Abstract:
The invention relates to a can end for a can, such as an easy opening can, comprising: a central panel; a can end radius for connection to a body of the can; and a countersink connected via a transition wall to the can end radius and via a panel wall to the panel; wherein a panel wall angle is 2°-45°; a panel radius is larger than 0.5 mm; a panel depth is 1 mm-7 mm; and a countersink radius is less than 5 mm; and to cans provided with at least one such a can end.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to a can end for a can, such as an easy opening can, and to such a can provided with at least one such a can end. 
     Such cans are intended for use as a beverage can and as a food can. 
     2) Description of Related Art 
     Generally, beverage cans are thin walled (0.04-0.15 mm). Such a beverage can obtains its strength (after filling and closure) by an internally build up pressure. To that extent the can is filled and provided with gas generating material. After closure, gas formation results in the internal build up of pressure. 
     Generally, food cans are provided with food which may have to be subjected to a pasteurization or sterilization procedure. Accordingly, pressure build up may be temporary during such procedure. However, due to undesired circumstances bacterial growth might result in internal pressure build up after the food can was filled and closed. 
     In relation to both food cans and beverage cans improper processing filling and handling of such cans may result in temporary or continuous pressure build up which may result in a deformation of in particular the can closure at the top end and/or the bottom end. Accordingly, overfilling the can with the content material, too high processing temperatures, unsatisfactory cooling operations, insufficient vacuum drawing in the can, pre-process spoilage of content, gas formation due to an undesired reaction between can metal and the content resulting in gas formation such as hydrogen gas, and incorrect handling resulting in impacting on the can may result in continuous or temporary pressure build up. These pressure build ups may result in a deformation of the can ends to an extent dependent on the pressure build up. 
     One form of localized distortion of the can end is buckling or pleating resulting in a local distortion which could extent into the counter sink and seaming region. The bulked portion may even locally extent beyond the perimeter of the can. Higher pressure build up may result in bulging or even the formation of a so called springer. Such bulges may be forced back into the normal can end position. A hard blow will result in a severe and permanent outbulging of one or both ends of the can. 
     In this respect it is noted that can ends may be designed such that due to pressure build up the concave can end flips out into a convex form (see for instance EP 0 906 222). 
     SUMMARY OF THE INVENTION 
     The present invention has for its object to provide a can end for a can, such as an easy opening can, which sustains higher internal pressures than a conventional can end while managing volume expansion. The can end of the invention has a form such that the resistance of the can end to distortion due to pressure build up is improved. For instance, a can provided with a can end according to the invention having a diameter ranging from 45-260 mm may resist pressures built up to more than 2 bar preferably up to more than 3-4 bar or even up to more than 5 bar. But, if a pre-designed pressure build up is surpassed, then the can end will distort but such that its form will not transform from a concave form into a convex form but will be provided with irregular distortions. Accordingly, the consumer could appreciate that due to the irregular buckled or pleated can end the content may be spoilt and should not be consumed. 
     The form and shape of the can end according to the invention is having a form and shape designed such that high pressure resistance and/or expansion is obtained preferably at minimum thickness of closure and/or body of the can. The pressure resistance is such that the can end and/or can may undergo a temporary deformation due to the pressure built up. Such a deformation allows temporary increase of internal volume of the can thus minimizing the actual pressure. It also allows inspection of the cans according to the invention at different stages during filling, closing, processing and storing using classical detector systems monitoring the outer shape properties. Accordingly, the opportunity is provided to inspect the cans for too low or too high internal pressure. This will provide relevant information in relation to the closing of the cans in pressurization processes and could detect undesired pressure loss due to leakages or pressure raises due to spoilage. 
     The present invention is the result of insights based on experimental research so that by particular shaping and dimensioning the can end the above objectives are fulfilled and the above mentioned drawbacks substantially overcome. 
     Accordingly, the present invention provides a can end for a can, such as an easy opening can, comprising
         a central panel,   a can end radius for connection to a body of the can; and   a countersink connected via a transition wall to the can end radius and via a panel wall to the panel, wherein   a panel wall angle (A 2 , P 2 ) is 2°-45°,   a panel radius (R 4 ) is larger than 0.5 mm   a panel depth (H 2 ) is 1 mm-7 mm, and   a counter sink radius (R 3 ) is less than 5 mm.       

     The panel wall angle A 2 , P 2  is selected within the range of 2°-45°. At a lower angle connecting, such that seaming the can end onto the body may be difficult or problematic. An angle beyond 45° will have an adverse effect on the pressure performance. 
     The panel radius R 4  is larger than 0.5 mm. Below 0.5 mm lacquer applied on the metal may be damaged during the forming of the metal, whereas the resistance to small pleats in the adjacent region towards the panel is insufficient. The panel radius R 4  is preferably selected within the range of 1.0-1.5 mm. A panel radius R 4  larger than 2 mm may result in a reduction of strength and thereby the occurrence of pleating and buckling in the region towards the counter sink. 
     The panel depth H 2  is within the range of 1 mm-7 mm. Below 1 mm panel depth H 2  the panel wall angle A 2 , P 2  will become too large. This will have a negative impact on the pressure resistance. Beyond a panel depth H 2  of 7 mm the panel wall angle P 2  will become too small whereby the pressure resistance will not be affected anymore. 
     For a can end intended as a can bottom the optimum panel depth H 2  is between 2-5 mm and for a top closure is H 2  optimal 2.0-2.5 mm. 
     The counter sink radius R 3  should be less than 5 mm. Otherwise, the strength would be insufficient. A counter sink radius R 3  lower than 0.5 mm could result in lacquer cracking during the forming of the metal. 
     For a can bottom is the counter sink radius R 3  preferably within the range of 0.5-1.5 mm. For a can lid is the optimum counter sink radius R 3  from 0.5-0.7 mm. 
     A can end according to the invention having the indicated dimensions and structure will be improved in sustaining higher internal pressures in combination with (temporary) elastic deformation. Pleats and buckles will appear at higher internal pressures and in localized predetermined locations. Furthermore, early buckling or bursting in the case of an easy open end is avoided and still (due to high internal pressures) total can volume expansions up to 30 cm 3  (at a can diameter of 73 mm) allowed before failure. Generally the internal pressure resistence ranges to at least 2 bar or more, frequently to more than 3-4 bar and even to more than 5 bar. This applies to cans having a diameter of generally 45-260 mm, preferably in the range of 52-153 mm, such as a practical diameter of 73 mm, 83 mm and/or 99 mm. 
     For a optimal pressure performance it is preferred that the panel wall angle A 2 , P 2  is 5°-35°. 
     Smaller pleats and less buckles are formed when the panel radius R 4  is selected in the preferred range of 1.0-1.5 mm, or even at 1.25-1.5 mm. 
     Optimally, the panel depth H 2  is selected between 2.0-2.5 mm. 
     According to one general embodiment the can end according to the invention is a can bottom for a can. In such can bottom the can end radius is connected to the body of the can and forms a foot of the ultimate can. According to an embodiment of the can bottom according to the invention the foot has an end foot radius R 2  which is less than 5 mm, preferably 0.5-1.5 mm. The upper limit for the end foot radius R 2  is such that an axial load does not generate a rolling in of the profile. Thus this can bottom provides less deformability against axial load. Furthermore, when the can end is used for a can which is subjected to thermal processing of the filled can, the closure according to the invention allows the use in continuous cookers, preferably with a can of which its body wall is provided with a rolling bead. For these applications and handling conditions it is preferred that the end foot radius R 2  is within the range of 0.5-1.5 mm. 
     According to a preferred embodiment of the can bottom according to the invention, the foot has a foot radius R 13  of less than 5 mm, preferably of 0.5-1.5 mm. Preferably in combination with a food height H 11  in the range of 1-7 mm, preferably 2-5 mm, the can bottom provides a improved or even perfect stackability of the filled can, in particular those provided with an easy opening top closure. Specially when the load of the upper can is on the top of the seam connecting the can lid to the can body and prevents excess wear on the tab of the can lid and thereby prevention of undesired opening of the can lid. 
     It is noted that the foot of the can bottom may have an outer foot radius R 14 . The dimensions of the outer foot radius R 14  depends on the distance between the foot radius R 13  and the end foot radius R 2 . 
     In addition, the properties and resistance to internal pressure and/or allowance of expansion at various can diameters and wall thicknesses, may be further improved when the unit depth (H 1 ) is 2-10 mm, preferably is 5-7 mm. 
     It is preferred that the can end is provided with a panel outer ring. Such panel outer ring will decrease the sensitivity to pleat formation. 
     For a can bottom it is preferred that in the can bottom a panel outer ring slope (A 3 ) is 0°-35° and a panel outer ring width (L 1 ) is 0-15 mm. The panel outer ring slope A 3  may be up to 35°. A minimum A 3  is about 1°. Preferably the panel outer ring slope A 3  ranges from 2°-20°. The panel outer ring width L 1  is up to 15 mm. A minimum panel outer ring width for improved properties starts from about 0.5 mm or from 1 mm. Preferably L 1  is within the range of 1-5 mm. 
     According to another general embodiment according to the present invention the can end according to the invention is a can lid. It could be an easy opening can lid or any other type of can lid which may require an opener for opening the can. 
     For optimal properties the can lid according to the invention has the unit depth (H 1 ) is 5-7 mm. 
     When the can lid is provided with a panel outer ring then it is preferred that in the can lid the panel outer ring slope (P 3 ) is 0°-35° and the panel outer ring width (L 1 ) is 0-15 mm, preferably 1-3 mm, more preferably 1-2 mm. The panel outer ring width L 1  for the can lid is less than 15 mm and a minimum width is about 0.5 mm. A preferred range for the outer ring width L 1  for the can lid is 1-3 mm, more preferably 1-2 mm. 
     The panel outer ring slope P 3  of the can lid according to the invention is preferably up to 35°. A minimum slope P 3  is as from 0.5° more preferably as from 1° or 2°. The general range is therefore from 0.5°-35° preferably 2°-20°. 
     In both can lid and can bottom there may be an angle with the transition wall. This foot wall angle A 1  ranges from 0°-45°, preferably from 2°-35°. 
     When present the panel outer ring L 1  has a width of more than about 0.1 to 0.2 mm. When present the panel outer ring may be provided with the score line. Preferably, the score line is located closer to the panel center than to the counter sink which is optimal for the burst resistance. 
     Preferably, the panel ring has a slope A 3 , P 3  such that higher internal pressures will less distort the form and structure of the can end. The panel ring slope A 3 , P 3  may be up to 35° which results in a reduction of the formation of pleats. Preferably, the panel ring slope A 3 , P 3  is within the range of 2°-20° whereby the panel is provided with a well rounded shape which is least distorted due to internal pressure build up. 
     The can end according to the invention may be an easy opening can end for an easy opening can. Thus, for opening the can via a preformed opening defined by a score line in the can end it is preferred that the can end is provided with an opening tab. 
     According to another aspect of the invention is provided a can which comprises a body and at least one can end according to the invention as described above. In one embodiment of the can according to the invention, the body may be provided at both ends with a can end according to the invention. In another embodiment only the can lid is a can end according to the invention. The can bottom or can lid may be integral with the body of the can and formed by any conventional process such as DWI, DRD and (deep) drawing. In another embodiment the can may be provided with a body and a can lid and with a can bottom which is a can end according to the invention. 
     Another preferred can according to the invention is a can which is composed of a can lid as described above (preferably with an opening tab and cooperating score line) and with another can lid as described above (not provided with opening means) but functioning as a can bottom. Accordingly, the advantage is obtained that the can lid functioning as a can bottom due to its design has a larger radius and therefore better in internal pressure resistance and allowing more expansion within elastic limits. According to another embodiment the can is provided with a can lid and with a can bottom as described above in relation to the present invention. Either of the can ends may be integral with the body of the can. The other can end is connected to the body of the can by traditional techniques such as seaming. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Mentioned and other features and characteristics of the can end and can according to the present invention will be further illustrated by means of several embodiments which are given for illustrative purposes and are not intended to limit the present invention to any extend. In particular, cans are illustrated with an easy open end, but of course, such cans could also be realized with one or more sanitary end or more generally a non-easy open end. These embodiments will be described with reference to the annexed drawings in which: 
         FIGS. 1 ,  2  and  3  partial cross-sections of can lid according to the invention; 
         FIG. 4  at a smaller scale a can provided with a can lid according to the invention; 
         FIG. 5  at a larger scale the can lid of a can having a localized pleated or buckled region due to internal pressure build up; 
         FIG. 6  shows in cross section a can bottom according to the invention; 
         FIGS. 7-8  are details VII and VIII of  FIG. 6 ; 
         FIG. 9  is an alternative embodiment of the can bottom of  FIG. 7 ; 
         FIGS. 10 and 11  are an alternative embodiment of the can bottom of  FIG. 8 ; 
         FIG. 12  is an alternative embodiment of the can bottom of  FIG. 6 ; 
         FIG. 13  is in cross section a can according to the invention provided with a can lid of  FIG. 3  and as a can bottom the can lid of  FIG. 1  (integrally formed with the can body); 
         FIG. 14  is a can according to the invention as an alternative to the can of  FIG. 4  having as a can bottom the can bottom of  FIG. 6 ; 
         FIG. 15  is a can according to the invention provided with a can lid according to  FIG. 3  and a can bottom according to  FIG. 12 ; and 
         FIG. 16  is a can according to the invention with two can ends seamed to the can body. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a can lid or can bottom  1  according to the invention. The can end has a central panel  2  and a can end radius or curl  3  for attachment, for instance by seaming, to a body of a can. The can end  1  further comprises a counter sink  4  which is connected via a transition wall  5  to a seaming panel  6  of the curl  3 . The counter sink  4  is also connected via a panel wall  7  to the panel  2 . 
     The panel wall angle P 2  is determined by the slope  8  of the panel wall  7  relative to the vertical line  9 . The panel radius R 4  determines the curvature of the connection between the panel wall  7  and the panel  2 . The counter sink radius R 3  determines the internal curvature of the section between the panel wall  7  and the chuck wall  5 . Finally, the panel depth H 2  is the distance between the underside of the counter sink and the panel  2  and unit depth H 1  the distance between seaming panel  6  and the counter sink underside. 
     In the can end  1  is the panel wall angle P 2  15°, the panel radius R 4  1.30 mm, the panel depth H 2  2.3 mm and the counter sink radius R 3  0.6 mm. 
       FIG. 2  shows another can end  10  according to the invention. 
     In comparison to the can end  1  of  FIG. 1  is the panel wall angle P 2  increased. The panel radius R 4  is also increased as well as the counter sink radius R 3 . The panel depth is also reduced. 
     As shown in  FIG. 2  is the can end  10  further provided with a panel outer ring  11  at the circumference of the panel  2  and connected via the panel wall  7  to the counter sink  4 . The outer ring  11  has a width L 1  of 1 mm and is provided with a score line  12 . The panel outer ring  11  has a slope with the horizontal  13 . This panel outer ring slope P 3  is 20°. 
     The dimensions of the can end  10  are panel wall angle P 2 =30°, panel radius R 4 =0.8 mm, panel depth H 2 =1.2 mm, counter sink radius R 3  0.9 mm and panel outer ring width L 1  1.5 mm. 
       FIG. 3  shows a can end  14  according to the invention. In comparison to the can end  10  illustrated in  FIG. 2 , the panel wall angle P 2  is 10°, the panel radius R 4  is 1.8 mm, the panel depth H 2  is 2.4 mm and the counter sink radius R 3  is 0.6 mm. Furthermore, the outer ring width L 1  is 1.5 mm and the outer ring panel slope P 3  is 10°. 
     The following table shows buckle resistance of the can ends  1 ,  10  and  14  (made of steel) dependent on metal range and metal temper. 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 case identification 
                 metal gauge 
                 metal temper 
                 burst pressure 
               
               
                   
               
             
             
               
                 closure 1 of FIG. 1 
                 0.23 mm 
                 TH 580 
                 4.9 bar 
               
               
                 closure 10 of FIG. 2 
                 0.23 mm 
                 TH 580 
                 4.0 bar 
               
               
                 closure 14 of FIG. 3 
                 0.23 mm 
                 TH 580 
                 5.1 bar 
               
               
                 closure 1 of FIG. 1 
                 0.24 mm 
                 TH 435 
                 4.1 bar 
               
               
                 closure 10 of FIG. 2 
                 0.24 mm 
                 TH 435 
                 3.2 bar 
               
               
                 closure 14 of FIG. 3 
                 0.24 mm 
                 TH 435 
                 4.4 bar 
               
               
                   
               
             
          
         
       
     
       FIG. 4  shows a can according to the invention. The can  15  is provided with a body  16  and an integral concave can bottom  16  of greater wall thickness and a seamed can end  18  according to  FIG. 1  (although can ends  10  or  14  of respectively  FIGS. 2 and 3  could also have been applied). The panel  19  of the can end  18  is provided with an opening tab  20  connected via a rivet  21  to the panel  19 . The panel  19  is further provided with a circular score line  22 . Accordingly, the can  15  is an easy opening can for beverage and/or food content. 
       FIG. 5  shows at a larger scale the can of  FIG. 4 . Due to undesired pressure development in the closed container  15  a buckle  23  formed locally (over a part of the circumference) in the region between the counter sink and the panel. As illustrated the other regions of the can end  18  are not distorted. 
       FIG. 6  shows a can bottom  24  of the invention which is integrally connected to a body of the can. The can bottom  24  comprises a central panel  25  which is provided with a outer panel ring  26  which is connected via a panel radius  27  to a panel wall  28  which via a counter sink radius  29  is connected to a transition wall  30 . The transition wall  30  is connected via an end/foot radius  31  to the body wall  32 . The details of the can bottom  24  are shown in  FIGS. 7 and 8 . 
     The minimal value of the outer radius R 14  is dependent on the distance between the food radius R 13  and the end food radius R 2 . 
     The following table shows the buckle (pressure) resistance of the can end  24  of  FIGS. 6-8  at a wall thickness of 0.22 mm and dependent on the unit depth H 1  and the panel depth H 2 . 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                   
                   
                   
                 Buckle 
               
               
                   
                 Thickness 
                 H1 (mm) 
                 H2 (mm) 
                 pressure (bar) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0.22 
                 5.6 
                 3 
                 52 
               
               
                   
                 0.22 
                 6 
                 3 
                 53 
               
               
                   
                 0.22 
                 6.4 
                 3 
                 54 
               
               
                   
                 0.22 
                 6.8 
                 3 
                 55 
               
               
                   
                 0.22 
                 6 
                 2.6 
                 52 
               
               
                   
                 0.22 
                 6 
                 2.8 
                 52 
               
               
                   
                 0.22 
                 6 
                 3 
                 53 
               
               
                   
                 0.22 
                 6 
                 3.2 
                 54 
               
               
                   
                   
               
             
          
         
       
     
       FIG. 9  shows an alternative can bottom  33  according to the invention. This can bottom  33  comprises a panel  34  which is directly connected to a panel radius  35 . Accordingly, this panel  34  does not comprise a panel ring. 
       FIG. 10  shows still another embodiment of a can bottom  36  according to the invention. In this embodiment the can end/foot radius  31  is directly connected to the body wall  32  of the can. Accordingly, this can bottom  36  does not comprise the foot radius R 13  and the outer foot radius R 14  (see  FIG. 7 ). 
       FIG. 11  shows still another alternative embodiment in the form of a can bottom  37  in comparison to the can bottom  24  of  FIG. 8 , the can bottom  37  comprises in the body wall  32  a rolling bead  38  for guiding the closed can provided with the can bottom  37  during processing in a continues cooker. 
       FIG. 12  shows another embodiment of a can bottom  39  of the invention. This can bottom  39  comprises a body wall  32  and a can end/foot radius  31  connected via a transition or chuck wall  30  and a counter sink radius  29  to a panel wall  28 . The panel wall  28  is connected via a panel radius  27  to a central panel  40 . In comparison to the can bottom  24  of  FIG. 6  this panel has a convex shape as the integral can bottom  17  (not according to the invention) as illustrated for the can  15  of  FIG. 4 . 
       FIG. 13  shows a can  41  comprising a body wall  42  provided with a can lid  43  and an integral can bottom  44 . The can lid  43  is a can lid  14  as shown in  FIG. 3 . The can lid  14  is connected by a seam  45  to the body wall  42 . The can lid  14  is provided with an opening tab  46  for opening the can  41  via an opening determined by a score line  12  formed in panel outer ring  11 . The can bottom  44  is a can end  1  as presented in  FIG. 1  as a can lid but integrally formed with the body wall  42 . The can end  1  comprises the panel  2  connected via the panel wall  7  and the counter sink  4  and the transition wall  5  to the curl or can end radius  3  which integrally is connected to the body wall  42 . 
       FIG. 14  shows another can  47  according to the invention. It is an alternative to the can  15  shown in  FIG. 4 . In this alternative the can bottom  48  is formed by the can bottom  24  as shown in  FIG. 6 . 
       FIG. 15  shows another can  49  according to the invention which is an alternative to the can  44  of  FIG. 13 . In this case the can bottom  50  has the form of the can bottom  39  as illustrated in  FIG. 12 . 
     Finally,  FIG. 16  shows a can  51  according to the invention in which a can lid  54  and a can bottom  52  are both seamed to a can body  53 . 
     It is noted that the various can lids and can bottoms could be manufactured by standard technologies by drawing from a disc shape metal part using various dies for forming the various can end structures. Each can end may be used as can lid and/or can bottom as is desired. 
     The metal used may be of any suitable metal such as aluminum, steel, plated steel. The metal may be provided with a coating in the form of a lacquer or plastic layer as is traditionally used for food and beverage cans.