Method for the extrusion of thermoplastic material composites

Method of producing a thermoplastic composite by dispersing fluid additive within only a portion of a stream of thermoplastic comprising the initial steps of:

• (a) flowing said thermoplastic material into a channel having walls of substantially circular cross section, into which there has been placed a rotating mixer head having an upstream end and a downstream end and at least two pluralities of alternate lands and grooves arranged at different portions of the mixer head with respect to the direction of flow, each of said lands and grooves having an upstream end and a downstream end and said lands alternating with said grooves and being arranged in pairs, each of said pairs having a land in loose clearance with said wall followed by a land in close clearance with said wall, said mixer head having an unobstructed internal passage positioned therein over a substantial portion of its terminal length and a plurality of elongated conduits severally connecting elongated zones between said land pairs and said internal passage, said mixer head having separate passages for conveying polymeric material to the upstream ends of said pluralities of alternate lands and grooves, and
• (b) injecting said fluid additive into said channel where said mixer head is located with the result that within the mixer head, depending upon the point of injection of the fluid additive, the core of the composite contains no fluid additive and the shell about the core has fluid additive dispersed in it or the core of the composite contains fluid additive and the shell about the core contains no fluid additive or the composite has a layer, into which additive is dispersed, disposed between the core and the shell which contain no additive.