Multi-stage process for producing multimodal linear low density polyethylene polymers

1. A process for the manufacture of a multimodal linear low density polyethylene polymer comprising:

in a first stage polymerising ethylene and optionally at least one α-olefin in the presence of a Ziegler-Natta catalyst which comprises a solid catalyst component which is formed at least from

(a) a compound of group 1 to 3 of the periodic table;

(b) a transition metal compound of group 4 to 10 of the periodic table or an actinide or lanthanide;

(c) a compound of group 13 of the periodic table;

wherein the catalyst component of said Ziegler Natta catalyst is formed by an emulsion/solidification method, and is modified by one or more organic ligand compounds which are selected from organic compounds comprising a cyclopentadienyl anion backbone;

so as to form 30 to 60 wt % of a lower molecular weight component (A) wherein (A) is an ethylene homopolymer or a copolymer of ethylene and at least one α-olefin; and

transferring the product of the first stage to a second stage and

in a second stage polymerising ethylene and at least one α-olefin in the presence of the same catalyst to form 70 to 40 wt % of a higher molecular weight component (B);

wherein (B) is a copolymer of ethylene and at least one α-olefin, wherein said α- olefin is the same or different from any α-olefin used in component (A) but wherein both components (A) and (B) are not polymers of ethylene and butene alone;

so as to form a multimodal linear low density polyethylene polymer which has a final density of 900 to 940 kg/m 3 ; and

wherein the multimodal linear low density polyethylene polymer has a dart drop of at least 700g, and the molecular weight distribution of the multimodal linear low density polyethylene polymer is in the range 7 to 22.

2. A process as claimed in claim 1 wherein the final density of the polymer is 910 to 925 kg/m 3 .

3. A process as claimed in claim 1 wherein said process is carried out in the presence of a cocatalyst and said cocatalyst is TIBA.

4. A process as claimed in claim 1 wherein the dart drop of the multimodal linear low density polyethylene polymer is at least 900 g.

5. A process as claimed in claim 1 wherein the LMW component forms 35 to 48 wt % of the multimodal linear low density polyethylene polymer and the HMW component forms 65 to 52 wt % of the multimodal linear low density polyethylene polymer.

6. A process as claimed in claim 1 further comprising forming said multimodal linear low density polyethylene polymer into an article.

7. A process as claimed in claim 6 wherein the article is a film.

8. A process as claimed in claim 7 wherein said film has a dart drop of at least 700 g.