Patent Document

TECHNICAL FIELD 
     The present invention relates to end closures for two-piece beer and beverage metal containers having a non-detachable operating panel. More specifically, the present invention relates to forming techniques for improving the openability of a lightweight end closure. 
     BACKGROUND OF THE INVENTION 
     Common end closures for beer and beverage containers have a central panel that has a frangible panel (sometimes called a “tear panel,” “opening panel,” or “pour panel”) defined by a score formed on the outer surface, the “consumer side,” of the end closure. Popular “ecology” can ends are designed to provide a way of opening the end by fracturing the scored metal of the panel, while not allowing separation of any parts of the end. For example, the most common such beverage container end has a tear panel that is retained to the end by a non-scored hinge region joining the tear panel to the remainder of the end, with a rivet to attach a leverage tab provided for opening the tear panel. This type of container end, typically called a “stay-on-tab” (“SOT”) end has a tear panel that is defined by an incomplete circular-shaped score, with the non-scored segment serving as the retaining fragment of metal at the hinge-line of the displacement of the tear panel. 
     The container is typically a drawn and ironed metal can, usually constructed from a thin plate of aluminum. End closures for such containers are also typically constructed from a cut-edge of thin plate of aluminum or steel, formed into a blank end, and manufactured into a finished end by a process often referred to as end conversion. These ends are formed in the process of first forming a cut-edge of thin metal, forming a blank end from the cut-edge, and converting the blank into an end closure which may be seamed onto a container. Although not presently a popular alternative, such containers and/or ends may be constructed of plastic material, with similar construction of non-detachable parts provided for openability. 
     These containers are typically filled with carbonated beverages that create a substantial pressure within the container. Upon opening the container, this pressure must be quickly and safely vented. For this reason can ends are constructed for venting or releasing the internal pressure of the container during the initial opening of the container. 
     When the tab is lifted, an upward force is placed on a rivet that attaches the tab to the end, and a downward force is placed on the tear panel. This causes an initial opening of the tear panel beneath the nose of the tab in an area referred to as the vent region of the can end. Further lifting of the tab causes the tear panel to separate progressively along the score. 
     Upon fracturing of the vent region, rapid disassociation of the tear panel from the end panel, or more simply, the “missiling” of the tear panel may occur. For this reason, some manufacturers place anti-missile features on the consumer side of the can end. 
     One such feature consists of a vent coin inside the score line. This feature causes localized compression. This score compression causes the edge of the tear panel to move over the end panel as illustrated in FIG. 4 of the drawings. Thus, the anti-missile feature and score help prevent the rapid disassociation of the tear panel from the end panel when the end is opened under the pressure provided by the carbonated beverage in the can. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an end closure for a container having an improved openability and resistance to missiling. The end closure includes a vent coin. The vent coin is a substantially obround shaped coin located adjacent to a score groove. The vent coin displaces metal of a large enough area to cold work a residual metal between the score groove and a product side of the end closure. This causes an elastic, compressive state. 
     The vent coin of the present invention collapses the score groove. This is accomplished by moving the vent coin outside of a tear panel defined by the score groove and on the public side of the end closure. A similar result is reached when the vent coin is provided on the tear panel but on the product side of the end closure rather than the public side. 
     The tear panel is slightly tucked below the adjacent portion of the end closure. A first plane of metal defined by the tear panel underlaps a second plane of metal defined by the region of the end closure on the opposite side if the score groove as the tear panel. This is accomplished by placing the vent coin in a location where the residual metal between the score groove and the product side is cold worked such that a flow of plastically deformed residual metal is forced inwardly and over the tear panel. 
    
    
     Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a can end of the present invention; 
     FIG. 2 is a top view of a can end of the present invention without a tab; 
     FIG. 3 is a bottom view of a can end of the present invention; 
     FIG. 4 is a photomicrograph of a prior art score groove; 
     FIG. 5 is a photomicrograph of a score groove of the present invention; 
     FIG. 6 is a photomicrograph of a score groove of the present invention showing the vent coin on the public side and beyond the perimeter of the tear panel; and 
     FIG. 7 is a photomicrograph of a score groove of the present invention showing the vent coin on the product side and within the perimeter of the tear panel. 
    
    
     DETAILED DESCRIPTION 
     While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated. 
     The container end of the present invention is a stay-on-tab end member  10  with improved physical properties including strength. Essentially, the present invention provides a lightweight end member  10  which embodies the physical characteristics and properties required in the beverage container market, as explained below. 
     Referring to FIGS. 1 and 2, the end member  10  for a container (not shown) has a central panel  12  having a seaming curl  14  for joining the wall to the container. The container is typically a drawn and ironed metal can, usually constructed from a thin plate of aluminum or steel, such as the common beer and beverage containers. End closures for such containers are also typically constructed from a cut edge of thin plate of aluminum or steel, formed into blank end, and manufactured into a finished end by a process often referred to as end conversion. In the embodiment shown in the Figures, the central panel  12  is joined to a container by a seaming curl  14  which is joined to a mating curl of the container. The seaming curl  14  of the end closure  10  is integral with the central panel  12  by a countersink area  16  which is joined to the panel outer peripheral edge of the central panel  12 . This type of means for joining the central panel  12  to a container is presently the typical means for joining used in the industry, and the structure described above is formed in the process of forming the blank end from a cut edge of metal plate, prior to the end conversion process. However, other means for joining the central panel  12  to a container may be employed with the present invention. 
     The central panel wall  12  has a displaceable tear panel  20  defined by a curvilinear frangible score  22  with an adjacent anti-fracture score  24  on the tear panel  20 , and a non-frangible hinge segment  26 . The hinge segment  26  is defined by a generally straight line between a first end  28  and a second end  30  of the frangible score  22 . The tear panel  20  of the central panel  12  may be opened, that is the frangible score  22  may be severed and the tear panel  20  displaced at an angular orientation relative to the remaining portion of the central panel  12 , while the tear panel  20  remains hingedly connected to the central panel  12  through the hinge segment  26 . In this opening operation, the tear panel  20  is displaced at an angular deflection, as it is opened by being displaced away from the plane of the panel  12 . 
     The frangible score  22  is preferably a generally V-shaped groove formed into the public side  34   a  of the panel wall  12 . Similarly, the anti-fracture score  24 , is preferably a generally V-shaped groove formed into the public side  34   a  of the panel wall  12  on the tear panel  20 . As is explained in more detail below, the frangible score groove  22  is preferably deeper than the anti-fracture score groove  24 . Accordingly, the score residual, being the amount of frangible material remaining below the frangible score groove  22 , is less than the adjacent anti-fracture score residual. This difference between score residual and adjacent anti-fracture score residual is the score residual differential. 
     The frangible score  22  and the second groove or anti-fracture score  24  are formed using conventional-type of scoring operation during the can end forming process, using tools that include an upper (public side) die with a score knife and a lower (product side) die with an anvil surface. 
     The score residual differential is adapted to provide a tear panel  20  with a score  22  more readily frangible than the anti-fracture score  24 , a significant factor for providing efficient opening of the end member  10 . Having a double score of a frangible score  22  and an anti-fracture score  24  wherein there is a score residual differential is common in the industry. 
     The stay-on-tab end member  10  has a tab  44  secured to the end panel  12  adjacent the tear panel  20  by a rivet  46 . The tab  44  has a lift end  48 , a central region  50 , and a nose portion  52 . The lift end  48  and the nose portion  52  are generally aligned along a central longitudinal axis passing through the rivet  44 . A bead  56  is optionally formed in the tear panel  20  inward of the score  22  and the anti-fracture score  24 . The tear panel bead  56  is useful to draw excess metal, or slack of metal, from the tear panel  20  to tighten the metal of the tear panel  20  and improve opening characteristics of the end member  10  by the tab  44  being lifted to push against the tear panel  20 . 
     The rivet  46  is formed in the typical manner. It is the conventional practice to coin the metal on the central panel  12  proximate the base of the rivet  46  during formation thereof. When the rivet  46  is completely formed in the central panel  12 , a button coin band having a generally circular periphery is also formed and is located about the rivet  46 . 
     During opening of the end member  10  by the user, the user lifts the lift end  48  of the tab  44  to displace the nose portion  52  downward against the tear panel  20 . The force of the nose portion  52  against the tear panel  20  causes the score  22  to fracture, typically in a vent region  58  of the tear panel  20 . As the tab  44  displacement is continued, the fracture of the score  22  propagates around the tear panel  20 , preferably in progression from the first end  28  of the score  22  toward the second end  30  of the score  22 . 
     The frangible score  22  includes a check slot region  62  within the vent region  58 . The check slot region  62  includes an area of thickened residual. The thickened residual causes the propagation of the fracture of the frangible score  22  to slow naturally as the fracture reaches the check slot region  62 . This allows the container to vent safely before the fracture of the frangible score  22  continues. 
     Preferably, the check slot region  62  includes a duel step residual differential. The dual step residual differential includes two levels of residual thickness. Thus, the check slot region  62 , rather than having a constant residual thickness, includes a first step wherein the residual is approximately 0.0023 inches and greater and a second step wherein the residual is approximately 0.0016 inches greater than the score residual. 
     The end member  10  also includes a vent coin  65  (see FIG.  2 ). The vent coin  65  is a substantially obround shaped coin, as differentiated from a score, placed near the frangible score  22 . The vent coin  65  may also be curved slightly to approximate the shape of the frangible score  22 . The vent coin  65  differs from a vent score in that the vent coin  65  causes displacement of the metal on the bottom or product side of the can end  10 . Further, the vent coin  65  can be rectangular or other shapes without departing from the spirit of the invention. 
     One purpose of the vent coin  65  is to prevent the tear panel  20  from missiling during the opening of the container. Missiling is a jutting upward of the tear panel  20  upon venting. Missiling is caused when the frangible score  22  fracture propagates beyond the vent region  58 , before the container pressure is fully relieved. The loose tear panel  20  is then forced upward due to the internal pressure of the container. 
     As the lift end  48  of the tab  44  is raised, a downward force is applied by the nose of the tab  44  to the tear panel  20 . This action also creates an upward force at the rivet  46 . These actions sever the frangible score  22  only in the vent region  58 . This allows a small portion of the tear panel  20  metal to be pushed below the deboss panel  13  to open and vent the pressure within the container. 
     As shown in FIG. 5, the vent coin  65  displaces or compresses the metal near in the score residual, adjacent to the vent region  58  and is of a large enough area to cold work the residual metal between the score  22  and the product side of the can end. This causes an elastic, compressive state. As such, when the frangible score  22  is severed in the vent region  58 , the metal of the tear panel  20  springs out to underlap the metal of the deboss panel  13  in that region. This underlapping portion of the tear panel  20  is believed to keep the remainder of the tear panel  20  in place so as to avoid premature fracture of the remainder of the frangible score  22  and thereby prevent the tear panel  20  from missiling, without appreciably increasing the force necessary to propagate the fracture of the score  22  about the tear panel  20 . This underlapping of the metal may eliminate the need for the check slot  62 , or raised residual area which is typically employed with anti-missiling features in this area. 
     As illustrated in FIG. 4, the vent coin  65  is typically located within the tear panel  20  on the public side of the can end  10 . Placing the vent coin  65  in this location causes the score  22  to collapse which “locks” the tear panel. This design causes the tear panel  20  to overlap the adjacent portion of the can end  10  as the residual metal between the frangible score  22  and the product side is cold worked so that a flow of metal is displaced outwardly toward the deboss panel  13 . This increases the opening push force required to propagate the fracturing of the score  22  because it is more difficult to push the tear panel  20  down through the collapsed score  22  configuration. The missile resistance is also limited because the tear panel  20  side of the score  22  collapses over, rather than under, the adjacent metal of the can end. 
     As shown in FIGS. 5-7, the vent coin  65  of the present invention collapses the score  22  in the opposite manner. This is accomplished by moving the vent coin  65  outside of the tear panel  20  and on the public side of the can end as shown in FIG.  6 . In an alternate embodiment shown in FIG. 7, a similar result is reached when the vent coin  65  is provided on the tear panel  20  but on the product side of the can end  10  rather than the public side. 
     It is believed that the opening of an end be improved by moving the vent coin  65  to a location where the tear panel  20  is slightly tucked below the adjacent portion of the can end. In other words, a first plane of metal defined by a portion of the tear panel  20  underlaps a second plane of metal defined by a portion of the non-frangible portion of the central panel  12  of the can end. This is accomplished by placing the vent coin  65  in a location wherein the residual metal between the frangible score  22  and the product side is cold worked such that a flow of plastically deformed residual metal from the tear panel  20  is forced under the end metal  10 . 
     Resistance to missiling is increased because the tear panel  20  metal is naturally tucked under the adjacent metal of the can end  10 . This arrangement may also eliminate the need for the check slot  62  which is provided to improve resistance to missiling but has the disadvantage of increasing opening force. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the broader aspects of the invention. Also, it is intended that broad claims not specifying details of a particular embodiment disclosed herein as the best mode contemplated for carrying out the invention should not be limited to such details.

Technology Category: 7