Stable hydrosilylation-curable resin-linear silicone hot-melt film

Abstract

An ultraviolet light-triggered hydrosilylation-curable composition contains: (a) a resin-linear polysiloxane containing on average at least 2 alkenyl groups per molecule and an average of less than 1.0 mole-percent SiOZ per moles of Si atoms; (b) a crosslinker containing an average of at least two SiH groups per molecule; (c) an ultraviolet light triggerable platinum catalyst; (d) greater than zero mass parts of platinum that is not part of the ultraviolet light triggerable platinum catalyst per million mass parts resin-linear polysiloxane; and (e) thiuram disulfide; where the concentration of crosslinker is sufficient to achieve a molar ratio of SiH to alkenyl groups from the resin-linear polysiloxane that is in a range of 0.25 to 2.0.

Description

[0001] STABLE HYDROSILYLATION-CURABLE RESIN-LINEAR SILICONE HOT-MELT FILM FIELD The present invention is in the field of curable hydrosilylation-curable silicone hot-melt films. INTRODUCTION Silicone hot-melt films (SHF) are particularly desirable materials for use as encapsulants in mini and micro light emitting diode (LED) applications. In such applications SHFs are positioned on a patterned substrate having three-dimensional surface contour and then warmed to induce flowing of the SHF to fill the surface contour while creating a flat surface. Unlike liquid injection compositions, SHFs can advantageously cover large areas at once without need for damming to prevent overflow and are easier to apply. Resin-linear polysiloxanes are particularly desirable for use in SHFs due to their thermoplastic-like behavior. A “resin-linear polysiloxane” refers to a block copolymer comprising one or more than one block of linear polysiloxane bound to one or more than one block of resinous polysiloxane. A “block” refers to a repeating section of multiple units of the same basic type. Preparation of resin-linear polysiloxanes typically involves coupling a SiOH group in a siloxane resin with an acetoxy group of an acetoxy-functional linear siloxane. The resulting resin-linear polysiloxane tends to have a large amount (typically greater than 10 mole-percent (mol%)) SiOH content relative to moles of resin-linear polysiloxane. That high of an SiOH content undesirably makes the resin-linear polysiloxane thermally unstable by facilitating post- curing reactions such as silanol condensation. Additionally, the SiOH containing resin-linear materials can experience warping after curing on flexible substrates. Therefore, it is desirable to minimize SiOH functionality in resin-linear polysiloxanes in SHF compositions. SUMMARY On one level, the present invention provides a solution to providing SHF compositions containing resin-linear polysiloxanes containing an average of less than one mol% SiOZ groups based on moles of silicon atoms (Si) in the resin-linear polysiloxanes, where SiOZ groups refer to a combination of SiOH and SiOR groups and where R corresponds to hydrocarbyl groups. In other words, the “Z” in SiOZ can be H or R. The invention is partly the result of using an alkenyl-functional resin-linear polysiloxane prepared by a hydrosilylation reaction between a resinous polysiloxane and a linear polysiloxane instead of coupling SiOH groups on the resin siloxane and acetoxy groups on the linear siloxane. US10167418B2 already describes examples of hydrosilylation-curable SHFs made with alkenyl functional resin-linear polysiloxanes prepared by hydrosilylation. The SHFs cure through a hydrosilylation reaction between the alkenyl-functional resin-linear polysiloxane and SiH functional crosslinker. However, the present invention is also a result of discovering undesirable stability problems with hydrosilylation-curable SHFs comprising alkenyl-functional resin-linear polysiloxanes and SiH functional crosslinkers when the resin-linear polysiloxanes are made by hydrosilylation. The present invention further provides a solution to those viscosity stability problems. Hydrosilylation reactions utilize a platinum catalyst that usually remains as a residual component of the resulting polymer. Combining alkenyl-functional resin-linear polysiloxanes made using hydrosilylation with crosslinkers containing SiH groups to form a SHF composition results in premature curing of the SHF due to the presence of the residual platinum catalyst from the previous hydrosilylation reaction (used to make the resin-linear polysiloxane). The premature curing causes the viscosity to undesirably increase, particularly at elevated temperatures, undesirably inhibiting the SHF from flowing and conforming to contoured surfaces of a substrate. The SHFs of US10167418 contain 2-phenyl-3-butyn-2-ol (PBO) inhibitor, which one might expect would help with viscosity stability, but as comparative examples herein illustrate, PBO does not help with key desirable viscosity properties. It is desirable to identify a SHF formulation that comprises a resin-linear polysiloxane with multiple alkenyl groups, platinum, and a SiH functional crosslinker that does not flow appreciably (does not flow to any visible extent over a period of 7 days) at 25 degrees Celsius (°C) but that flows readily so as to conform to contoured surfaces of a substrate at temperatures of 120 °C or higher. The SHF formulation can have a viscosity at 25 °C that is 50,000 Pascal*seconds (Pa*s) or more, preferably 100,000 Pa*s or more, 150,000 Pa*s or more, 200,000 Pa*s or more, 250,000 Pa*s or more, even 500,000 Pa*s or more. At the same time, it is desirable if the SHF formulation has a viscosity at 120 °C that is 5,000 Pascal*seconds (Pa*s) or less, and that can be 4,000 Pa*s or less, 3,000 Pa*s or less, 2,000 Pa*s or less even 1,000 Pa*s or less. At the same time, it is desirable for the SHF formulation to have a ratio of viscosity (in Pa*s) at 25 °C to viscosity (in Pa*s) at 120 °C that is 100 or more, 250 or more, 500 or more, even 700 or more so that the viscosity difference is large to maximize the difference between solid-like performance at 25°C and fluid like performance at 120 °C. Even more, it is desirably for the SHF to further be stable to exposing to 70 °C for 1 hour without curing to allow temperature ranges in storage and for drying if needed. It is further desirable for the composition to have a modulus at 25 °C that is greater than 0.01 MegaPascals (MPa), preferably greater than 0.10 MPa and a Tan(δ) value at 25 °C that is less than 5.0, preferably 2.5 or less, and that can be 1.0 or less. The present invention provides a SHF that achieves these desirable properties. Surprisingly, use of a thiuram disulfide as an inhibitor in the SHF allows the SHF to achieve all of these desirable properties. While US10167418B2 describes of examples SHFs made with resin-linear polysiloxanes made by hydrosilylation in combination with SiH functional crosslinker, platinum hydrosilylation catalyst and PBO inhibitor, there is no discussion on the properties targeted by the present invention, particularly the desirably viscosity ratio at 25 °C to 120 °C being 100 or more and stability from curing after 1 hour at 70 °C. Comparative examples herein reveal that the formulation that achieves these desirable properties with thiuram disulfide inhibitor do not achieve these desirable properties when using PBO inhibitor instead. In fact, comparative examples herein demonstrate the inability of common inhibitors such as 1- ethynyl-1-cyclohexanol (ETCH), PBO, and dioctyl maleate (DOM) to achieve the viscosity stability performance achieved by thiuram disulfide. In a first aspect, the present invention is an ultraviolet light-triggered hydrosilylation- curable composition comprising: (a) 85 to 99.5 parts by mass of resin-linear polysiloxane containing, on average, at least 2 alkenyl groups per molecule and, on average, less than 1.0 mole-percent SiOZ per molecule based on moles of Si atoms in the resin-linear polysiloxane; (b) 5 to 14.9 parts by mass of crosslinker containing, on average, at least two SiH groups per molecule;(c) 0.001 to 0.1 part by mass of ultraviolet light triggerable platinum catalyst; (d) greater than zero parts by mass of platinum that is not part of the ultraviolet light triggerable platinum catalyst per million mass parts resin-linear polysiloxane; and (e) thiuram disulfide at a molar concentration that is greater than the molar concentration of platinum that is not part of the ultraviolet light triggerable platinum catalyst in the ultraviolet light trigger hydrosilylation- curable composition; where parts by mass are relative to mass of ultraviolet light-triggered hydrosilylation-curable composition unless otherwise stated and wherein the concentration of crosslinker is sufficient to achieve a molar ratio of SiH to alkenyl groups from the resin-linear polysiloxane that is in a range of 0.25 to 2.0. In a second aspect, the present invention is a process for coating a substrate with a cured polysiloxane layer, the process comprising placing a film of the ultraviolet light-triggered hydrosilylation-curable composition of the first aspect onto a surface of a substrate at a temperature of 70 °C or lower, heating the film to a temperature of greater than 80 °C to cause the film to conform to the surface of the substrate while exposing the film to ultraviolet light to facilitate curing of the ultraviolet light-triggered hydrosilylation-curable composition. The present invention is useful as a silicone hot-melt formulation for use, as an example, as an encapsulant in LED applications. DETAILED DESCRIPTION “Multiple” means two or more. “And / or” means “and, or as an alternative”. All ranges include endpoints unless otherwise indicated. Identification of materials by trademark or tradename refers to materials having the composition as sold under that trademark or tradename at the priority date of this document. Polysiloxanes comprise multiple siloxane units linked together through siloxane bonds. Siloxane units can be characterized by the designation M, D, T or Q. There are two generally accepted usages of MDTQ nomenclature: GE method and an NMR method. Usage herein is in accordance with the following NMR method. Unless expressly stated otherwise: “M” correspond to R3SiO1 / 2siloxane units. “D” correspond to the combination of R2SiO2 / 2and R2(OZ)SiO1 / 2siloxane units. “T” corresponds to the combination of RSiO3 / 2, R(OZ)SiO2 / 2, and R(OZ)2SiO1 / 2siloxane units. “Q” corresponds to a combination of (OZ)3SiO1 / 2, (OZ)2SiO2 / 2, (OZ)SiO3 / 2, and SiO4 / 2siloxane units. “R” is independently in each occurrence selected from hydrocarbyl groups and can be an alkyl or aryl. Preferably, R is selected from a group consisting of C1-C8 alkyls (such as methyl, ethyl, propyl, methyl, butyl, pentyl, hexyl, heptyl and octyl) and C6-C20 aryls (including phenyl and benzyl). “OZ” is -OH or -OR, where R is as described above. Notably, an oxygen atom having a multiple of “1 / 2” subscript is an oxygen of a siloxane bond that is shared with a silicon atom of two siloxane units including the one of the subject siloxane unit. The numerator of the subscript indicates how many shared oxygen atoms are attached to the silicon atom. For example SiO3 / 2has three siloxane bonded oxygen atoms. The M, D and T notations can include a superscript indicating what R groups are bound to the silicon atom of the siloxane unit. If no superscript notation is used then it is assumed the R groups are all methyl groups. For instance, TArrefers to a T unit where the R group is an aryl group. When the aryl group of a TAris phenyl, the siloxane is TPh. DHand MHrefer to D siloxane units and M siloxane units, respectively, where one of the R groups bound to the silicon atom is a hydrogen. Similarly, DViand MVirefer to D siloxane units and M siloxane units, respectively, where one of the R groups bound to the silicon atom is a vinyl group. Chemical formula designations for polysiloxanes using M, D, T, Q nomenclature typically have subscripts associated with the siloxane unit designator that can either refer to the average mole ratio of that siloxane unit relative to all siloxane units in the molecule or the average number of the associate siloxane units in the molecule. When the subscript associated with a siloxane unit is greater than or equal to one, then the subscript refers to the average number of those siloxane units in the molecule. When the subscript associated with a siloxane unit is less than one then the subscript refers to the average mole ratio of that siloxane unit relative to the number of moles of all siloxane units in the molecule. An absence of a subscript implies a subscript value of one. Determine viscosity (herein, viscosity refers to complex viscosity), modulus and Tan(δ) values for SHF samples using a rotational rheometer (ARES-G2 from TA instrument) using parallel plates, samples having a thickness of 1 millimeter and a forced convection oven to measure dynamic shear as a function of temperature. Load the samples onto the parallel plates, equilibrate the samples to 20 °C for 5 minutes, ramp the temperature up to 120 °C at a rate of 3 °C per minute while measuring small-strain oscillatory rheology (frequency 1 Hz). In a first aspect the present invention is an ultraviolet (UV) light-triggered hydrosilylation-curable composition. The composition is stable to hydrosilylation curing until exposed to UV light. After exposure to UV light, the composition can undergo hydrosilylation. The hydrosilylation curing reaction typically occurs more rapidly the warmer the temperature of the composition, but tends to not undergo hydrosilylation at or below 70 °C to any meaningful extent unless exposed to UV light. The UV light releases a platinum catalyst that facilitates hydrosilylation. The UV light-triggered hydrosilylation-curable composition comprises: (a) a resin-linear polysiloxane; (b) crosslinker polysiloxane; (c) UV light-triggerable platinum catalyst; (d) platinum that is not part of the UV light-triggerable platinum catalyst; and (e) thiuram disulfide. (a) Resin-Linear Polysiloxane The resin-linear polysiloxane contains, on average, at least 2 alkenyl groups per molecule. The alkenyl groups are desirably terminally unsaturated, meaning that the alkenyl group resides between carbon atoms most remove from the polysiloxane backbone. The alkenyl groups are desirably alkenes, preferably terminally unsaturated alkenes. The alkenyl group typically has 2 or more, and can have 3 or more, 4 or more, 5 or more, even 6 or more carbon atoms while at the same time typically has 20 or fewer, and can have 18 or fewer, 16 or fewer, 14 or fewer, 12 or fewer, 10 or fewer, 8 or fewer, 6 or fewer, even 4 or fewer carbon atoms. Most typically, the alkenyl group is a vinyl group. The resin-linear polysiloxane contains, on average, less than 1.0 mole-percent (mol%) and can contain 0.8 mol% or less, 0.6 mol% or less, 0.4 mol% or less, 0.2 mol% or less, or even 0.0 mol% SiOZ per molecule where mol% is relative to silicon atoms (Si) in the resin-linear polysiloxane. Determine mol% OZ by Silicon-29 (29Si) nuclear magnetic resonance (NMR) spectroscopy using standard procedures. The resin-linear polysiloxane can be a MViTAr-D based polysiloxane block copolymer. An MViTAr-D based polysiloxane block copolymer is a form of resin-linear polysiloxane with a resinous block of MViTArgroups linked to a linear block of D siloxane units through an M group on the resinous block. The MViTAr-D based polysiloxane block copolymer is typically prepared using a hydrosilylation reaction between a resinous polysiloxane having MViTArgroups and a linear polysiloxane having terminal SiH groups, such as SiH terminal polydimethylsiloxane. The molar ratio of MVigroups on the resin to SiH group on the linear polysiloxane is greater than one such that there are excess MVigroups to ensure some remain as functional groups on the resulting resin-linear polysiloxane. For avoidance of doubt, the general name “MViTAr-D based polysiloxane block copolymer” implies that there are multiple TArsiloxane units with MVigroups bound thereto in the resinous blocks and multiple D siloxane units in each of the linear blocks. In the MViTAr-D based polysiloxane block copolymer for use in the present invention it is typical for there to be 75 mol% or more, 80 mol% or more, or even 85 mol% or more while at the same time 90 mol% or less TArgroups in the MViTArresinous block of the polysiloxane block copolymer. At the same time, it is typical to have an average of 50 or more, even 60 or more, 70 or more, 80 or more, 90 or more, 100 or more, 110 or more, 120 or more, 130 or more, even 140 or more while at the same time typically 150 or fewer, even 140 or fewer, 130 or fewer, 120 or fewer, 110 or fewer, 100 or fewer, 90 or fewer, 80 or fewer, 70 or fewer, or even 60 or fewer D siloxane units in the D linear block. There is also generally an M siloxane unit between the MViTArresinous block and the D linear block. Typically, the aryl (Ar) group on the T siloxane units are phenyl groups. The concentration of resin-linear polysiloxane in the UV light-triggered hydrosilylation- curable composition is typically 85 parts by mass or more and can be 90 parts by mass or more, even 93 parts by mass or more while at the same time is typically 99.5 parts by mass or less, and can be 99 parts by mass or less where parts by mass are relative to mass of UV light-triggered hydrosilylation-curable composition. (b) Crosslinker Polysiloxane The crosslinker polysiloxane is a polysiloxane that contains, on average, at least SiH groups per molecule. The crosslinker polysiloxane can be a siloxane resin. The crosslinker polysiloxane can be a siloxane resin having the molecular formula MHmTPh t, where: (a) subscript m is the molar ratio of MHunits in the resin and has a value in a range of 0.4 to 0.8, and can be 0.4 or more, 0.5 or more, 0.6 or more, even 0.7 or more while at the same time is typically 0.8 or less, and can be 0.7 or less, 0.6 or less, even 0.5 or less; and (b) and subscript t is the molar ratio of TPhunits in the resin and has a value in a range of 0.6 to 0.2, and can be 0.6 or less, 0.5 or less, 0.4 or less, even 0.3 or less, while at the same time is typically 0.2 or more, and can be 0.3 or more, 0.4 or more, even 0.5 or more. The concentration of crosslinker polysiloxane in the UV light-triggered hydrosilylation- curable composition is typically 0.5 parts by mass or more, and can be 0.75 parts by mass or more, even one part by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, even 5 parts by mass or more while at the same time is typically 14.9 parts by mass or less, and can be 10 parts by mass or less, even 7 parts by mass or less where parts by mass is relative to mass of UV light-triggered hydrosilylation-curable composition. Desirably, the concentration of crosslinker polysiloxane relative to the resin-linear polysiloxane is sufficient to achieve a molar ratio of silicon-hydride group to alkenyl group (SiH / Si(C=C)) from the resin-linear polysiloxane that is in a range of 0.5 to 2.0. For example, when the alkenyl group in the resin-linear polysiloxane is a vinyl group the SiH / Si(C=C) ratio corresponds to a SiH / SiVi ratio. The SiH / Si(C=C) molar ratio can be 0.25 or more, 0.50 or more, 0.75 or more, 1.0 or more, 1.25 or more, 1.50 or more, even 1.75 or more, while at the same time is typically 2.0 or less, and can be 1.75 or less, 1.50 or less, 1.25 or less, 1.0 or less, even 0.75 or less. Determine SiH / Si(C=C) ratio by proton nuclear magnetic resonance (1H NMR) spectroscopy. Prepare samples for analysis by combining a known amount of sample with a known amount of an internal standard (1,4-dioxane) in deuterated chloroform. Collect spectra using an Aligent 400- MR NMR instrument equipped with a 5 millimeter ONeNMR probe. Analyze data using MesReNova x64 software. Calculate weight percentages of alkenyl (C=C) and SiH groups by integrating the relevant proton resonances against those of the internal standard. (c) UV Light-Triggerable Platinum Catalyst The UV light-triggerable platinum catalyst is a platinum compound that does not appreciably facilitate hydrosilylation reaction, but that when exposed to UV light releases platinum in a form that does facilitate hydrosilylation reactions. Examples of UV light triggerable platinum catalyst include platinum (II) acetylacetonate, methylcyclopentadienyl- platinum (that is, (CpMe)Pt) complexes, and derivatives of cyclopentadienyl-platinum complexes such as CpPt, Cp(Et)Pt, (CpMe5)Pt where Cp refers to cyclopentadienyl, Et refers to ethyl, Me refer to methyl and Pt refer to platinum. The concentration of UV light-triggerable platinum catalyst in the UV light-triggered hydrosilylation-curable composition is typically sufficient to provide a concentration of platinum that exceeds [(concentration of thiuram disulfide) – (concentration of platinum that is not part of UV light-triggerable platinum catalyst)]. That concentration of platinum is “thiuram-free” platinum and is available to catalyze curing of the ultraviolet light-triggered hydrosilylation- curable composition. The concentration of thiuram-free platinum is in a range of one to 1000 parts by mass, and can be one or more, 5 or more 10 or more, 50 or more, 100 or more, 250 or more, 500 or more, even 750 or more mass parts while at the same time is typically 1000 mass parts or less, and can be 750 mass parts or less, 500 mass parts or less, 250 mass parts or less, 100 mass parts or less, 50 mass parts or less, or even 10 mass parts or less where mass parts of platinum are relative to million mass parts of UV light-triggered hydrosilylation-curable composition. (d) Platinum That Is Not Part of UV Light-Triggerable Platinum Catalyst The UV light triggered hydrosilylation-curable composition further comprises platinum that is not part of the UV light-triggerable platinum catalyst. This platinum component can prove to be problematic in the stability of the UV light-triggered hydrosilylation-curable composition because it can catalyst the hydrosilylation curing prematurely without UV light exposure. The platinum that is not part of the UV light-triggerable platinum catalyst is typically residual catalyst from synthesis of the resin-linear polysiloxane and enters the composition with the resin-linear polysiloxane. Platinum catalysts, such as Karstedt’s catalyst, are often used to accelerate hydrosilylation reactions, such as that commonly used to make the resin-linear polysiloxane. After the reaction is completed, the platinum remains in the product mixture but it is unclear in what form the platinum exists. Hence, remaining platinum from a hydrosilylation reaction is identified herein as “residual platinum catalyst from catalyzing a previous hydrosilylation reaction” or by a similar language. In the present invention, the platinum that is not UV light triggerable is typically residual platinum catalyst from catalyzing a previous hydrosilylation reaction used to prepare the resin-linear polysiloxane. The amount of platinum that is not part of the UV light-triggerable platinum catalyst can vary, but is greater than zero mass parts per million mass parts of resin-linear polysiloxane. Typically, the amount of platinum that is not part of the UV light-triggerable platinum catalyst is in a range of one to 100 mass parts per million mass parts of UV light-triggered hydrosilylation- curable composition. The amount of platinum that is not part of the UV light-triggerable platinum catalyst can be one mass part or more, 5 mass parts or more, 10 mass parts or more, 20 mass parts or more, 30 mass parts or more, 40 mass parts or more, 50 mass parts or more, 60 mass parts or more, 70 mass parts or more, 80 mass parts or more, even 90 mass parts or more while at the same time can be 100 mass parts or less, 90 mass parts or less, 80 mass parts or less, 70 mass parts or less, 60 mass parts or less, 50 mass parts or less, 40 mass parts or, 30 mass parts or less, 20 mass parts or, even 10 mass parts or less per million mass parts resin-linear polysiloxane. (e) Thiuram Disulfide Thiuram disulfide is a class of organosulfur compounds having the formula (R2NCSS)2and the general structure: S R RSN R where each R is a hydrocarbyl group. also referred to as tetrahydrocarbylthiuram disulfide. Examples of common suitable thiuram disulfides include tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetra(iso-butyl)thiuram disulfide, and tetra(n-butyl)thiuram disulfide. The thiuram disulfide surprisingly interacts with the platinum that is not part of the UV light triggerable platinum catalyst thereby inhibiting that platinum from facilitating hydrosilylation between the resin-linear polysiloxane and the crosslinker. This is particularly surprising because the platinum that is not part of the UV light triggerable platinum catalyst is residual platinum from catalyzing a hydrosilylation reaction and it is unclear just what form or state the platinum is in at that point. The molar concentration of thiuram disulfide greater than the molar concentration of platinum that is not part of the UV light triggerable platinum catalyst in the UV light-triggered hydrosilylation-curable composition in order to provide sufficient thiuram disulfide to combine with all of the platinum that is not part of the UV light triggerable platinum. At the same time, the concentration of thiuram disulfide that exceeds the concentration of platinum that is not part of the UV light triggerable platinum catalyst is less than the concentration of UV light triggerable platinum catalyst in order to ensure that there is UV light triggerable platinum catalyst uninhibited by the thiuram disulfide. Preferably, the amount of thiuram disulfide is 1.1 times or more, and can be 1.2 times or more, 1.3 times or more, 1.4 times or more, 1.5 times or more, even 2.0 times or more, while at the same time is typically 20 times or less, and can be 15 times or less, 10 times or less, even 5 times or less the molar concentration of platinum that is not part of the UV light triggerable platinum catalyst in the UV light-triggered hydrosilylation-curable composition. The molar concentration of thiuram disulfide is less than the molar concentration of platinum from the combination of UV light triggerable platinum catalyst and platinum that is not part of the UV light triggerable platinum catalyst so the thiuram disulfide does not complex with all of the UV light triggerable platinum catalyst. Optional Components The UV light-triggered hydrosilylation-curable composition can further comprise or be free of any one or any combination of more than one additional optional component. Examples of suitable optional components include stabilizers, additional platinum inhibitors, and adhesion promoters. The UV light-triggered hydrosilylation-curable composition of the present invention does not flow appreciably at 25 °C, but flows readily so as to conform to contoured surfaces of a substrate at temperatures of 120 °C or higher. The UV light-triggered hydrosilylation-curable composition of the present invention has a viscosity at 25 °C that is 50,000 Pa*s or more at 25 °C and at the same time 5,000 Pa*s or less at 120 °C. The ratio of viscosity (in Pa*s) at 25 °C to viscosity (in Pa*s) at 120 °C is 100 or more. The UV light-triggered hydrosilylation-curable composition of the present invention is stable to exposure to 70 °C for one hour without curing, has a modulus greater than 0.01 MPa at 25 °C and a Tan(δ) value at 25 °C that is less than 5.0. The UV light-triggered hydrosilylation-curable composition of the present invention can take the form of a film at 25 °C for easy placement over a substrate. A process for coating a substrate with the UV light-triggered hydrosilylation-curable composition of the present invention can comprise placing a film of the UV light-triggered hydrosilylation-curable composition onto the surface of a substrate at a temperature of 70 °C or lower, then heating the film to a temperature of greater than 80 °C to cause the film to conform to the surface of the substrate. At the same time as the film conforms to the surface of the substrate expose the film to UV light to facilitate curing of the UV light-triggered hydrosilylation-curable composition. The UV light-triggered hydrosilylation-curable composition cures to a coating over the surface of the substrate that has conformed to the contour(s) of the substrate surface. EXAMPLES Table 1 lists the components for use in the following examples. “Vi” refers to vinyl. “Ph” refers to phenyl. “Me” refers to methyl. Table 1 Component Description Source Resin 1 MVi0.18TPh0.82Synthesize according to teaching in n n n Preparation of Crosslinker 2 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask 330.0 grams (g) phenyltrimethoxylsilane (available from Gelest) and 693 milligrams (mg) trifluoromethanesulfonic acid (available from Sigma-Aldrich). Add 75 g acetic acid (from Fisher Scientific) using an additional funnel over 5 min at 50 °C. After addition, heat the reaction mixture for 30 min. Insert a Dean Stark apparatus and remove volatile by-products we by heating at 85 °C. Cool the flask to 25 °C and then add 202 g tetramethyldisiloxane (available from Gelest). Heat the reaction mixture to 40 °C and then add 150 g acetic acid (from Fisher Scientific)) using an addition funnel over 30 min. After addition is complete, heat the reaction mixture at 50°C for 30 min. Then, slowly add 128 g acetic anhydride (from Fisher Scientific) over 50 min using an addition funnel. After addition, stir the mixture for 2 hrs at 50 °C and then cool to 25 °C. Add 20 milliliters of deionized water and 100 ml of toluene, resulting in the formation of two layers. Remove the bottom layer. Add another 100 ml of toluene and the wash the product mixture with 60 milliliters of deionized water six times. Remove volatiles under reduced pressure (8 kiloPascals, 60 mm Hg) and filter through a 0.45micrometer filter. The resulting clear, low viscosity liquid is Crosslinker 2. Preparation of Resin-Linear Polysiloxane 1 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask Resin 1 (182.98 grams (g) as a solution in toluene, corresponding to 100 g solids), SiH- Terminated PDMS 2 (100.0 g) and toluene solvent (217.02 g). Heat the contents of the 1-L round bottom flask to 90 °C and add Karstedt’s catalyst (enough to provide 5 weight-parts per million platinum weight parts of combined resin and PDMS). Then, heat the contents of the 1-L round bottom flask to 110 °C for 2 hours, then cool to 100 °C. Add Crosslinker 1 (12.18 g) and heat to 110 °C for 20 hours. Filter the resulting mixture through a 142 millimeter (mm) diameter Magna filter (5 micrometers filter). Remove a portion of the toluene by roto-evaporation to obtain a translucent solution (RL Solution 1) having a non-volatile content of 69.72 weight- percent. The resulting Resin-Linear Polysiloxane 1 contains less than 0.2 mol% SiOZ by29Si NMR. Preparation of Resin-Linear Polysiloxane 2 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask Resin 1 (165 grams (g) as a solution in toluene, corresponding to 90 g solids), SiH- Terminated PDMS 2 (110.0 g) and toluene solvent (225 g). Heat the contents of the 1-L round bottom flask to 90 °C and add Karstedt’s catalyst (5 weight-parts platinum per million weight parts of combined weight of Resin and PDMS). Then, heat the contents of the 1-L round bottom flask to 110 °C for 2 hours, then cool to 100 °C. Add Crosslinker 1 (9.8 g) and heat to 110 °C for 20 hours. Filter the resulting mixture through a 142 millimeter (mm) diameter Magna filter (5 micrometers filter). Remove a portion of the toluene by roto-evaporation to obtain a translucent solution (RL Solution 2) having a non-volatile content of 73.41 weight-percent. The resulting Resin-Linear Polysiloxane 2 contains less than 0.2 mol% SiOZ by29Si NMR. Preparation of Resin-Linear Polysiloxane 2 with Inherent Inhibitor 1 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask Resin 1 (165 grams (g) as a toluene solution, corresponding to 90 g solids), SiH- Terminated PDMS 2 (110.0 g) and toluene solvent (225 g). Heat the contents of the 1-L round bottom flask to 90 °C and add Karstedt’s catalyst (5 weight-parts platinum per million weight parts of combined weight of Resin and PDMS). Then, heat the contents of the 1-L round bottom flask to 110 °C for 2 hours, then cool to 100 °C. Add Crosslinker 1 (9.8 g) and heat to 110 °C for 20 hours. Add 1.5 milligrams of Inhibitor 1 and stir overnight at 23-25 °C. Filter the resulting mixture through a 142 millimeter (mm) diameter Magna filter (5 micrometers filter). Remove a portion of the toluene by roto-evaporation to obtain a translucent solution (RL Solution 2 containing Inhibitor 1) having a non-volatile content of 73.48 weight-percent. The Resin-Linear Polysiloxane 2 contains less than 0.2 mol% SiOZ by29Si NMR. Preparation of Resin-Linear Polysiloxane 3 with Inherent Inhibitor 1 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask Resin 1 (165 grams (g) solution in toluene, corresponding to 90 g solids), SiH-Terminated PDMS 3 (100.0 g) and toluene solvent (225 g). Heat the contents of the 1-L round bottom flask to 90 °C and add Karstedt’s catalyst (5 weight-parts platinum per million weight parts combined weight of Resin and PDMS). Then, heat the contents of the 1-L round bottom flask to 110 °C for 2 hours, then cool to 100 °C. Add Crosslinker 1 (7.3 g) and heat to 110 °C for 20 hours. Add 1.5 milligrams of Inhibitor 1 and stir overnight at 23-25 °C. Filter the resulting mixture through a 142 millimeter (mm) diameter Magna filter (5 micrometers filter). Remove a portion of the toluene by roto-evaporation to obtain a translucent solution (RL Solution 3 containing Inhibitor 1) having a non-volatile content of 76.00 weight-percent. The Resin-Linear Polysiloxane 3 contains less than 0.2 mol% SiOZ by29Si NMR. Preparation of Resin-Linear Polysiloxane 4 Equip a one-liter (1-L) four-neck round bottom flask with a thermocouple, polytetrafluoroethylene stir paddle, and a water-cooled condenser. Add to the 1-L round bottom flask Resin 1 (184 grams (g) solution in toluene, corresponding to 100 g solids), SiH-Terminated PDMS 1 (100.0 g) and toluene solvent (216 g). Heat the contents of the 1-L round bottom flask to 90 °C and add Karstedt’s catalyst (5 weight-parts platinum per million weight parts combined weight of Resin and PDMS). Then, heat the contents of the 1-L round bottom flask to 110 °C for 2 hours, then cool to 100 °C. Add Crosslinker 1 (6.8 g) and heat to 110 °C for 20 hours. Filter the resulting mixture through a 142 millimeter (mm) diameter Magna filter (5 micrometers filter). Remove a portion of the toluene by roto-evaporation to obtain a translucent solution (RL Solution 4) having a non-volatile content of 77.45 weight-percent. Resin-Linear Polysiloxane 4 contains 0.32 mol% SiOZ by29Si NMR. UV-Triggered Hydrosilylation-Curable Silicone Hot-Melt Films Prepare samples of UV-triggered hydrosilylation-curable silicone hot-melt films using the procedures below. The UV-triggered hydrosilylation-curable silicone hot-melt films compositions are summarized in Table 2 along with their composition characteristics and measured properties. Example 1: Resin-Linear Polysiloxane 1 with Inhibitor 1 Add 40 g of RL Solution 1 and 0.21 milligrams of Inhibitor 1 (1.2 molar equivalents relative to Pt in RL Solution 1) to a 60 milliliter (mL) dental cup. Mix five times at 3000 revolutions per minute for 30 seconds. Filter the solution through a 1.2 micrometer filter to obtain Inhibitor 1-treated Resin-Linear Polysiloxane 1. Combine in a dental cup 98.3 weight-parts (solids) of Inhibitor 1-treated Resin-Linear Polysiloxane 1, 1.7 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 1. Example 2: Resin-Linear Polysiloxane 2 with Inherent Inhibitor 1 Combine in a dental cup 97.8 weight-parts (solids) of RL Solution 2 containing Inhibitor 1, 2.2 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 2. Example 3: Resin-Linear Polysiloxane 2 with Inherent Inhibitor 1 and 0.5X Crosslinker (relative to Example 2) Combine in a dental cup 98.9 weight-parts (solids) of RL Solution 2 containing Inhibitor 1, 1.1 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 3. Example 4: Resin-Linear Polysiloxane 3 with Inherent Inhibitor 1 Combine in a dental cup 95.4 weight-parts (solids) of RL Solution 3 containing Inhibitor 1, 4.6 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 4. Example 5: Resin-Linear Polysiloxane 4 with Inhibitor 2 Add 35 g of RL Solution 4 in a 60 mL dental cup and 0.25 milligrams of Inhibitor 2 (1.2 molar equivalents relative to Pt in RL Solution 4) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 2 treated Resin-Linear Polysiloxane 4 solution. Combine in a dental cup 98.9 weight-parts (solids) of Inhibitor 2-treated Resin-Linear Polysiloxane 4 solution, 2.4 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 5. Example 6: Resin-Linear Polysiloxane 4 with Inhibitor 3 Add 30 g of RL Solution 4 in a 60 mL dental cup and 0.29 milligrams of Inhibitor 3 (1.2 molar equivalents relative to Pt in RL Solution 4) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 3 treated Resin-Linear Polysiloxane 4 solution. Combine in a dental cup 97.6 weight-parts (solids) Inhibitor 3-treated Resin-Linear Polysiloxane 4 solution, 2.4 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Example 6. Comparative Example A: Resin-Linear Polysiloxane 1 with No Inhibitor Combine in a dental cup 96.3 weight-parts (solids) RL Solution 1, 1.7 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example A. Comparative Example B: Resin-Linear Polysiloxane 1 with Inhibitor 4 Add 40 g of RL Solution 1 in a 60 mm dental cup and 0.13 milligrams of Inhibitor 4 (1.2 molar equivalents relative to Pt in RL Solution 1) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 4 treated Resin-Linear Polysiloxane 1 Solution. Combine in a dental cup 98.3 weight-parts (solids) Inhibitor 4-treated Resin-Linear Polysiloxane 1 Solution, 1.7 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example B. Comparative Example C: Resin-Linear Polysiloxane 1 with Inhibitor 4 (higher concentration) Add 40 g of RL Solution 1 in a 60 mL dental cup and 0.39 milligrams of Inhibitor 4 (5.0 molar equivalents relative to Pt in RL Solution 1) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 4 treated Resin-Linear Polysiloxane 1 HC Solution. Combine in a dental cup 98.3 weight-parts (solids) Inhibitor 4-treated Resin-Linear Polysiloxane 1 HC Solution, 1.7 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example C. Comparative Example D: Resin-Linear Polysiloxane 2 with No Inhibitor Combine in a dental cup 97.9 weight-parts (solids) RL Solution 2, 2.1 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example D. Comparative Example E: Resin-Linear Polysiloxane 4 with Inhibitor 5 Add 35 g of RL Solution 4 in a 60 mm dental cup and 0.125 milligrams of Inhibitor 5 (1.2 molar equivalents relative to Pt in RL Solution 4) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 5 treated Resin-Linear Polysiloxane 4 Solution. Combine in a dental cup 97.6 weight-parts (solids) Inhibitor 5-treated Resin-Linear Polysiloxane 4 Solution, 2.4 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example E. Comparative Example F: Resin-Linear Polysiloxane 4 with Inhibitor 6 Add 30 g of RL Solution 4 in a 60 mL dental cup and 0.22 milligrams of Inhibitor 6 (1.2 molar equivalents relative to Pt in RL Solution 4) together. Mix the components five times at 3000 revolutions per minute for 30 seconds to prepare Inhibitor 6 treated Resin-Linear Polysiloxane 4 Solution. Combine in a dental cup 96.73 weight-parts (solids) Inhibitor 6-treated Resin-Linear Polysiloxane 4 Solution, 2.4 weight-parts Crosslinker 2, 10 weight-parts UV-Triggered Pt Catalyst 1 per million weight-parts final composition and 200 weight parts Inhibitor 7 per million weight-parts final composition. Mix three times at 3000 revolutions per minute for 30 seconds. Coat the resulting formulation onto an ethylene tetrafluoroethylene (ETFE) film to obtain a 200 micrometer thick film of composition and dry at 70 °C for one hour. The resulting dry film of composition is Comparative Example F. Sample Characterization 25°C Flowability A sample is considered not to be “flowable” if it appears as a hard solid. Formally, flowability correlates to softening temperature, which can be measured using a Ring-and-Ball method according to Japanese Industrial Standard (JIS) test method K6863 (1994) entitled “Testing Methods for the Softening Point of Hot Melt Adhesives”. A material is considered to be flowable above its softening point and non-flowable at and below its softening point. Therefore, materials with a softening point of less than 25 °C are considered flowable at 25 °C, while materials having a softening point of 25 °C or higher are not considered flowable at 25 °C. Viscosity, Storage Modulus and Tan(δ) Measure viscosity, storage modulus and Tan(d) on films of the samples prior to UV triggered curing of the samples. Determine viscosity (herein, viscosity refers to complex viscosity), modulus and Tan(δ) values for samples using a rotational rheometer (ARES-G2 from TA instrument) using parallel plates, samples having a thickness of 1 millimeter and a forced convection oven to measure dynamic shear as a function of temperature. Load the samples onto the parallel plates, equilibrate the samples to 20 °C for 5 minutes, ramp the temperature up to 120 °C at a rate of 3 °C per minute while measuring small-strain oscillatory rheology (frequency 1 Hz). Solubility in Toluene / Gel Percentage Take a sample of a film (approximately 1.0 g) and measure its mass (“original mass”), and place it into a 40 milliliter dental cup. Add 25.0 g of toluene and shake for one hour. Decant off the toluene solution from the dental cup and transfer undissolved sample to an aluminum pan. Dry the sample in the aluminum pan at 120 °C for one hour. weigh the dried sample to get the mass of undissolved gel. Gel percentage (Gel%) = 100% x (mass of undissolved gel) / (original mass). If a sample has no measured gel (Gel% is zero) then the sample is deemed soluble in toluene. If the sample has a measurable gel (Gel% is greater than zero) then the sample is not deemed soluble in toluene. 70 °C for 1 Hour Curing Determine whether a sample cured during the film drying step of the sample film, which occurs at 70 °C for one hour. Curing is determined by measuring gel%. A sample is considered “cured” if the Gel% exceeds zero percent. In other words, if the sample is soluble in toluene then the sample did not cure, but if there is a measurable Gel% for the sample in toluene then the sample is considered to have cured. UV-triggered Curing Irradiate sample films by placing the films in a VU chamber and then exposing them to UV radiation at 365 nanometer wavelengths (total dosage 4 Joules per square centimeter with 667 milliWatt exposure for 6 seconds) using a UVitron SkyRay with Raven device. Then cure the sample in an oven at 120 °C for two hours.

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Claims

CLAIMS:

1. An ultraviolet light-triggered hydrosilylation-curable composition comprising: (a) 85 to 99.5 parts by mass of resin-linear polysiloxane containing, on average, at least 2 alkenyl groups per molecule and, on average, less than 1.0 mole-percent SiOZ per molecule based on moles of Si atoms in the resin-linear polysiloxane; (b) 0.5 to 14.9 parts by mass of crosslinker containing, on average, at least two SiH groups per molecule; (c) ultraviolet light triggerable platinum catalyst at a concentration sufficient to provide thiuram-free platinum at a concentration in a range of one to 1000 mass parts per million mass parts of ultraviolet light-triggered hydrosilylation-curable composition, where thiuram-free platinum is the amount of platinum provided by the ultraviolet light triggerable platinum catalyst that exceeds [(concentration of thiuram disulfide)-(concentration of platinum that is not part of the ultraviolet light triggerable platinum catalyst)]; (d) greater than zero parts by mass of platinum that is not part of the ultraviolet light triggerable platinum catalyst per million mass parts resin-linear polysiloxane; and (e) thiuram disulfide at a molar concentration that is greater than the molar concentration of platinum that is not part of the ultraviolet light triggerable platinum catalyst in the ultraviolet light trigger hydrosilylation-curable composition; where parts by mass are relative to mass of ultraviolet light-triggered hydrosilylation- curable composition unless otherwise stated and wherein the concentration of crosslinker is sufficient to achieve a molar ratio of SiH to alkenyl groups from the resin-linear polysiloxane that is in a range of 0.25 to 2.

0.

2. The ultraviolet light-triggered hydrosilylation-curable composition of claim 1, wherein the platinum (d) that is not part of the ultraviolet light triggerable platinum is residual platinum catalyst from catalyzing a previous hydrosilylation reaction.

3. The ultraviolet light-triggered hydrosilylation-curable composition of any one previous claim, wherein the resin-linear polysiloxane is a MViTAr-D based polysiloxane block copolymer where the D blocks have an average of 50 to 150 D siloxane units, the resin block has 75 to 90 mole-percent TArsiloxane units relative to the combination of MViTArsiloxane units, and there is an M siloxane unit between TArMViand D siloxane blocks.

4. The ultraviolet light-triggered hydrosilylation-curable composition of claim 3, wherein the aryl group in the T siloxane unit is a phenyl group.

5. The ultraviolet light-triggered hydrosilylation-curable composition of any one previous claim, wherein the thiuram disulfide is any one or any combination of more than one component selected from a group consisting of tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetra(iso-butyl)thiuram disulfide, and tetra(n-butyl)thiuram disulfide.

6. The ultraviolet light-triggered hydrosilylation-curable composition of any one previous claim, wherein the crosslinker polysiloxane is a siloxane resin.

7. The ultraviolet light-triggered hydrosilylation-curable composition of claim 6, wherein the crosslinker polysiloxane has the molecular formula: MHmTPh t, where subscript m is the molar ratio of MHunits in the resin and has a value in a range of 0.4 to 0.8 and subscript t is the molar ratio of TPhunits in the resin and has a value in a range of 0.6 to 0.

2.

8. The ultraviolet light-triggered hydrosilylation-curable composition of any one previous claim, wherein the ultraviolet light-triggered hydrosilylation-curable composition further comprises at least one of a stabilizer, additional Pt inhibitor, and adhesion promoter.

9. The ultraviolet light-triggered hydrosilylation-curable composition of any one previous claim, wherein the ultraviolet light-triggered hydrosilylation-curable composition is in the form of a film.

10. A process for coating a substrate with a cured polysiloxane layer, the process comprising placing a film of the ultraviolet light-triggered hydrosilylation-curable composition of claim 9 onto a surface of a substrate at a temperature of 70 °C or lower, heating the film to a temperature of greater than 80 °C to cause the film to conform to the surface of the substrate while exposing the film to ultraviolet light to facilitate curing of the ultraviolet light-triggered hydrosilylation-curable composition.

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