Preparation method of ultraviolet curing antibacterial coating

Abstract

The invention relates to the technical field of antibacterial coatings, and discloses a preparation method of an ultraviolet curing antibacterial coating, which comprises the following steps: (1) preparing a core-shell structure antibacterial agent; (2) constructing a gradient photocuring system; (3) a step-by-step curing process; through the collaborative design of the core-shell structure antibacterial agent, the gradient light curing system and the step-by-step curing process, the antibacterial property, the curing efficiency and the mechanical property are synchronously improved. The prepared core-shell antibacterial agent solves the problems of dispersion and durability of a traditional antibacterial agent, component matching of a gradient system optimizes curing dynamics and a paint film structure, a step-by-step process guarantees the stability of the overall performance through regulation and control of a curing process, and the three components form an organic whole; the problems that the antibacterial property and the mechanical property of a traditional ultraviolet curing antibacterial coating are difficult to consider, and the contradiction exists between the curing efficiency and the quality are solved. And the final product can meet the requirements in the fields of medical instruments, furniture, electronic equipment and the like.

Description

Technical Field

[0001] This invention relates to the field of antibacterial coating technology, specifically a method for preparing an ultraviolet-cured antibacterial coating. Background Technology

[0002] UV-curable coatings are a type of functional coating that uses UV light to induce rapid cross-linking and curing of a resin system. They offer significant advantages such as solvent-free curing, low energy consumption, and high production efficiency, and are widely used in furniture coating, medical device surface protection, and electronic device casing coatings, among other fields. The core principle involves UV light exciting a photoinitiator to generate active free radicals or cations, which then promote polymerization of the double bonds in the resin and reactive diluent, forming a three-dimensional network cross-linked structure. This results in rapid film formation and stable performance.

[0003] With the increasing demand for hygiene in living environments and antibacterial properties on product surfaces, antibacterial coatings have gradually become a research hotspot in the coatings industry. In the medical device field, antibacterial coatings can effectively inhibit the growth of pathogenic bacteria such as Escherichia coli and Staphylococcus aureus on equipment surfaces, reducing the risk of cross-infection. In the furniture and household goods field, they can reduce the spread of bacteria during daily contact, and are especially suitable for high-frequency contact scenarios such as children's furniture and kitchen utensils. In the coating of public facilities surfaces, they can also improve the hygiene of public environments through continuous antibacterial effects. Therefore, the market demand and application scope of antibacterial coatings are continuously expanding.

[0004] However, existing UV-curable antibacterial coatings still face two major problems in practical applications that urgently need to be addressed. On the one hand, the curing efficiency is insufficient: to ensure film thickness and coverage, some coatings often use high-viscosity resin systems, which results in a slow diffusion rate of the photoinitiator in the system, thus prolonging the overall curing time.

[0005] On the other hand, the antibacterial performance and durability are unsatisfactory: existing antibacterial coatings mostly add antibacterial components such as nano-silver and titanium dioxide directly, resulting in poor dispersibility and stability. Nano-silver is prone to agglomeration, forming antibacterial dead zones, leading to an antibacterial rate generally below 90%, and it is easily lost with paint film wear during long-term use, resulting in a short antibacterial effect. Although titanium dioxide has photocatalytic antibacterial function, its light response range is narrow and its catalytic efficiency is low at conventional particle sizes, making it difficult to achieve a long-lasting antibacterial effect. In addition, the interfacial bonding force between conventional antibacterial agents and the resin matrix is ​​weak, which not only reduces the mechanical properties of the paint film but also further aggravates the shedding of antibacterial agents, restricting the application and promotion of antibacterial coatings. Summary of the Invention

[0006] To address the problems in the prior art, the present invention provides a method for preparing an ultraviolet-curable antibacterial coating.

[0007] The technical solution adopted by this invention to solve its technical problem is: a method for preparing a UV-curable antibacterial coating, comprising the following steps: (1) Preparation of core-shell structured antibacterial agent: Nano silver particles are surface modified by silane coupling agent, antibacterial functional monomers containing double bonds are grafted onto the modified nano silver surface, and then titanium dioxide quantum dots doped with rare earth elements are coated to form a core-shell structure with graft layer and doped coating layer, and the particle size of the core-shell structure is controlled at 50-80nm. (2) Constructing a gradient photocuring system: Based on a total mass of 100%, the core-shell antibacterial agent of step (1) is mixed with 34-40wt% bisphenol A epoxy acrylate, 26-30wt% hyperbranched polyurethane acrylate, 10-15wt% reactive diluent containing phenyl double bonds, and 3-4wt% free radical / cationic bifunctional photoinitiator system; (3) Step-by-step curing process: Curing is completed by using two-stage ultraviolet light irradiation.

[0008] As a further technical solution, the preparation of the core-shell structured antibacterial agent in step (1) includes: (a) Disperse nano-silver in ethanol at a concentration of 0.5-0.8 g / L, add KH-550 silane coupling agent, stir and react at 50-60℃ for 2 hours, and obtain amino-modified nano-silver after centrifugation and washing. (b) Add 12-15% by mass of antibacterial functional monomers containing double bonds to the amino-modified nano-silver dispersion in step (a), and keep it at 70-80°C for 1.5 hours to form a surface graft layer. The antibacterial functional monomer containing double bonds is a compound of N-vinylcaprolactam and glycidyl methacrylate, with a compound mass ratio of 2:1. (c) Tetrabutyl titanate and rare earth element compound are mixed at a mass ratio of 120:1.2-1.4 and dissolved in deionized water. The pH is adjusted to 2-3 with hydrochloric acid. Grafted modified nano-silver from step (b) is added, and the mixture is hydrothermally reacted at 60-80℃ for 4 hours to form a titanium dioxide quantum dot coating layer doped with rare earth elements. The rare earth element compound is cerium nitrate or lanthanum nitrate. (d) The product from step (c) is ultrasonically dispersed to obtain a core-shell structured antibacterial agent.

[0009] As a further technical solution, the centrifugal washing speed in step (a) is 3000-5000 r / min, the number of washing cycles is 3-5, and ethanol is used as the washing solution for each washing.

[0010] As a further technical solution, in step (b), the compound of N-vinylcaprolactam and glycidyl methacrylate needs to be filtered through a 0.22 μm organic filter membrane before being added to the dispersion to remove impurity particles and avoid affecting the grafting uniformity.

[0011] As a further technical solution, the volume ratio of tetrabutyl titanate to deionized water in step (c) is 1:8-12.

[0012] As a further technical solution, the ultrasonic dispersion power in step (d) is 300-500W, and the time is 10-15 minutes.

[0013] As a further technical solution, the reactive diluent containing phenyl double bonds in step (2) is 4-phenyl dimethacrylate or 2-phenyl ethyl acrylate.

[0014] As a further technical solution, the free radical / cationic bifunctional photoinitiator system in step (2) is a compound system of 1-hydroxycyclohexylphenyl ketone and diaryliodonium salt mixed in a mass ratio of 1:1-3.

[0015] As a further technical solution, the parameters of the stepwise curing process in step (3) are as follows: Pre-curing stage: UV light wavelength 365nm, light intensity 15mW / cm², curing time 30 seconds; Main curing stage: UV wavelength 395nm, light intensity 90mW / cm², curing time 60 seconds; The curing process is based on a wet film thickness of 50 μm.

[0016] As a further technical solution, when the wet film thickness of the coated paint is 50-100μm, the pre-curing time is adjusted as follows: for every 10μm increase in wet film thickness beyond the base thickness, the pre-curing time is increased by 5 seconds.

[0017] The beneficial effects of this invention are as follows: 1. This invention provides a core-shell structured antibacterial agent constructed through silane modification, double bond grafting, and rare earth-doped titanium dioxide quantum dot coating, which solves the defects of traditional antibacterial agents from both the aspects of composition optimization and structure optimization. The nano-silver core, acting as a rapid antibacterial component, achieves immediate sterilization by disrupting bacterial cell membranes and inhibiting enzyme activity. The amino modification of the silane coupling agent KH-550 forms an organic-friendly phase layer on the nano-silver surface, resolving the aggregation problem of nano-silver in the resin and providing reaction sites for subsequent grafting of antibacterial functional monomers. The grafted layer formed by N-vinylcaprolactam and glycidyl methacrylate not only participates in the UV curing reaction through double bonds, enabling the antibacterial agent to form chemical bonds with the resin matrix and preventing detachment during use, but also enhances the bactericidal effect through its own antibacterial groups. The outer layer of titanium dioxide quantum dots doped with rare earth elements broadens the photoresponse range, generating active substances such as hydroxyl radicals under both UV and visible light, achieving photocatalytic long-lasting antibacterial effects. Furthermore, the small particle size of the quantum dots allows for uniform dispersion in the paint film, eliminating antibacterial dead zones. Ultimately, this results in a coating with high antibacterial rates and strong stability against Escherichia coli and Staphylococcus aureus.

[0018] 2. The synergistic effect of the components in the gradient photocuring system solves the problem of long curing time while ensuring the mechanical properties of the coating film. Bisphenol A epoxy acrylate, as the main resin, has high reactivity and good rigidity, providing basic mechanical support for the coating film. Hyperbranched polyurethane acrylate, with its low viscosity, reduces the overall viscosity of the system, accelerates the diffusion of photoinitiators and reactive diluents, and shortens the curing reaction time. The reactive diluent containing phenyl double bonds not only adjusts the viscosity of the system, but its phenyl structure also enhances the weather resistance and adhesion of the coating film. The free radical / cationic bifunctional photoinitiator system can initiate the double bond polymerization and epoxy group ring-opening polymerization in the resin and reactive diluent respectively, forming a denser three-dimensional cross-linked network. Free radical polymerization achieves rapid surface drying, while cationic polymerization ensures complete deep curing. The two work synergistically to improve the surface quality of the cured coating.

[0019] 3. The step-by-step curing process achieves orderly curing—first fixing, then cross-linking—by controlling the wavelength, intensity, and time of ultraviolet light. The pre-curing stage uses low-intensity, short-wavelength ultraviolet light to initiate only the initial cross-linking of the surface resin, preventing sagging and deformation of the wet film during subsequent processing, while preserving the reactivity of the internal resin. The main curing stage uses high-intensity, long-wavelength ultraviolet light, which penetrates deep into the film, stimulating the photoinitiator to fully react and ensuring uniform overall cross-linking. Compared to traditional single-stage curing, this invention effectively avoids the problems of surface curing blocking ultraviolet light and incomplete internal curing, reducing internal stress in the film and lowering the risk of cracking and peeling. Furthermore, the adjustment mechanism of "increasing the pre-curing time by 5 seconds for every 10μm increase in thickness" can adapt to the curing requirements of coatings of different thicknesses, further ensuring the stability of curing quality.

[0020] 4. This invention achieves simultaneous improvement in antibacterial properties, curing efficiency, and mechanical properties through the synergistic design of a core-shell structured antibacterial agent, a gradient photocuring system, and a stepwise curing process. The core-shell antibacterial agent prepared by this invention solves the dispersion and durability problems of traditional antibacterial agents. The component matching of the gradient system optimizes curing kinetics and film structure, while the stepwise process ensures the stability of overall performance through curing process control. These three elements form an organic whole, overcoming the problems of traditional UV-cured antibacterial coatings where antibacterial properties and mechanical properties are difficult to balance, and where curing efficiency and quality are contradictory. The final product can meet the requirements of high antibacterial properties and high mechanical properties in fields such as medical devices, furniture, and electronic equipment, and has practical value and market prospects. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a method for preparing a UV-curable antibacterial coating. The core of this method lies in the synergistic design of customized core-shell structured antibacterial agents, the construction of a gradient photocuring system, and the matching of step-by-step curing processes. This addresses the problems of poor antibacterial durability, uneven curing, and insufficient mechanical properties in traditional UV-curable coatings. Specifically, it includes: All raw materials used in this invention are commercially available conventional products. Specific models and suppliers are listed below to ensure experimental repeatability: Nano silver particles: particle size 20-30nm, Nanjing Xianfeng Nanomaterials Technology Co., Ltd., model XF-NAg-20; KH-550 silane coupling agent: Sinopharm Chemical Reagent Co., Ltd., analytical grade (AR); N-Vinylcaprolactam: Aladdin Reagent (Shanghai) Co., Ltd., purity 98%; Glycidyl methacrylate: Sigma-Aldrich (Shanghai) Trading Co., Ltd., 97% purity; Tetrabutyl titanate: Tianjin Kemei Chemical Reagent Co., Ltd., analytical grade (AR); Cerium nitrate / Lanium nitrate: Shanghai Maclean Biochemical Technology Co., Ltd., purity 99.9%; Bisphenol A epoxy acrylate: Changxing Chemical Industry (China) Co., Ltd., model 6101-100; Hyperbranched polyurethane acrylate: Mitsui Chemicals (China) Investment Co., Ltd., model UA-306H; 4-Phenylacetyl dimethacrylate / 2-Phenylacetyl ethyl acrylate: Tokyo Chemical Industry (Shanghai) Co., Ltd., purity 98% / 97%; 1-Hydroxycyclohexylphenyl ketone (Photoinitiator 184): BASF (China) Co., Ltd., model Irgacure 184; Diaryl iodonium salt: Changzhou Huatai Chemical Co., Ltd., model CD-1012.

[0023] Preparation of core-shell structured antibacterial agents Strictly control the particle size to 50-80nm: Step (a): The concentration of nano-silver in ethanol is 0.5-0.8 g / L, and the amount of KH-550 added is 5%-8% of the mass of nano-silver to ensure sufficient amino modification. After stirring the reaction at 50-60℃ for 2 hours, centrifuge and wash 3-5 times at 3000-5000 r / min, each time with 50 mL of anhydrous ethanol. Step (b): The monomer containing double bond antibacterial function (N-vinylcaprolactam: glycidyl methacrylate in a ratio of 2:1) needs to be filtered through a 0.22μm organic filter membrane. The amount added is 12-15% of the mass of the nano silver. The reaction is carried out at 70-80℃ for 1.5h. Step (c): Tetrabutyl titanate to deionized water volume ratio 1:8-12, rare earth element compound (cerium nitrate / lanthanum nitrate) to tetrabutyl titanate mass ratio 1.2-1.4:120, after adjusting the pH to 2-3 with hydrochloric acid, hydrothermal reaction at 60-80℃ for 4h. Step (d): Use ultrasonic dispersion power of 300-500W for 10-15 minutes to ensure that the core-shell particles are uniformly dispersed without agglomeration.

[0024] Construction of gradient photocuring system Based on a total mass of 100%, the proportion of each component needs to be precisely controlled: Bisphenol A epoxy acrylate (34-40wt%), hyperbranched polyurethane acrylate (26-30wt%), reactive diluent (10-15wt%), photoinitiator system (3-4wt%), and balance of core-shell antibacterial agent; Photoinitiator system: 1-hydroxycyclohexylphenyl ketone and diaryliodonium salt in a mass ratio of 1:1-3, to achieve free radical / cationic synergistic curing.

[0025] Step-by-step curing process Based on a wet film thickness of 50 μm, the parameters are as follows: Pre-curing: 365nm UV light, 15mW / cm², 30s (to avoid wet film sagging and subsequent shrinkage); Main curing: 395nm ultraviolet light, 90mW / cm², 60s (to ensure complete deep curing); When the wet film thickness is 50-100μm, the pre-curing time should be adjusted by increasing the time by 5 seconds for every 10μm increase. Specific Implementation

[0026] Example 1: Preparation of core-shell structured antibacterial agent (a) Disperse 0.6 g of nano-silver in 1000 mL of anhydrous ethanol, add 0.03 g of KH-550, stir and react at 55 °C for 2 h; then centrifuge and wash 4 times at 4000 r / min (each time with 50 mL of anhydrous ethanol) to obtain amino-modified nano-silver. (b) Add 0.08 g of antibacterial functional monomer (N-vinylcaprolactam: glycidyl methacrylate in a ratio of 2:1) filtered through a 0.22 μm filter membrane to the amino-modified silver nanoparticle dispersion, and incubate at 75 °C for 1.5 h. (c) Take 120g of tetrabutyl titanate and 1.3g of cerium nitrate, mix them, dissolve them in 1200mL of deionized water (volume ratio 1:10), adjust the pH to 2.5 with hydrochloric acid, add the product from step (b), and hydrothermally react at 70℃ for 4h. (d) Disperse the mixture under ultrasonic pressure at 400W for 12 minutes to obtain a core-shell antibacterial agent with a particle size of 60-70nm.

[0027] Construction of gradient photocuring system Mix the following components based on a total mass of 100g: 16.5g core-shell antibacterial agent, 37g bisphenol A epoxy acrylate, 30g hyperbranched polyurethane acrylate, 13g 4-phenyl dimethacrylate, and 3.5g photoinitiator system (184:CD-1012 is 1:2). Stir at 25°C for 30 minutes until homogeneous.

[0028] Step-by-step curing process A wet film with a thickness of 50 μm was coated, pre-cured (365 nm, 15 mW / cm², 30 s), and then cured (395 nm, 90 mW / cm², 60 s) to obtain a UV-curable antibacterial coating. Example 2: Preparation of core-shell structured antibacterial agent (a) Disperse 0.5 g of nano silver in 1000 mL of anhydrous ethanol, add 0.025 g of KH-550, stir at 50 °C for 2 h; centrifuge at 3000 r / min and wash 3 times to obtain amino-modified nano silver; (b) Add 0.075g of filtered antibacterial functional monomer and incubate at 70°C for 1.5h; (c) 120g tetrabutyl titanate and 1.2g lanthanum nitrate were mixed and dissolved in 960mL deionized water (volume ratio 1:8), pH 2, and hydrothermally heated at 60℃ for 4h. (d) After 15 minutes of ultrasonication at 300W, a core-shell antibacterial agent with a particle size of 50-60nm was obtained.

[0029] Construction of gradient photocuring system Total mass 100g: 19g core-shell antibacterial agent, 34g bisphenol A epoxy acrylate, 28g hyperbranched polyurethane acrylate, 15g ethyl 2-phenyl acrylate, 4g photoinitiator (184:CD-1012 is 1:1).

[0030] Step-by-step curing process The wet film was 50 μm thick, pre-cured for 30 seconds, and then cured for 60 seconds to complete the preparation.

[0031] Example 3: Preparation of core-shell structured antibacterial agent (a) 0.8 g of nano silver was dispersed in 1000 mL of ethanol and 0.064 g of KH-550, stirred at 60 °C for 2 h; centrifuged 5 times at 5000 r / min. (b) 0.12g of antibacterial monomer, incubated at 80℃ for 1.5h; (c) 120g tetrabutyl titanate and 1.4g cerium nitrate were mixed and dissolved in 1440mL water (1:12), pH 3, and hydrothermally heated at 80℃ for 4h. (d) 500W ultrasound for 10 minutes, particle size 70-80nm.

[0032] Construction of gradient photocuring system Total mass 100g: core-shell 21g, bisphenol A 40g, hyperbranching 26g, 4-phenyldimethyl acrylate 10g, photoinitiator 3g (184:CD-1012 ratio is 1:3).

[0033] Step-by-step curing process Wet film thickness 60μm (overbase thickness 10μm), pre-curing 35s, main curing 60s.

[0034] Example 4: Preparation of core-shell structured antibacterial agent (a) 0.7 g nano silver / 1000 mL ethanol, 0.042 g KH-550, stirred at 55 °C for 2 h; centrifuged 4 times at 4500 r / min; (b) 0.098g of antibacterial monomer, incubated at 75℃ for 1.5h; (c) 120g tetrabutyl titanate and 1.3g cerium nitrate were mixed and dissolved in 1100mL water (1:9.2), pH 2.5, and hydrothermally heated at 75℃ for 4h; (d) 450W ultrasound for 13 minutes, particle size 65-70nm.

[0035] Construction of gradient photocuring system Total mass 100g: core-shell 18g, bisphenol A 36g, hyperbranching 29g, ethyl 2-phenylacrylate 12g, photoinitiator 3.5g (1:2).

[0036] Step-by-step curing process Wet film thickness 50μm, pre-curing 30s, main curing 60s.

[0037] Example 5: Preparation of core-shell structured antibacterial agent Same as Example 1, particle size 65-75nm.

[0038] Construction of gradient photocuring system Total mass 100g: core-shell 17g, bisphenol A 38g, hyperbranching 27g, 4-phenyldimethacrylate 14g, photoinitiator 3.5g (1:2).

[0039] Step-by-step curing process The wet film thickness is 80μm (overbase thickness is 30μm), the pre-curing time is 45s (30+3×5), and the main curing time is 60s.

[0040] Comparative Example 1: Preparation of antibacterial agent: 0.6g of nano-silver was directly dispersed in 1000mL of ethanol without silane modification, grafting or TiO2 coating, and used directly after ultrasonic dispersion.

[0041] Photocuring system: Same as in Example 1 (the core-shell antibacterial agent is replaced with an equal amount of nano-silver).

[0042] Curing process: Same as in Example 1.

[0043] Comparative Example 2: Preparation of core-shell antibacterial agent: Same as Example 1.

[0044] Photocurable system: Total mass 100g, core and shell 16.5g, bisphenol A epoxy acrylate 67g (37+30), 4-phenyl dimethacrylate 13g, photoinitiator 3.5g (1:2), non-hyperbranched resin.

[0045] Curing process: Same as in Example 1.

[0046] Comparative Example 3: Preparation of core-shell antibacterial agent: Same as Example 1.

[0047] Photocuring system: Same as in Example 1.

[0048] Curing process: For a wet film of 50μm, a single-stage curing process (395nm, 50mW / cm², 90s) is used, with no pre-curing step; for a wet film of 80μm, the curing time is still 90s without adjustment.

[0049] test Antibacterial performance test (refer to GB / T21866-2008 "Determination of antibacterial properties and antibacterial effects of antibacterial coatings (films)") Test methods Tested bacterial strains: Escherichia coli, Staphylococcus aureus; Bacterial concentration: 106 CFU / mL, each sample plate was inoculated with 0.2 mL of bacterial solution and covered with sterile polyethylene film; Culture conditions: After incubation at 37℃ for 24 hours, wash and count the number of viable bacteria; Antibacterial rate calculation: Antibacterial rate (%) is (number of viable bacteria in blank sample - number of viable bacteria in paint sample) / number of viable bacteria in blank sample × 100%; Each sample was tested in triplicate, and the average value was taken. The results are as follows:

[0050] As shown in Table 1, the antibacterial rate of all examples is ≥99.4%. The core reason is the synergistic effect of the core-shell structure antibacterial agent, the combination of nano silver (rapid sterilization) and rare earth-doped TiO2 quantum dots (photocatalytic long-lasting antibacterial), and the silane grafting layer improves the dispersibility of the antibacterial agent in the resin, avoiding antibacterial dead zones caused by agglomeration; step-by-step curing ensures deep curing of the coating, and the antibacterial agent is evenly distributed in the paint film.

[0051] Comparative Example 1: Using only nano-silver without a TiO2 coating layer, the nano-silver is prone to agglomeration (precipitation occurs in the ethanol dispersion after standing for 24 hours), and it lacks long-lasting photocatalytic antibacterial function, resulting in a low antibacterial rate; Comparative Example 2: The system had high viscosity, uneven dispersion of antibacterial agent, and no coverage of antibacterial agent in some areas, resulting in a decrease in antibacterial rate; Comparative Example 3: Single-stage curing results in the surface layer of the paint film curing first, while the interior is not fully cured. The antibacterial agent is encapsulated in the uncured resin and cannot contact the bacteria, thus reducing the antibacterial efficiency.

[0052] Curing rate test (refer to GB / T1728-2020 "Determination of drying time of paint film and putty film") Test methods Test indicators: Surface drying time (finger touch method, no adhesion when lightly touched with a finger), complete drying time (indentation method, no mark when pressed with a 1kg weight for 5 seconds). Test conditions: wet film thickness 50μm and 80μm, room temperature 25℃, relative humidity 50%; Each sample was tested in triplicate, and the average value was taken. The results are as follows:

[0053] Note: "-" indicates that the thickness was not tested. Examples 1, 2, and 4 focus on verifying the 50μm base thickness, while Examples 3 and 5 verify the performance after thickening.

[0054] As shown in Table 2, the surface drying time of the 50μm wet film is 27-30s and the actual drying time is 84-88s, while the actual drying time of the 80μm wet film is 86-92s. This is because the synergistic effect of bisphenol A and hyperbranched resin in the gradient system, combined with stepwise curing, allows for rapid fixation of the wet film during pre-curing and deep cross-linking during main curing, resulting in high curing efficiency.

[0055] Comparative Example 1: Nano-silver agglomeration hinders ultraviolet light penetration, reduces the amount of light absorbed by the photoinitiator, and decreases the curing rate; Comparative Example 2: The system with high viscosity, without hyperbranched resin, has hindered the movement of photoinitiator and resin molecules, resulting in a slow cross-linking reaction; Comparative Example 3: Single-stage curing without pre-curing, the surface layer cures rapidly to form a light shielding layer, but the internal ultraviolet light intensity is insufficient. The 80μm wet film requires 150s to fully dry, and there is uncured resin inside, resulting in incomplete drying.

[0056] Mechanical property testing (pencil hardness GB / T6739-2022; adhesion GB / T9286-1998) Test methods Pencil hardness: Using a 45° angle and a 1kg load, pencils from 6B to 9H were used to scratch the surface in sequence. The highest hardness without scratches was the test result. Adhesion: With a 1mm grid spacing, the paint film is crisscrossed to the substrate. After applying 3M tape, it is quickly peeled off. The paint film is rated according to the area of ​​peeling off (0: no peeling; 5: complete peeling). Five points were tested on each sample, and the average value was taken. The results are as follows:

[0057] As shown in Table 3, the pencil hardness reaches H-2H and the adhesion is grade 0. The reasons are: ① The TiO2 coating layer of the core-shell antibacterial agent forms chemical bonds with the resin (the double bonds of the grafted layer participate in cross-linking), which enhances the interfacial bonding force; ② The branched structure of the hyperbranched resin can disperse stress and reduce the brittleness of the paint film; ③ Stepwise curing reduces curing shrinkage and avoids the decrease in adhesion caused by internal stress in the paint film.

[0058] Comparative Example 1: Nano-silver without grafting layer, only physically mixed with resin, weak interfacial bonding, and agglomerates become stress concentration points, pencil hardness only grade B, adhesion grade 2; Comparative Example 2: No hyperbranched resin, uneven cross-linking density of the paint film, paint film peels off in pieces when the tape is torn off after cross-cutting, adhesion level 3; Comparative Example 3: Single-stage curing resulted in uncured resin inside, loose film structure, pencil hardness of 2B, adhesion of 4, and severely insufficient mechanical properties.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a UV-curable antibacterial coating, characterized in that, Includes the following steps: (1) Preparation of core-shell structured antibacterial agent: Nano silver particles are surface modified by silane coupling agent, antibacterial functional monomers containing double bonds are grafted onto the modified nano silver surface, and then titanium dioxide quantum dots doped with rare earth elements are coated to form a core-shell structure with graft layer and doped coating layer, and the particle size of the core-shell structure is controlled at 50-80nm. (2) Constructing a gradient photocuring system: Based on a total mass of 100%, the core-shell antibacterial agent of step (1) is mixed with 34-40wt% bisphenol A epoxy acrylate, 26-30wt% hyperbranched polyurethane acrylate, 10-15wt% reactive diluent containing phenyl double bonds, and 3-4wt% free radical / cationic bifunctional photoinitiator system; (3) Step-by-step curing process: Curing is completed by using two-stage ultraviolet light irradiation.

2. The method according to claim 1, characterized in that, The preparation of the core-shell structured antibacterial agent in step (1) includes: (a) Disperse nano-silver in ethanol at a concentration of 0.5-0.8 g / L, add KH-550 silane coupling agent, stir and react at 50-60℃ for 2 hours, and obtain amino-modified nano-silver after centrifugation and washing. (b) Add 12-15% by mass of antibacterial functional monomers containing double bonds to the amino-modified nano-silver dispersion in step (a), and keep it at 70-80°C for 1.5 hours to form a surface graft layer. The antibacterial functional monomer containing double bonds is a compound of N-vinylcaprolactam and glycidyl methacrylate, with a compound mass ratio of 2:

1. (c) Tetrabutyl titanate and rare earth element compound are mixed at a mass ratio of 120:1.2-1.4 and dissolved in deionized water. The pH is adjusted to 2-3 with hydrochloric acid. Grafted modified nano-silver from step (b) is added, and the mixture is hydrothermally reacted at 60-80℃ for 4 hours to form a titanium dioxide quantum dot coating layer doped with rare earth elements. The rare earth element compound is cerium nitrate or lanthanum nitrate. (d) The product from step (c) is ultrasonically dispersed to obtain a core-shell structured antibacterial agent.

3. The method according to claim 2, characterized in that, The centrifugation washing in step (a) is performed at a speed of 3000-5000 r / min, and the number of washing cycles is 3-5, with ethanol used as the washing solution for each wash.

4. The method according to claim 2, characterized in that, In step (b), the compound of N-vinylcaprolactam and glycidyl methacrylate needs to be filtered through a 0.22 μm organic filter membrane before being added to the dispersion.

5. The method according to claim 2, characterized in that, The volume ratio of tetrabutyl titanate to deionized water in step (c) is 1:8-12.

6. The method according to claim 2, characterized in that, The ultrasonic dispersion in step (d) has a power of 300-500W and a duration of 10-15 minutes.

7. The method according to claim 1, characterized in that, The reactive diluent containing phenyl double bonds mentioned in step (2) is 4-phenyl dimethacrylate or 2-phenyl ethyl acrylate.

8. The method according to claim 1, characterized in that, The free radical / cationic bifunctional photoinitiator system mentioned in step (2) is a compound system of 1-hydroxycyclohexylphenyl ketone and diaryliodonium salt mixed in a mass ratio of 1:1-3.

9. The method according to claim 1, characterized in that, The parameters for the stepwise curing process described in step (3) are: Pre-curing stage: UV light wavelength 365nm, light intensity 15mW / cm², curing time 30 seconds; Main curing stage: UV wavelength 395nm, light intensity 90mW / cm², curing time 60 seconds; The curing process is based on a wet film thickness of 50 μm.

10. The method according to claim 9, characterized in that, When the wet film thickness of the coating is 50-100μm, the pre-curing time should be adjusted as follows: for every 10μm increase in wet film thickness beyond the base thickness, the pre-curing time should be increased by 5 seconds.

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