Silica / Silane Mixing for Modern Tread Compounds-Influences of the Mixer Type

The market share of silica filled tire tread compounds for passenger cars is continuously growing. New developments are being introduced focusing on environmental aspects since ecological
requirements become more and more stringent. As a consequence, the new rubber silane VP Si 363 was introduced to the rubber industry reducing the rolling resistance by more than 10%. This is reached by a higher coupling yield of the silane-polymer reaction based on a more efficient interaction of this silane with the accelerator system.  Compared to carbon black the use of silica requires a more controlled mixing procedure because this is crucial for the chemical process of the silica silane reaction. For compounds containing the new silane an even more advanced mixing process with high shear forces is necessary to guarantee low compound viscosities. This contribution deals with the influence of the mixer type on the processing behavior of silica-silane compounds in general and in particular with its influence on compounds containing the new silane. Differences between mixer with tangential and intermeshing rotor geometry are emphasized. Examples are given and detailed in-rubber investigations are discussed. It is shown that significant differences in compound viscosities, surface appearance and various inrubber data can be obtained depending on the choice of the mixer type and mixing routine. Recommendations regarding adjustment of the formulation and mixing routine according to the mixer type are given.