One piece self-standing blow molded plastic bottles

Claim 1

In a blow molding process for producing a one-piece plastic container by expanding an elongated preform containing the plastic material for the neck, body and base of the container into a blow mold cavity, the method for forming the container of the champagne base variety having an annular peripheral chime surrounding an inwardly sloping base portion wherein the container is resistant to inversion of the base from internal pressure comprising the steps of: (a) forming a preform on a core rod in an injection mold cavity, the preform having an axial length less than the distance from the top to the bottom of the blow mold cavity and having a body-forming portion of constant thickness material along the length thereof for forming constant thickness sidewalls of the container and having a thicker base-forming portion such that during blowing of the preform, the material of the base-forming portion is blown to form the inwardly sloping base portion of a thickness sufficient to resist self-deformation and to form the annular peripheral chime having a moment arm therearound tending to create an integral reinforcing hoop within the chime sufficient for preventing inversion of the inwardly sloping base portion by preventing unrolling and radial stretching of the chime; (b) forming an annular contacting surface on the inner surface of the preform which contacting surface extends between the body-forming portion and the thicker base-forming portion of the preform; (c) positioning the preform within the blow mold cavity defining the finished container shape; (d) inserting a stretch rod having a shoulder portion into the preform and contacting the shoulder portion of the stretch rod with the annular contacting surface of the preform; (e) extending the stretch rod within the preform to move the bottom of the preform toward the bottom of the blow mold cavity to longitudinally stretch the material of the sidewall portion of the preform while minimizing stretching of the base-forming portion such that the preform extends from the top to adjacent the bottom of the blow mold cavity; and, (f) injecting pressurized gas into the preform adjacent the neck of the preform whereby the preform is radially stretched outwardly to fill the blow mold cavity and to form the container.