US20090032535A1

US20090032535A1 - Container

Info

Publication number: US20090032535A1
Application number: US12/281,024
Authority: US
Inventors: Robert Paul Dunwoody; Philip Alan Marriott; Paul Claydon; James Leslie Bullock
Original assignee: Crown Packaging Technology Inc
Current assignee: Crown Packaging Technology Inc
Priority date: 2006-03-01
Filing date: 2007-02-23
Publication date: 2009-02-05
Also published as: CA2642569A1; GB0604097D0; WO2007099066A1; MX2008011172A; CN101395067A; AU2007220536A1; EP1989121A1

Abstract

A container (1) particularly for food products comprising a metal can body (2) and a combination of a ring (12) and a foil membrane (14), the combination being attached to the can body, in which the ring is made of a plastics material, wherein 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.

Description

TECHNICAL FIELD

This invention relates to a container. In particular, it relates to a container which comprises the combination of a can body for products 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

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.
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 relics on numerous factors for seam integrity, of which the sealing compound is one important feature.
Cans for other products 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. Such 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.

avoid wasting the centre of the ring, but include additional manufacturing stages which, in turn, involve extra process time and/or capital equipment costs.

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.
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.
This invention seeks to overcome 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 described above.

DISCLOSURE OF INVENTION

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 reduced cost in comparison with traditional peelable closures.
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.
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, 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.
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 product from the container. The can body may have a generally cylindrical 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.
Preferably however, the edge of the can body to which the ring/foil membrane combination 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. Consequently, the inner sidewall of the ring extends smoothly into the inner sidewall of the can body. This is beneficial in enabling full release of product from the container and is particularly useful for solid or semi-solid food products, such as cooked meats, thick soups or pet food
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 conventional 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 precoated onto the can body and/or the ring. The ring may be heat sealed to the can body, for example using induction heating, with the application 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 induction 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.
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 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, induction 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.
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 induction heating (or other means involving application of heat to the ring), because it compensates for any thermal expansion or contraction of the plastic ring relative to the metal can body.
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.
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 embodiment, 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 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°.
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 reduce peel force requirements.
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.
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 product from the container.
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 such that all or part of the ring is located within the expanded portion.
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 subsequently fixed to the can body.
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.
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 the plastic ring compared to the foil membrane may enable the container to be recloseable by locating the ring/foil membrane combination back onto the can body.
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

Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

FIG. 1 is a side section of a first embodiment of a container according to the invention;

FIG. 2 is a perspective view of the container of FIG. 1;

FIG. 3 is a side section of a second embodiment of a container according to the invention;

FIG. 4 is a perspective view of the container of FIG. 3;

FIG. 5 is side section of a third embodiment of a container according to the invention;

FIG. 6 is a perspective view of the container of FIG. 5;

FIG. 7 is a side section of a fourth embodiment of a container according to the invention;

FIG. 8 is a side section of a fifth embodiment of a container according to the invention; and

FIG. 9 is a perspective view of the container of FIG. 8.

MODE FOR THE INVENTION

FIGS. 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 conventional 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 2 mm) at its upper end to provide a stepped portion 5 and terminates in a flange or curl 6.
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, such as one including a dispersion lacquer, used only for coating that part of the can wall and weld which is to contact the plastic ring 12.
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 substantially cylindrical and shaped to be seated within the stepped portion 5. In the embodiment 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 product release. However, alternative 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 product from the container 1, but instead promotes full product 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.
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 permanently bonded to the can body, for example by induction heating. The bonded region may also include the curl or flange 6.
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 FIG. 1 is domed inwardly due to negative pressure (so-called “vacuum”) within the container following filling or processing.
The container 1 of FIGS. 1 and 2 is typically formed in two separate stages. In one stage, the can body 2 has the flange or curl 6 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 induction 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 induction heating process and the induction heating does not interfere with the peelable bond between the foil 14 and plastic ring 12.
The example of FIGS. 3 and 4 is similar to that of FIGS. 1 and 2 but includes a shoulder portion 21 which slopes downwardly from the horizontal by an angle α (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 product in the container and enables use in reel and spiral retorts (or similar processes). By inclining the shoulder portion 21 downwardly, the angle α 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 FIGS. 1 and 2) which would be loaded in peel mode when subject to positive internal pressure. For barometric shoulders, preferred bonding surface angles α are up to 45° to give sufficient dome size, although in theory angles α of up to 60° are possible.
Although the centre region of the foil 14 of FIGS. 3 and 4 has been shown with a plain surface, decoration for customisation or beading for improving barometric performance may be used to allow for movement of the foil 14 whilst avoiding foil wrinkling.
This embodiment may be formed in the same way as that of FIGS. 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 subsequently 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.
In the alternative container shown in FIGS. 5 and 6, like features of the can body 2 are given the same reference numerals as in FIGS. 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 curl 6, 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 FIGS. 1 to 4. However, in FIGS. 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 described in

Patent Citation 0005 EP 0819086 B (GRABHER). 1998-12-23.

Tab 16 of FIGS. 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.
FIG. 7 shows an alternative container 1 which has a generally cylindrical can body 2 terminating at its upper end with flange or curl 6 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 curl 6 to assist in retaining the ring 12 on the can body 2. The ring 12 is permanently bonded to the can body, with the bonded region including the exterior surface of the curl or flange 6. As can be seen from FIG. 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. Consequently, release of product from the resulting container is not impeded.
FIGS. 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 FIGS. 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.

Claims

1. 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, the ring is formed of a material comprising a plastic 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.

2. A container as claimed in claim 1, wherein the edge of the can body to which the ring/foil membrane combination 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.

3. A container according to claim 2, wherein the height of the ring corresponds to the axial length of the expanded part of the can body.

4. A container according to claim 1, wherein the ring is directly bonded to the sidewall of the can body.

5. A container according to claim 1, wherein the ring comprises at least one of polypropylene or modified polypropylene.

6. A container according to claim 5, wherein the modified polypropylene comprises polypropylene grafted with maleic anhydride.

7. A container according to claim 1, in which the plastic ring is bonded permanently to the can body and the foil membrane is bonded peelably to the ring.

8. A container according to claim 1 wherein the can body comprises a curl or flange and the ring comprises a shoulder, the shoulder extending into an outer peripheral wall which depends from the shoulder over the outside of the can body curl or flange.

9. A container according to claim 8, in which the outer peripheral wall comprises a hook portion which clips over the can body curl or flange to retain the ring on the can body.

10. A container according to claim 1 wherein the ring comprises a portion which projects upwardly to provide a rim, the base of the container and the rim each being formed such that the base of a first container may be located within the rim of a second container.

11. A container according to claim 1, wherein the ring is provided with a substantially flat bonding surface, and the foil membrane is bonded to this flat surface.

12. A container according to claim 1, wherein 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.

13. A container according to claim 1, wherein the ring is provided with a bonding surface inclined downwardly at an angle of up to 45°, and the foil membrane is bonded to this inclined surface.

14. A container according to claim 1, wherein the foil membrane is cup shaped and the sidewall of the foil cup is bonded to the inner sidewall of the ring.

15. A method of forming a container, the method comprising:

forming a metal can body;

fixing a ring formed of a material comprising a plastic 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 product from the container.

16. A method according to claim 15, wherein 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 such that all or part of the ring is located within the expanded portion.

17. A method according to claim 15, in which the step bonding the foil occurs before the step of fixing the ring such that the foil is first bonded to the ring and the combined ring and foil is subsequently fixed to the can body.

18. 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,

the ring is formed of a material comprising a plastic,

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.