Structures for providing a removable closure

摘要

A membrane lid with a surface with a substantially triangular-shaped perimeter. The perimeter includes first, second and third corner portions, wherein each corner portion is bisected by an imaginary line. The membrane lid further includes a projection with a tab and adapted to initially direct a lifting force to at least one of the corner portions. The projection either extends outwardly from the perimeter such that the projection is non-symmetrically disposed with respect to the imaginary line of any adjacent corner portion, or the projection extends non-continuously from an adjacent corner portion and is substantially symmetrically disposed with respect to the imaginary line of the adjacent corner portion. Containers are also provided with a lip having a substantially triangular-shaped horizontal cross-section. The lip includes three corner portions and three sides, wherein the sides of the lip are structured differently than the corner portions of the lip to increase the relative rigidity of the sides with respect to the corner portions such that the corner portions and the sides are adapted to exhibit a substantially uniform reaction pressure when applying a membrane lid to the lip of the container.