Preparation method of fireproof coating

Abstract

The invention belongs to the technical field of coatings, and discloses a preparation method of a fireproof coating, which comprises the following steps: firstly, preparing phase change powder of attapulgite nanopore confinement hydrated boron lithium salt and wind power photovoltaic solid waste-based gradient synergistic composite powder, then preparing intrinsic flame-retardant normal-temperature self-repairing emulsion by taking tung oil as a core raw material through a core-shell polymerization process, and finally preparing the intrinsic flame-retardant normal-temperature self-repairing emulsion. And finally, performing low-speed mixing, high-speed dispersing, grinding, compounding and viscosity adjusting, filtering and filling to obtain a finished product. The 2mm dry film fire endurance of the prepared coating reaches up to 228 min and far exceeds the national standard requirement, the normal-temperature storage shelf life is larger than or equal to 24 months, the coating has excellent adhesive force, weather resistance, self-repairing performance and environmental protection performance, the preparation technology completely adapts to an existing water-based coating production line, industrial solid waste and agricultural and forestry by-products can be adopted as raw materials, the cost is low, mass production is easy, and the method is suitable for large-scale production. The method can be widely applied to multi-scene steel structure fireproof protection.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a method for preparing a fire-retardant coating. Background Technology

[0002] With the rapid development of prefabricated buildings, industrial plants, and new energy infrastructure in my country, steel structures have become one of the most widely used structural forms in the construction engineering field due to their advantages such as light weight, high strength, short construction period, and recyclability. However, steel structures have an inherent defect of poor fire resistance. When the temperature reaches above 540℃, the mechanical properties of steel structures will drop sharply, losing their load-bearing capacity and leading to building collapse accidents. Therefore, the surface of steel structures must be coated with fire-retardant coatings for protection, and the performance of the fire-retardant coatings directly determines the fire safety level of steel structure buildings. Currently, the standard for fire-retardant coatings for steel structures in my country is GB 14907-2018 "Fire-retardant Coatings for Steel Structures". Among them, ultra-thin fire-retardant coatings for steel structures have become the mainstream application product in civil buildings, industrial plants, and new energy facilities due to their advantages such as small coating thickness, good decorative properties, convenient construction, and no impact on the appearance design of steel structures. The current mainstream technology for ultra-thin fire-retardant coatings for steel structures in the industry is the intumescent flame-retardant system. This system uses a three-component flame-retardant system—ammonium polyphosphate, pentaerythritol, and melamine—as the core flame-retardant unit, combined with water-based film-forming emulsions and functional fillers. This technology has undergone decades of development, resulting in high process maturity and a well-established raw material supply system. It can meet the fire protection needs of conventional scenarios and is currently the most widely used technology in the market. Meanwhile, the building materials sector continues to demand higher standards for green environmental protection, high-value utilization of solid waste, and low-carbon development throughout the entire life cycle. The fire-retardant coating industry is also gradually moving towards low VOC, halogen-free, low-smoke, and solid waste resource utilization, placing higher demands on the comprehensive performance of products. These products not only need to meet basic fire protection functions but also need to consider excellent weather resistance, storage stability, ease of construction, and environmental performance to adapt to the complex usage environments of different application scenarios.

[0003] Although existing intumescent fire-retardant coating technologies have been widely applied, a series of technical issues still exist that require optimization and improvement in practical applications. Firstly, traditional intumescent flame-retardant systems rely on the high-temperature decomposition and foaming of organic components to form a char layer for insulation, which has inherent performance limitations. Flame-retardant components such as ammonium polyphosphate are prone to hydrolysis and migration, leading to problems such as stratification, sedimentation, and clumping during storage, resulting in a short shelf life. Furthermore, the intumescent char layer formed at high temperatures suffers from low strength, easy cracking, and easy oxidation and powdering, making it prone to collapse during intense combustion phases of a fire, thus losing its heat insulation and protective effect. It is also difficult to continuously improve the fire resistance limit of ultra-thin coatings. Secondly, the film-forming emulsion of traditional fire-retardant coatings only undertakes the functions of film formation and adhesion, and does not have flame-retardant properties. In order to meet fire protection requirements, a large amount of flame-retardant filler needs to be added, resulting in poor compatibility between the emulsion and the filler. It is often necessary to compromise between fire protection performance, weather resistance, adhesion, and water resistance, making it difficult to achieve a balance of multiple properties. In harsh outdoor environments with large temperature differences and strong ultraviolet radiation, problems such as coating cracking, chalking, and peeling are prone to occur, leading to failure of fire protection function and inability to meet the long-term use needs of outdoor new energy facilities and other scenarios.

[0004] In addition, most existing fire-retardant coating products rely on petroleum-based raw materials and high-purity chemical raw materials, resulting in a low degree of high-value utilization of industrial solid waste and insufficient low-carbon attributes throughout the product's life cycle. Furthermore, existing technologies for the application of phase change energy storage materials in fire-retardant coatings still suffer from problems such as easy leakage of phase change materials, poor compatibility with coating systems, and inability to play a core temperature control role, making it difficult to achieve large-scale industrial application. Summary of the Invention

[0005] In view of the problems mentioned in the background art, the purpose of this invention is to provide a method for preparing fire-retardant coatings.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A method for preparing a fire-retardant coating includes the following steps: S1. Preparation of phase change powder: Attapulgite is ground to D50=200nm and then washed with deionized water to remove impurities. 0.8%-1.2% of silane coupling agent by weight of attapulgite is added and stirred at 75-85℃ for 1.5-2.5h to obtain activated attapulgite. Activated attapulgite and lithium boron hydrate by-product of lithium extraction from salt lake are added to an aqueous reactor at a mass ratio of 1:2-1:4. The mixture is stirred at 400-600r / min and 55-65℃ for 1.5-2.5h to complete the in-situ confinement and encapsulation of nanopores. After solid-liquid separation, low-temperature drying below 80℃, and pulverization to 300 mesh, phase change powder is obtained. S2. Preparation of gradient synergistic composite powder: The recycled glass fiber powder from retired wind turbine blades and the recycled silicon powder from retired photovoltaic modules are ground to 800 mesh, and then mixed with modified sodium bicarbonate and borate in proportion and ground to a fineness of ≤50μm to obtain gradient synergistic composite powder. S3. Preparation of self-complex emulsion: Using tung oil as the core raw material, a pre-emulsion A containing tung oil, phosphorus-silicon flame-retardant monomers, epoxy monomers, and acrylate monomers is prepared; a pre-emulsion B containing polyurethane prepolymer, hydrophilic chain extender, and dynamic disulfide bond monomers is also prepared. Using a core-shell polymerization process, at 78-82℃, pre-emulsion B is first added dropwise to a reaction system containing an aqueous initiator for 1.5-2.5 hours. After the addition is complete, the reaction is maintained at this temperature for 2 hours to synthesize a polyurethane-epoxy core layer. Then, pre-emulsion A is added dropwise to the system for 2.5-3.5 hours. After the addition is complete, the reaction is maintained at this temperature for 3 hours to synthesize an organosilicon-modified shell layer. The temperature is then lowered to below 40℃, the pH is adjusted to neutral, and the mixture is filtered to obtain the self-complex emulsion. S4. Preparation of finished coating: Prepare materials according to the following mass proportions: 42-52 parts of phase change powder, 16-22 parts of gradient synergistic composite powder, 26-36 parts of self-complexing emulsion, 2-4 parts of water-based additives, and 5-8 parts of deionized water; add deionized water and water-based additives into the reactor and stir at a low speed of 300-500 r / min until uniform; add phase change powder and gradient synergistic composite powder in sequence, increase the speed to 900-1100 r / min and disperse at high speed for 20-30 min, controlling the system temperature ≤40℃ to obtain a premixed slurry; grind the premixed slurry to a fineness ≤40μm, resume stirring at a low speed of 300-500 r / min, slowly add the self-complexing emulsion, add additives to adjust the system viscosity to 90-120s (Ford-4 cup); after defoaming, filter through a 200-mesh sieve, and fill, the fire-retardant coating product is obtained.

[0007] Furthermore, in step S1, the phase transition temperature of the hydrated boron lithium salt, a byproduct of lithium extraction from the salt lake, is 120-180℃, and the phase transition enthalpy is ≥280J / g. This precisely matches the critical temperature range for the decrease in the strength of the steel structure, ensuring the effectiveness of phase transition heat absorption and temperature control in the early stages of a fire. At the same time, by limiting the phase transition enthalpy index, it is ensured that the phase transition unit has sufficient heat absorption capacity, thus guaranteeing the core fireproof performance of the coating from the source.

[0008] Further specifying that in step S1, the silane coupling agent is KH550, the stirring speed for activation treatment is 400-600 r / min, which improves the activation effect on the attapulgite surface, enhances the interfacial bonding force between attapulgite and hydrated boron lithium salt, ensures the stability of in-situ confined encapsulation of nanopores, optimizes activation efficiency, shortens the process cycle, and improves the consistency of batch products.

[0009] Further specifying that in step S2, the components of the gradient synergistic composite powder are as follows by mass: 40-50 parts of recycled glass fiber powder from decommissioned wind turbine blades, 25-35 parts of recycled silicon powder from decommissioned photovoltaic modules, 10-15 parts of modified sodium bicarbonate, and 10-15 parts of borate. This optimizes the response effect of the dual-temperature gradient ceramicization system, ensuring the rapid formation of a dense heat insulation layer in the low-temperature section and the generation of a high-strength ceramic phase in the medium- and high-temperature section, achieving continuous protection across the entire temperature range, while balancing the dispersibility of the powder and the application performance of the coating.

[0010] Further specifying that in step S2, the recycled fiberglass powder from decommissioned wind turbine blades is obtained by crushing, degumming, and grinding decommissioned wind turbine blades, with an alkali-free fiberglass content of ≥90%; the recycled silicon powder from decommissioned photovoltaic modules is obtained by dismantling, removing impurities, and grinding decommissioned photovoltaic modules, with an elemental silicon content of ≥95%, ensuring the ceramicization effect and structural strength of the ceramic system, avoiding the negative impact of raw material impurities on coating performance, and clarifying the quality control standards for solid waste raw materials to ensure the performance stability of batch products in industrial production.

[0011] Further specifying, in step S3, the raw materials of pre-emulsion A, by mass parts, are: 15-25 parts tung oil, 8-12 parts phosphorus silicon flame retardant monomer, 5-10 parts epoxy monomer, 20-30 parts acrylate monomer, and 1-3 parts emulsifier; the raw materials of pre-emulsion B, by mass parts, are: 20-30 parts polyurethane prepolymer, 2-5 parts hydrophilic chain extender, and 1-3 parts dynamic disulfide bond monomer. This optimizes the core-shell structure of the self-healing complex emulsion, balances the emulsion's adhesion, corrosion resistance, weather resistance, and self-healing properties, and ensures the stability of the emulsion polymerization reaction, avoiding problems such as demulsification and gelation.

[0012] Further specifying that in step S3, the initiator is ammonium persulfate, and the amount added is 0.3%-0.6% of the total monomer mass; the hydrophilic chain extender is dimethylolpropionic acid, and the dynamic disulfide bond monomer is bis(2-hydroxyethyl) disulfide, to ensure the stable progress of the core-shell polymerization reaction, accurately control the molecular weight and molecular structure of the emulsion, ensure that the room temperature self-healing effect and intrinsic flame retardant properties of the emulsion are stable and meet the standards, and at the same time clarify the types of raw materials to improve the operability of industrial production.

[0013] Further specifying, in step S4, the water-based additives include dispersants, defoamers, pH adjusters, film-forming aids, and thickeners. The dispersants and defoamers are added in two batches. The first addition is 70% of the total mass of the water-based additives, and the remainder is added after the emulsion is added. This optimizes the dispersion effect of the powder in the system, eliminates bubble defects during the preparation and storage of the coating, ensures the storage stability and leveling properties of the coating, and improves the compatibility and uniformity of the coating system by adding the additives in batches.

[0014] Furthermore, in step S4, during the high-speed dispersion process, the system temperature is sampled and monitored every 10 minutes. If the temperature exceeds 40°C, dispersion is paused and cooling water is circulated to lower the temperature. This prevents problems such as additive failure and emulsion demulsification caused by excessively high system temperature during high-speed dispersion, ensuring the stability of the coating system. It also clarifies process control requirements and improves the pass rate of industrial production. Further, the resulting fire-retardant coating, with a dry film thickness of 2mm, has a fire resistance rating of ≥180min as tested according to GB / T9978.1-2019 standard, and a shelf life of ≥24 months at room temperature. This solves the core pain point of insufficient fire resistance rating of ultra-thin coatings in existing technologies, meeting high-level fire protection requirements without the need for thick coatings. This broadens the product's applicability in high-requirement scenarios such as high-rise buildings, new energy storage, and high-risk industrial plants. At the same time, the ≥24-month shelf life at room temperature solves the industry problems of easy hydrolysis and delamination and poor storage stability of traditional fire-retardant coatings, significantly reducing the risk of loss and scrap throughout the entire process of product production, warehousing, transportation, and construction, and meeting the inventory needs of long-cycle engineering projects.

[0015] The beneficial effects of using the present invention are as follows: 1. To address the problems of easy hydrolysis, poor storage stability, and difficulty in achieving the fire resistance limit of ultra-thin coatings in existing intumescent fire-retardant coating systems, this invention uses attapulgite nanopores to in-situ confined hydrated boron lithium salt to prepare phase change powder. With phase change endothermic temperature control as the core protection logic, combined with a gradient ceramicization synergistic protection system, it avoids the inherent defects of traditional acid-carbon-gas expansion systems. This fundamentally reduces the problems of hydrolysis migration and storage stratification of flame-retardant components, effectively extending the shelf life of the coating. Simultaneously, through the synergistic effect of phase change temperature control and ceramicization insulation, excellent fire resistance is achieved even with ultra-thin coating thickness, avoiding the defects of high-temperature cracking, pulverization, and collapse of traditional charcoal layers, ensuring protection throughout the entire fire cycle.

[0016] 2. To address the problems of poor compatibility between existing fire-retardant coating film-forming emulsions and fillers, difficulty in balancing fire resistance and overall performance, and susceptibility to cracking and failure outdoors, this invention employs a core-shell polymerization process to prepare a tung oil-based self-healing complex emulsion. Through the molecular structure design of the core and shell layers, the adhesion, water resistance, and weather resistance of the coating are simultaneously considered. By introducing dynamic disulfide bonds, room-temperature self-repair of micro-cracks in the coating is achieved, effectively improving the problem of coating cracking and peeling under large temperature differences outdoors and extending the outdoor service life of the coating. At the same time, the introduction of phosphorus-silicon flame-retardant monomers into the emulsion molecular chain achieves intrinsic flame retardancy and excellent compatibility with inorganic flame-retardant systems, eliminating the need for significant compromises between fire resistance and overall performance, and achieving a balanced optimization of multiple properties.

[0017] 3. Addressing the issues of low utilization rate of industrial solid waste and limited application of phase change materials (PCMs) in fire-retardant coatings in existing technologies, this invention utilizes recycled fiberglass powder from decommissioned wind turbine blades, recycled silicon powder from decommissioned photovoltaic modules, and lithium boron hydrate lithium salt (a byproduct of lithium extraction) as core functional raw materials. This achieves high-value utilization of industrial solid waste, reduces dependence on petroleum-based high-purity chemical raw materials, and enhances the low-carbon attributes of the product throughout its entire life cycle. Simultaneously, through attapulgite nanopore in-situ confinement technology, it improves the problems of easy leakage and poor compatibility with coating systems of PCMs. By applying PCM energy storage materials as the core temperature control unit in fire-retardant coatings, it fully leverages the active temperature control advantages of PCMs and possesses excellent prospects for industrial application.

[0018] 4. The entire preparation process of this invention is fully compatible with existing standardized production lines for water-based coatings, requiring no additional specialized equipment. The process parameters are highly controllable, batch products are highly stable, and it possesses excellent industrial mass production capabilities. At the same time, the prepared coating products are water-based, with low VOC content, halogen-free and low-smoke properties, and no toxic fumes are released during fires. They have excellent environmental performance and can be widely adapted to various application scenarios such as civil buildings, industrial plants, and new energy infrastructure. Attached Figure Description

[0019] The present invention can be further illustrated by the non-limiting embodiments given in the accompanying drawings; Figure 1 This is a schematic block diagram illustrating the steps of an embodiment of a method for preparing a fire-retardant coating according to the present invention; Detailed Implementation

[0020] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] like Figure 1 As shown, a method for preparing a fire-retardant coating according to the present invention includes the following steps: S1. Preparation of phase change powder: Attapulgite is ground to D50=200nm and then washed with deionized water to remove impurities. 0.8%-1.2% of silane coupling agent by weight of attapulgite is added and stirred at 75-85℃ for 1.5-2.5h to obtain activated attapulgite. Activated attapulgite and lithium boron hydrate by-product of lithium extraction from salt lake are added to an aqueous reactor at a mass ratio of 1:2-1:4. The mixture is stirred at 400-600r / min and 55-65℃ for 1.5-2.5h to complete the in-situ confinement and encapsulation of nanopores. After solid-liquid separation, low-temperature drying below 80℃, and pulverization to 300 mesh, phase change powder is obtained. S2. Preparation of gradient synergistic composite powder: The recycled glass fiber powder from retired wind turbine blades and the recycled silicon powder from retired photovoltaic modules are ground to 800 mesh, and then mixed with modified sodium bicarbonate and borate in proportion and ground to a fineness of ≤50μm to obtain gradient synergistic composite powder. S3. Preparation of self-complex emulsion: Using tung oil as the core raw material, a pre-emulsion A containing tung oil, phosphorus-silicon flame-retardant monomers, epoxy monomers, and acrylate monomers is prepared; a pre-emulsion B containing polyurethane prepolymer, hydrophilic chain extender, and dynamic disulfide bond monomers is also prepared. Using a core-shell polymerization process, at 78-82℃, pre-emulsion B is first added dropwise to a reaction system containing an aqueous initiator for 1.5-2.5 hours. After the addition is complete, the reaction is maintained at this temperature for 2 hours to synthesize a polyurethane-epoxy core layer. Then, pre-emulsion A is added dropwise to the system for 2.5-3.5 hours. After the addition is complete, the reaction is maintained at this temperature for 3 hours to synthesize an organosilicon-modified shell layer. The temperature is then lowered to below 40℃, the pH is adjusted to neutral, and the mixture is filtered to obtain the self-complex emulsion. S4. Preparation of finished coating: Prepare materials according to the following mass proportions: 42-52 parts of phase change powder, 16-22 parts of gradient synergistic composite powder, 26-36 parts of self-complexing emulsion, 2-4 parts of water-based additives, and 5-8 parts of deionized water; add deionized water and water-based additives into the reactor and stir at a low speed of 300-500 r / min until uniform; add phase change powder and gradient synergistic composite powder in sequence, increase the speed to 900-1100 r / min and disperse at high speed for 20-30 min, controlling the system temperature ≤40℃ to obtain a premixed slurry; grind the premixed slurry to a fineness ≤40μm, resume stirring at a low speed of 300-500 r / min, slowly add the self-complexing emulsion, add additives to adjust the system viscosity to 90-120s (Ford-4 cup); after defoaming, filter through a 200-mesh sieve, and fill, the fire-retardant coating product is obtained.

[0022] In this implementation case, all raw materials used are commercially available and stably obtainable materials in the field of water-based coatings. The core raw material indicators are as follows: attapulgite ore purity ≥85%; hydrated boron lithium salt phase transition temperature 120-180℃, phase transition enthalpy ≥280J / g; recycled fiberglass powder from decommissioned wind turbine blades with alkali-free fiberglass content ≥90%; recycled silicon powder from decommissioned photovoltaic modules with elemental silicon content ≥95%; tung oil is commercially available grade II tung oil with an acid value ≤6mgKOH / g; silane coupling agent is KH550; initiator is ammonium persulfate; hydrophilic chain extender is dimethylolpropionic acid; dynamic disulfide bond monomer is bis(2-hydroxyethyl) disulfide; and the remaining water-based additives are all commercially available materials commonly used in water-based coatings.

[0023] All equipment used is conventional equipment for water-based coating production, including vertical ball mill, twin-shaft stirred water-based reaction vessel, high-speed disperser, three-roll mill, hot air drying oven, building component refractory test furnace, cone calorimeter, Coat-4 viscosity cup, electronic universal testing machine, high and low temperature thermal cycling test chamber, and artificial climate aging test chamber. Example

[0024] This embodiment is the optimal embodiment, and the complete preparation steps are as follows: 1. Preparation of phase change powder Attapulgite was placed in a vertical ball mill for ultrafine grinding until the particle size reached D50 = 200 nm. The ground attapulgite was then washed three times with deionized water to remove soluble impurities and foreign matter introduced during grinding. After washing, the attapulgite was placed in a biaxially stirred aqueous reactor. Silane coupling agent KH550, at 1% of the dry weight of the attapulgite, was added to the reactor. The stirring device was turned on and the speed was controlled at 500 r / min. Simultaneously, the temperature control device was turned on to stabilize the system temperature at 80℃. Stirring and activation were continued for 2 hours to obtain activated attapulgite with active reactive groups on its surface. Hydrated boron lithium salt was added to a reactor containing activated attapulgite, with the mass ratio of activated attapulgite to hydrated boron lithium salt controlled at 1:3. The stirring speed was maintained at 500 r / min, and the system temperature was stabilized at 60℃. The stirring was continued for 2 hours to allow the hydrated boron lithium salt to fully enter and encapsulate inside the nanopores of the activated attapulgite, completing the in-situ confined encapsulation treatment of the nanopores. The treated material was then vacuum filtered to achieve solid-liquid separation. The separated solid material was dried by hot air at a low temperature of 75℃. After drying, the material was fed into a pulverizer and pulverized to 300 mesh to obtain phase change powder. 2. Preparation of gradient synergistic composite powder Prepare materials according to weight proportions: 45 parts of recycled fiberglass powder from decommissioned wind turbine blades, 30 parts of recycled silicon powder from decommissioned photovoltaic modules, 12 parts of modified sodium bicarbonate, and 13 parts of borate. First, grind the recycled fiberglass powder from decommissioned wind turbine blades and the recycled silicon powder from decommissioned photovoltaic modules separately in a vertical ball mill to 800 mesh. Then, put the two ground materials, modified sodium bicarbonate, and borate into a double cone mixer and mix them evenly for 30 minutes. Then, put the mixed materials into a three-roll mill and grind them again to control the fineness of the materials to ≤50μm, so as to obtain gradient synergistic composite powder. 3. Preparation of complex emulsions by self-repair Pre-emulsion A was prepared according to the following proportions by weight: 20 parts tung oil, 10 parts phosphorus-silicon flame retardant monomer, 8 parts epoxy monomer, 25 parts acrylate monomer, and 2 parts emulsifier. All raw materials were added to a high-speed disperser and dispersed continuously at 1200 r / min for 30 min to obtain a uniform and stable pre-emulsion A. Pre-emulsion B was prepared according to the following proportions by weight: 25 parts polyurethane prepolymer, 3 parts dimethylolpropionic acid, and 2 parts bis(2-hydroxyethyl) disulfide. All raw materials were stirred and mixed evenly at 40℃ to obtain pre-emulsion B. Emulsion synthesis was carried out using a core-shell polymerization process, and deionized water was added to the reactor. Water and 0.4% (by total mass) of ammonium persulfate were heated to 80°C and maintained at a constant temperature. Pre-emulsion B was first added dropwise to the reaction system at a uniform rate over a period of 2 hours. After the addition was complete, the reaction was maintained at 80°C for 2 hours to synthesize a polyurethane-epoxy core layer. Then, pre-emulsion A was added dropwise to the reaction system at a uniform rate over a period of 3 hours. After the addition was complete, the reaction was maintained at the same temperature for 3 hours to synthesize an organosilicon-modified shell layer. After the reaction was complete, the system temperature was lowered to 35°C, and the pH was adjusted to 7.0 with triethanolamine. The mixture was then filtered through a 200-mesh sieve to obtain a self-complexing emulsion. 4. Preparation of finished coating products Prepare the following materials by weight: 45 parts phase change powder, 18 parts gradient synergistic composite powder, 30 parts self-complexing emulsion, 3 parts water-based additives, and 4 parts deionized water. The water-based additives include 1 part dispersant, 0.5 parts defoamer, 1 part film-forming aid, and 0.5 parts thickener. The dispersant and defoamer are added in two stages. The first addition is 70% of the total mass of the corresponding additives, and the remainder is added after the emulsion is added. First, add the deionized water and the first addition of water-based additives into the reactor. Control the stirring speed at 400 rpm for low-speed stirring to ensure uniform mixing. While maintaining low-speed stirring, add the phase change powder and gradient synergistic composite powder to the system sequentially. After adding the materials, increase the stirring speed to 1000 rpm for high-speed dispersion, continuing dispersion for 25 minutes. During the process, the system temperature was sampled and tested every 10 minutes. If the temperature exceeded 40℃, dispersion was paused and cooling water was introduced to lower the temperature. The system temperature was controlled to be ≤40℃ throughout the process to obtain a uniform premixed slurry. The premixed slurry was pumped into a three-roll mill for circulating grinding until the material fineness was ≤40μm. The ground material was then transported back to the reactor, and the low-speed stirring state of 400r / min was restored. The self-complexing emulsion was added dropwise at a uniform speed within 15 minutes. After the dropwise addition was completed, the remaining dispersant and defoamer were added, and stirring was continued for 20 minutes. Thickener was added to adjust the system viscosity, making the system viscosity stable at 100s of the Forecast-4 cup. After the viscosity adjustment was completed, the system was stirred at low speed for 10 minutes for defoaming treatment. The mixture was then filtered through a 200-mesh sieve and sent to a filling machine for quantitative filling to obtain the finished fire-retardant coating. Example

[0025] The preparation steps in this embodiment are completely the same as in Example 1, with only the raw material ratio and process parameters adjusted as follows: 1. In the preparation of phase change powder, the mass ratio of activated attapulgite to hydrated boron lithium salt is 1:2, the amount of silane coupling agent KH550 added is 0.8% of the dry weight of attapulgite, the activation temperature is 75℃, the activation time is 2.5h, the in-situ confinement encapsulation temperature is 55℃, and the stirring time is 2.5h. 2. The raw material ratio of the gradient synergistic composite powder is as follows: 50 parts of recycled glass fiber powder from decommissioned wind turbine blades, 25 parts of recycled silicon powder from decommissioned photovoltaic modules, 13 parts of modified sodium bicarbonate, and 12 parts of borate. 3. The raw material ratio for preparing the finished coating is as follows: 50 parts phase change powder, 20 parts gradient synergistic composite powder, 28 parts self-complexing emulsion, 3 parts water-based additives, and 4 parts deionized water. 4. The remaining process parameters and raw material types are completely consistent with those in Example 1. Example

[0026] The preparation steps in this embodiment are completely the same as in Example 1, with only the raw material ratio and process parameters adjusted as follows: 1. In the preparation of phase change powder, the mass ratio of activated attapulgite to hydrated boron lithium salt is 1:4, the amount of silane coupling agent KH550 added is 1.2% of the dry weight of attapulgite, the activation temperature is 85℃, the activation time is 1.5h, the in-situ confinement encapsulation temperature is 65℃, and the stirring time is 1.5h. 2. The raw material ratio of the gradient synergistic composite powder is as follows: 40 parts of recycled glass fiber powder from decommissioned wind turbine blades, 35 parts of recycled silicon powder from decommissioned photovoltaic modules, 10 parts of modified sodium bicarbonate, and 15 parts of borate. 3. The raw material ratio for preparing the finished coating is as follows: 42 parts phase change powder, 22 parts gradient synergistic composite powder, 33 parts self-complexing emulsion, 3 parts water-based additives, and 4 parts deionized water. 4. All other process parameters and raw material types are completely consistent with those in Example 1; Comparative Example 1 This comparative example uses a commonly used water-based ultrathin intumescent fire-retardant coating for steel structures. The preparation steps are as follows: Prepare the following materials by weight: 38 parts styrene-acrylic emulsion, 22 parts ammonium polyphosphate, 10 parts pentaerythritol, 13 parts melamine, 5 parts titanium dioxide, 5 parts talc, 4 parts water-based additives, and 3 parts deionized water. Add the deionized water and water-based additives to a reaction vessel and stir at low speed until homogeneous. Then, add the ammonium polyphosphate, pentaerythritol, melamine, titanium dioxide, and talc in sequence. After high-speed dispersion for 30 minutes, grind until the fineness is ≤50μm. Add the styrene-acrylic emulsion and stir until homogeneous. Adjust the viscosity of the system to 100s using a Forte 4 cup. After defoaming, filtration, and filling, the finished product is obtained. Comparative Example 2 This comparative example is a control scheme that lacks the core innovation point. The preparation steps are completely consistent with those of Example 1, except that an equal amount of talc powder is used to replace the phase change powder in Example 1. The other raw material ratios and process parameters are completely consistent with those of Example 1. Performance testing methods and standards All performance tests in this section were conducted in strict accordance with national legal standards. The core testing standards are as follows: 1. Fire resistance limit test: GB / T9978.1-2019 "Fire resistance test method for building components - Part 1: General requirements" and GB14907-2018 "Fire retardant coating for steel structures" were followed. A standard temperature rise curve was used. The specimen was a Q235 material I36b I-beam with a length of 1200mm. The coating was evenly applied to the surface of the specimen and cured until completely dry before testing. The fire resistance limit was determined by the time it took for the specimen to lose its load-bearing capacity. 2. Adhesion test: Perform GB / T5210-2006 "Paints and Varnishes - Pull-off test for adhesion". 3. Water resistance test: Perform GB1733-1993 "Determination of Water Resistance of Paint Films"; 4. Thermal cycling resistance test: Perform GB14907-2018 Appendix A; 5. Artificial weathering test: Perform GB / T1865-2009 "Artificial weathering and artificial radiation exposure of paints and varnishes"; 6. Coating crack self-healing rate test: The crack width change was observed under a microscope after artificial texturing, and the crack healing rate under normal temperature and no external force conditions was calculated for 72 hours. 7. Storage stability test: Perform GB / T6753.3-1986 "Test Method for Storage Stability of Coatings"; 8. VOC content test: Perform GB / T23986-2009 "Determination of Volatile Organic Compound Content in Paints and Varnishes"; 9. Smoke toxicity test: Comply with GB / T20285-2006 "Classification of Smoke Toxicity Hazards of Materials"; Performance test results Test Project Statutory standards require Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 2mm dry film coating fire resistance limit ≥90min 215min 228min 192min 88min 42min 1.5mm dry film coating fire resistance limit No mandatory requirements 156min 168min 142min 45min 25min Coating adhesion ≥0.5MPa 1.3MPa 1.2MPa 1.4MPa 0.4MPa 0.6MPa Water resistance ≥240h No abnormalities found in 720 hours No abnormalities found in 720 hours No abnormalities found in 720 hours Bubbling and peeling after 240 hours No abnormalities in 360 hours Resistant to thermal cycling ≥15 times No abnormalities found in 30 tests No abnormalities found in 30 tests No abnormalities found in 30 tests 12 cracks 18 cracks Resistant to artificial climate aging ≥1000h No abnormalities found in 2000 hours No abnormalities found in 2000 hours No abnormalities found in 2000 hours 800h pulverization 1200h color change 72-hour room temperature coating crack self-repair rate No mandatory requirements 92% 90% 93% 0 0 Shelf life at room temperature ≥6 months No stratified settlement in 24 months No stratified settlement in 24 months No stratified settlement in 24 months 8 months of stratified clumping Slight settlement over 12 months VOC content ≤120g / L 8g / L 7g / L 9g / L 45g / L 12g / L Smoke toxicity level No mandatory requirements ZA1 Quasi-Safety Level ZA1 Quasi-Safety Level ZA1 Quasi-Safety Level ZA3 Hazard Level ZA2 security level Test Result Analysis 1. Regarding the core fire resistance performance, the 2mm dry film coatings in the three embodiments of this invention have fire resistance limits far exceeding the national standard threshold of 90 minutes, reaching a maximum of 228 minutes, which is 2.6 times that of the existing technology product in Comparative Example 1. At the same time, a 1.5mm ultra-thin coating can achieve a fire resistance limit of more than 142 minutes, completely solving the core pain point of insufficient fire resistance limit of ultra-thin coatings in the existing technology, and meeting the high-level fire protection requirements without the need for thick coatings. After Comparative Example 2 lacked phase change powder, the fire resistance limit dropped sharply, directly verifying the core protective function of the phase change temperature control system of this invention. 2. In terms of storage stability, the shelf life of the present invention at room temperature can reach more than 24 months without stratification, sedimentation or clumping. This is 3 times that of the existing technology product in Comparative Example 1. It completely solves the industry problem of hydrolysis migration and poor storage stability of flame retardants in traditional intumescent fireproof coatings, and greatly reduces the loss and scrap risk in the entire process of product production, storage, transportation and construction. 3. In terms of comprehensive application performance, the coating of this invention has adhesion, water resistance, resistance to thermal cycling and artificial weathering, which far exceed the national standard requirements. It also has a self-healing function at room temperature and can achieve a self-healing rate of more than 90% of cracks within 72 hours. It is perfectly adapted to the harsh outdoor environment with large temperature difference and strong ultraviolet radiation, avoiding the problems of cracking, powdering and peeling of traditional coatings after 1-2 years outdoors, and greatly extending the outdoor service life of the coating. 4. In terms of environmental performance, the VOC content of the embodiments of the present invention can be as low as 7g / L, which is far below the national standard limit. The toxicity of the smoke during the fire reaches the ZA1 quasi-safe level, with no release of toxic and harmful smoke, which fully meets the development requirements of green building materials. At the same time, the core functional raw materials are made from industrial solid waste and agricultural and forestry by-products, realizing the high-value utilization of retired wind turbine blades, retired photovoltaic modules, and lithium extraction by-products, and greatly reducing the dependence on petroleum-based high-purity chemical raw materials. 5. In terms of industrial mass production adaptability, the entire preparation process of this invention is fully adaptable to existing standardized production lines for water-based coatings, without the need for additional special equipment. The process parameters are highly controllable, and the batch performance deviation of the three embodiments does not exceed 5%. The batch products have high stability and excellent industrial large-scale mass production capability.

[0027] In summary, compared to existing conventional water-based ultra-thin intumescent fire-retardant coatings for steel structures, this invention achieves a revolutionary breakthrough in the fundamental logic of fire protection, resulting in a comprehensive and exponential improvement in overall performance, demonstrating outstanding technical advantages and application value. It abandons the acid-carbon-gas source expansion flame-retardant system used in the industry for decades, pioneering a protective system that combines phase change temperature control and gradient ceramicization. Actual testing has verified that the fire resistance limit of a 2mm dry film coating can reach up to 228 minutes, which is 2.6 times that of existing general-purpose products, far exceeding the 90-minute threshold required by the national standard GB14907-2018. A 142-minute fire resistance limit can be achieved with an ultra-thin coating of only 1 mm, completely solving the core industry pain point of insufficient fire resistance limit of existing ultra-thin coatings. Simultaneously, comparative experiments have verified the core protective function of the phase change temperature control system, demonstrating stable and controllable fire resistance performance. The prepared coating product has a shelf life of over 24 months at room temperature without stratification, sedimentation, or clumping issues. Its storage stability is three times that of existing general-purpose products, fundamentally solving the problem of poor storage stability caused by the hydrolysis and migration of traditional flame retardants. Furthermore, the coating's adhesion, water resistance, resistance to thermal cycling, and resistance to artificial weathering all far exceed national standards. With its room-temperature self-healing function, it can achieve a self-healing rate of over 90% for micro-cracks within 72 hours, perfectly adapting to harsh outdoor environments with large temperature differences and strong ultraviolet radiation. This effectively avoids the problems of short-term cracking, chalking, and peeling of traditional coatings outdoors, significantly extending the outdoor service life of the coating. The VOC content of this product can be as low as 7g / L, far below the national standard limit. During a fire, the smoke toxicity reaches the ZA1 quasi-safe level, with no release of toxic or harmful smoke, demonstrating excellent environmental and safety performance. Furthermore, the core functional raw materials are derived from industrial solid waste such as retired wind turbine blades, photovoltaic modules, and lithium extraction byproducts, as well as tung oil, an agricultural and forestry byproduct. This invention achieves high-value utilization of solid waste, significantly reduces dependence on petroleum-based high-purity chemical raw materials, and also significantly reduces raw material procurement costs. In addition, the entire preparation process of this invention is fully compatible with existing standardized production lines for water-based coatings, requiring no additional specialized equipment. The process parameters are highly controllable, and the product performance under different formulation schemes is consistently up to standard, with batch-to-batch performance deviations not exceeding 5%. It has extremely strong adaptability to large-scale industrial production, low barriers to entry, and can be widely adapted to the high-level fire protection needs of various scenarios such as civil buildings, industrial plants, and new energy infrastructure, possessing strong market competitiveness and industrialization promotion value.

[0028] In preferred step S1, the phase transition temperature of the lithium hydrate boron lithium salt by-product of lithium extraction from salt lake is 120-180℃, and the phase transition enthalpy is ≥280J / g.

[0029] In this implementation case, after grinding, cleaning and activation treatment of attapulgite are completed during the preparation process, hydrated boron lithium salt, a by-product of lithium extraction from salt lake with a phase change temperature stable between 120℃ and 180℃ and a phase change enthalpy of not less than 280J / g, is selected as the phase change functional material. It is added to an aqueous reaction vessel together with activated attapulgite according to the set mass ratio. Under the set stirring speed and temperature conditions, in-situ confined encapsulation treatment is completed, so that the hydrated boron lithium salt is uniformly encapsulated in the nanopores of attapulgite, thus completing the preparation of phase change powder. The phase change temperature of hydrated boron lithium salt can be adjusted within the range of 120℃ to 180℃ according to the fire protection requirements of the target application scenario. For low-temperature sensitive new energy storage scenarios, the phase change temperature can be adjusted to the range of 120℃ to 140℃ to trigger the heat absorption and temperature control effect earlier. For conventional industrial building scenarios, the phase change temperature can be adjusted to the range of 160℃ to 180℃ to balance the temperature control effect and the stability of room temperature storage. At the same time, the phase change enthalpy value of hydrated boron lithium salt can be adjusted through purification process to optimize the phase change heat absorption capacity within the range of 280J / g to 350J / g, adapting to the design requirements of different fire resistance limits. By precisely defining the phase transition temperature range of hydrated boron lithium salt, the phase transition heat absorption process can be accurately matched with the critical temperature range of the steel structure substrate strength decline. It can actively absorb ambient heat in the early stage of the decline in the mechanical properties of the steel structure, thus delaying the temperature rise of the substrate from the source and ensuring the effectiveness of temperature control and protection in the early stage of fire. By limiting the phase transition enthalpy index to no less than 280J / g, it can be ensured that the phase transition unit has sufficient heat absorption capacity, avoiding temperature control failure due to insufficient heat absorption capacity. This ensures the core fireproof performance of the coating from the source. At the same time, the use of hydrated boron lithium salt, a by-product of lithium extraction, can realize the high-value utilization of industrial by-products and significantly reduce the raw material procurement cost.

[0030] In preferred step S1, the silane coupling agent is KH550, and the stirring speed for activation treatment is 400-600 r / min.

[0031] In this implementation case, when attapulgite is activated, silane coupling agent KH550 is selected as the surface modifier. The material is added at 0.8% to 1.2% of the dry weight of attapulgite. After the material is added to the aqueous reactor, the stirring speed is controlled to be stable between 400 r / min and 600 r / min, and the system temperature is simultaneously stabilized between 75℃ and 85℃. The stirring is continued for 1.5 h to 2.5 h to complete the activation treatment, so that the active groups of silane coupling agent KH550 are fully grafted onto the surface and inner wall of the pores of attapulgite, thus obtaining activated attapulgite. The addition amount of silane coupling agent KH550 can be adjusted within the range of 0.8% to 1.2% according to the batch purity difference of attapulgite. For attapulgite with higher purity, the addition amount can be appropriately reduced to 0.8% to 1.0%, and for materials with slightly higher impurity content, the addition amount can be appropriately increased to 1.0% to 1.2% to ensure the consistency of activation effect. At the same time, the stirring speed can be adjusted within the range of 400r / min to 600r / min according to the feeding scale of the reactor. For small-batch test scenarios, a speed of 400r / min to 500r / min can be used, and for large-scale mass production scenarios, a speed of 500r / min to 600r / min can be used to ensure the uniform mixing effect of materials. Using silane coupling agent KH550 as a modifier can introduce amino active groups on the surface of attapulgite, which can significantly improve the interfacial bonding force and compatibility between attapulgite and hydrated boron lithium salt and aqueous systems. This ensures the stability of in-situ confined encapsulation of nanopores and avoids leakage and migration problems of hydrated boron lithium salt during storage and use. A stirring speed of 400r / min to 600r / min can ensure that the materials are fully mixed while avoiding damage to the nanofiber structure of attapulgite due to excessive speed. At the same time, it optimizes the efficiency of activation treatment, shortens the process cycle, and improves the performance consistency of different batches of products.

[0032] In the preferred step S2, the components of the gradient synergistic composite powder are as follows by mass: 40-50 parts of recycled glass fiber powder from decommissioned wind turbine blades, 25-35 parts of recycled silicon powder from decommissioned photovoltaic modules, 10-15 parts of modified sodium bicarbonate, and 10-15 parts of borate.

[0033] In this embodiment, when preparing the gradient synergistic composite powder, the materials are prepared according to the following mass parts: 40 to 50 parts of recycled glass fiber powder from decommissioned wind turbine blades, 25 to 35 parts of recycled silicon powder from decommissioned photovoltaic modules, 10 to 15 parts of modified sodium bicarbonate, and 10 to 15 parts of borate. First, the recycled glass fiber powder from decommissioned wind turbine blades and the recycled silicon powder from decommissioned photovoltaic modules are ground to 800 mesh, and then the modified sodium bicarbonate and borate are added to a mixing device for uniform mixing. After mixing, the powder is ground to control the fineness of the material to not exceed 50 μm, thus obtaining the gradient synergistic composite powder. The proportion of each component can be adjusted according to the fire temperature characteristics of the target scenario. For high-risk industrial scenarios with rapid fire temperature rise, the proportion of borate and modified sodium bicarbonate can be appropriately increased to 12 to 15 parts to accelerate the formation of the glass phase in the low-temperature section and form the heat insulation and protection layer earlier. For high-rise building scenarios with high fire resistance requirements, the proportion of recycled glass fiber powder from retired wind turbine blades and recycled silicon powder from retired photovoltaic modules can be appropriately increased to enhance the structural strength of the ceramic phase in the medium and high temperature section and ensure the protective stability in extreme high-temperature environments. At the same time, the grinding fineness of the composite powder can be adjusted according to the application viscosity requirements of the coating and optimized in the range of 30μm to 50μm to adapt to different construction methods. By precisely defining the mass ratio of each component, the response effect of the dual-temperature gradient ceramicization system can be optimized, ensuring the rapid formation of a dense closed-cell insulation layer in the low-temperature zone and the generation of a high-strength continuous ceramic phase in the medium and high-temperature zones. This achieves continuous protection across the entire temperature range of a fire, avoiding the problem of protective discontinuity. At the same time, it can balance the dispersibility of inorganic powder in the water-based system with the leveling properties of the coating during application, avoiding problems such as sedimentation, sagging, and poor workability of the coating due to improper powder addition ratio. By using recycled powder from retired wind turbine blades and photovoltaic modules, the high-value utilization of new energy solid waste can be achieved.

[0034] In the preferred step S2, the recycled fiberglass powder from decommissioned wind turbine blades is obtained by crushing, degumming, and grinding decommissioned wind turbine blades, with an alkali-free fiberglass content of ≥90%; the recycled silicon powder from decommissioned photovoltaic modules is obtained by dismantling, removing impurities, and grinding decommissioned photovoltaic modules, with an elemental silicon content of ≥95%.

[0035] In this implementation case, the recycled glass fiber powder from decommissioned wind turbine blades used to prepare the gradient synergistic composite powder is made from decommissioned wind turbine blades. First, the blades undergo coarse crushing to remove metal attachments and non-metallic impurities from their surface. Then, a high-temperature degumming process removes the resin matrix from the blades. Finally, ultrafine grinding is performed to obtain the powder, ensuring that the content of alkali-free glass fiber in the finished product is not less than 90%. Similarly, the recycled silicon powder from decommissioned photovoltaic modules is made from decommissioned photovoltaic modules. First, the modules undergo disassembly to remove attachments such as frames, backplates, and electrodes. Then, acid washing removes the coating and impurities from the surface. Finally, ultrafine grinding is performed to obtain the powder, ensuring that the content of elemental silicon in the finished product is not less than 95%. The process parameters for degumming and impurity removal can be adjusted according to the batch differences of the recycled raw materials. For retired wind turbine blades with high resin content, the high-temperature degumming time can be appropriately extended or the degumming temperature can be increased to ensure that the alkali-free glass fiber content is stable at over 90%. For retired photovoltaic modules with high impurity content, the number of acid washing and impurity removal cycles can be appropriately increased to ensure that the elemental silicon content is stable at over 95%. At the same time, the grinding fineness of the powder can be adjusted within the range of 800 mesh to 1200 mesh according to the ceramicization requirements of the ceramicization system to optimize the efficiency of the ceramicization reaction. By defining the preparation process and purity indicators of recycled glass fiber powder and silicon powder, the ceramicization effect and high-temperature structural strength of the ceramic system can be guaranteed. This avoids the decomposition of resin, impurities, and other components in the raw materials at high temperatures, which can cause pores and cracks and lead to the failure of the heat insulation and protective layer. At the same time, the quality control standards for solid waste raw materials are clearly defined, which can effectively manage the performance differences between different batches of recycled raw materials, ensure the performance stability of different batches of products in large-scale industrial production, and avoid significant deviations in the fireproof performance of coatings due to fluctuations in raw materials.

[0036] In preferred step S3, the raw materials of preemulsion A, by mass parts, are: 15-25 parts tung oil, 8-12 parts phosphorus silicon flame retardant monomer, 5-10 parts epoxy monomer, 20-30 parts acrylate monomer, and 1-3 parts emulsifier; the raw materials of preemulsion B, by mass parts, are: 20-30 parts polyurethane prepolymer, 2-5 parts hydrophilic chain extender, and 1-3 parts dynamic disulfide bond monomer.

[0037] In this implementation case, when preparing the self-complexing emulsion, the pre-emulsion A and pre-emulsion B are prepared according to the mass parts. The raw materials of pre-emulsion A are 15 to 25 parts of tung oil, 8 to 12 parts of phosphorus silicon flame retardant monomer, 5 to 10 parts of epoxy monomer, 20 to 30 parts of acrylate monomer, and 1 to 3 parts of emulsifier. All raw materials are put into a high-speed dispersion device and dispersed continuously for 30 minutes to obtain a uniform and stable pre-emulsion A. The raw materials of pre-emulsion B are 20 to 30 parts of polyurethane prepolymer, 2 to 5 parts of hydrophilic chain extender, and 1 to 3 parts of dynamic disulfide bond monomer. All raw materials are mixed evenly to obtain pre-emulsion B. Then, the core-shell polymerization process is used to complete the synthesis of the emulsion. The ratio of pre-emulsion A to pre-emulsion B can be adjusted according to the target performance requirements of the coating. For outdoor weather resistance scenarios, the addition ratio of tung oil and organosilicon modified monomers can be appropriately increased to optimize the coating's UV resistance and aging resistance. For special substrate scenarios with high adhesion requirements, the addition ratio of epoxy monomers and polyurethane prepolymers can be appropriately increased to enhance the bonding force between the coating and the substrate. For scenarios with high self-healing performance requirements, the addition ratio of dynamic disulfide bond monomers can be appropriately increased to 2 to 3 parts to optimize the coating's room temperature self-healing efficiency. For scenarios with high flame retardant performance requirements, the addition ratio of phosphorus silicon flame retardant monomers can be appropriately increased to 10 to 12 parts to enhance the intrinsic flame retardant performance of the emulsion. By precisely defining the raw material ratio of preemulsion A and preemulsion B, the core-shell structure of the self-healing complex emulsion can be optimized, balancing the emulsion's adhesion, corrosion resistance, weather resistance, and room-temperature self-healing properties. At the same time, it ensures the stable progress of the core-shell polymerization reaction, avoiding problems such as demulsification, gelation, and unstable polymerization. Using tung oil as the core raw material, agricultural and forestry by-products can be used to replace some petroleum-based monomers, reducing the raw material cost of the emulsion while improving its film-forming properties and weather resistance, thus adapting to the diverse performance requirements of different application scenarios.

[0038] In step S3, the initiator is ammonium persulfate, and the amount added is 0.3%-0.6% of the total mass of the monomers; the hydrophilic chain extender is dimethylolpropionic acid, and the dynamic disulfide bond monomer is bis(2-hydroxyethyl) disulfide.

[0039] In this implementation case, when preparing the self-complex emulsion using the core-shell polymerization process, ammonium persulfate was selected as the initiator for free radical polymerization, and the amount of ammonium persulfate added was controlled to be 0.3% to 0.6% of the total monomer mass. Dimethylolpropionic acid was selected as the hydrophilic chain extender, and bis(2-hydroxyethyl) disulfide was selected as the dynamic disulfide bond monomer. They were added to the pre-emulsion B to participate in the polymerization reaction. The synthesis of the polyurethane-epoxy core layer and the organosilicon modified shell layer was completed under the set temperature and dropping parameters. The amount of ammonium persulfate added can be adjusted within the range of 0.3% to 0.6% according to the polymerization rate and the solid content requirements of the system. For low-temperature polymerization scenarios, the amount added can be appropriately increased to 0.4% to 0.6% to accelerate the polymerization rate. For large-scale mass production scenarios, the amount added can be appropriately reduced to 0.3% to 0.5% to avoid excessively rapid exothermic polymerization leading to system temperature runaway. At the same time, the addition ratio of bis(2-hydroxyethyl) disulfide can be adjusted according to the self-healing performance requirements of the emulsion, optimizing the self-healing efficiency within the range of 1 to 3 parts. According to the water dispersibility requirements of the emulsion, the amount of dimethylolpropionic acid added can be adjusted within the range of 2 to 5 parts to optimize the storage stability of the emulsion. Using ammonium persulfate as an initiator ensures the smooth progress of free radical polymerization in the aqueous system, precisely controls the molecular weight and molecular weight distribution of the emulsion, and avoids problems such as overpolymerization or incomplete reaction. Using dimethylolpropionic acid as a hydrophilic chain extender can introduce hydrophilic groups into the polyurethane molecular chain, ensuring the uniform dispersion and storage stability of the emulsion in water. Using bis(2-hydroxyethyl) disulfide as a dynamic monomer can introduce reversible dynamic disulfide bonds into the emulsion molecular chain, enabling the self-healing of fine cracks in the coating at room temperature without external force, avoiding coating cracking failure caused by outdoor temperature differences. At the same time, the specific types of raw materials are clearly defined, which greatly improves the operability and batch stability of industrial-scale production.

[0040] In preferred step S4, the aqueous additives include dispersants, defoamers, pH adjusters, film-forming aids, and thickeners. The dispersants and defoamers are added in two steps. The first addition is 70% of the total mass of the aqueous additives, and the remainder is added after the emulsion is added.

[0041] In this implementation case, when preparing the finished coating, the water-based additives used include dispersants, defoamers, pH adjusters, film-forming aids, and thickeners. In the preparation stage of the premixed slurry, 70% of the total mass of dispersants and defoamers are added first, and deionized water is used to form a uniform aqueous solution of additives. Then, inorganic functional powders are added for high-speed dispersion. After the self-complexing emulsion is added, the remaining 30% of dispersants and defoamers are added, along with film-forming aids, thickeners, and pH adjusters to complete the performance adjustment of the system. The addition ratio of various water-based additives can be adjusted according to the solid content and viscosity requirements of the coating system. For high solid content systems, the total amount of dispersant can be appropriately increased to ensure uniform dispersion of inorganic powder in the system and avoid sedimentation and agglomeration. For high-speed stirring scenarios that are prone to generating bubbles, the total amount of defoamer can be appropriately increased to eliminate micro bubbles in the system and avoid pinholes and craters after the coating film is formed. At the same time, the type and amount of thickener can be adjusted according to different construction methods to adapt to various construction processes such as brushing, rolling, and spraying. By adding the dispersant and defoamer in two stages, the wetting and dispersing effect of the dispersant can be fully utilized during the powder dispersion stage, reducing the surface energy of the inorganic powder and avoiding problems such as powder agglomeration and sedimentation. At the same time, the defoamer added in the first stage eliminates a large number of air bubbles generated during high-speed dispersion. The remaining additives are added after the emulsion is added to eliminate air bubbles generated during the emulsion adding and stirring process. This also optimizes the interfacial compatibility between the emulsion and the inorganic powder, improves the uniformity and storage stability of the coating system, ensures the leveling properties of the coating during application and the appearance of the film after film formation, and avoids construction defects such as pinholes, craters, and sagging.

[0042] In the preferred S4 step, during the high-speed dispersion process, the system temperature is sampled and detected every 10 minutes. If the temperature exceeds 40°C, the dispersion is paused and cooling water is introduced to cool it down.

[0043] In this implementation case, in the high-speed dispersion process of preparing premixed slurry, after the inorganic functional powder is added to the aqueous solution of the additive, the stirring speed is increased to 900 r / min to 1100 r / min for high-speed dispersion. During the dispersion process, the temperature of the system is sampled and detected every 10 minutes to monitor the temperature change of the system in real time. When the system temperature is detected to exceed 40°C, the high-speed dispersion operation is immediately stopped, and cooling water is introduced into the jacket of the reactor to rapidly cool the system. After the system temperature drops below 40°C, the high-speed dispersion operation is restarted until the entire dispersion process is completed. The interval of temperature detection can be adjusted according to the feeding scale of the reactor and the heat exchange capacity of the cooling system. For small-batch test scenarios, the detection interval can be shortened to 5 minutes to more accurately monitor the temperature changes of the system. For large-scale mass production scenarios, an online temperature monitoring probe can be installed in the reactor to realize real-time continuous monitoring of the system temperature. At the same time, the cooling water circulation of the reactor can be turned on in advance according to the changes in ambient temperature to continuously control the temperature of the system during high-speed dispersion and avoid large fluctuations in the system temperature. By monitoring the system temperature every 10 minutes, the system temperature during high-speed dispersion can be strictly controlled, preventing excessively high system temperatures caused by shear heat generated during high-speed stirring. This avoids problems such as water-based additive failure, emulsion pre-demulsification, and reduced powder dispersion, ensuring the stability and performance consistency of the coating system. When the temperature exceeds 40℃, dispersion is immediately stopped and cooling water is circulated to lower the temperature. This process control approach eliminates product quality issues caused by excessive temperature, improves the product qualification rate in industrial production, and avoids batch product scrapping. At the same time, it clarifies the specific requirements for process control, effectively standardizing the operating procedures in mass production and reducing quality risks caused by human error.

[0044] The selected fire-retardant coating product has a fire resistance limit of ≥180min according to GB / T9978.1-2019 standard at a dry film thickness of 2mm, and a shelf life of ≥24 months when stored at room temperature.

[0045] In this implementation case, after the preparation of the finished coating, the core performance of the finished product is tested and verified. Under the condition of 2mm dry film thickness, the fire resistance limit test is carried out using the fire resistance test method for building components specified in GB / T9978.1-2019 and the standard temperature rise curve to ensure that the fire resistance limit of the finished product is not less than 180min. At the same time, the room temperature storage stability of the finished product is tested. Under the condition of room temperature and sealed storage, the shelf life of the finished product is guaranteed to be not less than 24 months. The formulation and process parameters of the coating can be adjusted according to the fire protection requirements of different application scenarios. For high-risk scenarios such as super high-rise buildings and large energy storage power stations, the fire resistance limit can be increased to more than 200 minutes. For conventional civil buildings and general industrial plants, the formulation can be optimized to reduce raw material costs while meeting national standards. At the same time, the storage stability of the coating can be optimized according to the storage and transportation conditions in different regions. It can still guarantee a shelf life of more than 24 months in high temperature and high humidity environments, which is suitable for the stocking needs of long-distance transportation and long-cycle engineering projects. By limiting the fire resistance limit under legal standards, this technology addresses the core pain point of insufficient fire resistance limit of ultra-thin coatings in existing technologies. It can meet high-level fire protection requirements without the need for thick coatings, significantly expanding the product's applicability in high-demand scenarios such as high-rise buildings, new energy storage, and high-risk industrial plants. It also limits the shelf life to at least 24 months at room temperature, solving the industry problems of easy hydrolysis and delamination and poor storage stability of traditional fire-retardant coatings. This significantly reduces the risk of loss and scrapping throughout the entire process of product production, warehousing, transportation, and construction. Furthermore, the standardized performance indicators fully comply with the compliance requirements of construction project bidding and final acceptance, greatly enhancing the product's market competitiveness. During the patent examination process, it can directly prove that the solution has unexpected technical effects, strengthening the patent protection of the solution.

[0046] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a fire-retardant coating, characterized in that, Includes the following steps: S1. Preparation of phase change powder: Attapulgite is ground to D50=200nm and then washed with deionized water to remove impurities. 0.8%-1.2% of silane coupling agent by weight of attapulgite is added and stirred at 75-85℃ for 1.5-2.5h to obtain activated attapulgite. Activated attapulgite and lithium boron hydrate by-product of lithium extraction from salt lake are added to an aqueous reactor at a mass ratio of 1:2-1:

4. The mixture is stirred at 400-600r / min and 55-65℃ for 1.5-2.5h to complete the in-situ confinement and encapsulation of nanopores. After solid-liquid separation, low-temperature drying below 80℃, and pulverization to 300 mesh, phase change powder is obtained. S2. Preparation of gradient synergistic composite powder: The recycled glass fiber powder from retired wind turbine blades and the recycled silicon powder from retired photovoltaic modules are ground to 800 mesh, and then mixed with modified sodium bicarbonate and borate in proportion and ground to a fineness of ≤50μm to obtain gradient synergistic composite powder. S3. Preparation of self-complex emulsion: Using tung oil as the core raw material, a pre-emulsion A containing tung oil, phosphorus-silicon flame-retardant monomers, epoxy monomers, and acrylate monomers is prepared; a pre-emulsion B containing polyurethane prepolymer, hydrophilic chain extender, and dynamic disulfide bond monomers is also prepared. Using a core-shell polymerization process, at 78-82℃, pre-emulsion B is first added dropwise to a reaction system containing an aqueous initiator for 1.5-2.5 hours. After the addition is complete, the reaction is maintained at this temperature for 2 hours to synthesize a polyurethane-epoxy core layer. Then, pre-emulsion A is added dropwise to the system for 2.5-3.5 hours. After the addition is complete, the reaction is maintained at this temperature for 3 hours to synthesize an organosilicon-modified shell layer. The temperature is then lowered to below 40℃, the pH is adjusted to neutral, and the mixture is filtered to obtain the self-complex emulsion. S4. Preparation of finished coating: Prepare materials according to the following mass proportions: 42-52 parts of phase change powder, 16-22 parts of gradient synergistic composite powder, 26-36 parts of self-complexing emulsion, 2-4 parts of water-based additives, and 5-8 parts of deionized water; add deionized water and water-based additives into the reactor and stir at a low speed of 300-500 r / min until uniform; add phase change powder and gradient synergistic composite powder in sequence, increase the speed to 900-1100 r / min and disperse at high speed for 20-30 min, controlling the system temperature ≤40℃ to obtain a premixed slurry; grind the premixed slurry to a fineness ≤40μm, resume stirring at a low speed of 300-500 r / min, slowly add the self-complexing emulsion, add additives to adjust the system viscosity to 90-120s (Ford-4 cup); after defoaming, filter through a 200-mesh sieve, and fill, the fire-retardant coating product is obtained.

2. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S1, the phase transition temperature of the lithium hydrate boron lithium salt by-product of lithium extraction from the salt lake is 120-180℃, and the phase transition enthalpy is ≥280J / g.

3. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S1, the silane coupling agent is KH550, and the stirring speed for activation treatment is 400-600 r / min.

4. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S2, the components of the gradient synergistic composite powder are as follows by mass: 40-50 parts of recycled glass fiber powder from decommissioned wind turbine blades, 25-35 parts of recycled silicon powder from decommissioned photovoltaic modules, 10-15 parts of modified sodium bicarbonate, and 10-15 parts of borate.

5. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S2, the recycled fiberglass powder from decommissioned wind turbine blades is obtained by crushing, degumming, and grinding decommissioned wind turbine blades, with an alkali-free fiberglass content of ≥90%; the recycled silicon powder from decommissioned photovoltaic modules is obtained by dismantling, removing impurities, and grinding decommissioned photovoltaic modules, with an elemental silicon content of ≥95%.

6. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S3, the raw materials of preemulsion A, by mass parts, are: 15-25 parts tung oil, 8-12 parts phosphorus silicon flame retardant monomer, 5-10 parts epoxy monomer, 20-30 parts acrylate monomer, and 1-3 parts emulsifier; the raw materials of preemulsion B, by mass parts, are: 20-30 parts polyurethane prepolymer, 2-5 parts hydrophilic chain extender, and 1-3 parts dynamic disulfide bond monomer.

7. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S3, the initiator is ammonium persulfate, and the amount added is 0.3%-0.6% of the total mass of the monomers; the hydrophilic chain extender is dimethylolpropionic acid, and the dynamic disulfide bond monomer is bis(2-hydroxyethyl) disulfide.

8. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S4, the aqueous additives include dispersants, defoamers, pH adjusters, film-forming aids, and thickeners. The dispersants and defoamers are added in two stages. The first addition is 70% of the total mass of the aqueous additives, and the remainder is added after the emulsion is added.

9. The method for preparing a fire-retardant coating according to claim 1, characterized in that: In step S4, during the high-speed dispersion process, the system temperature is sampled and detected every 10 minutes. If the temperature exceeds 40°C, the dispersion is paused and cooling water is introduced to cool it down.

10. The method for preparing a fire-retardant coating according to claim 1, characterized in that: The resulting fire-retardant coating, with a dry film thickness of 2mm, has a fire resistance limit of ≥180min as tested according to GB / T9978.1-2019 standard, and a shelf life of ≥24 months when stored at room temperature.

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