LAMINATED PACKAGING MATERIAL AND OPENING MEMBRANE MATERIAL, PACKAGING CONTAINERS MANUFACTURED THEREFROM AND METHOD FOR MANUFACTURING THE LAMINATED MATERIAL

Abstract

The present invention relates to a laminated cellulose-based liquid food packaging material, comprising a cellulose-based bulk material layer, having through-going holes, openings or slits, an aluminium metal foil and outer layers of thermoplastic polymers. The invention further relates to the method for manufacturing the laminated packaging material and to a packaging container for liquid food packaging, comprising the laminated packaging material.

Claims

1. Laminated cellulose-based, liquid food packaging material, comprising a bulk material layer with through-going holes, openings or slits, each defining an opening area, further comprising an outermost, transparent and protective thermoplastic polymer layer arranged on the outside of the bulk material layer, i.e. on the side to be directed outwards from a packaging container made from the laminated material, and an innermost, heat sealable and liquid-tight thermoplastic polymer layer, which is intended to be in direct contact with the packed food product, an aluminium metal foil for providing gas barrier properties, which is laminated between the bulk material layer and the innermost thermoplastic polymer layer, wherein a thermo-mechanically stable polymer layer is also laminated between the bulk material layer and the innermost thermoplastic layer, the thermomechanically stable polymer layer being of a polymer composition having a melting point higher than 150 C. and comprising at least 70 wt-% of a polymer selected from the group consisting of ethylene vinyl alcohol copolymer (EVOH) and polyamide (PA) resulting from polymerization of monomers selected from the group consisting of Caprolactam, Laurolactam, Undecanolactam, Adipic Acid, Azelaic Acid, Sebacic Acid, Dodecanedioic Acid, Terephatalic Acid, Isophathalic Acid, Butanediamine, Hexamethylene diamine, Trimethylhexamethylene diamine and Metaxyxylene diamine (MXDA) monomer, or of a blend of two or more polyamidesobtained from different such monomer combinations, the amount of MXDA monomer included in the polyamide being in total 80 mol % or less, and wherein the aluminium metal foil, the inner- and outermost thermoplastic polymer layers and the thermo-mechanically stable polymer layer, all extend throughout the areas of the holes, openings or slits of the bulk material layer, such that they are laminated and sealed to each other to form a laminated opening membrane material, not containing the bulk material layer, within the opening areas.

2. Laminated packaging material as claimed in claim 1, wherein the aluminium metal foil is 6 m or thinner, such as 5 m or thinner.

3. Laminated packaging material as claimed in claim 1, wherein the thermo-mechanically stable layer is applied at an amount from 0.5 to 10 g/m.sup.2, such as from 1 to 6 g/m.sup.2, such as from 2 to 4 g/m.sup.2.

4. Laminated packaging material as claimed in claim 1, wherein the bulk material layer has a grammage from 100 to 350 g/m.sup.2.

5. Laminated packaging material as claimed in claim 1, wherein the thermo-mechanically stable layer is laminated between the aluminium metal foil and the bulk material layer, together with at least one intermediate bonding layer of a thermoplastic polymer.

6. Laminated packaging material as claimed in claim 1, wherein the bulk material layer is laminated to the aluminium metal foil, in the following order, by a first intermediate bonding layer of polyethylene, which is adhered to and contacting the bulk material layer, a first adhesive polymer layer, which is adhered to and contacting the opposite side of the first intermediate bonding layer of polyethylene, the thermo-mechanically stable layer, which is adhered to and contacting the opposite side of the first adhesive polymer layer, and a second adhesive polymer layer, which is adhered to and contacting the opposite side of the thermo-mechanically stable layer and binding the thermo-mechanically stable layer to the aluminium metal foil.

7. Laminated packaging material as claimed in claim 6, wherein the adhesive polymer is a polyethylene graft-modified with maleic anhydride (MAH-g-PE).

8. Laminated packaging material as claimed in claim 6, wherein the intermediate bonding layer of polyethylene is applied at an amount from 5 to 10 g/m.sup.2, such as from 6 to 8 g/m.sup.2.

9. Laminated opening membrane material (L), covering an opening area of a laminated packaging material, the opening area being defined by a through-going hole, opening or slit in a bulk material layer comprised in the laminated packaging material, the laminated membrane material comprising the following laminated layers from the outside of the laminated opening membrane material to the inside, i.e. corresponding to the outside and inside of a package comprising the laminated opening membrane material, an outermost, transparent and protective thermoplastic polymer layer, at least one intermediate bonding layer of a thermoplastic polymer, a thermo-mechanically stable layer, of a polymer composition having a melting point higher than 150 C. and comprising at least 70 wt-% of a polymer selected from the group consisting of ethylene vinyl alcohol copolymer (EVOH) and polyamide (PA) resulting from polymerization of monomers selected from the group consisting of Caprolactam, Laurolactam, Undecanolactam, Adipic Acid, Azelaic Acid, Sebacic Acid, Dodecanedioic Acid, Terephatalic Acid, Isophathalic Acid, Butanediamine, Hexamethylene diamine, Trimethylhexamethylene diamine and Metaxyxylene diamine (MXDA) monomer, or of a blend of two or more polyamides obtained from different such monomer combinations, the amount of MXDA monomer included in the polyamide being in total 80 mol % or less, an aluminium metal foil, at least one adhesive polymer layer and an innermost, heat sealable and liquid-tight thermoplastic polymer layer.

10. Laminated opening membrane material, as claimed in claim 9, wherein the laminated membrane material (L) comprises the following sequence of laminate layers, from the outside of the laminated opening membrane material to the inside, i.e. the outermost thermoplastic polymer layer, an intermediate bonding layer of a thermoplastic polymer, a first adhesive polymer layer, a thermo-mechanically stable layer, a second adhesive layer, the innermost thermoplastic layer.

11. Laminated opening membrane material, as claimed in claim 10, wherein the intermediate bonding layer of a thermoplastic polymer is a low density polyethylene and the first and second adhesive polymers are maleic-anhydride graft-modified polyethylene.

12. Liquid food packaging container comprising the laminated packaging material as defined in claim 1.

13. Method for manufacturing the laminated cellulose-based, liquid food packaging material as defined in claim 1, comprising the steps, in any order or in any combination, of a) forwarding a first web of a bulk material layer having through-going holes, openings or slits, each defining an opening area, and a second web of an aluminium metal foil towards a lamination roller nip, b) laminating the first and second webs to each other, c) laminating an innermost heat sealable thermoplastic polymer layer on the inner side of the web of the aluminium metal foil, opposite the side of the bulk material layer, d) laminating between the bulk material layer and the innermost thermoplastic polymer layer, a thermo-mechanically stable polymer layer, of a polymer composition having a melting point higher than 150 C., and comprising at least 70 wt-% of a polymer selected from the group consisting of ethylene vinyl alcohol copolymer (EVOH) and polyamide (PA) resulting from polymerization of monomers selected from the group consisting of Caprolactam, Laurolactam, Undecanolactam, Adipic Acid, Azelaic Acid, Sebacic Acid, Dodecanedioic Acid, Terephatalic Acid, Isophathalic Acid, Butanediamine, Hexamethylene diamine, Trimethylhexamethylene diamine and Metaxyxylene diamine (MXDA) monomer, or of a blend of two or more polyamides obtained from different such monomer combinations, the amount of MXDA monomer included in the polyamide being in total 80 mol % or less, e) laminating an outermost thermoplastic polymer layer on the outer side of the web of the bulk material layer, opposite the side of the aluminium metal foil, thus laminating the aluminium metal foil, the inner- and outermost thermoplastic polymer layers and the thermo-mechanically stable polymer layer to each other within the areas of the through-going holes, openings or slits, to form a laminated opening membrane material (L), not containing the bulk material layer, within the opening areas.

14. Method as claimed in claim 13, wherein the thermo-mechanically stable polymer layer is laminated into the laminated material structure by means of co-extrusion lamination together with at least one other thermoplastic polymer layer.

15. Method as claimed in claim 13, wherein step b) is carried out by melt co-extruding a molten multilayer of at least one intermediate bonding layer of a thermoplastic polymer together with the thermo-mechanically stable polymer, between the web of the aluminium metal foil and the web of the bulk material layer, and then pressing the layers to adhere to each other in the lamination roller nip.

Description

EXAMPLES AND DESCRIPTION OF DRAWINGS

[0093] In the following, embodiments of the invention will be described with reference to the drawings, of which:

[0094] FIG. 1a is showing a schematic, cross-sectional view of a laminated packaging material with an opening area, where there is no bulk material layer, but a membrane of the further laminate layers, according to the invention,

[0095] FIG. 1b shows a schematic, cross-sectional view of a further embodiment of such a laminated packaging material,

[0096] FIG. 1c shows a schematic, cross-sectional view of yet a further embodiment of such a laminated packaging material,

[0097] FIG. 2a shows schematically an example of a method, for laminating the aluminium metal foil to the bulk material layer, in accordance with the invention,

[0098] FIG. 2b shows schematically an example of a method, for laminating the innermost thermoplastic polymer layer to the previously laminated bulk material and aluminium foil, resulting from the operation described in FIG. 2a, in accordance with the invention,

[0099] FIG. 3a, 3b, 3c show typical examples of packaging containers produced from the laminated packaging material according to the invention,

[0100] FIG. 4 shows the principle of how packaging containers may be manufactured from the packaging laminate in a continuous, roll-fed, form, fill and seal process,

[0101] FIG. 5 is shows at which applied pressure a laminated opening membrane breaks when subject to a quick pressure puff on one side of the membrane, and

[0102] FIG. 6 shows how an overpressure, applied to one side of a laminated opening membrane, influences the OTR of the membrane.

TEST METHODS

[0103] Oxygen transmission (OTR) was measured according to ASTM F1927-14 och ASTM F1307-14, at 23 C. temperature with air as testgas, and a relative moisture content RH of 50.

[0104] The unit of measured values is accordingly: cm.sup.3 per sample/(0.2 atm, 24 hrs) at 23 C. and 50% RH. The sample is a piece of the packaging material comprising the opening membrane, which has a diameter of 20 mm.

[0105] The method for determining OTR identifies the amount of oxygen per surface and time unit at passing through a material at a defined temperature, given atmospheric pressure, and chosen driving force.

[0106] Membrane strength at burst was tested by fastening a piece of the packaging material comprising the opening membrane, in a position such that it may be pressurised from the inside (i.e. the inside of packaging material and resulting packaging container when made from the packaging material) with air during a certain time. For these tests, the time was set to 0.250 seconds. Starting from 0.7 bar above the surrounding atmospheric pressure at which the experiment was done, the pressure was gradually and stepwise increased by incremental steps of 0.1 bar (at each step the pressure was applied for 0.250 seconds) until the membrane broke.

[0107] In FIG. 1a, there is thus shown, in cross-section, a first embodiment of a laminated packaging material, 10a, of the invention. It comprises a bulk material layer 11a of a paperboard for liquid packaging, having a grammage of about 270 g/m.sup.2.

[0108] On the inner side of the bulk material layer 11a, which side is to be directed towards the inside of a packaging container formed from the laminated material, the laminated material comprises an aluminium metal foil 12a. The aluminium metal foil has a thickness of 5 m. The aluminium metal foil is laminated to the bulk material layer by a multilayer bonding structure comprising a first bonding layer 13a of 8 g/m.sup.2 of LDPE adhering to and directly contacting the bulk material paperboard, a first tie layer 14a of 3 g/m.sup.2 of a MAH-g-LDPE adhesive polymer adjacent and directly contacting the other side of the LDPE layer, a thermo-mechanically stable layer of 4 g/m.sup.2 of a PA-6 polyamide 15a applied adjacent and in direct contact with the first layer of adhesive polymer, and a second adhesive polymer or so-called tie layer 16a of 3 g/m.sup.2 of a MAH-g-LDPE adhesive polymer adjacent and directly contacting the thermo-mechanically stable PA layer. The second layer of adhesive polymer adheres also directly to the outer side of the aluminium metal foil, i.e. binds the thermo-mechanically stable layer 15a to the aluminium foil 12a.

[0109] On the other, inner side of the aluminium metal foil, there is an innermost, heat sealable thermoplastic layer 17a, which is also the layer of the packaging laminate that will be in direct contact with the filled food product in a final packaging container. The innermost, heat sealable polymer layer 17a is melt co-extrusion coated onto the aluminium foil together with an intermediate adhesive layer of EAA 18a.

[0110] The lamination of the bulk material layer 11a and the aluminium metal foil 12a by the (co-)extrusion lamination of the polyamide thermo-mechanically stable layer 15a, the LDPE bonding layer and the first and second adhesive polymer layers was done before the coextrusion coating of the innermost thermoplastic polymer layer 17a onto the aluminium metal foil.

[0111] This laminating layer configuration has the advantage of providing high adhesion to the bulk material layer, since the LDPE may be extrusion coated onto the cellulose surface at a higher temperature than any adhesive polymers or thermo-mechanically stable polymers. Furthermore, the adhesion to the outside LDPE layer on the outer side of the bulk material layer, through the opening hole in the laminated membrane, will be better due to this higher temperature. It is a further advantage to include the thermo-mechanically stable polymer layer between the bulk material layer and the barrier layer, rather than on the inside of the barrier layer, thus avoiding any interference with the heat sealing of the inner layers at package formation.

[0112] The innermost thermoplastic polymer layer is a heat sealable polymer selected from polyolefins, such as polyethylenes, such as in this case a composition comprising a blend of a metallocene-catalysed linear low density polyethylene (m-LLDPE) and a low density polyethylene (LDPE). Alternatively, or also, the heat sealable material on the innermost side of the laminated packaging material may be divided in two part-layers of different kinds of polyethylenes, e.g. there may be a first intermediate layer of LDPE contacting the adhesive polymer and a second innermost layer of the above blend.

[0113] On the other side, the outside of the bulk material layer 11a, the packaging material comprises an outermost liquid-tight and transparent layer 19a of an LDPE, which was extrusion coated onto the bulk material layer.

[0114] In FIG. 1b, a similar cross-section, of a second embodiment of a laminated packaging material, 10b, is shown. The laminated material is the same as the material in FIG. 1a, except from the layer configuration between the bulk material layer and the aluminium metal foil. The multilayer bonding layer configuration does not include the LDPE layer towards the inner side of the paperboard bulk as in FIG. 1a, but only the middle, thermo-mechanically stable layer 15b of polyamide, in an amount of 4 g/m.sup.2, surrounded by the first and second adhesive polymer layers 14b and 16b of EAA at an amount of from 3 to 4 g/m.sup.2 each. The first adhesive polymer layer 14b is thus directly and adjacently contacting the paperboard, and the second adhesive polymer layer 16b is directly and adjacently contacting the aluminium foil 12b.

[0115] In a different embodiment, the first layer of adhesive polymer could also be removed, such that the thermo-mechanically stable polymer layer 15, being a polyamide, would instead directly adhere to and be in direct contact with the bulk paperboard 11. Instead, for extrusion-lamination process purposes, the thicknesses of the layers of adhesive polymer may be increased, or an additional layer of LDPE 13 is added to bond the second layer of adhesive polymer 16 to the aluminium foil. The adhesion of the polyamide of the thermo-mechanically stable layer to the outermost layer of LDPE 19, on the opposited side of the paperboard, through the hole, within the membrane layer configuration, may not be less good, but may work sufficiently well for small straw holes, perforations and the like.

[0116] FIG. 1c shows a cross-section, of a third embodiment of a laminated packaging material according to the invention, 10c. The laminated packaging material has the same paperboard and the same outer- and innermost thermoplastic polymer layers as described in FIGS. 1a and 1b, however with the thermo-mechanically stable layer 15c instead located on the inner side of the aluminium metal foil 12c. The thermo-mechanically stable polyamide layer 15c is melt co-extrusion coated onto the aluminium foil together with surrounding, first and second adjacent adhesive polymer layers 14c and 16c being EAA, and with the innermost heat sealable layer 17c of LDPE/mLLDPE blend.

[0117] The aluminium foil 12c is bonded to the bulk paperboard 11c by means of a single intermediate bonding layer 13c of LDPE.

[0118] In FIG. 2a it is schematically illustrated how a web of the paperboard bulk layer 11, as described in FIG. 1, is forwarded from a reel 21 and extrusion laminated to a web of the aluminium metal foil 12, which is forwarded from a reel 22 in a lamination roller nip 25. A molten polymer curtain 23 of the bonding layers comprising the multilayer configuration of FIG. 1a or 1b, or the single layer of LDPE of FIG. 1c, is extruded 24 into the lamination nip 25, between the bulk material layer 11 and the aluminium foil 12, to be pressed together and cooled to solidify the molten lamination polymers, thus permanently adhering the paperboard and the aluminium foil to each other to produce a pre-laminate 26. The resulting pre-laminate is forwarded to the next operation of the lamination process, in this case as further described in connection with FIG. 2b.

[0119] In FIG. 2b it is schematically illustrated how the web of the pre-laminate 26 of the bulk material layer, the aluminium metal foil and the intermediate bonding layer or layers of thermoplastic polymers as in FIGS. 1a-1c is forwarded to a further lamination roller nip 27. At the roller nip 27, a molten curtain 28 of the inside polymer layers, i.e. the adhesive polymer layer 18a; 18b; 14c and 16c, thermo-mechanically stable layer 15c, and the innermost layer 19a; 19b; 19c, are co-extruded 29 down into the lamination roller nip 27, and being cooled to be coated as a multilayer film coating onto the opposite, inner side of the aluminium foil 12, by pressing and solidifying the polymer layers 18, 19, 14-16, to the inner surface of the web of the aluminium foil. The resulting laminate 30 may be forwarded to a further, similar lamination operation for extrusion-coating lamination of the outside layer 19 of LDPE onto the opposite, outer side of the paperboard layer 11, or if this was already done before the above lamination steps, to a reeling station for further transport and storage of the packaging laminate on a reel.

[0120] FIG. 3a shows an embodiment of a packaging container 30a produced from the packaging laminate 10a;10b;10c according to the invention. The packaging container is particularly suitable for beverages, sauces, soups or the like. Typically, such a package has a volume from about 100 to 1000 ml. It may be of any configuration, but is preferably brick-shaped, having longitudinal and transversal seals 31a and 32a, respectively, and optionally an opening device 33. In another embodiment, not shown, the packaging container may be shaped as a wedge. In order to obtain such a wedge-shape, only the bottom part of the package is fold formed such that the transversal heat seal of the bottom is hidden under the triangular corner flaps, which are folded and sealed against the bottom of the package. The top section transversal seal is left unfolded. In this way the half-folded packaging container is still is easy to handle and dimensionally stable when put on a shelf in the food store or on a table or the like.

[0121] FIG. 3b shows an alternative, preferred example of a packaging container 30b produced from an alternative packaging laminate according to the invention. The alternative packaging laminate is thinner by having a thinner cellulose bulk layer 11, and thus it is not dimensionally stable enough to form a cuboid, parallellepipedic or wedge-shaped packaging container, and is not fold formed after transversal sealing 32b. It will thus remain a pillow-shaped pouch-like container and be distributed and sold in this form.

[0122] FIG. 3c shows a gable top package 30c, which is fold-formed from a pre-cut sheet or blank, from the laminated packaging material comprising a bulk layer of paperboard and the durable barrier film of the invention. Also flat top packages may be formed from similar blanks of material.

[0123] FIG. 4 shows the principle as described in the introduction of the present application, i.e. a web of packaging material is formed into a tube 41 by the longitudinal edges 42 of the web being united to one another in an overlap joint 43. The tube is filled 44 with the intended liquid food product and is divided into individual packages by repeated transversal seals 45 of the tube at a pre-determined distance from one another below the level of the filled contents in the tube. The packages 46 are separated by incisions in the transversal seals and are given the desired geometric configuration by fold formation along prepared crease lines in the material.

[0124] FIG. 5 is a diagramme, which shows at which pressure the laminated opening membrane breaks, in a test measuring the Membrane strength at burst test, as explained above. The measured values are shown with the standard deviation indicated. The openings have a diameter of 20 mm. It can be seen that a laminated opening membrane with an aluminium foil which is not supported, i.e. only laminated to the conventional low density polyethylene layers, breaks earlier, at a lower applied membrane pressure. An identical membrane, however also laminated with a few grams per squaremeter of polyamide (PA6), as a co-extruded layer together with further intermediate thermoplastic bonding layers between the bulk layer material and the aluminium metal foil, does not break until at a higher applied membrane pressure. This is still the case, even if the aluminium metal foil is thinner, i.e. 5 m instead of 6.3 m. This effect is also notable on the quality of the laminated opening membranes, in packaging containers produced from the laminated packaging materials. It can be seen as improved openability of the membranes that have support by an additional polyamide layer, as fewer occurrences of frayed edges around the opening hole, as well as on the absence of any defects in unopened opening membranes. This shows that the laminated opening membrane material of the invention provides better support to the aluminium metal foil barrier and prevents damages from the mechanical stress that the packaging material is exposed to in a filling machine. It is known that the further application of heat to the membrane has a further detrimental effect to such an un-supported aluminium foil in opening membranes. The higher melting point of the thermo-mechanically polyamide composition, normally around or above 200 C., provides sufficient support to the aluminium foil to still resist such mechanical damage and stress even though the other polyolefin-based layers softens and become too flexible to provide mechanical support.

[0125] FIG. 6 is a diagramme showing the influence of overpressure applied to a laminated opening membrane, on the OTR of the membrane. Thus, the OTR was measured (23 C., 50% RH) on samples comprising the laminated opening membrane, before and after exerting a pressure of 1 bar on one side of the membrane. The two laminated opening membranes tested in FIG. 5 were also tested here, regarding influence on the OTR. In addition, a sample having no polyamide, but a thinner aluminium foil was also tested.

[0126] It may be concluded from the results, that a laminated membrane having a thinner aluminium foil of 5 m is significantly more sensitive to such stress from pressure acting on the membrane, than the thicker aluminium metal foil of 6.3 m. It can also be concluded that a few grams per squaremeter of polyamide-6 may prevent any damage on the laminated membrane, also when the aluminium metal foil is as thin as 5.0 m.

[0127] Thus, the packaging material according to the invention, as defined in the appended claims, provides more robust packaging containers made therefrom, with improved package integrity and improved gas barrier properties. According to preferred embodiments, the packaging material also provides for improved openability of a packaging container made from the material of the invention.

[0128] The invention is not limited by the embodiments shown and described above, but may be varied within the scope of the claims. As a general remark, the proportions between thicknesses of layers, distances between layers and the size of other features and their relative size in comparison with each other, should not be taken to be as shown in the figures, which are merely illustrating the order and type of layers in relation to each other all other features to be understood as described in the text specification.