Uniform minimization of plastic foam cell size

Claim 1

In the making of expandable bead and the like or equivalent physical forms of intermediate, blowing agent-containing masses of thermoplastic organic polymer material suitable for conversion to fine celled plastic foam product upon subjection of such expandable thermoplastic material to heat at a temperature at least equal to the glass transition temperature of the polymerizate therein but below its decomposition temperature, wherein (i) the involved blowing agent is a volatile normally-gaseous or readily-vaporizable substance selected from the group consisting of: at least monochlorinated or mono-fluorinated but incompletely-halogenated lower hydrocarbon halo-alkanes of C 1 to C 3 content; C 1 to C 3 chlorofluorocarbons; C 1 to C 5 aliphatic hydrocarbons; and mixtures thereof, with (ii) the expandable particle containing from about 5 to about 35 weight percent blowing agent impregnated in said thermoplastic organic polymer material; the step of improvement consisting essentially of: (iii) a quick-quench tempering treatment for the imbibed physical form of said thermoplastic material containing said impregnated blowing agent which involves rapidly cooling said bead or the like form in a quench media after completion of blowing agent imbibation at a temperature as indicated of at least about 65° C. to a rapidly-diminished chill temperature of said beads as a result of the said quench of less than about 10° C., wihtin not more than a minute whereupon and whereby the said expandable beads or the like are adapted to be converted upon expansion into foam body product characterized in having a density of from about 0.25 to about 10 pounds per cubic foot and having cells of about 0.02 to about 0.08 millimeter.