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WO2024141419A1 - Papier cristal comprenant de la bctmp et de la pâte recyclée - Google Patents

Papier cristal comprenant de la bctmp et de la pâte recyclée Download PDF

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Publication number
WO2024141419A1
WO2024141419A1 PCT/EP2023/087419 EP2023087419W WO2024141419A1 WO 2024141419 A1 WO2024141419 A1 WO 2024141419A1 EP 2023087419 W EP2023087419 W EP 2023087419W WO 2024141419 A1 WO2024141419 A1 WO 2024141419A1
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WIPO (PCT)
Prior art keywords
paper
range
recycled
pulp
glassine paper
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.)
Ceased
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PCT/EP2023/087419
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English (en)
Inventor
Jukka KOTILAINEN
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 US18/091,505 external-priority patent/US12188183B2/en
Priority claimed from EP22217245.4A external-priority patent/EP4394124A1/fr
Priority claimed from US18/113,743 external-priority patent/US12473693B2/en
Priority claimed from PCT/EP2023/075765 external-priority patent/WO2024141186A1/fr
Application filed by UPM Kymmene Oy filed Critical UPM Kymmene Oy
Priority to CN202380091159.6A priority Critical patent/CN120530245A/zh
Priority to EP23837340.1A priority patent/EP4623149A1/fr
Publication of WO2024141419A1 publication Critical patent/WO2024141419A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/14—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
    • 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
    • D21H11/08—Mechanical or thermomechanical pulp
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D21H11/10—Mixtures of chemical and mechanical pulp
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration
    • 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
    • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
    • D21H25/005—Mechanical treatment
    • 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
    • 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

Definitions

  • a glassine paper comprising BCTMP and recycled pulp
  • the invention relates to a calendered glassine paper suitable for use as a substrate layer of an industrial release liner for adhesive labels having a basis weight in the range of 40 to 120 g/m 2 , which contains bleached chemical pulp, bleached chemithermomechanical pulp, and recycled pulp obtained from a release liner wherein calendered glassine paper has been used as a substrate layer.
  • the invention further relates to a method for manufacturing such calendered glassine paper and to a release liner, which contains such calendered glassine paper.
  • a release liner refers to a product comprising a substrate layer and a release coating, such as a silicon polymer based compound, applied on at least one side of the substrate layer.
  • Release liners are widely used as backing materials in labelling applications with adhesive labels, which explains the expectation of high quality.
  • the substrate layer should have sufficient characteristics to withstand the stresses applied at today’s high-speed automated labelling processes.
  • the substrate layer typically comprises a paper and a primer coating applied on at least one side of the paper. Examples of paper types suitable for use as release liner substrate layers are glassine paper, supercalendered kraft paper, also denoted as SCK paper, and clay coated paper.
  • BKP bleached kraft pulp
  • the amount of bleached chemical pulp from hardwood in the pulp mixture is typically high, in order to obtain a good formation and a paper having sufficient incompressibility, smoothness and dense structure.
  • Prior to release coating the paper is also supercalendered, to increase the transparency and to provide a dense and smooth surface and a desired target thickness which meets the tolerance level set by the die-cutting system.
  • Label producers use a release liner as a substrate for producing a face stock, from which the adhesive labels are cut.
  • Minimal variation of release liner thickness is desired, to facilitate an even die strike pattern at a depth needed for the intended application. Different depth of impression left by the blades is used for different applications. High level of transparency is needed from the paper, since optical sensors are widely used for tracking the position of the labels on the release liner. Typically the optical sensors measure the brightness variation of a light beam, such as an infrared light beam, which is transmitted through a release liner.
  • a light beam such as an infrared light beam
  • one option for the paper manufacturer to alleviate the shortage of raw material could be to simply reduce the basis weight of the paper upon manufacturing, whereby less amount of pulp would be consumed.
  • the basis weight refers to the grammage of the paper, in grams per square meter.
  • the loss of fiber furnish would require compensation by calendering the paper more, which would lead into downgauging, that is, reduction of the paper thickness.
  • a thinner paper having less basis weight would be a different product, in many aspects.
  • a different die strike depth would likely be needed, for the die-cutting system.
  • the paper product would no longer have the same properties as earlier, either, and the risk of inducing adverse effects downstream, when the paper is part of a release liner, is increased.
  • the mechanical properties of the paper may suffer to an extent that a release liner manufactured from such paper would not function properly, when exposed to the conditions present in a labelling process. This is of particular concern with papers having a basis weight in the range of 40 to 120 g/m 2 ; the relative tolerance levels set by the label converter due to the die-cutting systems become stricter towards the lower end of this basis weight range.
  • Glassine paper is an example of a product type from which superior runnability and almost standardized target values are demanded, throughout the whole value chain.
  • BCTMP Bleached chemithermomechanical pulp
  • BCTMP is material which is appreciated by paper manufacturers as it offers a costefficient way to increase the bulk of the paper and to maintain the ratio between the basis weight and the thickness within a desired range. While this may reduce the basis weight, the risk remains that the produced paper does not meet the label converter’s expectations in respect of other quality characteristics, when considering use as a substrate layer of an industrial release liner.
  • BCTMP is high yield pulp manufactured by a hybrid process, wherein wood chips are first pre-treated with chemicals, heated for a short period and subsequently refined by mechanical means. This produces pulp having a yield typically in the range of 80 to 95 wt.%, wherein compounds other than cellulose present in the wood material have been preserved to a large extent.
  • Sustainability comprises both environmental aspects related to preserving biodiversity and aspects related to circular economy, by increasing the recycling of materials.
  • Sustainability may also include responsible sourcing of raw material for an industrial production process. The nature and origin of the wood-based raw material has a significant effect on the sustainability of an industrially produced paper product, since the production volumes are large, as explained above.
  • the invention solves the challenges disclosed above by providing a method for manufacturing calendered glassine paper having a basis weight in the range of 40 to 120 g/m 2 , wherein an optimal combination of non-recycled BCP, BCTMP, and recycled pulp obtained from release liner wherein the substrate has been glassine paper, is used to adjust the properties of the fiber furnish.
  • Glassine paper is a distinguished type of paper that is used as a release liner substrate due to its outstanding characteristics.
  • glassine paper is typically produced of highly refined BCP produced in a kraft process.
  • BCP produced in a kraft process may be referred to as bleached kraft pulp and denoted as BKP.
  • BHKP bleached hardwood kraft pulp
  • BSKP bleached softwood kraft pulp
  • the chemical cooking preserves the characteristics of the fibers in the pulp better in comparison to mechanical pulping methods, whereby the chemically pulped fibers may be better used for providing strength to the produced paper.
  • Bleaching removes residual lignin still present after the chemical cooking operation, which increases the pulp whiteness and brightness.
  • the whiteness of glassine paper may be obtained without external dyes or colorants.
  • a glassine paper typically contains a fiber furnish that includes both BSKP as well as BHKP. Different wood species produce different type of fibers, hence the origin of the pulp, in addition to the pulping method, may be used for adjusting the characteristics of the produced paper. For instance, BHKP in general is advantageous, in comparison to BCTMP, for the brightness and transparency of the product. The specifications of the produced paper may thus be altered by means of adjusting the share of pulp in a fiber furnish.
  • the challenge is that when the amount of a given pulp component is adjusted, it typically has an effect to several other paper characteristics.
  • a dilemma lies in the multivariable optimization - how to improve desired paper characteristics without deteriorating others to the extent that the paper no longer meets the set quality specifications for the intended purpose.
  • Glassine paper is manufactured on a paper machine by forming a paper web from selected pulp types which have been mixed together, such that a pulp mixture has been obtained. Automated optical analysis using unpolarized light may be used for determining the properties and fiber furnish of the pulp mixture, whereby for example fibers produced by chemical or mechanical pulping methods and their dimensions may be identified.
  • the moisture content of the paper web is reduced in a press section, after which the paper web is dried in a drying section, whereby paper is formed.
  • the ultimate properties of glassine paper manufactured at a paper machine, such as transparency and target thickness, are obtained by calendering, which is performed using a line pressure, heat and moisture content that are higher than conventionally used during an ordinary calendering treatment.
  • Supercalendering enables to produce glassine paper having high density surface and high transparency.
  • the level of compression used in the glassine calendering process is higher than is typically used for SCK paper, whereby the surface is smoother and the fiber structures of calendered glassine paper are more damaged during the calendering.
  • glassine paper is distinguished from SCK paper.
  • BCTMP the manufacturing method of BCTMP differs from BKP.
  • the two pulp types thus differ in many aspects. This can be seen in the mass of the particles in fiber length fractions in BCTMP, for instance.
  • the distribution of the mass of the particles in fiber length fractions differs considerably from those in BHKP. It also differs significantly from the mass of the particles in fiber length fractions in BSKP.
  • the mass of the particles in shorter fiber length fractions up to 1 .2 mm in length, forms majority of the total mass, while in BSKP, the opposite seems to be the case.
  • Uncalendered paper sheets which contained BCTMP in the range of 5 to 50 wt.%, when determined as dry matter content of the paper, demonstrated a considerable increase of bulk.
  • the uncalendered paper sheets when exposed to conditions corresponding to industrial supercalendering, can also be calendered into the same thickness as corresponding industrial glassine papers, which contain only BHKP and BSKP.
  • the bulk increase obtainable when replacing BHKP with BCTMP is particularly interesting in calendered glassine paper grades having a density in the range of 1050 to 1190 kg/m 3 , wherein the bulk may be flexibly controlled with the share of BCTMP in the fiber furnish, while using the share of BSKP to adjust other paper characteristics, such as tear strength of the paper. Further, the substitution of BHKP with BCTMP enables to maintain or even increase bending stiffness of the calendered glassine paper, whereby a good potential to resist compression, which facilitates an even die strike pattern during a diecutting operation, is obtainable.
  • a method for manufacturing calendered glassine paper suitable for use as a substrate of a release liner comprising - mixing pulps such that a stock comprising a fiber furnish is obtained, the fiber furnish determinable with standard ISO 9184-4 in conjunction with standard ISO 9184-1 , the fiber furnish comprising o an amount equal to or higher than 5 wt.% of non-recycled bleached chemithermomechanical pulp, o an amount equal to or higher than 5 wt.% of recycled pulp obtained from release liner glassine paper, and o non-recycled bleached chemical pulp produced from hardwood, o non-recycled bleached chemical pulp produced from softwood or o non-recycled bleached chemical pulp produced from hardwood and softwood the amounts determinable as dry matter content according to SCAN-P 39:80,
  • a release liner comprising a substrate layer and a release coating, wherein the substrate layer is a calendered glassine paper as indicated above, which comprises a primer coating applied on at least one side of the calendered glassine paper.
  • the primer coating is typically a surface sizing applied in the range of 1 to 5 g/m 2 per side.
  • the prime coating typically contains water-soluble polymers, such as starch, polyvinyl alcohol and/or carboxymethyl cellulose, which are compatible with addition-curing silicone systems used in release coatings.
  • the calendered glassine paper has a fiber furnish that contains BCTMP in the range of 5 to 40 wt.%, preferably in the range of 10 to 35 wt.%, most preferably in the range of 15 to 30 wt.%.
  • the fiber furnish further contains recycled pulp obtained from release liner wherein the substrate has been glassine paper in the range of 5 to 40 wt.%, preferably in the range of 10 to 35 wt.%, most preferably in the range of 15 to 30 wt.%.
  • the fiber furnish further contains non-recycled BCP produced from softwood at least 15 wt.%, preferably in the range of 15 to 20 wt.% of the fiber furnish.
  • a bulky glassine paper may be produced, wherein the fiber furnish enables calendering of the paper to typical target thickness used for corresponding glassine paper grade having a higher basis weight, which therefore has a higher density and sufficient quality characters for use as a substrate in a release liner.
  • the recycled pulp obtained from release liner wherein the substrate has been glassine paper enables to balance the paper manufacturing process and reduce the dimensional changes and shrinkage of the calendered glassine paper, which may also be seen in the paper quality.
  • the presence of recycled pulp obtained from release liner wherein the substrate has been glassine paper further improves the water removal from the fibers during the paper manufacturing.
  • the presence of non-recycled BCP produced from softwood in the fiber furnish has an effect to the formation of the paper web and runnability.
  • the formation and runnability of the paper web on the paper machine may be improved.
  • a calendered glassine paper with optimal shares of BCTMP and recycled pulp in the fiber furnish may be produced into a thickness range typical for higher basis weight products, while maintaining other quality characteristics of the paper sufficient for use as a substrate layer of an industrial release liner.
  • the calendered glassine paper as disclosed above has a fiber furnish comprising
  • S x , S z and S y refer to coordinate directions orthogonal to each other.
  • Figure 1 is a diagram showing comparative data of the difference in average mass of fractions (relative share, %) between BCTMP, BHKP and BSKP, when determined with Valmet Fiber Image Analyzer (Valmet FS5), according to the manufacturer’s instructions.
  • Figure 2 is a diagram showing the effect of BSKP to average length weighted fiber length (mm) in glassine papers having different fiber furnishes.
  • Figure 3 is a multivariable diagram showing how tear index (mNm 2 /g) and basis weight (g/m 2 ) correlate in calendered glassine papers as a function of the BCTMP share (wt.%), determined as dry matter content of the paper according to SCAN-P 39:80.
  • Figure 4 is a multivariable diagram showing how tear index (mNm 2 /g) and basis weight (g/m 2 ) correlate in calendered glassine papers as a function of the BSKP share (wt.%), determined as dry matter content of the paper according to SCAN-P 39:80.
  • Figure 5 is a multivariable diagram showing how transparency (%) and basis weight (g/m 2 ) correlate in calendered glassine papers as a function of the BCTMP share (wt.%), determined as dry matter content of the paper according to SCAN-P 39:80.
  • Figure 6 is a diagram that illustrates how the characteristics of calendered glassine paper having a basis weight in the range of 50 to 70 g/m 2 provide an optimization range RNG1 , wherein the basis weight of the paper to be produced may be adjusted by means of a fiber furnish composition, while maintaining the target thickness and without inducing adverse effects to other paper properties, which would prevent its use as substrate layer of an industrial release liner for adhesive labels.
  • Figure 7 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 8 shows, by way of an example, a method for manufacturing glassine paper, wherein the method a paper is formed from a stock that contains non-recycled bleached chemical pulp and recycled pulp obtained from glassine paper that has been used as a substrate of a release liner.
  • the calendered glassine paper may be used as a substrate for a release liner.
  • the release liner glassine paper may be recycled and reused in the method for manufacturing glassine paper.
  • Figure 9 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 11 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 13 is a trend diagram representing 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, when determined as the F ⁇ 2oo fraction with McNett classifier according to SCAN-CM 6:05.
  • Figure 15 is a trend diagram representing the drainage as a function of pulp content, when measured as the main steam group pressure level on a paper machine.
  • the addition of recycled pulp obtained from RGP reduces the need for steam in the pre-dryer.
  • Figure 16 shows comparative data of the development of paper width in centimetres at the reeler of a paper machine, when measured using ABB Web Imaging System (WIS).
  • WIS ABB Web Imaging System
  • the results demonstrate that paper shrinkage in the cross-direction S y correlates inversely with the amount of recycled pulp obtained from RGP in the paper.
  • Figure 17 shows comparative data of induced curl of calendered glassine paper, when measured from test pieces in the cross-direction S y .
  • the results demonstrate that the magnitude of curl correlates inversely with the amount of recycled pulp obtained from RGP in the furnish. Test pieces which contained higher amount of recycled pulp obtained from RGP displayed less curl.
  • Figure 18 shows data of an experimental study performed with computational modelling, which compares effects of different fiber furnish recipes on a calendered glassine paper.
  • Figure 19 is data from an experimental study, which compares effect of different fiber furnish recipes on the transparency of calendered glassine paper.
  • Figure 20 is data from an experimental study, which compares effect of different fiber furnish recipes on the opacity of calendered glassine paper.
  • a release liner glassine paper is used to describe a release liner, wherein the substrate is calendered glassine paper. Multiple aspects distinguish RGP from other paper types collected for recycling.
  • Calendered glassine paper denotes a specific paper type which is suitable for use as a substrate of a release liner.
  • Calendered glassine paper is conventionally prepared from highly refined bleached chemical pulp that has been strongly calendered, whereby it possesses an exceptional combination of high density, strength and transparency, which are beneficial characteristics for a release liner substrate. Typical characteristics defining a calendered glassine paper are
  • a method for manufacturing a release liner REL1 comprises applying a release coating SIL1 on a paper substrate GLA1.
  • the dehesive properties of the release coating SIL1 are typically obtained by means of an addition-curing silicone system in the presence of a suitable metal catalyst, such as platinum.
  • An addition-curing silicone system comprises a reactive silicone polymer and a silane hydride cross-linker comprising functional vinyl groups, which are provided in a fluid form and may be spread on the paper substrate GLA1 in an amount of ca. 1 g/m 2
  • the reactive silicone polymer is typically a hydrophobic, silicon-based organic polymer, such as polydimethylsiloxane.
  • a calendered glassine paper in general comprises a primer coating POL1 , such as a surface sizing applied on at least one side of the paper. Surface sizing improves the glassine paper surface characteristic, such as barrier properties.
  • An advantageous primer coating POL1 is a water-soluble polyvinyl alcohol comprising hydroxyl groups. Some of the hydroxyl groups of the polyvinyl alcohol may have been modified to comprise reactive groups, such as vinyl groups. This enables the polymer to participate into the cross-linking reaction of the addition-curing silicone system. The primer coating POL1 thereby improves the anchorage of the dehesive surface coating layer to the paper substrate GLA1 .
  • 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 finishing of the formed paper is done by surface sizing and calendering treatment.
  • the ultimate properties of glassine paper such as transparency and target thickness, are typically obtained by supercalendering, which is performed using a line pressure, heat and moisture content that are higher than conventionally used during an ordinary calendering treatment.
  • the calendering of glassine paper is typically performed in a temperature in the range of 100 to 200°C.
  • the line pressure used for calendering a glassine paper is generally in the range of 300 to 500 kN/m.
  • composition of the pulp mixture upon manufacturing glassine paper may thus be used for adjusting the properties of the fiber furnish, thereby enabling formation of a paper, which may be further treated by supercalendering such that predefined properties, such as sufficient transparency and target thickness are achieved.
  • the characteristics of the BCTMP for the glassine paper production may be evaluated, for instance, based on the bulk, brightness, pH and drainability of the pulp.
  • the bulk of the BCTMP is equal to or higher than 1 .8 cm 3 /g, preferably at least 2.0 cm 3 /g, such as in the range of 1.8 to 3.2 cm 3 /g, when determined according to ISO 534.
  • the brightness of the BCTMP is equal to or higher than 60%, preferably equal to or higher than 80%, such as in the range of 60 to 85%, when determined according to ISO 2470.
  • the bulkiness of the formed chemithermomechanical pulp may be increased such that less amount of refining may be required for providing the desired water retention value and fiber length distribution.
  • high intensity refining is used upon producing BCTMP, less energy is needed for the fibrillation of the fibers.
  • the amount of short fibers, such as fine particles, in the BCTMP may be increased, which increases the bulk.
  • the bleached chemithermomechanical pulp advantageously has a Canadian Standard Freeness (hereafter denoted as CSF) value of equal to or more than of 90 ml, such as in the range of 90 to 500 ml and the pH of aqueous extracts equal to or above pH 7.0, preferably a CSF value equal to or more than 130 ml, such as in the range of 130 to 425 ml and the pH of aqueous extracts equal to or above pH 7.1 , most preferably a CSF value equal to or more than 325 ml, such as in the range of 325 to 435 ml and the pH of aqueous extracts equal to or above pH 7.3.
  • CSF Canadian Standard Freeness
  • the Canadian Standard Freeness value may be determined in accordance with ISO 5267-2:2001.
  • the pH of the pulp may be determined from aqueous pulp extracts according to ISO 6588-2 (2020).
  • the pulp pH is measured from an aqueous extract having a temperature in the range of 20 to 25°C, by means of a pH meter, using two buffer solutions having pH 4 and pH 7, respectively.
  • Suitable pH meters are, for example, pH-meter CG 840 with electrode N 1042A, Knick pH-meter 766 Calimatic with electrode SE 103 or Mettler-Toledo MP 120, used according to the manufacturer’s instructions.
  • the glassine paper contains the BCTMP in an amount in the range of 5 to 50 wt.%, when determined as dry matter content of the paper according to SCAN-P 39:80.
  • the share of BCTMP in the fiber furnish has an effect to the bulk of the uncalendered glassine paper, as well as to the bending stiffness of the calendered glassine paper.
  • a higher BCTMP share also increases the roughness variation of glassine paper, whereby a BCTMP content in the range of 25 to 45 wt.% may be optimal, when paper smoothness is desired, in addition to bulk.
  • a calendered glassine paper which contains the BCTMP in an amount in the range of most preferably in the range of 30 to 40 wt.%, when determined as dry matter content of the paper according to SCAN- P 39:80, is preferred.
  • the transparency of calendered glassine paper in general, is lower in paper grades, wherein the BCTMP content is higher.
  • a calendered glassine paper having a basis weight of 68 g/m 2 , a density of 1105 kg/m 3 and which contains 15 wt.% of BSKP and 50 wt.% of BCTMP, determined as dry matter content of the paper according to SCAN-P 39:80 may have a transparency of 48%, which is sufficient for measuring brightness variation through a release liner by means of optical sensors and a light beam, such as an infrared light beam.
  • the optimal combination of BSKP and BCTMP thus enables a production of calendered glassine paper wherein the optical quality is maintained sufficiently such that the paper is suitable for use as a substrate layer of a release liner.
  • the calendered glassine paper has a transparency equal to or higher than 42%, preferably equal to or higher than 44%, such as in the range of 42 to 56% or in the range of 44 to 53%, determinable by standard ISO 2469.
  • the calendered glassine paper contains the BSKP at least 15 wt.%, preferably at least 20 wt.%, most preferably at least 30 wt.%, such as in the range of 15 to 65 wt.%, preferably in the range of 20 to 60 wt.%, most preferably in the range of 30 to 55 wt.%.
  • the experimental setup contained several trial points TP1 to TP9, wherein the trial points were divided into three groups, based on whether the share of BSKP was less than 20 wt.%, equal to or higher than 20 wt.% or equal to or higher than 30 wt.%.
  • the content of BSKP was either 15 wt.% (TP7, TP8) or 18 wt.% (TP9).
  • the content of BSKP was 22.5 wt.% (TP4, TP5, TP6).
  • the content of BSKP was 30 wt.% (TP1 , TP2, TP3).
  • each trial point TP1 to TP9 was increased by producing calendered glassine paper specimens in three different basis weight of 58, 62 and 68 g/m 2 .
  • a trial point with higher BCTMP content was produced by increasing the share of BCTMP and reducing the share of BHKP, as indicated in table 1 (below).
  • the addition of BCTMP was performed as a replacement such that the relative amount of BHKP in the fiber furnish was reduced.
  • Calendered glassine paper specimens for the trial points TP1 to TP9 used in the experimental study were prepared according to the ISO 5269-3 (2008) standard, using a conventional sheet-former method as described in ISO 5269-1 (2005), wherein a closed water system was used. The pulps were refined to levels typically used in glassine paper production. BCTMP refining was performed with a (Voith-Sulzer) laboratory refiner at 4% pulp consistency that corresponds well to mill refining and the °SR determined according to ISO 5267-1 (1999). The BCTMP was refined to a target °SR-value 45.
  • the BSKP was refined to a target °SR 20-35 at a paper mill and the BHKP was refined to a target °SR 30-45 at a paper mill as well.
  • the glassine paper specimens were calendered in conditions of 100°C roll temperature, 4000 dN pressure, using 2 passes, which produced specimens corresponding to industrial glassine paper and having a target thickness typical for the respective basis weight.
  • Example 1 comparison of fiber fractions and average dimensions
  • Valmet Fiber Image Analyzer Valmet FS5
  • a fiber furnish analysis is capable of identifying papermaking fibers from a sample.
  • Another example of a fiber furnish analysis is the Graff “C” stain test according to ISO 9184-4:1990(en), in conjunction with ISO 9184-1 and, if necessary, ISO 9184-2, wherein 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 may further be used for an analysis of fiber dimensions, such as fiber length and fiber width, as well as to quantify fiber fractions, such as mass of fractions and length weighted fiber length distributions of a sample, by means of automated optical analysis using unpolarized light, according to ISO 16065-2: 2014.
  • the analysis is based on an ultra high resolution (UHD) camera system equipped with image analysis software, which is used to acquire a greyscale image of a sample, of which image the properties of the fibers in the sample may be determined.
  • the greyscale image is acquired from a sample placed in a transparent sample holder, such as a cuvette, using a 0.5 millimetre depth of focus according to ISO 16505-2 standard.
  • pulp types used in the study were characterised based on their fiber properties. Below are listed the pulp types and their abbreviation in the experimental study:
  • BSKP northern bleached softwood kraft pulp (Picea, Pinus)
  • BHKP bleached hardwood kraft pulp (Betula)
  • the fiber mass fraction analysis was performed with Valmet Fiber Image Analyzer (Valmet FS5), using fiber length weighted distribution for classifying the fibers, according to the manufacturer’s instructions and implementing ISO 16065-2: 2014, ISO 9184-4 and ISO 9184-1.
  • Valmet Fiber Image Analyzer Valmet FS5
  • - fines were defined to be particles having a width over 10 micrometers and a length of less than 0.2 millimeters
  • - fibers were defined to be particles having a width in the range of 10 to 75 micrometers and a length above 0.2 millimeters.
  • the mass fraction distribution of BCTMP sample differs considerably from the mass fraction distributions of the two BKP samples.
  • the mass of the shorter fiber fractions up to 1 .2 mm in length, forms 86% of the total mass
  • BSKP the opposite is the case.
  • close to 75 % of the mass is in fractions having a length equal to or higher than 1 .2. mm.
  • BHKP only 20,6 % of the mass is in fractions having a length equal to or higher than 1.2. mm
  • BCTMP only 14 % of the mass is in fractions having a length equal to or higher than 1.2. mm.
  • most of the mass of BCTMP is in particles having a small average fiber length.
  • FIG. 2 shows the advantageous effect of BSKP to the average fiber length in calendered glassine paper.
  • the average length weighted fiber length of the fiber furnish was less than 1 mm.
  • the calendered glassine paper contained BSKP in an amount equal to or higher than 20 wt.%, when determined as dry matter content of the paper according to SCAN-P 39:80, an average length weighted fiber length equal to or higher than 1.03 mm is obtainable.
  • the bulking thickness therein refers to the thickness of the uncalendered paper, determined as single sheet thickness according to ISO 534:2011 .
  • the apparent bulk density therein refers to the mass per unit volume of the uncalendered paper, which is expressed in kilograms per cubic meters (kg/m 3 ).
  • the apparent bulk density has been calculated from a single sheet thickness according to ISO 534:2011 .
  • the bulk, as used therein, refers to the volume per unit mass, expressed in cubic centimeters per gram (cm 3 /g). The bulk therefore represents the inverse of the paper density.
  • the results also evidence that glassine papers with low basis weight, particularly in the range of 50 - 70 g/m 2 , are exceptionally suitable for the adjustment of density with BCTMP. This was observed throughout the studied range of 5 to 50 wt.% of BCTMP additions to the fiber furnish, determined as dry matter content of the paper (SCAN P 39:80). Thus, a considerable increase of bulk was obtainable.
  • the obtained increase in the bulk enabled calendering of the paper sheets into the same thickness as corresponding glassine papers, which contain only BHKP and softwood, while maintaining a lower density than in the corresponding glassine papers, due to the obtained increase of bulk.
  • Example 3 comparison of water retention value in the in glassine paper specimens
  • WRV water retention value
  • ISO 23714:2014(en) The glassine paper specimens in trial points TP1 to TP9 were also characterized in respect of their water retention value, abbreviated as WRV, according to ISO 23714:2014(en).
  • WRV is an empirical measure of the capacity of a pulp sample to hold water. The WRV was determined as an average of two parallel samples, each sample amount consisting of 1 g of dry pulp diluted into 500 ml of water and having a temperature of 23 ⁇ 3 °C. Materials and methods as listed below were used:
  • the amount BCTMP content may be varied significantly, in the range of 5 to 50 wt.%, without corresponding alteration in the capacity of the pulp mixture to hold water.
  • an optimum range exists, wherein the amount of BSKP may be arranged to interact with the amount of BCTMP in the fiber furnish.
  • a WRV equal to or higher than 1.58 g/g, preferably equal to or higher than 1.60 g/g may be obtained.
  • a fiber furnish containing BCTMP in the range of 5 to 50 wt.% may be used to provide a pulp composition having WRV, which is in the range of 1.50 to 1.90 g/g, preferably in the range of 1.54 to 1.88 g/g, most preferably in the range of 1 .58 to 1 .84 g/g, from a sample having a dry matter content of 1 gram (ISO 23714:2014).
  • Tensile, bending and tear strength properties, as well as optical properties of the prepared calendered glassine paper specimens were determined to evaluate the suitability of the produced calendered glassine paper for use as a substrate layer of an industrial release liner.
  • Tensile index refers to the tensile strength divided by the basis weight, determinable according to standard ISO 1924-3:2005(en), in units of Newton meter per gram.
  • Tensile index is indicative of the strength of the paper derived from factors such as fiber strength, fiber length, and bonding. It can also be used as an indication of the potential of a paper substrate to resist web breaking during a labelling operation.
  • Release liner glassine papers share a common history of treatments. This enables to use RGP as raw material in a recycling process, which may be arranged to produce pulp with exceptional characteristics.
  • the raw material used for the recycling process should contain at least 75 wt.%, more preferably at least 85 wt.%, most preferably at least 90 wt.% of release liner glassine paper.
  • the raw material used for the recycling process consists substantially of release liner glassine paper.
  • a method for manufacturing recycled pulp from a release liner glassine paper therefore contains a step for sorting RGP for recycling.
  • 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 other 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 nonlight or non-white RGP grades.
  • a white glassine paper in this context, refers to CIE L* a* b* colour space coordinate values of the paper, wherein
  • 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.
  • 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, is used for facilitating the detachment of silicone-based particles and other hydrophobic impurities from the fibers.
  • 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 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 REP1 may then be used in a method for manufacturing glassine paper.
  • 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 glassine paper on a paper machine.
  • pulp properties of recycled pulp obtained from RGP were measured and compared to properties of non-recycled bleached chemical pulps and mill broke used at a paper mill for glassine paper production. Below are listed the pulp types and their abbreviation in the experimental study:
  • 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.
  • automated optical analysis such as an ultra high resolution (UHD) camera system equipped with image analysis software, may be used to acquire a greyscale image of a sample, of which image the properties of the fibers in the sample may be determined.
  • the greyscale image may be acquired from a sample placed in a transparent sample holder, such as a cuvette, using a 0.5 millimetre depth of focus according to ISO 16505-2 standard.
  • Valmet Fiber Image Analyzer (Valmet FS5) may further be used to determine fiber dimensions, such as fiber length and fiber width, as well as length weighted distribution of the pulp fibers, by means of automated optical analysis using unpolarized light, according to ISO 16065-2: 2014.
  • FIG 10 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 11 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 average fiber length and width of recycled pulp obtained from RGP is closer to the average fiber length of non-recycled BCP made of hardwood or broke, but clearly distinguished from the average fiber length of nonrecycled BCP made of softwood.
  • 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 content of fines in a bleached chemical pulp varies naturally depending on the used wood species.
  • the content of the fines in a pulp varies also due to pulp treatments, such as refining and recycling, as disclosed above.
  • the length weighted distribution of fines is a fundamental property of pulp, which affects inter alia the formation of paper web during manufacturing.
  • the pulp characteristics also have an effect on the tensile strength, the burst strength, the fold endurance and the tear resistance of a paper.
  • 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 glassine paper that has been used as a substrate of a release liner 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.
  • 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 13-17 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 13-17 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 13-17 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 12 (below). Table 12. Composition of stock at reference and trial points 1 and 2 in experimental studies.
  • 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 sample was weighed first time after the centrifugation.
  • the sample was then dried overnight (12h) at 105 ⁇ 2 °C and cooled down to a room temperature of 23 ⁇ 3 °C in an excicator.
  • the sample was then weighed a second time.
  • a laboratory scale (0,0001 g precision) was used for the weighing.
  • the calendered glassine paper advantageously contains recycled pulp obtained from glassine paper that has been used as a substrate of a release liner 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 stock 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.
  • 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 13 (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 simulation trial points STP9 and STP10 indicated that a calendered glassine paper comprising a fiber furnish, wherein the majority of the fiber furnish was BCP SW (25 wt.%) and REP1 (in the range of 35 to 45 wt.% of the fiber furnish), the paper freeness and bulk were lower. On the other hand, the strength properties, tear index in particular, were very good.
  • the simulation trial points STP6 to STP8 wherein the majority of the fiber furnish was BCP HW (in the range of 40 to 45 wt.%) and BCTMP (in the range of 25 to 45 wt.%), the paper bulk was high. However, the strength properties were reduced and the sheet more porous, based on behaviour of the air permeability.
  • the simulation trial points STP16 to STP20 indicated that when the combined amount of BCTMP and REP1 was increased from 50 to 70 wt.% of the fiber furnish in a calendered glassine paper, the water removal from the fibers could be further improved. This was particularly the case for the simulation trial points STP18 to STP20, wherein the amount BCTMP was at least 2 fold to the amount of REP1 in the fiber furnish. However, a decrease in the strength properties was observed.
  • BCTMP has a very high potential for providing bulk into a glassine paper, in comparison to nonrecycled BCP, and also in comparison to recycled pulp obtained from RGP. Due to relatively short but wide fibers and a relatively high lignin content of the BCTMP, the fibers are more rigid and support the glassine paper structure better than BCP, during supercalendering. The exceptional characteristics are also reflected in the water retention value, which BCTMP is able to suppress remarkably well, in particular when used in high amount and together with high amount of recycled pulp obtained from RGP, as demonstrated by the series 4 samples STP17-STP20. This feature is reflected as easier water removing at the paper machine, during glassine paper production.
  • a further study was arranged to study the effects of recycled pulp obtained from RGP, BCTMP, and their combination in calendered glassine papers prepared in a laboratory scale.
  • a test specimen comprising 35 wt.% BSKP (pine) and 65 wt.% BHKP (eucalyptus) was prepared.
  • a set of 11 different calendered glassine paper test specimens LPT1 to LPT11 were prepared.
  • the reference and the set were prepared in two different basis weights of 58 g/m 2 and 62 g/m 2
  • the fiber furnish composition of the test specimens used in the study are defined in Table 15 (below).
  • BSKP bleached softwood kraft pulp (pine)
  • the BCTMP used in the experiment was a mixture made of hardwood (aspen) and softwood (spruce), wherein the share of softwood was 20 wt.%.
  • the test specimens were prepared according to ISO 5269-3 (2008) standard, using a conventional sheet-former as described in ISO 5269-1 (2005). Refining of BSKP, BHKP and BCTMP was performed with a Voith-Sulzer laboratory refiner (4% pulp consistency) to defined target °SR.
  • Tear index expressed in millinewton square metres per gram (mN m 2 /g), refers to the tearing resistance of the paper divided by its gram mage. Tearing resistance is defined as the mean force per sheet required to continue the tearing started by an initial cut in the test piece and is determinable according to ISO 1974:2012(en). The results of the laboratory tests thus further strengthened the perception already received from the computational modelling disclosed above.
  • BCTMP non-recycled BCP produced from softwood and recycled pulp obtained from RGP enables to maintain quality characteristics of calendered glassine paper at a sufficient level, with enhanced sustainability and without reducing the basis weight of the paper upon manufacturing.

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Abstract

La présente invention concerne un procédé de fabrication de papier cristal calandré ayant un poids de base dans la plage de 40 à 120 g/m2, une combinaison optimale de BCP non recyclée, de BCTMP et de pâte recyclée obtenue à partir de papier cristal à revêtement antiadhésif étant utilisée pour ajuster les propriétés de la teneur en fibres. Tandis que l'utilisation de BCTMP permet d'obtenir un produit ayant une masse plus élevée, le composant de pâte recyclée, qui présente une compatibilité élevée avec le processus de fabrication de papier, permet d'équilibrer le processus de fabrication et de réduire les changements dimensionnels et le retrait du papier formé. La présence combinée de la BCTMP et du composant de pâte recyclée dans la teneur en fibres améliore l'élimination de l'eau des fibres pendant la fabrication du papier cristal, tandis que la présence de la BCP non recyclée produite à partir de bois tendre améliore la formation et le comportement de la bande de papier sur la machine à papier. Ceci permet de produire du papier cristal calandré avec une durabilité améliorée, la densité pouvant être commandée au moyen de la teneur en fibres, sans réduction de taille et sans effets indésirables sur d'autres propriétés de papier, ce qui empêcherait l'utilisation du papier cristal calandré en tant que couche de substrat dans un revêtement antiadhésif.
PCT/EP2023/087419 2022-12-30 2023-12-21 Papier cristal comprenant de la bctmp et de la pâte recyclée Ceased WO2024141419A1 (fr)

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CN202380091159.6A CN120530245A (zh) 2022-12-30 2023-12-21 包含bctmp和再生纸浆的玻璃纸
EP23837340.1A EP4623149A1 (fr) 2022-12-30 2023-12-21 Papier cristal comprenant de la bctmp et de la pâte recyclée

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US18/091,505 US12188183B2 (en) 2022-12-30 2022-12-30 Supercalendered kraft paper comprising recycled fiber
US18/091,505 2022-12-30
EP22217245.4A EP4394124A1 (fr) 2022-12-30 2022-12-30 Papier cristal comprenant des fibres recyclées
FI20226184 2022-12-30
EP22217245.4 2022-12-30
FI20226184 2022-12-30
US18/113,743 2023-02-24
US18/113,743 US12473693B2 (en) 2023-02-24 2023-02-24 BCTMP-tailored SCK paper for release liner
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
EPPCT/EP2023/075765 2023-09-19

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