Expandable polyolefin compositions and preparation process utilizing isobutane blowing agent

Claim 1

An expanded polyolefin foam comprising an olefin polymer resin selected from the group consisting of ethylene homopolymers and copolymers of ethylene and a copolymerizable monomer, a stability control agent selected from the group consisting of partial esters of long chain fatty acids with polyols, higher alkyl amines, fatty acid amides, and olefinically unsaturated carboxylic acid copolymers, and a blowing agent selected from the group consisting of (i) isobutane, (ii) a mixture of from 5%-95% isobutane on a molar basis with from 95%-5% of a physical blowing agent selected from the group consisting of chlorofluorocarbons and fluorocarbons having from 1 to 4 carbon atoms, boiling points between -50° and 50° C., and a permeation rate through said olefin polymer resin modified with said stability control agent of less than about 1.2 times the permeation rate of air, and (iii) a mixture of at least 70% isobutane with a physical blowing agent selected from the group consisting of hydrocarbons, chlorocarbons, and chlorofluorocarbons having from 1 to 5 carbon atoms, boiling points between -50° C. and 50° C., and a permeation rate through said olefin polymer resin modified with said stability control agent of greater than about 1.2 times the permeation rate of air.