Multi-layer composite intumescent fire-retardant coating, and preparation method and usage method therefor

Abstract

A multi-layer composite intumescent fire-retardant coating, and a preparation method and a usage method therefor. The coating comprises a bottom fire-retardant coating and a surface fire-retardant coating, which are laminated into a single layer or in an ABAB form. The bottom fire-retardant coating contains a physical intumescent agent, and the surface fire-retardant coating contains a gas foaming type intumescent agent. By laminating the bottom fire-retardant coating containing the physical intumescent agent and the surface fire-retardant coating containing the gas foaming type intumescent agent, a multi-layer composite fire-retardant coating system is formed, the filling effect of the physical intumescent agent and the expansion effect of the gas foaming type intumescent agent are fully exerted, and the size of pores in an expansion layer formed under flames is greatly reduced, thereby both improving the compactness and strength of the expansion layer and enhancing the heat insulation performance of the expansion layer.

Description

A multi-layer composite intumescent fire-retardant coating, its preparation method and application method Technical Field

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

[0002] Current intumescent fire-retardant coatings suffer from poor thermal insulation performance of the intumescent layer. Adding non-foaming intumescent agents to fire-retardant coatings is one way to improve the quality of the intumescent layer in epoxy-based fire-retardant coatings. Expanded graphite is the most commonly added material. The worm-like graphite fills the intumescent layer, preventing the formation of large pores and weakening the heat transfer through convection. It also generally has high strength. However, the high thermal conductivity of graphite in this type of intumescent layer increases the overall thermal conductivity, and it often forms open pores, which weakens its thermal insulation capacity to some extent. Therefore, the effect of using expanded graphite to improve the fire resistance of coatings is limited. Some studies have used composite fire-retardant coatings, such as epoxy-based and acrylic-based fire-retardant coatings, to create visible coatings, but their fire resistance performance has not improved. Coatings prepared by combining aluminum foil with fire-retardant coatings show a reduced rate of temperature increase in the substrate under flame conditions, but the final temperature remains unchanged. Patent ZL202210867325.4 proposes a composite solution of intumescent fire-retardant coating and non-intumescent sealing coating. It mainly uses the bottom intumescent fire-retardant coating system to ensure the heat insulation performance of the coating, and uses the high-temperature resistant and dense sealing layer on the surface to block the combustion of the coating. However, it cannot solve the problem of weak fire resistance of the coating caused by the large-sized pores in the substrate of epoxy fire-retardant coating.

[0003] To address the inherent problem of high viscosity and high density at high temperatures in epoxy resin-based intumescent fire retardant coatings, which easily leads to large-sized pores and poor thermal insulation performance of the intumescent layer, there is an urgent need to research an epoxy-based intumescent fire retardant coating with high density after expansion. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0005] To address the aforementioned technical problems, this application discloses a multilayer composite intumescent fire-retardant coating, its preparation method, and its application method. By utilizing the full filling characteristics of the bottom fire-retardant coating and the excellent expansion performance of the top fire-retardant coating, the problem of poor adhesion to the substrate caused by large pores appearing at the bottom of the expansion layer after a high expansion ratio is avoided. This achieves a epoxy-based intumescent fire-retardant coating that combines high strength and high expansion ratio, resulting in excellent fire-retardant performance.

[0006] To achieve the above objectives, this application adopts the following technical solution:

[0007] The first aspect of this application proposes a multi-layer composite intumescent fire-retardant coating.

[0008] In one optional embodiment, the multilayer composite intumescent fire retardant coating includes a base fire retardant coating containing a physical expanding agent and a surface fire retardant coating containing a gas foaming expanding agent.

[0009] Optionally, the composite method of the base fire-retardant coating and the surface fire-retardant coating is a single layer or an ABAB… type, wherein the single-layer composite method is a layer of base fire-retardant coating-surface fire-retardant coating, and the ABAB… type refers to base fire-retardant coating-surface fire-retardant coating / base fire-retardant coating-surface fire-retardant coating / base fire-retardant coating-surface fire-retardant coating…

[0010] Optionally, the underlying fire-retardant coating comprises two components, A and B, wherein component A is composed of the following raw materials in parts by weight: 20-60 parts adhesive and 1-40 parts acid catalyst;

[0011] Component B consists of the following raw materials in parts by weight: 5-35 parts curing agent and 0.2-20 parts physical expansion agent.

[0012] The physical expanding agent refers to an inorganic substance or modifier that expands on its own at high temperatures and does not decompose at high temperatures. Preferably, the physical expanding agent is at least one of expanded graphite, vermiculite, perlite, resinstone, and obsidian, with expanded graphite being the most preferred.

[0013] Epoxy resin adhesives may contain one or more epoxy resins, such as the commonly used E22, E44, and E51, as well as mixtures thereof such as E44 / E51, E22 / E51, and E22 / E44. Epoxy resin adhesives may contain commercially available epoxy resins or modified epoxy resins, such as bisphenol A, bisphenol F, phenolic modified epoxy, and silicone modified epoxy. When selecting solid resins such as E22 as epoxy resin adhesives, reactive diluents can be used to dissolve them into a liquid state, serving as the resin adhesive for the base layer fire-retardant coating. Alternatively, low molecular weight resins can be compounded with solid resins to create a liquid state, which can also be used as a resin adhesive.

[0014] Acid catalysts primarily refer to substances that form acids during thermal decomposition, promoting polymer dehydration and char formation. Polyphosphates are preferred, and phosphoric acid catalysts containing nitrogen (N) are particularly suitable. Suitable catalysts are well-known to those skilled in the art, including ammonium polyphosphate, ammonium polyphosphate, melamine ammonium phosphate, and phosphates that have been modified or coated to improve water resistance and other durability properties. Acid catalysts also include boric acid and borates, such as boric acid, zinc borate, and ammonium pentaborate.

[0015] The curing agent is mainly a room temperature curing amine curing agent, including one or more of aromatic amines, alicyclic amines, and imides, as well as their corresponding modified amine curing agents.

[0016] Optionally, the underlying fire-retardant coating components A and B may further include an intumescent layer reinforcing agent.

[0017] Depending on the strength of the expansion layer, an expansion layer reinforcing agent may be added. Expansion layer reinforcing agents include surface ceramicizing materials or fibrous materials. Ceramicizing reinforcing materials include low-melting-point glass, silicon dioxide, kaolin, silicates, and natural minerals such as wollastonite, whetstone, and basalt, in granular or lamellar form. Fiber materials include organic fibers, carbon fibers, glass fibers, mineral fibers, and man-made inorganic fibers, with lengths ranging from a few micrometers to several thousand micrometers.

[0018] Optionally, the underlying fire-retardant coating comprises two components, A and B.

[0019] Component A consists of the following raw materials in parts by weight: 20-60 parts adhesive, 1-40 parts acid catalyst, and 0-20 parts expansion layer reinforcing agent;

[0020] Component B consists of the following raw materials in parts by weight: 5-35 parts curing agent, 0.2-20 parts physical expansion agent, and 0-20 parts expansion layer reinforcing agent.

[0021] Optionally, the surface fire-retardant coating comprises a first component and a second component, wherein the first component is composed of the following raw materials in parts by weight: 20-60 parts of adhesive and 1-40 parts of acid catalyst;

[0022] The second component consists of the following raw materials in parts by weight: 5-35 parts curing agent and 1-20 parts gas foaming expansion agent.

[0023] Gas-blowing expanders play a major role. These gas-blowing expanders refer to materials that release non-flammable, non-flammable gases at high temperatures, causing the coating to expand. They include one or more nitrogen-containing compounds, polymers, derivatives, or coatings, such as melamine, melamine salts, urea, guanidine, and their derivatives or mixtures, with melamine being preferred; or compounds capable of releasing water, carbon dioxide, or other flame-retardant gases, such as magnesium hydroxide, aluminum hydroxide, carbonates, and natural minerals, such as talc, magnesite, and dolomite.

[0024] Optionally, the first and second components of the surface fire-retardant coating further include an intumescent layer reinforcing agent.

[0025] Optionally, the surface fire-retardant coating includes a first component and a second component, wherein the first component is composed of the following raw materials in parts by weight: 20-60 parts adhesive, 1-40 parts acid catalyst, and 0-20 parts expansion layer reinforcing agent;

[0026] The second component consists of the following raw materials in parts by weight: 5-35 parts curing agent, 1-20 parts gas foaming expansion agent, and 0-20 parts expansion layer reinforcing agent.

[0027] The epoxy resin adhesive, acid catalyst, curing agent, and expansion layer reinforcing agent are the same as the base layer fireproof coating.

[0028] The second aspect of this application discloses a method for preparing a multilayer composite intumescent fire-retardant coating.

[0029] In an optional embodiment, the preparation method of the multilayer composite intumescent fire-retardant coating includes the following steps:

[0030] Preparation of the base fire-retardant coating;

[0031] Prepare a surface fire-retardant coating.

[0032] Optionally, the steps for preparing the underlying fire-retardant coating specifically include:

[0033] Add rheology modifiers, plasticizers and other additives to the epoxy resin adhesive in sequence, and stir at 400-1000 rpm for 1-20 minutes;

[0034] Add acid catalyst and stir at 2000-4000 rpm for 10-40 min;

[0035] If necessary, add an expansion layer strengthening agent and stir at 2000-4000 rpm for 10-40 min to obtain component A;

[0036] Add a physical expansion agent to the curing agent and stir at 100-4000 rpm for 1-20 minutes;

[0037] If necessary, add an expansion layer strengthening agent and stir at 1000-4000 rpm for 10-40 min to obtain component B;

[0038] Mix component A and component B evenly to obtain the base fire-retardant coating.

[0039] Optionally, the steps for preparing the surface fire-retardant coating specifically include:

[0040] Add rheology modifiers, plasticizers and other additives to the epoxy resin adhesive in sequence, and stir at 400-1000 rpm for 1-20 minutes;

[0041] Add acid catalyst and stir at 2000-4000 rpm for 10-40 min;

[0042] If necessary, add an expansion layer strengthening agent and stir at 2000-4000 rpm for 10-40 min to obtain the first component;

[0043] Add a gas-blowing expansion agent to the curing agent and stir at 100-4000 rpm for 1-20 minutes;

[0044] Add an expansion layer strengthening agent and stir at 1000-4000 rpm for 10-40 min to obtain the second component;

[0045] The first and second components are mixed evenly to obtain a surface fireproof coating.

[0046] The third aspect of this application discloses the application of a multilayer composite intumescent fire-retardant coating.

[0047] In one optional embodiment, the multilayer composite intumescent fire retardant coating is applied to fire retardant structures or components such as steel, concrete, and wood.

[0048] The fourth aspect of this application discloses a fire-retardant treatment method for a substrate, comprising the following steps:

[0049] S1. Substrate surface pretreatment;

[0050] S2. Stir the bottom layer of the fire-retardant coating described in the first aspect at 400-4000 rpm and apply it to the surface of the substrate until the desired thickness is achieved.

[0051] S3. Stir the surface fire-retardant coating of the fire-retardant coating described in the first aspect at 400-4000 rpm, and apply the surface fire-retardant coating on the gelled bottom fire-retardant coating until the desired thickness is achieved.

[0052] In step S1, the substrate surface pretreatment includes: removing rust, dust and other attachments from the substrate surface, cleaning the surface with ethanol or treating it with sandblasting / shot blasting to a Ra level of 2.5, and the construction is required to be completed within 8 hours.

[0053] Coating methods include spraying, brushing, rolling, and troweling.

[0054] Optionally, the underlying fire-retardant coating and the surface fire-retardant coating are overlapped multiple times in sequence to form an ABABAB type coating.

[0055] Optionally, an anti-aging layer coating may be applied to the surface of the fire-retardant coating. The anti-aging layer coating should be selected based on the overall aging resistance and compatibility with the surface fire-retardant coating, and its thickness should be controlled between 20-50 μm.

[0056] If the coating thickness is too thick, multiple layers of metal, organic, or inorganic wire mesh can be added between the layers during the coating application process. This means adding wire mesh inside the coating to improve the coating application quality and enhance the strength of the coating after curing.

[0057] The beneficial effect of this application is that by combining a base fire-retardant coating containing a physical expanding agent with a surface fire-retardant coating containing a gas-foaming expanding agent, a multi-layer composite fire-retardant coating system is formed. This fully utilizes the filling effect of the physical expanding agent and the expansion effect of the gas-foaming expanding agent, significantly reducing the pore size in the expansion layer formed under flame. This not only improves the density and strength of the expansion layer but also enhances its thermal insulation performance, reduces the rate of heat transfer through the expansion layer to the protected material, delays the failure time of the protected material, and ultimately improves the overall fire-retardant performance of the fire-retardant coating.

[0058] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0059] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0060] Figure 1 is a cross-sectional view of the coating expansion layer prepared in Example 1 of this application;

[0061] Figure 2 is a cross-sectional view of the coating expansion layer prepared in Example 2 of this application;

[0062] Figure 3 is a cross-sectional view of the coating expansion layer prepared in Example 3 of this application;

[0063] Figure 4 is a cross-sectional view of the coating expansion layer prepared in Comparative Example 1 of this application;

[0064] Figure 5 is a cross-sectional view of the coating expansion layer prepared in Comparative Example 2 of this application;

[0065] Figure 6 is a cross-sectional view of the coating expansion layer prepared in Comparative Example 3 of this application;

[0066] Figure 7 shows the back temperature curve of the coating prepared under flame in Example 1 of this application;

[0067] Figure 8 shows the back temperature curve of the coating prepared under flame in Example 2 of this application;

[0068] Figure 9 shows the back temperature curve of the coating prepared under flame in Example 3 of this application;

[0069] Figure 10 shows the back temperature rise curve of the coating prepared in Comparative Example 1 of this application under flame;

[0070] Figure 11 shows the back temperature rise curve of the coating prepared in Comparative Example 2 of this application under flame;

[0071] Figure 12 shows the back temperature rise curve of the coating prepared in Comparative Example 3 of this application under flame. Detailed Implementation

[0072] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0073] Example 1

[0074] A multi-layer composite intumescent fire-retardant coating comprises a base fire-retardant coating containing a physical expanding agent and a top fire-retardant coating containing a gas-foaming expanding agent.

[0075] 1. Preparation of the base layer fire-retardant coating

[0076] (1) Preparation of component A

[0077] Take 48.07g of E51 epoxy resin, add 18.76g of ammonium polyphosphate, and stir with a high-speed disperser at 2000rpm for 15min;

[0078] Add 1.43 g of basalt fiber to the above mixture and stir it for 10 min at 3000 rpm using a high-speed disperser to prepare component A;

[0079] (2) Preparation of component B

[0080] Take 19.93g of polyamide curing agent, add 11.53g of expanded graphite, and stir with a high-speed disperser at 1000rpm for 10min;

[0081] Add 1.54 g of basalt fiber to the above mixture and stir at 1000 rpm for 10 min using a high-speed disperser to prepare component B.

[0082] 2. Preparation of surface fire-retardant coating

[0083] (1) Preparation of the first component

[0084] Take 38.61g of E51 epoxy resin, add 14.39g of ammonium polyphosphate, and stir with a high-speed disperser at 2000rpm for 15min;

[0085] Add 15.23 g of calcium silicate to the above mixture and stir at 2000 rpm for 20 min using a high-speed disperser to prepare the first component;

[0086] (2) Preparation of the second component

[0087] Take 15.34g of polyamide curing agent, add 12.3g of melamine, and stir with a high-speed disperser at 1000rpm for 10min;

[0088] Add 3.32 g of basalt fiber to the above mixture and stir it for 10 min at 3000 rpm using a high-speed disperser to prepare the second component.

[0089] Paint application

[0090] The steel plate substrate was cleaned with ethanol to remove surface oil. The steel plate dimensions were 150×100×3mm.

[0091] Mix components A and B of the base fireproof coating at a mass ratio of 1:1, stir evenly with a mechanical stirrer at a speed of 400 rpm, and apply the coating to the steel plate substrate with a scraper; the thickness of the base fireproof coating should be about 1.5 mm.

[0092] Once the base layer fire retardant coating has gelled, meaning it has solidified on its own without sagging, mix the first and second components of the surface fire retardant coating in a 1:1 mass ratio. Stir the mixture evenly using a mechanical stirrer at 400 rpm. Apply the coating to the base layer fire retardant coating using a scraper. The thickness of the surface fire retardant coating should be approximately 1.5 mm.

[0093] The overall average thickness of the coating applied in Example 1 was 3.21 mm. The target thickness was 3 mm, but in actual application, the coating thickness cannot be precisely controlled and deviations are common.

[0094] Example 2

[0095] The coating preparation method is the same as in Example 1.

[0096] Regarding the coating application, Example 2 follows the same method as Example 1. During application, a base layer of fire-retardant coating of approximately 0.75 mm is applied to the steel plate, followed by a top layer of fire-retardant coating of approximately 0.75 mm, then a base layer of fire-retardant coating of approximately 0.75 mm, and finally a top layer of fire-retardant coating of approximately 0.75 mm.

[0097] The overall average thickness of the coating applied in Example 2 was 3.34 mm.

[0098] Example 3

[0099] A multi-layer composite intumescent fire-retardant coating comprises a base fire-retardant coating containing a physical expanding agent and a top fire-retardant coating containing a gas-foaming expanding agent.

[0100] 1. Preparation of the base layer fire-retardant coating

[0101] (1) Preparation of component A

[0102] Take 48.13g of E51 epoxy resin, add 16.93g of ammonium polyphosphate, and stir with a high-speed disperser at 2000rpm for 15min;

[0103] Add 1.33 g of basalt fiber to the above mixture and stir it for 10 min at 3000 rpm using a high-speed disperser to prepare component A;

[0104] (2) Preparation of component B

[0105] Take 20.02g of polyamide curing agent, add 14.02g of expanded graphite, and stir with a high-speed disperser at 1000rpm for 10min;

[0106] Add 0.94 g of basalt fiber to the above mixture and stir at 1000 rpm for 10 min using a high-speed disperser to prepare component B.

[0107] 2. Preparation of surface fire-retardant coating

[0108] (1) Preparation of the first component

[0109] Take 38.28g of E51 epoxy resin, add 14.56g of ammonium polyphosphate, and stir with a high-speed disperser at 2000rpm for 15min;

[0110] Add 13.13 g of calcium silicate to the above mixture and stir at 2000 rpm for 20 min using a high-speed disperser to prepare the first component;

[0111] (2) Preparation of the second component

[0112] Take 15.69g of polyamide curing agent, add 15.61g of melamine, and stir with a high-speed disperser at 1000rpm for 10min;

[0113] Add 2.55g of basalt fiber to the above mixture and stir it for 10min at 3000rpm using a high-speed disperser to prepare the second component.

[0114] Paint application

[0115] The construction of Example 3 is the same as that of Example 2. The overall average thickness of the coating applied in Example 3 is 3.42 mm.

[0116] Comparative Example 1

[0117] Coating preparation

[0118] (1) Preparation of component A

[0119] Take 48.23g of E51 epoxy resin, add 19.01g of ammonium polyphosphate to it, and stir with a high-speed disperser at 2000rpm for 15min;

[0120] Add 1.46 g of basalt fiber to the above mixture and stir at 3000 rpm for 10 min using a high-speed disperser to prepare component A;

[0121] (2) Preparation of component B

[0122] Take 19.98g of polyamide curing agent, add 11.48g of expanded graphite to it, and stir with a high-speed disperser at 1000rpm for 10min;

[0123] Add 1.58 g of basalt fiber to the above mixture and stir at 1000 rpm for 10 min using a high-speed disperser to prepare component B.

[0124] Paint application

[0125] The steel plate substrate was cleaned with ethanol to remove surface oil. The steel plate dimensions were 150×100×3mm.

[0126] Mix components A and B of the above fire-retardant coating, stir evenly with a mechanical stirrer at 400 rpm, and apply the coating to the steel plate substrate with a scraper. The thickness of the fire-retardant coating should be about 3 mm.

[0127] The overall average thickness of the coating applied in Comparative Example 1 was 3.29 mm.

[0128] Comparative Example 2

[0129] Coating preparation

[0130] (1) Preparation of component A

[0131] Take 38.43g of E51 epoxy resin, add 14.46g of ammonium polyphosphate to it, and stir with a high-speed disperser at 2000rpm for 15min;

[0132] Add 15.19 g of calcium silicate to the above mixture and stir at 2000 rpm for 20 min using a high-speed disperser to prepare component A;

[0133] (2) Preparation of component B

[0134] Take 15.41g of polyamide curing agent, add 12.25g of melamine to it, and stir with a high-speed disperser at 1000rpm for 10min;

[0135] Add 3.41 g of basalt fiber to the above mixture and stir for 10 min at 3000 rpm using a high-speed disperser to prepare component B.

[0136] Paint application

[0137] The steel plate substrate was cleaned with ethanol to remove surface oil. The steel plate dimensions were 150×100×3mm.

[0138] Mix components A and B of the above fire-retardant coating, stir evenly with a mechanical mixer at 400 rpm, and apply the coating to the steel plate substrate with a scraper. The thickness of the fire-retardant coating should be approximately 3 mm.

[0139] The overall average thickness of the coating applied in Comparative Example 2 was 3.34 mm.

[0140] Comparative Example 3

[0141] Coating preparation

[0142] 1. Preparation of the base coat

[0143] (1) Preparation of component A

[0144] Take 38.59g of E51 epoxy resin, add 14.45g of ammonium polyphosphate, and stir with a high-speed disperser at 2000rpm for 15min;

[0145] Add 15.27 g of calcium silicate to the above mixture and stir at 2000 rpm for 20 min using a high-speed disperser to prepare component A;

[0146] (2) Preparation of component B

[0147] Take 15.38g of polyamide curing agent, add 12.23g of melamine, and stir with a high-speed disperser at 1000rpm for 10min;

[0148] Add 3.36 g of basalt fiber to the above mixture and stir at 3000 rpm for 10 min using a high-speed disperser to prepare component B.

[0149] 2. Preparation of surface coating

[0150] (1) Preparation of the first component

[0151] Take 48.12g of E51 epoxy resin, add 18.69g of ammonium polyphosphate to it, and stir with a high-speed disperser at 2000rpm for 15min;

[0152] Add 1.47 g of basalt fiber to the above mixture and stir at 3000 rpm for 10 min using a high-speed disperser to prepare the first component.

[0153] (2) Preparation of the second component

[0154] Take 19.89g of polyamide curing agent, add 11.58g of expanded graphite to it, and stir with a high-speed disperser at 1000rpm for 10min;

[0155] Add 1.58g of basalt fiber to the above mixture and stir it for 10 minutes at 1000rpm using a high-speed disperser to prepare the second component.

[0156] Paint application

[0157] The construction process is the same as that in the example.

[0158] The overall average thickness of the coating applied in Comparative Example 3 was 3.27 mm.

[0159] Coating performance testing

[0160] The fire resistance test method for the above-described embodiments and comparative coatings is the same, specifically: Ignite an alcohol torch with the flame pointing vertically upwards. Once the flame stabilizes, place the cured coating sample 90 mm above the torch nozzle, with the coating facing the flame. Weld a thermocouple to the back of the sample, directly opposite the flame, to measure the temperature of the sample's back side. After the temperature on the sample's back side stabilizes, extinguish the flame and measure the thickness of the expansion layer. Divide the expansion layer thickness by 3 to obtain the coating expansion ratio.

[0161] Table 1 shows the expansion ratio and the highest back surface temperature of the steel plate obtained from testing the above coatings.

[0162] In the examples and comparative examples, the expansion ratio of the A+B composite coating in Example 1 was relatively small, while the expansion ratios of the ABAB composite coatings in Examples 2 and 3 were higher, and both maintained a low maximum back temperature. With increasing the number of composite layers, the expansion ratio of the coating actually increased, and the maximum back temperature further decreased, indicating that the composite method of this application has a better synergistic effect. Comparative Example 1, prepared with a fire-retardant coating identical to the bottom layer in the examples, had the smallest expansion ratio and the highest maximum back temperature, exhibiting the worst fire resistance. Comparative Example 2, prepared with a fire-retardant coating identical to the top layer in the examples, had a higher expansion ratio than Example 1, but its high back temperature was higher than all examples; the high expansion ratio of the top layer did not provide superior fire resistance. Comparative Example 3, prepared by interchanged bottom and top layers in the examples, had a slightly better expansion ratio than the examples, but its maximum back temperature was also significantly higher, resulting in slightly poorer fire resistance.

[0163] Table 1. Coating Test Results

[0164] Cross-sectional views of the expanded layers formed under flame are shown in Figures 1-6. The expanded layer coating obtained in Example 1 of this application shows a more obvious expansion effect of both the bottom layer and the top layer. The bottom layer expanded layer is denser than the layer in Comparative Example 1 where the expansion is mainly caused by a physical expanding agent, and its adhesion to the substrate is also better. Examples 2 and 3 used the ABAB construction method, with thinner layers. During construction, the diffusion layer between layers was more pronounced, leading to unclear distinction between the bottom and top layers after expansion. However, this composite method actually increased the overall expansion ratio of the coating and further reduced the back temperature, resulting in a synergistic and enhanced fire-retardant effect. Furthermore, the expanded layers in all examples expanded sufficiently, and the internal pores of the expanded layers were much smaller than those in the comparative examples. The adhesion between the expanded layers in the examples and the substrate was also superior to that in the comparative examples.

[0165] Corresponding to the aforementioned expansion layer, the temperature rise curves of the back side of the sample under flame are shown in Figures 7-12. The temperature rise curves of the examples all show lower back temperatures and relatively smaller heating rates, while the comparative examples show relatively larger heating rates and maximum back temperatures. This is because, when coatings with gas-foaming expanders as the main expansion component expand at high temperatures, they easily expand near the flame to form fine foam structures; however, in the deeper layers of the coating further from the flame, gas expansion is more difficult, and it is more likely to aggregate to form larger pores. These large pores provide conditions for thermal convection, increasing the heating rate and raising the back temperature, which is why Comparative Example 2 has poor fire resistance. When all physical expanders are used, the thermal conductivity of the expansion layer formed by the coating is high, and it cannot form a closed, insulating space, resulting in a high heating rate and high back temperature, which is why Comparative Example 1 has poor fire resistance. In the examples, the surface coating used a gas-expanding agent, while the deep coating used a physical expanding agent. Although physical expanding agents such as expanded graphite have high thermal conductivity, they expand uniformly at high temperatures, forming a uniform expanded heat insulation layer. Compared to an expanded layer with large pores, this actually reduces the heating rate and lowers the back temperature. In Comparative Example 3, the coatings using physical expanding agents and those using gas-expanding agents were used in reverse order; neither of the advantages was utilized, resulting in poor fire resistance.

[0166] Of course, the above description is not intended to limit this application, and this application is not limited to the examples given above. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of this application should also fall within the protection scope of this application.

Claims

1. A multi-layer composite intumescent fire-retardant coating, comprising a base fire-retardant coating containing a physical expanding agent and a surface fire-retardant coating containing a gas-foaming expanding agent.

2. The multi-layer composite intumescent fire-retardant coating as described in claim 1, wherein, The underlying fire-retardant coating comprises component A and component B. Component A comprises the following raw materials in parts by weight: 20-60 parts of adhesive 1-40 parts of acid catalyst; Component B comprises the following raw materials in parts by weight: 5-35 parts of curing agent Physical expansion agent 0.2-20 parts.

3. The multi-layer composite intumescent fire-retardant coating as described in claim 2, wherein, The underlying fire-retardant coating, components A and B, also contain an intumescent layer reinforcing agent.

4. The multi-layer composite intumescent fire-retardant coating as described in claim 3, wherein, The underlying fire-retardant coating comprises two components, A and B. Component A is composed of the following raw materials in parts by weight: 20-60 parts of adhesive 1-40 parts of acid catalyst 0-20 parts of expansion layer reinforcing agent; Component B consists of the following raw materials in parts by weight: 5-35 parts of curing agent Physical expansion agent 0.2-20 parts 0-20 parts of expansion layer reinforcing agent.

5. The multilayer composite intumescent fire-retardant coating as described in claim 1, wherein, The physical expansion agent is at least one of expanded graphite, vermiculite, perlite, resinstone, and obsidian.

6. The multi-layer composite intumescent fire-retardant coating as described in claim 1, wherein, The surface fire-retardant coating comprises a first component and a second component, wherein the first component comprises the following raw materials in parts by weight: 20-60 parts of adhesive and 1-40 parts of acid catalyst; The second component comprises the following raw materials in parts by weight: 5-35 parts of curing agent 1-20 parts of gas-blown expanding agent.

7. A multi-layer composite intumescent fire-retardant coating as described in claim 6, wherein, The first and second components of the surface fire-retardant coating also include an intumescent layer reinforcing agent.

8. The multilayer composite intumescent fire-retardant coating as described in claim 7, wherein, The surface fireproof coating comprises a first component and a second component, wherein the first component is composed of the following raw materials in parts by weight: 20-60 parts adhesive, 1-40 parts acid catalyst, and 0-20 parts expansion layer reinforcing agent; The second component consists of the following parts by weight of raw materials: 5-35 parts of curing agent 1-20 parts of gas-blown expanding agent 0-20 parts of expansion layer reinforcing agent.

9. A multi-layer composite intumescent fire-retardant coating as described in claim 1, wherein, The gas-foaming expander includes one or more of nitrogen-containing compounds, polymers, derivatives, or coatings, or the gas-foaming expander includes compounds capable of releasing water, carbon dioxide, or flame-retardant gases, or the gas-foaming expander includes natural minerals.

10. A method for preparing a fire-retardant coating as described in any one of claims 1 to 9, comprising the following steps: Preparation of the base fire-retardant coating; Prepare a surface fire-retardant coating.

11. The method for preparing a multilayer composite intumescent fire-retardant coating as described in claim 10, wherein, The steps for preparing the base fire-retardant coating specifically include: All components except the curing agent and physical expansion agent are mixed in proportion and dispersed at high speed to obtain component A; A physical expansion agent is added to the curing agent and dispersed at high speed to obtain component B; Mix component A and component B evenly to obtain the base fire-retardant coating.

12. The method for preparing a multilayer composite intumescent fire-retardant coating as described in claim 10, wherein, The steps for preparing a surface fire-retardant coating specifically include: All components except the curing agent and the gas-blowing expansion agent are mixed in proportion and dispersed at high speed to obtain the first component; A gas-blowing expansion agent is added to the curing agent and dispersed at high speed to obtain the second component; The first and second components are mixed evenly to obtain a surface fireproof coating.

13. The multilayer composite intumescent fire-retardant coating as described in any one of claims 1 to 9 is applied to the fire protection of steel, concrete, and wooden structures or components.

14. A method for fireproofing a substrate, comprising the following steps: S1. Substrate surface pretreatment; S2. Apply the bottom fire-retardant coating of any one of claims 1 to 9 to the surface of the substrate until the desired thickness is achieved; S3. Apply the top layer of fire-retardant coating according to any one of claims 1 to 9 onto the base fire-retardant coating after gelation until the desired thickness is achieved.

15. The fireproofing treatment method as described in claim 14, wherein, The bottom fireproof coating and the top fireproof coating are overlapped in sequence multiple times to form an ABAB… type coating.

16. The fireproofing treatment method as described in claim 14, wherein, Apply an anti-aging coating to the surface of the fire-retardant coating, with a thickness of 20-50μm.

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