Technical field This invention relates to a support layer for a release liner. This invention further relates to a method for providing coating layers on a paper suitable for use as a layer of a release liner.

Background

A label laminate typically comprises a face layer and a release liner, which are laminated together. A release liner refers to a product comprising typically a support layer and a release coating layer applied on at least one side of the support layer.

Release liners are typically made of cellulosic materials or plastic film materials, which are siliconized to enable smooth release of an applied adhesive layer. For the silicone to function properly, it must be properly anchored to the underlying substrate. Some level of anchorage can be achieved by weak interactions (e.g. hydrogen bonding) between silicone and hydroxyl groups of cellulose. However, these interactions are not very stable and deteriorate over a period of time. Typically, rub-off tests are used for determining the anchorage level of the silicone. Values from the rub-off tests can be used to determine how easily the silicone can be rubbed off from the surface of the release liner.

Summary

This invention relates to a support layer for a release liner, which support layer comprises a paper. This invention further relates to a method for providing a coating layer on a paper suitable for use as a layer of a release liner.

Aspects of the invention are characterized by what is stated in the independent claims. Preferred embodiments are disclosed in the dependent claims. These and other embodiments are disclosed in the description and figures. According to a first aspect, there is provided a support layer for a release liner, which support layer comprises a paper. According to a second aspect, there is provided a method for manufacturing a support layer suitable for use as a layer of a release liner.

A method for providing a coating layer comprising polyvinyl alcohol derivative on a paper suitable for use as a support layer of a release liner can comprise the following steps

- providing a paper having a first side and a second side,

- forming a first coating layer by applying a first coating on the first side of the dry paper, thereby obtaining the first coating layer, which first coating layer has a coat weight in a range between 0.6 g/m ² and 5 g/m ² , preferably in a range between 1 g/m ² and 3 g/m ² , when measured as a dry weight of the first coating layer,

- forming a second coating layer by applying a second coating having a temperature of less than 90°C on the first coating layer, thereby obtaining the second coating layer, wherein a contacting element, such as an applicator roll or a metering element, is used to apply and/or meter the second coating, wherein the second coating is aqueous solution, which aqueous solution contains polyvinyl alcohol derivative, which polyvinyl alcohol derivative

- has a degree of hydrolysis in the range of 60% to 100%, and

- contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative, the second coating layer having a coat weight in the range of 3 mg/m ² to 200 mg/m ² when measured as a dry weight of the polyvinyl alcohol derivative.

The step wherein the dry paper is provided may comprise the following steps:

- forming a paper web on a forming section of a paper machine, and

- drying the paper web on a drying section of the paper machine thereby obtaining a dry paper having a first side and a second side. Advantageously, the coatings are applied before calendering the support layer with at least one calender, preferably with a supercalender. This may improve the quality of the second coating and, hence, the quality of the manufactured support layer.

A support layer for a release liner can have a paper comprising a first side and a second side. The support layer can comprise

- a first coating layer on the first side of the paper,

- a second coating layer on the first coating layer, which second coating layer contains polyvinyl alcohol derivative which has a degree of hydrolysis in the range of 60% to 100%, the polyvinyl alcohol derivative containing pendant vinyl groups which are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative, wherein

- the first coating layer has a coat weight in the range of 0.6 to 5 g/m ² , when measured as a dry weight of the coating, and

- the second coating layer has a coat weight in the range of 3 to 200 mg/m ² , when measured as a dry weight of the polyvinyl alcohol derivative.

In an example, the polyvinyl alcohol derivative has a degree of hydrolysis of at least 60%, preferably in the range of 70% to 100% and contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative. This structure and length of the catenated carbon structure, which is preferably a linear hydrocarbon chain, is advantageous for reducing the polarity of the formed compound. This may enable using lower amounts of platinum catalyst and fast curing silicone compounds, which facilitates the manufacturing of a release liner with improved release characteristics.

The first coating is applied at least on the first side of the paper. The first coating can be applied on the first side or on the both sides of the dry paper. Further, the second coating can be applied on the first side or on the both sides of the dry paper. However, the second coating is applied, at least, on the first coating layer on the first side of the paper.

The temperature of the aqueous solution may be less than 90°C, preferably equal to or less than 80°C, more preferably less than 75°C, such as equal to or less than 70°C and most preferably equal to or less than 65°C. Thus, the aqueous solution is not preferably in a form of steam. The technical effect of the temperature is to provide substantially even coating comprising polyvinyl alcohol derivative on the first coating layer. Thanks to said temperature of the aqueous solution, the second layer may not have big holes. For example, by using too hot temperatures, such as steam, the second layer may not be as even as it could be by using said temperature level. Still further, by using low temperatures, the manufacturing costs may be decreased. Still further, temperature has an effect on solubility of the (partially) hydrolyzed polyvinyl alcohol derivative. Thus, the temperature can be selected according to suitable solubility of the polymer.

Further, said temperature of the aqueous solution is preferably at least 25°C, more preferably at least 35°C, and most preferably at least 45°C. The technical effect of said minimum temperatures is to decrease viscosity of the aqueous solution, which can improve the pumping process of the aqueous solution. Therefore, easiness of applying the second coating can be improved. Still further, temperature has an effect on solubility of the (partially) hydrolyzed polyvinyl alcohol derivative. Thus, the temperature can be selected according to suitable solubility of the polymer.

Therefore, by controlling the temperature level so that the temperature of the aqueous solution is not too high or too low, it may be possible to obtain both, good viscosity for the aqueous solution and good evenness for the second layer. Further, the production costs can be decreased. Thus, advantageously, the temperature level is not too low nor too high.

The first coating layer can comprise polyvinyl alcohol, and/or starch, and/or carboxymethyl cellulose, and/or ethylene-vinyl alcohol copolymer.

Advantageously, said polymers comprise at least 25 dry wt.%, such as from 25 dry wt.% to 80 dry wt.%, more preferably equal to or more than 30 wt.%, such as from 35 wt.% to 60 wt.%, and most preferably equal to or more than 40 dry wt.% of the first coating layer, calculated from the total dry weight of the first coating layer. The first coating layer can further comprise e.g. additives and mineral pigments.

Preferably, the first coating comprises polyvinyl alcohol, and/or carboxymethyl cellulose, and/or ethylene-vinyl alcohol copolymer. More preferably, the first coating comprises, at least, polyvinyl alcohol and/or ethylene-vinyl alcohol copolymer. Most preferably, the first coating comprises, at least, polyvinyl alcohol.

The method can further comprise the following step: drying the obtained first coating layer before applying the second coating on the first coating layer.

A technical effect is that it can be possible to obtain a very thin second coating layer on the first coating layer, wherein the vinyl groups are mainly on the surface of the coated paper and the second coating is not penetrated into the first coating layer. The drying step may be particularly advantageous due to the contacting element, which contacting element may cause some load on the second coating which has been applied on the first coating. However, in some application, the first coating layer may not be dried before the second coating is applied on the first coating layer.

The first coating may be applied by using a first application unit.

The first coating may be applied by using a blade coating or a rod coating, wherein the blade or the rod is directly in contact with the first side of the paper, and there may be a backing roll on the second side of the dry paper.

Alternatively, the first coating may be applied by using a film transfer coating, wherein the first coating is first applied onto a first applicator roll of the first application unit and then transferred onto the first side of the paper in a roll nip. Alternatively, the first coating can be applied by using a surface sizing, wherein the first application unit comprises a first sizer. In this embodiment, the first coating may be first applied onto a first applicator roll of the first sizer and then transferred to the first side of the dry paper. Alternatively, the first coating may be fed to a pond and then transferred to the first side of the dry paper from the pond. Alternatively, the first coating can be sprayed directly to the first side of the dry paper by using spraying nozzles of the first sizer. The second coating containing the water-soluble polyvinyl alcohol derivative may be applied onto the first coating layer by using a second application unit. The second application unit may comprise a contacting element. By using a coating method with a contacting element, it is possible to apply a thin coating layer on to the surface of the first coating layer.

Thus, the second coating can be applied onto the first coating layer by using a contacting element. The contacting element may comprise a blade or a rod. In this case, the contacting element can be directly in contact with the substate having the first coating. In this embodiment, said blade or rod is preferably on the first side of the paper and there can be a backing roll on the second side of the paper. This kind of direct coating method can be used to decrease manufacturing costs of the release liner. Further the direct coating method can improve the evenness of the surface of the product. Still further, the direct coating method may provide improved properties for the support layer.

The second application unit may comprise a sizer, and the contacting element may comprise a roll nip. In this embodiment, the second coating may be fed to a pond. The second coating can be applied via the pond on the first coating layer after which the paper may be led through the roll nip. For this method, a high drying capacity may be needed. However, the sizer may be suitable for coating both sides of the paper simultaneously. Thus, thanks to the sizer comprising the pond and the roll nip, it may be possible to apply coatings for both sides of the paper at the same time. Therefore, this application method may be particularly suitable for coating both sides of the paper. Alternatively, the second coating may be applied onto the first coating layer by using film transfer coating. In this embodiment, the second coating can be first evened out onto the surface of the applicator roll and then transferred onto the first coating layer. In this embodiment, the contacting element may comprise a roll nip. There may be backing roll forming a roll nip together with the applicator roll and the paper may be led through the roll nip. With said film transfer coating, it is possible to obtain thin, substantially even, continuous layer on the surface of the first coating layer. This method can be particularly suitable for coating only one side of the paper.

The second coating, i.e., the aqueous solution, may be applied onto the first coating layer in a form of foam. Alternatively, the second coating can be applied onto the first coating layer in a form of liquid.

Thus, the second coating can be applied onto the first coating layer in a form of foam, thereby forming a foam layer on the first coating layer. By using the foam layer, the second coating can be easily applied onto the first coating layer so that the polyvinyl alcohol derivative can effectively stay on the surface of the coatings. Further, thanks to the foam, the aqueous solution may have substantially high dry matter content, hence, the drying of the paper having the second coating may be easier than with other kind of applying methods. Advantageously, foam to be used as the second coating is first formed after which it is applied on the surface of the first coating layer. In this embodiment, the contacting element may comprise a roll nip, and the foam layer is preferably led through the roll nip.

A dry matter content of the first coating layer can be equal to or more than 90%, when the second coating is applied onto the first coating layer. This may improve the quality of the second coating. Further, the polyvinyl alcohol derivative may stay well on the surface of the substrate if the first coating layer is substantially dry when the second coating is applied on to the first coating layer.

The solids content of said polyvinyl alcohol derivative in the aqueous solution to be applied onto the first coating can be between 0.05% and 7%, wherein polyvinyl alcohol derivative - has a degree of hydrolysis equal to or more than 60%, preferably in the range of 70% to 100%, and

- contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative.

Thus, the solids content of said polyvinyl alcohol derivative in the aqueous solution is preferably equal to or more than 0.05%, more preferably equal to or more than 0.1 %, and most preferably equal to or more than 0.5% Thus, the drying costs of the second coating layer are not increased too much. Yet further, the rub-off properties of the release liner may be improved.

Further, the solids content of the polyvinyl alcohol derivative in the aqueous solution may be less than 7%, such as equal to or less than 5%, more preferably equal to or less than 3% or , and most preferably equal to or less than 2%. Thus, the production costs of the release liner having good and/or improved rub-off properties can be decreased. Further, within said range, it may be easier to obtain a thin, substantially even second coating layer, wherein the second coating is not having big holes. The second coating may also comprise other components, such as agents having an effect on the coating. Said agent may be used e.g. for improving strength or dispersibility of the coating. The second coating may comprise e.g. thickening agent(s). In an example, the second coating comprises carboxymethyl cellulose (CMC).

A support layer for a release liner can comprise a paper. The paper of the support layer comprises a first side and a second side. Further, the support layer can comprise a first coating layer on the first side of the paper, and a second coating layer on the first coating layer. The first coating may be applied on the first side or on the both sides of the paper. Further, the second coating can be applied on the first side or on the both sides of the paper, preferably on the first coating layer.

The second coating layer can contain polyvinyl alcohol derivative which has a degree of hydrolysis equal to or more than 60%, more preferably equal to or more than 70%, or equal to or more than 80%, and most preferably equal to or more than 90%. Thus, the polyvinyl alcohol derivative can be soluble in water. The solubility of the polyvinyl alcohol derivative depends on temperature. Thus, the degree of hydrolysis is preferably selected so that the solubility of the polyvinyl alcohol derivative is at a suitable level at the temperature of the second coating. For example, less than 80% hydrolyzed polyvinyl alcohol derivative may be poorly soluble at temperatures above 30- 35°C. Thus, in an advantageous example, the degree of hydrolysis is equal to or more than 80%, such as in a range between 80% and 100%. Further, said degree of hydrolysis is equal to or less than 100%, more preferably equal to or less than 99% or equal to or less than 98%, and most preferably equal to or less than 97%. The fully hydrolyzed PVOFI at degree of hydrolysis of 99-99.8% may not dissolve in water below 80°C. Further, less than 98% hydrolyzed polyvinyl alcohol, such as 97% hydrolyzed polyvinyl alcohol, may have better solubility than 98% hydrolyzed polyvinyl alcohol. Thus, in an advantageous example, the degree of hydrolysis is equal to or less than 97%, such as in a range between 80% and 97%.

The polyvinyl alcohol derivative can contain pendant vinyl groups which are part of catenated carbon structures which contain at least 4 carbon atoms, such as from 4 to 15 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative. Said structure of the polyvinyl alcohol derivative can improve the rub-off properties of the obtained product.

The first coating layer can have a coat weight in the range of 0.6 g/m ² to 5 g/m ² , when measured as a dry weight of the first coating layer. Thus, a first coating layer having substantially even surface can be obtained. Further, the second coating layer can have a coat weight in the range of 3 mg/m ² to 200 mg/m ² , when measured as a dry weight of the second coating layer. Thus, it is possible to obtain a cost-effective product having good rub-off properties.

The polyvinyl alcohol derivative used in the invention may have been obtained by means of acetalization in aqueous solvent, and/or esterification in organic solvent, and/or esterification by reactive extrusion without a solvent in a melt state. The technical effect of said acetalization in aqueous solvent is that there is no need for organic solvents. The technical effect of said esterification in organic solvent is a very low reagent residue level. Further, said esterification in organic solvent can be done off-site.

The technical effect of said esterification by reactive extrusion without a solvent in a melt state is that there are no solvents. Further, said reactive extrusion can be done off-site. Polyvinyl alcohol derivative obtained by said esterification by reactive extrusion may have very good properties, hence, advantageously, the polyvinyl alcohol derivative used in the invention has been obtained by means of esterification by reactive extrusion without a solvent in a melt state.

The second coating layer can have a vinyl group molality (b _V in) in the range of 0.05 mmol/g to 2.00 mmol/g, preferably in the range of 0.10 mmol/g to 1.10 mmol/g, and most preferably in the range of 0.15 mmol/g to 0.80 mmol/g, determined as millimoles per gram of dry polyvinyl alcohol. Thus, it is possible to obtain a product having good rub-off properties. Further, the amount of a release coating containing silicone compound may be reduced. Still further, less amount of release coating also requires less platinum catalyst for curing to take place. Because siliconizing a reactive surface layer may require less platinum catalyst for silicone curing to take place, the manufacturing costs of the release liner may be reduced.

A particular advantage of the second coating layer that contains catenated carbon structures with a vinyl group molality (b _V in) in an amount of equal to or higher than 0.05 mmol/g, preferably an amount of equal to or higher than 0.10 mmol/g, and most preferably equal to or higher than 0.15 mmol/g is that the high amount of functional vinyl groups enables the use of very fast curing silicone compounds in the release coating.

Further, the first and the second coating layers can have a total vinyl group molality (bvin) in the range of 0.00005 mmol/g to 0.33 mmol/g (i.e., 5x1 O ⁸ mol/ g to 0.33 mmol/g), preferably in the range of 0.0001 mmol/g to 0.17 mmol/g, and most preferably equal to or more than 0.00015 mmol/g and equal to or less than 0.013 mmol/g, determined as millimoles per gram of the dry polyvinyl alcohol. Thus, it is possible to obtain a support layer having very small amount of polyvinyl alcohol derivative which product has good rub-off properties. Thanks to the small total vinyl group molality, the manufacturing costs of the release liner may be reduced.

Preferably, the vinyl groups, or at least most of the vinyl groups, are on the surface of the substrate, i.e., within the second coating layer. The first coating layer can have a vinyl group molality (bvin) of less than 0.00005 millimoles per gram of the dry coating layer. This can decrease the amount of the polyvinyl alcohol derivative that is needed for good rub-off properties. Further, this may decrease the manufacturing costs of the product. Further, the production efficiency can be improved.

The polymer used for the second coating layer may have (but not need to have) sufficiently low molecular weight in order to avoid high viscosity. The polyvinyl alcohol derivative may have weight average molecular weight (M _w ) of less than 100000 g/mol, more preferably equal to or less than 80000 g/mol, and most preferably equal to or less than 50000 g/mol. Typically, the lower is the weight average molecular weight (M _w ) of the polymer, the lower is the viscosity of the polymer. Thus, an easiness of the manufacturing process of the product may be improved. However, in another example, the polymer does not have said sufficiently low molecular weight.

A grammage of the support layer can be from 35 to 120 gsm. Thus, the support layer can be easily treated in a production line.

A total grammage of coatings on the paper can be, e.g. from 0.6 g/m ² to 5.2 g/m ² . A grammage of the polyvinyl alcohol derivative on the support layer can be at least 5 mg/m ² , preferably at least 10 mg/m ² , and/or

100 mg/m ² at the most, preferably equal to or less than 60 mg/m ² when calculated as total dry weight of the polyvinyl alcohol derivative. Thus, the coatings can mainly comprise cheaper coating(s) having good properties for the product and only minor amounts of more expensive polyvinyl alcohol derivative providing good rub-off properties for the product. Silicone anchorage can be drastically improved by coating the substrate with a layer of water-soluble functionalized polymer that contains terminal carbon- carbon double bonds, i.e. vinyl groups.

Conventional coating methods are using large amounts of modified polymer (typically 1-2 gsm) to ensure sufficient functionality at the surface. Therefore, an on-site modification reactor is typically required. The novel solution can decrease the amount of vinyl groups needed for the silicone anchorage; hence, the novel solution can decrease the amount of polyvinyl alcohol derivative needed for the product. Thus, the novel solution can decrease the manufacturing costs and improve the production efficiency of the product. Further, number of pinholes may be reduced. Further, air permeability properties of the coating(s) may be improved.

Brief description of the drawings

In the following, the invention will be illustrated by drawings in which

Fig. 1a shows, by way of an example, a label laminate comprising a release liner, an adhesive layer, and a face layer,

Fig. 1b illustrates a support layer for a release liner, Figs 2a-b show, by way of an example, methods for providing a coating layer on a paper, and

Figs 3a-4b show some results from experimental tests. The Figures are intended to illustrate the general principles of the disclosed solution. Therefore, the illustrations in the Figures are not necessarily in scale or suggestive of precise layout of system components. Detailed description In the text, references are made to the Figures with the following numerals and denotations:

10 forming a paper web,

20 drying a paper web, 30 applying a first coating,

40 applying a second coating,

LABEL1 label laminate, REL1 release liner, FACE1 face layer, PAP1 paper, SUP1 support layer comprising a paper PAP1 , ADH1 adhesive layer, RELCT1 release coating layer, COAT coating on the paper, COAT1 first coating layer on the paper, and COAT2 second coating layer on the first coating layer.

In this application the term “label laminate” LABEL1 refers to so called pressure sensitive label laminates and self-adhesive label laminates. The label laminate LABEL1 can comprise two layers which are laminated together, i.e. a release liner REL1 and a face layer FACE1 , wherein an adhesive layer ADH1 is provided between the release liner REL1 and the face layer FACE1.

The term “face layer” FACE1 refers to “the top layer” of the label laminate, also called as the face stock. The face layer FACE1 comprises at least one layer that is attached to another surface with an adhesive layer ADH1, when the label laminate LABEL1 is used. The face layer FACE1 may consist of plastic layer(s), for example polypropylene film(s) and/or polyethylene film(s). The product consisting of the face layer(s) FACE1 and the adhesive layer(s) ADH1 is called a lineriess label. In other words, it is not same product as the label laminate LABEL1 , which also comprises the release liner REL1. The term “release liner” REL1 refers to a product comprising a support layer SUP1 as base material and at least one release coating layer RELCT1 on the support layer SUP1. In other words, the support layer SUP1 may be coated with a thin layer of release agent, such as silicone. Therefore, the release liner REL1 may be easily removed from the face layer FACE1 when the label is adhered to a substrate. The release liner REL1 is used to protect the adhesive layer ADH1 of the label laminate LABEL1 and to allow efficient handling up to the point where the label is dispensed and adhered to a substrate surface.

A release liner comprising a plurality of adhesive labels is referred to as a label stock. A label stock may be wound on a roll and used in a labelling process. The number of products to be labelled in a labelling process may be very large. A roll of release liner may comprise even several kilometers of winded release liner.

The term “support layer” refers to a coated paper suitable for use as a layer of a release liner. The paper is typically manufactured on a paper machine. The term “label” refers to a die-cut face layer.

In this application, the term “CCK paper” relates to a clay coated kraft paper. CCK paper are known to a person skilled in the art. In this application, the term “glassine paper” refers to a heavily calendered, substantially smooth and glossy paper. Glassine papers are known to a person skilled in the art.

In this application, the weight average molecular weight is referred as M _w

Unless otherwise stated, the following standards refer to methods which may be used in obtaining stated values of parameters representing paper or pulp quality:

Grammage: ISO 536, and Thickness: ISO 534. The novel solution relates to a coating method for applying polymers onto cellulosic release liner base materials. The coating method may be an offline coating method. Preferably, the coating method is an online coating method.

Silicon anchorage is typically mainly relying on OH groups on top of the coating. The OH groups can bond the silicon on the coating and, hence, on the paper. For example, moisture and heat together can affect the bond between silicon and the substrate. Thus, one object of the invention is to form vinyl groups sticking out of the substrate so that they can connect to a silicon polymer structure and have a better hold out through aging, despite of moisture and heat.

In the novel method, a first coating layer is first applied onto the cellulosic release liner base material, after which a second coating layer, which may be a very thin layer having a grammage of equal to or less than 200 mg/m ² , is applied onto the first coating layer. Thanks to the second coating layer, a paper may have on its surface high amount of vinyl groups that are attached to polyvinyl alcohol side chain.

The second coating may be applied by using a direct coating method comprising a contacting element, which may be either an applicator or a metering element. The applicator may comprise a roll, onto which the coating film is either applied in desired thickness or applied in excess and metered down to desired thickness. The roll then transfers the coating film onto paper web by direct contact. The coating may also be applied as a pond on top of a roll nip and the paper substrate passes through this pond and the underlying nip. Coaters with contacting applicator include metering size press, roll coater, roll moisturizer, and pond application coater. The metering element preferably comprises a blade or a rod on the first side of the paper. Further, there may be a backing roll on the second side of the paper. The contacting element is preferably the applicator, because it can apply coating with any viscosity, even water. Metering coaters need sufficient viscosity because coating color must remain on the web for a brief period of time before reaching the metering element. In the direct coating, the second coating may be fed in excess onto the paper, after which the coat layer can be metered down to the final thickness by using a contacting element in order to obtain the desired coat weight.

Alternatively, the second coating may be metered before it is applied on the first coating. The second coating may be applied on the first coating by using a contacting element, such as an applicator roll.

The contacting element preferably comprises a blade, a rod, or a roll on the first side of the paper. Further, there may be a backing roll on the second side of the paper. Thanks to the novel method, wherein the second coating is applied on to the first coating by using a coating method comprising a contacting element, several advantages may be obtained. For example, it may be possible to obtain improved properties of the product as well as cost effective manufacturing method.

The second coating unit may comprise an applicator, which feeds the second coating onto the first coating.

In an example, there is a certain (i.e., predetermined) distance between a first location wherein the second coating is applied and a second location wherein the second coating is metered down. Said distance may give some time for the second coating to set on the paper (i.e., dwell time), after which the second coating layer can be metered down to the final thickness by using a contacting element in order to obtain the desired coat weight.

In another example, the second coating is metered before applying on the first coating. In this example, the second coating may be applied on the first coating by using a contacting element, such as an applicator roll.

Advantageously, the second coating is applied by the applicator roll. Thus, the second coating can be applied on the first coating by using the applicator roll, wherein the second coating is first evened out onto the applicator roll and then transferred onto the first coating. There may also be a backing roll forming a roll nip with the applicator roll. This kind of coating method may be used to improve evenness of the second coating layer, even with a substantially thin coating layer. Further, the applicator roll may improve the easiness of the application processes. Still further, the applicator roll may be used with aqueous solutions having very low viscosity. Thus, viscosity of the second coating may be low if the applicator roll is used. In an example, the second coating may be applied onto the first coating layer with a roll moisturizer.

Thanks to said contacting element, the anchoring of the second coating onto the first coating may be improved. Thus, the surface strength of the support layer may be improved.

The density of the support layer SUP1 comprising the coatings COAT may be equal to or less than 1300 kg/m ³ , preferably in the range of 1000 to 1200 kg/m ³ , most preferably in the range of 1035 to 1150 kg/m ³ . This density can be particularly suitable for release libers.

It may be good for manufacturing and transportation costs to reduce the grammage of the paper to reduce the weight of a release liner. This, however, may often result in adverse effects, since typically paper having less grammage is also thinner and may have poor strength properties. Therefore, it may not be suitable for the intended purpose, such as use as a support layer in an automated high-speed labelling process. When the grammage is reduced, the specific volume and tearing resistance of a conventional paper are typically also reduced. The smoothness of the paper surface may thus decrease, which may have a negative effect on the subsequent release coating.

The support layer SUP1 suitable for a release liner REL1 preferably have a grammage equal to or less than 160 g/m ² , preferably equal to or less than 80 g/m ² , and most preferably equal to or less than 70 g/m ² .The support layer SUP1 suitable for a release liner preferably has a grammage equal to or higher than 30 g/m ² , such as equal to or higher than 40 g/m ² , for example in the range of 30 g/m ² to 120 g/m ² , or in the range of 40 g/m ² to 100 g/m ² . The support layer SUP1 having a grammage in the range of 40 to 80 g/m ² , most preferably in the range of 50 to 70 g/m ² , may benefit of the increase in bulk. Grammage in this context refer to the basis weight, given in grams per square meter (g/m ² ). Therefore, grammage of the support layer SUP1 is preferably at least 35 g/m ² and more preferably at least 40 g/m ² · and preferably less than 100 g/m ² , more preferably equal to or less than 90 g/m ² . Grammage may be, for example, in the range of 38 to 100 g/m ² or between 40 and 90 g/m ² .

Figure 1a presents an example of the label laminate LABEL1 . The label laminate LABEL1 comprises a face layer FACE1 , a release liner REL1 and an adhesive layer ADH1 between said layers. The release liner REL1 refers to a product comprising a support layer SUP1 and a release coating layer RELCT 1 . It is possible to apply the adhesive layer ADH1 on the face layer FACE1 and/or on the release liner REL1 .

The label laminate LABEL1 preferably consists of the release liner REL1 and the face layer FACE1 , which are laminated together with the adhesive layer(s) ADH1 in between. The release liner comprises at least the support layer SUP1 and the release coating layer RELCT 1 . After removal of the release liner REL1 , the label (comprising the face layer FACE1 ) can be attached to the surface of an item through said at least one adhesive layer ADH1 .

When the label laminate LABEL1 is used, the adhesive layer ADH1 bonds the label to the surface of an item. The structure of the label may have one adhesive layer or a multilayer adhesive structure including additional adhesive layer(s). The adhesive layer is applied on the face layer FACE1 and/or on the release liner REL1 during the manufacturing process of the label laminate LABEL1 . The adhesive layer ADH1 of the produced label laminate LABEL1 may have a thickness of at least 10 microns or at least 12 microns, preferably at least 14 microns or at least 16 microns. Advantageously, the thickness is not greater than 40 microns or 35 microns, preferably not greater than 30 microns, more preferably not greater than 25 microns or not greater than 20 microns. The thickness of the adhesive layer may be, for example, between 16 and 20 microns. Therefore, it is possible to obtain an adhesive layer that is good enough to attach the label to the surface of an item without being too expensive. The amount of the adhesive used in the label laminate may be, for example, 16 to 22 g/m ² (dry grammage). Figure 1b presents an example of a support layer SUP1 (shown also in Figure 1 a) that is suitable for a release liner.

The release liner REL1 comprises a support layer SUP1 and a release coating layer RELCT1 . There may be at least one adhesive layer on the release liner REL1 .

The release liner REL1 is a paper-based liner having a paper-based support layer SUP1 . The release liner REL1 can be used to prevent a sticky surface from prematurely adhering. The support layer SUP1 is preferably coated on one side, or both sides, with a release agent to form a release liner REL1 comprising a release coating layer RELCT1 .

The support layer SUP1 comprises a cellulose fibre-based layer, i.e. the paper PAP1 . The cellulose fiber-based layer refers to a paper containing cellulose fibers. The paper PAP1 may comprise, for example, coated paper such as clay coated kraft paper (CCK), machine finished kraft paper (MFK), machine glazed paper (MG), super calendered kraft paper (SCK), vegetable parchment, glassine, or greaseproof paper.

For coated papers, a coat weight in the range of 1 to 12 g/m ² per side (on one or both sides) may be used. The coating layer may comprise pigments, such as calcium carbonate and/or kaolin, and binders, such as starch and/or polyvinyl alcohol.

Vegetable parchment paper is a paper typically made of waterleaf sheet (unsized sheet of paper, made from chemical wood pulp) by treating it in a bath of sulfuric acid. The treated paper is washed thoroughly to remove the acid and then dried. This chemical treatment forms a very tough, stiff paper with an appearance similar to a genuine parchment. However, a paper treated in this manner has a tendency to become brittle and to wrinkle upon drying. Vegetable parchment may therefore be treated with a plasticizing agent, such as glycerine or glucose.

Glassine paper is widely used in release liner for self-adhesive materials. Glassine is typically made of bleached chemical pulp, having preferably a grammage in the range of 30 to 160 g/m ² . When producing giassine paper, the pulp is typically refined to obtain a dense surface, which may be resistant to air and liquids such as oil and water. When manufacturing giassine paper, the pulp slurry is typically first refined to a high level, the formed paper web is then pressed and dried, and the coating is applied on the paper web surface. Giassine is typically calendered with a multi-nip calender or a supercalender before or after applying the first coating layer, to obtain a product having high density surface, high impact strength, high tear resistance and transparency. Giassine, however, has typically a lower dimensional stability than a conventional coated paper. Therefore, shrinkage of the formed fiber web when manufacturing giassine paper is typically higher than with conventional coated paper.

Greaseproof paper is similar to giassine in grammage. The main difference between greaseproof paper and giassine is in the calendering treatment. While giassine is typically supercalendered, greaseproof paper is not. Hence, greaseproof paper has typically a diminished tearing resistance when compared to giassine.

Of the above-mentioned papers, giassine is preferred for industrial manufacturing of high-quality release liner REL1 , due to the mechanical properties of the paper obtained in the manufacturing process.

A paper PAP1 which may be used for the support layer SUP1 of the release liner REL1 is typically so called woodfree coated paper, made of chemical pulp, such as Kraft pulp.

The paper PAP1 comprises cellulose fibers containing pulp, wherein the cellulose fibers preferably originate from wood. Wood species differ from each other in their mechanical properties and chemical compositions. The wood material used for the support layer can be from softwood trees, such as spruce, pine, fir, larch, douglas-fir or hemlock, or from hardwood trees, such as birch, aspen, poplar, alder, eucalyptus or acacia, or from a mixture of softwoods and hardwoods. The pulp used in the support layer SUP1 may comprise cellulose fibers from both hardwood and softwood. Pulp comprising a mixture of hardwood and softwood may be used to improve the internal bond strength of the paper web during manufacturing process.

Thus, in this context, cellulose pulp preferably refers to material originating from wooden material, which has been processed into fibrous form, such as fibers, using chemical, mechanical, thermomechanical, or chemithermo - mechanical pulping process(es). In accordance with an embodiment, a pulp used for making the support layer SUP1 suitable for a release liner does not contain any kind of mechanical pulp due to high quality requirements of the release liner REL1 .

The support layer SUP1 of the release liner REL1 may also comprise other components, such as fillers. For example, at least one kind of mineral filler may be used in the support layer SUP1 . Mineral filler can comprise, for example, at least one of the following: clay, calcined clay, kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide. In addition, the support layer may comprise a mineral coating layer.

The total amount of the mineral filler in the support layer SUP1 may be equal to or more than 0 wt.% for example at least 0.5 wt.-% based on the total weight of the support layer SUP1 . The total amount of the mineral filler in the support layer SUP1 is preferably less than 10 weight-%, more preferably less than 5 weight-%, and most preferably less than 3 weight-%, for example between 0.5 and 5 wt.-%, or between 0 wt.-% and 3 wt.-%, based on the total weight of the support layer SUP1 . The mineral fillers may decrease costs of the manufactured product. However, in addition to the decreased strength properties, mineral fillers may also decrease transparency level of the product.

The support layer SUP1 can be arranged to have a first coating layer COAT1 applied on the paper PAP1 . The first coating layer COAT1 of the support layer SUP1 on the paper PAP1 may be, e.g., a water-based emulsion or water- based dispersion, which is applied as a coating on to the paper PAP1 . The support layer SUP1 can comprise the first coating layer and the second coating layer on one or two sides of the paper PAP1 . Thus, the support layer SUP1 comprises the first coating layer COAT1 applied on at least one side of the paper PAP1 . Thanks to the first coating layer, the surface penetration of the second coating can be reduced.

The paper PAP1 may also comprise other coating layer(s) on one or two sides of the paper PAP1 , such as 1 or 2 other coating layers on one or two sides of the paper PAP1 . Therefore, the support layer SUP1 may contain one, two or more coating layers on the paper PAP1 before the first coating layer and the second coating layer are applied on to the surface of the paper PAP1 . The coating layer(s) may be configured to reduce the porosity of the support layer SUP1 surface, thereby improving the smoothness of the support layer SUP1 . However, the second coating layer on the first coating layer are the top coating layers of the support layer SUP1 .

The paper PAP1 may be calendered with a calender or a supercalender before or after applying the first coating layer, to obtain a product having high density surface.

The first coating layer COAT1 can comprise polymer(s). The first coating layer may comprise water soluble binders. Preferably, the first coating layer COAT1 comprises or consists of

- polyvinyl alcohol (PVA), and/or

- carboxymethyl cellulose (CMC), and/or

- starch, and/or

- ethylene-vinyl alcohol copolymer (EVOH).

The amount of these polymers can be equal to or more than 30 wt.%, preferably equal to or more than 35 wt.%, more preferably equal to or more than 40 wt.%, and most preferably equal to or more than 45 wt.%, calculated from the total dry weight of the first coating layer. The first coating layer may thereby have capability to provide barrier properties for the cellulose fibre- based support layer SUP1 . The first coating layer COAT 1 can further comprise mineral pigments and/or synthetic thickener and/or other additional components. Mineral pigments can comprise, for example, at least one of the following: clay, calcined clay, kaolin, mica, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide.

The ethylene-vinyl alcohol copolymer (EVOH) is a copolymer of ethylene and vinyl alcohol. In this application, the content of the ethylene may be in a range between 1 and 20 mole percent calculated from the ethylene-vinyl alcohol copolymer. The ethylene-vinyl alcohol copolymer preferably comprises ethylene at least 1 mol-%, more preferably at least 3 mol-%, and most preferably at least 5 mol-%, such as in a range between 3 mol-% and 20 mol- %. Further, the ethylene-vinyl alcohol copolymer preferably comprises ethylene equal to or less than 20 mol-%, more preferably equal to or less than 17 mol-%, and most preferably equal to or less than 15 mol-%, such as in a range between 5 mol-% and 15 mol-%. Ethylene content makes the copolymer more hydrophobic, decreasing its water solubility. Thus, it is possible to obtain improved properties for the support layer. However, the ethylene content is preferably selected so that the water solubility of the first coating is suitable for the selected coating method.

Polyvinyl alcohol, ethylene-vinyl alcohol copolymer, starch and carboxymethyl cellulose are polymers having a film-forming nature which can provide a barrier between the release coating layer RELCT1 and the paper PAP1 . As discussed above, the first coating layer COAT1 may also comprise e.g. additives and fillers.

In an example, the first coating layer COAT 1 comprises starch. In an example, the first coating layer comprises carboxymethyl cellulose.

In an advantageous example, the first coating layer COAT 1 on the paper PAP1 comprises at least ethylene-vinyl alcohol copolymer. The amount of the ethylene-vinyl alcohol copolymer can be equal to or more than 25 wt.%, preferably equal to or more than 30 wt.%, more preferably equal to or more than 35 wt.%, and most preferably equal to or more than 40 wt.%, calculated from the total dry weight of the first coating layer COAT 1 . The ethylene-vinyl alcohol copolymer may be particularly compatible with the second coating layer COAT2 comprising polyvinyl alcohol derivative. Further, the amount of the ethylene-vinyl alcohol copolymer in the first coating layer can be equal to or less than 70 wt.%, calculated from the total dry weight of the first coating layer COAT 1 .

In another advantageous example, the first coating layer COAT1 on the paper PAP1 comprises, alternatively or in addition, at least polyvinyl alcohol. The amount of the polyvinyl alcohol can be equal to or more than 25 wt.%, preferably equal to or more than 30 wt.%, more preferably equal to or more than 35 wt.%, and most preferably equal to or more than 40 wt.%, calculated from the total dry weight of the first coating layer COAT 1 . The polyvinyl alcohol may be particularly compatible with the second coating layer COAT2 comprising polyvinyl alcohol derivative. Further, the amount of the polyvinyl alcohol in the first coating layer may be equal to or less than 70 wt.%, calculated from the total dry weight of the first coating layer COAT 1 .

Advantageously, the total amount of the first and second coatings on the first side of the paper PAP1 is at least 0.6 g/m ² , more preferably at least 0.8 g/m ² , and most preferably equal to or more than 1 .0 g/m ² . Further, the amount of said coatings on the first side of the paper PAP1 is preferably less than 5.5 g/m ² , more preferably equal to or less than 3 g/m ² , and most preferably equal to or less than 2 g/m ² .

The first coating layer and/or the second coating layer may comprise mineral pigments. Mineral pigments can comprise, for example, at least one of the following: clay, calcined clay, kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulphate, and titanium dioxide. The total amount of the mineral pigments in the first coating layer is preferably less than 80 wt.%, such as from 0 to 50 weight-%, more preferably equal to or less than 40 wt.%, such as from 5 wt.% to 40 wt.% and most preferably equal to or less than 20 wt.%, such as between 1 wt.% and 20 wt.%, based on the total dry weight of said coating layer. The mineral pigments may decrease the manufacturing costs of the release liners. However, if the coatings comprise too much mineral pigments, some properties of the release layer can be compromised. Thus, in an example, the first coating layer and/or the second coating layer do(es) not comprise mineral pigments. The first coating layer can be applied onto the first or both sides of the paper PAP1 by using a first application unit.

The first coating can be applied on the first side of the dry paper by using a direct coating, such as a blade coating or a rod coating, wherein the first application unit of the first coating is directly in contact with the first side of the dry paper, and there is preferably a backing roll on the second side of the dry paper. This kind of coating method can be used to decrease manufacturing costs of the release liner due to substantially simply coating device. Further, smoothness of the first coating may be improved. Thus, it may be easier to apply the thin second coating layer on the first coating layer.

The first coating can be applied on the first side of the dry paper by using a film transfer coating, wherein the first coating is first evened out onto an applicator roll of the first application unit and then transferred onto the first side of the dry paper in a roll nip. This kind of coating method can be used to improve evenness of the first coating layer, even with a substantially thin coating layer.

Alternatively, the first coating can be applied on the first side of the dry paper by using a surface sizing, hence, the first application unit may comprise a sizer. Thus, the first coating can be first fed to a pond and then transferred to the first side of the dry paper from the pond. Therefore, the coating can be partly penetrated into the paper. Therefore, strength properties of the support layer may be improved. With this method, the costs may be increased.

Alternatively, the first coating can be sprayed directly to the first side of the dry paper by using spraying nozzles, thus, it is possible to obtain a coating layer having substantially even thickness of the coating.

Alternatively, the first coating layer can be formed by using a curtain coating. In this embodiment, the method can comprise the following steps: applying a first curtain of fluid comprising the first coating, which first curtain of fluid falls on the first side of the dry paper.

Thanks to the curtain coating, the coating layer can be substantially uniform, continuous layer, hence, number of holes may be decreased. Still further, the curtain coating is very easy coating method for the paper web, hence, the curtain coating may decrease the number of paper web breaks on the paper machines. Yet further, quality of the base paper PAP2 may not be as critical for curtain coating as for many other coating methods.

The second coating layer COAT2 is applied onto the first coating layer COAT 1 . Thus, the support layer SUP1 comprising the paper PAP1 further comprises at least the first coating layer and the second coating layer.

The second coating layer COAT2 comprises a polymer, which is modified to contain functional groups that are able to improve silicone adhesion. These functional groups are vinyl groups.

The second coating layer COAT2 of the support layer SUP1 is a polymer containing layer comprising polyvinyl alcohol derivative which

- has a degree of hydrolysis in the range of 60% to 100%, and

- contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative.

The second coating layer preferably has a coat weight in the range of 3 mg/m ² to 200 mg/m ² , when measured as a dry weight of the water-soluble polyvinyl alcohol derivative.

The second coating layer can be applied as aqueous polymer solution. Thanks to the novel solution, a full surface coverage of functional groups may be obtained with minimal amount of modified polymer. In an example, the second coating layer is applied during a paper manufacturing process before a pope reel.

Conventionally, the accessible groups at the surface are only a small fraction of all groups in the modified polymer layer, causing most of the modified polymer to be "wasted". The novel solution discloses an improved application technique that introduces the modified polymer on top of unmodified polymer, which may ensure that substantially all modified polymer is on the surface and readily available for the silicone curing reaction.

Thanks to the novel solution, the required amount of modified polymer can thus be very low, allowing e.g. 20-200 times larger production of release liner with the same polymer modification capacity.

In an example, the polymer used for the second coating layer may be of sufficiently low molecular weight, hence, too high viscosity can be avoided.

In an advantageous embodiment, the modified polymer, i.e., the polyvinyl alcohol derivative, is soluble in cold water. In this embodiment, a partially hydrolyzed PVA may be preferred over fully hydrolyzed polyvinyl alcohol.

The second coating layer is preferably a continuous coating layer, i.e., there may not be any un coated areas having a surface area greater than 2 cm ² . More advantageously, there is not any un coated areas having a surface area greater than 1 .5 cm ² . Thus, there may not be any weak areas having decreased rub-off values, hence, rub-off properties of the release liner may be improved.

The second coating having the polyvinyl alcohol derivative therein is the top layer of the support layer SUP1 . The release coating layer will be applied on the second coating layer to form the release liner.

The second coating, i.e., the aqueous solution containing the water-soluble polyvinyl alcohol derivative, can be applied on the first coating layer by using a second application unit. The second application unit can comprise a contacting element.

Thus, the second coating can be applied onto the first coating layer by using a contacting element, such as a roll, a blade or a rod, which is directly in contact with the first side of substrate, and there may be a backing roll on the second side of the dry paper. This kind of coating method can be used to decrease manufacturing costs of the release liner due to substantially simply coating device. Further, smoothness of the coating may be improved. Thanks to the contacting element, an evenness of the surface of the product can be improved. Further, manufacturing costs of the release liner can be decreased due to substantially simply coating device. Still further, evenness of the substrate may be improved.

The contacting element may comprise a blade. In this embodiment, the blade is directly in contact with the substrate, and there is preferably a backing roll on the second side of the paper. The second coating can be fed in excess onto the first coating layer after which the second coating layer is metered down to a predetermined thickness by using the blade. This kind of coating method can be used to decrease manufacturing costs of the release liner due to substantially simply coating device. Further, second coating may be evenly distributed. Furthermore, if the first coating comprises any small holes, these may be filled with the second coating. Thus, the coated support layer may have improved smoothness. Suitable thickener(s) known by a skilled person may be used to improve the runnability of the coating process.

Alternatively, the contacting element may comprise a rod. In this embodiment, the rod is directly in contact with the substrate, and there is preferably a backing roll on the second side of the paper. The second coating can be fed in excess onto the first coating layer after which the second coating layer is metered down to a predetermined thickness by using the rod. This kind of coating method can be used to decrease manufacturing costs of the release liner due to substantially simply coating device. Further, the second coating may be evenly distributed. Furthermore, if the first coating comprises any small holes, these may be filled with the second coating. Thus, the coated support layer may have improved smoothness. Still further, the rod may cause less web breaks than the blade. Suitable thickener(s) known by a skilled person may be used to improve the runnability of the coating process.

The contacting element can comprise an applicator roll. The applicator roll may form a roll nip with a backing roll. The second coating can be first applied to a surface of the applicator roll and then transferred onto the first coating layer, preferably, but not necessarily, in the roll nip. Thus, in this case, it is possible to obtain a very thin, substantially continuous coating layer. Further, the second coating may be evenly distributed. Furthermore, if the first coating comprises any small holes, these may be filled with the second coating. Thus, the support layer may have improved smoothness. Further, the second coating layer can be a substantially even and continuous coating layer.

In an example, the total solid content of the second coating is controlled so that the moisture content of the support layer does not exceed 22% after the second coating is applied onto the first coating. This may decrease the production costs.

The second application unit may comprise a sizer. In this embodiment, the contacting element may comprise a roll nip. Further, there may be a pond near the nip. With the sizer, the both sides of the paper PAP1 can be coated simultaneously. Thus, this method is particularly suitable when manufacturing a support layer having coatings on both sides of the paper. However, if only one side of the support layer has the coating comprising polyvinyl alcohol derivative, this embodiment may not be as advantageous as other coating methods.

The second coating can be applied onto the first coating layer in a form of liquid and/or in a form of foam by using an applicator feeding the coating.

Therefore, the second coating can be applied onto the first coating layer in a form of foam by using the applicator and the contacting element, thereby forming a foam layer on the first coating layer. Thus, it is possible to obtain a very thin coating layer having substantially high dry matter content and viscosity level, hence, the drying costs of the support layer may be decreased. In this example, the contacting element may comprise a roll nip.

The second coating may be applied in a form of foam by using e.g. a narrow slot type applicator. Thus, the second application unit can comprise a narrow slot type applicator. The applicator may have an open gap between the slot and the paper to be coated. The gap may have a width e.g. between 300 pm and 500 pm. Further, the second application unit may comprise a roll nip which destruct at least part of the applied foam. In the foam coating process, the coat weight can be controlled by adjusting the following parameter(s):

Solids content of the coating material, and/or Pumping speed of the foam, and/or Application width, and/or Running speed of the coater.

The coat weight can be adjusted by changing the solids content of the coating and the application speed of the coating to the applicator. The manufacturing costs of the support layer may be decreased by using the foam.

The dry matter content of the dry paper PAP1 is preferably at least 90%, when the second coating is applied onto the first coating layer.

Further, the dry matter content of the first coating layer may be at least 90%, when the second coating is applied onto the first coating layer.

When applying the second coating on the first coating, the solids content of the aqueous solution comprising the polyvinyl alcohol derivative can be between 0.01 % and 7%, preferably from 0.05% to 3%, and most preferably at least 0.1%, calculated as dry weight of the polyvinyl alcohol derivative in the aqueous solution, wherein the polyvinyl alcohol derivative has a degree of hydrolysis in the range of 60% to 100%, and contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative. Advantageously, the second coating layer has a vinyl group molality (b _V in) in the range of 0.05 to 2.00, preferably in the range of 0.10 to 1 .00, most preferably in the range of 0.15 to 0.80 millimoles per gram of the dry polyvinyl alcohol. Thus, it is possible to manufacture an improved release liner with decreased manufacturing costs.

The polyvinyl alcohol derivative can be obtained e.g. by means of acetalization in aqueous solvent, esterification in organic solvent, or esterification by reactive extrusion without a solvent in a melt state. Advantageously, the esterification by reactive extrusion without a solvent in a melt state has been used to obtain the polyvinyl alcohol derivative.

In an example, the support layer SUP1 having the first and second coating layers COAT 1 , COAT2 on the paper PAP1 may be arranged to have hydrophobicity. 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. Hydrophobic surface may improve the orientation of vinyl functional groups so that they may be promoting the formation of covalent bonds with a silicone-based release layer, when a release coating layer RELCT1 is applied on top of the support layer SUP1 . However, thanks to the thin second coating layer comprising the vinyl functional groups, the vinyl groups may always be substantially near the surface of the coating layer. The hydrophobic effect is dependent of the amount of linear chains grafted onto the polyvinyl alcohol. The non-polar, catenated carbon structures that end into a terminal vinyl group may also acts as a surfactant. While a hydrophobic polyvinyl alcohol, as such, may have a poor adhesion to silicone, the catalytic hydrosilation reaction enables chemical bonding of the silicone.

The support layer SUP1 preferably comprises

- a paper PAP1 having a first side and a second side,

- a first coating layer COAT1 on the first side of the paper having a coat weight in the range of 0.6 to 5 g/m ² , when measured as a dry weight of the coating, and

- a second coating layer COAT2 on the first coating layer, which second coating layer has a coat weight in the range of 3 to 200 mg/m ² when measured as a dry weight of the polyvinyl alcohol derivative, and contains polyvinyl alcohol derivative which has a degree of hydrolysis in the range of 60% to 100%, the polyvinyl alcohol derivative containing pendant vinyl groups which are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative. The second coating layer can have a vinyl group molality (b _V in) in the range of 0.05 mmol/g to 2.00 millimoles per gram of the dry polyvinyl alcohol, preferably in the range of 0.10 mmol/g to 1 .00 millimoles per gram of the dry polyvinyl alcohol, most preferably in the range of 0.15 mmol/g to 0.80 millimoles per gram of the dry polyvinyl alcohol. Due to thin second coating layer, the amount of vinyl groups in the surface may be increased while the total amount of the vinyl groups can be substantially small.

The first and the second coating layers can have a total vinyl group molality (bvin) in the range of 0.00005 mmol/g to 0.33 mmol/g. Preferably, the first and the second coating layers have a total vinyl group molality (bvin) in the range of 0.0001 mmol/g to 0.17 mmol/g, most preferably in the range of 0.00015 mmol/g to 0.013 millimoles per gram of the dry coating layer. Thus, the total amount of the vinyl groups can be substantially small, but the rub-off properties of the release liner can be very good due to the novel solution.

The first coating layer may not have vinyl groups at all to improve the cost efficiency of the product. Thus, the first coating layer preferably has a vinyl group molality (bvin) of less than 0.00005 millimoles per gram of the dry coating layer.

The polyvinyl alcohol derivative in the second coating may have a weight average molecular weight (M _w ) of less than 50000 g/mol, preferably less than 40 000 g/mol. The polymer used for the second coating layer can be of sufficiently low molecular weight, hence, too high viscosity can be avoided.

As discussed above, grammage of the polyvinyl alcohol derivative on the paper is at least 3 mg/m ² and it can be at least 5 mg/m ² , preferably at least 10 mg/m ² ' and most preferably at least 15 mg/m ² when calculated as dry weight of the polyvinyl alcohol derivative to obtain good rub-off properties. Further, a grammage of the polyvinyl alcohol derivative on the paper is equal to or less than 200 mg/m ² and it can be equal to or less than 100 mg/m ² , more preferably equal to or less than 60 mg/m ² when calculated as dry weight of the polyvinyl alcohol derivative. Thus, the total amount of the expensive chemical can be decreased, hence, costs of the release liner can be decreased. Advantageously, but not necessarily, the grammage of the support layer SUP1 is from 38 gsm to 80 gsm, a total grammage of first and second coatings on the paper is from 0.6 g/m ² to 5.2 g/m ² , the first coating layer has a vinyl group molality (b _V in) of less than 0.00005 millimoles per gram of the dry coating layer, and the second coating layer can have a vinyl group molality (bvin) in the range of 0.05 mmol/g to 2.00 millimoles per gram of the dry polyvinyl alcohol. Therefore, a product having decreased manufacturing costs as well as good properties for the release liner, such as excellent rub-off properties, can be provided.

Fig. 2 shows, by way of an example, a method for manufacturing the support layer SUP1 . The support layer SUP1 can be manufactured by providing a paper PAP1 , applying a first coating COAT1 on the paper PAP1 , and applying a second coating COAT2 on the first coating COAT 1 .

Advantageously, the method for providing a coating layer comprising water- soluble polyvinyl alcohol derivative on a paper suitable for use as a support layer of a release liner can comprise the following steps: forming a paper web on a paper machine, drying the paper web on a drying section of the paper machine thereby obtaining a dry paper having a first side and a second side, forming a first coating layer by applying a first coating on the first side of the dry paper, thereby obtaining the first coating layer, which first coating layer has a coat weight in a range between 0.6 g/m ² and 5 g/m ² , preferably in a range between 1 g/m ² and 3 g/m ² , when measured as a dry weight of the first coating layer, forming a second coating layer by applying a second coating having a temperature of less than 90°C on the first coating layer, thereby obtaining the second coating layer, wherein a contacting element, such as an applicator roll or a metering element, is used to apply and/or meter the second coating, wherein the second coating is aqueous solution, which aqueous solution contains polyvinyl alcohol derivative, which polyvinyl alcohol derivative has a degree of hydrolysis in the range of 60% to 100%, and contains pendant vinyl groups, which pendant vinyl groups are part of catenated carbon structures which contain at least 4 carbon atoms, preferably in the range of 5 to 15 carbon atoms, and which are covalently bound to the polyvinyl alcohol derivative, wherein the second coating layer has a coat weight in the range of 3 mg/m ² to 200 mg/m ² when measured as a dry weight of the polyvinyl alcohol derivative.

The paper may be dried after the first coating has been applied, before applying the second coating. Thus, the dry matter content of the first coating layer may be equal to or more than 90% when applying the second coating on the first coating. Thus, advantageously the second coating is a wet coating which is applied on a dried first coating layer. This may improve the effect of the second coating layer, i.e., more vinyl groups may be remained on the surface of the support layer SUP1 , hence, the rub-off properties of the release liner may be improved.

Therefore, the method can further comprise the following step: drying the obtained first coating layer before applying the second coating on the first coating layer.

In an example, the drying step is used together with such liquid application system, wherein the second coating is applied via another roll to a transfer roll, which may be a hydrophilic transfer roll. The hydrophilic transfer roll may be run in the same direction as the paper web to apply the liquid film to the web.

The second coating may have a dry matter content in a range between 0.01% and 7% when it is applied on to the first coating. The technical effect of this solids content is to provide substantially same amount of vinyl groups onto the whole surface of the support layer SUP1 . Further, if the coating has too much water, the drying costs of the release liner may be increased.

The surface penetration of the release coating layer RELCT1 can further be reduced by calendering the support layer SUP1 . Therefore, the support layer comprising the first and second coatings is preferably calendered, more preferably supercalendered. Calendering improves the surface smoothness but reduces the specific volume and the paper thickness. Reduction in the paper thickness may, in some cases, lead to problems in the label manufacturing process, as the stencils used to die cut the label stock may have been designed to operate at a predefined paper thickness.

Therefore, the support layer SUP1 may be calendered into a desired thickness, such that the ratio of grammage to thickness of the paper in micrometers is maintained at a level equal to or higher than 1 .0. This may enable manufacturing of low grammage paper, which has a high surface density suitable for a release coating. Due to high surface density, also the amount of other raw materials beside fibers, such as coating material and additives used in the release liner manufacturing process, may be reduced.

The support layer SUP1 may have a thickness in the range of 35 pm to 100 pm. Thickness of the support layer SUP1 is preferably at least 35 pm, more preferably at least 40 pm or at least 45 pm. Thus, the manufacturing process of the support layer may be easier to control. In addition, the thickness of the support layer SUP1 may not be greater than 100 pm, more preferably not greater than 80 pm or 60 pm. Thus, the release liner may have suitable thickness for many end products in the market. Advantageously, the thickness of the support layer SUP1 is between 40 and 68 pm, more preferably between 42 and 60 pm.

The release liner REL1 should withstand the functional requirements set by the end purpose, such as a labelling system. In particular, the mechanical properties of the release liner, such as surface smoothness, surface density and tearing resistance, should be suitable for the release liner to function properly.

A release liner REL1 can be obtained from the support layer SUP1 by applying a release coating layer RELCT1 on said support layer SUP1 . Therefore, the support layer SUP1 is preferably coated with a release agent in order to form a release coating layer RELCT1 . The release coating layer RELCT1 is used in order to achieve a release effect for the release liner REL1 against the adhesive layer ADH1 . A typical example of a release coating contains silicone polymer. The release coating layer may comprise a silicone polymer-based compound, applied on at least one side of the substrate layer. Release coatings based on silicone compounds are typically easily applicable and flow readily. Therefore, the release liner REL1 preferably comprises a silicone release coating layer on the support layer. The chemistry of the silicone defines the force required to release the adhesive (and therefore the face layer) from the support layer SUP1 .

The release coating layer RELCT1 on the support layer can comprise cross- linkable silicone. The silicone used in the release coating layer RELCT1 may be, for example, UV curable. The UV curable silicone may be most preferably used because it may allow the use of lower temperatures for the curing process of the silicone.

Low temperature curable silicone compound (LTC silicone compound), refers to an addition-curable compound comprising silicone polymer with silane hydride groups and a cross-linker component with functional vinyl groups, which components are configured to cross-link in a catalytic hydrosilylation reaction at a low temperature. In the presence of precious metal catalysts such as platinum or rhodium complexes, 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 hydrosilylation 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 release coating layer RELCT1 may consist of silicone. The amount of silicone in the release coating layer RELCT1 can be at least 90 wt.-%. The amount of silicone on the release coating layer is preferably equal to or less than 2 g/m ² per side. Advantageously the amount of the silicone is at least 0.3 g/m ² , or at least 0.4 g/m ² · more preferably at least 0.5 g/m ² or at least 0.6 g/m ² (dry grammage) to provide a functional release coating on the support layer SUP1 . Advantageously the amount of the silicone is 2.0 g/m ² at the most, or 1 .6 g/m ² at the most, more preferably 1 .4 g/m ² at the most or 1 .2 g/m ² at the most (dry grammage) in order to provide cost effective solution. The amount of the silicone on the release coating layer may be, for example, between 0.3 and 1 .5 g/m ² , or between 0.6 and 1 .2 g/m ² (dry grammage). The silicone coating used is preferably recyclable. The release agent used in the release liner REL1 may be, but is not limited to, a one-part or two-part silicone system, preferably a 3- to 5-part silicone system.

The release coating layer RELCT1 is formed of a release coating applied on the support layer SUP1 . The release coating can be applied as an uncured composition, which is a liquid polymer solution that is subsequently cured to form the release coating layer RELCT1 . Advantageously, the cured release coating layer RELCT1 has a non-blocking surface. Further, the release coating layer RELCT1 can have a low surface energy. The surface energy level of a release coating layer RELCT1 is preferably in the range of 21 to 25 dynes/cm. The release coating layer may be used to protect adhesive material that is in contact with the coated release surface. Adhesive material of a label laminate web from premature adhesive bonding may be protected by a non-blocking surface of the cured release coating layer.

Due to the need to increase silicone coating line productivity and, thus, speed, there is an aim to reduce the silicone curing time. The silicone curing time, however, 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. Thanks to the novel solution, the silicone curing time of the novel method can be significantly reduced, allowing high coating speeds, such as coating speed exceeding 1000 m/m in. Further, the release liner comprising the novel support layer has shown improved rub-off values.

Anchorage is a term used in the field to describe the attachment of the release coating to the paper substrate. Anchorage may be measured as relative rub- off of the silicone from the paper substrate. A high relative rub-off value of 100% refers to a perfect anchorage of the silicone, such that the release coating is fully anchored to the substrate. A low relative rub-off value less than 90%, particularly values less than 85% or less than 80%, means that the release coating could not hold on to the paper substrate sufficiently.

The release coating may be applied on the support layer directly by the paper manufacturer or later by a label manufacturer, when manufacturing the face layer, i.e. “the face stock”.

The first coating layer COAT1 can be used to close the existing pores and cover the surface of the paper. The second coating layer COAT2 can provide the functionality of the support layer. Thanks to the novel solution, the amount of water-soluble polyvinyl alcohol derivative can be substantially small while still providing the functionality for the support layer.

Advantageously, the polyvinyl alcohol derivative is produced by using acid anhydrides for polyvinyl alcohol modification.

Advantageously, the polyvinyl alcohol modification is implemented by reactive extrusion in order to obtain polyvinyl alcohol derivative. An example for manufacturing polyvinyl alcohol derivative

According to an example, thermoplastic polyvinyl alcohol derivative that contains ester bonded pendant chains which end into a vinyl group can be obtained. Further, organic acid anhydrides can be suitable for use as a reagent in said method.

During the condensation reaction, one of the two acyl groups of the organic acid anhydride forms an ester bond with a hydroxyl group of the thermoplastic polyvinyl alcohol, thereby forming thermoplastic polyvinyl alcohol derivative, while the other acyl group becomes a carboxylic acid residue. The condensation reaction of the organic anhydride in a melt state is unselective, such that either of the acyl groups may participate in the ester bond forming reaction. A melt state condensation reaction of organic acid anhydride and thermoplastic polyvinyl alcohol that contains hydroxyl groups may be provided by heating solid thermoplastic polyvinyl alcohol having hydroxyl groups, wherein the thermoplastic polyvinyl alcohol has been dried and has a degree of hydrolysis in the range of 65 to 90 mol-%. By admixing organic acid anhydride with the thermoplastic polyvinyl alcohol at a temperature above the melting point of the mixture, a reaction in a melt state may occur, wherein at least some of the organic acid anhydride reacts with the hydroxyl groups of the thermoplastic polyvinyl alcohol in an ester bond forming condensation reaction. Mixing facilitates higher reaction rate and more uniform degree of modification. Typically, a temperature in a range of 150 to 210°C may be used for the condensation reaction. The suitable temperature range is limited from the lower end by the melting point of the thermoplastic polyvinyl alcohol and the mixture. The suitable temperature range is limited from the upper end by the decomposition temperature of the polyvinyl alcohol and/or its derivative. Preferably the temperature during the condensation reaction in a melt state is in a range of 150 to 210°C. Most preferably, said temperature is in a range of 170 to 190°C, which reduces the likelihood of thermal decomposition of the thermoplastic polyvinyl alcohol and/or its derivative. The lack of added solvents enables a small reaction volume. The lack acid halides in the reaction in a melt state further avoids formation of corrosive residues such as HCI into the reaction product.

The duration of the reaction in a melt state may be less than 5 minutes, preferably less than 1 minute, more preferably less than 20 seconds. The reaction may be carried out in an extruder or in a hot-cold mixer, which conveniently provides sufficient energy for the heating and/or sufficient shearing force for the mixing. Various kinds of extruders are commercially available and well known in the art. Common names for such a melt extruder include screw extruder, extruder-reactor, or extruder. Examples of suitable commercially available extruders include single screw extruders, twin screw extruders and multi-screw extruder. Preferably, the method is carried out in a twin-screw extruder, which brings to advantages of more uniform shearing, larger conveying capacity of screw, and more stable extrusion. More preferably, the method is carried out in a co-rotating twin-screw extruder to achieve better mixing. Compared to water-based modification, a melt state reaction can be done in large volumes with a compact device, in a short span of time which enables centralized production and easy distribution of solid, water soluble reaction product to paper manufacturing sites all over the world.

Thermoplastic polyvinyl alcohol which has been dried may be fed into the barrel of the extruder, for example from a hopper, such that the thermoplastic polyvinyl alcohol is gradually melted as temperature increases above its melting point . The reagent may be fed from the same source, or from another source, such as another hopper or side feeder unit or liquid feeding unit, in which case the thermoplastic polyvinyl alcohol may be admixed with the reagent before heating. When the reagent is fed from another source downstream of the barrel of the extruder, the thermoplastic polyvinyl alcohol may be heated at least partially to a melt state, prior to admixing the reagent. The latter case is more preferable, as more friction may be provided which facilitates melting of the material.

If desired, an inhibitor may be used to inhibit spontaneous radical polymerization of vinyl groups and/or to inhibit a cross-linking reaction of the thermoplastic polyvinyl alcohol and/or its derivative. An example of such an inhibitor is butylated hydroxytoluene, which can act as a free radical scavenger that suppresses radical reactions, such as polymerization and cross-linking through double bonds. The inhibitor may be added before the mixing or during the mixing, i.e. before the ester bond forming condensation reaction or during the ester bond forming condensation reaction. The inhibitor, when used, is typically added in minor amounts, such as in an amount of equal or less than 5 wt.-% of the total weight of the mixture.

Further, if desired, a homogeneous or heterogeneous catalyst may be used to accelerate the ester bond forming condensation reaction. A suitable catalyst may be, for example, a Bronsted acid (e.g. sulfuric acid), a Lewis acid (e.g. tin(ll) octoate), or a Bronsted/Lewis base (e.g. alkaline metal alkoxide or carbonate). Further, pyridine may be used as such a catalyst. A preferred catalyst is 1-methylimidazole, which has a high catalytic activity. The catalyst may be added before the mixing or during the mixing, i.e. before the ester bond forming condensation reaction or during the ester bond forming condensation reaction. The catalyst, when used, is typically added in minor amounts, such as in an amount of equal or less than 1 wt.-% of the total weight of the mixture. When an asymmetrical acid anhydride reacts in an ester bonding condensation reaction, it is equally likely for either of the acyl groups to become the ester bonded pendant chain of the thermoplastic polyvinyl alcohol derivative. A benefit of using a symmetrical anhydride therefore, is in obtaining thermoplastic polyvinyl alcohol derivative which may contain a higher amount of ester bond pendant chains that end into vinyl groups, than by using an asymmetrical anhydride, unless both of the acyl groups in the asymmetrical anhydride end into a vinyl group.

The reagent may be admixed with the thermoplastic polyvinyl alcohol in an amount in the range of 1 to 10 wt.-%, more preferably in the range of 3 to 6 wt.-% when determined of the total weight of the mixture. A higher amount of the reagent may decrease the melt viscosity of the mixture to a level, which complicates the operation of the reactor, in particular, when the reactor is an extruder.

The reagent may comprise one or more organic acid anhydrides, which may be different. The organic acid anhydride may be a fatty acid-based anhydride. A fatty acid based anhydride, as referred herein, comprises at least one chain which has a catenated carbon structure of at least 4 carbon atoms that ends into a vinyl group. The organic acid anhydride may be symmetrical or asymmetrical anhydride. The fatty acid-based anhydrides may contain one acyl group or two acyl groups derived from 3-butenoic acid, 2,2’-dimethyl-4- pentenoic acid, 4-pentenoic acid, 7-ocenoic acid, 8-nonenoic acid, 10- undecenoic acid, or 12-tridecenoic acid. A symmetrical fatty acid-based anhydride may be derived from a single fatty acid. An asymmetrical fatty acid- based anhydride may be derived from two or more fatty acids, which are different. The organic acid anhydride may be, for example, acetylundecenoyl anhydride, which is an asymmetrical anhydride comprising one acyl group having a vinyl group, wherein the acyl group has been derived from 10- undecenoic acid. Alternatively, or in addition, the organic acid anhydride may be 10-undecenoyl anhydride, which is a symmetrical anhydride comprising two identical acyl groups, each having a vinyl group at the end wherein both acyl groups are derived from 10-undecenoic acid, or 4-pentenoic octanoic anhydride wherein one acyl group is derived from 4-pentenoic acid. After the reaction product is formed, it may be extruded, for example through a die. The extrudate may be cooled, preferably by means of air or inert gas flow, such that the temperature of the reaction product decreases and a solid reaction product is obtained. Alternatively, the cooling may be performed, for example, as a water bath cooling. The solid reaction product may then be shaped into compact form which is suitable for transportation, such as pellets, granulates or powder. The method thus enables an efficient and an elegant way of producing solid reaction product by a melt state reaction, where separation and/or purification of the reaction product is not needed. The solid reaction product is easy to shape into granulate or powder form for transportation. The solid reaction product may be later dissolved into water, for example when used for preparing a coating composition.

EXAMPLE 1 _ effect of aging on products Different coating configurations were tested on glassine paper (UPM Brilliant 59 gsm) to determine their effect on silicone adhesion

The manufactured products comprised one coating layer or two coating layers on the glassine paper. The total amount of coatings comprising polyvinyl alcohol and/or polyvinyl alcohol derivative was approximately 2 gsm. The coatings were applied on the paper sheet by using a metered size press as an applicator. After applying the coating layer(s), the glassine paper was supercalendered. The substrate of trial points 1-6 comprised glassine paper (UPM Brilliant 59) which had one coating layer containing polyvinyl alcohol. The total amount of the coating was 2 gsm. This paper was manufactured without the polyvinyl alcohol derivative. Trial points 7-8 comprised similar glassine base paper as the trial points from 1 to 6. For the trial points 7 and 8, the glassine paper was coated with aqueous PVA solution comprising polyvinyl alcohol derivative containing vinyl groups. Said trial points 7 and 8 had one coating layer having a grammage of 2 gsm. The amount of polyvinyl alcohol derivative was approximately 300 mg/m ² .

Trial point 9 comprised similar glassine base paper as the trial points 1 to 8. Samples of this trial point 9 were manufactured according to the novel solution. Said glassine base paper was first coated with the same coating as trial points 1-6, comprising PVA solution. The first coating layer was dried, after which aqueous solution comprising the PVA derivative was applied onto the first coating layer, thereby obtaining the second coating layer. The polyvinyl alcohol derivative was applied at 1 .7 % solids content. The total amount of the polyvinyl alcohol derivative in the trial point 9 was 50 mg/m ² . The polyvinyl alcohol derivative was applied onto the first coating layer with a roll moisturizer.

Trial point 10 comprised similar glassine base paper as trial points 1 to 9. Further, the trial point 10 comprised one coating layer comprising PVA. The amount of coating was 2 gsm. Further, for this trial point, water was applied onto the first coating layer with a roll moisturizer.

Each supercalendered substrate was coated with an amount of approximately 1 g/m ² of the silicone resin to obtain a release liner. Silicone resin was mixed from 94.23 parts per weight of Syl-Off™ SL161 polymer, 5.21 parts per weight of Syl-Off™ 7678 crosslinker, and 0.57 parts per weight of Syl-Off™ 4000 catalyst (all components provided by Dow).

The silicone adhesion was tested immediately after the silicon ization from the formed release liner. This is referred to as the initial rub off level. Further, release liners were stored at 50°C and 70% RH and the silicone adhesion of said liners was tested after a period of 28 days. These results are shown in Figs 3a-3b.

To further observe the combined effect of tropical conditions and label adhesive as a function of time to the silicone adhesion level, an adhesive label was attached on each formed release liner immediately after siliconization and the laminates thus formed were stored at 50°C and 70% RH. Silicone adhesion was tested after a period of 14, and 28 days. These results are shown in Figures 4a-4b.

The level of silicone adhesion in each release liner sample was determined with a semi-automatic 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. In the case of face layer (i.e. , face label), the release liner was tested after removing the face layer from the laminate. Thus, the measurements, in which the face layer had been laminated, performed on surfaces of release liners that had been in contact with an adhesive. For each sample, 3 parallel rub-off measurements were performed, of which the arithmetic average was calculated.

The results of the rub-off tests are shown in Figures 3a-4b, wherein the values are the calculated arithmetic average values, given in units of relative rub-off value in percent (%). A relative rub-off value of at least 80%, preferably at least 85% represents a minimum level which is considered to be acceptable and a relative rub-off value of at least 90%, preferably 95% or above is considered as a good result.

An example of a device suitable for producing rub-off on a release liner surface is a Satra rub tester, which has a rotating head holding a circular felt pad under a standard load, which enables semi-automated testing of abrasion resistance of a release layer.

As can be seen from the test results shown in Figures 3a-4b, the novel product comprising only very small amount of polyvinyl alcohol derivative was showing excellent rub-off values. For example, the novel product (trial point 9) having only 50 mg/m ² of polyvinyl alcohol derivative had better rub-off values than a product comprising only one coating layer and having around 300 mg/m ² polyvinyl alcohol derivative (trial points 7 and 8). As shown in Figs 3a to 3b, all samples without the face label had good performance, if tested immediately after the siliconization from the formed release liner. However, additional 4 weeks in moist conditions started to show differences. After 4 weeks, only samples 7 to 9 which were having the polyvinyl alcohol derivative on the surface of the support layer had good rub-off values of above 90%. The trial point 9 comprising the small amount of 50 mg/m ² of polyvinyl alcohol derivative had as good rub-off values as the samples having greater amount of polyvinyl alcohol derivative of 300 mg/m ² of polyvinyl alcohol derivative in the support layer.

Said differences were, however, small compared to those samples with face labels on the test pieces (Figs 4a to 4b). In fact, in difficult environments (high temperature and moisture and aging against adhesive), the novel product had better rub-off values than conventional products, even if compared with those products comprising a great amount of expensive polyvinyl alcohol derivative.

From 70% to almost 90 % of silicon was removed after two weeks from the test points 1 to 6 and almost nothing was left after 4 weeks (see Figs 4a and 4b). Test points 7 and 8 having a quite large amount of 300 mg/m ² of polyvinyl alcohol derivative lost approximately 60% of silicon after four weeks. Further, the novel product (Test point 9) comprising two coating layers and only small amount of polyvinyl alcohol derivative was able to hold almost all silicon even after 4 weeks. The reference point 10 lost approximately 40 % of silicon after four weeks.

Thus, most of those samples which were stored with a face label laminated on the release liner, had poor rub-off values. The only trial point having good rub- off values after 4 weeks, i.e., values above 90%, was the trial point 9. Even the trial points 7 and 8 having the approximately 300 mg/m ² of polyvinyl alcohol derivative in the support layer had quite poor rub-off values after aging.

Thus, only the novel product (trial point 9) having only 50 mg/m ² of polyvinyl alcohol derivative in the support layer had good rub-off values after 4 weeks, when aging against adhesive. Therefore, thanks to the novel solution, the novel product comprising only small amount of 50 mg/m ² of expensive polymer had great properties and much better properties than conventional products having greater amount of approximately 300 mg/m ² expensive polymer in the release liner. Thus, a release liner having improved properties may be manufactured with decreased manufacturing costs.

EXAMPLE 2 _ effect of the second coating on the product

Example 1 illustrated the excellent rub-off properties of the novel product having an amount of 50 mg/m ² polyvinyl alcohol derivative on its surface. However, not only said 50 mg/m ² , but also other amounts of polyvinyl alcohol derivative were tested.

Experimental tests with the novel coating structure were done by applying a thin second coating layer on previously applied first coating layer. The substrate comprised commercial glassine paper (UPM Golden 57 gsm), containing the first coating layer comprising polyvinyl alcohol. Water soluble polyvinyl alcohol derivative was applied on top of the first coating layer, using a laboratory blade coater, and dried at 105 ° for 60 s. Coat weight of polyvinyl alcohol derivative was calculated from the solids content of the solution, and the mass of solution applied on the substrate. The total amounts of the polyvinyl alcohol derivative, calculated as total dry weight of the polyvinyl alcohol derivative in the release liner, were

Trial point 1 : 100 mg/m ² Trial point 2: 20 mg/m ² Trial point 3: 10 mg/m ² Trial point 4: 5 mg/m ² , and Trial point 5: 0 mg/m ² (reference)

The coated glassine sheets were then siliconized with the following fast-curing Wacker silicone system:

100 parts of SFX251 polymer 11 .9 parts of V58 cross-linker 2.5 parts of COS catalyst Silicone was cured in oven at 105 ° for 60 s, and silicone curing and rub-off were evaluated by manual rub test immediately. Commercial labels with aqueous adhesive were attached on siliconized substrates and the laminates were aged at 45 °C and 75% relative humidity. Rub-off was periodically evaluated from siliconized area covered by labels.

For the rub-off tests, the paper to be tested was measured with Oxford XRF to determine base silicon amount, after which the silicon was rubbed with an element with standard weight and revolutions. After rubbing, the silicon amount was again measured to check how much silicon was still on paper. The test results are shown in Table 1.

Table 1 curing:

1 = high friction, complete curing

2 = low friction, mildly sticky, incomplete curing

3 = wet, sticky, un cured rub-off:

1 = silicone withstands strong rubbing without detaching

2 = silicone detaches with strong rubbing

3 = silicone detaches easily with mild rubbing

The first four trial points having a second coating layer comprising 5-100 mg/m ² polyvinyl alcohol derivative had excellent rub-off properties. The excellent properties also retained during the 4-week aging test. Trial point 5 started showing rub-off after 2 days, indicating that regular PVA coating of glassine provided poor adhesion for this silicone system.

EXAMPLE 3 _ testing rub-off of the novel product after certain aging

Polyvinyl alcohol derivative containing functional vinyl groups was applied on glassine paper having a first coating layer comprising polyvinyl alcohol.

First coating containing polyvinyl alcohol was applied on glassine base paper (grammage 59 gsm) by a metering size press. Same paper was coated again with dilute modified PVA solution, in amount of 40 mg/m ² of dry polyvinyl alcohol derivative. The resulting paper was supercalendered to yield glassine paper. Sample sheets were cut across the web cross direction and siliconized with the fast-curing Wacker silicone system described in Example 2, and cured at 140 °C for 10 s. The silicone curing and rub-off were then evaluated by the method described in Example 4. The results are shown in Table 2. As can be seen from the Table 2, the trial points had excellent rub-off properties. Table 2 EXAMPLE 4 Testing rub-off of the foam coated product after certain aging

Polyvinyl alcohol derivative containing functional vinyl groups was applied on glassine base paper having a first coating layer comprising 2 gsm polyvinyl alcohol. The polyvinyl alcohol derivative was applied on the first coating layer in a form of foam.

First coating containing polyvinyl alcohol was applied on glassine base paper (grammage 59 gsm) by a metering size press, and the coated paper was supercalendered. The paper was coated again with solutions of polyvinyl alcohol and polyvinyl alcohol derivative containing vinyl groups. Solutions were applied in a form of foam . Foam was prepared from polyvinyl alcohol solutions with 5 wt.% solids content, and 0.1 % “Wey!C!ean®" foaming agent was added to improve foam stability. Coat weight was varied from 0.16 to 0.4 g/m ² (calculated as dry weight). Small amount of coating (0.16 g/m ² ) was evenly applied onto the paper surface and it clearly reduced the number of pinholes.

For the application of the foam to the web, a narrow slot type applicator manufactured by J. Zimmer Maschinenbau GmbH (Klagenfurt, Austria) was used. There was a 400 pm open gap between the slot and the moving web. The foam was applied onto the base paper ca. 15 cm before a smoothening nip to obtain a dwell time of 110 ms. A part of the foam destruction was done in the nip. The web speed was kept at a constant level of 80 m/min, and the coat weight was adjusted by changing the pumping rate of the foam to the applicator.

Sample sheets were siliconized with the fast-curing Wacker silicone system described in Example 2, and cured at 105 °C for 60 s. The silicone curing and rub-off were then evaluated by the method described previously, aging with labels attached at 45 °C and 75% RH.

Table 3

Each trial point having even the smallest amount of polyvinyl alcohol derivative applied on the surface of the first coating layer had excellent rub-off properties. None of the reference trial points, coated with unmodified polyvinyl alcohol, passed the rub-off test after 4 weeks of aging. As can be seen from the experimental tests, the rub-off of the novel release liner was improved even with a very small layer with polyvinyl alcohol derivative.

EXAMPLE 5 melt state reaction of polyvinyl alcohol with 10-undecenoyl anhydride

An experimental study was carried out, wherein a mixture containing thermoplastic polyvinyl alcohol and 10-undecenoyl anhydride was arranged to react in an ester bond forming condensation reaction in melt state such that reaction product containing thermoplastic polyvinyl alcohol derivative and carboxylic acid residue was obtained. 10-undecenoyl anhydride is a symmetrical anhydride condensed from two 10-undecenoic acid molecules having a vinyl group at the end. 10-undecenoyl anhydride therefore has two chains which have a catenated carbon structure and which end into a vinyl group. The amount of 10-undecenoyl anhydride that was admixed with the thermoplastic polyvinyl alcohol was 5 wt.-%, determined of the total weight of the mixture. The reaction was carried out using a twin-screw extruder (Brabender ^® , counter-rotating, 32 mm screw diameter, 330.7 mm screw length) which contained a feeding unit, three heating zones and a die zone for extruding the material.

In the experimental study, an amount of 1 ,9 kg of thermoplastic polyvinyl alcohol (Kuraray POVAL® 3-80 grade) having a degree of hydrolysis of 80 mol-% was first dried in an oven at a temperature of 60°C for 24 hours, thereby obtaining dry thermoplastic polyvinyl alcohol. The dry thermoplastic polyvinyl alcohol was then fed via the feeding unit to the extruder, together with 0.1 kg of 10-undecenoyl anhydride. The extruder screws were rotated at 30 rpm. The three heating zones were adjusted to have a temperature profile that provided smooth runnability. The first heating zone adjacent to the feeding unit had a temperature of 190°C, the second heating zone had a temperature of 190°C, as well, and the third heating zone had a temperature 195°C. The extrusion die zone was set to have a temperature of 200°C. Thus, the 10-undecenoyl anhydride was reacted in an ester bond forming condensation reaction with the thermoplastic polyvinyl alcohol in a melt state, yielding thermoplastic polyvinyl alcohol derivative which contained ester bonded 10-undecenoyl groups. The reaction product was extruded through the die and air cooled below the melting point of the mixture and granulated to form a solid reaction product, i.e. an extrudate.

Thanks to the novel solution, the novel support layer, having only small amount of modified PVA on top of the first coating, may enable the silicone and substrate to bond together enabling very low rub-off. The novel support layer and a release liner comprising the novel support layer can have several advantages. A release liner having the novel support layer may have excellent rub-off properties with very small amount of polyvinyl alcohol derivative. Thus, the production costs may be significantly reduced. The method using only small amount of polyvinyl alcohol derivative may enable higher production speeds at coaters. Further, the novel product may need less activating heat for silicon. Further, thanks to the novel solution, it may be possible to save costs caused by platinum. Still further, the novel solution may enable a centralized polyvinyl alcohol modification production as the granulated modified PVA can be eluctrated and applied the to the paper on paper machine separately or even afterward.

The invention has been described with the aid of illustrations and examples. The methods or any product obtained by the methods are not limited solely to the above presented embodiments but may be modified within the scope of the appended claims.