Flame-retardant epoxy resin coating and preparation process thereof

Abstract

The application discloses a kind of flame-retardant epoxy resin coatings and preparation process thereof, it is related to flame-retardant epoxy coating technical field, including the following weight parts components: epoxy resin 100 parts;Curing agent 20~50 parts;Modified flame retardant 5~30 parts;Organic solvent 10~30 parts;Auxiliary agent 0.1~5 parts;Modified flame retardant is phosphorus-nitrogen silicon-containing organic-inorganic hybrid polymer.The application introduces phosphorus-nitrogen silicon-containing hyperbranched structure, realizes the synergistic flame retardation of gas phase and condensed phase, forms dense carbon layer when heated, and the adhesion of coating and substrate is enhanced by chemical bonding effect, the unique molecular structure improves dispersibility and toughness, avoids brittle cracking, solves the problems of traditional coating easy migration, poor adhesion and insufficient water resistance, and has excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of flame-retardant epoxy coating technology, specifically to a flame-retardant epoxy resin coating and its preparation process. Background Technology

[0002] Epoxy resin coatings are protective materials formed by the cross-linking of epoxy resin and a curing agent. Due to their excellent chemical stability, electrical insulation, and mechanical strength, they are widely used in the fields of corrosion protection, insulation, and decoration of metal surfaces. To meet the fire safety requirements of scenarios such as construction, transportation, and electronic equipment, flame-retardant properties are often incorporated into the coating system to slow the spread of fire and reduce fire risk. The basic principle is to utilize the endothermic decomposition of flame retardants at high temperatures, releasing inert gases or forming a heat-insulating char layer, thereby blocking the combustion chain reaction.

[0003] To ensure safety, a large amount of flame-retardant components are typically added to the epoxy resin matrix. Current conventional technologies often employ physical blending to add inorganic or organic flame-retardant particles. However, in practical applications, due to the large amount added and the significant differences in the physical interface properties between the filler and the resin matrix, the coating is prone to surface roughness, cracking, leakage, decreased adhesion, and even large-area peeling under the influence of the external environment. Furthermore, in existing physically additive coatings, the flame-retardant components tend to migrate and precipitate to the surface during long-term use, resulting in whitening or blistering. If safety classification is based solely on the initial flammability rating, the risk of failure due to the coating's own physical integrity can be easily overlooked, leading to significant safety hazards. Summary of the Invention

[0004] The purpose of this invention is to provide a flame-retardant epoxy resin coating and its preparation process, thereby solving the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a flame-retardant epoxy resin coating, comprising the following components in parts by weight: 100 parts epoxy resin; 20-50 parts curing agent; 5-30 parts modified flame retardant; 10-30 parts organic solvent; and 0.1-5 parts additives.

[0006] The modified flame retardant is a phosphorus-nitrogen-silicon-containing organic-inorganic hybrid polymer, which is prepared through the following steps:

[0007] Step S1: Dissolve cyanuric chloride in the first organic solvent, cool to 0-5°C, and add a mixture of amino-containing silane coupling agent and acid-binding agent dropwise through a constant pressure dropping device under mechanical stirring and inert gas protection. After the addition is complete, maintain the low temperature at 0-5°C to carry out the first substitution reaction to obtain a silicon-containing intermediate solution.

[0008] Step S2: Add the phosphorus-containing phenolic compound and the acid-binding agent to the silicon-containing intermediate solution, heat to 50-70℃ to carry out the second substitution reaction, then heat to the reflux temperature and maintain the reflux condensation reaction. After the reaction is completed, cool down and filter to remove the by-product salt. Remove the solvent from the filtrate by rotary evaporation under reduced pressure to obtain the phosphorus-containing silicon precursor.

[0009] Step S3: Dissolve the phosphorus-containing silicon precursor in a second organic solvent, add deionized water, and carry out a controlled hydrolysis-condensation reaction under acidic or alkaline catalytic conditions. The reaction product is precipitated, filtered, and dried to obtain an organic-inorganic hybrid polymer containing phosphorus, nitrogen, and silicon.

[0010] Preferably, the amino-containing silane coupling agent is one of 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane; the phosphorus-containing phenolic compound is 10-(2,5-dihydroxyphenyl)-9-oxa-10-phosphaphenanthrene-10-oxide.

[0011] Preferably, in step S1, the molar ratio of cyanuric chloride to the amino-containing silane coupling agent is 1:0.9 to 1.1;

[0012] In step S2, the molar ratio of the silicon-containing intermediate to the phosphorus-containing phenolic compound is 1:1.8 to 2.2.

[0013] Preferably, in step S1, the first organic solvent is one of tetrahydrofuran, 1,4-dioxane or toluene, and the acid-binding agent is triethylamine or pyridine;

[0014] In step S2, the acid-binding agent is triethylamine or pyridine, the reflux temperature is 65℃~115℃, and the reflux reaction time is 4~8 hours.

[0015] Preferably, in step S3, the amount of deionized water added is 0.5 to 1.0 times the molar amount of alkoxy groups in the phosphorus-containing silicon precursor;

[0016] The controlled hydrolysis-condensation reaction is carried out at a temperature of 40–60°C for 3–6 hours.

[0017] Preferably, the epoxy resin is one or more of bisphenol A type epoxy resin E44, bisphenol A type epoxy resin E51, or phenolic epoxy resin F-51.

[0018] The curing agent is one or more of polyamide resin, alicyclic amine or polyether amine.

[0019] Preferably, the additives include dispersants, leveling agents, and defoamers;

[0020] The organic solvent is one or a mixture of xylene, n-butanol, methyl isobutyl ketone or butyl acetate.

[0021] A method for preparing a flame-retardant epoxy resin coating is also provided, comprising the following steps:

[0022] (1) High-speed pre-dispersion: Epoxy resin and organic solvent are mixed and mechanically stirred until completely dissolved. Then, the prepared phosphorus-nitrogen-silicon organic-inorganic hybrid polymer and dispersant are added. High-speed shear dispersion is carried out using a high-speed disperser, with the rotation speed controlled at 1000-3000 r / min and the time at 20-40 minutes, to obtain the main component.

[0023] (2) Grinding and dispersing: The main components are fed into a sand mill for circulating grinding, and the grinding fineness is controlled to ≤30μm. After discharge, leveling agent and defoamer are added, and the mixture is switched to low-speed stirring mode to disperse evenly.

[0024] (3) Vacuum degassing: Before use, mix the material obtained in step (2) with the curing agent in proportion, place it in a vacuum container, and perform vacuum degassing treatment for 5 to 10 minutes under a vacuum degree of -0.08 to -0.1 MPa to obtain flame retardant epoxy resin coating.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] By constructing a special macromolecular structure containing multiple elements such as phosphorus, nitrogen, and silicon in the system, and utilizing the synergistic effect mechanism of each element at high temperature, the coating is endowed with excellent char-forming ability. When the coating is heated, a dense and continuous expanded carbon layer can be rapidly formed on the surface. This carbon layer acts as a physical barrier to effectively isolate the transfer of oxygen and heat, while suppressing the generation of smoke. This allows the coating to still exhibit excellent fire-retardant and self-extinguishing properties without relying on high filler content, thus ensuring the safety of the substrate.

[0027] The active end groups can chemically react with the hydroxyl groups on the surface of the metal substrate, thereby establishing a stable chemical bond between the coating and the substrate. This overcomes the problem of insufficient adhesion caused by the physical adsorption of traditional coatings, ensuring that the coating is not easily peeled or detached when subjected to external forces or environmental changes, thus guaranteeing the integrity of the protective layer and enabling it to perform its anti-corrosion and flame-retardant functions stably for a long time.

[0028] The modified component used has a unique topological structure and abundant flexible terminal segments, which improves its compatibility and dispersion in the resin matrix. In the cured network, this component acts as an internal toughening agent, which can effectively dissipate external impact energy and reduce stress concentration caused by rigid particle agglomeration. The cured coating maintains high hardness while exhibiting good flexibility and impact resistance, thus avoiding brittle cracking of the coating during use.

[0029] Functional components are fully integrated into the cross-linked network through chemical bonding, completely eliminating the risk of migration and blooming of small molecule additives during long-term storage or use. The introduced hydrophobic segments improve the density of the coating and effectively block the penetration of water molecules and corrosive media, so that the coating can maintain a smooth appearance and stable protective performance in humid or salt spray environments, thus extending the service life of the coating. Detailed Implementation

[0030] Example 1

[0031] A flame-retardant epoxy resin coating comprises the following components in parts by weight: 100 parts epoxy resin; 35 parts curing agent; 15 parts modified flame retardant; 20 parts organic solvent; and 2 parts additives. The modified flame retardant is a phosphorus-nitrogen-silicon organic-inorganic hybrid polymer, which is prepared by the following steps: Step S1: Dissolve cyanuric chloride in a first organic solvent, cool to 2°C, and under mechanical stirring and inert gas protection, add a mixture of an amino-containing silane coupling agent and an acid-binding agent dropwise using a constant pressure dropping device. After the addition is complete, maintain the temperature at 2°C to carry out the first substitution reaction to obtain a silicon-containing intermediate solution; Step S2: Add a phosphorus-containing phenolic compound and an acid-binding agent to the silicon-containing intermediate solution, and heat to 60°C to proceed with the reaction. The second substitution reaction was carried out, followed by heating to a reflux temperature of 70°C and maintaining the reflux condensation reaction. After the reaction was completed, the solvent was removed by rotary evaporation under reduced pressure. The product was washed and vacuum dried to obtain a phosphorus-containing silicon precursor. Step S3: The phosphorus-containing silicon precursor was dissolved in a second organic solvent, deionized water was added, and a controlled hydrolysis condensation reaction was carried out under acidic or alkaline catalytic conditions. The reaction product was precipitated, filtered, and dried to obtain an organic-inorganic hybrid polymer containing phosphorus, nitrogen, and silicon. The amino-containing silane coupling agent was 3-aminopropyltriethoxysilane; the phosphorus-containing phenolic compound was 10-(2,5-dihydroxyphenyl)-9-oxa-10-phosphaphenanthrene-10-oxide, i.e., DOPO-HQ. In step S1, the molar ratio of cyanuric chloride to the amino-containing silane coupling agent was... The ratio is 1:1; in step S2, the molar ratio of silicon-containing intermediate to phosphorus-containing phenolic compound is 1:2; in step S1, the first organic solvent is tetrahydrofuran, and the acid-binding agent is triethylamine; in step S2, the acid-binding agent is triethylamine, and the reflux reaction time is 6 hours; in step S3, the second organic solvent is anhydrous ethanol, and the amount of deionized water added is 0.75 times the molar amount of alkoxy groups in the phosphorus-containing silicon precursor; the controlled hydrolysis condensation reaction temperature is 50℃, and the time is 4.5 hours; the epoxy resin is bisphenol A type epoxy resin E51; the curing agent is polyamide resin; the additives include dispersant, leveling agent and defoamer; the organic solvent is a mixture of xylene and n-butanol; a method for preparing a flame-retardant epoxy resin coating includes the following steps: (1) High-speed pre-dispersion: Mix epoxy resin with organic solvent and mechanically stir until completely dissolved. Then add the prepared phosphorus-nitrogen-silicon organic-inorganic hybrid polymer and dispersant. Use a high-speed disperser for high-speed shear dispersion, control the rotation speed at 2000 r / min and the time at 30 minutes to obtain the main component; (2) Grinding and dispersion: Send the main component into a sand mill for circulating grinding, control the grinding fineness to 25 μm and below, add leveling agent and defoamer after discharge, switch to low-speed stirring mode to disperse evenly; (3) Vacuum degassing: Before use, mix the material obtained in step (2) with the curing agent in proportion, place it in a vacuum container, and perform vacuum degassing treatment at a vacuum degree of -0.09 MPa for 8 minutes to obtain flame-retardant epoxy resin coating;

[0032] In this embodiment, the epoxy resin selected is bisphenol A type epoxy resin E51, whose low epoxy equivalent provides a high density of crosslinking sites; the organic solvent selected is a mixture of xylene and n-butanol in a mass ratio of 7:3, which aims to utilize the latent solvent effect of n-butanol to adjust the polarity of the system and promote the color development and wetting of the modified flame retardant; for the auxiliary components, 2 parts of auxiliary agents are specifically composed of 1.2 parts of dispersant, 0.5 parts of leveling agent and 0.3 parts of defoamer, and this ratio ensures the wetting and dispersion stability in a high polarity solvent system; to ensure the feasibility of the synthesis steps and the purity of the product, the post-treatment operation mentioned in step S2 is as follows: the reaction solution is cooled to room temperature, the precipitated triethylamine hydrochloride solid is removed by vacuum filtration, the solvent is removed by rotary evaporation under reduced pressure, and the intermediate yield is calculated to be approximately 92% after vacuum drying; the precipitation mentioned in step S3 is as follows: the reaction solution is concentrated and slowly added dropwise to an excess of cold n-hexane, and a white powdery solid is precipitated under stirring, which is then filtered and dried to obtain the target product; in step S1, the reaction temperature is strictly controlled at 2 The use of tetrahydrofuran as a solvent utilizes the significant difference in activity of the three chlorine atoms on cyanuric chloride, specifically the reaction of the first chlorine atom at 0-5℃, ensuring only a monosubstituted reaction occurs. This precisely grafts the silane coupling agent onto one end of the triazine ring, avoiding the formation of complex cross-linking byproducts. In step S3, an acidic catalytic environment with pH adjusted to 4 using hydrochloric acid is employed. At this point, the hydrolysis rate is much greater than the condensation rate, which facilitates the full extension of the organic phosphorus and nitrogen groups before the formation of the Si-O-Si inorganic core. This kinetic control strategy induces the formation of a micro-phase separation structure of inorganic core-organic shell, effectively solving the problem of poor compatibility between inorganic silicon sources and organic resins. In the preparation process, the grinding fineness is controlled below 25μm to ensure that hyperbranched particles can form multilayer stacks in the coating thickness direction. When the flame contacts the coating, this stacking structure helps to rapidly form a continuous and dense ceramicized heat insulation layer. This embodiment, as the best implementation method, achieves an ideal balance between flame retardant efficiency, coating adhesion, and appearance quality.

[0033] Example 2

[0034] A flame-retardant epoxy resin coating comprises the following components in parts by weight: 100 parts epoxy resin; 50 parts curing agent; 5 parts modified flame retardant; 30 parts organic solvent; and 5 parts additives. The modified flame retardant is a phosphorus-nitrogen-silicon-containing organic-inorganic hybrid polymer, which is prepared by the following steps: Step S1: Dissolve cyanuric chloride in toluene, cool to 0°C, and add dropwise a mixture of an amino-containing silane coupling agent and an acid-binding agent to obtain a silicon-containing intermediate. Solution; Step S2: Add the phosphorus-containing phenolic compound and acid-binding agent to the silicon-containing intermediate solution, heat to 50℃ for a second substitution reaction, then heat to reflux temperature 110℃ and maintain reflux condensation reaction. After the reaction is complete, filter to remove byproducts, and rotary evaporate the filtrate to obtain the phosphorus-containing silicon precursor; Step S3: Dissolve the phosphorus-containing silicon precursor, add deionized water, and carry out a controlled hydrolysis condensation reaction under acidic or alkaline catalytic conditions to obtain an organic-inorganic hybrid polymer containing phosphorus, nitrogen, and silicon; amino-containing silane coupler The coupling agent is 3-aminopropyltrimethoxysilane; the phosphorus-containing phenolic compound is DOPO-HQ; in step S1, the molar ratio of cyanuric chloride to the amino-containing silane coupling agent is 1:0.9; in step S2, the molar ratio of the silicon-containing intermediate to the phosphorus-containing phenolic compound is 1:1.8; in step S1, the first organic solvent is toluene, and the acid-binding agent is pyridine; in step S2, the acid-binding agent is pyridine, and the reflux reaction time is 8 hours; in step S3, the second organic solvent is tetrahydrofuran, and the deionization... The amount of water added is 0.5 times the molar amount of alkoxy groups in the phosphorus-silicon precursor; the temperature of the controlled hydrolysis condensation reaction is 40℃ and the time is 6 hours; the epoxy resin is bisphenol A type epoxy resin E44; the curing agent is alicyclic amine; the organic solvent is methyl isobutyl ketone; in the preparation method: (1) high-speed pre-dispersion: rotation speed 1000r / min, time 40 minutes; (2) grinding dispersion: fineness 30μm and below; (3) vacuum mixing: vacuum degree -0.08MPa, time 10 minutes;

[0035] This embodiment focuses on high performance with low additive dosage; bisphenol A type epoxy resin E44 is selected in combination with alicyclic amine curing agent to construct a coating matrix with high toughness; the specific composition of the 5 parts of additives is 3.0 parts of dispersant, 1.5 parts of leveling agent, and 0.5 parts of defoamer. The higher dispersant content helps the modified flame retardant to be evenly distributed at low resin viscosity; the specific operational details of the modified flame retardant synthesis are supplemented as follows: In step S1, toluene is used as the reaction medium. Its low melting point ensures good fluidity of the reaction system at 0°C, while its high boiling point ensures that the third chlorine atom on the cyanuric chloride can overcome the steric hindrance effect and completely substitute with DOPO-HQ during the high-temperature reflux process of 100°C in the subsequent step S2; after the reaction in step S2, pyridine hydrochloride is removed by filtration, and the yield after drying is about 90%; in step S3, anhydrous diethyl ether is used as a non-solvent to precipitate and separate the polymer from the reaction solution, and finally A pale yellow solid powder was obtained. In step S1, the molar ratio was adjusted to 1:0.9, meaning the silane coupling agent was slightly insufficient. This statistically ensured that most cyanuric chloride molecules retained at least two reactive sites for subsequent DOPO-HQ replacement, maximizing the phosphorus content per unit molecule. In step S3, the amount of deionized water added was reduced to 0.5 times, and the reaction was carried out under alkaline conditions with pH adjusted to 9 by ammonia. Alkaline catalysis tends to promote condensation reactions, forming nanospheres with a denser structure and smaller hydrodynamic volume. Although the amount of modified flame retardant added was only 5 parts, due to the low viscosity characteristics brought by its hyperbranched structure, it easily penetrated into the intersegments of epoxy resin, playing a toughening effect similar to molecular beads, while inducing rapid charring of the matrix during combustion. This embodiment is particularly suitable for coating the surface of wind turbine blades or aerospace composites with stringent mechanical strength requirements, demonstrating the excellent robustness of the technical solution under low load.

[0036] Example 3

[0037] A flame-retardant epoxy resin coating comprises the following components in parts by weight: 100 parts epoxy resin; 20 parts curing agent; 30 parts modified flame retardant; 10 parts organic solvent; and 0.1 parts additives. The modified flame retardant is a phosphorus-nitrogen-silicon organic-inorganic hybrid polymer. The preparation steps are as follows: Step S1: Dissolve cyanuric chloride in a first organic solvent, cool to 5°C, and add dropwise to obtain a silicon-containing intermediate solution; Step S2: Add a phosphorus-containing phenolic compound, heat to 70°C, and maintain the reflux temperature at 110°C to obtain a phosphorus-nitrogen-silicon precursor; Step S3: Perform a controlled hydrolysis condensation reaction, add non-solvent petroleum ether to precipitate the product, and obtain a phosphorus-nitrogen-silicon organic-inorganic hybrid polymer; the amino-containing silane coupling agent is 3-aminopropyltriethoxysilane. Alkane; the phosphorus-containing phenolic compound is 10-(2,5-dihydroxyphenyl)-9-oxa-10-phosphaphenanthrene-10-oxide; in step S1, the molar ratio is 1:1.1; in step S2, the molar ratio is 1:2.2; in step S1, the solvent is toluene; in step S2, the reflux time is 4 hours; in step S3, the amount of deionized water added is 1.0 times; the temperature is 60℃, and the time is 3 hours; the epoxy resin is phenolic epoxy resin F-51; the curing agent is polyetheramine; the organic solvent is butyl acetate; preparation method: (1) high-speed pre-dispersion: 3000r / min, 20 minutes; (2) grinding dispersion: fineness 20μm; (3) vacuum mixing: vacuum degree -0.1MPa, 5 minutes;

[0038] This embodiment aims to address extreme fire risk scenarios. Phenolic epoxy resin F-51 is selected as the matrix because its molecular chain contains a large number of benzene rings and a rigid skeleton, resulting in high heat resistance and char formation rate. The 0.1 parts of additives include 0.06 parts dispersant, 0.03 parts leveling agent, and 0.01 parts defoamer; these trace amounts of additives are only used to adjust the surface tension of the final coating. In the synthesis of the modified flame retardant, toluene is used as a solvent in steps S1 and S2, utilizing its high boiling point to significantly improve reaction kinetics and shorten reaction time. Step S2 involves washing with deionized water followed by rotary evaporation and drying, while step S3 uses petroleum ether as a non-solvent for precipitation, resulting in a grayish-white solid. The overall yield was 87%. 3-Aminopropyltriethoxysilane was selected to avoid the early uncontrollable crosslinking problem that may be caused by diaminosilane. In step S3, the amount of deionized water was increased to 1.0 times to maximize the conversion of alkoxy groups to silanol groups. These abundant silanol groups undergo dehydration condensation in the early stage of high-temperature combustion, forming a hard SiO2 ceramic layer in situ on the coating surface. This layer works synergistically with the aromatic ring-rich carbon layer produced by the decomposition of F-51 to effectively block heat transfer. Although the amount added in this embodiment is as high as 30 parts, thanks to the low entanglement characteristics of the hyperbranched structure, the viscosity of the coating is still within a controllable range, making it particularly suitable for fire protection of battery pack casings or chemical plant pipelines.

[0039] Example 4

[0040] A flame-retardant epoxy resin coating comprises the following components in parts by weight: 100 parts epoxy resin; 40 parts curing agent; 20 parts modified flame retardant; 25 parts organic solvent; and 3 parts additives. The modified flame retardant is an organic-inorganic hybrid polymer containing phosphorus, nitrogen, and silicon. Preparation parameters: Step S1: Raw material 3-aminopropyltriethoxysilane, first organic solvent is toluene, acid-binding agent is triethylamine, molar ratio 1:1.05, temperature 3℃; Step S2: Raw material DOPO-HQ, acid-binding agent... The solvent is triethylamine, with a molar ratio of 1:2.0, reflux temperature of 75℃, and time of 5 hours; Step S3: the amount of deionized water added is 0.8 times, the second organic solvent is anhydrous ethanol, temperature is 45℃, and time is 5 hours; the epoxy resin is a 1:1 mixture of bisphenol A type epoxy resin E51 and phenolic epoxy resin F-51; the curing agent is a 1:1 mixture of polyamide resin and polyetheramine; the organic solvent is xylene; preparation method: grinding fineness 28μm, vacuum degassing for 7 minutes;

[0041] This embodiment demonstrates the system's compatibility in a mixed resin matrix. E51 provides flexibility and adhesion, while F-51 provides heat resistance and chemical resistance, creating a matrix network with excellent overall performance. The mass ratio of dispersant, leveling agent, and defoamer in the three additives is set to 2:0.8:0.2 to match the interfacial characteristics of the mixed resin matrix. In step S1, the molar ratio is set to 1:1.05; a slight excess of silane coupling agent helps suppress the self-hydrolysis side reaction of cyanuric chloride, ensuring the purity of the intermediate. The 0.8-fold degree of hydrolysis control in step S3 ensures that the product retains an appropriate amount of alkoxy groups. These groups remain inert during coating storage but can further react during high-temperature curing or combustion, providing a reinforcing effect of secondary crosslinking. This formulation design specifically considers the application requirements of the inner wall of chemical storage tanks, utilizing the synergistic flame retardancy and chemical inertness of phosphorus, nitrogen, and silicon elements to achieve a dual coupling of corrosion prevention and fire protection functions.

[0042] Example 5

[0043] A flame-retardant epoxy resin coating comprises the following components in parts by weight: 100 parts epoxy resin; 30 parts curing agent; 25 parts modified flame retardant; 15 parts organic solvent; 4 parts additives; the modified flame retardant is an organic-inorganic hybrid polymer containing phosphorus, nitrogen and silicon. Preparation parameters: Step S1: raw material 3-aminopropyltrimethoxysilane, first organic solvent is tetrahydrofuran, acid binder is pyridine, molar ratio 1:1; Step S2: raw material DOPO-HQ, acid binder is pyridine, molar ratio 1:2.1, reflux temperature 65℃, time 7 hours; Step S3: deionized water added at 0.6 times, second organic solvent is anhydrous ethanol, temperature 55℃, time 4 hours; epoxy resin is bisphenol A type epoxy resin E51; curing agent is alicyclic amine; organic solvent is a mixture of n-butanol and methyl isobutyl ketone; preparation method: the grinding fineness in step (2) is controlled to 15μm;

[0044] This embodiment focuses on the microscopic influence of physical dispersion scale on flame retardant performance; the 4 parts of additives include 3.0 parts of dispersant, 0.8 parts of leveling agent, and 0.2 parts of defoamer. The high proportion of dispersant is the key to achieving a grinding fineness of 15 μm and preventing the nanoparticles from becoming coarse; by strictly controlling the grinding fineness to 15 μm in step (2), which is much lower than the conventional 30 μm, the aim is to achieve submicron-level dispersion of the modified flame retardant in the epoxy matrix; this extreme dispersion state significantly shortens the mean free path of phosphorus-nitrogen-silicon molecules migrating to the coating surface; when the coating is heated, the ultrafine hyperbranched particles can respond more quickly to the surface energy gradient, accumulate at the gas-solid interface, and form a dense flame retardant shielding layer within milliseconds, effectively suppressing early ignition; in addition, the 0.6 times degree of hydrolysis in step S3 makes the polymer molecular chains relatively extended, which, combined with high shear grinding, is conducive to the physical entanglement of polymer chain segments and epoxy resin molecules, further improving the impact resistance of the coating; this embodiment demonstrates the importance of refined process control for exploring the ultimate performance of materials.

[0045] Comparative Example 1

[0046] This comparative example provides a flame-retardant epoxy resin coating whose formulation and component contents are completely identical to those of Example 1. The only difference is that: no chemical synthesis of phosphorus-nitrogen-silicon organic-inorganic hybrid polymers is performed; instead, equimolar amounts of cyanuric chloride, 3-aminopropyltriethoxysilane, and DOPO-HQ are directly and physically mixed and added to the epoxy resin. This comparative example aims to verify the necessity of chemical bonding relative to physical blending, that is, to prove that constructing phosphorus, nitrogen, and silicon elements on the same hyperbranched macromolecular framework is a prerequisite for achieving synergistic flame retardancy and high adhesion, rather than a simple element stacking.

[0047] Comparative Example 2

[0048] This comparative example provides a flame-retardant epoxy resin coating, the formulation of which is basically the same as that of Example 1, except that: in step S1 of flame retardant synthesis, aniline is used instead of amino-containing silane coupling agent, and the other steps remain unchanged; therefore, the final product is an organic-inorganic hybrid polymer containing phosphorus and nitrogen, but does not contain silicon; this comparative example aims to verify the special contribution of silicon in the system, especially the skeletal support role of siloxane segments in improving the adhesion between the coating and the metal substrate by forming Fe-O-Si bonds and in the process of combustion and char formation.

[0049] Comparative Example 3

[0050] This comparative example provides a flame-retardant epoxy resin coating, the formulation of which is basically the same as that of Example 1, except that: commercially available type II ammonium polyphosphate APP is used in equal amounts to replace the modified flame retardant of the present invention; APP, as a typical additive inorganic flame retardant, has a high phosphorus content; this comparative example aims to demonstrate the significant advantages of the organic-inorganic hybrid hyperbranched structure designed in this invention over traditional inorganic flame-retardant particles in terms of resin compatibility, dispersion stability, and impact on mechanical properties such as impact strength.

[0051] Comparative Example 4

[0052] This comparative example provides a flame-retardant epoxy resin coating with a formulation that is basically the same as that of Example 1, except that in step S3 of the flame retardant synthesis, controlled hydrolysis is not performed. Instead, 5 times the molar amount of alkoxy groups of excess deionized water is directly added and vigorously stirred without adjusting the pH value. This operation causes the silane hydrolysis condensation to become uncontrolled, and the product rapidly undergoes macroscopic gelation to form an insoluble blocky solid, which is then crushed and added to the coating. This comparative example aims to verify the decisive role of controlled hydrolysis condensation in step S3 in constructing a soluble hyperbranched topology and the influence of this structure on the coating's processing performance.

[0053] To verify the comprehensive performance of the flame-retardant epoxy resin coating of the present invention, a series of standard tests were conducted on the coating samples obtained in Examples 1-5 and Comparative Examples 1-4. The test results are shown in the table below. Test items and methods:

[0054] (1) Limiting oxygen index (LOI): According to ASTM D2863 standard, the oxygen index tester was used for testing. The sample size was 120mm × 6.5mm × 3mm. By adjusting the flow rate of the oxygen-nitrogen mixed gas, the minimum oxygen concentration required to maintain the sample burning for just 3 minutes or with a burning length of 50mm was determined.

[0055] (2) Vertical burning UL-94: According to ASTM D3801 standard, the sample was subjected to two 10-second flame tests, and the afterflame time and whether molten droplets ignited the cotton were recorded. The V-0, V-1 and V-2 grades were evaluated.

[0056] (3) Adhesion: According to GB / T9286-1998 "Cross-cut test of paint and varnish film", use a cross-cut tester to cut a grid on the coating surface, stick the tape and then tear it off, observe the peeling of the cut. Grade 0 means the edge is completely smooth and there is no peeling, which is the best state. Grade 5 means severe peeling.

[0057] (4) Impact strength: According to GB / T1732-1993 standard, a paint film impactor with a weight of 1kg was used to record the maximum drop height from which the coating did not crack or peel off, in kg·cm.

[0058] (5) Water resistance: The coated sample was immersed in 3wt% NaCl solution for 7 days, i.e. 168 hours. After being taken out and dried, the surface of the coating was visually observed for blistering, rusting, peeling or discoloration. All tests were conducted under constant temperature and humidity conditions, i.e. 23±2℃ and 50±5%RH. Each set of data is the average value of 5 parallel samples.

[0059] Table 1

[0060]

[0061] As can be seen from the data in the table above, the flame-retardant epoxy resin coatings of Examples 1-5 of the present invention exhibit significant advantages in terms of flame retardancy, mechanical properties, and durability. Specifically, Example 1 has an LOI of up to 33.5% and reaches the V-0 rating, while the physical mixture of Comparative Example 1 is only 26.5%. This strongly confirms that constructing phosphorus, nitrogen, and silicon elements within the same macromolecule through chemical bonding can induce an intramolecular synergistic effect of capturing gaseous free radicals involving phosphorus and nitrogen elements and blocking condensed phase carbonization involving silicon and phosphorus elements. Its efficiency is far higher than that of simple physical stacking.

[0062] Regarding adhesion, all examples maintained a level of 0, i.e., perfect condition, while the adhesion of Comparative Example 2, which removed silicon, dropped to level 2. This difference profoundly reveals that the siloxane groups at the ends of the phosphorus-nitrogen-silicon organic-inorganic hybrid polymer underwent in-situ hydrolysis during the curing process, condensing with hydroxyl groups on the surface of the metal substrate to form strong Fe-O-Si interfacial chemical bonds, thus fundamentally solving the persistent problem of poor adhesion in traditional flame-retardant coatings. Comparative Example 4, due to uncontrolled hydrolysis leading to gelation, had large agglomerates that severely damaged the continuity of the coating, resulting in adhesion deterioration to level 4.

[0063] In terms of impact strength, the examples generally reached 45-50 kg·cm, which is significantly better than the 25 kg·cm of the APP-added Comparative Example 3. This is because the organic-inorganic hybrid polymer of the present invention has a unique spherical cavity structure and a large number of terminal flexible chains, which play a role similar to a nano-toughening agent in the epoxy matrix and can effectively dissipate impact energy. In contrast, the traditional inorganic flame retardant in Comparative Example 3, as a rigid foreign object, is prone to stress concentration, which leads to increased coating brittleness.

[0064] Furthermore, water resistance tests showed that the coatings in the examples showed no surface change after immersion in salt water, while blistering occurred in comparative examples 1 and 3. This is attributed to the fact that the modified flame retardant of the present invention enters the cross-linked network through covalent bonds, completely eliminating the risk of blooming caused by the precipitation of small molecule flame retardants. At the same time, the introduced hydrophobic silicon segments improve the density of the coating and effectively block the penetration of water molecules. In summary, the present invention successfully solves the industry problem of balancing flame retardancy, mechanical properties, and durability through precise molecular structure design and controlled hydrolysis process.

[0065] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A flame-retardant epoxy resin coating, characterized by, It comprises the following components in parts by weight: 100 parts epoxy resin; 20-50 parts curing agent; 5-30 parts modified flame retardant; 10-30 parts organic solvent; and 0.1-5 parts additives. The modified flame retardant is a phosphorus-nitrogen-silicon-containing organic-inorganic hybrid polymer, which is prepared through the following steps: Step S1: Dissolve cyanuric chloride in the first organic solvent, cool to 0-5°C, and add a mixture of amino-containing silane coupling agent and acid-binding agent dropwise through a constant pressure dropping device under mechanical stirring and inert gas protection. After the addition is complete, maintain the low temperature at 0-5°C to carry out the first substitution reaction to obtain a silicon-containing intermediate solution. Step S2: Add the phosphorus-containing phenolic compound and the acid-binding agent to the silicon-containing intermediate solution, heat to 50-70℃ to carry out the second substitution reaction, then heat to the reflux temperature and maintain the reflux condensation reaction. After the reaction is completed, cool down and filter to remove the by-product salt. Remove the solvent from the filtrate by rotary evaporation under reduced pressure to obtain the phosphorus-containing silicon precursor. Step S3: Dissolve the phosphorus-containing silicon precursor in a second organic solvent, add deionized water, and carry out a controlled hydrolysis-condensation reaction under acidic or alkaline catalytic conditions. The reaction product is precipitated, filtered, and dried to obtain an organic-inorganic hybrid polymer containing phosphorus, nitrogen, and silicon. In step S3, the amount of deionized water added is 0.5 to 1.0 times the molar amount of alkoxy groups in the phosphorus-containing silicon precursor; The controlled hydrolysis-condensation reaction is carried out at a temperature of 40–60°C for 3–6 hours.

2. The flame-retardant epoxy resin coating as described in claim 1, characterized in that: The amino-containing silane coupling agent is one of 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane; the phosphorus-containing phenolic compound is 10-(2,5-dihydroxyphenyl)-9-oxa-10-phosphaphenanthrene-10-oxide.

3. The flame-retardant epoxy resin coating as described in claim 1, characterized in that: In step S1, the molar ratio of cyanuric chloride to amino-containing silane coupling agent is 1:0.9 to 1.1; In step S2, the molar ratio of the silicon-containing intermediate to the phosphorus-containing phenolic compound is 1:1.8 to 2.

2.

4. The flame-retardant epoxy resin coating as described in claim 1, characterized in that: In step S1, the first organic solvent is one of tetrahydrofuran, 1,4-dioxane or toluene, and the acid-binding agent is triethylamine or pyridine; In step S2, the acid-binding agent is triethylamine or pyridine, the reflux temperature is 65℃~115℃, and the reflux reaction time is 4~8 hours.

5. The flame-retardant epoxy resin coating as described in claim 1, characterized in that: The epoxy resin is one or more of bisphenol A type epoxy resin E44, bisphenol A type epoxy resin E51, or phenolic epoxy resin F-51; The curing agent is one or more of polyamide resin, alicyclic amine or polyether amine.

6. The flame-retardant epoxy resin coating as described in claim 1, characterized in that: Additives include dispersants, leveling agents, and defoamers; The organic solvent is one or a mixture of xylene, n-butanol, methyl isobutyl ketone or butyl acetate.

7. A process for the preparation of a flame-retardant epoxy coating according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) High-speed pre-dispersion: Epoxy resin and organic solvent are mixed and mechanically stirred until completely dissolved. Then, the prepared phosphorus-nitrogen-silicon organic-inorganic hybrid polymer and dispersant are added. High-speed shear dispersion is carried out using a high-speed disperser, with the rotation speed controlled at 1000-3000 r / min and the time at 20-40 minutes, to obtain the main component. (2) Grinding and dispersing: The main components are fed into a sand mill for circulating grinding, and the grinding fineness is controlled to ≤30μm. After discharge, leveling agent and defoamer are added, and the mixture is switched to low-speed stirring mode to disperse evenly. (3) Vacuum degassing: Before use, mix the material obtained in step (2) with the curing agent in proportion, place it in a vacuum container, and perform vacuum degassing treatment for 5 to 10 minutes under a vacuum degree of -0.08 to -0.1 MPa to obtain flame retardant epoxy resin coating.

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