Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
  • D21H11/06—Sulfite or bisulfite pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
  • D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
  • D21C9/02—Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/14—Secondary fibres
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/03—Non-macromolecular organic compounds
  • D21H17/05—Non-macromolecular organic compounds containing elements other than carbon and hydrogen only
  • D21H17/17—Ketenes, e.g. ketene dimers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/62—Rosin; Derivatives thereof
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
  • D21H17/68—Water-insoluble compounds, e.g. fillers, pigments siliceous, e.g. clays
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/06—Paper forming aids
  • D21H21/10—Retention agents or drainage improvers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/16—Sizing or water-repelling agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
  • D21H21/20—Wet strength agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/10—Packing paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
  • D21H27/40—Multi-ply at least one of the sheets being non-planar, e.g. crêped

Definitions

• the present invention relates to a fluting or liner comprising neutral sulfite semi chemical (NSSC) pulp.
• NSC neutral sulfite semi chemical
• Corrugated board (sometimes referred to as corrugated cardboard or corrugated fiberboard) is a packaging material which can be converted to different types of packaging solutions.
• Corrugated board is a fiber based material made from cellulose fibers, virgin or recycled from used corrugated cardboard or other materials.
• the corrugated board comprises a corrugated medium (fluting) and at least non-corrugated medium (liner or linerboard) glued onto a surface of the corrugated medium.
• the corrugated board may consist of a layer of fluting glued between two layers of liner to form a sandwich structure.
• the sandwich structure can be formed in different ways such as in single, double, and triple walls as described, e.g., in Kirwan M., J., Paper and Paperboard. Packaging Technology, Blackwell Publishing 2005.
• liners examples include kraftliner and testliner.
• Kraftliner is typically produced from kraft pulp that can be bleached or unbleached and may comprise one or more layers/plies wherein the top layer/ply is often optimized to provide a good printing surface and good moisture resistance.
• Testliner is mainly produced from recycled corrugated board and is commonly manufactured in two layers/plies. Due to the presence of recycled fibers, testliner may typically have lower mechanical strength, particularly lower burst strength, than kraftliner. Kraftliner is frequently used in packaging boxes with higher demands on strength properties.
• Fluting is formed from paper or paperboard which has been corrugated using heat, moisture and pressure using a corrugator.
• NSSC neutral sulfite semi chemical
• NSSC pulp which is normally made from hardwood species, is noted for exceptional stiffness and high rigidity making it suitable for use in fluting.
• Neutral Sulfite Semi-Chemical (NSSC) pulping is an old process that it is well known in the field of paper pulping.
• the cooking liquor comprises sulfite, such as Na 2 SO 3 or (NH 4 ) 2 SO 3 and a base, such as NaOH or Na 2 CO 3 .
• “Neutral” means that the pH of the NSSC cooking liquor is generally between 6 and 10. The pulp can be cooked in a batch or continuous cooker.
• the cooking time is between 5 minutes and 3 hours and the cooking temperature is 160-200° C.
• the NSSC pulp comprises comparatively high amounts of residual lignin, such as 15-20%, which makes the NSSC pulp stiff.
• the Kappa number of the NSSC pulp is typically above 70.
• the NSSC pulping is “semi-chemical” in the sense that it also comprises mechanical refining of the pulp. Refining may for example be done using a disc refiner at digester pressure or at atmospheric pressure.
• the fluting and liner(s) are attached to each other by arranging an adhesive between the corrugated medium and liner(s).
• the liner is attached to at least one surface of the corrugated medium by the adhesive.
• the adhesive is preferably applied on a least one surface of the fluted corrugated medium and the liner is thereafter attached to said surface. Any conventional adhesives in the area may be used.
• the adhesive may for example be a glue that is based on starch that can be extracted from a wide variety of plants. Some of the most common plants are maize, wheat, barley, rice, potato, tapioca and peas.
• the starch is preferably native, i.e. no modification of the starch has been done.
• the adhesive may also comprise water, sodium hydroxide and boric acid.
• additives such as additives to improve the wet strength or adhesive bond strength may also be added.
• other functional chemicals in order to improve e.g. moisture resistance or gelling behavior can be added, e.g. borax, glyoxal or mixtures thereof.
• corrugated medium and corrugated board One important challenge when making corrugated medium and corrugated board is the resistance to humidity. When the corrugated board is exposed to humidity, water and water vapor may diffuse through the liners and soften the corrugating medium. A common solution to this problem is to increase grammage of the fluting and/or liner, but this is in conflict with environmental demands requiring lower grammage materials consuming less raw material.
• Another solution is to provide a barrier layer on the liner to reduce the penetration of water and water vapor.
• this is only a partial solution since moisture diffusion may still occur on the opposite side or via the edges and consequently impact the mechanical stability of the corrugated board.
• Barrier layers also increase cost and typically reduce recyclability of the materials.
• the fluting or corrugating medium may also be treated with hydrophobizing chemicals or coated, but this generally adds costs and may also impact the mechanical properties of the fluting negatively.
• High levels of hydrophobizing chemicals may also compromise the adhesion between the fluting and the liner(s).
• NSSC pulps require high levels of hydrophobizing chemicals to obtain a required level of water resistance in the finished fluting.
• the present invention is based on the inventive realization that if the ash content of a NSSC pulp used in a fluting or liner is reduced, the amount of hydrophobizing internal sizing agent required to obtain a required level of water resistance in the finished fluting or liner can be significantly reduced. Reducing the ash content of the pulp has also been found to reduce the required amounts of other wet end chemicals, e.g. drainage/retention chemicals in the fluting or liner.
• Reduction of the ash content can be achieved by washing of the pulp.
• the ash content can also be reduced by more efficient removal of bark prior to the pulping process.
• a fluting or liner for corrugated board comprising a neutral sulfite semi chemical (NSSC) pulp, wherein said NSSC pulp has an ash content of less than 1.8 wt %, as determined according to standard ISO 1762:2019.
• NSSC neutral sulfite semi chemical
• “NSSC pulp” is obtained from “NSSC pulping”, which in turn is defined in the background section.
• the NSSC pulp can be hardwood pulp or softwood pulp, or a mixture thereof.
• the NSSC pulp is preferably hardwood pulp or a hardwood/softwood pulp mixture with less than 15 wt % softwood, preferably less than 10 wt % softwood, and more preferably less than 5 wt % softwood.
• the hardwood may for example be aspen, alder, poplar, eucalyptus, birch, acacia, or beech.
• the NSSC pulp is preferably prepared cooked using a cooking liquor comprising sulfite, preferably Na 2 SO 3 or (NH 4 ) 2 SO 3 and a base, preferably NaOH or Na 2 CO 3 .
• the yield from the NSSC pulping is above 60%, preferably above 65%, preferably above 70%, and more preferably above 75%.
• neutral means that the pH of the NSSC cooking liquor is in the range of 6-10.
• the cooking time preferably in the range of 5 minutes to 3 hours.
• the cooking temperature is preferably in the range of 160-200° C.
• the NSSC pulp may comprise comparatively high amounts of residual lignin, such as 15-20%.
• the Kappa number of the NSSC pulp is typically above 70, preferably above 80, preferably above 95, and more preferably above 100, according to ISO 3260.
• the NSSC pulping is “semi-chemical” in the sense that it also comprises mechanical refining of the pulp. Refining may for example be done using a disc refiner at digester pressure or at atmospheric pressure. The refining can be done in one or more steps at the same or different pulp consistencies. A first refining step may preferably be done at higher consistency such as 5-35%, and a second refining step may preferably be done at lower consistency ⁇ 5%.
• said NSSC pulp in the fluting or liner has been subjected to washing to reduce the ash content.
• the purpose of washing is to separate the pulp from black liquor to wash out the residual substances such as alkali-lignin produced in the cooking process, and purify the pulp. Washing can be done using one or more conventional pulp washing methods and washing equipment, including, but not limited to a rotary vacuum washer, a rotary pressure washer, a pressure and atmospheric diffusion washer, a horizontal belt washer and/or dilution/extraction equipment. Washing involves diluting the NSSC pulp with water, and subsequently removing the water together with diluted colloidal substances, salts, impurities, and fines through a wire.
• the NSSC pulp has been prepared from wood comprising less than 3 wt %, less than 2.5 wt %, less than 2 wt %, or preferably less than 1 wt % or less than 0.8 wt % bark.
• the reduction of the ash content can be measured by measuring the ash content according to standard ISO 1762:2019.
• said NSSC pulp has an ash content of less than 1.6 wt %, preferably less than 1.4 wt %, and more preferably less than 1.2 wt % or less than 1.0 wt % or less than 0.9 wt %, as determined according to standard ISO 1762:2019.
• said fluting or liner has an ash content of less than 1.6 wt %, preferably less than 1.4 wt %, and more preferably less than 1.2 wt % or less than 1.0 wt % or less than 0.9 wt %, as determined according to standard ISO 1762:2019.
• the reduction of the ash content can also be measured by measuring the hot water extract conductivity of the NSSC pulp according to ISO 6587.
• said NSSC pulp has a hot water extract conductivity of less than 15 mS/cm, preferably less than 10 mS/cm, and more preferably less than 8 mS/cm, as determined according to ISO 6587.
• said fluting or liner has a hot water extract conductivity of less than 15 mS/cm, preferably less than 10 mS/cm, and more preferably less than 8 mS/cm, as determined according to ISO 6587.
• the conductivity of the NSSC pulp used in the fluting or liner is less than 1200, less than 1000, less than 800, or less than 600, and more preferably less than 500, less than 450, less than 400, less than 350 or less than 300 mS/m, when disintegrated at 3.5 wt % in distilled water.
• the NSSC pulp comprises less than 2%, preferably less than 1.8%, more preferably less than 1.6%, Pulmac shives (slot size 0.1 mm). It has been found advantageous to use a pulp with low amount of shives.
• cellulose fines generally refers to cellulosic particles significantly smaller in size than cellulose fibers.
• fines as used herein refers to fine cellulosic particles, which are able to pass through a 200 mesh screen (equivalent hole diameter 76 ⁇ m) of a conventional laboratory fractionation device (SCAN-CM 66:05).
• the reduction of fines in the NSSC pulp may for example be in the range of 0.1-10 wt %, or in the range of 0.5-7 wt %.
• the inventors have found that by reducing the ash content of the NSSC pulp, the amount of a hydrophobizing internal sizing agent required to obtain a required level of water resistance in the finished fluting or liner can be significantly reduced.
• the NSSC pulp is employed in a pulp composition for use in fluting or liner for corrugated board, wherein the pulp composition further comprises at least one internal sizing agent.
• pulp composition refers to an aqueous dispersion of cellulose fibers and non-fibrous additives used as a furnish for making paper or paperboard in a paper machine.
• the pulp of the pulp composition of the fluting or liner preferably mainly comprised of NSSC pulp.
• at least 50 wt % of the pulp of the pulp composition is NSSC pulp, based on dry weight.
• at least 55 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt % or 98 wt % of the pulp is NSSC pulp, based on dry weight.
• the part of the pulp of the pulp composition not being NSSC pulp may comprise any kind of fibers, such as hardwood and/or softwood fibers and may include, e.g., chemical pulp, mechanical pulp, thermomechanical pulp or chemi-thermomechanical pulp (CTMP).
• CTMP chemi-thermomechanical pulp
• the part of the pulp composition not being NSSC pulp may also for example comprise recycled fibers.
• the pulp of the present disclosure may consist essentially of NSSC pulp or a mixture of NSSC pulp and recycled fibers.
• “Recycled fibers” refers to fiber material that has previously been incorporated in some paper or board product.
• the part of the pulp not being NSSC pulp may for example comprise reject pulp.
• the pulp of the present disclosure may consist essentially of NSSC pulp and reject pulp.
• “Reject pulp” refers to pulp prepared by refining the screen reject from a pulping process.
• the pulp pf the pulp composition comprises less than 10 wt %, preferably less than 5 wt %, more preferably less than 2 wt % of recycled fibers.
• a low amount of recycled fibers is preferred, since high amounts of inorganic materials are typically added via recycled fiber.
• said fluting comprises less than 10 wt %, preferably less than 5 wt %, more preferably less than 2 wt % of recycled fibers.
• the fluting and/or liner may further comprise an internal sizing agent.
• the internal sizing agent is preferably a hydrophobizing sizing agent.
• the internal sizing agent is selected from the group consisting of alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin sizes, and mixtures thereof.
• the internal sizing agent is alkyl ketene dimer (AKD).
• the amount of the internal sizing agent in the fluting or liner is in the range of 0.5-6 kg/tn, preferably in the range of 0.5-4 kg/tn, preferably in the range of 0.5-3 kg/tn and more preferably in the range of 1-2 kg/tn, based on dry weight. Consequently, the amount sizing agent in the fluting or liner is quite low.
• At least one side of the fluting or liner preferably has a Cobb 30 s value below 30, preferably below 25, and more preferably below 22, as determined according to standard ISO 535. It may be preferred that both sides of the fluting or liner has a Cobb 30 s value below 30, preferably below 25, and more preferably below 22, as determined according to standard ISO 535. It has surprisingly been found that the addition of clean NSSC pulp to the bottom or top ply of the liner or fluting will not affect the Cobb value negatively. Consequently, the side/s of the liner or fluting comprising clean NSSC pulp preferably has a Cobb 30 s value below 30, preferably below 25, and more preferably below 22, as determined according to standard ISO 535.
• NSSC pulp is often used in the back ply of a fluting or liner and it is then preferred that the back side of the fluting or liner has a Cobb 30 s value below 30, preferably below 25, and more preferably below 22, as determined according to standard ISO 535.
• the fluting or liner further comprises a microparticle retention aid system, preferably a multi-component microparticle retention aid system.
• the microparticles of the microparticle retention aid system is selected from the group consisting of silica microparticles, bentonite microparticles and cellulose nanoparticles.
• the microparticle retention aid system comprises a water soluble polymer, preferably a cationic polymer.
• the amount of the microparticle retention aid system in the fluting or liner is in the range of 50 g/tn to 5 kg/tn, and more preferably in the range of 100 g/tn to 2 kg/tn, based on dry weight.
• the fluting or liner may further include additional components commonly used in fluting or liner production, such as such as native starch or starch derivatives, microfibrillated cellulose (MFC), 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 agents, dyes and colorants, wet strength resins, fixation agents, de-foaming aids, microbe and slime control aids, or mixtures thereof.
• MFC microfibrillated cellulose
• the fluting or liner is typically a single ply product, but it may also be a multiply product.
• the fluting or liner is typically formed in a gap former, but it may also be formed in a fourdrinier type former.
• the press section may be provided with a shoe press to maximize production.
• the basis weight of the fluting or liner may preferably be in the range of 80-300 gsm.
• said fluting or liner has an equilibrium moisture content (EMC) of less than 10 wt %, preferably less than 8 wt % at 50% RH, as determined according to standard ISO 287.
• EMC equilibrium moisture content
• said fluting or liner has a cd/md stretch value greater than 1.8, preferably greater than 1.9, and more preferably greater than 2.0, as determined according to standard ISO 1924-3.
• said fluting or liner has a kinetic friction of less than 0.5, preferably less than 0.45, and more preferably less than 0.4, as determined according to standard ASTMD 1894-63
• corrugated board comprising a fluting and/or liner according to the first aspect.
• Corrugated board comprises at least one layer of liner, which is non-corrugated, and at least one layer of fluting.
• fluting is corrugated and then glued to linerboard.
• corrugated board may consist of a layer of fluting sandwiched between two layers of liner.
• the examples show that a washed NSSC pulp can be used in sheet making and provides improved mechanical properties and different response to liquid absorption.
• NSSC beech pulp as used in Example 1 was refined to a higher SR value and a web was prepared as in Example 1.
• the increased SR due to the refining increased especially tensile index (Geom).
• NSSC beech pulp as used in Example 1 was washed with water (40 m 3 fresh water per ton of pulp) using an Eimco belt washing unit. 2.7% of the fines were removed together with colloidal substances and impurities in the liquid phase, including electrolytes. As a consequence of the washing, the pH of the pulp suspension increased, confirming the removal of electrolytes and reduction of the ash content. A web was prepared as in Example 1. A small improvement in both tensile strength and stretch was noticed.
• NSSC beech pulp as used in Example 1 was mixed with washed NSSC birch broke pulp (washed as described in Example 3). The pulps were mixed in a 50-50 ratio. A web was prepared as in Example 1. A significant improvement in both tensile strength and stretch was observed.
• Example 4 washed NSSC birch broke pulp as used in Example 4 was used without any other fibers.
• a web was prepared as in Example 1. The tensile strength properties and stretch were further improved.
• washed NSSC pulp was added to a liner.
• the washed pulp has an ash content below 1.8 wt %.
• Un-washed NSSC pulp was added to another liner as a comparison.
• the unwashed NSSC pulp has an ash content higher than 1.8 wt %.
• All the liner produced comprised unbleached kraft pulp (100%) in the top ply and recycled fiber (RCF) pulp in the back ply with or without NSSC pulp addition.

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• 2022
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