Intumescent coating composition and use thereof

Abstract

Intumescent coating composition comprising a binder and at least one intumescent material, wherein the binder comprises a polymer chain provided with C1-C4-alkoxysilane end groups, Characterized in that the binder is a blend of a first binder polymer and a second binder polymer both having a polymer chain provided with C1-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.

Description

[0001] Intumescent coating composition and use thereof

[0002] FIELD OF THE INVENTION

[0003] The invention relates to an intumescent coating composition comprising a binder material and at least one intumescent material, wherein the binder material comprises a polymer chain provided with Cl-C4-alkoxysilane end groups.

[0004] The invention also relates to the use of such an intumescent coating composition for coating or printing a substrate.

[0005] The invention further relates to a substrate provided with an intumescent coating obtainable by applying the coating composition onto the substrate and crosslinking thereof.

[0006] BACKGROUND OF THE INVENTION

[0007] Intumescent material imparts to an intumescent composition the ability to swell when exposed to heat. The intumescent material is typically provided in the form of a filler composition which comprises two or more ingredients, which together result in intumescence. Intumescent coating compositions are usually intended for application to steel framework for buildings either off-site (in the steel yard) or on-site (to the erected framework). Prior to application of the coating, the steel framework that normally has been blast cleaned, is usually provided with a primer coating. Suitable primers are for instance based on epoxy, suitably in a thickness of 25 to 100 microns, after which the coating is usually applied in separate layers. A decorative topcoat may be applied on the intumescent coating.

[0008] Such an intumescent composition is known from W02010 / 131037A1. The binder material of the known composition is a silane terminated polyurethane or a silane terminated polyether. The silane termination is for instance coupled to the polyurethane or the polyether with a terminal urethane group. The composition additionally comprises a plasticizer and a crosslinker, which is a siloxane compound. The composition is preferably provided as a two-part composition, with the binder polymer making up to 100% by weight of the first part and the intumescent ingredient being present in an amount of l-80wt% of the second part. The crosslinker is typically in the first part of the two-part composition, but it may also be added into the second part. Upon mixing the two parts together and allowing mixture to be exposed to atmospheric moisture, this moisture will initiate crosslinking of the polymer.

[0009] According to the examples, the one-part coating is applied in a dry film thickness of 0.65 mm, whereas the two-part coating is applied in a dry film thickness of almost 4 mm, and wherein the first and second part were applied in a ratio of 1:9. However, the time to reach 500°C is merely 35 minutes for the one-part coating, whereas 95 minutes are needed for the thicker two-part coating to reach a critical temperature of 550°C.

[0010] The known composition has the benefit of crosslinking via silanes, but still the composition has limitations. First of all, the two-part composition is practically a three-part composition, since the intumescent material and the remainder of the second composition are provided separately. This is cumbersome for a customer and may result in a less uniform distribution of the intumescent material. Furthermore, as specified in WO2014 / 095834, the use of humidity for the crosslinking initiation implies that the crosslinking starts at the surface, and that crosslinking degree will depend on the layer thickness and the actual humidity. Furthermore, the curing would not be uniform and the degree of crosslinking may strongly vary. WO2014 / 095834 thereto proposes the addition of water as the separately provided second part of the composition, with all remaining ingredients in the first part. However, this does not exclude the start of crosslinking by means of ambient humidity. Moreover, the sudden addition of a significant amount of water lead to strong hydrolysis and crosslinking, which is not necessarily uniform either.

[0011] Furthermore, as specified in WO2018 / 224317, the use of a plasticizer in the composition is on the one hand necessary to ensure an adequate viscosity, but on the other hand leads to introduction of volatile organic components therein. Moreover, when leaving out the plasticizer and formulating a one-part composition, the storage stability is insufficient. WO2018 / 224317 thereto proposes that the polyol component in the intumescent material, should be kept separately and be provided in the form of a liquid polyol or liquid epoxide. Such a separate composition may further comprise a conventional solid polyol compound, such as penta-erythritol. However, liquid epoxides and liquid polyols do not necessarily have optimum intumescent properties. Particularly, the resulting expansion ratios are probably low, and are not disclosed in WO2018 / 224317.

[0012] SUMMARY OF THE INVENTION

[0013] It is therefore a first object of the present invention to provide an intumescent composition with a binder polymer comprising silane end groups for crosslinking, which however does not have the above-mentioned disadvantages.

[0014] It is a further object of the present invention to use such coating for coating on substrates, such as steel substrates.

[0015] According to a first aspect, the invention provides an intumescent coating composition comprising a binder and at least one intumescent material, wherein the binder comprises a polymer chain provided with Cl-C4-alkoxysilane end groups, characterized in that the binder is a blend of a first binder polymer and a second binder polymer both having a polymer chain provided with C1-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, wherein the polymer chain of the binder polymers comprises a polyurethane.

[0016] According to a second aspect, the invention provides use of the intumescent coating composition of the invention for protecting a substrate.

[0017] According to a third aspect, the invention provides a method of applying an intumescent coating onto a substrate, such as a steel substrate, wherein the intumescent composition of the invention is applied, and which is subsequently crosslinked.

[0018] According to a further aspect, the invention provides a substrate provided with an intumescent coating obtainable by applying and crosslinking the intumescent coating composition of the invention. The resulting coating thus comprises a polymer network formed by crosslinking the binder material, and the at least one intumescent material.

[0019] The invention is based on the insight that a plasticizer is redundant when using a combination of a linear and a branched binder polymer. 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. Additionally, and not the least important, the performance in a fire test of coatings prepared with the intumescent coating composition was good. The test was performed with coating thicknesses of 1.0 mm and 1.5 mm, which thickness is relatively thin in the art.

[0020] According to the invention, the polymer chain of the binder polymers comprises a polyurethane. The term 'comprising a polyurethane' is chosen to specify that the binder polymer may contain further units than only polyurethane. In one implementation, the polyurethane would be prepared as a prepolymer, that is subsequently used for further reaction and optional polymerization into the binder polymer. Such further units are for instance urea joint unit and may also be comonomeric units, so as to obtain a polyurethane copolymer. Polyurethane chemistry has been found to allow for variations in the binder polymer by selection of the diol for the reaction with the isocyanate. Additionally, the polyurethane prepolymer may be further polymerized with a different diol than the one(s) in the prepolymer. In this manner, physical properties of the resulting binder polymer may be tuned, for instance with respect to hydrophilicity and adhesion to predetermined substrates, rigidity of the first polymer and so on. By further preference, aliphatic polyurethanes are used, i.e. polyurethanes based on aliphatic diisocyanates rather than aromatic diisocyanates. This is deemed preferable to avoid foaming, which hinders the application as a coating. It is observed for sake of clarity that the aliphatic polyurethanes may be based on cycloalkyl diisocyanates, such as isophorone diisocyanate (IPDI).

[0021] In a further embodiment, the second binder polymer is a branched polyurethane that comprises a branched ester, and especially an aliphatic branched ester. Preferably, it is obtainable from reacting an isocyanate with a - branched - ester-diol compound, preferably a polyester-polyol. Such a branched polyester has been found feasible from synthesis perspective.

[0022] In a further implementation, the branched polyester comprises a hydroxyl-group at a sidechain. This implementation is useful to ensure that the alkoxysilane end groups are arranged at a distance from the polymer chain, rather than on or at the polymer chain. A distance may be 1-20 atoms along a side chain, for instance 2-12 atoms along a side chain,, such as 3-8 atoms. By absence of a separate crosslinker siloxane, the location of the alkoxysilane end groups at the side chains contributes to defining the length of crosslinking bridges between different polymer chains. A larger length reduces the rigidity of the material during expansion of the intumescent material and therewith increases the expansion ratio.

[0023] In another embodiment, the first binder polymer is a linear polyurethane, wherein said linear polyurethane is 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. Good results have been obtained with a blend of a first binder polymer being a polyurethane based on a carbonate diol or polycarbonate diol and a second binder polymer being a polyurethane based on a polyester-diol compound.

[0024] 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. A typical indicator of molecular weight is viscosity. This is for instance in the range from 0.1 to 50,000 Pa.s, preferably between 1,000 and 40,000 Pa.s, such as between 5,000 and 35,000 Pa.s, all when measured at 25°C.

[0025] Preferably, the weight ratio of the first binder polymer over the second binder polymer is in the range of 2-20, preferably 3-10. For instance, the first, linear binder polymer is present in an amount of 15-40 % by weight of the first part of the intumescent composition and the second, branched binder polymer is present in an amount of 2-15% by weight. The total amount of binder polymer in the composition is preferably from 10 to 50% by weight, and more preferably from 30 to 40% by weight. The weight percentage herein refers to the weight relative to the dry weight of the composition.

[0026] In an important implementation, an acid catalyst is present for catalysis of cross-linking via the Cl-C4-alkoxysilane end groups, wherein the binder polymers are contained in a first component and wherein the acid catalyst is contained in a second component that is separated from the first component in a way that inhibits reaction. As the acid catalyst is in a separate part of the composition, there is no risk of premature activation of crosslinking. A preferred acid catalyst is an alkyl phosphate, more preferably mono- or dialkyl phosphoric acid. The preferred length of the alkyl group is C4-C12, such as C6-C10. One good example is di(2-ethylhexyl) phosphoric acid (CgH O -PO. OH). By further preference, both the first and second binder polymer and the intumescent material is provided in one part of the composition. This is easy for a customer. Moreover, the intumescent material and the binder polymers may be mixed during preparation of the intumescent composition, which contributes to uniformity. In one implementation, the acid catalyst is present in an amount in the range of 0.1%-10wt% based on the total binder content. The acid catalyst is preferably present in an amount of 0.5-5wt% based on the total binder content, more preferably 0.5-2 wt%, for instance 0.8-1.5 wt% based on binder content.

[0027] It is deemed most preferable, that the Cl-C4-alkoxysilane end groups are coupled to the polymer chain with urea junction units. The urea junction units contribute to chemical and scratch resistance of the coating. It is obtained by reaction of aminosilanes with an isocyanate in the polyurethane prepolymer. The silane is preferably coupled to the junction unit via a C2-C6-alkyl group, especially C2-C6 linear alkyl. More preferably, use is made of a so-called gamma-silane, such that there is a propylene-group between the silicon atom and the junction group. This is deemed beneficial over a so-called alpha-silane, so as to avoid electronic interaction between the junction group and the siloxane (Si-OR) binding. Furthermore, this longer alkyl group allows physical distance of the alkoxysilane group to the polymer chain, facilitating crosslinking reactions between alkoxysilane groups. Additionally, the resulting crosslinking-bridge is longer than in case of alphasilanes. The C1-C4 alkoxy-groups of the alkoxysilanes are preferably either methoxy or ethoxy groups. Ethoxy-groups are deemed preferred to avoid formation of methanol.

[0028] According a preferred embodiment of the invention, the intumescent coating composition is free of any siloxane cross-linking agent. This significantly reduces the risk of premature hydrolysis and crosslinking due to ambient humidity. Nevertheless, it is not excluded to add a siloxane crosslinking agent. In such a case, the siloxane cross-linking agent, which is typically a tetraalkoxysilane or a trialkoxyalkylsilane as known in the art, is preferably used in small quantities, for instance in an amount of up to 2% by weight of the dry weight of the intumescent composition. The amount may be less than 1% or even less than 0.5%. In the invention, the primary function of the crosslinking agent is not just to crosslink, but rather to modify the network and to extend the length of crosslinking bridges between the polymer chains. It may further be used to accelerate crosslinking. In view hereof, it appears preferably to use trialkoxyalkylsilanes and dialkoxydialkylsilanes. The number of bonds that may be generated with these types of compounds is smaller than with tetraalkoxysilanes.

[0029] According to another embodiment of the invention, the intumescent material preferably comprises three components: an acid source, a carbon source and a spumific or gas source. The acid source may be selected from, for instance, ammonium polyphosphate, melamine phosphate, magnesium sulphate and boric acid. The preferred acid source is ammonium polyphosphate. In one implementation, ammonium phosphate is used in coated form, such as for instance coated with melamine formaldehyde. Any phosphate added as an acid catalyst may further be an acid source for the purpose of intumescence. The acid source preferably constitutes from 35 to 65% by weight of the intumescent material. For sake of clarity, the term 'intumescent material' refers to any ingredient or combination of ingredients that has or contributes to intumescent behaviour. Each of said at least three components may be referred to as an intumescent ingredient alternatively.

[0030] Examples of suitable carbon sources include polyhydric alcohols, wherein the compound may have both linear, branched and even cyclic structure. Examples are pentaerythritol and dipentaerythritol. Starch and expandable graphite are other possible carbon sources. The carbon source preferably constitutes from 5% to 40% by weight of the intumescent material.

[0031] Suitable gas sources include melamine, melamine compounds preferably chosen from the group of melamine phosphate, melamine polyphosphate, melamine borate, melamine formaldehyde and melamine cyanurate, tris-(hydroxyethyl)-isocyanurate, ammonium polyphosphate and chlorinated paraffin. The gas source preferably constitutes from 5 to 40% by weight of the intumescent material.

[0032] Optionally, inorganic agents may be present that act as nucleating agents for the formation of char from the intumescent material upon heating during a fire. Examples of such nucleating agents include titanium dioxide, zinc oxide, aluminium oxide, silica, silicates, zirconium oxide, mica and clay. Titanium dioxide is generally preferred. The nucleating agent preferably constitutes from 1% to 25% by weight of the intumescent material.

[0033] While it is true that certain materials may have multiple functions for intumescence, such as acid source and gas source, it is generally preferred to include at least three individual compounds in the intumescent material. The combination of different materials has been found to lead to meet the various requirements of processability, stability at low temperatures, intumescence in case of fire with an acceptable expansion ratio. A typical intumescent material comprises titanium dioxide, pentaerythritol and / or dipentaerythritol, ammonium polyphosphate, melamine and / or melamine compounds. The total amount of intumescent material in the composition is typically in the range of 30-80% by weight, preferably 40-70% by weight of the total dry weight of the intumescent composition.

[0034] For sake of clarity, the term 'intumescent material' refers to any ingredient or combination of ingredients that has or contributes to intumescent behaviour. 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.

[0035] 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.

[0036] 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.

[0037] 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. BRIEF INTRODUCTION OF THE FIGURES

[0038] In Figures:

[0039] Fig. 1 shows the average temperature of the furnace during the fire tests specified in Example 3. The average temperature corresponded almost entirely to the setpoint.

[0040] Fig. 2 shows the temperature development of three samples of a coating with a thickness of 1.5 mm during heating in the fire test;

[0041] Fig. 3 shows the temperature development of three samples of a coating with a thickness of 1.0 mm during heating in the fire test.

[0042] EXAMPLES

[0043] Example 1

[0044] An intumescent coating composition was prepared as a two-part coating composition as specified in Table 1. Merely the acid catalyst was provided in the second part of the coating composition. The silane-modified aliphatic polymers being the first and second binder polymers were available from Worlee Chemie GmbH in Hamburg under the trade names WorleePur VP Si 4011 and WorleePur VP Si 2021 respectively. These are polyurethane polymers synthetized with aliphatic diisocyanates to and provided with urea joint units to which a propyltriethoxysilane is coupled. Ammonium phosphate was sourced as Exolit AP422 from Clariant. Titanium dioxide was sourced as Kronos 2300 from Kronos. Solvent was a mixture of butyl-acetate and propanol. Other ingredients are common and sourced from common sources such as specified in W02010 / 131037A1 and WO2018 / 224317A1.

[0045] Table 1 - intumescent coating composition

[0046] Example 2

[0047] Steel sections were coated with the intumescent coating composition specified in Table 1. The coating was applied in Coating 1 in a dry coating thickness of approximately 1.5 mm and in Coating 2 in a dry coating thickness of approximately 1.0 mm. The coatings were cured by mixing the first and second part of the composition. The resulting coatings were characterized. Coating 1 had a thickness of 1.366 mm, and Coating 2 had a thickness of 1.043 mm.

[0048] Example 3

[0049] 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 furnace temperature is shown in Fig. 1. The starting temperature was 19.0 °C and the relative humidity (RH) at the start of the test was 43.0%. The duration of the fire test was 135 minutes. The results are shown in Fig 2 and Fig 3 for Coatings 1 and 2 respectively.

[0050] For Coating 1 the critical temperature of 650 °C was reached after 87, 90 and 78 minutes for the three different samples. For Coating 2, the critical temperature of 650 °C was reached after 70, 62 and 69 minutes for the three different samples. All samples survived the 135 mm test duration. For Coating 1, the final temperatures were 817, 788 and 827 °C for the three samples. For Coating 2, the final temperatures were 887, 924 and 907 °C.

Claims

CLAIMS1. Intumescent coating composition comprising a binder and at least one intumescent material, wherein the binder comprises a polymer chain provided with Cl-C4-alkoxysilane end groups, Characterized in that 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, and the polymer chain of the binder polymers comprises a polyurethane, preferably wherein the polyurethane is aliphatic.

2. Intumescent coating composition as claimed in any of the claims 1, characterized in that the Cl- C4-alkoxysilane end groups are coupled to the polymer chain with urea junction units, preferably wherein the Cl-C4-alkoxysilane is coupled to the urea junction unit via a C2-C6 al kyl-bridge, and preferably wherein the Cl-C4-alkoxysilane is a gamma-silane.

3. Intumescent coating composition as claimed in claim 2, wherein the second binder polymer is a branched polyurethane that comprises a branched ester, such as an aliphatic branched ester, and wherein preferably the branched ester is obtainable from reacting an isocyanate with a branched ester-diol compound, preferably a polyester-polyol.

4. Intumescent coating composition as claimed in claim 1-3, wherein the first binder polymer is a linear polyurethane, wherein said linear polyurethane is based on a diol-compound chosen from the group of polyether, carbonate diols, polycarbonate diols, ester-diol, polyester-diol, polyetheresterdiol, more preferably a diol-compound chosen from the group of polyether, carbonate diols and polycarbonate diols.

5. Intumescent coating composition as claimed in claim 4, wherein the first binder polymer is a linear polyurethane based on a diol-compound chosen from the group of polyether, carbonate diols and polycarbonate diols, and the second binder polymer is a branched polyurethane that comprises an branched ester-diol compound.

6. Intumescent coating composition as claimed in claim 5, wherein the first binder polymer is a linear polyurethane based on a diol-compound chosen from the group of carbonate diols andpolycarbonate diols, and the second binder polymer is a branched polyurethane that comprises an aliphatic branched ester-diol compound.

7. Intumescent coating composition as claimed in any of the preceding claims, wherein the weight ratio of the first binder polymer over the second binder polymer is in the range of 2-20, preferably 3- 10.

8. Intumescent coating composition as claimed in any of the claims 1-7, wherein the binder material is present in an amount of 10-50wt% based on total dry weight of the coating composition, preferably 30-50wt%.

9. Intumescent coating composition as claimed in any of the preceding claims, further comprising an acid catalyst for catalysis of cross-linking via the Cl-C4-alkoxysilane end groups, wherein the binder polymers are contained in a first component and wherein the acid catalyst is contained in a second component that is separated from the first component, especially in a way that inhibits reaction, and preferably wherein the acid catalyst is an alkyl phosphate compound, preferably a mono- or dialkyl phosphoric acid.

10. Intumescent coating composition as claimed in any of the preceding claims, wherein the at least one intumescent material is chosen from the group of ammonium- and aminophosphates, melamine and melamine compounds, polyols such as penta-erythritol and dipentaerythritol, and aluminiumtrihydroxide.

11. Intumescent coating composition as claimed in any of the claims 1-10, wherein the amount of intumescent material is 40-80% by weight based on the total dry weight of the intumescent coating composition, preferably 45-60% by weight.

12. Intumescent coating composition as claimed in any of the preceding claims, wherein the intumescent coating composition is provided in two parts, to be mixed prior to coating a substrate.

13. Use of the intumescent coating composition as claimed in any of the preceding claims for coating a substrate, preferably a substrate with a hydrophilic surface, preferably wherein the substrate is chosen from a steel substrate, a fiber cement substrate, a calcium silicate, a concrete substrate and a wood substrate.

14. Substrate provided with an intumescent coating obtained by applying and crosslinking the intumescent coating composition as claimed in any of the preceding claims 1-12.

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