Heterophasic propylene copolymer with improved stiffness and stress whitening

Abstract

The invention relates to a composition comprising a heterophasic propylene copolymer, to a process for obtaining such composition, to the use of such composition and an article comprising such composition.

Description

[0001] HETEROPHASIC PROPYLENE COPOLYMER WITH IMPROVED STIFFNESS AND STRESS WHITENING

[0002] The invention relates to a composition comprising a heterophasic propylene copolymer, to a process for obtaining such composition, to the use of such composition and an article comprising such composition.

[0003] Heterophasic propylene copolymer, also known as impact propylene copolymers or propylene block copolymers, are an important class of polymers due to their attractive combination of mechanical properties, such as impact strength over a wide temperature range and their low cost. These copolymers find a wide range of applications ranging from the consumer industry (for example packaging and housewares), the automotive industry to electrical applications. For applications e.g. electrical application and electrical appliance, a part made of a heterophasic propylene copolymer is prone to suffer from whitening after a mechanical impact on the surface. This phenomena is named stress whitening which is not desired for applications requiring surface aesthetics. Upon improving the stress whitening performance, other properties e.g. mechanical properties of a heterophasic propylene copolymer are often compromised.

[0004] Therefore there is still a need to have a heterophasic propylene copolymer having improved stress whitening performance without deterioration of mechanical properties. Specifically, it is desired to have a heterophasic propylene copolymer having improved stress whitening performance while having even improved stiffness without compromising impact performance at low temperature.

[0005] This need is satisfied by a heterophasic propylene copolymer comprising a propylene based matrix and an ethylene copolymer as dispersed phase, wherein the amount of ethylene copolymer is in the range of 8.5 to 12.5 wt% basing on the total amount of the heterophasic propylene copolymer, wherein the amount of ethylene in the ethylene copolymer is in the range of 32.0 to 40.0 wt% basing on the total amount of the ethylene copolymer, wherein the melt flow index of the heterophasic propylene copolymer is in the range from 15 to 35 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 230 °C.

[0006] Propylene based matrix

[0007] The propylene based matrix may be a propylene homopolymer or a propylene random copolymer of ethylene or a C4 -C20 a-olefin. Preferably the propylene based matrix is a propylene homopolymer.

[0008] Ethylene copolymer as dispersed phase

[0009] The ethylene copolymer according to the invention is preferably an ethylene-a-olefin copolymer wherein the a-olefin is selected from C3-C8 a-olefin. Most preferably the ethylene copolymer is an ethylene-propylene copolymer.

[0010] The ethylene copolymer differs from the propylene based matrix to form as dispersed phase.

[0011] The amount of ethylene in the ethylene copolymer is in the range of 32.0 to 40.0 wt%, preferably 34.0 to 40.0 wt%, more preferably 35.0 to 39.0 wt% basing on the total amount of the ethylene copolymer.

[0012] Nucleating agent

[0013] Preferably the heterophasic propylene copolymer comprises a nucleating agent, wherein the nucleating agent comprises talc and a cyclic dicarboxylate salt compound.

[0014] The cyclic dicarboxylate salt compound has the formula (I):

[0015] Such nucleating compositions are as described in WO2014202603 and WO201 4202604.

[0016] Hyperform® HPN-20E™ nucleating agent commercialized by Milliken comprises such a calcium cis-hexahydrophthalate compound of Formula (I) and a stearate-containing compound as acid scavenger, e.g. zinc stearate.

[0017] Preferably ratio between the amount of talc and the amount of the cyclic dicarboxylate salt compound is in the range between 13 to 26, more preferably from 15 to 23, even more preferably from 18 to 22.

[0018] Heterophasic propylene copolymer

[0019] The amount of ethylene copolymer is in the range of 8.5 to 12.5 wt%, preferably 8.5 to 11 .5 wt%, even more preferably from 8.5 to 10.4 wt%, most preferably from 8.5 to 9.5 wt% basing on the total amount of the heterophasic propylene copolymer. In the context of the present invention, the amount of ethylene copolymer in the heterophasic propylene copolymer and the amount of ethylene comonomer in the ethylene copolymer may be determined by FT-IR during the polymerization process.

[0020] The amount of the cyclic dicarboxylate salt compound may be from 0.0025 to 0.1 wt% based on the total amount of the heterophasic propylene copolymer; preferably at least 0.004, 0.005, 0.008, 0.01 wt% and / or at most 0.08, 0.06, 0.05, 0.03 wt%, based on the total amount of the heterophasic propylene copolymer. The amount of talc in the polymer composition is preferably of from 0.1 to 5 wt%, more preferably from 0.2 to 4 wt%, more preferably from 0.3 to 3 wt%, most preferably from 0.3 to 1 wt% based on the total composition based on the total amount of the heterophasic propylene copolymer.

[0021] Preferably the total amount of the propylene based matrix, the ethylene copolymer and the nucleating agent is at least 96 wt%, preferably at least 98 wt%, even more preferably at least 99 wt% basing on the total amount of the heterophasic propylene copolymer.

[0022] The melt flow index of the heterophasic propylene copolymer is in the range from 15 to 35 g / 10min, preferably from 17 to 29 g / 10min, more preferably from 18 to 25 g / 10min, even more preferably from 19 to 22 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 230 °C.

[0023] To concentrate the rubber content of the heterophasic propylene copolymer, preparative temperature rising elution fractionation (p-TREF) was performed. Around 1 gram of material was completely dissolved in 150 mL of Xylene at 130 °C after which the solution was slowly cooled down at 0.1 °C / min to 30 °C. After this cooling down the solution is heated up again and the rubber fraction is collected at 98 °C while the second fraction which is mainly iPP is collected by further increasing the temperature to 130 °C. The fractions were dried to a constant weight and measured.

[0024] The first fraction collected as 98 °C was further measured using High-temperature two- dimensional liquid chromatography (HT-2D-LC). HT-2D-LC provides information on the chemical composition and molar mass distributions (CCD and MMD) of sample components. While these two microstructural parameters can be obtained independently, HT-2D-LC directly correlates them in a single experiment. The two dimensions are combined using a modulator valve which transfers the fractions the fractions from the first dimension (solvent gradient interaction chromatography, SGIC) to the second dimension (size exclusion chromatography, SEC).

[0025] In the first dimension, separation is according to chemical composition i.e. , in this case short chain branching. Copolymer components are retained according to the ethylene segment length (i.e., from random to block copolymers with long ethylene sequence lengths). So differences in ethylene build in in the EPR phase are quantified with this method. In the second dimension, separation is according to the size of the copolymer chains.

[0026] The data from the HT-2D-LC result calculation is converted to projected profile information using the GPC-1 software. The profiles are plotted as elution volume in the first dimension against the IR5 detector response. The elution volume dimension is converted to chemical composition distribution information using the first dimension calibration.

[0027] Preferably, the heterophasic propylene copolymer according to the invention has a C2 (ethylene) content at peak elution volume of at least 3.5 mol%, more preferably at most 4.5 mol%, more preferably at least 5 mol%, even more preferably at least 5.5 mol%. The elution volume may for example determined by High-temperature two-dimensional liquid chromatography (HT-2D-LC). Suitable device to carry out the measurement may for example be PolymerChar (Valencia, Spain) solvent gradient chromatograph equipped with an integrated IR5 detector, a binary gradient pump as well as an isocratic pump (both model 1260, Agilent, Waldbronn, Germany). In the context of the present invention, the elution volume of the heterophasic propylene copolymer was determined as following: Sample concentrations of ~ 4.2 mg / mL (solvent 1 -decanol) were used. For dissolution, the samples were first heated in an offline autosampler at 160 °C with shaking until dissolution. Prior to injection, the sample was allowed a further one hour of dissolution under shaking. The following experimental parameters were chosen: Elution temperature: 160 °C, SGIC flow rate: 0.01 mL / min, injection loop: 200 pL, SGIC stationary phase: Hypercarb® (particle size: 5 pm, column dimensions: 100 x 4.6 mm (L x I.D.) (Thermofisher Scientific, Dreieich, Germany)). As eluent, a 1-decanol TCB gradient was used with the following program: 0 - 1000 min linear gradient from 1 - decanol to TCB, 1000 - 1200 min pure TCB. The column was then purged for 40 min with 1 -decanol at a flow velocity of 0.8 mL / min in order to establish the original adsorption equilibrium in the column again. The mobile phase coming from the Hypercarb® column was collected in 100 pL sample loops. These were injected into the SEC column (PLGel Olexis, 300 x 7.8 mm (L x |.D.) (Agilent Technologies, Waldbronn, Germany) every 10 minutes. SEC was analysis in the second dimension was done in TCB at 160 °C, using a flow rate of 1 .5 mL / min. Calibration of the first dimension is based on the a set narrowly distributed ethylene-propylene copolymers with different amounts of ethylene. Calibration of the second dimension is based on a set of narrowly distributed polystyrene standards (PolymerChar, (Valencia, Spain)). Data collection and anlysis was performed using the PolymerChar software and processed in the GPC 1 software as well as OriginPro version 2019b.

[0028] For evaluation of the chromatograms, the peak and center of distribution (COD) of the eluting rubber components were chosen. Peak elution volumes are typically used in chromatography as a characteristic representative of the eluting species where peaks are symmetrical in shape. On the other hand, where peaks show a lack of symmetry or skewness, the center of gravity (COG), center of mass (COM) or COD becomes a better descriptor. After the calibration of the first dimension using narrowly distributed ethylene-propylene copolymers, the following linear calibration equation was established for the system:

[0029] Calibration equation

[0030] [C] mol.% = 21.6996 x (First dimension elution volume) - 65.9464

[0031] Intercept -65.9464 ±1.1325 mol.%

[0032] Slope 21.6996 ± 0.2108

[0033] Therefore ethylene content at peak elution volume is a parameter linked to the manner that ethylene comonomer builds in a heterophasic propylene copolymer. Surprisingly it was found that the heterophasic propylene copolymer with preferred ethylene content at peak elution volume has improved mechanical property and stress whitening behaviour. Preferably the heterophasic propylene copolymer has a flexural modulus of at least

[0034] 1700 MPa, more preferably at least 1750 MPa as measured according to ASTM D790.

[0035] Preferably the heterophasic propylene copolymer has a notched Izod value of at least 2.5 kJ / m2 as measured according to ISO 180 / 4A.

[0036] Preferably the heterophasic propylene copolymer has a stress whitening value of at most 210 mm2, preferably at most 200 mm2.

[0037] The heterophasic propylene copolymer may be prepared by a process comprising

[0038] - polymerizing propylene in the presence of a catalyst to obtain the propylene-based matrix and

[0039] - subsequently polymerizing ethylene with a-olefins in the presence of a catalyst in the propylene-based matrix to obtain the heterophasic propylene copolymer. These steps are preferably performed in different reactors. The catalysts for the first step and for the second step may be different, but are preferably the same.

[0040] The catalyst used for the preparation for the polypropylene composition according to the invention is the catalyst described in detail in WO2021 / 063930, incorporated herein by reference. The catalyst comprises a procatalyst, a co-catalyst and optionally an external electron donor.

[0041] The procatalyst is obtainable by a process comprising contacting a magnesium- containing support with a halogen-containing titanium compound, and an internal electron donor according to Formula I:

[0042] Formula I wherein R1is a secondary alkyl group and R2is a non-secondary alkyl group having at least 5 carbon atoms, preferably R2is a non-secondary alkyl group having at least 5 carbon atoms and being branched at the 3-position or further positions.

[0043] The process for providing said procatalyst comprises the steps of: i) contacting a compound R4zMgX42-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(0Ra)xX12-x, wherein: Rais a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms; wherein R4is a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms, preferably R4is butyl; wherein X4and X1are each independently selected from the group of consisting of fluoride (F-), chloride (Cl—), bromide (Br-) or iodide (I-), preferably chloride; z is in a range of larger than 0 and smaller than 2, being 0 < z < 2, x is an integer between 0 and 2; ii) optionally contacting the solid Mg(ORa)xX12-x obtained in step i) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M1(0Rb)v-w(0R3)w or M2(ORb)v-w(R3)w, to obtain a second intermediate product; wherein: M1is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; v is the valency of M1; M2is a metal being Si; v is the valency of M2; Rband R3are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms, and preferably has from 1 to 20 carbon atoms; wherein w is smaller than v, preferably v being 3 or 4; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with a halogen-containing Ti-compound and said compound represented Formula I, as the internal electron donor.

[0044] In an embodiment, during step ii) as activating compounds an alcohol is used as activating electron donor and titanium tetraalkoxide is used as metal alkoxide compound.

[0045] In an embodiment, an activator is present. In an embodiment, said activator is ethyl benzoate. In an embodiment, said activator is a benzamide according to formula X:

[0046] Formula X wherein R70and R71are each independently selected from hydrogen or an alkyl, and R72, R73, R74, R75, R76are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group, preferably selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof, more preferably wherein R70and R71are both methyl and wherein R72, R73, R74, and R75are all hydrogen, being N,N’- dimethylbenzamide (Ba-2Me).

[0047] In some preferred embodiment the activating compound is N-N-dimethylbenzamide.

[0048] Preferably, the internal electron donors used are according to Formula I:

[0049] Formula I wherein R1is a secondary alkyl group having at least three carbon atoms (C3) and R2is a non-secondary alkyl group having at least 5 carbon atoms, preferably R1et R2is having at most seven carbon atoms (C7), preferably at most six carbon atoms (C6), preferably iso-propyl, iso-butyl, iso-pentyl, cyclopentyl, n-pentyl, and isohexyl, preferably R2is being branched at the 3-position or further positions

[0050] In another embodiment, the internal electron donor is 3,3-bis(methoxymethyl)-2,6- dimethyl heptane, according to Formula I wherein R1is iso-propyl being secondary alkyl and R2is iso-pentyl being non-secondary and having a branch on the third carbon atom (abbreviated as iPiPen, wherein iP stands for iso-propyl and iPen stands for iso-pentyl, also known as 3-methyl-butyl). This compound iPiPen has a chemical formula of C13H28O2; an exact mass of 216.21 and a molecular weight of 216.37. In a more preferred embodiment of the invention, iPiPen is used as internal donor and N,N-dimethylbenzamide is preferably used as activator. iPiPen

[0051] In another embodiment, the internal electron donor is (1 -methoxy-2-(methoxymethyl)-5- methylhexan-2-yl)cyclopentane, according to Formula I wherein R1is secondary alkyl cyclopentyl and R2is secondary cyclopentyl (abbreviated as CPiPen, wherein CP stands for cyclopentyl and iPen stands for iso-pentyl, also known as 3-methyl-butyl). This compound CPiPen has a chemical formula of C15H30O2; an exact mass of 242.22 and a molecular weight of 242.40. In a more specific embodiment, CPiPen is used as internal donor and N,N-dimethylbenzamide is preferably used as activator.

[0052] CPIPen

[0053] In another embodiment, the internal electron donor is 3,3-bis(methoxymethyl)-2,7- dimethyloctane, according to Formula I wherein R1is the secondary alkyl iso-propyl and R2is non-secondary iso-hexyl with a branch on the third carbon atom (abbreviated as iPiHex, wherein iP stands for iso-propyl and iHex stands for iso-hexyl, also known as 4- methyl-pentyl). This compound iPiHex has a chemical formula of C14H30O2; an exact mass of 230.22 and a molecular weight of 230.39. In a more specific embodiment, iPiHex is used as internal donor and N,N-dimethylbenzamide is preferably used as activator. iPiHex

[0054] In another embodiment, the internal electron donor is 3,3-bis(methoxymethyl)-2- methyloctane, according to Formula I wherein R1is secondary alkyl iso-propyl and R2is non-secondary non-branched n-pentyl (abbreviated as iPnPen, wherein iP stands for isopropyl and nPen stands for n-pentyl). This compound iPnPen has a chemical formula of C13H28O2; an exact mass of 216.21 and a molecular weight of 216.37. In a more specific embodiment, iPnPen is used as internal donor and N,N-dimethylbenzamide is preferably used as activator. iPnPen In another embodiment, the internal electron donor is 3,3-bis(methoxymethyl)-2,6- dimethyloctane, according to Formula I wherein R1is secondary alkyl iso-propyl and R2is non-secondary branched iso-hexyl having a branch at the third carbon atom (abbreviated as iPiHex, wherein iP stands for iso-propyl and wherein iHex stands for isohexyl, also known as 3-methyl-pentyl). This compound iPiHex has a chemical formula of C14H32O2 ; an exact mass of 230.22 and a molecular weight of 230.39. In a more specific embodiment, iPiHex is used as internal donor and N,N-dimethylbenzamide is preferably used as activator. iPiHex

[0055] In an embodiment, the substituent R1is isopropyl or cyclopentyl. In an embodiment, the substituent R2is isopentyl or isohexyl. The below table shows the embodiments above with their abbreviations and the R1and R2groups as well if these groups are secondary or not and branched or not.

[0056] According to the present invention, it is further preferred that R1is a secondary alkyl group and R2is a non-secondary alkyl group being branched at the 3-position or further positions.

[0057] In some preferred embodiment, the co-catalyst is selected from the group consisting of trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, di isobutylaluminum hydride, trioctylaluminium, dihexylaluminum hydride and mixtures thereof.

[0058] Preferably, the external electron donors are chosen from the group of compounds having a structure according to:

[0059] - Formula III : (R90)2N— Si(OR91)3,

[0060] - Formula IV: (R92)Si(OR93)3,

[0061] Formula V: Si(ORa)4-nRbn, and

[0062] - mixtures thereof, wherein each of R90, R91, R92and R93groups are each independently a linear, branched or cyclic, substituted or unsubstituted alkyl having between 1 and 10 carbon atoms, preferably wherein R90, R91, R92and R93groups are each independently a linear unsubstituted alkyl having between 1 and 8 carbon atoms, wherein n can be from 0 up to 2, and each of Raand Rb, independently, represents an alkyl or aryl group, optionally containing one or more hetero atoms for instance 0, N, S or P, with, for instance, 1 -20 carbon atoms.

[0063] For example the external electron donors maybe ethyl, methyl or n-propyl, for example diethylaminotriethoxysilane (DEATES), n-propyl triethoxysilane, (nPTES), n-propyl trimethoxysilane (nPTMS), diisobutyl dimethoxysilane (DiBDMS), t-butyl isopropyl dimethyxysilane (tBuPDMS), cyclohexyl methyldimethoxysilane (CHMDMS), dicyclopentyl dimethoxysilane (DCPDMS) or di(iso-propyl) dimethoxysilane (DiPDMS). More preferably, the external electron donor is chosen from the group of di(iso-propyl) dimethoxysilane (DiPDMS) or diisobutyl dimethoxysilane (DiBDMS).

[0064] Preferably, the external donor comprises or consists of a compound selected from the list comprising organo-silicon compounds, silanes, alkoxy silanes, alkyl silane, alkyl alkoxy silane and aliphatic / aromatic ester, for example dicyclopentyldimethoxysilane, di-tert- butyldimethoxysilane, methylcyclohexyldimethoxysilane, ethylcyclohexyldimethoxysilane, diphenyldimethoxysilane, diisopropyldimethoxysilane, di-n-propyldimethoxysilane, diisobutyldimethoxysilane, di-n-butyldimethoxysilane, cyclopentyltrimethoxysilane, isopropyltrimethoxysilane, npropyltrimethoxysilane, n-propyltriethoxysilane, ethyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, cyclopentylpyrrolidinodimethoxysilane, bis(pyrrolidino )-dimethoxysilane, and mixtures thereof, preferentially di(iso-propyl) dimethoxysilane (DiPDMS)

[0065] The compounds mentioned above as examples of the external electron donor are sometimes referred as Selectivity Control Agent (SCA). The external electron donor may consist of SCA. Alternatively, in addition to SCA, the external electron donor may further comprise compounds known as an activity limiting agent (ALA). Preferably, the Activity Limiting Agent (ALA) is selected from the group consisting of: ethyl acetate, ethyl benzoate, p-ethoxy ethyl benzoate, methyl trimethylacetate, isopropyl myristate, di-n- butyl sebacate, (poly)(alkylene glycol) mono- or diacetates, (poly)(alkylene glycol) mono- or di-myristates, (poly)(alkylene glycol) mono- or di- laurates, (poly)(alkylene glycol) mono- or di-dioleates, glyceryl tri(acetate), mixed glycerides of linoleic, oleic, palmitic and stearic acids, and mixtures thereof. More preferably, the Activity Limiting Agent (ALA) is isopropyl myristate.

[0066] The ratio of Selectivity Control Agent (SCA) to Activity Limiting Agent (ALA) is in principle not critical, best results are obtained for a SCA / ALA ratio in the range from 0.010 to 100, more preferably in the range from 0.10 to 20.

[0067] The molar ratio of Al in the co-catalyst to Si in the external electron donor may e.g. be 1 to 120.

[0068] In a preferred embodiments, the molar ratio of Al in the co-catalyst to Si in the external electron donor is 1 to 25, preferably 1 to 15, preferably 3 to 10, more preferably 3.5 to 8. The relatively low molar ratio of Al / Si results in a higher stiffness of the composition.

[0069] It was surprisingly found that use of the preferred catalyst leads to the ethylene content at peak elution in the desired range.

[0070] Peroxide Preferably the heterophasic propylene copolymer is prepared in a process comprising a peroxide shifting step.

[0071] The term “peroxide shifting” or "visbreaking" is well known in the field of the invention. For example methods of visbreaking polypropylene have been disclosed in US 4,282,076 and EP 0063654 .

[0072] Several different types of chemical reactions which are well known can be employed for visbreaking propylene polymers. An example is thermal pyrolysis, which is accomplished by exposing a polymer to high temperatures, e.g., in an extruder at 350 °C or higher. Another approach is exposure to powerful oxidizing agents. A further approach is exposure to ionizing radiation. It is preferred however that visbreaking is carried out using a peroxide. Such materials, at elevated temperatures, initiate a free radical chain reaction resulting in beta-scission of the polypropylene molecules. The visbreaking may be carried out directly after polymerisation and removal of unreacted monomer and before pelletisation (during extrusion in an extruder wherein shifting of the intermediate heterophasic propylene copolymer occurs). However, the invention is not limited to such an embodiment and visbreaking may also be carried out on already pelletised polypropylene, which polypropylene generally contains stabilisers to prevent degradation.

[0073] Examples of suitable peroxides include organic peroxides having a decomposition halflife of less than 1 minute at the average process temperature during the visbreaking step. Suitable organic peroxides include but are not limited to dialkyl peroxides, e.g. dicumyl peroxides, peroxyketals, peroxycarbonates, diacyl peroxides, peroxyesters and peroxydicarbonates. Specific examples of these include benzoyl peroxide, dichlorobenzoyi peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5- di(peroxybenzoato)-3-hexene, 1 ,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-butyl peracetate, a,a'-bis(tert-butylperoxy)diisopropylbenzene (Luperco® 802), 2,5- dimethyl-2,5-di(tert-butylperoxy)-3-hexene, 2,5-dimethyl-2,5-di(tert- butylperoxy)-hexane, tert-butyl perbenzoate, tert-butyl perphenylacetate, tert-butyl per- sec-octoate, tert-butyl perpivalate, cumyl perpivalate, cumene hydroperoxide, diisopropyl benzene hydroperoxide, 1 ,3-bis(t-butylperoxy- isopropylbenzene, dicumyl peroxide, tert-butylperoxy isopropyl carbonate and any combination thereof. Preferably, a dialkyl peroxides is employed in the process according to the present invention. More preferably, the peroxide is a,a'-bis-(tert-butylperoxy)diisopropylbenzene, 2,5- dimethyl-2,5-di(tert- butylperoxy)-hexane or 3,6,9-Triethyl-3,6,9-trimethyl-1 ,4,7-triperoxonane. Preferably, the peroxide is selected from the group of non-aromatic peroxides.

[0074] It can easily be determined by the person skilled in the art through routine experimentation how much peroxide should be used to obtain a composition having the desired melt flow rate. This also depends on the half-life of the peroxide and on the conditions used for the melt-mixing, which in turn depend on the exact composition.

[0075] Preferably the MFI of the heterophasic propylene copolymer is in the range from 6 to 10 g / 10min, preferably from 7 to 9 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 230 °C prior to the peroxide shifting step.

[0076] Forming process and suitable applications

[0077] The heterophophasic propylene copolymer according to the invention may be extrusion moulded or injection moulded in to an article.

[0078] The article may be a home appliance, or furniture part, or food packaging.

[0079] Material

[0080] For the preparation of the resin part of the inventive example (IE), the procatalyst was prepared according to the method disclosed in W02021 / 063930A1 , example 1. The cocatalyst for the preparation of lEs is TEA and external electron donor is DiPDMS. The Al / Si ratio is 5, Al / Si is the molar ratio of the co-catalyst (TEA) to the external donor (DiPDMS).

[0081] For the preparation of the resin part of the comparative example (CE), the procatalyst is INcat P420 commercially available from INEOS Polyolefin Catalyst and prepared according to the instructions of the manufacturer.

[0082] Both IE and CE are heterophasic propylene copolymers. The examples were produced in a gas-phase polymerization process which was performed in two horizontally stirred gas-phase reactors (R1 and R2) with downstream powder processing units (= degassing & catalyst deactivation) for powder collection. Then the powder was introduced in an extruder for peroxide shifting, adding an additive package consisting of 1500 ppm stabilizers, 5250 ppm nucleating agents (5000 ppm talc and 250 ppm HPN20 from Milliken) and 2000 ppm molding agent basing on the total amount of the example and palletization.

[0083] Tern R1 63 to 73, Temp R2 63, Pressure R1 R2 22 bar The composition of IE and CE is shown in Table 1 :

[0084] Measurement

[0085] Stress Whitening Stress whitening is the appearance of a white area on an object when the object is stressed by a blushing operation. The appearance of the white area indicates that there is an onset of failure of the corresponding material.

[0086] The blushing on the samples was created according to PV3905, by dropping a ball of 500 grams from a height of 230 mm on a test piece with dimension 65*65*3.2mm injected on the machine Arburg 60T, mould: 1-1-1-108, by ISO 37 / 2.

[0087] Photos of these test pieces were taken with a SLR digital camera (Canon 6D; 100 macro lens including an extender) with fixed settings and illumination conditions such that no under or over exposure is present.

[0088] Image analysis of the photos was done using a Matlab Graphical Interface (GUI) in order to determine the values of the parameters “spot size”.

[0089] Parameter “spot size” indicates the dimensional visibility of the white area.

[0090] The spot size was determined as follows:

[0091] The total whiteness of the whole photo is calculated as the sum of the whiteness of each pixel in the whole photo. The whiteness of the intrinsic material is defined as 0. Each pixel constituting the sample has a whiteness of 0-255. The spot size is defined as the size of the area which has 99.5% of the whiteness of the whole photo.

[0092] Stiffness (flex modulus)

[0093] The flexural -modulus was measured in accordance with ASTM D790. The test specimen was injection moulded and prepared to a length of 63.5 mm, a width of 12.7 mm and a thickness of 3.2 mm. The flexural-modulus was determined by measuring in the flow direction. To allow after-crystallization to occur, the test specimen was stored for 14 days under standard conditions of 23 °C 150 atmospheric humidity. A test unit model Z010 from Zwick-Roell was used for testing. The testing velocity in the determination of the flexural modulus was 13.5 mm / min. The yield point in the determination of the modulus was in the range 0.05% - 0.25 %.

[0094] Impact resistance The notched Izod was measured in accordance with ISO 180 / 4A. The test specimen was injection moulded and prepared to a length of 63.5 mm, a width of 12.7 mm and a thickness of 3.2 mm. The notched Izod was determined by measuring in the perpendicular direction on the flow direction. To allow after-crystallization to occur, the test specimen was stored for 14 days under standard conditions of 0 °C and -20 °C 150 atmospheric humidity.

[0095] Melt flow rate (MFR)

[0096] MFR measurements are carried out in accordance with ISO1133 using a 2.16 kg weight and a temperature of 230 °C.

[0097] High-temperature two-dimensional liquid chromatography (HT-2D-LC)

[0098] Elution volume of the samples were measured by HT-2D-LC performed on PolymerChar (Valencia, Spain) solvent gradient chromatograph equipped with an integrated IR5 detector, a binary gradient pump as well as an isocratic pump (both model 1260, Agilent, Waldbronn, Germany). Sample concentrations of ~ 4.2 mg / mL (solvent 1 -decanol) were used. For dissolution, the samples were first heated in an offline autosampler at 160 °C with shaking until dissolution. Prior to injection, the sample was allowed a further one hour of dissolution under shaking. The following experimental parameters were chosen: Elution temperature: 160 °C, SGIC flow rate: 0.01 mL / min, injection loop: 200 pL, SGIC stationary phase: Hypercarb® (particle size: 5 pm, column dimensions: 100 x 4.6 mm (L x I.D.) (Thermofisher Scientific, Dreieich, Germany)). As eluent, a 1 -decanol TCB gradient was used with the following program: 0 - 1000 min linear gradient from 1 -decanol to TCB, 1000 - 1200 min pure TCB. The column was then purged for 40 min with 1 -decanol at a flow velocity of 0.8 mL / min in order to establish the original adsorption equilibrium in the column again. The mobile phase coming from the Hypercarb® column was collected in 100 pL sample loops. These were injected into the SEC column (PLGel Olexis, 300 x 7.8 mm (L x I.D.) (Agilent Technologies, Waldbronn, Germany) every 10 minutes. SEC was analysis in the second dimension was done in TCB at 160 °C, using a flow rate of 1.5 mL / min. Calibration is based on a set of polystyrene standards (PolymerChar, (Valencia, Spain)). Data collection and analysis was performed using the PolymerChar software and processed in the GPC 1 software as well as OriginPro version 2019b.

[0099] Herein, the peak and center of distribution (COD) of the eluting rubber component were chosen to evaluate the differences in the ethylene contents. The peak elution volumes are typically used in chromatography as a characteristic representative of the eluting species where peaks are symmetrical in shape. On the other hand, where peak show lack of symmetry or skewness, the center of gravity (COG), center of mass (COM) or COD becomes a better descriptor.

[0100] The calibration of the 100x4.6mm Hypercarb® column was executed with narrowly distributed ethylene-propylene standards. So based on the elution volume, it was possible to calculate the peak and center of distribution composition of the EPR phase. The following equation was obtained from the calibration of the first dimension with narrowly distributed ethylene propylene standards:

[0101] [C] mol.% = 21.6996 x (First dimension elution volume) - 65.9464

[0102] Intercept -65.9464 ±1.1325 mol.%

[0103] Slope 21.6996 ± 0.2108

[0104] Example: For IE the calculation of peak elution C2 content is as follows,

[0105] [C] mol.% = 21 .6996 x 3.30 mL - 65.9464

[0106] = 5.66 mol.%

[0107] Result

[0108] The HT-2D-LC results of IE and CE are shown in Table 2.

[0109] As clearly illustrated in Table 3, IE according to the invention has maintained impact performance at low temperature while has improved stiffness and stress whitening performance.

Claims

CLAIMS1 . A heterophasic propylene copolymer comprising a propylene based matrix and an ethylene copolymer as dispersed phase, wherein the amount of ethylene copolymer is in the range of 8.5 to 12.5 wt% basing on the total amount of the heterophasic propylene copolymer, wherein the amount of ethylene in the ethylene copolymer is in the range of 32.0 to 40.0 wt% basing on the total amount of the ethylene copolymer, wherein the melt flow index of the heterophasic propylene copolymer is in the range from 15 to 35 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 230 °C.

2. The heterophasic propylene copolymer according to claim 1 , wherein the amount of ethylene copolymer is in the range of 8.5 to 11 .5 wt%, preferably from 8.5 to 10.4 wt%, more preferably from 8.5 to 9.5 wt%basing on the total amount of the heterophasic propylene copolymer.

3. The heterophasic propylene copolymer according to claim 1 or 2, wherein the amount of ethylene in the ethylene copolymer is in the range of 34.0 to 40.0 wt%, preferably 35.0 to 39.0 wt% basing on the total amount of the ethylene copolymer.

4. The heterophasic propylene copolymer according to any one of the previous claims wherein the MFI of the heterophasic propylene copolymer is in the range from 17 to 29 g / 10min, preferably from 18 to 25 g / 10min, even more preferably from 19 to 22 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 2305. The heterophasic propylene copolymer according to any one of the previous claims wherein the heterophasic propylene copolymer comprises a nucleating agent, wherein the nucleating agent comprises talc and a cyclic dicarboxylate salt compound6. The heterophasic propylene copolymer according to claim 5 wherein, wherein the ratio between the amount of talc and the amount of the cyclic dicarboxylate salt compound is in the range between 13 to 26.7 The heterophasic propylene copolymer according to any one of the previous claims wherein the heterophasic propylene copolymer is prepared in a process comprising a peroxide shifting step.8 The heterophasic propylene copolymer according to any one of the previous claims wherein the MFI of the heterophasic propylene copolymer is in the range from 6 to 10 g / 10min, preferably from 7 to 9 g / 10min as measured according to ISO1133 using a 2.16 kg weight and a temperature of 230 °C prior to the peroxide shifting step.

9. The heterophasic propylene copolymer according to any one of the previous claims wherein the heterophasic propylene copolymer is produced in a process comprises the step of polymerizing propylene and ethylene comonomers in the presence of a catalyst in a gas phase, wherein said catalyst comprises a procatalyst, a co-catalyst and optionally an external electron donor, wherein the procatalyst is obtainable by a process comprising the steps of: contacting a magnesium-containing support with a halogen-containing titanium compound, and an internal electron donor according to Formula I:wherein R1is a secondary alkyl group and R2is a non-secondary alkyl group having at least 5 carbon atoms, preferably R2is a non-secondary alkyl group having at least 5 carbon atoms and being branched at the 3-position or further positions; said procatalyst is prepared according to the following steps: i) contacting a compound R4zMgX42-z with an alkoxy- or aryloxy-containing silane compound to give a first intermediate reaction product, being a solid Mg(0Ra)xX12-x, wherein: Rais a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms; wherein R4is a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted or unsubstituted, may contain one or more heteroatoms and preferably has from 1 to 20 carbon atoms, preferably R4is butyl; wherein X4and X1are each independently selected from the group of consisting of fluoride (F-), chloride (Cl—), bromide (Br-) or iodide (I-), preferably chloride; z is in a range of larger than 0 and smaller than 2, being 0 < z < 2, x is an integer between 0 and 2; ii) optionally contacting the solid Mg(ORa)xX12-x obtained in step i) with at least one activating compound selected from the group formed by activating electron donors and metal alkoxide compounds of formula M1(0Rb)v-w(0R3)w or M2(ORb)v-w(R3)w, to obtain a second intermediate product; wherein: M1is a metal selected from the group consisting of Ti, Zr, Hf, Al or Si; v is the valency of M1; M2is a metal being Si; v is the valency of M2; Rband R3are each a linear, branched or cyclic hydrocarbyl group independently selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof; wherein said hydrocarbyl group may be substituted orunsubstituted, may contain one or more heteroatoms, and preferably has from 1 to 20 carbon atoms; wherein w is smaller than v, preferably v being 3 or 4; iii) contacting the first or second intermediate reaction product, obtained respectively in step i) or ii), with a halogen-containing Ti-compound and said compound represented Formula I, as the internal electron donor.

10. The heterophasic propylene copolymer according to claim 9, wherein the co-catalyst is selected from the group consisting of trimethylaluminum, triethylaluminum, triisobutylaluminum, trihexylaluminum, di-isobutylaluminum hydride, trioctylaluminium, dihexylaluminum hydride and mixtures thereof.11 . The heterophasic propylene copolymer according to any one of claims 9 or 10, the catalyst comprises an external donor, wherein the external electron donor is a silane containing external donor, preferably wherein the external electron donor is selected from the group of compounds having a structure according to:- Formula III : (R90)2N— Si(OR91)3,- Formula IV: (R92)Si(OR93)3,Formula V: Si(ORa)4-nRbn, and- mixtures thereof, wherein each of R90, R91, R92and R93groups are each independently a linear, branched or cyclic, substituted or unsubstituted alkyl having between 1 and 10 carbon atoms, preferably wherein R90, R91, R92and R93groups are each independently a linear unsubstituted alkyl having between 1 and 8 carbon atoms, wherein n can be from 0 up to 2, and each of Raand Rb, independently, represents an alkyl or aryl group, optionally containing one or more hetero atoms for instance 0, N, S or P, with, for instance, 1 -20 carbon atoms12. The heterophasic propylene copolymer according to any one of claims 9 to 11 , wherein the molar ratio of co-catalyst to external electron donor is in the range from 1 to 25, preferably 1 to 15, preferably 3 to 10, more preferably 3.5 to 8.

13. The heterophasic propylene copolymer according to any one of claims 9 to 12, wherein an activator is present in the process for the preparation of the procatalyst, the activator preferably being a benzamide according to formula X:wherein R70and R71are each independently selected from hydrogen or an alkyl, and R72, R73, R74, R75, R76are each independently selected from hydrogen, a heteroatom or a hydrocarbyl group, preferably selected from alkyl, alkenyl, aryl, aralkyl, alkoxycarbonyl or alkylaryl groups, and one or more combinations thereof, more preferably wherein R70and R71are both methyl and wherein R72, R73, R74, and R75are all hydrogen, being N,N’-dimethylbenzamide (Ba-2Me).

14. The heterophasic propylene copolymer according to any one of the previous claims wherein the heterophasic propylene copolymer has an ethylene content at peak elution volume of at least 3.5 mol%, preferably at most 4.5 mol%, more preferably at least 5 mol%, even more preferably at least 5.5 mol% according to the High-temperature two- dimensional liquid chromatography method in the description.

15. An article comprising the heterophasic propylene copolymer according to any one of the previous claims wherein the article is a home appliance, or furniture part, or food packaging.

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