Patent Publication Number: US-6705479-B2

Title: Tamper evident closure

Description:
This application is a continuation of U.S. patent application Ser. No. 09/268,324, filed Mar. 16, 1999, now U.S. Pat. No. 6,325,225, which is a continuation of U.S. patent application Ser. No. 08/922,453, filed Sep. 3, 1997, now U.S. Pat. No. 6,089,390, which is a continuation of application Ser. No. 08/374,534, filed Mar. 7, 1995, now abandoned, which is a 371 of International Application No. PCT/AU93/00352, filed Jul. 14, 1993. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to closures for containers having an externally screw threaded neck and more particularly to such closures which are formed with a tamper evident band. 
     BACKGROUND ART 
     Manufacturers of foodstuffs, beverages, medicaments, dentifrice and the like are concerned to ensure that products they place on the market are not tampered with before being opened by the ultimate consumer of the goods. For this purpose it has become conventional to include in closures for such goods means which will indicate whether the closure has been tampered with before purchase. In the case of containers having an externally screw threaded neck it is common to provide the closure with a tamper evident band which engages behind a retaining flange formed on the neck of the container. The tamper evident band is joined to a depending skirt forming part of the closure by a number of frangible bridges. On application of the closure to the container the band is forced over the retaining flange, however, when the closure is unscrewed from the container the bridges are sheared as the band is trapped behind the retaining flange while the closure moves up the neck of the container. 
     While such tamper evident bands have been widely accepted there is a delicate balance between the two conflicting requirements. On the one hand, one must be able to apply the closures to containers at very high speed without inadvertently breaking the bridges, or breaking or deforming the band itself, or deleteriously affecting the seal between the closure and the container. On the other hand, the band must be sufficiently tightly secured behind the retaining flange and the bridges and/or the band must be sufficiently easily broken that the closure cannot be removed from the container without rupturing the bridges and/or the band. 
     Another problem is that-an unauthorized person might attempt to remove the closure and tamper evident band, without damaging the band or frangible bridges, in order to contaminate or replace the container contents and then reapply the closure. Such operation might be attempted with the assistance of a thin device, such as a knife blade, wedged up between the tamper evident band and the neck of the container to which the closure has been applied. The devices might then be levered outwardly in order to expand the inner diameter of the band so that it may be passed back over the retaining flange of the container. In such a process the device will be edged around the circumference of the band so as to gradually ease the band over the retaining flange at a continuously lengthening portion of the band circumference. 
     Closures of the type mentioned above are used around the world in extremely large numbers. To be commercially acceptable such closures must be capable of being produced very rapidly in automated machinery. This itself may produce a conflict with the functionality of the closure and/or its tamper evident band. 
     The arrangement according to the present invention is designed to provide the public with an alternative form of closure having a tamper evident band. 
     Disclosure of the Invention 
     The present invention in its broadest aspect consists in a closure for a container having an externally screw threaded neck, the closure comprising a top portion and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the body portion being provided with projections or other localised areas of thickening to enhance the longitudinal stiffness of the body portion while still permitting it to expand radially as it is forced over the retaining flange on a container. 
     In a first preferred aspect the present invention consists in a closure for a container having an externally screw threaded neck, the closure comprising a top and a depending skirt which has on its internal surface a complementary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a continuous or segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the closure being characterized in that the upper side of the rib comprises a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly from the top, and a second surface which is positioned radially inwardly from the first surface, the second surface having a slope angle more nearly normal to the longitudinal axis of the closure than the first surface is to that longitudinal axis. 
     In the prior art closures the upper side of the rib has always been linear in cross-section. The upper side has either lain in a plane normal to the longitudinal axis of the closure or it has been a simple frusto-conical surface inclined to that axis. In the former case it has been difficult to mold as the planar surface is normal to the direction in which the core of the mold must be withdrawn from the cap. In the latter case there is more likelihood of the rib being able to be forced upwardly over the flange on the container neck. The present invention has resolved these problems by providing the upper side of the rib with a compound surface having a more steeply angled radially outer surface which assists molding of the rib and, preferably, a substantially planar radially inner surface which increases the difficulty of removing the closure intact from a container. There is preferably a relatively clearly defined junction between the first and second surfaces on the upper side of the rib. However, they may merge together gradually such that the upper side of the rib is generally arcuate in cross-section. It has been found that improved resistance to removal of the closure from the container can be obtained in this way while facilitating the molding of the closure. This latter aspect is important as for economic reasons, it is necessary that the closures and their associated tamper evident bands must be capable of being molded at extremely high rates. 
     The first surface on the upper side of the rib preferably comprises from 25% to 75% and more preferably 45% to 55%, of the radial width of the upper side of the rib. The first surface preferably has a slope angle to a plane normal to the longitudinal axis of the closure of from 10° to 60°, more preferably 12° to 40° and most preferably 15° to 25°. The second surface on the upper side of the rib preferably comprises from 75% to 25% and more preferably 55% to 45% of the radial width of the upper side of the rib. The second surface preferably lies in a plane normal to the longitudinal axis of the closure or at an angle of up to 10° to that plane, most preferably it lies in that plane. 
     In carrying out the present invention it has been found that during the injection moulding of closures from an injection mould which defines a rib having an upper side comprising a first annular surface and a second annular surface the clear distinction between the first and second surfaces may be lost, or at least difficult to discern, in the moulded product. It is thought that this may be due to the second annular surface being distorted and dragged into a slope angle similar to that of the first surface as the closure is ejected from the mould. Despite the anomaly that the mould clearly displays the two surfaces but the moulded closure does not, it has been found that the closures moulded from such a mould show superior resistance to being tampered with as compared to similar closures moulded in a mould not defining the upper side of the rib as having first and second surfaces. 
     Therefore in another aspect the present invention consists in a closure for a container having an externally screw threaded neck, the closure comprising a top and a depending skirt which has on its external surface a complimentary screw thread, a free edge of the depending skirt being joined by a plurality of frangible bridges to a tamper evident band, the band comprising a generally cylindrical body portion and a continuous or segmented rib extending inwardly of the body portion and adapted to provide a lip to engage under a retaining flange extending outwardly from the neck of the container below the screw thread thereon, the rib having an upper side facing generally towards the top of the closure and an under side facing generally away from the top, the closure being characterised in that the closure is formed by injection moulding from a synthetic plastics material in a mould which defines the upper side of the rib as comprising a first surface contiguous with the body portion of the band, which surface slopes inwardly and downwardly from the top, and a second surface which is positioned radially inwardly from the first surface, the second surface having a slope angle more nearly normal to the longitudinal axis of the closure than the first surface is to that longitudinal axis. The mould surface preferably has the other characteristics previously described as being preferred for the upper side of the rib itself. 
     In another embodiment of the invention the radially inner surface of the band is provided with an array of radially spaced apart inwardly extending projections positioned between the rib and a free edge of the band. The projections, or some of them, may, if desired, make contact with the under side of the rib across the longitudinal width of the band or they may stop short of the lower free edge of the band. They preferably are aligned parallel with the longitudinal axis of the closure but may be inclined to that axis. These inwardly extending projections make it difficult for a person deliberately trying to expand the diameter of the band and to ease it off the neck of the container intact by inserting a blade or other tool between the band and the container. 
     In a particularly preferred arrangement, the rib is segmented and alternate ones of the projections are spaced below the gaps between adjacent segments and are not connected to the rib. The remaining projections preferably abut at the upper ends with respective ones of the segments. These remaining projections preferably abut the segments at their respective mid-points. The projections are preferably inclined radially inwardly as they approach the rib, however they preferably do not extend inwardly from the radially inner surface of the body portion of the band as far as the rib does. The rib preferably extends inwardly beyond the projection by a distance substantially equal to the width of the second surface on the upper side of the rib. 
     The rib formed to engage with the retaining flange on the container may be continuous or segmented about the band, however if it is segmented it will still extend about a majority of the circumferential extent of the inside surface of-the band. The rib segments, when present, are preferably evenly spaced about the inside circumference of the band and occupy at least 50%, preferably at least 65% and most preferably at least 80%, of the internal circumference of the band. The rib preferably has a sufficiently broad base where it joins the body portion of the band that the rib is resistant to flexing upwardly as it is forced past the retaining flange during application of the closure to a container. 
     Each of the rib segments is preferably formed with two substantially planar end surfaces which are inclined to the axis of the closure and face away from the closure top, i.e., they face in a direction that a mould core used to mould the closure was withdrawn. The planar end surfaces are also preferably inclined to a notional radial plane extending from the longitudinal axis of the closure to the end of the respective rib segment such that the ends are inclined to the skirt of the closure by an included angle that is less than the included angle that the respective notional plane makes with the skirt. 
     The tamper evident band is further preferably provided with areas of localised thickening which extend outwardly from an external surface of the body portion of the band. The areas of thickening further preferably extend parallel to the longitudinal axis of the closure and across the longitudinal width of the band. 
     The areas of outer thickening serve to reinforce and strengthen the tamper evident band. The reinforcement of the band preferably enhances the vertical stiffness of the band whilst retaining a sufficient flexibility to facilitate application of the closure to the container. The reinforcement also allows sufficient axial force to be applied to the free end of the band in order to successfully eject the closure from a core portion of a mould used in the closure production. The reinforcement of the band further reduces the possibility of the closure being tampered with and the band stretched in order that it may be eased back over the retaining flange on a container to which the closure has been applied. 
     The bridges are preferably evenly spaced about the circumference of the closure but may be optionally arranged in two groups which are diametrically opposed to one another. Each group may preferably occupy from one quarter to one third of the circumference of the closure while each of the spaces between the groups occupies from one quarter to one sixth of that circumference. Each group of bridges is preferably made up of from 4 to 10 bridges equally spaced apart within the group. 
     The individual bridges in each group may have an axis parallel to the axis of the closure. Preferably, however, the axis of each bridge is inclined to the axis of the closure, more preferably it is inclined such that when seen in side elevation the upper end of the bridge is inclined to the left relative to its lower end. This particularly preferred arrangement is predicated by the fact that most screw threads tighten in a clockwise direction. The preferred inclination of the bridges allows them to bend as the closure is screwed onto a container. This stabilizes the band and reduces the likelihood of it, or the bridges, breaking or distorting during application. Conversely this preferred inclination of the bridges means that as the closure is unscrewed the bridges are straightened out and this serves to concentrate the forces tending to rupture the bridge at the point of attachment of each bridge to the band and to the skirt. 
     The thread on the internal surface of the skirt of the closure is preferably formed of a series of thread segments arranged, starting from a first thread segment distal to the top, along a helical thread locus. Each of the thread segments, except the first, is preferably formed with two substantially planar end surfaces which are inclined to the axis of the closure and face away from the closure top, ie, they face in the direction that a mould core used to mould the closure was withdrawn. The term “substantially planar surface” is used to mean a surface which is actually planar or which is cured provided that it all faces in the defined direction. The first of the thread segments is preferably pointed at its end distal to its one adjacent thread segment to assist in mating the thread on the closure with a corresponding thread on the neck of a container. 
     The substantially planar ends of the thread segments are also preferably inclined to a notional radial planes of the closure extending from the longitudinal axis of the closure to the end of the respective thread segment such that the ends are inclined to the cylindrical skirt by an included angle that is less than the included angle that the respective notional radial plane makes with that skirt. 
     To assist in the venting of gas between the thread segment the spaces between the segment in adjacent turns of the thread are aligned. A groove may be provided on the inside surface of the skirt of the closure extending longitudinally thereof through the aligned spaces. 
     In another embodiment the present invention consists in an injection moulded article including a cylindrical wall having a thread formed on its radially inner surface, the thread being comprised of a plurality of segments arranged in spaced apart array along the helical locus of the thread, at least some of the thread segments terminating at at least one end in a substantially planar surface inclined to the axis of the thread and facing the direction in which a mould core used in the moulding of the article was withdrawn. 
     The closure is preferably formed with means for sealingly engaging with the container to prevent leakage therefrom. Any one of the large number of alternative sealing arrangements known may be used with the closure according to the present invention. These include integral sealing ribs or flanges, wadding or flowed-in gaskets. 
     The sealing arrangement preferably comprises an annular sealing rib which projects downwardly from an underside of the top of the closure, the rib including a first portion having a substantially cylindrical inner surface, the first portion being contiguous with the top and lying adjacent to the skirt of the closure and a second, frusto-conical, portion contiguous with an end of the first portion distal to the top and extending radially inwardly to terminate in a circular free edge, the first portion having an internal diameter at least equal to an external diameter of the neck of the container to which the closure is to be attached such that during threaded engagement of the closure with the neck, the second, frusto-conical, portion will be engaged by a free end of the neck and folded back against the substantially cylindrical inner surface of the first portion of the rib to form a gas-tight seal between at least an outer surface of the neck of the container and the closure. 
     The closure most preferably has a skirt having a substantially cylindrical form carrying on its outside surface a series of fine vertical ribs terminating at the lower edge of the skirt in a narrow circumferential rib. The frangible bridges are preferably considerably thinner in their radial dimensions than the skirt and the band and the inner surface of the bridges lie flush with the respective radially inner surfaces of the skirt and the band. The radially outer surface of the band is of a slightly smaller diameter than the skirt except in the areas of local thickening which project radially outwardly beyond the radial extent of the skirt. 
     In this most preferred embodiment of the inside surface of the skirt is preferably generally cylindrical with a helical array of thread segments extending radially inwardly of that surface. The thread segments are separated from one another by axially aligned spaces. The inside of the band is preferably defined by a smooth upper cylindrical surface above the rib of the same diameter as the inside surface of the skirt. The rib is preferably formed of rib segments in axial alignment with the thread segments on the inside surface of the skirt and with the spaces between the rib segments in axial alignment with the spaces between the thread segments. Below the rib the inside surface of the band is inclined downwardly and outwardly so that the band is a little thinner at its lower end than it is at the upper end. This inclined surface carries an array of projections which are axially aligned and of a thickness less than that of the rib segments. Alternate ones of the projections abut at their upper end against the mid point of one of the rib segments, while the other projections are each aligned with one of the spaces between the rib segments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a diametric sectional view through one embodiment of the closure according to this invention; 
     FIG. 2 is a view along section II—II of the closure of FIG. 1; 
     FIG. 3 is a view along section III—III of the closure of FIG. 1; 
     FIG. 4 is a view along section IV—IV of the closure of FIG. 1; 
     FIG. 5 is a view along section V—V of the closure of FIG. 1; 
     FIG. 6 is a view along section VI—VI of FIG. 4; 
     FIG. 7 is a view along section VII—VII of FIG. 4; 
     FIG. 8 is a side elevational view of the closure of FIG. 1 seen in the direction of arrow A of FIG. 3; 
     FIG. 9 is a side elevational view of the closure of FIG. 1 seen in the direction of arrow B of FIG. 3; 
     FIG. 10 is a longitudinal cross-sectional view of another embodiment of the closure on an enlarged scale and shows the closure in relation to a neck of a container, as the closure is screwed onto the container; and 
     FIG. 11 is a longitudinal cross-sectional view of the closure of FIG. 10 with the closure sealingly engaged with the neck of the container. 
     FIG. 12 is a vertical sectional view through a part of a mould used for the injection moulding of closures according to the present invention with the area defining the rib being also shown as an enlarged seal. 
    
    
     The tamper evident closure  10  includes a continuous tamper evident band  11  having a generally cylindrical body portion  12  attached by frangible bridges  13  to a cap portion  14  of the closure  10 . The cap portion  14 , frangible bridges  13  and tamper evident band  11  are formed integrally by injection molding from suitable material such as polyethylene or polypropylene. The cap portion  14  includes a circular top  15  and a depending skirt  16 . The inside of the skirt  16  is screw threaded and adapted to be attached to containers commonly made from glass or a plastics material such as poly(ethylene terephthalate) (PET) which have an externally screw threaded neck. 
     The container  29  (a portion of which is shown in FIGS. 10 and 11) to which the closure  10  will be attached includes a continuous generally annular retaining flange  30  immediately below the screw thread  31  of the container  29  so as to form an outwardly radially directed lip. The band  11  includes a rib  18  about its inside surface being sized and shaped so as to provide an inwardly extending lip which will engage under the retaining flange  30  of the container  29  once the closure  10  is fully closed onto the container  29 . 
     The rib  18  is made up of a series of rib segments  19  separated by short breaks  20  however the rib segments  19  constitute about 85% of the circumference of the band and act together as though the rib  18  were substantially continuous. The breaks  20  provide circumferential flexibility to the band and allow the rib  18  to pass over the retaining flange  30  without stress, sufficient to break the frangible bridges. 
     The rib  18  has an upper side  21  directed towards the top portion  15  and an under side  22  directed away from it. The upper side  21  includes a radially outer frusto-conical surface  23  and a radially inner annular surface  24 . The annular surface  24  lies in a plane normal to a longitudinal axis of the closure  10  while the frusto-conical surface  23  is inclined inwardly and downwardly away from the top portion  15  and makes an angle of about 20° with the plane normal to the longitudinal axis of the closure. The outer frusto-conical surface  23  and the inner annular surface  24  each comprise about one half of the radial width of the upper surface of the rib  18 . In use it is the annular surface  24  which engages under the flange  30  on the neck of the container  29  to which the closure  10  is attached. The presence of the frusto-conical surface  23  assists in the molding of the closure  10  as it prevents or at least substantially reduces the production of closures having deformed ribs  18 . It also ensures rigidity of the rib  18  and thereby prevents distortion of the rib  18  as it is forced over the retaining flange  30  as the closure  10  is screwed down onto the container  29 . The rib  18  is sufficiently robust that it can, on its own, withstand the forces applied to it during application to the container  29  and also prevents the cap  14  from being removed without breaking the frangible bridges  13  either by normal removal of the cap  14  or due to tampering with the container  29 . It has been found that there is no deleterious effect in not having the annular surface  24  extend across the full width of the upper surface  21  of the rib  18 . 
     Below the rib  18 , and still on the inside surface of the body portion  12  of the band  11 , is an arrangement of a plurality of inwardly extending projections  25  and  28 , each having a long axis generally aligned with the longitudinal axis of the closure  10 . The projections  25  and  28  extend radially inwardly from the inner surface of the body portion  12  sufficiently to come into contact with the retaining flange  30  during application of the closure  10  to the container  29  and once the container is capped to lie close to the outer neck surface of the container  29 . Each alternate inwardly extending projection  28  is spaced below the break  20  in the substantially continuous rib  18  and is not connected to the rib  18 . Each of the remaining inwardly extending projections  25  are connected at one end to the centre of a rib portion  19 . 
     The radially inner free edge of each rib segment  19  projects inwardly well beyond the innermost extent of the projections  25  and  28  and must be sufficiently sturdy to be self-supporting during application of the closure  10  to the container  29  and in preventing the band  11  from riding up over the retaining flange  30 . 
     The projections  25  and  28  prevent a person from introducing a device such as a knife blade radially inwardly of the body portion  12  of the band  11  and progressively moving the device circumferentially around the band  11  in an effort to gradually prise the rib  18  up and over its mating flange  30  on the container  29 . 
     Along the outside surface of the band  11  are a number of reinforcements or thickenings  26 . Each thickening  26  extends from a region adjacent the level of rib  18  to a region at the free end of the band  11 . The thickenings  26  in conjunction with the inwardly extending projections  25  and  28  strengthen the band  11  and thus enhance the vertical stiffness of the band  11  whilst retaining a sufficient horizontal or radial flexibility. This also allows sufficient axial force to be applied to the free end of the closure  10  to successfully eject the closure  10  from a core portion of a mold used in its production. 
     The outer surfaces of the thickenings  26  present substantially flat lands  27  which lie radially just outside the radial extent of the rest of the closure  10  to allow the land to be mechanically gripped or otherwise contacted without necessarily contacting the skirt. 
     The closure  10  is formed with a sealing arrangement which includes a concentric annular rib  32  which extends from the underside of the top portion  15  of the cap portion  14 . The annular sealing rib  32  includes a first or root portion  33  which extends downwardly from the top portion  15  approximately parallel to the skirt  16  with a second portion  34  which, prior to engagement with the neck of the container  29 , tapers inwardly and away from the skirt  16 . 
     The second portion  34  of the rib  32  contacts the end  35  of the container  29  as the closure  10  is being screwed onto the container  29 , and the second portion  34  is caused to fold up against the surface of the first portion  33 . Thus there is formed a continuous gas tight seal between the closure  10  and the container  29  extending up the side wall  36  of the container  29  to the end  35  of the container  29 . 
     As the closure  10  is screwed onto the neck of the container  29 , the second portion  34  of the sealing rib  32  is deformed by being bent towards the top  15 . The deformation continues and contact is made between the second portion  34  and an inner rib  37  on the inside surface of the top  15 . The inner rib  37  in fact is not essential to the invention and can be dispensed with if desired. 
     Once the second portion  34  has contacted the top portion  15 , further movement attaching the closure  10  will press and grip the contacting part of the second portion  34  between the container end  35  and the top portion  15 . As the movement attaching the closure  10  continues, it tends to pinch the free edge of rib  32  between the container  29  and the top portion  15  and to “pull” the first portion  33  of the annular rib  32  tightly in towards the container end  35  to produce a tight seal about the curved edge surface of the container  29  extending from its extreme end annular surface  35  down the side wall  36 . 
     As the closure  10  is screwed onto the neck of the container  29 , the screw thread  31  also engages the thread  39  on the interior surface of the skirt  16 . As the closure  10  moves down the neck of the container  29  the frangible bridges  13  form an annular weak zone which allows the rib  18  to diametrically expand over the retaining flange  30  of the container  29 . 
     In this embodiment the frangible bridges are equally spaced about the circumference of the closure  10  and the axis of each frangible bridge  13  is inclined such that when seen in side elevation the upper end of each bridge  13  is inclined to the left relative to its lower end. The bridges  13 , therefore, bend as the closure  10  is screwed clockwise onto the container  29 . As the rib  18  expands over the flange  30 , the lower edge  42  of the skirt  16  and the upper edge  41  of the band  11  have room to flex towards each other whilst still having the bridges  13  therebetween. This stabilises the band  11  and reduces the likelihood of the bridges  13  breaking during application. 
     Once the rib  18  has passed over and engaged under the flange  30 , the frangible bridges  13  return to their extended orientation (FIG.  11 ). As the closure  10  begins to be unscrewed from the neck of the container  29 , the rib  18  detains the band  11  under the flange  30 . As the closure  10  is unscrewed further, the bridges  13  are straightened which serves to concentrate the forces tending to rupture the bridges  13  at the point of attachment of each bridge  13  to the band  11  and to the skirt  16 . 
     As is best seen in FIG. 1, inside the skirt  16  is a thread made up of a plurality of thread segments  51  arranged in spaced apart array along the locus of the thread. Each thread segment, except the first segment  52 , is bounded at each end by a planar surface  53 . Each of the planar surfaces  53  is inclined to the longitudinal axis of the closure  10  so that it faces away from the top  15 . Each planar surface  53  is also inclined relative to a notional radial plane extending from the axis of the closure  10  to the planar surface  53  in question such that the minimum included angle between the planar surface  53  and the skirt  16  is acute and is less than the angle that a notional radial plane makes with the skirt  16 . 
     The first thread segment  52  is formed with a planar surface  53  on its trailing edge, however it is formed with a point  54  on its leading edge to assist in mating the thread on the closure  10  with a corresponding thread on the neck of the container  29 . 
     The thread segments  51  in each turn of the thread are aligned as are the spaces between them. A groove  43  is formed on the inside surface of the skirt  16  in each of the aligned spaces between adjacent thread segments  51 . The grooves  43  serve to assist in venting gas from a carbonated beverage container as the closure  10  is unscrewed. 
     The end faces of each of the rib segments  19  are each angled as has been described in respect of thread segments. This reduces the likelihood of the ends of the rib segments  19  being damaged as the closure  10  is ejected from a mould. 
     The closure  10  is moulded on a mould core which defines, inter alia, the inside surface of the skirt  16 , the thread segments  51  and the grooves  43 . It has been found that by forming the thread segments  51  with planar surfaces  53 , damage to the thread segments  51  upon theclosure  10  being ejected off the mould core has been significantly reduced as compared with forming each of the thread segments with a pointed end similar to point  54 . 
     FIG. 12 depicts that part of a mould  44  used to mould the rib segments  19 . It can be seen that the mould defines a recess  45  corresponding in cross-sectional shape to the desired slope of the rib segments  19  and is divided into an outer first surface  47  and an inner second surface  48 . The first surface  47  is contiguous with a cylindrical surface  49  of the mould which defines the inside surface of the band  11 . This first surface  47  is inclined to a plane normal the axis of the mould by an angle of 20°. The second surface  48  lies in the plane normal to the axis of the mould. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.