Process for producing high-flow heterophasic propylene copolymer compositions

Process for producing a heterophasic propylene copolymer composition, the process comprising the steps of

• a) preparing a bimodal matrix phase (A) of a heterophasic propylene copolymer by
• a1) polymerizing propylene in a first reactor to obtain a first propylene polymer fraction having a melt flow rate MFR2 of 25 to 85 g/10 min determined according to ISO 1133 at 230° C. and 2.16 kg load,
• a2) transferring the first propylene polymer fraction to a second reactor, and polymerizing propylene in the second reactor to obtain a second propylene polymer fraction, the combined first and second propylene polymer fractions having an MFR2 determined according to ISO 1133 at 230° C. and 2.16 kg load being at least 2.2 times higher than the MFR2 of the first propylene polymer fraction,
• b) preparing a disperse phase (B) of the heterophasic propylene copolymer by
• b1) transferring the first propylene polymer fraction and the second propylene polymer fraction to a third reactor, and polymerizing in the third reactor propylene and an alpha-olefin having 2 or 4 to 12 carbon atoms to obtain a third propylene polymer fraction,
• c) withdrawing from the third reactor the heterophasic propylene copolymer comprising the first, second and third propylene polymer fraction, and
• d) obtaining the heterophasic propylene copolymer composition comprising the heterophasic propylene copolymer,
• wherein the heterophasic propylene copolymer composition has a melt flow rate MFR2 of 70 to 250 g/10 min determined according to ISO 1133 at 230° C. and 2.16 kg load, and
• wherein polymerizing in steps a1), a2) and b1) is conducted in the presence of a metallocene catalyst system, the metallocene catalyst system comprising a metallocene complex and a support, wherein the support comprises silica and wherein the metallocene complex is of formula (I):
• wherein each X independently is a sigma-donor ligand,
• L is a divalent bridge selected from —R′2C—, —R′2C—CR′2—, —R′2Si—, —R′2Si—SiR′2—, and —R′2Ge—, wherein each R′ is independently a hydrogen atom or a C1-C20-hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 of the periodic table or fluorine atoms, or optionally two R′ groups taken together can form a ring,
• each R1 are independently the same or different and are hydrogen, a linear or branched C1-C6-alkyl group, a C7-20-arylalkyl, C7-20-alkylaryl group or C6-20-aryl group or an OY group, wherein Y is a C1-10-hydrocarbyl group, and optionally two adjacent R1 groups can be part of a ring including the phenyl carbons to which they are bonded,
• each R2 independently are the same or different and are a CH2—R3 group, with R3 being H or linear or branched C1-6-alkyl group, C3-3-cycloalkyl group, or C6-10-aryl group,
• R3 is a linear or branched C1-C6-alkyl group, C7-20-arylalkyl, C7-20-alkylaryl group or C6-C20-aryl group,
• R4 is a C(R9)3 group. with R9 being a linear or branched C1-C6-alkyl group.
• R5 is hydrogen or an aliphatic C1-C20-hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 of the periodic table;
• R6 is hydrogen or an aliphatic C1-C20-hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16 of the periodic table;
• or
• R5 and R6 can be taken together to form a 5 membered saturated carbon ring which is optionally substituted by n groups R10, n being from 0 to 4;
• each R10 is same or different and is selected from a C1-C20-hydrocarbyl group and a C1-C20-hydrocarbyl group optionally containing one or more heteroatoms belonging to groups 14-16 of the periodic table;
• R7 is H or a linear or branched C1-C6-alkyl group or an aryl or heteroaryl group having 6 to 20 carbon atoms optionally substituted by one to three groups R11,
• each R11 are independently the same or different and are hydrogen, a linear or branched C1-C6-alkyl group, a C7-20-arylalkyl, C7-20-alkylaryl group or C6-20-aryl group or an OY group, wherein Y is a C1-10-hydrocarbyl group.