CLOSURE Technical Field

[0001] This invention relates to a closure in the form of an annular component that defines an aperture, the aperture closed by a membrane of peelable lidding material. The lidding material has a tab for removal of the lidding material. In one aspect, the closure is adapted to reduce the risk of damage to the tab during handling or processing. In another aspect, the closure is adapted to provide improved peelability.

Background Art

[0002] WO 2004/014758 A (CROWN CORK) 19.02.2004 describes a peelable closure suitable for food cans. This closure is a can end in the form of an annular metal ring defining an aperture, to which is sealed a membrane of peelable lidding material. The lidding material has a cover portion and an integral tab extending from the periphery of the cover portion. The cover portion is sealed to a sealing surface provided on the can end to define a continuous annular seal about the aperture. Outward of the seal, the can end has a chuck wall extending first upwardly and then outwardly to provide a seaming panel. The seaming panel allows the closure to be attached to a container body by a conventional seaming operation. The full length of the tab is folded back over the cover portion and secured in a folded position on the cover portion. Securing the tab in a folded position is intended to minimise the risk of the tab becoming disturbed and damaged during subsequent processing and/or handling operations; for example, by disturbance from jets of water, steam or air during retort processing. As discussed in WO 2004/014758A, adhesive or heat sealing may be used to secure the tab to the cover portion. However, the use of adhesive/heat sealing to separately secure the folded tab is potentially messy. Further, it requires an additional manufacturing operation to that required to seal the cover portion to the can end, thereby increasing the complexity and cost of manufacture of the closure.

[0003] Alternatively, folding the full length of the tab of WO 2004/014758A without securing it against the cover portion has been found to leave the tab vulnerable to being disturbed during processing and handling. During retort processing, jets of water, steam or air have been found to get between the folded tab and the cover portion, thereby tending to distort the tab upwards. A distorted tab is vulnerable to further damage during subsequent handling operations, thereby making it more difficult or impossible to peelably remove the lidding material.

[0004] It is a first object of the present invention to provide an improved peelable closure having a membrane of peelable lidding material and a tab for removal of the lidding material, the tab being less vulnerable to damage during subsequent processing and/or handling operations.

[0005] A further problem with known peelable closures is that the requirement of peelability can limit the aperture size, seal width and intended application(s) for the closure. These limitations are explained below for a typical peelable closure, such as that described in WO 2004/014758A.

[0006] In use, the tab would first be lifted and then pulled along its longitudinal axis (i.e. the "pull" axis) to detach the lidding material from the can end. It has been found that a high force is required to initiate and propagate peeling when the radial inner and outer edges of the continuous annular seal under and on either side of the "pull axis" extend generally linearly and perpendicular to that axis. This is because this seal configuration results in a high effective length resisting peeling, the required peel force peaking where the effective seal length is greatest. "Initiation" of peeling (or "peel initiation") is defined as when peeling first breaks through to the radial inner edge of the seal.

[0007] The effects of seal profile and seal width upon peel initiation force are best illustrated in figures 1 , 2 & 3, with reference also to figures 9, 10 & 10a, b for clarity. Each figure is a plan view of part of a closure and shows a portion of a seal or bond (13) between a membrane of peelable lidding material (10) and a can end. The periphery of the lidding material (10) is shown in these figures as a solid line, as is the outline of an integral tab (12). The tab's "pull" axis (15) is also indicated. Figure 1 shows a seal (13) having edges extending linearly and perpendicular to the pull axis (15), defining a seal width w _s1 . Figures 2 and 3 show part of a circular annular seal (13), only differing in that the seal width of figure 3 is wider than that of figure 2, i.e. w _s3 > w _s2 . For the purpose of the present invention, the "chord" of the seal is defined as that (or those) portion(s) of a line perpendicular to the "pull" axis and extending through the area of the seal. The chord length at the location of where peel initiation occurs provides a measure of the peel initiation force: the greater the chord length, the greater the peel initiation force (all other factors being equal). The chord length at the peel initiation location is marked up as c _m1 , c _ιn2 and c _m3 for figures 1 , 2 & 3 respectively.

[0008] Figure 1 , with its linear edged seal, corresponds to the extreme theoretical case of an infinite chord length (c, _n i), for which the peel initiation force would be highest. It also closely resembles the situation of having a seal (13) with a very large radius of curvature. The seal profile of figure 1 with its high peel initiation force will result in tab damage (e.g. tearing) when pulling back on the tab, sometimes resulting in the tab being torn off before any peeling has commenced. Figures 2 & 3 with their circular annular seals, have a much reduced chord length (c _ιn2 , c _m3 ) at the peel initiation location and therefore have a reduced peel initiation force relative to figure 1. However, comparing figures 2 & 3, it can clearly be seen that increasing the seal width w _s whilst keeping the other parameters unchanged results in an increase in chord length at the peel initiation location, and thereby a higher effective seal length resisting peel initiation. This is obviously undesirable.

[0009] There is also a problem with the openability of peelable closures intended for "in-can pressure" applications, i.e. for cans subject to a positive internal pressure. In the context of can ends for food packaging, positive internal pressure may arise, for example, during retort processing due to expansion of both the can contents and any headspace gases. Inside some retorts, there is insufficient pressure balancing outside of the can to compensate for the expansion of the can contents/headspace gases during the heating cycle. Therefore, any pressure increase within the can has to be resisted by the seal between the can end and the lidding material. Consequently, for in-can pressure applications, the seal between the can end and the lidding material has to be particularly strong to prevent the seal rupturing. A strong seal is conventionally achieved by using one or more of i) materials that form a strong bond between the can end and the lidding material; ii) a wider seal (w _s ); and/or iii) an inclined sealing surface. As described in EP 0683110 B (METALBOX PLC) 22.11.1995 and WO 2005/005277 A (CROWN PACKAGING TECHNOLOGY, INC) 20.01.2005 , an inclined sealing surface helps to ensure that on expansion of the peelable lidding material into a domed profile (due to expansion of can contents/headspace gases during processing), the seal is predominantly loaded in shear rather than in peel and is therefore better able to resist in-can pressurisation. However, options (ii) and (iii) each increase the peel force required to remove the peelable lidding material from the can end. In particular, the peel force required can be so great that the tab may be torn from the lidding material during peeling.

[0010] It is therefore a second object of the present invention to provide a more easily peelable closure which may, for example, be particularly suitable for i) large apertures and/or ii) positive internal pressure applications.

Disclosure of Invention

[0011] To satisfy the first object of the present invention, there is provided a closure for a container, the closure comprising an annular component, the annular component defining an aperture and provided with an upwardly extending annular wall radially-outward of the aperture and a panel extending generally laterally between the aperture and the wall, the closure further comprising a membrane of peelable lidding material, the membrane having a cover portion and a tab extending from the periphery of the cover portion, the cover portion sealed to a sealing surface of the annular component to provide a continuous annular seal about the aperture, characterised in that: the tab is arranged to be fold-free in whole or part, thereby having at least a fold-free portion which extends radially-outwardly from the periphery of the cover portion against the panel. [0012] When referring to the "length" of a tab, the "length" is defined as the total combined length of the fold-free portion and (if applicable) any folded portion.

[0013] By "fold-free" is meant being free of any fold, even if the tab did at some earlier point in its life contain a fold.

[0014] By "free edge" of the tab is meant the free edge which extends generally perpendicular to the tab's longitudinal axis.

[0015] Locating the free edge of the tab in the proximity of the upwardly extending wall results in the wall shielding the free edge of the tab from impact damage during processing or handling operations. An advantage of the tab being fold-free in whole or part is that for the closure of the present invention, the free edge of the tab may be positioned closer to the upwardly extending annular wall than the free edge of a fully-folded tab of the same length. Preferably, the free edge of the tab extends to within a lateral distance of 10 mm from the upwardly extending wall. More preferably the free edge of the tab extends to within a lateral distance of 5 mm from the upwardly extending wall.

[0016] Conveniently, the lateral distance between the free edge of the tab and the upwardly extending wall is less than the height of the uppermost part of the annular component measured relative to the panel.

[0017] In contrast, where a tab of the same length is folded over its entire length back over the lidding material (as in WO 2004/014758A), the free edge of the tab is at its maximum distance away from the wall of the can end and therefore exposed and vulnerable to impact damage (for example, from jets of steam, air or water during processing).

[0018] In the context of the present invention, the term "annular component" applies to both: i. where the lidding material is attached to an intermediate component (e.g. a can end incorporating the aperture), the intermediate component being fastenable to the open end of a container body. In this case, the intermediate component is the "annular component"; and ii. where the lidding material is attached directly to the sidewall of a container body (for example, as described in WO 2006/092364 A (CROWN PACKAGING TECHNOLOGY, INC ) 08.09.2006 ). In this case, the sidewall of the can body is the "annular component".

[0019] In the case of an entirely fold-free tab, the "fold-free portion" is the full length of the tab, i.e. there is no folded portion. The use of an entirely fold-free tab avoids having to fold the tab at all and therefore allows the use of a peelable lidding material without an inherent deadfold characteristic. In its simplest form, the entire length (l _tab ) of the fold-free tab would be laid flat against the surface of the panel outward of the aperture. This would allow the free edge of the tab to be located very close to the upwardly extending annular wall, thereby providing optimal shielding of the free edge of the tab from disturbance during processing and/or handling operations. It has been found beneficial for the free edge of the tab to be located less than 2 mm away from the upwardly extending wall.

[0020] The alternative case of a part-folded tab (i.e. having both folded and fold-free portions) enables the use of a larger aperture (as a proportion of the closure area) than where the same tab is entirely fold-free, because less room is required on the panel for location of the tab. Therefore, for a closure of a given nominal diameter, a part-folded tab allows the use of a larger aperture (and smaller panel) than when having an entirely fold-free tab configuration. The folded portion may comprise a plurality of folds extending back and forth over the fold-free in a concertina-like manner. Where more than one fold is present, it is preferred that there is an even number of folds because this enables the free edge of the tab to locate close to and benefit from the shielding effect of the upwardly extending annular wall. Most preferably, the folded portion is folded back over the fold-free portion of the tab as a single layer. A single layer folded portion has the advantage of minimising the distance that the tab's folded portion protrudes above the surface of the panel of the annular component, thereby reducing the likelihood of damage from impacts during processing/handling. In use, a consumer would first engage their fingers with the folded portion of the part-folded tab at the tab's free edge and pull to separate the full length of the tab from the surface of the panel of the annular component. To enable a consumer to engage their fingers with the folded portion of the tab, it has been found beneficial for the distance from the free edge of the tab to i) the single fold line (for a single layer fold), or ii) the nearest adjacent fold line (for a tab having a plurality of folds), to be at least 5 mm.

In a second step, the consumer would then grasp the full length (l _tab ) of the tab to better allow the lidding material to be peelably removed from the annular component.

[0021] Dependent on the deadfold limitations of the lidding material, even where the tab incorporates a fold it may still be inclined relative to the underlying lidding material. Further, the folded portion may become (further) inclined due to disturbance during handling after folding of the tab. Figures 4a & 4b each show a lidding material bonded to a can end (2), the lidding material having a cover portion (11) and an integral folded tab (12) of a given length, the tab subjected to a lateral force component F _L from a jet of water, steam or air during retort processing. The can end (2) is adapted to be seamed to a can body, having an annular chuck wall (4) which extends upwardly and outwardly to define a seaming panel (5). The integral tab (12) is shown as a solid line, whereas the cover portion (11) from which it extends is shown as a dashed line. The figures differ in that for figure 4a (the present invention) the tab (12) incorporates a part-fold, whereas for figure 4b (the prior art) the tab is folded back along its full length.

[0022] An advantage of the part-folded tab of the present invention (figure 4a) over the fully-folded tab of the prior art (figure 4b) is that where the tab (12) is or becomes inclined (relative to the underlying lidding material) by a given angle α, any lateral force F _L applied to the free edge (12a) of the tab would have a reduced bending moment on the tab compared to a fully-folded tab of the same length inclined at the same angle. This is because the part-fold reduces the moment arm 'd' (i.e. the height between the free edge (12a) of the tab (12) and the exterior surface of the underlying lidding material) and consequently the turning effect of any lateral force on the free edge of the tab. Further, to protrude above the chuck wall (4) of the can end (2) and therefore be at higher risk of damage, the part-folded tab would need to be deflected by a greater angle than its fully-folded equivalent. Consequently, relative to a fully-folded tab of the same length, the part-folded tab of the present invention is better able to withstand the effects of jets of water/steam/air during retort processing, and is therefore less vulnerable to damage.

[0023] Additionally, with a part-folded tab it is possible for the free edge (12a) of the tab (12) to be positioned closer to the chuck wall (4) of the can end (2) than the free edge of a fully-folded tab of the same length. Consequently, as for the entirely fold-free tab, the "wall" provides a degree of shielding to the tab, thereby reducing the risk of the tab becoming snagged and damaged during subsequent processing and handling.

[0024] Conveniently, the continuous annular seal extends under the fold-free portion of the tab, to thereby also bond all or part of the fold-free portion to the panel. This provides the dual advantages of ensuring that a common sealing area both: i) establishes a hermetic seal between the lidding material and the annular component; and ii) secures the fold-free portion of the tab to the panel to reduce the risk of tab disturbance during subsequent handling operations.

[0025] In contrast with the separate manufacturing step required for the fully-folded tab of WO 2004/014758, the above seal configuration allows the use of a single common manufacturing operation to both form the hermetic seal (see (i) above) and secure the fold-free tab portion against subsequent tab disturbance (see (ii) above).

[0026] Alternatively, a separate discrete seal region may be used to bond all or part of the fold-free portion of the tab to the panel.

[0027] Use of a common manufacturing operation to cover & seal the aperture and secure the tab may be enabled by providing the lower surface of the lidding material (both the cover portion and tab) with a heat sealable coating.

[0028] Where an entirely fold-free tab configuration is used, it is important for at least part of the underside of the tab to remain unadhered to the panel so that a consumer can engage their fingers with the underside of the tab.

[0029] Preferably, the continuous annular seal has a tongue-shaped region extending under the fold-free portion of the tab and centred either on, or within a distance of half the tab's base width (w _tbase ) from the tab's longitudinal axis. For the purpose of the present invention, the tab's "base width" (designated w _tbase ) is the width of the tab measured at the location where it joins the cover portion of the lidding material. w _tbase is indicated on figures 1-3, 9, 10 & 13. Such a tongue-shaped region has been found to act as a natural and space-efficient stress-raising feature, and to assist in minimising the chord length at the peel initiation location (see figure 10).

[0030] The tongue-shaped region may consist of the radial outer edge of the continuous annular seal being generally triangular in configuration, having two linear or curved portions converging to a point or apex (see figures 9 & 10). Alternatively, rather than an apex, the peak of the tongue may have a tightly curved profile (see figure 10a, b).

[0031] Minimising the chord length at the peel initiation location and thereby the peel force is best achieved by correspondingly profiling the radial inner and outer edges of the continuous annular seal in the tongue-shaped region (see figures 9, 10 & 10b) so that each edge defines a tongue shape. This has the benefit of removing a portion of the seal that would otherwise increase both the chord length and thereby the required peel initiation force. Additionally, this feature also permits the use of a wider seal width w _s , with negligible increase in peel force required to initiate peelable removal of the lidding material.

[0032] Conventional polypropylene-based coatings have been found suitable as coating materials for the corresponding surfaces of the lidding material and the annular component due to their heat-sealability.

[0033] The annular component and its aperture must be shaped to provide a panel of adequate size to allow the fold-free portion of the tab to be located against the panel. However, the size and shape of aperture may be dependent on the nature of the product to be stored in the can. This will, in turn, determine whether a wholly fold-free or part-folded tab configuration is used. For certain products, it will be desirable to maximise the area of the aperture (as a proportion of the closure area) to avoid impeding the release of product from the container; for example, when the product contains chunks of material (for example, portions of fruit) or viscous materials (for example, treacle).

[0034] The annular component may be formed of any metal suitable for conventional forming/shaping operations. The invention is equally suitable for use with annular components that are either round or non-round in shape.

[0035] Conveniently, the annular component is a can end, with the wall provided by a chuck wall of a seaming panel, the seaming panel enabling the can end to be seamed onto a can body. Conventional seaming technology may be used to attach the can end to a can body. The seaming operation would typically occur after sealing of the peelable lidding material to the can end, with conventional double seaming technology being particularly suitable.

[0036] The peelable lidding material may be any conventional flexible multi-layered structure. Typically, the peelable lidding material comprises a metal foil substrate layer for strength (for example, of aluminium), with a layer of heat sealable material (for example, a polypropylene-based material) on its inward facing surface to enable bonding of the lidding material to the annular component. The foil substrate layer provides strength and a gas-tight and light-tight barrier. Optionally, there may also be a further layer of a polymer material (for example, a layer of polyethylene terephthalate (PET) or nylon) on the outward facing surface of the foil substrate suitable for printing of graphics or text.

[0037] To provide improved peelability and meet the second object of the invention, a further aspect of the invention provides a closure for a container, the closure comprising an annular component, the annular component defining an aperture, the closure further comprising a membrane of peelable lidding material, the membrane having a cover portion and a tab extending from the periphery of the cover portion, the cover portion sealed to a sealing surface of the annular component to provide a continuous annular seal about the aperture, the continuous annular seal generally symmetrically disposed about the tab's longitudinal axis, characterised in that: the continuous annular seal is non-circular in plan and is profiled such that the radial outer edge of the seal defines an apex or region of high curvature under or adjacent the tab and centred either on, or within a distance of half the tab's base width (w _tbase ) from the tab's longitudinal axis, the continuous annular seal extending away from the apex or region of high curvature as two linear or reduced curvature portions which extend to or beyond a line which is in the plane of the closure, normal to the tab's longitudinal axis and passes through the centroid of the continuous annular seal, until increasing in curvature to join together to define the continuous annular seal.

[0038] By "region of high curvature" is meant a tight curve having a smaller radius of curvature relative to the linear or reduced curvature portions of the continuous annular seal outward of the base of the tab (see arrows 'A' in figures 9, 10, 12, 13 & 20). For example, the region of high curvature is preferably provided by profiling the radial inner and outer edges of the continuous annular seal with a radius of curvature of in the range 10 mm to 15 mm adjacent or under the tab - this has been found effective in reducing the chord length resisting peel initiation.

[0039] Conveniently, the linear or reduced curvature portions converge to a point location under / adjacent the tab to define the apex. This results in a continuous annular seal with the general profile of a shield (see for example figure 20).

[0040] Preferably, the apex or region of high curvature is defined by the radial outer edge of the continuous annular seal being profiled to define a tongue-shaped region - as described above.

[0041] The provision of an apex or region of high curvature on the radial outer edge of the continuous annular seal provides a natural stress-raising feature to help break the bond at the outer edge of the seal. However, ensuring that radial inner and outer edges of the continuous annular seal are correspondingly profiled helps to reduce the peel initiation force, i.e. the force required for peeling to break through to the radial inner edge of the seal. Ensuring that the radial inner and outer edges of the seal are correspondingly profiled reduces the chord length at the initiation location, thereby reducing the peel initiation force relative to use of a wholly circular annular seal. Once peeling has broken through to the radial inner edge of the continuous annular seal (i.e. peel initiation has occurred), it has been found that the inherent flexibility of the lidding material assists in propagating peeling and overcoming any resistance from the geometry of the seal radially outward of the tab.

[0042] The generally symmetric disposition of the continuous annular seal about the tab's longitudinal axis has the effect of reducing any asymmetric forces on peeling that could result in tearing of the tab from the lidding material.

[0043] In this aspect of the invention, the tab is preferably an integral part of the lidding material. Alternatively however, the tab may be a separate entity fixed to the lidding material by conventional means (for example, by means of adhesive or a rivet).

[0044] In this aspect of the invention, the whole length of the tab may be folded back over the lidding material (as shown in WO 2004/014758A), in which case the apex or region of high curvature would be located under the cover portion but adjacent the tab (see the embodiment shown in figure 20).

[0045] Preferably however, the tab is arranged to be fold-free in whole or part, thereby having at least a fold-free portion which extends outwardly from the periphery of the cover portion against a surface of the annular component, the apex / region of high curvature of the continuous annular seal extending under the fold-free portion of the tab to bond the fold-free portion to the annular component (see the embodiments shown in figures 9, 10 & 12). In this configuration, the fold-free portion of the tab has the advantage that a common seal establishes the hermetic seal between the lidding material and the annular component, whilst also helping to secure the tab to the annular component.

[0046] The reduction in peel force due to the present invention can be used to offset the increase in peel force that would generally accompany: i. inclining the sealing surface upwardly (as may be done when adapting the closure for "in-can" pressure applications); and/or ii. the use of an increased seal width w _s (to provide a stronger seal); and/or iii. using sealing material(s) with an inherently higher peel force characteristic.

[0047] Therefore, whilst the present invention is applicable for use with closures having a planar or flat sealing surface (i.e. not inclined), the invention is particularly advantageous when used on a closure having an inclined sealing surface.

[0048] In summary, the present invention achieves the second object of providing an improved peelable closure, and is particularly suitable for i) large apertures (for example, > 100 mm in diameter) and/or ii) "in-can pressure" applications, in either case adapted such that the lidding material remains easily peelable by a consumer.

[0049] To maximise aperture size as a proportion of the closure area (and thereby product release), the continuous annular seal is generally formed to border the aperture with zero or minimal (for example, 1 -2 mm) gap between the aperture periphery and the radial inner edge of the seal. However, the shape of the aperture does not directly affect how the invention works. It is the profile of the continuous annular seal that is important to the present invention because it is the profile of the seal adjacent/under the tab and local to the tab's longitudinal axis that affects peelability (rather than the shape of the aperture that the seal surrounds).

[0050] Where maximising aperture size as a proportion of the closure area is not essential, it has been found convenient to use a circular aperture with the non-circular seal of the present invention. The advantage of this is that for an aperture incorporating a peripheral curl (commonly used to protect against cuts and corrosion), the tooling for a circular aperture is very much simpler than the tooling for a non-circular aperture.

[0051] On conventional peelable can ends of 60 to 85 mm nominal diameter having a circular continuous annular seal, the seal width w _s is typically limited to around 1.5 to 3 mm because this allows the lidding material to remain easily peelable. The present invention has instead permitted the use of a seal width w _s of between 3-5 mm whilst preserving peelability. Brief Description of Figures in the Drawings [0052] Various embodiments of the present invention will be described with reference to the following figures: [0053] FIGURE 1 is a plan view of part of a first closure and indicates the chord length c _m i at the peel initiation location for a seal extending linearly and perpendicular to the tab's longitudinal axis. [0054] FIGURE 2 is a plan view of part of a second closure and indicates the chord length c _m2 at the peel initiation location for a circular annular seal. [0055] FIGURE 3 is a plan view of part of a third closure and indicates the chord length c _m3 at the peel initiation location for a circular annular seal corresponding to that of figure 2, but having a wider seal width. [0056] FIGURE 4 shows a side elevation view of a part-folded tab of the present invention (figure 4a) and a fully-folded tab of the prior art (figure 4b), each showing a lateral force F _L acting on the free edge of the tab. [0057] FIGURE 5 shows a perspective view of the top of a closure according to a first embodiment of the present invention - having a fold-free tab. [0058] FIGURE 6 shows a perspective view of the underside of the closure of figure 5.

[0059] FIGURE 7 shows a cross-section view through section X-X of figure 5. [0060] FIGURE 8 shows a cut-out view of the closure of figure 5 along section

X-X. [0061] FIGURE 9 shows a plan view of the embodiment of figures 5-8, also indicating the outline of the continuous annular seal between the peelable lidding material and the can end. [0062] FIGURE 10 shows a detail view of the tongue-shaped region of the continuous annular seal of figure 9. [0063] FIGURES 10a and 10b show detail views of two alternative profiles of tongue-shaped region to that shown in figures 9 and 10. [0064] FIGURE 11 shows a perspective view of the top of a closure according to a second embodiment of the present invention, this second embodiment having a part-folded tab.

[0065] FIGURE 12 shows a plan view of the embodiment of figure 11 , also indicating the outline of the continuous annular seal between the peelable lidding material and the closure.

[0066] FIGURES 13 & 14 show plan views of third and fourth embodiments of a closure according to the present invention, both having an entirely fold-free tab.

[0067] FIGURE 15 & 16 show plan views of fifth and sixth embodiments of a closure according to the present invention, both having a part-folded tab.

[0068] FIGURE 17 shows a perspective view of a seventh embodiment of a closure according to the present invention, but including an inclined sealing area.

[0069] FIGURE 18 shows a cross-section view of the closure of figure 17 through section Y-Y.

[0070] FIGURE 19 corresponds to figure 17, but with the lidding material removed.

[0071] FIGURE 20 shows a plan view of the closure of figure 17.

Mode(s) for Carrying Out the Invention

[0072] Figures 1 to 4 have already been described above.

[0073] A first embodiment of the invention is shown in figures 5 to 10. A closure 1 includes a can end 2 of 73 mm nominal diameter (see figure 5). The can end 2 is formed from sheet metal which has undergone a number of mechanical forming and cutting operations. The can end 2 has a panel 3, with a chuck wall 4 extending first upwardly and then radially outwardly from the periphery of the panel to define a seaming panel 5 (see figures 5, 7 & 8). The seaming panel 5 is suitable for enabling the closure 1 to be seamed onto a metal can body (not shown). In an alternative embodiment (not shown in the figures), the can end 2 includes a circumferential countersink between the panel 3 and the chuck wall 4.

[0074] During manufacture of the can end 2, a portion of the sheet metal is punched out of the panel 3 to define an aperture 6 (see figure 6). The exposed cut edge of the aperture 6 terminates in a curl 7 to reduce both the risk of cuts to consumers and corrosion from product inside a can incorporating the closure 1 (see figures 6 to 8).

[0075] This first embodiment has a membrane of flexible peelable lidding material 10 that includes a cover portion 11 and an integral tab 12 (see figures 5 & 9). The lidding material 10 of this embodiment includes a foil substrate layer of aluminium. The corresponding opposing surfaces of the panel 3 and the lidding material 10 each include a coating of heat sealable material (not shown). By way of example, conventional polypropylene-based lacquer systems may be used to provide heat sealability. The lidding material 10 is heat sealed to the can end 2 to provide a continuous annular hermetic seal 13 about the aperture 6 (see figure 9).

[0076] This first embodiment has an entirely fold-free tab 12, with the full length (I tab) of the tab laid flat against the surface of the panel 3 outward of the aperture 6 so as to be almost flush with the panel (see figures 5, 9 & 10). In the embodiment shown, the tab 12 has a full length l _tab of approximately 18 mm (see figure 5). The free edge 12a of the tab 12 terminates approximately 2 mm radially inwards of the chuck wall 4 (shown as distance a-i on figure 5).

[0077] Figure 9 shows - using dashed lines - the radial inner and outer edges

13a, 13b of the continuous annular seal 13. From figures 9 & 10, it can be seen that the continuous annular seal 13 extends under the tab 12, with the radial inner and outer edges of the seal being correspondingly profiled to provide a tongue-shaped region 14 centred on the tab's longitudinal axis 15. This axis 15 is also referred to as the "pull" axis because the tab 12 is pulled back along this axis in order to peelably remove the lidding material 10 from the can end 2. The tip or apex 30 of the tongue-shaped region 14 provides a natural stress-raising feature when pulling back on the tab 12. The tongue-shaped geometry also reduces the chord length c _ιn at the peel initiation location, thereby reducing the peel initiation force requirements (see figure 10). In summary, the tongue-shaped region 14 helps: i) to ensure that a hermetic seal is maintained between the can end 2 and the lidding material 10; ii) to secure the underside of the tab 12 to the panel 3 outward of the aperture 6, thereby inhibiting disturbance of the tab during processing and handling operations; and iii) to provide a way of minimising the chord length at the peel initiation location (see c _ιn on figure 10) and, consequently, the force required to initiate peeling of the lidding material 10 when pulling the tab 12 back along the "pull" axis 15.

[0078] In the example shown in figures 9 & 10, the tongue-shaped region (14) is defined by the radial outer edge of the continuous annular seal being generally triangular in configuration, having two linear portions converging to a point or apex (30) under the tab (see figures 9 & 10). Figures 10a, b show two alternative configurations for the tongue-shaped region (14). In figure 10a the radial outer edge of the seal peaks with a tightly curved profile, to provide a natural stress-raising feature. Figure 10b differs from figure 10a in the radial inner and outer edges of the tongue-shaped region being correspondingly profiled to provide a tongue shape on both the inner and outer edges of the seal. The embodiment of figure 10b will result in a reduced chord length c, _n at the peel initiation location relative to the embodiment of figure 10a.

[0079] In the example shown in figures 5 to 10, the tongue-shaped region 14 of the seal would be formed using the same tooling and simultaneously as the rest of the continuous annular seal 13, therefore avoiding the need for a separate heat-sealing operation to secure the tab in position. The entire periphery of the continuous annular seal 13 (including the tongue-shaped region 14) is symmetrical about the "pull" axis 15, having a uniform width w s of approximately 2.5 mm.

[0080] The second embodiment shown in figures 11 & 12 is similar in most respects to that of figures 5 to 10. However, it has a part-folded tab 12. Like features are designated with the same reference numbers. The tab 12 incorporates a single fold line 12b defining a (part-)folded portion 12c which extends from the fold line 12b as a single layer back over the fold-free portion of the tab to terminate at free edge 12a. As seen in figure 12, the continuous annular seal 13 incorporates a tongue-shaped region 14 similar to that shown in the first embodiment of figures 9 & 10 and providing the same advantages. The fold line 12b is located adjacent to the chuck wall 4, with the part-folded portion 12c having a length l _p of approximately 5 mm - measured from the fold line 12b to the free edge 12a (see figure 12). When unfolded, the tab 12 would have a full length l _tab of approximately 18 mm, i.e. as for the fold-free tab of figures 5 to 10. In use, a consumer would first grasp hold of the folded-portion 12c of the tab 12 and then pull back along axis 15 to initiate peeling at the tip or apex 30 of the tongue-shaped region 14 and separate the full length of the tab from the panel 3. In a second stage, the consumer would then grasp hold of the full length of the tab 12, being better able to apply the necessary force to peel the remainder of the lidding material 10 from the can end 2.

[0081] Figures 13 & 14 show alternative configurations of lidding material 10 and continuous annular seal 13 to the embodiment of figures 9 & 10, i.e. with a fold-free tab. However, for both configurations the continuous annular seal 13 does not extend under the tab 12. Further, neither configuration includes a tongue-shaped region on the continuous annular seal 13. For the embodiment shown in figure 13 the radial inner and outer edges 13a, 13b of the continuous annular seal 13 adjacent the tab 12 are correspondingly profiled to define a region of high (tight) curvature relative to those portions (indicated by arrows A in figure 13) of the continuous annular seal immediately outward of the tab 12. This again has the effect of reducing both the chord length at the peel initiation location and the peel force required to initiate peeling of the lidding material 10 from the can end 2. However, the reduction in peel force is not as great as would occur when using the tongue-shaped region of the embodiment shown in figures 9 & 10.

[0082] Figures 15 & 16 show alternative configurations of lidding material 10 and continuous annular seal 13 to the embodiment of figures 11 & 12, i.e. with a part-folded tab. However, for both configurations the continuous annular seal 13 does not extend under the tab 12.

[0083] A closure 1 is shown in figures 17-20. As for the closures shown in figures 5-16, like features are designated with the same reference numbers. The can end 2 is an annular metal ring of 73 mm nominal diameter. The can end 2 has an upwardly inclined sealing surface 20 for bonding of the lidding material 10 to define the continuous annular seal 13. The continuous annular seal 13 has a uniform width w _s of 4 mm and the sealing surface 20 is inclined at an angle β of 25° to the horizontal plane generally defined by the can end 2 (see figure 18). The continuous annular seal 13 is symmetric about the longitudinal axis 15 of the tab 12 (see figure 20), i.e. the "pull" axis. In the embodiment shown, the full length l _tab of the tab 12 is folded back over the cover portion 11 of the lidding material 10.

[0084] It can be seen that the continuous annular seal 13 is non-circular in plan (see figure 20). Reduced curvature portions of the continuous annular seal outward of the base of the tab 12 (indicated by arrows 'A') converge to a region of high curvature 30 located on the "pull" axis 15 and adjacent the tab. The reduced curvature portions 'A' are wholly curved outwardly from the centroid C so that they each progressively curve towards the tab's longitudinal axis 15 when moving further along the axis. The portions 'A' extend beyond line C-C (see figure 20). Line C-C represents the line which lies in the plane of the closure, is normal to the tab's longitudinal axis 15 and which passes through the centroid C of the continuous annular seal 13. The portions 'A' extend to the line D-D, after which point they increase in curvature to join together to define the continuous annular seal 13. This results in a continuous annular seal with the general profile of a shield.

[0085] In an alternative embodiment, the continuous annular seal 13 may instead incorporate a tongue-shaped region as described above. Obviously, the can end 2 must provide sufficient space outward of the aperture for such a tongue-shaped region; for example, by the can end 2 incorporating a panel between the wall 4 and the aperture 6 as for the embodiments of figures 5-16. This space would also enable the use of a tab that is fold-free in whole or part (as detailed in the embodiments of figures 5-16).