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
  • 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
  • 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
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
  • D21H27/38—Multi-ply at least one of the sheets having a fibrous composition differing from that of other sheets

Definitions

• the present disclosure relates to the field of paperboard and production thereof.
• the objective of the present disclosure is to include recycled fibres in paperboard while maintaining or even improving properties characteristic of high-quality paperboard.
• a method of producing a paperboard comprising a top layer, a back layer and a middle layer, said method comprising the steps of:
• a paperboard comprising a top layer, a back layer and a middle layer
• the method and paperboard recipe defined above enables the formation of a paperboard of equal bending resistance as that of a prior art paperboard (formed from virgin pulp only) at a lower total fibre consumption.
• the present disclosure not only enables the introduction of a significant portion of recycled fibres in high-quality paperboard without sacrificing the bending resistance of the board, but it also enables a reduction of the amount of fibres needed to reach the desired bending resistance.
• a method of producing a paperboard comprising a top layer, a back layer and a middle layer.
• the middle layer is arranged between the top layer and the back layer.
• the top layer may be intended for printing.
• the top layer may be provided with a pigment-based coating, which may consist of several sublayers applied in consecutive coating steps.
• the top layer may be bleached.
• the method comprises the steps of:
• OCC pulp is formed by pulping and cleaning OCC, which is a well-known type of recycled material in the field of paper and paperboard.
• the amount of OCC pulp is higher than the amount of CTMP (as per dry weight).
• the amount of CTMP is higher than the amount of broke pulp (as per dry weight).
• the combined amount of OCC pulp, CTMP and broke pulp constitutes at least 88% as per dry weight of the middle layer furnish. In one embodiment, said combined amount constitutes at least 90%, such as at least 92%, as per dry weight of the middle layer furnish.
• the OCC pulp constitutes more than 35% by dry weight of the middle layer furnish, such as at least 40% by dry weight of the middle layer furnish.
• An upper limit may be 55%.
• the CTMP constitutes at least 25% by dry weight of the middle layer furnish, such as at least 30% by dry weight of the middle layer furnish.
• broke pulp constitutes at least 13% by dry weight of the middle layer furnish, such as at least 15% by dry weight of the middle layer furnish.
• the middle layer furnish may further comprise one or more strength agents, such as starch (preferably cationic starch), carboxymethyl cellulose (CMC) and/or microfibrillated cellulose (MFC).
• starch preferably cationic starch
• CMC carboxymethyl cellulose
• MFC microfibrillated cellulose
• the paperboard is a liquid packaging board (LPB).
• LPB liquid packaging board
• each of the (fibre-based) layers of the paperboard comprise hydrophobic size.
• the hydrophobic size is preferably selected from the group consisting of ASA, AKD, rosin size and combinations thereof.
• the amount of hydrophobic size in the middle layer furnish may for example be at least 2.5 kg/tonne dry fibre, such as at least 3.0 kg/tonne dry fibre.
• the amount of hydrophobic size in the outer layers is preferably lower than the amount of hydrophobic size in the middle layer.
• the hydrophobic size in each of the furnishes of the method of the first aspect is a combination of AKD and rosin size.
• the headbox pH of the furnishes is preferably in the range of 6.6-7.2, such as 6.9-7.1.
• the density according to ISO 534:2011 of the OCC pulp is below 620 kg/m 3 after sheet forming according to ISO 5269-2:2004.
• this density may be 500-616 kg/m 3 , such as 526-616 kg/m 3 .
• the tensile stiffness index according to ISO 1924-3:2011 of the OCC pulp is at least 4.3 MNm/kg after sheet forming according to ISO 5269-2:2004.
• this tensile stiffness index may be 4.5-5.7 MNm/kg.
• the OCC pulp is a fraction obtained by a fractionating operation, such as screening (see Example 2 below) or hydrocyclone fractionation (see Example 2 below).
• the fraction may (on average) have coarser or longer fibres than the OCC pulp subjected to the fractionation operation. Accordingly, a sheet formed from the fraction typically has lower density than a sheet formed from the OCC pulp subjected to the fractionation operation.
• the density according to ISO 534:2011 of the fraction pulp may for example be below 575 kg/m 3 after sheet forming according to ISO 5269-2:2004. In one embodiment, this density is 500-570 kg/m 3 , such as 526-570 kg/m 3 .
• the tensile stiffness index according to ISO 1924-3:2011 of the fraction may for example be at least 3.9 MNm/kg after sheet forming according to ISO 5269-2:2004. In one embodiment, this tensile stiffness index is 3.9-5.0 MNm/kg.
• the remainder of the fractionated OCC pulp (typically a fraction of finer or shorter fibres) is preferably used in another process of making paper or paperboard, such as a process of making containerboard to be used as fluting or testliner.
• the method of the first aspect may further comprise the steps of:
• the fibres of the top layer furnish may be bleached.
• the method of the first aspect may further comprise the steps of:
• the back layer furnish further comprises broke pulp.
• the method of the first aspect typically comprises a step of couching to join the paperboard layers to each other.
• the grammage, excluding any coating layers, of the paperboard formed by the method of the first aspect may for example be 120-400 g/m 2 when measured according to ISO 536:2019. If pigment-coating layers are included, the grammage may be 140-420 g/m 2 , such as 150-350 g/m 2 .
• the grammage of the middle layer is higher than the grammage of each of the top layer and the back layer.
• each of the top layer and the back layer may have a grammage below 80 g/m 2
• the grammage of the middle layer is above 100 g/m 2 , such as at least 115 g/m 2 , such as 115-150 g/m 2 .
• the grammage of the top layer is below 80 g/m 2
• the grammage of the back layer is below 65 g/m 2
• the grammage of the middle layer is higher than the grammage of each of the top layer and the back layer, e.g. above 100 g/m 2 .
• OCC pulp constitutes 18%-32% by dry weight of the total amount of fibres used to form the paperboard according to the first aspect.
• the top layer furnish and the back layer furnish comprise no OCC pulp or broke pulp.
• CTMP constitutes 16%-22% by dry weight of the total amount of fibres used to form the paperboard according to the first aspect.
• broke pulp constitutes 10%-20%, such as 10%-16%, by dry weight of the total amount of fibres used to form the paperboard according to the first aspect.
• a paperboard comprising a top layer, a back layer and a middle layer, wherein the middle layer comprises an OCC pulp, a chemithermomechanical pulp (CTMP) and broke pulp.
• the middle layer comprises the OCC pulp, the CTMP and the broke pulp means that it is formed from a mixture comprising these three pulps.
• the middle layer is arranged between the top layer and the back layer.
• the top layer may be intended for printing.
• the top layer may be provided with a pigment-based coating, which may consist of several sublayers. Further, the top layer may be bleached.
• the amount of OCC pulp is higher than the amount of CTMP as per dry weight.
• the amount of CTMP is higher than the amount of broke pulp as per dry weight.
• the combined amounts of OCC pulp, CTMP and broke pulp constitutes at least 88% as per dry weight of the middle layer. In one embodiment, said combined amount constitutes at least 90%, such as at least 92%, as per dry weight of the middle layer.
• the middle layer may further comprise one or more strength agents, such as starch (preferably cationic starch), carboxymethyl cellulose (CMC) and/or microfibrillated cellulose (MFC).
• starch preferably cationic starch
• CMC carboxymethyl cellulose
• MFC microfibrillated cellulose
• the paperboard of the second aspect is a liquid packaging board (LPB).
• LPB liquid packaging board
• each of the (fibre-based) layers of the paperboard comprise hydrophobic size.
• the hydrophobic size is preferably selected from the group consisting of ASA, AKD, rosin size and combinations thereof.
• the amount of hydrophobic size in the middle layer may for example be at least 2.5 kg/tonne dry fibre, such as at least 3.0 kg/tonne dry fibre.
• the amount of hydrophobic size in the outer layers is preferably lower than the amount of hydrophobic size in the middle layer.
• the hydrophobic size in each of the fibre-based layers of the LPB of the second aspect is a combination of AKD and rosin size.
• the top layer comprises at least 80% by dry weight of kraft pulp, such as least 90% by dry weight of kraft pulp.
• the back layer comprises at least 60% by dry weight of kraft pulp, such as at least 75% by dry weight of kraft pulp.
• the grammage, excluding any coating layers, of the paperboard of the second aspect may for example be 120-400 g/m 2 when measured according to ISO 536:2019. If pigment-coating layers are included, the grammage may be 140-420 g/m 2 , such as 150-350 g/m 2 .
• the grammage of the middle layer is higher than the grammage of each of the top layer and the back layer.
• each of the top layer and the back layer may have a grammage below 80 g/m 2
• the grammage of the middle layer is above 100 g/m 2 , such as at least 115 g/m 2 , such as 115-150 g/m 2 .
• the grammage of the top layer is below 80 g/m 2
• the grammage of the back layer is below 65 g/m 2
• the grammage of the middle layer is higher than the grammage of each of the top layer and the back layer, e.g. above 100 g/m 2 .
• OCC pulp preferably constitutes a significant part of the paperboard of the second aspect.
• the paperboard comprises 18%-32% by dry weight of OCC pulp, such as 18%-28% by dry weight of OCC pulp.
• the top layer and the back layer comprise no OCC pulp or broke pulp.
• CTMP preferably constitutes a significant part of the paperboard of the second aspect.
• the paperboard comprises 16%-22% by dry weight of CTMP.
• OCC 90/10 An OCC product sourced in the The Netherlands and called "OCC 90/10" was purchased from the company Prezero.
• the OCC product was slushed in a pulper for 15 minutes to produce a crude OCC pulp that was stored in a tank.
• the crude OCC pulp was subjected to coarse screening using a screen having 2 mm diameter holes to obtain an OCC pulp and a coarse reject. The main reason for the coarse screening was to remove trash and impurities.
• OCC pulp was fractionated by screening to obtain a long fibre fraction and a short fibre fraction (see Example 2 below) or by hydrocyclones to obtain a coarse fibre fraction and a fine fibre fraction (see Example 3 below).
• the bending resistance may be considered the most important parameter.
• the effect on bending resistance of including recycled pulp in a board structure was calculated based on layer grammage and density and tensile stiffness index (TSI) values in accordance with the method devised by Carlsson and Fellers in a journal article titled FLEXURAL STIFFNESS OF MULTI-PLYPAPERBOARD (Fibre Science and Technology 13 (1980) 213-223 ).
• the reference board is a 250 g/m 2 prior art liquid packaging board (LPB) structure having the composition of table 1.
• LPB liquid packaging board
• the proportion of broke pulp is about 13% to reflect a full-scale process in which a broke pulp stream corresponding to 13% of the total amount of fibres is generated and subsequently accommodated by the full-scale process.
• the OCC pulp has higher TSI and lower density than the less refined bleached softwood kraft pulp (BSKP low).
• Example 1.1 The proportion of recycled fibres was reduced compared to Example 1.1. Thereby, all recycled pulp and all broke pulp could be accommodated by the middle layer (without having to reduce the proportion of CTMP in the middle layer) to avoid that any recycled fibres end up in the back layer, which may be desirable in food- or liquid packaging applications.
• the resulting board composition is shown in table 4 below. Table 4.
• the OCC pulp was fractionated by screening using a screen having 1 mm diameter holes to obtain a long fibre fraction and a short fibre fraction in a 42:58 mass flow ratio. Properties of the fractions are presented in Table 6 below. Table 6. "Gsm” means grammage. “Gurley” means Gurley porosity. “TS” means tensile stiffness. “TSI” means tensile stiffness index. “Brightn.” means Brightness D65. Property Unit Gsm ⁇ g/m 2 Caliper ⁇ ⁇ m Density ⁇ kg/m 3 Brightn.
• the long fraction has slightly higher TSI and much lower density than the less refined bleached softwood kraft pulp (BSKP low).
• the OCC pulp was fractionated by hydrocyclones to obtain a coarse fibre fraction and a fine fibre fraction in a 41:59 mass flow ratio. Properties of the fractions are presented in Table 8 below. Table 8. "Gsm” means grammage. “Gurley” means Gurley porosity. “TS” means tensile stiffness. “TSI” means tensile stiffness index. “Brightn.” means Brightness D65. Property Gsm ⁇ Caliper ⁇ Densi ty ⁇ Brightn.
• the sheet formed from the coarse fraction has much lower density than the sheet formed from the less refined bleached softwood kraft pulp (BSKP low).
• TL 70 g/m 2 250 g/m 2 221.1 mN 13.0 0 18.2 ML: 130 g/m 2 BL: 50 g/m 2 1.1 TL: 70 g/m 2 244 g/m 2 (-6 g/m 2 ) 222.0 mN 12.9 24.4 17.8 ML: 124 g/m 2 BL: 50 g/m 2 1.2 TL: 70 g/m 2 243 g/m 2 (-7 g/m 2 ) 220.1 mN 12.7 20.2 17.7 ML: 123 g/m 2 BL: 50 g/m 2 1.3 TL: 70 g/m 2 243 g/m 2 (-7 g/m 2 ) 220.2 mN 12.5 24.4 19.9 ML: 138 g/m 2 BL: 35 g/m 2 2 TL: 70 g/m 2 241 g/m 2 (-9 g/m 2 ) 222.0 mN 12.9 24.1 17.6 ML:
• the inventive concept not only enables a replacement of a significant portion of virgin fibres by recycled fibres, it also allows for a reduction of the total fibre consumption without a loss of bending resistance.
• all the OCC pulps of table 11 have higher TSI and lower density than the less refined bleached softwood kraft pulp (BSKP low).

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Citations (3)

• 2022
  • 2022-10-19 EP EP22202546.2A patent/EP4357520B1/fr active Active
• 2023
  • 2023-10-19 WO PCT/EP2023/079158 patent/WO2024083989A1/fr not_active Ceased
  • 2023-10-19 EP EP23793780.0A patent/EP4605595A1/fr active Pending

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