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 cellulose-based bulk material layer and outer layers of thermoplastic polymers on both sides, having a dcorative print pattern arranged beneath one of the outer thermoplastic polymer layers. The invention further relates to the method for manufacturing the laminated packaging material and to a packaging container for liquid food packaging, comprising the laminated packaging material.

Claims

1. Laminated packaging material for packaging of liquid food, comprising a cellulose-based bulk material layer possessing an outer side, an outermost transparent and protective thermoplastic polymer layer arranged on an outside of the bulk material layer that is to be directed to the exterior of a packaging container made from the laminated packaging material, a decorative print pattern arranged between the bulk material layer and the outermost transparent and protective thermoplastic polymer layer, and visible through the outermost transparent and protective thermoplastic polymer layer, an innermost heat sealable and liquid-tight thermoplastic polymer layer, to be in direct contact with the liquid food in the packaging container, wherein the bulk material layer is a containerboard, which has been calendered to a Bendtsen outside surface roughness value lower than 200 ml air/min, and has an SCT index greater than 30 Nm/g in MD as determined in accordance with ISO 9895 and ISO 536 the outside surface of the containerboard having the Bendtsen outside surface roughness value lower than 200 ml air/min being the surface facing towards the outermost transparent and protective thermoplastic polymer layer, and wherein the laminated packaging material further comprises a cellulose-based print substrate paper, having an outside print surface carrying the decorative print pattern, the print substrate paper being adhered to the outer side of the bulk material layer by way of 1-4 g/m.sup.2 adhesive, dry weight, the print substrate paper having a surface weight of 100 g/m.sup.2 or lower (ISO 536), the outside print surface having a Bendtsen surface roughness value lower than 100 ml air/min (ISO 8791-2).

2. Laminated packaging material as claimed in claim 1, wherein a gas barrier film or foil comprising an oxygen barrier layer or coating is laminated on an inner side of the bulk material layer, between the bulk material layer and the innermost thermoplastic polymer layer.

3. Laminated packaging material as claimed in claim 1, wherein the bulk material layer has Bendtsen outside surface roughness lower than 150 ml air/min, before the bulk material layer is laminated to the print substrate paper.

4. Laminated packaging material as claimed in claim 1, wherein the outside print surface has a Bendtsen surface roughness value of below 80 ml air/min.

5. Laminated packaging material as claimed in claim 1, wherein the print substrate paper has a surface weight of lower than 80 g/m.sup.2.

6. Laminated packaging material as claimed in claim 1, wherein the outside print surface has a Cobb value from 20 to 30 g/m.sup.2 water.

7. Laminated packaging material as claimed in claim 1, wherein the print substrate paper has a density higher than 650 kg/m.sup.3, a surface weight of 100 g/m.sup.2 or lower (ISO 536), a tensile strength index (GM) of at least 40 Nm/g and a tear strength index (GM) of at least 6.0 mNm.sup.2/g, and comprising at least one sizing agent at from 0.1 to 0.4 wt-%, the outside print surface having a Bendtsen surface roughness value lower than 100 ml air/min (ISO 8791-2), and a Cobb value greater than 20 g/m.sup.2 and lower than 30 g/m.sup.2 (water).

8. Laminated packaging material as claimed in claim 1, wherein the print substrate paper is a paper selected from the group consisting of MG (Machine Glazed) paper, MF (Machine Finished) paper, LWC (Light-weight coated) paper, Flexible Packaging paper, digital printing paper and ink jet printing paper.

9. Laminated packaging material as claimed in claim 1, wherein the outside print surface of the print substrate paper is metallised and has a Bendtsen surface roughness value lower than 100 ml air/min.

10. Laminated packaging material as claimed in claim 1, wherein the outside print surface of the print substrate paper is natural brown.

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

12. Method for manufacturing a laminated packaging material for packaging of liquid food, the method comprising a) providing a first web of a cellulose-based bulk material layer, being a calendered containerboard having a Bendtsen outside surface roughness value lower than 200 ml air/min, and an SCT index greater than 30 Nm/g in MD as determined in accordance with ISO 9895 and ISO 536, the outside surface of the containerboard having the Bendtsen outside surface roughness value lower than 200 ml air/min being the surface directed to an exterior of a packaging container made from the laminated material, b) providing a second web of a cellulose-based print substrate paper, having a surface weight of 100 g/m.sup.2 or lower (ISO 536), and an outside print surface to carry a decorative print pattern, with a Bendtsen surface roughness value lower than 100 ml air/min (ISO 8791-2), c) applying an aqueous adhesive composition comprising an adhesive polymer at an amount from 1 to 4 g/m.sup.2, dry content, onto at least one of the outside of the first web and the inside of the second web, the inside of the second wet being the surface directed to an interior of said packaging container made from the aminated material, d) forwarding the first and second webs, from step c), towards a pressure roller nip to join and laminate the first and second webs together by the interjacent aqueous adhesive composition while passing the nip, and while the aqueous adhesive composition is partly absorbed into a surface of at least one of the first and second webs, e) printing a dcorative print pattern onto the outside print surface of the print substrate paper, f) laminating an innermost heat sealable thermoplastic polymer layer on the inner side of the first web of the bulk material layer, opposite the side of the print substrate paper, the innermost heat sealable thermoplastic polymer layer being the surface in contact with the liquid food in said packaging container made from the laminated material, g) laminating an outermost, transparent and protective thermoplastic polymer layer on the outer side of the second web of the print substrate paper that is opposite the side of the bulk material layer.

13. Method as claimed in claim 12, wherein step e) is carried out before steps c) and d), such that the print substrate paper is first printed with the dcorative print pattern onto the outside print surface in a separate printing operation.

14. Method as claimed in claim 12, further comprising laminating a gas barrier film or foil comprising an oxygen barrier layer or coating on an inner side of the bulk material layer so that the gas barrier film or foil is between the bulk material layer and the innermost thermoplastic polymer layer.

15. Method as claimed in claim 12, wherein the bulk material layer is calendered to the Bendtsen outside surface roughness value lower than 200 ml air/min in a separate step before step a) at a nip load from 80 to 120 kN/m and a surface temperature above 200 C., and at a calendaring speed from 500 to 1200 m/min.

16. Method as claimed in claim 12, wherein the laminating of the outermost, transparent and protective thermoplastic polymer layer on the outer side of the web of the print substrate paper occurs before the laminating of the innermost heat sealable thermoplastic polymer layer on the inner side of the web of the bulk material layer, and the printing of the dcorative print pattern onto the print surface of the print substrate paper occurs before the laminating of the outermost, transparent and protective thermoplastic polymer layer on the outer side of the web of the print substrate paper.

17. Laminated packaging material as claimed in claim 1, wherein the containerboard is linerboard.

18. Laminated packaging material as claimed in claim 1, wherein the containerboard is linerboard having a Cobb water adsorption value of lower than 35 g/m.sup.2 measured in accordance with ISO 535.

19. Method as claimed in claim 12, wherein the containerboard is a flat linerboard having a Cobb water adsorption value of lower than 35 g/m.sup.2 measured in accordance with ISO 535.

20. Method as claimed in claim 12, wherein the containerboard is linerboard.

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. 1a is showing a schematic, cross-sectional view of a first laminated packaging material according to the invention,

(3) FIG. 1b shows a schematic, cross-sectional view of a further embodiment of a laminated packaging material according to the invention,

(4) FIG. 1c shows a schematic, cross-sectional view of another embodiment of a laminated packaging material according to the invention,

(5) FIG. 2a shows schematically a method step in accordance with the invention, for laminating a web of print substrate paper to a web of bulk material layer,

(6) FIG. 2b shows schematically a preferred example of a method, for laminating a barrier film or foil to a bulk layer in accordance with the invention,

(7) FIG. 2c shows schematically a further method step, for laminating an innermost thermoplastic polymer layer to a web comprising the laminated bulk material layer, e.g. the laminated web resulting from the method step described in FIG. 2a. Alternatively, FIG. 2c may describe a further method step for laminating an outermost thermoplastic polymer layer to the outer side of a web comprising the print substrate paper with a printed dcor thereon, 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, and

(10) FIG. 5 shows how the high surface roughness of a linerboard bulk material layer may be reduced to support a good print surface of the final laminated packaging material.

(11) FIG. 6 shows the principle of a metal belt calendering operation.

TEST METHODS

(12) Grammage or surface weight (in (g/m.sup.2) is determined according to ISO 536.

(13) Bendtsen surface roughness may be measured by clamping a test piece between a flat glass plate and a circular metal head and measuring the rate of airflow in ml/minute between the paper and head. The Bendtsen technique is designed to work in the range 30-1500 ml/minute. Applicable test methods are BS 4420, ISO 8791/2, DIN 53108 and SCAN P21.

(14) The Cobb test is used to determine the water absorptivity of paper, cardboard and corrugated cardboard. The Cobb Test is carried out according to the following standards: ISO 535, EN 20535 and TAPPI T 441. One Cobb unit is 1 g/m.sup.2 (water) adsorbed onto the surface in 60 seconds while exposed to water. The Cobb value of a paper or paperboard is largely dependent on its degree of sizing. Other factors may play a role, such the degree of beating of the fibres in the pulp etc. In the print substrate papers that are suitable for the present invention, the Cobb value is mainly reflecting the degree of sizing of the paper. A quick version Cobb test may be done in half the absorption time above, i.e. at 30 seconds. The values then have to be adjusted to be comparable, i.e. doubled, but otherwise, the test is essentially the same.

(15) Tensile strength is measured according to ISO 1924-3, the measured unit being kN/m and presented as a geometrical mean (GM) value between the values of machine direction (MD) and cross direction (CD). The tensile strength index of a cellulose material will be its tensile strength normalized by its surface weight. Thus, the tensile strength index is presented by the unit Nm/g (GM).

(16) Tear strength is measured according to ISO 1974:2012, the unit being kN, also presented as GM value. The tear strength index is the value normalised by surface weight of the test sample, and presented by the unit mNm.sup.2/g.

(17) In FIG. 1a, there is thus shown a first embodiment of a laminated packaging material, 10a, of the invention. It comprises a bulk material layer 11a of a linerboard, having a surface weight of about 220 g/m.sup.2, a density of 780 kg/m.sup.3, an SCT index MD of 34 Nm/g, a Bendtsen value of 900 ml air/min, not yet calendered. By metal belt calendering at a surface temperature of about 200 C., and at high pressure in the metal belt nip, the surface roughness was reduced to 200 ml/min.

(18) On the outer side of the bulk material layer 11a, the packaging material comprises a separate layer of a print substrate paper 12a. The print substrate paper has an outer surface for receiving and carrying a printed ink dcor 12a-1, which is to provide the dcor of the final packaging container made from the packaging material. In this embodiment, the print surface paper is a natural brown (unbleached) MG (machine-glazed) paper having a surface weight of 40 g/m.sup.2, a density of 650 kg/m.sup.3, a Cobb value of 27 g/m.sup.2 water, tensile strength index GM of 49 Nm/g and tear strength index of 6 mNm.sup.2/g.

(19) The printed dcor is protected towards the external surroundings of the package by an outermost liquid-tight and transparent layer 13a of an LDPE, which was extrusion coated onto the printed print substrate paper 12a, i.e. the print substrate paper is provided with a printed dcorative pattern 12a-1.

(20) The print substrate paper 12a is laminated to the bulk paperboard by a low amount of starch adhesive 16a at between 1 and 4 g/m.sup.2.

(21) On the inner side of the bulk material layer 11a, which side is to be directed towards the inside of a packaging container formed from the laminated material, the laminated material comprises an aluminium metal foil 14a. The aluminium metal foil has a thickness of 6.3 m. The aluminium metal foil is laminated to the bulk material layer by a bonding layer 17a of 20 g/m.sup.2 of LDPE adhering and thus contacting the bulk material paperboard.

(22) Although the bulk material layer, i.e. the linerboard, is a cheap and more bulky layer than a conventional LPB paperboard, and providing less dimensional support to the packaging material, it may when laminated between the outer print substrate paper and the inside aluminium foil provide a sandwich layer contribution such that the resulting laminate has high and reliable bending stiffness, and in addition high compression strength.

(23) On the opposite, inner side of the aluminium metal foil, there is 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 melt co-extrusion coated onto the aluminium foil together with an intermediate adhesive polymer layer of EAA 18a.

(24) The lamination of the bulk material layer 11a and the aluminium metal foil 14a by extrusion lamination of the LDPE bonding layer 17a was done before the step of coextrusion coating of the innermost thermoplastic polymer layer 15a and the adhesive polymer layer 18a onto the aluminium metal foil.

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

(26) In FIG. 1b, a second embodiment of a similar laminated packaging material, 10b, is shown. The laminated material is principally the same as the material in FIG. 1a. A print substrate paper 12b, being a bleached white MG paper having a density of 785 kg/m.sup.3, a surface weight of 70 g/m.sup.2, a Cobb value of 24 g/m.sup.2, and a surface roughness on its outer side of 100 ml air/min (Bendtsen), a tear strength index GM of 7 mNm.sup.2/g and a tensile strength index of 60 Nm/g, to be printed with a printed dcor 12b-1, is laminated on the outside of the bulk material layer 11b by a starch adhesive at from 1 to 4 g/m.sup.2.

(27) The bulk material layer is the same linerboard as used in connection with FIG. 1a, of which the surface roughness was reduced to 200 ml/min by calendering.

(28) The gas barrier layer 14b is a substrate film 14b-1 of a biaxially oriented polyethylene terephthalate (BOPET) which has been coated with a nanometer-thin continuous coating 14b-2 of an amorphous diamond-like carbon coating (DLC) by means of plasma-enhanced chemical vapour deposition. The DLC coating is turned to be on the outer side of the BOPET film, and bonded to the bulk material layer by an intermediate bonding layer 17b of polyethylene. On its inner side, the BOPET film has a primer or adhesion promoting coating (not shown) to render its PET surface more compatible with extrusion-coated polyolefin based layers. The thus primed or treated BOPET film is co-extrusion coated on its inner side with an innermost layer 15b of a blend of an mLLDPE and an LDPE and an intermediate adhesive layer 18b of EAA.

(29) Although the bulk material layer, i.e. the linerboard, is a cheap and more bulky layer than a conventional LPB paperboard, and providing less dimensional support to the packaging material, it may when laminated to the outer print substrate paper and the inside layers provide a sandwich layer contribution such that the resulting laminate anyway achieves a high and reliable bending stiffness, and in addition high compression strength.

(30) FIG. 1c shows a third embodiment of a laminated packaging material according to the invention, 10c. The laminated packaging material has the same linerboard bulk layer 11c as in FIG. 1a and the same outer- and innermost thermoplastic polymer layers 13c and 15c as described in FIGS. 1a and 1b, but does not have a further gas barrier layer on the inner side of the bulk material layer.

(31) Such laminates are for example suitable for chilled dairy products not needing very high gas barrier properties of the packaging material.

(32) The laminated packaging materials 10a, 10b and 10c thus offer an opportunity for dairies and food fillers to easily differentiate food products and brands from each other by the exchangeable outside appearance of different print substrate papers having different print background effects.

(33) FIG. 2a shows how a first web of the bulk material layer A, being a liquid-food grade paperboard, was laminated to a second web of the print substrate paper B by cold aqueous adhesive absorption lamination. A low amount of an aqueous adhesive solution is applied onto the non-print surface of the web of the print substrate paper B in an adhesive application operation 21. The wet coated web of the print substrate paper is laminated to the first web of the paperboard A at lamination operation 22 in a nip of two lamination rollers, the aqueous adhesive solution then being absorbed into one or both of the two paper surfaces while pressing and adhering them together, by simultaneously forwarding the webs through the lamination nip 22.

(34) In FIG. 2b it is shown how the obtained web of the laminated layers AB in FIG. 2a is subsequently forwarded to a further lamination roller nip for lamination 25 to a third web C comprising a gas barrier layer, such as the aluminium foil of FIG. 1a, 14a, or the DLC-coated film of FIG. 1b, 14b. Thus, the web of the semi-laminate AB and the web C comprising the gas barrier layer are forwarded to a lamination roller nip, while at the same time, a molten curtain of the thermoplastic bonding polymer 23 is extruded 24 down into the lamination roller nip and cooled while pressing the two webs together, such that sufficient adhesion is obtained between the surfaces of the two webs AB and C, i.e. between the inner surface of the bulk material layer and the outer surface of the barrier foil or film, to form a laminated web 26.

(35) Alternatively, a cold aqueous adhesive absorption lamination method, as described in FIG. 2a, may be used when laminating the bulk material layer AB to the web C.

(36) The method step of FIG. 2b is not needed in the case of the packaging material of FIG. 1c, which is then instead wound up onto a reel for intermediate storage or transport to a different time or place, where final lamination and finishing steps may take place.

(37) In FIG. 2c it is principally shown how a web of the laminated print substrate paper and the bulk layer AB, or a web ABC of the bulk material layer, the print substrate paper and the gas barrier film or foil, resulting from FIG. 2a or 2b, respectively, is forwarded to a further lamination operation 27 at a roller nip. At the roller nip, a molten curtain 28 of the inside polymer layers, i.e. the adhesive polymer layer 18a; 18b; optionally 18c, and the innermost layer 15a; 15b; 15c, are co-extruded 29 down into the lamination roller nip, and being cooled to be coated as a multilayer film coating onto the inner side of the web AB or ABC, by pressing and solidifying the polymer layers 18, 19 to the inner surface. The resulting laminate 30 may be forwarded to a further, similar lamination operation for extrusion-coating lamination of the outside layer 13a, 13b, 13c of LDPE onto the opposite, outer side of the print substrate paper 12a, 12b, 12c or if this was already done before the above lamination steps, to a reeling station for winding onto a reel, for further transport and storage of the packaging laminate.

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

(39) 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, 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.

(40) 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.

(41) 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.

(42) 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.

(43) FIG. 5 shows the Surface Roughness values (Bendtsen ml air/min) of the different cellulose-based materials employed in the invention. A typical linerboard (SCA Kraftliner) having a surface weight of 135 g/m.sup.2 and an SR value of 640 ml air/min, was laminated to a print substrate paper being a Flexible Packaging paper (Lennoflex from Feldmuehle) having a surface weight of 70 g/m.sup.2, and an original measured surface roughness of the print surface of about 15 (marketed as 20) ml air/min. Lamination was carried out by means of an aqueous adhesive composition comprising starch, applied wet to yield a dry amount of about 1.4 g/m.sup.2. The dry content of the aqueous composition was 16 wt %. The resulting surface roughness after lamination, of the print surface of the laminated print substrate paper, was then decreased to 146 ml air/min, which is, however, considered too high to be acceptable.

(44) In a further experiment, the above linerboard was calendered in a metal belt calender at a nip load of 100 kN/m and a surface temperature of about 200 C. The resulting surface roughness on the metal belt side was 141 ml air/min, i.e. about the same as the previously described linerboard laminate. When instead laminating this calendered linerboard (the linerboard loses some surface weight at calendering due to loss of moisture, i.e. to instead have a surface weight of 125 g/m.sup.2), to the same print substrate paper in the same way, the resulting surface acquired a roughness value of only 42 ml air/min, i.e. much less than half of the maximum acceptable value for a print substrate paper, i.e. 100 ml air/min, although the initial surface roughness value of the print substrate paper was the same in both experiments. Consequently, it is possible to obtain a print surface that is similar to, or even smoother than, conventional liquid packaging paperboard, such as a clay-coated Duplex LPB, by calendering a rough linerboard before laminating it to a print substrate paper. Furthermore, it is possible to obtain a sufficiently smooth print surface of the laminated print substrate paper and linerboard bulk material layer, to ensure that the metallised surface may maintain its mirror-like, smooth appearance, and not be negatively affected by the roughness of the different bulk material layer.

(45) FIG. 6 shows the principle of a metal belt calendering operation. The containerboard 61, such as a linerboard, is forwarded into a nip 62 between a metal belt 63 and a metal roller 64, while pressure force is applied by a pressure roller 65 and while heat is supplied to the nip and the surface of the linerboard, by the heated metal roller 64. In heated roller calendering, usually directly applied in-line after the paper-manufacturing line (not shown here) the board is simply passing a series of heated hard pressure roller nips.

(46) 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.