Container closure
FIELD OF THE INVENTION 
     This invention relates to a plastics material closure for attachment to the rim of a plastics material container. 
     BACKGROUND OF THE INVENTION 
     The achievement of an ideal container closure requires application of seemingly conflicting design criteria. Thus, a closure must be configured to engage in positive sealing relationship with the rim of its container and yet be capable of relatively convenient removal. Also, the closure must possess sufficient flexural capacity to absorb impact forces (from any direction) which are likely to be encountered in service, without the sealing relationship being broken, and yet be sufficiently rigid to support static loads imposed by stacking of loaded containers. 
     Australian Patent Specification No. 435,466 (W.H. Roper et al) discloses a container-closure arrangement which, apparently, meets some but not all of the above requirements. The referenced patent specification describes one structure in particular (see FIG. 8 of the drawings of the patent specification) which provides for sealing of the closure to the rim of the container and for transfer of a static load from the closure to the wall of the container, the load transfer being provided for by a channel portion of the closure engaging in compression against a ledge portion of the container wall. The load transfer effect is enhanced by the walls of the channel being interconnected by radially extending ribs, but it is thought that these must have the effect of reducing the capacity of the structure to withstand impact forces without the closure-to-container seal being broken. 
     OBJECT OF THE INVENTION 
     The present invention seeks to provide a closure for a container and which is configured to accommodate the application of impact forces as well as providing static load carrying capacity. 
     SUMMARY OF THE INVENTION 
     In broad terms, the present invention provides a closure for a container which has a rim surrounding its opening and a ledge forming a portion of the internal wall of the container. The closure is formed from a resilient plastics material and comprises: 
     a central well having a base and a bordering wall, 
     an inverted first channel which is at least substantially annular and which borders the well, the first channel having a radially inner wall which constitutes the peripheral wall of the well, a radially outer wall, and means interconnecting the inner and outer walls, 
     a non-inverted annular second channel bordering the first channel, the second channel having a radially inner wall which is constituted by the outer wall of the first channel and a radially outer wall, and the second channel having a base portion which is arranged to seat on the ledge of the container when the closure is fitted to the container, 
     an inverted annular third channel bordering the second channel and arranged to receive the rim of the container, the third channel having a radially inner wall which is constituted by the outer wall of the second channel and a radially outer wall which surrounds the rim of the container when the closure is fitted to the container. 
     The closure in accordance with the invention and as above defined is characterized by the provision of the two (first and second) mutually inverted channels in addition to the container rim-receiving (third) channel, with the walls of the first channel being interconnected. The means which interconnect the two walls of the first channel may comprise radially extending ribs. 
     The first channel may be continuous, in which case it would be partitioned by a series of said radially extending ribs, or it may be discontinuous. In the latter case, the first channel would be constituted by at least two and preferably four or more circumferentially aligned trough-like inverted channel segments. 
     An important feature of the closure of the present invention is that the second (non-inverted) channel does not incorporate any radially extending elements such as ribs interconnecting its walls and hence the walls of that channel may flex toward and away from one another should the closure be subjected to radially directed impact forces. 
     The invention will be more fully understood from the following description of two explemplary embodiments of container-closure arrangements. The description is given with reference to the accompanying drawings. 
    
    
     DESCRIPTION OF DRAWINGS 
     In the drawings, FIG. 1 shows a perspective view of two stacked container-closure assemblies, 
     FIG. 2 shows a sectional elevation view of the portion of the container-closure assembly which is encircled in FIG. 1 and identified by the arrow A, the Figure illustrating a first embodiment of the invention, 
     FIG. 3 shows a view of a portion of the underside of the closure which is illustrated in FIG. 2, as viewed in the direction of arrow B, 
     FIG. 4 shows a view which is similar to that shown in FIG. 2, but illustrating a second embodiment of the invention, and 
     FIG. 5 shows a view of the top side of the closure which is illustrated in FIG. 4, as viewed in the direction of arrow C. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     FIG. 1 of the drawings shows two containers 10, each of which is fitted with a closure 11. The containers 10 each have a wall which is slightly conical and the base of the upper container nests within a well of the closure of the lower container. 
     As is shown in FIGS. 2 and 4, the container 10 has a surrounding wall 12 and a base 13 which incorporates an integral annular support portion 14. 
     The upper part of the wall 12 incorporates an inwardly directed annular ledge 15 and, above the ledge, the wall 12 diverges toward the rim 16 of the container. A beading 17 is provided on the outside of the container wall, above the level of the ledge 15, and the beading connects with the rim 16 of the container by way of a slightly concave portion 18. 
     Referring now to the closure as shown in FIGS. 2 and 3 of the drawings: 
     This closure comprises a central well portion 20 having a base 21 and a peripheral wall 22. A first channel 23 having an inverted V-shape borders the well, the channel having a radially inner wall which is constituted by the wall 22 and a radially outer wall 24. The channel 23 is continuous, in the sense that its walls 22 and 24 completely encircle the well 20, but the interior of the channel is partitioned by radially projecting ribs 25. The ribs interconnect the walls 22 and 24 and serve to prevent any change occurring in the angle between the two walls of the channel. 
     A second channel 26 which has a non-inverted V-shape borders the first channel 23, the second channel having a radially inner wall constituted by the wall 24 and a radially outer wall 27. The second channel is open-topped and it is not formed with any interior ribs. 
     The wall 27 has a negatively inclined portion which engages with the inner margin of the container rim 16. 
     Also, the second channel 26 has a base portion 30 which rests on the container ledge 15, this arrangement providing for transfer of loads which are imposed on the closure to the wall 12 of the container. 
     A third, inverted, channel 31 surrounds the second channel and provides a recess for receiving the rim 16 of the container in sealing interengagement. The third channel has a radially inner wall constituted by the wall 27 of the second channel and a radially outer or peripheral wall 32. The wall 32 is formed with an annular inwardly directed projection 33 which snap-fits below and is trapped by the container beading 17 when the closure is fitted to the container. 
     Removal of the closure from the container is effected by prising the projection 33 outwardly and upwardly with respect to the container beading 17, this operation being accommodated by the inherent resiliency of the closure material. 
     Reference is now made to the closure construction that is shown in FIGS. 4 and 5 of the drawings. 
     This closure is similar to that which is shown in FIGS. 2 and 3, except that the first (inverted) channel 23 is not continuous and does not (or need not) incorporate radially extending ribs. Instead, the channel 23 is constituted by four circumferentially aligned trough-like channel segments 23-1, 23-2, 23-3, and 23-4 as best seen in FIG. 5. The channel segments are each terminated by end walls 34 which interconnect the channel walls 22 and 24, and a planar bridge 35 extends between the end walls 34 of adjacent channel segments to join the well base 21 to the base 30 of the second channel 26. 
     Although not so shown in the drawings, each of the channel segments 23-1 to 23-4 may have its walls joined by radially projecting ribs in the same manner as the continuous channel structure as shown in FIGS. 2 and 3. 
     Also, although the closure as shown in the drawings has four of the channel segments 23-1 to 23-4, six such channel segments are preferably provided.