Polymer-coated paper and cardboard

Abstract

The present invention relates to a paper or cardboard-based packaging laminate comprising a paper or cardboard base layer and a gas barrier layer, wherein the gas barrier layer comprises i) a barrier coating layer containing polyvinyl alcohol (PVOH) or a polysaccharide, and ii) an extruded coating polymer layer containing ethylene vinyl alcohol (EVOH).

Description

Technical Field

[0001] The present disclosure relates to polymer-coated paper and cardboard. More particularly, the present disclosure relates to paper or cardboard comprising at least one extruded coating polymer layer comprising ethylene vinyl alcohol (EVOH).

Background Art

[0002] Coating of paper and cardboard with plastics is often used to combine the mechanical properties of cardboard with the barrier and sealing properties of plastic films. Furthermore, cardboard conditioned with a relatively small amount of suitable plastic material can provide the properties necessary to produce cardboard suitable for many required applications.

[0003] Extrusion coating is a process by which a molten plastic material is applied to a substrate such as paper or cardboard to form a very thin, smooth and uniform layer. The coating can be formed by the extruded plastic itself, or the molten plastic can be used as an adhesive to laminate a solid plastic film onto the substrate. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

[0004] Extrusion coating and lamination can be used, for example, to achieve barrier properties against moisture, water vapor, oxygen, aroma, etc., stain or oil resistance, heat sealability, and / or to impart a desired finish or texture to the substrate surface.

[0005] Paper or cardboard is generally suitable for packaging dry products. However, untreated cardboard has limited use when in direct contact with moist or oily products because moisture affects the mechanical properties of the packaging and the absorbed oil causes staining of the paper. These effects will impair the protective function and their packaging appearance.

[0006] Extrusion coating or lamination dramatically expands the scope of application for paper and cardboard. The thin plastic layer provides resistance to oil and moisture and, in some cases, heat resistance. The plastic coating can also be used for heat sealing. Depending on the application, the paper or cardboard may be extrusion coated on one or both sides.

[0007] Polymer-coated cardboard often has insufficient gas barrier properties, although it has excellent resistance to oil and moisture. Therefore, to ensure acceptable gas barrier properties, one or more layers of aluminum foil are often provided on polymer-coated cardboard. However, due to its high carbon footprint, there is a general desire to replace aluminum foil in packaging materials, especially in cardboard for liquid packaging. Also, the combination of polymer and aluminum foil layers makes it difficult to efficiently recycle the packaging material.

[0008] Therefore, there is still a need for improved solutions to replace the aluminum layer in packaging cardboard while maintaining acceptable liquid, water vapor, and oxygen barrier properties. SUMMARY OF THE INVENTION

[0009] An object of the present disclosure is to provide a polymer-based gas barrier layer-containing paper or cardboard-based packaging laminate.

[0010] A further object of the present disclosure is to provide a polymer-based gas barrier layer that can be used to replace the aluminum layer in packaging cardboard.

[0011] The above objects, and other objects that will be understood by those skilled in the art in light of the present disclosure, are realized by various aspects of the present disclosure.

[0012] According to a first aspect illustrated herein: A paper or cardboard base layer, and a gas barrier layer A paper or cardboard-based laminate comprising: wherein the gas barrier layer comprises i) a barrier coating layer containing polyvinyl alcohol (PVOH) or a polysaccharide, and ii) an extruded coating polymer layer containing ethylene vinyl alcohol (EVOH) There is provided a paper or cardboard-based laminate comprising.

[0013] Paper is generally a material made into a thin sheet from wood pulp or other fibrous substances containing cellulose fibers, and refers to a material used for writing, drawing, or printing on a surface, or as a packaging material.

[0014] Cardboard generally refers to a strong and thick paper or cardboard containing cellulose fibers used for boxes and other types of packaging. Cardboard can be bleached or not, can be coated or not, and can be produced in various thicknesses according to end-use requirements.

[0015] In some embodiments, the base layer has a basis weight in the range of 20 - 500 g / m 2 preferably in the range of 80 - 400 g / m 2 of the range.

[0016] In some embodiments, the base layer comprises multi-ply cardboard.

[0017] In some embodiments, the base layer comprises at least 10 wt%, preferably at least 30 wt%, more preferably at least 50 wt% recycled fibers, based on the total fiber weight of the base layer.

[0018] The surface of the base layer of paper or paperboard, to which an aqueous barrier coating is to be applied, may preferably be pretreated, for example, by surface sizing or dispersion coating, in order to reduce the surface porosity. In this way, the coating weight of the barrier coating layer can be reduced.

[0019] In some embodiments, the base layer is preferably surface sized on one or both sides with starch or a starch-based sizing agent.

[0020] In some embodiments, the paper or paperboard base layer includes a mineral coating layer on one or both sides.

[0021] The inventors have finally found that a combination of a barrier coating layer containing polyvinyl alcohol (PVOH) or a polysaccharide and an extruded coating polymer layer containing ethylene vinyl alcohol (EVOH) provides an effective gas barrier layer that can be used to replace the aluminum layer of packaging paperboard. It has been found that a combination of a barrier coating layer containing polyvinyl alcohol (PVOH) and an extruded coating polymer layer containing ethylene vinyl alcohol (EVOH) causes excellent oxygen barrier properties that are significantly better than the additive effects that can be predicted from the combination of the layers.

DETAILED DESCRIPTION OF THE INVENTION

[0022] As used herein, the term "coating" refers to the operation of covering the surface of a substrate with a composition to impart desired properties, finish, or texture to the substrate.

[0023] As used herein, the term "extrusion coating" refers to the operation of applying a molten plastic material to a substrate such as paper or paperboard to form a very thin, smooth, and uniform layer.

[0024] In some embodiments, a barrier coating layer is applied on the base layer and an extruded coating polymer layer is applied on the barrier coating layer.

[0025] The barrier coating layer can be a single-layer or multi-layer coating that can have PVOH or polysaccharides present in one or several layers.

[0026] The barrier coating layer can be applied by any suitable application method. The barrier coating layer can be applied, for example, by a liquid or foam coating method or by a melt extrusion coating method. In a preferred embodiment, the barrier coating layer is applied by a liquid or foam coating of a liquid solution or dispersion containing PVOH or polysaccharides onto the base layer and subsequent drying of the liquid solution or dispersion to obtain the barrier coating layer. The liquid of the liquid solution or dispersion is preferably water or an aqueous solution.

[0027] The liquid solution or dispersion can be applied to the paper or paperboard base layer using conventional coatings or application methods known in the art. Examples of suitable coatings or application methods include, but are not limited to, size press, film press, dipping, spray coating, curtain coating, printing such as flexo or rotogravure printing, or anilox or gravure or rod coating. Curtain coating is a preferred application method.

[0028] In some embodiments, the liquid solution or dispersion is applied in the form of foam. Foam coating is advantageous as it allows film formation with a higher solids content and a lower water content compared to non-foam coatings. The lower water content of the foam coating also reduces the problem of rewetting of the base layer. The foam can be formed using a polymeric or non-polymeric foaming agent. Examples of polymeric foaming agents include PVOH, hydrophobically modified starch, and hydrophobically modified ethyl hydroxyethyl cellulose.

[0029] In some embodiments, the PVOH or polysaccharide of the barrier coating layer is water-soluble or water-dispersible.

[0030] In some embodiments, the barrier coating layer comprises at least 50 wt%, preferably at least 70 wt%, of PVOH or polysaccharide based on the dry weight of the barrier coating layer. The remainder of the barrier coating layer can consist of other polymeric or non-polymeric coating components. In some embodiments, the remainder comprises latex. In some embodiments, the remainder comprises pigment. The barrier coating layer may consist of or consist essentially of PVOH or polysaccharides.

[0031] In some embodiments, the PVOH of the barrier coating layer is selected from the group consisting of PVOH, copolymers of ethylene and PVOH, and combinations thereof, preferably PVOH.

[0032] In some embodiments, the PVOH of the barrier coating layer has a degree of hydrolysis in the range of 80 - 99 mol%, preferably in the range of 85 - 99 mol%. PVOH having such a degree of hydrolysis has been demonstrated to provide exceptional gas barrier properties.

[0033] In some embodiments, the polysaccharide of the barrier coating layer is selected from the group consisting of hemicellulose, carboxymethyl cellulose (CMC), starch, and combinations thereof, preferably CMC.

[0034] Short water-soluble polysaccharides having a degree of polymerization (DP) of 100 or less, such as anionic hemicelluloses like xylan, can form good barrier films when combined with longer water-soluble polysaccharides having a degree of polymerization (DP) of 150 or more, such as carboxymethyl cellulose. In addition to providing barrier films and coatings with excellent oxygen and oil barrier properties, the combination of a relatively high amount of relatively short water-soluble polysaccharides and longer water-soluble polysaccharides enables the preparation of aqueous barrier coating compositions having a high total solids content, such as 10, 20, or even 30 wt% or more, while maintaining a reasonably low viscosity. This allows the aqueous barrier coating composition to be efficiently applied to paper or paperboard-based layers using conventional coating methods. The high solids content combined with low viscosity reduces the transportation cost of the coating composition and enables the preparation of coatings with a high basis weight in a single coating step. The high solids content also reduces the amount of water to be removed when drying the film or coating, which can reduce the drying energy requirements of the coating process.

[0035] Thus, in some embodiments, the barrier coating layer comprises 20 - 80 wt% of a first polysaccharide having a first degree of polymerization (DP1) of at least 150, based on the total solids content of the barrier film or coating; and 20 - 80 wt% of a second polysaccharide having a second degree of polymerization (DP2) of 100 or less, based on the total solids content of the barrier film or coating; The ratio of DP1:DP2 is at least 10:1.

[0036] In some embodiments, the barrier coating layer comprises a polysaccharide and xylan. In some embodiments, the barrier coating layer comprises CMC and xylan.

[0037] In some embodiments, the barrier coating layer further comprises a pigment. The pigment includes, for example, inorganic particles such as talcum, silicate, carbonate, alkaline earth metal carbonate, and ammonium carbonate, or oxides such as transition metal oxides and other metal oxides. The pigment may include those selected from the group consisting of nano-sized pigments such as nanoclays of layered inorganic silicates and nanoparticles such as montmorillonite, bentonite, kaolinite, hectorite, and halloysite.

[0038] In some embodiments, the coating weight of the barrier coating layer is in the range of 4 - 12 g / m 2 preferably in the range of 5 - 10 g / m 2 and is within this range.

[0039] In some embodiments, the barrier coating layer contains PVOH, and the coating weight of the barrier coating layer is in the range of 4 - 8 g / m 2 and is within this range.

[0040] In some embodiments, the barrier coating layer contains a polysaccharide, and the coating weight of the barrier coating layer is in the range of 6 - 10 g / m 2 preferably in the range of 8 - 10 g / m 2 and is within this range.

[0041] The extruded coating polymer layer can be a single-layer or multi-layer coating, and EVOH can be present in one or several layers.

[0042] In some embodiments, the extruded coating polymer layer contains at least 50 wt%, preferably at least 70 wt%, more preferably at least 90 wt% of EVOH based on the dry weight of the extruded coating polymer layer. The remainder of the extruded coating polymer layer can be composed of other polymers or non-polymer coating components. The extruded coating polymer layer may consist of or be substantially composed of EVOH.

[0043] In some embodiments, the EVOH of the extrusion coating polymer layer has an ethylene content of at least 27 mol%, preferably at least 32 mol%, more preferably at least 44 mol%. A high ethylene content of at least 27 mol% facilitates the recycling of paper or paperboard-based packaging laminates and causes good processability by allowing for lower temperatures for extrusion. Further, by including at least 27 mol% ethylene in the EVOH, the moisture resistance is improved, thereby preserving the high gas barrier properties of PVOH or polysaccharides even under high relative humidity conditions. A higher ethylene content typically reduces the oxygen barrier properties of the EVOH film, but by combining the EVOH of the extrusion coating polymer layer with a barrier coating layer containing PVOH or polysaccharides, the laminate still exhibits excellent oxygen barrier properties. In a preferred embodiment, the laminate includes a barrier coating layer containing PVOH having a degree of hydrolysis in the range of 80-99 mol% in combination with an extrusion coating polymer layer containing EVOH having an ethylene content of at least 27 mol%. This specific combination has been shown to provide exceptionally high oxygen barrier properties, particularly under high relative humidity conditions.

[0044] In some embodiments, the EVOH of the extrusion coating polymer layer has a melt flow index (MFI, 190 °C and 2.16 kg) in the range of 2-10 g / 10 min, preferably in the range of 3-7 g / 10 min.

[0045] In some embodiments, the coating weight of the extrusion coating polymer layer is in the range of 10-60 g / m 2 preferably in the range of 10-30 g / m 2 more preferably in the range of 10-25 g / m 2 of.

[0046] In some embodiments, the extrusion coating polymer layer contains 2-12 g / m 2 preferably 2-10 g / m 2 of EVOH.

[0047] In some embodiments, the extrusion coating polymer layer consists of two or more extrusion coating sub-layers, and at least one of the sub-layers is EVOH of 2 to 12 g / m 2 , preferably EVOH of 2 to 10 g / m 2 .

[0048] In some embodiments, the extrusion coating polymer layer consists of two or more extrusion coating sub-layers, and at least two of the sub-layers are each EVOH of 2 to 12 g / cm 2 , preferably EVOH of 2 to 10 g / m 2 .

[0049] In some embodiments, a paper- or cardboard-based packaging laminate further comprises a protective polymer layer applied to the extrusion coating polymer layer. The protective polymer layer preferably has a composition different from that of the extrusion coating polymer layer.

[0050] In some embodiments, the protective polymer layer is formed by extrusion coating or by extrusion film lamination.

[0051] In some embodiments, the protective polymer layer comprises a layer of a thermoplastic polymer, preferably a polyolefin, more preferably polyethylene or polypropylene, or a combination thereof. Polypropylene can provide even better moisture resistance at high humidity, for example in a tropical state.

[0052] In some embodiments, the protective polymer layer further comprises a tie layer that improves the adhesion between the extrusion coating polymer layer and the protective polymer layer. The tie layer is preferably based on polyethylene, which means that the tie layer contains >80 wt%, preferably >95 wt%, more preferably >98 wt% polyethylene. The high polyethylene content in the tie layer facilitates the recycling of the packaging laminate because the tie layer can be recycled at the same rate as the outermost polyolefin layer.

[0053] In some embodiments, a paper or paperboard-based packaging laminate has an oxygen transmission rate (OTR) of less than 5 cc / m 2 / 24 hours, preferably less than 3 cc / m 2 / 24 hours, more preferably less than 2 cc / m 2 / 24 hours, as measured in accordance with standard ASTM D-3985 at 50% relative humidity and 23 °C.

[0054] In some embodiments, a paperboard-based packaging laminate has a rejection rate of less than 30%, preferably less than 20%, more preferably less than 10%, in accordance with PTS RH 021 / 97.

[0055] In some embodiments, a paperboard-based packaging laminate has a residual ash content of less than 5 wt%, preferably less than 2 wt%, by combustion at 525 °C or 900 °C in accordance with Tappi standards T211 or T413, respectively.

[0056] According to a second aspect illustrated herein, a method for manufacturing a paper or paperboard-based packaging laminate, comprising: a) providing a paper or paperboard-based layer, b) applying an aqueous coating composition comprising polyvinyl alcohol (PVOH) or polysaccharides to the paper or paperboard-based layer and drying the applied aqueous coating composition to form a barrier coating layer, and c) applying a polymer layer comprising ethylene vinyl alcohol (EVOH) to the barrier coating layer by extrusion coating is provided.

[0057] The polyvinyl alcohol (PVOH) or polysaccharides of the second aspect may be further defined as described above with reference to the first aspect.

[0058] The ethylene vinyl alcohol (EVOH) of the second aspect may be further defined as described above with reference to the first aspect.

[0059] Although the present 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 without departing from the scope of the present invention and equivalents may be substituted for its elements. Further, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from the essential scope thereof. Accordingly, the present invention is not limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present invention, but the present invention is intended to include all embodiments falling within the scope of the appended claims.

Example

[0060] Example 1 - Preparation of Paperboard-Based Packaging Laminate Containing a Paperboard Base Layer and a Gas Barrier Layer Paperboard substrates (Performa Light RS, Koppargloss RS, Performa Light PS, and CKB Nude PS) were coated with various coating dispersions shown in Table 1. RS (reverse side) and PS (printing side) refer to the sides of the substrate to be coated. The dispersions used were starch-based coatings (Perfectafilm X115, Avebe), PVOH (Poval 15-99, Kuraray), carboxymethylcellulose (CMC, CPKelco), combinations of PVOH and CMC, and combinations of CMC with xylan and sorbitol. The dispersions were applied in two layers by rod (R20 or R15) and / or InvoTip (IT) coating, and IR drying was performed between applications. TIFF2025522900000001.tif172170

[0061] Next, the dispersion-coated substrate was extrusion-coated on the dispersion-coated surface at the top of the dispersion barrier layer with either LDPE / HDPE / LDPE (10 gsm / 15 gsm / 10 gsm, coating samples 302a, 305a, 307a, 313a, 314a, 317a, ZS02a, and XS04a are shown) or EVOH / MAH-grafted LDPE / LDPE (6 gsm / 5 gsm / 20 gsm, coating samples 302c, 305c, 307c, 313c, 314c, 317c, XS02c, and XS04c are shown).

[0062] Example 2 - Analysis of Gas Barrier Properties of Prepared Paperboard-Based Packaging Materials The paperboard-based packaging laminate prepared in Example 1 was analyzed to determine the oxygen and water vapor barrier properties. The oxygen transmission rate (OTR) was measured according to standard ASTM D-3985 at 50% relative humidity and 23 °C, and at 90% relative humidity and 38 °C. The water vapor transmission rate (WVTR) was measured according to standard ASTM F1249 at 50% relative humidity and 23 °C. The results are presented in Table 2. TIFF2025522900000002.tif179170

Claims

1. A paper or cardboard base layer, Gas barrier layer and A paper or cardboard-based packaging laminate, including, The aforementioned gas barrier layer i) A barrier coating layer comprising polyvinyl alcohol (PVOH) or polysaccharides, and ii) Extruded coating polymer layer containing ethylene vinyl alcohol (EVOH) Packaging laminates based on paper or cardboard, including [the specified material].

2. The base layer is 20-500 g / m². ２ Preferably in the range of 80 to 400 g / m² ２ A packaging laminate based on paper or cardboard according to claim 1, having a basis weight in the range of [specified range].

3. A paper or cardboard-based packaging laminate according to claim 1, wherein the base layer contains at least 10% by weight, preferably at least 30% by weight, and more preferably at least 50% by weight of recycled fibers, based on the total fiber weight of the base layer.

4. The paper or cardboard-based packaging laminate according to claim 1, wherein the base layer is preferably surface-sized on one or both sides with starch or a starch-based sizing agent.

5. A paper or cardboard-based packaging laminate according to claim 1, wherein the base layer includes a mineral coating layer on one or both sides.

6. A paper or cardboard-based packaging laminate according to claim 1, wherein a barrier coating layer is applied to a base layer and an extruded coating polymer layer is applied to the barrier coating layer.

7. The paper or cardboard-based packaging laminate according to claim 1, wherein the barrier coating layer contains at least 50% by weight, preferably at least 70% by weight, of PVOH or polysaccharides based on the dry weight of the barrier coating layer.

8. The paper or cardboard-based packaging laminate according to claim 1, wherein the PVOH in the barrier coating layer has a degree of hydrolysis in the range of 80 to 99 mol%, preferably in the range of 85 to 99 mol%.

9. The paper or cardboard-based packaging laminate according to claim 1, wherein the polysaccharide of the barrier coating layer is selected from the group consisting of hemicellulose, carboxymethylcellulose (CMC), starch, and combinations thereof, and is preferably CMC.

10. A paper or cardboard-based packaging laminate according to claim 1, wherein the barrier coating layer comprises a polysaccharide and xylan.

11. The paper or cardboard-based packaging laminate according to claim 1, wherein the barrier coating layer further comprises a pigment.

12. The coating weight of the barrier coating layer is 4 to 12 g / m². ２ Preferably within the range of 5 to 10 g / m ２ A paper or cardboard-based packaging laminate according to claim 1, within the range of [the specified range].

13. The barrier coating layer contains PVOH, and the coating weight of the barrier coating layer is 4-8 g / m². ２ A paper or cardboard-based packaging laminate according to claim 1, within the range of [the specified range].

14. The barrier coating layer contains polysaccharides, and the coating weight of the barrier coating layer is 6-10 g / m². ２ Preferably within the range of 8 to 10 g / m ２ A paper or cardboard-based packaging laminate according to claim 1, within the range of [the specified range].

15. The paper or cardboard-based packaging laminate according to claim 1, wherein the extruded coating polymer layer contains at least 50% by weight, preferably at least 70% by weight, and more preferably at least 90% by weight of EVOH, based on the dry weight of the extruded coating polymer layer.

16. The paper or cardboard-based packaging laminate according to claim 1, wherein the EVOH in the extruded coating polymer layer has an ethylene content of at least 27 mol%, preferably at least 32 mol%, and more preferably at least 44 mol%.

17. The paper or cardboard-based packaging laminate according to claim 1, wherein the EVOH of the extruded coating polymer layer has a melt flow index (MFI, 190°C, and 2.16 kg) in the range of 2 to 10 g / 10 min, preferably in the range of 3 to 7 g / 10 min.

18. The extruded coating polymer layer contains EVOH of 2 to 12 g / m ２ preferably 2 to 10 g / m ２ of EVOH, and the laminate for packaging based on the paper or cardboard according to claim 1.

19. The extruded coating polymer layer consists of two or more extruded coating sublayers, and at least one of the sublayers contains 2 to 12 g / m². ２ EVOH, preferably 2 to 10 g / m ２ A paper or cardboard-based packaging laminate according to claim 1, comprising EVOH.

20. The paper or cardboard-based packaging laminate according to claim 1, further comprising a protective polymer layer applied on an extruded coated polymer layer.

21. 5 cc / m³ measured according to ASTM D-3985 standard at 50% relative humidity and 23°C. ２ Less than 24 hours, preferably 3 cc / m³ ２ Less than 24 hours, more preferably 2 cc / m³ ２ A paper or cardboard-based packaging laminate according to claim 1, having an oxygen transport rate (OTR) of less than 24 hours.

22. A paper or cardboard-based packaging laminate according to claim 1, having a rejection rate of less than 30%, preferably less than 20%, and more preferably less than 10%, in accordance with PTS RH 021 / 97.

23. A method for manufacturing a paper or cardboard-based packaging laminate, a) To provide a paper or cardboard base layer, b) Applying an aqueous coating composition containing polyvinyl alcohol (PVOH) or polysaccharides to a paper or cardboard base layer, drying the applied aqueous coating composition to form a barrier coating layer, and c) Applying a polymer layer containing ethylene vinyl alcohol (EVOH) to a barrier coating layer by extrusion coating. Methods that include...