Styrene-butadiene rubber (SBR) and natural rubber (NR) blend with 30 mm thickness was press cured in a metal mold by heat conduction. Peroxide and D-nitrosopentamethylenetetramine (DTP) were used as the curing and blowing agents, respectively. The heating surface temperatures of 413 K and 423 K were adopted and heating time was ranged from 180 minutes to 480 minutes in nine steps in order to study the effects of heating conditions on the relation between the curing and blowing characteristics. The other side of the rubber was set to be adiabatic condition. Typical temperature field of one-dimensional, transient heat conduction was observed in the rubber. The degree of cure ε changed depending on the heating conditions and the distance from the heating surface, showing lower values for lower heating wall temperature with increasing distance from the heating surface. Observation studies for the foaming characteristics showed that the cell structure changed depending on both the distance from the heating surface and the heating conditions, and two extreme cell structure, open-cell foam and closed-cell foam, were clearly observed. Results of the image analyses of the cell structure can be well related to the degree of cure. The open-cell foam was found in the region ε < 0.05, the closed-cell foam in the region 0.14 < ε and the two types of cells coexisted in the region 0.05 < ε < 0.14.
