A foam sheet comprising polypropylene with high melt resistance and its preparation process.

Description

[0001] The invention relates to a foam sheet comprising a polymer composition comprising a polypropylene with high melt strength, to an article comprising said foam sheet, as well as to a process for preparing said foam sheet and to the use of said foam sheet.

[0002] Polymer foams are used in a wide range of applications, such as building and construction, automotive applications, residential applications such as food packaging and protective packaging; and consumer applications. Foams are popular because of their good mechanical stiffness, their good insulating properties, and their mechanical damping. Furthermore, the use of foams makes a significant contribution to reducing the use of raw materials. Moreover, the use of foams allows for a lightweight solution, which is not only advantageous from a cost perspective but also from a transportation standpoint, as less energy is required to transport a lighter material.

[0003] Polypropylene foams are advantageous compared to other polymer foams for several reasons: polypropylene has good mechanical properties, in particular stiffness (hardness), allows for easy recycling (whereas polystyrene, for example, requires additional steps in waste separation processes), has good chemical resistance (oil and acid), good thermal resistance, and does not absorb water.

[0004] Document No. US2019 / 276653 A1 discloses a foaming composition that includes a polypropylene-based copolymer and a polyolefin.

[0005] Document No. US2020 / 087478A1 reveals a process Petition 870240080479, dated 09 / 20 / 2024, page 8 / 37 2 / 22 for the production of a foam that has low emissions of organic compounds, products with polypropylene foam obtainable by the process and a process for the manufacture of articles with low emissions of organic compounds comprising a foam for use in cars and food packaging.

[0006] Document No. US2018 / 0201752A1 discloses cups based on a multi-layered sheet comprising at least one layer of foam based on polypropylene with high melt strength and a nucleating agent.

[0007] Document No. US2004 / 0258902A1 discloses an article with foam comprising a polymer foam base layer having at least one outer face, wherein said outer face contains, in at least one area, a plurality of integrally foamed surface microstructures comprising voids, wherein said microstructures have at least one dimension greater than 10 microns and the voids form the foam having an average cross-sectional dimension smaller than the smallest cross-sectional dimension of the microstructure.

[0008] For polypropylene foam, long-chain branched polypropylenes are commonly used. An example of such a long-chain branched polypropylene is DaployMWB140HMS, commercially available from Borealis.

[0009] Meanwhile, there is a continuing desire to improve long-chain branched polypropylenes. For example, there is a desire to improve the processing, recyclability and / or properties of foam produced with long-chain branched polypropylenes. In addition, there is also pressure to reduce the environmental impact of polypropylene foams, for example, by further reducing dimensions and / or increasing recyclability.

[0010] The objective of this invention is to achieve the preparation of Petition 870240080479, dated 09 / 20 / 2024, p. 9 / 37 3 / 22 foam sheets that have superior flexural toughness while not increasing the environmental impact (i.e., while not increasing the amount of raw materials required).

[0011] This objective is achieved by means of a foam sheet comprising a polymer composition comprising a high-melt-strength polypropylene, wherein the high-melt-strength polypropylene has a melt strength > 0.45 N (> 45 cN); preferably, > 0.5 N (> 50 cN); more preferably, > 0.55 N (> 55 cN); even more preferably, > 0.6 N (> 60 cN); with maximum preference, > 0.65 N (> 65 cN), where the fusion resistance is determined according to ISO 16790:2005 at a temperature of 200°C, using a cylindrical capillary part that has a length of 20 mm and a width of 2 mm, a starting velocity vo of 0.0098 m / s (9.8 mm / s) and an acceleration of 0.006 m / s2 (6 mm / s2).

[0012] The foam sheets of the invention exhibit increased overall flexural toughness. This means that the high-melt-strength polypropylene having a melt strength > 0.45 N (> 45 cN) in the foam sheets of the invention allows a) the production of foams that have increased flexural toughness (same thickness) and b) the production of foams using less raw material while still achieving the same flexural toughness (lower thickness and / or lower foam density). The use of less raw material (reduced dimensions) is advantageous from an environmental point of view in terms of carbon footprint (less material and lower transport and energy costs), as well as from an economic (cost) perspective.

[0013] As defined herein, a sheet has a shape that is longer than it is wide and wider than it is thick. The thickness of the sheet is not, in principle, critical, but may be, for example, > 5 µm and < 100 cm.

[0014] In the context of the invention, by 'with foam' or 'foam', Petition 870240080479, dated 09 / 20 / 2024, page 10 / 37 4 / 22 It is understood that the format has a lower density due to the presence of gas bubbles (such as air), compared to the density of the same material without gas bubbles. Polypropylene composition with high melt strength.

[0015] High melt-strength polypropylene having a melt strength > 0.45 N (> 45 cN) can, for example, be obtained by the process disclosed in document no. W02009 / 003930A1. Document no. 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 the mixture in a reduced oxygen environment. Furthermore, a high melt-strength polypropylene having a melt strength > 0.45 N (> 45 cN) has been available from SABIC as SABIC® PP UMS 561P since February 18, 2021.

[0016] Preferably, polypropylene with high melt strength is prepared by a) Irradiation of a polypropylene with at least one non-phenolic stabilizer, wherein, preferably, the non-phenolic stabilizer is chosen from the group of hindered amines, wherein the irradiation is carried out with an electron beam radiation of > 20000 J / kg and < 200000 J / kg (> 2.0 and < 20 Megarad) in a reduced oxygen environment, wherein the amount of active oxygen is < 15% by volume relative to the total volume of the reduced oxygen environment for a time sufficient to obtain a long-chain branched polypropylene and b) deactivation of free radicals in long-chain branched polypropylene to form polypropylene with high melt strength.

[0017] The way in which free radicals are deactivated is known in Petition 870240080479, dated 09 / 20 / 2024, page 11 / 37 5 / 22 technique, for example, by means of heating, as described in document no. W02009003930A1.

[0018] Examples of non-phenolic stabilizers are known in the art and are, for example, disclosed on pages 37-60 of document no. W02009 / 003930A1, incorporated herein by reference. Preferably, the non-phenolic stabilizer is chosen from the group of hindered amines.

[0019] 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, separately or in combination with at least one hydroxylamine, nitrone, amine oxide or benzofuranone selected from N,N-di(hydrogenated 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-α-heptadecylnitrone, Genox™ EP, a di(C16-C18)alkylmethylamine oxide, 3-(3,4-dimethylphenyl)-5,7-di-tert-butyl-benzofuran-2-one, Irganox® HP-136 (BFI) and mixtures thereof, separately or in combination with at least one organic phosphite or phosphonite selected from tris(2,4-di-tert-butylphenyl)phosphite (Irgafos® 168).More preferably, the non-phenolic stabilizers of the present matter may 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.

[0020] Preferably, the melt strength of high-melt-strength polypropylene is > 0.5 N (> 50 cN); more preferably, > 0.55 N (> 55 cN); even more preferably, > 0.6 N (> 60 cN); most preferably, > 0.65 N (> 65 cN) and / or, preferably, the melt strength of high-melt-strength polypropylene is < 0.95 N (< 95 cN); for example, < 0.9 N (< 90 cN); for example, < 0.87 N Petition 870240080479, dated 09 / 20 / 2024, p. 12 / 37 6 / 22 (< 87 cN).

[0021] The melt strength of high melt strength polypropylene is determined in accordance with ISO 16790:2005 at a temperature of 200°C, using a cylindrical capillary part that has a length of 20 mm and a width of 2 mm, a starting velocity vo of 0.0098 m / s (9.8 mm / s) and an acceleration of 0.006 m / s2 (6 mm / s2).

[0022] As used in this document, "polypropylene" means a propylene homopolymer, a propylene copolymer with an α-olefin, or a heterophasic propylene copolymer.

[0023] Preferably, the high-melt-strength polypropylene is a polypropylene chosen from the group of propylene homopolymers and propylene copolymers comprising propylene-derived chemical moieties and one or more co-monomers chosen from the group of ethylene and alpha-olefins with > 4 and < 12 carbon atoms.

[0024] Preferably, the propylene copolymer comprises chemical moieties derived from one or more co-monomers chosen from the group of ethylene and alpha-olefins with > 4 and < 12 carbon atoms in an amount of < 10 % by weight, for example, in an amount of > 1.0 and < 7.0 % by weight, based on the propylene copolymer, wherein the % by weight is determined using 13C NMR.For example, the propylene copolymer comprises chemical moieties derived from one or more co-monomers selected 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 chemical moieties derived from ethylene.

[0025] Polypropylenes and 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 co-monomers, for example, ethylene, under Petition 870240080479, dated 09 / 20 / 2024, page 13 / 37 7 / 22 suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is, for example, described in Moore, EP (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.

[0026] Propylene homopolymers, propylene copolymers and heterophasic propylene copolymers can be made from any known polymerization technique, as well as with any known polymerization catalyst system. With reference to techniques, reference can be made to flow paste, solution or gas phase polymerizations; with reference to the catalyst system, reference can be made to Ziegler-Natta, metallocene or single-site catalyst systems. All are, in themselves, known in the art.

[0027] Preferably, the polypropylene with high melt strength has a VOC value as determined and in accordance with VDA278 (2011-10) < 250 pg / g; preferably, a VOC value < 50 pg / g, and / or a FOG value as determined and in accordance with VDA278 (2011-10) < 500 pg / g; preferably, a FOG value < 100 pg / g.

[0028] Preferably, the polypropylene with high melt strength has a melt flow index > 0.50 and < 8.0 g / 10 min; more preferably, > 0.70 and < 5.0 g / 10 min; most preferably, > 1.0 and < 4.0 g / 10 min; with the highest preference, > 1.5 and < 4.0, as determined in accordance with ASTM D1238 (2013) at a temperature of 230°C under a load of 2.16 kg.

[0029] Preferably, high-melt-strength polypropylene is present in an amount > 10% by weight based on the polymer composition, wherein, preferably, high-melt-strength polypropylene is present in an amount > 10% by weight based on the polymer composition; more preferably, in an amount < 99.5% by weight based on the composition of Petition 870240080479, dated 09 / 20 / 2024, page 14 / 37 8 / 22 polymer. For example, the amount of high-melt-strength polypropylene based on the polymer composition is > 15% by weight, > 20% by weight, > 25% by weight; preferably, > 30% by weight; preferably, > 40% by weight; preferably, > 50% by weight; preferably, > 60% by weight; preferably, > 70% by weight; preferably, > 80% by weight; preferably, > 90% by weight, and / or < 99.5% by weight, < 99% by weight, < 98.5% by weight, < 98.0% by weight, < 97.0% by weight, < 96.0% by weight, < 95.0% by weight.

[0030] The polymer composition may additionally comprise additives such as, for example, flame retardants, pigments, lubricants, slip agents, flow promoters, antistatic agents, processing stabilizers, durable stabilizers and / or UV stabilizers. The additives may be present in any desired amount to be determined by a person skilled in the art, but are preferably present > 0.001% by weight and < 5.0% by weight; more preferably, > 0.01% by weight and < 4.0% by weight; even more preferably, > 0.01% and < 3.0% by weight; even more preferably, > 0.01% and < 2.0% by weight, based on the polymer composition.

[0031] In one embodiment, the polymer composition further comprises additional polypropylene, preferably additional polypropylene in an amount > 10% by weight and < 40% by weight based on the foam sheet. The additional polypropylene may be a propylene homopolymer, a propylene copolymer, for example, a propylene copolymer with an α-olefin, as described in this document, or a heterophasic propylene copolymer, for example, a heterophasic propylene copolymer as described in this document.

[0032] The polymer composition may additionally comprise Petition 870240080479, dated 09 / 20 / 2024, page 15 / 37 9 / 22 a nucleating agent. A nucleating agent may be desired to increase 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 be, for example, > 0.010% by weight and < 5.0% by weight; for example, > 0.030% by weight and < 4.0% by weight; for example, > 0.050% by weight and < 3.0% by weight; preferably, > 0.10% by weight and < 2.5% by weight; more preferably, > 0.30% by weight and < 1.5% by weight, based on the polymer composition; most preferably, > 0.50% by weight and < 1.2% by weight, based on the polymer composition.

[0033] 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, azodicarbonamide, amines and / or esters of a saturated or unsaturated (C10-C34) aliphatic carboxylic acid. Examples of suitable amides include fatty acid (bis)amides, such as 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 ethylene bistearamide (EBS), butylene bistearamide, hexamethylene bistearamide, ethylene bisbehenamide and mixtures thereof. Suitable amines include, for example, (C2-C18)alkylene diamines, such as ethylene biscaproamine and hexamethylene biscaproamine.The preferred esters of a saturated or unsaturated (C10-C34) aliphatic carboxylic acid are the esters of a (C16-C24) aliphatic carboxylic acid. Preferably, the nucleating agent is chosen from the group of talc, sodium bicarbonate, citric acid, azodicarbonamide and mixtures thereof, most preferably, the nucleating agent is talc. Petition 870240080479, dated 09 / 20 / 2024, page 16 / 37 10 / 22

[0034] For the preparation of the foam sheet, it may be desirable to use a cell stabilizer. Cell stabilizers are permeability modifiers that retard the diffusion of, for example, hydrocarbons such as isobutane, to create dimensionally stable foams. (Gendron, Thermoplastic Foam Processing, 2005, pages 31 and 149), wherein 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, if a cell stabilizer is used, the cell stabilizer is glycerol monostearate or stearamide.

[0035] The amount of cell stabilizer to be added depends on the desired cell size and the polymer composition used for the preparation of the foam sheet. Generally, the cell stabilizer can be added in an amount > 0.10 and < 3.0% by weight relative to the polymer composition. Preferably, the polymer composition is present in the foam sheet in an amount > 95% by weight based on the foam sheet. For example, the polymer composition is present in the foam sheet in an amount > 96% by weight, > 97% by weight, > 98% by weight, > 99% by weight, > 99.5% by weight based on the foam sheet. The foam sheet may also consist of the polymer composition.

[0036] Preferably, the density of the foam sheet is < 650 kg / m3 and > 20 kg / m3; preferably, < 500 kg / m3 and > 30 kg / m3, wherein the density is determined in accordance with ISO 845 (2006).

[0037] Preferably, the foam sheet has a content of Petition 870240080479, dated 09 / 20 / 2024, page 17 / 37 11 / 22 open cells < 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 in accordance with ASTM D6226-10.

[0038] The processes for preparing polypropylene foams and foam sheets are part of the knowledge of a person skilled in the art. In such a process, a melt of a polypropylene composition with high melt strength mixed with a gaseous or liquid blowing agent is suddenly expanded through a pressure drop. Continuous foaming processes, as well as discontinuous processes, can be applied. In a continuous foaming process, the polymer composition is melted and gas-charged in an extruder 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 polypropylene foam formation in such a foam extrusion process is explained, for example, in H. E. Naguib, C.B. Park, No.Reichelt, Fundamental foaming mechanisms governing the volume expansion of extruded polypropylene foams, Journal of Applied Polymer Science, 91, 2661-2668 (2004). The processes for foam formation are described in ST Lee, Foam Extrusion, Technomic Publishing (2000). In a batch foaming process, the (micro)pellets of polypropylene composition are loaded with the foaming agent under pressure and heated below the melting temperature before the pressure in the autoclave is suddenly reduced. The dissolved foaming agent forms bubbles and creates a foam structure.

[0039] Preferably, the foam sheet of the invention is Petition 870240080479, dated 09 / 20 / 2024, page 18 / 37 12 / 22 prepared by a foam extrusion process.

[0040] In another aspect, the invention relates to a process for preparing the foam sheet of the invention. In particular, the invention also relates to a process for preparing the foam sheet of the invention comprising the sequential steps of: a) provide the polymer composition of any one of claims 1 to 9, and b) adding a blowing agent to the polymer composition, wherein, for example, the blowing agent is added in an amount >0.10% by weight and <20% by weight based on the polymer composition, and c) subjecting the mixture of polymer composition and blowing agent to a foaming process, preferably a foam extrusion process, to form the foam sheet.

[0041] The amount of blowing agent depends, for example, on the desired density and the polymer composition used. For example, the blowing agent can be used in an amount >0.10% by weight and <20% by weight based on the polymer composition.

[0042] 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, with isobutane being the most preferred option.

[0043] 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 azodicarbonamide. Such chemical blowing agents are, for example, commercially available from Clariant Corporation under, for example, the name Hydrocerol™ CF-40E™ or Hydrocerol™ CF-40E™. (Reference 870240080479, dated 20 / 09 / 2024, page 19 / 37) 13 / 22 05E™.

[0044] Foam sheets prepared in this way can be stretched monoaxially or biaxially using a method known to oneself.

[0045] Therefore, the invention also relates to a process for preparing the foam sheet of the invention comprising the sequential steps of: a) provide the polymer composition of the invention, and b) adding a blowing agent to the polymer composition, wherein, for example, the blowing agent is added in an amount >0.10% by weight and <20% by weight based on the polymer composition, and c) subjecting the mixture of polymer composition and blowing agent to a foaming process, preferably a foam extrusion process to form the foam sheet, and d) stretching the foam sheet in at least one direction.

[0046] The invention also relates to the foam sheet of the invention in which the foam sheet is stretched in at least one direction, for example, the invention relates to the foam sheet of the invention in which the foam sheet is monoaxially stretched (e.g., in the machine direction) or, for example, the invention relates to the foam sheet of the invention in which the foam sheet is biaxially stretched, for example, in both the machine direction (MD) and the transverse direction (TD). As is known to one skilled in the art, stretching in MD and TD can be performed simultaneously or in consecutive steps.

[0047] The stretch ratio in MD can be, for example, >1.1 and < 7.0; for example, > 1.1 and < 3.0. The stretch ratio in the transverse direction can be, for example, >1.1 and < 7.0; for example, >1.1 and < Petition 870240080479, dated 09 / 20 / 2024, p. 20 / 37 14 / 22 3.0.

[0048] The blades of the invention can be suitably used in applications such as building and construction, automotive applications, residential applications such as food packaging and protective packaging; and consumer applications. For example, the blades can be used for the preparation of cups, trays, containers, bottles, seals, returnable boxes. Other applications of the blades of the invention are, for example: sandwich panels, pipe insulation, concrete joint fillers, insulation materials for residences, water tanks or floors (subfloors).

[0049] The very good cushioning properties of the foam of the invention offer safety and comfort to the user. The foam is applicable in multiple applications that require non-slip performance, such as footwear, protective gear, sports floor mats and foam rollers.

[0050] Therefore, in another aspect, the invention relates to an article comprising the foam sheet of the invention. In yet another aspect, the invention relates to the use of the foam sheet of the invention in applications such as building and construction, automotive applications, residential applications, such as food packaging and protective packaging; and consumer applications.

[0051] The invention also relates to the use of the foam sheet of the invention for the preparation of an article, for example, wherein the article is a cup, a tray, a container, a bottle, a seal, reusable boxes, a sandwich panel, pipe insulation, a concrete joint filler, insulation material for residences, water tanks or floors (subfloors), footwear, a protection, a floor mat (for sports) or a foam roll.

[0052] The sheets can be used as a replacement for applications where polystyrene foam is typically used, Petition 870240080479, dated 09 / 20 / 2024, p. 21 / 37 15 / 22 like disposable food containers.

[0053] 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 in this document, in particular, those combinations of features that are present in the claims are preferred. Therefore, it will be recognized that all combinations of features relating to compositions according to the invention; all combinations of features relating to processes according to the invention and all combinations of features relating to compositions according to the invention and features relating to processes according to the invention are described in this document.

[0054] Furthermore, it should be noted that the term “comprising” does not exclude the presence of other elements. However, it should also be understood that a description of a product / composition comprising certain components also reveals a product / composition consisting of those components. The product / composition consisting of those components may be advantageous because it offers a simpler and more economical process for preparing the product / composition. Similarly, it should also be understood that a description of a process comprising certain steps also reveals a process consisting of those steps. The process consisting of those steps may be advantageous because it offers a simpler and more economical process.

[0055] The invention is now elucidated by way of the following examples, without, however, being limited to them. Examples Methods used: melt flow index Petition 870240080479, dated 09 / 20 / 2024, page 22 / 37 16 / 22

[0056] The melt flow index of the polymers was determined according to ASTM D1238 (2013) at a temperature of 230°C (MFR230) under a load of 2.16 kg. Resistance to fusion

[0057] Fusion resistance was measured according to ISO standard 16790:2005. Fusion resistance is defined as the maximum force (downward stretch) (in N (cN)) by which a cast thread can be stretched before breaking, for example, during a Rheotens measurement. Measurements were made on a Göttfert 6000 rheograph at a temperature of 200°C with a configuration similar to that shown in Figure 1 of ISO standard 16790:2005. The rheometer has a furnace with a diameter of 12 mm. A capillary part 20 mm long and 2 mm wide was used. The entry angle of the capillary part was 180° (plane). The piston in the rheometer was moved at a speed of 0.00272 m / s (0.272 mm / s) to obtain an exit velocity, vO, of 0.0098 m / s (9.8 mm / s). After filling the rheometer, the melt was held in the rheometer for 5 minutes to stabilize the temperature and complete melting of the polymer.The filament exiting the capillary section was stretched with a Goettfert Rheotens II at an acceleration of 0.006 m / s² (6 mm / s²) until breakage occurred. The distance between the exit of the capillary section and the Rheotens II absorption wheels (= stretching length) was 100 mm.

[0058] The pressure required to push molten polymer through the capillary portion, the maximum stretching force (= resistance to melting) and the maximum stretch-at-break ratio were recorded. Bending modulus

[0059] The flexural modulus of the foam sheet samples was determined using a three-point bending test in accordance with ISO1209-2, Rigid cellular plastics — Determination of flexural properties, using a testing speed of 0.00033 m / s (20 mm / min). Petition 870240080479, dated 09 / 20 / 2024, page 23 / 37 17 / 22 Samples with a spacing of 60 mm and a width of 20 mm were cut from foam sheets. The samples were cut in the machine direction (MD, extrusion direction) and in the transverse direction (TD, direction perpendicular to the extrusion direction and perpendicular to the thickness direction), so that the thickness of the foam sheet (as indicated in Table 2) was maintained. As used in this document, the thickness direction is the size of the foam sheet with the smallest dimension. The mean flexural modulus is the average of the MD flexural modulus and the TD flexural modulus. Foam density

[0060] The foam density (kg / m3) is the apparent overall density and was determined in accordance with ISO 845:2006. Thickness and width

[0061] The thickness and width of the foam sheets were determined without applying pressure to the sheets. Open cell content

[0062] The open cell content was determined using a Quantachrome Pentapyc 5200e gas pycnometer and using a method based on ASTM D6226-10. The volume of the sample's external dimensions was determined using Archimedes' principle by immersing the sample in water. It is assumed that water absorption by the sample can be neglected. After drying the sample of adhering water, the sample volume (Vespec.) was determined by the pycnometer according to ASTM D6226-10 at different pressures.

[0063] All pressures applied were below 0.1 bar to minimize foam compression. Δ_ Vespec. — VCAMARA— VEXP / \— 1] '2 where: Vespec. = volume sample V-chamber - volume sample chamber Petition 870240080479, dated 09 / 20 / 2024, page 24 / 37 18 / 22 VEXP = expansion volume

[0064] The sample volume of the foam was plotted against the applied pressures (0.090 bar; 0.075 bar, 0.060 bar, 0.045 bar, 0.035 bar, 0.020 bar and 0.010 bar). A straight line was fitted through the measurement points using linear regression. The intercept of the linear regression line with the geometric Y-axis at p = 0 bar is the volume (Vespec_o) used in the equation below.

[0065] The Vaberto open cell content (%) was calculated using the following formula: Oy — [(^—^ESPEC_o) / ^l * 100 where: Ov = open cell content [%] V = geometric volume Vespec_o = sample volume measured at a pressure of 0 bar Materials used:

[0066] PP-UMS1 is a long-chain branched propylene homopolymer, commercially available from SABIC as SABIC® PPUMS 561P since February 18, 2021, without confidentiality restrictions, having an MFR230 melt flow index of 2.5 g / 10 min and a melt strength of 0.71 N (71 cN). SABIC® PPUMS 561P has a VOC value as measured according to VDA278 (2011-10) over 7 days of its production of 10.9 pg / g. SABIC® PPUMS 561P has a FOG value as measured according to VDA278 (2011-10) over 7 days of its production of 56.4 pg / g.

[0067] PP-HMS is a long-chain branched propylene homopolymer that is commercially available from Borealis as Daploy™ WB140HMS. It has a melt flow index of MFR230 of 2.2 g / 10 min and a melt strength of 0.42 N (42 cN).

[0068] PP-UMS2 is a branched propylene homopolymer of Petition 870240080479, dated 09 / 20 / 2024, p. 25 / 37 19 / 22 experimental long chain that has a melt flow index MFR230 of 0.23 g / 10 min and a melt strength of 0.62 N (62 cN). This PP-UMS2 is prepared as described in document no. W02009 / 003930A1, sample 11 (polymer B) with 0.05 PPH from Genox EP.

[0069] The talc is TALCOLIN PP70+ which is a masterbatch of propylene homopolymer with 70% by weight of talc (d50 of 9 pm), which is commercially available from JM Polymers.

[0070] The blowing agent is isobutane. Preparation of foam sheets

[0071] The preparation of the foam sheets was carried out in a 30 mm Theysohn twin-screw foam extruder that has a length-to-diameter (c / d) ratio of 40. This extruder consists of nine electric heating zones equipped with water cooling, followed by a cooling section, static mixer, and a die. For CE5, the temperature at the front of the cooling section is expected to increase by approximately 5 °C compared to experiments with PP-UMS1. Isobutane was added as a physical blowing agent in an amount of 2.5% by weight based on the composition in Table 1 and introduced into the polymer melt in zone 8 of the extruder. An adjustable thickness slit die was used for the production of the foam sheets. The die pressure was adapted by adjusting the thickness of the slit die so that the pressure in the die was 50 bar. A slit die with a width of 35 mm was used.

[0072] The foam sheets were then stretched in the machine direction at the stretch ratio indicated in Table 2 using a double belt stretching unit. The sheets thus obtained were then cooled in a water-cooled calibration unit to correct the dimensions of the prepared foam sheets. The stretch ratio was adjusted by adjusting the speed of the unit. Petition 870240080479, dated 09 / 20 / 2024, page 26 / 37 20 / 22 of double belt in relation to the foam output speed in free expansion. At a stretch ratio of 1, the foam output speed in free expansion (voutput) equals the speed of the double belt drive unit (Vline speed).

[0073] Table 1 reports the polymer compositions, conditions and foaming extrusion results. Conclusion

[0074] As can be seen from Table 1, when preparing the foam sheets according to the invention, a higher flexural modulus is obtained. The average flexural modulus is a measure of overall flexural hardness.

[0075] The foam sheets of the invention (containing a polymer composition based on a high-melt-strength polypropylene having a melt strength > 0.45 N (> 45 cN) (E1-E4)) exhibit superior overall flexural toughness compared to sheets containing a polymer composition based on a high-melt-strength polypropylene having a melt strength < 0.45 N (< 45 cN) (CE1-CE4).

[0076] Therefore, the foam sheets of the invention can be used for applications requiring superior overall bending toughness. For applications requiring the same overall bending toughness, it is possible to use thinner foam sheets of the invention and / or sheets with a lower foam density. The so-called “reduction in dimensions” is advantageous from an environmental point of view in terms of carbon footprint (less material and lower transport and energy costs), as well as from an economic (cost) perspective.

[0077] In addition, the foam sheets of the invention are prepared from a polypropylene with high melt strength having a melt flow index > 1.0 and < 4.0 g / 10 min; preferably, > 1.5 and < 4.0 Petition 870240080479, dated 09 / 20 / 2024, page 27 / 37 21 / 22 g / 10 min, as determined according to ASTM D1238 (2013) at a temperature of 230 °C under a load of 2.16 kg, will lead to a better surface appearance of the blades (see examples E1E4), compared with blades prepared from a high melt strength polypropylene that has a melt flow index of < 1.0 g / 10 min (see CE5 which has a melt flow index of 0.23 g / 10 min).

[0078] Another advantage of using a polypropylene composition with high melt strength having a melt flow index > 0.5 and < 8.0 g / 10 min; preferably, a melt flow index > 0.70 and < 5.0 g / 10 min; more preferably, a melt flow index > 1.0 and < 4.0 g / 10 min; most preferably, a melt flow index > 1.5 and < 4.0 g / 10 min, as determined according to ASTM D1238 (2013) at a temperature of 230 °C under a load of 2.16 kg, is that the extruder can be operated at a lower temperature, compared to CE5, when the temperature at the front of the cooling section is expected to increase by approximately 5 °C, compared to E1-E4 and CE1-CE4. In commercial foam extruders, this temperature increase is undesirable, as it limits maximum output. Table 1. Polymer compositions used, conditions and foam formation results. E1 E2 E3 E4 CE1 CE2 CE3 CE4 CE5 Composition PP-UMS1 % by weight 97.9 97.9 97.9 97.9 PP-HMS % by weight 97.9 97.9 97.9 97.9 PP-UMS2 % by weight 97.9 Talc % by weight 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Conditions Die pressure bar 50 50 50 50 50 50 50 50 50 Ratio of 1 1.31 1.63 1.95 1 1.34 1.66 1.95 1 Petition 870240080479, dated 09 / 20 / 2024, pp. 28 / 37 22 / 22 Stretching Speed ​​of the line m / min 7.5 9.9 12.3 14.7 7.3 9.8 12.2 14.3 5 Results Density kg / m3 100 100 100 100 100 100 100 100 100 Thickness mm 2.3 2.0 1.9 1.6 2.5 2.2 1.9 1.8 2.5 Width mm 112 91 79 74 95 83 77 71 95 Flexural modulus MD MPa 88 106 142 159 90 120 135 163 Flexural modulus TD MPa 54 50 36 45 42 30 27 21 Average flexural modulus MPa 71 78 92 104 66 75 82 93 Superficial appearance + + + + + + + + - +: the surface of the blades was smooth - : the surface of the blades was expected to be irregular.

Claims

1. Foam sheet characterized in that it comprises a polymer composition comprising a polypropylene with high melt strength, wherein the polypropylene with high melt strength has a melt strength > 0.45 N (> 45 cN); preferably, > 0.5 N (> 50 cN); more preferably, > 0.55 N (> 55 cN); even more preferably, > 0.6 N (> 60 cN); with the highest preference, > 0.65 N (> 65 cN), wherein the melt strength is determined in accordance with ISO 16790:2005 at a temperature of 200°C, using a cylindrical capillary part that has a length of 20 mm and a width of 2 mm, a starting velocity vo of 0.0098 m / s (9.8 mm / s) and an acceleration of 0.006 m / s2 (6 mm / s2), wherein the amount of high melt strength polypropylene based on the polymer composition is > 70% by weight.

2. Foam sheet, according to claim 1, characterized in that the melt strength of the high melt strength polypropylene is < 0.95 N (< 95 cN); for example, < 0.9 N (< 90 cN); for example, < 0.87 N (< 87 cN).

3. Foam sheet, according to claim 1 or 2, characterized in that the polypropylene with high melt strength is chosen from the group of propylene homopolymers and propylene copolymers comprising chemical moieties derived from propylene and one or more co-monomers chosen from the group of ethylene and alpha-olefins with > 4 and < 12 carbon atoms.

4. Foam sheet, according to any one of claims 1 to 3, characterized in that the polypropylene with high melt strength has a melt flow index > 0.5 and < 8.0 g / 10 min; preferably, a melt flow index > 0.70 and < 5.0 g / 10 min; most preferably, a melt flow index > 1.0 and < 4.0 g / 10 min, as determined in accordance with ASTM D1238 (2013) to Petition 870240080479, dated 20 / 09 / 2024, page 30 / 37 2 / 4 at a temperature of 230 °C under a load of 2.16 kg.

5. Foam sheet, according to any one of claims 1 to 4, characterized in that the polypropylene with high melt strength is prepared by a) irradiating a polypropylene with at least one non-phenolic stabilizer, wherein, preferably, the non-phenolic stabilizer is chosen from the group of hindered amines, wherein the irradiation is carried out with an electron beam radiation of > 20000 J / kg and < 200000 J / kg (> 2.0 and < 20 Megarad) in a reduced oxygen environment, wherein the amount of active oxygen is < 15% by volume relative to the total volume of the reduced oxygen environment for a time sufficient to obtain a long-chain branched polypropylene and b) deactivation of free radicals in the long-chain branched polypropylene to form the polypropylene with high melt strength.

6. Foam sheet, according to any one of claims 1 to 5, characterized in that polypropylene with high melt strength is present in an amount > 10% by weight based on the polymer composition, wherein, preferably, the polypropylene with high melt strength is present in an amount > 10% by weight based on the polymer composition, for example, in an amount < 99.5% by weight based on the polymer composition.

7. Foam sheet, according to any one of claims 1 to 6, characterized in that the polymer composition additionally comprises an additional polypropylene.

8. Foam sheet, according to any one of claims 1 to 7, characterized in that the polymer composition further comprises a nucleating agent, wherein, preferably, the nucleating agent is present in an amount > 0.01% by weight and < 5.0% by weight based on the composition and / or wherein, preferably, the nucleating agent is the nucleating agent that is chosen from the group of talc, sodium bicarbonate, citric acid, azodicarbonamide and mixtures thereof.

9. Foam sheet, according to any one of claims 1 to 8, characterized in that the polymer composition additionally comprises > 0.001% by weight and < 5.0% by weight of additives based on the polymer composition.

10. Foam sheet, according to any one of claims 1 to 9, characterized in that the polymer composition is present in the foam sheet in an amount > 95% by weight based on the foam sheet.

11. Foam sheet, according to any one of claims 1 to 10, characterized in that the density of the foam sheet is < 650 kg / m3 and > 20 kg / m3, wherein the density is determined in accordance with ISO 845 (2006) and / or wherein the foam sheet has an open cell content of < 15.0 %, wherein the open cell content is determined in accordance with ASTM D6226-10.

12. Foam sheet, according to any one of claims 1 to 11, characterized in that it is prepared by a foam extrusion process.

13. Foam sheet, according to any one of claims 1 to 12, characterized in that the polymer composition is present in the foam sheet in an amount > 95% by weight based on the foam sheet and / or in that the amount of polypropylene with high melt strength based on the polymer composition is > 80% by weight; preferably, > 90% by weight.

14. Article characterized by the fact that it comprises the foam sheet, as defined in any of claims 1 to 13. Petition 870240080479, dated 09 / 20 / 2024, pp. 32 / 37 4 / 4 15. Process for preparing foam sheeting, as defined in any one of claims 1 to 13, characterized in that it comprises the sequential steps of: a) providing the polymer composition, as defined in any one of claims 1 to 9, and b) adding a blowing agent to the polymer composition, wherein, for example, the blowing agent is added in an amount > 0.10% by weight and < 20% by weight based on the polymer composition, and c) subjecting the mixture of the polymer composition and the blowing agent to a foaming process, preferably a foam extrusion process to form the foam sheet, and optionally, d) stretching the foam sheet in at least one direction.

16. Use of the foam sheet, as defined in any one of claims 1 to 13, characterized in that it is intended for the preparation of an article.