Heterophasic polypropylene copolymer composition

Process for the preparation of heterophasic polypropylene compositions, comprising the steps of:

• producing a polypropylene polymer matrix (A) in the presence of a catalyst system comprising a Ziegler-Natta procatalyst in combination with an external donor and a cocatalyst in at least one slurry reactor
• transferring the slurry reactor product into a first gas phase reactor (GPR),
• (i) a Ziegler-Natta procatalyst which contains a trans-esterification product of a lower alcohol and a phthalic ester as internal donor and
• (ii) an organometallic cocatalyst and
• (iii) an external donor represented by formula (III)
• Si(OCH2CH3)3(NR1R2)
• wherein R1 and R2 can be the same or different a represent a hydrocarbon group having 1 to 12 carbon atoms
• or formula (IV)
• R3nR4mSi(OR6)z
• wherein R3 and R4 are identical or different hydrocarbon residues, R5 is methyl or ethyl, z is 2 or 3;
• m is 0 or 1;
• n is 0 or 1;
• with the proviso that n+m+z=4,
• said procatalyst being modified by polymerizing it with a vinyl compound of the formula CH2═CH—CHR6R7
• wherein R6 and R7 together form a 5- or 6-membered saturated, unsaturated or aromatic ring or independently represent an alkyl group comprising 1 to 4 carbon atoms,
• in the presence of the cocatalysts and the external donor,
• wherein the slurry reactor product is further polymerized in the presence of the catalyst system in said first GPR
• transferring the first GPR product into a 2nd GPR producing an ethylene/propylene-copolymer (B) in the polymer matrix (A) in the presence of the catalyst system in said 2nd GPR
• transferring the 2nd GPR product into a 3rd GPR and further producing an ethylene/propylene-copolymer (B) in the polymer matrix (A) in the presence of the catalyst system in said 3rd GPR, said ethylene/propylene copolymers having the same composition ratios and
• recovering the polymer product for further processing,
• yielding a polypropylene polymer matrix (A) containing said ethylene/propylene copolymers (B) having the same composition ratios, respectively having same ethylene content and intrinsic viscosities, so that an unimodal rubber composition is obtained
• adding (C) 0-15 wt % of an elastomeric ethylene/alpha-olefin random copolymer and (D) 3-25 parts per weight of inorganic filler.