Polypropylene composition suitable for healthcare applications

Abstract

The present invention relates to a polypropylene composition suitable for healthcare applications comprising from 87.5 to 100.0 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer, wherein the polypropylene composition in a first aspect has a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, an ethylene content of from 2.5 to 4.0 wt.-%, content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, and a zero shear viscosity at 200°C, eta0, of from 925 to 1400 Pa·s, the polypropylene composition in a second aspect has an ethylene content of from 2.5 to 4.0 wt.-%, a zero shear viscosity at 200°C, eta0, of from 925 to 1400 Pa·s, a polydispersity index at 200°C, PDI, of from 2.5 to 5.5, a flexural modulus of from 950 to 1450 MPa, and an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, a process for producing said polypropylene composition, an article comprising said polypropylene composition and the use of said polypropylene composition for the production of an injection moulded article for healthcare applications.

Description

[0001] Polypropylene composition suitable for healthcare applications

[0002] The present invention relates to a polypropylene composition suitable for healthcare applications comprising from 87.5 to 100.0 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer, wherein the polypropylene composition in a first aspect has a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, an ethylene content of from 2.5 to 4.0 wt.-%, content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, and a zero shear viscosity at 200°C, etao, of from 875 to 1400 Pa s, the polypropylene composition in a second aspect has an ethylene content of from 2.5 to 4.0 wt.-%, a zero shear viscosity at 200°C, etao, of from 875 to 1400 Pa s, a polydispersity index at 200°C, PDI, of from 2.5 to 5.5, a flexural modulus of from 950 to 1450 MPa, and an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, a process for producing said polypropylene composition, an article comprising said polypropylene composition and the use of said polypropylene composition for the production of an injection moulded article for healthcare applications.

[0003] Technical background

[0004] Polypropylene is used in many applications, like automotive applications, packaging applications or healthcare applications.

[0005] For moulding applications processability is a key feature together with softness and toughness.

[0006] Healthcare applications, especially moulded healthcare applications, such as two-parts syringes or three-parts syringes require a material which is able to provide a faster crystallization behaviour and an improved flowability in order to reduce the production cycle and enable a cost efficient production. In most of the cases, the better processability and advanced flowability of the material comes at the expenses of mechanical properties, which are negatively affected. However, the stiffness is equally important in moulding process, since the material requires a good flexural modulus to guarantee an efficient de-gating from the mould. At the same time, the final article is required to have good impact properties for the final application. The materials currently in market are not fulfilling all the requirement at the same time.

[0007] WO 2021 / 043784 A1 discloses a healthcare article comprising a phthalate-free random propylene-ethylene copolymer, which shows a good irradiation resistance. Mechanical properties and impact properties are not disclosed.

[0008] EP 3263613 A1 discloses a composition of hydrogenated block copolymer made from mixture of isoprene and butadiene. This is used in medical devices (in particular moulded as a tube shape), where a high flexibility is required (resistance to bend). JP 4928741 B2 discloses a film or laminated film based on a polypropylene resin with a good flexibility and balance of transparency, blocking resistance, tear strength, impact resistance, heat resistance, low temperature heat sealability, and bending whitening resistance. The film can be used for medical packaging. The polypropylene resin, however, does not exhibit sufficient processability and flowability for injection moulding applications in the healthcare field.

[0009] Thus, there is a need in the art for new polymer compositions, which show an improved balance of properties in regard of processability, flowability, mechanical properties and impact properties for the production of injection moulded healthcare articles.

[0010] In the present invention it has surprisingly been found that by carefully designing a propylene-ethylene random copolymer, a polypropylene composition can be provided which shows an improved balance of properties in regard of processability, flowability, mechanical properties and impact properties, which allows for injection moulded healthcare applications such as two-parts syringes or three-parts syringes.

[0011] Summary of the invention

[0012] In a first aspect the present invention relates to a polypropylene composition comprising from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer,

[0013] wherein the polypropylene composition has

[0014] • a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, preferably from 24.0 to 36.0 g / 10 min, more preferably from 25.0 to 35.0 g / 10 min, determined according to ISO 1133 at230°C and 2.16 kg;

[0015] • an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy;

[0016] • a content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, preferably from 3.4 to 7.6 wt.-%, more preferably from 3.8 to 7.2 wt.-%, based on the total weight of the polypropylene composition and determined according to ISO 16152; and a zero shear viscosity at 200°C, etao, of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10.

[0017] In a second aspect the present invention relates to a polypropylene composition suitable for healthcare applications comprising from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer,

[0018] wherein the polypropylene composition has

[0019] • an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy;

[0020] • a zero shear viscosity, etao, of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C;

[0021] • a polydispersity index PDI of from 2.5 to 5.5, preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C;

[0022] • a flexural modulus of from 950 to 1450 MPa, preferably from 1000 to 1400 MPa, more preferably from 1050 to 1350 MPa, determined according to ISO 178 on injection moulded specimens of 80x10x4 mm3prepared in accordance with ISO 294-1; and

[0023] • an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, more preferably from 1.02 to 1.35, still more preferably from 1.05 to 1.30,

[0024] wherein the Enhanced Medical MAterial (EMMA) index is calculated according to formula (III)

[0025]

[0026] wherein

[0027] C2 is the ethylene comonomer content in the polypropylene composition in wt.-%; Flex modulus is the flexural modulus of the polypropylene composition in MPa; a is a constant with the value 4200 (MPa wt.-%)'1;

[0028] PDI is the polydispersity index at 200°C; etao is the zero shear viscosity at 200°C in Pa s;

[0029] Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

[0030] In a third aspect the present invention relates to a process for producing the polypropylene composition in all aspects as described above or below, comprising the following steps:

[0031] a) polymerizing propylene monomer units and optionally ethylene comonomer units in a first polymerization reactor in the presence of a Ziegler-Natta catalyst system to produce a first polymerization mixture comprising a propylene homopolymer fraction or a propylene-ethylene random copolymer fraction and the Ziegler-Natta catalyst system, wherein the first polymerization reactor is preferably a slurry reactor, more preferably a loop reactor;

[0032] b) withdrawing said first polymerization mixture from the first polymerization reactor and transferring the first polymerization mixture into a second polymerization reactor; preferably a gas phase reactor;

[0033] c) polymerizing propylene monomer units and ethylene comonomer units in said second polymerization reactor in the presence of said Ziegler-Natta catalyst system to produce a second polymerization mixture comprising a propylene-ethylene random copolymer fraction, the propylene homopolymer fraction or the propylene- ethylene random copolymer fraction and the Ziegler-Natta catalyst system; a) withdrawing said second polymerization mixture from said second polymerization reactor and obtaining the propylene-ethylene random copolymer; and

[0034] d) compounding the propylene-ethylene random copolymer optionally with the addition of additives to form the polypropylene composition.

[0035] In a fourth aspect the present invention relates to an article comprising the polypropylene composition in all aspects as described above or below.

[0036] In a fifth aspect the present invention relates to the use of the polypropylene composition in all aspects as described above or below for the production of an injection moulded article for healthcare applications.

[0037] Definitions A propylene homopolymer is a polymer, which essentially consists of propylene monomer units. Due to impurities especially during commercial polymerization processes a propylene homopolymer can comprise up to 0.1 mol-% comonomer units, preferably up to 0.05 mol-% comonomer units and most preferably up to 0.01 mol-% comonomer units.

[0038] A propylene random copolymer is a copolymer of propylene monomer units and comonomer units in which the comonomer units are distributed randomly over the polypropylene chain. Thereby, a propylene random copolymer does not contain an elastomeric polymer phase dispersed therein.

[0039] Usually, a propylene polymer comprising at least two propylene polymer fractions (components), which have been produced under different polymerization conditions resulting in different (weight average) molecular weights and / or different comonomer contents for the fractions, preferably produced by polymerizing in multiple polymerization stages with different polymerization conditions, is referred to as “multimodal”. The prefix “multi” relates to the number of different polymer fractions the propylene polymer is consisting of. As an example of multimodal propylene polymer, a propylene polymer consisting of two fractions only is called “bimodal”, whereas a propylene polymer consisting of three fractions only is called “trimodal”.

[0040] A unimodal propylene polymer only consists of one fraction.

[0041] Thereby, the term “different” means that the propylene polymer fractions differ from each other in at least one property, preferably in the weight average molecular weight - which can also be measured in different melt flow rates of the fractions - or comonomer content or both.

[0042] Figures

[0043] Figure 1 shows an example of Time Temperature Superposition from the data of the storage and loss module (G', G"(w)) made by using IRIS Rheo Hub 2008 needed for the determination of the activation energy Ea. Figure 2 shows the plot of the mechanical properties index over processability index of the polypropylene compositions of examples IE1 , CE1 , CE2 and CE3 thereby visualizing the Enhanced Medical MAterial (EMMA) index.

[0044] Detailed description of the invention

[0045] Polypropylene composition

[0046] In a first aspect the present invention relates to a polypropylene composition.

[0047] In the following the properties of the polypropylene composition of said first aspect are described:

[0048] The polypropylene composition comprises the propylene-ethylene random copolymer in an amount of from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition.

[0049] The polypropylene composition can further comprise polymeric components, which are different from the propylene-ethylene random copolymer, in an amount of preferably 0.0 to 5.0 wt.-% based on the total weight of the polypropylene composition.

[0050] In a preferred embodiment the polymeric components of the polypropylene composition consist of the propylene-ethylene random copolymer.

[0051] Besides these polymeric components the polypropylene composition can comprise one or more additives in an amount of from 0.0 up to 5.0 wt.-%, such as from 0.1 to 4.7 wt.-%, preferably from 0.2 to 4.5 wt.-%, based on the total weight of the polypropylene composition. The one or more additives are preferably selected from acid scavengers, antioxidants, processing aids, alpha nucleating agents, beta nucleating agents, etc. Such additives are commercially available and for example described in “Plastic Additives Handbook”, 6thedition 2009 of Hans Zweifel (pages 1141 to 1190).

[0052] Usually, these additives are added in quantities of 1.0 to 50000 ppm for each single component. The one or more additives can be added to the polymeric components in a blending step.

[0053] Thereby, the one or more additives can be added to the polymeric components in form of master batches in which one or more additives are blended with a carrier polymer in concentrated amounts. Any optional carrier polymer is calculated to the amount of additives, based on the total weight of the propylene copolymer composition.

[0054] The polypropylene composition has a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, preferably from 24.0 to 36.0 g / 10 min, more preferably from 25.0 to 35.0 g / 10 min, determined according to ISO 1133 at 230°C and 2.16 kg.

[0055] Further, the polypropylene composition has an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy.

[0056] It is preferred that the monomer units of the polymeric components of the polypropylene composition, preferably of the propylene-ethylene random copolymer consist of propylene monomer units and ethylene comonomer units.

[0057] Consequently, it is preferred that the polypropylene composition has a propylene content of from 96.0 to 97.5 wt.-%, preferably from 96.1 to 97.4 wt.-%, more preferably from 96.2 to 97.3 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy.

[0058] Preferably the amount of propylene monomer units and ethylene comonomer units make up 100 wt.-% of the polypropylene composition, or the propylene-ethylene random copolymer.

[0059] Still further, the polypropylene composition has a content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, preferably from 3.4 to 7.6 wt.-%, more preferably from 3.8 to 7.2 wt.-%, based on the total weight of the polypropylene composition and determined according to ISO 16152. Furthermore, the polypropylene composition has a zero shear viscosity etao of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

[0060] Additionally, the polypropylene composition preferably has a polydispersity index PDI of from 2.5 to 5.5, preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

[0061] Still further, the polypropylene composition preferably has a flexural modulus of from 950 to 1450 MPa, more preferably from 1000 to 1400 MPa, still more preferably from 1050 to 1350 MPa, determined according to ISO 178 on injection moulded specimens of 80x10x4 mm3prepared in accordance with ISO 294-1.

[0062] The high melt flow rate MFR2 is a measure for a good flowability of the polypropylene composition, which ensures that upon injection moulding the mould is properly filled. The polypropylene composition thus qualifies for injection moulding applications.

[0063] The flexural modulus is an indication fora good stiffness. Stiffness important to ensure a proper and consistent de-gating during the final moulding of the material, i.e. injection moulding application.

[0064] The rather high ethylene comonomer content results in an increase of toughness, which enhances the impact properties of the polypropylene composition.

[0065] Further, the moderate zero shear viscosity and the rather broad polydispersity index are rheological properties, which are an indication fora good processability of the polypropylene composition.

[0066] The above described properties can be put into relations to each other which illustrate the improved balance of properties.

[0067] Thus it is preferred that the polypropylene composition has a mechanical properties index of from 0.85 to 1.50, more preferably from 0.87 to 1.40, still more preferably from 0.90 to 1.35.

[0068] The mechanical properties index is calculated according to formula (I) Mechanical properties index = (C2X Flex modulus / a)3(I) wherein

[0069] C2 is the ethylene comonomer content in the polypropylene composition in wt.-%;

[0070] Flex modulus is the flexural modulus of the polypropylene composition in MPa; and a is a constant with the value 4200 (MPa wt.-%)’1.

[0071] The mechanical properties index thus shows the relation of toughness and stiffness.

[0072] Further, it is preferred that the polypropylene composition has a processability index of from 0.68 to 1.35, more preferably from 0.72 to 1.30, still more preferably from 0. 75 to 1.25.

[0073] The processability index is calculated according to formula (II)

[0074]

[0075] wherein

[0076] PDI is the polydispersity index at 200°C;

[0077] etao is the zero shear viscosity at 200°C in Pa s;

[0078] Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

[0079] The processability index thus shows an improved processability attributed to the rheological properties - i.e. the higher polydispersity index and the lower zero shear viscosity - and the low sensitivity to temperature variation during processing attributed to the lower activation energy.

[0080] Still further, it is preferred that the polypropylene composition has an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, more preferably from 1.02 to 1.35, still more preferably from 1.05 to 1.30.

[0081] The Enhanced Medical MAterial (EMMA) index is calculated according to formula (III)

[0082]

[0083] wherein

[0084] C2 is the ethylene comonomer content in the polypropylene composition in wt.-%;

[0085] Flex modulus is the flexural modulus of the polypropylene composition in MPa;

[0086] a is a constant with the value 4200 (MPa wt.-%)'1;

[0087] PDI is the polydispersity index at 200°C;

[0088] etao is the zero shear viscosity at 200°C in Pa s; Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

[0089] The Enhanced Medical MAterial (EMMA) index is the product of the mechanical properties index and the processability index and thus it reflects the balance of properties in regard of stiffness, toughness and processability.

[0090] As already discussed above in the technical background section, an improvement in mechanical properties usually results in impaired processability and vice versa.

[0091] In the present invention a polypropylene composition has been developed which shows excellent mechanical properties and at the same time surprisingly maintains good processability, which results in an EMMA index, which is preferably at least 1.00.

[0092] The propylene-ethylene random copolymer preferably comprises at least two fractions, which differ in at least one property, such as the comonomer distribution or the molecular weight.

[0093] Thus, the propylene-ethylene random copolymer preferably is multimodal, more preferably bimodal.

[0094] The propylene-ethylene random copolymer preferably comprises a propylene homopolymer fraction and a propylene-ethylene random copolymer fraction.

[0095] Consequently, the propylene-ethylene random copolymer preferably is bimodal in regard of the comonomer distribution.

[0096] It is preferred that the weight ratio of the propylene homopolymer fraction to the propylene-ethylene random copolymer fraction propylene-ethylene random copolymer in the is from 65 : 35 to 35 : 65, more preferably 60 : 40 to 40 :60, still more preferably from 55 : 45 to 45 : 55.

[0097] Since the polypropylene composition comprises at least 87.5 wt.-% of the propylene-ethylene random copolymer it is preferred that the propylene-ethylene random copolymer exhibits the comparable properties as the polypropylene composition.

[0098] It is preferred that the propylene-ethylene random copolymer independently has a melt flow rate MFR2, an ethylene content, a content of xylene cold solubles (XCS) fraction, a zero shear viscosity qo, a rheological polydispersity index PDI, and / or a flexural modulus in the same range as the polypropylene composition.

[0099] In a second aspect the present invention relates to a polypropylene composition.

[0100] In the following the properties of the polypropylene composition of said first aspect are described:

[0101] The polypropylene composition comprises the propylene-ethylene random copolymer in an amount of from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition.

[0102] The polypropylene composition can further comprise polymeric components, which are different from the propylene-ethylene random copolymer, in an amount of preferably 0.0 to 5.0 wt.-% based on the total weight of the polypropylene composition.

[0103] In a preferred embodiment the polymeric components of the polypropylene composition consist of the propylene-ethylene random copolymer.

[0104] Besides these polymeric components the polypropylene composition can comprise one or more additives in an amount of from 0.0 up to 5.0 wt.-%, such as from 0.1 to 4.7 wt.-%, preferably from 0.2 to 4.5 wt.-%, based on the total weight of the polypropylene composition. The one or more additives are preferably selected from acid scavengers, antioxidants, processing aids, alpha nucleating agents, beta nucleating agents, etc. Such additives are commercially available and for example described in “Plastic Additives Handbook”, 6thedition 2009 of Hans Zweifel (pages 1141 to 1190).

[0105] Usually, these additives are added in quantities of 1.0 to 50000 ppm for each single component.

[0106] The one or more additives can be added to the polymeric components in a blending step.

[0107] Thereby, the one or more additives can be added to the polymeric components in form of master batches in which one or more additives are blended with a carrier polymer in concentrated amounts. Any optional carrier polymer is calculated to the amount of additives, based on the total weight of the propylene copolymer composition.

[0108] The polypropylene composition has an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy.

[0109] It is preferred that the monomer units of the polymeric components of the polypropylene composition, preferably of the propylene-ethylene random copolymer consist of propylene monomer units and ethylene comonomer units.

[0110] Consequently, it is preferred that the polypropylene composition has a propylene content of from 96.0 to 97.5 wt.-%, preferably from 96.1 to 97.4 wt.-%, more preferably from 96.2 to 97.3 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy.

[0111] Preferably the amount of propylene monomer units and ethylene comonomer units make up 100 wt.-% of the polypropylene composition, or the propylene-ethylene random copolymer.

[0112] Furthermore, the polypropylene composition has a zero shear viscosity etao of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

[0113] Additionally, the polypropylene composition preferably has a polydispersity index PDI of from 2.5 to 5.5, preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

[0114] Further, the polypropylene composition preferably has a flexural modulus of from 950 to 1450 MPa, more preferably from 1000 to 1400 MPa, still more preferably from 1050 to 1350 MPa, determined according to ISO 178 on injection moulded specimens of 80x10x4 mm3prepared in accordance with ISO 294-1. It is preferred that the polypropylene composition has a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, more preferably from 24.0 to 36.0 g / 10 min, still more preferably from 25.0 to 35.0 g / 10 min, determined according to ISO 1133 at 230°C and 2.16 kg.

[0115] Still further, the polypropylene composition preferably has a content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, more preferably from 3.4 to 7.6 wt.-%, still more preferably from 3.8 to 7.2 wt.-%, based on the total weight of the polypropylene composition and determined according to ISO 16152.

[0116] The flexural modulus is an indication fora good stiffness. Stiffness important to ensure a proper and consistent de-gating during the final moulding of the material, i.e. injection moulding application.

[0117] The rather high ethylene comonomer content results in an increase of toughness, which enhances the impact properties of the polypropylene composition.

[0118] Further, the moderate zero shear viscosity and the rather broad polydispersity index are rheological properties, which are an indication fora good processability of the polypropylene composition.

[0119] The high melt flow rate MFR2 is a measure for a good flowability of the polypropylene composition, which ensures that upon injection moulding the mould is properly filled. The polypropylene composition thus qualifies for injection moulding applications.

[0120] The above described properties can be put into relations to each other which illustrate the improved balance of properties.

[0121] Thus it is preferred that the polypropylene composition has a mechanical properties index of from 0.85 to 1.50, more preferably from 0.87 to 1.40, still more preferably from 0.90 to 1.35.

[0122] The mechanical properties index is calculated according to formula (I) Mechanical properties index = (C2X Flex modulus / a) ’ (I) wherein

[0123] C2 is the ethylene comonomer content in the polypropylene composition in wt.-%;

[0124] Flex modulus is the flexural modulus of the polypropylene composition in MPa; and a is a constant with the value 4200 (MPa wt.-%)’1. The mechanical properties index thus shows the relation of toughness and stiffness.

[0125] Further, it is preferred that the polypropylene composition has a processability index of from 0.68 to 1.35, more preferably from 0.72 to 1.30, still more preferably from 0. 75 to 1.25.

[0126] The processability index is calculated according to formula (II)

[0127]

[0128] wherein

[0129] PDI is the polydispersity index at 200°C;

[0130] etao is the zero shear viscosity at 200°C in Pa s;

[0131] Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

[0132] The processability index thus shows an improved processability attributed to the rheological properties - i.e. the higher polydispersity index and the lower zero shear viscosity - and the low sensitivity to temperature variation during processing attributed to the lower activation energy.

[0133] The polypropylene composition is characterized by an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, more preferably from 1.02 to 1.35, still more preferably from 1.05 to 1.30.

[0134] The Enhanced Medical MAterial (EMMA) index is calculated according to formula (III)

[0135]

[0136] wherein

[0137] C2 is the ethylene comonomer content in the polypropylene composition in wt.-%; Flex modulus is the flexural modulus of the polypropylene composition in MPa;

[0138] a is a constant with the value 4200 (MPa wt.-%)'1;

[0139] PDI is the polydispersity index at 200°C;

[0140] etao is the zero shear viscosity at 200°C in Pa s;

[0141] Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

[0142] The Enhanced Medical MAterial (EMMA) index is the product of the mechanical properties index and the processability index and thus it reflects the balance of properties in regard of stiffness, toughness and processability. As already discussed above in the technical background section, an improvement in mechanical properties usually results in impaired processability and vice versa.

[0143] In the present invention a polypropylene composition has been developed which shows excellent mechanical properties and at the same time surprisingly maintains good processability, which results in an EMMA index, which is at least 1.00.

[0144] The propylene-ethylene random copolymer preferably comprises at least two fractions, which differ in at least one property, such as the comonomer distribution or the molecular weight.

[0145] Thus, the propylene-ethylene random copolymer preferably is multimodal, more preferably bimodal.

[0146] The propylene-ethylene random copolymer preferably comprises a propylene homopolymer fraction and a propylene-ethylene random copolymer fraction.

[0147] Consequently, the propylene-ethylene random copolymer preferably is bimodal in regard of the comonomer distribution.

[0148] It is preferred that the weight ratio of the propylene homopolymer fraction to the propylene-ethylene random copolymer fraction propylene-ethylene random copolymer in the is from 65 : 35 to 35 : 65, more preferably 60 : 40 to 40 :60, still more preferably from 55 : 45 to 45 : 55.

[0149] Since the polypropylene composition comprises at least 87.5 wt.-% of the propylene-ethylene random copolymer it is preferred that the propylene-ethylene random copolymer exhibits the comparable properties as the polypropylene composition.

[0150] It is preferred that the propylene-ethylene random copolymer independently has a melt flow rate MFR2, an ethylene content, a content of xylene cold solubles (XCS) fraction, a zero shear viscosity qo, a rheological polydispersity index PDI, and / or a flexural modulus in the same range as the polypropylene composition.

[0151] Process

[0152] In a second aspect the present invention relates to a process for producing the polypropylene composition of all aspects as described above or below. The propylene-ethylene random copolymer of polypropylene composition of all aspects as described above or below is produced in a sequential multistage polymerization process, i.e. in a polymerization process in which two or more polymerization reactors are connected in series. Preferably, in the sequential multistage polymerization process, two or more, such as two or three, more preferably two polymerization reactors are connected in series. The term “polymerization reactor” shall indicate that the main polymerization takes place. Thus, in case the process consists of two polymerization reactors, this definition does not exclude the option that the overall process comprises for instance a pre-polymerization step in a pre-polymerization reactor.

[0153] The propylene-ethylene random copolymer can be polymerized in the presence of a Ziegler-Natta catalyst system, in particular a high yield Ziegler-Natta catalyst system (so-called fourth and fifth generation type to differentiate from low yield, so called second generation Ziegler-Natta catalysts). A suitable Ziegler-Natta catalyst system to be employed in accordance with the present invention comprises a catalyst component, a co-catalyst component and at least one electron donor (internal and / or external electron donor, preferably at least one external donor). Preferably, the catalyst component is a Ti-Mg-based catalyst component and typically the co-catalyst is an Al-alkyl based compound. Suitable catalysts are in particular disclosed in US 5,234,879, WO 92 / 19653, WO 92 / 19658 WO 99 / 33843, WO2016 / 066446 A and WO2015 / 117948.

[0154] Suitable external donors are the known silane-based donors, such as dicyclopentyl dimethoxy silane or cyclohexyl methyldimethoxy silane.

[0155] The process comprises the following steps:

[0156] a) polymerizing propylene monomer units and optionally ethylene comonomer units in a first polymerization reactor in the presence of a Ziegler-Natta catalyst system to produce a first polymerization mixture comprising a propylene homopolymer fraction or a propylene-ethylene random copolymer fraction and the Ziegler-Natta catalyst system, wherein the first polymerization reactor is preferably a slurry reactor, more preferably a loop reactor;

[0157] b) withdrawing said first polymerization mixture from the first polymerization reactor and transferring the first polymerization mixture into a second polymerization reactor; preferably a gas phase reactor; c) polymerizing propylene monomer units and ethylene comonomer units in said second polymerization reactor in the presence of said Ziegler-Natta catalyst system to produce a second polymerization mixture comprising a propylene-ethylene random copolymer fraction, the propylene homopolymer fraction or the propyleneethylene random copolymer fraction and the Ziegler-Natta catalyst system;

[0158] d) withdrawing said second polymerization mixture from said second polymerization reactor and obtaining the propylene-ethylene random copolymer; and

[0159] e) compounding the propylene-ethylene random copolymer optionally with the addition of additives to form the polypropylene composition.

[0160] Preferably, the polymerization reactors are selected from slurry phase reactors, such as loop reactors and / or gas phase reactors such as fluidized bed reactors, more preferably from loop reactors and fluidized bed reactors.

[0161] A preferred sequential multistage polymerization process is a “loop-gas phase”-process, such as developed by Borealis A / S, Denmark (known as BORSTAR® technology) described e.g. in patent literature, such as in EP 0887379, WO 92 / 12182

[0162] WO 2004 / 000899, WO 2004 / 111095, WO 99 / 24478, WO 99 / 24479 or in WO 00 / 68315.

[0163] A further suitable slurry-gas phase process is the Spheripol® process of LyondellBasell.

[0164] It is preferred that the operating temperature in the first polymerization reactor is in the range from 62 to 85°C, more preferably in the range from 65 to 82°C, still more preferably in the range from 67 to 80°C.

[0165] Alternatively or additionally to the previous paragraph it is preferred that the operating temperature in the second polymerization reactor is in the range from 75 to 95°C, more preferably in the range from 78 to 92°C.

[0166] Typically, the pressure in the first polymerization reactor, preferably in the loop reactor (LR), is in the range from 20 to 80 bar, preferably 30 to 70 bar, like 35 to 65 bar, whereas the pressure in the second polymerization reactor, i.e. in the gas phase reactor (GPR), is in the range from 5 to 50 bar, preferably 15 to 40 bar. Preferably hydrogen is added in each polymerization reactor in order to control the molecular weight, i.e. the melt flow rate MFR2.

[0167] It is preferred that the hydrogen is added to the first polymerization reactor in step a) with a molar ratio of hydrogen to propylene monomer units H2 / C3 of from 2.5 to 15.0 mol / kmol, more preferably from 4.5 to 12.5 mol / kmol, still more preferably from 6.0 to 10.0 mol / kmol.

[0168] It is further preferred that wherein hydrogen is added to the second polymerization reactor in step c) with a molar ratio of hydrogen to propylene monomer units H2 / C3 of from 25.0 to 75.0 mol / kmol, more preferably from 35.0 to 65.0 mol / kmol, still more preferably from 40.0 to 60.0 mol / kmol.

[0169] It is preferred that ethylene comonomer units are added to the first polymerization reactor in step a) in an amount of from 0.1 to 5.0 wt.-%, more preferably from 0.5 to 4.0 wt.-%, still more preferably from 1.0 to 3.5 wt.-%, based on the total weight of monomer units introduced to the first polymerization reactor.

[0170] It is further preferred that the molar ratio of ethylene comonomer units to propylene monomer units in the second polymerization reactor in step c) is from 5.0 to 25.0 mol / kmol, more preferably from 7.5 to 22.5 mol / kmol, still more preferably from 10.0 to 20.0 mol / kmol.

[0171] The preparation of the propylene-ethylene random copolymer can comprise in addition to the (main) polymerization of the propylene-ethylene random copolymer in the at least two polymerization reactors prior thereto a pre-polymerization in a pre-polymerization reactor upstream to the first polymerization reactor.

[0172] In the pre-polymerization reactor a polypropylene is produced. The pre-polymerization is conducted in the presence of the Ziegler-Natta catalyst system. According to this embodiment, the Ziegler-Natta catalyst system is introduced to the pre-polymerization step. However, this shall not exclude the option that at a later stage for instance further co-catalyst is added in the polymerization process, for instance in the first reactor. In one embodiment, all components of the Ziegler-Natta catalyst system are only added in the pre-polymerization reactor, if a pre-polymerization is applied.

[0173] The pre-polymerization reaction is typically conducted at a temperature of 0 to 60°C, preferably from 15 to 50°C, and more preferably from 20 to 45°C.

[0174] The pressure in the pre-polymerization reactor is not critical but must be sufficiently high to maintain the reaction mixture in liquid phase. Thus, the pressure may be from 20 to 100 bar, for example 30 to 70 bar.

[0175] In a preferred embodiment, the pre-polymerization is conducted as bulk slurry polymerization in liquid propylene, i.e. the liquid phase mainly comprises propylene, with optionally inert components dissolved therein. Furthermore, according to the present invention, an ethylene feed is employed during pre-polymerization as mentioned above.

[0176] It is possible to add other components also to the pre-polymerization stage. Thus, hydrogen may be added into the pre-polymerization stage to control the molecular weight of the polypropylene as is known in the art. Further, antistatic additive may be used to prevent the particles from adhering to each other or to the walls of the reactor.

[0177] The precise control of the pre-polymerization conditions and reaction parameters is within the skill of the art.

[0178] In a final process step the propylene-ethylene random copolymer is compounded optionally with the addition of additives to form the polypropylene composition.

[0179] As compounder usual extruders as known in the art can be used. No specific requirements or precautions need to be taken for the compounding conditions.

[0180] It is preferred that all aspects and embodiments of the polypropylene composition also apply to the process of said second aspect.

[0181] Article

[0182] In a third aspect the present invention relates to an article comprising the polypropylene composition of all aspects as described above or below. It is preferred that all aspects and embodiments of the polypropylene composition and the process for producing the polypropylene composition also apply to the article of said third aspect.

[0183] The article preferably comprises the polypropylene composition an amount of from 80 to 100 wt.-%, preferably from 90 to 100 wt.-%, more preferably from 95 to 100 wt.-%, based on the total weight of the article.

[0184] The article is preferably an injection moulded article for healthcare applications, more preferably a syringe, still more preferably a two-parts syringe or a three-parts syringe.

[0185] Use

[0186] In a fourth aspect the present invention relates to the use of the polypropylene composition of all aspects as described above or below for the production of an injection moulded article for healthcare applications, preferably a syringe, more preferably a two-parts syringe or a three-parts syringe.

[0187] It is preferred that all aspects and embodiments of the polypropylene composition, the process for producing the polypropylene composition and the article also apply to the use of said fourth aspect.

[0188] Examples

[0189] The following definitions of terms and determination methods apply for the above general description of the invention as well as to the below examples unless otherwise defined.

[0190] 1. Measurement methods

[0191] Density

[0192] Density of the polymer was determined according to ISO 1183-1 Method A on compression moulded specimen prepared according to ISO 19069-2 and is given in kg / m3.

[0193] Melt flow rate The melt flow rate (MFR) was determined according to ISO 1133 Procedure B and is indicated in g / 10 min. The MFR is an indication of the flowability and hence the processability of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 of polypropylene is determined at a temperature of 230°C. and under a load of 2.16 kg.

[0194] Comonomer content in polypropylene

[0195] The comonomer content was determined by quantitative Fourier transform infrared spectroscopy (FTIR) after basic assignment calibrated via quantitative13C nuclear magnetic resonance (NMR) spectroscopy in a manner well known in the art. Thin films were pressed to a thickness of 250 pm and spectra recorded in transmission mode. Specifically, the ethylene content of a polypropylene-co-ethylene copolymer was determined using the baseline corrected peak area of the quantitative bands found at 720-722 and 730-733 cm-1. Propylene-1-butene-copolymers were evaluated at 767 erm1. Quantitative results were obtained based upon reference to the film thickness.

[0196] Xylene Cold Soluble Fraction

[0197] Xylene cold soluble matter in polypropylene was determined according to ISO 16152 (Plastic - determination of xylene soluble matter in polypropylene). A weighed quantity of a sample was dissolved in hot xylene under reflux conditions, then cooled and maintained at 25 °C to ensure controlled gel formation of the insoluble fraction. The solution was filtrated, and the xylene soluble fraction was recovered by evaporation of the xylene and determined by weighing the residue.

[0198] Dynamic Rheology

[0199] The characterization of polymer melts by dynamic shear measurements complies with ISO standards 6721-1 and 6721-10. The measurements were performed on an Anton Paar MCR501 stress controlled rotational rheometer, equipped with a 25 mm parallel plate geometry. Measurements were undertaken on compression moulded plates using nitrogen atmosphere and setting a strain within the linear viscoelastic regime. The oscillatory shear tests could be done at 200°C or other temperature at which the material is molten, applying a frequency range between 0.05 and 500 rad / s and setting a gap of 1.2 mm. In a dynamic shear experiment the probe is subjected to a homogeneous deformation at a sinusoidal varying shear strain or shear stress (strain and stress-controlled mode, respectively). On a controlled strain experiment, the probe is subjected to a sinusoidal strain that can be expressed by

[0200] y(t) = yo sin(wt) (1)

[0201] If the applied strain is within the linear viscoelastic regime, the resulting sinusoidal stress response can be given by

[0202] o(t) = oo sin (cot +5) (2)

[0203] where oo, and yo are the stress and strain amplitudes, respectively; co is the angular frequency; 5 is the phase shift (loss angle between applied strain and stress response); t is the time.

[0204] Dynamic test results are typically expressed by means of several different rheological functions, namely the shear storage modulus, G’, the shear loss modulus, G”, the complex shear modulus, G*, the complex shear viscosity, q*, the dynamic shear viscosity, q', the out-of-phase component of the complex shear viscosity, q" and the loss tangent, tan q, which can be expressed as follows:

[0205] "

[0206] "

[0207]

[0208] The determination of so-called Shear Thinning Index, which correlates with MWD and is independent of Mw, is done as described in equation 9.

[0209] >

[0210]

[0211] For example, the SHI(2.7 / 2io) is defined by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 2.7 kPa, divided by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 210 kPa and the SHI(5 / 2oo) is defined by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 5 kPa, divided by the value of the complex viscosity, in Pa s, determined for a value of G* equal to 200 kPa.

[0212] The values of storage modulus (G'), loss modulus (G"), complex modulus (G*) and complex viscosity (q*) were obtained as a function of frequency (co).

[0213] Thereby, e.g. q*3oorad / s (eta*3oorad / s) is used as abbreviation for the complex viscosity at the frequency of 300 rad / s and q*o.o5rad / s (eta*o.osrad / s) is used as abbreviation for the complex viscosity at the frequency of 0.05 rad / s, and q*orad / s (eta*orad / s) is used as abbreviation for the complex viscosity at the frequency of 0 rad / s or zero shear viscosity. The loss tangent tan (delta) is defined as the ratio of the loss modulus (G") and the storage modulus (G') at a given frequency. Thereby, e.g. tano.osis used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G') at 0.05 rad / s and tansoo is used as abbreviation for the ratio of the loss modulus (G") and the storage modulus (G') at 300 rad / s.

[0214] The elasticity balance tano.os / tansoo is defined as the ratio of the loss tangent tano.os and the loss tangent tansoo.

[0215] Besides the above-mentioned rheological functions one can also determine other rheological parameters such as the so-called elasticity index El(x). The elasticity index Ei(x) is the value of the storage modulus, G’ determined fora value of the loss modulus, G” of x kPa and can be described by equation 10.

[0216] EI(x) = G' for (G" = x kPa) [Pa] (10)

[0217] For example, the EI(5kPa) is the defined by the value of the storage modulus G’, determined for a value of G” equal to 5 kPa.

[0218] The polydispersity index, PDI, is defined by equation 11.

[0219] "

[0220]

[0221] where WCOP is the cross-over angular frequency, determined as the angular frequency for which the storage modulus, G’(wCOp) in Pa, equals the loss modulus, G".

[0222] The values were determined by means of a single point interpolation procedure, as defined by Rheocompass software (Anton Paar rheometer software). In situations for which a given G’(wCOp) value is not experimentally reached, the value is determined by means of an extrapolation, using the same procedure as before. In both cases (interpolation or extrapolation), the option from Rheocompass "Interpolate y-values to x-values from parameter" and the "logarithmic interpolation type" were applied.

[0223] Zero shear viscosity

[0224] The determination of the so-called Zero Shear Viscosity at 200°C, etao, is determined in the RheoCompass software (Anton Paar rheometer software) by the use of the Carreau-Yasuda model. The Carreau-Yasuda equation describes the viscosity curve of a material with Newtonian regions at low shear rates and a shear thinning region (power law region) at medium shear rates.

[0225] Time-Temperature Superposition

[0226] The determination of the Time-Temperature Superposition horizontal shift factor (a-r) from the data of the storage and loss module (G', G"(w)) was made by using IRIS Rheo Hub 2008.

[0227] The flow activation energy (Ea) is a numerical value calculated according to an Arrhenius type equation from a shift factor (a-r) in making a master curve showing the dependency of melt complex viscosity (unit: Pa sec) at 200 °C on angular frequency (unit: rad / sec), based on the temperature-time superposition principle, and is a value obtained by a method described below. That is, melt complex viscosity-angular frequency curves of polymer sample at four temperatures (T, unit: °C.) including 200 °C. among temperatures of 190 °C, 200 °C, 210 °C, 220 °C, and 230 °C. are superposed on a melt complex viscosity-angular frequency curve of the copolymer at 200 °C., for each melt complex viscosity-angular frequency curve at each temperature (T), based on the temperature-time superposition theory, thereby obtaining shift factors (a-r) at respective temperatures (T), and a primary approximation formula (the following formula (12)) of [In(a-r)] and [1 / (T+273.16)] is calculated by a least square method from respective temperatures (T) and shift factors (a-r) at respective temperatures (T). Then, Eais obtained from the inclination m of the primary formula and the following formula (13).

[0228] ln(aT)=mx(1 / (T+273.16))+n (12)

[0229] Ea=Rxm (13) where R is the universal gas constant and Ea: flow activation energy (unit: kJ / mol)

[0230] An example of Time Temperature Superposition from the data of the storage and loss module (G', G"(w)) made by using IRIS Rheo Hub 2008 is shown in Figure 1.

[0231] Linear viscoelastic data (G', G"(w)) were obtained by sequence sweep measurements made at four different temperatures in an Anton Paar MCR 501 coupled with 25 mm parallel plates by applying a 1.2 mm gap within the linear viscoelastic regime, as described in Dynamic Rheology section.

[0232] References:

[0233] [1] “Rheological characterization of polyethylene fractions", Heino, E.L., Lehtinen, A., Tanner J., Seppala, J., Neste Oy, Porvoo, Finland, Theor. Appl. Rheol., Proc. Int. Congr. Rheol, 11th (1992), 1, 360-362.

[0234] [2] “The influence of molecular structure on some rheological properties of polyethylene", Heino, E.L., Borealis Polymers Oy, Porvoo, Finland, Annual Transactions of the Nordic Rheology Society, 1995.

[0235] [3] “Definition of terms relating to the non-ultimate mechanical properties of polymers”, Pure & Appl. Chem., Vol. 70, No. 3, pp. 701-754, 1998.

[0236] [4] C. W. Macosko, Rheology: Principles, Measurements, and Applications, VCH, Germany, 1994

[0237] [5] Structure and Rheology of Molten Polymers, John Dealy & Ronald G. Larson, Hanser 2006, pp 120-125.

[0238] Flexural modulus

[0239] Flexural Modulus was determined in 3-point-bending according to ISO 178 on injection moulded specimens of 80x10x4 mm prepared in accordance with ISO 294-1.

[0240] 2. Polypropylene compositions

[0241] Polymerization catalyst

[0242] The catalyst used in the polymerization process for propylene-ethylene random copolymer was the phthalate-free Ziegler-Natta type catalyst used in the inventive examples of WO2015 / 117948 A1, with triethyl-aluminium (TEAL) as co-catalyst and dicyclopentyl dimethoxy silane (donor “D”) as donor. Polymerization of the propylene-ethylene random copolymer

[0243] The propylene-ethylene random copolymer was polymerized in a Borstar® plant comprising a prepolymerization loop reactor, a loop reactor and a gas phase reactor, whereby the slurry from the prepolymerization reactor was withdrawn intermittently and directed into the loop reactor. Finally, the polymer was directed to the gas phase reactor (GPR). The polymerization conditions are listed in Table 1 below.

[0244] Table 1: Polymerization conditions of the propylene-ethylene random copolymer

[0245]

[0246] The propylene-ethylene random copolymer obtained from the Borstar® plant is compounded with 500 ppm pentaeryth rityl-tetrakis(3-(3’ ,5’-di-tert. butyl-4-hydroxyphenyl)-propionate (CAS-no. 6683-19-8), 500 ppm tris (2,4-di-f-butylphenyl) phosphate (CAS-no. 31570-04-4), 500 ppm calcium stearate (supplied by Croda Polymer Additives, CAS-no. 1592-23-0) and 1700 ppm 1,3 : 2,4 bis(3,4-dimethylbenzylidene) sorbitol (CAS- no. 135861 -56-2, supplied by Milliken) and pelletized in a W&P ZSK 70 twin-screw extruder (Coperion) to obtain the polypropylene composition of inventive example IE1. As comparative examples the following commercially available polypropylene compositions have been used:

[0247] CE1 a propylene random copolymer composition, commercially available from Sinopec under the tradename GM1600E.

[0248] CE2 a propylene random copolymer composition, commercially available from Natpet under the tradename R40MLT.

[0249] CE3 a propylene random copolymer composition, commercially available from Borouge under the tradename RG568MO

[0250] The properties of the polypropylene compositions of examples IE1, CE1, CE2 and CE3 are shown in Table 2.

[0251] Table 2: Properties of examples IE1, CE1, CE2, and CE3

[0252]

[0253] The polypropylene composition of the inventive example shows an improved balance of rheological properties in regard of processability as can be seen from the PDI and etao values, flowability as can be seen from the MFR2 values, and stiffness as can be seen from the flexural modulus value.

[0254] The increase of ethylene comonomer content results in an increase of toughness, which enhances the impact properties of the polypropylene composition of inventive example IE1.

[0255] As a consequence, the inventive example shows a superior stiffness / toughness balance, which can be seen in the mechanical properties index, which is calculated according to formula (I) and includes the ethylene comonomer content and the flexural modulus. The flexural modulus, and consequently the stiffness, are very important to ensure a proper and consistent de-gating during the final moulding of the material, i.e. injection moulding application. Thus, the higher the mechanical properties index, the better the final properties.

[0256] However, usually a material showing superior mechanical properties, are less easy to process, which will result in a lower benefit to the value chain.

[0257] The superior processability is illustrated by the processability index, which is calculated according to formula (II) and includes the PDI, etao and the activation energy Ea.

[0258] The higher is the polydispersity index, the better is the final processability. The lower is the zero shear viscosity the better is the processability. The activation energy should be as low as possible to consider the rheological behaviour of the material less sensitive to temperature variation during the material processing.

[0259] Superior stiffness / toughness balance and superior processability of the inventive example IE1 results in a superior enhanced medical material (EMMA) index, which is calculated according to formula (III) and is the product of mechanical properties index and processability index.

[0260] Figure 2 illustrates the improvement of the balance of properties in the plot of the mechanical properties index over processability index of the polypropylene compositions of examples IE1 , CE1 , CE2 and CE3 thereby visualizing the Enhanced Medical MAterial (EMMA) index.

[0261] Thereby the dashed line shows the EMMA index of 1.00. As it can be seen from the graph, the inventive example IE1 is excellent in mechanical properties index, maintaining a good processability index. Comparative examples CE2 and CE3 show better processability but poor mechanical properties, which results in an EMMA index below 1.00. Comparative example CE1 shows poor processability and poor mechanical properties.

Claims

Claims1. A polypropylene composition suitable for healthcare applications comprising from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer,wherein the polypropylene composition has• a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, preferably from 24.0 to 36.0 g / 10 min, more preferably from 25.0 to 35.0 g / 10 min, determined according to ISO 1133 at 230°C and 2.16 kg;• an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy;• a content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, preferably from 3.4 to 7.6 wt.-%, more preferably from 3.8 to 7.2 wt.-%, based on the total weight of the polypropylene composition and determined according to ISO 16152; and• a zero shear viscosity, etao, of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

2. The polypropylene composition according to claim 1 having a polydispersity index PDI of from 2.5 to 5.5, preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C.

3. The polypropylene composition according to claims 1 or 2 having a flexural modulus of from 950 to 1450 MPa, preferably from 1000 to 1400 MPa, more preferably from 1050 to 1350 MPa, determined according to ISO 178 on injection moulded specimens of 80x10x4 mm3prepared in accordance with ISO 294-1.

4. The polypropylene composition according to any one of the preceding claims having an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, more preferably from 1.02 to 1.35, still more preferably from 1.05 to 1.30, wherein the Enhanced Medical MAterial (EMMA) index is calculated according to formula (III)whereinC2 is the ethylene comonomer content in the polypropylene composition in wt.-%; Flex modulus is the flexural modulus of the polypropylene composition in MPa; a is a constant with the value 4200 (MPa wt.-%)’1;PDI is the polydispersity index at 200°C;etao is the zero shear viscosity at 200°C in Pa s;Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

5. A polypropylene composition suitable for healthcare applications comprising from 87.5 to 100.0 wt.-%, preferably from 90.0 to 99.9 wt.-%, more preferably from 95.0 to 99.8 wt.-%, based on the total weight of the polypropylene composition, of a propylene-ethylene random copolymer,wherein the polypropylene composition has• an ethylene content of from 2.5 to 4.0 wt.-%, preferably from 2.6 to 3.9 wt.-%, more preferably from 2.7 to 3.8 wt.-%, determined by quantitative FTIR spectroscopy, calibrated by quantitative13C-NMR spectroscopy;• a zero shear viscosity, etao, of from 925 to 1400 Pa s, preferably from 925 to 1300 Pa s, more preferably from 925 to 1200 Pa s, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C;• a polydispersity index PDI of from 2.5 to 5.5, preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5, determined by dynamic shear measurements complying with ISO 6721-1 and ISO 6721-10 at a temperature of 200°C; • a flexural modulus of from 950 to 1450 MPa, preferably from 1000 to 1400 MPa, more preferably from 1050 to 1350 MPa, determined according to ISO178 on injection moulded specimens of 80*10*4 mm3prepared in accordance with ISO 294-1; and• an Enhanced Medical MAterial (EMMA) index of from 1.00 to 1.50, more preferably from 1.02 to 1.35, still more preferably from 1.05 to 1.30, wherein the Enhanced Medical MAterial (EMMA) index is calculated according to formulawhereinC2 is the ethylene comonomer content in the polypropylene composition in wt.- %;Flex modulus is the flexural modulus of the polypropylene composition in MPa; a is a constant with the value 4200 (MPa wt.-%)’1;PDI is the polydispersity index at 200°C;etao is the zero shear viscosity at 200°C in Pa s;Ea / R is the ratio of the activation energy over the universal gas constant in K; andb is a constant with the value 1.100-106K Pa s.

6. The polypropylene composition according to claim 5 having one or more or all of the following properties:• a melt flow rate MFR2 of from 23.0 to 37.0 g / 10 min, preferably from 24.0 to 36.0 g / 10 min, more preferably from 25.0 to 35.0 g / 10 min, determined according to ISO 1133 at 230°C and 2.16 kg;• a content of xylene cold solubles (XCS) fraction of from 3.0 to 8.0 wt.-%, preferably from 3.4 to 7.6 wt.-%, more preferably from 3.8 to 7.2 wt.-%, based on the total weight of the polypropylene composition and determined according to ISO 161527. The polypropylene composition according to any one of the preceding claims having a mechanical properties index of from 0.85 to 1.50, more preferably from 0.87 to 1.40, still more preferably from 0.90 to 1.35,wherein the mechanical properties index is calculated according to formula (I) Mechanical properties index = (C2X Flex modulus / a)3(I)whereinC2 is the ethylene comonomer content in the polypropylene composition in wt.-%; Flex modulus is the flexural modulus of the polypropylene composition in MPa; and a is a constant with the value 4200 (MPa wt.-%)’1.

8. The polypropylene composition according to any one of the preceding claims having a processability index of from 0.68 to 1.35, more preferably from 0.72 to 1.30, still more preferably from 0. 75 to 1.25,wherein the processability index is calculated according to formula (II)whereinPDI is the polydispersity index at 200°C;etao is the zero shear viscosity at 200°C in Pa s;Ea / R is the ratio of the activation energy over the universal gas constant in K; and b is a constant with the value 1.100-106K Pa s.

9. The polypropylene composition according to any one of the preceding claims, wherein the propylene-ethylene random copolymer comprises a propylene homopolymer fraction and a propylene-ethylene random copolymer fraction, wherein the weight ratio of the propylene homopolymer fraction to the propylene- ethylene random copolymer fraction preferably is from 65 : 35 to 35 : 65, more preferably 60 : 40 to 40 :60, still more preferably from 55 : 45 to 45 : 55.

10. A process for producing the polypropylene composition according to any one of the preceding claims comprising the steps ofa) polymerizing propylene monomer units and optionally ethylene comonomer units in a first polymerization reactor in the presence of a Ziegler-Natta catalyst system to produce a first polymerization mixture comprising a propylene homopolymer fraction or a propylene-ethylene random copolymer fraction and the Ziegler-Natta catalyst system, wherein the first polymerization reactor is preferably a slurry reactor, more preferably a loop reactor;b) withdrawing said first polymerization mixture from the first polymerization reactor and transferring the first polymerization mixture into a second polymerization reactor; preferably a gas phase reactor;c) polymerizing propylene monomer units and ethylene comonomer units in said second polymerization reactor in the presence of said Ziegler-Natta catalyst system to produce a second polymerization mixture comprising a propyleneethylene random copolymer fraction, the propylene homopolymer fraction or the propylene-ethylene random copolymer fraction and the Ziegler-Natta catalyst system;d) withdrawing said second polymerization mixture from said second polymerization reactor and obtaining the propylene-ethylene random copolymer; ande) compounding the propylene-ethylene random copolymer optionally with the addition of additives to form the polypropylene composition.

11. The process according to claim 10, wherein hydrogen is added to the first polymerization reactor in step a) with a molar ratio of hydrogen to propylene monomer units H2 / C3 of from 2.5 to 15.0 mol / kmol, preferably from 4.5 to 12.5 mol / kmol, more preferably from 6.0 to 10.0 mol / kmol and / or hydrogen is added to the second polymerization reactor in step c) with a molar ratio of hydrogen to propylene monomer units H2 / C3 of from 25.0 to 75.0 mol / kmol, preferably from 35.0 to 65.0 mol / kmol, more preferably from 40.0 to 60.0 mol / kmol.

12. The process according to claims 10 or 11, wherein the molar ratio of ethylene comonomer units to propylene monomer units in the second polymerization reactor in step c) is from 5.0 to 25.0 mol / kmol, preferably from 7.5 to 22.5 mol / kmol, more preferably from 10.0 to 20.0 mol / kmol.

13. An article comprising the polypropylene composition according to any one of the preceding claims, preferably in an amount of from 80 to 100 wt.-%, preferably from 90 to 100 wt.-%, more preferably from 95 to 100 wt.-%, based on the total weight of the article.

14. The article according to claim 13, being an injection moulded article for healthcare applications, preferably a syringe, more preferably a two-parts syringe ora three- parts syringe.

15. Use of the polypropylene composition according to any one of claims 1 to 12 for the production of an injection moulded article for healthcare applications, preferably a syringe, more preferably a two-parts syringe or a three-parts syringe.

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