Laminate structure with improved barrier

Abstract

The present invention relates to a laminated sheet material for making a container, comprising, as layers of a layer sequence, a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer. The present invention further relates to a blank comprising the laminated sheet material and a container comprising the laminated sheet material. Even further, the present invention relates to the use of a gas barrier layer in a laminated structure.

Description

[0001] Laminate structure with improved barrier

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a laminated sheet material for making a container, comprising, as layers of a layer sequence, a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer. The present invention further relates to a blank comprising the laminated sheet material and a container comprising the laminated sheet material. Even further, the present invention relates to the use of a gas barrier layer in a laminated structure.

[0004] BACKGROUND

[0005] Within the technical field of packaging, it is known to produce a laminated sheet material for the manufacturing of a blank which is used to fold and assemble the blank to produce a container. The container may then be utilized to hold a pourable food product, like pastry or liquid food product like e.g. dairy products as milk or yoghurt, or juices.

[0006] The laminated sheet material typically comprises a carrier layer imparting dimensional stability to the packaging, typically a paperboard sheet, on which is laminated one or a plurality of barrier layers for holding the food product and / or prevent migration of air and flavors through the paperboard. A barrier layer may typically comprise a polymer layer or an aluminum layer.

[0007] The application of food products is associated with multiple challenges. The packaging must be dimensionally stable. At the same time, the laminate sheet material must enable an easy way of opening. Besides the mechanical properties of the packaging material, the materials must enable a blocking of chemical species in both directions, i.e. a chemical blocking to prevent species to permeate into the container and contaminate the product, and a chemical blocking to prevent constituents from passing the laminated sheet material from the inside to the outside.

[0008] Further, there are environmental concerns in the development of superior packaging products. An environmental concern relates to the use of materials from renewable resources. An increase of the proportion of fibrous materials from natural resources compared to synthetic polymers means an improvement in terms of environmental concerns. For that purpose, there is provided a paper substrate with a metal or metal oxide layer deposited via physical vapor deposition (PVD) method, with an optional intermediate layer, for the purpose of manufacturing a laminated sheet material fulfilling the above-mentioned challenges, in particular in view of chemical blocking properties and environmental concerns. However, liquid packaging made of laminate sheet materials containing a barrier film or barrier paper with a thin physical vapor deposition (PVD) layer exhibits a low mechanical stability as the thin barrier layer is very sensitive for cracks. There are not only mechanical stability issues but also chemical stability issues. In particular, acidic ingrediencies of containers attack the aluminum layer of laminate sheet materials. Acids may even permeate through layers of laminated sheet materials. This effect limits the long-time stability on the food inside the container.

[0009] Further, at the half-cut operation, creasing, side sealing and folding at the package forming the thin barrier layer is very sensitive for cracks. As for the term half-cut, it means that the laminated sheet material is cut in thickness direction in a non-penetrating way. At the half-cut, a spout can be arranged where the product in the container is poured out.

[0010] The thin PVD layer comprising a metal or metal oxide will also be very sensitive for chemical attacks when acidic food stuff may be used.

[0011] There is a need for laminated sheet materials which are environmentally friendly and provide a high mechanical strength and chemical resistivity.

[0012] Problems solved by the invention relate to the provision of a laminated sheet material for manufacturing a food container, which laminated sheet material makes use of environmentally friendly materials, wherein the container shows a high mechanical strength, good barrier properties and resistances in terms of chemical and mechanical attacks.

[0013] SUMMARY OF THE INVENTION

[0014] The invention’s underlying problems are solved by the subject-matter of claim 1. A first aspect of the invention therefore relates to a laminated sheet material for making a container, comprising, as layers of a layer sequence, a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer.

[0015] The laminated sheet material of the invention mandatorily comprises at least three layers, i.e. a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer.

[0016] The laminated sheet material solves the above problems since the gas barrier layer fulfills two functions: On the one hand, the gas barrier layer serves as a further gas barrier layer. On the other hand, the gas barrier layer serves as a protection layer for the metal layer respectively the metal oxide layer. The mechanism of the protection could be as follows: The paper substrate has different dynamic mechanical properties compared to the metal layer or metal oxide layer. The radius of kinks when appearing is such small that the metal or metal oxide layer tends to break at a location close to the crease lines, folding, deformation, embossing, irregularities or the like as well as the location where the half cut is provided. At locations where the kinks in the paper substrate appear, there is a support of the metal layer or metal oxide layer which seem to help that the cracks in the metal layer or metal oxide layer do not appear. A further protection effect refers to chemical attacks. To a certain amount, acids may pass layer such that the metal layer is exposed to chemical attacks. The gas barrier layer acts as further protection layer for acidic substances present in the food stuff.

[0017] The term “as layers of a layer sequence” is understood such that it includes the information on the order of the layers. The order is the sequence of reading. The term does not mean that the respective layers are directly attached to one another.

[0018] Principally, the order of the layers can be from the external side to the internal side, i.e. the gas barrier layer could be facing the interior part of the container to be manufactured from the laminated sheet material and the paper substrate could be facing the interior part of the container to be manufactured with the metal layer or the metal oxide layer, or the other way around, i.e. from the internal side to the external side. While the layers of the laminated sheet material do not have per se a direction in view of the orientation of facing the internal side or the external side of the container to be manufactured, the laminated sheet material may have further attributes which determine what side of the laminated sheet material becomes the internal side and what side becomes the external side relative to the interior of the container to be manufactured of the laminated sheet material.

[0019] The term “metal” of the feature “metal oxide layer” or “metal layer” may comprise a metalloid. In other words, in the framework of this disclosure, a metalloid is understood as metal. Therefore, boron, silicon, and germanium are metals in the sense of the present disclosure. There is thus an emphasis on the properties of a metal which are inherent in all metalloids.

[0020] The term “paper substrate” is understood in the sense that it comprises a plant-based fibrous material, especially pulps. The term “paper substrate” distinguishes from the term “paperboard”. The distinction between “paper substrate” and “paperboard” refers to its main function. While the function of the paperboard refers to rigidity and mechanical stability, the main function of the paper substrate does not aim at serving these main functions.

[0021] The metal layer or metal oxide layer as well as the gas barrier layer impart barrier properties. The term “barrier” means that that the layer imparting barrier properties inhibit or reduces the permeation of chemical species through the layer. Predominantly, the layer imparting barrier properties inhibits or reduces the permeation of moisture, i.e. water, oxygen or carbon dioxide. As used herein, the term "gas barrier layer" in general refers to a layer that limits the passage of one or more gases (e.g. oxygen, carbon dioxide, etc.) through the layer. The gas barrier properties can refer to the oxygen transmission rate (OTR), evaluated at 23°C and 50 % relative humidity. The oxygen transmission rate of laminate sheet materials is measured in the framework of the present application according to ASTM D- 3985.

[0022] But again, the function of the gas barrier layer is not reduced to the barrier properties only. The gas barrier layer additionally protects the metal layer from breakage, and also the gas barrier layer serves as a protection against acidic components stored in the container to be manufactured from the laminated sheet material of the invention.

[0023] The term “polymer” in the framework of the present application is understood as any macromolecule composed of monomeric repeating units, i.e. the term implies the meaning as understood by a person skilled in the art. The monomeric units may comprise distinguishing repeating units, i.e. a copolymer is understood as a polymer in the framework of the present application.

[0024] The term “comprising a polymer” in the framework of the present application is understood as comprising at least 50 wt.-%, at least 60 wt.-%, at least 70 wt.-%, at least 80 wt.-%, at least 90 wt.-%, at least 95 wt.-% or at least 99 wt.-% of a polymer based on the total weight of the gas barrier layer. It is particularly preferred that the gas barrier layer consists of a polymer.

[0025] In one aspect, the layers have the layers of sequence in the order from an external side to an internal side. According to this aspect, the paper substrate is facing the outside of the container to be manufactured of the laminated sheet material and the gas barrier layer is facing the inside of the container to be manufactured of the laminated sheet material.

[0026] The terms “facing the internal side” and “facing the external side” relates to the arrangement relative the further layers, it does not necessarily mean that the respective layers are in direct contact with the interior or the exterior of the container to be manufactured from the laminated sheet material.

[0027] In one aspect, the present invention relates to the laminated sheet material, wherein the metal layer or the metal oxide layer is in direct contact with the paper substrate. When the paper substrate is subjected to a modification, the metal layer or the metal oxide layer is in direct contact with that side of the substrate being subjected to the modification.

[0028] This aspect of the invention is the most affected by the risk of cracks appearing in the laminated sheet material. The paper substrate has different dynamic mechanical properties compared to the metal layer or metal oxide layer. The radius of kinks when appearing is such small that the metal or metal oxide layer tends to break at a location close to the crease lines, folding, deformation, embossing, irregularities or the like. Nevertheless, there is still a risk of breakage even if there are one or more layers between the paper substrate and the metal layer.

[0029] In one aspect, the present invention relates to the laminated sheet material, wherein paper substrate is subjected to a surface modification, preferably wherein the paper substrate is a paper substrate which is provided with a coating, more preferred wherein the paper substrate is a paper substrate which is provided with a primer coating. In one aspect, the paper substrate is a paper substrate which is provided with a coating comprising a composition comprising a clay. It is of course understood by a skilled person that the surface modification is performed before the deposition of the metal (oxide).

[0030] This aspect of the invention refers to an improvement of the metallized paper. The surface modification could be any kind of physical or chemical modification. The surface modification aims at a smoothening the surface and at improving the adhesion forces between the metal (oxide) and the paper. A preferred surface modification is a coating of the paper substrate, which could be more preferred any kind of primer coating, also briefly designated as primer, known in paper technology. Exemplarily, the surface modification represents the coating with a composition comprising a clay. Such a coating is performed by applying a composition, in particular a dispersion, comprising a clay. As for the clays, kaolin clay, bentonite clay, talcum particles, or their mixtures are preferred, in particular. The preferred feature according to which the metal (oxide) layer is in direct contact with the paper substrate preferably includes the aspect where the paper substrate is subjected to a surface modification. The surface modification may possibly be such that a structural change of the paper surface is left, only.

[0031] As for the primer, acrylic-based primers may be used. These primers contain acrylic polymers that help in improving adhesion and providing a suitable surface for further coatings of any kind. Further types of coating compositions which can be applied on the paper substrate for modifying the paper surface comprise polyvinyl alcohol (PVOH), water dispersible ethylene vinyl alcohol (EVOH), polyvinylidenechloride (PVDC), water dispersible polyamide (PA), water dispersible polyester, polysaccharide, polysaccharide derivatives, including starch and starch derivatives, and combinations thereof.

[0032] A preferred way of performing a surface modification is calendaring the paper surface to be provided with the metal layer. After drying, the paper may go through a calendaring process. This involves pressing the paper between rollers to smooth its surface and improve its finish. A further preferred way of performing a surface modification refers to a glazing process. To achieve a glazed finish, the paper goes through additional rollers or cylinders. One of these rollers is typically coated with a substance like starch or a clay mixture. The paper is pressed against this roller, transferring a thin layer of the coating onto the surface of the paper, creating the glazed paper.

[0033] In one aspect, the laminated sheet material further comprises a carrier layer, preferably a paperboard layer.

[0034] The carrier layer ensures the rigidity and mechanical stability of the container. This aspect concerns a favorable container in cases where a non-pouch container is to be manufactured from the laminated sheet material. Containers typically manufactured from the laminated sheet materials as disclosed herein distinguish from pouches or bags produced from thin laminated sheet materials. A carrier layer is, however, not essential for the present invention.

[0035] Typically, the carrier layer is made of a plant-based fibrous material, especially pulps, preferably bleached, unbleached and / or limed pulps, more preferred a plant-based fibrous material having a basis weight of 130 to 450 g / m2, even more preferred 140 to 410 g / m2, most preferred 150 to 370 g / m2, in particular 200 to 300 g / m2. The paperboard has per definition a thickness of more than 100 pm. The carrier layer, especially the paperboard, distinguishes per definition from the paper substrate. The paper substrate per definition distinguishes from the paperboard.

[0036] The basis weight is influenced by the porosity of the paper which in turn influences the mechanical stiffness. The paperboards having the preferable basis weight are beneficial in terms of mechanical stability.

[0037] In one aspect, the paperboard layer has a thickness of 200 to 800 pm, preferably a thickness of 250 to 600 pm, preferred a thickness of 300 to 500 pm, most preferred a thickness 325 to 450 pm. The thickness gives an appropriate mechanical stiffness.

[0038] In one aspect, the carrier layer, preferably the paperboard layer, is arranged on an external side of the paper substrate, of the metal layer or metal oxide layer, and of the gas barrier.

[0039] According to this aspect, the carrier layer, especially the paperboard layer, faces towards the exterior side of the container to be manufactured of the laminated sheet material. This does not necessarily mean that the paperboard layer is the outermost layer, i.e. the layer being in contact with the surrounding of the container to be manufactured. According to this aspect, the further layers, i.e. the paper substrate and / or the metal (oxide) layer and or the gas barrier layer, are arranged closer to the interior part of the container to be manufactured of the laminated sheet material.

[0040] In one aspect, the laminated sheet material comprises, as layers of the layer sequence, the carrier layer, preferably the paperboard layer, the paper substrate, the metal layer or the metal oxide layer, and the gas barrier layer.

[0041] This preferred laminated sheet material is used for non-pouch containers. The carrier layer imparts rigidity and mechanical strength to the container to be manufactured of the laminated sheet material.

[0042] In one aspect, the laminated sheet material according to the invention further comprises an adhesive layer between the carrier layer, preferably the paperboard layer, and the paper substrate. The adhesive layer is the most favorable way of attaching the paperboard layer to the paper substrate. The adhesive layer is defined by its function, i.e. a layer fulfilling the function of adhering the paper substrate with the paperboard is an adhesive layer. A further designation for the term “adhesive layer” is “tie layer”, “bonding layer” or “lamination layer”. It is preferred that the adhesive layer is an extrusion lamination layer or a water-based adhesive layer. It is further preferred that the adhesive layer comprises low density polyethylene (LDPE). LDPE is typically used in extrusion-based lamination techniques. Suitable adhesive polymers used for adhesive layers are the so-called adhesive thermoplastic polymers, such as modified polyolefins, which are mostly based on LDPE or LLDPE co-polymers or, graft co- polymers with functional group containing monomer units, such as carboxylic or glycidyl functional groups, e.g. (meth)acrylic acid monomers or maleic anhydride (MAH) monomers.

[0043] In one aspect, the gas barrier layer is in direct contact with the metal oxide layer or wherein the gas barrier layer is in direct contact with the metal layer.

[0044] This aspect is associated with the beneficial effect that the production is easier when the gas barrier layer is in contact with metal layer or metal oxide layer.

[0045] According to an alternative aspect, the laminated sheet material according to the invention further comprises a tie polymer layer between the gas barrier layer and the metal oxide layer, respectively a tie polymer layer between the gas barrier layer and the metal layer. The tie polymer layer improves the adhesion between the metal (oxide) layer and the gas barrier layer. It is to be understood that the tie polymer layer distinguishes from the tie layer, i.e. the adhesive layer between the paperboard layer and the paper substrate.

[0046] In one aspect, the tie polymer layer comprises an ethylene vinyl acetate, a functionalize polyethylene, a ethylene / propylene copolymer, ethylene methacrylic acid copolymer, ethylene acrylic acid copolymer, a maleic anhydride-modified polyolefin or blends thereof, preferably a maleic anhydride-modified polyolefin.

[0047] As for the material for the tie polymer layer, a variety of materials may be used. One type of material refers to adhesive resins. Examples thereof include ethylene vinyl acetate (EVA), polyethylene, polypropylene, or ethylene / propylene copolymers. A further type refers to functionalized polymers, i.e. polymers functionalized, i.e. modified, to enhance their bonding properties. Examples thereof include maleic anhydride-modified polyolefins, ethylene methacrylic acid copolymer, or ethylene acrylic acid copolymer. These exhibit improved adhesion characteristics in a very beneficial way.

[0048] In one aspect, the gas barrier layer is a biobased material. The term “biobased” characterizing the material of the gas barrier layer is to be understood in its broadest sense: A biobased material can be a material obtained from natural sources, like e.g. plants or bacteria. Biobased materials of that kind are e.g. polyhydroxyalkanoates. Also, a biobased material is a polymer constituted by monomers obtained from natural sources. A polymer being a biobased material in that sense is polylactide acid (PLA). Also, biobased materials in the sense of the present disclosure are materials being destructible to biocompatible species. In other words, a biobased material could be a biodegradable material.

[0049] The higher the amount of biobased materials in the laminated sheet material, the more environmentally friendly the laminated sheet material.

[0050] In one aspect, the gas barrier layer of the present laminated sheet material comprises an ethylene vinyl alcohol copolymer (EVOH), preferably an ethylene vinyl alcohol copolymer with an ethylene content of 25 to 50 wt.-%, preferably 27 to 45 wt.-%, more preferred 30 to 36 wt.-%, based on the total weight of the ethylene vinyl alcohol copolymer. Thus, the polymer of the gas barrier layer comprises an EVOH and preferably an EVOH with an ethylene content of 25 to 50 wt.-%, preferably 27 to 45 wt.-%, more preferred 30 to 36 wt.-%, based on the total weight of the ethylene vinyl alcohol copolymer. It is particularly preferred that the gas barrier layer consists of EVOH, especially EVOH with an ethylene content of 25 to 50 wt.-%, preferably 27 to 45 wt.-%, more preferred 30 to 36 wt.-%, based on the total weight of the ethylene vinyl alcohol copolymer.

[0051] As for an alternative aspect, the gas barrier layer of the present laminated sheet material comprises an ethylene vinyl alcohol copolymer (EVOH) with an ethylene content of 25 to 50 mol-%, preferably 27 to 45 mol-%, more preferred 30 to 36 mol-%, based on the ethylene vinyl alcohol copolymer as a whole.

[0052] As a favorable material for the gas barrier layer, the ethylene vinyl alcohol copolymer (EVOH) is used. EVOH barriers comprise various extrudable plastic barrier materials with excellent barrier properties for oxygen and a variety of other gases and volatile products. The comonomer ratio has an influence on the oxygen transmission rate (OTR). The higher the ethylene content the higher the OTR.

[0053] EVOH is commercially available with distinguishing contents of the ethylene comonomer in the EVOH. Typically, commercially available ethylene vinyl alcohol copolymers are those having an ethylene content of 24 wt.-%, 27 wt.-%, 29 wt.-%, 32 wt.-%, 35 wt.-%, 38 wt.-%, 44 wt.-%, and 48 wt.-%. The most preferred EVOH for the present laminated sheet material is the EVOH with an ethylene content of 32 wt.-%. The content of the ethylene comonomer is given in wt.-% based on the total weight of the copolymer. The rest is the vinyl alcohol comonomer with potentially some residues of a further comonomer.

[0054] In one aspect, the gas barrier layer comprises a polyamide or a blend of polyamides, preferably an aliphatic polyamide, an aromatic polyamide, or a blend thereof, more preferred polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, or a blend thereof, in particular a polyamide 6, an aromatic polyamide or a blend thereof. Thus, according to this aspect the polymer of the gas barrier layer comprises a polyamide or a blend of polyamides, more preferred polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, or a blend thereof, in particular a polyamide 6, an aromatic polyamide or a blend thereof. It is particularly preferred that the gas barrier layer consists of the polyamide or the blend of polyamides, more preferred polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, or the blend thereof, in particular a polyamide 6, an aromatic polyamide or the blend thereof.

[0055] The term "polyamide" as used herein refers to both homo- and co- or terpolyamides. The term specifically includes aliphatic polyamides or co-polyamides, e.g., polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, and specifically includes aromatic and partially aromatic polyamides or co-polyamides, such as polyamide 61, polyamide 6I / 6T, polyamide MXD6, polyamide MXD6 / MXDI, and blends thereof. It may comprise blends of one or more aliphatic polyamides with one or more aromatic polyamides.

[0056] It is possible that the gas barrier layer comprises a blend of EVOH and a polyamide or the gas barrier layer consists of a blend of EVOH and a polyamide.

[0057] As for environmental concerns, it can be beneficial to use less than 100 wt.% of the EVOH, wherein the difference up to 100 wt.-% is filled up with a biobased polymer.

[0058] In one aspect, the laminated sheet material comprises the gas barrier layer comprising the polymer wherein the gas barrier layer may be applied by extrusion coating.

[0059] According to a preferred aspect, the gas barrier layer, more preferred the gas barrier layer comprising the ethylene vinyl alcohol copolymer or comprising the polyamide or the blend of polyamides, is applied by extrusion coating.

[0060] The term “extrusion” is understood as known by a person skilled in the art: An extrusion or extrusion step is a process step used to create objects, in the framework of the present application the gas barrier layer, of a fixed cross- sectional profile by pushing material through a die of the desired cross-section.

[0061] According to this aspect, the polymer representing the gas barrier layer is subjected to an extrusion step. On the contrary to the present laminated sheet material, in those laminated sheet materials of the state of the art making use of a metal layer or metal oxide layer attached to a paper substrate which laminated sheet material comprise a polymer layer adjacent or indirectly attached to the metal layer or metal oxide layer, the polymer layers are casted polymer layers or layers deposited via polymer solution or polymer dispersion. The term “indirectly attached” in this context means that the polymer layer is attached to the metal layer or metal oxide layer via an intermediate layer.

[0062] In case of laminated sheet materials where layers are deposited via polymer solution or polymer dispersion, the polymer solution or polymer dispersion may contain a metal salt, especially with the aim of improving the adhesion to the adjacent layers. Accordingly, in a preferred embodiment, the gas barrier layer is essentially devoid of a metal compound or a metal salt.

[0063] It has surprisingly been found that gas barrier layers comprising a polymer, preferably an EVOH, a polyamide or a blend of polyamides, has beneficial effects if the polymer layer is applied by an extrusion coating process.

[0064] It is known in the art that extruded sheet materials structurally distinguish from casted sheet materials or sheet materials made from solutions or dispersions. Those layers being applied via extrusion coating have a higher thickness and they are devoid of pin holes. This makes the gas barrier layer comprising ethylene vinyl alcohol copolymer, a polyamide or a blend of a polyamide applied by extrusion coating superior over layers deposited via other method steps like solution or dispersion casted films.

[0065] In one aspect, the laminated sheet material comprises the gas barrier layer comprising the polymer wherein the gas barrier layer is applied by an extrusion step. In cases, where the polymer constituting the gas barrier layer comprises a polymer blend, the polymer blend is made before the extrusion step by mixing the polymers constituting the polymer blend.

[0066] In one aspect, the gas barrier layer is provided on both sides with the tie polymer layer. In this aspect, the laminated sheet material comprises as layers of the layer sequence the tie polymer layer, the gas barrier layer, and the tie polymer layer. This layer sequence is embedded in the further layer architecture in line with the present disclosure.

[0067] In one aspect, the gas barrier layer has a thickness of 0,5 to 20 pm, preferably 1 to 10 pm, more preferred more than 1 pm to less than 10 pm, even more preferred 2 to 8 pm, most preferred 3 to 6 pm; and / or wherein the gas barrier layer has an oxygen transmission rate of 0.1 to 50 g / m2d bar, preferably 0.5 to 25 g / m2d bar, more preferred 1 to 10 g / m2d bar as measured according to the above ASTM.

[0068] The thickness and the kind of the polymer used in the gas barrier layer have a beneficial influence in view of the oxygen transmission rate (OTR).

[0069] In one aspect, the metal layer or the metal oxide layer has a thickness of 5 to 200 nm, preferably 10 to 100 nm, more preferred 15 to 80 nm, most preferred 20 to 50 nm.

[0070] There is an optimal thickness of the metal (oxide) layer. If the layer is too thin the barrier quality is too poor. If on the other hand the layer becomes too thick, the metal layer is more sensitive to cracks.

[0071] In one aspect, the metal layer or the metal oxide layer is deposited on the paper substrate via physical vapor deposition. In one further aspect, the metal layer or the metal oxide layer is deposited on the paper substrate via chemical vapor deposition.

[0072] In particular, the deposition of metals, especially aluminum, is preferably performed via physical vapor deposition. These techniques (PVD and CVD) offer the best way of depositing a thin layer of a metal onto the paper substrate. In one aspect, the metal layer or the metal oxide layer is a metal oxide layer which metal oxide is aluminum oxide, e.g. AI2O3, silicon oxide, e.g. SiCh, magnesium oxide, e.g. MgO, titanium oxide, e.g. TiCh, a tin oxide, e.g. SnO, Sn20s, or SnCh, an indium oxide, e.g. InO, In2Os, or InCh, a zinc oxide, e.g. ZnO, or a combination of at least two metal oxides, e.g. indium tin oxide or Zn2SnO4, wherein the most preferred are aluminum oxide and silicon oxide (SiOxand / or A1OX). The silicon oxide is preferably silica.

[0073] As can be clearly gathered from the above aspect and the above disclosure, the metal of the metal oxide layer may comprise silicon. In the framework of this disclosure, a metalloid is understood as metal. Therefore, boron, silicon, and germanium are metals in the sense of the present disclosure.

[0074] In one aspect, the metal layer or the metal oxide layer is a metal layer which metal layer is a metallized layer, preferably which metal layer is a layer of aluminum.

[0075] If the metal layer is a layer of aluminum, the two-fold beneficial effects can be exhibited in the best way. The gas barrier layer protects the aluminum layer against a mechanical impact and against chemical species. Further, it is a gas barrier additional to the barrier layer consisting of the metal. The metal additionally works as a light barrier.

[0076] In one aspect, the paper substrate has a thickness of 30 pm to less than 100 pm, preferably 35 pm to 80 pm, more preferred 40 pm to 60 pm,

[0077] The invention’s underlying problems are solved by the subject-matter of claim 13. A second aspect of the invention therefore relates to blank comprising the laminated sheet material according to the invention.

[0078] In the production of the container, the laminate sheet material is cut to form a substantially rectangular blank, which is folded, filled and sealed to form the container filled with the food product. Therefore, the blank represents an intermediate product in the manufacturing process of the container for the food product.

[0079] The invention’s underlying problems are solved by the subject-matter of claim 14. A third aspect of the invention therefore relates to a container for holding a pourable food product, the container comprises a laminate sheet material according to the invention, wherein the laminate sheet material is folded to form said container. In one aspect, the container comprises the laminate sheet material according to the invention, wherein the laminate sheet material is folded, sealed and filled to form said container filled with a food product.

[0080] In one aspect, the laminate structure comprising a cut extending partway through the laminate structure from an outside surface thereof, along which cut the laminate structure is configured to be broken along the cut during a first opening of the container revealing an opening in the container.

[0081] The container may be provided with an opening arrangement allowing a consumer to open the container to access the food product. In the prior art, it is known to use plastic opening arrangements, such as arrangements comprising plastic pour spouts and lid portions. A particular advantageous opening arrangement for such containers is based on the known half-cut method. Details of the half-cut method are disclosed in EP1786618B1. The major advantage of the half-cut method is that the barrier layer is fully intact until the container is opened by an end user. Another advantage of the half-cut method during production is that the laminate may initially be produced as a homogenous sheet without any cutouts. In similar methods for obtaining an opening having an intact barrier layer, the paperboard is provided with openings before lamination and at least the barrier layer is subsequently laminated over the paperboard including the openings.

[0082] The invention’s underlying problems are solved by the subject-matter of claim 15. A fourth aspect of the invention therefore relates to a method of manufacturing a laminate sheet material for a container for holding a pourable food product, which method comprises the steps of

[0083] • providing a paper substrate, having a first and a second side, the paper substrate being metallized on the first side;

[0084] • bonding the second side of the metallized paper to a paperboard layer, using an adhesive layer; and

[0085] • adding a gas barrier layer onto the metal surface of the metallized paper substrate.

[0086] The method of the invention results in a laminate sheet material which is provided with a gas barrier layer arranged on the metal layer or the metal oxide layer, either directly or via an intermediate layer. The beneficial effects associated with the product of the method according to the invention are the same as those achieved with the laminated sheet material of the invention. According to one aspect, the laminated sheet material is a laminated sheet material according to the first aspect of the invention. In one aspect, the gas barrier layer is a polymer layer is applied by extrusion coating.

[0087] The application of the gas barrier layer is performed as follows: The material to be applied is extruded as a melt to obtain a coating curtain to be attached onto the substrate prior to the nip. Thereafter, the melted polymer film together with the substrate is subjected to a chill rolling. The film forming the gas barrier layer is on the side towards the chilled roller and the metalized paper substate is on the side towards the pressure roller. In practice, the film comprising the ethylene vinyl alcohol copolymer is not in direct contact with chill roller. A tie polymer layer or a tie polymer layer and a sealing layer is in between the ethylene vinyl alcohol polymer and the chill roller.

[0088] In view of a comparison between an ethylene vinyl alcohol copolymer (EVOH) solution or dispersion coating versus EVOH extrusion coating, the following is detailed:

[0089] EVOH coated papers are typically produced from aqueous solutions or dispersions. As the polymer is dissolved in water, it has great impact on viscosity and is used in relatively low concentrations (10-20%). This put high demands on the application methods and a high drying capacity to evaporate the water used to dissolve and carry the EVOH copolymer.

[0090] For a metalized paper including an EVOH gas barrier layer applied from aqueous solution, there is thus at least one extra process step applying the water based EVOH solution required. Further, thickness and quality of layers applied from solution or dispersion is not as desired.

[0091] By co-extrusion coating applying the EVOH from the melt together with a tie polymer layer or a tie polymer layer and a sealing layer, there is no need for any extra process step or any additional energy intensive process for drying out applied water. By co-extrusion coating with said layers, it is easy to steer coating and thickness of the layers to secure a pinhole free coating to get desired barrier properties and to facilitate an easier recycling.

[0092] An alternative to the extrusion coating of the gas barrier layer, an extrusion lamination can be performed to attach the gas barrier layer to the metalized paper. According to this aspect, the gas barrier layer is made separately from the metallization of the paper substrate and then laminated to the metalized paper substrate. The manufacturing of the polymer layer by the extrusion lamination imparts the gas barrier layer beneficial effects. The gas barrier properties are improved. According to an alternative aspect, the gas barrier layer is provided as a separate film; the film can be made by an initial extrusion step, optionally followed by a biaxial stretching step, more preferred by a biaxial stretching step simultaneously in machine direction and transversal direction. The biaxial stretching to obtain the gas barrier layer imparts improved properties to the gas barrier layer. The properties are even more improved if the biaxial stretching is performed simultaneously. This means that the extruded layer is stretched in machine direction and transversal direction at the same time. Further aspects and detailed description on the method of manufacturing the gas barrier layer are disclosed in connection with the laminated sheet material.

[0093] The biaxial stretching is performed in that the extruded polymer sheet is stretched, preferably simultaneously stretched in machine direction, i.e. MD, and in transversal direction, i.e. TD. In a first step, a such manufactured gas barrier layer is made, and in a further step the manufactured gas barrier layer is attached to the metalized paper. It is preferred that an intermediate layer, such as a tie polymer layer or an adhesive layer, is present between the metal surface and the gas barrier layer. Such an intermediate layer is preferably attached to the metal or metal oxide layer before the manufactured gas barrier layer is attached to the metalized paper. In a less preferred embodiment, the intermediate layer is formed on the manufactured gas barrier layer.

[0094] In one aspect, the adding of the gas barrier layer is performed using a tie polymer layer between the gas barrier layer and the metallized paper substrate.

[0095] The tie polymer layer has the characteristics as described above.

[0096] The invention’s underlying problems are solved by the subject-matter of claim 16. A fifth aspect of the invention therefore relates to a use of a ethylene vinyl alcohol copolymer or a polyamide or a blend of polyamides as gas barrier layers in a laminate sheet material comprising a metallized paper.

[0097] In one aspect the laminate sheet material is a laminate sheet material according to the invention.

[0098] Features being solely disclosed in connection with the first aspect of the invention are deemed to be disclosed in connection with any one of the second to fifth aspect of the invention and vice versa. BRIEF DESCRIPTION OF THE DRAWING

[0099] Certain aspects of the presently disclosed subject-matter will be described with reference to the accompanying drawing, which is representative and schematic in nature and is not considered to be limiting in any respect as it relates to the scope of the subject-matter disclosed herein:

[0100] Figure 1 depicts the basic principle of the layered architecture according to the present invention.

[0101] Figure 2 depicts an example of a laminate sheet material.

[0102] Figure 3 depicts a further example of a laminate sheet material.

[0103] Figure 4 depicts a further example of a laminate sheet material.

[0104] Figure 5 depicts a manufacturing line applying the extrusion coating.

[0105] Figure 6 depicts a manufacturing line applying the extrusion lamination.

[0106] DESCRIPTION OF EMBODIMENTS

[0107] Figure 1 shows the basic principle of the layer architecture of the present invention which mandatorily comprises a paper substrate 11, a metal layer 12 on the paper substrate 11, and a gas barrier layer 13. According to the invention, it is not required that the layers are compulsory adjacent to one another, it might be the case, that the layers have intermediate layers. Also, paper substrate 11 might be subjected to a surface modification in line with the above description.

[0108] Figure 2 shows an exemplary laminated sheet material comprising a paper substrate 11, a metal layer 12 on the paper substrate 11, and a gas barrier layer 13. Further, in order to imply mechanical stiffness, the laminated sheet material, a paperboard 14 is provided at the side of the paper substrate 11 opposite of the metal layer 12. The paperboard 14 and the paper substrate 11 are attached to one another via adhesive layer 15. The external side and the internal side are provided with sealing layers 17 which may be made of LDPE. The sealing layers are the outermost and innermost layers.

[0109] Figures 3 and 4 are further examples which make use of the tie polymer layer 16. As shown in Fig. 3, a tie polymer layer may be provided between the metal layer 12 and the gas barrier layer 13. This tie polymer layer strengthens the adhesion between the metal layer 12 and gas barrier layer 13. The beneficial effect associated with the gas barrier layer 13 at the side of the metal layer 12 are promoted by the tie polymer layer 16. The laminated sheet material shown in Fig. 4 comprises a tie polymer layer on both sides of the gas barrier layer 13.

[0110] For laminated sheet materials in practice, it is most favorable to provide a tie polymer layer 16 between the gas barrier layer 13 and the sealing layer 17.

[0111] Figure 5 shows a manufacturing line in which the step of extrusion coating of the gas barrier layer is performed. Extruder structure 18 represents a device enabling the provision of a coextruded film comprising at least the melted copolymer forming the gas barrier layer 13 in the laminate, i.e. the ethylene vinyl alcohol copolymer or the (blend of) polyamide(s), together with a composition forming a tie polymer layer 16. It is also possible that the extruder structure 18 represents a device enabling the provision of a coextruded film comprising the melted copolymer forming the gas barrier layer 13 in the laminate together with the composition forming the tie polymer layer 16 and together with a composition forming the sealing layer 17 which latter composition comprises e.g. a polyethylene. The coextrudate provided through extrusion die 19 comprises extruded polymer film 20 in which the two resp. three compositions are present in two resp. three distinguishing layers. In practice, the extruded polymer film 20 forms a coating curtain moving predominantly by gravity towards the gap between pressure roller 22 and chill roller 23.

[0112] The extruded polymer film 20 is immediately pressed onto the surface of the paper substrate with metal (oxide) 21. Paper substrate 21 is typically fed through the process at a controlled speed. Extruded polymer film 20 is immediately directed onto the surface of the moving paper substrate 21 using a chill roll laminator. Thereby, the layer of the extruded polymer film 20 which forms the gas barrier layer in the laminate is on the side towards the metalized paper and the layer of the extruded polymer film 20 which forms the tie polymer layer is on the side of the chill roller 23. In cases where the sealing layer is also extrusion coated, the layer forming the sealing layer faces the chill roller 23 and the layer forming the tie polymer layer 16 is in the middle of the coextrudate.

[0113] Paper substrate 21 and the extruded polymer film 20 pass through pressure roller 22 that ensure intimate contact and adhesion between the polymer film forming the gas barrier layer 13 and the paper substrate 21. As the thermoplastic polymer film comes into contact with the chill roller 23, it quickly solidifies and bonds with the paper substrate 21. In the manufacturing line shown in Figure 5, laminate 24 is obtained which comprises at least the paper substrate 11 with the metal (oxide) layer 12, the gas barrier layer 13, the tie polymer layer 16 and, if the coextrudate comprises the above three layer, the sealing layer 17. Fig. 6 depicts a manufacturing line applying the extrusion lamination. Distinguishing from the method of manufacturing a laminate structure using the manufacturing line shown in Fig. 5, the method of manufacturing a laminate structure using the manufacturing line shown in Fig. 6 makes use of an extruded film 20 forming the gas barrier layer being prepared prior to a lamination step. In that case, the film forming the gas barrier layer is firstly extruded and then biaxially stretched (using devices not shown in Fig. 6). Film 20 prior to lamination has basically the same size as the gas barrier layer 13 after having laminated to the metalized paper substrate. The method performed with the manufacturing line shown in Fig. 6 makes use of an extrusion coating of lamination layer 25 which comprises a tie polymer layer 16. Lamination layer 25 is immediately directed onto the surface of the moving paper substrate 21 using a chill roll laminator. There, lamination layer 25 bonds the metalized paper substrate and the biaxially stretched film such that laminate 24 is formed.

[0114] The following items are disclosed herewith:

[0115] 1. A laminated sheet material for making a container, comprising, as layers of a layer sequence, a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer.

[0116] 2. The laminated sheet material of item 1, wherein the metal layer or the metal oxide layer is in direct contact with the paper substrate.

[0117] 3. The laminated sheet material of item 1, wherein the paper substrate is subjected to a surface modification, preferably wherein the paper substrate is a paper substrate which is provided with a coating, more preferred wherein the paper substrate is a paper substrate which is provided with a primer coating.

[0118] 4. The laminated sheet material according to any one of the preceding items, wherein the layers have the layers of sequence in the order from an external side to an internal side.

[0119] 5. The laminated sheet material according to any one of the preceding items, further comprising a carrier layer, preferably a paperboard layer.

[0120] 6. The laminated sheet material according to item 5, wherein the carrier layer, preferably the paperboard layer, is arranged on an external side of the paper substrate, of the metal layer or metal oxide layer, and of the gas barrier.

[0121] 7. The laminated sheet material according to item 5 or item 6, wherein the laminated sheet material comprises, as layers of the layer sequence,

[0122] - the carrier layer, preferably the paperboard layer,

[0123] - the paper substrate,

[0124] - the metal layer or the metal oxide layer, and

[0125] - the gas barrier layer.

[0126] 8. The laminated sheet material according to any one of items 5 to 7, further comprising an adhesive layer between the carrier layer, preferably the paperboard layer, and the paper substrate.

[0127] 9. The laminated sheet material according to any one of the preceding items, further comprising a tie polymer layer between the gas barrier layer and the metal layer, or further comprising a tie polymer layer between the gas barrier layer and the metal oxide layer.

[0128] 10. The laminated sheet material according to any one of the preceding items, wherein the gas barrier layer is a biobased material, or wherein the gas barrier layer comprises an ethylene vinyl alcohol copolymer, preferably an ethylene vinyl alcohol copolymer with an ethylene content of 25 to 50 wt.-%, preferably 27 to 45 wt.-%, more preferred 30 to 36 wt.-% based on the total weight of the ethylene viny alcohol copolymer; and / or wherein the gas barrier layer comprises a polyamide or a blend of polyamides, preferably an aliphatic polyamide, an aromatic polyamide, or a blend thereof, more preferred polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, or a blend thereof, in particular a polyamide 6, an aromatic polyamide or a blend thereof.

[0129] 11. The laminated sheet material according to any one of the preceding items, wherein the gas barrier layer has a thickness of 0,5 to 20 pm, preferably 1 to 10 pm, more preferred 2 to 8 pm, most preferred 3 to 6 pm; and / or wherein the gas barrier layer has an oxygen transmission rate of 0.1 to 50 g / m2d bar, preferably 0.5 to 25 g / m2d bar, more preferred 1 to 10 g / m2d bar.

[0130] 12. The laminated sheet material according to any one of the preceding items, wherein the metal layer or the metal oxide layer has a thickness of 5 to 200 nm, preferably 10 to 100 nm, more preferred 15 to 80 nm, most preferred 20 to 50 nm.

[0131] 13. The laminated sheet material according to any one of the preceding items, wherein the metal layer or metal oxide layer is deposited on the paper substrate via physical vapor deposition.

[0132] 14. The laminated sheet material according to any one of the preceding items, wherein the metal layer or the metal oxide layer is a metal oxide layer which metal oxide is aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, a tin oxide, an indium oxide, a zinc oxide, or a combination of at least two metal oxides, wherein the most preferred metal oxides are aluminum oxide and silicon oxide.

[0133] 15. The laminated sheet material according to any one of items 1 to 13, wherein the metal layer or the metal oxide layer is a metal layer being a metallized layer, preferably a layer of aluminum.

[0134] 16. The laminated sheet material according to any one of the preceding items, wherein the paper substrate has a thickness of 30 pm to less than 100 pm, preferably 35 pm to 80 pm, more preferred 40 pm to 60 pm.

[0135] 17. A blank comprising the laminated sheet material according to any one of the preceding items.

[0136] 18. A container for holding a pourable food product, the container (1) comprises a laminate sheet material according to any one of claims 1 to 16, wherein the laminate sheet material being folded to form said container.

[0137] 19. The container according to item 18, wherein the laminate structure comprising a cut extending partway through the laminate structure from an outside surface thereof, along which cut the laminate structure is configured to be broken along the cut during a first opening of the container revealing an opening in the container. 0. A method of manufacturing a laminate structure for a container for holding a pourable food product, which method comprises the steps of

[0138] • providing a paper substrate, having a first and a second side, the paper substrate being metallized on the first side; • bonding the second side of the metallized paper to a paperboard layer, using an adhesive layer; and

[0139] • adding a gas barrier layer onto the metal surface of the metallized paper substrate. 21. The method according to item 20, wherein the adding of the gas barrier layer is performed using an adhesive layer between the gas barrier layer and the metallized paper substrate.

[0140] 22. A use of a laminate structure as a gas barrier layer in a laminated sheet material, which laminate structure comprises a gas barrier layer and a metallized paper, the metallized paper having at least one metallized side, the gas barrier layer being in contact with the metallized side of a metallized paper.

[0141] 23. The use of item 22, the laminate sheet material is a laminate sheet material according to any one of claims 1 to 16.

[0142] REFERENCE LIST

[0143] 11 Paper substrate 12 Metal (oxide)

[0144] 13 Gas barrier layer

[0145] 14 Paperboard

[0146] 15 Adhesive layer

[0147] 16 Tie polymer layer 17 Sealing layer

[0148] 18 Extruder structure

[0149] 19 Extruder die

[0150] 20 extruded polymer film

[0151] 21 Paper substrate with metal (oxide) 22 Pressure roller

[0152] 23 Chill roller

[0153] 24 Laminate comprising gas barrier on metalized paper

[0154] 25 Lamination layer, e.g. tie polymer layer, in particular polyethylene

Claims

CLAIMS1. A laminated sheet material for making a container, comprising, as layers of a layer sequence, a paper substrate, a metal layer or a metal oxide layer, and a gas barrier layer comprising a polymer.

2. The laminated sheet material of claim 1, wherein the metal layer or the metal oxide layer is in direct contact with the paper substrate.

3. The laminated sheet material of claim 1, wherein the paper substrate is subjected to a surface modification, preferably wherein the paper substrate is a paper substrate which is provided with a coating, more preferred wherein the paper substrate is a paper substrate which is provided with a primer coating.

4. The laminated sheet material according to any one of the preceding claims, wherein the gas barrier layer comprises an ethylene vinyl alcohol copolymer, preferably an ethylene vinyl alcohol copolymer with an ethylene content of 25 to 50 wt.-%, preferably 27 to 45 wt.-%, more preferred 30 to 36 wt.-% based on the total weight of the ethylene viny alcohol copolymer; and / or wherein the gas barrier layer comprises a polyamide or a blend of polyamides, preferably an aliphatic polyamide, an aromatic polyamide, or a blend thereof, more preferred polyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 69, polyamide 610, polyamide 612, copolyamide 6 / 9, copolyamide 6 / 10, copolyamide 6 / 12, copolyamide 6 / 66, copolyamide 6 / 69, or a blend thereof, in particular a polyamide 6, an aromatic polyamide or a blend thereof.

5. The laminated sheet material according to any one of the preceding claims, wherein the gas barrier layer has a thickness of 0,5 to 20 pm, preferably 1 to 10 pm, more preferred 2 to 8 pm, most preferred 3 to 6 pm; and / or wherein the gas barrier layer has an oxygen transmission rate of 0.1 to 50 g / m2d bar, preferably 0.5 to 25 g / m2d bar, more preferred 1 to 10 g / m2d bar.

6. The laminated sheet material according to any one of the preceding claims, wherein the gas barrier layer, preferably the gas barrier layer comprising theethylene vinyl alcohol copolymer or comprising the polyamide or the blend of polyamides, is applied by extrusion coating.

7. The laminated sheet material according to any one of the preceding claims, wherein the layers have the layers of sequence in the order from an external side to an internal side.

8. The laminated sheet material according to any one of the preceding claims, further comprising a carrier layer, preferably a paperboard layer.

9. The laminated sheet material according to any one of the preceding claims, further comprising a tie polymer layer between the gas barrier layer and the metal layer, or further comprising a tie polymer layer between the gas barrier layer and the metal oxide layer.

10. The laminated sheet material according to any one of the preceding claims, wherein the metal layer or the metal oxide layer has a thickness of 5 to 200 nm, preferably 10 to 100 nm, more preferred 15 to 80 nm, most preferred 20 to 50 nm.

11. The laminated sheet material according to any one of the preceding claims, wherein the metal layer or the metal oxide layer is a metal oxide layer which metal oxide is aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, a tin oxide, an indium oxide, a zinc oxide, or a combination of at least two metal oxides, wherein the most preferred metal oxides are aluminum oxide and silicon oxide.

12. A blank comprising the laminated sheet material according to any one of the preceding claims.

13. A container for holding a pourable food product, the container (1) comprises a laminate sheet material according to any one of claims 1 to 11, wherein the laminate sheet material being folded to form said container.

14. A method of manufacturing a laminate structure for a container for holding a pourable food product, which method comprises the steps of• providing a paper substrate, having a first and a second side, the paper substrate being metallized on the first side; bonding the second side of the metallized paper to a paperboard layer, using an adhesive layer; and• adding a gas barrier layer onto the metal surface of the metallized paper substrate.

15. The method according to claim 14, wherein the gas barrier layer, preferably the gas barrier layer comprising the ethylene vinyl alcohol copolymer or comprising the polyamide or the blend of polyamides, is a polymer layer applied by extrusion coating.

16. Use of a ethylene vinyl alcohol copolymer or a polyamide or a blend of polyamides as gas barrier layers in a laminate sheet material comprising a metallized paper.

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