Improved resin systems for intumescent fire-resistant coatings.

Abstract

The present invention relates to a novel reactive resin system for intumescent coatings and a method for producing said resin system. Intumescent coatings are used in particular for fire protection of metal components such as steel girders in building construction. Here, reactive foaming of said coatings occurs in the event of a fire, forming a fire-resistant insulating layer with low thermal conductivity on the metal girders, which, due to the associated thermal insulation, prevents premature thermally induced destruction of said components. Here, the present invention relates in particular to a methacrylate-based resin system produced by a novel method in which a first monomer fraction is polymerized to a degree of up to 95% by weight and then diluted with a second monomer mixture. The glass transition temperature of the polymer component of the composition formed in this case is particularly low compared to the prior art. Furthermore, the organic acid incorporated in the resin system has a surprising synergistic effect with the filler system. It has been found that the resin system produced in this way is particularly efficient in temperature-induced foaming due to its small pore and closed cellular foam structure.

Description

[Technical field]

[0001] The present invention relates to a novel reactive resin system for intumescent coatings and a method for producing said system, which is used in particular for fire protection of metal components such as steel girders in building construction, where reactive foaming of said coatings occurs in the event of a fire, forming a fire-resistant insulating layer with low thermal conductivity on the metal girders, the associated thermal insulation preventing premature thermally induced destruction of said components.

[0002] Here, the invention relates in particular to methacrylate-based resin systems produced by a novel method in which a first monomer mixture is polymerized to a degree of up to 95% by weight and then diluted with a second monomer mixture. The glass transition temperature of the polymer component of the composition formed in this case is particularly low compared to the prior art. Furthermore, the organic acid incorporated in the resin system exerts a surprising synergistic effect with the filler system. The resin system produced in this way has been found to be particularly efficient in temperature-induced foaming due to its small pore and closed cellular foam structure.

[0003] prior art First generation intumescent coating systems were based on high molecular weight thermoplastic resins based on acrylate, methacrylate and / or vinyl monomers and required large amounts of solvent or water to apply to suitable metal surfaces, with correspondingly long drying times.

[0004] Such intumescent coatings are typically applied on-site during the construction phase, but are preferably applied ex-situ before transport to the construction site, as this can be done under controlled conditions, but can also result in inefficient processing times if the drying times are long, especially since coatings must be applied successively on different sides to ensure completeness.

[0005] CN 112029367 describes, for example, an intumescent system in the form of an emulsion containing core-shell particles in water, the core of which is crosslinked.

[0006] CN111995919 discloses an emulsion of acrylic polymer as an ultra-thin intumescent coating, as does CAN3028431. The acrylic polymer is present in the form of core-shell particles, and the core is crosslinked.

[0007] JP 2003-171579 A relates to a mixture of an unpolymerized (meth)acrylic monomer mixture and a (meth)acrylic polymer. This mixture can be used as an intumescent coating. There is no disclosure of terminating the polymerization at a predetermined degree of polymerization.

[0008] DE 19630063 A1 relates to interior parts for rail vehicles. No intumescent coating is disclosed.

[0009] Epoxy-based intumescent coatings are advantageously used in the offshore industry. They are characterized by good resistance to ageing and relatively short drying times. Polyurethane systems have also been intensively studied. They are likewise characterized by relatively short drying times and good water resistance. However, the results of fire tests have been unsatisfactory due to poor adhesion of the coatings to the steel. Details are given in Development of alternative technologies for off-site applied intumescent, Longdon, PJ, European Commission, [Report] EUR (2005), EUR 21216, 1-141.

[0010] Another generation of intumescent coatings is based on (meth)acrylate reactive resins. The application of these resins has the great advantage that no solvent is required and the resins cure relatively quickly after application compared to the above-mentioned systems. This not only allows for faster processing but also, in particular, a lower content of residual volatile components in the applied coating. Such an intumescent coating system was first disclosed in EP 1 636 318 B1.

[0011] Further improvements of (meth)acrylate-based systems were subsequently described, for example in EP 2171004. These are characterized by a particularly high proportion of acid groups in order to improve metal adhesion. EP 2171005 discloses a development of such systems, which is characterized in particular by the copolymerization of diacids or copolymerizable acids with spacer groups. This makes it possible to further improve metal adhesion.

[0012] However, all these systems leave room for further improvement: for example, the formulation freedom is very limited, and only relatively thick layers can be applied, which, combined with other drawbacks, means that for example the foam height when needed or in case of fire can only be set to a minimum.

[0013] A further disadvantage is the relatively complex manufacturing process for the resin. What all the (meth)acrylate systems described in the prior art, which are otherwise very advantageous, have in common is that the solid thermoplastic polymer contained in the resin is first manufactured separately, then dissolved in the monomer components, preformed with additives and then finally compounded just before application as a two-component system. This process sequence is relatively complex and there is a great interest in simplifying it.

[0014] WO 2021 / 180488 describes for the first time the preparation of methacrylate-based reactive resins for intumescent coatings by the syrup process. Here, the monomer mixture is polymerized to a degree of polymerization of 70% and then the polymerization is terminated. Here, the composition is essentially similar to known reactive resins obtained by dissolving suspension polymers or granules in a monomer mixture. Differences arise in particular due to the type of polymer chain.

[0015] assignment It was therefore an object of the present invention to provide a significantly simplified process for the production of (meth)acrylate-based intumescent coatings.

[0016] In particular, there was a need for a simplified production process which, compared to the processes for producing (meth)acrylate-based intumescent coatings described in the prior art, allows the omission of at least one isolation or compounding step.

[0017] Furthermore, the challenge was to provide new formulations for two-component intumescent coatings which, in addition to very good metal adhesion and easy processability, also allow greater freedom in terms of the application of additives and the subsequent adjustment of the foaming control, in particular in terms of the subsequent presetting of the foam height and foam quality, e.g. the proportion of particularly high closed-cell foams.

[0018] Further problems not explicitly mentioned may become apparent below from the detailed description or examples of the invention and from the overall context of the invention.

[0019] solution These problems are solved by providing a novel method for the preparation of reactive resins for intumescent coatings. In this method, a first monomer mixture, which comprises at least one acid-functional monomer, is polymerized to a degree of polymerization of 70% to 95% by weight. The polymerization is then terminated once the desired degree of polymerization has been reached. The polymer formed according to the invention has a glass transition temperature, calculated according to the Fox formula, of less than 23° C., which is clearly lower than that reported for the corresponding resins in the prior art. Furthermore, the method according to the invention is characterized in that, after the end of the polymerization, the mixture comprising 70% to 95% by weight of polymer is diluted with a second monomer mixture, which is different from the first monomer mixture.

[0020] The intumescent fireproof coatings described in the prior art consist in particular of multi-component systems, which are formulated primarily from thermoplastic polymers dissolved in monomers. However, the present invention shows that liquid polymers, i.e. polymers with a glass transition temperature such that they are liquid in the undissolved state at room temperature below 23° C., are also suitable for use. Furthermore, polymerized acid components, such as 2-carboxyethyl acrylate in particular, play a role in improving adhesion to the substrate, and additionally formulated acid components, such as acrylic acid or methacrylic acid in particular, play a role in controlling the surprising foam height in the final use as a fireproof coating.

[0021] The Fox equation is a very simple and yet realistic method for calculating the glass transition temperature of homogeneous (i.e., statistically distributed repeat units) copolymers, and has proven to be particularly useful for (meth)acrylate copolymers (optionally with styrene), where the notation (meth)acrylate includes co-acrylates, co-methacrylates, and copolymers containing acrylates and methacrylates. Here, for two monomers, the Fox equation is as follows, but can be extended to many different comonomers as well: T g =T g1 (x1 )+T g2 (x 2 )…+T gy (x y ) Where: T g : Theoretically calculated glass transition temperature of copolymer T gy : Glass transition temperature of homopolymer of monomer y x y : weight fraction of monomer y in a monomer mixture or in a repeat unit in a polymer.

[0022] According to the present invention, all glass transition temperature data relate to polymers prepared by free radicals at the conventional polymerization temperatures of 40°C to 120°C. Exotic polymers prepared at much lower temperatures, for example by anionic polymerization or stereoselectively by GTP, are not relevant to the present invention. For such polymers, the Fox formula cannot be used in selected form, since the stereoregularity is significantly different. The glass transition temperatures of homopolymers prepared by radical polymerization are known from the literature.

[0023] In the scope of the present invention, a monomer mixture is generally understood to mean a monomer mixture that does not contain a solvent. In particular, a monomer mixture in the sense of the present invention does not contain water. Thus, a monomer mixture is preferably a mixture of monomers. These statements and preferred forms apply independently to both the first monomer mixture and the second monomer mixture.

[0024] The first monomer mixture is preferably composed of acrylates and / or methacrylates to an extent of at least 90% by weight, based on the total weight of the first monomer mixture. Here, likewise preferably, the acid-functional monomers in the first monomer mixture are acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, preferably methacrylic acid and / or 2-carboxyethyl acrylate. Furthermore, the first monomer mixture preferably comprises, besides the acid-functional monomers, as further monomers, methyl (meth)acrylate (MMA), n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, ethylhexyl (meth)acrylate and / or styrene. The first monomer mixture is particularly preferably composed of at least 95% by weight, based on the total weight of the first monomer mixture, very particularly preferably exclusively, of the monomers mentioned here.

[0025] Here, the monomer mixture very particularly preferably comprises 20% to 45% by weight, particularly preferably 25% to 40% by weight, of methacrylate, for example in particular ethylhexyl methacrylate. Preferably, up to 10% by weight of acid-functional monomers are used in the monomer mixture, each based on the total weight of the first monomer mixture.

[0026] In one embodiment of the present invention, the first monomer mixture does not include styrene. Thus, the first monomer mixture is preferably free of styrene.

[0027] It is further preferred that the first monomer mixture as acrylates and / or methacrylates does not contain a crosslinking agent. It is particularly preferred that the first monomer mixture does not contain a crosslinking agent.

[0028] "Crosslinker" is understood within the scope of the present invention to mean a monomer which contains two or more functional groups capable of polymerizing in a polymerization according to the invention, in particular in a radical polymerization.

[0029] The degree of polymerization at the end of the polymerization is preferably 85% to 95% by weight. Particularly preferably, the polymer formed from the first monomer mixture according to the present invention contains 1% to 10% by weight, preferably 2.5% to 5% by weight of repeating units of acid-functional monomers, based on the total weight of the formed polymer. More preferably, the formed polymer has a weight average molecular weight M of 10000 to 200000 g / mol, preferably 20000 to 150000 g / mol, particularly preferably 30000 to 100000 g / mol. w and has a glass transition temperature of -20°C to 20°C, preferably -5°C to 15°C.

[0030] Here, these data on the glass transition temperatures also relate to the values ​​preset by the Fox formula. The glass transition temperatures finally obtained in practice can be determined after polymerization, for example by DSC (differential scanning calorimetry, for example according to ISO 11357-1, in particular -2). When using the above-mentioned monomers, the values ​​determined in this way usually differ only minimally from the values ​​preset by the Fox formula. In the case of monomers other than these, it is very rare that the repeating units in the chain are distributed in blocks. Here, in very rare cases, the block formation can become significant and the polymer can have more than one glass transition temperature. In such very rare and unfavourable cases according to the invention, it is important not to calculate the glass transition temperature according to the Fox formula anymore, but to determine the most significant glass transition temperature according to the above-defined standard ISO 11357-2.

[0031] Here, the weight average molecular weight is determined by GPC against PMMA standards using THF as the eluent and at least two appropriate columns.

[0032] Surprisingly, it has been found to be particularly advantageous if the polymer formed by the process according to the invention has a glass transition temperature below ambient room temperature, i.e., is liquid at room temperature even in isolated form.

[0033] The polymerization can in particular be carried out batchwise or continuously in a continuously operated stirred tank with a connecting flow line, where the reaction can in principle be terminated regardless of the operating mode, but in a manner adapted to the operating mode in each case, by lowering the temperature, adding an inhibitor and / or simply consuming the initiator.

[0034] Preferably, the second monomer mixture comprises 50% to 90% by weight, particularly preferably 75% to 85% by weight, of methyl (meth)acrylate (MMA) based on the total weight of the second monomer mixture. More preferably, the second monomer mixture comprises at least 90% by weight of acrylates and / or methacrylates and optionally styrene, preferably MMA, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate and / or ethylhexyl (meth)acrylate, up to 5% by weight of acid-functional monomers, preferably acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, and optionally up to 5% by weight of styrene, each based on the total weight of the second monomer mixture.

[0035] In an alternative preferred embodiment of the present invention, the second monomer mixture comprises 55% to 80% by weight, particularly preferably 60% to 75% by weight, of methacrylate, each relative to the total weight of the second monomer mixture, whereby methyl (meth)acrylate and n-butyl (meth)acrylate are used, for example, in a ratio of about 80% by weight:20% by weight to 50% by weight:50% by weight.

[0036] In one embodiment, the second monomer mixture comprises in the range of 0.5% to 2% by weight of the acid functional monomer, based on the total weight of the second monomer mixture.

[0037] "Acid-functional monomer" is understood within the scope of the present invention to mean not just one acid-functional monomer, but also a mixture of two or more acid-functional monomers.

[0038] More preferably, the second monomer mixture does not contain styrene. Therefore, the second monomer mixture preferably does not contain styrene. Particularly preferably, the reactive resin does not contain styrene.

[0039] It is further preferred that the second monomer mixture does not contain a crosslinking agent. It is particularly preferred that the reactive resin does not contain a crosslinking agent. For the term "crosslinking agent", the above-mentioned explanations and preferred forms apply.

[0040] Particularly preferably, the second monomer mixture is selected so as to result in a polymer which, when fully polymerized, has a glass transition temperature according to the Fox formula of 50° C. to 120° C., preferably 60° C. to 90° C. Here, it should be clarified that the polymer in the finished intumescent coating, formed mainly from these monomers of the second monomer mixture, will in most cases deviate from the theoretical glass transition temperature of the second monomer mixture calculated by the Fox formula, since this second polymerization takes place during curing on the basis of a mixture of the second monomer mixture with the remaining first monomer mixture, different from the second monomer mixture, up to 30% by weight relative to the total weight of the reactive resin.

[0041] In addition to the method according to the invention, novel formulations for two-component intumescent coatings are also the subject of the invention. These formulations are in particular characterized in that after mixing of the two components, they contain 20% to 40% by weight of reactive resin produced by the method according to the invention, 35% to 60% by weight of blowing agent, 0.1% to 2.5% by weight of peroxide and / or azo initiator, preferably only peroxide, for example benzoyl peroxide, optionally up to 2% by weight of accelerator, optionally 4.9% to 15% by weight of additives, and 5% to 30% by weight of filler. Optionally, the formulations can contain additional pigments, each relative to the total weight of the two-component system.

[0042] The additives may in particular be wetting agents, film-forming agents, degassing agents and / or dispersing agents. The optionally used accelerators are usually secondary amines.

[0043] The fillers are, for example, silicon dioxide, titanium dioxide, quartz or other inorganic compounds, which are particularly thermally stable. In order to avoid uncontrolled additional expansion of the coating in the event of fire, inorganic fillers, such as carbonates, which may undergo thermal decomposition, can be used only to a relatively small extent. A particularly preferred filler is titanium dioxide.

[0044] There are various options for the blowing agent. In one particularly preferred alternative, polyphosphate can be used, which is converted to phosphoric acid at 190°C to 300°C. The formulation further comprises pentaerythritol, which then forms a carbon foam above 300°C in the presence of phosphoric acid, with the elimination of water and carbon dioxide. Here, water and carbon dioxide act as blowing agents. Here, a further advantage of this alternative is that both polyphosphate and phosphoric acid act as additional flame retardants.

[0045] In a second alternative, melamine is used as the blowing agent base, which above 350° C. decomposes into ammonia, nitrogen and carbon dioxide, where all three act as blowing agents.

[0046] In a third, particularly preferred variant, these two options are combined, which allows additional benefits beyond the flame retardant effect to be realized. In this way, the degree of foaming can be more finely tuned. Moreover, foaming takes place gradually, which also provides advantages in terms of foam stability.

[0047] When polyphosphate and melamine are mixed in parallel with the reactive resin according to the invention in a ratio of 3:1 to 1:1, for example 2:1, surprisingly, particularly small-pore and closed-cell foams are obtained.

[0048] The initiator is usually one or more peroxides and / or azo initiators, preferably peroxides.The initiator can be used together with an accelerator, usually one or more tertiary amines, especially aromatic tertiary amines, as initiator system.A particularly suitable example of such an initiator is dibenzoyl peroxide, which can also be used, for example, as a reliable premixed paste, in which the auxiliary of this paste, for example paraffin, does not interfere if it is at a suitable concentration in the formulation.

[0049] Examples of accelerators are especially N,N-dialkyl-p-toluidines, such as N,N-bis(2-hydroxypropyl)-p-toluidine or N,N-dimethyl-p-toluidine or N,N-dimethylaniline.

[0050] The actual formulation of the coating composition can be carried out as follows: the reactive resin is blended with the blowing agent, additives, optional fillers and further optional fillers. This intermediate blend is then split, for example, into two equal-sized fractions. One of these fractions is then further mixed with the accelerator. Thus, these two fractions are storage stable for a long period of time.

[0051] The accelerator-free fraction is then mixed with an initiator or initiator mixture before the actual application. After long storage or transport, it may first be necessary to stir both fractions once more, since for example fillers may have settled out. After the initiator has been stirred or mixed differently, the two fractions of the two-component system are then mixed together. In the process, polymerization of the monomer components of the reactive resin begins, which is the start of the so-called pot life, within which application to the substrate, i.e., to steel beams for example, must take place. In modern application equipment, mixing of the two fractions of the two-component system can also take place in the mixing chamber of the application nozzle immediately before pressure-induced spraying.

[0052] The pot life is a function of the type and concentration of initiator and accelerator, the monomer mixture, and external influences such as ambient temperature. These factors can be easily estimated and adjusted by those skilled in the art. It is common to work with pot lives of a few minutes to a few hours, and sometimes even more than 20 hours.

[0053] Furthermore, a method for the intumescent coating of metal surfaces is also the subject of the invention, in which the above-mentioned two-component intumescent coating formulation is prepared and applied to the metal surface within 1 to 20 minutes, where it is cured within 60 minutes at temperatures between -5°C and 30°C, preferably between 0°C and 30°C. Here, the preferred layer thickness of the unfoamed coating is 1 to 20 mm, particularly preferably 1.5 to 7.5 mm. Here, this is formulated in such a way that the coating gives rise in fire to a specific layer thickness of foam, preferably 5 to 100 mm per mm of layer thickness, preferably 15 to 50 mm per mm of layer thickness.

[0054] Working Example Example 1 Monomer supply process: A first monomer mixture of polymer components consisting of 23% by weight MMA, 33% by weight ethylhexyl methacrylate, 36% by weight n-butyl methacrylate and 8% by weight β-CEA (2-carboxyethyl acrylate) is mixed with 1% by weight thioglycolic acid 2-ethylhexyl ester and 0.6% by weight di-(4-tert-butylcyclohexyl) peroxydicarbonate or 2,2'-azobis(isobutyronitrile) at room temperature with a target molecular weight of about 60,000 g / mol. A 25% portion of the first monomer mixture is heated to 74 ° C as a pre-batch with stirring, the heating is stopped and at 86 ° C, the mixture is polymerized autothermally at about 90 ° C to 149 ° C by continuously adding a 75% portion of the first monomer mixture. After a metering time of about 30 to 60 minutes, the process is completed. After a post-reaction time of about 45 minutes, the batch is diluted by mixing a second monomer mixture consisting of 79% by weight methyl methacrylate, 20% by weight ethylhexyl acrylate and 1% by weight methacrylic acid in a ratio of 30% by weight polymer proportion and 70% by weight monomer mixture, cooled to 30° C., stabilized with 15 ppm (15 mg / kg) of 2,6-di-tert-butyl-4-methylphenol (Topanol O) and then compounded with 1.2% by weight wax (dropping point about 60° C.) and 1.9% by weight N,N-bis-(2-hydroxypropyl)-p-toluidine.

[0055] The viscosity was determined by DIN cup 4 over a flow time of 30 seconds, which corresponds to 30-150 mPa·s at 20°C. The target polymer content is about 30-35%. The formed polymer has a glass transition temperature of about -5°C and is not crosslinked.

[0056] Example 2 Initiator supply step A first monomer mixture of polymer components consisting of 23% by weight MMA, 33% by weight ethylhexyl methacrylate, 36% by weight n-butyl methacrylate and 8% by weight β-CEA (2-carboxyethyl acrylate) is mixed with about 2% by weight thioglycolic acid 2-ethylhexyl ester at room temperature. The first monomer mixture is heated to 74°C with stirring, the heating is turned off and the mixture is polymerized self-heatingly at about 90°C-120°C by successive addition of 0.6% by weight di-(4-tert-butylcyclohexyl) peroxydicarbonate or 2,2'-azobis(isobutyronitrile) as a 10% by weight solution in n-butyl acetate at 86°C with a target molecular weight of about 60,000 g / mol. After a metering time of about 60-120 minutes the process is complete. After a post-reaction time of about 45 minutes, the batch is diluted by mixing a second monomer mixture consisting of 79% by weight methyl methacrylate, 20% by weight ethylhexyl acrylate and 1% by weight methacrylic acid in a ratio of 30% by weight polymer proportion and 70% by weight monomer mixture, cooled to 30° C., stabilized with 15 ppm (15 mg / kg) of 2,6-di-tert-butyl-4-methylphenol (Topanol O) and then compounded with 1.2% by weight wax (dropping point about 60° C.) and 1.9% by weight N,N-bis-(2-hydroxypropyl)-p-toluidine.

[0057] The viscosity was determined by DIN cup 4 over a flow time of 30 seconds, which corresponds to 30-150 mPa·s at 20°C. The target polymer content is about 30-35%. The formed polymer has a glass transition temperature of about -5°C and is not crosslinked.

[0058] Comparative Example 1: DEGALAN® 1710 and DEGALAN® 1720 are mixed in equal amounts.

[0059] Resin system curing: 2% by weight of benzoyl peroxide to the resin mixture.

[0060] Comparative Example 1: Pot life: 18 minutes Tmax: 85℃ after 34 minutes, target: 70℃~130℃ after 15~40 minutes Glass transition temperature: 64°C.

[0061] Example 1: Pot life: 18 minutes Tmax: 90℃ after 42 minutes, target: 70℃~130℃ after 15~40 minutes Glass transition temperature: about -5°C and about 74°C.

[0062] Here, the lower glass transition temperature is for the polymer resulting from partial polymerization of the first monomer mixture, and the higher glass transition temperature is for the polymer formed upon final curing of the coating.

[0063] Fire-resistant coating formulation Usage example: 33.8% by weight of reactive resin according to Example 1 and Comparative Example 1 are premixed with 30.0% by weight of ammonium phosphate, 9.2% by weight of pentaerythritol, 15.0% by weight of melamine, 10.0% by weight of titanium dioxide, and 1% by weight of each of kaolin and wetting agent. These mixtures are then divided into two equal fractions, with one fraction receiving 0.5% by weight of benzoyl peroxide based on the total mixture. These two fractions are then mixed together and a small portion is taken out. The larger portion is used for coating a steel sheet with a layer thickness of 2000 μm, and the smaller sample is used for measuring the pot life and the maximum temperature after mixing.

[0064] Foaming experiment Testing in a High Therm VMK 39 muffle furnace The starting resin-filler system is applied with a 3000 μm blade to a degreased steel plate with a thickness of 0.8 mm. After curing for 24 hours, it is placed in a muffle furnace at a low temperature and heated to the desired temperature. After reaching this temperature, it is held at this temperature for 1 hour and then allowed to cool.

[0065] [Table 1]

[0066] The results of Example 1 and Example 2 show a higher specific foam height, which can provide better fire protection.

Claims

1. In a method for producing a reactive resin for intumescent coating, a first monomer mixture containing at least one acid-functional monomer is polymerized to a degree of polymerization of 70% to 95% by weight, and then the polymerization is terminated. The polymer formed at that time has a glass transition temperature of less than 23 °C calculated according to Fox's equation. After the termination of the polymerization, a mixture containing 70% to 95% by weight of the polymer is diluted with a second monomer mixture different from the first monomer mixture. A method characterized by this.

2. At least 90% by weight of the first monomer mixture consists of acrylate and / or methacrylate, and the acid-functional monomer in the first monomer mixture is acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, preferably methacrylic acid and / or 2-carboxyethyl acrylate. The method according to claim 1.

3. The polymer formed contains 1% to 10% by weight, preferably 2.5% to 5% by weight, of the repeating unit of the acid-functional monomer based on the total weight of the polymer formed. The method according to claim 2.

4. The second monomer mixture contains 50% to 90% by weight of MMA based on the total weight of the second monomer mixture. The method according to claim 1.

5. The first monomer mixture consists of the acid-functional monomer and a further monomer selected from MMA, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, ethylhexyl (meth)acrylate and / or styrene. The method according to claim 1.

6. The formed polymer has a weight average molecular weight M of 10,000 to 200,000 g / mol ｗ The method according to claim 1, having a glass transition temperature of -20°C to 20°C, preferably -10°C to 15°C.

7. The polymerization is carried out discontinuously in a batch mode or continuously in a continuously operated stirred tank having a connected flow tube, where the reaction is terminated by a decrease in temperature, addition of an inhibitor and / or consumption of an initiator. The method according to claim 1.

8. The degree of polymerization at the end of the polymerization is 85% to 95% by weight. The method according to claim 1.

9. The method according to claim 1, wherein the second monomer mixture comprises at least 90% by weight of acrylate and / or methacrylate, preferably MMA, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate and / or ethylhexyl (meth)acrylate, up to 5% by weight of acid-functional monomers, preferably acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, and optionally styrene, each based on the total weight of the second monomer mixture.

10. The method according to claim 1, wherein the second monomer mixture is selected such that, when fully polymerized, it results in a polymer having a glass transition temperature according to Fox's equation of 50°C to 120°C, preferably 60°C to 90°C.

11. A formulation for a two-component intumescent coating, wherein the formulation comprises, after mixing of the two components, 20% to 40% by weight of a reactive resin producible by the method according to claim 1, 35% to 60% by weight of a blowing agent, 0.1% to 2.5% by weight of a peroxide and / or an azo initiator, optionally up to 2% by weight of an accelerator, optionally 4.9% to 15% by weight of additives, and 5% to 30% by weight of a filler, each based on the total weight of the two-component system.

12. A formulation for a two-component intumescent coating, wherein the formulation has a blowing agent ratio of polyphosphate to melamine = 1:1 to 3:1 after mixing of the two components of the reactive resin producible by the method according to claim 1.

13. The formulation according to claim 11, wherein the formulation further comprises a pigment.

14. A method for intumescent coating of a metal surface, comprising producing the formulation according to claim 11 or 12, applying it to the metal surface within 1 to 20 minutes, and curing it at a temperature of -5°C to 30°C within 60 minutes.