GB2551566A

GB2551566A - Tamper evident screw closures

Info

Publication number: GB2551566A
Application number: GB1610987.8A
Authority: GB
Inventors: Abraham Pierre; Micallef Kevin
Original assignee: Greif International Holding BV
Current assignee: Greif International Holding BV
Priority date: 2016-06-23
Filing date: 2016-06-23
Publication date: 2017-12-27
Also published as: GB201610987D0; CN109641682A; BR112018076625A2; US20200317406A1; WO2017220785A1; EP3475181A1

Abstract

A pawl 18c attaches to a tamper indicating band 14 at its base 44c and at link 38c. The band is frangibly attached to a screw closure for a container. When the closure is screwed on for the first time the link can buckle to allow a cooperating lug past but can extend during attempts to unscrew to resist collapse of the pawl when it engages the lug, prevent rotation of the band and detach the band from the closure. The link can be curved towards the pawls other attachment or include thinned portions 46 to aid buckling. The link ideally attaches to the tip of the pawl. The band can be formed of segments and/or partially enclosed by a cover. The pawl can be thin 44c where it attaches to the band and thick at its tip. A guard stop thinner than the band width could limit excess flexing of the pawl instead of the link 38c. The pawl can have a flat face to engage a tooth of the container.

Description

Tamper Evident Screw Closures

Closure caps are known which include a so-called tamper indicating band, which is broken off from the remainder of the cap the first time that the cap is removed from a filled container. An intact band provides assurance that the container contents have not been interfered with after application of the cap to the container for the first time.

One form of tamper indicating band widely used in injection moulded plastics screw caps is attached to the remainder of the cap by a set of frangible links. The band is provided on its inner circumference with a series of flexible blades which act as “antibackoff’ ratchet pawls, in co-operation with a set of teeth, usually moulded into the container neck, which act as the ratchet rack. The blades extend radially inwardly from the band and slope obliquely rearwardly from root to tip in the screwing-on direction of the cap. Thus when the cap is viewed from below, for a right hand threaded cap, there is an acute included angle between the clockwise side of the blade and the band. Correspondingly, the container rack teeth each have a (clockwise-facing, when the container is viewed from above) flank lying substantially in a radial plane, to provide a surface which faces forwardly in the cap screwing-on direction; and a further flank which slopes from the tooth tip to the base of the tooth. Therefore when the cap is screwed onto the container towards its final position, the blade tips ride up along, and are cammed outwardly by, the teeth sloping flanks and then spring inward behind the teeth radial flanks. This ratcheting process can continue until the cap is fully tightened. The frangible links are sufficiently strong to move the band in unison with the remainder of the cap as a screwing-on torque is applied, pulling the flexible blades past the rack teeth in succession. When the cap is unscrewed, the blade tips jam against the teeth radial flanks and hold the tamper-indicating band stationary on the container. Continued unscrewing of the cap therefore breaks the frangible links. When the cap is removed, the band remains behind on the container. A user can therefore easily tell from a detached or missing band that the container has already been opened.

However this form of tamper indicating band can be defeated by a technique which involves gripping both the band and the remainder of the cap in a way which ensures that these two components move in unison in the unscrewing direction, thereby relieving any strain on the frangible links. A sufficiently high torque can be applied to the band in this way, to cause the flexible blades to bend abnormally and opposite to their normal flexing direction, so that their clockwise sides when viewed from below, make an acute angle with the band, at least at the blade tips. Hence the blades can be forcibly snapped past the neck teeth (perhaps distorting the container radially inwardly and/or stretching and expanding the band), and the cap can be unscrewed with the frangible links left intact. This forcing process may bend and break the blade tips, but the blades may be left sufficiently intact so that when the cap is re-applied to the container, they are bent back towards their proper positions and may even serve to hold the band stationary the next time the cap is unscrewed. This provides a false indication that the cap has not previously been opened. Importantly, the forcing process leaves the frangible links intact and so requires very close and careful inspection of the blade tips in order to be detected, if detectable at all. A variant of this tamper indicating band is known which is less vulnerable to the above-described forcing process, in that the pawl members on the band are formed as solid, substantially triangular teeth, each having a radial flank for lockable cooperation with the container rack teeth radial flanks, and a sloping flank for cooperation with the container rack teeth sloping flanks. The band itself flexes radially outwardly to allow the band tooth and rack tooth sloping flanks to slide past each other as the container cap is screwed on. As the cap is unscrewed, the band tooth and rack tooth radial flanks lock together to hold the band stationary and break the frangible links. The solid band teeth are too stiff to bend back on themselves under attempted forced unscrewing. Instead, the forcing tool tends to slip relative to the band and sufficient movement is generated between the band and the remainder of the cap to cause the frangible links to break. However, with this cap design, in normal use quite high torques are applied to the frangible links as the cap is screwed on. Therefore there is a danger that the links may break to give a false positive tamper indication the first time that the cap is screwed on, and/or a danger that the frangible links must be made so strong that the cap is difficult to remove for the first time. Further improvements in such tamper indicating bands are therefore desirable.

Accordingly the present invention provides a screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; wherein the screw closure further comprises a flexible link connecting the flexible anti-backoff pawl and the tamper indicating band. If an attempt is made to force the tamper indicating band to rotate together with the remainder of the screw closure in the unscrewing direction, the flexible link constrains the anti-backoff pawl and increases its resistance to being bent in an abnormal direction when it encounters the rack tooth on the container. The forcing tool is therefore more likely to slip relative to the tamper indicating band, causing the frangible links to break as intended. At the same time, both the flexible anti-backoff pawl and the flexible link can be made to be relatively easily deformable in comparison to a solid tooth on the tamper indicating band, whereby screwing on of the closure is easier and imposes lower stresses on the frangible link.

The flexible link may be made sufficiently thin whereby it readily undergoes buckling collapse during screwing on of the closure. Additionally or alternatively it may be provided with one or more thinned sections along its length, to form more flexible sections or “living hinges”, for the same purpose. A flexible link which buckles easily will offer less mechanical resistance to screwing the closure onto or into the container and impose a lower shear load upon the frangible link.

Additionally or alternatively, the flexible link may be curved or bent along its length in the relaxed state. This again encourages the flexible link to collapse or deform under lengthwise compression, in order to allow the flexible anti-backoff pawl to flex and more easily move past the rack tooth in the closure screwing-on/in direction. The resulting lower screwing on torque which then needs to be applied to the remainder of the closure means that a weaker frangible link can be used. This ensures that the closure is easier to remove on the first occasion.

For example the flexible link may have a bowed shape between its ends. The centre of the bowed shape may face towards or away from the root end of the flexible antibackoff pawl. On unscrewing the closure for the first time, the flexible anti-backoff pawl encounters the rack tooth and begins to bend radially inwards of the closure. This tends to straighten the bowed flexible link and allows the flexible anti-backoff pawl to engage more deeply behind the rack tooth on the container.

The flexible link may be joined to the flexible anti-backoff pawl at or near to the distal end thereof, so as to provide favourable mechanical advantage and favourable control against excessive bending of the flexible anti-backoff pawl under an unscrewing torque..

Although flexible so as to allow movement past the rack tooth in the screwing-on direction, the anti-backoff pawl may be sufficiently stiff so as to act as a strut which is resistant to buckling collapse. It thereby provides a high resistance to movement of the tamper indicating band in the unscrewing direction, when the distal end is wedged against the container rack tooth. The flexible anti-backoff pawl thus may be flexibly attached to the tamper indicating band, for example comprising a thinned section, or even a living hinge, at or near to its root end. This allows the necessary normal flexing of the pawl so that it can move past the rack teeth as the closure is screwed onto the container. Either the flexible attachment at the root end, or the flexible link, or both, may provide the flexible anti-backoff pawl with resilient bias so that it engages behind and jams against the rack tooth when the closure is moved in the unscrewing direction.

The tamper indicating band may be interrupted to form segments, with ends of adjacent segments connected in series by the flexible anti-backoff pawl and the flexible link.

Provision of a flexible link as described above is not the only solution to the problem of improving the resistance to abnormal bending of the anti-backoff pawl if forced unscrewing of the tamper indicating band is attempted. As one alternative, the present invention provides a screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; and a guard stop attached to the tamper-indicating band adjacent to the flexible antibackoff pawl and positioned to contact and support the flexible anti-backoff pawl so as to resist bending thereof driven by contact with the rack tooth as the closure is torqued in the unscrewing direction. Thus the guard stop may be positioned behind the anti-backoff pawl in the closure unscrewing direction.

The guard stop may be thinner than the width of the tamper indicating band in the closure axial direction and positioned adjacent to the upper edge of the tamper indicating band; or the guard stop may be thinner than the width of the tamper indicating band in the closure radial direction and positioned adjacent to the inner or outer edge of the tamper indicating band; in each case so as to provide a clearance space for passage of the rack tooth formed on the container.

As another alternative, the present invention provides a screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; wherein the distal end of the flexible anti-backoff pawl has an enlarged cross-section whereby it is stiffened to resist bending.

For example, the flexible anti-backoff pawl may progressively increase in cross-sectional thickness along its length from the root end towards the distal end. The flexible anti-backoff pawl may be flexibly attached to the tamper indicating band, for example comprising a thinned section, at or near to its root end.

The distal end of the flexible anti-backoff pawl may comprise a first, substantially flat face configured for substantially face-to-face engagement with a generally radially or vertically extending face of the rack tooth on the container, and optionally a second face for engagement with the container (on the part of the container onto which the closure is being screwed, typically a neck), adjacent to the rack tooth.

The closure may further comprise a flexible link as described above, connecting the flexible anti-backoff pawl and the tamper indicating band.

As yet another alternative, the present invention provides a screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; and a flexible anti-backoff pawl attached to the tamper indicating band; wherein the screw closure further comprises a cover overlying at least a part of the outer circumference of the tamper indicating band. The cover thereby prevents access to the full circumferential extent of the tamper indicating band, making driving engagement with the tamper indicating band for forced bending and disengagement of the flexible anti-backoff pawl more difficult.

The cover may leave at least one section of the tamper indicating band exposed and visible, so that its presence or absence can readily be seen when the closure is screwed onto or into the container. The cover may comprise one or more sections. The or each section may stand out radially from the tamper indicating band to an extent that at least 50% of the band lies between tangents to the band and the outer portion of the envelope of the or each cover section. In this way, the band may be provided with at least 50% protection against the action of the forcing tool but remains easily seen. A plurality of cover sections may be spaced around the band circumference and stand out radially from the band to a distance at which tangents to the outer envelopes of adjacent cover sections do not intersect the tamper indicating band. In this way, the band may be provided with 100% protection against the action of the forcing tool but remains easily seen.

Such a cover may be used in conjunction with any of the screw closures having a tamper indicating band, a frangible link and an anti-backoff pawl as described above.

For a more complete understanding of the invention and some of its further features and advantages, illustrative and non-limiting embodiments are described below with reference to the drawings in which:

Figure 1 shows a prior art screw cap and tamper-indicating band, viewed from below, after forced removal using a driving force applied to the tamper-indicating band;

Figure 2 shows a prior art screw cap and tamper indicating band provided with solid, generally triangular anti-backoff pawls;

Figure 3 is a sectioned view of a first embodiment of a screw cap according to the invention in position on a container neck;

Figure 4 is an enlarged view from below of a portion of the screw cap shown in Figure 3;

Figure 5 provides an enlarged view of one of the flexible anti-backoff pawls shown in Figure 4;

Figure 6 is a schematic view from above, illustrating screwing of the cap of Figures 3-5 onto the container neck;

Figure 7 corresponds to Figure 6, but illustrates the action of a cap unscrewing torque; Figure 8 shows an alternative form of anti-backoff pawl;

Figure 9 shows a plan view of a second embodiment of a screw cap according to the invention;

Figure 10 is an underplan view corresponding to Figure 9;

Figure 11 is a scrap view showing a portion of Figure 10 drawn to a larger scale;

Figure 12 is a perspective view from below of a third embodiment of a screw cap according to the invention;

Figure 13 is a partial top plan view corresponding to Figure 12 and drawn to a larger scale;

Figure 14 is a scrap sectional view from below, showing the interengagement between rack teeth on a container neck and a tamper indicating band comprising a fourth embodiment of the invention;

Figure 15 is a scrap view corresponding to Figure 14, showing the tamper indicating band and an adjacent portion of the screw cap, viewed in the radial direction from inside the cap;

Figure 16 is a scrap view showing a portion of a tamper indicating band and a flexible anti-backoff pawl having a profile comprising a fifth embodiment of the invention; Figure 17 is a schematic side view showing a container screw cap in accordance with a sixth embodiment of the invention, and

Figure 18 corresponds to Figure 4, but shows an embodiment having differently orientated anti-backoff pawls.

Referring to Figure 1, there is shown a container screw closure in the form of a screw cap 10 of known kind, injection moulded in one piece from suitable plastics, such as LDPE. The cap has an internal screw thread 12 for engagement with an external thread formed e.g. on a container neck (not shown). A tamper indicating band 14 is attached to the remainder of the screw cap 10 by a circumferentially spaced series of frangible links 16. A series of blade-shaped, flexible, anti-backoff pawls 18 have root ends 20 attached to the tamper indicating band 14. The pawls 18 extend obliquely radially inward from the band 14, so as to provide freely projecting tips 22. The tips are chamfered to provide a cam surface 24. In normal use, the tip 22 and cam surface 24 co-operate with a series of rack teeth provided on the container [typically distributed about the base of the container neck) so as to provide an anti-backoff action for the tamper indicating band 14. That is, the anti-backoff pawls 18 flex past the rack teeth so as to allow the screw cap to be screwed onto the container external thread with relatively little mechanical resistance. Hence the shear stress imposed on the frangible links 16 is kept reasonably low, so that they will not break prematurely during cap application and provide a false positive tamper indication. This is the case even if the frangible links 16 are designed to be quite delicate, with a low breaking strength in shear. On the other hand, when the cap 10 is first unscrewed, the pawl tips 22 jam against the rack teeth on the container and strongly resist rotation of the tamper indicating band 14 on the container in the unscrewing direction. As increasing unscrewing torque continues to be applied to the remainder of the cap 10, the frangible links 16 will break [shear off). The band 14 thereby becomes detached from the remainder of the cap 10, and this provides the desired tamper indication. Because the frangible links do not have to be robust [due to the low stress generated in them by the anti-backoff pawls 18 during cap application), the band 14 will detach at a correspondingly low unscrewing torque, making the screw cap 10 easy to open on the first occasion.

However the tamper indicating band 14 may be circumvented by gripping it and turning it together with the remainder of the cap 10 in the unscrewing direction. As the band and the rest of the cap are turned substantially in unison, insufficient shear strain is applied to the frangible links 16 to break them. At the same time, a sufficiently high torque may be applied to the band 14 to violently force the pawls 18 past the container rack teeth. The cap shown in Figure 1 has been subjected to this treatment. Forcibly overcoming the pawl’s jammed condition in this way involves flexing at least the tip 22 in a direction opposite to the normal flexure direction, with a strain many times greater than the designed normal flexural strain. The abnormal strain will usually exceed the cap material’s elastic limit and possibly its failure strain, whereby the pawl tips are permanently bent (22a) and / or broken (22b). Nevertheless, the anti-backoff pawls 18 may remain sufficiently intact to allow the cap 10 (notably with the frangible links 16 still intact) to be re-applied to the container. The anti-backoff pawls 18 may even still act in the normal way to lock the tamper indicating band 14 against rotation on the container as the cap 10 is unscrewed again. In that case the frangible links 16 will break and the band 10 will detach to provide an otherwise normal, but false negative, tamper indication. Without careful inspection of the anti-backoff pawls 18, the end user will have no idea that this has occurred.

Figure 2 shows another known form of container screw cap 10 made from injection moulded plastics, but which is less vulnerable to circumvention of its tamper indicating band 14 than the cap as described with reference to Figure 1. This is because the anti-backoff pawls 18a have a robust, substantially triangular cross-section in the plane normal to the axis of the tamper indicating band 14. The antibackoff pawls 18a are “solid” in the sense that, compared to the flexible blades 18 of Figure 1, the acute angled gaps present between the clockwise side of each blade 18 and the adjacent portion of the tamper indicating band 14 have been substantially “filled in”. The anti-backoff pawls 18a as shown in Figure 2 are therefore too stiff to bend contrary to their usual displacement direction and cannot act as rotating levers interposed between the band 14 and the container circumference. Therefore they cannot be forced out of their jamming contact with the container rack teeth by torque applied to the tamper indicting band 14 in the unscrewing direction. Instead the torque applying tool tends to slip on the tamper indicating band 14. This causes relative rotation between the remainder of the cap 10 (which is being driven at the same speed as the tool applying the torque to the band 14) and the (stationary) band 14. Hence the frangible links 16a, 16b are broken as intended by the cap manufacturer. However, as the cap 10 is screwed onto the container, the rigid antibackoff pawls 18a can only move past the container rack teeth by flexing or stretching of the tamper-indicating band 14 in the radially outward direction. This gives rise to quite a high mechanical resistance to screwing on of the cap. This resistive torque has to be transmitted through the frangible links 16a, 16b. Therefore either the frangible links 16a, 16b must be made more robust than for the flexible, blade-like anti-backoff pawls 18 of Figure 1, which leads to an undesirably high initial opening torque necessary to break the frangible links 16a, 16b; or there is a danger that the frangible links 16a, 16b will break prematurely as the cap is being screwed onto the container for the first time. Figure 2 shows the cap in a condition where some of the frangible links (16a) are still intact, while the remainder (16b) are broken. The tamper indicating band 14 has an open or unprotected style, in which the frangible links are carried at the corners of lugs 26 projecting radially from the bottom edge of the cap threaded side wall. In contrast, the tamper indicating band shown in Figure 1 has a relatively enclosed or protected configuration, in which a radially projecting, circumferential flange 28 at the bottom of the cap side wall overlies and at least partially shields the band 14, pawls 18 and frangible links 16. Either style or configuration (open or enclosed) may be used in any of the screw caps 10 described in this specification.

Figure 3 shows a screw closure in the form of a screw cap 10 embodying the present invention screwed onto a threaded neck or pouring spout 30 of a container 32 by an internal thread 12. The illustrated cap 10 is formed as a one piece injection moulding of suitable plastics material, but any suitable material and fabrication method may be used. A series of rack teeth 34 are formed on the container, circumferentially distributed around the base of the container neck. These co-operate with a series of flexible anti-backoff pawls (described in more detail below) formed on a tamper indicating band 14. A series of frangible links 16 separably connect the tamper indicating band 14 to the remainder of the cap 10. An integrally moulded sealing lip 36 is illustrated depending from the inner surface of the cap top. However this is not essential, and any other suitable sealing element (or none) may be used, depending on the container contents and customer requirements. The illustrated tamper indicating band 14 and its associated components such as the frangible links 16 have a “closed” configuration, in which they are shielded by an overlying circumferential flange 28; but again this is not essential.

As best seen in Figure 4, the frangible links 16 connect the tamper indicating band 14 to the remainder of the screw cap 10. For example, they may have an L-shape as illustrated, so as to connect the bottom edge of the cap threaded side wall, or the bottom surface of the flange 28, to a top edge region on the interior of the band 14. Many other forms and configurations of frangible links are known and may be used, e.g. (but not limited to) those shown and described with reference to Figure 2.

The tamper-indicating band carries a series of flexible anti-backoff pawls on its inner surface. Some of these (18) may be blade shaped with a freely extending tip 22 and chamfer 24, similar to the pawls 18 shown in Figure 1. Others 18b (see also Figure 5) of the anti-backoff pawls comprise a root end 20 attached to the tamper-indicating band, and a distal end 22b co-operable with the rack teeth 34 (Figure 3) so as to resist relative rotation between the band 14 and container 32 in the cap unscrewing direction. A flexible link 38 connects the distal end 22b of the pawl 18b to the inner surface of the tamper indicating band 14. If an attempt is made to force the tamper indicating band 14 to rotate together with the remainder of the screw cap 10 in the unscrewing direction, the flexible link 38 constrains the anti-backoff pawl 18b and increases its resistance to being bent back on itself contrary to its normal (screwing on) flexing direction, when it encounters the rack tooth 34 on the container neck 30. The forcing tool is therefore more likely to slip on the tamper indicating band, causing the frangible links 16 to break as intended. At the same time, both the flexible antibackoff pawl 18b and the flexible link 38 can be made relatively easily deformable in comparison to a solid tooth on the tamper indicating band, whereby they do not significantly increase the screwing-on resistance of the cap 10. This imposes lower stresses on the frangible link than e.g. the solid, triangular sectioned anti-backoff pawls 18a shown in Figure 2.

The flexible link 38 may be made sufficiently thin whereby it readily undergoes buckling collapse. At the same time it is strong enough to prevent the anti-backoff pawl 18a from being bent back on itself in the opposite direction to its normal deflection direction, when an attempt is made to forcibly unjam it from behind the rack tooth 34 by applying torque to the tamper-indicating band 14 in the unscrewing direction. The flexible link 38 may be curved or bent along its length in the relaxed state, as illustrated in Figure 2. This again encourages the flexible link 38 to collapse under lengthwise compression, in order to allow the flexible anti-backoff pawl 18b to flex and move past the rack tooth 34 in the cap screwing-on direction; again without unduly stressing the frangible link 16 under the drive torque applied to the remainder of the cap 10. For example the flexible link 38 may have a bowed shape between its ends. The centre of the bowed shape may face towards the root end of the flexible anti-backoff pawl (as shown in Figures 4 and 5] or away from it.

Figure 6 is a view from above of the container neck 30 and the associated rack teeth 34 at its base. The tamper indicating band 14, flexible anti-backoff pawls 18, 18b and flexible links 38 are indicated schematically in dotted lines, showing their interactions with the rack teeth 34 as the cap is screwed onto the container neck (arrow 40 showing the cap rotation direction]. It can be seen that the pawl 18 on the extreme right hand side of the Figure is undeflected, as it is positioned opposite to a rack tooth-free portion of the container neck 30. The remaining pawls 18, 18b have been cammed radially outward (their tip/distal ends 22/22b bent towards the band 14) after their clockwise faces have encountered and ridden up along the sloping, anticlockwise faces of the rack teeth 34. This also causes the flexible links 38 to collapse lengthwise by bowing further outwardly in the anticlockwise direction, as shown.

On unscrewing the cap for the first time (see arrow 42, Figure 7), the tips/distal ends 22/22b of the flexible anti-backoff pawls 18/18b encounter and jam against the radially directed faces of correspondingly positioned rack teeth 34 and begin to bend radially inwards compared to their relaxed state. This tends to straighten the bowed flexible links 38 and allows the flexible anti-backoff pawls 18/18b to engage more deeply behind their respective rack teeth 34. That is, the pawls 18/18b deflect radially inward (see straight arrows in Figure 7) and jam in the corners formed at the bases of the rack teeth radial faces, where these project from the container neck 30.

The flexible link 38 may be joined to the associated flexible anti-backoff pawl 18b at or near to the distal end 22b thereof as shown in Figures 4-7, so as to provide favourable mechanical advantage and favourable control against excessive bending back of the flexible anti-backoff pawl 18b. However any joining position may be used in which the flexible link 38 is effective to prevent reverse bending of the pawl 18b to an extent that it disengages from the rack teeth radial faces, when an attempt is made to subvert the tamper indicating band 14 by applying unscrewing torque to it.

Although flexible so as to allow movement past the rack tooth in the screwing-on direction, the anti-backoff pawl 18b can be made sufficiently stiff so as to act as a strut which is resistant to buckling collapse. It thereby provides a high resistance to movement of the tamper indicating band 14 in the unscrewing direction, when the distal end 22b is wedged against the container rack tooth 34. The flexible anti-backoff pawl may be flexibly attached to the tamper indicating band, as shown in Figure 8. Here a thinned section 44c, or even a living hinge, is shown at or near to the root end of the anti-backoff pawl 18c. Similarly, the flexible link 38c may be provided with one or more thinned sections 46 along its length, to form more flexible sections or “living hinges”, for the same purpose. The flexible link need not be bowed. The centre flexible section 46 is shown to be out of alignment with the end flexible sections, to encourage the flexible link to bend and collapse predictably in the outward direction away from the anti-backoff pawl 18c; although inwardly collapsing arrangements and arrangements with unpredictable directions of collapse may also be used.

Figures 9 and 10 respectively are top and underplan views of a further container screw cap embodying the present invention. The screw cap 10 is similar to that shown in Figure 2, in that an open or unprotected style of tamper indicating band 14 is attached to the outer corners of six projecting lugs 26 by frangible links (not clearly visible). Finger grip ribs 48 extend from side edges of each lug, up the side wall of the cap and into a curved transition region between the cap side wall and top wall.

An inner surface of the tamper indicating band 14 is formed with anti-backoff pawls 18d, one of which appears in region E of Figure 10; region E being drawn to a larger scale in Figure 11. Near to its distal end 22d, the pawl 18d is attached to the band 14 inner wall by an inwardly curving strut 38d. This provides a flexible link between the pawl distal end and the tamper indicating band 14. As the pawl 18d rides up the sloping faces of the rack teeth 34, the distal end 22d is able to flex radially outwardly so as to move closer to the band 14. In doing so, the strut 38d also flexes to a more curved shape. In this condition, the majority of the pawl 18d has a convex curvature at its radially inner surface, with a degree of inflection towards its root end 20d. The overall result is that as it passes the rack teeth 34, the flexible anti-backoff pawl 18d is deformed to adopt a lower profile [as compared not only to its unstressed profile, but also as compared to a solid pawl such as 18a of Figure 2). It therefore offers less mechanical resistance and does not impose as high stresses on the frangible links, with the advantages for reliability and ease of use as discussed above. The radially inner face of the pawl 18d is angled in the cap axial direction, sloping radially inwardly from bottom to top, as can be seen in Figure 11. This also helps the pawls 18d to ride smoothly past the rack teeth 34 as the cap 10 is screwed down onto the container neck.

As the cap 10 is torqued in the unscrewing direction, the pawl distal ends 22d jam against the radially directed faces of the rack teeth 34. The strut 38d may straighten slightly e.g. if torque is applied directly to the tamper indicating ring 14 in an attempt to circumvent it. This allows the pawl distal ends 22d to flex radially inward to jam in the corners formed at the bases of the rack teeth radial faces, where these project from the container neck 30; but the struts 38d constrain any further flexing and do not allow the pawl distal ends 22d to be forcibly bent past the rack teeth 34. The torque applying tool therefore slips relative to the tamper indicating band 14 and breakage of the frangible links is assured.

Figures 12 and 13 show a modification of the screw cap shown in Figures 9-11, in which the tamper indicating band is interrupted to form segments 14e. Ends of adjacent segments are connected in series by the flexible anti-backoff pawl 18e and the flexible link/curved strut 38e. In other words, in Figures 12 and 13 the ring/strut/pawl structure is as if the parts of the ring 14 in Figures 9-11 between each pawl 18d and its corresponding strut 18d have been removed. The resulting segmented ring structure is able to expand circumferentially, which allows the pawls 18d to ride past the rack teeth 34 even more easily in the screwing-on direction. In the unscrewing direction, any torque applying tool used to grip the ring segments: a) has less surface area to gain a purchase on, and b) tends to constrain the ring segments against radial expansion, so that the struts 38e, pawls 18e and pawl distal ends 22e behave in the same way as the components 38d, 18d and 22d described with reference to Figures 9-11, insofar as is material. The frangible links 16 are also more clearly visible in Figure 12; those used in the embodiment of Figures 9-11 may be similar.

Figure 14 shows portions of another embodiment of the invention viewed from below the container neck and screw cap. Here the tamper-indicating band 14 is equipped with anti-backoff pawls 18 shaped as blades, e.g. similar to those used in the screw cap 10 shown in Figure 1. A guard stop 50 is rigidly attached to the tamper-indicating band adjacent to at least one of [and optionally all or a substantial proportion of] the flexible anti-backoff pawls 18fi. The guard stop 50 is positioned to contact and support the flexible anti-backoff pawl 18fi so as to resist bending thereof driven by contact with the rack tooth 34fi, as the cap is torqued in the unscrewing direction. Thus the guard stop 50 is positioned in the obtuse angled space anticlockwise of the pawl 18fi as viewed in Figure 14. The gap 52 between the guard stop 50 and the pawl 18fi may be kept as small as is practicable according to the moulding process, and in any event should be kept sufficiently small to avoid excessive deformation of the pawl 18fi to the point at which it can be forced past the rack tooth 34fi in the cap unscrewing direction. The gap 54 between the other side of the guard stop 50 and the next pawl 18f2 [if such a pawl is present), must be large enough to accommodate the normal flexing of the pawl 18f2 as the cap is screwed onto the container. That is to say, the gap 54 is necessary to allow the pawl 18f2 to clear the rack tooth 34f2.

Referring to Figure 15, it can be seen that the illustrated guard stop 50 is thinner than the width [height) of the tamper indicating band 14 in the cap axial direction and positioned adjacent to the upper edge 56 of the tamper indicating band 14, so as to provide a clearance space 58 below the guard stop 50 for passage of the rack teeth 34fi, 34f2 formed on the container.

Another embodiment of the invention is shown in Figure 16, in which the distal end 22g of the flexible anti-backoff pawl 18g has an enlarged cross-section whereby it is selectively stiffened to resist bending. In the illustrative example shown, the flexible anti-backoff pawl 18g progressively increases in cross-sectional thickness along its length from the root end 20 towards the distal end 22g. The flexible anti-backoff pawl comprises a thinned section 44g by which it is flexibly attached to the tamper indicating band 14, for example, at or near to its root end 20. Like the solid pawls 18a of the cap shown in Figure 2, the pawl 18g is too stiff in the critical areas most vulnerable to excessive reverse bending, i.e. at and towards the distal end 22g, to bend contrary to its usual displacement direction. Therefore the pawl 18g cannot be forced out of jamming contact with the adjacent container rack tooth 34 by torque applied to the tamper indicting band 14 in the unscrewing direction. However, rather than being rigidly attached to the tamper indicating band 14, the anti-backoff pawl 18g can flex relative to the tamper indicating band 14 in a manner similar to the blade-shaped pawls 18 of Figure 1, in order to pass the rack teeth in the screwing-on direction. (Except that the flexing is concentrated mainly at the thinned section 44g, rather than taking place along the entire length of the pawl 18g). The result is that the pawl 18g presents less mechanical resistance to screwing on of the cap than do the solidly attached pawls 18a of Figure 2; with the corresponding advantages for reliability and ease of use as discussed above. A sufficiently large gap 64 is provided between the outer, clockwise side of the pawl 18g and the adjacent inner surface of the tamper indicating band 14, so as to allow flexing of the pawl 18g so that it may pass the rack teeth 34 in the screwing on direction, without substantial outward flexing of the band 14 itself.

The distal end 22g of the flexible anti-backoff pawl 18g may comprise a first, substantially flat face 60 configured for substantially face-to-face engagement with the generally radially extending face of the rack tooth 34 on the container, and a second, curved face 62 for engagement with the container (on the part of the container onto which the cap is being screwed, typically the neck 30), adjacent to the rack tooth 34. This configuration helps to reduce stress concentrations arising under axial compressive loading of the pawl 18g when abnormally high backoff forces are imposed on the pawl 18g e.g. as a result of attempts to circumvent the tamper indicating ring 14. It also helps to further stabilise the pawl 18g against abnormal reverse bending. The widely spaced edges of the contact region between the face 60 of the pawl 18g and the rack tooth radial flank, and the similarly widely spaced edges of the contact region between the face 62 and the container side wall at the base of the rack tooth radial flank, stabilise the pawl 18g against pivoting on the rack tooth and/or container wall when subjected to loading in the unscrewing direction. The pawl 18g is therefore less liable to break, permanently deform or be forced past the rack tooth 34 in the unscrewing direction under such abnormal loading, than the pawls shown in Figure 1.

Figure 17 shows a further embodiment of the invention in which the screw cap 10 comprises a cover overlying at least a part of the outer circumference of the tamper indicating band 14. The cover thereby prevents access to the full circumferential extent of the tamper indicating band, making driving engagement with the tamper indicating band for forced bending and disengagement of the flexible anti-backoff pawls more difficult.

The cover comprises a number of sections 66, between which the tamper indicating band 14 is left exposed and visible, so that its presence or absence can readily be seen when the cap 10 is screwed onto the container. Each section 66 may stand out radially from the tamper indicating band 14 to an extent that for example 50% of the band lies between tangents to the band and the outer portion of the envelope of each cover section. In this way, the band 14 may be provided with 50% protection against the action of the forcing tool, but remains easily seen. Other extents of coverage or protection are also possible. The bars 68 in Figure 17 schematically indicate the circumferential extent of the protection afforded by the cover sections 66 and the “shadows" at their ends. The plurality of cover sections 66 may be spaced around the band 14 circumference and stand out radially from the band to a distance at which tangents to the outer envelopes of adjacent cover sections do not intersect the tamper indicating band. In this way, the band may be provided with 100% protection against the action of the forcing tool but remains easily seen. The various cover sections 66 have open bottoms (thereby for example having a generally L-shaped radial cross-section). This allows the remainder of the cap 10 to be lifted away while leaving the tamper indicating band 14 behind on the container when the cap 10 is unscrewed for the first time.

Figure 18 illustrates a screw cap generally similar to that shown in Figures 3-7, except that the orientation of the anti-backoff pawls 18, 18h of Figure 18 differs from the orientation of those 18, 18b of Figures 3-7, and the tamper indicating band 14h is correspondingly modified. Thus a tamper indicating band 14h of generally L-shaped cross section is attached to the remainder of the screw cap 10 by a circumferentially spaced series of frangible links 16h. A series of blade-shaped, flexible, anti-backoff pawls 18, 18h have root ends 20 attached to the tamper indicating band 14h. The pawls 18, 18h extend obliquely axially downward from the band 14h, so as to provide freely projecting tips 22 and distal ends 22h respectively. The tips are chamfered to provide a cam surface 24. In normal use, the tips 22/distal ends 22h and the cam surfaces 24 co-operate with a series of rack teeth provided on the container (typically distributed about the base of the container neck) so as to provide an anti-backoff action for the tamper indicating band 14. The rack teeth are still typically distributed circumferentially about the base of a neck or pouring spout of the container, but are correspondingly re-orientated compared to those shown and described in Figures 3, 6 and 7, so that they extend axially relative to the screw cap, with their locking flanks extending axially upward from root to tip, rather than radially outwardly from root to tip. The rack teeth are therefore arranged below the anti-backoff pawls 18, 18h, about pitch circles of the same diameter, rather than being arranged generally radially inward of the anti-backoff pawls 18,18b as shown in Figures 3, 6 and 7. The pawls 18, 18h of Figure 18 therefore flex in a generally axial direction, instead of in a generally radial direction as is the case for the pawls 18,18h of Figures 3-7. The operation of the screw cap shown in Figure 18 is otherwise generally similar to the screw cap shown and described with reference to Figures 3-7. The embodiments shown in Figures 9-17 may be correspondingly modified, as regards the directions of projection and of deflection of their anti-backoff pawls (with appropriate corresponding modification of the rack teeth orientation, and of the position and orientation of the guard stop 50 in the case of Figures 14 and 15. That is, the modified guard stop is thinner than the width of the tamper indicating band in the radial direction and positioned adjacent to a radially inner or outer edge of the band to allow for passage of the rack teeth. A position adjacent to the band outer edge is preferred, but not essential).

Although the various embodiments particularly described above concern container screw caps, the invention may be more broadly applied to any suitable screw closure for a container, such as a screw plug provided with a tamper-indicating band.

Claims

1. A screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; wherein the screw closure further comprises a flexible link connecting the flexible anti-backoff pawl and the tamper indicating band.

2. The screw closure of claim 1, in which the flexible link undergoes buckling collapse during screwing on or in of the closure.

3. The screw closure of claim 1 or 2, in which the flexible link is provided with one or more thinned sections along its length, to form more flexible sections.

4. The screw closure of any preceding claim, in which the flexible link comprises a curve or bend along its length in the relaxed state.

5. The screw closure of any preceding claim, in which the flexible link comprises a bowed shape between its ends.

6. The screw closure of claim 5, in which the centre of the bowed shape faces away from the root end of the flexible anti-backoff pawl.

7. The screw closure of any preceding claim, in which the flexible link is joined to the flexible anti-backoff pawl at or near to the distal end thereof.

8. The screw closure of any preceding claim, in which the anti-backoff pawl is configured to act as a strut which resists buckling collapse as the closure is unscrewed.

9. The screw closure of any preceding claim, in which the flexible anti-backoff pawl is flexibly attached to the tamper indicating band.

10. The screw closure of any preceding claim, in which the flexible anti-backoff pawl comprises a thinned section at or near to its root end.

11. The screw closure of any preceding claim, in which the tamper indicating band is interrupted to form segments.

12. A screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; and a guard stop attached to the tamper-indicating band adjacent to the flexible antibackoff pawl and positioned to contact and support the flexible anti-backoff pawl so as to resist bending thereof driven by contact with the rack tooth as the closure is torqued in the unscrewing direction.

13. The screw closure of claim 12, in which the guard stop is thinner than the width of the tamper indicating band in the closure axial direction and positioned adjacent to the upper edge of the tamper indicating band; or in which the guard stop is thinner than the width of the tamper indicating band in the closure radial direction and positioned adjacent to the inner or outer edge of the tamper indicating band.

14. A screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; a flexible anti-backoff pawl having: a root end attached to the tamper-indicating band, and a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the band and container in the closure screwing-on or -in direction and so as to resist relative rotation between the band and container in the closure unscrewing direction; wherein the distal end of the flexible anti-backoff pawl has an enlarged cross-section whereby it is stiffened to resist bending.

15. The screw closure of claim 14, in which the flexible anti-backoff pawl progressively increases in cross-sectional thickness along its length from the root end towards the distal end.

16. The screw closure of claim 14 or 15, in which the flexible anti-backoff pawl is flexibly attached to the tamper indicating band.

17. The screw closure of claim 14, 15 or 16, in which the flexible anti-backoff pawl comprises a thinned section, at or near to its root end.

18. The screw closure of claim 14, 15, 16 or 17, in which the distal end of the flexible anti-backoff pawl comprises a first, substantially flat face configured for substantially face-to-face engagement with a generally radially extending or generally vertically extending face of the rack tooth on the container.

19. The screw closure of claiml8, in which the distal end of the flexible anti-backoff pawl comprises a second face for engagement with the container adjacent to the rack tooth.

20. The screw closure of any of claims 14-19 and any of claims 1-11.

21. A screw closure for a container, the screw closure comprising: a tamper indicating band; a frangible link connecting the band to the remainder of the screw closure; and a flexible anti-backoff pawl attached to the tamper indicating band; wherein the screw closure further comprises a cover overlying at least a part of the outer circumference of the tamper indicating band.

22. The screw closure of claim 21, in which the cover leaves at least one section of the tamper indicating band exposed and visible.

23. The screw closure of claim 21 or 22, in which the cover comprises one or more sections.

24. The screw closure of claim 23, in which the or each section stands out radially from the tamper indicating band to an extent that at least 50% of the band lies between tangents to the band and the outer portion of the envelope of the or each cover section.

25. The screw closure of claim 23, in which a plurality of cover sections are spaced around the band circumference and stand out radially from the band to a distance at which tangents to the outer envelopes of adjacent cover sections do not intersect the tamper indicating band.

26. The screw closure of any of claims 20-25 and any of claims 1-18.