Non-foil packaging laminate, method for manufacturing of the packaging laminate and packaging container produced thereof

Abstract

A non-foil packaging laminate for liquid food packaging comprises a layer of paper or other cellulose-based material, outermost liquid tight, heat sealable layers of polyolefin-based polymers and, vapour-deposition coated onto the inner side of the layer of paper or cellulose-based material, an induction heat susceptible metal coating. Also disclosed is a method for manufacturing of the packaging laminate, a packaging container that is made from the packaging laminate and a method of induction heat sealing the packaging laminate into packaging containers.

Claims

1. A non-foil packaging laminate for induction heat sealing into packages for liquid food or beverage, the non-foil packaging laminate comprising at least one, first layer of paper or other cellulose-based material, which first layer of paper or other cellulose-based material possesses an inner side and is pre-coated with an induction sealing durable coating layer so that the induction sealing durable coating layer is in direct contact with the inner side of the first layer of paper or other cellulose-based material to form a pre-coated first paper layer, an induction heat susceptible metal layer, the induction heat susceptible metal layer being deposited by vapour deposition directly on the pre-coated first paper layer so that the induction heat susceptible metal layer is directly deposited on the induction sealing durable coating layer, and at least one layer of liquid-tight, heat sealable thermoplastic polymer material applied onto an inner side of the induction heat susceptible metal layer, the induction heat susceptible metal layer causing heating and melting of the heat sealable thermoplastic polymer material to induce heat sealing in the heat sealable thermoplastic polymer material when the induction heat susceptible metal layer is subjected to a magnetic field during a heat sealing operation, the induction sealing durable coating layer providing a receiving surface for the induction heat susceptible metal layer and supporting the induction heat susceptible metal layer during the heat sealing operation, the induction sealing durable coating layer being formed from a composition mainly comprising a polymer selected from the group consisting of PVOH, water dispersible EVOH or starch, and the liquid-tight, heat sealable thermoplastic polymer material being polyethylene.

2. The non-foil packaging laminate according to claim 1, wherein the at least one layer of liquid-tight, heat sealable thermoplastic polymer material includes an innermost layer of the liquid-tight, heat sealable thermoplastic material, and the induction sealing durable coating layer possesses a higher melting point than the innermost layer of the liquid-tight, heat sealable thermoplastic material.

3. The non-foil packaging laminate according to claim 2, wherein the induction sealing durable coating layer is formed by liquid film coating of a liquid composition onto said first paper layer and subsequent drying, the liquid composition containing a polymer binder dispersed or dissolved in an aqueous or solvent medium.

4. The non-foil packaging laminate according to claim 3, wherein said liquid composition further comprises inorganic particles.

5. The non-foil packaging laminate according to claim 4, wherein said liquid composition comprises about 1 to about 40 wt % inorganic particles based on dry weight, wherein said inorganic particles comprise laminar compounds with an aspect ratio of 50 to 5000.

6. The non-foil packaging laminate according to claim 3, wherein said liquid composition further comprises about 20 to about 50 wt % based on dry weight of inorganic particles comprising laminar talcum particles having an aspect ratio from 10 to 500.

7. The non-foil packaging laminate according to claim 2, wherein said induction sealing durable coating layer is applied at a total amount of from 0.5 to 7 g/m.sup.2, dry weight.

8. The non-foil packaging laminate according to claim 2, wherein the induction sealing durable coating layer is applied at a total amount of from 0.5 to 3 g/m.sup.2, dry weight.

9. The non-foil packaging laminate according to claim 2, wherein the induction sealing durable coating layer is formed by liquid film coating of a first liquid composition onto said first paper layer and subsequent drying to form a first induction sealing durable coating part-layer, liquid film coating of a second liquid composition onto said first induction sealing durable coating part-layer and subsequent drying, the first and second liquid compositions containing a polymer binder dispersed or dissolved in an aqueous or solvent medium, wherein the first induction sealing durable coating part-layer is applied at a total amount of 0.3 to 3.5 g/m.sup.2, and wherein the second induction sealing durable coating part-layer is applied at a total amount of 0.3 to 3.5 g/m2.

10. The non-foil packaging laminate according to claim 9, wherein at least one of the induction sealing durable coating part-layers is applied at a total amount of 0.5 to 2 g/m.sup.2.

11. The non-foil packaging laminate according to claim 1, wherein the induction heat susceptible metal layer is a layer substantially consisting of aluminium.

12. The non-foil packaging laminate according to claim 1, wherein the induction heat susceptible metal layer has an optical density of from 1 to 5.

13. The non-foil packaging laminate according to claim 1, wherein the first layer of paper or other cellulose-based material is an innermost situated layer of paper or other cellulose-based material and has a surface weight of from 20 to 100 g/m.sup.2.

14. The non-foil packaging laminate according to claim 1, wherein the induction heat susceptible metal layer has an optical density of from 2 to 3.

15. The non-foil packaging laminate according to claim 1, wherein the induction sealing durable coating layer is formed from a composition comprising PVOH and inorganic particles.

16. A non-foil packaging laminate for induction heat sealing into packages for liquid food or beverage, the non-foil packaging laminate comprising at least one, first, layer of paper or other cellulose-based material, which first paper layer possesses an inner side and is pre-coated with an induction sealing durable coating layer so that the induction sealing durable coating layer is in direct contact with the inner side of the first layer of paper or other cellulose-based material to form a pre-coated first paper layer, an induction heat susceptible metal layer, the induction heat susceptible metal layer being deposited by vapour deposition directly on the pre-coated first paper layer so that the induction heat susceptible metal layer is directly deposited on the induction sealing durable coating layer, at least one layer of liquid-tight, heat sealable thermoplastic polymer material applied onto an inner side of the induction heat susceptible metal layer, the induction heat susceptible metal layer causing heating and melting of the heat sealable thermoplastic polymer material to induce heat sealing in the heat sealable thermoplastic polymer material when the induction heat susceptible metal layer is subjected to a magnetic field during a heat sealing operation, and a second layer of paper or carton laminated to the outside of the first layer of paper or other cellulose-based material, which second paper layer has a surface weight of from 50 to 500 g/m.sup.2, the induction sealing durable coating layer providing a receiving surface for the induction heat susceptible metal layer and supporting the induction heat susceptible metal layer during the heat sealing operation, the induction sealing durable coating layer being formed from a composition mainly comprising a polymer selected from the group consisting of polyvinyl alcohol, water dispersible ethylene vinyl alcohol, polyvinylidenechloride, water dispersible polyimide, polysaccharide, polysaccharide derivatives, starch, starch derivatives and combinations of two or more thereof, and the liquid-tight, heat sealable thermoplastic polymer material being polyethylene.

17. The non-foil packaging laminate according to claim 16, comprising an intermediate polymer layer between the first layer of paper or other cellulose-based material and the second layer of paper or other cellulose-based material to laminate the second layer of paper or other cellulose-based material to the first layer of paper or other cellulose-based material.

18. The non-foil packaging laminate according to claim 16, wherein the second layer of paper or other cellulose-based material is laminated to the outside of the first layer or other cellulose-based material after the first layer of paper or other cellulose-based material is pre-coated with the induction sealing durable coating layer.

19. A packaging laminate for induction heat sealing into packages for liquid food or beverage, the packaging laminate comprising at least one, first, layer of paper or other cellulose-based material, an induction sealing durable coating layer in direct contact with an inner side of the first layer of paper or other cellulose-based material, an induction heat susceptible metal layer deposited by vapour deposition on an inner side of said induction sealing durable coating layer, and at least one layer of liquid-tight, heat sealable thermoplastic polymer material applied onto an inner side of the induction heat susceptible metal layer, the at least one layer of liquid-tight, heat sealable thermoplastic polymer material including an innermost layer of the liquid-tight, heat sealable thermoplastic material, the induction heat susceptible metal layer causing heating and melting of the heat sealable thermoplastic polymer material to induce heat sealing in the heat sealable thermoplastic polymer material when the induction heat susceptible metal layer is subjected to a magnetic field during a heat sealing operation, the induction sealing durable coating layer providing a receiving surface for the induction heat susceptible metal layer and supporting the induction heat susceptible metal layer during the heat sealing operation, the induction sealing durable coating layer possessing a higher melting point than the innermost layer of the liquid-tight, heat sealable thermoplastic material, and the liquid-tight, heat sealable thermoplastic polymer material being polyethylene.

20. The packaging laminate of claim 19, wherein the induction heat susceptible metal layer has an optical density of from 1 to 5.

21. The packaging laminate of claim 19, wherein the first layer of paper or other cellulose-based material is an innermost situated layer of paper or other cellulose-based material and has a surface weight of from 20 to 100 g/m.sup.2.

22. The packaging laminate of claim 19, wherein the induction heat susceptible metal layer has a thickness of from 5 to 100 nm.

23. The packaging laminate of claim 19, wherein the induction heat susceptible metal layer has a thickness of from 5 to 50 nm.

24. The packaging laminate of claim 23, wherein the induction heat susceptible metal layer is a layer substantially consisting of aluminium.

Description

BRIEF DESCRIPTION OF DRAWING FIGURES

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

(2) FIGS. 1a, 1b, 1c and 1d are schematically showing, in cross-section, first, second, third and fourth embodiments of a packaging laminate produced according to the invention,

(3) FIG. 2 is grammatically showing a method of liquid film coating of a polymer composition onto a paper substrate layer,

(4) FIG. 3 is showing a diagrammatic view of a plant for vapour deposition of a preferred metal layer onto a substrate,

(5) FIGS. 4a, 4b and 4c are schematically showing example methods of manufacturing the packaging laminates described in FIG. 1,

(6) FIGS. 5a and 5b are showing examples of packaging containers produced from the packaging laminate according to the invention, and

(7) FIG. 6 is showing the principle of how such packaging containers are manufactured from the packaging laminate in a continuous form, fill and seal process.

EXAMPLES AND DETAILED DESCRIPTION

Example 1

(8) Preparation of an aqueous coating composition for the induction heat sealing durable layer: An aqueous dispersion of exfoliated laminar montmorillonite particles (Kunipia F from Kunimine Kogyo Co.) having an aspect ratio of about 50-5000, is blended with an aqueous solution of about 30 weight-% of PVOH (Mowiol 15-99, having a saponification degree of above 99%) at 60-90° C. during 1-8 hours. The dispersion of exfoliated laminar mineral particles may be stabilised by means of a stabiliser additive. Alternatively, the laminar mineral particles are exfoliated directly in the PVOH-solution at 60-90° C. during 1-8 hours.

(9) An aqueous composition of aqueous dissolved and dispersed PVOH and 30 weight-% exfoliated bentonite clay, was thus coated by means of liquid film coating, in two consecutive steps with drying in between, onto a thin paper web having a surface weight of 50 g/m2, with 3 g/m2 PVOH coating in total. The wet applied coating is dried by hot air to evaporate the water.

(10) In a subsequent step, the PVOH-coated paper was coated with an aluminium metal coating by means of a vapour deposition process up to optical density 3, onto the PVOH layer.

(11) The thus metallised, PVOH-coated paper was laminated to a thick paperboard of 260 mN (about 270 g/m2) by means of an extrusion laminating thermoplastic bonding layer of low density polyethylene (LDPE), and the thus laminated paper sandwich was subsequently coated with thermoplastic heat sealable layers (LDPE) on both sides and tested for heat seal quality in a Tetra Brik Aseptic® conventional filling machine, employing adapted induction heat sealing of the packaging containers produced. It has for example been seen that to reach sufficient heating efficiency by a very thin metallised layer, the frequency used in the induction sealing process needs to be increased significantly.

(12) The appearance and characteristics of the seals of the thus filled and sealed packaging containers were studied, by tearing the seals apart again. The appearance was noted and compared between the samples. The seal width and evenness in alignment was determined and compared by a further test, in which all packaging material is dissolved around the seal, except for the heat sealed thermoplastics. Finally, the package integrity of a filled and sealed packaging container was tested by using the red ink test. These are all tests well known by dairies and filling sites for Tetra Brik Aseptic® packages, for sealing quality control of the daily produced, filled packaging containers.

(13) The weighed properties and qualities of the samples of sealed packaging containers were evaluated based on many years experience from quality control of conventional packaging laminates for Tetra Brik® Aseptic packaging containers.

(14) The heat seal quality and the integrity of the produced packages was very good, and on par with the seal quality of today's Tetra Brik Aseptic, aluminium foil based packages, according to evaluations by the test panel. In the red ink test, all 300 out of 300 filled and sealed packages, were liquid tight, without leakage points.

Example 2

(15) An aqueous composition of aqueous dissolved and dispersed PVOH, having a saponification degree of above 99%, and 10 weight-% exfoliated bentonite clay, was prepared in a similar way to Example 1 and coated by means of liquid film coating, in two consecutive steps with drying in between, onto a thin paper web having a surface weight of 50 g/m2, with 3 g/m2 PVOH coating in total. The wet applied coating is dried by hot air to evaporate the water.

(16) In a subsequent step, the PVOH-coated paper was coated with an aluminium metal coating by means of a vapour deposition process up to optical density 3, onto the PVOH layer.

(17) The thus metallised, PVOH-coated paper was laminated to a thin paper of 50 g/m2 by means of an extrusion laminating thermoplastic bonding layer of low density polyethylene (LDPE), and the thus laminated paper sandwich was subsequently coated with thermoplastic heat sealable layers (LDPE) on both sides and tested for heat seal quality in a Tetra Brik Aseptic® conventional filling machine, employing adapted induction heat sealing of the packaging containers produced.

(18) Alternatively, it would be technically possible to metallise a thicker paper layer, e.g. of about 100 g/m2, and not laminating it to any further paper layers but keeping it as a single paper layer laminate, coated with outer heat sealable thermoplastic layers. Presently, however, it would not be cost efficient to vapour deposition coat a metallised layer onto such a thick paper substrate, why the above sandwich laminate was made in order to provide a laminate with a corresponding required thickness and stiffness.

(19) The heat seal quality and the integrity of the produced packages was equally very good, according to the same evaluation by the same test panel. Out of 300 tested packages, none had any leakage point relating to the quality of the seals.

Comparative Example 1

(20) A 12 um substrate film of an oriented PET (polyethylene terephthalate), was coated with an aluminium metal coating by means of a vapour deposition process to an optical density of about 3.

(21) The thus metallised, PET-film was laminated to a thick paperboard of about 260 mN (or about 270 g/m2) by means of an extrusion laminating thermoplastic bonding layer of low density polyethylene (LDPE), and subsequently coated with thermoplastic heat sealable layers (LDPE) on both sides and tested for heat seal quality in a Tetra Brik Aseptic® conventional filling machine, employing adapted induction heat sealing of the packaging containers produced.

(22) The heat seal quality and the integrity of the produced packages was acceptable according to evaluation by a test panel of tearing properties of the seals and of the package integrity using the red ink test, in comparison to the above examples. However, the sealing results from test run to test run were not as consistent and reliable as for laminated material with thin paper substrates.

Comparative Example 2

(23) A thin paper web having a surface weight of 50 g/m2 was co-extrusion coated by a first layer of LDPE at 10 g/m2 and a second layer of EAA (ethylene acrylic acid copolymer) at 5 g/m2.

(24) In a subsequent step, the extrusion-coated paper was further coated with an aluminium metal coating by means of a vapour deposition process, onto the EAA layer.

(25) The thus metallised, LDPE/EAA-coated paper was laminated with thermoplastic heat sealable layers on both sides and tested for heat seal quality in a test rig, simulating the real conditions in a conventional filling machine of the Tetra Brik Aseptic® type, employing adapted induction heat sealing of the packaging containers produced. Furthermore, the laminated paper was tested in the conventional filling machine of the Tetra Brik Aseptic® type, employing adapted induction heat sealing of the packaging containers produced.

(26) The weighed properties and qualities of the samples of sealed packaging material and containers were evaluated based on many years experience from quality control of conventional packaging laminates for Tetra Brik® Aseptic packaging containers, and it was seen that no properly sealed packages could be formed in the TBA filling machine, why any further testing of package integrity was unnecessary. Moreover, the results from the tear evaluation from sealing samples from the test rig showed that the seals were not good enough.

(27) Thus, the heat seal quality and the integrity of the produced packages was not good, and not at all on par with the seal quality of today's Tetra Brik Aseptic, aluminium foil based packages, according to evaluations by the same test panel.

Example 3

(28) Thin paper webs of different surface weights were coated by means of liquid film coating in two consecutive steps, with drying in between, with an aqueous composition of aqueous dissolved and dispersed PVOH, having a saponification degree of above 99%, and 10 weight-% exfoliated bentonite clay, as set out in Table 1. The wet applied coatings were dried by hot air to evaporate the water.

(29) In a subsequent step, the PVOH-coated paper webs were coated with an aluminium metal coating by means of a vapour deposition process, onto the PVOH layer.

(30) The thus metallised, PVOH-coated papers were laminated with thermoplastic heat sealable layers on both sides and tested for heat seal quality in a test rig, simulating the real conditions in a conventional filling machine of the Tetra Brik Aseptic® type, employing adapted induction heat sealing of the packaging containers produced.

(31) The results are shown in Table 1, as a ranking list of the various tested samples of thin-paper based packaging materials. The evaluation was made by a test panel for evaluation of seal quality. From the results it can be seen that a thicker paper provides for better sealing results, than a thinner paper. It can also be seen that metal vapour deposition coating of a higher optical density (OD) provides for a somewhat better sealing result than a metal vapour deposition coating of a lower OD. Furthermore, it can be seen that thicker layers of PVOH provides for somewhat better sealing results than thinner layers. All the samples from Table 1, provided very good seal quality in the rig tests, and should provide equally good results of package integrity in filling machine tests, similarly to what was shown in Example 1. Although, better sealing results were perceived by the thicker paper substrates of 70 g/m2, the thinner substrates of 50 g/m2 have been been generally used in the tests, because the thicker ones become much more expensive.

(32) TABLE-US-00001 TABLE 1 Sample No Paper g/m2 PVOH g/m2 OD Ranking 1 50 2 × 0.7 3 6 2 50 2 × 1.5 1.5 5 3 50 2 × 1.5 3 4 4 70 2 × 1.5 3 1 5 70 2 × 0.7 1.5 3 6 70 2 × 0.7 3 2

(33) There are of course still possibilities to further increase the gas barrier properties a little by coating thicker or further layers of the PVOH composition, or to fill the PVOH layer with higher amount of inorganic particles. There is, however, a more significant gain in odour barrier properties, by coating a thicker and more densely filled gas barrier layer composition. An excellent example of such a barrier composition comprises PVOH and from 10 to 50, preferably from 20 to 40 weight-% of talcum particles.

(34) In FIG. 1a, there is shown, in cross-section, a first embodiment of a packaging laminate 10a for aseptic packaging and long-term storage under ambient conditions, produced according to the invention. The laminate comprises a first paper layer 11, having a surface weight of 50 g/m2,

(35) The paper is prepared to receive a metal vapour deposition coating 12, which can work as an induction heat susceptible material and transmit heat to effect heat sealing in the innermost heat sealable layer 14.

(36) The thin paper, subsequently to be metal vapour-deposition coated, may be prepared by means of coating or by means of impregnating the paper layer or by means of mixing chemicals into the paper pulp at the stage of manufacturing of the paper web, or by any combination of these means or other means, for preparation.

(37) The prepared thin paper web is subsequently vapour deposition metallised to an optical density (OD) of about 3.

(38) An outer liquid tight and heat sealable layer 15 of polyolefin is applied on the outside of the core layer 11, which side is to be directed towards the outside of a packaging container produced from the packaging laminate. The polyolefin of the outer layer 15 may be a conventional low density polyethylene (LDPE) of a heat sealable quality. An innermost liquid tight and heat sealable layer 14 is arranged on the inside of the vapour deposited layer 12, which is to be directed towards the inside of a packaging container produced from the packaging laminate, and the layer 14 will be in contact with the packaged product. The innermost heat sealable layer comprises a polymer based on low density polyethylene, preferably including also an LLDPE produced by polymerising an ethylene monomer with a C4-C8, more preferably a C6-C8, alpha-olefin alkylene monomer in the presence of a metallocene catalyst, i.e. a so called metallocene-LLDPE (m-LLDPE). The innermost heat sealable layer 14 may consist of two or several part-layers of the same or different kinds of polymers and may alternatively constitute a polymer film 14.

(39) According to a preferred embodiment of the invention, the innermost heat sealable layer 14 is bonded to the metal vapour deposition layer by means of a tie layer, preferably of an ethylene acrylic acid copolymer. Alternatively, other tie layers may be used. Alternative examples of polyolefins suitable as tie layers, for bonding the heat sealable innermost layer to the metal-coated paper layer, are modified polyolefins based on LDPE or LLDPE co-polymers or, preferably, graft co-polymers with functional-group containing monomer units, such as carboxylic or glycidyl functional groups, e.g. (meth)acrylic acid monomers or maleic anhydride (MAH) monomers, (i.e. ethylene acrylic acid copolymer (EAA) or ethylene methacrylic acid copolymer (EMAA)), ethylene-glycidyl(meth)acrylate copolymer (EG(M)A) or MAH-grafted polyethylene (MAH-g-PE). Another example of such modified polymers or adhesive polymers are so called ionomers or ionomer polymers. Preferably, the modified polyolefin is an ethylene acrylic acid copolymer (EAA) or an ethylene methacrylic acid copolymer (EMAA).

(40) In special cases, where a thicker heat sealable layer is needed, it is of course possible, although not preferred from a cost perspective, to apply a further heat sealable polyethylene layer onto the inside of the innermost layer 14.

(41) In FIG. 1b, there is shown, in cross-section, a second embodiment of a packaging laminate 10b for aseptic packaging and long-term storage under ambient conditions, produced according to the invention. The laminate comprises a first paper layer 11, having a surface weight of 50 g/m2, and a thin induction sealing durable layer 13 formed by liquid film coating of a liquid polymer composition, and subsequent drying, onto the paper layer 11. The composition comprises an aqueous solution of PVOH and 10 weight-% bentonite, and after drying, the coated layer thus comprises PVOH and exfoliated bentonite particles homogeneously distributed in a laminar fashion within the PVOH layer. Preferably, the PVOH has a saponification degree of at least 99%.

(42) The coated thin paper web is subsequently vapour deposition metallised on its coated side to an optical density (OD) of about 3. The resulting packaging laminate thus comprises a thin paper substrate 11, first coated with PVOH with bentonite and then a thin vapour deposition coating layer 12 of aluminium metal at a thickness of about 50 nm.

(43) An outer liquid tight and heat sealable layer 15 of polyolefin is applied on the outside of the core layer 11, which side is to be directed towards the outside of a packaging container produced from the packaging laminate. The polyolefin of the outer layer 15 may be a conventional low density polyethylene (LDPE) of a heat sealable quality. An innermost liquid tight and heat sealable layer 14 is arranged on the inside of the vapour deposited layer 12, which is to be directed towards the inside of a packaging container produced from the packaging laminate, and the layer 14 will be in contact with the packaged product. The innermost heat sealable layer comprises low density polyethylene, preferably including an LLDPE produced by polymerising an ethylene monomer with a C4-C8, more preferably a C6-C8, alpha-olefin alkylene monomer in the presence of a metallocene catalyst, i.e. a so called metallocene-LLDPE (m-LLDPE). The innermost heat sealable layer 14 may consist of two or several part-layers of the same or different kinds of polymer and may alternatively constitute a polymer film 14.

(44) In special cases, where a thicker heat sealable layer is needed, it is of course possible, although not preferred from a cost perspective, to apply a further heat sealable polyethylene layer onto the inside of the innermost layer 14.

(45) In FIG. 1c, there is shown, in cross-section, a third embodiment of a packaging laminate 10c for aseptic packaging and long-term storage under ambient conditions, produced according to the invention. The laminate comprises a first paper layer 11, having a surface weight of 50 g/m2, and a thin induction sealing durable layer 13 formed by liquid film coating of a liquid polymer composition, and subsequent drying, onto the paper layer 11. The composition comprises an aqueous solution of PVOH and 30 weight-% bentonite particles, and after drying, the coated layer thus comprises PVOH and exfoliated bentonite particles homogeneously distributed in a laminar fashion within the PVOH layer. Preferably, the PVOH has a saponification degree of at least 99%.

(46) The prepared thin paper web is subsequently vapour deposition metallised to an optical density (OD) of about 3.

(47) The packaging laminate thus comprises a thin paper substrate 11, first coated with PVOH and then coated with a thin vapour deposition coating layer 12 of aluminium metal at a thickness of about 50 nm.

(48) In addition, the packaging laminate comprises a second core, paperboard layer 16 having a surface weight of at least 200 g/m2 or, preferably of about 300 g/m2. The first and second paper layers are suitably bonded to each other by means of an intermediate layer 17 of a polyolefin-based polymer, preferably a low density polyethylene (LDPE). The intermediate bonding layer 16 is preferably formed by means of extrusion laminating the metal-coated first paper layer and the second paperboard layer to each other.

(49) The outer liquid tight and heat sealable layers 14 and 15 are defined as in FIGS. 1a and 1b.

(50) In FIG. 1d, there is shown, in cross-section, a fourth embodiment of a packaging laminate 10d, which is similar to the packaging laminate of FIG. 1c, however with an additional layer from liquid film coated PVOH composition with bentonite, 18, on the other, outer side of the first paper layer 11, and, or alternatively, with an additional layer from liquid film coated PVOH composition with bentonite, 19, on the inner side of the second paperboard layer 16. The layer(s) 18, 19 of PVOH provide further gas barrier properties to the packaging laminate.

(51) In order to reduce the amount of moisture released from the paper layer into the vacuum chamber during the metallisation process, the first paper layer, which is to be metal vapour deposition coated, may be coated also on the other, outer side by a liquid film composition of a polymer in aqueous or solvent based dispersion or solution, before the metallisation process step. It is desirable to avoid moisture in the vacuum chamber for metallisation, because it may reduce the speed at which the metallisation process can be carried out. Furthermore, any back transfer of paper dust in the subsequent handling of coated paper webs on reels may be prevented.

(52) According to FIG. 1a and FIG. 1b, the first paper layer 11 may be a thin paper layer of about 50 g/m2 or even less. Since the paper layer is very thin, it may need an additional light barrier by added pigments in one or more of the layers of the laminate. There may, for example, be light reflecting white pigments, such as for example titanium dioxide (TiO2), and/or light absorbing pigments, such as for example carbon black, added to the liquid film coated induction heat sealing durable layer 13. Such pigments are advantageously hidden towards the inside by the metal vapour deposition coating 12, and at least to some extent by the paper layer 11, towards the outside.

(53) In FIG. 2, the method of liquid film coating of a polymer composition onto a paper or paperboard layer is grammatically shown. The paper layer 21a is fed from a storage reel towards a liquid film coating station 22a, where the liquid polymer composition is applied at an amount such that the amount of coated and dried layer is about 1-3 g/m2, when the coated paper has passed the drying station 22b. Preferably, the liquid film coating operation is carried out in two steps, i.e. by first coating 0.5-1.5 g/m2, drying in an intermediate step and then coating a second time at 0.5-1.5 glm2 and finally drying the total liquid film coated layer to obtain a coated paper layer 21b.

(54) FIG. 3 is a diagrammatic view of an example of a plant for vapour deposition coating of a metal layer 12 onto the coated thin first paper layer produced in FIG. 2. The thin paper web 21b from FIG. 2 is subjected, on the coating receiving side, to continuous evaporation deposition 30, of a metallised layer of aluminium, possibly in a mixture with aluminium oxide, and the coating is given a thickness of 5-100 nm, preferably 5-50 nm, so that the metal coated paper of the invention 34a is formed. The aluminium vapour comes from a solid piece evaporation source 31.

(55) In FIG. 4a, the coating process 40a is shown, wherein the induction heat sealing durable and/or oxygen barrier coated paper layer 21b, further coated with a thin metal vapour deposited coating 34a, is extrusion laminated to an inside polymer film 43, having an adhesive layer 43a on the side facing towards the paper layer, by extruding an intermediate bonding layer of LDPE 44 from an extrusion station 44a and pressing together in a roller nip 45. Subsequently, the laminated paper and film passes a second extruder 47 and lamination nip 48, where an outermost heat sealable layer of LDPE 46 is coated onto the outer side of the paper layer. Finally, the finished packaging laminate 49a is wound onto a storage reel, not shown.

(56) In FIG. 4b, an alternative embodiment is shown, wherein the metal coated paper layer 34a is directly extrusion coated with the innermost polymer layer(s) 14; 43b, in a first extrusion coating station 44b, and pressed together in a roller nip 45b, similar to the extruder 47 and lamination nip 48. Finally, the finished packaging laminate 49b is wound onto a storage reel, not shown.

(57) When the packaging laminate comprises an additional, second paperboard layer 16, as shown in FIG. 1c, there is a further lamination step in which the metal coated paper is extrusion laminated to the paperboard layer 43c; 16. The outermost and innermost heat sealable polymer layers of low density polyethylene(s) may be subsequently coated, in any order, by means of extrusion coating as in FIG. 4b above, or alternatively, by means of extrusion laminating an innermost heat sealable film, as shown in FIG. 4a above.

(58) FIG. 5a shows one example of a packaging container 50 produced from the packaging laminate 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 of about 100 to 1000 ml. It may be of any configuration, but is preferably brick-shaped, having longitudinal and transversal seals 51 and 52, respectively, and optionally an opening device 53. 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.

(59) FIG. 5b shows an alternative, example of a packaging container 50b produced from the packaging laminate 10b according to the invention. Since the packaging laminate 10b is thinner by having a thinner paper core layer, it is not dimensionally stable enough to form a parallellepipedic or wedge-shaped packaging container, and is not fold formed after transversal sealing 52b. It will thus remain a pillow-shaped pouch-like container and distributed and sold like this.

(60) FIG. 6 shows the principle as described in the introduction of the present application, i.e. a web of packaging material is formed into a tube 61 by the longitudinal edges 62, 62′ of the web being united to one another in an overlap longitudinal joint 63. The tube is filled 64 with the intended liquid food product and is divided into individual packages by repeated transversal seals 65 of the tube at a pre-determined distance from one another below the level of the filled contents in the tube. The packages 66 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.

(61) The invention is not limited by the embodiments shown and described above, but may be varied within the scope of the claims.