AQUEOUS FIRE RETARDANT COMPOSITION AND AQUEOUS COATING COMPOSITION COMPRISING SAID FIRE RETARDANT COMPOSITION

Abstract

The invention relates to an aqueous fire-retardant composition comprising particles dispersed in an aqueous phase, wherein the particles comprise a brominated fire-retardant epoxy polymer and an organic polymer comprising ionic dispersing groups. The invention further relates to an aqueous fire-retardant coating composition comprising said fire-retardant composition and a substrate coated with a coating deposited from said coating composition.

Description

AQUEOUS FIRE RETARDANT COMPOSITION AND AQUEOUS COATING COMPOSITION COMPRISING SAID FIRE RETARDANT COMPOSITION Field of invention The present invention relates to an aqueous fire retardant composition, to an aqueous fire retardant coating composition comprising said fire retardant composition, and to a substrate coated with a coating deposited from said coating composition. Background of the invention Fire-retardant coatings have been developed to control fire by various means, including raising the combustion temperature, reducing the rate of combustion, reducing flame spread, and reducing smoke generation. For the commercial aviation industry, aircraft interior components are typically interleaved, comprising a core structural panel sandwiched between outer skins. Such interior components, including floors, side walls, panel covers, window frames, partitions, bulkheads, ceilings, and storage compartments, must be fire-resistant and emit minimal amounts of smoke and other toxic fumes during combustion. The coating thickness for aircraft interiors typically ranges from 50 to 100 microns due to weight restrictions. These weight restrictions limit the use of intumescent coatings, as these are only effective at large film thicknesses, generally greater than 200 microns. Fire resistance standards in the United States are established by the Federal Aviation Administration. For interior aircraft components, FAR 25.853 includes flammability requirements for materials used in many aircraft operated in the United States. Specifically, FAR 25.853 requires that the material's flame time not exceed fifteen seconds, a burn length not exceed six inches (15.24 cm), and a dripping flame not exceed three seconds. Developing effective flame-retardant coatings that meet the FAR heat release rate and have the desired aesthetics for decorative parts has been challenging. It is also desirable that coating compositions be formulated as water-transmitted compositions. Brominated epoxy polymers are known as fire retardants and have been proposed for water-based textiles and wood coatings. US 2018 / 298229 describes an aqueous fire retardant formulation comprising a brominated epoxy polymer that is micronized to an average particle size in the range of approximately 1 to 10 microns using milling techniques. The aqueous fire retardant formulation is used in transparent aqueous wood coatings. The subject matter requires fire-retardant aqueous compositions that can be used in aqueous coating compositions in quantities such that the fire resistance requirements are met, without affecting the mechanical, stain resistance and aesthetic properties of the coating. pzRcnn / zznz / E / viAi Brief description of the invention It has recently been discovered that brominated epoxy polymers can be incorporated into aqueous coating compositions in sufficient quantities if provided as an aqueous fire-retardant composition. This can be obtained by first providing an organic liquid phase in which both the brominated epoxy polymer and an organic polymer with ionic dispersing groups are dissolved, and then emulsifying the organic phase in water. This results in small particles dispersed in water. These particles contain the fire retardant (brominated epoxy polymer) and an organic polymer with dispersing groups, and their small size allows them to produce, when used in an aqueous coating composition, a coating with very good aesthetic properties, particularly gloss, even when used in large quantities. Accordingly, the invention provides, in a first aspect, an aqueous fire-retardant composition comprising particles dispersed in an aqueous phase, wherein the particles comprise: a fire-retardant brominated epoxy polymer; and an organic polymer comprising ionic dispersing groups. The aqueous fire retardant composition can be properly used in an aqueous coating composition, for example, as a mixture, in any suitable quantity. Accordingly, the invention provides in a second aspect an aqueous fire-retardant coating composition comprising the fire-retardant composition according to the first aspect of the invention. In a third aspect, the invention provides a substrate coated with a coating deposited from a coating composition according to the second aspect of the invention. Detailed description of the invention The fire-retardant composition according to the invention is an aqueous composition comprising particles dispersed in an aqueous phase. The particles comprise a brominated fire-retardant epoxy polymer and an organic polymer with ionic dispersing groups. Both the brominated fire-retardant epoxy polymer and the organic polymer with ionic dispersing groups are present in the same particle. Brominated epoxy polymers are known as fire retardants (also called flame retardants) and, for example, are described in US 2018 / 298229. The fire retardant brominated epoxy polymer in the composition according to the invention is preferably an end-terminated brominated epoxy polymer, more preferably a tribromophenol end-terminated brominated epoxy polymer, in particular a bis(2,4,6-tribromophenyl ether) tetrabromobisphenol A-epichlorohydrin polymer. The brominated epoxy polymer preferably has a weight average molecular weight in the range of 700 to 20,000 g / mol, more preferably from 700 to 3,000 g / mol. Brominated epoxy polymers terminated at the ends with tribromophenol are commercially available, for example, as TexFRon® 4002 (e.g., ICL Industrial Products).The brominated fire-retardant epoxy polymer can be a mixture of two or more brominated fire-retardant epoxy polymers. Reference hereto to molecular weight is to the molecular weight determined by gel permeation chromatography (GPC) analysis with tetrahydrofuran (THF) (+ 0.1% acetic acid) as eluent (1 mL / min) on a styrene-divinylbenzene column combination, using polystyrene standards for calibration. The organic polymer with ionic dispersing groups can be any suitable organic polymer, preferably a film-forming polymer. Examples of suitable organic polymers include polyacrylate, polyester, polyurethane, polyurea, polyimide, polyamide, or a hybrid of two or more of these. Preferably, the polymer is a polyacrylate, a polyurethane, or a polyurethane-urea hybrid. The reference herein to a polyacrylate is to a copolymer obtainable by radical polymerization of acrylate and / or methacrylate monomers, optionally with other copolymerizable vinyl monomers such as styrene monomers, substituted styrene monomers, or vinyl ethers or esters such as vinyl acetate. The reference herein to acrylate or methacrylate monomers is to monomers with acrylate or methacrylate functionality. Examples of (meth)acrylate monomers include acrylic acid, methacrylic acid, aliphatic and cycloaliphatic esters of acrylic acid or methacrylic acid, and hydroxyalkyl esters of acrylic acid or methacrylic acid. Ionic dispersion groups are groups that are ionic in water and thereby provide water dispersibility to the polymer. Ionic dispersion groups are well known in the field. Preferably, ionic dispersion groups are carboxyl groups, sulfonate groups, or phosphonate groups. Ionic dispersion groups are preferably covalently bonded to a carbon atom of the polymer. Preferably, the organic polymer has an organic polymer backbone and dangling ionic groups directly or indirectly covalently bonded to a carbon atom of the polymer backbone. If the ionic groups are indirectly bonded to a carbon atom of the polymer backbone, that group is bonded to a carbon atom of the polymer backbone by a divalent organic radical, more preferably a divalent hydrocarbon radical comprising one to six carbon atoms.More preferably, the ionic dispersing groups are carboxyl groups, even more preferably carboxyl groups directly covalently bonded to a carbon atom in the main structure of the polymer. The organic polymer may have any suitable number of ionic dispersing groups to provide water dispersibility. The number of ionic dispersing groups is preferably such that the dispersing polymer has an acid value in the range of 5 to 50 mg KOH / g of polymer, more preferably 10 to 45 mg KOH / g of polymer, and even more preferably 20 to 40 mg KOH / g of polymer. The reference hereto to the acid value is to the acid value determined in accordance with ISO 2114. If the organic polymer with ionic dispersing groups is a polyacrylate, the ionic dispersing groups can be suitably incorporated by copolymerizing acid comonomers such as acrylic acid, methacrylic acid, or lyaconic acid in the radical polymerization reaction. If the organic polymer with ionic dispersing groups is a condensation polymer such as, for example, a polyester, a polyurethane, or a polyurethane-urea hybrid, the ionic dispersing groups can be suitably incorporated into the polymer by using, as a comonomer in the polycondensation reaction, a polyol or polyamine, preferably a diol or diamine, with a dispersing group. Examples of such comonomers are dimethylolpropionic acid and 2-[(2-aminoethyl)amino]ethanesulfonate. Dimethylolpropionic acid is a particularly preferred comonomer for preparing condensation polymers with ionic dispersing groups. The aqueous fire retardant composition according to the invention can be suitably obtained by a process comprising: a) providing a solution of the fire retardant polymer and an organic dispersing polymer comprising ionic dispersing groups in an organic solvent; b) neutralizing at least part of the ionic dispersing groups to obtain a neutralized solution of the fire retardant polymer and the dispersing polymer; and c) emulsify in water the neutralized solution obtained in b) to obtain particles comprising the fire retardant polymer and the dispersing polymer dispersed in an aqueous phase. In (a), a solution of the brominated flame-retardant epoxy polymer and a dispersing polymer comprising ionic dispersing groups in an organic solvent is provided. The organic solvent can be any organic solvent or mixture of organic solvents in which both the brominated epoxy polymer and the dispersing polymer are dissolved at a temperature at which the neutralized solution emulsifies in (c), typically within a temperature range of 15 to 95 °C. Preferably, the organic solvent is an oxygenated organic solvent, such as, for example, an alcohol, glycol ether, glycol ester, alkyl acetate, ketone, ester, or glycol ether / ester, or a mixture of two or more thereof. More preferably, the solvent comprises a polyalkylene glycol dialkyl ether, and even more preferably, di(propylene glycol)dimethyl ether. The solution provided in (a) can be obtained in any suitable way, for example, by dissolving both the brominated flame-retardant epoxy polymer and the dispersing polymer in the same organic solvent, or by first preparing two different solutions, i.e., a solution of the brominated flame-retardant epoxy polymer in a first organic solvent and a solution of the dispersing polymer in a second organic solvent, and then combining the two solutions. The first and second organic solvents may be the same or different. Alternatively, the solution can be provided by preparing the dispersing polymer in the organic solvent and then dissolving the brominated epoxy polymer in the polymer solution.A dispersion polyacrylate can be prepared, for example, by the copolymerization of acrylic monomers including acrylic monomers with ionic groups such as (meth)acrylic acid or itaconic acid in a suitable organic solvent such as, for example, butyl acetate or methyl ethyl ketone. In the solution provided in a), both the brominated epoxy polymer and the dispersing polymer are dissolved in the organic solvent. Preferably, the two polymers are not linked to each other but rather by covalent bonds. In one embodiment, the dispersion polymer provided in step a) is a polyurethane and the organic solvent is a polyalkylene oxide dialkyl ether, more preferably dl(propylene glycol)dlmethyl ether. In another embodiment, the dispersing polymer provided in step a) is a polyacrylate and the organic solvent comprises a ketone or ester, for example, butyl acetate or methyl ethyl ketone. For effective emulsification in c), at least some of the ionic dispersing groups in the dispersing polymer are neutralized in b). Preferably at least 50%, more preferably at least 65%, even more preferably at least 90%, even more preferably at least 95%, particularly preferably 100% of the ionic dispersing groups are neutralized before emulsification in c). The neutralization of acidic ionic groups before emulsification is well known in the field and can be carried out in any suitable manner using common neutralizing agents, for example, sodium hydroxide, ammonia, an amine such as diethylamine or triethylamine, an amino alcohol such as dimethylaminoethanol or diisopropanolamine, or a morpholine or N-alkylmorpholine. In c), the neutralized solution of fire retardant polymer and dispersing polymer is emulsified in water to obtain particles comprising the fire retardant polymer and the dispersing polymer dispersed in an aqueous phase. The particles thus obtained are solid particles or viscous liquid droplets. The emulsification can be carried out by any suitable technique known in the field. Typically, water is added to the neutralized solution of fire retardant polymer and dispersing polymer under shearing conditions until phase inversion occurs. The emulsification can be carried out at any suitable temperature, preferably in the range of 15 to 95 °C, more preferably 35 to 80 °C. Throughout this specification, the term dispersed particles is used for both dispersed solid particles and emulsified liquid droplets that have a defined shape and volume under ambient conditions (293 K, 1 bar (100 kPa) (absolute)). The terms emulsion and dispersion, and the terms dispersed and emulsified, are used interchangeably herein. The particles obtained in c) are small, generally in the submicron range. Preferably, the dispersed particles have a volume mean diameter D [4:3] determined by laser diffraction in the range of 50 to 500 nm, more preferably 100 to 200 nm. The small particle size can also be obtained by other methods known to the skilled worker, for example, by nanomilling or hot melt extrusion. The skilled worker can select the appropriate size of milling beads or extrusion die to achieve the desired particle size. Optionally, additional organic solvent can be added in b) and / or oc). The dispersion obtained in c), optionally after removing at least part of the organic solvent, for example, by evaporation under reduced pressure, can be the aqueous fire-retardant composition according to the invention. In one embodiment, the dispersing polymer provided in a) is a polyacrylate, and the emulsion obtained in c), optionally after removing at least part of the organic solvent, is the aqueous fire-retardant composition according to the invention. rzRcnn / zznz / E / YiAi In another embodiment, the dispersing polymer provided in (a) comprises free isocyanate groups, and the process for obtaining the aqueous fire-retardant composition comprises a further step (d) in which the dispersing polymer in the particles obtained in (c) is chain-extended by reacting at least some of its free isocyanate groups with a diamine or triamine. The reaction between the free isocyanate groups of the polymer and the amine groups of the di- or triamine results in urea bonding and, in a higher molecular weight polymer, ionic dispersing groups. In this embodiment, the dispersing polymer provided in (a) is preferably a polyurethane or polyurethane-urea hybrid, more preferably a polyurethane. The chain-extended organic polymer obtained in step (d) is preferably a polyurethane-urea hybrid. It has been found that a polyurethane-urea hybrid, obtainable by chain extension of a polyurethane or polyurethane-urea hybrid with free isocyanate groups, is particularly suitable for use as the organic polymer with ionic dispersing groups in the fire-retardant composition according to the invention. It has been found that using a fire-retardant composition comprising this chain-extended polymer in a coating composition results in a coating film with very good mechanical properties and chemical resistance. In this document, the reference to free isocyanate groups refers to isocyanate groups that have unlocked isocyanate functionality. The content of free isocyanate groups in the dispersing polymer provided in a) is preferably in the range of 2 to 12 wt%, more preferably 3 to 10 wt%, based on the solid weight of the polymer. The isocyanate content can be suitably determined according to DIN EN ISO 11909 by reacting the polymer with excess dibutylamine and back-titrating with hydrochloric acid against bromophenol blue. Preferably, the dispersing polymer with free isocyanate groups is reacted with the diamine or triamine using a substoichiometric amount of reactive amine groups to avoid the presence of unreacted amine. Preferably, the diamine or triamine is added in such an amount that the amount of reactive amine groups is equivalent to 50 to 90% of the free isocyanate groups, more preferably 60 to 80%. Therefore, the chain-extended polymer obtained in step d) may comprise some free isocyanate groups, for example, up to 3 wt%, more preferably up to 2.5 wt%. Such free isocyanate groups will react with water to form additional urea groups and carbon dioxide. Suitable diamines or triamines for chain-extending functional isocyanate polymers are known in the art.Diamines may have two or three primary and / or secondary amine groups that are reactive with the free isocyanate groups in the dispersing polymer. Preferably, the diamine or triamine is an aliphatic diamine or triamine, more preferably an aliphatic diamine or triamine with two primary amine groups. The diamine preferably has up to 16 carbon atoms, more preferably in the range of 2 to 12 carbon atoms. Particularly preferred amines are ethylenediamine, isophorone-diamine, and diethylenediamine. The organic dispersed polymer provided in a) is preferably a polyurethane or urea polyurethane that can be obtained by condensation polymerization of one or more monomers with at least two isocyanate-reactive functional groups with a polyisocyanate, wherein one or more monomers with at least two isocyanate-reactive functional groups comprise a polyol or polyamine with an ionic dispersing group and a polycarbonate diol or a polyester diol, preferably a polycarbonate diol. The dispersing polymer provided in a) and present during the emulsification step c) preferably has a numerical average molecular weight in the range of 500 to 6,000 g / mol, more preferably from 1,000 to 4,000 g / mol. If the dispersing polymer is chain-extended in step d) to obtain the final organic polymer with ionic dispersing groups, the final organic polymer preferably has a numerical average molecular weight of at least 10,000 g / mol, more preferably in the range of 20,000 to 10,000,000 g / mol, and even more preferably in the range of 50,000 to 1,000,000 g / mol. The aqueous phase of the fire retardant composition comprises water as the main liquid, preferably at least 50%, more preferably at least 70% by weight, and even more preferably at least 80% by weight. The aqueous phase may comprise up to 95% by weight, or even up to 100% by weight, of water. It will be considered that some of the organic solvent used in the preparation of the fire retardant composition may be present in the aqueous phase, particularly if that organic solvent is an oxygenated organic solvent that is miscible with water. At least some of the organic solvent can be removed, for example, by distillation under reduced pressure, after step c) or d). The weight ratio of brominated flame-retardant epoxy polymer to organic polymer in the dispersed particles can be any suitable ratio. The desired ratio will depend on the final application of the fire-retardant composition. If the fire-retardant composition is to be applied in a coating composition that requires a large amount of fire retardant to meet the fire retardancy requirements, a higher ratio is desired. Submicron dispersed particles have been found to be obtainable with brominated epoxy to organic polymer ratios with ionic dispersing groups of up to 80:20, depending on the organic polymer used. Preferably, the weight ratio of the brominated flame-retardant epoxy polymer to the organic polymer in the dispersed particle ratio is in the range of 5:95 to 80:20, more preferably from 10:90 to 78:22. The aqueous fire retardant composition may have any suitable solids content, preferably in the range of 10 to 60% by weight, more preferably 20 to 55% by weight. Reference hereto to solids content is to the solids content determined in accordance with ISO 3251 with an initial sample mass of 1.0 g, a test duration of 60 minutes, at a temperature of 125 °C. The aqueous fire-retardant composition according to the invention can be suitable for use in an aqueous fire-retardant coating composition. The rzRcnn / zznz / E / YiAi fire-retardant composition is particularly suitable for coating compositions for decorative coatings, since the submicron particle size of the dispersed fire-retardant polymer results in coatings with very good aesthetic properties, particularly gloss. Therefore, the invention relates in a second aspect to an aqueous fire retardant coating composition comprising the aqueous fire retardant composition. The coating composition can be any type of aqueous coating composition that requires a fire retardant. The organic polymer with ionic dispersing groups can serve as a film-forming binder polymer in the coating composition. Preferably, the coating composition comprises one or more additional film-forming polymers. Reference herein to additional film-forming polymers is to film-forming polymers in addition to the organic polymer with ionic dispersing groups comprising the fire-retardant composition. Reference herein to a film-forming polymer (also called a binder polymer or resin) refers to a polymer that forms a film, i.e., forms a coating film when applied to a surface and then dries and / or cures. The coating composition is an aqueous coating composition. The particles of the fire-retardant composition and any additional film-forming polymer are dissolved or dispersed in an aqueous phase, preferably a dispersed one. The aqueous phase comprises water as the main liquid, preferably more than 50%, more preferably more than 70% by weight, and even more preferably more than 80% by weight. The aqueous phase may comprise up to 95% by weight, or even up to 100% by weight, of water. Examples of suitable additional film-forming polymers include polyacrylates, alkyds, polyesters, polyurethanes, polyureas, polyethers, and hybrids of two or more of these. Such film-forming polymers are known in the art. The coating composition may comprise the additional film-forming polymer(s) in any suitable amount, preferably in the range of 10 to 80% by weight of polymeric solids based on the total weight of the coating composition, more preferably 15 to 70% by weight, even more preferably 20 to 50% by weight. If the additional film-forming polymer(s) comprise a polymer with crosslinking functionality, the coating composition may comprise a crosslinking agent. Such a coating composition may be a one-component system where all reactive components are present in the same component and are stable to storage. Alternatively, such a coating composition may be a two-component system comprising a first component comprising the polymer with crosslinking functionality and a second component comprising the crosslinking agent. If the additional film-forming polymer(s) comprise an oxidative drying polymer, such as, for example, an alkyd resin, a fatty acid-modified polyacrylate, or another unsaturated film-forming polymer, the coating composition preferably comprises rzRcnn / zznz / E / YiAi plus a dryer (drier). The organic polymer with ionic dispersing groups in the fire retardant composition is preferably a film-forming polymer that can act as a binding polymer in the coating composition and will become part of the dried or cured coating, resulting in improved film properties. The coating composition may comprise one or more additional fire retardants, such as, for example, ammonium polyphosphate (APP), preferably encapsulated APP, silicone-containing fire retardants such as polyorganosylesquioxane (a compound of general chemical formula (RS₂O₃ / ₂)ₙ where R is a hydrogen atom or an alkyl, aryl, or alkoxy radical), aluminum trihydrate, or magnesium hydroxide. If one or more additional fire retardants comprise APP, it is preferably encapsulated APP, for example, in a melamine-formaldehyde layer (commercially available as Exolit® AP 462 from Clariant). The coating composition may also comprise an additional brominated epoxy polymer as an additional fire retardant, i.e., in addition to the brominated epoxy polymer incorporated into the fire retardant composition according to the first aspect of the invention.Generally, the additional brominated epoxy polymer will have a larger particle size than the brominated epoxy polymer in the fire-retardant composition according to the first aspect of the invention. To control the gloss level of the coating, the amount of additional brominated epoxy polymer is preferably less than 50% by weight, and more preferably less than 20% by weight, based on the total weight of the brominated epoxy polymer. In one embodiment, the coating composition comprises APP and polyorganosylesquioxane as additional fire retardants. The amount of brominated fire-retardant epoxy polymer in the coating composition can be any suitable amount. It should be noted that the desired amount of fire-retardant polymer will depend on the type of coating composition and its application. In a coating composition for interior aircraft components, for example, the amount of brominated fire-retardant epoxy polymer is generally in the range of 1 to 30% by weight, preferably 3 to 25% by weight (total solids by weight). The coating composition may comprise additional ingredients commonly used in coating compositions such as color and effect pigments, diluent pigments, coalescing solvents, and one or more additives such as, for example, surfactants, antifoaming agents, rheology modifiers, thickeners, leveling agents, and biocides. If the coating composition includes APP as an additional fire retardant, it is preferred that the coating composition contain microfibrillated cellulose as a rheology modifier. Microfibrillated cellulose is commercially available, for example, as Exilva Forte 10. The microfibrillated cellulose is preferably present in an amount in the range of 0.1% to 20% by weight, more preferably 0.5% to 10% by weight based on the total weight of the coating composition. The solids content of the coating composition is preferably in the range of 10 to 85% by weight, more preferably from 15 to 80% by weight, even more preferably from rzRcnn / zznz / E / YiAi to 75% by weight, even more preferably from 40 to 70% by weight. The coating composition is preferably formulated as a one-component (1K) coating composition. This means that all ingredients of the coating composition are stored in the same container after manufacturing and have a reasonable shelf life in this state. The coating composition can be used to apply a single coating directly to a substrate, or in a multi-layer system, particularly as a topcoat applied over a primer layer. A significant advantage of the present coating composition is that it can be applied in thin layers (<200 µm) while maintaining high performance as regulated by standard tests FAR 25.853 and ABD 0031. The coating thickness obtained from the coating composition according to the invention is preferably less than 200 µm, more preferably in the range of 20 to 100 µm. The coating composition can be further formulated with any gloss level, such as low or semi-gloss. The coating composition can be a clear coat or tinted in any color, without affecting other performance properties such as fire retardancy, heat retardancy, or water resistance. In a particularly preferred embodiment, the additional film-forming polymer(s) in the coating composition comprise a dispersed polyacrylate having a glass transition temperature (Tg) of at least 45 °C and a dispersed polyurethane based on a polycarbonate polyol. This coating composition has been found to be particularly suitable for aircraft interior applications, more specifically on a composite substrate. Polyacrylate has a glass transition temperature (Tg) of at least 45 °C, preferably at least 50 °C, and more preferably in the range of 55 to 90 °C. Without intending to limit itself to any particular theory, it is believed that the relatively high Tg of polyacrylate contributes to good stain resistance of the resulting coating. The reference herein to the glass transition temperature Tges is to the glass transition temperature as determined by modulated differential scanning calorimetry (MDSC) using a modulation amplitude of 1 °C, a modulation period of 40 seconds, and an underlying heating rate of 5 °C / min. Helium is used as a purge gas at a flow rate of 50 mL / min. Two runs are performed; the second immediately following the first, and the glass transition temperature Tges is the value determined in the second run. The polyacrylate preferably has a number-average molecular weight (Mn) and a weight-average molecular weight (Mw) of at least 100,000 g / mol, more preferably in the range of 500,000–5,000,000 g / mol. The high molecular weight makes it possible to formulate the coating composition as a one-component composition without the need for a crosslinker. The polyacrylate preferably has some acid functionality, i.e., it is prepared from a mixture of monomers containing a functional acid comonomer such as acrylic acid or methacrylic acid, in order to provide water dispersibility. More preferably, the polyacrylate has an acid number in the range of 1 to 20 mg KOH / g of polymer, even more preferably from 1 to 10 mg KOH / g of polymer, and even more preferably from 1 to 7 mg KOH / g of polymer. The polyacrylate preferably has a hydroxyl number of less than 5 mg KOH / g of polymer. In some embodiments, the (meth)acrylate polymer has no OH functionality and has a hydroxyl number of 0 mg KOH / g of polymer. The hydroxyl number can be measured according to ISO 4629-2. Suitable polyacrylates are commercially available as water dispersions. Examples of such dispersions (also called emulsions) include Setaqua® 6770, Setaqua® 6756, and Setaqua® 6766 from Allnex; Bayhydrol® A2427 from Covestro; Ottopol® KX-99 from Gellner Industrial, LLC; Joncryl® 540, Joncryl® 1532, and Joncryl® 1982 from BASF; and Picassian® AC-122, Picassian® AC-126, Picassian® AC-169, and Picassian® AC-176 from Stahl. Polyacrylate preferably has crosslinking functionality, more preferably self-crosslinking functionality. Commercial polyacrylate emulsions with self-crosslinking functionality include, for example, Setaqua® 6766 and Setaqua® 6770, both from Allnex, and Picassian® AC-122 and Picassian® AC-169 from Stahl. Polyacrylate is preferably present in an amount ranging from 5 to 50% by weight, more preferably from 8 to 40% by weight, of the total weight of the coating composition. Polyacrylate is preferably present in an amount of 30 to 85% by weight, more preferably from 50 to 80% by weight, of the total weight of one or more additional film-forming polymers. Polycarbonate diol-based polyurethane preferably has an average molecular weight (Mn) in the range of 2,000 to 100,000 g / mol, more preferably from 5,000 to 50,000 g / mol. Preferably, the polyurethane contains acid functionality to aid water dispersibility. The polyurethane preferably has an acid number in the range of 1 to 30 mg KOH / g of polymer, more preferably from 1 to 25 mg KOH / g of polymer. Polyurethane may have hydroxyl functionality. In some embodiments, polyurethane has little hydroxyl functionality and a hydroxyl number of 0 mg KOH / g of polymer. In other embodiments, polyurethane has hydroxyl functionality and may have any suitable hydroxyl number, preferably in the range of 1 to 120 mg KOH / g of polymer, more preferably 1 to 100 mg KOH / g of polymer. Suitable polymers are commercially available as water dispersions. Examples of such dispersions (also called emulsions) include Picassian® PU461, PU676, and Relea PU 655, all from Stahl; Bayhydrol® UH 2557 and Bayhydrol® UH 2593 / 1, both from Covestro; SILIKOPUR® 8081 from Evonik; and Hauthane L-2897 from Hauthaway. Polyurethane is preferably present in the coating composition in an amount ranging from 1 to 50% by weight, more preferably from 3 to 40% by weight, of the total weight of the coating composition. Polyurethane is preferably present in an amount of 15 to 70% by weight, more preferably from 20 to 50% by weight, of the total weight of one or more additional film-forming polymers. The weight ratio of polyacrylate to polyurethane is preferably in the range of 1:5 to 5:1, more preferably in the range of 1:1 to 4:1, depending on the solid weight of the polymers. In a final aspect, the invention relates to a substrate coated with a coating deposited from a coating composition according to the invention. The substrate can be any suitable substrate, such as, for example, a wood, polymer, composite, metal, or mineral substrate. The substrate can be a bare substrate on which the coating composition can be used as a primer or pore filler, or a pre-primed substrate on which the coating composition can be used as a top coating. The coating composition can be applied to substrates commonly used for interior applications in aircraft, trains, or other vehicles. The substrate is preferably selected from the group consisting of plastic, composite, and metallic substrates. Particularly preferred substrates include plastic substrates such as polycarbonate, polyetherimide (PEI), polyether ether ketone (PEEK), and polyphenylsulfone (PPSU); composite substrates such as honeycomb composites and laminates (e.g., polyvinyl fluoride laminates); and pre-treated metal (e.g., chrome-plated aluminum). An example of a honeycomb composite is DuPont's NOMEX® aramid paper, widely used in aircraft structural panels due to its high strength-to-weight ratio and resistance to fatigue failure. The coating composition is particularly useful for interior aircraft applications. The invention is further illustrated by the following non-limiting examples. Examples EXAMPLE 1 - Preparation of the aqueous fire retardant composition 1 (invention) A polyurethane dispersion in di(propylene glycol) dimethyl ether was prepared by reacting polycarbonate diol (Eternacoll UM-90; OH number 125 mg KOH / g), dimethylolpropionic acid, and poly(ethylene glycol) 600 with isophorone diisocyanate and 4,4'-methylene dicyclohexyl diisocyanate in di(propylene glycol) dimethyl ether as solvent in a 1.0 L double-walled reactor (under a nitrogen blanket, stirring at 200 rpm) at 100°C for 4 hours. The resulting polyurethane dispersion had a number mean molecular weight of 1,200 g / mol, a free isocyanate content of 7 wt%, an ethylene oxide content of 1 wt%, and an acid number of 29 mg KOH / g of polymer (determined according to ISO 2114). The polyurethane dispersion thus prepared in di(propylene glycol)dimethyl ether was cooled to 40 °C and combined with a 70 wt% solution of brominated epoxy polymer (TexFRon 4002) in di(propylene glycol)dimethyl ether to obtain a weight ratio of brominated epoxy polymer solids to polyurethane dispersion of 75 / 25. The solids content of the polymer blend was reduced to 69% by the addition of additional di(propylene glycol)dimethyl ether. All acidic carboxyl groups of the polyurethane were neutralized with triethylamine. The neutralized rzficnn / zznz / E / YiAi solution was then emulsified at 40 °C for 15 minutes by adding water while stirring at 600 rpm. To extend the polyurethane chain, a 33% (w / w) solution of ethylenediamine in water was added dropwise for 60 seconds. The resulting emulsion was then filtered through an 80 µm nylon filter. The chain-extended polyurethane-urea hybrid thus obtained had a free isocyanate content of 2.4 wt%. The resulting fire retardant composition comprised 50% by weight of solids, a fire retardant polymer weight ratio to polyurethane-urea hybrid of 75:25, and dispersed particles with a volume mean diameter D [4:3] determined by 128 nm laser diffraction. EXAMPLE 2 - Preparation of aqueous fire retardant compositions 2 to 5 (invention) Aqueous fire retardant compositions were prepared as described in EXAMPLE 1, except that the weight ratio of the fire retardant polymer (FR) to the dispersing polyurethane was varied. The volume mean diameter D [4:3] of the particles in the resulting fire retardant compositions was determined as described in EXAMPLE 1. The results are shown in Table 1. EXAMPLE 3 - Preparation of aqueous fire retardant composition 6 with polyacrylate (invention) To 58 grams of methyl amyl ketone, which was kept in a 1.0 L round-bottom flask at 145°C under a nitrogen blanket, 102 grams of isoboyl methacrylate (IBOMA), 67 grams of 2-hydroxyethyl methacrylate (HEMA), 19 grams of ethenyl ester of neonononanoic acid (VEOVA 9), 5 grams of acrylic acid, 5 grams of methacrylic acid, and 10 grams of tert-butyl-3,5,5-trimethylhexanoate peroxide (Trigonox 42S) were slowly added. The addition was carried out for 90 minutes with continuous stirring. After the addition was complete, the reaction mixture was cooled to 125°C, and an additional 1 gram of Trigonox 42S dissolved in 7 grams of methyl amyl ketone was added over 10 minutes. The reaction was then continued for 60 minutes at 125°C. Therefore, a polyacrylate solution with hanging dispersing groups in methyl amyl ketone was obtained. The polyacrylate had a number-average molecular weight of 3.550 g / mol, and an acid number of 33 mg KOH / g of polymer, determined according to ISO 2114. The polyacrylate thus prepared in methyl amyl ketone was cooled to 80 °C, 12 grams of triethylamine were added, and the resulting neutralized polyacrylate solution was mixed with 33 grams of a 70% by weight solution of brominated epoxy polymer (TexFRon 4002) in di(propylene glycol) dimethyl ether. The polymer mixture was then emulsified by adding 750 grams of water while stirring at 600 rpm at 80 °C for 30 minutes. The resulting emulsion was then cooled to 300 °C and filtered through an 80 µm nylon filter. The resulting fire retardant composition comprised 22 wt% solids, a weight ratio of fire retardant polymer to polyacrylate of 10:90, and dispersed particles with a volume mean diameter D [4:3] determined by 110 nm laser diffraction. rzRcnn / zznz / E / YiAi EXAMPLE 4 - Preparation of aqueous fire retardant compositions 7 and 8 (invention) Aqueous fire retardant compositions were prepared as described in EXAMPLE 3, except that the weight ratio of the fire retardant polymer to the polyacrylate was varied. The volume mean diameter D [4:3] of the particles in the resulting fire retardant compositions was determined as described in EXAMPLE 3. The results are shown in Table 1. rzRcnn / zznz / E / YiAi Table 1 - Fire retardant compositions organic polymer composition with ionic dispersant groups FR / organic polymer ratio (w / w) D [4:3] (nm) 1 Polyurethane-urea hybrid 75 / 25 128 2 Polyurethane-urea hybrid 70 / 30 117 3 Polyurethane-urea hybrid 60 / 40 106 4 Polyurethane-urea hybrid 40 / 60 74 5 Polyurethane-urea hybrid 10 / 90 77 6 polyacrylate 10 / 90 110 7 polyacrylate 20 / 80 160 8 polyacrylate 30 / 70 500 EXAMPLE 5 - Coating compositions with FR composition (invention) The coating compositions according to the invention were prepared by mixing 37.4 grams of fire retardant composition 1 prepared as described in EXAMPLE 1 with 100 grams of an aqueous white or black color fixative composition. The ingredients of the aqueous colorant compositions used are provided in Table 2. The resulting coating compositions are designated as compositions 5 (white) and 5 (black). EXAMPLE 6 - Coating compositions with TexFRon 4002 as supplied (comparison) A comparator aqueous dispersion comprising: 30.6% by weight of aqueous polyacrylate emulsion (Setaqua 6766; 40.7% solids) 15.0 7% by weight of aqueous polyurethane dispersion (Picassian PU 461; 35 7% solids) 0.09 7o by weight of ammonia 4.3 7th by weight of solvent (2.6 7th by weight of propoxy-propanol and 1.7 7th by weight of 1 (2-butoxy-1-methylethoxy)propan-2-ol) 0.05 7o by weight of antifoaming agents 70 by weight of brominated epoxy polymer (TexFRon 4002) was prepared by adding solid brominated epoxy polymer to the other ingredients in a dissolving mixer and mixing for 20 minutes at 2,000 rpm. The comparison coating compositions were prepared by adding 37.4 grams of the aqueous dispersion comprising brominated epoxy polymer to 100 grams of a white or black dye composition from Table 2. The resulting coating compositions are listed as compositions 6 (white) and 6 (black). Table 2 - Dye Compositions White dye Black dye Aqueous polyacrylate emulsion (40% solids) 3 34 32 Aqueous polyurethane dispersion (35% solids) 0 17 16 Ammonia (25% solution) 0.44 0.42 Defoaming agents 0.41 0.40 Solvent 0 4.7 4.5 Dispersant 0.22 0.20 Titanium dioxide 23 21 Carbon black - 5.7 Microfibrillated cellulose 1.8 1.8 Polymethylsilsesquioxane 9.3 9.3 Encapsulated APP 2.5 2.5 Water 2.2 2.2 Polyethylene wax dispersion 4.6 4.6 rzRcnn / zznz / E / YiAiaSetaqua 6766: Allnex self-crosslinking styrene-acrylic emulsion (40 wt. solids, adipic dihydrazide (ADH) crosslinking agent, MFFT 50SC, Tg 65SC, estimated Mn and Mw greater than 1,000,000 g / mol, acid number 4.4 mg KOH / g of resin)bPicassian PU 461: a polycarbonate diol-based polyurethane dispersion from Stahl (35 wt. solids, 14 wt. solvents, Tg 65 °C, Mn 7,380 g / mol, Mw 37,700 g / mol)cpropoxy-propanol and 1-(2-butoxy-1-methylethoxy)propan-2-ol EXAMPLE 7 - brightness The coating compositions prepared in EXAMPLES 5 and 6 were manually applied to a Lenata opacity chart using a threaded rod pull-out applicator (S = 0.5 mils (0.0127 mm)) to a wet film thickness of 150 µm and allowed to dry at 23 °C and 50% relative humidity. After one day, the dried coatings were analyzed for gloss. Gloss at a 60° angle was determined using a Byk Gardner tri-gloss gloss meter. Low gloss was defined as having a gloss in the range of 8–12 units at a 60° angle; medium gloss as having a gloss in the range of 12–30 units at 60°. Table 3 - Brightness at 60° Coating composition Fire retardant particle size Brightness at 60° (brightness units) 5 (white) - invention 128 nm 25 5 (black) - invention 128 nm 23 6 (white) - comparison 3.1 pm 9 6 (black) - comparison 3.1 pm 6 EXAMPLE 8 - Properties of spray coatings The diluted coating compositions were prepared for spraying by adding 10 parts by weight of water to the coating compositions prepared in EXAMPLES 5 (invention) and 6 (comparison). The diluted compositions were then sprayed using a DeVilbiss GTI PRO spray gun at 2 bar (200 kPa) and a 16 mm nozzle width onto a polycarbonate substrate (Lexan 9604 sheet). The coatings were allowed to dry at 23 °C and 50% relative humidity. After 1 day, the brightness at a 60° angle was determined using a Byk Gardner tri-gloss brightness meter. After two days of drying, stain resistance was determined by applying mustard and coffee stains to the dry coating and cleaning the coating after two hours with a mixture of water and Turkish Aircraft Cleaner 5948-DPM (e.g., Henkel) in a 20:1 wt / wt ratio. Staining was rated on a scale of 0–5, where 0 indicates no staining and 5 indicates severe staining. Adhesion to the substrate was determined after one day of drying (dry adhesion) and after two days of drying and one day of immersion in water (wet adhesion). Adhesion was determined in a cross-hatching test according to ISO 2409 using six scraping points spaced 2 mm apart. Adhesion was rated from 0 (excellent adhesion) to 5 (very poor adhesion) as follows: 0% of coating area removed, maximum 5% of coating area removed 5 to 15% of coating area removed 15 to 35% of coating area removed 15-35% of coating area removed more than 65% of coating area removed. Table 4 provides the dry film thickness of the applied coatings (after one day of drying), 60° gloss, stain resistance, and dry and wet adhesion. rzRcnn / zznz / E / YiAi Table 4 - Coating properties: gloss, stain resistance and adhesion DFT coating composition (pm) gloss at 60° (ub) corrosion resistance Adhesion mustard coffee dry wet 5 (white) - invention 20 22 0 2 0 0 5 (Black) - invention 22 19 0 0 0 0 6 (white) - comparison 30 8 0 4 0 2 6 (Black) - comparison 31 5 0 0 0 2 EXAMPLE 9 - rate of heat release The coating compositions prepared as described in EXAMPLE 8 were spray-applied as described in EXAMPLE 8 in raised film construction over a resin-impregnated laminate commonly used in aerospace interiors (Type 12 laminate as described in AIMS-04-08-000) and over an aluminum substrate (2024-T3 aluminum, bare, 0.5 mm). Heat release was tested using OSU burn equipment. The maximum heat release rate (PHHR) and the total amount of heat released (THR) are shown in Table 5. rzRcnn / zznz / E / YiAi Table 5 - OSU Heat Release Test Results Coating Composition Substrate Film Weight (g)* PHRR (kW / m2) THR (kW-min / m2) 5 black (inv.) composite 2.81 52.1 28.9 6 black (comp.) composite 2.78 51.3 28.3 5 black (inv.) aluminum 2.26 28.5 12.8 6 black (comp.) aluminum 2.29 28.3 11.2 on a 15.24 cm x 15.24 cm (6x6 inch) panel The results show that the heat release for the coating compositions according to the invention is comparable to the heat release of the comparison coating compositions with the same amount of fire retardant as a function of the solid weight of the additional film-forming polymers.

Claims

1. An aqueous fire retardant composition comprising particles dispersed in an aqueous phase, wherein the particles comprise: a brominated fire retardant epoxy polymer; and an organic polymer comprising ionic dispersing groups.

2. An aqueous fire retardant composition according to claim 1, wherein the brominated epoxy polymer is a brominated epoxy polymer terminated at the ends with tribromophenol.

3. An aqueous fire retardant composition according to claim 1 or 2, wherein the organic polymer comprising ionic dispersing groups is a film-forming polymer.

4. An aqueous fire retardant composition according to any of the preceding claims, wherein the organic polymer comprising ionic dispersing groups is a polyacrylate, a polyurethane, or a polyurethane-urea hybrid.

5. An aqueous fire retardant composition according to any of the preceding claims, wherein the particles comprising the fire retardant polymer and the organic polymer comprising ionic dispersing groups have a volume mean diameter D [4:3] determined by laser diffraction in the range of 50 to 500 nm, preferably 100 to 200 nm.

6. An aqueous fire retardant composition according to any of the preceding claims, wherein the weight ratio of the brominated fire retardant epoxy polymer and the organic polymer comprising ionic dispersing groups in the particles is in the range of 10:90 to 80:

20.

7. An aqueous fire retardant composition according to any of the preceding claims, wherein it can be obtained by a process comprising: a) providing a solution of the fire retardant polymer and an organic dispersing polymer comprising ionic dispersing groups in an organic solvent; b) neutralizing at least some of the ionic dispersing groups to obtain a neutralized solution of the fire retardant polymer and the dispersing polymer; and c) emulsifying the neutralized solution obtained in b) in water to obtain particles comprising the fire retardant polymer and the dispersing polymer dispersed in an aqueous phase.

8. An aqueous fire retardant composition according to claim 7, wherein the dispersing polymer provided in a) comprises free isocyanate end groups, and wherein the process further comprises: d) extending the chain of the dispersing polymer comprising free isocyanate end groups in the particles obtained in c) by reacting at least some of the free isocyanate end groups with a diamine or triamine. rzRcnn / zznz / E / YiAi 9. An aqueous fire retardant composition according to claim 7 or 8, wherein the organic dispersing polymer is a polyurethane or polyurethane-urea hybrid obtainable by condensation polymerization of one or more monomers with at least two isocyanate-reactive functional groups with a polyisocyanate, wherein one or more monomers with at least two isocyanate-reactive functional groups comprise a polyol or polyamine with an ionic dispersing group and a polycarbonate diol or a polyester diol, preferably a polycarbonate diol.

10. An aqueous fire retardant composition according to any of claims 7 to 9, wherein the organic solvent is an oxygenated organic solvent, preferably a polyalkylene oxide dialkyl ether, more preferably di(propylene glycol) dimethyl ether.

11. An aqueous fire retardant composition according to any of the preceding claims, wherein the ionic dispersing groups are carboxyl groups, sulfonate groups or phosphonate groups, preferably carboxyl groups.

12. An aqueous fire retardant coating composition comprising the fire retardant composition according to any of the preceding claims.

13. An aqueous fire retardant coating composition according to claim 12, further comprising one or more additional film-forming polymers.

14. An aqueous fire-retardant coating composition comprising the fire-retardant composition according to claim 13, wherein the additional film-forming polymer(s) comprise: a dispersed (meth)acrylate polymer, wherein the glass transition temperature of the (meth)acrylate polymer is at least 45 °C as determined by modulated differential scanning calorimetry using a modulation amplitude of 1 °C, a modulation period of 40 seconds, and an underlying heating interval of 5 °C / min; and a dispersed polyurethane based on a polycarbonate polyol.

15. A substrate coated with a coating deposited from a coating composition according to claim 13 or 14.