CA2039204A1

CA2039204A1 - Container for a product to be heated or cooked in an oven such as a microwave oven, closed by a heat sealing lid

Info

Publication number: CA2039204A1
Application number: CA002039204A
Authority: CA
Inventors: Marianne Boehrer
Original assignee: Individual
Current assignee: Amcor Flexibles Selestat SAS
Priority date: 1990-03-28
Filing date: 1991-03-27
Publication date: 1991-09-29
Also published as: JPH05278764A; FR2660287A1; ES2069231T3; AU639085B2; AU7389191A; EP0457629A1; DE69107338T2; EP0457629B1; DE69107338D1; ATE118665T1; PT97178A; FR2660287B1; DK0457629T3

Abstract

ABSTRACT OF THE DISCLOSURE

A container is disclosed for a product to be heated or cooked in an oven such as a microwave oven, whose lid comprises an upper sub-assembly (I) with a metal layer and a lower sub-assembly (II) comprising an upper heat reactivatable layer (4) affixed initially so as not to adhere against the metal layer (3) and a lower heat sealing layer (5) sealed against the peripheral flange (1). The heat reactivatable layer (4) and the heat sealing layer (5) are layers of a synthetic material which can be peeled respectively off the metal layer (3) and the peripheral flange (1). In addition the heat reactivatable layer (4) has, vertically in line with the peripheral flange (1) , a peripheral portion (6) adhering to the metal layer (3) following heating thereof during sealing of the heat sealing layer (5) on the peripheral flange (1).

Description

2~3~204 Container for a product to be heated or cooked in an oven such as a microwave oven, closed by a heat sealing lid.

The present invention relates to a container for products to be heated or cooked in an oven such as a microwave oven, comprising a peripheral flange on which a lid is fixed by heat sealing.
The lids of containers containing food or medical products in general comprise a metal layer for making them perfectly impermeable. However, this metal layer opposes the passage of waves in a microwave oven and, promoting the formation of an electric arc, prohibits the introduction of such containers in this type of oven for heatin~ or cooking their contents.
~5 'rhe present invention proposes bringing a solution to this problem and, for this, it provides a container which is characterized in that its lid comprises an upper sub-assembly with a metal layer and a lower sub-assembly comprising an upper heat reactivatable layer affixed initially so as not to adhere against the metal layer and a lower heat sealing layer sealed against the peripheral flange, in that the heat reactivatable layer and -the heat sealing layer are layers of a synthetic material which can be peeled respactively off the metal layer and the peripheral flange and in that the heat reactivatable layer has, verticall~ in line with the peripheral flange, a peripheral portion adhering to the metal layer following heating there.of during sealing of the heat sealing layer on the peripheral flange.
The upper sub-assembly of this lid may be readily separated from the heat reactivatable layer. It is then suff~cient to remove it to be ableto remove the metal layer and introduce the containers containing the products to be heated or cooked in a microwave oven without any problem.
Advantageously, the heat reac-tivatable layer has with respect to the metal layer an adhesive strength less ,; .

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than that of the heat sealing layer with respect to the peripheral flange.
The risks of the heat sealing layer being accidentally separated from the peripheral flange of the container during removal of the upper sub-assembly are thus avoided.
The thickness of the lid is preferably chosen as a function of the dimensions of the container. For e~ample, for a container of the size of a yoghourt pot, -the heat reactivatable layer and the hea-t sealing layer may be applied inseparably one against the other. On the other hand, for a container whose dimensions are appreciably larger, the heat reactivatable layer and the heat sealing layer may be situated on each side of at least one intermediate layer from which they are inseparable.
In a particular embodiment of the invention, the upper and lower sub-assemblies each comprise an opening tongue ex-tending beyond the peripheral flange, the two tongues being superimposed but not adhering to each other.
~0 It then suffices to exert a pull, irst of all on the upper tongue to remove the upper sub-assembly just before introducing the container into a microwave oven, then on the lower tongue to remove the lower sub-assembly and open the container after heating or cooking.
In another embodiment, -the upper and lower sub-assemblies each comprise two opening tongues each having a root substantially at the level of the free edge of the peripheral flange, the tongues of the upper sub-assembly adhering to the tongues of the lower sub-assembly whereas one of the latter is weakened at its root.
I~l thi~ case it i9 re~o[nnended to affix, on the upper ~ace of the Lid, on the tongue of -the upper sub-assembly which covers the weakened tongue, an indication informing the user to exert first of all a tractive force on these two tongues, so as to remove the metal layer before placing the container in a microwave oven. Under the action of this force, the .

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weakened tongue will readily be separated from the lower sub-assembly but will remain fas-t with the tongue of the upper sub-assembly which covers it during removal of the latter.
The user will have to exert secondly a tractive force on the remaining tongue to remove -the lower sub-assembly and open the con~ainer after hea-ting or cooking.
When the container comprises a lateral indentation, it is desirable for the upper and lower sub-assemblies -to project above the lateral inden-tation and each comprise an opening tongue having a root substantially at the level of the free edge of the peripheral flange, the two tongues being remote from the lateral indentation and adhexing together, the tongue of the lower sub-assembly being further weakened at its root.
It is again advisable here to a~fix, on the upper face of -the lid, on the tongues, an indication informing the user to exert first of all a tractive force on the tongues to remove the upper sub-assembly before introducin~ the container into a microwave oven.
Since the part of the lower sub-assembly which overhangs the lateral indentation forms a sort of tongue, the user will secondly instinctively exert a tractive force on this part to open the container after heating or cooking.
When the peripheral flange of the container has an external projection defined by a weakened line, it is desirable for the upper and lower sub-assemblies to each have two opening tongues each having a root substantially at the level of the free edge of the peripheral flange, for the opening tongues of the upper sub-assembly to adhere to the tongues of the lower sub-assembly, for the external projection to be covered by two of the tongues adhering to each other and for the tongue of the lower sub-assembly resting on the external projec-tion to be weakened at its root.

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It is here again recommended to affix on the upper face of the lid, on the tongue of the uppar sub-assembly which overhangs the external projec-tion, an indication informing the user to first of all break this external projection and exert a tractive force on the corresponding tongues to remove the upper sub-assembly.
In the second place, the user will instinctively exert a tractive force on the remaining tongue to open the container after heating or cooking.
When the peripheral flange has two external projections each defined by a weakened line, it is desirable for the upper and lower sub-assemblies to each have two opening tongues each with a root substan-tially at the level of the free edge of the peripheral 1ange, for the tongues of the lower sub-assembly to cover the external projections and adhere to the tongues of the upper sub-assembly and for one of the tongues of the lower sub-assembly to be weakened at its root.
It is still advisable to state on the lid the position from which the user must remove the upper sub-assembly before introducing the container into a microwave oven.
To the extent that the container has large dimensions, the metal layer may advantageously be coated on the outside with at least one reinforcement layer, this layer making the lid rigid and more resistant, particularly so that it may withstand a sterilisa-tion operation.
Other characteristics and advantages of the present invention will be clear from the description of several embodiments, which will be gi.ven hereafter by way of non limitative examples, with reference to the accompan~ing drawings in which :
Figure ~ is a schematic sectional view of a container according to a first embodiment;
Figure 2 is a top view of the container shown in ' ' ` :~, , .,-,.
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Figure 1;
Figure 3 is a schematic sectional view of a container according to a second embodiment;
Figure 4 is a top view of the container shown in Figure 3;
Figure 5 is a schematic sectional view of a container according to a third embodiment;
Figure 6 is a top view of ~he container shown in Figure 5;
Fi~ure 7 is a schematic sectional view of a container according to a fourth embodiment, -the flange of this container possibly comprisin~ a second external projection, which is shown with a dash-dot line;
Figure 8 is a top view of the container shown in Figure 7;
Figure 9 is a diagram illustrating a method of manufacturing a laminated strip material from which the lids shown in Figures 1 and 7 may be obtained; and Figures 10 to 12 are diagrams illustrating three s-teps of a method for manufacturing a laminated strip material from which other lids may be obtained.
The containers according to the invention have been designed to receive long-life products, for example food products, intended to be heated or cooked in a microwave oven. These con-tainers comprise, as is known, a periph0ral flange 1 surrounding the en~rance of their cavity and are sealingly closed by a lid 2 heat sealed to their peripheral flange. They are in general made from a synthetic material but they could possibly be made from metal provided that the upper face of the peripheral flange 1 is coated with a synthetic material film allowing their lid 2 to be heat sealed.
Generally, the lid of the containers according to the invention comprises an upper sub-assembly I with a metal layer 3 and a lower sub-assembly II with a heat reactivatable layer upper layer 4 applied against the , ~- :, , .

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metal layer 3 and a lower heat sealing layer 5 sealed against the peripheral flange 1.
The heat reactivatable layer 4 and the heat sealing layer 5 are made from a synthetic material and may be separated, by peeling, respectively from the metal layer 3 and from the peripheral flange 1.
Furthermore, the heat reactivatable layer 4 has, vertically in line with the peripheral flange 1, a peripheral portion 6 which is reactivated, i.e. adhering -to the metal layer 3, following heating thereof during sealing of the heat sealing layer 5 to the peripheral flange.
Lid 2 is fixed to the peripheral flange of a container by applying a conventional heat sealing tool on the portion of the lid which overhangs said peripheral flange.
Under the effect of the heat which i-t releases during its operation, this tool activates portion 6 of the heat reactiva-table layer 4 whi.c~ extends thereunder and thus allows this portion to adhere to the metal layer 4 while forming a sealed connection. It further allows the heat sealing layer 5 to be fixed sealingly on flange 1 by causing melting of portion 7 situated between these two elements.
It will in any case be noted that the heat sealing tool causes a slight deformation of the portion of the lid which overhangs flange 1 and causes a slightly hollow annular impression 8.
It will be further noted that when a lid 2 is sealed on a container, the heat reactivatable layer 4 has, with respect to the metal layer 3, a lower adhesive power than that of the heat seating layer 5 with respect to flange 1.
In the embodiment shown in figures 1 and 2, the heat reactivatable layer 4 and the heat sealing layer 5 are applied against each other inseparably.

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Furthermore, the upper I and lower II sub-assemblies comprise openin~ tongues 9, 10 extending beyond ~lange 1, these tongues being superimposed but not adhering to each other since they are situated outside the annular impression 8 of the heat sealing tool.
Before introducing the container into a microwave oven, the user may readily separate the metal layer 3 ~rom the rest o~ the lid since i-t is sufficient ~o exert a pull on tongue 9.
In the embodiment shown in Figures 3 and 4, the heat reactivatable layer ~ and the heat sealing layer 5 of the lower sub-assembly II are situated on each side of an intermediate layer 11 with which they are fast.
Furthermore, the upper I and lower II sub-assemblies each comprise two opening tongues 12, respectively 13, spaced apart from each other and each haviny a root substantially at the level of the free edge of the flange 1 of the container.
In this embodiment, tongues 12 and 13 are adhered together during application of the heat sealing tool, one of tongues 13 being further weakened along a line 14 adjacent its root. Moreover, as is shown in Figure 4, tongue 12 which is situated above the weakened tongue 13 carries an indication s-tating that the user will have to remove these tongues before introducing the container into a microwave oven.
When the user exerts a -tractive force on these tongues, the ~eakened tongue 13 will be readily separated from the lower sub-assembly IIalong the weakened line 14, but will remain fast with the upper sub-assembly I which may thus be separated from the rest of the lid.
In the em~odiment shown in Figures 5 and 6, the container comprises a lateral indentation 15 at one o~ its corners, the width of its peripheral ~lange being the same at the level of its lateral indentation as in its other portions.

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Furthermore, the upper sub-assembly I of lid 2 comprises an additional reinforcement layer 16 fi~ed to the upper face of the metal layer 3.
In this embodiment, the upper I and lower II sub-assemblies project above the lateral indentation 15 sothat the existence of the latter cannot be discerned when the lid is seen from the top. They comprise two tongues 17, 18 distant from the lateral indentation 15 and adhering together, tongue 18 of the lower sub-assembly II
being weakened along a line 19 adjacent its root which is substantially at -the level of the free edge of flange 1 of the container.
In addition, tongue 17 carries an indication telliny the user that he must exert a tractive force on the pair of tongues 17, 18 to remove the upper sub assembly I.
It will be noted here that the lid forms a sort of tongue outside the lateral indentation 15 and which the user may use to open the container, after the contents thereof have been heated or cooked in a microwave oven.
In the embodiment shown in Figures 7 and 8, the peripheral flange 1 of the container has an external projection 20 defined by a weakened line 21.
Furthermore, the upper I and lower II sub-assemblies each comprise two opening tongues 22, respectively ~3, spaced apart from each other and each having a root substantially at the level of the free edge of -the peripheral flange 1.
The tongues 22 are adhered to tongues 23 during heat sealing. Furthermore, the external projection 20 is covered by the two tongues 22, 23 adhering together, tongue 23 resting on the e~ternal projection being weakened along a line 2~ adjacent its root.
An indication on tongue 22 situated at the level of projection 20 is further provided for informing the user that he must e~ert a tractive force on the assembly formed by the projection and the corresponding tongue3 22, 23 ~. , , ;

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before introducing the con~ainer into a microwave oven.
In a variant, the peripheral flange 1 of the container could have a second external projection 20 defined by a weakened line 21, as shown with a dash-dot line in Figure 7.
In this case, the second pair of tongues 22, 23 would rest then on this second external projection.
The materials will now be mentioned which may be used for constructing the lid 2 of containers according to the invention, with the thicknesses of the layers forming these lids.
Thus, the me-tal layer 3 may be a layer of aluminium or aluminium alloy, its thickness being of the order of 10 to 200 microns (10-5 to 2.10~4m).
The heat reactivatable layer ~ may be formed by a material chosen from the group comprising a grafted polypropylene, a grafted high density polyethylene, a grafted linear low density polyethylene, a graf~ed ethylene - vinyl acetate copolymer, a grafted ethylene -butyl acrylate copolymer, or a grafted ethylene me-thyl acrylate copolymer, the grafting element being an unsaturated monomer comprising at least one carboxylic acid group, su~h as acrylic acid or malic anhydride, its thickness being of the order of 10 to 200 microns (10-5 to 25 2.10~4m).
The heat sealing layer 5 may be formed by a material chosen from the group comprising a polyester varnish or an extrudable layer having a polypropylene, high density polyethylene or polyester basis~ i-ts thickness bein~ of 30 the order of 5 to lO0 microns (5 10-6 to 10~4m).
The intermedia-te layer 11 is formed by a material having an affinity with the heat reactivatable layer and with the heat sealing layer, its thickness being of the order of lO to 200 microns (10-5 to 2.10~4m).
As for the reinforcement layer 16, it may be formed by a material chosen from the group comprising polyester .. . ~
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or a polypropylene and i-ts thickness being of the order of 10 to 200 microns (10-5 to 2.10~4m).
It will be fllr-ther noted that the lower sub-assembly II of lids 2 could comprise perforations avoiding the formation of an overpressure in the containers during heating or cooking by microwaves of the products contained therein.
Figure 9 illustrates a method of manufacturing a laminated strip from which -the lids for closing the containers shown in Figures 1 to 7 may be cut out.
It shows ~hat this laminated material may be obtained in a way known per se by coextruding a heat reactivatable layer 4 and a heat sealing layer 5 on a metal strip 3 moving in the direction of arrow F, the coextrusion taking place continuously through a die 25.
Figures 10 to 12 illustrate a method of manufacturing a laminated material strip from which lids may be cut out whose upper sub-assembly I comprises a metal layer 3 and a reinforcement layer 16 and whose lower sub-assembly II comprises an intermediate layer 11 between a heat reactivatable layer 4 and a heat sealing layer 5, More precisely, Figure 10 illustrates the first step of the manufacturing method, during whic~ an elementary laminated strip material corresponding to the upper sub-assembly I is ob-tained :
- by applying, in a coating station 26, a film of adhesive on a reinforcement foil 16 driven continuously in the direction of arrow F1;
- by drying, in a drying station 27, the adhesive deposited on the reinforcement foil 16;
- by applying, against the coated face of foil 16, in a ~oining station 28, a metal foil 3 driven in the direction of arrow F2 in synchronism with said foil 16; and - by winding the resultant elementary laminate in the form of a reel 29.
Figure 11 illustrates a second step of the ~3~

manufacturing method, during which a second elementary strip laminate is obtained by extruding material forming the heat reactivatable layer ~ between the elementary laminate obtained in the first step and an in~ermediate 5 layer 16, the material ~ forming the heat reactivatable layer being extruded from a die 30 while the first elementary laminate and layer 16 are driven in synchronism respectively in the direction of arrows F3 and F4.
Figure 12 illustrates -the third step of the 10 manufacturing method, during which the final strip laminate is obtained by extruding a material forming the heat reactivatable layer 5 on the second elementary laminate obtained in the second step, the material forming layer 5 being extruded from a die 31 while the second elementary laminate moves in the direction of arrow F5.

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Claims

1. A container for a product to be heated or cooked in an oven such as a microwave oven, comprising a peripheral flange (1) on which a lid (2) is heat sealed, characterized in that the lid comprises an upper sub-assembly (I) with a metal layer and a lower sub-assembly (II) comprising an upper heat reactivatable layer (4) affixed initially so as not to adhere against the metal layer (3) and a lower heat sealing layer (5) sealed against the peripheral flange (1), in that the heat reactivatable layer (4) and the heat sealing layer (5) are layers of a synthetic material which can be peeled respectively off the metal layer (3) and the peripheral flange (1) and in that the heat reactivatable layer (4) has, vertically in line with the peripheral flange (1) , a peripheral portion (6) adhering to the metal layer (3) following heating thereof during sealing of the heat sealing layer (5) on the peripheral flange (1).

2. Container according to claim 1, characterized in that the heat reactivatable layer (4) has with respect to the metal layer (3) an adhesive strength less than that of the heat sealing layer (5) with respect to the peripheral flange (1).

3. Container according to claim 1 or 2, characterized in that the heat reactivatable layer (4) and the heat sealing layer (5) are applied inseparably one against the other.

4. Container according to claim 1 or 2, characterized in that the heat reactivatable layer (4) and the heat sealing layer (5) are situated on each side of at least one intermediate layer (11) from which they are inseparable.

5. Container according to claim 1, characterized in that the upper (I) and lower (II) sub-assemblies each comprise an opening tongue (9, 10) extending beyond the peripheral flange (1), the two tongues (9, 10) being superimposed but not adhering to each other.

6. Container according to claim 1, characterized in that the upper (I) and lower (II) sub-assemblies each comprise two opening tongues (12, 13) each having a root substantially at the level of the free edge of the peripheral flange, the tongues (13) of the upper sub-assembly (I) adhering to the tongues (12) of the lower sub-assembly (II) whereas one of the latter is weakened at its root.

7. Container according to claim 1, comprising a lateral indentation (15), characterized in that the upper (I) and lower (II) sub-assemblies project above the lateral indentation (15) and each comprise an opening tongue (17, 18) having a root substantially at the level of the free edge of the peripheral flange (1), the two tongues (17, 18) being remote from the lateral indentation (15) and adhering together, the tongue (18) of the lower sub-assembly (II) being further weakened at its root.

8. Container according to claim 1, whose peripheral flange has an external projection (20) defined by a weakened line (21), characterized in that the upper (I) and lower (II) sub-assemblies each have two opening tongues (22, 23) each having a root substantially at the level of the free edge of the peripheral flange (1), in that the tongues (22) of the upper sub-assembly (I) adhere to the tongues (23) of the lower sub-assembly (II), in that the external projection (20) is covered by two of the tongues (22, 23) adhering to each other and in that the tongue (23) of the lower sub-assembly (II) resting on the external projection (20)) is weakened at its root.

9. Container according to claim 1, whose peripheral flange (1) has two external projections (20) each defined by a weakened line (21), characterized in that the upper (I) and lower (II) sub-assemblies each have two opening tongues (22, 23) each with a root substantially at the level of the free edge of the peripheral flange (1), in that the tongues (23) of the lower sub-assembly (II) cover the external projections (20) and adhere to the tongues (22) of the upper sub-assembly (I) and in that one (23) of the tongues of the lower sub-assembly (II) is weakened at its root.

10. Container according to claim 1, characterized in that metal layer (3) is coated on the outside with at least one reinforcement layer (16).

11. Container according to claim 10, characterized in that the reinforcement layer (16) is formed by a material comprising a polyester or a polypropylene.

12. Container according to claim l or 10, characterized in that the metal layer (3) is an aluminium or aluminium alloy layer.

13. Container according to claim 1 or 2, characterized in that the heat reactivatable layer (4) is formed by a material chosen from the group comprising a grafted polypropylene, a grafted high density polyethylene, a grafted linear low density polyethylene, a grafted ethylene - vinyl acetate copolymer, a grafted ethylene - butyl acrylate copolymer, or a grafted ethylene - methyl acrylate copolymer, the grafting element being an unsaturated monomer comprising at least one carboxylic acid group.

14. Container according to claim 1 or 2, characterized in that the heat sealing layer (5)is formed by a material chosen from the group comprising a polyester varnish or an extrudable layer having a polypropylene, high density polyethylene or polyester basis.

15. Container according to claim 4, characterized in that the intermediate layer ( 11) is formed by a material having an affinity with the heat reactivatable layer and with the heat sealing layer.

16. Container according to claim 1 or 10, characterized in that the metal layer (3) has a thickness of the order of 10 to 200 microns (10-5 to 2.10-4 )

17. Container according to claim 1 or 2, characterized in that the heat reactivatable layer (4) has a thickness of the order of 10 to 80 microns (10-5 to 8.10-5m).

18. Container according to claim 1 or 4, characterized in that the heat sealing layer (5) has a thickness of the order of 5 to 100 microns (5.10-6 to 10-4m).

19. Container according to claim 10 or 11, characterized in that the reinforcement layer (16) has a thickness being of the order of 10 to 200 microns (10-5 to 2.10-4m).

20. Container according to claim 4, characterized in that the intermediate layer (11) has a thickness being of the order of 10 to 200 microns (10-5 to 2.10-4m).

21. Container according to claim 1, characterized in that lower sub-assembly (II) comprises perforations.