Process for preparing a polypropylene composition

1. 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 C 4 -C 10 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 C 4 -C 10 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 C 4 -C 10 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 MFR 2 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.

2. The process according to claim 1 , wherein the polypropylene composition has a comonomer content in the range of from 1.5 to 5.0 wt %, relative to the total amount of monomers present in the polypropylene composition.

3. The process according to claim 1 , wherein the melt-mixing of the pelletized second propylene polymer fraction is carried out at a temperature in the range of 190° C. to 260° C.

4. The process according to claim 1 , wherein the melt-mixing of the pelletized second propylene polymer fraction is carried out in a single-screw extruder or a twin-screw extruder.

5. The process according to claim 1 , wherein the second propylene polymer fraction and the propylene polymer (PP-c) are free of a phthalic compound.

6. The process according to claim 1 , wherein the first reactor is a slurry reactor.

7. The process according to claim 1 , wherein the second reactor is a gas-phase reactor.

8. A polypropylene composition obtainable by the process according to claim 1 .

9. The polypropylene composition according to claim 8 , wherein the polypropylene composition has a xylene soluble content (XCS) in the range of from 5.5 to 18.0 wt %, as determined according to ISO 16152 at 25° C.

10. The polypropylene composition according to claim 8 , wherein the polypropylene composition has a melting temperature >152° C. and a crystallization temperature >120° C. as measured according to ISO 11357/3.

11. The polypropylene composition according to claim 8 , wherein the polypropylene composition has a Charpy notched impact strength >4.8 kJ/m 2 , as measured according to ISO 179/1eA at 23° C. on injection moulded test specimens as described in EN ISO 1873-2.

12. The polypropylene composition according to claim 8 , wherein the polypropylene composition is free of a phthalic compound.

13. An article comprising the polypropylene composition according to claim 8 .

14. The article according to claim 13 , wherein the article is a cast film, an injection moulded article, a closure cap, a screw cap, or a closure system for food or fluid packaging.