Process for heat treating thermoplastic containers

A process for preparing a thermoplastic container, comprising the steps of:

• providing a biaxially oriented, crystallized precontainer having a first contained volume by expanding said precontainer from a tubular preform;
• selectively further crystallizing said precontainer by applying heat thereto while the precontainer is substantially unconstrained, including the step of protecting from heating those portions of the precontainer that have been deformed less than 2-fold in the course of expanding the preform to form said precontainer, and forming a deformed precontainer having a second contained volume;
• controlling deformation of the precontainer by closing the precontainer prior to further crystallizing in a manner permitting the controllable air escape from the precontainer and while the precontainer remains substantially unconstrained to create a predetermined increased air pressure in the deformed precontainer;
• reshaping the deformed precontainer by blow molding into a final container shape;
• wherein the increased air pressure in the deformed precontainer is controlled so as to provide said second contained volume of the deformed precontainer to be sufficiently close to the volume of the final container such that during reshaping, stresses are minimized, and wherein the deformation of the precontainer is controlled so as to obtain a size and shape capable of being transformed into a predetermined final shape without further substantial deformation by changing the shape of said crystallized precontainer in a blow mold into that of said container;
• and
• wherein the increased air pressure limits the amount of deformation of the precontainer and permits only symmetrical shrinking;
• and
• wherein said precontainer has a level of orientation, and wherein said second contained volume being defined by a shape such as to substantially maintain the level of orientation of the precontainer.