Two-part addition cure thermal control coating

Abstract

A thermal control coating is shown and described herein. The thermal control coating is provided by a two-part, addition cure silicone composition. The composition includes a curable siloxane and titanium dioxide. The composition is a fast curing composition that, when cured, exhibits low solar absorptance, high solar reflectance, and / or high infrared emissivity. Additionally, the composition, when cured exhibits good flexibility and can be applied to surfaces without the aid of a primer.

Description

TWO-PART ADDITION CURE THERMAL CONTROL COATINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of U.S. Provisional Application No. 63 / 448,691, titled “TWO-PART ADDITION CURE THERMAL CONTROL COATING,” filed on February 28, 2023, the disclosure of which is incorporated herein by reference in its entirety.FIELD OF INVENTION

[0002] The present invention relates to an addition cure siloxane coating. In particular, the present invention relates to an addition cure siloxane coating that exhibits low absorptivity, high infrared emissivity, as well as relatively quick curing. The coatings may find use in a variety of applications including those where low solar absorptivity and high infrared emissivity are desired.BACKGROUND

[0003] Thermal management systems provide a way to maintain thermal properties such as temperature, temperature fluctuations, and humidity. Thermal management can occur by active or passive means. Active temperature control may involve machinery or electrical devices, such as electrical heaters and / or coolers. Passive temperature controls are techniques that do not involve machinery or electrical devices, but include thermal control coatings or structural designs. Aircraft and aeronautical vehicles, for example, may include components that generate a large amount of heat that must be dissipated by thermal radiation through their external surfaces. In addition, the radiating surfaces are subjected to thermal radiation from incident sunlight, which degrades the thermal efficiency of the surface. At higher altitudes where the atmosphere is low or even outside the earth’s atmosphere, there is little or no atmosphere to conduct heat to or from the components of the vehicle. In operation, one side ofan article may be directly exposed to the sun, while another side faces away from the sun. Thus, there becomes the possibility of extreme temperature differences for different parts of the vehicles as well as the possibility of extreme temperature changes as the vehicle changes position relative to the sun and parts of the vehicle become directly heated by the sun. Radiation may be accomplished through the use of thermal control surfaces which can absorb solar radiation and emit radiation. These surfaces have a range of desirable values for solar absorptivity (a) and infrared emissivity (e). For surfaces such as radiators, it is important to absorb as little solar radiation as possible (low a) while radiating as much heat as possible (high e).SUMMARY

[0004] The following presents a summary of this disclosure to provide a basic understanding of some aspects of the invention. This summary is intended to neither identify key or critical elements nor define any limitations of embodiments or claims. Furthermore, this summary may provide a simplified overview of some aspects that may be described in greater detail in other portions of this disclosure.

[0005] Provided is a siloxane composition that is suitable for use as a thermal control coating. The composition exhibits one or more of low solar absorptivity, high infrared emissivity, and / or high solar reflectance. The composition is, in one aspect, an addition curable siloxane. In embodiments, the composition is provided as a two-part composition.

[0006] In one aspect, provided is a curable coating composition comprising: an alkenyl functional siloxane; a hydride functional siloxane; titanium dioxide particles; an addition cure catalyst; and optionally an adhesion promoter.

[0007] In one embodiment, the titanium dioxide is present in an amount of from about 20 wt.% to about 50 wt.% based on the total weight of the composition.

[0008] In one embodiment in accordance with any of the previous embodiments, the titanium dioxide particles have a particle size of from about 1 nm to about 500 nm.

[0009] In one embodiment in accordance with any of the previous embodiments, the titanium dioxide particles are selected from rutile titanium dioxide, anatase titanium dioxide, or a mixture thereof.

[0010] In one embodiment in accordance with any of the previous embodiments, the titanium dioxide particles comprise fumed anatase / rutile titanium dioxide.

[0011] In one embodiment in accordance with any of the previous embodiments, the alkenyl functional siloxane is present in an amount of from about 40 vrt.% to about 80 wt.% based on the total weight of the composition.

[0012] In one embodiment in accordance with any of the previous embodiments, the alkenyl functional siloxane is selected from a compound of the formula: M'a M^ D^D^ T^ T^Q g (I) wherein:M1= RiR^SiO 1 / 2M2= R4R5R6SiOi / 2D1= R7R8SiO2 / 2D2= R9R10SIO2 / 2T^ RHSIOMT2= R12SIO3 / 2Q = S1O4 / 2 where R1, R2, R3, R7, R8, and R11are independently chosen from a C1-C30 hydrocarbon, a C6- C30 aromatic group, or C1-C30 alkoxy group;R4, R5R6, R9, R10, and R12are independently chosen from a C1-C30 hydrocarbon, a C6-C30 aromatic group, C1-C30 alkoxy group, and a C2-C30 alkenyl group, with the proviso that one or more of the R4, R5, R6, R9, and / or R12groups are selected from a C2-C30 alkenyl group; the subscripts a, b, c, d, e, f, g, are zero or positive subject to the following limitations: 2 < a+b+c+d+e+f+g < 2000, and b+d+f > 0.

[0013] In one embodiment, the alkenyl functional siloxane is selected from an alkenyl functional siloxane of the formula M2D1CM2, the formula MJaD2dQg, or a combination thereof.

[0014] In one embodiment, the alkenyl functional siloxane comprises a first alkenyl functional siloxane having the formula M2D1CM2; and a second alkenyl functional siloxane having the formula M1aD2dQg. In one embodiment, the first alkenyl functional siloxane comprises is present in an amount of from about 50 wt. % to about 80 wt. %, and the second alkenyl functional siloxane is present in an amount of from about 20 wt. % to about 50 wt. % based on the total weight of the alkenyl functional siloxane.

[0015] In one embodiment in accordance with any of the previous embodiments, the composition comprises fumed silica. In one embodiment, the fumed silica is present in an amount of from about 0.1 wt.% to about 10 wt.% based on the total weight of the composition.

[0016] In one embodiment in accordance with any of the previous embodiments, wherein the catalyst is a platinum based catalyst.

[0017] In one embodiment in accordance with any of the previous embodiments, the adhesion promoter is selected from a cyclosiloxanes comprising Si-H functional groups.

[0018] In one embodiment in accordance with any of the previous embodiments, the adhesion promoter is present in an amount of from about 0 to about 30 wt.% based on the total weight of the composition.

[0019] In one embodiment in accordance with any of the previous embodiments, the composition is provided as a two-part composition comprising: a first part comprising the alkenyl functional siloxane; titanium dioxide, and the catalyst; and a second part comprising the alkenyl functional siloxane, the hydride functional siloxane, titanium dioxide, and the optional adhesion promoter.

[0020] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (cts) of 0.35 or less.

[0021] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (cts) about 0. 1 to 0.35

[0022] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a infrared emissivity (e) of 0.89 or greater.

[0023] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (cts) of 0.89 to about 0.98.

[0024] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has solar reflectance (ps) of 0.65 or greater.

[0025] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (cts) of from about 0.65 to about 0.9.

[0026] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (cQ.

[0027] In one embodiment in accordance with any of the previous embodiments, a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm an elongation of from about 100% to about 195%.

[0028] In another aspect, provided is a method of forming a coating on a substrate comprising curing the composition of any of the previous embodiments.

[0029] In one embodiment, the composition is a two-part composition comprising (i) a first part comprising the alkenyl functional siloxane; titanium dioxide, and the catalyst; and (ii) a second part comprising the alkenyl functional siloxane, the hydride functional siloxane, titanium dioxide, and the optional adhesion promoter, and the method comprises combining the first part and the second part, heating at a temperature of from about 80 °C to about 150 °C.

[0030] In one embodiment in accordance with any of the previous embodiments, curing is accomplished in about 1 hour.

[0031] In still another aspect, provided is a substrate comprising a surface coated with the composition of any of the previous embodiments.

[0032] In one embodiment, the composition is cured to form a coating.

[0033] The following description and the drawings disclose various illustrative aspects. Some improvements and novel aspects may be expressly identified, while others may be apparent from the description and drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings illustrate various systems, apparatuses, devices and related methods, in which like reference characters refer to like parts throughout, and in which:

[0035] FIG 1 is a graph showing the total reflectance spectra of films in the examples; and

[0036] FIG 2 is a graph showing the total reflectance spectra of the film produced by formulation 9.DETAILED DESCRIPTION

[0037] Reference will now be made to exemplary embodiments, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made. Moreover, features of the various embodiments may be combined or altered. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments. In this disclosure, numerous specific details provide a thorough understanding of the subject disclosure. It should be understood that aspects of this disclosure may be practiced with other embodiments not necessarily including all aspects described herein, etc.

[0038] As used herein, the words "example" and “exemplary” means an instance, or illustration. The words “example” or “exemplary” do not indicate a key or preferred aspect or embodiment. The word “or” is intended to be inclusive rather than exclusive, unless context suggests otherwise. As an example, the phrase “A employs B or C,” includes any inclusive permutation (e.g., A employs B; A employs C; or A employs both B and C). As another matter, the articles “a” and “an” are generally intended to mean “one or more” unless context suggest otherwise.

[0039] Viscosity, unless noted otherwise, can be evaluated, for example, using a Brookfield HATDV-II, spindle 2 at 50 rpm.

[0040] Provided is an addition cure siloxane composition. The composition may generally be provided as a two-part composition. The present compositions provide a material that, when cured, exhibits excellent properties suitable for a wide range of applications. The materials are particularly suitable for applications where the material will be exposed to extreme changes in temperature as well as prolonged exposure to solar light and radiation. The material formed from the compositions may exhibit, for example, one or more of low solar absorptivity, high infrared emissivity, high solar reflectance, and the like.

[0041] The composition comprises: (i) an alkenyl functional polysiloxane; (ii) a hydnde functional siloxane; (iii) a silicone hydride adhesion promoter; (iv) a titanium dioxide filler; and (v) an addition cure catalyst. The composition may be provided as a two-part composition, as is discussed in further detail herein.

[0042] Alkenyl functional polysiloxane

[0043] The composition includes an alkenyl functional siloxane. The alkenyl functional siloxane includes an alkenyl functional group, comprising a C=C bond, attached to a silicone atom of the siloxane.

[0044] In one embodiment, the composition includes an alkenyl functional silicone compound of the formula:wherein:M1= RiR^SiOi^M2= R4R5R6SiOi / 2D1= R7R8SIO2 / 2D2= R9R10SIO2 / 2T1= R11SiO3 / 2T2= R12SIO3 / 2Q = S1O4 / 2 where R1, R2, R3, R7, R8, and R11are independently chosen from a C1-C30 hydrocarbon, a C6-C30 aromatic group, or C1-C30 alkoxy group;R4, R5’ R6, R9, R10, and R12are independently chosen from a C1-C30 hydrocarbon, a C6- C30 aromatic group, C1-C30 alkoxy group, and a C2-C30 alkenyl group, with the proviso that one or more of the R4, R5, R6, R9, and / or R12groups are selected from a C2-C30 alkenyl group; the subscripts a, b, c, d, e, f, g, are zero or positive subject to the following limitations: 2 < a+b+c+d+e+f+g < 2000, and b+d+f > 0.

[0045] In embodiments, one or more of the R4, R5, R6, R9, and / or R12is selected from a C2-C30 alkenyl group, a C4-C20 alkenyl group, a C6-C15 alkenyl group, or a C8-C10 alkenyl group. In embodiments, the alkenyl group is a selected from a C2-C8 alkenyl group, a C3-C6 alkenyl group, or a C4-C6 alkenyl group. In one embodiment, the alkenyl group is selected from a C2 or a C3 alkenyl group.

[0046] Rx-R12can be independently selected from a C1-C30 hydrocarbon, a C2-C20 hydrocarbon, a C3-C15 hydrocarbon, or a C4-C10 hydrocarbon; a C6-C30 aromatic group, a C8-C20 aromatic group, or a C10-C15 aromatic group; or a C1-C30 alkoxy group, a C2-C20 alkoxy group, a C3-C15 alkoxy group, or a C4-C10 alkoxy group. In embodiments, R1-R12 are selected from a C1-C4 hydrocarbon, a C1-C3 hydrocarbon, or a C1-C2 hydrocarbon. The aromatic groups can be single ring or multi-ring structures. Where the aromatic groups comprisemultiple aromatic rings, the rings can be separated by a bond or a spacer group (e.g., an alkylene group) or two or more rings can be fused rings. In embodiments, the aromatic group is selected from a phenyl group. In embodiments, the alkoxy group is selected from a C1-C6 alkoxy, a Cl- C4 alkoxy, a C1-C3 alkoxy, or a C1-C2 alkoxy. In embodiments, the alkoxy group is methoxy.

[0047] In one embodiment, the alkenyl functional silicone comprises two or more alkenyl functional groups (i.e., b+d+f > 2). In one embodiment, the alkenyl functional silicone is of the formula M2D1CM2. In one embodiment, the alkenyl functional siloxane is of the formula M’aD^Qg.

[0048] The alkenyl functional siloxane can be present in an amount of from about 40 wt.% to about 80 wt.%, from about 45 wt.% to about 75 wt.%, or from about 50 wt.% to about 65 wt.% based on the total weight of the composition.

[0049] Further, it will be appreciated that the composition can include a mixture of two or more alkenyl functional silicones. Where a plurality of alkenyl functional silicones are used, the alkenyl functional silicones may be of different types (e.g., have a different overall makeup in terms of the M, D, T, and Q units), of different sizes (e.g., have similar M, D, T, Q structures but differ in terms of the number of the respective unit) and / or different viscosities. The composition may include a mixture of different types of siloxanes in terms of the M, D, T, and Q units. For example, the composition could include a mixture of two or more of an MD, MDT, MQ, and / or an MDQ type alkenyl functional resin in accordance with Formula (I).

[0050] In one embodiment, the composition comprises a first alkenyl functional silicone with terminal alkenyl functional groups (i.e., end-capped with one or more alkenyl functional groups) having the formula M2D1CM2; and a second alkenyl functional silicone having the formula M1aD2dQgwith alkenyl functional groups pendent to the siloxane chain. In one embodiment, the alkenyl functional siloxane comprises from about 50 wt. % to about 80 wt. % of an alkenyl functional terminated siloxane and from about 20 wt. % to about 50 wt. % of an alkenyl functional siloxane with pendent alkenyl functional groups based on the total weight of the alkenyl functional siloxane.

[0051] It will also be appreciated that the alkenyl functional siloxane can be provided as a mixture of two or more alkenyl functional siloxanes of different sizes and / or viscosities. In one embodiment, the composition comprises a first alkenyl functional siloxane of a first viscosity, and a second alkenyl functional siloxane of a second viscosity. In one embodiment, the first viscosity is a relatively low viscosity, and the second viscosity is a viscosity higher thanthe first viscosity. In one embodiment, the composition comprises a first alkenyl functional siloxane having a viscosity of from about 500 cps to about 10,000 cps, from about 1,000 cps to about 7,500 cps, from about 2,000 cps to about 5,000 cps, or from about 3,000 cps to about 4,000 cps, and a second alkenyl functional siloxane having a viscosity of from about 12,000 cps to about 100,000 cps, from about 15,000 cps to about 90,000 cps, from about 20,000 cps to about 80,000 cps, or from about 30,000 cps to about 70,000 cps. Where a mixture of alkenyl functional siloxanes is employed of different viscosities, the alkenyl functional siloxanes can be of the same or different base types or formulas. For example, the alkenyl functional siloxane may be all of the same type, e.g., MD, MDQ, MDT, MQ, etc., or they may be a mixture of different types. In one embodiment, the composition comprises a mixture of alkenyl functional siloxane of different viscosities where the alkenyl functional siloxane are of the structure M'aD^Qg.

[0052] Hydride Functional Siloxane

[0053] The composition includes a hydride functional siloxane. The hydride functional siloxane may function as, and may also be referred to herein as, a crosslinker. The hydride functional siloxane may be chosen from a compound of the formula:wherein:M3= R13R14R15SiOi / 2M4= R16R17R18SiOi / 2D3= R19R20SiO2 / 2 D4= R21R22SIO2 / 2T3= R23SIO3 / 2T4= R24SIO3 / 2 Q = S1O4 / 2 where R13, R14, R15, R19, R20, R23, and are independently chosen from a C1-C30 hydrocarbon, a C6-C30 aromatic group, or C1-C30 alkoxy group;R16, R17, R18, R21, R22, and R24are independently chosen from hydrogen, a C1-C30 hydrocarbon, a C6-C30 aromatic group, C1-C30 alkoxy group, or a C2-C30 alkenyl group, with the proviso that one or more of R16, R17, R18, R21, R22, and / or R24are hydrogen; the subscripts a, b, c, d, e, f, g, are zero or positive subject to the following limitations: l< h+i+j+k+m+n+o < 100, and i+k+n > 0.

[0054] R13-R24can be independently selected from a C1-C30 hydrocarbon, a C2-C20 hydrocarbon, a C3-C15 hydrocarbon, or a C4-C10 hydrocarbon; a C6-C30 aromatic group, a C8-C20 aromatic group, or a C10-C15 aromatic group; or a C1-C30 alkoxy group, a C2-C20 alkoxy group, a C3-C15 alkoxy group, or a C4-C10 alkoxy group. In embodiments, R1-R12 are selected from a C1-C4 hydrocarbon, a C1-C3 hydrocarbon, or a C1-C2 hydrocarbon. The aromatic groups can be single ring or multi-ring structures. Where the aromatic groups comprise multiple aromatic rings, the rings can be separated by a bond or a spacer group (e.g., an alkylene group) or two or more rings can be fused rings. In embodiments, the aromatic group is selected from a phenyl group. In embodiments, the alkoxy group is selected from a C1-C6 alkoxy, a Cl- C4 alkoxy, a C1-C3 alkoxy, or a C1-C2 alkoxy. In embodiments, the alkoxy group is methoxy.

[0055] In one embodiment, the hydride functional siloxane is of the type M3hD4kM3h.

[0056] The hydride functional silicone (or mixture of two or more alkenyl functional silicones) is present in an amount of from about 0.01 to about 20 weight %; from about 0.1 to about 5 weight %; or from about 0. 1 to about 3 weight % based on the total weight of the composition.

[0057] Titanium Dioxide

[0058] The present compositions include titanium dioxide particles. The titanium dioxide particles can be provided in any suitable form / morphology including the rutile form, anatase form, or mixtures thereof. In one embodiment, the composition comprises rutile titanium dioxide particles. In one embodiment, the composition comprises anatase titanium dioxide particles. In one embodiment, the composition comprises a mixture of rutile titanium dioxide particles and anatase titanium dioxide particles.

[0059] The titanium dioxide particles may have a particle size as desired for a particular purpose or intended application. In one embodiment, the titanium dioxide particles may have a particle size between about 1 nm and about 500 nm. In some embodiments, titanium dioxide particles will have a particle size of from about 5 nm to about 400, from about 10 nm to about 300 nm, from about 20 nm to about 250 nm, from about 30 nm to about 200 nm, from about 40 nm to about 150 nm, or from about 50 nm to about 100 nm. In one embodiment, the particle size of the titanium dioxide will be from about 50 nm to about 200 nm, from about 60 nm to about 75 nm. Reference herein to the size of titanium dioxide particles (or crystallites) will be understood to mean the average particle size of the titanium dioxide particulates. Where the particle size is modified by the term “about,” it will be understood to embrace somewhat largeror smaller particles sizes than the indicated value to account for experimental errors inherent in the measurement and variability between different methodologies for measuring particle size, as will be apparent to one skilled in the art. The diameters may be measured by, for example, transmission electron microscopy (TEM) and also X-ray diffraction (XRD).

[0060] Alternatively, the particles may be characterized by surface area. Typically, the titanium dioxide will have a surface area, as measured by any suitable method, including 5- point BET, of greater than about 20 m2 / g. More typically, the titanium dioxide particles have surface areas of greater than about 50 m2 / g or greater than about 70 m2 / g. In embodiments, the titanium dioxide particles have surface areas greater than about 100 m2 / g, and even greater than about 150 m2 / g. In some embodiments, the titanium dioxide photocatalyst will have a surface area greater than about 200 m2 / g, greater than about 250 m2 / g, or even greater than about 300 m2 / g. In embodiments, the titanium dioxide has a surface area of from about 20 m2 / g to about 500 m2 / g, from about 50 m2 / g to about 400 m2 / g, from about 75 m2 / g to about 300 m2 / g, from about 100 m2 / g to about 250 m2 / g, or from about 150 m2 / g to about 200 m2 / g.

[0061] It will be appreciated that the composition can comprise a mixture of titanium dioxide particles of different particle sizes. For example, the composition can include a mixture of a first set of titanium dioxide particles of a first average particle size, and a second set of titanium dioxide particles having a second average particles size, where the first average particle size is different from the second average particle size.

[0062] It may be desirable to employ titanium dioxide particles of a relatively small average particle size. The use of larger concentration of larger particles, while not negatively impacting the performance and properties of the compositions, may affect the appearance of the composition when cured on a surface. In particular, the use of larger particles may provide more of a matte or textured finish.

[0063] The titanium dioxide can be treated or untreated. In one embodiment, the titanium dioxide particles include a surface treatment. The surface treatment can be a hydrophobic or hydrophilic surface treatment. In one embodiment, the titanium dioxide particles are surface treated with a tetraalkoxy silane. In one embodiment, the titanium dioxide particles are surface treated with polydimethylsiloxane. In one embodiment, the titanium dioxide particles are treated with alumina. The titanium dioxide particles can also be treated with a polymer selected from carboxymethyl starch, carboxymethyl dextran, carboxymethylcellulose, polycarboxylic acids, and copolymers containing carboxyl units.Other suitable surface treatments include, but are not limited to, polycarboxylic acids such as polyacrylic acid and polymaleic acid, and copolymers such as acrylic acid / maleic acid copolymer and acrylic acid / sulfonic acid monomer copolymer, and the like.

[0064] The titanium dioxide can be present in an amount of from about 20 wt.% to about 50 wt.%, from about 25 wt.% to about 45 wt.%, or from about 30 wt.% to about 40 wt.% based on the total weight of the composition.

[0065] Filler

[0066] The compositions optionally comprise one or more fillers other than titanium dioxide. The fillers can be selected as desired for a particular purpose. They may, for example contribute toward other properties of the composition as may be desired, e.g., strength. The optional fillers should not diminish or hinder the compositions reflectance, emissivity, etc. So, common fillers such as, carbon black, graphene, graphite, or other dark fillers, may be less desirable in, and in embodiments are excluded from, the present compositions.

[0067] Examples of suitable fillers include, but are not limited to, silicone resins, silica, nanosilica, fumed silica, particulate forms of oxides of cerium, aluminum, zinc, zirconium and other metals and metalloids present with or without surface modification; glass fibers, inorganic fillers such as talc, carborundum, mica, boron nitride, inorganic fillers such as clay, kaolin, calcium carbonate, and the like. In one embodiment, the composition includes a filler selected from silica and / or zinc oxide.

[0068] In one embodiment, the composition comprises fumed silica. The fumed silica can be functionalized as desired. In one embodiment, the fumed silica is functionalized with a functionalizing agent such as a halosilane; an organosilane having at least one silanol group and / or an alkoxy group, an aryloxy group, or a cycloalkoxy group; an organosilazane, a cyclic organosiloxane, a low-viscosity polyorganosiloxane that has a silanol group and / or an alkoxy group, an aryloxy group, or a cycloalkoxy group, or a silicone resin that has a silanol group and / or an alkoxy group, an aryloxy group, or a cycloalkoxy group. Examples of alkoxy groups include those groups having 1 to 6 carbon atoms, examples of aryloxy groups include groups having 6 to 10 carbon atoms, and examples of cycloalkoxy groups include groups having 6 to 10 carbon atoms. In an embodiment, the fumed silica is functionalized with a functionalizing agent selected from the group consisting of a silanol — stopped polydimethylsiloxane, octaphenylcyclotetrasiloxane, octamethylcyclotetrasiloxane and hexamethyldisilazane (HMDZ). Other examples of the first organosilicon functionalizing agent includediphenylsilanediol, dimethylsilanediol, methyltriethoxysilane, and phenyltrimethoxysilane. The low-viscosity polyorganosiloxane may contain one or more kinds of organic groups selected from the group consisting of a methyl group, a phenyl group, a vinyl group, and a 3,3,3- trifluoropropyl group. Suitable low-viscosity polyorganosiloxanes have a viscosity, as measured at 25° C., in a range of from about 1 to about 300 centipoises in an embodiment, and from about 5 to about 100 centipoises in another embodiment. Examples of the halosilanes include halotrialkylsilanes, such as chlorotrimethylsilane; halotriarylsilanes, such as chlorotriphenylsilane; dichlorodimethylsilane, bis(chlorodimethylsilyl)methane, trichloromethylsilane, bromotrimethylsilane, and the like.

[0069] In one embodiment, the composition comprises fumed silica in an amount of from about 0.1 wt.% to about 10 wt.%, from about 0.5 wt.% to about 7.5 v .%, from about 1 wt.% to about 5 v .%, or from about 2 wt.% to about 4 wt.% based on the total weight of the composition.

[0070] In one embodiment of the invention, the amount of filler is from 0.1 wt.% to about 90 wt.% of the total composition. In yet another embodiment of the invention, the amount of filler is from about 5 wt.% to about 60 wt.% of the total composition. In still another embodiment of the invention, the amount of filler is from about 10 wt.% to about 40 wt.% of the total composition. The filler may be a single species or a mixture of two or more species.

[0071] Catalyst

[0072] The composition includes a hydrosilylation catalyst. In one embodiment, the hydrosilylation catalyst may be a platinum based catalyst. The hydrosilylation catalyst may be, for example, a Speier's catalyst or a Karstedf s catalyst. Suitable Speier's catalysts may include chloroplatimc acid and FbPtCk as known in the art. Suitable Karstedf s catalysts may include a (Pt2{[CH2=CH)Me2Si]2O}3) catalyst as known in the art. In one embodiment, the hydrosilylation catalyst is selected from a Karstedfs catalyst having the formula (Pt2{[CH2=CH)Me2Si]2O}3), wherein Me is a methyl group. Karstedt's catalyst shows better productivity than Speier's catalyst for hydrosilylation reaction. Additionally, Karstedt's catalyst is commercially available in solution to control catalyst concentration, stability, viscosity and inhibition. More preferably platinum(0)-l,3-divinyl-l,l,3,3-tetramethyldisiloxane (0.1 M in xylene), as the Karstedt's catalyst is employed. The catalyst can be employed in an amount to provide the platinum metal concentration in an amount of from about 0.0008 and 0.01 wt. %, preferably between 0.0001 and 0.005 and more preferably between 0.001 and 0.002.

[0073] Inhibitor

[0074] Optionally, the composition can include an inhibitor to slow or retard the catalytic activity of the platinum catalyst. Examples of suitable inhibitors include, but are not limited to, 1-ethynyl-l -cyclohexanol, 2-methyl-3-butyn-2-ol, 3,5-dimethyl-l-hexyn-3-ol, 3- methyl-l-dodecyn-3-ol, polymethylvinylcyclosiloxanes such as 1,3, 5, 7- tetravinyltetramethyltetracyclosiloxane, divinyltetramethyldisiloxane, tetravinyldimethyldisiloxane, trialkyl cyanurates, alkyl maleates, organic sulfoxides, organic amines, diamines, phosphanes and phosphites, nitriles, diaziridines, and oximes, acetylene compounds, phosphites, maleates, amines or alcohols, by means of which a targeted adjustment can be made to the processing life, onset temperature, and crosslinking rate of the compositions of the invention.

[0075] Adhesion Promoter

[0076] The composition may optionally include an adhesion promoter. Suitable adhesion promoters can be selected from alkoxy- or aryloxysilanes, such as, but not limited to, y-ami nopropyl tri methoxy si lane. 3-glycidoxypropyltrimethoxysilane, bis(trimethoxysilylpropyl)fumarate, or tetracyclosiloxanes modified with acryloxytrimethoxysilyl or methaciyloxypropyltrimethoxysilyl functional groups, oligosiloxanes containing an alkoxy silyl functional group, oligosiloxanes containing an aryloxysilyl functional group, polysiloxanes containing an alkoxysilyl functional group, polysiloxanes containing an aryloxysilyl functional group, cyclosiloxanes containing an alkoxysilyl functional group, cyclosiloxanes containing alkoxysilyl and Si — H functional groups, cyclosiloxanes containing an aryloxysilyl functional group, titanates, trialkoxy aluminum, tetraalkoxysilanes, and mixtures thereof.

[0077] Adhesion promoters may be added in an amount from 0 to about 30 wt.%, from about 0.001 wt.% to about 15 wt.%, from about 0.1 wt.% to about 10 wt.%, or from about 0.5 wt.% to about 5 wt.% based on the total weight of the composition.

[0078] UV Stabilizer

[0079] The composition may optionally include a UV stabilizer. In embodiments, the UV stabilizer is selected from an organic UV stabilizer. The organic UV stabilizer may be selected from the group consisting of, but not limited to, triazines, benzotriazoles or benzoxazinones. When the triazines 2- (4,6-diphenyl-l ,3,5-triazin-2-yl)-5-(hexyl) oxy-phenol (Tinuvin® 1577) or 2- (2'-hydroxyphenyl) -4,6-bis (4-phenylphenyl) marketed by BASF underthe tradename Tinuvin® 1600 are used, a transparency below 370 nm can be achieved at lower UV stabilizer levels, while simultaneously a higher transparency at wavelengths above 390 nm is achieved.

[0080] Two-Part Composition

[0081] The present composition may generally be provided as a two-part composition. Providing as a two-part composition may prevent any premature curing of the composition. In one embodiment, the two-part composition is provided as a first part (part A) comprising (i) the alkenyl functional polysiloxane, (ii) catalyst, (iii) titanium dioxide, (iv) optional fillers, and (v) optional diluent; and a second part (part B) comprising (i) the alkenyl functional siloxane, (ii) hydride functional siloxane, (iii) titanium dioxide), (iv) adhesion promoter, (v) optional catalyst inhibitor, (vi) optional fillers, and (vii) optional diluent.

[0082] The components are provided in each part in amounts to provide the desired overall concentration of the components when the parts are combined. Where a component is provided in each of the two parts, the amount of the component in the first part can be provided in a roughly equal amount as the amount of that component in the second part. In one embodiment, the first part and the second part are provided to have the same or a relatively similar specific gravity. This may facilitate better mixing of the two-parts when combined to form the coating. In one embodiment, the first part and the second part have a specific gravity within about 8%, 5%, 3%, 2%, or 1% or less of each other.

[0083] The first part and the second part are stored in separate containers or cartridges prior to use. The first and second part can be stored at room temperature, e.g., from about 18 °C to about 25 °C.

[0084] A coating formed from the two-part composition is prepared by mixing the first part and the second part, applying the composition to a target surface, and exposing the coating composition to elevated temperatures. In one embodiment, the coatings can be cured at room temperature (e.g., from about 18 °C to about 25 °C). In one embodiment, the coating is exposed to temperatures of from about 80 °C to about 150 °C. Additionally, curing can be affected in about 1 hour.

[0085] The coating can be applied in any suitable manner as is now known or later developed in the art. In embodiments, the coating may be applied by spraying, brushing, rolling, dipping, blade coating, curtain coating, skiv coating, or a combination thereof. Spray coating can be employed with the compositions that further include a solvent such as a non-volatilesolvent. Further, the means of spraying includes, but is not limited to, the use of a High Volume Low Pressure (HVLP) spraying systems, air-assisted / airless spraying systems, or electrostatic spraying systems. In further or alternative embodiments, the coating is applied in a single application, or in multiple applications.

[0086] The present compositions allow for the use of direct coating of a substrate surface. That is, in embodiments, the coating can be applied to and sufficiently adhere to a surface without the need for a primer. For primerless coating of the composition, the target surface is generally treated prior to coating the composition. The surface can be treated in any suitable manner such as, but not limited to, solvent washing, flame treatment, corona discharge, chemical etching. Chemical etching may include etching with an acidic material. In one embodiment, acid etching can be accomplished using any protonic acid such as, for example, sulfuric, hydrochloric or nitric acids or organic acids such as acetic acid, and the like. The length of time required to effect etching with an acid depends upon the acid employed, concentration of the acid, the substrate material and the coating composition. The precise conditions required for acid etching can readily be determined by a worker skilled in the art. Spraying may also allow for the application of relatively thin coatings onto the target surface.

[0087] Further, the compositions have been found to allow for coating of curved surfaces. In particular, the flexibility and properties of the compositions allow for the ability to more readily coat curved surfaces and provide good surface coverage.

[0088] In another embodiment, a surface may be pre-treated with a primer to promote adhesion of the coating. Examples of suitable primer materials include, but are not limited to, ethyl orthosilicate and tetra-n-butyl titanate in mineral spirits. Such a primer is commercially available from Momentive Performance Materials under the designation SS4155 primer.

[0089] The coating can be provided in a thickness as desired for a particular purpose or intended application. In one embodiment, the coating is provided at a wet thickness of about 50 microns or greater. At this level, excellent solar absorptivity is observed in the coatings in accordance with the present technology. Thicker coatings can be employed if desired, which may lower the solar absorptivity. In one embodiment, the coating, after curing, may have a thickness of from about 5 mils or greater, about 7 mils or greater, or about 10 mils or greater.

[0090] The coatings can be employed on a variety of substrates including, but not limited to, metal substrates and plastic substrates. In one embodiment, the substrate is selected from an aluminum substrate, a magnesium substrate, a titanium substrate, or the like. Examplesof aluminum substrates include, but are not limited to, bare aluminum, cast aluminum, aluminum alloys, and the like.

[0091] The coatings formed from the present compositions exhibit a wide range of properties that allow the coatings to be used in various applications including in applications. The coatings produced from the compositions may exhibit one or more of low solar absorptivity (cis), high infrared emissivity (e), and high solar reflectance (ps). Solar absorptance at To (initial absorptance after curing) and after 1000 hours at 150 °C was measured using ASTM E903-20 with a UV Vis spectrometer with integrating spheres, and solar reflectance at To and after 1000 hours at 150 °C was measured using ASTM E903-20 with a UV Vis spectrometer with integrating spheres. Emissivity may be measured according to ASTM E408. In one embodiment, the coating has one or more of the following properties at a coating thickness of from about 1.5 mm to about 2 mm:• solar absorptivity (as) of 0.35 or less; 0.25 or less; 0.2 or less; 0. 15 or less; about 0. 1 to 0.35; about 0. 12 to about 0.30; about 0. 15 to about 0.25; about 0. 17 to about 0.20; and / or• infrared emissivity (e) of 0.89 or greater, 0.9 or greater, 0.92 or greater, 0.95 or greater, or 0.98 or greater; 0.89 to about 0.98, about 0.9 to about 0.95, 0.89 to about 0.92, or about 0.9 to about 0.92; and / or• solar reflectance (ps) of 0.65 or greater, 0.75 or greater, 0.8 or greater, or 0.85 or greater to from about 0.65 to about 0.9, from about 0.7 to about 0.88, from about 0.75 to about 0.85, or from about 0.8 to about 0.83.

[0092] The coatings of the present technology also exhibit good flexibility. In one embodiment, the coating has an elongation of from about 100% to about 195%, from about 110% to about 185%, from about 120% to about 175%, from about 130% to about 160%, or from about 140% to about 150%.

[0093] Examples

[0094] Two-part compositions were prepared according to the formulas described in Tables 1 and 2. Coating compositions were prepared by mixing parts A and B of the respective formulations, applying the composition to a surface, and exposing the composition to a temperature of 80 °C for about one hour. Solar absorptance at To (initial absorptance after curing) and after 1000 hours at 150 °C was measured using ASTM E903-20 with a UV Vis spectrometer with integrating spheres, and solar reflectance at To and after 1000 hours at 150°C was measured using ASTM E903-20 with a UV Vis spectrometer with integrating spheres. Those results are shown in Table 3. Table 4 shows the reflectometer data for formulations 1-8 showing total absorptance, total reflectance, and emissivity after 1000 hours of exposure to a temperature of 150 °CTable 1Table 2Table 3Table 4

[0095] Figure 1 shows the total reflectance spectra for films prepare from formulations 1-8. Figure 2 shows the total reflectance of a film from formulation 9.

[0096] As shown in the tables and figures the films formed from compositions in accordance with the present technology exhibit high solar reflectance, high emissivity, and low solar absorptance. These properties are observed after extended periods of time. This is particularly the case compared to formulation 5, which did not include titanium dioxide, and formulation 9 having a relatively low concentration of titanium dioxide.

[0097] What has been described above includes examples of the present specification. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present specification, but one of ordinary skill in the art may recognize that many further combinations and permutations of the present specification are possible. Accordingly, the present specification is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either thedetailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.

[0098] The foregoing description identifies various, non-limiting embodiments of a thermal control coating. Modifications may occur to those skilled in the art and to those who may make and use the invention. The disclosed embodiments are merely for illustrative purposes and not intended to limit the scope of the invention or the subject matter set forth in the claims.

Claims

CLAIMSWhat is claimed is:

1. A curable coating composition comprising: an alkenyl functional siloxane; a hydride functional siloxane; titanium dioxide particles; an addition cure catalyst; and optionally an adhesion promoter.

2. The curable coating composition of claim 1, wherein the titanium dioxide is present in an amount of from about 20 wt.% to about 50 wt.% based on the total weight of the composition.

3. The curable composition of claim 1 or 2, wherein the titanium dioxide particles have a particle size of from about 1 nm to about 500 nm.

4. The curable composition of any of claims 1 to 3, wherein the titanium dioxide particles are selected from rutile titanium dioxide, anatase titanium dioxide, or a mixture thereof.

5. The curable composition of claim 4, wherein the titanium dioxide particles compnse fumed anatase / rutile titanium dioxide.

6. The curable composition of any of claims 1 to 5, wherein the alkenyl functional siloxane can be present in an amount of from about 40 wt.% to about 80 wt.% based on the total weight of the composition.

7. The curable composition of any of claims 1 to 5, wherein the alkenyl functional siloxane is selected from a compound of the formula:wherein:M1= i R^SiOi^M2= R4R5R6SiOi / 2D1= R7R8SiO2 / 2D2= R9R10SIO2 / 2^ = ^03 / 2T2= R12SiO3 / 2Q = S1O4 / 2 where R1, R2, R3, R7, R8, and R11are independently chosen from a C1-C30 hydrocarbon, a C6-C30 aromatic group, or C1-C30 alkoxy group;R4, R5’ R6, R9, R10, and R12are independently chosen from a C1-C30 hydrocarbon, a C6- C30 aromatic group, C1-C30 alkoxy group, and a C2-C30 alkenyl group, with the proviso that one or more of the R4, R5, R6, R9, and / or R12groups are selected from a C2-C30 alkenyl group; the subscripts a, b, c, d, e, f, g, are zero or positive subject to the following limitations: 2 < a+b+c+d+e+f+g < 2000, and b+d+f > 0.

8. The curable composition of claim 7, wherein the alkenyl functional siloxane is selected from an alkenyl functional siloxane of the formula M2D1CM2, the formula MJaD2dQ , or a combination thereof.

9. The curable composition of claim 8, wherein the alkenyl functional siloxane compnses a first alkenyl functional siloxane having the formula M2D1CM2; and a second alkenyl functional siloxane having the formula M1aD2dQg.

10. The curable composition of claim 9, wherein the first alkenyl functional siloxane comprises is present in an amount of from about 50 wt. % to about 80 wt. %, and the second alkenyl functional siloxane is present in an amount of from about 20 wt. % to about 50 wt. % based on the total weight of the alkenyl functional siloxane.

11. The curable composition of any of claims 1 to 10 comprising fumed silica.

12. The curable composition of claim 11, wherein the fumed silica is present in an amount of from about 0.1 wt.% to about 10 wt.% based on the total weight of the composition.

13. The curable composition of any of claims 1 to 12, wherein the catalyst is a platinum based catalyst.

14. The curable composition of any of claims 1 to 13, wherein the adhesion promoter is selected from a cy closiloxanes comprising Si-H functional groups.

15. The composition of any of claims 1 to 14, wherein the adhesion promoter is present in an amount of from about 0 to about 30 wt.% based on the total weight of the composition.

16. The composition of any of claims 1 to 15, wherein the composition is provided as a two-part composition comprising: a first part comprising the alkenyl functional siloxane; titanium dioxide, and the catalyst; anda second part comprising the alkenyl functional siloxane, the hydride functional siloxane, titanium dioxide, and the optional adhesion promoter.

17. The composition of any of claims 1-16, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (as) of 0.35 or less.

18. The composition of any of claims 1-16, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (ou) about 0.1 to 0.3519. The composition of any of claims 1-18, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a infrared emissivity (e) of 0.89 or greater.

20. The composition of any of claims 1-18, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (c ) of 0.89 to about 0.98.

21. The composition of any of claims 1-20, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has solar reflectance (ps) of 0.65 or greater.

22. The composition of any of claims 1-20, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (as) of from about 0.65 to about 0.9.

23. The composition of any of claims 1-22, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm has a solar absorptivity (o ).

24. The composition of any of claims 1-22, wherein a coating formed from the composition at thickness of from about 1.5 mm to about 2 mm an elongation of from about 100% to about 195%.

25. A method of forming a coating on a substrate comprising curing the composition of any of claims 1-24.

26. The method of claim 25, wherein the composition is a two-part composition comprising (i) a first part comprising the alkenyl functional siloxane; titanium dioxide, and the catalyst; and (ii) a second part comprising the alkenyl functional siloxane, the hydride functional siloxane, titanium dioxide, and the optional adhesion promoter, and the method comprisescombining the first part and the second part, heating at a temperature of from about 80 °C to about 150 °C.

27. The method of claim 25 or 26, wherein curing is accomplished in about 1 hour.

28. A substrate comprising a surface coated with the composition of any of claims 1 to 24.

29. The substrate of claim 28, wherein the composition is cured to form a coating.

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