The present invention relates to improvements in flexible containers, and in particular, to modifications of the zipper elements for an easy open container.
Recloseable, flexible containers are well-known in the art. Such containers normally comprise a bag-like structure made from a folded web of thermoplastic film, and typically include interlocking male and female zipper elements fused, extruded or attached to the bag side walls. The bag-like structure is created when the thermoplastic film is folded, severed and sealed along its side edges. The zipper elements are positioned on the opposing bag side walls and close to seal the bag mouth.
Because recloseable, flexible containers are, by definition, accessible, positive means to completely seal the bag mouth have been developed to preserve freshness, prevent accidental opening, and inhibit intentional tampering. In turn, means to open such sealed containers have also been developed. For example, tear strips are known which comprise weakened lines for tearing across sealed webs to gain access to the mouth of the bag. Naito, U.S. Pat. No. 3,198,228 and Uramoto, U.S. Pat. No. 3,780,781 (the '781 patent) both show tear strips having such weakened regions.
Problems have arisen, however, in the use of containers having weakened regions for tear lines. Such problems include consumers' inability to tear the thermoplastic material; the need, despite the weakened regions, to use scissors to open the container, obviating the value of the tear strip; and irregular tearing down the bag lips, which compromises the strength, shape and operation of the zipper elements. Modifications, such as the inclusion of perforations along the weakened lines of tearing, have enhanced the efficacy of tear strips, but eliminate the airtight and tamper-proof features desired in completely sealing the mouth in such containers.
Other tear strips comprised of a thin thread or string of fiber placed within the container at its top are shown by Staller, U.S. Pat. No. 3,543,343, as a means to open sealed containers along a single tear line. The drawback of such tear strips is that the tear line may deviate from the top of the bag and propagate into the zipper elements, again compromising their strength, shape and operation. In an apparent effort to avoid such problems, Uramoto, in U.S. Pat. No. 3,827,427 (the '427 patent), defines two tear lines, one on each lip of the bag mouth, between pairs of ribs. Further development is needed, however, to improve the design of tear strips for the easy opening of sealed flexible containers of thermoplastic material.