AU2022397928A1

AU2022397928A1 - Can lid and method for producing a can lid

Info

Publication number: AU2022397928A1
Application number: AU2022397928A
Authority: AU
Inventors: Gregor Anton Piech
Original assignee: Top Cap Holding GmbH
Current assignee: Top Cap Holding GmbH
Priority date: 2021-11-29
Filing date: 2022-11-18
Publication date: 2024-06-13
Also published as: WO2023094281A1; KR20240095287A; AR127794A1; DE102021131239A1; TW202335918A; EP4416070A1; MX2024006296A; CN118339082A; EP4420994A2; PE20241661A1; CA3238375A1

Abstract

A can lid comprises a metallic lid face in which an opening is formed, which opening is delimited by a closed edge of the lid face and is closed by a closure piece of the metallic lid face, wherein the closure piece is separated from the surrounding lid face by a micro-gap which extends at least in some sections around the edge of the lid face. A first end region of the closure piece is connected to the surrounding lid face via a pivot bearing. The can lid also comprises a tear-open element which acts on a second end region, opposite the pivot bearing, of the closure piece, so that it is possible to pivot the closure piece out of the plane defined by the opening by pulling on the tear-open element. The micro-gap is interrupted between the first end region and the second end region by at least one holding piece by which the closure piece and the surrounding lid face are integrally bonded to one another.

Description

Can end and method of manufacturing a can end

The invention relates to a can end, in particular for beverage cans, comprising a metallic end surface in which an opening is formed that is bounded by a closed margin of the end surface and that is closed by a closure piece of the metallic end surface, wherein the closure piece is separated from the surrounding end surface by a microgap extending at least sectionally along the margin of the end surface, wherein a first end region of the closure piece is connected to the surrounding end surface via a pivot bearing; and a tear-open member that engages at a second end region of the closure piece, said second end region being opposite the pivot bearing, so that a pivoting of the closure piece out of the plane defined by the opening is made possible by pulling at the tear-open member.

Can ends of this type are used on a large scale in the manufacture of beverage cans, food cans and the like. They are simple and inexpensive to manufacture, enable a space-saving stacking of similar cans and can be easily opened and, if necessary, closed again by manually moving the closure piece. Due to the microgap, an entry of metal particles into the can interior that is hazardous to health does not occur on the opening of the can.

When opening beverage cans and the like, a spraying, a foaming over and/or even a popping can occur, in particular if the can contents are a carbonated beverage. To avoid this, some users attempt to tap the can wall before the opening or to pull at the tear-open member as slowly and as carefully as possible. However, such measures are a nuisance and furthermore only have limited effectiveness.

It is an object of the invention to enable an easier and smoother opening of can ends of said kind and in particular to counteract a spraying, a foaming over and/or a popping.

The object is satisfied by a can end having the features of claim 1.

The invention provides that the microgap is interrupted between the first end region and the second end region by at least one holding web via which the closure piece and the surrounding end surface are connected to one another in a bonded manner. When the closure piece is pivoted upwardly by pulling at the tear open member, initially only a relatively small opening is produced that starts from the second end region and extends at most up to the holding web. The holding web initially counteracts a further opening. Due to the relatively small initial opening, a ventilation of the can already takes place, which is also designated as "venting". In the further course of the opening movement, the holding web tears so that it is possible to completely unfold the closure piece and thereby to release the total opening. Due to the ventilation that has already taken place, a noticeable spraying or foaming over no longer occurs in this respect. For the user, the pre ventilation before the complete opening may not even be perceivable under certain circumstances. A particular advantage lies in the simple design of a can end in accordance with the invention since it is sufficient not to design the microgap present as completely peripheral, but to provide it with a recess for forming the holding web. It is therefore not necessary to provide a separate additional holding apparatus.

A further advantageous effect of the invention is that the holding web increases the stability of the end closure. It has been shown that, due to the metallic holding web, no leakage or even a chipping of the closure piece occurs even at a greatly increased internal pressure in the can and/or at high temperatures. A high temperature and an associated high internal pressure not only occur in the case of solar radiation on cans including carbonated beverages, but in the case of a pasteurization that is mandatory for many applications. A sealing film possibly provided for covering the microgap is in this respect protected from an overloading by the holding web.

Furthermore, the holding web is also advantageous in that it ensures a reliable hold of the closure piece in the opening during the production.

In accordance with an embodiment of the invention, the at least one holding web has a width from 0.1 mm to 6 mm, preferably from 1.5 mm to 4 mm. It has been shown that with such a web width, a sufficiently strong holding effect is ensured for a ventilation effect, on the one hand, but the holding web is sufficiently easy to break, on the other hand, in order to avoid an impairment of the opening process. The width of the holding web can be measured along the margin bounding the opening or along the course of the microgap.

The at least one holding web can have a notch. On the first upward pivoting of the closure piece, the notch ensures a defined tearing of the holding web, namely along the notch. An unwanted tearing of the closure piece or of the surrounding end surface is thus avoided. The notch can extend along the margin of the end surface and/or of the microgap. The shape and the depth of the notch can be adapted such that a desired tearing force results. The notch preferably has a depth of at least 0.03 mm and/or of at least one quarter of the thickness of the metallic end surface.

The microgap region is preferably interrupted between the first end region and the second end by a web arrangement comprising at least two holding webs via which the closure piece and the surrounding end surface are connected to one another in a bonded manner. This ensures a uniform fixing of the closure piece in the opening. The web arrangement can be designed such that a relatively small initial opening is formed during the opening process. The smaller the initial opening, the more controlled and more smoothly the excess pressure can escape.

The web arrangement can comprise holding webs arranged at both sides of the second end region. Thus, a separation of the microgap is opposed at both sides of the point of engagement of the tear-open member so that the holding effect is uniform.

The web arrangement preferably comprises at least one pair of holding webs arranged disposed opposite one another with respect to a central region of the closure piece. This provides a symmetrical resistance to the opening movement.

The web arrangement can comprise at least four and at most eight holding webs, preferably six holding webs, arranged distributed along the margin of the end surface. This results in a particularly stable hold of the closure piece in the opening and counteracts an overloading of a coating or film covering the microgap.

The holding webs of the web arrangement can be of identical design to ensure a particularly simple design.

A further embodiment of the invention provides that the microgap is a punched gap and the at least one holding web is formed by a punched recess. A particularly simple and inexpensive manufacture is thereby made possible. In the punched recess, an embossing apparatus, such as an embossing stamp, can be arranged that is configured to produce a notch, in particular a notch as described above, in the respective holding web.

In accordance with a specific embodiment, the microgap has a maximum width of 0.01 mm. This has proven to be particularly favorable in practice. The closure piece can also be held in the surrounding end surface by clamping.

A coating composed of a plastic material can be applied to a flat side of the metallic end surface in a manner covering the microgap. The leak tightness of the can end is ensured by a coating covering the microgap despite the lack of a continuous metallic connection between the closure piece and the surrounding end surface. On the moving of the closure piece out of the plane defined by the opening, the coating composed of a plastic material tears in the region of the microgap such that the opening is subsequently free.

The coating is preferably applied to an inner side of the metallic end surface. The coating is therefore preferably located at the end side facing the can interior. In general, this is the lower side of the metallic end surface.

The coating can be applied over the full area to the flat side of the metallic end surface. This is of advantage from a technical production aspect and ensures a particularly high sealing effect. The coating can be designed as a film and/or can be applied, for example sealed on, in a firmly adhering manner to the metallic end surface. The plastic material can be polypropylene suitable for use with food.

In accordance with a further embodiment of the invention, the coating has a weakening, in particular a regionally reduced material thickness, that is arranged at a spacing from the microgap. The weakening can be produced in a sealing process by means of which the coating is applied. In general, a notch or an at least partial opening notch such as a perforation could be provided as a weakening. The weakening reduces the force effort required for opening the can. Due to the spacing between the weakening and the microgap, a high leak tightness is ensured.

The tear-open member can be a gripping, pulling and/or lever element, in particular composed of a plastic material. A user can actuate the gripping, pulling and/or lever element in order thus to pivot the closure piece upwardly about the pivot bearing axis that is defined by the pivot bearing. A two-armed lever member composed of a plastic material can in particular be provided and is fixedly connected to the metallic end surface. The gripping, pulling and/or lever element preferably has an annular gripping section such as a ring tab. A ring tab is particularly advantageous in the practical handling since it can be easily gripped and enables an opening of the respective can via a pulling movement that can be performed comfortably.

A further embodiment of the invention provides that a sealing frame composed of a plastic material and surrounding the opening is connected to the surrounding end surface and a closure unit composed of a plastic material and supporting the closure piece is pivotably attached to the surrounding end surface, with the sealing frame and the closure unit being releasably connectable in a fluid-tight manner to one another via sealing and latching ribs and associated reception grooves. Such a can end has a reclosable opening. The sealing and latching ribs as well as the reception grooves are preferably designed such that a complete reclosing by the snap-in connection can be felt and, if necessary, perceived acoustically. Unlike so called standard can ends, which are not reclosable, the closure piece of a reclosable can end cannot be deformed to a sufficient degree to provide a venting via the deformation. Therefore, the invention is suitable to a special degree, but not exclusively, for reclosable can ends.

The invention also relates to a method of manufacturing a can end, in particular a can end for beverage cans, preferably a can end in accordance with any one of the preceding claims, wherein an at least regionally areal metal element is provided, and wherein a closure piece is punched out of the metal element and is reinserted into the opening formed by the punching process.

In accordance with the invention, the punching out is performed by means of a punching die that has a cutting edge having at least one recess. This enables a particularly simple provision of a holding web in the form of a bonded connection between the closure piece and the surrounding end surface.

The invention also relates to a can end, in particular for beverage cans, comprising a metallic end surface in which an opening is formed that is bounded by a closed margin of the end surface and that is closed by a closure piece of the metallic end surface, wherein the closure piece is separated from the surrounding end surface by a microgap extending at least sectionally along the margin of the end surface, in particular a can end as described above.

In accordance with the invention, an arrangement of venting notches is formed in the metallic end surface and is in connection with the microgap.

On an application of a sealing film to the metallic end surface, the venting notches ensure a venting via the microgap and thus counteract an unwanted bubble formation between the sealing film and the metallic end surface. The venting notches can be embossed into the metallic end surface. In accordance with an embodiment of the invention, the venting notches have a V-shaped cross-section and/or a depth from 0.005 mm to 0.2 mm, preferably from 0.03 mm to 0.1 mm.

The arrangement of venting notches is preferably formed in an inner side of the metallic end surface, in particular with a coating composed of a plastic material being applied to the inner side of the metallic end surface in a manner covering the microgap and at least partly covering the arrangement of venting notches.

Provision can be made that the venting notches define a radial pattern and/or that each of the venting notches extends at least from the microgap up to a marginal region of the metallic end surface. This enables an effective venting across the total film surface or end surface.

Further developments of the invention can also be seen from the dependent claims, from the following description, and from the enclosed drawing.

The invention will be described in the following by way of example with reference to the drawing.

Fig. 1 is a plan view of a can end in accordance with the invention for a beverage can, said can end comprising a reclosable opening system;

Fig. 2 shows the can end in accordance with Fig. 1 with the opening system omitted;

Fig. 3 is an enlarged part representation of the can end shown in Fig. 2 that shows a holding web;

Fig. 4 shows a can end in accordance with a further embodiment of the invention; and

Fig. 5 shows, in a simplified form, the lower side of a can end in accordance with the invention.

Fig. 1 shows a can end 11 which is in particular intended for a beverage can and into whose metallic end surface 13 a reclosable opening system 15 is integrated. The can end 11 can be connected to an associated container, not shown, via a beaded rim 12. An opening is provided in the metallic end surface 13, which opening is closed by a section of the metallic end surface 13 in the form of a closure piece 19 in the delivery state of the can end 11 shown in Fig. 1.

As can be recognized in Fig. 2, the closure piece 19 is separated from the surrounding end surface 23 by a microgap 21. In the region of the microgap 21, the outer margin 25 of the closure piece 19 and the inner margin 27 of the surrounding end surface 23 adjoin one another.

The metallic end surface 13 is preferably formed from a sheet metal layer composed of aluminum or tin plate. A coating composed of a plastic material and covering the microgap 21 is applied to an inner flat side of the metallic end surface 13, which is not visible in Figs. 1 and 2, however. An adhesive lacquer layer, which is likewise not visible in the Figures, can be provided for a fixed connection of this coating to the metallic end surface 13. The coating is preferably applied over the full area to the inner flat side of the metallic end surface 13. In certain applications, it could, however, also be sufficient to provide a coating only in the environment of the microgap 21. The coating can be a plastic film, for example, composed of propylene. A notch, which extends along the microgap 21 at a predefined spacing therefrom, is formed in the coating.

The can end 11 can be opened by moving the closure piece 19 out of the plane defined by the opening (in Figs. 1 and 2, the paper plane). Since there is no bonded connection between the closure piece 19 and the surrounding end surface 23 in the region of the microgap 21, no noticeable metal separation has to take place on the first opening of a can provided with the can end 11 in accordance with the invention so that the otherwise unavoidable formation of metallic microparticles is reduced or completely prevented. This avoidance of the creation of microparticles in the opening process, in particular microparticles composed of aluminum, is of importance under health aspects since such microparticles unavoidably also enter into the product contained in the respective can and thus also into the human body.

The coating reliably seals the microgap 21. The notch, which can have a uniform depth or, if applicable, can also locally have different depths, ensures that only a comparatively small force is required to open the can end 11. The spacing between the microgap 21 and the notch 35, which preferably amounts to approximately 0.2 to 0.5 millimeters, improves the sealing effect.

The reclosable opening system 15 (Fig. 1) comprises a sealing frame, not recognizable in the plan view in accordance with Fig. 1, composed of a plastic material and surrounding the opening, said sealing frame being fixedly connected to the surrounding end surface 23. A closure unit 40 composed of a plastic material and supporting the closure piece 19 is further provided and is pivotably attached to the surrounding end surface 23. A releasable fluid-tight connection between the sealing frame and the closure unit 40 is made possible by means of a latch device that is formed by sealing and latching ribs 43 and associated reception grooves. The can end 11 is therefore reclosable.

A tear-open member 47 that is annular here, preferably likewise composed of plastic, is connected to or directly molded to the closure unit 40 and is accordingly fastened to the closure piece 19. By pulling at the tear-open member 47, a user can pivot the closure piece 19 upwardly out of the plane defined by the opening and can thus release the opening while separating the coating. A molded-on pivot bearing 48 (Fig. 1) is formed at the closure unit 40 in a manner disposed diametrically opposite the closure unit 40 and is fixedly connected to the surrounding end surface 23. Thus, a first end region 61 of the closure piece 19 is connected to the surrounding end surface 23 via the pivot bearing 48, while the tear-open member 47 engages at a second end region 62 of the closure piece 19, said second end region 62 being opposite the pivot bearing 48.

Between the first end region 61 and the second end region 62, the microgap 21 is interrupted by two holding webs 65 (Fig. 2) via which the closure piece 19 and the surrounding end surface 23 are connected to one another in a bonded manner. The two holding webs 65 form a web arrangement 70. As shown, the two holding webs 65 are arranged disposed opposite one another with respect to a central region 66 of the closure piece 19. The width of the identically designed holding webs 65 is preferably in a range from 0.5 mm to 6 mm and, for example, amounts to at least approximately 3 mm. Depending on the application, more than two holding webs 65 can also be provided. A detailed view of one of the holding webs 65 is shown in Fig. 3, wherein the microgap 21 is shown here with an exaggerated width for clarification.

The holding webs 65 preferably have respective notches 75 to avoid an undefined tearing of the metallic end material.

On the first opening of the can, a user pulls at the tear-open member 47 and thereby upwardly pivots the closure unit 40 with the closure piece 19. In this respect, the latch connection between the closure unit 40 and the sealing frame is released. Furthermore, the coating is separated along the microgap 21.

Due to the holding webs 65, only a relatively small opening is produced in the end surface 13 at the start of the pivoting process, said opening extending starting from the second end region 62 up to the region of the holding webs 65. The holding webs 65 at least briefly counteract a further opening. The relatively small opening in the environment of the second end region 62 provides a ventilation of the can. In the further course of the pivoting process, the holding webs 65 tear, in particular since they are of a relatively narrow design. After the tearing of the holding webs 65, the closure piece 19 can be pivoted completely upwardly to release the total opening. Due to the opening graduated by the holding webs 65 and the associated venting effect, no significant spraying, popping or foaming over occurs in this respect.

The contents of the can can be removed through the opening produced. When the closure unit 40 with the closure piece 19 is pivoted back again, the latch connection between the closure unit 40 and the sealing frame is established again such that the opening is sealed tightly again despite the separated coating. The opening and closing can be repeated as often as desired.

In the alternative embodiment of a can end 11 in accordance with the invention shown in Fig. 4, a web arrangement 70' comprising a total of six holding webs 65 is provided that are arranged distributed along the margin 27 of the metallic end surface 13. Specifically, an arrangement of three holding webs 65 is located at each side of a line 72 extending through the first end region 61 and the second end region 62. This enables a more finely graduated venting, on the one hand, and, on the other hand, ensures a particularly stable hold of the closure piece 19 at the intended position before the initial opening of the closure. It is understood that the number, the distribution, and the width of the holding webs 65 can vary in dependence on the respective application.

Fig. 5 shows, in a simplified form, a can end 13 in accordance with the invention from below. An arrangement of venting notches 80 is formed in the lower side, i.e. the inner side, of the metallic end surface 13. As shown, each of the venting notches 80, in particular rectilinear venting notches, extends from a marginal region 87 of the metallic end surface 13 up to the microgap 21. They could also extend slightly beyond the marginal region 27. The course of the venting notches 80 is radial. In the embodiment shown, the venting notches 80 define a radial pattern, i.e. the radially extending venting notches 80 are arranged distributed over the periphery of the metallic end surface 13 that is circular in this case. The venting notches 80 are preferably embossed into the metallic end surface 13 by means of an embossing tool, for example with an embossing depth of 0.07 mm.

The microgap 21 and the arrangement of venting notches 80 are covered by a sealing film, not visible in Fig. 5, that is composed of plastic and that is applied to the inner side of the metallic end surface 13. In particular on the application of the sealing film, the venting notches 80 cause a venting of the intermediate space between the metallic end surface and the sealing film via the microgap 2. The microgap 21 present is therefore used for a venting. In this way, the formation of bubbles and the like is prevented, and indeed across the total metallic end surface 13 due to the radiating pattern.

The effect of the holding webs 65 is independent of the presence of the reclosable opening system 15. Therefore, the provision of one or more holding webs 65 as described is also advantageous for non-reclosable can ends without a sealing frame and a closure unit, i.e. for standard can ends.

Furthermore, the effect of the venting notches 80 is independent of the presence of the holding webs 65 so that the provision of venting notches 80 is also advantageous for standard can ends and reclosable can ends whose microgaps are not interrupted by holding webs.

To manufacture a can end 11 in accordance with the invention, an areal metal element, for example a sheet metal layer composed of aluminum or tin plate, is provided and is fed to an embossing apparatus in which the beaded rim 12, the venting notches 80 as well as grooves, reinforcement beads and the like are molded into the areal metal element. The stamped metal element is fed to a punching apparatus in which the closure piece 19 is punched out of the metal element and reinserted into the opening formed by the punching process. Specifically, in the course of the return stroke of the punching die, the punched-out closure piece 19 is immediately pressed directly into the sheet metal layer again by a spring force and is held there in a force-fitted manner.

To produce the holding webs 65, the punching out is performed by means of a punching die whose cutting edge is not of a closed peripheral design, but has corresponding recesses having respective embossing stamps for producing the notches 75. The inner flat side of the metal element is subsequently provided with the coating, in particular the sealing film. The embossing apparatus and the punching apparatus can be integrated into a progressive tool, if necessary, together with further processing apparatus.

Reference numeral list

11 can end 12 beaded rim 13 metallic end surface 15 reclosable opening system 19 closure piece 21 microgap 23 surrounding end surface 25 outer margin 27 inner margin 40 closure unit 47 tear-open member 48 pivot bearing 61 first end region 62 second end region 65 holding web 66 central region 70, 70' web arrangement 72 line 75 notch 80 venting notch 87 marginal region

Claims

1. A can end (11), in particular for beverage cans, comprising a metallic end surface (13) in which an opening is formed that is bounded by a closed margin (27) of the end surface (13) and that is closed by a closure piece (19) of the metallic end surface (13), wherein the closure piece (19) is separated from the surrounding end surface (23) by a microgap (21) extending at least sectionally along the margin (27) of the end surface (13), wherein a first end region (61) of the closure piece (19) is connected to the surrounding end surface (23) via a pivot bearing (48); and a tear-open member (47) that engages at a second end region (62) of the closure piece (19), said second end region (62) being opposite the pivot bearing (48), so that a pivoting of the closure piece (19) out of the plane defined by the opening is made possible by pulling at the tear-open member (47), characterized in that the microgap (21) is interrupted between the first end region (61) and the second end region (62) by at least one holding web (65) via which the closure piece (19) and the surrounding end surface (23) are connected to one another in a bonded manner.

2. A can end in accordance with claim 1, characterized in that the at least one holding web (65) has a width from 0.5 mm to 6 mm, preferably from 1.5 mm to 4 mm.

3. A can end in accordance with claim 1 or claim 2, characterized in that the at least one holding web (65) has a notch (75).

4. A can end in accordance with any one of the preceding claims, characterized in that the microgap (21) is interrupted between the first end region (61) and the second end region (62) by a web arrangement (70, 70') comprising at least two holding webs (65) via which the closure piece (19) and the surrounding end surface (23) are connected to one another in a bonded manner.

5. A can end in accordance with claim 4, characterized in that the web arrangement (70, 70') comprises holding webs (65) arranged at both sides of the second end region (62).

6. A can end in accordance with claim 5, characterized in that the web arrangement (70, 70') comprises at least one pair of holding webs (65) arranged disposed opposite one another with respect to a central region (66) of the closure piece (19).

7. A can end in accordance with any one of the claims 4 to 6, characterized in that the web arrangement (70') comprises at least four and at most eight holding webs (65), preferably six holding webs (65), arranged distributed along the margin (27) of the end surface (13).

8. A can end in accordance with any one of the claims 4 to 7, characterized in that the holding webs (65) of the web arrangement (70, 70') are of identical design.

9. A can end in accordance with any one of the preceding claims, characterized in that the microgap (21) is a punched gap and the at least one holding web (65) is formed by a punched recess.

10. A can end in accordance with any one of the preceding claims, characterized in that the microgap (21) has a maximum width of 0.01 mm.

11. A can end in accordance with any one of the preceding claims, characterized in that a coating composed of a plastic material is applied to a flat side of the metallic end surface (13) in a manner covering the microgap (21).

12. A can end in accordance with claim 11, characterized in that the coating is applied to an inner side of the metallic end surface (13).

13. A can end in accordance with claim 11 or claim 12, characterized in that the coating is applied over the full area to the flat side of the metallic end surface (13).

14. A can end in accordance with any one of the claims 11 to 13, characterized in that the coating has a weakening that is arranged at a distance from the microgap (21).

15. A can end in accordance with any one of the preceding claims, characterized in that the tear-open member (47) is a gripping, pulling and/or lever element, in particular composed of a plastic material.

16. A can end in accordance with any one of the preceding claims, characterized in that a sealing frame composed of a plastic material and surrounding the opening is connected to the surrounding end surface (23) and a closure unit (40) composed of a plastic material and supporting the closure piece (19) is pivotably attached to the surrounding end surface (23), with the sealing frame and the closure unit (40) being releasably connectable in a fluid-tight manner to one another via sealing and latching ribs and associated reception grooves.

17. A method of manufacturing a can end (11), in particular a can end for beverage cans, preferably a can end in accordance with any one of the preceding claims, wherein an at least regionally areal metal element is provided, and wherein a closure piece (19) is punched out of the metal element and is reinserted into the opening formed by the punching process, characterized in that the punching out is performed by means of a punching die that has a cutting edge having at least one recess.

18. A can end (11), in particular for beverage cans, comprising a metallic end surface (13) in which an opening is formed that is bounded by a closed margin (27) of the end surface (13) and that is closed by a closure piece (19) of the metallic end surface (13), wherein the closure piece (19) is separated from the surrounding end surface (23) by a microgap (21) extending at least sectionally along the margin (27) of the end surface (13), in particular a can end in accordance with any one of the preceding claims, characterized in that an arrangement of venting notches (80) is formed in the metallic end surface (13) and is in connection with the microgap (21).

19. A can end in accordance with claim 18, characterized in that the arrangement of venting notches (80) is formed in an inner side of the metallic end surface (13), in particular with a coating composed of a plastic material being applied to the inner side of the metallic end surface (13) in a manner covering the microgap (21) and at least partly covering the arrangement of venting notches (80).

20. A can end in accordance with claim 18 or claim 19, characterized in that the venting notches (80) define a radial pattern and/or in that each of the venting notches (80) extends at least from the microgap (21) up to a marginal region (87) of the metallic end surface (13).