Foaming container

Abstract

The invention relates to a foamed container prepared by foam injection molding of a polymer composition comprising a high melt strength polypropylene having a melt strength of > = 30 cN, determined according to ISO 16790: 2005 at a temperature of 200 DEG C using a cylindrical capillary tube of length 20 mm and width 2 mm, a start velocity v0 of 9.8 mm / s and an acceleration of 6 mm / s2. Foam injection molding may comprise the following sequential steps: 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; injection molding the molten mixture into a mold; applying a pressure to the molten mixture in the mould; optionally, at least partially opening the mould to form the molten mixture into a soft foamed article; and-curing the soft foamed article to form a foamed container and discharging the foamed container from the mold.

Description

[0001] The present invention relates to a foamed container and a method for preparing such a foamed container.

[0002] Plastic crates or containers are currently widely used in many applications. Crates are often used to package and protect products in consumer products, food and groceries, automotive, and other fields. Some crates need to insulate or isolate the products they protect from heat or cold. A typical example is a food crate for fast food delivery. The product being delivered should be warm when it reaches the consumer.

[0003] Another example is a food crate for fresh fish. These crates are on fishing boats. After the fish are caught and cleaned, they are packed into the crates together with ice. The crates will be stored in a refrigerator. After reaching the port, the fish are sold and delivered.

[0004] In the example of a fish crate, a crate made of polystyrene bead foam is typically used. Polystyrene bead foam has excellent insulating properties. The insulating property is inversely proportional to the thermal conductivity (k) of the material; that is, the lower the k value, the better the insulating performance. The typical k value of polystyrene bead foam is 0.035 W / m.K. Typically, solid HDPE has a k value of 0.44 W / m.K and solid polypropylene has a k value of 0.21 W / m.K.

[0005] The disadvantage of crates made of polystyrene bead foam is that these crates can only be used once. Due to the particulate structure, microorganisms will hide in the pore structure of the material and affect the food.

[0006] The object of the present invention is to provide a container that has good heat insulating properties, is easy to clean, and can be reused.

[0007] Therefore, the present invention provides a foamed container prepared by foam injection molding of a polymer composition comprising high melt strength polypropylene.

[0008] The foamed container according to the present invention is easy to clean and can be reused because it does not have a particulate structure that makes it difficult to remove microorganisms. After its lifespan, for example, after being used 30 times, the container can be advantageously recycled.

[0009] According to the present invention, the use of high melt strength polypropylene in combination with foam injection molding allows for the obtaining of a foamed container with a very low density. The low density of the foamed container results in high insulating properties and can even result in insulating properties comparable to those of a foamed container made of polystyrene beads.

[0010] Foam injection molding

[0011] Generally, to prepare a foamed article such as a foamed container, 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.

[0012] Preferably, foam injection molding comprises the following sequential steps:

[0013] - Providing a mixture of a blowing agent and a polymer composition comprising high melt strength polypropylene;

[0014] - Melting the mixture to obtain a molten mixture;

[0015] - Injecting the molten mixture into a mold;

[0016] - Optionally applying pressure to the molten mixture in the mold;

[0017] - At least partially opening the mold to allow the molten mixture to form a soft foamed article; and

[0018] - Curing the soft foamed article to form a foamed container and discharging the foamed container from the mold.

[0019] Preferably, foam injection molding comprises the following sequential steps:

[0020] - 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;

[0021] - Injecting the molten mixture into a mold;

[0022] - Optionally applying pressure to the molten mixture in the mold;

[0023] - At least partially opening the mold to allow the molten mixture to form a soft foamed article; and

[0024] - Curing the soft foamed article to form a foamed container and discharging the foamed container from the mold.

[0025] Preferably, the step of injecting the molten mixture into the mold is carried out such that the mold is completely filled. This results in a greater density reduction.

[0026] The pressure application step is preferred because this results in a greater density reduction.

[0027] This process is sometimes referred to as the core-back injection molding process or the mold movement process. It has been found that particularly large density reductions and good insulation properties are achieved. The density reduction achieved can be at least 75%, i.e., the density of the foamed container can be at most 240 kg / m 3 .

[0028] Preferably, the foamed container has a density of at most 240 kg / m 3 , preferably 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).

[0029] In some preferred embodiments, the foamed container has a density of 160 to 320 kg / m 3 , more preferably 160 to 240 kg / m 3 , where the density is determined according to ISO 845 (2006). Such foamed containers have a combination of good thermal insulation properties and mechanical properties.

[0030] Preferably, the foamed container has a thermal conductivity value k of at most 0.100 W / mK, preferably 0.090 W / m.K, more preferably at most 0.080 W / m.K, more preferably at most 0.070 W / mK, as determined by ASTM C518.

[0031] Preferably, the foamed container has a thermal conductance value U of at most 10.0 W / m 2 .K, more preferably at most 7.0 W / m 2 .K, more preferably at most 5.0 W / m 2 .K, as determined by ASTM C518.

[0032] Preferably, the foam injection molding according to the present invention is carried out by expanding a molten mixture having a thickness of t0 in a mold into a foamed container having a wall thickness of t1 at an expansion ratio EXP of 2.0 to 7.5, preferably 2.5 to 7.0, more preferably 3.0 to 6.5, more preferably 3.5 to 6.0, where EXP = t1 / t0. Such a process results in a foamed container having a combination of good thermal insulation properties and mechanical properties.

[0033] In some preferred embodiments, foam injection molding is carried out by expanding a molten mixture having a thickness t0 in a mold to a foamed container having a wall thickness t1 at an expansion ratio EXP, and wherein the foamed container has a thermal conductivity value k [W / mK] as determined by ASTM C518, where the following relationship is satisfied:

[0034] 0.10*(1 / EXP)+0.025 ≤ k ≤ 0.50*(1 / EXP)-0.0085,

[0035] where EXP = t1 / t0

[0036] Such a process results in a foamed container having a combination of good thermal insulation properties and mechanical properties.

[0037] The present invention also provides a foamed container prepared by: preparing a foamed sheet by foam injection molding of a polymer composition comprising high melt strength polypropylene and assembling the foamed sheets to obtain a foamed container, wherein the foam injection molding comprises the following sequential steps:

[0038] - 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;

[0039] - injecting the molten mixture into a mold;

[0040] - optionally applying pressure to the molten mixture in the mold;

[0041] - at least partially opening the mold to allow the molten mixture to form a soft foamed article; and

[0042] - curing the soft foamed article to form a foamed sheet and discharging the foamed sheet from the mold.

[0043] The foamed sheets can be assembled into a foamed container by any known method, such as by using an adhesive or by thermal bonding.

[0044] Preferably, foam injection molding is carried out by expanding a molten mixture having a thickness t0 in a mold to a foamed sheet having a thickness t1 at an expansion ratio EXP of from 2.0 to 7.5, preferably from 2.5 to 7.0, more preferably from 3.0 to 6.5, even more preferably from 3.5 to 6.0, where EXP = t1 / t0.

[0045] In some preferred embodiments, foam injection molding is carried out by expanding a molten mixture having a thickness of t0 in a mold at an expansion ratio EXP into a foamed sheet having a wall thickness of t1, and wherein the foamed sheet has a thermal conductivity value k [W / mK] as determined by ASTM C518, where the following relationship is satisfied:

[0046] 0.10*(1 / EXP)+0.025 ≤ k ≤ 0.50*(1 / EXP)-0.0085,

[0047] where EXP = t1 / t0

[0048] 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 a 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.

[0049] Preferably, the blowing agent is a chemical blowing agent because it is easier to uniformly disperse the chemical blowing agent in the polymer composition, which results in a more uniform foam structure. The chemical blowing agent can be in the form of a powder or a masterbatch.

[0050] Typical physical blowing agents include, but are not limited to, fluids such as hydrocarbons in the gaseous or supercritical state (e.g., butane, pentane), carbon dioxide, nitrogen, and mixtures thereof.

[0051] 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 in the range of 0.2 - 5.0 wt% based on the total weight of the polymer composition.

[0052] 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% relative to the foaming container.

[0053] Polymer composition

[0054] 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 unbranched 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.

[0055] Branching can generally be achieved by using a specific catalyst (i.e., a specific single-site catalyst) or by chemical modification. For the preparation of branched polypropylene obtained by using a specific catalyst, reference is made to EP1892264. For 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.

[0056] 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).

[0057] Another suitable example of a commercially available product of high melt strength polypropylene is Achieve TM Advanced PP6302E1 from Exxon Mobil.

[0058] Preferably, the high melt strength polypropylene has a melt strength of ≥30 cN. In this article, 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 speed v0 of 9.8 mm / s, and an acceleration of 6 mm / s2.

[0059] High melt strength polypropylene having 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, 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.

[0060] Preferably, the high melt strength polypropylene is prepared by

[0061] 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

[0062] b) deactivating the free radicals in the long-chain branched polypropylene to form high melt strength polypropylene.

[0063] The deactivation of free radicals is known in the art, for example by heating as described in WO2009003930A1.

[0064] 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), N,N-bis(alkyl)hydroxylamine directly oxidized from N,N-bis(hydrogenated tallow)amine ( FS-042), 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), and alone or in combination with at least one organic phosphite / ester or phosphonite (selected from tris(2,4-di-tert-butylphenyl)phosphite ( 168)). Even more preferably, the non-phenolic stabilizer of the present subject matter may include those described in U.S. Pat. Nos. 6,664,317 and 6,872,764, which are incorporated herein in their entirety by reference.

[0065] Preferably, the melt strength of the high melt strength polypropylene is ≥37 cN, preferably ≥40 cN, preferably ≥45 cN, more preferably ≥50 cN, more preferably ≥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.

[0066] As used herein, polypropylene means a propylene homopolymer, a copolymer of propylene and an α-olefin or a heterophasic propylene copolymer.

[0067] 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.

[0068] 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, for example in 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 selected from ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-decene, and 1-dodecene, preferably structural moieties derived from ethylene.

[0069] Polypropylene and methods for its synthesis 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.

[0070] 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.

[0071] 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.

[0072] Preferably, the high melt strength polypropylene has a VOC value ≤250 μg / g (preferably a VOC value ≤50 μg / g) as measured according to VDA278 (2011-10) and / or a FOG value ≤500 μg / g (preferably a FOG value ≤100 μg / g) as measured according to VDA278 (2011-10).

[0073] Preferably, the high melt strength polypropylene has a molecular weight distribution Mw / Mn of from 5 to 20, preferably from 7 to 17, and most preferably from 10 to 15. Mw and Mn can be measured by conventional size exclusion chromatography (SEC) as described in ASTM D6474-12 using the following:

[0074] · Chromatography: PolymerChar GPC-IR system operating at 160 °C

[0075] · Detection: Polymer Char IR5 infrared detector; PolymerChar viscometer

[0076] · IR5 is used as a concentration detector.

[0077] · Column set: Three Polymer Laboratories 13 μm PLgel Olexis, 300 × 7.5 mm

[0078] · PE molar mass calibration is performed using linear PE standards (narrow and broad (Mw / Mn = 4 to 15)) in the range of 0.5–2800 kg / mol

[0079] · The concentration of the injected sample is 0.03% m / m and is stabilized using Irgafos 168 and Topanol CA (weight ratio, sample: Irgafos: Topanol = 1:1:1)

[0080] · The solvent and eluent are 1,2,4-trichlorobenzene and are stabilized using 1 g / L BHT

[0081] 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%, 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.

[0082] 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.

[0083] For example, the amount of the additional polypropylene is from 5 to 40 wt% or from 40 to 80 wt% based on the total polymer composition.

[0084] Preferably, the total amount of the high melt strength polypropylene and the additional 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.

[0085] 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.

[0086] The polymer composition may also comprise a nucleating agent. The nucleating agent may be desirable to increase the pore density and alter the kinetics of bubble formation and growth. (Gendron, Thermoplastic foam Processing, 2005, page 209).

[0087] 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.

[0088] 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 (C2-C 32 )alkylenediyl-bis-(C2-C 32 )alkanamides such as ethylene bisstearamide (EBS), butylene bisstearamide, hexamethylene bisstearamide, ethylene bisbehenamide, and mixtures thereof. Suitable amines include or are exemplified by (C2-C 18)Alkylenediamines such as ethylenebishexylamine and hexamethylenebishexylamine. Preferred saturated or unsaturated aliphatic (C 10 -C 34 ) esters of carboxylic acids are esters of aliphatic (C 16 -C 24 ) 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.

[0089] For preparing the foamed container, 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 glyceryl monostearate (GMS), glyceryl 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 glyceryl monostearate or stearamide.

[0090] The amount of cell stabilizer to be added depends on the desired cell size and the polymer composition used to prepare the foamed container. Generally, the cell stabilizer can be added in an amount of ≥0.10 and ≤3.0 wt% based on the polymer composition.

[0091] Preferably, the foamed container 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 a foamed container has a good combination of heat insulation properties and mechanical properties.

[0092] The foamed container according to the present invention can have any shape (such as a cube having a bottom wall and side walls) and any internal volume (such as 1.0 to 100 liters or 5.0 to 20 liters). For example, the internal volume can be 1 to 15 liters (such as 10 liters), 15 to 45 liters (such as 32 liters), or 45 to 100 liters (such as 70 liters).

[0093] The foamed container can have a wall thickness of 0.1 to 20 cm, 0.3 to 10 cm, or 0.5 to 5.0 cm. For example, the wall thickness can be 0.1 to 3.0 cm, 3.0 to 10 cm, or 10 to 20 cm.

[0094] The foamed container according to the present invention has an opening through which the product can be placed in the foamed container. The opening can be closed by a lid.

[0095] The invention also provides a container with a lid, which comprises a foamed container according to the present invention and a foamed lid for closing the foamed container.

[0096] Preferably, the foamed lid is also prepared by foam injection molding of a polymer composition comprising high melt strength polypropylene.

[0097] Suitable polymer compositions for preparing the lid are those described for the foamed container according to the present invention. Preferably, the polymer composition of the foamed container and the polymer composition of the lid are of the same type. It will be understood that this means using the same polymer composition to obtain the foamed container and the foamed lid.

[0098] Suitable methods for foam injection molding are those described for the foamed container according to the present invention. Preferably, the lid is prepared by a core-back injection molding method.

[0099] The lid can have a wall thickness of 0.1 to 20 cm, 0.3 to 10 cm or 0.5 to 5.0 cm. For example, the wall thickness can be 0.1 to 3.0 cm, 3.0 to 10 cm or 10 to 20 cm.

[0100] The present invention also provides the use of the foamed container according to the present invention or the container with a lid according to the present invention for storing and / or transporting food.

[0101] The present invention also provides a method for preparing a foamed container, which comprises foam injection molding of a polymer composition comprising high melt strength polypropylene.

[0102] It should be noted that the present invention relates to the subject matter defined in the independent claims, which are combined alone or in any possible combination with the features described herein (particularly preferably those combinations of features present in the claims). Therefore, it will be understood that all combinations of features related to the composition according to the present invention are described herein; all combinations of features related to the method according to the present invention, and all combinations of features related to the composition according to the present invention and features related to the method according to the present invention.

[0103] 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 some components also discloses a product / composition consisting of these components. The product / composition consisting of these components can 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 some steps also discloses a method consisting of these steps. The method consisting of these steps can be advantageous because it provides a simpler and more economical method.

[0104] 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.

[0105] The present invention is now illustrated by the following examples, which are, however, not limited thereto.

[0106] Figure 1 illustrates an example of a container with a lid, which includes a foamed container according to the present invention in an open state, and

[0107] Figure 2 illustrates an example of a container with a lid, which includes a foamed container according to the present invention in a closed state.

[0108] The performance of a container having the same internal dimensions (13 liters) of 360 mm × 360 mm × 100 mm was modeled via a Fourier heat transfer model:

[0109]

[0110] The heat (E) absorbed or transferred to the box per second to heat 5 kg of ice contents is related to the following: the thermal conductivity (U) across the foam container wall; the total external surface area (A) of the container including the lid; and the temperature difference between the external and internal surfaces of the container. Assuming that the external surface (T o ) of the container is at a constant temperature of 20 °C and the internal temperature (T i ) of the container is maintained at 0 °C until the complete melting of the ice contents, the equation will be simplified to

[0111] E = UA(20)

[0112] The U-value of the container wall is related to the thermal conductivity or k-value (k) and thickness (t) of the wall material:

[0113]

[0114] For each kilogram of ice, it requires 333550 J of thermal energy to melt; thus, it requires 1667750 J to completely melt 5 kg of ice contents. Therefore, the total amount of time that the container can prevent the complete melting of 5 kg of ice contents can be evaluated:

[0115]

[0116] Based on the above calculations, the time to melt 5 kg of ice placed in a container with a lid made of different materials was determined.

[0117] Comparative Example 1 represents an injection-molded container of unfoamed PP with a wall thickness of 2 cm. The typical k-value of such a material is 0.21 W / m.K. Such a container will prevent the complete melting of 5 kg of ice contents for only 4.1 hours.

[0118] Comparative Example 2 represents a foam-injection molded container of linear polypropylene with a 50% density reduction (i.e., 475 kg / m 3 ) and a wall thickness of 2 cm. The typical k-value of such a material is 0.1032 W / m.K. Even with foaming, such a container (with only a 50% density reduction) will prevent 5 kg of ice contents from completely melting for only 8.3 hours.

[0119] Comparative Example 3 represents a foam-injection molded container using the same material as Comparative Example 2 (i.e., 475 kg / m 3 ) but with a thicker wall thickness of 4 cm. Even doubling the wall thickness, such a container will prevent 5 kg of ice contents from completely melting for 12.8 hours.

[0120] Example 1 represents a foam-injection molded container of high melt strength polypropylene (PP-UMS) with a 75% density reduction (i.e., 235 kg / m 3 ) and a wall thickness of 2 cm. The typical k-value of such a material is 0.0628 W / m.K. This container will prevent 5 kg of ice contents from completely melting for 13.6 hours.

[0121] Example 2 represents a foam-injection molded container based on a PP-UMS resin with an 80% density reduction (i.e., 190 kg / m 3 ) and a wall thickness of 2 cm. The typical k-value of such a material is 0.0551 W / m.K. This container will prevent 5 kg of ice contents from completely melting for 15.5 hours.

[0122] Example 3 represents a foam-injection molded container based on a PP-UMS resin with an 80% density reduction (i.e., 190 kg / m 3 ) and a wall thickness of 3 cm. This container will prevent 5 kg of ice contents from completely melting for 20.3 hours.

[0123] Example 4 represents a foam-injection molded container based on a PP-UMS resin with an 83% density reduction (i.e., 158 kg / m 3 ) and a wall thickness of 3 cm. The typical k-value of such a material is 0.0504 W / m.K. This container will prevent 5 kg of ice contents from completely melting for 22.2 hours.

[0124] Example 5 represents a foam-injection molded container based on a PP-UMS resin with an 83% density reduction (i.e., 190 kg / m 3 ) and a wall thickness of 4 cm. This container will prevent 5 kg of ice contents from completely melting for 23.9 hours.

[0125] Comparative Example 4 represents an injection-molded container of unfoamed HDPE with a wall thickness of 2 cm. The typical k value for such a material is 0.44 W / m.K. Such a container will prevent 5 kg of ice contents from completely melting for only 1.9 hours.

[0126] Comparative Example 5 represents a foam injection-molded container of conventional HDPE with a 4 cm wall thickness and a 50% density reduction (i.e., 478 kg / m 3 ). The typical k value for such a material is 0.195 W / m.K. Even with foaming and a doubled wall thickness, such a container will prevent 5 kg of ice contents from completely melting for only 6.7 hours.

[0127] Comparative Example 6 represents a container made of particulate polystyrene foam with a 2 cm wall thickness. The typical k value for such a material is 0.035 W / m.K. This container will prevent 5 kg of ice contents from completely melting for 24.3 hours.

[0128] The results are summarized in the following table. By using the lower density achieved with PP-UMS, foam injection-molded containers with improved insulation properties can thus be obtained, enabling the possibility of using these containers as returnable and recyclable insulated crates / containers.

[0129]

[0130] Polypropylene (SABIC PP-UMS 561P) having a melt strength greater than 65 cN is premixed with 0.5 wt% Avient Hydrocerol CF 40E (a masterbatch containing a mixture of bicarbonate and citrate derivatives) as a foaming agent and a nucleating agent to obtain a polypropylene composition to be subjected to foam injection molding. Carbon black and an impact copolymer polypropylene SABIC PP FPC45 are also used to obtain the polypropylene compositions in some of the examples as shown in Table 2.

[0131] The obtained polypropylene composition was loaded into an injection molding machine with 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 consisted of 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. First, the gas-laden PP material was injected to fill the closed mold cavity. In a subsequent step, the movable half of the mold tool was partially retracted to an intermediate position, causing the gas-laden material in the cavity to foam and expand from the initial (cavity) thickness t0 to the final foam thickness t1. Foams with different densities were achieved by controlling the ratio between t1 and t0 (expansion ratio EXP). The foam was further cooled in the mold to solidify and then ejected from the mold.

[0132] The thermal conductivity (k) values of the obtained flat plates were measured using a heat flow meter (HFM 446 Lambda Small from NETZSCH) under the conditions of ASTM C518. The results are shown in Table 2.

[0133] Table 2

[0134] 100% UMS 100% UMS 100% UMS 100% UMS 30% UMS + 70% FPC45 Natural Natural Natural Black Black Initial thickness t0 [mm] 3 3 3 3 3 Foamed thickness t1 [mm] 9 12 15 15 15 Total expansion EXP[x] 3 4 5 5 5 Foam density ρ [kg / m3] 302 226 181 181 181 Thermal conductivity k [W / mK] 0.079 0.071 0.064 0.066 0.056 Thermal conductance U [W / m2K] 8.8 5.9 4.3 4.4 3.8

[0135] Even with a relatively low expansion ratio, low thermal conductivity (k value) and low heat conductance (U value) were obtained.

Claims

1. A foamed container prepared by 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 at a temperature of 200 °C according to ISO 16790:2005 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 2. The foamed container according to claim 1, wherein the high melt strength polypropylene has a melt strength of ≥ 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 determined at a temperature of 200 °C according to ISO 16790:2005 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 and / or the melt strength of the high melt strength polypropylene is ≤ 100 cN, for example ≤ 95 cN, for example ≤ 90 cN, for example ≤ 87 cN.

3. The foamed container 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. 2 4. The foamed container 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 into the foamed container having a wall thickness of t1 at an expansion ratio EXP of 2.0 to 7.5, preferably 2.5 to 7.0, more preferably 3.0 to 6.5, more preferably 3.5 to 6.0, where EXP = t1 / t0.

5. The foamed container according to any one of the preceding claims, wherein the foamed container has a thermal conductivity value k of at most 0.100 W / mK, preferably 0.090 W / mK, more preferably at most 0.080 W / mK, more preferably at most 0.070 W / mK and / or a heat transfer coefficient value U of at most 10.0 W / m 6. The foamed container 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 into the foamed container having a wall thickness of t1 at an expansion ratio EXP, and wherein the foamed container has a thermal conductivity value k [W / mK] determined by ASTM C518, wherein the following relationship is satisfied:

7. The foamed container 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 into the foamed container having a wall thickness of t1 at an expansion ratio EXP, and wherein the foamed container has a heat transfer coefficient value U [W / m²K] determined by ASTM C518, wherein the following relationship is satisfied: 2 8. The foamed container according to any one of the preceding claims, wherein the polymer composition further comprises a nucleating agent, preferably a talc nucleating agent. 2 9. The foamed container according to any one of the preceding claims, wherein the polymer composition further comprises a blowing agent, preferably a physical blowing agent. 2 10. The foamed container according to any one of the preceding claims, wherein the polymer composition further comprises a stabilizer, preferably a heat stabilizer.

11. The foamed container 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 into the foamed container having a wall thickness of t1 at an expansion ratio EXP, and wherein the foamed container has a thermal conductivity value k [W / mK] determined by ASTM C518, wherein the following relationship is satisfied: 0.10*(1 / EXP)+0.025 ≤ k ≤ 0.50*(1 / EXP)-0.0085, where EXP = t1 / t0.

7. The foamed container according to any one of the preceding claims, wherein the foamed container has an open cell content of ≤ 15.0%, preferably ≤ 12.0%, more preferably ≤ 10.0%, even more preferably ≤ 7.0%, even more preferably ≤ 5.0%, even more preferably ≤ 4.0%, even more preferably ≤ 3.0%, even more preferably ≤ 2.0%, wherein the open cell content is determined according to ASTM D6226 - 10.

8. The foamed container 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 the 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 apply pressure to the molten mixture in the mold; - At least partially open the mold to allow the molten mixture to form a soft foamed article; and - Cure the soft foamed article to form the foamed container and discharge the foamed container from the mold.

9. The foamed container according to any one of the preceding claims, wherein 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%, 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.

10. The foamed container according to any one of the preceding claims, wherein the polymer composition comprises additional polypropylene that is not high melt strength polypropylene, for example having a melt strength of < 10 cN determined at a temperature of 200 °C according to ISO 16790:2005 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 total amount of the high melt strength polypropylene and the additional 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.

11. The foamed container according to any one of the preceding claims, wherein the foamed container has a wall thickness of 0.1 to 20 cm, such as 0.3 to 10 cm or 0.5 to 5.0 cm.

12. The foamed container according to any one of the preceding claims, wherein the foamed container has an internal volume of 1 to 100 liters, such as 1 to 15 liters, 15 to 45 liters or 45 to 100 liters.

13. A container with a lid, which comprises the foamed container according to any one of the preceding claims and a foamed lid for closing the foamed container. Preferably, the foamed lid is prepared by foam injection molding of a polymer composition comprising high melt strength polypropylene. Preferably, the polymer composition of the foamed container and the polymer composition of the foamed lid are of the same type.

14. Use of the foamed container according to any one of claims 1 to 12 or the container with a lid according to claim 13 for storing and / or transporting food.

15. A method for preparing a foamed container, which comprises foam injection molding of a polymer composition comprising high melt strength polypropylene. Preferably, the foam injection molding comprises the following sequential steps: - a) providing a mixture of a foaming agent and the 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; - Apply pressure to the molten mixture in the mold; - Optionally, at least partially open the mold to allow the molten mixture to form a soft foamed article; and - Cure the soft foamed article to form the foamed container and discharge the foamed container from the mold, wherein the high melt strength polypropylene has a melt strength of ≥ 30 cN measured at a temperature of 200 °C according to ISO 16790:2005 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 .

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