UV curable polyorganosiloxane release coating compositon and methods for the preparation and use thereof

Abstract

An ultra-violet radiation curable polyorganosiloxane release coating composition includes a photoacid generator and an epoxycyclohexylalkyl-functional polydiorganosiloxane. The photoacid generator includes a silylated diaryliodonium cation and a fluorinated aryl borate anion. The composition is curable via exposure to ultra-violet radiation at low temperature. The composition is useful for preparing polyorganosiloxane release coatings on thermally sensitive substrates, such as thermal paper. The composition, and the release coating made therefrom, are useful for forming linerless labels.

Description

UV CURABLE POLYORGANOSILOXANE RELEASE COATING COMPOSITON AND METHODS FOR THE PREPARATION AND USE THEREOF CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefits under 35 U.S.C. §119 (e) of U.S. Provisional Patent Application Serial No.63 / 557024 filed 23 February 2024 and U.S. Provisional Patent Application Serial No.63 / 557032 filed on 23 February 2024. U.S. Provisional Patent Application Serial Numbers 63 / 557024 and 63 / 557032 are hereby incorporated by reference. FIELD

[0002] A polyorganosiloxane release coating composition is curable via exposure to ultra- violet radiation at low temperature. Said composition is useful for preparing polyorganosiloxane release coatings on thermally sensitive substrates, such as thermal paper. Said composition and said release coating are useful for forming products such as linerless labels. INTRODUCTION

[0003] Thermally curable silicone release coatings are often prepared by platinum catalyzed hydrosilylation of a curable composition including a vinyl terminated polydiorganosiloxane base polymer, a polyorganohydrogensiloxane crosslinker, a platinum catalyst, and other additives. The compositions may be stored under conditions to avoid premature cure and are typically mixed shortly before use. The curable composition can then begin to cure.

[0004] The substrates for release liners have traditionally been paper, and the temperature at which the polysiloxane based release coating is cured is usually at least 130 °C. There is a need in the release coating industry for curable compositions to cure efficiently and effectively at lower temperatures for several reasons. First, there is a growing desire in the release coating industry to use thermally sensitive substrates, which cannot withstand high curing temperature. For example, thermal paper may change color at temperature above 100 °C. And, lowering curing temperature can save energy from oven heating and improve sustainability. Finally, high curing temperature can cause paper substrates to lose moisture, leading to a paper curling problem, which creates a need for an additional re-moisturization process step after curing the release coating composition. An efficient lower curing temperature is desired to mitigate the moisture loss issue and avoid the re-moisturization, which would simplify the production process and reduce production cost.

[0005] Commercially available thermally curable silicone release coating compositions typically do not perform well at lower cure temperatures due to the competing desires to achieve both 1) fast cure with good anchorage and 2) long bath life. Generally, in the release coating industry, it is desirable for a silicone release coating layer to be fully cured and well anchored tothe substrate to avoid silicone transfer after 1-5 seconds of heating on a coater. At the same time, sufficient working time at typical working temperatures (e.g., RT to 40 °C) is desired to allow operators to prepare the coater and finish the coating process. Thermally curable silicone release coating compositions which cure via hydrosilylation reaction typically are stored in two parts, e.g., a base part including a base polymer and crosslinker, and a curing agent part including a platinum catalyst. An inhibitor, such as 1-ethynyl-1-cyclohexanol (ETCH) is typically added to one or both parts, and the parts are mixed shortly before use in a coating bath. The catalyst and inhibitor work together to afford longer enough coating bathlife after the parts are mixed to afford acceptable working times of the release coating bath before cure. If coating bath life of a release coating composition is too short, there is a risk of gelling the coating bath, piping, or other parts of the coating equipment.

[0006] Commonly, fast cure and sufficient bath life are achieved by selecting a catalyst / inhibitor combination and optimizing their relative amounts to achieve desired bulk bath life at the working temperature. The curable release coating composition is coated on a substrate to form a layer, which is cured at a temperature (e.g., ≥ 130 °C) much higher than the than working temperature to achieve fast cure. However, at lower curing temperatures, the difference between working temperature and curing temperature may be too narrow to achieve both long bathlife and fast cure with good anchorage. Thus, the lower temperature curing release coating market is occupied by irradiation curable systems, such as UV curable silicone release coating. However, the UV cure systems have cost and performance issues.

[0007] Therefore, this is an industry need for a new thermally curable silicone release coating composition that can afford fast, complete cure, with good anchorage to substrates while curing at relatively low temperatures. SUMMARY

[0008] An ultra-violet radiation curable polyorganosiloxane release coating composition (composition) comprises: (A) a photoacid generator and (B) an epoxycyclohexyl-functional polydiorganosiloxane. The photoacid generator comprises a silylated diaryliodonium cation and a fluorinated aryl borate anion. The composition may be prepared by a method comprising mixing starting materials (A) and (B), and optionally an additional starting material. The composition may be used in a method comprising coating the composition on a substrate and curing the composition via exposure to ultra-violet radiation, thereby forming a polyorganosiloxane release coating. The substrate may be thermally sensitive, such as thermal paper. The product prepared by this method may be, for example, a linerless label. DETAILED DESCRIPTION

[0009] An ultra-violet radiation curable polyorganosiloxane release coating composition(composition) comprises: (A) a photoacid generator and (B) an epoxycyclohexyl-functional polydiorganosiloxane. The composition may comprise starting materials (A) and (B). Alternatively, the composition may consist essentially of starting materials (A) and (B). Alternatively, the composition may consist of starting materials (A) and (B). The composition may consist of 0.1% to 5% of starting material (A) and a balance to 100% of starting material (B).

[0010] Alternatively, the composition may optionally further comprise an additional starting material selected from the group consisting of (C) a photosensitizer, (D) an alcohol, (E) a reactive diluent, (F) a filler, (G), a release modifier, and a combination of two or more of (C), (D), (E), (F), and (G). The starting materials may be present in amounts of 0.1% to 5% of (A) the photoacid generator, 0 to 1% of (C) the photosensitizer, 0 to 10% of (D) the alcohol, 0 to 25% of (E) the reactive diluent, 0 to 12% of (F) the filler, 0 to 40% of (G) the release modifier, and a balance to 100% of (B) the epoxycyclohexyl-functional polydiorganosiloxane. However, combined weights of the optional additional starting materials (e.g., (C) the photosensitizer, (D) the alcohol, (E) the reactive diluent, (F) the filler, and (G) the release modifier) may total 0 to 40%, based on combined weights of all starting materials in the composition. (A) Photoacid Generator

[0011] Starting material (A) in the composition is the photoacid generator. The photoacid generator comprises a silylated diaryliodonium cation and a fluorinated aryl borate anion. The silylated diaryliodonium cation has formula: anatoms, R7is an alkyl group of 8 or more carbon atoms, R8is an alkyl group of 8 or more carbon atoms, and R9is an alkyl group of 8 or more carbon atoms.

[0012] Suitable alkyl groups for R3, R4, and R6are exemplified by methyl, ethyl, propyl (including n-propyl and isopropyl), and butyl (including n-butyl, isobutyl, sec-butyl, and tert- butyl), as well as linear and branched saturated hydrocarbyl groups of 5 to 12 carbon atoms.Alternatively, R3may be methyl or ethyl. Alternatively, R3may be methyl. Alternatively, R4may be methyl or ethyl. Alternatively, R4may be methyl. Alternatively, R6may be methyl or ethyl. Alternatively, R6may be methyl.

[0013] Suitable divalent hydrocarbyl groups for R5are exemplified by alkane-diyl groups of 2 to 12 carbon atoms, alternatively 2 to 6 carbon atoms, and alternatively 2, 3, or 6 carbon atoms. The alkane-diyl groups may be linear or branched. Alternatively, R5may be linear, e.g., -CH2- CH2-.

[0014] In the formula for the silylated diaryliodonium cation above, R7, R8, and R9are each independently selected alkyl groups of 8 or more carbon atoms, alternatively 8 to 12 carbon atoms, alternatively 8 to 10 carbon atoms, and alternatively 8 carbon atoms. The alkyl groups for R7, R8, and R9may be linear or branched, alternatively linear. R7, R8, and R9may each be an octyl group, such as an n-octyl group. Without wishing to be bound by theory, it is thought that the longer chain (e.g., 8 or more carbon atoms) alkyl groups R7, R8, and R9may improve compatibility of the photoacid generator with (B) the epoxycyclohexyl-functional polydiorganosiloxane (as compared to a photoacid generator with shorter chain alkyl groups, e.g., 2 carbon atoms, corresponding to R7, R8, and R9).

[0015] The fluorinated aryl borate anion has R10, R11, R12, R13, and R14are each independentlyCF3, with the proviso that at least one, per anion, is R12, R13, and R14per aryl moiety in the fluorinated aryl borate anion is selected from the group consisting of F and CF3. Alternatively, 2 to 5, alternatively 2 to 4, and alternatively 2 to 3 of R10, R11, R12, R13, and R14per aryl moiety are selected from the group consisting of F and CF3. For example, the fluorinated aryl borate anion may be selected from the group consisting of [B(C6H3(CF3)2)4]-, [B(C6F5)3(C6H5) ]-, [B(C6F5)2(C6H5)2]-, [B(C6H2(CF3)3)4]-, [B(C6F5)4]-, and [B(C6H2F3)4]-. Alternatively, the fluorinated aryl borate anion may be [B(C6H3(CF3)2)4]-.

[0016] The photoacid generator described above may be prepared by a method as described in U.S. Provisional Patent Application Serial Numbers 63 / 557024 and 63 / 557032, which are hereby incorporated by reference. The method is illustrated below in Scheme 1, and further exemplified in Synthesis Example 1, below.Scheme 1:

[0017] In Z represents aR5described above. X1represents a halogen atom such as Br. X2represents a halogen atom, such as Cl. In Scheme 1, a method for preparing the photoacid generator for starting material(A) comprises: in a first step, a (2-alkoxyphenyl)dialkyl(alkenyl)silane (intermediate 2a) exemplified by (2-methoxyphenyl)dimethyl(vinyl)silane may be synthesized by a method comprising reacting an alkoxy-functional aryl halide (intermediate 1a), such as 2-bromoanisole with an alkenyl-, dialkyl-functional halosilane (intermediate 1b), such as vinyldimethylchlorosilane, in the presence of a solvent (such as diethyl ether) and an organometallic reagent (such as n-butyl lithium). This step may be performed with cooling, e.g., at a temperature of -20 °C to 0 °C.

[0018] In a second step, intermediate 2a may then be reacted with a trialkylhydridosilane (intermediate 2b), exemplified by trioctylsilane via hydrosilylation reaction with a platinum group metal catalyst, optionally in the presence of a solvent. The resulting product of this step is a (2-alkoxyphenyl)dialkyl(2-(trialkylsilyl)alkane-diyl silane (intermediate 3a) exemplified by (2- methoxyphenyl)dimethyl(2-(trioctylsilyl)ethyl)silane.

[0019] In a third step, intermediate 3a may then be reacted with PhI(OH)(OTs) (intermediate 3b) in the presence of a solvent such as 2,2,2-trifluoroethanol to form a 3-(dialkyl(2- (trialkylsilyl)alkyl)silyl-4-alkoxyphenyl iodonium tosylate (intermediate 4a), exemplified by (3- (dimethyl(2-(trioctanoylsilyl)ethyl)silyl)-4-methoxyphenyl)(phenyl)iodonium tosylate.

[0020] In a fourth step, intermediate 4a may be reacted with a sodium tetrakis(fluorinated aryl)borate compound (intermediate 4b), such as sodium tetrakis[3,5- bis(trifluoromethyl)phenyl]borate, in a solvent such as diethyl ether to form the photoacid generator useful as starting material (A) herein.

[0021] Starting material (A) the photoacid generator may be used in the composition in an amount of 0.1% to 5%, based on combined weights of all starting materials in the composition. Alternatively, the amount of starting material (A) may be at least 0.1%, alternatively at least 0.2%, alternatively at least 0.3%, alternatively at least 0.4%, and alternatively at least 0.5%; while at the same time, the amount of starting material (A) may be up to 5%, alternatively up to 4%, alternatively up to 3%, alternatively up to 2%, and alternatively up to 1%, on the same basis. (B) Epoxycyclohexyl-functional Polydiorganosiloxane

[0022] Starting material (B) in the composition is the epoxycyclohexyl-functional polydiorganosiloxane having a degree of polymerization up to 845 and having an epoxy content of 8.5 mol % to < 15 mol %, based on molar amount of the epoxycyclohexyl-functional polydiorganosiloxane. The epoxycyclohexyl-functional polydiorganosiloxane has sufficient epoxycyclohexyl groups to cure to form a polyorganosiloxane release coating.

[0023] The epoxycyclohexyl-functional polydiorganosiloxane comprises unit formula: (R13SiO1 / 2)a(R12R2SiO1 / 2)b(R12SiO2 / 2)c(R1R2SiO2 / 2)d, wherein each R1is an independentlyselected monovalent hydrocarbyl group of 1 to 12 carbon atoms; each R2is an epoxycyclohexyl- alkyl group; subscripts a, b, c, and d represent average numbers of each unit per molecule, and subscripts a, b, c, and d have values such that 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, a quantity (a + b) = 2, c ≥ 0, d ≥ 0, a quantity (b + d) ≥ 2, and a quantity (a + b + c + d) ≤ 845, and the values for a, b, c, and d are sufficient to give the epoxycyclohexyl-functional polydiorganosiloxane the epoxy content of 8.5 mol % to < 15 mol %. Subscripts a, b, c, and d have values sufficient to render the composition curable to form the polyorganosiloxane release coating. For example, the quantity (b + d) may be at least 3, alternatively at least 5, alternatively at least 7, alternatively at least 9, and alternatively at least 10; while at the same time, the quantity (b + d) may be up to 25, alternatively up to 23, alternatively up to 20, alternatively up to 15, and alternatively up to 12.

[0024] In the unit formula for the epoxycyclohexyl-functional polydiorganosiloxane, each R1is an independently selected monovalent hydrocarbyl group of 1 to 12 carbon atoms, alternatively 1 to 8 carbon atoms, and alternatively 1 to 4 carbon atoms. The monovalent hydrocarbyl group may be free of aliphatic unsaturation. The monovalent hydrocarbyl group may be an alkyl group or an aryl group. For example, suitable alkyl groups include methyl, ethyl, propyl (including n-propyl and isopropyl), and butyl (including n-butyl, isobutyl, sec-butyl and tert-butyl); alternatively methyl or ethyl; and alternatively methyl. Suitable aryl groups include phenyl, tolyl, xylyl, styryl, naphthyl, and anthracenyl, alternatively phenyl. Alternatively, each R1may be an alkyl group, such as methyl.

[0025] Each R2is an epoxycyclohexylalkyl group of , wherein D1is a divalent hydrocarbyl group, such as anatoms, alternatively 2, 3, or 6 carbon atoms, which may be or linear. Alternatively, each R2may be a 2-(3,4-epoxycyclohexyl)ethyl group of formula: . epoxycyclohexyl-functional polydiorganosiloxane,average numbers of each siloxy unit per molecule. Subscripts a, b, c, and d need not be whole numbers. The subscripts may be selected to give theepoxycyclohexyl-functional polydiorganosiloxane a DP ≤ 845. Alternatively, DP may be at least 54, alternatively at least 55, alternatively at least 60, alternatively at least 65, and alternatively at least 70; while at the same time, DP may be up to 845, alternatively up to 250, alternatively up to 233, alternatively up to 225, alternatively up to 200, alternatively up to 195, and alternatively up to 192. The subscripts may be selected to give the epoxycyclohexyl-functional polydiorganosiloxane an epoxy content of 8.5 mol % to < 15 mol %, alternatively 9 mol % to < 12 mol %, and alternatively 9 mol % to 11.9 mol %. Alternatively, epoxy content may be at least 8.5 mol %, alternatively at least 9 mol %, alternatively at least 9.5 mol %, and alternatively at least 10 mol %; while at the same time, epoxy content may be up to 12 mol %, alternatively < 12 mol%, and alternatively up to 11.9 mol %. Alternatively, in the unit formula for the epoxycyclohexyl-functional polydiorganosiloxane, each R1may be alkyl, subscript a may be 2, subscript b may be 0, and subscripts c and d may have values such that 60.5 ≤ c ≤ 169; and 7.5 ≤ d ≤ 23.

[0027] Alternatively, the epoxycyclohexyl-functional polydiorganosiloxane may be selected from the group consisting of: b-1): (R1SiO ) (R1 SiO ) (R1R2SiO ) (a CEP 3 1 / 2 2 2 2 / 2 108 2 / 2 10 bbreviated MD108D 10M); b-2): (R13SiO1 / 2)2(R12SiO2 / 2)117(R1R2SiO2 / 2)11.8(abbreviated MD117DCEP11.8M); b-3): (R11 3SiO1 / 2)2(R 2SiO2 / 2)169(R1R2SiO CEP 2 / 2)23 (abbreviated MD169D 23M); b-4): (R13SiO1 / 2)2(R12SiO2 / 2)60.5(R1R2SiO2 / 2)7.5(abbreviated MD60.5DCEP7.5M); and a combination of two or more thereof; wherein in the unit formulas b-1) to b-4), above, each R1is methyl, and each R2is 2-(3,4-epoxycyclohexyl)ethyl group. One skilled in the art would recognize that one epoxycyclohexyl-functional polydiorganosiloxane may be used as starting material (B). Alternatively, two or more epoxycyclohexyl-functional polydiorganosiloxanes that differ in at least one property such as structure, DP, molecular weight, and epoxy content may be used as starting material (B), provided that the combination has an average DP ≤ 845 and an average epoxy content of 8.5 mol % to < 15 mol %. For example, a bis-epoxycyclohexylethyl- terminated polydimethylsiloxane and a bis-trimethylsiloxy-terminated poly(dimethyl / methyl, epoxycyclohexylethyl)siloxane may be used in combination.

[0028] Epoxycyclohexyl-functional polydiorganosiloxanes are known in the art and are commercially available. For example, MD117DCEP 11.8M is available as ECMS-924 from Gelest, Inc. of Morrisville, Pennsylvania, USA. Alternatively, epoxycyclohexyl-functional polydiorganosiloxanes may be prepared by known methods, such as hydrosilylation of an organic epoxy-functional alkene such as 4-vinylcyclohexene-1,2-epoxide and a polyorganohydrogensiloxane, as described, for example, in US Patents 4279717, 4313988, 5391676, and 5703137. Epoxy-functional alkenes such as 4-vinylcyclohexene-1,2-epoxide,which has CAS No.106-86-5, are commercially available, e.g., from Sigma-Aldrich, Inc. and suitable polyorganohydrogensiloxanes are commercially available, e.g., from Gelest, Inc. or may be prepared by known methods, such as described in US Patent US5516870. (C) Photosensitizer

[0029] Starting material (C) is an optional photosensitizer that may be added to the composition. Suitable photosensitizers are disclosed, for example, in US Patent 4977198 and US Patent Application Publication 20230046737 and include xanthones such as isopropylthioxanthone. (D) Alcohol

[0030] Starting material (D) is an optional alcohol that may be added to the composition. The alcohol may be a monohydric alcohol such as ethanol, isopropanol, 2-butanol, or isobutyl alcohol. Suitable alcohols are as disclosed in US Patent Application Publication 20230046737. The alcohol may act as a solvent to facilitate compatibilization of another starting material in the composition, such as the photosensitizer described above. Alternatively, the alcohol may act as a reactive diluent. (E) Reactive Diluent

[0031] Starting material (E) is an optional reactive diluent that may be added to the composition as an accelerator. The reactive diluent may be a monohydric alcohol as described above for starting material (D), a diol, a polyol, an oxetane, or a combination thereof. Suitable reactive diluents are disclosed, for example, in US Patent Application Publication 20220251287. (F) Filler

[0032] Starting material (F) is an optional filler that may be added to the composition. Suitable fillers include silica, mica, quartz, calcium carbonate, talc, alumina, titania, zirconia and a combination thereof. Fillers are disclosed, for example, in US Patent Application Publications 20220251287 and 20230046737. (G) Release Modifier

[0033] Starting material (G) is an optional release modifier that may be added to change the release force of a polyorganosiloxane release coating prepared from the composition. Starting material (G) may comprise an epoxycyclohexyl-functional polyorganosiloxane resin. Suitable epoxycyclohexyl-functional polyorganosiloxane resins include MMCEPQ, MDCEPQ, and MTCEPQ resins, which may be prepared as described in US Patent 9976041 to Fu, et al. and US Patent Application Publication 20110070438 to Bahadur, et al.

[0034] The ultra-violet radiation curable polyorganosiloxane release coating composition may be free of conventional release modifiers that have been used in the past to control (decrease) the level of release force (the adhesive force between the release coating and an adherend thereto,such as a pressure sensitive adhesive. Examples of such release modifiers include trimethylsiloxy-terminated dimethyl, phenylmethylsiloxanes. Without wishing to be bound by theory, it is thought that including a trimethylsiloxy-terminated dimethyl, phenylmethylsiloxane in a release coating composition may lower subsequent adhesion strength and / or increase migration of the release coating prepared from the composition described herein.

[0035] When selecting starting materials for the composition described above, there may be overlap between types of starting materials because certain materials described herein may have more than one function. For example, certain alcohols may be useful as solvents, reactive diluents and / or accelerators. Certain particulates may be useful as fillers and as pigments, e.g., titania. When adding additional starting materials to the composition, the additional starting materials are distinct from one another.

[0036] The composition may be free of fluoroorganosilicone compounds. It is believed that, during cure, due to its low surface tension a fluorocompound will rapidly migrate to the interface of a composition and a substrate, for example a polyorganosiloxane release coating composition / PET film interface, and prevent adherence of the release coating (prepared by curing the composition) to the substrate by making a fluorine containing barrier. By making a barrier, the fluorocompound prevents other components from reacting at the interface. Moreover, fluorosilicone compounds are usually expensive, which may be undesirable for cost effectiveness of the composition. Method of Making the UV Curable Polyorganosiloxane Release Coating Composition

[0037] The composition described above may be prepared by any convenient means, such as mixing, under ambient conditions, amounts of starting materials comprising (A) and (B), and any optional additional starting materials, as described above. Mixing may be performed in any convenient equipment, such as a batch vessel equipped with mixing means (such as an agitator, baffles, or both). Without wishing to be bound by theory, it is thought that one of the benefits of the present invention is that (A) the photoacid generator is compatible with (B) the epoxycyclohexyl-functional polydiorganosiloxane, such that these starting materials are miscible, and use of a solvent is not required. Method of Making a Polyorganosiloxane Release Coating

[0038] The composition can be used to prepare a polyorganosiloxane release coating in a method comprising applying the composition to a surface of a substrate and curing the composition. The composition can for example be applied to the substrate by any convenient means such as spraying, doctor blade, dipping, screen printing or by a roll coater, e.g. an offset web coater, kiss coater or etched cylinder coater.

[0039] The substrate may be, for example a polymer film substrate such as polyester,particularly polyethylene terephthalate (PET); polyethylene, e.g., high density polyethylene (HDPE) or low density polyethylene (LDPE); polypropylene (PP); biaxially oriented polypropylene (BOPP); or polystyrene films. Alternatively, the substrate may be a paper substrate, including plastic coated paper, for example paper coated with polyethylene (such as polyethylene coated Kraft Paper), glassine, super calendar paper, or clay coated Kraft. Alternatively, the substrate may be a thermally sensitive substrate such as thermal paper, LDPE, HDPE, PP, BOPP, or polyethylene coated Kraft paper. Alternatively, the substrate may comprise thermal paper.

[0040] The method may further comprise: 3) treating the surface of the substrate before applying the composition thereto. Treating the substrate may be performed by any convenient means such as a plasma treatment or a corona discharge treatment. Alternatively, the substrate may be treated by applying a primer. Without wishing to be bound by theory, it is thought that anchorage of the polyorganosiloxane release coating may be improved if the substrate is treated before applying the composition.

[0041] The method may further comprise: 4) curing the composition to form a polyorganosiloxane release coating on the surface of the substrate. Curing may be performed by irradiation with ultra-violet radiation. The ultra-violet radiation has a wavelength of 100 nanometers to 400 nanometers, alternatively 200 nanometers to 400 nanometers, and alternatively 300 nanometers to 400 nanometers. Exposure dose of ultra-violet radiation may be 1 J / cm2to 4 J / cm2.

[0042] Curing may be performed at a temperature of < 100 °C, alternatively no more than 95 °C, alternatively no more than 90 °C, alternatively no more than 85 °C, and alternatively no more than 80 °C. Alternatively, curing may be performed at RT to < 100 °C; alternatively RT to 70 °C.

[0043] Irradiating may be performed for a time sufficient to cure the composition to form a polyorganosiloxane release coating. The time depends on various factors including the thickness of composition on the substrate and the temperature; however, the time may be 1 second to 1 minute, alternatively 10 seconds to 50 seconds. Under production coater conditions, cure can be effected in a residence time of 1 second to 6 seconds, alternatively from 1.5 seconds to 3 seconds, at an air temperature described above. Thickness of the composition is not specifically restricted, but may range from 0.3 µm to 5 µm, alternatively 1 µm to 3 µm, after step 1). EXAMPLES

[0044] The following examples are provided to illustrate the invention to one skilled in the art and are not to be construed as limiting the scope of the invention set forth in the claims. The starting materials used in these examples are summarized below in Table 1.Table 1 – Starting Materials . ., 4.,7, , , , , , ,, ,(vinyl)silane (2a) was synthesized as follows: Awith one equivalent of 2-Bromoanisole (1a) under nitrogen atmosphere, followed by addition of diethyl ether to make the concentration approximately 0.5 M. The mixture was cooled to -20 °C. Next, 1.1 equivalent of n-butyl lithium(1.6 M in hexane) was added to the solution. The reaction mixture was then stirred at -20 °C for 3 h. Next, 1.1 equivalent of dimethylvinylchlorosilane was slowly added to the reaction mixture. Once the addition was complete, the reaction was slowly warmed up to room temperature. After stirring overnight, the reaction was quenched by saturated NH4Cl (30 mL), and the mixture was then transferred to a separatory funnel. The organic layer was separated, and the aqueous layer was further washed with diethyl ether. The organic layers were combined and dried over anhydrous MgSO4. The solvent was removed under reduced pressure to yield the crude product. Next, the material was purified via silica gel column chromatography (5% ethyl acetate in hexane) to isolate the pure material 2a in 66% yield.

[0047] Step 2: (2-methoxyphenyl)dimethyl(2-(trioctylsilyl)ethyl)silane (3a) was synthesized as follows: In a nitrogen-purged glove box, a 40 mL glass vial was charged with (2- methoxyphenyl)dimethyl(vinyl)silane (2a, 1 equivalent) and 10 ppm of Karstedt’s catalyst (2 wt% in xylene). The reaction mixture was warmed up to 50 °C. Next, 1.1 equivalent of Octylsilane was slowly added to the reaction mixture. The hydrosilylation reaction is highly exothermic. After the addition was complete, the heat block was removed and the mixture was allowed to stir at room temperature for an hour, after which, an aliquot of the reaction mixture was removed and analyzed by 1H NMR. Once the reaction showed full conversion to the hydrosilylated product, the reaction mixture was removed from the glovebox and was further purified by silica gel column chromatography (100% hexane) to isolate the pure hydrosilylated product 3a over 90% yield.3: (3-(dimethyl(2-(trioctanoylsilyl)ethyl)silyl)-4- methoxyphenyl)(phenyl)iodonium tosylate (4a) was synthesized as follows: To a stirred solution of arene 3a (1.0 mmol) in 2,2,2-trifluoroethanol (5 mL), PhI(OH)OTs (392 mg, 1.0 mmol) was added in one portion at room temperature under air, and it was stirred for 3 h. Next, the solvents were removed under vacuum. The resulting oily crude product (4a) was characterized by1HNMR and directly used for the next step.- (phenyl)iodonium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (PAG-Si-1) was synthesized as follows: In a nitrogen purged glove-box, the tosylate salt (4a, 1 mmol) was dissolved in 5 mL of anhydrous diethyl ether, 1 equiv. of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (1.0 equiv.) was added and stirred for 12 h at room temperature. The solvent was removed in vacuo and the mixture was dissolved in 30 mL toluene and vacuum filtered. The filtrate was then concentrated and kept in under vacuum to remove excess toluene to isolate the pure product over 50% yield.

[0050] In this Synthesis Example 2, PAG-Si-2 was prepared as follows:Triethyl(2-((2-methoxyphenyl)dimethylsilyl)ethyl)silane (5a): In a nitrogen- purged glove box, a 40 mL glass vial was charged with (2-methoxyphenyl)dimethyl(vinyl)silane (2a prepared as described in Synthesis Example 1, 1 equivalent) and 10 ppm of Karstedt’s catalyst (2 wt% in xylene). The reaction mixture was warmed up to 50 °C. Next, 1.1 equivalent of triethylsilane was slowly added to the reaction mixture. The hydrosilylation reaction was highly exothermic. After the addition was complete, the heat block was removed and the mixture was allowed to stir at room temperature for an hour, after which, an aliquot of the reaction mixture was removed and analyzed by1H NMR. Once the reaction showed full conversion to the hydrosilylated product, the reaction mixture was removed from the glovebox and was further purified by silica gel column chromatography (100% hexane) to isolate the pure hydrosilylated product 5a over 90% yield.

[0052] Step 2: (3-(dimethyl(2-(triethylsilyl)ethyl)silyl)-4-methoxyphenyl)(phenyl)iodonium tosylate (6a): To a stirred solution of arene 5a (1.0 mmol) in 2,2,2-trifluoroethanol (5 mL), PhI(OH)OTs (392 mg, 1.0 mmol) was added in one portion at room temperature under air, and it was stirred for 3 h. Next, the solvents were removed under vacuum. The resulting oily crude product (6a) was characterized by1H NMR and directly used for the next step. OMe NaB[C6H3(CF3)2]4OMe 4(phenyl)iodonium tetrakis(3,5-bis(trifluoromethyl)phenyl)borate (bPAG-Si-2): In a nitrogen purged glove-box, the tosylate salt (6a, 1 mmol) was dissolved in 5 mL of anhydrous diethyl ether, 1 equiv. of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (1.0 equiv.) was added and stirred for 12 h at room temperature. The solvent was removed in vacuo and the mixture was dissolved in 30 mL toluene and vacuum filtered. The filtrate was then concentrated and kept in under vacuum to remove excess toluene to isolate the pure product over 50% yield.

[0054] In Reference Examples 1 to 11, epoxy-functional polydiorganosiloxanes were synthesized using the following general procedure. To a 500 mL 3N dry flask were added a polyorganohydrogensiloxane (SiH polymer), Karstedt’s catalyst, and toluene, followed by heating to 80 °C. A solution of epoxy-functional reactant in toluene was added dropwise within 20-30 min at 80 °C, and then the reaction mixture was heated to reflux (at 90 - 110°C) for 3-6 hours. Sampling to NMR showed the completion of the reaction, and then the toluene solvent and excess epoxy-functional reactant were removed with a rotary evaporator. Amounts and starting materials used and epoxy-functional polydiorganosiloxanes formed are summarized below in Table 2.Table 2 – Synthesis of Epoxy-Functional Polydiorganosiloxanes M M M M PPPM

[0055] In Table 2, the epoxy-functional reactant was AGE in Reference Example 1, and the epoxy-functional reactant was VCHO in all other Reference Examples. Amt SiH means the weight parts of SiH polymer. Amount Pt refers to ppm by weight of platinum provided by the amount of Karstedt’s catalyst added. Amt toluene added to flask refers to the weight parts of toluene solvent added to the flask. Amt epoxy means the weight parts of epoxy-functional reactant (AGE or VCHO). Amt toluene delivered means the weight parts of toluene solvent delivered dropwise with the AGE or VCHO. Product means the epoxy-functional polydiorganosiloxane formed.

[0056] In this Reference Example 12, UV Curable Release Coating Composition Samples were prepared as follows: All UV curable release coating composition samples were developed by mixing 0.1 % of a photoacid generated and 99.9 % of an epoxy-functional polydiorganosiloxane, as shown below in Table 3. The appearance was evaluated visually, with clear being a desirable result indicating good compatibility of the photoacid generator and the epoxy-functional polydiorganosiloxane. Table 3 - Compatibility between different photoacid generators and epoxycyclohexylethyl- functional polydiorganosiloxanes epoxycyclohexylethyl (CEP)-functional CEP PAG-Si- PAG- mol% 1 PAG-Si-2 PAG-3 2 PAG-1 l di r n il x n

[0057] Table 3 shows the compatibility between photoacid generators and different epoxycyclohexyl-functional polydiorganosiloxanes. The CEP mol% equals the mole number of Si atoms attached with epoxycyclohexylethyl groups divided by the total mole number of Si atoms in the epoxycyclohexyl-functional polydiorganosiloxanes. PAG-2 and PAG-1 showed the worst solubility in epoxycyclohexyl-functional polydiorganosiloxanes and were only compatible with epoxycyclohexyl-functional polydiorganosiloxanes with CEP mol% > 10%. However, the new PAG-Si-1 showed consistent compatibility with all epoxycyclohexyl-functional polydiorganosiloxanes tested. PAG-Si-2 showed compatibility with epoxycyclohexyl-functional polydiorganosiloxanes having CEP mol% > 8.

[0058] In this Reference Example 13, compositions containing 0.1 weight % of PAG-Si-1 and the balance to 100 weight % of an epoxy-functional polydiorganosiloxane were coated on thermal paper substrates as 3 µm thick films, and then cured under 365 nm LED UV light for 10 seconds (the UV power was1.5 J / cm2). The cured release coatings were measured for adhesion and release force. The samples and results are in Table 4.

[0059] The release force was categorized as premium, modified and tight, depending on the different applications. The premium release force ranges from 1-10 g / cm or 2.5 to 25 g / inch, the modified force ranges from 10-50 g / cm or 25-125 g / inch, and the tight force ranges from 50-500 g / cm or 125-1250 g / inch. Typically release coatings on thermal paper liners or thermal labels require premium or modified force. The release force of each sample was measured by using IMASS SP-2100 instrument. Tesa-7475 acrylic tape was laminated against the coating surface and stored under 40 pounds weight at RT for 24 hours. The release force was measured bypeeling the tape off with 180 degree and 0.3 meter per min peeling rate. Table 4 - The release force and ROR% values measured for UV cured release coating compositions based on various CEP-PDMS polymers. UV cure: 365nm LED UV light, 10 seconds (2J / cm2UV power), 0.1 wt% of PAG-Si-1 was used for most formulations except C8 and C9. Note: a: 0.1 wt% PAG-Si-2 was used for C8, b: 0.1 wt% PAG-3 was used for C9. Peel-V curable polyorganosiloxane release coating compositions with different epoxy contents. All the coatings were UV cured by using 365 nm LED light with UV power of 2 J / cm2. Samples 1-5 and C1-C6 cured rapidly in 10 seconds under UV irradiation. From Samples C1, C2, 1 to 6, and C3 to C5, the CEP mol% increased from 4.8 mol% to 100 mol%, and the release force measured increased from 7.9 to 200.6 g / inch. All compositions except C8 and C9 showed good bath life at RT and under darkness (with no cure over 60 days). C8 used 0.1% PAG-Si-2 and showed lowerROR% (or lower cure%), higher Peel-off% and short bath-life. Without wishing to be bound by theory, is thought that these results occurred with PAG-Si-2 because some PAG-Si-2 crystallized and precipitated from the composition. C9 used 0.1 wt% PAG-3 and also showed lower cure or lower ROR% and relatively higher Peel-off% than Example 3 because it is thought that the UV activity of PAG-3 is lower than the activity of PAG-Si-1. Example C7 contained epoxypropyl (PEP) functional polydiorganosiloxane, and this sample had slower cure than sample 3, which used epoxycyclohexylethyl-functional polydiorganosiloxane with the same mol% epoxy and DP.

[0061] ROR% is the percentage of rub off resistance which was measured and calculated as the weight percentage of the film that remained on the substrate after a rubbing off test. ROR% was measured for each coating sample to show the adhesion or anchor performance of the films on thermal paper substrates. The higher the ROR%, the stronger the adhesion of the coating to the substrate. Table 4 shows the increase of the ROR% with the increase of epoxy content. The desired ROR% values (> 80 %) were achieved by the coatings prepared from compositions containing polydiorganosiloxanes with epoxy content ≥ 9 mol%.

[0062] Peel-off % indicates the amount of the coating materials migrating from the substrate coated with a release coating prepared as described herein to the adhesive surface of 3M scotch tape when a strip of scotch tape is pushed against the release coating surface and then peeled off. The lower the Peel-off %, the less the migration of the coating materials from coated substrate to tape. The migration of coating materials occurred for the coatings prepared from compositions containing polydiorganosiloxanes with high epoxy content (e.g., > 18 mol%). For example, Sample C6 in Table 3 was the composition with MCEPMCEP, 100 mol% CEP, causing the migration of 100% of coating materials from the thermal paper substrate to 3M scotch tape. The release coating compositions with CEP content lower than 15 mol% did not show any material migration.

[0063] The notes in the last column in Table 4 indicated how the tape was smoothly peeled off from the coating surface during the release force measurement. “Smooth” means that the tape was peeled off from the surface with a very even force and a constant speed. “Chattery” means that the tape was peeled off from the coating surface unevenly with a chattering speed. High epoxy content in the coating compositions generally resulted in “chattery” under the conditions tested. The epoxy content lower than 15 mol% provided “smooth” peeling off for release force measurement under the conditions tested.

[0064] In this Reference Example 14, effect of storage time on release force was studied. The release force was measured from the release coating prepared from Sample 5 in Table 4 at different storage time at RT.Table 5 – The effect of storage time on release force.

[0065] Table 5 shows the variation of the release force with the increase of storage time at RT. One of the common issues for UV curable epoxy functional silicone release coating products is the insufficient cure and often requires post-cure, resulting in the significant release force change of the UV cured coatings with storage time. The release force data in Table 5 were measured from the release coating prepared from the composition of Sample 5 in Table 4 at different storage time at RT. In the first two weeks, the release force did not vary much and only slightly increased from 26.7 to 30.3 after one month storage. The relatively stable release force of the coatings indicated the fast UV cure of the release coating compositions of this invention.

[0066] In this comparative example 15, a sample was prepared by mixing 0.5% PAG-1 and 99.5% MCEPD100MCEP.

[0067] In this comparative example 16, a sample was prepared by mixing 0.5% PAG-3 and 99.5% MCEPD100MCEP.

[0068] The samples prepared in comparative example 15 and comparative example 16 were coated in a 1-mm thick film on an aluminum panel and exposed to 365 nm LED UV light for 10 seconds (the UV power was 1.5 J / cm2). Both samples exhibited no cure. Industrial Applicability

[0069] The UV curable release coating compositions described herein are useful for thermal paper applications. The compositions a photoacid generator that is compatible with the epoxycyclohexyl-functional polydiorganosiloxane, and these compositions cure via UV exposure to form a release coating with appropriate and stable release force, good adhesion on thermal paper substrates (high ROR%) and no material migration from thermal paper to the tape. DEFINITIONS AND USAGE OF TERMS

[0070] All amounts, ratios, and percentages herein are by weight, unless otherwise indicated by the context of the specification. The SUMMARY and ABSTRACT are hereby incorporated by reference. The articles, “a”, “an”, and “the” each refer to one or more, unless otherwise indicated by the context of the specification. The singular includes the plural unless otherwise indicated by the context of the specification. The transitional phrases “comprising”, “consisting essentially of”, and “consisting of” are used as described in the Manual of Patent Examining Procedure Ninth Edition, Revision 08.2017, Last Revised January 2018 at section §2111.03 I., II., and III. The use of “for example,” “e.g.,” “such as,” and “including” to list illustrative examples does not limit to only the listed examples. Thus, “for example” or “such as” means “for example, but not limited to” or “such as, but not limited to” and encompasses other similaror equivalent examples. The symbol “<” denotes “less than”, the symbol “>” denotes “greater than”, the symbol “≤” denotes “less than or equal to”, and the symbol “≥” denotes “greater than or equal to”.

[0071] Fluorinated aryl borate anions are abbreviated as shown in Table 6. Abbreviation StructureFTable 7 – Abbreviations

Claims

CLAIMS 1. A method for preparing a polyorganosiloxane release coating comprises: 1) applying, on a surface of a substrate, an ultra-violet radiation curable polyorganosiloxane release coating composition comprising (A) a photoacid generator comprising a silylated diaryliodonium cation and a fluorinated aryl borate anion, wherein the silylated diaryliodonium cation has formulaR4is an alkyl group of 1 to 12 carbon atoms, R5is a divalent hydrocarbyl group of 2 to 12 carbon atoms, R6is an alkyl group of 1 to 6 carbon atoms, R7is an alkyl group of 8 or more carbon atoms, R8is an alkyl group of 8 or more carbon atoms, and R9is an alkyl group of 8 or more carbon atoms; and the fluorinated aryl borate anion has R10, R11, R12, R13, and R14are each consisting of H, F, and CF3, with the(B) an epoxycyclohexyl-functional polydiorganosiloxane having a degree of polymerization ≤ 845 and having an epoxy content of 8.5 mol% to < 15 mol%, based on molar amount of the epoxycyclohexyl-functional polydiorganosiloxane; and2) irradiating the ultra-violet radiation curable polyorganosiloxane release coating composition with ultra-violet radiation, thereby curing the ultra-violet radiation curable polyorganosiloxane release coating composition to form the polyorganosiloxane release coating.

2. The method of claim 1, wherein the diaryliodonium cation has R6is methyl, each R10is methyl, each R11is octyl, and R12is octyl.

3. The method of claim 1 or claim 2, wherein the fluorinated aryl borate anion is selected from the group consisting of: -,]-,nd4]-.

4. The method of claim 3, wherein the fluorinated aryl borate anion is [B(C6H3(CF3)2)4]-.

5. The method of any one of claims 1 to 4, wherein (B) the epoxycyclohexyl-functional polydiorganosiloxane comprises unit formula: (R13SiO1 / 2)a(R12R2SiO1 / 2)b(R12SiO2 / 2)c(R1R2SiO2 / 2)d, wherein each R1is an independently selected monovalent hydrocarbyl group of 1 to 12 carbon atoms, each R2is an epoxycyclohexylalkyl- group, subscripts a, b, c, and d represent average numbers of each unit per molecule, and subscripts a, b, c, and d have values such that 0 ≤ a ≤ 2, 0 ≤ b ≤ 2, a quantity (a + b) = 2, c ≥ 0, d > 0, a quantity (b + d) ≥ 2, and a quantity 54 < (a + b + c + d) ≤ 233, and the values for a, b, c, and d are sufficient to give the epoxycyclohexyl-functional polydiorganosiloxane the epoxy content of 9 mol % to 11.9 mol %.

6. The method of claim 5, wherein each R1is alkyl, a = 2, b = 0, 60.5 ≤ c ≤ 169; and 7.5 ≤ d ≤ 23.

7. The method of any one of claims 1 to 6, wherein the epoxycyclohexyl-functional polydiorganosiloxane is selected from the group consisting of: (R13SiO1 / 2)2(R12SiO2 / 2)108(R1R2SiO2 / 2)10; (R13SiO1 / 2)2(R1 2SiO2 / 2)117(R1R2SiO2 / 2)11.8; (R11 3SiO1 / 2)2(R 2SiO2 / 2)169(R1R2SiO2 / 2)23; (R13SiO1 / 2)2(R1 2SiO2 / 2)60.5(R1R2SiO2 / 2)7.5; and a combination of two or more thereof; wherein each R1is methyl, and each R2is epoxycyclohexylethyl.

8. The method of any one of claims 1 to 7, wherein the composition comprises 0.1 weight % to 5 weight % of (A) the photoacid generator; and a balance to 100 weight % of (B) the epoxycyclohexyl-functional polydiorganosiloxane.

9. The method of any one of claims 1 to 8, wherein the composition further comprises an additional starting material selected from the group consisting of up to 1 weight % of (C) a photosensitizer, up to 10 weight % of (D) an alcohol, up to 25 weight % of (E) a reactive diluent, up to 12 weight % of (F) a filler, up to 40 weight % of (G) a release modifier, and a combination of two or more thereof; with the proviso that combined weights of the additional starting materials is > 0 weight % to 40 weight %, based on combined weights of all starting materials in the composition.

10. The method of any one of claims 1 to 9, wherein the ultra-violet radiation curable polyorganosiloxane release coating composition has a thickness of 0.3 µm to 5 µm after step 1).

11. The method of any one of claims 1 to 10, wherein step 2) comprises a condition selected from the group consisting of: (i) the ultra-violet radiation has a wavelength of 100 nanometers to 400 nanometers, (ii) step 2) is performed at a temperature < 100 °C, (iii) irradiating is performed for a time of 1 second to 1 minute, and(iv) a combination of two or more of conditions (i), (ii), and (iii).

12. The method of any one of claims 1 to 11, wherein the substrate comprises thermal paper.

13. A linerless label prepared by the method of any one of claims 1 to 12.

14. An ultra-violet radiation curable polyorganosiloxane release coating composition comprises: 0.1 weight % to 5 weight % of a photoacid generator comprising a silylated diaryliodonium cation and a fluorinated aryl borate anion, wherein the silylated diaryliodonium cation has formulaR4is an alkyl group of 1 to 12 carbon atoms, R5is a divalent hydrocarbyl group of 2 to 12 carbon atoms, R6is an alkyl group of 1 to 6 carbon atoms, R7is an alkyl group of 8 or more carbon atoms, R8is an alkyl group of 8 or more carbon atoms, and R9is an alkyl group of 8 or more carbon atoms; and the fluorinated aryl borate anion has R10, R11, R12, R13, and R14are each consisting of H, F, and CF3, with the0 to 1 weight % of a photosensitizer,0 to 10 weight % of an alcohol, 0 to 25 weight % of a reactive diluent, 0 to 12 weight % of a filler, 0 to > 40 weight % of a release modifier, and a balance to 100 weight % of an epoxycyclohexyl-functional polydiorganosiloxane having a degree of polymerization of 54 to 233 and having an epoxy content of 9 mol % to < 12 mol %, based on molar amount of the epoxycyclohexyl-functional polydiorganosiloxane; with the proviso that combined weights of the photosensitizer, the alcohol, the reactive diluent, the filler, and the release modifier total 0 weight % to 40 weight %, based on combined weights of all starting materials in the ultra-violet radiation curable polyorganosiloxane release coating composition.

15. The ultra-violet radiation curable polyorganosiloxane release coating composition claim 14, wherein ultra-violet radiation curable polyorganosiloxane release coating composition consists of: 0.1 weight % to 5 weight % of the photoacid generator; and a balance to 100 weight % of the epoxycyclohexyl-functional polydiorganosiloxane.

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