IMPROVED RESIN SYSTEM FOR INFLATABLE FIRE PROTECTION COATINGS

Description

Field of the invention

[0001] The present invention relates to a novel reaction resin system for intumescent coatings and a process for producing this resin system. Intumescent coatings are used in particular for fire protection of metallic components, such as steel beams in building construction. In the event of a fire, these coatings are reactively foamed, forming a fire-resistant insulating layer with low thermal conductivity on the metal substrate. The resulting insulation delays premature, thermally induced failure of this component.

[0002] The present invention relates in particular to methacrylate-based resin systems produced by a novel process in which a first monomer mixture is polymerized to a maximum degree of 95 wt% and subsequently diluted with a second monomer mixture. The glass transition temperature of the polymeric component of the resulting composition is particularly low compared to the prior art. Furthermore, the organic acids incorporated into the resin system act surprisingly synergistically with the filler system. The resin systems produced in this way prove particularly efficient in temperature-induced foaming due to their fine-pored and closed-pore foam structure. State of the art

[0003] A first generation of intumescent coating systems was based on high-molecular-weight thermoplastic resins based on acrylates, methacrylates and / or vinyl monomers and required a large proportion of solvent or water for application to the corresponding metal surface with correspondingly long drying times.

[0004] Typically, such intumescent coatings are applied on-site during the construction phase. However, off-site applications prior to delivery to the construction site are preferred, as they can be performed under controlled conditions. Slow drying, however, results in inefficient processing times, especially since the coating must be applied consecutively from different sides to be complete.

[0005] CN 112 029 367 A, for example, describes an intumescent system in the form of an emulsion containing core-shell particles in water. The core of the core-shell particles is cross-linked.

[0006] CN 111 995 919 A, like CA 3 028 431, discloses emulsions of acrylic polymers as ultra-thin intumescent coatings. The acrylic polymers are present as core-shell particles, with the core being cross-linked.

[0007] JP 2003 171 579 relates to a mixture of an unpolymerized (meth)acrylic monomer mixture and a (meth)acrylic polymer. The mixture can be used as an intumescent coating. Termination of polymerization at a certain degree of polymerization is not disclosed.

[0008] DE 196 30 063 concerns interior fittings for rail vehicle components. Intumescent coatings are not disclosed.

[0009] Epoxy-based intumescent coatings are primarily used in the offshore industry. They are characterized by good aging resistance and relatively short drying times. Polyurethane systems have been extensively studied. They also feature a relatively short drying time and good water resistance. However, the fire tests failed because the coating does not adhere well to steel. Details can be found in "Development of alternative technologies for off-site applied intumescent," Longdon, PJ, European Commission, [Report] EUR (2005), EUR 21216, 1-141.

[0010] A further generation of intumescent coatings is based on (meth)acrylate reactive resins. Their application has the significant advantage that no solvents are required, and the resin cures relatively quickly after application compared to the previously described systems. This not only results in faster processing but also, in particular, a lower proportion of residual volatile components in the applied coating. Such intumescent coating systems were first disclosed in EP 1 636 318.

[0011] A further improvement of (meth)acrylate-based systems is described, for example, in EP 2 171 004. This system is characterized by a particularly high proportion of acid groups to improve metal adhesion. EP 2 171 005 discloses a further development of such a system. This system is characterized in particular by the copolymerization of di-acids or copolymerizable acids with spacer groups. This can further improve metal adhesion.

[0012] However, all of these systems still require improvement. The degree of freedom regarding formulation is severely limited. Furthermore, only relatively thick layers can be applied. These disadvantages, for example, also result in only a limited degree of pre-adjustment of the foam height when needed or in the event of a fire.

[0013] Furthermore, disadvantages arise from the relatively complex manufacturing process for the resins. All of the otherwise very advantageous (meth)acrylate systems described in the prior art have in common that the solid, thermoplastic polymer contained in the resin is first produced discretely, then dissolved in the monomer components and preformulated with additives, and finally formulated as a two-component system shortly before application. This process chain is relatively complex, and there is great interest in simplifying it.

[0014] WO 2021 / 180488 describes for the first time the production of a methacrylate-based reactive resin for intumescent coatings using a syrup process. A monomer mixture is polymerized to a degree of polymerization of 70% and then polymerization is terminated. The composition is fundamentally similar to previously known reactive resins obtained by dissolving a suspension polymer or granules in a monomer mixture. Differences arise primarily in the type of polymer chains. Task

[0015] The present invention was therefore based on the object of providing a significantly simplified process for producing (meth)acrylate-based intumescent coatings. In particular, there was a need for a simplified production process in which at least one isolation or formulation step can be eliminated compared to the processes described in the prior art for producing (meth)acrylate-based intumescent coatings.

[0016] Furthermore, the task was to provide a novel formulation for the 2-component intumescent coating, which, in addition to very good metal adhesion and easy processing, also allows greater freedom with regard to additives and the setting of subsequent foaming control, in particular with regard to the presetting of subsequent foam heights and foam quality, such as a particularly high proportion of closed-pore foam.

[0017] Further objects not explicitly listed may arise from the description or examples below, as well as from the overall context of the invention. Solution

[0018] The objects are achieved by providing a novel process for producing reactive resins for intumescent coatings. In this process, a first monomer mixture containing at least one acid-functional monomer is first polymerized to a degree of polymerization of 70 wt.% to 95 wt.%. Subsequently, upon reaching the desired degree of polymerization, the polymerization is terminated. According to the invention, the polymer formed has a glass transition temperature of less than 23°C, calculated according to the Fox equation, which is significantly lower than that described for corresponding resins in the prior art. Furthermore, the process according to the invention is characterized in that, after the polymerization is terminated, the mixture containing 70 to 95 wt.% polymer is diluted with a second monomer mixture that differs from the first monomer mixture.

[0019] Intumescent fire-protection coatings described in the prior art consist, among other things, of multi-component systems formulated from thermoplastic polymers dissolved in monomers. The present invention, however, demonstrates that liquid polymers—i.e., polymers with a glass transition temperature that would be liquid in their undissolved state at room temperature below 23°C—are also suitable for this application. Furthermore, polymerized acid components, such as 2-carboxyethyl acrylate, improve adhesion to the substrate, and additionally formulated acid components, such as acrylic acid or methacrylic acid, provide surprising foam height control in the final application as a fire-protection coating.

[0020] The Fox equation is a relatively simple, yet realistic method for calculating glass transition temperatures of homogeneous (i.e., with randomly distributed repeating units) copolymers, which has proven particularly useful for (meth)acrylate copolymers (optionally with styrene). The notation (meth)acrylate includes co-acrylates, co-methacrylates, and copolymers containing acrylates and methacrylates. For two monomers, the Fox equation is as follows, although it can be extended to a variety of different comonomers: T g = T g 1 x 1 + T g 2 x 2 … + T gy x y These include T g : The determined theoretical glass transition temperature of the copolymer T gy : The glass transition temperature of a homopolymer of the monomer yxy : The mass fraction of the monomer y in the monomer mixture or of the repeating units in the polymer

[0021] According to the invention, all glass transition temperatures stated refer to polymers prepared by free-radical polymerization at typical polymerization temperatures between 40 and 120 °C. Exotic polymers prepared at significantly lower temperatures, for example, by anionic polymerization or stereoselectively by GTP, are not relevant to the invention. The Fox equation is also not applicable to these polymers due to significantly different tacticities in the chosen form. The glass transition temperatures of homopolymers prepared by free-radical polymerization are known from the literature.

[0022] In the context of the present invention, a monomer mixture is typically understood to mean a monomer mixture that is free of solvent. In particular, a monomer mixture within the meaning of the present invention contains no water. Therefore, a monomer mixture is preferably a mixture consisting of monomers. These statements and preferences apply independently of one another to both the first monomer mixture and the second monomer mixture.

[0023] The first monomer mixture preferably consists of at least 90% by weight of acrylates and / or methacrylates, based on the total weight of the first monomer mixture. The acid-functional monomer in the first monomer mixture is just as preferably acrylic acid, methacrylic acid, itaconic acid, and / or 2-carboxyethyl acrylate, preferably methacrylic acid and / or 2-carboxyethyl acrylate. Furthermore, in addition to the acid-functional monomer, the first monomer mixture preferably contains, 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. More preferably, the first monomer mixture consists of at least 95% by weight, based on the total weight of the first monomer mixture, and most preferably exclusively, the monomers mentioned here.

[0024] The monomer mixture most preferably contains 20 to 45 wt.%, particularly preferably 25 to 40 wt.%, of a methacrylate, such as, in particular, ethylhexyl methacrylate. Preferably, up to 10 wt.% of the acid-functional monomer(s) are used in the monomer mixture, based in each case on the total weight of the first monomer mixture.

[0025] In one embodiment of the invention, the first monomer mixture contains no styrene. The first monomer mixture is therefore preferably free of styrene.

[0026] It is further preferred that the first monomer mixture, as acrylate and / or methacrylate, does not contain a crosslinker. Particularly preferably, the first monomer mixture does not contain a crosslinker.

[0027] In the context of the present invention, a "crosslinker" is understood to mean a monomer which comprises two or more functional groups which can polymerize in the polymerization according to the invention, in particular in a radical polymerization.

[0028] The degree of polymerization upon termination of the polymerization is preferably between 85 and 95 wt.%. Particularly preferably, the polymer formed according to the invention from the first monomer mixture has between 1 and 10 wt.%, preferably between 2.5 and 5 wt.%, of repeat units of the acid-functional monomer, based on the total weight of the polymer formed. Furthermore, the polymer formed preferably has a weight-average molecular weight Mw between 10,000 and 200,000 g / mol, preferably between 20,000 and 150,000 g / mol, and particularly preferably between 30,000 and 100,000 g / mol, and a glass transition temperature between -20°C and 20°C, preferably between -5 and 15°C.

[0029] These glass transition temperature specifications also refer to a value preset using the Fox equation. The actual glass transition temperature obtained at the end can be determined after polymerization, e.g., by DSC (differential scanning calorimetry, for example, according to ISO 11357-1 and especially -2). When using the above-mentioned monomers, the value determined generally deviates only minimally from the value preset using the Fox equation. Deviations from these monomers can, in very rare cases, lead to a blocky distribution of the repeating units in the chain. In very rare cases, the block formation can be so pronounced that the polymer exhibits two or more glass transition temperatures.For these very rare, non-preferred cases according to the invention, the calculation of the glass transition temperature using the Fox equation is no longer decisive, but rather the determination of the most pronounced glass transition temperature according to the aforementioned standard ISO 11357-2.

[0030] The weight-average molecular weight is determined by GPC against a PMMA standard using at least two suitable columns with THF as eluent.

[0031] It has surprisingly proven particularly advantageous if the polymer formed in the process according to the invention has a glass transition temperature below the ambient room temperature, i.e. would be liquid at room temperature even in the isolated state.

[0032] In particular, the polymerization can be carried out discontinuously in a batch mode or continuously in a continuous stirred tank with a connected flow tube. Termination of the reaction can be carried out independently of the mode of operation, but can be adapted to the specific mode by lowering the temperature, adding an inhibitor, and / or simply by consuming the initiator.

[0033] The second monomer mixture preferably contains 50 to 90 wt.%, particularly preferably 75 to 85 wt.% methyl (meth)acrylate (MMA), based on the total weight of the second monomer mixture. Furthermore, the second monomer mixture preferably consists of at least 90 wt.% 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 wt.% acid-functional monomers, preferably acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, and optionally at most 5 wt.% styrene, in each case based on the total weight of the second monomer mixture.

[0034] In an alternative preferred embodiment of the present invention, the second monomer mixture contains 55 to 80 wt.%, particularly preferably 60 to 75 wt.% methacrylate, in each case based on the total weight of the second monomer mixture, wherein methyl (meth)acrylate and n-butyl (meth)acrylate are used here, for example, in a ratio of approximately 80 to 20 wt.% to 50 to 50 wt.%.

[0035] In one embodiment, the second monomer mixture contains in the range of 0.5 to 2 wt.% acid-functional monomers, based on the total weight of the second monomer mixture.

[0036] In the context of the present invention, "acid-functional monomers" means both precisely one acid-functional monomer and a mixture of two or more acid-functional monomers.

[0037] Furthermore, the second monomer mixture preferably contains no styrene. The second monomer mixture is therefore preferably free of styrene. The reaction resin is particularly preferably free of styrene.

[0038] It is further preferred that the second monomer mixture not contain a crosslinker. Particularly preferably, the reaction resin does not contain a crosslinker. The previously described explanations and preferences apply to the term "crosslinker."

[0039] Particularly preferably, the second monomer mixture is selected such that, when polymerized, it would result in a polymer with a glass transition temperature according to the Fox equation between 50 °C and 120 °C, preferably between 60 and 90 °C. It should be clarified at this point that the polymer of the finished intumescent coating formed predominantly from these monomers of the second monomer mixture must deviate from the theoretical glass transition temperature of the second monomer mixture calculated using the Fox equation in the vast majority of cases, since this second polymerization takes place during curing on the basis of a mixture of the second monomer mixture and up to 30 wt.% of the remaining first monomer mixture which differs from the second, based on the total weight of the reaction resin.

[0040] In addition to the process according to the invention, the present invention also provides a novel formulation for a 2K intumescent coating. This formulation is particularly characterized in that, at a time after mixing the 2K system, it comprises 20 to 40 wt.% of the reactive resin produced by the process according to the invention, 35 to 60 wt.% of a blowing agent, 0.1 to 2.5 wt.% of a peroxide and / or azo initiator, preferably only peroxides, such as benzoyl peroxide, optionally up to 2 wt.% of an accelerator, optionally 4.9 to 15 wt.% of additives, and 5 to 30 wt.% of fillers. Optionally, the formulation can comprise additional pigments, each based on the total weight of the 2K system.

[0041] The additives can include wetting agents, film formers, deaerating agents, and / or dispersing agents. Optional accelerators are usually secondary amines.

[0042] The fillers can be, for example, silicon dioxide, titanium dioxide, quartz, or other, particularly thermally stable, inorganic compounds. Inorganic fillers such as carbonates, which can decompose thermally, may only be used in small quantities to prevent uncontrolled additional foaming of the coating in the event of a fire. A particularly preferred filler is titanium dioxide.

[0043] There are various alternatives regarding blowing agents. A particularly preferred alternative involves the use of polyphosphates, which convert to phosphoric acid at temperatures of 190 to 300 °C. The formulation also contains pentaerythritol, which forms a carbon foam at temperatures above 300 °C in the presence of phosphoric acid, releasing water and carbon dioxide. Water and carbon dioxide act as blowing agents. An additional advantage of this alternative is that the polyphosphates, like the phosphoric acid, act as additional flame retardants.

[0044] In a second alternative, melamine is used as the basic material for the blowing agent, which decomposes at temperatures above 350 °C into ammonia, nitrogen and carbon dioxide, all three of which in turn act as blowing agents.

[0045] By combining these two alternatives as a third, particularly preferred variant, additional advantages can be realized in addition to the flame retardant effect. This allows for more precise adjustment of the foaming level. It also results in gradual foaming, which in turn provides advantages in terms of foam stability.

[0046] Particularly fine-pored and closed-pore foams are obtained when, surprisingly, polyphosphates and melamine are mixed in parallel with the reaction resin according to the invention in a ratio between 3 to 1 and 1 to 1, such as 2 to 1.

[0047] The initiator typically consists of one or more peroxides and / or azo initiators, preferably a peroxide. It can be used as an initiator system together with an accelerator, typically one or more tertiary amines, particularly an aromatic tertiary amine. A particularly suitable example of such an initiator is dibenzoyl peroxide, which can also be used, for example, as a safe, pre-formulated paste. The excipients of this paste, such as paraffins, do not interfere with the formulation at the appropriate concentrations.

[0048] Examples of accelerators include, in particular, N,N-dialkyl-para-toluidines, such as N,N-bis-(2-hydroxypropyl)-para-toluidine or N,N-di-methyl-para-toluidine or N,N-di-methylaniline. The actual coating composition can be formulated as follows: the reactive resin is formulated with the blowing agents, additives, optional fillers, and other optional fillers. These intermediate formulations are then divided into two equal fractions. One of these fractions is then additionally mixed with the accelerator. These two fractions are then stable for extended storage periods.

[0049] Before the actual application, the accelerator-free fraction is then mixed with the initiator or initiator mixture. After extended storage or transport, it may be necessary to stir both fractions again beforehand, as fillers, for example, may have settled. After the initiator has been stirred or otherwise mixed in, both fractions of the 2K system are then mixed together. This starts the polymerization of the monomer components of the reactive resin and begins the so-called pot life, within which application to the substrate, e.g. a steel support, must take place. With modern application devices, the two fractions of the 2K system can also be mixed in a mixing chamber of an application nozzle directly before pressure-induced spraying.

[0050] Pot lives are determined by a combination of the type and concentration of initiator and accelerator, the monomer mixture, and external factors such as ambient temperature. These factors are easy to estimate and adjust for a professional. Pot lives typically range from several minutes to several hours, sometimes even exceeding 20 hours.

[0051] Furthermore, a method for intumescent coating a metal surface is the subject of the present invention. In this method, the previously described formulation for the 2-component intumescent coating is prepared, applied to the metal surface within 1 to 20 minutes, and cured there within 60 minutes at a temperature between -5 and 30°C, preferably between 0 and 30°C. The preferred layer thickness of the non-foamed coating is 1 to 20 mm, particularly preferably 1.5 to 7.5 mm. This would be formulated such that, in the event of a fire, the coating would preferably result in a specific foam layer thickness of 5 to 100 mm / mm layer thickness, preferably 15 to 50 mm / mm layer thickness. Examples Example 1 Monomer feed process:

[0052] The first monomer mixture for the polymer component, consisting of 23 wt.% MMA, 33 wt.% ethylhexyl methacrylate, 36 wt.% n-butyl methacrylate, and 8 wt.% beta-CEA (2-carboxyethyl acrylate), is mixed at room temperature with 1 wt.% 2-ethylheyl thioglycolate and 0.6 wt.% di-(4-tert.-butylcyclohexyl) peroxydicarbonate or 2,2'-azobis(isobutyronitrile) for the target molecular weight of approximately 60,000 g / mol. A 25 wt.% portion of the first monomer mixture is heated to 74 °C as a prebatch with stirring, the heating is turned off, and the mixture is polymerized autothermally at approximately 90 to 149 °C at 86 °C by continuously adding the 75 wt.% portion of the first monomer mixture. After approximately 30 to 60 minutes of dosing time, the process is complete. After a post-reaction time of approximately 45 minutes, the mixture is diluted with the second monomer mixture, consisting of 79 wt.% methyl methacrylate, 20 wt.% ethylhexyl acrylate, and 1 wt.% methacrylic acid in a ratio of 30 wt.%.% polymer content and 70 wt.% monomer mixture for dilution, cooled to 30 °C and stabilized with 15 ppm (15 mg / kg) 2,6-di-tert-butyl-4-methyl-phenol (Topanol O) and formulated with 1.2 wt.% waxes (dropping point approx. 60 °C) and 1.9 wt.% N,N-bis-(2-hydroxypropyl)-para-toluidine.

[0053] The viscosity is determined using a flow time of 30 s (DIN cup 4), corresponding to 30–150 mPa*s at 20 °C. The target polymer content is approximately 30–35%. The resulting polymer has a glass transition temperature of approximately -5 °C and is not crosslinked. Example 2 Initiator feed process

[0054] The first monomer mixture for the polymer component, consisting of 23 wt.% MMA, 33 wt.% ethylhexyl methacrylate, 36 wt.% n-butyl methacrylate, and 8 wt.% beta-CEA (2-carboxyethyl acrylate), is mixed at room temperature with approximately 2 wt.% 2-ethylheyl thioglycolate. The first monomer mixture is heated to 74 °C with stirring, the heating is turned off, and the polymerization is carried out autothermally at approximately 90 to 120 °C at 86 °C by continuously adding 0.6 wt.% di-(4-tert.-butylcyclohexyl)peroxydicarbonate or 2,2'-azobis(isobutyronitrile) as a 10 wt.% solution in n-butyl acetate to a target molecular weight of approximately 60,000 g / mol. After approximately 60 to 120 minutes of dosing time, the process is complete. After a post-reaction time of approximately 45 minutes, the mixture is diluted with the second monomer mixture, consisting of 79 wt.% methyl methacrylate, 20 wt.% ethylhexyl acrylate, and 1 wt.% methacrylic acid in a ratio of 30 wt.% polymer and 70 wt.% acrylate.% monomer mixture for dilution, cooled to 30 °C and stabilized with 15 ppm (15 mg / kg) 2,6-di-tert-butyl-4-methyl-phenol (Topanol O) and formulated with 1.2 wt.% waxes (dropping point approx. 60 °C) and 1.9 wt.% N,N-bis-(2-hydroxypropyl)-para-toluidine.

[0055] The viscosity is determined using a flow time of 30 s (DIN cup 4), corresponding to 30–150 mPa*s at 20 °C. The target polymer content is approximately 30–35%. The resulting polymer has a glass transition temperature of approximately -5 °C and is not crosslinked. Comparison example 1:

[0056] DEGALAN ®< 1710 and DEGALAN ®< 1720 are mixed in equal parts. Curing the resin systems:

[0057] 2 wt.% benzoyl peroxide on resin mixture Comparison example 1:

[0058] Pot life: 18 min Tmax: 85 °C after 34 min Target: 70 - 130 °C after 15 - 40 min Glass transition temperature: 64 °C Example 1:

[0059] Pot life: 18 min Tmax: 90 °C after 42 min Target: 70 to 130 °C after 15 to 40 min Glass transition temperature: approx. -5 °C and approx. 74 °C

[0060] The lower glass transition temperature relates to the polymer from the partial polymerization of the first monomer mixture, while the higher glass transition temperature relates to the polymer formed during the final curing of the coating. Formulating a fire-resistant coating Application example:

[0061] 33.8 wt.% of the reaction resin according to Example 1 and Comparative Example 1 are each preformulated with 30.0 wt.% ammonium phosphate, 9.2 wt.% pentaerythritol, 15.0 wt.% melamine, 10.0 wt.% titanium dioxide, and 1 wt.% each of kaolin and wetting agent. These formulations are then divided into two equal fractions, with 0.5 wt.% benzoyl peroxide being added to one fraction, based on the total formulation. These two fractions are then mixed together, and a smaller portion is removed. A steel plate is coated with the larger portion in a layer thickness of 2000 µm, while the pot life and maximum temperature after mixing are measured on the smaller sample. Foaming test Tests in the muffle furnace High Therm VMK 39

[0062] The initiated resin-filler system was applied to a degreased, 0.8 mm thick steel sheet using a 3000 µm doctor blade. Allowed to cure for 24 hours, then placed in a cold muffle furnace and heated to the desired temperature. Once the temperature was reached, the system was held at this temperature for one hour, then allowed to cool.

[0063] Evaluation of the intumescent coating after thermal foaming, specific foam height, foam quality and adhesion to the steel sheet. Example Designation T / °C Coating height after polymerization / mm Specific foam height mm / mm coating height Foam quality in cross section Overhead adhesion after thermal foaming VB1 Comparison example 500 2,7 16,7 Large to medium porous, open porous No adhesion to the steel sheet VB2 Comparison example 1000 2,8 18,2 Large to medium porous, open porous No adhesion to the steel sheet 1 Inventive example 500 2,4 20,6 Fine-pored, closed-pored Adhesion to the steel sheet 2 Inventive example 1000 2,7 19,8 Fine-pored, closed-pored Adhesion to the steel sheet

[0064] The results of examples 1 and 2 show a higher specific foam height and can therefore develop a better fire insulating effect.

Claims

1. Process for producing reactive resins for intumescent coatings, characterized in that a first monomer mixture comprising at least one acid-functionalized monomer is polymerized to a degree of polymerization of 70% by weight to 95% by weight, after which the polymerization is terminated, in that the polymer thereby formed has a glass transition temperature, calculated according to the Fox equation, of less than 23°C, and in that, after termination of the polymerization, the mixture containing 70 to 95% by weight of polymer is diluted with a second monomer mixture that differs from the first monomer mixture.

2. Process according to Claim 1, characterized in that the first monomer mixture consists to an extent of at least 90% by weight of acrylates and / or methacrylates, and in that the acid-functionalized 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.

3. Process according to Claim 2, characterized in that the formed polymer contains between 1 and 10% by weight, preferably between 2.5 and 5% by weight, of repeat units of the acid-functionalized monomer, based on the total weight of the formed polymer.

4. Process according to at least one of Claims 1 to 3, characterized in that the second monomer mixture contains 50 to 90% by weight of MMA, based on the total weight of the second monomer mixture.

5. Process according to at least one of Claims 1 to 4, characterized in that the first monomer mixture consists of the acid-functionalized monomer and further monomers selected from MMA, n-butyl (meth)acrylate, isobutyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, ethylhexyl (meth)acrylate and / or styrene.

6. Process according to at least one of Claims 1 to 5, characterized in that the formed polymer has a weight-average molecular weight Mw of between 10 000 and 200 000 g / mol and glass transition temperature of between -20°C and 20°C, preferably between -10 and 15°C.

7. Process according to at least one of Claims 1 to 6, characterized in that the polymerization is carried out discontinuously in a batchwise process or continuously in the continuously operated stirred-tank reactor with connecting flow tube, with the reaction terminated by lowering the temperature, adding an inhibitor and / or through consumption of the initiator.

8. Process according to at least one of Claims 1 to 7, characterized in that the degree of polymerization on termination of the polymerization is between 85 and 95% by weight.

9. Process according to at least one of Claims 1 to 8, characterized in that the second monomer mixture contains to an extent of at least 90 % by weight of acrylates and / or methacrylates, 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-functionalized monomers, preferably acrylic acid, methacrylic acid, itaconic acid and / or 2-carboxyethyl acrylate, and optionally styrene, based in each case on the total weight of the second monomer mixture.

10. Process according to at least one of Claims 1 to 9, characterized in that the second monomer mixture is selected such that, when fully polymerized, it has to a polymer having a glass transition temperature according to the Fox equation of between 50°C and 120°C, preferably between 60 and 90°C.

11. Formulation for the 2C intumescent coating, characterized in that, after mixing the 2C system, the formulation contains 20 to 40% by weight of the reactive resin producible according to Claims 1 to 10, 35 to 60% by weight of a blowing agent, 0.1 to 2.5% by weight of a peroxide and / or 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 fillers, based in each case on the total weight of the 2C system.

12. Formulation for the 2C intumescent coating, characterized in that, after mixing the 2C system of the reactive resin producible according to Claims 1 to 10, the formulation has a blowing agent ratio of polyphosphate to melamine of between 1 to 1 and 3 to 1.

13. Formulation according to Claim 11, characterized in that the formulation additionally comprises pigments.

14. Process for the intumescent coating of a metal surface, characterized in that the formulation prepared according to Claim 11 or 12 is applied to the metal surface within 1 to 20 minutes and cured thereon at a temperature of between -5 and 30°C within a period of 60 minutes.