Polymer composition and expanded polypropylene beads made of that polymer composition

Abstract

To provide a polymer composition with a stable foaming ratio over a certain range of temperature.SOLUTION: The present invention relates to a polymer composition comprising (85 to 100 wt.%) of a propylene copolymer based on the total amount of the polymer composition, where the comonomer in the propylene copolymer is selected from a moiety derived from ethylene, an α-olefin having (4) to (20) carbon atoms or a combination thereof, where the amount of the comonomer is in the range of (0.50 to 4.5) wt.% based on the propylene copolymer, where the fraction of melted propylene copolymer in the temperature range of (116 to 151°C) is in the range of (65 to 90) wt.% based on the total weight of the propylene copolymer. The present invention also relates to expanded polypropylene (EPP) beads comprising the polymer composition. The invention further relates to the use of such EPP beads. The invention further relates to a process for preparing such EPP beads. The present invention also relates to an article made of the EPP beads. The invention further relates to the use of such an article. The invention further relates to a process for preparing such an article.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a polymer composition containing a propylene copolymer. The present invention further relates to the use of such a polymer composition. The present invention further relates to a process for preparing such a polymer composition.

[0002] The present invention also relates to expanded polypropylene (EPP) beads containing the polymer composition. The present invention further relates to the use of such EPP beads. The present invention further relates to a process for preparing such EPP beads.

[0003] The present invention also relates to an article made from such EPP beads. The present invention further relates to the use of such an article. The present invention further relates to a process for preparing such an article.

Background Art

[0004] EPP beads are foamed particles. These can be produced in an autoclave process using polypropylene pellets and foaming the pellets into EPP beads. The shapes of both the polypropylene pellets and the EPP beads are quasi-spherical. The diameter of the polypropylene pellets ranges from 0.5 to 1.5 mm, while the diameter of the EPP beads ranges from 1.0 to 5.5 mm. The degree of foaming can be represented by the foaming ratio, which is the volume ratio between the EPP beads before foaming and the polypropylene pellets. Articles can be produced in a steam molding process using EPP beads.

[0005] It is known that steam-molded articles made from EPP beads are used in various fields such as automobiles, buildings, furniture, and toys because they have characteristics such as being lightweight, having excellent heat insulation, good chemical resistance, and high impact resistance.

[0006] Patent Document 1 discloses EPP beads containing a propylene copolymer produced by a metallocene polymerization catalyst, which has a melting point exceeding 140°C and a melt flow rate of 12 g / 10 min or less. Patent Document 1 states that EPP beads containing such a propylene copolymer have good moldability.

[0007] Patent Document 2 discloses that from a polypropylene resin having at least two melting peaks (the at least two melting peaks include (i) a lowest temperature melting peak of 100°C or higher and 130°C or lower and (ii) a highest temperature melting peak of 140°C or higher and 160°C or lower) on a DSC curve obtained by measuring the melting point using a differential scanning calorimeter (DSC), by producing EPP beads as a base resin, (i) a foamed product in the mold can be produced at a very low mold heating steam pressure, (ii) even when the mold heating steam pressure rises, it shows low distortion, low shrinkage, and a wide range of heating conditions for molding, (iii) when foamed particles are molded using a mold having a complex shape, a large mold, etc., it shows satisfactory moldability, and (iv) when a polypropylene resin in-mold foamed product is prepared from EPP beads, it was possible to obtain EPP beads that maintain their properties such as compressive strength without significant loss.

[0008] Patent Document 3 discloses a foamed olefin resin containing a copolymer resin and a foaming agent, where the copolymer resin is composed of about 90 to 99.999 weight percent of an olefin and about 0.001 to 10 weight percent of an α-ω diene, and the copolymer resin has a weight average molecular weight in the range of about 30,000 to 500,000 daltons, a crystallization temperature in the range of 115°C to 135°C, and a melt flow rate in the range of 0.1 dg / min to 100 dg / min when determined using ASTM D - 1238 at a load of 230°C and 2.16 kg. According to Patent Document 3, it has been found that such a resin has improved physical, mechanical, and rheological properties.

[0009] Since a temperature deviation of even 0.5 °C can result in a ten-fold difference in the expansion ratio, it is known that the production process of EPP beads usually requires high-standard temperature control. In reality, it is technically difficult to completely eliminate temperature fluctuations and keep the temperature perfectly stable during the EPP bead production process. Temperature fluctuations can lead to a high defect rate of the final product due to a significant change in the expansion ratio. From this aspect, an object of the present invention is to provide a polymer composition having a stable expansion ratio over a certain temperature range.

[0010] Also, it is known that steam molding is an energy-consuming process. Since the temperature setting of the steam molding process can be lowered, it is possible to reduce energy consumption by using EPP beads made from a polymer composition having a lower melting temperature in the steam molding process. However, this type of polymer composition often causes a decrease in the rigidity of the steam-molded article. Therefore, a further object of the present invention is to provide an article prepared in a steam molding process with reduced energy consumption while maintaining the same level of rigidity.

Prior Art Documents

Patent Documents

[0011]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0012] The inventors of the present invention have found that the above technical problem is solved by a polymer composition comprising 85 to 100% by weight of a propylene copolymer based on the total amount of the polymer composition, wherein the comonomer in the propylene copolymer is selected from a moiety derived from ethylene, an α-olefin having 4 to 20 carbon atoms, or a combination thereof, and the amount of the comonomer ranges from 0.50 to 4.5% by weight based on the propylene copolymer, and the fraction of the molten propylene copolymer in the temperature range of 116 to 151 °C ranges from 65 to 90% by weight based on the total weight of the propylene copolymer.

[0013] Surprisingly, it has been found that such a polymer composition has a stable expansion ratio even when the temperature change exceeds 1 °C during the EPP bead production process. It has also been found that steam-molded articles made from EPP beads made from such a polymer composition require less energy during molding while maintaining the same level of rigidity.

Brief Description of the Drawings

[0014]

Figure 1

Modes for Carrying Out the Invention

[0015] Propylene copolymer In the context of the polyolefin industry, propylene copolymers fall into two well-known categories, namely propylene random copolymers and heterophasic propylene copolymers. The difference between these two types of propylene copolymers is that the former is homogeneous and the latter is heterophasic. For the purposes of the present invention, the propylene copolymer is preferably a propylene random copolymer.

[0016] Comonomer The comonomer in the propylene copolymer is selected from a moiety derived from ethylene, an α-olefin having 4 to 20 carbon atoms, or a combination thereof.

[0017] The amount of the comonomer in the propylene copolymer ranges from 0.50 to 4.5% by weight, preferably 1.0 to 4.4% by weight, preferably 2.0 to 4.3% by weight, preferably 3.0 to 4.2% by weight, preferably 3.6 to 4.1% by weight, preferably 3.7 to 4.0% by weight, based on the propylene copolymer.

[0018] The preferred comonomer in the propylene copolymer is a moiety derived from ethylene.

[0019] Melt Flow Index (MFI) The MFI of the propylene copolymer, when determined in accordance with ISO 1133-1:2011 at a load of 2.16 kg at 230 °C, can range from 5 to 15 g / 10 min, preferably 6 to 12 g / 10 min, preferably 7 to 10 g / 10 min.

[0020] Thermo-mechanical behavior The thermo-mechanical behavior of the propylene copolymer is determined by dynamic mechanical analysis (DMA). For stable foaming during the EPP bead production process, using a vibration temperature ramp from 27 °C to 160 °C at a rate of 5 °C / min, 1 Hz, 6% vibration strain, in an environment of vibration temperature rise using 17.5 mm single cantilever geometry in accordance with ASTM D4092-07(2013), the tan δ of the propylene copolymer at 151 °C can range from 0.160 to 0.080, preferably 0.155 to 0.090, more preferably 0.150 to 0.100, more preferably 0.140 to 0.110, and most preferably 0.135 to 0.115.

[0021] The DMA test can be carried out, for example, on a TA Instrument DMA 850 instrument with a sample size of 4 * 10 * 40 mm.

[0022] Thermal behavior The fraction of the molten propylene copolymer in the temperature range of 116 to 151 °C is in the range of 65 to 90% by weight, preferably 68 to 90% by weight, preferably 70 to 90% by weight, based on the total weight of the propylene copolymer.

[0023] The fraction of the molten propylene copolymer in the temperature range of 116 to 151 °C can be determined by SSA (Successive Self-nucleation and Annealing) measurement.

[0024] SSA (Successive Self-nucleation and Annealing) is a methodology for differential scanning calorimetry (DSC) thermal fractionation and was developed by Mueller et al. (A.J. Muller, Z.H.H. Hernandez, M.L. Arnal, J.J. Sanchez; Successive self-nucleation / annealing (SSA): A novel technique to study molecular segregation during crystallization; Polym Bulletin, 1997, 39, 465 - 472.). By using this method, the inventors were able to accurately indicate the fraction of the polymer melted in a specific temperature range.

[0025] The SSA test can be carried out on a DSC instrument, for example, a DSC TA Q1000.

[0026] For example, the fraction of the molten propylene copolymer in the temperature range of 116 to 151 °C can be calculated as the ratio of the melting enthalpy in the range of 116 to 151 °C to the total melting enthalpy, where the enthalpy values can be obtained in a test carried out in accordance with ISO 11357-3:2018 using the following temperature settings: a) Isothermal at 0 °C for 5 minutes. b) Heating from 0 °C to 230 °C at a temperature change rate of 10 °C / min c) Isothermal at 230 °C for 5 minutes. d) Cooling from 230 °C to 25 °C at a temperature change rate of 10 °C / min e) Isothermal at 25 °C for 5 minutes. f) Heating from 25 °C to 166 °C at a temperature change rate of 10 °C / min g) Isothermal at 166 °C for 5 minutes. h) Cooling from 166 °C to 25 °C at a temperature change rate of 10 °C / min i) Isothermal at 25 °C for 5 minutes. j) Heating from 25 °C to 161 °C at a temperature change rate of 10 °C / min k) Isothermal at 161 °C for 5 minutes. l) Cooling from 161 °C to 25 °C at a temperature change rate of 10 °C / min m) Isothermal at 25 °C for 5 minutes. n) Repeat the steps from j) to m) in a continuous loop using an isothermal time of 5 minutes, while gradually decreasing the maximum temperature during heating by 5 °C each time (decreasing the step size by 5 °C each time) until the maximum temperature reaches 41 °C.

[0027] Alternatively, the fraction of the molten propylene copolymer in the temperature range of 116 - 151 °C can be calculated as the ratio of the area between the heat flow - temperature curve and the temperature axis in the range of 116 - 151 °C to the total area between the heat flow - temperature curve and the temperature axis, where the heat flow - temperature curve can be obtained in a test conducted in accordance with ISO 11357 - 3:2018 using the following temperature settings: a) Isothermal at 0 °C for 5 minutes. b) Heating from 0 °C to 230 °C at a temperature change rate of 10 °C / min c) Isothermal at 230 °C for 5 minutes. d) Cooling from 230 °C to 25 °C at a temperature change rate of 10 °C / min e) Isothermal at 25 °C for 5 minutes. f) Heating from 25 °C to 166 °C at a temperature change rate of 10 °C / min g) Isothermal at 166 °C for 5 minutes. h) Cooling from 166 °C to 25 °C at a temperature change rate of 10 °C / min i) Isothermal at 25 °C for 5 minutes. j) Heating from 25 °C to 161 °C at a temperature change rate of 10 °C / min k) Isothermal at 161 °C for 5 minutes. l) Cooling from 161 °C to 25 °C at a temperature change rate of 10 °C / min m) Isothermal at 25 °C for 5 minutes. n) Steps j) to m) are repeated in a continuous loop using an isothermal time of 5 minutes, while gradually decreasing the maximum temperature during heating by 5 °C each time (decreasing the step size by 5 °C each time) until the maximum temperature reaches 41 °C.

[0028] To illustrate this alternative method, the SSA results of commercially available SABIC PP 9421 are shown in Figure 1. The total area under the total heat flow curve is taken as Y J / g, the area under the heat flow curve between 115 °C and 155 °C (dashed line) is taken as X J / g, and then the fraction of molten SABIC PP 9421 between 115 °C and 155 °C can be calculated as X / Y.

[0029] Catalyst Also, catalysts for producing propylene copolymers are known in the art, for example, Ziegler-Natta catalysts, metallocene catalysts. Preferably, the catalyst used for producing the polypropylene of the present invention does not contain phthalate. For example, the catalyst contains a compound of a transition metal of Groups 4 to 6 of the IUPAC, a Group 2 metal compound, and an internal donor, where the internal donor is a compound selected from malonate, maleate, succinate, glutarate, cyclohexene-1,2-dicarboxylate, benzoate, and their derivatives and / or mixtures, which are optionally substituted, and preferably, the internal donor is citraconate.

[0030] Process for preparing propylene copolymer Processes for producing propylene copolymers are known in the art and include bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization, or any combination thereof. Preferably, the polypropylene of the present invention is produced in a sequential polymerization process comprising at least two reactors, and more preferably, the polypropylene of the present invention is produced in a sequential polymerization process comprising at least three reactors.

[0031] Polymer composition The polymer composition according to the present invention comprises 85 to 100% by weight of the above-mentioned propylene copolymer based on the total amount of the polymer composition.

[0032] In addition to the propylene copolymer, the polymer composition may further contain additives. Examples of additives include stabilizers such as heat stabilizers, antioxidants, UV stabilizers; colorants such as pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame retardants; mold release agents; flow improvers; plasticizers; antistatic agents; external elastomeric impact modifiers; foaming agents; inorganic fillers such as talc and reinforcing agents; and / or components that enhance the interfacial bond between the polymer and the filler, such as maleated polypropylene. The amount of the additives depends on their type and function and ranges from 0 to 15% by weight based on the total amount of the polymer composition.

[0033] In one embodiment, the polymer composition contains an agent that can improve the thermal conductivity of the polymer composition, and this agent can be, for example, carbon black.

[0034] The polymer composition according to the present invention preferably has high toughness. Preferably, the elongation at break of the propylene copolymer is 500 to 5000% when determined in accordance with ISO527-1(2012).

[0035] Process for preparing the polymer composition The polymer composition can be prepared by mixing a propylene copolymer and an additive in an extrusion step. The settings of the extruder for preparing the polymer composition are known to those skilled in the art. The polymer composition obtained in this process is in pellet form, where the shape of the pellets of the polymer composition is quasi-spherical and the diameter of the polymer composition ranges from 0.5 to 1.5 mm.

[0036] EPP beads EPP beads can be produced by placing the pellets of the polymer composition in a pressurized sealed container such as an autoclave and dispersing them in an aqueous medium. If necessary, a dispersant can be added.

[0037] Next, a necessary amount of a blowing agent is supplied to the sealed container, the mixture is stirred under pressure, and heated to impregnate the pellets of the polymer composition with the blowing agent.

[0038] After the pellets of the polymer composition are impregnated with the blowing agent, the temperature and pressure of the sealed container are gradually and optionally lowered to room temperature and atmospheric level to foam the pellets into EPP beads.

[0039] The aqueous medium is usually water, and the mass ratio between the pellets of the polymer composition and the aqueous medium ranges from 1:5 to 5:1, preferably from 1:3 to 3:1, and most preferably from 1:2 to 2:1.

[0040] The optional dispersant can be an inorganic material poorly soluble in water such as alumina, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica, or a protective colloid agent based on a water-soluble polymer, such as polyvinylpyrrolidone, polyvinyl alcohol, and methylcellulose. Further, an anionic surfactant such as sodium dodecylbenzenesulfonate or sodium alkanesulfonate can be used as the dispersant.

[0041] The blowing agent used in the present invention is a physical blowing agent, such as an organic physical blowing agent like halogenated hydrocarbon, ethane, or dichloromethane, or an inorganic gas such as carbon dioxide, nitrogen, or air, or a mixture thereof. Among these blowing agents, it is preferable to use an inert gas such as carbon dioxide, nitrogen, or air as the main component. Most preferably, the blowing agent is carbon dioxide. The amount of the blowing agent can be adjusted according to the volume of the container, the mass ratio between the polymer composition and the aqueous medium, the temperature of the container, and the pressure setting.

[0042] For the purpose of the present invention, during the impregnation step, the temperature inside the pressure-sealed container is in the range of 140 to 165 °C, preferably 145 to 160 °C, preferably 148 to 157 °C, preferably 149 to 155 °C. For example, the temperature inside the pressure-sealed container is 151 °C during the impregnation step. Those skilled in the art can adjust the temperature so as to obtain EPP beads having a desired foaming ratio.

[0043] The pressure inside the pressure-sealed container during the impregnation step is in the range of 0.5 to 6.0 MPa, preferably 1.5 to 5.0 MPa. Those skilled in the art can adjust the pressure so as to obtain EPP beads having a desired foaming ratio.

[0044] A typical period of the impregnation step is in the range of 10 to 60 minutes. Those skilled in the art can adjust the impregnation period so as to obtain EPP beads having a desired foaming ratio.

[0045] For example, the process for preparing EPP beads includes the following steps in sequence: - The step of preparing the above-mentioned polymer composition - The step of placing the above-mentioned polymer composition and water into a pressure-sealed container, wherein the mass ratio between the polymer composition and water is in the range of 1:5 to 5:1 - The step of heating the container to a temperature range of 140 to 165 °C and injecting an inert gas such as a required amount of carbon dioxide, nitrogen, or air into the container so as to obtain a pressure range of 0.5 to 6.0 MPa - If the target temperature and pressure are reached, maintain the temperature and pressure for a time in the range of 10 to 60 minutes. - Release the container to room temperature 25 °C and atmospheric pressure level 1 bar. - Remove the EPP beads from the container and dry the EPP beads.

[0046] For example, the preparation process of EPP beads includes the following steps in sequence: - Prepare the above-mentioned polymer composition. - Place the above-mentioned polymer composition and water into a pressure-sealed container, wherein the mass ratio between the polymer composition and water is in the range of 1:3 to 3:1. - Heat the container to a temperature range of 149 to 155 °C and inject the required amount of carbon dioxide into the container to reach a pressure range of 1.5 to 5.0 MPa. - If the target temperature and pressure are reached, maintain the temperature and pressure for a time in the range of 10 to 60 minutes. - Release the container to room temperature 25 °C and atmospheric pressure level 1 bar. - Remove the EPP beads from the container and dry the EPP beads.

[0047] The density of the polymer composition pellets and the EPP beads is tested according to ISO845:2006. The expansion ratio is calculated as the ratio between the density of the polymer composition pellets and the density of the EPP beads produced therefrom. The typical expansion ratio of the EPP beads is in the range of 10 to 50.

[0048] The EPP beads according to the present invention contain 95 to 100% by weight of the above-mentioned polymer composition.

[0049] The present invention further relates to the use of EPP beads for the preparation of steam-molded articles.

[0050] Steam-molded article The steam-molded article is prepared in a process having the following steps: - Step of preparing the above EPP beads - Step of steam-molding EPP beads into an article by placing the EPP beads in a mold and fusing them, wherein the temperature range of this step is 130°C to 150°C, the pressure range of this step is 2.7 to 4.5 MPa, and the period of this step is in the range of 5 to 20 minutes.

[0051] The present invention also relates to a steam-molded article prepared using the above EPP beads.

[0052] The present invention further relates to the use of the steam-molded article for applications to automobiles, building structures, and toys.

[0053] The present invention further relates to the use of the above polymer composition for producing EPP beads having a stable expansion ratio or for reducing energy consumption in a steam molding process using EPP beads made from the polymer composition.

Example

[0054] Materials Polymer Composition 1: Polymer Composition 1 contains 100% by weight of a polypropylene random copolymer produced by the Sperizone technology using a Ziegler-Natta catalyst. The comonomer in Polymer Composition 1 is a portion derived from ethylene. The amount of the portion derived from ethylene is 3.80% by weight based on the total amount of Polymer Composition 1.

[0055] Polymer Composition 2: Polymer Composition 2 contains 100% by weight of a polypropylene random copolymer with the trade name COSMOPLENE® W331, which is available from The Polyolefin Company (Singapore). The comonomer in Polymer Composition 2 is a portion derived from ethylene. The amount of the portion derived from ethylene is 3.00% by weight based on the total amount of Polymer Composition 2.

[0056] Both polymer compositions were prepared in the form of quasi-spherical pellets, and the diameter of these pellets ranged from 0.5 to 1.5 mm.

[0057] Preparation of Samples Injection Molding The pellets of the polymer composition were injection molded into specimens with dimensions of 4 * 10 * 40 mm to be used in the DMA test according to ASTM D4092-07(2013), and specimens with a shape according to ISO527-1A(2012) to be used in the tensile test.

[0058] EPP Preparation 25 kg of polymer composition pellets were placed into an autoclave with an internal volume of 150 L together with 25 kg of water. Then, the autoclave was sealed, heated, and CO 2 was injected to maintain a pressure of 3 MPa at the temperature settings shown in Table 1. Once the temperature and pressure reached the target levels, CO 2 was maintained for 20 minutes to impregnate the polymer composition pellets. Thereafter, the autoclave was released to atmospheric pressure of 1 Bar and room temperature of 25 °C. While the autoclave was being released, the polymer composition pellets expanded into EPP beads. Finally, the EPP beads were taken out of the autoclave and dried. [Table 1]

[0059] Preparation of Steam-Molded Articles The EPP beads made from Polymer Compositions 1 and 2 having a foaming ratio of 25 times were steam molded into articles with dimensions of 50 × 50 × 5 cm under the conditions in Table 2 for 10 minutes. [Table 2]

[0060] Test Methods MFI The MFI of the pellets of the polymer composition was tested in accordance with ISO 1133-1:2011 at a load of 2.16 kg at 230 °C.

[0061] Breaking strain The breaking strain was tested on injection-molded specimens of the polymer composition in a tensile test according to ISO 527-1 (2012).

[0062] Thermo-mechanical test DMA measurements according to ASTM D4092-07 (2013) were carried out on injection-molded specimens on a TA Instrument DMA 850 instrument in a vibrating temperature rise environment using 17.5 mm single cantilever geometry at 1 Hz, 6% vibration strain, and a heating rate of 5 °C / min from 27 °C to 160 °C. The tan δ of the polymer composition at 151 °C was obtained in this test.

[0063] Thermal behavior The fraction of the polymer composition melted in the range of 116 to 151 °C was measured by SSA according to the protocol of ISO 11357-3:2018 using the following temperature settings: a) Isothermal at 0 °C for 5 minutes. b) Heating from 0 °C to 230 °C at a temperature change rate of 10 °C / min c) Isothermal at 230 °C for 5 minutes. d) Cooling from 230 °C to 25 °C at a temperature change rate of 10 °C / min e) Isothermal at 25 °C for 5 minutes. f) Heating from 25 °C to 166 °C at a temperature change rate of 10 °C / min g) Isothermal at 166 °C for 5 minutes. h) Cooling from 166 °C to 25 °C at a temperature change rate of 10 °C / min i) Isothermal at 25 °C for 5 minutes. j) Heating from 25 °C to 161 °C at a temperature change rate of 10 °C / min k) Isothermal at 161 °C for 5 minutes. l) Cooling from 161 °C to 25 °C at a temperature change rate of 10 °C / min m) Isothermal at 25°C for 5 minutes. n) Repeat the steps from j) to m) in a continuous loop using an isothermal time of 5 minutes, gradually decreasing the maximum temperature during heating by 5°C each time until the maximum temperature reaches 41°C.

[0064] The SSA test was performed on a DSC TA Q1000.

[0065] The fraction of the polymer composition melted at 116 - 151°C was calculated as the ratio of the melt enthalpy within the range of 116 - 151°C to the total melt enthalpy. The enthalpy values were directly exported via software combined with the DSC TA Q1000.

[0066] Compression modulus of the steam - formed article The compression modulus of the steam - formed article was tested in accordance with ISO844:2014.

[0067] Density The density of the pellets of both polymer compositions, as well as the density of the EPP beads made from both polymer compositions in EPP production 1, 2, and 3, were tested in accordance with ISO845:2006.

[0068] Results and discussion The results of the above - mentioned tests are shown in Table 3.

Table 3

[0069] According to Table 3, Polymer Composition 1 has a larger fraction of melted material in the temperature range of 116 to 151°C than Polymer Composition 2, and Polymer Composition 1 has a lower tan δ value at 151°C than Polymer Composition 2. As a result, the change in the foaming ratio of Polymer Composition 1 is significantly improved compared to Polymer Composition 2. Furthermore, although the steam molding conditions for EPP beads made from Polymer Composition 1 are at lower temperatures and pressures than those for EPP beads made from Polymer Composition 2, the compression elastic modulus of the final steam-molded article based on Polymer Composition 1 and the final steam-molded article based on Polymer Composition 2 is the same. This means that an article can be obtained that is prepared in a steam molding process with reduced energy consumption while maintaining the same level of rigidity. Additionally, Polymer Composition 1 exhibits better toughness than Polymer Composition 2 by having a higher fracture strain. Finally, the preferred embodiments of the present invention will be described item by item.

[0070] [Embodiment 1] A polymer composition comprising 85 to 100% by weight of a propylene copolymer based on the total amount of the polymer composition, wherein the comonomer in the propylene copolymer is selected from a moiety derived from ethylene, an α-olefin having 4 to 20 carbon atoms, or a combination thereof, and the amount of the comonomer ranges from 0.50 to 4.5% by weight based on the propylene copolymer, and the fraction of the molten propylene copolymer in the temperature range of 116 to 151°C ranges from 65 to 90% by weight based on the total weight of the propylene copolymer.

[0071] [Embodiment 2] When tested in an environment of vibration temperature rise using 17.5 mm single cantilever geometry with a temperature ramp from 27°C to 160°C at a rate of 5°C / min, 1 Hz, and 6% vibration strain in accordance with ASTM D4092-07(2013), the tan δ of the propylene copolymer is in the range of 0.160 to 0.080, preferably 0.155 to 0.090, more preferably 0.150 to 0.100, more preferably 0.140 to 0.110, and most preferably 0.135 to 0.115 at 151°C. The polymer composition according to Embodiment 1.

[0072] [Embodiment 3] The polymer composition according to Embodiment 1 or 2, wherein the comonomer in the propylene copolymer is a moiety derived from ethylene.

[0073] [Embodiment 4] The amount of the comonomer is in the range of 1.0 to 4.4% by weight, preferably 2.0 to 4.3% by weight, preferably 3.0 to 4.2% by weight, preferably 3.6 to 4.1% by weight, preferably 3.7 to 4.0% by weight based on the propylene copolymer. The polymer composition according to any one of Embodiments 1 to 3.

[0074] [Embodiment 5] When the melt flow index (MFI) of the propylene copolymer is determined in accordance with ISO1133-1:2011 under a load of 2.16 kg at 230°C, it is in the range of 5 to 15 g / 10 min, preferably 6 to 12 g / 10 min, preferably 7 to 10 g / 10 min. The polymer composition according to any one of Embodiments 1 to 4.

[0075] [Embodiment 6] When the elongation at break of the propylene copolymer is determined in accordance with ISO527-1(2012), it is 500 to 5000%. The polymer composition according to any one of Embodiments 1 to 5.

[0076] [Embodiment 7] The fraction of the molten propylene copolymer in the temperature range of 116 to 151°C is in the range of 68 to 90% by weight, preferably 70 to 90% by weight, based on the total weight of the propylene copolymer, the polymer composition according to any one of Embodiments 1 to 6.

[0077] [Embodiment 8] A process for preparing foamed polypropylene beads, in the following order, - A step of preparing the polymer composition according to any one of Embodiments 1 to 7 - A step of placing the polymer composition according to any one of Embodiments 1 to 7 and water in a pressure-sealed container, wherein the mass ratio between the polymer composition and water is in the range of 1:5 to 5:1 - A step of heating the container to a temperature range of 140 to 165°C and injecting a required amount of an inert gas such as carbon dioxide, nitrogen, or air into the container so as to obtain a pressure range of 0.5 to 6.0 MPa - A step of maintaining the temperature and pressure for a time in the range of 10 to 60 minutes once the target temperature and pressure are reached - A step of releasing the container to room temperature and an atmospheric pressure level of 1 bar - A step of taking out the foamed polypropylene beads from the container and drying the foamed polypropylene beads A process comprising.

[0078] [Embodiment 9] Foamed polypropylene beads containing 95 to 100% by weight of the polymer composition according to any one of Embodiments 1 to 7.

[0079] [Embodiment 10] A steam-molded article prepared using the foamed polypropylene beads according to Embodiment 9.

[0080] [Embodiment 11] A process for preparing a steam-molded article, - A step of preparing the foamed polypropylene beads according to Embodiment 9 - A step of placing the foamed polypropylene beads in a mold and fusing them to steam-mold the foamed polypropylene beads onto the article, wherein the temperature range of this step is 130°C to 150°C, the pressure range of this step is 2.7 to 4.5 MPa, and the period of this step is in the range of 5 to 20 minutes A process comprising this step

[0081] [Embodiment 12] Use of the polymer composition according to any one of Embodiments 1 to 7, for producing foamed polypropylene beads having a stable expansion ratio or for reducing energy consumption in a steam molding process using the foamed polypropylene beads produced from the polymer composition

Claims

[Claim 1] 1. A polymer composition comprising 85 to 100 wt % of a propylene copolymer based on the total weight of the polymer composition, a comonomer in the propylene copolymer is selected from an ethylene derived moiety, an α-olefin having 4 to 20 carbon atoms, or a combination thereof, the amount of the comonomer being in the range of 0.50 to 4.5 wt % based on the propylene copolymer, and a fraction of molten propylene copolymer in a temperature range of 116 to 151° C. being in the range of 65 to 90 wt % based on the total weight of the propylene copolymer.

Images