Tamper evident closure

Details Tamper evident closure Tamper evident closure

1999-03-16

2001-12-04

Newhouse, Nathan J. (Department: 3727)

Bottles and jars

Closures

Frangible member or portion

C264S334000, C425S547000

Reexamination Certificate

active

06325225

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to closures for containers having an externally screw threaded neck and more particularly to such closures which are formed with a tamper evident band.
BACKGROUND ART
Manufacturers of foodstuffs, beverages, medicaments, dentifrice and the like are concerned to ensure that products they place on the market are not tampered with before being opened by the ultimate consumer of the goods. For this purpose it has become conventional to include in closures for such goods means which will indicate whether the closure has been tampered with before purchase. In the case of containers having an externally screw threaded neck it is common to provide the closure with a tamper evident band which engages behind a retaining flange formed on the neck of the container. The tamper evident band is joined to a depending skirt forming part of the closure by a number of frangible bridges. On application of the closure to the container the band is forced over the retaining flange, however, when the closure is unscrewed from the container the bridges are sheared as the band is trapped behind the retaining flange while the closure moves up the neck of the container.
While such tamper evident bands have been widely accepted there is a delicate balance between the two conflicting requirements. On the one hand, one must be able to apply the closures to containers at very high speed without inadvertently breaking the bridges, or breaking or deforming the band itself, or deleteriously affecting the seal between the closure and the container. On the other hand, the band must be sufficiently tightly secured behind the retaining flange and the bridges and/or the band must be sufficiently easily broken that the closure cannot be removed from the container without rupturing the bridges and/or the band.
Another problem is that an unauthorized person might attempt to remove the closure and tamper evident band, without damaging the band or frangible bridges, in order to contaminate or replace the container contents and then reapply the closure. Such operation might be attempted with the assistance of a thin device, such as a knife blade, wedged up between the tamper evident band and the neck of the container to which the closure has been applied. The devices might then be levered outwardly in order to expand the inner diameter of the band so that it may be passed back over the retaining flange of the container. In such a process the device will be edged around the circumference of the band so as to gradually ease the band over the retaining flange at a continuously lengthening portion of the band circumference.
Closures of the type mentioned above are used around the world in extremely large numbers. To be commercially acceptable such closures must be capable of being produced very rapidly in automated machinery. This itself may produce a conflict with the functionality of the closure and/or its tamper evident band.
The arrangement according to the present invention is designed to provide the public with an alternative form of closure having a tamper evident band.
DISCLOSURE OF THE INVENTION
The present invention in its broadest aspect consists in a closure for a container having an externally screw threaded neck, the closure comprising a top portion and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the body portion being provided with projections or other localised areas of thickening to enhance the longitudinal stiffness of the body portion while still permitting it to expand radially as it is forced over the retaining flange on a container.
In a first preferred aspect the present invention consists in a closure for a container having an externally screw threaded neck, the closure comprising a top and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a continuous or segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the closure being characterized in that the upper side of the rib comprises a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly from the top, and a second surface which is positioned radially inwardly from the first surface, the second surface having a slope angle more nearly normal to the longitudinal axis of the closure than the first surface is to that longitudinal axis.
In the prior art closures the upper side of the rib has always been linear in cross-section. The upper side has either lain in a plane normal to the longitudinal axis of the closure or it has been a simple frusto-conical surface inclined to that axis. In the former case it has been difficult to mold as the planar surface is normal to the direction in which the core of the mold must be withdrawn from the cap. In the latter case there is more likelihood of the rib being able to be forced upwardly over the flange on the container neck. The present invention has resolved these problems by providing the upper side of the rib with a compound surface having a more steeply angled radially outer surface which assists molding of the rib and, preferably, a substantially planar radially inner surface which increases the difficulty of removing the closure intact from a container. There is preferably a relatively clearly defined junction between the first and second surfaces on the upper side of the rib. However, they may merge together gradually such that the upper side of the rib is generally arcuate in cross-section. It has been found that improved resistance to removal of the closure from the container can be obtained in this way while facilitating the molding of the closure. This latter aspect is important as for economic reasons, it is necessary that the closures and their associated tamper evident bands must be capable of being molded at extremely high rates.
The first surface on the upper side of the rib preferably comprises from 25% to 75% and more preferably 45% to 55%, of the radial width of the upper side of the rib. The first surface preferably has a slope angle to a plane normal to the longitudinal axis of the closure of from 10° to 60°, more preferably 12° to 40° and most preferably 15° to 25°. The second surface on the upper side of the rib preferably comprises from 75% to 25% and more preferably 55% to 45% of the radial width of the upper side of the rib. The second surface preferably lies in a plane normal to the longitudinal axis of the closure or at an angle of up to 10° to that plane, most preferably it lies in that plane.
In carrying out the present invention it has been found that during the injection moulding of closures from an injection mould which defines a rib having an upper side comprising a first annular surface and a second annular surface the clear distinction between the first and second surfaces may be lost, or at least difficult to discern, in the moulded product. It is thought that this may be due to the second annular surface being distorted and dragged into a slope angle similar to that of the first surface as the closure is ejected from the mould. Despite the anomaly that the mould clearly displ

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