Importance

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Abstract

An improved preform is disclosed for molding plastic containers having a self-supporting base structure. The preform has a reinforcing section of concentric annular ribs near its closed end. The wall thickness of the preform is increased in the reinforcing section by a plurality having an increasing thickness in a direction toward the closed end of the preform. When blow molded into a final container, these concentric ribs form annular reinforcing ribs on the inner surface of the container base. These ribs are substantially concentric about the longitudinal axis of the container and are of decreasing thickness radially outward from the center. The ribs coact with other reinforcing ribs in the base structure to further increase the strength of the container base. During stretching of the preform prior to blow molding, the concentric ribs act to reduce the stretching of the preform in the reinforcing section thus increasing the wall thickness of the base and thereby increasing the base strength.

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First Claim