Plastic containers for storage of goods under pressure

Claim 1

A form-retaining container made of a thermoplastic polymer material selected from the group consisting of polyethylene terephthalate, polyhexamethylene adipamide, polycaprolactam, polyhexamethylene sebacamide, polyethylene 2,6 and 1,5 naphthalate, polyetramethylene-1,2-dioxybenzoate, and copolymers of ethylene terephthalate and ethylene isophthalate; said container comprising in succession a mouth, a neck, a main body portion, and a bottom including a central portion and a peripheral portion, said container having a first region inclusive of said mouth and part of said neck, a second region inclusive of the remainder of said neck, said main body portion and said peripheral portion of said bottom, and a third region constituted by said central portion of said bottom, said polymer material being selectively heated, inflated and cooled so that said second region is obtained by stretching said material in said second region in more than one direction to achieve biaxial stretching and orientation of the material while the material in said first and third regions is substantially unoriented, whereafter the material is heated while being internally pressurized to effect thermal crystallization and release of internal stresses such that the first and third regions are in a thermocrystallized state and provide an opaque appearance while the second region has only a small crystallization to provide a transparent appearance, whereby the container is form stable when reheated.