Patent ID: 7868096

Claim:
A process for producing thermoplastic vulcanizates, the process comprising: (i) dynamically vulcanizing a rubber with a curative in a first stage, where the rubber is within a blend that includes the rubber, a polypropylene exhibiting a melt flow rate less and or equal to 0.5 dg/min, a number average molecular weight of about 120,000 and a weight average molecular weight of about 590,000, and the curative, where said step of dynamically vulcanizing occurs at a temperature at or above the melting point of the polypropylene, where said step of dynamically vulcanizing employs a peroxide curative, and where said rubber includes polymeric units deriving from 5-vinyl-2-norbornene, and where the weight ratio of polypropylene to rubber is at least 0.3:1, but less than 0.4:1; (ii) continuing said step of dynamically vulcanizing to cause phase inversion of the blend to thereby convert the polypropylene into a continuous phase, where the rubber has a degree of cure where less than 3 weight percent of the rubber is extractable by cyclohexane at 23° C., and where the rubber is in the form of finely-divided and well-dispersed particles where at least 75% of the rubber particles have an average diameter of less than 1 micron (μm); (iii) maintaining the blend at or above the melting point of the polypropylene after the phase inversion; and (iv) introducing additional molten polypropylene into the blend in a second stage, where said step of introducing additional molten polypropylene occurs after phase inversion and after greater then 90% consumption of the curative but before the blend is cooled to a temperature below the melting point of the polypropylene, where the additional molten polypropylene is the molten form of the same polypropylene used in the dynamically vulcanizing step and where the amount of additional molten polypropylene added is from 30 to 150 parts by weight polypropylene per 100 parts by weight rubber.