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
  • D21H11/16—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only modified by a particular after-treatment
  • D21H11/18—Highly hydrated, swollen or fibrillatable 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
  • 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
  • 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
  • D21C9/001—Modification of pulp properties
  • D21C9/007—Modification of pulp properties by mechanical or physical means
• • 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
  • D21H11/08—Mechanical or thermomechanical 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
  • D21H11/10—Mixtures of chemical and mechanical 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
  • 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
  • D21D—TREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
  • D21D1/00—Methods of beating or refining; Beaters of the Hollander type
  • D21D1/20—Methods of refining
  • D21D1/30—Disc mills
• • 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
  • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
• • 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 invention relates to a pulp mixture for board production in order to provide high strength in Z-direction, i.e. out of plane. It also relates to a method for producing such a pulp and to products obtained by means of said mixed pulp.
• Paperboard comprises a plurality of layers, also known as plies, of pulp and optional additives.
• the layers are purposively selected and arranged to achieve the desired properties of the paperboard as such.
• An essential property of the paperboard is the bending stiffness.
• the bending stiffness in paperboard is usually built up by having outer plies with high tensile stiffness and one or several bulky plies in between, so that the outer plies are placed at a desired distance from each other.
• the bulky ply/plies is/are often a middle layer/middle layers.
• the middle layer in paperboard may comprise by a mechanical pulp, such as thermomechanical pulp TMP.
• a mechanical pulp such as thermomechanical pulp TMP.
• CTM P chemithermomechanical pulp
• CTMP CTMP
• wood chips are impregnated with a lignin softening chemical prior to pressurized refining. This results in softening of lignin and the fiber rupture during refining will therefore be concentrated to the lignin rich middle lamella. This results in higher amounts of long fibers and lower amount of fines and shives at a certain energy input compared to TM P.
• CTMP is more advantageous than TMP in paperboard.
• the strength of paper is measured in three dimensions: the grain direction, also known as the X- direction; the cross-grain direction, also known as Y-direction; and the direction perpendicular to the paper surface plane, also known as the Z-direction.
• the force needed to delaminate a sample of a paper is recorded as its internal bond strength, or Z-directional tensile strength.
• a high Z-strength in the middle layer of paperboard is desired in order to avoid delamination of the middle layer and hence delamination of the paperboard as such. Such a Z-strength must however be achieved without deteriorating the bending stiffness, that is without having to increase the paper web density.
• Z-strength and density of a paperboard layer is usually optimized by altering the raw materials, by choosing different operation conditions in stock preparation and on the board machine and by addition of paper chemicals.
• strength in Z-direction increases with increased density and the effect comes from increase of bonded area between the fibers.
• the relationship between density and out-of-plane strength may vary depending on pulp type and densification method. Refining increases strength more than wet pressing.
• the main purpose of refining is to improve the bonding properties of the fibers. Changes that improve fiber-to-fiber bonding are internal and external fibrillation together with fines creation.
• WO 95/34711 Al discloses a CTMP pulp for use in the manufacture of paper or paperboard products.
• the pulp is produced by impregnating chips with a lignin softening chemical, preheating the chips, and refining the chips to papermaking pulp. This results in a high temperature
• HTCTM P chemithermomechnical pulp
• Klinga et al. Energy efficient high quality CTMP for paperboard, Journal of Pulp and Paper Science, 34 (2008), 2, 98-106, discusses the relationship between bulk and internal bond strength in paper sheets and their dependency on fiber length. Furthermore, this article suggests manufacturing energy efficient high quality CTMP for paperboard. More specifically, Klinga et al. conclude that LC refining of spruce HTCTMP yields high quality pulp at low total energy input and thus is an interesting process concept for production of pulps intended for paperboard.
• EP 1835075 discloses a method for forming at least one ply of a paperboard from a slurry of cellulose fibers comprising crosslinked fibers.
• the internal bond strength of the paperboard is improved by the addition of additives. Furthermore, it is shown that the addition of mechanically refined fiber increases the strength of the paperboard and increases the Scott Bond.
• Sack paper is often produced by subjecting a chemical pulp to HC refining followed by LC refining as this gives the excellent strength properties needed for such an application.
• pulps are generally not used in other types of paper products as the energy needed for refining often is quite high.
• the object of the present invention is to be able to provide a paperboard product with a high Z- strength at the same time as enabling a low grammage.
• the invention is focused on providing the desired properties in terms of Z-strength, bending stiffness and bulk to a layer, such as a middle layer, of paperboard.
• a high Z-strength of a paperboard layer can be achieved at a low density, and thus a low grammage, by means of the pulp mixture in accordance with the present invention.
• the pulp mixture comprising a first pulp constituting a chemical softwood pulp, which has been subjected to high consistency refining followed by low consistency refining, and a second pulp constituting a bulk increasing pulp.
• the pulp mixture according to the present invention it is possible to tailor the properties with regard to Z-strength, density, and bending stiffness as desired of a paperboard product obtained by means of said pulp mixture.
• the pulp mixture it is for example possible to produce a paper web with high strength in Z-direction and high bulk.
• High consistency refining of a chemical pulp results in higher Z-strength properties compared to low consistency refining for the same density.
• HC refining produces pulps with lower density at the same Z-tensile strength.
• HC refining does not result in sufficient tensile stiffness and surface smoothness.
• subsequent LC refining it has been found that low consistency refining of a high consistency refined pulp (the resulting pulp hereinafter also denominated HC/LC refined pulp) does not reduce the Z-strength. If fact, the subsequent LC refining results in retained or even increased Z-strength.
• HC/LC refined pulps may replace LC refined pulps in paperboard products to improve Z-strength. Furthermore, with maintained Z-strength compared to LC refined pulps, more CTMP can be included in a paperboard layer formed from a pulp mixture based on HC/LC refined pulp, which enables reduced grammage and thus reduced fibre consumption.
• the excellent properties in Z-direction of HC/LC refined pulp extend the possibility to optimise paperboard density by combining such a pulp with bulk increasing pulps.
• Test results have shown that bleached and unbleached HC and LC refined chemical pulps can be mixed with for example LC refined pulps and/or CTMP.
• the results show that improved Z-strength versus density relation of the HC/LC pulp mixtures in comparison with LC refined pulps. That implies wider operating window for optimisation of paperboard properties in cross-direction (out-of-plane) and possible raw material savings for board producers.
• the pulp mixture according to the present invention comprises a first pulp and a second pulp.
• pulped broke is a pulp prepared by the defibration of broke from a board-making process. Pulped broke is often included in the pulp mixture forming a layer, such as a middle layer, of paperboard, When the pulp mixture comprises pulped broke, the pulped broke is normally present in an amount of 5-40 %, such as 10-35 % of the total dry weight of the pulp mixture. Additives (e.g. strength agents), are discussed below.
• the first pulp and the second pulp are preferably each never dries pulps.
• the first pulp is a chemical softwood pulp which has been subjected to HC refining followed by LC refining.
• the second pulp is a bulk increasing pulp selected from the group consisting of a chemi- thermomechanical pulp (CTMP), a thermomechanical pulp (TMP) or a chemical softwood pulp refined solely by low consistency refining.
• CMP chemi- thermomechanical pulp
• TMP thermomechanical pulp
• the pulp mixture may comprise at least one strength agent.
• the at least one strength agent can for example be selected from carboxymethyl cellulose ("CMC”), starch, microfibrillated cellulose ("MFC”, see e.g. WO 2008/076056), polyacrylamide and polyvinylamine (“PVAm”),
• the pulp may comprise a inorganic microparticle, such as silica or [other examples].
• Preferred combinations of strengths chemicals comprise:
• the first pulp is present in an amount of 20-90 %, such as 25-90 %, such as 30-90 %, such as 50-90 % by dry weight of the total dry weight of the first pulp and the second pulp in case the second pulp is CTM P or TM P.
• the first pulp is present in an amount of 5-90 %, such as 10-70 %, such as 40-70 %, by dry weight of the total dry weight of the first pulp and the second pulp in case the second pulp is a chemical softwood pulp refined solely by low consistency refining.
• the second pulp is CTMP and the first pulp is present in an amount of 60-90 %, preferably 75-88 %, by dry weight of the total dry weight of the first pulp and the second pulp.
• a pulp mixture it has for example been found to be possible to obtain a layer or paper having a density of less than 700 kg/m 3 and a Z-tensile strength of more than 650 kPa (both in case of the first pulp being a bleached pulp and in the case of the first pulp being an unbleached pulp).
• the pulp mixture comprises:
• the first pulp in an amount of 15-40 %, such as 20-35 %, by dry weight;
• CTMP as the second pulp in an amount of 30-50 %, such as 40-50 %, by dry weight
• the second pulp is a chemical softwood pulp refined solely by low consistency refining and the first pulp is present in an amount of 8-85 %, preferably 10-60 %, by dry weight of the total dry weight of the first pulp and the second pulp.
• a pulp mixture it has for example been found to be possible to obtain a layer or paper having a density of less than 750 kg/m 3 and a Z-tensile strength of at least 550 kPa, typically of at least 600 kPa. It has also been found to be possible to obtain a layer or paper of said pulp mixture having a density of less than 780 kg/m 3 and a Z-tensile strength of at least 650 kPa at least for a bleached pulp mixture.
• the pulp mixture comprises:
• the first pulp in a mount of 25-55 %, such as 35-50 %, by dry weigh;
• the first pulp may suitably be a bleached chemical softwood pulp which has been subjected to high consistency refining followed by low consistency refining with a total refining energy of the high consistency refining and the low consistency refining of 70-250 kWh/t, preferably 130-220 kWh/t.
• the first pulp may alternatively suitably be an unbleached chemical softwood pulp which has been subjected to high consistency refining followed by low consistency refining with a total refining energy of the high consistency refining and the low consistency refining of 150-400 kWh/t, preferably 200-360 kWh/t.
• Low consistency refining of the high consistency refined chemical softwood pulp to obtain the first pulp may suitably be performed at a quite moderate refining energy, such as 15-40 kWh/t, preferably 15-30 kWh/t.
• the first pulp may suitably have a Schopper ielger (SR) number according to SO 5267-1:1999 of above 15.0, preferably 15.2-18.8, and/or a water retention value (WRV) according to SCAN-C 62:00 of above 1.55 g/g, preferably 1.58-1.90 g/g.
• SR Schopper ielger
• WRV water retention value
• the WRV may optionally be equal to or above 1.80 g/g, whereas in the case of the first pulp is a bleached pulp, the WRV may optionally be less than 1.80 g/g.
• the pulp mixture may suitably have a Schopper Rielger (SR) number according to SO 5267-1:1999 of 14.0-19.0, and/or a water retention value (WRV) according to SCAN-C 62:00 of 1.45-1.85 g/g.
• SR Schopper Rielger
• WRV water retention value
• the pulp mixture may comprise additional components, in particular one or more fillers, to thereby reduce the amount of fibrous fiber raw material at preserved strength in Z-direction.
• the pulp mixture may be produced by firstly providing the first pulp and providing the second pulp.
• the first pulp is provided by subjecting a chemical softwood pulp to a high consistency refining step and a subsequent low consistency refining step.
• the first pulp is thereafter mixed with the second pulp and any optional additional component(s), such as the at least one strength agent and/or the inorganic microparticle, thereby providing the pulp mixture.
• the preparation of the pulp mixture may also comprise mixing the first and/or the second pulp with pulped broke.
• At least part of the pulped broke is preferably obtained by pulping broke obtained from a board-making process in which the pulp mixture is used for a layer, such as a middle layer, of the board.
• the fibre composition of the pulped broke thus depend on the types of fibres that are used for the different layers of the board product.
• the first pulp may suitably be provided by subjecting a bleached chemical softwood pulp to high consistency refining followed by low consistency refining, and wherein the total refining energy used during the high consistency refining and the low consistency refining thereof is 70-250 kWh/t, preferably 130-220 kWh/t.
• the first pulp may alternatively suitably be provided by subjecting an unbleached chemical softwood pulp to high consistency refining followed by low consistency refining, and wherein the total refining energy used during the high consistency refining and the low consistency refining thereof is 150-400 kWh/t, preferably 200-360 kWh/t.
• the refining energy during the low consistency refining of the chemical softwood pulp subjected to high consistency refining followed by low consistency refining may suitably be quite moderate, such as 15-40 kWh/t, preferably 15-30 kWh/t.
• the second pulp may suitably be provided by subjecting a chemical softwood pulp to a low consistency refining step at a refining energy of 20-60 kWh/t, preferably 25-55 kWh/t.
• the refining energy during said low consistency refining step may be 20-40 kWh/t, more preferably 25-35 kWh/t, in case the chemical softwood pulp is a bleached chemical softwood pulp, or 35-60 kWh/t, more preferably 40-55 kWh/t, in case the chemical softwood pulp is an unbleached chemical softwood pulp.
• the pulp mixture and the method for producing said pulp mixture it is possible to tailor the properties of a paperboard layer, such as a middle layer, especially with respect to Z-strength and density.
• the chemical softwood pulp refined solely by low consistency refining and the first pulp are provided concurrently by co-refining at a low consistency an unrefined chemical softwood pulp and a chemical softwood pulp refined by high consistency refining.
• the present invention also relates to a paperboard comprising a layer made of the pulp mixture described above and optionally at least one additional layer, suitably at least two additional layers.
• Said layer made of the pulp mixture according to the present invention is suitably a middle layer of the paperboard and interposed between two outer layers.
• the present invention also relates to a method of producing a multi-layered board, such as paperboard, having a middle layer.
• the middle layer is formed from the pulp mixture as disclosed above, or formed from a pulp mixture produced as disclosed above.
• Figure 1 illustrates experimental results of Z-tensile strength and Scott Bond in relation to density for HC- and LC-refined bleached pulp.
• Figure 2 illustrates experimental results of Z-tensile strength and Scott Bond in relation to density for HC- and LC-refined unbleached pulp.
• Figure 3 illustrates experimental results of density and Z-tensile strength in relation to refining energy for HC and HC/LC refined bleached pulp.
• Figure 4 illustrates experimental results of density and Z-tensile strength in relation to refining energy for HC and HC/LC refined unbleached pulp.
• Figure 5 illustrates experimental results of the relation between Z-tensile strength and density for mixtures of HC/LC pulps with low LC refined samples for bleached and unbleached pulp in comparison with LC refined pulps.
• Figure 6 illustrates experimental results of the relation between density and Z-tensile strength for mixtures of bleached HC/LC pulp with low LC refined pulp in comparison with LC refined pulps.
• Figure 7 illustrates experimental results of the density and strength in Z-direction for a mixture of 80% bleached HC/LC pulp with 20 % CTMP in comparison with LC refined bleached pulp.
• Figure 8 illustrates experimental results of the density and strength in Z-direction for a mixture of 85% unbleached HC/LC pulp with 15 % CTMP in comparison with LC refined unbleached pulp.
• Low consistency refining in the present disclosure is intended to mean refining at a consistency of about 2 % to 8 %, such as 2 % to 5 %, unless explicitly disclosed otherwise.
• High consistency refining is intended to mean refining at a consistency of about 25 % to 38 %, such as 28 % to 38 %, unless explicitly disclosed otherwise.
• Low consistency refined pulp (or LC refined pulp) is herein intended to mean a pulp which has not been subjected to any preceding high consistency refining or medium consistency refining, but solely to low consistency refining, unless explicitly disclosed otherwise.
• High consistency refined pulp (or HC refined pulp) is herein intended to mean a pulp which has not been subjected to any other type of refining, but solely to high consistency refining, unless explicitly disclosed otherwise.
• HC/LC refined pulp is considered to mean a pulp which has been subjected to a high consistency refining followed by a low consistency refining.
• any of the refining steps high consistency refining and low consistency refining may be executed in a plurality of sub-steps. Such a procedure is intended to be encompassed by the scope of the invention, as well as a procedure wherein each refining step is performed in a single step.
• a pulp mixture comprising a first pulp and a second pulp.
• the first pulp consists of a chemical softwood pulp which has been subjected to high consistency refining followed by low consistency refining (i.e. a HC/LC pulp).
• the second pulp is a bulk increasing bulk, meaning that it constitutes a pulp which compared to the first pulp increases the bulk, i.e. reduces the density, of the pulp mixture when added.
• the first pulp is a chemical softwood pulp, inter alia in order to ensure that the cellulose fibers have an appropriate length.
• High consistency refining of said pulp is performed by conventional methods.
• low consistency refining of said high consistency refined pulp is performed by conventional methods.
• Such a HC/LC refined softwood pulp is as such previously known for the purpose of making sack paper. It has however not been previously considered for purposes such as board.
• the second pulp may suitably be a chemi-thermomechanical pulp, CTMP.
• CTMP chemi-thermomechanical pulp
• the first pulp is present in an amount of 20- 90 %, such as 25-90 %, such as 30-90 %, such as 50-90% by dry weight of the total dry weight if the first pulp and the second pulp.
• CTMP may be present in an amount of at least 60 % by dry weight of the total dry weight of the first and the second pulp, such as at least 75 % by dry weight of the total dry weight of the first and the second pulp.
• a too high addition of CTMP would reduce the Z-strength to such a degree that other pulps or pulp mixtures would be a better option from a cost perspective.
• an upper limit for the amount of CTM P may be 50 % or 60 % by dry weight based on the total dry weight of the pulp mixture.
• the first pulp is present in an amount of up to and including 90 % by dry weight, preferably up to and including 88 % by dry weight.
• CTMP thermomechanical pulp
• the second pulp may be a thermomechanical pulp (TMP) as such pulp would also likely increase the bulk of a paper web obtained by such pulp mixture.
• the first pulp should be present in an amount of 50-90 % by dry weight of the total dry weight of the first and the second pulp in case the second pulp is TMP.
• the embodiment wherein the second pulp is TMP is however less preferred than CTMP since TMP results in a lower amount of long fibers and a higher amount of shives at the same energy input compared to CTMP.
• the second pulp is a chemical softwood pulp which has been subjected to a low consistency refining without preceding high consistency refining, i.e. a LC refined pulp.
• the first pulp may preferably be present in an amount of at least 8 by dry weight of the total dry weight of the first pulp and the second pulp, more preferably at least 10% by dry weight of the total dry weight of the first pulp and the second pulp.
• the first pulp may is such a case preferably be present in an amount of up to and including 85 % by dry weight of the total dry weight of the first and the second pulp, more preferably up to and including 60 % or 70 % by dry weight of the total dry weight of the first and second pulp.
• the pulp mixture may comprise one or more further components, more specifically fillers.
• the filler selected is not limiting the scope of the present invention and any previously known filler for the paper products concerned may be used. Examples of such fillers are calcium carbonate (PCC and GCC) and clay.
• the pulp mixture according to the present invention may also exclusively consist of the first and the second pulp without any further additives or pulps.
• the pulp mixture normally comprises additives and/or at least one other pulp. Such as pulped broke.
• CTMP may be produced in accordance with any previously known techniques without departing from the scope of the invention.
• mixing of the first and the second pulp may be performed in accordance with any previously known technique.
• a paperboard product may be produced by conventional means by the pulp mixture according to the present invention and thus includes production of a paper web of the pulp mixture.
• HC-refining trials of bleached and unbleached pulps were performed in Gavle mill.
• the refiner used for bleached pulp was a Sprout-Bauer 50-1B refiner equipped with refining fillings with an edge length of 182 km/rev.
• HC-refining of unbleached pulp was performed in a Sunds Defibrator RGP 254 refiner with refining fillings with an edge length of 105 km/rev.
• the pulp consistency during HC refining of both pulps was kept at 30 % to 35 %.
• Bleached and unbleached LC refining curves were performed at Innventia in a Beloit 24" double disc refiner at a flow rate of 500 l/min. Refining segments used has an edge length of 8.38 km/rev and the refiner operated at 750 rpm. Refining consistency was 3.3% for both bleached and unbleached pulp. Refining was done as a single-stage refining and the energy input varied up to 145 kWh/t (six stages at 10, 30, 55, 80, 115 and 145 kWh/t) for bleached pulp and up to 140 kWh/t for unbleached pulp (six stages at 10, 30, 50, 80, 110 and 140 kWh/t). Individual mill LC-refined pulp samples were also delivered during the project time.
• LC-refining of HC-refined pulp was performed in a Voith laboratory conical refiner (conical fillings 3-1, 0-60) at energy input of 20 kWh/t for all samples.
• the pulp consistency during refining was kept on the level of approximately 4 % and in all cases; the refiner speed was 1500 rpm.
• All pulp samples were analysed with respect to SR, WRV-whole pulp and fiber dimensions using a L&W FiberTester Analyser. Standard laboratory sheets with a grammage of 60 g/m2 were tested with respect to density, tensile strength, Z-strength, Scott Bond and surface roughness. Fibre and pulps were characterized in accordance to the following standards
• Figure 1 illustrates Z-tensile strength and Scott Bond in relation to density for HC- and LC-refined bleached pulp.
• HC-refining was done up to approximately 200 kWh/t and LC-refining up to 145 kWh/t. It should be noted that the Scott Bond was not determined for LC refining at 145 kWh/t
• Figure 2 illustrates Z-tensile strength and Scott Bond in relation to density for HC- and LC-refined unbleached pulp.
• HC-refining was done up to 350 kWh/t and LC-refining up to 140 kWh/t.
• HC-refining produces pulps with high strength in Z-direction but with a poorer tensile stiffness and lower surface smoothness than LC-refining. It is common general knowledge that LC-refining as a post-stage after HC-refining straightens the fibers, increases density and pulp properties related to tensile strength in-plane and improves surface properties. However, it is not previously known how the LC refining affects the out-of-plane properties of HC-refined pulp. Therefore, experimental tests of LC refining of HC-refined pulp was performed.
• the HC-refined pulps were treated in a Voith laboratory refiner at low energy input of 20 kWh/t. After this stage, the pulp samples are noted HC/LC pulp.
• the effects of LC refining on density and Z-tensile strength in relation to refining energy are shown in Figure 3 for bleached pulp and in Figure 4 for unbleached pulp.
• the points shown in the Figures relating to HC/LC pulp correspond to the total refining energy of HC refining and LC refining.
• the amount of HC/LC-refined pulp in the mixtures was varied at five levels: 10%, 20%, 30%, 40% and 50% by weight, respectively.
• the SR for the bleached pulp mixtures ranged from 14.8 to 16.4, the highest value corresponding to the mixture comprising 50 % HC/LC-refined pulp.
• WRV was about 1.6 g/g for all of the bleached pulp mixtures.
• the amount of HC/LC-refined pulp was varied at 20%, 40% and 60% by weight, respectively.
• the SR for the mixtures ranged from 14.1 to 14.9, the highest value corresponding to the lowest amount of HC/LC refined pulp in the mixtures.
• WRV was about 1.7-1.8 g/g for the unbleached pulp mixtures.
• the grammage can be reduced.
• CTMP 475 90 160 The results are shown in Figure 7 illustrating the density and strength in Z-direction measured as Z- tensile strength and Scott Bond for the mixture of HC/LC pulp with 20 % CTMP in comparison with LC refined bleached pulp.
• the decrease in Z-strength which was expected by the addition of CTMP was balanced by the high Z-strength of HC/LC refined pulp.
• HC/LC pulp mixture with CTMP showed similar Z-strength measured as Scott Bond and Z-tensile strength at lower density that LC refined pulp.
• the grammage can be reduced.
• the pulp mixture for the top layer comprised bleached softwood chemical pulp (40 %) and bleached hardwood chemical pulp (60 %)
• the pulp mixture for the middle layer comprised unbleached softwood chemical pulp (about 75-80 %) and pulped broke (about 20-25 %).
• the bottom layer comprised unbleached chemical pulp and a small amount of pulped broke.
• the unbleached softwood chemical pulp of the middle layer pulp was subjected to LC refining only.
• part of the unbleached softwood chemical pulp of the middle layer was subjected to HC refining before the LC refining was carried out.
• the HC refined pulp was thus co-refined with non-HC refined pulp at low consistency. Details of the preparations of middle layer pulps are presented in table 5 below.

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• 2016
  • 2016-02-25 WO PCT/SE2016/050138 patent/WO2016140609A1/en active Application Filing
  • 2016-02-25 EP EP16710843.0A patent/EP3265609B1/de active Active

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