Patent Publication Number: US-2009230129-A1

Title: Tear-open seal packaging

Description:
The present invention relates to a tear-open seal packaging with a packaging element having an opening and a tear-open film which closes the opening according to the preamble of claim  1 . 
     Seal packagings of this type are used for food, for example. A container to accommodate the product is closed with a sealing film made of aluminium, plastic or a composite material. An impermeable connection is created along the sealing seam between the opening edge of the container and the outer edge of the film, e.g. by melting a sealing coating onto the underside of the film, or onto the top of the container or packaging element. In this way, the film and the edge of the packaging enter into a material-locking connection with each other. 
     Whilst in many cases, the container is formed as a single moulded part, one may also provide one part of the packaging only with tear-open film, and then connect this part to the rest of the packaging. Such a part may be an intermediate ring, whose opening is initially seal with the tear-open film, before it is then impermeably connected with another part of the container by means of crimping or some other prior art method. Within the meaning of this invention, then, the term packaging element is understood to designate both entire packagings such as pots, sealed bowls or such like, as well as parts thereof, such as the aforementioned intermediate rings. 
     Seal packagings must satisfy various requirements. On the one hand, the contents must be reliably protected. The packaging must, therefore, be impermeable, stable and resistant to damage. On the other hand, it should also be easy to open. Meeting both needs simultaneously is problematic in some cases, especially in terms of the shape and strength of the sealing seam. Reliable sealing can be achieved by widening the sealing seam, but this makes the film more difficult to tear open. The sealing seam in the vicinity of any tear-open tab part of the film is especially critical. As a general rule, this is where, at the start of the opening process, the greatest tear-open forces occur, and yet the consumer is only given a small tab to grip and pull on the film. If an arc-shaped seam is torn open from the exterior, the force required to continue tearing open initially increases considerably because the length of the tear-open edge, i.e. the width of the seal connection between the film and the opening edge of the packaging, is very large at the outset. 
     A high tear-open force at the outset of the opening process may cause the already detached part to become torn off from the rest of the film, thereby making it far more difficult, or even impossible, to open the packaging further, because the consumer can no longer grip the film. Frequently, a hole therefore has to be made in the film with a sharp object, from where the film can then be pulled off. 
     When a high tear-open force is applied, the film also frequently tears on one side of the tab, so that the film can then only be partly removed, whilst the rest remains seal to the packaging and has to be removed in a second tear-open operation. 
     Various proposals have therefore been made to contrive the sealing seam in such a way that the tear-open force is reduced, especially at the outset of the opening process. The seam can, for example, have a tapering or wave-shaped section in the vicinity of the tab, thereby departing from the arc-shaped path of the seam. This does, however, weaken the seam on the inside. This is a problem, particularly in packagings which have to withstand high interior pressure. At points where the path of the seam is not curved, i.e. where it zig-zags, stress peaks may occur if the tear-open film bulges towards the outside, and said peaks may destroy the seam, causing impermeability. The path of the seam on such packagings should therefore be as curved as possible in order to distribute the occurring inner pressure forces as evenly as possible along the seam. This type of seam path is not compatible with the use of pre-determined tear-open points in the above-described manner. 
     The task of this invention is, therefore, to create a seal packaging of the aforementioned type which is capable of withstanding a relatively high interior pressure and yet can still be easily torn open by the consumer with a low level of force that is as evenly spread as possible. 
     This task is solved according to the invention by a tear-open seal packaging with the features of claim  1 . 
     According to the invention, the sealing seam has at least one indentation from the exterior, extending inwards from the outer edge of the sealing seam. The depth of extension is less than the width of the sealing seam at the location in question. 
     As a result of the indentation or indentations, the sealing seam is slightly weakened in places from the exterior in such a way that when the film is torn open at the point where there is an indentation towards the middle of the film, the force is reduced to the level required to break the seam connection. The length of the tear-open edge, i.e. the width of the seal connection between film and opening edge of the packaging, is reduced by the indentations as will be explained in more detail further on in the description. As the depth of extension of the indentations is less than the width of the seam, the sealing seam is not weakened from its inner edge and is capable of withstanding even high degrees of stress such as those which may be caused by high pressure on the inside of the seal packaging. 
     In particular, such indentations can be applied without difficulty to curved sealing seams. 
     In the context of this invention, the term “indentation” designates a recess of any shape in the outer edge of the sealing seam, without the shape of said recess being specified. The person skilled in the art may adapt the shape, width and depth of this recess in suitable manner to the respective requirements of the seal packaging. 
     The indentation or indentations are preferably disposed on an approximately circular-shaped section of the sealing seam. 
     The indentation(s) is/are preferably disposed in a portion between an imaginary tangent of the outer edge of the sealing seam and a parallel imaginary tangent of the inner edge of the sealing seam. 
     Further, the indentation(s) is/are preferably shaped as a recess with an arc-shaped edge. 
     In a preferred form of embodiment, the tear-open film is provided with a free tear-open tab along an edge portion at an indentation in the sealing seam. 
     The sealing seam preferably has at least two indentations at a distance from each other along the sealing seam. 
     In this case, the tab can preferably be disposed between two indentations. 
     Pulling on the tab thus produces a tear-open edge which extends between the indentations and is shortened at both ends by the latter. This decisively reduces the material resistance, and hence the tensile force required to continue pulling the tab back further. 
     According to another preferred form of embodiment, recesses are disposed at opposite points on the sealing seam. 
     Whilst the tear-open film can be torn open at a point at which there are notches to reduce the required tear-open force, in this form of embodiment opposite indentations additionally ensure that the process of fully detaching the film from the opening edge proceeds evenly, rather than causing, here too, a sudden increase in the level of force required. 
     In one preferred form of embodiment, the packaging element is an intermediate ring which forms the upper edge of a container and is mechanically or materially connected to the other part of the container. 
    
    
     
       A preferred example of an embodiment will be described in more detail below with reference to the drawings, in which 
         FIG. 1  is a top-plan view of an embodiment of the tear-open seal packaging according to the invention; 
         FIG. 2  is a view of parts of the seal packaging as seen in  FIG. 1 , before being joined together; 
         FIG. 3  shows the parts of the seal packaging as seen in  FIG. 2 , during joining-up; 
         FIG. 4  is a section through the seal packaging as seen in  FIG. 1 ; 
         FIG. 5  shows the sealing seam of the seal packaging as seen in  FIG. 1 to 4 ; 
         FIG. 6 to 8  show a perspective view of a conventional seal packaging as per  FIG. 1 , during the tear-open process; 
         FIG. 9  shows the seal packaging according to the invention, in a tear-open position as per  FIG. 7 ; and 
         FIG. 10  is a force-path diagram to illustrate the forces during the tear-open process. 
     
    
    
     The tear-open seal packaging  10  shown in  FIG. 1  comprises a ring-shaped packaging element  12 , namely an intermediate ring forming the top edge of a packaging. The ring opening is sealed by a tear-open film  14  with an essentially circular peripheral edge  16 . To this end, the outer edge portion  16  of tear-open film  14  is connected to the opening edge of packaging element  12  by a circular-shaped sealing seam  18 . This sealing seam  18  is created, for example, by melting a meltable coating onto the underside of tear-open film  14  by means of a stamp tool, so that tear-open film  14  and packaging element  12  enter into a material-locking connection with each other. Sealing seam  18  can therefore be created under the action of heat. Another means of connection, such as adhesion, could conceivably also be used. 
     Along the edge portion disposed uppermost in  FIG. 1 , tear-open film  14  is provided with a free tear-open tab  20 . This tear-open tab  20  lies folded on the top side of tear-open film  14  and can be finger-gripped by the user of seal packaging  10 . By pulling on tear-open tab  20 , tear-open film  14  can be torn open, thereby exposing the opening of packaging element  12 . 
     In this figure, the path of sealing seam  18  (not visible in the top-plan view shown in  FIG. 1 ) underneath the edge  16  of tear-open film  14  is diagrammatically illustrated by hatching. The inner edge  22  of sealing seam  18  is circular. Along its outer edge  24 , sealing seam  18  has an indentation  26 , 28  on each side of tear-open tab  20 . Indentations  26 , 28  are thus distanced from each other along sealing seam  18 , and extend inwards from the outer edge  24  of sealing seam  18 . The depth of this extension is less than the width of sealing seam  18  between its inner edge  22  and outer edge  24 . Thus sealing seam  18  is not completely broken by indentations  26 , 28 , but rather the seal remains intact from the inside. As will be explained in more detail below, indentations  26 , 28  make it easier to tear open tear-open film  14  by pulling on tear-open tab  20  disposed between indentations  26 , 28 . 
     At this point, the manufacturing process used for the seal packaging  10  according to the invention will be described.  FIG. 2 and 3  show the ring-shaped packaging element  12 , namely the intermediate ring, with, at its centre, a circular opening  30 . The edge  32  of this opening  30  is formed by an inward and downward graduation of the cross-section of packaging element  12 , i.e. towards the interior of the packaging, which is not shown. Packaging element  12  can, however, also have a different cross-section to the one shown in  FIG. 3 . 
     The unit shown in  FIG. 1 , comprising packaging element  12  and tear-open film  14 , is formed by lowering the punched-out tear-open film  14  onto packaging element  12 , so that the outer edge portion  16  of tear-open film  14  rests on the opening edge  32  of packaging element  12 , and by material-locking connection of superposed edges  16  and  32 , resulting in the configuration in  FIG. 4 . The material-locking connection creates sealing seam  18 , which seals edges  16  and  32  together impermeably. In particular, the sealing is impermeable to liquid and/or gas. 
     As shown in  FIG. 2 , tear-open film  14  and tear-open tab  20  are contrived from a single blank. Tear-open tab  20  can be folded back onto the circular surface of tear-open film  14  in a manner not illustrated in more detail as film  14  is sealed onto packaging element  12 . 
     Edges  16  and  32  can be sealed together with a suitable stamp tool, by means of which tear-open film  14  and packaging element  12  are pressed together from above and below. The sealing point is heated during the pressing process. Alternatively, the heat required for sealing can be supplied to packaging element  12  before pressing. 
     The unit shown in  FIG. 4 , comprising packaging element  12  and tear-open film  14 , is then connected to a container not shown in more detail, e.g. by crimping the outer edge  34  of packaging element  12  with the top edge of the container. Alternatively, one may contrive the packaging as one piece and seal off its opening with a tear-open film  14 . Hence the term “packaging element” refers, in the context of this invention, both to parts of the packaging, such as the intermediate ring of this form of embodiment, as shown in the figures, or to packagings contrived as one piece. 
     The shape of the sealing seam is shown in more detail in  FIG. 5 . As already explained in connection with  FIG. 1 , sealing seam  18  is essentially circular. The width B of sealing seam  18 , i.e. the distance between its inner edge  22  and its outer edge  24  in the radial direction remains the same around the greater part of its circumference. In one portion  36  only, which is disposed at the top in  FIG. 5 , sealing seam  18  has two indentations  26 , 28 , which are located at a distance from each other along the path of sealing seam  18 . As already illustrated in  FIG. 1 , the tear-open tab  20  of the tear-open film  14  on seam  18  is disposed in the gap between the two indentations  26 , 28 . 
     Indentations  26 , 28  are each contrived as an arc-shaped recess in the outer edge  24  of sealing seam  18 . The depth of each recess is less than the width B of the sealing seam at the point of each indentation. Thus the path of sealing seam  18  is never completely broken at any point. In particular, the inner edge  22  of sealing seam  18  retains its round shape and is not touched by indentations  26 , 28 . Indentations  26 , 28  are relatively flat, i.e., their width in the circumferential direction is substantially greater than their depth in the radial direction. The radii of the arcs of the recess edges of indentations  26 , 28  are greater than the width B of sealing seam  18 , i.e. the centre point of these arcs  38  lies relatively far outside seam  18 . 
     Indentations  26 , 28  need not necessarily have the recess shape shown here, the shape may differ. In particular, flatter, or less flat, indentations  26 , 28  are also conceivable, as well as V-shaped recesses, etc. The distance between indentations  26 , 28  may also vary. 
     The mode of functioning of indentations  26 , 28  will now be explained in more detail with reference to the following figures. For the sake of better comprehension, the mode of functioning of a conventional seal packaging will be described first. 
       FIGS. 6 to 8  show a top plan view of a conventional seal packaging  110 , whose packaging element  112  is contrived like the intermediate ring  12  of the seal packaging  10  according to the invention, and whose tear-open film  114  has the same shape as tear-open film  14  of seal packaging  10 . Tear-open film  114  is also provided with a tear-open tab  120 . Running underneath the edge portion  116  of tear-open film  114  there is a round sealing seam  118  to seal tear-open film  114  onto the opening edge of packaging element  112 . In contrast to sealing seam  18  according to the invention, the conventional sealing seam  118  is not provided with indentations, i.e. both its inner edge  122  and outer edge  124  are circular and unbroken, and the width B around the complete periphery of sealing seam  118  is the same as that of sealing seam  18  according to the invention. 
     If one pulls on tear-open tab  120 , thereby exerting tensile force F on tab  120  towards the opposite edge area of tear-open film  114 , this force F acts along a line separating the already detached part of tear-open film  114  from the surface area of film  114  that is still firmly connected to packaging element  112  by means of sealing seam  118 , and lies flat on the opening thereof. This line, which will be referred to below as separating line  50 , runs perpendicular to the direction of pull of tab  120  and corresponds to a chord connecting two points on the circular outer edge  116  of tear-open film  114 . As the pulling movement progresses, tab  120  grows longer by the detached part of the film as sealing seam  118  gives way to tensile force F, and separating line  50  moves towards the middle of tear-open film  114 , becoming longer as it does so. 
     The amount of force required to pull tab  120  further depends on the momentary material resistance along separating line  50 . This in turn depends on the length of the section(s) of separating line  50  running over sealing seam  118 , i.e. via which there is contact with sealing seam  118 , contact which has to be overcome by exerting tensile force. In  FIG. 6 , tab  120  is partially pulled away from sealing seam  118 , but only to the extent that separating line  50  has not yet moved inwards beyond the full width B of sealing seam  118 . That is, sealing seam  118  is still intact from the inside of the sealing packaging, and the opening is still closed. Separating line  50  therefore cuts through two points  52  and  54  on the outer edge  124  of sealing seam  118 , but not inner edge  122 . The required tensile force F is thus determined by the length L 1  of a tear-open edge  56  between these points  52  and  54 , which is only slightly shorter than the entire length of separating line  50 . Tear-open edge  56  corresponds to a chord connecting the two points  52 , 54  on the arc of the outer edge  124  of sealing seam  118 . 
     As can be seen in  FIG. 7 , separating line  50  lengthens as tab  120  is pulled further, as does tear-open edge  56 , as the latter moves radially inward together with separating line  50 , and the chord between points  52  and  54  on the outer edge  124  of sealing seam  118  becomes longer. The tensile force F required for tearing open also increases as this happens. This is clearly illustrated in the force-path diagram in  FIG. 10 . The section of curve designated by a  1  in a circle indicates the position in  FIG. 6 , the maximum in position  2  equates with  FIG. 7 , etc. The curve increases sharply on the way from the not yet torn-open position in which sealing seam  118  is still intact, to the position in  FIG. 7 , in which separating line  50  touches the inner edge  122  of sealing seam  118 . As tearing-open proceeds, separating line  50  moves beyond inner edge  122  of sealing seam  118  (see  FIG. 8 ). As a result, only the end portions of separating line  50  remain in contact with sealing seam  118 . The contact is reduced to two narrow tear-open edges  58 , 60 , which cut through sealing seam  118  at two points around the circumference positioned at a distance from each other. As tab  120  is pulled back further, tear-open edges  58 , 60  move, together with separating line  50 , further along sealing seam  118 , without substantially changing in length. Thus the force F required for tearing open is hardly any greater, as the flat section of curve clearly shows in  FIG. 10  (position  3 ). 
     The above description reveals that the force, F, required for tearing open, increases with the length L 1  of tear-open edge  56 . The maximum force occurs in the situation in  FIG. 7 , in which length L 1  of tear-open edge  56  is at its maximum, and sealing seam  118  offers the greatest amount of material resistance. 
     The way in which the present invention considerably reduces this force peak, thereby substantially facilitating the process of opening seal packaging  10 , will be described below. 
       FIG. 9  shows the seal packaging  10  with the sealing seam  18  of  FIG. 5 , provided with the two indentations  26 , 28 . The situation in  FIG. 9  coincides with that in  FIG. 7 , in which separating line  50  between the detached and the still attached part of tear-open film  14  has just gone beyond the full width B of sealing seam  18  and reached the inner edge  22  of seam  18 . Note here that tear-open edge  62  is substantially shorter than tear-open edge  56  in  FIG. 7 . This is achieved by indentations  26 , 28 , past which separating line  50  moves during the pulling open movement. In the situation shown in  FIG. 9 , indentations  26 , 28  shorten the length of tear-open edge  62  from the lateral ends, and diminish the contact area with film  14 . This lessens the material resistance, and the force F required for pulling back is less (see path of curve marked  2 ′ in  FIG. 10 ). 
     Indentations  26 , 28  are disposed at an angular distance around the periphery of sealing seam  18  in such a way that separating line  50 , which moves inwards during the pulling back movement, parallel to the progression thereof, passes just beyond indentations  26 , 28  at the moment at which the inner edge  22  of sealing seam  18  has already been reached, and no further critical force peaks can occur. Hence indentations  26 , 28  are advantageously disposed in a strip-shaped area limited by two parallel straight lines, of which one straight line is a tangent of outer edge  24  of sealing seam  18  and the other straight line forms a tangent of inner edge  22 , which simultaneously forms a secant of outer edge  24 . 
     As can be seen in the force-path diagram in  FIG. 10 , a further force peak can occur at the end of the opening path, just before tear-open film  14  is completely torn off, caused by separating line  50  coming into contact with the opposite inner edge  22  of sealing seam  18 . As this happens, the two tear-open edges  58  and  60  join up to re-become a single tear-open edge with a width as shown in  FIG. 7 , requiring, once again, application of maximum force. By providing indentations opposite indentations  26 , 28  on the side of tear-open tab  20  on sealing seam  18 , the width of the tear-open edge can be reduced here too, and hence the tear-open resistance of film  14  as well. 
     Indentations  26 , 28  have virtually no weakening impact on sealing seam  18  on the inside portion of the opening of seal packaging  10 . The invention is therefore especially well suited for use with seal packagings which have to resist a high level of inner pressure, as the pressure force can distribute itself evenly along the circular inner edge  22  of sealing seam  18 , and no stresses occur in tear-open film  14 . And yet the tear-open process is made considerably easier, and proceeds more evenly, by providing indentations  26 , 28 . 
     Departing from the embodiment described in connection with the Figures, the desired effect of weakening the material resistance at the tear-open point can also be achieved with a single indentation. If, for example, one omits one of the two indentations  26  or  28  of the above-described embodiment, so that the other indentation remains, tear-open edge  56  is shortened at one end only. The effect of reducing the required tensile force may be slightly less in this case. The user will still, however, find the process of tearing open the film much easier. 
     Further, the indentations can of course be contrived in sealing seams shaped differently to that shown in  FIG. 5 , and are not circular. It would be conceivable, for example, to contrive indentations in an arc-shaped rounded corner in an essentially square sealing seam, or in an oval sealing seam or such like. In this respect, too, the above-described embodiment deriving from  FIGS. 1 to 10  is not limiting for the invention.