Polymer-coated cellulose release liner substrate

Abstract

The present invention relates to a polymer-coated cellulose substrate (S2) for a release liner (REL1), comprising: a cellulose support layer (PAP1); a first coating layer (PO1) comprising a first composition comprising a polyolefin; and an extrusion primer layer (PRIM1) comprising a second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group; wherein the first coating layer (PO1) is located between the cellulose support layer (PAP1) and the extrusion primer layer (PRIM1).

Description

TECHNICAL FIELD

[0001] The present invention relates to a polymer coated paper for release liner. The present invention also relates to a method of manufacturing a polymer coated paper for release liner. BACKGROUND

[0002] A release liner is a paper or plastic / polymer based film sheet used to prevent premature adhesion of a tacky surface. Typical release liners in pressure sensitive laminates or other materials such as tapes are based on either cellulose or film (polymer) substrates which are carrier materials for a release agent. A commonly used release agent for release liners is a cross-linkable silicone. These substrates are coated with silicone in order to achieve the desired release value for various facestocks containing adhesives.

[0003] Cellulose substrates can be coated with a thin layer of a polymer such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) or similar to achieve a smooth finish and prevent the silicone resin from penetrating into the substrate.

[0004] A good performing silicone network must be able to peel off any coated adhesive layer smoothly, but it must also adhere well to the carrier substrate. This anchoring is usually achieved through weak interactions such as hydrogen bonding. In order to achieve any level of hydrogen bonding, the substrate must have some polar groups on its surface. Polyolefin coated cellulose substrates usually do not contain such polar groups on their surface and most commonly are corona treated to change their surface energy and thus improve the silicone anchoring. Corona treatment is a process by which a discharge is used to increase the critical surface tension of a polymer coating to improve the adhesion of other coatings, adhesives, inks, etc. to the polyolefin coated cellulose substrate.

[0005] However, very high corona treatment of the polymer coating can lead to polymer chain scission or pinholes in the film surface which can lead to silicone anchoring issues. Furthermore, anchoring based purely on weak interactions tends to be quite unstable over longer periods of time leading to issues of silicone transfer and loss of specific peel performance. SUMMARY

[0006] The present application represents a new approach to provide a polymer coated cellulose substrate for release liner with improved performance and simplification of steps and chemicals involved in its manufacturing process.

[0007] In one aspect, the present application provides a polymer coated cellulose substrate for release liner comprising:

[0008] - a cellulose support layer,

[0009] - a first coating layer comprising a first composition comprising a polyolefin,

[0010] - an extrusion primer layer comprising a second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group; thus, the extrusion primer layer comprises a functional vinyl group;

[0011] wherein the first coating layer is located between the cellulosic support layer and the extrusion primer layer.

[0012] Preferably, the thermoplastic polymer covalently bound to the functional vinyl group has been obtained from the reaction product of a molten thermoplastic material and a grafting agent comprising a functional vinyl group. This is beneficial because the reaction product is a solid substance that does not require any processing prior to further melt processing. Moreover, the improvement can also be done in-line in a film extruder.

[0013] Optionally, the polymer coated cellulosic substrate can further comprise a tie layer located between the first coating layer and the extrusion primer layer.

[0014] The polymer coated cellulosic substrate according to the present application has a number of effects as described below.

[0015] On the one hand, the extrusion primer layer has excellent adhesion to the underlying first coating layer when the adjacent polymer compositions used, i.e. the first composition and the second composition, have similar polarity or have covalent bonds at their interface, because the thermoplastic melt adheres firmly to the first coating layer after solidification.

[0016] On the other hand, the extrusion primer layer comprising a functional vinyl group provides an excellent basis for siliconization as the second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group of the extrusion primer layer, because, when forming a release liner comprising the polymer coated cellulosic substrate of the extrusion primer layer, the functional vinyl groups present in the thermoplastic polymer structure of the extrusion primer layer are able to form covalent bonds with addition-cured silicones. Thus, the silicone anchoring is significantly improved.

[0017] The extrusion primer layer according to the present application helps to improve the surface coverage of a subsequent silicone coating, in turn improving the consistency of the release values. A high quality silicone coating requires a good coverage of the substrate.

[0018] Furthermore, a problem specific to polyolefin-coated cellulose substrates is the presence of pinholes. Pinholes are one of the coating defects. Pinholes are hole-like penetrations present in the coating. In the manufacturing process of polyolefin-coated cellulose substrates, the polymer can be extrusion coated or laminated onto the cellulose substrate to produce a coating or a laminate initially free of pinholes, but usually, when the coated or laminated substrate is subsequently subjected to a substantial heat treatment, the polymer coating re-melts, while volatile substances entrapped in the cellulose substrate evaporate, pinholes frequently form in the coating, and these pinholes remain after the substrate has cooled and the polymer coating material has re-solidified. Furthermore, when a polyolefin-coated cellulose substrate is subjected to a corona treatment, pinholes can form in the polyolefin coating.

[0019] Pinholes on the surface of the substrate can lead to uncoated areas of the silicone coating, which increase the release value and lead to poor release stability over time. There is also a risk that the silicone penetrates through the pinholes and contaminates the underlying cellulose substrate.

[0020] Pinholes in the polyolefin coating can lead to poor anchoring of the silicone coating area and silicone rub-off, resulting in poor release stability over time. The polyolefin-coated cellulose substrate according to the present application is pinhole-free. The extruded primer layer is free of water or solvents, thus avoiding the entrapment of moisture or volatile solvents. Furthermore, since there are fewer holes to be filled with the silicone coating, the polyolefin-coated cellulose substrate according to the present application can be siliconized with a smaller silicone coating weight compared to a polyolefin-coated, e.g. PE-coated, cellulose substrate without an extruded primer layer. Thus, the cost-effectiveness of producing the silicone coating can be improved. Furthermore, the risk of silicone penetration and contamination of the cellulose support substrate through pinholes is greatly reduced.

[0021] The present application provides a method for the manufacture of a polyolefin-coated cellulose substrate for release liners, the method comprising:

[0022] - providing a cellulose support layer,

[0023] - extruding a molten first composition comprising a polyolefin, thereby obtaining an extruded first composition,

[0024] - extruding a molten second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group, thereby obtaining an extruded second composition; thus, the extruded primer layer comprises a functional vinyl group,

[0025] - reducing the temperature of the extruded molten first composition to below its melting point, thereby forming a first coating,

[0026] - reducing the temperature of the extruded molten second composition to below its melting point, thereby forming an extruded primer layer, and

[0027] - forming a polymer-coated cellulose substrate comprising a cellulose support layer, an extruded primer layer and a first coating layer between the cellulose support layer and the extruded primer layer.

[0028] Preferably, the method can further comprise:

[0029] - extruding a third composition comprising a compatibilizing agent, thereby obtaining an extruded third composition, and

[0030] - reducing the temperature of the extruded molten third composition to below its melting point, thereby forming a tie layer,

[0031] such that the tie layer is located between the first coating layer and the extruded primer layer.

[0032] According to the method of the present application, at least two of the above-mentioned molten compositions can be co-extruded. For example, the first composition and the second composition can be co-extruded to coat the cellulose support layer. In another example, the first composition, the second composition and the third composition can be co-extruded to coat the cellulose support layer. In another example, the second composition and the third composition can be co-extruded to coat the polyolefin-coated cellulose support layer, which has been coated with the first composition.

[0033] In the method according to the present application, extruding the molten second composition comprising at least one thermoplastic polymer covalently bound to a functional vinyl group has several effects, as explained below.

[0034] The step of extruding the molten second composition can

[0035] - be a subsequent step after forming the polyolefin coating on the cellulose substrate before or after the polyolefin coating is solidified; or

[0036] - be combined with extruding the molten first composition comprising a polyolefin-based material by co-extruding the first and second compositions.

[0037] The corona treatment forms hydroxyl groups, carboxyl groups and free radicals. Since these reactive moieties would further react rapidly in an uncontrolled manner, it is recommended to perform the in-line corona treatment even on substrates that have been pretreated at a high level. Therefore, the film after corona treatment should be silicone coated as soon as possible. The filamentary corona discharge also creates pinholes in the polymer coating, making the surface less suitable for siliconization.

[0038] In contrast, in the method according to the present application, extruding a molten second composition comprising at least one thermoplastic polymer containing a functional vinyl group facilitates the polymer coated cellulosic substrate to provide a stable surface for the subsequent silicone coating. The surface of the extruded primer layer is chemically stable until the silicone coating is applied onto it and reacts with it and forms a stable release liner upon curing. This provides great flexibility to the industrial line-up.

[0039] According to the present method, during the manufacturing process of the polymer coated cellulosic substrate, volatile organic compounds are reduced or eliminated and drying or curing steps are eliminated. Harmful chemicals are reduced and manufacturing steps are greatly simplified. Furthermore, the polymer coated cellulosic substrate according to the present application has a predictable thickness as the extruded primer layer does not lose thickness during the setting process, whereas solvent borne primer layer compositions can lose up to 50-70% of the layer thickness during the drying process. Thus, the guaranteed performance and quality of the polymer coated cellulosic substrate produced on an industrial scale can be better managed.

[0040] The main embodiments are defined in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples described in the claims and the specification can be freely combined with each other unless explicitly stated otherwise. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 a A schematic representation of a cross-sectional view of a release liner REL1 according to the present application is shown by way of example, which comprises a polymer coated cellulosic substrate S2 and a release layer, i.e. a silicone coating SIL1.

[0042] Figure 1 b A schematic representation of a cross-sectional view of an example of a polymer coated cellulosic substrate S2 for a release liner according to the present application is shown.

[0043] Figure 2 A polyolefin coated cellulosic substrate is shown without an extruded primer layer.

[0044] Figure 3 A release liner is shown comprising a polyolefin coated cellulosic substrate without an extruded primer layer.

[0045] Figure 4 An example of a release liner according to the present application is shown.

[0046] Figure 5 A general formula and some variants of an organic acid anhydride having at least one acyl group with a chain-like carbon structure of at least 4 carbon atoms and ending in a vinyl group are exemplified, which are suitable for use as a reagent in a method for preparing a thermoplastic poly(vinyl alcohol) derivative by a reaction in the molten state.

[0047] Figure 6 condensation reaction of an organic anhydride with a thermoplastic poly(vinyl alcohol) in a molten state is exemplified, wherein at least some of the organic anhydride reacts with a hydroxyl group of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester linkages, thereby forming a reaction product comprising carboxylic acid residues and a thermoplastic poly(vinyl alcohol) derivative, wherein at least some of the carboxylic acid residues comprise a chain terminating in a vinyl group and at least some of the ester-linked side chains terminate in a vinyl group.

[0048] Figure 7 condensation reaction of an undecylenic anhydride with a thermoplastic poly(vinyl alcohol) in a molten state is exemplified, the undecylenic anhydride being a symmetrical anhydride comprising two identical acyl groups derived from 10-undecylenic acid, each acyl group having a vinyl group at the terminus, wherein at least some of the undecylenic anhydride reacts with a hydroxyl group of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester linkages, such that a reaction product comprising 10-undecylenic acid residues and a thermoplastic poly(vinyl alcohol) derivative is formed, wherein at least some of the ester-linked side chains terminate in a vinyl group.

[0049] Figure 8 condensation reaction of an acetyl undecylenic anhydride with a thermoplastic poly(vinyl alcohol) in a molten state is exemplified, the acetyl undecylenic anhydride being an asymmetrical anhydride comprising one acyl group derived from 10-undecylenic acid having a vinyl group at the terminus and another acyl group derived from acetic acid, wherein at least some of the acetyl undecylenic anhydride reacts with a hydroxyl group of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester linkages, such that a reaction product comprising acetic acid residues, 10-undecylenic acid residues, and a thermoplastic poly(vinyl alcohol) derivative is formed, wherein at least some of the ester-linked side chains terminate in a vinyl group.

[0050] It should be noted that the drawings are not drawn to scale.

[0051] Reference numerals:

[0052] REL1 - release liner

[0053] S2 - polymer coated cellulosic substrate

[0054] SIL1 - silicone coating

[0055] PRIM1 - extruded primer layer

[0056] TIE1 - tie layer

[0057] PO1 - first coating layer

[0058] PAPA1 - cellulosic support layer

[0059] AH1 - grafting agent, general formula

[0060] AH2 - Grafting agent, general formula

[0061] AH3 - Grafting agent, example

[0062] AH4 - Grafting agent, example

[0063] AH5 - Grafting agent, example

[0064] PVA1 - Thermoplastic PVA

[0065] CMP1 - Thermoplastic polymer covalently bound to functional vinyl groups, example

[0066] CMP2 - Thermoplastic polymer covalently bound to functional vinyl groups, example

[0067] CMP3 - Thermoplastic polymer covalently bound to functional vinyl groups, example

[0068] RD1 - Carboxylic acid residue, example

[0069] RD2 - Carboxylic acid residue, example

[0070] RD3 - Carboxylic acid residue, example

[0071] R 1 - organic group

[0072] R 2 - organic group DETAILED DESCRIPTION

[0073] The present application provides a polymer-coated cellulose substrate for a release liner and a method for preparing a polymer-coated cellulose substrate for a release liner.

[0074] Definition of the polymeric cellulose substrate

[0075] As described herein, a polymer-coated cellulose substrate refers to one of the three main categories of carrier substrates for industrially manufactured release liners: paper and paperboard, polymer films, and cellulose materials coated with a polymer layer.

[0076] A polymer coating can be applied on one or both sides of the cellulose material to make it, for example, smooth and moisture resistant. Commonly used materials for the polymer coating include polyolefins, such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), polypropylene (PP), and the like, and mixtures thereof. For example, the polymer coating can comprise a mixture of HDPE and LDPE.

[0077] The coating weight of the polymeric material used for the coating can vary depending on the application, for example, in the range of 5-32 g / m 2within the range of 10-15 g / m 2 In some examples, when the cellulose substrate is to be coated on one side only, the coating weight can be within the range of 10-15 g / m 2 In some examples, when the cellulose substrate is to be coated on both sides, the coating weight of each coating can be within the range of 18-20 g / m 3 In some examples, when the target density is 1 g / cm 2 The polymeric material corresponds to a thickness of 1 pm. The thickness of the polymer coated cellulose substrate varies depending on the desired basis weight / grammage and other end use considerations. The desired grammage of the polymer coated cellulose substrate can be achieved by lamination machines known to those skilled in the art.

[0078] Definition of the cellulose support layer

[0079] The cellulose support layer refers to a wide range of substrates which mainly comprise cellulose material, suitable for use as a carrier material for the release agent after being coated on one or both sides. The purpose of the cellulose support layer is to provide a dimensionally stable and compact surface on which a coating can be applied.

[0080] The cellulose support layer can be paper, preferably industrial paper, such as natural, bleached or semi-bleached kraft paper, calendered or super-calendered kraft paper (SCK paper), parchment paper, glassine paper, machine-finished paper, machine-glazed paper, high-grade paper or paperboard, having a basis weight of 18-400 g / m 2 (ISO 536), and a thickness of 30-500 pm.

[0081] Definition of the extrusion primer layer

[0082] The term "extrusion primer layer" as described herein refers to a layer structure made from thermoplastic substances by extrusion. Extrusion is a manufacturing process known to those skilled in the art. In the extrusion process of manufacturing the layer structure of the extrusion primer layer, the raw material is melted by the mechanical energy generated by the rotating screw and the heaters arranged along the barrel of the extruder, and then the molten material is pressed into a die, the molten material is shaped into the form of a continuous profile, which solidifies during the cooling process, thus forming the extrusion primer layer. A variety of dies are used in extrusion to form the layer structure, such dies include but are not limited to those used in blown film extrusion, sheet / film extrusion, co-extrusion and extrusion coating, all of which are known to those skilled in the art. Of course, the extrusion primer layer can be achieved by blown film extrusion, extrusion coating, co-extrusion, lamination, film transfer coating, etc. The extrusion primer layer has properties different from the solvent-based primer layer, as will be further explained in the present specification.

[0083] Description of the polymeric cellulose substrate according to the present application

[0084] Reference can be made to Figures 1 and Figure 4It should be noted that Figure 1 and... Figure 4 The examples shown are not intended to limit any specific implementation, but are only used to explain the relative positions of features indicated by the reference numerals in the accompanying drawings. Furthermore, Figure 1 and... Figure 4 The example shown is a schematic diagram, not a scale diagram.

[0085] This application provides a polymer-coated cellulose substrate S2 for release liner REL1, comprising:

[0086] - Cellulose support layer PAP1

[0087] - First coating PO1, which comprises a first composition containing a polyolefin.

[0088] - An extruded primer layer PRIM1 comprising a second composition containing a thermoplastic polymer covalently bonded to functional vinyl groups;

[0089] The first coating PO1 is located between the cellulose support layer PAP1 and the extruded primer layer PRIM1.

[0090] As described herein, the term "thermoplastic polymer covalently bonded to functional vinyl groups" refers to a thermoplastic polymer in which the main chain of the polymer has at least one type of functional side group comprising a vinyl group having the formula -CH=CH2. Such functional groups include, for example, vinyl, allyl, acrylate, 4-pentenyl, and 10-undecenyl. For extrusion to be possible, the material must be thermoplastic, meaning the polymer material becomes flexible or moldable at a certain high temperature and solidifies upon cooling.

[0091] Furthermore, for any polymer-coated cellulose substrate according to this application as presented herein, the thermoplastic polymer covalently bonded to the functional vinyl groups can preferably be obtained from the reaction product of molten thermoplastic material and a grafting agent containing functional vinyl groups, for example, by reactive extrusion. This reaction is rapid and inexpensive. More preferably, the reaction is a solvent-free reaction. Since the reaction does not require any organic solvents or water, obtaining the resulting reaction product also does not require any solvent separation or drying. The reaction product can also be in melt form, which can be extruded, or simply used for direct coating, or cooled and granulated for easy transport and storage for later use. Therefore, the application is more extensive when the thermoplastic polymer has already been obtained from the reaction product of molten thermoplastic material and a grafting agent containing functional vinyl groups.

[0092] Examples of grafting agents can be organic acid anhydrides, which can be derived from... Figure 5 The chemical formulas represented as AH1, AH2, AH3, AH4, and AH5 are used, where R... 1 and R 2 They represent different organic groups.

[0093] Organic anhydride refers to an organic compound having two acyl groups bonded to the same oxygen atom. The organic anhydride can be an aliphatic symmetrical anhydride or an asymmetrical anhydride. As used herein, symmetrical anhydride refers to an anhydride having two identical acyl groups, each acyl group ending in a vinyl group. As used herein, asymmetrical anhydride refers to an anhydride having different acyl groups, wherein at least one acyl group ends in a vinyl group.

[0094] Furthermore, according to the present application, for any polymer coated cellulose substrate as presented herein, the vinyl group containing thermoplastic polymer is formed from a thermoplastic poly(vinyl alcohol) (PVA) having a degree of hydrolysis of 65 to 95 mole %, for example 65, 70, 75, 80, 85, 90 or 95 mole %. A degree of hydrolysis lower than 95% is required to keep the melting point of the PVA below 200°C to avoid thermal degradation. PVA is a stable, non-toxic synthetic polymer that has excellent film forming, emulsifying and adhesive properties. It is made by hydrolysis of poly(vinyl acetate), which is a soft and sticky polymer at ambient temperature. The degree of hydrolysis should be at least 65% to ensure that the extruded PVA containing vinyl groups forms a solid, non-sticky film that can be wound into a reel. Therefore, the expression “thermoplastic poly(vinyl alcohol)” herein refers to a poly(vinyl alcohol) having thermoplastic properties. A degree of hydrolysis in the range of 65 to 95 mole % also contributes to the thermoplastic properties of the poly(vinyl alcohol). Decomposition of the thermoplastic PVA during extrusion should be avoided, because when the polymer decomposes to water and free vinyl groups, the former causes die blowouts and leads to holes in the extruded primer layer and / or a non-uniform surface of the extruded primer layer, while the latter starts crosslinking reactions, which in turn leads to a reduction of functional vinyl groups in the extruded primer layer. The risk of decomposition of the poly(vinyl alcohol) at high temperatures in the extruder can be reduced by selecting a thermoplastic poly(vinyl alcohol) grade with a degree of hydrolysis high enough, for example equal to or higher than 65 mole %. However, a grade with a degree of hydrolysis equal to or higher than 95 mole % can be less preferred, because also the coloration of the poly(vinyl alcohol) can occur due to excessive heating, especially when the amount of hydroxyl groups in the poly(vinyl alcohol) is very high.

[0095] Furthermore, according to the present application, for any polymer coated cellulose substrate as presented herein, the thermoplastic, preferably thermoplastic PVA, derivative comprises ester-bonded side chains, wherein at least some of the side chains end in a vinyl group, wherein the side chains ending in a vinyl group contain a chain-like carbon structure of at least 4 carbon atoms, preferably at least 9, most preferably 10 to 18 carbon atoms. A chain-like carbon structure with a chain length of less than 4 carbon atoms is less preferred, because a short chain length can result in a less easy accessibility of the vinyl group for reaction with the silicone. Also a longer chain length of more than 18 carbon atoms is not desirable, because it can result in folding of the chain itself, thereby also making the vinyl group less accessible.

[0096] Examples of thermoplastic PVA covalently bound to functional vinyl groups can beFigure 6 The Chinese version is represented as CMP1. Figure 7 The Chinese version is represented as CMP2 and Figure 8 The chemical formula for CMP3 is represented in Chinese.

[0097] Preferably, the organic acid anhydride participating in the condensation reaction to form the ester bond should have an acyl group with a chain-like carbon structure having a chain length of at least 4 carbon atoms and a vinyl terminus. This acyl group can thus form an ester bond with the hydroxyl group of the thermoplastic poly(vinyl alcohol) during the condensation reaction. Chain-like carbon structures with a chain length of less than 4 carbon atoms in the organic acid anhydride hydrocarbon chain are unsuitable because short chain lengths may interfere with the thermoplastic polyvinyl alcohol during the condensation reaction to form the ester bond. Preferably, the chain-like carbon structure contains 5 or more, preferably at least 9, and most preferably 10 to 18 carbon atoms. Longer chain lengths are undesirable because they may cause chain folding problems during or after the condensation reaction to form the ester bond.

[0098] like Figure 5 As shown, in asymmetric anhydrides AH1, AH3, and AH5, the two acyl groups of the anhydride are different. In symmetric anhydrides AH2 and AH4, the two acyl groups of the anhydride are the same. (Symbol R) 1 and R 2 Each represents a functional group individually, and at least one or two of them may have a chain-like carbon structure having a carbon chain length of at least 3 carbon atoms and a vinyl group at the end.

[0099] Furthermore, according to this application, for any polymer-coated cellulose substrate as presented herein, the thermoplastic (preferably thermoplastic PVA) derivative comprises ester-bonded side chains, wherein at least some of the side chains are vinyl-terminated, and the vinyl-terminated side chains contain a chain-like carbon structure of at least four carbon atoms. The extruded primer layer PRIM1 also comprises carboxylic acid residues, wherein the carboxylic acid residues are organic compounds containing a chain-like carbon structure of at least four carbon atoms of the same type as the side chains of the thermoplastic poly(vinyl alcohol) derivative, and are vinyl-terminated. The carboxylic acid residues have been observed to act as surfactants on the polymer-coated cellulose substrate S2. This effect has been observed even when some of the carboxylic acid residues on the extruded primer layer PRIM1 have been neutralized to the corresponding carboxylate salts, i.e., salts of the carboxylic acid residues. When arranged on the extruded primer layer PRIM1 of the polymer-coated cellulose substrate S2, the carboxylic acid residues can be configured to improve the spreading of the subsequent silicone-based composition, which can be used as a release coating SIL1, on the polymer-coated cellulose substrate S2.

[0100] Examples of carboxylic acid residues can be derived from... Figure 6 In, it is represented as RD1, in Figure 7 In, it is represented as RD2 and in Figure 8 The chemical formula for RD3 is represented in Chinese.

[0101] The second composition can also comprise a salt of a carboxylic acid residue, i.e. a carboxylate.

[0102] Furthermore, according to the present application, for any polymer coated cellulose substrate presented herein, the second composition comprising a thermoplastic polymer comprising functional vinyl groups can also comprise:

[0103] - one or more additives, such as plasticizers, and / or

[0104] - one or more non-thermoplastic materials, such as starch or carboxymethylcellulose (CMC).

[0105] The use of plasticizers results in better processing properties. Examples of such plasticizers are ethylene glycol, polyethylene glycol, glycerol, etc.

[0106] If the first coating PO1 and the extrusion primer layer PRIM1 have polymers of different polarity, it would be beneficial to use a compatibilizer.

[0107] In one example, the extrusion primer layer PRIM1 comprises a thermoplastic PVA covalently bound to functional vinyl groups and the first coating PO1 comprises a polyolefin such as a mixture of polyethylene, e.g. HDPE and LDPE. The use of a compatibilizer improves the interfacial adhesion by making the first coating PO1 surface more polar and able to form hydrogen bonds or covalent bonds with the hydroxyl groups of the thermoplastic PVA. The extrusion primer layer PRIM1 can form an improved interfacial adhesion with a surface of sufficient polarity. The additional tie layer TIE 1 is a better option compared to a mixture of a non-polar polymer and a compatibilizer as it results in a higher density of available polar groups on the surface.

[0108] Furthermore, according to the present application, for any polymer coated cellulose substrate presented herein, wherein the thermoplastic polymer covalently bound to vinyl groups is formed by a thermoplastic poly(vinyl alcohol),

[0109] At least one of the first coating PO1 and the extrusion primer layer PRIM1 further comprises at least one compatibilizer which is a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate; and additionally or alternatively,

[0110] The polymer coated cellulose substrate S2 can further comprise a tie layer TIE1 between the first coating PO1 and the extrusion primer layer PRIM1, such as an adhesion promoting layer comprising at least one compatibilizer, such as a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

[0111] In some examples, the extrusion primer layer PRIM1 can comprise a compatibilizer, such as an anhydride-modified polyolefin. The anhydride reacts with an alcohol to form an ester crosslink.

[0112] In some examples, the first coating PO1 comprises a compatibilizer, such as an anhydride-modified polyolefin. The anhydride present on the surface of the first coating PO1 reacts with the alcohol present in the extrusion primer layer PRIM1 to form ester crosslinks, thus, further improving the adhesion between the extrusion primer layer PRIM1 and the first coating PO1.

[0113] Furthermore, according to the present application, for any polymer coated cellulose substrate presented herein, the cellulose support layer PAP1 comprises cellulose fibers comprising pulp, wherein the cellulose fibers are preferably derived from wood. Wood species differ in mechanical properties and chemical composition. The wood material used for the cellulose support layer PAP1 can be from softwood trees, such as spruce, pine, fir, larch, Douglas fir or hemlock, or from hardwood trees, such as birch, poplar, aspen, alder, eucalyptus or acacia, or from a mixture of softwood and hardwood.

[0114] The pulp used in the cellulose support layer PAP1 can comprise cellulose fibers from both hardwood and softwood. Pulp comprising a mixture of hardwood and softwood can be used to increase the internal bond strength of the paper web during the manufacturing process.

[0115] Thus, herein, cellulose pulp preferably refers to a material derived from a lignocellulosic material that has been processed into a fibrous form, such as fibers, using a chemical, mechanical, thermo-mechanical or chemi-thermo-mechanical pulping process. According to one embodiment, the pulp used for manufacturing the cellulose support layer PAP1 suitable for the release liner REL1 does not contain any kind of mechanical pulp due to the high quality requirements of the release liner REL1.

[0116] The cellulose support layer PAP1 of the release liner REL1 can also comprise other ingredients, such as fillers. For example, at least one mineral filler can be used in the support layer SUP1. The mineral filler can comprise, for example, at least one of the following: clay, calcinated clay, kaolin, natural ground calcium carbonate, precipitated calcium carbonate, talc, calcium sulfate and titanium dioxide. Furthermore, the cellulose support layer PAP1 can comprise a mineral coating.

[0117] The total amount of mineral filler in the cellulose support layer PAP1 can be equal to or greater than 0 wt.%, such as at least 0.5 wt.%, based on the total weight of the cellulose support layer PAP1. The total amount of mineral filler in the cellulose support layer PAP1 is preferably less than 10 wt.%, more preferably less than 5 wt.%, most preferably less than 3 wt.%, such as 0.5 to 5 wt.%, or 0 wt.% to 3 wt.%, based on the total weight of the cellulose support layer PAP1. The mineral filler can reduce the cost of manufacturing the product. However, in addition to reducing the strength properties, the mineral filler can also reduce the transparency level of the product.

[0118] The cellulose support layer PAP1 can be calendered before or after the first coating to obtain a product with a high-density surface.

[0119] Reducing the basis weight of paper to lighten the release liner may be beneficial for manufacturing and shipping costs. However, this often leads to adverse effects because paper with a lower basis weight is typically thinner and may have poorer strength properties. Therefore, it may not be suitable for its intended use, such as as a support layer in automated high-speed labeling processes. When the basis weight is reduced, the specific volume and tear resistance of conventional paper also typically decrease. The smoothness of the paper surface may also decrease, which can negatively impact subsequent release coatings.

[0120] The basis weight of the cellulose support layer PAP1 suitable for release liner REL1 is preferably equal to or less than 160 g / m². 2 Preferably equal to or less than 80g / m 2 The optimal value is equal to or less than 70 g / m 2 The basis weight of the cellulose support layer PAP1 suitable for release liner is preferably equal to or greater than 30 g / m². 2 For example, equal to or greater than 40g / m 2 For example, at 30g / m 2 Up to 120g / m 2 Within the range, or at 40g / m 2 Up to 100g / m 2 Within the range. Weight is between 40 and 80 g / m³. 2 Within the range, the optimal value is 50 to 70 g / m³. 2 The cellulose support layer PAP1 within this range may benefit from an increase in bulk. Weight in this article refers to basis weight, expressed in grams per square meter (g / m²). 2 ).

[0121] Therefore, the basis weight of the cellulose support layer PAP1 is preferably at least 35 g / m³. 2 More preferably at least 40g / m 2 And preferably less than 100g / m 2 More preferably equal to or less than 90 g / m 2 For example, the weight can range from 38 to 100 g / m³. 2 Within the range, or between 40 and 90 g / m 2 between.

[0122] Furthermore, according to this application, for any polymer-coated cellulose substrate presented herein, the cellulose support layer PAP1 comprises kraft pulp fibers, and the basis weight of the cellulose support layer is 35 g / m². 2 Up to 100g / m2 .

[0123] The extrusion primer layer PRIM1 has excellent adhesion to the overlying silicone coating SIL1. On the polymer coated cellulose substrate S2 according to the present application, a silicone resin coating SIL1, i.e. a release coating, can be applied on the surface of the extrusion primer layer PRIM1 of the polymer coated cellulose substrate S2, which is subsequently heat cured in a catalytic hydrosilylation reaction, thereby forming a release liner REL1 comprising the silicone resin coating SIL1, the cellulose support layer PAP1, the first coating PO1 on the cellulose support layer PAP1 and the extrusion primer layer PRIM1 between the silicone resin coating SIL1 and the first coating PO1.

[0124] The catalytic hydrosilylation reaction, also known as hydrosilylation, refers to the formation of a covalent bond between the functional vinyl groups in the silicone base polymer and the silicon-hydrogen (Si-H) groups in the crosslinker compound in the presence of a platinum catalyst. This reaction forms the solid release layer SIL1 on the surface of the extrusion primer layer PRIM1. Due to the presence of the functional vinyl groups on the surface of the extrusion primer layer PRIM1, a covalent bond also forms between the functional vinyl groups in the extrusion primer layer PRIM1 and the silicon-hydrogen (Si-H) groups in the crosslinker during the catalytic hydrosilylation reaction. The covalent bond between the silicone coating SIL1 and the extrusion primer layer PRIM1 contributes to a strong interaction and thus facilitates the anchoring of the silicone coating SIL1 to the polymer coated cellulose substrate S2.

[0125] Furthermore, the extrusion primer layer PRIM1 contributes to an improved surface coverage of the subsequent silicone coating and thus to an improved consistency of the release value. The release value is used to indicate the minimum force required to separate a label or excess substrate material from the release liner. A high quality silicone coating SIL1 requires a good coverage to the polymer coated cellulose substrate S2. Reference can be made to Figure 2 and Figure 3 . As Figure 2The shown uncoated areas and pinholes and contaminations increase the release value and give a poor release stability over time. The surface of the polymer coated cellulose substrate S2 with less defects, such as pinholes, also promotes a good coverage of the silicone coating. Pinholes are a kind of pore penetration that occurs in solvent-borne coatings, usually due to the entrapment of moisture, air, solvents or other liquids. The number of pinholes on the surface of the extrusion primer layer PRIM1 according to the present application has been significantly reduced. This is because the primer layer composition used for the extrusion primer layer PRIM1 does not contain water or solvents, thus avoiding the entrapment of moisture or volatile solvents. Furthermore, no corona treatment is required, which can also cause pinholes on the polyolefin coating. Since the silicone coating fills fewer pores, the polymer coated cellulose substrate S2 according to the present application can be siliconized with a lower silicone coating weight. The cellulose support layer PAP1 is also protected from silicone contamination. Thus, the cost efficiency of the production of the silicone coating can be improved.

[0126] Furthermore, according to the present application, for any polymer coated cellulose substrate presented herein, the polymer coated cellulose substrate has at least one of the following properties:

[0127] - the PPS roughness value is less than 2 pm,

[0128] - the extrusion primer layer PRIM 1 comprising a thermoplastic polymer covalently bound to functional vinyl groups has a coating weight of at least 0.6 g / m 2 ,

[0129] - the extrusion primer layer PRIM1 contains at least 0.06 mmol / m 2 of functional vinyl groups,

[0130] - the thermoplastic polymer comprises a molar concentration of vinyl groups b vin 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, most preferably in the range of 0.15 mmol / g to 0.80 mmol / g, determined as millimoles per gram of dry thermoplastic polymer when determined by iodometric titration according to standard ISO 396 1 :2009(E),

[0131] Polyolefin coated paper, such as PE coated paper, typically has a Parker Print-Surf (PPS) average roughness value of 1-2 μm. PPS roughness can be measured using a PPS (Parker Print Surface) roughness tester known to those skilled in the art. The polymer-coated cellulose substrate with a PPS roughness value of less than 2 μm, according to this application, contributes to a smooth surface for subsequent silicone coatings. Furthermore, as mentioned above, polyolefin coated paper, such as PE coated paper, may contain pinholes. Such pinholes... Figure 2 As shown. Therefore, when applying the silicone coating solution, as... Figure 3 As shown, the coating solution fills the pores, leading to the waste of expensive coating solution and the risk of contaminating the cellulose support layer.

[0132] According to this application, if the first coating PO1 contains any pores, these pores can be filled with an extruded primer layer PRIM1, such as... Figure 4 As shown. Therefore, the polymer-coated cellulose substrate S2 can have improved smoothness. Thus, the polymer-coated cellulose substrate according to this application is pinhole-free. This helps to provide a smooth surface for subsequent silicone coatings. A smoother surface requires less silicone coating solution. According to this application, the extruded primer layer provides a smooth surface for subsequent silicone coatings. The polymer-coated cellulose substrate according to this application can be siliconeized with a smaller silicone coating weight, for example, 0.6 to 0.8 g / m³. 2 Or even smaller. Therefore, this is an economically ideal solution. Furthermore, the extruded primer layer has a consistent surface roughness, which contributes to a consistent release value for the silicone coating.

[0133] The polymer-coated cellulose substrate according to this application is pinhole-free. This facilitates good coverage for subsequent silicone coatings. This ensures a good release value for the release layer.

[0134] According to this application, the disclosed amount of thermoplastic polymer covalently bonded to functional vinyl groups has been shown to contribute to good silicone anchoring. The coating weight can be, for example, 0.5–10.0 g / m². 2 Preferably 0.5–4.0 g / m 2 More preferably 1.0–2.0 g / m 2 Experimental results show that the extruded primer layer PRIM1 contains 0.6 g / m 2 Thermoplastic polymers covalently bonded to functional vinyl groups, such as thermoplastic PVA, contribute to excellent adhesion between the polymer-coated cellulose substrate and the silicone layer in a wipe test.

[0135] The same effect has been observed, proving that the disclosed amount of vinyl groups contributes to good silicone anchoring. The functional vinyl groups contained in the extrusion primer layer PRIM1 comprising a thermoplastic PVA covalently bound to the functional vinyl groups, for example, can have the following vinyl group density: for example, 0.025 - 20 mmol / m 2 , preferably 0.05 - 4.0 mmol / m 2 , more preferably 0.15 - 1.6 mmol / m 2 .

[0136] measured in millimoles per gram of dry thermoplastic polymer (e.g. functional vinyl group containing thermoplastic PVA) when determined by iodometric titration according to standard ISO 3961 :2009(E), when the thermoplastic polymer comprises a molar concentration b vin of vinyl groups 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, most preferably in the range of 0.15 mmol / g to 0.80 mmol / g, the same effect is observed. This is thus an economically desirable solution. As a result, a product with good rub-off properties can be obtained. Furthermore, the amount of release coating containing silicone compounds can be reduced. Furthermore, less platinum catalyst is needed for the curing of the less amount of release coating. Because the siliconization of the reactive surface layer can require less platinum catalyst for the silicone curing to take place, the manufacturing costs of the release liner can be reduced.

[0137] Furthermore, according to the present application, for any polymer coated cellulose substrate as presented herein, the first coating PO1 can comprise polypropylene or polyethylene, for example low density polyethylene (LDPE) and / or high density polyethylene (HDPE), because these polymers are particularly suitable for release liners and are inexpensive. The extrusion primer layer according to the present application is suitable for various polymer coated papers.

[0138] In some examples, the polymer coated cellulose substrate can further comprise a tie layer TIE1 between the extrusion primer layer PRIM1 and the first coating PO1. The thermoplastic polymer covalently bonded to the functional vinyl groups is formed from a thermoplastic poly(vinyl alcohol), the first coating PO1 comprises a polyolefin, for example polyethylene, and the tie layer TIE1 comprises a polyethylene grafted with maleic anhydride.

[0139] Detailed description of the method according to the present application

[0140] The present application also provides a method for manufacturing a polymer coated cellulose substrate S2 for a release liner, the method comprising:

[0141] - providing a cellulose support layer PAP1,

[0142] - extruding a molten first composition comprising a polyolefin, thereby obtaining an extruded first composition,

[0143] - extruding a molten second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group, thereby obtaining an extruded second composition,

[0144] - reducing the temperature of the extruded molten first composition to below its melting point, thereby forming a first coating PO1,

[0145] - reducing the temperature of the extruded molten second composition to below its melting point, thereby forming an extrusion primer layer PRIM1, and

[0146] - forming a polymer-coated cellulose substrate S2 comprising a cellulose support layer PAP1, an extrusion primer layer PRIM1 and a first coating PO1 located between the cellulose support layer PAP1 and the extrusion primer layer PRIM1.

[0147] The product obtained according to the process of the present application, i.e. the polymer-coated cellulose substrate S2, has the effects as described above.

[0148] The second composition comprising an extrudable polymeric material, including a thermoplastic polymer covalently bound to a functional vinyl group as defined above, and possible additives, such as plasticizers or compatibilizers, can be fed into an extruder to form a molten second composition. This can be applied to extrusion coating the resulting extrusion primer layer PRIM1 onto the surface of the first coating PO1 of the cellulose support layer PAP1, the cellulose support layer PAP1 with the first coating PO1 thereon can be a carrier sheet moving through the extruder die. The die extrudes the polymeric material through a narrow slot vertically, forming a low viscosity thin coating of uniform thickness of the melt, which is uniformly coated on the carrier sheet moving continuously at high speed through the extruder die. As described above, due to the presence of the functional vinyl group on the surface of the extrusion primer layer PRIM1, a covalent bond is formed between the functional vinyl group in the extrusion primer layer PRIM1 and the silicon-hydrogen (Si-H) group in the crosslinker in the silicone coating composition during the catalytic silicon-hydrogenation reaction to cure the silicone coating. The surface of the extrusion primer layer is only reactive to the silicone coating during the application of the silicone coating. This provides great flexibility for the industrial line-up of the production. The thickness of the extrusion primer layer PRIM 1 can be controlled by the winding speed. Therefore, the guaranteed performance and quality of the polymer-coated cellulose substrate produced at an industrial scale can be better managed. Furthermore, the extrusion coating operation uses high melt temperature to reduce the melt viscosity. This improves the coating thickness uniformity and adhesion.

[0149] Preferably, the process can further comprise:

[0150] - extruding a third composition comprising a compatibilizing agent, thereby obtaining an extruded third composition, and

[0151] - reducing the temperature of the extruded molten third composition below its melting point, thereby forming a tie layer TIE1,

[0152] such that the tie layer TIE1 is located between the first coating PO1 and the extruded primer layer PRIM1.

[0153] According to the process of the present application, at least two of the above-mentioned molten compositions can be co-extruded. For example, the first composition and the second composition can be co-extruded to be coated on the cellulose support layer. In another example, the first composition, the second composition and the third composition can be co-extruded to be coated on the cellulose support layer. In another example, the second composition and the third composition can be co-extruded to be coated on the polyolefin coated cellulose support layer, which support layer has already been coated with the first composition.

[0154] The product obtained according to the process of the present application, i.e. the polymer coated cellulose substrate S2, has the effects as described above.

[0155] The extrusion equipment used to carry out the co-extrusion process of the present application can comprise, for example, at least two extruders, a film die, a cooling cylinder, optionally a orientation / stretching unit and a rewinder. The molten first composition and the molten second composition and optionally the third composition are fed from the extruders, converge in the die and are laminated together into a single film. As described above, due to the presence of the functional vinyl groups on the surface of the extruded primer layer PRIM1, covalent bonds are formed between the functional vinyl groups in the extruded primer layer PRIM1 and the silicon-hydrogen (Si-H) groups in the crosslinking agent in the silicone coating composition during the catalytic silicon-hydrogenation reaction that cures the silicone coating. The surface of the extruded primer layer is only reactive towards the silicone coating during the application of the silicone coating. This provides great flexibility for the industrial line-up. The layer ratio can be controlled by the screw speed and the total film thickness can be controlled by the winding speed. Thus, the predictability and guaranteed performance and quality of the polymer coated cellulose substrate produced on an industrial scale can be better managed.

[0156] To carry out one of the processes described herein according to the present application, an extruder can be used to convert a solid composition comprising a thermoplastic polymer containing a vinyl group into a melt at the appropriate temperature required for coating, thereby obtaining a molten second composition comprising a thermoplastic polymer containing a vinyl group. Preferably, the thermoplastic polymer has been obtained from the reaction product of a molten thermoplastic material and a grafting agent containing a functional vinyl group.

[0157] The chemical reaction to modify the thermoplastic material can be performed using the same or another extruder to produce a molten state of the vinyl group containing thermoplastic polymer at the appropriate temperature required for coating, to obtain a molten second composition comprising the vinyl group containing thermoplastic polymer. The thermoplastic polymer can be obtained from the reaction product of the molten thermoplastic material and the grafting agent, for example by reactive extrusion.

[0158] Further, according to the present application, for any of the methods described herein, the thermoplastic polymer can be obtained from the reaction product of the molten thermoplastic material and the grafting agent containing functional vinyl groups. This method is fast and cost effective. The reaction is more advantageously a solvent-free reaction. Since the reaction does not require any organic solvent or water, the resulting reaction product is also obtained without any solvent separation or drying. The reaction product is also in the form of a melt, which can be extruded, or simply used for direct coating, or cooled and pelletized for ease of transportation and storage for later use. The reaction is easily performed in a reactor such as an extruder, so there are no mixing issues, which can exist in solvent-based reactions.

[0159] Further, according to the present application, for any of the methods as presented herein, the vinyl group containing thermoplastic polymer is formed from a thermoplastic polyvinyl alcohol) (PVA) having a degree of hydrolysis of 65 to 95 mole %, for example 65, 70, 75, 80, 85, 90, or 95 mole %. The definition of such a thermoplastic polyvinyl alcohol) and the effects that come with it have been described above. The resulting product, i.e. the polymer coated cellulose substrate S2, has the effects as described above.

[0160] Further, according to the present application, for any of the methods as presented herein, the thermoplastic polymer (preferably thermoplastic PVA) comprises ester-bonded side chains, wherein at least some of the side chains terminate in a vinyl group, wherein the side chains that terminate in a vinyl group contain a chain-like carbon structure of at least 4 carbon atoms, the extrusion primer layer PRIM1 further comprises carboxylic acid residues, wherein the carboxylic acid residues are organic compounds that contain a chain-like carbon structure of at least 4 carbon atoms of the same kind as the side chains of the thermoplastic polyvinyl alcohol) derivative, which terminate in a vinyl group. It has been observed that the carboxylic acid residues act as a surfactant on the polymer coated cellulose substrate S2. This effect has been observed even when some of the carboxylic acid residues on the extrusion primer layer PRIM1 have been neutralized to the corresponding carboxylic acid salt, i.e. the salt of said carboxylic acid residues. The carboxylic acid residues can be configured to improve the spreading of a silicone-based composition that can be used as a release coating SIL1 on the polymer coated cellulose substrate S2 when arranged on the extrusion primer layer PRIM1 of the polymer coated cellulose substrate S2. The resulting product, i.e. the polymer coated cellulose substrate S2, has the effects as described above.

[0161] Examples of thermoplastic PVA covalently bound to functional vinyl groups can be obtained fromFigure 6 is denoted as CMP1, Figure 7 is denoted as CMP2 and Figure 8 is denoted as CMP3. Examples of carboxylic acid residues can be represented by the chemical formulae Figure 6 denoted as RD1, in Figure 7 denoted as RD2 and in Figure 8 denoted as RD3.

[0162] As shown in Figure 6 , 7 and 8, when the aliphatic organic acid anhydride AH1, AH2, AH3, AH4, AH5 is reacted in a condensation reaction in the molten state with the hydroxyl groups of the thermoplastic poly(vinyl alcohol) PVA1, one of the acyl groups forms an ester bond with a hydroxyl group of the poly(vinyl alcohol) PVA1, while the other acyl group becomes a carboxylic acid residue RD1, RD2, RD3. The formed thermoplastic poly(vinyl alcohol) derivative CMP1, CMP2, CMP3 thus comprises ester-bonded side chains, at least some of which terminate in a vinyl group, wherein the side chains which terminate in a vinyl group comprise a chain-like carbon structure of at least 4 carbon atoms. Statistically, the likelihood of either acyl group of the aliphatic acid anhydride to participate in the condensation reaction to form an ester bond is the same. Thus, the carboxylic acid residue RD1, RD2, RD3 is also an organic compound which contains a chain-like carbon structure of at least 4 carbon atoms of the same type as the chain-like carbon structure of the ester-bonded side chains of the thermoplastic poly(vinyl alcohol) derivative CMP1, CMP2, CMP3, which terminates in a vinyl group.

[0163] Furthermore, according to the present application, for any of the methods described herein, the second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group can further comprise:

[0164] - one or more additives, such as plasticizers, and / or

[0165] - one or more non-thermoplastic materials, such as starch or carboxymethylcellulose (CMC).

[0166] The use of plasticizers leads to better processing properties. Examples of such plasticizers are ethylene glycol, polyethylene glycol, glycerol, etc. The resulting product, i.e. the polymer-coated cellulose substrate, has the effects as described above.

[0167] Furthermore, according to the present application, for any of the methods presented herein, wherein the thermoplastic polymer containing a vinyl group is formed from a thermoplastic poly(vinyl alcohol),

[0168] The polymer-coated cellulose substrate S2 can further comprise a tie layer TIE1 between the first coating layer PO1 and the extrusion primer layer PRIM1, said tie layer TIE1 comprising at least one compatibilizer, such as a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

[0169] In some examples, the extrusion primer layer PRIM1 can comprise a compatibilizer, such as an anhydride-modified polyolefin. The anhydride, typically maleic anhydride, reacts with an alcohol to form an ester crosslink.

[0170] In some examples, the first coating PO1 can comprise a compatibilizer, such as an anhydride-modified polyolefin. The anhydride present on the surface of the first coating PO1 reacts with the alcohol present in the extrusion primer layer PRIM1 to form an ester crosslink, thus, further improving the adhesion between the extrusion primer layer PRIM1 and the first coating PO1.

[0171] Furthermore, according to the present application, for any method presented herein, the extrusion primer layer PRIM1 has at least one of the following properties:

[0172] - a PPS roughness value of less than 2 pm,

[0173] - a coating weight of the thermoplastic polymer covalently bound to the functional vinyl group of 0.5 - 10.0 g / m 2 , preferably 0.5 - 4.0 g / m 2 , such as at least 0.6 g / m 2 , more preferably 1.0 - 2.0 g / m 2 ,

[0174] - the extrusion primer layer PRIM1 contains 0.025 - 20 mmol / m 2 , preferably 0.05 - 4.0 mmol / m 2 , such as at least 0.06 mmol / m 2 , more preferably 0.15 - 1.6 mmol / m 2 of functional vinyl groups,

[0175] - the thermoplastic polymer contains a vinyl molar concentration b vin equal to or higher than 0.01 millimole per gram of thermoplastic polymer, preferably equal to or higher than 0.03 millimole per gram of thermoplastic polymer, when determined by iodometric titration according to standard ISO 3961 :2009(E).

[0176] The effects of these properties have been described above. The resulting product, i.e. the polymer-coated cellulose substrate, has the effects as described above.

[0177] Furthermore, according to the present application, for any method as presented herein, the first coating PO1 can comprise polypropylene or polyethylene, such as low-density polyethylene (LDPE) and / or high-density polyethylene (HDPE), as these polymers are particularly suitable for release liners and are inexpensive. The extrusion primer layer according to the present application is suitable for various polymeric coating papers.

[0178] In some examples, the polymer-coated cellulose substrate can further comprise a tie layer TIE1 between the extrusion primer layer PRIM1 and the first coating layer PO1. The thermoplastic polymer covalently bonded with the functional vinyl groups is formed from a thermoplastic poly(vinyl alcohol), the first coating layer comprises a polyolefin, such as polyethylene, and the tie layer TIE1 comprises a polyethylene grafted with maleic anhydride.

[0179] Further, according to the present application, for any method described herein, the method can further comprise, prior to providing the molten second composition:

[0180] - reacting the molten thermoplastic material with a grafting agent containing functional vinyl groups, preferably in a solventless reaction, thereby obtaining a thermoplastic polymer covalently bonded with the functional vinyl groups.

[0181] The resulting product, i.e. the polymer-coated cellulose substrate S2, has the effects as described above.

[0182] Further, according to the present application, for any method presented herein, wherein the thermoplastic polymer covalently bonded with the vinyl groups is formed from a thermoplastic poly(vinyl alcohol), can further comprise at least one compatibilizer, such that:

[0183] At least one of the first coating layer PO1 and the extrusion primer layer PRIMA1 further comprises at least one compatibilizer which is a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate; and additionally or alternatively,

[0184] The polymer-coated cellulose substrate S2 further comprises a tie layer TIE1 between the first coating layer PO1 and the extrusion primer layer PRIM1, said tie layer TIE1 comprising at least one compatibilizer, such as a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

[0185] In some embodiments, the extrusion primer layer PRIM1 comprises a compatibilizer, such as an anhydride-modified polyolefin. The anhydride reacts with an alcohol to form an ester crosslink.

[0186] In some examples, the first coating layer PO1 comprises a compatibilizer, such as an anhydride-modified polyolefin. The anhydride present on the surface of the first coating layer PO1 reacts with an alcohol present in the extrusion primer layer PRIM1 to form an ester crosslink, thus further improving the adhesion between the extrusion primer layer PRIM1 and the first coating layer PO1.

[0187] Furthermore, according to the present application, for any method presented herein, the step of extruding the molten second composition or at least the step of co-extruding the molten first composition and the molten second composition comprises co-extruding a molten third composition, thereby forming a adhesion promoting layer comprising the third composition between the first coating layer PO1 comprising the first composition and the extrusion primer layer PRIM1 comprising the second composition.

[0188] Furthermore, according to the present application, for any method described herein, the step of providing a molten second composition is performed:

[0189] - heating a thermoplastic poly(vinyl alcohol) having hydroxyl groups, wherein the thermoplastic poly(vinyl alcohol) has been dried and has a degree of hydrolysis in the range of 65 to 95 mol-%,

[0190] and

[0191] - mixing a grafting agent with the thermoplastic poly(vinyl alcohol), wherein the grafting agent is an organic acid anhydride having at least a chain having a chain-like carbon structure of at least 4 carbon atoms and ending in a vinyl group,

[0192] thereby obtaining a mixture comprising the molten thermoplastic poly(vinyl alcohol) having hydroxyl groups and the organic acid anhydride containing a chain ending in a vinyl group, and

[0193] - mixing the mixture at a temperature above the melting point of the mixture, thereby causing a reaction in the molten state, wherein at least some of the organic acid anhydride reacts with the hydroxyl groups of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester bonds,

[0194] thereby forming a reaction product as the second composition comprising:

[0195] - carboxylic acid residues of the condensation reaction forming ester bonds, wherein at least some of the carboxylic acid residues comprise a chain ending in a vinyl group, and

[0196] - thermoplastic poly(vinyl alcohol) derivatives comprising ester-bonded side chains, wherein at least some of the side chains end in a vinyl group.

[0197] Examples of providing a molten second composition can be illustrated by the chemical equations in Figure 6 to Figure 8

[0198] ​Generally, temperatures in the range of 170 to 210 °C can be used for the condensation reaction. The lower limit of the suitable temperature range is limited by the melting point of the thermoplastic poly(vinyl alcohol) PVA1 and the mixture. The upper limit of the suitable temperature range is limited by the decomposition temperature of the poly(vinyl alcohol) PVA1 and / or its derivatives. Most preferably, the temperature is in the range of 170 to 190 °C, which reduces the likelihood of thermal decomposition of the thermoplastic poly(vinyl alcohol) PVA1 and / or its derivatives. The reaction is preferably carried out in the molten state without the addition of a solvent. The non-addition of a solvent allows for a smaller reaction volume. The duration of the reaction in the molten state can be less than 5 minutes, preferably less than 1 minute, more preferably less than 20 seconds. If desired, an inhibitor can be used to inhibit the spontaneous radical polymerization of the vinyl groups and / or to inhibit the crosslinking reaction of the thermoplastic poly(vinyl alcohol) PVA1 and / or its derivatives. One example of such an inhibitor is butylated hydroxytoluene, which can act as a radical scavenger, inhibiting radical reactions such as polymerization and crosslinking. Furthermore, if desired, a homogeneous or heterogeneous catalyst can be used to accelerate the condensation reaction of the ester bond formation. Suitable catalysts can be, for example, Bronsted acids (such as sulfuric acid), Lewis acids (such as tin(II) octoate) or Bronsted / Lewis bases (such as alkali metal alkoxides or carbonates). Furthermore, pyridine can be used as such a catalyst. The preferred catalyst is 1-methylimidazole, which has a high catalytic activity, 4x 10 2 times higher than that of pyridine.

[0199] If desired, at least some of the carboxylic acid residues in the reaction product can be neutralized with a basic agent such as NaOH, thereby forming a salt of the carboxylic acid residue, i.e. a carboxylate.

[0200] The thermoplastic poly(vinyl alcohol) derivative comprised in the reaction product can have a degree of hydrolysis of 60% to 90%. The thermoplastic poly(vinyl alcohol) derivative comprised in the reaction product can further have a melt flow index in the range of 0.5-300 g / 10 min. The melt flow index can be determined according to standard ISO 1133-1 :2011 (210 °C, 2.16 kg) using a melt point measuring device or using differential scanning calorimetry.

[0201] In contrast, the melt state reaction can be accomplished in large quantities in a short time using compact equipment, thereby enabling centralized production and easy distribution of the solid water-soluble reaction product to paper mills all over the world.

[0202] The polymer-coated cellulose substrate (S2) and the method of manufacturing the polymer-coated cellulose substrate (S2) are particularly suitable for a release liner. Therefore, a release liner is also provided, comprising:

[0203] - a polymer-coated cellulose substrate according to the present application, or obtainable by a method according to the present application, and

[0204] - silicone coating on a polymeric coated cellulose substrate.

[0205] Example

[0206] Example 1 : melt state reaction of poly (vinyl alcohol) with 10-undecenoic anhydride

[0207] An experimental study was performed in which a mixture containing thermoplastic polyvinyl alcohol and 10-undecylenic anhydride was reacted in a condensation reaction forming ester bonds in the molten state, resulting in a reaction product containing a thermoplastic polyvinyl alcohol derivative and carboxylic acid residues. 10-Undecylenic anhydride is a symmetrical anhydride resulting from the condensation of two 10-undecylenic acid molecules with a vinyl group at both ends. Thus, 10-undecylenic anhydride has two chains with a chain-like carbon structure and a vinyl group at both ends. The amount of 10-undecylenic anhydride mixed with the thermoplastic polyvinyl alcohol was 5% by weight, determined from the total weight of the mixture. The reaction was performed using a twin-screw extruder (ZSK 25, Coperion®) counter-rotating with a screw diameter of 32 mm and a screw length of 330.7 mm, which contained one feeding unit, three heating zones and one die zone for extruding the material.

[0208] In the experimental study, first 1.9 kg of thermoplastic polyvinyl alcohol with a degree of hydrolysis of 80 mol% (Kuraray 3-80 grade) was dried in an oven at a temperature of 60 °C for 24 hours, resulting in dried thermoplastic polyvinyl alcohol. Then the dried thermoplastic polyvinyl alcohol was fed together with 0.1 kg of 10-undecylenic anhydride via the feeding unit into the extruder. The screw of the extruder was rotated at a speed of 30 rpm. The three heating zones were adjusted to have a temperature profile providing a smooth running performance. The temperature of the first heating zone adjacent to the feeding unit was 190 °C, the temperature of the second heating zone was also 190 °C and the temperature of the third heating zone was 195 °C. The temperature of the extrusion die zone was set to 200 °C. Thus, the 10-undecylenic anhydride reacted with the thermoplastic polyvinyl alcohol in a condensation reaction forming ester bonds in the molten state, resulting in a thermoplastic polyvinyl alcohol derivative containing ester-bonded 10-undecenoyl groups. The reaction product was extruded through the die and air-cooled to below the melting point of the mixture, pelletized to form a solid reaction product, i.e. an extrudate. In the following examples, the extrudate is denoted mPVA.

[0209] Example E1 : polymeric cellulose substrate made by extrusion coating mPVA on PE coated kraft paper Kraft paper

[0210] A commercially available PE-coated kraft paper was provided. The PE- uncoated kraft paper had the following properties:

[0211] Basis weight Caliper 80 g / m 2 ]] 90 pm Bendt. roughness T 133 ml / min Bendt. roughness B 140 ml / min Opacity Brightness, D65 81.7％ Tensile strength MD 87.5 8.3 kN / m Tensile strength CD 3.1 kN / m Tear strength MD 652 mN Tear strength CD 838 mN Example E2: polymeric cellulose substrate made by co-extrusion of polypropylene and mPVA on kraft paper ​

[0212] The coating weight of the PE coating on one side of the Kraft paper was 10 g / m 2 .

[0213] The mPVA obtained from Example 1 in pellet form was vacuum dried at 65 °C for 16 hours prior to extrusion. The pellets were fed from a hopper into an extruder with a narrow film die capable of applying a polymer melt to the surface of a passing film moving from an unreefer to a rewinder. The PE coated Kraft paper traveled past the extruder die opening and continued through a cooling nip to the rewinder. The die extruded the mPVA through a narrow slot vertically forming a low viscosity thin coating of uniform thickness melt that uniformly coated the PE coated Kraft paper moving continuously through the extruder die slot at a speed of 2.5 m / min. The coated PE coated Kraft paper passed through a nip between a pressure roller and a cooling roller. The nip pressure applied by the pressure roller smoothed the exposed face of the coating. Upon contact with the cooling roller the extruded coating was immediately cooled causing the extruded coating to harden resulting in a polymer coated cellulosic substrate comprising an extruded mPVA primer layer on the first polyethylene coating on the Kraft paper.

[0214] The coating weight of the mPVA used was 4 g / m 2 corresponding to a density of 0.68 g / m 2 of ethylene.

[0215] Example E3: polymeric cellulose substrate made by co-extrusion of PE, mPVA and compatibilizer on kraft paper

[0216] The mPVA obtained from Example 1 and a commercially available polypropylene (Moplen EP 310D HP) were provided as starting materials in pellet form.

[0217] Prior to extrusion the polymers were dried in a vacuum oven at 65 °C for 16 hours. A thin film extruder suitable for extruding 1-3 layers included three extruders, a three channel feed block, a film die, a cooling cylinder, a orientation unit and a rewinder. The extruders had single screws with diameters of 30, 45 and 30 mm with L / d ratios of 30, 25 and 30 respectively. The feed rates of all components were controlled by weight feeders. The polypropylene was fed into the larger extruders and the mPVA was fed into the smaller extruder. The extruders had ten heating zones adjusted to a steadily increasing temperature profile. The range was 225-235 °C for the polypropylene and 150-200 °C for the mPVA. The film nozzle was adjusted to 230 °C. The polymer melt feeds from all extruders converged in the feed block and were fused together into a single film through the nozzle. The feed rates of the polypropylene and mPVA were 10 and 2 kg / hour respectively.

[0218] A commercially available Kraft paper was provided having properties as shown in Example E1.

[0219] The extruded single film was coated on kraft paper which was continuously moved through the extruder die at a certain speed. The coated kraft paper passed through the nip between a pressure roller and a cooling roller. The nip pressure applied by the pressure roller smoothed the exposed surface of the coating. The extrusion coating was immediately cooled by contact with the cooling roller set at 55°C, causing the extrusion coating to harden, resulting in a polymer coated cellulose substrate comprising an extruded mPVA primer layer on a first polypropylene coating layer on the kraft paper. The thickness of the co-extruded first coating and the extruded primer layer was 45 pm, the coating weight of the extruded primer layer containing mPVA was 8.9 g / m 2 , the vinyl density was 1.5 mmol / m 2 .

[0220] Comparative example C1 : polymeric cellulose substrate made by co-extrusion of PP, compatibilizer and unmodified PVA on kraft paper Example 3: method to determine silicone adhesion

[0221] The mPVA obtained from Example 1, a commercially available polyethylene (CA9150) and a commercially available PE-MAH (Dow Amplify GR204) were provided as starting materials in pellet form.

[0222] The process of co-extrusion on paper was repeated as described in Example E2, except that polyethylene was used instead of polypropylene, and a third composition based on PE-MAH (polyethylene grafted with maleic anhydride) compatibilizer (Dow Amplify GR 204) was co-extruded as a tie layer, resulting in a three-layer film. The temperature range for PE was 190-220°C, for PE-MAH 180-205°C, and for mPVA 150-200°C. The film nozzle was adjusted to 230°C. The feed ratio was 10 kg / h for PE, 4 kg / h for PE-MAH and 2 kg / h for mPVA. The final film thickness was 45 pm, the coating weight of the extruded primer layer containing mPVA was 6.7 g / m 2 , the vinyl density was 1.2 mmol / m 2 .

[0223] Sample Wiping

[0224] The co-extrusion was repeated as described in Example E3, except that a commercially available PVA (Poval 3-80) was used instead of the mPVA of Example 1. PE, PE-MAH and PVA (Poval 3-80) were co-extruded using the same film extruder, resulting in a three-layer film. The coating weight of the PVA layer was 6.7 g / m 2 , and contained no vinyl groups.

[0225] Example E1

[0226] The polymer coated cellulose substrates obtained from Examples E1, E2, E3 and C1 were siliconized.

[0227] Siliconization refers to coating the substrate with a silicone resin prepared from Wacker Dehesive SFX 251 and V58 crosslinker using C05 catalyst (all components supplied by Wacker). The silicone resin applied to the paper substrate was prepared by stirring 100 parts by weight of Dehesive SFX 251 with 1 1.9 parts of V58 crosslinker for 2 minutes, then adding 2.5 parts of C05 platinum catalyst and stirring for 5 minutes. The silicone resin thus prepared was then applied to the paper substrate by a laboratory knife coater and cured at 105°C for 1 minute, thereby curing the silicone resin into a release layer and forming a release liner. Each sample sheet was coated with approximately 0.7 g / m2of the silicone resin thus prepared. 2

[0228] The silicone coating on the samples was tested for anchorage using a rub-off test. Anchorage is a term used in the art to describe the adhesion of a release coating to a substrate. The rub-off test is used to test the ability to remove a silicone release coating from the substrate on which it was coated under applied pressure. The samples were tested by a manual rub-off test using a piece of rubber. The silicone adhesion of the release liner formed was tested immediately after siliconization.

[0229] The results are listed in the table below. The adhesion rating is represented by the numbers 1, 2 and 3. "1 " means that the silicone resisted strong rubbing without coming off; "2" means that the silicone surface was soiled after strong rubbing; "3" means that the silicone came off after strong rubbing.

[0230] Example E2 Example E3 Example C1 2 ​ 2 ​ 1 ​ 3 ​

Claims

1. A polymer coated cellulose substrate for a release liner, comprising: - a cellulose support layer, - a first coating layer comprising a first composition comprising a polyolefin, - an extruded primer layer comprising a second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group; wherein the first coating layer is located between the cellulose support layer and the extruded primer layer, wherein the thermoplastic polymer comprising a vinyl group is formed from a thermoplastic polyvinyl alcohol having a degree of hydrolysis in the range of 65-95 mole%.

2. The polymer coated cellulose substrate according to claim 1, further comprising: a tie layer between the first coating layer and the extruded primer layer.

3. The polymeric coated cellulosic substrate of claim 1 or 2, wherein, the thermoplastic polymer covalently bound to a functional vinyl group is a reaction product of a molten thermoplastic material and a grafting agent comprising a functional vinyl group.

4. The polymer coated cellulose substrate according to claim 1 or 2, wherein, the thermoplastic polymer covalently bound to a vinyl group comprises ester-bonded side chains, wherein at least some of the side chains terminate in a vinyl group, wherein the side chains terminating in a vinyl group comprise a chain-like carbon structure of at least 4 carbon atoms.

5. The polymer coated cellulose substrate according to claim 1 or 2, wherein, the second composition further comprises: - one or more plasticizers, and / or - a non-thermoplastic material.

6. The polymer-coated cellulose substrate of claim 2, wherein, the tie layer comprises a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

7. The polymeric coated cellulosic substrate of claim 1 or 2, wherein, The cellulose support layer comprises kraft pulp fibers, the grammage of the cellulose support layer being 35 g / m 2 up to 100 g / m 2 .

8. The polymeric coated cellulosic substrate of claim 1 or 2, wherein, the extruded primer layer has at least one of the following properties: - a PPS roughness value of less than 2 pm, - the extrusion primer layer comprising a thermoplastic polymer covalently bound to functional vinyl groups has a coating weight of at least 0.6 g / m 2 2. - the extruded primer layer contains at least 0.06 mmol / m 2 of functional vinyl groups, - the thermoplastic polymer comprises a molar concentration of vinyl groups b determined in millimoles per gram of dry thermoplastic polymer when determined by iodometric titration according to standard ISO 3961 :2009(E) vin in the range of 0.05 mmol / g to 2.00 mmol / g.

9. The polymeric coated cellulosic substrate of claim 1 or 2, wherein, the first coating layer comprises polypropylene or polyethylene.

10. The polymer coated cellulose substrate according to claim 2, wherein, the first coating layer comprises polypropylene, and the tie layer comprises polyethylene grafted with maleic anhydride.

11. A method of manufacturing a polymer coated cellulose substrate for a release liner according to claim 1, the method comprising: - providing a cellulose support layer, - extruding a molten first composition comprising a polyolefin, thereby obtaining an extruded first composition, - extruding a molten second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group, thereby obtaining an extruded second composition, - reducing the temperature of the extruded molten first composition below its melting point, thereby forming a first coating layer, - reducing the temperature of the extruded molten second composition below its melting point, thereby forming an extruded primer layer, and - forming a polymer coated cellulose substrate comprising the cellulose support layer, the extruded primer layer and the first coating layer located between the cellulose support layer and the extruded primer layer.

12. The method according to claim 11, further comprising: - extruding a molten third composition comprising a compatibilizer, thereby obtaining an extruded third composition, and - reducing the temperature of the extruded molten third composition below its melting point, thereby forming a tie layer, - such that the tie layer is located between the first coating layer and the extruded primer layer.

13. The method according to claim 11 or 12, wherein, - at least two of the molten compositions are co-extruded.

14. The method of claim 11 or 12, wherein, the thermoplastic polymer covalently bound to a functional vinyl group is a reaction product of a molten thermoplastic material and a grafting agent comprising a functional vinyl group.

15. The method according to claim 11 or 12, wherein The thermoplastic polymer covalently bound to the vinyl groups comprises ester-bonded side chains, wherein at least some of the side chains terminate in a vinyl group, wherein the side chains terminating in a vinyl group comprise a chain-like carbon structure of at least 4 carbon atoms.

16. The method according to claim 11 or 12, wherein The second composition further comprises: - one or more plasticizers, and / or - a non-thermoplastic material.

17. The method of claim 12, wherein, The tie layer comprises a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

18. The method of claim 11 or 12, wherein, The extrusion primer layer has at least one of the following properties: - a PPS roughness value of less than 2 pm, - the extrusion primer layer comprising a thermoplastic polymer covalently bound to functional vinyl groups has a coating weight of at least 0.6 g / m 2 2. - the extruded primer layer contains at least 0.06 mmol / m 2 of functional vinyl groups, - the thermoplastic polymer comprises a molar concentration of vinyl groups b determined in millimoles per gram of dry thermoplastic polymer when determined by iodometric titration according to standard ISO 3961 :2009(E) vin in the range of 0.05 mmol / g to 2.00 mmol / g.

19. The method of claim 11 or 12, wherein, The first coating layer comprises polypropylene or polyethylene.

20. The method according to claim 12, wherein The first coating layer comprises polypropylene, and The tie layer comprises polyethylene grafted with maleic anhydride.

21. The method according to claim 11 or 12, further comprising, before extruding the molten second composition: - reacting the molten thermoplastic material with a grafting agent containing functional vinyl groups, thereby obtaining the second composition, which is a thermoplastic polymer covalently bound to the functional vinyl groups.

22. The method according to claim 21, wherein The step of reacting the molten thermoplastic material with a grafting agent containing functional vinyl groups comprises: - heating a 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 95 mole percent, and - mixing the grafting agent with the thermoplastic polyvinyl alcohol, wherein the grafting agent is an organic anhydride having at least a chain having a chain-like carbon structure of at least 4 carbon atoms and terminating in a vinyl group, thereby obtaining a mixture comprising the molten thermoplastic polyvinyl alcohol having hydroxyl groups and the organic anhydride containing a chain terminating in a vinyl group, and - mixing the mixture at a temperature above the melting point of the mixture, thereby causing a reaction in the molten state, wherein at least some of the organic anhydride reacts with the hydroxyl groups of the thermoplastic polyvinyl alcohol in a condensation reaction forming ester bonds, thereby forming a reaction product as the second composition, which comprises: - carboxylic acid residues of the condensation reaction forming ester bonds, wherein at least some of the carboxylic acid residues comprise a chain terminating in a vinyl group, and - a thermoplastic polyvinyl alcohol derivative comprising ester-bonded side chains, wherein at least some of the side chains terminate in a vinyl group.

23. A release liner, comprising: - the polymer-coated cellulose substrate according to claim 1 or 2, and - a silicone coating on the polymer-coated cellulose substrate.

24. A release liner, comprising: - the polymer-coated cellulose substrate obtained by the method according to claim 11 or 12, and - a silicone coating on the polymer-coated cellulose substrate.

Images