CA2217311C

CA2217311C - Tin can with a foil closure membrane, and a process, device and foil for manufacturing the can

Info

Publication number: CA2217311C
Application number: CA002217311A
Authority: CA
Inventors: Werner Grabher
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-04-02
Filing date: 1996-03-30
Publication date: 1999-05-25
Anticipated expiration: 2016-03-30
Also published as: KR20050038655A; JPH11509810A; AU694023B2; EP0819086B1; AU5398796A; GR3029457T3; KR19980703504A; WO1996031406A1; DE59601055D1; CA2217311A1; CN1185138A; BR9604869A; NZ305862A; KR100526838B1; ZA962628B; ATE174859T1; ES2127634T3; CN1063401C; DK0819086T3; JP3689115B2

Abstract

The tin can is closed by a paper, plastic or metal-foil membrane (2) on at least one end face in such a way that the outer side of the foil edge region (5) raised in the direction of the can's axis (A) is joined to the essentially cylindrical inner surface of the wall of the can (1) to form a seal, without covering the wall edge of the can. The membrane foil (2) with the raised foil edge region (5) is introduced into the can and forced against the inner wall of the can (1) by a die (8) with an expandable periphery (17). Heat is then applied to create a sealing join between the raised foil edge region (5) and the inner wall of the can (1) without any external pressure-absorbing device.

Description

CA 022l73ll l998-03-ll Process and apparatus for the production of a can having a foil closure diaphragm, and sheet metal can having a diaphragm foil closure This invention relates to a process and an apparatus for the production of sheetmetal cans having a diaphragm foil closure, as well as to a sheet metal can having a diaphragm foil closure.
Metal cans have to date been closed either by fl~ngin~ together the cut can edgewith a sheet metal lid (for example as claimed in WO 83/02577 or US-A-3,952,677) or by employing a sheet metal ring provided with a foil (as claimed in AT-A-368.919).
Alternatively, the inner surface of the can wall was conically shaped (for example as o claimed in DE-U94 14 440), at least in the region ofthe raised foil edge. This required a more complicated can production and high tolerances to enable the same position of the diaphragm disc relative to the can edge always to be achieved on introduction of the punch.
Discs with a raised edge that does not overlap the cut edge of the can have been15 disclosed for plastic cans (for example, DE-A133 05 144 or CH-A-629 984), but these were always relatively stable lid parts for the bottom of cans capable of bearing a pressure load or those having a relatively soft wall (for example as claimed in US-A4,599,123), which required an external pressure absorption apparatus for the sealing process.
Such discs have also been proposed for metal cans (CH-A5-659633). However, 20 they can only be fixed by means of a heat conductive (metal) lid, through which the heat for sealing the diaphragm has to be applied and which remains in the can.
WO-A-84/04507 describes an apparatus in which the can is closed by a diaphragm foil which is pressed against the can inner wall by means of a rubber ring mechanically expanded outwards and is connected to the wall by means of a heat-seal coating.
25 However, this requires a very complicated design of the rubber ring and of the welding tool brought to the can wall from the outside.
It is an object of the invention to provide a process for the production of a can, in particular one comprising tin plate or alllminum sheet, having a simple and especially cheap closure.

Accordingly the present invention provides a process for producing a sheet metalcan having a closure diaphragm of paper, plastic film, or metal foil provided on at least one end face thereof, said diaphragm foil having a raised foil edge region introduced into the can and closing the one or more end faces so that the outer surface of said edge region, which is raised in the direction of the can axis, is tightly connected to the inner surface of the can wall, wherein said foil edge region is pressed against the inner surface of the can by means of a punch having an expandable circumference and thereafter the raised foil edge region is tightly connected substantially over its total vertical extent to the inner surface of the can under the action of heat, the expansion being effected without being o opposed by a force from an external pressure absorption apparatus.
The closure consists of only one diaphragm foil, optionally of plastic and/or paper (in particular l~min~tecl with thin alllminllm foil), but preferably a metal foil, in particular of aluminum, everything also being denoted below merely as foil for the sake of simplicity, and optionally permits the can opening to be exposed in a manner known per 15 se with the aid of pull tabs. The diaphragm disc edge raised in the direction of the can axis does not overlap the preferably flanged can edge, and thus facilitates pulling off and therefore leaves the can edge with its robust outside or standing surface.
The diaphragm foil, which is preferably not more than 0.2 mm, and most preferably not more than 0.1 mm, thick, consists, for example, of a 50 ,um al~ foil 20 with a 20 ,um heat-seal coating on the inner surface and a 10-20 ~m antifriction coating on the outer surface and is therefore suitable for the closure of the subsequent withdrawal opening. Depending on the contents or on the lid used, however, the can bottom, too, may be produced as claimed in the invention, if required. Also preferred is the use of embossed foils because they can be more easily fitted closely to cans with ch~n~ing tolerance and 25 also give better stability.
In general, it is preferable if the diaphragm foil - at least in the region intended for connection to the inner surface of the can - is coated with a heat-seal coating. In principle, however, the inner surface of the can may also be provided with a primer or a heat-sealable coat in the region mentioned - as in the case of the inner surface of 30 combination cans (for example, l~min~ted with alulllhlulll foil); otherwise, tight connection frequently requires the use of special - in particular multicomponent -CA 022l73ll l998-03-ll adhesives or heat-seal coatings. In any case, bright or coated cans can thus also be closed with a tight seal.
In an inconvenient procedure employed to date, it was necessary to exert pl'eS~iUle externally against a fixed, stable punch applied in the interior of the (relatively soft) cardboard can by bringing together annular segments or bringing together two conical surfaces. This is no longer the case in the process as claimed in the invention. The improved and less inconvenient method of applying pressure from the inside is not possible in the case of conventional soft cans since the diameter tolerances of the can were too large for exact external holding directed against the internal pressure, or it was o necessary for the can inner edge and punch to have a conical shape. In the case of the can as claimed in the invention, ext~m~l holding is no longer required at all; loose centering is sufficient.
Of course, the diaphragm foils used for closing the cans as claimed in the invention are preferably produced beforehand from suitable material and are then applied 15 to -the corresponding can opening with the aid of the process as claimed in the invention, so that they can also be easily introduced into cans having different tolerances and in some cases are in the desired position simply owing to the conical foil edge region.
As mentioned above, Swiss Patent 659,633 discloses a sheet metal can whose end face is closed by means of a raised diaphragm. However, an essential feature of the 20 invention disclosed in this patent is a heat conducting lid which remains in the can until the latter is opened by the end user, whereupon the diaphragm is also removed. However, the can as claimed in the present invention is closed only at one end by means of a diaphragm foil and is free from a heat-conducting lid there (as is usual in the industry, and it is thus suitable at the opposite end for filling, i.e. an intermediate product, whereas the 25 comparable intermediate product as claimed in Swiss Patent 695,633 has a heat-conducting lid which makes the can more expensive and more complicated).
In a pl~f~lled embodiment, the foil used here is in fact, for example, one having a slightly conical foil edge region which, after thermoforming, is heat-sealed to the can inner wall in a broad gap between punch and can inner wall by expansion of the punch 30 circumference.

CA 022l73ll l998-03-ll A broad collar parallel to the diaphragm disc, as described, for example, in US-A-4,599,123, has proved to be extremely disadvantageous since, on introduction into the can - without overlapping the cut edge of the can - it must result in the formation of creases, which make it more difficult, or even impossible, to achieve a tight connection between the foil and the inner surface of the can.
There are of course a large number of possibilities as claimed in the prior art for final mounting. However, since the foil used as claimed in the invention is relatively thin and is preferably a foil having good thermal conductivity, use is made of a high-temperature joining process, for example the application of a heat-seal coating on the o outer surface.
The invention will now be described in more detail, by way of example only, withreference to the accompanying drawings, in which:-Fig. 1 shows the sequence of the process as claimed in the invention;
Fig. 2-3 show enlarged details II and III from Fig. la and lb, respectively;
Fig. 4 shows a section through the apparatus as claimed in the invention; and Fig. 5a and b show a horizontal section through the apparatus as claimed in the invention, in two different operating positions.
As shown in Fig. 1, a can 1 of sheet metal is to be closed with a diaphragm foil 2.
The diaphragm foil 2 may be connected to a pull tab 3 in any desired manner, for example by adhesive bonding. In contrast to conventional pull tabs, the tab 3 can be used for pulling offthe entire diaphragm foil 2 introduced into the can 1 and connected to it at the edge. This arrangement is more advantageous because, in the prior art, it was necessary to provide either a predetermined breaking point, for example by punching, or separating the diaphragm foil edge overlapping the cut edge of the can from the diaphragm foil disc stretched over the can opening. In the case of a thin foil of preferably not more than 0.2 mm, in general even not more than 0.1 mm, this always gave rise to difficulties.
Such a thin foil which serves merely for m~ ing freshness or preserving aroma or for preventing col-t~ i r-~tion is relatively difficult to handle. As claimed in the invention, it now has, along the circumference of a cover region 4, a foil edge region 5 CA 022l73ll l998-03-ll which is raised all around and imparts a certain rigidity to the diaphragm disc stretched over the can opening. For imparting rigidity (and also for achieving a slight, radial elasticity during deep drawing and/or sealing), the diaphragm foil 2 closing the bottom of the can preferably has at least one annular bead. The diaphragm foil 2 reinforced in this manner can now be picked up in an interlocking manner (so that the foil shape is not changed on insertion into the can opening), for example by means of a suction gripper, and can be mounted on the top of the can 1 in a first step. Here, a further difficulty associated with a thin foil is encountered: it is necessary to ensure that the foil remains on the top of the can 1 so that it can be tightly connected to the inner surface of the can in the o next step. It would be possible in principle to provide the upper edge of the can 1 with an adhesive so that the film remains attached thereto in the desired position. However, this is advantageously effected as claimed in the invention in a manner more readily evident from Fig. 2.
In Figure 2, the raised edge is at least slightly conically divergent, i.e. there is an angle ,B with the vertical V, which angle, although only very small is still measurable and has a magnitude of less than 5~, in particular less than 2~. In a practical embodiment, the diameter of the lower surface of the diaphragm disc, i.e. in the region of the cover surface 4, is only a few tenths of a millimetre smaller than the opening diameter of the diaphragm disc, it being necessar,v for the height measured along the vertical V to be only about 5 mm.
The upper, larger diameter of the diaphragm foil 2 is of course expediently chosen so that, when mounted, it is held on the top of the can 1 by the suction gripper by means of frictional force. A further measure for securing the diaphragm foil 2 on the top of the can 1 may consist in a collar 6 which has a hook-shaped cross-section and interacts with the upper edge of the can 1 . The upper, generally sharp edge of the can 1 is furthermore preferably flanged towards the outside (7 in Fig. la, 3), in order to prevent damage to the thin foil or injury to the user.
The diaphragm foil 2 thus fits with this collar 6 firmly on the edge of the can.However, this is only an intermediate step in the closing of the can 1 and should not hinder the subsequent steps. This includes the action of a punch 8 which is shown only schematically in Fig. lb and which presses the diaphragm foil 2 into the position shown CA 022l73ll l998-03-ll in Fig. lb. The collar 6 slides from the position indicated by a dash-dot line in Fig. 3, in which it was present before being pressed down by the punch 8, into the interior of the can and, owing to the ductility of the foil material (with simultaneous sufficient toughness), assumes the position, indicated in Fig. 3 by solid lines, at the inner circumference of the can 1. The conical shape of the film edge region 5 with the small angle ,B, which shape is shown in Fig. 2, becomes a cylindrical shape, so that the film edge region 5 is in close contact with the can circumference. As a result of the slightly conical shape, the formation of creases and wrinkles as mentioned expressly in US-A-4,599,123 - is avoided.
As described below, the process as claimed in the invention and the apparatus asclaimed in the invention result in a tight connection between the diaphragm foil 2 and the cylindrical region of the inner surface of the can immediately below the (preferably flanged) can edge.
In a preferred embodiment, the punch 8 is formed as claimed in the section shownin Fig. 4. It consists of several parts, namely the actual punch surface 9, which is connected to the lug 11 of a punch head 12 by means of upward-projecting pins 10 (only one is shown, but there are preferably three). A centering ring 13 is placed around the punch surface 9 and can be moved along guide pins 14 against the action of at least one pleS~ e spring 15. Usually, the ring 13 assumes the lowered position on the left in Fig. 4, in which, for example, it is supported on the upper side of the punch surface 9 in a manner not shown, but optionally is also held by other means.
In this position, the centering ring 13 holds the can edge, and has a recess 13' for this purpose. The process can now take place in such a way that the can 1 stands on a lifting table and is raised, with the result that the centering ring 13is displaced against the action of the spring 15 to the upper position shown on the right. At the same time, the punch surface 9 emerges from the interior of the ring 13 and thus presses the diaphragm foil 2 into the position shown in Fig. lb and 3.
Alternatively the ring 13 could also be stationary and the can held in a centered position while the punch surface 9 is moved dowllw~ds. In this case, it would benecessary, for example, for the lug 11 to be in the form of a piston rod of a fluidic aggregate, preferably of a pneumatic piston/cylinder aggregate. However, it is clear that in this case further latitude is allowed as a result of design considerations, since in fact only the relative movement of the parts shown and the can is important. Furthermore, the centering of the can, or of the diaphragm foil 2 relative to it, could be carried out in 5 varlous ways.
From the above explanation, it is clear that it is important to position the raised foil edge region 5 of the diaphragm foil 2 as close as possible to the inner circumference of the can (as shown in Fig. 3) in order to connect said edge region firmly to said inner circumference. For this purpose, the punch 8 has a spreading device, which is formed by a lO wedge arrangement in the embodiment as claimed in Fig. 4. A row of wedge segments 16 is guided along the upper side of the punch surf ace 9 in such a way that they can be displaced radially outwards with respect to the central axis A of the punch 8. For guidance, the back of the punch surface 9 could have, for example, grooves or slots (not shown). However, the flat back of the punch surface may also be sufficient for guidance.
Although the wedge segments 16 as such could themselves be used for pressing the raised foil edge region 5 of the diaphragm foil 2 against the inner circumference of the can 1, it is advantageous if elastic piston rings 17 or Seeger circlip rings are stretched around them. This provides a more uniform circumferential area when these rings 17 are pressed against the foil edge region S of the diaphragm foil 2 and moreover performs a 2 0 dual function by also generating a restoring force which acts on the segments 16.
A conical wedge 18 is provided for pressing the wedge segments 16 radially outwards, which wedge can be moved dowllw~ds and between the wedge segments withtheir wedge surfaces 20, by means of an actuating rod 19 of a drive, preferably of pneumatic type. The reason for ~rerelling a pneumatic drive is that there is scarcely any 2 5 danger of soiling by oil or leaked liquid and it is particularly easy to set a maximum ples:jul'e which does not extend the can. When the conical wedge 18 is moved dowllw~ds against the punch surface 9, it spreads apart the wedge segments 16 and thus presses the elastic rings 17 against the foil edge region 5 (which is partially indicated in the bottom right of Fig. 4) in an outward direction, where the can edge fits firmly in the recess 16'.

3 0 The position of the diaphragm foil 2 as claimed in Fig. lb is reached in this way.

* Trademark CA 022l73ll l998-03-ll In this position, however, the diaphragm foil 2 must also be secured and in general also sealed. This can be effected in a conventional manner by means of adhesive bonding, preferably by means of heat-sealing, because the thin diaphragm foil 2 does in fact lralls~ the heat relatively readily. For this purpose, the outside of the film edge can be provided with a heat-seal coat 21 (Fig. 2). A heating means is then coordinated with the spreading apparatus 16-18. Said heating means could be formed by heating coils housed in the wedge segments 16, but space is very limited there, and it is also necessary to provide movable connections. Although this possibility should therefore not be ruled out, it is possible to provide a radiant heat source 22 (for example, an annular one), for o example above the wedge segments 16 and the ring 177 which heat source heats these parts in order to warm up the heat-seal coat 21 (Fig. 2) and to fuse it with the inner surface of the can 1. The wedge segments 16 may be formed, for example, from a ceramic material having good heat storage-properties, which also improves the wear properties.
Fig. Sa shows the wedge segments 16 and a spring ring 17 in the closed position and Fig. Sb shows them in the position in which they are spread (by the wedge pieces 18 of the punch 8 which is not shown here and is moved at right angles to the plane of the drawing) for the purpose of heat-sealing the diaphragm foil 2 to the inner surface of the can.
It is clear that the wedge arrangement shown is only one possible embodiment which may be preferred, and that many modifications are possible within the scope of the invention. For example, the conical wedge 18 could simply be formed by a pressure plate which is movable relative to the punch surface 9, it being possible to provide a rubber bellows between the upper side of the punch surface 9 and the pressure plate. The bellows expands laterally from the top on being supplied with a pressure medium through the pl'eS:jUl'e plate which is used instead of the part 18 and which then would also be connected to the rod 19 for actuating the latter, and thus presses on the displaceable parts 16 or directly on the ring 17. A horizontal drive extending radially outwards would also be possible for the individual segments 16, but would be of complicated design.
Particularly in this case, but also in other cases, heating of the upper can edge from the outside for heat sealing may be the simpler solution.

As soon as the can 1 is closed in the position as claimed in Fig. lb, further, additional measures may be advantageous. For example, in order to protect the vulnerable diaphragm foil 2, a lid 23 or 24 (Fig. lc) can also be mounted.
Another particular advantage of the present invention is that the foils can be separately produced and, if necessary, kept in stock, and - where the cans 1 are of identical diameter - cans having different volumes can be equipped with the foils 2 which are produced beforehand and, owing to their design with the foil edge region 5, are in fact sufficiently stable. This foil edge region 5 can also be readily coated with the a&esive 21, which would be difficult to apply to the inner circumference of the can, owing to the 10 danger of soiling. On the other hand, the invention is of course not limited to the use of an a&esive, as already explained.
The invention is not limited to the embodiments described. Thus, the output of the apparatus as claimed in the invention with multiple tools - for example, arranged on a turntable - can be increased in a manner known per se.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for producing a sheet metal can having a closure diaphragm of paper, plastic film, or metal foil provided on at least one end face thereof, said diaphragm foil having a raised foil edge region introduced into the can and closing the one or more end faces so that the outer surface of said edge region, which is raised in the direction of the can axis, is tightly connected to the inner surface of the can wall, wherein said foil edge region is pressed against the inner surface of the can by means of a punch having an expandable circumference and thereafter the raised foil edge region is tightly connected substantially over its total vertical extent to the inner surface of the can under the action of heat, the expansion being effected without being opposed by a force from an external pressure absorption apparatus.

2. A process as claimed in claim 1, wherein said outer surface of said edge region is adhesively bonded or heat-sealed to the inner surface of the can wall, and said can wall is of cylindrical shape.

3. A process as claimed in claim 1 or 2, wherein the expansion of the punch circumference is effected by the transformation of the axial movement of the punch into a radial movement of pressure elements.

4. A process as claimed in claim 3, wherein said pressure elements are wedge segments and/or piston rings or spring rings.

5. A process as claimed in claim 1, wherein the expansion of the punch circumference is effected by a pneumatically operated rubber bellows.

6. A process as claimed in any one of claims 1 to 5, wherein the foil has, on its radial outer side, said raised film edge region.

7. A process as claimed in claim 6, wherein said raised film edge region is conically divergent by 0.2 to 0.3 mm upwards.

8. A process as claimed in any of claims 6 or 7, wherein said raised film edge region has an adhesive coat on its outside.

9. A process as claimed in claim 8, wherein said adhesive coat is a heat-seal coat.

10. A process as claimed in any one of preceding claims 1 to 9, wherein the foil has, at the free end of the foil edge region, a collar which points radially outwards and is approximately hook-shaped in cross-section.

11. A process as claimed in any one of claims 1 to 10, wherein the foil is embossed or grained.

12. An apparatus for producing a sheet metal can having a closure diaphragm of paper, plastic film, or metal foil provided on at least one end face thereof, comprising a displaceably mounted punch with a circumference expandable transversely to the displacement direction, a displacement means for the punch, and an expansion means for expanding said punch, said punch being displaceably mounted inside a centering means for the diaphragm foil and the can, and a heating means for the circumference of the punch or for the upper can edge provided on the outside.

13. An apparatus for producing a sheet metal can having a closure diaphragm of paper, plastic film, or metal foil provided on at least one end face thereof, comprising a displaceably mounted punch with a circumference expandable transversely to the displacement direction, means for displacing said punch in a longitudinal direction, a centering means for the diaphragm foil and the can, and a heating means for the circumference of the punch.

14. An apparatus as claimed in claim 12, wherein said expansion means comprises a combination of, at least two radially expandable piston rings or spring rings having mutually staggered openings, and at least three arranged in an annular manner.

15. An apparatus as claimed in claim 12 or 13, wherein the expansion means consists of an elastic ring arranged along the punch circumference.

16. An apparatus as claimed in claim 15, wherein the expansion means consists of at least one fluidic or pneumatic unit or a rubber bellows.

17. A sheet metal can having a diaphragm foil, which is provided at one end face thereof, of paper or plastic or metal foil and closing said opening so that the outside of a foil edge region raised in the direction of the can axis is tightly connected with the inside of the can wall without overlapping the can wall edge, wherein the inside of the can wall, at least in the raised foil edge region, is substantially cylindrical and the foil edge region is free of a heat-conducting lid.

18. A sheet metal can as claimed in claim 17, wherein the foil edge region is adhesively bonded or heat-sealed to the inside of the can wall.

19. A sheet metal can as claimed in claim 17, wherein the can wall edge is flanged on the outside and/or the foil edge region rests against the inner wall of the can substantially without creases and wrinkles.

20. An intermediate can structure having a sheet metal sidewall that is open at one end and fillable at the open end prior to sealing and closing of the can structure, the intermediate can structure having a closed end opposite said open end, the closed end being sealed by a closure diaphragm of a material selected from the group consisting of paper, plastic film and metal foil, the intermediate can structure having an axis, the closure diaphragm having a diaphragm edge region which is raised in a direction of said axis, the diaphragm edge region being tightly connected to an inner surface of said sidewall without overlapping an edge of said sidewall at said closed end, wherein an inner surface of said sidewall has a cylindrical shape in an area of the sidewall that is tightly connected to said diaphragm edge region, and wherein the diaphragm edge region is free from a heat-conducting cover.

21. An intermediate can structure as claimed in claim 21, having a configuration selected from the group consisting of 1) a can structure wherein the edge of the can sidewall is flanged in an outward direction, and 2) a can structure wherein the diaphragm edge region rests against the inner surface of the can substantially without creases or wrinkles.

22. An intermediate can structure as claimed in claim 21, wherein the closure diaphragm is not more than about 0.2 mm in thickness, and is selected from the group consisting of embossed diaphragm material and grained metal foil.

23. In the manufacture of a sheet metal can, the use of an intermediate can structure as claimed in any one of claims 20 to 22 to form a finished can.