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    33ABSTRACT Process for the production of a cured pulp product suitable for use in the production of paper,paperboard, tissue paper, filter paper or f|uff pulp, comprising the steps of attaching ananionic or amphoteric carboxymethyl ce|u|ose (CMC) to ce|u|osic fibres in acidic conditions orin the presence of divalent metal ions. Aluminium ions or divalent ions are then added to theslurry to a total molar concentration of from 0.0001 M to 0.5 M in the first pulp slurry. The firstpulp slurry is then dewatered and cured in acidic conditions and a cured pulp product isprovided. The cured pulp product is subsequently used in a paper making process to provide apaper-based product, whereby higher bulk is provided for the final paper-based product.Alternatively, the curing step is omitted and instead aluminium ions are added to the first pulp slurry and the pulp is directly used in a paper making process. Pig. 1
    公开号:SE1550654A1
    申请号:SE1550654
    申请日:2015-05-22
    公开日:2016-11-23
    发明作者:Ankerfors Mikael；Lindström Tom；Glad-Nordmark Gunborg
    申请人:Innventia Ab；
    IPC主号:
    专利说明:

    1Process for the production of paper or paperboard, paper or paperboard product obtainedand uses thereofTECHNICAL FIELDThe present invention relates to a process for the production of a cured pulp product suitablefor use in the production of paper, paperboard, tissue paper or fluff pulp, to a cured pulpproduct obtained by the process, to a use of the cured pulp product for the production ofpaper or paperboard, fluff pulp, filter paper, or tissue, to a process for the production of paperor paperboard and to a use of the produced paper or paperboard as a packaging material.BACKGROUNDPackaging materials of paperboard have been used for a long time for packaging of differentgoods to provide mechanical and/or chemical protection for the goods. There is a growingdemand for light weight packaging materials, which have good mechanical strength to ensuresufficient protection ofthe goods.
    Bulking fibres have historically been used and developed in the field of tissue manufacture,where soft structures have a particular consumer value. Bulky fibres can also be used for themanufacture of fluff pulps. Typical treatments involve cross-linking agents, such as citricacid/catalysts and/or curling treatments. Also, some development work to lower the densityof board materials has been made in connection with cellulosic fibre board materials used asheat insulating, sound insulating, or cushioning materials. However, such materials do nothave the same requirements for mechanical properties as packaging materials. For example,document JP S54-138060 discloses a method for manufacturing low-density flame-retardantcellulosic fibreboard for use as heat or sound insulation material or as a cushioning material. lnthe method a wood pulp is first impregnated with an aqueous solution of ammoniumphosphate to render the board material incombustible. The wood pulp is then dried andheated to 130-170°C to obtain cellulose phosphate. The cellulose phosphate is then re-slushedto a concentration of 2.5 wt-% and the cellulose phosphate is beaten in water. The pH is thenadjusted to pH 2.7 to 6.5 by using a multivalent metal salt, such as aluminium sulphate, in an2amount of about 20-30% by weight of water. The slurry is then formed to a fibre board,dewatered and dried at a temperature of 100-125°C for 1 to 3 hours. The metal group isattached to the phosphate group after curing, whereby the fibre bundle can get an increasedvolume and thus the board may get a low density. However, the metal salt is added to theobtained cellulose phosphate after the cured phosphate-impregnated web is re-slushed andbefore the dewatering ofthe final board material web. Ammonium phosphate is used as aflame retardant and therefore, there is a need to find materials that are suitable for use inpackaging materials and which are environmentally friendly and safe to use in workingenvironments.
    Thus, even though there are known methods to increase bulk of fibres, there is a need toprovide a process suitable for use in connection with the production of paper and packagingboard.SUMMARY OF THE INVENTIONlt is an object ofthe present invention to provide a process for the production of a cured pulpproduct that can be used for the production of paper or paperboard with low density and highbulk.lt is a further object ofthe present invention to provide a low density paper or paperboardproduct suitable for use as packaging material.lt is also an object of the present invention to minimize problems identified in connection withthe production of prior art low density materials. According to the present invention, cellulosicfibres are treated to obtain light-weighting of a cellulosic material. The treatment provides”bulking fibres", which can be used to make bulky paper and paperboard materials while thebending stiffness can be maintained with a lower basis weight. The bulking fibres can also beused in the manufacture of tissue paper, filter paper, and fluff pulp, which can be used forexample in absorbent products.
    Thus, it is an object with the present invention to provide a process for the production of acured pulp product through which bulking fibres can be obtained.lt is also an object ofthe present invention to provide a treatment of pulp, which results in asignificant reduction of the water retention value, which is beneficial for the dewatering and3pressing efficiencies during paper/paperboard making, resulting in a higher dry content afterthe press-section. Thereby, the need for drying energy in the drying process duringpaper/paperboard manufacture can be decreased. Hence, if the treatment step according tothe invention takes place in a pulp mill, and the pulp is used in a non-integrated paper/boardmill, the resource efficiency in the paper or paperboard mill will be much higher both in termsof material and energy efficiency.
    Further objects and advantages will be apparent from the following disclosure of the presentinvention.
    The objects above are attained by a process according to the first embodiment of theinvention relating to a process for the production of a cured pulp product suitable for use inthe production of paper, paperboard, tissue paper, filter paper, or fluff pulp, comprising thesteps of:i) providing a first aqueous pulp slurry comprising cellulosic fibres and having apulp consistency of from 0.1 to 40 % by weight, calculated as dry weight of thecellulosic fibres in the first pulp slurry;ii) adjusting the pH of the first pulp slurry to a pH of from pH 1.5 to pH 4.5, oralternatively treating the first pulp slurry with a metal salt containing divalentmetal ions selected from Zn2+, Mg2+, Ca2+ or mixtures thereof, to a total molarconcentration of from 0.0001 M to 0.5 M in the first pulp slurry;iii) attaching an anionic or an amphoteric carboxymethyl cellulose (CMC) or aderivative thereof to the cellulosic fibres in the first pulp slurry by treating thepulp with the CMC at a temperature of at least 50°C;iv) adding to the first pulp slurry a metal salt comprising Al3+ ion to a total molarconcentration of aluminium ions of from 0.0001 M to 0.5 M in the first pulpslurry, or alternatively controlling the concentration of the divalent metal ionsin the pulp slurry and adjusting the total molar concentration of the divalentmetal ions to a range of from 0.0001 M to 0.5 M in the first pulp slurry, if thetotal molar concentration is not within the range of from 0.0001 M to 0.5 M inthe first pulp slurry;4v) controlling the pH and adjusting the pH of the first pulp slurry to a pH of frompH 3.0 to pH 6.0 if the pH is not within the range of from 3.0 to 6.0;vi) dewatering and curing the first pulp slurry at a temperature of at least 60°C andthus provide a cured pulp product.
    This process is also herein below referred to as a ”dry” process since it includes a step ofcuring. ln the process, when the fibres are treated with multivalent metal ions (cations) inacidic conditions in steps iv) and v), the hornification ofthe fibres increases and thereby stifferfibres are obtained.
    Hornification refers to an irreversible internal bonding in lignocellulosic fibre materials thattakes place upon water removal or drying/curing. The hornified fibres do not swell to thesame extent as the non-hornified fibres (i.e. they cannot take up as much water) and thisdifference can e.g. be measured as a decrease in water retention value. The irreversiblebonding also leads to a stiffening of the polymer structure in the fibres and papers made fromstiffer fibres are bulkier. .Thus, the process according to the first aspect of the inventionprovides bulking fibres and leads to webs that are easy to dewater during a papermakingpFOCeSS.
    By the attachment of CI/IC to the fibres the charge density, or the anionic charge density ofthe fibres can be increased, which is beneficial in the following paper making process.lt should be noted that in the present application, when an interval from a first value to asecond value is described, it is meant that any individual value within the claimed interval maybe chosen. For example, regarding the pulp consistency in the interval ”of from 0.1 to 40 % byweight", it is meant that any value within the interval, such as 1%, 10%, or 40% may be chosenfor the pulp consistency. Further as an example and in a corresponding way the pH may bechosen to be any pH value within the claimed interval of from 3.0 to 6.0 and can be forexample pH 3.5, pH 5.0, or pH 6.0.
    According to one embodiment the first pulp slurry is dewatered and subsequently orconcurrently cured by means of flash drying. Flash drying is suitably performed at atemperature that is higher than for example when drying by means of heated cylinders, and5the temperature can be from 100 to 300°C, depending on the at sensitivity of the first pulpslurry. Also the curing time is normally shorter when flash drying is used. By flash drying afurther bulking effect, i.e. a higher bulk with lower density, may be obtained. Thus, in the stepvi) the first pulp slurry can be cured by means of flash drying at a temperature from 100°C to300°C, preferably from 150°C to 270°C and most preferably from 180°C to 240°C. The curingtime can be less than 5 minutes, preferably less than one minute. Therefore, essentiallyshorter curing time may be obtained compared to traditional curing methods.
    According to another embodiment, in the step vi) the first pulp slurry is cured at atemperature from 60 to 150°C by means of heated air or steam, wherein the heated air orsteam is lead directly to heat the first pulp slurry or indirectly to heat the first pulp slurry, forexample heated cylinders. The higher the temperature during the curing is, the higher will thebulk be, and thus the bulking effect. By using these curing methods in the step vi), it is possibleto provide the cured pulp product in the form of a web, i.e. a cured web. The web may then becollected and rolled up to web rolls and then provided to a papermaking mill. The process maythen further comprise a step vii) comprising cutting the cured web into sheets and stackingthe sheets to provide bales of pulp. The bales of pulp are easy to transport to a paper mill andcan be readily used in a papermaking process.ln the process in the step vi) the first pulp slurry is preferably cured until a moisture content ofbelow 50%, suitably below 30%, and preferably below 15% is obtained. The moisture contentmay be 0%, but usually the moisture content is from about 1 to 10%. The more the web iscured, the greater will the density decrease ofthe material be and thus the greater the bulkingeffect obtained.
    The metal salt comprising the multivalent, i.e. divalent or trivalent, metal ion is preferablyadded to the first pulp slurry in the step iv) at a molar concentration of from 0.0001 M to 0.05M which is sufficient to obtain bulking effect while the risk for deteriorating the quality of thefibres is minimized. According to one preferable variant the multivalent metal ion added in thestep iv) is Al3+, which is commonly known in papermaking.
    The pulp consistency ofthe first aqueous pulp slurry is of from 0.5% to 30%, preferably offrom 1% to 20%, calculated as dry weight of the cellulosic fibres in the first pulp slurry.
    Preferably, the pulp concentration is as high as possible, whereby a more effective ion6exchange can be achieved, and thus the concentration ofthe added metal salt can be kept at alow level.
    The CMC can be amphoteric and have a cationic molar substitution degree of from 0.00001and 0.4 and an anionic molar substitution degree of from 0.3 to 1.2, and wherein a net chargeof the CI/IC is anionic. By using amphoteric CI/IC, the amount of the CI/IC used can bedecreased and still a sufficient amount can be attached to the fibres. However, the CI/IC mayalso be anionic and have an anionic molar substitution degree of from 0.3 to 1.2. Generally,anionic CI/IC is cheaper, and even though larger amount of anionic CI/IC is needed forattaching an equal amount of CMC to fibres than amphoteric CI/IC, a more economical processcan be provided if anionic CMC is used. The amount ofthe anionic or amphoteric CMCattached during the treatment is suitable of from 1 mg/g to 100 mg/g, based on the weight ofthe cellulosic fibres in the first pulp slurry.
    The first aqueous pulp slurry may comprise a pulp selected from a kraft, soda, sulfite,mechanical, thermomechanical, semi-chemical or chemi-thermomechanical pulp, or mixturesthereof, and will be explained more in detail below.The present invention also relates to a cured pulp product obtained by the process.
    The cured pulp product may then be used in several applications, such as in the production ofpaper or paperboard, tissue paper, filter paper, or fluff pulp. According to one aspect, theinvention further relates to a process for the production of paper or paperboard comprisingthe steps of:a. providing a cured pulp product as defined above to a paper making process;b. re-slushing the cured pulp product to provide a second pulp slurry;c. dewatering the second pulp slurry to provide a web of paper or paperboard;d. drying the web of paper or paperboard to provide a dried web of paper orpaperboard.
    The processes for the production of paper or paperboard described above may furthercomprise adding a dry strength aid or a wet strength resin to the first pulp slurry, suitably forexample between the steps b. and c. ln this way the strength ofthe paper or paperboard canbe improved, while still maintaining an improved bulking effect.7According to a second embodiment ofthe invention, paper or paperboard may be produced inan integrated paper mill, i.e. a mill that comprises both a pulp mill and a paper mill withoutdrying the pulp before the paper/board machine. In an integrated paper mill it has been foundthat it is not necessary to cure the pulp before a paper or paperboard making process. Thus,the present invention also relates to a process for the production of paper or paperboardsuitable for use as a packaging board. The definition paper also includes e.g. tissue paper andfilter paper. The process according to a further embodiment comprises the steps of:I. providing a first aqueous pulp slurry comprising cellulosic fibres and having apulp consistency of from 0.1 to 40 % by weight, calculated as dry weight of thecellulosic fibres in the first pulp slurry;II. adjusting the pH ofthe first pulp slurry to a range between pH 1.5 to pH 4.5, oralternatively treating the first pulp slurry with a metal salt containing divalentmetal ions selected from Zn2+, Mg2+, Ca2+ or mixtures thereof, to a total molarconcentration ofthe metal salt of from 0.0001 to 0.5 M in the first pulp slurry;III. attaching an anionic or amphoteric carboxymethyl cellulose (CMC) or aderivative thereof to the cellulosic fibres in the first pulp slurry by treating thepulp with the CMC at a temperature of at least 50°C;IV. adding to the first pulp slurry a metal salt comprising an Al3+ metal ion to amolar concentration of from 0.0001 M to 0.5 M in the first pulp slurry, wherebyan ion-exchange occurs;V. providing the first pulp slurry to a papermaking process and thus provide asecond pulp slurry;VI. dewatering the second pulp slurry to provide a web of paper or paperboard;VII. drying the web of paper or paperboard to provide a dried web of paper orpaperboard.
    This process is also referred to as a ”wet” process, since the curing step before the papermaking process is omitted.
    In the process, in the step IV) it has been found that aluminium containing metal saltcomprising is suitable for use. Without binding the applicant to any specific theory, onepossible explanation is that by the presence of aluminium ions it is possible to increase the8friction between the fibres on the surface. Therefore, it is possible to maintain the network ofthe fibres during drying and thus it is possible to provide higher bulk. Thus, according to thisembodiment, the addition of aluminium ion Al3+ is essential, while the curing step before thepapermaking process is not essential. Thus, in this way pulp slurry with a high bulk can beprovided for the use in an integrated mill.ln the dry and wet processes described above, the first aqueous pulp slurry may comprise achemical pulp selected from a sulfate, kraft, soda, or sulfite pulp, a mechanical pulp, athermomechanical pulp, a semi-chemical pulp (e.g., a neutral sulphite semi-chemical pulp;NSSC), or a chemi-thermomechanical pulp, or mixtures thereof. According to one variant, thefirst pulp slurry comprises kraft pulp, whereby a high quality raw material for the process canbe provided.
    The pulp consistency ofthe first aqueous pulp slurry is suitably from 0.5% to 30% andpreferably from 1% to 20%. Preferably, the pulp concentration is as high as possible, wherebya more effective ion exchange can be achieved, and thus the concentration of the added metalsalt can be kept at a low level.
    The CMC can be anionic or amphoteric. According to one embodiment, the CMC is amphotericand has a cationic molar substitution degree between 0.00001 and 0.4, and an anionic molarsubstitution degree from 0.3 to 1.2.
    According to another embodiment, the CI/IC is anionic and has an anionic molar substitutiondegree of from 0.3 to 1.2. Anionic CMC is cheaper to produce and thus a more economicalprocess can be provided if anionic CMC is used.
    The amount of CMC used during the treatment can be from 1 to 100 mg/g, based on theweight of the cellulosic fibres in the first pulp slurry. By using the specific amount, all CMC canbe attached to the cellulosic fibres. Thus, the attached amount of CI/IC can be from 1 to 100mg/g-Further in the wet process described above, in the step iv) a metal salt comprising an Al3+metal ion can be added to the first pulp slurry to a total molar concentration of aluminiumions of from 0.0001 M to 0.05 M, whereby ion-exchange occurs. The concentration of the9aluminium salt in the specific range is sufficient to obtain a bulking effect on different bulkinglevels.
    The processes for the production of paper or paperboard described above may furthercomprise adding a dry strength aid or a wet strength resin to the first pulp slurry, suitably forexample between the steps V. and VI. ln this way the strength of the paper or paperboard canbe improved, while still maintaining an improved bulking effect.
    Further, the present invention relates to a paper or paperboard obtained by the processes asdescribed above. The paper or paperboard product may have a structural density of from 150to 600 kg/m3 according to SCAN-P-88:01, whereby a low density product can be provided forpackaging purposes. Preferably, the paper or paperboard product is used as a packagingmaterial, and more preferably as a middle layer in a paper board, whereby the bulk of theboard can be increased.lt has also been found that the cured pulp product obtained according to the firstembodiment of the process, the ”dry” process described process in steps i)-vi) can also beused for the production of a fluff pulp or filter or tissue paper. The fluff pulp may be furtherused for example in absorbent products.
    Further features and advantages of the present invention are described in the followingdetailed description and examples with reference to the appended drawings.BRIEF DESCRIPTION OF THE DRAWINGSFig. 1 is a flow chart which shows the main steps of the present process according to a firstembodiment, ”dry process";Fig. 2 is a flow chart which shows the main steps of the present process according to a secondembodiment, ”wet process";Fig. 3 shows a graph which illustrates effects on the water retention value of a pulp obtainedfrom a process according to the first embodiment of the invention, the ”dry process", withattachment levels of 20 mg/g and 40 mg/g amphoteric CI/IC and drying the sheets at 120°C for2 h and re-slushing the pulp and forming sheets.
    Fig. 4 shows a graph which illustrates effects on the sheet density of a pulp obtained from aprocess according to the first embodiment of the invention, the ”dry process", withattachment levels of 20 mg/g and 40 mg/g amphoteric CI/IC and drying the sheets at 120°C for2 hrs and re-slushing the pulp and forming sheets.
    Fig. 5 shows a graph which illustrates the effect of curing temperature on water retentionvalue when pulp is treated with 20 mg/g amphoteric CI/IC and the pulp is in its Al3+-form(0.005 M) and pH 3.5 and dried at 120 °C for 2 hrs (”dry process").
    Fig. 6 shows a graph which illustrates the effect of different metal ions on water retentionvalue when pulp is treated with 20 mg/g anionic CI/IC and the pulp is in its Al3+-form (0.005 M)and pH 3.5 and the curing temperature at 120°C for 2 hrs (”dry process").
    Fig. 7 shows a graph which illustrates the tensile index versus structural density of papersheets pressed to different densities when the pulp was treated with 20 mg/g anionic CMCand the pulp is in its different ionic forms (Na+, Ca2+ and Al3+), ”wet process".DETÅILED DESCRIPTIONThere is a long-time felt need for lighter and stronger packaging materials. The inventors ofthe present invention have found an economical and efficient method to treat fibres in aprocess that increases the bulk of paper or paperboard materials and thus provides lighterpackaging materials while the mechanical properties ofthe material can be maintainedsufficiently by using chemical additives for packaging purposes.Below, general descriptions for some of the used definitions in this application are given.
    Definitions paper or paperboard are used equally in this context and are meant to relate to amaterial made from pulp and which comprises cellulosic fibres. Paper is manufactured fromcellulosic fibres by pressing the moist fibres together and then dewatering and/or drying thefibres into a thin, flexible material. Paper may be a single layer product or it may containseveral layers. By paper is also meant equally e.g. printing paper, tissue paper, filter paper andpaperboard. Paperboard or packaging board is a cardboard product made from a pulp, andcan be made of several layers of paper.11By tissue paper is meant a very thin or light weight paper often produced with a papermachine comprising a steam heated drying cylinder (yankee cylinder) or by through-air-drying(TAD) of the tissue paper. Tissue paper has often good absorbent capacity, for example fromabout 1 g liquid/1 g fibre, but may be more or less depending on the quality of the tissuepa per.
    Fluff pulp is pulp having absorbent properties. Fluff pulp is often based on a chemical pulp,preferably kraft pulp or a chemi-thermomechanical pulp (CTMP). Preferably, the raw materialused comprises long fibres, and can be derived from soft wood material, such as spruce, pine,fir, larch, cedar, and hemlock.
    Filter paper is a paper used for filter applications where a passing fluid is passed through thepaper to capture for instance particles. The passing fluid may be a gas such as air or a liquidsuch as water. Fluff pulp is pulp having absorbent properties.
    Cellulosic fibres are fibres originating from unbleached or bleached pulp comprising a pulpselected from a kraft, soda, sulfite, mechanical, a thermomechanical pulp (TI/IP), a semi-chemical pulp (e.g., neutral sulfite semi-chemical pulp; NSSC), recycled pulp or a chemi-thermomechanical pulp (CTMP). The raw material for the pulps can be based on softwood,hardwood, recycled fibres or non-wood fibres suitable for making paper orpaperboard/cardboard. The softwood tree species can be for example, but are not limited to:spruce, pine, fir, larch, cedar, and hemlock. Examples of hardwood species from which pulpuseful as a starting material in the present invention can be derived include, but are notlimited to: birch, oak, poplar, beech, eucalyptus, acacia, maple, alder, aspen, gum trees andgmelina. Preferably, the raw material mainly comprises softwood. The raw material maycomprise a mixture of different softwoods, e.g. pine and spruce. The raw material may alsocomprise a non-wood raw material, such as bamboo and bagasse. The raw material may alsobe a mixture of at least two of softwood, hardwood and/or non-woods.
    By pulp consistency is meant dry content in an aqueous pulp slurry. That is, for example aconsistency of 10% means that the weight of the dry matter is 10%, based on the total weightof the pulp slurry.12By curing is meant that a physical or chemical reaction occurs in the material in addition toevaporation of water. By drying is meant evaporation or draining away water or other liquidsfrom a material.
    Dewatering is a procedure by which water is removed from a wet pulp web. Dewatering canbe performed mechanically during the web formation on a wire for example by means ofvacuum or centrifugal forces. Dewatering may also be performed by means of mechanicalforces, e.g. by means of pressing, e.g. in a pressing section of a paper machine. Afterdewatering on a wire and/or mechanical dewatering, the web can be forwarded to a dryingsection, in which the remaining water/moisture in the web is evaporated by means of heat,which is also called thermal dewatering. The drying section may be designed in different waysand can comprise e.g. multi-cylinder dryer, yankee cylinder drying, through-air drying or flashdrying equipment.
    By moisture content is meant the water content of the material expressed in weight %, andbased on the total weight of the material.
    By water retention value is meant a test value that provides an indication of fibres' ability totake up water and swell, and is in this application measured by means of a standard methodSCAN-C 62:00 unless otherwise stated.ln this application, the definition of re-slushing is used equally with re-pulping and re-slurryingand means that a cured pulp is re-suspended in water to provide an aqueous suspensioncontaining cellulosic fibres.ln the present application by bulking fibres are meant fibres that after treatment obtain amore bulky material structure than fibres that have not been treated. By bulking effect ismeant an effect which decreases the density of a material compared to a material that has notbeen treated.
    By molar concentration is meant the concentration or the amount of a substance (mole) inone dm3 or litre of a mixture, e.g. molar concentration of metal ions equals to moles of theions in one litre of an aqueous solution/suspension containing water and a metal salt.
    By ”degree of substitution" or ”DS”, is meant the number of substituted ring sites of beta-anhydroglucose rings of the carboxymethyl cellulose, CMC. Since there are three hydroxyl13groups on each anhydroglucose ring ofthe cellulose that are available for substitution, themaximum value of DS is 3.0.
    The carboxymethylcellulose (CI/IC) used in the present invention is anionic or amphoteric. lt isessential that the CMC is charged, however, the reaction agent to render the CMC chargedneeds not be of any specific kind. The amphoteric CMC has an anionic net charge. Any anionicor amphoteric CI/IC suitable for use in papermaking industry could be used in theembodiments of the present process. Anionic or amphoteric CI/IC and reaction agents torender the CMC charged are known to the skilled person in the art and examples, whichshould not be considered to be limiting, of the CI/IC usable in the present invention aredescribed below.
    The anionic carboxymethyl cellulose (CMC) useful in the process of the present invention has adegree of substitution of up to the theoretical limit of 3.0, but preferably from about 0.30 to1.20 carboxymethyl substituents per anhydroglucose unit of cellulose.
    The CI/IC usable in the present invention has a net anionic charge, but may comprise alsocationic groups whereby the CI/IC is amphoteric. An amphoteric CMC can have a cationicdegree of substitution in the range of from 0.00001 to 1.0, preferably from 0.00001 to 0.4. Theamphoteric CI/IC can also have an anionic degree substitution in the range of from 0.3 toabout 1.20.
    Examples of suitable anionic groups include carboxylate, e.g. carboxyalkyl, sulphonate, e.g.sulphoalkyl, phosphate and phosphonate groups in which the alkyl group can be methyl, ethylpropyl and mixtures thereof. The CI/IC suitably contains an anionic group comprising acarboxylate group, e.g. a carboxyalkyl group. The counter-ion ofthe anionic group can be analkali metal or alkaline earth metal ion, such as sodium.
    Examples of suitable cationic groups of CMC can include salts of amines, suitably salts ofsecondary ammonium groups, tertiary amines, and quaternary ammonium groups. Thesubstituents attached to the nitrogen atom of secondary ammonium groups, amines andquaternary ammonium groups can be the same or different and can be selected from e.g.alkyl, cycloalkyl, and alkoxyalkyl groups. The substituents can comprise from 1 to about 24carbon atoms, independently of each other. The nitrogen of the cationic group can beattached to the CI/IC directly or by means of a linking chain of atoms which can comprise14carbon and hydrogen atoms, and optionally oxygen and/or nitrogen atoms. For example thelinking chain of atoms can be an alkylene group with from 2 to 18 carbon atoms, and maycontain one or more O or N atoms. Examples of CMC containing cationic groups include thoseobtained by reacting CMC with a quaternization agent selected from 2,3-(epoxypropyl)trimethylammonium chloride, (4-chlorobutene-2)-trimethylammonium chloride, 2-diethylaminoethyl chloride and mixtures thereof.
    The cationic groups are suitably quaternary ammonium groups and then the cationic degree ofsubstitution referred to herein is the same as the degree of substitution of quaternaryammonium groups.
    The anionic and/or amphoteric CMC usually has an average molecular weight which is at least20 000 Dalton, preferably at least 50 000 Dalton, and up to about 1 000 000 Dalton, preferablyup to about 500 000 Dalton.
    The amount of CMC added to the pulp slurry during the treatment can be from 5 to 100 mg/gfibres, based on the weight of the cellulosic fibres in the first pulp slurry. Suitably, the amountis from about 10 to 30 mg/g, based on the weight of the cellulosic fibres in the first pulp slurry.All CI/IC can be attached to the fibres, and therefore the attached amount of CI/ICcorresponds to the added amount, e.g. from 5 to 100 mg/g fibres.
    Process descriptionAs already mentioned above, it is desirable to produce packaging materials with a higher bulk.However, despite prior art solutions there is still a need to improve processes to producebulky paper, such as tissue paper or filter paper, paperboard, or fluff pulp in an economicaland efficient way. lt is also desirable that existing process equipment can be used to producepaper or paperboard. lt is thus essential that the characteristics of the treated pulp material orproduct used in paper mills do not negatively affect the papermaking process. lt is desirablethat the paperboard production in the existing paper mills can be run with as fewmodifications as possible.
    According to the first embodiment of the present process, which is also in this contextreferred to as a ”dry process", it is possible to provide a cured pulp product in the form of aweb of pulp, bales of pulp or flakes of pulp for a further production of paper or paperboard ina paper mill or factory. The flakes may be in the form of a free flowing material or the flakesmay be gathered to bales. ln the process the pulp is treated with multivalent metal ions, suchas aluminium, calcium, magnesium or zinc ions (cations) so as to obtain bulking fibres.
    When the pulp is cured, the physical/chemical reactions that occur during curing render theinternal structure of the pulp material stabilized before further processing of the cured pulpproduct. Therefore, the fibres show less swelling when re-slushed during paper or paperboardmanufacture than fibres that are not treated. Thus, for example significant lowering of thewater retention value can be obtained when the cured pulp product ofthe invention is usedcompared to a pulp material that is not cured. This is beneficial for the pressing efficiency.Thereby, a higher dry content after the press section in a paper machine may be obtained,which is especially beneficial in paper mills having limited drying capacity.
    When the pulp is provided in an integrated paper mill, according to the second embodimentof the present invention the pulp is not cured before it is provided to the paper or paperboardmaking process. By the treatment with aluminium salts during the paper or paperboardmaking process it is possible to increase the bulk ofthe obtained paper or paperboard.Without binding the applicant to any specific theory, this may be caused by the increasedfriction between fibres on the surface of the pulp product and therefore, it is possible tomaintain the network of the fibres during curing and thus it is possible to provide a structurewith higher bulk.
    The processes according to the embodiments of the present invention have been found to beefficient to produce paper-based products having a higher bulk than pa per-based productsproduced from non-treated pulps. Also, during the paper making process the pulp can bemechanically pressed to higher solids content and therefore drying energy is saved during thepaper or paperboard making processes. As mentioned above, a further advantage is that thatthe productivity of drying-limited paper/board machines can be enhanced.
    A first embodiment ofthe present process is illustrated in Fig. 1 in which steps ofthe processare illustrated in a flow chart. The first embodiment of the present process is also referred toas a ”dry process”. A second embodiment ofthe present process is illustrated in Fig. 2 in whichsteps ofthe process are illustrated in a flow chart. The second embodiment ofthe presentprocess is also referred to as a ”wet process”. By the first embodiment of the present processa cured pulp product suitable for use for the production of paper, paperboard, tissue or filter16paper or fluff pulp can be provided. Fluff pulps are commonly used in for example absorbentproducts.
    By the second embodiment of the present process it is possible to provide a treated pulpusable directly in a papermaking process, e.g. in an integrated pulp and paper mill, andprovide paper or paperboard with increased bulk. ln the second embodiment of the invention,no curing is performed between the pulp treatment and the papermaking process.
    ”D ry” processReturning to Fig. 1 and the first embodiment ofthe present invention, in the first step i) of theprocess an aqueous first pulp slurry is provided. The first pulp slurry comprises cellulosic fibresand has a pulp consistency of from about 0.1 to 40 wt-%, calculated as a dry content ofcellulosic fibres in the first pulp slurry. The first pulp slurry may thus be a low consistency pulphaving a dry content of from 1 to 4%, medium consistency pulp having a dry content of from 8to 12 % or high consistency pulp having a dry content of from about 20 to 40%. Suitably theconsistency is from 0.5 to 30 %, and preferably from 1 to 20%, calculated as a dry content ofcellulosic fibres in the first pulp slurry.
    The raw material may be selected from any of softwood, hardwood, recycled fibres or non-wood fibres that are suitable for making paper or paperboard/cardboard or mixtures thereof.The first pulp slurry may comprise or consist of an unbleached or a bleached pulp which cancomprise or consist of a chemical pulp such as a kraft (sulfate), soda or sulfite pulp. The pulpmay also comprise or consist of a mechanical pulp, thermomechanical pulp (TMP), semi-chemical pulp (e.g., neutral sulfite semi-chemical pulp; NSSC), recycled pulp or chemi-thermomechanical pulp (CTMP). The pulp may consist of one type of pulp or the pulp maycomprise two or more pulps as a mixture. Preferably, the cellulosic fibres originate from achemical pulping process, which provides high quality pulps. Suitably, the fibres are derivedfrom a kraft pulping process.
    The next step ii) of treating the first pulp slurry can be performed in two alternative ways.According to a first alternative, the pH ofthe pulp slurry is adjusted to an acidic range, i.e. to apH value of from 1.5 to 4.5. The pH adjustment can be performed by using any suitable acid,preferably an inorganic acid such as sulphuric acid. According to a second alternative in the17step ii) the first pulp slurry is treated with a metal salt containing divalent metal ions (cations).The total metal ion concentration in the first pulp slurry is adjusted to a total concentration offrom 0.0001 to 0.05 M in the first pulp slurry, preferably from 0.0005 to 0.05. The divalentmetal salt may comprise a metal ion selected Zn2+, Mg2+ or Ca2+, or combinations thereof.ln the following step iii) an anionic or amphoteric carboxymethyl cellulose (CMC) or aderivative thereof is attached to the cellulosic fibres in the first pulp slurry. The CMC can beattached to the cellulosic fibres by treating the pulp with CMC at a temperature of at least50°C and in the specific conditions created during the alternative steps ii), i.e. at acidicconditions or in the presence of electrolytes, i.e. in the presence of divalent metal ions.Method for the CMC attachment is known in the prior art and can be performed as describedfor example in one ofthe applicant's previous patents, EP1240389B1.ln the following step iv) a metal salt comprising a multivalent metal ion selected from Al3+,Zn2+, Mg2+, Ca2+ or mixtures thereof, is added to the first pulp slurry. The metal ion added to atotal molar concentration ofthe metals ion in the first slurry of from 0.0001 M to 0.5 M. |ftheconcentration ofthe divalent metal ions added in the step ii) is within the desired range, nofurther addition of a metal salt is necessary. By adding the multivalent metal salt to the firstpulp slurry, which is never-dried, it is possible to provide a bulking structure for a cured pulpproduct. The cured pulp product is obtained in the following curing step under acidicconditions whereby the structure of the fibres is stabilized and thus a paper or paperboardproduct with higher bulk can be provided. Therefore, it is possible to obtain low density paperor pa perboa rd materials.
    The counter ion in the multivalent metal salt may be any suitable counter ion and can be forexample selected from Cl", N03' or S042' or any other suitable counter-ion, which is dissociatedfrom the multivalent metal ion in water. Such salts are also often used in papermaking and aresuitable for the processes thereof.
    Preferably, the amount of the added metal salt in step iv) is kept as low as possible so that thequality of the pulp material is not degraded. Thus, the multivalent metal salt comprising ametal ion is preferably added to the pulp to a molar concentration of from 0.0001-0.05 M.
    Preferably, the multivalent metal salt is an aluminium salt and is added to the first pulp slurry18in addition to the divalent metal ions and to a total molar concentration of from 0.0001 M to0.05 l/l.
    The pH of the first pulp slurry is adjusted after or before the addition ofthe metal saltcomprising the metal ion if necessary as described in the step v) of the process. lt is essentialthat the pH is acidic during curing and the pH of the first pulp slurry should be from pH 3.5 topH 6.0. The adjustment can be performed by using an acid or base other than the metal saltused in steps ii) and/or iv), e.g. by using sulphuric acid.
    After the addition of the multivalent metal ions and the adjustment of the pH in step v) ifneeded, the first pulp slurry is dewatered and cured under acidic conditions in the step vi) ofthe process to provide a cured web, which is to be distinguished from a dried web obtainedfrom the final paper/paperboard process. The acidic condition during the curing in the step vi)of the first pulp slurry further increases the bulk of a paper, paperboard, tissue paper, filterpaper, or fluff pulp made from the cured pulp product. This is caused by an increasedhornification of the cellulosic fibres when cured under acidic conditions and especially goodresults have been obtained in the presence of Al3+ ions. This means that the fibres becomestiffer in aqueous suspensions than non-treated fibres. The curing temperature is at least60°C, and the first pulp slurry is cured until the moisture content is below 50%. Preferably, themoisture content is below 30%, and most preferably below 15%. Normally, the pulp is cureduntil a moisture content level of from 0 to 5% is obtained. Due to practical reasons, the pulpoften contains small amounts of moisture.lt has also been noted that the curing temperature influences the bulk of the cured pulpproduct, i.e. a lower density may be obtained by increasing the curing temperature. Therefore,according to an embodiment ofthe invention, the curing temperature of the first pulp slurrycan be from about 60°C and up to about 150°C, preferably from 80 to 120°C, when the curingis performed by means of heated air/steam or by means of steam heated drying cylinders.Suitably, the first pulp slurry is cured for less than about 3 hours at the specific temperature.The cured pulp product continues to cure when it is rolled into a web roll or when stacked intobales of sheets, since the temperature ofthe cured pulp product decreases slowly, and thiscuring time is also included in the curing period of less than about 3 hours.19Alternatively or additionally to the drying by means of heated air or steam or steam heatedcylinders, the first pulp slurry can be cured by means of flash drying, also called swirlfluidisizing. Such driers are known in the art and provided e.g. by the company GEA ProcessEngineering A/S or Andritz AG. By using flash drying, the drying temperature can be higherthan when drying by means of heated cylinders, and the temperature can be of from 100 to300°C, depending on the sensitivity of the first pulp slurry to the curing conditions. Also thecuring time can be shorter when flash drying is used. By flash drying a further bulking effect,i.e. a higher bulk with lower density, may be obtained, and a free-flowing material may beobtained. Further, the bulk of the first pulp product may be further increased.
    Thus, in the ”dry process” the first pulp slurry containing the multivalent metal salt is curedbefore re-slushing it in a paper- or paperboard making process. lt is thus possible to lower thewater retention value significantly during the paper or paperboard production. The pressingefficiency can be improved significantly and a higher dry content after the press section can beobtained and therefore less energy for drying is needed. The treatment suitably takes place ina pulp mill, and the pulp is used in a non-integrated paper/board mill, and therefore theresource efficiency will be much higher both in terms of material and energy efficiency at thenon-integrated pa per/pa perboa rd mill.
    The cured web obtained in the step vi) can be used as such or e.g. rolled into a web roll havinga pre-determined web length. Optionally, in a step vii) the cured web of pulp can be cut intosheets and the sheets are stacked to provide bales of pulp.
    The cured pulp product may be used for the production of paper or paperboard, but may alsobe used for the production of tissue paper, filter paper, or fluff pulp.ln case of a non-integrated paper mill, it is possible to transport the cured pulp product to thepaper mill from the pulp mill in the form of bales, rolls orflakes. The cured pulp product isthen re-slushed in a headbox of a papermaking machine.
    According to a further aspect, the present invention also relates to a process for theproduction of paper or paperboard. After collecting the cured web in a suitable manner in thestep vi) or vii) described above, the cured web is provided to the papermaking process in aprocess step a). The providing is illustrated by two broken lines between the process steps i) tovi) or vii) and the process steps a) to d) in Fig. 1.
    The cured pulp product is then subjected to re-slushing in step b) to provide a second pulpslurry. The second slurry is then dewatered in the step c) and a web of paper or paperboard isprovided. The web is then dried in a step d) and thus a dried, bulky web of paper orpaperboard that is suitable for use as a packaging material is obtained. The paper orpapermaking process can be performed in a traditional way, and dry contents, additives andother papermaking process parameters known in the art can be used.
    Since the cellulosic fibres become stiffer due to the treatment in steps i)-vii) above in aqueoussuspensions after re-slushing, the fibres swell less during the re-slushing of the cured pulpproduct. This leads to webs that are easily dewatered during the papermaking process. This isa huge advantage and makes the process energy efficient while higher bulk can be obtained.ln the paper or paperboard material comprising the bulking fibres treated with a multivalentmetal ion there may be a risk that the mechanical properties (e.g. z-strength for instancemeasured according to SCAN-P 80:98) are weakened. Thus, in order to enhance the strengthof paper/board made from bulking fibres, there are several different groups of suitable drystrength aids including, but not limited to, nanocellulosic materials, such as microfibrillarcellulose, cellulose nanofibrils, cellulose filaments, nanocrystalline cellulose, fines and finesenriched pulps, starch and gum derivatives, synthetic copolymers with acrylamide, such asacrylic acid, vinyl pyridine, 2-aminoethyl methacrylate, diallyl-dimethyl ammonium chloride,dimethyl-amino-propylacryl amide, diamine ethyl acrylate, styrene and glyoxalatedpolyacrylamides. The latter group is also suitably copolymerized with cationic monomers. Wetstrength resins such as urea-formaldehyde resins, melamine-formaldehyde resins orpolyamide-polyamine-epichlorohydrine resins are also useful in order to enhance the drystrength of bulking fibres. Such dry strength aids or wet strength resins are suitably added tothe second pulp slurry during paper or paperboard production, whereby the strength of thefinal paper or paperboard product can be improved.l'Wet rocess"21A second embodiment of the present invention is illustrated in Fig. 2. This process relates to aprocess for the production of paper or paperboard suitable for use as a packaging board and isalso called a ”wet process", since the curing step (vi) ofthe first embodiment is notperformed. The steps I, ll and | in the process are similar to the process steps i) to iii) in Fig. 1and reference is made to the description above in connection with Fig. 1. ln short, the steps Ito | comprise:I. providing a first aqueous pulp slurry comprising cellulosic fibres and having apulp consistency of from 0.1 to 40 % by weight, calculated as dry weight of thecellulosic fibres in the first pulp slurry;ll. adjusting the pH of the first pulp slurry to a range from pH 1.5 to pH 4.5, oralternatively treating the first pulp slurry with a metal salt containing divalentmetal ions selected from Zn2+, Mg2+, Ca2+ or mixtures thereof, to a total molarconcentration of the metal salt of from 0.0001-0.5 M in the first pulp slurry|. attaching an anionic or amphoteric carboxymethyl cellulose (CMC) or aderivative thereof to the cellulosic fibres in the first pulp slurry by treating thefirst pulp slurry with the CMC at a temperature of at least 50°C;After the steps I to |, in the following step IV, the cellulosic fibres with the attached CMC inthe first pulp slurry is ion-exchanged to counter-ions with high valency. This means that amultivalent metal salt comprising aluminium Al3+- metal ion is added to the first pulp slurry toa total molar concentration from 0.0001 M to 0.5 M, whereby an ion-exchange occurs.Without binding to any specific theory, it is believed that when the ion-exchange occurs, thefibre to fibre friction increases significantly in the presence ofAl3+-ions on the surface of thefibres. The higher friction between the fibres in the wet state will partly prevent sheetconsolidation and result in a paper/paperboard product with a higher bulk. lt is also believedthat the fibres thus form a network of fibres and this network can be maintained during adrying process in a papermaking process.
    After the addition ofthe aluminium salt, the first pulp slurry is provided to a papermakingprocess in step V. The paper making process may be of any known kind and chemicals andother papermaking parameters suitable for the process in question can be used. ln a usual22manner, the first pulp slurry is then dewatered in step VI) to provide a web and finally, in thestep VII) the web is dried to provide a web of paper or paperboard.ln a similar manner as mentioned above, the process may further comprise adding a drystrength aid or a wet strength resin to the first pulp slurry. The same aids or resins asmentioned above can be used for the purpose.
    The present invention also relates to a paper or paperboard product suitable for use as apackaging material which is obtained by the processes described above. lt is possible to obtaina high quality paper or paperboard with low density having a structural density according toSCAN-P-88:01 of from 150 to 600 kg/m3. The paper or paperboard product is suitably used as apackaging material. Preferably, the paper or paperboard product can be used as a middle layerin a paperboard to provide increased bulk for the paperboa rd product.
    The present process is suitable for use in both pulping and papermaking mills/factories thatare integrated or non-integrated, since the curing step after metal-ion addition is not essentialfor the bulking effect in the second embodiment ofthe invention.The invention will now be further described and illustrated in the following examples.EXAMPLESThe following exampled illustrate the effects of the present invention, but should not beregarded as limiting the scope of invention in any way.Example 1A never-dried bleached softwood kraft pulp was treated with 20 and 40 mg/g amphoteric CI/IChaving degree of substitution of anionic groups= 0.48 and degree of substitution of cationicgroups = 0.027, whereby the amphoteric CI/IC has a total net anionic charge, whereby theamount of carboxylic groups on the surface of fibres can be enhanced. The pulps were treatedwith the CI/IC under conditions given in Table 1 below.23Table 1 CI/IC Grafting conditions.
    Water type Deionised waterPulp concentration 25 g/litre (2.5% by weight)Electrolyte concentration (CaClz) 0.05 MCI/IC addition 20 mg CMC/g fibre, or40 mg CMC/g fibrepH 8Temperature during CI/IC 120 °CtreatmentTime for CMC treatment 2 hrsThe amount of attached CMC was quantitative, i.e. all CI/IC became attached to the fibresurface. After the CI/IC-attachment, the pulp was treated with AlClg to a total molarconcentration of 0.005 M AlClg and the pH was adjusted to 4.0 and 5.0, respectively. After thepH adjustment, the pulp was dewatered on a Buchner funnel to a solids content of around20%. The pulp was then cured at 120°C for 2 h (oven drying), after which the pulp was re-slushed and formed into sheets in accordance with ISO 5269-1:2005, except that the sheetswere pressed at 400 kPa for 5 min.
    The water retention value (WRV) was measured according to SCAN-C62:00 before the sheetforming. The structural density (SCAN-P 88:01) was then determined on the prepared andpressed sheets. The effects on the WRV and resulting sheet density obtained by the process,also referred to as a ”dry process” are shown in Fig. 3 and Fig. 4 respectively. ln the processamphoteric CMC is attached to the cellulosic fibres in an amount of 20 mg/g and 40 mg/g.
    From Fig. 3 it can be concluded that ifthe CMC is attached to the cellulosic fibres and thefibres are transferred to their aluminium form and dried under acidic conditions, the waterretention value can be lowered and thus improved. lt can also be concluded that the WRV24decreases and thus improves when the pH decreases. Thus, the lower the pH value is, thelower the obtained WRV is.
    From Fig. 4 it can be concluded that if the CI/IC is attached to the cellulosic fibres and thefibres are transferred to their aluminium form and dried under acidic conditions a higher bulkof the sheets is obtained compared to pulps not treated with CI/IC. lt can also be concludedthat the density decreases leading to improved bulk when the pH decreases.Example 2This example shows the effects of different treatment temperatures and times on WRV, whichare believed to occur due to hornification.
    Never-dried bleached softwood kraft pulp was treated with 20 mg/g amphoteric CMC having adegree of substitution of anionic groups= 0.48 and degree of substitution of cationic groups =0.027, wherein the CMC has a net anionic charge, whereby the amount of carboxylic groupson the surface of fibres can be enhanced. The pulps were treated with the CMC underconditions given in Table 1 above and in Example 1. The fibres were then transferred to theiraluminium form and cured at different temperatures, 60°C, 80°C, and 120°C. After the curingthe pulps were re-slushed and their WRV values according to SCAN-C62:00 were determined.
    Fig. 5 shows in a graph the effect ofthe curing (oven curing) temperature on WRV due tohornification of a pulp treated with 20 mg/g amphoteric CI/IC pulp in its Al-form (i.e. a totalmolar concentration of Al-ions 0.005 M) and pH 3.5.lt can be concluded that the higher the curing temperature is, the more the WRV decreasesand thus improves the bulk of the paper/board.
    Example 3A never-dried bleached softwood kraft pulp was treated with 20 mg/g amphoteric CMC havinga degree of substitution of anionic groups = 0.48 and a degree of substitution of cationicgroups = 0.027, and thus having a net anionic charge, whereby the amount of carboxylicgroups on the surface of fibres can be enhanced. The treatment was performed under theconditions given in Table 1 above and Example 1. After the treatment the pulps were broughtin contact with different metal ion salts (i.e. electrolytes; as chloride salts) for 20 min at a totalmolar concentration ofthe salts in the pulp slurry as follows:Nat; 0.005 |v|,-cazt; 0.005 |v|Mgzt; 0.005 |v|zn 2% 0.005 |v|AP 0.005 |v|The pulps were then cured at 120° C for various times and re-slushed, after which the WRVwas determined. The results are shown in Fig 6.lt can be concluded that when the valency of the metal ion increases, the WRV decreases andthus improves the bulk of the paper/board. Therefore, e.g. much lower WRV values wereobtained with Al3+ metal ions than with Na+ metal ions.Example 4This example illustrates that it is not always necessary to cure the pulp in order to enhance thebulk of formed sheets and that bulk can also be obtained by the treatment according to the”wet process” as described above. lt is possible to attach CI/IC (anionic) or amphoteric CI/IC,whereby the amount of carboxylic groups on the surface of fibres can be enhanced. Hence, apulp slurry of unbeaten bleached softwood kraft pulp was treated with 20 mg/g fibre ofanionic CI/IC (degree of substitution = 0.4, Aquasorb A-500, Hercules, Sweden) under the sameconditions as shown in table 1 above in connection with Example 1.
    Before the attachment ofthe CI/IC the pulp was set to its calcium form. The pulp was given anacidic treatment at pH 2, after which the pulp was washed with deionized water and the pHwas increased to pH 8, again washed with deionized water and treated with a 10'2 M CaClzsolution and then finally washed with deionized water.
    The pulp was then mixed with the CMC solution and with CaClz. The pH was adjusted to 8using NaOH. The mixture was then inserted in an autoclave. The autoclave was heated upunder constant agitation in a glycol bath which had a constant temperature of 120 °C. After26the two hour long attachment process, the pulp was washed with deionised water on aBuchner funnel until the conductivity in the filtrate was below 5 uS/cm.
    The results from the treatment are shown in Table 2. The total amount ofthe attached CI/ICwas calculated from the total charge density increase to be 20.6 mg/g (+/- 1 mg/g), that is, theattachment efficiency can be considered as quantitative. The surface selectivity of theattachment, i.e. the amount of charges accessible on the surface of fibres as determined bypolyelectrolyte titration using high molecular weight poly-DADMAC (poly-DiallylDiMethyl-AmmoniumChloride was found to be 87.7 %, i.e. most ofthe CI/IC was being attached ontothe surface ofthe fibres. As reference an untreated pulp washed to its Ca2+ form was used.The method has been described by Horvath A E, Lindström T and Laine J. Langmuir, 22(2)(2006), 824-830.
    Table 2. Total and surface charge of reference pulp and pulp with attached CI/IC (20 mg/g)pulp.
    Pulp Total Charge Surface Charge ratio(eqv./g) Charge (surface/total)(eqv-/slReference pulp(Untreated pulp 39 5 1 6 0 04washed to its Ca2+ ' ' 'form)CI/IC grafted pulp 83.6 37.2 0.4427The pulp treated with CMC 20 mg/g fibre was transferred to its Na+, Ca2+ and Al3+-form,respectively. Different structural densities were obtained by forming sheets in accordancewith ISO 5269-112005, except that different pressing levels were used. Each sheet was pressedfor 5 minutes with different pressing levels, respectively (50, 100, 200, 400, 600, and 800 kPa).
    Fig. 7 shows a tensile strength index (ISO 1924-3: 2005) versus structural density of papersheets pressed to different densities. The pulps were grafted with 20 mg/g CI/IC and thentransferred to different ionic forms (Na+, Ca2+, Al3+) together with a reference pulp without anyattached CI/IC in its Cazïform.
    Fig. 7 shows how the tensile strength index of reference sheets and sheets (ISO 5269-1:2005)made from the bleached kraft pulp with the attached CI/IC is affected by the ionic form of thepulp. Apart from the strength development, the sheets in their Na+-form and Cazïform haveapproximately the same sheet density irrespective of pressing pressure, whereas the sheets intheir aluminium form have significantly lower sheet density. This example shows that it ispossible to make bulky sheets without curing before forming sheets by transferring papersheets with attached CI/IC to their Al3+-form before drying. However, curing of the pulp toinduce hornification is not a requirement, but stronger bulking effect can be achieved by the”d ry procedure".
    It is clear to the skilled person in the art that the invention may be varied within the scope ofthe appended claims. The examples and embodiments above are not intended to limit thescope ofthe invention in any way. Instead the invention may be varied within the scope of theappended claims.
    权利要求:
    Claims (31)
    [1] 1. Process for the production of a cured pulp product suitable for use in the production of paper, paperboard, tissue paper, filter paper or f|uff pulp, comprising the steps of: i) m) vi) providing a first aqueous pulp slurry comprising ce|u|osic fibres and having apulp consistency of from 0.1 to 40 % by weight, calculated as dry weight of thece|u|osic fibres in the first pulp slurry; adjusting the pH of the first pulp slurry to a pH of from 1.5 to 4.5, oralternatively treating the first pulp slurry with a metal salt containing divalentmetal ions selected from Zn2+, Mg2+, Ca2+ or mixtures thereof, to a total molarconcentration of from 0.0001 to 0.5 M in the first pulp slurry; attaching an anionic or an amphoteric carboxymethyl cellulose (CMC) or aderivative thereof to the ce|u|osic fibres in the first pulp slurry by treating thepulp slurry with the CMC at a temperature of at least 50°C; adding to the first pulp slurry a metal salt comprising Al3+ ions at a total molarconcentration of from 0.0001 M to 0.5 M in the first pulp slurry, or alternativelycontrolling the concentration of the divalent metal ions in the pulp slurry andadjusting the total molar concentration of the divalent metal ions selected fromZn2+, Mg2+, Ca2+ or mixtures thereof to a range of from 0.0001 M to 0.5 M in thefirst pulp slurry, ifthe total molar concentration is not within the range of from0.0001 M to 0.5 M in the first pulp slurry; controlling the pH and adjusting the pH of the first pulp slurry to a pH of frompH 3.0 to pH 6.0 if the pH is not within the range of from pH 3.0 to pH 6.0;dewatering and curing the first pulp slurry at a temperature of at least 60°C and thus provide a cured pulp product.
    [2] 2. Process according to claim 1, wherein in the step vi) the first pulp slurry is cured by means of flash drying at a temperature of from 100°C to 300°C, preferably from 150°C to 270°C and most preferably from 180°C to 240°C. 10. 29Process according to claim 2, wherein the curing time is less than 5 minutes, preferably less than one minute. Process according to claim 1, wherein in the step vi) the first pulp slurry is cured at a temperature of from 60 to 150°C by means of heated air or steam. Process according to claim 4, wherein in the step vi) the cured pulp product is provided in the form of a cured web. Process according to claim 5, wherein the process further comprises a step vii)comprising cutting the cured web of pulp into sheets and stacking the sheets to bales of pulp. Process according to any one of the preceding claims, wherein in the step vi) the curedpulp product is cured until a moisture content of below 50%, preferably below 30%and most preferably below 15%, based on the total weight of the cured pulp product, is obtained. Process according to any one of the preceding claims, wherein in the step iv) the metalsalt is a metal salt containing Al3+ ions which is added to the first pulp slurry to a total molar concentration of from 0.0001 M to 0.05 M in the first pulp slurry. Process according to any one of the preceding claims, wherein the pulp consistency ofthe first aqueous pulp slurry is of from 0.5% to 30%, preferably of from 1% to 20%, calculated as dry weight ofthe cellulosic fibres in the first pulp slurry. Process according to any one of the preceding claims, wherein the CI/IC is amphotericand has a cationic molar substitution degree of from 0.00001 to 0.4 and an anionicmolar substitution degree of from 0.3 to 1.2, and wherein a net charge ofthe CMC is anionic.
    11. Process according to any one ofthe preceding claims 1-9, wherein the CMC is anionic and has an anionic molar substitution degree of from 0.3 to 1.2.
    12. Process according to any one of the preceding claims, wherein the amount of theanionic or amphoteric CI/IC attached during the treatment is of from 1 to 100 mg/g, based on the weight of the ce|u|osic fibres in the first pulp slurry.
    13. Process according to any one of the preceding claims, wherein the first aqueous pulpslurry comprises a pulp selected from a kraft, soda, sulfite, mechanical,thermomechanical, semi-chemical or chemi-thermomechanical pulp, recyc|ed pulp or mixtures thereof.
    14. A cured pulp product obtained according to the process of any one of claims 1-13.
    15. Process for the production of paper or paperboard comprising the steps of: a. providing a cured pulp product according to c|aim 14 to a paper makingprocess; b. re-slushing the cured pulp product to provide an aqueous second pulp slurry; c. dewatering the aqueous second pulp slurry to provide a web of paper orpaperboard; d. drying the web of paper or paperboard to provide a dried web of paper or paperboard.
    16. Process according to any c|aim 15, wherein the process further comprises adding a dry strength aid or a wet strength resin to the second pulp slurry.
    17. Process for the production of paper or paperboard comprising the steps of: I. providing a first aqueous pulp slurry comprising ce|u|osic fibres and having apulp consistency of from 0.1 to 40 % by weight, calculated as dry weight of thece|u|osic fibres in the first pulp slurry; ll. adjusting the pH of the first pulp slurry to a pH of from 1.5 to 4.5, or alternatively treating the first pulp slurry with a metal salt containing divalent 18. 19. 20. 21. 22. 31metal ions selected from Zn2+, Mg2+, Ca2+ or mixtures thereof, to a total molarconcentration of the metal salt of from 0.0001 to 0.5 M in the first pulp slurry; III. attaching an anionic or amphoteric carboxymethyl cellulose (CMC) or aderivative thereof to the cellulosic fibres in the first pulp slurry by treating thefirst pulp slurry with the CMC at a temperature of at least 50°C; IV. adding to the first pulp slurry a metal salt comprising an Al3+ metal ion to a totalmolar concentration of from 0.0001 M to 0.5 M in the first pulp slurry wherebyan ion-exchange occurs; V. providing the first pulp slurry to a papermaking process and thus provide a second pulp slurry; VI. dewatering the second pulp slurry to provide a web of paper or paperboard;VII. drying the web of paper or paperboard to provide a dried web of paper orpaperboard. Process according to claim 17, wherein the first pulp slurry comprises a pulp selectedfrom a kraft, soda, sulfite, mechanical, thermomechanical, semi-chemical or chemi- thermomechanical pulp, or mixtures thereof. Process according to any one of the claims 17 or 18, wherein the pulp consistency ofthe first pulp slurry is of from 0.5 to 30%, preferably of from 1 to 20%, calculated as dry weight of the cellulosic fibres in the first pulp slurry. Process according to any one ofthe preceding claims 17-19, wherein the CMC isamphoteric and has a cationic molar substitution degree of from 0.00001 to 0.4 and an anionic molar substitution degree of from 0.3 to 1.2. Process according to any one ofthe preceding claims 17-19, wherein the CMC is anionic and has an anionic molar substitution degree of from 0.3 to 1.2. Process according to any one ofthe preceding claims 17-21, wherein the amount of the anionic or amphoteric CMC attached during the treatment is of from 1 to 100 23. 24. 25. 26. 27. 28. 29. 30. 31. 32 mg/g, based on the weight of the cellulosic fibres in the first pulp slurry. Process according to any one ofthe preceding claims 17-22, wherein the multivalentmetal salt comprising an Al3+ metal ion is added to the pulp in the step IV) to a totalmolar concentration of from 0.0001 to 0.05 M. Process according to any one of the preceding claims 17-23, wherein the processfurther comprises adding a dry strength aid or a wet strength resin to the first pulpslurry. Paper or paperboard obtained by the process according to any one of claims 15-24. Paper or paperboard according to claim 25 having a structural density of from 150 to 600 kg/m3 according to SCAN-P-88:01. Use ofthe paper or paperboard of claim 25 or 26 as a packaging material. Use of the paper or paperboard product of claim 25 or 26 as a middle layer in a paper board. Use ofthe cured pulp product according to claim 14 for the production of fluff pulp. Use ofthe cured pulp product according to claim 14 for the production of tissue paper. Use ofthe cured pulp product according to claim 14 for the production of filter paper.
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    同族专利:
    公开号 | 公开日
    JP2018515696A|2018-06-14|
    CA2986087A1|2016-12-01|
    EP3298197A1|2018-03-28|
    CN107849824A|2018-03-27|
    US20180155875A1|2018-06-07|
    BR112017024581A2|2018-07-31|
    CL2017002959A1|2018-05-11|
    WO2016190801A1|2016-12-01|
    SE538863C2|2017-01-10|
    EP3298197A4|2019-01-09|
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    法律状态:
    2020-05-12| NUG| Patent has lapsed|
    优先权:
    申请号 | 申请日 | 专利标题
    SE1550654A|SE538863C2|2015-05-22|2015-05-22|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|SE1550654A| SE538863C2|2015-05-22|2015-05-22|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|
    EP16800385.3A| EP3298197A4|2015-05-22|2016-05-19|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|
    CN201680029507.7A| CN107849824A|2015-05-22|2016-05-19|Method, obtained paper or board product for producing paper or cardboard and application thereof|
    PCT/SE2016/050460| WO2016190801A1|2015-05-22|2016-05-19|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|
    CA2986087A| CA2986087A1|2015-05-22|2016-05-19|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|
    JP2017560761A| JP2018515696A|2015-05-22|2016-05-19|Paper or paperboard manufacturing method, resulting paper or paperboard product and use thereof|
    BR112017024581A| BR112017024581A2|2015-05-22|2016-05-19|process for the production of paper or paperboard, paper product or paperboard obtained and uses thereof|
    US15/575,410| US20180155875A1|2015-05-22|2016-05-19|Process for the production of paper or paperboard, paper or paperboard product obtained and uses thereof|
    CL2017002959A| CL2017002959A1|2015-05-22|2017-11-21|Process for the production of paper or cardboard, products obtained from paper or cardboard and their related uses.|
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