Method for producing laminated film

Claim 1

In the process for the manufacture of a tubular, laminated film consisting of extruded thermoplastic materials, the improvement which comprises: (a) providing an unoriented, tubular, collapsible, thermoplastic substrate which has been extruded and cooled below its melt temperature; (b) inflating the substrate into an approximately circular cross-section subsequent to said extrusion and cooling thereof, the inflation alone of the tubular substrate providing said circular cross-section and, after inflation, said tubular substrate having no internal, mechanical supporting means and said tubular substrate not being substantially expanded by said inflation; (c) providing a circular laminating die; (d) passing said inflated tubular substrate through said die; (e) trapping the portion of said inflated, tubular substrate that passes through said die between two spaced apart pairs of pinch rollers; and, (f) extruding a molten coating layer of thermoplastic material onto and uniformly around said inflated, tubular substrate thereby producing a laminated tubular film product which is substantially unstretched and is flexible and collapsible.