Foamed article

Abstract

The invention relates to a foamed article comprising a polymer composition comprising a propylene copolymer having a comonomer selected from moiety derived from ethylene, an α-olefin having 4 to 20 carbon atoms or a combination thereof, wherein the propylene copolymer has a comonomer content of 2.5 to 5.0 wt% based on the propylene copolymer and the propylene copolymer has a xylene soluble fraction determined according to ISO 16152:2005 of 3.0 to 7.5 wt% based on the propylene copolymer.

Description

[0001] FOAMED ARTICLE

[0002] The present invention relates to a foamed article and a process for making such article. The invention further relates to use of such article.

[0003] CN102167840A discloses a method for preparing polymer microcellular foamed material by supercritical press molding foaming, which comprises the following steps: heating up a foaming mould on a mould pressing machine, then putting a polymer into a mould after a foaming temperature is reached, closing the mould pressing machine, sealing the mould, introducing supercritical fluid into the mould so that the supercritical fluid is swelled and diffused toward the polymer, and then opening the mould pressing machine for pressure relief and foaming, so as to obtain a polymer microcellular foamed material. In Embodiment 2, a polypropylene microporous foam bead was obtained.

[0004] It is an object of the present invention to provide a foamed article having good mechanical properties such as high compressive stress.

[0005] Accordingly, the invention provides a foamed article comprising a polymer composition comprising a propylene copolymer having a comonomer selected from moiety derived from ethylene, an a-olefin having 4 to 20 carbon atoms or a combination thereof, wherein the propylene copolymer has a comonomer content of 2.5 to 5.0 wt% based on the propylene copolymer and the propylene copolymer has a xylene soluble fraction determined according to ISO16152:2005 at 25 °C of 3.0 to 7.5 wt% based on the propylene copolymer.

[0006] It was surprisingly found that the foamed article according to the invention has good mechanical properties such as high compressive stress.

[0007] The invention further provides a process for making the foamed article according to the invention, comprising the steps of a) forming the polymer composition into a shaped article, b) impregnating the shaped article with a supercritical gas and c) degassing the impregnated article of step b) to obtain the foamed article. It was observed that step b) can be performed in the process of the invention at a relatively low temperature to obtain desirable properties of the foamed article. This is advantageous in terms of energy consumption and for the process efficiency. Further, similar low densities are obtained over a wide range of temperatures of step b), which is advantageous in that the process tolerates a relatively high temperature fluctuation during step b).

[0008] Propylene copolymer

[0009] In the context of polyolefin industry, there are two well-known categories of propylene copolymer: propylene random copolymer and heterophasic propylene copolymer. The difference between these two types of propylene copolymer is that the former is homogeneous and the latter is heterophasic. For the purpose of the present invention, the propylene copolymer is preferably a propylene random copolymer.

[0010] The comonomer in the propylene copolymer is selected from moiety derived from ethylene, an a-olefin having 4 to 20 carbon atoms and combinations thereof. Preferably, the comonomer in the propylene copolymer is moiety derived from ethylene, i.e. the propylene copolymer is a propylene-ethylene copolymer. Most preferably, the propylene copolymer is a propylene-ethylene random copolymer.

[0011] The comonomer content of the propylene copolymer is 2.5 to 5.0 wt%, preferably 2.7 to 4.5 wt%, more preferably 3.0 to 4.0 wt%, more preferably 3.2 to 3.7 wt%, based on the propylene copolymer. This leads to good mechanical properties of the foamed article. The comonomer content in the propylene copolymer is determined by13C NMR.

[0012] The propylene copolymer has a xylene soluble fraction determined according to ISO16152:2005 at 25 °C of 3.0 to 7.5 wt%, preferably 3.5 to 7.0 wt%, more preferably 4.0 to 6.5 wt%, based on the propylene copolymer. Such relatively low xylene soluble fraction leads to good mechanical properties of the foamed article, such as high stiffness.

[0013] Preferably, the propylene copolymer has Mw / Mn of 5.0 to 9.0, preferably 6.0 to 8.0, more preferably 6.5 to 7.5, wherein Mw and Mn are determined in accordance with ASTM D6474-12. This leads to good mechanical properties of the foamed article. Preferably, the propylene copolymer has Mz / Mw of 2.5 to 3.5, preferably 2.8 to 3.2, wherein Mz and Mw are determined in accordance with ASTM D6474-12. This leads to good mechanical properties of the foamed article.

[0014] Preferably, the propylene copolymer has a melt flow index determined according to ISO1133-1 :2011 with 2.16kg load at 230°C of 0.5 to 5.0 dg / min, more preferably 1.0 to 3.0 dg / min. This allows the process for making the foamed article to be performed easily, especially the step of forming the polymer composition into a shaped article.

[0015] Preferably, the propylene copolymer has a melting temperature of 140.0 to 148.0 °C, preferably 142.0 to 146.0 °C. The melting temperature is determined by differential scanning calorimetry (DSC) by heating a sample of 5 mg from room temperature to 200 °C at a rate of 10 °C / min, holding at 200 °C for 5 mins, then cooling to room temperature at a rate of 10 °C / min, then heating to 200 °C at a rate of 10 °C / min, wherein the melting temperature is taken from the second temperature increase.

[0016] The process to produce propylene copolymer is known in the art such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combination thereof. Preferably the propylene copolymer of the present invention is produced in a sequential polymerization process comprising at least two reactors, for example two reactors, three reactors, four reactors or five reactors.

[0017] The catalyst to produce propylene copolymer is also known in the art, for example Ziegler-Natta catalyst, metallocene catalyst. The catalyst used to produced the propylene copolymer of the present invention may comprise phthalate. Preferably the catalyst used to produced the propylene copolymer of the present invention is free of phthalate, for example the catalyst comprises compounds of a transition metal of Group 4 to 6 of IUPAC, a Group 2 metal compound and an internal donor wherein said internal donor is a compound selected from optionally substituted malonates, maleates, succinates, glutarates, cyclohexene- 1 ,2-dicarboxylates, benzoates and derivatives and / or mixtures thereof, preferably the internal donor is a citraconate.

[0018] Preferably, the amount of the propylene copolymer in the polymer composition is 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% with respect to the total polymer composition. Polymer composition

[0019] The polymer composition of the present invention may optionally include additives which do not interfere with the previously mentioned desirable properties but enhance other favorable properties.

[0020] Optional additives that may be compounded or blended into the composition of the invention in customary amounts include stabilisers, e.g. heat stabilisers, anti-oxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame-retardants; mould-release agents; flow improving agents; plasticizers; anti-static agents; external elastomeric impact modifiers; blowing agents; inorganic fillers such as talc and reinforcing agents; and / or components that enhance interfacial bonding between polymer and filler, such as a maleated polypropylene.

[0021] The amount of the additives may e.g. be 0.0 to 5.0 wt%, for example 0.1 to 1.0 wt%, with respect to the polymer composition. Preferably, the total amount of polymer and the additives is 100 wt% of the total composition. Preferably, the total amount of the propylene copolymer and the additives is 100 wt% of the total composition.

[0022] In some preferred embodiments, the foamed article is obtainable by subjecting a shaped article to a foaming process, wherein the foamed article has a density of less than 0.100 g / cm3, preferably less than 0.050 g / cm3, more preferably 0.010 to 0.040 g / cm3, wherein the foaming process is performed at temperatures in the range of 120 to 160 °C. This can mean that during the foaming process the shaped article is impregnated with a supercritical gas at temperatures in the range of 120 to 160 °C.

[0023] In some preferred embodiments, the foamed article is obtainable by subjecting a shaped article to a foaming process, wherein the density of the foamed article is less than 10 wt%, preferably less than 5.5 wt%, more preferably 1.0 to 4.5 wt%, of the density of the shaped article.

[0024] In some preferred embodiments, the amount of the polymer composition in the foamed article is at least 98.0 wt%, preferably at least 99.0 wt%, more preferably at least 99.5 wt% basing on the total weight of the foamed article, most preferably the foamed article consists essentially of the polymer composition. Process

[0025] The invention further provides a process for making the foamed article according to the invention, comprising the steps of a) forming the polymer composition into a shaped article, b) impregnating the shaped article with a supercritical gas and c) degassing the impregnated article of step b) to obtain the foamed article.

[0026] Step a)

[0027] The step for obtaining a shaped article may be performed by any known method, such as injection molding and extrusion.

[0028] The shaped article may in principle have any form of dimension. In some preferred embodiments, the shaped article is a sheet. The sheet may have a straight surface or a curved surface. The sheet may have a thickness of 1 .0 to 10.0 mm, for example 1 .5 to 5.0 m.

[0029] Preferably, the shaped article has a density of 0.85 to 1 .00 g / cm3, more preferably 0.88 to 0.92 g / cm3.

[0030] Step b)

[0031] The process according to the invention comprises the step of impregnating the shaped article with a supercritical gas. This step may involve placing the shaped article in a mold, closing the mold, introducing the supercritical fluid into the mold and maintaining the closure of the mold for a desired period of time. The mold may be heated to reach the desired temperature before placing the shaped article in the mold or the mold may be heated to reach the desired temperature after placing the shaped article in the mold.

[0032] An impregnated shaped article impregnated with the supercritical gas is obtained by step b). A supercritical gas has a state that shows intermediate properties between gas state and liquid state. A gas reaches a supercritical state when its pressure and temperature go beyond a given point (critical point) that is specific for the gas.

[0033] Any gas can be used for impregnation as long as the gas can penetrate into the composition in its supercritical state. For example, the supercritical gas can e.g. be gases of carbon dioxide, nitrogen, air, oxygen, hydrogen or inert gas like helium. Preferably, the supercritical gas is carbon dioxide gas, nitrogen gas or a gas of a mixture of carbon dioxide and nitrogen.

[0034] It was observed that according to the invention step b) can be performed at a relatively low temperature to obtain a shaped article with good mechanical properties.

[0035] Preferably, step b) is performed at a temperature of 120 to 160 °C, preferably 135 to 154 °C, more preferably 142 to 150 °C. i.e. during the step of impregnating the shaped article with a supercritical gas the shaped article is situated in a closed mold having a temperature of 135 to 154 °C, more preferably 142 to 150 °C.

[0036] Preferably, step b) is performed at a pressure of 1 .0 to 15 MPa, more preferably 5.0 to 12 MPa, i.e. during the step of impregnating the molded article with a supercritical gas the pressure in the closed mold in which the shaped article is situated is 1.0 to 15 MPa, more preferably 5.0 to 12 MPa.

[0037] Preferably, step b) is performed for a duration of 20 minutes to 8 hours, more preferably 30 minutes to 4 hours, i.e. the duration between the introduction of the supercritical fluid into the closed mold and degassing is 20 minutes to 8 hours, more preferably 30 minutes to 4 hours.

[0038] Step c)

[0039] The process according to the invention comprises the step of degassing the impregnated shaped article to obtain the foamed article.

[0040] In this step, the pressure is reduced to a pressure below the critical pressure of the impregnated gas, typically to ambient pressure.

[0041] Step c) may be performed at a relatively high pressure release rate for obtaining uniform closed cells. For example, step c) is performed at a pressure release rate of at least 10 MPa / s. In other embodiments, step c) is performed at a pressure release rate of 1 .0 to 10 MPa / s, more preferably 2.0 to 6.0 MPa / s.

[0042] The foamed article may have a density of less than 0.100 g / cm3, preferably less than 0.050 g / cm3, more preferably 0.010 to 0.040 g / cm3. Preferably, the density of the foamed article is less than 10 wt%, preferably less than 5.5 wt%, more preferably 1.0 to 4.5 wt%, of the density of the shaped article.

[0043] In some preferred embodiments, the foamed article according to the invention is a component of an electric vehicle battery such as a cushion layer of an electric vehicle battery or a component in an automotive interior. In other preferred embodiments, the foamed article according to the invention is a panel for a building, a transportation or recreation vehicle or a shipping container.

[0044] It is noted that the invention relates to the subject-matter defined in the independent claims alone or in combination with any possible combinations of features described herein, preferred in particular are those combinations of features that are present in the claims. It will therefore be appreciated that all combinations of features relating to the composition according to the invention; all combinations of features relating to the process according to the invention and all combinations of features relating to the composition according to the invention and features relating to the process according to the invention are described herein.

[0045] It is further noted that the term ‘comprising’ does not exclude the presence of other elements. However, it is also to be understood that a description on a product / composition comprising certain components also discloses a product / composition consisting of these components. The product / composition consisting of these components may be advantageous in that it offers a simpler, more economical process for the preparation of the product / composition. Similarly, it is also to be understood that a description on a process comprising certain steps also discloses a process consisting of these steps. The process consisting of these steps may be advantageous in that it offers a simpler, more economical process.

[0046] When values are mentioned for a lower limit and an upper limit for a parameter, ranges made by the combinations of the values of the lower limit and the values of the upper limit are also understood to be disclosed.

[0047] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0048] Materials Three types of propylene-ethylene random copolymer shown in Table 1 were used, produced by Spherizone technology using a Ziegler-Natta catalyst.

[0049] Table 1

[0050] Xylene soluble fraction was determined according to 18016152:2005: 2g of pellets sample is dissolved in 200 ml xylene under reflux conditions, then cooled under controlled conditions and maintained at 25 °C for 30 minutes to ensure controlled crystallization of the insoluble fraction. The xylene-soluble fraction is then recovered by evaporation of 100 ml aliquot of the filtrate and determined by weighing the residue.

[0051] Ethylene content was determined by 13C NMR: The sample was dissolved at 130°C in C2D2CI4 containing DBPC as stabilizer. The NMR spectra was recorded on a Bruker Avance500 spectrometer equipped with a cryogenically cooled probe head operating at 125°C. Mw, Mn and Mz were all determined in accordance with ASTM D6474-12 (Standard Test Method for Determining Molecular Weight Distribution and Molecular Weight Averages of Polyolefins by High Temperature Gel Permeation Chromatography). Mw stands for the weight average molecular weight and Mn stands for the number average weight. Mz stands for the z-average molecular weight. The measurement was performed using a configuration in which a Polymer Char IR5 infrared concentration detector and a Polymer Char online viscosity detector were used to gain ‘absolute’ or accurate molar masses. Three columns of Polymer Laboratories 13 pm PLgel Olexis, 300 x 7.5 mm (3 x Agilent PLgel Olexis 13pm, 7.5 x 300mm columns) were used in series with 1 ,2,4-trichlorobenzene stabilized with 1 g / L butyl hydroxytoluene (also known as 2,6-di-fert-butyl-4-methylphenol or BHT) as eluent. The molar mass was determined based on a calibration using linear PE standards (narrow and broad (Mw / Mn = 4 to 15)) in the range of 0.5 - 2800 kg / mol.

[0052] Melt flow index was determined according to ISO1133-1 :2011 with 2.16kg load at 230°C.

[0053] Flexural modulus was determined by ISO 178.

[0054] Tensile modulus was determined by ISO 527.

[0055] Tensile strength at yield was determined by ISO 527.

[0056] Charpy impact strength was determined by ISO179 at 23 °C.

[0057] HDT (heat deflection temperature) was determined by ISO75 at a load of 0.45MPa.

[0058] Melting temperature Tm was determined by differential scanning calorimetry (DSC) by heating a sample of 5 mg from room temperature to 200 °C at a rate of 10 °C / min, holding at 200 °C for 5 mins, then cooling to room temperature at a rate of 10 °C / min, then heating to 200 °C at a rate of 10 °C / min, wherein the melting temperature is taken from the second temperature increase.

[0059] Example set 1 PP1 , PP2 and PP3 shown in Table 1 were injection molded into sheets (plaques) having a thickness of 4 mm. The sheets were placed into a cavity of a mold having a temperature shown in Table 2. The cavity was closed. The cavity was filled with N2 gas and CO2 gas at a pressure of 5 MPa and this was maintained for 30 minutes. The cavity was subsequently depressurized and opened. Foamed sheets were obtained. The density of the foamed sheet was determined by measuring the mass and the volume of the sheet.

[0060] Table 2 Density of foamed sheets (g / cm3)

[0061] It can be understood that foaming PP3 leads to a foamed sheet with a low density at a relatively low temperature. It can further be understood that PP3 allows achieving low density of the foamed article over a wide range of temperatures.

[0062] Example 2

[0063] PP1 , PP2 and PP3 shown in Table 1 were extruded into sheets. The sheets were placed into a cavity of a mold and the cavity was closed. The cavity was filled with CO2 gas at a pressure of 10 MPa and this was maintained for 2.5 hours. The cavity was subsequently depressurized and opened. Foamed sheets were obtained.

[0064] The density of the foamed sheet was determined by ASTM D 792.

[0065] Compression stress at 10%, 25%, 50% and 75 compression in the thickness direction were determined by ISO 844.

[0066] Flexural strength was determined by ISO 1209-2: 2007.

[0067] Flexural modulus was determined by ISO 1209-2: 2007. Tensile strength© break was determined by ASTM D 412.

[0068] Elongation @ break was determined by ASTM D 412.

[0069] Table 3-1 shows the values as determined by the relevant methods. Table 3-2 shows the values which have been standardized to the density of PP1 , i.e. 0.057 g / cm3, for the purpose of more meaningful comparison. The results show that the foamed sheet made from PP3 according to the invention has better mechanical properties than the foamed sheets made from PP1 and PP2. Table 3-1

[0070] Table 3-2

Claims

CLAIMS1 . A foamed article comprising a polymer composition comprising a propylene copolymer having a comonomer selected from moiety derived from ethylene, an a- olefin having 4 to 20 carbon atoms or a combination thereof, wherein the propylene copolymer has a comonomer content of 2.5 to 5.0 wt% based on the propylene copolymer and the propylene copolymer has a xylene soluble fraction determined according to ISO 16152:2005 at 25 °C of 3.0 to 7.5 wt% based on the propylene copolymer.

2. The foamed article according to claim 1 , wherein the propylene copolymer is a propylene-ethylene random copolymer.

3. The foamed article according to any one of the preceding claims, wherein the comonomer content in the propylene copolymer is 2.7 to 4.5 wt%, preferably 3.0 to 4.0 wt%, more preferably 3.2 to 3.7 wt%, based on the propylene copolymer.

4. The foamed article according to any one of the preceding claims, wherein the xylene soluble fraction determined according to ISO 16152:2005 at 25 °C is 3.5 to 7.0 wt%, preferably 4.0 to 6.5 wt%, based on the propylene copolymer.

5. The foamed article according to any one of the preceding claims, wherein the propylene copolymer has a melt flow index determined according to IS01133- 1 :2011 with 2.16kg load at 230°C of 0.5 to 5.0 dg / min.

6. The foamed article according to any one of the preceding claims, wherein the propylene copolymer has Mw / Mn of 5.0 to 9.0, preferably 6.0 to 8.0, more preferably 6.5 to 7.5, wherein Mw and Mn are determined in accordance with ASTM D6474-12 and / or the propylene copolymer has Mz / Mw of 2.5 to 3.5, preferably 2.8 to 3.2, wherein Mz and Mw are determined in accordance with ASTM D6474-12.

7. The foamed article according to any one of the preceding claims, wherein the amount of the propylene copolymer in the polymer composition is 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% with respect to the total polymer composition.

8. The foamed article according to any one of the preceding claims, wherein the foamed article is obtainable by subjecting a shaped article to a foaming process, wherein the foamed article has a density of less than 0.100 g / cm3, preferably less than 0.050 g / cm3, more preferably 0.010 to 0.040 g / cm3, and the foaming process has been performed at temperatures in the range of 120 to 160 °C.

9. The foamed article according to any one of the preceding claims, wherein the foamed article is obtainable by subjecting a shaped article to a foaming process, wherein the density of the foamed article is less than 10 wt%, preferably less than 5.5 wt%, more preferably 1.0 to 4.5 wt%, of the density of the shaped article.

10. The foamed article according to any one of the preceding claims, wherein the foamed article is a component of an electric vehicle battery such as a cushion layer of an electric vehicle battery or a component in an automotive interior.11 . A process for making the foamed article according to any one of the preceding claims, comprising the steps of a) forming the polymer composition into a shaped article, b) impregnating the shaped article with a supercritical gas and c) degassing the impregnated article of step b) to obtain the foamed article.

12. The process according to claim 11 , wherein step b) is performed at temperatures in the range of 120 to 160 °C.

13. The process according to any one of claims 11-12, wherein the supercritical gas is carbon dioxide gas, nitrogen gas or a gas of a mixture of carbon dioxide and nitrogen.

14. The process according to any one of claims 11-13, wherein the shaped article has a density of 0.85 to 1 .00 g / cm3, preferably 0.88 to 0.92 g / cm3.

15. The process according to any one of claims 11-14, wherein the density of the foamed article is less than 10 wt% of the density of the shaped article, preferably less than 5.5 wt%, more preferably 1 .0 to 4.5 wt%.

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