Propylene-Based Polymer Additives for Improved Tire Tread Performance

#The present invention relates to propylene-ethylene-diene terpolymers useful as modifiers for tire treads.

#The tire tread compound is an important compound in a tire that dictates wear, traction, and rolling resistance. It is a technical challenge to deliver excellent traction, low rolling resistance while providing good tread wear. The challenge lies in the trade-off between wet traction and rolling resistance/tread wear. Raising the compound Tg would provide better wet traction but, at the same time, increase the rolling resistance and tread wear. There are needs to develop a tread compound additive that can provide good wet traction without increasing the rolling resistance and tread wear.

#Functionalized SBR (styrene butadiene rubber) is one method to improve this trade-off by improving filler dispersion. Nanoprene™, sub-micron to micron sized gels from Lanxess with cross-linked butadiene cores and acrylic shells, is another additive used to increase the wet traction without affecting rolling resistance. However, Nanoprene can only deliver limited improvement in wet traction.

#FIG. 1 are Dynamic Mechanical Thermal Analysis (DMTA) curves of several embodiments of tire tread compositions disclosed herein.

#This invention is directed to the use of propylene-ethylene-diene terpolymers in tire tread compositions. The propylene-ethylene-diene terpolymers are prepared by polymerizing propylene with at least one of ethylene and C4-C20 α-olefins, and, optionally, one or more dienes such as ethylidene norbornene. The propylene-ethylene-diene terpolymers contain from 5 wt % to 40 wt % of ethylene and/or C4-C20 α-olefins derived units and having a heat of fusion, as determined by DSC, of from 0 J/g to 80 J/g.

#The tire tread composition is an important aspect in a tire that dictates wear, traction, and rolling resistance. It is a technical challenge to deliver excellent traction and low rolling resistance while providing good tread wear. The challenge lies in the trade-off between wet traction and rolling resistance/tread wear. Raising the composition's Tg would provide good wet traction but, at the same time, increase the rolling resistance and tread wear. The embodiments described herein provide a tread compound additive that can accomplish wet traction without lowering the rolling resistance and tread wear.

#The problem has been approached by developing an additive, a polypropylene-ethylene-diene terpolymer that increases hysteresis in the wet traction region (0° C.) and lowers hysteresis in the rolling resistance region (60° C.) without changing the overall compound Tg.