The present invention relates generally to tamper-evident and so-called tamper-resistant closures and, more particularly, to tamper-evident closures for containers whose contents are maintained at an overpressure with respect to atmospheric pressure.
Recent unfortunate instances of tampering with the contents of containers intended for human consumption have resulted in the design of a variety of container closures provided with tamper-evident features. Such closures attempt to provide readily visible evidence that the closure seal has at some time been disturbed.
The present invention is specifically directed to providing tamper-evident closure apparatus for containers whose contents are maintained at an overpressure with respect to atmospheric pressure. An example to which the present invention is especially suited is carbonated beverage containers.
Tamper-evident packaging presently used in conjunction with closures for sealing internally pressurized containers generally fall into one of several types. Shrink seals comprise bands or wrappers, some with distinctive designs, which are shrunk by heat or drying to seal the union of the closure and container. The seal must be cut or torn to open the container. Another type of tamper-evident closure is the breakable closure. The container is sealed by a plastic or metal closure that either breaks away completely when removed from the container or leaves part of the closure attached to the container. The closure must be broken to open the container and remove the product. A metal closure is disclosed in U.S. Pat. No. 3,303,955 issued Feb. 14, 1967 to Osborne, et al. which is provided with a locking band connected to the closure by frangible bridges which fracture to leave the band on the container upon initial removal of the closure from the container to thereby provide visible evidence of initial closure removal. Another metal closure is disclosed in U.S. Pat. No. 3,601,273 issued Aug. 24, 1971 to Kutcher which is similar to the previously described closure but wherein the locking band has several spaced vertical weakening lines formed therein so that upon rotation of the closure during initial removal thereof, the weakening lines rupture dividing the locking band into outwardly flared sectors which remain with the closure upon removal.
Plastic closures are available which have locking bands which remain connected to the container upon removal of the closure. For example, such a closure is available from Alcoa Corp. under the trademark Drop-Lok.
Shrink seals have the disadvantage of requiring additional assembly operations including the application of heat which is relatively expensive. Moreover, shrink seals are not considered desirable from the point of view of the purchaser since they usually require a separate removal operation to be performed. Closures which leave a locking band on the container are not entirely satisfactory, especially where the containers are returnable and refillable or recycleable, since such bands must first be removed by clippers, knives or the like which is a costly and tedious operation.