Liquid resistant multilayer sheet paper and paperboard

Abstract

The present invention relates to a liquid resistant multilayer sheet paper or paperboard comprising: a cellulose-based back ply, wherein the back ply comprises at least two different internal sizing agents in a total amount of 2 - 10 kg / ton, based on the total dry weight of the back ply; a cellulose-based top ply, wherein the top ply comprises a single internal sizing agent in a total amount of 0.1 - 5 kg / ton, based on the total dry weight of the top ply, and wherein the total amount of internal sizing agent in the top ply is lower than the total amount of internal sizing agent in the back ply; and a first surface sizing layer applied on the outermost surface of the back ply, wherein the first surface sizing layer has a coating weight of 0.5 - 3 g / m 2 and comprises at least one hydrophobic surface sizing agent and at least one binder. The present invention also relates to a method of manufacturing a liquid resistant multilayer sheet paper or paperboard.

Description

Technical Field

[0001] This disclosure relates to repulpable and compostable liquid-resistant paper or paperboard suitable for use in single-use packaging containers (e.g., cups, boxes, and trays) for food and beverages. Background Technology

[0002] Liquid resistance, and especially water resistance, is an important property in many paper and paperboard applications. Important examples include single-use packaging containers for food and beverages, such as cups, boxes, and trays.

[0003] Plastic coating of paper and paperboard is often used to combine the mechanical properties of paper and paperboard with the barrier and transformation properties of plastic films (such as thermal sealability and shape forming). However, from a sustainability and recycling perspective, plastics are undesirable and negatively impact the efficiency of repulping pre- and post-consumer waste. Furthermore, only a small number and less common types of plastics can be considered compostable, particularly for home composting. Additionally, plastic coating typically must be done offline, significantly increasing production time and costs.

[0004] Paper and paperboard used in food and beverage packaging applications are typically hydrophobically treated with hydrophobic agents (often also called sizing agents) to increase resistance or repulsion to wetting and penetration of water and other liquids into the cellulose-based substrate. This hydrophobic treatment (often called sizing) is important for maintaining the function of the substrate under wet or damp conditions. There are two main types of sizing: internal sizing and surface sizing. When a sizing agent is added to the cellulose formulation, it is called internal sizing, and when a sizing agent is applied to the surface of the paper or paperboard, it is called surface sizing. Common internal sizing agents include alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), and rosin. Common surface sizing components include starch and starch derivatives, styrene maleic anhydride, polyurethane, styrene acrylate (SA), and acrylic copolymers.

[0005] It is also known that traditional sizing concepts do not provide any permanent water or liquid resistance, but the technical effect is more often used to provide controlled wetting behavior of the substrate.

[0006] To achieve repulpable and compostable paper and paperboard suitable for use in single-use packaging containers, it is desirable to replace plastic coatings with sizing methods. However, existing sizing concepts are insufficient to meet the requirements of food and beverage packaging applications, including acceptable product performance, recyclability, and compostability, when the plastic coating is removed. Increasing the dosage of sizing agent can be one approach to improve product performance, but this improvement typically comes at the cost of reduced recyclability and / or compostability. Furthermore, simply increasing the dosage is insufficient to provide acceptable product performance for different types of food and beverages.

[0007] Another issue related to sizing agents is the migration of sizing chemicals, which can lead to deposition on production machinery and / or the final product, limiting technical feasibility and industrial applicability. From a food safety perspective, sizing agent migration can also be harmful, as each sizing agent has its own usage restrictions.

[0008] Sizing agents can also affect the friction of paper or paperboard, resulting in excessively low friction. This can in turn lead to difficulties in handling and / or converting paper and paperboard, and is exemplified by so-called telescope reels.

[0009] Further solutions are still needed to make paper and paperboard for food and beverage packaging applications liquid-resistant without compromising the material's repulping and compostability. The solution should be industrially applicable, preferably avoiding problems such as sizing agent migration or excessively low friction, and the resulting paper or paperboard should be easily convertible and safe for food contact use. Summary of the Invention

[0010] The purpose of this disclosure is to provide a liquid-resistant paper or paperboard with good repulping and compostability.

[0011] Another objective of this disclosure is to provide a liquid-resistant paper or paperboard with good repulping and compostability, which can be used in food and beverage packaging applications.

[0012] Another object of this disclosure is to provide a liquid-resistant paper or cardboard for food and beverage packaging applications that is free of plastic coating.

[0013] The above objectives, as well as other objectives that a person skilled in the art would recognize based on this disclosure, are achieved through various aspects of this disclosure.

[0014] According to a first aspect shown herein, a liquid-resistant multiply paper or paperboard is provided, comprising:

[0015] Cellulose-based backsheet, wherein the backsheet contains at least two different internal sizing agents in a total amount of 2-10 kg / ton, based on the total dry weight of the backsheet;

[0016] A cellulose-based top sheet, wherein the top sheet contains a single internal sizing agent in a total amount of 0.1-5 kg / ton, based on the total dry weight of the top sheet, and wherein the total amount of internal sizing agent in the top sheet is less than the total amount of internal sizing agent in the back sheet; and

[0017] A first surface adhesive layer is applied to the outermost surface of the backsheet, wherein the first surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

[0018] Paper generally refers to a material made from pulp of wood or other fibrous materials containing cellulose fibers in sheets or rolls, used for writing, drawing or printing, or as packaging material.

[0019] Cardboard generally refers to sturdy, thick paper or cardboard used, for example, in containers (such as cups, boxes, and trays) and / or other types of packaging for food and beverages.

[0020] Paper or paperboard can typically be a single-ply material or a multi-ply material containing two or more layers. Paperboard can be bleached or unbleached, pigment-coated or uncoated, and is produced in a variety of thicknesses depending on the requirements of the end use.

[0021] The multi-layer sheet paper or paperboard disclosed herein comprises at least two layers. The paper or paperboard can be manufactured in a paper machine or paperboard machine suitable for manufacturing multi-layer sheet paper or paperboard. Paper machines or paperboard machines for manufacturing multi-layer sheet paper or paperboard are well known in the art. Typically, the machine layout includes a feed handling section, a wet-end section, a press section, a drying section, and optionally a calendering and / or coating section. In the wet-end section, the layers may be formed individually using different headboxes and stacked in a wet state, or formed together using multi-layer sheet headboxes. If formed individually, these layers are typically stacked before entering the press section of the paper machine.

[0022] This disclosure is based on the understanding that the aforementioned problems can be solved by differentiating the sizing processes in different layers of multilayer paper or paperboard in a controlled manner, thereby combining resistance to a wide range of liquids and food types with good repulping and compostability. Multilayer paper or paperboard comprises at least two cellulose base sheets, a cellulose-based back sheet, and a cellulose-based top sheet, and a surface sizing layer applied to the outermost surface of the back sheet. The cellulose base sheets preferably comprise sheets or webs of material formed primarily of wood pulp or other fibrous materials containing cellulose fibers.

[0023] It has been found important to provide a backing sheet comprising a combination of at least two different internal sizing agents and having a surface sizing layer comprising at least one hydrophobic surface sizing agent applied to its outermost surface, intended for direct contact with the packaged food or beverage. The use of a combination of at least two different internal sizing agents in the backing sheet, combined with the surface sizing layer, allows for combinations of different sizing agents that provide resistance to a wide range of different liquids and food types, such as hot and cold beverages, hot and cold foods, frozen foods, and complex food or liquid mixtures with different phases (e.g., water, grease, oil, or emulsion phases). The combination of at least two different internal sizing agents in the backing sheet, combined with the surface sizing layer preferably applied by a sizing pressing method, also supports the retention of sizing agents in the paper or paperboard and reduces potential migration of sizing agents, as the amount of each sizing agent can be reduced or maintained at a relatively low level, and because the surface sizing layer acts as a barrier against the migration of internal sizing agents.

[0024] When different sizing agents are added simultaneously to cellulose formulations during the raw material processing or wet-end section of paper or paperboard manufacturing, competitive adsorption between sizing agents can occur. Therefore, if the dosage of one sizing agent increases, the retention of another sizing agent can become reduced. Since adjusting the retention system is insufficient to address this problem, surface sizing becomes a viable method for adding additional hydrophobic sizing agents to paper or paperboard, improving the retention and dosage of a particular hydrophobic sizing agent or providing the possibility of introducing other types of sizing agents with different functions to further reduce the penetration of different liquids and food types.

[0025] In top sheets not intended for direct contact with packaged food or beverages, a lower amount of a single internal sizing agent provides moderate liquid resistance, but offers good printability, high resizing and compostability.

[0026] In addition to the back sheet and the top sheet, the paper or paperboard may further comprise at least one cellulose-based intermediate sheet disposed between the top sheet and the back sheet. In some embodiments, the paper or paperboard further comprises:

[0027] A cellulose-based intermediate layer sheet is disposed between the top layer sheet and the back layer sheet, wherein the intermediate layer sheet contains a single internal sizing agent in a total amount of 0.1-5 kg / ton based on the total dry weight of the intermediate layer sheet, and wherein the total amount of internal sizing agent in the intermediate layer sheet is less than the total amount of internal sizing agent in the back layer sheet, and preferably more than the total amount of internal sizing agent in the top layer sheet.

[0028] Additional or multiple intermediate sheets allow for further differentiation of the adhesive application process.

[0029] In addition to the first surface sizing layer applied to the outermost surface of the back sheet, the paper or paperboard may further include a second surface sizing layer applied to the outermost surface of the top sheet.

[0030] Therefore, in some embodiments, the paper or paperboard further comprises:

[0031] A second surface adhesive layer is applied to the outermost surface of the top sheet, wherein the second surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

[0032] A second surface sizing layer applied to the outermost surface of the top sheet can add further liquid resistance to surfaces of paper or paperboard that are not intended to come into direct contact with the packaged food or beverage (often also known as the printed surface).

[0033] Each cellulose base sheet of paper or paperboard may contain a composition of pulp fibers, such as bleached and / or unbleached Kraft pulp, sulfite pulp, dissolving pulp, thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), high-temperature CTMP (HT-CTMP), pressure-ground wood pulp (PGW), and / or mixtures thereof. In some embodiments, the paper or paperboard contains a significant amount of recycled cellulose fibers, such as waste paper or fibers recycled from pre- or post-consumer waste. In some embodiments, the amount of recycled cellulose fibers in the paper or paperboard, based on the total dry weight, 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%. The paper or paperboard product may also contain only recycled fibers. Recycled cellulose is particularly preferred in the interlayer sheet. Thus, in some embodiments, the cellulose-based interlayer sheet contains a significant amount of recycled cellulose fibers. In some embodiments, the amount of recycled cellulose fibers in the interlayer sheet 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 interlayer sheet. The interlayer sheet may also contain only recycled fibers.

[0034] In some embodiments, the paper or paperboard has a back sheet comprising bleached kraft pulp, an intermediate sheet comprising a mixture of bleached kraft pulp and CTMP, and a top sheet comprising bleached kraft pulp, wherein the intermediate sheet has a lower density than the back sheet and the top sheet, respectively. The lower-density intermediate sheet may typically have a density of 750 kg / m³. 3 Below, 700 kg / m is preferred. 3 Below, or at 650 kg / m 3 Below, or at 600 kg / m 3 Below, or at 550 kg / m 3 Below or at 500 kg / m 3 The following densities. In examples, lower-density intermediate sheets may have a density of 550-650 kg / m³. 3 The density between the layers. Higher-density backing and top layers typically have at least 100 kg / m³ higher density than intermediate layers. 3 Preferably, it is at least 200 kg / m higher than the intermediate layer. 3 The density. In some embodiments, the total weight of the liquid-resistant multilayer paper or paperboard according to the invention is 600-900 kg / m³. 3 Between, for example, 700-850 kg / m 3 between.

[0035] The multilayer sheets or paperboards disclosed herein are liquid resistant. The term "liquid resistant" generally means that multilayer sheets or paperboards having internal sizing and surface sizing layers have greater resistance or repulsion to liquid penetration and absorption than the same multilayer sheets or paperboards without said internal sizing and surface sizing layers.

[0036] The multilayer sheets or paperboards of this disclosure are preferably at least water-resistant. The term "water-resistant" generally means that multilayer sheets or paperboards having an internal sizing agent and a surface sizing agent have a higher resistance to water absorption than the same multilayer sheets or paperboards without said internal sizing agent and surface sizing agent (e.g., expressed by the difference between water Cobb 300 and water Cobb 30 measured at 300 and 30 seconds respectively according to standard ISO 535:2014).

[0037] Liquid-resistant multilayer sheet paper or paperboard substrates are preferably suitable for use as packaging materials intended to come into contact with food and liquids. In some embodiments, cellulose-based substrates are used in single-use packaging containers (e.g., boxes, cups, lids, containers, and trays) for food and beverages.

[0038] Internal sizing agents are included in the backing sheet, top sheet, and optional intermediate sheets of paper or paperboard. Internal sizing agents are commonly used in paper or paperboard to control wetting. An internal sizing agent is a hydrophobic agent added to cellulose formulations during the raw material handling or wet-end portion of the paper or paperboard manufacturing process. The most common internal sizing agents are alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), and rosin sizing agents, the latter being used as a soap glue or rosin emulsion or as a cationic or anionic dispersion. However, other agents that increase resistance to liquid penetration into cellulose-based substrates, such as water and other liquids, can also be used as internal sizing agents. Examples include natural waxes, fatty acids, fatty acid derivatives, and / or combinations thereof. Internal sizing agents are typically added to cellulose formulations in emulsion form or as a dispersion.

[0039] In some embodiments, the internal sizing agents in the back sheet, top sheet, and optional intermediate sheet of the paper or paperboard are each selected from alkyl ketene dimers (AKD), alkenyl or alkyl succinic anhydrides (ASA), rosin (soap or emulsion), stearic anhydride, and waxes, wherein said waxes have a melting temperature above 50°C, above 55°C, or above 60°C. The waxes are preferably natural waxes, i.e., waxes derived from natural sources (e.g., plant, animal, or mineral). Non-limiting examples of natural waxes include beeswax, carnauba wax, and shellac wax. Unless otherwise specified, the melting temperature of the wax is determined according to standard ASTM D3418-21.

[0040] In some embodiments, the internal sizing agents in the back sheet, top sheet, and optional intermediate sheet of the paper or paperboard are each selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and rosin.

[0041] In some embodiments, each internal sizing agent in the backing sheet is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature above 50°C, 55°C, or 60°C. In some embodiments, the backing sheet comprises a dual sizing agent selected from AKD and rosin, ASA and rosin, ASA and AKD, or AKD and stearic anhydride. These combinations of internal sizing agents are particularly useful, but not limited to, because the liquid resistance properties of different internal sizing agents complement each other.

[0042] Different internal sizing agents can be used in different amounts due to their different chemical and physical properties. Internal sizing agents are typically added to cellulose formulations in the form of emulsions or dispersions. Internal sizing agents can be added to cellulose formulations sequentially, simultaneously, or as premixed blends. Preferably, they are added sequentially or simultaneously. If premixed, the emulsions or dispersions preferably have similar charge or net charge signs and are electrostatically stable, such that the mixture is colloidally stable when the emulsions are blended together.

[0043] In some implementations, the backing sheet contains an internal sizing agent in a total amount of 2-8 kg / ton, based on the total dry weight of the backing sheet.

[0044] In some implementations, the backing sheet contains 1-4 kg / ton of AKD, based on the total dry weight of the backing sheet.

[0045] In some implementations, the backing sheet contains 1-2 kg / ton of ASA, based on the total dry weight of the backing sheet.

[0046] In some implementations, the backing sheet contains 2-6 kg / ton of rosin, based on the total dry weight of the backing sheet.

[0047] In some embodiments, the internal sizing agent in the top sheet is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature above 50°C, above 55°C, or above 60°C.

[0048] In some embodiments, the top sheet contains an internal sizing agent in a total amount of 1-6 kg / ton, preferably 1-4 kg / ton, based on the total dry weight of the top sheet.

[0049] In some implementations, the top layer contains 1-4 kg / ton of AKD, based on the total dry weight of the top layer.

[0050] In some implementations, the top layer contains 1-2 kg / ton of ASA, based on the total dry weight of the top layer.

[0051] In some implementations, the top layer contains 2-6 kg / ton of rosin, based on the total dry weight of the top layer.

[0052] In some embodiments, the internal sizing agent in the interlayer sheet is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature of 50°C or higher, more preferably 55°C or higher, and most preferably 60°C or higher.

[0053] In some embodiments, the interlayer sheet contains an internal sizing agent in a total amount of 1-6 kg / ton, preferably 1-4 kg / ton, based on the total dry weight of the interlayer sheet.

[0054] In some implementations, the interlayer contains 1-4 kg / ton of AKD, based on the total dry weight of the interlayer.

[0055] In some implementations, the interlayer contains 1-2 kg / ton of ASA, based on the total dry weight of the interlayer.

[0056] In some implementations, the interlayer sheet contains 2-6 kg / ton of rosin, based on the total dry weight of the interlayer sheet.

[0057] To improve the wet strength of paper or paperboard, internal sizing agents can be combined with wet strength agents. Wet strength agents improve the tensile properties of paper or paperboard in a wet state by, for example, covalent bonding with cellulose fibers and by forming a cross-linked network within the fiber network. This cross-linked network does not break down upon wetting and reduces swelling, thereby also reducing liquid absorption. Common wet strength agents include urea-formaldehyde (UF), melamine-formaldehyde (MF), polyamide-epimerol (PAE), glyoxal, cross-linked cationic polyalkyleneamines, vinylformamide-vinylamine copolymers, dialdehyde starch, and copolymers of acrylamide and diallylamine. Other wet strength agents provide wet strength through other mechanisms, and some of these wet strength agents may also have temporary wet strength functions, such as glyoxalized polyacrylamide (G-PAM). In some embodiments, the paper or paperboard contains 0.1-10 kg / ton of wet strength agent, preferably 0.1-4 kg / ton, based on the total dry weight of the paper or paperboard.

[0058] In some embodiments, the backsheet is formed from pulp having a higher Schopper Riegler (SR) value (as determined according to standard ISO 5267-1) than the pulp used for the top sheet and the pulp used for the optional intermediate sheet (when present). Pulp with a higher Schopper Riegler value generally has a higher internal sizing agent retention than pulp with a lower Schopper Riegler value. The higher Schopper Riegler value of the backsheet pulp can be obtained, for example, by refining or beating the pulp, or by adding a fine cellulose material (e.g., fine cellulose particles, highly refined cellulose, or microfibrillated cellulose) to the pulp. The fine cellulose material is preferably obtained from bleached or unbleached softwood or hardwood kraft pulp. As determined according to standard ISO 5267-1, the fine cellulose material preferably has a Schopper Riegler value in the range of 30-85, preferably in the range of 55-85. The fine cellulose material is preferably present in the backsheet in an amount of 0.1-15 wt%, based on the total dry weight of the backsheet. To prevent the board material from curling, the top sheet can also be formed from pulp with a high Schopper Riegler (SR) value. The high Schopper Riegler value of the top sheet pulp can be obtained in the same way as the back sheet.

[0059] Multilayer sheets of paper or paperboard include a first surface sizing layer applied to the outermost surface of a back sheet, and optionally a second surface sizing layer applied to the outermost surface of a top sheet. Surface sizing enhances the surface properties of the paper or paperboard and, depending on the type of surface sizing layer applied, can make the surface more resistant to water penetration, improve printability, and increase the overall surface strength and appearance of the material. The primary purpose of the surface sizing layer of the paper or paperboard of the present invention is to improve the liquid resistance of the paper or paperboard, particularly for contact with hot and cold foods and beverages. Liquid resistance is improved by increasing hydrophobicity and by sealing the surface by reducing the size and number of pores on the surface of the fibrous matrix. Surface sealing also helps prevent compounds from migrating from the paper or paperboard sheets to the food or beverages in contact with the paper or paperboard surface, especially when using hot foods and beverages. The surface sizing layer can also facilitate subsequent conversion of multilayer sheets of paper or paperboard by improving adhesion to adhesives used to form containers from the paper or paperboard. The surface strength provided by the surface sizing layer facilitates the application of adhesives and also reduces adhesive absorption into the paper or paperboard.

[0060] Surface sizing is typically achieved by applying a sizing composition, which contains chemicals that form a film on the surface of paper or paperboard fibers. The two main methods for applying a surface sizing layer are sizing press and membrane press, but surface sizing layers can also be applied using a wet-end applicator or by any other surface sizing, coating, or spraying method known in the paper industry. Sizing press involves applying a surface sizing composition directly to the surface of the paper or paperboard as it passes through a set of rolls. First, the paper or paperboard is coated with a liquid mixture containing the surface sizing composition. Excess liquid mixture is then removed by passing the paper or paperboard through the gap between two rolls, leaving a thin, uniform sizing layer on the surface of the paper or paperboard fibers. Another option is to apply a flooded gap. In membrane press, a membrane press is typically used to form a film of the surface sizing composition separately, where a film is produced on a transfer roll using bars, doctor blades, or metering rolls. Pressure is then used to transfer the film onto the surface of the paper or paperboard. In addition to layers obtained through conventional surface sizing methods, the term surface sizing as used herein is also intended to cover other methods for providing a thin, water-resistant layer on a paper or paperboard surface without forming a plastic coating. Accordingly, the term surface sizing as used herein is also intended to cover impregnating a surface with a hydrophobic agent and applying a hydrophobic agent or sizing agent wet-on-wet.

[0061] The formulation of surface sizing compositions and surface sizing layers depends on the specific requirements of the paper or paperboard, such as desired levels of water resistance, printability, and strength. The selection of hydrophobic surface sizing agents and binders, as well as optional other additives, can be adjusted to meet the requirements of different paper or paperboard grades and end-use applications.

[0062] The first surface adhesive layer has a density of 0.5-3 g / m². 2 The coating weight comprises at least one hydrophobic surface sizing agent and at least one binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 1-80 wt% hydrophobic surface sizing agent and 20-99 wt% binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 1-50 wt% hydrophobic surface sizing agent and 50-99 wt% binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 1-15 wt% hydrophobic surface sizing agent and 75-99 wt% binder.

[0063] In some embodiments, the first surface sizing layer comprises at least two hydrophobic surface sizing agents, such as two or three hydrophobic surface sizing agents.

[0064] In some embodiments, each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, latex dispersions, styrene-maleic anhydride copolymers (SMA), styrene-acrylate copolymers (SAE), modified polyurethane dispersions, and combinations thereof.

[0065] In some embodiments, each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and latex dispersions and combinations thereof.

[0066] In some embodiments, each binder is selected from water-soluble polymers, preferably from polyvinyl alcohol (PVOH), water-soluble polysaccharides and water-soluble polysaccharide derivatives, and more preferably from water-soluble starch, water-soluble starch derivatives and water-soluble cellulose derivatives. In some embodiments, each binder is selected from 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 ethyl or methyl modified cellulose.

[0067] In some implementations, the first surface adhesive layer further comprises 0.1-20 wt% filler based on the total dry weight of the first surface adhesive layer.

[0068] In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer further comprises 0.1-10 wt% of fine cellulose material, preferably selected from cellulose fine particles, highly refined cellulose, microfibrillated cellulose (MFC), cellulose microcrystals, and cellulose nanocrystals.

[0069] In some embodiments, the first surface adhesive layer further comprises 0.1-20 wt% of a crosslinking agent based on the total dry weight of the first surface adhesive layer. In some embodiments, the crosslinking agent is selected from polyamide-epimeric alcohol (PAE) and polyfunctional organic acids or aldehydes, such as citric acid, glyoxal, and glutaraldehyde.

[0070] In some embodiments, the first surface sizing layer contains 0.1-10 wt%, preferably 0.1-4 wt%, of a wet strength agent based on the total dry weight of the first surface sizing layer.

[0071] In some embodiments, the first surface sizing layer further comprises 0.1-5 wt% of other additives based on the total dry weight of the first surface sizing layer. Other additives may include, but are not limited to, fixatives such as polyethyleneamine (PVAm), polyaluminum chloride (PAC), and alum.

[0072] The second surface adhesive layer may be further defined as described with reference to the first surface adhesive layer. The coating weight and composition of the second surface adhesive layer may be the same as or different from those of the first surface adhesive layer.

[0073] In a more specific embodiment, the liquid-resistant multilayer sheet or paperboard comprises:

[0074] Cellulose-based backsheet, wherein the backsheet contains 2-10 kg / ton, preferably 5-8 kg / ton, of AKD and rosin, based on the total dry weight of the backsheet;

[0075] A cellulose-based interlayer sheet, wherein the interlayer sheet contains 0.2-5 kg / ton, preferably 2-4 kg / ton, of rosin based on the total dry weight of the interlayer sheet, and wherein the total amount of internal sizing agent in the interlayer sheet is less than the total amount of internal sizing agent in the back layer sheet; and

[0076] A cellulose-based top sheet, wherein the top sheet contains a single internal sizing agent in a total amount of 0.1-5 kg / ton, preferably 1-3 kg / ton, based on the total dry weight of the top sheet, and wherein the total amount of internal sizing agent in the top sheet is less than the total amount of internal sizing agent in the intermediate layer sheet; and

[0077] A first surface adhesive layer is applied to the outermost surface of the backsheet, wherein the first surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight and comprising SA latex and at least one adhesive, and optionally

[0078] A second surface adhesive layer is applied to the outermost surface of the top sheet, wherein the second surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes SA latex and at least one adhesive.

[0079] In some embodiments, the backing sheet of the liquid-resistant multilayer paper or paperboard with surface sizing has a strength of 30 g / m². 2 The following is preferred at 25 g / m 2 Below, more preferably at 20 g / m 2 The following are the differences between water Cobb300 and water Cobb30 measured for 300 and 30 seconds respectively, according to standard ISO 535:2014.

[0080] In some embodiments, the backing sheet of the liquid-resistant multilayer paper or paperboard with surface sizing has a water penetration depth of less than 40 μm, preferably less than 30 μm, and more preferably less than 20 μm, said water penetration depth being optically determined by cross-sectional analysis of a sample treated with dyed water for 300 seconds according to standard ISO 535:2014.

[0081] In some embodiments, the backing sheet of the liquid-resistant multilayer paper or paperboard with surface sizing has a water contact angle of 90° or higher, preferably 100° or higher. In some embodiments, the contact angle difference between the top sheet and the backing sheet is >10°, more preferably >15°. Unless otherwise specified, the water contact angle is determined after 10 seconds using a 4 μL droplet and the Young-Laplace model as the water droplet model, according to the standard TAPPI T558 om-15 method.

[0082] In some embodiments, the backing sheet of the liquid-resistant multilayer paper or paperboard with surface sizing has a strength of <25 g / m² as determined by SCAN-P37:77. 2 More preferably <15g / m 2 or even better <10g / m 2 The Cobb-Unger 15 s value.

[0083] In a preferred embodiment, the multilayer sheet paper or paperboard does not contain a plastic layer, such as a plastic coating or plastic film layer formed by extrusion coating or dispersion coating, having a density of 5 g / m². 2 The above is usually closer to 8-15 g / m³. 2Or higher basis weights. As used herein, the term "plastic" generally refers to water-insoluble synthetic polymers, typically made from hydrocarbons such as ethylene, propylene, and other similar compounds. These plastics can be classified into various types based on their chemical composition and properties, including but not limited to polyethylene (PE), such as low-density polyethylene (LDPE) and high-density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC). Examples of common polymer compounds that can be used in the above-mentioned dispersion coatings are polyvinylidene chloride, poly(vinyl acetate), styrene-acrylic latex and styrene-butadiene latex, polyethylene, and these or other substances are used at least 50 wt% of the dispersion coating.

[0084] In some embodiments, based on the total dry weight of the paper or paperboard, the multilayer sheet or paperboard may contain an additional polymer compound (which may be defined as a plastic, such as processing chemicals, additives, binders and / or retention aids) in a total content of less than 5 wt%, preferably less than 1 wt%, and more preferably less than 0.5 wt%.

[0085] Multi-layer paper sheets or paperboards preferably have high repulping reproducibility, which facilitates recycling. Repulping involves breaking down paper and paperboard products into pulp to produce their new products. In some embodiments, for Class II products, according to the PTS RH 021 / 97 test method, the total scrap rate of multi-layer paper sheets or paperboards is less than 5%, preferably less than 1%, and more preferably less than 0.5%.

[0086] Multi-layered paper or paperboard is preferably compostable, and more preferably home compostable. Compostable material is a material that is biodegradable in a composting system, a controlled environment designed to promote the decomposition of organic matter. Composting involves breaking down 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 decompose at lower temperatures and in shorter timeframes compared to industrially compostable materials, making them suitable for home composting systems. In some embodiments, the paper or paperboard is compostable, as determined according to standard ASTM D6868-11.

[0087] In some implementations, the paper or paperboard has a density of 150 g / m². 2 The above basis weight. In some embodiments, the paper or paperboard has a basis weight of 200 g / m³. 2 The above are basis weights. In some embodiments, the paper or paperboard has a basis weight of 200-400 g / m³. 2 The basis weight is within the range of 220–320 g / m³. In some embodiments, the paper or paperboard has a basis weight of 220–320 g / m³. 2Basis weight within the range of 220 g / m³. It has been observed that... 2 The above weight results in good rigidity, which is advantageous when using this material for food and / or beverage packaging containers.

[0088] The basis weights of the backsheet, topsheet, and intermediate sheets can be the same or different. In some embodiments, the basis weights of the backsheet and topsheet are 20-100 g / m³, respectively. 2 Within this range. In some implementations, the basis weight of the intermediate layer sheet is 50-250 g / m³. 2 Within a certain range. In some embodiments, the backing sheet has a higher density but lower basis weight than the top sheet. This allows for a denser backing sheet while preventing curling of multiple layers of paper or paperboard due to density differences between the layers.

[0089] According to a second aspect thereof, a method for manufacturing liquid-resistant multilayer sheets or paperboards is provided, the method comprising:

[0090] a) A cellulose-based backsheet is formed from a first cellulose ingredient, wherein the first cellulose ingredient comprises at least two different internal sizing agents in a total amount of 2-10 kg / ton, based on the total dry weight of the first cellulose ingredient;

[0091] b) A cellulose-based top sheet is formed from a second cellulose formulation, wherein the second cellulose formulation contains a single internal sizing agent in a total amount of 0.1-5 kg / ton, based on the total dry weight of the second cellulose formulation, and wherein the total amount of internal sizing agent in the second cellulose formulation is less than the total amount of internal sizing agent in the first cellulose formulation; and

[0092] c) Form a first surface adhesive layer on the outermost surface of the backing sheet.

[0093] The first surface adhesive layer has a content of 0.5-3 g / m 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

[0094] In some implementations, the method further includes:

[0095] A cellulose-based intermediate layer is formed between the top layer and the back layer by a third cellulose ingredient, wherein the third cellulose ingredient contains a single internal sizing agent in a total amount of 0.1-5 kg / ton based on the total dry weight of the third cellulose ingredient, and wherein the total amount of internal sizing agent in the third cellulose ingredient is less than the total amount of internal sizing agent in the first cellulose ingredient, and preferably more than the total amount of internal sizing agent in the second cellulose ingredient.

[0096] In some implementations, the method further includes:

[0097] A second surface adhesive layer is formed on the outermost surface of the top layer, wherein the second surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

[0098] In some embodiments, each of the internal sizing agents in the first cellulose formulation is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature above 50°C, above 55°C, or above 60°C.

[0099] In some embodiments, the first cellulose ingredient comprises AKD and rosin, ASA and rosin, ASA and AKD, or AKD and stearic anhydride.

[0100] In some implementations, the first cellulose ingredient contains an internal sizing agent in a total amount of 2-8 kg / ton, based on the total dry weight of the first cellulose ingredient.

[0101] In some implementations, the first cellulose ingredient contains 1-4 kg / ton of AKD based on the total dry weight of the first cellulose ingredient.

[0102] In some implementations, the first cellulose ingredient contains 1-2 kg / ton of ASA based on the total dry weight of the first cellulose ingredient.

[0103] In some implementations, the first cellulose ingredient contains 2-6 kg / ton of rosin based on the total dry weight of the first cellulose ingredient.

[0104] In some embodiments, the internal sizing agent in the second cellulose formulation is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature above 50°C, above 55°C, or above 60°C.

[0105] In some embodiments, the second cellulose ingredient contains an internal sizing agent in a total amount of 1-6 kg / ton, and preferably 1-4 kg / ton, based on the total dry weight of the second cellulose ingredient.

[0106] In some implementations, the second cellulose ingredient contains 1-4 kg / ton of AKD, based on the total dry weight of the second cellulose ingredient.

[0107] In some implementations, the second cellulose ingredient contains 1-2 kg / ton of ASA based on the total dry weight of the second cellulose ingredient.

[0108] In some implementations, the second cellulose ingredient contains 2-6 kg / ton of rosin based on the total dry weight of the second cellulose ingredient.

[0109] In some embodiments, the internal sizing agent in the third cellulose formulation is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and waxes having a melting temperature above 50°C, above 55°C, or above 60°C.

[0110] In some embodiments, the third cellulose ingredient comprises an internal sizing agent in a total amount of 1-6 kg / ton, and preferably 1-4 kg / ton, based on the total dry weight of the third cellulose ingredient.

[0111] In some implementations, the third cellulose ingredient contains 1-4 kg / ton of AKD based on the total dry weight of the third cellulose ingredient.

[0112] In some implementations, the third cellulose ingredient contains 1-2 kg / ton of ASA based on the total dry weight of the third cellulose ingredient.

[0113] In some implementations, the third cellulose ingredient contains 2-6 kg / ton of rosin based on the total dry weight of the third cellulose ingredient.

[0114] In some implementations, the first cellulose ingredient has a higher Schopper Riegler value than the second ingredient and optionally the third ingredient, as determined according to standard ISO 5267-1.

[0115] The first surface adhesive layer has a density of 0.5-3 g / m². 2 The coating weight comprises at least one hydrophobic surface sizing agent and at least one binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 1-80 wt% hydrophobic surface sizing agent and 20-99 wt% binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 1-50 wt% hydrophobic surface sizing agent and 50-99 wt% binder. In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer comprises 2-30 wt% hydrophobic surface sizing agent and 70-98 wt% binder.

[0116] In some embodiments, the first surface sizing layer comprises at least two hydrophobic surface sizing agents, such as two or three hydrophobic surface sizing agents.

[0117] In some embodiments, each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, latex dispersions, styrene-maleic anhydride copolymers (SMA), styrene-acrylate copolymers (SAE), modified polyurethane dispersions, and combinations thereof. The latex may be, for example, styrene-acrylate (SA) latex, styrene-butadiene (SB) latex, polyvinyl acetate (PVAc) latex, and preferably SA latex.

[0118] In some embodiments, each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and latex dispersions and combinations thereof.

[0119] In some embodiments, each binder is selected from water-soluble polymers, preferably from polyvinyl alcohol (PVOH), water-soluble polysaccharides and water-soluble polysaccharide derivatives, and more preferably from water-soluble starch, water-soluble starch derivatives and water-soluble cellulose derivatives. In some embodiments, each binder is selected from water-soluble starch and water-soluble starch derivatives.

[0120] In some implementations, the first surface adhesive layer further comprises 0.1-20 wt% filler based on the total dry weight of the first surface adhesive layer.

[0121] In some embodiments, based on the total dry weight of the first surface sizing layer, the first surface sizing layer further comprises 0.1-10 wt% of fine cellulose material, preferably selected from cellulose fine particles, highly refined cellulose, microfibrillated cellulose (MFC), cellulose microcrystals, and cellulose nanocrystals.

[0122] In some embodiments, the first surface sizing layer further comprises 0.1-5 wt% of a crosslinking agent based on the total dry weight of the first surface sizing layer. In some embodiments, the crosslinking agent is selected from polyamide-epimeric alcohol (PAE) and polyfunctional organic acids or aldehydes, such as citric acid, glyoxal, dialdehyde starch, and glutaraldehyde.

[0123] In some embodiments, the first surface sizing layer contains 0.1-10 kg / ton, preferably 0.1-4 kg / ton, of wet strength agent based on the total dry weight of the first surface sizing layer.

[0124] In some embodiments, the first surface sizing layer further comprises 0.1-5 wt% of other additives based on the total dry weight of the first surface sizing layer. Other additives may include, but are not limited to, fixatives such as polyethyleneamine (PVAm), polyaluminum chloride (PAC), and alum.

[0125] The second surface adhesive layer may be further defined as described with reference to the first surface adhesive layer. The coating weight and composition of the second surface adhesive layer may be the same as or different from those of the first surface adhesive layer.

[0126] Competition between sizing agents can occur when different sizing agents are added simultaneously to cellulose formulations during the raw material handling or wet-end portion of the paper or paperboard manufacturing process. Therefore, if the dosage of one sizing agent increases, the retention of another sizing agent may decrease. Since adjustments to the retention system are insufficient to address this issue, surface sizing becomes a viable method for adding additional hydrophobic sizing agents to paper or paperboard, improving the retention of a particular hydrophobic sizing agent or providing the possibility of introducing other types of sizing agents with different functions to further improve durability and reduce penetration by different liquids and food types.

[0127] Depending on the function of the sizing chemicals, different internal sizing agents cure in different ways. The term "curing" refers to the process that allows the sizing agent to fully react, anchor, spread, and / or orient itself on the fibers within the paper or fiber matrix to produce the desired sizing effect. On-machine curing typically occurs in the drying section of a paper or paperboard machine, prior to the surface sizing unit. ASA and rosin are examples of sizing agents that primarily exhibit on-machine curing, while AKD sizing agents typically exhibit a pronounced post-curing characteristic, meaning that the sizing effect continues to develop even after production, for example, even weeks after production, in storage reels. Preferred is the curing of at least one internal sizing agent prior to surface sizing, meaning that the sizing effect of at least one sizing agent has been fully or almost fully realized before the application of surface sizing, to minimize the penetration of the surface sizing solution into the interior portions of the board.

[0128] In some embodiments, at least one of the internal sizing agents in the backing sheet is cured before the surface sizing layer is applied. More specifically, ASA or rosin may be used in combination with AKD as part of a dual sizing process in the backing sheet, with the aim of both reducing the adsorption of surface sizing agent into the board and providing increased hydrophobicity to the final product. In some embodiments, all internal sizing agents are cured before the surface sizing layer is applied.

[0129] According to the third aspect described herein, a container is provided formed from liquid-resistant multilayer paper or paperboard obtained according to the first aspect or by means of the second aspect, wherein the outermost surface of the backing sheet, which is glued, forms the inner surface of the container.

[0130] While products, polymers, materials, plies, layers, and methods are typically described in terms of "comprising" various components or steps, they can also be described as "consisting substantially of various components and steps" or "comprised of various components and steps". Detailed Implementation

[0131] Figure 1 A cross-sectional view of an example of a paper or paperboard substrate according to the present invention is shown. It should be understood that... Figure 1 The accompanying drawings are schematic and not to scale. A multilayer sheet material 1 comprising three layers can be seen: a top layer 3, a back layer 4, and an intermediate layer 5. The material has a first printed surface 2 and a second inner surface 6. According to the invention, the cellulose-based top layer 3 of the multilayer sheet material 1 contains an internal sizing agent, for example, in the form of rosin sizing. Furthermore, the cellulose-based back layer 4 of the multilayer material 1 contains two internal sizing agents, for example, in the form of AKD and rosin. In this embodiment, the material 1 also includes an internally sizing intermediate layer 5. Both the first printed surface 2 and the second inner surface 6 have been surface-sizingd, for example, with starch and SA-latex.

[0132] Example

[0133] According to a first embodiment, the cellulose-based top sheet of the multilayer sheet material contains an internal sizing agent in the form of 4 kg / ton rosin sizing. Furthermore, the cellulose-based back sheet of the multilayer sheet material contains a dual internal sizing agent in the form of 5 kg / ton modified AKD and 2 kg / ton rosin. In this first embodiment, the material also includes an intermediate sheet containing 6 kg / ton rosin sizing. Both the first printed surface and the second inner surface have been surface-sizingd with a mixture of starch and SA latex, wherein the SA latex content is 10 wt% based on the starch solids content. The surface sizing coating weight is 0.9 g / m². 2 / side. The basis weight of the multi-layer sheet paperboard in the first embodiment is 255 g / m². 2 .

[0134] According to the second and comparable reference embodiments, the cellulose-based top sheet of the multilayer sheet material contains an internal sizing agent in the form of rosin sizing at a rate of 4 kg / ton. Furthermore, the cellulose-based back sheet of the multilayer sheet material contains only one internal sizing agent in the form of rosin at a rate of 2 kg / ton. In this embodiment, the material also includes an intermediate sheet containing 6 kg / ton of rosin sizing. Neither the first printed surface nor the second inner surface is surface-sized. The basis weight of the multilayer sheet paperboard in the second embodiment is 266 g / m². 2 .

[0135] According to the third embodiment, the monolayer sheet material contains an internal sizing agent in the form of AKD sizing at a rate of 2.5 kg / ton. No surface sizing is applied. The basis weight of the monolayer sheet material in the third embodiment is 120 g / m². 2 .

[0136] According to the fourth embodiment, the single-layer sheet material contains an internal sizing agent in the form of AKD sizing at a rate of 2.5 kg / ton. Both sides are surface-sizinged with a mixture of starch and SA latex, wherein the SA latex content is 7.5 wt% based on the starch solids content. The surface sizing coating weight is 1.45 g / m². 2 / face. The basis weight of the single-layer sheet material in the fourth embodiment is 120 g / m². 2 .

[0137] According to the fifth embodiment, the single-layer sheet material comprises an internal dual sizing system in the form of 2 kg / ton ASA and 6 kg / ton rosin. No surface sizing is applied. The basis weight of the single-layer sheet material in the fifth embodiment is 120 g / m³. 2 .

[0138] According to the sixth embodiment, the single-layer sheet material comprises an internal double sizing system in the form of 2 kg / ton ASA and 6 kg / ton rosin. Both sides are surface-sizingd with a mixture of starch and SA-latex, wherein the SA latex content is 7.5 wt% based on the starch solids content. The surface sizing coating weight is 0.6 g / m². 2 / face. The basis weight of the single-layer sheet material in the sixth embodiment is 120 g / m². 2 .

[0139] According to the seventh embodiment, the single-layer sheet material comprises an internal double sizing system in the form of 2.5 kg / ton AKD and 6 kg / ton rosin. No surface sizing is applied. The basis weight of the single-layer sheet material in the seventh embodiment is 120 g / m³. 2 .

[0140] According to the eighth embodiment, the single-layer sheet material comprises an internal dual sizing system in the form of 2.5 kg / ton AKD and 6 kg / ton rosin. Both sides are surface-sizingd with a mixture of starch and SA latex, wherein the SA latex content is 7.5 wt% based on the starch solids content. The surface sizing coating weight is 0.5 g / m². 2 / face. The basis weight of the single-layer sheet material in the eighth embodiment is 120 g / m². 2 .

[0141] result

[0142] The Cobb values ​​of the three-layer sheet structure (Examples 1-2) were measured according to standard ISO 535:2014 (determination of water absorption), but absorbent paper was used under the test sample to prevent condensation from wetting the sample from the reverse side.

[0143] Cobb measurements of the 1-layer sheet structure (Examples 3-8) were performed according to standard ISO 535:2014, but with free space below the test sample created by removing the base plate in the Cobb apparatus. Furthermore, different liquids were tested to demonstrate the effects of varying properties of the test liquids and the need for multi-applied plates protected by this invention.

[0144]

[0145] Table 1. Adhesive dosage and Cobb value measured at the surface of the backing sheet (in g / m2)

[0146] The results of the Cobb measurements are shown in Table 1. Compared to Example 1, which has a double sizing process combined with a hydrophobic surface sizing, the three-layer sheet without internal double sizing or surface sizing showed very poor performance compared to Reference Example 2. It is equally evident that Example 1 provided significant improvement not only for water but also for hot cream coffee, which can be considered the most demanding condition the sheet can withstand, as it is both acidic and fatty, and has a high temperature (i.e., 80°C).

[0147] The results for the single-layer sheet structures in Examples 3-8 showed a similar trend (Table 1). For Examples 3 and 4, which contained only AKD without any double sizing, the additional surface sizing with SA-latex did not provide any improvement in Cobb value for hot water or Cobb for creamy coffee.

[0148] In contrast, other examples 5-8 with dual sizing showed significant improvements for hot water, and particularly for creamy coffee Cobb when additionally surface-sizing with SA-latex (Examples 6 and 8). This is thought to be related to the ability of rosin to provide sufficient sizing effect before surface sizing is applied, an effect not achievable by using AKD alone. However, the presence of AKD as part of the sizing concept is also desirable, as it is believed to provide a greater sizing effect when properly cured over time, since AKD sizing typically exhibits significant post-curing characteristics. This observed effect is important for the present invention and the performance of the materials, because insufficient on-machine curing before pressing can lead to increased surface sizing penetration into the board structure, resulting in poorer results.

[0149] While the invention has been described with reference to various exemplary embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for its elements without departing from the scope of the invention. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the essential scope of the invention. Therefore, it is intended that the invention will not be limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. Liquid-resistant multilayer sheets or paperboard, comprising: Cellulose-based backsheet, wherein the backsheet contains at least two different internal sizing agents in a total amount of 2-10 kg / ton, based on the total dry weight of the backsheet; A cellulose-based top sheet, wherein the top sheet contains a single internal sizing agent in a total amount of 0.1-5 kg / ton, based on the total dry weight of the top sheet, and wherein the total amount of internal sizing agent in the top sheet is less than the total amount of internal sizing agent in the back sheet; and A first surface adhesive layer is applied to the outermost surface of the backsheet, wherein the first surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

2. The paper or paperboard according to claim 1, further comprising: A cellulose-based intermediate layer sheet is disposed between the top layer sheet and the back layer sheet, wherein the intermediate layer sheet contains a single internal sizing agent in a total amount of 0.1-5 kg / ton based on the total dry weight of the intermediate layer sheet, and wherein the total amount of internal sizing agent in the intermediate layer sheet is less than the total amount of internal sizing agent in the back layer sheet, and preferably more than the total amount of internal sizing agent in the top layer sheet.

3. The paper or paperboard according to any one of the preceding claims, further comprising: A second surface adhesive layer is applied to the outermost surface of the top sheet, wherein the second surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

4. The paper or paperboard according to any one of the preceding claims, wherein each internal sizing agent is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride and wax, wherein the wax has a melting temperature of 50°C or above, or 55°C or above, or 60°C or above.

5. The paper or paperboard according to any one of the preceding claims, wherein the backing sheet comprises AKD and rosin, ASA and rosin, ASA and AKD, or AKD and stearic anhydride.

6. The paper or paperboard according to any one of the preceding claims, wherein the backing sheet contains an internal sizing agent in a total amount of 2-8 kg / ton, based on the total dry weight of the backing sheet.

7. The paper or paperboard according to any one of the preceding claims, wherein the top sheet contains an internal sizing agent in a total amount of 1-6 kg / ton, and preferably 1-4 kg / ton, based on the total dry weight of the top sheet.

8. The paper or paperboard according to any one of claims 2-7, wherein the interlayer sheet contains an internal sizing agent in a total amount of 1-6 kg / ton, and preferably 1-4 kg / ton, based on the total dry weight of the interlayer sheet.

9. The paper or paperboard according to any one of the preceding claims, wherein the first surface sizing layer comprises 1-80 wt% of a hydrophobic surface sizing agent and 20-99 wt% of a binder, preferably 1-50 wt% of a hydrophobic surface sizing agent and 50-99 wt% of a binder, and more preferably 1-15 wt% of a hydrophobic surface sizing agent and 75-99 wt% of a binder, based on the total dry weight of the first surface sizing layer.

10. The paper or paperboard according to any one of the preceding claims, wherein each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and latex dispersions and combinations thereof.

11. The paper or paperboard according to any one of the preceding claims, wherein each binder is selected from water-soluble polymers, preferably from water-soluble polysaccharides and water-soluble polysaccharide derivatives.

12. The paper or paperboard according to any one of the preceding claims, wherein the outermost surface of the backing sheet is sized at 30 g / m². 2 The following is preferred: 25 g / m 2 Below, more preferably at 20 g / m 2 The following are the differences between water Cobb300 and water Cobb30 measured for 300 and 30 seconds respectively, according to standard ISO 535:2014.

13. The paper or paperboard according to any one of the preceding claims, wherein the outermost surface of the back sheet with surface sizing has a water penetration depth of less than 40 μm, preferably less than 30 μm and more preferably less than 20 μm, said water penetration depth being optically determined by cross-sectional analysis of a sample treated with dyed water for 300 seconds according to standard ISO 535:2014.

14. The paper or paperboard according to any one of the preceding claims, wherein the outermost surface of the backing sheet with adhesive has a water contact angle of 90° or more, preferably 100° or more.

15. The paper or paperboard according to any one of the preceding claims, wherein the paper or paperboard has a total scrap rate of less than 5%, preferably less than 1%, and more preferably less than 0.5%, according to the PTS RH021 / 97 test method for Class II products.

16. 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.

17. The paper or paperboard according to any one of the preceding claims, wherein the paper or paperboard has a density of 150 g / m³. 2 The above, for example, at 200 g / m 2 Above, and at 400g / m 2 The following are the basis weights.

18. A method for manufacturing liquid-resistant multilayer sheets or paperboards, the method comprising: a) A cellulose-based backsheet is formed from a first cellulose ingredient, wherein the first cellulose ingredient comprises at least two different internal sizing agents in a total amount of 2-10 kg / ton, based on the total dry weight of the first cellulose ingredient; b) A cellulose-based top sheet is formed from a second cellulose formulation, wherein the second cellulose formulation contains a single internal sizing agent in a total amount of 0.1-5 kg / ton based on the total dry weight of the second cellulose formulation, and wherein the total amount of internal sizing agent in the second cellulose formulation is less than the total amount of internal sizing agent in the first cellulose formulation. and c) A first surface adhesive layer is formed on the outermost surface of the backsheet, wherein the first surface adhesive layer has a content of 0.5-3 g / m 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

19. The method of claim 18, further comprising: A cellulose-based intermediate layer is formed between the top layer and the back layer by a third cellulose ingredient, wherein the third cellulose ingredient contains a single internal sizing agent in a total amount of 0.1-5 kg / ton based on the total dry weight of the third cellulose ingredient, and wherein the total amount of internal sizing agent in the third cellulose ingredient is less than the total amount of internal sizing agent in the first cellulose ingredient, and preferably more than the total amount of internal sizing agent in the second cellulose ingredient.

20. The method according to any one of claims 18-19, the method further comprising: A second surface adhesive layer is formed on the outermost surface of the top layer, wherein the second surface adhesive layer has a content of 0.5-3 g / m². 2 The coating weight includes at least one hydrophobic surface sizing agent and at least one adhesive.

21. The method according to any one of claims 18-20, wherein each internal sizing agent is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and wax, wherein the wax has a melting temperature of 50°C or above, or 55°C or above, or 60°C or above.

22. The method according to any one of claims 18-21, wherein the first cellulose ingredient has a higher Schopper Riegler value than the second ingredient and optionally the third ingredient, as determined according to standard ISO 5267-1.

23. The method according to any one of claims 18-22, wherein each hydrophobic surface sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, stearic anhydride, and latex dispersions and combinations thereof.

24. The method according to any one of claims 18-23, wherein each binder is selected from water-soluble polymers, preferably from water-soluble polysaccharides and water-soluble polysaccharide derivatives.

25. A container formed from any one of claims 1-17 or obtained by the method according to claims 18-24, wherein the outermost surface of the backing sheet, to which adhesive is applied, forms the inner surface of the container.

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