Low temperature fast curing coating material, its preparation method and application

Abstract

The application relates to the technical field of coatings, in particular to a low-temperature rapid curing coating as well as a preparation method and application thereof. The low-temperature rapid curing coating comprises the following raw materials: a polyurethane modified epoxy emulsion, a low-temperature curing agent, a filler, a toughening agent, a dispersing agent, a defoaming agent, a leveling agent, an anti-settling agent and deionized water; the low-temperature curing agent is a modified dicyandiamide microcapsule. The modified dicyandiamide is coated by a low-temperature phase change wall material to form a microcapsule structure. At low temperature, the wall material undergoes solid-liquid phase change and releases the modified dicyandiamide, the active amine hydrogen in the molecule of the modified dicyandiamide can trigger ring-opening polymerization of an epoxy group, meanwhile, the tertiary amine structure in the molecule can synchronously catalyze crosslinking reaction of -NCO groups and hydroxyl groups in a polyurethane phase at low temperature, and a uniform and dense interpenetrating network structure can be formed at low temperature, thereby improving the technical problems of slow curing rate, mismatching of double-network curing and poor film compactness of an epoxy-polyurethane composite coating in a low-temperature environment.

Description

Technical Field

[0001] This application relates to the field of coating technology, and in particular to a low-temperature rapid curing coating, its preparation method, and its application. Background Technology

[0002] Cold chain logistics is a crucial mode of transportation for ensuring the quality and safety of temperature-sensitive goods such as fresh food and pharmaceutical products. With rising consumer demands and increasing food safety requirements, the need for energy conservation, emission reduction, and lightweighting in cold chain transportation equipment is becoming increasingly urgent. The cold chain transport container is the core equipment in cold chain logistics; its insulation performance and weight directly affect transportation energy consumption and loading efficiency. Currently, cold chain transport containers mainly adopt a composite structure of polyurethane (PU) foam insulation layer combined with a metal or fiberglass (FRP) outer shell. The container panels are made by bonding the inner and outer skins to the insulation layer. To reduce the refrigeration energy consumption of cold chain transport containers, the industry commonly adopts a technical solution of coating the outer surface of the container with a radiation-insulating coating.

[0003] In related technologies, during the winter in northern regions and in the low-temperature environment around cold storage facilities, the ambient temperature is often below 10℃ or even below 0℃. The coating curing reaction is very slow, and the viscosity increases significantly, making it impossible to guarantee the construction quality and film-forming performance. This severely limits the construction window for radiation insulation coatings on cold chain transport containers in cold regions, especially for retrofitting existing cold chain vehicles, which is often difficult to implement due to seasonal temperature limitations.

[0004] In conclusion, how to provide a coating that can cure rapidly at low temperatures is a technical problem that urgently needs to be solved.

[0005] It should be noted that the above content is not necessarily prior art, nor is it intended to limit the scope of patent protection of this application. Summary of the Invention

[0006] This application provides a low-temperature rapid curing coating, its preparation method, and its application to solve or alleviate one or more of the technical problems mentioned above.

[0007] In a first aspect, embodiments of this application provide a low-temperature rapid-curing coating, characterized in that it comprises the following raw materials in parts by weight: The composition includes 80-120 parts of polyurethane modified epoxy emulsion, 8-12 parts of low-temperature curing agent, 25-30 parts of filler, 6-10 parts of toughening agent, 0.3-0.7 parts of dispersant, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of leveling agent, 0.8-1.2 parts of anti-settling agent, and 15-25 parts of deionized water. The low-temperature curing agent is a modified dicyandiamide microcapsule.

[0008] Optionally, the filler includes one or more of the following: radiation barrier factor, silica aerogel powder, and hollow glass microspheres.

[0009] Optionally, when the filler is a radiation barrier and silica aerogel powder, the mass ratio of the radiation barrier to silica aerogel powder is (2~5):1.

[0010] Optionally, the toughening agent comprises core-shell MBS elastomer particles and hydroxyl-terminated polybutadiene HTPB, and the mass ratio of the core-shell MBS elastomer particles to the hydroxyl-terminated polybutadiene HTPB is (1~3):1.

[0011] Optionally, the coating may further include 2 to 6 parts by weight of n-tetradecane@mesoporous silica core-shell structured nano-phase change capsules.

[0012] Optionally, the coating may further include 0.3 to 1.5 parts by weight of polydopamine-modified bacterial cellulose nanofibers.

[0013] Secondly, embodiments of this application provide a method for preparing the low-temperature rapid-curing coating described in any one of the above claims, characterized in that the preparation method includes the following steps: S1. Pre-dispersion stage: Deionized water, dispersant, and defoamer are added to a high-speed dispersion kettle in sequence and stirred at 800-1200 r / min. Filler is added, and the speed is increased to 2000-3000 r / min. The mixture is dispersed for 30-45 min until the fineness is ≤30μm to obtain pigment paste. S2. Emulsion preparation stage: Add polyurethane modified epoxy emulsion to the paint mixing tank and stir at 400-600 r / min. Then add toughening agent and stir until uniform to obtain emulsion.

[0014] S3. Mixing stage: Slowly add the pigment paste from step S1 to the emulsion from step S2, stir at 600-800 r / min, add leveling agent, anti-settling agent and low-temperature curing agent, stir until uniform, and the coating can be obtained.

[0015] Optionally, in step S1, the n-tetradecane@mesoporous silica core-shell structured nanophase change capsules are added together with the filler and dispersed together at high speed.

[0016] Optionally, in step S1, the polydopamine-modified bacterial cellulose nanofibers are added to deionized water and pre-dispersed evenly by stirring at a speed of 800~1200 r / min, and then the dispersant and defoamer are added in sequence.

[0017] Thirdly, embodiments of this application provide an application of the low-temperature rapid curing coating described in any of the above claims in radiation heat insulation protection of the surface of cold chain logistics transportation equipment.

[0018] The embodiments of this application employing the above-described technical solution may have the following advantages: 1. By adding polyurethane-modified epoxy emulsion and modified dicyandiamide microcapsules, the modified dicyandiamide is encapsulated by the low-temperature phase change wall material to form a microcapsule structure, which is in a dormant state at room temperature. When the ambient temperature reaches 5~10℃, the wall material undergoes a solid-liquid phase change and releases the modified dicyandiamide. The active amine hydrogen in its molecule can trigger the ring-opening polymerization of epoxy groups. At the same time, the tertiary amine structure in the molecule can simultaneously catalyze the cross-linking reaction of -NCO groups and hydroxyl groups in the polyurethane phase at low temperature, so that the curing start-up time and cross-linking rate of the epoxy and polyurethane dual network are highly matched. A uniform and dense interpenetrating network structure can be formed at low temperature, thereby effectively improving the technical problems of slow curing rate, dual network curing mismatch, and poor film density of epoxy-polyurethane composite coatings at low temperature of about 5℃. 2. The radiation barrier can form a continuous radiation functional pathway in the coating, ensuring the efficiency of infrared radiation heat dissipation; at the same time, the silica aerogel can fully fill the gaps between the radiation barrier particles to build a continuous low thermal resistance barrier. The two form a gradient heat flow regulation mechanism of "surface radiation as the main component and internal barrier as the auxiliary component", maximizing the synergistic effect of heat insulation; in addition, the overall oil absorption of the filler is matched with the wetting ability of the polyurethane modified epoxy emulsion, and the resin can fully encapsulate the filler particles, avoiding interface voids and defects, and ensuring the density and mechanical properties of the coating film. 3. The hydroxyl groups at both ends of the HTPB molecule can participate in the cross-linking reaction of -NCO in the polyurethane phase, covalently integrating the flexible long chain into the IPN network, thereby improving the matrix flexibility at the molecular scale and reducing the brittle-tough transition temperature of the coating; the core-shell MBS elastomer particles are uniformly distributed in the matrix as a micron-scale dispersed phase, absorbing impact energy and terminating crack propagation by inducing crazes and shear bands, thus achieving toughening and reinforcement at the particle scale; without significantly reducing the cross-linking density, hardness and corrosion resistance, the core-shell MBS elastomer particles and hydroxyl-terminated polybutadiene HTPB can significantly improve low-temperature toughness. Detailed Implementation

[0019] The present application will be further described in detail below with reference to the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments shall be performed under conventional conditions or conditions recommended by the manufacturer, and the raw materials used in the following embodiments shall be commercially available unless otherwise specified.

[0020] In a first aspect, embodiments of this application disclose a low-temperature rapid-curing coating, which comprises the following raw materials in parts by weight: The composition comprises 80-120 parts of polyurethane-modified epoxy emulsion, 8-12 parts of low-temperature curing agent, 25-30 parts of filler, 6-10 parts of toughening agent, 0.3-0.7 parts of dispersant, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of leveling agent, 0.8-1.2 parts of anti-settling agent, and 15-25 parts of deionized water; wherein the low-temperature curing agent is modified dicyandiamide microcapsules. It should be noted that the particle size of the modified dicyandiamide microcapsules is 5-15 μm, the activation temperature of the modified dicyandiamide microcapsules is 5-10℃, and the microcapsules use a low-temperature phase change material as the wall material to encapsulate the modified dicyandiamide active component, which is used to trigger epoxy ring-opening and simultaneously catalyze polyurethane crosslinking at an environment of 5-10℃, achieving simultaneous curing of the dual networks. The epoxy equivalent in the polyurethane-modified epoxy emulsion is 500-800 g / mol, and the solid content is 45-55%.

[0021] In this embodiment, by adding polyurethane-modified epoxy emulsion and modified dicyandiamide microcapsules, the modified dicyandiamide is encapsulated by a low-temperature phase change wall material to form a microcapsule structure, which remains dormant at room temperature. When the ambient temperature reaches 5~10℃, the wall material undergoes a solid-liquid phase change and releases the modified dicyandiamide. The active amine hydrogen in the molecule can trigger the ring-opening polymerization of the epoxy group, while the tertiary amine structure in the molecule can simultaneously catalyze the cross-linking reaction of the -NCO group and hydroxyl group in the polyurethane phase at low temperature. This results in a high degree of matching between the curing start-up time and cross-linking rate of the epoxy and polyurethane dual networks, forming a uniform and dense interpenetrating network structure at low temperature. This allows the coating to be surface-dry within 4~8 hours, fully dry within 24 hours, and completely cured after 7 days at 5℃. This effectively improves the technical problems of slow curing rate, dual-network curing mismatch, and poor film density of epoxy-polyurethane composite coatings at low temperatures around 5℃.

[0022] In optional embodiments, the filler includes one or more of the following: radiation barrier factor, silica aerogel powder, and hollow glass microspheres. The radiation barrier factor is formed by doping with metal oxides such as Fe2O3, MnO2, Co2O3, and CuO, and SiO2 aerogel, with a particle size D50 of 2~5 μm.

[0023] In this embodiment, the radiation barrier factor can generate high infrared emissivity through lattice vibration in the 8~14μm atmospheric window band, dissipating the heat absorbed by the coating outward in the form of long-wave radiation, thus achieving active radiative heat dissipation. The silica aerogel, with its nanoporous structure, restricts the thermal motion of gas phase molecules and the thermal conduction of the solid phase, constructing a low thermal resistance barrier at the nanoscale. The hollow glass microspheres reduce the overall thermal conductivity of the coating through the internal static air layer, achieving macroscale barrier heat insulation. The combination of the three forms a multi-level thermal regulation system of radiative heat dissipation, nano-barrier, and hollow heat insulation. The different heat insulation mechanisms work synergistically to significantly improve the overall heat insulation efficiency of the coating.

[0024] In an optional embodiment, when the filler is a radiation barrier and silica aerogel powder, the mass ratio of the radiation barrier to the silica aerogel powder is (2~5):1. For example, the mass ratio of the radiation barrier to the silica aerogel powder is 2:1, 3:1, or 5:1.

[0025] In this embodiment, when the mass ratio of the radiation barrier factor to the silica aerogel powder is (2~5):1, the radiation barrier factor can form a continuous radiation functional pathway in the coating, ensuring the efficiency of infrared radiation heat dissipation; at the same time, the silica aerogel can fully fill the gaps between the radiation barrier factor particles, constructing a continuous low thermal resistance barrier. The two form a gradient heat flow regulation mechanism of "surface radiation as the main component and internal barrier as the auxiliary component", maximizing the heat insulation synergy effect; in addition, the overall oil absorption of the filler under this ratio matches the wetting ability of the polyurethane modified epoxy emulsion, and the resin can fully encapsulate the filler particles, avoiding interface voids and defects, and ensuring the film density and mechanical properties of the coating.

[0026] It should be further explained that, according to Kirchhoff's radiation law, Planck's radiation distribution law, the Stefan-Boltzmann law, and Wien's displacement law, within a specific ambient temperature range of -60℃ to 70℃, the main energy radiation band is 8~14μm. The radiation barrier in the coating has an inverse spinel structure, and the outermost electrons of the special metal oxides are easily excited, resulting in active radiation performance. When the coating is heated, the internal molecular motion is excited, generating spontaneous radiation and releasing energy to the outside, preventing heat from entering the chamber through the heat transfer interface. Thermal radiation accounts for 65%~75% of the total heat dissipation (in still air, windless environment), of which the 8-14μm long-wave infrared accounts for 92-98% of the total radiated heat.

[0027] In optional embodiments, the toughening agent comprises core-shell MBS elastomer particles and hydroxyl-terminated polybutadiene HTPB, and the mass ratio of the core-shell MBS elastomer particles to the hydroxyl-terminated polybutadiene HTPB is (1~3):1. For example, the mass ratio of the core-shell MBS elastomer particles to the hydroxyl-terminated polybutadiene HTPB is 1:1, 5:3, or 3:1.

[0028] In this embodiment, when the mass ratio of core-shell MBS elastomer particles to hydroxyl-terminated polybutadiene HTPB is less than 1:1, HTPB has a long-chain hydrophobic structure. Excessive HTPB will disrupt the charge balance of the aqueous hybrid emulsion, leading to flocculation and stratification of the coating and a significant reduction in shelf life. Simultaneously, a large number of flexible long chains will significantly reduce the IPN crosslinking density, lowering the coating pencil hardness to below 2B, decreasing scratch resistance and salt spray resistance, and resulting in insufficient matrix strength at low temperatures. Cracks are prone to plastic propagation, and vibration fatigue life is reduced. When the mass ratio of core-shell MBS elastomer particles to hydroxyl-terminated polybutadiene HTPB is greater than 3:1, the resin matrix itself is brittle, the stress concentration effect around the MBS particles is significant, and crazes easily develop directly into macroscopic cracks. The elongation at break is insufficient, failing to meet the requirements for low-temperature vibration. The coating requires resistance to cracking; excessive MBS particles are prone to agglomeration, forming interface defects, reducing coating density, and deteriorating water resistance and salt spray resistance. At the same time, an excessively high proportion of organic particles will slightly increase the thermal conductivity, crowding out the volume ratio of functional fillers and indirectly weakening the thermal insulation effect. Therefore, when the ratio of the two is within the above range, the HTPB flexible segments first improve the flexibility of the IPN matrix at the molecular level, reduce the brittle-ductile transition temperature of the coating, and maintain high ductility at -10℃. MBS elastic particles, as micron-sized second phases dispersed in the matrix, induce a large number of micro-silver streaks and shear bands, absorb vibration and impact energy, and terminate crack propagation. The two form a multi-scale synergy of molecular-level toughening and particle-level toughening, which can significantly improve the elongation at break of the coating and increase the impact strength at -10℃, with a significant synergistic effect.

[0029] In an optional embodiment, the coating further includes 2 to 6 parts by weight of n-tetradecane@mesoporous silica core-shell structured nanophase change capsules.

[0030] In this embodiment, the phase transition temperature of n-tetradecane is precisely matched with the curing trigger temperature. When the modified dicyandiamide microcapsules release the active amine, the phase transition capsule undergoes a solid-liquid phase transition simultaneously. The phase transition process is accompanied by an increase in molecular mobility and local volume expansion, which can reduce the local viscosity of the resin around the microcapsules and reduce the diffusion resistance of the active amine molecules. At the same time, the continuous pores of the mesoporous silica shell can serve as molecular diffusion channels, guiding the active amine to penetrate deep into the resin matrix, avoiding excessive concentration of crosslinking points around the microcapsules, and making the overall crosslinking density distribution more uniform.

[0031] In an optional embodiment, the coating further includes 0.3 to 1.5 parts by weight of polydopamine-modified bacterial cellulose nanofibers. It should be noted that the polydopamine-modified bacterial cellulose nanofibers can be prepared by in-situ self-polymerization using Tris buffer solution.

[0032] In this embodiment, polydopamine (PDA) contains a large number of catechol and amino active groups. On the one hand, it firmly binds to the hydroxyl groups on the surface of the inorganic filler through coordination bonds and hydrogen bonds. On the other hand, its active groups can undergo covalent reactions with epoxy groups and polyurethane-NCO groups, building a "molecular bridge" between the filler and the resin, upgrading the physical bond to a chemical bond, and significantly improving the interfacial bonding strength. At the same time, bacterial cellulose nanofibers are one-dimensional nanostructures that can form a three-dimensional continuous network inside the coating, dispersing vibration stress and inhibiting the initiation and propagation of microcracks. Furthermore, the fiber network can fix the filler particles and reduce filler displacement under vibration. This improves the peel strength of the filler-resin interface.

[0033] Secondly, this application also discloses a method for preparing the low-temperature rapid-curing coating according to any of the above-mentioned methods, the method comprising the following steps: S1. Pre-dispersion stage: Deionized water, dispersant, and defoamer are added to a high-speed dispersion kettle in sequence and stirred at 800-1200 r / min. Filler is added, and the speed is increased to 2000-3000 r / min. The mixture is dispersed for 30-45 min until the fineness is ≤30μm to obtain pigment paste. S2. Emulsion preparation stage: Add polyurethane modified epoxy emulsion to the paint mixing tank and stir at 400-600 r / min. Then add toughening agent and stir until uniform to obtain emulsion.

[0034] S3. Mixing stage: Slowly add the pigment paste from step S1 to the emulsion from step S2, stir at 600-800 r / min, add leveling agent, anti-settling agent and low-temperature curing agent, stir until uniform, and the coating can be obtained.

[0035] In this embodiment, the pre-dispersion stage first disperses the filler at high speed, which effectively breaks up filler agglomeration and ensures that the fineness of the pigment slurry meets the standard. In the emulsion preparation stage, low-speed stirring is used to mix the toughening agent and resin emulsion to avoid high shear damaging the colloidal stability of the emulsion. In the mixing stage, medium-low speed stirring is used to mix the pigment slurry and emulsion, and finally, a low-temperature curing agent is added. This reduces the risk of high-speed shear causing the hollow glass microspheres to break and lose their thermal insulation function, while also ensuring that the heat generated by shear causes the modified dicyandiamide microcapsules to release their curing activity prematurely, thus ensuring the storage stability of the coating. The preparation method of this application, through a phased process with gradient speeds, balances filler dispersibility, functional component integrity, and curing agent latency, exhibiting strong process adaptability and industrialization potential.

[0036] In an optional embodiment, in step S1, the n-tetradecane@mesoporous silica core-shell structured nano-phase change capsules are added together with the filler and dispersed at high speed.

[0037] In this embodiment, the n-tetradecane@mesoporous silica phase change capsules use silica as a rigid shell, which has good shear resistance and will not leak during pre-dispersion at room temperature. When dispersed at high speed together with fillers, the agglomeration of phase change capsules can be broken by the collision and shearing action of filler particles, so as to achieve uniform dispersion of nano-phase change capsules in the system.

[0038] In an optional embodiment, in step S1, polydopamine-modified bacterial cellulose nanofibers are added to deionized water and pre-dispersed evenly by stirring at a speed of 800~1200 r / min, and then dispersant and defoamer are added in sequence.

[0039] In this embodiment, the surface of the polydopamine-modified bacterial cellulose is rich in hydrophilic groups. It is first pre-dispersed in an aqueous phase at low rotation speed, which allows the nanofibers to fully swell and deagglomerate, forming a uniform fiber dispersion system. Subsequently, dispersants and other additives are added to further stabilize the fiber dispersion state, reduce fiber breakage and structural damage caused by direct dispersion under high shear, ensure the integrity of the three-dimensional network structure of the nanofibers, and give full play to their interface reinforcement and stress dispersion effects.

[0040] Thirdly, embodiments of this application also disclose the application of any of the above-mentioned low-temperature rapid curing coatings in radiation heat insulation protection of the surface of cold chain logistics transportation equipment.

[0041] In this embodiment, the coating can be rapidly cured into a film at a low temperature of 5°C, which greatly expands the construction window for low-temperature scenarios such as autumn and winter in the north and around cold storage facilities, and meets the construction needs of retrofitting existing cold chain vehicles; at the same time, the coating has multi-level heat insulation function and high toughness and vibration resistance, and can stably exert radiation heat insulation effect for a long time under low temperature vibration conditions on the vehicle, reducing the refrigeration energy consumption of cold chain transportation.

[0042] It should be noted that current cold chain transport containers mainly adopt a composite structure of polyurethane (PU) foam insulation layer combined with a metal or fiberglass outer shell. In high-temperature summer environments, the outer surface temperature of the container can reach 60-70℃, and solar radiation heat load accounts for approximately 60% of refrigeration energy consumption. Traditional container insulation layer thickness is typically 60-100mm, resulting in a large container weight and severely limiting effective loading capacity. Currently, the industry mainly addresses energy conservation and consumption reduction in cold chain transport containers through two approaches: one is to increase the insulation layer thickness to improve thermal insulation performance, but this increases the container weight; the other is to coat the outer surface of the container with a radiation-insulating coating, utilizing the thermal radiation blocking properties of special metal oxides in the long-wave infrared band to reduce the surface temperature of the container. This application involves spraying a coating onto the surface of a polyurethane (PU) foam insulation layer, thereby forming a coating with radiative heat insulation and flexible protective functions. This results in a three-layer structure consisting of a metal or fiberglass shell, an insulation layer, and a coating. The radiative heat insulation effect of the coating compensates for the reduced thickness of the insulation layer, achieving lightweight cold chain transport containers without compromising insulation performance.

[0043] To further illustrate, taking a standard 9.6-meter refrigerated truck as an example, the traditional box body uses an 80mm thick PU insulation layer. The coating proposed in this application forms a 300μm thick layer on the insulation layer, reducing the insulation layer to 60mm. Tests show that after coating, the heat flux density on the outer surface of the box body decreases by ≥30% (summer noon, ambient temperature 38℃), and the equivalent thermal resistance increases by approximately 0.08 (m²·K) / W, compensating for the thermal resistance loss (approximately 0.05 (m²·K) / W) due to the 20mm reduction in insulation layer thickness. The overall insulation performance is no less than the original design. The weight of a single vehicle is reduced by approximately 120-180kg, and the effective loading capacity increases by approximately 2-3%.

[0044] The following specific embodiments provide a more detailed description of this application, but should not be construed as limiting the application. Any modifications or substitutions made to the methods, steps, or conditions of this application without departing from the spirit and substance of this application are within the scope of this application.

[0045]

Example

[0046] Table 1: Raw materials of low-temperature rapid curing coatings in Examples 1-6 Comparative Examples 1-8 The difference from Example 1 is that Comparative Example 1 uses a free amine curing agent.

[0047] The difference from Example 1 is that Comparative Example 2 uses 9.25 parts of added radiation barrier factor and 9.25 parts of SiO2 aerogel powder, with a weight ratio of 1:1.

[0048] The difference from Example 1 is that Comparative Example 3 uses 15.86 parts of added radiation barrier factor and 2.64 parts of SiO2 aerogel powder, with a weight ratio of 6:1.

[0049] The difference from Example 1 is that Comparative Example 4 did not add HTPB.

[0050] The difference from Example 1 is that Comparative Example 5 did not add MBS.

[0051] The difference from Example 1 is that Comparative Example 6 did not include n-tetradecane@mesoporous silica core-shell structured nanophase change capsules.

[0052] The difference from Example 1 is that Comparative Example 7 did not add polydopamine-modified bacterial cellulose nanofibers.

[0053] Comparative Example 8 used a commercially available conventional water-based acrylic radiation insulation coating.

[0054] The following tests were conducted on the coatings formed by the paints provided in Examples 1-6 and Comparative Examples 1-9 of this application. All test samples (coatings) were cured for 7 days in a constant temperature and humidity environment of 5℃±1℃ and 50%±5% relative humidity before testing. The test data are shown in Table 2. The specific test conditions for each item are as follows: 1. Drying time at 5℃: Refer to Method A (filter paper method) of GB / T1728-1979, with a wet film coating thickness of 150μm, and record the time when the filter paper can fall freely and the paint film leaves no sticky marks.

[0055] 2. Relative standard deviation (RSD) of microhardness: Vickers microhardness tester was used with a load of 10gf and a holding time of 10s. Ten test points were randomly selected from each sample to test the hardness value and calculate the relative standard deviation to reflect the uniformity of crosslinking density.

[0056] 3. 2-hour simulated internal temperature rise: A self-made standard simulated cold chain box (300mm×200mm×200mm, 50mm thick polyurethane insulation board) was coated with a 200μm dry film coating on the outer surface; the ambient temperature was 35℃±1℃, the xenon lamp simulated light intensity was 1000W / m², the initial internal temperature was 5℃±0.5℃, and the difference between the internal temperature and the initial value was recorded after 2 hours of sealed testing.

[0057] 4. Elongation at break and tensile strength: Type I dumbbell specimens were prepared according to GB / T528-2009 and tested at room temperature (23℃±2℃) with a tensile rate of 50mm / min.

[0058] 5. Impact resistance at -10℃: Refer to GB / T1732-1993 and use a 1kg hammer; the test plate is placed in a constant temperature environment of -10℃±1℃ for 2 hours before being taken out and tested immediately, and the maximum impact energy without cracking of the coating is recorded.

[0059] 6. Initial adhesion (cross-cut test): Refer to GB / T9286-1998, with a cross-cut spacing of 1mm, and adopt a rating of 0 to 5 (0 being the best).

[0060] 7. 2000h neutral salt spray test: Refer to GB / T1771-2007, use 50±5g / L NaCl solution, pH value 6.5~7.2, test temperature 35℃±2℃, continuous spraying; place the test plate at 20° to the vertical plane, evaluate the coating blistering and rusting level after 2000h (level 0 with no change is the best).

[0061] 8. Color difference ΔE after 800h UV accelerated aging: A UVB-313 lamp was used, with an irradiance of 0.63W / (m²・nm)@313nm. The cycle regime was 4h UV irradiation at 60℃ / 4h condensation at 50℃. The CIELab color difference of the coating after 800h was tested. The smaller the color difference value ΔE, the better the weather resistance.

[0062] Table 2: Test data of coatings prepared from low-temperature rapid-curing coatings of Examples 1-6 and Comparative Examples 1-8 As can be seen from Table 1 and Examples 1-3, the coatings of Examples 1-3 can dry quickly at 5°C, form a dense and uniform film, have excellent salt spray resistance and weather resistance, and have high heat insulation efficiency and strong toughness.

[0063] Based on Examples 2 and 4 and Table 1, it can be seen that Example 4 added n-tetradecane@mesoporous silica core-shell structured nano-phase change capsules. During the curing start-up, n-tetradecane undergoes a solid-liquid phase change simultaneously, locally reducing viscosity and guiding the diffusion of active amines through mesoporous channels. This completely improves the problem of short diffusion distance of amine molecules and concentrated crosslinking points under low temperature and high viscosity conditions. Therefore, the hardness RSD is reduced, but the uniformity of crosslinking density is improved, internal defects of the coating are greatly reduced, and the drying speed, salt spray resistance, and weather resistance are effectively improved.

[0064] As can be seen from Examples 2 and 5 and Table 1, Example 5 added polydopamine-modified bacterial cellulose nanofibers, which effectively enhanced the coating's tensile strength, low-temperature impact resistance, salt spray resistance, aging resistance, and significantly improved long-term service stability.

[0065] Based on Examples 2 and 4-5, as well as Table 1, it can be seen that Example 5 added polydopamine-modified bacterial cellulose nanofibers. The tetradecane@mesoporous silica core-shell structured nano-phase change capsules improved crosslinking uniformity from the curing source and reduced initial film defects. The polydopamine-modified bacterial cellulose nanofibers enhanced long-term service reliability at the interface level. The combination of the two resulted in better coating performance in terms of curing speed, crosslinking uniformity, mechanical toughness, thermal insulation stability, corrosion resistance, and weather resistance.

[0066] Based on Example 2, Comparative Example 1, and Table 1, it can be seen that the free amine in Comparative Example 1 immediately triggers the reaction after being added to the system, without any latency. Furthermore, the catalytic rate of the free amine on epoxy is not matched with the catalytic rate on polyurethane, which easily leads to the asynchronous problem of polyurethane curing first and epoxy crosslinking later. This results in aggravated separation of the two microphases, an increase in internal defects in the coating, and a decrease in resistance to media penetration.

[0067] Based on Example 2, Comparative Examples 2-3, and Table 1, it can be seen that when the mass ratio of the radiation barrier factor to the silica aerogel powder is (2-5):1, the heat insulation efficiency is better.

[0068] As can be seen from Example 2, Comparative Examples 4-5 and Table 1, the compound toughening system not only improves the toughness of the matrix through HTPB, but also retains the strength and corrosion resistance through the highly cross-linked matrix of MBS and IPN.

[0069] Based on Example 5, Comparative Example 6, and Table 1, it can be seen that the tetradecane@mesoporous silica core-shell structured nano-phase change capsules in this example utilize the viscosity-reducing effect of solid-liquid phase change and the guiding effect of mesoporous channels to promote uniform diffusion of curing agent molecules, thereby improving the uniformity of low-temperature curing from the root. Therefore, the microhardness relative standard deviation RSD / % in Comparative Example 6 is relatively large, and the local hardness of the coating fluctuates greatly, indicating uneven distribution of crosslinking points and the existence of problems of "local over-crosslinking and local under-curing".

[0070] As can be seen from Example 5, Comparative Example 7 and Table 1, the addition of polydopamine-modified bacterial cellulose nanofibers can effectively improve properties such as salt spray resistance, aging resistance and low-temperature impact resistance.

[0071] It should be noted that the above are merely preferred embodiments of this application and do not limit the scope of patent protection of this application. Any equivalent structural or procedural changes made using the specification and content of this application, or any direct or indirect application in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A low-temperature, rapid-curing coating, characterized in that, Including the following parts by weight of raw materials: The composition includes 80-120 parts of polyurethane modified epoxy emulsion, 8-12 parts of low-temperature curing agent, 25-30 parts of filler, 6-10 parts of toughening agent, 0.3-0.7 parts of dispersant, 0.1-0.3 parts of defoamer, 0.1-0.3 parts of leveling agent, 0.8-1.2 parts of anti-settling agent, and 15-25 parts of deionized water. The low-temperature curing agent is a modified dicyandiamide microcapsule.

2. The low-temperature rapid-curing coating according to claim 1, characterized in that, The filler includes one or more of the following: radiation barrier factor, silica aerogel powder, and hollow glass microspheres.

3. The low-temperature rapid-curing coating according to claim 2, characterized in that, When the filler is a radiation barrier and silica aerogel powder, the mass ratio of the radiation barrier to silica aerogel powder is (2~5):

1.

4. The low-temperature rapid-curing coating according to claim 1, characterized in that, The toughening agent comprises core-shell MBS elastomer particles and hydroxyl-terminated polybutadiene HTPB, and the mass ratio of the core-shell MBS elastomer particles to the hydroxyl-terminated polybutadiene HTPB is (1~3):

1.

5. The low-temperature rapid-curing coating according to claim 1, characterized in that, The coating also includes 2-6 parts by weight of n-tetradecane@mesoporous silica core-shell structured nano-phase change capsules.

6. The low-temperature rapid-curing coating according to claim 1, characterized in that, The coating also includes 0.3 to 1.5 parts by weight of polydopamine-modified bacterial cellulose nanofibers.

7. A method for preparing the low-temperature rapid-curing coating according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: S1. Pre-dispersion stage: Deionized water, dispersant, and defoamer are added to a high-speed dispersion kettle in sequence and stirred at 800-1200 r / min. Filler is added, and the speed is increased to 2000-3000 r / min. The mixture is dispersed for 30-45 min until the fineness is ≤30μm to obtain pigment paste. S2. Emulsion preparation stage: Add polyurethane modified epoxy emulsion to the paint mixing tank and stir at 400-600 r / min. Then add toughening agent and stir until uniform to obtain emulsion. S3. Mixing stage: Slowly add the pigment paste from step S1 to the emulsion from step S2, stir at 600-800 r / min, add leveling agent, anti-settling agent and low-temperature curing agent, stir until uniform, and the coating can be obtained.

8. The method for preparing the low-temperature rapid-curing coating according to claim 7, characterized in that, In step S1, the n-tetradecane@mesoporous silica core-shell structured nano-phase change capsules are added together with the filler and dispersed at high speed.

9. The method for preparing the low-temperature rapid curing coating according to claim 1, characterized in that, In step S1, polydopamine-modified bacterial cellulose nanofibers are added to deionized water and pre-dispersed evenly by stirring at a speed of 800~1200 r / min. Then, dispersant and defoamer are added in sequence.

10. The application of the low-temperature rapid curing coating according to any one of claims 1 to 6 in radiation heat insulation protection of the surface of cold chain logistics transportation equipment.

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