GB2618569A

GB2618569A - Screw cap core seal structure

Info

Publication number: GB2618569A
Application number: GB2206828.2A
Authority: GB
Inventors: Miguel De Oliveira Pedro; Moreno Marin Jaime
Original assignee: Greif International Holding BV
Current assignee: Greif International Holding BV
Priority date: 2022-05-10
Filing date: 2022-05-10
Publication date: 2023-11-15
Also published as: WO2023217656A1

Abstract

A screw cap for containers comprises a screw cap body 10, neck 26, and an expandable core seal 24 with an annular sealing element 30; a peripheral part 36 of a resilient seal energizing element 38 expands radially when compressed as the screw cap body is screwed onto a container; the peripheral part 36 joined to a stiff backing 34 and encased in a more yielding facing 44 which comprise a plurality of separate, axially extending segments (42, Fig. 4); a detent 32; this structure creating a more evenly distributed sealing pressure of the annular sealing element 30. The seal energizing element 38 may be dome shaped and have a central recess 43 which may form a snap-fit connection with protrusions 28 present on the bottom of the cap body. The seal 24 may be segmented by slots 40 that extend from the detent 32 to the seal energizing element 38. An aperture or membrane 62 for liquids or gasses may be in a recess that may be the same recess as the one housing the snap-fit connection 43.

Description

Screw Cap Core Seal Structure This invention concerns screw caps for containers. More particularly, the invention relates to screw caps provided with a core seal which is expandable to engage the inner surface of a container neck Such expandable core seals are known in various forms from GB2280895. In one form shown there, the expandable core has a face sealing ring which in use rests against the rim of the container neck, and a central section which projects above the face sealing to ring when the core is in a relaxed (contracted, unsealed) state. The central section of the expandable core therefore rests against the inner surface of the top wall of a cap applied to the container neck. A somewhat flexible outer skirt depends generally vertically from the inner margin of the face sealing ring to lie against the inner surface (bore) of the container neck in use. A flared (trumpet-shaped) inner skirt joins the lower periphery of the outer skirt to the outer periphery of the central section. At least the lower, outer peripheral part of the inner skirt is somewhat flexible. As the cap is applied to the container neck, the face sealing ring comes to rest against the rim of the container neck. Then as the cap moves axially further onto the container neck, the central section of the core seal continues to move with the cap, axially into the container neck. The outer skirt and the lower periphery of the inner skirt are constrained against axial movement relative to the container neck by the engagement of the face sealing ring against the container neck rim. Continued application of the cap therefore causes compressive collapse and corresponding radial expansion of the lower periphery of the inner skirt Such radial expansion causes corresponding radial expansion of the outer skirt, particularly at and towards its lower (inner) end. The outer skirt is thereby expanded into sealing engagement with the inner surface of the container neck In another form shown in GB2280895, the inner skirt has a shallow frustoconical shape and is apparently connected to the lower periphery of the outer skirt and to the outer periphery of the central section, by respective outer and inner circumferential living hinges. The cap top wall is secured to the central section of the expandable core. In the relaxed, contracted, unsealed state of the core seal, the outer circumferential living hinge lies below the inner circumferential living hinge. As the cap is applied to the container neck, the shallow frustoconical inner skirt begins to flatten, resisting the application of the cap and again expanding at least the lower portion of the outer skirt towards, and then into sealing engagement with, the inner surface of the container neck. When the inner skirt has been distorted to a substantially flat shape, it reaches an "overcentre" condition, in which it snaps into an everted shape, in which the inner circumferential living hinge lies below the outer circumferential living hinge. This pulls the cap top wall towards (or, absent any other cap-to-neck securing means, into) engagement with the face sealing ring and the container neck rim; at the expense of some relaxation of the to sealing expansion of the outer skirt Such expandable core seals may be used to seal otherwise conventional internally screw-threaded caps to conventionally externally threaded container necks. The outer skirt may have a facing layer made from a relatively yielding material, to take up and seal against any irregularities in the container neck inner surface. A backing structure for the outer skirt, and the entire inner skirt, may be formed from a relatively stiffer, more creep resistant material. A final screwing-on torque limit may be selected (a "target torque") which ensures that the facing layer is properly deformed into full circumferential sealing engagement with the container neck inner surface. At this torque, there will be considerably more deformation in the inner skirt than in the outer skirt facing layer. Thus expansion of the container neck e.g. due to a rise in temperature, or thinning of the facing layer due to creep, does not result in any significant relaxation of the energizing force pressing the facing layer against, and maintaining it in sealing contact with, the container neck inner surface. If the cap is screwed on to a higher torque than that which is necessary to first achieve a good circumferential seal, the excess strain is largely taken up by further deformation of the inner skirt The facing layer is thereby protected against overstraining, improper distortion, and extrusion. The expanding core container closure seals disclosed in GB2280895 therefore have good fault tolerance against poor neck inner surface finishes and inaccurate tightening torques.

The amount of radial expansion of the outer skirt which is possible, is limited by the elastic limit of the material(s) from which the outer skirt is formed. The maximum amount that the outer skirt can expand also largely depends upon the distance that the central section projects above the face sealing ring when the core is in the relaxed state, or the axial distance between the inner and outer circumferential living hinges when the core is in the relaxed state, for the two expandable core seal types described above, respectively.

In the case of screw-threaded container caps, expansion of the expandable core seal io from the relaxed, fully contracted, unsealed condition to the sealed condition, best takes place during the final few turns (or even during a fraction of the final turn) of the screw cap. This ensures that the cap is in a predictable axial position when tightened to the target torque, with sufficient length of the cap and neck threads inter-engaged. A secure interconnection between the cap and container results, so that the cap will not "pop off" under rough handling or under internal pressure, e.g. due to heating or agitation of gas-evolving container contents, or storage or transportation of an at least partly gas-filled container at low ambient pressure, such as in aircraft or at altitude. Accurate final axial positioning of the cap is also often necessary to ensure correct inter-engagement and secure operation of co-operating anti-tamper features provided on the cap and container neck respectively. The face sealing ring is therefore axially positioned relative to the screw cap so that it contacts the container neck rim and begins expansion of the outer skirt only when less than one turn of the screw cap remains (or perhaps a few turns, in the case of screw caps having a fine thread) before the cap is fully screwed on to the container neck. The necessity for such an arrangement therefore further restricts the possible range of expansion of the core seal. On occasion, where the container neck is particularly oversized (out of tolerance, as can occur in the case of blow-moulded containers for example, which are inherently quite variable in neck internal diameter; and/or because nominally standard manufacturing dimensions in fact vary between different manufacturers), the available range of expansion of the core seal is inadequate to form a reliable seal inside the container neck bore. On the other hand, if the core were allowed to begin expanding many turns before the cap is fully screwed on, the possible range of expansion of the core seal is increased, but the final axial position of the screw cap when the target torque is reached then becomes unacceptably unpredictable.

W02020/200619 discloses a screw cap and core seal arrangement in which a resiliently deformable seal energizing element has a rotational coupling with a cap body end wall.

The coupling includes cam surfaces which transform relative rotation between the cap body and the seal energizing element as the cap body is screwed onto the container neck, into axial movement of the seal energizing element This axial movement is added to the movement of the cap body end wall as the cap is screwed onto the container neck..

The cap can therefore provide a highly expandable core seal operated by little rotation as the cap is torqued into its final, fully screwed on position on the container neck.

However the resiliently deformable seal energizing element disclosed in W02020/200619 again acts primarily, if not exclusively, at a lower end of the sealing element disposed furthest within the container neck. If more even loading of the sealing element is required, according to one embodimentthe opposite, upper end of the sealing element (closest to the mouth of the container neck) may be expanded outwardly by a separate annular wall which optionally depends from the inner surface of the cap body end wall. Oblique sections at the upper end of the sealing element are urged to expand radially, as they are urged against the depending annular wall during final tightening of the screw cap body onto the container neck. Effective operation of the core seal of W02020/200619 may also be hindered if there is rotational slippage between the resiliently deformable seal energizing element and the container neck.

US3788510 relates to a cap liner which can be energized to wrap around the upper marginal zone of the neck of a container. An upper part of an annular wall portion of the liner is energized by a shallow conical web whose apex is forced downwardly by the inner face of the cap end panel. The lower edge of the wall portion has a hook-like form including a bevelled downwardly and outwardly directed face and an upwardly facing internal shoulder. The upwardly facing shoulder sealingly engages a downwardly facing flat shoulder within the bottle neck, essentially perpendicular to the neck principal axis. The base of the conical web is remote from the hooked lower edge of the wall portion and therefore has little or no ability to expand or provide a tighter sealing interengagement between the shoulders. The pliability of the wall portion, necessary for it to conform to and seal against the container neck, also means that the stress and strain at the base of the of the conical web remains localised there.

The present invention aims to mitigate at least some of these issues, and accordingly provides a screw cap comprising: a cap body comprising an end wall and an internally threaded, annular side wall depending from the end wall; an annular sealing element disposed concentrically within and spaced from the annular side wall so as to be receivable within an externally threaded container neck when the screw cap is screwed onto the container neck; a detent engageable with the container neck so as to support the annular sealing element within the container neck as the screw cap is screwed onto the container neck; a resiliently deformable seal energizing element comprising a central part braced against the cap body end wall and a peripheral part joined to the annular sealing element; the seal energizing element being constructed and operatively arranged within the cap body so that axial compression of the seal energizing element between central part and the peripheral part as the cap body is screwed onto the container neck causes radial expansion of the seal energizing element at the peripheral part, thereby radially expanding the annular sealing element towards the inner surface of the container neck; the annular sealing element comprising a backing formed from a relatively stiff but resilient material and a facing of a relatively more yielding material, wherein the backing extends in a direction away from the cap body end wall to below the level of the detent; characterised in that: the peripheral part of the seal energizing element is joined to the backing at a level at or below the detent, and the backing below this level comprises a plurality of separate, axially extending segments. With this arrangement, the axial compression of the seal energising element not only makes the peripheral part of the seal energizing element and adjacent part of the sealing element tend to expand radially, but also makes the axially extending segments tend to rotate upwardly and outwardly. Both of these tendencies are resisted by the surrounding container neck as the cap is screwed onto it. The tendency of the backing segments to rotate upwardly and outwardly, when added to the tendency of the annular sealing element to expand radially at the level of the seal energizing element periphery, causes the sealing pressure of the annular sealing element against the inner surface of the container neck to be more evenly distributed across the entire axial extent of the sealing element. This improves sealing performance of the sealing element If the cap is screwed on to a higher torque than that which is necessary to first achieve a good circumferential seal, the excess strain is largely taken up not only by further deformation of the seal energizing element but also by bending to stress in the segments of the backing. The facing is thereby protected against overstraining, improper distortion, creep relaxation, and extrusion. The screw caps of the present invention therefore have excellent sealing performance and fault tolerance against poor neck inner surface finishes and inaccurate tightening torques.

The seal energising element, annular sealing element, detent, backing, and facing may comprise parts of an expandable plug seal subassembly within the screw cap. The plug seal subassembly and cap body may comprise a snap-fit connection by which the plug seal subassembly is held in the cap body even when the screw cap is not screwed onto the container neck. The snap-fit connection may comprise a recess at the central part of the seal energizing element, into which a projection extending from the cap body end wall is snap-fittingly received. The projection may comprise a plurality of axially extending fingers or segments. The projection may comprise an enlarged end which is snap-fittingly received in an undercut portion of the recess at the central part of the seal energizing element The snap-fit connection may allow relative rotation between the seal energizing element and the cap body, whereby normally there is substantially no relative rotation between the annular sealing element and the container neck as the screw cap is screwed on or unscrewed.

The detent maybe integrally formed with the expandable plug seal subassembly, e.g. as an annular flange extending radially from an upper portion of the backing. The backing and seal energizing element may comprise through-going slots extending radially in the seal energizing element and axially in the annular sealing element; thereby allowing easier radial expansion of the plug seal by widening of the slots to take up much of the resulting strain. The axially extending through-going slots may serve to define the plurality of separate, axially extending segments of the backing. These slots may continue into the annular flange which forms the detent Additionally or alternatively these slots may be united with, run into, or become, the radial through-going slots in the seal energizing element The facing may cover at least the outer circumference of the annular sealing element and may sealingly cover the through-going slots in it, so that when the plug seal is expanded, the facing is sealingly pressed against the inner surface of the container neck around its entire circumference, to thereby hermetically seal the to container. The facing may also cover a lower surface of the annular flange forming the detent, so as to hermetically seal against the rim of the container neck, when the cap body is screwed onto it A bottom surface of the seal energizing element may have a covering of a softer and more compliant material to seal the slots therein. Such a covering may be continuous with the facing so as to prevent contact between the packaged material and the other components of the screw cap. PCR materials may therefore be used to make these other components, while still allowing the screw cap to be used in food-grade or similar hygienic applications. The backing and the facing may be formed by insert moulding (bi-injection). The seal energizing element may comprise a domed shape which becomes flatter and expands radially as the detent engages the container neck, the cap body is screwed onto the container neck and the cap body end wall presses down on the central part of the seal energizing element The expandable plug seal subassembly may comprise a through-going aperture, over which a gas permeable, liquid impermeable membrane is secured, to provide a gas venting path. For example, the through-going aperture may be formed in the seal energizing element. The through-going aperture may be formed in a recess at the central part of the seal energizing element This recess may be part of the snap-fit connection as described above. The detent and/or the inside surface of the cap body end wall maybe provided with grooves or projections which space the detent away from the inside surface of the cap body end wall when the screw cap is fully tightened, thereby providing a gas flow path connecting the space between the seal energizing element and the cap body end wall to the atmosphere via the cap body internal thread.

The invention and some of its further optional features and advantages are described below with reference to illustrative embodiments shown in the drawings, in which: Figure 1 is an exploded perspective view from one side and above, of a screw cap body, an expandable plug subassembly, and a corresponding container neck, embodying the present invention; Figure 2 is an exploded perspective view from below of the components shown in Figure 1; Figure 3 corresponds to Figure 1 but shows the components in part-section; Figures 4 and 5 are part-sectional perspective views from one side and above, showing the screw cap body and expandable plug subassembly snap-fitted together and the resulting screw cap partly screwed onto the container neck; Figure 6 is a part-sectional perspective view from one side and below, with the components assembled as in Figures 4 and 5; Figure 7 is a side view of an expandable plug body subassembly similar to the one shown in the preceding Figures, and Figure 8 is a diametral cross-sectional view through a modified form of expandable plug body plug assembly useable as a component in screw caps embodying the present invention.

Turning first to Figure 1, the illustrative screw cap comprises a cap body 10 within which an expandable plug seal subassembly 24 is relatively rotatably housed, as further explained below. Figure 1 also shows a complementary container neck 26 which can be closed and sealed by the cap body 10 and attached plug seal subassembly 24. The cap body 10 comprises a disc-shaped end wall 12 and a generally cylindrical side wall 14 depending from the periphery of the end wall 12. The bottom of the side wall 14 opposite to the end wall 12 is provided with a radially outwardly extending protective flange 16, beneath which an anti-tamper ring 18 is frangibly attached, in known manner. The screw cap body 10 and anti-tamper ring 18 may be manufactured as a single component, e.g. by injection moulding from a suitable plastics material such as PE or a PCR plastic. As best shown in Figures 2 and 3, the cap body side wall 14 is formed with an internal screw thread 20. A projection 22 formed by a pair of axially extending fingers or segments 28 depends centrally from the inner face of the cap body end wall 12. The projection 22 forms a part of a snap-fit connection by which the plug seal subassembly 24 is rotatably held in the cap body 10 even when the screw cap is not screwed onto the container neck 26. Each of the axially extending fingers or segments 28 has an enlarged end 28a.

Figures 3 -6 show the annular sealing element 30 of the plug seal subassembly 24. More particularly the sectional views of these Figures show the structure of the annular sealing element 30, comprising its backing 34 and its facing 44. The backing 34 is formed of a relatively stiff and resilient material, such a suitable PCR plastic material.

which is sufficiently resilient so as to return to or towards its original shape when external stresses are removed. The facing 441s of a softer, more compliant material, for example a suitable elastomer such as NBE, EPDM, neoprene or a silicone elastomer. For example, the material used to form the facing 44 may be selected to be compatible with (e.g. inert to) the container contents.

The detent for supporting the annular sealing element 30 within the container neck 26 as the screw cap 10, 24 is screwed on, may comprise an annular flange 32 projecting radially outward from at or near the upper end of the backing 34.

The seal energizing element 38 illustrated in the drawings has a shallow, generally frustoconical configuration, although this is not essential to the invention. Other (usually generally dome-shaped) configurations are also possible, which allow radial expansion of the seal energizing element to arise from compression applied axially between its central and peripheral parts as the cap body 10 is screwed onto the container neck 26.

The apex or central part 39 of the seal energizing element 38 is directed towards the centre of the cap body end wall 12 in use. A pocket 43 of circular cross-section is provided, having an entrance at, and a depth extending axially below, this apex. The pocket 43 has an inwardly extending peripheral retaining lip SO which forms an undercut or re-entrant portion at the bottom of the pocket, into which the enlarged ends 28a of the axially extending fingers or segments 28 are snap-fittable. The plug seal subassembly 24 is thereby rotatably retained in the cap body 10. The apex or central portion 39 of the seal energizing element, the pocket 43, and the projection 22 also form a rotary thrust bearing, allowing the cap body 10 to rotate relative to the plug seal subassembly 24 as the cap is screwed onto or unscrewed from the container neck 26 and the plug seal subassembly 24 is held stationary within the container neck 26. However the described snap-fit interconnection 22, 43 between the cap body 10 and plug seal subassembly 24 is not essential to the invention. The apex 39 of the seal energizing element 38 may simply bear directly or indirectly against the inner face of the cap body end wall 12 to form a rotary thrust bearing. Other retention mechanisms/rotary thrust bearings disposed between the cap body 10 and plug seal subassembly 24 are also possible, as known to those skilled in the art The peripheral part 36 of the resiliently deformable seal energizing element 38 is joined to the backing 34 of the annular sealing element 30 at a position at or below the level of the detent (radially projecting annular flange) 32. The backing 34 extends below this junction and is divided by a plurality of circumferentially distributed, axially extending, through-going slots into a corresponding plurality of axially extending, radially distributed segments 42 (Figure 4). As illustrated in Figures 3 and 6, the part of the backing 34 extending below the junction or seal energizing element periphery 39 is about twice as deep as the part of the backing extending between this junction up to the level of the flange. However other configurations are also effective in providing the beneficial sealing effects of the invention. For example, the junction or seal energizing element periphery 36 may be provided at the level of the flange 32, whereby all of the backing 34 extends below the junction 36; or the junction 36 may be provided at a level about three quarters of the way down the backing 34 below the flange 32; or the junction 36 may be provided at a level anywhere within this range.

The edges of the slots 40 and the corresponding edges of the axially extending segments 42 are indicated in dotted lines in Figure 4, being still covered by the facing 44 in this part-sectional view. In Figure 3, the left hand side of the plug seal subassembly 24 is shown sectioned through the material of the backing 34 and of the seal energizing element 38. However, the right hand side is shown sectioned through one of the slots 40 in the backing 34. Normally this slot may be filled with the facing material 44. (The slot 40 widens during the required deformation of the annular sealing element 30, allowing separation from any filler material, whereby interference from compression resistance of such material is not an issue). For clarity of illustration, the right hand side of Figure 3 shows this slot 40 empty. To make the frustoconical or dome shaped seal energizing element 38 more easily radially expandable under axial compression, it may be provided with a plurality of radially distributed, radially extending, through-going slots 40a. The slots 40 in the backing 34 may run into the seal energizing element 38, to e.g. so as to be united with, run into, or become, the radial through-going slots 40a, as shown in Figure 3. The upper ends 40b of the slots 40a terminate near to the apex or central part 39 of the seal energizing element, e.g. at or near to the pocket 43. The slots 40 in the backing 34 may also have upwardly extending, through going continuations 40c, which may terminate in the radially projecting annular flange (detent) 32, so as to leave a series of relatively small bridging pieces 32a (Fig 3) holding the flange 32 together. This increases the out-of-plane flexibility of the flange 32, allowing it to more easily accommodate corresponding irregularities in the upper end surface of the container neck 26. The slots 40c and 40a also increase the radial flexibility of the annular sealing element 30, allowing it to better accommodate out-of-roundness of the container neck bore. The facing 44 may continue radially outwards onto the lower surface of the annular flange 32 so as to help to form a seal with the upper end surface of the container neck 26. The backing 34 together with the detent flange 32 and the seal energizing element 38 may be formed as a one-piece component e.g by injection moulding.

In its relaxed state, the annular sealing element 30 tapers slightly in diameter in the axial direction away from the flange 32. This enables the expandable plug seal subassembly 24 to be guided and more easily pushed into the bore of the container neck 26 as the cap body 10 is screwed into place on the container neck. As a result the flange (detent) 32 eventually comes to rest on the upper end surface of the container neck 26. When the plug seal subassembly 24 in its relaxed state is first secured to/hilly inserted within the cap body 10, a gap 52 exists between the upper surface of the flange 32 and the adjacent part of the cap body end wall 12 (Figure 4). After the flange (cletent) 32 comes to rest on the upper end surface of the container neck 26, continued screwing on of the cap body 10 causes the gap 52 to diminish and the domed seal energizing element 38 to become flatter. Such flattening causes the seal energizing element 38 to expand radially, the flattening and radial expansion being aided by the presence of the radial through-going slots 40a. The radial expansion of the seal energizing element 38 forces the adjacent upper part of the annular sealing element 30 more tightly into engagement within the bore of the container neck 26. Because they are joined to its periphery 36, flattening of the seal energizing element 38 also causes the axially extending segments 42 of the backing 34 to pivot upwardly and outwardly. The unslotted part of the flange (detent) 32 and/or the adjacent rim of the container neck may assist such pivoting movement by acting as a fulcrum. The taper of the annular sealing element 30 therefore diminishes as the cap body continues to be screwed on. The annular sealing element 30 is therefore pressed against the bore of the container neck 26 with a more even pressure across its axial extent (as well as evenly around its circumference). A point is reached at which further expansion of annular sealing element 30 is substantially fully constrained by the container neck Further screwing on of the cap body 10 beyond this point (e.g. to fully eliminate the gap 52) mainly results in further bending of, and hence additional locked-in bending stresses within, the segments 42 and seal energizing element 38. These locked in stresses (prestresses) are available to maintain the even sealing pressure between the annular sealing element 30 and the bore of the container neck 26, even if there is creep in the facing 44 and/or in the container neck 26. A low and predictable tightening torque (to fully eliminate the gap 52 and cause the anti-tamper ring 18 to engage one way teeth 54 on the container neck 26, Figure 5) therefore results in a reliable and long-lasting sealed closure, able to accommodate wide variations in the container neck bore size and profile. With the gap 52 eliminated, when the final tightening torque is applied to the screw cap body 10, the facing 44 on the underside of the flange 32 is forced into tighter sealing engagement of the corresponding rim surface of the container neck 26.

A covering 44a of a softer and more compliant material (such as, but not limited to, the material of the facing 44) may be applied to the bottom surface of the seal energizing element 38 to seal the slots 40a, without significantly affecting the ability of the seal energizing element 38 to expand radially under axial compression. This covering 44a may be continuous with the facing 44 and therefore also cover the radially inner surfaces of the axially extending segments 42, the slots 402 and the lower edge of the backing 34. For example the facing 44 and covering 44a may be insert moulded (hi-injected) onto the underside of the flange 32, onto both sides of the backing 34, and onto the bottom surface of the seal energizing element 38, in a single operation. The facing 44 and covering 44a therefore may seal not only the slots 40 and the slots 40a, but also the slots 40c (where present). The facing 44 and covering 44a may also provide a continuous, uninterrupted layer which seals around the entire circumference of the bore of the container neck 26, and spans this bore so as to isolate the container contents from the other components of the screw cap. These other components may therefore be made from PCR plastics, without risk of contaminating the container contents, even when the screw cap is used in pharmaceutical, food, or other similar hygienically demanding applications.

The plug seal 24 shown in Figures 2 and 6 differs slightly from the version shown in Figure 3, in that in Figures 2 and 6 a central region of the seal energizing element 38 (e.g. the bottom wall 43a (Fig. 6) of the pocket 43 enclosure) where present) is not covered by the covering 44a. This exposed portion 43a is provided with a number of through-going apertures 62. Three such apertures maybe used, although other numbers are also suitable, including one. In Figure 6, only two of the three apertures 62 are visible; the third being cut away by the sectioning. A microporous, gas permeable, liquid impermeable membrane 64 is sealingly secured at its periphery to the exposed central region 43a of the seal energizing element 38 so as to cover and surround the apertures 62.

For the purposes of illustration rather than any technical necessity, in Figures 2 and 6 the microporous membrane 64 is shown as being partially transparent, so that the apertures 62 can be seen through it For "venting out" applications, the membrane 64 may be secured to the exposed region of the seal energizing element 38 immediately surrounded by the covering 44a (e.g to the lower surface of the bottom wall 43a of the pocket 43 enclosure, where present). For "venting in" applications (not illustrated), the membrane may be secured to the opposite side of the seal energizing element 38, e.g. on the upper surface of the bottom wall 43a of the pocket 43 enclosure, where present. In each case, the seal energizing element 38 thereby supports and protects the membrane 64 against bursting by overpressure.

Further gas venting channels may be provided in the form of shallow grooves 66 (or other appropriately shaped channels) extending across the radial width of the flange/detent 32 on its side facing away from the container. These channels therefore lead from the space between the plug seal 24 and the cap body end wall 12, to the annular region occupied by the container neck 26. They therefore provide a gas venting path between the inside of the container and the atmosphere, via the screw cap body 10 internal thread 20. Additionally or alternatively, to complete the gas venting pathway, similar gas venting channels, conduits, spacing ridges, or the like may be provided in or on: the projection 22, the interior surfaces of the pocket 43, the apex 39 of the seal energizing element 38, and/or the interior surface of the cap body end wall 12. Optionally, as shown on Figure 3, in non-gas venting applications, the apertures 62 may be present in the seal energizing element 38, but are covered and sealed e.g. by the covering 44a. In this way the same moulding tools may be used to form the seal energizing element 38 in both gas venting and non-gas venting versions of the screw cap.

Referring to Figure 7, the radially outer surface of the annular sealing element 30 tapers substantially constantly from the detent (radially projecting annular flange) 32, to a rounded bottom edge formed where the facing 44 and covering 44a enfolds the distal tips of the segments 42. This profile allows the plug seal assembly 30 to be easily guided into the bore of the container neck as the screw cap is screwed onto it Other profiles are also possible. A further non-limiting example is shown in Figure 8, in which a lower part of the annular sealing element's radially outer surface is tapered, and an upper part of this surface (adjacent to the detent/flange 32 and adjacent to the junction 36) is substantially cylindrical. Expansion of the plug seal assembly 24 as the cap is screwed onto the container neck may lead to a substantially even pressure on this cylindrical portion of the facing 44 as it is pressed against the bore of the container neck.

Tests have ben conducted using core seal subassemblies 24 as shown in Figures 7 and 5 8, in each case fitted to a 60 mm screw cap (a modified 60 mm "Plasticap" (RTM) cap from the applicants). The test caps were screwed onto a simulated jelly can neck to a torque of 5 Nm. The simulated jerry can neck was machined internally to mimic a 3mm bore ovalisation -i.e. a difference in major and minor diameters of the bore of 3mm, the major and minor diameters being at right angles to each other. No leakage was 10 observed when the caps/neck were submerged in a water tank and pressurised to 318 mbar using compressed air. In another test, the caps were screwed onto ordinary sample jenycans to a 5 Nm torque. The jerry cans were filled with water at room temperature and held upside down for a 24 hour period. Again no leakage was observed. In a third test, two ordinary empty jerry cans fitted with the test caps according to Figs. 7 and 8 respectively (again at the 5 Nm closing torque) were pressurised with air until visibly distended ("blown up"). The air pressure required to do this was recorded (5.5 and 6.0 bar respectively). The jerry cans were then submerged in a water tank. Again no leakage was observed. The test caps therefore performed well at low closing torques, even with a substantial deformity in the container neck bore.

Claims

CLAIMS1. A screw cap comprising: a cap body comprising an end wall and an internally threaded, annular side wall 5 depending from the end wall; an annular sealing element disposed concentrically within and spaced from the annular side wall so as to be receivable within an externally threaded container neck when the screw cap is screwed onto the container neck; a detent engageable with the container neck so as to support the annular sealing element within the container neck as the screw cap is screwed onto the container neck; a resiliently deformable seal energizing element comprising a central part braced against the cap body end wall and a peripheral part joined to the annular sealing element; the seal energizing element being constructed and operatively arranged within the cap body so that axial compression of the seal energizing element between central part and the peripheral part as the cap body is screwed onto the container neck causes radial expansion of the seal energizing element at the peripheral part, thereby radially expanding the annular sealing element towards the inner surface of the container neck; the annular sealing element comprising a backing formed from a relatively stiff but resilient material and a facing of a relatively more yielding material, wherein the backing extends in a direction away from the cap body end wall to below the level of the detent; characterised in that: the peripheral part of the seal energizing element is joined to the backing at a level at or below the detent, and the backing below this level comprises a plurality of separate, axially extending segments.
2. The screw cap of claim 1, in which the seal energising element annular sealing element, detent, backing, and facing comprise parts of an expandable plug seal subassembly positionable within the screw cap.
3. The screw cap of claim 2, in which the plug seal subassembly and cap body comprise a snap-fit connection by which plug seal subassembly is held in the cap body even when the screw cap is not screwed onto the container neck
4. The screw cap of claim 3, in which the snap-fit connection comprises a recess at the central part of the seal energizing element, into which a projection extending from the cap body end wall is snap-fittingly received.
5. The screw cap of claim 4, in which the projection comprises a plurality of axially extending fingers or segments.
6. The screw cap of claim 4 or 5, in which the projection comprises an enlarged end which is snap-fittingly received in an undercut portion of the recess at the central part of the seal energizing element.
7. The screw cap of any of claims 3-6, in which the snap-fit connection allows relative rotation between the seal energizing element and the cap body, whereby normally there is substantially no relative rotation between the annular sealing element and the container neck as the screw cap is screwed on or unscrewed.
8. The screw cap of any of claims 2-7, in which the detent is integrally formed with the expandable plug seal subassembly as an annular flange extending radially from an upper portion of the backing.
9. The screw cap of any preceding claim, in which the backing and seal energizing element comprise through-going slots extending radially in the seal energizing element and axially in the annular sealing element
10. The screw cap of claim 9, in which the axially extending through-going slots serve to define the plurality of separate, axially extending segments of the backing.
11. The screw cap of claim 9 or 10, in which the axially extending through-going slots continue into an annular flange which forms the detent
12. The screw cap of any of claims 9-11,111 which the axially extending through-going slots are united with, run into, or become, the radial through-going slots in the seal energizing element
13. The screw cap of any of claims 9-12, in which a bottom surface of the seal energizing element has a covering of a softer and more compliant material to seal the to slots therein.
14. The screw cap of claim 13, in which the covering is continuous with the facing.
15. The screw cap of any preceding claim, in which the seal energizing element 15 comprises a domed shape which becomes flatter and expands radially as the detent engages the container neck, the cap body is screwed onto the container neck and the cap body end wall presses down on the central part of the seal energizing element
16. The screw cap of claim 2, in which the expandable plug seal subassembly comprises a through-going aperture, over which a gas permeable, liquid impermeable membrane is secured, to provide a gas venting path.
17. The screw cap of claim 16, in which the through-going aperture is formed in the seal energizing element.
18. The screw cap of claim 17, in which the through-going aperture is formed in a recess at the central part of the seal energizing element
19. The screw cap of claim 18, in which the recess comprises the recess of the snap-fit connection as defined in any of claims 4-6.
20. The screw cap of ally of claims 16-19, in which the detent and/or the inside surface of the cap body end wall are provided with grooves or projections which space the detent away from the inside surface of the cap body end wall when the screw cap is fully tightened.