Method and apparatus for altering the flow characteristics of a melt in an extrusion die

摘要

The invention relates to method in a process for preparing extruded articles by flowing heat plastified stream of extrudable resinous thermoplastic material through an extrusion orifice. The invention relates further to an extrusion process and an apparatus. In the invention the stream can be separated into a central core stream and at least one boundary stream on the outside of the core stream. Modifying additives are added to the boundary streams while maintaining physical separation of the core and boundary streams. The streams are recombined prior expelling the material out of the extrusion orifice (2), said boundary streams being applied as a relatively thin surface layer having altered properties between the core layer and the surfaces of the extrusion orifice (2). The additives can alternatively be added directly to the surface portion of the material stream without any physical separation step. <IMAGE>