Intumescent fire retardant coating for steel structure, and preparation method and performance testing method of intumescent fire retardant coating

Abstract

The invention discloses an intumescent fireproof coating for a steel structure and a preparation method and a performance testing method thereof, and relates to the technical field of building materials and fireproofing. The intumescent fireproof coating comprises modified epoxy resin, a foaming agent, a charring agent, a specific inorganic flame-retardant filler, a compatible aid and the like, and the intumescent fireproof coating is prepared by optimizing the components and proportion and improving the preparation process. The mechanical property, the fire resistance and the compatibility with intermediate paint of the coating are remarkably improved. The foaming agent and the charring agent have a synergistic effect to form a heat insulation carbon layer, and the specific inorganic flame-retardant filler not only enhances the flame-retardant effect, but also assists the compatible auxiliary agent in improving the interface bonding force with the epoxy micaceous iron oxide intermediate paint, so that the situation that the overall protection performance is reduced due to interface failure is avoided.

Description

Technical Field

[0001] The present invention relates to the field of building materials and fire protection technology, and in particular to an intumescent steel structure fire retardant coating and a preparation method and a performance testing method thereof. Background Art

[0002] When steel structures are used as the primary structural material for buildings, they must be treated with fire and corrosion protection. To achieve this, a specific coating system is often designed based on the application environment. For example, in outdoor environments, an epoxy zinc-rich primer and an epoxy micaceous iron intermediate are often used as the corrosion protection system, with an intumescent fire retardant coating serving as the fireproof protective layer, supplemented by a polyurethane or acrylic-polyurethane topcoat as the protective surface layer. The epoxy micaceous iron intermediate utilizes a lamellar zinc powder structure to improve sealing and adhesion. In indoor environments, however, neither an intermediate nor a topcoat is typically used for economic and durability reasons. Current research focuses on the mechanical and fire resistance properties of intumescent fire retardant coatings for steel structures. However, the fire resistance testing in the current national standard GB 14907-2018, "Fire Retardant Coatings for Steel Structures," does not fully incorporate real-world application scenarios. In particular, there is a lack of clear specifications for the performance of fire retardant coatings under different systems. For example, the standard divides fire resistance grades into 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, and 3.0h grades, but does not specify minimum fire resistance performance requirements, and the fire resistance performance test results are applicable to substrates of the same type with a smaller cross-sectional coefficient.

[0003] To improve the overall performance of intumescent fire-retardant coatings for steel structures, existing technologies have optimized their mechanical and fire-resistant properties by adjusting their formulations and exploring compatibility with intermediate coatings. However, in practical applications, the performance of intumescent fire-retardant coatings still faces certain limitations. For example, some coatings exhibit poor adhesion to the intermediate coating at high temperatures, affecting the overall protective effect. Other coatings, while exhibiting excellent fire-resistant properties through good adhesion to the intermediate coating, lack mechanical strength. These issues highlight the need to develop an intumescent fire-retardant coating for steel structures that combines both mechanical properties and good compatibility with intermediate coatings. Summary of the Invention

[0004] In response to the above-mentioned problems in the prior art, the present invention provides an intumescent fire retardant coating for steel structures, a preparation method thereof, and a performance testing method, so as to solve the technical difficulty that the intumescent fire retardant coating in the prior art is difficult to have both mechanical properties and good compatibility with intermediate paint.

[0005] The technical solution adopted in the present invention is as follows:

[0006] One of the purposes of the present invention is to provide an intumescent fire-retardant coating for steel structures, comprising the following components in weight percentage: 20% to 30% of a modified epoxy resin, 5% to 15% of a foaming agent, 5% to 15% of a carbonizing agent, 20% to 30% of an inorganic flame-retardant filler, 1% to 5% of a compatibilizer, 0.5% to 2% of a dispersant, 0.2% to 1% of a leveling agent, and the balance being a solvent; the modified epoxy resin is chemically modified by introducing siloxane groups into an epoxy resin, has a molecular weight between 8000 and 15000, and has a glass transition temperature between 40°C and 60°C; the inorganic flame-retardant filler is composed of aluminum hydroxide, zinc borate, and iron oxide in a mass ratio of 1:1 to 2:1 to 2, and the particle sizes of the aluminum hydroxide, zinc borate, and iron oxide are all 1 to 10 μm.

[0007] Furthermore, the preparation process of the modified epoxy resin is as follows: epoxy resin and γ-aminopropyltriethoxysilane are stirred and reacted at 80-100° C. for 3-5 hours to obtain the modified epoxy resin, wherein the addition amount of γ-aminopropyltriethoxysilane is 5%-10% of the mass of the epoxy resin, and the epoxy resin is bisphenol A epoxy resin.

[0008] Furthermore, the foaming agent is melamine phosphate and / or pentaerythritol phosphate, and the decomposition temperature is between 200 and 300°C.

[0009] Furthermore, the carbon-forming agent is dipentaerythritol and / or ammonium polyphosphate, and the thermal decomposition temperature is between 250 and 350°C.

[0010] Furthermore, the compatibilizing agent is a silane coupling agent and / or a titanate coupling agent containing at least one active group selected from amino, epoxy or carboxyl groups.

[0011] Furthermore, the dispersant is a polycarboxylate compound and / or a polyether compound, and has a molecular weight between 1000 and 3000.

[0012] Preferably, the leveling agent is silicone-modified acrylate and / or fluorine-modified acrylate, and has a surface tension of 20 to 30 mN / m.

[0013] A second object of the present invention is to provide a method for preparing the above-mentioned intumescent fire retardant coating for steel structures, comprising the following steps:

[0014] (1) Add the modified epoxy resin into a stirring container and stir at a speed of 500 to 1000 r / min at room temperature, then slowly add the dispersant and leveling agent, and continue stirring for 10 to 20 minutes until uniform;

[0015] (2) Add the foaming agent, carbonizing agent and inorganic flame retardant filler to the stirring container in sequence, adjust the stirring speed to 1500-2000 r / min, and stir for 30-60 minutes to fully mix the components;

[0016] (3) Reduce the stirring speed to 500-800 r / min, add the compatibilizer and solvent, and continue stirring for 10-15 minutes until a uniform slurry is formed;

[0017] (4) The slurry is ground by a three-roll mill to control the fineness of each component to no more than 40 μm.

[0018] A third object of the present invention is to provide a performance testing method for the above-mentioned intumescent steel structure fire retardant coating, comprising the following steps:

[0019] (1) Adhesion test

[0020] (101) Sample preparation: Steel was used as the substrate, and oil stains and rust were removed. The steel was then sandblasted to a surface roughness Ra of at least 80 μm.

[0021] (102) Coating matching: Apply primer, intermediate paint, fire retardant paint and topcoat according to the actual use scenario, and control the average dry film thickness of each layer;

[0022] (103) Test operation: Referring to GB / T 5210-2006 standard, an adhesion tester with a spindle size of 20 mm was used, and a two-component epoxy slow-drying adhesive was used to test the adhesion between the coating and the substrate at a tensile rate of 0.2 to 1 MPa / s;

[0023] (2) Fire resistance test

[0024] (201) Using an imaging sintering point tester, CCD camera and computer image processing system, the test and observation were carried out in the following three stages:

[0025] Stage 1: Room temperature to 300°C, heating rate 10°C / min, observing initial expansion behavior;

[0026] Stage 2: 300-800°C, heating rate 15°C / min, capturing interface failure characteristics;

[0027] Stage 3: 800°C constant temperature for 30 min, recording the integrity of the carbon layer;

[0028] (202) The length, width, and height of the samples before and after each stage of the test were measured and recorded as l 前 d 前 、h 前 With l 后 d 后 、h 后 ; Sample volume before test V 前 According to formula (1), the shape of the sample is evaluated after the test. If the shape after expansion is approximately a cube, the sample volume V后 Calculate according to formula (2); if the shape after expansion is approximately spherical, the sample volume V 后 Calculate according to formula (3); the expansion / contraction ratio n of the sample before and after the test is calculated according to formula (4):

[0029] V 前 =l 前 ×d 前 ×h 前 Formula (1)

[0030] V 后 =l 后 ×d 后 ×h 后 Formula (2)

[0031]

[0032] n=V 后 / V 前 Formula (4);

[0033] (203) The expansion ratio n of the coating with and without the matching system 原始 / n 配套 Compare and judge the compatibility of the coatings, and calculate the coating system expansion ratio attenuation α according to the following formula:

[0034] α=|n 配套 -n 原始 | / n 原始 ×100%

[0035] If the average expansion ratio of the coating after the application of the matching system decreases by more than 25% compared with the original sample, it can be determined that the fire compatibility of the matching system with the fire retardant coating is poor.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] The intumescent steel structure fire retardant coating designed by the present invention introduces an inorganic flame retardant filler of a specific composition by chemically modifying the base resin, and optimizes the ratio of multiple components such as the modified resin, foaming agent, carbonizing agent and inorganic flame retardant filler. This significantly improves the mechanical strength and fire resistance of the coating. The decomposition behavior of the foaming agent at high temperature and the carbonization process of the carbonizing agent work together to form a stable and dense insulating carbon layer, which effectively inhibits the conduction of heat to the substrate. In addition, the addition of specific inorganic flame retardant fillers not only enhances the flame retardant properties of the coating, but also synergizes with the compatibilizer to optimize the interfacial bonding strength between the coating and the intermediate paint, thereby avoiding the reduction of overall protective performance due to interface failure.

[0038] Furthermore, the fire-retardant coating designed in the present invention rapidly expands under high temperatures to form a dense carbonaceous insulation layer, effectively blocking heat transfer and significantly extending the durability of steel structures in fires. The chemically modified base resin enhances the coating's adhesion and weather resistance, ensuring it maintains excellent fire protection even in complex environments. The optimized multicomponent ratio further enhances the synergistic effects of the components, further improving the overall performance of the coating. Therefore, the intumescent steel structure fire-retardant coating designed in the present invention has broad application potential in the field of steel structure fire protection. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with various embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. That is, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments.

[0040] The preparation process of the intumescent steel structure fire retardant coatings prepared in the following embodiments and comparative examples includes the following steps:

[0041] (1) Add epoxy resin to a stirring container and stir at a speed of 500-1000 r / min at room temperature, then slowly add dispersant and leveling agent, and continue stirring for 10-20 minutes until uniform;

[0042] (2) Add the foaming agent, carbonizing agent and inorganic flame retardant filler to the stirring container in sequence, adjust the stirring speed to 1500-2000 r / min, and stir for 30-60 minutes to fully mix the components;

[0043] (3) Reduce the stirring speed to 500-800 r / min, add the compatibilizer and solvent, and continue stirring for 10-15 minutes until a uniform slurry is formed;

[0044] (4) The slurry is ground by a three-roll mill to control the fineness of each component to no more than 40 μm.

[0045] Among them, the solvent used in each embodiment is an aromatic hydrocarbon composite solvent, and the coating prepared in the embodiment comprises a modified epoxy resin, a foaming agent, a carbonizing agent, an inorganic flame retardant filler, a compatibilizer, a dispersant, a leveling agent and a solvent. The weight percentages of each component are 20% to 30% of modified epoxy resin, 5% to 15% of foaming agent, 5% to 15% of carbonizing agent, 20% to 30% of inorganic flame retardant filler, 1% to 5% of compatibilizer, 0.5% to 2% of dispersant, 0.2% to 1% of leveling agent, and the balance is solvent.

[0046] The modified epoxy resins described in the following examples are chemically modified by introducing siloxane groups into epoxy resins. They have a molecular weight between 8,000 and 15,000 and a glass transition temperature between 40 and 60°C. Each group of examples of the present invention uses bisphenol A epoxy resin as the base resin. The modification process is as follows: bisphenol A epoxy resin and γ-aminopropyltriethoxysilane are stirred and reacted at 80 to 100°C for 3 to 5 hours to obtain the modified epoxy resin, wherein the added amount of γ-aminopropyltriethoxysilane is 5% to 10% by mass of the bisphenol A epoxy resin.

[0047] The foaming agent is melamine phosphate and / or pentaerythritol phosphate, the decomposition temperature is between 200 and 300 DEG C, and the decomposition product is nitrogen or carbon dioxide.

[0048] The carbonizing agent is dipentaerythritol and / or ammonium polyphosphate, and the thermal decomposition temperature is between 250 and 350° C., and a stable carbon layer is generated after decomposition.

[0049] The inorganic flame retardant filler consists of aluminum hydroxide, zinc borate and iron oxide in a mass ratio of 1:1-2:1-2. The particle sizes of the aluminum hydroxide, zinc borate and iron oxide are all 1-10 μm.

[0050] The compatibilizer is a silane coupling agent and / or a titanate coupling agent, which contains active groups such as amino, epoxy or carboxyl groups in the molecular chain and can react chemically with the functional groups in the base resin and the intermediate paint.

[0051] The dispersant is a polycarboxylate compound or a polyether compound, and the molecular weight thereof is controlled within the range of 1000 to 3000.

[0052] The leveling agent is selected from silicone-modified acrylate and / or fluorine-modified acrylate, and the surface tension is in the range of 20 to 30 mN / m (millinewton / meter).

[0053] Example 1

[0054] 1. Coating preparation

[0055] In order to explore the effect of different component ratios on the coating, this example was prepared according to the ingredient list shown in Table 1. The modified epoxy resin in the table is obtained by modifying bisphenol A epoxy resin as the base resin, and its average molecular weight is 10,000. Six groups of intumescent steel structure fire retardant coatings were prepared:

[0056] Table 1 Sample feeding table for Example 1

[0057] project Y1 Y2 Y3 Y4 Y5 Y6 Modified epoxy resin (g) 25 15 35 25 25 25 Melamine phosphate (g) 10 10 10 10 10 10 Dipentaerythritol (g) 10 10 10 10 10 10 Aluminum hydroxide / zinc borate / iron oxide (1:1:1) (g) 25 25 25 15 35 25 Silane coupling agent (g) 3 3 3 3 3 0 Polycarboxylate compounds (g) 1 1 1 1 1 1 Silicone modified acrylate (g) 1 1 1 1 1 1

[0058] 2. Sample preparation

[0059] The primer, intermediate paint and topcoat information to be used in this step are as follows: GZH208 epoxy zinc-rich primer and GZH206 epoxy micaceous iron intermediate paint were purchased from Chengdu Tianhe Hongye Technology Development Co., Ltd.; Interthane 870 acrylic polyurethane topcoat was purchased from Akzo Nobel Protective Coatings (Suzhou) Co., Ltd.

[0060] Q215 steel was used as the substrate for the specimens, measuring 10 mm × 10 mm × 5 mm. Oil and rust stains were thoroughly removed to a cleanliness level of Sa 2.5, and the surface roughness Ra was reduced to approximately 80 μm by sandblasting. The epoxy zinc-rich primer and epoxy micaceous iron intermediate were sprayed sequentially according to the manufacturer's instructions, using a thickness gauge to ensure that the average dry film thickness of each layer was between 80 and 100 μm. The fire retardant coating and topcoat were applied evenly with a wool brush according to the manufacturer's instructions, and the average dry film thickness of the fire retardant coating was approximately 1.5 mm, and the average dry film thickness of the topcoat was also between 80 and 100 μm using a thickness gauge. The sample codes for each group in this experiment, based on the different fire retardant coating systems, are shown in Table 2.

[0061] Table 2 Composition and code of each sample

[0062] Paint code S SP SPI ST SP-T SPI-T primer × √ √ × √ √ Intermediate paint × × √ × × √ Topcoat × × × √ √ √ Fire retardant coatings √ √ √ √ √ √

[0063] Note: “S”—fire retardant coating applied directly to sandblasted steel plate; “SP”—fire retardant coating applied to sandblasted steel plate + primer; “SPI”—fire retardant coating applied to sandblasted steel plate + primer + intermediate paint; “T”—topcoat applied; ×—uncoated; √—coated.

[0064] The 6 groups of fire retardant coatings prepared were made into 36 groups of samples according to Table 2, and the following tests were carried out simultaneously:

[0065] (1) Adhesion test

[0066] Adhesion testing of coatings was conducted with reference to GB / T 5210-2006, using a 20mm spindle, a two-component slow-drying epoxy adhesive, and a tensile rate of 0.2 to 1 MPa / s. Adhesion of different coating systems (Y1 to Y6) to substrates was tested using a KS-M (20mm) adhesion tester in accordance with relevant design standards. The results are shown in Table 3.

[0067] Table 3 Adhesion test results of different sample compositions of Y1~Y6 fire retardant coatings

[0068] project S SP SPI ST SP-T SPI-T Y1 2.51 2.72 2.55 2.55 2.79 2.61 Y2 1.24 1.28 1.21 1.28 1.33 1.27 Y3 1.39 1.41 1.35 1.41 1.44 1.37 Y4 1.57 1.51 1.53 1.59 1.54 1.55 Y5 1.45 1.47 1.41 1.48 1.49 1.46 Y6 1.36 1.29 1.24 1.38 1.33 1.29

[0069] By comparing the adhesion data of different supporting systems (e.g., direct application of substrate S, application of primer SP, application of primer + intermediate paint SPI, etc.) (as shown in Table 3, the SPI system adhesion of Y1 reached 2.55 MPa, significantly higher than the 1.21 to 1.41 MPa of Y2 to Y6), this example effectively verified the optimization effect of the compatibilizer, modified epoxy resin and inorganic flame retardant filler on the interfacial bonding strength, and also solved the problem of coating shedding caused by insufficient interfacial adhesion (for example, the SPI system adhesion of Y6 without the addition of a compatibilizer was only 1.24 MPa, which was prone to reduce the protective performance due to interface failure in actual use), significantly improving the overall durability of the coating and the supporting system.

[0070] (2) Fire resistance test

[0071] Test equipment: An imaging sintering point tester. Specifications include: maximum test temperature range: room temperature to 1400°C; heating rate: up to 1400°C in 1.5 hours, adjustable according to experimental requirements; image magnification: 8x to 9x, with an image screen equipped with a coordinate system for easily quantifying expansion and contraction data; maximum power consumption: 2kW; maximum specimen size: 7 x 8mm; equipped with a CCD camera and computer image processing system.

[0072] Test process: Phase 1: Room temperature to 300°C (heating rate 10°C / min), observing initial expansion behavior; Phase 2: 300-800°C (heating rate 15°C / min), capturing interface failure characteristics; Phase 3: Constant temperature at 800°C for 30 minutes, recording the integrity of the carbon layer.

[0073] Data Analysis:

[0074] Use digital display vernier calipers to measure the length, width and height of the sample before and after each stage of the test, and record them as l 前 d 前 、h 前 With l 后 d 后 、h 后 . Sample volume before test V 前 According to formula (1), the shape of the sample is evaluated after the test. If the shape after expansion is approximately cubic, the sample volume V 后 According to formula (2), if the shape after expansion is approximately spherical, the sample volume V 后 Calculate according to formula (3), and the expansion / contraction ratio n of the sample before and after the test is calculated according to formula (4):

[0075] V 前 =l 前 ×d 前 ×h 前 Formula (1)

[0076] V 后 =l 后 ×d 后 ×h 后 Formula (2)

[0077]

[0078] n=V 后 / V 前 Formula (4)

[0079] The expansion ratio n of the coating with and without the matching system 原始 / n 配套 Compare and judge the compatibility of coatings, and calculate the coating system expansion ratio attenuation α.

[0080] α=|n 配套 -n 原始 | / n 原始 ×100%

[0081] If the average expansion ratio of the coating after applying the matching system decreases by more than 25% compared with the original sample, it is judged that the matching system has poor fire resistance compatibility with the fire retardant coating.

[0082] Among the 36 groups of samples prepared in this embodiment, the average expansion ratio of the Y2-Y6 fire retardant coatings after the supporting system was applied was basically more than 25% lower than that of the original samples, indicating poor fire compatibility between the supporting system and the fire retardant coatings. Furthermore, by extracting the sample contours and interface bonding before and after expansion using an image segmentation algorithm, it was found that the Y2-Y6 fire retardant coating systems were spherical after expansion and had a small bonding area with the substrate, indicating that the Y2-Y6 fire retardant coatings affected their high-temperature interface adhesion with the substrate. The high-temperature interface bonding performance of the system was poor, and interface defects were prone to occur during the fire test, leading to fire failure. The Y1 fire retardant coating system was cubic after expansion and had good bonding with the substrate, indicating that the system had good high-temperature interface bonding performance and could achieve excellent interface compatibility in the fire test.

[0083] It can be seen that the introduction of siloxane groups significantly optimizes the interfacial bonding and weather resistance of fire retardant coatings, which is mainly manifested in:

[0084] (1) The polarity of the siloxane groups (-Si-O- bonds) forms hydrogen bonds or covalent bonds with the epoxy groups (-O-) in the epoxy iron oxide intermediate, enhancing the interfacial adhesion between the fire retardant coating and the intermediate. In this example, the Y1 sample (containing a compatibilizer) with the addition of a silane coupling agent exhibited an adhesion of 2.55 MPa in the SPI system (primer + intermediate + fire retardant coating), while the Y6 sample without the addition of a compatibilizer exhibited only 1.24 MPa (Table 3), representing an improvement in interfacial adhesion of over 100%.

[0085] (2) The high bond energy of the siloxane group (Si-O bond energy is about 452 kJ / mol, which is higher than the 347 kJ / mol of the C-C bond) gives the coating stronger resistance to UV aging, avoiding interfacial debonding caused by long-term exposure.

[0086] Example 2

[0087] This example explores the effects of different epoxy resins on coatings, and sets up experimental groups or control groups with different epoxy resins. Based on the Y1 sample, the experimental group or control group only replaces the modified resin whose base resin is bisphenol A epoxy resin with resins with different average molecular weights, including 10,000 bisphenol A, 5,000 bisphenol A, 20,000 bisphenol A, 5,000 modified bisphenol A, 20,000 modified bisphenol A, 10,000 phenolic epoxy resin and 10,000 modified phenolic epoxy resin (Note: except for the epoxy resin substrate, the modification process is the same as in Example 1), and samples Y7 to Y13 are prepared respectively.

[0088] The adhesion of different coating systems of Y7~Y13 fire retardant coatings to the substrate was tested using an adhesion tester, and the results are shown in Table 4.

[0089] Table 4 Adhesion test results of different sample compositions of Y7~Y13 fire retardant coatings

[0090] project S SP SPI ST SP-T SPI-T Y7 1.71 1.72 1.65 1.73 1.78 1.69 Y8 1.19 1.18 1.16 1.21 1.23 1.21 Y9 1.69 1.61 1.65 1.71 1.67 1.71 Y10 1.51 1.53 1.52 1.53 1.57 1.55 Y11 1.75 1.79 1.72 1.78 1.81 1.76 Y12 1.64 1.76 1.74 1.69 1.84 1.76 Y13 2.43 2.53 2.61 2.49 2.63 2.65

[0091] Among the 42 groups of samples prepared in this embodiment, among the 36 groups of samples of Y7~Y12 fire retardant coatings, the average expansion ratio of the coating after applying the supporting system was more than 25% lower than that of the original samples in more than 90% of the cases; the Y13 fire retardant coating system was cubic after expansion and had good bonding with the substrate, and the average expansion ratio of the coating after applying the supporting system did not exceed 25% lower than that of the original sample.

[0092] Example 3

[0093] This example provides the effects of different inorganic flame retardant fillers on the properties of the coating, and sets up control groups containing different inorganic flame retardant filler components. The details of the inorganic flame retardant filler feeding in each control group are shown in Table 5.

[0094] Table 5 Inorganic flame retardant filler feeding situation in different control groups

[0095] sample Feed ratio of aluminum hydroxide / zinc borate / iron oxide Y14 1∶1∶0 Y15 1∶0∶1 Y16 0∶1∶1 Y17 1∶0∶0 Y18 0∶1∶0 Y19 0∶0∶1 Y20 1∶1∶2 Y21 1∶2∶1 Y22 2∶1∶1

[0096] The adhesion of different coating systems of Y14~Y22 fire retardant coatings to the substrate was tested using an adhesion tester, and the results are shown in Table 6.

[0097] Table 6 Adhesion test results of different sample compositions of Y14~Y19 fire retardant coatings

[0098] project S SP SPI ST SP-T SPI-T Y14 1.42 1.41 1.39 1.43 1.48 1.42 Y15 1.39 1.36 1.31 1.42 1.43 1.37 Y16 1.12 1.11 1.09 1.21 1.27 1.11 Y17 1.21 1.23 1.21 1.26 1.28 1.24 Y18 1.15 1.19 1.22 1.18 1.22 1.25 Y19 1.04 1.07 1.02 1.07 1.09 1.05 Y20 2.47 2.52 2.51 2.51 2.53 2.55 Y21 2.41 2.43 2.49 2.43 2.48 2.55 Y22 1.91 1.98 1.97 1.95 2.03 2.05

[0099] Among the 54 groups of samples prepared in this embodiment, among the 36 groups of samples of Y14~Y19 fire retardant coatings, the average expansion ratio of the coating after applying the matching system was more than 25% lower than that of the original sample; the Y20 and Y21 fire retardant coating systems were cubic after expansion and had good bonding with the substrate, and the average expansion ratio of the coating after applying the matching system was less than 25% lower than that of the original sample; the Y22 fire retardant coating system tended to be spherical after expansion, but the average expansion ratio of the coating after applying the matching system was attenuated by 10% to 22% compared with the original sample, and the fire resistance compatibility between the matching system and the fire retardant coating was not completely lost.

[0100] It can be seen that under the synergistic effect of aluminum hydroxide, zinc borate and iron oxide, the carbon layer formation rate is increased (the expansion starting temperature in stage one is advanced to 220°C), the carbon layer thickness is increased (after constant temperature at 800°C in stage three, the carbon layer thickness reaches 8 to 10 times that of the original coating), and the density of the carbon layer is improved (the porosity is reduced by about 30%). In addition, the particle sizes of aluminum hydroxide, zinc borate, and iron oxide are all 1-10 μm. This design, on the one hand, evenly disperses the filler in the resin, avoiding local interface defects caused by agglomeration (for example, the SPI system adhesion of Y17-Y19 is only 1.02-1.25 MPa due to the large particle size of the single filler, see Table 6); when the particle size is greater than 1 μm, the reaction efficiency of the active sites (hydroxyl groups, silanol groups) on the filler surface and the compatibilizer (silane coupling agent) is higher, thereby enhancing the interfacial bonding between the filler and the resin (Y20-Y21 has an SPI system adhesion of 2.41-2.55 MPa due to the ternary filler particle size of 1-10 μm, see Table 6); on the other hand, fillers with uniform particle size can reduce the obstruction to the decomposition gas of the foaming agent, making the expansion process more uniform (Y20 becomes a cube after expansion, and the expansion ratio is attenuated by less than 25%, while Y14-Y16 becomes spherical after expansion due to the lack of a certain component, and the attenuation is greater than 25%).

[0101] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

Claims

1. An intumescent fire retardant coating for steel structures, characterized in that: The invention comprises the following components in weight percentage: 20% to 30% of modified epoxy resin, 5% to 15% of foaming agent, 5% to 15% of carbonizing agent, 20% to 30% of inorganic flame retardant filler, 1% to 5% of compatibilizer, 0.5% to 2% of dispersant, 0.2% to 1% of leveling agent, and the balance is solvent; the modified epoxy resin is chemically modified by introducing siloxane groups into epoxy resin, and its molecular weight is between 8000 and 15000 and its glass transition temperature is between 40°C and 60°C; the inorganic flame retardant filler is composed of aluminum hydroxide, zinc borate and iron oxide in a mass ratio of 1:1 to 2:1 to 2, and the particle size of the aluminum hydroxide, zinc borate and iron oxide is 1 to 10 μm.

2. The intumescent fire retardant coating for steel structures according to claim 1, characterized in that: The preparation process of the modified epoxy resin is as follows: epoxy resin and γ-aminopropyltriethoxysilane are stirred and reacted at 80-100° C. for 3-5 hours to obtain the modified epoxy resin, wherein the addition amount of γ-aminopropyltriethoxysilane is 5%-10% of the mass of the epoxy resin, and the epoxy resin is bisphenol A epoxy resin.

3. The intumescent fire retardant coating for steel structures according to claim 1, characterized in that: The foaming agent is melamine phosphate and / or pentaerythritol phosphate, and the decomposition temperature is between 200 and 300°C.

4. The intumescent fire retardant coating for steel structures according to claim 1, wherein: The carbonizing agent is dipentaerythritol and / or ammonium polyphosphate, and the thermal decomposition temperature is between 250 and 350°C.

5. The intumescent fire retardant coating for steel structures according to claim 1, characterized in that: The compatibility aid is a silane coupling agent and / or a titanate coupling agent containing at least one active group selected from amino, epoxy or carboxyl groups.

6. The intumescent fire retardant coating for steel structures according to claim 1, characterized in that: The dispersant is a polycarboxylate compound and / or a polyether compound, and has a molecular weight between 1000 and 3000.

7. The intumescent fire retardant coating for steel structures according to claim 1, characterized in that: The leveling agent is organic silicon modified acrylate and / or fluorine modified acrylate, and the surface tension is 20-30 mN / m.

8. The method for preparing the intumescent fire retardant coating for steel structures according to any one of claims 1 to 7, characterized in that: The steps include: (1) Add the modified epoxy resin into a stirring container and stir at a speed of 500 to 1000 r / min at room temperature, then slowly add the dispersant and leveling agent, and continue stirring for 10 to 20 minutes until uniform; (2) Add the foaming agent, carbonizing agent and inorganic flame retardant filler to the stirring container in sequence, adjust the stirring speed to 1500-2000 r / min, and stir for 30-60 minutes to fully mix the components; (3) Reduce the stirring speed to 500-800 r / min, add the compatibilizer and solvent, and continue stirring for 10-15 minutes until a uniform slurry is formed; (4) The slurry is ground by a three-roll mill to control the fineness of each component to no more than 40 μm.

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