Method of forming laminated preforms

A method of forming laminated preforms of the type including an interior barrier layer, said method comprising the steps of providing a conventional injection mold unit for a preform wherein the injection mold unit includes a core with there being a cavity surrounding the core, providing separate supplies of at least one flowable thermoplastic resin and a flowable barrier material, injecting into that end of said mold cavity which defines a preform bottom a limited quantity of said thermoplastic resin with the surface portions of said limited quantity of thermoplastic resin cooling due to contact with said mold and said core to define first solidified layers while there is tunnel flow of the thermoplastic resin between said solidified layers, next injecting a limited quantity of said barrier material into said mold cavity behind said limited quantity of thermoplastic resin with said barrier material forcing said thermoplastic resin further into said cavity with said barrier material having tunnel flow between said thermoplastic resin solidified layers with surface portions of said barrier material in contact with said thermoplastic resin solidified layers also cooling and forming second solidified layers, and then injecting other flowable thermoplastic resin into said mold cavity behind said barrier material sufficient to complete filling of said mold cavity with said other flowable thermoplastic resin forcing said limited quantities of said thermoplastic resin and said barrier material to flow toward the other end of said mold cavity, and permitting all of the injected material to solidify.