In one aspect there is disclosed a method of improving shot repeatability in a multilayer reciprocating screw injection molding apparatus by preventing pressure communication or cross-talk between melt channels. In the first aspect an outlet nozzle valve is closed prior to closing a check valve within an injection unit of the multilayer reciprocating screw injection molding apparatus. In another aspect there is disclosed a method of improving shot repeatability in a reciprocating screw injection molding apparatus by recording a first position of a screw within the barrel of an injection unit of a reciprocating screw injection molding apparatus, the first position corresponding to a volume of melt within the barrel of the material injection unit. A second position of the screw is then calculated based on the first position, the second position corresponding to a transition position of the screw within the barrel of the injection unit of the reciprocating screw injection molding apparatus.

A method of injection molding a test tube-shaped preform for biaxial stretch blow molding includes supplying a major material resin from outer and inner flow paths to a combined flow path for a predetermined time and rate. For a period of time within a range of the predetermined time period during which the major material resin is supplied, the intermediate layer resin is simultaneously supplied from the middle flow path to the combined flow path at a second predetermined supplying rate. A columnar laminated molten resin is injected into a cavity of a metal mold connected to a tip of the nozzle through a gate to fill the cavity, the columnar laminated molten resin being composed of the major material resin and the intermediate layer resin formed in the major material resin in a laminated manner that are combined into a columnar shape at the combined flow path.

In one aspect, a method of coinjection molding a multilayer article having a multi-segment internal layer is disclosed. A surface layer material is injected into a mold cavity from at least one of an inner outlet and an outer outlet of a multi-channel nozzle. An internal layer material is intermittently injected into the mold cavity from an intermediate outlet of the multi-channel nozzle that is between the inner and outer outlets. The intermittent injecting of the internal layer material is controlled, at least in part, by intermittent opening and closing of the intermediate outlet. An apparatus for coinjection molding the multilayer article with the segmented internal layer is also disclosed.