Importance

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Abstract

Disclosed is a process for producing a multiple-layered sheet of film comprising at least two thermoplastic materials by coextrusion through a slot die, comprising the steps of heat plastifying a first, second, third and fourth thermoplastic material; joining a stream of the first heat plastified thermoplastic material and a stream of the second heat plastified thermoplastic material to form a first combined stream having a generally rectangular cross-section and having an upper layer of the first thermoplastic material and a lower layer of the second thermoplastic material mechnically anchored together by means of profiles formed on the contact surfaces of the two layers; joining a stream of the third heat plastified thermoplastic material and a stream of the fourth heat plastified thermoplastic material to form a similar second combined stream, reducing the width of the first and second combined stream; joining the first and second combined streams in edge-to-edge fashion in a single plane to form a composite stream; introducing the composite stream into the inlet channel of the slot die; coextruding the composite stream through the slot die to form a multiple layer film or sheet; and cooling the film or sheet. Also disclosed is an apparatus for carrying out this process.

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First Claim