Recyclable paper packaging material including a metallized layer and a polymeric barrier layer attached with a binder - Patents.com

Abstract

The present invention relates to a barrier multi-layer packaging material structure (1) formed as a flexible or semi-rigid single sheet and comprising a metallized paper (2), said metallized paper (2) further coated on the inside of said material structure (1) with a polymeric binder (5) selected from pure ethylene-acrylic acid, pure methacrylic acid copolymer, pure polyester, pure polyvinyl acetate, pure polyurethane, and further coated on its innermost side with a water-resistant oxygen barrier layer (6) of pure polyvinylidene chloride (PVDC).

Description

[Technical field]

[0001] The present invention relates to a paper-based packaging material that has high barrier properties to moisture and oxygen and is recyclable in the paper recycling stream. [Background technology]

[0002] Plastic packaging is often used in economic activities and people's daily lives. It has several advantages, such as flexibility and light weight. Light weight contributes, for example, to fuel savings and CO2 reduction during transportation. The barrier properties of plastic packaging help to reduce food waste, as they have a positive effect on extending shelf life. The barrier properties also help to ensure food safety.

[0003] However, according to the European Strategy for Plastics in a Circular Economy recently published by the European Commission, around 25.8 million tonnes of plastic waste is generated in Europe every year, less than 30% of this waste is recovered for recycling, and as much as 150,000-500,000 tonnes of plastic waste enters the oceans every year.

[0004] There are great efforts in industry and commerce to ensure the reduction of plastic waste. Some supermarkets, for example, have replaced plastic bags with paper-based bags. However, replacing plastic with paper in food packaging is not an easy task. The change in packaging material must not compromise consumer safety. The packaging must not only serve to protect the food, but also be sturdy enough to be handled by machines during the production process and such that the food product can be effectively presented.

[0005] Thus, there is a need for paper-based materials with improved barrier properties, in particular paper-based materials with improved barrier properties that can be recycled in conventional paper recycling processes.

[0006] Solutions have been developed that involve metallizing the paper to achieve a certain level of barrier against moisture or grease. Polymer film layers may be added by extrusion or lamination processes to also achieve gas (especially oxygen) barrier properties. However, when such polymers are deposited in thick layers by extrusion or lamination processes, the material has a high polymer content, which makes it non-recyclable in the paper recycling process.

[0007] Also, current metallized barrier paper solutions, while they may provide high levels of oxygen and water vapor barrier, have been found to lack robustness against mechanical action such as folding (when forming packages), and further, such paper-based structures have been found to wrinkle when exposed to very high levels of relative humidity.

[0008] Thus, there was a need for a packaging material that was paper-based, did not contain significant amounts of polymeric materials that would make it incompatible with paper recycling processes, and had an excellent barrier to moisture and oxygen while at the same time being resistant to mechanical stresses such as those encountered during the packaging manufacturing process.

[0009] Polyvinylidene chloride or polyvinylidene dichloride (PVDC) has been found to be a very good barrier to oxygen in polymeric film structures while also providing excellent heat seal capabilities since it does not substantially degrade when exposed to heat generated by sealing tools of the type used in packaging manufacturing processes. However, it has also been found that PVDC does not adhere adequately to aluminum metal layers in multi-layer structures, and therefore, it has long been commonly believed by those skilled in the art that metal layers should not be combined with PVDC to achieve high barriers to both moisture and oxygen in packaging.

[0010] WO 9211952 A1 (applicant DUPONT de NEMOURS Company) discloses a metallized material having a metal coating on one or more surfaces, which exhibits improved barrier layer coating adhesion and heat seal properties. The material comprises at least 80% vinylidene chloride (PVDC), a coating of at least 4% polyvinylidene copolymer of ethylenically unsaturated acrylic monomers, as well as a coating additive for modifying the film properties. PVDC achieves good resistance to mechanical stress while providing good oxygen barrier properties. In this patent publication, the inventors found that by mixing PVDC with additives, a reasonably good bond can be achieved between the metal layer and the PVDC oxygen barrier layer. More precisely, the metallized material described in WO '952 is produced by treating a substrate material (e.g. paper) having at least one metal surface thereon with a combined solution of coating additive and vinylidene chloride copolymer, and thus exhibits improved barrier layer coating adhesion and heat seal properties. The polyvinylidene chloride copolymers described above contain at least 80% by weight of polyvinylidene chloride and at least 4% by weight of an ethylenically unsaturated acrylic acid ester.

[0011] Although the invention disclosed in WO 9211952 improves the adhesion of PVDC to metals, the inventors have found that mixing vinylidene chloride with the same additives that enable adhesion of PVDC to metals causes the PVDC to undergo extensive modification. This chemical modification results in a substantial reduction in the barrier properties of PVDC.

[0012] In view of the above, there is a need for a packaging material that avoids the main drawbacks of already available solutions and that is recyclable in the paper recycling process, metallized for high moisture barrier, and further includes an additional layer for excellent oxygen barrier and heat seal properties.

[0013] [Summary of the Invention] The object of the present invention is to provide a barrier multi-layer packaging material structure formed as a single flexible or semi-rigid sheet having from its outer surface to its inner surface: (i) 40 g / m 2 ~150g / m 2 a flexible or semi-rigid paper layer having a basis weight of (ii) a pre-metallization layer between the paper layer and the metal layer, having a density of 1 to 10 g / m 2 a layer outside the metallic coating, the layer being present in an amount falling within the range of (iii) Physical vapor deposition of aluminum with an optical density equivalent to 1.5-4; a thin metal layer selected from the list consisting of physical or chemical vapor deposition of aluminum oxide (AlOx) or silicon oxide (SiOx), said metal or oxide layer having a thickness comprised between 7 nm and 100 nm; (iv) a polymeric binder selected from the list consisting of pure ethylene-acrylic acid, pure methacrylic acid copolymer, pure polyester, pure polyvinyl acetate, pure polyurethane, having a density of 0.1 g / m 2 ~10g / m 2 a polymeric binder present in an amount comprised between (v) 4g / m 2 ~20g / m 2 , preferably 5 g / m 2 ~8g / m 2 a water-resistant oxygen barrier layer of pure polyvinylidene chloride (PVDC) in an amount of This is accomplished by a barrier multi-layer packaging material structure comprising:

[0014] Unlike prior art structures in which the PVDC chemical structure has been modified by additives, the barrier and heat resistance properties of the structure are unaltered and have proven to be superior due to the fact that the PVDC layer is pure. Furthermore, it has been found that the presence of an intermediate tie layer between the metal layer and the PVDC layer provides excellent adhesion between these two layers. No solution available in the prior art is able to provide all of these benefits simultaneously.

[0015] The outer layer of the metal coating specifically smoothes the surface of the paper, allowing the metal layer to adhere properly to the surface of the paper and providing a chemically compatible interface for the deposited metal atoms.

[0016] By "inside" of a packaging structure is meant the side of a package produced from said packaging structure that is intended to face the filled food contents.

[0017] By "pure polyvinylidene chloride (PVDC) layer" is meant a layer made entirely of PVDC, that is, the polymer excluding binders, fillers, and especially excluding any other type of polymer or material.

[0018] A "pure ethylene acrylic acid layer" or "pure" methacrylic acid means that the layer is composed entirely and exclusively of ethylene acrylic acid or methacrylic acid, respectively, and in particular contains only one type of polymer and is free of any other type of polymer or component.

[0019] The multi-layer metallized paper-based material according to the present invention can be recycled together with other paper packaging materials in normal paper recycling processes, preferably in processes according to PTS test method PTS-RH 021:2012 Category II. This recyclability is due to the fact that the material contains a certain amount of polymer (HDPE) that is applied by a dispersion coating process.

[0020] Thanks to the dispersion coating of the polymer layer, the overall thickness of the polymeric material in the structure is greatly reduced compared to the thickness of the paper material. Thus, the inventors have achieved a packaging multi-layer structure with excellent barrier properties against oxygen and moisture transfer, as well as resistance to liquid contact, while at the same time achieving a very high percentage of total cellulosic fiber content relative to the total material weight. Furthermore, the dispersion coating of the polymer avoids high polymer cohesion and adhesion, which solves the problem of recyclability (the substrate is coated with polymeric solid particles dispersed in a water carrier medium, rather than with a liquid polymer). The inventors have succeeded in forming a multi-layer structure entirely free of polymer layers formed by extrusion (extrusion lamination or extrusion coating), providing a multi-layer structure with a very high fiber content, with a ratio of cellulosic fibers to non-cellulosic materials. The polymer layer is easily disintegrated in the repulping process of the paper recycling stream, due to the relatively low cohesive strength of the polymer and its relatively low adhesion to the rest of the substrate, especially the cellulosic fibers. Thus, the resulting structure shows excellent repulping ability and high fiber yield, making it acceptable for waste paper recovery in most countries of the world. Unlike existing structures known in the art, vacuum deposited metal layers with very low content of non-cellulosic polymeric and metallic materials readily disintegrate, dissolve and separate from the cellulose.

[0021] Advantageously, in a paper-based barrier multilayer structure according to the invention, the total fibre content of said structure is between 85% and 95% by weight.

[0022] In one embodiment, the packaging structure further comprises an outermost coating layer comprising an ink printing, overprint varnish, said outermost layer having a coating density of 0.1 g / m 2 ~6g / m 2 is applied in an amount of

[0023] Preferably, the layer that is outer than the metal coating comprises a component selected from the list consisting of ethylene acrylic acid copolymer, polyvinyl alcohol (PVOH), butenediol vinyl alcohol (BVOH) copolymer, nitrocellulose-propylene-acrylic acid copolymer, polyurethane, or combinations thereof.

[0024] In order to provide a packaging structure with a sufficiently low level of polymer content to enable recycling in paper recycling processes, the layers outer than the metal coating are preferably applied by a polymer dispersion coating process, more preferably using a direct or reverse gravure application or a semi-flexographic printing process.

[0025] Optionally, the packaging structure of the present invention may also advantageously comprise an innermost layer having a heat seal lacquer, a liquid-tight polyolefin dispersion coating, or a combination thereof, said innermost layer having a coating density of 1 to 10 g / m 2 is present in an amount of

[0026] The present invention further relates to a package made with the paper-based barrier multi-layer structure as described above. [Brief description of the drawings]

[0027] Additional features and advantages of the present invention are described in, or will be apparent from, the following description of the presently preferred embodiments which take place in conjunction with the drawings. [Figure 1] 1 is a schematic diagram of a cross-section of a first embodiment of a multi-layer barrier structure according to the present invention; [Diagram 2] FIG. 2 is a schematic diagram of a cross-section of a second embodiment of a multi-layer barrier structure according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Generally, as used herein, "extrusion coating" refers to a process for providing a thick layer of polymer by using an extruder to force a molten thermoplastic resin (e.g., polyethylene) through a horizontal slot die onto a moving web of substrate (e.g., paper). The product is a permanently coated web structure.

[0029] "Extrusion lamination" refers to a process akin to extrusion coating in which a polymer resin is extruded between two substrates (eg, a layer of paper and another layer of polymer film) to act as a binder.

[0030] "Adhesive lamination" refers to a process in which one paper material is coated with an adhesive and laminated to a second paper or paperboard material.

[0031] In the lamination process, two thick layers of material are combined by either extrusion lamination or adhesive lamination, resulting in a thickness for each layer that is much greater than that obtainable by dispersion coating.

[0032] "Dispersion coating" or "polymer dispersion coating" refers to a coating technique in which an aqueous dispersion of fine polymer particles or a polymer solution is applied neat to the surface of paper or paperboard to form a solid, non-porous film after drying. Dispersion coating can be performed by gravure, flexo-gravure, rod, blade, slot die, curtain air knife, or any other known paper coating method. Because the polymer is mixed into an aqueous solution, dispersion coating can produce a much thinner layer than extrusion. This provides advantages in terms of polymer usage, its barrier performance, and the recyclability of the resulting paper structure. The goal of dispersion coating is to provide a barrier layer against water, water vapor, grease, oil, gas, etc., through an environmentally friendly coating. Another goal is to prepare the surface of cellulosic materials for the vacuum deposition process.

[0033] Figure 1 illustrates a first embodiment of the invention, showing a multi-layer structure 1 comprising several layers, starting from the outer layer (i.e. the layer in contact with the external atmosphere after the structure is formed into a package) to the inner layer (i.e. the layer in contact with the final packed product after the structure is formed into a package).

[0034] In this first embodiment of the structure 1 according to the invention, as shown in FIG. 1, the first outermost layer 2 has a thickness of 80 g / m 2 The paper is an uncoated, supercalendered, wood-free kraft paper obtained from UPM Company.

[0035] The paper-based barrier multilayer structure 1 then further comprises a layer 3, outer than the metallization, of butenediol vinyl alcohol (BVOH) copolymer, disposed between the paper layer 2 and the next layer, which is a vacuum deposited metal layer 4, said layer 3 outer than the metallization having a weight of about 3 g / m 2 is applied by polymer dispersion coating in an amount of

[0036] The layer 3 external to the metallization is then metallized with a thin metal layer 4 which is a physical vapor deposition of aluminum having an optical density corresponding to 3, said aluminum layer having a thickness of about 45 nm.

[0037] The inside of the aluminum layer 4 is then coated with a polymeric adhesion primer coating 5 comprising a water-based dispersion of polyester, said primer (also referred to in the remainder of this specification as "binder") being applied at a rate of about 2 g / m by a dispersion coating process. 2 is applied in an amount of

[0038] Finally, the innermost layer of the structure 1 according to this first embodiment is a water-resistant oxygen barrier layer 6 of pure polyvinylidene chloride (PVDC), said barrier layer 6 having a thickness of about 8 g / m 2 and is deposited by a polymer dispersion coating process using direct gravure application.

[0039] In a second embodiment of the structure 1 according to the invention, as shown in Figure 2, the structure is similar to the structure of the first embodiment described above in relation to Figure 1. However, in this embodiment, the paper-based barrier multi-layer structure 1 has a weight of about 5 g / m 2 The material further comprises an outermost coating layer 7 comprising an amount of ink printing and an overprint varnish. In the innermost part of the material structure, the PVDC layer functions as a heat seal lacquer, especially if the material requires sealing in a heat seal process for producing a package from the material.

[0040] The flexible packaging structure of the present invention may be designed to form a packaging material for food products. The packaging material is preferably a primary packaging material, but can also be used to produce a secondary or tertiary packaging material. A primary packaging material for a food product is in direct contact with the actual food product. A secondary packaging material for a food product may be a packaging material for a food product that serves to secure one or more food products contained in a primary package. A secondary packaging material is typically used when multiple food products are individually packed in a single container and provided to the consumer. A tertiary packaging material for a food product is a packaging material for a food product that serves to secure one or more food products contained in the primary package and / or in the primary and secondary packages during transportation.

[0041] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. Accordingly, such changes and modifications are intended to be covered by the appended claims.

Claims

1. A barrier multi-layer packaging material structure (1) formed as a flexible or semi-rigid single sheet, having from its outer surface to its inner surface: (i) 40 g / m ２ ~150g / m ２ A flexible or semi-rigid paper layer (2) having a basis weight of (ii) a layer (3) located between the paper layer (2) and the metal layer (4) and located outside the metal coating, said layer (3) having a thickness of 1 to 10 g / m ２ a layer (3) located outside the metal coating, said layer (3) being present in an amount of (iii) Physical vapor deposition of aluminum having an optical density equivalent to 1.5 to 4; a thin metal layer (4) selected from the list consisting of physical or chemical vapor deposition of aluminum oxide (AlOx) or silicon oxide (SiOx), having a thickness of 7 nm to 100 nm; (iv) a polymeric binder selected from the list consisting of ethylene-acrylic acid, methacrylic acid copolymers, polyesters, polyvinyl acetates, and polyurethanes, the binder having a density of 0.1 g / m ２ ~10g / m ２ a polymeric binder (5) present in an amount of (v) 4 g / m ２ ~20g / m ２ Or 5 g / m ２ ~8g / m ２ a water-resistant oxygen barrier layer (6) of polyvinylidene chloride (PVDC) in an amount of A barrier multi-layer packaging structure (1).

2. 2. The barrier multi-layer packaging structure (1) according to claim 1, wherein the total fibre content of said structure is between 85% and 95% by weight.

3. The outermost coating layer (7) further comprises an ink printing and an overprint varnish, the outermost coating layer (7) having a coating thickness of 0.1 g / m ２ ~6g / m ２ The barrier multilayer packaging structure (1) according to claim 1, wherein

4. 2. The barrier multi-layer packaging structure (1) of claim 1, wherein the layer (3) that is outer than the metal coating comprises a component selected from the list consisting of ethylene acrylic acid copolymer, polyvinyl alcohol (PVOH), butenediol vinyl alcohol (BVOH) copolymer, nitrocellulose-propylene-acrylic acid copolymer, polyurethane, or combinations thereof.

5. 2. The barrier multi-layer packaging structure (1) according to claim 1, wherein the layer (3) outside the metal coating is applied by a polymer dispersion coating process.

6. The innermost layer (8) may further comprise a heat seal lacquer, a liquid-tight polyolefin dispersion coating, or a combination thereof, the innermost layer (8) having a coating weight of 1 to 10 g / m ２ The barrier multilayer packaging structure (1) according to claim 1, wherein

7. A package comprising a barrier multi-layer packaging material structure (1) according to any one of claims 1 to 6.

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