Patent Publication Number: US-7721906-B2

Title: Easy open can end with high pressure venting

Description:
This is a continuation-in-part of Ser. No. 11/533,114, filed Sep. 19, 2006, the entire disclosure of which is hereby incorporated by reference as if set forth fully herein. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates broadly to the field of convenience closures for full-open type can ends. More specifically, this invention relates to an improved rivet formation for attaching a gripping tab to an end panel of such a can end. 
   2. Description of the Related Technology 
   One form of self-opening can which is in wide use is the so called full-open can, in which a peripheral score, generally circular in configuration, is formed in the end panel at or adjacent to the periphery thereof to permit its complete removal. 
   Full-open type cans are to be distinguished from those self opening cans which have a comparatively small removable section which, when opened, provide a comparatively small hole for dispensing the product. The latter type of can end is only appropriate for packaging soda, beer, or other liquids. Full-open type cans, on the other hand, are suitable for packaging solid products such as candy, nuts, meats, or ground coffee. 
   A conventional full-open type can end of the type disclosed in U.S. Pat. No. 5,232,114 to Zysset is depicted in  FIG. 1 . Can end  10  conventionally includes an end panel  12  and an edge-curled peripheral flange  14  that is adapted to be interfolded with an end flange of a can body. At or adjacent to the periphery of end panel  12  is a peripheral score  16  which is indented into the end panel  12  and defines a fixed can end portion  18  and a removable portion or panel  20 . A gripping tab  22  is mounted to the end panel  12  by means of a rivet formation  24 . 
   The gripping tab  22  is positioned close enough to the peripheral score  16  so that when its inner end is rocked upwardly to cause its outer end to move downwardly and exert a downward force on the end panel  12  at or near the peripheral score  16 , a portion of the end panel  12  is bent downwardly to initiate rupture of the peripheral score  16 . Thereafter, an upward and backward pull on the gripping tab  22  by the user induces tearing of the metal in the peripheral score  16  on both sides of the area of initial rupture to complete detachment from the can of the removable portion or panel  20  of the end panel  12 . 
   It is also known within the prior art to employ a vent score behind the rivet formation  24  toward the center of the end panel  12  in order to relieve internal pressure or vacuum that exists within the container, and thereby avoid implosion or explosion as the container  12  is opened by rotation of the gripping tab  22  about the rivet formation  24 . The most frequently used shape for the vent score is curved like a man&#39;s mustache and therefore these scores are generally known as “mustache scores.” 
   For the aforesaid purposes and to promote flexibility and to provide a hinge point for the tab  22  when it is lifted, a mustache score  34  may be formed in the end panel  12 , as is illustrated in  FIG. 1 . Mustache score  34  typically has an inner portion  36  that is defined on a raised area  26  of rivet formation  24  having an outer edge  27 , and at least one outer portion  38  that is defined on the outer surface of end panel  12 . Raised area  26  includes an oval shaped first operation bubble  40 , which is elongated along an axis which is a chord perpendicular to a radius of end panel  12 . Raised area  26  further includes a second operation bubble  30 , which is defined centrally with respect to the first operation bubble  40 . 
   The inner portion  36  of mustache score  34  may be curved about the radial inner periphery of the second operation bubble  30 . The outer portions  38  of the mustache score  34  would typically be shaped so as to flare outwardly from the respective inner portions  36 , and would typically end up at their extreme outer ends to be substantially parallel or slightly curved away from the peripheral score  16 . 
   Although conventional mustache scores such as the one that is described above are generally effective in preventing violent explosions or implosions during the opening of containers that are moderately pressurized or underpressurized, they tend to be ineffective in preventing explosions during the opening of highly pressurized containers. A highly pressurized container for purposes of this document is a container that is pressurized at least 25 pounds per square inch over ambient pressure conditions. 
   A need exists for an improved easy open can end that can be used with highly pressurized containers and that is capable of effectively reducing the likelihood of a violent explosion or implosion occurring when such a highly pressurized container is opened. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the invention to provide an improved easy open can end that can be used with highly pressurized containers and that is capable of effectively reducing the likelihood of a violent explosion or implosion occurring when such a highly pressurized container is opened. 
   In order to achieve the above and other objects of the invention, a full open type of convenience closure which is adapted for sealing an end of a can according to a first aspect of the invention includes an end panel; a peripheral score defined in the end panel, the peripheral score defining fixed and removable portions of the end panel; a tab having a nose portion for exerting a downward force on the end panel in an area that is proximate to the peripheral score; a rivet formation for securing said tab to the end panel; and a flex line score defined in the end panel adjacent to the rivet formation, the flex line score having a first linear portion and a second curved portion. 
   A full-open type of convenience closure which is adapted for sealing an end of a can according to a second aspect of the invention includes an end panel; a peripheral score defined in the end panel, the peripheral score defining fixed and removable portions of the end panel; a tab having a nose portion for exerting a downward force on said end panel in an area that is proximate to the peripheral score; a rivet formation for securing said tab to the end panel; a mustache score defined in the end panel, the mustache score including a central portion that is positioned radially inwardly on the end panel relative to the rivet formation and is curved about the rivet formation and first and second end portions that are curved away from the rivet formation; and a flex line score defined in the end panel adjacent to said rivet formation, the flex line score having a first linear portion and a second curved portion. 
   These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatical view of a previously known easy open can end configuration; 
       FIG. 2  is a perspective view of an easy open can end that is constructed according to a preferred embodiment of the invention; 
       FIG. 3  is a fragmentary cross-sectional view of the easy open can end that is depicted in  FIG. 2 ; 
       FIG. 4  is a fragmentary cross-sectional view of a press assembly that is preferably used in accordance with a preferred embodiment of the invention; 
       FIG. 5  is a diagrammatical depiction of an opening score pattern and a forming tool according to a preferred embodiment of the invention; 
       FIG. 6  is a diagrammatical depiction of an opening score pattern and a forming tool according to a modified embodiment of the invention; 
       FIG. 7  is a diagrammatical depiction of the opening score pattern that is shown in  FIG. 5 ; 
       FIG. 8  is a fragmentary cross-sectional view depicting a forming tool according to the preferred embodiment of the invention; 
       FIGS. 9(   a ) through  9 ( g ) are a series of diagrammatical depictions of a cross-section of the end panel showing seven forming operations in a preferred method of forming an easy open can end according to a preferred embodiment of the invention; and 
       FIG. 10  is a photograph depicting an easy open can end according to the preferred embodiment of the invention after an initial opening step. 
       FIG. 11  is a diagrammatical depiction of an improved opening score pattern and a forming tool according to the preferred embodiment of the invention; 
       FIG. 12  is a fragmentary cross-sectional view depicting a forming tool according to the preferred embodiment of the invention; and 
       FIG. 13  is a diagrammatical depiction of the opening score pattern that is shown in  FIG. 11 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to  FIGS. 2 and 3 , a full open convenience closure or easy open can end  50  that is constructed according to a preferred embodiment of the invention includes an end panel  52  that has pictorial opening instructions  54  embossed thereon. As is conventional, a peripheral score  72  has been formed in the end panel  52  and defines a fixed portion  74  of the end panel  52  and a removable portion  76  of the end panel  52 . A finger well  56  is defined in an upper surface of the end panel  52 . 
   Full open convenience closure  50  further includes a circumferentially extending end curl  58  that is constructed and arranged to be secured to a container using the double seaming process. It also includes a tab  60  that has a main body portion  62  including a nose portion  63  that is constructed and arranged to exert a downward force on the end panel  52  in area that is proximate to the peripheral score  72  when a lifting ring  64  of the tab  60  is lifted by a consumer. A rivet formation  66  secures the tab  60  to the end panel  52 . Convenience closure  50  further preferably includes a double fold  68  that is defined in the end panel  52  adjacent to the peripheral score  72  in order to provide cut protection for the consumer. 
   According to one particularly advantageous feature of the invention, a plurality of opening scores  70  are preferably defined in the end panel  52  in an area that is generally proximate to the location of the rivet formation  66 . The opening scores  70  preferably include a mustache score  78 , a flex line score  80  and a pair of break line scores  98 ,  100 , which are best shown in  FIG. 7 . Although in the preferred embodiment the end panel  52  has all of these scores defined therein it should be understood that in alternative embodiments of the invention the mustache score  78  could be provided without a flex line score, with or without a break line score. 
     FIG. 7  provides a more detailed view of the opening scores  70  in the preferred embodiment. As  FIG. 7  shows, the mustache score  78  preferably includes a central portion  84  that is positioned radially inwardly on the end panel  52  relative to the rivet formation  66  and is curved about the rivet formation  66  in such a manner that a concave side of the central portion  84  faces the rivet formation  66 . The curvature of the central portion  84  is preferably a constant radius of curvature. 
   Mustache score  78  further preferably includes first and second end portions  86 ,  88  that are preferably symmetric with respect to each other about a diametric axis of symmetry  82  that extends through the center  90  of the rivet formation  66 . Each of the first and second end portions  86 ,  88  preferably includes a convex side of curvature that faces the nearest portions of the peripheral score  72 . 
   Each of the first and second end portions  86 ,  88  preferably have a constant radius of curvature R 1  that preferably extends along an arc section that is at least about 150°. The constant radius of curvature R 1  is preferably substantially within a range of about 0.07 inches to about 0.2 inches. 
   The distal ends of the first and second end portions  86 ,  88  in the preferred embodiment point away from the nearest portion of the peripheral score  72 , and a tangent line extending through the distal ends would preferably be substantially perpendicular to a tangent line of the peripheral score  72  at a location where the first tangent line would intersect the peripheral score  72 . 
   Preferably, a transition location  92  between the central portion  84  and the first and portion  86  is located at a transitional angle α from the diametric axis of symmetry  82  that is preferably substantially within a range of about 45° to about 60°. More preferably, this angle is substantially within a range of about 50° to about 55°. 
   The flex line score  80  preferably has a first portion  94  that is located on a first side of the rivet formation  66  and a second portion  96  that is located on a second, opposite side of the rivet formation  66 . The first and second portions  94 ,  96  of the flex line score  80  are preferably aligned and symmetric with respect to each other. The flex line score  80  and its components  94 ,  96  are preferably substantially perpendicular with respect to the diametric axis of symmetry  82 . 
   The flex line score  80  preferably has a residual thickness (i.e., a thickness that remains in the end panel  52  at the location of the score line  80 ) that is substantially the same as a residual thickness of the mustache score  78 . The flex line score  80  further preferably has a residual thickness that is within a range of about 25% to about 40% of a thickness of the end panel  52 . More preferably, the flex line score  80  has a residual thickness that is substantially within a range of about 30% to about 35% of the thickness of the end panel  52 . 
   The mustache score  78  has a residual thickness that is preferably substantially within a range of about 25% to about 40% of the thickness of the end panel  52 . More preferably, the mustache score  78  has a residual thickness that is substantially within a range of about 30% to about 35% of the thickness of the end panel  52 . The mustache score  78  preferably has a residual thickness that is no greater than about 0.0045 inches, and more preferably no greater than about 0.0035 inches. 
   As  FIG. 7  shows, the portions of the mustache score  78  that most closely approach the flex line score  80  present a convex side of curvature that faces the flex line score  80 . 
   In the preferred embodiment of the invention, a pair of break line scores  98 ,  100  are defined in the end panel  52  in order to provide a pre-weakened tearing path between the mustache score  78  and the flex line score  80  that is utilized by the convenience closure  50  during the preliminary stages of opening. The break line scores  98 ,  100  are positioned between the mustache score  78  and the flex line score  80 . Each of the break line scores  98 ,  100  are preferably substantially perpendicular to the flex line score  80  and are aligned with the locations on the respective first and second end portions  86 ,  88  of the mustache score  78  that most closely approach the flex line score  80 . 
   The break line scores  98 ,  100  are preferably substantially perpendicular with respect to tangent lines that would pass through the locations on the respective first and second end portions  86 ,  88  of the mustache score  78  that most closely approach the flex line score  80 . The break line scores  98 ,  100  preferably have a residual thickness that is greater than a residual thickness of the flex score line  80  and that is greater than a residual thickness of the mustache score  78 . The residual thickness of the break line scores  98 ,  100  is preferably substantially within a range of about 30% to about 95% of the thickness of the end panel  52 , with a more preferred range of about 50% to about 80% of the thickness of the end panel  52 . 
   When the convenience closure  50  is used in conjunction with a can body to package contents under high pressure (i.e. over 20 psi), it may be opened by a consumer by gripping the lifting tab and pulling the lift ring  64  upwardly. 
   As the gripping tab  60  pivots about the rivet formation  66 , the nose portion  63  will move downwardly and exert a downward force on the end panel  52  at or near the peripheral score  72 . Before the end panel  52  is bent downwardly enough to initiate rupture of the peripheral score  74 , however, sufficient tension is formed in the end panel  52  in the area near the central portion  84  of the mustache score  78  to cause a rupture of the end panel at the central portion  84 . 
   Pressurized gas within the container will be permitted to harmlessly vent through the rupture in the central portion  84  of the mustache score  78  without affecting the integrity of the peripheral score  72  or accelerating the opening process. The flow of pressurized gas will tend to be directed harmlessly at an oblique angle beneath the fingers of the consumer across the top of the end panel  52  so as not to present a hazard to the consumer. 
   The presence of the flex score line  80  reduces the amount of force that will need to be exerted by the consumer to cause the initial rupture of the central portion  84  of the mustache score  78 . 
   After the convenience closure  50  has vented, the consumer will continue to pull the lifting ring  64  upwardly, which causes the tear or rupture in the central portion  84  of the mustache score  78  to enlarge. The tearing will progressively advance into the first and second end portions  86 ,  88  of the mustache score. At the location on the first and second end portions  86 ,  88  that are closest to the flex line score, the tear line will leave the mustache score and advance directly to the respective first and second portions  94 ,  96  of the flex line score  80  along the path of the break line scores  98 ,  100 . This will occur even in embodiments of the invention where the break line scores  98 ,  100  are not present. 
   The tearing will then move laterally outwardly along the respective first and second portions  94 ,  96  of the flex line score  80 . As this occurs, sufficient downward force will be exerted by the nose portion  63  of gripping tab to rupture the peripheral score  74 . This stage of opening is shown in the photograph that is provided as  FIG. 10 . The consumer at this time may pull the lift ring  64  back to cause the peripheral score  74  to tear, thus removing the removable portion  76  of the end panel  52  from the fixed portion  74 . 
   Referring now to  FIG. 4 , the tooling assembly for forming the convenience closure  50  according to the preferred embodiment includes a third operation press assembly  101  including an upper portion  102  and a lower portion  104  that are mounted for movement with respect to each other. The tooling assembly further preferably includes a first forming tool  106  for forming a top surface of the end panel  52  of the convenience closure  50 . 
   Looking now to  FIG. 5 , it will be seen that the first forming tool  106  preferably includes a first tool surface  108  that is constructed and arranged to form the mustache score  78  and a second tool surface  110  that is constructed and arranged to form the flex line score  80 . The second tool surface  110  includes a first portion  112  for forming the first portion  94  of the flex line score  80  and a second portion  114  for forming the second portion  96  of the flex line score  80 . 
   First forming tool  106  also preferably includes a third tool surface  116  for forming the first break line score  98  and a fourth tool surface  118  for forming the second break line score  100 . As is shown in  FIG. 8 , both the first tool surface  108  and the second tool surface  110  are formed as projections that extend outwardly from the substantially flat, horizontal base surface of the first forming tool  106 . 
     FIG. 6  depicts a first forming tool  120  according to a modified embodiment of the invention. First forming tool  120  is identical in all respects to the first forming tool  106  described above, except that it lacks the third and fourth tool surfaces  116 ,  118  for forming the first and second break line scores  98 ,  100 . First forming tool  120  would be used to manufacture a convenience closure according to a modified embodiment of the invention in which the break line scores  98 ,  100  are not present. 
   A method of making such a convenience closure  50  according to the preferred embodiment of the invention would include a step of providing an end panel blank and providing the tooling discussed above in relation to  FIGS. 4-6 . The tooling would be used in otherwise conventional fashion to form the convenience closure that is discussed in detail above. 
   The preferred method of making the convenience closure  50  utilizes a seven operation manufacturing process. A cross-sectional view of the end panel after each operation is shown diagrammatically in  FIGS. 9(   a ) through  9 ( g ). 
   The first forming operation shown in  FIG. 9(   a ), is used to form the rivet bubble formation on the end panel blank. 
   The second forming operation, shown in  FIG. 9(   b ), completes the formation of the rivet button and begins the formation of a lower safety fold. 
   The third forming operation, shown in  FIG. 9(   c ), forms the score lines that have been described in detail above and pre-folds an upper safety fold. 
   The fourth operation, shown in  FIG. 9(   d ), completes the folding of the lower safety fold. 
   The fifth operation, shown in  FIG. 9(   e ), involves the staking of the tab to the end panel and a final rivet operation. 
   The sixth operation, shown in  FIG. 9(   f ), includes a tab detect function as well as a step of forming an upper fold pre-bulge. 
   The seventh and final operation, shown in  FIG. 9(   g ), involves a step of completing the folding of the upper fold into a position where it will afford cut protection. 
   Referring now to  FIGS. 11-13 , an easy open can end that is constructed according to a second, preferred embodiment of the invention is identical to that described above with regard to the first embodiment of the invention except as otherwise described herein. 
   As  FIG. 13  shows, a plurality of opening scores  270  are preferably defined in the end panel of the can end in an area that is generally proximate to the location of the rivet formation  224 , shown in  FIG. 11 . The opening scores  270  preferably include a mustache score  278 , a flex line score  280  and a pair of break line scores  298 ,  300 , which are best shown in  FIG. 13 . Although in the preferred embodiment the end panel has all of these scores defined therein it should be understood that in alternative embodiments of the invention the mustache score  278  could be provided without a flex line score, with or without a break line score. 
   As  FIG. 13  shows, the mustache score  278  preferably includes a central portion  284  that is positioned radially inwardly on the end panel relative to the rivet formation  224  and is curved about the rivet formation  224  in such a manner that a concave side of the central portion  284  faces the rivet formation  224 . The curvature of the central portion  284  is preferably a constant radius of curvature. 
   Mustache score  278  further preferably includes first and second end portions  286 ,  288  that are preferably symmetric with respect to each other about a diametric axis of symmetry  282  that extends through the center of the rivet formation  224 . Each of the first and second end portions  286 ,  288  preferably includes a convex side of curvature that faces the nearest portions of the peripheral score  272 . Each of the first and second end portions  286 ,  288  preferably have a constant radius of curvature R 1  that preferably extends along an arc section that is at least about 150°. The constant radius of curvature R 1  is preferably substantially within a range of about 0.07 inches to about 0.2 inches. 
   The distal ends of the first and second end portions  286 ,  288  in the preferred embodiment point away from the nearest portion of the peripheral score  272 , and a tangent line extending through the distal ends would preferably be substantially perpendicular to a tangent line of the peripheral score  272  at a location where the first tangent line would intersect the peripheral score  272 . 
   Preferably, a transition location  292  between the central portion  284  and the first end portion  286  is located at a transitional angle α from the diametric axis of symmetry  282  that is preferably substantially within a range of about 45° to about 60°. More preferably, this angle is substantially within a range of about 50° to about 55°. 
   The flex line score  280  preferably has a first portion  294  that is located on a first side of the rivet formation  224  and a second portion  296  that is located on a second, opposite side of the rivet formation  224 . The first portion  294  in this embodiment of the invention preferably includes a substantially linear portion  304  that is proximate to the rivet formation  224  and a second, curved portion  306  at an end of the first portion  294  that is distal from the rivet formation  224 . 
   Similarly, the second portion  294  in this embodiment of the invention preferably includes a substantially linear portion  308  that is proximate to the rivet formation  224  and a second, curved portion  310  at an end of the second portion  296  that is distal from the rivet formation  224 . 
   One purpose of the curved portions  306 ,  310  is to deter possible tearing from occurring near the outer distal ends of the first and second flex line score portions  294 ,  296  during and after opening of the easy open end by a consumer. 
   The first and second portions  294 ,  296  of the flex line score  280  are preferably aligned and symmetric with respect to each other. 
   The linear portions  304 ,  308  of the flex line score  280  and its components  294 ,  296  are preferably substantially perpendicular with respect to the diametric axis of symmetry  282 . 
   The flex line score  280  preferably has a residual thickness (i.e., a thickness that remains in the end panel at the location of the score line  280 ) that is substantially the same as a residual thickness of the mustache score  278 . The flex line score  280  further preferably has a residual thickness that is within a range of about 25% to about 40% of a thickness of the end panel. More preferably, the flex line score  280  has a residual thickness that is substantially within a range of about 30% to about 35% of the thickness of the end panel. 
   The mustache score  278  has a residual thickness that is preferably substantially within a range of about 25% to about 40% of the thickness of the end panel. More preferably, the mustache score  278  has a residual thickness that is substantially within a range of about 30% to about 35% of the thickness of the end panel. The mustache score  278  preferably has a residual thickness that is no greater than about 0.0045 inches, and more preferably no greater than about 0.0035 inches. 
   As  FIG. 13  shows, the portions of the mustache score  278  that most closely approach the flex line score  280  present a convex side of curvature that faces the flex line score  280 . 
   In this preferred embodiment of the invention, a pair of break line scores  298 ,  300  are defined in the end panel in order to provide a pre-weakened tearing path between the mustache score  278  and the flex line score  280  that is utilized by the convenience closure during the preliminary stages of opening. The break line scores  298 ,  300  are positioned between the mustache score  278  and the flex line score  280 . Each of the break line scores  298 ,  300  are preferably substantially perpendicular to the flex line score  280  and are aligned with the locations on the respective first and second end portions  286 ,  288  of the mustache score  278  that most closely approach the flex line score  280 . 
   The break line scores  298 ,  300  are preferably substantially perpendicular with respect to tangent lines that would pass through the locations on the respective first and second end portions  286 ,  288  of the mustache score  278  that most closely approach the flex line score  280 . 
   The break line scores  298 ,  300  preferably have a residual thickness that is greater than a residual thickness of the flex score line  280  and that is greater than a residual thickness of the mustache score  278 . The residual thickness of the break line scores  298 ,  300  is preferably substantially within a range of about 30% to about 95% of the thickness of the end panel, with a more preferred range of about 50% to about 80% of the thickness of the end panel. 
   The presence of the flex score line  280  reduces the amount of force that will need to be exerted by the consumer to cause the initial rupture of the central portion  284  of the mustache score  278 . 
   Looking now to  FIG. 11 , it will be seen that the first forming tool  206  preferably includes a first tool surface  208  that is constructed and arranged to form the mustache score  278  and a second tool surface  210  that is constructed and arranged to form the flex line score  280 . The second tool surface  210  includes a first portion  212  for forming the first linear portion  304  of the first portion  294  of the flex line score  280  and a second portion  220  for forming the curved portion  306  of the first portion  294  of the flex line score  280 . It further includes a third portion  214  for forming the linear portion  308  of the second portion  296  of the flex line score  280  and a fourth portion  220  for forming the curved portion  310  of the second portion  296  of the flex line score  280 . 
   First forming tool  206  also preferably includes a third tool surface  216  for forming the first break line score  298  and a fourth tool surface  218  for forming the second break line score  300 . As is shown in  FIG. 12 , both the first tool surface  208  and the second tool surface  210  are formed as projections that extend outwardly from the substantially flat, horizontal base surface of the first forming tool  206 . 
   It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.