GAS BARRIER AND LIQUID ABSORBENT CONTAINER FOR THE PACKAGING OF FOOD PRODUCTS

Abstract

The present invention relates to a gas barrier and liquid absorbent container (1) for use in the modified atmosphere packaging of food products which tend to release liquids. The container of the invention comprises a base and upwardly extending side walls terminating in a continuous flange horizontally projecting from the side walls, and comprising an inner part of a liquid pervious material (20), and an outer part of a liquid and gas barrier material (10), said inner and outer parts being joined together at the side walls and being spaced apart from each other at the base to define an interspace (30). A circumferentially extending continuous portion (11) of the surface of the liquid and gas barrier material is exposed to provide an area for a gas barrier closing lid to be sealed. The invention further relates to a method of manufacture of said container, to its use in the packaging of food products under a modified atmosphere and to the gas-tight packages thus obtained.

Description

TECHNICAL FIELD

The present invention relates to gas barrier and liquid absorbent containers for use in modified atmosphere packaging of food products, in particular products that tend to release liquids. The invention further relates to a method of manufacture of said containers, to their use in the packaging of food products and to the food packages thus obtained.

DISCLOSURE OF INVENTION

It is common practice in retail stores to display certain types of foods, such as meat, poultry, fish and some vegetables, in individually wrapped containers. To improve the shelf life of the packaged product it is also common practice to package the food product under a modified atmosphere, that is an atmosphere other than air selected to prolong the shelf-life of the packaged product. In order to maintain such a modified atmosphere within the package gas barrier packaging materials are used. In general the term “gas barrier” is used with reference to the ability of a material to serve as a barrier to one or more gases, typically oxygen. This type of package offers the advantage that food packages, e.g. meat packages, can be prepared at a central location and then distributed to supermarkets and small shops. The appeal for the consumer is the possibility to see and inspect the packaged product.

However, in the case of liquid containing products, such as meat, poultry or fish, the liquids exuded from the food can create a negative visual impression on the consumer. Furthermore, the presence of these liquids in direct contact with the food product may promote the growth of bacteria inside the package, thus reducing the shelf-life of the product.

These problems have been generally overcome by the use of absorbent pads, which are introduced in the package between the product and the bottom of the container. Typically absorbent pads comprise a mat of an absorbent material enveloped in a moisture impermeable film that has a number of perforations on the surface not in contact with the product. The use of an absorbent pad suffers from the disadvantage of the labour cost involved in inserting it into a container, including the cost of a padding machine specifically designed for this purpose. Another disadvantage of this system is the poor aesthetics of the pad when filled with liquids, particularly blood. Furthermore when the pad is saturated with liquids it tends to stick to the food product and must be manually removed by the consumer when the package is opened.

As an alternative to the use of absorbent pads the use of double walled containers, provided with an internal reservoir for the collection of the exuded liquids, has been proposed in the prior art. WO 86/00275 discloses a rigid container comprising two or more thermoformed trays nested together; each tray is provided with a flange and all the flanges have the same size and are sealed together when a closing lid is sealed to the container for closing it.

WO 2007/059187 similarly discloses a container comprising a first tray and a second tray, provided with at least one hole, nested within the first tray to define a reservoir between the two, the flange of the first tray being completely covered by the flange of the second tray. The container is not provided with gas barrier properties.

FR 2,564,807 discloses a container comprising a tray and an insert, provided with a central opening, defining a reservoir at the bottom of the tray. The container is not provided with gas barrier properties.

It is therefore an object of the present invention to provide a gas barrier container for food packaging which is capable of absorbing, retaining and hiding the fluids exuded from the food product placed thereon without requiring the use of a separate pad and that at the same time provides an end package, obtained by sealing a gas barrier closing lid to the container flange, which is gas-tight.

In a first aspect the present invention is directed to a container suitable for food packaging which comprises: a first part made of a liquid and gas barrier material comprising a base and upwardly extending side walls terminating in a continuous flange outwardly projecting from the side walls, said flange being provided with an upper surface and a lower surface, a second part made of a liquid pervious material, comprising a base and upwardly extending side walls optionally terminating in a flange outwardly projecting from the side walls, said second part being coaxially positioned into said first part in such a way that the bases of said first and second parts are spaced apart from each other to define an interspace and said first and second parts are joined together at the side walls and, when a flange is present in said second part, at the flanges provided that a circumferentially extending continuous portion of said upper surface of the flange of the liquid and gas barrier material is exposed to provide an area for a closing lid to be sealed to the container.

When a gas barrier closing lid is sealed all around the exposed upper surface of the flange of the liquid and gas barrier material in the container of the present invention a gas-tight and liquid absorbent package is obtained.

In a second aspect the present invention is related to a method of manufacturing a container suitable for food packaging comprising:

• • forming a first part made of a liquid and gas barrier material, said first part comprising a base and upwardly extending side walls terminating in a continuous flange outwardly projecting from the side walls, said flange being provided with an upper surface and a lower surface;
  • forming a second part made of a liquid pervious material, said second part comprising a base and upwardly extending side walls optionally terminating in a flange outwardly projecting from the side walls;
  • coaxially inserting said second part into said first part in such a way that the bases of said first and second parts are spaced apart from each other to define an interspace and said first and second parts are joined together at the side walls and, when a flange is present in said second part, at the flanges provided that a circumferentially extending continuous portion of said upper surface of the flange of the liquid and gas barrier material is exposed to provide an area for a closing lid to be sealed to the container.

In a third aspect the present invention is related to a method of packaging a food product, said method comprising loading the product into the storage compartment of the container of the invention, optionally vacuumizing and/or gas flushing the container with a selected gas or gas mixture suitable to extend the shelf-life of the product and sealing a gas barrier closing lid to the circumferentially extending continuous portion of the upper surface of the flange of the liquid and gas barrier material exposed all around the container.

In a fourth aspect the present invention is directed to a gas-tight package for food products comprising a food product loaded in a container according to the present invention and a gas barrier closing lid, disposed over the food product, and sealed to the circumferentially extending continuous portion of the upper surface of the flange of the liquid and gas barrier material exposed all around the container. The product is held under a modified atmosphere suitable to prolong its shelf-life. The modified atmosphere is maintained within the package due to the gas barrier properties of both the container and the lid and to the gas-tight seal that they form in the circumferentially extending continuous portion of the upper surface of the liquid and gas barrier material exposed all around the container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a first embodiment of the container of the present invention;

FIG. 2 is a top view of a first embodiment of the container of the present invention;

FIG. 3 is a sectional view of a second embodiment of the container of the present invention;

FIG. 4 is a top view of the second embodiment of the container of the present invention with a first perforation pattern;

FIG. 5 is a top view of the second embodiment of the container of the present invention with a different perforation pattern;

FIG. 6 A-C are sectional views showing alternative perforation arrangements for the central area of the inner part of the container;

FIG. 7 is a sectional view of a first embodiment of the package of the present invention;

FIG. 8 is vertical cross-sectional view showing a first step of a first embodiment of the manufacturing method of the container of the present invention;

FIG. 9 is vertical cross-sectional view showing a second step of a first embodiment of the manufacturing method of the container of the present invention.

FIG. 1 shows a container 1 according to the present invention which comprises a first, or outer, part 10 and a second, or inner, part 20 coaxially inserted into the first part 10.

First part 10 of the container comprises a base 12 and upwardly extending side walls 13 terminating in a continuous flange 14. Flange 14 extends horizontally all around the contour of the container, outwardly projecting from the side walls. Flange 14 is provided with a lower surface 15. Flange 14 is provided with an upper surface 16 for the sealing of a closing lid.

Relative to the container as a whole first part 10 represents the outer part of the container. That is, base 12 and side walls 13 of the first part correspond to the base and the side walls of the container. In the remainder of the text, the term “outer part” may be exchanged with the term “first part” to indicate component 10 of the container.

As shown in FIG. 1, second part 20 comprises a base 22 and upwardly extending side walls 23 terminating in a flange 24. Typically flange 24 extends continuously around the perimeter of second part 20.

Relative to the container as a whole second part 20 represents the inner part of the container, that is base 22 and side walls 23 are the internal, food-contact surfaces of the container. In the remainder of the text, the term “inner part” may be exchanged with the term “second part” to indicate part 20 of the container.

In the embodiment shown in FIGS. 1 and 2 inner part 20 is provided with a flange 24 and the inner and outer parts are joined together at the side walls and in part of the flange area. Flange 24 of inner part is sized and/or positioned in such a way that it does not completely cover flange 14 of the outer part. As shown in FIG. 2, flange 24 of the inner part covers only partially flange 14 of the outer part of the container 10. A continuous portion 11 of the upper surface 16 of flange 14 is not covered by flange 24 providing an area for a closing lid to be sealed all around the circumference of the container. By sealing a gas barrier closing lid to the exposed surface 11 of the liquid and gas barrier material making up outer part 10 of the container it is thus possible to obtain a gas-tight package.

The feature of the container of the invention whereby the circumferentially extending continuous portion 11 of the liquid and gas barrier material of the outer part is available on the upper surface of the flange of the container for sealing to a closing lid is advantageous when the inner part of the container is made of a foamed material. If flange 24 were to cover completely flange 14 of the outer part the gas barrier closing lid would be sealed to the upper surface of flange 24. However, if inner part 20 is made of a foamed material the lateral edges of the foamed material would allow air to permeate and distribute through the inner part to eventually equilibrate the atmosphere inside the package with the atmosphere outside of it. It is only by providing an accessible surface of the liquid and gas barrier material of the outer part 10 that a gas-tight package can be obtained when sealing a gas barrier lid onto the container, regardless of the nature of the material used to make the inner part.

In an alternative embodiment of the container of the present invention, shown in FIGS. 3 to 5, inner part 20 does not comprise a flange. Thus, the container will comprise a first part 10 made of a liquid and gas barrier material with a base and upwardly extending side walls terminating in a continuous flange outwardly projecting from said side walls, said flange being provided with an upper surface and a lower surface, a second part 20 made of a liquid pervious material, comprising a base and upwardly extending side walls, said second part being coaxially inserted into said first part in such a way that the base of said second part is spaced from the base of said first part to define an interspace and said first and second parts are joined together at the side walls. According to this embodiment the flange of the container consists only of the liquid and gas barrier material making up the outer part.

The width of the continuous surface 11 of liquid and gas barrier material exposed along a closed line all around the flange area may vary depending on the size of the container but it is at least 1 mm, at least 1.5 mm, preferably at least 2 mm, even more preferably at least 3 mm. The width of the exposed surface 11 varies from the entire width of flange 14 of the first part, when the second part of the container has no flange, to at least 10%, 30%, 50% of the total width of flange 14, when the second part of the container has a flange 24. Typically the total width of the flange is at least 3 mm, at least 4 mm, at least 5 mm and up to 10 mm, 11 mm, 15 mm.

The size and position of inner part 20 is selected in such a way that, when inner part 20 is coupled to outer part 10, its base 22 does not contact base 12 of outer part. An interspace 30 is created between the two parts of the container to collect the fluids exuded from a product placed in the container.

As shown in FIG. 3 base 12 of outer part 10 may be provided with ribs to separate the interspace in compartments which may restrict the mobility of the collected fluids. Features other than ribs may be present in base 12 to obtain the same effect. When ribs or other equivalent features are present in base 12 it is preferred that they do not contact base 22 of the inner part. Thus the compartments within the interspace 30 are in fluid communication with each other. Known absorbent materials, e.g. absorbent pads, or polymers, such as salts of homo- or co-polymers of acrylic or methacrylic acids or partially saponified polyacrylate or polymethacrylate polymers, can be placed in interspace 30 to further restrict or eliminate the mobility of the collected fluids.

The side walls 23 of inner part 20 may have any length relative to the side walls of the outer part of the container, provided that when the two parts are coupled an interspace is left in the base area of the container and the side walls of the inner part do not exceed the length of the side walls of the outer part. Typically, the side walls 23 of the inner part are at least 1 mm, 2 mm, 5 mm long to allow joining of the outer and the inner parts of the container together. Preferably side walls 23 are at least 10 mm, 12 mm long. Even more preferably the length of side walls 23 coincide with the length of the part of side walls 13 of the outer part comprised between the flange of the container and the base 22 of the inner part as shown in FIG. 3.

Inner and outer parts 20 and 10 are firmly joined together at the side walls' area, for example by heat-sealing, radiofrequency sealing or gluing. Suitable adhesives may be placed between the side walls to improve the bonding between the outer and inner parts of the container.

Typically the distance between inner part 20 and outer part 10, i.e. the height of the interspace 30 ranges from 1 to 40 mm, from 1.5 to 30 mm, from 2 to 25 mm, from 2 to 20 mm. The distance between the bases of inner and outer parts of the container of the present invention may depend on the overall size of the container.

The base and the side walls of inner portion 20 define the storage area 40 of the container. Base 22 provides the resting surface for the packaged product. Inner part 20 is made of a liquid pervious material which allows the passage of liquids from the storage area 40 of the container into interspace 30. When container 1 is used for packaging food products which exude liquids, the liquid exuded from the product permeates through inner part 20 into interspace 30 and is effectively removed from the storage area of the container. The exuded liquid is therefore efficiently removed from direct contact with the product and from the sight of the consumer, improving both the shelf-life of the product and the appeal of the package.

Inner part 20 is liquid pervious. The term “liquid pervious” is used herein to indicate a material that allows the passage of a liquid from the storage area of the container to the interspace. The term applies equally to materials which are inherently capable to permit the passage of a liquid as well as to materials which require physical modifications, such as perforations, in order to permit the passage of a liquid.

Inherently pervious materials are for instance some porous materials. Examples of porous materials that may be pervious to liquids are some non-woven films or some void-containing films where the pattern of voids in the polymer matrix allows the passage of liquids by capillarity. Typically these liquid pervious films are made of polyolefin resins.

Pervious materials obtained by physical modification of an impervious substrate are preferably made of a thermoplastic material provided with perforations in at least part of its surface. Examples of suitable thermoplastic materials include polyethylenes, either homo- or co-polymers, such as ethylene-α-olefin copolymers, ethylene-cyclic olefin copolymers and ethylene-vinyl acetate copolymers, propylene homo- or co-polymers, styrene homo- or co-polymers, polyesters, polyamides, starches and the like polymers.

The thermoplastic material used to produce inner part 20 can be a monolayer or a multilayer structure.

In a preferred embodiment of the container of the present invention inner part 20 comprises at least one layer of a foamed material.

Any type of polymer than can be foamed can suitably be employed for inner part 20. Non-limiting examples of suitable polymers include ethylene homo- and/or co-polymers, such as ethylene-α-olefin copolymers and ethylene-vinyl acetate copolymers, propylene-based polymers, styrene homo- and/or co-polymers, polyesters, starches and the like polymers. Preferably the foamed material is made of a material selected from the group of styrene homo- and/or co-polymers, propylene-based polymers, and starches. The foamed material is made of styrene homo- and/or co-polymers. Alternatively, the foamed material is made of polyesters homo- and/or co-polymers, preferably of poly(lactic acid).

The thickness of the foamed layer is typically comprised between 0.1 mm and 10 mm, preferably between 0.5 mm and 7 mm, between 1 and 6 mm, between 1 and 4 mm.

The foamed material used for inner part 20 may have an open cell structure, that is a structure in which the cells are at least for their majority open, that is intercommunicating. Open cell foam materials may absorb and store liquids similarly to a sponge and facilitate the removal of liquid from the storage area of the container of the present invention. Suitable polymers used to make open cell foam materials are as indicated above for the foamed material layer. Generally, open cell foam sheets with an absorbency in the range of from 500 to 1,500 ml/m² can be obtained by suitably selecting the percentage of open cells, the size of the cells and the thickness of the layer itself.

Typically, the thermoplastic material used to produce inner part 20 is a multilayer structure comprising a foamed layer and at least one solid layer.

Said solid layer can be positioned on the side of the material that will be in contact with outer part 10. In this case the solid layer provides better adhesion between the inner and the outer parts of the container. Said adhesion layer can be of any thermoplastic material and the preferred ones are those providing a good adhesion to the surface layer of the gas barrier material making up outer part 10. The thickness of said adhesion layer is typically comprised between about 5 μm and about 90 μm, preferably between about 10 μm and about 85 μm, more preferably between about 15 μm and about 70 μm.

Inner part 20 can be made of a multilayer structure comprising a styrene homo- and/or co-polymer foamed layer and a solid adhesive layer. The adhesive layer comprises a material selected from the group consisting of polystyrene, high impact polystyrene, styrene-butadiene-styrene block copolymer, styrene-ethylene/butene-styrene block terpolymer, styrene-isoprene-styrene block copolymer and blends thereof, ethylene-unsaturated ester copolymers, such as ethylene-vinyl acetate copolymers, ethylene-butyl acrylate copolymers and the like. Preferably the solid adhesive layer comprises a blend of high impact polystyrene and styrene-butadiene-styrene block copolymer. More preferably the solid adhesive layer comprises a blend of from 50%, 60%, 70%, 80%, 90% by weight of high impact polystyrene and of from 10%, 20%, 30%, 40%, 50% by weight of styrene-butadiene-styrene block copolymer.

When the foamed layer has an open cell structure the solid layer is generally the food-contact layer and may improve the thermal molding behaviour of the open cell foam sheet when it is thermoformed. The solid layer, particularly an opaque one, may also provide an aesthetic function hiding from view the liquid absorbed in the open cell foam layer. Said solid food-contact layer can be of any thermoplastic material and the preferred ones are those providing for a good bond with the underlying open cell foam layer. Generally the same resin used for the open cell foam layer can be employed as a thick non-foamed layer for the food-contact layer. The thickness of said food-contact layer is typically comprised between about 5 μm and about 100 μm, preferably between about 10 μm and about 85 μm, more preferably between about 15 μm and about 80 μm.

The thermoplastic material used to produce inner part 20 may be provided with two solid layers, a food contact layer and an adhesive layer.

Inner part 20 can be made of a multilayer structure comprising a styrene homo- and/or co-polymer foamed layer, a styrene homo- and/or co-polymer solid food-contact layer and a solid adhesive layer. The adhesive layer comprises a material selected from the group consisting of polystyrene, high impact polystyrene, styrene-butadiene-styrene block copolymer, styrene-ethylene/butene-styrene block terpolymer, styrene-isoprene-styrene block copolymer and blends thereof, ethylene-unsaturated ester copolymers, such as ethylene-vinyl acetate copolymers, ethylene-butyl acrylate copolymers and the like. Preferably the solid adhesive layer comprises a blend of high impact polystyrene and styrene-butadiene-styrene block copolymer. More preferably the solid adhesive layer comprises a blend of from 50%, 60%, 70%, 80%, 90% by weight of high impact polystyrene and of from 10%, 20%, 30%, 40%, 50% by weight of styrene-butadiene-styrene block copolymer. The foamed layer can have an open cell structure.

Additional layers may be present in the multilayer material used to produce inner part 20. For instance the material may comprise an adhesive solid layer as described above, styrene homo- and/or co-polymer foamed layer (with a closed cell structure) and a styrene homo- and/or co-polymer foamed layer with an open cell structure in contact with the product as shown in FIGS. 6A and 6B.

In the embodiments of the container of the invention shown in FIGS. 1 to 5, perforations 28 are provided in inner part 20 to allow the fluids to pass from the storage space of the container into interspace 30. Preferably the perforations have a small diameter, typically lower than 5 mm. When inner part 20 of the container is mostly comprised of a close cell foamed material the perforations have a diameter of at least 2 mm, preferably of at least 3 mm. When inner part 20 of the container is mostly comprised of an open cell foamed material the perforations can have a smaller diameter of about 1.0 mm, preferably of about 1.5 mm.

Any number of perforations may be present to render inner part 20 liquid pervious. One single perforation could be used, although two or more perforations are preferred. The perforations may have all the same diameter or they may have different diameters. The perforations may be regularly distributed on the portion of inner part 20 which defines the internal base of the container. Alternatively, the perforations may be distributed across the base portion of inner part 20 according to a specific pattern. Many different perforation patterns can be devised depending for instance on the type of product to be packaged, the size of the container, the materials making up the inner part of the container and so on. A first pattern, shown in FIG. 2, comprises one perforation centrally located in the base portion of inner container 20 and a number of smaller perforations regularly positioned around the perimeter of said base portion. Alternative patterns are shown in FIGS. 4 and 5, wherein the perforations are localised in the central area of inner part 20.

Typically the number of perforations will depend on the average diameter of the perforations and may suitably be comprised between 20 and 40,000 per m², between 50 and 30,000 per m², between 50 and 20,000 per m², preferably between 100 and 10,000 per m². The perforations are preferably funnel-shaped towards the interspace and may have a round or slightly oval section.

When an open cell foam material is used to make inner part 20 perforations that extend only partially through the foam layer may be sufficient to allow the passage of the fluids from the storage area of the container to the interspace. Different perforation arrangements are shown in FIG. 6 A-C. Particularly advantageous is the use of partial perforations made in a staggered relationship on both the upper and the lower surface of the inner part (shown in the FIGS. 6A-C).

Inner part 20 can also be provided with channels (as the ones indicated with numeral 29 in FIGS. 4 and 5) or other equivalent features which guide the exuded fluids towards the apertures.

Outer part 10 of the container of the present invention is made of a liquid and gas barrier material. The liquid and gas barrier material may be a monolayer material of a gas barrier resin or, preferably, a multi-layer material wherein at least one layer has gas barrier properties, the whole structure being also liquid impervious. Polymers that are typically employed for the gas barrier layer in packaging applications are EVOH, polyesters, polyamides and blends thereof.

As used herein, the term EVOH includes saponified or hydrolyzed ethylene-vinyl acetate copolymers, and refers to vinyl alcohol copolymers having an ethylene comonomer content preferably comprised from about 28 to about 48 mole %, more preferably, from about 32 to about 44 mole % ethylene, and even more preferably, from about 36 to about 42 mole % ethylene, and a saponification degree of at least 85%, preferably at least 90%.

The term polyesters refers to polymers obtained by the polycondensation reaction of dicarboxylic acids with dihydroxy alcohols or alternatively by the ring-opening polycondensation reaction of lactones or lactides. Suitable dicarboxylic acids are, for instance, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid and the like. Suitable dihydroxy alcohols are for instance ethylene glycol, diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Examples of useful polyesters include poly(ethylene terephthalate), copolyesters obtained by reacting one or more dicarboxylic acids with one or more dihydroxy alcohols, poly(lactic acid), polycaprolactone, poly(butylene succinate) and the likes.

The term polyamide is intended to refer to polymers obtained by the polycondensation reaction of dicarboxylic acids with diamines or alternatively by the ring-opening polycondensation reaction of lactams. The term polyamide refers to both homo- and co- or ter-polyamides. This term specifically includes aliphatic polyamides or co-polyamides, aromatic polyamides or co-polyamides, and partially aromatic polyamides or co-polyamides, modifications thereof and blends thereof.

The thickness of the gas barrier layer in the outer part of the container will be set in order to provide the outer part of the container with an Oxygen Transmission Rate (OTR) lower than 20, lower than 15, preferably lower than 10 cm³/24 h per unit, when measured at 23° C. and 50% of relative humidity.

Preferably the liquid and gas barrier material is a multilayer material comprising in addition to a gas barrier layer at least a heat-sealable layer to give a hermetic seal with the closing lid by a conventional heat-sealing step. Said heat-sealable layer can comprise any thermoplastic material that can be heat-sealed to the sealing layer of the closing lid that will close the package. The preferred material will therefore depend on the material used for the heat-sealing layer of the closing lid. Generally said heat-sealable thermoplastic material will be selected among the polyolefins, such as ethylene homo- or co-polymers, propylene homo- or co-polymers, etc., the styrene homo- or co-polymers, such as for instance polystyrene, styrene-butadiene-styrene block copolymer, styrene-ethylene/butene-styrene block terpolymer, and styrene-isoprene-styrene block copolymer, and the hydrogenated derivatives thereof, and the polyester homo- and co-polymers, such as PETG, a glycol-modified polyethylene terephthalate, poly(lactic acid). Suitable blends may also include peelable blends to provide the container with an easy-to-open feature.

The thickness of said heat-sealable layer will be typically comprised between about 2 μm and about 100 μm, preferably between about 6 μm and about 80 μm, more preferably between about 10 μm and about 50 μm.

Additional layers, such as tie layers, to better adhere the gas barrier layer to the adjacent layers, may be present in the liquid and gas barrier film and are preferably present depending in particular on the specific resins used for the gas barrier layer and on the possible presence of a structural layer.

The liquid and gas barrier material used for the outer part of the container should have a sufficient rigidity to provide structural integrity to the whole container. When the liquid and gas barrier material is a monolayer structure this can be obtained by using a material of a sufficient thickness, e.g. higher than about 100 μm, 150 μm, 200 μm, 300 μm, or even 400 μm.

When the liquid and gas barrier material used for the outer part of the container is a multilayer structure the required rigidity is generally obtained by means of a structural layer. The structural layer can be made of any suitable thermoplastic material, such as for instance styrene homo- and/or copolymers, propylene homo- and/or copolymers, polyesters, polyethylenes, and the like polymers, and be either foamed or solid. The structural layer typically represents the outer surface of the end container.

The structural layer can be made of a foamed polymer. The structural layer can be of foamed polystyrene. Alternatively, the structural layer can be of foamed poly(ethylene terephthalate). Still alternatively the structural layer can be of foamed poly(lactic acid).

Alternatively, the structural layer can be made of a solid, cast polymer. The structural layer can be of cast polypropylene, poly(ethylene terephthalate), poly(lactic acid), high density polyethylene, polystyrene or high impact polystyrene.

The thickness of the structural layer is typically comprised between about 0.1 and 7 mm, depending mainly on whether it is a foamed or a cast material. Structural layers made of a cast solid material are preferably from 0.1 to 4 mm, from 0.5 to 3 mm thick. Structural layers of a foamed material are preferably from 1 to 7 mm, 2 to 6 mm thick. Thicker layers can however be employed, if needed, to get the required stiffness, provided that the end multilayer sheet can still be formed into a container of the desired shape.

In a first embodiment of the present invention the multilayer sheet used to form outer part 10 of the container will comprise (from the outermost layer to the innermost layer) a structural layer, typically of a material such as foamed polystyrene, foamed polyester or foamed polypropylene, or a cast monolayer sheet of e.g. polypropylene or polyester, a liquid and gas barrier thermoplastic film comprising a gas barrier layer and a heat-sealable layer.

In a second embodiment of the present invention the multilayer sheet used to form outer part 10 of the container will comprise (from the outermost layer to the innermost layer) a structural layer, typically of a material such as foamed poly(ethylene terephthalate) or foamed poly(lactic acid), or a cast monolayer sheet of e.g. poly(ethylene terephthalate) or poly(lactic acid) and a liquid and gas barrier heat-sealable layer.

The multilayer sheet can be obtained either by coextrusion of all the layers using well-known coextrusion techniques or by heat- or glue-lamination of the structural layer with the liquid and gas barrier film. The overall thickness of this multilayer sheet will typically be up to 9 mm, preferably it will be comprised between 0.1 and 8 mm and more preferably between 0.5 and 7 mm.

A container according to the present invention which may be particularly suitable for the packaging of food products like meat, poultry and fish comprises a first part made of a liquid and gas barrier material comprising a structural layer of foamed polystyrene, a gas barrier layer preferably comprising EVOH and a heat-sealable layer comprising a polyolefin and a second part made of a thermoplastic material comprising a foamed polystyrene layer provided with one or more perforations. Preferably, the second part is made of a thermoplastic material comprising a foamed polystyrene layer and an adhesive layer comprising a blend of from 50%, 60%, 70%, 80%, 90% by weight of high impact polystyrene and of from 10%, 20%, 30%, 40%, 50% by weight of styrene-butadiene-styrene block copolymer. The foamed polystyrene layer may optionally have an open cell structure.

A second container according to the present invention which may also be suitable for the packaging of food products like meat, poultry and fish comprises a first part made of a liquid and gas barrier material comprising a structural layer of foamed poly(lactic acid) and a second part made of a thermoplastic material comprising foamed poly(lactic acid) layer provided with one or more perforations.

A second object of the invention is a method for manufacturing a liquid and gas barrier container.

In the method of the present invention first and second parts of the container are formed into a tray-like shape comprising a base, upwardly extending side walls and a flange outwardly projecting from the side walls (optional for the second part) by means of known forming techniques. Suitable forming techniques are vacuum forming by which a preheated softened sheet is disposed on a molding portion having the shape of a desired product, the air present in the gap between the molding portion of the molding die and the sheet is eliminated by pulling vacuum so that the sheet conforms to the contours of the mold; match mold assist forming in which a plug matching the internal shape of the mold is used to guide the deformation of the sheet. Different techniques may be used to form first and second part of the container.

Once formed, second part is coaxially inserted into and joined to the first part in such a way that the base of said second part is parallel to and spaced from the base of the first part to define an interspace. The two parts are joined together at least along the side walls and in the flange area, when the second part of the container is provided with a flange.

Joining of the two parts can be done by heat-sealing, said term indicating the pressing of the two parts together with a heated tool, or alternatively the pressing of the two parts together when still in a heated state right after the forming operation has taken place. Alternatively, the two parts may be joined together by radiofrequency welding. Still alternatively the two parts may be joined together by gluing, for instance by means of a hot-melt adhesive provided on either one of the two parts or by means of a suitable heat-activated or light-activated adhesive. Preferably, the two parts of the container are joined together by heat-sealing. Joining by heat-sealing is facilitated by the presence of an adhesive layer between the inner and outer parts of the container, preferably of an adhesive layer positioned on the side of the inner part of the container facing the outer part (i.e. the side facing away from the product in the final package).

When second, or inner, part of the container is made of a thermoplastic material rendered liquid pervious by perforations, said perforations can be made in the thermoplastic material at any time before, during or after the forming of the second part. Typically the thermoplastic material is perforated in the mold during the forming operation. Alternatively, the perforations can be made in the already formed part after cooling of the thermoplastic material.

Forming of the two parts can be done separately and the parts brought together and joined afterwards, in a separate step. Alternatively forming of the inner and outer parts can take place substantially simultaneously in one single forming operation.

In a first embodiment of the manufacturing method of the present invention first and second parts are formed independently of each other in separate forming operations and are then coupled together in a third operation. Joining of the two parts to provide the final container may be done by heat-sealing, radiofrequency welding, gluing or the like.

In an alternative embodiment, first and second parts are formed simultaneously in the same mold with the base of the first part oppositely facing the base of the second part. At the end of the forming operation the second part is inverted, coaxially inserted into and firmly joined to the first part. Joining can be done by anyone of the methods discussed for the first embodiment.

In still another alternative embodiment of the manufacturing method of the present invention, first and second parts of the container are coaxially formed and joined together simultaneously in the same mold in one single operation. The forming and joining steps of the method according to this embodiment are schematically illustrated in FIGS. 8 and 9 which are vertical cross-sectional views taken through a forming mold suitably designed to carry out the coaxial forming operation. As shown in FIGS. 8 and 9 forming is done using a vacuum forming technique.

FIG. 8 shows the mold 200 in its closed state during the forming step of the cycle. Mold 200 comprises a female cavity 201 and a male plug 202. Male plug 202 is designed so that at its maximum extension into female cavity 201 there will be no contact between their respective surfaces, in particular in the area defining the base of the final container. This will produce a gap between the two formed webs of material in the area of the base and an interspace will be formed in the final container.

Mold 200 further comprises a platen 203 positioned between female cavity 201 and male plug 202. Platen 203 is provided with an aperture which is aligned with both the female cavity and the male plug.

A first web of a thermoplastic material 205 and a second web of liquid and gas barrier material 206 are positioned on opposite sides of platen 203. In particular first web 205 is positioned between platen 203 and male plug 202, whereas second web 206 is positioned between platen 203 and female cavity 201. Platen 203, or any other suitable equivalent mean, ensures that first and second webs 205 and 206 are not joined together in the area of the flange and its immediate vicinity during the forming operation.

At the stage shown in FIG. 8 both first and second webs 205 and 206 have been preheated to a suitable forming temperature. For instance, when both the first and the second web are mostly made of foamed polystyrene material the webs are preheated to a temperature of from about 120° C. to about 160° C. Heating of the two webs is carried out with conventional heating means, such as an heated oven. If required further heating may be provided to the webs at this stage of the forming process, for instance by introducing heated air between the webs through a suitably designed aperture provided in platen 203 (not shown). Such an aperture could be used also to introduced pressurised air between the webs to assist with the forming of the parts.

As shown in FIG. 8 first web of thermoplastic material 205 is deformed to the surface shape of the male plug 202, and second web of liquid and gas barrier material 206 is deformed to the surface shape of the female cavity 201. To facilitate shaping, vacuum may be applied to the underside of both female cavity and male plug.

As shown in FIG. 9, once male plug 202 reaches its maximum extension into female cavity 201 first web 205 is pressed into contact with second web 206 which is still in contact with the inner surface of female cavity 201. Male plug 202 and female cavity 201 are so designed that the two webs of material are pressed into contact only in the area of the side walls and partially in the area of the flange, when the inner part of the container is provided with a flange. The pressure exerted at this stage on the still heated webs effectively joins together the two webs. The two webs are separated the one from the other in the area of the base of the container to define an interspace for collecting the liquids exuded by the product that will be packaged in the container.

To facilitate the joining of first and second part of the container within the mold the formed portion of thermoplastic material which corresponds to the inner part of the container (20) may be severed from the web 205 while still in the mold. Typically the cutting of the formed portion 20 from web 205 takes place during the extension of male plug 202 into female cavity 201, for instance by means of a cutting blade positioned in a gap between male plug 202 and platen 203. Alternatively, platen 203 may function as a cutting tool to severe the formed portion 20 of first web 205 from the web itself.

At the end of the forming cycle container 1 is released from the mold. Generally at this stage container 1 is still connected to second web 206 and ready to be severed from said web in a subsequent cutting station.

When second, or inner, part of the container is made of a thermoplastic material rendered liquid pervious by perforations, said perforations can be made at any time before, during or after the forming of the container. The perforations in the inner part of the container can be produced with conventional perforating means in a separate step after the container has been released from the mold. Alternatively, the perforations can be produced during the thermoforming step, by providing male plug 202 with suitable perforating means. Still alternatively, a thermoplastic web 205 already provided with perforations can be fed to the forming operation.

A further specific object of the invention is the use of a container according to the present invention in the packaging of a food product under a modified atmosphere.

Modified atmosphere packaging is defined as “the packaging of a perishable product in an atmosphere which has been modified so that its composition is other than that of air”. The air surrounding the food product in the package is changed to another composition selected among those capable to prolong the shelf-life of perishable products like meat, poultry, fish and some vegetables.

In the packaging method according to the present invention the food product is loaded in the storage compartment 40 of container 1 (FIG. 7).

The atmosphere inside the package is modified before a gas barrier closing lid is heat-sealed to the container. The atmosphere can be modified either by simply flushing with a suitable gas or gas mixture or by firstly evacuating and then back-filling with a suitable gas or gas mixture the space between the container and the closing lid. The gas or the gas mixture is selected to maximize the shelf-life of the product. Preferred gases to replace evacuated air include oxygen, carbon dioxide, nitrogen, argon and mixtures thereof.

Once this step has been completed, the gas barrier closing lid is heat-sealed along a continuous sealing line to the portion 11 of the upper surface of the flange of the liquid and gas barrier material exposed of the all around the container. A gas-tight hermetic seal is obtained that allows to maintain the modified atmosphere within the package.

Products which typically exude liquids and for which the use of the container of the present invention would be advantageous are for instance meat, poultry, fish and some vegetable products.

The packaging method of the invention may be performed on currently available tray lidding machines, either automatic or manual, like the ones commercially supplied by, e.g., Sealpac GmbH, Multivac GmbH or Mondini SpA. In this type of machines pre-formed containers are loaded onto the machine and, after loading of the product in the container, sealing of a closing lid is carried out by means of a sealing frame, which forms a continuous seal around the circumferentially extending upper surface 11 of the liquid and gas barrier material on the flange of the container. When inner part of the container has a flange that extends partially over the flange of the outer part the closing lid may be heat-sealed also to the portion of the liquid pervious material present on the flange.

FIG. 7 shows an example of a package 100 thus obtained, wherein a product 101 is placed into a tray-shaped container 1 (as illustrated in FIG. 3). The package is then closed by sealing a gas barrier closing lid 102 to the circumferentially extending portion 11 of the upper surface of the flange of the liquid and gas barrier outer part 10 along a closed line around the container. The closing lid can be a flexible, semi-rigid or rigid film or sheet. The closing lid may have a thickness ranging from 10 to 250 μm, from 12 to 150 μm, from 15 to 80 μm, from 15 to 60 μm. It can be stretchable or not, oriented or non-oriented and if oriented it can be heat-shrinkable or heat-set.

Closing lid 102 may be a monolayer or a multilayer material. Closing lid 102 is provided with gas barrier properties in order to preserve the modified atmosphere inside the package. Suitable gas barrier lids typically have an oxygen transmission rate at 23° C. and 0% relative humidity lower than 150, lower than 130, preferably lower than 100 cm³/m²·24 h·atm (evaluated according to ASTM method D-3985 and using an OX-TRAN instrument by Mocon). Preferably closing lid 102 is a multilayer structure comprising at least a gas barrier layer and a heat-sealable layer. The heat-sealable layer will be selected to create with the exposed upper surface of the flange of the liquid and gas barrier outer part of the container a hermetic, gas-tight seal. Suitable resins for the heat-sealable and the gas barrier-layers being as indicated above for the liquid and gas barrier layer of the container. Typically closing lid 102 will be provided with antifog properties. Suitable films to be used as gas barrier lid 102 are for instance those described in EP-A-692,374, EP-A-739,398, EP-A-797,507, EP-A-801,046, EP-A-881,966, EP-A-987,103 or WO 2001/68363.

In a preferred embodiment of the package of the invention gas barrier closing lid 102 is a multilayer heat-shrinkable film provided with antifog properties. The film comprises a gas barrier layer comprising EVOH and at least one heat-sealable layer comprising one or more polymers selected from the group of ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers and propylene-α-olefin copolymers.

In an alternative embodiment gas barrier closing lid 102 is a polyester based film provided with a heat-sealing layer capable of sealing to a polyester sealing surface on the container.

Without prejudice to the principle of the invention, the details of execution and the embodiments may vary from what has been described by way of illustration, while remaining within the scope of the invention as defined by the appended claims.

Claims

1. A container for the packaging of food products comprising a first part made of a liquid and gas barrier material comprising a base and upwardly extending side walls terminating in a continuous flange outwardly projecting from said side walls said flange being provided with an upper surface and a lower surface, a second part made of a liquid pervious material, comprising a base and upwardly extending side walls optionally terminating in a flange outwardly projecting from said side walls, said second part being coaxially positioned into said first part in such a way that the bases of said first and second parts are spaced apart from each other to define an interspace and said first and second parts are joined together at the side walls and, when a flange is present in said second part, at the flanges provided that a circumferentially extending continuous portion of said upper surface of the flange of the liquid and gas barrier material is exposed to provide an area for a closing lid to be sealed to the container.

2. The container according to claim 1 wherein no flange is present in said second part and said first and second parts are joined together only at the side walls.

3. The container according to any preceding claim wherein the liquid pervious material is a thermoplastic material provided with one or more perforations.

4. The container according to any preceding claim wherein the liquid pervious material comprises a foamed material.

5. The container according to any preceding claim wherein the liquid and gas barrier material of said first part is a multilayer material comprising a structural layer, a gas barrier layer and a heat-sealable layer.

6. The container according to any preceding claim comprising a first part made of a liquid and gas barrier material comprising a structural layer of foamed polystyrene, a gas barrier layer and a heat-sealable layer and a second part made of a thermoplastic material comprising a foamed polystyrene layer provided with one or more perforations.

7. The container according to claim 6 wherein said second part is made of a material further comprising an adhesive layer positioned on the side of said second part facing said first part and wherein said adhesive layer comprises a blend of high impact polystyrene and styrene-butadiene-styrene block copolymer.

8. The container according to any one of claims 1 to 4 comprising a first part made of a liquid and gas barrier material comprising a structural layer of foamed poly(lactic acid) and a second part made of a thermoplastic material comprising a foamed poly(lactic acid) layer provided with one or more perforations.

9. A method of producing a container of any one of claims 1 to 8 comprising the steps of:

forming a first part made of a liquid and gas barrier material, said first part comprising a base and upwardly extending side walls terminating in a continuous flange outwardly projecting from said side walls, said flange being provided with an upper surface and a lower surface;

forming a second part made of a liquid pervious material, said second part comprising a base and upwardly extending side walls optionally terminating in a flange outwardly projecting from said side walls;

bringing said second part coaxially into said first part in such a way that the bases of said first and second parts are spaced apart from each other to define an interspace and said first and second parts are joined together at the side walls and, when a flange is present in said second part, at the flange provided that a circumferentially extending continuous portion of said upper surface of the flange of the liquid and gas barrier material is exposed to provide an area for a closing lid to be sealed to the container.

10. The method according to claim 9 wherein no flange is present in said second part and said first and second parts are joined together only at the side walls.

11. The method according to claim 9 or 10 wherein said first and second parts are formed simultaneously and joined coaxially together in the same mold.

12. The method according to any one of claims 9 to 11 wherein said first and second parts are joined together by heat-sealing.

13. A method of packaging a food product comprising loading said product in the container of any one of claims 1 to 8; optionally vacuumizing and/or gas flushing the container with a suitably selected gas or gas mixture and closing said container by means of a gas barrier closing lid sealed to the circumferentially extending continuous portion of the upper surface of the flange of the liquid and gas barrier material exposed around the circumference of the container.

14. A gas-tight package for food products comprising a food product loaded in a container of any one of claims 1 to 8 closed by a gas barrier closing lid, disposed over the food product, and sealed to the circumferentially extending continuous portion of the upper surface of the flange of the liquid and gas barrier material exposed around the circumference of the container.

15. The package according to claim 14 wherein the food product is meat, poultry or fish.