Coextrusion die

Claim 1

An extrusion die for the coextrusion of plural plastic materials into the form of a tubular film, said die comprising: (A) means for separately supplying at least two extrudable plastic materials in a fluid state; (B) a material distribution section comprising an array of annular elements providing a plurality of pairs of mutually contacting surfaces, at least one of said surfaces of each pair being recessed to define a labyrinthine distribution channel system for each such material, each said system having an inlet opening connected to one of said supply means and dividing into generally oppositely directed peripherally extending passages terminating in axially extending connecting passages which in turn divide into generally oppositely directed peripherally extending passages terminating in axially extending connecting passages which in turn divide into oppositely peripherally extending passages terminating in axially connecting passages, the number of said passage divisions being sufficient to provide for each extrudable material an array of at least eight peripherally spaced apart connecting passages opening generally axially through an end wall of said distribution section, the plural distribution channel systems being arranged in radially displaced relation at different radial distances from the center axis of the extrusion die; (C) an extrusion die section having one end wall contacting said distribution section end wall and comprising a plurality of concentric generally annular elements including generally spaced parallel concentric surfaces adjacent pairs of which define at least one axially elongated generally annular collecting chamber in communication with the open ends of the arrays of said connecting passages from said distribution sections, at least one of said annular elements defining said collecting chamber being mounted for rotation about its axis relative to said material distribution section and relative to at least the other of said annular elements defining said chamber, a common continuous annular extrusion orifice opening through the opposite end wall of said die section and connecting with the downsteam end of each such annular collecting chamber; (D) mechanical engagement means uniting the annular elements of said distribution and extrusion die sections, respectively, and maintaining said sections together and at least one of said annular sections free for said relative rotation with said end faces in contact; and (E) means for rotating said at least one rotatably mounted annular element of said die section about its axis relative to said distribution section and relative to said at least one other annular element.