WO2026009023A1 - Multiply paper substrate comprising a barrier mid-ply - Google Patents

Abstract

The present invention relates to a method for manufacturing a multiply paper substrate comprising, in order, a first outer ply, a first bulk ply, a barrier mid-ply, a second bulk ply, and a second outer ply, wherein the barrier mid-ply is obtained by forming and dewatering a web layer from a pulp suspension comprising at least 70 wt% (based on dry weight) of microfibrillated cellulose (MFC) having a Schopper-Riegler (SR) value in the range of 80-100, and wherein each of the first and second bulk plies are obtained by forming and dewatering a web layer from a pulp suspension comprising at least 65 wt% (based on dry weight) of high-bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High-Temperature Chemi-ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp obtained from the method for manufacturing a multiply paper substrate.

Description

MULTIPLY PAPER SUBSTRATE COMPRISING A BARRIER MID-PLY

Technical field

The present disclosure relates to paper substrates, e.g. useful in paper and paperboard-based packaging materials. More specifically, the present disclosure relates to methods for manufacturing paper substrates comprising microfibrillated cellulose (MFC).

Background

Effective gas, aroma, and grease barriers are required in paper and paperboardbased packaging materials for food packaging. Paper and paperboard-based packaging materials should also have suitable mechanical properties allowing them to be used in converting lines for manufacturing packaging containers.

Coating of paper with plastics is often employed to combine the mechanical properties of the paper with the barrier and sealing properties of a plastic film or layer. Paper provided with even a relatively small amount of a suitable plastic material can provide the properties needed to make the paper suitable for many demanding applications, for example as liquid or food packaging. In liquid or food packaging, polyolefin coatings are frequently used as liquid barrier layers, heat sealing layers and adhesives. However, the recycling of such polymer coated paper is difficult since it is difficult to separate the polymers from the fibers. Also, in many cases the water vapor barrier properties of the polymer coated paper are still insufficient unless the coating layers are thick or combinations of different polymer coating layers are used. Therefore, in order to ensure high water vapor barrier properties, the polymer coated paper is often combined with one or more layers of aluminum foil. The aluminum foil is typically bonded to the laminate using one or more polymeric tie layers. However, the addition of polymer and aluminum foil add significant costs and the combination of polymeric layers and aluminum foils makes repulping and recycling of the materials more difficult. Also, due to its high carbon footprint there is a wish to replace aluminum foils in paper or paperboard based packaging materials. In the prior art, attempts have been made to replace the aluminum foil with more environmentally friendly and/or easier to recycle solutions. For example, microfibri Hated cellulose (MFC) films and coatings have been developed, in which cellulosic fibrils provided by fibrillation of cellulose fibers have been dispersed e.g. in water and thereafter re-organized and rebonded together to form a dense film or coating with excellent gas, aroma, and grease barrier properties. The MFC films are typically laminated to a paper or paperboard based substrate in the same manner as aluminum foils. However, challenges still remain in terms of providing sufficient barrier properties, mechanical strength, durability, repulpability and recyclability, at an acceptable cost, in order to effectively replace aluminum foils and plastic films with cellulose based alternatives.

MFC films are typically relatively weak, and the films are therefore often formed or laminated with paper or paperboard substrate to improve the mechanical strength. However, the MFC films in such laminates are also prone to cracking and delamination during converting of the laminates into packaging containers. Due to the shrinking properties of the MFC films, the forming or lamination with other cellulose based layers may also often result in problems with curling of the formed multilayer structures.

There remains a need for improved solutions to replace the combinations of plastic films and aluminum foils commonly used in paper and paperboard-based packaging materials, while maintaining acceptable gas, aroma, and grease barrier properties, as well as acceptable mechanical properties for converting into packaging containers. At the same time, there is a need to replace the combination of plastic films and aluminum foils with alternatives that facilitate repulping and recycling of the used packaging materials. Description of the invention

It is an object of the present disclosure to provide a method for manufacturing a paper substrate comprising a microfibrillated cellulose (MFC), which alleviates at least some of the above-mentioned problems associated with prior art methods.

It is a further object of the present disclosure to provide an improved method for manufacturing a paper substrate comprising MFC in a paper- or paperboard machine type of process.

It is a further object of the present disclosure to provide a paper substrate with gas, aroma, and grease barrier properties useful in paper and paperboard-based packaging materials for food packaging.

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.

According to a first aspect illustrated herein, there is provided a method for manufacturing a multiply paper substrate comprising, in order, a first outer ply, a first bulk ply, a barrier mid-ply, a second bulk ply, and a second outer ply in a paper machine, the method comprising the steps: a) forming and dewatering a first web layer from a first pulp suspension comprising at least 70 wt% (based on dry weight) of Kraft pulp to obtain a first outer ply of the multiply paper substrate; b) forming and dewatering a second web layer from a second pulp suspension comprising at least 65 wt% (based on dry weight) of high-bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High-Temperature Chemi- ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp, to obtain a first bulk ply of the multiply paper substrate; c) forming and dewatering a third web layer from a third pulp suspension comprising at least 70 wt% (based on dry weight) of microfibrillated cellulose (MFC) having a Schopper-Riegler (SR) value in the range of 80-100, to obtain a barrier mid-ply of the multiply paper substrate; d) forming and dewatering a fourth web layer from a fourth pulp suspension comprising at least 65 wt% (based on dry weight) of high-bulk pulp selected from CTMP, HT-CTMP, high yield pulp, PGW, or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp, to obtain a second bulk ply of the multiply paper substrate; e) forming and dewatering a fifth web layer from a fifth pulp suspension comprising at least 70 wt% (based on dry weight) of Kraft pulp to obtain a second outer ply of the multiply paper substrate; wherein the broke pulp in the second and fourth pulp suspension is obtained from the method for manufacturing a multiply paper substrate.

Each ply of the obtained multiply paper substrate is designed to provide specific properties to the final product.

The first and second outer plies of the multiply paper substrate comprise a high amount of Kraft pulp ensuring structural integrity, smoothness, printability and aesthetics.

The first and second bulk plies of the multiply paper substrate comprise a high amount of high-bulk pulp selected from CTMP, HT-CTMP, high yield pulp, PGW, or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp, adding thickness and rigidity without significantly increasing weight of the multiply paper substrate.

The barrier mid-ply of the multiply paper substrate comprises a high amount of microfibri Hated cellulose (MFC) having a Schopper-Riegler (SR) value in the range of 80-100, which forms a dense layer with low permeability, providing gas, aroma, and grease barrier properties to the multiply paper substrate.

The barrier mid-ply of the multiply paper substrate improves the barrier properties of the multiply paper substrate to gases, aromas, and grease, which is very useful in packaging applications. In addition, the barrier mid-ply of the multiply paper substrate also acts as a barrier for migration of internal contaminants between the outer and bulk plies on one side of the barrier mid-ply to the outer and bulk plies on the other side of the barrier mid-ply. Such internal contaminants may for example include saturated hydrocarbons (MOSH) and alkylated aromatic hydrocarbons (MOAH). This is advantageous as it may allow for using higher amounts of recycled fibers, which often contain elevated levels of MOSH and/or MOAH, in the outer and bulk plies of the multiply paper substrate.

The present invention is based on the realization that a barrier layer with excellent gas, aroma, and grease barrier properties can advantageously be formed as a mid-ply in a multiply paper substrate from a pulp suspension comprising at least 70 wt% (based on dry weight) of microfibrillated cellulose (MFC). Forming this MFC barrier layer as a mid-ply in the multiply paper substrate minimizes the stress on the barrier layer during transport, handling and converting of the multiply paper substrate. The barrier layer arranged as a mid-ply in the multiply paper substrate does not need to stretch as much during folding and converting as a barrier layer arranged as an outer ply in a multiply paper substrate. This reduces the risk of cracking the sensitive barrier layer during folding and converting.

The inventive method also allows for efficient manufacturing of a multilayer paper substrate comprising MFC in a paper machine type of process as broke obtained from the method for manufacturing a multiply paper substrate is recycled in intermediate plies, or bulk layers, of the multiply paper substrate. The method thus allows for a high degree of broke recycling which also contributes to the overall properties of the obtained product. Thanks to the MFC in the barrier mid-ply, the broke obtained from the method for manufacturing a multiply paper substrate will also comprise a significant amount of MFC. This has been found to make the broke ideal for use in the intermediate plies, or bulk layers, of the multiply paper substrate, where the MFC imparts improved internal bond strength and/or compression strength to the high-bulk pulp.

The obtained multiply paper substrates have been found to be very useful in packaging applications requiring gas, aroma, and grease barrier properties, as well as acceptable mechanical properties for converting into packaging containers. The obtained multiply paper substrates may optionally be coated or laminated with one or more polymer layers to provide additional resistance to liquids, gases, aromas and grease. The multiply paper substrates of the present disclosure provided with one or more polymer layers may be especially suited as substrates for packaging laminates, such as liquid packaging board (LPB).

The obtained multiply paper substrates have high repulpability, providing for high recyclability of the paper substrates and packaging products comprising the paper substrates.

The term “web” or “web layer” as used herein refers to a sheet formed cellulose- based material obtained by applying a suspension comprising a cellulose-based fibrous material and/or MFC on a surface, preferably a porous surface, and dewatering the applied suspension to increase the dry solids content of the suspension until a cellulose-based web layer is formed on the surface.

The term “ply” as used herein refers generally to the dewatered and dried web layer which may form part of a “multiply paper substrate”.

The “multiply paper substrate” as used herein refers generally to a multilayer sheet formed material obtained by co-formation or wet lamination of two or more cellulose-based web layers. Depending on the thickness and composition of the multiply paper substrate, it can be considered as a multiply paper or a multiply paperboard.

The multiply paper substrate can be used as such, or it can be combined with one or more other layers. The multiply paper substrate may for example be useful as a barrier layer in a paperboard-based packaging material.

Although different arrangements for performing the steps of the inventive method could be contemplated by the skilled person, the inventive method may advantageously be performed in a paper machine, more preferably in a Fourdrinier type paper machine, i.e. a paper machine based on the principles of the Fourdrinier Machine.

A paper machine (or paper-making machine) is an industrial machine which is used in the pulp and paper industry to create paper or fiber-based substrates in large quantities at high speed. Modern paper machines are typically based on the principles of the Fourdrinier machine, which uses a moving dewatering fabric or woven mesh, commonly referred to as a “wire”, to create a continuous web layer by filtering out the fibers held in a pulp suspension and producing a continuously moving wet web layer of fiber. This wet web layer is dried in the machine to produce paper or film. Paper machines for manufacturing a multiply paper substrate in accordance with the present disclosure are well known and available to the skilled person. The pulp suspension is preferably applied to the wire using a so-called headbox. The dewatering fabric of the wire can be a single ply or multiply fabric, made of plastic, non-woven, composite, or metal. The paper machine may be provided with various devices for facilitating dewatering of the web on the wire, such as blade, table and/or foil elements, suction boxes, friction less dewatering, ultra-sound assisted dewatering, couch rolls, or a dandy roll.

The first pulp suspension is an aqueous suspension comprising a water- suspended mixture of cellulose-based fibrous material, or pulp, and optionally non- fibrous additives. The first pulp suspension comprises at least 70 wt% (based on dry weight) of Kraft pulp. The Kraft pulp may be softwood pulp or hardwood Kraft pulp. The Kraft pulp may be bleached or unbleached Kraft pulp. In a preferred embodiment, the Kraft pulp of the first pulp suspension is unbleached Kraft pulp. The pulp of the first pulp suspension can further include pressurized groundwood pulp (PGW), thermomechanical (TMP), chemi-thermomechanical pulp (CTMP), neutral sulfite semi chemical pulp (NSSC), broke, or recycled fibers, or combinations thereof. The pulp of the first pulp suspension may comprise up to 30 wt% (based on dry weight), such as in the range of 5-30 wt% (based on dry weight), of recycled fibers. In a preferred embodiment, the pulp of the first pulp suspension comprises or consists of unbleached Kraft pulp. The pulp of the first pulp suspension can be unrefined or refined. Refining, or beating, of cellulose-based fibrous materials refers to mechanical treatment and modification of the cellulose fibers in order to provide them with desired properties. The pulp of the first pulp suspension is preferably unrefined or only slightly refined, such that the pulp will have a relatively high drainage rate and low water retention. The drainage rate is expressed as a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1. In some embodiments, the pulp of the first pulp suspension has an SR value in the range of 10-50, preferably in the range of IQ- 40 and more preferably in the range of 10-30. In some embodiments, the pulp of the first pulp suspension has an SR value in the range of 18-50. In some embodiments, the pulp of the first pulp suspension has an SR value in the range of 20-35. The water retention of the pulp is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the pulp of the first pulp suspension has a WRV in the range of 100-220%, preferably in the range of 120-190%.

The dry solids content of the first pulp suspension is typically in the range of 0.1- 1.5 wt%, preferably in the range of 0.1-1 wt%, more preferably in the range of 0.1- 0.5 wt%.

The dry solids content of the first pulp suspension may be comprised solely of the pulp, or it can comprise a mixture of pulp and other ingredients or additives.

The first pulp suspension includes the Kraft pulp as its main component, based on the total dry weight of the suspension. In some embodiments, the first pulp suspension comprises at least 80 wt% (based on dry weight) or at least 90 wt% (based on dry weight), of the Kraft pulp.

Kraft pulp will typically comprise at least 10 wt% (based on dry weight) of hemicellulose. Thus, in some embodiments the first pulp suspension comprises hemicellulose at an amount of at least 10 wt%, such as in the range of 10-25 wt%, based on the dry weight of Kraft pulp. The first pulp suspension may further comprise additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, a filler, retention and/or drainage chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cross-linking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, de-foaming aids, microbe and slime control aids, or mixtures thereof.

In some embodiments, the first pulp suspension comprises a hydrophobizing chemical such as an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA), or a rosin size in an amount of 0-10 kg/ton, preferably 0.1-5 kg/ton and more preferably 0.2-2 kg/ton based on the total dry weight of the suspension.

In some embodiments, the first pulp suspension comprises unbleached pulp to give the multiply paper substrate a natural look.

In some embodiments, the first pulp suspension comprises less than 15 wt% (based on dry weight), and more preferably less than 10 wt% (based on dry weight), of broke pulp. In some embodiments, the first pulp suspension comprises no broke pulp.

The second pulp suspension is an aqueous suspension comprising a water- suspended mixture of cellulose-based fibrous material, or pulp, and optionally non- fibrous additives. The second pulp suspension comprises at least 65 wt% (based on dry weight) of high-bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High-Temperature Chemi-ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp.

The high-bulk pulp may be bleached or unbleached high-bulk pulp. In a preferred embodiment, the high-bulk pulp of the second pulp suspension is unbleached high-bulk pulp. The high-bulk pulp of the second pulp suspension is preferably unrefined or only slightly refined since the purpose of this pulp is to provide bulk to the multiply paper substrate.

The broke pulp in the second pulp suspension is obtained from the method for manufacturing a multiply paper substrate. Accordingly, the broke pulp comprises a combination of the pulps of the first, second, third, fourth and fifth pulp suspensions. Particularly, the broke pulp in the second pulp suspension comprises MFC from the barrier mid-ply of the multiply paper substrate. In some embodiments, the broke pulp in the second pulp suspension comprises at least 0.1 wt% (based on dry weight), preferably at least 0.5 wt% (based on dry weight), and more preferably at least 1 wt% (based on dry weight), of MFC.

The pulp of the second pulp suspension can further include Kraft pulp, thermomechanical pulp (TMP), neutral sulfite semi chemical pulp (NSSC), or recycled fibers, or combinations thereof. The pulp of the second pulp suspension may comprise up to 30 wt% (based on dry weight), such as in the range of 5-30 wt% (based on dry weight), of recycled fibers. In a preferred embodiment, the pulp of the second pulp suspension consists of the high-bulk pulp and the broke pulp.

Since the high-bulk pulp of the second pulp suspension is preferably unrefined or only slightly refined, the pulp of the second pulp suspension will have a relatively high drainage rate and low water retention. The drainage rate is expressed as a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1. In some embodiments, the pulp of the second pulp suspension has an SR value in the range of 10-30, preferably in the range of 10-25 and more preferably in the range of 10-20. The water retention of the pulp is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the pulp of the second pulp suspension has a WRV in the range of 100-220%, preferably in the range of 120-190%.

The dry solids content of the second pulp suspension is typically in the range of 0.1 -1.5 wt%, preferably in the range of 0.1-1 wt%, more preferably in the range of 0.1 -0.5 wt%. The dry solids content of the second pulp suspension may be comprised solely of the high-bulk pulp and the broke pulp, or it can comprise a mixture of the high-bulk pulp, the broke pulp, and other ingredients or additives.

The second pulp suspension includes the high-bulk pulp as its main component, based on the total dry weight of the suspension. In some embodiments, the second pulp suspension comprises at least 70 wt% (based on dry weight) or at least 75 wt% (based on dry weight) or at least 80 wt% (based on dry weight) or at least 85 wt% (based on dry weight), of the high-bulk pulp.

The second pulp suspension includes the broke pulp as its second main component. The second pulp suspension comprises at least 2 wt% (based on dry weight) of the broke pulp. In some embodiments, the second pulp suspension comprises at least 5 wt% (based on dry weight), at least 10 wt% (based on dry weight), at least 15 wt% (based on dry weight), at least 20 wt% (based on dry weight) of the broke pulp. In some embodiments, the second pulp suspension comprises 2-30 wt% (based on dry weight), preferably 2-25 wt% (based on dry weight), of broke pulp.

The second pulp suspension may further comprise additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, a filler, retention and/or drainage chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cross-linking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, de-foaming aids, microbe and slime control aids, or mixtures thereof.

In some embodiments, the second pulp suspension comprises a hydrophobizing chemical such as an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA), or a rosin size in an amount of 0-10 kg/ton, preferably 0.1-5 kg/ton and more preferably 0.2-2 kg/ton based on the total dry weight of the suspension.

The third pulp suspension is an aqueous suspension comprising a water- suspended mixture of highly refined cellulose-based material, referred to herein as microfibri Hated cellulose (MFC), and optionally other fibrous or non-fibrous additives. The third pulp suspension comprises at least 70 wt% (based on dry weight) of MFC having an SR value in the range of 80-100.

MFC shall in the context of the patent application mean a cellulose particle, fiber or fibril having a width or diameter of from 20 nm to 1000 nm. Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pretreatment steps is usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp used when producing MFC may thus be native or pre-treated enzymatically or chemically, for example to reduce the quantity of hemicellulose or lignin. The cellulose fibers may be chemically modified before fibrillation, wherein the cellulose molecules contain functional groups other (or more) than found in the original cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), or quaternary ammonium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC. The MFC of the third pulp suspension can be produced from wood cellulose fibers, both from hardwood and softwood fibers or a combination thereof. The MFC is preferably produced from wood cellulose fibers sourced from trees such as pine, spruce, and other softwoods, although hardwoods can also be used. It can also be made from microbial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources.

The MFC of the third pulp suspension may be obtained from bleached or unbleached Kraft pulp. In some embodiments, the MFC of the third pulp suspension comprises or consists of MFC obtained from bleached Kraft pulp. In some embodiments, the MFC of the third pulp suspension comprises or consists of MFC obtained from unbleached Kraft pulp.

The MFC of the third pulp suspension is preferably obtained from virgin Kraft pulp. Virgin Kraft pulp refers to a type of pulp made from wood chips that have not been previously used or recycled. Virgin Kraft pulp has a consistent chemical composition free from contaminants and impurities, such as additives and fillers, that are often found in recycled pulp. This purity ensures that the MFC produced is of high quality, with consistent properties. This consistency is important for producing MFC with predictable and reliable properties. Virgin Kraft pulp contains long, strong fibers that are ideal for producing MFC. The strength of the fibers contributes to the mechanical strength and durability of webs and plies formed of the MFC and the consistent properties of the formed MFC contributes to improved barrier properties of the webs and plies formed of the MFC.

The dry solids content of the third pulp suspension may consist solely of the MFC, or it can further comprise other ingredients or additives. The third pulp suspension includes the MFC as its main component based on the total dry weight of the suspension. Having a high content of the MFC in the third pulp suspension ensures good barrier properties in the finished multiply paper substrate.

The MFC of the third pulp suspension has an SR value in the range of 80-100 as determined by standard ISO 5267-1. In some embodiments, the MFC of the third pulp suspension has an SR value in the range of 85-100, and preferably in the range of 90-100. In some embodiments, the MFC of the third pulp suspension has an SR value in the range of 80-98. preferably in the range of 85-98, and more preferably in the range of 90-98. The water retention of the MFC is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the MFC of the third pulp suspension has a WRV of >200%, preferably >250%.

The third pulp suspension comprises at least 70 wt% (based on dry weight) of the MFC. In some embodiments, the third pulp suspension comprises at least 80 wt% (based on dry weight), preferably at least 90 wt% (based on dry weight), and more preferably at least 95 wt% (based on dry weight) of the MFC. In some embodiments, the third pulp suspension comprises 100 wt% (based on dry weight) of the MFC.

The third pulp suspension may further comprise additives such as fillers, deflocculating additives, dry strength additives, latexes, softeners, cross-linking aids, sizing chemicals, dyes and colorants, wet strength resins, de-foaming aids or foaming aids, microbe and slime control aids, or mixtures thereof.

Having a high total content of the MFC in the third pulp suspension ensures good barrier properties in the finished multiply paper substrate. Thus, the third pulp suspension comprises no more than 30 wt% (based on dry weight), preferably no more than 20 wt% (based on dry weight), and more preferably no more than 10 wt% (based on dry weight), of additives in total, based on the total dry weight of the suspension.

In addition to the MFC, the third pulp suspension may also comprise a certain amount of unrefined or slightly refined cellulose fibers. The term “unrefined or slightly refined fibers” as used herein preferably refers to cellulose fibers having a Schopper-Riegler (SR) value below 30, preferably below 28, as determined by standard ISO 5267-1. Unrefined or slightly refined cellulose fibers are useful to enhance dewatering and may also improve strength and fracture toughness of the barrier mid-ply. In some embodiments, the third pulp suspension comprises 0.1-30 wt% (based on dry weight), preferably 0.1-20 wt% (based on dry weight), and more preferably 0.1-10 wt% (based on dry weight) of unrefined or slightly refined cellulose fibers, based on the total dry weight of the pulp suspension. The unrefined or slightly refined cellulose fibers may for example be obtained from bleached or unbleached Kraft pulp, bleached or unbleached or mechanical or chemi-mechanical pulp, or other high yield pulps.

In some embodiments, the third pulp suspension comprises up to 20 wt% (based on dry weight), preferably up to 10 wt% (based on dry weight), of a filler, e.g. a phyllosilicate such as bentonite, based on the total dry weight of the suspension. The filler is preferably a platy filler. In some embodiments, the filler has a shape factor higher than 20, preferably higher than 30, and more preferably higher than 40. "Shape factor" as used herein is a measure of an average value (on a weight average basis) of the ratio of mean particle diameter to particle thickness for a population of particles of varying size and shape, as measured using the electrical conductivity method and apparatus described in, for example, patent publications US 5 128 606 and US 5 576 617. The pH value of the third pulp suspension may typically be in the range of 4-10 preferably in the range of 5-8, and more preferably in the range of 5.5-7.5.

The temperature of the third pulp suspension may typically be in the range of 40- 80 °C, preferably in the range of 50-80 °C, and more preferably in the range of 60- 80 °C.

The fourth pulp suspension is an aqueous suspension comprising a water- suspended mixture of cellulose-based fibrous material, or pulp, and optionally non- fibrous additives. The fourth pulp suspension comprises at least 65 wt% (based on dry weight) of high-bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High-Temperature Chemi-ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp.

The high-bulk pulp may be bleached or unbleached high-bulk pulp. In a preferred embodiment, the high-bulk pulp of the fourth pulp suspension is unbleached high- bulk pulp.

The high-bulk pulp of the fourth pulp suspension is preferably unrefined or only slightly refined since the purpose of this pulp is to provide bulk to the multiply paper substrate.

The broke pulp in the fourth pulp suspension is obtained from the method for manufacturing a multiply paper substrate. Accordingly, the broke pulp comprises a combination of the pulps of the first, second, third, fourth and fifth pulp suspensions. Particularly, the broke pulp in the fourth pulp suspension comprises MFC from the barrier mid-ply of the multiply paper substrate. In some embodiments, the broke pulp in the fourth pulp suspension comprises at least 0.1 wt% (based on dry weight), preferably at least 0.5 wt% (based on dry weight), and more preferably at least 1 wt% (based on dry weight), of MFC. The pulp of the fourth pulp suspension can further include Kraft pulp, thermomechanical pulp (TMP), neutral sulfite semi chemical pulp (NSSC), or recycled fibers, or combinations thereof. The pulp of the fourth pulp suspension may comprise up to 30 wt% (based on dry weight), such as in the range of 5-30 wt% (based on dry weight), of recycled fibers. In a preferred embodiment, the pulp of the fourth pulp suspension consists of the high-bulk pulp and the broke pulp.

Since the high-bulk pulp of the fourth pulp suspension is preferably unrefined or only slightly refined, the pulp of the fourth pulp suspension will have a relatively high drainage rate and low water retention. The drainage rate is expressed as a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1. In some embodiments, the pulp of the fourth pulp suspension has an SR value in the range of 10-30, preferably in the range of 10-25 and more preferably in the range of IQ- 20. The water retention of the pulp is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the pulp of the fourth pulp suspension has a WRV in the range of 100-220%, preferably in the range of 120-190%.

The dry solids content of the fourth pulp suspension is typically in the range of 0.1- 1.5 wt%, preferably in the range of 0.1-1 wt%, more preferably in the range of 0.1- 0.5 wt%.

The dry solids content of the fourth pulp suspension may be comprised solely of the high-bulk pulp and the broke pulp, or it can comprise a mixture of the high-bulk pulp, the broke pulp, and other ingredients or additives.

The fourth pulp suspension includes the high-bulk pulp as its main component, based on the total dry weight of the suspension. In some embodiments, the fourth pulp suspension comprises at least 70 wt% (based on dry weight) or at least 75 wt% (based on dry weight) or at least 80 wt% (based on dry weight) or at least 85 wt% (based on dry weight), of the high-bulk pulp.

The fourth pulp suspension includes the broke pulp as its second main component. The fourth pulp suspension comprises at least 2 wt% (based on dry weight) of the broke pulp. In some embodiments, the fourth pulp suspension comprises at least 5 wt% (based on dry weight), at least 10 wt% (based on dry weight), at least 15 wt% (based on dry weight), at least 20 wt% (based on dry weight) of the broke pulp. In some embodiments, the fourth pulp suspension comprises 2-30 wt% (based on dry weight), preferably 2-25 wt% (based on dry weight), of broke pulp.

The fourth pulp suspension may further comprise additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, a filler, retention and/or drainage chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cross-linking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, de-foaming aids, microbe and slime control aids, or mixtures thereof.

In some embodiments, the fourth pulp suspension comprises a hydrophobizing chemical such as an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA), or a rosin size in an amount of 0-10 kg/ton, preferably 0.1-5 kg/ton and more preferably 0.2-2 kg/ton based on the total dry weight of the suspension.

The fifth pulp suspension is an aqueous suspension comprising a water- suspended mixture of cellulose-based fibrous material, or pulp, and optionally non- fibrous additives. The fifth pulp suspension comprises at least 70 wt% (based on dry weight) of Kraft pulp. The Kraft pulp may be softwood pulp or hardwood Kraft pulp. The Kraft pulp may be bleached or unbleached Kraft pulp. In a preferred embodiment, the Kraft pulp of the fifth pulp suspension is unbleached Kraft pulp. The pulp of the fifth pulp suspension can further include pressurized groundwood pulp (PGW), thermomechanical (TMP), chemi-thermomechanical pulp (CTMP), neutral sulfite semi chemical pulp (NSSC), broke, or recycled fibers, or combinations thereof. The pulp of fifth pulp suspension may comprise up to 30 wt% (based on dry weight), such as in the range of 5-30 wt% (based on dry weight), of recycled fibers. In a preferred embodiment, the pulp of the fifth pulp suspension comprises or consists of unbleached Kraft pulp. The pulp of the fifth pulp suspension can be unrefined or refined. Refining, or beating, of cellulose-based fibrous materials refers to mechanical treatment and modification of the cellulose fibers in order to provide them with desired properties. The pulp of the fifth pulp suspension is preferably unrefined or only slightly refined, such that the pulp will have a relatively high drainage rate and low water retention. The drainage rate is expressed as a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1. In some embodiments, the pulp of the fifth pulp suspension has an SR value in the range of 10-50, preferably in the range of IQ- 40 and more preferably in the range of 10-30. In some embodiments, the pulp of the fifth pulp suspension has an SR value in the range of 18-50. In some embodiments, the pulp of the fifth pulp suspension has an SR value in the range of 20-35. The water retention of the pulp is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the pulp of the fifth pulp suspension has a WRV in the range of 100-220%, preferably in the range of 120-190%.

The dry solids content of the fifth pulp suspension is typically in the range of 0.1- 1.5 wt%, preferably in the range of 0.1-1 wt%, more preferably in the range of 0.1- 0.5 wt%.

The dry solids content of the fifth pulp suspension may be comprised solely of the pulp, or it can comprise a mixture of pulp and other ingredients or additives.

The fifth pulp suspension includes the Kraft pulp as its main component, based on the total dry weight of the suspension. In some embodiments, the fifth pulp suspension comprises at least 80 wt% (based on dry weight) or at least 90 wt% (based on dry weight), of the Kraft pulp.

Kraft pulp will typically comprise at least 10 wt% (based on dry weight) of hemicellulose. Thus, in some embodiments the fifth pulp suspension comprises hemicellulose at an amount of at least 10 wt%, such as in the range of 10-25 wt%, based on the dry weight of Kraft pulp. The fifth pulp suspension may further comprise additives such as native starch or starch derivatives, cellulose derivatives such as sodium carboxymethyl cellulose, a filler, retention and/or drainage chemicals, flocculation additives, deflocculating additives, dry strength additives, softeners, cross-linking aids, sizing chemicals, dyes and colorants, wet strength resins, fixatives, de-foaming aids, microbe and slime control aids, or mixtures thereof.

In some embodiments, the fifth pulp suspension comprises a hydrophobizing chemical such as an alkyl ketene dimer (AKD), an alkenyl succinic anhydride (ASA), or a rosin size in an amount of 0-10 kg/ton, preferably 0.1-5 kg/ton and more preferably 0.2-2 kg/ton based on the total dry weight of the suspension.

In some embodiments, the fifth pulp suspension comprises unbleached pulp to give the multiply paper substrate a natural look.

In some embodiments, the fifth pulp suspension comprises less than 15 wt% (based on dry weight), and more preferably less than 10 wt% (based on dry weight), of broke pulp. In some embodiments, the fifth pulp suspension comprises no broke pulp.

The method of the present disclosure comprises forming and dewatering a first web layer from a first pulp suspension to obtain a first outer ply, forming and dewatering a second web layer from a second pulp suspension to obtain a first bulk ply, forming and dewatering a third web layer from a third pulp suspension to obtain a barrier mid-ply, forming and dewatering a fourth web layer from a fourth pulp suspension to obtain a second bulk ply, and forming and dewatering a fifth web layer from a fifth pulp suspension to obtain a second outer ply of the multiply paper substrate.

Dewatering of the web layers may be performed using methods and equipment known in the art. Examples include but are not limited to table roll and foils, friction less dewatering and ultra-sound assisted dewatering. Dewatering means that the dry solids content of the web layers is reduced compared to the dry solids content of the pulp suspensions, but the dewatered web layer may still comprise some water. In some embodiments, dewatering of the web layer means that the dry solids content of the dewatered web layer is above 1 wt% but below 15 wt%. In some embodiments, dewatering of the web layer means that the dry solids content of the dewatered web layer is above 1 wt% but below 10 wt%. A dry solids content of the dewatered webs in this range has been found to be especially suitable for joining the wet webs into a multilayer web.

The different web layers can be formed and dewatered separately, on different wires, or together, on the same wire. In some embodiments two or more of the web layers are formed and dewatered on different wires, and subsequently joined.

The dewatered web layers are preferably joined by wet lamination. When the pulp suspension is dewatered on the wire a visible boundary line will appear at a point where the web layer goes from having a reflective water layer to where this reflective layer disappears. This boundary line between the reflective and non- reflective web layer is referred to as the waterline. The waterline is indicative of a certain solids content of the web. The webs are preferably joined after the water line. Joining the web layers while they are still wet ensures good adhesion between the layers. The joining can be achieved by applying one of the dewatered web layers on top of the other. The joining may be done non-wire side against non-wire side, or wire-side against non-wire side. Joining and further dewatering of the formed multilayer web may be improved by various additional operations. In some embodiments, the joining further comprises pressing the dewatered web layers together. In some embodiments, the joining further comprises applying suction to the joined dewatered web layers. Applying pressure and/or suction to the formed multilayer web improves adhesion between the web layers.

In some embodiments two or more of the web layers are formed and dewatered on the same wire. In some embodiments, the second, third and fourth web layers are formed and dewatered on the same wire using a multilayer headbox or using three separate head boxes.

In some embodiments, the first, second, third, fourth and fifth web layers are all formed and dewatered on the same wire using a multilayer headbox or using several separate headboxes.

In some embodiments, the third web layer is formed directly on the second web layer by applying the third pulp suspension on the wet or dewatered second web layer. The second web layer is preferably dewatered before the third web layer is formed or applied. In some embodiments, the third web layer is formed simultaneously with the second web layer, e.g. using a multilayer headbox or two headboxes arranged at the same wire. In some embodiments, the second web layer and the third web layer are formed simultaneously using a multilayer headbox. The water of the third pulp suspension can be removed by dewatering through the less drainage resistant second web layer, or by drying, or by a combination thereof. The dewatering and/or drying of the third web layer results in the formation of the barrier mid-ply on the first bulk ply.

In some embodiments, the method further comprises the step f) dewatering and/or drying the multiply paper substrate to a moisture content below 10 wt%, preferably in the range of 5-9 wt%, as determined according to ISO 287.

The further dewatering typically comprises pressing the multiply paper substrate to squeeze out as much water as possible. The further dewatering may for example include passing the formed multiply paper substrate through a press section of a paper machine, where the web passes between large rolls loaded under high pressure to squeeze out as much water as possible. In some embodiments the further dewatering comprises passing the web through one or more shoe presses. The removed water is typically received by a fabric or felt. In some embodiments, the dry solids content of the multiply paper substrate after the further dewatering is in the range of 15-48 wt%, preferably in the range of 18-40 wt%, and more preferably in the range of 22-35 wt%.

The drying may for example include drying the multiply paper substrate by passing the multiply paper substrate around a series of heated drying cylinders. Drying may typically remove the water content down to a level of about 1-15 wt%, preferably to about 2-10 wt%.

Each of the first and second outer plies of the multiply paper substrate is obtained by forming and dewatering a web layer from a pulp suspension comprising at least 70 wt% (based on dry weight) of Kraft pulp.

The first and second outer plies of the multiply paper substrate thus comprise a high amount of Kraft pulp ensuring structural integrity, smoothness, printability and aesthetics. In some embodiments, one of the outer plies is the top ply, intended to serve as the outer and primary printing surface of a packaging formed from the multiply paper substrate, and the other outer layer is the bottom ply, intended to serve as the inner surface of a packaging formed from the multiply paper substrate and provides structural integrity and additional strength. Although the first and second outer plies may be identical, or at least formed from the same pulp suspension, one of the outer plies will often focus more on appearance and print quality, while the other outer ply provides additional strength and durability.

In some embodiments, each of the first and second outer plies have a grammage in the range of 20-100 g/m².

In some embodiments, each of the first and second outer plies have a density in the range of 700-950 kg/m³.

Each of the first and second bulk plies of the multiply paper substrate is obtained by forming and dewatering a web layer from a pulp suspension comprising high- bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High- Temperature Chemi-ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, as well as broke pulp obtained from the method for manufacturing a multiply paper substrate.

High-bulk pulp refers to a type of paper pulp characterized by its lower density and higher volume compared to regular pulp. This type of pulp is designed to create paper products that are bulkier and thicker while maintaining a lower weight. The high-bulk pulp in the present disclosure is selected from Chemi- ThermoMechanical Pulp (CTMP), High-Temperature Chemi-ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof.

The term “broke” as used herein refers to paper that is discarded at any point in the manufacturing process. This can include dry or wet web layer, multilayer web, or paper trimmings, off-spec dry or wet web layer, multilayer web, or paper, or any dry or wet web layer, multilayer web, or paper that is damaged or defective during production, as well as combinations thereof. The term “broke pulp” as used herein refers to pulp obtained from broke. Essentially, broke encompasses all forms of paper waste generated within a paper mill. Accordingly, the broke pulp may comprise pulp obtained from all plies of the multiply paper substrate.

Recycling broke within the paper manufacturing process typically involves several steps to reintegrate it back into the production cycle. Broke is collected from various points in the manufacturing process. This includes trimmings from paper cutting, rejected rolls, and damaged sheets. It is sorted based on its quality and type.

The sorted broke is sent to a repulper, where it is mixed with water and agitated to break it down into its fibrous components. This creates a broke pulp suspension. The broke pulp suspension can be screened and cleaned to remove any contaminants, such as filler, adhesives, ink, or debris. This step ensures that the broke pulp is of high quality and suitable for reuse. The optionally cleaned broke pulp suspension will typically have an SR value in the range of 20-50. The broke pulp is mixed and optionally co-refined with the high-bulk pulp and optionally other components to obtain a pulp suspension with the desired quality and characteristics for use in the first and second bulk ply. The pulp suspension comprising the mixture is then fed back into the papermaking machine, where it is formed and dewatered to obtain the intermediate plies of the multiply paper substrate.

The second and fourth pulp suspension comprises 2-35 wt% (based on dry weight) of broke pulp obtained from the method for manufacturing a multiply paper substrate. In some embodiments, the second and fourth pulp suspension comprises 2-30 wt% (based on dry weight), preferably 2-25 wt% (based on dry weight), of broke pulp obtained from the method for manufacturing a multiply paper substrate. In some embodiments, the second and fourth pulp suspension comprises at least 5 wt% (based on dry weight) or at least 10 wt% (based on dry weight) of broke pulp obtained from the method for manufacturing a multiply paper substrate. In some embodiments, the second and fourth pulp suspension comprises 5-30 wt% (based on dry weight), preferably 5-20 wt% (based on dry weight), of broke pulp obtained from the method for manufacturing a multiply paper substrate. In some embodiments, the second and fourth pulp suspension comprises 10-30 wt% (based on dry weight), preferably 10-20 wt% (based on dry weight), of broke pulp obtained from the method for manufacturing a multiply paper substrate.

The use of broke pulp obtained from the method for manufacturing a multiply paper substrate leads to an increased amount of MFC in the second and fourth pulp suspension. In some embodiments, the broke pulp in the second and fourth pulp suspension comprises at least 0.1 wt% (based on dry weight), preferably at least 0.5 wt% (based on dry weight), and more preferably at least 1 wt% (based on dry weight), of MFC. In some embodiments, the broke pulp in the second and fourth pulp suspension comprises in the range of 0.1-5 wt% (based on dry weight), preferably in the range of 0.5-5 wt% (based on dry weight), and more preferably in the range of 1-5 wt% (based on dry weight), of MFC.

Due to the MFC content, the broke pulp obtained from the method for manufacturing a multiply paper substrate will have a relatively low drainage rate and a relatively high water retention. The drainage rate is expressed as a Schopper-Riegler (SR) value, as determined by standard ISO 5267-1. In some embodiments, the broke pulp in the second and fourth pulp suspension has an SR value in the range of 20-50, preferably in the range of 20-40, and more preferably in the range of 25-40. The water retention of the pulp is expressed as the water retention value (WRV), as determined by standard ISO 23714:2014. In some embodiments, the broke pulp in the second and fourth pulp suspension has a WRV in the range of 120-180%.

In some embodiments, each of the first and second bulk plies have a grammage in the range of 20-120 g/m².

In some embodiments, each of the first and second bulk plies have a density below 700 kg/m³.

The barrier mid-ply of the multiply paper substrate is obtained by forming and dewatering a third web layer from the third pulp suspension comprising at least 70 wt% (based on dry weight) of microfibrillated cellulose (MFC) having a Schopper- Riegler (SR) value in the range of 80-100.

The barrier mid-ply of the multiply paper substrate comprises a high amount of microfibrillated cellulose (MFC) having a Schopper-Riegler (SR) value in the range of 80-100, which forms a dense layer with low permeability, providing gas, aroma and grease barrier properties to the multiply paper substrate.

Forming the MFC barrier layer as a mid-ply in the multiply paper substrate allows dewatering and drying in both directions which helps to retain the barrier properties of the barrier mid-ply.

Forming the MFC barrier layer as a mid-ply in the multiply paper substrate also allows the barrier mid-ply of the multiply paper substrate to act as a barrier for migration of internal contaminants between the outer and bulk plies on one side of the barrier mid-ply to the outer and bulk plies the other side of the barrier mid-ply. Such internal contaminants may for example include saturated hydrocarbons (MOSH) and alkylated aromatic hydrocarbons (MOAH). This is advantageous as it may allow for using higher amounts of recycled fibers, which often contain elevated levels of MOSH and/or MOAH, in the outer and bulk plies of the multiply paper substrate.

Forming the MFC barrier layer as a mid-ply in the multiply paper substrate also protects the barrier layer and minimizes the stress on the sensitive barrier ply during transport, handling and converting of the multiply paper substrate. The barrier layer arranged as a mid-ply in the multiply paper substrate does not need to stretch as much during folding and converting as a barrier layer arranged as an outer ply in a multiply paper substrate. This reduces the risk of cracking the sensitive barrier layer during folding and converting.

One advantage of forming the MFC barrier layer as a barrier mid-ply in the multiply paper substrate is that the grammage of the ply can be low. This is possible as the barrier mid-ply is supported and protected by the adjacent bulk plies. In some embodiments, the barrier mid-ply has a grammage in the range of 5-35 g/m², preferably in the range of 5-30 g/m², and more preferably in the range of 5-25 g/m².

The density of the barrier mid-ply in the formed multiply paper substrate is preferably above 850 kg/m³, and more preferably above 950 kg/m³. The density of the barrier mid-ply in the formed multiply paper substrate may for example be in the range of 850-1300 kg/m³ or in the range of 950-1300 kg/m³. The density of the barrier mid-ply is typically significantly higher than the density of the first and second outer plies and the first and second bulk plies in the formed multiply paper substrate. In some embodiments, the density of the barrier mid-ply is at least 100 kg/m³ higher, and more preferably at least 150 kg/m³ higher, than the density of the first and second outer plies in the formed multiply paper substrate. In some embodiments, the density of the barrier mid-ply is at least 200 kg/m³ higher, and more preferably at least 250 kg/m³ higher, than the density of the first and second bulk plies in the formed multiply paper substrate.

The multiply structure of the formed multiply paper substrate may preferably be at least partially symmetrical. This means that the first outer ply may have the same or similar composition and/or properties as the second outer ply, or that the first bulk ply may have the same or similar composition and/or properties as the second bulk ply, or both. This symmetrical structure helps to prevent curling of the formed multilayer structures.

The term “similar properties” as used herein generally means that the value of a property of the first outer ply differs from the corresponding value of the property of the second outer ply by less than 10 %, and preferably less than 5 %, or that the value of a property of the first bulk ply differs from the corresponding value of the property of the second bulk ply by less than 10 %, and preferably less than 5 %, or both, when the values are measured by the same method.

In some embodiments, the pulp in the first and fifth pulp suspensions have the same or similar SR values. In some embodiments, the Kraft pulp in the first and fifth pulp suspensions have the same or similar SR values. The term "similar SR values” as used herein means that the difference between the SR values of the pulp in the first and fifth pulp suspensions is less than 10 %, and preferably less than 5 %. Having the same or similar SR values of the pulp in the first and fifth pulp suspensions leads to the same or similar shrinkage during dewatering or drying of the first and the fifth web layers.

In some embodiments, the first and fifth web layers exhibit the same or similar shrinkage during dewatering or drying. The term "similar shrinkage” as used herein means that the difference between the shrinkage of the first and the fifth web layer is less than 10 %, preferably less than 5 % in both the machine direction and in the cross direction.

In some embodiments, the first and fifth web layers have the same or similar composition. The term "similar composition” as used herein means that the first and fifth web layers are composed of the same or equivalent components, such as Kraft pulp and optional additives. The amounts of the components preferably differ by less than 10 %, and preferably less than 5 %. In some embodiments, the amount of Kraft fibers in the first and fifth web layers layers (based on dry weight) differ by less than 10 %, and preferably less than 5 %. In some embodiments, the first and fifth web layers have the same or similar grammage. In some embodiments, the same pulp suspension is used for the first and fifth web layers. In other words, in some embodiments the first and fifth pulp suspension are the same. The term "similar grammage” as used herein means that the grammages of the first and fifth web layers differ by less than 10 %, and preferably less than 5 %. In some embodiments, the first and fifth web layers have the same composition. In some embodiments, the first and fifth web layers have the same grammage. In some embodiments, the first and fifth web layers have the same density.

In some embodiments, the pulp in the second and fourth pulp suspensions have the same or similar SR values. In some embodiments, the high-bulk pulp in the second and fourth pulp suspensions have the same or similar SR values. The term "similar SR values” as used herein means that the difference between the SR values of the pulp in the second and fourth pulp suspensions is less than 10 %, and preferably less than 5 %. Having the same or similar SR values of the pulp in the second and fourth pulp suspensions leads to the same or similar shrinkage during dewatering or drying of the second and the fourth web layers.

In some embodiments, the second and fourth web layers exhibit the same or similar shrinkage during dewatering or drying. The term "similar shrinkage” as used herein means that the difference between the shrinkage of the second and the fourth web layer is less than 10 %, preferably less than 5 % in both the machine direction and in the cross direction.

In some embodiments, the second and fourth web layers have the same or similar composition. The term "similar composition” as used herein means that the second and fourth web layers are composed of the same or equivalent components, such as high-bulk pulp and broke pulp, and optional additives. The amounts of the components preferably differ by less than 10 %, and preferably less than 5 %. In some embodiments, the amount of high-bulk pulp in the second and fourth web layers (based on dry weight) differ by less than 10 %, and preferably less than 5 %. In some embodiments, the amount of broke pulp in the second and fourth web layers (based on dry weight) differ by less than 10 %, and preferably less than 5 %. In some embodiments, the same pulp suspension is used for the second and fourth web layers. In other words, in some embodiments the second and fourth pulp suspension are the same. In some embodiments, the second and fourth web layers have the same or similar grammage. The term "similar grammage” as used herein means that the grammages of the second and fourth web layers differ by less than 10 %, and preferably less than 5 %. In some embodiments, the second and fourth web layers have the same composition. In some embodiments, the second and fourth web layers have the same grammage. In some embodiments, the second and fourth web layers have the same density.

In some embodiments, the grammage of the formed multilayer web and obtained multiply paper substrate is in the range of 50-300 g/m², preferably in the range of 50-200 g/m², more preferably in the range of 50-150 g/m².

Thanks at least in part to the MFC in the broke pulp of the first and second bulk plies, the obtained multiply paper substrate will typically have a relatively high internal bond strength, as measured by Scott bond. In some embodiments, the multiply paper substrate has a Scott bond above 110 J/m², preferably above 120 J/m², and more preferably above 130 J/m² as determined according to TAPPI 569.

The structure of the obtained multiply paper substrate, particularly the first and second bulk plies, provides the multiply paper substrate with a relatively high bending resistance. In some embodiments, the multiply paper substrate has a bending resistance (L&W 15° according to ISO 2493-1) in the machine direction (MD), above 220 mN, preferably above 250 mN, and more preferably above 300 mN, and a bending resistance (L&W 15° according to ISO 2493-1) in the cross direction (CD), above 120 mN, preferably above 140 mN, and more preferably above 160 mN.

The obtained multiply paper substrate will typically exhibit good resistance to grease and oil. Grease resistance of the multiply paper substrate can be determined by the KIT-test according to standard ISO 16532-2. The test uses a series of mixtures of castor oil, toluene and heptane. As the ratio of oil to solvent is decreased, the viscosity and surface tension also decrease, making successive mixtures more difficult to withstand. The performance is rated by the highest numbered solution which does not darken the sheet after 15 seconds. The highest numbered solution (the most aggressive) that remains on the surface of the paper without causing failure is reported as the "kit rating" (maximum 12). In some embodiments, the KIT value of the obtained multiply paper substrate is at least 6, preferably at least 8, as measured according to standard ISO 16532-2.

In some embodiments, the obtained multiply paper substrate has a Gurley Hill value of at least 10 000 s/100ml, preferably at least 25000 s/100ml, and more preferably at least 40 000 s/100ml, as measured according to standard ISO 5636/6.

In addition to barrier properties, the obtained multiply paper substrate also has a high compressive strength. In some embodiments, the obtained multiply paper substrate has a compressive strength (SOT index in cross direction) of at least 15 Nm/g, preferably at least 18 Nm/g, and more preferably at least 20 Nm/g or at least 22 Nm/g, as measured according to ISO 9895.

The obtained multiply paper substrate preferably also has high repulpability. In some embodiments, the obtained multiply paper substrate exhibits less than 30 %, preferably less than 20 %, and more preferably less than 10 % residues, when tested as a category II material according to the PTS-RH 021/97 test method.

The multiply paper substrates of the present disclosure are especially suited as substrates for packaging laminates, such as liquid packaging board (LPB), when coated or laminated with one or more polymer layers. Thus, the multiply paper substrate may preferably be coated or laminated with one or more polymer layers.

In some embodiments one or more polymer layer(s) are applied on one side or on both sides of the multiply paper substrate. The one or more polymer layer(s) may of course interfere with repulpability but may still be required or desired in some applications. Polymer layers may for example be applied by extrusion coating, film lamination or dispersion coating. In some embodiments, the one or more polymer layer(s) comprises a PVOH coating layer. The PVOH coating layer improves the barrier properties of the coated multiply paper substrate. The PVOH coating layer may also provide an additional barrier against migration of low molecular weight substances, such as MOAH and MOSH from the multiply paper substrate. The PVOH coating layer may also improve the adhesion of a further polymer coating layer applied on the PVOH coating layer.

The PVOH coating layer may be applied by any suitable method known in the art. The PVOH coating layer may for example be applied as a solution or dispersion in an aqueous or organic solvent carrier using liquid coating methods known in the art, in melt form using extrusion coating, or in the form of a solid film by lamination.

The PVOH coating layer is preferably formed by means of a liquid film coating process, i.e. in the form of a solution or dispersion which, on application, is spread out to a thin, uniform layer on the substrate and thereafter dried. The liquid phase of the solution or dispersion is preferably water or an aqueous solution, but organic solvents or mixtures of water or aqueous solutions and organic solvents may also be used. The one or more polymers may be present in the solution or dispersion in dissolved form or in the form of polymer particles, such as a latex. The PVOH coating layer can be applied by contact or non-contact coating methods. Examples of useful coating methods include, but are not limited to rod coating, curtain coating, film press coating, cast coating, transfer coating, size press coating, impregnation, flexographic coating, gate roll coating, twin roll HSM coating, blade coating, such as short dwell time blade coating, jet applicator coating, spray coating, gravure coating or reverse gravure coating.

To minimize the risk of pinholes in the PVOH coating layer, the PVOH coating layer may preferably be applied in at least two different coating steps with drying of the coated film between the steps.

In some embodiments, the PVOH coating layer comprises at least 50 wt% of a PVOH, preferably at least 70 wt% of a PVOH, based on the total dry weight of the PVOH coating layer. In some embodiments, the PVOH coating layer comprises at least 50 wt% of a water-soluble PVOH based on dry weight. The water-soluble PVOH of the PVOH coating layer is soluble in cold water or soluble in hot water, e.g. at a temperature below 100 °C or even above 100 °C, for a given period of time. The water-soluble PVOH coating layer in addition to providing barrier properties and improving the adhesion of a further polymer coating layer applied on the PVOH coating layer, can also facilitate separation of a further polymer coating layer applied on the PVOH coating layer during repulping.

In some embodiments, the PVOH has a degree of hydrolysis in the range of 80-99 mol%, preferably in the range of 85-99 mol%.

In some embodiments, the PVOH coating layer further comprises a crosslinking agent capable of crosslinking the water-soluble polymer. The crosslinking agent may advantageously be applied together with the water-soluble polymer, and then activated, e.g. by heat or radiation, when the PVOH coating layer is in contact with the inorganic thin film coating. Crosslinking improves the water vapor barrier properties of the PVOH coating layer. Suitable crosslinking agents include, but are not limited to polyfunctional organic acids or aldehydes, such as citric acid, glyoxal, and glutaraldehyde. In some embodiments, the crosslinking agent is an organic acid, and more preferably citric acid. The concentration of the crosslinking agent may for example be 1-20 wt%, preferably 1-15 wt%, based on the total dry weight of the PVOH coating layer.

In some embodiments, the grammage of the PVOH coating layer is in the range of 1-20 g/m², preferably in the range of 2-15 g/m², more preferably in the range of 2- 12 g/m², based on dry weight.

In some embodiments, the one or more polymer layer(s) comprises a thermoplastic polymer layer comprising any of the thermoplastic polymers commonly used in paper or paperboard based packaging materials in general or polymers used in liquid packaging board in particular. Examples include polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polyhydroxyalkanoates (PHA), polylactic acid (PLA), polyglycolic acid (PGA), starch and cellulose. Polyethylenes, especially low density polyethylene (LDPE) and high density polyethylene (HDPE), are the most common and versatile polymers used in liquid packaging board.

Thermoplastic polymers are useful since they can be conveniently processed by extrusion coating techniques to form very thin and homogenous films with good liquid barrier properties. In some embodiments, the polymer layer comprises polypropylene or polyethylene. In preferred embodiments, the polymer layer comprises polyethylene, more preferably LDPE or HDPE.

In some embodiments, the polymer layer is formed by extrusion coating of the polymer onto a surface of the multiply paper substrate. Extrusion coating is a process by which a molten plastic material is applied to a substrate to form a very thin, smooth and uniform layer. Common plastic resins used in extrusion coating include polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET).

In some embodiments, the polymer layer is formed by laminating a plastic film to a surface of the multiply paper substrate using an adhesive tie layer. The adhesive tie layer may for example comprise PVOH. The adhesive tie layer may be further defined as described for the PVOH coating layer.

In some embodiments, the polymer layer is vacuum deposition coated, preferably metallized. Vacuum deposition coating refers to a family of processes used to deposit layers of metals, metal oxides and other inorganic and organic compositions, typically atom-by-atom or molecule-by-molecule, on a solid surface. Vacuum deposition of a metal or metal oxide may also be referred to as metallization. In some embodiments, the vacuum deposition coating comprises a metal or metal oxide selected from the group consisting of aluminum, magnesium, silicon, copper, aluminum oxides, magnesium oxides, silicon oxides, and combinations thereof, preferably aluminum or an aluminum oxide. Multiple layers of the same or different materials can be combined. The process can be further specified based on the vapor source; physical vapor deposition (PVD) uses a liquid or solid source and chemical vapor deposition (CVD) uses a chemical vapor. Vacuum deposition coating typically results in very thin coatings. In some embodiments, the vacuum deposition coating has a thickness in the range of IQ- 600 nm, preferably in the range of 10-250 nm, and more preferably in the range of 50-250 nm. This should be compared to conventional aluminum foils used in packaging laminates, which foils typically have thickness in the range of about 3- 12 pm.

In some embodiments, the polymer layer is formed by laminating a vacuum deposition coated, preferably metallized, plastic film to a surface of the multiply paper substrate using an adhesive tie layer. The adhesive tie layer may for example comprise PVOH. The adhesive tie layer be further defined as described for the PVOH coating layer.

The polymer layer may comprise one or more layers formed of the same polymeric resin or of different polymeric resins. In some embodiments the polymer layer comprises a mixture of two or more different polymeric resins. In some embodiments the polymer layer is a multilayer structure comprised of two or more layers, wherein a first layer is comprised of a first polymeric resin and a second layer is comprised of a second polymeric resin, which is different from the first polymeric resin. For example in some embodiments, the multiply paper substrate comprises a PVOH coating layer and a polymer layer applied by extrusion coating or a plastic film or a metallized plastic film applied by lamination onto the PVOH coating layer. When a plastic film or a metallized plastic film is applied by lamination, the PVOH coating layer may advantageously be used as the adhesive tie layer.

The grammage of each polymer layer of the multiply paper substrate is preferably less than 50 g/m². In order to achieve a continuous and substantially defect free film, a grammage of the polymer layer of at least 8 g/m², preferably at least 12 g/m² is typically required. In some embodiments, the grammage of the polymer layer is in the range of 8-50 g/m², preferably in the range of 12-50 g/m². Unless otherwise specified, parameters discussed in the present disclosure are measured according to the following standards:

Grammage ISO 536

Density ISO 534

Drainability (SR) ISO 5267-1

Water retention (WRV) ISO 23714:2014 Fiber length (Lc(l)) ISO 16065-2 Grease resistance (KIT) ISO 16532-2 Viscosity SCAN-P 50:84

Porosity (Gurley Hill) ISO 5636/6 SGT (CD) ISO 9895

Repulpability (PTS) PTS-RH 021/97

Generally, while the products, polymers, materials, layers, and processes are described in terms of “comprising” various components or steps, the products, polymers, materials, layers and processes can also “consist essentially of” or “consist of” the various components and steps.

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

Claims

1. A method for manufacturing a multiply paper substrate comprising, in order, a first outer ply, a first bulk ply, a barrier mid-ply, a second bulk ply, and a second outer ply in a paper machine, the method comprising the steps: a) forming and dewatering a first web layer from a first pulp suspension comprising at least 70 wt% (based on dry weight) of Kraft pulp to obtain a first outer ply of the multiply paper substrate; b) forming and dewatering a second web layer from a second pulp suspension comprising at least 65 wt% (based on dry weight) of high-bulk pulp selected from Chemi-ThermoMechanical Pulp (CTMP), High-Temperature Chemi- ThermoMechanical Pulp (HT-CTMP), high yield pulp, pressurized groundwood (PGW), or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp, to obtain a first bulk ply of the multiply paper substrate; c) forming and dewatering a third web layer from a third pulp suspension comprising at least 70 wt% (based on dry weight) of m icrofibril lated cellulose (MFC) having a Schopper-Riegler (SR) value in the range of 80-100, to obtain a barrier mid-ply of the multiply paper substrate; d) forming and dewatering a fourth web layer from a fourth pulp suspension comprising at least 65 wt% (based on dry weight) of high-bulk pulp selected from CTMP, HT-CTMP, high yield pulp, PGW, or a combination thereof, and 2-35 wt% (based on dry weight) of broke pulp, to obtain a second bulk ply of the multiply paper substrate; e) forming and dewatering a fifth web layer from a fifth pulp suspension comprising at least 70 wt% (based on dry weight) of Kraft pulp to obtain a second outer ply of the multiply paper substrate; wherein the broke pulp in the second and fourth pulp suspension is obtained from the method for manufacturing a multiply paper substrate.

2. The method according to claim 1 , wherein the second and fourth pulp suspension comprises 2-30 wt% (based on dry weight), preferably 2-25 wt% (based on dry weight), of the broke pulp obtained from the method for manufacturing a multiply paper substrate.

3. The method according to any one of the preceding claims, wherein the broke pulp in the second and fourth pulp suspension comprises at least 0.1 wt% (based on dry weight), preferably at least 0.5 wt% (based on dry weight), and more preferably at least 1 wt% (based on dry weight), of MFC.

4. The method according to any one of the preceding claims, wherein the broke pulp in the second and fourth pulp suspension has an SR value in the range of 20- 50, preferably in the range of 20-40, and more preferably in the range of 25-40.

5. The method according to any one of the preceding claims, wherein the broke pulp in the second and fourth pulp suspension has a water retention value (WRV) value in the range of 120-180%.

6. The method according to any one of the preceding claims, wherein the second, third and fourth web layers are formed and dewatered on the same wire using a multilayer headbox or using three separate headboxes.

7. The method according to any one of the preceding claims, further comprising the step f) dewatering and/or drying the multiply paper substrate to a moisture content below 10 wt%, preferably in the range of 5-9 wt%, as determined according to ISO 287.

8. The method according to any one of the preceding claims, wherein each of the first and second outer plies have a grammage in the range of 20-100 g/m².

9. The method according to any one of the preceding claims, wherein each of the first and second outer plies have a density in the range of 700-950 kg/m³.

10. The method according to any one of the preceding claims, wherein each of the first and second bulk plies have a grammage in the range of 20-120 g/m².

11. The method according to any one of the preceding claims, wherein each of the first and second bulk plies have a density below 700 kg/m³.

12. The method according to any one of the preceding claims, wherein the barrier mid-ply has a grammage in the range of 5-35 g/m², preferably in the range of 5-30 g/m², and more preferably in the range of 5-25 g/m².

13. The method according to any one of the preceding claims, wherein the barrier mid-ply has a density above 850 kg/m³, preferably above 950 kg/m³.

14. The method according to any one of the preceding claims, wherein the Kraft pulp in the first and fifth pulp suspensions have the same or similar SR values.

15. The method according to any one of the preceding claims, wherein the high- bulk pulp in the second and fourth pulp suspensions have the same or similar SR values.

16. The method according to any one of the preceding claims, wherein the first and fifth web layers have the same or similar grammage.

17. The method according to any one of the preceding claims, wherein the second and fourth web layers have the same or similar grammage.

18. The method according to any one of the preceding claims, wherein the multiply paper substrate has a Scott bond above 110 J/m², preferably above 120 J/m², and more preferably above 130 J/m² as determined according to TAPPI 569.

19. The method according to any one of the preceding claims, wherein the multiply paper substrate has a bending resistance (L&W 15° according to ISO 2493-1) in the machine direction (MD), above 220 mN, preferably above 250 mN, and more preferably above 300 mN, and a bending resistance (L&W 15° according to ISO 2493-1) in the cross direction (CD), above 120 mN, preferably above 140 mN, and more preferably above 160 mN.

20. The method according to any one of the preceding claims, further comprising applying a polymer layer to the multiply paper substrate by laminating a vacuum deposition coated, preferably metallized, plastic film to a surface of the multiply paper substrate using an adhesive tie layer.

21. The method according to claim 20, wherein the adhesive tie layer comprises polyvinyl alcohol (PVOH).