WO2025153683A1

WO2025153683A1 - Intumescent coating composition

Info

Publication number: WO2025153683A1
Application number: PCT/EP2025/051147
Authority: WO
Inventors: Paul Stefan REISS; Stian BLAKSTAD ISAKSEN
Original assignee: Jotun AS
Current assignee: Jotun AS
Priority date: 2024-01-19
Filing date: 2025-01-17
Publication date: 2025-07-24
Anticipated expiration: 2026-07-19

Abstract

An intumescent coating composition comprising: a) i) at least one Michael addition acceptor with a functionality of two or lower; and ii) at least one Michael addition acceptor with a functionality of four or higher; b) at least one Michael donor; and c) at least one catalyst.

Description

Intumescent Coating Composition

Field of Invention

The invention relates to ultra-high solids intumescent coatings involving the use of a binder system that cures by a Michael addition reaction and the use thereof to protect a substrate, such as a metal substrate, from fire and/or extreme heat damage. In particular, the invention requires the use of a combination of Michael addition acceptors to maximise char performance, intumescence and heat resistance.

Background

In order to protect substrates from fire, it is well known to apply an intumescent coating. An intumescent coating is defined as a coating that swells in the case of fire to produce a carbon based insulating char and has many advantages over other available forms of passive fire protection, such as their light weight and environmental durability.

An intumescent coating usually is in the form of either a waterborne acrylic coating or a solventbome acrylic coating. Waterborne acrylic technologies are preferred from an environmental and health and safety perspective, but solventbome acrylic technologies can withstand environments where there is a higher risk of corrosivity, such as C4 internal environments.

In any case, both solvent and waterborne acrylic technologies are unsuitable where rain, pooling water or constant high humidity and condensation can occur, even if they are used as a coating system which additionally comprises a top coat layer.

Traditionally, one-component intumescent coating technologies have been used, which have demonstrated reliable and efficient fire protection performance over decades. However, one-component coatings suffer from significant limitations such as: slow application throughput; long drying times; and poor durability.

As an alternative, two-component epoxy-based intumescent coating technologies are extremely durable and fast curing. However, in order to achieve an acceptable fire protection performance, a much higher film thickness must be used. Additionally, epoxy-based intumescent coating compositions are highly viscous and typically require a plural feed pump with heating to enable spray application. W02016/170122 describes epoxy binders in intumescent coatings with improved expansion factor.

In light of the above, there is interest to develop an ultra-high solids intumescent coating, which is more durable than one-component intumescent coating systems while at the same time exhibits an improvement in fire performance and a simplified application procedure compared to two-component epoxy-based intumescent coatings. There is also a need for the intumescent coating composition to have a sufficient pot life when the components are mixed to allow for application by a single feed airless spray pump.

Technical solutions employed in the development of ultra-high solid, fastcuring and weather-resistant intumescent coatings are known in the literature, and generally involve the use of reactive binder systems whose unique structural properties determine the efficacy of the overall intumescent system. Typical reactive binder systems involve silane-modified polymers, as disclosed in EP2430102A1 or methacrylate resins, such as those disclosed in US8461244B2.

The inventors have surprisingly found that a binder system that cures by a Michael addition reaction effectively protects substrates from a rise in temperature over time, wherein the formulations expand upon exposure to fire to generate efficient chars.

The use of a Michael addition binder system is not new in intumescent coating compositions. US2016/0068689 discloses an intumescent composition comprising polyfunctional Michael addition donors and acceptors and a catalyst. Upon heating the compositions to initiate expansion, the intumescent factor and mechanical stability of the resulting char were significantly higher than comparative epoxy-amine based systems, and the curing rates were significantly reduced.

US2016/0312042 reports Michael addition cured coating compositions and has a similar disclosure to US2016/0068689. In both pieces of prior art, only trifunctional donors and acceptors are exemplified.

EP2960276 describes ablative coating compositions (but not intumescent coatings) that comprise Michael donors and acceptors. Ablative compositions are ones that when exposed to fire, release water vapor which helps prevent the spread of fire. The coating may also form a char that insulates the area and protects nearby components.

DE102012223514 refers to an intumescent coating composition comprising: A) a multifunctional Michael acceptor having at least two electron-deficient carbon multiple bonds per molecule; B) a multifunctional Michael donor having at least two thiol groups per molecule; and C) an insulation layer-forming additive. The heart of the invention appears to be the use of a thiol-functionalised Michael donor.

The present invention demonstrates how the char performance of the intumescent coating can be influenced through the binder composition. A specific blend of Michael acceptors can be used to improve char but when tetrafunctional or trifunctional Michael acceptors are used alone, brittle and void-filled chars are generated when exposed to fire, and a poor thermal insulation barrier allows the temperature rise of the underlying substrate.

When the defined blend of acceptors is used the inventors see improvement in char expansion, resulting in softer, denser chars with a lower propensity for void formation and an improvement in thermal insulation performance. This is not at the expense of other coating properties such as intumescence factor and time of failure rates. The intumescent coating composition of the invention is ideally suited to mitigate cellulosic fire scenarios.

In one embodiment, the invention uses a latent base catalyst, e.g. as described in WO2011/124663. This document describes a curable, but non- intumescent coating composition without plasticisers. The use of a latent base catalyst, i.e. a compound that converts in situ into a strong base, offers advantages in terms of pot life. W02013/050623 also uses a latent base catalyst in combination with a tetrafunctional acrylate acceptor. The advantages of the blend are not disclosed.

Summary of Invention

Viewed from one aspect, the present invention provides an intumescent coating composition comprising: a) i) at least one Michael addition acceptor with a functionality of two or lower; and ii) at least one Michael addition acceptor with a functionality of four or higher; b) at least one Michael donor; and c) at least one catalyst.

It is preferred if the at least one Michael donor has a functionality of at least two.

Viewed from another aspect, the present invention provides a substrate, preferably a metallic substrate, coated with an intumescent coating composition as herein described.

Viewed from another aspect, the present invention provides a process for the application of an intumescent coating composition as herein described to a substrate, comprising applying the intumescent coating composition to a primer layer on a substrate, or directly on a substrate, e.g. by airless spraying, and allowing said intumescent coating composition to cure.

Viewed from another aspect, the present invention provides a coated substrate obtained from the process as herein defined.

Viewed from another aspect, the present invention provides the use of an intumescent coating composition as herein defined for protecting a substrate from exposure to fire.

Detailed Description of Invention

Coating Composition

The present invention refers to an intumescent coating composition comprising a binder system based on Michael donors and acceptors and a catalyst. The coating composition is intumescent and therefore expands upon exposure to fire. Such a coating therefore contains well known intumescent additives which are described in detail below.

The intumescent coating composition of the present invention is not an ablative composition, as described in EP2960276. The binder system herein will comprise at least one Michael donor, and at least two Michael acceptors. At least one catalyst, such as a latent base catalyst, is also present to ensure that the Michael reaction proceeds and a cured coating is obtained. The coating composition described herein is therefore that which can be applied to a substrate. It may be that the coating composition is transported as a kit to prevent premature reaction and mixed shortly before application to a substrate. On application to a substrate, the coating composition undergoes a reaction to form a cured coating on the substrate. The resulting coating will be called the cured coating herein and contains therefore the cured reaction products of the intumescent coating composition.

The intumescent coating composition should have a high solid content, preferably above 70.0 wt%, such as in the range of 80.0 to 98.0 wt%, especially 85 to 95 wt% solids (calculated according to ASTM D5201-05).

It is preferable if the Michael acceptors are present in an amount between 3.0 to 20.0 wt% of the intumescent coating composition, more preferably between 4.0 to 15 wt%, especially, 7.0 to 13 wt%. These percentages refer to the total content of Michael acceptors present.

It is preferable if the Michael acceptors are present in an amount between 4.0 to 20.0 dry wt% of the intumescent coating composition, more preferably between 5.0 to 16 dry wt%, especially, 8.0 and 14 dry wt%. These percentages refer to the total content of Michael acceptors present. The term dry wt% is used herein to define the percentage of components within the intumescent coating composition but with solvents discounted.

It is preferable if the mono or difunctional Michael acceptor is present in an amount between 1.0 to 12 wt% of the intumescent coating composition, more preferably between 1.5 to 10 wt%.

It is preferable if the tetrafunctional or higher Michael acceptor is present in an amount between 1.5 to 12 wt% of the intumescent coating composition, more preferably between 2.0 to 10 wt%.

It is preferable if the Michael donor is present in an amount of 5.0 to 20 wt% of the intumescent coating composition, such as 7.0 to 18 wt%, especially 8.0 to 15 wt%. If two or more Michael donors are used then these percentages refer to the total content of Michael donors present.

It is preferable if the Michael donor is present in an amount of 6.0 to 20 dry wt% of the intumescent coating composition, such as 8.0 to 18 dry wt%, especially 8.0 to 16 dry wt%. If two or more Michael donors are used then these percentages refer to the total content of Michael donors present.

The stoichiometric ratio between the donor and acceptor is often 1:1 for a standard Michael addition top coat composition but deviation from a 1 : 1 ratio is possible. Possible stoichiometric ratios are 0.8: 1 to 1.2: 1 donor to acceptor. It is however preferred if the stoichiometric ratio is close to 1:1, such as 0.95:1 to 1.05:1 donor to acceptor.

It will be appreciated that the ratio required reflects the number of active acceptor groups and active donor groups on the reactants. If a Michael acceptor is difunctional then it requires two Michael donor reactive functional groups per molecule of Michael acceptor for a 1 : 1 stoichiometric ratio to be achieved. The skilled person can readily add the correct amounts of acceptor and donor depending on the functionality of the reactants such that a stoichiometric ratio is achieved.

The amount of catalyst can vary, but it will typically form 0.1 to 5.0 wt% of the intumescent coating composition, preferably 0.25 to 4.0 wt% of the intumescent coating composition, most preferably 0.5 to 3.0 wt%. If two or more catalysts are used then these percentages refer to the total content of catalyst present. The catalyst may be supplied in a solvent. These percentages refer to the actual catalyst present and not any solvent.

The amount of catalyst can vary, but it will typically form 0.1 to 5.0 dry wt% of the intumescent coating composition, preferably 0.2 to 5.0 dry wt% of the intumescent coating composition, most preferably 0.25 to 3.0 dry wt%. If two or more catalysts are used then these percentages refer to the total content of catalyst present.

The plasticiser, if present, may form 0.5 to 15 wt% of the intumescent coating composition, such as 1.0 to 12 wt%, preferably 1.5 to 8.0 wt%. If two or more plasticisers are used then these percentages refer to the total content of plasticisers present. Other substances commonly used in coating formulations, such as solvents, dispersants, defoamers, thixotropic agents, char reinforcers may also be included in the intumescent coating composition.

The intumescent coating should also contain well known components that create the intumescence. The intumescent additives will typically comprise: an acid generating compound, a blowing/expansion agent and a carbon donor, such as a polyalcohol.

In a preferable embodiment, the intumescent additives will comprise all three of a carbon donor, an acid generating compound and a blowing agent. In a preferable embodiment, the intumescent coating composition will comprise a mixture of melamine, ammonium polyphosphate and pentaerythritol.

The amount of intumescent additives may vary, but they will typically form 25 to 70 wt%, preferably 40 to 65 wt% of the total intumescent coating composition.

The amount of intumescent additives may vary, but they will typically form 25 to 75 dry wt%, preferably 40 to 70 dry wt% of the total intumescent coating composition.

The amount of carbon donor may vary, but it will typically make up between 0.0 to 20 wt%, preferably 3.0 to 20 wt%, especially 7.0 to 14 wt% of the intumescent coating composition. Typically, the carbon donor will make up 10 to 30 wt% of the total intumescent additives.

The amount of acid generating compound may vary, but it will typically make up between 20 to 50 wt%, preferably 25 to 35 wt% of the intumescent coating composition. Typically, the acid generating compound will make up 55 to 75 wt% of the total intumescent additives.

The amount of blowing agent may vary, but it will typically make up between 5.0 to 20 wt%, preferably 9.0 to 15 wt% of the total intumescent coating composition. Typically, the blowing agent will make up 10 to 30 wt% of the total intumescent additives.

In one embodiment the intumescent coating composition comprises: a) 3.0 to 20 wt% of the Michael acceptors; b) 5.0 to 20 wt% of at least one Michael donor; and c) 0.1 to 5.0 wt% of at least one catalyst. In one embodiment the intumescent coating composition comprises: a) 7.0 to 13 wt% of the Michael acceptors; b) 7.0 to 18 wt% of at least one Michael donor; and c) 0.25 to 4.0 wt% of at least one catalyst.

Michael Addition

“Michael addition” refers to the reaction between a Michael donor and a Michael acceptor, in the presence of a catalyst such as a strong base. A classic Michael addition mechanism is depicted below:

A “Michael acceptor”, depicted above as MA, refers to a compound having at least one activated unsaturated group; and a “Michael donor”, depicted above as MD, refers to a compound with at least one acidic proton in activated methylene or methine groups.

In organic chemistry terms, the mechanism proceeds via deprotonation of the acidic proton from the Michael donor by a suitable base to form a carbanion, which is stabilised through its electron-withdrawing groups. The anion additionally can be represented by any one of the two possible resonance structures, which are the corresponding enolate ions. This nucleophilic species can then react with the electrophilic Michael acceptor in a conjugate addition reaction, which is followed by proton abstraction from the protonated base to yield the product.

Michael addition is activated by base catalysis, but also inhibited by the presence of acidic species that will consume these basic catalysts. In tuning the reactivity of coating systems in view of achieving a desirable drying profile, there are various requirements to balance. The drying profile (also referred to as the reaction profile or as the curing profile) is the progress of the crosslinking reaction as a function of time. It is preferred that the drying profile allows build-up of mechanical properties as fast as possible. It is further preferred to have a drying profile that is robust, i.e. the reactivity (and hence the resulting drying profile) is not strongly influenced by accidental low levels of acidic contaminants being present.

The “binder system” referred to herein comprises the Michael acceptors and the Michael donor. The binder system is preferably free from any epoxide or epoxycontaining compound. The intumescent coating composition as a whole is preferably free from any epoxide or epoxy-containing compound.

The functionality of a Michael reaction component defined herein is the number of Michael reactive functional groups per molecule for that component. For Michael acceptors, the functional groups are the activated unsaturated groups and for Michael donors, the functional groups are the acidic protons.

Michael Acceptor

The intumescent coating composition of the invention contains at least two Michael acceptors. The Michael acceptor in the present invention will be a compound having at least one activated unsaturated group which is activated by an electron withdrawing group, such as by a carbonyl group in the alpha position. In particular, the Michael acceptor is an alpha beta unsaturated carbonyl compound.

The intumescent coating composition contains: i) at least one Michael addition acceptor with a functionality of two or monofunctional; and ii) at least one Michael addition acceptor with a functionality of four or higher, such as 4.

The weight ratio of components (i) to (ii) may be 1:10 to 10:1, such as 1:5 to 5:1, preferably 1 : 4 to 4 : 1 , more preferably 1 : 3 to 3 : 1. Where the first Michael acceptor is mono functional there is a preference that the polyfunctional Michael acceptor (ii) is in excess. Each Michael acceptor contains at least one unsaturated group. The unsaturated group is typically a non-aromatic functional group, such as an alkene or an alkyne, especially an alkene.

Each Michael acceptor is preferably a (meth)acrylate, fumarate, or maleate, which all comprise an acryloyl functionality. Michael acceptors which comprise (meth)acrylate (i.e. (meth)acrylic ester) functionality are most preferred. Whilst methacrylates are possible, the use of acrylates is preferred.

The Michael addition esters used may optionally contain hydroxyl groups, however it is preferred if the only functional groups present are unsaturated group(s), especially alkenes and ester group(s). It is most preferred that the Michael acceptor contains the motif -C=C-COO-C.

Michael addition acceptor with a functionality of two or lower (i.e. difunctional or monofunctional)

In some embodiments, the Michael acceptor is an acrylic ester containing 1 to 2 ester groups and up to 40 carbon atoms, e.g. 1 to 2 ester groups and 10 to 30 carbon atoms.

Representative examples of Michael acceptors are disclosed in US2759913 (column 6, line 35 through column 7, line 45), DE-PS-835809 (column 3, lines 16- 41), US4871822 (column 2, line 14 through column 4, line 14), US4602061 (column 3, line 14 through column 4, line 14), US4408018 (column 2, lines 19-68) and US4217396 (column 1, line 60 through column 2, line 64). Acrylates, fumarates, and maleates are preferred. Most preferably, the Michael acceptor is an unsaturated acryloyl functional component.

A preferred first group of Michael acceptors are the acrylic esters of components containing 1-2 ester groups and up to 30 carbon atoms, such as up to 25 carbon atoms.

In some embodiments, the Michael acceptor comprises a difunctional acrylate of the following formula:

Formula (I) wherein Zi and Z2 are independently selected from any (CH2)_n group where n is an integer between 1 and 10, and R is selected from either hydrogen, or any linear or branched alkyl, aryl, aralkyl, or alkaryl groups, which may optionally be substituted. R preferably represents an alkyl group, such as -CH3 or -(CH2)_mCH3 where m can be any integer from 1 to 10.

In a preferable embodiment, the Michael acceptor comprises a difunctional acrylate of Formula (I) wherein R is either hydrogen or a linear, unsubstituted alkyl group and Zi and Z2 are a -(CH2)_n group where n is an integer from 2 to 5.

In a preferable embodiment, the Michael acceptor comprises a difunctional acrylate of Formula (I) wherein R is hydrogen and the Zi and Z2 groups are -(012)4 and -( 12)5, such as 1,10-decanediol diacrylate.

In a preferable embodiment, the Michael acceptor comprises a difunctional acrylate of Formula (I) wherein R is -CH3 and both Z groups are -(012)2, such as 3- methyl-l,5-pentanediol diacrylate. The use of 1 ,4-butanediol diacrylate or 1,6- hexanediol diacrylate is also preferred.

A mono functional acrylate preferably has the following formula:

Formula (II) wherein Z is selected from any (CH2)_n group where n is an integer between 0 and 10 (such as 1 to 6), and R1/R2 are each independently selected from either hydrogen, or a linear or branched alkyl, aryl, alkaryl or aralkyl group, which may optionally be substituted. R1/R2 preferably represents a -CH3 or -(CH2)_mCH3 group where m can be any integer from 1 to 10. R1/R2 may also be taken together to form a ring such as a cycloalkyl ring, e.g. cyclohexyl which may be optionally substituted, e.g. by one or more alkyl groups.

In a preferable embodiment, the mono functional acrylate is of Formula (II) wherein Z is -CEE, and R1/R2 are each linear Cl-10-alkyl groups, more preferably when Ri is -(CH2)_nCH3 where n = 2, and R2 is -(CH2)_nCH3 where n = 4.

In some embodiments the -CH2- repeating unit in Z, Zi and Z2 groups may instead be an alkylene glycol, such as ethylene glycol or propylene glycol (the oxygen of carbonyl forming therefore the first oxygen of the glycol). Structures include: where Z3 is an alkylene glycol (e.g. CH2CH2-O or CH2CH2CH2-O) and Rc is H or a Cl -6 alkyl. Multiple alkylene glycol units may be present.

Especially preferred examples of the first Michael acceptor include 2- propylheptyl acrylate, lauryl acrylate, iso-butyl acrylate, tert-butyl acrylate, isodecyl acrylate, tridecyl acrylate, isobomyl acrylate, dihydrocyclopentadienyl acrylate, ethyldiglycol acrylate, heptadecyl acrylate, 4-hydoxybutyl acrylate, tetrahydrofurfuryl acrylate, 2 -phenoxy ethyl acrylate, 2 -hydroxy-3 -phenoxypropyl acrylate, 2-hydroxyethyl acrylate, 2-(2-ethoxyethoxy) ethyl acrylate, hydroxypropyl acrylate, 3-acryloxypropyl trimethoxy silane, 1,4-butanediol diacrylate, 1,6- hexanediol diacrylate, 3-methyl-l,5-pentanediol diacrylate, 1,5 -pentanediol diacrylate, 1,8-octanediol diacrylate, 1,10-decanediol diacrylate, 1,12- dodecanediol diacrylate, bisphenol A diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, triethylene glycol diacrylate, butylene glycol diacrylate, dipropylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexane dimethanol diacrylate, tertbutyl cyclohexyl acrylate, 3,3,5- trimethylcyclohexyl acrylate, stearyl acrylate, behenyl acrylate and tricyclodecane dimethanol diacrylate.

The first Michael acceptor might also be based on maleic, fumaric and/or itaconic acid esters (and maleic and itaconic anhydride).

Michael addition acceptor with a functionality of four or higher

The second Michael acceptor can be an acrylic ester containing 4 or more, such as 4 to 6 ester groups and up to 40 carbon atoms, e.g. 4 to 6 ester groups and 10 to 30 carbon atoms.

A preferred group of the second Michael acceptors are the acrylic esters of components containing 4 ester groups and up to 40 carbon atoms, such as up to 30 carbon atoms. Especially preferred examples include di-trimethylolpropane tetraacrylate and pentaerythritol tetraacrylate,

Also of interest are dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate which are 5 and 6 functional respectively.

It is preferred if the Michael acceptor package is a mixture of at least one tetrafunctional acrylate and at least one difunctional acrylate or at least one tetrafunctional acrylate and at least one monofunctional acrylate.

One Michael acceptor has a functionality of at least four, especially a tetrafunctional acrylate such as an ethoxylated pentaerythritol tetraacrylate.

A tetrafunctional acrylate preferably has the following formula:

Formula (IV) wherein Zi to Z4 are independently selected from any (CH2)_n group where n is an integer between 1 and 10, and Ri and R2 are independently selected from either hydrogen, or a linear or branched Cl-6-alkyl, C6-10-aryl, C7-10-alkylaryl or C7-10- arylalkyl group, which may optionally be substituted. Ri and R2 preferably represent a -CH3 or -(CH2)_mCH3 group where m can be any integer from 1 to 6. Preferably, the tetrafunctional acrylate is of Formula (IV) where each of Zi to Z4 are -CH2 and each of Ri and R2 are -(Ch^CFR

In a further embodiment, the tetrafunctional acrylate preferably has the following formula:

Formula (V) wherein a-d independently can be an integer of 1 to 10, such as 1 to 4. Preferably a-d are all the same.

As a second preferred example may be mentioned polyesters based upon maleic, fumaric and/or itaconic acid (and maleic and itaconic anhydride), and di- or polyvalent hydroxyl components, optionally including a monovalent hydroxyl and/or carboxyl component.

As a third preferred example may be mentioned resins as polyesters, polyurethanes, polyethers and/or alkyd resins containing pendant activated unsaturated groups. These include, for example, urethane acrylates obtained by reaction of a polyisocyanate with an hydroxyl group-containing acrylic ester, e.g., an hydroxyalkyl ester of acrylic acid or a component prepared by esterification of a polyhydroxyl component with less than a stoichiometric amount of acrylic acid; polyether acrylates obtained by esterification of an hydroxyl group-containing polyether with acrylic acid; polyfunctional acrylates obtained by reaction of an hydroxyalkyl acrylate with a poly carboxylic acid and/or a polyamino resin; polyacrylates obtained by reaction of acrylic acid with an epoxy resin; and polyalkylmaleates obtained by reaction of a monoalkylmaleate ester with an epoxy resin and/or an hydroxy functional oligomer or polymer.

Most preferred activated unsaturated group-containing components are the unsaturated acryloyl functional components. It is also especially preferred that the acid value of the activated unsaturated group-containing components is sufficiently low to not substantially impair activity of the catalyst, so preferably less than about 2, most preferably less than 1 mg KOH/g. As exemplified by the previously incorporated references, these and other activated unsaturated group-containing components, and their methods of production, are generally known to those skilled in the art, and need no further explanation here. Preferably the functionality is 4-20.

The equivalent weight (EQW: average molecular weight per reactive functional group) is 100-2000 g/eq, and the number average molecular weight preferably is Mn 200-5000.

The viscosity of the Michael acceptor with a functionality of two or lower may be less than 1000 mPas, such as less than 500 mPas, preferably less than 250 mPas. In some embodiments, the viscosity may be 100 mPas or less.

The viscosity of the Michael acceptor with a functionality of four or higher may be 30 to 1000 mPas, such as 80 to 800 mPas.

In some embodiments, the Michael acceptor does not comprise a trifunctional (i.e. functionality of three) Michael acceptor. If a trifunctional (i.e. functionality of three) Michael acceptor is present it may be trimethylol propane triacrylate, pentaerythritol triacrylate, or glyceryl triacrylate.

In some embodiments, it is preferable if the Michael acceptor is present in between 20 to 50 wt% of the total binder system (i.e. based on the weight of the Michael donors and acceptors combined), such as 25 to 45 wt%.

In some embodiments, the Michael acceptor is a mixture of at least one tetrafunctional Michael acceptor and at least one difunctional Michael acceptor.

In some embodiments, the Michael acceptor is a mixture of at least one tetrafunctional Michael acceptor and at least one difunctional Michael acceptor, wherein the percentage of tetrafunctional Michael acceptor is between 20.0 to 80.0 wt% of the total Michael acceptor content.

In some embodiments, the Michael acceptor is a mixture of at least one tetrafunctional Michael acceptor and at least one monofunctional Michael acceptor.

In some embodiments, the Michael acceptor is a mixture of at least one tetrafunctional Michael acceptor and at least one monofunctional Michael acceptor wherein the percentage of tetrafunctional Michael acceptor is between 50.0 to 90.0 wt% of the total Michael acceptor content, such as between 70.0 and 80.0 wt%.

It is most preferred if the binder comprises a first Michael addition compound comprising one group only containing the motif -C=C-COO-C and a second Michael addition compound comprising 4 groups only comprising the motif -C=C-COO-C or the binder comprises a first Michael addition compound comprising two groups only containing the motif -C=C-COO-C and a second Michael addition compound comprising 4 groups only comprising the motif -C=C- coo-c.

It is most preferred if the Michael acceptor is a (meth)acrylic ester, preferably a (meth)acrylate, especially a combination of a tetrafunctional acrylate and either a difunctional or monofunctional acrylate.

Michael Donor

The Michael donor in the present invention will comprise at least one acidic proton, preferably at least two acidic protons. That proton is preferably located between two carbonyl groups and hence the Michael donor comprises the motif - CO-CRH-CO- where R is H or a hydrocarbyl group, such as a Cl -10 hydrocarbyl group.

A preferable Michael donor will have the following formula:

Formula (VI) wherein R is selected from hydrogen, a linear or branched alkyl, aryl, alkaryl or aralkyl group which are optionally substituted, and each of Yi and Y2 are independently selected from: linear or branched Cl-6- alkyl, C6-10-aryl, C7-10-alkylaryl or C7-10-arylalkyl groups; Cl-6-alkoxy groups; or amido groups which are optionally substituted.

If any of the aforementioned groups are substituted, no substituents should be included which substantially interfere with the crosslinking reaction.

Suitable Michael donors include activated C-H derivatives having a structure according to formula (VII): wherein Ra is hydrogen or an Cl-6-alkyl or C6-10-aryl group; and

Y and Y' are Cl-6-alkyl, C7-10-aralkyl or C6-10-aryl (R*), Cl-6-alkoxy or C6-10-aryloxy (OR*) or wherein in formula (VII) the -C(=O)-Y and/or -C(=O)-Y' group(s) is replaced by CN, NH2 or aryl.

Most preferred is that formula (VII) comprises malonate (Y and Y' are alkoxy or -OR*) or acetoacetate (Y is alkoxy or -OR* and Y' is alkyl or -R*). R* is preferably a C6-10 aryl group such as phenyl. The preferred malonates are polymers, preferably a polyester, polyurethane, acrylic or polycarbonate polymer. Also, mixtures or hybrids of these polymer types are possible.

In a most preferred embodiment, the Michael donor is a malonate containing compound (i.e. comprising -OCO-CH2-COO-). It is preferred that in the intumescent coating composition the majority of the activated C-H groups are from malonate, that is more than 50%, preferably more than 60%, more preferably more than 70%, most preferably more than 80% of all activated C-H groups in the crosslinkable composition are from malonate.

Examples of suitable components containing activated methylene or methine groups are generally disclosed in US4871822 (see especially column 4, lines 15-28), in which components contain a methylene and/or monosubstituted methylene group in the alpha-position to two activating groups such as, for example, carbonyl, cyano, sulfoxide and/or nitro groups. Preferred are components containing a methylene group in the alpha-position to two carbonyl groups, such as malonate and/or acetoacetate group-containing components, malonates being most preferred.

Suitable examples of malonate group-containing components may be mentioned malonic acid esters as disclosed in US2759913 (column 8, lines 51-52), and malonate group-containing oligomeric and polymeric components as disclosed in US4602061 (column 1, line 10 through column 2, line 13). Preferred are the oligomeric and/or polymeric malonate group-containing components such as, for example, polyesters, polyurethanes, polyacrylates, epoxy resins, polyamides and polyvinyl resins containing malonate groups in the main chain, pendant or both. The malonate group-containing polyesters can be obtained preferably by the transesterification of a methyl or ethyl diester of malonic acid, with multifunctional alcohols that can be of a polymeric or oligomeric nature. Malonate group-containing polyurethanes can be obtained, by reacting a polyisocyanate with a hydroxyl group- containing ester of a polyol and malonic acid, or e.g. by transesterification of an hydroxy functional polyurethane with a dialkylmalonate. Malonate group-containing epoxy esters can be obtained by esterifying an epoxy resin with malonic acid or a malonic monoester, or acid functional malonate polyester, or by transesterification with a dialkyl malonate, optionally with other carboxylic acids and derivatives thereof. Malonate group-containing polyamides, or polyamide-esters, can be obtained in the same manner as the polyesters, wherein at least a part of the hydroxy component is replaced with a mono- and/or polyfunctional primary and/or secondary amine. The malonate group-containing polyamides with malonamide functionality are less preferred. Other malonate group-containing polymers may be obtained by the transesterification of an excess of a dialkyl malonate with hydroxy-functional acrylic polymer. In this manner, a polymer with malonate group-containing sidechains may be formed. Any excess dialkyl malonate may be removed under reduced pressure or, optionally, be used as a reactive solvent.

Especially preferred malonate group-containing components for use with the present invention are the malonate group-containing oligomeric or polymeric esters, ethers, urethanes, and epoxy esters containing 1-50, more preferably 2-10, malonate groups per molecule. In practice polyesters and polyurethanes are preferred.

It is also preferred that such malonate group-containing components have a number average molecular weight (Mn) in the range of from about 100 to about 5000, more preferably, 250-2500, and an acid number of about 2 or less. Also, monomalonates can be used as they have 2 reactive C-H per molecule. Monomeric malonates can, in addition, be used as reactive diluents.

Acetoacetate groups may contain the motif C-CO-CHR-COO-C where R is H or an alkyl group.

Suitable acetoacetate group-containing components are acetoacetic esters as disclosed in US2759913 (column 8, lines 53-54), diacetoacetate components as disclosed in US4217396 (column 2, line 65 through column 3, line 27), and acetoacetate group-containing oligomeric and polymeric components as disclosed in US4408018 (column 1, line 51 through column 2, line 6). Preferred are the oligomeric and/or polymeric acetoacetate group-containing components.

Suitable acetoacetate group-containing oligomeric and polymeric components can be obtained, for example, from polyalcohols and/or hydroxyfunctional polyether, polyester, polyacrylate, vinyl and epoxy oligomers and polymers by reaction with diketene or transesterification with an alkyl acetoacetate. Such components may also be obtained by copolymerization of an acetoacetate functional (meth)acrylic monomer with other vinyl- and/or acrylic-functional monomers.

Especially preferred of the acetoacetate group-containing components for use with the present invention are the acetoacetate group-containing oligomers and polymers containing at least 1, preferably 2-10, acetoacetate groups. It is also especially preferred that such acetoacetate group-containing components should have an Mn in the range of from about 100 to about 5000, and an acid number of about 2 or less.

Components containing both malonate and acetoacetate groups in the same molecule are also suitable. Additionally, physical mixtures of malonate and acetoacetate group-containing components are suitable. Alkylacetoacetates can, in addition, be used as reactive diluents.

Again, as exemplified by the previously incorporated references, these and other malonate and/or acetoacetate group-containing components that can be used in the composition, and their methods of production, are generally known to those skilled in the art, and need no further explanation here.

The equivalent weight (EQW: average molecular weight per reactive functional group) of the Michael donor is preferably 100-2000, such as 100 to 500, preferably 125 to 250 g/eq.

The viscosity of the Michael donor may be 800 to 12000 rnPas, such as 1000 to 10000 rnPas.

In a preferred embodiment, the Michael donor has Formula (VI) which comprises malonate ester functionality, wherein both Yi and Y2 will be alkoxy groups.

In a further preferred embodiment, Formula (VI) will comprise acetoacetate functionality, wherein Y 1 will be an alkoxy group and Y2 will be an alkyl or aryl group, or vice versa.

In certain embodiments, the Michael donor will comprise a polymer with acetoacetate functionality, preferably wherein the polymer is polyester, polyether, polyurethane, polyacrylate, polyamide, polycarbonate or mixtures thereof.

In a highly preferred embodiment, the Michael donor will comprise a malonate containing polymer, preferably a polyester, polyurethane, polyacrylate, polyamide, polycarbonate or mixtures thereof, most preferably a polyester.

Malonate functional polymers can be obtained commercially or synthesised through transesterification reactions. For example malonate functional polymers can be prepared through the synthesis of one or more multi-hydroxyl functional reactants such as a diol and/or triol, one or more multicarboxylic acids (such as a dicarboxylic acid, and one or more malonate esters. The products are formed therefore by esterification /transesterification and can be complex but will contain the malonate functionality.

In certain embodiments, the Michael donor will comprise both malonate ester and acetoacetate functionality, optionally within the same compound.

In the most preferred embodiment, the Michael donor is a malonate functional polyester, preferably comprising functionality of 1 to 50, such as 2 to 10.

In some embodiments, the Michael donor will be at least one malonate functional polyester.

In some embodiments, the Michael donor will be at least one malonate functional polyester additionally comprising succinimide, where the amount of succinimide can vary, but will typically be present in an amount of 1.0 and 5.0% of the total malonate polyester by weight.

In a preferred embodiment, the Michael donor will comprise at least one trifunctional Michael donor. In an alternative embodiment, the Michael donor may have functionality lower than 3 or higher than 3. Most preferred Michael donors are malonate esters, malonate functional polyesters or acetoacetate functional polyesters. These can therefore be malonated and acetoacetylated resins.

In some embodiments, it is preferable if the Michael donor is present in between 50 to 80 wt% of the total binder system, preferably between 55 and 75.0 wt%.

In some embodiments, it is preferable if two Michael donor compounds are used. These may be present in a weight ratio of 1.0 to 10 to 10 to 1.0, more preferably wherein at least one compound is a malonate ester compound comprising succinimide and the other is a malonate ester compound free of succinimide.

The person skilled in the art will appreciate that succinimide and other kinetic control compounds with a pKa value lower than the C-H of the malonate can be used to adjust the open time of the coating composition. Such compounds include ethylacetoacetate, IH-benzotriazole, 1,2,4-triazole and malonate.

Latent Base Catalyst

The catalyst for the Michael addition reaction is a base, such as a strong base. In one embodiment, the catalyst is a latent base catalyst. A latent base catalyst is one that converts into a strong base during the crosslinking/curing process (these terms are used interchangeably herein). It is therefore a protected base. The latent base catalyst is preferably a carbonate salt of the following formula:

X -OCOO-R_b

Formula (VIII) wherein X represents a cation, such as an alkali or earth alkali metal ion, ammonium or phosphonium ion, and Rb is a hydrogen, or a linear or branched alkyl, aryl, alkaryl or aralkyl group, which may optionally be substituted. If Rb is substituted, the substituents should not interfere with the crosslinking reaction. Rb is preferably a Cl-6-alkyl, C6-10-aryl, C7-10-alkaryl or C7-10-aralkyl group, which may optionally be substituted.

The catalyst should be substantially free of acidic substituents, such as carboxylic acids or acidic cations. It will be appreciated that the valency of the metal ion balances the valency of the carbonate part of the molecule. It may be therefore that there are two carbonate ions if an alkaline earth ion is used.

A mixture of catalysts may be used.

In some embodiments, the catalyst is free of water.

For basic catalyst of Formula (VIII), X preferably represents a lithium, sodium or potassium ion, or more preferably a quaternary ammonium or phosphonium ion, such as NQ4 or PQ4 where Q represents an alkyl, aryl or aralkyl group. In a preferable embodiment, Rb is an alkyl group having 1 to 4 carbon atoms such as diethylcarbonate. The catalyst of Formula (VIII) is a latent base because, on drying, the carbonate salt decomposes releasing carbon dioxide to produce a strong base, such as a hydroxy-, alkoxy- or aralkoxy- base. The curing rate is thus dependent on the release of carbon dioxide, which can readily occur for a coating composition which covers a high surface area. The catalyst unblocks with the release of carbon dioxide and alcohol.

In a preferred embodiment, the catalyst is a latent base which is formed from the reaction mass of tetraalkylammonium hydroxide (such as tetrabutylammonium hydroxide) and a dialkyl carbonate (such as dimethyl carbonate or diethyl carbonate). Preferably the latent base catalyst is formed from diethyl carbonate.

In a preferred embodiment, the intumescent coating composition of the present invention comprises: a) i) at least one (meth)acrylic ester, preferably acrylate, Michael addition acceptor with a functionality of two or lower; and ii) at least one (meth)acrylic ester, preferably acrylate, Michael addition acceptor with a functionality of four or higher; b) at least one malonate ester or malonate functional polyester resin Michael donor; and preferably c) at least one latent base catalyst comprising an anion of formula

-OCOO-Rb

Rb is a hydrogen, or a linear or branched Cl-6-alkyl, C6-10-aryl, C7-10- alkaryl or C7-10-aralkyl group, which may optionally be substituted; and a cation, such as an alkali or earth alkali metal ion, ammonium or phosphonium ion.

In a further preferred embodiment, the intumescent coating composition of the present invention comprises: a) i) at least one (meth)acrylic ester, preferably acrylate. Michael addition acceptor with a functionality of two or lower; and ii) at least one (meth)acrylic ester, preferably acrylate. Michael addition acceptor with a functionality of four or higher; b) at least one acetoacetate ester or acetoacetate functional polyester resin Michael donor; and preferably c) at least one latent base catalyst comprising an anion of formula

-OCOO-Rb

In a further preferred embodiment, the intumescent coating composition of the present invention comprises: a) i) at least one diacrylate or monoacrylate Michael addition acceptor (i.e. with a functionality of one or two); and ii) at least one tetraacrylate Michael addition acceptor (i.e. with a functionality of four); b) at least one malonate functional polyester resin Michael donor; and preferably c) at least one latent base catalyst comprising an anion of formula

-OCOO-Rb

In a further preferred embodiment, the intumescent coating composition of the present invention comprises: a) i) at least one diacrylate or monoacrylate Michael addition acceptor (i.e. with a functionality of one or two); and ii) at least one tetraacrylate Michael addition acceptor (i.e. with a functionality of four); b) at least one acetoacetate functional polyester resin Michael donor; and preferably c) at least one latent base catalyst comprising an anion of formula

-OCOO-Rb

Plasticiser

The intumescent coating composition of the invention may comprise a plasticiser. A plasticiser is a substance that is added to soften and make more flexible, i.e. to increase its plasticity. The plasticiser should be compatible with the Michael donor, the Michael acceptor and the catalyst, and should mix with the binder system without precipitating out. The plasticiser can act as a softener by increasing the mobility of the crosslinked matrix which is influential on the melting temperature and the viscosity of the material.

Suitable plasticisers include derivatives (such as esters) of hydrocarbons, e.g alkyl esters, such as esters of benzoic acid, phthalic acid (e.g. phthalates such as dibutyl-, dioctyl-, dicyclohexyl-, diisooctyl-, diisodecyl-, dibenzyl-, or butylbenzyl phthalate), trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, citric acid and alkylsulfonic acid, alkyl phosphate esters and derivatives of polyester, polyether and epoxy and the like. Preferred plasticisers are alkyl esters for example phthalates, adipates, sebacates and benzoates or alkyl phosphate esters, which may be blended together or used solely.

An especially preferred plasticiser is di-2-ethylhexyladipate, known commercially as EFKA PL 5643 from BASF. This is a near colourless anhydrous liquid which is soluble in common organic solvents and almost insoluble in water and shows good behavior at low temperatures.

A further preferred plasticiser is 2-ethylhexyl diphenyl phosphate, known commercially as DISFLAMOLL DPO from Lanxess, which is highly efficient as a plasticiser, has a low viscosity and good low temperature properties. This plasticiser also shows a significant lower smoke density than other common plasticisers.

A further preferred plasticiser is dipropylene glycol dibenzoate, known commercially as Benzoflex 9-88 from Eastman, which is a non-phthalate plasticiser which offers low cure interference and reduced loading rate.

A further preferred plasticiser is a cyclohexanoate plasticiser, such as diisononyl- 1,4-cyclohexane dicarboxylate, known commercially as Elatur DINCD from Evonik or the 1 ,2-cyclohexane dicarboxylate Hexamoll DINCH from BASF. This is a plasticiser with excellent low-temperature flexibility and high UV resistance, thus contributing significantly to the weather resistance and durability of the products made thereof.

In certain embodiments, it is preferred if more than one different type of plasticiser is present in the intumescent coating composition, such as a mixture of an alkyl phosphate ester and an alkyl ester.

The plasticizer should not react with the Michael donor. The plasticizer should not react with any other component of the intumescent coating. Ideally therefore the plasticizer should be free of acid groups, hydroxyl groups, amine groups or thiol groups. The plasticiser is ideally not a fatty acid, fatty alcohol, fatty thiol or fatty amine. The plasticiser is ideally free of a fatty group.

Intumescent Additives

Carbon Donor

In some embodiments the intumescent coating composition comprises a carbon donor compound. The carbon donor is present to enable the formation of a carbonaceous char. The carbon donor can comprise an organic polyhydroxide compound (i.e. an organic polyol) and/or expandable graphite. For example, the carbon donor compound can comprise pentaerythritol, dipentaerythritol, tripentaerythritol, a polysaccharide (i.e. starch, cellulose, glycogen, and the like), a disaccharide sugar (i.e. sugar, lactose, maltose, and the like), a monosaccharide sugar (i.e. glucose, fructose, galactose, and the like), glycerol, or expandable graphite, or a combination of any thereof.

When present the carbon donor is preferably pentaerythritol or dipentaerythritol.

Acid Generating Compound

The intumescent coating composition comprises an acid-generating compound. The acid-generating compound can comprise 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 some examples, the acid-generating compound comprises a phosphoric acid ester of a polyhydroxy compound, or an ammonium phosphate (e.g., APP), or an amine phosphate (e.g., melamine phosphate), or a combination of any thereof.

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 above. Thus, APP produces phosphoric acid that is readily available to participate in the charring reactions.

APP compounds are polymeric phosphates, having P-O-P linkages, which may be represented by the formula:

[NH4PO3] wherein the average value of n is at least about 10, such as at least 100. Particularly useful APP compounds in the intumescent coating compositions of the present invention include those having values of n>1000.

The acid-generating compound can also comprise 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 can comprise, for example, borate salts such as ammonium pentaborate, zinc borate, sodium borate, lithium borate, aluminium borate, magnesium borate, borosilicate compounds, and combinations of any thereof.

Blowing or Expansion Agent

The intumescent coating composition comprises an expandable intumescent material (also known as a blowing agent or expansion agent). The blowing agent will produce non-flammable gases, generally nitrogen, when exposed to fire or heat. The produced gases will expand the char derived from the carbon source, forming a foam-like protective layer. Suitable examples of commercially available blowing agents include but are not limited to nitrogen-containing compounds such as glycine, melamine, melamine salts, melamine derivatives, urea, urea derivatives, dicyandiamide, guanidine, and isocyanurate derivatives, especially melamine.

Melamine derivatives include for example melamine formaldehyde, methylolated melamine, hexamethoxymethylmelamine, melamine monophosphate, di-melamine phosphate, melamine biphosphate, melamine polyphosphate, melamine pyrophosphate, melamine cyanurate, melamine borate, melam (N2-(4,6-diamino- l,3,5-triazin-2-yl)-l,3,5-triazine-2,4,6-triamine), melem (2,5,8-triamino- l,3,4,6,7,9,9b-heptaazaphenalene), and melon (poly[8-amino-l,3,4,6,7,9,9b- heptaazaphenalene-2,5-diyl)imino).

Urea derivatives include, for example, N-alkylureas such as methyl urea; N,N'-dialkylureas such as dimethylurea; and N,N,N'-trialkylureas such as trimethylurea; guanylurea; guanylurea phosphate; formamide amino urea; guanylurea phosphate; 1,3-diamino urea; biurea; and the like.

Isocyanurate derivatives of interest include tris-(2-hydroxyethyl)isocyanurate (THEIC). Boron-containing compounds useful as blowing agents in the present invention include, but are not limited to, boric acid, and borates, such as ammonium pentaborate, zinc borate, sodium borate, lithium borate, aluminium borate, magnesium borate, and borosilicate.

The blowing agent may also comprise monomeric or polymeric compounds such as meso-lactide, polylactide, a polysulfone, a polycarbonate, a polyester, a 1,1- di-activated vinyl compound, or an addition polymer of a 1 , 1 -di-activated vinyl compound, or a combination of any thereof.

A physical blowing agent such as expandable graphite and/or gas incorporating expandable microspheres may also be used.

Pigments and Fillers

The intumescent coating composition may comprise pigments and fillers well known in the art. Suitable fillers include barium sulfate, titanium dioxide, zinc oxide, aluminium oxide, aluminium hydroxide, magnesium hydroxide, carbonates, 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 fibrous fillers is especially preferred. The fibers useful in the intumescent coating composition of the present invention include, but are not limited to, inorganic fibers and organic fibers. Typical inorganic fibers include: carbide fibers, such as boron carbide fibers, silicon carbide fibers, niobium carbide fibers, etc.; nitride fibers, such as silicon nitride fibers; boron containing fibers, such as boron fibers, boride fibers; silicon containing fibers, such as silicon fibers, alumina- boron silica fibers, E-glass (non-base aluminium borates) fibers, C-glass (non-base or low base sodalime-aluminiumborosilicate) fibers, A-glass (basic-sodalime- silicate) fibers, S-glass fibers, inorganic glass fibers, quartz fibers, etc. The glass fibers may include E-glass fibers, C-glass fibers, A-glass fibers, S-glass fibers, etc. Useful inorganic fibers also include ceramic fibers and basalt fibers. Kevlar (para-aramid fibres) may also be used. Mineral fibres like CoatForce CF10 or Roxul MS 675 are preferred.

A preferred organic fibre is carbon fibre.

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

The fillers preferably constitutes from 5% to 40% by weight of the intumescent coating composition.

These components may act as a char reinforcer. In a preferred embodiment, the intumescent coating composition will comprise all three of an inorganic compound, a mineral fibre and a mineral clay.

The amount of char reinforcer can vary, but it will typically form 1.0 to 20 wt% of the total intumescent coating composition. If two or more char reinforcers are used then these percentages refer to the total content of char reinforcers present.

Colour pigments may also be used. Examples of the colour pigments include titanium white, red iron oxide, yellow iron oxide, black iron oxide, carbon black and organic colour pigments.

Additives

The intumescent and non-intumescent coating compositions may also comprise various other additives. Suitable additives will depend on the binder used and whether the coating composition is solventbome, waterborne or solvent free.

Examples of additives that may be present in the intumescent coating composition of the invention include, rheology modifiers, surfactants, antifoaming agents, pH adjusting agents, dispersing agents, biocides, wetting agents, coalescing agents, adhesion promoters and anticorrosive agents.

Suitable rheology modifiers may be polyamide wax, polyethylene wax, polysaccharide rheology modifiers, associative rheology modifiers, clays, organoclays such as organophilic phyllosilicates, cellulosic rheology modifiers, fumed silica or a mixture thereof. Various surfactants may also be used. This is especially relevant for the waterborne coating compositions. A number of different surfactants may be suitable. The surfactant may be non-ionic, anionic, cationic or amphoteric.

The intumescent 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.

In order to improve or facilitate dispersion of the 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.

Further optional additives may be included to aid char formation and to strengthen the char and prevent char degradation. Such additives include solids such as zinc borate, zinc stannate, zinc hydroxystannate, glass flake, glass spheres, polymeric spheres, fibres (ceramic, mineral, glass/silica based, carbon fibres as described above), aluminium hydroxide, aluminium oxide, boron phosphate, and fumed silica.

It may also be 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, and lead oxide. Auxiliary corrosion inhibitors include, for example a molybdate, phosphate, tungstate or vanadate, ultrafme titanium dioxide, and/or zinc oxide and/or a filler such as silica, calcined clay, alumina silicate, talc, barytes or mica.

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 65% by weight in the intumescent coating composition, such as 0.5 to 50 wt%, preferably 0.5 to 30 wt%. Organic Solvents

The coating compositions of the present invention preferably contains low amounts of organic solvent. The coating compositions of the present invention may also contain small amounts of water.

The nature of the organic solvent is not restricted, and publicly known solvents having boiling points of wide range are employable. Examples of such solvents include xylene, toluene, naphtha, white spirit, MIBK, methoxypropanol, MAK, MEK, n-butyl acetate, t-butyl acetate, benzyl alcohol, octyl phenol, resorcinol, ethyl acetate, ethylene glycol mono butyl ether acetate, diethylene glycol n-butyl ether acetate, propylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, dipropylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, ethanol, n-butanol, isobutanol, n-propanol, and isopropanol. The above solvents can be used singly or in combination of two or more kinds.

Solvents can be changed to tune the pot life and drying time properties of the Michael Addition composition.

Preparation of the Coating Composition

The intumescent coating composition may be prepared by any suitable technique that is commonly used in the field. Thus, the various constituents may be mixed together using a high-speed disperser, a ball mill, a pearl mill, a three-roll foam mill etc. The intumescent coating composition according to the invention may be filtered using bag filters, patron filters, wire gap filters, wedge wire filters, metal edge filters, EGLM tumoclean filters (ex Cuno), DELTA strain filters (ex Cuno), and Jenag Strauber filters (ex Jenag), or by vibration filtration.

The coating composition may be supplied as a kit of parts in which the Michael donor and Michael acceptor are kept separate or in which the catalyst is kept separate to prevent premature reaction.

In one embodiment part (A) comprises the Michael acceptor and part (B) the Michael donor. Other components can be supplied in either part (A) or (B). Alternatively, part (A) comprises the Michael acceptor and donor and part (B) the latent base catalyst. Other components can be supplied in either part (A) or (B). The skilled person will be able to design an appropriate kit to supply the components for transport.

Application of the Coating Composition

The intumescent coating composition can be applied to a substrate, preferably a steel substrate, by well-known standard application methods like conventional air spraying or by airless- or airmix- spraying equipment (or alternatively by means of a brush or a roller, in particular when used as a stripe coat).

The coating compositions may be applied in several layers in order to buildup layer thickness.

The pot life of the coating composition, once mixed is at least 20 mins, such as 60 mins, such as at least 90 mins, preferably up to four hours when measured as described in the methods section. Pot lives much longer than 4 hours are also possible, e.g. up to 20 hours.

Film Thickness

The intumescent coating composition is 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.

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 steel thicknesses and geometries might need different thicknesses. Substrates might be subject to different fire testing minimums and hence require different levels of protection. These values are however generally suitable.

The intumescent coating may be applied several times to achieve the appropriate dry film thickness. The intumescent coating composition is applied to a substate such as a metallic substrate such as a steel substrate. Any substrate that requires fire protection is possible. The intumescent coating composition can be applied directly to a substrate but ideally the substrate is protected with a primer layer.

Primer Layer

In some embodiments the substrate has a primer layer therein onto which the intumescent coating composition is applied. Alternatively, the coating composition of the invention may be used direct to substrate, e.g. direct to metal.

The primer layer is conventional and is typically formed from an epoxy resin, but other options may be used. The primer layer preferably comprises at least 20 wt% epoxy resin, preferably at least 25 wt% epoxy resin.

Examples of suitable primer layers are coatings based on epoxy, modified epoxy (such as modified with polyvinyl butyral), polyurethane, acrylic, vinyl and chlorinated rubber. Preferably the primer layer is an epoxy-based primer or a zinc- rich epoxy-based primer.

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

The dry film thickness of the primer is ideally in the range of 15 to 500 pm. In one embodiment therefore the invention provides a substrate with a primer layer and a layer of a cured intumescent coating obtained by curing the coating composition defined herein.

Top Coat

A top coat layer may be applied over the intumescent coating composition. In one embodiment however there is no top coat present and hence the intumescent coating of the invention acts as the top coat.

A top coat is generally present for aesthetics but also helps protect the underlying layers from the weather and sun damage. The top coat layer is obtained by the application of a top coat composition onto the intumescent coating layer. This is typically cured or partially cured before application of the top coat composition. The top coat composition may be solventbome or waterborne.

The top coat is preferably non-intumescent, e.g. it should be free of an acid generating compound and/or expansion agent, for example.

Preferably, the top coat composition has a volume solids content of at least 35%, such as at least 50%, e.g. 60 to 70% volume solids.

The top coat composition may comprise an (meth)acrylic-based binder, polyurethane-based binder, alkyd-based binder, vinyl-based binder or a silicone- based binder. The top coat composition may also be one prepared using Michael addition reactions similar to that of the intumescent coating composition of the invention. The use of an (meth)acrylic-based binder, silicone-based binder and a polyurethane-based binder is preferred.

The top coat composition may also contain standard additives such as pigments and fillers, thickening agents, dispersants and biocides. Suitable pigments and fillers include titanium dioxide, zinc oxide, aluminium oxide, barium sulphate, carbonates, borates, silica, silicates, heavy metal oxides such as cerium oxide, lanthanum oxide and zirconium oxide, mica, diatomaceous earth and bentonite clay. Preferred fillers are carbonate type fillers.

The fillers preferably constitute from 1% to 50% by dry weight of the top coat composition.

The invention will now be described with reference to the following nonlimiting examples and figure.

Figure 1 is a graphic representation of the time-to -failure (400 °C) test. The figure shows time-temperature curves for examples CE1, E2, E4, and a solvent-free 2K epoxy-based intumescent.

Methods

Determination of the solids content of the compositions

The solids content in the compositions are calculated in accordance with ASTM D5201-05.

Determination of the pot life The pot life of the intumescent coating composition is determined by measuring the viscosity increase directly after mixing 3.20 kg of the intumescent coating composition and spraying part of the mixture into a 1 L tin (total length = 136 mm and total diameter = 108 mm). The pot life is set to the time where the viscosity has doubled. All formulations have sufficient pot life that they were sprayable with a single leg pump, and all panels for fire testing were prepared this way.

Fire Performance Testing

The thermal insulation properties are evaluated using a mass loss calorimeter from Fire Testing Technology Ltd. Each formulation is applied via single leg airless spray to blasted and unprimed 100x100x3 mm steel panels at a wet film thickness of 1100 pm The coating is left to cure for 14 days at ambient temperature, and the resulting dry film thickness (DFT) is measured using a PosiTector 6000 Paint Thickness Gauge from DeFelsko to ensure that a consistent film thickness has been achieved. A Type K thermocouple is fixed into place on to the backside of the panel using aluminium tape, and the panel is then fitted inside a stainless-steel sample holder. The coated panel is exposed to a temperature of 735 °C at a distance of 25 mm (50 kW/m² heat flux) until the temperature of the panel reaches 405 °C. The temperature curve data is recorded using a Squirrel SQ2010 Universal Input Data Logger from Grant Instruments. The time- to -failure is recorded as the time taken for the panel to reach a temperature of 400 °C.

Intumescence Factor

The intumescence factor is determined by letting the expanded coating cool and recording the degree of char expansion (char height) using a hydrocone (fireproofing depth gauge). The intumescence factor is calculated by dividing the average char height by the average DFT. The intumescence factor provides an indication on the ability of a coating to expand when exposed to high temperatures which can cause a fire.

Char Rating

The char rating is determined from the fire performance testing. The char rating is highly important to determine the effectiveness of the internal char structure for protecting the substrate upon exposure to fire. The char is rated on a scale ranging from 0 to 4. A rating of 3 or 4 is considered to be acceptable and good, whereas a rating of 2 or less is considered to be unacceptable.

Examples

Table 1: Materials

*Grouped as “Additives” in Table 2. Table 2: Results

The data from Table 2 indicates that the key to efficient intumescent coating performance is the formation of a dense, expanded insulation layer, whereas brittle and void-filled char structures offer less thermal protection in the event of a fire. While the degree of expansion and char stability are important, the internal char structure is of utmost important when protecting steel specimens from fire exposure. The time-to-failure (400 °C) results are also important and are an indication of how well the intumescent coating composition is able to protect the substrate from the heat generated by a fire.

Intumescence Factor taken alone does not provide any conclusive information about the protective capabilities of the intumescent coating composition, but it is important that a coating intumesces during a fire - that is, expands when exposed to the high temperatures caused by a fire.

The efficiency of the compositions is dependent on the functionality of the Michael acceptor resin and the degree of polymer cross-linking. The best results are achieved when the amount of tetra-functional acrylate (i.e. Acure 550-105) is limited by using lower functional acrylates which are chemically incorporated into the polymeric structure. The reduction in cross-linking degree encourages the initiation of intumescence and char expansion, resulting in softer, denser chars with a lower propensity for void formation and an improvement in thermal insultation performance. The best examples are E3 and E4, as they combine good expansion, char structure, and thermal insulation properties.

All inventive examples in Table 2 are superior to a commercialised solvent- free epoxy-based intumescent product designed specifically for cellulosic fire scenarios.

Acure 550-105 (diTMPTA- tetra-functional acrylate) is required for effective curing performance, but when used alone, brittle and void-filled chars are generated when exposed to fire, and a poor thermal insulation barrier allows the temperature rise of the underlying steel to accelerate.

No comparative example was made next to the composition of EP2978779, as the pot life was too short for this coating composition and thus could not be applied by the conventional airless spray pump method. However, we highlight CE1-CE4, which features a tetrafunctional or trifunctional acrylic ester alone, wherein the results reflect a poorer performance when compared with the inventive examples, with regard to time-to-failure at 400 °C, char rating and intumescence factor.

Claims

1. An intumescent coating composition comprising: a) i) at least one Michael addition acceptor with a functionality of two or lower; and ii) at least one Michael addition acceptor with a functionality of four or higher; b) at least one Michael donor; and c) at least one catalyst.

2. An intumescent coating composition as claimed in claim 1 wherein the Michael acceptor aii) has a functionality of 4.

3. An intumescent coating composition as claimed in any preceding claim comprising an acid generating compound and a blowing agent.

4. An intumescent coating composition as claimed in any preceding claim comprising a carbon donor.

5. An intumescent coating composition as claimed in any preceding claim wherein the weight ratio of the Michael acceptor(s) ai to Michael acceptor(s) aii is 1 :5 to 5:1.

6. An intumescent coating composition as claimed in any preceding claim wherein the Michael acceptors are all (meth)acrylic esters, preferably acrylates.

7. An intumescent coating composition as claimed in any preceding claim wherein the Michael donor is a malonate ester or a malonate functional polyester.

8. An intumescent coating composition as claimed in any preceding claim wherein the Michael acceptor ai is 2-propylheptyl acrylate, lauryl acrylate, iso-butyl acrylate, tert-butyl acrylate, iso-decyl acrylate, tridecyl acrylate, isobomyl acrylate, dihydrocyclopentadienyl acrylate, ethyldiglycol acrylate, heptadecyl acrylate, 4-hydoxybutyl acrylate, tetrahydrofurfuryl acrylate, 2-phenoxyethyl acrylate, 2 -hydroxy-3 -phenoxypropyl acrylate, 2 -hydroxy ethyl acrylate, 2(2- ethoxyethoxy) ethyl acrylate, hydroxypropyl acrylate, 3 -acryloxypropyl trimethoxysilane, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 3 -methyl - 1,5-pentanediol diacrylate, 1,5 -pentanediol diacrylate, 1,8-octanediol diacrylate, 1,10-decanediol diacrylate, 1,12-dodecanediol diacrylate, bisphenol A diacrylate, neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, triethylene glycol diacrylate, butylene glycol diacrylate, dipropylene glycol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, cyclohexane dimethanol diacrylate, tertbutyl cyclohexyl acrylate, 3,3,5- trimethylcyclohexyl acrylate, stearyl acrylate, behenyl acrylate or tricyclodecane dimethanol diacrylate.

9. An intumescent coating composition as claimed in any preceding claim wherein the Michael acceptor aii is an acrylic ester containing 4 ester groups and up to 40 carbon atoms such as di-trimethylolpropane tetraacrylate and pentaerythritol tetraacrylate or is dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate.

10. An intumescent coating composition as claimed in any preceding claim comprising a) 3.0 to 20 wt% of Michael acceptors; b) 5.0 to 20 wt% of at least one Michael donor; c) 0.1 to 5.0 wt% of at least one catalyst.

11. An intumescent coating composition as claimed in any preceding claim wherein the at least one catalyst c) is a latent base catalyst preferably comprising an anion of formula -OCOO-Rb wherein Rb is a hydrogen, or a linear or branched Cl-6-alkyl, C6-10-aryl, C7-10-alkaryl or C7-10-aralkyl group, which may optionally be substituted; and a cation, such as an alkali or earth alkali metal ion, ammonium or phosphonium ion.

12. An intumescent coating composition as claimed in any preceding claim wherein the Michael acceptors are (meth)acrylic esters; the Michael donor is a malonate ester, malonate functional polyester or acetoacetate functional polyester; and preferably the at least one catalyst c) comprises an anion of formula

-OCOO-Rb wherein Rb is a hydrogen, or a linear or branched Cl-6-alkyl, C6-10-aryl, C7-10-alkaryl or C7-10-aralkyl group, which may optionally be substituted.

13. An intumescent coating composition as claimed in any preceding claim comprising: a) i) at least one diacrylate or monoacrylate Michael addition acceptor (i.e. with a functionality of one or two); and ii) at least one tetraacrylate Michael addition acceptor (i.e. with a functionality of four); b) at least one malonate functional polyester resin Michael donor; and preferably c) at least one latent base catalyst comprising an anion of formula

-OCOO-Rb wherein Rb is a hydrogen, or a linear or branched Cl-6-alkyl, C6-10-aryl, C7-10-alkaryl or C7-10-aralkyl group, which may optionally be substituted; and a cation, such as an alkali or earth alkali metal ion, ammonium or phosphonium ion.

14. An intumescent coating composition as claimed in any preceding claim further comprising at least one char reinforcer, preferably wherein the char reinforcer comprises: an inorganic compound, such as titanium dioxide; and/or a mineral fibre; and/or a mineral clay.

15. A substrate coated with an intumescent coating composition as claimed in any preceding claim which has been cured, preferably wherein the substrate is a steel substrate.

16. A process for the application of an intumescent coating composition to a substrate, comprising applying an intumescent coating composition as claimed in any of claims 1 to 14 to a primer layer on a substrate or directly on a substrate, e.g. by airless spraying, and allowing said coating system to cure.

17. Use of the intumescent coating composition as claimed in any of claims 1 to 14 for protecting a metal substrate e.g. from fire damage.