Polymer composition and a process for production of the polymer composition

1. A polyethylene composition comprising a base resin which comprises

(a) an ethylene homo- or copolymer fraction (A1); and

(b) an ethylene homo- or copolymer fraction (A2), wherein

(I) fraction (A1) has a lower weight average molecular weight than fraction (A2);

(II) the base resin has a density of 930 to 950 kg/m 3 ;

(III) the base resin has a melt flow rate MFR 21 of equal to or less than 8.0 g/10 min;

(IV) the polyethylene composition has a melt flow rate MFR 5 of 0.01 to 0.3 g/10 min;

(V) the polyethylene composition has a flow rate ratio FRR 21/5 of equal to or more than 25;

(VI) the ratio of the weight average molecular weight and the number average molecular weight (M w /M n ) of the polyethylene composition is equal to or less than 30; and

(VII) the polyethylene composition has a tensile modulus of less than 1000 MPa.

2. A polyethylene composition according to claim 1 , wherein the ratio of the weight average molecular weight and the number average molecular weight (M w /M n ) of the polyethylene composition is 5 to 30.

3. A polyethylene composition according to claim 1 , wherein the polyethylene composition has a tensile modulus of not more than 950 MPa.

4. A polyethylene composition according to claim 1 , wherein the polyethylene composition has a tensile modulus of at least 700 MPa.

5. A polyethylene composition according to claim 1 , wherein the base resin has a density of 933 to 947 kg/m 3 .

6. A polyethylene composition according to claim 1 , wherein the polyethylene composition has a viscosity at a shear stress of 747 Pa (eta747) of 300 to 700 kPas.

7. A polyethylene composition according to claim 1 , wherein a ratio of ETA 0.05rad/s to ETA 300rad/s of the polyethylene composition is 110 to 180.

8. A polyethylene composition according to claim 1 , wherein the polyethylene composition has the melt flow rate MFR 5 of 0.05 to 0.3 g/10 min.

9. A polyethylene composition according to claim 1 , wherein the base resin has a melt flow rate MFR 21 of equal to or less than 7.0 g/10 min.

10. A polyethylene composition according to claim 1 , wherein the polyethylene composition has a strain hardening modulus of more than 75 MPa.

11. A polyethylene composition according to claim 1 , wherein the polyethylene composition has a time to failure of at least 400 h.

12. An article made of polyethylene composition as defined in claim 1 .

13. Method for production of an article using a polyethylene composition as defined in claim 1 .

14. A process for the production of a polyethylene composition comprising a polyethylene base resin, which comprises steps of

(a) polymerising ethylene and optionally at least one comonomer in the presence of a polymerisation catalyst to form an ethylene homo- or copolymer fraction (A1); and

(b) polymerising ethylene and optionally at least one comonomer in the presence of same or different polymerisation catalyst(s) as polymerising the fraction (A1) to form an ethylene homo- or copolymer fraction (A2); and wherein

(I) fraction (A1) has a lower weight average molecular weight than fraction (A2), and at least one of the catalyst(s) is a Ziegler-Natta (ZN) catalyst;

(II) the base resin has a density of 930 to 950 kg/m 3 ;

(III) the base resin has a melt flow rate MFR 21 of equal to or less than 8.0 g/10 min;

(IV) the polyethylene composition has a melt flow rate MFR 5 of 0.01 to 0.3 g/10 min;

(V) the polyethylene composition has a flow rate ratio FRR 21/5 of equal to or more than 20;

(VI) the ratio of the weight average molecular weight and the number average molecular weight (M w /M n ) of the polyethylene composition is equal to or less than 30; and

(VII) the polyethylene composition has tensile modulus less than 1000 MPa, wherein the Ziegler-Natta (ZN) catalyst comprises an internal organic compound having the formula (I):

wherein in the formula (I) R 1 to R 5 are the same or different and can be hydrogen, a linear or branched C1 to C8-alkyl group, or a C3-C8-alkylene group, or two or more of R 1 to R 5 can form a ring, and the two oxygen-containing rings are individually saturated or partially unsaturated or unsaturated.

15. A process according to claim 14 comprising the additional steps of

(a) providing solid carrier particles of MgCl 2 *mROH adduct;

(b) pre-treating the solid carrier particles of step (a) with a compound of Group 13 metal;

(c) treating the pre-treated solid carried particles of step (b) with a transition metal compound of Group 4 to 6;

(d) recovering the solid catalyst component;

(e) contacting the solid carrier particles with the internal organic compound having the formula (I) prior to the step (c); and

(f) passing the solid catalyst component into the first polymerisation stage, wherein R in the adduct MgCl 2 *mROH is a linear or branched alkyl group with 1 to 12 carbon atoms and m is a number from 1 to 6.