Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/10—Packing paper
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/03—Non-macromolecular organic compounds
  • D21H17/05—Non-macromolecular organic compounds containing elements other than carbon and hydrogen only
  • D21H17/17—Ketenes, e.g. ketene dimers
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/21—Macromolecular organic compounds of natural origin; Derivatives thereof
  • D21H17/24—Polysaccharides
  • D21H17/28—Starch
  • D21H17/29—Starch cationic
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/71—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes
  • D21H17/72—Mixtures of material ; Pulp or paper comprising several different materials not incorporated by special processes of organic material
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents

Definitions

• the present disclosure relates to the field of stretchable papers, in particular to stretchable papers with wet strength properties.
• FibreForm ® Billerud AB (Sweden) has marketed a highly stretchable paper under the name FibreForm ® since 2009. The stretchability of FibreForm ® in both the machine direction (MD) and the cross direction (CD) allows it to replace plastics in many applications, such as bags.
• paper bags loose mechanical stability upon contact with water, such as when put down on wet ground.
• the present disclosure aims to provide an stretchable paper having wet strength properties.
• a stretchable paper comprising at least 90% by dry weight of kraft pulp fibres, wherein the stretchability according to ISO 1924-3:2011 of the paper is at least 8.0 % in the machine direction (MD) and the cross direction (CD) and wherein the paper comprises 5-10 kg/tonne of cationic starch based on dry weight of the paper, 0.25-1.00 kg/tonne of AKD or ASA based on dry weight of the paper, 1.00-3.00 kg/tonne of rosin size based on dry weight of the paper and 0.5-5.0 kg/tonne of glyoxylated polyacrylamide (G-PAM) based on dry weight of the paper.
• G-PAM glyoxylated polyacrylamide
• the pulp is a kraft pulp since such pulp provides mechanical strength. Kraft pulp is also known as sulphate pulp.
• Alkyl Ketene Dimers (AKD), Alkenyl Succinic Anydrides (ASA) and rosin size are internal sizing agents that provides ability to resist wetting and penetration by liquids.
• the paper comprises AKD or ASA in an amount of 0.25-1.00 kg/tonne, preferably 0.3-0.7 kg/tonne, based on dry weight of the paper.
• the paper comprises rosin size an amount of 0.5-5.0 kg/tonne, preferably 0.7-3.0 kg/tonne, based on dry weight of the paper.
• the paper comprises cationic starch in an amount of 5-10 kg/tonne, preferably 5-9 kg/tonne paper, based on dry weight of the paper.
• the cationic starch provides strength properties, in particular dry strength properties, as well as retention of the AKD or ASA.
• the dry strength properties are important are, amongst others, for the strainability.
• the paper may further comprise alum, for example in an amount of 5-10 kg/tonne based on dry weight of the paper. Although not necessary, it is beneficial to include alum since the role of the aluminium ion is to aid anchoring of the rosin size onto the anionic fibre surfaces. Alum therefore improves the retention of the rosin size.
• the grammage of the paper according to ISO 536:2020 is typically 50-200 g/m 2 , such as 90-175 g/m 2 . Below 50 g/m 2 the strength and rigidity are typically insufficient. The inventors have also realized that if the grammage is at least 90 g/m 2 , the wet strength properties, such as the immediate tensile strength, are at a level where a SOS paper bag can be produced and dipped into water several hundreds of time without breaking.
• the paper has a stretchability of at least 8 % in the machine direction (MD) and cross direction (CD).
• Compacting in a Clupak unit or Expanda unit increases the stretchability of the paper, in particular in MD.
• the Clupak unit typically comprises a steel cylinder or a chromed cylinder and a rubber blanket.
• the Expanda unit typically comprises a venturi section formed in a nip between a rubber and a steel roll. On running the rubber roll more slowly than the steel roll, the web will shrink in MD and become micro-creped.
• the stretchability in MD is even higher than 8 %, such as at least 10 %, such as at least 11% or at least 12 %.
• the stretchability enables formation of three-dimensional (double curvature) shapes in the paper, e.g. by press forming, vacuum forming or deep drawing.
• the formability of the paper in such processes is further improved by that the stretchability is relatively high also in the cross direction (CD).
• the stretchability in CD is at least 9 %.
• An upper limit for the stretchability in MD may for example be 20 % or 25 %.
• An upper limit for the stretchability in CD may for example be 15 %.
• the stretchability (in both MD and CD) is determined according to the standard ISO 1924-3:2011.
• the paper web is preferably allowed to dry freely after the Clupak unit. During such "free drying", which improves the stretchability, the paper web is not in contact with a dryer screen (often referred to as a dryer fabric).
• a forced, optionally heated, air flow may be used in the free drying, which means that the free drying may comprise fan drying.
• a stretchability of at least 8% in MD in particular in MD is beneficial also in production and usage of paper bags produced from the paper.
• the Bendtsen roughness according to ISO 8791-2:2013 of at least one side of the paper is 2000 ml/min or lower, such as 1850 ml/min or lower. It is desired to be able to produce a stretchable paper with a relatively fine surface.
• the wet immediate tensile strength in the machine direction (MD) according to ISO 3781:1983 using 10 min immerse time is at least 1 kN/m, such as at least 1.3 kN/m, such as at least 1.6 kN/m.
• the wet immediate tensile strength in CD according to ISO 3781:1983 using 10 min immerse time is at least 1 kN/m, such as at least 1.15 kN/m, such as at least 1.25 kN/m.
• the ratio of wet immediate tensile strength in MD to dry tensile strength in MD, wherein the wet tensile index is tested according to ISO 3781:1983 using 10 min immerse time is at least 10%, such as at least 12%, such as at least 14%.
• the result is presented as percentage, i.e. the percentage of wet strength out of dry strength. If the number is 100 %, the paper is be performing equally good wet as dry with respect to tensile index.
• the air resistance according to Gurley i.e. the Gurley value or the Gurley porosity
• Gurley porosity is a measurement of the time (s) taken for 100 ml of air to pass through a specified area of a paper sheet. Short time means highly porous paper.
• Gurley porosity of the paper of the present disclosure is typically at least 25 s, such as at least 30 s according to ISO 5636-5:2013. The inventors have realized that the wet strength properties are improved if the Gurley value is not too low, in particular if the Gurley value is at least 25 s it is beneficial for provision of a paper bag produced from the paper that can be put down on wet ground several hundreds of times.
• the Cobb 60 s value measured according to ISO 535:2014 of both sides of the paper is typically below 30 g/m 2 , such as 18-25 g/m 2 .
• the density of the paper according to ISO 534:2011 is typically 620-900 kg/m 3 . Higher density typically means reduced bending stiffness, which is often undesired.
• the tensile strength is the maximum force that a paper will withstand before breaking.
• Tensile energy absorption (TEA) that is the area under the cure tensile strength vs stretch, is a measure of how tough the material is.
• the TEA index is the TEA value divided by the grammage.
• the TEA index in MD according to ISO 1924-3:2011 is typically at least 4.0 J/g, such as at least 4.3 J/g.
• the TEA index in CD according to ISO 1924-3:2011 is typically at least 3.0 J/g.
• a paper of higher tensile strength and stretch has higher TEA value. Thus, a paper of higher grammage typically has a higher TEA value.
• TEA index For TEA index, on the other hand, this effect is substantially insignificant as a higher TEA value is balanced by a higher grammage and a lower TEA value is compensated for in the division by a lower grammage. Consequently, the TEA index does not vary to any great extent depending on grammage.
• the TEA value on the other hand, is typically varied with grammage. Accordingly, the grammage of the paper according to ISO 536:2020 maybe 50-125 g/m 2 and TEA in MD according to ISO 1924-3:2011 is then least 375 J/m 2 , such as at least 425 J/m 2 .
• the grammage of the paper according to ISO 536:2020 may be 126-200 g/m 2 and TEA in MD according to ISO 1924-3:2011 is at least 600 J/m 2 , such as at least 650 J/m 2 .
• a method of producing a kraft paper having a stretchability according to ISO 1924-3:2011 in the MD and CD of at least 8 % comprising the following steps:
• the G-PAM is added in an amount of 1.0-4.0 kg/tonne based on dry weight of the pulp stock, such as 1.8-3.0 kg/tonne based on dry weight of the pulp stock.
• step c) further comprises adding retention aid(s) to the pulp stock, wherein the/each retention aid is added in an amount of 0.03-0.12 kg/tonne based on dry weight of the pulp stock; and the dilution in step d) is conducted with a headbox dilution ratio of 9-13 %, wherein the headbox dilution ratio is the dilution water flow into the headbox divided by the pulp stock flow into the headbox.
• the inventors have realized that surface roughness is improved, i.e. lowered, by using a dilution ratio of 9-13% in the headbox.
• a low surface roughness is beneficial for printing properties and lamination with a plastic film or glue, and in particular for low amounts of glue the roughness should be low.
• the headbox dilution ratio is 9.5-12 %, such as 9.5-11.5 %. This is an increased dilution ratio compared with what is customary for paper and identified as an optimum in combination with the amount of retention aid(s) for obtaining a smooth paper. The dilution of the stock will, thereby, to a greater extent be conducted in the headbox instead of before the headbox.
• the dilution is typically conducted by using a headbox having actuators as well as several dilution zones in the headbox. Further, the actuator average dilution percentage is typically 56-64 % open, such as 60-62% open.
• the headbox dilution ratio is the dilution water flow into the headbox divided by the pulp stock flow into the headbox. Typically, the dilution ratio is increased by increasing the dilution water flow without making any significant adjustments of the pulp stock flow.
• the final consistency of the pulp stock in the headbox is 0.20-0.30 % based on dry weight when added to the forming wire.
• Such consistency is comparable to consistencies regularly used when forming paper. That is, even though the dilution ratio is higher than is customary for paper, the final consistency is not substantially altered.
• the amount of pulp stock that is applied on the wire per second is controlled by a slice opening arrangement of the headbox.
• the slice opening arrangement consists of two lips that are parallel to each other, a stationary lip and a regulating lip. Depending on the distance between the lips i.e. vertical lip opening, the pulp stock flow from the headbox to the wire can be varied.
• the headbox has a vertical lip opening of 42-60 mm, such as 45-56 mm.
• the lip opening is lower when the grammage is lower and higher when the grammage is higher.
• the lip opening is typically 42-50 mm
• the intended grammage is 120-200 g/m 2 , such as 120-175 g/m 2
• the lip opening is typically 50-60 mm.
• retention aid(s) may be added to the pulp stock, wherein the/each retention aid is added in an amount of 0.03-0.12 kg/tonne based on dry weight of the pulp stock.
• the/each retention aid is added an amount of 0.04-0.10 kg/tonne based on dry weight of the pulp stock, such as 0.04-0.08 kg/tonne based on dry weight of the pulp stock.
• one retention aid is cationic, such as a cationic polymer, such as cationic polyacrylamide (cPAM), polyethyleneimine (PEI) or mixtures thereof. If a cationic retention aid is added in such amount, the paper will be less open, which is beneficial for low surface roughness.
• one other retention aid is anionic, such as anionic inorganic particles, such as silica microparticles, bentonite clay, or mixtures thereof.
• anionic retention aid it is preferred that this type is an anionic retention aid.
• the inventors have realized that there is a synergistic effect with respect to improved roughness of the addition of retention aid(s) wherein the/each retention aid is added in an amount of 0.03-0.12 kg/tonne, preferably 0.04-0.10 kg/tonne, such as 0.04-0.08 kg/tonne, based on dry weight of the pulp stock and using the specific dilution ratio in the headbox.
• the kraft pulp is a softwood pulp as the long fibres of softwood provides mechanical strength. Accordingly, the kraft pulp may comprise at least 50 % softwood pulp, preferably at least 75 % softwood pulp and more preferably at least 90 % softwood pulp. The percentages are based of the dry weight of the pulp.
• the kraft pulp may be bleached or unbleached. If the kraft pulp is unbleached, typically less than 0.05 kg/tonne of anionic polymer is added to the pulp stock, such as no anionic polymer is added to the pulp stock. The inventors have realized that since unbleached pulp is inherently anionic there is no need for adding an additional anionic polymer to the pulp stock, which is beneficial from a cost and environmental perspective. On the other hand, in case the kraft pulp is bleached, typically an anionic polymer, such as anionic polyacrylamide (A-PAM), is added to the pulp stock to balance the charge of the pulp.
• A-PAM anionic polyacrylamide
• the anionic polymer, such as A-PAM may be added in a total amount of 0.20-1.00 kg/tonne dry fibre, such as 0.25-0.75 kg/tonne dry fibre, such as 0.35-0.55 kg/tonne dry fibre.
• the paper may be calendered after being compacted in the Clupak unit or the Expanda unit.
• the calender is preferably a soft nip calender.
• a soft nip calender comprises a soft, resilient, calender roll and a hard backing roll, typically a steel roll.
• the steel roll may be heated, by e.g. steam or oil. If the paper is calendered, the Bendtsen roughness according to ISO 8791-2:2013 of at least one side of the paper typically becomes 200-700 ml/min.
• the kraft pulp is subjected to high consistency (HC) refining followed by low consistency (LC) refining before dilution into a pulp stock in step b).
• HC refining and the LC refining increase the stretchability in both MD and CD.
• the consistency of the pulp subjected to HC refining is typically 25-40 %, such as 30-40 %, such as 33-40 %.
• the consistency of the pulp subjected to LC refining is typically 2-6 %.
• the total energy supply energy supply in the HC and LC refining may be 500-1000 kWh per ton paper.
• a kraft paper wherein the paper is having a stretchability according to ISO 1924-3:2011 in MD and CD of at least 8 %, and an approved water-resistant carrying capacity according to a modified version of EN13590:2003, wherein the modified version of EN13590:2003 is conducted accordingly:
• the wet immediate tensile strength evaluates the short-term wet strength properties. However, also the long-term wet strength properties are important.
• the long-term wet strength properties were evaluated by producing paper bags from the papers. The paper bags were filled with filling material simulating what one would carry in a paper bag, and the bag was alternating between lifting and be put on the ground into water to simulate one lifting the bag form the ground and placing the bag on a wet ground over and over again, just as a typical consumer uses a paper bag.
• a paper according to the present disclosure provides a combination of stretchability and short-term as well as long-term wet strength properties.
• Unbleached softwood kraft pulp was provided.
• the pulp was diluted into a pulp stock and subjected to high consistency (HC) refining (240-280 kWh per ton pulp) at a consistency of about 33-36 % followed by low consistency (LC) refining to a total energy consumption of 790-810 kWh/ton pulp.
• HC high consistency
• LC low consistency
• cPAM cationic acrylamide
• Glyoxylated polyacrylamide was either added in an amount of 2.4 kg/tonne or not added at all to the refined pulp stock.
• the pulp stock was forwarded into a headbox (Voith Sulzer type ModuleJet SD year 1998), wherein the pulp stock was diluted.
• the stock flow into the headbox was 2469 l/s, and the dilution water flow was 207 l/s or 257 1/s.
• 207 l/s provides a dilution ratio of 8.4 % (207/2469*100) and 257 l/s provides a dilution ratio of 10.4% (257/2469*100).
• the stock was diluted to a final headbox consistency of 0.23-0.25 % based on dry weight.
• the stock was, thereafter, added to a forming wire with a speed of 440 m/min to obtain a paper web.
• the vertical lip of the headbox was set to 48 mm, 50 mm or 52-56 mm.
• the paper web was dewatered in a press section having three nips.
• the dewatered paper web was then dried in a subsequent drying section including one Clupak unit to obtain a paper.
• Papers were produced having a grammage of 100 g/m 2 , 120 g/m 2 and 150 g/m 2 .
• the index values are obtained by dividing respective property with grammage.
• the wet immediate tensile index measured according to ISO 3781:1983 using 10 min immerse time was divided by the dry, i.e. regular, tensile index measured according to 1924-3:2011.
• the result is presented as percentage, i.e. the percentage of wet strength out of dry strength. If the numbers would be 100 %, the paper would be performing equally good wet as dry with respect to tensile index.
• kraft paper having therein G-PAM in combination with cationic starch, AKD and rosin size in the particular amounts used herein provides for a high wet strength in combination with high stretch at break in both MD and CD, which is shown for papers 4-5.
• the wet tensile index in CD also is comparable to the one in paper 5 since it contains the same additives.
• smooth papers in terms of low Bendtsen roughness was obtained for papers 3-5.
• the inventors also realized that the amount of retention aids and headbox dilution ratio provides for the low roughness, which is beneficial for printing.
• the inventors have further realized that due to the inherent anionic charge of unbleached pulp, the G-PAM can be added without addition of an anionic wet strength polymer, which is beneficial form a cost and environmental perspective.
• the test is passed if the average times of lifting the bag before breakage according to EN13590:2003 was at least 500 times.
• the papers used for producing the bags were paper #1 (100 g/m 2 ), paper# 4 (150 g/m 2 ) and paper# 5. Up to three bags per paper were produced and tested. The results from the test are shown in Table 4 below. Table 4. Number of lifts of the different bags. Paper# 1 (100 g/m 2 ) Paper# 3 (150 g/m 2 ) Paper# 4 Bag #1 15 38 163 Bag #2 16 999 Bag #3 18 999 Average 16.3 38 720.3
• the long-term wet strength properties were evaluated by producing paper bags from the papers. The paper bags were filled with filling material simulating what one would carry in a paper bag, and the bag was alternating between lifting and be put on the ground into water to simulate one lifting the bag form the ground and placing the bag on a wet ground over and over again.

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• 2023
  • 2023-11-03 EP EP23207625.7A patent/EP4549650A1/fr active Pending
• 2024
  • 2024-10-18 WO PCT/EP2024/079594 patent/WO2025093338A1/fr active Pending

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