THE EFFECT OF CHEMICAL-COMPOSITION AND SURFACE CHARACTERISTICS OF MOLD STEELS ON THE RELEASE OF NITRILE RUBBER

Interactions between the metal of the mould and the rubber during vulcanisation lead to the formation of a complex interfacial layer which influences release processes and may generate mould fouling. Measurements of adhesion between a nitrile rubber compound and various steel surfaces showed a strong influence of both surface roughness and alloy hardness: the sticking index increased with increasing surface roughness and with decreasing hardness. Investigations of the crosslinking reaction in the elastomer using a differential scanning calorimeter showed that the composition of the steel alloy present affected the cure rate and, by inference, the crosslink structure in adjacent rubber layers and thence the mould release of the vulcanisates. The experimental results were interpreted in terms of a theory developed by Good that links the work of fracture of such adhesive bonds to thermodynamic work of adhesion, and plastic and viscoelastic dissipation terms.