The Use of Zinc Dibutyldithiocarbamate in the Manufacture of Cellular Rubber

Abstract

Abstract One conclusion to be drawn from the present work is that a combination of zinc dibutyldithiocarbamate and benzothiazolyl disulfide is a particularly advantageous one for the manufacture of cellular rubber. By means of this combination of accelerators it is possible, by proper balancing of their proportions and of the percentage of sulfur, to adjust at will the stability of the rubber mixture with respect to blowing and to the rate of vulcanization as soon as blowing is complete. The good solubility of zinc dibutyldithiocarbamate in rubber guarantees a very rapid onset of vulcanization after the blowing action. It is evident that the most suitable method for manufacturing cellular rubber products is stepwise vulcanization. At the beginning, for example, heating may be at a temperature corresponding to 2 kg. per sq. cm. steam pressure, which allows satisfactory blowing of the rubber mixture; following this the temperature is raised rapidly to a point corresponding to 4 kg. per sq. cm. steam pressure as soon as the blowing effect is complete. At this higher temperature, vulcanization of the cellular rubber becomes very rapid. By this method it was found possible to manufacture cellular rubber shoes by an initial heating of 5 minutes at 2 kg. per sq. cm. steam pressure and a final heating of 5 minutes at 4 kg. per sq. cm. steam pressure. However, even if such a stepwise change in temperature during the heating is impracticable, as is the case when shoe soles are vulcanized in an electrically heated press, it is still possible, by choosing the proper proportions of sulfur, zinc dibutyldithiocarbamate, and benzothiazolyl disulfide, as well as the temperature of vulcanization, to obtain perfect blowing and rapid vulcanization.