Patent Publication Number: US-6213321-B1

Title: Threaded closure for pressurized containers

Description:
This application is a continuation of my application, Ser. No. 08/490,533 filed Jun. 14, 1995 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to the field of threaded closures for containers, and more particularly to synthetic resinous closures of relatively small diameter employed to seal containers of pressurized contents, typically soft drinks, beer and other carbonated comestibles. Traditionally, such containers have been sealed using metallic caps commonly referred to as crown closures requiring the use of a tool for removal. Over the past fifteen to twenty years, such closures have been almost completely replaced by a synthetic resinous closure either injection molded, or, more commonly, compression molded. Such closures are usually provided with a tamper-evident ring which depends from the lower edge of the cylindrical side wall of the closure, and is interconnected to said edge by frangible bridges formed during the molding operation, or by a separate slitting operation. Annual production of said closures surpasses that of other types of closures, and, not surprisingly, the art relating to such closures is in a highly developed state. 
     Although synthetic resinous closures of this type have many advantages, including the ability to be removed without the use of a tool, and the ability to reseal the container where all of the contents are not consumed upon first opening, they do present significant problems during manufacture. 
     One of the problems concerns the formation of a sealing liner beneath the inner surface of the end wall of the closure. The material used in forming the closure, while possessing a degree of resilience, is normally not possessed of adequate cold flow properties to form a gas tight seal against the mouth of the container neck or finish. This function is normally provided by forming a liner of softer synthetic material in situ using the closure as a female part of the mold in conjunction with a reciprocating male part which flattens and shapes a measured quantity of material. The closure is provided with an inwardly projecting lip which is of lesser diameter than the internal thread diameter forming an undercut or recess which shapes the rim of the flattened seal. That portion of the rim of the seal disposed immediately inwardly of the lip engages the end surface of the mouth of the finish to effect a gas tight seal. It is usual to form that portion to a slightly thicker cross section for greater resiliency. This construction does not permit the formation of a sealing effect which extends outwardly beyond the inner edge of the lip. 
     A more serious problem lies in the provision of frangible ribs or bridges which interconnect the lower edge of the side wall or skirt of the closure with the tamper-indicating band or ring. The bridges must be sufficiently strong so as to avoid breaking when the closures are installed, either by threading or pressing the closures into position, and yet be capable of readily fracturing when the closure is unthreaded. To this end, designs have included the provision of some bridge members which are stronger than other bridge members and are positioned in specific locations, this construction being partially successful when the tamper-evident ring is split and remains attached to the skirt during removal of the closure. Other constructions provide for a camming action utilizing inclined surfaces at the lower edge of the skirt and the upper edge of the tamper-indicating ring. 
     The most common construction used for fracturing the bridges is the use of flexible wings or tabs. One form uses tabs which engage the outer surface of the finish to prevent rotation of the ring relative to the skirt. More commonly, the tabs are pivoted about an axis normal to the axis of the closure and have free ends which engage beneath a radially projecting bead on the outer surface of the container finish. The tabs are not only pivoted relative to the inner surface of the ring, but are flexible as well to permit easy removal without damage from a forming mold. The relatively thin cross section required to produce this flexibility has an adverse result in that the tabs are occasionally not sufficiently rigid to assure prompt breakage of the bridges when the closure is unthreaded. This problem is accommodated by the provision of a radially inwardly extending band on the inner surface of the ring against which the tabs are engaged after being folded through approximately 135 degrees. This engagement reduces the effective diameter of the bead on the tamper-indicating ring to less than that of the corresponding bead on the outer surface of the container, so that it cannot pass the bead on the container, and continued unthreading of the closure serves to break the bridges. The use of this construction is almost mandatory where the bridges are of unequal strength. However, this construction in its so-called second mode of operation requires a substantial degree of unthreading of the closure before the bridges are broken, and no substantial leverage is obtained. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the invention contemplates the provision of an improved closure of the type described in which the above-mentioned problems have been either eliminated or substantially ameliorated. 
     At the upper part of the closure, the seal retaining lip forming an undercut portion which retains the seal in position has been eliminated through the use of superior seal-forming materials permitting the seal to be of greater diameter than heretofore possible to present a greater sealing surface to the peripheral edge of the mouth of the closure. The seal, once cold formed within the closure, bonds to the inner surface of the end wall thereof without the necessity of interlocking projections or surfaces, and is incapable of relative rotation therebetween. 
     At the opposite end of the closure, the above-described relatively complicated flexible tab construction is substituted by hingedly interconnected tabs which are of sufficient cross section to preclude flexing, so as to assure that the free ends thereof will exert an unyielding leveraged force to the undersurface of the container bead to positively fracture the tamper-indicating ring bridges, without the necessity of providing a secondary mode for that purpose. The cross-sectional shape of the tabs is such that they can be readily removed from a mold without damage or difficulty. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, to which reference will be made in the specification, similar reference characters have been employed to designate corresponding parts throughout the several views. 
     FIG. 1 is a side elevational view of an embodiment of the invention, partly in central section. 
     FIG. 2 is an enlarged fragmentary sectional view corresponding to the upper left-hand portion of FIG.  2 . 
     FIG. 3 is a fragmentary enlarged view in perspective showing the structure of hingedly mounted tabs for fracturing frangible bridge structures interconnecting a closure skirt with a tamper-indicating ring. 
     FIG. 4 is a fragmentary view in perspective showing a first alternate construction. 
     FIG. 5 is a fragmentary view in perspective showing a second alternate construction. 
     FIG. 6 is a fragmentary view in perspective showing a third alternate construction. 
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENT 
     In accordance with the invention, the device, generally indicated by reference character  10  is of conventional configuration, including an end wall  11 , a side wall or skirt  12 , a tamper-indicating ring  13  interconnected by frangible bridges  14 , and a resilient liner  15 . Most conveniently, the device, exclusive of the liner  15 , is either compression molded or insert molded from polypropylene or synthetic resinous materials having similar properties. Using techniques known in the art, the liner  15  is formed by depositing a measured quantity of polymeric material in a recess in the inner surface of the end wall. 
     The end wall  11  is bounded by an outer surface  20  and an inner surface  21  which defines a recess  22  in which the liner  15  is formed. It meets with the side wall  12  at a rounded edge  24 . The side wall  12  is bounded by an outer surface  25 , preferably having finger-engaging striations  26  thereon, as well as an inner surface  27  having an upper threaded portion  28 . The tamper-indicating ring  13  is interconnected to the lower edge of the side wall  12  by frangible bridges  40 . The ring  13  includes an upper tapered section  42  bounded by an outer surface  43  and a rounded surface  44  which terminates in a lower edge  45 . An inner surface  46  is slightly tapered and extends downwardly to the area of the edge  45 . A medially positioned section  48  is of relatively thin cross section, and is bounded by an outer surface  49  and an inner surface  50 . A lower section  52  includes an annular main body  53  of relatively thicker cross section bounded by an upper radially extending surface  54  and an inner cylindrical surface  55  which extends to a lower tapered surface  56  which meets a downwardly extending bead  57 . The surfaces  54  and  55  meet in an area of relatively thin cross section indicated by reference character  60 , from which extend a plurality of hinged tabs  61 , conveniently eight in number. The tabs, in unstressed condition, extend inwardly at approximately thirty degrees with respect to the principal axis of the closure and are generally triangular in cross section. Each tab is bounded by an outwardly extending surface  65 , an end surface  66  which meets the surface  65  in a rounded bead  67 . An inner surface  68  extends downwardly from the end surface  66  from an edge  69  to the area of thin cross section  60  which forms a hinge for the tab which is relatively rigid. Extending from the surface  68  are a pair of shaped projections  70  bounded by first and second surfaces  71  and  72  and end surfaces  73 . Referring to FIG. 4 in the drawing, it will be observed that these projections are adapted to contact the surface  55  which determines the limit of the path of travel which the tabs may execute when the container is unthreaded. In this position, the outer surface  65  is disposed at approximately 49 degrees with respect to the principal axis of the closure, whereas in unstressed condition, the surface is disposed at approximately 20 degrees from the principal axis. Thus, the tabs operate only in a single mode in which they are in relatively upright condition, thus assuring a rapid breaking of the frangible bridges during the initial portion of the unthreading operation which removes the closure from the container. While pivoting inwardly, a considerable degree of leverage is obtained whereby the manually transmitted force exerted by the user to unthread the closure is substantially reduced. 
     Turning now to FIGS. 4,  5 , and  6  in the drawings, there are illustrated three alternate constructions, in which, to avoid needless repetition, certain of the component parts corresponding to those of the principal embodiment have been designated by similar reference characters with the additional prefixes “1”, “2”, and “3”. 
     In the form illustrated in FIG. 4, the projections  70  have been replaced by a single projection  170  to provide slightly greater rigidity to the tab when flexed to its inward limit of travel. 
     In the form shown in FIG. 5, the annular main body  253  is shortened in height, to form a somewhat larger bead  257 , thereby saving a degree of material from which the device is molded. 
     In the form illustrated in FIG. 6, the annular main body  353  is extended inwardly beneath the area of thin cross section  360 , so that the tab contacts the upper radial surface  354  rather than the inner cylindrical surface  355  when flexed, this construction being particularly suitable where the tamper ring is not split upon removal of the closure. 
     The invention will be best understood from a comparison of the disclosed structure herein with that disclosed in my prior U.S. Pat. No. 5,107,998 granted Apr. 28, 1992 under the title “Tamper Proof Ring For Threaded Containers”. 
     In my prior patent, the disclosed tamper-indicating ring includes an inwardly directed lower flange which supports a plurality of hook-like members, i.e. tabs, against movement past a predetermined point when the closure is unthreaded. The base of the tabs is formed to interconnect with a curved outer portion of the upper surface of the supporting flange (See FIG.  3 ), so that when the tab is forced downwardly as shown in FIG. 4, an inwardly oriented side surface moves against the more inwardly disposed upper surface of the flange, at which point further downward movement is prevented. This movement develops substantial leverage against the outer surface of the container finish, and results in the splitting of the tamper indicating ring prior to the breaking of some of the frangible bridge members, so that with further unthreading, some of the bridges remain unbroken and the split tamper indicating ring remains attached to the skirt of the closure. The entire cross section of the tabs is, therefore, of relatively thick cross section, so that a compressive force is exerted against the relatively thin medially disposed portion of the tamper ring to result in splitting the ring in that area. 
     By contrast, the presently disclosed structure is directed to the separation of the tamper indicating ring from the closure skirt without splitting the ring, so that it will remain attached to the container as the closure is unthreaded. This is accomplished without the tabs being pivoted to a degree wherein they overlie an inwardly disposed generally vertical surface of a bead to decrease the effective internal diameter of the tamper indicating ring to less than that of the corresponding bead on the container finish as described, e.g. in the McBride U.S. Pat. No. 4,938,370 of Jun. 3, 1990. That structure necessitates a relatively flexible or flabby tab which very often is too thin in cross section to permit operation in a so-called first mode. As a result, the closure must be unthreaded to a considerably greater degree before the frangible bridges interconnecting the ring with the skirt of the closure are broken, often at the limit of the threaded engagement, and without the obtaining of substantial leverage possible only in the first mode of operation. 
     The present construction, therefore, is directed to the provision of tabs which are of substantial cross section along the length thereof, but which have a hinged interconnection at a location of relatively thin cross section, so that they will pivot instead of flex relative to the tamper indicating ring body as the closure is unthreaded to a relatively limited degree, and exert a force against the tamper ring body which is, for the most part, axially directed relative to the axis of the closure, and results in prompt separation of the tamper ring, substantially at the initiation of the unthreading action. 
     To accomplish this result, it is necessary that the tab be free to pivot outwardly to readily clear the tamper ring bead on the container finish when the closure is unthreaded, but be limited in inward pivotal movement in an opposite arcuate path of movement to no more than 40 degrees from the axis of the closure. This can be accomplished using a variety of structures. In the principal embodiment, the triangularly shaped projections contact the inner surface of the tamper ring at the lower main body thereof to prevent further movement. This is equally true in the case of the first and second alternate forms. In the third alternate form contact by the tab is made with a radially inwardly extending surface of the lower main body to create a similar effect. 
     I wish it to be understood that I do not consider the invention to be limited to the precise details of structure illustrated and described in the specification, for obvious modifications will occur to those skilled in the art to which the invention pertains.