A PACKAGING LAMINATE POSSESSING SUPERIOR BARRIER PROPERTIES TO GASES, A METHOD OF PRODUCING THE PACKAGING LAMINATE AND PACKAGING CONTAINERS PRODUCED FROM THE PACKAGING LAMINATE

Abstract: The disclosure relates to a packaging laminate comprising a core layer (31) of paper and a gas barrier layer (32) disposed on one side of the core layer and containing polyketone, the polyketone being an aliphatic linear copolymer of olefin monomer and carbon monoxide (CO). The packaging laminate possesses good internal strength and packaging containers produced from the packaging laminate obtain superior gas and aroma barrier properties as well as good mechanical properties at a lower cost. The polyketone copolymer consists of 100 percent alternating olefin monomer and carbon monoxide units, preferably of alternating ethylene and carbon monoxide units and up to approx. 15 weight percent of alpha -olefin units with 3-12 carbon atoms. The polyketone may also be mixed with another thermoplastic polymer such as, for example, polyolefin, and is incorporated in the mixture in a quantity of 1-99, preferably 30-70 weight percent. The gas barrier layer (32) may be bonded to the core layer (31) by means of an adhesive layer (35) of an adhesion promoting polymer or alternatively by means of a lamination layer (34) of a thermoplastic and an adhesive layer (35) disposed between the thermoplastic layer and the gas barrier layer. One or more inside layers (33') of a liquid-tight plastic may be provided on the opposite side of the gas barrier layer, for the formation of the inside layer in a packaging container produced from the packaging laminate, by means of an interjacent adhesion layer (36).

Description: A PACKAGING LAMINATE POSSESSING SUPERIOR BARRIER PROPERTIES TO GASES, A METHOD OF PRODUCING THE PACKAGING LAMINATE AND PACKAGING CONTAINERS PRODUCED FROM THE PACKAGING LAMINATE TECHNICAL FIELD The present invention relates to a packaging laminate comprising a core layer of paper and a gas barrier layer of plastic. The present invention also relates to a method of producing the packaging laminate according to the invention, as well as packaging containers produced from the packaging laminate according to the invention. BACKGROUND ART Within the packaging industry, use has long been made of packages of the single-use disposable type for packaging and transporting, for example, liquid foods. A large group of these single-use disposable packages is produced from a laminated packaging material comprising a core layer of paper or paperboard and outer, liquid-tight coatings of plastic on both sides of the core layer. The composition of the packaging material is intended to afford to the packed product the best possible protection, at the same time as it is intended to render the package both easy to manufacture and easy to handle. A core layer of paper or paperboard imparts to the package good mechanical configurational stability such that the package may be distributed in a simple, rational manner and be conveniently handled, at the same time as outer, liquid-tight coatings of plastic effectively protect the core layer against penetration by moisture and wet which otherwise would rapidly weaken and destroy the core layer and thereby render the package sloppy and impossible to handle. Preferably, the outer, liquid-tight coatings consist of a thermoplastic such as, for example, polyethylene which, in addition, gives the laminated packaging material excellent heat-sealing properties so that the packages may be closed and permanently sealed in the desired geometric configuration by means of conventional heat-sealing methods. Packaging containers from such a laminated packaging material are often produced in that a continuous web of the packaging material is reformed into a tube by the longitudinal edges of the web being united to one another, whereafter the tube is filled with intended contents and is sealed along repeated transverse sealing zones. The package units containing their contents are separated from the tube by means of incisions in the transverse sealing zones and are formed to the desired geometric configuration by a fold-forming operation. In order to supplement such a packaging material with barrier properties against light or gases such as carbon dioxide or oxygen gas, it is known in the art to apply different types of barrier layers between the core layer and the one outer plastic coating of the packaging material. Conventionally, use is often made of a light and gas barrier layer of an aluminium foil (Alifoil). In itself, Alifoil is practically entirely gas-tight, but because of its slight ductility, there is a tendency to crack formations and ruptures in particularly exposed areas which occur on reforming of the packaging laminate into packaging containers. Alternatively, a layer of a polymer possessing superior gas barrier properties may be employed as the gas barrier layer. Examples of known gas barrier polymers are ethylene vinyl alcohol copolymers (EVOH), polyvinyl alcohol (PVOH) and polyamide. Such polymers possess superior gas barrier properties, but must, because of their sensitivity, be protected against moisture and wet, for example by being encapsulated in between layers of a liquid-tight polymer such as, for example, polyethylene. In addition the prior art conventional gas barrier layers are relatively expensive, which entails a higher manufacturing cost per package. OBJECTS OF THE INVENTION - THE LAMINATE One object of the present invention is therefore to realise a novel packaging laminate of the type described by way of introduction, without any consequential problems of the type linked to the prior art technology. Another object of the present invention is to realise a well-integrated packaging laminate possessing superior gas barrier properties at a lower cost. Yet a further object of the present invention is to realise a well- integrated packaging laminate possessing superior oxygen gas barrier properties as well as superior aroma barrier properties at a lower cost. Still a further object of the present invention is to realise a well- integrated packaging laminate possessing superior oxygen gas barrier properties also in environments of high relative humidity. One particular object of the present invention is to realise a well- integrated packaging laminate possessing superior oxygen gas barrier properties and, compared with the prior art technology, at least equivalent mechanical properties such as strength and flexibility, at a lower cost. SOLUTION These objects will be attained in that a laminated packaging material of the type described by way of introduction has been given the characterizing features as set forth in appended Claim 1. Preferred embodiments of the laminated packaging material according to the present invention will be apparent from appended subclaims 2 to 16. OBJECTS OF THE INVENTION - THE METHOD A further object of the present invention is to realise a simple, rational method of producing, with existing process equipment and at lower cost, a packaging laminate possessing superior oxygen gas barrier properties and also superior aroma barrier properties and, compared with the prior art technology, at least equivalent mechanical properties. The method of producing the packaging laminate according to the present invention has the characterizing features as set forth in appended Claims 17 and 18, respectively. Furthermore, there will be realised according to the present invention mechanically strong and configurationally stable packaging containers according to appended Claim 19, possessing superior gas and aroma barrier properties. SUMMARY OF THE INVENTION The core layer in the packaging laminate according to the invention consists of a fibre material such as, for example, paper or paperboard of a suitable packaging quality. The plastic layer which constitutes the gas barrier layer in the packaging laminate according to the invention includes a so-called aliphatic polyketone, i.e. a linear copolymer with perfectly alternating carbon monoxide and olefin monomer. The term "perfectly alternating" is here taken to signify that carbon monoxide monomers and olefin monomers respectively essentially constitute every second linear building block in the polymer chains so that the polymer molecules include roughly 50 mol per cent of each of carbon monoxide and α-olefin. Such polymers are semi- crystalline thermoplastic materials with high molecular weight. Preferably, the linear copolymer is a perfect 100 per cent alternating copolymer of carbon monoxide and ethylene, and, where applicable, may encompass a minor quantity of additionally one or more randomly copolymerised α- olefins with at least 3 carbon atoms. Suitable additional copolymerised α- olefins have 3-12 carbon atoms, preferably 3-6 carbon atoms, such as, for example, propylene 1-butene or isobutene. Such aliphatic polyketones are distinguished not only from randomly alternating copolymers of ethylene and carbon monoxide which are produced by means of free radical polymerisation and contain a considerably lower proportion of carbon monoxide than 50 mol per cent, but also from aromatic polyketones, for example polyether ketones. Preferably, the aliphatic polyketone in a gas barrier layer in a packaging laminate according to the present invention is such a tercopolymer of carbon monoxide, ethylene and a minor quantity of α-olefin with at least 3 carbon atoms such as, for example, propylene and may be represented by the repeating unit -(-CO-(-CH2-CH2))x-(-CO-(-G))y- wherein G is a moiety of the additional copolymerised α-olefin. Suitably, the terpolymer contains up to approx. 15 weight per cent, preferably approx. 1-10 weight per cent of α-olefin, preferably propylene. The aliphatic polyketone in a gas barrier layer in the packaging laminate according to the present invention preferably has a molecular weight (number average) which lies between approx. 1,000 and approx. 250,000, more preferably between approx. 20,000 and approx. 150,000, a melting point from about 175 to about 300°C and a melt index of between 5 and 2,000 g/ 10 min., at 5 kg and 240°C. Preferably, it has a glass transition temperature Tg of between 10 and 15°C and a density of approx. 1.22-1.24. Such aliphatic polyketones have, in addition to excellent gas barrier properties and aroma barrier properties, also good mechanical properties, good chemical resistance, good heat resistance and also good processing properties, making it suitable for gas and aroma barrier materials in packages for foods. Moreover, it may be produced at a low cost in relation to other prior art polymer gas barrier materials. In addition, it has noλv surprisingly proved that such aliphatic polyketones possess unexpectedly good adhesive properties in direct coating onto a core layer of untreated paper, and that a well-integrated packaging laminate consisting of a core layer of paper or paperboard with correspondingly improved properties may simply and rationally be produced using existing process equipment. The gas barrier layer consists, according to one embodiment of the present invention, substantially of the above-described aliphatic polyketone, but may also contain a mixture of this polyketone and a second thermoplastic such as, for example, a polyolefin. As a result, the properties of the gas barrier layer may be adapted to suit precisely those circumstances as are required in a specific packaging laminate. The mixing ratio between the aliphatic polyketone and the second thermoplastic polymer may suitably vary between 1:99 and 99:1. Preferably, the mixture contains approx. 30-70 weight per cent polyketone and, most preferably approx. 40-60 weight per cent of polyketone. According to one special embodiment of the present invention, the mixture may be such that the aliphatic polyketone forms a dispersed phase in a matrix of the second thermoplastic polymer, in the form of multiple, thin, substantially parallel and overlapping layers, a so-called laminar blend. Such laminar blends of, for example, EVOH and polyolefin are known by persons skilled in this art, see for example W096/ 10053, and are produced by means of attenuation of the dispersed phase in the polymer melt during the extrusion process. The packaging laminate according to the invention may also include outer layers of a heat-sealable polymer on one or both sides, normally polyethylene of a suitable quality, for example low density polyethylene (LDPE). Other heat-sealable plastics known to persons skilled in this art may also advantageously be provided as outer layers in the packaging laminate according to the present invention. The adhesion between the polyketone-containing gas barrier layer and adjacent layers may be further improved by means of an interjacent layer of an adhesive polymer such as, for example, a copolymer of olefin and (meth)acrylic acid, acid- or anhydride-modified polyolefin or a so-called ionomer. Alternatively, the adhesion between the polyketone layer and adjacent layers may be improved by a surface active pre-treatment by means of, for example, flash treatment techniques or corona and / or plasma techniques, in which event lamination of the polyketone layer to the remainder of the packaging laminate may be put into effect by means of film lamination of prefabricated film and/ or semi-manufactured packaging laminate. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail hereinbelow, with particular reference to the accompanying Drawings, in which: Fig. 1 schematically illustrates a cross section through a laminated packaging material 10a and 10b, respectively, according to the present i vention; Fig. 2 schematically illustrates a cross section through a laminated packaging material 20a and 20b, respectively, according to the present invention; and Fig. 3 schematically illustrates a cross section through a laminated packaging material 30a and 30b, respectively, according to the present invention. It should be observed that the polymer compositions and laminate structures specifically selected in the Figures merely constitute examples among numerous other conceivable alternatives to a person skilled in this art, and that various modifications and variations may be made, for example, by adding further material layers with or without interjacent adhesive or lamination layers, with a view to satisfying the requirement of best possible product protection, without departing from the spirit and scope of the inventive concept as this is defined in the appended Claims. DESCRIPTION OF PREFERRED EMBODIMENTS Fig. 1 thus schematically illustrates a cross section of a packaging laminate according to the present invention, carrying the generic reference numerals 10a and 10b, respectively. The packaging laminate 10a comprises a core layer 11 of paper or paperboard of suitable packaging quality, and, directly applied on the one side of the core layer corresponding to the inside of the packaging container produced from the packaging laminate, a gas barrier layer 12 of a perfectly alternating linear copolymer of carbon monoxide and ethylene, with up to approx. 15 weight per cent propylene monomer randomly copolymerised and incorporated into the polymer structure instead of ethylene monomer. On its opposite side corresponding to the outside of the packaging container produced from the packaging laminate, the core layer is coated with a liquid-tight plastic layer 13 of, for example, LDPE. The gas barrier layer 12 is disposed on the core layer 11, for example by means of direct extrusion coating. In a packaging container produced from the packaging laminate 10a, the gas barrier layer 12 is thus in direct contact with the packed product. In addition to the layers and materials incorporated in the packaging laminate 10a, the packaging laminate 10b moreover includes an inside layer 13' consisting of one or more part layers, of a liquid-tight, heat-sealable plastic such as, preferably, polyethylene of a well-functioning quality (for example LDPE). The adhesion between the gas barrier layer 12 and the inside layer 13' is improved by means of an interjacent adhesion layer 14, a so-called "tie-layer", of an adhesion-promoting polymer. The inside layer 13' and the tie layer 14 are applied, for example, by co-extrusion. Fig. 2 shows an alternative packaging laminate 20a, 20b, respectively in which the core layer 21, the gas barrier layer 22 and the outer layer 23 are of the same type as layers 11, 12 and 13, respectively, in Fig. 1, but in which the gas barrier layer 22 is bonded to the core layer 21 by means of an interjacent adhesion layer 24 of an adhesive polymer. The interjacent adhesive layer functions, on the one hand, as an adhesion-promoting layer and, on the other hand, as a smoothening layer for the coarse, rough paper surface of the core layer, whereby the quantity of applied polyketone in the gas barrier layer 22 may be reduced while retaining oxygen gas and aroma barrier effects. The adhesion layer 24 and the gas barrier layer 22 are applied, for example, by means of co-extrusion onto the core layer 21. Like the packaging laminate 10b, the packaging laminate 20b moreover includes an inside layer 23' consisting of one or more part layers of a liquid-tight, heat-sealable plastic such as, preferably, polyethylene of a well-functioning quality (for example LDPE), and an interjacent adhesion layer 25. The four layers 24, 22, 25 and 23' may be applied simultaneously by co-extrusion or as separate or partly co-extruded layers. Fig. 3 shows a packaging laminate 30a, 30b, respectively in which the core layer 31, the gas barrier layer 32 and the outer layer 33 are of the same type as layers 11, 12 and 13, respectively, in Fig. 1, but in which the gas barrier layer 32 is laminated to the core layer 31 by means, on the one hand, of an interjacent lamination layer 34 of a thermoplastic such as, for example, polyethylene, bonded to the core layer, and, on the other hand, an adhesion layer 35 of an adhesive polymer provided between the thermoplastic layer 34 and the gas barrier layer 32. The thermoplastic layer 34, the adhesion layer 35 and the gas barrier layer 32 are coated, for example, by means of co- extrusion onto the core layer 31. Like the packaging laminate 10b, the packaging laminate 30b moreover includes an inside layer 33' consisting of one or more part layers of a liquid-tight, heat-sealable plastic such as, preferably, polyethylene of a well-functioning quality (for example LDPE), and an interjacent adhesion layer 36. The five layers 34, 35, 32, 36 and 33' may be applied simultaneously by co-extrusion or as separate or partly co-extruded layers. It will be obvious to a person skilled in this art that the gas barrier layer 12; 22; 32 may alternatively be incorporated into the packaging laminate structure by means of film lamination of the gas barrier layer alone or in combination with one or more adhesive layers and/ or lamination layers of thermoplastic, even though extrusion or co-extrusion is the most preferred method of applying the gas barrier layer. It will thus be apparent from the foregoing disclosure that the present invention, in a simple manner and with simple means, at lower cost, attains the established objects and realises an efficient, well-integrated laminate packaging material possessing both superior oxygen gas and aroma barrier properties and also at least retained mechanical properties such as strength and flexibility, as well as heat resistance.

Claims: WHAT IS CLAIMED IS: 1. A packaging laminate (10; 20; 30) comprising a core layer (11; 21; 31) of paper and a gas barrier layer (12; 22; 32) of plastic, characterized in that the gas barrier layer includes a polyketone, said polyketone being an aliphatic linear copolymer of olefin monomer and carbon monoxide (CO). 2. The packaging laminate as claimed in Claim 1, characterized in that said polyketone is an aliphatic linear copolymer of a 100 percent alternating olefin monomer and carbon monoxide (CO). 3. The packaging laminate as claimed in Claim 1 or 2, characterized in that said polyketone contains at least 50 mol per cent CO. 4. The packaging laminate as claimed in any of Claims 1 to 3, characterized in that said polyketone is a copolymer of ethylene and carbon monoxide units. 5. The packaging laminate as claimed in any of Claims 1 to 4, characterized in that said polyketone is a terpolymer of carbon monoxide units and ethylene- or α-olefin units, respectively, with 3-12 carbon atoms. 6. The packaging laminate as claimed in Claim 5, characterized in that said α-olefin unit is propylene. 7. The packaging laminate as claimed in Claim 6, characterized in that said polyketone terpolymer contains up to 15 weight per cent propylene units. 8. The packaging laminate as claimed in any of Claims 1 to 7, characterized in that the gas barrier layer substantially consists of a mixture of said polyketone and a second thermoplastic polymer. 9. The packaging laminate as claimed in Claim 8, characterized in that the mixture contains approx. 30-70 weight per cent polyketone. 10. The packaging laminate as claimed in Claim 8, characterized in that the mixture contains approx.40-60 weight per cent polyketone. 11. The packaging laminate as claimed in any of Claims 8 to 10, characterized in that the thermoplastic polymer is a polyolefin. 12. The packaging laminate as claimed in any of Claims 8 to 11, characterized in that the mixture is a laminar blend. 13. The packaging laminate as claimed in any of the preceding Claims, characterized in that the gas barrier layer (12; 22; 32) is directly laminated to the core layer (11; 21; 31). 14. The packaging laminate as claimed in any of the preceding Claims, characterized in that the gas barrier layer (22) is bonded to the core layer (21) by means of an interjacent adhesion layer (24). 15. The packaging laminate as claimed in any of the preceding Claims, characterized in that the gas barrier layer (32) is bonded to the core layer (31) by means of a lamination layer (34) provided adjacent the core layer and consisting of a thermoplastic, and an adhesion layer (35) disposed between the thermoplastic layer and the gas barrier layer. 16. The packaging laminate as claimed in any of the preceding Claims, characterized in that one or more inside layers (13'; 23'; 33') of a liquid-tight plastic are disposed on the opposite side of the gas barrier layer, for the formation of an inside layer in a packaging container produced from the packaging laminate, by means of an interjacent adhesion layer (14; 25; 36). 17. A method of producing a packaging laminate as claimed in any of Claims 1 to 16, characterized in that a layer of an aliphatic linear polymer from 100 per cent alternating olefin monomer and carbon monoxide (CO) is applied on one side of a core layer of paper by means of extrusion coating or coating by co-extrusion. 18. A method of producing a packaging laminate as claimed in any of Claims 1 to 16, characterized in that a layer of an aliphatic linear polymer from 100 per cent alternating olefin monomer and carbon monoxide (CO) is applied on one side of a core layer of paper by means of film lamination. 19. A packaging container produced from a packaging laminate as claimed in any of Claims 1 to 16.

Inventors: LOEFGREN LARS, OVEBY CLAES, LOEFGREN, LARS, OVEBY, CLAES
Applicants: LOEFGREN LARS, OVEBY CLAES, TETRA LAVAL HOLDINGS & FINANCE, LOEFGREN, LARS, OVEBY, CLAES, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1998
Main classification: B32B27
IPC codes: B32B27