A PACKAGING MATERIAL WITH AN O2 BARRIER

Abstract: A packaging material with an O2 barrier, in particular for flexible packagings, comprises a plastic film (1) coated with an organic coating (4) comprising at least one of the materials ethylene vinyl alcohol (EVOH) and polyvinyl alcohol (PVOH) applied to the plastic film (1) in fluid form. The organic coating (4) is coated with an inorganic coating (5) comprising a metal oxide or a non-metal oxide.

Description: Title: A packaging material with an O 2 barrier. Technical Field The invention relates to a packaging material with an O 2 barrier, in particular for flexible packagings. Background Art When packaging certain products such as foodstuffs which are sensitive to oxygen and/or water vapour it is known to use packaging materials in form of plastic laminates having a barrier against ingress of oxygen and/or water vapour. It is also known to use such laminates with barrier properties for packaging foodstuffs in a gas atmosphere in order prevent the gas from leaving the package. Said barrier properties can be obtained by means of a metallisation layer forming part of the plastic laminate. It is further from US-A-4.457.977 and EP-A-2-0 340 910 known that improved barrier properties are obtained by coating a plastic film with an organic coating subsequently being metallised. In order to provide transparent or translucent packaging materials with barrier proper¬ ties it has been suggested to coat plastic films with transparent metal oxides or non- metal oxides by vacuum deposition (confer GB-B-22 108 826, GB-B-2 246 794, GB-B- 22 46 795 and EP-B-00 70 875). An O 2 barrier greater than 1 cm 3 /m 2 /24 hours is obtained thereby. Finally EP-B-0070 875 and EP-A-0437 946 disclose the combination of metal coating and metal oxide coating to obtain improved barrier properties while maintaining the transparent or translucent character of the packaging material. It further appears from the publications that the plastic film can be primed prior to the metal/metal oxide deposition. Brief Description of the Invention The present invention provides a packaging material with an O 2 barrier, in particular for flexible packagings, and which comprises a plastic film coated with an organic coating applied to the plastic film in fluid form, said organic coating overcoated with an inorganic coating comprising a metal oxide or a non-metal oxide and which packag¬ ing material is characterised in that the organic coating comprises at least one of the materials ethylene vinyl alcohol (EVOH) and polyvinyl alcohol (PVOH). By applying the metal oxide or non-metal oxide coating to an EVOH or PVOH coating, improved barrier properties have surprisingly been obtained compared to a direct application of the metal oxide or non-metal oxide coating to the plastic film or to a primer without barrier properties coated on the plastic film. An O 2 permeability of 0.1 cm 3 /m 2 /24 hours has thus been obtained. Moreover it has been found that said good O 2 barrier properties are maintained after flexure (Gelbo flexures) in spite of the high brittleness of the non-metal oxide coating. The good barrier properties are believed to be caused by a more smooth surface provided by the EVOH or PVOH coating providing a more smooth and uniform metal oxide or non-metal oxide coating and by a synergistic effect between the EVOH or PVOH coating and the metal oxide or non-metal oxide coating. The good O 2 barrier properties obtained after flexure are believed to be caused by the elasticity of the EVOH or PVOH layer and a surprisingly good adhesion between the EVOH or PVOH coating and the metal oxide or the non-metal oxide coating as well as by the above synergistic effect of the two coatings. According to the invention a primer layer may be provided between the plastic film and the organic coating (EVOH or PVOH coating) to increase the adhesion of the orgamc coating to the plastic film. Furthermore according to the invention the organic coating per se may have an O 2 permeability of less than 10 cm 3 /m 2 /24 hours, preferably of less than 5 cm 3 /m 2 /24 hours. Moreover according to the invention the organic coating may be prepared from a dispersion or a solution comprising at least one of the materials EVOH and PVOH and be of a thickness of preferably 0.5 to 3 μm, most preferably of between 0.7 to 1.8 μm. In practice, excellent results have been obtained at a thickness of 1.2 μm corresponding to an O 2 permeability of about 3 cm 3 /m 2 /24 hours of said coating. The coating may be provided by means of any known coating process such as roll coating, for instance smooth roller coating, gravure roller coating, spray coating and dip coating. In practice excellent results have been obtained by smooth roll coating. Furthermore according to the invention the organic coating may comprise EVOH applied by extrusion coating or co-extrusion coating and have a thickness of between 2 to 10 μm, preferably of between 3 to 5 μm. Moreover according to the invention the plastic film may be oriented in the machine direction and preferably biaxially oriented. Furthermore according to the invention the plastic film preferably being a transparent film may comprise at least one material chosen from among polyolefines, polyamides, polyesters and polycarbonates. In mis connection it should be noted that the transparent film advantageously may be reverse printed and provided with an intermediary primer layer before being coated with the organic coating and the inorganic coating on the printed side. Moreover according to the invention the organic coating may comprise an oxide chosen from the group comprising aluminium oxides, magnesium oxides and silicon oxides. In this connection it should be noted that in addition to the said oxides the inorganic coating may also comprise the corresponding metals or non-metals, preferably the amount of the latter being such that the inorganic coating remains transparent or at least translucent. Furthermore according to the invention the inorganic coating may have a thickness of between 50-1000 Angstrom, preferably of between 100-300 Angstrom. Finally according to the invention when seen in the direction from the plastic film towards the coatings the packaging material may comprise an inner sealing medium layer arranged after the coatings and comprising a polyolefme, preferably polyethylene or polypropylene or copolymers thereof. Brief Description of the Drawing The invention is explained in detail below with reference to the drawing whose only illustration is a sectional view through an embodiment of the packagaging material according to the invention. Best Mode for Carrying Out the Invention When seen from the outer face towards the inner face of a package the shown packag¬ ing material comprises an outer, substantially transparent film 1 , which may be a single layered film or a laminate formed of several films, and preferably comprises a polyole¬ fme, a polyamide or a polyester being biaxially oriented. The outer film 1 is reverse printed on its inwardly facing surface. A primer 3 is coated on the print 2 to provide good adhesion to an organic coating 4 comprising EVOH or PVOH. The organic coating 4 is applied to the primer either by extrusion coating or in form of a solution or dispersion which is dried after application by roller coating. An inorganic coating 5 is vacuum deposited on the PVOH layer 4, said coating 5 comprising metal oxide, preferably in form of an aluminium oxide or magnesium oxide, or a non-metal oxide, preferably in form of a silicon oxide. An inner sealing medium layer 7 is adhered to the inorganic coating 5 by means of an adhesive 6. The inner heat sealing layer 7 is typically a polyolefme, preferably a polyethylene or a copolymer thereof. The invention is further illustrated by means of the following examples: Example 1 A biaxially oriented polyester (PETP) film 1 having a thickness of 12 μm was coated with a polyurethane-based primer 3 on its inwardly facing side. The primer 3 was coated with an EVOH coating in form of an alcohol/water solution of an EVOH granulate. An amount of about 1.2 g/m 2 (dry weight) was deposited corresponding to a thickness of about 1 μm (dried). The EVOH coating was dried. An Al 2 O 3 coating of a thickness of about 150 Angstrom was vacuum deposited on the EVOH coating. A PE film was laminated to the Al 2 O 3 coating 5 by means of a two-component polyureth¬ ane adhesive 6. The prepared laminate was transparent and had an O 2 permeability < 0.1 cm 3 /m 2 /24 hours. A Gelbo flexure test showed that the O 2 barrier remained unchanged after twenty Gelbo flexures performed according to MIL-V-131G, FED-STD-101, Method No 2017. Example 2 A laminate was made as described in Example 1, the EVOH coating being omitted. The laminate had an O 2 permeability of about 4 cm 3 /m 2 /24 hours prior to flexure. After twenty Gelbo flexures the laminate had an O 2 permeability of about 25 cm 3 / m 2 /24 hours. The two Examples show that a significantly improved O 2 barrier was obtained by the combined EVOH and Al 2 O 3 coating both before and after flexure compared to an Al 2 O 3 coating without an EVOH coating. The high O 2 barrier both before and after flexure is considered surprising although the used EVOH coating per se has an O 2 permeability of about 3 cm 3 /m 2 /24 hours.

Claims: Claims. 1. A packaging material with an O 2 barrier, in particular for flexible packagings, and which comprises a plastic film (1) coated with an organic coating (4) applied to the plastic film in fluid form, said organic coating (4) overcoated with an inorganic coating (5) comprising a metal oxide or a non-metal oxide, characterised in that the organic coating (4) comprises at least one of the materials ethylene vinyl alcohol (EVOH) and polyvinyl alcohol (PVOH). 2. A packaging material according to claim ^characterised by a primer layer (3) provided between the plastic film (1) and the organic coating (4) (the EVOH or PVOH coating). 3. A packaging material according to claims 1 or 2, characterised in that the organic coating per se has an O 2 permeability of less than 10 cm 3 /m 2 /24 hours, preferably of less than 5 cm 3 /m 2 /24 hours. 4. A packaging material according to one or more of the preceding claims, characterised in that the organic coating (4) is prepared from a dispersion or a solution comprising at least one of the materials EVOH and PVOH and of a thickness of preferably 0.5 to 3 μm, most preferably of between 0.7 to 1.8 μm. 5. A packaging material according to one or more of the claims 1-3, characterised in that the organic coating (4) comprises EVOH applied by extrusion coating or co-extrusion coating and of a thickness of between 2 to 10 μm, preferably of between 3 to 5 μm. 6. A packaging material according to one or more of the preceding claims, characterised in that the plastic film (1) at least is oriented in the machine direction and preferably biaxially oriented. 7. A packaging material according to claim 6, characterised in that the plastic film (1) comprises at least one material chosen from among polyolefines, polyamides, polyesters and polycarbonates. 8. A packaging material according to one or more of the preceding claims, characterised in that the inorganic coating (5) comprises an oxide selected from the group comprising aluminium oxides, magnesium oxides and silicon oxides. 9. A packaging material according to claim 8, characterised in that the inorganic coating has a thickness of between 50-1000 Angstrom, preferably of between 100-300 Angstrom. 10. A packaging material according one or more of the preceding claims, characterised in that when seen in direction from the plastic film (1) towards the coatings it comprises an inner sealing medium layer (7) arranged after the coatings and comprising a polyolefme, preferably polyethylene or polypropylene or copolymers thereof.

Inventors: LYKKE KIRSTEN, LYKKE, KIRSTEN
Applicants: DANISCO, LYKKE KIRSTEN, DANISCO A/S, LYKKE, KIRSTEN
Application year: 1997
Main classification: B32B27
IPC codes: B32B9, B32B27, B65D65, C08J7