Low density, extruded ethylenic polymer foams

Claim 1

A method for making foam planks from a non-crosslinked, ethylenic polymer resin, said planks having a density of from about 0.8 to about 1.9 pounds per cubic foot, dimensional stability, substantially closed-cell structure, a cross-sectional area of at least 6 square inches and a minimal cross-sectional dimension of at least 0.5 inch and said method comprising the steps of forming under heat and pressure a flowable gel composition comprising (1) a non-crosslinked polyethylene resin composition consisting essentially of low density polyethylene or a blend of a major proportion of low density polyethylene with one or more other ethylenic polymer resins and (2) at least one fluorocarbon blowing agent selected from fluorocarbons having normal boiling point between -30° and 30° C., from 2 to 4 carbon atoms in its molecular structure, and a value for the critical quantity T b -0.5V c of between 110 to 145 where T b is the normal boiling point temperature of the fluorocarbons in degrees Kelvin and V c is its critical volume in cubic centimeters per gram-mole, and extruding the resulting flowable gel to ambient air atmosphere whereby the blowing agent separates from the gel and forms gas cells in the ethylenic polymer resin, particularly characterized in that the flowable gel is mixed sufficiently to disperse the fluorocarbon blowing agent in the gel to an amount from 13.5 to about 35×10 -4 moles per gram of the ethylenic polymer resin.

Claim 2

A method for making foam planks from a non-crosslinked, ethylenic polymer resin, said planks having a density of from about 0.8 to about 1.9 pounds per cubic foot, dimensional stability, substantially closed-cell structure, a cross-sectional area of at least 6 square inches and a minimal cross-sectional dimension of at least 0.5 inch and said method comprising the steps of forming under heat and pressure a flowable gel composition comprising (1) a non-crosslinked polyethylene resin composition consisting essentially of low density polyethylene or a blend of a major proportion of low density polyethylene with one or more other ethylenic polymer resins and (2) at least one fluorocarbon blowing agent selected from fluorocarbons having normal boiling point between -30° and 30° C., from 2 to 4 carbon atoms in its molecular structure, and a value for the critical quantity T b -0.5V c of between 110 to 145 where T b is the normal boiling point temperature of the fluorocarbons in degrees Kelvin and V c is its critical volume in cubic centimeters per gram-mole, and extruding the resulting flowable gel to ambient air atmosphere whereby the blowing agent separates from the gel and forms gas cells in the ethylenic polymer resin, particularly characterized in that the flowable gel is mixed sufficiently to disperse the fluorocarbon blowing agent in the gel to an amount from 13.5 to about 35×10 -4 moles per gram of the ethylenic polymer resin.