Moisture and liquid resistand paper or paperboard arranged with sealant and liquid resistant layers comprising renewable polymers

Abstract

The present invention relates to a moisture- and liquid-resistant paper or paperboard, comprising: an internally-sized cellulose-based substrate with a basis weight between 100-500 g / m2 and a density between 400-850 kg / m3, said substrate having a first main surface and a second main surface; at least one sealant layer applied on said first main surface of the substrate protecting the substrate at least against moisture penetration; at least one liquid-resistant layer applied on said sealant layer, protecting the substrate at least against liquid penetration; wherein said sealant layer is made up by unmodified and / or modified renewable polymers in an amount of 70-100 wt% calculated on the total dry weight of said layer; liquid-resistant layer is made up by unmodified and / or modified renewable polymers in an amount of 30-100 wt% calculated on the total dry weight of said layer; and said moisture- and liquid-resistant paper- or paperboard has a total renewable content >90 wt%, preferably >95 wt% as calculated on the total dry weight of the paper or paperboard.

Description

[0001] MOISTURE AND LIQUID RESISTAND PAPER OR PAPERBOARD ARRANGED WITH SEALANT AND LIQUID RESISTANT LAYERS COMPRISING RENEWABLE POLYMERS

[0002] Technical field

[0003] The present disclosure relates to renewable and compostable moisture- and liquid resistant paper or paperboard suitable for use in disposable packaging containers, such as cups, boxes and trays, for food and beverages.

[0004] Background

[0005] Fiber-based material used in containers, such as cups, bowls, and boxes, for liquids (hot and cold), fatty or frozen food, is usually provided with barrier coatings primarily on the inside (facing the packed item) but also on the outside (print-side). The barrier coating applied on the inside makes the material resistant against e.g. liquids, grease, and / or aroma and enables it to withstand the influence of the packed item on the package material. The barrier on the outside is applied to protect the packed item from the surrounding, especially from water vapor and condensation that is formed on the surface due to temperature fluctuations or temperature differences between container outside vs container inside.

[0006] Coating of paper and paperboard with plastics is often employed to combine the mechanical properties of the paper and paperboard with the barrier and converting properties of a plastic film, such as sealability and shape forming. However, plastics are undesirable from a sustainability and recycling point of view and negatively affect for example the repulping efficiency of pre- and post-consumer waste. Also, only few and less common plastics can be considered as compostable, especially home compostable. The most common coating materials for creating barrier- and heat-sealable properties on fiber-based packaging materials include polyolefins, such as polyethylene (PE) or polypropylene (PP). Paperboard intended for e.g. cups is often provided with a polyolefin coating to provide barrier and heat sealability at least on the inside of the packaging, and in some cases both on the inside and on the outside.

[0007] Environmental concerns and recent directives and legislations have created a demand that disposable fiber-based containers, such as cups, should contain no or very low amounts of plastics manufactured from biobased, fossil or synthetic starting substances. Barrier coatings based on natural polymers have been tested in the art, but many of these have not been considered to provide high enough barrier properties. These solutions often tend to be more expensive and also require higher coat weights, which further increases the price and limits the applicability and commercialization of the material.

[0008] Therefore, it remains a need for a renewable and compostable container for liquid, fatty- and / or frozen food that provides enough barrier properties but contains no or low amounts of plastics.

[0009] Description of the invention

[0010] It is an object of the invention to provide a moisture- and liquid-resistant paper or paperboard made from mainly renewable resources and that exhibits good repulpability.

[0011] It is a further object of the invention to provide a moisture- and liquid-resistant paper or paperboard with good repulpability, which is useful in food and beverage packaging applications.

[0012] It is a further object of the invention to provide a moisture- and liquid-resistant paper or paperboard for food and beverage packaging applications, which is free from conventional plastic-barrier coatings.

[0013] It is a further object of the invention to provide a compostable container, such as a cup, which provides barrier functionality against moisture- and liquid penetration, particularly against hot beverages such as coffee or tea.

[0014] The above-mentioned objects, as well as other objects as will be realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

[0015] Accordingly, the present invention relates to a paper or paperboard that is resistant to both moisture and liquid. The inventive material comprises an internally sized cellulose-based substrate with a basis weight between 100-500 g / m2and density between 400-850 kg / m3. The substrate has a first main surface and a second main surface. To protect the cellulose substrate from moisture penetration, at least one sealant layer is applied on the first main surface of the substrate, i.e. the sealant layer is in direct contact with the substrate. The purpose of the sealant layer is primarily to seal any pores in the substrate and provide a moisture-resistant material to prevent or at least delay penetration of moisture into the substrate. It also provides a smoother surface on the first main surface, or on both first and second main surfaces, of the paperboard, rendering it suitable for receiving a further layer. The sealant layer provides a continuous covering over the desired surface of the substrate. The reduced moisture permeability provided by the sealant layer protects the substrate from too high losses in mechanical rigidity and stiffness, and ensures that the initial structural properties of the paperboard remain largely unaffected throughout the intended usage period of an end product, such as a paper cup for hot beverage. Moisture resistance can be evaluated by measuring water vapor transmission rate (WVTR).

[0016] Further protection against liquid penetration is provided by applying at least one liquid-resistant layer on top of the existing sealant layer. According to the present invention, a key feature of these layers (i.e. the sealant layer and the liquidresistant layer) lies in their composition and their combination as they cannot function on their own for the intended use and removal of a plastic-barrier layer. The sealant layer is made up by unmodified and / or modified renewable polymers in amounts between 70-100 wt% calculated on the total dry weight of said layer, and furthermore the liquid resistant layer is made up by unmodified and / or modified renewable polymers in amounts between 30-100 wt% calculated on the total dry weight of said layer. This contributes significantly to the overall renewable content of the paper or board, which exceeds 90 wt% or even exceeds 95 wt% as calculated on its total dry weight.

[0017] Another important aspect of this invention is the performance of the paper or paperboard under testing conditions. The material exhibits high resistance to water with a Cobb300 value less than 30 g / m2according to ISO 535:2023 standard, preferably less than 25 g / m2. Furthermore, the Cobb-Unger (15 s) value is less than 10 g / m2, measured according to SCAN-P 37:77. Additionally, said material displays significant resistance against water vapor transmission rate (WVTR) with values less than 35g / m2 / h at 38°C and 80% RH, measured according to standard ASTM E96-00 but where the value is recorded after 1h (one hour) instead of the usual 24h.

[0018] In a preferred embodiment, the paper or paperboard is free from pigment coating. Pigment coatings are normally used to improve the surface performance of the board, such as smoothness, whiteness, and printability. However, the need of pigment coating increases the cost, environmental footprint, and production complexity. The present invention functions without the requirement of such pigment coating, further increasing the sustainability, cost competitiveness, and production efficiency of the paper or paperboard.

[0019] In some embodiments, the sealant layer is applied only on the first main surface, and on top of that, a liquid-resistant layer is applied. The total amount of the combined sealant- and liquid resistant layers applied on the first main surface is preferably below 10 gsm. In this embodiment, the second main surface is free from at least the sealant layer, resulting in that any moisture having entered the substrate is not trapped therein but may exit through said second main surface. The second main surface may in this case comprise a liquid-resistant layer in direct contact with the substrate.

[0020] In some embodiments, at least one sealant layer protecting the substrate against moisture penetration is applied also on said second main surface of the substrate in addition to the first main surface. Preferably, also a liquid-resistant layer is applied on top of the sealant layer at said second main surface of the substrate, resulting in that a core fiber-based substrate is sandwiched between outer moisture- and liquid-resistant layers, i.e. both the top- and main surfaces of the substrate are covered with moisture- and liquid-resistant layers.

[0021] Thanks to the invention, there is achieved a material free from conventional plastic coating that provides moisture and liquid resistance, meeting the requirements for containers holding liquids, including hot liquids above 75°C, during usage. Moreover, the material is made mainly from renewable resources, and is repulpable.

[0022] The innovative combination of moisture and liquid resistant layers described in this invention further results in a significantly reduced Cobb-Unger value (i.e. oil Cobb). This has several benefits when it comes to additional processes like coating, lamination, or printing on the material surface.

[0023] As used herein, the term “renewable polymer” refers to a polymer that is derived from a renewable resource. Furthermore, the term “renewable resource” refers to a resource that is produced via a natural process at a rate comparable to its rate of consumption (e.g., within a 100-year time frame). The resource can be replenished naturally, or via agricultural techniques, i.e. they are renewable, reusable and recyclable. Non-limiting examples of renewable resources include plants (e.g., woody plants, lignocellulose, hemicellulose, cellulosic waste sugar cane, beets, corn, potatoes, citrus fruit), bacteria, fungi, and forestry products. These resources can be naturally occurring, hybrids, or genetically engineered organisms. Fossil-based resources, such as crude oil, coal, natural gas, and peat, which take longer than 100 years to form, are not considered renewable resources.

[0024] The moisture- and liquid-resistant paper or paperboard according to the invention is preferably suitable for use as packaging material intended for contact with food and liquids, such as hot liquids. In some embodiments, the moisture- and liquidresistant paper or paperboard according to the invention is suitable for use in disposable packaging containers, such as cups, lids, boxes and trays for food and beverages.

[0025] Paper generally refers to a material manufactured in thin sheets or rolls from the pulp of wood or other fibrous substances comprising cellulose fibers, used for writing, drawing, or printing on, or as a packaging material. Paperboard generally refers to strong, thick paper or cardboard, typically comprising more than one ply, used for example in containers such as cups, boxes and trays for food and beverages, and / or other types of packaging.

[0026] Paper or paperboard may generally be a single-ply material or a multiply material, i.e. comprising two or more plies. Paperboard can either be bleached or unbleached paperboard, uncoated paperboard, and produced in a variety of thicknesses, depending on the end-use requirements.

[0027] The paper or paperboard can be manufactured in a paper or paperboard machine. Typically, the machine layout comprises a stock handling section, a wet-end section, a press section, a drying section, a calendaring and / or coating section, and a surface sizing unit.

[0028] The paper or paperboard can have a certain composition of pulp fibers, such as bleached and / or unbleached Kraft pulp, sulfite pulp, dissolving pulp, thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), high- temperature CTMP (HT-CTMP) and / or mixtures thereof. In some embodiments, the paper or paperboard comprises a substantial amount of recycled cellulose fibers, such as broke or fibers recycled from pre- or post-consumer waste. In some embodiments, the amount of recycled cellulose fibers in the paper or paperboard is in the range of 1-50 wt%, preferably in the range of 5-45 wt%, and more preferably in the range of 10-35 wt%, based on the total dry weight of the paper or paperboard. It is also possible that the paper or paperboard product comprises only recycled fibers.

[0029] In some embodiments, the paper or paperboard is a multiply material having a multilayer structure comprising a back ply comprising bleached Kraft pulp, a mid ply comprising a mixture of bleached Kraft pulp and CTMP, and a top ply comprising bleached Kraft pulp, wherein the mid ply has a lower density than both the back and top plies, respectively. The multiply paper or paperboard of the present disclosure is liquid repellent. The term “liquid repellent” generally means that the multiply paper or paperboard with the internal sizing agents and barrier layers has a higher resistance or repellence to liquid penetration and absorption than the same multiply paper or paperboard without said internal sizing agents and barrier layers.

[0030] The substrate of the paper or paperboard preferably comprises internal sizing agent / s. Internal sizing agents are often used in paper or paperboard in order to control wetting. An internal sizing agent is a hydrophobic agent which is added to the cellulose furnish in the stock handling or wet-end section of the paper or paperboard manufacturing process. The most common internal sizing agents are alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA) and rosin sizing agents, where the latter can be used as soap size or rosin emulsion or as cationic or anionic dispersions. However, other agents that increase the resistance to liquid surface- and raw-edge penetration of water and other liquids into the cellulose- based substrate may also be used as internal sizing agents. Examples include natural waxes, fatty acids, fatty acid derivatives, and / or combinations thereof. The internal sizing agents are typically added to the cellulose furnish in emulsion form or as a dispersion.

[0031] The sealant layer is arranged to at least slow down unwanted absorption of atmospheric or incidental moisture into the substrate during the intended use of the product, i.e. provide moisture resistance. Said sealant layer comprises at least one binder in the form of one or more renewable polymer / s (modified and / or unmodified) as main component, selected from: microfibrillated cellulose (MFC), water-soluble polysaccharides, modified polysaccharides, hydrophobically modified polysaccharides, and cellulose derivatives, such as hydroxypropyl starch, n-octenyl succinic anhydride (n-OSA) starch, dialdehyde starch, oxidized starch, sodium carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose and / or chitosan.

[0032] In some embodiments of this invention, there can be addition of a crosslinker in the sealant layer to improve the functionality. In some embodiments, the sealant layer comprises 0.1-20 wt% crosslinker, based on the total dry weight of the sealant layer. In some embodiments, the crosslinker is selected from the group consisting of polyamide-epichlorohydrin (PAE), zirconium carbonates such as ammonium zirconium carbonate or potassium zirconium carbonate, and / or polyfunctional organic acids or aldehydes, such as citric acid, tartaric acid, glyoxal, sodium trimetaphosphate and glutaraldehyde or combinations thereof.

[0033] In some embodiments, the sealant layer also comprises particles that are impermeable to moisture to slow down the transmission rate. In some embodiments, the sealant layer comprises 0.1-20 wt% particles, based on the total dry weight of the sealant layer. In some embodiments, the impermeable particles are selected from the group consisting of clay, silica, calcium carbonate, cellulose nanocrystals, microcrystalline cellulose and / or combinations thereof.

[0034] In some embodiments, the sealant layer also comprises at least one hydrophobic agent to reduce the wetting from condensed moisture and / or upon application of the subsequent liquid-resistant layer. In some embodiments, the sealant layer comprises 0.1-10 wt% of at least hydrophobic agent, based on the total dry weight of the sealant layer. In some embodiments, the hydrophobic agents are preferably selected from the group consisting of rosin, AKD, wax, and / or SA-latex.

[0035] The sealant layer can be applied as a surface sizing composition, said surface sizing layer comprising one or more of said renewable polymers. Surface sizing enhances the surface properties of the paper or paperboard, and can, depending on the type of surface-sizing layer applied, make the surface more resistant to liquid penetration and increase the overall strength and appearance of the material. The primary objective of the surface sizing layer(s) of the inventive paper or paperboard is to create a sealant layer on the paper or paperboard, particularly for use in contact with hot and cold food and beverages. To improve the moisture resistance of the paper or paperboard material, a sealant layer is needed to prevent or at least delay the moisture from reaching the underlying substrate. The sealant layer should thereby have a structural design with low permeability towards water vapor and sufficient hydrophobicity to minimize the wetting as a result of liquid condensation. By the addition of different additives, the moisture resistance of the layer can be further improved, for example additives in the form of impermeable particles that create a tortuous pathway for the moisture molecules and / or a crosslinker that prevents the structure from swelling. Surface sizing is typically achieved through the application of a sizing composition, which comprises chemicals on a paper web. The two main methods for applying surface sizing layers are the size-press method and the film-press method, but surface sizing layers may also be applied using a wet-end applicator, or by any other surface sizing or coating or spraying method known in the paper industry. The size press method involves applying the surface sizing composition directly or indirectly onto the surface of the paper or paperboard as it passes through a nip or a set of rollers. In the film press method, a film of the surface sizing composition is formed separately, typically using a film press machine wherein a rod, blade or metering roll is used to create a thin film on a transfer roll. This film is then transferred onto the surface of the paper or paperboard using pressure. In addition to traditional surface sizing methods, other methods can also be applied for providing a thin sealant layer on a paper or paperboard surface, without forming a plastic coating. Accordingly, for example impregnation as well as wet-on-wet application of a composition as described above can also be utilized and the invention is not limited to the specific application method to form the sealant layer, but preferably, the application method should be included as an online application in the paperboard machine.

[0036] In some embodiments of this invention, the sealant layer has a coat weight of at least 0.2 g / m2such as at least 0.3 g / m2. Furthermore, to ensure optimal functionality while keeping material usage minimalistic, the sealant layer is applied in amounts less than 5 g / m2, preferably less than 3 g / m2, and comprises at least one of said renewable polymers. In some embodiments, the sealant layer comprises at least 70 wt% renewable polymers and 1-30 wt% of additional compounds based on the total dry weight of the layer.

[0037] In some embodiments, the paper or paperboard substrate with the sealant layer has a moisture content of less than 10 wt%, preferably less than 8 wt%, such as between 3-7 wt%, based on the total weight of the substrate prior to the application of the liquid-resistant layer.

[0038] In some embodiments, the sealant layer comprises at least two renewable polymers, such as two or three renewable polymers. In some embodiments, the sealant layer can be calendered prior to application of further layer / s.

[0039] As previously stated, at least one liquid-resistant layer is applied on top of the existing sealant layer for further protection against liquid penetration e.g. in case of direct and persistent water contact. The liquid-resistant layer comprises at least one hydrophobic agent. In some embodiments, the liquid-resistant layer comprises above 10 wt%, such as between 10-70 wt% of at least one hydrophobic agent, such as 10-50 wt%, based on the total dry weight of the layer. In some embodiments, the liquid-resistant layer comprises between 50-100 wt% hydrophobic agent. In some embodiments, the at least one hydrophobic agent is preferably selected from the group consisting of: rosin resin, ASA, AKD, wax, fatty acids and fatty acid derivatives, water-dispersible latex such as styrene-acrylate latex, silane, cationic modified silanes, hydrophobic particles and organosilicons among others for performance against liquids, preferably SA-latex. The hydrophobic agent of the liquid-resistant layer is added in amounts to overcome any hydrophilic character of other components that may be present in the layer composition, such as e.g. binders and / or optional crosslinkers etc., resulting in that the surface of the liquid-resistant layer preferably presents a water-contact angle above 100°, suitable above 105° based on the ISO standard TC 6 / SC 2 / WG 41: Paper and board - Measurement of water contact angle by optical methods.

[0040] In some embodiments, the hydrophobic agent of the liquid-resistant layer is further combined with a binder or carrier and / or optionally also one or more additional property-enhancing agents, for example in the form of a crosslinker and / or a fixator and / or flocculant. In some embodiments, the binder is selected from the group consisting of water-dispersible and / or water-soluble polymers, preferably selected from the group consisting of water-dispersible polysaccharides and water-soluble polysaccharide derivatives, more preferably selected from the group consisting of water-soluble starch, water-dispersible starch derivatives, and water- dispersible cellulose derivatives. In some embodiments, the binder is selected from the group consisting of water-soluble starch and water-soluble starch derivatives. In some embodiments, the binder is a hydrophobically modified polysaccharide, such as n-octenyl succinic anhydride modified starch (n-OSA starch), or an ethyl- or methyl-modified polysaccharide, such as an ethyl- or methyl-modified cellulose. Furthermore, in some embodiments, the crosslinker is selected from the group consisting of polyamide-epichlorohydrin (PAE), and polyfunctional organic acids or aldehydes, such as citric acid, glyoxal, and glutaraldehyde.

[0041] The hydrophobicity of the liquid-resistant layer can also be induced by application of various varnishes, water-based or organic solvent-based compositions. Varnish is also referring to dispersions, i.e. not fully solved compounds. It can further include cellulose-based derivatives.

[0042] Said liquid-resistant layer may be applied in any conventional way, on-line as well as off-line, in one or multiple layers such as 2-3 layers on top of each other. Examples of conceivable coating methods include surface sizing preferably by using film size press, blade coaters, curtain coaters or spray coaters, and various printing or off-line coaters such as gravure, reverse gravure and flexography.

[0043] Like the sealant layer protecting against moisture penetration, the liquid-resistant layer’s applied amount is maintained between 0.2 - 5 g / m2, preferably lower than 3 g / m2.

[0044] One advantageous aspect of the invention lies in its environmental sustainability credentials since the inventive paper or paperboard does not have a plastic coating-layer and it has high repulpability, which facilitates recycling. Repulping involves breaking down paper and paperboard products into pulp to create new products thereof. In some embodiments, the paper or paperboard has a total reject according to PTS RH 021 / 97 test method for Category II products below 5 %, preferably below 1 %. Furthermore, the paper or paperboard is preferably compostable, and more preferably also home compostable. Compostable materials are those that can biodegrade in a composting system, which is a controlled environment designed to facilitate the decomposition of organic matter. Composting involves the breakdown of organic materials, such as food waste and certain biodegradable products, into nutrient-rich compost that can be used to enrich soil and promote plant growth. Home compostable materials are designed to break down at lower temperatures and shorter timeframes compared to industrial compostable materials, making them suitable for household composting systems. In some embodiments, the paper or paperboard is compostable as determined according to standard ASTM D6868-11. In some embodiments, the paper or paperboard is compostable as determined according to standard EN 13432. In embodiments, the container is home compostable, preferably according to the Australian standard AS 5810.

[0045] The invention also extends to a method for manufacturing paper or paperboard according to the invention. This involves forming a cellulose-based substrate from a cellulose furnish, followed by application of at least one sealant layer on the first main surface of the substrate to protect against moisture penetration. Next, at least one liquid-resistant layer is applied on top of the existing sealant layer to protect against liquid penetration.

[0046] The paper or paperboard according to the invention can be used for manufacturing containers wherein the first main surface which is applied with sealant- and liquid resistant layers forms an inside surface of the container offering resistance against both moisture and liquid ingress. One example of a container formed from paper or paperboard according to the first aspect is a paper cup for containing hot liquid such as hot tea or coffee.

[0047] Examples

[0048] In the following examples, reference is made to Figs. 1 and 2, which are schematic cross-sectional views of paper or paperboard according to two board-structure examples according to the invention. Fig. 1 shows a moisture- and liquid-resistant paper or paperboard 1 comprising an internally sized cellulose-based substrate 2 with a basis weight between 100-500 g / m2and a density between 400-850 kg / m3. The substrate 2 may be single-ply or multiply. The substrate comprises a first main surface 20 and a second main surface 21. A sealant layer 3 protecting the substrate against damaging moisture penetration is applied on said first main surface 20 of the substrate 2. The sealant layer 3 provides the function of at least substantially reducing penetration of moisture into the substrate 2. On top of said sealant layer 3, there is applied a liquid-resistant layer 4 protecting the substrate 2 against liquid penetration.

[0049] Fig. 2 shows an alternative arrangement of a paper or paperboard according to the invention. In this arrangement, a sealant layer 3, as described for Fig. 1, is applied to both sides of the paper substrate 2. A liquid-resistant layer 4 as described for Fig. 1 , is further applied to each of the sealant layers 2.

[0050] According to the invention, both the moisture- and liquid-resistant layers 3, 4 are made from unmodified and / or modified renewable polymers, preferably in amounts ranging between 50-100 wt% calculated on the total dry weight of said barrier layers. In addition, the paper- or paperboard 1 has a total renewable content >90 wt% as calculated on the total dry weight of the paper- or paperboard.

[0051] In the following, three non-limiting examples are provided of compositions for the sealant layer and its combination with the liquid-resistant layer. In addition to what has already been mentioned, these combinations offer benefits in terms of simplified processing and improved cost competitiveness.

[0052] 1)

[0053] The first main surface of a 3-ply board structure is surface-sized by applying a mixture of a binder that consists of 90:10 weight ratio of n-OSA starch and carboxymethylated cellulose (CMC) to which 10 wt% PAE and 2 wt% AKD are added, based on total solids content of the binder, by using a size press. The pH of such mixture is 8, adjusted by sodium bicarbonate. The surface sizing is applied in an amount of around 2.5 gsm based on its dry weight. The treated board is dried to a moisture content <10% prior to application of the liquid-resistant layer with 3 gsm dry weight to the first and second main surface. The liquid-repellant layer is composed of 75 wt% of low-cationic starch and 25 wt% of carnauba wax.

[0054] 2) The first main surface of a 3-ply board structure is surface sized by applying a mixture of n-OSA starch that further contains 5 wt% glyoxal; and 10 wt% SA-latex based on starch solids content, using a size press. The pH of such mixture is 4. Surface sizing is applied in an amount of around 2.5 gsm. The moisture content of the board material is <10% prior to that 3 gsm of the liquid-resistant layer is applied to the first main surface by applying a water-repellent coating that is composed of 70 wt% of a styrene-based latex and 30 wt% of a wax.

[0055] 3)

[0056] The first main surface of a 3-ply board structure is surface sized by applying a mixture of n-OSA starch that further contains 25 wt% citric acid and 10 wt% SA- latex based on starch weight, using a size press. The pH of such mixture is 4. The surface size coat weight is 2.5 gsm. The moisture content of the board material is <10% prior to that 3 gsm of the liquid-resistant layer is applied to the first main surface by printing of a liquid-repellant varnish comprising at least 30 wt% of a renewable polymer.

[0057] The moisture- and liquid-resistant paper or paperboard 1 is suitable for use as packaging material intended for contact with food and liquids, such as hot liquids. Thanks to the combined moisture- and liquid-resistant layers, the material provides a moderate barrier without use of any plastic barrier layer, and thus may offer a solution for replacing products which today require >5 wt% plastic content, for example hot liquid cups.

[0058] 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 will 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.

Claims

CLAIMS1. A moisture- and liquid-resistant paper or paperboard, comprising:-an internally-sized cellulose-based substrate (2) with a basis weight between 100- 500 g / m2and a density between 400-850 kg / m3, said substrate having a first main surface (20) and a second main surface (21);-at least one sealant layer (3) applied on said first main surface (20) of the substrate (2) protecting the substrate at least against moisture penetration;-at least one liquid-resistant layer (4) applied on said sealant layer (3), protecting the substrate at least against liquid penetration; wherein:-said sealant layer (3) is made up by unmodified and / or modified renewable polymers in an amount of 70-100 wt% calculated on the total dry weight of said layer;-liquid-resistant layer (4) is made up by unmodified and / or modified renewable polymers in an amount of 30-100 wt% calculated on the total dry weight of said layer;-said moisture- and liquid-resistant paper- or paperboard (1) has a total renewable content >90 wt%, preferably >95 wt% as calculated on the total dry weight of the paper or paperboard; and-wherein the moisture- and liquid-resistant paper or paperboard (1) comprises:-a water Cobb300 value <30 g / m2, preferably <25 g / m2according to ISO 535:2023;-a modified water Cobb300 measurement at 80°C with blotting paper <30 g / m2, preferably <25 g / m2according to ISO 535:2023;-a Cobb-Unger (15s) value <10 according to SCAN-P 37:77; and-a water vapor transmission rate (WVTR) <35 g / m2 / h at 38°C and 80% RH according to standard ASTM E96-00.

2. The paper or paperboard according to claim 1, wherein the sealant layer (3) and liquid-resistant layer (4) are made up by unmodified and / or modified renewable polymers in an amount of 75-100 wt%, more preferably 85-100 wt% as calculated on the total dry weight of said layers.

3. The paper or paperboard according to claim 1 or 2, wherein the sealant layer (3) comprises unmodified or modified polysaccharides.

4. The paper or paperboard according to any one of claims 1, 2 or 3, wherein the sealant layer (3) comprises at least one renewable polymer selected from the group comprising: MFC, modified starch such as hydroxypropyl starch, cellulose derivatives such as CMC and methyl cellulose, chitosan and guar gum.

5. The paper or paperboard according to any one of the previous claims, wherein the sealant layer (3) further comprises a crosslinker selected from the group consisting of polyamide-epichlorohydrin (PAE); polyfunctional organic acids or aldehydes, such as citric acid, tartaric acid, glyoxal, glutaraldehyde and sodium trimetaphosphate; and zirconium carbonates, such as ammonium zirconium carbonate (AZC) and potassium zirconium carbonate (KZC).

6. The paper or paperboard according to any one of the previous claims, wherein the sealant layer further comprises at least one hydrophobic agent, such as 0.1-10 wt% of a hydrophobic agent based on the total dry weight of the sealant layer preferably selected from the group consisting of rosin, wax, AKD and / or SA- latex.

7. The paper or paperboard according to any one of the previous claims, wherein the sealant layer (3) further comprises 0.1-20 wt% of at least one impermeable particle selected from the group consisting of clay, silica, calcium carbonate, cellulose nanocrystals and / or combinations thereof.

8. The paper or paperboard according to any one of the previous claims, wherein the sealant layer (3) is applied in amounts between 0.2 - 5 g / m2, preferably 0.5 - 3 g / m2.

9. The paper or paperboard according to any one of the previous claims, wherein the liquid-resistant layer (4) comprises at least one hydrophobic agent,preferably in amounts of at least 10 wt% based on the total dry weigh of the layer, where said hydrophobic agent preferably is selected from the group comprising: rosin resin, ASA, AKD, wax, fatty acids and fatty acid derivatives, water-dispersible latex such as styrene-acrylate latex, silane, cationic modified silanes, hydrophobic particles and organosilicons.

10. The paper or paperboard according to any one of the previous claims, wherein the liquid-resistant layer (4) further comprises a binder and optionally one or more additional property-enhancing agent / s.

11. The paper or paperboard according to any one of the previous claims, wherein the liquid-resistant layer (4) is composed of a varnish or lacquer.

12. The paper or paperboard according to any one of the previous claims, wherein the liquid-resistant layer (4) is applied in amounts between 0.2 - 5 g / m2, preferably 0.2 - 3 g / m2or 0.3 - 3g / m2.

13. The paper or paperboard according to anyone of the previous claim, wherein the substrate (2) comprises more than one ply.

14. The paper or paperboard according to any one of the preceding claims, wherein the paper or paperboard has a total reject according to PTS RH 021 / 97 test method for Category II products below 5 %, preferably below 1 %, and more preferably below 0.5 %.

15. The paper or paperboard according to any one of the preceding claims, wherein the paper or paperboard is compostable as determined according to standard ASTM D6868-11.

16. The paper or paperboard according to any one of the preceding claims, wherein the paper or paperboard has a basis weight above 150 g / m2.

17. The paper or paperboard according to any one of the previous claims, wherein at least one sealant layer protecting the substrate against moisture penetration applied on said second main surface (21) of the substrate (2).

18. The paper or paperboard according to claim 17, wherein at least one liquid-resistant layer protecting the substrate against liquid penetration is applied on top of said sealant layer at said second main surface (21) of the substrate (2).

19. The paper or paperboard according to any one of the previous claims, wherein the paper or paperboard is free from any heat-sealable barrier layer.

20. The paper or paperboard according to any one of the previous claims, which is free from pigment coating.

21. A method for manufacturing a moisture-resistant and liquid-resistant paper or paperboard according to anyone of claims 1-20, said method comprising: a) forming a cellulose-based substrate (2) from a cellulose furnish; b) applying on said first main surface (20) of the substrate (2), at least one sealant layer (3) protecting the substrate against moisture penetration; and c) apply on said sealant layer (3), at least one liquid-resistant layer (4) protecting the substrate against liquid penetration.

22. A method according to claim 20, wherein the substrate with the applied sealant layer (3) is dried to a moisture content <10 wt% before application of said liquid-resistant layer (4).

23. A container formed from liquid-resistant multiply paper or paperboard according to any one of claims 1-20 or obtained by the method according to claim 15, wherein the outermost surface of the barrier layered first main surface (20) of the substrate (2) forms an inside surface of the container.

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