Method and apparatus for manufacturing biaxially oriented, thermally

Abstract

A method of producing a blow-molded PET container suitable for hot-filling includes the steps of injection molding a preform, blow-molding the preform into a primary molded article larger than the desired final container, heating the primary article in a series of oven chambers while its mouth is sealed so that pressure builds within the article to thereby control shrinkage, and blow-molding the shrunken article into the desired container. The two molds are preferably heated, and the mold contact time is as long as allowed by the manufacturing process to help remove internal stresses in the article. An apparatus for carrying out the method includes a first machine having an injection station, a thermal conditioning station, a primary blow-molding station, and an exit station. A second machine includes the oven chambers and a final blow-molding station. The primary article is sealed by a cap member that has a pressure relief valve connected to it to limit the internal pressure during heating, an air supply passage for final blow-molding, and a tensioning rod for insertion into the primary article and engaging a pocket in the center of the article's bottom. In some applications, it is necessary to stiffen the neck, particularly when hot-filling at about 200.degree. F. or higher, or when using a closure roll-on die or a lugged neck finish to apply a bottle cap to the final container.