Patent Publication Number: US-2002003142-A1

Title: Container closures

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to container closures and particularly, but not exclusively, to tamper-evident closures for containers and to methods of forming such closures.  
       BACKGROUND OF THE INVENTION  
       [0002] The invention stems from our desire to produce a tamper-evident (hereinafter referred to as ′te&#39;) closure that can be produced from sheet plastics material by a thermo-forming process rather than by an injection moulding process. The invention may, however, be applied to injection moulded closures if desired. The containers will usually be tubs for food products, but the invention may be applied to other containers. The invention may also be applied to so-called ′permanent&#39; closures for containers.  
       SUMMARY OF THE INVENTION  
       [0003] According to one aspect of the invention we provide a closure for a container, the container having a mouth surrounded by an external flange extending generally away from the mouth, the closure comprising a closure body adapted to extend across the mouth, a skirt which is disposed below the level of the container flange when the closure is initially secured to the container and the mouth is uppermost, the skirt being connected to the margin of the body by a plurality of spaced-apart bridges which lie adjacent to the outer margin of the flange in the initially secured condition of the closure, and a plurality of upwardly-facing latching formations depending from the skirt and each disposed circumferentially between adjacent bridges as viewed in plan and adapted to latch under the flange, the upper portion of the latching formations each lying vertically beneath a respective tool access aperture provided in the margin of the closure body.  
       [0004] The tool access apertures may be completely open, but they may, at least prior to application of the closure to a container, be covered by flash. In a first embodiment each latching formation comprises a latch wall supported on the skirt in an inclined position by a pair of substantially triangular fillets connected to opposite side edges of the latch wall, the latch wall being of substantially trapezoidal shape.  
       [0005] In a second embodiment each latching formation is defined by a pair of triangular latch walls having a common edge which is inclined inwardly and upwardly of the closure.  
       [0006] When the closure has been produced from a flat sheet of plastics material by thermo-forming, said upper portion of the latching formations has preferably been formed from the material that occupied the tool access apertures in the sheet material.  
       [0007] According to a second aspect of the invention we provide a method of forming a latch formation during thermo-forming of a closure in accordance with the first aspect of the invention, comprising creating a tool access aperture in the margin of the closure body, and causing a tool projection to extend axially through the tool access aperture in the direction normal to the plane of the closure body, the tool projection being shaped to assist in deforming the sheet material to provide an inclined latching formation, and relatively separating the tool projection and closure body by relative axial movement apart.  
       [0008] It will be appreciated that in the absence of the tool access apertures, a tool for forming the upper portion of the inclined latching formation would need to be provided with retractable tool parts to facilitate relative separation of the formed closure body and tool, which of course leads to substantially increased costs. The present invention can enable thermo-forming to be carried out in a two-part tool assembly using matched tools.  
       [0009] The tool projection preferably comprises a narrow shoulder which provides a forming surface to define the upper margin of the upper portion of the latch formation in the closed condition of the tools, and the tool shoulder is preferably bounded by a cutting edge of the tool projection that creates the respective tool access aperture.  
       [0010] In order to provide a cutting action the other tool of the tool assembly is preferably provided with a complementary cutting edge to that of said cutting edge.  
       [0011] The inclined walls of the latching formation may be thermo-formed from sheet material between complementary tool formations on a two-part tool assembly, or said walls may be formed by the action of differential pressure acting against a tool surface on just one of the tool parts. The central portion of the closure body is preferably shaped to have a plug-fit with the container, and the closure body is detachably connected to the skirt by frangible connections which have to be broken on or prior to initial removal of the closure body from the container.  
       [0012] The frangible connections are preferably defined by a plurality of slits which are positioned in the margin of the closure body between the tool access apertures, and the tool access apertures are preferably of substantially trapezoidal shape as viewed in plan, the slits extending substantially lengthwise of said margin.  
       [0013] In one embodiment the skirt is provided with a pull-tab and with a weakened region adjacent to the pull-tab, to enable the skirt to be broken on firm pulling of the pull-tab, and then the skirt and bridges can be peeled away from the container, the peeling action breaking the frangible connections in the margin of the closure body. Once the skirt has been removed, it is then evident that the closure has been subject to attention. In a second embodiment the skirt remains on the container after initial opening of the closure, this being facilitated, for example, by provided a pull-tab which is fast with the central portion of the closure body, and the skirt is left substantially intact.  
       PREFERRED EMBODIMENTS OF THE INVENTION  
       [0014] Various container and tamper-evident closure assemblies in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] In the drawings:  
     [0016]FIG. 1 is a perspective view of a first container and closure assembly prior to initial opening of the closure,  
     [0017]FIG. 2 is an enlargement of the portion  2  of FIG. 1,  
     [0018]FIG. 3 is a front elevation of the unopened assembly of FIG. 1,  
     [0019]FIG. 4 is a plan view of the unopened assembly of FIG. 1,  
     [0020]FIG. 5 is a computer simulation of the assembly corresponding to the view of FIG. 1, and in which the container is of darker material than the closure,  
     [0021]FIG. 6 is a vertical section on the line  6 - 6  of FIG. 4,  
     [0022]FIG. 7 is a vertical section of the line  7 - 7  of FIG. 4, a forming tool projection being indicated in the upper part of the drawing,  
     [0023]FIG. 8 is a perspective view of a second container and closure assembly prior to initial opening of the closure,  
     [0024]FIG. 9 is a front elevation of the second container and closure assembly of FIG. 8,  
     [0025]FIG. 10 is a plan view of the second container and closure assembly of FIG. 8,  
     [0026]FIG. 11 is a side view of the second container and closure assembly of FIG. 8,  
     [0027]FIG. 12 is an enlarged cross-section on the line  12 - 12  of FIG. 10,  
     [0028]FIG. 13 is an enlarged cross-section on the line  13 - 13  of FIG. 10,  
     [0029]FIG. 14 is a CAD perspective view of the upper tool of a two-part tool set for thermo-forming the lid of FIGS.  8  to  13 , FIG. 15 is a CAD perspective view of the lower tool of the two-part  
     [0030] tool set which comprises the upper tool of FIG. 14,  
     [0031]FIG. 16 is a CAD enlargement of part of the view of FIG. 14, boundary lines having been inserted to show the transition between one surface shape and a different surface shape,  
     [0032]FIG. 17 is a CAD enlargement of part of the view of FIG. 15,  
     [0033]FIGS. 18 and 19 are perspective views from different directions of a modified closure to that shown in FIGS.  8  to  13  and suitable for use with the second container, and  
     [0034]FIG. 20 is a plan view of the closure of FIGS. 18 and 19. 
    
    
     [0035] With reference to FIGS. 1 and 6, a thermo-formed plastics container is in the form of a tub  1  sealably closed by a tamper-evident closure in the form of a circular thermo-formed lid  3 .  
     [0036] The shape of the tub is substantially conventional which highlights an advantageous feature of the invention, that the inventive closure can be used with this well-known type of tub. The tub  1  comprises a sloping sidewall  4  connected by annular step  5  with a hook-shaped (in transverse cross-section) rim  6  which terminates in a downwardly and outwardly directed flange or lip  7 , the sidewall  4  in its upper region being expanded in this example to provide an annular sealing land  8 .  
     [0037] The lid  3  comprises a closure body  9  of shallow cup shape and a downwardly directed skirt  10 , the circular base  11  of the closure body being connected to the vertical wall  12  of the body  9  by means of a substantially U-shaped corner  12  provided with two vertically-spaced apart sealing ribs  13 ,  14  which effect a liquid tight seal with the sealing land  8 , in known manner.  
     [0038] The lower portion  14  of skirt  10  is flared downwardly and outwardly, that is, away from the mouth  16  of the tub, defined essentially by the encircling land  8 , whereas the upper portions of skirt  10  are substantially vertical wall elements  17  of oblong-shape connected to the radially outer margin  18  of closure body  12  by respective vertical bridges  19 .  
     [0039] As best shown in FIGS. 2, 5 and  7  a plurality of latch formations  20  are each located substantially circumferentially, as viewed in plan, between respective adjacent pairs of bridges  19  and are supported by the skirt  10 . The latch formations  20  have been thermo-formed from the embryo sheet material of the lid, as will be described later. Each latch formation  20  comprises an inclined latch wall  21  of substantially symmetrical trapezoidal shape and a pair of triangular fillets  22  which interconnect opposite side edges of the latch wall  21  with the respectively adjacent pairs of vertical wall elements  17 , each latch wall  21  being directed upwardly and inwardly with respect to the closure body  9 , so as to define a horizontal latch abutment  23 , FIG. 7, which is positioned radially inwards relative to bridges  19  for latching engagement under the lip  7  of the tub rim  6 .  
     [0040] The latch abutment  23  is provided by the narrow upper edge of the latch wall  21 .  
     [0041] The margin  18  of the formed closure body  9  is cut-away by a series of circumferentially-spaced apart tool access apertures  25  of symmetrical trapezoidal shape, the apertures  25  extending between bridges  19  and in plan view being in register with the upper portions of the respective latch formations  20 , to enable a sloping nose  26  and abutment-forming shoulder  26 ′, FIG. 7, of an upper thermo-forming tool  27  to be retracted axially upwardly of the lid following forming, through the apertures  25 , the nose  26  having assisted in shaping the walls  21 ,  22 , and the shoulder  26 ′ having assisted in shaping of the latch abutment  23 . It will be seen that the apertures  25  leave the margin  18  of the closure body  9  as a series of trapezoidal radial projections, and each of these projections  28  is connected to the remainder of the closure body  9  by a pair of frangible connecting limbs  29  defined in part by the opposite ends of a series of circumferentially-extending slits  30 .  
     [0042] A first pull-tab  31  on the skirt  10  enables the skirt  10  with depending latch formations  20 , bridges  19  and projections  28  to be separated from the main portion of closure body  9  by a firm pull exerted on tab  31 , break line  32  in skirt  10  and break line  32 ′ in margin  18  enabling initial separation of the skirt  10 .  
     [0043] After removal of the skirt  10  and depending members, the main part of closure body  3  can be removed from the tub by pulling upwards on a second tab  40 , and the tub can be re-sealed by reapplication of the closure body  3  to the tub, sealing being effected by ribs  13 ,  14 .  
     [0044] It will be appreciated that the lid  3  can be thermo-formed from sheet plastics material. The tools may be designed to produce the cut-outs  25  in one closure of the tools, or the cut-outs  25  may be produced during a pre-forming operation. It is preferred, however, that the cut-outs  25  are produced during one closure of the tools, and that all of the cut material is utilised in forming the latch formation.  
     [0045] By suitable modification of the break lines  32 ,  32 ′, by omitting tab  31  and reducing the size of tab  40 , it can be arranged, as in the embodiment of FIGS.  8  to  13 , that the skirt  10  and depending members remain on the tub after initial opening of the lid, by prizing tab  40  from skirt  10  and pulling on tab  40 .  
     [0046] The tenature of the lid is provided by the fact that tab  40  once released from skirt  10  will project from the skirt  10 .  
     [0047] FIGS.  8  to  13  show a second embodiment which differs from the embodiment of FIGS.  1  to  7  principally in the modified configuration of the latching formations  20 .  
     [0048] In FIGS.  8  to  13  parts corresponding to those of the embodiment of FIGS.  1  to  7  have been given corresponding reference numerals.  
     [0049] It will be seen from FIG. 8 that the latching formations  20  are each defined by a pair of triangular walls  22 ′ which have a common edge  21 ′ that is inclined upwardly and inwardly of the lid  3 , so as to be roughly of beak shape.  
     [0050] In effect, by comparison with the construction of FIG. 2, the latch walls  21  of FIG. 2 are replaced by the inclined edge  21 ′ and the vertical wall elements  17  of FIG. 2 are omitted, the bridges  19  being of reduced height in the second embodiment.  
     [0051] It will be appreciated that the latching formations  20  of the second embodiment of FIGS.  8  to  13  are formed in a similar manner to those of the first embodiment of FIG. 1 to  7 , the tool portions  27  (FIG. 7) being suitably modified, as shown in FIGS. 14 and 16 described below. In the second embodiment reduced-thickness tear formations  30 ′ are provided to enable the body  9  of the lid to be removed from the tub  1  by firm pulling on tab  40 , the skirt  10  being left on the tub  1 .  
     [0052] As shown in FIGS. 14 and 16, the upper tool  27  of a two-part tool assembly is provided with a plurality of circumferentially spaced-apart forming noses  26  each of which is surmounted by a respective abutment-forming shoulder  26 ′ of V-shape in underplan view. The shoulders  26 ′ are each bounded in FIG. 16 by a first line  51  at the junction between nose  26  and the shoulder  26 ′, and a second line  52  at the junction between an interrupted frieze  53  of internal gear-teeth form, and the shoulder  26 ′.  
     [0053] Importantly, the line  52  extending along the radially inner, lower margin of each element of the frieze  53  is in the form of a V-shaped cutting edge that acts, in conjunction with a matched cutting edge  54  on the lower tool, to produce the respective cut-outs in the sheet material. The depth of the frieze  53  determines the vertical distance of the latch abutments  23  below the closure body margin  18 . In order to provide the latch abutments  23  with an inclined face, as seen in FIG. 12, to provide an enhanced latch grip, the tool surfaces  26 ′ are part of a frusto-conical surface of large cone angle.  
     [0054] The lower tool part  50  is provided with a series of circumferentially-spaced recesses  55  of complementary shape to that of the noses  26 , but of larger dimensions to take account of the required thickness of the latch walls  22 ′. The recesses  55  are surmounted by a frieze  60  of complementary shape to that of frieze  53  of the upper tool part  27 , the upper edge  54  of the frieze providing the matched cutting edge for cooperation with edge  52  on the upper tool part  27 .  
     [0055] It will be seen from FIG. 16 that the cutting edges  52  are discontinuous in the narrow regions  61  intermediate the radially inwardly-directed teeth of the frieze  53  in order to create the bridges  19 .  
     [0056] The upper and lower tool parts  27 ,  50  are provided with ports  56 ,  57  respectively for connection to suitable pressure/vacuum sources to assist in thermo-forming of the sheet material.  
     [0057] The upper tool part  27  is provided with additional circumferentially-spaced blades  58  to provide weakened lines in the lid to define the vertical sides of tab  40 .  
     [0058] FIGS.  18  to  20  show a modification to the closure of FIG. 8 which differs principally in the configuration of the pull tab  40 . In the construction of FIGS.  18  to  20  the pull tab  40 , in the as-formed condition shown, is directed horizontally outwards from the closure body  9  and lies substantially in register with an upwardly-facing aperture  70  defined by an outward bulge  71  of skirt  15 .  
     [0059] Bulge  71  is of similar depth to the remainder of skirt  15  and accordingly retains the integrity of the skirt when the tab  40  has been pulled to initiate separation of the closure body  9  from the remainder of the closure along the line of weakness  30 ”.  
     [0060] It will be appreciated from what has been previously discussed in relation to the forming of the latching formations  20 , that the tab  40  and skirt bulge  71  can be formed from sheet material by the provision of suitable cutting edges and forming surfaces on the axially movable tools.  
     [0061] Whilst the invention is of particular value in relation to tamper-evident closures, it should be appreciated that the latch formation disclosed can be employed with permanent closures, those that do not have a frangible connection for separating a removable closure body.