WO1998030390A1

WO1998030390A1 - A packaging laminate

Info

Publication number: WO1998030390A1
Application number: PCT/GB1998/000044
Authority: WO
Inventors: Andrew David Rothwell Baxter; Geir Morten Johansen; Jørn Erland OLSEN; Harald Riiber
Original assignee: Elopak Systems Ag
Priority date: 1997-01-10
Filing date: 1998-01-08
Publication date: 1998-07-16
Also published as: ZA98181B; AU5491798A; GB9700433D0

Abstract

A packaging laminate comprises a first layer of EVOH or greaseproof paper, to provide a good barrier to oxygen and/or aroma, but a poor barrier to visible light, and a second layer of bleached/unbleached, duplex paper or board, or of a tie substance incorporating a dye pigment, to provide a good barrier to visible light. The laminate may form a carton or a pouch for packaging a dairy product.

Description

A PACKAGING LAMINATF.

This invention relates to a packaging laminate. EP-A-0313356 discloses a carton blank from which can be formed a carton for a food product, for example a fruit juice. The blank is so composed as to provide security against leakage from the carton and against passage of gas through the wall of the carton. To achieve these purposes, the blank consists of a laminate comprising, from the outside to the inside, a polyolefin heat-sealing layer (specific

2 ₂ weight 8 to 40g./m ) a paperboard layer (100 to 500g./m ), a

₂ polyolefin adhesive layer (8 to 50g./m ), a greaseproof paper

₂ layer (25 to lOOg./m ), and a polyolefin heat-sealing product-contacting layer (10 ' to 50g./m ) . The three polyolefin layers may have dye pigments added to provide impermeability to light. The degree of dyeing depends upon the product to be protected and on its light sensitivity. In a sample of the blank according to the invention of EP-A- 0313356 used for comparative testing purpose, the laminate consisted of LDPE (14g. /m²) /duplex paperboard (224g. /m²) /LDPE (20g./m²) /greaseproof paper (50g . /m²) /LDPE (40g./m²).

The TAPPI "Dictionary of Paper", 5th Edition, 1996, defines "DUPLEX BOARD" as "A general term for a board made of two different stocks or colors on a cylinder machine, or a combination cylinder-fourdrinier machine, or a fourdrinier machine equipped to receive two different pulp furnishes. It is a combination board limited to two stocks or colors"; and defines "DUPLEX PAPER" as "any paper showing different colors, textures, or finishes on the two sides of the sheet".

WO-A-92/01558 discloses a packaging carton consisting of a laminate comprising inner and outer layers which serve to stiffen the laminate, and an intermediate layer intermediate the inner and outer layers and by way of which the inner and outer layers are tied together. In one embodiment, the inner layer and the intermediate layer both serve as relatively good barriers to 0₂ migration, the intermediate layer being ethylene vinyl alcohol (EVOH) or polyamide (PA) extruded or co-extruded onto the inner layer, which comprises metallized polyethylene terephthalate (M-PET) , glass-coated PET (G-PET) , metallized oriented polypropylene (M-OPP) , G-OPP, or greaseproof paper, the coated surface of the M-PET, G-PET, M- OPP, or G-OPP, facing outwards. In another embodiment an aluminium-metallized EVOH film constitutes the inner stiffening layer and has been extrusion-laminated by an intermediate low density polyethylene (LDPE) layer to the outer stiffening layer. If the outer layer is semi-bleached multilayer paperboard and the inner layer is unbleached greaseproof paper, the laminate gives very good protection against light. The innermost, heat-sealing, product- contacting layer of the laminate consists of LDPE, as does an outermost, heat-sealing layer if provided. The layer arrangement of a preferred version of the one embodiment, progressing inwards, is LDPE (10 'to 30g./m )/ paperboard (150 to 400g./m ) /0₂ barrier polymer (3 microns to 15 microns) (e.g. thin tie layer/EVOH or PA/thin tie layer) /M-PET, G-PET,

M-OPP, G-OPP (6 microns to 25 microns), or greaseproof paper

(25 to 100 microns) /LDPE (10 to 70g./m²). An example of the one embodiment is LDPE (14g. /m²) /duplex board (230g. /m²) /LDPE

(20g. /m²) /"BYNEL" tie layer (5g. /m²) /EVOH (7g. /m²) /greaseproof paper (50g./m 2 ) /LDPE (35g./m2) . In the other embodiment, the layer arrangement is preferably LDPE (10 to 30g./m ) /duplex paperboard (150 to 400g . /m²) /LDPE (10 to 50g. /m²) /aluminium- metallized material, such as Al-metallized greaseproof paper or polymer film, for example Cellophane (regenerated cellulose) film or EVOH film (7 microns to 20 microns) /LDPE

2

10 to 70g./m ) . An example of this other embodiment is LDPE (14g./m²)/ duplex board (230g. /m²) /LDPE (25g. /m²) /"SURLYN" tie layer (5g./m²)/ metallized EVOH film (12 microns)/ "BYNEL" tie layer (5g. /m²) /LDPE 30g./m²). O93/02862 discloses a laminating method comprising (a) applying a moisture barrier layer of LDPE to the outside of a relatively stiff substrate of paperboard to form a preliminary laminate, (b) extrusion laminating the preliminary laminate, a thermoplastics layer of LDPE and a film comprised of a barrier polymer layer, by applying the thermoplastics layer in a molten state to between the inside of the preliminary laminate and the film, and (c) applying a second moisture barrier layer of LDPE to the inside of the film. The film may consist of an inner, oxygen barrier layer of EVOH and an outer, tie layer of modified LDPE; or of inner and outer, tie layers of modified LDPE and an intermediate, oxygen barrier layer of EVOH. The packaging laminate, progressing inwardly, may consist of the following layers: LDPE (14g./m²) /paperboard/LDPE (10 to 25g. /m²) /modified LDPE (3 microns) /oriented EVOH (6 microns) /modified LDPE (6g./m² or 3 microns) /LDPE (10 to 50g./m²).

According to one aspect of the present invention, there is provided a packaging laminate comprising a first layer which provides a relatively good barrier to oxygen and/or aroma but a relatively poor barrier to visible light, a second layer which provides a relatively good barrier to visible light, and respective opposite surface layers which provide respective heat-sealing layers, characterized in that said surface layers provide relatively poor barriers to visible light.

Owing to this aspect of the invention, it is possible to avoid the problem that incorporation of light barrier material, particularly a dye pigment, into the surface layers has a deleterious effect upon one or more desirable properties of those layers, particularly their heat-sealing properties .

According to a second aspect of the present invention, there is provided a packaging laminate comprising a first layer which provides a relatively good barrier to oxygen and/or aroma but a relatively poor barrier to visible light, and a second layer which provides a relatively good barrier to visible light, characterized in that said second layer is comprised of a stratum of bleached pulp and a stratum of unbleached pulp.

Owing to these two aspects of the invention, it is possible to provide a laminate which allows use of a transparent or translucent material, such as EVOH or bleached greaseproof paper, providing a good barrier to transmission of oxygen and/or aroma, with a light-sensitive product, such as fresh milk, ultra-heat-treated (UHT) milk, mineral water, and fruit juice.

According to a third aspect of the present invention, there is provided a packaging laminate comprising a first layer which provides a relatively poor barrier to visible light, and a second layer which provides a relatively good barrier to visible light and which is a thermoplastics adhesion layer including a dye pigment providing relatively good impermeability to visible light, characterized in that the laminate further comprises, at the opposite side of said first layer from said adhesion layer, a thermoplastics adhesion layer including a dye pigment providing a desired colour. Owing to this aspect of the present invention, it is possible to ensure that, in spite of the incorporation of a dye pigment, for example carbon black, into an adhesion layer spaced from the interior of a container, for example a carton or a pouch, by layers which are relatively transparent, the visual appearance of the inside surface of the container is attractive to a customer. The adhesion layer can be, for example, an extruded thermoplastics used in extrusion lamination of two webs to each other or a tie layer which is a very thin layer of adhesive between two other layers of the laminate.

According to a fourth aspect of the present invention, there is provided a packaging pouch formed of a laminate comprising a thermoplastics layer and, outwardly of the thermoplastics layer, a second layer, characterized in that said second layer comprises paper.

Owing to this aspect of the invention, the inclusion of a paper layer in the laminate from which the pouch is formed has not only the advantage that the laminate has increased stiffness, giving easier handling of the laminate by the machinery used in its manufacture and by the machinery used in its conversion into pouches. The paper layer can be mould paper which is relatively strong and which it is known per se to include in laminar sheets to be blow thermoformed, since the paper is elongatable to a limited extent without rupturing. There is the additional advantage that the paper layer can take the form of a light barrier paper layer in the event that the product to be filled into the pouch is light- sensitive. When relatively low stiffness of the laminate for the pouch is acceptable, the paper layer could be a layer of unbleached greaseproof paper and thus constitute a good barrier to visible light as well as to oxygen and/or aroma. On the other hand, where greater stiffness of the laminate is required, it is preferred that the paper layer provide stiffness in particular, while an additional layer, between the paper layer and the thermoplastic layer, provides in particular an oxygen and/or aroma barrier. That additional layer may be bleached greaseproof paper or a polymer such as EVOH. The product which is improvedly protected, and thereby has its shelf life extended, is preferably milk or a milk- based product .

The oxygen and/or aroma barrier layer is at least translucent. The layer should be of a material which is suitable for extrusion coating or lamination, particularly bleached greaseproof paper, or regenerated cellulose, or a polymer, for example EVOH, PA, or PET, or a polymer film having an inorganic surface coating, e.g. PET coated with silicon oxide (SiO or aluminium oxide (A10 , or OPP coated with SiO_x or A10_x.

The visible light barrier layer is advantageously such that the transmission of light of a wavelength of 400nm does not exceed 2% and the transmission of light of a wavelength of 500nm is below 8%. The layer may comprise duplex paper or board containing unbleached chemical thermomechanical pulp (CTMP) . The unbleached stratum of the duplex paper or board is preferably at the inner side of the paper or board, with the oxygen and/or aroma barrier layer located to the inside thereof. In this way, the visually more attractive bleached stratum is located at the outer side of the duplex paper or board. The proportion of the thickness of the paper or board which is not bleached is advantageously between 20% and 70%, the higher the proportion of unbleached thickness, the better the barrier to light, which, for example in the case of milk or a milk-based product, causes the taste of the same to change .

We have ascertained that good protection against light and transfer of oxygen and/or aroma can be achieved by combining a light barrier consisting of a layer of duplex paper or board containing unbleached CTMP and an oxygen and/or aroma barrier consisting of a layer of EVOH, or of a layer of bleached greaseproof paper.

Advantageously, the laminate does not include any metal foil layer.

A polymer constituting the oxygen and/or aroma barrier can be applied by, for example, extrusion coating (including co-extrusion coating), or film lamination.

In the event that the laminate is to be formed and sealed to provide a container, a sealing layer is included at the very inside of the laminate, whilst another sealing layer may be included at the very outside of the laminate.

The laminate may additionally include a layer comprised of a mixture of a polymeric material and an inorganic filler to improve the water vapour barrier property of the laminate and to improve its pin-hole resistance. In this respect, filled LDPE is particularly useful.

At one or each side of the oxygen and/or aroma barrier layer may be provided a tie layer, which may be such as to improve environmental stress crack resistance (ESCR) . In this respect, linear low density polyethylene (LLDPE) is particularly useful for improving ESCR and toughness of the laminate. The tie layer, or one or each of the tie layers may incorporate a dye pigment, to provide a barrier to visible light.

A further layer may be included in the laminate to provide an additional barrier to water vapour and/or to add stiffness and/or to reduce scalping of flavour. Polypropylene (PP) or PP-blend is particularly suitable for this purpose. Where the further layer comprises PP, it is advantageous to use polyolefin plastomer (POP) as a low temperature sealing layer readily adherent to PP.

In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: - Figures 1 to 6 are respective diagrams of differing versions of a packaging laminate, and giving materials, exemplary "thicknesses", advantageous "thickness" ranges, and properties of layers of each version; and Figure 7 is a side elevation of a pouch made from the laminate of Figure 2 or 3.

The laminate may take a relatively simple form, for example as shown in Figure 1, where an EVOH layer is in direct contact with an unbleached stratum of duplex board, which stratum serves as a light barrier and which board provides stiffness, and is attached by a tie layer to an inside heat-sealing layer of low density polyethylene (LDPE) , a bleached stratum of the duplex board, which stratum provides a white surface for printing, being covered by an outside heat-sealing layer of LDPE. The duplex board may be of the type consisting of the following strata: bleached sulphate/unbleached CTMP/ unbleached sulphate. In the manufacture of the laminate according to Figure 1, a duplex board web is brought to a first extrusion laminator where the outside layer of LDPE is extrusion-coated onto the duplex board web. The LDPE/board web is then forwarded to a second extrusion laminator where the inside of the web is co- extrusion coated with a molten film consisting of the three layers EVOH/tie/LDPE . This laminate is suitable for forming liquid-packaging cartons.

The laminate may be of another simple form, shown in Figure 2, which differs from the form shown in Figure 1 solely in that duplex paper is included instead of duplex board, the duplex paper having an outer, bleached stratum and an inner, unbleached stratum, each of CTMP for example. The manufacture of the laminate of Figure 2 corresponds to that of the laminate of Figure 1. The laminate of Figure 2 is employed where relatively high stiffness of the laminate is not sought and is suitable for forming liquid-packaging pouches .

Figure 3 shows a laminate of a character similar to that of the laminate of Figure 2 except that bleached greaseproof paper is laminated by a layer of LDPE to the duplex paper. In manufacture thereof, the outside LDPE layer is formed by extrusion-coating onto the light barrier paper, the inside LDPE layer is formed by extrusion-coating onto the greaseproof paper, and then the LDPE/light barrier paper web and the LDPE/greaseproof paper web so formed are extrusion- laminated together at a nip by the intermediate LDPE. Again, this laminate is suitable for forming packaging pouches.

However, the laminate may be of a more complex structure, for example as illustrated in Figure 4, where, to the inside, unbleached stratum of the duplex board, is a layer of filled LDPE, for example as disclosed in our co- pending British Patent Application 9603448.3), with that layer being attached by an LLDPE tie layer to the EVOH layer, which in this case is in the form of a film, itself attached through another LLDPE tie layer to an inside, heat-sealing layer of LDPE. In the manufacture of the laminate according to Figure 4, a duplex board web is brought to a first extrusion laminator where the outside heat-sealing layer of LDPE is extrusion-coated onto the board web. The LDPE/board web is then forwarded to a second extrusion laminator where filled LDPE is extruded into a nip between the LDPE/board web and an LLDPE tie/EVOH/LLDPE tie web of film form. The LDPE/board/ filled LDPE/LLDPE/EVOH/LLDPE web is then forwarded to a third extrusion laminator where the inside layer of LDPE is extrusion-coated onto the exposed LLDPE layer.

In a slightly more complex version shown in Figure 5, a PP-blend layer and a POP layer (which may be DPT1450.00 from Dow Chemical Company) co-extrusion coated onto the exposed LLDPE-tie layer are provided instead of the inside LDPE layer, with the POP layer constituting the inside heat- sealing layer of the laminate.

The laminates of Figures 4 and 5 are again suitable for forming packaging cartons.

The deliberate provision of a light barrier is not necessarily in the stiffness-providing layer of the laminate; it could be in another layer which is not one of the surface layers of the laminate, for example in a tie layer as illustrated in Figure 6, in which, in a laminate as disclosed in WO93/02862, a visible-light-absorbing, dye pigment, in this case carbon black, has been incorporated into the modified LDPE of the outer tie layer so that the outer tie layer serves as a good barrier to invisible light. So that the carbon black is not visible through the relatively transparent, inner, LDPE heat-sealing layer and the relatively transparent, EVOH layer, a dye pigment giving a desired colour, in this case titanium oxide (Ti0₂) giving a white appearance, has been incorporated into the modified LDPE of the inner tie layer. Referring to Figure 7, the filled and sealed pouch 20 illustrated therein has been produced by forming into a tube a web of laminate according to Figure 2 or 3, with the inner, LDPE sealing layer on the inside of the tube, forming a longitudinal sealing seam 21 along the tube while lowering the tube, continually topping-up the tube with product to below the top of the seam as the tube lowers, and repeatedly sealing the lowering tube transversely below the surface level of the product therein to ^'trap doses of product among the transverse seals 22, and severing the transverse seals centrally transversely to separate the pouches from each other. The consumer of the product opens the pouch 20 by cutting open a corner thereof.

Claims

I . A packaging laminate comprising a first layer which provides a relatively good barrier to oxygen and/or aroma but a relatively poor barrier to visible light, a second layer which provides a relatively good barrier to visible light, and respective opposite surface layers which provide respective heat-sealing layers, characterized in that said surface layers provide relatively poor barriers to visible light.

2. A laminate according to claim 1, wherein said second layer is comprised of a stratum of bleached pulp and a stratum of unbleached pulp.

3. A laminate according to claim 2, wherein said stratum of unbleached pulp is nearer to said first layer than is said stratum of bleached pulp.

4. A laminate according to claim 2 or 3, wherein between 20% and 70% of the thickness of said second layer is constituted by said stratum of unbleached pulp.

5. A laminate according to any one of claims 2 to 4, wherein said second layer is of a weight of between 30 and

80g./m².

6 . A laminate according to claim 5 , wherein said second

2 layer is of a weight of between 40 and 60g./m .

7. A laminate according to claim 6, wherein said second

2 layer is of a weight of substantially 60g./m .

8. A laminate according to any one of claims 5 to 7 and in the form of a pouch.

9. A laminate according to any preceding claim and further comprising, between the first and second layers, another layer comprised of a mixture of a polymeric material and an inorganic filler.

10. A laminate according to any preceding claim, and further comprising, at that side of second layer further from said first layer, a further layer providing a relatively good barrier to water vapour and/or relatively high stiffness and/or a relatively good barrier to scalping of flavour.

II. A laminate according to claim 10, wherein said further layer comprises polypropylene.

12. A laminate according to claim 11, wherein said further layer is immediately adjacent to one of said surface layers, which comprises polyolefin plastomer.

13. A laminate according to claim 1, wherein said second layer is a tie layer in face-to-face contact with said first layer and including a dye pigment providing relatively good impermeability to visible light.

14. A laminate according to claim 13, and further comprising, in face-to-face contact with said first layer oppositely to said tie layer, a tie layer including a dye pigment providing a desired colour.

15. A laminate according to claim 13 or 14, wherein the or each tie layer is of a weight of between 3 and lOg./m .

16. A laminate according to claim 15, wherein the or each

2 tie layer is of a weight of substantially 3g./m .

17. A laminate according to any preceding claim, wherein said first layer comprises bleached greaseproof paper, regenerated cellulose, a polymer, or a coated polymeric film having an inorganic surface coating.

18. A laminate according to claim 17, wherein said polymer comprises ethylene vinyl alcohol, polyamide, or polyethylene terephthalate .

19. A laminate according to claim 17, wherein said coated polymeric film comprises polyethylene terephthalate coated with silicon oxide or aluminium oxide, or oriented polypropylene coated with silicon oxide or aluminium oxide.

20. A laminate according to any preceding claim, wherein the transmission, through said second layer, of light of a wavelength of 400nm does not exceed 2% and the transmission, through said second layer, of light of a wavelength of 500nm is below 8%.

21. A packaging laminate comprising a first layer which provides a relatively good barrier to oxygen and/or aroma but a relatively poor barrier to visible light, and a second layer which provides a relatively good barrier to visible light, characterized in that said second layer is comprised of a stratum of bleached pulp and a stratum of unbleached pulp.

22. A laminate according to claim 21, wherein said stratum of unbleached pulp is nearer to said first layer than is said stratum of bleached pulp.

23. A laminate according to claim 21 or 22, wherein between 20% and 70% of the thickness of said second layer is constituted by said stratum of unbleached pulp.

24. A laminate according to any one of claims 21 to 23, wherein said second layer is of a weight of between 30 and 80g./m².

25. A laminate according to claim 24, wherein said second layer is of a weight of substantially 60g./m².

26. A laminate according to claim 24 or 25 and in the form of a pouch.

27. A laminate according to any one of claims 21 to 26, wherein said first layer comprises bleached greaseproof paper, regenerated cellulose, a polymer, or a coated polymeric film having an inorganic surface coating.

28. A laminate according to any one of claims 21 to 27, wherein the transmission, through said second layer, of light of a wavelength of 400nm does not exceed 2% and the transmission, through said second layer, of light of a wavelength of 500nm is below 8%.

29. A packaging laminate comprising a first layer which provides a relatively poor barrier to visible light, and a second layer which provides a relatively good barrier to visible light and which is a thermoplastics adhesion layer including a dye pigment providing relatively good impermeability to visible light, characterized in that the laminate further comprises, at the opposite side of said first layer from said adhesion layer, a thermoplastics adhesion layer including a dye pigment providing a desired colour.

30. A packaging laminate according to claim 29, wherein said first layer provides a relatively good barrier to oxygen and/or aroma.

31. A laminate according to claim 29 or 30, wherein the adhesion layers are respective tie layers in face-to-face contact with respective opposite surfaces of said first layer which is a polymeric layer.

32. A laminate according to claim 31, wherein each tie layer

2 is of a weight of between 3 and lOg./m .

33. A laminate according to claim 32, wherein each tie layer is of a weight of substantially 3g./m .

34. A laminate according to claim 31, 32, or 33, wherein said first layer comprises a polymeric film.

35. A laminate according to any one of claims 31 to 34, wherein said polymeric layer comprises ethylene vinyl alcohol .

36. A packaging pouch formed of a laminate comprising a thermoplastics layer and, outwardly of the thermoplastics layer, a second layer, characterized in that said second layer comprises paper.

37. A pouch according to claim 36, wherein said paper provides a relatively good barrier to visible light and is comprised of a stratum of bleached pulp and a stratum of unbleached pulp.

38. A pouch according to claim 37, wherein said stratum of unbleached pulp is nearer to said thermoplastics layer than is said stratum of bleached pulp.

39. A pouch according to claim 37 or 38, wherein between 20% and 70% of the thickness of said second layer is constituted by said stratum of unbleached pulp.

40. A pouch according to any one of claims 37 to 39, wherein

2 said second layer is of a weight of between 30 and 80g./m .

41. A pouch according to claim 40, wherein said second layer

2 is of a weight of between 40 and 60g./m .

42. A pouch according to claim 41, wherein said second layer

2 is of a weight of substantially 60g./m .

43. A pouch according to any one of claims 36 to 42, and further comprising an adhesion layer including a dye pigment providing relatively good impermeability to visible light.

44. A pouch according to claim 43, and further comprising, inwardly of said adhesion layer, an adhesion layer including a dye pigment providing a desired colour.

45. A pouch according to claim 43 or 44, wherein the or each

2 adhesion layer is of a weight of between 3 and lOg./m .

46. A pouch according to any one of claims 36 to 45, wherein the transmission, through said second layer, of light of a wavelength of 400nm does not exceed 2% and the transmission, through said second layer, of light of a wavelength of 500nm i s be l ow 8 % .

47. A pouch according to any one of claims 36 to 46, and further comprising, between said thermoplastics layer and said second layer, an additional layer providing a relatively good barrier to oxygen and/or aroma but a relatively poor barrier to visible light.

48. A pouch according to claim 47, wherein said additional layer comprises a polymer or bleached greaseproof paper.