GB2393091A

GB2393091A - Food container with heat sensitive seal released by microwave susceptor

Info

Publication number: GB2393091A
Application number: GB0221025A
Authority: GB
Inventors: Frank Ian Taylor
Original assignee: NORTHERN FOODS Ltd
Current assignee: NORTHERN FOODS Ltd
Priority date: 2002-09-11
Filing date: 2002-09-11
Publication date: 2004-03-17
Also published as: GB0221025D0; EP1398278A1

Abstract

A food package is disclosed which is easy to open after heating in either a conventional oven or a microwave oven. The package comprises a thermally stable rigid container 101 with an opening, a film membrane 302 configured to close the opening of the rigid container, a heat sensitive seal 304 to adhere the film membrane to the rigid container, and a microwave susceptor material 303 in close proximity to at least a portion of the heat sensitive seal. When the package is heated in a microwave oven, the microwave susceptor material heats up, and heat is transferred to the heat sensitive seal. The heat sensitive seal is thereby weakened, allowing the user easily to separate the film membrane from the rigid container, avoiding the risk of spillage. The susceptor material may be placed in various locations near the seal, and may take the form of a packaging label.

Description

-1- 239309 1

FOOD CONTAINER WITH EASY OPEN SEAL

Field of the Invention

The present invention relates to the field of packaging materials suitable for

conventional or microwave cooking.

Background to the Invention

It is estimated that in the UK, around 70,000 people per year are admitted to accident and emergency departments of hospitals with injuries involving non o medicine packaging. It is thought that only around 35% of all packaging relating accidents are reported to hospitals, giving around 200,000 accidents per year in the UK related to packaging (source: DTI, Domestic Accidents Related to Packaging, November 1997). At particular risk are elderly people, and people suffering from visual impairment or arthritis. Several studies have been carried out in an effort to increase the safety of food packaging ('Packaging Openability and the Elderly Consumer' Institute of Grocery Distribution (IGD) 1992, Packaging Openability: Recommendations for Immediate Improvement' IGD 1993, 'An Open and Shut Case' IGD 1995).

o Fig. 1 shows a schematic perspective view of a prior art container for food

for use in either a conventional oven or a microwave oven. This comprises a thermally stable rigid container 101 (or tray), which has a rim 102 and an internal space 103 in which the food is positioned. It also comprises a film membrane 104 (or lid). The film membrane 104, in a cross-section view 106, comprises layers of thermally stable film 107, and a polymer sealing layer 108.

The film membrane 104 is heat sealed to the rim 102 of the container 101.

A cross section of the seal 109 comprises the top layer of thermally stable film 107, the layer of heat sensitive seal 108 and the rim 102.

30 The film membrane typically has a region 105 that overhangs the rim 102 of the container 101 to allow the user to grip the film membrane 104 and separate it from the rim 102 of the container.

-2 A thermally stable material does not alter its dimensions significantly at temperatures around 200 C.

5 For the container to be useable in either conventional or microwave ovens, it must be able to withstand temperatures in excess of 200 C. The rigid container is typically manufactured from crystallized polyethylene terephthalate (cPET), which has a melting point of above 250 C. The inner layer of the rigid container, and therefore the surface of the rim of the rigid container, comprises amorphous To polyethylene terephthalate (aPET), which forms part of the seal. The upper layer 107 of the film membrane 104 typically comprises a biaxial orientated polyester PET film. The adhesive surface 108, also comprises a layer of aPET.

A heat sensitive seal between aPET layers is one that loses strength at :s elevated temperatures. This allows for the seal to be strong at room temperature, but weaken after cooking the contents of the container 101 to facilitate separation of the film 104 from the rim 102 of the container 101.

The end-user of the container requires the seal to be as weak as possible o after cooking thereby making it easier to remove the film membrane 104 from the container101 after cooking.

The manufacturer of the food requires the seal to be as strong as possible to prevent contamination and minimize spillage and leaks during processing, transportation and display of the product.

The retailer of the food pack prefers to display the container on end in order to maximise the impact of the sleeve, which normally shows a serving suggestion of the product. Packs that leak through faulty seals onto the retailer's shelves are o totally unacceptable and often removed from sale and returned to the manufacturer.

-3 A strong seal is also desirable in order to make the package tamper evident.

A strong seal makes it more difficult for a person to interfere with the food content when the package is on display, and tampering with a package having a relatively stronger seal is more evident.

Different persons handling the food package in the supply chain from initial packaging of the food, through display of the food, to final heating and opening of the container by the end user therefore have conflicting requirements. The retailer and food producer need an easier to open seal so that the package is o easier to open reducing the risk of accident to consumers.

When a ready meal is cooked in a conventional oven, the food, the prior art

rigid container, the film membrane and the seal are all heated in the same environment to the same temperature. This temperature is typically hot enough 15 to significantly soften the aPET seal, and allow the user to easily remove the film membrane. However, when the ready meal is heated in a microwave oven, the water molecules in the food absorbs microwave radiation, gain energy and heats the go food accordingly. Heat is transferred by conduction and/or convection from the food towards the seal, and as the temperature of the seal increases, it becomes softened, and makes the file membrane easier to remove than when in a cold condition. However, in the prior art package, because the conduction and

convection does not efficiently transfer heat to the seal when the package is in a microwave cooker, once the food has been reheated the user finds it very difficult to remove the film membrane, as the seal has not been softened sufficiently.

Therefore, there is a specific problem for prior art food packages which are

designed to be cooked either in a conventional oven, or in a microwave oven, o that the type of seal which may be suitable for a conventional oven, where the seal is heated directly by ambient temperature all around the package, does not perform as well when the food package is placed in a microwave oven, where

heating is by direct heating of the food, rather than direct heating of the container, film and seal themselves.

The problem with film lids that do not easily peel off from the container is specifically pointed out in the DTI report on Domestic Accidents Related to Packaging, November 1997, wherein a survey response was "there are some that say peel like on yogurt packs, but it often doesn't work and that is annoying".

Accidents where the user is scalded as they remove the film lid from ready o meals after they have been heated in the microwave oven have been reported to the Home Accident Surveillance System.

European Patent application 0 470 771 A2 and US Patent 4,911,938 both disclose a microwave package with a microwave susceptor incorporated into the seal to aid opening. However, these packages comprise film, and do not comprise a rigid container. They are therefore only suitable for cooking foodstuffs with a relatively low water content (for example pies or pastries), as foodstuffs with a high water content (for example lasagne or shepherd's pie) could not be easily removed after cooking without risk of scalding the user, and o the foodstuff losing its shape.

Furthermore, these packages are configured only for use in microwave ovens, and not conventional ovens.

: The inventor has realised that there is a need to provide a container for ready meals that can be used in either conventional ovens or microwave ovens, but which minimises the risk of opening to the user when the contents have been cooked in a microwave oven. Furthermore, the present invention is suitable to contain foodstuffs regardless of the liquid content.

-5 Summarv of the Invention According to a first aspect of the present invention there is provided a device for containing food in a microwave oven or a conventional oven, comprising; a thermally stable rigid container with an opening; a film membrane configured to substantially close the opening of the rigid container; a heat sensitive seal to substantially adhere the film membrane to the rigid container, such the opening of the rigid container is substantially closed by the film membrane, wherein the heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; a microwave susceptor material in close proximity to at least a portion of the heat sensitive seal, wherein the microwave susceptor material is operable to heat up in response to an applied microwave field, such that the susceptor material

heats up to cause the heat sensitive seal to have a reduced adhesion.

According to a second aspect of the present invention there is provided a device configured for containing food in a conventional oven or a microwave oven, comprising; 5 a thermally stable rigid container with an opening; a film membrane configured to substantially close the opening of the rigid container; so a microwave susceptor material incorporated into at least a portion of the film membrane, wherein the microwave susceptor material is operable to heat up in response to a microwave field;

-6 a heat sensitive seal to substantially adhere the film membrane to the rigid container, such that the opening of the rigid container is substantially closed by the film membrane, wherein the heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; wherein the susceptor material heats up in response to an applied microwave field to cause the heat sensitive seal to have a reduced adhesion.

According to a third specific embodiment of the invention, there is provided To a device configured for containing food in a microwave oven or a conventional . oven, comprising; a thermally stable rigid container with an opening; 15 a film membrane configured to substantially close said opening of the rigid container; a heat sensitive seal to substantially adhere the film membrane to the rigid container, such that the opening of the rigid container is substantially closed by 2 o the film membrane, wherein the heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; a label affixed to the film membrane in close proximity to at least a portion of the heat sensitive seal; a microwave susceptor material incorporated into at least a portion of the label, wherein the microwave susceptor material is operable to heat up in response to an applied microwave field, such that the susceptor material heats

up to cause the heat sensitive seal to have a reduced adhesion.

According to a fourth specific embodiment of the invention, there is provided a device configured for containing food in a microwave oven or a conventional oven, comprising;

-7 a thermally stable rigid container with an opening; a thermally stable rim around the opening of the rigid container comprising an upper surface and a lower surface; a film membrane configured to substantially close the opening of the rigid container; To a heat sensitive seal positioned between the upper surface of the rim and the film membrane, such that the opening of said rigid container is substantially closed by the film membrane, wherein the heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; 5 a border that can be affixed to said lower surface of said rim; a microwave susceptor material incorporated into at least a portion of the border, wherein the microwave susceptor material is operable to heat up in response to an applied microwave field, such that the susceptor material heats

2 o up to cause the heat sensitive seal to have a reduced adhesion.

According to a fifth specific embodiment of the invention, there is provided a device configured for containing food in a microwave oven or a conventional oven, comprising; a thermally stable rigid container with an opening; a film membrane configured to substantially close the opening of the rigid container; a heat sensitive seal to substantially adhere the film membrane to the rigid container, such that the opening of the rigid container is substantially closed by

-8 the film membrane, wherein the heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; a sleeve positioned around the device, comprising at least one upper surface, wherein the upper surface further defines an inner surface and an outer surface, wherein the inner surface of the upper surface is in close proximity to the film membrane; a label affixed to the inner surface of the upper surface of the sleeve To positioned in close proximity to at least a portion of the heat sensitive seal; a microwave susceptor material incorporated into at least a portion of the label, wherein the microwave susceptor material is operable to heat up in response to an applied microwave field, such that the susceptor material heats

:s up to cause the heat sensitive seal to have a reduced adhesion.

According to a further specific embodiment of the invention, there is provided a method for manufacturing a food package suitable for cooking in a conventional oven and/or microwave oven, comprising; applying adhesive material to a food container, the food container having an opening wherein the adhesive material is applied adjacent to a periphery of the opening; applying a film membrane across the opening, such that the opening becomes bonded to the container by the adhesive material; wherein the adhesive material comprises a microwave susceptor material capable of releasing the bond when subjected to microwave radiation.

Brief Description of the Drawinas

For a better understanding of the invention and to show how the same may be carried into effect, there will now be described by way of example only,

-9- specific embodiments, methods and processes according to the present invention with reference to the accompanying drawings in which: Fig. 1 illustrates schematically a perspective view of a prior art container for

5 cooking food in a conventional or microwave oven.

Fig. 2 illustrates schematically the heating of a container in both conventional and microwave ovens.

o Fig. 3 illustrates schematically a cross-section view through a film membrane incorporating a microwave susceptor material and a rigid container.

Fig. 4 illustrates schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a microwave susceptor material is 15 incorporated into the film membrane.

Fig. 5 illustrates schematically a cross-section view through a rigid container, a film membrane and a sticker incorporating a microwave susceptor material. Fig. 6 illustrates schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a microwave susceptor material is incorporated into a sticker and positioned in close proximity to a portion of the seal between the film membrane and the rigid container.

Fig. 7 illustrates schematically a cross-section view through a rigid container, a film membrane and a border that incorporates a microwave susceptor material.

o Fig. 8 illustrates schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a microwave susceptor material is incorporated into a border which is positioned in close proximity to the seal between the film membrane and the rigid container.

-10 Fig. 9 illustrates schematically a cross-section view through a rigid container, a film membrane, a cardboard sleeve and a sticker that incorporates a microwave susceptor material.

Fig. 10 illustrates schematically a perspective view of a food container for use in a microwave oven, wherein a microwave susceptor material is incorporated into a portion of a cardboard sleeve and placed in close proximity to the seal between the film lid and the rigid container.

Detailed Description of the Best Mode for Carrvinu Out the Invention

There will now be described by way of example the best mode contemplated by the inventors for carrying out the invention. In the following description numerous specific details are set forth in order to provide a thorough

understanding of the present invention. It will be apparent however, to one skilled in the art, that the present invention may be practiced without limitation to these specific details. In other instances, well known methods and structures have not been described in detail so as not to unnecessarily obscure the present invention.

go In a first specific embodiment of the invention, a microwave susceptor material is positioned in close proximity to the heat sensitive seal between a thermally stable rigid container and a film membrane. When placed in a microwave field, the microwave susceptor heats up in response to incident

microwave radiation. Heat generated by the microwave susceptor material is transferred to the heat sensitive seal, which consequently weakens.

Referring to Fig. 2 herein, there is illustrated schematically the heating of a container in both conventional and microwave ovens. In Figs. 2a, 2b and 2c, there is shown the rim 102 of a thermally stable rigid container that is sealed to a so film membrane 104. The film membrane comprises a heat sensitive seal 107 and a further layer to impart strength 106. Fig. 2c shows a microwave susceptor material 209 in close proximity to the heat sensitive seal 107.

-11 When microwave radiation 210 - 213 is incident upon the microwave susceptor material 209, the microwave susceptor material 209 gains energy and consequently heats up. The heat is transferred 214 - 217 to the heat sensitive seal 109, which consequently weakens. The weakening of the heat sensitive seal 107 allows a user to easily separate the film membrane 104 from the rim 102 of the container.

For comparison, Fig. 2a shows the same container without the presence of a microwave susceptor material in a conventional oven. The heat from the JO conventional oven 201 - 204 heats the film membrane 104, the rim 102 of the thermally stable rigid container, and the food in the container to the same temperature. This heat therefore softens the heat sensitive seal 107, allowing a user to easily remove the film membrane 104 from the rim 102 of the container.

s Fig. 2b shows the same container in an applied microwave field without the

presence of a microwave susceptor material. The film membrane 104 and the rim 102 of the thermally stable rigid container are substantially transparent to microwave radiation. No heat is generated, and so the heat sensitive seal 107 does not reach a sufficiently high temperature to weaken. The user will therefore go encounter difficulty in removing the film membrane 104 from the rim 102 of the thermally stable rigid container.

In a second specific embodiment of the invention, a microwave susceptor material is incorporated into the film membrane. This ensures that the microwave susceptor material is in very close proximity to the heat sensitive seal, and that heat generated by the microwave susceptor material is transferred directly to the heat sensitive seal by solid conduction.

Referring to Fig. 3 herein, there is illustrated schematically a crosssection So view through a rigid container and a film membrane incorporating a microwave susceptor material. The film membrane 301 comprises an upper layer 302 to impart strength, a microwave susceptor material layer 303 and a heat sensitive seal layer 304. Where the heat sensitive seal layer 304 is in contact with the rim

-12 102 of the container 101, the film membrane 301 is sealed to the rim of the container 102.

The heat sensitive seal layer 304 comprises a layer of aPET, and the microwave susceptor layer 303 comprises a metallized layer or a carbon layer.

The upper layer 302 of the film membrane comprises any suitable material to impart mechanical strength and thermal stability, including aPET, cPET or cellulose. JO When heated using a conventional oven, the heat sensitive seal 304 will heat up and therefore weaken, thereby allowing the user to easily separate the film membrane 301 from the rim 102 of the container 101.

When placed in an applied microwave field, incident microwave radiation

s 305 will be absorbed by the microwave susceptor material 303, which will consequently heat up. The heat 306 generated by microwave susceptor material 303 is sufficient to soften the heat sensitive layer 304, thereby allowing the user to easily separate the film membrane 301 from the rim 102 of the container 101 after the contents have been cooked.

The food contents in the internal space 103 of the container must be subject to incident microwave radiation in order to heat up and cook. However, incident microwave radiation 307 at a distance from the rim 102 of the container 101 will also be absorbed by the microwave susceptor layer 303, and therefore will not efficiently cook the food positioned in the internal space 103 of the container. To minimize the amount of microwave radiation 307 that is absorbed in a region away from the rim 102, the microwave susceptor material 303 is applied in a throughout the film, or may be applied in a pattern throughout the film, or may be applied throughout the film and then demetallized to form a o pattern. This allows incident microwave radiation to pass through the unmetallized regions of the film membrane 301 that do not comprise a microwave susceptor layer without being absorbed. This microwave radiation can therefore be absorbed by the food contents, and contribute to the cooking of the food.

-13 The microwave susceptor layer pattern may be either applied in a pattem to an unmetallized film 301, or a film comprising a microwave susceptor layer may have the microwave susceptor layer partially removed to form a pattern.

Referring to Fig. 4 herein, there is illustrated schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a microwave susceptor material is incorporated into the film membrane. For clarity, the film membrane 301 is shown above the thermally stable rigid container 101, Jo although during storage and cooking of the contents the film membrane 301 is sealed to the rim of the container 101. The shaded region 402 shows the area of the rim that is heated by the microwave susceptor material.

In this specific embodiment, the entirety of the seal is weakened by the heat 5 generated by the microwave susceptor material when the contents are cooked in a microwave oven. Owing to the weakened seal, the film membrane 301 can easily be separated from the container 101. The heat sensitive seal is weak at every point around the rim of the container 101, and so the user can initiate peeling of the film membrane 301 from any point.

In a third specific embodiment of the invention, a microwave susceptor material is incorporated into a label, which is affixed to the film lid in proximity to the seal between the film membrane and the rim of the container.

25 Referring to Fig. 5 herein, there is illustrated schematically a crosssection view through a rigid container, a film membrane, and a sticker incorporating a microwave susceptor material. The label 501 comprises a printable surface layer 508 comprising paper or cardboard, a layer to impart strength 502, a microwave susceptor layer 503, and an adhesive layer 504. The adhesive layer 504 is used 30 to affix the label to the film membrane 104, which comprises an aPET surface layer to impart strength 106 and a heat sensitive seal layer 107 comprising aPET.

The film membrane is sealed to the rim 102 of a thermally stable rigid container

-14 101 by the heat sensitive seal 107, and the label 501 is positioned in proximity to the rim 102 of the container 101.

When the container is placed in a conventional oven, the label 501, the film 5 membrane 104 and the container 101 will all heat up together, and the heat sensitive seal 107 will weaken sufficiently to allow the user to easily separate the film membrane 104 from the rim 102 of the container 101.

When the container is placed in a microwave field, microwave radiation 505

JO that is incident on the label 501 is absorbed by the microwave susceptor layer 503. The microwave susceptor layer 503 consequently heats up, and the heat 506 is transferred predominantly by solid conduction from the microwave susceptor layer 503 to the heat sensitive seal 107. The printable surface layer 508 comprises paper, which insulates the top of the label 501 and encourages 5 the heat 506 to escape down towards the heat sensitive seal 107 instead of away from the heat sensitive seal. The heat sensitive seal 107 weakens sufficiently to allow the user to easily separate the film membrane 104 from the rim 102 of the container 101.

So As the film membrane 104 is transparent to microwave radiation 507, the microwave radiation 507 in a region away from the rim 102 of the container 101 is not absorbed by the film membrane 104 and can be absorbed by and cook the food positioned the internal volume 103.

5 A further advantage of the printable paper layer 508 on the label 501 is that it can be printed with instructions for the user, for example "peel here".

Referring to Fig. 6 herein, there is illustrated schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a o microwave susceptor material is incorporated into a label and positioned in close proximity to a portion of the seal between the film membrane and the rigid container. For clarity, the film membrane 104 is shown above the rigid container

-15 101, although in storage and during cooking, the film membrane 104 would be sealed to the rim 102 of the container 101.

The label 501 is positioned in close proximity to the rim 102. The region 5 that is heated by the microwave susceptor material incorporated in the label 501 is shown as a shaded region 601. In this region, the heat sensitive seal will soften sufficiently to allow the user to easily separate the film membrane 104 from the rim 102 of the container 107. It is known that once peeling of the film membrane 104 from the rim 102 of the container 101 has been initiated from the JO softened region 601, the rest of the film membrane 104 will easily separate from the rim 102 of the container 101, even in regions away from the heated (and therefore weakened) area 606.

If the user does not comply with the instruction printed on the label 501, but :s tries to separate the film membrane 104 from the rim 102 of the container 101 in a region away from the label, the heat sensitive seal will not have weakened sufficiently to allow easy separation of the film membrane 104 from the rim 102 of the container 101.

So In a fourth specific embodiment of the invention, a microwave susceptor material is incorporated into a border that is affixed below the rim of the thermally stable rigid container.

Referring to Fig. 7 herein, there is illustrated schematically a crosssection view through a rigid container, a film membrane and a border that incorporates a microwave susceptor material. The border 701 comprises a cPET layer to impart mechanical strength 702, a microwave susceptor material 703, and means to affix the border to the rim 102 of the container 101. A film membrane 104 comprising an aPET layer to impart mechanical strength 106 and an aPET heat 3 o sensitive seal 107 is sealed to the rim 102 of the container 101.

When microwave radiation 705 is incident on the border 701, the microwave susceptor material 703 heats up. The heat 706 is transferred to the heat

-16 sensitive seal 107 predominantly by solid conduction. The heat is sufficient to weaken the heat sensitive seal such that the user can easily separate the film membrane 104 from the rim 102 of the container 101.

5 Microwave radiation 707 can pass through the film membrane 104, and heat up and cook the food contained in the internal volume 103 of the container.

Referring to Fig. 8 herein, there is illustrated schematically a perspective view of a food container for use in a conventional or microwave oven, wherein a JO microwave susceptor material is incorporated into a border which is positioned in close proximity to the seal between the film membrane and the rigid container.

For clarity, the film membrane 104 is shown above the rigid container 101,and the border 701 is shown below the rigid container 101, although in storage and during use the border 701 would be affixed below the rim of the container 101 15 and the film membrane 104 would be sealed to the rim of the container 101.

The shaded region 801 shows the area that is heated by the microwave susceptor material during microwave cooking. It can be seen that the entire area of the rim is heated, thereby allowing the user to easily separate the film go membrane 104 from the rigid container 102 regardless of where the user begins to peel the film membrane 104.

Preferably, the means 704 to affix the border 701 to the rim 102 comprise an adhesive layer. However, other means of affixing, such as mechanical clips, 5 may be used to affix the border 701 to the rim 102 of the container.

In a fifth specific embodiment of the invention, a microwave susceptor material is affixed to a sleeve, which is placed around the container, such that the microwave susceptor material is in close proximity to the rim of the container.

Referring the Fig. 3 herein, there is illustrated schematically a crosssection view through a rigid container, a film membrane, a cardboard sleeve and a label that incorporates a microwave susceptor material. A layer of cardboard 901 is

-17 positioned over the rigid container 101, and a label 902 incorporating a microwave susceptor layer 904 is affixed to the lower surface of the cardboard layer 901 using an adhesive layer 903. The microwave susceptor layer 904 is in close proximity to the film membrane 104, which comprises an aPET upper layer 5 to impart strength 106 and an aPET heat sensitive seal layer 107. The film membrane is heat sealed to the rim 102 of a thermally stable rigid container 101.

When microwave radiation 905 is incident on the microwave susceptor layer 904, heat 906 is generated. The cardboard layer 901 has insulating properties, Jo and therefore the heat 906 predominantly escapes downwards towards the heat sensitive seal 107. This weakens the heat sensitive seal 107, thereby allowing the user to easily separate the film membrane 104 from the rim 102 of the container 101.

15 In a region away from the microwave susceptor 904, the cardboard layer 901 and the film membrane 104 are predominantly transparent to incident microwave radiation 907, and so the microwave radiation 907 is absorbed by the food contained in the internal volume 103 of the container 101.

2 o Referring to Fig. 10 herein, there is illustrated schematically a perspective of a food container for use in a microwave oven, wherein a susceptor material is incorporated into a portion of a cardboard sleeve and placed in close proximity to the seal between the film lid and the rigid container. For clarity, the cardboard sleeve and the microwave susceptor material are shown transparent.

The cardboard sleeve 1001 is positioned around the thermally stable rigid container 101, with the upper surface 901 of the cardboard sleeve 1001 positioned over the film membrane 104. The microwave susceptor material 902 is affixed to the lower side of the upper surface 901 of the cardboard sleeve 1001 so in close proximity to a portion of the rim of the container 101. The shaded area 903 shows the portion of the rim that is heated by the microwave susceptor material 902. If the user initiates peeling from this region, the microwave susceptor 902 will have heated up the heat sensitive seal sufficiently to weaken it

-18 thereby allowing easy separation of the film membrane 104 from the rigid container 101.

If the user attempts to initiate removal of the film membrane 104 from the 5 rigid container 101 in a region away from the heated area 903, the heat generated by the microwave susceptor material 902 will not have heated and weakened the heat sensitive seal, and so the user will have difficulty removing the film membrane 104 from the rigid container 101.

10 The food package can be manufactured by a method comprising: applying an adhesive material to a food container, the food container having an opening, wherein the adhesive material is applied adjacent a periphery of said opening; applying a film membrane across the opening, such that the opening becomes bonded to said container by said adhesive material; wherein the adhesive material comprises a microwave susceptor material o capable of releasing the bond when subjected to microwave radiation.

Claims

-19 Claims:

1. A device configured for containing food in a microwave oven or a conventional oven, comprising; s a thermally stable rigid container with an opening; a film membrane configured to substantially close said opening of said rigid container; To a heat sensitive seal to substantially adhere said film membrane to said rigid container, such that said opening of said rigid container is substantially closed by said film membrane, wherein said heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; Is a microwave susceptor material in close proximity to at least a portion of said heat sensitive seal, wherein said microwave susceptor material is operable to heat up in response to an applied microwave field, such that said susceptor

material heats up to cause said heat sensitive seal to have a reduced adhesion.

20

2. A device as claimed in claim 1 wherein said thermally stable rigid container comprises crystalline polyethylene terephthalate.

3. A device as claimed in claims 1 or 2 wherein said film membrane comprises amorphous polyethylene terephthalate.

4. A device as claimed in claims 1 or 2 wherein said film membrane comprises cellulose.

5. A device as claimed in any preceding claim wherein said heat 3 o sensitive seal comprises a amorphous polyethylene terephthalate.

6. A device as claimed in any preceding claim wherein said microwave susceptor material comprises a metal layer.

-20

7. A device as claimed in any one of claims 1 to 5 wherein said microwave susceptor material comprises carbon.

8. A device configured for containing food in a conventional oven or a microwave oven, comprising; a thermally stable rigid container with an opening; To a film membrane configured to substantially close said opening of said rigid container; a microwave susceptor material incorporated into at least a portion of said film membrane, wherein said microwave susceptor material is operable to heat s up in response to a microwave field;

a heat sensitive seal to substantially adhere said film membrane to said rigid container, such that said opening of said rigid container is substantially closed by said film membrane, wherein said heat sensitive seal is operable to o have a reduced adhesion in response to elevated temperature; wherein said susceptor material heats up in response to an applied microwave field to cause said heat sensitive seal to have a reduced adhesion.

:

9. A device as claimed in claim 8 wherein said thermally stable rigid container comprises crystalline polyethylene terephthalate.

10. A device as claimed in claim 8 or claim 9 wherein said film membrane comprises amorphous polyethylene terephthalate.

11. A device as claimed in claim 8 or claim 9 wherein said film membrane comprises cellulose.

-21

12. A device as claimed in any one of claims 8 to 11 wherein said microwave susceptor material comprises a layer of vacuum deposited metal.

13. A device as claimed in any one of claims 8 to 11 wherein said 5 microwave susceptor layer comprises carbon.

14. A device as claimed in any one of claims 8 to 13 wherein said microwave susceptor material forms a continuous layer on said film membrane.

To

15. A device as claimed in any one of claims 8 to 13 wherein said microwave susceptor material forms a discontinuous pattern on said film membrane.

16. A device as claimed in any one of claims 8 to 15 wherein said heat 15 sensitive seal comprises: amorphous polyethylene terephthalate.

17. A device configured for containing food in a microwave oven or a 2 o conventional oven, comprising; a thermally stable rigid container with an opening; a film membrane configured to substantially close said opening of said rigid 2 5 container; a heat sensitive seal to substantially adhere said film membrane to said rigid container, such that said opening of said rigid container is substantially closed by said film membrane, wherein said heat sensitive seal is operable to o have a reduced adhesion in response to elevated temperature; a label affixed to said film membrane in close proximity to at least a portion of said heat sensitive seal;

-22 a microwave susceptor material incorporated into at least a portion of said label, wherein said microwave susceptor material is operable to heat up in response to an applied microwave field, such that said susceptor material heats

5 up to cause said heat sensitive seal to have a reduced adhesion.

18. A device as claimed in claim 17 wherein said thermally stable rigid container comprises crystalline polyethylene terephthalate.

10

19. A device as claimed in claim 17 or claim 18 wherein said film membrane comprises amorphous polyethylene terephthalate.

20. A device as claimed in claim 17 or claim 18 wherein said film membrane comprises cellulose.

21. A device as claimed in any one of claims 17 to 20 wherein said heat sensitive seal comprises amorphous polyethylene terephthalate.

22. A device as claimed in any one of claims 15 to 19 wherein said 2 o label comprises: a first layer configured to be printed; a second layer to impart strength; a third layer comprising a microwave susceptor material, which is operable to heat up in response to an applied microwave field;

a fourth layer comprising an adhesive material, configured to affix said 3 o label to said full membrane.

23. A device configured for containing food in a microwave oven or a conventional oven, comprising;

-23 a thermally stable rigid container with an opening; a thermally stable rim around said opening of said rigid container comprising an upper surface and a lower surface; a film membrane configured to substantially close said opening of said rigid container; To a heat sensitive seal positioned between said upper surface of said rim and said film membrane, such that said opening of said rigid container is substantially closed by said film membrane, wherein said heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; 5 a border that can be affixed to said lower surface of said rim; a microwave susceptor material incorporated into at least a portion of said border, wherein said microwave susceptor material is operable to heat up in response to an applied microwave field, such that said susceptor material heats

o up to cause said heat sensitive seal to have a reduced adhesion.

24. A device as claimed in claim 23 wherein said thermally stable rigid container comprises crystalline polyethylene terephthalate.

25. A device as claimed in claim 23 or claim 24 wherein said thermally stable rim comprises crystalline polyethylene terephthalate.

26. A device as claimed in any one of claims 23 to 25 wherein said film membrane comprises amorphous polyethylene terephthalate.

27. A device as claimed in any one of claims 23 to 25 wherein said film membrane comprises cellulose.

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28. A device as claimed in any one of claims 23 to 27 wherein said heat sensitive seal comprises amorphous polyethylene terephthalate.

29. A device as claimed in any one of claims 23 to 28 wherein said 5 boarder is affixed to said lower surface of said rim using an adhesive.

30. A device as claimed in anyone of claims 23 to 28 wherein said border is affixed to said lower surface of said rim using mechanical means.

To

31. A device as claimed in any one of claims 23 to 30 wherein said border comprises: a rigid layer to impart mechanical strength 15 a microwave susceptor layer operable to heat up in response to an applied microwave field.

32. A device configured for containing food in a microwave oven or a conventional oven, comprising; a thermally stable rigid container with an opening; a film membrane configured to substantially close said opening of said rigid container; a heat sensitive seal to substantially adhere said film membrane to said rigid container, such that said opening of said rigid container is substantially closed by said film membrane, wherein said heat sensitive seal is operable to have a reduced adhesion in response to elevated temperature; a sleeve positioned around said device, comprising at least one upper surface, wherein said upper surface further defines an inner surface and an outer

-25 surface, wherein said inner surface of said upper surface is in close proximity to said film membrane; a label affixed to said inner surface of said upper surface of said sleeve positioned in close proximity to at least a portion of said heat sensitive seal; a microwave susceptor material incorporated into at least a portion of said label, wherein said microwave susceptor material is operable to heat up in response to an applied microwave field, such that said susceptor material heats

o up to cause said heat sensitive seal to have a reduced adhesion.

33. A device as claimed in claim 32 wherein said thermally stable rigid container comprises crystalline polyethylene terephthalate.

:s

34. A device as claimed in claim 32 or claim 33 wherein said film membrane comprises amorphous polyethylene terephthalate.

35. A device as claimed in claim 32 or claim 33 wherein said film membrane comprises cellulose.

36. A device as claimed in any one of claims 32 to 35 wherein said heat sensitive seal comprises amorphous polyethylene terephthalate.

37. A device as claimed in any one of claims 32 to 36 wherein said sleeve comprises cardboard.

38. A device as claimed in any on of claims 32 to 37 wherein said label is affixed to said inner surface of said surface of said sleeve using an adhesive.

30

39. A food package capable of being heated in a conventional oven and/or a microwave oven, said food package comprising: a rigid container suitable for containing food products;

-26 a film membrane extending adjacent to said container; and an adhesive seal extending between said container and said film, said 5 adhesive seal comprising a microwave susceptor material, said adhesive seal operating to bond said film membrane to said container.

40. The food package as claimed in claim 39, wherein: 10 said rigid container comprises a rim portion surrounding an opening of said container, and said film membrane extends across said opening and adjacent to said rim portion, said adhesive seal being disposed there between.

41. The food package as claimed in claim 39 or claim 40, wherein: said adhesive seal operates to bond said film membrane to said container in a first bonding state, in which said container is exposed to a temperature which is substantially at a natural ambient level; and 20 said adhesive seal operates to release said film membrane from said container, when said adhesive seal is exposed to a predetermined temperature above said ambient temperature level.

42. A food package as claimed in claim 39 or 40, wherein; said adhesive seal operates to bond said film membrane to said container when exposed to a microwave radiation level substantially at an ambient natural microwave radiation level; and 30 said adhesive seal operates to release said film membrane from said container, when said adhesive seal is exposed to a pre-determined microwave radiation level, above a natural ambient microwave radiation level

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43. The food package as claimed in claim 42, wherein said predetermined microwave level, is of a level found within an operating microwave oven 5

44. A method of manufacturing a food package, said food package suitable for cooking in a conventional oven and/or microwave oven, said method comprising; applying an adhesive material to a food container, said food container 10 having an opening, wherein said adhesive material is applied adjacent a periphery of said opening; applying a film membrane across said opening, such that said opening becomes bonded to said container by said adhesive material; wherein said adhesive material comprises a microwave susceptor material capable of releasing said bond when subjected to microwave radiation.

45. A method as claimed in claim 44, wherein said step of applying a go film membrane across said opening comprises heat sealing said film membrane to a rim of a thermally stables rigid said food container.