Abstract:
An easy open end for a pressurized food container, having an end panel and a conventional aperture score, surrounding the periphery of an aperture through which the contents of the container may be dispensed. A tab is provided to facilitate easy opening of the aperture. The easy open end also includes a vent score, which is arranged to rupture before the main aperture score, to vent the internal pressure in the container, before the container is opened. The end panel and/or tab also defines a shield to prevent the egress of product from the vent opening, when the vent score is severed.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an end adapted for use on a pressurised container. In particular, the invention provides an easy open end suitable for use on a pressurised food can or the like. In a pressurised food can, the food product is inserted into the can and stored therein under pressure. The increased pressure in the can is achieved by pressurising the headspace above the food product. 
     This may be achieved in a number of different ways. For example, a droplet of liquefied, inert gas may be inserted into the can just prior to sealing, as described in U.S. Pat. No. 2,894,844. The liquid evaporates and the resultant gas pressurises the headspace. Alternatively, a portion of the can may be designed such that it can be irreversibly deformed inwardly. After filling the can and sealing the open end thereof, the deformable portion of the can is deformed inwardly, thereby reducing the volume of the headspace and pressurising the headspace gases. This technique is described in European Patent No. EP 0 521 642. 
     The advantage of pressurising a food can is that the can may be made of substantially thinner gauge metal, which is deformable under normal conditions. The increased internal pressure in the can helps to support the walls of the can, providing the rigidity required for handling and transport. The use of thinner gauge metal has significant cost benefits to the can manufacturer and also has significant environmental benefits. 
     Conventional food cans comprise a body, in which a food product is stored, and at least one separate end, which is connected to the free edge of the body, conventionally by seaming and in particular by a technique known as “double seaming”. Conventional ends comprise a flat plate-like centre panel connected to a seaming portion (often referred to as the “cover hook”) via a chuck wall, which supports a seaming chuck during the double seaming operation. At the base of the chuck wall a concave reinforcing bead (looking from the outside of the can) is normally provided, to strengthen the end and support the seam. 
     Some food cans are provided with an easy open end, which is connected to the can body in the same manner as a conventional end. An easy open end differs from the convention end in that a thinned score line is provided on the flat plate-like centre panel, around the periphery of a desired aperture. A tab is connected to the end, usually by a rivet, and the tab has a tail portion and a nose portion arranged on either side of the rivet. The tab is located on the plate-like centre panel with the nose portion overlying or adjacent to the thinned score line, defining the desired aperture. On opening, a consumer lifts the tail portion of the tab, which causes the tab to pivot (axially) about the rivet, pressing the nose portion against the score line area of the can end. This pressure causes the score line to rupture around the periphery of the aperture. The aperture panel may then be pulled free from the remainder of the can, allowing access to the contents of the container. 
     A container, whose contents are held under pressure, has the disadvantage that upon first opening by a consumer, the pressure inside the container is rapidly released to atmosphere and the stream of released gases may carry a quantity of product. This problem is particularly difficult when the product in the container is coloured and/or viscous, as this may spoil a consumers clothes, or where the product is potentially harmful to a consumer. This problem is referred to as “spurting” and is highly undesirable for the consumer. In extreme circumstances, such “spurting” may have explosive force making the can dangerous. The present invention is concerned with controlling “spurting” i.e. controlling the forceful ejection of headspace gases and entrained product particles upon first opening of a pressurised container. 
     A further problem with containers having so called easy open ends is that once rupture of the score line is initiated the rapid release of pressured gases from inside the container may result in uncontrolled severing of the score line, causing the aperture panel to missile. Such missiling is potentially very dangerous. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides an easy open end for sealing a pressurised container, such as a food can or the like. 
     The end has a vent score, which is ruptured to form a vent opening, before the main aperture score begins to rupture. The vent opening allows the internal pressure in the container to be released whilst the aperture score, remains largely intact. This two-stage opening prevents missiling of the aperture panel, because the pressure in the container is largely released, before the container is opened. Furthermore, the end panel and/or tab is designed to define a shield, which ensures that any product entrained within the pressurised gases ejected from the vent opening is retained in the area surrounding the vent opening and does not make contact with the consumer. 
     With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a conventional food can filled with product after the associated end has been sealed to the food can. 
         FIG. 2  shows a side section view of a conventional easy-open food can end prior to opening, having a tab and a “moustache” score vent. 
         FIG. 3  shows a side section of the same end as shown in  FIG. 2 , after the tail portion of the tab has been lifted to the extent necessary to open the vent score, but prior to severing of the main aperture score. 
         FIG. 4  shows a plan view of a portion of the can end shown in  FIGS. 2 and 3  prior to attachment of the tab, showing the layout of the vent score and main aperture score in relation to the position of the rivet. 
         FIG. 5  shows a side section view of a first embodiment of an easy-open food can end according to the invention prior to opening, having a vent score arranged to be overlain by the nose portion of the tab. 
         FIG. 6  shows a side section of the same end as shown in  FIG. 5 , after the tail portion of the tab has been lifted to the extent necessary to open the vent score, but prior to severing of the main aperture score. 
         FIG. 7  shows a plan view of a portion of the can end shown in  FIGS. 5 and 6  prior to attachment of the tab, showing the layout of the vent score and main aperture score in relation to the position of the rivet. 
         FIG. 8  shows a plan view of an alternative embodiment of the can end according to the invention prior to opening, with the vent aperture provided distant from the aperture score and sealed by a tape. 
         FIG. 9  shows a side section view of the same end as shown in  FIG. 8 , prior to opening. 
         FIG. 10  shows a side section view through a portion of a food can end prior to opening, according to another embodiment of the invention. In this embodiment, the end  3  has a vent score overlain by the tail portion of the tab and a ridge in the plate-like portion of the end, surrounding the vent score to act as a shield. 
         FIG. 11  shows the same side section as shown in  FIG. 10  after the tail portion of the tab has been lifted to the extent necessary to open the vent score, but prior to severing of the main aperture score. 
         FIG. 12  shows a plan view of a portion of the can end shown in  FIGS. 10 and 11  prior to attachment of the tab, showing the layout of the vent score and main aperture score in relation to the position of the rivet. 
         FIG. 13  shows a side section view through a portion of a food can end according to another embodiment of the invention prior to opening, having a vent score and a catching feature defined on the underside of the tail portion of the tab. 
         FIG. 14  shows the same side section view as shown in  FIG. 13 , after tail portion of the tab has been lifted to the extent necessary to open the vent score, but prior to severing of the main aperture score. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a conventional food can  1  includes a body  2  and an associated end  3 . The end  3  has a flat plate-like centre panel  31 , a reinforcing bead  42  and a cover hook  41 . The food can  1  is filled with a product  5  to a predetermined fill height, thus leaving an unfilled headspace  6 . The end  3  is placed over the free end of the can body  2  and supported thereon by the cover hook  41 . Thereafter, a portion of the cover hook  41  and the free edge of the can body  2  is rolled together, to form a double seam  4  in a known process. 
     Referring to  FIGS. 2 ,  3  and  4  a conventional easy-open food can end further defines an aperture score  32 , which ruptures to release an aperture panel (not shown), to allow access to the contents of the food can without the need to use a separate opening device. The conventional easy open end again comprises a flat plate-like centre panel  31  on which the aperture score is defined. A tab  7  is fixed to the centre panel  31  by a rivet  8  and comprises a nose portion  71  and a tail portion  75 , arranged on either side of the rivet  8 . The free end of the nose portion  71  of the tab  7  defines a nose  72 , which is used to propagate severing of the aperture score  32  by pressing on or adjacent to it. Thus, the tab  7  is arranged on the centre panel  31  with the nose portion  71  lying in a position where the nose  72  can press on or adjacent to the aperture score. 
     On first opening, a user lifts the tail portion  75  of the tab  7  rotating it vertically about the rivet  8  and thereby pressing the nose  72  on or adjacent to the aperture score  32 , to propagate severing thereof. 
     The end panel  31  has a further vent score  33  overlain by the tail portion of the tab  75  adjacent to the rivet  8 . This vent score  33  (often referred to as a moustache score due to its shape) is arranged to sever before the nose  72  touches the area around the aperture score  32 . The vent score  33  severs to form a vent opening  34 , which allows the pressure in the can to equalise with atmospheric pressure. During processing, the product  5  in the can is heated and may release vapour. Upon cooling the vapour may condense creating a partial vacuum in the container  1 . The vent opening  34  allows the pressure inside the container  1  to equalise with atmospheric pressure prior to severing of the aperture score  32 , thus preventing implosion of the aperture panel. This two-stage opening (i.e. pressure equalisation then severing of the aperture score  32 ) is particularly important in pressurised food cans, where the pressure in the food can is substantially higher than atmospheric pressure. 
     In a first embodiment of the invention (as shown in  FIGS. 5 ,  6  and  7 ) the food can end has a cover hook  41 , reinforcing bead  42  and a tab  7  affixed to the centre panel  31  by a rivet  8 . An aperture score  32  and vent score  33  are provided, but in this embodiment the vent score  33  is overlain by the nose portion  71  of the tab  7 . The nose portion  71  of the tab  7  has a sinusoidal configuration and includes a depression  74 , which is the first part of the nose portion  71  to press against the end panel  31 , when the tail portion  75  of the tab  7  is lifted. The depression  74  is arranged to press adjacent to the vent score  33 , rupturing it to create a vent opening  34 . 
     As already mentioned, a problem with pressurised food cans is that upon first opening of the vent score  33 , the pressurised head space gases are released very rapidly and may entrain particles of product therein. If a conventional venting system is used (as described above), these entrained particles may be fired towards the user (“spurting”). Hence, it is an aim of the present invention to shield a user from contact with any product ejected from the vent opening  34 . 
     As shown in  FIG. 6 , upon opening a can end according to the first embodiment of the invention, the sinusoidal shape of the nose portion of the tab not only initiates severing of the vent score  33 , but also creates a natural shield  76 , to prevent entrained particles of product from being fired towards a user of the can. A disadvantage of this embodiment is that the shield  76  formed by the nose portion  71  of the tab  7  can only accommodate small amounts of product ejected from the container upon venting. Where the product is particularly viscous, large quantities of product may be entrained within the gases vented from the headspace, which cannot be adequately accommodated by this first embodiment. 
     The inventors have found that a greater quantity of “spurting” can be accommodated if the vent opening  34  is provided distant from the side wall of the body  2  of the can i.e. towards the centre of the end panel  31 . A vent in this position minimises the amount of product entrained within the headspace gasses. At the point where the product contacts the side wall of the can body, the product surface is attracted by the side wall and a meniscus forms. Thus, adjacent to the side wall the product surface is closer to the end panel  31  and a vent opening in this position has a greater likelihood of venting headspace gasses in which a large amount of product is entrained. 
     A simple arrangement of an embodiment having a vent opening positioned in the centre of the can  1  is shown in  FIGS. 8 and 9 . An easy open end according to this embodiment comprises an end panel  31  and a tab  7  affixed thereto by a rivet  8  as previously described. A vent opening  34  is provided in the centre of the end panel  31  (as shown in  FIG. 8 ). A tape  9 , at least adhesive in the vicinity of the vent opening  34  and at one end is affixed to the end panel  31 , covering the vent opening  34  and looped around the tail portion of the tab  75 . The tape may be removed by pulling its free end upwards (as shown in  FIG. 9 ), but this limits its shield effect when the pressurised headspace gases are released. Preferably therefore, the tape  9  is removed from the vent opening  34 , by lifting the tail portion of the tab  75 . This means that the tape remains fixed to the end panel  31  on the far side of the vent opening  34  (furthest from the tab  7 ) and the tape  9  itself shields the vent opening  34  and prevents ejected product from making contact with the user. 
     A disadvantage of this simple arrangement is that it requires assembly of the tape onto the finished end and tab and this is not cost effective for a mass-produced item. However, this idea inspired the last two embodiments of the invention, in which the vent score is overlain by the tail portion  75  of the tab  7  and is therefore further from the side wall of the can  1 . 
       FIGS. 10 to 12  show a further embodiment of the invention, which incorporates the principles discussed above, but is suitable for mass production. In this embodiment, the vent score  33  is defined in the area overlain by the tail portion  75  of the tab  7  (see FIG.  10 ). This allows the vent score  33  to be positioned further from the side wall of the can and thereby minimises the “spurting” likely to occur upon first opening of the container. 
     A user who wants to open the can lifts the tail portion  75  of the tab  7 , severing the vent score  33  to create a vent opening  34  (see  FIG. 11 ). The plate-like end panel  31  has a ridge  77  surrounding the vent score  33  and upon first opening, this ridge  77 , in conjunction with a catcher element  78  on the tail portion  75  of the tab  7  creates a shield  76 , which prevents and product ejected from the vent opening  34  from reaching the user. The orientation of the aperture score  32 , vent score  33  and ridge  77  in relation to the rivet  8 , can more clearly be understood from  FIG. 12 . The aperture score  32  is again severed by contact of the nose  72  on or adjacent to the aperture score  32  after the tail portion  75  of the tab  7  has been lifted and the vent score  33  severed to produce a vent opening  34 . 
     A final embodiment of the invention is shown in  FIGS. 13 and 14 . Again, the vent score  33  is overlain by the tail portion  75  of the tab  7 . A guard element on the underside of the tail portion  75  is folded flat against the end panel  31  and held in this folded configuration by the rivet  8 . However, the folded guard element is biased towards its upright orientation, orthogonal to the tail portion  75  of the tab  7  (as shown in  FIG. 14 ) and upon lifting of the tail portion, springs into this upright orientation, providing a shield  76  for the vent opening  34 . 
     As will be appreciated, the final two embodiments (shown in  FIGS. 10 to 14 ) are suitable for mass production as the shield  76  is provided by part of the tail portion  75  of the tab  7  and/or features defined on the end plate  31 . Further embodiments of the invention will be readily apparent to those skilled in the art, embodying the features described by the claims.