Process of preparing reinforced container

Claim 1

A process for the manufacture of a container of thermoplastic material comprising rapidly cooling a blank produced by extrusion or injection molding to form an amorphous structure, and reheating the blank while blowing the blank to effect biaxial stretching, said blank being subjected before said blowing to localized treatment in a zone to modify the structure of the material and produce subsequent reinforcing ribs on the container, the modification of the structure in said zone leading in the subsequent blowing and biaxial stretching operation to a lesser degree of expansion of the material in said zone and the formation of said ribs of a denser material structure in relation to the remainder of said container and wherein said ribs are formed as humped protuberances providing increasing thickness of the container in the wall thereof at said ribs and wherein said wall has an outer continuous surface at said ribs, said localized treatment being a mechanical treatment to form annular recesses in said blank, said ribs being formed at said recesses after said reheating and blowing.