Method for making partially crystalline biaxially oriented heat set

Abstract

A method including engaging the open end of a first plastic parison which is at a temperature within its molecular orientation temperature range, enclosing a hot mold which is at heat setting temperature about the parison at a first position, simultaneously enclosing a cold mold at a second position about a container previously blown in the hot mold to cool the previously blown container, expanding the plastic parison within the hot mold by internal pressurization through the open end to induce biaxial orientation of the plastic parison and force the plastic parison into intimate contact and conformance with the hot mold and to maintain contact by such internal pressurization between the mold and biaxially oriented container for a time sufficient to induce partial crystallization in the biaxially oriented container, moving the hot mold and the cold mold in unison to bring the hot mold to the second position and the cold mold to a third position during the expanding of the parison within the hot mold and during the cooling of the previously blown container in the cold mold, maintaining a lower internal pressurization of the container in the hot mold and exhausting the pressurization to atmospheric pressure in the cold mold, substantially simultaneously opening the hot mold and cold mold, moving the open hot mold to the first position and open cold mold to the second position.