EP3636833A1 - Papiersubstrat mit vinylalkohol-oligomeren, die zum enthalten von verketteten kohlenstoffstrukturen mit funktionellen vinylgruppen modifiziert sind - Google Patents

Papiersubstrat mit vinylalkohol-oligomeren, die zum enthalten von verketteten kohlenstoffstrukturen mit funktionellen vinylgruppen modifiziert sind Download PDF

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Publication number
EP3636833A1
EP3636833A1 EP18199296.7A EP18199296A EP3636833A1 EP 3636833 A1 EP3636833 A1 EP 3636833A1 EP 18199296 A EP18199296 A EP 18199296A EP 3636833 A1 EP3636833 A1 EP 3636833A1
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EP
European Patent Office
Prior art keywords
paper substrate
vinyl alcohol
compound
subst1
oligomeric
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.)
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Application number
EP18199296.7A
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English (en)
French (fr)
Inventor
Harri Kosonen
Mikko Rissanen
Kuisma Littunen
Jaakko Rautalahti
Janne ANTILA
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UPM Kymmene Oy
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UPM Kymmene Oy
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Publication date
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Priority to EP18199296.7A priority Critical patent/EP3636833A1/de
Priority to PCT/FI2019/050711 priority patent/WO2020074773A1/en
Publication of EP3636833A1 publication Critical patent/EP3636833A1/de
Pending legal-status Critical Current

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    • 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
    • D21H19/00—Coated paper; Coating material
    • D21H19/10—Coatings without pigments
    • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
    • D21H19/20—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • 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
    • D21H19/00—Coated paper; Coating material
    • D21H19/10—Coatings without pigments
    • D21H19/14—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12
    • D21H19/24—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H19/32—Coatings without pigments applied in a form other than the aqueous solution defined in group D21H19/12 comprising macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds obtained by reactions forming a linkage containing silicon in the main chain of the macromolecule
    • 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
    • D21H19/00—Coated paper; Coating material
    • D21H19/36—Coatings with pigments
    • D21H19/44—Coatings with pigments characterised by the other ingredients, e.g. the binder or dispersing agent
    • D21H19/56—Macromolecular organic compounds or oligomers thereof obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H19/60—Polyalkenylalcohols; Polyalkenylethers; Polyalkenylesters
    • 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

  • the invention relates to a paper substrate suitable for binding silicone in a catalytic hydrosilation reaction and to a method for manufacturing such paper substrate.
  • the invention further relates to use of oligomeric vinyl alcohol in a method for manufacturing a paper substrate and to products thereof.
  • Release liners comprising cellulose fiber-based support layers are widely used as non-blocking backing material for self-adhesive products, such as self-adhesive labels.
  • a typical cellulose fiber-based support layer suitable for use on release liner paper substrate is an industrially manufactured paper, which is manufactured from chemical pulp, such as bleached Kraft pulp. The purpose of a cellulose fiber-based support layer is to provide dimensionally stable and dense surface, on which a primer layer and a release coating may be applied.
  • a typical example of an industrially manufactured paper that is used in a release liner is glassine paper.
  • a label stock refers to multiple labels LAB1 on a release liner REL1.
  • a label stock may be formed of a label laminate web FILM1 by cutting the label laminate web FILM1 with a die cutting roll DIE1 and stripping excess matrix material MTX1 away from the release liner REL1, such that the labels LAB1 remain attached on the release liner REL1.
  • the strength of the bonding between the adhesive ADH1 layer and the release layer SIL1 resists the separation of the adhesive ADH1 layer from the release layer SIL1.
  • Release value refers to the minimum amount of force F N required to detach a label LAB1 or excess matrix material MTX1 from the release liner REL1.
  • Modern high-speed labelling applications which may operate at a very high velocity up to tens of thousands of labels dispensed per hour, demand that the release liner has a sufficiently low and stable high-speed release value, such that the dispensing of labels from the release liner may proceed without interruptions.
  • a paper substrate SUBST1 is used herein to denote a coated cellulose fiber-based support layer, comprising a cellulose fiber-based support layer PAP1 and a primer layer PRIM1. Up to 35% by weight of the primer layer composition may consist of binder material.
  • a mixture for coating a cellulose fiber-based support layer in general comprises water-soluble binders capable of forming a film, such as starch, polyvinyl alcohol (hereafter referred to also as PVA or polyvinyl alcohol) and carboxymethyl cellulose (hereafter referred to also as CMC).
  • the paper substrate SUBST1 serves as a surface for a subsequent release coating applied on the coated cellulose fiber-based support layer, which release coating is then cured to form a release layer SIL1.
  • Self-adhesive products may be manufactured by coating the release layer SIL1 of the formed release liner REL1 with an adhesive, thereby forming an adhesive layer ADH1 and subsequently adjoining a face material FACE1 on the adhesive layer ADH1 surface, thereby forming the label laminate web FILM1.
  • Thermally curable release coatings refer to specific type of release coatings, which are distinguished from radiation curable systems.
  • Low temperature curable silicone compound or "LTC" silicone compound refers to an addition-curable compound comprising a cross-linker component with silane hydride groups and a silicone polymer with functional vinyl groups, which components are configured to cross-link in a catalytic hydrosilation reaction at a low temperature.
  • a silane hydride group undergoes an addition reaction with a vinyl group.
  • the addition reaction is typically catalyzed by a platinum catalyst. Platinum-catalyzed addition reactions are fast, and the curing speed of the reaction can be controlled via the curing temperature.
  • a low temperature in this context refers to a catalytic hydrosilation reaction temperature of less than 120°C, preferably in the range of 55 to 110°C, wherein the silane hydride groups and the functional vinyl groups form covalently cross-linked structures within the release coating, thereby forming the cured release layer.
  • the silicone curing time should not adversely affect the relative rub-off values of the release layer, which should remain consistent over time, since a release liner may be stored for a period prior to its use.
  • This sets requirements for the paper substrate which should promote long-term stable anchorage of the silicone to the paper substrate at low platinum levels, while enabling the use of fast curing silicone compounds, which are advantageous in reducing the high-speed release values.
  • Publication WO 2011/104427 suggests functionalizing a PVA polymer that contains hydroxyl functionalities with undecylenic aldehyde. According to the publication, this functionalization of the PVA polymer can be done in a water-based process, before the modified PVA polymer is deposited on a cellulose fiber-based support layer.
  • a disadvantage of the water-based reaction of the PVA polymer is, however, that while water is a suitable solvent for certain grades of PVA polymer, for each grade of water-soluble PVA polymer, an increase in PVA concentration is accompanied by a rise in solution viscosity. A high degree of viscosity quickly impedes the reaction dynamics and eventually causes flocculation or micelle formation.
  • solvation of the PVA polymer to water is also slow and highly temperature-dependent, which limits the available reaction conditions.
  • the organic molecule presented in the prior art is not water soluble, unlike the PVA polymer.
  • Undecylenic aldehyde is commercially available, but the molecule is in an organic phase.
  • the density of undecylenic aldehyde is lower than the density of water, the reactant easily remains floating on the surface of an aqueous solution, despite stirring of the solution during the reaction. Therefore, the reaction of a mixture containing PVA polymer and undecylenic aldehyde is a two-phase reaction. To contact each other, the reactants need to reach over a phase interface, which reduces the reaction efficiency.
  • the prior art discloses a solution that has a maximum limit to the amount of organic molecule, which may be grafted onto a PVA polymer. This limit is set to a relatively low level.
  • the amount of functional vinyl groups grafted on a modified PVA polymer disclosed in the prior art is not optimal for a release liner which is used in modern high-speed release liner applications, wherein higher bonding strength and lower release values are needed between the paper substrate and the release layer. This requirement is enhanced as the base weight (grammage) of the paper substrate used in high-speed release liner applications with labels is decreasing.
  • the reduced base weight leads to also lighter label laminate web and subsequently weaker excess matrix material, which need to be stripped away from the release liner with lower amount of force than before.
  • the invention addresses the above disclosed problems by providing means to change the rheology of the aqueous solution upon grafting the organic molecule.
  • This enables the production of a coating composition comprising high amount of vinyl groups.
  • Novel fast-curing silicone compounds in particular, may require less time for the addition curing reaction to take place.
  • a paper substrate comprising a cellulose fiber-based support layer and a coated primer layer containing a high amount of vinyl groups thus provides an unprecedented means of improving the release characteristics of a subsequent release layer applicable on the primer layer.
  • the rheology of the aqueous solution upon grafting the organic molecule may be controlled by using oligomeric vinyl alcohol.
  • Oligomeric vinyl alcohol has a considerably lower hydrocarbon chain length and subsequently a lower molecular weight than a PVA polymer.
  • M w the weight average molecular weight
  • M w the weight average molecular weight
  • the weight average molecular weight represents the mean average weight of the oligomeric vinyl alcohol, weighted according to weight fractions.
  • a water-based acetalization reaction of an organic molecule comprising both an aldehyde group and a functional vinyl group may therefore be performed at a higher efficiency.
  • acetalization efficiency may be obtained with an organic molecule that has a terminal vinyl group and a catenated carbon structure containing at least 4 carbon atoms, preferably at least 5 carbon atoms.
  • the organic molecule is an aldehyde which contains a linear chain of 5 to 15 carbon atoms and which ends into a terminal vinyl group, such as 10-undecenal.
  • the length of the catenated carbon structure which preferably is a linear hydrocarbon chain, is advantageous for reducing the polarity of the formed acetal compound.
  • a cellulose fiber-based support layer may be coated with a compound based on oligomeric vinyl alcohol which contains unprecedently high amount of vinyl groups grafted onto the compound. This enables using lower amounts of platinum catalyst and fast curing silicone compounds, which facilitates the manufacturing of a release liner with improved release characteristics.
  • a paper substrate which is suitable for binding silicone in a catalytic hydrosilation reaction, the paper substrate comprising
  • a release liner which comprises a paper substrate as disclosed above, and a release layer based on a silicone compound that has been applied on the paper substrate.
  • 'catenated carbon structure' is used to denote a series of bonded carbon atoms, wherein the carbon atoms are bonded to other carbon atoms. Carbon is known to be suitable for catenation, which herein refers to the formation of chain having interconnecting carbon-carbon bonds. Catenated carbon structures may also be referred to as 'catenae'. A catenated carbon structure in this context includes a hydrocarbon chain. A catenated carbon structure may also comprise substituents, such as oxygen, hydrogen or alkane or alkene groups, such as a vinyl group. The catenated carbon structure may have 4 or more interconnecting carbon atoms in a series.
  • the catenated carbon structure of an organic molecule is a hydrocarbon chain having at least 7 carbon atoms, more preferably 11 carbon atoms, and which terminates into an aldehyde at the first end of the chain and into a functional vinyl group at the other end of the chain.
  • the catenated carbon structure terminates into an acetal at the first end of the chain.
  • the low M w of the oligomeric vinyl alcohol facilitates the covalent bonding of a high amount of catenated carbon structures to the oligomeric vinyl alcohol, such that on the surface of the paper substrate, the formed compound renders the primer layer hydrophobic and enables to produce a paper substrate surface that contains a vinyl group molality of equal to or higher than 0.2 millimoles per gram of the compound.
  • the primer layer may contain functional vinyl groups for example in the range of 0.20 to 1.41, preferably in the range of 0.23 to 1.21, most preferably in the range of 0.28 to 1.01 millimoles per gram of the compound.
  • the abbreviation 'mmol/g' used hereafter denotes millimoles per gram of the compound based on oligomeric vinyl alcohol, unless otherwise stated.
  • the abbreviation therefore denotes the molality of vinyl groups in the compound, which has been formed in a water-based acetalization reaction of the dissolved oligomeric vinyl alcohol and the reactant, which is an organic molecule that contains at least 4 carbon atoms and comprises both an aldehyde group and a functional vinyl group.
  • the high amount of organic molecules which contain a catenated carbon structure may be used to provide a hydrophobic surface on a cellulose fiber-based support layer.
  • a catenated carbon structure, linear hydrocarbon in particular is non-polar and therefore the oligomeric vinyl alcohol, when grafted to contain high amounts of such catenated carbon structures before coating onto a cellulose fiber-based support layer surface, has a tendency to avoid the hydrophilic surface of the cellulose fiber-based support layer beneath, which contains hydroxyl groups.
  • the hydrophobic effect is dependent of the amount of linear chains grafted onto the oligomeric vinyl alcohol.
  • the non-polar, catenated carbon structures that end into a terminal vinyl group may also acts as a surfactant.
  • a hydrophobic oligomeric vinyl alcohol may have a poor adhesion to silicone
  • the catalytic hydrosilation reaction enables chemical bonding of the silicone.
  • a compound based on the oligomeric vinyl alcohol comprising a high vinyl group content of equal to or above 0.2 mmol/g of the compound based on oligomeric vinyl alcohol on the surface of the cellulose fiber-based support layer has been observed to be advantageous in providing a hydrophobic effect to the cellulose fiber-based support layer surface.
  • the increased amount of non-polar catenated carbon structures reduces the effect of the hydroxyl groups present in the polyvinyl alcohol and on the cellulose fiber-based support layer surface.
  • the amount of a release coating containing silicone compound may be reduced. Less amount of release coating requires less platinum catalyst for curing to take place.
  • the primer layer contains catenated carbon structures with functional vinyl groups in an amount of equal to or higher than 0.3 mmol/g of the compound based on oligomeric vinyl alcohol, since the molality of catenated carbon structures with functional vinyl groups on the cellulose fiber-based support layer surface has been observed to correlate with high-speed release value, such that a higher molar amount provides a lower and more stable release value, particularly in high-speed labelling applications.
  • the primer layer contains catenated carbon structures with functional vinyl groups in an amount of equal to or higher than 0.5 mmol/g of the acetal compound, as this enables to further reduce the thickness of the release layer.
  • a particular advantage of the hydrophobic surface on the cellulose fiber-based support layer is that less adhesive may penetrate through a release layer into the primer layer beneath, when the cellulose fiber-based support layer is used as part of a release liner paper substrate.
  • a primer layer having a hydrophobic surface or barrier may be arranged to repel the adhesive. Thus, also the minimum amount of force required to detach a label or excess matrix material is reduced.
  • a further effect of the hydrophobic surface on the cellulose fiber-based support layer is that this enables the thickness of the release layer to be reduced, since the minimum amount of force required to detach a label from the release liner is dependent of the thickness of the release layer.
  • the hydrophobic surface therefore facilitates the reduction of the amounts of silicone and platinum required for providing a release layer.
  • a thinner release layer further enables a lower high-speed release value.
  • the silicone-based release layer may thereby remain thin, such as less than 1 micrometer in thickness.
  • a thinner release layer enables also reduction of the thickness of the cellulose fiber-based support layer, which is needed as a backing to give strength for the release layer.
  • the release value is therefore dependent of the behavior of the whole release liner wherein both the paper substrate comprising the cellulose fiber-based support layer and the viscoelastic behavior of the release layer determine the release properties.
  • a particular advantage of a primer layer that contains catenated carbon structures with functional vinyl groups in an amount of equal to or higher than 0.3 mmol/g, preferably an amount of equal to or higher than 0.5 mmol/g of the acetal compound is that the high amount of functional vinyl groups enables the use of very fast curing silicone compounds in the release coating.
  • the catenated carbon structure is thus configured to promote hydrophobicity and further configured to contain a functional vinyl group in one end, which vinyl group is suitable for catalytic hydrosilation reaction.
  • the catenated carbon structure is covalently bonded into the primer layer by having an acetal connectivity to the moiety of the compound, which is based on oligomeric vinyl alcohol.
  • Acetal connectivity of the catenated structure at one end enables the formation of the compound based on oligomeric vinyl alcohol in a water-based reaction.
  • the formed compound may be purified from the reaction solution prior to coating the compound on a cellulose fiber-based support layer.
  • a hydrophobic surface facilitates the even spreading of the uncured silicone polymer applied on the surface.
  • the release liner paper substrate comprises acetal compounds that contain catenated carbon structures with functional vinyl groups in an amount of equal to or higher than 0.2 millimoles per gram of the acetal compound
  • the release layer is this more evenly spread and firmly bonded to the paper substrate.
  • a hydrophobic primer layer may further be used to resist the penetration of water-based or hot-melt adhesive material, which may be used in the manufacturing of a label laminate web and may thus become into contact with the paper substrate surface.
  • a hydrophobic acetal compound evens out the characteristics, for example release characteristics, of the whole surface, despite the existence of possible defects, such as holes, which may sometimes be present in the cellulose fiber-based support layer.
  • the method for manufacturing a paper substrate which is suitable for binding silicone in a catalytic hydrosilation reaction may comprise at least the steps of
  • a further issue addressed by a primer layer that contains high amounts of oligomeric vinyl alcohol with functional vinyl groups is the migration of uncured silicone compounds.
  • the component comprising silane hydride groups When coating a paper substrate with a fast-curing silicone compound, the component comprising silane hydride groups is added in excess amount relative to the amount of the component comprising vinyl groups to ensure a proper cross-linking between the two components that cures the coating into a release layer.
  • the excess amount of silane hydride groups all these groups are not cured in the catalytic hydrosilation reaction.
  • the uncured silane hydride groups may later migrate into the cellulose fiber-based support layer.
  • a conventional film-forming primer layer may provide some barrier effect
  • the unreacted cross-linker has despite a film-forming primer layer been observed to migrate through the primer layer and to the opposite side of the cellulose fiber-based support layer underneath the primer layer.
  • Industrially manufactured cellulose fiber-based support layers such as glassine papers, are never completely closed or impermeable and may contain some openings or pores, thereby allowing the uncured cross-linker compound to penetrate the cellulose fiber-based support layer and reach the opposite side of the release liner, thereby contaminating the adjacent surface of the label laminate web on a reel.
  • the uncured cross-linker compound may smear portions of the face material surface and subsequently cause problems with printing quality, such as poor intensity of the printed surface, especially when the face material is a filmic face substrate, such as polyethylene, polypropylene, polyethylene terephthalate or a similar synthetic thermoplastic polymer, which are widely in use.
  • a filmic face substrate such as polyethylene, polypropylene, polyethylene terephthalate or a similar synthetic thermoplastic polymer, which are widely in use.
  • the primer layer may contains a compound based on oligomeric vinyl alcohol, wherein the compound comprises catenated carbon structures with functional vinyl groups in an amount of equal to or higher than 0.2 millimoles per gram, preferably equal to or higher than 0.3 millimoles per gram, most preferably equal to or higher than 0.5 millimoles per gram of the acetal compound, such as in the range of 0.20 to 1.41 millimoles per gram of the compound based on oligomeric vinyl alcohol.
  • a high vinyl group molality of equal to or above 0.23 mmol/g is also efficient in binding unreacted cross-linker component, when the cross-linker component is added in excess stoichiometric amount.
  • a high vinyl group content of equal to or above 0.23 mmol/g of the compound on the surface of the paper substrate may thus be configured to bind release coating components and thereby used to increase the printing intensity of a filmic face material, such as polyethylene, polypropylene, polyethylene terephthalate, polylactic acid or a similar film-forming thermoplastic polymer.
  • the amount of functional vinyl groups may be measured by an iodometric titration method from the acetal compound formed in the acetalization reaction.
  • Oligomeric vinyl alcohol may be obtained from polyvinyl alcohol by means of controlled chain scission, for example with Fenton's reagent. Oligomeric vinyl alcohol has specific characteristics, which may be used to provide a composition containing a high amount of grafted catenated carbon structures with vinyl groups on a cellulose fiber-based support layer, the paper substrate thus formed comprising remarkably high amount of functional vinyl groups, which functional vinyl groups are available for a subsequent release coating. Such a paper substrate is particularly suitable for use as a release liner paper substrate for fast-curing silicone compounds, which require high bonding strength between the release layer and the coated cellulose fiber-based support layer.
  • Oligomeric vinyl alcohol may be used to provide an acetal compound based on the oligomeric vinyl alcohol, having a low M w , such as a M w of less than 1000 g/mol, preferably in the range of 440-880 g/mol.
  • the number of repeat units in an oligomer is typically in the range of 4 to 22. In context of oligomeric vinyl alcohol, it has been observed that the number of repeat units is preferably in the range of 10-20.
  • the low M w of the oligomeric vinyl alcohol may be used to suppress the rise of viscosity of a solution during a water-based acetalization reaction. Viscosity in this context refers to the property of a fluid that resists a force tending to cause the fluid to flow.
  • the flow behavior of oligomeric vinyl alcohol in water is therefore related to the viscosity of the solution during a water-based acetalization reaction.
  • the flow behavior of oligomeric vinyl alcohol in water may further be controlled by selecting the degree of hydrolysis of the oligomeric vinyl alcohol grade. Therefore, the viscosity ⁇ of the water-based solution containing the vinyl alcohol oligomer may be low, such as less than 20000 mPa ⁇ s, during the water-based acetalization reaction.
  • the viscosity of the water-based solution containing the vinyl alcohol oligomer should be less than 8000 mPa ⁇ s, when measured as Brookfield viscosity at 100 rpm.
  • Experimental results have demonstrated that industrial applicability of PVA modified with undecylenic aldehyde in an acetalization reaction is limited by the solution viscosity.
  • a coating composition having a viscosity higher than 8000 mPa ⁇ s does not permit sufficient pumping on a coating machine, the viscosity thereby limiting the use of PVA modified with undecylenic aldehyde in an acetalization reaction as a coating composition.
  • a coating composition containing a higher amount of catenated carbon structures with functional vinyl groups which have been grafted onto the compound based on oligomeric vinyl alcohol may be applied on a surface of a cellulose fiber-based support layer, thereby forming a primer layer containing high amount of catenated carbon structures and a high vinyl group molality.
  • a paper substrate containing catenated carbon structures with high amount of functional vinyl groups may be used to improve the anchorage of a release coating containing fast-curing silicone compound.
  • the high density of functional vinyl groups on the paper substrate surface provides more anchoring points which are suitable for cross-linking reactions with silane hydride groups present in fast-curing silicone compounds, that may be applied on the paper substrate.
  • the viscosity of oligomeric vinyl alcohol has a significant effect on the flow behavior of the solution.
  • the oligomeric vinyl alcohol may be arranged to react at a higher efficiency with an organic molecule comprising both an aldehyde and a vinyl function in a water-based acetalization reaction, such that a high conversion of the aldehyde to an acetal product is obtainable. This has not been possible in the past, since the high average molecular weight of polyvinyl alcohol has rapidly caused rise in viscosity of the reaction mixture, when the molar fraction of the reactants in the reaction mixture has been increased.
  • the oligomeric vinyl alcohol may be arranged to provide a higher modification degree, thereby resulting into a primer layer containing more functional vinyl groups per surface area unit of the cellulose fiber-based support layer.
  • the affinity of the primer layer containing the acetal compound towards the cellulose fiber-based support layer may further be increased by selecting the degree of hydrolysis of the oligomeric vinyl alcohol.
  • the degree of hydrolysis of the oligomeric vinyl alcohol is above 70%, preferably equal to or higher than 80%.
  • the degree of hydrolysis of the oligomeric vinyl alcohol may be in the range of 70-99%, advantageously in the range of 85 to 99%.
  • the degree of hydrolysis in the oligomeric vinyl alcohol may thus be used to select the affinity of the oligomeric vinyl alcohol towards a hydrophilic layer, such as a further polymer containing layer containing a polymer having capability to provide barrier properties for the cellulose fiber-based support layer, such as polyvinyl alcohol, starch, and/or carboxymethyl cellulose.
  • a hydrophilic layer such as a further polymer containing layer containing a polymer having capability to provide barrier properties for the cellulose fiber-based support layer, such as polyvinyl alcohol, starch, and/or carboxymethyl cellulose.
  • the degree of hydrolysis in the oligomeric vinyl alcohol may be selected such that a water-based reaction of oligomeric vinyl alcohol with 10-undecenal yields an acetalized reaction product comprising a catenated carbon structure, wherein the reaction product has a very high vinyl group molality.
  • the lower viscosity of the solution during a water-based acetalization reaction further enables higher dry matter content of the starting material oligomeric vinyl alcohol to be used.
  • the acetalization reaction may proceed further and yield a compound based on oligomeric vinyl alcohol comprising 10-undecylenic groups acetalized into the structure, wherein the compound thus contains vinyl group molality of equal to or more than 0.20 mmol/g, preferably equal to or more than 0.23 mmol/g, such as equal to or more than 0.3 mmol/g, or more than 1.4 mmol/g of the compound.
  • the grafting reaction with the organic molecule may be arranged to proceed further, thereby obtaining a higher amount of catenated carbon structures with functional vinyl groups into the formed reaction product.
  • the lower viscosity of the reaction mixture further facilitates the mixing of the reactants, thereby allowing the reactants to be better in contact with each other, despite possible phase layer interfaces. This is the case in particular, when a non-water-soluble organic molecule, such as 10-undecenal, is used.
  • the amount of stirring correlates with the amount of surface area available for chemical reactions; the better the mixing of the reactants during the reaction is, the higher is the probability of the participating functional groups to be in contact for a reaction to take place.
  • a paper substrate having a higher density of catenated carbon structures with functional vinyl groups per unit area of the primer layer surface may be obtained.
  • the grafting reaction with the organic molecule may further be arranged to proceed towards a more complete reaction conversion, the reaction conditions may be arranged to yield more of the acetalized reaction product from the amount non-acetalized starting materials.
  • the higher conversion of reactants to a reaction product has a further effect of reducing the amount of unreacted reactant present in the reaction mixture after the reaction has taken place. Therefore, there is less need for purification of the reaction mixture of unreacted reactant which could be recycled, for example.
  • the acetalized reaction product is easier to purify. The purification would be much more challenging from a highly viscose gel. The method thereby provides a clear advantage over the prior art by facilitating purification, increasing the process safety and the recyclability of the process chemicals.
  • FIGS 1 to 5 are schematic. S x and S z represent orthogonal directions in the figures.
  • a release liner REL1 refers to a thin multilayer structure having width, length and thickness dimensions.
  • a release liner REL1 having a multilayer structure comprises at least a paper substrate SUBST1 and a release layer SIL1, such as a silicone-based release layer, applied on at least one side of the paper substrate SUBST1.
  • a paper substrate SUBST1 is used herein to denote a coated cellulose fiber-based support layer, wherein the cellulose fiber-based support layer PAP1 has been coated from at least one side with at least one primer layer PRIM1.
  • a primer layer PRIM1 in this context refers to a layer coated on a cellulose fiber-based support layer PAP1.
  • a paper substrate SUBST1 may contain one or more primer layers.
  • a primer layer PRIM1 is typically configured to reduce the porosity of the support layer surface, thereby improving the smoothness of the paper substrate SUBST1 surface.
  • An example of a primer layer PRIM1 is a polymer containing layer. When the primer layer PRIM1 is a polymer containing layer, it is typically applied as a coating composition on the cellulose fiber-based support layer PAP1, when manufacturing the paper substrate SUBST1.
  • a conventional technical effect of a polymer containing layer is to reduce the surface penetration of a subsequent release layer applied on the paper substrate SUBST1.
  • Polyvinyl alcohol, starch, and/or carboxymethyl cellulose are typically unmodified polymers POL1 having a film-forming nature which are widely used to provide a barrier between the release layer SIL1 and the cellulose fiber-based support layer PAP1 surface.
  • the primer layer PRIM1 may contain an acetal compound CMP1 based on oligomeric vinyl alcohol having a low M w , such as a M w of less than 1000 g/mol, and wherein the acetal compound CMP1 has been formed in a water-based acetalization reaction with an organic molecule comprising both an aldehyde group and a functional vinyl group, such that the acetal compound CMP1 based on the oligomeric vinyl alcohol on the primer layer PRIM1 contains functional vinyl groups.
  • the acetal compound CMP1 based on oligomeric vinyl alcohol may be coated on a cellulose fiber-based support layer PAP1 independently of any other polymer containing layer, such as a layer containing polyvinyl alcohol, starch, and/or carboxymethyl cellulose.
  • the cellulose fiber-based support layer PAP1 refers to a paper containing cellulose fibers, which paper is suitable for use as a layer of a release liner.
  • the pulp is typically derived from a chemical pulping process. Chemical pulping disintegrates the structure of the wood with strong chemicals in a cooking process, thereby producing fibrous material with a very high cellulose fiber content of equal to or higher than 70 wt.%, preferably equal to or higher than 80 wt.%, most preferably equal to or higher than 90 wt.%.
  • a chemical pulping process removes nearly all the lignin and at least part of the hemicelluloses, while preserving well the fiber structure and length.
  • Examples of chemical pulping processes are, for example, the sulphite pulping process or the Kraft pulping process.
  • the Kraft pulping process uses sodium sulphide and alkali to degrade and dissolve the lignin.
  • the remaining lignin in the chemical pulp while only in residual amounts of less than 5 wt.%, may still cause darkening of the pulp.
  • the remaining lignin can be further removed through bleaching processes, thereby providing bleached chemical pulp.
  • the first bleaching steps are further delignification stages, whereas the later steps are brightening stages, in which the brown-color inducing chromophores are removed, thereby increasing the pulp whiteness and brightness.
  • Bleached chemical pulp typically contains lignin in an amount of less than 2 wt.%, preferably less than 1 wt.%, most preferably less than 0.5 wt.% of the bleached chemical pulp. Bleaching is typically used to improve the brightness and whiteness of the pulp. In papers used for release liners, a high transparency level of the paper is desirable. The Kraft process, in particular, decreases considerably the amounts of hemicelluloses, lignin, wood extractives and inorganics in the pulp material such that only residual traces of these compounds remain; thereby bleached Kraft pulp may be denoted as essentially 'lignin free'.
  • a paper suitable for use as a layer of a release liner refers to paper manufactured on a paper machine.
  • paper quality and suitability for coating with a silicon compound may be determined based on the smoothness, density, porosity and transparency of the paper.
  • Typical characteristics of a paper suitable for use as a layer of a release liner are smoothness of at least 900 sec/min (ISO 5627), density of at least 1.0, such as in the range of 1.0 to 1.2, wherein the density refers to grammage (ISO536) per thickness (ISO534), porosity equal to or less than 15000 pm/Pas (ISO11004) and transparency of equal to or higher than 40%, preferably equal to or higher than 44% when the paper grammage is less than 70 g/m 2 , or equal to or higher than 28%, preferably equal to or higher than 33% when the paper grammage is equal to or higher than 70 g/m 2 (ISO2470), the parameter values corresponding to ISO standards referred in parentheses.
  • paper types lending themselves for release liner applications are vegetable parchment, greaseproof paper, coated papers and glassine.
  • glassine is preferred for industrial manufacturing of high-quality release liner, due to the mechanical properties of the paper obtained in the manufacturing process.
  • the paper may have been made essentially of bleached chemical pulp, such as bleached Kraft pulp. While hardwood is advantageous for increasing the brightness of the paper, softwood having a longer average fiber length is typically used together with the hardwood in bleached Kraft pulp to improve the internal bond strength and facilitate the formation of the paper web.
  • bleached chemical pulp comprising hardwood and softwood may also be used to improve the burst strength and tensile strength of the paper.
  • Glassine is paper typically made of bleached chemical pulp, having a grammage in the range of 30 to 160 g/m 2 .
  • the pulp is refined to obtain a fiber fineness, which enables a dense, nearly unporous, paper surface to be obtained. Such a surface is resistant to air and liquids such as oil and water.
  • the pulp slurry is first refined to a high level, the formed paper web is then pressed and dried, and a coating layer containing conventional sizing polymers having a film-forming nature such as unmodified polyvinyl alcohol, starch, and/or carboxymethyl cellulose is applied on the paper surface to provide barrier properties.
  • Glassine is calendered with a multi-nip calender or a supercalender before or after applying the coating layer, to obtain a product having high density surface, high impact strength, high tear resistance and transparency.
  • the coating layer may be applied as a separate layer or together with a compound based on oligomeric vinyl alcohol that contains functional vinyl groups.
  • the release layer SIL1 is formed of a release coating applied on the paper substrate surface.
  • the release coating is typically applied as an uncured composition, which is a liquid polymer resin that is subsequently cured to form the release layer SIL1.
  • a cured release layer SIL1 has a non-blocking surface.
  • the surface energy level of a cured release layer SIL1 is typically in the range of 21 to 25 dynes/cm.
  • the non-blocking surface of the cured release layer SIL1 may be used to protect adhesive material of a label laminate web FILM1 from premature adhesive bonding.
  • the release layer SIL1 may comprise fast-curing silicone compound.
  • a fast-curing silicone compound comprises a cross-linker component SH1 with silane hydride groups and silicone polymer VIN1 with functional vinyl groups, which components SH1, VIN1 are configured to cross-link in a catalytic hydrosilation reaction, preferably with a low amount of platinum-based catalyst.
  • An organic molecule MOL1 in this context refers to a reactant.
  • An organic molecule has a chemical structure which is defined by number or carbon atoms and functional groups.
  • An organic molecule MOL1 suitable for grafting oligomeric vinyl alcohol in this context further refers to a small molecule comprising a catenated carbon structure that terminates into an aldehyde at the first end of the chain and into a functional vinyl group at the other end of the chain.
  • the organic molecule MOL1 should have a catenated carbon structure having a carbon chain length of at least 4 carbon atoms.
  • the symbol R in Figure 4 is used to denote the part of the organic molecule which separates the functional vinyl group and the aldehyde group of the organic molecule MOL1 from each other such that the catenated carbon structure of the organic molecule MOL1 contains at least four carbon atoms.
  • a catenated carbon structure having a chain length of less than 4 carbon atoms in the organic molecule MOL1 hydrocarbon chain may lead to interference with the oligomeric vinyl alcohol OLG1 during the grafting reaction.
  • a catenated carbon structure having a chain length of equal to or less than 15 carbon atoms is preferred, as a longer chain length may lead to chain folding problems.
  • a suitable organic molecule MOL1 for a paper substrate has a catenated carbon structure, preferably a hydrocarbon chain, containing at least 4 carbon atoms, preferably in the range of 5 to 15.
  • the catenated carbon structure is aliphatic. More preferably, the catenated carbon structure is acyclic. When the catenated carbon structure is linear or branched, steric hindrances are better avoided. When the catenated carbon structure is a hydrocarbon, the non-polar effect of the carbon chain is very high.
  • a catenated carbon structure may also comprise substituents, such as oxygen, hydrogen or functional alkane or alkene groups, such as vinyl group.
  • the organic molecule MOL1 is 10-undecenal or 2,2'-dimethyl-4-pentenal, such that the acetalized compound comprises a hydrocarbon chain that contains 11 or 5 carbon atoms in a row, respectively.
  • the preferred is 10-undecenal, which is a commercial fine chemical available in industrial amounts.
  • the selection of the organic molecule further depends of the desired substitution degree of the oligomeric vinyl alcohol upon the grafting reaction.
  • a terminally unsaturated aldehyde having a shorter hydrocarbon chain has a better water-solubility and may therefore be used to provide a higher efficiency in the grafting reaction.
  • the higher water solubility allows the reagent to be better in contact with the oligomeric vinyl alcohol.
  • a shorter hydrocarbon chain length of the organic molecule therefore may increase the probability of the participating functional aldehyde groups to be in contact with hydroxyl groups of the oligomeric vinyl alcohol, such that a water-based acetalization reaction may take place at a high efficiency.
  • the oligomeric vinyl alcohol further improves the coatability of the formed acetal compound based on oligomeric vinyl alcohol.
  • the mass ratio R m refers to the amount of the aldehyde reactant in grams that is reacted per 100 grams of the oligomeric vinyl alcohol.
  • the mass ratio R m may also be expressed as degree of modification and the units given in percent by weight (wt.-%) of the oligomeric vinyl alcohol.
  • Table 1 shows correlation between degree of modification and coatability of the composition in a paper coating process.
  • the experimental study was comparative and used polyvinyl alcohol having an average molecular weight higher than 50000 g/mol. The results demonstrate a rapid rise in viscosity of the modified polymer, when the amount of 10-undecenal increases.
  • the coatability is preserved to a higher degree of modification, up to a vinyl group content of 1.41 mmol/g, when 10-undecenal is used as the organic molecule in the acetalization reaction.
  • Table 1 shows correlation between degree of modification and coatability of the composition in a paper coating process.
  • the experimental study was comparative and used polyvinyl alcohol having an average molecular weight higher than 50000 g/mol. The results demonstrate a rapid rise in viscosity of the modified polymer, when the amount of 10-undecenal increases.
  • the coatability is preserved to a higher degree of modification, up to a vinyl group content of 1.41 mmol/g, when 10-unde
  • the 'coatability' refers to the coatability of the reaction product to a cellulose fiber-based support layer, wherein the formed polymer product is either easy to coat ('1') such that reaction product viscosity is low enough to apply by conventional coating means, or the polymer is difficult to coat ('2') such that that reaction product forms a viscose gel which is not easy to apply by conventional coating means, or the polymer has lost its coatability ('3') to such a degree that the reaction product could no longer be applied as a coating.
  • Polyvinyl alcohol is commercially manufactured from polyvinyl acetate via hydrolysis.
  • the main structure and degree of polymerization of polyvinyl alcohol is established already when the vinyl acetate monomers are polymerized.
  • Polymerization in this context refers to the rapid chain extension reaction connecting the used individual monomer units together into a compound having a high M w , which consists of a large number of monomer units covalently bound together in the polymerization reaction.
  • a polymer hence refers to a product directly obtainable by a polymerization reaction.
  • the polymerized chains, when emerging, are 'live' only for a very short period and extend rapidly to their full length as polymers, the chain extension then terminating.
  • the chain extension is also most efficient immediately after chain emergence, when available monomers for chain extension are most abundant.
  • Oligomeric vinyl alcohol may be formed from fully or partly hydrolyzed polyvinyl alcohol. Oligomeric vinyl alcohol compound may be used, in particular, to reduce the viscosity behavior of an aqueous solution. Oligomeric chains have a low number of repeat units, thereby reducing the tendency for entanglement.
  • oligomeric vinyl alcohol compounds useful in the practice of this invention have flow and viscosity characteristics which permit use of the compound as part of a coating composition applicable on a cellulose fiber-based support layer.
  • oligomeric vinyl alcohol has a M w of less than 1000 g/mol, preferably in the range of 100 to 950 g/mol, advantageously in the range of 440 to 880 g/mol.
  • the number of repeat units may be in the range of 4 to 22.
  • a method to manufacture oligomeric vinyl alcohol may comprise, for example, reduction of the molecular weight of polyvinyl alcohol by controlled chain scission.
  • Oligomeric vinyl alcohol may be produced, for example, by treating polyvinyl alcohol with Fenton's reagent.
  • hydrogen peroxide (H 2 O 2 ) and iron salt which in this context refer to Fenton's reagent, are used to produce highly oxidizing reaction conditions to a solution containing dissolved polyvinyl alcohol, whereby the polyvinyl alcohol can be broken down into short, oligomeric fragments in a controllable manner.
  • the pH of the solution and the amounts of hydrogen peroxide and iron salt may be used to control the degradation rate of the polyvinyl alcohol into oligomeric vinyl alcohol.
  • a method to manufacture oligomeric vinyl alcohol by means of chain scission may comprise
  • a higher concentration of the Fenton's reagent improves the reaction kinetics and facilitates the degradation of the PVA.
  • the degradation reaction with Fenton's reagent typically occurs at a temperature in the range of 20 to 40°C and when the pH of the solution is between pH 3 and pH 6. A low pH value below 3 may inhibit the reaction.
  • the reaction temperature is in the range of 25 to 30°C.
  • the reaction efficiency declines, which is due to the accelerated decomposition of H 2 O 2 into oxygen and water.
  • Sequential addition of the hydrogen peroxide may be necessary to moderate the rise in temperature, which may occur as the oxidation reaction proceeds.
  • Aqueous solutions of FeSO 4 typically contains residual H 2 SO 4 , which has the effect of decreasing the solution pH.
  • the addition of H 2 O 2 has the effect of decreasing the solution pH.
  • concentrated polymer solutions it may thus be necessary to perform the oxidation in steps while monitoring the pH of the solution, such that after each step the pH of the solution is adjusted upwards, when necessary, for example with an aqueous solution of sodium hydroxide (NaOH).
  • Stepwise addition of the hydrogen peroxide facilitates to maintain the pH of the solution above 3, such as in the range of 4 to 5, while the reaction proceeds.
  • the oxidation reaction time may be selected on the basis of the desired oligomer length to be obtained.
  • a typical reaction time for Fenton's reagent is less than 3 hours, such as in the range of 15 to 120 minutes. However, the reaction time may be extended, if needed.
  • reaction solutions were stirred rapidly at 25°C and samples were taken at 10, 20, 30, 60, 90 and 120 minute time points from the reaction solution. Each sample that was taken was treated by a 1M solution of NaOH such that a pH 9 was reached. The insoluble phase formed thereby was removed by filtration or centrifuging.
  • the samples prepared had molar ratio of PVA : Fe 2+ : H 2 O 2 in the range of 1:2:0.2 to 1:20:2.
  • the reaction products were analyzed by means of an UV-VIS spectrophotometer (660 nm).
  • the oligomeric vinyl alcohol formed by controlled chain scission may purified, for example, by dissolving the precipitated reaction product into water and precipitating it in acetone. The purification procedure may be repeated, if needed.
  • the starting material i.e. the polyvinyl alcohol
  • the oligomeric vinyl alcohol may thereby have functional characteristics, which due to the lower molecular weight differ from the characteristics of conventional polymeric PVA.
  • the oligomeric vinyl alcohol may thus be provided with desired functionality.
  • vinyl acetate monomers may be oligomerized from vinyl acetate monomers in the presence of suitable initiator and chain transfer agent.
  • suitable initiator and chain transfer agent See US20030050394 A1 , which discloses an exemplary method for producing oligomeric vinyl acetate by radical polymerization of vinyl acetate monomers in the presence of di -tert- butyl peroxide as initiator and using isopropanol (2-propanol) as a chain transfer agent.
  • the formed vinyl acetate oligomer may be partially saponified in the presence of a base catalyst and an inert solvent, thereby forming oligomeric vinyl alcohol having a desired amount of hydroxyl groups.
  • the degree of oligomerization may be experimentally determined by the ratio of monomer (i.e. vinyl acetate) to chain transfer agent.
  • Suitable initiators for the oligomerization are common free-radical polymerization initiators, such as dibenzoyl peroxide or 2,2'-azo-bis-isobutyronitrile.
  • di- tert -butyl peroxide is used as the initiator because the tert-butanol that is produced during the initiation can easily be removed from the reaction mixture by distillation.
  • Concentrations of 0.5 to 4 mol.%, with respect to the amount of vinyl acetate are generally suitable, as the degree of oligomerization is affected only slightly by the concentration of initiator.
  • Isopropanol is a preferably used chain transfer agent, which also acts as a solvent and can easily be removed by distillation after the reaction.
  • the boiling point of the chain transfer agent may be selected as the reaction temperature.
  • the method enables manufacturing of oligomeric vinyl alcohol wherein the number of repeat units may be less than 30, preferably in the range of 2 to 15, most preferably 6 to 12.
  • a still alternative method to manufacture oligomeric vinyl alcohol is free radical polymerization of vinyl acetate monomers in the presence of a chain transfer agent such as chloroform and subsequent hydrolysis of the thereby formed oligomeric vinyl acetate, thereby forming oligomeric vinyl alcohol.
  • a chain transfer agent such as chloroform
  • the above-referred method is modified by reducing the concentration of the monomer used as a reagent, shorter oligomeric fractions of vinyl acetate may be produced.
  • the oligomeric vinyl acetate can be hydrolyzed into oligomeric vinyl alcohol.
  • chloroform as both solvent and chain transfer agent
  • Figure 5 illustrates, by way of an example, a water-based acetalization reaction of an organic molecule MOL1 comprising both an aldehyde group and a functional vinyl group with oligomeric vinyl alcohol OLG1, such that an acetal compound CMP1 based on the oligomeric vinyl alcohol OLG1 is formed, wherein the acetal compound CMP1 contains functional vinyl groups grafted onto the oligomeric structure.
  • Acetalization reaction as disclosed herein refers to a reversible chemical reaction comprising an acid catalyst, such as sulphuric acid, that is used to provide acidic condition to a water-based medium, thereby initiating a reaction wherein two hydroxyl groups of the oligomeric vinyl alcohol OLG1 are reacted with the aldehyde group of the organic molecule MOL1 which in acidic conditions leads to the formation of an acetal compound CMP1.
  • an acid catalyst such as sulphuric acid
  • the balance of the acetalization reaction is on the acetal side, thereby providing acetal compound CMP1 wherein two hydroxyl groups of the oligomeric vinyl alcohol have been covalently bonded to the carbonyl group of the aldehyde.
  • the water-based acetalization reaction may be performed in 1 hour or less, such as in the range of 20 to 60 minutes.
  • the reaction temperature may be above room temperature, such as in the range of 20 to 99°C.
  • the reaction temperature is above 50°C, as a higher reaction temperature correlates with accelerated reaction kinetics.
  • the acetalization reaction may be terminated by adjusting the solution pH to 7, for example by addition of a suitable neutralizing agent, such as sodium hydroxide.
  • a suitable neutralizing agent such as sodium hydroxide.
  • the neutralization step which terminates the acetalization reaction is preferably followed by a purification with acetone precipitation. Purification removes unreacted reactant and any by-products, such as inorganic salts, formed due to the neutralization step from the acetalized reaction solution.
  • Coating of the cellulose fiber-based support layer with unpurified acetalized reaction solution may result in further, undesired reactions on the surface of the cellulose fiber-based support layer. This may cause problems in novel high-speed release liner applications, wherein higher bonding strength and lower release values are needed between the paper substrate and the release layer.
  • Analytical method to evaluate the efficiency of the acetalization reaction from a reaction solution or from a paper substrate surface may comprise
  • the analytical method may be performed, for example, with HeadSpace-GC-MDS equipment, wherein e.g. unreacted 10-undecenal may be detected by its specific retention time, i.e. the time needed for this specific component to flow through the separation column of the gas chromatography device.
  • Analytical comparison of an unreacted solution and reacted solution may thus be used to provide a comparison, wherein the amount of unreacted 10-undecenal in the acetalization reaction is calculated from the integrated surface areas of the peaks of a solution before and after an acetalization reaction.
  • 1 H-NMR proton nuclear magnetic resonance
  • Molar fraction of vinyl groups per vinyl alcohol unit can be determined using the 1 H-NMR spectrum by calculating the relative peak areas for one proton from both vinyl group and PVA backbone.
  • the NMR results may further be used to determine how much of the aldehyde reactant has been consumed in the acetalization reaction.
  • lodometric titration in this context refers to a method based on the Wijs method according to standard ISO 3961:2009(E) wherein a known excess of iodine monochloride is added to a sample, which results in a reaction between the iodine monochloride and any double bonds present in the sample.
  • the quantity of iodine monochloride that has reacted with the double bonds present in the sample is determined by reacting the remaining residual iodine monochloride with a known excess of potassium iodide to form iodine, the stoichiometric quantity of which is then determined by titration with a solution of sodium thiosulphate of known concentration.
  • an iodine value of the sample is obtained that specifies the amount of iodine in grams that can formally be added to the double bonds in a known amount of the sample and from which the quantity of double bonds in the sample may then be determined.
  • Vinyl groups are double bonds and low molecular weight polyvinyl alcohol, as such, does not contain double bonds. Therefore, iodometric titration is a specific method that can be used to investigate the amount of vinyl groups present in a sample of acetalized polyvinyl alcohol and to determine the vinyl group molality of the sample.
  • the iodometric titration method based on the Wijs method may be used to measure the total number of vinyl double bonds present in a sample of oligomeric vinyl alcohol compound that has been acetalized with an aldehyde that contains a functional vinyl group, such as 10-undecenal or 2,2'-dimethyl-4-pentenal.
  • the iodometric titration method is based on a measured volume of iodine monochloride in acetic acid (Wijs solution) which may be added to the reaction solution containing the acetalized oligomeric vinyl alcohol compound, whereby the iodine monochloride reacts according to Equation 3 (below) with the double bonds of the vinyl groups present in the oligomeric vinyl alcohol compound that has been acetalized such that the electrophilic addition reaction produces a dihalogenated single bond, of which one carbon has bound an atom of iodine.
  • acetic acid Wijs solution
  • the iodine monochloride is a light-sensitive reagent and needs to be stored and incubated in the dark. After 1-hour incubation in the dark, the quantity of iodine that has reacted in the electrophilic addition reaction is determined by adding a measured volume of potassium iodide solution (15%, weight/volume) to the reaction solution, which causes the remaining unreacted iodine chloride in the reaction solution to form molecular iodine according to Equation 4 (below). Equation 4: ICl + KI ⁇ KCl + I 2
  • Equation 5 I 2 + 2 Na 2 S 2 O 3 ⁇ 2 NaI + Na 2 S 2 O 4
  • the iodometric titration thus enables to determine an iodine value, which is a measure of the amount of iodine in grams that have reacted with the functional vinyl groups in a known amount of the oligomeric vinyl alcohol compound, as presented in Equation 6 (below).
  • Iodine value B ⁇ A N ⁇ 12 , 7 g 100 g m
  • A is thiosulfate consumption in milliliters of a test sample (oligomeric vinyl alcohol compound that has been acetalized)
  • B is thiosulfate consumption of a blank sample containing only the measured volume of iodine monochloride in acetic acid and the measured volume of potassium iodide solution
  • N is the normality (mol/l) of the thiosulfate solution
  • m is the mass in grams of the test sample (oligomeric vinyl alcohol compound that has been acetalized).
  • a sample containing only the low molecular weight polyvinyl alcohol used in the acetalization reaction may be used as a blank sample, instead. Blank samples containing only low molecular weight polyvinyl alcohols may also be used if the samples have been obtained from different types of low molecular weight polyvinyl alcohols.
  • b vin B ⁇ A N m
  • the thiosulfate consumption of a 2.5 g test sample of oligomeric vinyl alcohol compound that has been acetalized in iodometric titration is 35 milliliters
  • the thiosulfate consumption of a blank sample is 48 milliliters and the normality of the thiosulfate solution is 0.1 mol/l
  • the reaction solution is first cleaned by purification, which comprises:
  • the quantity of functional vinyl groups (i.e. the vinyl group molality) may then be measured by iodometric titration method, which comprises:
  • the starch indicator is added before the titration to visualize the end-point, which is observed as fading of the dark blue or purple color of the solution.
  • the M w of oligomeric vinyl alcohol compounds can be determined by gel permeation chromatography (GPC) combined with static light scattering.
  • the M w is measured from re-acetylated specimens by methods known from the literature, for example in a pyridine/acetic anhydride mixture.
  • the M w represents the mean average weight of the oligomeric vinyl alcohol compound.
  • viscosity herein refers to a measure of the internal friction occurring in the displacement of two adjacent liquid layers, as defined in standard DIN 51 550. Viscosity is a property of a fluid that resists the force tending to cause the fluid to flow. Viscosity of a polymer solution is dominated by short-range attractive intermolecular forces within the solution. The viscosity behavior of a solution during a reaction may be measured with a viscometer. Unless otherwise stated, the values refer to viscosity ⁇ given in units of mPa ⁇ s (millipascal-second) according to the international system of units (SI). The viscosity values have been determined by using a Brookfield viscometer from aqueous solutions having a temperature of 25°C at 100 rpm, according to the manufacturer's instructions.
  • Figure 6 illustrates the results of a comparative experimental study, wherein the viscosity was measured from water-based acetalization reaction products as a function of modification degree, using 10-undecenal as reactant.
  • the vertical axis in Figure 6 represents the viscosity value of the reaction mixture in millipascal-seconds (mPa ⁇ s) on a logarithmic scale.
  • the horizontal axis in Figure 6 represents the vinyl group molality b vin (mmol/g).
  • the viscosity ⁇ was measured as a function of the vinyl group molality b vin from reaction solutions denoted as samples A, B, C, D, E or F.
  • Each sample A, B, C, D, E and F contained polyvinyl alcohol of a specific grade.
  • the specific grade refers to the degree of hydrolysis and the degree of polymerization of the polyvinyl alcohol.
  • Table 2 discloses the characteristics of the grades of polyvinyl alcohol used in samples A-F. Samples A, B, C, D and E represented fully hydrolyzed grades having a degree of hydrolysis equal to or higher than 97%, whereas sample F was a partially hydrolyzed grade having a degree of hydrolysis of 88%, respectively.
  • Sample A was a reference sample containing commercial polyvinyl alcohol with a degree of hydrolysis of 98%, the degree of polymerization P w of ca. 2800 and a M w of ca. 125000 g/mol. Table 2. M w (g/mol) and degree of polymerization P w of the polyvinyl alcohol grades used in the comparative experimental study. Sample M w (g/mol) P w A 125000 2800 B 61000 1400 C 47000 1000 D 27000 600 E 16000 360 F 14000 270
  • Each sample A-F was prepared in the same manner by mixing polyvinyl alcohol into water and heating and stirring the mixture for 2 hours at 90°C until a solution was obtained that contained a 12% solids content (i.e. dry matter content) and subsequently adjusting the pH of the solution with sulfuric acid.
  • the pH of the solution was measured to be 1.5 prior to adding 10-undecenal, which was used as the reactant for the water-based acetalization reaction.
  • the solution was stirred vigorously during the synthesis to ensure a reaction with the reactant, which was not water-soluble.
  • the synthesis was continued for 25 minutes at a temperature of 90°C and the pH was then adjusted to 7 by adding sodium hydroxide (1M solution).
  • the solution containing the reaction product was subsequently allowed to cool down to room temperature before measurement of the viscosity of the sample thus prepared.
  • sample B at a vinyl group molality of 0.09 mmol/g correlates with a 1.5 wt.-% degree of modification.
  • the leftmost dashed vertical line p1 denotes a sample with a vinyl group molality of 0.06 mmol/g.
  • the viscosity of sample A was already 50000 mPa ⁇ s, whereas the viscosity of sample B was ca.1200 mPa ⁇ s.
  • the vertical line denotes a vinyl group molality of 0.12 mmol/g.
  • the viscosity of sample A was too high for measurement.
  • the viscosity of sample B had also increased rapidly and was already around 7200 mPa ⁇ s, which had a significant effect on the flow behavior of the solution.
  • the degree of modification of sample B was 0.15 mmol/g. the viscosity of the solution had already risen to 26000 mPa ⁇ s, which rendered the sample unsuitable for coating on a cellulose fiber-based support layer by conventional means used in the industry.
  • the dashed vertical line p2 denotes a vinyl group molality of 0.17 mmol/g.
  • the viscosity of sample B was already ca.100000 mPa ⁇ s and the viscosity of sample C was already ca.20000 mPa ⁇ s.
  • the dashed vertical line p3 denotes a vinyl group molality of 0.42 mmol/g.
  • the viscosity of fully hydrolyzed sample E was already above 10000 mPa ⁇ s.
  • the viscosity of the partially hydrolyzed sample F was ca.3000 mPa ⁇ s.
  • the comparative experimental study demonstrates how the viscosity ⁇ behaved as a function of vinyl group molality in the samples A-F, when 10-undecenal was used as a reactant.
  • the examples 1 to 4 below illustrate in practice how the invention may be carried out and present some advantageous effects that the use of a compound based on oligomeric vinyl alcohol may provide on a paper substrate primer layer.
  • the abbreviation w/v denotes weight per volume
  • the abbreviation w/w denotes weight per weight.
  • the modified oligomeric vinyl alcohol refers to a compound based on oligomeric vinyl alcohol that has been modified to contain vinyl groups.
  • the solution was subjected to Fenton oxidation reaction by adding an amount of 1.87 grams of aqueous iron(II) sulfate solution (1% w/v) and 2.49 grams of aqueous hydrogen peroxide (30% w/w) into the solution.
  • the mixture thus obtained was then stirred for 16 hours, thereby allowing the polyvinyl alcohol to degrade into oligomeric vinyl alcohol by means of a controlled chain scission of the polymer.
  • the chain scission reaction was stopped by adjusting the pH of the mixture to 7.
  • the obtained reaction product was an oily solution of oligomeric vinyl alcohol wherein the solution, at a temperature of 25°C, had a Brookfield viscosity of 75 mPa ⁇ s, when measured at 100 rpm.
  • the agitation was continued for 2 hours at the temperature of 90°C, thereby reacting the reactant with the dissolved oligomeric vinyl alcohol in a water-based acetalization reaction such that compound based on the oligomeric vinyl alcohol was formed.
  • the pH of the reaction mixture was then adjusted to a pH value 7 with sodium hydroxide and cooled down to 25°C.
  • the formed compound had a Brookfield viscosity of 450 mPa ⁇ s, when measured at 100 rpm.
  • solutions containing oligomeric vinyl alcohol having a very low M w of less than 1000 g/mol, such as in the range of 440-880 g/mol, may be used to suppress the rise of viscosity during an acetalization reaction with organic molecule.
  • Glassine paper sheets (UPM Golden) were coated with the aqueous PVA solutions using a laboratory blade coater, thereby obtaining paper substrates with a primer layer that contained either unmodified polyvinyl alcohol, polyvinyl alcohol grafted with 10-undecenal or a compound based on oligomeric vinyl alcohol.
  • the amount of coating applied on each glassine paper sheet was 2 g/m 2 .
  • the paper substrates thus prepared were dried at 105°C for 1 minute. All paper substrates were subsequently subjected to siliconization, which refers to coating of a paper substrate with silicone resin prepared of Wacker Dehesive SFX 251 and V525 cross-linker, using C05 catalyst (all components provided by Wacker).
  • the silicone resin applied on the paper substrate was prepared by stirring 100 parts per weight of the Dehesive SFX 251 with 14.4 parts of the V525 cross-linker for 2 minutes, then adding 1 part of the C05 platinum catalyst and stirring for 5 minutes. Thus the amount of platinum in the formed silicone resin was 10 ppm.
  • the silicone resin thus prepared was then applied on top of the paper substrate by blade coater and cured for 30 seconds at 105°C, thereby curing the silicone resin into a release layer and forming a release liner. Each paper substrate was coated with an amount of 1.2 g/m 2 of the silicone resin thus prepared.
  • the silicone adhesion was tested immediately after the siliconization from the formed release liner. This is referred to as the initial rub off level.
  • the level of silicone adhesion in each release liner sample was determined with a semi-automatized method, wherein the amount of silicone was measured using an x-ray fluorescence spectrometer (Oxford Lab-X-3000) before and after a defined amount of rubbing of the release liner sample.
  • the release liner sample was placed on top of a felt, such that the siliconized surface of the release liner sample was facing the felt.
  • the rubbing was performed by pressing the sample with constant pressure against a felt and rotating the sample 10 times around its axis, to increase reliability and comparability of the result.
  • 2- and 7-day measurements the release liner was tested after removing the label from the laminate. Thus the 2- and 7-day measurements were performed on surfaces that had been in contact with an adhesive.
  • the release coating applied on the paper substrate was a fast curing silicone system (SFX251 dehesive, V525 cross-linker) wherein the amount of platinum was 10 ppm.
  • sample type vinyl group molality (mmol/g) relative rub-off value (%) 0 d 2 d 7 d unmodified polyvinyl alcohol 0 10 9 10 modified polyvinyl alcohol 0.09 15 7 9 modified oligomeric vinyl alcohol 0.5 98 97 95 modified oligomeric vinyl alcohol 0.9 99 99 100
  • the release liner samples containing compound based on oligomeric vinyl alcohol presented good relative rub-off values, which remained relatively consistent over time, unlike the samples containing either unmodified or modified polyvinyl alcohol.
  • the paper substrates containing compound based on oligomeric vinyl alcohol demonstrated a surprisingly large difference in silicone adhesion levels, when relative rub-off was measured, and thus provided better anchorage capability for the silicone system.
  • a compound based on oligomeric vinyl alcohol thus enabled the use of a fast curing silicone resin with a very low platinum level.
EP18199296.7A 2018-10-09 2018-10-09 Papiersubstrat mit vinylalkohol-oligomeren, die zum enthalten von verketteten kohlenstoffstrukturen mit funktionellen vinylgruppen modifiziert sind Pending EP3636833A1 (de)

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EP18199296.7A EP3636833A1 (de) 2018-10-09 2018-10-09 Papiersubstrat mit vinylalkohol-oligomeren, die zum enthalten von verketteten kohlenstoffstrukturen mit funktionellen vinylgruppen modifiziert sind
PCT/FI2019/050711 WO2020074773A1 (en) 2018-10-09 2019-10-03 A paper substrate comprising vinyl alcohol oligomers modified to contain catenated carbon structures with functional vinyl groups

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WO2021255333A1 (en) * 2020-06-15 2021-12-23 Upm-Kymmene Corporation Support layer for a release liner

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WO2011104427A1 (en) 2010-02-23 2011-09-01 Ahlstrom Corporation Cellulose fibre - based support containing a modified pva layer, and a method its production and use
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WO2021255333A1 (en) * 2020-06-15 2021-12-23 Upm-Kymmene Corporation Support layer for a release liner

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