Patent ID: 6329439
Filing Date: 2001-12-11
Classification: B29C,B29K,B60J,Y10T

Abstract:
A foamed extrudate of an elastomer formed by, extruding a mixture of an elastomer and a chenmical blowing agent in a long-barrel extruder comprising plural temperature zones including a feed zone, a discharge zone near said extruder's die, and intermediate zones, wherein said elastomer comprises a vulcanized blend of a polyolefin and a rubber copolymer, wherein said polyolefin contains a repeating unit derived from an .alpha.-olefin having from 2 to 4 carbon atoms, and said elastomer contains no more than an equal amount by weight of said polyolefin relative to said rubber copolymer, and said chemical blowing agent is present in an amount from about 1 to 10% by weight of the elastomer;maintaining a chosen temperature profile within said barrel wherein temperature in said feed zone is no lower than the temperature in said intermediate and discharge zones; and,discharging said extrudate from said die through a stepped land having a lateral portion having a length L' to diameter D' ratio in the range from 3:1 to 1:3, extending from a choked funnel portion having a conical angle in the range from 60.degree. to 120.degree. and extending longitudinally in the range from 0.25 to 1.5 times said barrel's diameter, length of said flinnel portion being measured from said upstream face to the upstream end of said lateral land portion; and,forming said extrudate with a core of essentially closed cells sheathed with a dense non-porous smoothly continuous sdin self-produced by said elastomer and formed integrally with said cells, said skin having a thickness in the range from 0.01 mm to 1 mm.