ABSTRACT
Blowing agents are used to make soft, light, impact-resistant sponge rubber. Most often used alone, but occasionally with other materials, they form gases at curing temperatures which put holes in the rubber and make it spongelike. One of the growth industries peripheral to rubber goods manufacturing during the last decade or so has been dispersion of rubber chemicals. Buying rubber chemicals in dispersed form is more costly than mixing from scratch. Incidentally, dispersion in plasticizers are somewhat cheaper than those using a polymeric binder, but usually the former have more extraneous matter and handle less easily. Chemically, pigments for rubber coloration should not interact with the polymer or other ingredients. They should be free of impurities like certain manganese salts, which would catalyze oxidation of the rubber. Physically, the colorants should disperse easily and should be insoluble to the extent that they won't bleed to surface, for example, if the rubber compound has oil in it.
