Foamed article

Abstract

The present invention relates to an article comprising a foamed sheet prepared from foam injection molding of a polymer composition comprising a high melt strength polypropylene wherein the high melt strength polypropylene has a melt strength at a temperature of 200 DEG C according to ISO 16790: 2005, and a melt strength at a temperature of 200 DEG C according to ISO 16790: 2005. A melt strength of > = 30 cN as determined using a cylindrical capillary tube of 20 mm in length and 2 mm in width, a start velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s2.

Description

[0001] The present invention relates to an article comprising a foamed sheet, in particular a panel for construction, transport or leisure vehicles or containers.

[0002] For many years, boards and panels of wood and its derivatives have been widely used as structural elements in construction and transport. However, wood is prone to mould and may require treatment to prevent bugs and pests. There is a need in the industry for structural panels that are recyclable and have good mould and pest resistance, flexural rigidity and compressive strength, which can be prepared in a simple and sustainable manner.

[0003] Structural foam sheets have been available on the market as an alternative to wood, medium density fibreboard (MDF, 600 - 800 kg / m3) and low density fibreboard (LDF, 300 - 500 kg / m3), offering better mould and pest resistance.

[0004] Examples of structural foam sheets are extruded foam sheets from PP, PET, PU and moulded expanded PP (EPP) sheets. The foam core can also be covered with a face sheet to become a multi - layer composite, providing improved aesthetics and other properties such as scratch and abrasion resistance. Examples of face sheets are wood, MDF, plastics, and glass fibre reinforced layers. Additional steps are required to bond the face sheet to the foam core; this can include using glue, adhesives and / or thermal lamination. Such steps incur additional costs, complexity, and reduce the recyclability of the composite (hybrid material).

[0005] WO2023118202A1 discloses a sheet having improved compressive yield stress in the thickness direction. The sheet is produced by orienting and assembling a plurality of elongated foam elements generated by foam extrusion. Due to the anisotropic elliptical holes, a composite material with improved compressive properties in the thickness direction is obtained. A multi - layer composite comprising such a sheet and a cover layer is also disclosed, which can be a panel for construction or transport or leisure vehicles.

[0006] EP4140723 discloses a multi - layer composite for containers comprising an assembly of elongated foam elements.

[0007] WO2023143926A1 discloses a moulded polymer article used as a cup or container for liquids and / or food. The article comprises a single - piece wall portion made of a polymer, the single - piece wall portion comprising a core layer of expanded porous foam made of a polymer. The core layer is multi - layer and comprises a first layer of expanded porous foam adjacent to a first solid skin, a second layer of expanded porous foam adjacent to a second solid skin, and an intermediate layer of expanded porous foam between and adjacent to the first and second layers. Expansion is carried out at an expansion coefficient of 2 to 4.

[0008] The object of the present invention is to provide articles, in particular panels for use in construction, transport or leisure vehicles or containers, which have a low density and good compression properties.

[0009] Accordingly, the present invention provides articles, in particular panels for use in construction, transport or leisure vehicles or containers, which comprise a foamed sheet prepared by foam injection molding of a polymer composition comprising a high melt strength polypropylene, wherein the high melt strength polypropylene has a melt strength of ≥ 30 cN determined according to ISO 16790:2005 at a temperature of 200 °C using a cylindrical capillary of 20 mm in length and 2 mm in width, an initial velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 .

[0010] Surprisingly, it has been found that the high melt strength polypropylene in the polymer composition for preparing the foamed sheet allows the foamed sheet according to the invention to have a low density and good compression properties. It has been found according to the invention that the high melt strength polypropylene allows foam injection molding at a relatively high expansion ratio to achieve a low density without pore rupture, which results in good compression properties.

[0011] The foamed sheet prepared by foam injection molding of a polymer composition comprising a high melt strength polypropylene has a non-porous skin layer on its surface and a porous structure having foam cells oriented perpendicular to the thickness direction of the sheet. The oriented cells provide the foam with improved compression strength in this critical load-bearing direction, making them a viable alternative to conventional structural panels, flat sheets or floors made of wood (logs), MDF, LDF and their composites. The non-porous skin layer provides flexural rigidity to the foamed sheet.

[0012] Foam injection molding

[0013] Generally, in order to prepare a foamed article such as a foamed sheet, a polymer composition is mixed with a blowing agent. The mixture is then heated to cause the polymer composition to melt and cause the blowing agent to generate gas. Instead of first providing a mixture of the blowing agent and the polymer composition and then melting the mixture to obtain a molten mixture, a melt of the polymer composition can also be provided and the blowing agent can be mixed into the melt of the polymer composition to obtain a molten mixture. Depending on the process, the resulting mixture is maintained as a gas-laden melt until it is dispensed through an orifice or into a molding cavity in a controlled manner. When foaming is complete, the foamed article is cured by cooling. Such processes are known in the art, for example from Thermoplastic Foams, by James L. Throne, Sherwood Publishers 1996, which is incorporated herein by reference.

[0014] Preferably, foam injection molding is carried out by expanding a molten mixture having a thickness of t0 into a foamed sheet having a thickness of t1 in a mold at an expansion ratio t1 / t0 greater than 4, preferably from 4.1 to 20, more preferably from 4.3 to 15, more preferably from 4.5 to 12, and even more preferably from 4.8 to 10.

[0015] Preferably, foam injection molding includes the following sequential steps:

[0016] - a) providing a mixture of a blowing agent and a polymer composition and melting the mixture to obtain a molten mixture or b) providing a melt of the polymer composition and mixing the blowing agent into the melt of the polymer composition to obtain a molten mixture;

[0017] - injecting the molten mixture into a mold;

[0018] - optionally applying pressure to the molten mixture in the mold;

[0019] - at least partially opening the mold to allow the molten mixture to form a soft foamed article; and

[0020] - curing the soft foamed article to form a foamed sheet and discharging the foamed sheet from the mold.

[0021] This process is sometimes referred to as the core-back injection molding process or the mold movement process. The achieved density reduction can be at least 75%, for example, the density of the foamed sheet can be at most 345 kg / m 3 .

[0022] Preferably, the foamed sheet has a density of at most 340 kg / m 3 , at most 320 kg / m 3 , at most 300 kg / m 3 , at most 280 kg / m 3 , at most 260 kg / m 3 , at most 240 kg / m 3 , at most 226 kg / m 3 , at most 220 kg / m 3 , at most 200 kg / m 3 , at most 180 kg / m 3 or at most 160 kg / m 3 , where the density is determined according to ISO 845 (2006). In some preferred embodiments, the foamed sheet has a density of 170 to 210 kg / m 3 , where the density is determined according to ISO 845 (2006).

[0023] The foamed sheet may have a thickness of 0.1 to 20 cm, 0.3 to 10 cm, or 0.5 to 5.0 cm. For example, the thickness may be 0.1 to 3.0 cm, 3.0 to 10 cm, or 10 to 20 cm.

[0024] In some embodiments, the article is an inner wall panel and the foamed sheet has a thickness of at least 0.3 cm, such as at least 0.6 cm.

[0025] In some embodiments, the article is a (trailer) floor and the foamed sheet has a thickness of 1.0 to 5.0 cm, such as 1.5 to 3.5 cm.

[0026] In some embodiments, the article is a panel that is an interlocking brick for a soft foam floor and the foamed sheet has a thickness of 0.5 to 1.5 cm, such as 0.8 to 1.2 cm, such as 3 / 8 inch (9.525 mm).

[0027] The blowing agent used according to the present invention can be either a physical blowing agent or a chemical blowing agent, where the chemical blowing agent is a chemical that decomposes at a specific temperature to release gas, and where the physical blowing agent is either a volatile liquid or a volatile gas. Typical chemical blowing agents include, but are not limited to, azodicarbonamide, sodium bicarbonate, 5-phenyltetrazole, and citrate / ester derivatives.

[0028] Typical physical blowing agents include, but are not limited to, fluids such as hydrocarbons (e.g., butane, pentane) in a gaseous or supercritical state, carbon dioxide, nitrogen, and mixtures thereof.

[0029] The amount of the blowing agent used in the present invention can be varied according to its properties and the foaming performance of the blowing agent. In some cases, the amount of the blowing agent varies within the range of 0.2 - 5.0 wt% based on the total weight of the polymer composition.

[0030] Preferably, the amount of the polymer composition is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, or 100 wt% based on the foamed sheet.

[0031] Preferably, the foamed sheet according to the present invention has a compressive stress of at least 0.8 MPa, more preferably at least 1.0 MPa, more preferably at least 1.2 MPa under 10% compression (σ10) in the thickness direction as measured by ISO 844 (2014).

[0032] Preferably, the foamed sheet according to the present invention has a compressive stress of at least 0.8 MPa, more preferably at least 1.0 MPa, more preferably at least 1.2 MPa, more preferably at least 1.6 MPa under 20% compression (σ20) in the thickness direction as measured by ISO 844 (2014).

[0033] Preferably, the foamed sheet according to the present invention has a compressive stress of at least 0.8 MPa, more preferably at least 1.0 MPa, more preferably at least 1.2 MPa, more preferably at least 1.7 MPa under 25% compression (σ25) in the thickness direction as measured by ISO 844 (2014).

[0034] Preferably, the foamed sheet according to the present invention has a compressive modulus of at least 10.0 MPa, more preferably at least 15.0 MPa as measured by ISO 844 (2014).

[0035] Preferably, the foamed sheet according to the present invention has a flexural modulus of at least 250 MPa, more preferably at least 350 MPa, more preferably at least 400 MPa as measured by ISO 844 (2014).

[0036] Polymer composition

[0037] The polymer composition comprises high melt strength polypropylene (HMS-PP). High melt strength polypropylene is branched and thus differs from linear polypropylene in that the polypropylene main chain covers the side chains, whereas non-branched polypropylene, i.e., linear polypropylene, does not cover the side chains. The side chains have a significant effect on the rheology of polypropylene. Thus, linear polypropylene and high melt strength polypropylene can be clearly distinguished by their flow behavior under stress.

[0038] Branching can generally be achieved by using a specific catalyst (i.e., a specific single-site catalyst) or by chemical modification. Regarding the preparation of branched polypropylene obtained by using a specific catalyst, reference is made to EP1892264. Regarding the branched polypropylene obtained by chemical modification, reference is made to EP0879830A1. In such cases, the branched polypropylene is also referred to as high melt strength polypropylene.

[0039] Suitable examples of commercially available products of high melt strength polypropylene are available from Borealis AG under the trade name Daploy TM (e.g., Daploy TM WB140HMS).

[0040] Another suitable example of a commercially available product of high melt strength polypropylene is Achieve TM Advanced PP6302E1 from Exxon Mobil.

[0041] The high melt strength polypropylene used according to the present invention has a melt strength of ≥30 cN. In this text, the melt strength of the high melt strength polypropylene is determined according to ISO 16790:2005 at a temperature of 200 °C, using a cylindrical capillary with a length of 20 mm and a width of 2 mm, an initial velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 for determination.

[0042] The high melt strength polypropylene with a melt strength of ≥30 cN can be obtained, for example, by the method disclosed in WO2009 / 003930A1. WO2009 / 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 method comprising mixing the polyolefin resin with the non-phenolic stabilizer and irradiating this polymer in a reduced oxygen environment. Additionally, the high melt strength polypropylene with a melt strength of ≥45 cN was available from SABIC as of February 18, 2021 in the form of PP UMS 561P.

[0043] Preferably, the high melt strength polypropylene is prepared by

[0044] a) irradiating polypropylene with at least one non-phenolic stabilizer, preferably wherein the non-phenolic stabilizer is selected from hindered amines, wherein irradiation is carried out with an electron beam radiation of ≥2.0 and ≤20 Mrad in a reduced oxygen environment for a time sufficient to obtain long-chain branched polypropylene, wherein the amount of active oxygen is ≤15 vol% relative to the total volume of the reduced oxygen environment, and

[0045] b) deactivating the free radicals in the long-chain branched polypropylene to form the high melt strength polypropylene.

[0046] How to deactivate free radicals is known in the art, for example, by heating as described in WO2009003930A1.

[0047] Examples of non-phenolic stabilizers are known in the art and are disclosed, for example, on pages 37 - 60 of WO2009 / 003930A1, which is incorporated herein by reference. Preferably, the non-phenolic stabilizer is selected from hindered amines. More preferably, the non-phenolic stabilizer comprises at least one hindered amine (selected from 944, 622, 2020, 119, 770, and mixtures thereof), alone or in combination with at least one hydroxylamine, nitrone, amine oxide or benzofuranone (selected from N,N-bis(hydrogenated tallow)amine( FS-042), consisting of N,N-bis(hydrogenated tallow)amine( FS-042) N,N-bis(alkyl)hydroxylamine produced by direct oxidation, N-octadecyl-α-heptadecyl nitrone, Genox TM EP, di(C16-C18)alkylmethylamine oxide, 3-(3,4-dimethylphenyl)-5,7-di-tert-butylbenzofuran-2-one, HP-136 (BFl), and mixtures thereof), in combination with, and either alone or in combination with at least one organic phosphite / ester or phosphonite (selected from tris(2,4-di-tert-butylphenyl) phosphite / ester( 168)). Even more preferably, the non-phenolic stabilizers of the present subject matter may include those described in U.S. Pat. Nos. 6,664,317 and 6,872,764, both of which are incorporated herein by reference in their entirety.

[0048] Preferably, the melt strength of the high melt strength polypropylene is ≥35 cN, preferably ≥37 cN, preferably ≥40 cN, preferably ≥45 cN, more preferably ≥50 cN, more preferably ≥55 cN, even more preferably ≥60 cN, most preferably ≥65 cN and / or preferably the melt strength of the high melt strength polypropylene is ≤100 cN, such as ≤95 cN, such as ≤90 cN, such as ≤87 cN.

[0049] As used herein, polypropylene means a propylene homopolymer, a copolymer of propylene and an α-olefin or a heterophasic propylene copolymer.

[0050] Preferably, the high melt strength polypropylene is a polypropylene selected from propylene homopolymers and propylene copolymers, the propylene copolymers comprising structural moieties derived from propylene and one or more comonomers selected from ethylene and α-olefins having ≥4 and ≤12 carbon atoms.

[0051] Preferably, the propylene copolymer comprises structural moieties derived from one or more comonomers selected from ethylene and α-olefins having ≥4 and ≤12 carbon atoms, in an amount ≤10% by weight based on the propylene copolymer, such as an amount ≥1.0 and ≤7.0% by weight, where the % by weight is determined using 13 13C NMR. For example, the propylene copolymer comprises structural moieties derived from one or more comonomers (preferably structural moieties derived from ethylene), the comonomers selected from ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-decene and 1-dodecene.

[0052] The synthesis methods of polypropylene and polypropylene are known. Propylene homopolymers are obtained by polymerizing propylene under suitable polymerization conditions. Propylene copolymers are obtained by copolymerizing propylene and one or more other comonomers (such as ethylene) under suitable polymerization conditions. The preparation of propylene homopolymers and copolymers is described, for example, in Moore, E.P. (1996) Polypropylene Handbook. Polymerization, Characterization, Properties, Processing, Applications, Hanser Publishers: New York.

[0053] Propylene homopolymers, propylene copolymers, and heterophasic propylene copolymers can be prepared by any known polymerization technique and using any known polymerization catalyst system. Regarding the technique, slurry, solution, or gas-phase polymerization can be referred to; regarding the catalyst system, Ziegler-Natta, metallocene, or single-site catalyst systems can be referred to. All of them are known in the art.

[0054] Preferably, the high melt strength polypropylene has a melt flow rate of ≥0.50 and ≤8.0 g / 10 min, more preferably ≥0.70 and ≤5.0 g / 10 min, and most preferably ≥1.0 and ≤4.0 g / 10 min, as measured according to ASTM D1238 (2013) at a temperature of 230 °C under a load of 2.16 kg.

[0055] Preferably, the high melt strength polypropylene has a VOC value of ≤250 μg / g (preferably a VOC value of ≤50 μg / g) as measured according to VDA278 (2011 - 10) and / or a FOG value of ≤500 μg / g (preferably a FOG value of ≤100 μg / g) as measured according to VDA278 (2011 - 10).

[0056] Preferably, the high melt strength polypropylene has a molecular weight distribution Mw / Mn of 5 to 20, preferably 7 to 17, and most preferably 10 to 15. Mw and Mn can be measured by universal size exclusion chromatography (SEC) as described in ASTM D6474 - 12 using the following:

[0057] · Chromatography: PolymerChar GPC-IR system operating at 160 °C

[0058] · Detection: Polymer Char IR5 infrared detector; PolymerChar viscometer

[0059] · IR5 is used as a concentration detector.

[0060] · Column set: Three Polymer Laboratories 13μm PLgel Olexis, 300×7.5mm

[0061] · PE molar mass calibration was carried out using linear PE standards (narrow and wide (Mw / Mn = 4 to 15)) in the range of 0.5–2800 kg / mol

[0062] · The concentration of the injected sample was 0.03% m / m, and Irgafos 168 and Topanol CA were used for stabilization (weight ratio, sample: Irgafos: Topanol = 1:1:1)

[0063] · The solvent and eluent were 1,2,4-trichlorobenzene, and 1 g / L BHT was used for stabilization

[0064] Preferably, the amount of the high melt strength polypropylene is at least 20 wt%, at least 30 wt%, at least 40 wt%, at least 50 wt% based on the total polymer composition.

[0065] In some preferred embodiments, most of the polymer composition is high melt strength polypropylene. For example, the amount of the high melt strength polypropylene is at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.5 wt%, at least 99.9 wt% or 100 wt% based on the total polymer composition. This results in particularly low density and particularly good compression properties.

[0066] The polymer composition may comprise additional polypropylene that is not high melt strength polypropylene. The additional polypropylene has a melt strength of <30 cN. The melt strength of the additional polypropylene may be <10 cN. The additional polypropylene may be a propylene homopolymer, a propylene copolymer (e.g., a copolymer of propylene and an α-olefin as described herein), or a heterophasic propylene copolymer. This allows obtaining a desired combination of mechanical properties of the articles according to the present invention.

[0067] For example, the amount of the additional polypropylene is 5.0 to 80 wt%, such as 5.0 to 40 wt% or 40 to 80 wt% based on the total polymer composition.

[0068] In some preferred embodiments, most of the polymer composition is high melt strength polypropylene and additional polypropylene. For example, the total amount of high melt strength polypropylene and additional polypropylene is at least 60 wt%, or at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.5 wt% or at least 99.9 wt% or 100 wt% based on the total polymer composition. The polymer composition may be free or substantially free of reinforcing inorganic fibers such as glass fibers, meaning that the amount of reinforcing inorganic fibers is less than 0.1 wt% based on the polymer composition. This allows for obtaining a desired combination of mechanical properties without using reinforcing inorganic fibers such as glass fibers.

[0069] In some preferred embodiments, the polymer composition comprises glass fibers. Preferably, the amount of glass fibers is 0.1 to 40 wt%, 0.5 to 30 wt%, 1.0 to 25 wt%, 2.0 to 20 wt% or 5.0 to 15 wt% based on the total polymer composition. This results in good flexural properties of the foamed sheet.

[0070] Prior to compounding, the glass fibers may have an average fiber length of 1 - 10 mm, preferably 2 - 8 mm, more preferably 3 - 7 mm. Prior to compounding, the diameter of the glass fibers may be 5 - 50 μm, preferably 8 - 30 μm, more preferably 10 - 20 μm.

[0071] In some preferred embodiments, most of the polymer composition is high melt strength polypropylene and glass fibers. For example, the total amount of high melt strength polypropylene and glass fibers is at least 60 wt%, or at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.5 wt% or at least 99.9 wt% or 100 wt% based on the total polymer composition. This results in good flexural properties of the foamed sheet.

[0072] In some preferred embodiments, the polymer composition comprises additional polypropylene that is not high melt strength polypropylene and glass fibers. Preferably, the amount of high melt strength polypropylene is 20 to 90 wt%, the amount of additional polypropylene is 5.0 to 40 wt%, and the amount of glass fibers is 0.1 to 40 wt%. This allows for obtaining a desired combination of mechanical properties.

[0073] Preferably, the total amount of high melt strength polypropylene, additional polypropylene and glass fibers is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt%, at least 99.5 wt% or at least 99.9 wt% or 100 wt% based on the total polymer composition.

[0074] The polymer composition may further comprise additives such as flame retardants, pigments, lubricants, slip agents, flow promoters, antistatic agents, processing stabilizers, long-term stabilizers and / or UV stabilizers. The additives may be present in any desired amount to be determined by those skilled in the art, but are preferably present in an amount of ≥0.001 wt% and ≤5.0 wt%, more preferably ≥0.01 wt% and ≤4.0 wt%, even more preferably ≥0.01 wt% and ≤3.0 wt%, even more preferably ≥0.01 wt% and ≤2.0 wt% based on the polymer composition.

[0075] The polymer composition may further comprise a nucleating agent. The nucleating agent may be desirable to increase the pore density and to alter the kinetics of bubble formation and growth. (Gendron, Thermoplastic foam Processing, 2005, page 209).

[0076] The amount of the nucleating agent may be, for example, ≥0.010 wt% and ≤5.0 wt%, such as ≥0.030 wt% and ≤4.0 wt%, such as ≥0.050 wt% and ≤3.0 wt%, preferably ≥0.10 wt% and ≤2.5 wt%, more preferably ≥0.30 wt% and ≤1.5 wt%, and most preferably ≥0.50 wt% and ≤1.2 wt% based on the polymer composition.

[0077] 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 (such as azodicarbonamide), amines and / or esters of saturated or unsaturated aliphatic (C 10 -C 34 ) carboxylic acids. Examples of suitable amides include fatty acid (bis)amides such as stearamide, hexamide, octamide, undecanamide, lauramide, myristamide, palmitamide, behenamide and eicosanamide, hydroxystearamide and alkylenediyl-bis-alkanamides, preferably (C 2 -C 32 ) alkylenediyl-bis-(C 2 -C 32 ) alkanamides such as ethylene bisstearamide (EBS), butylene bisstearamide, hexamethylene bisstearamide, ethylene bisbehenamide and mixtures thereof. Suitable amines include or are exemplified by (C 2 -C 18 ) alkylenediamines such as ethylene bishexylamine and hexamethylene bishexylamine. Preferred saturated or unsaturated aliphatic (C 10 -C 34 ) carboxylic acid esters are aliphatic (C 16 -C 24) Esters of carboxylic acids. Preferably, the nucleating agent is selected from the following: talc, sodium bicarbonate, citric acid, azodicarbonamide, and mixtures thereof, and more preferably the nucleating agent is talc.

[0078] To prepare the foamed sheet, it is desirable to use a cell stabilizer. A cell stabilizer is a permeability modifier that slows down the diffusion of, for example, hydrocarbons (such as isobutane) to produce dimensionally stable foams. (Gendron, Thermoplastic foam Processing, 2005, pages 31 and 149) Preferred cell stabilizers include, but are not limited to, glycerol monostearate (GMS), glycerol monopalmitate (GMP), palmitide, and / or amides. Suitable amides are, for example, stearyl stearamide, palmitamide, and / or stearamide. Suitable mixtures include, for example, a mixture containing GMS and GMP or a mixture containing stearamide and palmitamide. Preferably, if a cell stabilizer is used, the cell stabilizer is glycerol monostearate or stearamide.

[0079] The amount of cell stabilizer to be added depends on the desired cell size and the polymer composition used to prepare the foamed sheet. Generally, the cell stabilizer can be added in an amount of ≥0.10 and ≤3.0% by weight based on the polymer composition.

[0080] Preferably, the foamed sheet has an open cell content of ≤15.0%, preferably ≤12.0%, more preferably ≤10.0%, even more preferably ≤7.0%, even more preferably ≤5.0%, even more preferably ≤4.0%, even more preferably ≤3.0%, even more preferably ≤2.0%, where the open cell content is determined according to ASTM D6226-10. Such foamed sheets have a good combination of thermal insulation properties and mechanical properties.

[0081] Preferably, the polymer composition has a density of 0.885 to 1.365 g / cm 3 、for example, 0.890 to 1.300 g / cm 3 、0.900 to 1.200 g / cm 3 、0.903 to 1.100 g / cm 3 、0.904 to 1.000 g / cm 3 、0.905 to 0.950 g / cm 3 .

[0082] Multi-layer composite material

[0083] An article according to the present invention may be a multi-layer composite material comprising a core layer that includes a foamed sheet. The multi-layer composite material further includes a first cover layer provided on the core layer. Preferably, the multi-layer composite material further includes a second cover layer on the side of the core layer opposite the first cover layer. Thus, the core layer is provided between the first cover layer and the second cover layer. Preferred embodiments relate to a multi-layer composite material comprising a first cover layer, a second cover layer, and a core layer provided between the first cover layer and the second cover layer, wherein the core layer includes a sheet according to the present invention. In some embodiments, the article according to the present invention does not include such a first cover layer and such a second cover layer.

[0084] Preferably, the core layer is directly adhered to the first cover layer and optionally the second cover layer without an adhesive layer. The direct adhesion can be achieved by thermal bonding.

[0085] First covering layer and second covering layer

[0086] The first cover layer and / or the second cover layer may have a thickness of, for example, from 0.1 to 4.0 mm, such as from 0.3 to 2.0 mm.

[0087] The first cover layer includes a first composition and the second cover layer includes a second composition. The first composition and the second composition may be the same or different from each other.

[0088] Preferably, the first composition and / or the second composition is an unfoamed composition, and more preferably the first composition is an unfoamed composition and the second composition is an unfoamed composition.

[0089] Preferably, the first composition and / or the second composition has a density of at least 0.903 g / cm 3 、more preferably at least 0.904 g / cm 3 、more preferably at least 0.905 g / cm 3 。

[0090] Preferably, the first composition and / or the second composition includes polypropylene and optionally reinforcing fibers.

[0091] Preferably, the amount of polypropylene is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% based on the total amount of polymers in the first composition. Preferably, the amount of polypropylene is at least 90 wt%, at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% based on the total amount of polymers in the second composition.

[0092] In some embodiments, the reinforcing fibers may be glass fibers. In other embodiments, the reinforcing fibers may be selected from basalt fibers, carbon fibers, aramid fibers, and natural fibers such as hemp, linen, and bamboo fibers.

[0093] In some cases, the first composition and the second composition do not contain reinforcing fibers. This is advantageous in view of recyclability.

[0094] Glass fiber

[0095] The glass fibers added to the first and / or second composition may comprise long and / or short glass fibers.

[0096] A composition filled with short glass fibers can be prepared by mixing chopped strands of a predetermined length with a thermoplastic polymer in an extruder, during which the glass fibers are dispersed in the molten thermoplastic. A composition filled with long glass fibers can be prepared by a cable-wiring process, a blending process, or by a pultrusion process. The length of the added glass fibers can be reduced during processing, and thus the final length of the glass fibers in the composition (and specifically after compounding) can be less than the length of the added glass fibers. Before compounding, the long glass fibers can have an average fiber length of 1 mm or greater. Preferably, before compounding, the long glass fibers can have an average fiber length of 1-50 mm, more preferably 1-20 mm, and even more preferably 5-15 mm. Before compounding, the short glass fibers can have an average fiber length of 1-10 mm, preferably 2-8 mm, more preferably 3-7 mm. Before compounding, the diameter of the glass fibers can be 5-50 μm, preferably 8-30 μm, more preferably 10-20 μm.

[0097] The aspect ratio of the fibers can be in the range of, for example, 200-2000, preferably in the range of 200-1000, for example in the range of 250-750. The aspect ratio refers to the ratio between the average fiber length and the average fiber diameter. Generally, the length of the glass fibers in the polymer composition decreases during a melt processing step such as injection molding. The average length of the glass fibers in a molded article made from the composition according to the invention (i.e., after compounding) is thus typically significantly shorter. Typically, after compounding, the glass fibers have an average fiber length of 1 mm or less. Preferably, the average fiber length in the molded article (after compounding) can be 0.05-0.9 mm, more preferably 0.1-0.6 mm, even more preferably 0.1-0.4 mm. Since the average glass fiber diameter does not change significantly during compounding, the average glass fiber diameter in a molded article made from the composition according to the invention (i.e., after compounding) can be in the range of 5-50 μm, preferably 8-30 μm, for example 10-20 μm.

[0098] Suitably, the glass fibers can be coated to improve the interaction with polypropylene. Such coated glass fibers are also known in the art as sized glass fibers. Such coatings typically include amino-silanes or silane coatings. Amino-silane and silane-coated glass fibers are commercially available. Some examples include ECS03-480H (from NEG), 03T480 (from NEG), HP3270 (from PPG Industries), HP3299 (from PPG Industries), ECS 305H (from CPIC), ECS 305K (from CPIC), DS2100-13P (from Binani 3Bfiberglass), DS2200-10P (from Binani 3B fiberglass), DS2200-13P (from Binani 3B fiberglass), OwensCorningSE4805SE4850, SE4849 Type 30.

[0099] The glass fibers can be treated with a coupling agent to improve the interaction between the glass fibers and polypropylene. Such coupling agents promote the adhesion of polypropylene to the polar glass fiber surface. Suitable coupling agents include functional organosilanes, transition metal coupling agents, Werner coupling agents containing amino groups, and mixtures thereof. Examples of functional organosilane coupling agents include 3-aminopropyldimethylethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, β-aminoethyltriethoxysilane, Ν-β-aminoethylamino-propyltrimethoxysilane, γ-isocyanatopropyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, mercaptopropyltrimethoxysilane, mercaptopropyltriethoxysilane, glycidoxypropyltriethoxysilane, glycidoxypropyltrimethoxysilane, 4,5-epoxycyclohexyl-ethyltrimethoxysilane, ureidopropyltrimethoxysilane, ureidopropyltriethoxysilane, chloropropyltrimethoxysilane, and chloropropyltriethoxysilane. Examples of transition metal coupling agents include chromium, titanium, and zirconium coupling agents.

[0100] Examples of Werner-type coupling agents containing amino groups include complex compounds in which a trivalent nuclear atom (such as chromium) is coordinated with an organic acid having an amino functional group. Such treated glass fibers are known in the art. The amount of glass fibers in the thermoplastic composition can vary depending on the specific application and requirements. For example, the amount of glass fibers in the thermoplastic composition can be 10-40 wt%, such as 20-30 wt% or 20-25%, based on the total composition.

[0101] Glass fibers can be prepared from continuous lengths of fiber by, for example, a sheath or wire coating process, by crosshead extrusion, or by pultrusion techniques. Using these techniques, fiber strands impregnated or coated with a polymer are formed. The fibers can then be cut into a desired length and optionally formed into pellets or granules. The fibers can be further processed into a composition, for example, by an injection molding or extrusion process.

[0102] In some preferred embodiments, the first cover layer and / or the second cover layer can be or can comprise a continuous glass fiber reinforced tape, as described, for example, in WO2021053180A1, which is incorporated herein by reference.

[0103] Preferably, if a continuous glass fiber reinforced tape is used, at least two (e.g., 2, 3, 4, 5, 6, 7, 8, 9, or 10) tape layers are applied in the first cover layer and / or the second cover layer. The stacking of the tape layers is preferably carried out such that the tapes are in a quasi-isotropic layup (e.g., a +0 90° layup).

[0104] Examples of glass fiber reinforced tapes include, but are not limited to, commercially available UDMAX TM tape and Polystrand TM tape. In addition, such tapes are also disclosed in WO2016 / 142786A1 (incorporated herein by reference), WO2016 / 142781A1 (incorporated herein by reference), and WO2016 / 142784A1 (incorporated herein by reference).

[0105] Thus, a continuous glass fiber reinforced tape can be a fiber reinforced composite material comprising:

[0106] a matrix material including polypropylene; and

[0107] a nonwoven fiber region comprising a plurality of continuous glass fibers dispersed in the matrix material;

[0108] wherein the width and length of the nonwoven fiber region are substantially equal to the width and length of the fiber reinforced composite material, respectively;

[0109] wherein the nonwoven fiber region has an average relative fiber area coverage (RFAC) (%) of 65 - 90 and a coefficient of variation (COV) (%) of 3 - 20; and

[0110] wherein each of the plurality of continuous fibers is substantially aligned with the length of the fiber reinforced composite material.

[0111] Another example of a continuous glass fiber reinforced tape is described, for example, in WO2019122317A1 (incorporated herein by reference) and in WO2019122318A1 (incorporated herein by reference).

[0112] In some preferred embodiments, the first cover layer and / or the second cover layer may be or may comprise a uniaxially drawn polypropylene multi-layer film or tape, such as described in WO0308190. The film or tape may have an AB or ABA type, have a draw ratio greater than 12, have an E-modulus of at least 10 GPa, and consist essentially of a central layer (B) of polypropylene and one or two other layers (A) of polypropylene, wherein the DSC melting point of the material of the other layer (A) is lower than the DSC melting point of the material of the central layer (B), where the central layer (B) is between 50 and 99 wt% of the material and the other layer (A) is between 1 and 50 wt%. The use of a uniaxially drawn polypropylene multi-layer film or tape is advantageous because it renders the use of fibers redundant, thereby improving the recyclability.

[0113] Typically, the thickness of the first cover layer and / or the second cover layer is less than the thickness of the foamed sheet according to the invention, for example the thickness of the first cover layer and / or the second cover layer is at most 90%, at most 70%, at most 50%, at most 30%, at most 10% or at most 5% of the thickness of the foamed sheet according to the invention.

[0114] Core layer

[0115] The core layer comprises the foamed sheet according to the invention. The foamed sheet according to the invention may be present in the core layer in an amount of 50 to 100 wt% of the core layer.

[0116] In some embodiments, the core layer consists of the foamed sheet according to the invention.

[0117] In other embodiments, the core layer comprises a part consisting of the foamed sheet according to the invention and one or more additional parts consisting of a third composition having a higher density than the density of the foamed sheet according to the invention. Such parts consisting of the third composition may be present, for example, in the peripheral part of the core layer and / or a plurality of such parts may be distributed over the core layer. In some embodiments, the core layer consists of a central part (the central part consisting of the foamed sheet according to the invention) and a peripheral part at least partially surrounding the perimeter of the central part, wherein the peripheral part consists of the third composition. In some embodiments, the peripheral part completely surrounds the perimeter of the central part.

[0118] The part consisting of the third composition may serve to reinforce the core layer, for example to ensure the connection of the core layer to the first cover layer and the second cover layer. This may be particularly useful in multi-layer composite materials in which the first cover layer, the second cover layer and the core layer are screwed together. By using a third composition having a higher density than the density of the components according to the invention for the peripheral part of the core layer, a more secure connection by means of a screw can be achieved.

[0119] Preferably, the third composition comprises polypropylene and optionally glass fibers.

[0120] Preferably, the third composition is an unfoamed composition.

[0121] Preferably, the third composition has a density of at least 903 g / cm 3 、preferably at least 904 g / cm 3 、more preferably at least 905 g / cm 3 of.

[0122] Suitable components of the third composition are those described for the first and second compositions. The third composition can be the same as or different from the first and / or second compositions.

[0123] The multilayer composite material may further comprise a surface layer provided over the first cover layer and / or the second cover layer. The surface layer can be, for example, a decorative layer and can comprise, for example, PVC, wood.

[0124] The present invention also provides a method for preparing a multilayer composite material according to the present invention, which comprises the following steps:

[0125] a) Providing a foamed sheet according to the present invention on the first cover layer,

[0126] b) Placing the second cover layer on the foamed sheet, and

[0127] c) Bonding the first cover layer, the foamed sheet, and the second cover layer to each other, for example, by a twin-belt press.

[0128] Product

[0129] The present invention provides a board for a building, a transportation vehicle, a recreational vehicle, or a container, wherein the board comprises a foamed sheet according to the present invention. On the other hand, the present invention relates to the use of a foamed sheet according to the present invention for preparing a board for a building, a transportation vehicle, a recreational vehicle, or a container. The board can be selected from floor boards, wall boards, roof boards, insulation boards, such as the inner wall or front wall board of a truck, the roof board of a house, the floor of a trailer, the door panel of a car, the bumper board of a car. The board can have a straight surface or a curved surface.

[0130] The present invention also provides a method for preparing an article comprising a foamed sheet, the method comprising foam injection molding of a polymer composition comprising high melt strength polypropylene, wherein the high melt strength polypropylene has a melt strength of ≥30 cN determined according to ISO 16790:2005 at a temperature of 200 °C, using a cylindrical capillary with a length of 20 mm and a width of 2 mm, an initial velocity v0 of 9.8 mm / s, and an acceleration of 6 mm / s 2 of.

[0131] It should be noted that the present invention relates to the subject matter defined in the independent claims, either alone or in combination with any possible combination of the features described herein (especially preferably those combinations of the features present in the claims). Thus, it will be understood that all combinations of features related to the compositions according to the invention are described herein; all combinations of features related to the methods according to the invention, and all combinations of features related to the compositions according to the invention and features related to the methods according to the invention.

[0132] It should also be noted that the term "comprising / including / containing" does not exclude the presence of other elements. However, it is also understood that the description of a product / composition containing certain components also discloses a product / composition consisting of these components. A product / composition consisting of these components may be advantageous because it provides a simpler and more economical method for preparing the product / composition. Similarly, it is also understood that the description of a method including certain steps also discloses a method consisting of these steps. A method consisting of these steps may be advantageous because it provides a simpler and more economical method.

[0133] When referring to the values of the lower and upper limits of a parameter, it is also understood that the range formed by the combination of the lower limit value and the upper limit value is disclosed.

[0134] The present invention is now illustrated by the following examples, without being limited thereto.

[0135] Examples 1 and 2

[0136] The composition shown in Table 1 was loaded into an injection molding machine having a 50 mm diameter screw and a 150 ton clamping unit. The machine was also equipped with a Trexel MuCell T-100 system for dosing 1.5 wt% carbon dioxide blowing agent for foam injection molding. The mold tool used comprised a fixed half and a movable half. When the two halves were closed, the tool had a mold cavity with a rectangular flat plate geometry of 90 mm wide × 160 mm long. The barrel and mold temperatures used were 190 °C and 85 °C, respectively. First, the gas-containing composition was injected to fill the closed mold cavity. In a subsequent step, the movable half of the mold tool was partially returned to an intermediate position, causing the gas-containing material in the cavity to foam and expand from an initial (cavity) thickness t0 of 3 mm to a final foam thickness t1 of 15 mm, with an expansion ratio of 5. The foam (sheet) was further cooled in the mold to solidify and was then ejected from the mold.

[0137] A cuboid test specimen is processed from a foamed sheet. The processed specimen includes a foam core covered with surface layers on the top and bottom sides. The morphology and surface layer thickness of the specimen are examined using a microscope manufactured by Zeiss. The densities of the specimens with and without two surface layers are measured and shown in Table 1. The compressive stresses (σ10, σ20, and σ25) at 10%, 20%, and 25% compression in the thickness direction are determined by ISO 844 (2014) and shown in Table 1. The compressive modulus and flexural modulus are also determined by ISO 844 (2014) and ISO 1209, respectively, and shown in Table 1.

[0138] Comparative Examples 1 and 2

[0139] The compositions shown in Table 1 are subjected to foam extrusion to obtain foams with a density similar to that of Example 1. The density of the sheet is measured and shown in Table 1. The foam extrusion is carried out in a co-rotating twin-screw foam extruder with a 30 mm diameter and a 40 length-to-diameter ratio (L / D). The extruder consists of nine electrically heated zones equipped with water cooling, a subsequent cooling section, a static mixer, and a slit die. PP-UMS 561P and the nucleating agent masterbatch are heated and homogenized in the extruder at a temperature above 230 °C. In the rear section of the extruder, the physical blowing agent (isobutane) is metered and mixed with the molten polymer. The mixture is cooled to the foaming temperature of 170 °C and extruded through the slit die at a production rate of 20 kg / hr for CEx 1 and 15 kg / hr for CEx 2. The foamed sheet is obtained after cooling with a water-cooled calibrator device. The extruded PP foam sheet is cut into cuboids with a thickness of 12 mm for CEx 1 and 20 mm for CEx 2 in the thickness direction for property measurement. The compressive stresses at 10%, 20%, and 25% compression in the thickness direction are determined by ISO 844 (2014) and shown in Table 1.

[0140] Table 1

[0141]

[0142]

[0143] PP-UMS 561P is a polypropylene with a melt strength greater than 65 cN.

[0144] PP compound G3220A is 20% short glass fiber-reinforced polypropylene. The base material is a PP homopolymer. The glass fiber is chemically coupled to the PP matrix.

[0145] Nucleating agent (talc): Representative FPE 50 T, which is a 50% masterbatch of a talc-based nucleating agent, is commercially available from LyondellBasell.

[0146] Nucleating agent (CF40E): represents HYDROCEROL TM CF 40 E, which is a 40% masterbatch of a foaming nucleating agent based on sodium bicarbonate and a citric acid derivative, is commercially available from Avient.

[0147] Colorant (black): represents PF48 / 92F, a black masterbatch commercially available from Colloids Ltd.

[0148] Table 1 shows that the foamed sheet according to the present invention prepared by foam injection molding of a polymer composition comprising high melt strength polypropylene has a combination of low density and good compression properties.

Claims

1. An article comprising a foamed sheet prepared by foam injection molding of a polymer composition, the polymer composition comprising a high melt strength polypropylene, wherein the high melt strength polypropylene has a melt strength of ≥ 30 cN determined according to ISO 16790:2005 at a temperature of 200 °C using a cylindrical capillary with a length of 20 mm and a width of 2 mm, an initial velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 .

2. The article according to claim 1, wherein the high melt strength polypropylene has, according to ISO 16790:2005, at a temperature of 200 °C, using a cylindrical capillary with a length of 20 mm and a width of 2 mm, a starting speed v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 a melt strength of ≥ 35 cN, preferably ≥ 37 cN, more preferably ≥ 40 cN, more preferably ≥ 45 cN, even more preferably ≥ 50 cN, even more preferably ≥ 55 cN, even more preferably ≥ 60 cN, most preferably ≥ 65 cN and / or a melt strength of the high melt strength polypropylene of ≤ 100 cN, for example ≤ 95 cN, for example ≤ 90 cN, for example ≤ 87 cN, as measured.

3. The article according to any one of the preceding claims, wherein the high melt strength polypropylene has a molecular weight distribution Mw / Mn of 5 to 20, preferably 7 to 17, most preferably 10 to 15, measured by the general size exclusion chromatography described in ASTM D6474-12.

4. The article according to any one of the preceding claims, wherein the amount of the high melt strength polypropylene is at least 20% by weight based on the total polymer composition.

5. The article according to any one of claims 1 to 4, wherein the amount of the high melt strength polypropylene is at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or at least 99.9% by weight or 100% by weight based on the total polymer composition.

6. The article according to any one of claims 1 to 4, wherein the polymer composition comprises additional polypropylene that is not high melt strength polypropylene, for example having a melt strength of < 10 cN as determined according to ISO 16790:2005 at a temperature of 200 °C using a cylindrical capillary with a length of 20 mm and a width of 2 mm, an initial velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 and preferably wherein the amount of the additional polypropylene is from 5.0 to 40% by weight relative to the total polymer composition.

7. The article according to claim 6, wherein the total amount of the high melt strength polypropylene and the additional polypropylene is at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or at least 99.9% by weight or 100% by weight based on the total polymer composition.

8. The article according to any one of claims 1 to 4, wherein the polymer composition further comprises glass fibers, preferably wherein the amount of the glass fibers is 0.1 to 40% by weight, 0.5 to 30% by weight, 1.0 to 25% by weight, 2.0 to 20% by weight, or 5.0 to 15% by weight.

9. The article according to claim 8, wherein the total amount of the high melt strength polypropylene and the glass fibers is at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, at least 95% by weight, at least 98% by weight, at least 99% by weight, at least 99.5% by weight, or at least 99.9% by weight or 100% by weight based on the total polymer composition.

10. The article according to any one of claims 1 to 4, wherein the polymer composition comprises additional polypropylene and glass fibers that are not high melt strength polypropylene, for example, the additional polypropylene has a melt strength of < 10 cN determined according to ISO 16790:2005 at a temperature of 200 °C, using a cylindrical capillary with a length of 20 mm and a width of 2 mm, an initial velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s 2 and preferably wherein the amount of the high melt strength polypropylene is 20 to 90% by weight, the amount of the additional polypropylene is 5.0 to 40% by weight, and the amount of the glass fibers is 0.1 to 40% by weight, based on the total polymer composition.

11. The article according to any one of the preceding claims, wherein the foamed sheet has a density of at most 345 kg / m 3 , at most 340 kg / m 3 , at most 320 kg / m 3 , at most 300 kg / m 3 , at most 280 kg / m 3 , at most 260 kg / m 3 , at most 240 kg / m 3 , at most 226 kg / m 3 , at most 220 kg / m 3 , at most 200 kg / m 3 , at most 180 kg / m 3 or at most 160 kg / m 3 , wherein the density is determined according to ISO 845 (2006).

12. The article according to any one of the preceding claims, wherein the foam injection molding is carried out by expanding a molten mixture having a thickness of t0 in a mold to the foamed sheet having a thickness of t1 with an expansion ratio t1 / t0 greater than 4, preferably 4.1 to 20, more preferably 4.3 to 15, more preferably 4.5 to 12, more preferably 4.8 to 10.

13. The article according to any one of the preceding claims, wherein the article is a multi-layer composite material, the multi-layer composite material comprising a core layer containing the foamed sheet, a first covering layer provided on the core layer, wherein preferably the multi-layer composite material further comprises a second covering layer and the core layer is provided between the first covering layer and the second covering layer, wherein the first covering layer comprises a first composition having a density of at least 0.903 g / cm 3 and comprising polypropylene and optionally reinforcing fibers such as glass fibers, and optionally the second covering layer comprises a second composition having a density of at least 0.903 g / cm 3 and comprising polypropylene and optionally reinforcing fibers such as glass fibers.

14. The article according to any one of the preceding claims, wherein the foam injection molding comprises the following sequential steps: - a) providing a mixture of a foaming agent and a polymer composition and melting the mixture to obtain a molten mixture or b) providing a melt of the polymer composition and mixing the foaming agent into the melt of the polymer composition to obtain a molten mixture; - injecting the molten mixture into a mold; - optionally applying pressure to the molten mixture in the mold; - at least partially opening the mold to allow the molten mixture to form a soft foamed article; and - curing the soft foamed article to form the foamed sheet and discharging the foamed sheet from the mold.

15. The article according to any one of the preceding claims, wherein the article is a panel for a building, a transportation or a recreational vehicle or a container.

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