US Patent 7225945 Self-adjusting re-sealable spring center closure

The application is directed to a leak-resistant closure for a plastic container having a generally planar central portion a peripheral portion, and a spring structure. The peripheral portion defines an annular recess with an inner wall having a secondary sealing formation for engaging a free edge of a container The outer wall of the peripheral portion has a primary sealing formation on an inner surface thereof and faces the annular recess, thereby defining the primary sealing formation. The spring structure biases the peripheral portion radially outward from the central portion, and the spring structure is positioned between the central portion and the peripheral portion.