PACKAGING LAMINATE, METHOD FOR PRODUCING SAME, AND PACKAGING CONTAINER PRODUCED FROM THE PACKAGING LAMINATE

Abstract

Packaging laminate for a packaging container for oxygen-sensitive liquid food, such as milk, juice, wine and cooking oil. The packaging laminate has a layer of paper or paperboard, and a layer serving as gas barrier and composed of a material with barrier properties against gases, in particular oxygen. The layer serving as gas barrier is bonded to the paper or paperboard layer by a lamination layer, which comprises at least one layer of an adhesive polymer or polymer composition, which comprises monomer units with carboxyl acid functional groups. The packaging laminate also has outer liquid-tight coatings on both sides of the paper or paperboard layer.

Claims

1. Packaging laminate for a packaging container for oxygen-sensitive liquid food, which packaging laminate comprises a layer of paper or paperboard, and a layer serving as a gas or vapour barrier layer, which layers are bonded to each other by a laminating material, comprising a first adhesive polymer composition in direct contact with the paper or paperboard, wherein the first adhesive polymer composition comprises a polymer material having ethylene monomer units and monomer units having carboxylic acid functional groups, at an amount lower than 1.5 mol % of the total first adhesive polymer composition.

2. Packaging laminate according to claim 1, wherein the amount of monomer units having carboxylic acid functional groups in the laminating material is from 0.15 to below 1.5 mol % of the total first adhesive polymer composition.

3. Packaging laminate according to claim 1, wherein the first adhesive polymer composition further comprises a low density polyethylene (LDPE) at an amount of up to 60 wt-%

4. Packaging laminate for a packaging container for oxygen-sensitive liquid food, according to claim 1, wherein the laminating material comprises a first layer of a first adhesive polymer composition with the ability to bind to the paper or paperboard layer and, on its other surface, has a second polymer layer with the ability to bind to the layer serving as a gas or vapour barrier, wherein the adhesive layer is in contact with the paper or paperboard layer, wherein the layer is in contact with the layer serving as a barrier, and wherein the first adhesive polymer composition comprises ethylene monomer units and monomer units having carboxylic acid functional groups, which amount to less than 1.5 mol % of the total first adhesive polymer composition.

5. Packaging laminate according to claim 4, wherein the second polymer layer is a second adhesive polymer comprising a polymer having ethylene monomer units and monomer units having carboxylic acid functionality, which amount to from 1.5 mol % and above of the second adhesive polymer.

6. Packaging laminate for a packaging container for oxygen-sensitive liquid food, according to claim 4, wherein the laminating material comprises a central polymer layer which, on one surface, has a first layer of a first adhesive polymer composition with the ability to bind to the paper or paperboard layer and, on its other surface, has a second layer of a second adhesive polymer with the ability to bind to the layer serving as gas barrier, wherein the adhesive layer on one surface of the polymer layer is in contact with the paper or paperboard layer, and wherein the adhesive layer on the other surface of the polymer layer is in contact with the layer serving as gas or vapour barrier, the first adhesive polymer composition comprising ethylene monomer units and monomer units having carboxylic acid functional groups, which amount to less than 1.5 mol % of the total first adhesive polymer composition.

7. Packaging laminate according to claim 4, wherein the amount of monomer units having carboxylic acid functional groups in the first adhesive polymer composition is from 0.15 to below 1.5 mol % of the first adhesive polymer composition.

8. Packaging laminate according to claim 1, wherein the first adhesive polymer or polymer composition comprises an adhesive polymer selected from the group consisting of ethylene-acrylic acid copolymer (EAA) and ethylene-methacrylic acid copolymer (EMAA) and blends thereof.

9. Packaging laminate according to claim 1, wherein the material layer serving as a barrier layer is aluminium.

10. Packaging laminate according to any one of the preceding claim 1, wherein the heat sealable food product contact layer comprises a polyethylene selected from the group consisting of LDPE, linear low density polyethylene (LLDPE) and linear low density polyethylene polymerised by a single site catalyst (m-LLDPE), and blends of two or more thereof.

11. Packaging laminate according to claim 1, wherein the central layer of the laminating material has a thickness of from 10 to 14 g/m.sup.2, and the outer adhesive polymer layers of the laminating material each have a thickness of from 2 to 5 g/m.sup.2.

12. Packaging laminate according to claim 1, wherein the material layer serving as a barrier layer is, on its opposite side, which is to form the inside of the packaging laminate in a packaging container, bonded to a heat sealable food product contact layer of polyethylene by an inside adhesive polymer, which is in direct contact with the barrier layer, the inside adhesive polymer consisting of a polymer having ethylene monomer units and monomer units having carboxylic acid functional groups, which amount to from 1.5 mol % and above of the inside adhesive polymer.

13. Packaging laminate according to claim 6, wherein the central polymer layer comprises a polyolefin, such as a polyethylene.

14. Packaging laminate according to claim 6, wherein the central polymer layer comprises a polyethylene chosen from a group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), very low-density polyethylenes (VLDPE), ultra low-density polyethylenes (ULDPE), linear low-density polyethylene which has been produced with a so-called single-site catalyst, metallocene catalyst or so-called constrained-geometry catalyst (m-LLDPE), medium-density polyethylene (MDPE) and high-density polyethylene (HDPE).

15. Packaging laminate according to claim 6, wherein the adhesive polymers in the two outer layers of the laminating material are identical to each other.

16. Packaging laminate according to claim 1, wherein the adhesion between the first adhesive composition and the paper or paperboard is so high that it generates fibre tear within the paper or paperboard layer, upon adhesion testing according to ASTMD903-98(2010).

17. Packaging laminate according to claim 9, wherein the adhesion between the aluminium barrier layer and the laminating material is higher than 105 N/m.

18. Packaging container for oxygen-sensitive liquid food, e.g. milk, juice, wine, cooking oil, etc., wherein it is produced from the packaging laminate according to claim 1.

19. Method of producing the packaging laminate according to claim 1, wherein the layer of paper or paperboard is laminated to the layer serving as a gas or vapour barrier layer, by melt (co-)extrusion lamination with the laminating material.

20. Method according to claim 18, wherein the melt co-extrusion lamination is done without any surface treatment.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0066] The invention will be described in more detail with reference to the attached drawings, in which:

[0067] FIGS. 1a, 1b and 1c are schematic cross-sectional views of packaging laminates according to the invention;

[0068] FIG. 2 schematically illustrates the production of the packaging laminates from FIG. 1a, 1b, 1c by the method according to the invention;

[0069] FIG. 2A is an enlarged view of the circled area A in FIG. 2 for the case when the packaging laminate of FIG. 1c is produced;

[0070] FIG. 3 schematically depicts a method for forming, filling and sealing packaging containers from a web on a reel of packaging material;

[0071] FIG. 4 is a schematic perspective view of a packaging container of the type Tetra Brik Aseptic, made from the packaging laminate according to the invention;

[0072] FIG. 5 is a schematic perspective view of a packaging container of the type Tetra Fino Aseptic, made from the packaging laminate according to the invention; and

[0073] FIG. 6 is a schematic perspective view of a packaging container of the gable-top type, a so-called Tetra Rex package, made from the packaging laminate according to the invention.

DETAILED DESCRIPTION OF THE FIGURES

[0074] FIG. 1a shows schematically a cross section through a general packaging laminate according to an embodiment of the invention. The packaging laminate, designated by the general reference sign 10, has a layer 11 of paper or paperboard, and a layer 12 which serves as gas barrier and is bonded to the paper or paperboard layer 11 by a laminating material layer 13. In the embodiment shown, the packaging laminate 10a also has an outer liquid-tight, heat sealable coating 14, 15 on both sides of the paper or paperboard layer 11, the heat sealable layer 15 on the inside of the packaging laminate being aimed to be in direct contact with the filled food product on the inside of a packaging container. The heat sealable product contact layer 15 is optionally bonded to the barrier layer 12 by means of an inside adhesive polymer 16, the inside adhesive polymer preferably being a polymer having ethylene monomer units and some monomer units having carboxylic acid functionality, which amounts to from 1.4 to 3.0 mol % of the inside adhesive polymer.

[0075] The lamination layer 13 has the ability to bind to the paper or paperboard layer 11, as well as to the layer 12 serving as gas barrier, most commonly an aluminium foil. The lamination layer may consist of an adhesive polymer, which is a copolymer comprising ethylene monomer units and monomer units having carboxylic acid functional groups at an amount of from 0.15 to 1.3 mol % of the total adhesive polymer. Alternatively, the lamination layer may comprise a blend of low density polyethylene and an adhesive polymer, the adhesive polymer being a copolymer comprising ethylene monomer units and monomer units having carboxylic acid functional groups, and the blend material comprising monomer units having carboxylic acid functional groups at an amount of from 0.15 to 1.3 mol %, more preferably from 0.15 to 0.7 mol %, of the total polymer blend.

[0076] FIG. 1b shows schematically a cross section through an alternative general packaging laminate according to an embodiment of the invention. The packaging laminate, designated by the general reference sign 10b, has a layer 11 of paper or paperboard, and a layer 12 which serves as gas barrier and is bonded to the paper or paperboard layer 11 by a laminating material layer 13. In the embodiment shown, the packaging laminate 10b also has an outer liquid-tight, heat sealable coating 14, 15 on both sides of the paper or paperboard layer 11, the heat sealable layer 15 on the inside of the packaging laminate being aimed to be in direct contact with the filled food product on the inside of a packaging container. The heat sealable product contact layer 15 is optionally bonded to the barrier layer 12 by means of an inside adhesive polymer 16, the inside adhesive polymer preferably being a polymer having ethylene monomer units and some monomer units having carboxylic acid functionality, which amounts to from 1.4 to 3.0 mol % of the inside adhesive polymer.

[0077] The laminating material 13 comprises a first layer 13b of a first adhesive polymer with the ability to bind to the paper or paperboard layer 11 and a second polymer layer 13c with the ability to bind to the layer 12 serving as a gas or vapour barrier, the adhesive layer 13b being in contact with the paper or paperboard layer 11, and the second polymer layer 13c being in contact with the layer 12 serving as a barrier.

[0078] The first layer 13b consists of an adhesive polymer, which is a copolymer comprising ethylene monomer units and monomer units having carboxylic acid functional groups at an amount of from 0.15 to 1.3 mol %, from 0.15 to 1.3 mol %, of the adhesive polymer. The second polymer layer 13c may be a layer of low density polyethylene (LDPE) or of a second adhesive polymer, which is a copolymer having ethylene monomer units and some monomer units having carboxylic acid functional groups, which amount to from 1.4 to 3.0 mol % of the second adhesive polymer. The two polymer layers 13b and 13c may be co-extruded together in the extrusion lamination operation, when laminating the paper or paperboard 11 to the barrier layer 12.

[0079] FIG. 1c shows schematically a cross section through a further embodiment of a general packaging laminate according to an embodiment of the invention. The packaging laminate, designated by the general reference sign 10c, has a layer 11 of paper or paperboard, and a layer 12 which serves as gas or vapour barrier and is bonded to the paper or paperboard layer 11 by a laminating material 13. In the embodiment shown, the packaging laminate 10 also has an outer liquid-tight coating 14, 15 on both sides of the paper or paperboard layer 11, the heat sealable layer 15 on the inside of the packaging laminate being aimed to be in direct contact with the filled food product on the inside of a packaging container. The heat sealable product contact layer 15 is optionally bonded to the barrier layer 12 by means of an inside adhesive polymer 16, the inside adhesive polymer preferably being a polymer having ethylene monomer units and some monomer units having carboxylic acid functionality, which amounts to from 1.4 to 3.0 mol % of the inside adhesive polymer.

[0080] The laminating material layer 13 has a central layer 13a, of which one surface has a layer 13b of an adhesive with the ability to bind to the paper or paperboard layer 11, and of which the other surface has a layer 13c of an adhesive with the ability to bind to the layer 12 serving as gas barrier. As is shown in FIG. 1c, the adhesive layer 13b on one side of the central layer 13a is in contact with the paper or paperboard layer 11, while the adhesive layer 13c on the other side of the central layer 13a is in contact with the layer 12 serving as gas barrier.

[0081] In one illustrative embodiment according to the invention, the central layer 13a can be a polymer layer of low-density polyethylene (LDPE) that can be produced by a polymerization reaction in either an autoclave reactor or a tube reactor. As has already been mentioned, a polymer layer of low-density polyethylene (LDPE) is preferably a low-density polyethylene (LDPE) that is produced in the latter type of reactor, i.e. a tube reactor, since a low-density polyethylene (LDPE) of this kind permits extrusion at a lower extrusion temperature and at a higher web speed (draw-down) than a low-density polyethylene (LDPE) that is produced in an autoclave reactor.

[0082] In another illustrative embodiment, the central layer 13a can be a polymer layer made of a linear polymer, which helps give the finished packaging laminate 10c improved mechanical properties when these are desired. Examples of linear polymers that can be used are high-density polyethylene (HDPE), or linear low-density polyethylene (LLDPE), very low-density polyethylenes (VLDPE), ultra low-density polyethylenes (ULDPE) produced with conventional catalysts or so-called single-site catalysts.

[0083] As has already been mentioned, a well-functioning adhesive polymer for the adhesive layers 13b and 13c has active binding sites (free carboxylic acid groups) to permit effective and permanent binding to the paper or paperboard layer 11 and to the layer 12 serving as gas barrier. A further requirement of a well-functioning adhesive polymer in the packaging laminate 10c according to the invention is that it is able to be applied at a sufficiently low temperature in order to avoid loss of quality as a result of degradation reactions upon contact with the warmer polymer in the central layer 13a of the lamination layer 13. Practical examples of adhesive polymers with active binding sites (acid groups) are ethylene-acrylic acid copolymer (EAA) and ethylene-methacrylic acid copolymer (EMAA) and blends thereof.

[0084] The adhesive layers 13b and 13c of the lamination layer 13 can be made from adhesive polymers of mutually different chemical compositions and of mutually different layer thicknesses, but they are preferably made from one and the same adhesive polymer with one and the same layer thickness. In any case, according to the invention, the first adhesive polymer of the first adhesive layer 13b being a copolymer having ethylene monomer units and monomer units having carboxylic acid functional groups at an amount of from 0.15 to 1.3 mol %, more preferably from 0.15 to 0.7 mol %, of the first adhesive polymer.

[0085] According to the invention, the material in the layer 12 serving as gas barrier can be of both organic and inorganic nature. Examples of organic materials are various types of polyamides (PA), and one example of inorganic material is an aluminium foil. Preferably, the layer 12 serving as gas barrier is an aluminium foil which, in addition to its excellent barrier properties against gases, in particular oxygen, also makes the packaging laminate 10 heat-sealable by means of induction sealing, which is a rapid and also effective sealing technique.

[0086] The outer liquid-tight coatings 14 and 15 of the packaging laminate 10 can be coatings of a polyolefin, such as polyethylene (PE) and polypropylene (PP). Examples of a usable polyethylene (PE) are low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) produced with conventional catalysts or so-called single-site catalysts, and high-density polyethylene (HDPE). In the present case, an outer liquid-tight coating, which is intended to be directed towards a food product packed in a packaging container, can be bonded to the barrier layer by a layer of an adhesive polymer of the same type as, or different from, the adhesive layers included in the laminating material 13. For the best performance of the packaging laminate, the inside adhesive polymer is as stated above, a polymer having ethylene monomer units and some monomer units having carboxylic acid functionality, which amounts to from 1.4 to 3.0 mol % of the inside adhesive polymer.

[0087] According to the invention, the packaging laminates 10a, 10b, 10c in FIGS. 1a, 1b and 1c, respectively, can be produced in the manner shown schematically in FIG. 2. A web 201 of paper or paperboard is unwound from a storage reel 200, and a corresponding web 203 of a material with barrier properties against gases, in particular oxygen, is unwound from a storage reel 202. The two webs 201 and 203 are brought together with each other and are guided together through a nip between two adjacent rotatable cylinders 204 and 205, while at the same time a laminating material 206 is applied between the webs in order to laminate them to each other and thereby form a durable laminated web 208.

[0088] In the example shown, the laminating material 13, 206 is applied by extrusion or co-extrusion by means of an extruder 207 arranged above the nip and will be described in more detail below.

[0089] The laminated web 208 is then conveyed via guide rollers 209 and 210 towards and through a nip between two further adjacent rotatable cylinders 211 and 212, while at the same time one surface of the web 208 is provided with an outer liquid-tight coating 213 of extrusion-coated polymer. In a subsequent nip between another two adjacent rotatable cylinders 217 and 218, the other surface of the web 208 is provided with an outer liquid-tight coating 214 of extruded polymer. These two extrusion-coating steps can be carried out in reverse order and also, wholly or partly, before the lamination step in the nip between the cylinders 204 and 205.

[0090] In the example shown, an outer liquid-tight coating 213 is applied to one surface of the web by extrusion with the aid of an extruder 215, and an outer liquid-tight coating 214 is applied to the other surface of the web 208 by extrusion with the aid of a corresponding extruder 216 arranged near the web 208.

[0091] Following further mechanical or other machining operations on the web thus coated, the latter is finally wound up for onward transport and further handling in which it is formed into dimensionally stable packaging containers for oxygen-sensitive liquid food, e.g. milk, juice, wine and cooking oil, as will be described hereinbelow.

[0092] According to the invention, the laminating material 206 with which the web 203 of the material with barrier properties against gases, in particular oxygen, is laminated to the paper or paperboard web 201 may be a three-layer structure as in FIG. 1c (or a two-layer structure as in FIG. 1b), as is shown on an enlarged scale in FIG. 2A. This three-layer structure has a central layer 206a of a polymer which, on one surface, has a first outer layer 206b of an adhesive polymer with the ability to bind to paper or paperboard and, on its other surface, has a second outer layer 206c of an adhesive polymer with the ability to bind to said material with barrier properties against gases, in particular oxygen. According to the invention, the three-layer structure serving as laminating material is preferably extruded by co-extrusion, in such a way that the outer adhesive layer 206b is brought into direct contact with the paper or paperboard web 201, while at the same time the outer adhesive layer 206c is brought into direct contact with the web 203 of the material with barrier properties against gases, in particular oxygen. There is no need for a surface treatment, such as ozone treatment or corona, or any further addition of chemicals to the lamination operation.

[0093] According to the invention, and as has already been mentioned, the polymer for the central layer 206a of the laminating material 206 can be chosen more or less freely and is thus not limited to any particular type of polymer. An example of a usable polymer for the central layer 206a of the laminating material 206 is a low-density polyethylene (LDPE) of the type which is produced by a polymerization reaction in an autoclave reactor, or a low-density polyethylene (LDPE) of the type which is produced by a polymerization reaction in a tube reactor. By virtue of the method according to the invention, low-density polyethylene (LDPE) produced in an autoclave reactor can, despite its poorer draw-down properties, also be extruded at a relatively high speed and even at lower temperatures, while at the same time the layers can be extruded more thinly, the total amount of laminating material is reduced, better adhesion can be achieved, and energy is saved.

[0094] Low-density polyethylene (LDPE) produced in a tube reactor permits co-extrusion coating at a relatively high production speed, for example ca. 400 m/min and over, by virtue of its good draw-down properties, compared with an LDPE produced in an autoclave reactor. It also has the added advantage that it can be co-extruded and coated at a lower extrusion temperature, for example 280 to 310° C., for example 290 to 300° C., than LDPE produced in an autoclave reactor and therefore requires less energy than the latter. In turn, extrusion of low-density polyethylene (LDPE) at a lower temperature such as this reduces the risk of the quality being impaired by degradation reactions, as has already been mentioned. Furthermore, no surface treatment such as ozone treatment is needed.

[0095] Other examples of usable polymers for the central layer 206a of the laminating material 206 are linear polymers, which have the advantage of helping to improve the mechanical properties of the finished packaging laminate. Examples of linear polymers that can be used in the method according to the invention are high-density polyethylene (HDPE), medium-density polyethylene (MDPE), linear low-density polyethylene (LLDPE), very low-density polyethylenes (VLDPE), ultra low-density polyethylenes (ULDPE) produced with conventional catalysts or so-called single-site catalysts, or constrained-geometry catalysts, including so-called metallocene catalysts.

[0096] The requirement to be met by usable adhesive polymers for both outer layers 206b and 206c of the laminating material 206 is of course that they must permit effective and permanent binding to the respective web 201 and 203. A further requirement is that they must also be able to be extruded at a sufficiently low temperature in order to avoid the risk of inadvertently increasing the temperature of the polymer layer 20 of the laminating material 206 such that it exceeds the critical temperature at which uncontrolled degradation reactions may be initiated that impair quality. Examples of adhesives that meet both of these requirements are ones which, in their natural state, have active acid groups on their surface, for example ethylene-acrylic acid copolymer (EAA) and ethylene-methacrylic acid copolymer (EMAA). Such an adhesive is commercially available under the trade name Primacor from Dow Chemical Company, and another such adhesive can be obtained from DuPont under the trade name Nucrel. A further example is obtainable from ExxonMobil Chemicals under the trade name Escor.

[0097] Other examples of adhesive polymers having free, active carboxylic acid groups, suitable for some aspects of the present invention, may be maleic-anhydride functionalised polyolefins, in particular maleic-anhydride functionalised polyethylenes, which also provide polyolefin-based polymers having free carboxylic acid functionality.

[0098] Although adhesives that are different from each other can be used in the outer layers 206b and 206c of the laminating material 206, it is advantageous, for reasons of processing technology, to use adhesive of the same composition and of the same quantity in each of the outer layers 206b and 206c.

[0099] Materials that have gas barrier properties and that are usable in the method according to the invention may be of both organic and also inorganic nature. Examples of organic materials are copolymers of ethylene and vinyl alcohol (EVOH) and various types of polyamides (PA). Examples of inorganic materials can be an aluminium foil or a polymer film which, on one or both of its sides, has a coating of metal, e.g. vapour-deposited or vacuum-metallized aluminium or a vapour-deposited coating of an oxide, e.g. aluminium oxide, or silicon oxide (SiOx). An aluminium foil is preferably used which, in addition to having excellent barrier properties against gases, also allows the packaging laminate to be sealed by so-called induction sealing, which is a rapid, simple and effective heat-sealing technique.

[0100] Examples of usable polymers for the liquid-tight, heat-sealable outer layers 213 and 214 applied to the web 208 in the method according to the invention are polyolefins, such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE) and polypropylene (PP).

[0101] From a web of the packaging laminates 10 in FIG. 1a, 1b, 1c for example, it is possible, as has already been mentioned, to produce dimensionally stable packaging containers of a disposable type for oxygen-sensitive liquid foods, such as milk, juice, wine and cooking oil, by folding and heat-sealing in a manner known per se. Such packaging containers are nowadays produced with the aid of modern packaging machines of the type in which finished packages are shaped, filled and sealed.

[0102] One way in which packaging containers made of the packaging laminate 10 in FIG. 1 can be shaped, filled and sealed is illustrated in FIG. 3. The so-called single-use packages are produced from a web by being shaped into a tube 31, in which the longitudinal edges 32, 32′ of the web are joined to each other in an overlap seam 33 by melting together the mutually facing surfaces of the plastic layers 14 and 15. The tube is filled 34 with the food product in question and is divided into contiguous pillow-shaped packaging units 36 by repeated pressing-together and heat-sealing of the tube transversely with respect to the longitudinal direction 35 of the tube, below the product level of the tube, and the packaging units are separated from each other and finally given the desired geometric shape, usually a parallelepipedal shape like a brick, by means of at least one further folding and heat-sealing step.

[0103] A well-known example of a single-use package of this type is the commercial package sold under the name Tetra Brik aseptic, which is shown in FIG. 4. In addition to the characteristic brick-like outer shape, a unique feature of this commercial type of packaging is that it is produced more or less completely by folding and heat-sealing 41, 42 of the web-shaped packaging laminate, without the use of extra packaging parts such as separate tops and/or bottoms. Such packaging containers 40 can also be provided with a suitable opening arrangement 43, for example a screw cap which, when opened, penetrates and removes the packaging material and permits emptying of the packaged product. For this purpose, the laminated packaging laminate can have perforations in the paperboard layer that has been laminated in between the polymers and barrier layers of the laminate. Alternatively, a hole is punched in the laminated packaging material immediately before the filling process, after which the hole is provided with a tape or pull-tab, on both sides of the packaging material. After the packaging container has been filled and sealed, an opening arrangement in the form of a hinge or screw cap can be applied on top of the covered hole. Alternatively, an opening arrangement is applied which is cast onto a punched hole directly during the filling process. It is not necessary to provide the packaging container with an opening device, it can also be torn open by means of a tear-perforation, or by cutting.

[0104] Alternatively, packaging containers can be produced as above but have, as their final shape, the pillow shape that is obtained directly after the packaging units have been separated from each other and that is not therefore further shaped by folding. Such a package is generally produced using a thinner paperboard material and therefore entails greater demands on adhesion and integrity of the packaging material with regard to the lamination layers and also to the mechanical strength characteristics, in particular the elastic characteristics, of the polymer layers. An example of one such package is shown in FIG. 5.

[0105] Packaging containers for oxygen-sensitive liquid food, for example juice, can also be produced from sheet-like blanks or prefabricated blanks of the packaging laminate 10 in FIG. 1. From a tubular blank of the packaging laminate 10 that is folded flat, packages are produced by first of all building the blank up to form an open tubular container capsule, of which one open end is closed off by means of folding and heat-sealing of integral end panels. The thus closed container capsule is filled with the food product in question, e.g. juice, through its open end, which is thereafter closed off by means of further folding and heat-sealing of corresponding integral end panels. An example of a packaging container produced from sheet-like and tubular blanks is shown in FIG. 6 and is a so-called gable-top package 60. There are also packages of this type which have a moulded top and/or screw cap made of plastic.

Comparative Example 1

[0106] Packaging laminate 10 was produced with the composition indicated in the following table:

TABLE-US-00001 Coating Coating quantity, Reference quantity, g/m.sup.2 (Example sign in g/m.sup.2 (reference 1 according to Laminate layer figures example 1) the invention) Low-density 14 12 12 polyethylene (LDPE) Paperboard 11 Ethylene-acrylic acid 13b —  3 copolymer (EAA) (Primacor 3540 Dow; with about 3, 2 mol-% carboxylic acid groups) Low-density 13a 20 10 polyethylene (LDPE) (Novex 19N730) (Novex 19N730) (Autoclave- LDPE) Ethylene-acrylic acid 13c — 3 (Primacor copolymer (EAA) 3540 Dow) Aluminium foil 12 6.3 μm 6.3 μm Ethylene-acrylic acid (not  6  6 copolymer (EAA) shown) Blend of LDPE and m- 15 19 19 LLDPE (weight ratio 30:70)

[0107] Packaging laminate 10 was produced by co-extrusion of the material layers 13a-13c as a three-layer structure, with the material layers included in the sequence 13b/13a/13c. This co-extrusion could generally be carried out at an extrusion speed of 200 m/min and at an extrusion temperature of below 310° C. and without the use of ozone or other extra chemicals to achieve and maintain a permanent binding of the aluminium foil 12, serving as gas barrier, to the paper or paperboard layer 11 of the packaging laminate. The paperboard material used throughout was CLC/C material with a flexural stiffness of 260 mN. The three layers were able to be co-extruded at the temperatures 290-310-290° C. and at a web speed of 650 m/min, with excellent (non-measurable, above the detection limit) adhesion to the paperboard layer or barrier layer.

[0108] The known packaging laminate of the prior art, constituting a further reference example 1, was produced in a similar manner by extrusion of only the material layer 13a, of LDPE only, but in this case an extrusion temperature as high as 325° C. was needed, together with addition of ozone, to achieve an acceptable binding between the aluminium foil 12 and the paper or paperboard layer 11. A packaging laminate produced by the method according to Comparative Example 1 thus has considerable environmental and health-related advantages over a corresponding packaging laminate produced in the known way, i.e. without use of adhesive chemicals in direct contact with the paper or paperboard layer and with the layer serving as gas barrier, in this case the aluminium foil. The adhesion obtained, in the example according to Comparative Example 1, between the laminating material and the aluminium foil was improved to such an extent that the layers could no longer be separated along the interfaces between these two materials, i.e. the adherence was higher than the detection limit in the peel test, which is about 200 N/m. By way of comparison, satisfactory adhesion between the laminating material and the aluminium foil was also obtained in the reference example, by means of a higher extrusion temperature and also surface treatment with ozone, but the adhesion was not so great that the layers could not be separated (mean value 105 N/m). After shaping into packaging containers, satisfactory packaging integrity was obtained, i.e. durability and tightness both to liquid and oxygen, with the packaging laminates from both Example 1 and the reference example.

[0109] In a peel test, strips of packaging laminate measuring 15 mm in width are cut, and the two layers between which the adherence is to be measured are separated/delaminated. The two flaps of the delaminated strips are clamped in a tension testing machine, where the strips are further delaminated under controlled conditions at a delamination angle of 90°. The force during the delamination is measured with a load cell, and the peel test value is indicated by the unit N/m. The method is a variation of ASTM D903-98 (2010) “Standard Test Method for Peel or Stripping Strength of Adhesive Bonds”, with the difference that the specimen width is 15 mm instead of 25 mm and the delamination angle is 90° instead of 180°.

[0110] Moreover, with the purpose of testing the ability of the packaging laminate to withstand impact or percussion, like when a packaging container falls down on the floor from a certain height, observations made by an internal test method surprisingly showed a significant improvement, up to more than 30%, of the durability of the packaging laminate of Comparative Example 1 compared to the packaging laminate of the reference example 1.

Comparative Example 2

[0111] Comparative Example 1 was repeated with the difference that Primacor™ 3460 (having about 3.6-4.0 mol-% of carboxlic acid groups) was used as adhesive polymer in both outer layers 13b and 13c of the laminating material. Conventional autoclave-LDPE Novex 19N 730 was used as central layer. The three-layers were co-extruded at the temperature setting 290-290-290° C. and were able to be coated at a web speed of 500 m/min.

[0112] In both Comparative Examples 1 and 2, there was gel formation occurring at difficult circumstances in the heated melting and extrusion equipment, due to degradation induced by the carboxylic acid groups of the adhesive polymers. By optimising the extrusion lamination conditions, this is possible to prevent to a sufficient extent by thorough surveillance of the extrusion process. The window of operation, within which a good lamination result may be obtained is however narrow, and needs careful attention by operators and control systems. Lowering the extrusion temperature further in order to avoid gel formation, was found not to be an option. At 280° C. there was no, or insufficient adhesion of the adhesive polymer layer to the paperboard (no fibre tear).

Example 3

[0113] Comparative Example 1 was repeated with the difference that Novex M21N (having a carboxylic acid group (methacrylic acid) content of about 0.4 mol-%) was used as adhesive polymer in both outer layers 13b and 13c of the laminating material. Conventional autoclave-LDPE Novex 19N 730 was used as central layer. Thus, the three-layers were co-extruded at the temperature setting 290-310-290° C. and were evenly coated at a web speed of 500 m/min, without using ozone treatment, and found to have lower adhesion to the adjacent paperboard layer as well as to the Aluminium foil. There was separation between the paperboard layer and the adhesive polymer layer, and very little tear within the fibrous paperboard layer, so-called “fibre-tear”. The adhesion was judged as “just satisfactory” at about 150 N/m between the laminating material and the aluminium foil, i.e. better than in the reference Example but not as good as with the higher acid content adhesive polymer of Comparative Example 1. There was no gel formation, regardless of (provoking) difficult circumstances in the melting and extrusion equipment, such as longer than usual holding times for the molten polymer, due to stops in the lamination operation or due to an occasional peak in the heating temperature of the equipment.

Example 4

[0114] Comparative Example 1 was repeated with the difference that Novex M21N (having a carboxylic acid group (methacrylic acid) content of about 0.4 mol-%) was used as adhesive polymer in both outer layers 13b and 13c of the laminating material. Conventional autoclave-LDPE Novex 19N 730 was used as central layer. Thus, the three-layers were co-extruded at the temperature setting 310-310-310° C. and were evenly coated at a web speed of 500 m/min, without using ozone treatment.

[0115] The results from Example 4 were very positive, regarding adhesion to paperboard as well as to aluminium foil and regarding gel formation. Improved adhesion to the aluminium foil (above 200 N/m, i.e. inseparable, as in Comparative Example 1) was seen, and in particular the adhesion result to the paperboard was improved. There was no separation between the paperboard layer and the adhesive polymer layer, but tear within the fibrous paperboard layer, so-called “Fibre-tear”. There was no trace of gel formation observed, neither in the adhesive layers nor in the extrusion equipment under the same conditions as in Example 3.

[0116] Thus, when lowering the amount of carboxylic acid monomer unit content in the adhesive polymer, it was surprisingly found that improved and more robust adhesion results were obtained, and in particular that the operating window could be widened such that higher extrusion temperatures in the adhesive polymer layers may be used, without risk for gel formation and particles in the adhesive polymer layer or in the extrusion equipment. Still, high extrusion temperatures as needed when extruding LDPE alone (Example 2) are not needed for achieving good adhesion.

[0117] Accordingly, the use of a an adhesive ethylene co-polymer having a lower carboxylic acid content, makes it possible to manufacture improved packaging laminates, without gel particles in the adhesive polymer applied, but still with excellent adhesion between the laminating material and the paperboard surface, and without need for surface treatments such as ozone treatment. Similar packaging laminates having a higher acid content in the laminating material will either have too low adhesion to paperboard, or a high risk for gel degradation particles present in the adhesive layers. At continuous and industrial production of packaging laminates, this is an evident and notable improvement.