Flame retardant coating

Abstract

A flame retardant coating for the outside of a building contains latex binder, inorganic filler and expandable graphite. The performance of the coating is improved if the aqueous coating formulation also contains (i) an isocyanate crosslinker; and (ii) less than 5 weight percent borate, based on the weight of solid components in the composition and excluding solvent.

Description

[0001] FLAME RETARDANT COATING

[0002] FIELD

[0003] This invention relates to the field of architectural coatings.

[0004] INTRODUCTION

[0005] Architectural coatings are paints, varnishes and other coatings that are applied to the exterior of buildings. Architectural coating compositions are frequently aqueous to minimize the emission of volatile organic compounds and contain:

[0006] • A water-insoluble filler. Many fillers contain inorganic powders such as silica, calcium carbonate, aluminum trihydrate, aluminosilicates and / or inorganic pigments.

[0007] • A binder that adheres the filler to an exterior substrate. The binder is typically a film-forming polymer that is insoluble but forms an emulsion in water, such as an acrylic polymer or vinyl ester copolymer.

[0008] • Optionally other additives such as emulsifiers, stabilizers, thickeners, surfactants, hydrophobic additives, levelling and coalescing agents, antioxidants, UV stabilizers, inorganic pigments or other additives.

[0009] • An aqueous solvent that suspends the filler and binder and any other components of the coating. The term “solvent” does not imply that the filler or binder dissolve in the aqueous solvent. Typically, the filler and binder are insoluble in the aqueous solvent, but the filler is suspended in the solvent and the binder forms an aqueous emulsion.

[0010] The fillers, binders and other water-insoluble additives are referred to as “solid components” or “solids”. The quantity of aqueous solvent is typically high enough to fully wet the solid components and to provide a homogeneous coating composition whose viscosity is suitable to apply by ordinary means such as spraying, brushing, or rolling. The quantity of aqueous solvent is typically low enough that the aqueous coating composition can dry quickly to leave a solid coating.

[0011] Architectural coating compositions should have good weatherability. They must withstand years of exposure to sun and rain and the expansion and contraction caused by temperature and humidity changes.

[0012] In addition, it is desirable that the architectural coating improves the flame resistance of the substrate. Many building materials are combustible, such as wood, asphalt shingles, and organic polymers. Flame resistant coatings can improve the safety of buildings made with combustible materials. Ideally, the coating will provide improved flame resistance even in the presence of gaps in the coating that may result from expansion and contraction of the substrate.

[0013] It is desirable to identify architectural coating compositions that can improve the flame resistance of an exterior combustible substrate, especially in the presence of gaps in the coated surface. SUMMARY

[0014] One aspect of this invention is an aqueous coating composition comprising the following solid components dissolved or suspended in an aqueous solvent:

[0015] (a) Latex binder in a concentration sufficient to bond solid components to a substrate:

[0016] (b) Inorganic filler;

[0017] (c) Expandable graphite in a concentration sufficient to improve the flame resistance of a cured coating;

[0018] (d) Isocyanate crosslinker in a concentration sufficient to provide crosslinking; and

[0019] (e) Less than 5 weight percent borate, based on the weight of solid components in the composition and excluding solvent.

[0020] A second aspect of this invention is a process to coat a combustible substrate comprising the steps of (a) applying an aqueous coating composition to the combustible substrate, and (b) allowing the aqueous coating composition to dry, leaving a solid coating, wherein the aqueous coating composition is a composition described in the first aspect of the invention.

[0021] A third aspect of this invention is a coated substrate comprising a combustible substrate and a solid coating adhering directly or indirectly to the combustible substrate, wherein the solid coating comprises:

[0022] (a) Latex binder in a concentration sufficient to bond solid components to the substrate;

[0023] (b) Inorganic filler;

[0024] (c) Expandable graphite in a concentration sufficient to provide flame retardancy to the solid coating;

[0025] (d) Residue of a cured isocyanate crosslinker; and

[0026] (e) From 0 to 5 weight percent borate, based on the weight of the solid coating.

[0027] Aqueous coating compositions of this invention provide improved flame resistance, especially when the coated surface has small gaps, and avoid the use of large quantities of borate salts, which can diminish the weatherability of the coating.

[0028] DETAILED DESCRIPTION

[0029] Aqueous coating compositions of this invention and the resulting coatings contain conventional ingredients for architectural coatings, dissolved or suspended in an aqueous solvent: inorganic filler, an organic binder and optionally additives. Aqueous coating compositions of this invention also comprise expandable graphite and an isocyanate crosslinker dissolved or suspended in the aqueous solvent, and contain little to no borate.

[0030] Binder

[0031] The aqueous coating composition and the resulting coatings contain one or more binders, which are film-forming water-insoluble polymers, in a concentration effective to bind the filler and other components of the aqueous coating composition to a substrate. Binders and aqueous dispersions that contain binders are known, and they are commercially available. They are described in publications such as “Paints” published by Department of Chemistry, University of York at https: / / www.essentialchemicalindustry.org / materials-and-applications / paints.html (March 18, 2013). The concept of “film-forming” polymers is well understood. “Film-forming” means that a substance is capable of forming a film upon application to a solid surface. The ability of polymers and their solutions or emulsions to be film-forming is known and described in publications such as: P.A. Steward et al., “An Overview of Polymer Latex Film Formation and Properties”, 86 Advances in Colloid and Interface Science at 195-267 (2000) and J. Guerts et al., “New Waterborne Acrylic Binders for Zero VOC Paints”, 5 J. Coating Technol. Res. at 57-63 (2008). Film-forming polymer latexes generally contain colloidal particles that can coalesce as they dry. Coalescence can arise from individual particles compacting, deforming, adhering to each other and / or having polymer chains diffuse with each other. Commonly, the film-forming ability of polymers increases with lower molecular weight and / or lower Tg and decreases with higher molecular weight and / or higher Tg.

[0032] Examples of known binders include acrylic polymers, vinyl ester copolymers, alkyd polymers and epoxy polymers. Other examples include copolymers of styrene, butadiene and isoprene.

[0033] In some embodiments, the binder comprises an acrylic polymer. An acrylic polymer is a homopolymer or copolymer that contains repeating units derived from acrylic monomers. Exemplary acrylic monomers include acrylic acid, methacrylic acid, and their esters. Exemplary esters used in acrylic monomers include alkyl esters, such as alkyl groups containing from 1 to 8 carbon atoms or from 1 to 4 carbon atoms or in some cases methyl groups or ethyl groups. Examples of useful acrylic monomers are acrylic acid, methacrylic acid, butyl acrylate, 2-ethylhexyl acrylate, methyl acrylate, ethyl acrylate, methyl methacrylate and ethyl methacrylate.

[0034] Exemplary acrylic polymer binders may contain at least 70 weight percent repeating units derived from acrylic monomers, or at least 80 weight percent or at least 90 weight percent or at least 95 weight percent. Exemplary acrylic polymer binders may contain up to 100 percent repeating units derived from acrylic monomers. Some exemplary acrylic polymer binders are copolymers containing units derived from two or more acrylic monomers, such as copolymers of butyl acrylate with methyl methacrylate and / or methacrylic acid.

[0035] Some exemplary acrylic polymer binders may contain a crosslinking monomer. For example, acetoacetoxyethyl methacrylate (AAEM), which is sold under the trademark: Eastman AAEM, can be incorporated in the acrylic polymer chain and reacts with dihydrazides or diamines to form cross-links. Alternatively, hydroxyl-functional monomers such as (hydroxyethyl)methacrylate can provide pendant hydroxyl groups that react readily with the isocyanate cross-linker to form cross-links. The crosslinking monomer enables the acrylic polymer binder to crosslink as it sets when applied as a coating. In some embodiments, no more than 10 mole percent of repeating units in the acrylic polymer binder are derived from crosslinking acrylic monomers or no more than 5 mole percent or no more than 3 mole percent or no more than 2 mole percent or no more than 1 mole percent. In some embodiments, 0 mole percent of repeating units in the acrylic polymer binder are derived from crosslinking acrylic monomers or at least 0.1 mole percent or at least 0.5 mole percent or at least 1 mole percent. An example of a suitable acrylic polymer binder containing a crosslinking acrylic monomer is sold as RHOPLEX™ VSR 1065. Some exemplary acrylic polymer binders contain only acrylic monomers. Suitable binders are commercially available under the RHOPLEX™ trademark.

[0036] Some exemplary acrylic polymer binders may contain repeating units derived from non-acrylic ethylenically unsaturated comonomers, such as ethylene, vinyl esters (such as vinyl acetate) or styrene. In some embodiments, the comonomer is an ethylene monomer. Suitable binders are commercially available under the RO V ACE™ trademark.

[0037] In some embodiments, the binder comprises a vinyl ester copolymer. Vinyl ester copolymers contain repeating units derived from one or more vinyl ester monomers, such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1- methylvinyl acetate, vinyl pivalate, and vinyl esters of C-branched monocarboxylic acids having 9 to 11 carbon atoms, such as vinyl versatate or vinyl neodecanoate. In some embodiments, the vinyl ester copolymer comprises vinyl acetate. In some embodiments, the vinyl ester copolymer comprises both vinyl acetate and vinyl esters of higher molecular weight monocarboxylic acids, such as vinyl versatate or vinyl neodecanoate; examples of such polymers are commercially available under the trademark VeoVa.

[0038] In some embodiments, the vinyl ester copolymer further comprises repeating units derived from ethylene. For example, vinyl ester-ethylene copolymers may contain at least 1 weight percent repeating units derived from ethylene or at least 5 weight percent or at least 10 weight percent, and vinyl ester-ethylene copolymers may contain at most 60 weight percent repeating units derived from ethylene or at most 50 weight percent.

[0039] In some embodiments, the vinyl ester copolymer further comprises repeating units derived from an acrylic or methacrylic ester such as n-butyl acrylate or 2-ethyl hexyl acrylate. For example, vinyl ester-acrylic ester copolymers may contain 30 to 90 weight percent repeating units derived from vinyl ester, 1 to 60 weight percent repeating units derived from acrylic ester and 1 to 40 weight percent repeating units derived from ethylene. In some embodiments, the vinyl ester copolymer comprises no measurable quantity of acrylic or methacrylic ester.

[0040] Examples of suitable vinyl ester copolymers are described in US Patent 6,890,975. In some embodiments, the vinyl ester copolymer is a vinyl acetate-ethylene (VAE) copolymer. In some embodiments, the vinyl ester copolymer is a vinyl ester of versatic acid (VeoVa) copolymer.

[0041] Aryl groups can make the binder polymers susceptible to degradation by ultraviolet light. In some embodiments, monomers that contain aryl groups, such as styrene and phenyl esters of acrylic and methacrylic acid, are minimized in the binder polymer. In some embodiments, less than 50 mole percent of monomers in the binder polymer contain aryl groups, or less than 30 mole percent or less than 20 mole percent or less than 10 mole percent or less than 5 mole percent or less than 2 mole percent. In some embodiments, the binder polymer contains no detectable level of aryl-containing monomers, which is essentially 0 percent. On the other hand, styrene monomer can provide other useful qualities to the binder polymer, such as increased hydrophobicity. In some embodiments, the binder is a styrene-acrylic copolymer, such as UCAR™ DL 424.

[0042] The binder should be film-forming when the aqueous coating composition is applied to the substrate, and the coating may be subjected to thermal expansion and contraction due to changes in outdoor temperature. In some embodiments, the binder may be selected to have a glass transition temperature (Tg) of at most 40°C or 35°C or 25°C or 15°C or 5 or 0°C or -10°C or -20°C or -30°C. There is no minimum desirable Tg, but Tg below -60°C are seldom necessary.

[0043] The binder may also need to remain non-molten in temperatures that exterior coatings are commonly exposed to. In some embodiments, the binder has a melting temperature of at least 60°C or at least 75°C or at least 80°C or at least 95°C or at least 110°C. There is no maximum desirable melting temperature, but melting temperatures above 200°C are seldom necessary.

[0044] It is known to adjust the glass transition temperature and melting temperature of binder polymers by adjusting the selection and ratio of monomers. For example, in acrylic polymers certain monomers, such as methyl methacrylate, increase Tg and melting point of the resulting polymer, and other monomers, such as butyl acrylate, reduce Tg and melting point of the resulting polymer. In some embodiments, an acrylic polymer binder contains at least 7 weight percent units derived from methyl methacrylate or at least 10 weight percent or at least 12 weight percent. In some embodiments, an acrylic polymer binder contains at most 50 weight percent units derived from methyl methacrylate or at most 45 weight percent or at most 40 weight percent. In some embodiments, an acrylic polymer binder contains at least 50 weight percent units derived from butyl acrylate or at least 55 weight percent or at least 60 weight percent. In some embodiments, an acrylic polymer binder contains at most 93 weight percent units derived from butyl acrylate or at most 90 weight percent or at most 88 weight percent. Likewise, in vinyl acetate-ethylene copolymers, increasing levels of ethylene reduce Tg and melting point of the resulting polymer, whereas increasing levels of vinyl acetate increase Tg and melting point of the resulting polymer.

[0045] In some embodiments, the particles of binder have an average diameter of at least 50 nm or at least 100 nm or at least 200 nm. In some embodiments, the particles of binder have an average diameter of at most 700 nm or at most 500 nm or at most 400 nm.

[0046] In the aqueous coating composition, the binder particles are emulsified in an aqueous dispersion. This is often accomplished using emulsifiers, which are usually surfactants. In some embodiments, the emulsifiers are anionic surfactants, and in some embodiments the emulsifiers are non-ionic surfactants. Examples of suitable emulsifiers are sodium dodecylbenzenesulfonate and sodium lauryl sulfate. Examples of suitable emulsifiers are available under the DOWFAX™, TRITON™, TERGITOL™, ECOSURF™, and Polystep trademarks. Suitable acrylic polymer binders are commercially available from the Dow Chemical Company under the ROVACE™, RHOPLEX™, PRIMAL™ and UCAR™ trademarks. Other acrylic polymer binders can be made by emulsion polymerization of suitable monomers in the presence of suitable emulsifiers. Emulsion polymerization processes are well-known and described in numerous publications, such as Emulsion Polymerization of Acrylic Monomers, published by Rohm and Haas Company (1966); Lovell et al, Fundamentals of Emulsion Polymerization, 21 Biomacromolecules 4396-4441 (2020); and Juaregui, Thesis: Synthesis and Optimization of Emulsion Polymers, published by California Polytechnic State University, San Luis Obispo (2016).

[0047] Suitable vinyl ester polymer binders are commercially available in the Vinnipas trademark. Other vinyl ester copolymers can be produced by aqueous emulsion polymerization at temperatures below 100°C between 20 and 120 bar of ethylene pressure.

[0048] The binder concentration should be high enough to effectively adhere the solid components of the aqueous coating composition to the substrate after the aqueous coating composition has dried. In some embodiments, the aqueous coating composition contains at least 5 weight percent binder, based on solid components excluding solvent, or at least 8 weight percent or at least 10 weight percent or at least 12 weight percent or at least 15 weight percent or at least 18 weight percent. (The “solid components” are the binder, the inorganic filler, the expandable graphite, the isocyanate crosslinker and any other water-insoluble additives in the aqueous coating composition.) In some embodiments, the aqueous coating composition contains at most 50 weight percent binder, based on solid components excluding solvent, or at most 40 weight percent or at most 35 weight percent or at most 30 weight percent or at most 27 weight percent. For example, the aqueous coating composition may contain from 12 to 35 weight percent binder, based on solid components excluding solvent, or from 15 to 30 weight percent or from 18 to 27 weight percent.

[0049] In some embodiments, the aqueous coating composition contains at least 5 weight percent binder, based on all components including solvent, or at least 7 weight percent or at least 9 weight percent or at least 10 weight percent. In some embodiments, the aqueous coating composition contains at most 30 weight percent binder, based on all components including solvent, or at most 20 weight percent or at most 15 weight percent. For example, the aqueous coating composition may contain from 7 to 20 weight percent binder, based on all components including solvent, or from 10 to 15 weight percent.

[0050] In some embodiments, the binder is added to the aqueous coating composition as an aqueous emulsion. For clarity, the weight percentages listed above refer to the weight of the binder only, excluding the weight of water in the emulsion that contains the binder. In some embodiments, the aqueous emulsion contains at least 30 weight percent binder or at least 40 weight percent and at most 70 weight percent binder or at most 60 weight percent or at most 50 weight percent. In some embodiments, the aqueous emulsion contains at least 30 weight percent water or at least 40 weight percent or at least 50 weight percent and at most 70 weight percent water or at most 60 weight percent. Filler

[0051] The aqueous coating composition and the resulting coatings contain one or more fillers. Fillers are solid particles added to a coating to improve properties and / or reduce cost. Suitable inorganic fillers for coatings are known and commercially available. In some embodiments, the inorganic fillers include oxides, carbonates and sulfates of silicon, calcium, titanium and / or aluminum. Examples of common inorganic fillers include silica and silicates, titanium dioxide, calcium carbonate, quartz, dolomite, kaolin, barium sulfate, wollastonite, mica, talc, feldspar, diatomaceous earth, glass powder and microspheres and aluminum hydroxide. Fillers and their production and use are described in publications such as: Gysau, Fillers for Paints (3rd Ed.), Vincentz Network GmbH & Co. (2017); and “Functional Silicate Fillers: Basic Principles”, Painting & Coatings Industry (August 1, 2002) (https: / / www.pcimag.com / articles / 84909-functional-silicate-fillers-basic-principles).

[0052] In some embodiments, the filler may contain materials that are classified as flame retardants, such as aluminum hydroxide, which is also known as alumina trihydrate or ATH. Aluminum hydroxide is commercially available, including from J. M. Huber Corporation.

[0053] In some embodiments, the filler may include materials that arc classified as inorganic pigments or pigment extenders. High reflectance pigments have a white color and a high refractive index. See for example “Titanium Dioxide for Coatings”, publication C-10416-2(2 / 19) published by The Chemours Company FC. Examples of light colored inorganic pigments and pigment extenders that may be included in the filler include titanium dioxide, antimony white, titanium white, zinc white, barium sulfate, chrome yellow, cobalt yellow and titanium yellow. The filler may also comprise dark colored inorganic pigments, such as iron and copper oxides and carbon black.

[0054] It is known in the coatings arts to select fillers that have a particle size suitable for the aqueous coating composition. In some embodiments, the filler has a median particle size of at least 2 microns or at least 5 microns or at least 8 microns or at least 9 microns. In some embodiments, the filler has a median particle size of at most 2 mm or at most 1.5 mm or at most 1 mm or at most 800 microns or at most 600 microns. Within this broad range, some embodiments of “coarse” filler have a median particle size of at least 100 microns or at least 200 microns or at least 300 microns. Within the broad range, some embodiments of “fine” fillers have a median particle size of at most 100 microns or at most 80 microns or at most 50 microns or at most 30 microns.

[0055] The inorganic fillers are typically insoluble in water. Dispersing and wetting agents may help to maintain a stable slurry or dispersion. Suitable dispersing and wetting agents are known and commercially available, such as under the following trademarks: TAMOL™, Calgon, and Dispex. In some embodiments, the dispersant may be a polycarboxylate, a polyphosphate or a block copolymer having blocks that interact with water and blocks that interact with the filler / pigment. In some embodiments, a wetting agent is a surfactant such as a salt of a fatty acid, a poly (ethylene oxide) surfactant or a silicone-based surfactant. In some embodiments, the aqueous coating composition contains at least 10 weight percent filler, based on the weight of solid components excluding solvent, or at least 20 weight percent or at least 30 weight percent or at least 35 weight percent or at least 38 weight percent or at least 40 weight percent. In some embodiments, the aqueous coating composition contains at most 80 weight percent filler, based on the weight of solid components excluding solvent, or at most 70 weight percent or at most 65 weight percent or at most 60 weight percent or at most 55 weight percent or at most 50 weight percent. For example, the aqueous coating composition may contain from 35 to 70 weight percent filler, based on solid components excluding solvent, or from 40 to 60 weight percent.

[0056] In some embodiments, the aqueous coating composition contains at least 15 weight percent filler, based on all components including solvent, or at least 18 weight percent or at least 20 weight percent or at least 22 weight percent or at least 24 weight percent. In some embodiments, the aqueous coating composition contains at most 60 weight percent filler, based on all components including solvent, or most 50 weight percent or at most 45 weight percent or at most 84 weight percent or at most 40 weight percent or at most 38 weight percent. For example, the aqueous coating composition may contain from 18 to 50 weight percent filler, based on all components including solvent, or from 20 to 40 weight percent or from 22 to 38 weight percent.

[0057] Please note that the expandable graphite component acts like a filler in the aqueous coating composition and resulting coatings, so in some embodiments the quantity of other inorganic fillers may be lower than some common architectural coating compositions.

[0058] Expandable Graphite

[0059] The aqueous coating composition and the resulting coatings contain expandable graphite. Expandable graphite is a graphite that has expansion agents such as acids inserted or “intercalated” within the graphite layers. The graphite contains layers of carbon. Examples of expansion agents that can be inserted withing the layers include halogens, alkali metals, sulfates, nitrates, various organic acids, aluminum chloride, ferric chloride and other metal halides. In some embodiments, the expansion agent is a sulfate such as sulfuric acid. In some embodiments, the expandable graphite contains at least 80 weight percent carbon or at least 85 weight percent. In some embodiments, the expandable graphite contains at most 99 weight percent carbon or at most 98 weight percent.

[0060] The expandable graphite has particle sizes that are suitable for the aqueous coating composition. In some embodiments, the expandable graphite may have a median particle size of at least 1 microns or at least 10 microns or at least 50 microns or at least 80 microns or at least 100 microns. In some embodiments, the expandable graphite may have a median particle size of at most 2 mm or at most 1 mm or at most 700 microns or at most 500 microns or at most 300 microns or at most 200 microns or at most 150 microns.

[0061] Expandable graphite is commercially available, such as from ACS Material LLC and Qingdao Yanhai Carbon Material Co. It can also be made by treating flake graphite with an intercalation reagent that migrates between the graphene layers in a graphite crystal and remain as stable species. For example, flake graphite can be treated with a mixture of sulfuric acid and oxidizing agents which assist the sulfate to intercalate into the graphite layers.

[0062] The expandable graphite expands rapidly when heated. It is theorized, without intending to be bound, that the expansion agents form gases when exposed to high heat, and the gases press the graphite layers apart. In some embodiments, the expandable graphite begins to expand at temperatures of at least 100°C or at least 120°C or at least 140°C or at least 160°C or at least 180°C. In some embodiments, the expandable graphite begins to expand at temperatures of at most 350°C or at most 320°C or at most 300°C or at most 280°C or at most 260°C.

[0063] In some embodiments, the expandable graphite can achieve volume expansion of at least 2x its original volume or at least lOx or at least 20x or at least 50x or at least lOOx or at least 150x or at least 200x or at least 250x or at least 300x. There is no maximum desired expansion, but in some embodiments expansion more than 400x or 350x may be unnecessary.

[0064] In some embodiments, the expandable graphite can achieve an increase in surface area of at least 2x or at least 3x or at least 5x or at least 7x or at least 9x. There is no maximum desired increase in surface area, but in some embodiments an increase more than 20x or 15x may be unnecessary.

[0065] Expandable graphite is generally insoluble in water. It may be suspended or emulsified in the aqueous coating composition using known suspension and emulsifying agents, such as those described in the description of fillers.

[0066] The concentration of expandable graphite in the aqueous coating composition and the resulting coating should be high enough to improve the flame resistance of the resulting coating. In some embodiments, the aqueous coating composition contains at least 5 weight percent expandable graphite, based on solid components excluding solvent, or at least 8 weight percent or at least 10 weight percent or at least 12 weight percent or at least 18 weight percent or at least 25 weight percent. In some embodiments, the aqueous coating composition contains at most 50 weight percent expandable graphite, based on solid components excluding solvent, or at most 40 weight percent or at most 35 weight percent or at most 30 weight percent. For example, the aqueous coating composition may contain from 8 to 50 weight percent expandable graphite, based on solid components excluding solvent, or from 10 to 50 weight percent or from 10 to 40 weight percent or from 20 to 35weight percent.

[0067] In some embodiments, the aqueous coating composition contains at least 5 weight percent expandable graphite, based on all components including solvent, or at least 7 weight percent or at least 10 weight percent or at least 15 weight percent. In some embodiments, the aqueous coating composition contains at most 30 weight percent expandable graphite, based on all components including solvent, or at most 25 weight percent or at most 20 weight percent. For example, the aqueous coating composition may contain from 5 to 30 weight percent expandable graphite, based on all components including solvent, or from 7 to 20 weight percent.

[0068] Before it is exposed to expansion temperatures, the expandable graphite behaves much the same as a filler. In some embodiments, the expandable graphite, inorganic pigments and other fillers together make up at least 60 weight percent of the solid components in the aqueous coating composition excluding solvent, or at least 65 weight percent or at least 70 weight percent or at least 71 weight percent. In some embodiments, the expandable graphite, inorganic pigments and other fillers together make up at most 85 weight percent of the solid components in the aqueous coating composition excluding solvent, or at most 80 weight percent or at most 75 weight percent. For example, the aqueous coating composition may contain from 60 to 85 weight percent expandable graphite, inorganic pigments and other fillers, based on solid components excluding solvent, or from 65 to 80 weight percent or from 70 to 75 weight percent.

[0069] In some embodiments, the expandable graphite, inorganic pigments and other fillers together make up at least 20 weight percent of the aqueous coating composition including solvent, or at least 25 weight percent or at least 30 weight percent or at least 35 weight percent or at least 40 weight percent. In some embodiments, the expandable graphite, inorganic pigments and other fillers together make up at most 70 weight percent of the aqueous coating composition including solvent, or at most 65 weight percent or at most 60 weight percent or at most 50 weight percent. For example, the aqueous coating composition may contain from 20 to 70 weight percent expandable graphite, inorganic pigments and other fillers or from 30 to 60 weight percent or from 40 to 50 weight percent.

[0070] The quantity of fillers in coating formulations can also be described using pigment volume concentration (“PVC”), which is the volume of pigment and filler as a percent of the total volume of solid components in the coating formulation. PVC is calculated by Formula 1 : wherein Vp is the dry volume of pigment, Ve is the dry volume of filler and Vb dry is the dry volume of binder. In some embodiments, the PVC of aqueous coating composition (counting expandable graphite, inorganic pigments and other fillers as pigment) is at least 10 or at least 25 or at least 40 or at least 50 or at least 60. In some embodiments, the PVC of aqueous coating composition (counting expandable graphite, inorganic pigments and other fillers as pigment) is at most 90 or at most 80 PVC or at most 75 PVC.

[0071] Expandable graphite is known to improve flame retardancy of materials. See, for example, US Patent 10,487,218 B2, US Patent Application 2014 / 0295164 Al, and Kmetova et al., Effect of Expandable Graphite Flakes on the Flame Resistance of Oak Wood, 12 Coatings 1908 (2022), available

[0072] Other Additives

[0073] Aqueous coating compositions and the resulting coatings may optionally contain other additives that are appropriate for architectural coatings. Many such components are described in the publication Johan Bieleman (ed.), Additives for Coatings, published by WILEY-VCH Verlag GmbH (2000). Some examples of common additives are listed below. All of the additives listed below are commercially available. The aqueous coating composition may optionally contain thickeners to make it easier to handle and apply. Examples of thickeners include inorganic materials, such as certain clays, and polymer thickeners, such as certain cellulose derivatives, starches, and acrylic polymers.

[0074] The aqueous coating composition may optionally contain surfactants for a number of purposes. Some surfactants are emulsifiers, wetting agents and dispersants, which help insoluble components to enter and remain in an emulsion or dispersion in the aqueous solvent. Some surfactants are antifoaming agents. Some surfactants can promote adhesion of the binder to the substrate.

[0075] The aqueous coating composition may optionally contain hydrophobic additives to improve its ability to resist water infiltration. Examples of hydrophobic components may include waxes and polymers, such as polypropylene.

[0076] The aqueous coating composition may optionally contain levelling and coalescing agents to provide complete coverage and a smooth surface on a substrate. Examples of levelling additives include certain polyacrylate polymers, which have a low glass-transition temperature such as 20°C or lower. Coalescing agents promote interaction of binder molecules as the coating dries on the substrate, to form a solid homogeneous film that docs not rcdissolvc when subjected to new water. Examples of coalescing agents include:

[0077] • certain branched and cyclic paraffins,

[0078] • certain esters such as 3-hydroxy-2,2,4-trimethylpentyl isobutyrate (TPiB), diesters of adipic acid (ADE), dimethyl phthalate (DMP), 2-hydroxypropyl ethylhexanoate (HPE) and benzyl benzoate, and

[0079] • certain ether alcohols such as ethylene glycol butyl ether, propylene glycol butyl ether, dipropylene glycol butyl ether (DPB) and propylene and ethylene glycol phenyl ether (PPH and EPH)

[0080] The aqueous coating composition may optionally contain antioxidants. Antioxidants may include a primary antioxidant, such as certain amines or sterically -hindered phenols, and / or a secondary antioxidant, such as certain organophosphates or thioesters.

[0081] The aqueous coating composition may optionally contain light and ultraviolet (UV) stabilizers. Examples of light and ultraviolet (UV) stabilizers may include:

[0082] • UV absorbers such as benzotriazoles and other compounds having coordinated double bonds; and

[0083] • Sterically hindered amines such as compounds containing a 2,2,6,6-tetramethylpiperidine group;

[0084] The aqueous coating composition may optionally contain antifouling additives, such as 4,5- dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), 2-n-octyl-4-isothiazolin-3-one (OIT) and zinc pyrithione (ZPT).

[0085] The aqueous coating composition may optionally contain dirt pickup resistance additives, such as benzophenone.

[0086] The aqueous coating composition may optionally contain a small amount of volatile organic solvent to help maintain all components dissolved or suspended until it is applied and dried.

[0087] In some embodiments, the other additives make up no more than 10 weight percent of the solid components in the coating composition (excluding solvent) or no more than 5 weight percent or no more than 3 weight percent or no more than 2 weight percent. In some embodiments, the other additives make up 0 weight percent of the solid components in the coating composition (excluding solvent) or at least 0.1 weight percent or at least 0.5 weight percent or at least 0.8 weight percent or at least 1 weight percent.

[0088] In some embodiments, the other additives make up no more than 5 weight percent of the coating composition including solvent or no more than 3 weight percent or no more than 2 weight percent or no more than 1 weight percent. In some embodiments, the other additives make up 0 weight percent of the coating composition including solvent, or at least 0.1 weight percent or at least 0.2 weight percent or at least 0.5 weight percent.

[0089] Isocyanate crosslinker

[0090] The aqueous compositions contain at least one isocyanate crosslinker in a concentration sufficient to provide crosslinking, and the resulting coatings contain the reaction product residue of the isocyanate crosslinkers.

[0091] The isocyanate crosslinkers contain on average more than one isocyanate group per molecule, linked by an organic moiety. In some embodiments, the isocyanate crosslinkers contain on average at least 1.5 isocyanate groups per molecule or at least 1.9 isocyanate groups per molecule or at least 2 isocyanate groups per molecule. In some embodiments, the isocyanate crosslinkers contain on average no more than 6 isocyanate groups per molecule or no more than 4 isocyanate groups per molecule or no more than 3 isocyanate groups per molecule or no more than 2.5 isocyanate groups per molecule or no more than 2 isocyanate groups per molecule.

[0092] The isocyanate groups in an isocyanate crosslinker are linked by an organic moiety (R1). The organic moiety may be aliphatic, aromatic or aliphatic-aromatic. In some embodiments, the organic moiety contains at least 4 carbon atoms or at least 6 carbon atoms. In some embodiments, the organic moiety contains at most 20 carbon atoms or at most 18 carbon atoms or at most 16 carbon atoms. In some embodiments, the organic moiety is a hydrocarbon. In some embodiments, aliphatic groups of the organic moiety are alkyl groups.

[0093] The isocyanate crosslinkers generally meet Formula 2

[0094] (2) R'-(NCO)Xwherein R1is an organic moiety as previously described and x is a number of isocyanate groups as previously described.

[0095] Examples of isocyanate crosslinkers include methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), methylene bis (4-cyclohcxylisocyanatc) (HMDI), naphthalene diisocyanatc (NDI), xylylcnc diisocyanatc, phenylene diisocyanate, substituted biphenyl diisocyanates, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate. In some embodiments, the isocyanate crosslinkers are selected from 4,4'-diphenylmethane diisocyanate (MDI), 2,4- or 2,6-toluene diisocyanate (TDI) and / or methylene bis (4- cyclohexylisocyanate) (HMDI). In some embodiments, the isocyanate crosslinker is 4,4’ diphenylmethane diisocyanate (MDI). In some embodiments, the isocyanate crosslinker is 2,4- or 2,6- toluene diisocyanate (TDI). In some embodiments, the isocyanate crosslinker is methylene bis (4- cyclohexylisocyanate) (HMDI).

[0096] In some embodiments, the isocyanate crosslinkers contain a single variety of isocyanate crosslinker. In some embodiments, the isocyanate crosslinkers contain a mixture of two or more varieties of isocyanate crosslinkers.

[0097] In some embodiments, the isocyanate crosslinkcr comprises a “polymeric isocyanate”. Polymeric isocyanates may be a polymer or an oligomer having on average more than 1 pendant isocyanate group per molecule. In some embodiments, the polymeric isocyanate crosslinker can be formed by reacting an excess of isocyanate monomer as previously described with a lesser amount of comonomer such as a polyol. In some embodiments, the polymeric isocyanate crosslinker has an isocyanate equivalent weight of at least 50 Da or at least 80 Da or at least 100 Da or at least 120 Da. In some embodiments, the polymeric isocyanate crosslinker has an isocyanate equivalent weight of at most 1000 Da or at most 500 Da or at most 300 Da or at most 200 Da.

[0098] Many isocyanate crosslinkers arc commercially available, such as under the PAPI™ and VORONATE™ trademarks. Others can be made by known processes, such as by phosgenation of diamines or by reacting a dicarboxylic acid with ammonia and hydrazoic acid.

[0099] In some embodiments, the isocyanate crosslinker comprises a water-dispersible isocyanate. Water-dispersible HDI crosslinkers and their emulsions are commercially available under the Bayhydur and Kowa trademarks.

[0100] The concentration of isocyanate crosslinker in the aqueous coating composition should be high enough to provide crosslinking among the components of the resulting coating. In some embodiments, the aqueous coating composition contains at least 0.5 weight percent isocyanate crosslinker, based on solid components excluding solvent, or at least 1 weight percent or at least 2 weight percent or at least 3 weight percent or at least 5 weight percent or at least 8 weight percent. In some embodiments, the aqueous coating composition contains at most 25 weight percent isocyanate crosslinker, based on solid components excluding solvent, or at most 20 weight percent or at most 15 weight percent or at most 12 weight percent or at most 10 weight percent. For example, the aqueous coating composition may contain from 1 to 20 weight percent isocyanate crosslinker, based on solid components excluding solvent, or from 3 to 15 weight percent or from 8 to 12 weight percent.

[0101] In some embodiments, the aqueous coating composition contains at least 0.1 weight percent isocyanate crosslinker, based on all components including solvent, or at least 0.5 weight percent or at least 1 weight percent or at least 2 weight percent. In some embodiments, the aqueous coating composition contains at most 15 weight percent isocyanate crosslinker, based on all components including solvent, or at most 10 weight percent or at most 7 weight percent. For example, the aqueous coating composition may contain from 5 to 30 weight percent isocyanate crosslinker, based on all components including solvent, or from 7 to 20 weight percent.

[0102] Isocyanate crosslinkers are often highly reactive. In some embodiments, the isocyanate crosslinker is not added to the aqueous coating composition until shortly before the aqueous coating composition is used. In some embodiments, the isocyanate crosslinker is added to the aqueous coating composition no more than 24 hours before the aqueous coating composition is used or no more than 12 hours or no more than 6 hours is used or no more than 4 hours or no more than 2 hours.

[0103] Aqueous Solvent

[0104] The aqueous coating composition contains an aqueous solvent. The aqueous solvent contains primarily water, but may contain a minor amount of other solvents that are miscible with water, such as ethanol. In some embodiments, the aqueous solvent contains at least 70 weight percent water or at least 80 weight percent water or at least 90 weight percent water or at least 95 weight percent water or at least 98 weight percent water. In some embodiments, the aqueous solvent may contain up to 100 percent water. (The weight percentages of water in the solvent are based on the weight of solvents, excluding solid components).

[0105] The aqueous coating composition has sufficient aqueous solvent to wet the solid components and form a homogeneous suspension that has a viscosity which makes it practical to apply. In many embodiments, its viscosity is low enough to apply evenly by brush, roller or spray and high enough to minimize running and dripping after the aqueous coating composition is applied. In some embodiments, the quantity of water is minimized in order to minimize the time needed for the aqueous coating composition to dry.

[0106] In some embodiments, the aqueous coating compositions contain at least 40 weight percent solid components or at least 45 weight percent or at least 50 weight percent or at least 55 weight percent or at least 60 weight percent. In some embodiments, the aqueous coating compositions contain at most 75 weight percent solid components or at most 70 weight percent or at most 65 weight percent. In some embodiments, the aqueous coating compositions contain at least 25 weight percent aqueous solvent or at least 30 weight percent or at least 35 weight percent. In some embodiments, the aqueous coating compositions contain at most 60 weight percent aqueous solvent or at most 55 weight percent or at most 50 weight percent or at most 45 weight percent or at most 40 weight percent.

[0107] Borate

[0108] The aqueous coating compositions and the resulting coatings contain less than 5 weight percent of borate. “Borate” means boric oxides, boric acids and boric acid salts. Examples of borates covered by this limit include sodium borate, zinc borate (ZB), disodium octaborate tetrahydrate (DOT), ammonium pentaborate, potassium pentaborate, borates of magnesium, potassium tetraborate, hydrated calcium borate hydroxide (colemanite), hydrated sodium calcium borate hydroxide (ulexite), boric oxide and boric acids.

[0109] In some embodiments, the aqueous coating compositions and the resulting coatings contain no more than 4 weight percent borate, based on solid components excluding solvent, or no more than 3 weight percent or no more than 2 weight percent or no more than 1 weight percent or no more than 0.5 weight percent. There is no minimum desired content of borate; borate may be at undetectable levels (essentially 0 weight percent).

[0110] Borates can reduce the weatherability of the resulting coating. In some embodiments, no borate is intentionally added to the aqueous coating composition or the resulting coatings.

[0111] Coating Composition

[0112] The aqueous coating composition is made by mixing the filler, binder, expandable graphite and other components in the aqueous solvent in the proportions previously described. As previously described, in some embodiments, the components other than the isocyanate crosslinker are mixed together first to form a storage-stable emulsion, and the isocyanate crosslinkcr is added to the storage stable emulsion to complete the aqueous coating composition shortly before the aqueous coating composition is used.

[0113] In some embodiments, the storage-stable emulsion is mixed in two stages, as described in European Patent EP 2 217 667 Bl. First, in a “grind” stage, the inorganic pigments and other fillers and optionally other components are mixed with water to fully wet and blend the solid components, fully disperse the solid components, and prevent them from re-agglomerating. Second, in a “let down” stage, the binder, expandable graphite and any remaining components are mixed in and blended to form a stable, homogeneous aqueous coating composition.

[0114] In some embodiments, the storage stable emulsion and / or the aqueous coating composition have a viscosity at 25°C of at least 70 KU or at least 80 KU or at least 85 KU or at least 90 KU. In some embodiments, the storage stable emulsion and / or the aqueous coating composition have a viscosity at 25°C of at most 150 KU or at most 145 KU or at most 141 KU or at most 135 KU or at most 130 KU or at most 125 KU or at most 120 KU.

[0115] Process and Coated Substrate

[0116] In the process of this invention, the aqueous coating composition is applied directly or indirectly onto a combustible substrate. In some embodiments, the combustible substrate comprises wood, such as a wooden plank, sheet, shake or stud, or a particle board, chipboard or plywood. In some embodiments, the substrate comprises other combustible materials, such as an asphalt shingle, a polymer membrane or a foamed polymer sheet or plank.

[0117] In some embodiments, the substrate is intended to be part of a building. In some embodiments, the substrate is intended to be directly exposed to weather, such as exterior panels, facing or roofing on a building. In some embodiments, the substrate is not intended to be directly exposed to weather but forms an underlayer on the building, such as an insulation, water-proofing or structural component on the building, or an interior surface.

[0118] In some embodiments, the aqueous coating composition is applied directly onto the combustible substrate. In some embodiments, the aqueous coating composition is applied onto an intervening layer that is adhered to the substrate. For example, a primer or tie layer may be applied to the substrate first, or a face sheet or membrane may be adhered to the substrate first.

[0119] The aqueous coating composition may be applied to the substrate by known means such as spraying, rolling, brushing or dipping. Application may be done before or after the substrate is fixed in position for its intended use. In most cases, the aqueous coating composition would be applied under dry conditions with a temperature high enough for the aqueous solvent to evaporate quickly leaving the dry coating behind. In some embodiments, the temperature will be at least 0°C or 5°C or 10°C or at least 15°C. Maximum temperature is not usually critical, but temperature is commonly below 50°C or 45°C or 40°C.

[0120] The aqueous coating composition is allowed to dry, leaving behind a solid dried coating on the substrate. Drying time may vary depending on many factors, such as the contents of the aqueous coating composition, temperature, humidity and air flow / wind. In some embodiments, at a temperature of 25°C and relative humidity of no more than 50 percent, the coating dries to the touch in no more than 24 hours or no more than 12 hours or no more than 6 hours or no more than 4 hours or no more than 2 hours. In some embodiments, at a temperature of 25°C and relative humidity of no more than 50 percent, the coating dries to the touch in at least 5 minutes or at least 10 minutes or at least 15 minutes or at least 20 minutes or at least 30 minutes.

[0121] The aqueous coating composition may be applied as a single coat, or two or more coats may be applied with each coat permitted to substantially dry before the next coat is applied.

[0122] The contents of the dry coating are essentially the same as the solid components of the aqueous coating composition in the same proportions as in the aqueous coating composition, except that the isocyanate crosslinker has usually reacted with other components in the aqueous coating composition to form crosslinks among the various components of the dried coating. The dry coating contains reaction products of the isocyanate crosslinker in about the same proportions that the crosslinker had in the aqueous coating composition. In some embodiments, the residual unreacted isocyanate crosslinker in the dry coating is undetectable (essentially 0 percent).

[0123] In some embodiments, the dry coating comprises no more than 5 weight percent water, or no more than 3 weight percent or no more than 1 weight percent or no more than 0.5 weight percent. There is no required content of water in the coating but in some cases, it may be impractical to remove solvent to a content below 0.01 weight percent.

[0124] In some embodiments, the average thickness of the coating is at least 10 mil (250 micron) or at least 20 mil (500 micron) or at least 25 mil (760 micron). In some embodiments, the average thickness of the coating is at most 120 mil (3000 micron) or 100 mil (2500 micron) or 75 mil (1900 micron) or 50 mil (1300 micron) or 45 mil (1200 micron).

[0125] In some embodiments, the coated substrate has a flame spread of no more than 12 ft or no more than 11 or no more than 10 ft or no more than 9 ft, when tested according to the Test Methods (30 minute extended test).

[0126] Test Methods

[0127] Unless stated otherwise, measurements listed in this application are made using the following test methods:

[0128] Cone Calorimetry: A thermocouple is taped to the center of the uncoated side of a coated substrate. The coated side of the substrate is exposed to 50 kW / m2of radiant energy using a cone calorimeter as described in the NIST publication at The temperature rise on the unexposed side is measured after 900s and 1800s of exposure. Lower measured temperature indicates a more efficient heat resistance.

[0129] Examples

[0130] The following examples illustrate specific embodiments of the invention, but do not limit the broadest scope of the invention. The materials in Table 1 are used for the Examples:

[0131] Table 1

[0132] * TDCC = The Dow Chemical Company Preparation of Coating Formulations:

[0133] Coatings formulations shown in Table 2 are mixed together as described below. Components listed in Table 2 under “Side A” are added to a container sequentially under continuous stirring by an overhead mixer, except Propylene Glycol and HMC are pre-mixed separately before adding to the mix. After all Side A components are added, the mixing is continued for 10 minutes to form storage stable emulsions. The resulting storage stable emulsions are stored in sealed containers. Note that comparative examples CE1-CE3 and inventive example IE 1 have extra binder added to maintain similar solids content to other examples.

[0134] Before applying the storage stable emulsions to a substrate, the components listed in Table 2 under “Side B” are added to the storage stable emulsions and mixed for 5 minutes using an overhead mixer.

[0135] Cone Calorimetry Testing:

[0136] Oriented Strand Board (OSB) blocks measuring 4 inch x 4 inch x 7 / 16 inch thick are cut from commercial OSB panels. The coating compositions for inventive examples IE1-IE5 and comparative examples CE1-CE3 are applied uniformly to cut OSB blocks using a draw down bar. The relevant coating composition is also applied to the edge of each OSB block with a brush. The samples are left to dry at ambient conditions overnight The dried samples are tested with the cone calorimetry test as described in the Test Methods. The temperature on the uncoated side of each test plaque is recorded at 900 and 1800 seconds and is recorded on Table 2. Table 2 shows that the inventive coatings have lower increase in temperature than similar comparative coatings.

[0137] Table 2

[0138] Flame Spread Testing:

[0139] Oriented Strand Board (OSB) panels of 2 ft x 8 ft x 7 / 16 inch thick are laid horizontally. The coating compositions in inventive example IE6 and comparative example CE4 are rolled onto the OSB panels using hand rollers. The coated panels are left to dry at ambient conditions overnight.

[0140] The coated panels are tested according to the 10 minute flame spread test (ASTM E84) and the extended 30 minute flame spread test (ASTM E2768), as listed in the Test Methods.

[0141] • In the case of comparative example CE4, three intact panels are placed end to end to cover the 2 ft by 24 ft tunnel.

[0142] • In the case of inventive example IE6, a gap is added to each panel before testing. Each coated 2 ft by 8 ft panel is cut along the length to obtain two 1 ft by 8 ft panels. Three pairs of the cut panels are placed in the flame testing tunnel so that each member of the pair is adjacent to the other member of the pair with a l / 8thgap running along the length and the pairs are placed end-to-end to cover the 24 foot length of the tunnel.

[0143] Test results are shown in Table 3. Table 3 shows that the inventive coating has less flame spread and smoke generation than a similar comparative coating, even when the inventive coating has a gap in the coating and the comparative coating does not.

[0144] Table 3

Claims

CLAIMS:

1. An aqueous coating composition comprising the following solid components dissolved or suspended in an aqueous solvent:(a) a latex binder in a concentration sufficient to bond solid components to a substrate;(b) inorganic filler;(c) a suspended expandable graphite in a concentration sufficient to improve the flame resistance of a cured coating;(d) an isocyanate crosslinker in a concentration sufficient to provide crosslinking; and(e) from 0 to 5 weight percent borate, based on the weight of solid components in the composition and excluding solvent.

2. The aqueous coating composition of Claim 1 wherein the latex binder comprises an acrylic polymer or vinyl ester copolymer having a glass transition temperature of no more than 30°C and is in a concentration from 30 to 70 weight percent based on the weight of solid components and excluding solvent.

3. The aqueous coating composition of Claim 1 which contains from 8 to 50 weight percent expandable graphite, based on the weight of solid components and excluding solvent.

4. The aqueous composition of Claim 3 wherein the expandable graphite has median particle size from 10 micron to 500 micron and expands in volume at least 10 times when subjected to a temperature up to 300°C.

5. The aqueous coating composition of Claim 1 which contains from 20 to 70 weight percent inorganic filler, based on the weight of solid components and excluding solvent.

6. The aqueous coating composition of Claim 5 wherein the filler comprises aluminum hydroxide.

7. The aqueous coating composition of Claim 1 which contains from 3 to 15 weight percent isocyanate cross-linker, based on the weight of solid components and excluding solvent.

8. The aqueous composition of Claim 7 wherein the isocyanate crosslinker comprises any one or more of a polymeric isocyanate, methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), methylene bis (4- cyclohexylisocyanate) (HMDI), naphthalene diisocyanate (NDI), xylylene diisocyanate, phenylene diisocyanate, substituted biphenyl diisocyanates, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate.

9. The aqueous composition of Claim 7 wherein the isocyanate crosslinker is water-dispersible.

10. The aqueous coating composition of Claim 1 which contains less than 1 weight percent borate, based on the weight of solid components and excluding solvent.

11. The aqueous coating composition of Claim 1 which further comprises an ultraviolet light stabilizer in a concentration of at least 0.1 weight percent, based on the weight of solid components and excluding solvent.

12. The aqueous coating composition of Claim 1 wherein:(a) the latex binder comprises an acrylic polymer or a vinyl ester copolymer having a glass-transition temperature of no more than 10°C in a concentration from 30 to 60 weight percent;(b) the expandable graphite is in a concentration from 10 to 50 weight percent;(c) the inorganic filler comprises any one or more of silica and silicates, titanium dioxide, calcium carbonate, quartz, dolomite, kaolin, barium sulfate, wollastonite, mica, talc, feldspar, diatomaceous earth, glass powder and microspheres, and aluminum hydroxide and is in a concentration from 20 to 70 weight percent;(d) the isocyanate crosslinker comprises any one or more of a polymeric isocyanate, methylenediphenyl diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), methylene bis (4-cyclohexylisocyanate) (HMDI), naphthalene diisocyanate (NDI), xylylene diisocyanate, phenylene diisocyanate, substituted biphenyl diisocyanates, dicyclohexylmethane diisocyanate, and hexamethylene diisocyanate and is in a concentration from 3 to 15 weight percent;(c) the composition further comprises at least 0.1 weight percent ultraviolet light stabilizer;(f) the concentration of borate is less than 1 weight percent; and(g) the quantities in (a) through (f) are based on the weight of solid components in the composition and excluding aqueous solvent, and wherein the aqueous composition comprises from 45 to 70 weight percent solid components and from 30 to 55 weight percent aqueous solvent.

13. A process to coat a combustible substrate comprising the steps of (a) applying an aqueous coating composition to the combustible substrate, and (b) allowing the aqueous coating composition to dry leaving a solid coating, wherein the aqueous coating composition is an aqueous coating composition of any one of Claims 1 to 12.

14. The process of Claim 13 wherein the combustible substrate is an exterior component of a building.

15. A coated substrate comprising a combustible substrate and a solid coating adhering directly or indirectly to the combustible substrate, wherein the solid coating comprises:(a) latex binder in a concentration sufficient to bond solid components to a substrate;(b) inorganic filler;(c) expandable graphite in a concentration sufficient to provide flame retardancy to the solid coating;(d) residue of a cured isocyanate crosslinker; and(e) from 0 to 5 weight percent borate, based on the weight of the solid coating.

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