Polypropylene composition

Abstract

A polypropylene composition (percentages being referred to the total A+B) comprising: A) from 80 to 94wt%, preferably from 82 to 92wt%, more preferably from 83 to 91wt% of polypropylene comprising more than 85wt% of propylene unit, and B) from 6 to 20wt%, preferably from 8 to 18%, more preferably from 9 to 17wt% of a copolymer of propylene and ethylene containing an average content of ethylene derived units from 20 to 50wt%, preferably from 25 to 45wt% and more preferably from 28 to 40wt%; said polypropylene composition being characterized by a fraction soluble in xylene at 25°C having an intrinsic viscosity in tetralin at 135°C of at least 80 dl / g.

Description

TITLEPOLYPROPYLENE COMPOSITIONFIELD OF THE INVENTION

[0001] The present disclosure relates to polypropylene heterophasic compositions having good foamability properties.BACKGROUND OF THE INVENTION

[0002] It is known in the art that, for certain applications, such as polymer foams, products having good melt flowability in combination with high melt strength are particularly desirable. Heterophasic copolymers for foaming are described for example in W02022 / 002514.

[0003] However, there is the need to further improve the foamability properties of the heterophasic polypropylene composition in order to make them useful for demanding foaming applications.SUMMARY OF THE INVENTION

[0004] The present disclosure therefore provides a polypropylene composition (percentages being referred to the total A+B) comprising: (percentages being referred to the total A+B) comprising:

[0005] A) from 80 to 94wt%, preferably from 82 to 92wt%, more preferably from 83 to 91wt% of polypropylene comprising more than 85wt% of propylene unit and having a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 5.0 to 80.0 g / 10’, preferably from 10.0 to 75.0 g / 10’, more preferably from 15.0 to 70.0 g / 10’ and especially from 18.0 to 65.0 g / 10’, and

[0006] B) from 6 to 20wt%, preferably from 8 to 18%, more preferably from 9 to 17wt% of a copolymer of propylene and ethylene containing an average content of ethylene derived units from 20 to 50wt%, preferably from 25 to 45wt% and more preferably from 28 to 40wt%; said polypropylene composition being characterized by a fraction soluble in xylene at 25°C having an intrinsic viscosity in tetralin at 135°C of at least 8.5 dl / g, more preferably at least 9.0 dl / g and especially ranging from 9.0 to 15.0 dl / g.DETAILED DESCRIPTION OF THE INVENTION

[0007] Preferably, the heterophasic polypropylene composition of the present disclosure has a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 0.1 to 30.0g / 10’, preferably from 0.5 to 25.0 g / 10’, more preferably from 1.0 to 20.0 g / 10’, and especially from 1.5 to 15.0 g / 10’.

[0008] It is also preferred that the component (A) has a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 10.0 to 75.0 g / 10’, more preferably from 15.0 to 70.0 g / 10’ and especially from 18.0 to 65.0 g / 10’.

[0009] Preferably, the intrinsic viscosity of the fraction soluble in xylene at 25°C (XSIV) is at least 9.0 dl / g and especially ranging from 9.0 to 15.0 dl / g.

[0010] Preferably component (A) contains at least 90wt% of propylene derived units, more preferably at least 95%wt of propylene derived units and, especially, from 96 to 100wt% of propylene derived units. In the most preferred embodiment, component (A) is propylene homopolymer.

[0011] For the purpose of the present disclosure, the term "copolymer" means polymers containing only ethylene and propylene.

[0012] It has been determined that the heterophasic composition of the present disclosure is endowed with high melt tension, determined with the method described in the experimental section, which preferably ranges from 150 to 350 mN preferably from 170 to 320 mN and especially from 175 to 300 mN.

[0013] In a preferred aspect, the values of the melt tension combined with the total MFR of the heterophasic compositions make it possible to simultaneously obtain good processability and foamability.

[0014] The polypropylene composition of the present disclosure may also show an interesting balance of physical mechanical properties. In particular, the impact properties (Charpy@23°C) of the polypropylene compositions ranges from 2 to 15 kJ / m2.

[0015] Preferably the Flexural Modulus is comprised between 1,400 and 2,200 MPa, preferably comprised between 1,600 and 2,200 MPa.

[0016] The polypropylene composition of the present disclosure is produced by sequential polymerization in at least two stages, with each subsequent polymerization stage being conducted in the presence of the polymeric material formed in the immediately preceding polymerization reaction.

[0017] In a preferred embodiment, propylene is polymerized in a first polymerization stage carried out in liquid propylene and in the presence of hydrogen as molecular weight regulator. In the second polymerization stage, carried out in the presence of the polypropylene produced in the first stage, ethylene and propylene are preferably polymerized in gas-phase thereby completing the preparation of the heterophasic propylene composition.

[0018] Both stages are carried out in the presence of a heterogenous ZN catalyst which preferably comprises the product of the reaction between:

[0019] a) a solid catalyst component comprising Ti, Mg, Cl, and an electron donor compound selected from structures containing at least a carbamic group which is present in an amount of higher than 50%wt based on the total amount of electron donors ;

[0020] b) an alkylaluminum compound and,

[0021] c) an external electron-donor compound having the general formula:

[0022] (R7)a(R8)bSi(OR9)c, where a and b are integers from 0 to 2, c is an integer from 1 to4 and the sum (a+b+c) is 4; R7, Rs, and R9, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms.

[0023] The electron donor present in the solid catalyst component (a) has preferably two carbamic groups. The preferred dicarbamates are those belonging to of formula (I):(I)Where R1and R2, independently, are selected from hydrogen and C1-C15 hydrocarbon groups, optionally contain a heteroatom selected from halogen, P, S, N, O and Si, which can be fused together to form one or more cycles and A is a bivalent bridging group.

[0024] Dicarbamate structures of formula (I) are described in WO2014048861 the relevant part of which is herein included by reference.

[0025] The solid catalyst component (a) may further contain Bi atoms in an amount ranging0.5 to 40% more preferably from 1 to 35, especially from 2 to 25%wt and in a very particular embodiment from 2 to 20%wt with respect to the total weight of solid catalyst component (a).

[0026] The particles of solid component (a) have substantially spherical morphology and average diameter ranging between 5 and 150 pm, preferably from 20 to 100 pm and more preferably from 30 to 90 pm. As particles having substantially spherical morphology, those are meant wherein the ratio between the greater axis and the smaller axis is equal to or lower than 1.5 and preferably lower than 1.3.

[0027] The amount of Mg may preferably range from 8 to 30% more preferably from 10 to 25%wt.

[0028] The amount of Ti may range from 0.5 to 7% and more preferably from 0.7 to 5%wt.

[0029] If present, the Bi atoms preferably derive from one or more Bi compounds not having Bi-carbon bonds. In particular the Bi compounds can be selected from Bi halides, Bi carbonate, Bi carboxylates, Bi nitrate, Bi oxide, Bi sulphate, Bi sulfide. Compounds in which Bi has the valence 3+are preferred. Among Bi halides, preferred are Bi trichloride and Bi tribromide. The most preferred Bi compounds are BiCh, Bi oxide, Bi carbonate and Bi neodecanoate.

[0030] The preparation of the solid catalyst component can be carried out according to several methods.

[0031] According to one method the solid catalyst component can be prepared by reacting a titanium compound of formula Ti(OR)q-yXy, where q is the valence of titanium and y is a number between 1 and q, preferably TiCh, with a magnesium chloride deriving from an adduct of formula MgCh’pROH, where p is a number between 0.1 and 6, preferably from 2 to 3.5, and R is a hydrocarbon radical having 1-18 carbon atoms. The adduct can be suitably prepared in spherical form by mixing alcohol and magnesium chloride, operating under stirring conditions at the melting temperature of the adduct (100-130°C). Then, the adduct is mixed with an inert hydrocarbon immiscible with the adduct thereby creating an emulsion which is quickly quenched causing the solidification of the adduct in form of spherical particles. Examples of spherical adducts prepared according to this procedure are described in USP 4,399,054 and USP 4,469,648. The so obtained adduct can be directly reacted with Ti compound or it can be previously subjected to thermal controlled dealcoholation (80-130°C) so as to obtain an adduct in which the number of moles of alcohol is of lower than 3, preferably between 0.1 and 2.5. The reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold TiCh; the mixture is heated up to 80-130°C and kept at this temperature for 0.5-2 hours. The treatment with TiCh can be carried out one or more times. The electron donor compound can be added in the desired ratios during the treatment with TiCh.

[0032] In a preferred method of producing the catalyst which may be used in the present disclosure, the reaction with the Ti compound can be carried out by suspending the adduct (dealcoholated or as such) in cold TiCh generally at 0°C. Preferably the adduct is used in an amount such as to have a concentration ranging from 20 to 100 g / 1, and preferably from 30 to 90 g / 1. According to a preferred embodiment, the 1,3 -di ether and the dicarbamate are added to the system at the beginning of this stage of reaction and preferably when the temperature of the mixture is in the range of -10° to 20°C. In a preferred embodiment, the 1,3 di ether is added first. The electron donors are used in amounts such as to meet the desired DE:DC molar ratio in the final catalyst taking into account the respective efficiency in being fixed on the catalyst. In an embodiment the Mg / diether molar ratio may range from 3:1 to 10: 1 and preferably from 4: 1 to 9: 1, while the Mg / dicarbamate molar ratio may range from 25: 1 to 200: 1 and preferably from 30: 1 to 180: 1. The temperature is then gradually raised up until reaching a temperature ranging from 90-130°C and kept at this temperature for 0.5-3 hours.

[0033] After completing the reaction time stirring is stopped, the slurry is let to settle, and liquid phase removed. A second stage of treatment with TiCh is performed, preferably carried out at a temperature ranging from 70 to 110°C. After completing the reaction time, stirring is stopped, the slurry is let to settle, and liquid phase removed. It is possible, although not necessary, to carry out additional reaction stage with the titanium compound and preferably with TiCh under the same conditions described above and in the absence of electron donors. The so obtained solid can then be washed with liquid hydrocarbon under mild conditions and then dried..

[0034] Preferably, the solid catalyst component (a) is endowed with a porosity determined by mercury method relating to pore with radius equal to or less than 1 pm of at least 0.30 cm3 / g. More preferably, the porosity is higher than 0.35 cm3 / g and especially higher than 0.40 cm3 / g.

[0035] The alkyl-Al compound (b) is preferably chosen among the trialkyl aluminum compounds such as for example triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides, such as AlEt2Cl and AhEtsCh, possibly in mixture with the above cited trialkylaluminums. The Al / Ti molar ratio ranges from higher than 1 to 250 and preferably range between 10 and 200. Values higher than 250 lead to produce heterophasic copolymers with a XSIV lower than 8.0 dl / g while values lower than 1 may cause a poor polymerization activity.

[0036] The external electron donor compound (c) is a silicon compound having the general formula (R?)a(R8)bSi(OR9)c, where a and b are integers from 0 to 2, c is an integer from 1 to 4and the sum (a+b+c) is 4; R7, Rs, and R9, are alkyl, cycloalkyl or aryl radicals with 1-18 carbon atoms optionally containing heteroatoms.

[0037] Particularly preferred are the silicon compounds in which a is 1, b is 1, c is 2, at least one of R7 and Rs is selected from branched alkyl, cycloalkyl or aryl groups with 3-10 carbon atoms optionally containing heteroatoms and R9 is a C1-C10 alkyl group, in particular methyl. Examples of such preferred silicon compounds are methylcyclohexyldimethoxy silane (C donor), diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane (D donor), diisopropyldimethoxysilane, (2-ethylpiperidinyl)t- butyldimethoxysilane, (2-ethylpiperidinyl)thexyldimethoxysilane, (3,3,3-trifluoro-n- propyl)(2-ethylpiperidinyl)dimethoxysilane, methyl(3,3,3-trifluoro-n- propyl)dimethoxysilane. Moreover, are also preferred the silicon compounds in which a is 0, c is 3, R8 is a branched alkyl or cycloalkyl group, optionally containing heteroatoms, and R9 is methyl. Examples of such preferred silicon compounds are cyclohexyltrimethoxy silane, t- butyltrimethoxysilane and thexyltrimethoxysilane.

[0038] The external electron donor compound (c) is used in such an amount to give a molar ratio between the organoaluminum compound and said external electron donor compound (iii) of from 0.1 to 20, preferably from 0.5 to 15 and more preferably from 1 to 10.

[0039] The catalyst forming components can be contacted with a liquid inert hydrocarbon solvent such as, e.g., propane, n-hexane or n-heptane, at a temperature below about 60°C and preferably from about 0 to 30°C for a time period of from about 6 seconds to 60 minutes.

[0040] The above catalyst components (a), (b) and optionally (c) can be fed to a precontacting vessel, in amounts such that the weight ratio (b) / (a) is in the range of 0.1-10 and if the compound (c) is present, the weight ratio (b) / (c) is weight ratio corresponding to the molar ratio as defined above. Preferably, the said components are pre-contacted at a temperature of from 10 to 20°C for 1-30 minutes. The precontact vessel is generally a stirred tank reactor.

[0041] Preferably, in large scale plants, the precontacted catalyst is then fed to a prepolymerization reactor where a prepolymerization step takes place. The prepolymerization step can be carried out in a first reactor selected from a loop reactor or a continuously stirred tank reactor, and is generally carried out in liquid-phase. The liquid medium comprises liquid alphaol efin monomer(s), optionally with the addition of an inert hydrocarbon solvent. Said hydrocarbon solvent can be either aromatic, such as toluene, or aliphatic, such as propane, hexane, heptane, isobutane, cyclohexane and 2,2,4-trimethylpentane. The amount of hydrocarbon solvent, if any, is lower than 40% by weight with respect to the total amount of alpha-olefins, preferably lowerthan 20% by weight. Preferably said step is carried out in the absence of inert hydrocarbon solvents.

[0042] The average residence time in this reactor generally ranges from 2 to 40 minutes, preferably from 10 to 25 minutes. The temperature ranges between 10°C and 50°C, preferably between 15°C and 35°C. Adopting these conditions allows to obtain a pre-polymerization degree in the preferred range from 60 to 800g per gram of solid catalyst component, preferably from 150 to 500 g per gram of solid catalyst component. Step (a) is further characterized by a low concentration of solid in the slurry, typically in the range from 50 g to 300 g of solid per liter of slurry.

[0043] The pre-contacted and optionally prepolymerized catalyst is fed to the reactor where the first polymerization step takes place. As mentioned, the first step is preferably carried out in liquid phase. Preferably, it is carried out in liquid propylene using reactors chosen from continuous stirred tank reactors or loop reactors. If a gas-phase is used, the reactor is preferably gas-phase reactor comprising two interconnected polymerization zones one of which, working under fast fluidization conditions and the other in which the polymer flows under the action of gravity.

[0044] The liquid polymerization is generally carried out at temperature of from 20 to 120°C, preferably of from 40 to 85°C. When the polymerization is carried out in gas-phase the operating pressure is generally between 0.5 and 10 MPa, preferably between 1 and 5 MPa. In the bulk polymerization the operating pressure is generally between 1 and 6 MPa preferably between 1.5 and 4 MPa. Preferably, the alkylaluminum component b) is used in amounts such that it ratio with propylene (ppm of Al per mol of propylene) ranges from 1 to 100, more preferably from 10 to 60 and in particular from 15 to 50.

[0045] The second polymerization stage, comprising the propyl ene / ethylene copolymerization, is preferably carried out in a conventional fluidized-bed gas-phase reactor in the presence of the polymeric material and the catalyst system coming from the preceding polymerization step.

[0046] The polypropylene composition of the present disclosure can be used for the manufacturing of foamed articles, such as laminated and un-laminated sheet, beads, and profiles. Foams having densities in the range from 30 to 700 Kg / m3, in particular from 100 to 600 Kg / m3, can be obtained from the polypropylene composition of the present disclosure, finding application for thermal and electrical insulation, for noise and vibration damping, shock absorption and weight reduction.

[0047] In particular they can find application in the automotive field for bumper interiors and impact panels, in marine field as floating devices or in electrical cables insulation. Foamed articles such as foamed coated or uncoated pipes and foamed packaging for foods can be manufactured using the polypropylene composition of the present disclosure. The polypropylene composition of the present disclosure may be manufactured into foamed article by conventional methods. They may be extruded in the presence of at least one foaming agent in conventional single screw or twin screw extruders, both in single and multilayer constructions.

[0048] Foaming agents can be physical foaming agents, such as CO2, gaseous hydrocarbons, H2O, CFCs or mixtures thereof, or chemical foaming agents, such as inorganic carbonates, citric acid or their mixtures. Alternatively, the polypropylene composition of the present disclosure can be firstly pelletized and foamed and subsequently molded for the manufacturing of foamed polypropylene beads according to processes well known in the art.As a method for continuously manufacturing foamed sheets used for food packaging and other purposes, it is known to mix a thermally decomposable foaming agent that generates gas upon heating or a volatile gas with resin and extrude it through a T-die or circular die using an extruder. In the case of a thermally decomposable foaming agent, the foaming agent is premixed with the resin before supplying it to the extruder, separately from the resin. For volatile foaming agents or gaseous foaming agents, the foaming agent is mixed with the melted resin by injecting it into the middle part of the extruder cylinder. The foaming agent used in the foamable composition can be added in a form of a foaming agent master batch using a polyolefin as a carrier. Examples of the polyolefin include polypropylene, polyethylene, and polystyrene. The carrier contained in the masterbatch corresponds to the above-described other components. The content of the decomposition type foaming agent or the solvent type foaming agent contained in the foaming agent masterbatch is usually 5 to 50 wt% and preferably 10 to 40 wt%, and a commercially available product can be used as it is.

[0049] The addition amount of the foaming agent is usually 1 to 10 phr, preferably 2 to 6 phr, and more preferably 2 to 4 phr, with respect to the composition. Further, within the above range, the optimum amount is selected in consideration of the amount of gas to be generated, the foaming ratio, and the like. In extrusion foaming as described above, it is important to foam the resin in a molten state with suitable viscoelasticity for foaming. If the resin’s melt viscosity is too high, foaming becomes difficult, while if it is too low, foamed cells may rupture, preventing gas retention within the resin and deteriorating the surface condition of the foamed sheet. Polypropylene, with its relatively high heat resistance, oil resistance, and mechanicalproperties, is also expected to be suitable for foamed sheet applications. However, due to significant change of the resin’s viscoelasticity with minor temperature variations, the optimal foaming temperature range during extrusion foaming is very narrow, making extrusion foaming a challenging process.

[0050] The following examples are given to illustrate and not to limit the present invention.EXAMPLES

[0051] The data of the propylene polymer materials were obtained according to the following methods:HECO composition

[0052] Total ethylene content and ethylene content of bipolymer portion (C2 in BIPO) in the sample were determined using a13C NMR. Bipolymer content in the sample was calculated from the total ethylene content and the C2 in BIPO.

[0053] A powder sample of a HECO was dissolved in a mixed solvent of 1, 2, 4- trichlorobenzene / deuterated benzene. A13C NMR spectrum of the sample solution was obtained using a Brucker AVANCE III HD400 spectrometer (13C resonance frequency 100 MHz) under conditions of a temperature of 120 °C, a flip angle of 45 °C, a pulse interval of 7 seconds, a sample rotation rate of 20 Hz, and a number of accumulations of 5000 times.

[0054] The total ethylene content (Total C2) of the HECO was determined from the spectrum obtained above by using the method described in M.Kakugo, Y.Naito, K.Mizunuma and T.Miyatake, Macromolecules, 15, 1150-1152 (1982).

[0055] The ethylene content of biopolymer portion (C2 in BIPO) in the HECO was determined in the same manner as Total C2, except that the integrated intensity T’ bb obtained by the following formula was used instead of the integrated intensity Tbbpp obtained by the method described in the above literature to determine Total C2.T’ PP = 0.98 x Say x A / (1 - 0.98 x A) where A = Say / (Say + Sa5), which is calculated from Sagay and Sad described in the above literature. The amount of bipolymer (Bipolymer content) in the HECO is determined by the following formula.Bipolymer content (wt%) = Total C2 (wt%) / (C2 in BIPO (wt%) / 100)

[0056] When component (A) is not a homopolymer and contains a monomer unit other than propylene, a powder sample is taken out after polymerization of component (A) inpolymerization of the HECO (A+B), and a NMR measurement is performed together with the HECO under the same conditions as the HECO. Compositions (C2 in BIPO and Bipolymer content) are determined by using a reduced integrated intensity obtained from integrated intensities of the respective peaks of the spectra of HECO (A+B) and component (A) by the following formula.[Reduced integrated intensity]= [Integrated intensity of HECO (A+B)] - f x [Integrated intensity of component (A)] Where, f is the weight fraction of component (A) in HECO (A+B), and can be from 0 to 1. The f is determined so that T' 00 obtained from reduced Say and Sa5 by the above formula is equal to reduced T00. Bipolymer content in the HECO is determined by the following formula.BIPO content (wt%) = 100 x (1-f)Further, C2 in BIPO is determined by the method described in the above mentioned literature using the reduced integrated intensity.PELLETIZING

[0057] 0.2 phr of B225, 0.12 phr of Sumilizer GP and 0.1 phr of calcium stearate were added to the polymerized powder, and the mixture was extruded at 230 °C with a 15 mm corotating twin- screw extruder (manufactured by Technovel Corporation) and was pelletized.Melt Flow Rate

[0058] For the pellets, measurement was performed under the conditions of a temperature of 230 °C and a load of 2.16 kg in accordance with JIS K7210-1 which is equivalent to ISO 1133.Melt Tension

[0059] Using a capillary rheometer (Capilograph ID manufactured by Toyo Seiki Seisaku- sho, Ltd, equipped with a cylindrical orifice having a length of 8.0 mm and a diameter of 2.095 mm and having a flat upper surface, a resin composition was melted at a temperature of 200 °C in a barrel with a diameter of 9.55 mm. The melted resin composition was discharged from the orifice at a resin extrusion rate of 15 mm / min in the barrel to form a strand. The strand was taken up using a rotating take-up device at a take-up speed of 6.5 m / min while the melt tension (unit: mN) was measured.Xylene soluble and insoluble fractions at 25 °C (room temperature)

[0060] Xylene Solubles according to ISO 16152; 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 °C under vacuum.Intrinsic Viscosity (I V.) of the Xylene Soluble fraction

[0061] A sample of the propylene powder or XS of HECO was dissolved in tetrahydronaphthalene (THN) containing 0.1% BHT at 135 °C to obtain a solution having a concentration of 0.01- 0.02% by weight. Using the solution, the intrinsic viscosity was measured using a capillary automatic viscosity measuring apparatus (SS-780-H1, manufactured by Shibayama Scientific Co., Ltd.).Foaming Test

[0062] Foaming performance was evaluated for several samples with high melt tension. To a pelletized sample, 2 phr of CELLMIC MB3064 manufactured by Sankyo Kasei Co., Ltd. was added as a foaming agent, which was then dry -blended to obtain a foamable composition. Subsequently, using the foamable composition, foamed sheet was formed under the following conditions, and the obtained foamed sheet was evaluated.- Extruder: single screw extruder TP- 15 manufactured by Thermo Plastics Industries, Co., Ltd.- Die portion shape: T-die- Die portion dimension: 60 x 1.2 mm2 Screw shape: full flight screw Screw rotation speed: 60 rpmCylinder set temperature: 200 / 220 / 190 °C Die portion set temperature: 175 °C[Foaming ratio]

[0063] The density of foamed sheet was measured based on ISO 1183 (JIS K7112). The foaming ratio was calculated by dividing 0.9 g / mL by the density of the foam.Procedure for the preparation of heterophasic copolymers Examples 1-3 and comparative examples C1-C2

[0064] A solid catalyst component prepared according to the procedure of Example 3 of WO202 1 / 048861 was brought into contact with the amounts of tri ethylaluminum (TEAL) anddi cyclopentyldimethoxy silane (DCPMS) reported in Table 1 and left at room temperature for 5 minutes. The suspension containing the catalyst prepared above was added into a reactor. Subsequently, liquefied propylene and optionally hydrogen were added to the reactor at room temperature. Then, while stirring the inside of the reactor, the temperature was raised to 70 °C. and polymerization was performed for a predetermined time.

[0065] After completion of the polymerization, the unreacted monomers were purged, and the inside of the reactor was sufficiently replaced with nitrogen, and subsequently a mixed gas of propylene and ethylene was continuously introduced into the reactor to polymerize an ethylene- propylene copolymer (Bipolymer). During the polymerization, the temperature and pressure inside the reactor were adjusted to be constant, and finally, the gas in the reactor was purged and obtained HECO powder.The detailed operative conditions and characterization data are reported in Table 1.The HECO powder of Example 3 was not produced directly in polymerization but was the result of blending the powders of Example 1 and 2 in a 1 :2 wt ratio.Foaming Tests

[0066] The compositions of Examples 1-3 and the commercial material of comparative example 1 were subject to the foaming test performed as previously described. The results are reported in Table 2.Table 1 HECO polymerization conditions and analysis resultsContinuedTABLE 2 FOAMING TEST RESULTThe data above show that Hecos with XSIV higher than 8 exhibited melt strength and foaming performances better than the commercial grades.

Claims

CLAIMSWhat is claimed is:

1. A polypropylene composition (percentages being referred to the total A+B) comprising: (percentages being referred to the total A+B) comprising:A) from 80 to 94wt%, preferably from 82 to 92wt%, more preferably from 83 to 91wt% of polypropylene comprising more than 85wt% of propylene unit and having a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 5.0 to 80.0 g / 10’, preferably from 10.0 to 75.0 g / 10’, more preferably from 15.0 to 70.0 g / 10’ and especially from 18.0 to 65.0 g / 10’, andB) from 6 to 20wt%, preferably from 8 to 18%, more preferably from 9 to 17wt% of a copolymer of propylene and ethylene containing an average content of ethylene derived units from 20 to 50wt%, preferably from 25 to 45wt% and more preferably from 28 to 40wt%; said polypropylene composition being characterized by a fraction soluble in xylene at 25°C having an intrinsic viscosity in tetralin at 135°C of at least 8.5 dl / g, more preferably at least 9.0 dl / g and especially ranging from 9.0 to 15.0 dl / g.

2. The polypropylene composition according to claim 1 wherein the total melt flow rate FR ranges from 0.1 to 30.0g / 10’, preferably from 0.5 to 25.0 g / 10’, more preferably from 1.0 to 20.0 g / 10’, and especially from 1.5 to 15.0 g / 10’.

3. The polypropylene composition according to claims 1 or 2 wherein the component A) the component (A) has a MFR L (Melt Flow Rate according to ISO 1133, condition L, i.e. 230°C and 2.16 kg load) ranging from 10.0 to 75.0 g / 10’, more preferably from 15.0 to 70.0 g / 10’ and especially from 18.0 to 65.0 g / 10’.

4. The polypropylene composition according to anyone of claims 1-3 wherein the intrinsic viscosity of the fraction soluble in xylene at 25°C is at least 9.0 dl / g and especially ranging from 9.0 to 15.0 dl / g.

5. The polypropylene composition according to anyone of claims 1-4 wherein component A) contains at least 90%wt of propylene derived units, more preferably at least 95wt% of propylene derived units and, especially, from 96 to 100 wt% of propylene derived units.

6. The polypropylene composition according to anyone of claims 1-5 having melt tension, determined with the method described in the experimental section, ranging from 150 to 350 mN preferably from 170 to 320 mN and especially from 175 to 300 mN.

7. A process for the preparation of the polypropylene composition according to anyone of claims 1-6 comprising sequential polymerization in at least two stages, wherein propylene is polymerized in a first polymerization stage carried out in liquid propylene and in the presence of hydrogen as molecular weight regulator and in the second polymerization stage, carried out in the presence of the polypropylene produced in the first stage, ethylene and propylene are polymerized in gas-phase, said process being carried out in the presence of a heterogenous ZN catalyst which preferably comprises the product of the reaction between: a) a solid catalyst component comprising Ti, Mg, Cl, and an electron donor compound selected from structures containing at least a carbamic group which is present in an amount of higher than 50%wt based on the total amount of electron donors; b) an alkylaluminum compound and, c) an external electron-donor compound having the general formula: (R?)a(R8)bSi(OR9)c, where a and b are integers from 0 to 2, c is an integer from 1 to 4 and the sum (a+b+c) is 4; R7, Rs, and R9, are alkyl, cycloalkyl or aryl radicals with 1- 18 carbon atoms optionally containing heteroatoms.

8. The process according to claim 7 wherein the electron donor present in the solid catalyst component (a) has two carbamic groups.

9. The process according to claim 8 in which the electron donor has formula (I)where R1and R2, independently, are selected from hydrogen and C1-C15 hydrocarbon groups, optionally contain a heteroatom selected from halogen, P, S, N, O and Si, which can be fused together to form one or more cycles and A is a bivalent bridging group.

10. Foamed articles comprising the polypropylene composition of claims 1-6.

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