A UV-responsive biodegradable acrylic self-healing coating and its preparation method

Abstract

This invention relates to the field of coating materials technology, specifically to a UV-responsive biodegradable acrylic self-healing coating and its preparation method. This coating introduces photoresponsive coumarin groups into the side chains of acrylic prepolymers and synergistically embeds polyethylene glycol nanogels containing o-nitrobenzyl photo-crack crosslinking points. At room temperature, using 365nm UV light, it achieves a dual response of surface self-healing and internal photodegradation. Under the crosslinking effect of the outer coumarin layer, the resulting coating can rapidly heal microcracks while maintaining high adhesion and hardness. Under long-term or high-energy UV irradiation, the photo-crack bonds within the nanogel break and become hydrophilic, gradually forming swellable soft domains in the coating, thereby achieving controlled peeling and degradation. This realizes a temporal transition from coating stability during service life to degradability in the later stages, exhibiting characteristics such as low-energy triggering, repeatable repair, and controllable desorption. It is suitable for intelligent protection, renewable surfaces, and environmentally friendly photocuring applications.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to a UV-responsive biodegradable acrylic self-healing coating and its preparation method. Background Technology

[0002] Acrylic photocurable coatings are widely used in metal protection, automotive coatings, and optical component protection due to their fast curing speed, high mechanical strength, and good weather resistance. However, after curing, these coatings form a highly cross-linked and dense structure, which makes it difficult for them to repair themselves once microcracks or surface scratches appear. Microcracks are also prone to propagate under sunlight and humid conditions, causing photoaging, loss of gloss, and corrosion failure.

[0003] To improve service reliability, researchers have attempted to introduce reversible chemical bonds or microcapsule-type repair systems into polymers, such as thermally reversible Diels-Alder bonds, hydrogen bond recombination, or flow repair agents. However, these solutions often require high-temperature triggering or the addition of external chemical components, making them unsuitable for outdoor ambient temperature environments. In addition, with the increasing demand for sustainable development, the degradability and peelability of traditional coatings have become new focuses of attention.

[0004] Currently, material degradation can be achieved by introducing hydrolyzable structures such as acid-sensitive or ester bonds. However, these chemical bonds are prone to premature decomposition due to moisture during the service life, resulting in insufficient durability. Traditional photodegradable systems mostly rely on strong UV or deep ultraviolet irradiation (such as the 254nm band), which has high energy requirements in practical applications and causes serious damage to the substrate and interface. Therefore, coating systems often face the dilemma of either being too stable to degrade or becoming brittle and losing their functionality.

[0005] Therefore, in acrylic photocurable systems, how to simultaneously achieve reversible crosslinking self-healing properties and time-triggered controllable photodegradation behavior under both room temperature and low-energy ultraviolet light irradiation remains a core problem that urgently needs to be solved in this technical field. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose an ultraviolet light-responsive biodegradable acrylic self-healing coating and its preparation method, so as to solve the problem of how to achieve the synergistic effect of self-healing and subsequent controllable photodegradation of acrylic coating under room temperature ultraviolet light irradiation.

[0007] To achieve the above objectives, the present invention provides a UV-responsive biodegradable acrylic self-healing coating, which is formed by coating a substrate surface with a UV-responsive biodegradable acrylic photocurable coating composition and curing it by UV irradiation;

[0008] Before coating, the substrate needs to be pretreated for rust and oil removal. The specific steps are as follows: First, use 200 and 400 grit sandpaper to sand the surface of the substrate in sequence to remove oxide scale and burrs. Then, wipe the surface with anhydrous ethanol to remove oil and let it dry at room temperature for 10 minutes before use.

[0009] Preferably, the thickness of the coated wet film is 55-65 μm.

[0010] Preferably, the wavelength of the ultraviolet light irradiation is 365 nm and the light intensity is 75-85 mW / cm². 2 .

[0011] The preparation steps of the UV-responsive biodegradable acrylic photocurable coating composition are as follows:

[0012] S1: In N,N-dimethylformamide, 7-hydroxy-4-methylcoumarin and 2-bromoethanol were subjected to a nucleophilic substitution reaction under nitrogen atmosphere and at 75-85°C for 15-17 h in the presence of anhydrous potassium carbonate. After the reaction was completed, the product precipitated and was filtered, washed, and dried to obtain an intermediate. The intermediate was then dispersed in anhydrous dichloromethane and reacted with methacryloyl chloride at room temperature for 5-7 h in the presence of triethylamine to carry out an esterification reaction. After the reaction was completed, the organic phase of the product was extracted, washed, dried, filtered, distilled under reduced pressure, and subjected to column chromatography to obtain the photoresponsive coumarin methacrylate monomer.

[0013] S2: In anhydrous dichloromethane, 2-hydroxy-5-nitrobenzyl alcohol and acryloyl chloride are reacted under a nitrogen atmosphere with triethylamine for 1 h, and then stirred at room temperature for 5-7 h to carry out acylation reaction. After the reaction is completed, the organic phase of the product is extracted, washed, dried, filtered, distilled under reduced pressure and recrystallized to obtain the ultraviolet crosslinking agent.

[0014] S3: In anhydrous ethanol, methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate and photoresponsive coumarin methacrylate monomers are used as reactants, 4-cyano-4-(phenylthiocarbamoylthio)valerate is used as a chain transfer agent and 2,2'-azobisisobutyronitrile is used as an initiator. The reaction is carried out under nitrogen atmosphere and stirred at 65-75℃ for 11-13h for free radical polymerization. After the reaction is completed, the solid precipitates from the reaction solution, and after filtration, washing and drying, acrylic prepolymer resin is obtained.

[0015] S4: In anhydrous ethanol, polyethylene glycol methyl ether methacrylate, ultraviolet crosslinking agent, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole were used as monomers, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid was used as chain transfer agent, and 2,2'-azobisisobutyronitrile was used as initiator. The reaction was carried out under nitrogen atmosphere and stirred at 65-75℃ for 7-9 h. After the reaction was completed, the reaction solution was dialyzed and lyophilized to obtain modified polyethylene glycol nanogel.

[0016] S5: Using acrylic prepolymer resin, butyl acrylate, and modified polyethylene glycol nanogel as reactive components, tripropylene glycol diacrylate as a crosslinking agent, 2-hydroxy-2-methyl-1-phenyl-1-propanone as a photoinitiator, and hydroxyethyl methacrylate as a supplement, the mixture is mechanically stirred at room temperature and 200-300 r / min for 25-35 min to form a UV-responsive biodegradable acrylic photocurable coating composition.

[0017] Preferably, the ratio of 7-hydroxy-4-methylcoumarin to 2-bromoethanol in step S1 is 18-22g:28-32g.

[0018] Preferably, the ratio of the intermediate, triethylamine, and methacrylamide chloride used in step S1 is 14-16g:18-22g:17-19g.

[0019] Preferably, the organic phase washing in step S1 is performed sequentially with 1 mol / L hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution.

[0020] Preferably, the column chromatography in step S1 is performed using a volume fraction of ethyl acetate:petroleum ether of 1:4.

[0021] Preferably, the ratio of 2-hydroxy-5-nitrobenzyl alcohol, acryloyl chloride, and triethylamine in step S2 is 18-22g:23-25g:25-27g.

[0022] Preferably, the organic phase washing in step S2 is performed sequentially with 1 mol / L hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution.

[0023] Preferably, the recrystallization in step S2 is carried out using ethyl acetate / petroleum ether (volume fraction 1:3).

[0024] Preferably, the ratio of methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate, photoresponsive coumarin methacrylate monomer, 4-cyano-4-(phenylthiocarbamoylthio)valerate, and 2,2'-azobisisobutyronitrile in step S3 is 48-52g:28-32g:18-22g:9-11g:480-520mg:190-210mg.

[0025] Preferably, the ratio of polyethylene glycol methyl ether methacrylate, ultraviolet crosslinking agent, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, and 2,2'-azobisisobutyronitrile in step S4 is 38-42g:2.5-3.5g:2.5-3.5g:350-450mg:180-220mg.

[0026] Preferably, the dialysis in step S4 is performed in a dialysis bag with a molecular weight cutoff of 10,000 Da.

[0027] Preferably, the ratio of acrylic prepolymer resin, butyl acrylate, modified polyethylene glycol nanogel, tripropylene glycol diacrylate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and hydroxyethyl methacrylate in step S5 is 48-52g:28-32g:14-16g:9-11g:2.5-3.5g:0.8-1.2g.

[0028] Furthermore, the present invention also provides a method for preparing a UV-responsive biodegradable acrylic self-healing coating, comprising the following steps:

[0029] After the substrate is treated to remove oil and rust, the UV-responsive biodegradable acrylic photocurable coating composition is applied to the substrate surface and cured under UV light to form a UV-responsive biodegradable acrylic self-healing coating.

[0030] Preferably, the substrate is Q235 cold-rolled steel sheet.

[0031] The beneficial effects of this invention are:

[0032] This invention creatively achieves a dynamic balance between "surface self-repair and internal photodegradation" in the same system by introducing reversibly photoresponsive coumarin groups into the side groups of acrylic prepolymers and synergistically introducing polyethylene glycol nanogels containing o-nitrobenzyl photo-cracked crosslinking points into the coating structure: the coumarin groups can undergo 2+2 photodimerization under ultraviolet light (e.g., 365 nm) to form reversible crosslinking points, promoting crack closure through local crosslinking and network reconstruction; under higher light doses or different ultraviolet bands, the crosslinking structure can be further reversibly regulated, thereby supporting repeatable repair; the o-nitrobenzyl photo-cracked bonds, as time-sequential activation points, only break under high light dose irradiation, promoting local hydrophilicization of the nanogel and forming microscale swellable regions.

[0033] This partitioned design allows for precise control of the self-repair and degradation processes under illumination conditions, achieving a time-series transition from "stable during service life to degradation at the end of service life." The structure not only maintains high adhesion and hardness but also preserves good mechanical stability after multiple light cycles. Compared to existing repair systems that require high temperatures or chemical triggering, this invention achieves rapid response using low-energy ultraviolet light, significantly reducing energy consumption and improving repeatability. Compared to conventional additive photodegradation systems, this invention localizes and controls degradation behavior by confining photodegradation units within the soft domain of the nanogel, avoiding overall failure.

[0034] In summary, this invention integrates three seemingly contradictory properties: low-energy photorepair, high adhesion, and controlled photodegradation. It achieves programmable switching between repair and degradation and has broad application potential in high-end protective coatings, peelable anti-corrosion protection, and intelligent surface reconstruction. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0036] Figure 1 The infrared spectrum of the UV-responsive biodegradable acrylic self-healing coating prepared in Example 2 of this invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0038] Example 1: A method for preparing a UV-responsive biodegradable acrylic self-healing coating, the specific preparation steps are as follows:

[0039] (1) Take a flask, add 18g of 7-hydroxy-4-methylcoumarin, 23g of anhydrous potassium carbonate and 180mL of N,N-dimethylformamide, purge with nitrogen for 30min, and then add 28g of N,N-dimethylformamide dropwise over 25min at 75℃ under a nitrogen atmosphere. 2-Bromoethanol was added dropwise, and the reaction was stirred for 15 hours after the addition was complete. After the reaction was completed and cooled to room temperature, the resulting reaction solution was slowly poured into ice water to precipitate the solid. After filtration and washing, the solid was dried in a vacuum oven at 40°C to obtain an intermediate. Subsequently, 14 g of the intermediate was dispersed in 140 mL of anhydrous dichloromethane and cooled to 0°C in an ice-water bath. 18 g of triethylamine was added and stirred for 10 min. Then, 17 g of methacryloyl chloride was added dropwise over 25 min. After the addition was complete, the ice bath was removed, and the reaction was stirred for 5 hours at room temperature. After the reaction was completed, ice water was added to the system, and the organic phase was separated by extraction. The organic phase was washed successively with 1 mol / L hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The product was dried over anhydrous magnesium sulfate, filtered, and the crude product obtained by vacuum distillation was purified by silica gel column chromatography (ethyl acetate:petroleum ether ratio of 1:4) to obtain the photoresponsive coumarin methacrylate monomer.

[0040] (2) Take a flask, add 18g of 2-hydroxy-5-nitrobenzyl alcohol and 140mL of anhydrous dichloromethane, cool to 0℃ in an ice-water bath, add 25g of triethylamine and stir evenly, purge with nitrogen for 30min, then add 23g of acryloyl chloride dropwise in a nitrogen atmosphere at 0℃ for 35min. After the addition is complete, continue stirring for 1h, then stir at room temperature for 5h. After the reaction is complete, add ice water and extract the organic phase by layering. Wash the organic phase with 1mol / L hydrochloric acid solution, saturated sodium bicarbonate solution and saturated brine solution in sequence. Dry with anhydrous magnesium sulfate, filter, and distill under reduced pressure. Recrystallize the crude product by ethyl acetate / petroleum ether (volume fraction 1:3) to obtain the ultraviolet crosslinking agent.

[0041] (3) Take a flask, add 48g of methyl methacrylate, 28g of butyl acrylate, 18g of hydroxyethyl methacrylate, 9g of photoresponsive coumarin methacrylate monomer and 90mL of anhydrous ethanol, then add 480mg of 4-cyano-4-(phenylthiocarbamoylthio)valerate as a chain transfer agent and 190mg of 2,2'-azobisisobutyronitrile as an initiator. Stir until completely dissolved, and then stir and react at 65°C for 11h under a nitrogen atmosphere. After the reaction is completed, the resulting reaction solution is cooled to room temperature and then slowly added dropwise to n-hexane for precipitation. After filtration, washing with n-hexane, and drying in a vacuum oven at 40°C for 20h, acrylic prepolymer resin is obtained.

[0042] (4) Take a three-necked flask, add 38g of polyethylene glycol methyl ether methacrylate (weight average molecular weight 1000), 2.5g of UV crosslinking agent, 2.5g of 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole and 180mL of anhydrous ethanol and stir until completely dissolved. Then add 350mg of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid as chain transfer agent and 180mg of 2,2'-azobisisobutyronitrile as initiator. Stir and react at 65℃ for 7h under nitrogen atmosphere. After the reaction is completed, cool to room temperature. The resulting reaction solution is placed in a dialysis bag with a molecular weight cutoff of 10000Da and dialyzed in deionized water for 48h, with the dialyzing water changed every 5h. After the dialyzing is completed, the dialysate is frozen and freeze-dried to obtain modified polyethylene glycol nanogel.

[0043] (5) Take a reaction vessel, add 48g of acrylic prepolymer resin, 28g of butyl acrylate, 14g of modified polyethylene glycol nanogel, then add 9g of tripropylene glycol diacrylate as a crosslinking agent, 2.5g of 2-hydroxy-2-methyl-1-phenyl-1-propanone as a photoinitiator, then add 0.8g of hydroxyethyl methacrylate and add 22g of butyl acrylate and 10g of anhydrous butyl acetate as solvents. Stir mechanically at room temperature and 200r / min for 25min to form a UV-responsive biodegradable acrylic photocurable coating composition.

[0044] (6) Q235 cold-rolled steel plate that has been degreased and derusted is selected as the substrate. The surface of the steel plate is first sanded with 200 and 400 grit sandpaper in sequence to remove oxide scale and burrs. After wiping the surface with anhydrous ethanol to remove oil, it is dried at room temperature for 10 minutes. The UV-responsive biodegradable acrylic photocurable coating composition is then uniformly applied to the surface of the steel plate, and the wet film thickness is controlled to be 55 μm. After application, the plate is left to stand at room temperature for 8 minutes. Then, the test plate is transferred to a light source with a wavelength peak of 365 nm and a light intensity of 75 mW / cm. 2 The coating was initially cured by irradiation under a UV LED surface light source for 4 minutes, followed by irradiation for another 9 minutes, resulting in a UV-responsive biodegradable acrylic self-healing coating.

[0045] Example 2: A method for preparing a UV-responsive, biodegradable acrylic self-healing coating, the specific preparation steps are as follows:

[0046] (1) Take a flask, add 20g of 7-hydroxy-4-methylcoumarin, 25g of anhydrous potassium carbonate and 200mL of N,N-dimethylformamide, purge with nitrogen for 30min, and then add 30g of N,N-dimethylformamide dropwise over 30min at 80℃ under a nitrogen atmosphere. 2-Bromoethanol was added dropwise, and the reaction was stirred for 16 hours after the addition was complete. After the reaction was completed and cooled to room temperature, the resulting reaction solution was slowly poured into ice water to precipitate the solid. After filtration and washing, the solid was dried in a vacuum oven at 40°C to obtain an intermediate. Subsequently, 15 g of the intermediate was dispersed in 150 mL of anhydrous dichloromethane and cooled to 0°C in an ice-water bath. 20 g of triethylamine was added and stirred for 10 min. 18 g of methacryloyl chloride was added dropwise over 30 min. After the addition was complete, the ice bath was removed, and the reaction was stirred for 6 hours at room temperature. After the reaction was completed, ice water was added to the system, and the organic phase was separated by extraction. The organic phase was washed successively with 1 mol / L hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The product was dried over anhydrous magnesium sulfate, filtered, and the crude product obtained by vacuum distillation was purified by silica gel column chromatography (ethyl acetate:petroleum ether ratio of 1:4) to obtain the photoresponsive coumarin methacrylate monomer.

[0047] (2) Take a flask, add 20g of 2-hydroxy-5-nitrobenzyl alcohol and 150mL of anhydrous dichloromethane, cool to 0℃ in an ice-water bath, add 26g of triethylamine and stir evenly, purge with nitrogen for 30min, then add 24g of acryloyl chloride dropwise in a nitrogen atmosphere at 3℃ for 40min. After the addition is complete, continue stirring for 1h, then stir at room temperature for 6h. After the reaction is complete, add ice water and extract the organic phase by layering. Wash the organic phase with 1mol / L hydrochloric acid solution, saturated sodium bicarbonate solution and saturated brine solution in sequence. Dry with anhydrous magnesium sulfate, filter, and distill under reduced pressure. Recrystallize the crude product by ethyl acetate / petroleum ether (volume fraction 1:3) to obtain the ultraviolet crosslinking agent.

[0048] (3) Take a flask, add 50g methyl methacrylate, 30g butyl acrylate, 20g hydroxyethyl methacrylate, 10g photoresponsive coumarin methacrylate monomer and 100mL anhydrous ethanol, then add 500mg 4-cyano-4-(phenylthiocarbamoylthio)valerate as chain transfer agent and 200mg 2,2'-azobisisobutyronitrile as initiator. Stir until completely dissolved, then stir and react at 70℃ for 12h under nitrogen atmosphere. After the reaction is completed, cool the resulting reaction solution to room temperature and slowly add it dropwise to n-hexane for precipitation. After filtration, washing with n-hexane, and drying in a vacuum oven at 40℃ for 22h, acrylic prepolymer resin is obtained.

[0049] (4) Take a three-necked flask, add 40g of polyethylene glycol methyl ether methacrylate (weight average molecular weight 1000), 3g of ultraviolet crosslinking agent, 3g of 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole and 200mL of anhydrous ethanol and stir until completely dissolved. Then add 400mg of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid as chain transfer agent and 200mg of 2,2'-azobisisobutyronitrile as initiator. Stir and react at 70℃ under nitrogen atmosphere for 8h. After the reaction is completed, cool to room temperature. Put the resulting reaction solution into a dialysis bag with a molecular weight cutoff of 10000Da and dialyze in deionized water for 48h, changing the dialysate every 6h. After the dialysate is completed, freeze and freeze-dry the resulting dialysate to obtain modified polyethylene glycol nanogel.

[0050] (5) Take a reaction vessel, add 50g of acrylic prepolymer resin, 30g of butyl acrylate, 15g of modified polyethylene glycol nanogel, then add 10g of tripropylene glycol diacrylate as a crosslinking agent, 3g of 2-hydroxy-2-methyl-1-phenyl-1-propanone as a photoinitiator, then add 1g of hydroxyethyl methacrylate and add 24g of butyl acrylate and 12g of anhydrous butyl acetate as solvents. Stir mechanically at room temperature and 250r / min for 30min to form a UV-responsive biodegradable acrylic photocurable coating composition.

[0051] (6) Q235 cold-rolled steel plate that has been degreased and derusted is selected as the substrate. The surface of the steel plate is first sanded with 200 and 400 grit sandpaper in sequence to remove oxide scale and burrs. After wiping the surface with anhydrous ethanol to remove oil, it is dried at room temperature for 10 minutes. The UV-responsive biodegradable acrylic photocurable coating composition is then uniformly applied to the surface of the steel plate, and the wet film thickness is controlled to be 60 μm. After application, the plate is left to stand at room temperature for 10 minutes. Then, the test plate is transferred to a light source with a wavelength peak of 365 nm and a light intensity of 80 mW / cm. 2 The coating was initially cured by irradiation under a UV LED surface light source for 5 minutes, followed by irradiation for another 10 minutes, resulting in a UV-responsive biodegradable acrylic self-healing coating.

[0052] Example 3: A method for preparing a UV-responsive, biodegradable acrylic self-healing coating, the specific preparation steps are as follows:

[0053] (1) Take a flask, add 22g of 7-hydroxy-4-methylcoumarin, 27g of anhydrous potassium carbonate and 220mL of N,N-dimethylformamide, purge with nitrogen for 30min, and then add 32g of N,N-dimethylformamide dropwise over 35min at 85℃ under a nitrogen atmosphere. 2-Bromoethanol was added dropwise, and the reaction was stirred for 17 hours after the addition was complete. After the reaction was completed and cooled to room temperature, the resulting reaction solution was slowly poured into ice water to precipitate the solid. After filtration and washing, the solid was dried in a vacuum oven at 40°C to obtain an intermediate. Subsequently, 16 g of the intermediate was dispersed in 160 mL of anhydrous dichloromethane and cooled to 0°C in an ice-water bath. 22 g of triethylamine was added and stirred for 10 min. 19 g of methacryloyl chloride was added dropwise over 35 min. After the addition was complete, the ice bath was removed, and the reaction was stirred for 7 hours at room temperature. After the reaction was completed, ice water was added to the system, and the organic phase was separated by extraction. The organic phase was washed successively with 1 mol / L hydrochloric acid solution, saturated sodium bicarbonate solution, and saturated sodium chloride solution. The product was dried over anhydrous magnesium sulfate, filtered, and the crude product obtained by vacuum distillation was purified by silica gel column chromatography (ethyl acetate:petroleum ether ratio of 1:4) to obtain the photoresponsive coumarin methacrylate monomer.

[0054] (2) Take a flask, add 22g of 2-hydroxy-5-nitrobenzyl alcohol and 160mL of anhydrous dichloromethane, cool to 0℃ in an ice-water bath, add 27g of triethylamine and stir evenly, purge with nitrogen for 30min, then add 25g of acryloyl chloride dropwise in a nitrogen atmosphere at 5℃ for 45min. After the addition is complete, continue stirring for 1h, then stir at room temperature for 7h. After the reaction is complete, add ice water and extract the organic phase by layering. Wash the organic phase with 1mol / L hydrochloric acid solution, saturated sodium bicarbonate solution and saturated brine solution in sequence. Dry with anhydrous magnesium sulfate, filter, and distill under reduced pressure. Recrystallize the crude product by ethyl acetate / petroleum ether (volume fraction 1:3) to obtain the ultraviolet crosslinking agent.

[0055] (3) Take a flask, add 52g methyl methacrylate, 32g butyl acrylate, 22g hydroxyethyl methacrylate, 11g photoresponsive coumarin methacrylate monomer and 110mL anhydrous ethanol, then add 520mg 4-cyano-4-(phenylthiocarbamoylthio)valerate as chain transfer agent and 210mg 2,2'-azobisisobutyronitrile as initiator. Stir until completely dissolved, and then stir and react at 75°C for 13h under nitrogen atmosphere. After the reaction is completed, the resulting reaction solution is cooled to room temperature and then slowly added dropwise to n-hexane for precipitation. After filtration, washing with n-hexane, and drying in a vacuum oven at 40°C for 24h, acrylic prepolymer resin is obtained.

[0056] (4) Take a three-necked flask, add 42g of polyethylene glycol methyl ether methacrylate (weight average molecular weight 1000), 3.5g of UV crosslinking agent, 3.5g of 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole and 220mL of anhydrous ethanol and stir until completely dissolved. Then add 450mg of 2-(dodecyltrithiocarbonate)-2-methylpropionic acid as chain transfer agent and 220mg of 2,2'-azobisisobutyronitrile as initiator. Stir and react at 75℃ for 9h under nitrogen atmosphere. After the reaction is completed, cool to room temperature. The resulting reaction solution is placed in a dialysis bag with a molecular weight cutoff of 10000Da and dialyzed in deionized water for 48h, with the dialyzing water changed every 7h. After the dialyzing is completed, the dialysate is frozen and freeze-dried to obtain modified polyethylene glycol nanogel.

[0057] (5) Take a reaction vessel, add 52g of acrylic prepolymer resin, 32g of butyl acrylate, 16g of modified polyethylene glycol nanogel, then add 11g of tripropylene glycol diacrylate as a crosslinking agent, 3.5g of 2-hydroxy-2-methyl-1-phenyl-1-propanone as a photoinitiator, then add 1.2g of hydroxyethyl methacrylate and add 26g of butyl acrylate and 14g of anhydrous butyl acetate as solvents. Stir mechanically at room temperature and 300r / min for 35min to form a UV-responsive biodegradable acrylic photocurable coating composition.

[0058] (6) Select Q235 cold-rolled steel plate that has been degreased and derusted as the substrate. First, use 200 and 400 grit sandpaper to sand the surface of the steel plate in sequence to remove oxide scale and burrs. Wipe the surface with anhydrous ethanol to remove oil and let it dry at room temperature for 10 minutes. Apply the UV-responsive biodegradable acrylic photocurable coating composition evenly to the surface of the steel plate, controlling the wet film thickness to be 65 μm. After coating, let it stand at room temperature for 8-12 minutes. Then, transfer the test plate to a light intensity of 85 mW / cm at a wavelength peak of 365 nm. 2 The coating was initially cured by irradiation under a UV LED surface light source for 6 minutes, followed by 11 minutes of irradiation to obtain a UV-responsive biodegradable acrylic self-healing coating.

[0059] Comparative Example 1: The difference from Example 2 is that no photoresponsive coumarin methacrylate monomer is added in step (3), while the other conditions are the same as in Example 2.

[0060] Comparative Example 2: The difference from Example 2 is that no ultraviolet crosslinking agent is added in step (4), and 3.5g of ultraviolet crosslinking agent is added directly in step (5). The other conditions are the same as in Example 2.

[0061] Comparative Example 3: The difference from Example 2 is that in step (4), 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole is replaced with the benzotriazole UV absorber Tinuvin P, and the other conditions are the same as in Example 2.

[0062] Comparative Example 4: The difference from Example 2 is that in step (4), polyethylene glycol methyl ether methacrylate is replaced with butyl acrylate, and the other conditions are the same as in Example 2.

[0063] Performance testing

[0064] The UV-responsive biodegradable acrylic photocurable coating compositions obtained in the examples and comparative examples were respectively coated on the surface of pretreated Q235 cold-rolled steel sheets, and the wet film thickness was controlled to be 60 μm. After curing, the samples were formed for testing. Each test experiment was performed in parallel three times and the average was taken.

[0065] Coating adhesion rate and mechanical strength test: The samples were tested according to GB / T 9286-2021 "Cross-cut test of paint and varnish film" and GB / T6739-2006 "Determination of pencil hardness of paint film".

[0066] Self-healing performance test under ultraviolet light: Each sample was scratched with a blade to create shallow scratches 0.1 mm wide. The scratch depth was then measured using a three-dimensional optical profilometer. The sample was then subjected to ultraviolet light at a wavelength of 365 nm and an intensity of 80 mW / cm². 2 Under intense ultraviolet LED irradiation, the scratch depth was measured using a three-dimensional optical profilometer after 10 min and 20 min of irradiation. The self-healing efficiency η was calculated based on the scratch depth recovery: η = (h0 - h t ) / h0×100%; where h0 is the scratch depth without irradiation, h t The depth of the scratch after irradiation for t minutes is given; at least 3 scratches are selected for each sample, and the values ​​are measured at 3 locations for each scratch and averaged.

[0067] Degradability and peel strength tests: Take a sample, measure and calculate the coating area A1 on the sample surface, and then test the sample at 365nm wavelength and 100mW / cm². 2 After continuous light irradiation for 40 minutes under light intensity, the sample was immersed in deionized water at 25℃ for 24 hours, and then a 90° peel test was performed. The maximum peel force required was recorded. After peeling was completed, the area of ​​the remaining coating on the sample surface, A2, was measured using the image method. The degradability index was calculated according to the formula: D=(A1-A2) / A1×100%, where A1 is the area of ​​the coating before peeling and A2 is the area of ​​the remaining coating after peeling.

[0068] Weathering resistance test: The sample was placed in a xenon lamp artificial climate aging chamber with a radiation intensity of 65W / m. 2An aging test was conducted at a blackboard temperature of 50℃ and a humidity of 50% for a period of 500 hours. After the test, the adhesion rate was tested again, and the aging resistance was calculated based on the ratio of the adhesion rate before and after the test.

[0069] The test results are shown in Table 1.

[0070] Table 1 Performance Test Results

[0071]

[0072] Data analysis: As can be seen from the data of Examples 1-3 in Table 1, the UV-responsive biodegradable acrylic self-healing coating prepared by the present invention shows an overall coordinated improvement trend in key properties such as adhesion, self-healing rate and aging stability. This composite system achieves a new balance between mechanical properties and photo-triggered self-healing properties, making it both highly tough and low-maintenance in long-term outdoor use.

[0073] As can be seen from the data in Example 2 and Comparative Example 1 in Table 1, the overall performance of the coating is significantly improved after introducing coumarin photoresponsive units into the side groups of the acrylic prepolymer. It can be inferred that the coumarin photocrosslinking structure is more sensitive to weak energy ultraviolet irradiation and can quickly achieve reversible cycloaddition and cleavage in the 365nm band, thereby completing stress recombination and crack closure without heating or chemical addition. Furthermore, the uniformly distributed coumarin side groups after polymerization can form a uniform and stable reversible crosslinking network under light irradiation, which provides short-range flexible energy buffer and avoids stress concentration caused by high temperature or local reaction lag in traditional thermally triggered systems.

[0074] As can be seen from the data of Example 2 and Comparative Example 2 in Table 1, Example 2 shows a significant difference in self-healing rate compared to Comparative Example 2. This is presumably because the cross-linking point structure containing o-nitrobenzyl photolysis is confined within the polyethylene glycol nanogel, rather than being randomly dispersed in the main resin. This localized design allows high-dose ultraviolet light to act first on the internal nanosoft domain, forming a controllable "first-crack-then-swell" channel within the coating, thus exhibiting low peeling force and high integrity under high-energy light irradiation. In addition, the slight improvement in adhesion and aging resistance indicates that this partitioned network fracture did not cause macroscopic structural damage, but instead improved the stability of the substrate-substrate interface through stress relief.

[0075] Table 1 shows that the data from Example 2 and Comparative Example 3 indicate that Example 2 significantly outperforms Comparative Example 3 in terms of aging resistance and self-healing efficiency. This is presumably because the design of introducing benzotriazole-type UV-absorbing monomers into the polyethylene glycol nanogel framework gives the coating a "first absorption, then conduction" light energy distribution characteristic. Compared to physical blending, the covalently fixed absorbing groups still have stable absorption capacity under long-term light exposure. Benzotriazole may be located in the nanoscale soft domain, forming a local UV shielding layer, so that short-wave UV energy is mainly concentrated inside to trigger o-nitrobenzyl photolysis, while the surface layer can still retain sufficient 365nm light for coumarin crosslinking and restoration. Thus, it achieves a partitioned response of simultaneous repair and internal degradation in the same wavelength band. This complex spatiotemporal light flux control is difficult to maintain stably in conventional additive absorption systems. Therefore, the coating can achieve a high level in both anti-aging and self-healing aspects.

[0076] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, Example 2 exhibits both high hardness and excellent self-healing and degradation coordination compared to Comparative Example 4. This is presumably due to the microphase separation structure formed between the hydrophilic segments of the polyethylene glycol nanogel and the hydrophobic segments of the acrylic substrate. This structure can generate a soft-hard phase distribution gradient in the vertical direction after high-energy ultraviolet irradiation, which disperses stress at the interface and reduces the overall peel force. In contrast, Comparative Example 4, which uses completely hydrophobic butyl acrylate, lacks flexible segments that can absorb energy and buffer in a wet environment, resulting in the inability to effectively close the cracks after repair and the inability to soften the optical crack interface.

[0077] from Figure 1 It can be seen that the cured coating obtained in Example 2 is at 1725cm. -1 A strong absorption peak for the C=O stretching vibration of the ester group was observed at 3400 cm⁻¹, proving the successful introduction of the acrylic resin backbone and coumarin lactone structure; -1 The broad peaks on the left and right correspond to the hydrogen bond association vibrations of the residual hydroxyl groups in the system, 2950-2870 cm⁻¹. -1 The range corresponds to the characteristic peaks of aliphatic -CH2- and -CH3 stretching vibrations. (1600 cm⁻¹) -1 The left and right aromatic ring skeleton vibration peaks and 1520 and 1350 cm⁻¹ -1 The asymmetric / symmetric stretching peaks of the aromatic nitro group (Ar-NO2) at 1240, 1160, and 1100 cm⁻¹ collectively characterize the aromatic ring structure containing the photolytic crosslinking point of the ortho-nitrobenzyl group; -1 The presence of strong COC and CO stretching vibration absorptions at various locations indicates that ether and ester bonds have been formed in both the polyethylene glycol nanogel and the acrylate side chains. The simultaneous presence of these characteristic peaks suggests that the coumarin photoresponsive unit, the o-nitrobenzyl photo-cleavage crosslinking point, and the flexible polyethylene glycol segment have all been introduced into the same acrylic acid network structure.

[0078] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A UV-responsive, biodegradable, self-healing acrylic coating, characterized in that, It is formed by coating a substrate surface with a UV-responsive biodegradable acrylic photocurable coating composition and curing it under UV light. The preparation steps of the UV-responsive biodegradable acrylic photocurable coating composition are as follows: S1: 7-hydroxy-4-methylcoumarin and 2-bromoethanol undergo a nucleophilic substitution reaction under nitrogen atmosphere and in the presence of anhydrous potassium carbonate at 75-85°C to form an intermediate; subsequently, the intermediate and methacryloyl chloride are subjected to an esterification reaction at room temperature in the presence of triethylamine to obtain the photoresponsive coumarin methacrylate monomer. S2: 2-Hydroxy-5-nitrobenzyl alcohol is acylated with acryloyl chloride in the presence of triethylamine to obtain a UV crosslinking agent; S3: Using methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate and photoresponsive coumarin methacrylate monomers as reactants, 4-cyano-4-(phenylthiocarbamoylthio)valerate as chain transfer agent and 2,2'-azobisisobutyronitrile as initiator, free radical polymerization reaction is carried out in a nitrogen atmosphere at 65-75℃ to obtain acrylic prepolymer resin; S4: Using polyethylene glycol methyl ether methacrylate, ultraviolet crosslinking agent, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole as the monomer, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid as the chain transfer agent, and 2,2'-azobisisobutyronitrile as the initiator, a free radical polymerization reaction was carried out in a nitrogen atmosphere at 65-75℃ to obtain modified polyethylene glycol nanogels; S5: An acrylic prepolymer resin, butyl acrylate, and modified polyethylene glycol nanogel are used as reactive components, tripropylene glycol diacrylate is used as a crosslinking agent, 2-hydroxy-2-methyl-1-phenyl-1-propanone is used as a photoinitiator, and hydroxyethyl methacrylate is added and stirred to form a UV-responsive biodegradable acrylic photocurable coating composition.

2. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, The ratio of 7-hydroxy-4-methylcoumarin to 2-bromoethanol in step S1 is 18-22g:28-32g.

3. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, The ratio of intermediate, triethylamine, and methacrylamide chloride used in step S1 is 14-16g:18-22g:17-19g.

4. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, In step S2, the ratio of 2-hydroxy-5-nitrobenzyl alcohol, acryloyl chloride, and triethylamine is 18-22g:23-25g:25-27g.

5. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, The ratio of methyl methacrylate, butyl acrylate, hydroxyethyl methacrylate, photoresponsive coumarin methacrylate monomer, 4-cyano-4-(phenylthiocarbamoylthio)valerate, and 2,2'-azobisisobutyronitrile in step S3 is 48-52g:28-32g:18-22g:9-11g:480-520mg:190-210mg.

6. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, In step S4, the ratio of polyethylene glycol methyl ether methacrylate, ultraviolet crosslinking agent, 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole, 2-(dodecyl trithiocarbonate)-2-methylpropionic acid, and 2,2'-azobisisobutyronitrile is 38-42g:2.5-3.5g:2.5-3.5g:350-450mg:180-220mg.

7. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, The ratio of acrylic prepolymer resin, butyl acrylate, modified polyethylene glycol nanogel, tripropylene glycol diacrylate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and hydroxyethyl methacrylate in step S5 is 48-52g:28-32g:14-16g:9-11g:2.5-3.5g:0.8-1.2g.

8. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, Before coating, the substrate needs to be pretreated for rust and oil removal. The specific steps are as follows: First, use 200 and 400 grit sandpaper to sand the surface of the substrate in sequence to remove oxide scale and burrs. Then, wipe the surface with anhydrous ethanol to remove oil and let it dry at room temperature for 10 minutes before use.

9. The UV-responsive biodegradable acrylic self-healing coating according to claim 1, characterized in that, The thickness of the coated wet film is 55-65 μm.

10. A method for preparing a UV-responsive biodegradable acrylic self-healing coating according to any one of claims 1-9, characterized in that, Includes the following steps: After the substrate is treated to remove oil and rust, the UV-responsive biodegradable acrylic photocurable coating composition is applied to the substrate surface and cured under UV light to form a UV-responsive biodegradable acrylic self-healing coating.

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