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United States Patent 5340304
Douris , ê et al. August 23, 1994

Mold for injection molding perform with undercut lip

Nakamura August 23, 1994

Abstract

The present invention provides an injection mold having an injection core mold for defining the inner wall of a lip portion in a preform having an undercut, a first lip cavity mold for defining the outer wall of the lip portion having no undercut, and a second lip cavity mold for defining the outer wall of the lip portion having the undercut. In the initial release after the injection molding process of the preform, the second lip cavity mold is first moved upwardly to secure a space wherein there is no obstruction around the outer periphery of the undercut. Thereafter, the injection core mold is upwardly moved such that the second injection core mold can be forcedly released from the molded preform while resiliently deforming the undercut in the outward direction, utilizing the space so formed. The barrel portion of the preform so molded is biaxially stretched to provide a so-called roll-on type biaxially oriented vessel having a ball received in the lip portion thereof.