A high-speed low-temperature curing coating for coil-coated panels and a method for preparing the same

Abstract

The application belongs to the technical field of coating and discloses a high-speed low-temperature curing coating for coil-coated plate and a preparation method thereof, raw materials of the coating include, by weight fraction, 50-65 parts of an epoxy resin matrix, 6-10 parts of a first toughening agent, 2-5 parts of a second toughening agent, 10-16 parts of a trisulfide polythiol curing agent, 3-5 parts of a filler, 1-3 parts of an antioxidant, 0.8-1.5 parts of a leveling agent and 0.5-1 part of benzoin, wherein the epoxy resin matrix is a compound of polyether modified bisphenol A epoxy resin and DOPO modified bisphenol A epoxy resin. Through the compound system of the polyether modified bisphenol A epoxy resin and the DOPO modified bisphenol A epoxy resin, the application realizes the precise balance between toughness and flame-retardant performance, guarantees the excellent fluidity of the coating in a low-temperature environment and endows the coating layer with stable and reliable flame-retardant function; the synergistic design of the double-toughening system greatly improves the bending resistance and impact resistance of the coating layer, solves the inherent brittleness defect of the traditional epoxy coating and meets the deformation requirement in the processing of the coil-coated plate.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, and specifically relates to a high-speed low-temperature curing coating for coil coating and its preparation method. Background Technology

[0002] Coated steel sheets, widely used in construction, home appliances, transportation, and other fields, rely on continuous high-speed coating processes for their production. This places stringent requirements on the high-speed, low-temperature curing of the coatings used in their production. Currently, while epoxy coatings for coated steel sheets on the market possess certain mechanical strength and corrosion resistance, many problems still need to be addressed in practical applications.

[0003] Traditional epoxy coatings often rely on high-temperature or long-term curing. Forcing a faster curing speed to match the pace of high-speed coil-coated sheet production lines often results in incomplete curing, poor surface finish, and defects such as pinholes and sagging. Conversely, low-temperature curing systems frequently suffer from low curing efficiency and insufficient cross-linking density, failing to meet the demands of continuous industrial production. Furthermore, the inherent brittleness of epoxy resins makes traditional coil-coated sheet coatings lack toughness, leading to cracking and peeling during bending and cutting processes, severely impacting product yield. Existing toughening agents added to improve toughness often have poor compatibility with the epoxy matrix, easily causing phase separation and resulting in uneven mechanical properties of the coating, further limiting their application in the coil-coated sheet field. Summary of the Invention

[0004] The present invention aims to improve at least one technical problem in the prior art.

[0005] The first aspect of this invention provides a high-speed, low-temperature curing coating for coil-coated steel sheets, the raw materials comprising, by weight: 50-65 parts epoxy resin matrix, 6-10 parts first toughening agent, 2-5 parts second toughening agent, 10-16 parts trisulfide polythiol curing agent, 3-5 parts filler, 1-3 parts antioxidant, 0.8-1.5 parts leveling agent, and 0.5-1 parts benzoin;

[0006] The epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin in a mass ratio of (3-5):1.

[0007] The first toughening agent is a prepolymer block copolymer of hydroxyl-terminated polybutadiene and bisphenol A epoxy resin;

[0008] The second toughening agent comprises a core and a shell, wherein the core is polybutadiene and the shell is obtained by copolymerizing methyl methacrylate and glycidyl acrylate.

[0009] The high-speed, low-temperature curing coating for coil-coated steel sheets provided in this application is designed for the high-speed production rhythm and low-temperature curing requirements of continuous coil-coated steel sheet processing. It achieves excellent comprehensive performance through the synergistic effect of its components. Specifically, the epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide)-modified bisphenol A epoxy resin in a specific ratio. The polyether-modified bisphenol A epoxy resin provides the coating with good toughness and low-temperature flowability, meeting the coating requirements under low-temperature curing conditions. The DOPO-modified bisphenol A epoxy resin, through chemical modification, introduces flame-retardant active groups, imparting flame-retardant functionality to the coating without affecting the mechanical properties of the matrix. The combination of these two components ensures both the structural strength of the coating and a balance between toughness and flame retardancy. The first toughening agent is a prepolymer block copolymer of hydroxyl-terminated polybutadiene and bisphenol A epoxy resin. It introduces flexible segments (derived from the long-chain hydrocarbon structure of hydroxyl-terminated polybutadiene) into the epoxy system through chemical bonding, effectively alleviating the inherent brittleness of epoxy resin and improving the coating's resistance to bending and impact, meeting the deformation requirements during coil coating processing. The second toughening agent adopts a core-shell structure design. The core polybutadiene provides excellent flexible support, while the shell is formed by copolymerizing methyl methacrylate and glycidyl acrylate, possessing both rigidity and reactivity. It can further enhance the coating's toughness through a particle toughening mechanism (the core-shell toughening agent absorbs impact energy through the flexible deformation of the core polybutadiene under stress), and it can also cross-link with the epoxy matrix through the active groups in the shell (derived from the epoxy groups of glycidyl acrylate), ensuring the compatibility of the toughening agent with the matrix and avoiding phase separation problems during use. Trisulfide-based polythiol curing agents exhibit excellent low-temperature reactivity, enabling rapid cross-linking reactions with epoxy groups at lower temperatures. This aligns with the curing rhythm of high-speed coil-coated sheet production lines, shortening production cycles. Furthermore, the addition of fillers optimizes the mechanical strength and corrosion resistance of the coating, synergistically enhancing its service life with other components. Antioxidants inhibit oxidative aging during curing and long-term use, delaying performance degradation. Leveling agents reduce surface tension, promoting rapid leveling during coating and preventing surface defects such as pinholes and orange peel during coil coating, ensuring a smooth and uniform coating. Benzoin, as an auxiliary agent, assists in degassing during curing, further improving the surface quality of the coating and ensuring its compatibility with the industrial production needs and practical application scenarios of coil-coated sheets.

[0010] The core of the low-temperature curing mechanism of the coating in this application revolves around the synergistic reaction between the trisulfide polythiol curing agent and the epoxy system. The trisulfide polythiol curing agent contains multiple active thiol groups in its molecular structure. These groups possess strong nucleophilicity and maintain high reactivity without requiring high temperatures. The activation energy of its reaction with the epoxy groups in the epoxy resin matrix and the second toughening agent shell is significantly lower than that of traditional curing systems, allowing for rapid initiation of the reaction without high-temperature drive. During the reaction, the thiol groups directionally attack the three-membered ring structure of the epoxy ring in the epoxy resin, promoting ring opening and forming stable thioether bonds. The multifunctionality of the trisulfide polythiol allows a single curing agent molecule to simultaneously undergo cross-linking reactions with multiple epoxy groups, rapidly constructing a dense and stable three-dimensional network polymer structure, thereby achieving rapid curing of the coating under low-temperature conditions. This curing mechanism not only ensures curing efficiency and adapts to the pace of high-speed continuous production of coil-coated sheets, but also avoids the damage of high-temperature environments to functional components such as the flexible segments of toughening agents and DOPO flame-retardant groups in the coating. This ensures that the performance advantages of each component are fully utilized, ultimately enabling the coating to maintain high-speed curing characteristics while possessing excellent toughness, strength, flame retardancy, and corrosion resistance.

[0011] The polyether-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and polyethylene glycol in a mass ratio of 100:(20-30); the DOPO-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and DOPO in a mass ratio of 100:(25-35).

[0012] The method for preparing the prepolymer block includes the following steps:

[0013] The hydroxyl-terminated polybutadiene and the bisphenol A epoxy resin were mixed at a mass ratio of 1:(2-4), a catalyst was added, and the mixture was reacted at 80℃-90℃ for 2-3 hours to obtain the prepolymer block.

[0014] The catalyst is dimethylbenzylamine or triphenylphosphine, and the mass of the catalyst accounts for 0.2%-0.5% of the sum of the mass of the hydroxyl-terminated polybutadiene and the bisphenol A epoxy resin.

[0015] Preferably, the mass ratio of the core to the shell is 1:(0.1-0.25).

[0016] Preferably, the mass ratio of methyl methacrylate to glycidyl acrylate is (15-20):(5-8).

[0017] The preparation method of the second toughening agent includes the following steps:

[0018] The polybutadiene was dispersed in water, and then the methyl methacrylate, glycidyl acrylate and initiator were added. The mixture was reacted at 60℃-70℃ for 1-2 hours, heated to 80℃ and held for 1 hour, cooled to room temperature and centrifuged. The solid product was then freeze-dried to obtain the second toughening agent.

[0019] Preferably, the filler comprises at least one of quartz powder, mica powder, talc powder, silica, and alumina.

[0020] Preferably, the antioxidant includes at least one of antioxidant 168, antioxidant 1010, and antioxidant 1017.

[0021] Preferably, the leveling agent includes at least one of leveling agent F-400, leveling agent F-401, and leveling agent DH-4036.

[0022] A second aspect of the present invention provides a method for preparing the above-mentioned high-speed low-temperature curing coating for coil-coated steel sheets, comprising the following steps:

[0023] The epoxy resin matrix, the first toughening agent, and the second toughening agent are added to a high-speed mixer for a first stirring and mixing to obtain mixture A;

[0024] Add the curing agent, the filler, the antioxidant, the leveling agent, and the benzoin to the mixture A, and perform a second stirring and mixing to obtain mixture B;

[0025] The mixture B is fed into a twin-screw extruder through a feed port for melt extrusion, cooling, tableting, crushing, and sieving to obtain the high-speed low-temperature curing coating for coil coating.

[0026] The first stirring and mixing speed is 800 r / min-1200 r / min, and the time is 30 min-40 min.

[0027] The second stirring and mixing speed is 1000r / min-1500r / min, and the time is 20min-30min.

[0028] The melt extrusion temperature is 120℃-150℃, and the screw speed is 300r / min-500r / min.

[0029] The beneficial effects of this invention are as follows: This invention achieves a precise balance between toughness and flame retardancy through a compound system of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin. This ensures excellent flowability of the coating at low temperatures while providing stable and reliable flame retardant properties. Combined with the synergistic design of the dual toughening system, it significantly improves the coating's resistance to bending and impact, overcoming the inherent brittleness of traditional epoxy coatings and meeting the deformation requirements during coil coating processing. The good compatibility and optimized interfacial bonding between the components of this invention further ensure the coating's adhesion stability, corrosion resistance, and surface smoothness, extending the service life of coil coating products. Overall, this invention balances product performance, production efficiency, and application reliability, broadening the application scenarios of coil coatings and providing technical support for high-quality, high-efficiency production in the coil coating industry. It has significant industrial promotion value and economic and social benefits. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the description of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0031] Example 1

[0032] A high-speed low-temperature curing coating for coil-coated steel sheets comprises the following raw materials by weight: 58 parts epoxy resin matrix, 8 parts first toughening agent, 3 parts second toughening agent, 13 parts trisulfide polythiol curing agent, 4 parts filler (nano silica), 2 parts antioxidant (antioxidant 168 and antioxidant 1010 are compounded in a mass ratio of 1:1), 1.2 parts leveling agent F-400, and 0.8 parts benzoin.

[0033] The epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin in a mass ratio of 4:1.

[0034] The polyether-modified bisphenol A epoxy resin is obtained by ring-opening addition reaction of bisphenol A epoxy resin (E-51) and polyethylene glycol (PEG-2000) in a mass ratio of 100:25. The preparation method of polyether-modified bisphenol A epoxy resin includes the following steps: adding bisphenol A epoxy resin and polyethylene glycol into a reaction vessel, purging with nitrogen for protection, heating to 125°C and stirring for 30 min to mix them evenly, then adding triphenylphosphine as a catalyst at 0.4% of the total raw material mass, heating to 155°C and reacting for 3.5 h, taking samples every 30 min to detect the epoxy value, and when the epoxy value drops to 0.5 eq / 100 g, cooling to 80°C and vacuum degassing for 30 min to obtain polyether-modified bisphenol A epoxy resin.

[0035] The DOPO-modified bisphenol A epoxy resin is obtained by ring-opening addition reaction of bisphenol A epoxy resin (E-44) and DOPO in a mass ratio of 100:30. The preparation method of DOPO-modified bisphenol A epoxy resin includes the following steps: adding bisphenol A epoxy resin to a reaction vessel, heating to 105°C to melt it, slowly adding DOPO powder while stirring and continuing to stir until completely dispersed, adding 0.3% of zinc 2-ethylhexanoate as a promoter, heating to 135°C and reacting for 2.5 hours, taking samples every 30 minutes to detect the phosphorus content, and when the phosphorus content reaches 5 wt%, cooling to 70°C, adding an appropriate amount of toluene to dilute to a solid content of 85%, filtering to remove unreacted DOPO particles, and vacuum desolventizing to remove toluene to obtain DOPO-modified bisphenol A epoxy resin.

[0036] The first toughening agent is a prepolymer block of hydroxyl-terminated polybutadiene and bisphenol A epoxy resin. The preparation method of the prepolymer block includes the following steps: hydroxyl-terminated polybutadiene and bisphenol A epoxy resin (E-51) are mixed at a mass ratio of 1:3, dimethyl benzylamine is added as a catalyst (the mass of dimethyl benzylamine accounts for 0.3% of the sum of the mass of hydroxyl-terminated polybutadiene and bisphenol A epoxy resin), and the mixture is reacted at 85°C for 2.5 h to obtain the prepolymer block.

[0037] The second toughening agent comprises a core and a shell. The core is polybutadiene, and the shell is obtained by copolymerizing methyl methacrylate and glycidyl acrylate at a mass ratio of 18:6. The preparation method of the second toughening agent includes the following steps: dispersing polybutadiene in 2.5 times its mass of deionized water, stirring to form a uniform emulsion, then adding methyl methacrylate, glycidyl acrylate, and ammonium persulfate accounting for 0.25% of the total mass of polybutadiene, methyl methacrylate, and glycidyl acrylate as an initiator, reacting at 65°C for 1.5 h, raising the temperature to 80°C and holding for 1 h, cooling to room temperature, centrifuging, and freeze-drying the solid product to obtain the second toughening agent.

[0038] The preparation method of this high-speed low-temperature curing coating for coil-coated steel sheets includes the following steps:

[0039] The epoxy resin matrix, the first toughening agent, and the second toughening agent were added to a high-speed mixer for the first stirring and mixing (the first stirring and mixing speed was 1000 r / min and the time was 35 min) to obtain mixture A;

[0040] Add curing agent, filler, antioxidant, leveling agent and benzoin to mixture A, and carry out a second stirring and mixing (the second stirring and mixing speed is 1200 r / min and the time is 25 min) to obtain mixture B;

[0041] Mixture B is fed into a twin-screw extruder through a feed port for melt extrusion (melt extrusion temperature is 135℃, screw speed is 400r / min), cooled, pressed into sheets, crushed, and sieved (200 mesh sieve) to obtain a high-speed low-temperature curing coating for coil coating.

[0042] Example 2

[0043] A high-speed, low-temperature curing coating for coil-coated panels, which differs from Example 1 in that:

[0044] The raw materials, by weight, include 50 parts epoxy resin matrix, 6 parts first toughening agent, 5 parts second toughening agent, 10 parts trisulfide polythiol curing agent, 3 parts filler (talc), 1 part antioxidant (antioxidant 168 and antioxidant 1010 are compounded in a mass ratio of 1:1), 0.8 parts leveling agent F-401, and 0.5 parts benzoin;

[0045] The epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin in a mass ratio of 3:1.

[0046] The polyether-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and polyethylene glycol in a mass ratio of 100:20.

[0047] DOPO-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and DOPO in a mass ratio of 100:25.

[0048] The mass ratio of hydroxyl-terminated polybutadiene to bisphenol A epoxy resin in the raw materials for preparing the first toughening agent is 1:2.

[0049] The mass ratio of methyl methacrylate to glycidyl acrylate in the second toughening agent shell is 15:5.

[0050] Everything else is the same as in Example 1.

[0051] Example 3

[0052] A high-speed, low-temperature curing coating for coil-coated panels, which differs from Example 1 in that:

[0053] The raw materials, by weight, include 65 parts epoxy resin matrix, 10 parts first toughening agent, 2 parts second toughening agent, 16 parts trisulfide polythiol curing agent, 5 parts filler (alumina), 3 parts antioxidant (antioxidant 168 and antioxidant 1010 are compounded in a mass ratio of 1:1), 1.5 parts leveling agent DH-4036, and 1 part benzoin;

[0054] The epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin in a mass ratio of 5:1; the polyether-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and polyethylene glycol in a mass ratio of 100:30; the DOPO-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and DOPO in a mass ratio of 100:35.

[0055] The mass ratio of hydroxyl-terminated polybutadiene to bisphenol A epoxy resin in the raw materials for preparing the first toughening agent is 1:4.

[0056] The mass ratio of methyl methacrylate to glycidyl acrylate in the second toughening agent shell is 5:2.

[0057] Everything else is the same as in Example 1.

[0058] Comparative Example 1

[0059] A coil coating differs from Example 1 in that the epoxy resin matrix is ​​solely bisphenol A epoxy resin (E-51), and the blending system of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin is not used. Otherwise, it is the same as Example 1.

[0060] Comparative Example 2

[0061] A coil coating differs from Example 1 in that the epoxy resin matrix consists only of polyether-modified bisphenol A epoxy resin and does not contain DOPO-modified bisphenol A epoxy resin. Otherwise, it is the same as Example 1.

[0062] Comparative Example 3

[0063] A coil coating differs from Example 1 in that the epoxy resin matrix is ​​solely DOPO-modified bisphenol A epoxy resin, without any polyether-modified bisphenol A epoxy resin compound. Otherwise, it is the same as Example 1.

[0064] Comparative Example 4

[0065] A coil coating for steel sheets differs from Example 1 in that the raw materials do not contain the first toughening agent, and the amount of the second toughening agent is adjusted to 11 parts. Otherwise, it is the same as Example 1.

[0066] Comparative Example 5

[0067] A coil coating differs from Example 1 in that the shell of the second toughening agent is formed solely by the polymerization of methyl methacrylate and does not contain glycidyl acrylate. Otherwise, it is the same as Example 1.

[0068] Comparative Example 6

[0069] A coil coating for steel sheets differs from Example 1 in that the raw materials do not contain a second toughening agent, and the amount of the first toughening agent is adjusted to 11 parts. Otherwise, it is the same as Example 1.

[0070] The coatings prepared in the examples and comparative examples were sprayed onto the surface of the coil coating sheet, and the performance of the coatings obtained after curing was tested, as shown in Table 1.

[0071] Table 1

[0072]

[0073] Referring to the data in Table 1, the high-speed low-temperature curing coating for coil-coated plates prepared in the embodiments of this application exhibits comprehensive and excellent performance due to the synergistic adaptation of each component. The performance differences with each comparative example clearly demonstrate the key role of the core components and the compound system.Compared to the examples, Comparative Example 1 used a single bisphenol A epoxy resin as the matrix without introducing polyether-modified and DOPO-modified components. This resulted in a lack of flexible chain segment support and flame-retardant active group activation in the system. Not only did the low-temperature curing efficiency decrease significantly, but the curing time was also significantly prolonged. Furthermore, the coating toughness was severely insufficient, and the elongation at break was drastically reduced. Simultaneously, the flame-retardant performance failed to meet standards, and the adhesion and corrosion resistance were significantly deteriorated due to poor compatibility between the matrix and other components. Surface quality also exhibited defects such as pinholes and roughness. Comparative Example 2 used only polyether-modified bisphenol A epoxy resin as the matrix, lacking the DOPO-modified component. Its performance compared to the examples showed a clear weakness in flame retardancy, failing to meet the limiting oxygen index and vertical burning rating standards. In terms of curing efficiency... The flame retardant properties, tensile strength, and surface quality of the epoxy resin were similar to those of the example. This difference clearly indicates that the polyether-modified component can effectively ensure the fluidity and basic mechanical properties of the system. However, only by combining it with the DOPO-modified component can a balance between flame retardant properties and other properties be achieved, confirming the necessity of the epoxy resin matrix compound system. Comparative Example 3 is exactly the opposite. It only uses DOPO-modified bisphenol A epoxy resin as the matrix and does not add the polyether-modified component. Although its flame retardant properties are excellent, and its limiting oxygen index and vertical burning rating are comparable to those of the example, the coating brittleness is significantly increased due to the lack of flexibility and low-temperature fluidity brought by the polyether segments. The elongation at break is much lower than that of the example, and the time required for low-temperature curing is also prolonged. At the same time, the adhesion and corrosion resistance are lower. The coating exhibited defects such as brittleness, bending, and powdering, demonstrating the crucial role of the polyether-modified component in improving system toughness, optimizing low-temperature curing efficiency, and enhancing interfacial bonding performance. Comparative Example 4 lacked the first toughening agent, resulting in significantly insufficient toughness, reduced elongation at break, and a decline in adhesion and corrosion resistance compared to the examples. This indicates a synergistic effect between the flexible segments introduced by the first toughening agent through chemical bonding and the particle toughening mechanism of the second toughening agent; a single toughening system cannot achieve the same superior toughness improvement. In Comparative Example 5, the second toughening agent shell was formed solely by the polymerization of methyl methacrylate, lacking the epoxy active groups provided by glycidyl acrylate. This prevented the second toughening agent from bonding with the epoxy through the shell's active groups. When the oxy-resin matrix undergoes effective cross-linking, the compatibility between the two decreases significantly, leading to phase separation. This results in insufficient toughness, a significantly reduced elongation at break, and markedly deteriorated adhesion and corrosion resistance. Defects such as localized cracking also appear on the surface. This contrasts sharply with the effect of the second toughening agent in the example, which achieves good bonding with the matrix and synergistically improves performance through shell epoxy groups. Comparative Example 6 lacks the second toughening agent, resulting in a lower elongation at break than the example, and its surface gloss is not uniform enough. This further confirms the functional compatibility of the two toughening agents in the dual toughening system. The chemical bonding toughening of the first toughening agent and the core-shell particle toughening of the second toughening agent complement each other, jointly ensuring the excellent toughness of the coating. A single toughening system cannot replace the performance improvement effect brought about by the synergy of the two.

[0074] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A high-speed, low-temperature curing coating for coil-coated steel sheets, characterized in that, The raw materials, by weight, include: 50-65 parts epoxy resin matrix, 6-10 parts first toughening agent, 2-5 parts second toughening agent, 10-16 parts trisulfide polythiol curing agent, 3-5 parts filler, 1-3 parts antioxidant, 0.8-1.5 parts leveling agent, and 0.5-1 parts benzoin; The epoxy resin matrix is ​​a compound of polyether-modified bisphenol A epoxy resin and DOPO-modified bisphenol A epoxy resin in a mass ratio of (3-5):

1. The first toughening agent is a prepolymer block copolymer of hydroxyl-terminated polybutadiene and bisphenol A epoxy resin; The second toughening agent comprises a core and a shell, wherein the core is polybutadiene and the shell is obtained by copolymerizing methyl methacrylate and glycidyl acrylate.

2. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The polyether-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and polyethylene glycol in a mass ratio of 100:(20-30); the DOPO-modified bisphenol A epoxy resin is obtained by a ring-opening addition reaction of bisphenol A epoxy resin and DOPO in a mass ratio of 100:(25-35).

3. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The method for preparing the prepolymer block includes the following steps: The hydroxyl-terminated polybutadiene and the bisphenol A epoxy resin were mixed at a mass ratio of 1:(2-4), a catalyst was added, and the mixture was reacted at 80℃-90℃ for 2-3 hours to obtain the prepolymer block. The catalyst is dimethylbenzylamine or triphenylphosphine, and the mass of the catalyst accounts for 0.2%-0.5% of the sum of the mass of the hydroxyl-terminated polybutadiene and the bisphenol A epoxy resin.

4. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The mass ratio of the core to the shell is 1:(0.1-0.25).

5. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The mass ratio of methyl methacrylate to glycidyl acrylate is (15-20):(5-8).

6. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The preparation method of the second toughening agent includes the following steps: The polybutadiene was dispersed in water, and then the methyl methacrylate, glycidyl acrylate and initiator were added. The mixture was reacted at 60℃-70℃ for 1-2 hours, heated to 80℃ and held for 1 hour, cooled to room temperature and centrifuged. The solid product was then freeze-dried to obtain the second toughening agent.

7. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The filler includes at least one of quartz powder, mica powder, talc powder, silica, and alumina.

8. The high-speed low-temperature curing coating for coil-coated steel sheets according to claim 1, characterized in that, The antioxidant includes at least one of antioxidant 168, antioxidant 1010, and antioxidant 1017; And / or, the leveling agent includes at least one of leveling agent F-400, leveling agent F-401 and leveling agent DH-4036.

9. A method for preparing a high-speed, low-temperature curing coating for coil-coated steel sheets as described in any one of claims 1 to 8, characterized in that, Includes the following steps: The epoxy resin matrix, the first toughening agent, and the second toughening agent are added to a high-speed mixer for a first stirring and mixing to obtain mixture A; Add the curing agent, the filler, the antioxidant, the leveling agent, and the benzoin to the mixture A, and perform a second stirring and mixing to obtain mixture B; The mixture B is fed into a twin-screw extruder through a feed port for melt extrusion, cooling, tableting, crushing, and sieving to obtain the high-speed low-temperature curing coating for coil coating.

10. The method for preparing high-speed low-temperature curing coating for coil-coated steel sheets according to claim 9, characterized in that, The first stirring and mixing speed is 800 r / min-1200 r / min, and the time is 30 min-40 min; And / or, the second stirring and mixing speed is 1000 r / min-1500 r / min, and the time is 20 min-30 min; And / or, the melt extrusion temperature is 120℃-150℃, and the screw speed is 300r / min-500r / min.

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