Abstract:
A tamper evident lid is provided for mounting over an opening of a container having sidewalls with a lip extending outwardly therefrom to define the opening. The lid has a base, a rim extending about a perimeter of the base for receiving the lip and at least one finger extending upwardly from the rim and toward the base for engaging an underside of the lip. A frangible membrane is associated with the fingers to facilitate outward tearing of the finger regions away from the sidewalls. Each finger has a length exceeding the distance between an inside of the lip and the sidewall.

Description:
[0001]     This application is a continuation-in-part of International Application No. PCT/CA03/00055, filed Jan. 17, 2003, and also a continuation-in-part of International Application No. PCT/CA02/01311, filed on Aug. 26, 2002, and also claims the benefit of U.S. Provisional Application No. 60/399,731, filed Aug. 1, 2002. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to injection moulded containers and their lids. More specifically this invention relates to tamper evident lids which may be applied to standard containers.  
       BACKGROUND OF THE INVENTION  
       [0003]     Tamper evident (TE) features are very important in the packaging industry. Unfortunately, packages having tamper evident features generally require specific container and lid designs making the container and the lid a unique combination. A disadvantage to this type of design is that expensive moulds are required not only for the container but for the lid and the moulds are often limited in design to a single product.  
         [0004]     Many applications in the food packaging industry currently use “standard” container sizes, which can be purchased from a multitude of suppliers. The containers are generally filled with packaging machinery adapted to those container sizes. If special containers and lids are to be used, it may be necessary to install additional machinery in a filling line to accommodate assembly limitations caused by the special tamper evident containers.  
         [0005]     U.S. Pat. No. 5,540,342 by Rathbun describes a lid having a dual locking system to retain the lid on a container. The lid uses a purality of primary beads and secondary locking ribs to retain the lid on the container.  
         [0006]     However, one disadvantage of Rathbun&#39;s lid is that the locking ribs are completely removed from the lid once the lid is initially from the container, thus removing all visual evidence of the released locking ribs.  
         [0007]     It is an object of the present invention to provide a tamper evident lid which may be used with a standard container. Preferably the lid may be mounted onto such a container using conventional packaging equipment currently available in most automated filling lines.  
       SUMMARY OF THE INVENTION  
       [0008]     A tamper evident lid is provided for mounting over an opening of a container having sidewalls with a lip extending outwardly therefrom to define an opening. The lid has a base, a rim extending about the base for receiving the lip and at least one resiliently flexible finger extending radially inwardly from the rim for engaging the lip. Each finger has a length exceeding the distance between an inside of the lip and the sidewall and extends towards the base when the lid is mounted on the container. At least one frangible membrane is formed in the rim and associated with at least one of the fingers for facilitating tearing of the rim to disengage the associated finger(s) from the lip thereby enabling removal of the lid from the container while leaving evidence of removal by way of a torn frangible membrane.  
         [0009]     The rim may have an upper end adjacent the base and a lower edge distal the base with the frangible membrane extending from the lower edge toward the upper end.  
         [0010]     A respective of the frangible membranes may be disposed on opposite sides of at least one finger. Alternatively, at least one pair of fingers may be provided with each one of the pair of fingers disposed on an opposite side of the frangible membrane.  
         [0011]     The frangible membrane may extend to a membrane hinge formed in at least one of the rim and the base. The membrane hinge may be positioned to facilitate disengagement of the associated finger from the lip upon tearing of the frangible membrane.  
         [0012]     The associated finger may be disposed between the membrane hinge and the lower edge.  
         [0013]     The frangible membrane may extend to at least one membrane hinge formed in the rim. Each such membrane hinge may extend from the lower edge toward the base with an associated finger disposed in any area bordered by the frangible membrane, a membrane hinge and a lower edge.  
         [0014]     A pair of fingers may be disposed between a pair of membrane hinges extending from the lower edge toward the base. A frangible membrane may extend from the lower edge to each one of the pair of the membrane hinges so that each of the fingers is disposed in an area bordered by at least part of the frangible membrane, one of the membrane hinges and the lower edge.  
         [0015]     A pair of radially spaced apart frangible membranes may be provided with at least one of the resilient fingers disposed therebetween. A membrane hinge may extend across the base between the frangible membranes to facilitate disengagement of the fingers from the lip upon tearing of the frangible membranes by bending a portion of the base away from the lip.  
         [0016]     A plurality of fingers may be disposed between the frangible membranes of the embodiment described in the preceding paragraph.  
         [0017]     At least one of the fingers may be a webbed finger having a web defined by a reduced thickness region extending toward the rim from a lip engaging end of the webbed finger which is distal the rim.  
         [0018]     Each webbed finger may be provided with a passage therethrough in the form of a window to promote drainage of fluid trapped between the webbed finger and the rim.  
         [0019]     The fingers may be of various profiles including rounded, parallel faced straight, tapered narrowing toward the rim and tapered narrowing toward the rim with a scallop facing the container at an outer end thereof distal the rim.  
         [0020]     Each finger may be curved in a direction generally corresponding to a curvature of the container to provide a lengthened contact zone with the lip.  
         [0021]     The rim may be a recess extending from the fingers to the lower edge to accommodate the fingers thereby facilitating stripping of the lid in an injection moulding process.  
         [0022]     The fingers may extend from the lower edge of the rim.  
         [0023]     At least one pull tab may extend from the lower edge of the rim to facilitate tearing of at least one of the frangible membranes.  
         [0024]     A stacking ring may extend about the base away from the rim to engage the lower edge of an adjacent tamper evident lid when the lids are stacked in order to resist lateral shifting therebetween. The stacking ring may be segmented or continuous.  
         [0025]     A chamfer may extend into the rim from the lower edge at the juncture of the frangible membranes and the lower edge to avoid a sharp corner at the juncture upon tearing of the frangible membrane. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]     Preferred embodiments of the present invention are described below with reference to the accompanying illustrations in which:  
         [0027]      FIG. 1  is a perspective view from below of a tamper evident lid according to the present invention;  
         [0028]      FIG. 2  is a perspective view from above of the lid of  FIG. 1 ;  
         [0029]      FIG. 3A  is a perspective sectional view taken at line  3 - 3  of  FIG. 1 ;  
         [0030]      FIG. 3B  is a view corresponding to  FIG. 3A  but taken from the inside rather than from the outside of the lid;  
         [0031]      FIG. 4  is a perspective sectional view taken on line  4 - 4  of  FIG. 1 ;  
         [0032]      FIG. 5  is an axial section of an outer portion of a lid according to the present invention illustrating how it mounts over a container;  
         [0033]      FIG. 6  is an axial sectional view of a lid according to the present invention being moulded and illustrating the associated mould components;  
         [0034]      FIG. 7  is a schematic view of an injection moulding arrangement for forming a lid according to the present invention;  
         [0035]      FIG. 8  is a perspective view from below illustrating an alternate embodiment for a temper evident lid according to the present invention;  
         [0036]      FIGS. 8   a  and  8   b  are scrap perspective views illustrating alternate features associated with the  FIG. 8  embodiment;  
         [0037]      FIG. 9  is a sectional perspective view illustrating a further alternate embodiment for a tamper evident lid according to the present invention;  
         [0038]      FIG. 10   a  is a perspective view from above illustrating a still further embodiment for a tamper evident lid according to the present invention;  
         [0039]      FIG. 10   b  is a perspective from below of the  FIG. 10   a  embodiment;  
         [0040]      FIGS. 11 and 11   a  illustrate alternate embodiments for a “finger” portion illustrating a tamper evident lid according to the present invention;  
         [0041]      FIGS. 12 and 12   a  are respectively scrap perspective views from below and above illustrating a “pull tab” feature of a tamper evident lid according to the present invention;  
         [0042]      FIGS. 13   a ,  13   b ,  13   c  and  13   d  are scrap perspective views illustrating further alternate embodiments for a “finger” portion of a tamper evident lid according to the present invention;  
         [0043]      FIG. 14  is a scrap perspective view illustrating a still further alternate embodiment for a “finger” portion of a tamper evident lid according to the present invention;  
         [0044]      FIG. 15  is a scrap perspective view illustrating an embodiment of a tamper evident lid according to the present invention wherein a “finger” portion extends from a lower edge thereof;  
         [0045]      FIG. 16  is a perspective view from above illustrating yet another alternate embodiment for a tamper evident lid according to the present invention;  
         [0046]      FIG. 17  is a perspective view from above illustrating the use of chamfered edges as a safety feature associated with “tab” portions of a tamper evident lid according to the present invention;  
         [0047]      FIG. 18  is a perspective bottom view of a further embodiment of the lid of  FIG. 1 ;  
         [0048]      FIG. 19  is an enlarged view of an operated tab portion of the lid of  FIG. 18 ;  
         [0049]      FIG. 20  is a side sectional view taken on the line  5 - 5  of  FIG. 18 ;  
         [0050]      FIG. 21  is a perspective bottom view of an alternative embodiment of the lid of  FIG. 18 ;  
         [0051]      FIG. 22  is a side sectional view taken on line  6 - 6  of  FIG. 21 ; and  
         [0052]      FIG. 23  is a top view of an alternative embodiment of the lid of  FIG. 18 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0053]     A tamper evident lid (“lid”) according to the present invention is generally illustrated by reference  10  in the accompanying illustrations. The lid  10  has a base  12  and a rim  14  which extends about the perimeter of the base  12 .  
         [0054]     Discrete fingers  20  extend from an inside of the rim  14 . The fingers extend radially inwardly and toward the base  12  (inwardly and upwardly as illustrated in the figures).  
         [0055]     The lid  10  is intended for mounting over a “standard container”  13  as illustrated in  FIG. 5 . A portion of a sidewall of such a container  13  is shown in dashed lines at reference  30 . As typical with such containers  13  which are commonly used for food and other applications, the sidewall  30  terminates in an outwardly and downwardly extending lip  32 . The lip  32  defines an opening  34  over which the lid  10  may be mounted.  
         [0056]     Each of the fingers  20  has a length which exceeds the distance or “gap” between the inside of the rim  14  and the outside of the sidewall  30  as illustrated at reference  41 . The length of the fingers  20  exceeds the breadth of the gap as illustrated by arrow  44 . Accordingly, when the lid  10  is forced over the lip  32 , the fingers  20  flex toward a retracted position against the inside of the rim  14 . Once fully past the lip  32 , the fingers flex inwardly, away from the rim  14 , to rest against the sidewall  30 . The direction of this spring bias is indicated by reference  31 . In order to enable the flexing of the fingers  20 , the material of the lid  10  must have a desired degree of resiliency which is characteristic of the type of plastics typically used for such lids (polyethylene for example). Basically the fingers  20  must be able to flex without breaking off.  
         [0057]     Once in place, removal of the lid  10  from the container  13  is resisted by the fingers  20  engaging an underside  36  of the lip  32 . As the ends of fingers  20  rest against the sidewall  30 , the fingers  20  can rely on the sidewall  30  for support and accordingly a tremendous amount of strength is not required from the fingers  20 . This proves advantageous in stripping the lid  20  from an injection moulding assembly, as discussed below.  
         [0058]     To either side of the fingers  20  is a frangible membrane  22  (see  FIG. 1 ) formed in the rim  14  to define “tear tabs”  24 . The tear tabs  24  may be pried away from the sidewall  30  by tearing the frangible membranes  22  to either side to move the fingers  20  out of engagement and away from the lip  32 . This enables removal of the lid  10  from the container  13  but only by leaving evidence in the form of torn frangible membranes  22 .  
         [0059]     A membrane hinge  26  (see  FIG. 3   a ) may be provided at the top of the tear tabs  24  to maintain the tear tabs  24  affixed to the remainder of the lid  10  after tearing of the frangible membranes  22 . This avoids having to tear the tear tabs  24  out entirely in order for the fingers  20  to be disengaged from the lip  32 . Without the hinge  26 , the resiliency of the lid  10  might otherwise keep urging the fingers  20  into engagement with the lip  32  even with the frangible membranes  22  torn.  
         [0060]     Alternatively the membrane hinge  26  may be substituted for a further frangible membrane  22  to allow complete removal of the tear tabs  24 .  
         [0061]     An inwardly extending rib  50  (see  FIG. 1 ) may be provided about the rim  14  of the lid  10  between the break tabs  24 . The ribs  50  serve to further secure the lid  10  over the opening  34  by engagement with the lip  32  (see  FIG. 5 ).  
         [0062]     Preferably the rim  14  at the tear tabs  24  is thinner below the finger  20  (distal the base  12 ) than above the finger  20  (proximal the base  12 ) by an amount corresponding to the thickness of the fingers  20 . This forms a recess  28  (see  FIG. 3   b ) which accommodates the fingers  20  during a stripping stage of the lid  10  in an injection moulding operation.  
         [0063]      FIGS. 6 and 7  illustrate a mould assembly for plastic injection moulding of the lid  10 . The mould assembly includes a cavity  100  which receives a two-part mould core made up of a removing core poppet  102  and a core base  104 . A stripper ring  110  extends about the core base  104  to engage a lower edge  18  of the rim  14  of the lid  10 . The cavity  100  and moving core poppet  102  are movable in opposite relative directions as are the core base  104  and moving core poppet  102 .  
         [0064]     After injection and solidification of a molten resin to form the lid  10 , the formed lid  10  will typically shrink onto the moving core poppet  102  and core base  104  enabling the lid  10  in combination with the core poppet  102  and core base  104  and stripper ring  110  to be moved away from the cavity  100  as the mould is opened. Next, the core poppet  102 , stripper ring  110  and lid  10  move away from the core base  104  toward the cavity  100 . The core poppet  102  stops moving and the stripper ring  110  pushes the lid  10  off of the poppet  102 .  
         [0065]     As shown by dashed lines in  FIG. 6 , the finger  20  flexes away from the base  12  of the lid  10  and is accommodated by the recess  28  as the lid  10  is lifted off of the moving core poppet  102 .  
         [0066]     The fingers  20  will generally retain enough “memory” to resiliently flex toward their original position as the formed lid  10  cools after stripping.  
         [0067]     Alternatively the fingers  20  may be configured to cool so as to point away from the base  12  (“down”) and be pushed into an “upwards” position mechanically after moulding.  
         [0068]     Although six tear tabs  24  are illustrated, other numbers are possible. Generally it is expected that six to eight will prove an optimal compromise between security and effort to remove the lid  10 . It may be possible to have as few as one tear tab  24  if it is broad enough to retain the lid  10  on the container  13 . Two or more is preferable. It is generally not necessary to lift away all of the tear tabs  24  for removal of the lid  10 . Lifting away the tear tabs  24  about half the perimeter and sometimes less of the lid  10  will generally prove sufficient to enable removal of the lid  10  when installed on the container  13 .  
         [0069]     As illustrated in  FIG. 8  it isn&#39;t necessary to provide a frangible membrane  22  on opposite sides of the fingers  20 . For example, more than one finger  20  may be provided between adjacent of the frangible membranes  22 . Alternatively, as illustrated in  FIG. 8   a , a single frangible membrane  22  may be provided adjacent the finger  20 . Whether the latter arrangement is truly effective will depend on the overall configuration of the lid  10  and how many fingers  20  have to be displaced in order to release the lid  10 . This arrangement may be less practical when several fingers  20  are used unless the frangible membrane  22  extends from a lower edge  29  (see  FIG. 11 ) of the rim  14  about the finger  20  to a membrane hinge  26  on an opposite side of the finger  20  as illustrated in  FIG. 8   b.    
         [0070]     In some instances it may be desirable to avoid the use of a membrane hinge  26  or to provide one with significant restorative force characteristics. This might for example be the case where it is desired for the fingers  20  to participate in “locking” the lid  10  to the container lip  32  upon reapplication of the lid  10 . Such an arrangement is illustrated in  FIG. 9 .  
         [0071]     As illustrated in  FIGS. 10   a  and  10   b , the membrane hinge  26  may extend across the base  12  between two frangible membranes  22 . This provides good opening characteristics and is particularly useful for spices and other pourable products.  
         [0072]      FIGS. 11 and 11   a  illustrate fingers  20  of considerably more span than in many of the other illustrations. In order to achieve such a span without interfering with flexing of the fingers  20  toward the base  12  and to maintain engagement between a lip engaging end  21  of the fingers  20  distal the rim  14 , webs  23  are provided. The webs  23  represent a thinner area (i.e. a reduced thickness region) extending toward the rim  14  from the lip engaging end  21 . The webs  23  enable the finger  20  to flex in a manner similar to a row of closely spaced individual fingers  20  of lesser span in side by side juxtaposition.  
         [0073]     The wider span fingers  20  of the  FIGS. 11 and 11   a  embodiment may be more prone to retaining moisture between the fingers  20  and the rim  12 . Accordingly passages or holes in the form of windows  25  may be provided through the fingers  20  as shown in  FIG. 11   a . The windows  25  are illustrated as being rectangular however any configuration may be used including circular and triangular and combinations of the foregoing.  
         [0074]     As illustrated in  FIGS. 12 and 12   a , one or more pull tabs  40  may be provided extending from the rim  14  of the lid  10  away from the base  12 . The pull tabs  40  assist in tearing of the frangible membranes  22  by providing an enhanced gripping surface for digital grasping. Preferably the pull tabs  40  should bend radially outwardly somewhat to assist in stacking of the lids  10 .  
         [0075]     A variety of configurations for the fingers  20  may be utilized.  FIGS. 13   a  through  13   d  illustrated a few representative examples.  FIG. 13   a  illustrates a rounded configuration.  FIG. 13   b  illustrates a straight parallel faced configuration.  FIG. 13   c  illustrates a tapered configuration narrowing toward the rim  14 .  FIG. 13   d  illustrates a configuration similar to that of  FIG. 13   c  but further having a scallop  42  for facing the container extending into its lip engaging end  21 .  
         [0076]      FIG. 14  illustrates a finger  20  which is curved facing the container in a direction generally corresponding to a curvature of the container. This provides a longer contact zone along the lip engaging end  21  than would be possible with a straight finger  20 . A straight finger  20  would have a tendency of only engaging the lip  22  along part of the length of the lip engaging end  21 .  
         [0077]      FIG. 15  illustrates a portion of a rim  14  having a finger  20  extending from its lower edge  29  thereby eliminating a “foot” portion  44  of the rim  14  which extends between the lower edge  29  and the finger  20  in the other illustrations. Such an arrangement is possible but wouldn&#39;t stack as well as the lids  10  having a foot portion  44  and would therefore apply more to large industrial containers than stackable filling lines.  
         [0078]     Referring to  FIG. 16 , to promote stacking a stacking ring  46  may be provided extending about the base  12  in a direction opposite to that of the rim  14 . The stacking ring  46  engages the foot portion  44  of an underlying lid  10  to resist lateral shifting therebetween. The stacking ring  46  may be segmented as illustrated in  FIG. 2  or continuous as illustrated in  FIG. 16 .  
         [0079]     A continuous stacking ring  46  can be easier to manufacture. To provide a continuous stacking ring  46  the membrane hinge  26  may be located on the rim  14  below the base  12 .  FIG. 16  shows two possible arrangements. In the first such arrangement the membrane hinge  26  is to the right of a tab  24  and a frangible membrane  22  extends from the lower edge  29  about the finger (not illustrated) to the frangible membrane  26 . The finger would extend radially inwardly from the tab  24 .  
         [0080]     Alternatively, as shown toward the right of  FIG. 16 , the tab  24  may be defined by a membrane hinge  26  between the lower edge  29  and the base  12  and a frangible membrane  22  to either side thereof. The frangible membranes  22  extend from the lower edge  29  to the membrane hinge  26 .  
         [0081]     As a safety precaution it is desirable to avoid sharp edges upon tearing of the frangible membranes  22 . One way of achieving this, as illustrated in  FIG. 17 , is to provide a chamfer  52  extending into the rim  14  from its lower edge  29  at the juncture of the frangible membrane  22  and the lower edge  29 . The chamfer will avoid a sharp point in the torn frangible membrane  22 . Different arrangements of the membrane hinge  26  and the frangible membranes  22  are illustrated in  FIG. 17  in association with the chamfer  52 .  
         [0082]     Referring to  FIG. 18 , an alternative embodiment of the lid  10  has the rim  14  extending around the periphery of the base  12  and depending from the base  12  to the lower edge  29 . A series of the tabs  24  are located at spaced locations around the rim  14  for indicating the sealing state of the lid  10  when mounted on the container  13  (see  FIG. 5 ), i.e. either previously opened or unopened. The tabs  24  have adjacent frangible membranes  22 , situated adjacent to each of the fingers  20 , between a main sidewall  25  of the rim  14  and the tabs  24 . The frangible membranes  22  extend between the lower edge  29  of the rim  14  and the base  12 . The inwardly extending ribs or undercuts  50  have extending portions  60  that extend past the membranes  22  and overlap onto the underside of the tabs  24 , while leaving sufficient spacing for the fingers  20  as an interrupted portion  62  between adjacent ones of the extending portions  60 . The interrupted portions  62  allow the fingers  20  to flex outwardly towards the retracted position against the inside of the rim  14 . It is noted that the tabs  24  have a first tab portion  24   a  including the overlapped extending portions  60 , and a second tab portion  24   b  positioned between the first tab portion  24   a  and the lower edge  29  of the rim  14 . Further, the lid  10  can also have vertical ribs  74  positioned on the first tab portion  24   a  to help alleviate bounce on the spin bars (not shown) during manufacture of the lid  10 .  
         [0083]     Referring to  FIG. 19 , in operation of the lid  10 , the extending portions  60  interrupt the tearing of the frangible membranes  22 , such that the second tab portion  24   b  separates from the main sidewall  25  of the rim  14 , while the first tab portion  24   a  remains attached thereto. The extending portions  60  of the rib  50  provide tear resistance of the membranes  22 , such that only part of the membranes  22  tears adjacent to the second tab portion  24   b . This partial tearing of the membrane  22  helps to maintain the integrity of the rim  14  between the ribs  50  and the base  12 , such that the lid  10  once opened can be resealed onto the container  13  (see  FIG. 5 ).  
         [0084]     Referring to  FIG. 20 , it can be seen that the first tab portion  24   a  is thinner in cross section than that of the second tab portion  24   b , thereby defining an offset sidewall that provides an offset hinge  64 . It is recognised that positioning of the offset hinge  64  between the portions  24   a  and  24   b  helps to promote bending of the tab portion  24   b  to one side of the extending portions  60 , providing a means for the finger  20  of the tab portion  24   b  to remain positioned away (see ghosted view) from the sidewall  30  of the container  13  (see  FIG. 5 ) once the membranes  22  are partially broken during opening of the lid  10 . Further, it can be seen that a local pocket  66  is provided by the first tab portion  24   a  between adjacent sections of the sidewall  25  (see  FIG. 19 ).  
         [0085]     Referring to  FIGS. 6 and 20 , it is recognised that forming the frangible membranes  22  from the lower edge  29  to the base  12  helps to provide for moulding efficiencies, such as but not limited to reducing the need for slider mould mechanisms (as is known in the art) as compared to forming piecewise membranes  22  (see  FIGS. 16 and 17 ) partway in the rim  14 , which extend from the lower edge  29  to approximately midway to the hinge  26 . Further, it is recognised that the offset sidewall of the tab  24  can help to position ejection forces of the moulding process away from the ribs  50 .  
         [0086]     Referring to  FIG. 21 , an alternative embodiment of the lid  10  is shown having both the offset tab  24  and an offset sidewall  25 , which consists of a first sidewall portion  25   a  and a second offset sidewall portion  25   b . Provision of the adjacent tab portions  24   a, b  and sidewall portions  25   a, b  gives a continuous offset around the rim  14 . For example, the outside surfaces of the tab portions  24   a, b  and the respective sidewall portions  25   a, b  can be flush with one another on either side of the intervening membrane  22 .  
         [0087]     Referring to  FIG. 22 , it is noted that the inside wall of the rim  14  has an inset region  68  located between the tab portions  24   a, b  to help maintain consistency of the thickness of the rim  14 . A tapered transition portion  70  positioned to either side of the tab  24  helps to locally stiffen the connection between the tab portions  24   a, b  (i.e. offset hinge  64 ) to help maintain the structural integrity of the lid  10  when installed on the container  13  (see  FIG. 5 ), as well as to help transfer ejection forces from the lower edge  29  to eject over the rib  50  and rib extending portions  60 . The lid  10  also has an angled abutment member  72  located adjacent to the lower edge  29  and oriented radially inwards from the inside surface of the rim  14 . The angled abutment member  72  increases the thickness of the rim  14  near the lower edge  29 , thereby helping to increase a tendency for toe-in of the lower edge  29  (warping of the lower edge  29  radially inwards) during cooling of the lid  10  in the moulding process. Further, the abutment member  72  can also enhance stackability of the lid  10  by providing a thicker lower edge  29  for placement on the base  12  of an adjacent lid  10  (not shown), outwardly of the stacking ring  46 .  
         [0088]     Accordingly, the lid  10  of FIGS.  18  to  22  includes an offset tab  24  (and optional offset sidewall  25 ) configuration for providing an offset hinge  64  at the point of offset. The extending portions  60  overlap the first tab portions  24   a  to interrupt the rupture of the frangible membranes  22 , such that the membrane  22  tearing is inhibited from damaging the integrity of the rim  14  between the ribs  50  and the base  12 . The thickness of the ribs  50  and corresponding extending portions  60  are sufficient to resist tear continuation of the membrane  22  past the ribs  50 , and therefore restrict or otherwise localise separation of the tabs  24  from the sidewall  25  primarily to the second tab portions  24   b . Maintaining integrity of the rim  14  near the base  12  helps to provide a resealing capability to the lid  10  once opened.  
         [0089]     Referring to  FIG. 23 , an alternative embodiment of lid  10  is shown in a rectangular (or square) configuration. The lid  10  can also have vertical ribs  74  positioned on the first tab portion  24   a.    
         [0090]     The above description is intended in an illustrative rather than a restrictive sense. Variations may be apparent to those skilled in the relevant art without departing from the spirit and scope of the invention as defined by the claims set out below.