There have been many proposals for self-heating or self-cooling beverage containers. WO 96/29255, for example, discloses a can having the same external dimensions and shape as conventional beverage cans, but having an indented base to define an external cavity in which means to cool or heat the contents of the can are received.

Heating or cooling of the contents of the can can be achieved by using two chemical reactants which are stable when separated, but which produce an exothermic reaction or an endothermic reaction when mixed. US patent No.

5,626,022 shows just one example, from many, of an insert for a self-heating or self-cooling can which enables mixing of the reactants when required. This construction, as is common, proposes the use of a module, which is pre- assembled and is then inserted into the can.

WO 01/24672 describes a self-heating or self-cooling metal can having an indented base defining an external cavity in which heating or cooling means are received. For example, heating means may comprise quicklime within a first chamber in the external cavity and water within a second chamber of the external cavity. A breakable membrane separates the first and second chambers and is piercable by the depression of a piercing member to activate the heating means. When the breakable membrane is pierced, the water from the second chamber flows over the quicklime in the first chamber to cause an exothermic reaction.

The arrangement described in WO 01/24672 has the advantage over earlier arrangements involving inserts and modules that there is no requirement to form the heating or cooling means into a sub-assembly. Instead, the individual components of the heating or cooling means are simply assembled within the external cavity of the container. This preferably occurs after the

container has been filled, and its contents have been subjected to any required treatments.

The breakable membrane extends across the external cavity of the metal can to define the first and second chambers. In addition, it is necessary to seal the membrane to surfaces of the metal can whereby the contents of the two chambers, for example, the quicklime and the water are reliably kept sealed from each other until the membrane is pierced to initiate the chemical reaction.

The present invention is concerned with a method of forming a reliably sealed chamber within a metal can, for example, to hermetically seal in the contents of cooling or heating means of a self-heating or a self-cooling container.

According to a first aspect of the present invention, there is provided a method of forming a sealed chamber within a cavity in a metal can body, the method comprising the steps of positioning a membrane within the cavity to extend thereacross and thereby define a chamber to be sealed, a circumferential portion of the membrane being in contact with a sealing surface of the can body, and applying the membrane to the can body by a heated sealing head such that heat and pressure are applied to the circumferential portion of the membrane arranged between the sealing head and the can body to seal the circumferential portion of the membrane to the sealing surface of the can body, wherein the surface of the sealing head which contacts the membrane has a conforma layer to ensure that the circumferential portion of the membrane accurately follows any contours in the sealing surface of the can body.

Metal cans may be formed by moulding, pressing, deep drawing, or reverse drawing operations. In many instances, the surfaces thereof are not perfectly flat and it is unlikely, for example, that a sealing surface in a cavity in a metal can will be perfectly flat. This can cause difficulties in achieving a reliable seal between a membrane and its sealing surface.

With a method according to an embodiment of the invention, the surface of the sealing head which contacts the membrane has a conformal layer to ensure that the circumferential portion of the membrane is, itself, conformed to accurately follow the contours in the sealing surface of the can body. In this way, it can be ensured that there is a perfect and reliable seal between the membrane and the sealing surface. This, in its turn, ensures that the sealed chamber is hermetically sealed.

In an embodiment, the sealing surface of the can body is an annular flange formed within said cavity.

In one embodiment, an adhesive is provided on the membrane and/or on the sealing surface of the can body prior to the sealing of the membrane to the can body by the sealing head.

The membrane may have a coating of, or be laminated with, a meltable material arranged to melt upon the application of heat and pressure thereto to seal the membrane to the can body. Alternatively, the membrane may have a coating of, or be laminated with, a weldable material arranged to weld the membrane to the can body upon the application of heat and pressure to the membrane. Additionally and/or alternatively, the membrane may have a layer of meltable material arranged to adhere the membrane to the can body upon the application of heat and pressure thereto.

Preferably, said meltable or weldable material is a polymeric material.

In an embodiment, the conforma layer on the contact surface of the sealing head is a thin layer of a compliant or resilient material.

The thin layer of compliant or resilient material may be of the order of 1- 2mm thick.

The thin layer of compliant or resilient material preferably comprises a polymeric material incorporating thermally conductive particles.

In an embodiment, the thin layer of compliant or resilient material may comprise a silicon material with an aluminium powder loading. Additionally and/or alternatively, the compliant or resilient material may be a rubber, with or without a loading of thermally conductive material. It would also be possible to provide a compliant mesh of metal or a woven metal material.

In an embodiment, the membrane may be of the order of 20 microns thick. The membrane may comprise a layer of metal foil having a plastics or cellulose lacquer on one or both surfaces thereof.

Alternatively, the membrane may comprise a laminated or layered material incorporating one or more of glass, waxed paper and frangible plastics material.

In a preferred embodiment, the metal can body has a tubular peripheral wall, a top membr closing one end of the peripheral wall, and a base member closing the other end of the peripheral wall. An internal cavity for the contents of the container is defined within the peripheral wall, and the base member is indented to define an external cavity which extends within the peripheral wall but is separated from the internal cavity. Preferably, the membrane is a breakable membrane which extends across the external cavity to divide it into first and second chambers, with a first reactant material being sealed within the first chamber by said breakable membrane.

Preferably, a disc shaped breakable membrane is sealed to the annular flange after a charge of the first reactant material has been filled into the first chamber.

According to a further aspect of the present invention, there is provided a metal can having a sealed chamber within a cavity within a metal can body, wherein the sealed chamber has been formed by a method as defined above.

The present invention also extends to a self-heating or self-cooling container having a tubular peripheral wall, a top member closing one end of the peripheral wall, and a base member closing the other end of the peripheral wall, an internal cavity for the contents of the container being defined within the

peripheral wall, wherein the base member is indented to define an external cavity which extends within the peripheral wall but is separated from the internal cavity, and wherein means for heating or cooling the contents of the container are received within said external cavity, said heating or cooling means comprising a breakable membrane dividing the external cavity into first and second chambers, a first reactant material sealed within the first chamber by said breakable membrane, a closure member closing said second chamber to retain a second reactant material therein, and piercing means movable to break or pierce the breakable membrane whereby said first and second reactant materials can mix, and wherein said breakable membrane has been sealed to a sealing surface of the external cavity by the application of heat and pressure to the breakable membrane when positioned between the sealing surface and a heated sealing head, and wherein the surface of the sealing head which contacts the membrane has a conforma layer to ensure that the circumferential portion of the membrane accurately follows any contours in the sealing surface of the external cavity.

Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 shows schematically an embodiment of a self heating beverage container, Figure 2 shows an example of a self-heating container, in the inverted position, and illustrates the shape of its external cavity and of its closure member, and Figure 3 illustrates a method of the invention for forming a sealed chamber in the external cavity of a container.

The invention will be described hereinafter specifically with reference to a self-heating beverage container. However, the container of the invention, which is described below, may alternatively be arranged to be self-cooling. In fact, and as set out above, a method of the invention finds general application whenever it is required to form a sealed chamber in a metal can.

The container shown in Figure 1 is a metal container 10 having a substantially cylindrical peripheral wall 12 which is closed at one end by a top

member 14. The container 10, for example, may have a can body of aluminium or steel. As described in WO 96/29255, a base member 16 of the container is indented to define an elongate external cavity 20 which extends within the peripheral wall 12. It will be appreciated that the peripheral wall 12 and the top and base members 14 and 16 of the container together define an internal cavity 22 in which contents, such as a beverage, are received. It will be seen that the external cavity 20 extends within this internal cavity 22, but is separated therefrom by the wall of the base member 16.

The container 10 illustrated in Figure 1 is configured to have the same external dimensions and shape as a conventional beverage can. This means that the can 10 can be filled and treated on existing filling lines.

The external cavity 20 of the can 10 is to be utilised to contain heating or cooling means. Where the can 10 is a self-heating can, for example, the heating means may comprise quicklime (calcium oxide) 26 filled within a first chamber within the cavity 20. A second chamber 32 within the cavity 20, separated from the first by a breakable membrane 24, is filled with water. The second chamber 32 is closed by a closure 30.

When it is required to heat the contents of the can 10, the can is inverted and stood on its top member 14 so that the base of the closure 30 is accessible. A button, described below, on the bottom of the base is depressed whereby an elongate piercing member 42 pierces the membrane 24 so that water from the chamber 32 flows over the quicklime 26 to cause the exothermic reaction. The steam which is generated is allowed to vent around the periphery of the closure 30 through vents or recesses (not illustrated) formed in either the periphery of the closure 30 or in the wall of the cavity 20 or in both. The user will retain the can in its inverted position until the exit of steam has been completed. At this stage the contents of the can will have been heated to a satisfactory temperature.

The structure of the heating means is apparent from Figure 2 in which it can be seen that the base member 16 is shaped to define at least one annular flange 34 in the wall of the external cavity 20. This flange 34 is used to support the breakable membrane 24 whereby the external cavity 20 is divided into a

first chamber 28 and a second chamber 32. It will be appreciated that the breakable membrane 24 may be piercable, rupturable or breakable in other manner.

In a preferred embodiment, the breakable membrane 24 is a disc of metal foil. After the first reactant material, for example, the quicklime 26 (not shown in Figure 3) has been charged into the first chamber 28, the membrane 24 is positioned in the cavity 20 and bonded or otherwise sealed along its periphery to the annular flange 34 as is described further below.

Preferably, and as shown in Figure 2, the closure 30 is formed from plastics material and is integral with the elongate piercing member 42. The closure 30 comprises a substantially circular member having an annular peripheral rim 36. This rim 36 defines an annular recess 38 which enables the closure 30 to be clipped on to the base of the can 10. It will be seen that in the embodiment illustrated, the free edge of the rim 36 carries an annular projection 40 which is arranged to engage within an annular groove provided externally of the base edge of the can 10.

For security of the connection, the peripheral area of the closure 30 is made to have a greater thickness of material than the central area thereof.

Substantially centrally thereof, the closure 30 carries an upstanding elongate piercing member 42. In the embodiment illustrated, this piercing member 42 is cylindrical and has a sharpened free end. The piercing member 42 is fixed to the closure 30 centrally of a button 50 defined within the closure 30 by an annular groove 48. It will be seen that in the condition shown in Figure 2, the button 50 is convex and is positioned radially inwardly of the annular groove 48.

After the quicklime 26 has been sealed within the first chamber 28 by the breakable membrane 24, an open second chamber 32 is defined. This second chamber 32 is filled with water which is retained therein by snap fitting the closure 30 into position on the base of the can 10. In order to ensure that the chamber 32 is substantially watertight, the periphery of the closure 30 is shown to have an integrally formed seal in the form of an annually extending wiper 52.

When self-heating of the can is required, it is inverted as described above. The button 50 is pressed to move the piercing member 42 in a direction to pierce or break the breakable membrane 24. Generally, it is expected that depression of the button 50 will cause a positive break in the membrane 24 whereby water is quickly released into the quicklime within the chamber 28 to commence the self-heating reaction. However, because the can 10 is inverted, it does not matter if there is some failure in the break provided as long as some rupture of the membrane 24 occurs. In this respect, with any rupture in the membrane 24, a flow of water from the chamber 32 into the chamber 28 will occur and this, in itself, will tend to ensure that a larger rupture in the membrane 24 is caused.

The reaction which takes place between the water and the quicklime will generate steam and it is necessary to ensure that air and steam can exit from the external cavity 20. For example, vent channels (not shown) may be provided through the material of the periphery of the closure 30 to open into the external cavity 20 radially outwardly of the wiper 52. The wiper 52 is thereby able to prevent egress of water whilst allowing air and steam to exit.

The self-heating container described and illustrated can be filled on conventional filling lines, and the contents thereof may be subjected to any treatment required. For example, contents of the container may be pasteurised and/or sterilised. Thereafter, it is a simple matter to invert each completed and fitted container and provide it with heating means in its external cavity 20.

Thus, the external cavity 20 is charged with a predetermined amount of quicklime, a breakable membrane 24 is inserted and is bonded or otherwise sealed to the annular flange 34, a charge of water is then filled into the thus defined second chamber 32, and the closure 30 is clipped onto the container 10.

The embodiment described above shows a particularly simple construction for the heating means and a similar construction can be used for cooling means. The final can is sufficiently robust to withstand normal transport and handling.

It is required that the membrane 24 hermetically seal the chamber 28 with its charge of quicklime whereby contamination of the quicklime is prevented. This increases the shelf life of the heating means of the can 10.

As indicated above, as the container 10 is a metal can, an annular flange, as 34, formed on the metal can body will not have a surface which is perfectly smooth. This means that it can be difficult to obtain a perfect seal between the circumferential portion of the membrane 24 and the externally facing sealing surface of the flange 34. Figure 3 indicates a method of sealing the membrane 24 to the flange 34 which overcomes the difficulties.

In the embodiment illustrated in Figure 3, the membrane 24 is a foil disc provided with appropriate means to enable its circumferential portion to be sealed to the flange 34 by the application of heat and pressure thereto. For example, the foil disc 24 may have a coating of, or be laminated with, a material which is arranged to melt upon the application of heat and pressure.

Alternatively, the foil disc may have a coating of, or be laminated with, a material arranged to weld the membrane to the annular flange upon the application of heat and pressure thereto. Additional and/or alternatively, the foil disc 24 may have a layer of meltable material arranged to adhere it to the flange 34. The meltable or weldable material may be any suitable material, such as a polymeric material or a cellulose material. It is also possible to apply an adhesive either to the foil disc or to the annular flange before the foil disc 24 is placed in position prior to sealing.

The foil disc 24 is placed in position in contact with the annular flange 34. This may be done, for example, by forming the foil disc with a die cutter having an integral sealing head. The foil disc may then be transported into position by the sealing head on which it is held by a small vacuum. An alternative is to cut the foil disc separately and use a pick and place machine to position the foil disk 24 on the externally facing sealing surface of the annular flange 34.

Once the foil disc 24 has been appropriately positioned, a heated sealing head 60 is introduced into the external cavity 20 and is moved downwardly such that it engages the foil disc 24 and presses its circumferential

portion against the sealing surface of the annular flange 34. This sealing head 60 may be the integral sealing heat of the die cutter, or a separate sealing head. It will be appreciated that the foil disc 24 is subjected to pressure by the reaction of the sealing head 60 with the annular flange 34, and that the foil disc is also subjected to heat. The application of heat and pressure seals the circumferential portion of the foil disc 24 to the flange 34.

To ensure that the seal is perfect, the contact surface of the sealing head 60 is provided with a conforma layer 62. As the sealing head applies pressure, the conforma layer 62 is arranged to deform such that its surface conforms exactly to the contours of the sealing surface of the annular flange 34. This, in its turn, means that the circumferential porition of the foil disc 24 is also deformed to. conform to the sealing surface and it is this conforming of the foil disc which leads to the achievement of a reliable seal between the foil disc 24 and the annular flange 34.

The conforma layer 62 may be of any appropriate material which is able to accurately conform to the sealing surface and also to ensure that the appropriate heating effect is applied to the foil disc. The conforma layer also needs to survive in the pressure and temperature applying environment.

It is preferred that the conforma layer 62 is a thin layer of a compliant or resilient material. For example, a layer having a thickness of the order of 1- 2mm is presently preferred.

Any appropriate material or combination of materials may be chosen for the conforma layer 62. For example, the compliant or resilient material may comprise a polymeric material incorporating thermally conductive particles.

Alternatively, the conforma layer may comprise a silicon material with an aluminium powder loading.

In the embodiment described above, the membrane 24 is said to be a disc of metal foil. Of course, any appropriate material or combination of materials may be utilised. For example, the membrane may incorporate one or more of glass, wax paper and frangible plastics. Any suitable material may

have a plastics based lacquer on the contact side and a protective cellulose lacquer or layer on its reverse.

In a preferred embodiment, the membrane may be of the order of 20 microns thick.

It will be appreciated that modifications to or variations of the embodiments described and illustrated may be made within the scope of this application as set out in the appended claims.