The problem of mould fouling is a common phenomenon in the rubber processing industry. A layer of deposits forms on the mold walls during the vulcanization process and gradually accumulates during the subsequent production cycle. Previous literature has discussed the influence of various factors that cause mold scaling. It has now been found that for the various vulcanizates (and zinc oxide) contained in polymeric rubber compounds, zinc sulfide is the most annoying reaction byproduct of the vulcanization process that causes fouling. There is no semi-permanent release agent or permanent (metallic) overlay that can avoid this deposition. The conclusion is that fouling is initially caused by zinc sulfide (inorganic deposits) adhering to the mold and forming a gray deposit layer. As a function of temperature, the lower molecular weight components of the mixture adhere to the microcrystals of zinc sulfide and cause a second stage of deposition (organic deposition). Oxidation products are formed over a certain period of time and cause the deposition of carbon.

By understanding the causes of mold fouling and the mechanisms inherent in the formation of zinc sulfide microcrystals on the metal surface of the mold, it is possible to generate an approach that is applicable to the current processing to reduce the formation of zinc sulfide and thus prevent mold fouling. By studying the causes of fouling, it is quite possible to reduce this phenomenon. There are two possible solutions to prevent or reduce the formation of fouling : change the composition of the mixture or improve the surface of the die. Changing the composition of the mixture to reduce die fouling due to zinc oxide or sulfide combination must be reduced or eliminated. Most deposits are associated with high levels of vulcanization and zinc oxide, which are often applied in tire rubber products. Tires are the largest of the global rubber products by volume (up to 75%). Therefore, most of the experiments were conducted with blends of NR/BR compounds and SBR compounds commonly used in tire production. The effect of zinc vulcanization, short-term vulcanization experiments, and the effect of compound composition were examined in terms of reducing mold scale by changing the mixture composition.