Medium modulus molded material comprising substantially linear polyethlene and fabrication method
AssigneeThe Dow Chemical Company
InventorsJeffrey J. Wooster, Theo L. V. Geussens, Jozef J. I. Van Dun
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Abstract
Medium modulus molded polyethylene materials with improved impact strength are made. The polyethylene material is molded to pipes, bars, and sheets. The molded material comprises high molecular weight linear polyethylene and a substantially linear ethylene/.alpha.-olefin interpolymer. The material is more than about 0.23 mm thick, has a density in the range of about 0.923 to about 0.95 grams/cubic centimeter (g/cc) and has an excellent impact resistance.
Claims20
A medium modulus, molded polyethylene material characterized as having a thickness greater than about 0.23 mm which comprises:
- (A) from about 70 to about 99 weight percent, based on the combined weight of components (A) and (B), of at least one high molecular weight linear ethylene polymer having a density in the range of about 0.93 to about 0.96 g/cc and an I.sub.5 melt index in the range of about 0.1 to about 3 g/10 minutes, and
- (B) from about 1 to about 30 weight percent, based on the combined weight of components (A) and (B), of at least one substantially linear ethylene/.alpha.-olefin interpolymer characterized as having:
- i. a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
- ii. a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation:
- M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, and
- iii. a critical shear rate at onset of surface melt fracture at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear olefin polymer having essentially the same I.sub.2 and M.sub.w /M.sub.n
- wherein the substantially linear ethylene/.alpha.-olefin polymer is further characterized as containing at least one .alpha.-olefin monomer and having a density in the range of about 0.85 to about 0.92 g/cc and an I.sub.2 melt index in the range of 0.3 to about 3 g/10 minutes.
A method for preparing a medium modulus molded polyethylene material comprising the steps of:
- (1) providing an extrudable thermoplastic composition containing (A) from about 70 to about 99 weight percent, based on the combined weights of components (A) and (B), of at least one high molecular weight linear ethylene polymer having a density in the range of about 0.93 to about 0.96 g/cc and an I.sub.5 melt index in the range of about 0.1 to about 3 g/10 minutes, and (B) from about 1 to about 30 weight percent, based on the combined weights of components (A) and (B), of at least one substantially linear ethylene/.alpha.-olefin interpolymer characterized as having:
- i. a melt flow ratio, I.sub.10 /I.sub.2, .gtoreq.5.63,
- ii. a molecular weight distribution, M.sub.w /M.sub.n, defined by the equation:
- M.sub.w /M.sub.n .ltoreq.(I.sub.10 /I.sub.2)-4.63, and
- iii. a critical shear rate at onset of surface melt fracture at least 50 percent greater than the critical shear rate at the onset of surface melt fracture of a linear olefin polymer having essentially the same I.sub.2 and M.sub.w /M.sub.n
- wherein the substantially linear ethylene/.alpha.-olefin interpolymer is further characterized as containing at least one .alpha.-olefin monomer and having a density in the range of about 0.85 to about 0.92 g/cc and an I.sub.2 melt index in the range of 0.3 to about 3 g/10 minutes,
- (2) introducing said composition of step (1) into an extrusion apparatus, and
- (3) extruding said composition of step (1) to form a material with a thickness greater than about 0.23 mm, and
- (4) conveying said material formed in step (3) for subsequent use down-line of the extrusion apparatus of step (2) or collecting said material formed in step (3) for subsequent use off-line.
Dependencies are inferred from the claim text.