Molded article comprising propylene copolymer

Abstract

A propylene ethylene copolymer containing from 1.2 to 6.2 wt% of ethylene derived units characterized in that: i) melting point, measured according to ISO 11357-3, 20°C / min, ranges from 130°C to 156°C; ii) the fraction soluble in xylene at 25°C is comprised between 3.3 wt% and 12.6 wt%; iii) the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 6.0 dl / g to 12.0 dl / g; iv) a melt flow rate (ISO 1133 (230° C, 21.6 kg). ranges from 1.2 g / 10min to 5.9 g / 10 min; v) the melt strength measured at 250°C and applying an acceleration equal to 6 mm / s2 is higher than 0.050 N.

Description

MOLDED ARTICLE COMPRISING PROPYLENE COPOLYMERFIELD OF THE INVENTION

[0001] The present disclosure relates to molded articles preferably compression molded articles comprising a polypropylene ethylene copolymer having high molecular weight and high abrasion resistant.BACKGROUND OF THE INVENTION

[0002] Propylene copolymer is widely used in the processing fields of molding such as injection molding or compression molding.

[0003] Abrasion resistance is an important characteristics of articles made from polymeric materials, Scratch and / or mar resistance are important characteristics of articles made from polymeric materials, in particular for polypropylene, for many applications. For example in automotive industry wherein there is the need of durable plastic products as exterior and interior parts especially if they are part of moving parts such as gears.

[0004] Therefore there is the need to develop a propylene copolymer to be used in molded object having an enhanced abrasion resistance.SUMMARY OF THE INVENTION

[0005] The present disclosure is directed to a propylene ethylene copolymer containing from 1.2 to 6.2 wt% of ethylene derived units characterized in that:i) the melting point, measured according to ISO 11357-3, 20°C / min, ranges from 130°C to 156°C;ii) the fraction soluble in xylene at 25°C is comprised between 3.3 wt% and 12.6 wt%;iii) the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 6.0 dl / g to 12.0 dl / g;iv) a melt flow rate (ISO 1133 (230° C, 21.6 kg), ranges from 1.2 g / lOmin to 5.9 g / 10 min;v) the melt strength measured at 250°C and applying an acceleration equal to 6 mm / s2is higher than 0.050 N.DETAILED DESCRIPTION OF THE INVENTION

[0006] The present disclosure is directed to a propylene ethylene copolymer containing from 1.2 to 6.2 wt%; preferably from 2.4 wt% to 5.6 wt% ; more preferably from 3.2 wt% to 4.8 wt% of ethylene derived units characterized in that:i) the melting point, measured according to ISO 11357-3, 20°C / min, ranges from 130°C to 156; preferably from 133°C to 148°C; more preferably form 136°C to 144°C;ii) the fraction soluble in xylene at 25 °C is comprised between 3.3 wt% and 12.6 wt%; preferably comprised between 6.0 wt% and 11.6 wt%; more preferably comprised between 7.9 wt% and 10.7 wt%;iii) the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 6.0 dl / g to 12.0 dl / g; preferably from 6.8 dl / g to 9.8 dl / g; more preferably from 7.1 dl / g to 8.6 dl / g;iv) a melt flow rate (ISO 1133 (230° C, 21.6 kg), ranges from 1.2 g / lOmin to 5.9 g / 10 min;preferably from 2.3 g / lOmin to 4.7 g / 10 min; more preferably from 3.1 g / lOmin to 4.3 g / 10 min;v) the melt strength measured at 250°C and applying an acceleration equal to 6 mm / s2is higher than 0.050 N; preferably is higher than 0.055 N; more preferably is higher than 0.061 N.

[0007] Preferably the propylene copolymer of the present disclosure is not nucleated.

[0008] Preferably the propylene copolymer of the present disclosure shows a value of melt strength lower than 0.5 N.

[0009] Preferably the propylene copolymer of the present disclosure shows a polydispersity index, PI, comprised between 4.5 and 7.5; more preferably between 5.0 and 7.2; more preferably from 5.5 to 6.5.

[0010] Preferably the propylene copolymer of the present disclosure shows a tensile modulus ranging from 550 MPa to 1200 MPa; preferably from 650MPa, to 1000 Mpa.

[0011] Preferably the propylene copolymer of the present disclosure shows a charpy impact test at 23°C ranging from 6.0 kJ / m2to 20.0 kJ / m2; preferably from 10.5 kJ / m2to 15.0 kJ / m2.

[0012] The propylene copolymer of the present disclosure is characterized by having an high melt strength and an high molecular weight. For this reason the homopolymer of the present disclosure preferably shows a low value of abrasion resistance measured according to ISO 15527 : 2007. The value of average abrasion index measured according to ISO 15527 : 2007, on compression molded plaque can be lower than 330 ; preferably lower than 305. The low value ofabrasion index renders the molded article of the present disclosure particularly fits for producing automotive articles especially articles subjected to movement.

[0013] The propylene copolymer disclosed herein can be prepared by a process comprising polymerizing propylene with ethylene, in the presence of Ziegler-Natta catalysts. An essential component of said catalysts is a solid catalyst component comprising a titanium compound having at least one titanium-halogen bond, and an electron-donor compound, both supported on a magnesium halide in active form. Another essential component (co-catalyst) is an organoaluminium compound, such as an aluminium alkyl compound. An external donor is optionally added.

[0014] Catalysts having the above mentioned characteristics are well known in the patent literature; particularly advantageous are the catalysts described in US patent 4,399,054 and European patent 45977. Other examples can be found in US patent 4,472,524.

[0015] The solid catalyst components used in said catalysts comprise, as electron- donors (internal donors), compounds selected from the group consisting of ethers, ketones, lactones, compounds containing N, P and / or S atoms, and esters of mono- and dicarboxylic acids.Particularly suitable electron-donor compounds are esters of succinic acid (succinates) Preferably, the succinate present in the solid catalyst component is selected from succinates of formula (I) below

[0016] in which the radicals Ri and R2, equal to, or different from, each other are a C1-C20 linear or branched alkyl, alkenyl, cycloalkyl, aryl, arylalkyl or alkylaryl group, optionally containing heteroatoms; and the radicals R3 and R4 equal to, or different from, each other, are Ci- C20 alkyl, C3-C20 cycloalkyl, C5-C20 aryl, arylalkyl or alkylaryl group with the proviso that at least one of them is a branched alkyl; said compounds being, with respect to the two asymmetric carbon atoms identified in the structure of formula (I), stereoisomers of the type (S,R) or (R,S)Ri and R2 are preferably Ci-Cs alkyl, cycloalkyl, aryl, arylalkyl and alkylaryl groups. Particularly preferred are the compounds in which Ri and R2 are selected from primary alkyls and in particular branched primary alkyls. Examples of suitable Ri and R2 groups are methyl, ethyl, n-propyl, n- butyl, isobutyl, neopentyl, 2-ethylhexyl. Particularly preferred are ethyl, isobutyl, and neopentyl.

[0017] Particularly preferred are the compounds in which the R3 and / or R4 radicals are secondary alkyls like isopropyl, sec-butyl, 2-pentyl, 3 -pentyl or cycloakyls like cyclohexyl, cyclopentyl, cyclohexylmethyl.

[0018] Examples of the above-mentioned compounds are the (S,R) (S,R) forms pure or in mixture, optionally in racemic form, of diethyl 2,3-bis(trimethylsilyl)succinate, diethyl 2,3-bis(2- ethylbutyl)succinate, diethyl 2,3 -dibenzylsuccinate, diethyl 2,3-diisopropylsuccinate, diisobutyl 2.3-diisopropylsuccinate, diethyl 2,3-bis(cyclohexylmethyl)succinate, diethyl 2,3- diisobutylsuccinate, diethyl 2,3-dineopentylsuccinate, diethyl 2,3-dicyclopentylsuccinate, diethyl 2.3-dicyclohexylsuccinate.

[0019] Particularly suitable electron-donor compounds are esters of phtalic acid and 1,3- diethers of formula:

[0020] wherein R1and Rnare the same or different and are Ci-Cis alkyl, C3-C18 cycloalkyl or C7-C18 aryl radicals; R111and RIVare the same or different and are C1-C4 alkyl radicals; or are the 1,3-diethers in which the carbon atom in position 2 belongs to a cyclic or polycyclic structure made up of 5, 6, or 7 carbon atoms, or of 5-n or 6-n' carbon atoms, and respectively n nitrogen atoms and n' heteroatoms selected from the group consisting of N, O, S and Si, where n is 1 or 2 and n' is 1, 2, or 3, said structure containing two or three unsaturations (cyclopolyenic structure), and optionally being condensed with other cyclic structures, or substituted with one or more substituents selected from the group consisting of linear or branched alkyl radicals; cycloalkyl, aryl, aralkyl, alkaryl radicals and halogens, or being condensed with other cyclic structures and substituted with one or more of the above mentioned substituents that can also be bonded to the condensed cyclic structures; one or more of the above mentioned alkyl, cycloalkyl, aryl, aralkyl,or alkaryl radicals and the condensed cyclic structures optionally containing one or more heteroatom(s) as substitutes for carbon or hydrogen atoms, or both.Ethers of this type are described in published European patent applications 361493 and 728769.

[0021] Representative examples of said diethers are 2-methyl-2-isopropyl-l,3- dimethoxypropane, 2,2-diisobutyl-l,3-dimethoxypropane, 2-isopropyl-2-cyclopentyl-l,3- dimethoxypropane, 2-isopropyl-2-isoamyl-l,3-dimethoxypropane, 9,9-bis (methoxymethyl) fluorene.

[0022] Other suitable electron-donor compounds are phthalic acid esters, such as diisobutyl, dioctyl, diphenyl and benzylbutyl phthalate.

[0023] The preparation of the above mentioned catalyst component is carried out according to various methods.

[0024] For example, a MgC12»nROH adduct (in particular in the form of spheroidal particles) wherein n is generally from 1 to 3 and ROH is ethanol, butanol or isobutanol, is reacted with an excess of TiC14 containing the electron-donor compound. The reaction temperature is generally from 80 to 120° C. The solid is then isolated and reacted once more with TiC14, in the presence or absence of the electron-donor compound, after which it is separated and washed with aliquots of a hydrocarbon until all chlorine ions have disappeared.

[0025] In the solid catalyst component the titanium compound, expressed as Ti, is generally present in an amount from 0.5 to 10% by weight. The quantity of electron-donor compound which remains fixed on the solid catalyst component generally is 5 to 20% by moles with respect to the magnesium dihalide.

[0026] The titanium compounds, which can be used for the preparation of the solid catalyst component, are the halides and the halogen alcoholates of titanium. Titanium tetrachloride is the preferred compound.

[0027] The reactions described above result in the formation of a magnesium halide in active form. Other reactions are known in the literature, which cause the formation of magnesium halide in active form starting from magnesium compounds other than halides, such as magnesium carboxylates.

[0028] The Al-alkyl compounds used as co-catalysts comprise the Al-trialkyls, such as Al- triethyl, Al-triisobutyl, Al-tri-n-butyl, and linear or cyclic Al-alkyl compounds containing two or more Al atoms bonded to each other by way of O or N atoms, or SO4 or SO3 groups.

[0029] The Al-alkyl compound is generally used in such a quantity that the Al / Ti ratio be from 1 to 1000.

[0030] The electron-donor compounds that can be used as external donors include aromatic acid esters such as alkyl benzoates, and in particular silicon compounds containing at least one Si-OR bond, where R is a hydrocarbon radical.

[0031] Examples of silicon compounds are (tert-butyl)2Si(OCH3)2, (cyclohexyl) (methyl) Si (OCH3)2, (cyclopentyl)2Si(OCH3)2 and (phenyl)2Si(OCH3)2 and (1,1,2- trimethylpropyl)Si(OCH3)3.

[0032] 1,3 -diethers having the formulae described above can also be used advantageously. If the internal donor is one of these diethers, the external donors can be omitted.

[0033] In particular, even if many other combinations of the previously said catalyst components may allow to obtain compositions according to the present invention, the component A) are preferably prepared by using catalysts containing a phthalate as internal donor and (cyclopentyl)2Si(OCH3)2 as outside donor, or the said 1,3-diethers as internal donors.

[0034] The polymerization is generally carried out at temperatures of from 20 to 120°C, preferably of from 40 to 80°C. When the polymerization is carried out in gas-phase, the operating pressure is generally between 0.5 and 5 MPa, preferably between 1 and 4 MPa. In bulk polymerization, the operating pressure is generally between 1 and 8 MPa, preferably between 1.5 and 5 MPa. Hydrogen is typically used as a molecular weight regulator. The polymerization can be in gas phase or in slurry or in solution. In one or more reactors. Preferably the polymerization is carried put in two slurry reactors operating in series.

[0035] The propylene copolymer of the present disclosure can be used for the production of molded article. The molded articles can be for example an injection molded article, a blow molded article or a compression molded article. Preferably the molded article of the present disclosure is a compression molded article.

[0036] The following examples are given in order to illustrate, but not limit the present disclosure.EXAMPLES CHARACTERIZATIONS

[0037] Xylene-insoluble and soluble fraction at 25°CXylene Solubles fraction has been measured according to ISO 16 152 - 2005; with solution volume of 250 ml, precipitation at 25°C for 20 minutes, 10 of which with the solution in agitation (magnetic stirrer), and drying at 70°.

[0038] Melt Flow Rate (MFR)Measured according to ISO 1133 at 230°C with a load of 21.6 kg, unless otherwise specified.

[0039] Polydispersity (PI)Some grams of molten homopolymer are submitted to a dynamic test in rate sweep with a parallel plate rheometer, at temperature of 200°C, according to the ISO 6721-10. G’ (storage modulus) and G” (loss modulus) are measured as function of frequency. From the rate sweep data, PI is defined by PI=105 / Gc, wherein Gc is the crossover modulus as value of modulus at G’ = G

[0040] Melting temperature via Differential Scanning Calorimetry (DSC)The melting points of the polymers (Tm) were measured by differential scanning calorimetry (DSC) on a Perkin Elmer DSC-1 calorimeter, previously calibrated against indium melting points, and according to ISO 11357-1, 2009 and 11357-3, 2011, at 20°C / min. The weight of the samples in every DSC crucible was kept at 6.0 ± 0.5 mg.In order to obtain the melting point, the weighted sample was sealed into aluminium pans and heated to 200°C at 20°C / minute. The sample was kept at 200°C for 2 minutes to allow a complete melting of all the crystallites, then cooled to 5°C at 20°C / minute. After standing 2 minutes at 5°C, the sample was heated for the second run time to 200°C at 20°C / min. In this second heating run, the peak temperature (Tp,m) was taken as the melting temperature.

[0041] 13C NMR of homopolymer and propylene / ethylene copolymers13C NMR spectra were acquired on a Bruker AV-600 spectrometer equipped with cryoprobe, operating at 160.91 MHz in the Fourier transform mode at 120°C.The peak of the Spp carbon (nomenclature according to “Monomer Sequence Distribution in Ethylene-Propylene Rubber Measured by 13C NMR. 3. Use of Reaction Probability Mode ” C. J. Carman, R. A. Harrington and C. E. Wilkes, Macromolecules, 1977, 10, 536) was used as internal reference at 29.9 ppm. The samples were dissolved in l,l,2,2-tetrachloroethane-d2 at 120°C with a 8 % wt / v concentration. Each spectrum was acquired with a 90° pulse, 15 seconds of delay between pulses and CPD to remove 1H-13C coupling. 512 transients were stored in 32K data points using a spectral window of 9000 Hz. The assignments of the spectra, the evaluation of triaddistribution and the composition were made according to Kakugo (“Carbon- 13 NMR determination of monomer sequence distribution in ethylene-propylene copolymers prepared with 8-titanium trichloride- diethylaluminum chloride” M. Kakugo, Y. Naito, K. Mizunuma and T. Miyatake, Macromolecules, 1982, 15, 1150) using the following equations:PPP = 100 Tpp / S PPE = 100 Tps / S EPE = 100 Tss / SPEP = 100 Spp / S PEE= 100 Sps / S EEE = 100 (0.25 Syg+0.5 S55) / SS = Tpp + Tps + Tss + Spp + Sps + 0.25 Syg + 0.5 SssThe molar percentage of ethylene content was evaluated using the following equation:E% mol = 100 * [PEP+PEE+EEE]The weight percentage of ethylene content was evaluated using the following equation:100 * E% mol * MWEE% wt. = >E% mol * MWE+ P% mol * MWpwhere P% mol is the molar percentage of propylene content, while MWE and MWp are the molecular weights of ethylene and propylene, respectively.The product of reactivity ratio nr? was calculated according to Carman (C.J. Carman, R.A. Harrington and C.E. Wilkes, Macromolecules, 1977; 10, 536) as:The tacticity of Propylene sequences was calculated as mm content from the ratio of the PPP mmTpp (28.90-29.65 ppm) and the whole Tpp (29.80-28.37 ppm).

[0042] Intrinsic viscosityThe sample is dissolved by tetrahydronaphthalene at 135 °C and then it is poured into the capillary viscometer. The viscometer tube (Ubbelohde type) is surrounded by a cylindrical glass jacket; this setup allows temperature control with a circulating thermostated liquid. The downward passage of the meniscus is timed by a photoelectric device. The passage of the meniscus in front of the upper lamp starts the counter which has a quartz crystal oscillator. The meniscus stops the counter as itpasses the lower lamp and the efflux time is registered: this is converted into a value of intrinsic viscosity through Huggins' equation, provided that the flow time of the pure solvent is known at the same experimental conditions (same viscometer and same temperature). One single polymer solution is used to determine IV],

[0043] Melt strengthThe melt strength is measured by Haul-off Melt Strength Meter produced by Geottfert Werkstoff Pruefmaschinen, Germany. This system measures the extensional properties of polymer melts by drawing a vertical melt strand at a constant pull-off speed or with a linear or exponentially accelerating velocity. The HAUL-OFF system measures the force needed to elongate the strand, and calculates elongation stress, draw ratio and apparent elongation rate and viscosity. Polymer is melt and plasticized through a capillary rheometer, then is extruded from a hole die with a 1 mm of diameter, 30 mm of length and 180° inlet angle. The test is performed at 250°C. The distance from the capillary outlet to the center of the transducer pulley is 150 mm. The monofilament is stretched at each temperature test applying an acceleration equal to 6 mm / s2and, passing through an angular transducer, its tension is measured. The draw ratio (dimensionless value) and force (cN) values are recorded as the final result in addition to the entire curve. The value of the melt strength is the maximum force value of the curve.

[0044] Charpy impact testCharpy impact test is measured according to ISO 179-leA, e ISO 1873-2, on compression sample

[0045] Tensile ModulusTensile Modulus is measured according to ISO 527-2, and ISO 1873-2 on compression sample

[0046] Examples 1 - Preparation of copolymerProcedure for the preparation of the solid catalyst componentThe solid catalyst used in the following examples was prepared according to the Example 10 of the International Patent Application WO 00 / 63261. Triethylaluminium (TEAL) was used as co-catalyst and dicyclopentyldimethoxysilane as external donor, with the weight ratios indicated in Table 1.PolymerizationThe polymerization run is carried out in continuous mode in a series of two reactors equipped with devices to transfer the product from one reactor to the one immediately next to it. The two reactorsare liquid phase loop reactors. Propylene is the main solvent, hydrogen is used as molecular weight regulator. The gas phase is continuously analyzed via gas-chromatography.At the end of the run the powder is discharged and dried under a nitrogen flow. The main polymerization conditions and the properties of the polymer are reported in Tables 1 and 2.Table 1 - Polymerization conditions<

[0047] The features of the polymers of example 1 and comparative example 2 are reported on table 2Table 2*(230°C / 2.16kg)

[0048] Comparative example 2 is PP H2150 is a nucleated propylene homopolymer sold by LyondellBasell. Nm not measured

[0049] Abrasion test, according to ISP 15527:2007, has been measure on compression molded plaque at 250°C, produced with polymers of example 1 and comparative example 2. The results are reported on table 3.Table 3

Claims

CLAIMSWhat is claimed is:

1. A propylene ethylene copolymer containing from 1.2 to 6.2 wt% of ethylene derived units, measured with13C NMR, characterized in that:i) melting point, measured according to ISO 11357-3, 20°C / min, ranges from 130°C to 156°C;ii) the fraction soluble in xylene at 25°C is comprised between 3.3 wt% and 12.6 wt%; iii) the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 6.0 dl / g to 12.0 dl / g;iv) a melt flow rate (ISO 1133 (230° C, 21.6 kg), ranges from 1.2 g / lOmin to 5.9 g / 10 min;v) the melt strength measured at 250°C and applying an acceleration equal to 6 mm / s2is higher than 0.050 N.

2. The propylene ethylene copolymer according to claim 1 wherein the melting point, measured according to ISO 11357-3, 20°C / min, ranges from 133°C to 148°C.

3. The propylene ethylene copolymer according to claims 1 or 2 wherein the fraction soluble in xylene at 25°C is comprised between 6.0 wt% and 11.6 wt%.

4. The propylene ethylene copolymer according to anyone of claims 1 -3 wherein the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 6.8 dl / g to 9.8 dl / g.

5. The propylene ethylene copolymer according to anyone of claims 1 -4 wherein the melt flow rate (ISO 1133 (230° C, 21.6 kg), ranges from 2.3 g / lOmin to 4.7 g / 10 min.

6. The propylene ethylene copolymer according to anyone of claims 1-5 wherein the melt strength measured at 250°C and applying an acceleration equal to 6 mm / s2is higher than 0.055 N.

7. The propylene ethylene copolymer according to anyone of claims 1-6 having a poly dispersity index, PI, comprised between 4.5 and 7.5.

8. The propylene ethylene copolymer according to anyone of claims 1-7 wherein in the propylene homopolymer the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 7.0 dl / g to 11.0 dl / g.

9. The propylene ethylene copolymer according to anyone of claims 1 -8 wherein the ethylene derived units content ranges from 2.4 wt% to 5.6 wt.

10. The propylene ethylene copolymer according to anyone of claims 1 -9 wherein the intrinsic viscosity (IV) measured in tetrahydronaphthalene at 135 °C ranges from 7.1 dl / g to 8.6 dl / g.

11. The propylene ethylene copolymer according to anyone of claims 1-10 wherein the melt flow rate (ISO 1133 (230° C, 21.6 kg), ranges from 3.1 g / lOmin to 4.3 g / 10 min.

12. The propylene ethylene copolymer according to anyone of claims 1-11 wherein the propylene homopolymer has the value of average abrasion index measured according to ISO 15527 : 2007, on compression molded plaque lower than 330.

13. The propylene ethylene copolymer according to anyone of claims 1-12 being not nucleated.14 A molded article comprising the propylene ethylene copolymer of claims 1-13.

15. A compression molded article comprising the propylene ethylene copolymer of claims 1-

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