The Goodyear Tire & Rubber Company (Akron, OH) has developed new core-shell type emulsion polymer nanoparticles that improve the ability of tires to grip wet roads, according to its U.S. Patent 7,645,511.
The core-shell polymer particle is comprised of a crosslinked elastomeric center portion (core) and an exterior portion (shell) which has a composition that is sufficiently different from the core. The core-shell polymer particles can be prepared with a controlled structure and size. The function of the crosslinked core is to provide a discrete polymer phase having a glass transition temperature which imparts better wet traction and lower rolling resistance.
According to Goodyear inventors Eric Sean Castner; Lei Zheng, Feng Anne Xie and Ping Zhang, polymeric nanoparticles are incorporated into rubbery polymers by a technique that involves (1) blending the solution of the hairy polymer particles made by the process of this invention with the cement of a rubbery polymer to produce a cement blend, and (2) coagulating the cement blend to recover the rubber composition.
The utilization of this technique further improves the level of incorporation and interaction between the nanoparticles and the rubbery polymer. This will further improve the physical properties of the rubber composition.
The advantage over the prior art is the inclusion of a vinyl aromatic-rich shell to the core. This modification has been found to impart improved mechanical and tear properties of a rubbery composite compared to the crosslinked elastomeric core alone.
Specifically the mixtures are rubbers that contain crosslinked elastomeric particles (diolefins and copolymers consisting of vinyl aromatic monomers and diolefins) grafted with a vinyl aromatic polymer or copolymer of vinyl aromatic monomers and diolefins, which can form a core-shell type structure.
The particles are generally described as a crosslinked elastomeric core and a shell, where the shell is covalently connected to the core. The crosslinked elastomeric core may be designed to have a composition which provides high damping in a particular temperature range so as to impart improved wet traction, and usually low damping at higher temperatures, for improved rolling resistance.
The advantage nanoparticle polymers is that the vinyl aromatic-rich shell reinforces the crosslinked elastomeric core, which enhances mechanical properties, e.g., high elastic modulus. In addition, the vinyl aromatic-rich shell is believed to increase the interactions between the particles to obtain better tear resistance.
The core-shell polymer particles can be used alone or in combination with other elastomers to prepare rubber compounds, such as a tire treadstock, sidewall stock or other tire component stock compounds.
The core-shell polymer particles can be used alone or in combination with other elastomers to prepare rubber compounds, such as a tire treadstock, sidewall stock or other tire component stock compounds.