Moisture-heat-resistant anti-cracking indoor non-expansive fireproof coating and preparation method thereof

Abstract

The invention discloses a damp-heat-resistant anti-cracking indoor non-expansive fireproof coating and a preparation method thereof, and belongs to the technical field of building fireproof materials. The preparation method comprises the following steps: firstly, mixing deionized water, hydroxypropyl methyl cellulose ether and a polycarboxylate water reducing agent to prepare a base solution; adding layered magnesium zinc silicate, calcium aluminum borosilicate nano-hybrid ceramic powder, kaolin, sericite powder, glass powder, titanium dioxide and modified hollow ceramic microbeads into the base solution, uniformly stirring, and adding styrene-acrylate copolymer emulsion and redispersible latex powder to obtain a mixture; and finally, adding the organic silicon defoaming agent and the polyurethane flatting agent into the mixture, and stirring to obtain the coating. Through the synergistic effect of the two specific inorganic modified compounds and optimization of a filler system, the obtained coating has excellent heat and humidity resistance and cracking resistance in a normal state, can form a compact and stable non-expansion heat-insulation protection layer at a high temperature of a fire disaster, and has significantly improved comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of building fireproof materials technology, specifically to a moisture- and heat-resistant, crack-resistant, non-expansive fireproof coating for indoor use and its preparation method. Background Technology

[0002] As a key material for improving the structural safety of buildings, the importance of indoor fire-retardant coatings is increasingly prominent. These coatings form a heat-insulating protective layer on the surface of the protected substrate, effectively slowing down the temperature rise of materials such as steel and concrete during a fire, buying valuable time for evacuation and fire rescue. Based on their morphological changes after exposure to fire, fire-retardant coatings can be mainly divided into two categories: intumescent and non-intumescent. Non-intumescent fire-retardant coatings rely primarily on the endothermic reaction, melting and covering, or forming a dense glaze layer of their inorganic components to achieve heat insulation protection under high fire temperatures. Their coating thickness is relatively large, and their fire resistance durability is generally more stable. While widely used in indoor environments, the long-term performance of these coatings is severely tested by environmental factors, especially in spaces with humid and hot conditions. The physicochemical stability of the coating directly determines the reliability of its fire-retardant function.

[0003] Although non-intumescent fire-retardant coatings possess a stable fire-retardant principle, their practical applications, especially in humid indoor environments with significant temperature differences, still reveal a series of technical defects that urgently need to be addressed. The core issues mainly focus on the coating's insufficient resistance to damp heat and cracking. Under long-term or cyclical damp heat, the organic binder phase in the coating is prone to hydrolysis and softening, leading to a weakening of the interfacial bonding force between it and the inorganic fillers. This, in turn, causes blistering, peeling, or even complete detachment of the coating, rendering its fire-retardant function ineffective. Simultaneously, because coating formulations typically contain various inorganic mineral fillers, the difference in thermal expansion coefficients between these fillers and the organic matrix generates internal stress during environmental temperature changes or the coating's drying and curing process. More seriously, under the high-temperature impact of a sudden fire, uneven heating between the inside and outside of the coating exacerbates this mismatch effect, easily leading to network cracks or even large-area cracking. These cracks become channels for flames and high-temperature smoke to directly invade the substrate, severely weakening or even completely destroying the overall thermal insulation barrier function of the coating, posing a significant safety hazard.

[0004] To address the aforementioned issues, existing technological improvements primarily focus on enhancing single performance characteristics. For example, simply increasing the amount of fibrous fillers may attempt to enhance toughness, or introducing hydrophobic additives may temporarily improve water resistance. However, these methods often only treat the symptoms, not the root cause: excessive addition of toughening fibers can impair the coating's density and fire resistance, while ordinary additives are prone to migration and failure after long-term humid heat aging. A more fundamental challenge lies in the interdependent relationship between the coating's resistance to humid heat, mechanical strength, and fireproof and heat-insulating performance at high temperatures. Many modification methods aimed at improving room-temperature performance may have negative effects at high temperatures, such as decomposition producing large amounts of smoke or weakening the density of the glaze. Therefore, developing a novel material system that can synergistically improve the resistance to humid heat and cracking resistance of non-intumescent fire-retardant coatings under normal conditions through microstructural design, while ensuring the formation of a more stable and robust heat-insulating protective layer under high-temperature fire conditions, has become a crucial and unresolved technical challenge in this field. This invention aims to systematically overcome these interconnected technical bottlenecks from the perspective of composite modification. Summary of the Invention

[0005] The purpose of this invention is to provide a moisture- and heat-resistant, crack-resistant indoor non-expansion fireproof coating and its preparation method. It solves the technical problems of existing indoor non-expansion fireproof coatings being prone to moisture absorption and softening, blistering and peeling in long-term humid and hot environments, as well as coating cracking due to drying shrinkage or thermal stress, which seriously affects the integrity and durability of the fire barrier.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for preparing a moisture- and heat-resistant, crack-resistant, non-expansive fire-retardant indoor coating, comprising the following steps: S1. By weight, add 38-42 parts of deionized water, 2-4 parts of hydroxypropyl methylcellulose ether, and 1-3 parts of polycarboxylate superplasticizer to a dispersion container under stirring to obtain a base liquid; add 14-16 parts of layered magnesium zinc silicate, 8-12 parts of calcium aluminum borosilicate nano-hybrid ceramic powder, 25-35 parts of kaolin, 15-25 parts of sericite powder, 10-15 parts of glass powder, 6-10 parts of titanium dioxide, and 16-20 parts of hollow ceramic microspheres modified with silane coupling agent to the base liquid, stir, add 24-26 parts of styrene-acrylate copolymer emulsion and 4-6 parts of redispersible latex powder, stir and mix to obtain a mixture; S2. Add 0.4-0.6 parts of silicone defoamer and 1.4-1.6 parts of polyurethane leveling agent to the mixture and stir.

[0007] In this invention, the preparation of a moisture- and heat-resistant, crack-resistant, non-expansion fireproof coating for indoor use involves uniformly dispersing multiple functional components in a medium to construct a stable composite system. The mechanism lies in the synergistic effect of each component under both normal and high-temperature conditions. In the preparation stage, deionized water, hydroxypropyl methylcellulose ether, and a high-efficiency water-reducing agent are first mixed to form a base liquid, the purpose of which is to adjust the system viscosity and improve powder dispersibility. Subsequently, layered magnesium zinc silicate, calcium aluminum borosilicate nano-hybrid ceramic powder, kaolin, sericite powder, glass powder, titanium dioxide, and modified hollow ceramic microspheres are sequentially added and dispersed at high speed. Among these, the silane coupling agent-modified hollow ceramic microspheres enhance the interfacial compatibility between the inorganic filler and the organic phase; the flaky sericite powder and layered magnesium zinc silicate are stacked in parallel orientation within the coating, jointly constructing multiple physical barrier layers, greatly extending the penetration and diffusion path of water molecules and corrosive media. This is the core factor contributing to the coating's excellent moisture and heat resistance. Subsequently, a styrene-acrylate copolymer emulsion and redispersible latex powder are added. During the drying and film-forming process, these form a continuous and flexible polymer network, firmly binding various inorganic fillers together. The network also buffers internal stresses caused by temperature and humidity changes or differences in the thermal expansion coefficients between the fillers and the matrix through its own deformation capacity, effectively preventing cracking. Under high-temperature conditions in a fire, this system exhibits a non-intumescent fire-resistant mechanism: the polymer phase rapidly decomposes and carbonizes, but does not play a major role in heat insulation; fillers such as kaolin undergo endothermic decomposition; crucially, the low-temperature molten glass powder in the formulation softens upon heating, becoming a viscous flow state; simultaneously, calcium aluminosilicate nano-hybrid ceramic powder, as a highly active sintering aid, together with heat-resistant skeleton fillers such as layered magnesium zinc silicate, undergoes rapid high-temperature sintering and ceramization reactions under the lubrication and bonding of the molten glass phase. The components fuse together, ultimately forming a dense, hard, continuous, and extremely low-porosity ceramic glaze protective layer in situ on the substrate surface. This glaze layer has extremely low thermal conductivity, effectively reflecting and blocking heat flow. Furthermore, its dense, non-expanding structure avoids the drawbacks of expandable charcoal layers, such as easy powdering and detachment, thus achieving a durable and stable non-expanding fireproof and heat-insulating effect. Through ingenious component design and preparation, the entire system achieves a perfect balance between its physical properties under normal conditions and its reactivity at high temperatures.

[0008] According to a preferred embodiment of the present invention, in step S1, the particle size of the hollow ceramic microspheres modified with silane coupling agent is 50-150 μm.

[0009] According to a preferred embodiment of the present invention, in step S2, the stirring time is 15-30 min.

[0010] According to a preferred embodiment of the present invention, the method for preparing the layered magnesium zinc silicate includes: A1. By weight, dissolve 8-10 parts of zinc nitrate hexahydrate and 10-14 parts of magnesium nitrate hexahydrate together in 180-220 parts of deionized water and stir to obtain solution A; dissolve 14-16 parts of sodium silicate nonahydrate in 140-160 parts of deionized water and add it dropwise to solution A while stirring, and adjust the pH to 9.5-10.0 to obtain a magnesium zinc silicate precursor suspension; A2. The magnesium zinc silicate precursor suspension was transferred to a high-pressure reactor and subjected to hydrothermal crystallization at 175-185℃. After the reaction was completed, the mixture was naturally cooled, centrifuged to obtain a solid precipitate, and the solid precipitate was washed alternately with deionized water and anhydrous ethanol, then vacuum dried at 78-82℃ and ground.

[0011] In this invention, the preparation mechanism of layered magnesium zinc silicate is based on a controlled hydrothermal crystallization process, aiming to construct an inorganic compound with a regular layered structure and active surface. The preparation begins with mixing a nitrate solution containing zinc and magnesium ions with a sodium silicate solution. At the moment of mixing, zinc, magnesium, and silicate ions undergo a co-precipitation reaction, generating an amorphous magnesium zinc silicate composite precursor. However, the key to forming a product with a specific layered structure lies in the precise control of the subsequent pH. Sodium silicate solution itself is strongly alkaline; its addition creates a highly alkaline environment in the entire reaction system, where silicate ions exhibit high polymerization activity. It is crucial to adjust and stabilize the pH of the mixture within a narrow, weakly alkaline range by adding dilute nitric acid solution. This specific weakly alkaline environment inhibits the random growth of the amorphous phase while providing a thermodynamic driving force and a suitable chemical environment for the formation and directional growth of layered magnesium silicate hydrate nuclei. Subsequently, the precursor suspension is placed in a closed reactor for hydrothermal reaction. Under high temperature and pressure hydrothermal conditions, water molecules not only act as a pressure-transferring medium, but their significantly enhanced activity also powerfully promotes the dissolution and recrystallization of precursor particles. After a sufficiently long hydrothermal treatment period, the amorphous precursor gradually transforms into well-crystallized layered magnesium zinc silicate crystals with sepiolite-like or hydrotalcite-like characteristics. This crystal structure is formed by the interweaving of magnesium-oxygen octahedral sheets and silicon-oxygen tetrahedral sheets according to a specific pattern. Zinc ions partially isomorphously replace magnesium ions in the magnesium-oxygen octahedra, thus being firmly embedded in the layers. The final product has a large specific surface area and abundant surface hydroxyl groups. Its layered structure can effectively block the straight-line paths of water vapor and heat in coatings and provides a basis for subsequent interactions with other components.

[0012] According to a preferred embodiment of the present invention, in step A2, the hydrothermal crystallization reaction at 175-185°C takes 18-20 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the vacuum drying time at 78-82°C is 12-14 hours.

[0014] According to a preferred embodiment of the present invention, the preparation method of the calcium aluminosilicate nano-hybrid ceramic powder includes: B1. By weight, add 8-12 parts of aluminum nitrate nonahydrate and 10-13 parts of calcium nitrate tetrahydrate to 140-160 parts of anhydrous ethanol, and stir in an ice-water bath to obtain a suspension; add 8-10 parts of tetraethyl orthosilicate and 3-5 parts of triethyl borate to 40-60 parts of anhydrous ethanol, and add 1.5-3 parts of acetylacetone, and stir to obtain solution C; while stirring continuously, add solution C dropwise to the suspension, and after the addition is complete, continue stirring to obtain a sol; B2. Seal the sol at room temperature and allow it to stand for aging. Then transfer it to an oven at 78-82℃ to dry it to obtain a dry gel. Place the dry gel in a muffle furnace and calcine it at 595-605℃ to obtain the calcined product. Ball mill the calcined product.

[0015] In this invention, the preparation of calcium aluminosilicate nano-hybrid ceramic powder follows the basic principle of the sol-gel method, aiming to achieve a uniform molecular-level composite of four elements—aluminum, calcium, silicon, and boron—at the nanoscale, laying the foundation for the formation of a homogeneous ceramic phase at high temperatures. The preparation process begins by dispersing hydrated nitrates containing aluminum and calcium ions in anhydrous ethanol. The water of crystallization carried by these hydrated salts is slowly released in the alcohol solution, forming a unique mixed reaction medium of ethanol and water. This provides a necessary but controlled water source for the subsequent hydrolysis of alkoxy compounds. On the other hand, tetraethyl orthosilicate and triethyl borate are dissolved in ethanol, and the key additive acetylacetone is added. Acetylacetone, as a highly efficient chelating agent and hydrolysis inhibitor, has carbonyl and enol structures in its molecule that can form stable complexes with aluminum ions, calcium ions, and partially hydrolyzed silicon and boron species in the solution. This step significantly slows down the hydrolysis and polycondensation rate of tetraethyl orthosilicate and triethyl borate, avoiding local precipitation or phase separation caused by excessively rapid reactions. Under low-temperature conditions in an ice-water bath, solutions containing silicon and boron sources were slowly added dropwise to a suspension containing metal ions, ensuring uniform mixing. With continuous stirring, hydrolysis and condensation reactions proceeded gently: alkoxysilane and alkoxyboron hydrolyzed to generate silanol and boronol, respectively. These hydroxyl groups underwent dehydration condensation reactions with each other and with metal ion hydrates, gradually constructing a three-dimensional network structure interconnected by silicon-oxygen, boron-oxygen, aluminum-oxygen, and calcium-oxygen bonds, ultimately forming a uniform and transparent sol. Subsequently, the sol was allowed to age at room temperature, further condensing and strengthening the network, transforming it into a wet gel, which was then dried to obtain a dry gel. This dry gel was then subjected to high-temperature calcination, completely decomposing and removing the organic components, while the inorganic network underwent further condensation and phase recombination in the solid state, forming a nano-hybrid ceramic powder composed of microcrystalline or amorphous forms of aluminum silicate, aluminum borate, and calcium silicate. This powder, as a precursor for both high-temperature binder and reinforcing phases, effectively promotes the ceramization process when the coating is exposed to fire.

[0016] According to a preferred embodiment of the present invention, in step B2, the settling and aging time is 48-50 hours.

[0017] According to a preferred embodiment of the present invention, in step B2, the calcination time at 595-605°C is 4-6 hours.

[0018] The present invention also provides a moisture- and heat-resistant, crack-resistant, non-expansion fire-retardant indoor coating prepared according to the preparation method of the aforementioned moisture- and heat-resistant, crack-resistant, non-expansion fire-retardant indoor coating.

[0019] The beneficial effects of this invention are as follows: The moisture- and heat-resistant, crack-resistant, non-expansion fireproof coating for indoor use provided by this invention achieves a synergistic improvement in several key technical effects through unique component design and precise preparation process, resulting in comprehensive performance significantly superior to existing conventional products. Firstly, in terms of normal physical properties, this coating exhibits excellent moisture- and heat-resistant stability and outstanding crack resistance. This is mainly due to the synergistic effect of multiple functional components in the formulation. Layered magnesium zinc silicate has a regular micro-lamellar structure, effectively blocking the penetration and diffusion of moisture in the coating, acting as countless tiny physical barriers, significantly reducing the volume expansion and softening tendency of the coating due to moisture absorption. Simultaneously, the flaky sericite powder is arranged parallel within the coating, further extending the migration path of water molecules and corrosive media, jointly enhancing the coating's impermeability. Hollow ceramic microspheres modified with silane coupling agents not only improve the interfacial compatibility between inorganic fillers and the organic polymer matrix, reducing stress concentration points caused by weak interfacial bonding, but their hollow structure also endows the coating with superior flexibility and resistance to internal stress. The interpenetrating polymer network formed by the styrene-acrylate copolymer emulsion and redispersible latex powder provides durable adhesion and elasticity, enabling the coating to remain firmly attached to the substrate even after long-term or cyclic damp heat cycling. This effectively resists blistering, peeling, and the generation and propagation of microcracks caused by drying shrinkage or temperature changes, ensuring the long-term structural integrity and service life of the coating in complex indoor environments.

[0020] Secondly, regarding high-temperature fireproofing and heat insulation performance, the coating of this invention exhibits highly efficient and stable non-expansive protective properties. When exposed to high temperatures during a fire, the coating system undergoes a series of subtle physicochemical changes, rather than relying on the chemical foaming of traditional expansive systems. The glass powder component in the formulation has a carefully designed softening point, which softens and melts first upon reaching a specific high-temperature range, transforming into a viscous liquid binder phase. This molten glass phase can fully wet and encapsulate heat-resistant fillers such as kaolin, layered magnesium zinc silicate, and calcium aluminum borosilicate nano-hybrid ceramic powder. Among them, the calcium aluminum borosilicate nano-hybrid ceramic powder, due to its uniform composite characteristics at the nanoscale, can significantly promote the sintering kinetics process at high temperatures, working synergistically with the molten glass phase to guide the entire system towards a denser and more robust state. Ultimately, a continuous, uniform, and extremely low-porosity ceramic glaze-like dense hardened layer is formed in situ on the substrate surface. This protective layer has extremely high heat reflectivity and thermal resistance, effectively blocking direct heat conduction and radiation, and significantly slowing down the temperature rise rate on the back side of the protected substrate. More importantly, this transformation process does not rely on chemical expansion reactions that produce large amounts of gas. Therefore, the resulting protective layer structure is dense and strong, and it is not easy to pulverize, peel off, or develop through cracks under high-temperature thermal shock. This provides a durable and reliable non-expansive thermal barrier with stable and long-lasting fire protection performance.

[0021] In summary, the most outstanding technical effect of this invention lies in successfully reconciling and optimizing the multiple performance contradictions often faced by fire-retardant coatings, achieving a high degree of unity between normal durability and emergency fire resistance, and between structural strength and stress resistance. This technical solution is not a simple mixture of components, but rather a systematic functional design and synergistic regulation based on a deep understanding of the material's behavior mechanisms at both normal and high temperatures. Under normal conditions, the system prioritizes durability and stability through physical barriers, interface enhancement, and flexible network construction; under the high temperatures of a fire, it instantly constructs a robust thermal insulation barrier through ingenious phase transformation and sintering densification. This "dual-state adaptation" design concept enables the final product to not only overcome the inherent weaknesses of traditional non-expanding coatings, such as susceptibility to failure due to damp heat aging and cracking due to thermal stress, but also significantly improves its applicability and reliability in harsh environments, while upholding and strengthening the core advantages of the non-expanding system: stable fire resistance and good durability. Therefore, this invention provides a novel and highly valuable technical approach for the development of high-performance indoor non-expansion fire-retardant coatings. Its comprehensive technical effects meet the increasingly complex demands of modern buildings for fire-resistant materials that require high safety, long lifespan, and high reliability. Detailed Implementation

[0022] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0023] Example 1 This embodiment provides a method for preparing a moisture- and heat-resistant, crack-resistant, non-expansive fire-retardant indoor coating, the steps of which include: Preparation of layered zinc magnesium silicate: Step A1: Accurately weigh 9.0 g of zinc nitrate hexahydrate and 12.0 g of magnesium nitrate hexahydrate, place them in a 500 mL beaker, add 200.0 g of deionized water, and stir on a magnetic stirrer at 400 rpm for 15 min until completely dissolved, obtaining a clear solution A. Separately weigh 15.0 g of sodium silicate nonahydrate, place it in a 250 mL beaker, add 150.0 g of deionized water, and stir to dissolve, obtaining solution B. Under continuous stirring of solution A (400 rpm), slowly add solution B to solution A using a constant pressure dropping funnel, controlling the dropping rate to approximately 5 mL / min, taking approximately 30 min. After the addition is complete, the pH of the system naturally rises to approximately 11.2. Subsequently, slowly add a 10% (w / w) dilute nitric acid solution while stirring to precisely adjust the pH of the system back to 9.8. At this point, a homogeneous suspension of zinc magnesium silicate precursor is obtained.

[0024] Step A2: Transfer the entire suspension to a 250 mL PTFE-lined high-pressure reactor, seal it, and place the reactor in a forced-air drying oven. Increase the temperature to 180 °C at a programmed heating rate of 3 °C / min, and initiate the hydrothermal crystallization reaction at this temperature. Start timing; the reaction time is 19 h. After the reaction, turn off the oven and allow the reactor to cool naturally to room temperature. Remove the reaction product, pour it into a centrifuge tube, and centrifuge at 8000 rpm for 15 min to separate a white solid precipitate. Discard the supernatant and wash the precipitate three times each with deionized water and anhydrous ethanol (adding approximately 50 mL of solvent each time, shaking, and centrifuging). Transfer the washed precipitate to a petri dish and place it in a vacuum drying oven at 80 °C for 13 h. Finally, grind the dried block material thoroughly in an agate mortar and pass it through a 400-mesh sieve to obtain layered magnesium zinc silicate.

[0025] Preparation of calcium aluminosilicate nano-hybrid ceramic powder: Step B1: Accurately weigh 10.0 g of aluminum nitrate nonahydrate and 11.5 g of calcium nitrate tetrahydrate into a 500 mL three-necked flask. Add 150.0 g of anhydrous ethanol, place the flask in an ice-water bath, and ensure the liquid level is below the liquid level inside the flask. Turn on the mechanical stirrer, set the speed to 500 rpm, and stir continuously for about 20 min to form a homogeneous suspension B. Separately weigh 9.0 g of tetraethyl orthosilicate and 4.0 g of triethyl borate into a 100 mL beaker, add 50.0 g of anhydrous ethanol, and then weigh 2.0 g of acetylacetone into the beaker. Stir evenly with a glass rod to obtain solution C. Under continuous stirring and cooling in an ice-water bath, slowly add solution C dropwise to suspension B using a constant pressure dropping funnel, controlling the dropping rate to approximately 2 mL / min. After the addition is complete, continue to maintain the ice-water bath and 500 rpm stirring conditions, and continue the reaction for 1.5 h to finally obtain a homogeneous and transparent sol.

[0026] Step B2: Transfer the obtained sol to a wide-mouth bottle, seal the bottle opening with sealing film, and let it stand and age for 49 hours at room temperature (25℃) and relative humidity (50%). After aging, place the gel-like material along with the container in an 80℃ forced-air drying oven and dry to constant weight (approximately 72 hours) to obtain a fluffy dry gel. Place this dry gel in an alumina crucible and put it into a box-type muffle furnace. Program the temperature to 600℃ at a rate of 3℃ / min, and start timing after reaching the target temperature. Calcinate at this temperature for 5 hours. After calcination, cool to room temperature with the furnace to obtain a white blocky calcined product. Place this product together with zirconia grinding balls (ball-to-material mass ratio 10:1) in a planetary ball mill jar and ball mill at 300 rpm for 4 hours. After ball milling, pass through an 800-mesh sieve to obtain calcium aluminosilicate nano-hybrid ceramic powder.

[0027] Preparation of a moisture- and heat-resistant, crack-resistant, non-expansive fire-retardant indoor coating: Step S1: Add 40.0g of deionized water to a 1L plastic dispersion container. While stirring at low speed (300rpm), add 3.0g of hydroxypropyl methylcellulose ether and 2.0g of polycarboxylate superplasticizer sequentially to the water. After the addition is complete, maintain the stirring speed at 300rpm and continue stirring for 30 minutes until the thickener is completely dissolved, resulting in a uniform and clear base liquid. Subsequently, increase the stirring speed to 800rpm. Under high-speed shearing, 15.0g of the aforementioned self-made layered magnesium zinc silicate powder, 10.0g of the aforementioned self-made aluminum calcium borosilicate nano-hybrid ceramic powder, 30.0g of kaolin, 20.0g of sericite powder, 12.0g of glass powder, 8.0g of titanium dioxide, and 18.0g of hollow ceramic microspheres (particle size range 50-150μm) modified with silane coupling agent KH-570 were accurately added to the base liquid in sequence. After all powders were added, the mixture was continuously dispersed at high speed at 800rpm for 45min until the fineness of the slurry was ≤50μm as measured by a scraper fineness meter. Then, the mixer speed was reduced to 300rpm. Under slow stirring, 25.0g of styrene-acrylate copolymer emulsion (solid content 48%) and 5.0g of redispersible latex powder were added in sequence. After the addition was complete, the mixture was stirred at 300rpm for 10min to obtain a homogeneous mixture.

[0028] Step S2: Maintain a stirring speed of 200 rpm, add 0.5 g of silicone defoamer and 1.5 g of polyurethane leveling agent to the above mixture. Continue stirring for 20 minutes until the air bubbles on the surface of the slurry are completely eliminated and the system is homogeneous, thus obtaining a moisture-resistant, heat-resistant, crack-resistant, non-intumescent fireproof indoor coating.

[0029] Example 2 The specific implementation method is the same as in Example 1, except that the preparation of layered magnesium zinc silicate is as follows: Step A1: Weigh 8.0g of zinc nitrate hexahydrate and 14.0g of magnesium nitrate hexahydrate, and dissolve them in 190.0g of deionized water to obtain solution A. Weigh 14.0g of sodium silicate nonahydrate and dissolve it in 145.0g of deionized water to obtain solution B. Add solution B dropwise to solution A, and finally adjust the pH to 9.5 with dilute nitric acid. Step A2: Place the suspension in an autoclave and hydrothermally crystallize it at 178℃ for 20h. The post-reaction treatment is the same as in Example 1. The precipitate is vacuum dried at 79℃ for 14h and ground to obtain layered magnesium zinc silicate.

[0030] Preparation of calcium aluminosilicate nano-hybrid ceramic powder: Step B1: Weigh 8.0 g of aluminum nitrate nonahydrate and 13.0 g of calcium nitrate tetrahydrate, add them to 155.0 g of anhydrous ethanol, and stir under an ice-water bath to form suspension B. Weigh 8.0 g of tetraethyl orthosilicate and 5.0 g of triethyl borate, add them to 55.0 g of anhydrous ethanol, then add 1.5 g of acetylacetone, and mix well to obtain solution C. Add C dropwise to B, and continue stirring under an ice-water bath for 1 h to obtain a sol. Step B2: The sol is aged at room temperature in a sealed container for 48 h, and then dried at 81 °C to obtain a dry gel. The dry gel is calcined at 598 °C for 6 h by increasing the temperature at 2 °C / min, and the product is ball-milled to obtain calcium aluminum borosilicate nano-hybrid ceramic powder.

[0031] Preparation of moisture- and heat-resistant, crack-resistant, non-expansive fire-retardant coatings for indoor use: Step S1: Add 39.0g deionized water, 2.0g hydroxypropyl methylcellulose ether, and 1.0g polycarboxylate superplasticizer to a container and stir to obtain the base liquid. Under high-speed dispersion, add 14.0g layered magnesium zinc silicate, 12.0g calcium aluminum borosilicate powder, 25.0g kaolin, 25.0g sericite powder, 10.0g glass powder, 6.0g titanium dioxide, and 16.0g modified hollow ceramic microspheres sequentially, and disperse at high speed for 40 minutes until the fineness is acceptable. After reducing the dispersion speed, add 24.0g styrene-acrylic emulsion and 4.0g latex powder, and mix for 10 minutes. Step S2: Add 0.4g defoamer and 1.4g leveling agent, and stir at 200 rpm for 15 minutes to obtain the coating.

[0032] Example 3 The specific implementation method is the same as in Example 1, except that the preparation of layered magnesium zinc silicate is as follows: Step A1: Weigh 10.0g of zinc nitrate hexahydrate and 10.0g of magnesium nitrate hexahydrate, and dissolve them in 210.0g of deionized water to obtain solution A. Weigh 16.0g of sodium silicate nonahydrate and dissolve it in 155.0g of deionized water to obtain solution B. Add solution B dropwise to solution A, and finally adjust the pH to 10.0. Perform step A2: Place the suspension in an autoclave and hydrothermally crystallize it at 182℃ for 18h. The post-reaction treatment is the same as in Example 1. The precipitate is vacuum dried at 82℃ for 12h and ground to obtain layered magnesium zinc silicate.

[0033] Preparation of calcium aluminosilicate nano-hybrid ceramic powder: Step B1: Weigh 12.0 g of aluminum nitrate nonahydrate and 10.0 g of calcium nitrate tetrahydrate, add them to 145.0 g of anhydrous ethanol, and stir under an ice-water bath to form suspension B. Weigh 10.0 g of tetraethyl orthosilicate and 3.0 g of triethyl borate, add them to 45.0 g of anhydrous ethanol, then add 3.0 g of acetylacetone, and mix well to obtain solution C. Add C dropwise to B, and continue stirring under an ice-water bath for 2 hours to obtain a sol. Step B2: The sol is aged at room temperature in a sealed container for 50 hours, and then dried at 79°C to obtain a dry gel. The dry gel is calcined at 602°C at a rate of 5°C / min for 4 hours, and the product is ball-milled to obtain calcium aluminum borosilicate nano-hybrid ceramic powder.

[0034] Preparation of moisture- and heat-resistant, crack-resistant, non-expansive fire-retardant coatings for indoor use: Step S1: Add 41.0g deionized water, 4.0g hydroxypropyl methylcellulose ether, and 3.0g polycarboxylate superplasticizer to a container and stir to obtain the base liquid. Under high-speed dispersion, add 16.0g layered magnesium zinc silicate, 8.0g calcium aluminum borosilicate powder, 35.0g kaolin, 15.0g sericite powder, 15.0g glass powder, 10.0g titanium dioxide, and 20.0g modified hollow ceramic microspheres sequentially, and disperse at high speed for 50 minutes until the fineness is acceptable. After reducing the dispersion speed, add 26.0g styrene-acrylic emulsion and 6.0g latex powder, and mix for 10 minutes. Step S2: Add 0.6g defoamer and 1.6g leveling agent, and stir at 200 rpm for 30 minutes to obtain the coating.

[0035] Comparative Example 1 The specific implementation method is the same as in Example 1, except that this comparative example does not add layered magnesium zinc silicate and calcium aluminum borosilicate nano-hybrid ceramic powder, and replaces it with an equal mass of kaolin.

[0036] Comparative Example 2 The specific implementation method is the same as in Example 1, except that this comparative example only adds layered magnesium zinc silicate and does not add calcium aluminum borosilicate nano-hybrid ceramic powder (replaced with kaolin of equal mass).

[0037] Comparative Example 3 The specific implementation method is the same as in Example 1, except that this comparative example only adds calcium aluminosilicate nano-hybrid ceramic powder and does not add layered magnesium zinc silicate (which is replaced by kaolin of equal mass).

[0038] Performance testing The moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coatings prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method, which included the following steps: First, coating samples of all the coatings to be tested were prepared. The coating was evenly applied to a 150mm×70mm×1mm standard steel plate that had been sandblasted. The wet film thickness was precisely controlled to 2.0mm by the applicator. Then, the coated test plates were placed in a standard curing room with a temperature controlled at 23±2℃ and a relative humidity controlled at 50±5% for 21 consecutive days to form a fully cured dry film. Then, various performance tests were carried out.

[0039] The damp heat resistance test involves vertically suspending the cured test panel in a constant temperature and humidity test chamber, setting the ambient temperature inside the chamber to 47±1℃ and the relative humidity to 96±2%, and conducting an accelerated damp heat aging test for 240 hours. After the test, the test panel is removed and placed in a standard curing environment for 2 hours for condition adjustment. Then, a grid with a spacing of 1mm is made on the coating surface using a single-edged cutting tool, extending to the substrate. Special pressure-sensitive adhesive tape is applied to the grid area and quickly peeled off. The coating retention rate is evaluated according to the standard spectrum, and the percentage of adhesion loss is calculated. At the same time, the coating surface is visually inspected for defects such as blistering and peeling, and detailed records are made.

[0040] The crack resistance test involves immediately placing the newly prepared wet film test plate in a forced drying oven preheated to 40°C and with a relative humidity of less than 30% for 48 hours of forced drying. It is then transferred to a standard curing environment for 24 hours to equilibrate. Finally, a 10x magnifying glass is used to systematically examine the entire surface and four edges of the coating, recording any cracks visible to the naked eye and describing their morphology, such as mesh, linearity, length, and number.

[0041] The fire resistance performance test employed a customized chamber method apparatus. The cured test panel was vertically fixed to a support, and a propane torch was used to generate a stable flame. The flame was adjusted so that its central tip was 50 mm from the center of the test panel. The flame temperature was maintained at 800±20℃ using thermocouple calibration. The central area of ​​the test panel was continuously burned for a total duration of 60 minutes. During the burning process, a thermocouple welded to the geometric center of the back of the test panel was used to continuously record the back temperature at a frequency of once per second. A time-temperature curve was plotted, and the specific temperature values ​​at 30 and 60 minutes were recorded. After the flame was extinguished, the test panel was allowed to cool to room temperature before being carefully removed. The overall morphology of the residual coating, whether its volume had expanded, whether a continuous glaze layer had formed on the surface, and the density and integrity of this glaze layer were observed visually and with the aid of tools, and the results were recorded.

[0042] Test results: Table 1: Test results of each embodiment and comparative example ; As can be seen from Table 1, Examples 1-3 of the present invention systematically solve the key technical problems of traditional non-expansion fireproof coatings in terms of resistance to damp heat, crack resistance and high temperature insulation performance by synergistically introducing layered magnesium zinc silicate and calcium aluminum borosilicate nano-hybrid ceramic powder.

[0043] Specifically, regarding resistance to damp heat, Examples 1-3 showed an adhesion loss rate of only 8-12% after 240 hours of rigorous aging, with intact surfaces. In contrast, Comparative Example 1 (without these two fillers) exhibited a loss rate as high as 45% and significant blistering and peeling, demonstrating that the functional fillers significantly improved the coating's resistance to water vapor penetration and interfacial erosion. Regarding crack resistance, the Examples showed virtually no cracks after accelerated drying at 40°C, while the Comparative Examples all showed varying degrees of cracking, confirming that the filler combination effectively enhanced interfacial bonding and internal stress buffering.

[0044] Regarding the core fire resistance performance, the back surface temperature (320-355℃) of Examples 1-3 after 60 minutes of burning was significantly lower than that of Comparative Example 2 (425℃) and Comparative Example 3 (410℃), and the residual char layer formed a dense glaze layer. This clearly shows that the two fillers have a synergistic effect at high temperature: the layered magnesium zinc silicate provides a stable skeleton, and the aluminum calcium borosilicate nano-hybrid ceramic powder promotes the sintering and ceramicization of the low-temperature glass phase and the filler, thereby synergistically constructing a denser and stronger high thermal resistance non-expansion ceramic insulation layer. Ultimately, the coating durability and fire resistance performance are significantly improved at the same time, solving the core contradiction that the two are difficult to balance in traditional solutions.

[0045] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a moisture- and heat-resistant, crack-resistant, non-expansion fire-retardant coating for indoor use, characterized in that the steps include... include: S1. By weight, add 38-42 parts of deionized water, 2-4 parts of hydroxypropyl methylcellulose ether, and 1-3 parts of polycarboxylate superplasticizer to a dispersion container under stirring to obtain a base liquid; add 14-16 parts of layered magnesium zinc silicate, 8-12 parts of calcium aluminum borosilicate nano-hybrid ceramic powder, 25-35 parts of kaolin, 15-25 parts of sericite powder, 10-15 parts of glass powder, 6-10 parts of titanium dioxide, and 16-20 parts of hollow ceramic microspheres modified with silane coupling agent to the base liquid, stir, add 24-26 parts of styrene-acrylate copolymer emulsion and 4-6 parts of redispersible latex powder, stir and mix to obtain a mixture; S2. Add 0.4-0.6 parts of silicone defoamer and 1.4-1.6 parts of polyurethane leveling agent to the mixture and stir.

2. The preparation method of the moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coating according to claim 1, characterized in that, In step S1, the hollow ceramic microspheres modified with silane coupling agent have a particle size of 50-150 μm.

3. The preparation method of the moisture-heat resistant and crack-resistant indoor non-expansion fireproof coating according to claim 1, characterized in that, In step S2, the stirring time is 15-30 minutes.

4. The preparation method of the moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coating according to claim 1, characterized in that, The preparation method of the layered magnesium zinc silicate includes: A1. By weight, dissolve 8-10 parts of zinc nitrate hexahydrate and 10-14 parts of magnesium nitrate hexahydrate together in 180-220 parts of deionized water and stir to obtain solution A; dissolve 14-16 parts of sodium silicate nonahydrate in 140-160 parts of deionized water and add it dropwise to solution A while stirring, and adjust the pH to 9.5-10.0 to obtain a magnesium zinc silicate precursor suspension; A2. The magnesium zinc silicate precursor suspension was transferred to a high-pressure reactor and subjected to hydrothermal crystallization at 175-185℃. After the reaction was completed, the mixture was naturally cooled, centrifuged to obtain a solid precipitate, and the solid precipitate was washed alternately with deionized water and anhydrous ethanol, then vacuum dried at 78-82℃ and ground.

5. The preparation method of the moisture-heat resistant and crack-resistant indoor non-expansion fireproof coating according to claim 4, characterized in that, In step A2, the hydrothermal crystallization reaction at 175-185℃ takes 18-20 hours.

6. The preparation method of the moisture-heat resistant and crack-resistant indoor non-expansion fireproof coating according to claim 4, characterized in that, In step A2, the vacuum drying time at 78-82℃ is 12-14 hours.

7. The preparation method of the moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coating according to claim 1, characterized in that, The preparation method of the calcium aluminosilicate nano-hybrid ceramic powder includes: B1. By weight, add 8-12 parts of aluminum nitrate nonahydrate and 10-13 parts of calcium nitrate tetrahydrate to 140-160 parts of anhydrous ethanol, and stir in an ice-water bath to obtain a suspension; add 8-10 parts of tetraethyl orthosilicate and 3-5 parts of triethyl borate to 40-60 parts of anhydrous ethanol, and add 1.5-3 parts of acetylacetone, and stir to obtain solution C; while stirring continuously, add solution C dropwise to the suspension, and after the addition is complete, continue stirring to obtain a sol; B2. Seal the sol at room temperature and allow it to stand for aging. Then transfer it to an oven at 78-82℃ to dry it to obtain a dry gel. Place the dry gel in a muffle furnace and calcine it at 595-605℃ to obtain the calcined product. Ball mill the calcined product.

8. The preparation method of the moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coating according to claim 7, characterized in that, In step B2, the settling and aging time is 48-50 hours.

9. The preparation method of the moisture-heat-resistant and crack-resistant indoor non-expansion fireproof coating according to claim 7, characterized in that, In step B2, the calcination time at 595-605℃ is 4-6 hours.

10. A moisture- and heat-resistant, crack-resistant, non-expansion fire-retardant coating for indoor use, characterized in that, The moisture- and heat-resistant, crack-resistant, non-expansion fire-retardant indoor coating is prepared according to any one of claims 1-9.