Involute embossment base structure for hot fill PET container

Claim 1

A PET container formed by blow molding and adapted to be filled with liquid at a temperature elevated above room temperature, said container comprising an upper portion defining a sealable closure, a sidewall portion, and a base structure closing the bottom of the container and formed integral with said sidewall portion, said base structure including a peripheral support ring, a dome, and a central disk, said support ring being formed with the lower end of said sidewall portion and being substantially concentric with said sidewall portion, said dome being formed integral with said support ring and extending upwardly into said container until terminating in said central disk, said disk also being substantially concentric with said sidewall portion, said dome including an annular wall extending between said disk and said support ring, a transition portion of said annular wall having present therein unrelaxed retractive stresses resulting from blow molding, said transition portion being subject to deformation by virtue of said unrelaxed retractive stresses and the heating effect of filling said container with liquid at an elevated temperature, said transition portion further being shaped to resist said stresses by the provision of a plurality of spaced involute embossments extending thereacross, each said embossment extending interiorly of said container and having substantially upright reinforcing walls with connecting portions therebetween, said embossments also extending in a direction radiating substantially outwardly and downwardly along said dome in three dimensional involute paths of substantially spiral shape from said disk to thereby reinforce the ability of said transition region to resist said deformation.