Propylene polymer composition having superior hexane extractables/impact balance

1. Process for the preparation of heterophasic polypropylene copolymers comprising the steps of:

producing a polypropylene polymer matrix (A) in the presence of a catalyst system in a first slurry reactor and optionally in a second slurry reactor or in a 1 st gas phase reactor (GPR), yielding a first polymerisation product, wherein the catalyst system comprises:

i) a Ziegler-Natta procatalyst which contains a trans-esterification product of a lower alcohol and a phthalic ester;

(ii) optionally an organometallic cocatalyst; and

(iii) an external donor represented by formula (I) or (II)

Si(OCH 2 CH 3 ) 3 (NR 1 R 2 )  (I)

or

R 3 n R 4 m Si(OR 5 ) z   (II)

wherein R 1 and R 2 can be the same or different and represent a hydrocarbon group having 1 to 12 carbon atoms,

R 3 and R 4 are identical or different hydrocarbon residues having 1 to 12 carbon atoms,

R 5 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;

transferring the first polymerisation product into a 1 st GPR or a 2 nd GPR, if the matrix is produced in a slurry/GPR combination;

producing an ethylene/propylene-copolymer in the polymer matrix in the presence of the catalyst system in said 1 st or 2 nd GPR;

optionally transferring the 1 st or 2 nd GPR product into a 2 nd respectively 3 rd GPR and producing a second ethylene/propylene-copolymer in the polymer matrix in the presence of the catalyst system in said 2 nd or 3 rd GPR, said 1 st and 2 nd ethylene/propylene mixtures may have the same or different composition ratios; and

recovering the polymer product for further processing, the recovered polymer product including heterophasic polypropylene copolymers having an MFR 2 (2.16 kg, 230° C.) of 15 to 200 g/10 min, determined according to ISO 1133 comprising a propylene homo- or copolymer matrix (A) with an MFR 2 (2.16 kg, 230° C.) of 80 to 500 g/10 min, determined according to ISO 1133 and an ethylene or C 4 -C 10 -alpha-olefin propylene rubber phase (B) dispersed within the matrix,

wherein the heterophasic polypropylene copolymers have a fraction soluble in p-xylene at 25° C. (XCS), having an intrinsic viscosity of 2.85 to 4.00 dl/g, determined according to DIN EN ISO 1628-1 and -3 and being composed of propylene monomer units in an amount of 70 wt % to 90 wt %.

2. The process of claim 1 , wherein the propylene matrix (A) is a propylene homopolymer with an MFR 2 (2.16 kg, 230° C.) of 90 to 400 g/10 min, determined according to ISO 1133 (A).

3. The process of claim 1 , wherein the rubber phase (B) is an ethylene/propylene copolymer.

4. The process of claim 1 , wherein the heterophasic polypropylene copolymers comprise:

a) 75 wt % to 95 wt % of the propylene matrix (A) based on the total amount of the heterophasic propylene copolymer and

b) 5 to 25 wt % of the ethylene or C 4 -C 10 -alpha-olefin propylene rubber phase (B) based on the total amount of the heterophasic propylene copolymer.

5. The process of claim 1 further comprising providing the heterophasic copolymers in a heterophasic polypropylene composition, wherein the propylene matrix (A) and the ethylene or C 4 -C 10 -alpha-olefin propylene rubber phase (B) contribute to at least 85 wt % to the composition and up to 15 wt % may be on or more additives selected from the group consisting of alpha-nucleating agents, antioxidants, stabilizers, acid scavengers, lubricants, mould release agents, flame retardants, pigments, dyes, fillers and plasticizers.

6. The process of claim 5 , wherein the composition has a Charpy notched impact strength at +23° C. of at least 4.0 kJ/m 2 , up to 80 kJ/m 2 , and a Charpy notched impact strength at −20° C. of at least 2.0 kJ/m 2 up to 50 kJ/m 2 , determined according to ISO 179-1eA:2000.

7. The process of claim 5 , wherein the composition has a flexural modulus of at least 600 MPa up to 2500 MPa determined according to ISO 178.

8. The process of claim 5 , wherein the composition has a fraction extractable in hexane (FDA 177, 1520) of less than 5.0 wt %.