Polypropylene composition

Abstract

The present invention relates to a polypropylene composition, a method for preparing the same, and an article comprising such a polyolefin composition. The polypropylene composition, based on a total weight thereof, comprises (A) 50-82 wt% of a polypropylene which is a propylene homopolymer or a propylene copolymer consisting of at least 90 wt% of propylene monomer units and at most 10 wt% of ethylene monomer units and / or α-olefin monomer units having 4 to 10 carbon atoms; (B) at most 5 wt% of an elastomer of ethylene and α-olefin comonomer having 4 to 10 carbon atoms; and (C) at least 18 wt% of a block copolymer comprising a terminal block comprising styrene or alpha-methyl styrene, with a polystyrene content of at least 22 wt%.

Description

[0001] 24POLY0089-WO-ORD 1

[0002] POLYPROPYLENE COMPOSITION

[0003] The present invention relates to a polypropylene composition, a method for preparing the same, and an article comprising such a polyolefin composition.

[0004] Polypropylene is a versatile thermoplastic material known for its excellent chemical resistance, high melting point, and good strength-to-weight ratio. It has been widely used in various applications, such as packaging, textiles, and automotive components. It is widely known in the art to add a polyolefin elastomer to the base polypropylene to improve its impact strength, flexibility, thermal resistance, and adhesion properties, making it more versatile and suitable for a wider range of applications.

[0005] However, the addition of the polyolefin elastomer has the disadvantage of deteriorating other properties such as transparency. For applications in need of a transparent appearance of the articles produced from such polypropylene compositions, a balance between mechanical properties and optical properties needs to be improved.

[0006] It is an objective of the present invention to provide a polypropylene composition with an improved balance between impact strength and transparency of the composition.

[0007] In one aspect, the present invention provides a polypropylene composition comprising:

[0008] (A) 50-82 wt% of a polypropylene which is a propylene homopolymer or a propylene copolymer consisting of at least 90 wt% of propylene monomer units and at most 10 wt% of ethylene monomer units and / or a-olefin monomer units having 4 to 10 carbon atoms;

[0009] (B) at most 5 wt% of an elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms;

[0010] (C) at least 18 wt% of a block copolymer comprising a terminal block comprising styrene or alpha- methyl styrene, with a polystyrene content of at least 22 wt%.

[0011] The polypropylene composition of the present invention optionally comprises:

[0012] (D) 0.1-20 wt%, preferably 5-15 wt%, more preferably 8-12 wt%, of an inorganic filler, which is mica.

[0013] The polypropylene composition of the present invention optionally comprises: 24POLY0089-WO-ORD 2

[0014] (E) 0.1-10 wt% of additives.

[0015] (A) Polypropylene

[0016] The composition according to the invention comprises a polypropylene (A), in other words, a propylene-based polymer.

[0017] The propylene-based polymer may be a propylene homopolymer or a propylene copolymer with at most 10 wt% of comonomer units, such as 8 wt%, 6 wt%, 5wt%, 4 wt%, 3 wt%, 2 wt%, 1 wt%, 0.5 wt%, or 0.1 wt%. The comonomer units may be ethylene monomer units and / or an a- olefin monomer units having 4 to 10 carbon atoms.

[0018] In an embodiment, the propylene-based polymer (A) is a propylene homopolymer.

[0019] In an embodiment, the propylene-based polymer (A) is a random propylene-ethylene copolymer consisting of 90 to 99 wt% of propylene monomer units and 1 to 10 wt% of ethylene monomer units. Preferably, the propylene-based polymer (A) is a random propylene-ethylene copolymer consisting of 96 to 99 wt% of propylene monomer units and 1 to 4 wt% of ethylene monomer units. A random copolymer with a low comonomer content retains a good stiffness and leads to a good mechanical property balance.

[0020] In one embodiment, the propylene-based polymer (A) has a density of 0.870-0.950 g / cm3, for example 0.900-0.910 g / cm3, measured in accordance with ASTM D1505.

[0021] In one embodiment, the propylene-based polymer (A) has a melt flow rate of 10 to 100 dg / min, for example 15 to 60 dg / min, such as 20 dg / min, 25 dg / min, 30 dg / min, 35 dg / min, 40 dg / min, 45 dg / min, 50 dg / min, 55 dg / min, measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

[0022] In one embodiment, the amount of the propylene-based polymer (A) in the composition is 62 to 80 wt% or 65 to 75 wt%, with respect to the total composition.

[0023] It will be appreciated that the propylene-based polymer (A), which is a propylene homopolymer or a random propylene copolymer with at most 10 wt% of comonomer units, is not a 24POLY0089-WO-ORD 3 heterophasic propylene copolymer, also known as impact propylene copolymer or propylene block copolymer. Heterophasic propylene copolymers are generally prepared in two or more than two reactors in series, by polymerization of propylene (or propylene and a-olefin) in the presence of a catalyst and subsequent polymerization of an ethylene-a-olefin mixture. The resulting polymeric materials consist of a propylene-based matrix and a dispersed ethylene-a- olefin copolymer. Heterophasic propylene copolymers are described e.g. in WO2014044680. Such heterophasic propylene copolymer is not understood as a random propylene copolymer wherein the comonomer is randomly distributed throughout the copolymer, since in a heterophasic propylene copolymer the non-propylene comonomer amount is generally different between the matrix phase and the dispersed phase (the dispersed phase is an ethylene copolymer and therefore has a higher ethylene content than the matrix phase). For the avoidance of any doubt, the propylene-based polymer (A) of the present invention is not a heterophasic propylene copolymer consisting of a propylene-based matrix and a dispersed ethylene-a-olefin copolymer. The composition according to the invention comprises little or no amount of a heterophasic propylene copolymer, e.g. at most 5 wt%, at most 3 wt%, at most 1 wt% or 0 wt% with respect to the total composition.

[0024] The use of the propylene-based polymer (A), which is a propylene homopolymer or a random propylene copolymer, is more advantageous than the use of a heterophasic propylene copolymer with respect to the optical performance, specifically with a lower haze.

[0025] In the context of the present invention, the polypropylene composition may also comprise two or more polypropylenes (A), each of which and / or a combination of which meets the definitions above.

[0026] (B) Elastomer

[0027] The composition according to the invention may or may not comprise an elastomer (B) of ethylene and a-olefin comonomer having 4 to 10 carbon atoms.

[0028] In any case, the amount of the elastomer (B) should not be higher than 5 wt% with respect to the total composition, such as at most 4 wt%, at most 3 wt%, at most 2 wt%, at most 1 wt%, at most 0.1 wt%, or 0 wt%. 24POLY0089-WO-ORD 4

[0029] In one embodiment, the (B) elastomer is a copolymer of ethylene and octene, preferably 1- octene. In one embodiment, the (B) first elastomer is a copolymer of ethylene and butylene, preferably 1 -butylene.

[0030] In one embodiment, the (B) elastomer has a density of 0.850-0.950 g / cm3, for example, 0.880- 0.900 g / cm3, measured in accordance with ASTM D1505.

[0031] In one embodiment, the (B) elastomer has a melt flow rate of 0.1 to 10 dg / min, for example 1 to 5 dg / min, measured in accordance with ASTM D1238 using a 2.16 kg weight and at a temperature of 190 °C.

[0032] In the context of the present invention, the polypropylene composition may also comprise two or more first elastomers (B), each of which and / or a combination of which meets the definitions above.

[0033] The composition according to the invention comprises a styrene block copolymer (C).

[0034] The styrene block copolymer used in the present invention is a block copolymer comprising a terminal block comprising styrene or alpha-methyl styrene. The block copolymer is preferably selected from the group consisting of polystyrene-polybutadiene, polystyrene- poly(ethylene- propylene) (SEP), polystyrene-polyisoprene, poly(alpha-methylstyrene)- polybutadiene, polystyrene-polybutadiene-polystyrene (SBS), polystyrene-poly(ethylene- butylene)-polystyrene (SEBS), polystyrene-poly(ethylene-propylene)-polystyrene, polystyrene-polyisoprene- polystyrene (SIS), poly(alpha-methylstyrene)-polybutadiene- poly(alpha-methylstyrene) and polystyrene- poly(ethylene-propylene-styrene)-polystyrene.

[0035] One preferred example of the block copolymer is polystyrene-polyisoprene-polystyrene (SIS). However, preferably, the block copolymer comprises a non-terminal block comprising ethylene, for example selected from the group consisting of polystyrene-poly(ethylene- propylene) (SEP), polystyrene-poly(ethylene-butylene)-polystyrene (SEBS), polystyrene- poly(ethylene-propylene)- polystyrene and polystyrene-poly(ethylene-propylene-styrene)- polystyrene. Most preferably, the block copolymer is polystyrene-poly(ethylene-butylene)- polystyrene (SEBS). 24POLY0089-WO-ORD 5

[0036] Typically, the block copolymer (C) has a melt flow rate of 0.1 to 10 dg / min, for example 1 to 5 dg / min as measured according to ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

[0037] In the context of the present invention, the amount of styrene or alpha-methyl styrene in the block copolymer (C) is at least 22 wt%, preferably 25 to 40 wt%, more preferably 28 to 35 wt%, based on the block copolymer.

[0038] The block copolymer (C) may comprise a non-terminal block comprising ethylene. In this case, the amount of ethylene in the block copolymer may typically be 10-60 wt% based on the block copolymer. The amount of components of the block copolymer (C), such as ethylene, butylene and styrene or alpha-methylstyrene, may be determined by13 C NMR measurements, for example according to the following method: The samples are dissolved in C2D2CI4 at 130°C. 2,6-Di-tert-butyl-p-cresol (DBPC) is added as an internal stabilizer. The13 C NMR measurements are performed on a Bruker500 Avance III NMR spectrometer equipped with a 10mm-diameter cryo-cooled probe head operating at 125°C. The weight percentage of ethylene, butylene and styrene are obtained by analyzing the13 C NMR spectra.

[0039] In one embodiment, the amount of the block copolymer (C) in the composition is at least 18 wt%, for example 20 to 40 wt%, preferably 22 to 30 wt%, with respect to the total composition.

[0040] In one embodiment, the total of (A), optional (B) and (C) is at least 85 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% of the total composition.

[0041] In the context of the present invention, the polypropylene composition may also comprise two or more block copolymers (C), each of which and / or a combination of which meets the definitions above.

[0042] (D) Inorganic filler

[0043] The composition according to the invention may comprise an inorganic filler. 24POLY0089-WO-ORD 6

[0044] Suitable examples of the inorganic filler include talc, calcium carbonate, wollastonite, barium sulphate, kaolin, glass flakes, laminar silicates (bentonite, montmorillonite, smectite) and mica.

[0045] For the purpose of the present invention, the inorganic filler comprises mica. In one embodiment, the inorganic filler is comprised of mica.

[0046] Mica is a group of silicate minerals that are known for their strong plate-like structures.

[0047] The production of mica can be broadly categorized into two methods: dry method and wet method.

[0048] In the dry method, mica is extracted from the rock in its natural state using hand tools or mechanical equipments. The rock containing mica is crushed and then sorted using screens to separate the mica plates from the other minerals. The mica plates are then washed and dried to remove any impurities and prepare them for use.

[0049] In the wet method, mica is extracted using water or a water-based solution. The rock containing mica is crushed and then mixed with water to create a slurry. The mica plates settle at the bottom of the tank, while the other minerals and impurities float on the top. The mica is then separated from the water using various methods, such as filtration or centrifugation, and then dried.

[0050] Mica produced using the dry method is often referred to as "natural mica" or "mined mica," while mica produced using the wet method is called "washed mica" or "processed mica."

[0051] For the purpose of the present invention, the mica used in the present polypropylene composition is a wet method mica, which is produced by a wet method comprising the step of grinding coarse mica in the presence of a liquid media, such as water.

[0052] In one embodiment, the amount of (D) inorganic filler is 0.1-20 wt%, preferably 5-15 wt%, more preferably 8-12 wt%, with respect to the total composition.

[0053] In one embodiment, the polypropylene composition comprises 0.1-20 wt%, preferably 5-15 wt%, more preferably 8-12 wt%, of mica. 24POLY0089-WO-ORD 7

[0054] In one embodiment, the mica used in the present invention has a narrow particle distribution, represented by a typical particle size span between 1.2-1.7, preferably between 1.4-1.5, as tested by a laser particle size analyzer. Particle size span is calculated by (D90-D10) / D50. which has typical span at 1.48 characterized by laser particle size analyzer.

[0055] In one embodiment, the mica used in the present invention has a thin layer thickness of less than 1 pm, preferably 200-700 nm.

[0056] In one embodiment, the mica used in the present invention has a D50 particle size of 5-50 pm, such as 9pm, 13 pm, 17pm, 21 pm, 25 pm, 29 pm, 33 pm, 37 pm, 41 pm, 45 pm, or 49pm, preferably 10-35 pm.

[0057] In one embodiment, the mica used in the present invention has a fluorine content of at least 5 wt%.

[0058] In one embodiment, the total of (A), optional (B), (C) and (D) is 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% of the total composition.

[0059] (E) Additives

[0060] The composition may further comprise optional components different from the polypropylene (A), the elastomer (B), the styrene block copolymer (C) and the inorganic filler (D), such as additives (E), wherein the total of (A), (B), (C), (D) and (E) is 100 wt% of the total composition. Accordingly, the invention relates to a composition consisting of (A), (B), (C), (D) and (E).

[0061] The additives may include nucleating agents, stabilizers, e.g., heat stabilizers, antioxidants, UV stabilizers; colorants, like pigments and dyes; clarifiers; surface tension modifiers; lubricants; flame-retardants; mold-release agents; flow improving agents; plasticizers; anti-static agents; blowing agents; and / or components that enhance interfacial bonding between polymer and filler, such as a maleated polypropylene. 24POLY0089-WO-ORD 8

[0062] The skilled person can readily select any suitable combination of additives and additive amounts without undue experimentation. The amount of the additives depends on their type and function and typically is of from 0 to about 10 wt%. The amount of the additives may e.g. be from about 0.1 to about 5 wt%, or from about 0.2 to about 3 wt%, based on the total composition.

[0063] Process

[0064] The composition of the invention may be obtained by a process comprising melt-mixing the components of the composition by using any suitable means. Accordingly, the invention further relates to a process for the preparation of the composition according to the invention comprising melt mixing component (A), optional component (B), component (C), optional component (D) and optional component (E). The melt-mixing step may be preceded by dry-mixing of the components (A), (B) and (C). This is especially preferred when the melt-mixing is performed by injection molding.

[0065] Preferably, the composition of the invention is made in a form that allows easy processing into a shaped article in a subsequent step, like in pellet or granular form. Preferably, the composition of the invention is in pellet or granular form as obtained by mixing all components in an apparatus like an extruder; the advantage being a composition with homogeneous and well- defined concentrations of the additives. With melt-mixing, it is meant that the components are mixed at a temperature that exceeds the melting point of the component (A). Melt-mixing may be done using techniques known to the skilled person, for example in an extruder. Generally, in the process of the invention, melt- mixing is performed at a temperature in the range of 200 to 260°C.

[0066] Suitable conditions for melt-mixing, such as temperature, pressure, amount of shear, screw speed and screw design when an extruder is used are known to the skilled person.

[0067] In one embodiment, the polypropylene composition of the present invention has a transmittance, measured in accordance with ASTM D1003A at 23°C, of at least 60%, preferably at least 65%, more preferably at least 70%, and at most 90%. 24POLY0089-WO-ORD 9

[0068] In one embodiment, the polypropylene composition of the present invention has a Charpy impact strength of at least 20 kJ / m2, preferably at least 25 kJ / m2, more preferably at least 30 kJ / m2, and at most 50 kJ / m2, as measured in accordance with ISO 179-1eA (II) (2010) at 23°C.

[0069] In one embodiment, the polypropylene composition of the present invention has a tensile modulus, measured according to ISO 527 2(1A) (2012) at 23°C, of at least 1400 Mpa, preferably at least 1500 Mpa.

[0070] In one embodiment, the polypropylene composition of the present invention has a flexural modulus, measured according to ISO 178 (2010) at 23°C, of at least 1400 Mpa, preferably at least 1800 Mpa.

[0071] Further aspects

[0072] The invention further relates to an article, preferably automotive exterior parts like panels and bumpers, and / or automotive interior parts like instrument panels and lighting, prepared from the composition according to the invention.

[0073] The invention further relates to use of the composition according to the invention for automotive exterior parts and / or automotive interior parts.

[0074] The composition according to the invention may be processed by any conventional technique known in the art into an article. Suitable examples of processing techniques wherein the composition according to the invention may be used include injection moulding, injection blow moulding, injection stretch blow moulding, rotational moulding, compression moulding, extrusion, extrusion compression moulding, extrusion blow moulding, sheet extrusion, film extrusion, cast film extrusion, foam extrusion, thermoforming and thin-walled injection moulding.

[0075] It is noted that the invention relates to all 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. It is further 24POLY0089-WO-ORD 10 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 / com position comprising certain components also discloses a product / com position 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.

[0076] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0077] Experiments

[0078] Components used in the experiments are summarized in Table 1. In all tables, “%” means “wt%”, unless indicated otherwise.

[0079] Table 1. 24POLY0089-WO-ORD 11

[0080] The PP homopolymer, elastomers, styrene block copolymers, mica, and additives were dry blended in accordance with the compositions reported in tables 2-3 and injection molded. The properties of the compositions were measured as summarized in Tables 2-3 as well. The measurements of the properties of the components and compositions were performed as follows:

[0081] • MFI was measured according to ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

[0082] • Charpy impact strength was measured according to ISO 179-1eA (II) (2010) at 23°C. • Tensile modulus was measured according to ISO 5272(1 A) (2012) at 23°C.

[0083] • Flexural modulus was measured according to ISO 178 (2010) at 23°C.

[0084] • Haze and Transmittance were measured by ASTM D1003A at 23°C. 24POLY0089-WO-ORD 12 Table 2.

[0085] As can be seen from table 2, the use of different amounts of various types of ethylene-based elastomers and styrene-based block copolymers in a PP homopolymer matrix brings about the advantage of increasing the Charpy impact strength substantively, however, the transmittance is greatly reduced. For applications in need of an excellent impact strength and transmittance at the same time, such solutions are not idea. The desired impact strength is at least 20 kJ / m2, preferably at least 30 kJ / m2, and the transmittance is at least 60%, preferably at least 65%.

[0086] 24POLY0089-WO-ORD 13 Table 3.

[0087] As can be seen from E1 , the use of a suitable amount of styrene-based block copolymer with a PS content of 30% achieved an improved Charpy impact strength and transmittance both, as opposed to CE9 with the same amount of styrene block copolymer with a PS content of 12.4% but insufficient in transmittance, and CE10 with a PS content of 19.2% but insufficient in impact strength. CE6 provides a further comparison in which 15 wt% of a styrene bock copolymer with a PS content of 21% brought about inferior impact strength and transmittance at the same time.

[0088] As revealed by E2-E4 in comparison with E1, further use of mica as an inorganic filler provides a substantive improvement in tensile modulus and flexural modulus, while mica produced by a wet method achieves the best balance between impact strength, tensile modulus, flexural modulus, and transmittance, as desired by the intended applications of the present invention.

Claims

24POLY0089-WO-ORD 14CLAIMS1. A polypropylene composition, based on a total weight thereof, comprising:(A) 50-82 wt% of a polypropylene which is a propylene homopolymer or a propylene copolymer consisting of at least 90 wt% of propylene monomer units and at most 10 wt% of ethylene monomer units and / or a-olefin monomer units having 4 to 10 carbon atoms;(B) at most 5 wt% of an elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms; and(C) at least 18 wt% of a block copolymer comprising a terminal block comprising styrene or alpha- methyl styrene, with a polystyrene content of at least 22 wt%.

2. The polypropylene composition of any of the preceding claims, wherein the (A) polypropylene, preferably a propylene homopolymer, has a density of 0.870-0.950 g / cm3, and / or a melt flow rate of 10 to 100 dg / min, for example 15 to 60 dg / min, measured in accordance with ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

3. The polypropylene composition of any of the preceding claims, wherein the (B) elastomer, preferably a copolymer of ethylene and octene or a copolymer of ethylene and butylene, has a density of 0.850-0.950 g / cm3, and / or a melt flow rate of 0.1 to 10 dg / min, for example 1 to 5 dg / min, measured in accordance with ASTM D1238 using a 2.16 kg weight and at a temperature of 190 °C.

4. The polypropylene composition of any of the preceding claims, wherein the amount of the (B) elastomer is at most 1 wt%, preferably 0 wt%.

5. The polypropylene composition of the preceding claim, wherein the (C) block copolymer has a polystyrene content of 25 to 40 wt%, preferably 28 to 35 wt%.

6. The polypropylene composition of the preceding claim, wherein the amount of the (C) block copolymer is 20 to 40 wt%, preferably 22 to 30 wt%.

7. The polypropylene composition of any of the preceding claims, further comprising:(D) 0.1-20 wt%, preferably 5-15 wt%, more preferably 8-12 wt%, of an inorganic filler, which comprises or consists of mica.

8. The polypropylene composition of claim 9, wherein the mica is produced by a wet method comprising the step of grinding coarse mica in the presence of a liquid media, such as water.

9. The polypropylene composition of any of the preceding claims, wherein the mica has a thin layer thickness of less than 1 pm, preferably 200-700 nm, and / or a D50 particle size of 5-50 pm, preferably 10-35 pm.24POLY0089-WO-ORD 1510. The polypropylene composition of any of the preceding claims, wherein the mica has a fluorine content of at least 5 wt%.

11. The polypropylene composition of any of the preceding claims, further comprising(E) 0.1-10 wt% of additives.

12. The polypropylene composition of any of the preceding claims, having a transmittance, measured in accordance with ASTM D1003A at 23°C, of at least 60%, preferably at least 65%, more preferably at least 70%, and at most 90% and a Charpy impact strength, measured in accordance with ISO179 / 1eA (II) at 23°C, of at least 20 kJ / m2, preferably at least 25 kJ / m2, more preferably at least 30 kJ / m2, and at most 50 kJ / m2.

13. The polypropylene composition of any of the preceding claims, having a tensile modulus, measured according to ISO 527 2(1A) (2012) at 23°C, of at least 1400 Mpa and / or a flexural modulus, measured according to ISO 178 (2010) at 23°C, of at least 1400 Mpa.

14. A process for preparing the polypropylene composition of any of the preceding claims, comprising melt-mixing the components (A), optional (B), (C), optional (D) and optional (E).

15. An article comprising the composition according to any one of claims 1-13, which is an automotive exterior or interior part.

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