Method for producing a thermoplastic container having a ring-shaped reinforcing zone at its bottom

A method of producing a container comprising providing a preform having a bottom closure of relatively thick material which is joined by an annular ring-shaped region to a tubular portion having a mouth remote from the bottom closure, said tubular portion defining an axis for the preform and consisting of material joined to said annular ring-shaped region oriented along the axis of the preform with an orientation corresponding to that produced in a sheet of material stretched monoaxially to cause material flow, forming the bottom closure inwardly into the preform towards said mouth while said ring-shaped region is stretched and axially stressed so that said ring-shaped region becomes axially oriented and of substantially the same thickness as the material of said tubular portion which is joined thereto such that said ring-shaped region tends to contract for preventing said bottom closure from straightening out or turning inside-out, and expanding the tubular portion of the preform after the stretching and stressing of the ring-shaped region to form the container, the forming of said bottom closure inwardly into the preform forming a standing surface for the container in the vicinity of said ring-shaped region whereat the relatively thick bottom closure is connected to the oriented material of said tubular portion via said ring-shaped region whereby to achieve uniformity of thickness and orientation between the material of the ring-shaped region and the material of the tubular portion joined thereto, and connection of the relatively thick bottom closure to said ring-shaped region, in the vicinity of the standing surface.