Patent ID: 7714072

Claim:
A multimodal polyethylene composition having; 1) a density of at least about 0.940 g/cm 3 as measured by ASTM Method D-1505; 2) a melt flow index (I 5 ) of from about 0.2 to about 1.5 g/10 min (as measured by ASTM D-1238, measured at 190° C. and 5 kilograms); 3) a melt flow index ratio (I 21 /I 5 ) of from about 20 to about 50; 4) a molecular weight distribution, Mw/Mn, of from about 20 to about 40; and 5) a bubble stability measured on an HS50S stationary extrusion system with an BF 10-25 die, HK 300 air ring, A8 take off, and WS8 surface winder, all commercially available from Hosokawa Alpine Corporation, with a 100 mm die diameter having a 50 mm 21:1 L/D grooved feed extruder used according to the conditions described herein for a film of about 6×10 −6 m thickness of at least about 1.22 m/s line speed, at least about 45 kg/hr (0.013 kg/sec) output rate, or at least about 0.5 lb/hr/rpm (0.0000011 kg/s/rps) specific output rate or a combination thereof; 6) a dart impact on 12.5 micron (1.25×10 −5 m) film of at least 300 g; measured according to ASTM 1709, Method A; the composition comprising a blend comprising; A) a high molecular weight fraction which; a) is present in an amount of from about 30 to about 70 weight percent (based on the total weight of the composition); b) has a density of at least about 0.860 g/cm 3 as measured by ASTM D-1505; c) has a melt flow index (I 21 ) of from about 0.01 to about 50 g/10 min (as measured by ASTM D-1238, measured at 190° C. and 21.6 kilograms); and d) a melt flow index ratio (I 21 /I 5 ) of from about 6 to about 12; and B) a low molecular weight fraction which; a) is present in an amount of from about 30 to about 70 weight percent (based on the total weight of the composition); b) has a density of at least about 0.900 g/cm 3 as measured by ASTM D-1505; c) has a melt flow index (I 2 ) of from about 0.5 to about 3000 g/10 min (as measured by ASTM D-1238, measured at 190° C. and 2.16 kilograms); d) a melt flow index ratio (I 21 /I 5 ) of from about 5 to about 15; and e) is prepared using a mole ratio of alpha olefin to ethylene less than that in the high molecular weight fraction of less than or equal to about 0.01:1; wherein said blend is melted in an extruder having a mixer vent, wherein the mixer vent has an oxygen concentration of from about 0.05 to about 6 volume percent oxygen in nitrogen; and the extrusion temperature is sufficient to melt the blend and result in tailoring the blend in the presence of the oxygen; and wherein said molten blend is passed through one or more active screens, wherein in the case of two or more active screens, the screens are positioned in series, each active screen having a micron retention size of from about 2 to about 70, at a mass flux of about 5 to about 100 lb/hr/in 2 (1.0 to 20 kg/s/m 2 ) to form a screened molten polymer blend.