Laminated packaging material, packaging containers manufactured therefrom and a method for manufacturing the laminate material

Abstract

The present invention relates to a laminated liquid food packaging material, comprising a bulk layer, and a barrier layer portion and a polymer layer structure for balancing package integrity vs openability of the package. 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. Liquid carton packaging laminate having the following laminated layer portions, a. an outermost liquid-tight and heat sealable layer of a thermoplastic polymer, outermost meaning directed to the outside of a packaging container made from the packaging laminate, b. a bulk layer of carton or paperboard, the bulk layer including an outer side and an opposite inner side, the outermost liquid-tight and heat sealable layer being applied on the outer side of the bulk layer, c. a barrier layer portion that includes an inner side, d. a lamination layer portion, which binds the inner side of the bulk layer to the barrier layer portion, e. an innermost layer portion of liquid-tight and heat sealable polymer, applied on the inner side of the barrier layer portion so that the lamination layer portion and the innermost layer portion are on opposite sides of the barrier layer portion, f. optionally, a layer of an adhesive polymer, which binds the innermost layer portion to the barrier layer portion, and has a thickness from 4 to 9 μm, the innermost layer portion having an intermediate layer of low density polyethylene (LDPE) and an innermost layer, which constitutes the inside surface of a packaging container made from the packaging laminate, of a linear low density polyethylene produced with a metallocene or metallocene-type catalyst, (mLLDPE), the innermost layer portion and the adhesive layer constituting inside polymer layers, wherein the lamination layer portion has a center layer of an mLLDPE, and a support layer of LDPE on each side of the center layer, the support layers of LDPE binding the center layer to the bulk layer and to the barrier layer portion, on the respective sides of the center layer, and wherein the thickness of the center layer is from 4 to 15 μm and constitutes not more than 40% of the total thickness of the lamination layer portion, the total thickness of the lamination layer portion being lower than 50 μm and wherein the thickness of the innermost layer of mLLDPE is from 6 to 20 μm and constitutes not more than 50% of the total thickness of the inside polymer layers, the total thickness of the inside polymer layers being up to 50 μm and wherein the mLLDPE of the innermost layer has at least one melting point from 95 to 105° C. and wherein the LDPE of the intermediate layer has a melting point from 105 to 115° C.

2. Liquid carton packaging laminate as claimed in claim 1, wherein the mLLDPE polymer has a melt flow index from 10 to 25 g/10 min at 190° C., 2.16 kg (ISO1133), while the LDPE polymer has a melt flow index from 4 to 12 g/10 min at 190° C., 2.16 kg (ISO1133).

3. Liquid carton packaging laminate as claimed in claim 1, wherein the mLLDPE of the innermost layer is the same as the one used in the center layer of the laminate layer portion.

4. Liquid carton packaging laminate as claimed in claim 1, wherein the LDPE polymer of the intermediate layer of the innermost layer portion is the same as the one used in the support layers of the laminate layer portion.

5. Liquid carton packaging laminate as claimed in claim 1, wherein the outermost liquid-tight and heat sealable layer comprises an LDPE polymer which is the same as the LDPE polymer of the intermediate layer of the innermost layer portion.

6. Liquid carton packaging laminate as claimed in claim 1, wherein the barrier layer portion is an aluminium foil.

7. Liquid carton packaging laminate as claimed in claim 1, wherein the adhesive polymer has a melt flow index from 4 to 12 g/10 min at 190° C., 2.16 kg (ISO1133) and has a content of carboxylic functional groups from 3 to 10 weight-%.

8. Liquid carton packaging laminate as claimed in claim 1, wherein thickness ratio of the total thickness of the inside polymer layers to the thickness of the laminate layer portion is greater than 1.

9. Liquid carton packaging laminate as claimed in claim 1, wherein the bulk layer is a paperboard having a surface weight from to 50 to 450 g/m.sup.2.

10. Liquid carton packaging laminate as claimed in claim 1, wherein the center layer of the laminate layer portion has a thickness from 4 to 8 μm, and constitutes not more than 40% thickness of the total laminate layer portion, which has a total thickness of 25 μm or lower, and the thickness of the innermost layer is from 6 to 15 μm, and constitutes not more than 50% of the total thickness of the inside polymer layers, which is 40 μm or lower.

11. Liquid carton packaging laminate as claimed in claim 10, wherein the thickness ratio of the total thickness of the inside polymer layers to the thickness of the laminate layer portion is greater than 1.3.

12. Liquid carton packaging laminate as claimed in claim 10, wherein the bulk layer is a paperboard having a surface weight from 100 to 400 g/m.sup.2.

13. Method for manufacturing of a liquid carton packaging laminate as claimed in claim 1, comprising a step of extrusion laminating a web of the bulk layer to a web of the barrier layer portion by means of melt co-extruding the center layer of mLLDPE together with at least one support layer of LDPE, between the webs, and press together while solidifying the molten polymer in a roller nip, and a further step of melt co-extrusion coating the innermost layer of mLLDPE together with at least the intermediate layer of LDPE onto a web surface comprising the barrier layer portion.

14. Method for manufacturing of a liquid carton packaging laminate as claimed in claim 13, wherein all the polymer layers of the laminate layer portion, are co-extruded together in one melt extrusion operation.

15. Method for manufacturing of a liquid carton packaging laminate as claimed in claim 13, wherein all the inside polymer layers are co-extruded together in one melt extrusion operation.

16. A packaging container manufactured from the liquid carton packaging laminate as defined in claim 1.

17. Liquid carton packaging laminate as claimed in claim 1, wherein the mLLDPE polymer has a melt flow index from 15 to 25 g/10 min at 190° C., 2.16 kg (ISO1133), while the LDPE polymer has a melt flow index from 4 to 12 g/10 min at 190° C., 2.16 kg (ISO1133).

18. Liquid carton packaging laminate as claimed in claim 10, wherein the thickness ratio of the total thickness of the inside polymer layers to the thickness of the laminate layer portion is greater than 1.5.

19. Liquid carton packaging laminate as claimed in claim 10, wherein the bulk layer is a paperboard having a surface weight from 100 to 350 g/m.sup.2.

Description

EXAMPLES AND DESCRIPTION OF DRAWINGS

(1) In the following, embodiments of the invention will be described with reference to the drawings, of which:

(2) FIG. 1 is showing a schematic, cross-sectional view of a laminated packaging material according to the invention,

(3) FIG. 2a shows schematically a preferred example of a method, for laminating an aluminium foil barrier to a bulk layer in accordance with the invention,

(4) FIG. 2b shows schematically a preferred example of a method, for laminating the inside layers including the inner layer portion of heat-sealable and liquid-tight thermoplastic polymers to the barrier layer portion, in accordance with the invention, FIG. 3a, 3b, 3c, 3d show typical examples of packaging containers produced from the laminated packaging material according to the invention,

(5) 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,

(6) FIG. 5 is a diagram showing how the openability varies between three different material structures, of which one is according to the invention,

(7) FIG. 6a is a diagram which shows the general influence of a thinner laminate layer portion on the peak plastic strain in the aluminium foil, and a comparison between a layer structure according to the invention and a layer structure according to a corresponding prior art layer structure,

(8) FIG. 6b is a diagram showing the peak plastic strain in the aluminium foil as a function of total thickness of the laminate layer portion,

(9) FIG. 6c is a diagram showing the plastic strain in the aluminium foil as a function of total thickness of the inside polymer layers,

(10) FIGS. 7a and 7b further respectively shows a diagram wherein the crack defects measured in the K-fold zone are plotted for a material structure of the invention, in comparison to a reference material structure,

(11) FIG. 8 shows the results of a rig test of heat sealing of different material structures at different power settings, and

(12) FIG. 9 shows an example of a possible melt diagram from analysing the two layers of the innermost layer portion together, with DSC according to ASTMD3418.

(13) In FIG. 1, there is thus shown, in cross-section, a first embodiment of a laminated packaging material, 10, of the invention. It comprises a bulk layer 11 of a paperboard, having a grammage of about 200 g/m.sup.2 and a bending stiffness of 260 mN.

(14) On the inside, of the paperboard layer 11, the laminated material comprises a barrier layer portion 12, in this case being an aluminium foil of 6.3 μm thickness.

(15) The barrier layer 12 is laminated to the bulk layer 11 by a laminate layer portion 13, consisting of a center layer of mLLDPE 14, having adjacent support layers of LDPE, 15, 16, on both sides. The support layer 15 bonds the center layer 14 to the bulk layer 11, while the support layer 16 bonds the center layer 14 to the barrier layer portion 12.

(16) An inner layer portion 17 of heat-sealable and liquid-tight thermoplastic polymer layers is applied on the inside of the barrier layer 12. The inner layer portion consists of an innermost layer of mLLDPE 18 and an intermediate layer of LDPE 19.

(17) In the case of the barrier layer portion 12 being an aluminium foil, the inner layer portion 17 is bonded to the aluminium foil 12 with an interjacent layer of an adhesive polymer 20.

(18) The outer side of the bulk layer of paperboard 11 is covered with an outside layer 21 comprising LDPE, for heat sealability and liquid tightness from the outside of a package made from the packaging laminate.

(19) In this example, the same mLLDPE polymer is used in the innermost layer 18, as in the center layer 14 of the laminate layer portion 13. The mLLDPE used in this specific example is from Dow, i.e. Elite® 5860.

(20) Furthermore, the same LDPE polymer is used in the intermediate layer 19 of the inner layer portion 17, as in the support layers 15, 16 of the laminate layer portion 13. The LDPE used was 19N730 from Ineos.

(21) Moreover, the same LDPE was used in the outermost, outside layer 21.

(22) 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 barrier layer 12 of aluminium foil, which is forwarded from a reel 22. A molten polymer curtain 23 of the laminate layer portion 13, of the center layer 14 and the support layer 15 and 16 on each side thereof, is extruded 24 into a lamination nip 25, between the bulk layer 11 and the barrier layer 12, to be pressed together and cooled to solidify the molten polymer, thus permanently adhering the bulk and the barrier layer portion 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.

(23) In FIG. 2b it is schematically illustrated how the web of the pre-laminate 26 of the bulk and barrier layers produced in FIG. 2a is forwarded to a lamination roller nip 27. At the roller nip 27, a molten curtain 28 of the three inside polymer layers, i.e. the adhesive polymer layer 20 and the inner layer portion 17 of the innermost layer 18 and the intermediate layer 19, 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 side of the barrier layer portion 12, i.e. on the inside of the aluminium foil, by pressing and solidifying the polymer layers 18, 19, 20 to the surface of the web of the aluminium foil. The resulting laminate 30 may be forwarded to further lamination of the outside layer of LDPE onto the outside of the bulk layer, or if already done, to a reeling station for further transport and storage of the packaging laminate on a reel.

(24) FIG. 3a shows an embodiment of a packaging container 30a produced from the packaging laminate 10 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 easy to handle and dimensionally stable when put on a shelf in the food store or on a table or the like.

(25) 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.

(26) 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.

(27) FIG. 3d shows a bottle-like package 30d, which is a combination of a sleeve 34 formed from pre-cut blanks of the laminated packaging material of the invention, and a top 35, which is formed by injection moulding plastics in combination with an opening device such as a screw cork or the like. This type of packages are for example marketed under the trade names of Tetra Top® and Tetra Evero®. Those particular packages are formed by attaching the moulded top 35 with an opening device attached in a closed position, to a tubular sleeve 34 of the laminated packaging material, sterilizing the thus formed bottle-top capsule, filling it with the food product and finally fold-forming the bottom of the package and sealing it.

(28) 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.

(29) The diagram in FIG. 5 shows the opening force required for the tearing open of a perforation opening of a 1-liter family package of the Tetra Brik® Slim type, made from a reference material structure and from a material structure according to the invention, as well as from a hybrid material structure.

(30) The X-axis represents the strain as measured in the material, while the Y-axis measures the force required to open the same, along a standard perforation tearing line.

(31) The three comparable laminate structures are as shown in Table 1.

(32) The reference laminated packaging material has a state-of-the-art two-layer inside with a blend of mLLDPE and LDPE and a laminate layer of LDPE.

(33) The laminated packaging material, No. 5210, has the same inside layer configuration as the reference, but a laminate layer portion as according to the invention.

(34) The comparable laminated packaging material, No. 5211, is according to the invention.

(35) TABLE-US-00001 TABLE 1 a) b) c) Ref TBA/ml 1000 S 5210 5211 12 g/m.sup.2/13.0 μm LDPE 12 g/m.sup.2/13.0 μm LDPE 12 g/m.sup.2/13.0 μm LDPE Board 260 mN Board 260 mN Board 260 mN 20 g/m.sup.2/21.7 μm LDPE 5 g/m.sup.2/5.4 μm LDPE 6 g/m.sup.2/6.5 μm LDPE 4 g/m.sup.2/4.4 μm mLLDPE 6 g/m.sup.2/6.6 μm mLLDPE 5 g/m.sup.2/5.4 μm LDPE 6 g/m.sup.2/6.5 μm LDPE 6.3 μm Al-foil 6.3 μm Al-foil 6.3 μm Al-foil 6 g/m.sup.2/6.4 μm EAA 6 g/m.sup.2/6.4 μm EAA 6 g/m.sup.2/6.4 μm EAA 19 g/m.sup.2/20.9 μm mPE 19 g/m.sup.2/20.9 μm mPE 12 g/m.sup.2/13.0 μm LDPE (70% 5860 + 30% 770 G) (70% 5860 + 30% 770 G) 6 g/m.sup.2/6.6 μm mLLDPE 100% 5860

(36) In all the three comparable laminate structures the paperboard bulk layer 51 is the same, the aluminium foil barrier layer 52 is the same, and the outermost heat sealable layer of LDPE 53 is the same and has the same thickness, i.e. 13.0 μm (12 g/m.sup.2). Also, all the three structures have a bonding layer of EAA 54 that binds the inner heat sealable layer(s) to the inside of the aluminium foil, at a thickness of 6.4 μm (6 g/m.sup.2).

(37) The reference sample material structure a) has the structure as shown in Table 1, i.e. it has one single laminate layer of 21.7 μm (20 g/m.sup.2) of LDPE 55, and an innermost layer 56 of a blend of 70 wt % of mLLDPE (Dow Elite 5860) and 30 wt % of LDPE (770G), at a thickness of 20.9 μm (19 g/m.sup.2).

(38) A different comparison material structure b) numbered as 5210, has the same inside layers structure as the reference sample, but has a different laminate layer portion, which is as the laminate layer according to the invention, having a center layer of mLLDPE at 4.4 μm (4 g/m.sup.2), and a support layer of LDPE on each side thereof, at 5.4 μm (5 g/m.sup.2).

(39) The laminate material structure according to the invention is numbered as 5211, and has a similar laminate layer portion as the structure b), but wherein the center and support layers each have a thickness of 6.5 μm. The inside layer portion has two heat sealable layers, i.e. an innermost layer of mLLDPE at 6.6 μm (6 g/m.sup.2), and an intermediate layer of LDPE, between the adhesive polymer layer and the innermost layer, at 13.0 μm (12 g/m.sup.2). Thus, the innermost layer contains in this case no LDPE, and is a considerably thinner layer, but has an adjacent, intermediate, thicker layer of LDPE, instead.

(40) The diagram of FIG. 5 thus shows that the reference sample material requires a higher initial force for opening of a perforation opening, and with a continued opening resistance clearly at a higher level than the other two samples. It can also be seen that the curves, representing the opening resistance from start of opening until the perforation is fully torn open, resemble each other, however at different levels of the force required and applied.

(41) Furthermore, the material structure according to the invention, 5211, has the lowest opening force required of all three samples.

(42) The sample 5210, which has the same inside layer configuration as the reference sample, but a different laminate layer portion, requires a lower opening force than the reference sample, probably due to that the laminate layer is considerably thinner at only 15.2 μm (14 g/m.sup.2) in total, but instead has an mLLDPE as a center layer, but at a low thickness of only 4.4 μm (4 g/m.sup.2).

(43) The material structure according to the invention thus lowered the required opening force further, by instead of a blend of mLLDPE and LDPE on the inside layer, having a thinner layer of only mLLDPE. This was a surprising and enlightening effect, considering that it has previously been thought necessary to blend an mLLDPE in order to not make it too strong to open and too hard to process, for liquid carton packaging laminates.

(44) In addition to the measured opening force, an independent panel of test openers found the sample packages made from material structure 5211 more “robust” to open, i.e. meaning that there were less plastic residues created around the opening laminate edge, as a result of opening a package.

(45) A similar test and similar findings were made regarding these three material structures, based on packages having a straw hole, to be penetrated by a straw, in order to be opened and accessed for drinking. The straw hole, to be opened, then comprised all the layers of the laminate except from the bulk layer, as described in the above.

(46) In a test series of different layer thickness configurations of laminated material structures of the invention, the peak plastic strain in the aluminium foil during folding was estimated by simulation and visualised in the diagrams 6a, 6b and 6c, as a function of polymer layer thicknesses. The material layer structures were as described in Tables 2 and 3, wherein the LDPE used in the intermediate layer of the innermost layer portion and in the laminate layer portion, was Novex® 19N730 from Ineos. The mLLDPE used was Elite® 5860 from Dow. When the mLLDPE was blended in the innermost layer portion, it was blended with the LDPE 770G from Dow. Also in the outside layer, the LDPE used was Novex® 19N730 from Ineos.

(47) The adhesive polymer used in all examples was Primacor® 3540 from Dow.

(48) Plastic strain is the strain obtained in the plastic region above the yield point where the metal does not return to its original shape after removal of stress. Higher plastic strains mean higher risk of foil cracks. An estimation of the peak plastic strain is thus a measure of the risk for strain that is effecting crack initiation in the aluminium barrier foil at fold-forming of packages to occur. Foil crack initiations have been observed to be connected to a higher oxygen transmission (OTR) through the aluminium foil barrier and the laminated packaging material. A lower peak plastic strain in the barrier material may thus result in improved oxygen barrier properties of the laminated packaging material comprising the barrier material layer, when fold-formed into packages.

(49) The diagram of FIG. 6a shows the peak plastic strain obtained in the aluminium foil, from test runs 2, 4, 3 and 5. The simulations were made based on a scenario of folding the laminated packaging materials producing the most single-folding strain in the aluminium foil, i.e. at folding the laminate such that the outside of the material is folded against itself (the aluminium foil being located on the inside of the thick bulk layer). The strain was tested at a folding angle of 100 degrees.

(50) It can be seen that at higher thickness of the laminate layer portion, by comparing runs 2 and 3 and 4 and 5, respectively, there is higher peak plastic strain in the aluminium foil and thereby likely also higher oxygen transfer or permeation through the laminate.

(51) Similarly, there is higher peak plastic strain in the aluminium foil from the prior art layer structure (run 2) than in a corresponding layer structure according to the invention (run 4), which has the same total thickness of polymer layers in the laminate layer portion, and on the inside of the aluminium foil, respectively. This is also the conclusion from comparing run 3 and run 5.

(52) The diagram of FIG. 6b shows the peak plastic strain in the aluminium foil as a function of total thickness of the laminate layer portion, structured according to the invention, (Runs 8-13). It may be concluded from the diagram, that when lowering the total thickness of the laminate layer portion from 20 to 9 μm, also the peak plastic strain of the aluminium foil was decreased from 22 to 15%, (expressed as the ratio of the sample length after deformation divided by the sample length at start). The cross represents a reference sample (Run 7) having a single innermost layer of a blend of mLLDPE and LDPE, the total inside layers being 27.4 μm (25 g/m.sup.2) thick, and a relatively thick laminate layer portion of LDPE of about 21.8 μm (20 g/m.sup.2).

(53) The diagram of FIG. 6c shows the plastic strain in the aluminium foil as a function of total thickness of the inside polymer layers. It may be concluded from this diagram, that when increasing the total thickness of the inside polymer layers the plastic strain in the aluminium foil was further decreased. The left square point represents a reference sample not according to the invention, which has a laminate thickness of 22 μm i.e. 20 g/m2. When increasing the inside layer thickness of the reference sample, the right upper square point was obtained, i.e. the plastic strain increased. However, when instead a laminate layer configuration according to the invention was used, the lower right point was obtained, i.e. the plastic strain remained unchanged. In further samples of the invention, having thinner laminate layer portions, the plastic strain instead decreased, with increasing inside layer thickness.

(54) The 20 g/m2 laminate layer portion samples are taken from runs 2, 4, and 7 in the Table. The 15 samples are taken from runs 9 and 10, while the 12 samples are taken from runs 11 and 12 in the table.

(55) The simulation test-runs resulting in the diagrams of FIGS. 6b and 6c are described further in Tables 2 and 3.

(56) TABLE-US-00002 TABLE 2 Board Outside Lam. 1 Lam. 2 Lam. 3 Inside 1 Inside 2:1 Inside 2:2 Run type Grade Grade Grade Grade Grade Grade Grade 2 CLC/C LDPE LDPE LDPE LDPE EAA LDPE mPE blend Duplex 3 CLC/C LDPE LDPE LDPE LDPE EAA LDPE mPE blend Duplex 4 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 5 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 7 CLC/C LDPE LDPE LDPE LDPE EAA — mPE blend Duplex 8 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 9 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 10 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 11 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 12 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex 13 CLC/C LDPE LDPE mLLDPE LDPE EAA LDPE mLLDPE Duplex

(57) TABLE-US-00003 TABLE 3 Package material spec Outside Board Total Total PE Stiffness Laminate 1 Laminate 2 Laminate 3 Laminate Aluminium Inside 1 Inside 2:1 Inside 2:2 inside Run [g/m.sup.2/μm] [mN] [g/m.sup.2/μm] [g/m.sup.2/μm] [g/m.sup.2/μm] [g/m.sup.2/μm] foil [μm] [g/m.sup.2/μm] [g/m.sup.2/μm] [g/m.sup.2/μm] [g/m.sup.2/μm] 2 16/17.4 370 5/5.4 10/10.9 5/5.4 20/21.3 6.3 6/6.4 14/15.2 15/16.5 35/37.7 3 16/17.4 370 6.25/6.8   12.5/13.5.sup.  6.25/6.8   25/27.1 6.3 6/6.4 17/18.5 17/18.7 40/43.2 4 16/17.4 370 7/7.6 6/6.6 7/7.6 20/21.8 6.3 6/6.4 23/25.0 6/6.6 35/37.6 5 16/17.4 370 9/9.8 7/7.7 9/9.8 25/27.3 6.3 6/6.4 27/29.3 7/7.7 40/43.0 7 12/13.0 260 5/5.4 10/11.0 5/5.4 20/21.8 6.3 6/6.4 — 19/20.9 25/27.3 8 12/13.0 260 6/6.5 6/6.6 6/6.5 18/19.6 6.3 6/6.4 12/13.0 6/6.6 24/25.6 9 12/13.0 260 5/5.4 5/5.5 5/5.4 15/16.3 6.3 6/6.4 11/12.0 7/7.7 24/25.7 10 12/13.0 260 5/5.4 5/5.5 5/5.4 15/16.3 6.3 6/6.4 14/15.2 7/7.7 27/28.9 11 12/13.0 260 4/4.4 4/4.4 4/4.4 12/13.2 6.3 6/6.4 10/10.9 8/8.8 24/25.7 12 12/13.0 260 4/4.4 4/4.4 4/4.4 12/13.2 6.3 6/6.4 13/14.1 8/8.8 27/28.9 13 12/13.0 260 3/3.3 3/3.3 3/3.3 9/9.9 6.3 6/6.4 12/13.0 9/9.9 27/28.9

(58) Thus, it is concluded from run 2-13 that thicker polymer layers in the laminate layer portion in general give higher peak plastic strain in the aluminium foil. It is indicated from runs 4-6 that a combination of a thinner laminate layer portion and a thicker total inside (i.e. thicker innermost layer portion) may give the lowest strain in the aluminium foil. It is also seen from runs 2-5 that the structure of the laminate layer portion according to the invention, i.e. including a center layer of mLLDPE at a certain proportional thickness, may give lower strain than the runs with LDPE.

(59) Again, from test runs 7-13, it may be concluded that a thinner laminate layer portion and a thicker total inside layer according to the invention (thicker innermost layer portion) may provide lower strain in the aluminium foil and accordingly, improved gas barrier properties should be obtainable.

(60) The diagram of FIG. 7a shows, the width of actual, detected cracks measured in the K-fold zone of an aluminium foil barrier in a laminated material structure of the invention, and in reference sample material structures, when fold-formed into cuboid packaging containers. A packaging material is exposed to a high strain in the K-fold zone, from fold-forming into a packaging container of a cuboid shape, such as a brick-shaped, parallelepipedic shape. The width of the formed cracks were measured and the values were plotted for the three sample laminate layer structures, which are equal, except from the features described below.

(61) The general structure is /(12 g/m.sup.2) 13.0 μm LDPE/260 mN paperboard/(12 g/m.sup.2) about 13 μm laminate layers/Al-foil 6 μm/total 25 g/m.sup.2 inside layers/

(62) Reference Sample No. 7465:

(63) A laminate layer of LDPE at (12 g/m.sup.2) 13.0 μm and an innermost layer portion of a blend heat sealable layer at (19 g/m.sup.2) 20.9 μm and an adhesive layer of (6 g/m.sup.2) 6.4 μm, the blend being 70 wt % mLLDPE and 30 wt % LDPE.

(64) Reference Sample 7466:

(65) A laminate layer of LDPE at (12 g/m.sup.2) 13.0 μm and a total inside sealing layer at (25 g/m.sup.2) 27.2 μm, however comprising a pure mLLDPE innermost layer. The inside layer structure is (6 g/m.sup.2) 6.4 μm adhesive polymer, (10 gm.sup.2) 10.9 μm LDPE intermediate layer, and (9 g/m.sup.2) 9.9 μm mLLDPE.
Sample According to the Invention 7467:
A laminate layer portion according to the invention, having a center layer of mLLDPE at (4 g/m.sup.2) 4.4 μm thickness and bonding and support layers of LDPE at (4 g/m.sup.2) 4.4 μm thickness each, on each side of the center layer, the total laminate layer portion being (12 g/m.sup.2) 13.2 μm thick, and a total inside sealing layer at (25 g/m.sup.2) 27.2 μm, comprising a pure mLLDPE innermost layer. The inside layer structure is (6 g/m.sup.2) 6.4 μm adhesive polymer, (10 g/m.sup.2) 10.9 μm LDPE and (9 g/m.sup.2) 9.9 μm mLLDPE.

(66) The larger the initial width of a crack appearing in the K-fold zone of the barrier layer, the higher is the risk for later formation of larger cracks in the barrier material, due to handling and distribution of the packages, such that ruptures and defects in the adjacent layers may be formed, potentially even worse, causing leakage of packed product content or ingress of bacteria into the filled product of the package interior. A crack in the K-fold zone of the barrier material may lead to loss of shelf life due to an increased amount of oxygen migrating into the filled packaging container. Thus, it is important to keep the width of the initial K-fold zone cracks formed by fold-forming into cuboid packages as low as possible in order to avoid or reduce the risk for package integrity or performance problems, after stressful handling and distribution.

(67) It is clearly shown, that a significant decrease of the width of the cracks formed in the aluminium foil barrier layer, in the K-fold zone, is obtained by sample 7467, i.e. the laminate layer structure of the invention. Such a laminate structure should thus also provide improved package performance, from the K-fold zone point-of-view.

(68) FIG. 7b shows the same relationship and conclusion regarding larger packaging containers having a corresponding laminated material structure, however thicker and stronger to be suitable for larger amounts of liquid food products, such as from 1.5 to 2 litres.

(69) The laminated packaging material samples were as described below, and were fold-formed into cuboid packages of a same parallel-epipedic shape (“Slim”), of 1.5 litre. The general structure is

(70) /(16 g/m.sup.2) 17.4 μm LDPE outside/370 mN paperboard/(20 g/m.sup.2) LDPE (or/7/6/7/ g/m.sup.2)/Alfoil 6 μm/(14 g/m.sup.2) 15.2 μm LDPE/(15 g/m.sup.2) mLDPE+LDPE blend (70+30 wt %)/(or /6/23/6/ g/m.sup.2).

(71) Reference Sample No. 6908:

(72) A laminate layer of LDPE at (30 g/m.sup.2) 32.6 μm and an innermost layer portion of a blend heat sealable layer at (19 g/m.sup.2) 20.9 μm, an adhesive layer of (6 g/m.sup.2) 6.4 μm, and an intermediate layer of LDPE at (20 g/m.sup.2) 21.7 μm, i.e. a total inside layer thickness of 49.0 μm, the innermost layer blend being a blend of 70 wt % mLLDPE and 30 wt % LDPE.
Reference Sample 6909:
A laminate layer of LDPE at (20 g/m.sup.2) 21.7 μm and an innermost layer portion of a blend heat sealable layer at (15 g/m.sup.2) 16.5 μm, an adhesive layer of (6 g/m.sup.2) 6.4 μm and an intermediate layer of LDPE at (14 g/m.sup.2) 15.2 μm, i.e. a total inside layer thickness of (35 g/m.sup.2) 38.1 μm, the blend being 70 wt % mLLDPE and 30 wt % LDPE.
Sample According to the Invention 6913:
A laminate layer portion according to the invention, having a center layer of mLLDPE at (6 g/m.sup.2) 6.6 μm thickness and bonding and support layers of LDPE at (7 g/m.sup.2) 7.6 μm thickness each, on each side of the center layer, the total laminate layer portion being (20 g/m.sup.2) 21.8 μm thick, and a total inside sealing layer at (39 g/m.sup.2) μm, having a pure mLLDPE innermost layer. The inside layer structure is (6 g/m.sup.2) 6.4 μm adhesive polymer layer, (27 g/m2) 29.3 μm intermediate LDPE layer and (7 g/m.sup.2) 7.7 μm innermost layer mLLDPE.

(73) Again, there was a significant decrease of the width of the cracks formed in the aluminium foil barrier layer, in the K-fold zone, obtained by sample 6913, i.e. the laminate layer structure of the invention. Such a laminate structure thus may have improved oxygen barrier properties and package integrity, from the K-fold zone point-of-view.

(74) The structures of the invention as shown by examples 7467 in FIG. 7a and 6913 in FIG. 7b, also have an improved resistance to puncture or break in the laminate layer portion, caused by fibres and uneven surfaces of bulk and barrier layers.

(75) FIG. 8 shows the results of a rig test of heat sealing at different power settings of different material structures. It can thus also be concluded that the heat sealing window is widened by the laminated material structure of the present invention, in comparison to a reference structure having a blended innermost layer of mLLDPE and LDPE. A wider heat sealing window is beneficial because the sealing operation can be initiated at a lower temperature, and allows more time for the polymer chains of the sealing polymer to disentangle and entangle again, across the interface of the two polymer surfaces to be sealed to each other.

(76) Legend:

(77) X: blocked seal

(78) O: tight seal

(79) Sample 6322: mLLDPE with melting point of 97° C. and density 907 kg/m.sup.3 as innermost sealing layer; Elite 5860 from Dow

(80) Material structure from outside to inside (g/m.sup.2): //16 LDPE/ppr 260 mN/9 LDPE/10 mLLDPE/9 LDPE/Alfoil 6.3/6 EAA/18 LDPE/10 mLLDPE//

(81) 6424: mLLDPE/LDPE blend as innermost sealing layer; mLLDPE: Elite 5860 from Dow and LDPE: 770G from Ineos

(82) Material structure from outside to inside (g/m.sup.2): //16 LDPE/ppr 260 mN/30 LDPE/Alfoil 6.3/6 EAA/17 LDPE/12 mLLDPE//

(83) 6425: mLLDPE with melting point of 106° C. and density 918 kg/m.sup.3 as sealing layer; Exceed 0019XC from Exxon Mobil

(84) Material structure from outside to inside (g/m.sup.2): //16 LDPE/ppr 260 mN/9 LDPE/10 mLLDPE/9 LDPE/Alfoil 6.3/6 EAA/18 LDPE/10 mLLDPE//.

(85) FIG. 9 thus shows an example of a possible melt diagram from analysing the two layers of the innermost layer portion together (i.e. one layer of LDPE and one layer of mLLDPE), with DSC according to ASTMD3418 at the second heating at 10° C./min. The melting point peaks of the mLLDPE “shine through” the melting curve 93 of the LDPE, since they lie rather close and the melt energy areas overlap each other. Thus, there is one melting point of the mLLDPE layer, visible as a “shoulder” on the slope of the LDPE curve at 92 in FIG. 9, and there is another mLLDPE melting point at the weakened slope 91 of the LDPE curve at the end of the melting process. A scanning ramp rate of 10° C./min, sometimes a lower ramp rate, is needed in order to “separate” the melting point peaks, to be visible in the DSC curve in this way.

(86) To conclude, the above embodiments and evaluations show that the invention as defined by the claims, makes it possible to produce liquid carton packages having both improved openability properties and improved package integrity properties, as well as improved gas barrier properties. The packaging material of the invention is suitable for high-speed lamination processes, as well as exhibiting increased robustness in high-speed filling and sealing processes. The invention also makes it possible to reduce the total amounts of polymer raw materials involved and thus provide a resource-efficient packaging material.

(87) 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 and all other features to be understood as described in the text specification.