Tamper evident screw closures

Abstract

A screw closure for a container includes a tamper indicating ring, a frangible link connecting the ring to the remainder of the screw closure, and a flexible anti-backoff pawl having a root end attached to the tamper-indicating ring. A distal end of the pawl co-operates with a rack tooth formed on the container so as to allow relative rotation between the ring and container in the closure screwing-on direction and so as to resist relative rotation between the ring and container in the closure unscrewing direction. The distal end of the pawl is connected to the ring by a flexible link. Alternatively the pawl is supported in the unscrewing direction by a guard stop or the distal end has an enlarged cross-section whereby it is stiffened to resist bending, and/or the ring is protected by radially projecting covers.

1 . A screw closure for a container, the screw closure comprising:
 a tamper indicating ring;   a frangible link connecting the ring to the remainder of the screw closure;   a flexible anti-backoff pawl having:
 a root end attached to the tamper-indicating ring, and 
 a flexibly movable distal end co-operable with a rack tooth formed on the container so as to allow in normal operation relative rotation between the ring and container in the closure screwing-on or -in direction by flexing of the pawl and so as to jam against a rack tooth and resist relative rotation between the ring and container in the closure unscrewing direction; 
   
       characterised in that the screw closure further comprises a flexible link connecting the flexible anti-backoff pawl and the tamper indicating ring; the flexible link being configured to undergo buckling collapse during screwing on or in of the closure; the flexible link being of a strength to remain unbroken when a forcing tool is used to attempt to move the ring and the remainder of the screw closure in unison in the unscrewing direction, whereby the anti-backoff pawl is constrained by the flexible link against being bent abnormally when the anti-backoff pawl encounters the rack tooth, whereby the forcing tool slips on the ring and causes the frangible link to break. 
     
     
         2 . The screw closure of  claim 1 , in which the flexible link is provided with one or more sections along its length which are thinner than other sections along its length, to form more flexible sections. 
     
     
         3 . The screw closure of any preceding claim, in which the flexible link comprises a curve or bend along its length in the relaxed state. 
     
     
         4 . The screw closure of any preceding claim in which, when the pawl is in the relaxed or normal flexed positions, the flexible link comprises a bowed shape. 
     
     
         5 . The screw closure of  claim 4 , in which the convex side of the bowed shape faces away from the root end of the flexible anti-backoff pawl. 
     
     
         6 . The screw closure of any preceding claim, in which the flexible link is joined to the flexible anti-backoff pawl at or near to the distal end thereof. 
     
     
         7 . The screw closure of any preceding claim, in which the flexible anti-backoff pawl is flexibly attached to the tamper indicating ring. 
     
     
         8 . The screw closure of any preceding claim, in which the flexible anti-backoff pawl comprises a section at or near to its root end which is thinner than a part of the anti-backoff pawl more distant from the root end. 
     
     
         9 . The screw closure of any preceding claim, in which the tamper indicating ring is interrupted to form segments. 
     
     
         10 . A screw closure for a container, the screw closure comprising:
 a tamper indicating ring;   a frangible link connecting the ring to the remainder of the screw closure;   a flexible anti-backoff pawl having:
 a root end attached to the tamper-indicating ring, and 
 a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the ring and container in the closure screwing-on or -in direction and so as to resist relative rotation between the ring and container in the closure unscrewing direction; 
   
       characterised in that a guard stop is formed on or attached to the screw closure adjacent to the flexible anti-backoff pawl and positioned to contact and support the flexible anti-backoff pawl so as to resist bending thereof driven by contact with the rack tooth as the closure is torqued in the unscrewing direction. 
     
     
         11 . The screw closure of  claim 10 , in which the guard stop is thinner than the width of the tamper indicating ring in the closure axial direction and formed on or attached to the tamper indicating ring adjacent to an upper edge thereof; or in which the guard stop is thinner than the width of the tamper indicating ring in the closure radial direction and formed on or attached to the tamper indicating ring adjacent an inner or outer edge thereof. 
     
     
         12 . The screw closure of  claim 10 , in which the guard stop comprises an extension of an annular side wall of the screw closure positioned opposite to the distal end of the anti-backoff pawl. 
     
     
         13 . A screw closure for a container, the screw closure comprising:
 a tamper indicating ring;   a frangible link connecting the ring to the remainder of the screw closure;   a flexible anti-backoff pawl having:
 a root end attached to the tamper-indicating ring, and 
 a distal end co-operable with a rack tooth formed on the container so as to allow relative rotation between the ring and container in the closure screwing-on or -in direction and so as to resist relative rotation between the ring and container in the closure unscrewing direction; 
   
       characterised in that the distal end of the flexible anti-backoff pawl has an enlarged cross-section compared to the remainder of the anti-backoff pawl, whereby the anti-backoff pawl is stiffened to resist bending. 
     
     
         14 . The screw closure of  claim 13 , in which the flexible anti-backoff pawl progressively increases in cross-sectional thickness along its length from the root end towards the distal end. 
     
     
         15 . The screw closure of  claim 13  or  14 , in which the flexible anti-backoff pawl is flexibly attached to the tamper indicating ring. 
     
     
         16 . The screw closure of  claim 13 ,  14  or  15 , in which the flexible anti-backoff pawl comprises a thinned section, at or near to its root end. 
     
     
         17 . The screw closure of  claim 13 ,  14 ,  15  or  16 , in which the distal end of the flexible anti-backoff pawl comprises a first, substantially flat face configured for substantially face-to-face engagement with a generally radially extending or generally vertically extending face of the rack tooth on the container. 
     
     
         18 . The screw closure of  claim 17 , in which the distal end of the flexible anti-backoff pawl comprises a second face for engagement with the container adjacent to the rack tooth. 
     
     
         19 . The screw closure of any of  claims 13 - 18  and any of  claims 1 - 9 . 
     
     
         20 . A screw closure for a container, the screw closure comprising:
 a tamper indicating ring;   a frangible link connecting the ring to the remainder of the screw closure; and   a flexible anti-backoff pawl attached to the tamper indicating ring;   characterised in that the screw closure further comprises a cover overlying at least a part of the outer, radially outwardly facing, circumference of the tamper indicating ring.   
     
     
         21 . The screw closure of  claim 20 , in which the cover leaves at least one section of the tamper indicating ring exposed and visible. 
     
     
         22 . The screw closure of  claim 20  or  21 , in which the cover comprises one or more sections. 
     
     
         23 . The screw closure of  claim 22 , in which the or each section stands out radially from the tamper indicating ring to an extent that at least 50% of the ring lies between tangents to the ring and the outer portion of the envelope of the or each cover section. 
     
     
         24 . The screw closure of  claim 22 , in which a plurality of cover sections are spaced around the ring circumference and stand out radially from the ring to a distance at which tangents to the outer envelopes of adjacent cover sections do not intersect the tamper indicating ring. 
     
     
         25 . The screw closure of any of  claims 20 - 24  and any of  claims 1 - 19 .