NOVEL COMPOSITION AND METHOD Russian patent published in 2020 - IPC C08L23/04 C08F210/16 C08K3/04 F16L9/12 

FIELD: manufacturing technology; chemical or physical processes.

SUBSTANCE: invention relates to a polyethylene composition for producing pipes or fittings, a method of producing a polyethylene composition, articles made from a polyethylene composition, as well as to use of polyethylene composition. Polyethylene composition contains a base resin and additives. Resin of base contains three polymer components: (a) polyethylene component with very high molecular weight as fraction A1; (b) a polyethylene component with low molecular weight as fraction A2 with weight-average molecular weight less than the weight-average molecular weight of the polyethylene component with very high molecular weight; (c) a polyethylene component with high molecular weight as fraction A3 with weight-average molecular weight higher than the weight-average molecular weight of the polyethylene component with low molecular weight, but lower than weight-average molecular weight of component with very high molecular weight. Fraction A3 is an ethylene copolymer with at least one C₃-C₂₀ alpha-olefin comonomer. Amount of polyethylene component with very high molecular weight in the base resin ranges from 0.5 to 8 wt %, and average molecular weight (Mv) of polyethylene component with very high molecular weight is higher than 1100 kg/mol, and less than 4000 kg/mol. Composition has FRR_21/5 from 38 to 70, melt flow rate MFR 21 from 6.5 to 15.0 g/10 minutes, viscosity at shear stress of 747 Pa (eta747) from 450 to 3000 kPa·s and molecular weight distribution, which is ratio of weight-average molecular weight to number-average molecular weight Mw/Mn, from 10 to 40. From said polyethylene composition pipe or fitting is produced. Said polyethylene composition is also used to produce film, fiber or cable sheath. Method of producing the polyethylene composition involves first obtaining a resin base. For this, at the first step, ethylene and optionally at least one comonomer are polymerised in the presence of a polymerisation catalyst to obtain a polyethylene component with very high molecular weight fraction A1. At the second step, ethylene and optionally at least one comonomer are polymerised in the presence of the same or different polymerisation catalyst and a polyethylene component with very high molecular weight of fraction A1 to obtain a polyethylene component with low molecular weight fraction A2. At the third step, ethylene and at least one comonomer are polymerised in the presence of the same or distinguishing catalyst in the presence of a polyethylene component of fraction A1 and a polyethylene component of fraction A2 to obtain a polyethylene component with high molecular weight fraction A3. Then, the base resin is mixed with additives and extruded to obtain granules.

EFFECT: invention enables to obtain a composition which has good resistance to runoff and high mechanical properties.

15 cl, 3 tbl, 2 ex