Process for the Production of a Bimodal Polypropylene Having Low Ash Content
The present invention relates to a process for making low ash propylene homo- or copolymers with improved properties, with “ash” denoting aluminium as well as residues of catalyst, cocatalyst or any additive, such as titanium (Ti) and silicium (Si) derivatives, used in the production of propylene polymers. The propylene polymers of the present invention are useful to make films, such as capacitor films, as well as fibers and nonwovens, such as for example staple fibers, spunbond nonwovens or meltblown nonwovens.
1 - 15 . (canceled)
16 . A process for production of propylene polymers with improved properties and a low ash content comprising:
polymerizing propylene and one or more optional comonomers in at least two sequential polymerization reactors in presence of:
a Ziegler-Natta catalyst comprising a titanium compound having at least one titanium-halogen bond, and an internal electron donor, both supported on a magnesium halide in active form;
triethyl aluminium;
an optional external electron donor (ED); and
hydrogen,
wherein the internal electron donor comprises at least 80 wt % of a diether, the molar ratio Al/Ti is at most 40, the propylene polymers are recovered from the polymerization reactor without any washing, as a powder and optionally converted to pellets, and wherein the propylene polymer fractions produced in the at least two of the sequential polymerization reactors differ in average molecular weight such that the ratio of the melt flow indices of the propylene polymer fractions with the highest and the lowest melt flow index is at least 10.
17 . The process of claim 16 further comprising an external electron donor (ED).
18 . The process of claim 17 , wherein the molar ratio Al/ED is at most 120.
19 . The process of claim 17 , wherein the external electron donor (ED) comprises a silane.
20 . The process of claim 16 , wherein the polymerization of propylene and one or more optional comonomers is done in two sequential polymerization reactors.
21 . The process of claim 20 , wherein the first polymerization reactor produces from 35 wt % to 65 wt % of the total weight of propylene polymer.
22 . Propylene polymer formed by the process of claim 16 .
23 . The propylene polymer of claim 22 comprising at most 2 ppm of titanium.
24 . The propylene polymer of claim 23 comprising a total ash content of at most 50 ppm.
25 . The propylene polymer of claim 22 comprising at most 2.5 wt % of xylene solubles, relative to the total weight of the propylene polymer.
26 . The propylene polymer of claim 22 having a polydispersity index (PI) in the range from 5 to 7.
27 . The propylene polymer of claim 22 having an isotacticity of at least 97.0% mmmm.
28 . Film formed by the polymer of claim 22 .
29 . Fiber or nonwoven comprising the propylene polymer of claim 22 .
30 . A capacitor film formed by the film of claim 29 .