Method for manufacturing heat resistant PET containers

Claim 1

A two-step biorientation method for manufacturing containers of polyethyleneterephthalate (PET) which are capable of subsequently being subjected, without substantial deformation, to relatively severe heat conditions during processes such as being filled with a hot liquid or the pasteurization of their contents, comprising, in sequence, the steps of: (a) on an amorphous PET container preform (1) comprising a body portion (5) and a neck portion (2) which is already conformed to its final shape and dimensions, heating at a first heating station only the neck to a temperature and for a time sufficient to crystallize the neck; (b) slowly cooling the neck; (c) at a second heating station, heating only the body (5) of the preform (9), exclusive of the neck, to the softening temperature of PET; (d) blow molding the hot preform body in a first blow mold having mold walls maintained at a temperature of from 5° to 40° C. to form a intermediate container whose body (22) has dimensions greater by approximately 20%in height and 0 to 30% in width than the dimensions of a final container to be obtained, a first biorientation occurring during this blow molding step; thereafter, (e) at a third heating station, heating only the body (22) of the intermediate container to a temperature of 180° to 220° C. for a period of 1 to 15 minutes, said intermediate container undergoing considerable deformation and shrinkage as a result of this heating step; and then, (f) transferring said hot intermediate container from step (e) to a second blow mold and blow molding said hot intermediate container to its final shape and dimensions in said second blow mold having mold walls maintained at a temperature of 80° to 100° C. for a period of 2 to 6 seconds, a second biorientation occurring during this blow molding step.