Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
PACKAGING TRAY AND METHOD FOR MANUFACTURING A PACKAGING TRAY
Document Type and Number:
WIPO Patent Application WO/2011/136641
Kind Code:
A1
Abstract:
A packaging tray (1) which is destined to be used for containing foodstuff (50) is manufactured by providing an undeformed piece of foil (11), and providing fluid plastic and moulding the plastic to the piece of foil (11). When the plastic cools down, the plastic shrinks, and the piece of foil (11) is forced to assume a more or less wrinkled state. When the packaging tray (1) is filled with foodstuff (50) and sealed by means of a piece of cover foil (60), loss of gas from an interior space (40) of the packaging tray (1) can be compensated for by straightening out of the piece of foil (11) of the packaging tray (1), which is advantageous because such a process does not involve a deterioration of barrier properties of the packaging tray (1), and does not affect the shielding function of the piece of cover foil (60) either.

Inventors:
NABER, Wilhelmus, Cornelis, Maria (Julianastraat 9, GL Waalwijk, NL-5141, NL)
Application Number:
NL2011/000035
Publication Date:
November 03, 2011
Filing Date:
April 29, 2011
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
NABER BEHEER B.V. (Van Hilststraat 12, RL Waalwijk, NL-5145, NL)
NABER, Wilhelmus, Cornelis, Maria (Julianastraat 9, GL Waalwijk, NL-5141, NL)
International Classes:
B29C45/14; B65D79/00; B65D81/20
Attorney, Agent or Firm:
DEKKER-GARMS, Alwine, Emilie (Octrooibureau Griebling B.V, Sportweg 10, AC Tilburg, NL-5037, NL)
Download PDF:
Claims:
CLAIMS

1. Method for manufacturing a packaging tray (1 ) which is destined to be used for containing foodstuff (50), and which is formed with an open side (30) which is destined to be sealed with a piece of cover foil (60), especially a piece of cover foil (60) which is suitable for constituting a fluid-tight and gas-tight barrier between an interior space (40) of the tray (1) and surroundings of the tray (1), wherein the method comprises a step of providing at least one piece of foil (11), and also a step of providing fluid plastic and moulding the fluid plastic to the piece of foil (11), wherein the piece of foil (11) is left in an undeformed state prior to the moulding process.

2. Method according to claim 1 , wherein the plastic is moulded to the piece of foil (11) along the entire circumference of the piece of foil (11).

3. Method according to claim 1 or 2, wherein the plastic is moulded to a circumferential rim of the piece of foil (11).

4. Method according to claim 1 or 2, wherein the plastic is moulded to the piece of foil (11) in an overlapping position with portions (14) of the piece of foil (11). 5. Method according to any of claims 1-4, wherein the fluid plastic is supplied to the piece of foil (11) from at least two positions.

6. Method according to any of claims 1-5, wherein a mould for injection moulding is applied, and wherein the piece of foil (11) is retained in the mould on the basis of electrostatic forces.

7. Method according to any of claims 1-6, wherein the piece of foil (11) is heated prior to supplying the plastic. 8. Method according to any of claims 1-7, wherein the piece of foil (11) is supplied in combination with an element arranged thereon for absorbing fluid.

9. Packaging tray (1) for containing foodstuff (50), provided with an open side (30) which is destined to be sealed with a piece of cover foil (60), especially a piece of cover foil (60) which is suitable for constituting a fluid-tight and gas-tight barrier between an interior space (40) of the tray (1) and surroundings of the tray (1), wherein the tray (1) comprises at least one piece of foil (11), and also plastic moulded to the piece of foil (11), and wherein the piece of foil (11) has an uneven appearance which has been obtained exclusively on the basis of shrinkage

differences which have occurred after the moulding process between the piece of foil (11 ) and the plastic moulded to the piece of foil (11 ).

10. Packaging tray (1 ) according to claim 9, wherein the piece of foil (11 ) is located in a bottom portion (10) of the tray (1), i.e. a portion (10) of the tray (1) which is destined to support the foodstuff (50), and wherein the plastic moulded to the piece of foil (11) is part of standing walls (20) of the tray (1), which are connected to the bottom portion (10), and of a transition area (21) between the bottom portion (10) and the standing walls (20).

11. Packaging tray (1 ) according to claim 9 or 10, wherein the piece of foil (11 ) is oversized, i.e. larger than necessary for a smooth appearance in the connection to the plastic moulded to the piece of foil (11 ).

12. Packaging tray (1 ) according to any of claims 9-11 , wherein the piece of foil (11) and the plastic moulded to the piece of foil (11) overlap at least partially. 13. Packaging tray (1 ) according to any of claims 9-12, wherein the foil (11 ) is a multilayered foil, which is practically fluid-tight and gas-tight.

14. Assembly (2) of a packaging tray (1) according to any of claims 9-13, foodstuff (50) located inside the tray (1), and a piece of cover foil (60) sealing an open side (30) of the tray (1), and constituting a fluid-tight and gas-tight barrier between an interior space (40) of the tray (1) and surroundings of the assembly (2).

15. Assembly (2) according to claim 14, wherein a protective gas is present in the interior space (40) of the tray (1).

Description:
Title: Packaging tray and method for manufacturing a packaging tray

The present invention relates to a method for manufacturing a packaging tray which is destined to be used for containing foodstuff, and which is formed with an open side which is destined to be sealed with a piece of cover foil, especially a piece of cover foil which is suitable for constituting a fluid-tight and gas-tight barrier between an interior space of the tray and surroundings of the tray.

Furthermore, the present invention relates to a packaging tray provided with an open side which is destined to be sealed with a piece of cover foil, especially a piece of cover foil which is suitable for constituting a fluid-tight and gas-tight barrier between an interior space of the tray and surroundings of the tray. Also, the present invention relates to an assembly of a packaging tray as mentioned, foodstuff located inside the packaging tray, and a piece of cover foil constituting a fluid-tight and gas- tight barrier between an interior space of the tray and surroundings of the assembly.

Packaging trays are well-known articles, which can be found in practically any supermarket. In many cases, the packaging trays are applied for containing foodstuff, for example, one or more pieces of meat or fish. In general, a packaging tray has a bottom portion and standing walls, wherein the standing walls form a closed ring, as it were, which is positioned on the bottom portion. The bottom portion serves for supporting the foodstuff, and the standing walls act like borders of an area which is defined by the bottom portion. At a top side of the packaging tray, a transparent piece of cover foil is arranged, which is connected to a top rim of the ring of standing walls. Due to the use of the transparent foil, the content of a packaging tray can be visible to a consumer, who is thereby enabled to make an appropriate choice. Furthermore, the foil prevents the foodstuff from falling out of the packaging tray when the tray is not in a normal, upright position, and protects the foodstuff against environmental influences which might cause the foodstuff to decay.

DE 20 2006 018 876 discloses an assembly of a packaging tray and a piece of cover foil arranged at a top side of the tray. In the following, for sake of clarity, such an assembly will be referred to as package. A process of sealing the packaging tray by means of the cover foil is performed under special conditions, in such a way that it is ensured that an interior space of the packaging tray is filled with a protective gas, i.e. a gas for protecting the foodstuff from decay, thereby prolonging the shelf life of the foodstuff. An example of the protective gas is air with an increased content of nitrogen, oxygen and/or carbon dioxide. For sake of completeness, it is noted that performing a packaging process of foodstuff which is aimed at trapping a protective gas inside the package is known as Modified Atmosphere Packaging (MAP).

In order to act like a barrier between the protective gas which is present inside a package and the ambient air surrounding the package, the cover foil needs to have special properties, which are referred to as barrier properties. In fact, it should be impossible for gas molecules to diffuse through the cover foil, so that a situation in which the gas which is present inside the package becomes more and more like normal air over time is prevented. An example of a foil having good barrier properties is a multilayered foil made of polypropylene or ethylene vinyl acetate.

Although the shelf life of foodstuff can be prolonged by using the protective gas and the piece of cover foil for keeping the gas inside the package, there is a problem which prevents the protective effect of the gas and the piece of cover foil from being optimal. The fact is that the foodstuff can play a role in absorbing some of the protective gas. As a result, underpressure is obtained inside the package, which causes the piece of cover foil to bulge in the direction of the interior space of the package. This is disadvantageous, as the barrier properties of the package are decreased when the piece of cover foil is in the bulged condition, and the process of diffusion through the cover foil, and especially through other portions of the package, is stimulated on the basis of the pressure difference.

It is an object of the present invention to provide a solution to the problem as mentioned. In particular, it is an object of the present invention to provide a way of having a package with a piece of cover foil as described in the foregoing, in which the barrier function of the cover foil is significantly less deteriorated over time than in a conventional package, or is not deteriorated over time at all.

The object of the present invention is achieved by a method for manufacturing a packaging tray, wherein at least one piece of foil is provided, wherein fluid plastic is provided and moulded to the piece of foil, and wherein the piece of foil is left in an undeformed state prior to the moulding process. Hence, according to the present invention, at least one piece of foil is used in the packaging tray. Furthermore, a more solid portion of the packaging tray, which provides the necessary stiffness of the tray, is formed by providing fluid plastic and moulding the fluid plastic to the piece of foil, wherein the plastic is made to capture the piece of foil, and to fuse to the piece of foil, as it were, such that a connection between the plastic and the piece of foil is obtained when the fluid plastic solidifies. The solidification of the plastic takes place automatically when the plastic is not subjected to any heating process after the moulding process has taken place, and the temperature drops below the melting point of the plastic.

A first advantage of the use of at least one piece of foil in the packaging tray is that material is saved, so that both costs and the environment are saved. In comparison with a conventional packaging tray, which is made of one type of plastic material, a portion of the plastic is removed and replaced by foil.

A second advantage of the use of the piece of foil in the packaging tray pertains to the use of the packaging tray with a piece of cover foil in order to form a sealed package as described in the foregoing. An insight underlying the present invention is that fluid plastic shrinks to a certain extent when its temperature decreases. When the fluid plastic is moulded to the piece of foil during the

manufacturing process of the packaging tray, in such a way that the piece of foil is at least partially surrounded by the plastic, and the fluid plastic is made to solidify under the influence of a decrease of the temperature, the foil is pressed to an uneven appearance due to the shrinking of the plastic, wherein the foil is wrinkled in order to compensate for the lack of space which arises. Hence, when the plastic has cooled down and has assumed its final shape, the piece of foil is oversized with respect to the window in the plastic.

When the packaging tray having the oversized piece of foil is used for accommodating foodstuff and is used in combination with a piece of cover foil in order to obtain a sealed package in which both the foodstuff and a protective gas are present, the effect that the foodstuff absorbs some of the protective gas over time still occurs. However, the oversized piece of foil, which is part of the packaging tray, is capable of compensating for this effect. When some of the protective gas disappears from the interior space of the packaging tray, it is no longer the piece of cover foil which is used in combination with the packaging tray that is made to deform. Instead, the piece of foil which is part of the packaging tray is made to deform, wherein wrinkles in the foil are straightened out to a certain extent. By being initially oversized, the piece of foil has the capability of compensating for a pressure difference by deforming and thereby decreasing the interior space of the sealed package, wherein the barrier properties of the package are not deteriorated, as the appearance of the piece of foil changes from oversized to normally sized.

According to the present invention, the piece of foil is left in an undeformed state prior to the moulding process, so that it is very well possible to retain the piece of foil in an appropriate position during the moulding process. In this respect, it is noted that WO 2005/002990 teaches a way of manufacturing a receptable, which includes the steps of placing a piece of foil in the mould cavity of a mould, and, through raised temperature and pressure, adhering the piece of foil to the rest of the receptacle to be formed by the mould. However, according to WO 2005/002990, prior to closing of the mould and forming of the receptacle, the piece of foil has greater dimensions than its projected area after forming the receptacle, whereafter the receptacle with a bottom part consisting of the piece of foil is removed, optionally after cooling, from the opened mould. Particularly, the shape of the mould is adapted to deforming the piece of foil when the mould is closed in order to achieve the effect of the piece of foil having greater dimensions prior to forming the receptacle than its projected area after forming the receptacle. A disadvantage of deforming the piece of foil prior to forming the rest of the receptacle is that undesired side-effects such as local wrinkling of the piece of foil occurs, and that there is no practical possibility of keeping the piece of foil properly positioned, and realizing a proper embedding of the piece of foil in the rest of the receptacle. Therefore, it is not possible to put the manufacturing method known from WO 2005/002990 to practice and yield

acceptable results.

When the method according to the present invention is carried out, the problems with the piece of foil do not occur. Still, a deformation of the piece of foil is obtained, but this is only done in a natural way after the moulding process has taken place, namely on the basis of differences in the extent to which shrinkage occurs in the piece of foil and the plastic which is moulded to the piece of foil. In any case, there is no deliberate, forced deformation of the piece of foil prior to the moulding process. On the basis of this fact, the method according to the present invention is very well suitable to be carried out in practice, contrary to the method known from WO 2005/002990. The achievement of the present invention resides in the

recognition that there are shrinkage differences which can be used in an advantageous manner, wherein there is no need for any further deformation process of the piece of foil.

In a practical embodiment, the piece of foil is applied in a bottom portion of the packaging tray, i.e. in a portion which is intended to support the foodstuff in a normal orientation of the packaging tray. In such an embodiment, the plastic which is moulded to the piece of foil may be part of standing walls of the packaging tray, which are connected to the bottom portion, and of a transition area between the bottom portion and the standing walls.

Advantageously, the fluid plastic is moulded to the piece of foil along the entire circumference of the piece of foil. In such a case, the effect of the shrinking process of the plastic on the piece of foil can be optimal. The plastic may be moulded to a circumferential rim of the piece of foil, but it is also possible that considerable overlap of the piece of foil and the plastic is created. An advantage of the overlap is that the barrier properties of the packaging tray as a whole can be improved, as a combination of plastic and foil is more effective in preventing diffusion than only plastic.

The process of moulding the plastic to the piece of foil may take place in any suitable way, wherein the plastic may be supplied to the piece of foil at various positions, i.e. at two or more positions. In practice, a mould for injection moulding may be applied, wherein the undeformed piece of foil is retained inside the mould on the basis of electrostatic forces. Furthermore, in practice, the plastic is heated during the supply of plastic to the piece of foil, so that the plastic is actually capable of filling up cavities of the mould.

In comparison with a conventional packaging tray, the packaging tray according to the present invention has at least one piece of foil. When the piece of foil is oversized, i.e. larger than necessary for a smooth appearance in the

connection to the moulded plastic, it is achieved that the shelf life of foodstuff can be prolonged to a considerable extent. As has been explained in the foregoing, the reason is that the oversized piece of foil can compensate for a loss of pressure inside the interior space, which is caused by absorption of some of the gas which is present in the interior space by the foodstuff, without losing the capability of acting like a fluid-tight and gas-tight barrier.

Various options which are applicable to the conventional packaging tray are also applicable to the packaging tray according to the present invention. For example, it is possible for the bottom portion of the packaging tray to be provided with a cushion-like element for absorbing fluid from the foodstuff.

The present invention will be further explained on the basis of the following description of a packaging tray for containing foodstuff and a process for

manufacturing such packaging tray, with reference to the drawing, in which equal reference signs indicate equal or similar components, and in which:

figures 1 and 2 diagrammatically show perspective views of the packaging tray according to the present invention;

figure 3 diagrammatically shows a piece of foil which is used in the process of manufacturing the packaging tray, and indicates how fluid plastic can be supplied to the piece of foil and can be made to surround the piece of foil;

figure 4 diagrammatically shows a cross-section of a portion of a piece of foil and a portion of plastic which is moulded to the piece of foil;

figure 5 diagrammatically shows a perspective view of an assembly of the packaging tray, foodstuff contained in the packaging tray, and a piece of cover foil sealing the packaging tray;

figure 6 illustrates how an appearance of the piece of foil of the packaging tray of the assembly shown in figure 5 may change over time; and

figure 7 diagrammatically shows an alternative shape of the piece of foil to be integrated in the packaging tray.

The present invention relates to a packaging tray 1 for containing foodstuff and a method for manufacturing such a packaging tray 1 , which is shown in figures 1 and 2. It is noted that figure 1 shows the packaging tray 1 in a normal, upright orientation, whereas figure 2 shows the packaging tray 1 in an upside down orientation.

Basically, the packaging tray 1 comprises a bottom portion 10 and a ring- shaped standing wall portion 20 which is connected to a circumference of the bottom portion 10. In the shown example, the circumference as mentioned is rectangular, which does not alter the fact that other shapes of the circumference are possible within the scope of the present invention. A top side of the packaging tray 1 is an open side 30. It is noted that the top side may be partially closed, as long as there is enough space for foodstuff to be placed in an interior space 40 of the packaging tray 1.

A special feature of the packaging tray 1 according to the present invention resides in the fact that the packaging tray 1 comprises a piece of foil 11. In the shown example, the piece of foil 11 is integrated in the bottom portion 10 of the packaging tray 1. Furthermore, the standing wall portion 20 is made of plastic, wherein the plastic is moulded to the piece of foil 11.

Figure 3 illustrates a way in which the manufacturing process of the packaging tray 1 can be performed. In particular, a piece of foil 11 is provided and left in an undeformed state, and fluid plastic is provided as well, which is supplied to the piece of foil 11 at appropriate positions, and which is used to form the standing wall portion 20, a transition area 21 between the standing wall portion 20 and the bottom portion 10, and a portion 12 of the bottom portion 10 surrounding and embedding the piece of foil 11. In figure 3, the supply of the fluid plastic is indicated by means of dots, and the flow of the fluid plastic is indicated by means of arrows. In the shown example, the fluid plastic is supplied to the piece of foil 11 at four positions on the

circumference of the piece of foil 11 , wherein the fluid plastic is made to flow around the piece of foil 11. Eventually, a closed, ring-shaped plastic unit is obtained on the basis of the fact that plastic which is supplied at one position meets plastic supplied at another position. In the shown example, the positions where this phenomenon takes place is close to the corners of the piece of foil 11. For sake of completeness, it is noted that the positions where the fluid plastic is supplied may be chosen freely, depending on practical possibilities for the moulding process, and depending on factors like the shape and the size of the packaging tray 1 to be manufactured.

An injection moulding process is a well-known process in which fluid plastic is used and is made to assume a predetermined shape. In the process, a suitable mould (not shown) is used, which comprises cavities for receiving the fluid plastic, wherein the shape of the cavities is adapted to the predetermined shape of the plastic. A most practical way of carrying out the manufacturing process according to the present invention involves carrying out an injection moulding process as mentioned. In the process, the undeformed piece of foil 11 is retained inside the mould, for example, by using electrostatic forces, and the fluid plastic is made to fill the mould containing the piece of foil 1. As soon as the entire cavity for forming the packaging tray 1 is provided with plastic, the plastic can be made to cool down. In the process, the plastic solidifies, and at a certain point in time, the packaging tray 1 can be released from the mould. At that point in time, the packaging tray 1 is ready, wherein there is a solid connection between the plastic and the piece of foil 11. Figure 4 illustrates how a circumferential rim 13 of the piece of foil 11 may be embedded in the plastic in the final product.

The packaging tray 1 is particularly suitable to be used for receiving and containing foodstuff, for example, one or more pieces of meat or fish, or vegetables. Such use of the packaging tray 1 is illustrated in figure 5, in which foodstuff is diagrammatically shown and indicated by reference numeral 50. The foodstuff 50 is positioned in the interior space 40 of the packaging tray 1 , and the open side 30 of the packaging tray 1 is closed by means of a piece of transparent cover foil 60, so that a closed assembly 2 is obtained. In order to promote preservation of the foodstuff 50, it is advantageous if the interior space 40 is not filled with air, but with a special protective gas, as is commonly known in the field of packing foodstuff 50. Furthermore, it is advantageous if the materials of the packaging tray 1 are chosen such that the foodstuff 50 is protected from environmental influences, and that diffusion of gas molecules is prevented. In view thereof, the foil may be a

multilayered foil, for example, and may comprise a material which is known for having excellent barrier properties, such as polypropylene or ethylene vinyl acetate. In the assembly of the packaging tray 1 , the foodstuff 50 and the piece of cover foil 60, the piece of foil 11 of the packaging tray 1 and the piece of cover foil 60 may be of the same type. A suitable material for the plastic of the packaging tray 1 , which is moulded to the piece of foil 11 of the packaging tray 1 , is polypropylene, wherein it is noted that many other materials are feasible as well within the scope of the present invention.

Figure 6 serves to illustrate a special aspect of the packaging tray 1 according to the present invention. The fact is that the plastic of the packaging tray 1 shrinks during the process of cooling down, i.e. during the solidification, which takes place at the end of the manufacturing process. For example, polypropylene has a shrinkage percentage of about 1.5%. As a result of this fact, the piece of foil 11 is pushed at its sides to a somewhat smaller space. The piece of foil 11 does not shrink, but can be deformed easily, and assumes a kind of wrinkled state in order to compensate for the loss of space. On the top side of figure 6, this state of the piece of foil 11 is diagrammatically shown. When the packaging tray 1 is filled with foodstuff 50 and protective gas, and sealed with the piece of cover foil 60, there is one factor resulting in a disappearance of some of the protective gas, and that is the gas absorbing capability of the foodstuff 50. Hence, as time passes, there is less protective gas in the interior space 40. In a conventional assembly comprising a packaging tray and a piece of cover foil 60, this phenomenon causes a deformation of the piece of cover foil 60, and possibly also a pressure difference over the piece of cover foil 60, as a result of which the barrier properties of the conventional assembly are deteriorated, and diffusion through the foil 60 and other portions of the assembly is more likely to occur. This has a negative impact on the shelf life of the foodstuff 50. However, in an assembly 2 according to the present invention, the oversized piece of foil 11 of the packaging tray 1

compensates for the loss of protective gas by straightening out to the necessary extent, wherein there is no reduction of the barrier capacity of the piece of foil 11. In fact, the loss of protective gas is compensated for by a decrease of the interior space 40, which only involves a change of the appearance of a portion of the packaging tray 1 , and which does not affect the piece of cover foil 60, as the wrinkled piece of foil 11 of the packaging tray 1 is deformed more easily than the piece of cover foil 60. Hence, using a packaging tray 1 according to the present invention for packing foodstuff 50 results in a prolonged shelf life, which is an important achievement of the present invention. The changed state of the piece of foil 11 of the packaging tray 1 is diagrammatically shown on the bottom side of figure 6.

Figure 7 illustrates the fact that the piece of foil 11 which is used in the packaging tray 1 according to the present invention may comprise portions 14 which are to be overlapped by the plastic. When the plastic is combined with the foil 11 , the barrier properties of the packaging tray 1 as a whole are even further improved.

It will be clear to a person skilled in the art that the scope of the present invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims.

An advantageous option existing within the scope of the present invention involves an additional step of heating the at least one piece of foil 11 that is used in the process of manufacturing a packaging tray 1. For example, an infrared heat source may be used to heat the piece of foil 11 to a certain temperature, just before the piece of foil 11 is positioned in a mould for injection moulding. By heating the piece of foil 11 first, before the plastic is provided and moulded to the piece of foil 11 , the extent to which the piece of foil 11 wrinkles when the plastic shrinks is

decreased. Hence, when it is desired to control the appearance of the piece of foil 11 in the packaging tray 1 in such a way that the extent to which the piece of foil 11 is wrinkled is not higher than necessary for fulfilling a barrier property conserving function, it is advantageous to perform a step of heating the piece of foil 11. When the piece of foil 11 is heated, it is achieved that the piece of foil 11 is expanded with respect to an unheated condition. Consequently, when the size of the window in the plastic which is moulded to the piece of foil 11 decreases, less wrinkles are obtained in the piece of foil 11 , as a shrinking process of the plastic starts at an expanded state of the piece of foil 11 , instead of a normal state of the piece of foil 11.

The present invention can be summarized as follows. A packaging tray 1 which is destined to be used for containing foodstuff 50, and which is formed with an open side 30 which is destined to be sealed with a piece of cover foil 60, especially a piece of cover foil 60 which is suitable for constituting a fluid-tight and gas-tight barrier between an interior space 40 of the tray 1 and surroundings of the tray 1 , is manufactured by providing a piece of foil 11 , and providing fluid plastic and moulding the plastic to the piece of foil 11. Prior to the moulding process, the piece of foil 11 is not deformed, so that it can be easily retained in an appropriate position. However, when the plastic cools down, the plastic shrinks, and the piece of foil 11 is forced to assume a more or less wrinkled state. Hence, deformation of the piece of foil 11 does take place, but only due to differences in shrinkage characteristics of the foil and the plastic, which occur after the moulding process. On the basis of the wrinkled appearance of the piece of foil 11 in the final packaging tray 1 , when the packaging tray 1 is filled with foodstuff 50 and sealed by means of a piece of cover foil 60, loss of gas from the interior space 40 of the packaging tray 1 can be compensated for by straightening out of the piece of foil 11 of the packaging tray 1 , which is

advantageous in view of the fact that such a process does not involve a deterioration of barrier properties of the packaging tray 1 , and does not affect the shielding function of the piece of cover foil 60 either.

For sake of completeness, it is noted that the term "undeformed" which is used in respect of the piece of foil 11 should be understood such as to indicate a state of the piece of foil 1 1 in which the piece of foil 1 1 has not deliberately been subjected to forces for pushing or pulling the piece of foil 1 1 from an initial state, which is mostly a flat state. For example, it may be so that the piece of foil 1 1 experiences forces during fixation in the mould, but such forces, which are caused by an action that is not primarily aimed at deforming the piece of foil 1 1 , are of another order, an should not be considered as influencing an undeformed state of the piece of foil 1 1 in the current context.