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) 60-85 wt% of a polypropylene which is a propylene homopolymer or a propylene copolymer with at most 1.5 wt% of ethylene monomer units and / or α-olefin monomer units having 4 to 10 carbon atoms; (B) 5-30 wt% of a first elastomer of ethylene and α-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of 0-3%, and (C) 0.1-20 wt% of a second elastomer of ethylene and α-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of above 3% to 10%.

Description

[0001] POLYPROPYLENE COMPOSITION

[0002] The present invention relates to a polypropylene composition, a method for preparing the same, and an article comprising such a polyolefin composition.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] In one aspect, the present invention provides a polypropylene composition comprising:

[0007] (A) 60-85 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 1.5 wt% of ethylene monomer units and / or a-olefin monomer units having 4 to 10 carbon atoms;

[0008] (B) 5-30 wt% of a first elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of 0-3%,

[0009] Dev = [(density of polypropylene)-(density of elastomer) ] / (density of polypropylene)*100%,

[0010] (C) 0.1-20 wt% of a second elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of above 3% to 10%.

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

[0012] (D) 0.1-10 wt% of a block copolymer comprising a terminal block comprising styrene or alpha- methyl styrene, with a polystyrene content of at most 25 wt%. The polypropylene composition of the present invention optionally comprises: (E) 0.1-10 wt% of additives.

[0013] The composition according to the invention comprises a polypropylene (A), in other words, a propylene-based polymer.

[0014] The propylene-based polymer may be a propylene homopolymer or a propylene copolymer with at most 1.5 wt% of comonomer units, such as 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.

[0015] The propylene copolymer with at most 1.5 wt% of comonomer units is in particular a minirandom propylene copolymer.

[0016] In an embodiment, the propylene-based polymer (A) is a mini-random propylene-ethylene copolymer consisting of 98.5 to 99.9 wt% of propylene monomer units and 0.1 to 1.5 wt% of ethylene monomer units. A mini-random copolymer with a low comonomer content retains a good stiffness and leads to a good mechanical property balance.

[0017] 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.

[0018] 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.

[0019] In one embodiment, the amount of the propylene-based polymer (A) in the composition is 60 to 85 wt%, for example 65 to 82 wt% or 70 to 80 wt%, with respect to the total composition.

[0020] It will be appreciated that the propylene-based polymer (A), which is a propylene homopolymer or a random propylene copolymer with at most 1.5 wt% of comonomer units, is not a 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 W02014044680. 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.

[0021] The use of the propylene-based polymer (A), which is a propylene homopolymer or a minirandom propylene copolymer, is more advantageous than the use of a heterophasic propylene copolymer with respect to the optical performance, specifically with a lower haze.

[0022] 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.

[0023] (B) First Elastomer

[0024] The composition according to the invention comprises a first elastomer (B) of ethylene and a- olefin comonomer having 4 to 10 carbon atoms.

[0025] The first elastomer has a density deviation Dev of 0-3%, in which Dev is calculated as follows: Dev = [(density of polypropylene)-(density of elastomer)] / (density of polypropylene)*100%. For example, when the polypropylene (A) has a density of 0.900 g / cm3, and the first elastomer (B) has a density of 0.890 g / cm3, the Dev of the first elastomer (B) is (0.900-0.890) / 0.900*100% = 1.1%.

[0026] In one embodiment, Dev of the first elastomer (B) is 0-3%, for example, 0-2%, or 0-1%.

[0027] In one embodiment, the (B) first 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.

[0028] In one embodiment, the (B) first elastomer has a density of 0.877-0.950 g / cm3, for example, 0.880-0.900 g / cm3, measured in accordance with ASTM D1505.

[0029] In one embodiment, the (B) first 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.

[0030] In one embodiment, the amount of the (B) first elastomer in the composition is 5 to 30 wt%, for example 8 to 25 wt%, 10 to 20 wt%, or 12 to 16 wt%, with respect to the total composition (100 wt%).

[0031] In one embodiment, the total of (A) and (B) 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.

[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] (C) Second Elastomer

[0034] The composition according to the invention may comprise a second elastomer (C) of ethylene and a-olefin comonomer having 4 to 10 carbon atoms. The second elastomer (C) and the first elastomer (B) may be the same type or different types. The second elastomer has a density deviation Dev of above 3% to 10%, in which Dev is calculated as follows:

[0035] Dev = [(density of polypropylene)-(density of elastomer)] / (density of polypropylene)*100%. For example, when the polypropylene (A) has a density of 0.900 g / cm3, and the second elastomer (C) has a density of 0.860 g / cm3, the Dev of the first elastomer (B) is (0.900-0.860) / 0.900*100% = 4.4%.

[0036] In one embodiment, Dev of the second elastomer (C) is 3.01-8%, for example, 3.01-6%, or 3.01-5%, such as 4%.

[0037] In one embodiment, the (C) second elastomer is a copolymer of ethylene and octene, preferably 1-octene. In one embodiment, the (C) second elastomer is a copolymer of ethylene and butylene, preferably 1 -butylene.

[0038] In one embodiment, the (C) second elastomer has a density of 0.850-0.875 g / cm3, for example, 0.860-0.870 g / cm3, measured in accordance with ASTM D1505.

[0039] In one embodiment, the (C) second 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.

[0040] In one embodiment, the amount of the (C) second elastomer in the composition is 0.1 to 20 wt%, for example 8 to 18 wt%, or 9 to 16 wt%, with respect to the total composition (100 wt%).

[0041] In one embodiment, the total of (A), (B) and (C) 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.

[0042] In one embodiment, the amount of an elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev above 5.5% is at most 2 wt%, for example at most 1wt%, or at most 0.1wt%.

[0043] In the context of the present invention, the polypropylene composition may also comprise two or more second elastomers (C), each of which and / or a combination of which meets the definitions above. (D) Styrene block copolymer

[0044] The composition according to the invention may comprise a styrene block copolymer (D).

[0045] 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.

[0046] 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).

[0047] Typically, the block copolymer (D) has a melt flow rate of 1 to 10 dg / min, for example 2 to 5 dg / min as measured according to ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

[0048] In the context of the present invention, the amount of styrene or alpha-methyl styrene in the block copolymer (D) is at most 25 wt%, preferably at most 21 wt%, more preferably at most 18 wt%, for example 10 to 16 wt% or 12 to 15 wt%, based on the block copolymer.

[0049] The block copolymer (D) 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.

[0050] In one embodiment, the amount of the block copolymer (D) in the composition is 0.1 to 10 wt%, for example 1 to 5 wt% with respect to the total composition.

[0051] In one embodiment, the total of (B), (C) and (D) is 20-30 wt%.

[0052] In one embodiment, the total of (A), (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.

[0053] In the context of the present invention, the polypropylene composition may also comprise two or more block copolymers (D), each of which and / or a combination of which meets the definitions above.

[0054] (E) Additives

[0055] The composition may further comprise optional components different from the polypropylene (A), the first elastomer (B), the second elastomer (C) and the styrene block copolymer (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).

[0056] 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.

[0057] 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.

[0058] Process

[0059] 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), 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.

[0060] 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.

[0061] 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.

[0062] 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 55%, preferably at least 60%, more preferably at least 65%, and at most 90%.

[0063] In one embodiment, the polypropylene composition of the present invention has a 100% YD curve type as measured in accordance with ISO 6603-2 at -10°C. In one embodiment, the polypropylene composition of the present invention has a Charpy impact strength above 20 kJ / m2, as measured in accordance with ISO 179-1eA (II) (2010) at 23°C.

[0064] In one embodiment, the polypropylene composition of the present invention has a flexural modulus above 1100 Mpa, preferably above 1150 Mpa, more preferably above 1200 Mpa, even more preferably above 1300 Mpa, as measured in accordance with ISO 178 (II) at 23°C.

[0065] Further aspects

[0066] 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.

[0067] The invention further relates to use of the composition according to the invention for automotive exterior parts and / or automotive interior parts.

[0068] 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.

[0069] 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 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.

[0070] The invention is now elucidated by way of the following examples, without however being limited thereto.

[0071] Experiments

[0072] Components used in the experiments are summarized in Table 1. In all tables, “%” means “wt%”, unless indicated otherwise.

[0073] Table 1. Components

[0074] The PP homopolymer, elastomers, styrene block copolymers and additives were dry blended and injection molded. The properties of the compositions were measured as summarized in Tables 2-3.

[0075] The measurements of the properties of the components and compositions were performed as follows:

[0076] • Density was measured according to ASTM D 1505.

[0077] • MFR was measured according to ISO 1133 using a 2.16 kg weight and at a temperature of 230 °C.

[0078] • Charpy impact strength was measured according to ISO 179-1eA (II) (2010) at 23°C and -20°C.

[0079] • Haze and Transmittance were measured by ASTM D1003A at 23°C.

[0080] • Flexural modulus was measured by in accordance with ISO 178 (II) at 23°C.

[0081] MAI (Multiaxial impact)

[0082] Multiaxial impact is also termed in Dutch as val energie meting (VEM). The MAI / VEM test was conducted respectively on five samples according to ISO 6603-2 at -10°C.

[0083] The ISO 6603-2 curve type evaluation is a common method to characterize the force / deflection data obtained by puncture test experiments. It provides four typical types of curve progression that can usually be observed during data evaluation. In general, these range from ductile to brittle and focus on information like yielding, crack initiation and crack propagation. Obtained data was divided into four break types summarized below:

[0084] YD: Yielding followed by deep drawing (Ductile) - most preferred

[0085] YS: Yielding followed by stable cracking (Semi-ductile) - preferred YU: Yielding followed by unstable cracking (Semi-brittle) - least preferred

[0086] NY: No yielding (Brittle) - not preferred.

[0087] The percentage of YD samples in the five samples tested was reported.

[0088] Table 2. Compositions and properties

[0089] As can be seen from a comparison between comparative example 1 (CE1) and CE2, CE3 and CE7, the addition of polyolefin elastomers, although improves Charpy impact strength, drastically deteriorates transmittance of the composition, and the reduction of transmittance is in positive correlation with the density Dev of the elastomers. From a comparison between CE3, E4, E5, E6, E7 and CE8, it can be seen that a polypropylene composition meeting the requirements of the present invention achieves a high flexural modulus of above 1100 Mpa, and an improved balance between impact strength and transmittance, especially a 100% VEM test result and a transmittance above 55, which meets industrial needs for related applications.

[0090] Table 3. Compositions and properties As can be seen from CE9-CE12, the sole use of various styrene block copolymers seriously deteriorates ductility of the PP composition, but the use of such copolymers in addition to the PP compositions of the present invention, as indicated in E13-E15, achieves a 100% YD curve type, representing a ductile VEM impact performance, and a transmittance above 60% at the same time, in the meanwhile, the flexural modulus is at an acceptable level of above 1100 Mpa. The Charpy impact strength is substantively improved if the styrene block copolymers have restricted PS content as specified in the present invention.

Claims

Claims:

1. A polypropylene composition, based on a total weight thereof, comprising:(A) 60-85 wt% of a polypropylene which is a propylene homopolymer or a propylene copolymer with at most 1.5 wt% of ethylene monomer units and / or a-olefin monomer units having 4 to 10 carbon atoms, the polypropylene has a density of 0.870-0.950 g / cm3;(B) 5-30 wt% of a first elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of 0-3%,Dev = [(density of polypropylene)-(density of elastomer) ] / (density of polypropylene)*100%,(C) 0.1-20 wt% of a second elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev of above 3% to 10%.

2. The polypropylene composition of any of the preceding claims, wherein the (A) polypropylene is a propylene homopolymer.

3. The polypropylene composition of any of the preceding claims, wherein the (A) polypropylene has a density of 0.900-0.910 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.

4. The polypropylene composition of any of the preceding claims, wherein the (B) first elastomer is a copolymer of ethylene and octene or a copolymer of ethylene and butylene.

5. The polypropylene composition of any of the preceding claims, wherein the (B) first elastomer has a density of 0.877-0.950 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.

6. The polypropylene composition of any of the preceding claims, wherein the (C) second elastomer is a copolymer of ethylene and octene or a copolymer of ethylene and butylene.

7. The polypropylene composition of any of the preceding claims, wherein the (C) second elastomer has a density of 0.850-0.875 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.

8. The polypropylene composition of claim 1 , further comprising:(D) 0.1-10 wt% of a block copolymer comprising a terminal block comprising styrene or alpha- methyl styrene, with a polystyrene content of at most 25 wt%.

9. The polypropylene composition of the preceding claim, wherein the (D) block copolymer has a polystyrene content of at most 18 wt%, preferably at most 15 wt%, and / or the (D) block copolymer is SEBS.

10. The polypropylene composition of any of the preceding claims, wherein the amount of (A) is 70-80 wt% and the sum of (B), (C) and (D) is 20-30 wt%.

11. The polypropylene composition of any of the preceding claims, wherein the amount of an elastomer of ethylene and a-olefin comonomer having 4 to 10 carbon atoms with a density deviation Dev above 5.5% is at most 2 wt%.

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

13. The polypropylene composition of any of the preceding claims, having a transmittance, measured in accordance with ASTM D1003A at 23°C, of at least 55%, preferably at least 60%, more preferably at least 65%, and at most 90%.

14. A process for preparing the polypropylene composition of any of the preceding claims, comprising melt-mixing the components (A), (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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