Patent ID: 7232541

Claim:
A method of vacuum thermoforming a container which includes an outer surface including an outwardly-projecting ridge, the container further including a base, side walls, and an inwardly-projecting cut lip, the method comprising: (a) providing a three-part mold defining a cavity conforming in shape to the outer surface of the container, the cavity including an undercut portion corresponding to the ridge of the container, the mold including separable first, second and third portions, the first portion including a planar upper surface and an upper lip, the first portion defining an upper part of the undercut portion, the second portion defining a lower part of the undercut portion and further defining a surface corresponding to the side walls of the container, the first and second portions of the mold being separable along a part line located along the ridge of the container, the third portion defining a surface corresponding to the base of the container, the cavity being shaped so that the separated thermoplastic material is a shell having a base surrounded by integrally formed side walls extending upward to a cut lip, the walls and base formed of a single thermoplastic sheet and defining a volume, the side walls including a ridge below the cut lip, the ridge protruding away from the volume and being sized to support the shell on a lower surface of the ridge against a cut lip of a second identical shell with the bases of the two shells spaced apart when the shell is nested within the second identical shell, the cut lip extending inward about the volume; (b) positioning a heated sheet of thermoplastic material over the mold; (c) drawing the heated sheet of thermoplastic material over the upper lip of the mold and down into the cavity and into the undercut portion of the mold; (d) allowing the drawn thermoplastic material to cool below its glass transition temperature; (e) after said allowing, cutting the thermoplastic material along the upper lip of the mold to separate the drawn thermoplastic material in the mold cavity from the remainder of the thermoplastic material to produce the thermoformed container; (f) separating the first, second, and third portions of the mold whereby the second and third portions move downwardly away from the first portion until the third portion contacts an ejector plug, the second portion thereafter continuing downward until clear of the thermoformed container; and (g) removing the thermoformed container from the second and third portions of the mold.