A low-temperature tank heat preservation anti-cracking foaming composite coating and a preparation method thereof

Abstract

This invention relates to the field of crack-resistant foamed composite coating technology, and discloses a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks and its preparation method; Step 1: Spray a low-temperature resistant epoxy paint onto the surface of the cargo tank, cure at room temperature to form an epoxy primer layer; Step 2: Apply a polyurethane composition to the surface of the epoxy primer layer to form a single-layer foam; lay a crack-resistant layer; repeat the "single-layer foam-crack-resistant layer" process until the required total thickness is reached to obtain the crack-resistant foamed composite coating. The raw materials of the polyurethane composition include component A and component B in a mass ratio of 1:(1~1.03); an epoxy-modified polyurethane containing imidazole groups is introduced into component A to improve the dispersibility of the CoO-loaded filler, thereby improving flame retardancy, and controlling the CoO loading to prevent an increase in thermal conductivity.

Description

Technical Field

[0001] This invention relates to the field of crack-resistant foamed composite coating technology, specifically a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks and its preparation method. Background Technology

[0002] The storage and transportation of cryogenic media such as liquefied natural gas (LNG) and liquid hydrogen are critical links in the energy supply chain, placing stringent requirements on the thermal insulation performance of storage containers. Inadequate insulation in storage tanks can lead to vaporization of the medium, causing a surge in pressure and potentially triggering safety valve activation or even an explosion. Currently, insulation technologies for cryogenic storage tanks mainly fall into two categories: one is the prefabricated insulation panel bonding method, which utilizes the panel seams as flow channels, but suffers from significant heat leakage at the seams, requires additional installation costs, and is not conducive to efficient utilization of tank capacity; the other is the on-site spraying of polyurethane foam, which, while achieving a tight bond with the tank body, is prone to shrinkage and cracking under long-term low-temperature alternating stress, forming through-cracks or even detaching.

[0003] To address the aforementioned issues, existing technologies improve crack resistance by setting up multi-layer composite structures or crack-resistant mesh layers, but the problem of not being able to simultaneously achieve both flame retardancy and thermal insulation performance of the foam layer itself still exists.

[0004] In summary, the preparation of a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks and its preparation method, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a crack-resistant foamed composite coating for insulation of cryogenic cargo tanks includes the following steps: Step 1: Spray a low-temperature resistant epoxy paint onto the surface of the cargo tank and cure it at room temperature to form an epoxy primer layer; Step 2: Form a single layer of foam with polyurethane composition on the surface of epoxy primer; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating.

[0007] In a more optimized manner, the spraying thickness of the polyurethane composition is 20~30mm; the error of the total thickness is 0~15mm; the single-layer foam-crack-stopping layer process is as follows: when the thickness reaches 40~60mm, the first crack-stopping layer is laid, and when the thickness reaches 200~220mm, the second crack-stopping layer is laid.

[0008] In the design, the total thickness of the crack-resistant foamed composite coating is 220~300mm; the thickness of a single spray coating of the polyurethane composition is 2~5mm.

[0009] Depending on the application environment, a protective coating can be sprayed onto the surface of the crack-resistant foamed composite coating; the crack-resistant layer is made of fiberglass mesh with a surface density of 80~200g / m². 2 Preferred concentration: 100~150g / m 2 .

[0010] In a more optimized form, the raw materials of the polyurethane composition include component A and component B in a mass ratio of 1:(1~1.03); The raw materials of component A include the following components: by mass parts, 40-50 parts polyether polyol, 10-15 parts polytetrahydrofuran ether diol, 5-10 parts polycarbonate diol, 5-8 parts epoxy modified polyurethane, 12-22 parts flame retardant, 1.5-2.5 parts foaming agent, 0.3-0.8 parts catalyst, and 10-15 parts foaming agent; The flame retardant comprises melamine cyanurate (CAS No. 14960-06-6) and filler in a mass ratio of 2:(0.5~1); Component B includes: polymethylene polyphenyl polyisocyanate (CAS No. 9016-87-9).

[0011] In the scheme, the mixing process of component A is as follows: 40-50 parts of polyether polyol (model: polyether 4110) are heated to 30-45℃, filler is added and dispersed evenly, followed by 5-8 parts of epoxy-modified polyurethane, 10-15 parts of polytetrahydrofuran ether diol (molecular weight 1500), and 5-10 parts of polycarbonate diol (molecular weight 2000), and mixed evenly; melamine cyanurate and 1.5-2.5 parts of foaming agent (foaming agent is polyurethane rigid foam silicone oil, AK8805) are added, and after cooling to room temperature, 0.3-0.8 parts of catalyst and 10-15 parts of blowing agent (HFO1233zd) are added, and mixed evenly to obtain component A; the catalyst is an organotin catalyst and an amine catalyst with a mass ratio of (1-2):(0.5-1). Component A is stored at room temperature.

[0012] A more optimized method for preparing the epoxy-modified polyurethane is as follows: (1) Epoxy resin E44 is added to acetone and mixed to obtain an epoxy resin solution; Aminated nano-silica is added to acetone and mixed evenly, then the epoxy resin solution is added, and the mixture is reacted at 40~60℃ for 2~3 hours, washed, and nano-silica-modified epoxy resin is obtained; (2) Nano-silica-modified epoxy resin is added to propylene glycol methyl ether acetate and mixed to obtain a modified epoxy resin mixture; In a nitrogen atmosphere, dicyclohexylmethane diisocyanate, polytetrahydrofuran ether diol, 2,2-diimidazolium methane, and catalyst (dibutyltin dilaurate) are added to propylene glycol methyl ether acetate, heated to 80~85℃, reacted for 6~10 hours, catalyst (dibutyltin dilaurate) and modified epoxy resin mixture are added, and stirring is continued for 2~4 hours, cooled to room temperature, and the solvent is removed to obtain epoxy-modified polyurethane.

[0013] Thin-layer chromatography (TLC) was used to monitor the reaction process, and the reaction endpoint was defined as the complete disappearance or very faint appearance of the dicyclohexylmethane diisocyanate spot.

[0014] More optimally, the mass ratio of the aminated nano-silica to epoxy resin E44 is 1:(0.2~0.4); the raw materials of the epoxy-modified polyurethane include the following components by mass: 20~25 parts dicyclohexylmethane diisocyanate, 15~20 parts polytetrahydrofuran ether diol, 1~3 parts 2,2-diimidazolium methane, 0.1~0.3 parts catalyst, 4~8 parts nano-silica modified epoxy resin, and 80~120 parts propylene glycol methyl ether acetate.

[0015] In the scheme, the aminated nano silica is prepared by modification with silane coupling agent; the preparation method of aminated nano silica is as follows: (1) Hydrolysis of KH-550 (γ-aminopropyltriethoxysilane): KH-550, deionized water and ethanol are mixed uniformly in a mass ratio of 21:7:72, acetic acid is added dropwise to adjust the pH to 5, and the mixture is mixed uniformly for 60 minutes to obtain KH-550 hydrolysis solution; (2) Ten parts by weight of nano-silica (particle size of 50 nm) were ultrasonically dispersed in 50 wt% ethanol aqueous solution, and 9.5 parts of KH-550 hydrolysis solution were added. The mixture was reacted at 65 °C for 6 hours, filtered, washed, and dried to obtain aminated nano-silica.

[0016] A more optimized method for preparing the packing material is as follows: cobalt acetylacetonate and hexadecyltrimethylammonium bromide are added to 1-octadecene and mixed. Porous silica, oleic acid, and oleylamine are added. The mixture is degassed with nitrogen for 20-30 minutes, heated to 220-260°C and refluxed for 2-4 hours. After cooling to room temperature, an ethanol / n-hexane mixture is added dropwise over two hours. The mixture is then centrifuged, washed, and dried to form CoO, thus obtaining the packing material.

[0017] In a more optimized form, the raw material for the filler comprises the following components: by mass parts, 0.1-0.3 parts cobalt acetylacetonate, 0.01-0.02 parts hexadecyltrimethylammonium bromide, 12-15 parts 1-octadecene, 2-5 parts porous silica (particle size 200 nm, pore size 2-3 nm), 3-5 parts oleic acid, 7-9 parts oleylamine, and 20-25 parts ethanol / n-hexane mixture; wherein the mass ratio of ethanol to n-hexane in the ethanol / n-hexane mixture is 1:(1-2); and the loading of CoO on the porous silica is 2-6 wt%.

[0018] While traditional polyurethane foam offers excellent thermal insulation, it suffers from poor flame retardancy and uneven filler dispersion. This solution addresses these issues by employing multi-component synergistic modification to improve performance: To address the issues of poor dispersibility and unsatisfactory flame retardant effect of porous silica, this solution involves coating the surface of porous silica with CoO to obtain a special filler. This not only solves the problems of easy agglomeration and uneven dispersion of porous silica in polyurethane matrix, but also endows the filler with good flame retardant properties. At the same time, the imidazole groups contained in the epoxy-modified polyurethane molecular chain can form a stable coordination effect with the cobalt ions on the filler surface, further improving the dispersion uniformity of the filler in the polyurethane system. This allows the filler and melamine cyanurate to form a highly efficient synergistic flame retardant system, significantly improving the flame retardant performance of polyurethane foam.

[0019] During the preparation process, polyether polyol, polytetrahydrofuran ether diol, and polycarbonate diol are heated to 40-50°C, and epoxy-modified polyurethane is added and mixed evenly before adding flame retardant. The coordination effect between cobalt ions on the surface of CoO and imidazole groups of epoxy-modified polyurethane is utilized to enhance the dispersion effect of porous silica, thereby ensuring the flame retardant performance of polyurethane foam. The CoO coating load must be strictly controlled to avoid excessive load damaging the thermal conductivity and insulation performance of the coating.

[0020] A more optimized low-temperature resistant epoxy paint contains the following components by weight: 40-60 parts bisphenol F type epoxy resin, 18-25 parts epoxy modified polyurethane, 3-6 parts liquid nitrile rubber (the liquid nitrile rubber is carboxyl-terminated nitrile rubber with a molecular weight of 3000), 13-20 parts amine curing agent, 0.1-0.5 parts defoamer (BYK-066N), 0.1-0.5 parts leveling agent (BYK-333), and 25-45 parts solvent.

[0021] In the solution, the raw material components of the low-temperature resistant epoxy paint are stored separately. Component A of the low-temperature resistant epoxy paint includes bisphenol F type epoxy resin, epoxy modified polyurethane, liquid nitrile rubber, defoamer, leveling agent, and solvent; Component B of the low-temperature resistant epoxy paint includes curing agent and solvent. When spraying the primer, components A and B are mixed on-site. The solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3.

[0022] In this scheme, aminated nano-silica reacts with the epoxy groups on epoxy resin E44 to obtain nano-silica-modified epoxy resin. By controlling the ratio of dicyclohexylmethane diisocyanate, polytetrahydrofuran ether diol, and 2,2-diimidazole methane, the system is made so that isocyanate groups are the main active groups before adding the nano-silica-modified epoxy resin. In this scheme, controlling the reaction ratio of aminated nano-silica and epoxy resin E44 consumes most of the epoxy groups in the system, avoiding excessive epoxy groups from reacting with 2,2-diimidazole methane first. However, the nano-silica-modified epoxy resin contains hydroxyl and amino groups, which can react rapidly with isocyanate, so it needs to be added slowly to prevent explosive polymerization.

[0023] In this scheme, the introduction of liquid nitrile rubber and nano silica can improve the low-temperature resistance of the epoxy primer layer; and the imidazole ring in the molecular structure of 2,2-diimidazolium methane contains electron-rich nitrogen atoms, which can form coordination and hydrogen bonding with metal atoms or metal oxide layers on the surface of the cargo tank, thereby enhancing the interfacial bonding between the primer and the metal substrate.

[0024] Compared with the prior art, the beneficial effects of the present invention are: 1. The epoxy primer layer uses bisphenol F type epoxy resin, epoxy modified polyurethane and liquid nitrile rubber in synergy, combined with aminated nano silica, to greatly improve the low temperature toughness and crack resistance of the coating, making it suitable for the long-term working environment of low temperature cargo tanks.

[0025] 2. Epoxy-modified polyurethane improves filler dispersion through coordination and forms a synergistic flame retardant system with melamine cyanurate. The CoO coating layer further enhances flame retardancy, solving the problem of poor flame retardancy in traditional polyurethane foam.

[0026] 3. The imidazole groups in the epoxy-modified polyurethane coordinate with the surface of the metal cargo tank, improving the adhesion strength between the epoxy primer layer and the substrate, and preventing the coating from peeling off or delaminating in low-temperature environments. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Raw material preparation: 1. The preparation method of epoxy-modified polyurethane is as follows: (1) Weigh the aminated nano-silica and epoxy resin E44 at a mass ratio of 1:0.4; add epoxy resin E44 to acetone and mix to obtain epoxy resin solution; add aminated nano-silica to acetone and mix evenly, add epoxy resin solution, react at 55°C for 3 hours, wash, dry, and obtain nano-silica-modified epoxy resin; (2) Add 6 parts of nano-silica-modified epoxy resin to A modified epoxy resin mixture was obtained by mixing 12 parts of propylene glycol methyl ether acetate; under a nitrogen atmosphere, 23 parts of dicyclohexylmethane diisocyanate, 20 parts of polytetrahydrofuran ether diol, 2 parts of 2,2-diimidazolium methane, and 0.15 parts of catalyst were added to 80 parts of propylene glycol methyl ether acetate, the mixture was heated to 80°C, and reacted for 6 hours. Then, 0.1 parts of catalyst and the modified epoxy resin mixture were added, and the mixture was stirred for another 3 hours. The mixture was then cooled to room temperature, and the solvent was removed to obtain epoxy-modified polyurethane.

[0029] 2. The preparation method of the filler is as follows: 0.15 parts of cobalt acetylacetonate and 0.018 parts of hexadecyltrimethylammonium bromide are added to 12 parts of 1-octadecene and mixed. 5 parts of porous silica, 3.6 parts of oleic acid and 7 parts of oleylamine are added. The mixture is degassed with nitrogen for 30 minutes, heated to 260℃ and refluxed for 3 hours. After cooling to room temperature, 20 parts of ethanol / n-hexane mixture (ethanol to n-hexane mass ratio of 1:2) are added dropwise over two hours. The mixture is then centrifuged, washed, and dried to form CoO, thus obtaining the filler. The loading amount of CoO on the porous silica is 3.2 wt%.

[0030] Example 1 Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components: by mass parts, 40 parts bisphenol F type epoxy resin, 18 parts epoxy modified polyurethane, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials for component A include the following components by mass: 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts epoxy-modified polyurethane, 13 parts flame retardant, 1.5 parts foam stabilizer, 0.3 parts catalyst, and 13 parts blowing agent (HFO-1233zd); the catalyst includes 0.2 parts dibutyltin dilaurate and 0.1 parts triethylenediamine. The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack-arresting layer process is as follows: when the thickness reaches 60mm, the first crack-arresting layer is laid (the crack-arresting layer is a fiberglass mesh with a surface density of 150g / m²). 2 When the thickness reaches 200mm, a second crack-resistant layer is laid; the total thickness is 260mm.

[0031] Performance testing: 1. Flame retardancy test: The crack-resistant foamed composite coating of Example 1 was cut into cubes (100mm×20mm×20mm) and its flame retardancy was tested according to GBT24061993 standard; the limiting oxygen index was 30.7%. 2. Thermal conductivity test: According to GB / T10294-2008, the thermal conductivity (w / m·k) of the crack-resistant foamed composite coating prepared in Example 1 was tested to be 0.0161 (w / m·k). 3. The pull-out adhesion (MPa) of the low-temperature resistant epoxy paint in Example 1 on the stainless steel substrate was tested according to GB / T-5210-2006; the pull-out adhesion of 10.3 MPa was measured. 4. After the low-temperature resistant epoxy paint is applied to the stainless steel base cloth and fully cured at room temperature, 5 samples are taken and treated at -162±2℃ for 1 hour. According to performance test 3, the pull-out adhesion is tested to be 8.1MPa.

[0032] Example 2 Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components: by mass parts, 40 parts bisphenol F type epoxy resin, 18 parts epoxy modified polyurethane, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials of component A include the following components: by mass parts, 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts epoxy modified polyurethane, 17 parts flame retardant, 1.5 parts foam stabilizer, 0.3 parts catalyst, and 13 parts blowing agent (HFO-1233zd). The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack arresting layer process is as follows: when the thickness reaches 60mm, the first crack arresting layer is laid; when the thickness reaches 200mm, the second crack arresting layer is laid; the total thickness is 260mm.

[0033] Performance testing: The methods for flame retardancy testing and thermal conductivity testing are the same as in Example 1; the limiting oxygen index was 33.1% and the thermal conductivity was 0.0169 (w / m·k).

[0034] Example 3 Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components: by mass parts, 40 parts bisphenol F type epoxy resin, 18 parts epoxy modified polyurethane, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials of component A include the following components: by mass parts, 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts epoxy modified polyurethane, 22 parts flame retardant, 1.5 parts foam stabilizer, 0.3 parts catalyst, and 13 parts blowing agent (HFO-1233zd). The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack arresting layer process is as follows: when the thickness reaches 60mm, the first crack arresting layer is laid; when the thickness reaches 200mm, the second crack arresting layer is laid; the total thickness is 260mm.

[0035] Performance testing: The methods for flame retardancy testing and thermal conductivity testing are the same as in Example 1; the limiting oxygen index was 36.3% and the thermal conductivity was 0.0183 (w / m·k).

[0036] Comparative Example 1 is based on Example 3, except that imidazole groups were not introduced into the epoxy-modified polyurethane; the other operating steps are the same. The preparation method of epoxy modified polyurethane is as follows: (1) Weigh the aminated nano silica and epoxy resin E44 at a mass ratio of 1:0.4; add epoxy resin E44 to acetone and mix to obtain epoxy resin solution; add aminated nano silica to acetone and mix evenly, add epoxy resin solution, react at 55°C for 3 hours, wash, dry, and obtain nano silica modified epoxy resin; (2) Add 6 parts of nano silica modified epoxy resin to 12 parts of propylene glycol methyl ether acetate and mix to obtain modified epoxy resin mixture; in a nitrogen atmosphere, add 23 parts of dicyclohexylmethane diisocyanate, 20 parts of polytetrahydrofuran ether diol, and 0.15 parts of catalyst to 80 parts of propylene glycol methyl ether acetate, heat to 80°C, react for 6 hours, add 0.1 parts of catalyst and modified epoxy resin mixture, continue stirring for 3 hours, cool to room temperature, remove solvent, and obtain epoxy modified polyurethane; Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components: by mass parts, 40 parts bisphenol F type epoxy resin, 18 parts epoxy modified polyurethane, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials of component A include the following components: by mass parts, 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts epoxy modified polyurethane, 22 parts flame retardant, 1.5 parts foam stabilizer, 0.3 parts catalyst, and 13 parts blowing agent (HFO-1233zd). The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack arresting layer process is as follows: when the thickness reaches 60mm, the first crack arresting layer is laid, and when the thickness reaches 200mm, the second crack arresting layer is laid.

[0037] Performance testing: 1. The methods for flame retardancy testing and thermal conductivity testing are the same as in Example 1; the limiting oxygen index was 28.1%; the thermal conductivity was 0.0215 (w / m·k). 2. The method for testing the pull-out adhesion of the low-temperature resistant epoxy paint is the same as in Example 1; the pull-out adhesion was tested to be 9.4 MPa.

[0038] 3. After the low-temperature resistant epoxy paint is applied to the stainless steel base cloth and fully cured at room temperature, 5 samples are taken and treated at -162±2℃ for 1 hour. According to the performance test 3 of Example 1, the pull-out adhesion is tested to be 6.9MPa.

[0039] Comparative Example 2 is based on Example 3, except that the nano-silica modified epoxy resin is used instead of epoxy modified polyurethane; the other operating steps are the same. Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components by weight: 40 parts bisphenol F type epoxy resin, 18 parts nano silica modified epoxy resin, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials of component A include the following components: by mass parts, 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts nano silica modified epoxy resin, 22 parts flame retardant, 1.5 parts foaming agent, 0.3 parts catalyst, and 13 parts foaming agent (HFO-1233zd). The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack arresting layer process is as follows: when the thickness reaches 60mm, the first crack arresting layer is laid, and when the thickness reaches 200mm, the second crack arresting layer is laid.

[0040] Performance testing: The methods for flame retardancy testing and thermal conductivity testing are the same as in Example 1; the limiting oxygen index was 27.0% and the thermal conductivity was 0.0234 (w / m·k).

[0041] Comparative Example 3 is based on Example 3, but with an increased CoO loading; the remaining operating steps are the same. The packing material was prepared as follows: 0.48 parts of cobalt acetylacetonate and 0.05 parts of hexadecyltrimethylammonium bromide were added to 23 parts of 1-octadecene and mixed. Then, 5 parts of porous silica, 9.7 parts of oleic acid, and 18.4 parts of oleylamine were added. The mixture was degassed with nitrogen for 30 minutes, heated to 260℃ and refluxed for 3 hours. After cooling to room temperature, 35 parts of an ethanol / n-hexane mixture (ethanol to n-hexane mass ratio of 1:2) were added dropwise over two hours. The mixture was then centrifuged, washed, and dried to form CoO, thus obtaining the packing material. The loading of CoO on the porous silica was 8.2 wt%. Step 1: Spray low-temperature resistant epoxy paint onto the surface of the cargo tank and cure at room temperature (35℃) to form an epoxy primer layer (100μm thick). The raw materials for the low-temperature resistant epoxy paint include the following components: by mass parts, 40 parts bisphenol F type epoxy resin, 18 parts epoxy modified polyurethane, 4 parts liquid nitrile rubber, 20 parts amine curing agent, 0.2 parts defoamer, 0.2 parts leveling agent, and 35 parts solvent; the solvent is toluene and propylene glycol methyl ether acetate in a mass ratio of 7:3. Step 2: Spray a 20mm thick polyurethane composition onto the epoxy primer layer to form a single layer of foam; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating. The raw materials of component A include the following components: by mass parts, 40 parts polyether polyol, 15 parts polytetrahydrofuran ether diol, 10 parts polycarbonate diol, 8 parts epoxy modified polyurethane, 22 parts flame retardant, 1.5 parts foam stabilizer, 0.3 parts catalyst, and 13 parts blowing agent (HFO-1233zd). The polyurethane composition comprises components A and B in a mass ratio of 1:1.03. The single-layer foam-crack arresting layer process is as follows: when the thickness reaches 60mm, the first crack arresting layer is laid, and when the thickness reaches 200mm, the second crack arresting layer is laid.

[0042] Performance testing: The methods for flame retardancy testing and thermal conductivity testing are the same as in Example 1; the limiting oxygen index was 37.2% and the thermal conductivity was 0.0301 (w / m·k).

[0043] Results and Discussion: Comparative Example 1 is based on Example 3, except that imidazole groups were not introduced into the epoxy-modified polyurethane; this resulted in reduced filler dispersibility, thus leading to decreased flame retardancy and thermal conductivity. Comparative Example 2 is based on Example 3, except that nano-silica-modified epoxy resin replaced epoxy-modified polyurethane; although the silica content was increased, the dispersibility decreased, resulting in decreased flame retardancy and increased thermal conductivity compared to Example 3. Comparative Example 3 is based on Example 3, but with increased CoO loading; although the flame retardancy was improved, the increased CoO loading led to increased filler thermal conductivity, thus affecting the thermal conductivity of the polyurethane foam.

[0044] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks, characterized in that: The following steps are included: Step 1: Spray a low-temperature resistant epoxy paint onto the surface of the cargo tank and cure it at room temperature to form an epoxy primer layer; Step 2: Form a single layer of foam with polyurethane composition on the surface of epoxy primer; lay a crack-resistant layer; repeat the "single layer foam-crack-resistant layer" process until the required total thickness is achieved to obtain a crack-resistant foamed composite coating.

2. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 1, characterized in that: The spraying thickness of the polyurethane composition is 20~30mm; the error of the total thickness is 0~15mm; the single-layer foam-crack-stopping layer process is as follows: when the thickness reaches 40~60mm, the first crack-stopping layer is laid, and when the thickness reaches 200~220mm, the second crack-stopping layer is laid.

3. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 1, characterized in that: The raw materials of the polyurethane composition include component A and component B in a mass ratio of 1:(1~1.03); The raw materials of component A include the following components: by mass parts, 40-50 parts polyether polyol, 10-15 parts polytetrahydrofuran ether diol, 5-10 parts polycarbonate diol, 5-8 parts epoxy modified polyurethane, 12-22 parts flame retardant, 1.5-2.5 parts foaming agent, 0.3-0.8 parts catalyst, and 10-15 parts foaming agent; The flame retardant comprises melamine cyanurate and filler in a mass ratio of 2:(0.5~1); Component B includes: polymethylene polyphenyl polyisocyanate.

4. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 3, characterized in that: The preparation method of the epoxy-modified polyurethane is as follows: (1) Epoxy resin E44 is added to acetone and mixed to obtain an epoxy resin solution; Aminated nano-silica is added to acetone and mixed evenly, epoxy resin solution is added, and the reaction is carried out at 40~60℃ for 2~3 hours. After washing, nano-silica modified epoxy resin is obtained; (2) In a nitrogen atmosphere, dicyclohexylmethane diisocyanate, polytetrahydrofuran ether diol, 2,2-diimidazolium methane and catalyst are added to propylene glycol methyl ether acetate, the temperature is raised to 80~85℃, the reaction is carried out for 6~10 hours, catalyst and nano-silica modified epoxy resin are added, stirring is continued for 2~4 hours, the temperature is lowered to room temperature, the solvent is removed, and epoxy-modified polyurethane is obtained.

5. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 4, characterized in that: The mass ratio of the aminated nano-silica to epoxy resin E44 is 1:(0.2~0.4); the raw materials of the epoxy-modified polyurethane include the following components by mass: 20~25 parts dicyclohexylmethane diisocyanate, 15~20 parts polytetrahydrofuran ether diol, 1~3 parts 2,2-diimidazolium methane, 0.1~0.3 parts catalyst, 4~8 parts nano-silica modified epoxy resin, and 80~120 parts propylene glycol methyl ether acetate.

6. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 3, characterized in that: The packing material is prepared as follows: cobalt acetylacetonate and hexadecyltrimethylammonium bromide are added to 1-octadecene and mixed. Porous silica, oleic acid, and oleylamine are added. The mixture is degassed with nitrogen for 20-30 minutes, heated to 220-260℃ and refluxed for 2-4 hours. After cooling to room temperature, an ethanol / n-hexane mixture is added dropwise over two hours. The mixture is then centrifuged, washed, and dried to form CoO, thus obtaining the packing material.

7. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 6, characterized in that: The raw materials for the filler include the following components: by mass parts, 0.1-0.3 parts cobalt acetylacetonate, 0.01-0.02 parts hexadecyltrimethylammonium bromide, 12-15 parts 1-octadecene, 2-5 parts porous silica, 3-5 parts oleic acid, 7-9 parts oleylamine, and 20-25 parts ethanol / n-hexane mixture; in the ethanol / n-hexane mixture, the mass ratio of ethanol to n-hexane is 1:(1-2); the loading of CoO on the porous silica is 2-6 wt%.

8. The method for preparing a crack-resistant foamed composite coating for insulation of low-temperature cargo tanks according to claim 1, characterized in that: The raw materials for low-temperature resistant epoxy paint include the following components: by weight, 40-60 parts bisphenol F type epoxy resin, 18-25 parts epoxy modified polyurethane, 3-6 parts liquid nitrile rubber, 13-20 parts amine curing agent, 0.1-0.5 parts defoamer, 0.1-0.5 parts leveling agent, and 25-45 parts solvent.

9. The anti-crack foamed composite coating for insulation of low-temperature cargo tanks is prepared by the method according to any one of claims 1 to 8.