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EP4623150A1 - Papier cristal comprenant une fibre recyclée - Google Patents

Papier cristal comprenant une fibre recyclée

Info

Publication number
EP4623150A1
EP4623150A1 EP23837652.9A EP23837652A EP4623150A1 EP 4623150 A1 EP4623150 A1 EP 4623150A1 EP 23837652 A EP23837652 A EP 23837652A EP 4623150 A1 EP4623150 A1 EP 4623150A1
Authority
EP
European Patent Office
Prior art keywords
range
paper
glassine paper
release liner
recycled
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23837652.9A
Other languages
German (de)
English (en)
Inventor
Jukka KOTILAINEN
Mikko Rissanen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UPM Kymmene Oy
Original Assignee
UPM Kymmene Oy
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from EP22217245.4A external-priority patent/EP4394124A1/fr
Priority claimed from PCT/EP2023/075765 external-priority patent/WO2024141186A1/fr
Application filed by UPM Kymmene Oy filed Critical UPM Kymmene Oy
Publication of EP4623150A1 publication Critical patent/EP4623150A1/fr
Pending legal-status Critical Current

Links

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
    • D21H27/06—Vegetable or imitation parchment; Glassine 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
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
    • D21H11/04—Kraft or sulfate pulp
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/14—Secondary fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/001—Release paper

Definitions

  • a glassine paper comprising recycled fiber
  • the invention relates to a glassine paper suitable for a release liner and a method to manufacture such paper, which contains both non-recycled bleached chemical pulps produced from hardwood and softwood, as well as recycled pulp produced from release liner glassine paper.
  • Glassine paper is a distinguished type of paper that is used as a release liner substrate due to its outstanding characteristics. Glassine paper is expensive, as it is typically produced of bleached chemical pulp, hereafter abbreviated as BCP, that has been highly refined.
  • BCP bleached chemical pulp
  • the production of glassine paper is a complex process, which requires skills, large amounts of virgin wood-based material and energy.
  • the BCP used for producing glassine paper is typically a pulp mixture that contains both BCP made of softwood and BCP made of hardwood.
  • Virgin BCP made of softwood in particular, is very expensive, whereby in general majority of the furnish, up to 70-80 % by weight, of the glassine paper is typically virgin BCP made of hardwood.
  • BCP made of softwood is preferred, due to the longer fibers in BCP made of softwood. Part of the longer average fiber length of BCP made of softwood, however, is lost due to the refining of the pulp, which is performed prior to introducing the furnish on the paper machine.
  • Refining is a mill operation performed on the BCP prior to manufacturing glassine paper, wherein the pulp fibers are subjected to high shear forces. This modifies the pulp fibers physically, for example by fibrillation, such that the fiber structures become looser.
  • the extent of refining of a pulp may be determined by a Schopper-Riegler test, which measures the drainability of a pulp suspension in water in terms of the Schopper-Riegler number, referred to as the SR number or °SR. Refining further reduces the average fiber length of the pulp fibers. Consequently, the specific volume of the formed glassine paper is also reduced, since shorter fibers may be packed together closer. This also enables to manufacture glassine paper having higher surface smoothness and density.
  • a smooth and dense paper surface is advantageous for reducing the consumption of a subsequent release coating, upon producing a release liner.
  • refining also increases the moisture uptake of the BCP, denoted as swelling, since the loosened fiber structure of refined BCP is better accessible for water molecules.
  • refining increases the amount of water to be removed from the formed paper web, when manufacturing glassine paper on a paper machine.
  • the excess water to be removed from the fibers may cause shrinkage, which changes the dimensions of the glassine paper and is also detrimental for the paper quality, such as paper strength.
  • Refining of the pulp thus causes multiple effects downstream on the glassine paper manufacturing process. While some effects of refining are positive and improve the glassine paper quality, others are not.
  • a glassine paper is typically surface sized and strongly calendered, by means of a multi-nip calender or a supercalender.
  • Label waste poses other types of challenges, as the material to be recycled may often contain plastic and adhesive label remnants.
  • a release liner contains cured silicone polymer that has been adhered on the paper surface.
  • release liner glassine paper A release liner, wherein the substrate is glassine paper, is hereafter referred to as release liner glassine paper and abbreviated as RGP.
  • RGP recycling provides means for glassine paper production to be more sustainable, while solving challenges mentioned above. Fibers of RGP display signs of damages due to extensive hornification and no longer have the same characteristics as fibers of virgin BCP made of softwood.
  • sorting of RGP apart from other paper waste provides specific and highly homogeneous material for recycling, which enables to better adjust characteristics of the material already during the recycling process. This is advantageous, as the compatibility of the recycled pulp can thus be adapted and optimized for glassine paper production. For instance, excessive refining of the recycled pulp may be avoided.
  • pulp produced from RGP may be used to replace non-recycled BCP in the composition of the glassine paper. Recycled pulp obtained from RGP may thus be circulated back to the manufacturing process. A more closed loop is therefore possible for the papermaking fibers.
  • the sorting may be performed based on the paper type to calendered glassine paper or supercalendered kraft paper, thereby obtaining sorted release liner substrate. For instance, excessive refining of the recycled pulp and/or bleaching may be avoided.
  • the recycled pulp obtained from a sorted release liner glassine paper is not bleached during or after the caustic loop and/or cleaning loop.
  • pulp produced from RGP may be used to replace non-recycled BCP in the composition of the glassine paper, respectively.
  • the release liner substrate is white calendered glassine paper
  • the method disclosed above may be arranged provide recycled pulp, which does not need to be bleached during the pulp recycling, prior to introducing it into a new glassine paper production.
  • a two-step sorting may further be used to facilitate the recycling of non-white RGP grades, such as light yellow, yellow, brown or blue shades.
  • a two-step sorting may be used to facilitate introduction of such recycled pulp into a glassine paper manufacturing process, wherein the same or similar paper colour is produced, without bleaching the papermaking fibers.
  • the sorting of RGP to white or non-white paper colour is therefore advantageous, as the compatibility of the recycled pulp can thus be adapted and optimized already during the recycling process for a further production of a specific glassine paper grade. A more closed loop is therefore possible for the papermaking fibers.
  • Recycled pulp obtained from RGP has a pH which is in an alkaline range, when determined from aqueous pulp extracts.
  • An alkaline pH during the recycling process softens the pulp, which thereby requires less energy for refining.
  • An alkaline pH may inhibit the subsequent drying of the pulp.
  • the pulp pH may thus be adjusted, as necessary, prior to mixing the pulp with other pulp components.
  • the recycled pulp obtained from RGP in a method for manufacturing calendered glassine paper suitable for use as a substrate of a release liner
  • the recycled pulp obtained from release liner glassine paper has a pH which is in the range of 6.0 to 9.1.
  • the pH is in the range of 7.0 to 8.5, since a highly alkaline pH may inhibit the functioning of cationic UV curing silicone systems. Most preferably, the pH in the range of 7.5 to 8.2, whereby the drying and the compatibility of the recycled pulp can be optimized for glassine paper production.
  • Recycled pulp obtained from RGP is very quick to refine, compared to nonrecycled pulp components.
  • Recycled pulp obtained from RGP also has a relatively high SR number, compared to non-recycled bleached chemical pulps, which have not been refined.
  • the recycled pulp obtained from RGP may be used in glassine paper production without further refining.
  • the recycled pulp obtained from RGP may be directly mixed with other non-recycled pulp components in a method for manufacturing glassine paper.
  • recycled pulp obtained from RGP has a SR number equal to or higher than 25, such as in a range from 25 to 65, preferably in the range of 30 to 60, most preferably in the range of 40 to 55, when determined according to ISO 5267-1 .
  • the recycled pulp obtained from RGP typically contains particles derived from the recycled pulp having a length less than 200 micrometers in an amount equal to or higher than 10 %, such as in a range from 10 to 30 %, preferably in the range of 12 to 20 %, most preferably in the range of 15 to 17 %, when determined as length weighted average fiber length by automated optical analysis using unpolarized light according to ISO 16065-2: 2014.
  • the fibers of the recycled pulp obtained RGP typically have an average fiber width of less than 25 micrometers, preferably in the range of 19-25 micrometers, most preferably in the range of 19-21 micrometers, when determined by automated optical analysis using unpolarized light according to ISO 16065-2: 2014.
  • Fiber furnish analysis according to ISO 9184-4 in conjunction with ISO 9184-1 may be used for fiber identification and to determine the fiber properties of a given pulp.
  • pulp drainage analyses such as measurement of the pulp water retention value and/or the SR number, these analyses distinguish recycled pulp obtained from release liner glassine paper.
  • the fibers of recycled pulp obtained from RGP are less accessible for water molecules. Recycled pulp obtained from RGP therefore inhibits the moisture uptake of the stock.
  • the water retention value of recycled pulp obtained from RGP is low, typically lower than in non-recycled BCP.
  • the amount of recycled pulp obtained from RGP may therefore be used to control the dry matter content of the stock, upon forming the paper web.
  • the reduced ability of the recycled pulp obtained from RGP to absorb moisture also leads to enhanced dewatering of the paper web, already at the press section of the paper machine. Upon entering the drying section, the paper web therefore contains less moisture which needs to be evaporated. Hence, less steam pressure is needed, which improves the energy efficiency of the drying section during the paper production.
  • the compounded effects of reduced refining, improved dewatering and more efficient drying are observable by methods, which measure the water retention and drying behaviour of the paper web. For instance, when the amount of recycled pulp obtained from RGP in the stock is increased, the water retention value decreases. This indicates that less water needs to be removed on the press section, during glassine paper production. Pulp analyses from a paper mill further indicate that replacement of non-recycled BCP with recycled pulp obtained from RGP in a pulp mixture results to an increase in the fines content in the pulp mixture, when determined as the F ⁇ 2oo fraction with McNett classifier according to SCAN-CM 6:05. This indicates, that recycled pulp obtained from RGP may be used to adjust the quality of the paper web formed on the paper machine.
  • paper machine off-line analyses demonstrate that the produced paper has less shrinkage and less variability of the grammage in the crossdirection at a paper machine, which correlates with the amount of the recycled pulp obtained from RGP.
  • the amount of shrinkage is an indicator of dimensional stability.
  • the smaller variability of the grammage in the crossdirection at a paper machine is an indicator of more homogeneous product.
  • a calendered glassine paper which comprises recycled pulp obtained from RGP thus has improved quality characteristics.
  • Experimental results also evidence of reduced curl in paper samples comprising recycled pulp obtained from RGP.
  • the improved properties of the calendered glassine paper are of importance, when considering the use of glassine paper as a substrate, on which a release coating is subsequently spread and cured.
  • the blades cut through the face material into a predefined depth, such that the face material comprising the adhesive layer may be stripped away around the cut area without damaging the substrate.
  • the combination of density and transparency therefore indicates the suitability of the calendered glassine paper to function as a release liner substrate for adhesive labels.
  • a calendered glassine paper suitable for use as a substrate of a release liner, the calendered glassine paper comprising fibers from
  • the calendered glassine paper comprising the recycled pulp obtained from release liner glassine paper in an amount equal to or higher than 5 wt.%, determinable as dry matter content according to SCAN-P 39:80.
  • a calendered glassine paper suitable for use as a substrate of a release liner, the calendered glassine paper comprising fibers from
  • An advantage of sorting the RGP based on a white or a non-white color shade of the paper is that recycled pulp obtained from RGP may be produced without bleaching. Further, the compatibility of the recycled pulp may be optimized for glassine paper production, respectively. Hence, advantageously, recycled pulp as disclosed above is obtained from release liner comprising calendered glassine paper as a substrate, wherein the colour of the calendered glassine paper is white.
  • recycled pulp as disclosed above may also be obtained from release liner comprising calendered glassine paper as a substrate, wherein the calendered glassine paper has a specific non-white colour, such as light yellow, yellow, brown or blue. Therefore, the colour of the calendered glassine paper suitable for use as a substrate of a release liner advantageously has the same or similar paper colour as the release liner glassine paper from which the recycled pulp obtained from release liner glassine paper has been prepared.
  • the recycled pulp obtained from RGP may be used to replace non-recycled BCP made of hardwood and/or softwood.
  • Non-recycled BCP in this context, may also be referred to as virgin BCP.
  • the refining of non-recycled BCP in the glassine paper manufacturing process may be reduced. Reduced refining of the non-recycled BCP preserves the quality of the fibers.
  • nonrecycled BCP made of softwood has a longer average fiber length than other components in the stock and can be used to improve the internal bond strength upon formation of the paper web.
  • the preserved quality of the BCP fibers may be used for compensating negative effects, which the damaged fibers in the recycled pulp obtained from RGP may cause to paper formation, when manufacturing glassine paper at a paper machine.
  • the preserved quality of the fibers in the nonrecycled BCP is used to increase the proportion of recycled pulp obtained from RGP in the composition of the glassine paper. Hence, a synergy is perceived, when using recycled pulp obtained from RGP together with non-recycled BCP in a method for manufacturing glassine.
  • the yellow refers to CIE L* a* b* colour space coordinate values of the paper, wherein o L* is in the range of 65 to 71 , o a* is in the range of +7 to +13, and o b* is in the range of +50 to +56,
  • Figure 1 shows, by way of an example, a cross-dimensional structure of a release liner, which comprises a surface sized paper substrate and a release coating.
  • Figure 3 shows, by way of an example, a method for manufacturing recycled pulp from a release liner glassine paper, which contains a sorting stage, a caustic loop and a cleaning loop for disintegrating fibers and for detaching and removing non-fiber material from the fibers.
  • the method has been arranged to improve the fiber characteristics such that the recycled pulp may be used without further refining for stock preparation in glassine paper manufacturing.
  • Figure 5 shows comparative data of average fiber width in micrometers of fibers in recycled pulp obtained from RGP vs. non-recycled pulp types, measured using the Valmet Fiber Image Analyzer (Valmet FS5).
  • Figure 6 shows comparative data of the average amount of hydrophobic particles in different pulp types, when measured by means of flow cytometry. The particles have been further sorted based on an average diameter.
  • Figure 8 is a trend diagram representing the development of water retention value as a function of pulp content, at machine chest of a paper machine.
  • the content of recycled pulp obtained from RGP correlates inversely with the water retention value.
  • the content of recycled pulp obtained from RGP increases, the water retention value decreases.
  • a calendered glassine paper suitable for release liner typically has
  • the thickness of a calendered glassine paper denotes thickness in micrometers after a calendering treatment, prior to applying a release coating. Thickness, unless otherwise stated, refers to the apparent thickness, determined as single sheet thickness (ISO 534:2011 ).
  • Glassine paper is calendered with a multi-nip calender or a supercalender before or after applying a primer coating. Calendering enables to produce a glassine paper having high density surface and high transparency, but may lead to moderate reduction in the burst, tensile, and tear strength of the glassine paper. Calendering also reduces the thickness of the glassine paper to a predefined target thickness.
  • FIG. 1 discloses a structural cross-dimensional view of release liner REL1 , wherein the substrate GLA1 is a glassine paper.
  • a release liner REL1 in this context, refers to an industrially manufactured paper product, which comprises a dehesive surface coating on at least one side of a calendered paper substrate GLA1.
  • the dehesive surface coating is generally referred to as release coating SIL1 .
  • the dehesive surface coating may be used as a protective layer for an adhesive label which contains a face material and an adhesive layer.
  • a stock MIX1 is obtained after mixing 12 together different pulps during stock preparation.
  • the mixing may be performed, for example by homogenising the stock MIX1 in a mixer.
  • Stock refers to a pulp mixture from which paper is manufactured on a paper machine.
  • Stock may also be referred to as furnish.
  • Stock is fed to the forming section of a paper machine when manufacturing paper.
  • a pulp suspension is needed to adjust loading upon stock preparation and to control fiber bonding, when forming a paper web 13 at a headbox of a paper machine.
  • the stock is typically first fed to a machine chest.
  • the nonrecycled pulp may be bleached chemical pulp from a Kraft process.
  • the stock MIX1 may contain broke BRK1 , which refers to material produced on a paper machine, which is not up to specification, such as paper trimmings. Broke may be recycled back to the paper manufacturing process. Broke may be refined prior to mixing 12. However, broke has undergone at least part of a paper manufacturing process on a paper machine, and hence is not considered to be virgin pulp material, when introduced again into the paper manufacturing process. Broke is not obtained from a release liner REL1 , either.
  • White water WHT1 may also be used, when preparing the stock MIX1 .
  • White water is used to describe slurry, which is formed at a forming section of a paper machine, when fine particles present in the stock drain from the formed paper web WEB1 into a pit below the paper machine.
  • White water contains fines suspended in the stock. Fines refers to particles having a width in the range of 10 to 75 micrometers and a length less than 0.2 millimeters.
  • White water may be circulated back into the stock preparation by means of a short circulation of the paper machine or treated and used elsewhere in the papermaking process. The amount of circulated fines defines a retention level, which describes the ability of the formed paper web to retain fines, and therefore the balance between drainage and formation 13 of the paper web.
  • the paper web WEB1 is formed 13 from the pulp suspension and dewatered
  • the press section of a paper machine typically comprises a number of rolls for guiding and/or pressing the paper web.
  • the paper web is then moved from the press section to a drying section of a paper machine.
  • the drying section the paper web is heated to evaporate most of the remaining moisture in the paper web.
  • the paper web may have a dry matter content level equal to or more than 90 wt.-%, for example in the range of 90 to 95 wt.-%, when determined according to SCAN-P 39:80.
  • the forming of paper 14 therefore comprises a step for reducing moisture content of the paper web in a press section, and a step for drying the paper web in a drying section, thereby forming paper from a stock MIX1 that contains non-recycled bleached chemical pulp from hardwood PULP1 , non-recycled bleached chemical pulp from softwood PLILP2 and recycled pulp obtained from release liner glassine paper PLILP3.
  • a weight percentage is used to describe a weight fraction of component in a composition.
  • a weight percentage of pulp is used to describe a weight fraction of a pulp in a material.
  • a weight percentage of pulp in a paper denotes the dry weight of the pulp in a dry paper, when determined according to SCANP-39:80 test method for dry matter content.
  • the dry weight of a sample is determined by weighing 20 grams of sample on a dish before and after oven drying at 105°C and eliminating the mass of the empty dish from the measurement. Oven dry pulp has been dried at 105°C until its mass is constant and cooled thereafter in an exicator to ambient temperature of 25°C, prior to weighing.
  • the stock used for manufacturing glassine paper in this context is distinguished, as it contains mainly bleached chemical pulp made of softwood and hardwood.
  • a recycled pulp obtained from RGP due to its origin, also contains mainly bleached chemical pulp made of softwood and hardwood.
  • the surface of the glassine paper is typically sized with a water-soluble polymer, such as polyvinyl alcohol in an amount ranging from 1 to 5 g/m 2
  • a RGP typically does not contain mineral fillers or coatings in significant amounts, such as kaolin (i.e. aluminium silicate dihydrate), clay pigments or calcium carbonate, when compared to other paper types, such as printing and writing papers.
  • a method for manufacturing recycled pulp from a release liner glassine paper comprises a sorting stage 20 for separating RGP apart from other papers, a first process stage, denoted as a caustic loop CL1 , having a principal function of disintegrating the RGP into pulp and detaching non-fiber material from fibers, and a second process stage, denoted as a cleaning loop NL1 , having a principal function of separating pulp fibers from non-fiber material, in particular silicone particles originating from the release coating.
  • Caustic loop CL1 provides conditions in which the pulp fibers are able to swell and fibrillate.
  • Cured silicon-based organic polymers, polydimethylsiloxanes in particular, are generally water-resistant and relatively inert chemically.
  • the release coating is typically fragmented into pieces, which are hereafter denoted as silicone-based particles.
  • the caustic loop CL1 and the cleaning loop NL1 are configured to adjust the fibrillation of the pulp suspension, such that the recycled pulp obtained from the release liner glassine paper PLILP3 has a pulp drainability in a range which enables the use of the recycled pulp obtained from the RGP in a method for manufacturing glassine paper without further refining.
  • the caustic loop CL1 and cleaning loop NL1 provide means to control the chemical load and temperature of the recycling process, as well as a means to adjust the consistency of the suspension.
  • Sorted RGP may be further separated based on a color shade of the paper. For example, light RGP shades, such as white and yellow shades, may be separated from dark RGP shades, such as blue and brown RGP shades.
  • white RGP grades wherein the paper furnish does not contain colorants, are separated apart from non-white RGP grades, such as yellow, blue and brown RGP grades.
  • a CIELAB color space may be used for measuring the colour of the RGP and for rejecting non-light or non-white RGP grades.
  • the colour information may further be used as a basis for accepting and/or rejecting paper having a specific colour, such as white, light yellow, yellow, blue or brown or a specific shade, such as non-white, non-light or dark, for recycling.
  • This provides highly homogeneous starting material for manufacturing of recycled pulp, wherein the paper is of the same type and further comprises the same or similar colour.
  • same kind of colourants are used to provide a specific colour shade for a glassine paper, such as yellow, brown or blue, whereby the combination of the same paper type and the same or similar colour is advantageous for a more closed-loop recycling of glassine paper.
  • Such recycling process is also less complex.
  • a two-step sorting may thus be used to facilitate the recycling of non-white RGP grades.
  • a two-step sorting may be further used to facilitate introduction of such recycled pulp into a glassine paper manufacturing process, wherein the same or similar paper colour is produced.
  • brown refers to CIE L* a* b* colour space coordinate values
  • - b* is in the range of +17 to +23, , the colour determinable from a sample of release liner glassine paper by means of diffuse reflectance method with the elimination of specular gloss, using standard ilium inant C and 2° standard observer, in accordance with ISO 5631 -1 :2022.
  • blue refers to CIE L* a*, b* colour space coordinate values of a calendered glassine paper, wherein
  • the pulping of RGP is performed in alkaline conditions to facilitate disintegration of the cellulose fibers from the RGP, since RGP comprises a dense surface, a polymeric primer coating and a release coating.
  • the pH is maintained in a range between 8.5 to 10.
  • the pH may be adjusted by addition of NaOH, referred to as caustic soda.
  • Caustic soda reacts with the hydrogen groups of the fiber and promotes fiber swelling, referred to as caustic swelling, which will loosen the fiber network of the RGP.
  • Caustic soda also acts as an activator for hydrogen peroxide, which may be used to facilitate oxidative bleaching, when the pulp suspension contains colourants, for example blue colorant from a non-white grade of RGP.
  • Hydrogen peroxide is also used to prevent yellowing during the pulping. Typically, hydrogen peroxide is added in the range of 0.5 - 2 wt.%.
  • Sodium silicate is typically added to buffer the pH of the pulp suspension and to prevent the pH of the suspension from rising excessively at the beginning of pulping. Sodium silicate thus contributes to the alkalinity of the pulp suspension, such that the conditions are suitable for the caustic swelling.
  • Sodium silicate may be also used as a stabilising agent for the hydrogen peroxide. Sodium silicate may further improve the detachment of release liner from the fibers. Typically, sodium silicate is added in the range of 1 - 6 wt.%.
  • a saponifying agent typically a fatty acid such as palmitic acid or stearic acid
  • a fatty acid such as palmitic acid or stearic acid
  • Fatty acids react first with caustic soda and then with calcium ions present in the pulp suspension and form calcium soap, which is water-insoluble and finely dispersed in an aqueous phase.
  • Soap particles which are strongly hydrophobic, facilitate maintaining the pulped fibers and the detached hydrophobic particles, such as silicone-based particles, apart from each other in the pulp suspension.
  • a fatty acid is used in a range of 0.1 to 1.5 wt.% of the RGP.
  • the fatty acid dose is advantageously matched with the water hardness, such that the amount of fatty acids is substantially equal with the amount of calcium ions present in the suspension.
  • a high consistency suspension sufficient time, temperature and chemical additives, such as hydrogen peroxide, sodium silicate (water glass) and caustic soda (NaOH), may be used to disintegrate and detach the fibers of the RGP and induce caustic swelling, despite the hornification of the fibers.
  • chemical additives such as hydrogen peroxide, sodium silicate (water glass) and caustic soda (NaOH)
  • a high-consistency cleaning unit 23 such as a cleaner using centrifugal field, is used to complement the coarse screening to separate pulp fibers from contaminants based on specific gravity.
  • a centrifugal cleaner can remove particles down to a dimension of 10 micrometers.
  • a centrifugal cleaner can separate also light-weight particles present in the RGP, such as polymer particles, release coating agglomerates or residual adhesive stickies, when their density differs sufficiently from the density of water.
  • PVA for example, has a density typically in the range of 1.19-1.35 g/cm 3 at 25°C, which differs significantly from the density of water.
  • the separation of particles having a density closer to 1 .00 g/cm 3 may be improved by raising the pulp suspension temperature, which decreases the density of the water.
  • the pulp suspension temperature during the high-consistency cleaning is typically in the range of 30 to 85°C, preferably in the range of 50 to 85°C, to facilitate the cleaning of the PVA.
  • a pulp consistency of 2-6 wt.% is used.
  • the consistency of the pulp suspension during the cleaning may be adjusted by means of adjusting the pulping and screening conditions.
  • the consistency of the pulp suspension may be further adjusted by reusing process water F4 downstream from the recycling process, as needed.
  • the cleaning loop NL1 comprises a dispersion unit 25, a flotation unit 26, a second screening unit 27, a washing unit 28 and a dewatering unit 29.
  • a dispersion unit is used for producing shear forces which are sufficient for detaching remaining contaminants, such as silicone-based polymer, from the fibers and to adjust the average size of the contaminant particles to below 100 micrometers, suitable for removal by means of flotation.
  • the dispersion unit may operate with a thickened pulp suspension received directly from the dewatering unit.
  • the method may further comprise a dilution chest prior to the dispersion unit, for adjusting the consistency and/or temperature of the dewatered pulp suspension.
  • Conical and disc type dispergers operate in a manner where inverse correlation between pulp fibrillation and temperature exists; a lower pulp suspension temperature at the inlet correlates with a higher decrease in fibrillation.
  • the temperature of the pulp suspension at the inlet to the disperger is in the is range of 50 to 130°C, preferably in the range of 50 to 85°C.
  • the fibrillation of the pulp is adjusted after the caustic loop CL1 by means of dispersion in a conical disperger or a disc disperger, prior to flotation, such that the temperature of the pulp suspension at the inlet to the disperger is in the is range of 50 to 130°C, preferably in the range of 50 to 85°C and the pulp suspension has been thickened into a consistency equal to or higher than 20 wt.%, preferably in the range of 20 to 50 wt.%, most preferably in the range of 25 to 40 wt.%.
  • the pH may be adjusted and buffered by addition of suitable alkaline agents, such as caustic soda and sodium silicate.
  • Soap such as sodium soap, or other surfactant comprising a hydrophilic and a hydrophobic part, is added to act as a collector.
  • a collector is used for promoting agglomeration of silicone particles and facilitate their charging and flotation. During flotation, a low water hardness in the range of 10-20 dH is preferred, for promoting the agglomeration further.
  • the flotation unit 26 may contain several flotation cells arranged into a series.
  • a second screening unit 27 is used for fine screening to separate debris from the fibers coming from the flotation, in particular silicone particles originating from the release coating.
  • the fine screening may use slot screens having a slot size equal to or less than 0.25 millimeters, such as in the range of 0.10 to 0.25 millimeters, preferably in the range of 0.10 to 0.20 millimeters.
  • the screening operates under pressure and pulp suspension passing through the slots is accepted.
  • a washing unit 28 such as a washing unit is a belt filter type machine, is used to separate particles from the pulp suspension by size. Washing is typically performed under wire pressure with a set of two or more rolls, wherein the wire has a mesh size in the range of 36 to 60 micrometers, such that particles with a maximum size less than 30 micrometers are removed.
  • a pulp suspension having a consistency equal to or less than 2 wt.%, such as in the range of 0.5 to 2 wt.% is typically used at the inlet of the washing unit.
  • Clear water F1 is used to wash the filtered fiber mat and to adjust the consistency of the suspension during the washing. Dissolved contaminants are removed with the filtrate. The filtrate may be used as process water F3 upstream in the recycling process.
  • a second dewatering unit 29 based on pressing or filtration is used to mechanically remove process water F2 from the washed pulp suspension. Due to the relatively low consistency of the pulp after the washing unit, a twin-wire press is preferred, such that the pulp consistency may be increased efficiently for transport or storage.
  • the pulp suspension is thickened into a consistency equal to or higher than 30 wt.%, preferably equal to or higher than 40 wt.%, such as in the range of 30 to 50 wt.%.
  • the recycled pulp thus obtained from release liner glassine paper PULP3 may then be used in a method for manufacturing calendered glassine paper.
  • the recycling process 16 is arranged to contain operations and conditions, which optimize the separation of fibers from non-fiber components in the pulp suspension.
  • the caustic loop and the cleaning loop have been configured to adjust the fibrillation of the pulp suspension, such that a pulp drainability is obtained, which is in a range enabling the use of the recycled pulp obtained from the RGP in a method for manufacturing glassine paper, preferably without further refining.
  • the recycling process 16 is arranged to improve the fiber characteristics such that the recycled pulp PULP3 may be used without further refining for preparing a stock for glassine paper manufacturing.
  • the operations and conditions homogenize the pulp and develop characteristics such as pulp fibrillation, drainability and pH, which improve the quality of the pulp for a method for manufacturing glassine paper.
  • a pulp consistency in the range of 30 to 50 wt.% is advantageous in that the pulp fibers are not exposed to a further drying treatment, which may cause further hornification.
  • a pulp consistency in the range of 30 to 50 wt.% is advantageous also when mixing the recycled pulp PULP3 together with different pulps, during stock preparation.
  • the dewatering unit 29 may be supplemented with a drying system, such as a fluffer, to increase the dryness of the pulp, such that a pulp consistency equal to or higher than 80, such as in the range of 80 to 90 wt.% is obtained.
  • recycled pulp obtained from RGP has a pH which is typically neutral or alkaline, when determined from aqueous pulp extracts.
  • An alkaline pH during the recycling is preferred, as a higher pH softens the pulp and facilitates the flotation.
  • Alkalinity of the pulp also facilitates the modification of pulp fibrillation and drainability.
  • Recycled pulp obtained from RGP when having alkaline pH, needs less energy for refining. The pH, however, may be adjusted, as necessary, prior to using the recycled pulp.
  • Recycled pulp obtained from RGP is also distinguished by its water drainage resistance, which is a measure of pulp fibrillation, and which may be determined by the Schopper-Riegler test.
  • the SR number is a measure of the extent of fibrillation in the recycled pulp PLILP3.
  • the recycled pulp obtained from RGP may have a SR number equal to or higher than 25, such as in a range from 25 to 65, when determined according to ISO 5267-1.
  • recycled pulp obtained from RGP has a SR number equal to or higher than 30, if the aqueous extract, from which the measurement is performed, is process water that contains electrolytes.
  • the SR number may be higher, such as equal to or higher than 40, since the concentration of electrolytes (salts) in a pulp suspension influences the drainability.
  • the SR number of the recycled pulp obtained from RGP develops very quickly. This is a feature of recycled pulp obtained from RGP, which may be used to distinguish it from other non-recycled pulp components used in a glassine paper.
  • Table 1 (below) demonstrates, by means of an example, the development of SR number (°SR) in recycled pulp obtained from RGP, as a function of specific energy consumption (SEC) in kWh/t.
  • SEC specific energy consumption
  • SEL specific edge load
  • the recycled pulp obtained from release liner glassine paper has a °SR equal to or higher than 25, such as in a range from 25 to 65, preferably in the range of 30 to 60, most preferably in the range of 40 to 55, when determined according to ISO 5267-1.
  • Standard ISO 6588-2 2020
  • the pH may be measured either directly from the pulp sample (when the consistency is 5 wt.% or less) or from a filtrate (when the consistency is higher than 5 wt.%).
  • a filtrate refers to an aqueous extract.
  • the sample thus obtained is heated to a boiling point and boiled for 60 minutes. After boiling, the sample is cooled down, such that the temperature of the sample is in the range of 20 to 25°C, and the sample is filtrated through a filter having a 200 mesh grid, for example by means of a Buchner-funnel, thereby obtaining a filtrate separated from the pulp. The pH is measured from the filtrate thus obtained.
  • silicone-based particles When manufacturing recycled pulp from a release liner glassine paper as disclosed above, the removal of silicone-based particles is not complete.
  • the recycled pulp obtained from RGP still contains traces of the cured release coating, in very small size particles, which are chemically rather inert.
  • the maximum particle size of the silicone-based particles is typically in the range of 100 to 150 micrometers and limited by the slot size used in the fine screening in the cleaning loop NL1. While detectable, the amount of silicone- based particles in the recycled pulp obtained from RGP has not been observed to cause difficulties, upon manufacturing calendered glassine paper on a paper machine.
  • the amount of silicone-based particles may be measured with an Energy Dispersive X-ray Spectroscopy from a test specimen which is combusted at 900°C, in accordance with Tappi standard T 413, which detects the oxides of silicon.
  • a calendered glassine paper comprising recycled pulp from RGP contains silicon in an amount of equal to or less than 0.3 wt.%, preferably equal to or less than 0.28 wt.%, most preferably equal to or higher than 0.25 wt.%, such as in the range of 0.01 to 0.3 wt.%, determinable as dry matter content from a paper specimen which is combusted at 900°C with an Energy Dispersive X-ray Spectroscopy, in accordance with Tappi standard T 413.
  • the consistency of the pulps in the study was 4 wt.%.
  • the properties of the non-recycled bleached chemical pulps were measured before and after refining, to compare the properties of the recycled RGP and the non-recycled bleached chemical pulps.
  • the results represent an average of measurements, during which the recycled pulp obtained from RGP varied in the range of 6.8 to 7.3.
  • the measured pH in the recycled pulp obtained from RGP was clearly higher than in the nonrecycled chemical pulps made of softwood or hardwood.
  • the measured pH in the recycled pulp obtained from RGP was clearly higher than in the mill broke, as well.
  • Pulps as disclosed above were further analysed by means of a fiber furnish analysis according to ISO standards ISO 9184-1 and 9184-4:1990.
  • a fiber furnish analysis is capable to identify papermaking fibers from a sample. The analysis may further be used to quantify average dimensions of the different fiber types detected in a sample.
  • the wood species used in a pulp may be distinguished by comparison method, wherein a sample fiber is compared against a known reference fiber.
  • Valmet Fiber Image Analyzer (Valmet FS5) is an example of a device, which can be used according to the manufacturer’s instructions to perform the fiber furnish analysis.
  • FIG 4 shows the average length in millimeters of fibers in recycled pulp obtained from RGP and other pulp types, measured as length weighted average fiber length, using a Valmet Fiber Image Analyzer (Valmet FS5).
  • the recycled pulp obtained from RGP comprises an average fiber length of 0.94 millimeters.
  • the non-recycled BCP made of hardwood comprises an average fiber length of 0.86 millimeters, which upon refining was reduced to 0.84 millimeters.
  • the average fiber length of recycled pulp obtained from RGP is higher than the average fiber length of non-recycled BCP made of hardwood.
  • the non-recycled BCP made of softwood comprises an average fiber length of 2.10 millimeters, which upon refining was reduced to 2.00 millimeters.
  • the average fiber length of recycled pulp obtained from RGP is significantly less than the average fiber length of non-recycled BCP made of softwood.
  • Mill broke had an average fiber length of 1.04 millimeters.
  • FIG. 5 shows comparative data of average fiber width in micrometers of fibers in recycled pulp obtained from RGP and other pulp types, measured, using the Valmet Fiber Image Analyzer (Valmet FS5).
  • the recycled pulp obtained from RGP comprises an average fiber width of 20 micrometers.
  • the non-recycled BCP made of hardwood comprises an average fiber width of 18 micrometers, which upon refining was increased to 19 micrometers.
  • the average fiber width of recycled pulp obtained from RGP is larger than the average fiber width of non-recycled BCP made of hardwood.
  • the non-recycled BCP made of softwood comprises an average fiber width of 28 micrometers, which upon refining was increased to 29 micrometers.
  • the average fiber width of recycled pulp obtained from RGP is significantly less than the average fiber width of non-recycled BCP made of softwood.
  • Mill broke had an average fiber width of 20 micrometers.
  • the length weighted distribution of the pulp fibers was further analysed using Valmet Fiber Image Analyzer (Valmet FS5), according to the manufacturer’s instructions.
  • fibers were defined to be the fraction of the pulp that included particles having a width in the range of 10 to 75 micrometers and a length in the range of 0.2 to 7.0 millimeters.
  • Fines were defined to be the fraction of the pulp that included particles having a width in the range of 10 to 75 micrometers and a length less than 0.2 millimeters.
  • Fibrils were defined to be the fraction of the pulp that included particles having a width less than 10 micrometers and a length longer than 0.2 millimeters.
  • Flakes were defined to be the fraction of the pulp that included particles having a width less than 200 micrometers and a length less than 0.2 millimeters. Fibrils are typically particles generated from the secondary wall of the wood cell layer structure, which due to their elongated shape may improve bonding properties of the pulp. Flakes are typically particles generated from the middle lamella and primary wall of the wood cell layer structure, which tend to decrease the bonding properties of the pulp. The flakes scatter light and may hence affect the optical properties of the pulp by increasing opacity and decreasing transparency.
  • the results of the analysis was, that the amount of fines in the recycled pulp obtained from RGP was 16.3 % of the total amount of fibers in the recycled pulp, when determined as length weighted average fiber length, by means of an automated optical analysis using unpolarized light according to ISO 16065- 2: 2014.
  • the amount of fines in the recycled pulp obtained from RGP was in the same level as in the mill refined non-recycled bleached chemical pulp made of hardwood.
  • the amount of fibrils in the recycled pulp obtained from RGP unexpectedly, was much higher than in the mill refined non-recycled bleached chemical pulp made of hardwood, but lower than in the mill refined non-recycled bleached chemical pulp made of softwood.
  • the recycled pulp obtained from release liner glassine paper contains particles derived from the recycled pulp having a length less than 200 micrometers in an amount equal to or higher than 10 %, such as in a range from 10 to 30 %, preferably in the range of 12 to 20 %, most preferably in the range of 15 to 17 %.
  • the Valmet Fiber Image Analyzer also provided results of the amount fiber deformations, such as fiber kinks and fiber curl, in the pulps. Fiber kinks and curls tend to decrease the tensile strength of the formed paper, due to reduced bonding ability of the fibers in a fiber network.
  • the number of kinks in the recycled pulp obtained from RGP was 3250 1/m, which was considerably higher than in the non-recycled bleached chemical pulps after refining or in the mill broke.
  • the number of kinks in the non-recycled bleached chemical pulp made of hardwood was 2880 1/m before refining and 2310 1/m after refining.
  • the number of kinks in the non-recycled bleached chemical pulp made of softwood was 3410 1/m before refining and 2730 1/m after refining.
  • a series of dilutions (in the range of 10-1000 fold) was prepared with ultrapure water such that a suitable dilution was obtained, which contained particles in an amount that resulted into 700-1000 events per second, when analysed with the flow cytometer.
  • a volume on 20 ml of the dilution to be analysed was mixed with 1 ml of Nile red stain, which was used as a fluorescent marker to selectively stain hydrophobic moieties in the samples.
  • the flow cytometry was calibrated to size standards with 3 pm commercial polystyrene beads. Relative hydrophobicity (>10) was used for gating the particles.
  • the particles in each sample were further sorted based on their size, such that hydrophobic particles with a diameter of 1 micrometer or less was denoted as small, whereas hydrophobic particles with a diameter over 1 micrometer were denoted as large.
  • the results indicate that the recycled pulp obtained from RGP contains in the range of 2-3 times higher amount of large and small hydrophobic particles than non-recycled BCP made of hardwood.
  • the recycled pulp obtained from RGP contains close to 10 times higher amount of large and small hydrophobic particles than non-recycled BCP made of softwood. The difference to mill broke was also clear.
  • calendered glassine paper having grammage of 53 g/m 2 and a thickness of 48 pm was produced, such that the amount of recycled pulp obtained from RGP in the stock was varied.
  • the amount of recycled pulp obtained from RGP was varied from 0 to 30 wt.%, referring to the dry matter content of the produced glassine paper, according to SCAN-P 39:80.
  • the ratio of non-recycled bleached chemical pulp produced from hardwood to the non-recycled bleached chemical pulp produced from softwood was maintained constant.
  • the non-recycled BCP contained 35 wt.% of non-recycled BCP produced from softwood and 65 wt.% of nonrecycled BCP produced from hardwood.
  • a composition which contained only non-recycled bleached chemical pulps and broke, but did not contain recycled pulp obtained from RGP, is marked in the Figures 7-11 as a reference point, and abbreviated as REF.
  • a composition which contained 15 wt.% of recycled pulp obtained from RGP, is marked in the Figures 7-11 as a trial point 1 , and abbreviated as TP1 .
  • a composition, which contained 30 wt.% of recycled pulp obtained from RGP, is marked in the Figures 7-11 as a trial point 2, and abbreviated as TP2.
  • the stock composition of the reference point and trial points 1 and 2 is described in Table 5 (below).
  • BCP tot. refers to the total amount of non-recycled bleached chemical pulp in the stock, in wt.%.
  • Broke refers to the amount of mill broke wt.% in the stock, in wt.%.
  • PLILP3 refers to the amount of recycled pulp obtained from RGP in the stock, in wt.%.
  • the last column on the right refers to the share of each component (BCP SW, BCP HW, broke, PLILP3) in the stock, which sums up to 100 wt.%.
  • the effect of the recycled pulp obtained from RGP on glassine paper production was assessed by measuring the development of fines content at the machine chest of a paper machine as a function of the amount of recycled pulp obtained from RGP in the stock.
  • the fines content refers to fibrous material in the pulp that was determined as the F ⁇ 2oo fraction with McNett classifier according to SCAN-CM 6:05, using a 20 minutes fractionation time, a set of 16, 28, 48 and 200 mesh wires, and weighed filter papers (Macherey-Nagel MN616, 125 mm diameter) for collecting the fibre fractions.
  • the method describes a fibre-fractionation procedure, wherein the fibres in a pulp suspension are grouped into fractions of different average fibre size.
  • the mass of the fibres retained in a fraction is expressed as a percentage of the dry mass of the original sample.
  • the retained F ⁇ 2OO fraction serves as an indication of how much the fines content changes in glassine paper production due to an increase in the amount of pulp obtained from RGP, when the relative ratio of the BCP SW and BCP SW is maintained, the amount of broke mill staying the same.
  • the results evidence that when the amount of recycled pulp obtained from RGP in the glassine paper is in the range of 0 to 10 wt.%, the fines content remains relatively stable, in the range of 10.2 wt.% to 10.5 wt.%.
  • the fines content begins to increase more rapidly.
  • the amount of recycled pulp obtained from RGP in the glassine paper is equal to or higher than 15 wt.%, such as in the range of 15 to 30 wt.%, the fines content in the fiber furnish of the glassine paper increases very rapidly.
  • the amount of recycled pulp obtained from RGP in the glassine paper was in the range of 0 to 30 wt.%, the fines content increased from 10.2 wt.% to 13.8 wt.%.
  • the fines content had an effect to the characteristics of the paper. The effect was detectable already upon forming the paper web.
  • the results indicate that the amount of recycled pulp obtained from RGP in the stock may be used for adjusting the retention level, which describes the ability of the formed paper web to retain fine particles on the web, and therefore the balance between drainage and formation of the paper web.
  • the water retention value was calculated according to equation 1 below:
  • the WRV was 1.72 g/g.
  • the water retention level analysis results support and validate the observations of the fines content analysis disclosed above.
  • the correlation of WRV as a function of the amount of recycled pulp obtained from RGP in the stock demonstrates that recycled pulp obtained from RGP in the stock may be used for adjusting the water retention level.
  • a reduced amount of water absorbed into the fiber network at the machine chest indicates a better dimensional stability of the glassine paper upon drying.
  • the calendered glassine paper advantageously contains recycled pulp obtained from release liner glassine paper equal to or less than 50 wt.%, such as in the range of 5 to 50 wt.%, preferably in the range of 10 to 45 wt.%, most preferably in the range of 15 to 40 wt.% of the paper, when determined as dry matter content according to SCAN-P 39:80.
  • the effect of the recycled pulp obtained from RGP on glassine paper production was further evaluated at the drying section.
  • the calendered glassine paper samples demonstrated a density in the range of 1100 ⁇ 11 g/m 3 and a transparency in the range of 50 ⁇ 1 %.
  • the characteristics of samples produced according to the reference and trial points compositions are presented in Table 6 (below). The trial points were run with the same speed and settings for all the compositions (REF, TP1 , TP2), such that the effect of recycled pulp obtained from RGP to the calendered glassine paper could be evaluated.
  • the paper width was measured from calendered glassine paper samples at the reference point, trial point 1 and trial point 2.
  • the paper width was measured at the reeler, in centimeters, by means of Web Imaging System, abbreviated as WIS, which is an automated image analysis system provided by ABB. The system was used according to manufacturer’s instructions.
  • the width of the paper indicated in Figure 10 is an average value of 8 measurements along the surface of the paper in the crossdirection S y , which is perpendicular to the machine direction S x .
  • the results evidence that a replacement of non-recycled BCP with recycled pulp obtained from RGP leads to reduced shrinkage of the glassine paper, which is directly proportional to the amount of the recycled pulp obtained from RGP in the glassine paper.
  • a replacement of 15 wt.% of non-recycled BCP by recycled pulp obtained from RGP resulted into a glassine paper, which demonstrated 3 cm less shrinkage than the reference.
  • a replacement of 30 wt.% of nonrecycled BCP by recycled pulp obtained from RGP resulted into a glassine paper, which demonstrated 4 cm less shrinkage than the reference.
  • the WIS results were validated in an independent trial run, wherein the paper was profiled off-line from 30 calendered and uncalendered paper samples at the reeler, by means of a Tapio PMA, which is an automated paper quality control system provided by Tapio technologies. The system was used according to manufacturer’s instructions. The results of the latter independent trial run with Tapio PMA validated the paper width results of the first trial run.
  • the grammage variability analysis indicated, that the standard deviation of samples at the trial points 1 and 2, containing recycled pulp obtained from RGP, was 0.5 g/m 2 This was on the same level as the standard deviation of samples at the reference point, which did not contain recycled pulp obtained from RGP (REF).
  • the grammage variability (max-min) was in the range of 3.1 to 3.6 g/m 2 , in all the measured sample compositions (REF, TP1 , TP2).
  • the thickness variability analysis indicated that the standard deviation of samples at the trial points 1 and 2, containing recycled pulp obtained from RGP (TP1 , TP2) was 0.4 pm, which was on the same level as the standard deviation of samples at the reference point, which did not contain recycled pulp obtained from RGP (REF).
  • a modified version of a test method ISO 11556:2005(en) was used for measuring the induced curl.
  • a rectangular test piece from the middle of a paper sheet that had been allowed to stabilize in NTP conditions (25°C, 1 bar) 24 hours after production was cut, having a shape with a length of 10 cm (in the cross-direction S y of the paper) and a width of 5 cm (in the machine direction S x of the paper).
  • the magnitude of curl was thus imprinted into the template as the angle of curvature of the curled test piece from a reference plane, in units of degree of angle.
  • the curl of the test piece was compared to the angle of curvature imprinted on the curl template; the curvature on both sides was recorded. Two test pieces were measured and the four recorded values were averaged. The result of the curl test was thus an average value of the recorded four values. If the recorded curl was towards wire-side, the curl was positive. If the recorded curl was towards top-side, the curl was negative.
  • the wire-side in this context, refers to the side of the paper that upon forming the paper web has been in contact with the papermaking machine's forming wire.
  • the top-side in this context, refers to the opposite side of the paper.
  • Tensile strength can be used as an indication of the potential resistance of the calendered glassine paper to a web break, when the calendered glassine paper is used as a substrate of a release liner in a labelling operation.
  • the strain at break can be used as an indication of how well the paper will conform to irregular shapes and, along with tensile energy absorption, as an indication of the paper’s performance under dynamic straining and stressing.
  • Tensile energy absorption is a measure of the ability of a paper to absorb energy. Tensile energy absorption thus expresses the toughness of the sheet. The parameters thus predict the performance of paper, especially when that paper is subjected to an uneven stress or a dynamic stress.
  • Table 7 indicates the results measured from calendered glassine paper samples that did not contain recycled pulp obtained from RGP (REF), from calendered glassine paper samples that contained 15 wt.% of the recycled pulp obtained from RGP (TP1 ) and from calendered glassine paper samples that contained 30 wt.% of the recycled pulp obtained from RGP (TP2). Table 7. Comparative results (MD and CD) from calendered glassine paper samples.
  • Example 1 A calendered glassine paper suitable for use as a substrate (GLA1 ) of a release liner, the calendered glassine paper comprising fibers from
  • calendered glassine paper having
  • Example 8 The method according to any of the Examples 2 to 7, wherein the stock (MIX1 ) at a machine chest of a paper machine has a water retention value which is in the range of 1 .5 to 1 .9 g/g, preferably in the range of 1 .55 to 1 .85, most preferably in the range of 1 .6 to 1 .8, determinable according to ISO 23714:2014 from a sample having a dry matter content of 1 gram.
  • a water retention value which is in the range of 1 .5 to 1 .9 g/g, preferably in the range of 1 .55 to 1 .85, most preferably in the range of 1 .6 to 1 .8, determinable according to ISO 23714:2014 from a sample having a dry matter content of 1 gram.
  • Example 10 The paper or the method according to any of the previous Examples, wherein the recycled pulp obtained from release liner glassine paper (PULP3) has not been bleached.
  • PULP3 release liner glassine paper
  • Example 11 The paper or the method according to any of the previous Examples, the calendered glassine paper comprising the recycled pulp obtained from release liner glassine paper (PLILP3) in an amount equal to or higher than 10 wt.%, preferably in an amount equal to or higher than 15 wt.%, most preferably in an amount equal to or higher than 30 wt.%, when determined as dry matter content according to SCAN-P 39:80.
  • PILP3 release liner glassine paper
  • Example 12 The paper or the method according to any of the Examples 1 to 10, the calendered glassine paper comprising the recycled pulp obtained from release liner glassine paper (PLILP3) in the range of 5 to 50 wt.%, preferably in the range of 10 to 45 wt.%, most preferably in the range of 15 to 30 wt.%, when determined as dry matter content according to SCAN-P 39:80.
  • PILP3 release liner glassine paper
  • Example 13 The paper or the method according to any of the previous Examples, the calendered glassine paper comprising non-recycled bleached chemical pulp produced from softwood (PLILP2) in an amount equal to or higher than 10 wt.%, preferably in the range of 10 to 50 wt.%, most preferably in the range of 10 to 30 wt.%, when determined as dry matter content according to SCAN-P 39:80.
  • PILP2 non-recycled bleached chemical pulp produced from softwood
  • Example 14 The paper or the method according to any of the previous Examples, the calendered glassine paper having
  • Example 15 A release liner (REL1 ) comprising a calendered glassine paper according to any of the Examples 1 or 9-14 and a release coating.
  • Example 16 Use of recycled pulp obtained from release liner glassine paper (PULP3) without further refining in a method for manufacturing calendered glassine paper suitable for use as a substrate of a release liner.
  • PULP3 release liner glassine paper

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Abstract

L'invention se rapporte à une production de papier cristal pour un revêtement antiadhésif, qui contient à la fois des pâtes chimiques blanchies non recyclées et de la pâte recyclée produite à partir de papier cristal de revêtement antiadhésif. Lorsqu'une matière première hautement spécifique est utilisée pour le recyclage, les caractéristiques de la pâte recyclée peuvent être ajustées déjà lors du recyclage. La pâte recyclée obtenue à partir de papier cristal de revêtement antiadhésive peut être utilisée sans autre raffinage pour la fabrication de papier cristal calandré. Un raffinage excessif peut ainsi être évité et la compatibilité de la pâte recyclée peut être optimisée pour la production de papier cristal. Les pâtes non recyclées peuvent également être raffinées. Ceci conduit à des effets positifs dans un processus de fabrication de papier cristal, tel qu'une déshydratation améliorée et un séchage écoénergétique. Le papier produit présente un retrait réduit et une stabilité dimensionnelle améliorée tout en conservant une qualité suffisante pour une utilisation comme substrat pour un revêtement antiadhésif. Un papier cristal calandré présentant une durabilité améliorée est produit.
EP23837652.9A 2022-12-30 2023-12-21 Papier cristal comprenant une fibre recyclée Pending EP4623150A1 (fr)

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EP22217245.4A EP4394124A1 (fr) 2022-12-30 2022-12-30 Papier cristal comprenant des fibres recyclées
FI20226184 2022-12-30
PCT/EP2023/075765 WO2024141186A1 (fr) 2022-12-30 2023-09-19 Recyclage de papier cristal et de papier kraft surcalandré de pellicule de protection en pâte à papier de haute qualité
PCT/EP2023/087425 WO2024141420A1 (fr) 2022-12-30 2023-12-21 Papier cristal comprenant une fibre recyclée

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US5316621A (en) 1990-10-19 1994-05-31 Kanzaki Paper Mfg. Co., Ltd. Method of pulping waste pressure-sensitive adhesive paper
JP4735271B2 (ja) * 2006-01-13 2011-07-27 王子製紙株式会社 光透過性を有する紙及び剥離紙
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