Abstract

Among the different processes for heat-sensitizing latex by the more or less direct action of zinc-ammonium complexes, one has the choice of inorganic and organic complexes. Among the inorganic complexes, zinc-ammonium nitrate seems to be the most effective. Prepared from a 5 N solution of zinc nitrate and 5 N ammonia, it gives good heat sensitization when a volume of 2 per cent, based on the volume of the latex, is used. Among the organic complexes, the formate and acetate are particularly to be recommended because of their great heat-coagulating power. Dicarboxylic amino acids give active compounds, but they are more troublesome. Fat acids containing double bonds, of the type zinc-ammonium undecylenate or the oleate, have the advantage of being applicable to the manufacture of sponge rubber, for the complex, because of its surface-active properties, acts both as a foaming agent and a heat-coagulating agent, and can be added at the moment of use or several hours earlier without difficulty. Thus, the range of heat sensitizing agents of the zinc-ammonium complex type is, in fact, reduced to two or three practical effective agents, namely, the formate and the acetate in the manufacture of solid objects, and the oleate in the manufacture of molded sponge objects. The stearate often used is much less effective.