Process for preparing a polypropylene composition

A process for producing a polypropylene composition by sequential polymerization, the process comprising the steps of:

• a) polymerizing in a first reactor monomers comprising propylene and optionally one or more comonomers selected from ethylene and C4-C10 alpha-olefins, to obtain a first propylene polymer fraction having a comonomer content in the range of 0.0 to 1.0 wt %,
• b) polymerizing in a second reactor monomers comprising propylene and one or more comonomers selected from ethylene and C4-C10 alpha-olefins, in the presence of the first propylene polymer fraction to obtain a second propylene polymer fraction having a comonomer content in the range of from 4.5 to 20.0 wt %,
• c) pelletizing the second propylene polymer fraction, and
• d) melt-mixing the pelletized second propylene polymer fraction in the presence of:
• i. a propylene polymer (PP-c) produced in a process comprising at least two reactors connected in series, the propylene polymer (PP-c) containing one or more comonomers selected from ethylene and C4-C10 alpha-olefins wherein the comonomer content is in the range of from 0.5 to 2.5 wt %, and
• ii. at least one alpha-nucleating agent,
• wherein the polypropylene composition has:
• i—an MFR2 in the range of from 11.0 to 60.0 g/10 min, as measured according to ISO 1133 at 230° C. under a load of 2.16 kg;
• ii—a haze value of <20%, as measured according to ASTM D1003 on injection moulded plaques having 1 mm thickness produced as described in EN ISO 1873-2;
• iii—a tensile modulus >950 MPa, as measured according to ISO 527-1:2012/ISO 527-2:2012 on an injection moulded test specimen at 23° C.;
• iv—15 to 84 wt % of the pelletized second polymer fraction relative to the total amount of polypropylene composition;
• v—15 to 84% of the propylene polymer (PP-c) relative to the total amount of polypropylene composition;
• and
• vi—0.01 to 1.0 wt % of at least one alpha-nucleating agent relative to the total amount of polypropylene composition.