Note: Descriptions are shown in the official language in which they were submitted.
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Description
CONTAINER
Technical Field
[0001] This invention relates to a container. In particular, it relates to a
container which
comprises the combination of a can body for prodirts such as food, and a
closure
element. The invention also includes a method of forming the combination of
can body
and closure element.
Background Art
[0002] Cans for the packaging food are typically of a two or three piece form,
comprising a
tubular can body, either cylindrical or irregular/polygonal in cross-section,
with a base
and closed by a can end, diaphragm, film, screw top or other closure. The base
may be
integral with the can body so as to form a so-called two-piece can body, or
the can
body may be formed from a tube of sheet metal with the edges of the sheet
metal
joined by a welded side seam, which is then closed at both ends to form a
three-piece
can.
[0003] Typical food cans which are closed by a can end, have sealing compound
in the
curled edge of a cover hook portion of the can end in order to provide a tight
hermetic
seam, usually known as a double seam due to the two thicknesses of metal in
the seam
- one from the can body and the other from the can end. A problem with a three
piece
can body is that the welded side seam provides an irregular sealing surface
for
seaming. The sealing compound needs to be precisely and uniformly placed so
that the
resultant ring of sealing compound within the seam has the right width,
thickness and
position to ensure that the seam has the required tightness. Double seam
technology is
a precise art, which relies on numerous factors for seam integrity, of which
the sealing
compound is one important feature.
[0004] Cans for other prodirts may use different closure arrangements; for
example, a
peelable foil is typically seated on an intermediate metal ring which, in
turn, is seamed
to the can body. Smh can and ring combinations are expensive to manufacture as
the
central disc from the ring element is generally scrapped, leading to material
wastage.
Proposals such as those described in
Patent Citation 0001: EP 1029613 A (IMPRESS GMBH & CO). 2000-08-23.
and
Patent Citation 0002: WO 2005063587 A (CROWN PACKAGING TECHNOLOGY
INC). 2005-07-14.
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avoid wasting the centre of the ring, but include additional manufacturing
stages
which, in turn, involve extra process time and/or capital equipment costs.
[0005]
Patent Citation 0003: EP 0819086 B (GRABHER, WERNER). 1998-12-23.
describes a semi-finished can which is open at one end and closed at its other
end by a
cup-shaped foil membrane. The sidewall of the foil cup extends in the
direction of the
can axis and is bonded directly to the inside of the can wall. The foil may
extend over
the can body edge, which has been formed into a hook or curl. Although
inexpensive
to manufacture, unfortunately when cans closed in this way are stacked, the
pressure of
the upper can bears directly onto the foil, risking damage to the foil. In
addition, the
foil is bonded to the can body over a side seam which presents an irregular
sealing
surface as described above.
[0006] Another problem with
Patent Citation 0004: EP 0819086 B (GRABHER, WERNER). 1998-12-23.
is that the container is unsuitable for use with foods which generate internal
positive
pressure within the can body during processing as this tends to peel the foil
from off
the sidewall of the container.
[0007] This invention seeks to oveicome the problems of EP 0819086 B whilst
still
providing a container that is less expensive and wasteful to manufacture than
the ring
and peelable foil membrane closures descxibed above.
Disclosure of Invention
[0008] This invention seeks to provide a can body and closure element for
closing by a
variety of closure panels (can end, diaphragm, disc etc.) at a redired cost in
comparison with traditional peelable closures.
[0009] Accordingly, a first aspect of the invention provides a container
comprising:
a metal can body, and
a combination of a ring and a foil membrane, the combination being attached to
the
can body,
in which the ring is made of a plastics material,
characterised in that the inside diameter of the plastic ring is no less than
the inside
diameter of the can body away from the attachment location of the ring on the
can
body.
[0010] Use of a plastic ring is more economical than using a metal ring from
which the
centre is generally discarded. The bond between the ring/foil membrane
combination
and the can body provides a strong connection to give a hermetic seal.
Furthermore,
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the ring/foil membrane combination covers any weld (for example, a welded side
seam
in the sidewall of a 3 piece can) and the plastic ring supports any container
stacked on
top, without risk of damage to the foil membrane.
[0011] Ensuring that the inside diameter of the plastic ring is no less than
the inside
diameter of the can body away from the attachment location of the ring on the
can
body is beneficial in maximising the opening aperture of the container and in
enabling
full release of prodirt from the container. The can body may have a generally
cyl-
indrical profile, i.e. with a straight or tapered sidewall. In such an
embodiment, the
ring may be retained by contact between the ring and the exterior surface of
the can
body; conveniently, retention of the ring on the can body is enabled by the
ring having
an outer peripheral wall and a hook portion as described below.
[0012] Preferably however, the edge of the can body to which the ring/foil
membrane com-
bination is attached comprises an expanded portion, all or part of the ring
locating
within the expanded portion, the inside diameter of the ring being no less
than the
inside diameter of the unexpanded portion of the can body. Usually the height
of the
ring corresponds to the axial length of the expanded part of the can body. Con-
sequently, the inner sidewall of the ring extends smoothly into the inner
sidewall of the
can body. This is beneficial in enabling full release of prodirt from the
container and
is particularly useful for solid or semi-solid food prodirts, such as cooked
meats, thick
soups or pet food.
[0013] In one embodiment, the ring is bonded permanently to the can body and
the foil
membrane is bonded peelably to the plastic ring. The ring may be formed from a
con-
ventional thermoplastic polymer, such as polypropylene. The bonding between
the ring
and the can body may be enhanced by selection of the coating on the can body;
for
example, a film of heat sealable lacquer may be applied at the interface
between the
ring and the can body or be pre-coated onto the can body and/or the ring. The
ring may
be heat sealed to the can body, for example using indirtion heating, with the
ap-
plication of heat causing the heat sealable lacquer to form a bond between the
ring and
the can body. When using induction heating to bond the ring to the can body,
the foil
membrane is typically peelably bonded to the ring subsequent to the bonding of
the
ring onto the can body, thereby ensuring that any metal in the foil membrane
will not
interfere with the indirtion heating process. The resulting container is more
easy to
open by peeling than that of EP 0819086 B, which is not in peel mode for
opening.
[0014] In a preferred embodiment, the ring is directly bonded to the sidewall
of the can
body. The plastic ring may be made from a thermoplastic polymer; it has been
found
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beneficial for the plastic ring to comprise polypropylene or modified
polypropylene.
The ring may then be placed in position on the can body and suitable heating
means
applied (for example, indirtion heating). The action of the heating causes the
surface
of the ring itself to directly bond with the surface of the can body, even
when the can
body surface includes protective lacquers/coatings (for example, epoxy-based
coatings). Advantageously, the modified polypropylene comprises polypropylene
grafted with maleic anhydride. Such a modified polypropylene has been found to
form
a strong bond with conventional lacquers of the type commonly used on metal
can
bodies to protect the metal substrate of the can body, such as epoxy-based
lacquers.
Polypropylene is a non-polar material, whereas the lacquers used to protect
the metal
substrate of a can body (e.g. epoxy-based lacquers) are often polar materials.
The
addition of maleic anhydride improves the ability of the non-polar
polypropylene of
the plastic ring to bond with polar lacquers provided on the can body.
[0015] The can body may comprise a curl or flange, and the ring may include a
shoulder
which is adapted to extend over the can body curl/flange. Preferably, the
shoulder
extends into an outer peripheral wall which depends from the shoulder over the
outside
of the can body curl/flange. Advantageously, the outer peripheral wall
comprises a
hook portion so as to clip over the can body curl/flange to retain the ring on
the can
body. The hook portion is useful for retaining the ring in position on the can
body if
the ring is to be fixed onto the can body by indirtion heating (or other means
involving application of heat to the ring), because it compensates for any
thermal
expansion or contraotion of the plastic ring relative to the metal can body.
[0016] Conveniently, the shoulder includes a portion which extends upwardly to
provide a
rim for handling and tab protection. Preferably, the base of the container and
the rim
are formed such that the base of a first container of the present invention
may be
located within the rim of a second container of the present invention, thereby
enhancing the ability to stack the containers on top of each other.
[0017] In one embodiment, the ring's shoulder is provided with a substantially
flat bonding
surface, and the foil membrane is bonded to this flat surface. In an
alternative em-
bodiment, the ring is provided with a bonding surface inclined downwardly at
an angle
of up to 60 , and the foil membrane is bonded to this inclined surface. The
provision of
such an inclined bonding surface has been found to enable retort processing of
the
container. When subject to internal positive pressure during processing, the
foil would
expand outwardly to form a curved profile. The inclined bonding surface
ensures that
the foil membrane is mainly loaded in shear rather than in peel when subject
to internal
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positive pressure, thereby inhibiting loss of seal between the foil membrane
and the
plastic ring. More preferably, the bonding surface is instead inclined
downwardly at an
angle of up to 45 .
[0018] The foil membrane usually includes a tab for gripping to peel the foil
membrane
from the ring. Ideally, this tab is situated towards one edge of the foil in
order to
redire peel foiue requirements.
[0019] Alternatively, the foil membrane may be formed in the shape of a cup
(i.e. cup-shaped) and the sidewall of the foil cup bonded to the inner
sidewall of the
ring. In this embodiment, it is beneficial for any tab to be situated away
from the
sidewall of the cup-shaped foil to assist in peelable removal of the foil.
[0020] In a second aspect of the present invention, there is provided a method
of forming a
container, the method comprising:
forming a metal can body;
fixing a ring of plastics material permanently to the can body, the inside
diameter of
the plastic ring being no less than the inside diameter of the can body away
from the
attachment location of the ring on the can body; and
bonding a foil to the ring such that, in use, the foil may be peeled from the
ring for
dispensing a prodirt from the container.
[0021] Preferably, the can body is formed with a radially expanded portion at
one end of
the can body, and the plastic ring is fixed permanently to the can body smh
that all or
part of the ring is located within the expanded portion.
[0022] Alternatively, the steps of fixing the ring and bonding the foil may be
reversed such
that the foil is first bonded to the ring and the combination of ring and foil
is sub-
sequently fixed to the can body.
[0023] According to a third aspect of the present invention, there is provided
a container
comprising:
a metal can body, and
a combination of a ring and a foil membrane, the combination being attached to
the
can body,
in which the ring is made of a plastics material,
characterised in that the ring/foil membrane combination comprises a permanent
bond
between the membrane foil and the ring, and the foil is peelably bonded to the
inside
of the can body sidewall.
[0024] In this aspect of the invention, the ring may include a tab or ring
pull for removing
the ring and foil together as a single entity from the container. The relative
rigidity of
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the plastic ring compared to the foil membrane may enable the container to be
re-
closeable by locating the ring/foil membrane combination back onto the can
body.
[0025] This aspect of the invention may also incorporate one or more of the
features
described above for the first aspect of the invention.
Brief Description of the Drawings
[0026] Preferred embodiments of the invention will now be descxibed, by way of
example
only, with reference to the drawings, in which:
Figure 1 is a side section of a first embodiment of a container acoording to
the
invention;
[0027] Figure 2 is a perspective view of the container of figure 1;
[0028] Figure 3 is a side section of a second embodiment of a container
according to the
invention;
[0029] Figure 4 is a perspective view of the container of figure 3;
[0030] Figure 5 is side section of a third embodiment of a container according
to the
invention;
[0031] Figure 6 is a perspective view of the container of figure 5;
[0032] Figure 7 is a side section of a fourth embodiment of a container
acoording to the
invention;
[0033] Figure 8 is a side section of a fifth embodiment of a container
acoording to the
invention; and
[0034] Figure 9 is a perspective view of the container of figure 8.
Mode for the Invention
[0035] Figures 1 and 2 show a container 1. The container 1 is of a so-called
"three piece"
type, comprising a cylindrical can body 2 that is closed at its lower end by a
con-
ventional closure 3. The closure 3 is joined to the can body 2 by a double
seam 4. The
can body 2 is radially expanded by an amount `a' (in this example,
approximately
2mm) at its upper end to provide a stepped portion 5 and terminates in a
flange or curl
6.
[0036] The can body 2 may be formed from a metal sheet which is coated with a
lacquer,
polypropylene being dispersed within the lacquer. The metal sheet may then be
formed
into a cylinder (for example, by welding) to provide the can body. The welded
side
seam thus formed on the can body is generally separately coated with a similar
internal
lacquer or with a polypropylene powder. Alternatively, the metal sheet could
be coated
with a conventional lacquer and a specific lacquer, smh as one including a
dispersion
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lacquer, used only for coating that part of the can wall and weld which is to
contact the
plastic ring 12.
[0037] The upper end of the can body 2 is closed off by a closure 10. The
closure 10
includes a plastic ring component 12, and a diaphragm or foil 14 with a
peripheral tab
16 for opening. The plastic ring 12 is moulded into a first annulus 18 that is
sub-
stantially cylindrical and shaped to be seated within the stepped portion 5.
In the em-
bodiment shown, the plastic ring 12 has an internal diameter which is the same
as that
of the unexpanded portion of the can body 2. This provides a smooth transition
from
i) the inner sidewall of the unexpanded portion of the can body 2 to ii) the
inner
sidewall of the plastic ring 12, thereby optimising prodirt release. However,
al-
ternative embodiments may have the plastic ring 12 having an internal diameter
which
is greater than that of the can body 2 beneath the stepped portion 5. In
either case, the
plastic ring 12 does not impede the release of prodirt from the container 1,
but instead
promotes full prodirt release. The plastic ring 12 is also typically of either
polypropylene for bonding to a polypropylene dispersion in the internal can
body
coating, or modified polypropylene for bonding to conventional lacquers.
[0038] The annulus 18 of the plastic ring 12 extends radially outwardly into a
flat shoulder
portion 20 which, in turn, extends outwardly and downwardly into a retention
portion
22 and upwardly into a rim 24. The plastic ring 12 may also be shaped (for
example,
with a hooked portion) so as to be snapped into position around the can body
flange or
curl 6 and thereby hide any exposed metal of the flange or curl. The annulus
18 is per-
manently bonded to the can body, for example by induction heating. The bonded
region may also include the curl or flange 6.
[0039] The foil 14 is bonded to the flat shoulder portion 20 which forms a
sealing surface
of 1.0 to 2.5 mm in width. The centre region of the foil 14 as shown in figure
1 is
domed inwardly due to negative pressure (somlled "vauum") within the container
following filling or processing.
[0040] The container 1 of figures 1 and 2 is typically formed in two separate
stages. In one
stage, the can body 2 has the flange or cur16 formed around the periphery to
which the
plastic ring 12 is to be bonded, and then the upper region of the can body 2
is radially
expanded to form the stepped portion 5. The plastic ring 12 is bonded to the
can body
2 by indirtion heating, and the foil 14 then fixed to the plastic ring. The
container 1 is
filled through its bottom end and the closure 3 seamed onto the filled
container. In this
method, the foil 14 does not interfere with the indirtion heating process and
the
indirtion heating does not interfere with the peelable bond between the foil
14 and
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plastic ring 12.
[0041] The example of figures 3 and 4 is similar to that of figures 1 and 2
but includes a
shoulder portion 21 which slopes downwardly from the horizontal by an angle a
(in
this example, 20 ). Downwardly extending or "barometric" shoulders are
preferred for
containers in which the lidding material is deflected by in-can pressure
during
processing of the food prodirt in the container and enables use in reel and
spiral
retorts (or similar processes). By inclining the shoulder portion 21
downwardly, the
angle a becomes greater than the angle subtended by the extremity of the
lidding
material in its outwardly domed position when subject to positive internal
pressure. As
a result, the sealing surface is predominantly loaded in shear rather than in
peel, which
effectively doubles the burst pressure performance from that of containers
with flat
shoulders (such as that of figures 1 and 2) which would be loaded in peel mode
when
subject to positive internal pressure. For barometric shoulders, preferred
bonding
surface angles a are up to 45 to give sufficient dome size, although in
theory angles a
of up to 60 are possible.
[0042] Although the centre region of the foil 14 of figures 3 and 4 has been
shown with a
plain surface, decoration for customisation or beading for improving
barometric per-
formance may be used to allow for movement of the foil 14 whilst avoiding foil
wrinkling.
[0043] This embodiment may be formed in the same way as that of figures 1 and
2. Of
course, either of these two embodiments could use a container drawn from a
blank of
sheet metal to form a sidewall and integral base (i.e. no welded side seam),
in which
case the plastic ring 12 and foil 14 may be formed as one component which is
sub-
sequently bonded to the can body 2 after filling. Alternatively, the ring 12
may first be
bonded to the can body 2, the can filled and the foil 14 then bonded to the
plastic ring.
[0044] In the alternative container shown in figures 5 and 6, like features of
the can body 2
are given the same reference numerals as in figures 1 to 4. The plastic ring
12 of this
embodiment comprises a shoulder 13 which extends over the edge of the can body
(here shown as a cur16, although the edge may be unshaped or a simple flange)
and
the annulus 18 is seated against and permanently bonded to the inner wall of
the can
body 2 in the same manner as the embodiments of figures 1 to 4. However, in
figures 5
and 6, the foil 14 is peelably bonded to the inner wall of the plastic ring
12, rather than
to a flat or downwardly inclined portion of the ring. In this embodiment, the
foil 14
defines a cup-shape profile. This avoids the problems of direct welding of
foil over a
weld margin as arises in processes such as that descxibed in
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Patent Citation 0005: EP 0819086 B (GRABHER). 1998-12-23.
. Tab 16 of figures 5 and 6 is bonded to the central part of foil 14. This
ensures that a
customer peels the foil 14, rather than trying to remove the whole of the
permanently
bonded plastic ring 12 from the can body 2.
[0045] Figure 7 shows an alternative container 1 which has a generally
cylindrical can
body 2 terminating at its upper end with flange or cur16 at the edge of the
can body.
The ring 12 includes a flat shoulder portion 20 which extends outwardly and
downwardly into a retention portion 22 and upwardly into a rim 24. The
retention
portion 22 terminates in a hooked portion 25 which partially extends
underneath the
flange or cur16 to assist in retaining the ring 12 on the can body 2. The ring
12 is per-
manently bonded to the can body, with the bonded region including the exterior
surface of the curl or flange 6. As can be seen from figure 7, in this
embodiment the
plastic ring 12 does not extend down along the interior surface of the can
body 2,
thereby avoiding the need to provide an expanded portion on the can body. Con-
sequently, release of prodirt from the resulting container is not impeded.
[0046] Figures 8 and 9 represent an embodiment of the invention in which a
plastic ring 30
is bonded permanently to the foil 14. As clearly seen from figures 8 and 9,
the foil 14
is bonded to the external sidewall of the plastic ring 30. The combination of
the plastic
ring 30 and foil 14 is attached to the can body 2 by peelably bonding the foil
to the
inner wall of the can body 2 around the upper sidewall 32 of the can body 2.
The
plastic ring 30 incorporates a large ring-pull style of tab 36 for ease of
gripping when
removing the foil (and ring) from the container 1.
