A fire-retardant coating, its preparation method and application

Abstract

This invention provides a fire-retardant coating, its preparation method, and its application. By adding black phosphorus nanosheets to a water-based polyvinyl acetate emulsion flame-retardant coating modified with hollow glass microspheres, and utilizing the layered structure of black phosphorus and the migration and heat insulation properties of the hollow glass microspheres, the flame-retardant properties, water resistance, and adhesion to steel of the prepared coating can be significantly improved.

Description

Technical Field

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

[0002] Steel structures are widely used in modern construction due to their lightweight, high strength, large span, large space, good seismic performance, convenient hoisting and construction, and short construction time. However, as a non-combustible building material, steel's mechanical properties, such as yield strength, tensile strength, and modulus of elasticity, decrease with increasing temperature under the influence of high temperatures during a fire. When the temperature rises to approximately 500℃, its mechanical strength decreases by 60%, causing bending deformation and loss of load-bearing capacity, leading to the bending of steel columns and beams and building collapse. To extend the load-bearing capacity of steel structures under high temperatures during a fire, directly spraying fire-retardant coatings onto steel components is the most practical, simple, and convenient method. Fire-retardant coatings for steel structures have good fireproofing and heat insulation properties, are not limited by the geometry of the steel structure during construction, generally do not require additional auxiliary facilities, and are lightweight, even offering some aesthetic decoration. However, existing fire-retardant coatings have poor water resistance; in high-humidity environments, their adhesion to steel weakens, making them prone to peeling off during fire protection, thus significantly reducing their fire-resistant effect.

[0003] Therefore, there is a need for a high-performance fireproof coating that is environmentally friendly, has excellent water resistance, adhesion, and flame retardant properties. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a high-performance fire-retardant coating that exhibits excellent water resistance, adhesion, flame retardancy, and is environmentally friendly. This invention achieves this through…

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A first aspect of the present invention provides a fire-retardant coating, comprising, based on 100 parts by weight, the following components in parts by weight:

[0007]

[0008]

[0009] In the fire-retardant coating of the present invention, black phosphorus nanosheets modified hollow glass microspheres utilize the layered structure characteristics of black phosphorus and the migration and heat insulation properties of hollow glass microspheres, which can significantly improve the flame retardant properties, water resistance properties and adhesion properties to steel of the prepared coating.

[0010] Specifically: (1) Black phosphorus decomposes only at temperatures above 500℃. This high-temperature stability provides an advantage of delayed thermal decomposition under fire conditions, allowing it to exert its flame-retardant effect for a longer period of time. After decomposition, black phosphorus releases products such as phosphoric anhydride, forming a fire-resistant isolation layer that prevents the flame from spreading to the internal matrix. The two-dimensional layered structure of black phosphorus enhances the interfacial interaction with the polymer matrix, improving the overall structural strength of the coating and avoiding the reduction in mechanical properties caused by traditional flame retardants. (2) Hollow glass microspheres, due to their low density and light weight, can move quickly in the matrix, driving the black phosphorus nanosheets on the surface to migrate to the surface of the coating, forming a protective layer with a certain density and strength, improving the surface crack resistance and water resistance of the coating. This protective layer can effectively prevent the decrease in adhesion to the steel substrate caused by the penetration of water vapor.

[0011] In addition, the coating containing black phosphorus nanosheets modified hollow glass microspheres can further reduce the melt viscosity of the substrate, making the application of the fireproof coating smoother, improving the processing performance of the material, and ensuring the quality and ease of application of the fireproof coating.

[0012] Preferably, in the black phosphorus nanosheet-modified hollow glass microspheres, the weight ratio of black phosphorus nanosheets to hollow glass microspheres is (0.005–0.02):1. Within this weight ratio range, the high flame-retardant properties of black phosphorus and the migration properties of hollow glass microspheres in the matrix can be fully utilized, significantly improving the flame retardancy, water resistance, and adhesion to steel of the prepared fire-retardant coating.

[0013] Preferably, the particle size D of the hollow glass microspheres is... n50 The diameter is 10–40 μm, D n50 This indicates the particle size corresponding to when the cumulative number of hollow glass microspheres reaches 50%.

[0014] Preferably, the black phosphorus nanosheet-modified hollow glass microspheres comprise a first black phosphorus nanosheet-modified hollow glass microsphere and a second black phosphorus nanosheet-modified hollow glass microsphere, satisfying: D n50-A >D n50-B D n50-A D represents the particle size of the first black phosphorus nanosheet-modified hollow glass microspheres, in μm; n50-B The particle size of the second black phosphorus nanosheet modified hollow glass microsphere is expressed in μm; the mass ratio of the first black phosphorus nanosheet modified hollow glass microsphere to the second black phosphorus nanosheet modified hollow glass microsphere is (1~1.5):1.

[0015] It should be noted that in this invention, the surface of hollow glass microspheres is modified with black phosphorus nanosheets. Since the particle size of hollow glass microspheres is at the micrometer level, while the particle size of the modifier black phosphorus nanosheets is at the nanometer level, the modification of the micrometer-sized hollow glass microspheres with nanometer-sized black phosphorus nanosheets does not affect the particle size of the hollow glass microspheres modified with black phosphorus nanosheets. In this invention, the particle size of the hollow glass microspheres modified with black phosphorus nanosheets can be expressed using the particle size of the hollow glass microspheres.

[0016] By adding two sizes of hollow glass microspheres to the coating system, and utilizing the different migration rates of the hollow glass microspheres of different sizes within the coating system, black phosphorus nanosheet-modified hollow glass microspheres can form a specific dispersed network structure in the system. This specific network structure exhibits superior flame-retardant properties. The first type of black phosphorus nanosheet-modified hollow glass microspheres (relatively larger in particle size and lower in density) has good migration in the coating. During coating and curing, it can carry the surface-modified black phosphorus nanosheets to the coating surface, forming a protective layer with a certain density and strength, improving the crack resistance of the coating surface and extending the fire resistance time of the coating. Conversely, the second type of black phosphorus nanosheet-modified hollow glass microspheres (relatively smaller in particle size and higher in density) settles closer to the substrate during the coating process, improving adhesion to the substrate and ensuring that it will not detach for a longer period, thus extending the fire protection time.

[0017] In this invention, the black phosphorus nanosheet-modified hollow glass microspheres are prepared by a method comprising the following steps:

[0018] (1) Dissolve black phosphorus nanosheets in a good solvent and disperse them evenly in an inert atmosphere to obtain a brown dispersion 1.

[0019] (2) Dissolve the silane coupling agent in a good solvent, adjust the pH of the system to 4-5, disperse it evenly, add hollow glass microspheres, disperse it evenly, and obtain dispersion 2.

[0020] (3) After mixing the dispersion 1 obtained in step (1) and the dispersion 2 obtained in step (2) evenly, heat to 40-60℃ and react for 30-60 minutes. After filtration, dry the obtained solid product to obtain the black phosphorus nanosheet modified hollow glass microspheres.

[0021] Preferably, the good solvent in steps (1) and (2) is an ethanol-water solution with a mass fraction of 50-75 wt%.

[0022] Preferably, the inert atmosphere described in step (1) is a gas atmosphere formed by at least one gas selected from helium, neon, argon, and nitrogen.

[0023] Preferably, in the dispersion 1 of step (1), the mass concentration of black phosphorus nanosheets is 0.05-0.4%.

[0024] Preferably, in the dispersion 2 of step (2), the mass concentration of the silane coupling agent is 0.5-2%.

[0025] Preferably, the drying temperature in step (2) is 70-90°C, and the product is dried to a constant weight.

[0026] Preferably, the black phosphorus nanosheets are prepared by mechanically grinding red phosphorus into black phosphorus powder, and then by liquid-phase exfoliation to obtain black phosphorus oxide (OBP) nanosheets. The black phosphorus nanosheets prepared in this way contain hydroxyl (-OH), carboxyl (-COOH), and carbonyl (-C=O-) groups on their surface, which can improve their adhesion to the steel surface.

[0027] Optionally, the silane coupling agent includes, but is not limited to, at least one of γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, N-(2-aminoethyl-3-aminopropyl)trimethoxysilane, and 3-glycidyl etheroxypropyltrimethoxysilane.

[0028] Preferably, the polyvinyl acetate emulsion comprises Emultex FR 797 and Emultex FR 728. More preferably, the weight ratio of Emultex FR 797 to Emultex FR 728 is (0.8-1.2):1, and even more preferably 1:1. The glass transition temperature of the blended emulsions is low, thus requiring only a small amount of film-forming aid to form a film in the coating formulation. Furthermore, both emulsions are environmentally friendly products, free of APEO and halogens.

[0029] In this invention, ammonium polyphosphate, pentaerythritol, and melamine are all flame-retardant fillers. The addition of black phosphorus nanosheets modified hollow glass microspheres can work together with them to significantly improve the flame-retardant performance of the coating with a small amount of flame-retardant filler. The addition of a small amount of flame-retardant filler can further improve the mechanical strength of the coating. Moreover, the reduced amount of melamine further improves the environmental performance.

[0030] Preferably, the weight ratio of ammonium polyphosphate, pentaerythritol, and melamine is (2-3):1:1. The polymer n of the ammonium polyphosphate is preferably greater than 1000, prepared via a type II crystal transformation, and has a decomposition temperature of 212°C. The pentaerythritol has a particle size of less than 40 μm, with a monopentaerythritol content of approximately 87%, a dipentaerythritol content of approximately 7%, and a hydroxyl content of approximately 48%-50%. The decomposition temperature of the pentaerythritol is 280°C. The pentaerythritol possessing the above characteristics can be dehydrated into carbon under the action of the acid produced by the decomposition of ammonium polyphosphate, ultimately forming a good foamed layer. Melamine has a decomposition temperature greater than 280°C, a sublimation temperature greater than 354°C, and contains abundant gas. Therefore, the above-mentioned mass ratio of ammonium polyphosphate, pentaerythritol, and melamine, when used as a flame retardant system, can make the expanded carbonaceous heat insulation layer formed by the coating at high temperatures dense and not easily detached, resulting in better fireproof and heat insulation effects.

[0031] Preferably, the reinforcing filler includes at least one of titanium dioxide, sepiolite, and ceramic fiber.

[0032] Preferably, the titanium dioxide is rutile titanium dioxide. Rutile titanium dioxide can significantly improve the fire resistance limit of thin-film steel structure fireproof coatings, and it is easy to disperse in water, has good hiding power, and high refractive index.

[0033] Preferably, the sepiolite has a particle size of less than 15 μm (greater than 800 mesh), and contains hydrous magnesium silicate clay minerals with a layered chain structure, forming a fibrous aggregate, which has the characteristics of being lightweight, heat-insulating, radiation-resistant and thermally stable.

[0034] Preferably, the ceramic fibers have an average diameter of 4.5 μm, a glass transition temperature of 731°C, a softening point of 875°C, and a melting point >1000°C. The ceramic fibers possessing these characteristics exhibit good toughness, thermal stability, and chemical stability, low thermal conductivity, high temperature resistance, high strength, and uniform dispersion.

[0035] The titanium dioxide, sepiolite, and ceramic fibers, when compounded according to the formulation of this invention, can significantly improve the fire resistance limit of the coating. The layered chain structure of sepiolite and the linear structure of ceramic fibers enable the expanded char layer to form a continuous solid-phase skeleton, while the gas phase continuously exists in the interstices of the fiber material skeleton. This special structure allows the char layer to withstand the impact of flames and airflow, improving the medium- and long-term fireproof and heat-insulating effect.

[0036] Commonly used film-forming aids, wetting and dispersing agents, mildew inhibitors, defoamers, pH adjusters, and thickeners in this invention can all be used in this invention.

[0037] Optionally, the film-forming aid includes, but is not limited to, at least one of triethylene glycol ethyl ether, triethylene glycol monobutyl ether, and tripropylene glycol monobutyl ether. The film-forming aid can lower the lowest film-forming temperature of the emulsion, allowing the emulsion to fuse and form a film at a lower temperature. After film formation, the film-forming aid gradually evaporates, restoring the mechanical properties and hardness of the coating to their original levels.

[0038] Optionally, the wetting and dispersing agent includes, but is not limited to, at least one of fatty acid ethylene oxide adducts, polyethylene glycol-type polyols, and polyethyleneimine derivatives, all of which are nonionic wetting and dispersing agents.

[0039] Optionally, the antifungal agent includes, but is not limited to, heat-resistant isothiazolinone antifungal agents.

[0040] Optionally, the defoamer includes, but is not limited to, polyether siloxane copolymers, which have good compatibility with aqueous polyvinyl acetate emulsions and good defoaming effect.

[0041] Optionally, the pH adjuster includes, but is not limited to, at least one of 2-amino-2-methyl-1-propanol and dimethylethanolamine.

[0042] Optionally, the thickener includes, but is not limited to, acrylic associative thickeners. It exhibits shear-thinning flow properties in high-solids systems.

[0043] A second aspect of the present invention provides a method for preparing the fire-retardant coating described in the first aspect of the present invention, comprising the following steps:

[0044] The fire-retardant coating is obtained by mixing and dispersing water, wetting and dispersing agent, pH adjuster, defoamer, black phosphorus nanosheet modified hollow glass microspheres, reinforcing filler, film aid, polyvinyl acetate emulsion, pentaerythritol, ammonium polyphosphate, melamine, mildew inhibitor, and thickener evenly.

[0045] Preferably, in order to further improve the dispersibility of each component in the fire-retardant coating system, the preparation method of the fire-retardant coating includes the following steps:

[0046] (1) Mix and disperse water, wetting and dispersing agent, pH adjuster and defoamer evenly;

[0047] (2) Add the black phosphorus nanosheets modified hollow glass microspheres and reinforcing fillers to the dispersion system of step (1);

[0048] (3) Add film-forming aid, polyvinyl acetate emulsion, pentaerythritol, ammonium polyphosphate and melamine to the dispersion system of step (2) and disperse evenly;

[0049] (4) Add antifungal agent and thickener to the dispersion system in step (3) and disperse evenly to obtain the fireproof coating.

[0050] A third aspect of the present invention provides the application of the fire-retardant coating described in the first aspect of the present invention. The fire-retardant coating is applied to a steel surface and cured to obtain a fire-retardant coating layer.

[0051] Compared with the prior art, the beneficial effects of the present invention are:

[0052] This invention improves the flame retardant properties, water resistance, and adhesion to steel of the prepared coating by adding black phosphorus nanosheets modified with hollow glass microspheres to an aqueous polyvinyl acetate emulsion flame retardant coating. This utilizes the layered structure of black phosphorus and the migration and heat insulation properties of hollow glass microspheres. Detailed Implementation

[0053] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further describe the invention below. However, these embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0054] The relevant raw materials and their sources used in the embodiments and comparative examples of this invention are as follows:

[0055]

[0056]

[0057] The black phosphorus nanosheet-modified hollow glass microspheres were prepared in-house using the present invention. The specific preparation method includes the following steps:

[0058] (1) Dissolve black phosphorus nanosheets in 75wt% ethanol-water solution and ultrasonically disperse them uniformly at room temperature (25±5℃) under nitrogen atmosphere to obtain a brown dispersion 1 with a concentration of 0.1wt%.

[0059] (2) Dissolve the silane coupling agent in a 75wt% ethanol-water solution. The concentration of the silane coupling agent γ-aminopropyltriethoxysilane in the solution is 1wt%. Adjust the pH of the solution to 4-5 with hydrochloric acid. After ultrasonic dispersion, add hollow glass microspheres and further ultrasonic dispersion to obtain dispersion 2.

[0060] (3) After mixing the dispersion 1 obtained in step (1) and the dispersion 2 obtained in step (2) evenly, heat to 40-60℃ and react for 30-60 minutes. After filtration, place the obtained solid product in an oven at 70-90℃ and dry to constant weight to obtain the black phosphorus nanosheet modified hollow glass microspheres.

[0061] In this embodiment of the invention, the black phosphorus nanosheets are prepared by mechanically grinding red phosphorus into black phosphorus powder, and then by liquid-phase exfoliation to obtain black phosphorus oxide (OBP) nanosheets. The specific preparation method is as follows:

[0062] (1) Fill an 80cm³ container with red phosphorus powder and zirconium oxide balls (powder to ball ratio 30:1). 3 The ceramic container was filled with argon gas and sealed. It was then mechanically ground for 58 hours at a speed of 1500 r / min. The ceramic container was then returned to the glove box to store the black phosphorus powder.

[0063] (2) Using DMF as a solvent, black phosphorus powder was subjected to ultrasonic liquid phase exfoliation at room temperature: First, black phosphorus powder and DMF (concentration of 1 mg / mL) were added to a centrifuge tube, and argon gas was injected into the centrifuge tube. Then, the tube was immediately sealed with polytetrafluoroethylene tape and paraffin film. During the ultrasonic process at room temperature, the tube was shaken once per hour to disperse the unexfoliated powder particles at the bottom into the solvent, thereby improving the exfoliation efficiency. After ultrasonic exfoliation for 12 hours, the upper half of the dispersion was collected by centrifugation, and the exfoliated black phosphorus oxide nanosheets were collected by filtration.

[0064] By selecting hollow glass microspheres of different sizes and adjusting the ratio of dispersion 1 and dispersion 2, a series of black phosphorus nanosheet-modified hollow glass microspheres can be prepared. Specific parameters are detailed in Table 1.

[0065] Table 1. Black phosphorus nanosheets modified hollow glass microspheres

[0066]

[0067]

[0068] Examples 1-13

[0069] This embodiment provides a fire-retardant coating, the preparation method of which includes the following steps, according to the raw material formulations in Tables 2 and 3:

[0070] (1) Mix and disperse water, wetting and dispersing agent, pH adjuster and defoamer evenly;

[0071] (2) Add the black phosphorus nanosheets modified hollow glass microspheres and reinforcing fillers to the dispersion system of step (1);

[0072] (3) Add film-forming aid, polyvinyl acetate emulsion, pentaerythritol, ammonium polyphosphate and melamine to the dispersion system of step (2) and disperse evenly;

[0073] (4) Add antifungal agent and thickener to the dispersion system in step (3) and disperse evenly to obtain the fireproof coating.

[0074] Table 2

[0075]

[0076]

[0077] Table 3

[0078]

[0079] Comparative Example 1

[0080] A fire-retardant coating is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that the black phosphorus nanosheet modified hollow glass microspheres are replaced with a mixture of black phosphorus nanosheets and hollow glass microspheres of equal weight. No chemical modification is performed, only physical mixing.

[0081] Comparative Example 2

[0082] A fire-retardant coating is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that in the black phosphorus nanosheet modified hollow glass microspheres, the black phosphorus nanosheets are replaced with red phosphorus.

[0083] Comparative Example 3

[0084] A fire-retardant coating is provided, which is prepared according to the method of Example 1. The difference from Example 1 is that in the preparation process of black phosphorus nanosheet modified hollow glass microspheres, after the red phosphorus is mechanically ground to obtain black phosphorus powder, it is not subjected to liquid phase exfoliation.

[0085] Comparative Example 4

[0086] A fire-retardant coating is provided, which is prepared according to the method of Example 1, except that the black phosphorus nanosheet modified hollow glass microspheres are replaced with site-modified hollow glass microspheres.

[0087] Performance testing

[0088] The performance of the fire-retardant coatings obtained in the above embodiments and comparative examples was characterized by testing in accordance with GB14907-2018. The test results are detailed in Table 4.

[0089] Table 4-1

[0090]

[0091]

[0092] Table 4-2

[0093]

[0094]

[0095] The results above show that:

[0096] This invention improves the flame retardant properties, water resistance, and adhesion to steel of the prepared coating by adding black phosphorus nanosheets modified with hollow glass microspheres to an aqueous polyvinyl acetate emulsion flame retardant coating. This utilizes the layered structure of black phosphorus and the migration and heat insulation properties of hollow glass microspheres.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A fire-retardant coating, characterized in that, Based on 100 parts by weight, it includes the following components in parts by weight: 35-50 parts of polyvinyl acetate emulsion; 16-20 parts of ammonium polyphosphate; Pentaerythritol 3-6 parts; 3-6 parts of melamine; 5-10 parts of black phosphorus nanosheets modified hollow glass microspheres; 4-5 parts of reinforcing filler; 1-2 parts of film-forming aid; 1-2 parts wetting and dispersing agent; 0.1-0.3 parts of antifungal agent; Defoamer 0.1-0.3 parts; pH adjuster 0.1-0.5 parts; Thickener 0.1-0.5 parts; Water balance; The black phosphorus nanosheet-modified hollow glass microspheres include a first type of black phosphorus nanosheet-modified hollow glass microspheres and a second type of black phosphorus nanosheet-modified hollow glass microspheres. The particle size D of the first type of black phosphorus nanosheet-modified hollow glass microspheres is... n50-A =35~40μm, the particle size D of the second black phosphorus nanosheet modified hollow glass microspheres n50-B =10~20μm, D n50 This indicates the particle size corresponding to when the cumulative number of hollow glass microspheres reaches 50%; In the black phosphorus nanosheet modified hollow glass microspheres, the weight ratio of black phosphorus nanosheets to hollow glass microspheres is (0.005~0.02):

1.

2. The fire-retardant coating according to claim 1, characterized in that, The mass ratio of the first black phosphorus nanosheet modified hollow glass microspheres to the second black phosphorus nanosheet modified hollow glass microspheres is (1~1.5):

1.

3. The fire-retardant coating according to claim 1, characterized in that, The reinforcing filler includes at least one of titanium dioxide, sepiolite, and ceramic fiber.

4. The fire-retardant coating according to claim 1, characterized in that, The film-forming aid includes at least one of triethylene glycol ethyl ether, triethylene glycol monobutyl ether, and tripropylene glycol monobutyl ether.

5. The fire-retardant coating according to claim 1, characterized in that, It satisfies at least one of the following characteristics: (1) The polyvinyl acetate emulsion includes Emultex FR 797 and Emultex FR 728; (2) The wetting and dispersing agent includes at least one of fatty acid ethylene oxide adducts, polyethylene glycol-type polyols, and polyvinylimide derivatives; (3) The antifungal agent includes heat-resistant isothiazolinone antifungal agents; (4) The defoamer includes a polyether siloxane copolymer; (5) The pH adjuster includes at least one of 2-amino-2-methyl-1-propanol and dimethylethanolamine; (6) The thickener includes an acrylic associative thickener.

6. The fire-retardant coating according to claim 1, characterized in that, The black phosphorus nanosheets modified hollow glass microspheres were prepared by a method comprising the following steps: (1) Dissolve black phosphorus nanosheets in a good solvent and disperse them evenly in an inert atmosphere to obtain a brown dispersion 1; (2) Dissolve the silane coupling agent in a good solvent, adjust the pH of the system to 4-5, disperse it evenly, add hollow glass microspheres, disperse it evenly, and obtain dispersion 2. (3) After mixing the dispersion 1 obtained in step (1) and the dispersion 2 obtained in step (2) evenly, heat to 40~60℃ and react for 30~60 min. After filtration, dry the obtained solid product to obtain the black phosphorus nanosheet modified hollow glass microspheres.

7. The method for preparing the fire-retardant coating according to any one of claims 1-6, characterized in that, Includes the following steps: The fire-retardant coating is obtained by mixing and dispersing water, wetting and dispersing agent, pH adjuster, defoamer, black phosphorus nanosheet modified hollow glass microspheres, reinforcing filler, film-forming aid, polyvinyl acetate emulsion, pentaerythritol, ammonium polyphosphate, melamine, mildew inhibitor, and thickener evenly.

8. The application of the fire-retardant coating according to any one of claims 1-6, characterized in that, The fire-retardant coating is applied to the surface of the steel and cured to obtain a fire-retardant coating.

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