceding clauses, wherein the decorative top structure comprises at least one basecoat layer, directly or indirectly, applied onto the top surface of the core layer, and at least one further layer applied onto said basecoat layer.

[0074] 27. Decorative panel (1) according to any of the preceding clauses, wherein the decorative top structure comprises at least one decorative layer, directly or indirectly, applied onto the top surface of the core layer, and preferably at least one further layer, such as a wear layer and / or anti-scratch layer, applied onto said decorative layer.

[0075] 28. Decorative panel (1) according to clause 27, wherein the decorative layer is a digitally printed decorative layer.

[0076] 29. Decorative panel (1) according to clause 27, wherein the decorative layer is formed by a veneer layer or by a decorative film.

[0077] 30. Decorative panel (1) according to any of clauses 27-29, wherein a top surface of the decorative top structure is provided with a relief pattern, wherein said relief pattern is preferably aligned with a decorative image of the decorative layer.

[0078] 31 . Decorative panel (1 ) according to any of the preceding clauses, wherein the panel comprises a backing layer attached, directly or indirectly, to a bottom surface of the core layer, wherein the backing layer is preferably at least composed of PET. 32. Decorative panel (1) according to any of the preceding clauses, wherein the panel comprises at at least one pair of opposing side edges complementary coupling profiles allowing intercoupling of adjacent decorative panels.

[0079] 33. Core layer (2) intended for use in a decorative panel (1) according to any of the preceding clauses, wherein said core layer comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0080] 34. Method for producing a decorative panel, in particular a decorative panel (1) according to any of the preceding clauses, comprising the steps of: a) mixing recycled PET material with at least one chain extender, said recycled PET material preferably having an intrinsic viscosity of between 0.50 dl / g and 0.80 dl / g, preferably between 0.50 and 0.60 dl / g, and / or having a molar mass of between 10,000 and 20,000 g / mol; b) loading said mixture in an extruder, preferably a twin screw extruder; c) extruding said mixture by said extruder, preferably at a temperature between 255 and 300 degrees Celsius, wherein at least a fraction of the PET material reacts with at least a fraction of the chain extender resulting in chain- extended polyethylene terephthalate (PET) wherein at least two polymer chains of recycled PET mutually are chemically bonded by said chain extender, wherein optionally water is generated, and wherein a core layer of the decorative panel is generated; d) cooling, preferably actively cooling, said extruded core layer to a temperature below 100 degrees Celsius, e) applying a decorative top structure on top of said core layer thereby forming the decorative panel.

[0081] 35. Method according to clause 34, wherein the mass ratio of recycled PET and chain extender mixed during step a) is between 100:1 and 100:2.

[0082] 36. Method according to clause 34 or 35, wherein during step a) at least two chain extenders are mixed, wherein a first chain extender is formed by at least one dianhydride, preferably pyromellitic dianhydride (PM DA) and / or mellophanic dianhydride (MEDA), and a second chain extender is formed by ADR, preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4.

[0083] Further embodiments of the invention are presented in the following non-limitative second set of clauses:

[0084] 1. Decorative panel (1 ), in particular a decorative floor panel, decorative ceiling panel, or decorative wall panel, comprising:

[0085] • at least one core layer (2),

[0086] • a decorative top structure (6) directly or indirectly affixed to a top surface said core layer (2); wherein said at least one core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0087] 2. Decorative panel (1) according to clause 1 , wherein at least a fraction of said PET based molecules each comprises at least four polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0088] 3. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least one polymer chain of recycled PET and at least one polymer chain of virgin PET mutually chemically bonded by at least one chain extender.

[0089] 4. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises unbonded recycled PET and / or unbonded virgin PET.

[0090] 5. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises unbonded chain extender molecules.

[0091] 6. Decorative panel (1) according to any of the preceding clauses, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least two different chain extenders.

[0092] 7. Decorative panel (1) according to any of the preceding clauses, wherein at least one chain extender comprises a multifunctional epoxide oligomer.

[0093] 8. Decorative panel (1) according to clause 7, wherein said multifunctional epoxide oligomer (ADR), prior to bonding to the PET chains, is represented by the chemical structure: wherein:

[0094] - R1-R5 are H, CH3, a higher alkyl group, or combinations of them;

[0095] - R6 is an alkyl group, and

[0096] - x, y, and z are each between 1 and 20.

[0097] 9. Decorative panel (1) according to any of the preceding clauses, wherein at least one chain extender, prior to bonding to PET chains, comprises at least one dianhydride, preferably pyromellitic dianhydride (PM DA) and / or mellophanic dianhydride (MEDA).

[0098] 10. Decorative panel (1) according to clause 8 and 9, wherein the core layer comprises a mixture of (i) at least one dianhydride, preferably pyromellitic dianhydride (PMDA) and / or mellophanic dianhydride (MEDA), and (ii) ADR, preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4.

[0099] 11 . Decorative panel (1 ) according to clauses 7 or 8 and clause 9 or 10, wherein at least a fraction of the PET based molecules, each molecule comprising: - a plurality of clusters, wherein each cluster comprises of a plurality of polymer chains of recycled PET mutually chemically bonded by a dianhydride, preferably PM DA and / or MEDA,

[0100] - wherein said clusters are mutually chemically bonded by said multifunctional epoxide oligomer.

[0101] 12. Decorative panel (1) according to any of the preceding clauses, wherein the panel comprises a plurality of laminated core layers, wherein at least one core layer, preferably each core layer comprises PET, more preferably chain-extended PET, wherein the panel comprises three laminated core layers in an A-B-A configuration, wherein the outer layers (A) have the same composition, and wherein the inner layer (B) has a different composition.

[0102] 13. Decorative panel (1) according to any of the preceding clauses, wherein the mutually bonded recycled PET chains each has an average molar mass smaller than 20,000, preferably smaller than 15,000, more preferably smaller than 12,000 g / mol.

[0103] 14. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one inorganic filler, such as limestone, and / or organic filler, such as wood particles wherein the amount of filler in the core layer is at least 50 percent by weight of the core layer, preferably in an amount of between 60 and 70 percent by weight of the core layer.

[0104] 15. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one lubricant formed by silicone oil, preferably in an amount of less than 1 percent by weight of the core layer.

[0105] 16. Decorative panel (1) according to any of the preceding clauses, wherein the core layer comprises at least one toughening agent, preferably in an amount of less than 10 percent by weight of the core layer, more preferably in an amount of between 3 and 8 percent by weight of the core layer.

[0106] 17. Decorative panel (1) according to any of the preceding clauses, wherein the decorative top structure comprises at least one decorative layer, directly or indirectly, applied onto the top surface of the core layer, and preferably at least one further layer, such as a wear layer and / or anti-scratch layer, applied onto said decorative layer.

[0107] 18. Decorative panel (1) according to any of the preceding clauses, wherein the panel comprises at at least one pair of opposing side edges complementary coupling profiles allowing intercoupling of adjacent decorative panels.

[0108] 19. Core layer (2) intended for use in a decorative panel (1) according to any of the preceding clauses, wherein said core layer comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

[0109] 20. Method for producing a decorative panel, in particular a decorative panel (1) according to any of clauses 1-18, comprising the steps of: a) mixing recycled PET material with at least one chain extender, said recycled PET material preferably having an intrinsic viscosity of between 0.50 dl / g and 0.80 dl / g, preferably between 0.50 and 0.60 dl / g, and / or having a molar mass of between 10,000 and 20,000 g / mol; b) loading said mixture in an extruder, preferably a twin screw extruder; c) extruding said mixture by said extruder, preferably at a temperature between 255 and 300 degrees Celsius, wherein at least a fraction of the PET material reacts with at least a fraction of the chain extender resulting in chain-extended polyethylene terephthalate (PET) wherein at least two polymer chains of recycled PET mutually are chemically bonded by said chain extender, wherein optionally water is generated, and wherein a core layer of the decorative panel is generated; d) cooling, preferably actively cooling, said extruded core layer to a temperature below 100 degrees Celsius, e) applying a decorative top structure on top of said core layer thereby forming the decorative panel.

[0110] The invention will be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures. Herein: - Figure 1 schematically shows a decorative panel according to the invention;

[0111] - Figure 2 shows the panel of figure 1 without the optional intermediate layer;

[0112] - Figures 3 and 4 schematically show possible configurations of complementary coupling profiles according to the invention;

[0113] - Figures 5 and 6 schematically show other possible coupling profiles according to the present invention

[0114] - Figure 7 schematically shows a p decorative panel according to the invention;

[0115] - Figure 8 shows a possible example of chain extensions according to the present invention; and

[0116] - Figure 9 shows another example embodiment of chain extensions according to the present invention.

[0117] Figure 1 schematically shows a panel (1) according to the invention, with a centrally located core layer (2), wherein said core layer (2) comprises an top surface (3) and a bottom surface (4), preferably on opposite sides of said core layer (2). A backing layer (5) is in this non-limitative embodiment attached to the bottom surface (4) of the core. Figure 1 also shows a decorative top layer (6), which is attached to the top surface (3) of the core (2). Although the decorative top structure (6) is indicated as a single layer in this non-limitative embodiment, it is conceivable that the decorative top structure (6) comprises more than one layer. For example, the decorative top structure (6) may be formed by; a printed decorative layer, such as a digital print layer, veneer layer, or decorative film, an embossing structure or pattern layer, which may form a relief of the panel, and optionally a wear or protective layer.

[0118] On two opposite sides (7, 8) of the panel (1), which may alternatively be referred to as a pair of opposing edges (7, 8), complementary coupling parts (9, 10) are provided. The first coupling part (7) is in the form of a downward tongue (11) and the second coupling part (9) is in the form of an upward tongue (12). The second coupling part (9) may comprise a single upward tongue (12), at least one upward flank (13) lying at a distance from the upward tongue and a single upward groove (14) formed between the upward tongue and the upward flank, wherein at least a part of a side (15) of the upward tongue facing toward the upward flank is inclined and extends in the direction of the normal (N1) of the upper side or top surface (3) of the core, and wherein optionally at least a part of a side (16) of the upward tongue facing away from the upward flank comprises a substantially rigid first locking element (17), and on a second or fourth edge, a single downward tongue (11), at least one downward flank (18) lying at a distance from the downward tongue, and a single downward groove (19) formed between the downward tongue and the downward flank, wherein at least a part of a side (20) of the downward tongue facing toward the downward flank is inclined and extends in the direction of the normal (N2) of the lower side or bottom surface (4) of the core, and wherein the downward flank optionally comprises a, preferably substantially rigid, second locking element (21) adapted for co-action with the first locking element of a third edge of yet a further panel.

[0119] Figure 1 further shows that an upper or front side (22) of the upward tongue (12) is inclined, from a top side (22A) downwards towards the outside (16). The transition from the inside (15) of the upward tongue (12) to the top side (22A) forms an aligning edge (23). A similar construction is present on the other side, with an upper side (24) of the groove (19) being inclined. The aligning edge (25) on the downward tongue (11) is arranged on the outside (26) thereof. On both sides, the transition between the tongue (11 , 12) and the core (2) is formed by a bridge, being an upper bridge (27) on the downward tongue (11) side and a lower bridge (28) on the upward tongue (12) side. The transition (29) from the downward tongue (11) towards the inside thereof is shown rounded, to facilitate deformation.

[0120] Figure 1 further shows that between the core layer (2) and the decorative top structure (6) an optional intermediate layer (30) is arranged, which is absent in figure 2.

[0121] The core layer (2) comprises chain-extended polyethylene terephthalate (PET) which is at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded through at least one chain extender. The chain extensions are shown in more detail with respect to figure 8.

[0122] Figure 2 schematically shows a layering of the panel (1) and the decorative top structure (6) in particular. The decorative top structure (6) comprises an adhesive primer (61), a base coat (62), a transition layer (63), a printed decor (64), a wear layer (65), a structured layer (66), and a scratch resistant layer (67), provided on top.

[0123] Figures 3 and 4 show possible other configurations of the complementary coupling parts and may also be usable for the invention as possible embodiments for the sideward tongue and groove combination.

[0124] Figure 3 for example shows on a first edge a sideward tongue (32) extending in a direction substantially parallel to the top surface of the panel, the bottom front region (33) of said sideward tongue being rounded at least partly, the bottom back region (24) of said tongue being configured as bearing region, wherein the bottom back region is located closer to the level of the top surface of the panel than a lowest part of the bottom front region, and on an opposite second edge (8) comprising a recess or sideward groove (35) for accommodating at least a part of the sideward tongue of a further panel, said recess being defined by an upper lip (36) and a lower lip (37), said lower lip being provided with a upwardly protruding shoulder (38) for supporting and / or facing the bearing region of the sideward tongue.

[0125] Figures 4a-4e show various variations on shapes usable for sideward tongues and grooves according to the present invention.

[0126] Figures 5 and 6 shows possible other configurations of the complementary coupling parts and may also be usable for the invention as possible embodiments for the downward and upward tongue combination. In figure 5 a similar locking system is shown compared to figures 1 and 2, with a slightly different shaping as well as with additional locking (31) on the outside of the downward tongue (11) and the upper side of the upward flank (13). In figure 6 the locking is shown as an open groove, wherein the insides (15, 20) of the tongues (11 , 12) are inclined, but not towards the cores but away from the cores. The angle of those insides (15, 20) is opposite to the one shown in figures 1 and 2.

[0127] Figure 7 schematically shows a panel (1) with a top surface (3) and a Sidebottom surface (4) on opposite sides of the core. The decorative panel (1) is rectangular with four edges. The opposite edges (7, 8) on the short sides and two opposite edges (7’, 8’) on the long sides. Along the cross section A-A indicated in figure 7 the coupling parts on the long sides would show up, represented for example by the figures 3 and 4. Along the cross section B-B the coupling parts on the short sides would be shown, represented by the other figures of the application.

[0128] Figure 8 schematically shows the chain extension according to the present invention. On the left a PM DA (71) is shown which reacts with a PET chain (72). The PET chain (72) may for example be a recycled PET chain. In the progress, the ring of PDMA opens and allows attachment of up to four PET chains (72) on the ends to obtain the first intermediate product (73). The first intermediate product (73) may also be an end product (73), however, even better results may be achieved when this intermediate product (73) is used in further chain extensions. This intermediate product (73), or rather multiple thereof, may subsequently react with an ADR group (74). The ends of the PET chain (72) that didn’t attach to the PMDA (71), hence the free ends of the intermediate product (73) now react with the ADR group (74) forming an ADB backbone with, preferably a plurality of, intermediate product (73) to further extend the chain.

[0129] The reaction products from PMDA are likely four-arm star polymer, and the formation of a comb-shaped PET with a very short backbone is possible for branching reactions with ADR. The reason why the backbone is considered relatively short is that PET (26,300 g / mol) is about nine times the number average molar mass of ADR (3000 g / mol). According to the different reaction mechanisms, ADR can easily induce branched structures compared to PMDA, because the branching can be achieved through only one step for ADR but two steps for PMDA, especially the secondary esterification or transesterification reaction of PMDA is relatively slow. This can be confirmed by the short reaction time of ADR during the batch mixing process.

[0130] Figure 9 shows an alternative example of the chain extension as shown in figure 8. This figure shows that an ADR group (74) reacts with a PET chain (72). In the final product (75) the PET chains (72) have attached to the ADR group (74). It is also imaginable that a combination of the chain extensions as indicated in figures 8 and 9 is formed. Hence, wherein a combination of PET chains (72) and intermediate product (73) attach to the ADR group (74). 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.

[0131] The ordinal numbers used in this document, like “first”, “second”, “third” and “fourth”, are used only for identification purposes. Hence, the use of the expression “third coupling profile” does therefore not necessarily require the co-presence of a “first coupling profile”. And likewise, the use of the expressions “third locking element” and “second locking element” does therefore not necessarily require the co-presence of a “first locking element”. By "horizontal", it is meant as a direction which extends parallel to a plane defined by the tile panel, and which may intersect a core layer of the tile panel. By “vertical”, it is meant as a direction which is perpendicular to said plane defined by the tile panel. By "complementary" coupling profiles, it is meant that these coupling profiles of adjacent tile panels can cooperate with each other. However, to this end, the complementary coupling profiles do not necessarily have to have fully complementary forms (inverted designs). By “proximal side”, it is meant a side which is positioned closest to a body of the tile panel, while by “distal side”, it is meant as a side which is positioned farther from a body of the tile panel than said proximal side. The proximal side may face said tile panel body, while the distal side may face away from said tile panel body.

[0132] In the above, the expression PET may selectively be replaced by at least one other suitable condensation polymer, in particular polyester and / or by a copolymer of PET and / or derivate from PET, such as PETG ((polyethylene terephthalate glycol), wherein the PET copolymer, for example, comprises, as comonomer, at least one comonomer chosen from the group consisting of: diethylene glycol (DEG), cyclohexanedimethanol (CHDM), isophthalic acid (IPA), naphthalene acid (NDC), and mixtures of at least two of these comonomers. PETG is an adaptation of PET, where the ‘G’ stands for glycol, which is added at a molecular level to offer different chemical properties and is therefore considered as copolymer of PET. Compared to (virgin or recycled) PET, (virgin or recycled) PETG has greater strength and durability, as well as being more impact resistant and better suited to higher temperatures, and is therefore a suitable alternative to PET. As indicated above, in this disclosure recycled PET may be replaced by either recycled PETG and / or virgin PETG, or a combination of recycled and virgin PETG. In this disclosure, virgin PET may be replaced by either recycled PETG and / or virgin PETG, or a combination of recycled and virgin PETG. A combination of (recycled and / or virgin) PET and (recycled and / or virgin) PETG may also be used in at least one panel layer, such as the core layer. It is imaginable that (recycled and / or virgin) PET is used at least one panel layer, while (recycled and / or virgin) PETG is used in at least one other panel layer. It is imaginable that a plurality of panel layers comprises PETG, such as for example the core layer, at least one wear layer, and / or at least one intermediate layer (intermediate film) situated in between said core layer and at least one wear layer. The PETG based material used in at least one panel layer may be foamed or unfoamed (solid). In particular, a PETG based core layer may be a foamed PETG based core layer to save weight.

[0133] In order to realize a foamed PETG (and / or foamed PET) layer, it may be favourable that this layer comprises at least one blowing agent, such as an azodicarbonamide (AC) blowing agent (foaming agent), and / or at least one foaming regulator, such as an acrylate (ACR) foaming regulator. For example, such a foamed layer may be prepared from a raw material including the following components in parts by mass: 100 parts of PET and / or PETG, 1-2 parts of the blowing agent, such as an AC blowing agent, and / or 14-16 parts of the foaming regulator, such as an ACR foaming regulator. Optionally, at least 100 parts, such as 150-350 parts, in particular 300 parts of inorganic filler, such as limestone and / or talc, may be added to the raw material composition. Optionally, wax, such as polyethylene wax, for example in a relative amount of 1-3 parts, may be added to the raw material composition. Optionally, the raw composition may comprise at least one releasing agent, such as 3-7 parts, in particular 5 parts, of releasing agent. Optionally, at least one reinforcement agent is added to the raw composition, for example in an amount of 5-15 parts, in particular 10 parts.

[0134] In the present disclosure, the foaming regulator preferably acts as chain extender. The foaming regulator preferably comprises a, preferably acrylate based, polymer with (reactive) epoxy groups and / or ester groups. The presence of ester groups provides a good compatibility to achieve uniform mixing of the foaming regulator and the PET (and / or PETG). A reaction between the foaming regulator and the polymer chain(s) of PET and / or PETG expands the molecular weight of PET and / or PETG, and significantly improves the melt strength of the mixture. An acrylate based foaming regulator moreover has a relatively good compatibility for mixing with an inorganic filler. Each epoxy group of the foaming regulator (chain extender) is capable to react with a hydroxyl group (of a carboxyl (end) group) to form an ester. In case the foaming regulator molecule comprises multiple epoxy groups, multiple PET (and / or PETG) chains can be bonded to said foaming regulator molecule, and hence can be mutually bonded, effectively leading to a chain extension.

[0135] In the present disclosure, the amount of the foaming agent in the raw material composition is preferably kept limited, such as an amount of 1 part of blowing agent with respect to 100 parts of PET (and / or PETG). This leads to sufficient foaming to reduce the layer density (e.g. between and including 0.8 and 1 .0 g / cm3) and hence the panel weight, while to keep sufficient (bending) strength, such as at least 180 MPa, and often leads to a relatively high noise reduction coefficient of at least 0.95, preferably measured in accordance with the ASTM C423(-23) standard.

[0136] In the present disclosure, the inorganic filler preferably is or comprises a mixture calcium carbonate (limestone) and talc powder, a mass ratio of calcium carbonate to talc powder preferably being in a range of (1 -9):(9-1 ), and more preferably 1 :1. In the present disclosure, in some embodiments, the inorganic filler may have a particle size of 200-400 mesh.

[0137] As a PETG melt is inclined to adhere to metal, which causes PETG to be inclined to adhere to a mould surface during extrusion processing, this would hinder a smooth flow of PETG and therefore would affect a smooth production of the PETG based panel layer. At the same time, due to PETG adhesion, decomposition under long-term heating could occur which would result in a relatively (and too) rough surface of the extruded layer. For this reason, it is advantageous that at least one release agent is added to the mixture (prior to extruding). Such as release agent forms a stable lubricating film between the metal mould surface and the PETG comprising melt during extrusion, eliminating the risk of adhesion between the mould and the melt mixture. Preferably, the release agent comprises ester groups which ensures that the release agent is absorbed and fixed onto the surface of PETG chain(s). The addition of release agent moreover ensures the smooth production of foamed PETG based layers. The release agent preferably comprises a long-chain alkane backbone. The release agent is preferably temperature resistant to temperature of at least 200 degrees Celsius.

[0138] It is imaginable that at least one chain extender is configured to chemically bond and / or actually chemically bonds at least one (virgin and / or recycled) PET chain and at least one (and / or recycled) PETG chain. It is imaginable that at least one chain extender is configured to chemically bond and / or actually chemically bonds (i) at least one (virgin and / or recycled) PET chain and / or at least one (and / or recycled) PETG chain, and (ii) at least one other (virgin and / or recycled) polymer chain.

[0139] 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

Claims1. Decorative panel (1 ), in particular a decorative floor panel, decorative ceiling panel, or decorative wall panel, comprising:• at least one core layer (2),• a decorative top structure (6) directly or indirectly affixed to a top surface said core layer (2); wherein said at least one core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender, and wherein said at least one core layer (2) is free of PVC, and wherein said at least one core layer (2) is free of polyolefins.

2. Decorative panel (1) according to claim 1 , wherein at least a fraction of said PET based molecules each comprises at least four polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

3. Decorative panel (1) according to any of the preceding claims, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least one polymer chain of recycled PET and at least one polymer chain of virgin PET mutually chemically bonded by at least one chain extender.

4. Decorative panel (1) according to any of the preceding claims, wherein the core layer (2) comprises unbonded recycled PET and / or unbonded virgin PET.

5. Decorative panel (1) according to any of the preceding claims, wherein the core layer (2) comprises unbonded chain extender molecules.

6. Decorative panel (1) according to any of the preceding claims, wherein the core layer (2) comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each comprising at least two polymer chains of recycled PET mutually chemically bonded by at least two different chain extenders.

7. Decorative panel (1) according to any of the preceding claims, wherein at least one chain extender comprises a multifunctional epoxide oligomer.

8. Decorative panel (1) according to claim 7, wherein said multifunctional epoxide oligomer, prior to bonding to the PET chains, is represented by the chemical structure:wherein:- R1-R5 are H, CH3, a higher alkyl group, or combinations of them;- R6 is an alkyl group, and- x, y, and z are each between 1 and 20.

9. Decorative panel (1) according to any of the preceding claims, wherein at least one chain extender, prior to bonding to PET chains, comprises at least one dianhydride, preferably pyromellitic dianhydride (PM DA) and / or mellophanic dianhydride (MEDA).

10. Decorative panel (1) according to claim 8 and 9, wherein the core layer comprises a mixture of (i) at least one dianhydride, preferably pyromellitic dianhydride (PMDA) and / or mellophanic dianhydride (MEDA), and (ii) said multifunctional epoxide oligomer , preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4.11 . Decorative panel (1 ) according to claims 7 or 8 and claim 9 or 10, wherein at least a fraction of the PET based molecules, each molecule comprising:- a plurality of clusters, wherein each cluster comprises of a plurality of polymer chains of recycled PET mutually chemically bonded by a dianhydride, preferably PMDA and / or MEDA,wherein said clusters are mutually chemically bonded by said multifunctional epoxide oligomer.

12. Decorative panel (1) according to any of the preceding claims, wherein the panel comprises a plurality of laminated core layers, wherein at least one core layer, preferably each core layer comprises PET, more preferably chain-extended PET, wherein the panel comprises three laminated core layers in an A-B-A configuration, wherein the outer layers (A) have the same composition, and wherein the inner layer (B) has a different composition.

13. Decorative panel (1) according to any of the preceding claims, wherein the amount of chain-extended polyethylene terephthalate (PET) in the core layer is situated between 25 and 45, preferably between 30 and 35, percent by weight of the core layer.

14. Decorative panel (1) according to any of the preceding claims, wherein the amount of chain extender in the core layer is situated between 0.25 and 4, preferably between 0.5 and 1 , percent by weight of the core layer.

15. Decorative panel (1) according to any of the preceding claims, wherein the panel comprises a plurality of laminated core layers, wherein at least one core layer, preferably each core layer comprises PET, more preferably chain-extended PET.

16. Decorative panel (1) according to claim 15, wherein the panel comprises three laminated core layers in an A-B-A configuration, wherein the outer layers (A) have the same composition, and wherein the inner layer (B) has a different composition.

17. Decorative panel (1) according to any of the preceding claims, wherein at least one core layer is unfoamed, and wherein at least one core layer is foamed.

18. Decorative panel (1) according to any of the preceding claims, wherein the mutually bonded recycled PET chains each has an average molar mass smallerthan 20,000, preferably smaller than 15,000, more preferably smaller than 12,000 g / mol.

19. Decorative panel (1) according to any of the preceding claims, wherein the core layer comprises at least one inorganic filler, such as limestone, and / or organic filler, such as wood particles wherein the amount of filler in the core layer is at least 50 percent by weight of the core layer, preferably in an amount of between 60 and 70 percent by weight of the core layer.

20. Decorative panel (1) according to claim 19, wherein the amount of filler in the core layer is at least 1 .5 times the amount of PET, preferably chain-extended PET, of said core layer.21 . Decorative panel (1 ) according to any of the preceding claims, wherein the core layer comprises at least one lubricant configured to withstand temperatures of at least 200 degrees Celsius, preferably in an amount of less than 1 percent by weight of the core layer.

22. Decorative panel (1) according to any of the preceding claims, wherein the core layer comprises at least one lubricant formed by silicone oil, preferably in an amount of less than 1 percent by weight of the core layer.

23. Decorative panel (1) according to any of the preceding claims, wherein the core layer comprises at least one toughening agent, preferably in an amount of less than 10 percent by weight of the core layer, more preferably in an amount of between 3 and 8 percent by weight of the core layer.

24. Decorative panel (1) according to any of the preceding claims, wherein the decorative top structure comprises a primer layer applied onto the top surface of the core layer, and at least one further layer applied onto said primer layer.

25. Decorative panel (1) according to any of the preceding claims, wherein the decorative top structure comprises at least one basecoat layer, directly or indirectly, applied onto the top surface of the core layer, and at least one further layer applied onto said basecoat layer.

26. Decorative panel (1) according to any of the preceding claims, wherein the decorative top structure comprises at least one decorative layer, directly or indirectly, applied onto the top surface of the core layer, and preferably at least one further layer, such as a wear layer and / or anti-scratch layer, applied onto said decorative layer.

27. Decorative panel (1) according to any of the preceding claims, wherein the decorative top structure is at least partially composed of at least one polyester, preferably polyethylene terephthalate (PET), more preferably chain-extended polyethylene terephthalate (PET) at least partially composed of PET based molecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

28. Decorative panel (1) according to claim 27, wherein the decorative layer is a digitally printed decorative layer.

29. Decorative panel (1) according to claim 27, wherein the decorative layer is formed by a veneer layer or by a decorative film.

30. Decorative panel (1) according to any of claims 27-29, wherein a top surface of the decorative top structure is provided with a relief pattern, wherein said relief pattern is preferably aligned with a decorative image of the decorative layer.31 . Decorative panel (1 ) according to any of the preceding claims, wherein the panel comprises a backing layer attached, directly or indirectly, to a bottom surface of the core layer, wherein the backing layer is preferably at least composed of PET32. Decorative panel (1) according to any of the preceding claims, wherein the panel comprises at at least one pair of opposing side edges complementary coupling profiles allowing intercoupling of adjacent decorative panels.

33. Core layer (2) intended for use in a decorative panel (1) according to any of the preceding claims, wherein said core layer comprises chain-extended polyethylene terephthalate (PET) at least partially composed of PET basedmolecules each molecule comprising at least two polymer chains of recycled PET mutually chemically bonded by at least one chain extender.

34. Method for producing a decorative panel, in particular a decorative panel (1) according to any of claims 1-32, comprising the steps of: a) mixing recycled PET material with at least one chain extender, said recycled PET material preferably having an intrinsic viscosity of between 0.50 dl / g and 0.80 dl / g, preferably between 0.50 and 0.60 dl / g, and / or having a molar mass of between 10,000 and 20,000 g / mol; b) loading said mixture in an extruder, preferably a twin screw extruder; c) extruding said mixture by said extruder, preferably at a temperature between 255 and 300 degrees Celsius, wherein at least a fraction of the PET material reacts with at least a fraction of the chain extender resulting in chain-extended polyethylene terephthalate (PET) wherein at least two polymer chains of recycled PET mutually are chemically bonded by said chain extender, wherein optionally water is generated, and wherein a core layer of the decorative panel is generated; d) cooling, preferably actively cooling, said extruded core layer to a temperature below 100 degrees Celsius, e) applying a decorative top structure on top of said core layer thereby forming the decorative panel.

35. Method according to claim 34, wherein the mass ratio of recycled PET and chain extender mixed during step a) is between 100:1 and 100:2.

36. Method according to claim 34 or 35, wherein during step a) at least two chain extenders are mixed, wherein (i) a first chain extender is formed by at least one dianhydride, preferably pyromellitic dianhydride (PMDA) and / or mellophanic dianhydride (MEDA), and (ii) a second chain extender is formed by a multifunctional epoxide oligomer, prior to bonding to the PET chains being represented by the chemical structure:wherein:R1-R5 are H, CH3, a higher alkyl group, or combinations of them;R6 is an alkyl group, and - x, y, and z are each between 1 and 20, preferably in a mass ratio of between 1 :1 and 2:1 , more preferably in a mass ratio of 6:4.

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