US Patent 7528181 Rubber composition and tire comprising same

The present invention is a rubber composition comprising microencapsulated sulfur and free sulfur. The composition is particularly useful as a cushion gum in retreading procedures. In one embodiment of the invention, the composition further comprises one or more ultra-accelerator curing agents for rubber. In another embodiment of the invention, the rubber composition has a t90 within twenty percent, more preferably within ten percent, and more preferably within five percent of the unaged green rubber composition, after 28 days aging at forty degrees Celsius. In another embodiment of the invention, the rubber composition has a t0 within twenty percent, more preferably within ten percent, and more preferably within five percent of the unaged green rubber composition, after 28 days aging at forty degrees Celsius. In another embodiment of the invention, approximately between forty and fifteen percent, more preferably between thirty and twenty percent, and more preferably approximately twenty-five percent by weight of the sulfur in the composition is encapsulated.