Intumescent composion and intumescent product obtained therewith

Abstract

Intumescent composition comprising an acid donor (A), a carbon donor (B), a binder polymer (C) and a blowing agent (D). The acid donor (A) is selected from the group consisting of ammonium polyphosphate, ammonium dihydrogen phosphate, ethylenediamine phosphate, ammonium pentaborate, guanylurea phosphate, diguanidine phosphate and mixtures thereof. The carbon donor (B) is selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, mannitol and other polyhydric alcohols and mixtures thereof. The blowing agent is provided in the form of microsphere particles comprising a thermoplastic polymer shell encapsulating a propellant, which microsphere particles are expandable microspheres.

Description

[0001] Intumescent composition and intumescent product obtained therewith

[0002] FIELD OF THE INVENTION

[0003] The invention relates to an intumescent composition comprising an acid donor (A), a carbon donor (B), a binder polymer (C) and a blowing agent (D), wherein:

[0004] The acid donor (A) is selected from the group consisting of ammonium polyphosphate, ammonium dihydrogen phosphate, ethylene-diamine phosphate, ammonium pentaborate, guanylurea phosphate, diguanidine phosphate and mixtures thereof;

[0005] The carbon donor (B) is selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, mannitol or other polyhydric alcohols and mixtures thereof;

[0006] The invention also relates to a method of applying an intumescent coating on a substrate using said intumescent composition, and to a method of forming a firestopping product comprising an intumescent body using said intumescent composition.

[0007] The invention further relates to products obtained with such methods.

[0008] BACKGROUND OF THE INVENTION

[0009] Such an intumescent composition is for instance known from W02010 / 131037A1. In the known intumescent composition, the acid donor may be selected from ammonium polyphosphate, melamine phosphate, magnesium sulphate and boric acid. The preferred acid donor is ammonium phosphate. Most preferred is an ammonium polyphosphate that is coated with melamine formaldehyde. The carbon donor is chosen from polyhydric alcohols, starch and expandable graphite, wherein the polyhydric alcohols pentaerythritol and dipentaerythritol are preferred. The blowing agent is preferably melamine or a melamine-containing compound such as melamine phosphate, melamine borate, melamine formaldehyde, melamine cyanurate. A nucleating agent may further be present, but is not deemed an essential ingredient in intumescent reactions. Examples thereof include titanium dioxide, zinc oxide, aluminium oxide, silica, silicates, heavy metal oxides, mica and bentonite clay. The preferred nucleating agent is titanium dioxide, which also provides opacity to the coating. Most preferred is a combination of titanium dioxide, pentaerythritol, ammonium polyphosphate and melamine, wherein each of these ingredients are present in an amount of 5-15% by weight of the intumescent composition, except for ammonium polyphosphate, which is present in an amount of 20-40% by weight of the intumescent composition.

[0010] During a fire, these ingredients will react to form a char. The char is an expanded and thermally resistant foamed structure, which is intended to replace elements that are molten away during the fire and ensure a sealing so that fire cannot pass the char. The said combination of ingredients works well and is widely used in coatings on steel, for instance. The behaviour of the intumescent composition during a fire is less well understood, but appears to include several steps.

[0011] When the temperature rises around and in an intumescent coating, the first step is that the binder polymer will soften or melt. For instance, a typical binder polymer is polypropylene with a melting point of 150°C. Polyethers have a melting point of or around 168=C. Other polymer bodies will typically collapse starting from these temperatures. It appears however that the intumescent fillers contribute to stability. Beyond 150°C, the intumescent fillers start to decompose. The acid donor starts to decompose to liberate acid. More specifically, ammonium polyphosphate will decompose into acidic polyphosphate, as well as ammonia (NH3). The decomposition reaction particularly proceeds above 250°C. The carbon donor starts to decompose to form aldehydes, which will react with the liberated acid. Carbon, typically polymerized, will be formed. The acidic polyphosphate may be hydrated.

[0012] A further step resides in the formation of a foam. Liberated gases such as ammonia, water and carbon dioxide will flow through the mixture, resulting in foam formation. This is believed to start at 200°C. Beyond foam formation, the generation of gases will give a cooling effect due to being an endothermic process. The decomposition of melamine, starting around 340°C further contributes to this gas formation, as it decomposes into NH3, CO2and H2O.

[0013] At the same time, a structure must be formed that is strong enough to withstand the fire for a long time and stabilize the gases in a foam-like structure called char. The melamine and titanium dioxide are believed to play a role here too. The melamine would react with ammonium polyphosphate, and the reaction product would have a thermal stability of up to 800°C prior to forming a ceramic coating. The titanium oxide would build an inorganic structure with released polyphosphate. This inorganic structure would facilitate solidification of material and crosslinking into the char.

[0014] In summary, it will be understood that the individual ingredients of an intumescent coating strongly interact with each other, and that hence it is not apparent for a skilled person that any modification would maintain intumescent properties. Nevertheless, certain ingredients are not deemed environmentally friendly and may even be banned through regulation. This especially applies to melamine. OBJECT OF THE INVENTION

[0015] It is therefore an object of the invention to provide an intumescent composition of the type mentioned in the opening paragraph with improved environmental impact, and particularly through reduction or complete removal of the melamine therein.

[0016] It is another object to use such an intumescent composition to provide an intumescent coating and / or a firestopping product comprising an intumescent body.

[0017] Further objects relate to the provision of substrates with intumescent coatings and to firestopping products comprising an intumescent body, wherein the intumescent coating or intumescent body has reduced melamine content and preferably is melamine-free.

[0018] According to a first aspect, the invention relates to an intumescent composition comprising an acid donor (A), a carbon donor (B), a binder polymer (C) and a blowing agent (D). The acid donor (A) is selected from the group consisting of ammonium polyphosphate, ammonium dihydrogen phosphate, ethylene-diamine phosphate, ammonium pentaborate, guanylurea phosphate, diguanidine phosphate and mixtures thereof. The carbon donor (B) is selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, mannitol or other polyhydric alcohols and mixtures thereof. The binder can be chosen broadly. According to the invention, the blowing agent is provided in the form of a microsphere particles comprising a thermoplastic polymer shell encapsulating a propellant. The microsphere particles are herein expandable microspheres.

[0019] It has been understood and confirmed by testing in preliminary experiments, that the provision of the blowing agent in the form of expandable microsphere particles may replace melamine in intumescent compositions. This result constitutes a big surprise, particularly since expandable microspheres as commercially available start to expand at relatively low temperatures, and typically lower than the melting temperature of the binder polymer of the intumescent composition. It is therefore not clear how such material with a low expansion temperature could replace the melamine. As discussed, melamine starts to decompose around 340°C, which is above the temperature at carbon is formed, which will be a skeleton of the char. Namely, the carbon is formed through the full carbonization of the polyalcohol with the acidic polyphosphate. How the expansion at low temperature may contribute to foam forming of the char, is not apparent. However, the inventor has understood that the expandable microspheres do not merely expand, but subsequently, i.e. at higher temperatures further decompose or at least react. Typically, expandable microspheres are based on polymers comprising acrylonitrile groups, or stated otherwise, are formed from acrylonitrile monomers, either as homopolymers or as copolymers. Like melamine, acrylonitrile includes nitrogen atoms that are connected to carbon atoms with multiple bonds. The inventor believes that these acrylonitrile groups may be converted during a heat treatment, creating a crosslinked network and potentially leaving a carbon structure or a carbonbased structure that includes nitrogen atoms. This conversion may liberate gases, such as water and potentially ammonia from the thermoplastic polymer, but also from the propellant contained within the thermoplastic polymer shell of the expandable microsphere. The first phase of such conversion of the thermoplastic polymer is understood to be a conversion of the triple carbon-nitrogen bonds into double carbon-nitrogen bonds, together with crosslinking and formation of a ladder structure comprising ringstructures, such as pyridine-rings. Additionally, dehydrogenation may occur.

[0020] Therefore, the thermoplastic polymer of the microsphere preferably is or comprises a polymer obtained from acrylonitrile monomers. The resulting polymer may be a homopolymer or a copolymer, and is formed by polymerization from ethylenically unsaturated monomers. Suitable acrylonitrile monomers include acrylonitrile, methacrylonitrile, alpha-ethoxyacrylonitrile, fumaronitrile and crotonitrile. Typical comonomers include acrylic esters, such as methyl-acrylate or ethyl-acrylate, methacrylic esters, such as methyl methacrylate, isobornyl methacrylate and ethyl methacrylate, acrylamides, vinyl pyridine, vinyl esters such as vinyl acetate, vinyl ether, styrene, dienes such as butadiene and isoprene. The ethylenically unsaturated monomers may further comprise crosslinking multifunctional monomers, typically in quantities from 0.1 to lwt% of the total amounts of ethylenically unsaturated monomers of the thermoplastic shell. Preferably, the thermoplastic polymer is halogen-free. Halogenic compounds may be converted at higher temperatures into dioxines and the like, which give a risk of cancer. Further information on the synthesis and monomers of microspheres can for instance be found in WO2013 / 178561, WO2016 / 091847, EP1592733B1, EP1981630B1, EP1981631B1, EP2026902B1, EP3484608B1. Such microspheres are for instance commercially available from Nouryon under the trade name Expancel®.

[0021] According to a preferred embodiment, the thermoplastic polymer of the microsphere comprises a copolymer made from ethylenically unsaturated monomers, wherein said monomers comprise methacrylonitrile and acrylonitrile. The total amount of methacrylonitrile and acrylonitrile monomers in the copolymer is suitably at least 80% by weight, preferably at least 90% by weight and may even be at least 95% by weight or 100% by weight. The mutual weight ratio of acrylonitrile and methacrylonitrile is for instance in the range of 1 (50% acrylonitrile) to 4 (80% acrylonitrile), such as 1.5 to 3. The use of microspheres based on both acrylonitrile and methacrylonitrile monomers is deemed advantageous in view of its thermal behaviour. The resulting microsphere has a starting temperature of expansion of above 100°C, such as in the range of 110-140°C and a maximum expansion temperature above 150°C, such as in the range of 150-220°C, preferably 160°C-200°C. Such a temperature range lies in the same range as the softening of the binder polymer. It ensures that the intumescent coating can expand quickly in case of fire, and fill any space even prior to transformation into a char. If expansion would start at a lower temperature, there is a risk of premature breakage of the microsphere, leading to loss of the propellant at a temperature where it will simply leak out. Moreover, the polymer decomposition occurs in a temperature range of 250°C -500°C, especially 300°C-400°C, as measured using thermogravimetric analysis (TGA). The decomposition temperature is in the range where the intumescent ingredients are transformed into a char, and wherein the skeleton of the shell may contribute to char formation. The high amount of acrylonitrile and methacrylonitrile groups allows transformation into a carbon skeleton. This is believed to occur by way of conversion of the nitrile groups into nitrogen-containing aromatic structures and removal of any nitrogen atoms therein.

[0022] It is observed for sake of clarity that the starting temperature Tstart and the maximum Tmax are typically provided by the manufacturer of the microsphere and may be determined using a Mettler TMA40 or TMA841 and a PC with STARe software, using a heating rate of 20oC / min and a load (net) of 0.06N. The starting temperature is the temperature at which expansion starts, the maximum expansion temperature is the temperature at which maximum expansion is obtained. The expansion continues to higher temperature. While the conditions during a fire and a fire test are significantly different from such controlled testing, this range nevertheless indicates the expansion relative to softening and melting of the binder polymer. It is furthermore believed that a wide expansion range is beneficial in a fire to accommodate the rather quick but continuous rise in temperature therein. With the term 'expansion range', reference is made to the range defined by the starting temperature Tstart and the maximum expansion temperature Tmax.

[0023] In one preferred implementation, the thermoplastic polymer of the expandable microsphere comprise a layer of colloidal silica, that is especially surface modified with organosilane groups. This addition is deemed beneficial for the use in intumescent compositions, as the colloidal silica enables network formation and therewith contributes to char formation. Furthermore, the choice of colloidal silica type can be used to tune the particle size of the unexpanded microspheres and as well as the size of the microspheres after expansion. The organosilane groups may be hydrophobic, hydrophilic or a mixture of hydrophilic and hydrophobic. Formation of expandable microspheres with such layer of colloidal silica is known from EP-B-3484608. Said layer is arranged at a surface of the microsphere and acts as a protective layer.

[0024] Fire tests have shown surprisingly that microspheres with a low expansion are preferred over microspheres with a high expansion. Expansion appears coupled to the size of the unexpanded microspheres and the size after expansion, as is typically reported in datasheets of suppliers. A preferred size of the unexpanded microspheres is in the range of 5-16 pm. A preferred size after expansion is 40 pm or below, such as 15-25 pm. These particle sizes are defined as average particle sizes measured by laser diffraction; Low Angle Laser Light Scattering (LALLS). The observed benefit of microspheres with low expansion may be due to one or more of following reasons: the expanded microsphere may break more quickly, thus supplying the propellant as a blowing gas into the char; the distribution of propellant through the intumescent composition is better, since smaller average particle size of the unexpanded particles implies also more particles; furthermore, the effective amount of polymer material is higher for the low expansion type, thus facilitating a formation of a stronger char that can withstand heat for a longer period.

[0025] The propellant is preferably a hydrocarbon. Suitable hydrocarbons are n-pentane, isopentane, neopentane, butane, isobutane, cyclopentane, hexane, isohexane, neohexane, cyclohexane, heptane, isoheptane, octane, isooctane, isodecane, isododecane or mixtures thereof, as well as petroleum ether. Preferred propellants comprise at least one of isobutane, isopentane, isohexane, cyclohexane and isooctane and mixtures thereof. Use of isobutane and / or isopentane, either as only propellant or in the form of a mixture, for instance with octane, isooctane or even isododecane is preferred. Use of a higher alkane as propellant will typically lead to some increase in the start temperature Tstart.

[0026] The acid donor used in the context of the invention is preferably ammonium polyphosphate (APP). It is preferably present in a range from 25% to 65% by weight, more preferably from 35% to 55% by weight of the intumescent ingredient of the intumescent composition. The term 'intumescent ingredient' is herein used to refer to carbon donor, acid donor, blowing agent and any nucleating agent. Examples of nucleating agents include titanium oxide, zinc oxide, aluminium oxide, silica, silicates, zirconium oxide, mica and clay. Titanium oxide is preferred. Such nucleating agent preferably constitutes from 1% to 25% by weight of the intumescent ingredient of the intumescent composition.

[0027] The carbon donor is preferably a polyhydric alcohol. Preferred embodiments include pentaerythritol and dipentaerythritol and a combination of both. The carbon donor preferably constitutes from 5% to 40% by weight of the intumescent ingredient of the intumescent composition. Preferably, the intumescent composition comprises the preferred acid donor in combination with the preferred carbon donor and the blowing agent of the invention. Preferably, titanium dioxide is present as nucleating agent.

[0028] In a further embodiment, the amount of melamine in the intumescent composition is at most 50% by weight relative to the total amount of blowing agent (melamine and microsphere), and preferably at most 25% by weight. More preferably, the amount of melamine is at most 10% by weight relative to the total amount of blowing agent, and by further preference the intumescent composition is free of melamine. For sake of clarity, this implies that melamine is neither present as such, nor in the form of a salt or compound, not in the form of a coating. It was found in experiments leading to the invention, that a combination of melamine and expandable microspheres led to less good results in the fire test that the use of expandable microspheres alone. This may be due to an interaction between the melamine and the microspheres, but also could be due to distribution of these components in the test composition, which used a binder polymer in the form of aqueous emulsion.

[0029] The binder polymer used in the intumescent composition of the invention can be chosen from a wide group of binder polymers known to the skilled person. Examples include polyacrylates, epoxies, polyethers, polyurethanes, polyureas, polypropylenes and copolymers thereof, as well as blends of binder polymers. Preferably, the binder polymer has a softening or melting temperature in the range of 130°C to 180°C.

[0030] In one preferred embodiment, the binder polymer is an aqueous polymer, in other words a polymer that is soluble or dispersible in an aqueous solution. Preferably, the binder polymer is provided as an aqueous emulsion. Examples of such binder polymers include polyacrylates, polymethacrylates, polyvinylacetates, polystyrene-acrylates including e.g., blends, copolymers and terpolymers thereof including, e.g., ethylene / vinyl acetate / acrylate terpolymer. Examples of suitable commercially available latices include acrylate polymer latex available under the trade designation RHOPLEX HA-8 from Rohm and Haas Co. (Philadelphia, Pa.), ELASTENE from Dow Chemicals and ethylene / vinyl acetate / acrylate terpolymer commercially available under the trade designations FLEXBOND 149 and AIRFLEX 600 BP from Air Products and Chemicals (Allentown, Pa.). Preferably the latex composition includes from about 30% by weight to about 75% by weight polymer. The use of such binder polymer facilitates coating of the intumescent composition on a variety of substrates and is environmentally friendly.

[0031] In another embodiment, the binder polymer is chosen from the group of polyethers, polyurethanes, polyureas, polypropylenes and copolymers thereof. These polymers have sufficient temperature stability and have been found to contribute to a high expansion factor, particularly when tested as coatings on steel. One preferred embodiment is a silane-terminated polymer, such as a silane- terminated polyether or polyurethane. Such binder polymers are known per se from W02010 / 131037 Al. In a further preferred embodiment, the binder polymer comprises a polymer chain provided with Cl- C4-alkoxysilane end groups, wherein the binder is a blend of a first binder polymer and a second binder polymer both having a polymer chain provided with Cl-C4-alkoxysilane end groups, wherein the first binder polymer comprises a linear polymer chain, and wherein the second binder polymer comprises a branched polymer chain, wherein at least of some of the side chains of said branched polymer chain are provided with C1-C4 alkoxysilane end groups. Such combination of a linear polymer chain and a branched polymer chain has been found to render a plasticizer redundant. At the same time, the branched binder polymer allows formation of a three-dimensional network without the need of a separate alkoxysilane crosslinking agent. Therewith the risk of premature crosslinking due to undesired hydrolysis of the alkoxysilane and the previously observed viscosity increases are avoided. The binder polymers are herein preferably polyurethane polymers or copolymers, and more preferably aliphatic polyurethanes. The first binder polymer is preferably a linear polyurethane based on a diol-compound chosen from the group of polyether, carbonate diols, polycarbonate diols, ester-diol, polyester-diol, polyetherester-diol, more preferably a diol-compound chosen from the group of polyether, carbonate diols and polycarbonate diols. The second polymer preferably comprises a branched ester. Molecular weights and chain lengths of the first and second binder polymer are set as known to the skilled person in the art of polyurethane chemistry and the weight ratio of the first binder polymer over the second binder polymer is preferably in the range of 2-20, more preferably 3-10. Further details hereof can be found in the non-prepublished application EP23215066.4 in the name of Applicant, which is herein included by reference.

[0032] The composition may further include one or more additives, such as antioxidants, colour pigments, UV absorbers, rheology modifiers, wetting agents, structuring fibers, additives to aid char formation and to strengthen the char and prevent char degradation, ash-crust stabilizers such as mineral fibers, carbon fibers or glass fibers, flame retardants, a dehydrogenation catalyst.

[0033] In a preferred embodiment, the composition is free of a plasticizer. However, use of a separate plasticizer is not excluded either. If used, its concentration in the intumescent composition may be lowered compared to the amounts specified in W02010 / 131037, which is preferably around 20% by weight of the total dry weight of the composition. Amounts of at most 10% by weight or even at most 5% by weight seem sufficient. In use, the intumescent coating composition will be applied as a protective coating onto a substrate. The substrate is for instance a steel body or steel frame for use in constructions. However, the composition is also deemed feasible for other substrates, including cement, fiber cement, calcium silicate, concrete and so on. The application of the intumescent coating composition may be preceded through the application of a primer, such as an epoxy primer. The need for a primer coating generally depends on the substrate and environment in which the substrate is going to be used. Close to sea, highways and industrial areas the risk of corrosion is higher than in rural areas and hence a primer may be necessary. The composition may be applied in thicknesses from generally 0.5 mm to 5 mm, and preferably in the range of 0.7 to 2.5 mm, more preferably 0.8 to 1.8 mm.

[0034] It is observed that any weight% hereinabove refers to total dry weight of the intumescent composition, unless otherwise specified or it would follow otherwise from the context. Embodiments discussed hereinabove apply to any and all aspects of the invention. Further preferred implementations are discussed hereinafter with respect to the examples. Where reference is made to alkyl-, alkoxy- and the like, the chain length can be chosen by the skilled person in the art and does not deviate from what is common in the art and / or functional for the desired chemical behaviour. As is known, an intumescent composition of the type of the invention, forms a char when exposed to high temperature, for instance above 200°C, such as in case of fire. It is thus a char-forming intumescent composition.

[0035] EXAMPLES Example 1 An intumescent coating composition was prepared that comprised an aqueous emulsion polymer commercially available from Dow Chemicals under the trade name Elastene™ 404, with 60 % by weight of solids. The acid donor was ammonium phosphate was sourced as Exolit AP422 from Clariant. The carbon donor was a micronized pentaerythritol derivative as commercially available from Perstorp under the tradename Charmor™ PM40. Titanium dioxide was sourced as Kronos 2300 from Kronos and served as nucleating agent. Other ingredients included the blowing agent as well as conventional wetting and dispersing agents (surface additives) and conventional rheology additives. Water was added to tune viscosity. Further details on the intumescent composition are given in Table 1.

[0036] Table 1 - intumescent coating composition

[0037] As blowing agent two different expandable microspheres from Nouryon Specialty Chemicals BV were used, either as sole blowing agent or in combination with melamine. The combinations are shown in Table 2 and the total amount of blowing agent was in each case identical at 9.4% by weight. Microsphere A is a product sold under the trade name Expancel™ 920 DU 20. Microsphere B is a product sold under the trade name Expancel™ 909 DU 80. According to information in safety data sheets on the 909 and 920 products, the products are based on the monomers acrylonitrile and methacrylonitrile and the propellant is isopentane. These microspheres typically expand in the range between 100°C and 250°C. Product B is listed in Nouryon's product specification (Technical Datasheet Expancel® DU Microspheres, 2024-09) with a starting temperature of 118°C -128°C and a maximum expansion temperature in the range of 172-187°C, as specified. It has an average particle size prior to expansion from 18-24 pm, an average particle size after expansion of around 80 pm and a density of at most 10 kg / m3. Product A is listed to have a starting temperature of 118°C -143°C and a maximum expansion temperature in the range of 152-172°C, as specified. It has an average particle size prior to expansion from 5-9 pm, an average particle size after expansion of around 20 pm and a density of at most 25 kg / m3. Product A has been referred to in marketing presentations of Nouryon as an example of a microsphere with low expansion, and Product B was referred to as a microsphere with high expansion.

[0038] Table 2 - blowing agents of test

[0039] Example 2

[0040] Steel sections were coated with the intumescent coating composition specified in Table 1 and the blowing agents 1-5 specified in Table 2. The intumescent was applied in in a wet coating thickness of 1.0 mm (dry coating thickness approximately 0.8 mm). The Coatings 1 and 2 were subjected to a fire test in line with ISO 1182. Each test was performed with three samples. Thereto, the steel sections were placed in a wall of 200 mm thickness and made of ytong blocks. The walls with the incorporated steel sections were put into a furnace. Six thermocouples are installed in plates using insulation pads, in order to control the furnace temperature. The furnace temperature was increased according to the fire curve specified in said ISO standard. The starting temperature was 19.0 °C and the relative humidity (RH) at the start of the test was 43.0%. Table 3 shows the results of the fire test in minutes duration. The duration is the time needed to reach a temperature of 500 °C.

[0041] Table 3 - duration needed to reach 500°C in a fire test for compositions 1-5

[0042] It is apparent from Table 3 that the intumescent compositions performed better with increasing content of microspheres (and decreasing content of melamine). This indicates that microspheres work properly as a blowing agent in an intumescent composition. The performance of the compositions with microsphere type B was less good than those with microsphere type A. It is observed that this is surprising, since the microsphere type B was one with high expansion, whereas type A was one with low expansion. Still, both worked well, and the difference when using the microspheres as sole blowing agent (examples 3 and 5) is merely six minutes. The overall satisfactory performance was confirmed by visual inspection of the samples after the fire test. No cracks or slits were observed in the formed crust. There were no parts of the coating that fell down. The crust was solid and compact and had a uniform thickness over across width and length of the samples. If any longer duration would be desired, this can for instance be achieved by means of a larger coating thickness. The 0.8 mm dry thickness is comparatively thin in the field of intumescent coatings. A typical dry thickness is 1.5 mm, which is rather the double.

Claims

Claims1. Intumescent composition comprising an acid donor (A), a carbon donor (B), a binder polymer (C) and a blowing agent (D), wherein:The acid donor (A) is selected from the group consisting of ammonium polyphosphate, ammonium dihydrogen phosphate, ethylene-diamine phosphate, ammonium pentaborate, guanylurea phosphate, diguanidine phosphate and mixtures thereof;The carbon donor (B) is selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, mannitol and other polyhydric alcohols and mixtures thereof; characterized in that the blowing agent is provided in the form of microsphere particles comprising a thermoplastic polymer shell encapsulating a propellant, which microsphere particles are expandable microspheres.

2. The intumescent composition as claimed in claim 1, wherein the propellant is at least one hydrocarbon with a boiling temperature, which is not higher than a glass transition temperature of the thermoplastic polymer.

3. The intumescent composition as claimed in any of the preceding claims, wherein the thermoplastic polymer shell comprises a thermoplastic polymer or copolymers obtained from nitrile containing monomers.

4. The intumescent composition as claimed in claim 3, wherein the thermoplastic polymer or copolymer is halogen-free.

5. The intumescent composition as claimed in claim 3 or 4, wherein the monomers comprise acrylonitrile and methacrylonitrile.

6. The intumescent composition as claimed in claim 5, wherein the amount of acrylonitrile and methacrylonitrile monomers is at least 80% by weight, and preferably at least 90% by weight of the total amount of monomers for the thermoplastic copolymer.

7. The intumescent composition as claimed in any of the preceding claims 3-6, wherein the microsphere further comprises a protective layer of colloidal silica, preferably modified with at least one of hydrophobic organosilane groups and hydrophilic organosilane groups.

8. The intumescent composition as claimed in any of the preceding claims, wherein the microsphere particles have an onset temperature in the range of 110°C to 160°C.

9. The intumescent composition as claimed in any of the preceding claims, wherein the binder polymer is chosen from a silane-terminated polyurethane, a silane- terminated polyether, a silane terminated polyurea or a copolymer of at least two of polyurethane, polyether and polyurea with a silane termination.

10. The intumescent composition as claimed in any of the claims 1-8, wherein the binder polymer is an aqueous emulsion polymer.

11. The intumescent composition as claimed in any of the preceding claims, wherein:The acid donor is present in an amount in the range of 15-35% by weight, The carbon donor is present in an amount in the range of 5-15% by weight, The binder is present in an amount in the range of 15-60% by weight, The blowing agent is present in an amount in the range of 5-15% by weight, wherein said amounts are weight percentages based on dry weight of the composition.

12. The intumescent composition as claimed in claim 11, wherein:The acid donor is present in an amount in the range of 22-28% by weight, The carbon donor is present in an amount in the range of 8-12% by weight, The binder is present in an amount in the range of 35-55% by weight,The blowing agent is present in an amount in the range of 8-12% by weight, wherein said amounts are weight percentages based on dry weight of the composition.

13. The intumescent composition as claimed in any of the preceding claims, especially claims 11 and 12, wherein the acid donor is ammonium polyphosphate and the carbon donor is selected from the groupcomprising erythritol, pentaerythritol and dipentaerythritol and mixtures thereof, and preferably further comprising a nucleating agent.

14. Method of providing an intumescent coating onto a substrate, comprising the steps of:- providing the intumescent composition as claimed in any of the preceding claims in an aqueous form- applying the intumescent composition onto at least a portion of the substrate- drying the intumescent composition to obtain said intumescent coating.

15. Substrate with an intumescent coating provided with an intumescent composition comprising an acid donor (A), a carbon donor (B), a binder (C) and a blowing agent (D) as claimed in any of the preceding claims 1-13, wherein: the acid donor (A) is selected from the group consisting of ammonium polyphosphate, guanylurea phosphate, diguanidine phosphate, ammonium dihydrogen phosphate, ethylene-diamine phosphate, ammonium pentaborate and mixtures thereof; the carbon donor (B) is selected from the group consisting of glucose, arabinose and other monosaccharides, lactose, maltose and other disaccharides, starch, cellulose, dextrin and other polysaccharides, sorbitol, erythritol, pentaerythritol, dipentaerythritol, mannitol and other polyhydric alcohols and mixtures thereof; the blowing agent is provided in the form of a microsphere particles comprising a thermoplastic polymer shell encapsulating a propellant.

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