Preparation method and application of low-temperature fast-curing coiled material powder coating

Abstract

The invention belongs to the technical field of coatings, and discloses a preparation method and application of a low-temperature fast-curing coiled material powder coating, and the preparation method comprises the following steps: S1, adding raw materials of the low-temperature fast-curing coiled material powder coating into a high-speed mixer, and mixing for 5-8 minutes at the rotating speed of 1200-1600r / min to ensure that the components are uniformly dispersed; s2, adding the mixture into a double-screw extruder for melt extrusion, wherein the temperature of the double-screw extruder is 80-90 DEG C in a first area, 100-110 DEG C in a second area, 120-130 DEG C in a third area and 110-120 DEG C in a fourth area, and the rotating speed is 200-250 r / min; s3, tabletting and cooling to 40 DEG C or below, after coarse crushing, adopting an ACM pulverizer and a grading screen of 80-120 meshes to obtain the low-temperature fast-curing coiled material powder coating, low-temperature curing and fast film forming are achieved through component cooperation, the process adaptability is high, meanwhile, functional filler modified sericite and modified nanometer aluminum oxide are added, and the low-temperature fast-curing coiled material powder coating is prepared. The two synergistically enhance the corrosion resistance, mechanical strength and environmental adaptability of the powder coating paint film.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coatings, and in particular relates to a preparation method and application of a low-temperature fast-curing coil powder coating. Background Art

[0002] As an efficient and energy-saving metal processing substrate, metal coils are widely used in construction, home appliances, transportation, furniture and other fields. The performance of their surface protective coating directly determines the service life and application scenarios of the metal coils. Therefore, metal coils need to be coated during processing. The pre-coating of metal coils is currently mainly liquid coatings, but the pressure caused by the large amount of volatile organic matter on the environment has greatly hindered its application. Powder coatings have become a new type of coating for metal coil surface protection due to their characteristics of solvent-free volatilization, good environmental protection, high coating utilization rate and excellent performance. Powder coatings are solid powdered synthetic resin coatings composed of solid resins and pigments, fillers and additives. Their dispersion medium is air. They are characterized by no solvent pollution, 100% film formation and low energy consumption.

[0003] Traditional metal powder coatings cure at high temperatures, making them poorly suited for coil production lines (thin substrates can deform at high temperatures). Low-temperature curing powders (such as UV curing) require specialized equipment, which is costly and lacks adhesion. Furthermore, deficiencies in traditional metal coil powder coatings, such as insufficient long-term corrosion protection, lack of self-healing capabilities, lack of antimicrobial properties, and weak self-cleaning capabilities, have become key bottlenecks restricting their application in high-end applications. Therefore, developing a new metal coil powder coating that rapidly cures at low temperatures and combines excellent antimicrobial, corrosion-resistant, and mechanical properties is crucial for extending the service life of metal coils and expanding their application scenarios. Summary of the Invention

[0004] In order to solve the deficiencies mentioned in the above-mentioned background technology, the purpose of the present invention is to provide a preparation method and application of low-temperature fast-curing coil powder coating, which realizes low-temperature curing and rapid film formation through the synergistic combination of components, has high process adaptability, and at the same time adds functional filler modified sericite and modified nano-alumina to enhance the corrosion resistance, mechanical strength and environmental adaptability of the powder coating film.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a low-temperature fast-curing coil powder coating comprises the following steps: S1. Add the raw materials of low-temperature fast-curing coil powder coating into a high-speed mixer at a speed of 1200-1600 r / min and mix for 5-8 minutes to ensure that the components are evenly dispersed. S2. Add the mixed material into a twin-screw extruder for melt extrusion. The temperature of the twin-screw extruder is 80-90°C in zone 1, 100-110°C in zone 2, 120-130°C in zone 3, and 110-120°C in zone 4. The speed is 200-250 r / min. S3. The tablets are cooled to below 40° C., and after coarse crushing, they are crushed using an ACM grinder with a grading screen of 80-120 mesh to obtain the low-temperature fast-curing coil powder coating.

[0006] Preferably, the raw materials of the low-temperature fast-curing coil powder coating include: 45-55 parts of carboxyl polyester resin, 3-6 parts of β-hydroxyalkylamide, 5-10 parts of epoxy resin, 0.1-0.3 parts of organic tin catalyst, 6-12 parts of modified sericite, 15-25 parts of barium sulfate, 1.0-1.5 parts of composite leveling agent, 0.8-1.2 parts of modified nano-alumina, and 0.3-0.6 parts of benzoin; The modified sericite is modified by intercalation of cerium salts, and then the surface is modified with tannic acid iron complex, and finally the polydopamine and benzotriazole corrosion inhibitor are formed by self-polymerization of dopamine. The modified nano-alumina is prepared by in-situ growing nano-zinc oxide coating on the surface of the nano-alumina by a hydrothermal method, then loading Ag and carbon quantum dots for co-modification, and finally grafting fluorosilane to achieve surface super-hydrophobic modification.

[0007] Preferably, the acid value of the carboxyl polyester resin is 40-50 mg KOH / g, the epoxy equivalent weight (EEW) of the epoxy resin is 800, the organic tin catalyst is dibutyltin dilaurate, and the composite leveling agent is a mixture of polybutyl acrylate, polydimethylsiloxane, and perfluoropolyether in a mass ratio of 6:3:1.

[0008] Preferably, the preparation method of modified sericite comprises the following steps: (1) Dispersing sericite in deionized water, ultrasonically treating for 20-40 min, adding cerium nitrate (5% by weight of the total mass of sericite), stirring at 80°C for 4-6 h, centrifuging and washing until neutral, and vacuum drying at 80°C to obtain cerium salt intercalated sericite; (2) The intercalated modified sericite was dispersed in a 50 vol% ethanol solution, tannic acid and ferric chloride were added, reacted at 60 ° C for 3-5 h, centrifuged, washed, and dried to obtain sericite surface-modified with tannic acid iron complex; (3) The surface-modified sericite was dispersed in Tris buffer, dopamine hydrochloride was added, and the mixture was stirred at room temperature for 18 to 24 hours. Benzotriazole was added and stirred for 2 to 4 hours to allow the benzotriazole to be adsorbed into the porous structure of polydopamine. The mixture was washed by centrifugation and dried in a vacuum at 40°C to obtain the modified sericite.

[0009] Preferably, the mass ratio of the intercalated modified sericite, tannic acid and ferric chloride is 5:2:0.5.

[0010] Preferably, the mass ratio of the surface-modified sericite, dopamine hydrochloride and benzotriazole is 6:1:0.4.

[0011] Preferably, the preparation method of modified nano-alumina comprises the following steps: A. Disperse nano-alumina in deionized water, ultrasonicate for 20-40 minutes, add zinc nitrate and hexamethylenetetramine, and hydrothermally react at 90°C for 3-5 hours to grow nano-zinc oxide on the surface of the alumina. Centrifuge, wash, and dry to obtain zinc oxide-coated nano-alumina. B. Disperse the zinc oxide-coated nano-alumina in deionized water, add silver nitrate and ascorbic acid, stir in the dark for 1-3 hours, add 1 mg / mL carbon quantum dot solution, stir at 60°C for 3-5 hours to allow the carbon quantum dots to adsorb in the gaps between the zinc oxide, and centrifuge and wash to obtain co-modified nano-alumina; C. Dispersing the co-modified nano-alumina in ethanol, adding heptadecafluorodecyltrimethoxysilane, refluxing at 80° C. for 4-6 hours to graft the fluorosilane onto the surface, washing by centrifugation, and curing at 120° C. to obtain the modified nano-alumina.

[0012] Preferably, the mass ratio of nano-alumina, zinc nitrate and hexamethylenetetramine is 5:2:1.5.

[0013] Preferably, the mass ratio of zinc oxide-coated nano-aluminum oxide, silver nitrate, and carbon quantum dots is 4:0.1:0.2.

[0014] The invention discloses an application of a low-temperature, fast-curing coil powder coating in the continuous coating of metal coils. The powder coating can be quickly cured at a low temperature of 130-160°C within 1-3 minutes, significantly reducing energy consumption and improving production efficiency.

[0015] Beneficial effects of the present invention: The low-temperature fast-curing coil powder coating of the present invention uses carboxyl polyester resin as the main resin, β-hydroxyalkylamide as the curing agent, and epoxy resin as the auxiliary resin. The organic tin catalyst significantly reduces the activation energy of the reaction between β-hydroxyalkylamide and polyester, promotes low-temperature curing, and the composite leveling agent balances wetting and anti-shrinkage. Benzoin inhibits the blisters produced by the reaction of β-hydroxyalkylamide. Low-temperature curing and rapid film formation are achieved through component synergy. At the same time, functional filler modified sericite and modified nano-alumina are added, and the two synergistically enhance the corrosion resistance, mechanical strength and environmental adaptability of the powder coating film. Compared with traditional coil coatings, the powder coating of the present invention improves salt spray resistance by more than 100% through physical barrier, chemical repair, and super-hydrophobic synergy. It also has self-repairing, antibacterial, and self-cleaning properties. It is suitable for building exterior walls, home appliance housings, automotive parts, etc. with anti-corrosion, weathering, and self-cleaning requirements. The powder coating of the present invention cures quickly at low temperature, is compatible with existing coil coating lines, does not require equipment modification, and has high process adaptability.

[0016] Among them, the modified sericite flake structure is stacked in parallel in the coating to form a maze effect, which prolongs the penetration path of corrosive media such as water, oxygen, and chloride ions, and improves the permeability resistance of the coating; when corrosion occurs on the metal surface (local pH fluctuates between acidic and alkaline), the structure of the polydopamine coating layer is destroyed, releasing the benzotriazole corrosion inhibitor, and at the same time, the interlayer It migrates to the corrosion site to form a Ce-based passivation film and a benzotriazole adsorption film to synergistically inhibit corrosion; the polar groups (hydroxyl and amino groups) of the iron tannate complex and the polydopamine coating layer can form hydrogen bonds with the carboxyl groups of the polyester resin, thereby enhancing the bonding strength between sericite and the resin matrix and reducing interface defects.

[0017] The modified nano-alumina is grafted with heptadecafluorodecyltrimethoxysilane to introduce low surface energy fluorocarbon chains. Combined with the micro-nano rough structure of nano-zinc oxide, the coating surface contact angle is greater than 150°, reducing water adhesion and penetration, and reducing the probability of corrosive medium invasion. Nano-alumina is evenly dispersed in the resin matrix, filling the microscopic pores of the coating, and improving the hardness and impact resistance of the coating through the nano-enhancement effect. Ag nanoparticles are slowly released. , inhibiting the growth of bacteria on the coating surface (especially in humid environments), carbon quantum dots regulate the interface charge to stabilize Ag nanoparticles, preventing them from oxidative agglomeration and extending the antibacterial life. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] Example 1 A modified sericite is prepared by modifying the sericite with a cerium salt intercalation layer, then modifying the surface with a tannic acid iron complex, and finally coating the surface with polydopamine and benzotriazole corrosion inhibitor by self-polymerization of dopamine. The preparation method comprises the following steps: (1) 10 g of sericite was dispersed in 200 mL of deionized water, ultrasonicated for 30 min, cerium nitrate (5% of the total mass of sericite) was added, and stirred at 80 ° C for 6 h. Insert the mixture between the layers, wash it by centrifugation until it is neutral, and dry it in vacuum at 80℃ to obtain cerium salt intercalated sericite; (2) 5 g of intercalated modified sericite was dispersed in 100 mL of 50 vol% ethanol solution, 2 g of tannic acid and 0.5 g of ferric chloride were added, the mixture was reacted at 60 °C for 4 h, centrifuged, washed, and dried to obtain sericite surface-modified with tannic acid iron complex; (3) Disperse 3 g of surface-modified sericite in 100 mL of Tris buffer, add 0.5 g of dopamine hydrochloride, and stir at room temperature for 24 h. Add 0.2 g of benzotriazole and continue stirring for 2 h to allow benzotriazole to be adsorbed into the porous structure of polydopamine. Wash by centrifugation and dry in vacuum at 40 °C to obtain modified sericite.

[0020] Example 2 A modified nano-alumina is prepared by in-situ growing nano-zinc oxide coating on the surface of the nano-alumina by a hydrothermal method, then co-modifying with Ag and carbon quantum dots, and finally grafting fluorosilane to achieve super-hydrophobic modification of the surface. The preparation method comprises the following steps: A. Disperse 5 g of nano-alumina in 100 mL of deionized water, sonicate for 30 min, add 2 g of zinc nitrate and 1.5 g of hexamethylenetetramine, and hydrothermally react at 90 ° C for 4 h to grow nano-zinc oxide on the surface of the alumina. Centrifuge, wash, and dry to obtain zinc oxide-coated nano-alumina. B. Disperse 2 g of zinc oxide-coated nano-alumina in 50 mL of deionized water, add 0.05 g of silver nitrate and 0.01 g of ascorbic acid, stir in the dark for 2 h, add 100 mL of 1 mg / mL carbon quantum dot solution, stir at 60°C for 4 h to allow the carbon quantum dots to adsorb in the gaps between the zinc oxide, and centrifuge and wash to obtain co-modified nano-alumina. C. Disperse 1 g of the co-modified nano-alumina in 50 mL of ethanol, add 0.5 mL of heptadecafluorodecyltrimethoxysilane, reflux at 80° C. for 6 h to graft the fluorosilane onto the surface, wash by centrifugation, and solidify at 120° C. to obtain the modified nano-alumina.

[0021] Example 3 A method for preparing a low-temperature fast-curing coil powder coating comprises the following steps: S1. Add the raw materials of low-temperature fast-curing coil powder coating into a high-speed mixer at a speed of 1200 r / min and mix for 8 minutes to ensure that the components are evenly dispersed; S2, adding the mixed material into a twin-screw extruder for melt extrusion, the temperature of the twin-screw extruder is 80°C in zone 1, 110°C in zone 2, 120°C in zone 3, and 120°C in zone 4, and the speed is 200r / min; S3. The tablets are cooled to below 40° C., and after coarse crushing, they are crushed using an ACM grinder and a grading screen of 80 mesh to obtain the low-temperature fast-curing coil powder coating.

[0022] The low-temperature fast-curing coil powder coating includes the following raw materials in parts by weight: 45 parts of a carboxyl polyester resin with an acid value of 50 mg KOH / g, 6 parts of β-hydroxyalkylamide, 5 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.3 parts of dibutyltin dilaurate, 6 parts of modified sericite, 25 parts of barium sulfate, 0.6 parts of polybutyl acrylate, 0.3 parts of polydimethylsiloxane, 0.1 parts of perfluoropolyether, 1.2 parts of modified nano-alumina, and 0.3 parts of benzoin. The modified sericite is prepared in Example 1, and the modified nano-alumina is prepared in Example 2.

[0023] Example 4 A method for preparing a low-temperature fast-curing coil powder coating comprises the following steps: S1. Add the raw materials of low-temperature fast-curing coil powder coating into a high-speed mixer at a speed of 1600 r / min and mix for 5 minutes to ensure that the components are evenly dispersed; S2, adding the mixed material into a twin-screw extruder for melt extrusion, the temperature of the twin-screw extruder is 90°C in zone 1, 100°C in zone 2, 130°C in zone 3, and 110°C in zone 4, and the speed is 250r / min; S3. The tablets are cooled to below 40° C., and after coarse crushing, they are crushed using an ACM grinder with a 120-mesh grading screen to obtain the low-temperature fast-curing coil powder coating.

[0024] The low-temperature fast-curing coil powder coating includes the following raw materials in parts by weight: 55 parts of a carboxyl polyester resin with an acid value of 40 mg KOH / g, 3 parts of β-hydroxyalkylamide, 10 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.1 parts of dibutyltin dilaurate, 12 parts of modified sericite, 15 parts of barium sulfate, 0.9 parts of polybutyl acrylate, 0.45 parts of polydimethylsiloxane, 0.15 parts of perfluoropolyether, 0.8 parts of modified nano-alumina, and 0.6 parts of benzoin. The modified sericite is prepared in Example 1, and the modified nano-alumina is prepared in Example 2.

[0025] Example 5 A method for preparing a low-temperature fast-curing coil powder coating comprises the following steps: S1. Add the raw materials of the low-temperature fast-curing coil powder coating into a high-speed mixer at a speed of 1450 r / min and mix for 6 minutes to ensure that the components are evenly dispersed; S2. Add the mixed material into a twin-screw extruder for melt extrusion. The temperature of the twin-screw extruder is 85°C in zone 1, 105°C in zone 2, 125°C in zone 3, and 115°C in zone 4. The speed is 225 r / min. S3. The tablets are cooled to below 40° C., and after coarse crushing, they are crushed in an ACM grinder with a 100-mesh grading screen to obtain the low-temperature fast-curing coil powder coating.

[0026] The low-temperature fast-curing coil powder coating includes the following raw materials in parts by weight: 50 parts of a carboxyl polyester resin with an acid value of 45 mg KOH / g, 4.5 parts of β-hydroxyalkylamide, 8 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.2 parts of dibutyltin dilaurate, 9 parts of modified sericite, 20 parts of barium sulfate, 0.72 parts of polybutyl acrylate, 0.36 parts of polydimethylsiloxane, 0.12 parts of perfluoropolyether, 1.0 parts of modified nano-alumina, and 0.5 parts of benzoin. The modified sericite is prepared in Example 1, and the modified nano-alumina is prepared in Example 2.

[0027] Comparative Example 1 The preparation method of a low-temperature fast-curing coil powder coating is the same as that of Example 5.

[0028] The low-temperature fast-curing coil powder coating includes the following raw materials in parts by weight: 50 parts of a carboxyl polyester resin with an acid value of 45 mg KOH / g, 4.5 parts of β-hydroxyalkylamide, 8 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.2 parts of dibutyltin dilaurate, 20 parts of barium sulfate, 0.72 parts of polybutyl acrylate, 0.36 parts of polydimethylsiloxane, 0.12 parts of perfluoropolyether, 1.0 parts of modified nano-alumina, and 0.5 parts of benzoin. The modified nano-alumina is prepared as in Example 2.

[0029] Comparative Example 2 The preparation method of a low-temperature fast-curing coil powder coating is the same as that of Example 5.

[0030] The low-temperature fast-curing coil powder coating includes the following raw materials in parts by weight: 50 parts of a carboxyl polyester resin with an acid value of 45 mg KOH / g, 4.5 parts of β-hydroxyalkylamide, 8 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.2 parts of dibutyltin dilaurate, 9 parts of modified sericite, 20 parts of barium sulfate, 0.72 parts of polybutyl acrylate, 0.36 parts of polydimethylsiloxane, 0.12 parts of perfluoropolyether, and 0.5 parts of benzoin. The modified sericite is prepared according to Example 1.

[0031] Comparative Example 3 The preparation method of a low-temperature fast-curing coil powder coating is the same as that of Example 5.

[0032] The low-temperature fast-curing coil powder coating comprises the following raw materials in parts by weight: 50 parts of a carboxyl polyester resin with an acid value of 45 mg KOH / g, 4.5 parts of β-hydroxyalkylamide, 8 parts of an epoxy resin with an epoxy equivalent weight (EEW) of 800, 0.2 parts of dibutyltin dilaurate, 20 parts of barium sulfate, 0.72 parts of polybutyl acrylate, 0.36 parts of polydimethylsiloxane, 0.12 parts of perfluoropolyether, and 0.5 parts of benzoin.

[0033] Performance testing Performance testing of the powder coatings prepared in Example 5 and Comparative Examples 1-3 was conducted on 150 mm × 70 mm × 0.8 mm cold-rolled steel sheets. These were degreased, derusted, washed to a neutral finish, and then dried for later use. Each set of powder coatings was evenly sprayed onto the substrate using electrostatic powder spraying equipment, maintaining a coating thickness of 60 ± 5 μm. The samples were cured in an oven according to the process, cooled naturally to room temperature, and then allowed to stand for 24 hours before the following performance tests were performed. The data obtained are shown in Table 1 below: (1) Neutral salt spray test: refer to GB / T1771-2007 standard, scratch the sample and place it in a salt spray chamber at 35±2℃. Spray 5% NaCl solution at a certain spray rate. Take out the sample after 500h, 800h, 900h and 1200h. Rinse the surface salt frost with deionized water. Observe after drying. Record the blistering and rust of the coating. Measure the width of corrosion spread at the scratch. (2) Water contact angle test: refer to GB / T30447-2013 standard, use contact angle meter to automatically analyze water drop profile and calculate contact angle; (3) Pencil hardness test: refer to GB / T6739-2006 standard and use pencils with hardness grades ranging from 2B to 3H to perform scratch test until the pencil can make continuous visible scratches on the coating surface (without penetrating the coating). The pencil hardness is the coating hardness grade; (4) Drop ball impact strength test: refer to GB / T2423.5-1995 standard, fix the sample coating surface upward on the drop ball impact tester, and release the steel ball with a mass of 1000g and a diameter of 16mm from a height of 30cm to freely drop and impact the coating surface (the impact point is ≥25mm from the edge of the sample). After each impact, observe whether the coating has cracks or peeling. If the coating is not damaged, increase the height (increase 10cm each time) and repeat the test until visible cracks or peeling appear on the coating. The height at this time is recorded as the impact strength. (5) Self-repair efficiency test, using electrochemical impedance spectroscopy (EIS), using a three-electrode system, the sample is the working electrode (exposed area 1cm 2 ), platinum sheet as counter electrode, saturated calomel electrode as reference electrode, electrolyte is 3.5% NaCl solution, test the electrochemical impedance spectroscopy of the unscratched coating (frequency range 10 -2 ~10 5 Hz, AC signal amplitude 10mV), record the low-frequency impedance modulus |Z|0, then use a blade to make a 1cm long scratch in the working electrode area (through the coating to the substrate), immerse the scratched sample in the electrolyte, measure the impedance spectrum at 0h, 24h, and 48h, and record the low-frequency impedance modulus |Z| at 48h. t , calculate the self-repair efficiency, self-repair efficiency = (|Z| t / |Z|0)×100%, reflecting the degree of coating impedance recovery (the higher the value, the better the self-healing effect); (6) Antibacterial test: referring to GB / T21510-2008 standard, Escherichia coli (ATCC25922) was inoculated into nutrient broth medium, cultured at 37℃ for 24h, and diluted with physiological saline to a bacterial concentration of 10 6 ~10 7 CFU / mL, take a 2cm×2cm coating sample, sterilize it with UV for 30 minutes, then place it in a sterile culture dish, add 0.2mL of bacterial solution, evenly spread it on the coating surface, cover it with sterile polyethylene film, and culture it at 37℃ for 24 hours. After culture, add 10mL of normal saline to rinse the coating surface, take 1mL of the washing solution for gradient dilution, spread it on nutrient agar medium, and culture it at 37℃ for 48 hours, then count the number of colonies and calculate the antibacterial rate, antibacterial rate = (number of colonies in the control group - number of colonies in the experimental group) / number of colonies in the control group × 100%.

[0034] Table 1 Performance test results of low temperature fast curing coil powder coatings

[0035] From the data in Table 1 we can see that: Example 5 has the best salt spray resistance and the largest water contact angle, which is due to the synergistic effect of modified sericite and nano-alumina. The flaky structure of modified sericite forms a physical barrier to delay the penetration of corrosive media; the benzotriazole released in response to pH A passivation film forms at scratches, enabling self-repair. The fluorocarbon chains (low surface energy) grafted with heptadecafluorodecyltrimethoxysilane on the surface of the modified nano-alumina work in synergy with the micro-nano rough structure of nano-zinc oxide to achieve super-hydrophobicity, further blocking corrosion pathways. Comparative Example 1's salt spray resistance drops to 800 hours. While the super-hydrophobicity of the nano-alumina still blocks water, it lacks the physical barrier and self-repairing properties of sericite. Corrosion at scratches cannot be suppressed, accelerating its spread. Comparative Example 2 withstands salt spray for 900 hours. The barrier and self-repair properties of sericite remain effective, but the lack of a super-hydrophobic layer allows moisture to easily adhere to and penetrate the coating surface, resulting in a shorter corrosion protection period than Example 5. Comparative Example 3 exhibits the worst performance. Lacking modified nano-alumina, the coating surface relies solely on the polar groups of the resin itself, failing to form a low surface energy and rough structure. It exhibits either hydrophobic or hydrophilic behavior, allowing moisture to spread and penetrate, allowing corrosive media to quickly invade.

[0036] The pencil hardness of Example 5 and Comparative Example 1 reached 3H, while that of Comparative Examples 2 and 3 was only 2H. This is because the modified nano-alumina is evenly dispersed in the resin matrix, refining the coating's microstructure through a "nano-filling effect" and improving hardness. The modified sericite contributes only slightly to the increased hardness. The impact resistance of Example 5 and Comparative Example 1 reached 50cm, but dropped to 40cm in Comparative Example 2 and only 30cm in Comparative Example 3. The modified nano-alumina enhances the toughness of the resin matrix through interfacial interactions, absorbing impact energy. While the modified sericite enhances flexural resistance, its impact strength improvement is minimal.

[0037] The self-repair efficiency of Example 5 and Comparative Example 2 is greater than 80%. Both contain modified sericite, and the polydopamine and benzotriazole coatings thereof release benzotriazole when the pH at the scratch fluctuates. The self-repair efficiency of Comparative Examples 1 and 3 was ≤10%, which was due to the lack of modified sericite and the absence of a responsive corrosion inhibitor release system. The scratches could not be repaired autonomously, and the impedance recovery was almost non-existent.

[0038] The antibacterial rate of Example 5 and Comparative Example 1 is greater than 98%. Both contain modified nano-alumina, and the nano-silver on its surface is slowly released. , destroying bacterial cell membranes and enzyme activity, achieving high antibacterial efficiency; the stabilizing effect of carbon quantum dots extends the antibacterial life of nanosilver. The antibacterial rates of Comparative Examples 2 and 3 are less than 66%, which is due to the lack of modified nano-alumina. Release system, the resin itself has only a weak antibacterial effect and the antibacterial effect is poor.

[0039] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0040] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing a low-temperature fast-curing coil powder coating, characterized in that: The following steps are involved: S1. Add the raw materials of low-temperature fast-curing coil powder coating into a high-speed mixer at a speed of 1200-1600 r / min and mix for 5-8 minutes to ensure that the components are evenly dispersed. S2. Add the mixed material into a twin-screw extruder for melt extrusion. The temperature of the twin-screw extruder is 80-90°C in zone 1, 100-110°C in zone 2, 120-130°C in zone 3, and 110-120°C in zone 4. The speed is 200-250 r / min. S3, cooling the tablets to below 40°C, crushing them roughly using an ACM grinder and grading screens of 80-120 mesh to obtain the low-temperature fast-curing coil powder coating; The low-temperature fast-curing coil powder coating comprises the following raw materials in parts by weight: 45-55 parts of carboxyl polyester resin, 3-6 parts of β-hydroxyalkylamide, 5-10 parts of epoxy resin, 0.1-0.3 parts of organotin catalyst, 6-12 parts of modified sericite, 15-25 parts of barium sulfate, 1.0-1.5 parts of composite leveling agent, 0.8-1.2 parts of modified nano-alumina, and 0.3-0.6 parts of benzoin; The modified sericite is modified by cerium salt intercalation, and then the surface is modified with tannic acid iron complex, and finally the polydopamine and benzotriazole corrosion inhibitor are formed by dopamine self-polymerization. The modified nano-alumina is prepared by in-situ growing nano-zinc oxide on the surface of the nano-alumina by a hydrothermal method, then co-modifying it with Ag and carbon quantum dots, and finally grafting fluorosilane to achieve surface super-hydrophobic modification.

2. The method for preparing a low-temperature fast-curing coil powder coating according to claim 1, characterized in that: The acid value of the carboxyl polyester resin is 40-50 mg KOH / g, the epoxy equivalent weight (EEW) of the epoxy resin is 800, the organic tin catalyst is dibutyltin dilaurate, and the composite leveling agent is a mixture of polybutyl acrylate, polydimethylsiloxane and perfluoropolyether in a mass ratio of 6:3:

1.

3. The method for preparing a low-temperature fast-curing coil powder coating according to claim 1, characterized in that: The preparation method of the modified sericite comprises the following steps: (1) Dispersing sericite in deionized water, ultrasonically treating for 20-40 min, adding cerium nitrate (5% by weight of the total mass of sericite), stirring at 80°C for 4-6 h, centrifuging and washing until neutral, and vacuum drying at 80°C to obtain cerium salt intercalated sericite; (2) The intercalated modified sericite was dispersed in a 50 vol% ethanol solution, tannic acid and ferric chloride were added, reacted at 60 ° C for 3-5 h, centrifuged, washed, and dried to obtain sericite surface-modified with tannic acid iron complex; (3) The surface-modified sericite was dispersed in Tris buffer, dopamine hydrochloride was added, and the mixture was stirred at room temperature for 18 to 24 hours. Benzotriazole was added and stirred for 2 to 4 hours to allow the benzotriazole to be adsorbed into the porous structure of polydopamine. The mixture was washed by centrifugation and dried in a vacuum at 40°C to obtain the modified sericite.

4. The method for preparing a low-temperature fast-curing coil powder coating according to claim 3, characterized in that: The mass ratio of the intercalation-modified sericite, tannic acid and ferric chloride is 5:2:0.

5.

5. The method for preparing a low-temperature fast-curing coil powder coating according to claim 3, characterized in that: The mass ratio of the surface-modified sericite, dopamine hydrochloride and benzotriazole is 6:1:0.

4.

6. The method for preparing a low-temperature fast-curing coil powder coating according to claim 1, characterized in that: The preparation method of the modified nano-alumina comprises the following steps: A. Disperse nano-alumina in deionized water, ultrasonicate for 20-40 minutes, add zinc nitrate and hexamethylenetetramine, and hydrothermally react at 90°C for 3-5 hours to grow nano-zinc oxide on the surface of the alumina. Centrifuge, wash, and dry to obtain zinc oxide-coated nano-alumina. B. Disperse the zinc oxide-coated nano-alumina in deionized water, add silver nitrate and ascorbic acid, stir in the dark for 1-3 hours, add 1 mg / mL carbon quantum dot solution, stir at 60°C for 3-5 hours to allow the carbon quantum dots to adsorb in the gaps between the zinc oxide, and centrifuge and wash to obtain co-modified nano-alumina; C. Dispersing the co-modified nano-alumina in ethanol, adding heptadecafluorodecyltrimethoxysilane, refluxing at 80° C. for 4-6 hours to graft the fluorosilane onto the surface, washing by centrifugation, and curing at 120° C. to obtain the modified nano-alumina.

7. The method for preparing a low-temperature fast-curing coil powder coating according to claim 6, characterized in that: The mass ratio of the nano-alumina, zinc nitrate and hexamethylenetetramine is 5:2:1.

5.

8. The method for preparing a low-temperature fast-curing coil powder coating according to claim 6, characterized in that: The mass ratio of the zinc oxide-coated nano-aluminum oxide, silver nitrate, and carbon quantum dots is 4:0.1:0.

2.

9. Use of a low-temperature, fast-curing coil powder coating prepared by the method according to any one of claims 1 to 8 in continuous coating of metal coils, characterized in that: The powder coating can be quickly cured at a low temperature of 130-160° C. within 1-3 minutes, significantly reducing energy consumption and improving production efficiency.

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