Process for the production of fine-cell polyolefin foams

Claim 1

A process for the production of a fine-celled foam which comprises forming a mixture of a polyolefin, a crosslinking amount of an organic peroxide capable of crosslinking the polyolefin, 2 to 30 percent by weight, based on the weight of the mixture, of a principal blowing agent having a decomposition point or decomposition range above about 190°C. and 0.1 to 1.5 percent by weight, based on the weight of said principal blowing agent, of an auxiliary blowing agent working up said mixture to form a shaped object under conditions that neither crosslinking nor appreciable foaming thereof takes place and subsequently crosslinking and foaming said shaped object by heating it to a temperature above 190°C., said auxiliary blowing agent being a disulfonylhydrazide of the formula H.sub.2 NHNO.sub.2 S-X-SO.sub.2 NHNH.sub.2 wherein X is an alkyl radical having up to 6 carbon atoms, a cycloalkyl radical having 4 to 7 carbon atoms, an aryl radical having 6 to 12 carbon atoms or an aromatic radical of the formula ##SPC2## wherein Y is 0, SO 2 , S or a bond or a sulfonylhydrazide of the formula X-SO.sub.2 -NH-NHR wherein X is as aforesaid and R is acyl having 3 to 6 carbon atoms or -R'COR" wherein R' and R" are the same or different aliphatic radicals having 1 to 5 carbon atoms.