Polyurethane coating and preparation method thereof

Abstract

The invention discloses a polyurethane coating and a preparation method thereof, and belongs to the technical field of antibacterial coatings. The preparation method of the polyurethane coating comprises the following steps: carrying out acyl chloride substitution reaction on a phenolic substance and a chlorine donor to obtain an intermediate reactant, and carrying out conjugate addition reaction on the intermediate reactant and an amine substance with hydroxyl groups at two ends to obtain antibacterial diol; reacting the antibacterial diol with isocyanate to obtain a polyurethane coating; the phenolic substance is selected from at least one of thymol, carvacrol, paeonol, catechol and theaflavin. The antibacterial coating is applied to the aspect of an antibacterial coating of a food contact part, the problem that the antibacterial property of an existing antibacterial coating is difficult to last is solved, and the antibacterial coating has the synergistic antibacterial effect of killing and defending bacteria.

Description

Technical Field

[0001] The invention belongs to the technical field of antibacterial coatings, and in particular relates to a polyurethane coating and a preparation method thereof. Background Art

[0002] Covalently bonding organic antibacterial groups to resin matrices is an important means of preparing antibacterial coatings, and has been widely studied in recent years. However, since the antibacterial groups are bonded to the resin molecular chains, covalently bonded antibacterial coatings rely more on direct contact between bacteria and their surfaces to exert their bactericidal effects. As the coating is used, the bacteria that are initially killed will inevitably accumulate on the coating surface, and eventually form a barrier between the coating surface and subsequent bacteria, resulting in a serious decrease in the antibacterial effect. Therefore, solving the problem of surface bacterial attachment of covalently bonded antibacterial coatings is crucial for their practical application.

[0003] Chinese patent CN117645859A discloses a formaldehyde-free and environment-friendly wood veneer board material and its preparation process, and specifically discloses: firstly, 3-mercapto-1,2-propylene glycol and eugenol are reacted in a molar ratio of 1:1, and then the reactant is reacted with 2-ethyl acryloyl chloride in a molar ratio of 1:1 to obtain a functional monomer; the functional monomer, water, methyl methacrylate, ethyl acrylate, cross-linking monomer, etc. are polymerized to obtain polyacrylate, and then a polyurethane prepolymer is introduced into its side chain to form a polyurethane-modified polyacrylate adhesive with a three-dimensional network structure through chemical cross-linking, and the polyurethane-modified polyacrylate adhesive is coated on the surface of a wooden panel, and after hot pressing and post-treatment, a wood veneer board material with strong adhesion and good antibacterial effect is obtained.

[0004] Although the above technical solution prepares a wood veneer board with antibacterial effect, the antibacterial coating obtained therefrom still cannot solve the problem that the antibacterial performance of the existing antibacterial coating is difficult to last. Summary of the invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to overcome the problem that the antibacterial performance of the existing antibacterial coating is difficult to sustain, and to propose a polyurethane coating with a bacterial "killing-defense" synergistic antibacterial effect and a preparation method thereof.

[0006] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0007] On one hand, the present invention provides a method for preparing a polyurethane coating, comprising: a phenolic substance and a chlorine donor undergo an acyl chloride substitution reaction to obtain an intermediate reactant, the intermediate reactant undergoes a conjugate addition reaction with an amine substance having hydroxyl groups at both ends to obtain an antibacterial diol; the antibacterial diol reacts with an isocyanate to obtain a polyurethane coating; the phenolic substance is selected from at least one of thymol, carvacrol, paeonol, catechol, and theaflavins.

[0008] In some embodiments, the chlorine donor is selected from at least one of acryloyl chloride, 4-pentenoyl chloride, allyl oxalyl chloride, methacryloyl chloride, and 3,3-dimethylacryloyl chloride.

[0009] In some embodiments, the antibacterial diol is prepared by the following method: a phenolic substance and an amine substance having hydroxyl groups at both ends are mixed, dry dichloromethane is added thereto, and the mixture is cooled to 0°C in an ice bath to obtain component A; a chlorine donor is dissolved in dichloromethane to obtain component B; component B is mixed with component A and reacted at 0°C, and then the mixture is transferred to room temperature for reaction to obtain the antibacterial diol.

[0010] In some embodiments, component B is added dropwise to component A, reacted at 0°C, and then transferred to room temperature for reaction, filtered, washed with dichloromethane, and then rotary evaporated to remove excess solvent, the solution is extracted with saturated sodium chloride solution, and dried with anhydrous sodium sulfate. The final product is further rotary evaporated to obtain antibacterial diol.

[0011] In some embodiments, the amount of the amine substance with hydroxyl groups at both ends is equal to the amount of hydroxyl groups contained in the phenolic substance; the ratio of the amount of the chlorine donor to the amount of the amine substance with hydroxyl groups at both ends is 1.01-1.1:1.

[0012] In some embodiments, the reaction of antimicrobial diol and isocyanate to obtain a polyurethane coating includes: dissolving an alcohol donor, dihydroxymethylpropionic acid and a neutralizer in dry 2-butanone, and reacting at 70°C to obtain component C; dissolving isocyanate in dry 2-butanone to obtain component D; mixing component D with component C and heating them at 70°C under argon protection to react to obtain component E; adding antimicrobial diol to component E and continuing the reaction, stirring and emulsifying, and reducing pressure and rotary evaporation to obtain a polyurethane coating.

[0013] In some embodiments, the alcohol donor is selected from at least one of isosorbic acid, 1,2-decanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 1,2-butanediol; and the neutralizer is selected from at least one of triethylamine, ammonia water, hydrochloric acid, sodium hydroxide, and acetic acid.

[0014] In some embodiments, the amount ratio of the alcohol donor, dimethylolpropionic acid, and neutralizing agent is 0.5-2:10:10.

[0015] In some embodiments, the isocyanate is selected from at least one of dimer acid diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, and lysine diisocyanate.

[0016] Another aspect of the present invention provides a polyurethane coating, which is prepared by the preparation method of the polyurethane coating of any of the above technical solutions.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a method for preparing a polyurethane coating. In the process of preparing an antibacterial diol, firstly, an acyl chloride substitution reaction is carried out between an acyl chloride and a phenolic hydroxyl group to obtain an intermediate reactant, and the structure of the phenolic substance is limited to contain no unsaturated bonds, so that the subsequent conjugate addition reaction between the intermediate reactant and an amine substance with hydroxyl groups at both ends will not be affected, thereby preparing the antibacterial diol, and preparing the coating by reacting the antibacterial diol with isocyanate, thereby ensuring the persistence of the subsequent antibacterial effect of the polyurethane coating.

[0019] The present invention provides a polyurethane coating, which can be hydrolyzed in water to produce organic antibacterial phenol with bactericidal activity, and can also form zwitterions with excellent antifouling ability at the release point, so that the coating has the synergistic antibacterial ability of "killing-defending" bacteria, and can be used as an antibacterial coating for parts in contact with food. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A reaction process diagram for preparing the antibacterial diol provided in an embodiment of the present invention;

[0021] Figure 2 This is a diagram of the "killing-defense" synergistic antibacterial mechanism of the polyurethane coating provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The technical scheme in the specific embodiment of the present invention will be described in detail and completely in conjunction with the accompanying drawings. Obviously, the described embodiments are only some specific implementation methods of the overall technical scheme of the present invention, rather than all implementation methods. Based on the overall concept of the present invention, all other embodiments obtained by ordinary technicians in this field fall within the scope of protection of the present invention.

[0023] The present invention provides a method for preparing a polyurethane coating, comprising: a phenolic substance and a chlorine donor undergo an acyl chloride substitution reaction to obtain an intermediate reactant, and the intermediate reactant undergoes a conjugate addition reaction with an amine substance having hydroxyl groups at both ends to obtain an antibacterial diol; the phenolic substance is selected from at least one of thymol, carvacrol, paeonol, catechol, and theaflavins. Figure 1 As shown, in the preparation process of antibacterial diol, firstly, acyl chloride and phenolic hydroxyl groups undergo acyl chloride substitution reaction to obtain an intermediate reactant, and it is limited that the phenolic substance structure does not contain unsaturated bonds (the phenolic substance structure is required to contain no unsaturated bonds, otherwise it will affect subsequent reactions), so that it will not affect the subsequent conjugate addition reaction between the intermediate reactant and the amine substance with hydroxyl groups at both ends, thereby preparing the antibacterial diol.

[0024] The present invention provides a method for preparing a polyurethane coating, comprising: reacting an antibacterial diol with an isocyanate to obtain a polyurethane coating. It should be noted that although the antibacterial diol can also produce phenolic substances that kill bacteria and anti-fouling and self-cleaning amphoteric substances after hydrolysis reaction in water, the antibacterial diol cannot form a coating on the surface of household appliances such as refrigerators and adhere to the surface of the refrigerator. Therefore, the technical solution uses the "one-pot method" between the antibacterial diol and the isocyanate to synthesize the polyurethane coating, which is then applied to the antibacterial process on the surface of household appliances such as refrigerators.

[0025] like Figure 2 As shown, the coating undergoes a hydrolysis reaction under the action of water to produce phenolic substances that kill bacteria and anti-fouling and self-cleaning amphoteric substances. Among them, due to the charged characteristics of the anti-fouling and self-cleaning amphoteric substances, they can repel charged bacterial particles, thereby achieving a "killing-defense" synergistic antibacterial effect. In addition, the coating has a slow release property and a long-lasting bactericidal effect, so it can be applied to the surface of food-contact parts in the home appliance industry such as refrigerators.

[0026] The antibacterial properties of traditional additive antibacterial coatings are difficult to last due to factors such as high initial release concentration, short release time, and coating surface contamination. The present invention discloses a polyurethane coating with a synergistic antibacterial effect of "killing and defending" bacteria. The coating is prepared from antibacterial diols and isocyanates, wherein the antibacterial diols are prepared by reacting active bactericidal phenolic substances and acyl chloride substances. The coating can be hydrolyzed in water to produce active bactericidal phenolic substances, which exert a bactericidal effect when in contact with bacteria. The amphoteric substances produced by hydrolysis have excellent antifouling ability, which can avoid the problem of reduced antibacterial effect due to the accumulation of killed bacteria on the coating surface, thereby making the coating have a synergistic antibacterial effect of "killing and defending" bacteria. In addition, the antibacterial diols contain a large benzene ring in their structure, which can effectively block the migration of isocyanate groups and can be used for coatings of food contact materials.

[0027] In some embodiments, the chlorine donor is selected from at least one of acryloyl chloride, 4-pentenoyl chloride, allyl oxalyl chloride, methacryloyl chloride, and 3,3-dimethylacryloyl chloride. The technical solution defines the type of chlorine donor, and the chlorine donor can undergo an acyl chloride substitution reaction with a phenolic hydroxyl group to obtain an intermediate reactant, thereby obtaining an antimicrobial diol.

[0028] In some embodiments, the antibacterial diol is prepared by the following method: mixing a phenolic substance and an amine substance with hydroxyl groups at both ends, adding dry dichloromethane thereto, cooling to 0°C in an ice bath, and obtaining component A; dissolving a chlorine donor in dichloromethane to obtain component B; mixing component B with component A and reacting at 0°C, and then transferring to room temperature for reaction to obtain antibacterial diol. This technical solution limits the mixing of phenolic substances and amine substances with hydroxyl groups at both ends and cooling to 0°C before mixing with a chlorine donor, rather than directly mixing phenolic substances, amine substances with hydroxyl groups at both ends, and chlorine donors, because at low temperatures, the amino group is protonated and its nucleophilicity is significantly reduced. At this time, when an acyl chloride is added, the acyl chloride will preferentially react with the phenolic hydroxyl group to form an ester. If mixed directly, the acyl chloride will preferentially react with the amine.

[0029] In some embodiments, component B is added dropwise to component A, reacted at 0°C, then transferred to room temperature for reaction, filtered, washed with dichloromethane, then rotary evaporated to remove excess solvent, extracted with saturated sodium chloride solution, dried with anhydrous sodium sulfate, and the final product is further rotary evaporated to obtain antibacterial diol. By defining the post-processing steps, the yield and purity of the prepared antibacterial diol are guaranteed.

[0030] In some embodiments, the amount of the amine substance with hydroxyl groups at both ends is equal to the amount of the hydroxyl group contained in the phenolic substance; the ratio of the amount of the chlorine donor to the amount of the amine substance with hydroxyl groups at both ends is 1.01-1.1: 1. This technical solution limits the amount of the relevant reactants, ensures sufficient reaction, reduces the use of excess substances, and ensures the purity of the product.

[0031] In some embodiments, the preparation of antibacterial diol includes: adding active bactericidal phenolic substances and diethanolamine in a certain ratio (the amount of hydroxyl substances contained in the active bactericidal substances and the amount of substances such as diethanolamine) to a three-necked round-bottom flask, and adding a certain amount of dry dichloromethane thereto, and cooling to 0°C in an ice bath. A certain amount of chlorine donor is dissolved in 10mL of dichloromethane and added dropwise to the reaction bottle. React at 0°C for a period of time, and then transfer to room temperature for a period of time. Filter, wash with dichloromethane, and then rotary evaporate to remove excess solvent. Afterwards, extract the solution with a saturated sodium chloride solution and dry with anhydrous sodium sulfate. The final product is further rotary evaporated and dried.

[0032] In some embodiments, the reaction of antimicrobial diol and isocyanate to obtain a polyurethane coating includes: dissolving an alcohol donor, dihydroxymethylpropionic acid and a neutralizer in dry 2-butanone, and reacting at 70°C to obtain component C; dissolving isocyanate in dry 2-butanone to obtain component D; mixing component D with component C and heating them at 70°C under argon protection to react to obtain component E; adding antimicrobial diol to component E and continuing the reaction, stirring and emulsifying, and reducing pressure and rotary evaporation to obtain a polyurethane coating.

[0033] In some embodiments, the alcohol donor is selected from at least one of isosorbic acid, 1,2-decanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 1,2-butanediol; the neutralizer is selected from at least one of triethylamine, ammonia, hydrochloric acid, sodium hydroxide, and acetic acid; the molar ratio of the alcohol donor, dimethylol propionic acid, and the neutralizer is 0.5-2:10:10; the isocyanate is selected from at least one of dimer acid diisocyanate, 1,5-pentane diisocyanate, 1,6-hexamethylene diisocyanate, and lysine diisocyanate. The above isocyanates are all bio-based isocyanates, so that the prepared polyurethane antibacterial coating is a bio-based polyurethane antibacterial coating.

[0034] In some embodiments, the preparation of the polyurethane antibacterial coating includes: the prepolymer of the polyurethane coating is synthesized by a "one-pot method". A certain proportion of alcohol donor, dimethylol propionic acid and neutralizer are dissolved in dry 2-butanone and reacted at 70°C for 30 minutes. Then, the bio-based isocyanate is dissolved in dry 2-butanone and heated at 70°C for 2 hours under argon protection. The antibacterial diol is then added to the reaction and then heated for another 2 hours. After the reaction is cooled to room temperature, 50 mL of deionized water is poured into the reaction flask and stirred and emulsified at 800 rpm for 12 hours. The final coating dispersion is decompressed and rotary evaporated for 2 hours to remove Voc.

[0035] Another aspect of the present invention provides a polyurethane coating, which is prepared by the preparation method of the polyurethane coating of any of the above technical solutions. The coating can be hydrolyzed in water to produce organic antibacterial phenols with bactericidal activity, and can also form zwitterions with excellent antifouling ability at the release point, so that the coating has a synergistic antibacterial ability of "killing-defending" bacteria, and because the antibacterial diol material structure contains a large benzene ring, it can effectively block the migration of isocyanate, and can be used for coatings of food contact materials, as antibacterial coatings for parts in contact with food.

[0036] In order to more clearly and in detail introduce the polyurethane coating and the preparation method thereof provided by the embodiments of the present invention, they will be described below in conjunction with specific embodiments.

[0037] Example 1

[0038] (1) Preparation of antimicrobial diols: 50 mmol of thymol and 50 mmol of diethanolamine were added to a three-necked round-bottom flask, 50 mL of dry dichloromethane was added, and the mixture was cooled to 0°C in an ice bath. 55 mmol of acryloyl chloride was dissolved in 10 mL of dichloromethane and added dropwise to the reaction flask. The mixture was reacted at 0°C for 2 h and at room temperature for 1 h. The mixture was filtered, washed with dichloromethane, and then rotary evaporated to remove excess solvent. Afterwards, the solution was extracted with a saturated sodium chloride solution and dried over anhydrous sodium sulfate. The final product was further rotary evaporated to dryness.

[0039] (2) Preparation of polyurethane antibacterial coating: The prepolymer of polyurethane coating was synthesized by "one-pot method". 5mmol isosorbide, 24mmol dihydroxymethylpropionic acid and 24mmol triethylamine were dissolved in 40mL dry 2-butanone and reacted at 70℃ for 30 minutes. Then, 52mmol dimer acid diisocyanate was dissolved in 15mL 2-butanone and heated at 70℃ for 2.5 hours under argon protection. Subsequently, 25mmol antibacterial diol was added to the reaction, which was then heated for another 2 hours. After the reaction was cooled to room temperature, 50mL deionized water was poured into the reaction flask and stirred at 800rpm for emulsification for 12 hours. The final coating dispersion was evaporated under reduced pressure at 45℃ for 2 hours to remove Voc.

[0040] Example 2

[0041] (1) Preparation of antimicrobial diols: 50 mmol of carvacrol and 50 mmol of diethanolamine were added to a three-necked round-bottom flask, and 50 mL of dry dichloromethane was added. The mixture was cooled to 0°C in an ice bath. 52 mmol of 4-pentenoyl chloride was dissolved in 10 mL of dichloromethane and added dropwise to the reaction flask. The mixture was reacted at 0°C for 2 h and at room temperature for 1 h. The mixture was filtered, washed with dichloromethane, and then rotary evaporated to remove excess solvent. Afterwards, the solution was extracted with a saturated sodium chloride solution and dried over anhydrous sodium sulfate. The final product was further rotary evaporated to dryness.

[0042] (2) Preparation of polyurethane antibacterial coating: The prepolymer of polyurethane coating was synthesized by "one-pot method". 4mmol 1,2-hexanediol, 25mmol dihydroxymethylpropionic acid and 25mmol ammonia water were dissolved in 40mL dry 2-butanone and reacted at 70℃ for 30 minutes. Then, 54mmol 1,5-pentanediisocyanate was dissolved in 15mL 2-butanone and heated at 70℃ for 2 hours under argon protection. Subsequently, 25mmol antibacterial diol was added to the reaction, which was then heated for another 2 hours. After the reaction was cooled to room temperature, 50mL deionized water was poured into the reaction flask and stirred at 800rpm for emulsification for 12 hours. The final coating dispersion was evaporated under reduced pressure at 45℃ for 2 hours to remove Voc.

[0043] Example 3

[0044] (1) Preparation of antimicrobial diol: Add 50 mmol of paeonol and 50 mmol of diethanolamine to a three-necked round-bottom flask, add 50 mL of dry dichloromethane, and cool to 0°C in an ice bath. Dissolve 52 mmol of methacryloyl chloride in 10 mL of dichloromethane and add dropwise to the reaction flask. React at 0°C for 2 h and at room temperature for 1 h. Filter, wash with dichloromethane, and then rotary evaporate to remove excess solvent. Thereafter, extract the solution with saturated sodium chloride solution and dry with anhydrous sodium sulfate. The final product is further rotary evaporated to dryness.

[0045] (2) Preparation of polyurethane antibacterial coating: The prepolymer of polyurethane coating was synthesized by a "one-pot method". 2mmol 1,2-butanediol, 20mmol dihydroxymethylpropionic acid and 20mmol triethylamine were dissolved in 40mL dry 2-butanone and reacted at 70°C for 30 minutes. Then, 44mmol 1,6-hexamethylene diisocyanate was dissolved in 15mL 2-butanone and heated at 70°C for 2 hours under argon protection. Subsequently, 22mmol of antibacterial diol was added to the reaction, which was then heated for another 2 hours. After the reaction was cooled to room temperature, 50mL of deionized water was poured into the reaction flask and stirred at 800rpm for emulsification for 12 hours. The final coating dispersion was rotary evaporated under reduced pressure at 45°C for 2 hours to remove Voc.

[0046] Example 4

[0047] (1) Preparation of antimicrobial diols: 50 mmol of carvacrol and 50 mmol of diethanolamine were added to a three-necked round-bottom flask, and 50 mL of dry dichloromethane was added. The mixture was cooled to 0°C in an ice bath. 50.5 mmol of 3,3-dimethylacryloyl chloride was dissolved in 10 mL of dichloromethane and added dropwise to the reaction flask. The mixture was reacted at 0°C for 2 h and at room temperature for 1 h. The mixture was filtered, washed with dichloromethane, and then rotary evaporated to remove excess solvent. The solution was then extracted with a saturated sodium chloride solution and dried over anhydrous sodium sulfate. The final product was further rotary evaporated to dryness.

[0048] (2) Preparation of polyurethane antibacterial coating: The prepolymer of polyurethane coating was synthesized by a "one-pot method". 4mmol 1,2-pentanediol, 20mmol dihydroxymethylpropionic acid and 20mmol ammonia water were dissolved in 40mL dry 2-butanone and reacted at 70°C for 30 minutes. Then, 44mmol lysine diisocyanate was dissolved in 15mL 2-butanone and heated at 70°C for 2 hours under argon protection. Subsequently, 21mmol of antibacterial diol was added to the reaction, which was then heated for another 2 hours. After the reaction was cooled to room temperature, 50mL of deionized water was poured into the reaction flask and stirred at 800rpm for emulsification for 12 hours. The final coating dispersion was evaporated under reduced pressure at 45°C for 2 hours to remove Voc.

[0049] Comparative Example 1

[0050] Preparation of polyurethane coating: 30mmol isosorbide, 24mmol dimethylol propionic acid and 24mmol triethylamine were dissolved in 40mL dry 2-butanone and reacted at 70°C for 30 minutes. Then, 52mmol lysine diisocyanate was dissolved in 15mL 2-butanone and heated at 70°C for 2 hours under argon protection. After the reaction was cooled to room temperature, 50mL deionized water was poured into the reaction flask and stirred at 800rpm for 12 hours. The final coating dispersion was evaporated under reduced pressure at 45°C for 2 hours to remove Voc.

[0051] Functional testing

[0052] (1) Antibacterial performance test

[0053] The antibacterial properties of the coatings were evaluated using Escherichia coli and Staphylococcus aureus as test bacteria. The coatings of Examples 1-4 and Comparative Example 1 were applied to a glass slide and solidified into a film, and then 100 μL of a bacterial suspension with a concentration of 108 CFU / mL was applied to the surface of the coating and cultured in a sterile environment at 37°C for 24 hours. The glass slide was taken out and repeatedly rinsed with a phosphate buffer solution. The wash solution was inoculated into a nutrient agar medium, and after culturing at 37°C for 24 hours, the bacterial survival was recorded as shown in Table 1.

[0054] Table 1 Antibacterial effect

[0055] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Escherichia coli 97.5％ 98.6％ 99.2％ 92.1％ No antibacterial effect Staphylococcus aureus 98.6％ 99.3％ 99.8％ 94.5％ No antibacterial effect

[0056] As can be seen from Table 1, the antibacterial rates of Escherichia coli and Staphylococcus aureus in Examples 1-4 are as high as over 97%, and the bio-based polyurethane coating prepared with antibacterial diol as raw material exhibits excellent antibacterial properties. Antibacterial diol hydrolyzes to produce active bactericidal phenolic substances. On the one hand, phenolic substances block the metabolic pathways of bacteria by interfering with key enzyme systems of bacteria, such as oxidase and dehydrogenase, to achieve a bactericidal effect. On the other hand, phenolic substances can also dissolve in the lipophilic body of the cell, accumulate on the surface of the bacterial cell, increase the permeability of the cell wall, cause the contents of the bacteria to overflow, further change the spatial structure of the cell protein and denature it, and finally kill the bacteria.

[0057] (2) Bacterial adhesion test

[0058] The coatings of Examples 1-4 and Comparative Example 1 were applied to a glass slide and cured into a film (2.5 cm * 2.5 cm) and immersed in 1 ml of sterile LB broth, then inoculated with a small amount of bacterial colonies, and then cultured at 37°C with shaking at 200 rpm for 24 hours. Subsequently, the solution culture was aspirated with a pipette and fresh LB broth was replenished every 24 hours. After 3 days, the sample was removed from the culture and gently rinsed with sterile saline. The attached bacteria were stained using the LIVE / DEAD bacterial viability detection kit and incubated for 25 minutes without ambient light. The biofilm formed on the coating surface was observed using CLSM (Nikon Eclipse Ti-U) at 200 times magnification. The images obtained were analyzed using Image J software, and the signal intensity in the red and green channels was quantified respectively.

[0059] Relative bacterial attachment (RBA) was calculated using Image J software, and the color channels of the confocal images were split into red, green, and blue channels to analyze the number of dead and live bacteria separately. In each channel, image thresholding was performed to accurately select the area covered by bacteria in the image. The bacterial coverage was then quantified by measuring the content of the selected pixels as a proportion of the total number of pixels in the image. The relative bacterial attachment (RBA) was calculated by the sum of the live and dead bacterial coverage, and the results are shown in Table 2.

[0060] Table 2 Bacterial attachment rate

[0061] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Escherichia coli 17.3％ 18.3％ 17.8％ 18.7％ 86.3％ Staphylococcus aureus 13.5％ 14.6％ 14.2％ 14.5％ 75.9％

[0062] As can be seen from Table 2, the antibacterial rate of the antibacterial polyurethane coatings in Examples 1-4 against Escherichia coli and Staphylococcus aureus is as high as over 97%, and the bio-based polyurethane coatings prepared with antibacterial diol as raw material exhibit excellent low bacterial adhesion. While the polyurethane coatings produce active bactericidal phenolic substances after hydrolysis, they also form antifouling zwitterions, which can avoid the problem of reduced antibacterial effect due to the accumulation of killed bacteria on the coating surface, further improving the sustainability and durability of the antibacterial polyurethane coatings.

[0063] (3) Migration experiment

[0064] In order to evaluate the compliance of food contact coating materials with national food safety standards, this experiment was carried out in accordance with the provisions of GB31604.1 and GB 50093156 to simulate the use in a frozen and refrigerated environment. The experimental conditions were 20°C for 10 days, and the coatings of Examples 1-4 and Comparative Example 1 were coated on a glass sheet and cured to form a film (6dm 2), 10% ethanol (v / v), 4% acetic acid (v / v), 50% ethanol (v / v) and vegetable oil were used to simulate aqueous food, acidic food, alcoholic food and fatty food, respectively. The results are shown in Table 3.

[0065] Table 3 Isocyanate migration amount (mg / kg)

[0066]

[0067]

[0068] It can be seen from Table 3 that the migration amount of isocyanate radicals in the antimicrobial polyurethane coatings in Examples 1-4 is less than 0.05 mg / kg, which meets the requirements of food contact coatings. The reason why the migration rate of isocyanate radicals is higher in an aqueous environment is that the hydrolysis of the ester group in the structure fully releases the antimicrobial phenolic substances, which reduces the barrier effect on isocyanate radicals, thereby increasing the migration rate of isocyanate radicals.

Claims

1. A method for preparing a polyurethane coating, characterized in that: include: A phenolic substance undergoes an acyl chloride substitution reaction with a chlorine donor to obtain an intermediate reactant, and the intermediate reactant undergoes a conjugate addition reaction with an amine substance having hydroxyl groups at both ends to prepare an antibacterial diol; The antimicrobial diol reacts with isocyanate to obtain a polyurethane coating; The phenolic substance is selected from at least one of thymol, carvacrol, paeonol, catechol and theaflavins.

2. The method for preparing the polyurethane coating according to claim 1, characterized in that: The chlorine donor is selected from at least one of acryloyl chloride, 4-pentenoyl chloride, allyl oxalyl chloride, methacryloyl chloride and 3,3-dimethylacryloyl chloride.

3. The method for preparing the polyurethane coating according to claim 1, characterized in that: The antibacterial diol is prepared by the following method: The phenolic substance and the amine substance with hydroxyl groups at both ends are mixed, and dry dichloromethane is added thereto, and the mixture is cooled to 0° C. in an ice bath to obtain component A; Dissolving the chlorine donor in dichloromethane to obtain component B; The component B and the component A are mixed and reacted at 0° C., and then transferred to room temperature for reaction to obtain the antibacterial diol.

4. The method for preparing the polyurethane coating according to claim 3, characterized in that: The component B is added dropwise to the component A, reacted at 0°C, and then transferred to room temperature for reaction, filtered, washed with dichloromethane, and then rotary evaporated to remove excess solvent, the solution is extracted with saturated sodium chloride solution, and dried with anhydrous sodium sulfate. The final product is further rotary evaporated to obtain the antibacterial diol.

5. The method for preparing the polyurethane coating according to claim 3, characterized in that: The amount of the amine substance with hydroxyl groups at both ends is equal to the amount of hydroxyl groups contained in the phenolic substance; the ratio of the amount of the chlorine donor to the amount of the amine substance with hydroxyl groups at both ends is 1.01-1.1:

1.

6. The method for preparing the polyurethane coating according to claim 1, characterized in that: The polyurethane coating obtained by reacting the antimicrobial diol with isocyanate comprises: The alcohol donor, dimethylol propionic acid and a neutralizing agent are dissolved in dry 2-butanone, and reacted at 70° C. to obtain component C; dissolving the isocyanate in dry 2-butanone to obtain component D; The component D and the component C are mixed and heated at 70° C. under argon protection to react, thereby obtaining component E; The antibacterial diol is added to the component E and the reaction is continued, followed by stirring and emulsification, and then rotary evaporation under reduced pressure is performed to obtain the polyurethane coating.

7. The method for preparing the polyurethane coating according to claim 6, characterized in that: The alcohol donor is selected from at least one of isosorbic acid, 1,2-decanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol, and 1,2-butanediol; the neutralizer is selected from at least one of triethylamine, ammonia water, hydrochloric acid, sodium hydroxide, and acetic acid.

8. The method for preparing the polyurethane coating according to claim 6, characterized in that: The molar ratio of the alcohol donor, the dimethylolpropionic acid and the neutralizing agent is 0.5-2:10:

10.

9. The method for preparing the polyurethane coating according to claim 6, characterized in that: The isocyanate is selected from at least one of dimer acid diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate and lysine diisocyanate.

10. A polyurethane coating, characterized in that: The polyurethane coating is prepared by the preparation method of any one of claims 1 to 9.

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