Forming molecularly oriented containers from reheated preforms

摘要

In forming containers from injection molded preforms of thermoplastic material such as nitrile-based polymers by a process which includes heating the preforms to orientation temperature followed by distension to container form in a mold, the improvement providing reduced thickness variability in lower portions of the containers which involves controlling preform shrinkage during such heating to between about 4 to 15% of the initial length for nitrile materials by maintaining the ratio of average thickness to inside preform surface area within defined limits and then axially and radially stretching such preforms during distension to predetermined levels. Nitrile preforms convertible to such improved quality containers have values of between about 0.005 to 0.011 inch-1 for the aforementioned ratio.