Method for preparing thermoplastic vulcanizates with improved extrusion surfaces

A process for the preparation of dynamically vulcanized thermoplastic elastomers comprising melt processing under shearing conditions in melt reaction extruder, A) at least one thermoplastic resin, B) at least one vulcanizable gas-phase elastomer having a Mooney viscosity (ML1+4(125° C.)) of from about 65 to about 450, C) at least one curing agent, and D) process oil, wherein said process oil D) is added to the extruder in at least three oil injection positions located:

• a. at least one location within the first 15% of the total length of the extruder;
• b. at least one other location prior to, at or within boo total extruder length after the onset of the vulcanization of said gas-phase elastomer;
• and
• c. at least one location subsequent to the point at which the vulcanization of said gas-phase elastomer is substantially completed;
• and
• wherein the direct oil injection locations into the extruder are positioned at or immediately before one or more distributive mixing elements, which distributive mixing elements are immediately followed by one or more dispersive mixing elements, wherein 9-18 phr oil is added in a), 36-45 phr oil is added in b), and 74.3-81 phr oil is added c), and wherein the total amount of oil added in a)-c) is less than or equal to 160 phr oil, wherein a curative in diluted liquid or molten state is injected prior to the b) onset of vulcanization and into injection locations in the extruder positioned at or immediately before one or more distributive mixing elements, which distributive mixing elements are immediately followed by one or more dispersive mixing elements, and wherein approximately 40% to 60% of the process oil is added prior to injection position c), and approximately 60% to 40% of the process oil is added after the curing agent.