Cutting – Other than completely through work thickness or through work... – Scoring
Patent
1997-04-11
1998-09-22
Shoap, Allan N.
Cutting
Other than completely through work thickness or through work...
Scoring
83879, 215252, 264154, 264163, 425291, B26D 308, B31B 125
Patent
active
058098607
DESCRIPTION:
BRIEF SUMMARY
This invention relates to closures for packaging containers, in particular, but not exclusively, to tamper-evident closures for such containers.
It is well known to provide a closure with a tamper-evident capability by forming the tubular skirt of the closure with a line of weakening so as to define a free marginal edge portion of the skirt as a security ring or band. In some closures the security ring has a snap-engagement formation, which enables it to make locking engagement with a complementary formation of the container, so that when the closure is removed it partially or wholly severs along the line of weakening, leaving the security ring either left behind on the container or attached to the closure but capable of clearly indicating that the closure has been operated. The snap-engagement formation may be a continuous annulus, or it may be formed of independantly movable, peripherally arranged, tabs.
When formed in plastics material the line of weakening may be provided by a simple peripheral groove leaving a residual thickness of plastics material which is capable of tearing when the closure is first opened. More usually, however, the line of weakening has the form of several (e.g. ten) frangible bridges of small cross-sectional area which are spaced around the closure and separated by slits at which the plastics material of the skirt is severed completely through its thickness.
Two alternative routes are commonly used for the formation of the line of weakening in a plastics skirt. In one route the line of weakening is a moulded feature of the skirt, being formed when the skirt itself is moulded. However, the moulding of the line of weakening often requires complicated and delicate tool parts which are expensive and liable to wear; moreover, the restriction to polymer flow presented by the residual plastics material (e.g the bridges) can create polymer starvation within the part of the closure which lies downstream of it in the direction of polymer flow.
The second possible route for forming the line of weakening avoids the particular shortcomings of the first route which are recited in the previous paragraph. In this further route the line of weakening is formed after the closure has been moulded, usually by means of a part-circular knife (or succession of part-circular knives) to which the closure is presented. If the line of weakening is of the kind having spaced bridges and slits separating the bridges, the knife is required to penetrate right through the wall of the closure skirt to form the slits, and hitherto it has been the practice to support the skirt internally by a roller or other support member which is inserted into it.
The support member may be made of a material, e.g rubber, with which the knife can come into contact without being blunted, or alternatively it may be arranged to cooperate with the knife by scissor action; however, in each case the contact with the knife causes degradation and wear, and the support member and/or the knife may need relatively frequent replacement or adjustment. Moreover, in those security rings having a snap-engagement formation in the form of a continuous flexible ring or a series of individual, flexibly mounted, elements which is (are) attached around the bottom free edge of the security ring and from there extend(s) upwardly and inwardly in a resilient manner for engagement with the container, the support member has hitherto being located at a sufficient height above the bottom edge of the closure skirt to ensure that it can reliably avoid contact with, and possible damage to, the snap-engagement formation as it (the support member) is being inserted into or removed from the closure or during its operation to support the closure skirt. This in turn has imposed a lower limit on the length of the skirt below the line of weakening, it being necessary to locate the line of weakening at a distance above the skirt free edge which is somewhat greater than the height of the snap-engagement formation within the closure. The skirt has accordingly been made to
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Crown Cork & Seal Technologies Corporation
Hylton Robin
Shoap Allan N.
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