Polymer films and a process for the production thereof

A blown polyethylene film comprising a polyethylene composition having

• (i) a low, molecular weight portion having a density of more than 960 kg/m3 and an MFR2 higher than 100 g/10 min;
• and
• (ii) a high molecular weight portion which has an MFR21 of less than 50 g/10 min,
• the polyethylene composition having a density between 935-939 and MFR21 between 7-20 g/10 min and said film exhibiting
• tensile strength in transverse direction of at least 20 Mpa;
• 1% secant modulus in machine direction of at least 400 MPa and in transverse direction at least 500 MPa;
• and,
• when run to a film having a thickness between 35-45 μm in a machine operating with a low neck, a dart drop of at least 5 g/μm;
• or
• when run to a film having a thickness between 20-30 μm in a machine operating with a high neck, a dart drop of at least 8 g/μm.

A process for producing a blown polyethylene film comprising the steps of

• producing a polyethylene composition in the presence of a catalytic system of an ethylene polymerizing catalyst and cocatalyst in a multistage reaction sequence consisting of successive polymerization stages where at least one stage is carried out in a gas phase by
• subjecting ethylene, optionally hydrogen and comonomers to a first polymerization or copolymerization reaction in a first reaction zone or reactor to produce a first polymer;
• recovering the first polymer and the catalyst therein from the first reaction zone;
• feeding the first polymer into a second polymerization zone or reactor;
• feeding additional ethylene and optionally hydrogen and comonomers to the second reaction zone;
• subjecting the additional ethylene and optionally additional monomer(s) and hydrogen to a second polymerization reaction in the presence of the first polymer and the catalyst therein to produce a second polymerization product having an MFR21 of less than 50 g/10 min.;
• and
• recovering the combined polymerization product from the second reaction zone, and
• blowing the thus obtained polyethylene composition into a film having a density of 929-939 kg/m3.

A process for producing a blown polyethylene film exhibiting

• a tensile strength at yield in transverse direction at least 15 MPa,
• a density of 929 to 939 kg/m3;
• a 1% secant modulus in machine direction at least 300 MPa and in transverse direction at least 400 MP a;
• and
• a dart drop at least 5 g/mm;
• comprising the steps of
• producing a polyethylene composition by
• subjecting ethylene, optionally hydrogen and comonomers to a first polymerization or copolymerization reaction in a first reaction zone or reactor to produce a polymer having a MFR2 of 100 g/10 min or more;
• recovering the first polymerization product from the first reaction zone;
• feeding the first polymerization product to a second reaction zone or reactor,
• feeding additional ethylene and optionally hydrogen and comonomers to the second reaction zone,
• subjecting the additional ethylene and optionally additional monomer(s) and hydrogen to a second polymerization reaction in the presence of the first polymerization product to produce a second polymerization product having a MFR21 of less than 50 g/10 min, and
• recovering the combined polymerization product from the second reaction zone, and
• blowing the thus obtained polyethylene composition into a film.