Recyclable paper packaging material containing a metallized layer bonded with a binder and a polymer barrier layer.

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

[0002] Plastic packaging is frequently used in economic activities and people's daily lives. Plastic packaging offers several advantages, including flexibility and light weight. Lightweight packaging contributes, for example, to fuel savings and CO2 reduction during transportation. The barrier properties of plastic packaging have a positive effect on extending shelf life, thus helping to reduce food waste. Barrier properties also help ensure food safety.

[0003] However, according to the European Strategy on Plastics in the Circular Economy, recently published by the European Commission, approximately 25.8 million tons of plastic waste are generated in Europe every year, less than 30% of which is recovered for recycling, and 150,000 to 500,000 tons of plastic waste end up in the oceans each year.

[0004] Significant efforts are being made in industry and commerce to ensure the reduction of plastic waste. Some supermarkets, for example, are replacing plastic bags with paper bags. However, replacing plastic with paper in food packaging is not an easy task. Changes to packaging materials must not compromise consumer safety. Packaging must not only protect food, but also be strong enough to withstand machine handling during the manufacturing process and allow food products to be presented effectively.

[0005] Therefore, paper-based materials with improved barrier properties are needed. In particular, paper-based materials with improved barrier properties that can be recycled in conventional paper recycling processes are required.

[0006] To achieve a certain level of barrier against moisture or grease, solutions including the metallization of paper have been developed. To also achieve gas (especially oxygen) barrier properties, polymer film layers may be added by extrusion or lamination processes. However, the deposition of such polymers in thick layers by extrusion or lamination processes increases the polymer content of the material, rendering it unrecyclable in paper recycling processes.

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

[0008] Therefore, there was a need for a packaging material that was paper-based, did not contain large amounts of polymer material that would make it unsuitable for paper recycling processes, had excellent barrier properties against moisture and oxygen, and was resistant to the mechanical stresses encountered during the packaging manufacturing process.

[0009] Polyvinylidene chloride or polyvinylidene dichloride (PVDC) has been found to provide an excellent barrier to oxygen in polymer film structures, while also offering superior heat-sealing capabilities, as it does not degrade substantially when exposed to the heat generated by the types of sealing tools used in packaging manufacturing processes. However, it has also been found that PVDC does not adhere well to aluminum metal layers in multilayer structures, and for this reason, it has long been generally 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] International Publication No. 9211952 (A1) (Applicant: DUPONT de NEMOURS Company) discloses a metallized material having a metal coating on one or more surfaces exhibiting improved barrier layer coating adhesion and heat seal properties. The material comprises a coating of polyvinylidene copolymer consisting of at least 80% vinylidene chloride (PVDC) and at least 4% ethylenically unsaturated acrylic monomer, as well as coating additives for modifying film properties. PVDC achieves excellent resistance to mechanical stress while providing good oxygen barrier properties. In this patent publication, the inventors have 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 International Publication No. 952 exhibits improved barrier layer coating adhesion and heat seal properties because it is produced by treating a substrate material (e.g., paper) having at least one metal surface thereon with a compound solution of coating additives and vinylidene chloride copolymer. The above polyvinylidene chloride copolymer contains at least 80% by weight of polyvinylidene chloride and at least 4% by weight of ethylenically unsaturated acrylic acid ester.

[0011] The invention disclosed in International Publication No. 9211952 improves the adhesion of PVDC to metals, but the inventors have found that mixing vinylidene chloride with the same additive that enables the adhesion of PVDC to metals causes extensive modification of the PVDC. This chemical modification results in a substantial decrease in the barrier properties of the PVDC.

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

[0013] [Overview of the prefecture] The above object is achieved by a barrier multi-layer packaging material structure formed as a flexible or semi-rigid single sheet, from its outer surface to its inner surface, (i) a flexible or semi-rigid paper layer having a basis weight of 40 g / m 2 ~150 g / m 2 ; and, (ii) a layer outside the metallization, disposed between the paper layer and the metal layer, present in an amount within the range of 1 to 10 g / m 2 ; and, (iii) a thin metal layer selected from the list consisting of physical vapor deposition of aluminum having an optical density corresponding to 1.5 to 4, physical vapor deposition or chemical vapor deposition of aluminum oxide (AlOx) or silicon oxide (SiOx), the layer of the metal or oxide having a thickness included between 7 nm and 100 nm, (iv) a polymer binder selected from the list consisting of pure ethylene-acrylic acid, pure methacrylic acid copolymer, pure polyester, pure polyvinyl acetate, pure polyurethane, present in an amount included between 0.1 g / m 2 ~10 g / m 2 ; and, (v) a water-resistant oxygen barrier layer of pure polyvinylidene chloride (PVDC) in an amount of 4 g / m 2 ~20 g / m 2 , preferably 5 g / m 2 ~8 g / m 2 ; and, The above object is achieved by a barrier multi-layer packaging material structure including the above components.

[0014] Unlike conventional structures in which the PVDC chemical structure has been modified by additives, the fact that the PVDC layer is pure demonstrates that the barrier and heat resistance properties of the above structure remain unchanged and are superior. Furthermore, it has been found that the presence of an intermediate bonding layer between the metal layer and the PVDC layer provides excellent adhesion between the two layers. No known solution available simultaneously offered all of these benefits.

[0015] The layer outside the metal coating, in particular, smooths the surface of the paper, allowing the metal layer to adhere properly to the paper surface and providing a chemically compatible interface for the deposited metal atoms.

[0016] The "inside" of the packaging structure refers to the side of the package manufactured from the above-mentioned packaging structure that is intended to face the filled food contents.

[0017] A "pure polyvinylidene chloride (PVDC) layer" means a layer made entirely of PVDC, from which binders, fillers, and especially any other types of polymers or materials have been removed.

[0018] "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 no other type of polymer or component.

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

[0020] Thanks to the dispersion coating of the polymer layer, the overall thickness of the polymer material in the structure is significantly reduced compared to the thickness of the paper material. Thus, the inventors have achieved a packaging multilayer structure with excellent barrier properties against oxygen and moisture transfer, as well as resistance to liquid contact, while simultaneously achieving a very high proportion of the total cellulose fiber content relative to the total material weight. Furthermore, the dispersion coating of the polymer avoids high polymer aggregation and high adhesion, and as a result, the problem of recyclability is solved (the substrate is coated with polymer solid particles dispersed in an aqueous carrier medium rather than a liquid polymer). By successfully forming a multilayer structure that completely eliminates the polymer layer formed by extrusion (extrusion lamination or extrusion coating), a multilayer structure is provided that has a certain ratio of cellulose-based fibers to non-cellulose-based materials and a very high fiber content. The polymer layer described above has a relatively low aggregation strength and a relatively low adhesion to the remaining part of the substrate (especially cellulose-based fibers), and thus easily disintegrates in the repulping process of the paper recycling stream. Therefore, the resulting structure exhibits excellent repulping ability and high fiber yield and is acceptable for waste paper collection in most countries of the world. Different from existing structures known in the art, the very low content of non-cellulose-based polymers and the vacuum-evaporated metal layer of the metal material easily disintegrate, dissolve, and separate from the cellulose.

[0021] Advantageously, in the paper-based barrier multilayer structure according to the present invention, the total fiber content of the structure is 85 wt% to 95 wt%.

[0022] In one embodiment, the packaging structure further includes an outermost coating layer including ink printing and overprint varnish, and the outermost layer is coated in an amount of 0.1 g / m 2 ~6 g / m 2 of.

[0023] Preferably, the layer outside the metal coating contains components 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] To enable recycling in the paper recycling process by providing a packaging structure with a sufficiently low polymer content, the layer outside the metal coating is preferably coated by a polymer dispersion coating process, more preferably by direct or reverse gravure coating or semi-flexographic printing process.

[0025] Optionally, the packaging structure of the present invention may also advantageously include an innermost layer having a heat-seal lacquer, a liquid-tight polyolefin dispersion coating, or a combination thereof, wherein the innermost layer is 1 to 10 g / m² 2 It exists in that quantity.

[0026] The present invention further relates to a package made of a paper-based barrier multilayer structure as described above. [Brief explanation of the drawing]

[0027] Additional features and advantages of the present invention are described below in the description of the currently preferred embodiments with reference to the drawings and will become apparent therefrom. [Figure 1] This is a schematic cross-sectional view of a first embodiment of a multilayer barrier structure according to the present invention. [Figure 2] This is a schematic cross-sectional view of a second embodiment of a multilayer barrier structure according to the present invention. [Modes for carrying out the invention]

[0028] In general, as used herein, “extrusion coating” means a method of providing a thick layer of polymer by using an extruder to extrude molten thermoplastic resin (e.g., polyethylene) through a horizontal slot die onto a moving web of a substrate (e.g., paper). The product is a permanently coated web structure.

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

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

[0031] In the lamination process, two thick layers of material are combined by either extrusion lamination or adhesive lamination, resulting in each layer being much thicker than the thickness achieved by dispersion coating.

[0032] "Dispersion coating" or "polymer dispersion coating" refers to a coating technique in which an aqueous dispersion or polymer solution of fine polymer particles is applied directly to the surface of paper or cardboard to form a solid, non-porous film after drying. Dispersion coating can be carried out by gravure, flexogravure, rod, blade, slot die, curtain air knife, or any other known paper coating method. Because the polymer is mixed in an aqueous solution, dispersion coating can produce much thinner layers than extrusion. This offers 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 an environmentally friendly barrier layer against water, water vapor, grease, oil, gas, etc. Another goal is to prepare the surface of cellulosic materials for vacuum deposition processes.

[0033] Figure 1 illustrates a first embodiment of the present invention. This figure shows a multilayer structure 1 comprising multiple layers, starting from an outer layer (i.e., the layer that comes into contact with the external atmosphere after the structure is formed into a package) to an inner layer (i.e., the layer that comes into contact with the finally packed product after the structure is formed into a package).

[0034] In this first embodiment of the structure 1 according to the present invention, as shown in Figure 1, the first outermost layer 2 is 80 g / m² 2 It is a flexible or semi-rigid paper layer having a basis weight of [amount missing]. This paper is uncoated supercalendered fine kraft paper obtained from UPM Company.

[0035] Next, the paper-based barrier multilayer structure 1 further includes a layer 3 of butenediol vinyl alcohol (BVOH) copolymer, which is located outside the metal coating and is positioned between the paper layer 2 and the next layer, which is a vacuum-deposited metal layer 4. The layer 3 outside the metal coating has a density of approximately 3 g / m². 2 It is applied by polymer dispersion coating in that quantity.

[0036] Next, layer 3, which is outside the metal coating, is metallized with a thin metal layer 4, which is an aluminum physical vapor deposition having an optical density corresponding to 3, and the aluminum layer has a thickness of approximately 45 nm.

[0037] Next, the inside of the aluminum layer 4 is coated with a polymer adhesive primer coating 5 containing an aqueous dispersion of polyester, the primer (also referred to as “binder” in the remainder of this specification) by the dispersion coating process at a rate of approximately 2 g / m². 2 It is applied in that amount.

[0038] Finally, the innermost layer of the structure 1 according to this first embodiment is a water-resistant oxygen barrier layer 6 made of pure polyvinylidene chloride (PVDC), and the barrier layer 6 is approximately 8 g / m² 2 It is applied in a certain quantity and deposited by a polymer dispersion coating process using direct gravure coating.

[0039] In a second embodiment of the structure 1 according to the present 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 multilayer structure 1 is approximately 5 g / m² 2 The outermost coating layer 7 further includes an amount of ink printing and overprint varnish. On the innermost part of the material structure, the PVDC layer acts as a heat seal lacquer, especially when the material requires a seal in the heat seal process to manufacture a package from the material.

[0040] The flexible packaging material 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 manufacture secondary or tertiary packaging materials. Primary packaging materials for food products are in direct contact with the actual food products. Secondary packaging materials for food products may be food product packaging materials that help to secure one or more food products contained in the primary packaging. Secondary packaging materials are typically used when multiple food products are individually packed in a single container and provided to the consumer. Tertiary packaging materials for food products are food product packaging materials that help to secure the primary packaging and / or one or more food products contained in the primary and secondary packaging during transport.

[0041] It should be understood that various changes and modifications to the current 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 invention and without diminishing the incidental advantages of the invention. Accordingly, such changes and modifications are intended to be covered by the appended claims.

Claims

1. A barrier multilayer packaging material structure (1), formed as a single sheet of flexibility or semi-rigidity, wherein 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, (ii) A layer (3) located between the paper layer (2) and the metal layer (4), which is outside the metal coating, and has a density of 1 to 10 g / m². ２ A layer (3) located outside the metal coating exists in an amount of, (iii) 1. Aluminum physical deposition having an optical density equivalent to 1.5 to 4, A thin metal layer (4) selected from the list consisting of physical or chemical deposition of aluminum oxide (AlOx) or silicon oxide (SiOx), having a thickness of 7 nm to 100 nm, (iv) A polymer binder selected from the list consisting of ethylene-acrylic acid, methacrylic acid copolymer, polyvinyl acetate, and polyurethane, in a quantity of 0.1 g / m². ２ ~10g / m ２ A polymer binder (5) is present in an amount of, (v) 4 g / m ２ to 20 g / m ２ or 5 g / m ２ to 8 g / m ２ and a water-resistant oxygen barrier layer (6) of polyvinylidene chloride (PVDC) in an amount of A barrier multilayer packaging material structure (1) including the above.

2. The barrier multilayer packaging material structure (1) according to claim 1, wherein the total fiber content of the structure is 85% to 95% by weight.

3. The outermost coating layer (7) further comprises ink printing and overprint varnish, wherein the outermost coating layer (7) is 0.1 g / m² ２ ~6g / m ２ A barrier multilayer packaging material structure (1) according to claim 1, which is present in the amount of .

4. The barrier multilayer packaging material structure (1) according to claim 1, wherein the layer (3) outside 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 a combination thereof.

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

6. The material further comprises an innermost layer (8) containing a heat-seal lacquer, a liquid-tight polyolefin dispersion coating, or a combination thereof, wherein the innermost layer (8) is 1 to 10 g / m² ２ A barrier multilayer packaging material structure (1) according to claim 1, which is present in the amount of .

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

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