Uniform stacking cup lid

摘要

A thin walled lid formed of a thermoplastic material having a generally circular center portion and an outer rim portion which fits over the cup bead and includes an integral peripheral skirt which makes up the outer side wall of the lid is disclosed. Located between the rim portion and the center portion is a recess or annular trough with an inner wall and an outer wall. The outer wall is separated into two shelves and three vertical sections. The lower shelf serves as a receiver ring upon which the lid above rests. The short vertical section located above the receiver ring effectively prevents any lateral movement of the lid above, while the lowest wall section forms the stacking ring and generally has a negative slope toward the lid skirt. Spaced periodically around the circumference of the stacking ring are positive draft flutes which have a positive slope away from the skirt and toward the center of the lid. The recess has a generally flat bottom which connects the stacking ring to the inner wall. The corner of the lid where the stacking ring and the recess bottom join rests in the receiver ring of the next lower lid in the stack to provide uniform nesting and full circumferential support. The inner wall of the recess has a positive slope and connects the bottom of the recess with the generally flat center portion. In an alternative embodiment, the negative stack ring and the receiver ring are provided on the inner wall of the lid. There are no positive draft flutes provided, in that as the plastic cools during the thermoforming process the negative stack ring will shrink towards the lid center a sufficient distance to allow the lid to clear the undercut of the mold during stripping.