LAMINATED PACKAGING MATERIAL COMPRISING A BARRIER LAYER AND PACKAGING CONTAINER MADE THEREFROM

Abstract

A laminated packaging material for packaging of liquid or semi-liquid food products comprises: a bulk layer comprising cellulose-based material, preferably paper or paperboard, a first outermost liquid-tight, heat-sealable thermoplastic layer, arranged on the outside of the bulk layer to constitute the outside of a package formed from the packaging material, a second innermost liquid-tight, heat-sealable thermoplastic layer arranged on the inside of the bulk layer to be in direct contact with the filled food product, and a barrier layer comprising a barrier substrate layer coated with a physical vapour deposited barrier coating comprising partially oxidised aluminium, the barrier coating having a thickness of 8 to 40 nm and a transmittance of 20 to 60%, the barrier layer being laminated between the bulk layer and the second, innermost liquid-tight, heat-sealable thermoplastic layer.

Claims

1. A laminated packaging material for packaging of liquid or semi-liquid food products, comprising: a bulk layer comprising cellulose-based material, preferably paper or paperboard, a first outermost liquid-tight, heat-sealable thermoplastic layer, arranged on the outside of the bulk layer to constitute the outside of a package formed from the packaging material, a second innermost liquid-tight, heat-sealable thermoplastic layer arranged on the inside of the bulk layer to be in direct contact with the filled food product, and a barrier layer comprising a barrier substrate layer coated with a physical vapour deposited (PVD) barrier coating comprising partially oxidised aluminium, the barrier coating having a thickness of 8 to 40 nm and a transmittance of 20 to 60%, as measured by a spectrophotometer at wavelengths over the visible spectrum and after stabilisation of the coating in air, the barrier layer being laminated between the bulk layer and the second, innermost liquid-tight, heat-sealable thermoplastic layer.

2. A laminated packaging material as claimed in claim 1, wherein the partially oxidised aluminium comprises a ceramic-metallic composite of aluminium particles and Al.sub.2O.sub.3.

3. A laminated packaging material as claimed in claim 1, wherein the barrier coating has a non-metallic appearance.

4. A laminated packaging material as claimed in claim 1, wherein the barrier substrate layer comprises a polymer film or a cellulose-based material.

5. A laminated packaging material as claimed in claim 4, wherein the polymer film is a polyolefin film or a polyester film.

6. A laminated packaging material as claimed in claim 5, wherein the polymer film is a pre-manufactured mono-axially or biaxially oriented film.

7. A laminated packaging material as claimed in claim 6, wherein the polymer film is a mono-axially orientated polyethylene terephthalate film or a biaxially orientated polyethylene terephthalate film.

8. A laminated packaging material as claimed in claim 4, wherein the barrier substrate layer is a paper layer.

9. A laminated packaging material as claimed in claim 1, wherein the surface of the barrier substrate layer to be PVD coated has been pre-treated by in-line plasma pre-treatment and/or corona, flame or atmospheric plasma during film manufacturing.

10. A laminated packaging material as claimed in claim 1, wherein the barrier coating has been post-treated by plasma treatment.

11. A laminated packaging material as claimed in claim 1, wherein the PVD barrier coating has been applied by plasma-assisted reactive evaporation.

12. A method of manufacturing the laminated packaging material as claimed in claim 1, comprising, in any order, laminating the barrier layer to the inner side of the bulk layer, applying the first outermost liquid-tight, heat-sealable thermoplastic layer onto the outer side of the bulk layer, and applying the second innermost liquid-tight, heat-sealable thermoplastic layer on the inner side of the barrier layer.

13. A method as claimed in claim 12, wherein the barrier layer is laminated to the bulk layer by melt (co-)extruding an interjacent laminating layer of a thermoplastic polymer between the bulk layer and the barrier layer, and subsequently applying pressure in a lamination roller nip.

14. A packaging container for liquid or semi-liquid food products comprising the laminated packaging material defined in claim 1.

15. A method of forming a packaging container as claimed in claim 14, comprising folding the laminated packaging material.

Description

DESCRIPTION OF PREFERRED EMBODIMENTS

[0084] In the following, preferred embodiments of the invention will be described with reference to the drawings, in which:

[0085] FIG. 1 shows a schematic, cross-sectional view of a laminated packaging material of a preferred embodiment of the invention.

[0086] FIG. 2 shows a schematic view of a plant for PVD of a partially oxidised aluminium barrier coating onto a barrier substrate layer for use in the material of FIG. 1.

[0087] FIG. 3 shows a schematic view of a plant for plasma surface pre-treatment of the barrier substrate layer for use in the material of FIG. 1.

[0088] FIG. 4 shows schematically a method for manufacturing the laminated packaging material of FIG. 1.

[0089] FIGS. 5a, 5b, 5c and 5d show typical examples of packaging containers produced from the laminated packaging material of FIG. 1.

[0090] FIG. 6 shows the principle of how the packaging containers of FIG. 5 are manufactured from the packaging laminate in a continuous roll-fed form, fill and seal process.

[0091] FIG. 7 shows a TEM image of the barrier coating 3a of the example.

[0092] FIG. 8 shows oxygen transmission rates for barrier layers of the example.

[0093] FIG. 9 shows oxygen transmission rates for barrier layers of the example after Gelbo flexing.

[0094] FIG. 10 shows graphs of oxygen transmission rates against strain for barrier layers of the example, indicating crack onset strain values. FIG. 10 (a) shows BOPET-based barrier layers and FIG. 10 (b) shows MOPET-based barrier layers.

[0095] FIG. 11 shows oxygen transmission rates for barrier layers and packaging laminates of the example.

[0096] FIG. 12 shows oxygen transmission rates for packages of the example.

[0097] In FIG. 1, a laminated packaging material (also referred to herein as a packaging laminate) for liquid carton packaging 10a of a preferred embodiment of the invention is shown, in which the laminated material comprises a bulk layer 11 of paperboard, and an outer liquid-tight and heat-sealable layer 12 of polyolefin applied on the outside of the bulk 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 12 is a conventional low density polyethylene (LDPE) of a heat-sealable quality. An innermost liquid-tight and heat-sealable layer 13 is arranged on the opposite side of the bulk layer 11, i.e. the layer 13 will be in direct contact with the packaged product. The thus innermost heat sealable layer 13, which is to form very strong seals of a liquid packaging container made from the laminated packaging material, comprises m-LLDPE.

[0098] The bulk layer 11 is laminated to a barrier layer 14 (also referred to herein as a barrier film), formed from an oriented BOPET film barrier substrate layer 14b, coated with a PVD barrier coating 14a comprising partially oxidised aluminium. The coating 14a is applied by PVD with reactive evaporation to a thickness of about 15 nm. The form of the partially oxidised aluminium is discussed in more detail in the example below.

[0099] FIG. 2 is a diagrammatic view of an example of a plant 20a for PVD formation of coating 14a on polymer film barrier substrate layer 14b; 24b-c. The thin film substrate 14b; 24b-c is subjected, on the coating receiving side, to continuous evaporation deposition, such that the coated barrier layer 14 of the invention is formed. The aluminium vapour comes from a solid piece aluminium evaporation source 21. The aluminum evaporation is thermal and occurs when the aluminum wire contacts a high temperature surface including boron-nitride (heated by joule heating to 1500-1700 C.).

[0100] A limited amount of oxygen is introduced into the chamber via injection nozzles. Reactive evaporation takes place between the aluminium and oxygen.

[0101] Before the PVD coating operation is initiated, the surface of the polymer film barrier substrate layer 14b is briefly pre-treated by a plasma to functionalise and clean the surface, in order to render the surface more susceptible to the coating and create better bonding between coating and substrate.

[0102] FIG. 3 is a diagrammatic view of an example of a plant for plasma surface pre-treatment of a polymer film barrier substrate layer. The film substrate 44 is subjected, on one of its surfaces, to an oxygen-argon plasma, in a plasma reaction zone 50 created in the space between magnetron electrodes 45, and a chilled film-transporting drum 46, which is also acting as an electrode, while the film is forwarded by the rotating drum, through the plasma reaction zone along the circumferential surface of the drum. The plasma is applied as a surface treatment only.

[0103] Post-treatment is also used to remove aluminium hydroxides and to oxidise the surface of the coating 14a.

[0104] Returning to the structure shown in FIG. 1, the first, outer side of the barrier layer 14 is laminated to the bulk layer 11 by an intermediate bonding layer 15 of LDPE. The innermost heat sealable layer 13 comprising m-LLDPE is adhered to the barrier layer 14 by means of a layer of LDPE 16 and optionally an adhesive polymer, such as a polyolefin having functional polar groups to enhance adhesion to adjacent layers.

[0105] In FIG. 4, the lamination process 30 is shown for the manufacturing of the laminated packaging material 10a of FIG. 1, wherein the bulk layer 11 is laminated to the barrier layer 14 by extruding an interjacent bonding layer of LDPE 15; 34 from an extrusion station 35 and pressing together in a roller nip 36. The barrier layer 14 has a pre-applied barrier coating 14a on one side of the substrate layer as discussed above, and this side is directed towards the bulk layer 11 as shown in FIG. 1. Thus, the laminated paper bulk layer and barrier layer pass a second extruder feedblock 37-2 and a lamination nip 37, where an outermost heat-sealable layer of LDPE 12; 37-3 is coated onto the outer side of the paper layer. Further, the laminate, including the outermost heat-sealable polymer layer 12; 37-3, passes a third extruder feedblock 38-2 and a lamination nip 38, where an innermost heat sealable polymer layer 13; 38-3 is coated onto the barrier layer side of the paper-film laminate forwarded from 37. As an alternative, this latter step may advantageously be performed before lamination at 37, to protect the barrier layer 14 on the inside as soon as possible, and according to a separate alternative embodiment, the lamination at 37 of the outermost layer to the paperboard may even be performed before the lamination at 36. The finished packaging laminate 39 is finally wound onto a storage reel, not shown.

[0106] FIG. 5a shows an embodiment of a packaging container (also referred to herein as a package) 50a produced from the packaging laminate 10a 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. The packaging container may be of any configuration, but is preferably brick-shaped, having longitudinal and transversal seals 51a and 52a, 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 easy to handle and dimensionally stable when put on a shelf in the food store or on a table or the like.

[0107] FIG. 5b shows an alternative, preferred example of a packaging container 50b produced from an alternative packaging laminate according to the invention. The alternative packaging laminate is thinner by having a thinner paper bulk layer, and thus 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 be distributed and sold in this form.

[0108] FIG. 5c shows a gable top package 50c, 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 layer of the invention. Alternatively, flat top packages may be formed from similar blanks of material.

[0109] FIG. 5d shows a bottle-like package 50d, which is a combination of a sleeve 54 formed from a pre-cut blanks of the laminated packaging material of the invention, and a top 55, which is formed by injection moulding plastics in combination with an opening device such as a screw cap or the like. This type of package is for example marketed under the trade names of Tetra Top and Tetra Evero. Those particular packages are formed by attaching the moulded top 55 with an opening device attached in a closed position, to a tubular sleeve 54 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.

[0110] FIG. 6 shows the form-fill-seal 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 of the web being united to one another in an overlap joint 63. The tube is filled (at 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.

EXAMPLES

[0111] A series of barrier layers 14 were produced by vapour coating of barrier substrate layers 14b. The barrier layers were included in packaging laminates, which were then formed into packages, as described below.

[0112] The barrier substrate layers were polymer films of BOPET (Mitsubishi primed film, BOPET RNK12-2DF) and MOPET (developed internally).

[0113] A plasma pre-treatment was applied to the barrier substrate layers as described in connection with FIG. 3. Direct current was used.

[0114] Barrier coatings 14a of partially oxidised aluminium were applied by PVD with reactive evaporation between aluminium and oxygen, as described in connection with FIG. 2. The film substrate web was of 1900 mm width and was coated at a reference speed of 7.8 m/s. Oxygen was injected into the evaporation zone at various flow rates to provide an atmosphere comprising evaporated oxygen and aluminium at different ratios. Test coatings were formed using lower ratios of oxygen to aluminium than the control coatings.

[0115] The amounts of oxygen and aluminium were varied as shown in Table 1 (sccm=standard cubic centimeter of gas volume flow):

TABLE-US-00001 TABLE 1 Oxygen Particles Recipe Control or Sample flow Al rate Transmittance Thickness seen in Substrate Number test Number (sccm) (g/min) value (%) (nm) TEM? BOPET 1a Control 2014-09-11-A1 12500 1.67 85 12.5 0.4 BOPET 2a Test 2014-09-11-A2 10000 1.67 70 10.3 0.7 (comparative) BOPET 3a Test 2014-09-11-A3 7000 4.2 18 22.8 1.6 ++ BOPET 4a Test 2014-09-11-A4 12000 4.2 25 24.7 0.6 ++ MOPET 1b Control 2014-09-12-A1 12300 1.67 85 13.4 0.7 MOPET 2b Test 2014-09-12-A2 12000 4.2 25 23.8 0.5 ++ MOPET 3b Test 2014-09-12-A3 25000 4.2 32 28.9 1.1 +

[0116] The barrier layers were used to manufacture packaging laminates. The laminated structure was as shown in FIG. 1 above, and the laminates were manufactured according to the method described in FIG. 4. Thus, all laminates produced had the same general structure, were formed of the same polymers and paperboard materials except where noted, and were laminated to each other in the same way:

[0117] /LDPE (12 g/m.sup.2) outermost/unbleached paperboard/LDPE optionally with adhesive (20 g/m.sup.2)/barrier coating/MOPET OR BOPET film substrate of 12 m thickness/[LDPE (12 g/m.sup.2)/m-LLDPE (13 g/m.sup.2) OR adhesive (6 g/m.sup.2)/m-LLDPE (19 g/m.sup.2)]/

[0118] The laminates were formed into cuboidal packages using a TETRA PAK A3 Flex/TBA1000 packaging apparatus with ultrasonic sealing.

[0119] The barrier layers, laminates and packages were evaluated.

TEM Images

[0120] TEM images were obtained of the barrier coatings. Dark particles were visible in some but not all coatings, as shown in Table 1. Particles were seen in coatings 3a (shown in FIG. 7), 4a and 2b. For coating 3b a grain-like structure was visible in TEM. For the control coatings 1a and 1b, and coating 2a, dark particles were not seen.

[0121] Without wishing to be bound by this theory, the inventors believe that the dark particles are particles of aluminium metal dispersed in aluminium oxide, Al.sub.2O.sub.3, so that the coating is of a ceramic-metallic (cer-met) composite. It is believed that where the amount of aluminium metal is small the particles may be present but be too small to be visible by TEM.

XPS Analysis

[0122] XPS analysis of the three MOPET-based samples 1b, 2b, 3b indicated that the surface composition of the barrier layer coatings was Al.sub.2O.sub.3.

Thickness

[0123] Thicknesses of the coatings were determined by TEM and are shown in Table 1. Coating thicknesses were in the range of 10.3-28.9 nm.

Transmittance Values of Coatings

[0124] Transmittance values for the coatings were measured online during coating formation and are shown in Table 1.

[0125] Transmittance values increased after coating and this was thought to be due to further oxidation and stabilisation of the coating during post-treatment and afterwards in air. Increases of 5 to 7 percentages points (or up 30-40% of initial value for low initial transmittance) were typical. The values provided in Table 1 thus increased to final, stabilised values being 5-7 percentage points higher, on each coating.

Oxygen Transmission Rates of Barrier Layers

[0126] FIG. 8 shows OTR for the barrier layers at 23 C. and 50% RH.

[0127] It can be seen that OTRs decrease as the coating is prepared with a lower oxygen ratio i.e. OTR for BOPET-based barrier layers is 1a (control, labelled BOPET AlOx (standard))>2a>>3a>4a and for MOPET-based barrier layers is 1b (control, labelled MOPET AlOx (standard))>2b>3b. Low OTRs are desirable.

[0128] Coatings 3a, 4a, 2b and 3b provided OTRs of less than 3 cm.sup.3/(m.sup.2.Math.24 h.Math.1 atm), which is desirable. For coatings 2b and 3b (on MOPET) OTRs were less than 2 cm.sup.3/(m.sup.2.Math.24 h.Math.1 atm), which is even more desirable.

[0129] FIG. 9 shows OTR at 23 C. and 50% RH for the barrier layers after 0, 10 and 50 cycles of Gelbo flexing. It can be seen that the good initial OTR performance of the partially oxidised aluminium coatings is maintained after Gelbo flexing. This indicates that the coatings have better mechanical properties than the control of standard AlOx, and are less brittle. Coating 4a is thicker and has less embedded aluminium (transmittance of 25% compared to 18%) which makes the coating more brittle.

Crack Onset Strain

[0130] FIG. 10 shows crack onset strain for (a) BOPET-based barrier layers and (b) MOPET-based barrier layers. Crack onset strain is the strain at which OTR (at 23 C. and 50% RH) starts to increase rapidly. A high crack onset strain indicates good mechanical properties and resistance to cracking.

[0131] Crack onset strain increases in the order 1a (control, labelled A1)<2a (A2)<3a (A3)<4a (A4) for BOPET-based barrier layers. For MOPET-based films, again films 2b (A2) and 3b (A3) performed better than the control (1b/A1).

Oxygen Transmission Rates of Laminates

[0132] FIG. 11 shows OTR (at 23 C. and 50% RH) for the BOPET-based laminates (packaging materials).

[0133] Again, it can be seen that OTR decreases as the coating is prepared with a lower oxygen ratio, with OTR for the control 1a (labelled BOPET AlOx (standard)) higher than for 4a.

[0134] It can also be seen that OTR for the 4a packaging material is similar to that for the barrier layer, indicating that the barrier layer maintains good properties even after extrusion lamination.

Oxygen Transmission Rates of Packages

[0135] FIG. 12 shows OTR (at 23 C. and 50% RH) for packages formed from the laminates (packaging materials).

[0136] Again, it can be seen that OTR decreases as the coating is prepared with a lower oxygen ratio. For each of MOPET and BOPET, the standard AlOx coating gives higher OTR than the modified AlOx coating.

Appearance

[0137] The appearance of the test coatings was visually evaluated. The coatings were usually grey, brown, dark brown or bluish but in one case the coating was purple.

[0138] It was found that coatings with a final transmittance value of less than 20% had a metallic appearance. Coatings with a higher transmittance value than 20% did not have a metallic appearance after lamination, particularly when unbleached board was used.

[0139] Without wishing to be bound by theory, the inventors believe that the appearance of the coatings is dependent on both the thickness of the coating and the size of the aluminium particles.

CONCLUSIONS OF EXAMPLE

[0140] The coatings of the examples had various advantages. [0141] The coatings were non-metallic in appearance, especially after lamination, and could thus be visually distinguished from metal and metallised films. This may be important in meeting market needs. For example, the Japanese market requires barrier layers which are non-metallic in appearance to enable package recycling. [0142] The coatings provided effective barrier properties as shown by OTRs. The good OTRs were maintained when the barrier layers were converted to form laminates (including extrusion coating) and when the laminates were formed into packages. The good OTRs were also maintained after a Gelbo flex test. Crack onset strain was high. Thus, the coatings showed better mechanical properties than conventional AlOx coatings, which tend to be brittle. Again without wishing to be bound by theory, the inventors believe that the cer-mat structure with its aluminium particles contributes to the good mechanical properties of the test coatings by reducing brittleness. The coatings are promising as a barrier layer for use in liquid packaging laminates (including those for long-term aseptic, ambient storage), where crack resistance is very important. The low thickness of the coatings contributes to the good mechanical properties: thicker coatings used in the prior art e.g. the coating of EP437946 (thickness around 5-7 times that of the example) would be likely to be more brittle. [0143] The coatings could be applied at a higher coating speed than PECVD coatings using standard PVD equipment. Again, low coating thickness allows for higher coating speed. These coatings thus offer a low-cost, scaleable option. [0144] The coatings use a low amount of metal compared with conventional aluminium foil, which also enables easier recycling of the laminated material, and generates less carbon dioxide in the manufacturing process. In addition, the PE used in the various layers may be bio-based. Therefore, the laminate of the examples has sustainability advantages. [0145] The coatings may be microwaveable.

[0146] As a final remark, the invention is not limited by the embodiments shown and described above, but may be varied within the scope of the claims.