Multilayer parison extrusion molding machine for blow molding

A multilayer parison extrusion molding machine for blow molding wherein one main extruder and one or more subextruders are mounted radially around one diehead at an angle of 25.degree. to 90.degree. relative to each other, said diehead comprises a core holder having a core pin at the lowermost end thereof, a cylindrical mandrel enclosing said core holder therein, a die portion including an extrusion die and adjusting means for adjusting the relative positions of said core pin and said extrusion die, said die portion constructed to surround said core holder so as to form a resin extrusion outlet opening, and at least two head portions provided on said die portion, each of said head portions form a resin layer and wherein each of said portions comprises:

• a. a sleeve surrounding said mandrel, the external surface of said sleeve being arranged to allow change of the flowing direction of resin and the internal surface thereof being arranged to surround the mandrel;
• b. a housing which surrounds said sleeve with a space therebetween to define a resin passage for forming a resin layer, and includes an internal surface parallel to the external surface of said sleeve, and a resin inlet opening connected to said resin passage and to one of said extruders;
• c. a pressure ring mounted on said housing downstream from said resin inlet opening for controlling the thickness and pressure of the molten resin layer formed by said resin passage, at least one surface of said pressure ring being arranged parallel to the external surface of said sleeve and shaped to change the flow direction of the resin layer, another surface of said pressure ring being arranged parallel to the external surface of said mandrel and spaced from the external surface of said sleeve, the pressure ring surface directions in cooperation with the internal surface of the housing being adapted to change the resin flowing direction two times;
• and
• d. means operatively associated with said pressure ring for adjusting said pressure ring to vary the size of said resin passage;
• and
• the resin passages of adjacent ones of said head portions arranged to merge at a respective junction so that the individual resin layers formed in each of said head portions flow together at the respective junction and subsequent downstream junctions so as to form a multilayer parison which is extruded from said resin extrusion outlet opening.