POLYETHYLENE MOLDING MASS AND TUBE WITH IMPROVED MECHANICAL PROPERTIES MADE THEREFROM Russian patent published in 2004 - IPC

FIELD: polymer materials.

SUBSTANCE: invention relates to polyethylene molding mass with bimodal molecular weight distribution, which is formed in two consecutive polymerization steps and has total density above 0.958 g/cm³ and melt index MFI_190/5 below 0.2 dg/min. It contains low-molecular ethylene homopolymers in amount 35-65% with coefficient of viscosity VZ_A 40-90 cm³/g, melt index MFI_190/2,16 40-2000 dg/min and density higher than or equal to 0.965 g/cm³; and high-molecular ethylene copolymer in amount 35-65% with coefficient of viscosity VZ_B 500-2000 cm³/g, melt index MFI_190/5 0.02-0.2 dg/min and density 0.922-0.944 g/cm³. Polyethylene fraction obtained on dissolving polyethylene molding mass in p-xylene, when performing TREF analysis at 78 ± 3 K, has average molecular weight higher than or equal to 200 000 g/mole. Tube made from molding mass according to invention is resistant to crack formation because of internal stress over a period of time more than 1500 h, crack resistance higher than or equal to 9 mJ/mm², and bend creeping modulus, as measured according to DIN 54852-24, higher than or equal to 1350 N/mm². Tube is especially suitable for transportation of gas and water.

EFFECT: increased action time and rigidity of molding mass and improved performance characteristics of tube.

8 cl, 1 dwg, 2 tbl