Polypropylene composition for cable insulation

Abstract

The present invention relates to a polypropylene composition comprising (A) a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms, the total amount of comonomer units of the copolymer being 10.0 to 16.0 wt.%, based on the total amount of monomer units in the polypropylene composition, and (B) an α-nucleating agent; wherein the polypropylene composition has: a xylene cold soluble (XCS) fraction in a total amount of 25.0 to 50.0 wt.%, based on the total weight of the polypropylene composition, the amount of comonomer units of the xylene cold soluble (XCS) fraction being at least 23.0 wt.%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction, a melt flow rate (MFR2) of 0.5 to 5.0 g / 10 min, and a flexural modulus of not more than 470 MPa, an article comprising the polypropylene composition, preferably a cable comprising an insulation layer comprising the polypropylene composition, and use of the polypropylene composition as cable insulation for medium and high voltage cables.

Description

Technical Field

[0001] The present invention relates to a flexible polypropylene composition, an article comprising the polypropylene composition, preferably a cable comprising an insulation layer comprising the polypropylene composition, and the use of the polypropylene composition as cable insulation for medium and high voltage cables. Background Art

[0002] Today, ethylene polymer products are used as insulation and semiconducting shielding for low-, medium-, and high-voltage cables due to their ease of processing and favorable electrical properties. In low-voltage applications, polyvinyl chloride (PVC) is also commonly used as insulation, often combined with a softener to achieve the desired softness. PVC is a thermoplastic that, through the addition of various plasticizers, can be used over a wide temperature range. For standard PVC, a maximum continuous conductor temperature of 70°C is normal. At low temperatures, PVC becomes rigid, and operating temperatures below -10°C should be avoided. At conductor temperatures above 100°C, the plasticizers migrate out, and the material loses its flexibility. However, by adding specialized plasticizers and stabilizers, PVC materials can be produced for conductor temperatures of 90-105°C. However, PVC is primarily used in the 1 kV range because the material's higher dielectric constant means that losses increase significantly at higher voltages. Therefore, PVC cables are typically used up to 1 kV. Furthermore, softeners must be added to PVC to maintain a high level of flexibility. Insufficient softener content can significantly reduce PVC's low-temperature performance. These softeners are not always considered to be unproblematic from an environmental perspective, so they need to be eliminated.

[0003] Cross-linked polyethylene (XLPE) products are currently the main insulation materials for medium-voltage, high-voltage, and extra-high-voltage (MV, HV, and EHV) cables, as well as high-voltage direct current (HVDC) cables. These products offer high operating temperatures, high electrical breakdown strength, and good mechanical properties. However, due to its cross-linking, XLPE cannot be recycled through remelting.

[0004] Therefore, attempts are being made to use thermoplastic materials, in particular thermoplastic propylene polymers, as insulation materials for medium voltage, high voltage and extra high voltage (MV, HV and EHV) cables as well as high voltage direct current (HVDC) cables. In addition, power grid owners are increasingly interested in cables that can be recycled by remelting.

[0005] Therefore, there is an increasing interest in polymer compositions based on thermoplastic propylene polymers for use in insulation layers of medium voltage (MV), high voltage (HV), extra high voltage (EHV) and high voltage direct current (HVDC) cables.

[0006] Therefore, propylene polymers need to show a good balance of properties with respect to flexibility, mechanical properties, impact properties and electrical breakdown strength.

[0007] Therefore, there is a need in the art for polypropylene compositions suitable for cable insulation and showing a good balance of properties with respect to flexibility, mechanical properties, impact properties and electrical breakdown strength. Summary of the Invention

[0008] In one aspect, the present invention relates to a polypropylene composition comprising

[0009] (A) a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms, the total amount of comonomer units being 10.0 to 16.0 wt%, preferably 10.5 to 15.0 wt%, most preferably 11.0 to 14.0 wt%, based on the total amount of monomer units in the polypropylene composition, and

[0010] (B) α-nucleating agent;

[0011] wherein the polypropylene composition has

[0012] % and most preferably 24.0 to 30.0 wt.-% of xylene cold soluble (XCS) fraction, based on the total weight of the polypropylene composition, the amount of comonomer units of the xylene cold soluble (XCS) fraction being at least 23.0 wt.-%, such as 23.0 to 35.0 wt.-%, preferably 23.5 to 32.5 wt.-%, and most preferably 24.0 to 30.0 wt.-%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction,

[0013] a melt flow rate MFR2 of 0.5 to 5.0 g / 10 min, preferably 0.8 to 4.5 g / 10 min, more preferably 1.0 to 4.3 g / 10 min, and most preferably 1.2 to 4.0 g / 10 min, and

[0014] A flexural modulus of no more than 470 MPa, such as from 200 to 470 MPa, preferably from 250 to 450 MPa, and most preferably from 300 to 430 MPa.

[0015] In another aspect the present invention relates to an article comprising the polypropylene composition as described above or below.

[0016] Preferably, the article is a cable comprising an insulation layer comprising the polypropylene composition as described above or below.

[0017] In a further aspect the present invention relates to the use of a polypropylene composition as described above or below as cable insulation for medium and high voltage cables.

[0018] definition

[0019] Heterophasic polypropylene is a propylene-based copolymer having a semicrystalline matrix phase and an elastomeric phase dispersed therein. The matrix phase can be a propylene homopolymer or a random copolymer of propylene and at least one α-olefin comonomer. The elastomeric phase can be a propylene copolymer with a high comonomer content, where the comonomer is not randomly distributed in the polymer chain but rather is distributed in comonomer-rich blocks and propylene-rich blocks.

[0020] Heterophasic polypropylene is generally distinguished from monophasic propylene copolymers in that it shows two different glass transition temperatures Tg due to the matrix phase and the elastomeric phase.

[0021] Propylene homopolymers are polymers consisting essentially of propylene monomer units. Due to impurities, especially in industrial polymerization processes, propylene homopolymers may contain up to 0.1 mol% of comonomer units, preferably up to 0.05 mol% of comonomer units, and most preferably up to 0.01 mol% of comonomer units.

[0022] Propylene random copolymer is a copolymer of propylene monomer units and comonomer units, wherein the comonomer units are randomly distributed on the polypropylene chain. Therefore, the propylene random copolymer includes a xylene-insoluble fraction - xylene cold insolubles (XCI) fraction - based on the total amount of the propylene random copolymer, in an amount of at least 85 wt %, most preferably at least 88 wt %. Therefore, the propylene random copolymer does not include an elastomeric polymer phase dispersed therein.

[0023] Typically, 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 of the fractions), preferably by polymerization in a plurality of polymerization stages with different polymerization conditions, is referred to as "multimodal". The prefix "multi" relates to the number of different polymer fractions comprising the propylene polymer. As an example of a multimodal propylene polymer, a propylene polymer consisting of only two fractions is referred to as "bimodal", whereas a propylene polymer consisting of only three fractions is referred to as "trimodal".

[0024] Unimodal propylene polymers consist of one fraction only.

[0025] Accordingly, the term "different" means that the propylene polymer fractions differ from each other in at least one property, preferably in weight average molecular weight (which can also be measured in the different melt flow rates of the fractions) or comonomer content or both.

[0026] "Functionalization" herein refers to chemical modification, preferably grafting or copolymerization with a mono- or poly-carboxylic acid compound or a derivative of a mono- or poly-carboxylic acid compound to provide the desired functional groups.

[0027] Visbreaking is a post-reactor chemical process used to modify semi-crystalline polymers, such as propylene polymers. During visbreaking, the propylene polymer backbone is degraded, for example, by peroxides such as organic peroxides, via beta scission. Degradation is typically used to increase melt flow rate and narrow molecular weight distribution.

[0028] Unless otherwise stated, the amounts below are given as % by weight (wt %). DETAILED DESCRIPTION

[0029] Polypropylene composition

[0030] In one aspect, the present invention relates to a polypropylene composition comprising

[0031] (A) a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms, the total amount of comonomer units being 10.0 to 16.0 wt%, preferably 10.5 to 15.0 wt%, most preferably 11.0 to 14.0 wt%, based on the total amount of monomer units in the polypropylene composition, and

[0032] (B) α-nucleating agent;

[0033] wherein the polypropylene composition has

[0034] % and most preferably 24.0 to 30.0 wt.-% of xylene cold soluble (XCS) fraction, based on the total weight of the polypropylene composition, the amount of comonomer units of the xylene cold soluble (XCS) fraction being at least 23.0 wt.-%, such as 23.0 to 35.0 wt.-%, preferably 23.5 to 32.5 wt.-%, and most preferably 24.0 to 30.0 wt.-%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction,

[0035] a melt flow rate MFR2 of 0.5 to 5.0 g / 10 min, preferably 0.8 to 4.5 g / 10 min, more preferably 1.0 to 4.3 g / 10 min, and most preferably 1.2 to 4.0 g / 10 min, and

[0036] A flexural modulus of no more than 470 MPa, such as from 200 to 470 MPa, preferably from 250 to 450 MPa, and most preferably from 300 to 430 MPa.

[0037] The polypropylene composition comprises an α-nucleating agent (B). Therefore, the α-nucleating agent (B) is not counted among the optional additives described herein.

[0038] Preferably, the polypropylene composition comprises 0.000001 to 5.00 wt.-%, more preferably 0.00001 to 2.50 wt.-% of the α-nucleating agent (B), based on the total amount of the polypropylene composition.

[0039] The amount of pure α-nucleating agent (B) in the polypropylene composition (without the optional masterbatch carrier polymer) is preferably in the range of 0.01 to 6000 ppm, more preferably 0.1 to 5000 ppm, based on the total amount of the polypropylene composition.

[0040] The α-nucleating agent (B) is preferably selected from soluble α-nucleating agents and particulate α-nucleating agents.

[0041] The α-nucleating agent (B) is preferably selected from the group consisting of:

[0042] (i) salts of monocarboxylic and polycarboxylic acids, for example sodium benzoate or aluminum tert-butylbenzoate, and

[0043] (ii) dibenzylidenesorbitol (e.g. 1,3:2,4-dibenzylidenesorbitol) and C1-C8-alkyl-substituted dibenzylidenesorbitol derivatives, such as methyldibenzylidenesorbitol, ethyldibenzylidenesorbitol or dimethyldibenzylidenesorbitol (e.g. 1,3:2,4-di(methylbenzylidene)sorbitol), or substituted nonitol derivatives, such as 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol, and

[0044] (iii) salts of phosphoric acid diesters, for example sodium 2,2'-methylenebis(4,6-di-t-butylphenyl)phosphate or aluminum-hydroxy-bis[2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate] (also known as 2,2'-methylene-bis(4,6-di-t-butylphenyl)phosphate) basic aluminum, and

[0045] (iv) vinylcycloalkane polymers and vinylalkane polymers (as discussed in more detail below), and

[0046] (v) mixtures thereof.

[0047] The α-nucleating agent is preferably selected from the group consisting of dibenzylidene sorbitol (e.g. 1,3:2,4 dibenzylidene sorbitol), dibenzylidene sorbitol derivatives, preferably dimethyldibenzylidene sorbitol (e.g. 1,3:2,4 di(methylbenzylidene)sorbitol), or substituted nonitol derivatives, such as 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol, vinylcycloalkane polymers, vinylalkane polymers and mixtures thereof.

[0048] Particularly preferred are vinylcycloalkane polymers, such as, for example, vinylcyclohexane (VCH) polymers. Such polymers can be added, for example, using Borealis Nucleation Technology (BNT).

[0049] The α-nucleating agent (B) can be added to the polypropylene composition as a separate raw material or in a mixture with a carrier polymer, ie in a so-called masterbatch. The amount of carrier polymer of the masterbatch is therefore calculated into the amount of α-nucleating agent.

[0050] Surprisingly it was found that the polypropylene composition as defined above comprising the α-nucleating agent (B), preferably in an amount as stated above or below, shows improved electrical breakdown strength behaviour, in particular the Weibull-β parameter.

[0051] The polypropylene composition preferably comprises the copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms (A) in an amount of 90.0 to 99.999999 wt%, more preferably 92.5 to 99.9 wt% and most preferably 95.0 to 99.8 wt%, based on the total amount of the polypropylene composition.

[0052] The polypropylene composition may further comprise polymer components other than the copolymer (A) of propylene with comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms in an amount of 0.0 to 10.0 wt.-%, based on the total amount of the polypropylene composition.

[0053] In one embodiment, the polymer component of the polypropylene composition consists of a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms.

[0054] In another embodiment, the polypropylene composition comprises a polyolefin functionalized with a mono- or polycarboxylic acid compound or a derivative of a mono- or polycarboxylic acid compound, wherein the functionalized polyolefin is different from a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms.

[0055] The mono- or polycarboxylic acid compound or the derivative of the mono- or polycarboxylic acid compound of the functionalized polyolefin is preferably selected from the anhydrides of mono- or polycarboxylic acids, wherein the anhydrides of mono- or polycarboxylic acids may be linear or cyclic.

[0056] The functionalized polyolefin is preferably an anhydride functionalized polyolefin, more preferably a maleic anhydride (MAH) functionalized polyolefin, still more preferably a maleic anhydride (MAH) functionalized polypropylene or polyethylene, even more preferably a maleic anhydride (MAH) functionalized polypropylene, most preferably a maleic anhydride (MAH) grafted polypropylene, wherein the polypropylene is selected from a homopolymer of propylene, a random copolymer of propylene or a heterophasic copolymer of propylene.

[0057] The functionalized polyolefin preferably has a high melt flow rate MFR2 of 100 to 750 g / 10 min, more preferably 150 to 500 g / 10 min, measured at a load of 2.16 kg and a temperature of 230° C. according to ISO 1133. Furthermore, the functionalized polyolefin preferably has a peak melting temperature of 140 to 180° C., more preferably 145 to 170° C.

[0058] The functionalized polyolefin is preferably commercially available, for example from ExxonMobil under the trade name Exxelor PO, such as for example Exxelor PO 1020.

[0059] In said embodiment the functionalized polyolefin is preferably present in the polypropylene composition in an amount of 0.5 to 3.0 wt.-%, preferably 0.7 to 2.5 wt.-%, most preferably 0.9 to 2.0 wt.-%, based on the total weight of the polypropylene composition.

[0060] In addition to these polymer components and the α-nucleating agent (B), the polypropylene composition may further comprise one or more additives in an amount of 0.0 to 5.0 wt. %, based on the total amount of the polypropylene composition. The one or more additives are preferably selected from acid scavengers, antioxidants, β-nucleating agents, etc. Such additives are commercially available and are described, for example, in the "Plastic Additives Handbook", 6 th edition 2009 of Hans Zweifel (pp. 1141–1190).

[0061] Typically, these additives are added in amounts of 1 to 50,000 ppm per single component.

[0062] One or more additives may be added to the polymer components during the blending step.

[0063] Thus, one or more additives may be added to the polymer component in the form of a masterbatch in which the one or more additives are blended in concentrated amounts with a carrier polymer. Any optional carrier polymer is calculated into the amount of additives based on the total amount of the propylene copolymer composition.

[0064] The term "β-nucleating agent" refers to any nucleating agent suitable for inducing crystallization of propylene polymers in the hexagonal or pseudo-hexagonal modification. Mixtures of such nucleating agents may also be used.

[0065] Suitable types of beta-nucleating agents are

[0066] (i) Dicarboxylic acid derivative-type diamide compounds derived from C5-C8-cycloalkylmonoamines or C6-C12-aromatic monoamines and C5-C8-aliphatic, C5-C8-alicyclic or C6-C12-aromatic dicarboxylic acids, for example, N,N'-di-C5-C8-cycloalkyl-2,6-naphthalenedicarboxylic acid compounds such as N,N'-dicyclohexyl-2,6-naphthalenedicarboxylic acid and N,N'-dicyclooctyl-2,6-naphthalenedicarboxylic acid, N,N'-di-C5-C8-cycloalkyl-4,4-biphenyldicarboxylic acid compounds Such as N,N'-dicyclohexyl-4,4-biphenyldicarboxamide and N,N'-dicyclopentyl-4,4-biphenyldicarboxamide, N,N'-di-C5-C8-cycloalkyl-terephthalamide compounds such as N,N'-dicyclohexylterephthalamide and N,N'-dicyclopentylterephthalamide, N,N'-di-C5-C8-cycloalkyl-1,4-cyclohexanedicarboxamide compounds such as N,N'-dicyclohexyl-1,4-cyclohexanedicarboxamide and N,N'-dicyclohexyl-1,4-cyclopentanedicarboxamide,

[0067] (ii) diamine derivative-type diamide compounds derived from C5-C8-cycloalkylmonocarboxylic acids or C6-C12-aromatic monocarboxylic acids and C5-C8-alicyclic or C6-C12-aromatic diamines, for example, N,N'-C6-C12-arylene-bis-benzamide compounds such as N,N'-p-phenylene-bis-benzamide and N,N'-1,5-naphthalene-bis-benzamide, N,N'-C5-C8-cycloalkyl-bis-benzamide compounds such as N,N'-1,4-cyclopentane-bis-benzamide N,N'-1,4-cyclohexane-bis-benzamide, N,N'-p-C6-C12-arylene-bis-C5-C8-cycloalkylcarboxamide compounds such as N,N'-1,5-naphthalene-bis-cyclohexanecarboxamide and N,N'-1,4-phenylene-bis-cyclohexanecarboxamide, and N,N'-C5-C8-cycloalkyl-bis-cyclohexanecarboxamide compounds such as N,N'-1,4-cyclopentane-bis-cyclohexanecarboxamide and N,N'-1,4-cyclohexane-bis-cyclohexanecarboxamide,

[0068] (iii) Amino acid derivative-type diamide compounds from the amidation reaction of C5-C8-alkyl, C5-C8-cycloalkyl- or C6-C12-arylamino acids, C5-C8-alkyl-, C5-C8-cycloalkyl- or C6-C12-aromatic monocarboxylic acid chlorides and C5-C8-alkyl-, C5-C8-cycloalkyl- or C6-C12-aromatic monoamines, for example N-phenyl-5-(N-benzylamino)valeramide and N-cyclohexyl-4-(N-cyclohexyl-carbonylamino)benzamide.

[0069] Other suitable β-nucleating agents are

[0070] (iv) quinacridone-type compounds, such as 5,12-dihydro-quinone[2,3-b]acridine-7,14-dione (i.e., quinacridone), dimethylquinacridone, and dimethoxyquinacridone,

[0071] (v) quinacridone quinone type compounds, such as quinone [2,3-b] acridine-6,7,13,14 (5H,12H) -tetraone (i.e., quinacridone quinone), and (vi) dimethoxyquinacridone quinone and dihydroquinacridone type compounds, such as 5,6,12,13-tetrahydroquinolino [2,3-b] acridine-7,14-dione (i.e., dihydroquinacridone), dimethoxydihydroquinacridone and dibenzodihydroquinacridone.

[0072] Still further suitable β-nucleating agents are dicarboxylates of metals from Group IIa of the Periodic Table, such as calcium pimelate and calcium suberate; and mixtures of dicarboxylic acids and salts of metals from Group IIa of the Periodic Table.

[0073] Still further suitable β-nucleating agents are salts of metals from Group IIa of the Periodic Table and imides of the formula

[0074]

[0075] wherein x=0 to 4; R=H, -COOH, C1-C12-alkyl, C5-C8-cycloalkyl or C6-C12-aryl, and Y=a divalent C6-C12-aromatic residue substituted by C1-C12-alkyl, C5-C8-cycloalkyl or C6-C12-aryl, for example

[0076] Calcium salts of phthaloylglycine, hexahydrophthaloylglycine, N-phthaloylalanine, phthalimidoacetic acid and / or N-4-methylphthaloylglycine.

[0077] Preferred β-nucleating agents are any one or a mixture of N,N′-dicyclohexyl-2,6-naphthalenedicarboxylic acid amide, the β-nucleating agents of EP 177961 and those of EP 682066.

[0078] Particularly preferred β-nucleating agents are any one or a mixture of the following

[0079] 5,12-Dihydro-quinone[2,3-b]acridine-7,14-dione (CAS 1047-16-1) (i.e., quinacridone), quinone[2,3-b]acridine-6,7,13,14(5H,12H)-tetraone (CAS 1503-48-6) (i.e., quinacridonequinone), 5,6,12,13-tetrahydroquinone[2,3-b]acridine-7,14-dione (CAS 5862-38-4) (i.e., dihydroquinacridone), N,N'-dicyclohexyl-2,6-naphthalenedicarboxamide (CAS 153250-52-3), and salts of dicarboxylic acids having at least 7 carbon atoms with metals of Group IIa of the Periodic Table, preferably calcium pimelate (CAS 19455-79-9).

[0080] Particularly preferred is quinolino[2,3-b]acridine-6,7,13,14(5H,12H)-tetraone (CAS 1503-48-6) (ie quinacridonequinone), which is commercially available as Cinquasia CGNA-7588 from BASF.

[0081] Typically, the amount of β-nucleating agent in the polypropylene composition is in the range of 1 ppm to 2500 ppm, preferably 10 ppm to 1000 ppm, most preferably 25 ppm to 500 ppm.

[0082] When the β-nucleating agent in the embodiment is selected from any one or a mixture of quinacridone-type compounds, quinacridonequinone-type compounds and dihydroquinacridone-type compounds, the β-nucleating agent is preferably present in the polypropylene composition in an amount of 1 ppm to 500 ppm, more preferably 10 ppm to 250 ppm, and most preferably 25 ppm to 150 ppm.

[0083] The acid scavenger may be for example calcium stearate or magnesium oxide.The acid scavenger is preferably present in the polypropylene composition in an amount of 10 to 50000 ppm, preferably 50 to 35000 ppm, most preferably 100 to 20000 ppm, based on the total weight of the polypropylene composition.

[0084] The antioxidant may be selected from any suitable antioxidant known in the art for use in polypropylene compositions suitable for cable insulation.

[0085] It is especially preferred that the polypropylene composition does not comprise (ie is free of) a dielectric fluid, such as described in EP 2 739 679.

[0086] The polypropylene composition has high flexibility as can be seen from a flexural modulus of not more than 470 MPa, such as from 200 to 470 MPa, preferably from 250 to 450 MPa and most preferably from 300 to 430 MPa.

[0087] Furthermore, the polypropylene composition preferably has good impact properties as evidenced by the Charpy notched impact strength at 23°C and -20°C.

[0088] Preferably, the polypropylene composition has a Charpy notched impact strength at 23°C of at least 70.0 kJ / m 2 , for example, 70.0 to 100.0 kJ / m 2 , more preferably 72.5 to 95.0 kJ / m 2 , and most preferably 75.0 to 90.0 kJ / m 2 .

[0089] Furthermore, the polypropylene composition preferably has a Charpy notched impact strength at -20°C of at least 3.5 kJ / m 2 , for example 3.5 to 10.0 kJ / m 2 , more preferably 3.7 to 9.0 kJ / m 2 , and most preferably 4.0 to 8.0 kJ / m 2 .

[0090] The polypropylene composition has a melt flow rate MFR2 of 0.5 to 5.0 g / 10 min, preferably 0.8 to 4.5 g / 10 min, still more preferably 1.0 to 4.3 g / 10 min and most preferably 1.2 to 4.0 g / 10 min.

[0091] Furthermore, the polypropylene composition has a melting temperature Tm of 140 to 159 °C, preferably of 143 to 157 °C and most preferably of 145 to 153 °C.

[0092] Additionally, the polypropylene composition has a crystallization temperature Tc of 105 to 130°C, preferably 107 to 128°C and most preferably 110 to 125°C.

[0093] The difference between the melting temperature and the crystallization temperature, Tm-Tc, is preferably in the range of 20 to 45°C, preferably 25 to 40°C and most preferably 27 to 37°C.

[0094] The polypropylene composition has a total amount of comonomer units of 10.0 to 16.0 wt%, preferably 10.5 to 15.0 wt%, most preferably 11.0 to 14.0 wt%, based on the total amount of monomer units in the polypropylene composition.

[0095] The comonomer units are selected from ethylene and α-olefins having 4 to 12 carbon atoms, such as ethylene, 1-butene, 1-hexene or 1-octene. The polypropylene composition may comprise one type of comonomer unit or two or more types, such as two types of comonomer units. Preferably, the polypropylene composition comprises one type of comonomer unit. Particularly preferred is ethylene.

[0096] Preferably the polypropylene composition has an intrinsic viscosity measured in decalin of from 185 to 350 cm 3 / g, preferably 200 to 325cm 3 / g, and most preferably 210 to 300 cm 3 / g.

[0097] The polypropylene composition has a xylene cold soluble (XCS) fraction in a total amount of 25.0 to 50.0 wt.-%, preferably 27.5 to 45.0 wt.-%, more preferably 30.0 to 42.5 wt.-% and most preferably 32.5 to 41.0 wt.-%, based on the total weight of the polypropylene composition.

[0098] The amount of comonomer units (preferably ethylene) of the xylene cold soluble (XCS) fraction is at least 23.0 wt%, for example from 23.0 to 35.0 wt%, preferably from 23.5 to 32.5 wt%, and most preferably from 24.0 wt% to 30.0 wt%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction.

[0099] Furthermore, the intrinsic viscosity of the xylene cold soluble (XCS) fraction, measured in decalin, is preferably from 150 to 350 cm 3 / g, preferably 165 to 325cm 3 / g, and most preferably 175 to 300 cm 3 / g.

[0100] Furthermore, the weight average molecular weight Mw of the xylene cold soluble (XCS) fraction is preferably from 185,000 to 350,000 g / mol, more preferably from 200,000 to 325,000 g / mol and most preferably from 210,000 to 315,000 g / mol.

[0101] Furthermore, the polydispersity index of the xylene cold soluble (XCS) fraction, which is the ratio of weight average molecular weight to number average molecular weight, Mw / Mn, is preferably from 3.5 to 8.5, preferably from 3.7 to 8.0, and most preferably from 4.0 to 7.5.

[0102] Furthermore, the polypropylene composition has a cold xylene insoluble (XCI) fraction, the total amount of which is preferably 50.0 to 75.0 wt.-%, preferably 55.0 to 72.5 wt.-%, more preferably 57.5 to 70.0 wt.-% and most preferably 59.0 to 67.5 wt.-%, based on the total weight of the polypropylene composition.

[0103] The amount of comonomer units, preferably ethylene, of the fraction insoluble in cold xylene (XCI) is preferably 3.0 to 9.0 wt.-%, more preferably 4.0 to 8.5 wt.-% and most preferably 4.5 to 7.5 wt.-%, based on the total amount of monomer units in the fraction insoluble in cold xylene (XCI).

[0104] Furthermore, the intrinsic viscosity of the fraction insoluble in cold xylene (XCI) as measured in decalin is preferably from 185 to 350 cm 3 / g, preferably 220 to 325cm 3 / g, and most preferably 210 to 300 cm 3 / g.

[0105] Furthermore, the weight average molecular weight Mw of the fraction insoluble in cold xylene (XCI) is preferably from 225,000 to 450,000 g / mol, more preferably from 240,000 to 425,000 g / mol and most preferably from 260,000 to 400,000 g / mol.

[0106] Furthermore, the polydispersity index of the fraction insoluble in cold xylene (XCI), which is the ratio of weight-average molecular weight to number-average molecular weight, Mw / Mn, is preferably from 3.5 to 7.5, preferably from 3.7 to 7.0, and most preferably from 4.0 to 6.5.

[0107] The ratio of the intrinsic viscosity of the XCI fraction to the XCS fraction is preferably in the range of 0.9 to 1.5, more preferably 1.0 to 1.4 and most preferably 1.0 to 1.3.

[0108] The ratio of the weight average molecular weight of the XCI fraction to the XCS fraction is preferably in the range of 1.05 to 1.50, more preferably 1.10 to 1.40 and most preferably 1.20 to 1.35.

[0109] Preferably, the polypropylene composition is prepared by melt blending a copolymer of propylene with comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms (A), an α-nucleating agent (B), optional further polymer components such as a propylene polymer grafted with an acid grafting agent and optional further additives such as antioxidants, β-nucleating agents and / or acid scavengers, all as described above or below.

[0110] Hereinafter, the copolymer (A) of propylene and a comonomer unit selected from ethylene and an α-olefin having 4 to 12 carbon atoms (abbreviated as "propylene copolymer") is described in more detail.

[0111] Propylene copolymer (A)

[0112] The polypropylene composition according to this invention comprises a copolymer (A) of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms (hereinafter "propylene copolymer").

[0113] The comonomer units are selected from ethylene and α-olefins having 4 to 12 carbon atoms, such as ethylene, 1-butene, 1-hexene or 1-octene. The propylene copolymer may comprise one type of comonomer unit or two or more types, such as two types of comonomer units. Preferably, the propylene copolymer comprises one type of comonomer unit. Particularly preferred is ethylene.

[0114] The total amount of comonomer units (preferably ethylene) of the propylene copolymer is preferably 10.0 to 16.0 wt%, preferably 10.5 to 15.0 wt%, most preferably 11.0 to 14.0 wt%, based on the total amount of monomer units in the propylene copolymer.

[0115] Preferably the propylene copolymer is a heterophasic copolymer of propylene.

[0116] The heterophasic propylene copolymer has a matrix phase and an elastomeric phase dispersed in the matrix phase.

[0117] The matrix phase is preferably a propylene random copolymer.

[0118] The comonomer units of the propylene random copolymer of the matrix phase are generally identical to the comonomer units of the propylene copolymer as described above. The comonomer units are preferably selected from ethylene and α-olefins having 4 to 12 carbon atoms, such as ethylene, 1-butene, 1-hexene or 1-octene. The propylene random copolymer of the matrix phase may comprise one type of comonomer units or two or more types, such as two types of comonomer units. Preferably, the propylene random copolymer of the matrix phase comprises one type of comonomer units. Particularly preferred is ethylene.

[0119] Heterophasic propylene copolymers are typically characterized by comprising at least two glass transition temperatures. The two glass transition temperatures are attributable to a matrix phase (Tg(matrix)) and an elastomeric phase (Tg(EPR)).

[0120] The glass transition temperature Tg(matrix) of the heterophasic propylene copolymer due to the matrix phase is preferably in the range of -1.0 to -15.0 °C, preferably -2.5 to -12.5 °C and most preferably -5.0 to -10.0 °C.

[0121] Furthermore the heterophasic propylene copolymer preferably has a glass transition temperature Tg(EPR) due to the elastomeric phase in the range of -40.0 to -55.0 °C, preferably -42.5 to -52.5 °C and most preferably -45.0 to -50.0 °C.

[0122] In propylene copolymers, for example heterophasic propylene copolymers, matrix phase and elastomeric phase can not be separated from each other accurately usually. In order to characterize the matrix phase and elastomeric phase of heterophasic polypropylene copolymers, several methods are known. One method is to extract the fraction comprising most of the elastomeric phase with xylene, thereby separating the xylene cold solubles (XCS) fraction from the xylene cold insolubles (XCI) fraction. The XCS fraction comprises most of the elastomeric phase and only a small portion of the matrix phase, while the XCI fraction comprises most of the matrix phase and only a small portion of the elastomeric phase.

[0123] The total amount of xylene cold soluble (XCS) fraction of the propylene copolymer is preferably 25.0 to 50.0 wt.-%, more preferably 27.5 to 45.0 wt.-%, still more preferably 30.0 to 42.5 wt.-% and most preferably 32.5 to 41.0 wt.-%, based on the total weight of the propylene copolymer.

[0124] The amount of comonomer units, preferably ethylene, of the xylene cold soluble (XCS) fraction is preferably from 23.0 to 35.0 wt%, more preferably from 23.5 to 32.5 wt% and most preferably from 24.0 to 30.0 wt%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction.

[0125] Furthermore, the intrinsic viscosity of the xylene cold soluble (XCS) fraction, measured in decalin, is preferably from 150 to 350 cm 3 / g, preferably 165 to 325cm 3 / g, and most preferably 175 to 300 cm 3 / g.

[0126] Furthermore the total amount of the cold xylene insoluble (XCI) fraction of the propylene copolymer is preferably from 50.0 to 75.0 wt.-%, more preferably from 55.0 to 72.5 wt.-%, still more preferably from 57.5 to 70.0 wt.-% and most preferably from 59.0 to 67.5 wt.-%, based on the total weight of the propylene copolymer.

[0127] The amount of comonomer units, preferably ethylene, of the fraction insoluble in cold xylene (XCI) is preferably 3.0 to 9.0 wt.-%, preferably 4.0 to 8.5 wt.-% and most preferably 4.5 to 7.5 wt.-%, based on the total amount of monomer units in the fraction insoluble in cold xylene (XCI).

[0128] Furthermore, the intrinsic viscosity of the fraction insoluble in cold xylene (XCI) as measured in decalin is preferably from 185 to 350 cm 3 / g, preferably 220 to 325cm 3 / g, and most preferably 210 to 300 cm 3 / g.

[0129] The ratio of the intrinsic viscosity of the XCI fraction to the XCS fraction of the propylene copolymer is preferably in the range of 0.9 to 1.5, more preferably 1.0 to 1.4 and most preferably 1.0 to 1.3.

[0130] The melt flow rate MFR2 of the propylene copolymer before mixing is preferably from 0.5 to 2.5 g / 10 min, preferably from 0.8 to 2.2 g / 10 min, still more preferably from 1.0 to 2.0 g / 10 min and most preferably from 1.2 to 1.9 g / 10 min.

[0131] The flexural modulus of the propylene copolymer is preferably from 130 MPa to 380 MPa, more preferably from 150 MPa to 365 MPa and most preferably from 175 MPa to 350 MPa.

[0132] Preferably, the propylene copolymer has a Charpy notched impact strength at 23°C of 40 to 110 kJ / m 2 , more preferably 50 to 100 kJ / m 2 , and most preferably 55 to 95 kJ / m 2 .

[0133] The propylene copolymer can be polymerized in a sequential multistage polymerization process, i.e., a polymerization process in which two or more polymerization reactors are connected in series. Preferably, in a sequential multistage polymerization process, two or more, more preferably three or more, for example three or four polymerization reactors are connected in series. The term "polymerization reactor" shall mean that the main polymerization occurs. Thus, in the case where a process consists of four polymerization reactors, this definition does not exclude the option of including a prepolymerization step in, for example, a prepolymerization reactor as the entire process.

[0134] When the propylene copolymer is a heterophasic propylene copolymer the matrix phase of the heterophasic propylene copolymer is polymerized in a first polymerisation reactor to produce a unimodal matrix phase or in a first and a second polymerisation reactor to produce a multimodal matrix phase.

[0135] The elastomeric phase of the heterophasic propylene copolymer is preferably polymerized in the presence of the matrix phase in one or two subsequent polymerisation reactors to produce a unimodal or multimodal elastomeric phase.

[0136] Preferably, the polymerization reactor is selected from slurry phase reactors, such as loop reactors and / or gas phase reactors, such as fluidized bed reactors, more preferably selected from loop reactors and fluidized bed reactors.

[0137] A preferred sequential multistage polymerization process is the "loop-gas phase" process, such as that developed by Borealis A / S of Denmark (known as technology), described, for example, in the patent literature, for example in EP 0 887 379, WO 92 / 12182, WO 2004 / 000899, WO 2004 / 111095, WO 99 / 24478, WO 99 / 24479 or WO 00 / 68315.

[0138] Another suitable slurry-gas phase process is LyondellBasell's method.

[0139] Suitable sequential polymerization processes for polymerizing propylene copolymers, preferably heterophasic propylene copolymers, are disclosed in e.g. EP 1 681 315 A1 or WO 2013 / 092620 A1.

[0140] The propylene copolymer, preferably the heterophasic propylene copolymer, may be polymerized in the presence of a Ziegler-Natta catalyst or a single site catalyst.

[0141] Suitable Ziegler-Natta catalysts are disclosed, for example, in US Pat. No. 5,234,879, WO 92 / 19653, WO 92 / 19658, WO 99 / 33843, WO 03 / 000754, WO 03 / 000757, WO 2013 / 092620 A1 or WO 2015 / 091839.

[0142] Suitable single-site catalysts are disclosed, for example, in WO 2006 / 097497, WO 2011 / 076780 or WO 2013 / 007650.

[0143] The propylene copolymer is preferably not subjected to a visbreaking step, such as described in WO 2013 / 092620 A1. In such an embodiment, the melt flow rate of the resulting polypropylene composition is preferably from 0.5 to 2.5 g / 10 min, preferably from 0.8 to 2.3 g / 10 min, more preferably from 1.0 to 2.0 g / 10 min, and most preferably from 1.2 to 1.9 g / 10 min.

[0144] In another embodiment, the propylene copolymer is preferably subjected to a visbreaking step, such as described in WO 2013 / 092620A1. In such an embodiment, the melt flow rate of the resulting polypropylene composition is preferably greater than 2.5 to 5.0 g / 10 min, preferably 3.0 to 4.5 g / 10 min, still more preferably 3.2 to 4.3 g / 10 min, and most preferably 3.5 to 4.0 g / 10 min.

[0145] Heterophasic propylene copolymer resins suitable as propylene copolymers are also commercially available. These resins typically already have stabilizer packages added. Therefore, when using commercially available resins as propylene copolymers, the addition of additives as described above may have to be adjusted to the additives already present.

[0146] Embodiments of the polypropylene composition

[0147] The polypropylene composition according to the present invention comprises different embodiments.

[0148] In one embodiment, the polypropylene composition has a melt flow rate of 0.5 to 2.5 g / 10 min, preferably 0.8 to 2.3 g / 10 min, still more preferably 1.0 to 2.0 g / 10 min, and most preferably 1.2 to 1.9 g / 10 min. In said embodiment, the polypropylene composition preferably does not undergo a visbreaking step.

[0149] The weight average molecular weight Mw of the xylene cold soluble (XCS) fraction of the polypropylene composition of this embodiment is preferably from 250,000 to 350,000 g / mol, more preferably from 260,000 to 325,000 g / mol and most preferably from 270,000 to 315,000 g / mol.

[0150] Furthermore, the polydispersity index of the xylene cold soluble (XCS) fraction, which is the ratio of weight average molecular weight to number average molecular weight, Mw / Mn, is preferably from 5.0 to 8.5, preferably from 5.5 to 8.0, and most preferably from 6.0 to 7.5.

[0151] Additionally the polypropylene composition of the embodiment has a weight average molecular weight Mw of the cold xylene (XCI) insoluble fraction of preferably 325,000 to 450,000 g / mol, more preferably 340,000 to 425,000 g / mol and most preferably 360,000 to 400,000 g / mol.

[0152] Furthermore, the polydispersity index of the fraction insoluble in cold xylene (XCI), which is the ratio of the weight-average molecular weight to the number-average molecular weight, Mw / Mn, is preferably from 4.0 to 7.5, preferably from 4.5 to 7.0, and most preferably from 5.0 to 6.5.

[0153] The ratio of the weight average molecular weight of the XCI fraction to the XCS fraction is preferably in the range of 1.05 to 1.50, more preferably 1.10 to 1.40 and most preferably 1.20 to 1.35.

[0154] In said embodiment the polypropylene composition may comprise an additional component selected from a beta-nucleating agent or a polyolefin functionalized with a mono- or polycarboxylic acid compound or a derivative of a mono- or polycarboxylic acid compound.

[0155] However, it is preferred that the polypropylene composition of the embodiment consists of a propylene copolymer as described above having a melt flow rate of 0.5 to 2.5 g / 10 min, preferably 0.8 to 2.3 g / 10 min, still more preferably 1.0 to 2.0 g / 10 min and most preferably 1.2 to 1.9 g / 10 min, an α-nucleating agent and optionally an antioxidant and / or acid scavenger as additives.

[0156] The polypropylene composition with a low melt flow rate preferably meets all properties as described above.

[0157] In another embodiment, the melt flow rate (MFR) of the polypropylene composition is greater than 2.5 to 5.0 g / 10 min, preferably 3.0 to 4.5 g / 10 min, still more preferably 3.2 to 4.3 g / 10 min, and most preferably 3.5 to 4.0 g / 10 min. Higher melt flow rate (MFR) can be obtained by visbreaking the polypropylene composition of the first embodiment. The visbreaking step usually not only affects the melt flow rate (MFR), but also affects the weight average molecular weight and polydispersity index (PDI).

[0158] The weight average molecular weight Mw of the xylene cold soluble (XCS) fraction of the polypropylene composition of another embodiment is preferably from 250,000 to 350,000 g / mol, more preferably from 185,000 to 300,000 g / mol, more preferably from 200,000 to 275,000 g / mol and most preferably from 210,000 to 250,000 g / mol.

[0159] Furthermore, the polydispersity index of the xylene cold soluble (XCS) fraction, which is the ratio of weight average molecular weight to number average molecular weight, Mw / Mn, is preferably from 3.5 to 6.0, preferably from 3.7 to 5.5, and most preferably from 4.0 to 5.0.

[0160] Additionally, the polypropylene composition of another embodiment has a cold xylene (XCI) insoluble fraction weight average molecular weight Mw of preferably 225,000 to 350,000 g / mol, more preferably 240,000 to 325,000 g / mol and most preferably 260,000 to 300,000 g / mol.

[0161] Furthermore, the polydispersity index of the fraction insoluble in cold xylene (XCI), which is the ratio of the weight-average molecular weight to the number-average molecular weight, Mw / Mn, is preferably from 3.5 to 6.0, preferably from 3.7 to 5.5, and most preferably from 4.0 to 5.0.

[0162] The ratio of the weight average molecular weight of the XCI fraction to the XCS fraction is preferably in the range of 1.05 to 1.50, more preferably 1.10 to 1.40 and most preferably 1.20 to 1.35.

[0163] In said further embodiment the polypropylene composition preferably has a flexural modulus of 200 MPa to less than 400 MPa, preferably 250 to 390 MPa and most preferably 300 to 380 MPa.

[0164] In said embodiment the polypropylene composition may comprise an additional component selected from a beta-nucleating agent or a polyolefin functionalized with a mono- or polycarboxylic acid compound or a derivative of a mono- or polycarboxylic acid compound.

[0165] However, it is preferred that the polypropylene composition of the embodiment consists of a propylene copolymer as described above having a melt flow rate of more than 2.5 to 5.0 g / 10 min, preferably 3.0 to 4.5 g / 10 min, still more preferably 3.2 to 4.3 g / 10 min, most preferably 3.5 to 4.0 g / 10 min, an α-nucleating agent and optionally an antioxidant and / or acid scavenger as additives.

[0166] The polypropylene composition having a high melt flow rate preferably meets all properties as described above.

[0167] Products

[0168] In another aspect the present invention also relates to an article comprising the polypropylene composition as defined above or below.

[0169] The article is preferably a cable comprising an insulation layer comprising the polypropylene composition as defined above or below.

[0170] The cable typically comprises at least one conductor and at least one insulation layer comprising the polypropylene composition as defined above or below.

[0171] The term "conductor" as used hereinabove and below means that the conductor comprises one or more wires. The wire can be used for any purpose and can be, for example, an optical wire, a telecommunication wire or an electric wire. In addition, the cable may comprise one or more such conductors. Preferably, the conductor is an electrical conductor and comprises one or more metal wires. The cable is preferably a power cable. A power cable is defined as a cable for transmitting energy that operates at any voltage, typically at a voltage higher than 1 kV. The voltage applied to the power cable may be alternating current (AC), direct current (DC) or transient (pulse). The polypropylene composition of the present invention is very suitable for power cables, in particular for power cables operating at voltages of 6 kV to 36 kV (medium voltage (MV) cables) and power cables operating at voltages higher than 36 kV, known as high voltage (HV) cables and extra high voltage (EHV) cables, and it is well known that EHV cables operate at very high voltages. These terms have well-known meanings and indicate the working levels of such cables.

[0172] For low voltage applications, the cable system usually consists of a conductor and an insulation layer comprising a polypropylene composition as described above or below, or a conductor, an insulation layer comprising a polypropylene composition as described above or below and an additional jacket layer, or a conductor, a semiconducting layer and an insulation layer comprising a polypropylene composition as described above or below.

[0173] For medium and high voltage applications the cable system usually consists of a conductor, an inner semiconductive layer, an insulation layer comprising a polypropylene composition as described above or below and an outer semiconductive layer, optionally covered by an additional sheath layer.

[0174] The semiconductive layer mentioned preferably comprises, more preferably consists of, a thermoplastic polyolefin composition, preferably a polyethylene composition or a polypropylene composition, which comprises a sufficient amount of electrically conductive solid fillers, preferably carbon black. Preferably, the thermoplastic polyolefin composition of the semiconductive layer is a polypropylene composition, more preferably a polypropylene composition comprising as polymer component a heterophasic propylene copolymer. Particularly preferably, the thermoplastic polyolefin composition of at least one semiconductive layer, preferably both semiconductive layers of the cable comprises the same propylene copolymer as the insulation layer, i.e. propylene copolymer (A) as described above or below.

[0175] The cable comprising an insulation layer comprising the polypropylene composition according to the present invention as described above shows good electrical properties in the form of Weibull alpha and Weibull beta values.

[0176] The Weibull alpha value of the cable is preferably at least 35 kV / mm, such as 35.0 to 65.0 kV / mm, more preferably 40.0 to 65.0 kV / mm, and most preferably 43.0 to 65.0 kV / mm, when measured on a 10 kV cable.

[0177] Still further, the Weibull beta value of the cable is preferably at least 7.5, such as from 7.5 to 250.0, more preferably from 8.0 to 250.0, most preferably from 8.5 to 250.0, when measured on a 10 kV cable.

[0178] Thus, the insulation layer comprising the polypropylene composition according to the present invention can be used in medium and high voltage cables.

[0179] In a further aspect the present invention relates to the use of a polypropylene composition as described above or below as cable insulation for medium and high voltage cables.

[0180] The medium and high voltage cables preferably meet all performance requirements described for the cables above and below.

[0181] Advantages of the present invention:

[0182] The polypropylene composition of the present invention shows a good balance of properties with respect to high flexibility, good mechanical strength, good impact properties and high crystallization and melting temperatures, which allows the use as cable insulation, e.g. for medium and high voltage cables at high operating temperatures.

[0183] The cables comprising an insulation layer comprising the polypropylene composition of the present invention surprisingly show good electrical breakdown strength in the form of Weibull alpha and Weibull beta values.

[0184] Thus, the presence of the α-nucleating agent in the polypropylene composition of the present invention further improves the electrical properties, in particular as manifested in a narrower distribution of electrical breakdown strength values ​​and consequently higher Weibull β values.

[0185] It has been found that the polypropylene of the present invention can be easily compounded to prepare insulation layers even at a melt flow rate as low as 0.5 to 2.5 g / 10 min, without the need to increase the melt flow rate by visbreaking.

[0186] Good electrical breakdown strength in the form of Weibull alpha and Weibull beta values ​​can be obtained without adding dielectric fluids as described in, for example, EP 2 739 679.

[0187] The electrical properties can be further improved when the semiconducting composition of the semiconducting layer is adapted to a propylene-based composition rather than an ethylene-based composition. This behavior is believed to be due to the increased adhesion between the semiconducting layer and the insulating layer due to the similar polymer composition.

[0188] Thus, the polypropylene composition as described above or below shows an excellent balance of properties with respect to high flexibility, good mechanical strength, good impact properties and high crystallization and melting temperatures, which allows the use as cable insulation, e.g. for medium and high voltage cables with good electrical breakdown strength at high operating temperatures.

[0189] Example

[0190] Unless otherwise indicated, the following definitions of terms and determination methods apply to the above general description of the invention as well as the following examples.

[0191] 1. Measurement method

[0192] a) Melt flow rate (MFR2)

[0193] Melt flow rate is the amount of polymer in grams that is extruded in 10 minutes at a specific temperature and a specific load using a test apparatus standardized to ISO 1133 or ASTM D1238.

[0194] The melt flow rate MFR2 of the propylene-based polymer and the polypropylene composition is measured according to ISO 1133 at 230°C and a load of 2.16 kg.

[0195] The melt flow rate MFR2 of the ethylene-based polymers and polyethylene compositions is measured according to ISO 1133 at 190°C and a load of 2.16 kg.

[0196] b) Comonomer content

[0197] Quantitative nuclear magnetic resonance (NMR) spectroscopy was used to quantify the comonomer content of the polymers.

[0198] Quantification of comonomer content of poly(propylene-co-ethylene) copolymers

[0199] for 1 H and 13 C, quantitative data were recorded in solution using a Bruker Advance III 400 NMR spectrometer operating at 400.15 and 100.62 MHz, respectively. 13 C{ 1 H} NMR spectra. All spectra were obtained using 13Recordings were made at 125°C using a C-optimized 10 mm extended temperature probe, with nitrogen used for all pneumatics. Approximately 200 mg of material was dissolved in 3 ml of 1,2-tetrachloroethane-d2 (TCE-d2) along with chromium(III) acetylacetonate (Cr(acac)3) to form a 65 mM solution of the relaxant in the solvent {8}. To ensure a homogeneous solution, the NMR tube was further heated in a rotary oven for at least 1 hour after initial sample preparation in a heating block. After insertion into the magnet, the tube was rotated at 10 Hz. This setup was chosen primarily due to the high resolution and quantitative requirements for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimized tip angle, a 1 s recycle delay, and a two-stage WALTZ16 decoupling scheme {3,4}. A total of 6144 (6k) transients were acquired for each spectrum.

[0200] Quantification was performed using a proprietary computer program 13 C{ 1 The H} NMR spectra were processed, integrated, and the relevant quantitative properties were determined from the integration. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This method allows for a comparable reference even when this structural unit is not present. Characteristic signals corresponding to ethylene incorporation were observed {7}.

[0201] Using the method of Wang et al. {6} 13 C{ 1 The comonomer fraction is quantified by integrating multiple signals over the entire spectral region of the H} spectrum. This method was chosen for its robustness and ability to account for the presence of regio defects when needed. The integration region is slightly adjusted to increase applicability over the full range of comonomer contents encountered.

[0202] For systems where only isolated ethylene is observed in the PPEPP sequence, the method of Wang et al. was modified to reduce the effect of nonzero integrals at sites known to be absent. This approach reduces the overestimation of ethylene content in such systems by reducing the number of sites used to determine absolute ethylene content:

[0203] E=0.5(Sββ+Sβγ+Sβδ+0.5(Sαβ+Sαγ))

[0204] Using this set of sites, the corresponding integral equation becomes:

[0205] E=0.5(I H +I G +0.5(I C +I D ))

[0206] The same symbols used in the article by Wang et al. {6} were used. The equations for absolute propylene content were not modified.

[0207] The mole percentage of comonomer incorporation is calculated from the mole fraction:

[0208] E[mol%]=100*fE

[0209] The weight percent of comonomer incorporation is calculated from the mole fraction:

[0210] E[weight%]=100*(fE*28.06) / ((fE*28.06)+((1-fE)*42.08))

[0211] bibliography:

[0212] 1) Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443.

[0213] 2) Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, AL, Macromolecules 30 (1997) 6251.

[0214] 3) Zhou, Z., Kuemmerle, R., Qiu,

[0215] 4) Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128.

[0216] 5)Resconi,L.,Cavallo,L.,Fait,A.,Pimontesi,F.,Chem.Rev.2000,100,1253.

[0217] 6) Wang, WJ., Zhu, S., Macromolecules 33 (2000), 1157.

[0218] 7)Cheng, HN, Macromolecules 17 (1984), 1950.

[0219] 8)Singh, G., Kothari, A., Gupta, V., Polymer Testing 28 5 (2009), 475.

[0220] 9) Kakugo, M., Naito, Y., Mizunuma, K., Miyatake, T. Macromolecules 15 (1982) 1150.

[0221] 10) Randall, J. Macromol. Sci., Rev. Macromol. Chem. Phys. 1989, C29, 201.

[0222] 11) Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253.

[0223] c) Differential scanning calorimetry (DSC) analysis, melting temperature (Tm) and crystallization temperature (Tc) :

[0224] The measurements were performed on 5 to 7 mg samples using a TA Instrument Q2000 Differential Scanning Calorimetry (DSC). The DSC was run according to ISO 11357 / Part 3 / Method C2 in a heating / cooling / heating cycle with a scan rate of 10°C / min over a temperature range of -30°C to +225°C.

[0225] The crystallization temperature and the heat of crystallization (Hc) are determined by the cooling step, while the melting temperature and the heat of fusion (Hf) are determined by the second heating step.

[0226] When a sample shows two or more melting temperatures and / or crystallization temperatures, only the main melting temperature (at the highest Hc) and the main crystallization temperature (at the highest Hf) are shown in the corresponding table. The difference between the melting temperature and the crystallization temperature (Tm-Tc) is given for the main melting temperature and the main crystallization temperature.

[0227] d) Xylene cold soluble matter (XCS) content

[0228] The amount of xylene solubles in polypropylene is determined according to ISO 16152 (first edition; 2005-07-01).

[0229] A weighed amount of sample is dissolved in hot xylene at reflux at 135°C. The solution is then cooled under controlled conditions and held at 25°C for 30 minutes to ensure controlled crystallization of the insoluble fraction. This insoluble fraction is then separated by filtration. The xylene is evaporated from the filtrate, leaving a soluble fraction as a residue. The percentage of this fraction is determined gravimetrically.

[0230]

[0231] in

[0232] m0 is the mass of the weighed test sample in grams

[0233] m1 is the mass of the residue in grams

[0234] v0 is the original volume of the solvent taken

[0235] v1 is the volume of the aliquot used for the assay.

[0236] e) Intrinsic viscosity (IV int )

[0237] The reduced viscosity (also called viscosity value) η was determined according to ISO 1628-3: "Determination of the viscosity of polymers in dilute solution using capillary viscometers" red and intrinsic viscosity [η].

[0238] The relative viscosities of diluted polymer solutions at a concentration of 1 mg / ml and the pure solvent (decalin stabilized with 200 ppm of 2,6-bis(1,1-dimethylethyl)-4-methylphenol) were measured using an automated capillary viscometer (Lauda PVS1) equipped with four Ubbelohde capillaries placed in a thermostatic bath filled with silicone oil. The bath temperature was maintained at 135°C. The sample was dissolved under constant stirring until complete dissolution was achieved (typically within 90 minutes).

[0239] The elution times of the polymer solutions and the pure solvents were measured several times until the difference between three consecutive readings did not exceed 0.2 seconds (standard deviation).

[0240] The relative viscosity of the polymer solution is determined as the ratio of the mean efflux times (in seconds) obtained for both the polymer solution and the solvent:

[0241] [dimensionless]

[0242] Reduced viscosity (η red ) is calculated using the following equation:

[0243] [dl / g]

[0244] Where C is the concentration of the polymer solution at 135°C:

[0245] And m is the mass of polymer, V is the volume of solvent, γ is the ratio of the density of solvent at 20℃ and 135℃ (γ=ρ 20 / ρ 135 =1.107).

[0246] Calculation of intrinsic viscosity [η] is performed from single concentration measurements using the Schulz-Blaschke equation:

[0247]

[0248] where K is a coefficient that depends on the polymer structure and concentration. To calculate an approximate value for [η], K = 0.27.

[0249] f) Average molecular weight, polydispersity (Mn, Mw, Mz, MWD) by GPC analysis (GPC)

[0250] For GPC analysis, the column set was calibrated using universal calibration (according to ISO 16014-2:2003) with 19 narrow MWD polystyrene (PS) standards ranging from 0.5 kg / mol to 11,500 kg / mol. The PS standards were dissolved at 160°C for 15 minutes, or alternatively at room temperature, at a concentration of 0.2 mg / ml for molecular weights greater than or equal to 899 kg / mol and 1 mg / ml for molecular weights less than 899 kg / mol. Conversion of polystyrene peak molecular weights to polyethylene molecular weights was accomplished using the Mark Houwink equation and the following Mark Houwink constants:

[0251] K PS =19x 10 -3 ml / g,α PS =0.655

[0252] K PE =39x 10 -3 ml / g,α PE =0.725

[0253] A third-order polynomial fit was used to fit the calibration data.

[0254] The molecular weight averages (Mz, Mw and Mn), the molecular weight distribution (MWD) and its breadth, which is described by the polydispersity index PD = Mw / Mn (where Mn is the number average molecular weight and Mw is the weight average molecular weight) are determined using the following formula:

[0255]

[0256]

[0257]

[0258] g) flexural modulus

[0259] Flexural modulus was measured according to ISO 178, Method A (three-point bend test) on 80 mm x 10 mm x 4 mm specimens. In accordance with the standard, a test speed of 2 mm / min and a span length of 16 times the thickness were used. The test temperature was 23 ± 2°C. Injection molding was performed according to ISO 19069-2 using a melt temperature of 230°C for all materials, regardless of melt flow rate.

[0260] h) Simple supported beam notched impact strength

[0261] Charpy notched impact strength was measured according to ISO 179-1 / 1eA on notched 80 mm x 10 mm x 4 mm specimens (samples prepared according to ISO 179-1 / 1eA). The test temperature was 23 ± 2°C or -20 ± 2°C. Injection molding was performed according to ISO 19069-2 using a melt temperature of 230°C for all materials, regardless of melt flow rate.

[0262] i) AC breakdown strength (ACBD)

[0263] AC breakdown tests are performed on 6 / 10 kV cables in accordance with CENELEC HD 605 5.4.15.3.4. Therefore, the cable is cut into six test specimens with an effective length of 10 meters (plus end caps). The specimens are subjected to breakdown tests at ambient temperature using a 50 Hz AC step test according to the following procedure:

[0264] Start at 18kV and continue for 5 minutes

[0265] The voltage is increased in steps of 6 kV every 5 minutes until breakdown occurs

[0266] The Weibull parameters for the six breakdown value (conductor stress, i.e., the electric field in the inner semiconductor layer) data sets were calculated using the least-squares regression procedure described in IEC 62539 (2007). The Weibull α parameter in this document refers to the scale parameter of the Weibull distribution, i.e., the voltage at which the probability of failure is 0.632. The Weibull β value refers to the shape parameter.

[0267] 2. Propylene copolymer composition

[0268] The following resins were used to prepare the propylene copolymer compositions of the examples:

[0269] a) Polymerization of heterophasic propylene copolymer powders A1 and A2

[0270] ·catalyst

[0271] The catalyst used during the polymerization of the heterophasic propylene copolymer powders A1 and A2 was a Ziegler-Natta catalyst which is described in patent publications EP 491566, EP 591224 and EP 586390. Triethylaluminium (TEAL) was used as cocatalyst and dicyclopentyldimethoxysilane (D-donor) as donor.

[0272] Polymerization of heterophasic propylene copolymer powder

[0273] A liquid phase loop reactor and two gas phase reactors connected in series were used under the conditions shown in Table 1 in the presence of the above polymerization catalyst at Borstar TM Heterophasic propylene copolymer powders A1 and A2 are produced in a plant. The first reaction zone is a loop reactor, and the second and third reaction zones are gas phase reactors. The matrix phase is polymerized in the loop reactor and the first gas phase reactor, and the elastomeric phase is polymerized in the second gas phase reactor. The catalyst as described above is fed to the prepolymerization reactor preceding the first reaction zone.

[0274] Table 1: Polymerization conditions of heterophasic propylene copolymer powders A1 and A2:

[0275] A1-Powder A2-Powder Prepolymerization TEAL / Ti ratio [mol / mol] 342 404 Donor / Ti ratio [mol / mol] 26.9 27.1 temperature [℃] 19.9 20.0 Dwell time [h] 0.16 0.15 Ring pipe temperature [℃] 70.0 70.0 pressure [barg] 55 55 Split ratio (loop + prepolymerization) [％] 33.7 32.6 H2 / C3 ratio [mol / kmol] 5.5 5.0 C2 / C3 Ratio [mol / kmol] 16.7 17.2 MFR (230℃ / 2.16kg) [g / 10min] 6.5 5.4 C2 content (calculated) [weight%] 2.0 2.0 GPR 1 temperature [℃] 74.9 74.9 pressure [barg] 21.0 21.1 Split ratio (GPR1) [％] 48.2 47.8 H2 / C3 ratio [mol / kmol] 21.3 19.3 C2 / C3 Ratio [mol / kmol] 53.4 58.0 MFR (230℃ / 2.16kg) [g / 10min] 1.3 1.3 C2 content (calculated) [weight%] 6.5 6.6 GPR 2 temperature [℃] 79.99 79.96 pressure [barg] 16.03 14.97 Split ratio (GPR2) [％] 18.2 19.5 C2 / C3 Ratio [mol / kmol] 401 432 H2 / C3 ratio [mol / kmol] 69 76 MFR (230℃ / 2.16kg) [g / 10min] 1.2 1.1 XCS [weight%] 35.3 39.2 C2 (calculated content) [weight%] 10.5 11.3

[0276] b) Preparation of polypropylene composition

[0277] In a first process, heterophasic propylene copolymer powders A1 and A2 from the polymerization were mixed in a twin screw extruder with different stabilizer packages to obtain the polypropylene compositions of examples CE1, IE1, IE2, IE3 and IE4.

[0278] Depending on the respective polypropylene composition, different α-nucleating agents are added.

[0279] The compositions of Examples IE2 to IE4 were visbroken to a melt flow rate MFR2 (230°C, 2.16 kg) of 3.8-3.9 g / 10 min as disclosed in the Examples section of WO 2017 / 198633.

[0280] An overview of the production of the polypropylene compositions of Examples CE1, IE1, IE2, IE3 and IE4 is shown in Table 2.

[0281] Table 2: Compounding of CE1, IE1, IE2, IE3 and IE4 in a twin-screw extruder:

[0282]

[0283] In a second method, the composite pellets of comparative example CE1 were mixed in a Buss 100MDK L / D 11D co-kneader in a second mixing step together with different α-nucleating agents to obtain the polypropylene compositions of examples CE2, IE5 and IE6.

[0284] An overview of the production of polypropylene compositions CE2, IE5 and IE6 is shown in Table 3.

[0285] Table 3: Mixing of CE2, IE5 and IE6 in a Buss 100MDK L / D 11D co-kneader:

[0286] CE2 IE5 IE6 Granules CE1 CE1 CE1 α-NA DMDBS [weight%] - 0.2 - α-NA NX8000 [weight%] - - 0.4 Mixer Zone Temperature Settings [C] 150-200 160-200 150-200 Mixer RPM 150 150 150 Specific energy input SEI [kWh / kg] 0.29 0.28 0.28

[0287] Stabilizer Package and Alpha-Nucleating Agent:

[0288] Stabilizer Single Pack 1 consists of 21.8 wt% pentaerythritol tetrakis(3-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate (CAS No. 6683-19-8), 43.6 wt% tris(2,4-di-tert-butylphenyl)phosphite (CAS No. 31570-04-4), and 34.6 wt% calcium stearate (CAS No. 1592-23-0), all of which are commercially available from various companies.

[0289] Stabilizer Single Pack 2 consists of 29 wt% pentaerythritol tetrakis(3-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate (CAS No. 6683-19-8), 58 wt% tris(2,4-di-tert-butylphenyl)phosphite (CAS No. 31570-04-4), and 13 wt% magnesium oxide (CAS No. 1309-48-4), all of which are commercially available from various companies.

[0290] Stabilizer Single Pack 3 consists of 15.6 wt% pentaerythritol tetrakis(3-(3',5'-di-tert-butyl-4-hydroxyphenyl)propionate (CAS No. 6683-19-8), 15.6 wt% tris(2,4-di-tert-butylphenyl)phosphite (CAS No. 31570-04-4), 15.6 wt% calcium stearate (CAS No. 1592-23-0), and 53.2 wt% of the α-nucleating agent 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS, CAS No. 135861-56-2), all of which are commercially available from multiple companies.

[0291] The α-nucleating agent DMDBS (1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol, CAS No. 135861-56-2) is commercially available from various companies.

[0292] • α-nucleating agent Millad NX8000, 1,2,3-trideoxy-4,6:5,7-bis-O-((4-propylphenyl)methylene)nonitol (CAS No. 882073-43-0) is commercially available from Milliken Chemical Company.

[0293] α-Nucleation via BNT was achieved by adding 2 wt% of a propylene homopolymer having an MFR2 (230°C) of 8.0 g / 10 min and a melting temperature of 162°C, produced with Borealis Nucleation Technology (BNT) using a Ziegler-Natta type catalyst, containing a polymeric α-nucleating agent, and distributed by Borealis AG (Austria).

[0294] The polypropylene compositions CE1-CE2 and IE1-IE6 showed the properties listed in Tables 4 and 5 below.

[0295] Table 4: Properties of polypropylene compositions CE1, IE1-IE4:

[0296] CE1 IE1 IE2 IE3 IE4 HECO powder A1 A1 A1 A2 A2 α-NA none BNT BNT BNT DMDBS <![CDATA[MFR2]]> [g / 10min] 1.2 1.3 3.9 3.8 3.8 flexural modulus [MPa] 335 370 378 361 351 Simply supported beam NIS (-20℃) <![CDATA[[kJ / m 2 ]]]> 6.3 6.5 4.2 5.2 6.8 Simply supported beam NIS (23°C) <![CDATA[[kJ / m 2 ]]]> 83.9 83.6 78.9 77.7 79.2 Tm [℃] 148.9 146.6 147.4 147.1 149.2 Tc [℃] 95.7 113.6 114.5 112.4 119.5 Tm-Tc [℃] 53.2 33.0 32.9 34.7 29.7 C2(Total) [weight%] 12.4 12.4 11.3 12.5 13.6 <![CDATA[V int (Total)]]> <![CDATA[[cm 3 / g]]]> 277 268 213 nm nm XCS fraction [weight%] 35.6 34.7 35.6 37.4 40.3 C2(XCS) [weight%] 26.1 26.3 24.5 25.0 26.0 <![CDATA[V int (XCS)]]> <![CDATA[[cm 3 / g]]]> 251 243 189 194 202 Mw(XCS) [g / mol] 294,500 285,000 215,000 211,500 219,000 Mn(XCS) [g / mol] 45,650 45,400 48,900 50,700 44,850 PDI (Mw / Mn) (XCS) [-] 6.4 6.3 4.4 4.2 4.9 XCI fraction [weight%] 64.4 65.3 64.4 62.6 59.7 C2(XCI) [weight%] 4.8 5.5 5.8 5.5 6.6 <![CDATA[V int (XCI)]]> <![CDATA[[cm 3 / g]]]> 286 275 216 217 212 Mw(XCI) [g / mol] 384,500 372,500 271,000 273,000 271,500 Mn(XCI) [g / mol] 69,500 68,100 62,000 59,250 60,050 PDI (Mw / Mn) (XCI) [-] 5.5 5.5 4.4 4.6 4.5 <![CDATA[V int Ratio (XCI / XCS) [-] 1.14 1.13 1.14 1.12 1.05 Mw ratio (XCI / XCS) [-] 1.31 1.31 1.26 1.29 1.24

[0297] Table 5: Properties of polypropylene compositions CE1, IE5 and IE6:

[0298] CE2 IE5 IE6 Granules CE1 CE1 CE1 α-NA none DMDBS NX8000 <![CDATA[MFR2]]> [g / 10min] 1.4 1.4 1.4 flexural modulus [MPa] 351 390 428 Simply supported beam NIS (-20℃) <![CDATA[[kJ / m 2 ]]]> 4.5 5.0 4.2 Simply supported beam NIS (23°C) <![CDATA[[kJ / m 2 ]]]> 79.9 79.3 77.2 Tm [℃] 149.9 148.4 151.8 Tc [℃] 97.4 119.0 123.2 Tm-Tc [℃] 52.5 29.4 28.2

[0299] nm = not measured

[0300] Production of 3.10kV cables

[0301] The 10kV test cable is produced on the catenary continuous vulcanization (CCV) type Maillefer test cable line.

[0302] The conductor of the cable core has a cross section of 50 mm 2 of stranded aluminum with a cross section of 50 mm 2 The inner semiconducting layer was produced from the semiconducting composition SC1, SC2 or SC3 described below and had a thickness of 1.0 mm. The insulating layer was produced from the above compositions C1 and CE2 and IE1 to IE6 and had a thickness of 3.4 mm. The inner semiconducting layer was produced from the semiconducting composition SC1, SC2 or SC3 described below and had a thickness of 1.0 mm.

[0303] The cable (i.e., the cable core) is produced using a three-head extrusion process. The insulation extruder is 100 mm in diameter, the conductor shield (inner semiconducting layer) extruder is 45 mm in diameter, and the insulation shield (outer semiconducting layer) extruder is 60 mm in diameter. The line speed is 6.0 m / min.

[0304] The total length of the vulcanization tube is 52.5 meters, consisting of a curing section followed by a cooling section. The curing section is filled with 10 bar nitrogen but is not heated. The 33-meter-long cooling section is filled with water at 20-25°C.

[0305] Then perform an AC breakdown test on the test cable.

[0306] The semiconducting layer 1 (SC1) was prepared from the ready-to-use semiconducting composition Borlink LE7710, a non-crosslinkable polyethylene-based composition comprising carbon black, commercially available from Borealis AG.

[0307] Semiconducting layer 2 (SC2) was prepared from 66.5 wt% of the polypropylene-based composition of CE1 with 33.0 wt% of carbon black Printex Alpha (commercially available from Orion Engineered Carbons GmbH) and 0.5 wt% of maleic anhydride-grafted propylene homopolymer Exxelor PO1020, which has a melt flow rate of 430 g / 10 min at 230° C. and a load of 2.16 kg and is commercially available from ExxonMobil.

[0308] Semiconductor layer 3 (SC3) was prepared from 70 wt% of the polypropylene-based composition of IE3 and 30.0 wt% of carbon black Printex Alpha (commercially available from Orion Engineered Carbons GmbH).

[0309] Table 6 shows the electrical properties of 10 kV cables of Examples C1-C8, wherein the insulation layers IE1-IE6 according to the invention are compared with the comparative insulation layers CE1 and CE2.

[0310] Table 6: Electrical properties of 10kV cables C1-C8

[0311] C1 C2 C3 C4 C5 C6 C7 C8 insulation layer CE1 IE1 IE2 IE3 IE4 CE2 IE5 IE6 Inner semiconductor layer SC1 SC1 SC2 SC3 SC3 SC2 SC2 SC2 Outer semiconductor layer SC1 SC1 SC1 SC3 SC3 SC1 SC1 SC1 Weibull-α (scale) [kV / mm] 48.7 47.0 50.8 48.1 44.6 43.8 46.7 47.6 Weibull-β (shape) 7.0 9.3 8.9 35.0 19.0 6.4 14.4 17.5

[0312] It can be seen that all tested cables C1 to C8 show good dielectric properties in terms of Weibull-α parameters. When comparing C1 with C2 to C5 and C6 with C7 and C8, it can be seen that the introduction of an α nucleating agent (BNT, DMDBS or Millad NX8000) increases the Weibull-β parameters.

Claims

1. A polypropylene composition comprising (A) a copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms, the total amount of comonomer units of the copolymer being 10.0 to 16.0 wt.%, based on the total amount of monomer units in the polypropylene composition, and (B) α-nucleating agent; wherein the polypropylene composition has a xylene cold soluble (XCS) fraction in a total amount of 25.0 to 50.0 wt.-%, based on the total weight of the polypropylene composition, the amount of comonomer units of the xylene cold soluble (XCS) fraction being at least 23.0 wt.-%, based on the total amount of monomer units in the xylene cold soluble (XCS) fraction, a melt flow rate MFR2 of 0.5 to 5.0 g / 10 min, and Flexural modulus not exceeding 470 MPa.

2. The polypropylene composition according to claim 1, wherein the xylene cold soluble (XCS) fraction has an intrinsic viscosity measured in decalin of from 150 to 350 cm 3 / g.

3. The polypropylene composition according to claim 1 or 2, having a xylene insoluble fraction (XCI), the amount of comonomer units in the xylene insoluble fraction being from 3.0 to 9.0 wt.-%, based on the total amount of monomer units in the xylene insoluble fraction (XCI).

4. The polypropylene composition according to claim 1 or 2, wherein the copolymer of propylene and comonomer units selected from ethylene and α-olefins having 4 to 12 carbon atoms is a heterophasic copolymer of propylene comprising a matrix phase and an elastomeric phase dispersed in the matrix phase.

5. The polypropylene composition according to claim 4, wherein the heterophasic copolymer of propylene comprises two glass transition temperatures attributable to the matrix phase and the elastomeric phase, wherein the glass transition temperature attributable to the matrix phase is in the range of -1.0 to -15.0°C and / or the glass transition temperature attributable to the elastomeric phase is in the range of -40.0 to -55.0°C.

6. The polypropylene composition according to claim 1 or 2, having a melting temperature Tm of 140 to 159°C.

7. The polypropylene composition according to claim 1 or 2, having a crystallization temperature Tc of 105 to 130°C.

8. The polypropylene composition according to claim 1 or 2, having a Charpy notched impact strength at -20°C of at least 3.5 kJ / m 2 .

9. The polypropylene composition according to claim 1 or 2, having a Charpy notched impact strength at 23°C of at least 70.0 kJ / m 2 .

10. The polypropylene composition according to claim 1 or 2, having a melt flow rate MFR2 of greater than 0.5 to 2.5 g / 10 min.

11. The polypropylene composition according to claim 1 or 2, having a melt flow rate MFR2 of greater than 2.5 to 5.0 g / 10 min.

12. The polypropylene composition according to claim 11, which is visbroken.

13. The polypropylene composition according to claim 1 or 2, which contains no dielectric fluid.

14. An article comprising the polypropylene composition according to any one of claims 1 to 13.

15. The article according to claim 14, which is a cable comprising an insulation layer comprising the polypropylene composition.

16. The article according to claim 14, which is a medium voltage cable or a high voltage cable comprising an insulation layer comprising the polypropylene composition.

17. The article according to claim 15 or 16, which is a cable comprising an insulation layer comprising the polypropylene composition and having a Weibull alpha value of at least 35 kV / mm and / or a Weibull beta value of at least 7.5, measured on a 10 kV cable.

18. Use of the polypropylene composition according to any one of claims 1 to 13 as cable insulation for medium and high voltage cables.

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