Patent ID: 7959426

Claim:
An apparatus connectable in fluid communication with a flow head fed molten polymer resin by at least a first extruder to continuously produce a parison in said flow head and flowing away therefrom, said apparatus comprising: a valve block having a duct therethrough with an inlet and an outlet, said outlet being connectable in fluid communication with said flow head; a second extruder in fluid communication with said inlet, said second extruder continuously supplying molten polymer resin to said duct; a valve positioned within said duct and controlling flow of said molten polymer resin directly from said second extruder to said flow head; a controller for opening and closing the valve to vary the thickness of the molten polymer resin by controlling the rate at which the resin continuously flows through the duct; an accumulator cylinder in fluid communication with said duct at a position between said valve and said outlet and having a piston reciprocably movable within said cylinder, wherein actuating said piston varies the thickness of the molten polymer resin by reducing and increasing the resin pressure; and, a continuously extruded parison having a plurality of polymer resin layers and at least one polymer resin layer having variable thickness along the length of the parison.