Note: Descriptions are shown in the official language in which they were submitted.
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.
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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.
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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
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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
CA 02217311 1998-09-09
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
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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.
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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.
