A packaging material with an oxygen barrier, based on organic polymers

COMPLETE SPECIFICATION

Title of Invention

A packaging material with an 02 barrier

Name, address and nationality of applicant(s) as in international application form*

DANISCO A/S, 1, Langebrogade, DK-1001 Copenhagen K, Denmark

Title A packaging matenal with an (λ barrier

Technical Field

The invention relates to a packaging matenal with an O₂ bamer, in particular for $ flexible packagings

Background Art

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When packaging certain products such as foodstuffs which are sensitive to oxygen and/or water vapour it is known to use packaging matenals in form of plastic laminates having a bamer against ingress of oxygen and/or water vapour It is also known to use such laminates with bamer properties for packaging foodstuffs m a gas atmosphere in 10 order prevent the gas from leaving the package

Said bamer 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 bamer properties are obtained by coating a plastic film with an organic coating subsequently being metallised

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In order to provide transparent or translucent packaging matenals with bamer properties it has been suggested to coat plastic films with transparent metal oxides or nonmetal oxides by vacuum deposition (confer GB-B-22 108 826, GB-B-2 246 794, GB-B22 46 795 and EP-B-00 70 875) An O₂ bamer greater than 1 cm³/m~/24 hours is obtained thereby

Further EP-B-00 70 875 and EP-A-0 437 946 disclose the combination of metal coating and metal oxide coating to obtain improved bamer properties while maintaining the transparent or translucent character of the packaging matenal It further appears from the publications that the plastic film can be pnmed pnor to the metal/metal oxide deposition.

amended

EP Ο 723 860 discloses a packaging matenal compnsing a film coated with an inorganic coating of silicon oxide and a film of polyolefine An adhesive disposed between the silicon oxide and the film of polyolefine is a thermoplastic resin containing at least one hydroxyl function The silicon oxide coating is not provided on an organic coating 5 comprising EVOH or PVOH

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Finally, WO 95/34396 discloses a transparent film composition comprising a polymeric substrate with a modified propylene surface, an organic skin layer (EVOH skin layer) on the modified propylene layer and a transparent metal oxide gas barrier layer deposited on the EVOH layer

The following processes are mentioned for the provision of the EVOH layer

1) coextrusion of a EVOH skin and the modified substrate,

2) extrusion coating of the EVOH layer onto the surface of the modified substrate, and

3) co-lamination of a thin film of EVOH onto the surface of the modified polypropylene sheet

Brief Description of the Invention

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The present invention provides a packaging matenal with an O₂ bamer, in particular for flexible packagings, and which compnses a plastic film coated with an organic coaung applied to the plastic film in fluid form, said organic coating overcoated with an inorganic coating compnsing a metal oxide or a non-metal oxide and which packag20 mg matenal is charactensed in that the organic coating compnses at least one of the matenals ethylene vinyl alcohol (EVOH) and polyvinyl alcohol (PVOH) and is prepared from a dispersion or a solution compnsing at least one of the matenals EVOH and PVOH By applying the metal oxide or non-metal oxide coating to an EVOH or PVOH coating, improved bamer properties have surpnsingly been obtained compared to a 25 direct application of the metal oxide or non-metal oxide coating to the plastic film or to a pnmer without bamer properties coated on the plastic film An O₂ permeability of 0 1 cm³/m²/24 hours has thus been obtained Moreover it has been found that said j

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good O₂ barrier properties are maintained after flexure (Gelbo flexures) in spite of the high brittleness of the metal oxide or 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 5 oxide coating and by a synergistic effect between the EVOH or PVOH coating and the metal oxide or non-metal oxide coating The good O₂ 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 10 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 organic coating to the plastic film

Furthermore according to the invention the organic coating per se may have an O₂ permeability of less than 10 cm³/m²/24 hours, preferably of less than 5 cm³/m²/24 hours

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Moreover according to the invention the organic coating may be of a thickness of 0 5 to 3 μπι, preferably of between 0 7 to 1 8 μπ\ In practice, excellent results have been obtained at an organic coating thickness of 1 2 gm corresponding to an O₂ permeability 20 of about 3 cm³/m²/24 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

According to the invention the plastic film may be oriented in the machine direction 25 and preferably biaxially oriented

According to the invention the plastic film preferably being a transparent film may comprise at least one matenal chosen from among polyolefines, polyamides, polyesters and polycarbonates In this 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

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t Moreover according to the invention the organic coating may comprise an oxide chosen from the group compnsing aluminium oxides, magnesium oxides and silicon oxides In this connection it should be noted that m addition to the said oxides the inorganic coating may also compnse the corresponding metals or non-metals, preferably the amount of the latter being such that the inorganic coating remains transparent or at , 10 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 m the direction from the plastic film towards the coatings the packaging matenal may compnse an inner sealing medium 15 layer arranged after the coatings and compnsing a polyolefine, preferably polyethylene or polypropylene or copolymers thereof

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Bnef Description of the Drawing

The invention is explained «η detail below with reference to the drawing whose only illustration is a sectional view through an embodiment of the packagagmg matenal 20 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 packaging matenal compnses an outer, substantially transparent film 1, which may be a single layered film or a laminate formed of several films, and preferably compnses a polyole25 fine, a polyamide or a polyester being biaxially onented The outer film 1 is reverse ___AMEiWn

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4α.

printed on its inwardly facing surface A primer 3 is coated on the print 2 to provide good adhesion to an organic coating 4 compnsing EVOH or PVOH The organic coating -I is applied to the pnmer m form of a solution or dispersion which is dried after application by roller coating An inorganic coating 5 is vacuum deposited on the 5 EVOH or PVOH layer 4, said coating 5 compnsing 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 by means of an adhesive 6 The inner heat sealing layer 7 is typically a polyolefine, preferably a polyethylene or a copolymer thereof

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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 p.m was coated

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with a polyurethane-based pnmer 3 on its inwardly facing side The primer 3 was coated with an EVOH coating m form of an alcohol/water solution of an EVOH granulate An amount of about 1 2 g/m² (dry weight) was deposited corresponding to a thickness of about 1 μτη (dned) The EVOH coating was dned. An A1₂O₃ coating of a thickness of 5 about 150 Angstrom was vacuum deposited on the EVOH coating A PE film was t laminated to the A1₂O₃ coating 5 by means of a two-component polyurethane adhesive

The prepared laminate was transparent and had an O₂ permeability &lt;01 cm³/m²/24 hours

A Gelbo flexure test showed that the O₂ bamer remained unchanged after twenty Gelbo flexures performed according to MIL-V-131G, FED-STD-101, Method No 2017

Example 2 - Comparative example

A laminate was made as descnbed in Example 1, the EVOH coating being omitted

The laminate had an O₂ permeability of about 4 cm³/m²/24 hours prior to flexure

After twenty Gelbo flexures the laminate had an O₂ permeability of about 25 cm³/ nr/24 hours

The two Examples show that a significantly improved O₂ bamer was obtained by the combined EVOH and A1₂O₃ coating both before and after flexure compared to an A1₂O₃coating without an EVOH coating The high O₂ bamer both before and after flexure is considered surprising although the used EVOH coating per se has an O₂ permeability of about 3 cm³/m²/24 hours

AMENDED SHEET