Thin film release substrate with improved silicone anchoring properties

Abstract

The present application relates to a polymer film (FILM 1) for a release liner (REL1), comprising a polymer support layer (S1) of a first composition comprising one or more polyolefins and / or polyesters, and an extruded primer layer (PRIM1) of a second composition comprising a thermoplastic polymer covalently bound to functional vinyl groups.

Description

TECHNICAL FIELD

[0001] The present application relates to a polymeric film for release liner. The present application also relates to a process for manufacturing a polymeric film for release liner. BACKGROUND

[0002] A release liner is a paper or plastic / polymeric 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 (polymeric) 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] A good performing silicone network must be able to smoothly peel off any coated adhesive layer, 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. Due to the different characteristics of cellulose and film substrates, the anchoring of silicone to these substrates surfaces is also different. Film substrates are most often corona treated in order to change its 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 film material to improve the adhesion of coatings, adhesives, inks, etc. to the substrate.

[0004] However, a very high corona treatment of plastic films can lead to polymer chain scission or pinholes in the film surface which can lead to anchoring issues. Furthermore, anchoring based purely on weak interactions tends to be quite unstable over time leading to issues of silicone transfer and loss of specific peel performance. SUMMARY

[0005] The present application represents a new approach to provide a polymeric film for release liner with improved performance and simplified steps and chemicals involved in its manufacturing process.

[0006] In one aspect, the present application provides a polymeric film for release liner comprising:

[0007] - a polymeric support layer comprising a first composition of one or more polyolefins and / or polyesters, and

[0008] - an extruded primer layer of a second composition comprising a thermoplastic polymer covalently bound to functional vinyl groups.

[0009] Thus, the extruded primer layer comprises functional vinyl groups.

[0010] Preferably, the thermoplastic polymer covalently bound with the functional vinyl group has been obtained from a reaction product of a molten thermoplastic material and a grafting agent containing a functional vinyl group. This is beneficial because the reaction product is a solid material that does not require any processing prior to further melt processing. Furthermore, the modification can also be performed in-line in a film extruder.

[0011] Optionally, the polymeric film can further comprise a tie layer between the polymeric support layer and the extrusion primer layer.

[0012] The extrusion primer layer according to the present application has a number of effects as described below.

[0013] On one hand, the extrusion primer layer according to the present application has excellent adhesion to the underlying polymeric support layer when the adjacent polymeric compositions (i.e. the first and second compositions) have similar polarity or have covalent bonds at their interface because the thermoplastic melt adheres firmly to the polymeric support layer upon solidification. On the other hand, the extrusion primer layer comprising a functional vinyl group provides an excellent foundation for siliconization as the second composition comprising a thermoplastic polymer covalently bound with the functional vinyl group of the extrusion primer layer because, when forming a release liner comprising the polymeric film 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. As a result, the silicone anchorage is significantly improved.

[0014] The extrusion primer layer according to the present application helps to improve the surface coverage of the subsequent silicone coating, which in turn improves the consistency of the release value. A high quality silicone coating requires good coverage to the substrate. Pinholes in solvent-borne or water-borne dispersion-borne primer layers can lead to poor anchorage of the silicone coating area and silicone rub-off, resulting in poor peel stability over time. Pinholes are coating defects where there are hole-like penetrations on the coating. Pinholes can occur in solvent-borne coatings due to entrapped moisture, air, solvent or other liquids in the coating solution. Pinholes on a clear film can be studied and quantified by optical microscopy. Since the primer layer composition used for the extrusion primer layer does not contain water or solvent, the number of pinholes on the surface of the extrusion primer layer according to the present application has been significantly reduced, thus avoiding the entrapment of moisture or volatile solvent. Furthermore, since there are fewer holes to be filled with the silicone coating, the polymeric film according to the present application can be siliconized with a smaller silicone coating weight compared to primer layers using water-borne dispersion-borne or solvent-borne coatings. As a result, the cost-effectiveness of preparing the silicone coating can be improved.

[0015] On the other hand, the present application provides a method of manufacturing a polymeric film for a release liner, the method comprising:

[0016] - extruding a molten first composition comprising one or more polyolefins and / or polyesters, thereby obtaining an extruded first composition,

[0017] - 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 the functional vinyl group,

[0018] - reducing the temperature of the extruded molten first composition to below its melting point, thereby forming a polymeric support layer,

[0019] - reducing the temperature of the extruded molten second composition to below its melting point, thereby forming an extruded primer layer, and

[0020] - forming a polymeric film comprising the polymeric support layer and the extruded primer layer.

[0021] Preferably, the method can further comprise:

[0022] - extruding a third composition comprising a compatibilizing agent, thereby obtaining an extruded third composition, and

[0023] - reducing the temperature of the extruded molten third composition to below its melting point, thereby forming a tie layer,

[0024] such that the tie layer is located between the polymeric support layer and the extruded primer layer.

[0025] 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. For example, the first composition, the second composition and the third composition can be co-extruded.

[0026] In the method according to the present application, extruding a molten second composition comprising at least one thermoplastic polymer covalently bound to a functional vinyl group has several effects, as explained below.

[0027] Corona treatment forms hydroxyl, carboxyl and 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.

[0028] In contrast, in the method according to the present application, extruding a molten second composition comprising at least one thermoplastic polymer covalently bound to a functional vinyl group facilitates that the polymeric film provides a stable surface for the subsequent silicone coating. The surface of the extruded primer layer is chemically stable until the silicone coating is applied on top of it and reacts with it, and forms a stable release liner after curing. This provides great flexibility for the industrial line-up.

[0029] According to the present method, volatile organic compounds are reduced or eliminated during the manufacturing process of the polymer film, and a drying or curing step is eliminated. Harmful chemicals are reduced, and manufacturing steps are greatly simplified. Furthermore, the polymer film according to the present application has a predictable thickness, as the extruded primer layer does not lose thickness during the solidification process, whereas solvent-based 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 film produced on an industrial scale can be better managed.

[0030] 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

[0031] Figure 1 A schematic diagram of a cross-sectional view of a release liner REL1 is shown by way of example, which comprises a polymer film FILM1 and a release layer, namely a silicone coating SIL1.

[0032] Figure 2 A schematic diagram of a cross-sectional view of another example of a release liner is shown, which comprises a polymer film FILM1 and a release layer, namely a silicone coating SIL1.

[0033] Figure 3 A general formula and some variants of an organic acid anhydride having at least one acyl group having a chain-like carbon structure of at least 4 carbon atoms and ending in a vinyl group are illustrated, which is suitable for use as a reagent in a process for preparing a thermoplastic poly(vinyl alcohol) derivative by a melt-state reaction.

[0034] Figure 4 A condensation reaction of an organic acid anhydride with a thermoplastic poly(vinyl alcohol) in a melt state to form ester bonds is illustrated, wherein at least some of the organic acid anhydride reacts with hydroxyl groups of the thermoplastic poly(vinyl alcohol) in a condensation reaction to form ester bonds, thereby forming a reaction product containing carboxylic acid residues and a thermoplastic poly(vinyl alcohol) derivative, wherein at least some of the carboxylic acid residues contain a chain ending in a vinyl group, and at least some of the ester-bonded side chains end in a vinyl group.

[0035] Figure 5A condensation reaction forming ester bonds between undecylenic anhydride and 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 terminal end, wherein at least some of the undecylenic anhydride reacts with hydroxyl groups of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester bonds, 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-bonded side chains have a vinyl group at the terminal end.

[0036] Figure 6 A condensation reaction forming ester bonds between acetyl undecylenic anhydride and 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 terminal end and another acyl group derived from acetic acid, wherein at least some of the acetyl undecylenic anhydride reacts with hydroxyl groups of the thermoplastic poly(vinyl alcohol) in a condensation reaction forming ester bonds, 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-bonded side chains have a vinyl group at the terminal end.

[0037] It should be noted that the drawings are not drawn to scale.

[0038] Reference numerals:

[0039] FILM1 - polymeric film

[0040] REL1 - release liner

[0041] S1 - polymeric support layer

[0042] PRIM1 - extruded primer layer

[0043] TIE1 - tie layer

[0044] AH1 - grafting agent, general formula

[0045] AH2 - grafting agent, general formula

[0046] AH3 - grafting agent, example

[0047] AH4 - grafting agent, example

[0048] AH5 - grafting agent, example

[0049] PVA1 - thermoplastic PVA

[0050] CMP1 - thermoplastic polymer covalently bound to functional vinyl groups, example

[0051] CMP2 - thermoplastic polymer covalently bound to functional vinyl groups, example

[0052] CMP3 - thermoplastic polymer covalently bound to a functional vinyl group, examples

[0053] RD1 - carboxylic acid residue, examples

[0054] RD2 - carboxylic acid residue, examples

[0055] RD3 - carboxylic acid residue, examples

[0056] R 1 - organic group

[0057] R 2 - organic group DETAILED DESCRIPTION

[0058] The present application provides a polymeric film for a release liner and a method for the production of a polymeric film for a release liner.

[0059] Definition of a polymer film

[0060] As described herein, a polymeric film refers to one of the three main categories of carrier substrates for industrially manufactured release liners: paper and paperboard, polymeric films and cellulose materials coated with polymeric films. A polymeric film mainly comprises polymeric materials. Paper-based substrates mainly comprising cellulose materials are not within the meaning of a polymeric film.

[0061] Definition of a polymer support layer

[0062] As described herein, the term "polymeric support layer" refers to a layer structure that is preferably capable of standing on its own in the absence of another support substrate. The polymeric support layer comprises any suitable film- forming polymeric material.

[0063] Plastics are suitable for this purpose. Illustrative examples include, but are not limited to, polyolefins such as high-density polyethylene (HDPE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET) and copolymers thereof.

[0064] The polymeric support layer can be made into a film by a plastic extrusion process and can be made from one single type of plastic material, a mixture of different plastic materials or a multilayer co-extrudate.

[0065] The polymeric support layer in the form of a film can already be oriented. Illustrative examples include, but are not limited to, oriented polypropylene (OPP), oriented polyethylene terephthalate (OPET), BOPET and BOPP, wherein BO indicates that the substrate has been biaxially oriented by sequential stretching in two mutually perpendicular directions. The film can also be oriented after the primer layer has been extruded to increase the film strength and to facilitate a thinner primer layer.

[0066] The polymeric support layer can comprise one or more suitable materials. For example, the polymeric support layer can be a BOPET film coated on both sides with a polyolefin material. In this way, the tough and dimensionally stable PET film is combined with an inexpensive polyolefin resin, making the film a better carrier web for special applications.

[0067] The polymeric support layer can comprise other additives, such as compatibilizers. Compatibilizers consist of two parts, one part is compatible with one of the two polymers to be compatibilized, the other part is compatible with the second polymer.

[0068] Definition of an extrusion primer layer

[0069] The term "extrusion primer layer" as described herein refers to a layer structure made from a thermoplastic by extrusion. Extrusion is a manufacturing process known to those skilled in the art. In the extrusion process to manufacture the layer structure of the extrusion primer layer, the raw material is melted by the mechanical energy generated by a rotating screw and heaters arranged along the barrel of the extruder, and then the molten material is pressed into a die, the molten material is shaped into a continuous profile shape, solidified during cooling, thereby forming the extrusion primer layer. Various 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 realized by blown film extrusion, extrusion coating, co-extrusion, lamination, etc. The extrusion primer layer has properties different from the solvent-based primer layer, as will be further explained in this specification.

[0070] Description of the polymer film according to the present application

[0071] Reference can be made to Figure 1 and Figure 2 It should be noted that the examples shown in Figure 1 and Figure 2 do not limit any specific embodiment, but are only used to explain the relative position of the features denoted by the reference numerals. Furthermore, Figure 1 and Figure 2 show schematic views of examples, not to scale.

[0072] The present application provides a polymeric film FILM1 for a release liner REL1, comprising:

[0073] - a polymeric support layer S1 comprising a first composition of one or more polyolefins and / or polyesters, and

[0074] - an extrusion primer layer PRIM1 of a second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group.

[0075] As described herein, the term "thermoplastic polymer covalently bound to a functional vinyl group" refers to a thermoplastic polymer, wherein the backbone 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, acrylic, 4-pentenyl, and 10-undecenyl groups. To be extrudable, the material must be thermoplastic, i.e., the polymeric material becomes pliable or moldable at certain elevated temperatures and solidifies upon cooling.

[0076] Further, for any polymer film according to the present application as presented herein, the thermoplastic polymer covalently bound to a functional vinyl group can preferably be obtained from the reaction product of a molten thermoplastic material with a grafting agent comprising a functional vinyl group, for example by reactive extrusion. The reaction is fast and cost-effective. More preferably, the reaction is a solvent-free reaction. Since the reaction does not require any organic solvent or water, the resulting reaction product also does not require any solvent separation or drying for its obtention. The reaction product can also be in the form of a melt, can be extruded, or simply used for direct coating, or cooled and pelletized for ease of transportation and storage for later use. Thus, the application of the thermoplastic polymer is more versatile when it has been obtained from the reaction product of a molten thermoplastic material with a grafting agent comprising a functional vinyl group.

[0077] Examples of grafting agents can be organic acid anhydrides, which can be represented by the chemical formulae AH1, AH2, AH3, AH4, and AH5 as represented in Figure 3 wherein R 1 and R 2 represent different organic groups.

[0078] Organic acid anhydrides refer to organic compounds having two acyl groups bonded to the same oxygen atom. Organic acid anhydrides can be aliphatic symmetric or asymmetric acid anhydrides. As used herein, symmetric acid anhydrides refer to acid anhydrides having two identical acyl groups, each acyl group ending in a vinyl group. As used herein, asymmetric acid anhydrides refer to acid anhydrides having different acyl groups, wherein at least one acyl group ends in a vinyl group.

[0079] Furthermore, according to the present application, for any polymeric film 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. The expression "thermoplastic poly(vinyl alcohol)" herein thus 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 thermoplasticity 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 can cause die blowouts and lead to holes and / or uneven surfaces of the extruded primer layer, while the latter can start cross-linking reactions, which in turn can lead 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, in particular when the amount of hydroxyl groups in the poly(vinyl alcohol) is very high.

[0080] Furthermore, according to the present application, for any polymeric film as presented herein, the thermoplastic, preferably thermoplastic PVA, derivative 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 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, thus also making the vinyl group less accessible.

[0081] Examples of thermoplastic PVA covalently bound to a functional vinyl group can be represented by the chemical formula Figure 4 CMP1 in Figure 5 CMP2 in and Figure 6 CMP3 in.

[0082] 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.

[0083] like Figure 3 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.

[0084] Furthermore, according to this application, for any polymer film 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 wherein the vinyl-terminated side chains contain a chain-like carbon structure of at least 4 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 4 carbon atoms of the same kind 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 film FILM1. 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 film FILM1, 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 film FILM1.

[0085] Examples of carboxylic acid residues can be derived from... Figure 4 In, it is represented as RD1, in Figure 5 In, it is represented as RD2 and in Figure 6 The chemical formula for RD3 is represented in Chinese.

[0086] The second composition may also contain a salt of a carboxylic acid residue, i.e., a carboxylate.

[0087] Furthermore, according to the present application, for any polymer film described herein, the second composition comprising a thermoplastic derivative covalently bound to a functional vinyl can further comprise:

[0088] - one or more additives, such as plasticizers, and / or

[0089] - one or more non-thermoplastic materials, such as starch or carboxymethylcellulose (CMC).

[0090] The use of plasticizers leads to better processing properties. Examples of such plasticizers are ethylene glycol, polyethylene glycol, glycerol, etc.

[0091] If the polymer support layer S1 and the extrusion primer layer PRIM1 have polymers of different polarity, it would be beneficial to use a compatibilizer.

[0092] In one example, the extrusion primer layer PRIM1 comprises a thermoplastic PVA covalently bound to a functional vinyl and the polymer support layer S1 comprises polyethylene and / or polypropylene. The use of a compatibilizer improves the interfacial adhesion by making the support layer 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 TIE1 is a better option than a mixture of non-polar polymers and compatibilizer as it would result in a higher density of available polar groups on the surface.

[0093] Furthermore, according to the present application, for any polymer film presented herein, wherein the thermoplastic polymer covalently bound to a vinyl is formed of a thermoplastic poly(vinyl alcohol), can further comprise at least one compatibilizer, such that:

[0094] At least one of the polymer support layer S1 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,

[0095] The polymer film FILM1 further comprises a tie layer TIE1 between the polymer support layer and the extrusion primer layer, said tie layer TIE1 comprising at least one compatibilizer, such as a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

[0096] In some examples, the extrusion primer layer PRIM1 can comprise a compatibilizer, such as an anhydride-modified polyolefin. Anhydrides, typically maleic anhydride, react with alcohols to form ester crosslinks.

[0097] In some examples, the support layer S1 can include a compatibilizer, such as an anhydride-modified polyolefin. The anhydride present on the surface of the polymeric support layer S1 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 polymeric support layer S1.

[0098] The extrusion primer layer PRIM1 has excellent adhesion to the overlying silicone coating SIL1. On the polymeric film FILM1 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 polymeric film FILM1, which is then thermally cured in a catalytic hydrosilylation reaction, thereby forming a release liner REL1 comprising the silicone resin coating SIL1, the polymeric support layer S1 and the extrusion primer layer PRIM1 between the silicone resin coating SIL1 and the polymeric support layer S1. Catalytic hydrosilylation, also known as hydrosilylation, refers to the formation of a covalent bond between a functional vinyl group in the silicone base polymer and a silicon-hydrogen (Si-H) group in the crosslinker compound in the presence of a platinum catalyst. This reaction forms a solid release layer SIL1 on the surface of the extrusion primer layer PRIM1. Due to the presence of the functional vinyl group on the surface of the extrusion primer layer PRIM1, a covalent bond also forms between the functional vinyl group in the extrusion primer layer PRIM1 and the silicon-hydrogen (Si-H) group 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, thus facilitating the anchoring of the silicone coating SIL1 to the polymeric film FILM1.

[0099] Furthermore, the extrusion primer layer PRIM1 helps to improve the surface coverage of the subsequent silicone coating, which in turn improves the 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 good coverage on the polymeric film FILM1. Uncoated areas, pinholes and contamination increase the release value and give poor peel stability over time. The surface of the polymeric film FILM1 with fewer defects, such as pinholes, also promotes good coverage of the silicone coating. Pinholes are a kind of pore-like penetration that often occur in solvent-borne coatings 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, since there are fewer holes to be filled with the silicone coating, the polymeric film FILM1 according to the present application can be siliconized at a lower silicone coating weight compared to primer layers using water-borne dispersion type or solvent-borne coatings. Thus, the cost-effectiveness of preparing the silicone coating can be improved.

[0100] Furthermore, according to the present application, for any polymer film presented herein, the polymer primer layer has at least one of the following properties:

[0101] - the PPS roughness value is less than 1 pm,

[0102] - 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 ,

[0103] - the extrusion primer layer PRIM 1 contains at least 0.06 mmol / m 2 of functional vinyl groups,

[0104] - the thermoplastic polymer comprises a molar concentration of vinyl groups b vin measured in millimoles per gram of dry thermoplastic polymer, when determined by iodometric titration according to standard ISO 396 1 :2009(E), is 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.

[0105] The polymer film according to the present application having a Parker Print-Surf (PPS) roughness value of less than 1 pm facilitates a smooth surface for the subsequent silicone coating. The measurement of PPS roughness can be obtained by using a PPS (Parker Print Surface) roughness tester known to the person skilled in the art. A smoother surface requires less silicone coating solution. According to the present application, the extrusion primer layer provides a smooth surface for the subsequent silicone coating. The polymer film according to the present application can be siliconized with a smaller silicone coating weight, for example 0.6 to 0.8 g / m 2 or even less. This is therefore an economically desirable solution. Furthermore, the extrusion primer layer has a consistent surface roughness which facilitates a consistent release value of the silicone coating.

[0106] The polymer film according to the present application is substantially pinhole free. This facilitates a good coverage for the subsequent silicone coating. This guarantees a good release value of the release layer.

[0107] According to the present application, the disclosed amount of thermoplastic polymer covalently bound to functional vinyl groups proves to facilitate a good silicone anchoring. The coating weight can be for example 0.5 - 10.0 g / m 2 , preferably 0.5 - 4.0 g / m 2 , more preferably 1.0 - 2.0 g / m 2 . Experimental results show that the extrusion primer layer PRIM 1 contains 0.6 g / m2 The thermoplastic polymer covalently bound to the functional vinyl groups, such as thermoplastic PVA, helps to achieve excellent adhesion between the polymer film and the silicone layer in the rub-off test.

[0108] The same effect has been observed, proving that the amount of disclosed vinyl groups helps to achieve good silicone anchoring. The functional vinyl groups contained in the extrusion primer layer PRIM1 comprising, for example, a thermoplastic PVA covalently bound to the functional vinyl groups 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 .

[0109] The same effect is observed when the molar concentration of vinyl groups b vin is 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, when the thermoplastic polymer comprises, when determined by iodometric titration according to standard ISO 3961 :2009(E) in millimoles per gram of dry thermoplastic polymer, such as thermoplastic PVA covalently bound to the functional vinyl groups. This is therefore 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.

[0110] Furthermore, according to the present application, for any polymer film as presented herein, the polymer support layer S1 can comprise one or more of high-density polyethylene (HDPE), polypropylene (PP), polybutylene, polyethylene terephthalate (PET) and PET copolymers, 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 polymer support layers.

[0111] In one example, the thermoplastic polymer covalently bound to the functional vinyl groups is formed from a thermoplastic poly(vinyl alcohol), and the polymer support layer S1 comprises a PET copolymer. The PET copolymer can be melt-processed at temperatures below 210 °C, which temperature can also be used for melt-processing the thermoplastic poly(vinyl alcohol) covalently bound to the functional vinyl groups. Common comonomers include cyclohexane dimethanol (denoted as PET-G) and isophthalic acid, which both interfere with the crystallization of PET, thus lowering its melting point.

[0112] In one example, the polymer film can further comprise a tie layer TIE1 between the extrusion primer layer PRIM1 and the polymer support layer S1. The thermoplastic polymer covalently bound to the functional vinyl groups is formed from a thermoplastic poly(vinyl alcohol), the polymer support layer S1 comprises a polypropylene, and the tie layer TIE1 comprises a polypropylene grafted with maleic anhydride.

[0113] Detailed description of the method according to the present application

[0114] The application also provides a method of preparing a polymer film FILM1 for a release liner REL1, the method comprising extruding a molten second composition, the second composition comprising at least one thermoplastic polymer covalently bound to functional vinyl groups.

[0115] The method according to the application can comprise:

[0116] - extruding a molten first composition comprising one or more polyolefins and / or polyesters, thereby obtaining an extruded first composition,

[0117] - extruding a molten second composition comprising a thermoplastic polymer covalently bound to functional vinyl groups, thereby obtaining an extruded second composition,

[0118] - reducing the temperature of the extruded molten first composition to below its melting point, thereby forming a polymer support layer S1,

[0119] - reducing the temperature of the extruded molten second composition to below its melting point, thereby forming an extrusion primer layer PRIM1, and

[0120] - forming a polymer film FILM1 comprising the polymer support layer S1 and the extrusion primer layer PRIM1.

[0121] The product, i.e. the polymer film FILM1, obtained according to the method of the application has the effects as described above.

[0122] The second composition comprises an extrudable polymeric material, including a thermoplastic polymer covalently bound to a functional vinyl group as defined above, and possibly additives, such as plasticizers or compatibilizers, which second composition can be fed into an extruder to form a molten second composition. This can be suitable for extrusion coating the resulting primer layer PRIM1 onto the surface of a polymeric support layer S1, which polymeric support layer S1 can be a carrier sheet that travels through the extruder die. The die extrudes the polymeric material through a narrow slot, forming a low viscosity thin coating of a uniform thickness of melt that is uniformly coated onto the carrier sheet that moves continuously at high speed through the extruder die. As mentioned above, due to the presence of the functional vinyl group on the surface of the primer layer PRIM1, a covalent bond is formed between the functional vinyl group in the primer layer PRIM1 and the silicon-hydrogen (Si-H) group in the crosslinker in the silicone coating composition during the catalytic silicon-hydrogenation reaction that cures the silicone coating. The surface of the primer layer is only reactive to the silicone coating during the process of applying the silicone coating. This provides great flexibility for the industrial line-up of the production. The thickness of the primer layer PRIM1 can be controlled by the winding speed. Thus, the guaranteed performance and quality of the polymeric film produced at an industrial scale can be better managed. Furthermore, the extrusion coating operation uses a high melt temperature to reduce the melt viscosity. This improves the coating thickness uniformity and adhesion.

[0123] Preferably, the method can further comprise:

[0124] - extruding a third composition comprising a compatibilizer, thereby obtaining an extruded third composition, and

[0125] - reducing the temperature of the extruded molten third composition to below its melting point, thereby forming a tie layer TIE1,

[0126] such that the tie layer TIE1 is located between the polymeric support layer S1 and the extruded primer layer PRIM1.

[0127] 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. For example, the first composition, the second composition and the third composition can be co-extruded.

[0128] The product, i.e. the polymeric film FIM1, obtained according to the method of the present application has the effects as described above.

[0129] The extrusion equipment used to implement the co-extrusion process of the present application can include, for example, at least two extruders, a film die, a cooling cylinder, an optional 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 to the silicone coating during the process of applying the silicone coating. This provides great flexibility for the industrial line-up of the production. The layer ratio can be controlled by the screw rotation speed, the total film thickness can be controlled by the winding speed. The film orientation can be performed as needed. Thus, the predictability and guaranteed performance and quality of the polymer film produced on an industrial scale can be better managed.

[0130] To implement one of the methods described herein according to the present application, a solid composition comprising a thermoplastic polymer containing a vinyl group can be converted into a melt using an extruder 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.

[0131] The chemical reaction to modify the thermoplastic material can be performed using the same or another extruder to produce a thermoplastic polymer containing a vinyl group in a molten state at the appropriate temperature required for coating, thereby obtaining a molten second composition comprising a thermoplastic polymer containing a vinyl group. The thermoplastic polymer can be obtained from the reaction product of a molten thermoplastic material and a grafting agent, for example, by reactive extrusion.

[0132] Furthermore, for any method according to the present application as presented herein, the thermoplastic polymer covalently bound to the functional vinyl group can be obtained from the reaction product of a molten thermoplastic material and a grafting agent covalently bound to the functional vinyl group. 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 also does not require any solvent separation or drying to be obtained. 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.

[0133] Furthermore, according to this application, for any method as presented herein, the vinyl-containing thermoplastic polymer is formed from thermoplastic poly(vinyl alcohol) (PVA) with a degree of hydrolysis of 65 to 95 mol%, for example 65, 70, 75, 80, 85, 90, or 95 mol%. The definition of this thermoplastic poly(vinyl alcohol) and the advantages it brings have been described above. The resulting product, namely polymer film FIM1, has the effects described above.

[0134] Furthermore, according to this application, for any method presented herein, the thermoplastic polymer (preferably thermoplastic PVA) 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 film FILM1. 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 film FILM1, 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 film FILM1. The resulting product, the polymer film FIM1, has the effects described above.

[0135] Examples of thermoplastic PVA covalently bonded to functional vinyl groups can be found in... Figure 4 The Chinese version is represented as CMP1. Figure 5 The Chinese version is represented as CMP2 and Figure 6 The chemical formula CMP3 is used to represent this. Examples of carboxylic acid residues can be found in... Figure 4 In, it is represented as RD1, in Figure 5 In, it is represented as RD2 and in Figure 6 The chemical formula for RD3 is represented in Chinese.

[0136] like Figure 4 , 5and 6, when the aliphatic organic acid anhydride AH1, AH2, AH3, AH4, AH5 is reacted in a condensation reaction with the hydroxyl groups of the thermoplastic poly(vinyl alcohol) PVA1 in the molten state, one of the acyl groups forms an ester bond with a hydroxyl group of the poly(vinyl alcohol) PVA1 and 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, wherein at least some of the side chains end in a vinyl group, wherein the side chains ending 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 forming 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, ending in a vinyl group.

[0137] Furthermore, according to the present application, for any method described herein, the second composition comprising a thermoplastic polymer covalently bound to a functional vinyl group can further comprise:

[0138] - one or more additives, such as plasticizers, and / or

[0139] - one or more non-thermoplastic materials, such as starch or carboxymethylcellulose (CMC).

[0140] 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 film FILM1, has the beneficial effects as described above.

[0141] Furthermore, according to the present application, for any method presented herein, wherein the thermoplastic polymer covalently bound to a vinyl group is formed from a thermoplastic poly(vinyl alcohol),

[0142] The polymer film FILM1 further comprises a tie layer TIE1 between the polymer support layer S1 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.

[0143] 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.

[0144] In some examples, the support layer S1 can comprise a compatibilizer, such as an anhydride-modified polyolefin. The anhydride present on the surface of the polymeric support layer S1 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 polymeric support layer S1.

[0145] Furthermore, according to the present application, for any method as presented herein, the extrusion primer layer PRIM1 has at least one of the following properties:

[0146] - the PPS roughness value is less than 1 pm,

[0147] - the coating weight of the extrusion primer layer PRIM 1 comprising a thermoplastic polymer covalently bound to a functional vinyl group is 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 ,

[0148] - 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,

[0149] - 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 in millimoles per gram of dry thermoplastic polymer when determined by iodometric titration according to standard ISO 396 1 :2009(E).

[0150] The effects of these properties have been described above. The resulting product, i.e. the polymeric film FIM1, has the beneficial effects as described above.

[0151] Furthermore, according to the present application, for any method as presented herein, the polymeric support layer S1 can comprise one or more of high-density polyethylene (HDPE), polypropylene (PP), polybutylene, polyethylene terephthalate (PET) and PET copolymers, 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 support layers.

[0152] In one example, the thermoplastic polymer covalently bound to the functional vinyl group is formed from a thermoplastic poly(vinyl alcohol), and the polymer support layer S1 comprises a PET copolymer. PET copolymers can be melt-processed at temperatures below 210 °C, which is also the temperature at which the thermoplastic poly(vinyl alcohol) covalently bound to the functional vinyl group can be melt-processed. Common comonomers include cyclohexane dimethanol (denoted as PET-G) and isophthalic acid, which both interfere with the crystallization of PET, thus lowering its melting point.

[0153] In one example, the polymer film can further comprise a tie layer TIE1 between the extrusion primer layer PRIM1 and the polymer support layer S1. The thermoplastic polymer covalently bound to the functional vinyl group is formed from a thermoplastic poly(vinyl alcohol), and the polymer support layer S1 comprises a polypropylene, and the tie layer TIE1 comprises a polypropylene grafted with maleic anhydride.

[0154] Further, according to the present application, for any method described herein, the method can further comprise, prior to providing the molten second composition:

[0155] - reacting the molten thermoplastic material with a grafting agent containing a functional vinyl group, preferably in a solventless reaction, thereby obtaining a thermoplastic polymer covalently bound to the functional vinyl group.

[0156] The resulting product, i.e. the polymer film FILM1, has the beneficial effects as described above.

[0157] Further, according to the present application, for any method presented herein, wherein the thermoplastic derivative covalently bound to the vinyl group is formed from a thermoplastic poly(vinyl alcohol), can further comprise at least one compatibilizer, such that:

[0158] At least one of the polymer support layer S1 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. In some examples, the polymer film FILM1 further comprises a tie layer TIE1 between the polymer support layer S1 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.

[0159] In some examples, the extrusion primer layer PRIM1 comprises a compatibilizer, such as an anhydride-modified polyethylene (AMP). The anhydride reacts with an alcohol to form an ester crosslink.

[0160] In some examples, the support layer S1 comprises a compatibilizer, such as an anhydride-modified polyethylene (AMP). The anhydride present on the surface of the polymeric support layer S1 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 polymeric support layer S1.

[0161] Further, according to the present application, for any method described herein, the step of providing a molten second composition is performed:

[0162] - 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%,

[0163] and

[0164] - mixing a grafting agent with the thermoplastic poly(vinyl 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 ending in a vinyl group,

[0165] thereby obtaining a mixture comprising the molten thermoplastic poly(vinyl alcohol) having hydroxyl groups and the organic anhydride containing a chain ending in a vinyl group, and

[0166] - 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 poly(vinyl alcohol) in a condensation reaction forming ester bonds,

[0167] thereby forming a reaction product as the second composition, which comprises:

[0168] - 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

[0169] - thermoplastic poly(vinyl alcohol) derivatives comprising ester-bonded side chains, wherein at least some of the side chains end in a vinyl group.

[0170] The example of providing a molten second composition can be illustrated by the chemical equation in Figures 4 to 6 .

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] Furthermore, according to the present application, for any of the methods described herein, the method can further comprise orienting the polymeric film (FILM1). The melt composition can first be extruded in the form of a relatively thick layer, thereby further eliminating surface defects such as pinholes, and then the orientation can further thin the polymeric film to the desired thickness and smoothness.

[0176] The polymer film (FILM1) and the method of manufacturing the polymer film (FILM1) are particularly suitable for a release liner. Therefore a release liner is also provided comprising:

[0177] - a polymer film according to the present application, or obtainable by a method according to the present application, and

[0178] - a silicone coating on the polymer film.

[0179] Example

[0180] Example 1 : melt state reaction of poly (vinyl alcohol) with 10-undecylenic anhydride

[0181] 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 wt.%, 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, comprising one feeding unit, three heating zones and one die zone for extruding the material. The screw 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.

[0182] 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 into the extruder via the feeding unit together with 0.1 kg of 10-undecylenic anhydride. 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.

[0183] Example E1 : polymer film made by extrusion coating of mPVA on PET

[0184] 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 unreeled roll to a rewinder. A commercially available PET film of 50 pm thickness was unreeled from one roll, passed through 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 of the melt which uniformly coated the PET sheet continuously moving through the extruder die slot at a speed of 2.5 m / min. The coated PET sheet passed through a 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 extruded coating was immediately cooled by contact with the cooling roller so that the extruded coating hardened.

[0185] The coating weight of the mPVA used was 4 g / m 2 corresponding to a vinyl group amount of 0.68 g / m 2 .

[0186] Example E2: polymer film made by co-extrusion of a PET copolymer (PET-G) and mPVA

[0187] The mPVA obtained from Example 1 and a commercially available PET copolymer (PET-G, Akestra 90) were provided as starting materials in pellet form.

[0188] Prior to extrusion, the polymers were dried in a vacuum oven at 65 °C for 16 hours. A 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 of 30, 45 and 30 mm diameter with respective L / d ratios of 30, 25 and 30. The feed rates of all components were controlled by weight feeders. The PET-G was fed into the larger extruder and the mPVA was fed into the smaller extruder. The extruders had ten heating zones which were adjusted to a steadily increasing temperature profile. The range 190-220 °C was used for the PET-G and 150-200 °C for the mPVA. The film nozzle was adjusted to 220 °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 PET-G and mPVA were 30 and 2.3 kg / hour respectively. After leaving the nozzle, the melt was rapidly cooled by a cooling roller set to 55 °C, thereby forming a polymer film. The polymer film thus had a polymer support layer of the PET copolymer and an extruded primer layer of the mPVA. The formed film precursor was passed through an orientation unit where it was stretched in the machine direction to a final thickness of 50 pm. Estimating from the feed ratios and the total thickness, the coating weight of the extruded primer layer containing the mPVA was 4.3 g / m 2, the vinyl density being 0.73 mmol / m 2 .

[0189] Example E3: polymer film made by co-extrusion of polypropylene and mPVA

[0190] The process of co-extrusion was repeated as described in Example E2, except that polypropylene (Moplen EP 310D HP) was used instead of the PET copolymer. The temperature range used was 225-235 °C for PP and 150-200 °C for mPVA. The film die was adjusted to 230 °C. The feed ratio was 10 kg / h for PP and 2 kg / h for mPVA. The final film thickness was 45 μm and the coating weight of the extruded primer layer comprising mPVA was 8.9 g / m 2 , the vinyl density being 1.5 mmol / m 2 .

[0191] Example E4: polymer film made by co-extrusion of PP, mPVA and compatibilizer

[0192] The process of co-extrusion was repeated as described in Example E3, except that a third composition based on a compatibilizer (Bynel 50E739) based on PP-MAH (polypropylene grafted with maleic anhydride) was co-extruded as a tie layer, resulting in a three layer film. The temperature range used was 225-235 °C for PP, 210-235 °C for PP-MAH and 150-200 °C for mPVA. The film die was adjusted to 230 °C. The feed ratio was 10 kg / h for PP, 4 kg / h for PP-MAH and 2 kg / h for mPVA. The final film thickness was 45 μm and the coating weight of the extruded primer layer comprising mPVA was 6.7 g / m 2 , the vinyl density being 1.1 mmol / m 2 .

[0193] Comparative Example C1 : polymer film made by co-extrusion of a PET copolymer and unmodified PVA

[0194] The process of co-extrusion was repeated as described in Example E2, except that a commercially available PVA (Poval 3-80) was used instead of the mPVA of Example 1. The PET-G copolymer (Akestra 90) and the PVA (Poval 3-80) were co-extruded using the same film extruder with the same settings, resulting in a two layer film. The coating weight of the PVA layer was 4.3 g / m 2 and did not contain vinyl groups.

[0195] Comparative Example C2: polymer film made by co-extrusion of PP, compatibilizer and unmodified PVA

[0196] A co-extrusion was repeated as described in Example E4, except that a commercially available PVA (Poval 3-80) was used instead of the mPVA of Example 1. PP, PP-MAH and PVA (Poval 3-80) were co-extruded using the same film extruder with the same settings to obtain a three-layer film. The coating weight of the PVA layer was 6.7 g / m 2 and is free of vinyl groups.

[0197] Example 3: method for determining silicone adhesion

[0198] The polymer films obtained from Examples E2, E3, E4, C1 and C2 were siliconized.

[0199] Siliconization refers to coating a 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 11.9 parts of V58 crosslinker for 2 minutes, followed by the addition of 2.5 parts of C05 platinum catalyst and stirring for 5 minutes. The silicone resin thus prepared was then applied to the substrate by means of 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 piece was coated with about 0.7 g / m 2 of the silicone resin thus prepared.

[0200] 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 a substrate on which it has been applied 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.

[0201] The results are listed in the table below. The adhesion rating is indicated by the numbers 1, 2 and 3. “1” means that the silicone withstands strong rubbing without coming off; “2” means that the silicone surface is soiled after strong rubbing; “3” means that the silicone comes off after strong rubbing.

[0202] Sample Wiping Example E2 1 Example E3 2 Example E4 1 Example C1 3 Example C2 3

Claims

1. A polymeric film for a release liner, comprising: - a polymeric support layer of a first composition comprising one or more polyolefins and / or polyesters, and - an extrusion primer layer of a second composition comprising a thermoplastic polymer covalently bound to functional vinyl groups, wherein the thermoplastic polymer covalently bound to functional vinyl groups is formed from a thermoplastic polyvinyl alcohol having a degree of hydrolysis in the range of 65-95 mol%.

2. The polymeric film according to claim 1, further comprising: - a tie layer between the polymeric support layer and the extrusion primer layer.

3. A method of manufacturing a polymeric film for a release liner, the method comprising: - extruding a molten first composition comprising one or more polyolefins and / or polyesters, thereby obtaining an extruded first composition, - extruding a molten second composition comprising a thermoplastic polymer covalently bound to functional vinyl groups, thereby obtaining an extruded second composition, wherein the thermoplastic polymer covalently bound to functional vinyl groups is formed from a thermoplastic polyvinyl alcohol having a degree of hydrolysis in the range of 65-95 mol%, - reducing the temperature of the extruded molten first composition below its melting point, thereby forming a polymeric support layer, - reducing the temperature of the extruded molten second composition below its melting point, thereby forming an extrusion primer layer, and - forming a polymeric film comprising the polymeric support layer and the extrusion primer layer.

4. The method according to claim 3, further comprising: - extruding a molten third composition comprising a compatibilizing agent, 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 positioned between the polymeric support layer and the extrusion primer layer.

5. The method of claim 3 or 4, wherein, The at least two molten compositions are co-extruded.

6. The polymeric film of any one of claims 1-2 or the method of any one of claims 3-4, wherein, The thermoplastic polymer covalently bound to functional vinyl groups is a reaction product of a molten thermoplastic material and a grafting agent containing functional vinyl groups.

7. The polymeric film of claim 1 or 2 or the method of claim 3 or 4, wherein, The thermoplastic polymer covalently bound to 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.

8. The polymeric film according to claim 1 or 2 or the method according to claim 3 or 4, wherein, The second composition further comprises: - one or more plasticizers, and / or - a non-thermoplastic material.

9. The polymeric film according to claim 1 or 2 or the method according to claim 3 or 4, wherein, The tie layer comprises a polyolefin grafted with maleic anhydride, acrylic acid or glycidyl methacrylate.

10. The polymeric film of claim 1 or 2 or the method of claim 3 or 4, wherein, The extrusion primer layer has at least one of the following properties: - a PPS roughness value of less than 1 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.

11. The polymeric film according to claim 1 or 2 or the method according to claim 3 or 4, wherein, The polymeric support layer comprises one or more of high-density polyethylene (HDPE), polypropylene (PP), polybutylene, polyethylene terephthalate (PET) and a PET copolymer.

12. The polymeric film of claim 1 or 2 or the method of claim 3 or 4, wherein, The polymeric support layer comprises a PET copolymer containing cyclohexane dimethanol or isophthalic acid comonomer.

13. The polymeric film according to claim 1 or 2 or the method according to claim 3 or 4, wherein - the polymeric support layer comprises polypropylene, and - the tie layer comprises polypropylene grafted with maleic anhydride.

14. The method according to claim 3, further comprising: prior to extruding the molten second composition, - reacting the molten thermoplastic material with a grafting agent containing a functional vinyl group, thereby obtaining a second composition which is a thermoplastic polymer covalently bound to a functional vinyl group.

15. The method according to claim 14, wherein the step of reacting the molten thermoplastic material with a grafting agent containing a functional vinyl group comprises: - 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%, and - mixing the 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, 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 - 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 an ester bond, thereby forming a reaction product as the second composition, which comprises: - carboxylic acid residues of the condensation reaction forming an ester bond, wherein at least some of the carboxylic acid residues comprise a chain ending in a vinyl group, and - a thermoplastic poly(vinyl alcohol) derivative comprising side chains bonded by an ester bond, wherein at least some of the side chains end in a vinyl group.

16. A release liner, comprising: - the polymeric film according to claim 1 or 2 or obtainable by the method according to claim 3 or 4, and - a silicone coating on the polymeric film.

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