Durable fireproof coating for steel structure and preparation method and application thereof

Abstract

This invention provides a durable fire-retardant coating for steel structures, its preparation method, and its application, belonging to the field of fire-retardant coating technology. The coating uses a water-based organosilicon-modified acrylic resin emulsion as the base material, combined with flame-retardant components such as ammonium polyphosphate and melamine, as well as functional components such as modified nano-silica, modified carbon nanotubes, self-healing microcapsules, and zinc molybdate, and is prepared through a specific mixing and dispersion process. This invention achieves integrated fire resistance, corrosion protection, and self-healing functions through the synergistic effect of its components. It possesses advantages such as high fire resistance limit, good char layer stability, smoke suppression and environmental friendliness, strong corrosion resistance, and rapid self-healing response. Furthermore, it is convenient to apply and forms a uniform film, meeting the protection needs of steel structures in various scenarios, including conventional, humid, high-temperature, and high-risk environments. It solves the problems of existing coatings having single functions and unbalanced performance, demonstrating significant practicality and promotional value.

Description

Technical Field

[0001] This invention relates to the field of fire-retardant coating technology, and in particular to a durable fire-retardant coating for steel structures, its preparation method, and its application. Background Technology

[0002] Steel structures, with their significant advantages such as light weight, high strength, excellent seismic performance, high degree of industrialization, and short construction period, have been widely used in various engineering fields such as architecture, transportation, and industrial plants, becoming one of the core forms of modern engineering structures. With the advancement of urbanization and the rapid development of prefabricated buildings and transportation hub projects, the scale of steel structure applications continues to expand. Among them, subways, as the core carrier of urban public transportation, extensively use steel structures in key parts such as the main structure of stations, tunnel supports, and entrance canopies, which are directly related to operational safety and stability.

[0003] However, steel structures have fatal flaws in fire resistance. Steel has a high thermal conductivity, causing it to heat up rapidly in a fire. Its strength begins to decrease significantly at 300℃, drops to half its normal strength around 500℃, and undergoes plastic deformation and loses its load-bearing capacity above 600℃. Unprotected steel structures have a fire resistance time of only 15-20 minutes, far below the requirements of engineering specifications, making them extremely prone to rapid collapse in a fire, leading to significant casualties and property damage.

[0004] To address this challenge, the "Technical Specification for Fire Protection of Steel Structures" (GB51249-2017) clearly stipulates that steel components whose fire resistance rating does not meet the requirements must be protected against fire. Currently, mainstream protection methods include applying fire-retardant coatings, covering with fire-resistant boards, and spraying fire-retardant concrete. Among these, applying fire-retardant coatings is the most widely used method due to its ease of application, controllable cost, strong adaptability, minimal increase in structural weight, and preservation of the steel structure's mechanical properties.

[0005] Fire-retardant coatings for steel structures are mainly divided into intumescent and non-intumescent types. Among them, intumescent coatings, with their advantages of thin-film application, high efficiency, and no impact on appearance, have become the preferred choice for medium and light steel structures and public transportation. Their core mechanism is the synergistic reaction of acid, gas, and carbon sources during a fire, resulting in rapid expansion and the formation of a dense, porous carbon layer, which delays the temperature rise of the steel through heat insulation and oxygen isolation. However, existing intumescent coatings still have many technical drawbacks: ordinary coatings generally have uneven performance; some excessively add flame-retardant components to pursue higher fire resistance limits, leading to poor film formation, insufficient adhesion, and easy cracking and peeling; others prioritize film formation performance but sacrifice fire resistance, resulting in substandard fire resistance limits. At the same time, traditional coatings have poor water resistance, weather resistance, and corrosion resistance, and are prone to aging, chalking, and peeling in outdoor or humid environments, resulting in high maintenance costs.

[0006] With increasingly stringent environmental protection requirements, high-VOC solvent-based coatings are gradually being phased out of the market. However, some water-based fire-retardant coatings suffer from poor film-forming properties, insufficient water resistance, and difficulty in application. Furthermore, most existing coatings lack self-healing capabilities, and micro-cracks that develop during application, transportation, or use cannot repair themselves. External moisture and corrosive media can easily penetrate through these cracks, reducing fire resistance, accelerating steel structure corrosion, and shortening service life.

[0007] Compared to ordinary scenarios, the fire protection requirements for subway steel structures are much more stringent. Subways are enclosed spaces with high passenger density, large passenger flow, and limited evacuation routes. In the event of a fire, smoke spreads rapidly and is highly toxic, making evacuation extremely difficult. Therefore, fire-retardant coatings must not only meet fire resistance limits but also control smoke production and toxicity. Subway steel structures are constantly exposed to the damp and dark underground environment, and are affected by train vibrations, corrosive media, and alternating temperature and humidity. This places higher demands on the water resistance, corrosion resistance, crack resistance, and adhesion of coatings, while ordinary coatings are prone to problems such as dampness, blistering, cracking, and peeling. Some critical areas have narrow spaces, requiring strict control over the ease of coating application and leveling. Existing coatings are prone to sagging and uneven coating thickness. Subways have long operating cycles and high maintenance costs, placing stringent requirements on the service life and durability of coatings. Existing coatings require frequent maintenance, increasing costs and affecting normal operations.

[0008] Currently, most fire-retardant coatings for steel structures used in subways are either directly reused from ordinary building coatings or simply modified. These coatings fail to adequately consider the unique environment of subways, characterized by enclosed humidity, high population density, frequent vibration, and strong corrosion. This results in unstable fire resistance, poor adhesion, easy aging and peeling, and excessive smoke production, failing to meet protection requirements and posing safety hazards. Furthermore, existing coatings have limited functionality, making it difficult to simultaneously address multiple needs such as fire resistance, corrosion prevention, self-healing, and weather resistance. They also cannot solve the problems of fire resistance failure and corrosion aging during long-term service.

[0009] With the rapid development of subway engineering, higher requirements are being placed on the environmental friendliness, functionality, and durability of fire-retardant coatings. These coatings must be water-based, low in VOCs, low in smoke and toxicity, and possess excellent fire resistance, water and corrosion resistance, crack resistance, and self-healing properties. They must also be adaptable to special construction environments and operational needs, extending service life and reducing maintenance costs. Therefore, developing a fire-retardant coating for steel structures that is suitable for the special environment of subways, combines multiple functions, and has stable and reliable performance, and addresses the pain points of existing technologies, has become an urgent technical problem to be solved in the field of steel structure fire protection. This has significant practical significance and application value for ensuring the safety of subway operations and promoting the upgrading of fire protection technology. Summary of the Invention

[0010] The purpose of this invention is to provide a durable fire-retardant coating for steel structures, its preparation method, and its application, in order to solve the above-mentioned technical problems.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a durable fireproof coating for steel structures, comprising the following raw materials in the indicated mass fractions: 35-45% water-based silicone-modified acrylic resin emulsion, 18-22% ammonium polyphosphate, 8-10% melamine, 6-8% pentaerythritol, 3-5% expandable graphite, 4-6% aluminum tripolyphosphate, 2-4% zinc phosphate, 1-2% aluminum silver paste, 1-1.5% modified nano-silica, 0.5-1% modified carbon nanotubes, 3-5% self-healing microcapsules, 1-2% zinc molybdate, 1-3% propylene glycol, 1-2% functional additives, and the balance being water; The self-healing microcapsule is composed of a melamine-formaldehyde resin shell and a self-healing core material in a mass ratio of 1:1.5~4. The self-healing core material includes polyamide resin or silane-terminated polymer.

[0012] Furthermore, the functional additives include wetting and dispersing agents, defoamers, and leveling agents; The self-healing microcapsules have a particle size of 5~30μm.

[0013] Furthermore, in the raw material system of the durable steel structure fireproof coating, the mass fraction of the wetting and dispersing agent is 0.5~1.5%, the mass fraction of the defoamer is 0.2~0.5%, and the mass fraction of the leveling agent is 0.2~0.5%.

[0014] This invention provides a method for preparing a durable fire-retardant coating for steel structures, comprising the following steps: Step 1) Mix modified nano-silica, modified carbon nanotubes, a portion of wetting and dispersing agent and water, and then treat with ultrasound to obtain a nano-slurry; Step 2) Under stirring conditions, add the remaining wetting and dispersing agent, propylene glycol and waterborne organosilicon-modified acrylic resin emulsion to water to obtain the base solution; Step 3) Under stirring conditions, ammonium polyphosphate, melamine, pentaerythritol, expandable graphite, aluminum tripolyphosphate and zinc phosphate are added sequentially to the base solution and continuously dispersed. Step 4) Under stirring conditions, add nano slurry, self-healing microcapsules and aluminum silver paste to the system obtained in step 3) in sequence until the materials are evenly dispersed. Then add defoamer and leveling agent, and adjust the viscosity to obtain the fireproof coating for steel structures.

[0015] Furthermore, in step 1), the frequency of the ultrasonic treatment is 20~80kHz, and the time is 15~20min.

[0016] Furthermore, in step 2), the stirring speed is 300~400 rpm; In step 3), the dispersion speed is 1200~1500 rpm and the dispersion time is 30~40 min.

[0017] Furthermore, in step 3), the stirring speed is 400~600 rpm; The viscosity is adjusted using an alkali-swellable thickener.

[0018] The present invention also provides an application of the above-mentioned durable steel structure fireproof coating in steel structure fireproofing, wherein the fireproof coating is stirred evenly and then applied in 2 to 3 coats on the treated steel structure substrate.

[0019] Furthermore, the total coating thickness is 80μm to 1.5mm, and the coating method includes one or more of spraying, brushing and roller coating.

[0020] Furthermore, the surface roughness Ra of the treated steel structure substrate is 30~75μm.

[0021] The beneficial effects of this invention are: This technical solution overcomes the shortcomings of existing fire-retardant coatings, such as loose char layer, passive corrosion protection, and high smoke generation, through the synergistic effect of nano-reinforcing phase, self-healing microcapsule components, and functional additives. Significant benefits are achieved: the synergistic flame-retardant system of nano-modified silica and modified carbon nanotubes significantly improves the compressive strength, density, and fire resistance limit of the char layer; the introduction of zinc molybdate effectively reduces smoke generation during fires; the self-healing microcapsules endow the coating with repair capabilities, constructing a multi-layered synergistic anti-corrosion defense system and greatly extending the coating's salt spray protection life; excellent coating adhesion; a single coating integrates multiple functions including fireproofing, corrosion protection, and smoke suppression, simplifying construction procedures and reducing overall costs; the all-water-based system is environmentally friendly and low in VOCs, making it particularly suitable for scenarios with stringent safety and environmental requirements, such as subways, significantly improving the safety and service life of steel structures. Detailed Implementation

[0022] This invention provides a durable fireproof coating for steel structures, comprising the following raw materials in the indicated mass fractions: 35-45% water-based silicone-modified acrylic resin emulsion, 18-22% ammonium polyphosphate, 8-10% melamine, 6-8% pentaerythritol, 3-5% expandable graphite, 4-6% aluminum tripolyphosphate, 2-4% zinc phosphate, 1-2% aluminum silver paste, 1-1.5% modified nano-silica, 0.5-1% modified carbon nanotubes, 3-5% self-healing microcapsules, 1-2% zinc molybdate, 1-3% propylene glycol, 1-2% functional additives, and the balance being water; The self-healing microcapsule is composed of a melamine-formaldehyde resin shell and a self-healing core material in a mass ratio of 1:1.5~4. The self-healing core material includes polyamide resin or silane-terminated polymer.

[0023] In this invention, the amount of the water-based organosilicon-modified acrylic resin emulsion added is preferably 38-42% by mass fraction.

[0024] In this invention, the amount of ammonium polyphosphate added is preferably 20% by mass fraction.

[0025] In this invention, the amount of melamine added is preferably 9% by mass fraction.

[0026] In this invention, the amount of pentaerythritol added is preferably 7% by mass fraction.

[0027] In this invention, the amount of expandable graphite added is preferably 4% by mass fraction.

[0028] In this invention, the amount of aluminum tripolyphosphate added is preferably 5% by mass fraction.

[0029] In this invention, the amount of zinc phosphate added is preferably 3% by mass fraction.

[0030] In this invention, the amount of aluminum silver paste added is preferably 1.5% by mass fraction.

[0031] In this invention, the amount of modified nano-silica added is preferably 1.2% by mass fraction.

[0032] In this invention, the amount of modified carbon nanotubes added is preferably 0.8% by mass fraction.

[0033] In this invention, the amount of the self-healing microcapsules added is preferably 4% by mass fraction.

[0034] In this invention, the amount of zinc molybdate added is preferably 1.5% by mass fraction.

[0035] In this invention, the amount of propylene glycol added is preferably 2% by mass fraction.

[0036] In this invention, the functional additive of expandable graphite is preferably 1.2 to 1.8% by mass fraction.

[0037] In this invention, the mass ratio of the shell material to the core material in the self-healing microcapsule is preferably 1:2~3.

[0038] In this invention, the self-healing core material comprises polyamide resin or silane-terminated polymer, preferably Versamid 115 or MS Polymer.

[0039] In this invention, the self-healing microcapsules are prepared by in-situ polymerization.

[0040] In this invention, waterborne organosilicon-modified acrylic resin emulsion is used as the main material. The organosilicon network can provide better heat resistance, hydrolysis resistance and elasticity. The introduction of long-chain alkyl groups can make the coating surface hydrophobic, greatly reducing the contact between water, electrolyte and substrate, and physically strengthening the anti-corrosion performance.

[0041] In this invention, the modified nano-silica is modified by using a silane coupling agent to reduce surface energy and reduce agglomeration.

[0042] In this invention, the modified carbon nanotubes are modified by using surfactants to improve dispersibility and enhance adhesion to the matrix.

[0043] In this invention, a small amount of flake alumina is added to the coating to facilitate rapid lateral heat diffusion in hot spots, preventing localized rapid heating and thus delaying the time it takes for the overall temperature to reach the critical temperature, thereby improving the fire resistance limit.

[0044] In this invention, zinc molybdate is added as a smoke suppressant synergist, which effectively reduces the amount of smoke generated in a fire.

[0045] In this invention, the functional additives include wetting and dispersing agents, defoamers, and leveling agents; The self-healing microcapsules have a particle size of 5-30 μm, preferably 10-40 μm, and more preferably 20-30 μm.

[0046] In this invention, when the coating develops microcracks or scratches, the microcapsules rupture and release a repair agent, which migrates to the metal surface, extending the service life of the coating in harsh environments.

[0047] In this invention, in the raw material system of the durable steel structure fireproof coating, the mass fraction of the wetting and dispersing agent is 0.5-1.5%, preferably 0.8-1.2%; the mass fraction of the defoamer is 0.2-0.5%, preferably 0.3%; and the mass fraction of the leveling agent is 0.2-0.5%, preferably 0.3-0.4%.

[0048] In this invention, the wetting and dispersing agent is preferably BYK-190, BYK-2155 or Tego Dispers 755 W.

[0049] In this invention, the defoamer is preferably BYK-022, BYK-024 or Tego Airex 902W.

[0050] In this invention, the leveling agent is preferably BYK-346, BYK-381, or Tego Flow 425.

[0051] This invention provides a method for preparing a durable fire-retardant coating for steel structures, comprising the following steps: Step 1) Mix modified nano-silica, modified carbon nanotubes, a portion of wetting and dispersing agent and water, and then treat with ultrasound to obtain a nano-slurry; Step 2) Under stirring conditions, add the remaining wetting and dispersing agent, propylene glycol and waterborne organosilicon-modified acrylic resin emulsion to water to obtain the base solution; Step 3) Under stirring conditions, ammonium polyphosphate, melamine, pentaerythritol, expandable graphite, aluminum tripolyphosphate and zinc phosphate are added sequentially to the base solution and continuously dispersed. Step 4) Under stirring conditions, add nano slurry, self-healing microcapsules and aluminum silver paste to the system obtained in step 3) in sequence until the materials are evenly dispersed. Then add defoamer and leveling agent, and adjust the viscosity to obtain the fireproof coating for steel structures.

[0052] In this invention, in step 1), the frequency of the ultrasonic treatment is 20~80kHz, preferably 30~50kHz; the time is 15~20min, preferably 18min.

[0053] In this invention, in step 2), the stirring speed is 300~400 rpm, preferably 320~380 rpm, and more preferably 350 rpm; In step 3), the dispersion speed is 1200~1500 rpm, preferably 1300~1400 rpm; the dispersion time is 30~40 min, preferably 32~38 min, and more preferably 35 min.

[0054] In this invention, in step 3), the stirring speed is 400~600 rpm, preferably 500 rpm; The viscosity is adjusted using an alkali-swellable thickener, preferably ASE-60.

[0055] The present invention also provides an application of the above-mentioned durable steel structure fireproof coating in steel structure fireproofing, wherein the fireproof coating is stirred evenly and then applied in 2 to 3 coats on the treated steel structure substrate.

[0056] In this invention, the construction environment temperature is preferably between 5 and 35°C, the relative humidity is ≤80%, and the surface temperature of the substrate is more than 3°C above the dew point temperature.

[0057] In this invention, the total coating thickness is preferably 80μm~1.5mm, and the coating method includes one or more of spraying, brushing and roller coating. Brushing or roller coating is preferred for complex corners or touch-up areas.

[0058] In this invention, the surface roughness Ra of the treated steel structure substrate is 30~75μm, preferably 40~60μm.

[0059] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0060] Example 1

[0061] 1.2 parts of modified nano-silica, 0.8 parts of modified carbon nanotubes, 0.3 parts of BYK-190 and water were mixed and ultrasonically treated at 30 kHz for 18 min to obtain a nano slurry. At a rotation speed of 350 rpm, 0.5% BYK-190, 2 parts propylene glycol and 38 parts waterborne organosilicon modified acrylic resin emulsion were added to water and stirred evenly to obtain a base solution. Adjust the stirring speed to 500 rpm, and add 20 parts ammonium polyphosphate, 9 parts melamine, 7 parts pentaerythritol, 4 parts expandable graphite, 5 parts aluminum tripolyphosphate and 3 parts zinc phosphate to the base solution in sequence. Then adjust the stirring speed to 1300 rpm and continue to disperse for 35 minutes. Adjust the rotation speed to 500 rpm, and continue to add nano slurry, 4 parts of self-healing microcapsules (core material is Versamid 115, and the mass ratio of shell material to core material is 1:2) and 1.5 parts of aluminum silver paste to the system in sequence. After dispersing evenly, add 0.3 parts of BYK-022 and 0.3 parts of BYK-346. Use ASE-60 alkali-swelling thickener to adjust the viscosity to about 2700 mPa·s to obtain a durable fireproof coating for steel structures.

[0062] Example 2

[0063] Mix 1 part modified nano silica, 0.5 parts modified carbon nanotubes, 0.4 parts BYK-2155 and water, and treat with ultrasonication at 40 kHz for 15 min to obtain nano slurry; At a rotation speed of 320 rpm, 0.8 parts of BYK-2155, 1 part of propylene glycol and 42 parts of waterborne organosilicon modified acrylic resin emulsion were added to water and stirred evenly to obtain a base solution. Adjust the stirring speed to 400 rpm, and add 18 parts ammonium polyphosphate, 8 parts melamine, 6 parts pentaerythritol, 3 parts expandable graphite, 4 parts aluminum tripolyphosphate and 2 parts zinc phosphate to the base solution in sequence. Then adjust the stirring speed to 1400 rpm and continue to disperse for 32 minutes. Adjust the rotation speed to 400 rpm, and continue to add nano slurry, 3 parts of self-healing microcapsules (core material is Versamid 115, and the mass ratio of shell material to core material is 1:3) and 1 part of aluminum silver paste to the system in sequence. After dispersing evenly, add 0.3 parts of BYK-024 and 0.3 parts of BYK-381. Use ASE-60 alkali-swelling thickener to adjust the viscosity to about 2500 mPa·s to obtain a durable fireproof coating for steel structures.

[0064] Example 3

[0065] 1.5 parts of modified nano-silica, 1 part of modified carbon nanotubes, 0.3 parts of Tego Dispers 755 W and water were mixed and ultrasonically treated at 50 kHz for 20 min to obtain nano-slurry; At a rotation speed of 380 rpm, 0.7 parts of Tego Dispers 755 W, 3 parts of propylene glycol and 40 parts of waterborne silicone-modified acrylic resin emulsion were added to water and stirred until homogeneous to obtain the base solution. Adjust the stirring speed to 600 rpm, and add 22 parts ammonium polyphosphate, 10 parts melamine, 8 parts pentaerythritol, 5 parts expandable graphite, 6 parts aluminum tripolyphosphate and 4 parts zinc phosphate to the base solution in sequence. Then adjust the stirring speed to 1400 rpm and continue to disperse for 38 minutes. Adjust the rotation speed to 600 rpm, and continue to add nano-slurry, 5 parts of self-healing microcapsules (core material is MS Polymer, and the mass ratio of shell material to core material is 1:4) and 2 parts of aluminum silver paste to the system in sequence. After uniform dispersion, add 0.4 parts of TegoAirex 902W and 0.4 parts of Tego Flow 425, and adjust the viscosity to about 2300 mPa·s using ASE-60 alkali-swelling thickener to obtain a durable fireproof coating for steel structures.

[0066] Example 4

[0067] 1.1 parts of modified nano-silica, 0.6 parts of modified carbon nanotubes, 0.3 parts of BYK-190 and water were mixed and ultrasonically treated at 35 kHz for 17 min to obtain nano-slurry. At a rotation speed of 340 rpm, 0.6 parts of BYK-190, 1.5 parts of propylene glycol and 35 parts of waterborne organosilicon modified acrylic resin emulsion were added to water and stirred evenly to obtain a base solution. Adjust the stirring speed to 450 rpm, and add 19 parts ammonium polyphosphate, 8.5 parts melamine, 6.5 parts pentaerythritol, 3.5 parts expandable graphite, 4.5 parts aluminum tripolyphosphate and 2.5 parts zinc phosphate to the base solution in sequence. Then adjust the stirring speed to 1350 rpm and continue to disperse for 34 min. Adjust the rotation speed to 450 rpm, and continue to add nano slurry, 3.5 parts self-healing microcapsules and 1.2 parts aluminum silver paste to the system in sequence. After even dispersion, add 0.3 parts BYK-022 and 0.3 parts Tego Flow 425. Use ASE-60 alkali-swelling thickener to adjust the viscosity to about 2600 mPa·s to obtain a durable fireproof coating for steel structures.

[0068] Example 5

[0069] 1.4 parts of modified nano-silica, 0.9 parts of modified carbon nanotubes, 0.3 parts of BYK-2155 and water were mixed and ultrasonically treated at 45 kHz for 19 min to obtain nano-slurry. At a rotation speed of 360 rpm, 0.8 parts of BYK-2155, 2.5 parts of propylene glycol and 45 parts of waterborne organosilicon modified acrylic resin emulsion were added to water and stirred evenly to obtain a base solution. Adjust the stirring speed to 550 rpm, and add 21 parts ammonium polyphosphate, 9.5 parts melamine, 7.5 parts pentaerythritol, 4.5 parts expandable graphite, 5.5 parts aluminum tripolyphosphate and 3.5 parts zinc phosphate to the base solution in sequence. Then adjust the stirring speed to 1380 rpm and continue to disperse for 36 minutes. Adjust the rotation speed to 550 rpm, and continue to add nano-slurry, 4.5 parts of self-healing microcapsules and 1.8 parts of aluminum silver paste to the system in sequence. After even dispersion, add 0.3 parts of Tego Airex 902W and 0.3 parts of BYK-381. Use ASE-60 alkali-swelling thickener to adjust the viscosity to about 2800 mPa·s to obtain a durable fireproof coating for steel structures.

[0070] Comparative Example 1

[0071] Unlike Example 1, in this comparative example, the addition of modified nano-silica, modified carbon nanotubes, self-healing microcapsules and zinc molybdate to the raw material system was omitted.

[0072] Comparative Example 2

[0073] Unlike Example 1, in this comparative example, the modified nano-silica and modified carbon nanotubes in the raw material system were omitted.

[0074] Comparative Example 3

[0075] Unlike Example 1, the addition of self-healing microcapsules to the raw material system was omitted in this comparative example.

[0076] Application Example 1

[0077] The durable fireproof coating for steel structures prepared in Example 1 was stirred evenly and applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, the total coating thickness was 1.5 mm, and the coating method was spraying. After each coat, the coating was allowed to dry to ensure that there were no bubbles or runs, and finally a uniform and dense fireproof coating was formed.

[0078] Application Example 2

[0079] The durable fire-retardant coating for steel structures prepared in Example 2 was stirred evenly and applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, and the total coating thickness was 1.5 mm. The coating method combined brushing and roller coating. First, brushing was used to coat the corners, gaps and other complex parts of the steel structure, and then roller coating was used to coat the large area of ​​the substrate. After each coating, the substrate was allowed to dry to ensure that there were no bubbles or runs in the coating, and finally a uniform and dense fire-retardant coating was formed.

[0080] Application Example 3

[0081] The durable fire-retardant coating for steel structures prepared in Example 3 was stirred evenly and applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, the total coating thickness was 1.5 mm, and the coating method was spraying. This method is suitable for the protection requirements of high-temperature and high-risk fire scenarios. After each coat, the coating was allowed to dry to ensure that there were no bubbles or runs, ultimately forming a uniform, dense fire-retardant coating with excellent fire resistance.

[0082] Application Example 4

[0083] The durable fire-retardant coating for steel structures prepared in Comparative Example 1 was stirred evenly to remove any possible lumps or impurities. It was then applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, the total coating thickness was 1.5 mm, and the coating method was spraying. After each coat, the coating was allowed to dry to ensure that there were no bubbles or runs, ultimately forming a uniform and dense fire-retardant coating.

[0084] Application Example 5

[0085] The durable fireproof coating for steel structures prepared in Comparative Example 2 was stirred evenly and applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, the total coating thickness was 1.5 mm, and the coating method was spraying. After each coat, the coating was allowed to dry to ensure that there were no bubbles or runs, and finally a uniform and dense fireproof coating was formed.

[0086] Application Example 6

[0087] The durable fire-retardant coating for steel structures prepared in Comparative Example 3 was stirred evenly and applied in three coats to the pretreated steel structure substrate. The surface roughness Ra of the pretreated steel structure substrate was 60 μm, the total coating thickness was 1.5 mm, and the coating method was spraying. After each coat, the coating was allowed to dry to ensure that there were no bubbles or runs, and finally a uniform and dense fire-retardant coating was formed.

[0088] Performance testing

[0089] The fire-retardant coatings obtained from Examples 1-6 were subjected to performance tests, and the experimental results are shown in Table 1.

[0090] Table 1. Test data of fire-retardant coating performance obtained from Application Examples 1-6 GB / T 9978.1, GB / T 15442.4 GB / T 1771 ISO 5660-1 As shown in Table 1, the durable fire-retardant coating for steel structures of the present invention is an environmentally friendly material. The modified nano-silica and modified carbon nanotubes in the raw material system have excellent synergistic effects in smoke suppression and flame retardancy, which can inhibit the release of toxic and harmful gases (such as formaldehyde and volatile organic compounds) during combustion. In contrast, Comparative Examples 1-3, due to the omission of key raw materials, resulted in insufficient degradation of components such as resin and flame retardant during coating combustion, leading to the generation of a small amount of toxic smoke. The coating of the present invention achieves synergistic effects of environmental protection, fire prevention, and corrosion resistance. The release of toxic smoke only occurs after the omission of key smoke-suppressing raw materials. Application Examples 1-3 (corresponding to Examples 1-3) exhibit excellent performance, with fire resistance limit, char layer stability, corrosion resistance, and smoke suppression performance all meeting the standards. Application Example 3 has the best fire resistance and smoke suppression effect, making it suitable for high-temperature and high-risk scenarios; Application Example 2 has outstanding corrosion resistance and self-healing properties, making it suitable for humid environments. After discarding key raw materials, Comparative Examples 1 to 3 all showed significantly worse performance than Application Example 1. Comparative Example 1 discarded four core raw materials and had the worst performance in all aspects. Comparative Example 2 lacked nano-modified raw materials, resulting in a decrease in fire resistance and smoke suppression. Comparative Example 3 lacked self-healing microcapsules and had insufficient anti-corrosion and repair capabilities.

[0091] As can be seen from the above embodiments, the present invention provides a durable fire-retardant coating for steel structures, its preparation method, and its application. The durable fire-retardant coating for steel structures of the present invention uses a water-based organosilicon-modified acrylic resin emulsion as the base material, combined with synergistic flame-retardant, corrosion-resistant, and functionally modified components, resulting in excellent comprehensive performance. Through the synergistic effect of modified nano-silica, modified carbon nanotubes, and self-healing microcapsules, the present invention achieves integrated fireproofing, corrosion protection, and self-healing functions. It exhibits outstanding smoke suppression during fires, releases no toxic fumes, and is environmentally friendly. The coating has a high fire resistance limit, good char layer stability, rapid self-healing after scratches, strong corrosion resistance, and is easy to apply with uniform film formation. It also provides multiple adaptable formulations, which can be flexibly selected according to different scenarios such as conventional, humid, high-temperature, and high-risk conditions, adapting to various steel structure protection needs, demonstrating significant practicality and promotional value.

[0092] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A durable fire-retardant coating for steel structures, characterized in that, It is composed of the following raw materials in the indicated mass percentages: 35-45% water-based organosilicon modified acrylic resin emulsion, 18-22% ammonium polyphosphate, 8-10% melamine, 6-8% pentaerythritol, 3-5% expandable graphite, 4-6% aluminum tripolyphosphate, 2-4% zinc phosphate, 1-2% aluminum silver paste, 1-1.5% modified nano-silica, 0.5-1% modified carbon nanotubes, 3-5% self-healing microcapsules, 1-2% zinc molybdate, 1-3% propylene glycol, 1-2% functional additives, and the balance being water; The self-healing microcapsule is composed of a melamine-formaldehyde resin shell and a self-healing core material in a mass ratio of 1:1.5~4. The self-healing core material includes polyamide resin or silane-terminated polymer.

2. The durable fireproof coating for steel structures according to claim 1, characterized in that, The functional additives include wetting and dispersing agents, defoamers, and leveling agents; The self-healing microcapsules have a particle size of 5~30μm.

3. The durable fireproof coating for steel structures according to claim 2, characterized in that, In the raw material system of the durable steel structure fireproof coating, the mass fraction of the wetting and dispersing agent is 0.5~1.5%, the mass fraction of the defoamer is 0.2~0.5%, and the mass fraction of the leveling agent is 0.2~0.5%.

4. The method for preparing the durable fire-retardant coating for steel structures according to any one of claims 2 to 3, characterized in that, Includes the following steps: Step 1) Mix modified nano-silica, modified carbon nanotubes, a portion of wetting and dispersing agent and water, and then treat with ultrasound to obtain a nano-slurry; Step 2) Under stirring conditions, add the remaining wetting and dispersing agent, propylene glycol and waterborne organosilicon-modified acrylic resin emulsion to water to obtain the base solution; Step 3) Under stirring conditions, ammonium polyphosphate, melamine, pentaerythritol, expandable graphite, aluminum tripolyphosphate and zinc phosphate are added sequentially to the base solution and continuously dispersed. Step 4) Under stirring conditions, add nano slurry, self-healing microcapsules and aluminum silver paste to the system obtained in step 3) in sequence until the materials are evenly dispersed. Then add defoamer and leveling agent, and adjust the viscosity to obtain the fireproof coating for steel structures.

5. The method for preparing a durable fire-retardant coating for steel structures according to claim 4, characterized in that, In step 1), the frequency of the ultrasonic treatment is 20~80kHz and the time is 15~20min.

6. A method for preparing a durable fire-retardant coating for steel structures according to claim 4 or 5, characterized in that, In step 2), the stirring speed is 300~400 rpm; In step 3), the dispersion speed is 1200~1500 rpm and the dispersion time is 30~40 min.

7. The method for preparing a durable fire-retardant coating for steel structures according to claim 6, characterized in that, In step 3), the stirring speed is 400~600 rpm; The viscosity is adjusted using an alkali-swellable thickener.

8. The application of the durable fire-retardant coating for steel structures according to any one of claims 1 to 3 in fire protection of steel structures, characterized in that, After stirring the fire-retardant coating evenly, apply it in 2 to 3 coats onto the treated steel structure substrate.

9. The application of the durable fire-retardant coating for steel structures according to claim 8 in fire protection of steel structures, characterized in that, The total coating thickness is 80μm to 1.5mm, and the coating method includes one or more of spraying, brushing and roller coating.

10. The application of the durable fire-retardant coating for steel structures according to claim 8 or 9 in fire protection of steel structures, characterized in that, The surface roughness Ra of the treated steel structure substrate is 30~75μm.

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