CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Serial No. 62/946,012 filed December 10, 2019, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The subject matter disclosed herein relates to intumescent fire- retardant (IFR) coatings and their application on substrates to provide protection against flame and heat.

BACKGROUND

A variety of substances can be added to combustible materials to prevent fires from starting or to slow the spread of fire and provide additional escape time. Intumescent flame retardant (IFR) technology is a promising approach to replace halogen-containing flame retardants while maintaining relatively high flame-retardant efficiency. IFR systems are generally composed of three components: an acid source such as ammonium polyphosphate (APP), a char forming agent such as pentaerythritol (PER), and a blowing agent such as melamine (MEL). However, traditional IFR additives are susceptible to migration to polymer surfaces during polymer processing due to their low molecular weight, which decreases flame- retardant efficiency.

Accordingly, there is an ongoing need for additional IFR compositions. There is also an ongoing need for IFR coating compositions that are water- based or have reduced levels of volatile organic solvents.

SUMMARY

This summary lists several embodiments of the presently disclosed subject matter, and in many cases lists variations and permutations of these embodiments. This summary is merely exemplary of the numerous and varied embodiments. Mention of one or more representative features of a given embodiment is likewise exemplary. Such an embodiment can typically exist with or without the feature(s) mentioned; likewise, those features can be applied to other embodiments of the presently disclosed subject matter, whether listed in this summary or not. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features.

In some embodiments, the presently disclosed subject matter provides a curable intumescent fire retardant (IFR) coating composition comprising a fluoropolymer, a curative, and a flame-retardant (FR) additive. In some embodiments, the fluoropolymer is a fluoropolymer elastomer. In some embodiments, the curative comprises dicinnamylidene hexamethylenediamine.

In some embodiments, the curable IFR coating composition further comprises a hydrogen fluoride scavenger. In some embodiments, the hydrogen fluoride scavenger comprises magnesium oxide.

In some embodiments, the FR additive comprises at least one of poly(piperazinyl, morpholinyl, triazine), ammonium polyphosphate (APP), melamine, and di-pentaerythritol. In some embodiments, the FR additive comprises expandable graphite. In some embodiments, the FR additive is free of halogen-containing materials.

In some embodiments, the curable IFR coating composition further comprises an adhesion promoter. In some embodiments, the adhesion promoter comprises an epoxy silane.

In some embodiments, the curable IFR coating composition further comprises water as a carrier fluid. In some embodiments, the curable IFR coating composition is free of volatile organic solvents (VOCs).

In some embodiments, the presently disclosed subject matter provides a substrate comprising at least one surface coated with a cured layer of a curable IFR coating composition comprising a fluoropolymer, a curative, and a FR additive. In some embodiments, the substrate comprises aluminum. In some embodiments, the cured layer comprises expandable graphite. In some embodiments, the cured layer has a thickness of at least about 200 microns (pm). In some embodiments, the presently disclosed subject matter provides a method of providing thermal protection to a substrate, wherein the method comprises: (a) applying a curable IFR coating composition comprising a fluoropolymer, a curative, and a FR additive to at least one surface of a substrate; and (b) drying and curing the IFR coating composition to provide a cured layer of the curable IFR coating composition. In some embodiments, the applying is performed via spraying. In some embodiments, the substrate comprises aluminum. In some embodiments, the cured layer has a thickness of at least about 200 pm. In some embodiments, the curable IFR coating composition comprises expandable graphite.

Accordingly, it is an object of the subject matter disclosed herein to provide a curable IFR composition, substrates coated with a cured layer of the curable IFR composition, and related methods. This and other objects are achieved in whole or in part by the presently disclosed subject matter. Further, an object of the presently disclosed subject matter having been stated above, other objects and advantages of the presently disclosed subject matter will become apparent to those skilled in the art after a study of the following description and examples.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a series of panels showing scanning electron microscopy (SEM) images and elemental mapping of a cross-section of a cured layer of an intumescent fire retardant (IFR) coating composition of the presently disclosed subject matter. Panel A is a SEM image of a cross-section of a cured IFR coating composition, while panels B, C, D, and E show the homogenous distribution of carbon, fluorine, silicon, and phosphorus, respectively, in the same cross-section.

Figure 2 shows microscope images of (left) a cured intumescent fire retardant (IFR) coating layer film installed on an aluminum substrate after cross-hatch tape was applied and pulled off; and (right) a cured IFR coating layer film installed on an aluminum substrate and subjected to a 45 degree (°) bending test. Figure 3 is a photographic image showing the experimental test setup for flame-testing of a cured intumescent fire retardant (IFR) coating film installed on an aluminum panel. The coated side of the panel is facing the torch tip (at left in the image), with the torch tip 10 millimeters (mm) offset from the coating, as indicated by the ruler. The section of coated aluminum being analyzed during the test is also 40 mm higher than the bottom edge of the torch tip.

Figure 4 is a graph showing the backside temperatures versus time (in minutes (min)) of a cured intumescent fire retardant (IFR) film coated aluminum panel subjected to a flame test using the test setup shown in Figure 3. Data is shown for panels coated with different film thicknesses: 100 microns (pm), 200 pm, 300 pm, and 400 pm.

Figure 5A is a photographic image of the front side of a cured intumescent fire retardant (IFR) film coated aluminum panel after exposure to flame, showing char formation.

Figure 5B is a photographic image of a side view of the same panel shown in Figure 5A.

DETAILED DESCRIPTION The presently disclosed subject matter now will be described more fully hereinafter, in which some, but not all embodiments of the presently disclosed subject matter are described. Indeed, the presently disclosed subject matter can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

L Definitions

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the presently disclosed subject matter.

All technical and scientific terms used herein, unless otherwise defined below, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. References to techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one of skill in the art. While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

In describing the presently disclosed subject matter, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques.

Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims.

Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims. Thus, for example, reference to "an additive" includes a plurality of such additives, and so forth.

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

As used herein, the term “about,” when referring to a value or to an amount of a composition, dose, mass, weight, thickness, temperature, time, volume, concentration, percentage, etc., is meant to encompass variations of in some embodiments ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1 %, in some embodiments ±0.5%, and in some embodiments ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods or employ the disclosed compositions.

The term “comprising”, which is synonymous with “including” “containing” or “characterized by” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. “Comprising” is a term of art used in claim language which means that the named elements are essential, but other elements can be added and still form a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of” appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

As used herein, the phrase “consisting essentially of” limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.

With respect to the terms “comprising”, “consisting of”, and “consisting essentially of”, where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.

As used herein, the term “and/or” when used in the context of a listing of entities, refers to the entities being present singly or in combination. Thus, for example, the phrase “A, B, C, and/or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.

As used herein, a “monomer” refers to a molecule that can undergo polymerization, thereby contributing constitutional units (or “monomeric units”), i.e., an atom or group of atoms, to the essential structure of a macromolecule.

As used herein, a “macromolecule” refers to a molecule of high relative molecular mass, the structure of which comprises the multiple repetition of units derived from molecules of low relative molecular mass, e.g., monomers and/or oligomers. An “oligomer” refers to a molecule of intermediate relative molecular mass, the structure of which comprises a small plurality (e.g., 2, 3, 4, 5, 6, 7, 8, 9, or 10) of repetitive units derived from molecules of lower relative molecular mass.

A “polymer” refers to a substance comprising macromolecules. In some embodiments, the term “polymer” can include both oligomeric molecules and molecules with larger numbers (e.g., > 10, > 20, >50, > 100) of repetitive units. In some embodiments, “polymer” refers to macromolecules with at least 10 repetitive units.

The term “fluoropolymer” refers to a polymer based on a fluorocarbon monomer and having multiple carbon-fluorine bonds. An exemplary fluoropolymer is polytetrafluoroethylene.

A “copolymer” refers to a polymer derived from more than one species of monomer. The different species of monomer can be arranged in blocks where each block comprises monomeric units that are all the same or be arranged in a sequential or random manner.

A “terpolymer” is a polymer derived from three different monomer species.

The term “intumescent” as used herein refers to a material that expands upon on exposure to heat, producing a char. This volume expansion and charring protects any underlying substrate as the char acts as a poor conductor of heat. Accordingly, intumescent coatings can be used in passive fire protection and applied to substrates as fire retardant coatings to improve fire resistance.

As used in this specification, the terms "cure" and "curing" refer to the chemical crosslinking of components in a curable coating composition applied as a coating layer over a substrate. Accordingly, the terms "cure" and "curing" do not encompass solely physical drying of coating compositions through solvent or carrier evaporation. In this regard, the term "cured," as used in this specification, refers to the condition of a coating layer in which at least one of the components of the curable coating composition forming the layer has chemically reacted to form new covalent bonds in the coating layer. N. IFR Compositions and Methods

In some embodiments, the presently disclosed subject matter provides a curable IFR coating composition comprising oligomeric or polymeric flame- retardant and/or IFR materials. In some embodiments the composition can be cured to provide an inherently flame-retardant (FR) matrix, thereby avoiding issues related to IFR materials where the IFR additives migrate to an IFR coating system polymer surface.

Moreover, the coating industry is becoming increasingly motivated to provide water-borne solutions and shift away from heavy use of volatile organic solvents (VOCs). This trend is motivated by cost, safety, government regulations, and environmental concerns. In some embodiments, the presently disclosed IFR coating composition uses water as a diluent/carrier fluid and/or is free of VOCs. There are no commercially available aqueous- based FR coating technologies with similar performance to that described in the examples below.

In some embodiments, the presently disclosed subject matter provides an aqueous-based curable IFR coating composition based on fluoropolymer elastomer (FKM) emulsions and further comprising halogen-free FR additives. FKM have good chemical, thermal and electrical stabilities; are inert to acids, bases, solvents, and oils; and are resistant to ageing and oxidation. The use of FKM and blowing agents (e.g., melamine or other blowing agents) produces a unique intumescent structure upon expansion. Without being bound to any one theory, outward stresses from the blowing agents coupled with inward stresses of the FKM backbone attempting to return to its originally cured structure can create a consistent, microcellular char. Unlike epoxies, urethanes, phenolic and alkyd materials, which revert when exposed to heat or disintegrate, FKM leaves a carbonized network which can hold intumescent additives in place, providing extended protection of any underlying substrate.

In addition to being VOC free, the presently disclosed IFR coating composition is advantageous in its replacement of environmentally undesirable halogen-containing FR additives with halogen free additives. In some embodiments, this replacement improves the performance and/or the economics of the corresponding cured IFR coating. In comparative testing, cured coating layers formed from the presently disclosed IFR coating compositions demonstrate comparable backside temperatures at lesser thicknesses than traditional thermoset solutions. Further, the ability to apply the coating compositions at a lower thickness expands the applications of the coating compositions to statically indeterminant substrates that expand and contract during normal operation. These applications include, for example, use in providing thermal and/or fire protection to substrates including battery cells and battery covers for electric vehicles, as well as oriented strand board (OSB) or other building materials utilized in infrastructure industries.

Accordingly, in some embodiments, the presently disclosed subject matter provides a curable IFR coating composition comprising a fluoropolymer, a curative, and a FR additive. In some embodiments, the fluoropolymer is a fluoropolymer elastomer (i.e., FKM, which can also be referred to as a fluoropolymer rubber or latex). Fluoropolymer elastomers are copolymers prepared from at least two species of monomer where vinylidene fluoride (VdF) is one of the at least two species of monomer. Other monomers that can be used with VdF to prepare FKM include perfluoromethylvinylether (PMVE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), propylene, and ethylene. For example, in some embodiments, the FKM is a copolymer of VdF and HFP; a terpolymer of VdF, HFP, and TFE; a terpolymer of VdF, PMVE, and TFE; a terpolymer of VdF, TFE, and propylene; or a pentapolymer of VdF, HFP, ethylene, PMVF, and TFE. FKM are commercially available, for example, as polymers sold under the tradename VITON™ from Chemours (Wilmington, Delaware, United States of America); polymers sold under the tradename DYNEON™ from 3M (St. Paul, Minnesota, United States of America); as well as fluoropolymers sold by Daikin Industries, Ltd (Osaka, Japan), Solvay Specialty Polymers USA, LLC (Alpharetta, Georgia, United States of America) and Solvay Specialty Polymers Italy S.p.A. (Milan, Italy).

In some embodiments, the fluoropolymer is present in about 10 weight % to about 45 weight % of the IFR coating composition based on the total weight of the coating composition. In some embodiments, the fluoropolymer is present in about 15 weight % to about 25 weight % of the IFR coating composition based on the total weight of the coating composition.

A curative is a substance which can induce any degree of crosslinking of the polymers in the presently disclosed compositions. Curatives are known in the art of polymer chemistry and include, for example, amines (e.g., diamines), acid acceptors, dihydroxyaromatic compounds (e.g., bisphenols), quaternary onium salts, peroxides, persulfates, triallyl imidazole, triallyl isocyanurate, and photoexcitable ketones. In some embodiments, the curative comprises one or more of the group comprising diamine crosslinking agents (e.g., blocked diamine compounds), peroxides, and dihydroxyaromatic crosslinking agents. In some embodiments, e.g., when a diamine crosslinking agent is used, a hydrogen and/or acid scavenger (e.g., a hydrogen fluoride scavenger), such as magnesium oxide, can also be added. In some embodiments, e.g., when dihydroxyaromatic compounds are used as crosslinking agents, a curing accelerant, such as a quaternary phosphonium salt, can be included as an additional curative. In some embodiments, the curative is present in about 0.1 weight % to about 5 weight % based on the total weight of the curable IFR coating composition. In some embodiments, the curative is present in about 0.2 weight % to about 1 .0 weight % based on the total weight of the curable IFR coating composition.

In some embodiments, the curative comprises dicinnamylidine hexamethylenediamine (which can also be referred to as DIAK 3, which is commercially available from several suppliers). In some embodiments, the composition further comprises a hydrogen and/or acid scavenger, such as a hydrogen fluoride scavenger. Suitable hydrogen fluoride scavengers include divalent and higher valency metal oxides and hydroxides, such as, but not limited to, calcium hydroxide, magnesium oxide, zinc oxide, titanium oxide, and lead oxide. In some embodiments, the hydrogen fluoride scavenger comprises or consists of magnesium oxide (MgO).

In some embodiments, the FR additive is free of halogen-containing materials. Halogen-free FR additives include, but are not limited to, nitrogen- containing compounds such as melamine, cyanuric acid and related triazine or triazine-containing compounds; condensation products of melamine (including melam, melem, and melon), reaction products of melamine with phosphoric acid (including melamine phosphate, melamine pyrophosphate, and melamine polyphosphate (MPP)), reaction products of condensation products of melamine with phosphoric acid (including melam polyphosphate, melem polyphosphate, melon polyphosphate), melamine cyanurate (MC), zinc diethylphosphinate (DEPZn), aluminum diethylphosphinate (DEPAI), calcium diethylphosphinate, calcium stearate, magnesium diethylphosphinate, bisphenol-A bis(diphenyphosphinate) (BPADP), resorcinol bis(2,6-dixylenyl phosphate) (RDX), resorcinol bis(diphenyl phosphate) (RDP), di-pentaerythritol, phosphorous oxynitride, zinc borate, zinc oxide, zinc stannate, zinc hydroxystannate, zinc sulfide, zinc phosphate, zinc silicate, zinc hydroxide, zinc carbonate, zinc stearate, magnesium stearate, ammonium octamolybdate, ammonium polyphosphate (APP), melamine molybdate, melamine octamolybdate, barium metaborate, ferrocene, boron phosphate, boron borate, magnesium hydroxide, magnesium borate, aluminum hydroxide, alumina trihydrate, melamine salts of glycoluril and 3-amino-1 ,2,4-triazole-5-thiol, urazole salts of potassium, zinc and iron, 1 ,2-ethanediyl-4-4'-bis-triazolidine-3,5,dione, silicone, oxides of Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Sn, Sb, Ba, W, and Bi, polyhedral oligomeric silsesquioxanes, silicotungstic acid (SiTA), phosphotungstic acid, melamine salts of tungstic acid, linear, branched or cyclic phosphates or phosphonates, spirobisphosphonates, spirobisphosphates and nanoparticles, such as carbon nanotubes and nanoclays (including, but not limited to, those based on montmorillonite, halloysite, and laponite).

In some embodiments, the FR additive comprises at least two, at least three, at least four, or at least five different FR additives. In some embodiments, the FR additive comprises one or more compounds selected from melamine (1 ,3, 5-triazine-2, 4, 6-triamine) and related triazine-based compounds such as, for example, melam (N-4,6-diamino-1 ,3,5-triazine-2-yl)- 1 , 3, 5-triazine-2, 4, 6-triamine), melem (2,5,8-triamino-1 ,3,4,6,7,9,9b- heptaazaphenalene), benzoguanamine (2,4-diamino-6-phenyl-1 ,3,5-triazine), and acetoguanamine (2, 4-diamino-6-methyl-1 ,3,5-triazine); cyanuric acid (1 ,3,5-triazine-2,4,6-triol) and related triazine-based compounds such as, for example, ammeline (1 ,3,5-triazine-2,4-diamine-6-ol) ammelide (1 ,3,5-triazine- 2-amine-4,6-diol), and melamine cyanurate; and reaction products of trichlorotriazine, piperazine and morpholine (i.e., poly(piperazinyl, morpholinyl, triazine)) as per CAS-No. 1078142-02-5 (e.g. MCA PPM triazine HF from MCA Technologies GmbH, Biel-Benken, Switzerland). In some embodiments, the FR additive comprises or consists of ammonium polyphosphate (APP) particles encapsulated within a melamine or melamine- containing resin. Melamine tends to expand when exposed to high temperatures, for example above 200°C, and flame. Exemplary commercially available FR particles include APP-melamine particles from Clariant AG (Muttenz, Switzerland) sold under the product names Exolit AP 462 and Exolit AP 740 F. For instance, Exolit AP 462 is a fine-particle white powder having a particle size (d50) of about 20 microns, composed of particles of ammonium polyphosphate micro-encapsulated (i.e., coated) with melamine resin, and is non-hygroscopic and non-flammable. Exolit AP 740 F is a fine-particle white powder having a size (d50) of 8-12 microns, based on ammonium polyphosphate which develops its effectiveness through phosphorus/nitrogen synergism and intumescence.

In some embodiments, the FR additive comprises at least one of poly(piperazinyl, morpholinyl, triazine), APP, melamine, and di-pentaerythritol. In some embodiments, the FR additive comprises at least two, at least three, or at least four of these additives.

In some embodiments, the FR additive further comprises expandable graphite. Upon exposure to high temperatures (e.g., 160°C to 260°C), expandable graphite can exfoliate and form a graphite char, which is more resistant to degradation than the carbon chars from other chemical intumescent materials. Expandable graphite can be produced using different processes. For example, it can be obtained by oxidation treatment of natural graphite or artificial graphite using an oxidation agent such as hydrogen peroxide, nitric acid or another oxidizing agent in sulfuric acid. Graphite can also be anodically oxidized in an aqueous acidic or aqueous salt electrolyte. Thus, the expandable graphite comprises a lamellar structure in which, for example, an acid is intercalated between the layers of graphite. Upon heating, the material intercalated between the layers is gasified and the graphite expands or exfoliates. In some embodiments, the expandable graphite has an expansion onset temperature of about 160°C to about 220°C. In some embodiments, the average particle size of the expandable graphite is about 0.01 micron (pm) to about 10,000 pm. In some embodiments the average particle size of the expandable graphite is about 0.1 pm to about 5,000 pm or about 0.1 pm to about 1 ,000 pm. In some embodiments, the expandable graphite comprises neutral flakes that are 100 mesh or larger. In some embodiments, the expandable graphite has a neutral surface chemistry. Expandable graphite is commercially available from several sources, for instance, from Neograph Solutions (Lakewood, Ohio, United States of America, formally part of GrafTech International), Asbury Carbons (Asbury, New Jersey, United States of America), and Nyacol Nano Technologies, Inc. (Ashland, Massachusetts, United States of America). In some embodiments, the expandable graphite can be present in about 1 weight % to about 20 weight % based on the total weight of the curable IFR coating composition. In some embodiments, the expandable graphite can be present in about 1 weight % to about 10 weight % based on the total weight of the curable IFR coating composition.

In some embodiments, the FR additives (including any expandable graphite) are present in about 10 weight % to about 60 weight % of the curable IFR coating composition based on the total weight of the curable IFR coating composition. In some embodiments, the FR additives are present in about 20 weight % to about 60% weight % of the IFR coating composition based on the total weight of the curable composition. In some embodiments, the FR additives are present in about 20 weight % to about 40 weight %. In some embodiments, the FR additives are present in about 20 weight % to about 30 weight %.

In some embodiments, the curable IFR coating composition further comprises an adhesion promoter. Any suitable adhesion promoter or combination of adhesion promoters can be used. Suitable adhesion promoters include compounds having a group that can participate in the crosslinking/curing reaction of the components of the coating composition (e.g., the fluoropolymer and/or the FR additives) and a group that adheres to metal or another type of substrate that the coating composition can be used to protect. Groups that adhere to metal include hydroxy, acid (e.g., carboxylic, phosphoric or sulphonic acid), phosphates, zirconate, titanate and silane. Thus, adhesion promoters include, but are not limited to, (meth)acrylate functionalized carboxylic or phosphoric acids. Exemplary suitable adhesion promoters include hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, di- or trialkoxy zirconates or titanates, vinyl trimethoxysilane, mercaptopropyltrimethoxysilane, isocyanotoalkyltrialkoxy-silanes, methacrylylalkyl trialkoxysilanes, amino alkyltrialkoxysilanes and epoxy alkyltrialkoxy silanes. Another suitable silane adhesion promoter is vinyltrimethoxysilane. Mercaptosilanes, such as mercaptopropyltrimethoxysilane and mercaptopropyltriethoxysilane, can also be used.

In some embodiments, the adhesion promoter comprises or consists of an epoxy silane. Examples of suitable epoxy functional silane compounds include, but are not limited to, 3-glycidoxypropyltrimethoxysilane, 3- glycidoxypropyldimethoxysilane, 3-glycidoxypropyldimethylmethoxysilane, 2- (3,4-epoxycyclohexyl)-ethyltrimethoxysilane and the like. Such compounds are generally available commercially (for example, 3-glycidoxypropyl- trimethoxysilane is available from Aldrich Chemical (part of MillaporeSigma, St. Louis, Missouri, United States of America) and 3- glycidoxypropyltrimethoxysilane and beta-(3,4- epoxycyclohexyl)ethyltrimethoxy-silane from Gelest Inc. (Morrisville, Pennsylvania, United States of America)). In some embodiments, the epoxy silane is gamma-glycidoxypropyltrimethoxy silane (sold under the tradename SILQUEST A-187™, Momentive Performance Materials, Waterford, New York, United States of America). In some embodiments, the adhesion promoter is present in about 1 weight % to about 20 weight % of the IFR coating composition based on the total weight of the curable composition. In some embodiments, the adhesion promoter is present in about 5 weight % to about 20 weight % of the IFR coating composition based on the total weight of the curable composition. In some embodiments, the adhesion promoter is present in about 5 weight % to about 10 weight % or in about 5 weight % to about 8 weight %. In some embodiments, the adhesion promoter not only acts as an adhesion promoter but also helps to consolidate char and avoid formation of a fluffy char layer.

In some embodiments, the curable IFR coating composition can include one or more additional additives, such as, but not limited to, surfactants, rheology modifiers, colorants, defoamers, etc. For example, the surfactant can be a non-ionic surfactant. Non-limiting examples of suitable nonionic surfactants include poloxamers and block copolymers (e.g., surfactants sold under the tradename PLURONICS™ (BASF Corporation, North Mount Olive, New Jersey, United States of America), fatty alcohols (e.g., 1-octanol, 1-dodecanol), ethoxylated fatty alcohols, alkylphenol ethoxylates, poly(oxyethylene)-alkyl ethers (e.g., TRITON X-100 or compositions sold under the tradename BRIJ™ (Croda Americas LLC, Wilmington, Delaware, United States of America), glycerol alkyl esters (e.g., glycerol laurate), polyoxyethylene glycol sorbitan alkyl esters (e.g., polysorbate), and silicone- based surfactants (e.g., silicone polyoxyalkylene copolymer). In some embodiments, the surfactant comprises or consists of a poly(oxyethylene)- alkyl ether, such as poly(oxyethylene) oleyl ether. In some embodiments, the defoamer is a non-silicon defoamer. In some embodiments, the rheology modifier comprises a urea-based compound. The additional additives are typically present in relatively minor amounts, such as up to about 5 weight % each based on the total weight of the curable IFR coating composition. In some embodiments, the total weight of all of the additional additives is about 5 weight % or less based on the total weight of the curable IFR coating composition.

In some embodiments, the curable IFR coating composition includes a carrier fluid. In some embodiments, the carrier fluid comprises or consists of water. In some embodiments, the carrier fluid is present at about 35 weight % to about 55 weight % based on the total weight of the curable IFR coating composition. In some embodiments, the carrier fluid is present at about 40 weight % to about 45 weight % based on the total weight of the curable IFR coating composition. The presently disclosed curable IFR coating composition can comprise no VOCs. Thus, in some embodiments, the curable IFR coating composition is free of VOCs.

The presently disclosed subject matter also provides substrates coated with the presently disclosed IFR coating compositions. Thus, in some embodiments, the presently disclosed subject matter provides a substrate comprising at least one surface coated with a cured layer of a curable IFR coating composition as described hereinabove (i.e., a composition comprising a fluoropolymer (e.g., a FKM), a curative, and a FR additive). In some embodiments, the FR additive comprises expandable graphite. In some embodiments, each surface (i.e., outer surface) of the substrate is coated with a layer comprising the cured IRF coating composition. In some embodiments, only one surface (e.g., one side of a substrate sheet or panel) is coated with the cured IFR coating composition. In some embodiments, the substrate comprises metal (e.g., steel or aluminum). In some embodiments, the substrate comprises aluminum. In some embodiments, the substrate is a wood composite material. In some embodiments, the substrate is a battery cell or pack component. In some embodiments, the substrate is a material used in a building application (e.g., a house, office building, or civil infrastructure). In some embodiments, the layer comprising the cured IFR coating has a thickness of at least about 200 microns (e.g., at least about 200, about 250, about 300, about 350, or about 400 microns). In some embodiments, the layer comprising cured IFR coating has a thickness between about 200 microns and about 400 microns.

In some embodiments, the presently disclosed subject matter provides a method of providing thermal protection to a substrate. In some embodiments, the method comprises: (a) applying a curable IFR coating composition as described hereinabove (i.e., a composition comprising a fluoropolymer (e.g., a FKM), a curative, and a FR additive) to at least one surface of a substrate; and (b) drying and curing the curable IFR coating composition to provide a cured layer of the IFR coating composition disposed on the at least one surface of the substrate. In some embodiments, the curable IFR coating composition (and thus, the cured layer) comprises expandable graphite. Any suitable application method can be used. For example, as the curable IFR coating composition can be a water-based composition, it can be applied to the surface of the substrate via spray coating, roll coating, or dip coating. In some embodiments, the applying is performed via spraying. In some embodiments, the applying is performed such that the cured layer of the IFR coating composition has a thickness of at least about 200 pm. In some embodiments, the thickness of the cured layer is between about 200 pm and about 400 pm.

In some embodiments, the substrate comprises aluminum or another metal (e.g., steel). In some embodiments, the substrate comprises fiber- reinforced plastic (FRP), bulk molding compound (BMC) or wood composites (e.g., OSB). In some embodiments, the substrate is heated immediately prior to application of the IFR coating composition. For example, in some embodiments, the substrate can be pre-heated to about 60°C for about 5 minutes to about 10 minutes prior to application of the coating composition.

The drying and curing is performed under conditions suitable for evaporating any carrier fluid (e.g., water) present in the curable IFR composition and that results in cross-linking of the fluoropolymer and/or other components of the coating composition. For example, in some embodiments, the coated substrate is dried at about 80°C for a period of time (e.g., about 30 minutes to about 60 minutes). Then, the coated substrate can be cured gradually, for instance, by heating to about 100°C for a period of time (e.g., about 30 minutes) and then by heating to a higher temperature, such as about 120°C, for a further period of time (e.g. about 1 hour). The heating and/or curing can be performed in an oven, such as an air circulation oven.

In some embodiments, the coated substrate is a substantially planar substrate, such as a sheet or board, and is coated on one side of the planar substrate. In some embodiments, the opposite side (i.e., the uncoated side of the substrate) can maintain a temperature below about 300°C when the coated substrate is exposed to flame for at least about 14 minutes. In some embodiments, the substrate is coated on one or more sides and an internal temperature of the substrate can be maintained below 300°C when the coated substrate is exposed to flame for at least about 14 minutes. EXAMPLES

The following examples are included to further illustrate various embodiments of the presently disclosed subject matter. However, those of ordinary skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the presently disclosed subject matter.

EXAMPLE 1 IFR Formulation

Table 1 , below, summarizes an exemplary curable IFR coating formulation which contains:

1. An FKM latex (i.e., a FKM latex sold under the tradename TECNOFLON™ TN (Solvay Specialty Polymers Italy S.p.A., Milan, Italy) with dicinnamylidene hexamethylenediamine (also known as “DIAK 3”) (from Chemours, Wilmington, Delaware, United States of America) as a curative and magnesium oxide (from Akrochem Corporation, Akron, Ohio, United States of America) as a hydrogen/fluoride scavenger.

2. An epoxy silane as adhesion promotor (i.e., gamma- glycidoxypropyltrimethoxy silane (sold under the tradename SILQUEST A- 187™, Momentive Performance Materials, Waterford, New York, United States of America); and

3. Flame retardant additives: a. Poly(piperazinyl, morpholinyl, triazine), ammonium polyphosphate, melamine, di-pentaerythritol; and b. Expandable graphite. Table 1. IRF coating composition. More particularly, the surfactant in the formulation described in Table 1 is that sold under the tradename BIRJ™ O20-SO-AP (Croda Americas LLC, Wilmington, Delaware, United States of America); the rheology modifier is that sold under the tradename BYK™-7420-ES (BYK-Chemie, GmbH, Wesel, Germany); the defoamer is sold under the product name Knockdown 155 (Palmer Holland, North Olmsted, Ohio, United States of America); Triazine 765 MCA PPM is commercially available from MCA Technologies GmbH, Biel- Benken, Switzerland); Exolit AP462 is commercially available from Clariant AG (Muttenz, Switzerland) and the expandable graphite is Graftech 210-140N from Neograph Solutions (Lakewood, Ohio, United States of America).

EXAMPLE 2

IFR COATING MORPHOLOGY

The curable IFR coating formulation described in Example 1 was applied at thicknesses up to 600 microns by spraying on a preheated Al substrate followed by drying at 80°C for 1h and curing gradually at 100°C for 30 min and 120°C for 1 hour in air circulation oven to give a film as shown in Figure 1 , panel A. Scanning electron microscopy (SEM) images were taken for a cross-section of the FR coating on the substrate to monitor elemental mapping, which reflects the distribution of the ingredients within the coating film or any sign of phase separation. Panels B, C, D, and E of Figure 1 show the homogenous distribution of carbon, fluorine, silicon, and phosphorus, respectively. Without being bound to any one theory, it is believed that this homogenous distribution of elements contributes to the consistent fire- resistance performance of the coating.

EXAMPLE 3

IFR COATING ADHESION

The adhesion of the coated film to an Al substrate was tested using a standard ASTM D3359 cross-hatch test. First, a cross-hatch was cut in the film on a substrate with a crosshatch cutter. A cross-hatch tape was applied to the area and pulled off. The cross-hatch test area was then compared with the ASTM adhesion standards. Figure 2 shows no film pull-off, representing ASTM class 5B as the highest level of adhesion. Also, a 45° bending test showed no sign of cracks, suggesting excellent flexibility of the IFR coating. Without being bound to any one theory, the flexibility is believed to be due to the high elongation at break of the FKM elastomer used in the coating formulation. EXAMPLE 4 FLAME TEST

A flame test was applied in which the coating-side of a coated aluminum panel was exposed to a flame source of 1100°C for 10 minutes while measuring the backside temperature. The experimental set up for the flame tests is shown in Figure 3. The torch tip of the torch at the left of Figure 3 is 10 mm offset from the coated aluminum panel as indicated by the ruler and the coated aluminum panel is positioned 40 mm higher than the bottom edge of the torch tip. A desired aim of the flame test is to maintain the backside temperature of the aluminum panel under 300°C. Various dry film thinness (DFT), ranging from 100-400 microns, were applied, cured, and tested. Coatings with DFTs over 200 microns passed the test successfully as shown in Figure 4. The coating system expanded up to 30-40 times of the original film thinness after exposure to the flame test, creating a condensed and thick char layer, which is held in place and acts as a thermal barrier to protect the substrate. See Figures 5A and 5B.

It will be understood that various details of the presently disclosed subject matter can be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.