Patent ID: 6306970
Filing Date: 2001-10-23
Classification: C08L

Abstract:
A process for making an irradiated polymer blend comprising(1) preparing a blend comprising:(a) a propylene polymer selected from the group consisting of (i) a propylene homopolymer and (ii) a copolymer of propylene and ethylene or a 4-8 C alpha-olefin, wherein the content of polymerized ethylene or polymerized alpha-olefin is 10% or less, the propylene polymer having an isotactic index of greater than 90, and(b) a propylene polymer made using a metallocene catalyst and selected from the group consisting of (i) a propylene homopolymer and (ii) a copolymer of propylene and ethylene or a 4-8 C alpha-olefin, wherein the content of polymerized ethylene or polymerized alpha-olefin is 10% or less, the propylene polymer having a crystallinity of less than 24% measured from the heat of crystallization,(2) irradiating the blend in an environment in which the active oxygen concentration is established and maintained at less than 15% by volume with high energy ionizing radiation at a radiation dose of 3 to 12 Mrad for a period of time sufficient for a substantial amount of radical formation to occur, but insufficient to cause gelation of the material;(3) maintaining the irradiated material in such an environment for a period of up to two hours; and(4) treating the irradiated material while in such an environment to deactivate substantially all of the free radicals present in the irradiated material, whereby the irradiated blend has a melt tension of greater than 7 centiNewtons at 200.degree. C. and a Young's modulus of less than 1000 MPa.