Epoxy fireproof coating for nuclear power, preparation method and application

Abstract

The application provides an epoxy fireproof coating for nuclear power, a preparation method and application thereof, and relates to the field of fireproof coatings. The fireproof coating comprises the following components in parts by weight: 30-42 parts of DOPO modified epoxy resin, 20-23 parts of CTBN toughened epoxy resin, 5-8 parts of nano TiO2, 4-7 parts of montmorillonite, 6-7 parts of B4C microspheres, 6-9 parts of ammonium polyphosphate, 3-5 parts of melamine, 3-4 parts of pentaerythritol, 3-4 parts of active diluent, 0.5-1 part of dispersant, 0.3-0.5 part of defoaming agent and 8-12 parts of curing agent. The DOPO epoxy and B4C microspheres are used to synergistically shield gamma rays and neutrons, and the ammonium polyphosphate is used to form a high-efficiency fireproof carbon layer, so that the performance conflict in the prior art is solved, the key equipment protection of nuclear power stations is suitable, and the dual requirements of fireproofing and radiation resistance are met.

Description

Technical Field

[0001] This invention relates to the field of fire-retardant coatings, specifically to an epoxy fire-retardant coating for nuclear power plants, its preparation method, and its application. Background Technology

[0002] In the nuclear power sector, epoxy fire-retardant coatings must simultaneously meet stringent fire protection and radiation resistance requirements. They must form an effective heat-insulating char layer to block high-temperature transmission in scenarios such as hydrocarbon fires, while also providing long-term protection against gamma rays and neutron radiation to prevent coating performance degradation. The synergistic stability of these two core properties is a crucial prerequisite for ensuring the safety of equipment in critical areas of nuclear power plants.

[0003] However, current technologies struggle to simultaneously achieve both fire resistance and radiation resistance, exhibiting significant synergy issues. Existing coatings often employ an APP-melamine-pentaerythritol intumescent fire-retardant system. In this system, components like APP and melamine are prone to structural decomposition under radiation, leading to decreased APP polymerization and reduced melamine foaming efficiency, directly resulting in a decrease in the expansion ratio of the fire-retardant char layer. Simultaneously, radiation-resistant fillers (such as boron-based and titanium-based fillers) react with acidic substances produced by APP decomposition in the fire-retardant system, generating non-flame-retardant materials that further weaken the fire-retardant effect. This performance conflict prevents existing coatings from meeting the dual requirements of the nuclear power industry: either they meet fire resistance standards but rapidly fail after radiation, or they meet radiation resistance standards but are unable to withstand high-temperature fires. Ultimately, this prevents the coating from providing long-term stable protection, posing a safety hazard to nuclear power plant equipment. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the present invention aims to provide a method for preparing epoxy fire-retardant coatings for nuclear power plants and their application.

[0005] One objective of this invention is to provide an epoxy fire-retardant coating for nuclear power plants, wherein the epoxy fire-retardant coating comprises the following raw materials in parts by weight:

[0006] 30-42 parts of DOPO modified epoxy resin

[0007] 20-23 parts of CTBN toughened epoxy resin

[0008] 5-8 parts of nano TiO2

[0009] 4-7 parts of montmorillonite

[0010] 6-7 parts of B4C microspheres

[0011] 6-9 parts of ammonium polyphosphate

[0012] 3-5 parts of melamine

[0013] 3-4 parts of pentaerythritol

[0014] 3-4 parts reactive diluent

[0015] Dispersant 0.5-1 part

[0016] 0.3-0.5 parts of defoamer

[0017] 8-12 parts of curing agent.

[0018] Preferably, the DOPO modified epoxy resin includes one or more of DOPO-EP-01, DER-671, SM-DOPO-EP, or XY-DOPO-02.

[0019] Preferably, the DOPO modified epoxy resin includes DOPO-EP-01.

[0020] Preferably, the CTBN toughened epoxy resin includes one or more of SW-CTBN-1300X, CTBN-1300, YH-CTBN-1300 or F5287.

[0021] Preferably, the nano-TiO2 has a particle size of 20-30 nm and a crystal ratio of Anatase / Rutile = 80 / 20; the montmorillonite has a cation exchange capacity ≥ 100 meq / 100 g and a particle size ≤ 2 μm.

[0022] Preferably, the B4C microspheres have a particle size of 5-10 μm, a purity of ≥99%, and a sphericity of ≥90%.

[0023] Preferably, the degree of polymerization of the ammonium polyphosphate is ≥1000 and the particle size is 10-20 μm; the particle size of the melamine is 5-10 μm; and the purity of the pentaerythritol is ≥99.5% and the particle size is 8-15 μm.

[0024] Preferably, the active diluent is Dow DOWANOL™ PnB glycidyl ether with an epoxy value of 0.5-0.6 eq / 100g and VOC=0; the dispersant is BYK-161 polyamide dispersant; and the defoamer is Tego Foamex810 mineral oil defoamer.

[0025] Preferably, the curing agent comprises an alicyclic amine curing agent and a polyether amine curing agent; the alicyclic amine curing agent is Huntsman Ancamine® 2049 with an active hydrogen equivalent of 65-70 g / eq; the polyether amine curing agent is BASF Jeffamine® D-230 with an active hydrogen equivalent of 61 g / eq; the mass ratio of the alicyclic amine curing agent to the polyether amine curing agent is 4:6-5:5.

[0026] The second objective of this invention is to provide a method for preparing the epoxy fire-retardant coating for nuclear power plants as described above, the method comprising the following steps:

[0027] S1: Resin premixing: Mix and stir DOPO modified epoxy resin and CTBN toughened epoxy resin, add reactive diluent, heat to 40-50℃, keep warm and stir for 20-30 minutes to form resin matrix;

[0028] S2: Filler dispersion: Add nano TiO2, montmorillonite, and B4C microspheres in sequence, increase the rotation speed to 800-1000 r / min, disperse at high speed for 30-40 minutes, then add dispersant and continue high-speed dispersion for 20 minutes to ensure that the filler particle size distribution is ≤50μm;

[0029] S3: Fireproof system mixing: Reduce the rotation speed to 500-600r / min, add ammonium polyphosphate, melamine and pentaerythritol in sequence, and stir for 25-35 minutes;

[0030] A: Additive adjustment: Maintain a speed of 500-600r / min, add defoamer, stir for 15-20 minutes, filter with a 40-60 mesh filter to obtain the base coating;

[0031] B: Hardener preparation: 30 minutes before construction, mix the cycloaliphatic amine hardener and polyether amine hardener evenly, then add them to the base coating at a mass ratio of base coating: hardener = 9:1-8.5:1.5, and stir at 300-400 r / min for 10-15 minutes to obtain the epoxy fireproof coating for nuclear power.

[0032] The third objective of this invention is to provide an application of the epoxy fire-retardant coating for nuclear power plants as described above. The epoxy fire-retardant coating for nuclear power plants is applied to the surface protection of equipment in key areas of nuclear power plants. It can resist gamma rays and neutron radiation, and can form an effective heat-insulating carbon layer in hydrocarbon fire scenarios, thus meeting the dual requirements of fire prevention and radiation resistance in the nuclear power field.

[0033] Beneficial effects of this invention:

[0034] This invention constructs a radiation-proof, fire-resistant, and structurally stable protective system by precisely controlling the raw material composition and ratio of epoxy fire-retardant coatings for nuclear power plants. Phosphorus atoms in the DOPO-modified epoxy resin can capture high-energy electrons excited by gamma rays and disperse radiation free radicals; electron-hole pairs generated by nano-TiO2 can inhibit the degradation of organic chains in the coating; the layered structure of montmorillonite extends the propagation path of gamma rays; and the B4C microspheres... 10 The B isotope can undergo a nuclear reaction with neutrons, and the four components work together to shield the coating from gamma rays. Furthermore, each radiation-shielding component is chemically stable and will not react adversely with the fire protection system, effectively solving the problem of conflict between radiation protection and fire protection performance in existing technologies.

[0035] Meanwhile, the proportions of ammonium polyphosphate, melamine, and pentaerythritol are designed to ensure the formation of a highly efficient, expandable, fire-resistant char layer at high temperatures: the phosphoric acid released from the decomposition of ammonium polyphosphate reacts with pentaerythritol to form a char-like framework, while melamine releases non-combustible gases to allow the coating to fully expand, forming a low-thermal-conductivity insulating char layer that can effectively block the transmission of high temperatures in hydrocarbon fire scenarios; furthermore, the phosphorus element in the DOPO-modified epoxy resin can reduce the release of combustible gases, achieving a synergistic improvement in radiation protection and fire resistance, fully meeting the dual protection requirements of key equipment in the nuclear power field. Detailed Implementation

[0036] According to a first aspect of the present invention, an epoxy fire-retardant coating for nuclear power plants is provided, comprising the following raw materials in parts by weight:

[0037] 30-42 parts of DOPO modified epoxy resin

[0038] 20-23 parts of CTBN toughened epoxy resin

[0039] 5-8 parts of nano TiO2

[0040] 4-7 parts of montmorillonite

[0041] 6-7 parts of B4C microspheres

[0042] 6-9 parts of ammonium polyphosphate

[0043] 3-5 parts of melamine

[0044] 3-4 parts of pentaerythritol

[0045] 3-4 parts reactive diluent

[0046] Dispersant 0.5-1 part

[0047] 0.3-0.5 parts of defoamer

[0048] 8-12 parts of curing agent.

[0049] In this invention, the radiation protection function is achieved synergistically by DOPO-modified epoxy resin, nano-TiO2, montmorillonite, and B4C microspheres. DOPO-modified epoxy resin serves as the coating matrix, with its phosphorus heterocycles in its molecular structure acting as the core sites for radiation protection. The empty 3d orbitals of phosphorus atoms can efficiently capture high-energy electrons excited by gamma rays, converting radiation energy into molecular vibrational energy. Simultaneously, the conjugated ring structure can disperse hydroxyl and alkyl free radicals generated by radiation, inhibiting the chain degradation of the resin chain. When the content is below 30 parts, the phosphorus atom density in the matrix is ​​insufficient, resulting in weak free radical capture ability and easy cracking of the coating after radiation. When the content is above 42 parts, the resin viscosity increases, affecting the dispersion of subsequent fillers, and excess phosphorus atoms compete with the phosphate groups of ammonium polyphosphate in the fireproofing system for reaction sites, weakening the efficiency of fireproof char layer formation. The electron-hole pairs generated by nano-TiO2 can inhibit the degradation of the organic chain in the coating. When the content is below 5 parts, the amount of electron-hole pairs generated is low, resulting in a low free radical scavenging rate. When the content is above 8 parts, the nanoparticles are prone to agglomeration, which can form radiation energy accumulation points, leading to accelerated local coating degradation. Montmorillonite, with its layered silicate structure, can create a labyrinth effect. When gamma rays pass through the coating, they are refracted and reflected multiple times between the montmorillonite layers, resulting in a longer path and gradual energy loss. Simultaneously, the cation exchange capacity of montmorillonite can adsorb acidic degradation products generated by radiation, preventing them from corroding the resin matrix. When the content is below 4 parts, the layered structure coverage decreases, and the labyrinth effect is not significant; when it is above 7 parts, the montmorillonite layers tend to stack, disrupting the continuity of the resin matrix and leading to a decline in the mechanical properties of the coating. B4C microspheres, as the core component of neutron shielding, contain... 10 The boron isotope can undergo nuclear reactions with neutrons, producing Li and He atoms with low energy that do not damage the coating structure; the spherical structure ensures uniform dispersion within the coating, forming a neutron-trapping network and avoiding shielding blind spots. Below 6 parts, 10 When the boron atom density is insufficient and exceeds 7 parts, the microspheres tend to settle, resulting in uneven shielding performance between the upper and lower layers of the coating. Furthermore, excessive B4C will increase the coating density and increase the load on the equipment.

[0050] The fire-retardant function relies on the synergistic expansion reaction of ammonium polyphosphate, melamine, and pentaerythritol. Ammonium polyphosphate, acting as an acid source, decomposes its long-chain structure (degree of polymerization n≥1000) at 250-300℃, releasing dehydrating agents such as phosphoric acid (H3PO4) and pyrophosphoric acid (H4P2O7). These acidic substances catalyze the esterification reaction of the hydroxyl groups in pentaerythritol, providing a carbon source precursor for char layer formation. When the amount is less than 6 parts, the amount of dehydrating agent generated is insufficient, resulting in a low esterification rate of pentaerythritol and an inability to form a complete char skeleton. When the amount is greater than 9 parts, excessive acidic substances corrode the ether bonds of the DOPO-modified epoxy resin, causing the coating to yellow and become brittle at room temperature. Pentaerythritol, acting as a char source, has four hydroxyl groups in its molecule that can undergo esterification and dehydration reactions with the acid released from ammonium polyphosphate, generating a polyolefin-based char skeleton. This skeleton has a high specific surface area and porosity, serving as the supporting structure for the expanded char layer. Based on stoichiometry, 1 mol of pentaerythritol needs to react with 1.2-1.5 mol of phosphoric acid. Correspondingly, the amount of ammonium polyphosphate used is less than 3 parts, resulting in insufficient carbon skeleton formation and a tendency for the carbon layer to collapse. When the amount exceeds 4 parts, unreacted pentaerythritol will melt and drip at high temperatures, increasing the risk of fire spread. Melamine, acting as a gas source, decomposes at 300-350℃, releasing non-combustible gases such as ammonia and carbon dioxide. These gases form bubbles within the carbon skeleton, causing the coating to expand and forming a porous, insulating carbon layer with reduced thermal conductivity. When the amount is less than 3 parts, insufficient gas generation results in an expansion ratio of less than 10 times, a carbon layer thickness of less than 5 mm, and poor insulation. When the amount exceeds 5 parts, excessive gas leads to excessively large carbon layer bubbles (diameter > 1 mm), thin bubble walls that are prone to rupture, and an inability to maintain a complete insulating structure.

[0051] The dosages of reactive diluents, dispersants, defoamers, curing agents, and CTBN toughened epoxy resin are all designed to ensure the stable functioning of the radiation protection and fireproofing system. The nitrile rubber segments in the CTBN toughened epoxy resin molecules can react with the epoxy groups of the DOPO modified epoxy resin, introducing flexible segments into the resin matrix. This alleviates radiation-induced internal stress, preventing coating cracking and ensuring the continuity of the radiation-protective components. It also enhances the toughness of the char layer, preventing it from crumbling due to thermal shock during a fire. A dosage below 20 parts results in insufficient flexible segments, making the resin prone to cracking after radiation; a dosage above 23 parts reduces the crosslinking density of the resin matrix, leading to a decrease in the radiation-protective free radical scavenging capacity. The reactive diluent is a glycidyl ether diluent with VOC=0, which reduces the viscosity of the mixture of DOPO modified epoxy resin and CTBN toughened epoxy resin, facilitating the dispersion of fillers such as nano-TiO2 and B4C microspheres. Simultaneously, its epoxy groups participate in the curing reaction, avoiding coating porosity caused by the evaporation of traditional solvents. Below 3 parts, the viscosity is too high, resulting in uneven filler dispersion; above 4 parts, it dilutes the concentration of radiation-proof and fire-retardant components in the resin matrix, weakening the functional effect. The dispersant prevents the aggregation of nano-TiO2 and B4C microspheres through electrostatic repulsion, ensuring uniform distribution of radiation-proof and fire-retardant components; the defoamer eliminates bubbles generated during stirring, preventing bubbles from becoming focal points of radiation energy or weak points in the char layer during a fire; the curing agent uses a compound system of alicyclic amines and polyether amines, whose active hydrogen can react with the epoxy groups of the epoxy resin to form a cross-linked network. The cross-linking density directly affects the radiation-proof performance and the integrity of the fire-retardant char layer. DOPO modified epoxy resin has an epoxy value of 0.42-0.48 eq / 100g, and CTBN toughened epoxy resin has an epoxy value of 0.28-0.32 eq / 100g. Based on the epoxy value, this dosage can achieve an epoxy group conversion rate of over 90%. If the dosage is less than 8 parts, the crosslinking is incomplete, and the coating has poor radiation resistance. If the dosage is more than 12 parts, there will be excessive curing agent residue, which will cause the coating to yellow and reduce adhesion.

[0052] In this invention, the DOPO modified epoxy resin is, for example, 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, or 42 parts.

[0053] In this invention, the CTBN toughened epoxy resin is, for example, 20 parts, 20.5 parts, 21 parts, 21.5 parts, 22 parts, 22.5 parts, or 23 parts by weight.

[0054] In this invention, the weight parts of nano-TiO2 are, for example, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, or 8 parts.

[0055] In this invention, the weight parts of montmorillonite are, for example, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, or 7 parts.

[0056] In this invention, the weight parts of B4C microspheres are, for example, 6 parts, 6.2 parts, 6.4 parts, 6.5 parts, 6.6 parts, 6.8 parts, or 7 parts.

[0057] In this invention, the ammonium polyphosphate is, for example, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts, 8.5 parts, or 9 parts by weight.

[0058] In this invention, the weight parts of melamine are, for example, 3 parts, 3.5 parts, 4 parts, 4.5 parts, or 5 parts.

[0059] In this invention, the pentaerythritol is, for example, 3 parts, 3.2 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.8 parts, or 4 parts by weight.

[0060] In this invention, the amount of active diluent by weight is, for example, 3 parts, 3.2 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.8 parts, or 4 parts.

[0061] In this invention, the weight of the dispersant is, for example, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, or 1 part.

[0062] In this invention, the defoamer is present in parts by weight, for example, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, or 0.5 parts.

[0063] In this invention, the curing agent is, for example, 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts or 12 parts by weight.

[0064] In a preferred embodiment of the present invention, the DOPO modified epoxy resin includes one or more of DOPO-EP-01, DER-671, SM-DOPO-EP, or XY-DOPO-02.

[0065] In this invention, the DOPO modified epoxy resin is, for example, DOPO-EP-01, DER-671, SM-DOPO-EP, XY-DOPO-02, DOPO-EP-01 and DER-671, DER-671 and SM-DOPO-EP, SM-DOPO-EP and XY-DOPO-02, XY-DOPO-02 and DOPO-EP-01, DOPO-EP-01 and SM-DOPO-EP, DOPO-EP-01, DER-671 and SM-DOPO-EP, or DER-671, SM-DOPO-EP and XY-DOPO-02.

[0066] In a preferred embodiment of the present invention, the DOPO modified epoxy resin comprises DOPO-EP-01.

[0067] In this invention, the DOPO-modified epoxy resin has an epoxy value of 0.42-0.48 eq / 100g and a DOPO content of ≥12%;

[0068] In a preferred embodiment of the present invention, the CTBN toughened epoxy resin includes one or more of SW-CTBN-1300X, CTBN-1300, YH-CTBN-1300 or F5287.

[0069] In this invention, the CTBN toughened epoxy resin is, for example, SW-CTBN-1300X, CTBN-1300, YH-CTBN-1300, F5287, SW-CTBN-1300X and CTBN-1300, CTBN-1300 and YH-CTBN-1300, YH-CTBN-1300 and F5287, F5287 and SW-CTBN-1300X, SW-CTBN-1300X and YH-CTBN-1300, SW-CTBN-1300X, CTBN-1300 and YH-CTBN-1300, or CTBN-1300, YH-CTBN-1300 and F5287.

[0070] In a preferred embodiment of the present invention, the nano-TiO2 has a particle size of 20-30 nm and a crystal ratio of Anatase / Rutile = 80 / 20; the montmorillonite has a cation exchange capacity ≥ 100 meq / 100 g and a particle size ≤ 2 μm.

[0071] In this invention, nano-TiO2 is a key auxiliary component of the coating radiation protection system. Its particle size and crystal structure ratio directly determine the gamma-ray shielding efficiency and compatibility with the resin matrix. The parameter design must simultaneously meet the dual requirements of efficient free radical scavenging and uniform dispersion.

[0072] A particle size of 20-30 nm represents the optimal range for balancing specific surface area and dispersibility. On one hand, a particle size of 20-30 nm allows for the formation of nano-TiO2 particles ≥50 nm in size. 2 With a specific surface area of ​​ / g, the surface has a sufficient number of exposed hydroxyl sites, enabling efficient adsorption of hydroxyl and alkyl free radicals generated by gamma-ray irradiation. These free radicals are converted into stable H₂O or small molecule alcohols by combining with surface hydroxyl groups, preventing them from attacking the resin molecular chains and causing degradation. If the particle size is >30nm, the specific surface area will decrease to 30nm. 2Below a certain size (e.g.), the number of free radical adsorption sites decreases, increasing the rate of coating degradation induced by gamma rays. Furthermore, large-diameter particles tend to aggregate in the resin matrix, forming localized areas of uneven density that become focal points for radiation energy, leading to localized cracking of the coating. On the other hand, if the particle size is <20 nm, the surface energy of the nanoparticles is too high, and even with the addition of dispersants, irreversible aggregation easily occurs, forming agglomerates with a particle size >100 μm. This disrupts the continuity of the coating, weakening its radiation protection effect and reducing its mechanical properties.

[0073] The synergistic effect of anatase and rutile is key to enhancing radiation protection performance. Anatase-type TiO2 has a band gap of 3.2 eV, making it easier to excite valence band electrons to transition to the conduction band under gamma-ray irradiation, forming electron-hole pairs. The holes have strong oxidizing properties, capable of oxidizing and decomposing small-molecule degradation products generated by radiation in the coating, preventing acidic substances from corroding the resin matrix. The electrons, on the other hand, react with oxygen in the coating to generate superoxide anions (O2). - Furthermore, the high specific surface area of ​​anatase-type TiO2 enhances the scattering of gamma rays, extending the propagation path of rays within the coating. While Rutile-type TiO2, with a band gap of 3.0 eV, has a lower electron-hole pair generation efficiency than anatase-type, its more stable crystal structure improves the anti-sintering properties of nano-TiO2 at high temperatures, preventing particle growth when anatase-type transforms into Rutile-type at high temperatures. If the anatase ratio is <80%, insufficient electron-hole pair generation leads to reduced free radical scavenging and significantly weakened radiation protection. If the anatase ratio is >80%, particles are prone to sintering and agglomeration at high temperatures, resulting in a decline in the coating's radiation protection performance after a fire, failing to meet the long-term protection requirements of the nuclear power industry.

[0074] Montmorillonite, as a dual-functional component for both structural reinforcement and radiation protection in coatings, directly influences its adsorption capacity for radiation degradation products and its interfacial bonding with the resin matrix through its cation exchange capacity and particle size parameters. Parameter design must serve the goals of inhibiting radiation corrosion and improving coating density. Cation exchange capacity (CEC) is a key indicator of montmorillonite's ability to adsorb cations and polar molecules. Under radiation conditions, the DOPO-modified epoxy resin and CTBN-toughened epoxy resin in the coating undergo minor degradation, generating acidic small-molecule products containing carboxyl groups (-COOH) and hydroxyl groups (-OH) (such as propionic acid and butanol). These acidic substances corrode the resin matrix and B4C microspheres, leading to the oxidation of the B4C microsphere surface to form B2O3, thus weakening neutron shielding efficiency. In the layered silicate structure of montmorillonite, exchangeable Na+ exists between the layers. + Ca 2+When montmorillonite has an isocation content (CEC) ≥ 100 meq / 100g, its interlayer cations can exchange with the H⁺ of acidic small molecules, fixing the acidic substances within the interlayer channels and preventing them from diffusing into the coating and causing corrosion. If CEC < 100 meq / 100g, the adsorption capacity of montmorillonite for acidic substances is insufficient, and the coating will deteriorate after 10 days. 6 After irradiation with Gy γ rays, the concentration of acidic substances will rise to above 0.5 mol / L, resulting in a decrease in the neutron shielding efficiency of B4C microspheres, while the resin matrix will show obvious yellowing and embrittlement.

[0075] A particle size ≤2μm is crucial for ensuring uniform dispersion of montmorillonite in the resin matrix and the formation of the labyrinth effect. On one hand, montmorillonite particles with a particle size ≤2μm can be uniformly dispersed in the mixed matrix of DOPO-modified epoxy resin and CTBN-toughened epoxy resin under the action of a dispersant. Their layered structure can form a tight interfacial bond with the resin molecular chains, improving the density of the coating and reducing the probability of direct penetration of gamma rays, i.e., the labyrinth effect. Gamma rays need to be refracted and reflected multiple times between the montmorillonite layers, extending the path by 3-5 times, and their energy is gradually consumed. If the particle size >2μm, the montmorillonite particles easily settle in the resin, forming localized aggregation areas. This not only fails to create a continuous labyrinth effect but also leads to pores within the coating, allowing gamma rays to directly act on the equipment substrate through these pores, weakening the protective effect. On the other hand, montmorillonite with a particle size ≤2μm can form a multi-scale filler synergistic dispersion system with nano-TiO2 and B4C microspheres, avoiding stratification due to excessive particle size differences between different fillers and ensuring the overall uniformity of the coating performance. If the particle size is >2μm, the particle size difference between montmorillonite and nano-TiO2 is more than 100 times, which easily leads to stratification phenomenon of large particles settling and small particles floating, resulting in excessive differences in radiation protection and mechanical properties between the upper and lower layers of the coating, which cannot meet the requirements for uniform protection of the surface of nuclear power equipment.

[0076] In a preferred embodiment of the present invention, the B4C microspheres have a particle size of 5-10 μm, a purity of ≥99%, and a sphericity of ≥90%.

[0077] In this invention, the core function of the B4C microspheres is through... 10 The B isotope undergoes a nuclear reaction with neutrons to achieve shielding. A particle size of 5-10 μm ensures the formation of a continuous trapping network in the coating. Based on an addition of 6-7 parts of B4C microspheres to the coating, the distribution density of these microspheres in a dry film coating typically 200-300 μm thick can reach 300-500 microspheres / mm². 2The spacing between adjacent microspheres is ≤20μm, which is less than the mean free path of neutrons in the coating, effectively intercepting most neutrons and avoiding shielding blind spots. If the particle size is <5μm, the specific surface area of ​​the microspheres increases sharply, and the surface energy is too high. Even with the addition of dispersants, they are still prone to agglomeration to form aggregates with a particle size >50μm, resulting in sparse distribution of microspheres in local areas and a 15%-20% decrease in neutron shielding efficiency. If the particle size is >10μm, the microspheres are prone to settling in the resin matrix due to gravity, causing a difference in microsphere concentration between the upper and lower layers of the coating. In addition, large-diameter microspheres will destroy the continuity of the coating, reducing the tensile strength by 10%-15%, making it unable to withstand the vibration loads during the operation of nuclear power plant equipment.

[0078] The 5-10μm particle size forms a multi-scale gradient distribution with other fillers, which can avoid the stratification of fillers with different particle sizes during high-speed dispersion and ensure the stability of the coating system. At the same time, this particle size will not clog 40-60 mesh filter screens, meeting the process requirements for filtration and impurity removal during the preparation process. If the particle size is >10μm, it is easy to get stuck in the filter screen pores, resulting in a decrease in filtration efficiency or even damage to the filter screen, affecting the continuity of coating production.

[0079] High purity is crucial for ensuring stable neutron shielding efficiency and preventing impurities from interfering with coating performance. The neutron shielding capability of B4C microspheres depends on... 10 For B content, a purity ≥99% means that the mass fraction of B4C is ≥99%, and the total impurity content is ≤1%. If the purity is <99%, the impurities will dilute the content. 10 The effective concentration of B is insufficient to meet the stringent requirements for neutron shielding in the nuclear power field; furthermore, metallic elements such as Fe and Si in the impurities can become scattering centers for gamma rays, accelerating the radiation degradation of the resin matrix and causing the coating to degrade after 10 years. 6 The degree of embrittlement increases after irradiation with Gy γ rays, and the elongation at break decreases from ≥5% to ≤3%.

[0080] The B2O3 contained in low-purity B4C reacts with melamine in the fire-retardant system to form melamine borate salt, which has no flame-retardant activity, thus weakening the formation efficiency of the expanded char layer. When the purity of B4C is <99% and the B2O3 content is >0.5%, the expansion ratio of the char layer will decrease from 15-20 times to 10-12 times, and the thermal conductivity will increase to 0.15-0.2 W / (m·K). In hydrocarbon fires, the substrate temperature is likely to exceed 200℃, failing to meet fire protection requirements. However, when the purity is ≥99% and the B2O3 content is ≤0.3%, such adverse reactions can be completely avoided, ensuring that fire protection and radiation protection performance work synergistically.

[0081] High sphericity is the core guarantee for optimizing microsphere dispersibility and reducing internal stress in the coating. Microspheres with a sphericity ≥90% have smooth surfaces, experience low shear resistance in the resin matrix, can disperse quickly and uniformly during high-speed dispersion, and are less prone to agglomeration due to mechanical entanglement between particles after dispersion. If the sphericity is <90%, hook structures are easily formed between particles, resulting in local agglomeration after dispersion, causing uneven distribution of B4C microspheres in the coating and fluctuations in neutron shielding performance exceeding 10%. At the same time, the sharp edges of irregular particles can scratch the resin molecular chains, forming stress concentration points after coating curing. These points are prone to microcracks after radiation or temperature changes, reducing the service life of the coating.

[0082] Spherical particles have a higher packing efficiency than irregular particles. B4C microspheres with a sphericity of ≥90% can bond more tightly with the resin matrix, reducing the porosity caused by loose particle packing inside the coating. If these pores exist, they will become "channels" for gamma rays and neutrons, accelerating the impact of radiation on the substrate. At the same time, they are easily broken down by high-temperature gases in a fire, damaging the thermal insulation structure of the carbon layer. High sphericity can effectively avoid this problem and ensure the protective stability of the coating in radiation and fire scenarios.

[0083] In a preferred embodiment of the present invention, the degree of polymerization of ammonium polyphosphate n≥1000 and the particle size is 10-20μm; the particle size of melamine is 5-10μm; and the purity of pentaerythritol is ≥99.5% and the particle size is 8-15μm.

[0084] In this invention, the degree of polymerization of ammonium polyphosphate (n) is ≥1000. A high degree of polymerization reduces the volatilization loss of phosphates at high temperatures, ensuring a complete carbon skeleton is formed through full reaction with pentaerythritol. If n < 1000, it easily decomposes and volatilizes at high temperatures, resulting in insufficient carbon source supply and easy collapse of the carbon layer. A particle size of 10-20 μm is suitable for coating dispersion processes, avoiding both agglomeration of small particles (<10 μm) leading to uneven fireproofing and large particles (>20 μm) affecting coating smoothness, while ensuring uniform release of acid source at high temperatures to support carbon layer expansion. Melamine has a particle size of 5-10 μm, which allows for uniform dispersion in the coating and simultaneous release of non-combustible gases at high temperatures, ensuring uniform bubble size (1-3 mm in diameter) in the carbon layer. If >10 μm, concentrated gas release easily leads to carbon layer rupture; if <5 μm, gas escapes quickly, resulting in insufficient expansion ratio (<10 times), weakening the heat insulation effect. A pentaerythritol purity ≥99.5% reduces the interference of impurities on the esterification reaction, ensuring efficient formation of a carbon skeleton with phosphates; a purity <99.5% results in impurities reducing carbonization efficiency and decreasing carbon layer strength. A particle size of 8-15μm matches the particle size of ammonium polyphosphate and melamine, achieving uniform mixing and simultaneous reaction at high temperatures; deviations from this range can lead to component stratification, resulting in uneven carbon layer structure and fluctuations in thermal insulation performance.

[0085] In a preferred embodiment of the present invention, the active diluent is Dow DOWANOL™ PnB glycidyl ether with an epoxy value of 0.5-0.6 eq / 100g and VOC=0; the dispersant is BYK-161 polyamide dispersant, and the defoamer is Tego Foamex810 mineral oil defoamer.

[0086] In a preferred embodiment of the present invention, the curing agent includes an alicyclic amine curing agent and a polyetheramine curing agent; the alicyclic amine curing agent is Huntsman Ancamine® 2049 with an active hydrogen equivalent of 65-70 g / eq; the polyetheramine curing agent is BASF Jeffamine® D-230 with an active hydrogen equivalent of 61 g / eq; the mass ratio of the alicyclic amine curing agent to the polyetheramine curing agent is 4:6-5:5.

[0087] In this invention, the alicyclic structure of the cycloaliphatic amine curing agent endows the coating with excellent radiation resistance, resisting the damage of gamma rays to the crosslinking network; its active hydrogen equivalent of 65-70 g / eq allows for efficient reaction with the epoxy groups of the epoxy resin, ensuring crosslinking density and preventing coating embrittlement after radiation. The flexible polyether segments of the polyether amine curing agent can absorb radiation stress and improve coating toughness; its active hydrogen equivalent of 61 g / eq matches that of the cycloaliphatic amine, ensuring simultaneous curing reaction and no unreacted groups remaining.

[0088] The mass ratio of alicyclic amine curing agent to polyetheramine curing agent is 4:6-5:5 to balance radiation resistance and toughness. The alicyclic amine accounts for 40%-50% to ensure that the tensile strength retention rate of the coating after radiation is ≥85%; the polyetheramine accounts for 50%-60% to prevent the coating from becoming brittle due to excessive cross-linking. If the alicyclic amine content is >50%, the coating toughness is insufficient and prone to cracking; if it is <40%, the radiation resistance decreases, failing to meet the long-term use requirements of nuclear power.

[0089] According to a second aspect of the present invention, a method for preparing the epoxy fire-retardant coating for nuclear power plants as described above is provided, the method comprising the following steps:

[0090] S1: Resin premixing: Add DOPO modified epoxy resin and CTBN toughened epoxy resin to a stainless steel mixing tank, start stirring at 200-300 r / min, add reactive diluent at the same time, heat to 40-50℃, keep warm and stir for 20-30 minutes to form resin matrix.

[0091] S2: Filler dispersion: Add nano TiO2, montmorillonite, and B4C microspheres in sequence, increase the rotation speed to 800-1000 r / min, disperse at high speed for 30-40 minutes, then add dispersant and continue high-speed dispersion for 20 minutes to ensure that the filler particle size distribution is ≤50μm;

[0092] S3: Fireproof system mixing: Reduce the rotation speed to 500-600r / min, add ammonium polyphosphate, melamine and pentaerythritol in sequence, and stir for 25-35 minutes;

[0093] A: Additive adjustment: Maintain a speed of 500-600r / min, add defoamer, stir for 15-20 minutes, filter with a 40-60 mesh filter to obtain the base coating;

[0094] B: Hardener preparation: 30 minutes before construction, mix the cycloaliphatic amine hardener and polyether amine hardener evenly, then add them to the base coating at a mass ratio of base coating: hardener = 9:1-8.5:1.5, and stir at 300-400 r / min for 10-15 minutes to obtain the epoxy fireproof coating for nuclear power.

[0095] According to a third aspect of the present invention, an application of the epoxy fire-retardant coating for nuclear power as described above is provided, characterized in that the epoxy fire-retardant coating for nuclear power is applied to the surface protection of equipment in critical areas of nuclear power plants, can resist gamma rays and neutron radiation, and can form an effective heat-insulating carbon layer in hydrocarbon fire scenarios, thus meeting the dual requirements of fire prevention and radiation resistance in the nuclear power field.

[0096] Example

[0097] This invention includes eight embodiments. Table 1 shows the raw material ratios for Examples 1-8 and Comparative Examples 1-4. The dispersant used in Examples 1-8 and Comparative Examples 1-4 was BYK-161, with a weight of 0.75 parts; the defoamer was Tego Foamex 810, with a weight of 0.4 parts; the reactive diluent was Dow DOWANOL™ PnB, with a weight of 3.5 parts; the curing agent was Huntsman Ancamine® 2049 and BASF Jeffamine® D-230, with a weight of 10 parts, and the mass ratio of Huntsman Ancamine® 2049 to BASF Jeffamine® D-230 was 4.5:5.5; the nano-TiO2 was Degussa P25; and the montmorillonite was Zhejiang Fenghong JH-1.

[0098] The proportions of other raw materials in Examples 1-8 and Comparative Examples 1-4 are shown in Table 1.

[0099] Table 1. Raw material ratios of Examples 1-8 and Comparative Examples 1-4

[0100]

[0101] Comparative Example 1 was replaced with ordinary bisphenol A epoxy E-51; Comparative Example 4 was replaced with 21.5 parts of ordinary nitrile rubber toughening agent.

[0102] The specific preparation method is as follows:

[0103] S1: Resin premixing: Add DOPO modified epoxy resin and CTBN toughened epoxy resin to a stainless steel mixing tank, start stirring at 200-300 r / min, add reactive diluent at the same time, heat to 40-50℃, keep warm and stir for 20-30 minutes to form resin matrix.

[0104] S2: Filler dispersion: Add nano TiO2, montmorillonite, and B4C microspheres in sequence, increase the rotation speed to 800-1000 r / min, disperse at high speed for 30-40 minutes, then add dispersant and continue high-speed dispersion for 20 minutes to ensure that the filler particle size distribution is ≤50μm;

[0105] S3: Fireproof system mixing: Reduce the rotation speed to 500-600r / min, add ammonium polyphosphate, melamine and pentaerythritol in sequence, and stir for 25-35 minutes;

[0106] A: Additive adjustment: Maintain a speed of 500-600r / min, add defoamer, stir for 15-20 minutes, filter with a 40-60 mesh filter to obtain the base coating;

[0107] B: Hardener preparation: 30 minutes before construction, mix the cycloaliphatic amine hardener and polyether amine hardener evenly, then add them to the base coating at a mass ratio of base coating: hardener = 9:1-8.5:1.5, and stir at 300-400 r / min for 10-15 minutes to obtain the epoxy fireproof coating for nuclear power.

[0108] Performance testing

[0109] The test indicators, parameters, and test methods are shown in Table 2:

[0110] Table 2 Performance Test Indicators

[0111]

[0112] Table 3 Performance Test Results

[0113]

[0114] Regarding fire resistance, in all examples, the substrate temperature after 120 minutes of a hydrocarbon fire at 1100℃ was ≤180℃, far below the critical protection temperature of steel (540℃). In Example 13 (9 parts ammonium polyphosphate, 5 parts melamine, 4 parts pentaerythritol, all upper limits in the specification), the substrate temperature was only 162℃, and in Example 15 (42 parts DOPO modified epoxy resin, 23 parts CTBN toughened epoxy resin, 7 parts B4C microspheres, all upper limits in the specification), the substrate temperature was as low as 160℃, demonstrating that the fire-resistant system can stably form a highly efficient heat-insulating carbon layer. Regarding radiation resistance, all examples, after a cumulative gamma-ray dose of 10... 6 After Gy irradiation, no peeling, powdering, or cracking was observed; only slight discoloration was present. The number of bubbles (≤50 per square meter), their diameter (≤2 mm), and the crack length (<1 cm) all met the requirements of the instructions. Furthermore, the adhesion strength was >4.5 MPa, far exceeding the acceptable standard of 0.2 MPa. Example 15 even achieved an adhesion strength of 5.4 MPa. All examples, due to the use of 6-7 parts of B4C microspheres, achieved a neutron shielding rate of 60%-65%, meeting the requirements for nuclear power. Comparative Example 2, lacking B4C microspheres, had a neutron shielding rate of only 25%, directly confirming that B4C microspheres are the core component of neutron shielding. This dual performance of meeting fire resistance standards and exhibiting excellent radiation resistance directly demonstrates that the presence of the radiation-resistant component did not interfere with the formation of the char layer in the fireproof system, and the fireproof system did not experience structural degradation due to radiation.

[0115] Comparative Example 1 used ordinary bisphenol A epoxy resin (E-51) instead of the DOPO-modified epoxy resin specified in the instructions. Although the substrate temperature reached 170℃ after 120 minutes (fire resistance performance qualified), localized powdering and two 1.5cm excessive cracks appeared after radiation resistance, and the adhesion was only 0.15MPa. Comparative Example 3 reduced the amount of ammonium polyphosphate to 4 parts. Although the radiation resistance performance was qualified, the substrate temperature rose sharply to 285℃ after 120 minutes, and the fire resistance failed. Comparative Example 4 used ordinary nitrile rubber toughening agent instead of the CTBN toughening epoxy resin specified in the instructions. After radiation resistance, 5% of the area of ​​localized peeling and one 2cm excessive crack appeared, and the adhesion was only 0.8MPa. Comparative Example 5 did not add the nano TiO2 and montmorillonite specified in the instructions. After radiation resistance, 80 / m 2 3mm of excessive air bubbles.

[0116] This invention constructs a multi-layered radiation shielding system using DOPO-modified epoxy resin, nano-TiO2, montmorillonite, and B4C microspheres. The 3d empty orbitals of phosphorus atoms in the DOPO-modified epoxy resin can capture high-energy electrons excited by gamma rays, slowly releasing radiation energy as molecular vibrational energy. Simultaneously, its conjugated structure disperses radiation-induced free radicals, preventing resin molecular chain breakage. The nano-TiO2 particles, with a diameter of 20-30 nm and an anatase / rutile ratio of 80 / 20, generate electron-hole pairs upon gamma ray irradiation, further capturing organic free radicals within the coating and inhibiting chain degradation reactions. The layered structure of montmorillonite extends the gamma ray propagation path through a maze effect. Together, these components increase the gamma ray shielding efficiency to 45%-50%. The B4C microspheres... 10 The B isotope undergoes a nuclear reaction with neutrons to generate low-energy Li and He nuclei, and its spherical structure forms a neutron trapping network, achieving a neutron shielding rate of 60%-65%. Simultaneously, this radiation protection system does not interfere with intumescent fire-retardant systems based on ammonium polyphosphate, melamine, and pentaerythritol. The radiation-resistant fillers, such as B4C microspheres and nano-TiO2, are chemically stable and will not react with the phosphoric acid substances produced by the decomposition of ammonium polyphosphate. Furthermore, the phosphorus heterocyclic structure of the DOPO-modified epoxy resin can catalyze the formation of a char layer at high temperatures, thereby enhancing the fire-retardant effect and completely solving the problem of radiation-resistant fillers weakening fire-retardant performance in existing technologies.

[0117] The end carboxyl groups of CTBN-toughened epoxy resin react with DOPO-modified epoxy resin to introduce flexible nitrile butadiene segments. Simultaneously, the curing system employs alicyclic amines and polyether amines in a 4:6-5:5 ratio, forming a cross-linked network that combines rigidity and flexibility. The cyclic structure of the alicyclic amine provides radiation stability, while the flexible segments of the polyether amine absorb radiation shock energy, preventing the coating from cracking due to internal stress caused by radiation. This allows it to withstand the vibrations and temperature fluctuations experienced during the long-term operation of nuclear power plant equipment.

[0118] This invention uses Dow DOWANOL™ PnB glycidyl ether (VOC=0) as an active diluent to replace traditional solvents. This diluent adjusts the coating viscosity to 5000-8000 mPa·s (25℃), meeting the requirements for brush and roller coating, and also participates in the curing reaction, improving coating density. BYK-161 dispersant promotes uniform filler dispersion, prevents agglomeration, and ensures the coating is free of noticeable particles. Tego Foamex 810 defoamer eliminates bubbles during stirring, preventing defects such as orange peel and pinholes. Furthermore, the hardener is formulated with a base coating to hardener mass ratio of 8.5:1-9:1, with a pot life of 8-12 hours (25℃), providing a wide application window to meet the continuous protection requirements of large nuclear power plant equipment.

[0119] The reactive diluent used in this invention has a VOC content of 0, with no solvent evaporation, meeting the environmental emission standards for the nuclear power industry. All raw materials exhibit excellent aging resistance, and the coating does not powder or peel off even under the long-term high-temperature and high-humidity environment of a nuclear power plant. Simultaneously, the overall performance of the coating is stable, requiring no frequent maintenance or replacement, thus avoiding equipment protection interruptions due to coating failure. This fundamentally reduces safety hazards in critical areas of the nuclear power plant, providing a reliable guarantee for the safe operation of nuclear power facilities.

Claims

1. An epoxy fire-retardant coating for nuclear power plants, characterized in that, Including the following parts by weight of raw materials: 30-42 parts of DOPO modified epoxy resin 20-23 parts of CTBN toughened epoxy resin 5-8 parts of nano TiO2 4-7 parts of montmorillonite 6-7 parts of B4C microspheres 6-9 parts of ammonium polyphosphate 3-5 parts of melamine 3-4 parts of pentaerythritol 3-4 parts reactive diluent Dispersant 0.5-1 part 0.3-0.5 parts of defoamer 8-12 parts of curing agent; The nano-TiO2 has a particle size of 20-30 nm and a crystal structure ratio of Anatase / Rutile = 80 / 20; The montmorillonite has a cation exchange capacity ≥100meq / 100g and a particle size ≤2μm; The B4C microspheres have a particle size of 5-10 μm, a purity of ≥99%, and a sphericity of ≥90%. The ammonium polyphosphate has a degree of polymerization n ≥ 1000 and a particle size of 10-20 μm; the melamine has a particle size of 5-10 μm; and the pentaerythritol has a purity ≥ 99.5% and a particle size of 8-15 μm. The curing agent includes alicyclic amine curing agents and polyetheramine curing agents; the active hydrogen equivalent of the alicyclic amine curing agent is 65-70 g / eq; the active hydrogen equivalent of the polyetheramine curing agent is 61 g / eq; the mass ratio of alicyclic amine curing agent to polyetheramine curing agent is 4:6-5:

5.

2. The epoxy fire-retardant coating for nuclear power plants as described in claim 1, characterized in that, The DOPO modified epoxy resin includes one or more of DOPO-EP-01, DER-671, SM-DOPO-EP, or XY-DOPO-02.

3. The epoxy fire-retardant coating for nuclear power plants as described in claim 1, characterized in that, The CTBN toughened epoxy resin includes one or more of SW-CTBN-1300X, CTBN-1300, YH-CTBN-1300 or F5287.

4. The epoxy fire-retardant coating for nuclear power plants as described in claim 1, characterized in that, The active diluent is Dow DOWANOL™ PnB glycidyl ether, with an epoxy value of 0.5-0.6 eq / 100g and VOC=0; the dispersant is BYK-161 polyamide dispersant, and the defoamer is Tego Foamex810 mineral oil defoamer.

5. The epoxy fire-retardant coating for nuclear power plants as described in claim 1, characterized in that, The alicyclic amine curing agent includes Huntsman Ancamine® 2049; the polyether amine curing agent includes BASF Jeffamine® D-230.

6. The method for preparing the epoxy fire-retardant coating for nuclear power plants according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: S1: Resin premixing: Mix and stir DOPO modified epoxy resin and CTBN toughened epoxy resin, add reactive diluent, heat to 40-50℃, keep warm and stir for 20-30 minutes to form resin matrix; S2: Filler dispersion: Add nano TiO2, montmorillonite, and B4C microspheres in sequence, increase the rotation speed to 800-1000 r / min, disperse at high speed for 30-40 minutes, then add dispersant and continue high-speed dispersion for 20 minutes to ensure that the filler particle size distribution is ≤50μm; S3: Fireproof system mixing: Reduce the rotation speed to 500-600r / min, add ammonium polyphosphate, melamine and pentaerythritol in sequence, and stir for 25-35 minutes; A: Additive adjustment: Maintain a speed of 500-600r / min, add defoamer, stir for 15-20 minutes, filter with a 40-60 mesh filter to obtain the base coating; B: Hardener preparation: 30 minutes before construction, mix the cycloaliphatic amine hardener and polyether amine hardener evenly, then add them to the base coating at a mass ratio of base coating: hardener = 9:1-8.5:1.5, and stir at 300-400 r / min for 10-15 minutes to obtain the epoxy fireproof coating for nuclear power.

7. The application of the epoxy fire-retardant coating for nuclear power plants as described in any one of claims 1-5, characterized in that, The epoxy fire-retardant coating for nuclear power plants is used for surface protection of equipment in critical areas of nuclear power plants.

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