Composite flame-retardant synergist with core-shell structure, preparation method and application of composite flame-retardant synergist, intumescent fire retardant coating, preparation of intumescent fire retardant coating and application of intumescent fire retardant coating

Abstract

The invention provides a core-shell structure composite flame-retardant synergist, a preparation method and application thereof, an intumescent fireproof coating, and preparation and application thereof, and belongs to the technical field of fire-fighting materials. Through a coprecipitation method, ammonium polyphosphate APP and melamine MEL which exist independently traditionally are compounded and assembled at a molecular level on the surface of a zinc borate particle serving as an anchor point to form a core-shell integrated functional particle. At the high temperature of a fire, due to close contact and extremely short reaction path of APP and MEL of the shell layer, violent dehydration, gasification and cross-linking reaction can be instantly generated, strong expansion driving force with more controllable directionality is generated, the expansion efficiency is greatly improved, and the coating fire resistance, carbon layer quality and durability of the fireproof coating can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of fire protection materials technology, and in particular to a core-shell structured composite flame retardant synergist, its preparation method and application, and an intumescent fire-retardant coating, its preparation and application. Background Technology

[0002] Steel structures are the core load-bearing structures of modern buildings, bridges, and industrial facilities. However, their fire resistance is poor, and they rapidly lose their load-bearing capacity under high temperatures during a fire, leading to structural collapse. Intumescent fire-retardant coatings are currently the most widely used method for fire protection of steel structures. Their mechanism of action lies in the fact that, under the influence of flames or high temperatures, the components of the coating undergo complex physicochemical changes, rapidly expanding and foaming to form a porous carbonaceous insulation layer tens to hundreds of times thicker. This effectively delays the transfer of heat to the steel substrate, buying valuable time for evacuation and fire rescue.

[0003] Traditional intumescent fire-retardant coatings typically consist of three main components: an acid source (such as ammonium polyphosphate, APP), a carbon source (such as pentaerythritol, PER), and a gas source (such as melamine, MEL), along with a film-forming matrix (such as epoxy resin, acrylic emulsion, etc.) that binds these components to the steel surface. Although this system is relatively mature, its inherent defects limit further performance improvements. Traditional processes involve the simple physical blending of APP, PER, and MEL as independent powders. During high-temperature reactions, these dispersed particles require thermal diffusion to contact and react, resulting in low reaction efficiency and incomplete or uncoordinated expansion due to uneven heating. Furthermore, the char layer formed by physically mixed systems is often loose, low-strength, and prone to cracking. Under the impact of high-temperature flames or thermal shock, it easily pulverizes and detaches, leading to the failure of the thermal insulation barrier.

[0004] To improve performance, synergists such as zinc borate and expandable graphite are often added. However, conventional physical addition methods result in these synergists being distributed in isolated dots within the coating, lacking a close physicochemical connection with the APP / MEL / PER bulk expansion system, thus limiting their synergistic effect and potentially affecting the mechanical properties of the coating.

[0005] While existing technologies include studies on modifying single components, most focus on encapsulating APP. Existing technologies (Yang Liu, Shen Jian, Luo Wensheng, Li Xinyu, Wang Mingzhi. Preparation of flame-retardant impregnated paper from MFAPP and its application in decorative high-density fiberboard [J]. Journal of Beijing Forestry University, 2023, 45(12): 134-148.) use melamine-formaldehyde resin to encapsulate APP to prepare microencapsulated APP, or optimize the carbon source. Although these methods can improve moisture absorption or increase char residue to some extent, they fail to fundamentally solve the problem of efficient "in-situ" synergy between acid source, carbon source, and gas source at high temperatures. Therefore, there is an urgent need to provide new high-performance intumescent fire-retardant coatings to overcome the defects of existing intumescent fire-retardant coatings, such as low reaction efficiency, poor synergy, and poor char layer quality caused by the physical mixing of multiple components. Summary of the Invention

[0006] The purpose of this invention is to provide a core-shell structured composite flame retardant synergist, its preparation method and application, and an intumescent fire retardant coating, its preparation and application, which can solve the defects of existing intumescent fire retardant coatings, such as low reaction efficiency, poor synergy and poor char layer quality caused by simple physical mixing of components.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a core-shell structured composite flame retardant synergist, comprising the following steps: Zinc borate was dispersed in water to obtain a zinc borate suspension; Ammonium polyphosphate and melamine were mixed with water to obtain an ammonium polyphosphate-melamine mixture. The pH of the zinc borate suspension was adjusted to 4.0-5.0, and the ammonium polyphosphate-melamine mixture was added. After a aging reaction, a core-shell structured composite flame retardant synergist was obtained.

[0008] Preferably, the dispersion temperature is 50~70℃, the rotation speed is 500~1000r / min, the time is 15~30min, and the solid content of the zinc borate suspension is 10~20wt%.

[0009] Preferably, the mass ratio of ammonium polyphosphate to melamine is 1.5~2.5:1; the mass ratio of the total mass of ammonium polyphosphate and melamine to zinc borate is 1.8~3:1; and the total mass concentration of the ammonium polyphosphate-melamine mixture is 15~25%.

[0010] Preferably, dilute hydrochloric acid or acetic acid is used to adjust the pH value; the ripening reaction temperature is 50~70℃ and the time is 90~150min.

[0011] This invention provides a core-shell structured composite flame retardant synergist prepared by the preparation method described in the above technical solution.

[0012] This invention provides the application of the core-shell structured composite flame retardant synergist described above in intumescent fire-retardant coatings.

[0013] This invention provides an intumescent fire-retardant coating based on a core-shell structured composite flame-retardant synergist, comprising the following raw materials by weight percentage: Film-forming matrix 25-35%, carbon source 8-15%, composite flame retardant synergist 17-30%, char formation promoter 8-15%, reinforcing filler 15-20%, additives 2-5%, water balance; The composite flame retardant synergist is the core-shell structure composite flame retardant synergist described in the above technical solution; The additives include wetting and dispersing agents, defoamers, leveling agents, thickeners, and anti-settling agents.

[0014] Preferably, the film-forming matrix includes one or more of aqueous epoxy resin emulsion, aqueous acrylic resin emulsion, and styrene-acrylic emulsion; The carbon source includes one or more of pentaerythritol, dipentaerythritol, starch, and sorbitol; The char formation accelerator includes one or more of melamine, dicyandiamide, melamine polyphosphate (MPP), and expandable graphite. The reinforcing filler includes one or more of titanium dioxide, aluminum hydroxide, magnesium hydroxide, silica powder, and sepiolite fiber.

[0015] This invention provides a method for preparing the intumescent fire-retardant coating described above, comprising the following steps: Water, wetting and dispersing agent, defoamer, carbon source, char formation accelerator and reinforcing filler are mixed in the first step to obtain a slurry; The slurry is mixed with the composite flame retardant synergist to obtain a mixture. After mixing the mixture with the film-forming matrix, leveling agent, thickener and anti-settling agent are added, and the mixture is cured to obtain an intumescent fire-retardant coating.

[0016] This invention provides the application of the intumescent fire-retardant coating described in the above technical solution or the intumescent fire-retardant coating prepared by the preparation method described in the above technical solution in the field of steel structure protection.

[0017] The beneficial effects of this invention are: This invention utilizes a co-precipitation method to hydrogen-bond and assemble traditionally independent ammonium polyphosphate (APP) and melamine (MEL) onto the surface of zinc borate particles, which serve as "anchors," forming integrated "core-shell" functional particles. Under the high temperatures of a fire, the APP and MEL in the outer shell, due to their close contact and extremely short reaction path, can instantly undergo intense dehydration, vaporization, and cross-linking reactions, generating a powerful and more directionally controllable expansion driving force, significantly improving expansion efficiency.

[0018] This invention introduces a core-shell structured composite flame-retardant synergist into intumescent fire-retardant coatings, achieving uniform compounding and functional synergy of different flame-retardant elements (phosphorus-nitrogen-boron-zinc), effectively suppressing the generation of toxic fumes and combustible gases during combustion. This invention achieves a programmed, integrated response of each functional component during thermal reaction, significantly improving the performance of intumescent fire-retardant coatings.

[0019] The intumescent fire-retardant coating provided by this invention introduces a specific "core-shell structure composite flame-retardant synergist" to tightly combine the acid source (ammonium polyphosphate), gas source (melamine), and synergist (zinc borate), achieving a faster, more efficient, and more synergistic expansion and char formation reaction under high fire temperatures, significantly improving the fire resistance performance and char quality of the fire-retardant coating.

[0020] Due to the aforementioned synergistic effect, the intumescent fire-retardant coating provided by this invention can form a high-quality char layer with a higher expansion ratio, more uniform and tougher structure, and more durable and stable heat insulation performance when exposed to fire. Compared with traditional coatings that use physical mixing of equal amounts of APP, MEL, and zinc borate, its fire resistance limit can be increased by more than 20% at the same coating thickness, and the integrity of the char layer is excellent.

[0021] This invention improves the processability of fire-retardant coatings by integrating three key functional components into a single particle, simplifying the formulation and reducing storage and application stratification problems caused by differences in the density and particle size of various powders. The storage stability and application leveling properties of the coating are improved, and the method is simple and easy to industrialize. Attached Figure Description

[0022] Figure 1 Infrared spectra of zinc borate and the core-shell structured composite flame retardant synergist prepared in Example 1; Figure 2 Thermogravimetric curve of the core-shell structured composite flame retardant synergist prepared in Example 1; Figure 3 The images show the expansion of the fire-retardant coatings prepared in Example 1 and Comparative Example 1 after being applied to steel plates and tested. Detailed Implementation

[0023] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0024] This invention provides a method for preparing a core-shell structured composite flame retardant synergist, comprising the following steps: Zinc borate was dispersed in water to obtain a zinc borate suspension; Ammonium polyphosphate and melamine were mixed with water to obtain an ammonium polyphosphate-melamine mixture. The pH of the zinc borate suspension was adjusted to 4.0-5.0, and the ammonium polyphosphate-melamine mixture was added. After a aging reaction, a core-shell structured composite flame retardant synergist was obtained.

[0025] In this invention, the dispersion temperature is preferably 50~70℃, more preferably 60~65℃, the rotation speed is preferably 500~1000r / min, more preferably 700~800r / min, the time is preferably 15~30min, more preferably 20~25min, and the dispersion is preferably carried out under ultrasonic conditions; the solid content of the zinc borate suspension is preferably 10~20wt%, more preferably 12.5~15wt%.

[0026] In this invention, the degree of polymerization of the ammonium polyphosphate (APP) is ≥1000, more preferably >2000.

[0027] In this invention, the mass ratio of ammonium polyphosphate (APP) to melamine (MEL) is 1.5~2.5:1, more preferably 2~2.2:1; the mass ratio of the total mass of ammonium polyphosphate and melamine to zinc borate is preferably 1.8~3:1, more preferably 2~2.5:1; the total mass concentration of the ammonium polyphosphate-melamine mixture is 15~25%, more preferably 20~22%. Preferably, ammonium polyphosphate and melamine are mixed with hot water at 70°C and stirred until clear to obtain the ammonium polyphosphate-melamine mixture.

[0028] The present invention preferably maintains the zinc borate suspension within the dispersion temperature range, and adjusts the pH value to 4.0~5.0, more preferably 4.5~4.8, using dilute hydrochloric acid or acetic acid; the present invention does not have a special limitation on the concentration of the dilute hydrochloric acid or acetic acid, and can adjust it to the required pH value as needed.

[0029] In this invention, the ammonium polyphosphate-melamine mixture is preferably added dropwise to a zinc borate suspension after pH adjustment using a constant pressure dropping funnel at a speed of 500-1000 r / min (more preferably 700-800 r / min). After the addition is complete, the temperature and pH are kept constant, and the ripening reaction continues to allow the coating layer to grow fully and stabilize. The dropping rate is preferably 1-2 mL / min, more preferably 1.5-1.8 mL / min, and the total dropping time is preferably 60-120 min, more preferably 80-100 min.

[0030] In this invention, the temperature of the ripening reaction is preferably 50~70℃, more preferably 60~70℃, and the time is preferably 90~150min, more preferably 100~120min.

[0031] After the curing reaction is completed, the product is naturally cooled to room temperature. The obtained product is filtered and washed with deionized water at 50-60°C (more preferably 55°C) until the washing liquid is neutral and no chloride ions are detected. The obtained filter cake is placed in a forced-air drying oven at 80-90°C (more preferably 85°C) and dried for 6-10 hours (more preferably 8 hours). After being crushed and passed through a 200-300 mesh sieve, a core-shell structured composite flame retardant synergist with good flowability is obtained.

[0032] The core-shell structured composite flame retardant synergist prepared in this invention uses zinc borate particles as the core and a co-precipitated composite of ammonium polyphosphate and melamine as the shell. This shell is not a simple mixture of ammonium polyphosphate and melamine, but rather a tightly interacting composite coating layer formed under specific conditions through an in-situ reaction on the surface of zinc borate.

[0033] This invention provides a core-shell structured composite flame retardant synergist prepared by the preparation method described in the above technical solution.

[0034] This invention provides the application of the core-shell structured composite flame retardant synergist described above in intumescent fire-retardant coatings.

[0035] This invention provides an intumescent fire-retardant coating based on a core-shell structured composite flame-retardant synergist, comprising the following raw materials by weight percentage: Film-forming matrix 25-35%, carbon source 8-15%, composite flame retardant synergist 17-30%, char formation promoter 8-15%, reinforcing filler 15-20%, additives 2-5%, water balance; The composite flame retardant synergist is the core-shell structure composite flame retardant synergist described in the above technical solution; The additives include wetting and dispersing agents, defoamers, leveling agents, thickeners, and anti-settling agents.

[0036] The intumescent fire retardant coating comprises 25-35% film-forming matrix, preferably 28-32%, and more preferably 30-31% by weight percentage.

[0037] In this invention, the film-forming substrate preferably includes one or more of the following: aqueous epoxy resin emulsion, aqueous acrylic resin emulsion, and styrene-acrylic emulsion; when the film-forming substrate is two or more of the above, this invention does not have a special limitation on the ratio of different types of film-forming substrates, and any ratio is acceptable.

[0038] The intumescent fire retardant coating comprises 8-15% carbon source by weight, preferably 9-13%, and more preferably 10-12%.

[0039] In this invention, the carbon source includes one or more of pentaerythritol, dipentaerythritol, starch, and sorbitol; when the carbon source is two or more of the above, this invention does not have a special limitation on the ratio of different types of carbon sources, and any ratio is acceptable.

[0040] The intumescent fire-retardant coating comprises, by weight percentage, 17-30% of a composite flame-retardant synergist, preferably 20-28%, and more preferably 23-25%. The composite flame-retardant synergist of this invention simultaneously provides an acid source (APP), an auxiliary gas source (MEL), and a synergist / smoke suppressant (zinc borate).

[0041] The intumescent fire retardant coating comprises 8-15% char-forming accelerator, preferably 8-12%, and more preferably 9-10%, by weight percentage.

[0042] In this invention, the char-forming accelerator includes one or more of melamine, dicyandiamide, melamine polyphosphate (MPP), and expandable graphite. When the char-forming accelerator is two or more of the above, this invention does not have a special limitation on the ratio of different types of char-forming accelerators, and any ratio is acceptable. The char-forming accelerator of this invention also serves as a supplementary gas source, used to optimize the expansion ratio and carbon layer structure.

[0043] The intumescent fire retardant coating comprises 15-20% reinforcing filler, preferably 15-18%, and more preferably 16-17% by weight percentage.

[0044] In this invention, the reinforcing filler includes one or more of titanium dioxide, aluminum hydroxide, magnesium hydroxide, silica fume, and sepiolite fiber. When the reinforcing filler is two or more of the above, this invention does not have a special limitation on the ratio of different types of reinforcing fillers, and any ratio is acceptable.

[0045] By weight percentage, the intumescent fire-retardant coating comprises 2-5% additives, preferably 3-4%, including wetting and dispersing agents, defoamers, leveling agents, thickeners, and anti-settling agents; wherein the wetting and dispersing agents comprise 0.4-1.1%, more preferably 0.5-0.6%, the defoamers 0.4-1%, the leveling agents 0.4-1%, more preferably 0.5-0.8%, the thickeners 0.4-1.2%, more preferably 0.6-0.7%, and the anti-settling agents 0.4-1%, more preferably 0.6-0.9%.

[0046] In this invention, the wetting and dispersing agent preferably includes one or more of sodium dodecyl sulfate, Tween-80, and ammonium polyacrylate; the defoamer preferably includes one or more of polyoxypropylene glycerol ether (GP type), polydimethylsiloxane, and polyether-modified organosilicon; the leveling agent preferably includes one or more of alkyl-modified polysiloxane, polyacrylate copolymer, and isophorone; the thickener preferably includes one or more of hydroxyethyl cellulose, sodium polyacrylate, and sodium carboxymethyl cellulose; and the anti-settling agent preferably includes one or more of polyamide wax paste, quaternary ammonium salt-modified montmorillonite, and hydrophilic fumed silica. When two or more of the corresponding types of wetting and dispersing agent, defoamer, leveling agent, thickener, or anti-settling agent are selected, the proportions of different types are not specifically limited and can be adjusted according to requirements.

[0047] The present invention does not impose any special limitations on the specific models and sources of the above-mentioned additives; commercially available products well known in the art are acceptable.

[0048] The intumescent fire-retardant coating of the present invention includes a water balance, more preferably 5-25%, which is replenished to 100%.

[0049] This invention provides a method for preparing the intumescent fire-retardant coating described above, comprising the following steps: Water, wetting and dispersing agent, defoamer, carbon source, char formation accelerator and reinforcing filler are mixed in the first step to obtain a slurry; The slurry is mixed with the composite flame retardant synergist to obtain a mixture. After mixing the mixture with the film-forming matrix, leveling agent, thickener and anti-settling agent are added, and the mixture is cured to obtain an intumescent fire-retardant coating.

[0050] Preferably, in this invention, water, a wetting and dispersing agent, and a defoamer are added to a dispersion tank. Under stirring at 300-700 r / min (more preferably 500-600 r / min), a carbon source, a char-forming promoter, and a reinforcing filler are added sequentially. The rotation speed is increased to 1200-1800 r / min (more preferably 1500 r / min), and the mixture is dispersed for 30-50 min (more preferably 40 min) until the slurry fineness is ≤100 μm (more preferably 55 μm). Then, the rotation speed is reduced to 400-600 r / min (more preferably 500 r / min), and a core-shell structured composite flame retardant synergist is added uniformly. The mixture is then continuously stirred and dispersed for 15-25 min (more preferably 20-22 min) to ensure uniform dispersion without significant damage. Stirring at 300-500 r / min (more preferably 350-450 r / min), add film-forming matrix, stir and mix for 10-15 min (more preferably 12-15 min), add leveling agent, thickener and anti-settling agent, adjust the coating with water to a suitable application viscosity (80-100 KU, more preferably 95 KU), mature under stirring at 50-100 r / min (more preferably 60-80 r / min) for 20-30 min (more preferably 25 min), filter with a 100-150 mesh (more preferably 120 mesh) sieve to obtain intumescent fire retardant coating.

[0051] This invention provides the application of the intumescent fire-retardant coating described in the above-described technical solution or the intumescent fire-retardant coating prepared by the above-described preparation method in the field of steel structure protection. This coating is suitable for various steel structure buildings and facilities requiring high-level fire protection, such as commercial complexes, transportation hubs, power facilities, data centers, historical buildings, and petrochemical plants.

[0052] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0053] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the raw materials used are all commercially available products, and the proportions are all by mass percentage.

[0054] Zinc borate was supplied by Jinan Shengfeng Industry and Trade (purity ≥ 99%), high-polymerization-degree ammonium polyphosphate was produced by Shandong Jinyingtai Chemical (polymerization degree ≥ 1000, conforming to HG / T 2770-2008 standard), melamine was industrial grade (purity 99.8%), waterborne acrylic resin emulsion was produced by Wuhan Jiyesheng Chemical (solid content 48%), dipentaerythritol was distributed by Guangzhou Haoyu International Trade under the Ruiyang brand (purity ≥ 90%), melamine polyphosphate (MPP-200) was produced by Zhenjiang Sanhe Chemical Co., Ltd., waterborne epoxy resin emulsion (3510-W-60A) was produced by Henson Chemical Company, USA, and waterborne acrylic emulsion (Joncryl 1984) and styrene-acrylic emulsion (ACRONAL ECO 7080 ap) were produced by BASF AG. Expandable graphite (80 mesh) is produced by Qingdao Nanshu Hongda Graphite, rutile titanium dioxide is produced by CITIC Titanium Industry (CR-300), and aluminum hydroxide is produced by Jiangyin Guangyuan Ultrafine Powder (purity ≥99.5%). In the following examples, the auxiliary products selected are: Tween-80 wetting and dispersing agent from Beijing Bio-Lab Technology Co., Ltd.; JYS15 defoamer from Wuhan Jiyesheng Chemical Co., Ltd.; SR-252 alkyl-modified polysiloxane leveling agent from Guangdong Leibang High-Tech Materials Co., Ltd.; HEC-XT60 thickener from Hubei Shiteng Chemical Technology Co., Ltd.; and Disparlon 6900-20X anti-settling agent from Kusumoto, Japan.

[0055] Example 1

[0056] Preparation of core-shell structured composite flame retardant synergists: 1. Weigh 100g of zinc borate (2ZnO·3B2O3·3.5H2O), add it to 800mL of deionized water at 60℃, and ultrasonically disperse it for 20min under stirring at 700r / min to obtain a zinc borate suspension with a solid content of 12.5wt%. 2. Preparation of coating solution: Dissolve 120g of ammonium polyphosphate (APP, degree of polymerization >1000) and 60g of melamine (MEL) in 900mL of 70℃ hot water and stir until clear to obtain a polyphosphate-melamine mixture with a total mass concentration of 20%, which is the coating solution; 3. Maintain the temperature of the zinc borate suspension at 70℃, adjust the pH of the system to 4.5 with 10% (v / v) dilute acetic acid and maintain this pH. While stirring at 700 rpm, add the coating solution dropwise into the zinc borate suspension at a rate of 1.5 mL / min using a constant pressure dropping funnel, for a total adding time of 100 min. After the addition is complete, continue the aging reaction at 70℃ and pH=4.5 for 120 min. After the reaction solution is cooled to room temperature, filter it and wash it four times with 55℃ hot water until the washing solution is neutral and no chloride ions are detected. Dry the resulting filter cake at 85℃ for 8 h, pulverize it through a 250-mesh sieve, and obtain the composite flame retardant synergist, labeled CF-A.

[0057] Intumescent fire-retardant coatings (by weight) provided using the above-mentioned composite flame retardant synergist: Film-forming matrix: Aqueous acrylic resin emulsion (48% solids content): 28% Carbon source: Dipentaerythritol: 10% Core-shell composite flame retardant synergist (CF-A): 25% Carbonization accelerator: Expandable graphite (80 mesh): 8% Reinforcing fillers: Titanium dioxide (rutile type): 8%, aluminum hydroxide: 7% Additives 3%: wetting and dispersing agent: 0.6%, defoamer: 0.4%, leveling agent: 0.4%, thickener: 0.7%, anti-settling agent: 0.9%; Deionized water: Balance (11%).

[0058] Preparation method of intumescent fire-retardant coating: 1. Add deionized water, wetting and dispersing agent and defoamer to a dispersion tank. Add dipentaerythritol, expandable graphite, titanium dioxide and aluminum hydroxide while stirring at 500 r / min. Disperse at high speed (1500 r / min) for 40 min until the fineness reaches 55 μm to obtain a slurry. 2. Reduce the rotation speed to 500 r / min, add CF-A synergist, disperse for 20 min, maintain stirring, add water-based acrylic resin emulsion, stir for 15 min, add leveling agent, anti-settling agent and thickener, adjust the viscosity to 95 KU with deionized water, mature for 25 min under stirring conditions of 100 r / min, filter through 120 mesh to obtain intumescent fire retardant coating A.

[0059] Structural characterization and performance testing

[0060] 1) Infrared spectroscopy was performed on zinc borate and the composite flame retardant synergist prepared in Example 1. The results are as follows: Figure 1 As shown, the composite flame retardant synergist has four more characteristic peaks compared to zinc borate, namely 3418 and 3131 cm⁻¹. -1 1653cm -1 1275cm-1 The corresponding functional groups are NH bond, C=N bond, and P=O bond. NH and C=N are functional groups unique to melamine, while P=O bond is a functional group unique to ammonium polyphosphate. This indicates that Example 1 successfully prepared a composite flame retardant synergist.

[0061] 2) Thermogravimetric analysis was performed on the composite flame retardant synergist prepared in Example 1, and the results are as follows: Figure 2 As shown, the initial thermal decomposition temperature of the composite flame retardant synergist is 291℃, indicating that it has good thermal stability. In the event of a fire, the synergist rapidly decomposes and releases gas, creating a solid-gas synergistic flame retardant effect. Its char residue is as high as 68.4%, forming a relatively stable char layer and preventing the protected substrate from further heating.

[0062] 3) The fire-retardant coatings prepared in Example 1 and Comparative Example 1 were respectively applied to steel plates, cured, and then placed in a test furnace for high-temperature treatment. The results are shown in [the table below]. Figure 3 .like Figure 3 As shown, the integrity of the expanded char layer differs between the two. The char layer in Example 1 is more complete, with no openings on the side, while the char layer in Comparative Example 1 has larger openings on the side, affecting the fire protection capability of the coating. This indicates that the char layer of the protective coating of the present invention is of high quality.

[0063] 4) According to GB 14907-2018 "Fire-retardant Coatings for Steel Structures" standard, coating A from Example 1 was applied to a standard I-beam to a dry film thickness of 2.0 ± 0.2 mm. The fire resistance limit was tested to be 163 minutes.

[0064] Cone calorimeter tests showed that its peak heat release rate (PHRR) was 138 kW / m³. 2 The total smoke emission was 13.2 MJ / m³. 2 Compared to control group 1, the emissions decreased by 23% and the total smoke emissions decreased by 15%.

[0065] Example 2

[0066] Preparation of composite flame retardant synergist: The only difference from Example 1 is that the mass ratio of APP:MEL is adjusted to 2.2:1, the mass of APP is 121g, the mass of MEL is 55g, and it is dissolved in 800mL of 70℃ hot water, that is, the concentration of coating solution is increased to 22%, and the curing time is shortened to 90min, to obtain composite flame retardant synergist powder, denoted as CF-B.

[0067] Intumescent fire-retardant coatings (by weight) provided using the above-mentioned composite flame retardant synergist: Film-forming substrate: Styrene-acrylic emulsion: 30% Carbon source: Pentaerythritol: 12% Core-shell composite flame retardant synergist (CF-B): 20% Charcoal formation accelerator: Melamine: 8% Reinforcing fillers: Magnesium hydroxide: 10%, Titanium dioxide: 5% Additives (same as in Example 1): 3% Deionized water: Balance (12%); The coating preparation method is the same as in Example 1.

[0068] Performance characteristics: This formula has a low viscosity, making it easy to spray. It expands rapidly, with an initial expansion ratio reaching 32 times, making it suitable for light steel structures requiring a fire resistance rating of 60-90 minutes. At a dry film thickness of 2.0 mm, the fire resistance rating can reach 82 minutes.

[0069] Example 3

[0070] High weather resistance and thick coating

[0071] Preparation of composite flame retardant synergist: The only difference from Example 1 is that the zinc borate suspension was subjected to ultrasonic dispersion treatment for a longer time (30 min) before the coating liquid was added, and APP (high degree of polymerization ammonium polyphosphate, XS-APPII-2000 produced by Zhejiang Xusen Flame Retardant Co., Ltd.) with a degree of polymerization >2000 was used to obtain composite flame retardant synergist powder, denoted as CF-C.

[0072] Intumescent fire-retardant coatings (by weight) provided using the above-mentioned composite flame retardant synergist: Film-forming matrix: Waterborne epoxy resin emulsion: 35% Carbon source: Dipentaerythritol: 9% Core-shell composite flame retardant synergist (CF-C): 23% Charcoal formation accelerator: melamine polyphosphate (MPP): 8% Reinforcing filler: Titanium dioxide: 10%, chopped sepiolite fiber: 5% Additives: 5%, including wetting and dispersing agent: 1.1%, defoamer: 0.9%, leveling agent: 0.8%, thickener: 1.2%, and anti-settling agent: 1.0%; Deionized water: 5%; The coating preparation method is the same as in Example 1.

[0073] Performance characteristics: With added fiber reinforcement, the coating's thixotropic index reaches 3.0, suitable for thick-coating without sagging. The epoxy group can withstand salt spray corrosion for up to 960 hours. Dry film thickness can reach over 3.0 mm, suitable for heavy-duty steel structures and ultra-high-rise buildings in outdoor or corrosive environments for high-level fire protection.

[0074] Comparative Example 1

[0075] Traditional physical coatings

[0076] Formulation: The same as in Example 1, consisting of waterborne acrylic resin emulsion (28%), dipentaerythritol (10%), expandable graphite (8%), titanium dioxide (8%), aluminum hydroxide (7%), and 3% additives. The 25% CF-A synergist in Example 1 is replaced with a physically mixed mixture of ammonium polyphosphate (APP) 15%, melamine (MEL) 6%, and zinc borate powder 4% (total mass of the three 25%), with deionized water as the balance.

[0077] Preparation method: The only difference between the preparation process and Example 1 is that ammonium polyphosphate, melamine and zinc borate powder are added sequentially in step 2.

[0078] Under the same dry film thickness (2.0 mm), the fire resistance limit was only 112 minutes. The char layer had a rough surface, large pores inside, and was brittle and easily broken after cooling.

[0079] The peak heat release rate (PHRR) is 179 kW / m². 2 The total smoke emission was 15.5 MJ / m³. 2 .

[0080] Comparative Example 2

[0081] Only use coatings for the APP

[0082] Formulation: The only difference from Example 1 is that 25% of the CF-A composite flame retardant synergist is replaced with an equal amount of commercially available microencapsulated ammonium polyphosphate (Clariant Exolit® AP 462, APP coated with melamine-formaldehyde resin).

[0083] Performance comparison: The coating exhibits better moisture resistance than Comparative Example 1, and its fire resistance limit (approximately 130 minutes) is better than Comparative Example 1 but significantly lower than Example 1. Due to the lack of an integrated core-shell structure with zinc borate and the fine composite with MEL, the strength and high-temperature stability of its expanded carbon layer remain insufficient.

[0084] Through the comparison of the above embodiments and comparative examples, it is demonstrated that the present invention, through its original core-shell structure composite flame retardant synergist, fundamentally changes the way each component of the expansion system works, achieving a strong synergistic effect of "1+1+1>3". The fireproof coating prepared has achieved breakthrough improvements in fire resistance, char layer quality and overall practicality, and has significant innovative and industrial application value.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell structured composite flame retardant synergist, characterized in that, Includes the following steps: Zinc borate was dispersed in water to obtain a zinc borate suspension; Ammonium polyphosphate and melamine were mixed with water to obtain an ammonium polyphosphate-melamine mixture. The pH of the zinc borate suspension was adjusted to 4.0-5.0, and the ammonium polyphosphate-melamine mixture was added. After a aging reaction, a core-shell structured composite flame retardant synergist was obtained.

2. The preparation method according to claim 1, characterized in that, The dispersion temperature is 50~70℃, the rotation speed is 500~1000r / min, the time is 15~30min, and the solid content of the zinc borate suspension is 10~20wt%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of ammonium polyphosphate to melamine is 1.5~2.5:1; the mass ratio of the total mass of ammonium polyphosphate and melamine to zinc borate is 1.8~3:1; and the total mass concentration of the ammonium polyphosphate-melamine mixture is 15~25%.

4. The preparation method according to claim 1, characterized in that, The pH value is adjusted using dilute hydrochloric acid or acetic acid; the ripening reaction is carried out at a temperature of 50-70℃ for 90-150 minutes.

5. The core-shell structured composite flame retardant synergist prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the core-shell structured composite flame retardant synergist as described in claim 5 in intumescent fire-retardant coatings.

7. An intumescent fire-retardant coating based on a core-shell structured composite flame-retardant synergist, comprising the following raw materials by weight percentage: Film-forming matrix 25-35%, carbon source 8-15%, composite flame retardant synergist 17-30%, char formation promoter 8-15%, reinforcing filler 15-20%, additives 2-5%, water balance; The composite flame retardant synergist is the core-shell structure composite flame retardant synergist as described in claim 5; The additives include wetting and dispersing agents, defoamers, leveling agents, thickeners, and anti-settling agents.

8. The intumescent fire-retardant coating according to claim 7, characterized in that, The film-forming matrix includes one or more of the following: aqueous epoxy resin emulsion, aqueous acrylic resin emulsion, and styrene-acrylic emulsion. The carbon source includes one or more of pentaerythritol, dipentaerythritol, starch, and sorbitol; The char-forming accelerator includes one or more of melamine, dicyandiamide, melamine polyphosphate, and expandable graphite; The reinforcing filler includes one or more of titanium dioxide, aluminum hydroxide, magnesium hydroxide, silica powder, and sepiolite fiber.

9. A method for preparing the intumescent fire-retardant coating according to any one of claims 7-8, characterized in that, Includes the following steps: Water, wetting and dispersing agent, defoamer, carbon source, char formation accelerator and reinforcing filler are mixed in the first step to obtain a slurry; The slurry is mixed with the composite flame retardant synergist to obtain a mixture. After mixing the mixture with the film-forming matrix, leveling agent, thickener and anti-settling agent are added, and the mixture is cured to obtain an intumescent fire-retardant coating.

10. The application of the intumescent fire-retardant coating according to any one of claims 7 to 8 or the intumescent fire-retardant coating prepared by the preparation method according to claim 9 in the field of steel structure protection.

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