Container closure overcap

Abstract

A molded plastics overcap (10) for a container closure comprises a top wall (12), a generally annular side wall (14) depending from the top wall, and a retention skirt (16) foldably attached to a rim of the side wall. The retention skirt is foldable between a first position in which it extends from the side wall away from the top wall, to an operative position in which it extends within the side wall towards the top wall. The retention skirt comprises a retention boss (20) which, when the retention skirt is in the operative position, extends radially inward and provides an engagement surface facing the top wall so as to be engageable beneath a closure flange retaining curl to retain the overcap thereon. An outer ring (42) is attached to side wall by frangible bridges (36) and is permanently connected to the top wall by a bridging piece (44). A gap (38) or line of weakness in the side wall surrounds the bridging piece at its sides and bottom to isolate the bridging piece from the remainder of the side wall and the retention skirt. The gap or line of weakness is contiguous with and merges into lines of weakness (38c1, 38d′) which define edges of a tear-out portion of the overcap top wall.

Description

FIELD OF THE INVENTION

[0001] The present invention concerns molded plastics overcaps for container closures.BACKGROUND OF THE INVENTION

[0002] Such overcaps are typically used to provide a degree of tamper resistance and physical protection for a container closure, such as a closure plug for a “200-litre” (“55 U.S. gallon”) steel drum or similarly sized industrial container. The overcap may for example restrict access to the plug extraction features and shield the plug against dirt and water ingress. The overcap may be designed to be broken upon removal, whereby the presence of an undamaged overcap provides some assurance that the container contents have not been interfered with in the supply chain.

[0003] Current polymer tamper evident overcaps used to protect the contents of steel drums rely on an internally projecting annular retention boss engageable beneath the drum closure flange retaining curl. Historically polymer tamper evident overcaps have been designed with a retention boss geometry that allows the overcap to be injection molded and then removed from the mold by being stripped away from the core tooling. To facilitate removal from the injection mold tooling the retention boss has a ramp angle that enables the overcap to expand out of the internal retention boss undercut in the core tooling without permanent deformation. See U.S. Pat. Nos. 7,080,749B2, 7,568,585B2, WO2005 / 056412A1 and USD963,811S1 for example. However, this angled retention feature also allows a determined individual a relatively easy means of prying the overcap off the drum opening and therefore affords minimal tamper evidence. With this design the contents of the drum may be compromised by an individual with ill intent. The large variability in nominally standard flange curl geometries among different manufacturers exacerbates the problem. The retention boss internal diameter is made to accommodate the largest flange curl dimensions (prevalent e.g. in the U.S.), which means in practice that the overcap will often be a relatively loose fit in other markets (e.g. in Asia, where flange curl dimensions tend to be on the smaller side).

[0004] U.S. Pat. No. 7,222,741 B2 concerns a tamper evident cover for engaging a container cap or drum bung, which cover has a plurality of locking teeth that snap under and engage a lip of the container cap. A frangible strip permits severing the cover to facilitate its removal, and a series of locking teeth extend from and bear against the outer periphery of the container cap to prevent any forcible removal of the cover without substantial damage or destruction.SUMMARY OF THE INVENTION

[0005] The present invention provides a molded plastics overcap for a container closure, the overcap comprising a top wall, a generally annular side wall depending from the top wall, and a retention skirt foldably attached to a rim of the side wall, whereby the retention skirt is foldable between a first position in which it extends from the side wall away from the top wall, to an operative position in which it extends within the side wall towards the top wall; the retention skirt comprising a retention boss which, when the retention skirt is in the operative position, extends radially inward and provides an engagement surface facing the top wall and engageable beneath a closure flange retaining curl or similar radially outwardly projecting part of the container (“retaining projection”) to retain the overcap thereon; the overcap further comprising an outer ring attached to side wall by frangible bridges; wherein the outer ring is permanently connected to the top wall by a bridging piece; a gap or a line of weakness (for example a membranous web) in the side wall surrounds the bridging piece at its sides and bottom to isolate the bridging piece from the remainder of the side wall and the retention skirt; and the gap or line of weakness in the side wall is contiguous with and merges into lines of weakness which define edges of a tear-out portion of the overcap top wall. The overcap may therefore be snapped onto the retaining projection of a container, over the container opening and any container closure received therein, with the retention skirt in the operative position. The engagement surface of the overcap's retention boss will then engage beneath the retaining projection. In contrast to the prior art, when the retention skirt is in the operative position, the engagement surface of the overcap's retention boss need not be angled away from the top wall in the radially inward direction, because the retention skirt may be configured to escape mold core tooling when in the first position. This may therefore be adopted as the as-molded position of the retention skirt. On the other hand, the retention boss need not slope radially inward away from the overcap top surface when the retention skirt is in the operative position, which means that the overcap will be firmly engageable beneath the retaining projection, and much more resistant to prying off the container opening. The radial extent of the engagement surface of the overcap's retention boss may also be larger than in the prior art, reducing the problem of loose-fitting overcaps. Because the engagement surface of the overcap's retention boss is thus improved, the cross-sectional areas of the retention boss and / or of the overcap side wall transverse to the hoop direction may be reduced in comparison to the prior art. This not only may lead to significant materials savings (e.g. of the order of 13%), but also may mean that the side wall and / or retention boss are circumferentially “stretchier”. Therefore they can be made to a smaller internal diameter that will closely hug and firmly engage “undersized” container flange retaining curls (or other retaining projections), and yet still can be snap-fitted to “oversized” flange curls etc. with acceptably low press-on forces.

[0006] The lines of weakness defining the tear-out portion of the overcap top wall may comprise a pair of parallel grooves molded into an inner face of the top wall to define edges of a tear strip. The grooves may terminate in the overcap top wall close to its junction with the side wall, diametrically opposite to the bridging piece. The gap or lines of weakness in the side wall may extend into the retention skirt, for example through the retention boss.

[0007] The engagement surface of the retention boss may comprise a hooked profile whereby in the operative position for engagement beneath the retaining projection, a radially inner portion of the engagement surface is closer to the overcap top wall than a radially outer portion thereof. Then an attempt to pry the overcap off the container opening will tend to draw the retention skirt into tighter engagement in the angle between the closure flange retaining curl and the neck of the container opening. Thus the pry-off attempt will be strongly resisted, making it extremely difficult to remove the overcap without leaving visible damage.

[0008] The retention skirt may comprise a locking projection which, when the retention skirt is in the operative position, projects towards the overcap's top wall between the overcap's side wall and the container's retaining projection. If an attempt is then made to pry the overcap off the retaining projection, this will tend to rotate the retention skirt towards its first position extending from the sidewall away from the top wall. However, such rotation is blocked by engagement of the locking projection with the retaining projection, which lies radially inward of the locking projection.

[0009] The retention boss may be formed as further projection extending radially inward and upward towards the overcap's top wall, inward of the locking projection when the retention skirt is in the operative position. The retention skirt including the locking projection and the further projection may therefore comprise a bifurcated or generally Y-shaped or generally V-shaped cross-sectional profile, with the base of the fork, Y or V corresponding to the foldable attachment to the rim of the side wall. An attempt to prise off the overcap to gain access to a container closure which it covers, will therefore cause the further projection to flex downward and inward, constricting about the container neck. The overcap will thereby tightly grip the container in the angle beneath its retaining projection, making the overcap very resistant to pry-off attempts. In this condition, total eversion of the further projection and remainder of the retention skirt back into the first position will be strongly resisted not only by the radial interengagement between the overcap's locking projection (if present) and the conainer's retaining projection, but also by the above-described constriction and tight grip of the further projection in the angle beneath the container's retaining projection.

[0010] For ease of removal from the mold core, the retention boss when the retention skirt is in its first position may comprise an inwardly-facing surface which tapers relatively gently inward in the direction away from the overcap top wall, is substantially cylindrical, and / or which flares outward in the direction away from the overcap top wall. For example, when the retention skirt is in its first position, the retention boss may comprise a generally frustoconical inwardly-facing surface sloping inward in the direction away from the overcap top wall at an angle to a central axis of the overcap of less than 45 degrees, for example at an angle to this central axis of 20-25 degrees, optionally about 23 degrees.

[0011] For ease of application of the overcap to the container closure, when the retention skirt is in the operative position, the retention boss may comprise an inwardly-facing surface which tapers relatively gently outward in the direction away from the overcap top wall. For example, when the retention skirt is in the operative position, the retention boss may comprise a generally frustoconical inwardly-facing surface sloping outward away from the overcap top wall at an angle to the central axis of the overcap of less than 30 degrees, for example at an angle to this central axis of 20-25 degrees, optionally about 23 degrees. This may again serve to reduce the required cap press-on force, or keep it to an acceptably low level when adopting a tighter fitting overcap design as regards the variance in nominally standard neck curl diameters or in other retaining projections of containers present in the marketplace. This measure may be applied together with or independently of a smaller overcap sidewall and / or retaining boss cross-section transverse to the hoop direction, as previously discussed.

[0012] The overcap comprises frangible features which break to allow tamper evident removal of the overcap from the container opening. The improved effectiveness of the retention boss means that higher pull-off forces can be generated before the overcap is unseated from the container closure. This allows the frangible features to be more robust and therefore less prone to accidental damage in the supply chain and hence less prone to giving false positive tamper indications.

[0013] The outer ring may be configured such that it is positionable closely adjacent to a surface of the container (e.g. the upper surface of a flange pocket in a drum head) when the overcap is seated on the container closure. Pry-off tools inserted beneath the overcap side wall are therefore also likely to lever up the outer ring and break one or more of the frangible bridges. When the end user desires to access the container contents for the first time, the frangible bridges can be deliberately broken, whereby the outer ring and permanent connection may then serve as a convenient handle for pulling the overcap off the container closure. The rim of the overcap side wall may be axially recessed within the outer ring, thereby making it less accessible to pry-off tools, without also disturbing the outer ring.

[0014] The invention and some of its optional features and advantages is further explained below with reference to illustrative embodiments shown in the drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 is a three-quarter perspective view from the top, rear and one side of an illustrative overcap embodying the present invention;

[0016] FIG. 2 is a top plan view of the overcap of FIG. 1;

[0017] FIG. 3 is a bottom plan view of the overcap of FIGS. 1 and 2, showing the retention skirt in the first position, extending outward from the cap, toward the viewer;

[0018] FIG. 4 is a view on arrow xxiv in FIG. 2, with the retention skirt in the first position;

[0019] FIG. 5 is a cross-sectional view taken on line XXXV-XXXV in FIG. 2, with the retention skirt shown in the first position;

[0020] FIG. 5a is a view drawn to an enlarged scale, of a portion of FIG. 5 shown circled in dotted lines;

[0021] FIG. 6 is a cross-sectional view taken on line XXXVI-XXXVI in FIG. 2, with the retention skirt shown in the first position;

[0022] FIG. 6a is a view drawn to an enlarged scale, of a portion of FIG. 6 shown circled in dotted lines;

[0023] FIG. 7 is a cross-sectional view taken on line XXXVI in FIG. 3;

[0024] FIG. 8 is a half-section on a radial plane, showing the overcap of FIGS. 1-7 in operative position, lockingly engaged with a container neck, across a container access opening;

[0025] FIG. 8a is a view drawn to an enlarged scale, of a portion of FIG. 8 shown circled in dotted lines, and

[0026] FIG. 9 is a partial radial cross-sectional view of another illustrative overcap embodying the present invention.DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0027] FIGS. 1-8a show an illustrative overcap 10 embodying the present invention. The overcap 10 may be injection molded from a suitable plastics material, such as PCR resin. It may be made in a relatively small size in the context of industrial-sized containers. For example, the overcaps shown in FIGS. 1-8a may be suitable for protecting an industry standard G¾ closure plug or the like, and corresponding container openings. The overcap 10 of FIGS. 31-38a may comprise a top wall 12, a generally annular side wall 14, a retention skirt 16 foldably attached to a rim 18 of the side wall 14, an outer ring 42, frangible bridges 36 and a pull tab 54. The retention skirt 16 may be evertably foldable about its annular line of attachment at the rim 18, between a first position (FIGS. 3-7) in which it extends from the side wall 14 away from the top wall 12, to an operative position (FIGS. 8 and 8a) in which it extends generally co-axially within and next to the side wall 14, towards the top wall 12. The retention skirt 16 may be configured so that in the operative position its outer surface lies closely adjacent to (e.g. in face-to-face contact with) the interior surface of the side wall 14. The retention skirt 16 may therefore be stably circumferentially supported in the operative position by the surrounding side wall 14.

[0028] The retention skirt 16 comprises a retention boss 20 (FIG. 5a). When the retention skirt 16 is in the operative position, the retention boss 20 is configured to extend radially inward to provide an engagement surface facing the overcap top wall 12. In this position, the engagement surface is engageable beneath retaining curl 24 of a container closure flange (not shown) or a similarly radially outwardly projecting part (24a, FIGS. 8 and 8a) of a container, container neck or container access opening, to retain the overcap 10 thereon. The retention skirt 16 may further comprise a locking projection 28 which projects towards the top wall 12 radially outward of the retention boss 20, when the retention skirt 16 is in the operative position within the side wall.

[0029] The overcap 10 may therefore be snapped onto the container, with the retention skirt 16 in the operative position. The overcap's retention boss 20 will then engage beneath the radially outwardly projecting part 24a of the container, container neck or container access opening, and the locking projection 28 (where present) will project towards the overcap's top wall 12 between the overcap's side wall 14 and the container's radially outwardly projecting part 24a. If an attempt is then made to pry off the overcap 10, this will tend to rotate the retention skirt 16 about the rim connection 18, towards the first position (FIGS. 3-7) in which the retention skirt 16 extends from the sidewall 14 away from the top wall 12. However, such rotation is blocked by engagement of the locking projection 28 with the container's radially outwardly projecting part 24a, which lies radially inward of the locking projection 28.

[0030] In contrast to the prior art, when the retention skirt 16 is in the operative position (FIGS. 8 and 8a), the engagement surface of the overcap's retention boss 20 need not be angled away from the top wall 12 in the radially inward direction, because the retention skirt 16 may be configured to escape mold core tooling when in the first position (FIGS. 3-7). Absence of a slope to the retention boss 20 radially inward away from the overcap top wall 12 when the retention skirt 16 is in the operative position (FIGS. 8 and 8a) on the other hand means that the overcap 10 will be firmly engageable beneath the container's radially outwardly projecting part 24a, and much more resistant to prying off the container opening. The radial extent of the overcap's retention boss 20 may also be larger than in the prior art, reducing the problem of loose-fitting overcaps. Because the retention boss 20 is thus improved, the cross-sectional areas of the retention boss 20 and / or of the overcap side wall 14 transverse to the hoop direction may be reduced in comparison to the prior art, providing concomitant advantages in materials usage and technical performance as previously mentioned.

[0031] FIGS. 3-7 show the retention skirt 16 in its first position in which it extends from the side wall 14 away from the overcap top wall 12. FIGS. 8 and 8a show the retention skirt 16 in its operative position in which it has been folded upwardly and inwardly inside the side wall 14, so that the locking projection 28 of the retention skirt 16 lies adjacent to the inner surface of the side wall 14, and the retention boss 20 extends radially inward. The retention boss 20 may be formed as further projection extending inward of the locking projection 28 radially inward and upward towards the overcap's top wall 12, when the retention skirt 16 is in the operative position. The retention skirt 16 may therefore have a bifurcated Y- or V-shaped cross-sectional profile, with the base of the Y or V being attached to the lower rim of the side wall 14 at the fold line 18. The locking projection 28 forms one limb of the bifurcated cross-sectional profile of the retention skirt 26, and the retention boss 20 forms the other limb of this bifurcated cross-sectional profile. The retention boss limb 20 may be somewhat shorter than the locking projection limb 28.

[0032] FIGS. 8 and 8a show the overcap 10 snap-fitted onto a venting neck profile 68 of a large blow-molded plastics container 70. The venting neck profile 68 has an upper rim zone 72 adapted to receive the head and sealing gasket of a threaded closure plug (not shown). The outer circumference of the upper rim zone 72 may be provided with the annular, radially outwardly extending retaining projection 24a. When the overcap 10 is snap-fitted into place over the venting neck profile 68, the retention boss limb 20 flexes and stretches to pass over and then lodge beneath the retaining projection 24a. The radially inner surface of the retention boss limb 20 forms a tapered ramp surface which, together with the flexibility of the retention boss limb 20, helps to minimise the axial force required to snap the overcap 10 into this position. The distal tip portion of the retention boss limb 20 forms the engagement surface which engages beneath the retaining projection 24a, in the angle between the retaining projection 24a and the adjacent outer surface of the upper rim zone 72. The retention boss limb 20 can thereby act like a barb. Attempts to pull or pry the overcap 10 off the venting neck profile 68 will rotate the retention boss limb 20 downwardly and inwardly about the fold line 18, constricting the engagement surface at its distal tip against the outer circumference of upper rim zone 72, in the angle beneath the retaining projection 24a. The applied pulling or prying forces therefore are strongly resisted and cause the overcap 10 to grip the venting neck profile 68 more tightly. Further downward and inward rotation of the retention skirt 16 is eventually limited as the locking projection limb 28 (if used) presses against the outer circumference of the retaining projection 24a. Eversion of the retaining skirt into the first position by full rotation about the fold line 18 is thereby resisted. The overcap 10 is thus firmly retained on the venting neck profile 68 and is highly resistant to pull-off or pry-off attempts.

[0033] In other embodiments, for example as shown in FIG. 9, the length of the retention boss limb may be reduced, or the retention boss 20 may be formed as part of the body of the retention skirt 16. The engagement surface of the retention boss 20 may comprise a hooked profile whereby in the operative position for engagement beneath the radially outwardly projecting part 24a of the container (FIGS. 8 and 8a), a radially inner portion 22a of the engagement surface is closer to the overcap top wall 12 than a radially outer portion 22b thereof. Then an attempt to pry the overcap off the container opening will tend to draw the retention skirt 16 into tighter engagement in the angle between the radially outwardly projecting part 24a and the remainder of the container neck profile 68. Thus the pry-off attempt will be strongly resisted, making it extremely difficult to remove the overcap 10 without leaving visible damage.

[0034] The overcap 10 may comprise an outer ring 42 attached to the side wall 14 by frangible bridges 36. The outer ring 42 may be configured such that it can be positioned closely adjacent to a surface 46 of the container (e.g. the upper surface of a flange pocket 48 in a drum head, when the overcap 10 is seated on the container closure. Pry-off tools inserted beneath the overcap side wall 14 are therefore also likely to lever up the outer ring42 and break one or more of the frangible bridges 36. When the end user desires to access the container contents for the first time, the frangible bridges 36 can be deliberately broken, whereby the outer ring 42 and permanent connection 44 may then serve as a convenient handle for pulling the overcap 10 off the container closure. The rim 18 of the overcap side wall 14 may be axially recessed within the outer ring 42 (see e.g. FIGS. 8, 8a and 9), thereby making it less accessible to pry-off tools, without also disturbing the outer ring 42.

[0035] For ease of removal from the mold core, the retention skirt 16 when in its first position (FIGS. 3-7) may comprise an inwardly-facing surface 32 which may taper relatively gently inward in the direction away from the overcap top wall 12, be substantially cylindrical (not shown), and / or flare outward in the direction away from the overcap top wall 12 (not shown). For example, the surface 32 when the retention skirt 16 is in its first position may be a generally frustoconical internal surface sloping inward in the direction away from the overcap top wall 12 at an angle to the central axis of the overcap 10 of less than 45 degrees, for example at an angle to this central axis of 20-25 degrees, optionally about 23 degrees. This shallower taper angle of the retention skirt allows it to escape from the undercut in the mold core tool under lower ejection forces than molded plastic overcaps of the prior art, and / or without excess ejection forces while providing a radially broader, and thus more effective, retention boss 20.

[0036] For ease of application of the overcap 10 to the container closure, and / or to provide other advantages as previously mentioned, when the retention skirt 16 is in the operative position (FIGS. 8, 8a, and 9), the retention boss 20 may be configured to provide an inwardly-facing surface 34 which tapers relatively gently outward in the direction away from the overcap top wall 12. For example, the internal surface 34 may be generally frustoconical, sloping outward away from the overcap top wall 12 at an angle to the central axis of the overcap 10 of less than 30 degrees, for example at an angle to this central axis of 20-25 degrees, optionally about 23 degrees.

[0037] The overcap 10 may comprise frangible features 36, 38, 38c′, 38d′, which break to allow tamper evident removal of the overcap 10 from the container opening. The improved effectiveness of the retention boss 20 means that higher pull-off forces can be generated before the overcap 10 is unseated from the container closure. This allows the frangible features to be more robust and therefore less prone to suffering accidental damage in the supply chain and hence less prone to providing false positive tamper indications.

[0038] The retention skirt 16 may comprise a frangible line of weakness. This line of weakness may lie adjacent to the permanent connection 44 e.g. being breakable to form a break in the circumference of the retention skirt 16 adjacent to the permanent connection 44. Additionally or alternatively, the retention skirt frangible line of weakness may extend to other parts of the retention skirt 16, e.g. around the foldable attachment 18 between the retention skirt 16 and the overcap's side wall 14, so as to disconnect the retention skirt 16 from the remainder of the overcap 10 when broken.

[0039] As best seen in FIGS. 3, 5, 5a, 6, and 6a, opposite to the pull tab 54, the outer ring 42 may be securely fixed to the overcap top wall 12 by a permanent connection in the form of a solid bridging piece 44. A generally U-shaped gap 38 (as shown) or a similarly shaped membranous web, or other line of weakess (not shown) in the side wall 14 may surround the bridging piece 44 at its sides and bottom, to isolate the bridging piece 44 from the side wall 14. The gap, line of weakness, or membranous web 38 may extend into the retention skirt 16 and through the retention boss 20, for example to leave only the locking projection 28 circumferentially intact.

[0040] The upper ends of the two limbs 38c, 38d of the U-shaped gap 38 or line of weakness in the side wall 14 (or the ends of the limbs of the corresponding U-shaped depression in the side wall 14 which defines the membranous web, where present) may be contiguous with and merge into a pair of parallel grooves 38c′, 38d′. The grooves 38c′, 38d′ are molded into the inner face of the top wall 12 to form lines of weakness which define edges of a tear strip 60. The tear strip 60 is isolated from the side wall 14 by the gap (or line of weakness or membranous web) 38 but has one end permanently secured to the outer ring 42 by the bridging piece 44. The opposite end of the grooves 38c′, 38d′ and hence also the tear strip 60 terminate in the overcap top wall 12 close to its junction with the side wall 14, diametrically opposite to the bridging piece 44. The outer ring 42 may be provided with a pull tab 54. With the overcap secured over a container opening to protect a container closure, pulling upwardly on the pull tab 54 can break the frangible bridges 36. The outer ring 42 remains attached to the tear strip 60 by the bridging piece 44. The outer ring 42 can then be used as a handle to tear out the tear strip 60 from the remainder of the overcap top wall 12 along the lines of weakness formed by the grooves 38c′, 38d′. The two parts of the cap 10a, 10b (FIG. 3) on either side of the tear strip 60, and the tear strip itself, will then remain connected together by a portion 14a of the cap side wall. But the cap parts 10a, 10b are free to pivot away from each other, because the top wall 12 and outer ring 42 no longer serve to hold the two parts of the side wall 14 together on either side of the gap 38. (Similarly, where a membranous web or line of weakness is used instead of the gap 38, the top wall 12 and outer ring 42 no longer serve to reinforce this, allowing it to rupture, and the two parts of the side wall on either side of it to move apart). A continued upward pull on the outer ring 42 will therefore dislodge the retention boss 20 from beneath the retaining projection 24a of the venting neck profile 68. The gap, line of weakness or membranous web 38 may make the retention boss 20 circumferentially discontinuous, allowing it to expand by movement together with the two pivotally separating cap parts 10a, 10b. The part 74 of the locking projection 28 which is not interrupted by the gap, line of weakness, or membranous web 38 is relatively weak, and may stretch or break to allow the required expansion of the retention boss 20.

Claims

1. A molded plastics overcap for a container closure, the overcap comprising a top wall, a generally annular side wall depending from the top wall, and a retention skirt foldably attached to a rim of the side wall, whereby the retention skirt is foldable between a first position in which it extends from the side wall away from the top wall, to an operative position in which it extends within the side wall towards the top wall; the retention skirt comprising a retention boss which, when the retention skirt is in the operative position, extends radially inward and provides an engagement surface facing the top wall and engageable beneath a retaining projection of the container to retain the overcap thereon; the ovecap further comprising an outer ring attached to side wall by frangible bridges; wherein the outer ring is permanently connected to the top wall by a bridging piece; a gap or line of weakness in the side wall surrounds the bridging piece at its sides and bottom to isolate the bridging piece from the remainder of the side wall and the retention skirt; and the gap or line of weakness in the side wall is contiguous with and merges into lines of weakness which define edges of a tear-out portion of the overcap top wall.

2. An overcap as claimed in claim 1, wherein the lines of weakness defining the tear-out portion of the overcap top wall comprise a pair of parallel grooves molded into an inner face of the overcap top wall to define edges of a tear strip.

3. An overcap as claimed in claim 2, wherein the grooves terminate in the overcap top wall close to its junction with the side wall, diametrically opposite to the bridging piece.

4. An overcap as claimed in any preceding claim, wherein the gap or line of weakness in the side wall extends into the retention skirt.

5. An overcap as claimed in claim 4, wherein the gap or line of weakness in the side wall extends through the retention boss.

6. An overcap as claimed in any preceding claim, wherein when the retention skirt is in the operative position, the engagement surface is not angled away from the top wall in the radially inward direction.

7. An overcap as claimed in any preceding claim, wherein the engagement surface comprises a hooked profile whereby in the operative position of the retention skirt, a radially inner portion of the engagement surface is closer to the overcap top wall than a radially outer portion thereof.

8. An overcap as claimed in any preceding claim, wherein the retention skirt further comprises a locking projection which projects towards the top wall radially outward of the engagement surface when the retention skirt is in the operative position within the side wall.

9. An overcap as claimed in claim 8, wherein the retention boss is formed as further projection extending radially inward and upward towards the top wall, inward of the locking projection when the retention skirt is in the operative position.

10. An overcap as claimed in claim 9, wherein the retention skirt comprises a bifurcated or generally Y-shaped or generally V-shaped cross-sectional profile, with the base of the fork, Y or V corresponding to the foldable attachment to the rim of the side wall.

11. An overcap as claimed in any preceding claim, wherein the retention boss when the retention skirt is in its first position comprises an inwardly-facing surface which tapers relatively gently inward in the direction away from the overcap top wall, is substantially cylindrical, and / or which flares outward in the direction away from the overcap top wall.

12. An overcap as claimed in any preceding claim, wherein the retention boss when the retention skirt is in its first position comprises a generally frustoconical internal surface sloping inward in the direction away from the overcap top wall at an angle to a central axis of the overcap of less than 45 degrees.

13. An overcap as claimed in any preceding claim, wherein the retention boss when the retention skirt is in its first position comprises a generally frustoconical inwardly-facing surface sloping inward in the direction away from the overcap top wall at an angle to a central axis of the overcap of 20-25 degrees, optionally about 23 degrees.

14. An overcap as claimed in any preceding claim, wherein when the retention skirt is in the operative position, the retention boss comprises an inwardly-facing surface which tapers gently outward in the direction away from the overcap top wall.

15. An overcap as claimed in any preceding claim, wherein when the retention skirt is in the operative position, the retention boss comprises a generally frustoconical inwardly-facing surface sloping outward away from the overcap top wall at an angle to the central axis of the overcap of less than 30 degrees.

16. An overcap as claimed in any preceding claim, wherein when the retention skirt is in the operative position, the retention boss comprises a generally frustoconical inwardly-facing surface sloping outward away from the overcap top wall at an angle to the central axis of the overcap of 20-25 degrees, optionally about 20 degrees.

17. An overcap as claimed in any preceding claim, wherein the outer ring is configured such that it is positionable closely adjacent to a surface of the container when the overcap is seated on the container closure.

18. An overcap as claimed in claim 17 wherein the rim of the overcap side wall is axially recessed within the outer ring.

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