WO2006011842A1

WO2006011842A1 - Permeable packaging material

Info

Publication number: WO2006011842A1
Application number: PCT/SE2005/001167
Authority: WO
Inventors: Karl Nideborn; Mattias Bragwad; Per-Axel Olsson
Original assignee: Amcor Flexibles Europe A/S
Priority date: 2004-07-30
Filing date: 2005-07-19
Publication date: 2006-02-02
Also published as: SE0401959D0; EP1771301A4; EP1771301A1; NO20070846L

Abstract

The present invention relates to a packaging material, and especially to a rigid permeable packaging material for perishables having a microbiological activity, a package of said packing material, and a method for packaging the perishables. The packaging material comprises a first material component of an ultra-high or high barrier material, and a second material component of a low barrier material, said first and second material components being configured to provide a carbon dioxide gas barrier and an oxygen gas barrier that can be controlled independently of the thickness of the packaging material.

Description

PERMEABLE PACKAGING MATERIAL

Technical field

The present invention relates to a packaging material, and especially to a rigid permeable packaging material for perishables having a microbiological activity, and a package and a method for packaging perishables.

Background of the invention

It is becoming more and more common that different types of perishables are packed in finished consumer package. Usually, the packaging operation of the perishables takes place centrally for outward distribution of the packages to supermarkets, or the like. It is important that the package and its subsequent handling and the storage of the packed perishables take place under such condition and employing such methods that the packed food is of a good quality and in a desired condition when reaching the consumer.

Some natural processes have to be slowed down in order not to deteriorate the quality of the packed perishables or the appearance of the package. For example, it is desirable to avoid oxidation, which could occur by a too large amount of oxygen coming into contact with the packed perishables. Certain foods continue to release gases even after packaging. For example, an unriped cheese releases carbon dioxide gas, CO₂, during the process of ripeness. The release of carbon dioxide gas can be a drawback, especially if the package has a low permeability for carbon dioxide gas, since the gas will build up in the package and forming a package having a balloon-like shape. For many customers, perishables stored in such a ballooned package would not be attractive to buy.

Flexible packaging materials for packing of cheese are known on the market and are commonly used for vacuum packaging. These flexible materials are low barrier material, often laminates, and are usually built up of a polyamide, PA, and polyethylene, PE, combination, or other polymers having a low E-modulus which make them unfeasible for rigid packages. Further, it is not sufficient to increase the thickness of the laminates to obtain a rigid package. Furthermore, these flexible materials usually have a carbon dioxide permeability that is larger than the oxygen permeability. For example, the oxygen permeability is approximately 30 - 50 cc/mf-day-atmosphere and the carbon dioxide permeability is approximately 100 - 200 cc/m²-day-atmosphere. The US patent US 6,746,762 discloses a film selectively permeable to carbon dioxide gas and a food packing film comprising the same. The film consists of a laminate film including at least three layers composed of an outer layer, an intermediate layer and an inner layer, in which the outer layer and the inner layer include a thermoplastic resin and the intermediate layer includes a film made of chitosan. Chitosan is a material providing a barrier in between the low and medium barriers as they are defined below. The selectively permeable film provides a ratio of the carbon dioxide gas transmission, CO₂TR, to the oxygen gas transmission, O₂TR₅ CO₂TR/O₂TR, of 15 or higher.

A drawback with the film disclosed by US 6,746,762 is that the carbon dioxide gas barrier and the oxygen gas barrier cannot be controlled independently of each other. The transmission of carbon dioxide gas through the film would for example be too large if a sufficient oxygen gas barrier is provided. When too much carbon dioxide gas, which provides a low pH in the package, diffuse through the packaging film, the pH will increase and the bacterial growth will be promoted. In order to retain a sufficient amount of carbon dioxide within the package, the oxygen gas barrier would have to be less. However, a smaller oxygen gas barrier would lead to the risk of the packed perishables going mouldy since the transmission of the oxygen gas through the packaging film would be too high.

Another drawback with the film disclosed by US 6,746,762 is that it is impossible to manufacture rigid packages of the film without increasing the thickness of the package.

The US patent 5,763,095 discloses a packaging film for packaging oxygen sensitive products which emit carbon dioxide gas, such as a high gassing cheese. The packaging film is a multilayer film having a CO₂:O₂ transmission rate higher than 3.0; and has a CO₂ transmission rate of at least 400 cc/m²-day-atmosphere. A drawback with the film disclosed by US 5,763,095 is that the packaging film is flexible and that it is impossible to manufacture rigid packages of the film without increasing the thickness of the package. Since an increased thickness will affect the carbon dioxide gas barrier and the oxygen gas barrier, the favourable barrier properties of the flexible material will be dramatically changed, either to be too high or too low, i.e. to provide a too low permeability or a too high permeability. Therefore, if the packaging film of US 5,763,095 was made rigid it would not be suitable for packaging oxygen sensitive products which emit carbon dioxide gas, since the gas barrier would be changed.

It would be desirable to provide a rigid package and a rigid package material that makes it possible to control the carbon dioxide gas barrier and the oxygen gas barrier independently of the package thickness.

For some perishables, e.g. cheese, it is desirable to provide a package allowing the cheese to mature without negatively affecting the appearance of the retailed product, i.e., without negatively affecting the shape of the package. In case the packed food is a cheese, it would be desirable to provide a package having a controlled permeability for carbon dioxide gas, whereby the cheese can be able to ripen when stored in the package without causing the package to deform into a ballooned package. Such a package would have the advantage that younger, i.e. immature, cheeses can be packed, transported and delivered to stores. When packaging cheese, several problems have to be solved. For example, young cheeses have, especially at summer time, a high production of carbon dioxide gas. In a common consumer package with sliced cheese, the emission of carbon dioxide gas can often exceed 3 — 5 cm³ per day. However, the emission of carbon dioxide gas from the cheese depends on several factors, such as the cheese type, season, storage time and temperature after packaging, and if the cheese is sliced, also the storage time before slicing. The emission of carbon dioxide gas depends also on the maturity of the cheese, since a younger, more immature cheese has a larger emission of carbon dioxide gas than an older more mature cheese.

If the emission of carbon dioxide is large, i.e. larger than the diffusion of carbon dioxide out from the package, the result would be packages having a balloon-like shape. It should also be noted that cheese is sensitive to oxygen and if the oxygen barrier of the package is too low, mould would occur in the package, i.e. the cheese would go mouldy. Therefore, it is desirable to provide a package and a method of packaging having a controlled permeability for carbon dioxide gas and oxygen gas. An object of the present invention is to provide a rigid packaging material feasible for packing of perishables having a microbiological activity without negatively affect the quality of the perishables or the appearance of the package and a packaging method feasible for packing perishables.

An aim of the object is to provide a packaging material having a chosen carbon dioxide and oxygen gas barrier, which barriers can be chosen independently of the thickness of the package material or package.

Another aim is to avoid ballooning of the package.

Yet another aim is to avoid collapsing of the package, which will occur if the carbon dioxide barrier is too low. A further aim is to avoid a too large amount of oxygen gas in the package, and thereby preventing the packed perishables from going mouldy.

Another aim is to provide a package that is transparent and thermo formable. Yet another aim is to provide a package wherein a packed cheese can ripen without deforming the package.

Summary of the invention

In the description, the following definitions will be used: A low barrier material, i.e. a high permeable material, is a material having an oxygen gas barrier of more than approximately 200 cm³/(m²-24h-atm) at 23⁰C and 50 % relative humidity on a flat film. Examples of such material are polystyrene (PS), polyethylene (PE), and polypropylene (PP), at commonly used thicknesses, i.e. in the range of 200 - 600 microns.

A medium barrier material is a material having an oxygen gas barrier in the interval of approximately 30 - 100 cm³/(m²-24h-atm) at 23⁰C and 50 % relative humidity on a flat film. Examples of such material are poly lactic acid (PLA) polymers, oriented polyamide (OPA), and polyamide (PA), at commonly used thicknesses, i.e. in the range of 50 — 500 microns. For OPA, it should be noted that the usual thicknesses are in the range of 9 - 15 microns.

A high barrier material is a material having an oxygen gas barrier in the interval of approximately 4 - 30 cm³/(m²-24h-atm) at 23⁰C and 50 % relative humidity on a flat film. Examples of such material are co-polyesters, such as amorphous polyethylene terephthalate (APET) or glycol modified polyethylene terephthalate (PETG); polyvinylchloride (PVC); and polyamide (PA), at commonly used thicknesses, i.e. in the range of 50 — 600 microns.

An ultra high barrier material is a material having an oxygen gas barrier of less than approximately 4 cm³/(m²-24h-atm) at 23⁰C and 50 % relative humidity on a flat film. Examples of such material are copolymers of ethylene and vinyl alcohol (EVOH, PVOH), high-gas barrier nylon such as MXD-6, at commonly used thicknesses, i.e. in the range of 2 - 20 microns. Other examples are inorganic coatings such as AlOx, and SiOx. The present invention fulfils the above-mentioned object and aims, amongst others, by providing a packaging material that comprises a low barrier material and a high barrier material. The low and high barrier materials can be co-extruded or laminated in such a fashion, that a barrier within a rather narrow barrier region is achieved. In order to provide a favourable environment for packed perishables, the region of the oxygen gas barrier is preferably in the range of approximately 20 - 100 cm /(m -24h-atm), more preferably in the range of approximately 30 — 90 cm³/(m²-24h-atm), and the carbon dioxide barrier in the range of approximately 80 - 400 cm³/(m²-24h-atm), more preferably in the range of approximately 120 - 360 cm³/(m²-24h-atm), i.e. providing a relationship of approximately 4:1 between the transmission of carbon dioxide and the transmission of oxygen. If the thickness of the packaging materials or laminates is in the interval of approximately 150 to 700 microns, a package that is rigid, transparent, thermo formable and stiff is obtained. The present invention is defined in the independent claims. Embodiments of the invention are set out in the dependent claims. Detailed description of the invention

The present invention will now be described in more detail. In this description text, perishables refer to food that go bad or whose quality deteriorate after a short length of storage time if not stored optimally. In order to exemplify perishables, embodiments of the invention are described with reference to a packaging material for cheese, a package and a method for packing cheese. However, it should be understood that the inventive packaging material, package and packaging method can be used for other types of food having a microbiological activity, or a tendency to generate or release carbon dioxide gas and to which oxygen gas could be harmful in a certain concentration. Examples of such foods are e.g., coffee, fruits, or vegetables.

The cheese can be natural cheese such as Cheddar, Gruyere, Emmenthaler, and Gouda, or process cheese containing these, sliced and non-sliced. The coffee includes bean-like and pulverised-like coffee after roasting. As mentioned above, the inventive packaging material comprises a low barrier material and a high barrier material selected such that the carbon dioxide gas barrier and the oxygen gas barrier can be controlled independently of the thickness of the packaging material. In other words, the barriers are controllable independently of the thickness of the packaging material. As understood by the skilled person, the carbon dioxide gas barrier and the oxygen gas barrier cannot be controlled independently of each other. The low and high barrier materials can be co-extruded or laminated in such a fashion, that a barrier within a rather narrow barrier region is achieved. In order to provide a favourable environment for the . packed perishables, the region of the oxygen gas barrier is preferably in the range of approximately 30 - 90 cm³/(m²-24h-atm) at 23⁰C and 50% relative humidity. If the thickness of the barrier materials is in the interval of approximately 150 to 700 microns, a package that is rigid, transparent, thermo formable and stiff is obtained. It should however be understood that the required thickness of the barrier materials varies with the size of the package. According to the invention, the rigid permeable packaging material for perishables having a microbiological activity, comprises a first material component of an ultra-high or high barrier material, and a second material component of a low barrier material, said first and second material components being configured to provide a carbon dioxide gas barrier and an oxygen gas barrier that can be controlled independently of the thickness of the packaging material. The first material component is configured to control the permeability of carbon dioxide gas and oxygen gas through said packaging material and the second material component is configured to provide stability to said packaging material.

Further, one of said first and second components is configured to control the mechanical stiffness and the strength of the packaging material.

Exemplifying embodiment APETZ(PE or PP)ZAPET

According to an embodiment of the invention, the first material component is configured to provide stability, thermo formability and transparency to the packaging material. The second material component is configured to provide a distance between two layers of the first material component. Further, the first material component can be a co-polyester such as amorphous polyethylene terephthalate, APET, or a PETG-type co-polyester, i.e. a co-polyester of glycol modified polyethylene terephthalate type. The second material component can be polyethylene, PE, or polypropylene, PP. The first material component can constitute an outer and an inner layer, each of which having a thickness in the range of approximately 20 - 80 microns, e.g. 50 microns, and the second material component can constitute an intermediate layer having a thickness in the range of approximately 230 — 600 microns, e.g. 300 microns. In this embodiment, a tie can be applied between the different layers. The tie can for example be MAH, i.e. Maleic AnHydride types of copolymer.

It should be noted that even a packaging material consisting of the layers: APETZPEZAPET is stiff even with a thick polyethylene layer, if the APET layers constitute more than 10+10% of the total structure, the E-modulus APET is 1900 NZmm² and the low density polyethylene, LDPE, is 300 NZmm². The PETG-type or other co-polyester mentioned above has preferably the property of remaining totally amorphous. Exemplifying embodiment PETG/PS or PETG/PS/PETG

According to yet another embodiment of the invention, the second material component can be configured to provide stability, thermo formability and transparency to said packaging material.

Further, the first material component can be a co-polyester such as glycol modified polyethylene terephthalate, PETG, and the second material component can be polystyrene, PS. The second material component can for example be a transparent polystyrene terpolymer. The first material component can constitute a first layer and the second material component can constitute a second layer of a packing material.

The first material component can further constitute a third layer. The first and third layers can constitute inner and outer layers of the packing material and the second layer can constitute an intermediate layer of the packing material. The second layer of the second material component is further configured to provide a distance between the two layers of the first material component.

The layer or layers of said first material component has preferably a total thickness in the range of approximately 40 — 140 microns, e.g. 90 microns. Thus, if the packing material comprises two layers of the first material component, each of the layers has a thickness in the range of approximately 20 — 70 microns, e.g. 45 microns. The second layer can have a thickness in the range of approximately 270 - 600 microns, e.g. 290 microns.

In this embodiment, a tie, e.g. a polystyrene terpolymer or ABS, can be applied between the different layers.

Exemplifying embodiment PA/PS and PAZ(PS or PP)TPA

According to yet another embodiment, the second material component further is configured to provide stability, thermo formability, transparency and a distance between two layers of said first material component. The first material component can be polyamide, PA, and the second material component can be polystyrene, PS, or polypropylene, PP. The first material component can constitute a first layer and the second material component can constitute a second layer of a packing material.

The first material can further constitute a third layer. The first and third layers can constitute inner and outer layers of the packing material and the second layer can constitute an intermediate layer of the packing material.

The layer or layers of the first material component has preferably a total thickness in the range of approximately 10 - 80 microns, e.g. 60 microns. Thus, if the packing material comprises two layers of the first material component, each of the layers has a thickness in the range of approximately 5 - 40 microns, e.g. 30 microns. The layer of the second material component can constitute an intermediate layer having a thickness in the range of approximately 150 - 700 microns, e.g. 350 microns.

Further, a suitable tie can be applied between the different layers.

Exemplifying embodiment PS/EVOH/PS

According to a further embodiment of the invention, the second material component is configured to provide stability, thermo formability, and transparency to the packing material. The first material component can be a copolymer of ethylene and vinyl alcohol, EVOH, and the second material component can be polystyrene, PS. In order to tailor-make the transmission rate of EVOH, the EVOH is preferably blended with an inorganic filling material or a polyethylene based copolymer. If not blended, the EVOH could be too tight for some applications. Further, the first material component, EVOH-blend, can constitute an intermediate layer having a thickness in the range of approximately 2 - 20 microns, e.g. 4 microns. The second material component can constitute an inner and an outer layer, each of which having a thickness in the range of approximately 75 — 350 microns, e.g. 200 microns.

Further, a tie, e.g. a polyethylene based copolymer, can be applied between the different layers.

The first and second material components of the inventive packing material can be co-extruded or laminated in order to form an end product, e.g. a package. The inventive packaging material is further intended for packing of perishables having a microbiological activity, such as cheese, coffee, fruits, or vegetables.

The present invention also refers to a permeable rigid package for perishables having a microbiological activity, which package comprises the inventive packaging material.

Further, the invention refers to a method for packaging perishables having a microbiological activity, the method comprises the step of using the inventive packaging material. The inventive packaging material can be used for packing products or perishables under vacuum or in a modified gas mixture, e.g. by modified atmosphere packaging (MAP).

It should be understood that the first and second material components can be selected among other ultra high or high barrier materials and low barrier materials, respectively, than those mentioned above. Further, it should be understood that embodiments of the inventive packing material described above can be provided with a sealing layer of polyethylene or polyethylene peel in order to provide an easy-open solution.

Claims

1. A rigid permeable packaging material for perishables having a microbiological activity, said packaging material comprising a first material component of an ultra- high or high barrier material, and a second material component of a low barrier material, said first and second material components being configured to provide a carbon dioxide gas barrier and an oxygen gas barrier that can be controlled independently of the thickness of the packaging material.

2. The packing material of claim 1, wherein said first material component is configured to control the permeability of carbon dioxide gas and oxygen gas through said packaging material.

3. The packaging material of claim 1 or 2, wherein one of said first and second components is configured to control the mechanical stiffness and the strength of the packaging material.

4. The packing material of any of claim 1 - 3 , wherein the region of the oxygen gas barrier is in the range of approximately 20 — 100 cm³/(m²-24h-atm) and the region of the carbon dioxide barrier is in the range of approximately 80 - 400 cm³/(m²-24h-atm), thereby providing a relationship of approximately 4:1 between the transmission of carbon dioxide and the transmission of oxygen.

5. The packing material of any of claim 1 — 4, wherein said first material component is configured to provide stability, thermo formability and transparency to said packaging material, and said second material component is configured to provide a distance between two layers of said first material component.

6. The, packaging material of claim 5, wherein said first material component is a co-polyester such as amorphous polyethylene terephthalate. APET, or a PETG-type or other co-polyester, and said second material component is polyethylene, PE, or polypropylene, PP, said first material component constitutes an outer and an inner layer, each of which having a thickness in the range of approximately 20 - 80 microns, e.g. 50 microns, and said second material component constitutes an intermediate layer having a thickness in the range of approximately 230 - 600 microns, e.g. 300 microns.

7. The packing material of any of claim 1 - 4, wherein said second material component is configured to provide stability, thermo formability and transparency to said packaging material.

8. The packing material of claim 7, wherein said second material component further is configured to provide a distance between two layers of said first material component.

9. The packaging material of claim 7 or 8, wherein said first material component is a co-polyester such as glycol modified polyethylene terephthalate, PETG, and said second material component is polystyrene, PS, or polystyrene terpolymer, said first material component constitutes a first layer and said second material component constitutes a second layer of said packing material.

10. The packaging material of claim 9, wherein said first material component further constitutes a third layer, said first and third layers being inner and outer layers and said second layer being an intermediate layer of said packing material.

11. The packing material of claim 9 or 10, wherein said layer or layers of said first material component has a total thickness in the range of approximately 40 — 140 microns, e.g. 90 microns, and said layer of said second material component has a thickness in the range of approximately 270 - 600 microns, e.g. 290 microns.

12. The packaging material of claim 7, wherein said first material component is polyamide, PA, and said second material component is polystyrene, PS, or poly¬ propylene, PP, said first material component constitutes a first layer and said second material component constitutes a second layer of said packing material.

13. The packing material of claim 12, wherein said first material component further constitutes a third layer, said first and third layers being inner and outer layers and said second layer being an intermediate layer of said packing material.

14. The packing material of claim 12 or 13, wherein said layer or layers of said first material component has a total thickness in the range of approximately 10 - 80 microns, e.g. 60 microns, and said layer of said second material component has a thickness in the range of approximately 150 - 700 microns, e.g. 350 microns.

15. The packing material of claim 7, wherein said first material component comprises copolymers of ethylene and vinyl alcohol, EVOH-blend, and said second material component is polystyrene, PS, said first material component constitutes an intermediate layer having a thickness in the range of approximately 2 — 20 microns, e.g. 5 microns, and said second material component constitutes an inner and an outer layer, each of which having a thickness in the range of approximately 75 - 350 microns, e.g. 200 microns.

16. The packaging material of any of claim 1 — 15, wherein said first and second material components are formed by means of co-extrusion.

17. The packaging material of any of claim 1 - 15, wherein said first and second material components are laminated.

18. The packing material of any of claim 1 — 17, wherein said packing material is intended for packing of perishables having a microbiological activity, such as cheese, coffee, fruits, or vegetables.

19. A permeable rigid package for perishables having a microbiological activity, said package comprises a packaging material according to any of claim 1 — 18.

20. A method for packaging perishables having a microbiological activity, said method for packing comprising a packaging material according to any of claim 1 - 18 or a package according to claim 19.