Expandable polyolefin compositions and polyolefin foam preparation process

Claim 1

A process for preparing closed-cell olefin polymer foamed articles having increased maximum achievable cross-sectional areas and having good dimensional stability which process comprises the steps of: (A) heat plastifying a normally solid olefin polymer resin selected from the group consisting of ethylene homopolymers and substantially non-neutralized ethylenic copolymers derived from at least about 50 weight percent of ethylene; (B) admixing said heat plastified resin under elevated temperature and pressure with (1) 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, complete esters of higher fatty acids, and substantially non-neutralized a-olefin-monoethylenically unsaturated carboxylic acid copolymers and (2) a mixed blowing agent (a) which comprises from about 50 to about 95 weight percent of dichlorodifluoromethane and from about 5 to about 50 weight percent of an aliphatic hydrocarbon compound or a halogenated hydrocarbon compound having a normal atmospheric boiling point of from about 0° C. to about 50° C., and (b) which has a saturated vapor pressure at 100° C. of less than about 32 kg/cm 2 but greater than about 25 kg/cm 2 ; and (C) extruding the resultant mixture into a zone of lower temperature and pressure to thereby form said olefin polymer foam.