PAPERBOARD AND LAMINATE COMPRISING A BIO-BARRIER

Abstract

The present invention relates to a paper or paperboard substrate having barrier properties, which substrate comprises a single or multiply structure with e.g. a top ply, a middle ply and a bottom ply, wherein at least one of said top ply and said bottom ply is provided with a high-density bio-barrier layer, and wherein said top or bottom ply provided with the high-density bio-barrier layer and said top or bottom ply not provided with the high-density bio-barrier layer have both been subjected to grafting with a fatty acid halide.

Claims

1. A paper or paperboard substrate having barrier properties, said substrate comprising: a first surface and a second surface opposite to said first surface; wherein at least said first surface is provided with a bio-barrier layer comprising at least 50 wt % of one or more renewable compounds having a film-forming capacity, and having a density which is higher than a density of the paper or paperboard substrate at the second surface; wherein both of said first surface provided with the bio-barrier layer and said second surface have been subjected to grafting with a fatty acid halide; and wherein the paper or paperboard substrate has an oxygen transmission rate below 500 cc/m.sup.2/24 h/atm, measured according to the standard ASTM F-1927 at 50% relative humidity and 23° C.

2. The paper or paperboard substrate according to claim 1, where said substrate comprises: a top ply, a middle ply and a bottom ply, wherein at least one of said top ply and said bottom ply is provided with the bio-barrier layer, and wherein said top or bottom ply provided with the bio-barrier layer and said top or bottom ply not provided with the bio-barrier layer have both been subjected to grafting with a fatty acid halide, and wherein the density of the bio-barrier layer is higher than the density of the top or bottom ply not provided with the bio-barrier layer.

3. The paper or paperboard substrate according to claim 1, wherein said one or more renewable compounds is selected from one or more of the following: (i) cellulose nanomaterial; (ii) cellulose derivative; (iii) hemicelluloses; (iv) monosaccharides; and (v) starch-based compounds.

4. The paper or paperboard substrate according to claim 3, wherein the bio-barrier layer comprises at least 50 wt % of the one or more renewable compounds.

5. The paper or paperboard substrate according to claim 1, wherein the density of the bio-barrier is above 700 kg/m.sup.3.

6. The paper or paperboard substrate according to claim 1, wherein the bio-barrier layer comprises a basis weight in a range of 2 to 55 g/m.sup.2.

7. The paper or paperboard substrate according to claim 1, wherein said bio-barrier layer comprises at least 50 wt % microfibrillated cellulose (MFC), said MFC having a Schopper-Riegler value in a range of 70-94, and wherein the bio-barrier layer further comprises a basis weight in a range of 5- to 35 g/m.sup.2.

8. The paper or paperboard substrate according to claim 3, wherein the bio-barrier layer comprises at most 50 wt % of different grades of poly(vinyl alcohol) (PVOH) and mixtures thereof.

9. The paper or paperboard substrate according to claim 1, wherein the bio-barrier layer, prior to grafting, has an oxygen transmission rate (OTR) below 500 cc/m.sup.2/24 h/atm measured according to the standard ASTM F-1927 at 50% relative humidity and 23° C.

10. The paper or paperboard substrate according to claim 1, wherein the fatty acid halide grafting results in a material having a Cobb60 value below 30 g/m.sup.2 (as determined according to standard ISO 535:2014 after 60 seconds).

11. The paper or paperboard substrate according to claim 1, wherein said substrate further comprises: at least one outer polymer layer forming an outer surface of said substrate, wherein said polymer comprises: polyethylene (PE), polyethylene terephthalate (PET), polyvinyl alcohol (PVOH), polylactic acid (PLA), polyvinyl acetate (PVA), polypropylene (PP), and/of polyamide (PA) or mixtures thereof.

12. A method for manufacturing a paper or paperboard substrate having barrier properties, said method comprising: a) providing a paper or paperboard substrate comprising a First surface and a second surface opposite to said first surface, wherein at least said first surface is provided with a bio-barrier layer having a density which is higher than a density of the paper or paperboard substrate at the second surface; and b) subjecting both said first surface provided with the bio-barrier layer and said second surface to grafting with a fatty acid halide.

13. The method according to claim 12, wherein said paper or paperboard substrate comprises a top ply, a middle ply and a bottom ply, wherein one of said top ply and said bottom ply is provided with the bio-barrier layer, and wherein both of said top ply and said bottom ply are subjected to grafting with a fatty acid chloride.

14. The method according to claim 12, wherein the fatty acid halide comprises an aliphatic chain length of 10-22 carbon atoms.

15. The method according to claim 12, wherein an applied amount of fatty acid halide is between 0.1-4 g/m.sup.2 of a total dry weight of the substrate.

16. A product produced from the paper or paperboard substrate according to claim 1, wherein the product is selected from a group consisting of: structures utilized for liquid packaging boards (LPB) for use in the packaging of liquids or liquid-containing products, paper or paperboard for dry, fat, fresh and/or frozen food, and laminates thereof; cup material and laminates thereof for hot and cold food stuff; general packaging, luxury packaging, and graphical board for their designated applications; products for non-food applications; well and wrapping paper; pouches; paper or paperboard for single-use items; and labels, grease-proof paper, high-density paper, sack paper and well structures.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings, wherein

[0040] FIG. 1 schematically illustrates two examples of producing a material according to the invention;

[0041] FIG. 2 shows a schematic view of the plies of a prior art multilayer paperboard material;

[0042] FIG. 3 shows a schematic view of an example of a multilayer paperboard according to the invention;

[0043] FIG. 4a shows a schematic view of another example of a multilayer paperboard according to the invention; and

[0044] FIG. 4b shows a schematic view of yet another example of a multilayer paperboard according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] FIG. 1 is a schematic view of two exemplary, step-wise manufacturing processes for producing paperboard material with a bio-barrier according to the invention.

[0046] As illustrated in FIG. 1, a multiply paperboard substrate is provided here in the form of a 3-ply web. (Herein, “multiply” refers to multiple plies/a plurality of plies >2 plies). Next, a bio-based barrier is applied to one of the surfaces and dried to moisture <10%. Then, grafting is performed by applying a fatty acid chloride in at least one step to both surfaces (top ply and bottom ply) with a direct-contact or non-contact method, after which the product is cured by heat. As an option, the obtained grafted substrate can be used for further lamination.

[0047] FIG. 2 illustrates an example of a multiply paperboard 1 in cross section according to prior art. Herein, a middle ply 5 corresponding to a bulking layer is attached to a porous top ply 4 and a bottom ply 6. All plies 4, 5, 6 are cellulose fiber-based layers. The top layer 4 has been subjected to treatment such as surface sizing, coating e.g. mineral coating etc. 3 for obtaining e.g. hydrophobic properties or a barrier function.

[0048] FIGS. 3, 4a and 4b illustrate three examples 8, 9, 10 of paperboard substrates according to the invention, all of which comprises a bio-barrier layer 7. Common for all of the three examples is that said substrate 8, 9, 10 comprises a middle ply 5 sandwiched between an attached top ply 4 and a porous bottom ply 6. A bio-barrier 7 is applied onto the top layer 4 of the substrate 8. Said bio-barrier 7 can be coated directly on the substrate as a dispersion or be added as a pre-made film. The bio-barrier 7 can be applied on a surface-sized board (a size-press can have applied starch on both sides). Grafting with fatty acid halide is performed by means of direct-contact or non-contact method to top ply 4 (coated with said bio-barrier 7) and bottom ply 6. The side 6 without the bio-barrier coating is more permeable than the coated barrier side, allowing for a higher penetration of the fatty acid chloride into the bulk of the board 8, 9, 10.

[0049] The substrates 9, 10 illustrated in FIGS. 4a-b differs from the one seen in FIG. 3 in that one or two surface/s are covered with a polymer layer 11a, 11b. In FIG. 4a, both the top and bottom sides of the paperboard substrate are covered with a polymer layer. The polymer layer may comprise any of the polymers commonly used in paper or paperboard based packaging materials in general or polymers used in liquid packaging board in particular. Examples include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polylactic acid (PLA). Polyethylenes, especially low density polyethylene (LOPE) and high density polyethylene (HDPE), are the most common and versatile polymers used in liquid packaging board. The basis weight (corresponding to the grammage) of the polymer layer of the inventive substrate is preferably in less than 50 gsm (grams per square meter). In order to achieve a continuous and substantially defect free film, a basis weight of the polymer layer of at least 8 gsm, preferably at least 12 gsm is typically required. In some embodiments, the basis weight of the polymer layer is in the range of 8-50 gsm, preferably in the range of 12-50 gsm. A multiply paperboard comprising outer polymer layers provides efficient barrier against gas, e.g. oxygen, and/or water as liquid or gas.

[0050] However, thanks to the grafting in combination with use of a bio-barrier according to the invention, the barrier properties of the paperboard can be improved to such a level that the need for plastic coatings can be significantly reduced in many applications. One example is showed in FIG. 3 where no plastic coating is applied. Another example is illustrated in FIG. 4b, wherein one polymer layer is removed leaving only the PE-layer on the side of the substrate 10 comprising the bio-barrier coating.

[0051] The basis weight (corresponding to the grammage) of the bio-barrier layer 7 is preferably in the range of less than 55 g/m.sup.2. The basis weight of the bio-barrier layer 7 may for example depend on the mode of its manufacture. For example, coating of an MFC dispersion onto a substrate may result in a thinner layer, whereas the formation of a free standing MFC film for lamination to a substrate may require a thicker layer. In some embodiments, the basis weight of the MFC layer is in the range of 5-50 g/m.sup.2. In some embodiments, the basis weight of the MFC layer is in the range of 5-20 g/m.sup.2.

[0052] Moreover, grafting of the fatty acid halide to a bio-barrier layer surface can be achieved by applying a fatty acid halide to the surface of the layer and heating the surface to form covalent bonds between the fatty acid residue and hydroxyl groups of the layer. The reaction between the fatty acid halide; e.g. fatty acid chloride, and the hydroxyl groups of the bio-barrier layer results in ester bonds between the reagent and the polysaccharides. Ungrafted and thereby unbound fatty acids may also be present to a certain extent. Upon the reaction with the hydroxyl groups on the substrate or with water in the substrate or in the air, hydrochloric acid (HCl) is formed as a reaction byproduct. The grafting may preferably be followed by removal of the formed HCl, and optionally by removal of the ungrafted residues.

[0053] One example of a grafting process which could be used in production of the gas barrier film of the present disclosure is described in detail in WO2012066015A1.

[0054] In some non-limiting embodiments, the paper or paperboard based packaging material has the following general structures: [0055] Grafting+Paper/Paperboard+Bio-barrier+Grafting [0056] Grafting+Paper/Paperboard+Bio-barrier+Grafting+Polymer [0057] Polymer+Grafting+Paper/Paperboard+Bio-barrier+Grafting [0058] Polymer+Grafting+Paper/Paperboard+Biobarrier+Grafting+Polymer [0059] The thickness of the outermost PE layer/s, is selected depending on if the layer is intended to form an outside or inside surface of a container manufactured for the packaging material. For example, an inside surface for a liquid packaging container may require a thicker PE layer to serve as a liquid barrier, whereas the outside surface a thinner PE layer or no PE layer may be sufficient. [0060] The material according to the invention is suitable for use in a vast number of applications. A non-limiting list of examples include:
structures utilized for liquid packaging boards (LPB) for use in the packaging of liquids or liquid-containing products, as well as paper or paperboard for dry, fat, fresh and/or frozen food, and laminates thereof;
cup material and laminates thereof for hot and cold food stuff;
general packaging, luxury packaging, and graphical board for their designated applications;
products for non-food applications, such as flora and fauna products, pharma products, beauty and personal care products and multi-pack products;
well and wrapping paper (food and non-food based);
pouches;
paper or paperboard for single-use items;
labels, grease-proof paper, high-density paper, sack paper and well structures.

[0061] While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.