Intumescent coating composition

Abstract

A water-borne intumescent coating composition comprising: a) at least 5.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl ester-based binder and / or a (meth)acrylic-based binder; b) an acid-generating agent; c) a carbon donor d) at least 4.0 wt% relative to the total weight of the intumescent coating composition of dicyandiamide; wherein the weight ratio of components b):c) is in the range of 2:1 to 4:1.

Description

[0001] Intumescent Coating Composition

[0002] Field of the Invention

[0003] The present invention relates to an intumescent coating composition and a substrate coated with an intumescent coating. The present invention also relates to a process for coating a substrate with an intumescent coating as well as the use of an intumescent coating composition for protecting a substrate from fire and / or heat. The invention also relates to a method of improving the quality of char produced by an intumescent coating when said intumescent coating is exposed to fire and / or heat.

[0004] Background

[0005] Steel is commonly used as a construction material and has many advantages. However, structural steel is known to quickly lose its structural integrity in the case of a fire if unprotected. It is, therefore, known to protect steel using some form of passive fire protection, of which intumescent coatings are an example. Passive fire protection is designed to slow the rate at which the structural steel increases in temperature, significantly delaying the time to any form of structural collapse and thereby giving time to evacuate personnel and preserve expensive assets.

[0006] At elevated temperatures, an intumescent coating (which is typically applied directly on a substrate or on top of a pre-existing coating that is disposed on a substrate) decomposes to form a cellular carbonaceous char that expands into a foam by the release of gases which become trapped within the char. The foamed char forms an insulating layer that protects the underlying substrate from heat damage. Intumescent coatings typically offer advantages over other available forms of passive fire protection e.g. in terms of their light weight and environmental durability.

[0007] The formed cellular carbonaceous char and its integrity are crucial to the quality and performance of the intumescent coating. Any defects could lead to cracks in the char and in the extreme cases the char will not be able to protect the substrate from the heat of a fire.

[0008] One particular type of defect is a nodule. A nodule is a structural feature of the char surface characterised by having a rounded or irregular shape. Nodules are weak points of the char which can lead to early detachment, cracks, and irregular performance. Nodules may be formed in a range of sizes, with larger nodules being more detrimental to the integrity of the char than smaller nodules. Larger nodules are also less efficient insulators than small nodules. Therefore, a char formed with large nodules will be a less efficient insulator.

[0009] It would thus be advantageous to provide an intumescent coating which (when exposed to heat e.g. from a fire) produces a char surface having improved quality; in particular having fewer and / or smaller nodules. At the same time, it would be desirable if these intumescent coatings had maintained or even improved fire resistance compared to existing coatings, e.g. in terms of a similar or higher (longer) time-to-failure (TTF).

[0010] The present inventors have now provided a solution to the afore-mentioned problems. Specifically, it has surprisingly been established that the use of dicyandiamide in the water-borne intumescent coating compositions of the present invention (hereinafter sometimes referred to simply as the “intumescent coating composition” or “intumescent coating compositions”) leads to the production of a char surface having a low number of nodules, especially a low number of large nodules. In particular, the number and size of nodules are improved (lower) than comparative compositions in which dicyandiamide is not used. At the same time, in some embodiments, the improved char surface quality is accompanied by a maintenance or even an increase in the time-to-failure of the intumescent coating formed from the intumescent coating composition. Advantageously, both these effects may be obtained without having to use melamine or any melamine derivatives.

[0011] Summary of the Invention

[0012] In one aspect, the present invention provides a water-borne intumescent coating composition comprising: a) at least 5.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl ester-based binder and / or a (meth)acrylic-based binder; b) an acid-generating agent; c) a carbon donor d) at least 4.0 wt% relative to the total weight of the intumescent coating composition of dicyandiamide; wherein the weight ratio of components b):c) is in the range of 2:1 to 4:1. In another aspect, the present invention provides a substrate, preferably a metal substrate such as steel, coated with an intumescent coating obtained by (i) applying an intumescent coating composition as hereinbefore defined to the substrate and then (ii) allowing the intumescent coating composition to harden.

[0013] In yet another aspect, the present invention provides a process for coating a substrate, preferably a metal substrate such as steel, with an intumescent coating, the process comprising:

[0014] (i) applying an intumescent coating composition as hereinbefore defined to the substrate; and then

[0015] (ii) allowing the intumescent coating composition to harden.

[0016] In yet another aspect, the present invention provides a use of an intumescent coating composition as hereinbefore defined for protecting a substrate, preferably a metal substrate such as steel, from fire and / or heat.

[0017] In yet another aspect, the present invention provides a method of improving the quality of char produced by an intumescent coating when said intumescent coating is exposed to fire and / or heat, the method comprising preparing the intumescent coating from a first intumescent coating composition comprising dicyandiamide, preferably an intumescent coating composition as hereinbefore defined, and wherein the improvement in the quality of char preferably includes a reduction in the size and / or number of nodules on the surface of the char, e.g. compared to the surface of a char produced by a reference intumescent coating prepared from a second intumescent coating composition which comprises melamine instead of dicyandiamide but is otherwise identical to the first intumescent coating composition.

[0018] Definitions

[0019] The present invention relates in one aspect to an intumescent coating composition. The term “intumescent coating composition” defines a composition which, upon application to a substrate and subsequent drying and / or hardening, forms an intumescent coating. It will be appreciated therefore that an intumescent coating prepared from the intumescent coating composition of the present invention ideally consists of the components of the intumescent coating composition, with the exception of any solvent and / or water present in the intumescent coating composition which typically evaporates during drying / hardening. The intumescent coating composition (and thus also the intumescent coating formed from the intumescent coating composition) comprises components to ensure intumescence. To “intumesce” means to char and expand. When exposed to heat from a fire, for example, components in an intumescent coating chemically react to produce gases and a cellular carbonaceous char that expands into a foam when the gases become trapped within the char. Intumescent coatings thus form a relatively thick and thermally insulating foam barrier on the surfaces of coated substrates exposed to the heat from a fire.

[0020] As used herein in relation to an intumescent coating, the term “expansion” is used to refer to the increase in the volume of a coating after contact with heat from a fire. It is preferably determined by measuring the char depth using a char depth gauge / hydrocone.

[0021] As used herein the term “binder” refers to a polymer which forms a continuous film on a substrate surface when applied thereto. The binder may be physically drying / hardening or it may cure. Preferably, physically drying binders are used.

[0022] The term “expansion agent” is used interchangeably with the term “blowing agent” herein.

[0023] The term “acid generating agent” might also be called an “acid-generating compound” or an “acid catalyst” herein.

[0024] The term “(meth)acrylate” or “(meth)acrylic” encompasses both methacrylate / methacrylic and acrylate / acrylic.

[0025] The term “dispersion” refers to both particles and droplets (emulsions) dispersed in water / solvent. As used herein, the term “solvent” refers to a solvent other than water, e.g. an organic solvent.

[0026] Unless otherwise stated, “%” means percent by weight (wt.% or wt%). Likewise, references to a “ratio” or “ratios” means weight ratio or weight ratios unless otherwise stated.

[0027] Brief Description of the Figures

[0028] Figure 1 : (Left) Image of the char surface after fire testing of the intumescent coating formed from the water-borne inventive example intumescent coating composition E1 ; (Right) Image of the char surface after fire testing of the intumescent coating formed from the water-borne comparative example intumescent coating composition C1. Detailed Description of the Invention

[0029] The present invention relates to an intumescent coating composition which can be used to produce an intumescent coating which has an improved char surface quality (e.g. fewer / smaller nodules) when exposed to heat, e.g. from a fire. In some embodiments, the intumescent coating formed from the intumescent coating composition of the present invention also has maintained or even improved fire resistance e.g. as measured by time-to-failure (TTF). The intumescent coating formed from the intumescent coating composition is intumescent and therefore expands upon exposure to heat, e.g. from a fire.

[0030] Component a) - Binder

[0031] The intumescent coating composition comprises at least 5.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl ester-based binder and / or a (meth)acrylic-based binder. Suitable binders of this type will be known to the skilled person and are commercially available. In one embodiment, the intumescent coating composition comprises a polyvinyl ester-based binder but is free from a (meth)acrylic-based binder; or comprises a (meth)acrylic-based binder but is free from a polyvinyl ester-based binder. Alternatively, the intumescent coating composition may comprise a polyvinyl ester-based binder and a (meth)acrylic-based binder.

[0032] In general, the binder is responsible for the film-forming properties of the coating composition. The binder may also contribute to the structural integrity and mechanical properties of the coating obtained from the coating composition.

[0033] In one embodiment, the amount of binder (component a)) relative to the total weight of the intumescent coating composition is in the range of 5.0 to 40.0 wt%, preferably in the range of 7.5 to 35.0 wt%, more preferably in the range of 10.0 to 30.0 wt%. In terms of dry wt%, i.e. ignoring the contributions of any non-solid components of the coating composition, the amount of binder a) in the intumescent coating composition may be in the range of 2.5 to 35.0 wt%, preferably in the range of 4.0 to 30.0 wt%, such as in the range of 5.0 to 25.0 wt%. For example, the intumescent coating composition may comprise at least 5.0 dry wt% binder a), such as at least 7.5 dry wt% binder a), such as at least 10.0 dry wt% binder a).

[0034] In one embodiment, a single binder a) is used in the intumescent coating composition. Alternatively, it is possible to use a mixture of different binders a). Where a mixture of binders is used, the afore-mentioned amount of binder refers to the total amount of binder in the intumescent coating composition i.e. the sum of the amount of binders.

[0035] In some embodiments, the binder(s) a) is / are the only binder(s) in the intumescent coating composition. Alternatively, in some embodiments the intumescent coating composition comprises further binder(s) other than the binder(s) a) i.e. other than polyvinyl ester-based binders and / or (meth)acrylic-based binders. Examples of suitable further binder components include paraffins such as halogenated paraffins e.g. chlorinated paraffins.

[0036] The binder may be provided as a dispersion in water and / or one or more other solvents, e.g. organic solvents. Alternatively, the binder may be provided as a solid which is subsequently combined with water and / or one or more other solvents, e.g. organic solvents. In one embodiment, the binder has a solids content in the range of 30.0 to 70.0 wt%, preferably 35.0 to 65.0 wt%, more preferably 40.0 to 60.0 wt%. For commercially available binders, the solids content of the binder may usually be determined by consulting the technical datasheet provided by the manufacturer of the binder.

[0037] Polyvinyl ester-based binder

[0038] In one embodiment, the intumescent coating composition comprises a polyvinyl ester-based binder. In general, any known polyvinyl ester-based binders can be used to prepare the intumescent coating composition. The use of a polyvinyl acetate-based binder is especially preferred.

[0039] In one embodiment, the polyvinyl ester-based binder is a polyvinyl ester based homopolymer, such as a polyvinyl acetate based homopolymer.

[0040] In another embodiment, the polyvinyl ester-based binder is a copolymer derived from a vinyl ester monomer, such as vinyl acetate, and at least one of ethylene, vinyl chloride, a different vinyl ester (e.g. a vinyl ester of one or more long- chain branched carboxylic acids), di-n-butyl maleate, (meth)acrylic acid and (meth)acrylic ester. Co-polymers of a vinyl ester monomer (especially vinyl acetate) and ethylene and optionally one or more other comonomers are particularly preferred, as are copolymers of a vinyl ester monomer (especially vinyl acetate) and vinyl chloride. Copolymers of two or more vinyl ester monomers, e.g. vinyl acetate and a different vinyl ester, optionally with one or more other comonomers (especially ethylene), are also preferred. As used herein, the term “copolymer” or “co-polymer” refers to polymers derived from two or more different comonomers. The term therefore includes both polymers derived from strictly two different comonomers (i.e. bipolymers) and polymers derived from more than two different comonomers (e.g. terpolymers). The term “comonomer” refers to a copolymerisable monomer.

[0041] In another preferred embodiment, the polyvinyl ester-based binder is a copolymer derived from vinyl acetate and vinyl versatate. The polyvinyl ester-based binder may also be a terpolymer such as a terpolymer derived from ethylene, vinyl acetate and (meth)acrylate. In a preferred embodiment, the binder is a terpolymer of vinyl acetate, ethylene and a different vinyl ester (i.e. a vinyl ester other than vinyl acetate). Suitable polyvinyl ester-based binders are commercially available.

[0042] The polyvinyl ester-based binder may be solvent-borne or water-borne. In an exemplified embodiment, the polyvinyl ester-based binder is water-borne.

[0043] The polyvinyl ester-based binder is preferably provided as a dispersion, e.g. in water. The polyvinyl ester-based binder is typically present in the dispersion in the form of particles or droplets with an average size of 4 to 1000 nm, preferably 25 to 500 nm, more preferably 50 to 450 nm, such as 100 to 400 nm.

[0044] The polyvinyl ester-based droplets or particles preferably form 30 to 70 wt% of the dispersion, relative to the total weight of the dispersion as a whole. Typical wt% ranges may be 35 to 60 wt%, such as 40 to 60 wt%, relative to the total weight of the dispersion as a whole.

[0045] The polyvinyl ester-based dispersions may in addition to water also comprise polar organic solvents such as acetone, methyl alcohol, ethyl alcohol, n- propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2- methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 1-methoxy-2-propanol, 1- ethoxy-2-propanol, diacetone alcohol, dioxane, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monopropyl ether, and ethylene glycol monohexyl ether. One or more of these can be used.

[0046] The polyvinyl ester-based dispersion may be prepared by any suitable known method in the art.

[0047] If the intumescent coating composition comprises a water-borne polyvinyl ester-based dispersion, the content of organic solvent is preferably low, such as less than 5.0 wt% organic solvent, especially less than 2.0 wt% organic solvent, more especially less than 1 .0 wt% organic solvent, e.g. 0.5 wt% or less. Examples of suitable commercially available polyvinyl ester-based binders are Emultex FR 797, Emultex FR 747 and Emultex FR 728 from Synthomer Vinnapas EZ3112, Vinnapas EZ3010, Vinnapas EZ3066 from Wacker, Mowilith® DC, Mowilith® LDM 1871 , Mowilith® LDM 1880, Mowilith LDM 2301 from Celanese, Dow DLP 212, Dow DLP 2141 from Dow, ENCOR 2341 and ENCOR 2326 from Arkema.

[0048] (Meth)acrylic-based binder

[0049] In another embodiment, the intumescent coating composition comprises a (meth)acrylic-based binder. Any known (meth)acrylic based binder can be used to prepare the intumescent coating composition. The (meth)acrylic-based binder may be used alone or in combination with the polyvinyl-ester based binder as previously described.

[0050] Typically (meth)acrylic-based binders of interest are those prepared using one or more monomers such as (meth)acrylic acids or esters such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3- hydroxypropyl (meth)acrylate, 2-hydroxy-1 -methylethyl (meth)acrylate, 4- hydroxybutyl (meth)acrylate and hydroxyisobutyl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-(2- ethoxyethoxy)ethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isopropylideneglycerol (meth)acrylate, glycerolformal (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, hydroxyethyl (meth)acrylate, glycidyl (meth)acrylate and 4-glycidyloxybutyl (meth)acrylate, 2-(dimethylamino)ethyl (meth)acrylate, 3-(dimethylamino)propyl (meth)acrylate, 2-(diethylamino)ethyl (meth)acrylate, 2-(diisopropylamino)ethyl (meth)acrylate, 2-(tert-butylamino)ethyl (meth)acrylate and (meth)acrylic acid.

[0051] (Meth)acrylic-based binders of use in the intumescent coating composition may be ones based on monomers containing two or more polymerizable ethylenically unsaturated bonds. Examples of monomers containing two or more polymerizable ethylenically unsaturated bonds include monomers such as 1 ,2- ethanediol di(meth)acrylate, 1 ,3-butanediol di(meth)acrylate, 1 ,4-butanediol di(meth)acrylate, 1 ,6-hexanediol di(meth)acrylate, 1 ,3-glycerol di(meth)acrylate, methacrylic anhydride, zinc di(meth)acrylate, and trimethylolpropane tri(meth)acrylate. (Meth)acrylic monomers comprising polyether or polysiloxane groups may also be used.

[0052] The monomers listed above may be combined with other non-(meth)acrylic monomers to prepare the desired polymer such as styrene and acrylonitrile. In one preferred embodiment the (meth)acrylic-based binder is a styrene-(meth)acrylate co-polymer.

[0053] The (meth)acrylic-based binder may be a physically drying binder. The (meth)acrylic binder may also be cured by radical polymerization using azo or peroxide initiators such as described in WO2021 / 180488 A1 and W02005 / 000975 A1. Crosslinking agents such as difunctional or trifunctional (meth)acrylates or triallyl cyanurates may be present.

[0054] In one embodiment, the (meth)acrylic-based binder may be dissolved in an organic solvent or dispersed in water.

[0055] In one embodiment, the binder may be dissolved in an organic solvent. Examples of suitable solvents include xylene, toluene, MIBK, methoxypropanol, MEK, butyl acetate, benzyl alcohol, octyl phenol, resorcinol, n-butanol, isobutanol and isopropanol. The use of a (meth)acrylic-binder dissolved in an organic solvent, e.g. xylene, is particularly preferred.

[0056] Examples of suitable commercially available (meth)acrylic-based binders are Pliolite AC80, Pliolite AC3H, Plioway Ultra 350LV, Pliolite LV72, Plioway EC1 , Plioway ECT and Pliolite AC5-G from Synthomer. Examples of monomeric (meth)acrylates that may be used in free radically polymerised systems are Methyl Acrylate (MA) and 2-Ethylhexyl Acrylate (2-EHA) from BASF, and also Methyl Methacrylate (MMA) from Dow.

[0057] Component b) - Acid-generating agent

[0058] The intumescent coating composition comprises an acid-generating agent (also known as an acid-generating compound). Typically, the acid-generating agent comprises a source of phosphoric or sulfonic acid that is capable of producing the phosphoric or sulfonic acid upon exposure to heat, particularly at temperatures greater than 200 °C. Examples of such sources include sodium phosphate, potassium phosphate (e.g. potassium tripolyphosphate), ammonium phosphate (e.g. ammonium polyphosphate (APP), monoammonium phosphate, diammonium phosphate), sodium sulfate, potassium sulfate, ammonium sulfate, magnesium sulfate, or para-toluene sulfonic acid, or a combination of any thereof. In general, it is the reaction between the acid (generated by decomposition of the acid-generating agent when exposed to high temperature) and the carbon donor compound that is responsible for the formation of the carbonaceous char. For example, an ammonium polyphosphate acid-generating agent may decompose at about 240 °C to form ammonia and phosphoric acid. The phosphoric acid can function as an acid for dehydration reactions of organic polyol compounds such as starch, cellulose, non-polymeric sugars (e.g., glucose, fructose, sucrose, and the like), pentaerythritol, dipentaerythritol, or tripentaerythritol, or combinations of any thereof, which may function as carbon donor compounds.

[0059] The phosphoric acid may then react with the hydroxyl groups to form heat- unstable phosphate esters, which decompose to release carbon dioxide and regenerate the phosphoric acid. The dehydrated carbon donor and / or the binder system then forms the carbonaceous char, and the carbon dioxide expands the char into a foam.

[0060] In one embodiment, the acid-generating compound comprises a phosphoric acid ester of a polyhydroxy compound, or an ammonium phosphate (e.g., APP), or an amine phosphate, or a combination of any thereof.

[0061] A particularly useful acid-generating compound is ammonium polyphosphate because APP yields phosphoric acid at temperatures generally below the decomposition temperatures of the carbon donor compounds described herein. Thus, APP produces phosphoric acid that is readily available to participate in the charring reactions.

[0062] In a preferred embodiment therefore, the acid-generating agent is an ammonium polyphosphate. Such compounds are generally polymeric phosphates, having P-O-P linkages, which may be represented by the formula:

[0063] [NH4PO3]nwherein the average value of n is at least about 10 preferably at least 500, more preferably at least 800, most preferably at least 1000, e.g. >1000. The upper limit for the average value of n is not particularly limited but may in one embodiment be as high as 10000. In one embodiment, the acid-generating agent is a coated or uncoated ammonium polyphosphate.

[0064] In another embodiment, the acid-generating compound is boric acid or a source of boric acid that is capable of producing boric acid upon exposure to heat, particularly at temperatures greater than 200 °C. The source of boric acid may comprise, for example, borate salts such as ammonium pentaborate, zinc borate, sodium borate, lithium borate, aluminum borate, magnesium borate, borosilicate compounds, or combinations of any thereof.

[0065] In one embodiment, the amount of acid-generating agent (component b)) relative to the total weight of the intumescent coating composition is in the range of 10.0 to 50.0 wt%, preferably in the range of 12.0 to 40.0 wt%, more preferably in the range of 15.0 to 35.0 wt%, most preferably in the range of 18.0 to 30.0 wt%.

[0066] In terms of dry wt%, the intumescent coating composition may comprise the acid-generating agent b) in an amount of 12.0 to 75.0 wt%, preferably in the range of 15.0 to 60.0 wt%, more preferably in the range of 20.0 wt% to 50.0 wt%, most preferably in the range of 25.0 wt% to 45.0 wt%.

[0067] Where a mixture of acid-generating agents is used, the afore-mentioned amount of acid-generating agent refers to the total amount of acid-generating agent in the intumescent coating composition i.e. the sum of the amount of acidgenerating agents.

[0068] In one embodiment, a single acid-generating agent b) (e.g. ammonium polyphosphate) is used in the intumescent coating composition. Alternatively, the intumescent coating composition may comprise a mixture of acid-generating agents, e.g. a mixture of ammonium polyphosphate and one or more other acidgenerating agents.

[0069] Component c) - Carbon donor

[0070] The intumescent coating composition comprises a carbon donor (also known as a carbon donor compound). Generally, the purpose of the carbon donor is to enable the formation of a carbonaceous char.

[0071] In one embodiment, the carbon donor is an organic polyhydroxide compound (i.e. an organic polyol) and / or expandable graphite. For example, in one embodiment the carbon donor compound is selected from the group consisting of pentaerythritol (i.e. monopentaerythritol), dipentaerythritol, tripentaerythritol, a polysaccharide (e.g. starch, cellulose, glycogen, and the like), a disaccharide sugar (e.g. sucrose, lactose, maltose, and the like), a monosaccharide sugar (e.g. glucose, fructose, galactose, and the like), glycerol, glycols, expandable graphite, or mixtures thereof. In a preferred embodiment, the carbon donor is selected from the group consisting of pentaerythritol (i.e. monopentaerythritol), dipentaerythritol, tripentaerythritol, and mixtures thereof. For example, in one embodiment the carbon donor is pentaerythritol, dipentaerythritol, or a mixture thereof. In an especially preferred embodiment, the carbon donor is pentaerythritol.

[0072] In one embodiment, the intumescent coating composition comprises at least one solid carbon donor. In another embodiment, the majority (e.g. at least 50 wt%) of the carbon donor(s) in the intumescent coating intumescent coating composition are solid carbon donors. In a preferred embodiment, at least 60 wt%, such as at least 75 wt% or at least 90 wt%, e.g. 60 to 99 wt%, 75 to 98 wt%, or 90 to 95 wt%, of the carbon donor(s) in the intumescent coating intumescent coating composition are solid carbon donors. In one embodiment, the intumescent coating composition is free from liquid carbon donors.

[0073] For the avoidance of doubt, the term “solid” as used herein means solid at room temperature (25 °C) and atmospheric pressure (1 atm) and the term “liquid” as used herein means liquid at room temperature (25 °C) and atmospheric pressure (1 atm). It will also be understood that the term “carbon donor” excludes those kinds of components which may be carbon based but which are counted towards other parts of the composition, e.g. the binder a). As used herein therefore, the term “carbon donor” excludes polymerizable film-forming components of the intumescent coating composition such as binders, e.g. epoxy resins.

[0074] In one embodiment, the amount of carbon donor (component c)) relative to the total weight of the intumescent coating composition is in the range of 2.5 to 25.0 wt%, preferably in the range of 3.0 to 20.0 wt%, more preferably in the range of 4.0 to 17.5 wt%, most preferably in the range of 5.0 to 15.0 wt%.

[0075] In terms of dry wt%, the intumescent coating composition may comprise the carbon donor c) in an amount of 3.5 to 40.0 wt%, preferably in the range of 4.0 to 30.0 wt%, more preferably in the range of 5.0 wt% to 25.0 wt%, most preferably in the range of 7.0 wt% to 22.5 wt%.

[0076] Where a mixture of carbon donors is used, the afore-mentioned amount of carbon donor refers to the total amount of carbon donor in the intumescent coating composition i.e. the sum of the amount of carbon donors.

[0077] In one embodiment, a single carbon donor, e.g. pentaerythritol, is used in the intumescent coating composition. Alternatively, the intumescent coating composition may comprise a mixture of carbon donors, e.g. a mixture of pentaerythritol and one or more other carbon donors.

[0078] Component d) - Dicyandiamide

[0079] The intumescent coating composition comprises at least 4.0 wt% relative to the total weight of the intumescent coating composition of dicyandiamide.

[0080] Dicyandiamide (also known as cyanoguanidine, 2-cyanoguanidine, DCD, or Dicy) is a nitrile derived from guanidine. It generally exists in the form of one of two tautomers the structure of which is shown below, although the skilled person will understand that a zwitterionic form also exists.

[0081] When exposed to heat, e.g. from a fire, as part of an intumescent coating, dicyandiamide will typically produce non-flammable gases, generally nitrogen, which act to expand the char derived from the carbon donor, thereby forming a foam-like protective layer over the substrate to be protected. Thus suitably, dicyandiamide acts as a blowing agent (also known as an expansion agent) in the intumescent coating compositions of the present invention.

[0082] The dicyandiamide of use in the intumescent coating composition of the present invention may suitably be synthesised from one or more precursors, e.g. by treating cyandiamide with a base, or may be obtained from a commercial source, typically in the form of a powder. In one embodiment, the intumescent coating composition comprises dicyandiamide in the form of particles having a median diameter (D50) in the range of 0.1 to 200 pm, preferably in the range of 0.1 to 100 pm such as 5 to 50 pm, e.g. 10 to 40 pm.

[0083] The amount of dicyandiamide in the intumescent coating composition is at least 4.0 wt%. Amounts below this level have been found to be insufficient to improve the char surface quality while maintaining fire performance, i.e. to reduce the number and / or size of nodules formed on the surface of the char generated by the intumescent coating formed from the intumescent coating composition of the present invention. In one embodiment, the amount of dicyandiamide (component d)) relative to the total weight of the intumescent coating composition is in the range of 4.0 to 25.0 wt%, preferably in the range of 5.0 to 20.0 wt%.

[0084] In an especially preferred embodiment, the amount of dicyandiamide present in the intumescent coating composition is less than 20.0 wt%. This is because it has been found that when an amount of 20.0 wt% or more dicyandiamide is used, the char surface quality is still improved but the time-to- failure (TTF) is low. Thus, in a preferred embodiment, the amount of dicyandiamide in the intumescent coating composition is in the range of 4.0 to 18.0 wt%, preferably 5.0 to 18.0 wt%, more preferably 6.0 to 18.0 wt%, most preferably in the range of 8.0 to 16.0 wt%. Within these ranges, the present inventors have surprisingly established that both the char surface quality and TTF is acceptable.

[0085] In terms of dry wt%, the intumescent coating composition may comprise dicyandiamide in an amount of 5.5 to 40.0 wt%, preferably in the range of 7.0 to 30.0 wt%, more preferably in the range of 8.5% to 25.0 wt%.

[0086] In one embodiment, dicyandiamide is the sole blowing agent in the intumescent coating composition.

[0087] Fibres

[0088] The intumescent coating composition optionally comprises fibres. The fibres may be inorganic fibres or organic fibres. Typical inorganic fibres include: carbide fibres, such as boron carbide fibres, silicon carbide fibres, niobium carbide fibres, etc.; nitride fibres, such as silicon nitride fibres; boron containing fibres, such as boron fibres, boride fibres; silicon containing fibres, such as silicon fibres, alumina- boron silica fibres, E-glass (non-base aluminum borates) fibres, C-glass (non-base or low base sodalime-aluminumborosilicate) fibres, A-glass (base -sodalime- silicate) fibres, S-glass fibres, inorganic glass fibres, quartz fibres, etc. The glass fibres may include E-glass fibres, C-glass fibres, A-glass fibres, S-glass fibres, etc.

[0089] Useful inorganic fibres also include ceramic fibres and basalt fibres. Kevlar (para-aramid fibres) may also be used.

[0090] A preferred organic fibre is carbon fibres.

[0091] Other suitable fibres include mineral fibres. Typically, the mineral fibres comprise aluminium oxide, calcium oxide, iron oxide, magnesium oxide and / or silica.

[0092] In one preferred embodiment the fibres are silicate fibres. If present, the fibres preferably form at least 0.25 wt% of the intumescent coating composition, preferably at least 0.5 wt%, preferably at least 1 .0 wt%.

[0093] In some embodiments the fibres form 0.25 to 20 wt% of the intumescent coating composition, preferably 0.5 to 15 wt%, more preferably 1.0 to 10 wt%.

[0094] In some embodiments the fibres form 0.3 to 30 dry wt% of the intumescent coating composition, preferably 0.6 to 20.0 dry wt%, more preferably 1 .2 to 15.0 dry wt%.

[0095] In some embodiments the average length of the fibres is from 10 to 6000 pm, preferably from 50 to 3000 pm, especially 100 to 1000 pm.

[0096] In one preferred embodiment fibers of different average length are used. Thus, a first fibre population of length X might be combined with a second fibre population of differing length Y. Using fibers of different average length helps to create a network of fibers which stabilises the char of the intumescent composition. The difference in average length between the fibre populations may be at least 200 pm. For example, a first fibre population of 125 pm might be combined with a second fibre population of 500 pm. A fibre population is a plurality of fibres of essentially the same length.

[0097] In one embodiment three or more fiber populations of different average length are used.

[0098] It is preferred if substantially all the fibres have an average length of 50 to 3000 pm. Fibers which have an average length less than 50 pm are generally not sufficiently long to provide a mesh effect.

[0099] In some embodiments the melting point of the fibres is above 800 °C, preferably above 1000 °C, especially above 1200 °C.

[0100] In a preferred embodiment, the intumescent coating composition comprises fibres, e.g. mineral fibres, in an amount of 0.1 to 10 wt%, preferably 0.5 to 8.0 wt%, such as 1 .0 to 5.0 wt%.

[0101] Pigments and fillers

[0102] The intumescent coating composition optionally comprises pigment(s) and / or filler(s). Suitable pigments and fillers are well known in the art. Suitable fillers include barium sulfate, titanium dioxide, zinc oxide, aluminium oxide, aluminium hydroxide, magnesium oxide, magnesium hydroxide, carbonates (e.g. dolomite), borates, silica, silicates, heavy metal oxides such as cerium oxide, lanthanum oxide and zirconium oxide, micronized iron oxide, kaolin, wollastonite, diatomaceous earth, bentonite clay, polymeric and inorganic microspheres such as uncoated or coated hollow and solid glass beads, uncoated or coated hollow and solid ceramic beads, porous and compact beads of polymeric materials. The use of a metal oxide in the intumescent coating composition, especially a transition metal oxide such as titanium dioxide (TiO2), is particularly preferred.

[0103] Flaky fillers such as mica, glass flakes and micaceous iron oxide (MiO) may also be used. Preferred fillers include titanium dioxide, kaolin and wollastonite.

[0104] When present, the filler preferably constitutes from 1 .0% to 30.0% by weight of the intumescent coating composition, more preferably 2.0 to 20 wt%, especially 5.0 to 15.0 wt%. In terms of dry wt%, the fillers preferably form 1 .2 to 45 wt%, more preferably 2.5 to 30.0 wt%, most preferably 7.0 to 20 wt% of the intumescent coating composition. If two or more fillers are used then these percentages refer to the total content of fillers present. As used herein, the term “filler” does not include fibres, e.g. mineral fibres.

[0105] As examples of pigments, colour pigments may be mentioned. Examples of the colour pigments include titanium white, red iron oxide, yellow iron oxide, black iron oxide, carbon black and organic colour pigments.

[0106] The fillers and / or pigments may act as char reinforcers. In a preferred embodiment, the intumescent coating composition will comprise both a mineral fibre and a metal oxide.

[0107] In a preferred embodiment, the intumescent coating composition comprises a metal oxide, e.g. TiO2, in an amount of 0.1-20.0 wt%, preferably 1.0 to 18.0 wt%, such as 5.0 to 15.0 wt%.

[0108] Additives

[0109] In addition to the binder(s), acid-generating agent(s), carbon donor(s), dicyandiamide, and optional fibres, fillers and pigments mentioned above, the intumescent coating composition optionally further comprises one or more additives conventionally used in intumescent coating compositions. Suitable additives will depend on the binder used and whether the coating composition is solvent-borne, water-borne or solvent free. In each case however, suitable additives are well known to the skilled person.

[0110] Examples of additives that may be present in the intumescent coating composition of the invention include rheology modifiers, surfactants, antifoaming agents, pH adjusting agents, biocides, coalescing agents and anticorrosive agents. Suitable rheology modifiers include polyamide wax, polyethylene wax, polysaccharides, associative rheology modifiers such as hydrophobically modified alkali swellable emulsions (HASE) or urethanes such as hydrophobically modified ethoxylate urethanes (HEUR), clays, cellulosic rheology modifiers, rheology modifiers based on acrylic polymers such as alkali swellable emulsions (ASE thickeners), fumed silica or mixtures thereof.

[0111] Various surfactants may also be used. This is especially relevant for the water-borne coating compositions. A number of different surfactants may be suitable. The surfactant may be non-ionic, anionic, cationic or amphoteric.

[0112] The coating compositions of the present invention may comprise an antifoaming agent. Antifoaming agents are sometimes also referred to as foam control agents or defoamers. A wide range of antifoaming agents are commercially available and may be used in the coating compositions of the invention. Representative examples of suitable antifoaming agents include organic siloxanes, polyethers, polyether-modified silicones, mineral oils and combinations thereof.

[0113] The coating compositions may comprise a pH adjusting agent such as ammonia, 2-amino-2-methyl-1 -propanol, sodium hydroxide (NaOH), sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3).

[0114] Coalescing agents may optionally be included. In a water-borne composition, the applied wet product is typically inhomogeneous, as opposed to a solvent-borne composition which will typically be homogenous when applied. Therefore, in order to form a film, the polymeric binder droplets or particles in a water-borne composition must generally coalesce. Coalescing agents aid this process in the water phase. Examples of suitable coalescing agents are 2,2,4- trimethyl-1 ,3-pentanediol monoisobutyrate (Texanol™ Ester alcohol), benzyl alcohol, propylene glycol monomethyl ether (PM), propylene glycol propyl ether (PnP), dipropylene glycol n-butyl ether (DPnB), propylene glycol phenyl ether (PPh), tripropylene glycol n-butyl ether (TPnB), ethylene glycol propyl ether (EP), ethylene glycol butyl ether (EB), diacetone alcohol (DAA) and dipropylene glycol methyl ether (DPM).

[0115] In one embodiment, one or more co-solvents are present in the coating composition. As used herein, the term “co-solvent” is used to refer to a solvent which is not the predominant solvent present in the intumescent coating composition and which is present in an amount of less than 7 wt% relative to the total weight of the coating composition. For example, in one embodiment, the amount of co-solvent is less than 5 wt%, such as less than 3 wt%, or less than 1 .0 wt%. Where more than one co-solvent is used, the above amounts refer to the total amount of co-solvents.

[0116] Suitable co-solvents include polar organic solvents such as acetone, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 1 -methoxylpropanol, 1-ethoxy-2-propanol, diacetone alcohol, dioxane, ethylene glycol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, dipropylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monohexyl ether, and mixtures thereof. The use of a co-solvent is particularly preferred in the water-borne intumescent coating composition.

[0117] In order to improve or facilitate dispersion of the optional pigments, fillers and fibres it may be desirable to incorporate wetting / dispersion additives. A wide range of dispersing agents is commercially available and may be used in the coating compositions of the invention. Suitable dispersing agents include conventional anionic, cationic, non-ionic, and amphoteric dispersing agents as well as combinations thereof.

[0118] It is to be understood that certain components, such as the fibres, fillers and pigments described above, may also serve to aid char formation and to strengthen the char and prevent char degradation. Such components include solids such as zinc borate, zinc stannate, zinc hydroxystannate, glass flake, glass spheres, polymeric spheres, further fibres (ceramic, mineral, glass / silica based), aluminium hydroxide oxide, aluminium trihydroxide, boron phosphate and fumed silica.

[0119] It is also possible to include anticorrosive components in the coating composition. Such components may be metal oxides, metal carbonates, talc, feldspar and so on to act as anti-corrosive materials. Specific anticorrosive functional pigments include zinc phosphate, zinc oxide, zinc dust, aluminium flakes, lead oxide. Auxiliary corrosion inhibitors, for example a molybdate, phosphate, tungstate or vanadate, ultrafine titanium dioxide, and / or zinc oxide and / or a filler such as silica, calcined clay, alumina silicate, talc, barytes or mica.

[0120] The total amount of the above-mentioned various additive components depends upon the use and cannot be determined indiscriminately, but they are frequently contained in the total amount of 0.1 to 50% by weight in the intumescent coating composition, such as 0.5 to 40 wt%, preferably 0.5 to 30 wt%. In dry weight the total amount of various additive components may range from 0.5 to 75% by weight in the intumescent coating composition, such as 2 to 60 by dry wt%.

[0121] In a preferred embodiment, the intumescent coating composition comprises 0.1 to 10.0 wt% of one or more additives selected from the group consisting of plasticisers, rheology modifiers, surfactants, antifoaming agents, pH adjusting agents, biocides, coalescing agents, and co-solvents.

[0122] Diluent

[0123] The intumescent coating composition typically comprises one or more diluents. Such diluents may aid in dissolving or dispersing the other constituents of the coating composition and / or aid in the application of the coating composition to a substrate, e.g. by ensuring that the viscosity of the coating composition is in range which is suitable for forming a layer of the coating composition when the coating composition is applied to a substrate.

[0124] As the intumescent coating composition is a water-borne intumescent coating composition, the diluent comprises water. In a solvent-borne intumescent coating composition, the diluent comprises a solvent other than water, e.g. an organic solvent.

[0125] In the water-borne intumescent coating composition, water typically forms a majority (e.g. at least 50 wt%, preferably at least 70 wt%, such as at least 90 wt%) of the one or more diluents present in the coating composition. In a solvent-borne intumescent coating composition, the solvent other than water, e.g. the organic solvent, typically forms a majority (e.g. at least 50 wt%, preferably at least 70 wt%, such as at least 90 wt%) of the one or more diluents present in the coating composition. In one embodiment, the diluent may consist essentially of water.

[0126] The amount of diluent in the intumescent coating composition is not particularly limited and may be adjusted to give the desired viscosity. In one embodiment, the diluent forms 5 to 50 wt% of the intumescent coating composition, such as 7.5 to 40 wt%, such as 10 to 30 wt%. For the avoidance of doubt, the amount of diluent does not include the amount of any co-solvent(s) which may be present. Instead, any co-solvent(s) present (which is defined as a solvent which is not the predominant solvent present in the intumescent coating composition and is present in an amount of less than 7 wt% relative to the total weight of the coating composition) is counted towards the amount of “additives”. The nature of the solvent other than water, e.g. the organic solvent, is generally not restricted, and known solvents having boiling points of wide range are employable. Examples of such solvents include xylene, toluene, methyl isobutyl ketone (MIBK), methoxypropanol, methyl ethyl ketone (MEK), n-butyl acetate, t- butyl acetate, benzyl alcohol, octyl phenol, resorcinol, n-butyl alcohol, isobutyl alcohol and isopropyl alcohol. The above solvents can be used singly or in combination of two or more kinds.

[0127] Intumescent Coating Composition

[0128] The intumescent coating composition comprising component a)-d) and optional further components as hereinbefore described, is one which is capable of forming an intumescent coating when applied to a substrate. Thus, as used herein the term “intumescent coating” refers to the coating formed by applying the intumescent coating composition as hereinbefore described to the surface of a substrate and allowing said composition to harden. As used herein, the term “coating” includes both partial and complete coatings, i.e. those which cover only a part of a surface of the substrate and those which cover the whole of a surface of the substrate. Irrespective of whether the coatings completely or partially cover the substrate however, the coatings are preferably continuous coatings.

[0129] The intumescent coating composition is water-borne. For example, in one embodiment the intumescent coating composition is an aqueous intumescent coating composition. Preferably the intumescent coating composition is a one- component intumescent coating composition, i.e. ready to use without addition of further components.

[0130] In one embodiment, the intumescent coating composition has a low content of melamine and / or derivatives thereof. For example, in one embodiment the intumescent coating composition comprises less than 1.0 wt% melamine and / or derivatives thereof, preferably than 0.5 wt%, more preferably less than 0.1 wt%. In one embodiment, the amount of melamine and / or derivatives therefore is in the range of 0.0 to 1 .0 wt%. Preferably the intumescent coating composition is free from or essentially free from melamine and / or derivatives thereof. For the avoidance of doubt, the term “melamine and / or derivatives thereof’ does not include dicyandiamide.

[0131] The intumescent coating composition preferably has a high solids content. In one embodiment, the intumescent coating composition has a solids content of at least 55 wt% relative to the total weight of the intumescent coating composition, preferably at least 60 wt%, more preferably at least 65 wt%, most preferably at least 70 wt%. In some embodiments, the intumescent coating composition has a solids content of up to 95 wt%, such as up to 90 wt%. A solids content of 70 to 90 wt%, e.g. 70 to 80 wt% is preferred. Solids content may be determined according to the method described herein under the heading “Determination Methods”.

[0132] The intumescent coating composition preferably has a low content of volatile organic compounds (VOCs). In one embodiment, the VOC content is less than 500 g / L, preferably less than 400 g / L, e.g. 0 to 400 g / L. The VOC content of the waterborne intumescent coating composition is preferably less than 250 g / L, more preferably less than 100 g / L, most preferably less than 60 g / L. In some embodiments, the VOC content might be 25 g / L or less. In this regard, volatile organic compounds include benzyl alcohol. VOC content may be measured according to US EPA method 24.

[0133] In one embodiment, the intumescent coating composition has a time-to- failure (500 °C) as measured according to the method under “Determination Methods” of at least 25 minutes, such as at least 30 minutes, such as at least 40 minutes, such as at least 50 minutes. In one embodiment, the time-to-failure of the intumescent coating composition is up to 120 minutes, such as up to 100 minutes, such as up to 80 minutes.

[0134] In one embodiment, the intumescent coating composition has a pigment volume concentration (PVC) in the range of 40% to 85%, such as 50% to 85%, preferably 60% to 85%, more preferably 65 to 80%. Pigment volume concentration may be determined according to the method described herein under the heading “Determination Methods”.

[0135] The weight ratio of components b):c) (i.e. the ratio of the weight of the acidgenerating agent to the weight of the carbon donor in the intumescent coating composition) is in the range of 2:1 to 4:1. In one embodiment, the weight ratio of b):c) is in the range of 2.5:1 to 3.5:1. A weight ratio of b):c) of about 3:1 is preferred. As will be understood by the skilled person, when there is more than one acidgenerating agent and / or more than one carbon donor in the intumescent coating composition, the weight ratio b):c) refers to the ratio of the total amount of acidgenerating agent(s) to the total amount of carbon donor(s) in the composition.

[0136] In one embodiment, the weight ratio of components d):c) (i.e. the ratio of the weight of dicyandiamide to the weight of the carbon donor in the intumescent coating composition) is at least 0.5:1 , preferably at least 0.75:1 such as at least 1 :1. In one embodiment, the weight ratio of d):c) is less than or equal to 4:1 , such as less than or equal to 3:1. A range of 0.75:1 to 2.5:1 , such as 1 :1 to 2:1 is preferred. As will be understood by the skilled person, when there is more than one carbon donor in the intumescent coating composition, the weight ratio d):c) refers to the ratio of the total amount of dicyandiamide to the total amount of carbon donor(s) in the composition.

[0137] In one embodiment, the weight ratio of components b):d) (i.e. the ratio of the weight of the acid-generating agent to the weight of dicyandiamide in the intumescent coating composition) is less than or equal to 6:1 , such as less than or equal to 5:1 , such as less than or equal to 4:1 . For example, the ratio of b):d) may be in the range of 1 : 1 to 6: 1 , such as in the range of 1 : 1 to 5 : 1 , such as in the range of 1 :1 to 4:1 , such as in the range of 1 .5:1 to 3:1. As will be understood by the skilled person, when there is more than one acid-generating agent in the intumescent coating composition, the weight ratio b):d) refers to the ratio of the total amount of acid-generating agent(s) to the total amount of dicyandiamide in the composition.

[0138] In one embodiment, the total amount of acid-generating agent(s) (including any APP), blowing agent(s) (including any melamine), and pigment(s) (including any TiC>2 and / or carbon black) is less than 55 wt% relative to the weight of the intumescent coating composition as a whole, such as 10 to 55 wt%, such as 15 to 52 wt%, such as 20 to 50 wt%.

[0139] In a preferred embodiment, the intumescent coating composition of the present invention comprises: a) 5.0 to 40.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl acetate-based binder and / or a (meth)acrylic-based binder, e.g. 10.0 to 30.0 wt%; b) 10.0 to 50.0 wt% ammonium polyphosphate, e.g. 18.0 to 30.0 wt%; c) 2.5 to 25.0 wt% pentaerythritol, e.g. 5.0 to 15.0 wt%; d) 4.0 to 25.0 wt% dicyandiamide, e.g. 8.0 to 16.0 wt%; e) 0.0 to 20.0 wt% of at least one metal oxide, preferably TiO2, e.g. 5.0 to 15.0 wt% f) 0.0 to 10.0 wt% fibres, e.g. 1 .0 to 5.0 wt%; and g) 0.0 to 10.0 wt% of one or more additives selected from the group consisting of plasticisers, rheology modifiers, surfactants, antifoaming agents, pH adjusting agents, biocides, coalescing agents, and co-solvents, e.g. 1 .0 to 5.0 wt%.

[0140] Preparation of the Coating Composition

[0141] The intumescent coating composition may be prepared by any suitable technique that is commonly used within the field. Thus, the various constituents may be mixed together using a high speed disperser, a ball mill, a pearl mill, a three-roll mill, an inline mixer etc.

[0142] Typically, the intumescent coating composition is supplied as a one- component coating composition, i.e. is ready to use. Before use, the intumescent coating composition may be stored. Suitable storage conditions for the intumescent coating composition include temperatures of 5-30 °C (water-borne).

[0143] Application of the Coating Composition

[0144] The intumescent coating composition may be applied to a substrate, e.g. a metal substrate such as steel. Optionally the substrate may already be coated e.g. with a primer layer. The resulting substrate coated with the intumescent coating composition as hereinbefore defined thus forms a further aspect of the present invention. Optionally the intumescent coating composition on the substrate has been hardened to form an intumescent coating.

[0145] In another aspect, the present invention relates to a substrate, preferably a metal substrate such as steel, coated with an intumescent coating. The intumescent coating is obtained by (i) applying an intumescent coating composition as hereinbefore defined to the substrate and then (ii) allowing the intumescent coating composition to harden. It will be understood that the intumescent coating ideally consists of the same components as the intumescent coating composition, with the exception of any volatile components e.g. water / solvent, lost through evaporation during hardening.

[0146] In another aspect, the present invention relates to a process for coating a substrate, preferably a metal substrate such as steel, with an intumescent coating, the process comprising:

[0147] (i) applying an intumescent coating composition as hereinbefore defined to the substrate; and then

[0148] (ii) allowing the intumescent coating composition to harden. The intumescent coating composition can be applied to the substrate, preferably a steel substrate, by well-known standard application methods like spraying, e.g. conventional air spraying or by airless- or airmix- spraying equipment, or manually e.g. by means of a brush or a roller. Application typically results in the formation of a layer of the coating composition. The coating compositions may be applied in several layers in order to build-up layer thickness.

[0149] Hardening of the coating composition may involve the loss of volatile components from the coating composition (i.e. drying) and / or curing reactions within the coating composition. Allowing the coating composition to harden may therefore involve passively allowing the coating composition to harden or alternatively encouraging hardening e.g. by the application of heat and / or drying means e.g. air.

[0150] In a yet further aspect, the present invention provides an intumescent coating obtainable, preferably obtained, from the intumescent coating composition as hereinbefore defined.

[0151] Film Thickness

[0152] The intumescent coating composition is typically applied in high dry film thickness to ensure a good fire protection. The applied film thickness might vary depending on the nature of the substrate being coated and its predicted fire exposure scenario.

[0153] The dry film thickness of the intumescent layer is preferably 100 pm - 10000 pm, preferably 150 pm - 7500 pm, more preferably 200 pm to 5000 pm. It will be appreciated that the film thickness is a function of the substrate to which the coating composition is applied. Different substrate thicknesses and geometries might need different thicknesses. Substrates might be subject to different fire testing minimums and hence require different levels of protection. The selection of a suitable film thickness is within the competencies of the skilled person.

[0154] The intumescent coating composition may be applied several times to achieve the appropriate dry film thickness.

[0155] The substrate is typically a metallic substrate such as a steel substrate. In general however, any substrate that requires fire protection may be used.

[0156] In one embodiment, the intumescent coating composition is applied directly on a surface of the substrate, i.e. direct to substrate e.g. direct to metal. In a preferred embodiment however, the intumescent coating composition is applied indirectly, e.g. on a primer layer which is disposed on the base substrate. Suitable primer layers are well known in the art and are typically formed from an epoxy resin, although other options may be used. The primer layer preferably comprises at least 20 wt% epoxy resin, preferably at least 25 wt% epoxy resin.

[0157] Examples of suitable primer layers are coatings based on epoxy, polyurethane, acrylic, alkyd, vinyl and chlorinated rubber. Preferably the primer layer is an epoxy-based primer or a zinc-rich epoxy-based primer. In one embodiment, the primer is a shop primer.

[0158] In another embodiment, the primer layer is a polysiloxane sol primer such as described in US2014 / 0106176.

[0159] When present, the dry film thickness of the primer is ideally in the range of 15 to 250 pm. In one embodiment therefore, the invention provides a substrate coated with a primer layer and the intumescent coating as hereinbefore defined, in that order. Optionally a topcoat layer is disposed on top of the intumescent coating. In general, any topcoat layer conventionally used in the art may be applied to the intumescent coating. Suitable topcoat layers are known to the skilled person.

[0160] Applications

[0161] The intumescent coating compositions of the present invention may be used to form intumescent coatings which protect substrates, e.g. steel substrates, from damage caused by extreme heat, e.g. as a result of fire. In one aspect therefore, the present invention relates to the use of the intumescent coating composition as hereinbefore defined for protecting a substrate, preferably a metal substrate such as steel, from fire and / or heat. The use may comprise preparing an intumescent coating composition as hereinbefore defined and subsequently applying said coating composition directly or indirectly (e.g. on a primer layer) to the substrate to be protected. The use may further comprise allowing said composition to harden after application to the substrate.

[0162] In another aspect, the present invention relates to a method of improving the quality of char produced by an intumescent coating when said intumescent coating is exposed to fire and / or heat, the method comprising forming the intumescent coating from a (first) intumescent coating composition comprising dicyandiamide, preferably an intumescent coating composition as hereinbefore defined. The improvement in the quality of char preferably includes a reduction in the size and / or number of nodules on the surface of the char, e.g. compared to the surface of a char produced by a reference intumescent coating prepared from a second intumescent coating composition which comprises melamine instead of dicyandiamide but is otherwise identical to the first intumescent coating composition.

[0163] Determination Methods

[0164] Solids content

[0165] The solids content of the binder or intumescent coating composition is calculated according to ASTM D5201 - 05a(2020). Solids content may be expressed in % by weight (wt%) or % by volume (vol%) relative to the total weight or volume of the binder / composition respectively.

[0166] Volatile Organic Compounds (VOC) content

[0167] VOC content of the intumescent coating compositions is measured according to US EPA method 24.

[0168] Pigment Volume Concentration (PVC)

[0169] Pigment volume concentration (PVC) for the compositions were determined by calculation according to the formula PVC = ((Vp + Vf) / (Vp+Vf+Vb))*100. Where Vp is the volume of pigments, Vf is the volume of fillers, including glass spheres, and Vb is the volume of binders. It is expressed as a percentage (%).

[0170] Fire testing of the intumescent coating compositions

[0171] For fire testing, the coating compositions were applied to carbon steel panels sandblasted to SSPC SP10, (size of 300 x 300 x 6 mm) and primed with MUKI EPS from Jotun to a dry film thickness (DFT) of approximately 30 pm. The intumescent coating compositions were applied to a wet film thickness corresponding to 1 mm DFT. The coatings were dried for a minimum 14 days at 23°C, 50%RH before being tested as per EN 1363-1 fire curve. The furnace temperature was measured and controlled using four bare wire type K chromel-alumel thermocouples located within the furnace and positioned close to the specimen, as per internal test procedure. Furnace pressure was continually monitored by a micro-meter and maintained at approximately 10 Pa for the test duration. The time to failure (TTF) was recorded as the average of 2 thermocouple type K chromel-alumel positioned as per EN16623. The fire test was conducted until the average steel temperature of the test samples has reached the set failure temperature of 500 °C. The time to reach this temperature was recorded in minutes and reported as TTF.

[0172] Char surface quality

[0173] The quality of the char surface resulting from the above-mentioned fire testing was evaluated. Evaluation involved assessing the size and density (number density) of nodules on a scale of 1-4. The following descriptors were used to assign a char surface quality score to each of the exemplified intumescent coatings:

[0174] A score of 1 or 2 is considered acceptable whereas a score of 3 or 4 is considered unacceptable.

[0175] Examples

[0176] Water-borne intumescent coating compositions according to the present invention were prepared and tested for their fire resistance according to the methods described under the heading “Determination Methods”.

[0177] Water-borne intumescent coating compositions

[0178] The following table (Table 1) lists the ingredients that were used in the inventive (E1-E7) and comparative (C1-C5) water-borne intumescent coating compositions. Table 1 :

[0179] The ingredients in Table 1 were mixed together in a high speed disperser in the proportions shown in Table 2 to form inventive (E1-E7) and comparative (C1-C5) water-borne intumescent coating compositions. The coating compositions were subjected to fire testing as described herein under the heading “Determination Methods”. The properties of the coating compositions and the results of the fire testing (char surface quality score and TTF) are also reported in Table 2. Images of the char surface of examples E1 (left) and C1 (right) are shown in Figure 1 . Table 3 reports the results of testing on further comparative examples (C6 and C7) which have a ratio of acid-generating agent : carbon donor (weight ratio of components b):c)) outside the range of 2:1 to 4:1. Table 2:

[0180] Table 2 continued:

[0181] Table 3: The following observations may be drawn from the above examples.

[0182] • Compared to C1 (melamine as blowing agent) and C2 (no blowing agent), E1 (dicyandiamide as blowing agent) shows an improvement (increase) in TTF. In addition, the char quality has improved from a score of 3-4 for C1 and C2 to a score of 1 for E1 . On E1 the surface is very smooth, there is no significant formation of nodules, and the char is controlled and dense. C1 and C2 in contrast show a surface with a high density of different sized nodules ranging from medium to large in size.

[0183] • E2 and E3 show that the same effects as observed for E1 (increase in TTF, reduction in number and size of nodules observed on char surface) are obtained when using different amounts / ratios of acid generating agent, dicyandiamide and carbon donor. TTF is lower than E1 but still significantly higher than C1 and C2.

[0184] • E4-E6 and C3-C4 use a different binder system to that used in E1-E3 and C1-C2. Compared to C3 (melamine as blowing agent) and C4 (no blowing agent), E4 shows an improvement in TTF and improvement in char quality (fewer nodules). E5 and E6 show that this same effect is obtained for different amounts / ratios of acid generating agent, dicyandiamide and carbon donor. E6 in particular has a very high TTF.

[0185] • C5 and E7 show the effect of using low and high contents of dicyandiamide respectively. E7 has good char surface quality although the TTF is poor. C5 on the other hand has both poor char surface quality and poor TTF.

[0186] • C6 and C7 are water-borne intumescent coating compositions comprising dicyandiamide but having a ratio of acid-generating agent : carbon donor outside the range of 2:1 to 4:1 . C6 does not provide an expanding char, while the char of C7 is completely detached. TTF is poor for both C6 and C7.

[0187] The above examples therefore show that the use of dicyandiamide as blowing agent instead of only melamine in the water-borne intumescent coating compositions of the present invention results in a significant improvement in the quality of the char (lower nodule size and density) generated by the resulting intumescent coatings. In addition, the intumescent coatings of the present invention have maintained or even improved TTF relative to the coatings comprising only melamine as blowing agent or the coatings comprising no blowing agent at all.

Claims

Claims1 . A water-borne intumescent coating composition comprising: a) at least 5.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl ester-based binder and / or a (meth)acrylic-based binder; b) an acid-generating agent; c) a carbon donor d) at least 4.0 wt% relative to the total weight of the intumescent coating composition of dicyandiamide; wherein the weight ratio of components b):c) is in the range of 2:1 to 4:1 .

2. The water-borne intumescent coating composition according to claim 1 , wherein the amount of component a) relative to the total weight of the intumescent coating composition is in the range of 5.0 to 40.0 wt%, preferably in the range of 7.5 to 35.0 wt%, more preferably in the range of 10.0 to 30.0 wt%.

3. The water-borne intumescent coating composition according to claim 1 or 2, wherein the amount of component b) relative to the total weight of the intumescent coating composition is in the range of 10.0 to 50.0 wt%, preferably in the range of 12.0 to 40.0 wt%, more preferably in the range of 15.0 to 35.0 wt%, most preferably in the range of 18.0 to 30.0 wt%.

4. The water-borne intumescent coating composition according to any preceding claim, wherein the amount of component c) relative to the total weight of the intumescent coating composition is in the range of 2.5 to 25.0 wt%, preferably in the range of 3.0 to 20.0 wt%, more preferably in the range of 4.0 to 17.5 wt%, most preferably in the range of 5.0 to 15.0 wt%.

5. The water-borne intumescent coating composition according to any preceding claim, wherein the amount of component d) relative to the total weight of the intumescent coating composition is in the range of 4.0 to 25.0 wt%, preferably in the range of 5.0 to 20.0 wt%, more preferably in the range of 6.0 to 18.0 wt%, most preferably in the range of 8.0 to 16.0 wt%.

6. The water-borne intumescent coating composition according to any preceding claim, wherein the weight ratio of components d):c) is at least 0.5:1 , preferably at least 1 :1 , such as in the range of 1 :1 to 4:1 , such as 1 :1 to 3:1.

7. The water-borne intumescent coating composition according to any preceding claim, wherein the weight ratio of components b):d) is less than or equal to 6:1 , such as less than or equal to 5:1 , such as less than or equal to 4:1 , such as in the range of 1 :1 to 4:1 , such as in the range of 1 :1 to 3:1.

8. The water-borne intumescent coating composition according to any preceding claim, wherein the acid-generating agent is an ammonium polyphosphate, preferably an ammonium polyphosphate represented by the formula:[NH4PO3]nwherein the average value of n is at least about 10, preferably at least 500, more preferably at least 800, most preferably at least 1000.

9. The water-borne intumescent coating composition according to any preceding claim, wherein the carbon donor is selected from the group consisting of pentaerythritol, dipentaerythritol, tripentaerythritol, and mixtures thereof, preferably pentaerythritol.

10. The water-borne intumescent coating composition according to any preceding claim, wherein the intumescent coating composition comprises less than 1.0 wt% melamine and / or derivatives thereof, preferably than 0.5 wt%, more preferably less than 0.1 wt%.11 . The water-borne intumescent coating composition according to any preceding claim, wherein the intumescent coating composition is free from melamine and / or derivatives thereof.

12. The water-borne intumescent coating composition according to any preceding claim, comprising: a) 5.0 to 40.0 wt% relative to the total weight of the intumescent coating composition of a polyvinyl acetate-based binder and / or a (meth)acrylic-based binder; b) 10.0 to 50.0 wt% ammonium polyphosphate; c) 2.5 to 25.0 wt% pentaerythritol; d) 4.0 to 25.0 wt% dicyandiamide; e) 0.0 to 20.0 wt% of at least one metal oxide, preferably TiO2; f) 0.0 to 10.0 wt% fibres; and g) 0.0 to 10.0 wt% of an additive selected from the group consisting of plasticisers, rheology modifiers, surfactants, antifoaming agents, pH adjusting agents, biocides, coalescing agents, co-solvents, and mixtures thereof.

13. The water-borne intumescent coating composition according to any preceding claim, wherein the intumescent coating composition has a solids content of at least 55 wt% relative to the total weight of the intumescent coating composition, preferably at least 60 wt%, more preferably at least 65 wt%, most preferably at least 70 wt%.

14. The water-borne intumescent coating composition according to any preceding claim, further comprising at least one metal oxide, preferably a transition metal oxide, especially titanium dioxide (TiO2).

15. The water-borne intumescent coating composition according to claim 14, wherein the intumescent coating composition comprises less than 1 .0 wt% melamine and / or derivatives thereof, preferably than 0.5 wt%, more preferably less than 0.1 wt%, or is free from melamine and / or derivatives thereof.

16. The water-borne intumescent coating composition according to any preceding claim, having a pigment volume concentration (PVC) in the range of 40% to 85%, such as 50% to 85%, preferably 60% to 85%, more preferably 65 to 80%.

17. A substrate, preferably a metal substrate such as steel, coated with an intumescent coating obtained by (i) applying a water-borne intumescent coating composition according to any preceding claim to the substrate and then (ii) allowing the intumescent coating composition to harden.

18. A process for coating a substrate, preferably a metal substrate such as steel, with an intumescent coating, the process comprising:(i) applying a water-borne intumescent coating composition according to any of claims 1 to 16 to the substrate; and then(ii) allowing the intumescent coating composition to harden.

19. Use of the water-borne intumescent coating composition according to any of claims 1 to 16 for protecting a substrate, preferably a metal substrate such as steel, from fire and / or heat.

20. A method of improving the quality of char produced by an intumescent coating when said intumescent coating is exposed to fire and / or heat, the method comprising preparing the intumescent coating from a first intumescent coating composition comprising dicyandiamide, preferably an intumescent coating composition as claimed in any of claims 1 to 16; wherein the improvement in the quality of char preferably includes a reduction in the size and / or number of nodules on the surface of the char, e.g. compared to the surface of a char produced by a reference intumescent coating prepared from a second intumescent coating composition which comprises melamine instead of dicyandiamide but is otherwise identical to the first intumescent coating composition.