Heterophasic polypropylene composition with high flexibility and softness

1. A heterophasic polypropylene composition comprising a polymer base resin which comprises a matrix phase and an elastomeric phase dispersed therein, wherein the matrix phase and the elastomeric phase are polymerized in the presence of a single-site catalyst; and

wherein the polymer base resin comprises:

(A) from 20 to 55 wt % of a crystalline fraction (CF), measured by Crystex QC in trichlorobenzene, which is a propylene homopolymer fraction or a copolymer fraction of propylene monomer units and comonomer units of ethylene or alpha-olefins with 4 to 12 carbon atoms with an amount of comonomer units of up to 6.0 wt %; and

(B) from 45 to 80 wt % of a soluble fraction (SF), measured by Crystex QC in trichlorobenzene, which is a copolymer of propylene monomer units and comonomer units of ethylene or alpha-olefins with 4-12 carbon atoms, with an amount of comonomer units of from 17 to 55 wt % and an intrinsic viscosity iV of from 1.2 to 7.0 dl/g,

wherein the heterophasic polypropylene composition has a tensile modulus of not more than 700 MPa and a total viscosity iV of from 1.2 to 7.0 dl/g.

2. The heterophasic polypropylene composition according to claim 1 , having a Shore D hardness of not more than 50.

3. The heterophasic polypropylene composition according to claim 1 , having a Shore A hardness of not more than 100.

4. The heterophasic polypropylene composition according to claim 1 , having a total amount of comonomer units of from 6.0 to 35.0 wt %, based on the total amount of the heterophasic polypropylene composition.

5. The heterophasic polypropylene composition according to claim 1 , having a melting temperature of from 135° C. to 165° C.

6. The heterophasic polypropylene composition according to claim 1 , having a melt flow rate MFR 2 (230° C., 2.16 kg) of from 0.05 to 100 g/10 min.

7. The heterophasic polypropylene composition according to claim 1 , wherein the crystalline fraction (CF) has an intrinsic viscosity iV of from 1.0 to 7.0 dl/g.

8. The heterophasic polypropylene composition according to claim 1 , wherein the crystalline fraction (CF) is a copolymer fraction of propylene monomer units and ethylene comonomer units.

9. The heterophasic polypropylene composition according to claim 1 , wherein the soluble fraction (SF) is a copolymer fraction of propylene monomer units and ethylene comonomer units.

10. A process for preparing the heterophasic polypropylene composition according to claim 1 , comprising the steps of:

a) polymerizing propylene and optionally comonomer units selected from ethylene or alpha-olefins with 4 to 12 carbon atoms in a first polymerization reactor in the presence of a single-site catalyst to produce a first polymerization mixture comprising a first propylene homo- or copolymer and the single-site catalyst;

b) transferring the first polymerization mixture into a second polymerization reactor;

c) polymerizing propylene and comonomer units selected from ethylene or alpha-olefins with 4 to 12 carbon atoms in said second polymerization reactor in the presence of said single-site catalyst to produce a second polymerization mixture comprising a second propylene copolymer, said first propylene homo- or copolymer and the single-site catalyst, wherein the weight ratio of said first propylene homo- or copolymer to said second propylene copolymer is in the range of 20:80 to 55:45;

d) withdrawing said second polymerization mixture from said second polymerization reactor; and

e) compounding said second polymerization mixture optionally with the addition of additives to form the heterophasic polypropylene composition.

11. The process according to claim 10 , wherein the single-site catalyst comprises (i) a complex formula (I):

wherein

M is zirconium or hafnium;

each X independently is a sigma-donor ligand

L is a divalent bridge selected from —R′ 2 C—, —R′ 2 C—CR′ 2 —, —R′ 2 Si—, —R′ 2 Si—SiR′ 2 —, —R′ 2 Ge—, wherein each R′ is independently a hydrogen atom or a C 1 -C 20 -hydrocarbyl group optionally containing one or more heteroatoms of Group 14-16 of the periodic table or fluorine atoms, or optionally two R′ groups taken together can form a ring;

R 1 and R 1′ are each independently hydrogen, C 5 -C 10 -aryl or a group —CH(R x ) 2 wherein each R x is independently H or a C 1-10 hydrocarbyl group, and optionally the two R x taken together can form a ring,

R 2 and R 2′ are each independently hydrogen, C 5 -C 10 -aryl or a group —C(R y ) 3

wherein each R y is independently H or a C 1-10 hydrocarbyl group, or optionally two or three R y groups taken together can form a ring,

whereby at least one of R 1 or R 2 and one of R 1′ or R 2′ is different from hydrogen and

whereby R 2 together with one of R 1 , as well as R 2′ together with one of R 1′ can be part of a further mono- or multicyclic ring condensed to the phenyl ring

R 3 and R 3′ are each independently a linear C 1 to C 6 hydrocarbyl group or a branched or cyclic C 4 to C 10 hydrocarbyl group, whereby the groups are not branched in α-position

R 4 and R 4′ are each independently a tertiary C 4 to C 10 hydrocarbyl group

R 5 and R 5′ are each independently a linear or branched C 1 to C 10 alkyl group or an C 5 -C 10 -aryl group and

(ii) a cocatalyst comprising a compound of a group 13 metal.

12. The process according to claim 10 , wherein the single-site catalyst comprises (i) a complex formula (II):

wherein

M is Zr or Hf;

each R 1 is a linear or branched C 1-10 alkyl;

L is ethylene or Si(R6) 2 ;

R 6 is C 1-10 alkyl, C 6-10 -aryl, C 7-12 -alkylaryl, or C 7-12 -arylalkyl;

each X is a hydrogen atom, C 1-6 -alkoxy, a halogen atom, or an R group;

R is C 1-10 alkyl

each R 4 is H or C 1-3 -alkyl;

W′ is phenyl, pyridyl, thiophenyl or furyl optionally substituted by up to 2 groups R 5 ;

each R 5 is C 1-10 -alkyl or two adjacent R 5 groups taken together form a phenyl ring fused to W′, and

(ii) at least an alumoxane or a compound able to form an alkylmetallocene cation.

13. An article comprising the heterophasic polypropylene composition according to claim 1 .