Method for producing laminated film

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.