Laminated packaging material, packaging containers manufactured therefrom

Abstract

The present invention relates to a method for manufacturing of a laminated cellulose-based liquid or semi-liquid food packaging material, wherein the laminated packaging material has a bulk material layer of paper, paperboard or other cellulose-based material, an innermost, heat sealable and liquid-tight layer of a thermoplastic polymer, the innermost polymer layer intended to be in direct contact with the packaged food product, a barrier layer laminated between the bulk layer and the innermost layer. The invention further relates the laminated packaging materials obtained by the method and to a packaging container for liquid food packaging, comprising the laminated packaging material or being made from the laminated packaging material obtained by the method.

Claims

1. Laminated cellulose-based, liquid- or semi-liquid food packaging material, for heat sealing into aseptic packaging containers, comprising a bulk material layer of paper, paperboard or other cellulose-based material, an innermost, heat sealable and liquid-tight layer of a thermoplastic polymer, the innermost polymer layer intended to be in direct contact with the packaged liquid- or semi-liquid food, a barrier layer laminated between the bulk layer and the innermost layer, wherein the barrier layer is a compact-surface barrier paper coated with a pre-coating material so that the compact-surface barrier paper has a pre-coating surface and subsequently further coated with a vapour deposition barrier coating onto the pre-coating surface, the pre-coating material being a barrier material selected from the group consisting of polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), starch and starch derivatives, cellulose and cellulose derivatives, and other polysaccharides and polysaccharide derivatives, polyvinylidene chloride (PVDC), and polyam ides, the compact-surface barrier paper having a density of 800 kg/m.sup.3 or higher, a surface smoothness value below 300 ml/minute Bendtsen (ISO 8791-2), a thickness of 60 μm or lower, a grammage of from 20 to 40 g/m.sup.2, a wet strength from 0.4 to 0.6 kN/m (ISO 3781) and an air permeance below 2.0 nm/Pas (SCAN P26).

2. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper has a thickness from 20 to 40 μm.

3. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper material has a tensile strength from 40 to 80 MPa in a cross direction, CD, and from 140 to 180 MPa in the machine direction, MD.

4. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper material has an air permeance of 0.1 to 1.7 nm/Pas (SCAN P26).

5. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper material has a tear resistance below 200 mN in MD as well as in CD (ISO1974).

6. Laminated packaging material as claimed in claim 1, wherein the thermoplastic polymer of the innermost heat sealable layer is a polyolefin.

7. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper is laminated to the bulk layer by a bonding layer of a thermoplastic polymer.

8. Laminated packaging material as claimed in claim 1, wherein the vapour deposition barrier coating is an aluminium metallization coating.

9. Laminated packaging material as claimed claim 1, wherein the pre-coating barrier material is PVOH and the vapour deposition coating is a metallised coating having an optical density higher than 1.5.

10. Laminated packaging material as claimed in claim 1, wherein the bulk layer comprises a cellulose material layer functioning as a spacer layer in a sandwich structure within the laminated packaging material, the density of the spacer layer being lower than 750 kg/m.sup.3.

11. Laminated packaging material as claimed in claim 10, wherein the spacer layer is a fibrous layer made by a foam-forming process, having a density from 100 to 600 kg/m.sup.3.

12. Liquid- or semi-liquid food packaging container comprising the laminated packaging material as defined in claim 1.

13. Laminated packaging material as claimed in claim 1, wherein the thermoplastic polymer of the innermost heat sealable layer is a blend of metallocene-catalysed linear low density polyethylene (m-LLDPE) and low density polyethylene (LDPE).

14. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper is laminated to the bulk layer by a bonding layer of low density polyethylene (LDPE).

15. Laminated cellulose-based packaging material to be heat-sealed into aseptic packaging containers containing liquid- or semi-liquid food product, comprising: a bulk material layer of paper, paperboard or other cellulose-based material; an innermost, heat sealable and liquid-tight layer of a thermoplastic polymer that directly contacts the liquid- or semi-liquid food product in the aseptic packaging containers when the laminated packaging material is heat-sealed into the aseptic packaging containers containing the liquid- or semi-liquid food product; a barrier layer between the bulk material layer of paper, paperboard or other cellulose-based material and the innermost, heat sealable and liquid-tight layer of thermoplastic polymer, the barrier layer being a compact-surface barrier paper, the compact-surface barrier paper having a density of 800 kg/m.sup.3 or higher, a surface smoothness value below 300 ml/minute Bendtsen (ISO 8791-2), a thickness of 60 μm or lower, a grammage of from 20 to 40 g/m.sup.2, a wet strength from 0.4 to 0.6 kN/m (ISO 3781) and an air permeance below 2.0 nm/Pas (SCAN P26); a pre-coating material applied to a surface of the compact-surface barrier paper facing the innermost, heat sealable and liquid-tight layer of thermoplastic polymer so that the compact-surface barrier paper has a pre-coating surface, the pre-coating material being a barrier material selected from the group consisting of polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), starch and starch derivatives, cellulose and cellulose derivatives, and other polysaccharides and polysaccharide derivatives, polyvinylidene chloride (PVDC), and polyamides; a vapour deposition barrier coating on the pre-coating surface of the compact- surface barrier paper, the vapour deposition barrier coating being a metallisation coating having an optical density higher than 1.5 or a diamond-like carbon coating.

16. Laminated packaging material as claimed in claim 15, wherein the compact-surface barrier paper has an air permeance of 0.1 to 1.7 nm/Pas (SCAN P26).

17. Laminated packaging material as claimed in claim 15, wherein the compact-surface barrier paper has a tear resistance below 200 mN in MD as well as in CD (ISO1974).

18. Laminated non-foil cellulose-based packaging material to be heat-sealed into aseptic packaging containers containing liquid- or semi- liquid food product, comprising: a bulk material layer of paper, paperboard or other cellulose-based material; an innermost, heat sealable and liquid-tight layer of a thermoplastic polymer that directly contacts the liquid- or semi-liquid food product in the aseptic packaging containers when the laminated packaging material is heat-sealed into the aseptic packaging containers containing the liquid- or semi-liquid food product; a barrier layer between the bulk material layer of paper, paperboard or other cellulose-based material and the innermost, heat sealable and liquid-tight layer of thermoplastic polymer, the barrier layer being a compact-surface barrier paper, the compact-surface barrier paper having a density of 800 kg/m.sup.3 or higher, a surface smoothness value below 300 ml/minute Bendtsen (ISO 8791-2), a thickness of 60 μm or lower, a grammage of from 20 to 40 g/m.sup.2, a wet strength from 0.4 to 0.6 kN/m (ISO 3781) and an air permeance below 2.0 nm/Pas (SCAN P26); a vapour deposition barrier coating providing barrier properties against oxygen and/or light, the vapour deposition barrier coating being between the compact-surface barrier paper and the innermost, heat sealable and liquid-tight layer of thermoplastic polymer.

19. Laminated packaging material as claimed in claim 18, further comprising a pre-coating material layer applied to the compact-surface barrier paper so that the pre-coating material layer is between the compact-surface barrier paper and the vapour deposition barrier coating, the pre-coating material layer being a barrier material selected from the group consisting of polyvinyl alcohol (PVOH), ethylene vinyl alcohol (EVOH), starch and starch derivatives, cellulose and cellulose derivatives, and other polysaccharides and polysaccharide derivatives, polyvinylidene chloride (PVDC), and polyamides.

20. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper has a grammage of from 25 to 30 g/m.sup.2.

21. Laminated packaging material as claimed in claim 1, wherein the compact-surface barrier paper has a surface smoothness value below 250 ml/minute Bendtsen (ISO 8791-2).

Description

EXAMPLES AND DESCRIPTION OF DRAWINGS

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

(2) FIG. 1a is showing a schematic, cross-sectional view of a specific example of a laminated packaging material which has a compact-surface barrier paper layer according to the invention,

(3) FIG. 1b shows a schematic, cross-sectional view of a further such specific embodiment of a laminated packaging material with a compact-surface barrier paper layer,

(4) FIG. 1c shows a schematic, cross-sectional view of yet a further embodiment of a laminated packaging material with a compact-surface barrier paper layer,

(5) FIG. 1d shows a schematic, cross-sectional view of yet another embodiment of a laminated packaging material with a compact-surface barrier paper layer,

(6) FIG. 2a shows schematically an example of a method, for laminating the compact-surface barrier paper layer to the bulk material in accordance with the invention,

(7) FIG. 2b shows schematically an example of a different method, for laminating the compact-surface barrier paper layer to the bulk material, in accordance with the invention,

(8) FIG. 3a, 3b, 3c, 3d show typical examples of packaging containers produced from the laminated packaging material according to the invention,

(9) 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,

(10) FIG. 5 is a diagram showing how the oxygen barrier properties of a laminated packaging material from a cellulose fluting material bulk layer is deteriorated in comparison to a conventional paperboard-based laminated liquid packaging material, when laminated with an aluminium foil barrier in the same way and formed into filled pouch packages of the same kind,

(11) FIG. 6 is a diagram which shows how the OTR may be improved in conjunction with extrusion coating/lamination metallised barrier layer with an adhesive polymer,

(12) FIG. 7 is a diagram which shows how the compact-surface barrier paper layer is capable of providing light barrier properties,

(13) FIG. 8 shows how the bending stiffness is improved in a sandwich structure having a low-stiffness spacer layer and a paper facing layer arranged or laminated onto each side of the spacer layer.

(14) 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 from a spacer layer 11a of a cellulose material, such as a foam-formed fibrous cellulose layer or a layer of a fluting material, or with any combination of a higher density paper or cellulose-based product with a foamed cellulose or fluting material. In this particular embodiment, the spacer layer is a layer of foam-formed cellulose material of grammage about 70 g/m.sup.2.

(15) On the inside, of the spacer layer 11a, the laminated material comprises a thin and high-density paper facing layer 12a, having a barrier coating 13a,14a applied to it, the paper facing layer thus interacting in a sandwich structure with the spacer layer 11a and an outside paper facing layer 16a. The paper facing layer 12a is a thin, high-density compact-surface barrier paper layer having a surface roughness of lower than 300 Bendtsen ml/min. In particular a greaseproof paper of the type Super Perga WS Parchment with grammage 32 g/m.sup.2 and surface roughness of about 200 ml/min, from Nordic Paper was used.

(16) The inside also comprises an innermost, heat sealable thermoplastic layer 15a, 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 15a is applied onto the paper facing layer by means of melt extrusion coating, or melt co-extrusion coating of a multilayer polymer structure onto the inside of the barrier paper facing layer 13a. The barrier paper may be first coated with one or more further barrier coatings. In this embodiment it is first coated with a PVOH barrier polymer, applied onto the paper surface layer by means of an aqueous dispersion in a preceding coating and drying operation. Subsequently, a metallisation coating 14a has been applied on top of the pre-coating surface 13a. The barrier coated paper facing layer 12a may alternatively be directed in the laminate such that the barrier coating 14a is facing outwards in the packaging laminate, towards the center and spacer layer 11a, but in this particular embodiment it is directed inwards, towards the the innermost sealing layer. In an alternative embodiment, the paper facing layer 13a provides some barrier properties in itself, when laminated between polymer layers, such that it may be uncoated and still provide some barrier properties and thus be the barrier layer without any further coating. Also the paper facing layer 16a in the outside module may be such, or a similar, greaseproof barrier paper, onto which a print surface is arranged by for example a thin clay-coat layer or a similar white coating layer.

(17) The (co-)extrusion coating of the innermost layer 15a may be done before or after lamination of the inside layers to the spacer layer 11a. The innermost heat sealable layer or multilayer 15a may alternatively be applied in the form of a pre-manufactured film, adding further stability and durability by being an oriented film to a higher degree than what is obtainable in extrusion coating operations. Again, the inside material layers may be pre-laminated as a separate module inside, before laminating it to the spacer layer 11c. In this particular embodiment, however, the barrier-coated paper facing layer 13a-14a is first laminated to the spacer layer 11a, or the rest of the laminated material, and subsequently melt extrusion coated on the inner side of the barrier-coated paper layer with the layer or multilayer 15a of a heat sealable polymer being a polyolefin, being a low density polyethylene composition comprising a blend of a metallocene-catalysed linear low density polyethylene (m-LLDPE) and a low density polyethylene (LDPE).

(18) On the other side, the outside of the spacer material layer 11a, the packaging material comprises a print substrate layer of a thin, high-density paper 16a, with a grammage of 70 g/m.sup.2 and having a smooth print surface. If a white print substrate is desired, the thin paper facing layer may be provided with a clay-coat or the like. The paper 16a also constitutes a facing layer on the outside of the sandwich structure in interaction with the spacer layer 11a. In the final laminated material, the substrate 16a is printed and decorated with a print pattern from various colours, images and text. The material outside of the bulk layer also comprises an outermost liquid-tight and transparent layer 17a of a plastic, preferably a heat sealable thermoplastic, such as a polyolefin, such as a polyethylene material layer. The print substrate and paper facing layer 16a may be printed before or after lamination to the spacer layer, and the outermost plastic layer 17a be applied onto the printed substrate layer in a separate operation before or after lamination to the spacer layer 11a. If coating of the décor print with the plastic layer 16a takes place before lamination to the spacer layer, the whole outside material is thus prepared as one module, i.e. as a pre-laminated outside, which is then laminated to the spacer layer or to the rest of the laminate, on the outside of the spacer layer. The lamination operation could be a melt extrusion lamination operation, thus applying an intermediate thermoplastic bonding layer 18a between the spacer layer and the print substrate and paper facing layer 16a. in this particular embodiment, however, the lamination of the print substrate paper facing layer 16a to the spacer layer 11a is carried out by applying a low amount of an aqueous solution of an adhesive that is partly absorbed into the respective cellulose layers and efficiently adheres the two paper-cellulose layers together, the adhesive being starch or nano-/micro-fibrillar cellulose or polyvinyl alcohol/polyvinyl acetate or similar hydrophilic substances, which readily bond to cellulose molecules. When the adhesive material has inherent barrier properties, of course such an adhesive, although applied by a very low amount, may contribute even further to the resulting oxygen barrier properties of the laminated packaging material.

(19) An aqueous adhesive will also aid in recycling processes to more easily delaminate the layers from each other, than when hydrophobic polyolefin bonding layers were employed.

(20) The stiffness of the laminated packaging material of this example, was 128 mN.

(21) In yet a different embodiment, the print substrate 16a may be a polymer film having a colour and a surface suitable for décor printing background, such as a coloured film or a metallised film. If no paper facing layer is employed with the print substrate, either there has to be an integrated paper facing layer in the bulk layer, on the outside of the spacer layer 11, or the spacer layer has to be of higher density and grammage, such as a layer of fluting material.

(22) In FIG. 1b, a similar cross-section, of a second embodiment of a laminated packaging material, 10b, is shown. The laminated material is substantially the same as the material in FIG. 1a, except from the barrier coating of the compact-surface barrier paper 12b. The spacer layer 11b is laminated to the barrier paper by an intermediate adhesive 19b. The innermost heat sealable layer 15b is the same or similar to 15a in the packaging material 10a.

(23) The spacer layer 11b is made of a cellulose material, such as a foam-formed fibrous cellulose layer or a layer of a fluting material, or with any combination of a higher density paper or cellulose-based product with a foamed cellulose or fluting material. In this particular embodiment, the spacer layer is a foamed cellulose of grammage of about 90 g/m.sup.2.

(24) On the inside, of the spacer layer 11b, the paper facing layer 12b is a compact-surface barrier paper layer having a surface roughness of lower than 300 Bendtsen ml/min. A greaseproof paper of the type Super Perga WS Parchment, 40 g/m.sup.2 and surface roughness of about 200 ml/min, from Nordic Paper was used. The barrier paper is first coated with a PVOH barrier polymer, applied onto the paper surface layer by means of an aqueous dispersion coating in a preceding coating and drying operation. Subsequently, a PECVD DLC coating 14b has been applied on top of the pre-coating surface 13b. The DLC coating is applied at a thickness from 5 to 50, such as from 10 to 40 nm. The barrier coating 14b is directed inwards, towards the the innermost sealing layer.

(25) The (co-)extrusion coating of the innermost layer 15b may be done before or after lamination of the inside layers to the spacer layer 11b. The innermost heat sealable layer or multilayer 15b may alternatively be applied in the form of a pre-manufactured film, adding some further stability and durability by being an oriented film to a higher degree than what is obtained in extrusion coating operations. The innermost layer or multilayer 15b being a heat sealable polymer material, is a low density polyethylene composition comprising a blend of a metallocene-catalysed linear low density polyethylene (m-LLDPE) and a low density polyethylene (LDPE).

(26) Also this material has excellent oxygen barrier properties and is suitable for the formation into carton packages for sensitive and/or long-term storage liquid food products. The material has good integrity resistance to migration of free fatty acid substances present in fruit juices and similar food products, and a bending stiffness of about 340 mN.

(27) FIG. 1c shows a cross-section, of a third embodiment of a laminated packaging material, 10c. The laminated packaging material is in principle the same as that described in FIG. 1a, however with the heat sealable innermost layer being laminated to the metallised layer 14c, by an adhesive polymer comprising a polyethlyene modified by copolymerisation with a monomer having a carboxylic functionality, i.e. ethylene acrylic acid copolymer EAA. By this simple feature of adding an adhesive polymer, the adhesion of the inside layers to the metal may be increased to some expected, suitable degree, but more importantly, the oxygen barrier properties of this high-barrier compact-surface paper may be increased even further when laminated into a packaging material, up to an unexpectedly improved level. The inside polymer layers are preferably applied onto the metallised layer by means of coextrusion coating of a multilayer melt curtain of layer configuration 22c in one simultaneous coating operation. When the spacer layer 11c is a fluting material of about 100 g/m.sup.2 and the outer paper facing layer is a thin paper of grammage 70 g/m.sup.2 in combination with a compact-surface barrier paper 12c of 40 g/m.sup.2, the final laminated packaging material obtains a bending stiffness of about 130 mN.

(28) FIG. 1d shows a cross-section, of a third embodiment of a laminated packaging material, 10d. This laminated material is the same as the one described in FIG. 1c, except for the configuration of the polymer layers on the inside of the barrier paper, and the feature of having an additional layer of a polyamide on the inside of the barrier paper 12d and its coatings 13d and 14d.

(29) The metallised coating 14d is co-extrusion coated with a multilayer structure of an EAA layer 21d closest to the metal surface, as described in laminated material 10c, the EAA layer 21d being adjacent on its other side to a layer of from 5-8 g/m2 polyamide 22d, which is further adjacent to an EAA layer 23d. Finally, the multilayer structure has the innermost heat sealable layer of a low density polyetheylene composition 15d on the inside of the second EAA layer 23d. The innermost layer 15d may be co-extruded together with the polyamide and EAA layers, or alternatively coated in a further extrusion step onto the polyamide extrusion layers. Preferably, in order to minimize the number of lamination roller nips, the inside layers are all applied in one single co-extrusion coating operation.

(30) In any one of the laminated packaging materials of the invention, the thin, high-density paper facing layer on the outside of the spacer layer may thus be a paper with a grammage from 20 to 100, such as from 30 to 80, such as from 30 to 60 g/m.sup.2, and having a density from 600 to 1500 kg/m.sup.3. In particular embodiments, also that paper facing layer may be a greaseproof paper, alone or coated with a further barrier coating, such as for example a metallisation coating. Some greaseproof papers provide a further gas barrier of lower than 2 cc/m2/day/atm at 23° C. and 50% RH, when laminated between plastic layers, such as polyethylene laminate layers.

(31) In FIG. 2a it is schematically illustrated how one layer or module of layers may be laminated to another layer/module by cold aqueous adhesive absorption lamination, such that a very low amount of an aqueous adhesive solution is applied onto one of the surfaces to be laminated to each other, the aqueous adhesive solution then being absorbed into one or both of the two surfaces while adhering them together under the application of pressure. Thus, in the embodiments for manufacturing the laminated packaging materials in FIGS. 1a-1d, an aqueous adhesive solution is applied onto the surface to be laminated, of the outside layer/material module 1B;2B;3B;4B representing the layer(s) on the outside of the bulk and spacer layer, i.e. onto the non-print surface of the print substrate layer 16a; 16b; 16c; 16d, in an adhesive application operation 21. At a lamination nip between two nip rollers, a web of the center module material 1A;2A;3A;4A representing the bulk layer comprising the spacer layer, is laminated at lamination station 22 to a web of the outside module material 1B;2B;3B;4B under simultaneous forwarding of the two webs through the lamination nip, at a pressure sufficiently high for adhereing the two surfaces together, but not so high that a low density spacer layer of the sandwich structure is collapsed. The obtained web of the intermediate pre-laminate of two layers/modules 1A+1B;2A+2B;3A+3B;4A+4B is forwarded to a further lamination station for lamination to the third module or parts of it as will be described herein below in FIG. 2b, or alternatively wound up onto a reel for intermediate storage or transport to a different time or place, where the final lamination and finishing steps will take place. The cold aqueous adhesive absorption lamination method may also or alternatively be applied when laminating the inside material module 1C;2C;3C;4C to the center layer/module material or pre-laminated center and outside modules.

(32) In FIG. 2b it is schematically illustrated how one layer/module may be laminated to another layer/module by melt extrusion lamination such that the two surfaces to be laminated are bonded to each other by an intermediate thermoplastic bonding layer. According to this example, the web of the pre-laminate of the two modules laminated in the example of FIG. 2a is forwarded to a lamination nip at the same time as a web of the inside material module 1C;2C;3C;4C. At the same time, a molten curtain of a thermoplastic bonding polymer 23;19a;19b;19c;19d is extruded down into the lamination roller nip, and being cooled while pressing the two webs together, such that sufficient adhesion is obtained between the cellulose-based center module, i.e. the surface of the spacer layer 11a;11b;11c;11d and the barrier paper 13a; 13b;13c;13d of the inside material module.

(33) FIG. 3a shows an embodiment of a packaging container 30a produced from the packaging laminate 10a; 10b; 10c; 10d 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.

(34) 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.

(35) 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.

(36) FIG. 3d shows a bottle-like package 30d, which is a combination of a sleeve 34 formed from a 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.

(37) 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.

(38) In FIG. 5 it is shown how the oxygen barrier of a laminated packaging material from a bulk layer of cellulose fluting material is deteriorated in comparison to a reference conventional paperboard-based laminated liquid packaging material, when laminated with an aluminium foil barrier in the same way and formed into filled 1 litre folded pouch packages of the same kind. It has been confirmed that there were numerous cracks in the aluminium foil, when laminated to the fluting layer and formed into packages, and this was identified as the reason for loss of oxygen barrier. This shows that when selecting low-cost cellulose-based spacer layers, thus altering the mechanical properties of the bulk layer, the oxygen barrier properties are as a consequence deteriorated and there is a need to increase or improve or replace the existing barrier materials.

(39) Reference laminate: //LDPE/80 mN paperboard/LDPE/al-foil 6 μm/EAA/blend LDPE+mLLDPE/

Example 1: //LDPE/200 g/m.SUP.2 .Fluting Material/LDPE/Al-Foil 6 μm/EAA/Blend LDPE+mLLDPE/

(40) In FIG. 6 it is shown that the OTR of a metallised layer/coating may be improved further in conjunction with extrusion coating/lamination of the metallised barrier layer to an adhesive polymer, such as EAA. Such an effect of course comes in handy when there is a need to improve barrier properties of metallised materials. The particular experiment behind this conclusion was made by coating a thin Duplex paper of 50 g/m.sup.2, with two layers of 1 g/m.sup.2 PVOH and subsequently metallisation coating onto the PVOH layer surface with an OD (optical density) of about 2. When laminating the thus barrier-coated paper into a laminate and to adjacent layers of LDPE laminate layer and a blend of LDPE and metallocene-LLDPE on the inside, the oxygen transmission became almost as high as 10 cc per m.sup.2, 24 h, 1 atm at 23° C. and 50% RH. When laminated in the same way, the metallised layer being adhered to an adjacent layer of EAA, thus further bonding to the LDPE-m-LLDPE blend, the oxygen transmission was lowered to 4 cc per m.sup.2, a surprising decrease by a factor 2.5.

(41) The laminate structure:

(42) /LDPE/paper 50 g/m.sup.2/LDPE/paper 50 g/m.sup.2 with 2×1 g/m.sup.2 PVOH-metallisation/EAA/LDPE+mLLDPE/

(43) In FIG. 7 it is shown how the compact-surface barrier paper layer is capable of providing light barrier properties when being metallised with a nanometer-thin layer of aluminium. The curve showing the light transmission of light of different wavelengths is thus a laminate comprising the non-metallised compact-surface barrier paper, i.e. the Super Perga WS parchment of 32 g/m.sup.2 and about 200 ml/min surface roughness, as tested above. The corresponding, similar laminate sample, with the only difference that the barrier paper is also metallised, shows virtually no light transmission within the tested wavelength range (including visible light). The compact surface of the barrier paper accordingly also increases the density and the quality of the metallised layer. It was also concluded that the a metal layer of an optical density of about 2-3 OD will also provide improved properties for heat sealing by means of induction heating, which also implies a higher quality coating. There are, accordingly, further important advantages obtainable by a laminate comprising a metallised compact-surface barrier paper as of the invention.

(44) FIG. 8 illustrates how the bending stiffness of a laminated packaging material increases with the incorporation of at least one paper facing layer on a side of a low-stiffness bulk paperboard or a low-density cellulose-based spacer layer. Such paper facing layers may thus improve the stiffness of a laminated material and thereby also support the material barrier properties in a better way.

(45) The laminated samples tested for bending stiffness were:

(46) 1: an 80 mN stiff paperboard intended for smaller packages

(47) 2: the paperboard of 1, laminated with a 6.3 μm thick aluminium foil

(48) 3: the paperboard of 1, laminated with a Super Perga WS parchment paper of 40 g/m.sup.2

(49) 4: a bulk layer of 165 g/m.sup.2 fluting material laminated with a 72 g/m.sup.2 paper on one side and with a 6.3 μm thick aluminium foil on the other side

(50) 5: a bulk layer of 165 g/m.sup.2 fluting material laminate with a 72 g/m.sup.2 paper on one side and with a Super Perga WS parchment paper of 40 g/m.sup.2 on its other side

(51) It can thus be seen that a low-cost and low-grade bulk layer can be more properly supported by a paper facing layer on at least one side, and clearly best with such a paper facing layer on each side of the bulk layer. The bending stiffness of the samples was measured by Lorentzen & Wettre according to ISO2493-1.

(52) We have accordingly seen that the new laminated packaging material of the invention, also enables the providing of packaging containers with good integrity properties also under wet conditions, i.e. for the packaging of liquid or wet food products with long shelf life.

(53) Generally, the grammages mentioned in the above and following description are as measured by SCAN P 6:75. The material densities and layer thicknesses were measured as by ISO 534:1988.

EXPERIMENTS

(54) A compact-surface (CS) barrier paper of the type from Nordic Paper identified as Super Perga WS Parchment 32 g/m.sup.2, was laminated into a structure as follows, with or without various barrier coatings applied:

(55) //outside 12 g/m.sup.2 LDPE/Duplex CLC 260 mN/20 g/m.sup.2 LDPE/barrier paper/20 g/m.sup.2/inside heat seal: 20 g/m.sup.2 blend of LDPE and m-LLDPE//

(56) The Duplex CLC paperboard is a clay-coated paperboard of the conventional type, and m-LLDPE is a metallocene-catalysed linear low density polyethylene. The barrier paper is thus laminated between thermoplastic polymer layers, i.e. polyethylene layers.

(57) The CS barrier paper was laminated 1) uncoated, 2) metallisation coated directly onto the cellulose paper surface, 3) pre-coated with PVOH with 1 g/m.sup.2 and subsequently metallisation coated onto the PVOH surface, 4) pre-coated with 1 g/m.sup.2 EAA and subsequently metallisation coated, and in a final experiment, 5) pre-coated with 1 g/m.sup.2 PVOH and subsequently PECVD-coated with a DLC barrier coating. Metallisation coatings were applied to an optical density of 2.5. A DLC coating was applied at 5-50 nm, such as from 10 to 40 nm.

(58) As may be seen from the results of oxygen transmission measurements made with an Oxtran equipment at 23° C. and at 50 and 80% RH, respectively, equipment based on coulometric sensors, with a standard deviation of the results being ±0.5 cm.sup.3/m.sup.2/day. the PVOH and metallisation coated barrier paper surprisingly has an oxygen barrier on par with aluminium foil, i.e. lower than 1, such as about 0.5 or lower, cc/m.sup.2/24 h/atm at 23° C. and 80% RH. Also, the water vapour transmission of the PVOH-metallisation coated barrier paper was the best obtained and on par with the requirements in order to reach the same performance as with aluminium foil packaging. Water vapour transmission was measured at 40° C. and 90% RH as g/m.sup.2, 24 h.

(59) It was seen that the metallisation of the un-coated barrier paper does not contribute further to oxygen barrier properties, but does on the other hand not subtract anything from oxygen barrier performance either. Furthermore, it was seen that a pre-coating of EAA did not contribute to the oxygen barrier of a laminated material, while the PVOH pre-coating interacts with the adjacent layers in a positive manner to improve the oxygen barrier.

(60) A coating combination of PVOH and a PECVD-coated DLC (diamond-like carbon) coating also provided very good oxygen barrier, and a good water vapour barrier, the latter which however leaves some small room for improvement up to the level of aluminium foil.

(61) From forming into heat sealed envelopes, simulating the re-forming and sealing of the laminated packaging material into package pouches, it was further also seen that the material which best withstood such handling best was the PVOH- and metallisation-coated compact-surface barrier paper. Such good oxygen barrier properties had not been seen before. As seen in table 1, the barrier paper when laminated uncoated into the laminate structure, also provides some barrier properties, which do not deteriorate with metallisation operations and/or subsequent heat sealing of envelopes. This means that the oxygen entered into the packages only via the planar surfaces of the packages, of which the oxygen barrier properties were not affected by the metallisation operation and not by the folding operation.

(62) The reference heat sealed envelope from a conventional aluminium-foil and paperboard laminate resulted in an OTR value of 0.024 cc/pack/day/0.2 atm, 23° C., 50% RH.

(63) TABLE-US-00001 TABLE 1 CS GPP: Super Perga WS Parchment FL109 CS GPP CS GPP CS GPP CS GPP CS GPP met PVOH-met EAA-met PVOH-DLC OTR 1-2 1.5 0.1-0.4 1.8 0.3 cc/m.sup.2/day/atm 23° C. 50% RH OTR  6-10 5.6 0.4 5.0 0.4 cc/m.sup.2/day/atm 23° C. 80% RH WVTR g/m.sup.2/day 6.4-6.8 8.1 0.5 (ok!) 1.2 2.0 40° C. 90% RH Heat sealed Not ok Not ok Ok Not ok Ok oxygen envelopes But the But very good barrier Ok/not Ok folding light barrier Almost ok vs reference did not and induction water 0.025 cc/ increase sealing was vapour pack/day/0.2 atm, the OTR enabled barrier 23° C. 50% RH of a flat sample!

(64) Earlier attempts to increase OTR of similar high-density papers, having a PVOH pre-coating, had shown that the subsequent metallisation coating increased the oxygen transmission, rather than reduced it.

(65) In order to find the optimally working compact-surface barrier paper layer of the invention, a number of different barrier papers were considered and investigated over time. It has been concluded that the grammage of the paper should be 60 g/m.sup.2 or lower, the thickness should be 60 μm or lower and the density 800 kg/m.sup.3 or higher. Preferably, the papers should have a grammage from 20 to 40 g/m.sup.2, and a thickness from 20 to 40 μm. These properties are all important for providing the right mix of mechanical properties, for laminating into a packaging material structure, as well as for enabling cost-efficient vapour deposition of barrier coatings. Furthermore, it has been seen that the surface of a barrier paper, should have a dense and smooth topography, below 450, such as below 300 ml/minute, such as below 250 ml/minute, such as below 200 ml/minute, as measured by ISO 8791-2 (Bendtsen) since it seems to have an impact on the final barrier properties of the coated material. The superior oxygen barrier and water vapour barrier properties of the PVOH-pre-coated and metallised compact surface barrier paper as defined above are very surprising, and believed to be the result of synergetic interaction between the paper type and its mechanical and surface qualities on the one hand, and the combination of the pre-coating and metallisation materials and possibly their optimal layer thicknesses, on the other hand. When employing higher thicknesses or amounts of the PVOH and metallisation, respectively, it has been seen that the barrier effect is not increasing much beyond a certain thickness, and that a thicker coated layer becomes more brittle and sensitive to cracking.

(66) Filled and sealed packaging containers Tetra Brik® Aseptic 1000 ml produced from the material as of Variant 21, showed excellent oxygen barrier of not more than 0.06 cc/package/24 hours, which is fully comparable to the same packages made from packaging laminate based on aluminium foil barrier. This had also never been seen before, when working with barrier materials on paper substrates.

(67) In table 2, the induction heating properties of various metallization-coated laminate samples are compared, and it may be seen that also in this respect the PVOH-coated and subsequently metallised specific CS barrier paper of the invention is optimized beyond what has been seen from other similar high-density papers. For the better function of induction heating of adjacent polymer layers, by means of the metallised layer, the SR value (sheet resistance) should be as low as possible at a reasonable optical density applied, of the metallization layer, and be able to provide heat sealing of thermoplastic polymers over a large range of power settings, i.e. be able to provide good heat seals quickly and reliable in a robust sealing operation.

(68) The evaluation of the different samples were rated according to a scale from 1-3, where 1 means “not acceptable”, 2 means “uncertain” and 3 means “acceptable”.

(69) The laminate samples tested were: (g/m.sup.2) metal layer towards the inside i.e. the LDPE+mLLDPE

(70) Variant 2: //LDPE 12/80 mN paperboard/LDPE 20/Super Perga 32 Metallised to OD 1.3/LDPE+mLLDPE 25//

(71) Variant 3: //LDPE 12/80 mN paperboard/LDPE 20/Super Perga 32 Metallised to OD 1.6/LDPE+mLLDPE 25//

(72) Variant 8: //LDPE 12/30 mN paperboard/LDPE 20/Super Perga 32 Metallised to OD 1.3/LDPE+mLLDPE 25//

(73) Variant 9: //LDPE 12/30 mN paperboard/LDPE 20/Super Perga 32 Metallised to OD 1.6/LDPE+mLLDPE 25//

(74) Variant 21: //LDPE 12/260 mN paperboard/LDPE 20/Super Perga 32+PVOH 1+Metallised to OD 3/LDPE+mLLDPE 25//

(75) TABLE-US-00002 TABLE 2 Power setting [W] SR** 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2500 OD [Ω□] Variant 2 1 1 1 2 2 2 1 1 1 1 1 1 1 1.3 4.3 Variant 3 1 1 1 2 2 2 2 3 3 3 2 3 3 1.6 3.0 Variant 8* 1 1 1 2 2 2 2 2 2 3 2 2 2 1.3 4.5 Variant 9* 1 3 3 3 2 2 2 3 2 2 2 3 3 1.6 2.9 Variant 21 1 3 3 3 3 3 3 3 3 3 3 3 3 2.5 0.7

(76) It may be concluded from the above tests that the metallised pre-coated compact-surface barrier paper of the invention, also shows great potential for robust and repeatable induction heat sealing at reasonable optical density of the metallization coating. An OD of at least 2.5 is sufficient for good induction properties. The differences of paperboard quality and innermost heat sealing polymer layer thickness, are known from experience not to affect the sealing results to a significantly. The pre-coating beneath the metallisation coating has proven to be necessary for the robust sealing results, and such pre-coatings should be selected that are sufficiently thermostable and resistant to melting or deterioration under influence of induction heating, such as e.g. PVOH.

(77) 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.