WO2013124674A1

WO2013124674A1 - A container for a self-heating device

Info

Publication number: WO2013124674A1
Application number: PCT/GB2013/050444
Authority: WO
Inventors: Jim Shaikh; David Hartwanger; Richard Thom
Original assignee: Feed Me Bottles Limited
Priority date: 2012-02-23
Filing date: 2013-02-22
Publication date: 2013-08-29

Abstract

The container (16) consists of a base (18), an upstanding wall (20) which is at least partially transmissive to microwave energy and a lid (24). The container (16) is suitable for use with a self-heating device(2) containing an exothermic phase change material that can be re-charged using microwave energy. The device (2) includes a diaphragm (6) to accommodate volumetric changes of the exothermic phase change material during the phase change process and the lid (24) of the container (16) includes a cavity (29) into which the diaphragm (6) can expand with the wall of the cavity (29) preventing the diaphragm (6) from expanding too far. The self-heating assembly enables the self-heating device (2) to be re-charged using microwave energy without the deleterious effects commonly encountered.

Description

A CONTAINER FOR A SELF-HEATING DEVICE

The present invention relates to a container for a self-heating device and to a self- heating assembly comprising a container and the self-heating device. In particular, this invention relates to a container for a self-heating device for use when recharging the device using microwave energy.

Self-heating devices, such as heat packs, are used in a wide variety of applications including, for example, as a therapeutic means to alleviate muscular pain. A popular version of the self-heating device comprises a flexible membrane containing an exothermic phase change material, which releases heat upon crystallisation, and a trigger mechanism for activating the exothermic phase change. After use, the phase change material of the self-heating device is left in a crystalline state and must be returned to a liquid state before the self-heating device can be re-used. This can be accomplished by, for example, submersing the self-heating apparatus in hot water or by exposure to microwave energy. The flexibility of the membrane containing the phase change material is necessary to enable external forces to be applied to the trigger mechanism within the flexible membrane and to accommodate the difference in the volume of the exothermic phase change material between its crystalline and liquid states.

A self-heating device that proposes using microwave energy to replenish the latent energy of the exothermic phase change material is described in US 5645749. This document describes a heat pack comprising two flexible plastic layers that are welded together along their edges to provide a flexible pouch closed on all sides by a water-tight seal. A saturated sodium acetate solution is contained in the pouch along with an activator which is in contact with the saturated sodium acetate solution. However, flexible pouches of self-heating device such as that described above are known to encounter reliability problems when the saturated sodium acetate solution is re-charged using microwave energy, which can result in the plastic layers or the seal failing.

Accordingly, a need exists for a means and a method for re-charging a self-heating device containing exothermic phase change material using microwave energy which avoids or minimises the reliability problems mentioned above.

A self-heating apparatus is described in EP 1871204 which is adapted for warming fluids, such as milk, in a baby's feeding bottle. The self-heating apparatus includes an exothermic phase change self-heating device positioned between a fluid reservoir and a feeding teat. With the heating device activated, fluid from the fluid reservoir flows over or through the heating device where the fluid is heated, and to the feeding teat. The heating device described in EP 1871204 differs from other conventional self-heating devices in that the walls used to contain the exothermic phase change material are substantially rigid. That is to say, the walls are inflexible under manually applied external forces. However, a flexible diaphragm is provided in one of the walls of the device to accommodate volume changes arising from the phase change process. This earlier patent is owned jointly with the present application and the content of this publication is incorporated herein by reference.

A need also exists for a means and a method enabling heating devices suitable for use in the self-heating apparatus of EP 1871204 to be recharged using microwave energy. In the context of this document, reference herein to recharging using microwave energy is intended as reference to exposing crystalline exothermic phase change material to electromagnetic energy in the microwave range of wavelengths (approximately 1 mm to 1 m) and in particular, but not exclusively, to those wavelengths and power levels commonly used in consumer microwave ovens so as to cause the exothermic phase change material to return to its liquid state.

The present invention therefore provides a container for a self-heating device containing an exothermic phase change material, the self-heating device including a flexible portion having a smoothly curving periphery capable of accommodating volumetric changes of the exothermic phase change material, the container comprising: a housing having one or more walls which at least partially define a cavity adapted to receive the self-heating device; an opening in the housing, said opening providing fluidic communication between the cavity and the environment external to the housing; and a dome-shaped expansion boundary the concave side of which is in fluidic communication with the cavity, and wherein the housing is at least partially transmissive to microwave energy whereby the expansion boundary conforms to and limits expansion of the flexible portion of the self-heating device when the self-heating device is mounted in the cavity and the housing is irradiated by electromagnetic energy.

The container described above enables the exothermic phase change material of the self-heating device to be recharged using microwave energy without the deleterious effects previously encountered.

Ideally, the expansion boundary comprises electromagnetic radiation shielding and the shielding may be shaped to substantially conform to the expansion boundary.

In a preferred embodiment, the housing includes a base with the one or more walls upstanding from the base and the one or more walls of the housing are arranged to accommodate the self-heating device orientated so that the flexible portion is uppermost and remote from the base of the housing. In the preferred embodiment the container additionally includes a lid adapted for engagement with the one or more walls the lid comprising the dome-shaped expansion boundary and having an outer surface shaped to prevent the container being stood with its base uppermost. The lid and the one or more walls are preferably releasably securable to form an air-tight seal such as, but not limited to, a threaded seal or an interference fit.

Preferably, the container further comprises a locking mechanism for restricting access to the cavity, the locking mechanism being actuated automatically when the internal force acting on the expansion boundary exceeds a predetermined threshold.

The container described above significantly reduces the risks of a user of the self- heating assembly being injured in the event excessive pressures build up within the container as a result of the self-heating device being over-exposed to microwave energy.

Preferably the locking mechanism comprises at least one movable arm adapted to bridge the junction between the upstanding wall and the lid and the movable arm having a free end engageable in an alcove with a depth substantially aligned with a container opening direction, whereby movement of the lid relative to the at least one upstanding wall in the container opening direction, in response to the force acting on the expansion boundary exceeding the predetermined threshold, automatically causes the free end of the movable arm to form a locking engagement with the alcove.

A second aspect of the present invention provides a self-heating assembly adapted for being irradiated by electromagnetic energy comprising: a container; and, a self- heating device containing an exothermic phase change material, the self-heating device including a flexible portion capable of accommodating volumetric changes of the exothermic phase change material, said container comprising: a housing at least partially transmissive to microwave energy, the housing having one or more walls which at least partially define a cavity adapted to receive the self-heating device; an opening in the housing, said opening providing fluidic communication between the cavity and the environment external to the housing; and an expansion boundary shaped to limit expansion of the flexible portion of the self-heating device when the self-heating device is mounted in the container and the assembly is irradiated by electromagnetic energy.

In a third aspect the present invention provides a method of using a self-heating assembly comprising a container which is at least partially transmissive to microwave energy and a self-heating device, the method comprising: mounting the self-heating device within the container; irradiating the self-heating assembly with microwave energy for between 30 and 120 seconds; re-irradiating the self-heating assembly with microwave energy for at least one additional discontinuous period of between 20 and 30 seconds; and manually shaking the self-heating assembly in at least one of the intervals between irradiation. The method described above enables the exothermic phase change material of the self-heating device to be fully re-charged in a safe and reliable manner.

Preferably the self-heating assembly is re-irradiated twice and the self-heating assembly may be manually shaken in each interval between irradiation. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of a known self-heating device;

Figure 2 is a perspective view of a first embodiment of a container in accordance with the present invention for use with the device of Figure 1 ; Figure 3 is a sectional view of the container of Figure 2;

Figure 4 is a sectional view of the container of Figure 2 with the self-heating device of Figure 1 located therein; Figure 5 is a perspective view of a second embodiment of a container in an open configuration which is in accordance with the present invention and is for use with the self-heating device of Figure 1 ;

Figure 6 is a perspective view of the container of Figure 5 in a closed configuration;

Figure 7 is a sectional view of the container of Figure 5 in a closed configuration; Figure 8 is a sectional view of the container of Figure 5 in a locked configuration; and, Figure 9 is a semi-transparent perspective view of the container of Figure 5. In the drawings, like reference numerals denote like features.

To assist understanding of the present invention, a self-heating device in accordance with EP 1871204 shall first be described with reference to Figure 1. The self-heating device 2 is for use with a liquid container, such as but not limited to a baby's feeding bottle, to enable liquid within the bottle to be heated On demand'. The device 2 is mounted in a device holder and positioned between a liquid reservoir and a liquid delivery port. In combination, the inner surface of the device holder and the outer surface of the device 2 define fluid pathways from the liquid reservoir to the liquid delivery port. In use, liquid is caused to flow, either under gravity or in response to reduced pressure applied via the liquid delivery port, from the liquid reservoir, along the liquid pathways over the device 2 where the liquid is heated, and on to the liquid delivery port.

In overview, the device 2 has a compartment containing an exothermic phase change material with the walls of the compartment being substantially rigid (namely resistant to flexure under manually applied external force) and consisting of a base 4 and a thermally transmissive wall 5. The exterior of the thermally transmissive wall 5 has a plurality of substantially rigid projections 12 defining labyrinthine fluid pathways over the surface of the thermally transmissive wall 5. In the compartment base 4, a flexible diaphragm 6 is provided which has a smoothly curving (preferably circular) outer edge or periphery and which is capable of accommodating changes in the volume of the exothermic phase change material. A seal 8 is provided which permanently closes an opening at the top of the compartment originally used during manufacture for filling the compartment with the exothermic phase change material. An initiator 14 extends through the thermally transmissive wall 5 and is mounted for movement substantially perpendicular to the thermally transmissive wall 5. The outer end of the initiator 14 is accessible for manual activation and the inner end of the initiator 14 is in contact with the exothermic phase change material within the compartment.

Manual activation of the initiator 14 commences crystallisation of the exothermic phase change material and the release of latent heat which is transmitted by the thermally transmissive wall 5 to any fluid flowing along the fluid pathways on the outer surface of the device 2. The volume of the exothermic phase change material is less in its crystalline state than in its liquid state and the diaphragm 6 responds to the volume reduction following activation of the initiator 14.

The latent energy can be replenished, i.e. the device 2 recharged, by submersing the device 2 in hot water for a sufficient length of time for the phase change material to revert to its liquid state. When the device 2 is recharged, the diaphragm 6 flexes outwardly from the compartment in a dome shape to accommodate the volumetric increase of the exothermic phase change material when it returns to its liquid state. Optionally, an agitator (not shown), in the form of, for example, a small ball, is provided within the compartment with the exothermic phase change material. The agitator is able to move freely within the compartment when the exothermic phase change material is in its liquid state. Shaking the compartment urges the agitator within the compartment to move, which agitates and hence aids mixing of the different phases of the exothermic phase change material. Additionally, the agitator may provide audible confirmation of when the exothermic phase change material is substantially in its liquid state because with the exothermic phase change material in its liquid state, the agitator is free to move within the compartment and will 'rattle' against the inside walls of the compartment when the compartment is manually shaken.

The device 2 can also be recharged using microwave energy. However, during recharging using microwave radiation, there is a risk of hot spots developing at isolated locations within the exothermic phase change material. Such non-uniform heat distribution in the device 2 can result in thermal runaway within the exothermal phase change material at the hot spots because the rate of absorption of electromagnetic energy increases as the temperature of the exothermal phase change material increases. If left unchecked, the exothermic phase change material at the hot spots can boil causing the diaphragm 6 to flex beyond its elastic limit to failure.

To enable the device 2 described above to be recharged using microwave energy, and at the same time avoiding or reducing any deleterious effects arising from the use of microwave energy, the container 16 of Figures 2 to 4 is used. As shown in Figure 2 the container 16 comprises housing consisting of a base 18 and an upstanding wall 20, and a lid 24 which together define a closable housing interior 22. The base 18 includes an inner concentric wall 36, which projects into the housing interior 22 and defines the outer perimeter of a central depression 23.

Inter-engaging means are provided for securing the lid 24 to the upstanding wall 20 preferably to form an air-tight seal to the housing interior 22. For example, the securing means may consist of a threaded engagement between the lid 24 and the upstanding wall 20. Of course, other means of securing the lid 24 to the housing 22 are also envisaged. For example, the lid 24 may be secured to the housing 22 by means of respective inter-engaging elements on the lid 24 and the upstanding wall 20 which latch or which form an interference fit with each other.

With reference to Figure 3, the lid 24 includes a substantially rigid central diaphragm expansion section 28, which will be referred to herein as a domed section, with an opening 30 at its apex. A one-way valve 34 is preferably positioned within the opening 30 to allow air to exit the container 16 but to prevent air entering the container 16 and thereby supporting an air-tight seal to the housing interior 22.

The domed section 28 of the lid 24 defines a cavity 29 on the underside of the lid 24 to accommodate expansion of the diaphragm 6 of the self-heating device 2 which will arise when the exothermic phase change material changes from a crystalline state to a liquid state. Thus, the smooth inner surface of the domed section 28 acts as a diaphragm expansion boundary, in that the inner surface of the domed section 28 is a barrier to excessive expansion of the diaphragm 6 at any point on the surface of the diaphragm. Ideally, the diaphragm expansion boundary substantially corresponds to the shape of the diaphragm 6 in its expanded state. The domed section 28 may be made from any material capable of resisting the internal forces acting on the inner surface of the diaphragm 6 likely to arise as the exothermic phase change material changes from a crystalline state to a liquid state. Moreover, the threaded engagement between the lid 24 and the upstanding wall 20 is adapted to withstand the increased force of the exothermic phase change material acting on the diaphragm 6.

The inner surface of the domed section 28 preferably also includes a shield 32, which may be made of any material suitable for reflecting substantially all or at least a significant portion of incident microwave energy, for example, but not limited to, aluminium. With the shield 32 mounted to the inner surface of the domed section 28, the diaphragm expansion boundary 31 is defined by the inner surface of the shield 32. It will, of course, be understood that the shielding may alternatively be provided on the outer surface of the domed section 28. The outer surface of the lid 24 is shaped to prevent the container 16 being stood with its base 18 uppermost. In Figures 2 to 4 the shape of the outer surface of the lid 24 is shown with a dome corresponding to the domed section 28. However the lid may, course, have an outer surface shaped differently from the domed section 28 illustrated in Figures 2 to 4. For example, but not by way of limitation, the outer surface of the lid 24 could have a high curvature resulting in a shape that converges to a point. Alternatively, the outer surface of the lid 24 could be shaped to include a protruding section positioned between the edge and the centre of the lid 24. Other configurations of the outer surface of the lid 24 are also envisaged. It should be understood from the above description that the shape of the outer surface of the lid 24 can be different from the shape of the cavity 29.

Use of the container 16 shall now be described with reference to Figure 4. The device 2 is mounted in the housing 22 of the container 16 in an inverted orientation, i.e. the top of the device 2 (that part closest to the fluid delivery port during use) is located in the central depression 23 in the base 18 of the container 16 and the bottom of the device 2 is located in the lid 24 of the container 16. This ensures that gravitational forces do not add to the forces on the diaphragm 6 arising from the volumetric changes of the exothermic phase change material. To prevent the device 2 being placed in the container 16 in the wrong, i.e. an upright, orientation, the inner diameter of the container 16 immediately adjacent the base 18 is less than the outer diameter of the bottom of the device 2. Hence the diameter of the upstanding wall 20 of the container 16 tapers inwardly from the lid 24 to the base 18. Alternatively, inwardly projecting lugs or an inwardly projecting shelf adjacent the base 18 of the container may be used to prevent or deter the device 2 being positioned in the container 16 in the wrong orientation.

The depression 23 in the base 18 of the container 16 functions to guide the positioning of the device 2 into the centre of the container 16 and the outward projections 12 closest to the seal 8 on the device 2 abut the raised concentric wall 36 at the base 18 of the container 16 to support the device 2 in the housing 22. With the device 2 correctly positioned within the container 16 and the lid 24 secured to the upstanding wall 20, the diaphragm 6 is aligned with the domed section 28 of the lid 24. When the lid 24 engages with the upstanding wall 20 of the container 16, a concentric ring region on the underside of the lid 24 engages with the base 4 of the device 2 to hold the device 2 in position. In Figure 4 a peripheral edge region of the shield 32 is shown engaging with the base of the device 2. It is not essential for the shield 32 to extend as far as the outside diameter of the device 2. Instead, the shield 32 may only extend beyond the domed section 28 sufficiently far to overlie the junction of the diaphragm 6 with the rigid base 4 of the device 2.

Once the device 2 is correctly mounted within the container 16 the lid 24 of the container 16 engages with the upstanding wall 20 to seal the interior of the container 16 against ingress of air and/ or contaminants. The container 16, with the device 2 inside, is placed in a conventional microwave oven (e.g. 12.5cm wavelength, 800W power) and irradiated with microwave energy for an initial time period of approximately 60 seconds. The container 16 is then removed from the microwave oven and manually shaken to encourage mixing of the exothermic phase change material so as to disperse any thermal gradients within the compartment of the device 2. This process is repeated twice more with the periods of irradiation successively reducing from 30 seconds to 20 seconds, so that the container 16 and the device 2 are irradiated with microwave energy for a total of approximately 1 10 seconds.

The device 2 of Figure 1 contains 100 mis of exothermic phase change material and the cumulative 1 10 second exposure to microwave energy is sufficient to complete the change of phase of the exothermic phase change material in the device 2 from a crystalline state to a liquid state. It will, of course, be appreciated that for different oven powers or for different volumes of the exothermic phase change material (most commonly between 40 mis and 120 mis of phase change material) the number of occasions of re-irradiation may be reduced or increased to complete the transformation of the exothermic phase change material to its liquid state. For example, for 100 mis of exothermic phase change material in a 700W oven, a total exposure time of approximately 140 seconds is envisaged. For volumes of exothermic phase change material less than 100 mis the initial exposure time may be as short as 30 seconds. The table below sets out different ranges of exposure timings for 100 mis of exothermic phase change material in a two stage re-charging process. Table 1

Additionally, the cumulative microwave energy exposure should be sufficient to render the device 2 and the interior of the container 16 sterile. The device 2 and the interior of the container 16 will remain sterile until the seal between the lid 24 and the upstanding wall 20 is released e.g. by the lid 24 being removed. The use of the oneway valve 34, as opposed to an opening, serves to maintain the interior of the container 16 at atmospheric pressure whilst ensuring that the device 2 and the interior of the container 16 can remain sterile until the seal between the lid 24 and the upstanding wall 20 is released.

The volume of the exothermic phase change material increases during the phase change process causing the diaphragm 6 to expand into the cavity 29. However, a non-uniform heat distribution within the exothermic phase change material can cause some areas of the diaphragm 6 to expand more than other areas. This, in turn, can lead to an uneven expansion of the diaphragm 6, which can result in areas of localised fatigue in the material of the diaphragm 6. Shaking of the container 16 and, of course, the device 2 urges the agitator within the compartment to move, which aids mixing of the exothermic phase change material to improve the heat distribution, resulting in a more uniform expansion the diaphragm 6. The diaphragm expansion boundary 31 , defined by the inner surface of the shield 32, is adapted to allow the diaphragm 6 to expand to a predetermined permitted limit, thereby ensuring a uniform expansion of the diaphragm 6. The predetermined expansion limit is selected to provide sufficient expansion of the diaphragm 6 to accommodate the volumetric change of the exothermic phase change material whilst preventing expansion of the diaphragm 6 beyond its elastic limit. This is achieved by ensuring the internal shape of the expansion boundary 31 conforms to the shape of the diaphragm when expanded uniformly and by ensuring the expansion boundary remains rigid at the forces likely to arise during the phase changes of the exothermic material. Limiting the expansion of the diaphragm 6 to the predetermined expansion limit provides the added benefit of raising the internal pressure of the exothermic phase change material within the compartment during the phase change process so as to minimise or substantially prevent micro-boiling of the exothermic phase change material during its exposure to microwave energy.

The expansion of the diaphragm 6 during the phase change process displaces the air occupying the cavity 29 through the one-way valve 34 causing the displaced air to exit the container 16. A one-way valve 34 is preferred so that the interior of the cavity can be sterilised. However, the one-way valve 34 may be replaced with any opening for a non-airtight version of the container or the opening may be in the form of a non air-tight interconnection between the lid 24 and the upstanding wall 22.

During exposure of the container 16 to microwave energy, the shield 32 serves to shield the diaphragm 6 from substantially all or at least a significant proportion of the incident microwave energy. Moreover, the shield 32 may additionally act as a thermal sump, protecting the flexible diaphragm 6 from substantial temperature fluctuations when, for example, the container 16 and the device 2 are manually shaken in the intervals between the periods of exposure to microwave energy.

Figure 5 illustrates a second embodiment of the container 16 for use when recharging the device 2 using microwave energy. This embodiment of the container 16 advantageously includes physical and visual safety features, in addition to the features and benefits described above with respect to the first of embodiment of the container 16.

The container 16 comprises a housing consisting of base 18 and an upstanding wall 20, and a lid 24, which together define a closable housing interior 22. The base 18 includes an opposed pair of arcuate walls 36, which project into the housing interior 22 and define, in part, the outer perimeter of a central depression 23. The interior of each of the inner arcuate walls 36 is hollow thereby defining an outwardly facing alcove in which the depth of the alcove is aligned with the opening direction of the container 16 i.e. with the container of Figure 5 the depth of each alcove is substantially orthogonal to the base 18. The upstanding wall 20 includes an opposed pair of outwardly facing recesses 38 that extend the height of the upstanding wall 20 and each meets on the underside of the base 18 with a respective one of the arcuate walls 36.

The lid 24 engages with the upper edge of the upstanding wall 20 by way of an interference fit, which allows easy access to the housing interior 22. Two hooked arms 40 (hereinafter "arms 40") are hingeably or pivotably mounted to opposing sides of the lid 24 and are moveable between an open position, as shown in Figure 5, and a closed position, as shown in Figure 6. In the closed position of Figure 6 the arms 40 overlie the junction between the lid 24 and the upstanding wall 20. When the arms 40 are in the open position, the housing interior 22 can be accessed by simply lifting the lid 24 from the upstanding wall 20 with sufficient force to overcome the interference fit. When the arms 40 are in the closed position, the arms 40 must first be moved to the open position before access can be gained to the housing interior 22. As such each arm 40 functions as a latch.

Figure 7 is a sectional view of the container 16 with the arms 40 in the closed position. With the arms 40 in the closed position, each of the hooked ends 40a of the arms 40 is arranged to be aligned with the opening to the alcove of a respective one of the arcuate walls 36. The recesses 38 are provided to receive and guide the arms 40 so as to ensure that the hooked ends 40a of the arms 40 align with the arcuate walls 36. That is to say, the lid 24 cannot be correctly fitted to the upstanding wall 20 if the arms 40 are not aligned with the recesses 38.

This embodiment of the container 16 is used in manner similar to that described above in relation to the first embodiment of the container 16. However, in this embodiment the one-way valve is omitted from the domed section 28 of the lid (alternative atmospheric equalisation is provided). The device 2 is mounted upside down within the container 16. With the arms 40 in the open position, the lid 24 of the container 16 engages with the upstanding wall 20 with the arms aligned with the recesses 38. The arms 40 are then moved to the closed position to close and seal the interior of the container 16. The container 16, with the device 2 inside, is placed in a microwave oven (e.g. 12.5cm wavelength, 800W power) and irradiated with microwave energy for an initial time period of 60 seconds. The container 16 is then removed from the microwave oven and manually shaken to encourage mixing of the exothermic phase change material so as to disperse any thermal gradients within the compartment of the device 2. This process is repeated twice more with the periods of irradiation successively reducing from 30 seconds to 20 seconds, so that the container 16 and the device 2 are irradiated by microwave energy for a total of approximately 1 10 seconds. As explained above, the volume of the exothermic phase change material increases during this process as the exothermic phase change material changes from a crystalline state to a liquid state. This causes the diaphragm 6 of the device 2 to expand into the cavity 29. The diaphragm expansion boundary 31 , defined by the inner surface of the shield 32, is adapted to prevent the diaphragm 6 from expanding beyond its elastic limit by providing structural support for the expanding diaphragm 6.

The diaphragm 6 will exert an increasing force on the diaphragm expansion boundary 31 if the device 2 is exposed to microwave energy for an excessive period of time so that volumetric expansion of the exothermic phase change material beyond that accommodated by the expansion boundary 31 will cause the lid 24 to lift away from the upstanding wall of the housing, when the force exerted by the diaphragm 6 on the expansion boundary exceeds the holding force of the interference fit of the lid 24.

In order to prevent the container 16 from being opened when the device 2 is under such pressure, the hooked ends 40a of the arms 40 are arranged to automatically move from the closed position to a locked position when a predetermined pressure threshold exerted on the diaphragm expansion boundary 31 is reached. The movement of the arms 40 to the locked position does not decrease the pressure being exerted on the device 2 or the container 16. Indeed, once the arms 40 are in the locked position, if the self-heating device 2 continues to be exposed to m icrowave energy the pressure within the self-heating device will continue to rise.

Figure 8 shows a sectional view of the container 16 with the hooked ends 40a of the arms 40 in the locked position but without the device 2. As mentioned earlier, when a force exceeding the predetermined threshold is exerted on the diaphragm expansion boundary 31 , the force is sufficient to overcome the interference fit of the lid with the upstanding wall 20. Consequently the lid 24 is caused to automatically move, in its opening direction, upwards away from the upper edge of the upstanding wall 20. As the arms 40 are attached to the lid 24, upwards movement of the lid 24 causes the hooked ends 40a of the arms to be drawn upwards into a locked position where the hooked ends 40a of the arms 40 are inserted into and engage with the alcoves of the arcuate walls 36. With the hooked ends 40a of the arms in the locked position, the housing interior 22 cannot be accessed.

The force exerted by the diaphragm 6 on the diaphragm expansion boundary 31 will fall if exposure to microwave radiation is halted and the container and the self-heating device are allowed to cool. In due course the pressure within the self-heating device 2 will fall sufficiently for the lid 24 to be moved easily manually. The lid 24 and the hooked ends 40a can then be moved downwards to the lid's closed position at which position the hooked ends 40a of the arms 40 can then be disengaged from the alcoves of the arcuate walls 36.

The upwards motion of the lid 24 to the locked position also exposes a contrasting coloured strip 42 extending around the outer surface of the upper edge region of the upstanding wall 20, which is hidden from view under the lid 24 during normal use. The exposure of the contrasting coloured strip 42 functions as a visual warning that the pressure within the device 2 is above the predetermined threshold. Preferably, therefore, the contrasting colour is red as the coloured strip 42 is being used as a warning of danger.

An additional green coloured strip (not shown) below and adjacent the red coloured strip may also be provided on the upstanding wall 20 and the green coloured strip is similarly hidden from view by the lid prior to the self-heating assembly being microwaved. The green coloured strip is used to indicate during the first exposure step in the re-charging process when the self-heating device has been exposed to sufficient microwave energy for the phase changing process to have commenced. When the green coloured strip becomes visible, the first exposure step should be halted and the self-heating assembly removed from the microwave oven for shaking, as described earlier. The green coloured strip ensures the self-heating assembly is able to safely accommodate variations in microwave oven power and can be used in association with the exposure timings set out earlier in Table 1 . Once in the locked position, further exposure of the container 16 and the device 2 to microwave energy will eventually cause the diaphragm 6 to fail, resulting in the exothermic phase change material in the device 2 filling the container 16. In this situation, the air occupying the container 16 is displaced by the exothermic phase change material through air vents 41 . The air vents 41 are shown in more detail in Figure 9. The air vents 41 are located at the upper edge of the upstanding wall 20 and are covered when the lid 24 is fitted to the upstanding wall 20. This ensures that any explosion of pressurised exothermic phase change material through the air vents 41 is shielded by the lid 24 and directed downwards. It is to be understood that the present invention is not limited to use with the self- heating device 2 of EP 1871204 and that the container 16 described herein and all of its attendant advantages and benefits can be adapted as so to be equally applicable to other self-heating devices which can be recharged using microwave energy. For example, but not by way of limitation, the container can be adapted to house conventional self-heating pads. As mentioned earlier, such pads are commonly used as hand warmers and are generally of a flat rectangular shape formed from two flexible layers that are welded together along their edges to provide a flexible pouch. The flexible pouch contains an exothermic phase change material, along with an activator. The housing of the container would be shaped to substantially conform to the shape of the pad. The expansion of the phase change material during the phase change process causes the pouch to expand in all directions but with the greatest expansion tending to be furthest away from the welded edges. Accordingly, a cavity is defined within the container to accommodate but restrict the expansion of the pouch. Preferably, fluidic communication is provided between the cavity and the external atmosphere, which may be in the form of a valve. Whilst not essential, shielding may be provided on the upper surface of the housing for absorbing substantially all or at least a significant portion of incident microwave energy. Also, the upper outer surface of the container can be shaped to ensure that the container cannot be stood with its base uppermost and, consequently, the shielding lowermost. Alternatively, it is envisaged that the shielding may extend intermittently to completely encase the flexible pouch and thereby restrict the amount of microwave energy incident on the pouch. This embodiment of the invention provides all of the attendant advantages and benefits described above in relation to the previously described embodiment.

Although the present invention has been described and illustrated in detail, it should be clearly understood that the same are by way of example only and it is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A container for a self-heating device containing an exothermic phase change material, the self-heating device including a flexible portion having a smoothly curving periphery capable of accommodating volumetric changes of the exothermic phase change material, the container comprising:

a housing having one or more walls which at least partially define a cavity adapted to receive the self-heating device;

an opening in the housing, said opening providing fluidic communication between the cavity and the environment external to the housing; and

a dome-shaped expansion boundary a concave side of which is in fluidic communication with the cavity,

and wherein the housing is at least partially transmissive to microwave energy whereby the expansion boundary conforms to and limits expansion of the flexible portion of the self-heating device when the self-heating device is mounted in the cavity and the housing is irradiated by electromagnetic energy.

2. A container as claimed in claim 1 , wherein the expansion boundary comprises electromagnetic radiation shielding.

3. A container as claimed in claim 2, wherein said shielding is shaped to substantially conform to the expansion boundary.

4. A container as claimed in any one of the preceding claims, wherein the opening comprises a one-way valve.

5. A container as claimed in any one of the preceding claims, wherein the one or more walls of the housing are arranged to accommodate the self-heating device orientated so that the flexible portion is uppermost.

6. A container as claimed in claim 5, wherein the container includes a base, at least one upstanding wall and a lid and wherein the outer surface of the lid of the container is shaped to prevent the container being stood with its base uppermost.

7. A container as claimed in any one of claims 1 to 5, wherein the container includes a base, at least one upstanding wall and a lid and wherein the lid and the at least one upstanding wall are releasably securable to form an air-tight seal.

8. A container as claimed in claim 7, wherein the air-tight seal is a threaded seal.

9. A container as claimed in claim 7, wherein the air-tight seal is an interference fit.

10. A container as claimed in claim 9, the container further comprising a locking mechanism for preventing access to the cavity, the locking mechanism being actuated automatically when the force acting on the expansion boundary exceeds a predetermined threshold.

1 1 . A container as claimed in claim 10, wherein the locking mechanism comprises at least one movable arm adapted to bridge the junction between the upstanding wall and the lid, the movable arm having a free end engageable in an alcove having a depth substantially aligned with a container opening direction, whereby movement of the lid relative to the at least one upstanding wall in the container opening direction, in response to the force acting on the expansion boundary exceeding the predetermined threshold, causes the free end of the movable arm to automatically form a locking engagement with the alcove.

12. A self-heating assembly adapted for being irradiated by electromagnetic energy comprising:

a container; and,

a self-heating device containing an exothermic phase change material, the self-heating device including a flexible portion capable of accommodating volumetric changes of the exothermic phase change material,

said container including:

a housing at least partially transmissive to microwave energy, the housing having one or more walls which at least partially define a cavity adapted to receive the self-heating device; an opening in the housing providing fluidic communication between the cavity and the environment external to the housing; and an expansion boundary shaped to limit expansion of the flexible portion of the self-heating device when the self-heating device is mounted in the cavity and the housing is irradiated by electromagnetic energy.

13. A method of using a self-heating assembly comprising a container and a self- heating device, adapted for being irradiated by microwave energy, the method comprising:

Mounting the self-heating device within the container;

irradiating the self-heating assembly with microwave energy for between 30 and 120 seconds;

re-irradiating the self-heating assembly with microwave energy for at least one additional discontinuous period of between 20 and 30 seconds; and

manually shaking the self-heating assembly in at least one of the intervals between irradiation.

14. A method as claimed in claim 13 wherein the self-heating assembly is re- irradiated twice.

15. A method as claimed in either of claims 13 or 14, wherein the self-heating assembly is manually shaken in each interval between irradiation.