Environment-friendly antibacterial paint and preparation method thereof

Abstract

This invention discloses an environmentally friendly antibacterial paint and its preparation method, belonging to the field of paint technology. It comprises the following raw materials in parts by weight: 40-50 parts water-based acrylic emulsion, 2-4 parts nano-zinc oxide, 3-6 parts antibacterial chitosan, 15-20 parts rutile titanium dioxide, 10-15 parts ultrafine talc, 1-2 parts dispersant, 0.5-1 part defoamer, 2-3 parts film-forming aid, 0.6-1.2 parts thickener, and 20-30 parts deionized water. The water-based acrylic emulsion, as the main film-forming substance, significantly reduces VOC emissions; the antibacterial chitosan and nano-zinc oxide construct a composite antibacterial system, prolonging the antibacterial durability and preventing the loss of organic antibacterial components, significantly improving the antibacterial properties of the paint; and the antibacterial chitosan has stronger hydrophilicity and antibacterial activity compared to ordinary chitosan; the rutile titanium dioxide and ultrafine talc, as fillers, improve the paint's wear resistance and durability.

Description

Technical Field

[0001] This invention belongs to the field of paint technology, specifically relating to an environmentally friendly antibacterial paint and its preparation method. Background Technology

[0002] Paint, as an important type of surface functional material, is widely used in various fields such as building decoration, furniture manufacturing, medical facilities, and food processing workshops. It plays a core role in decorative aesthetics, substrate protection, and extending service life, and its performance directly affects the user experience and environmental safety. With the increasing awareness of environmental protection and the growing demand for health, the shortcomings of traditional paints in terms of environmental protection and lack of antibacterial properties have become increasingly prominent, making it difficult to meet the stringent requirements of modern production and life.

[0003] Traditional paints are mostly solvent-based, using large amounts of volatile organic compounds (VOCs) such as benzene, toluene, and xylene as diluents. These substances are continuously released into the air during construction and use, causing air pollution and harming human health through inhalation and skin contact, leading to respiratory diseases, dizziness, nausea, and other symptoms. Long-term exposure may even pose a cancer risk. Furthermore, some traditional paints add heavy metals such as lead, mercury, and chromium to enhance their anti-corrosion properties. These substances easily accumulate in the environment, polluting soil and water sources and causing irreversible damage to ecosystems. Although environmentally friendly products such as water-based paints have gradually emerged in recent years, while reducing VOC content, they often face the problem of insufficient antibacterial properties. The hydrophilic environment of water-based systems easily becomes a breeding ground for bacteria, mold, fungi, and other microorganisms. Especially in humid and enclosed environments, paint surfaces are prone to mold spots and odors, affecting not only appearance but also potentially spreading bacteria and threatening public health and safety. This problem is particularly prominent in fields with extremely high hygiene requirements, such as medical and food industries.

[0004] To address the need for antibacterial properties, existing technologies often involve adding antibacterial agents to prepare antibacterial paints. However, this approach still has several drawbacks. On one hand, while commonly used inorganic antibacterial agents (such as silver ions and zinc ions) are relatively safe, they often require high dosages to achieve the desired effect. This not only increases production costs but may also affect the paint's film-forming properties, adhesion, and scrub resistance, leading to easy peeling and discoloration. On the other hand, organic antibacterial agents may be prone to migration, have a short shelf life, and may possess certain toxicity or irritant properties, raising concerns about environmental friendliness and safety. Therefore, there is an urgent need to solve these problems and invent a paint that combines environmental friendliness and antibacterial properties to meet the higher technical demands of the paint technology field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an environmentally friendly antibacterial paint and its preparation method.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] An environmentally friendly antibacterial paint comprises the following raw materials in parts by weight: 40-50 parts water-based acrylic emulsion, 2-4 parts nano zinc oxide, 3-6 parts antibacterial chitosan, 15-20 parts rutile titanium dioxide, 10-15 parts ultrafine talc, 1-2 parts dispersant, 0.5-1 part defoamer, 2-3 parts film-forming aid, 0.6-1.2 parts thickener, and 20-30 parts deionized water.

[0008] As a further technical solution, the dispersant is a polycarboxylate dispersant.

[0009] As a further technical solution, the defoamer is an organosilicone defoamer.

[0010] This invention uses water-based acrylic emulsion as the core film-forming component, which not only eliminates toxic solvents such as benzene and toluene, reducing environmental pollution at the source, but also exhibits excellent film-forming properties and strong compatibility with fillers, ensuring stable overall paint performance. The fillers selected are rutile titanium dioxide and ultrafine talc. Rutile titanium dioxide has extremely high hiding power and whiteness, enhancing the decorative effect of the paint while reflecting ultraviolet rays, delaying coating aging, and enhancing weather resistance. Ultrafine talc has a layered structure; its addition fills the internal voids of the coating, improving its wear resistance and leveling properties during application, reducing the amount of film-forming aids used, and further reducing VOC emissions.

[0011] As a further technical solution, the antibacterial chitosan is prepared through the following steps:

[0012] A1. In a dry round-bottom flask, 5-hydroxyisophthalic acid, sodium p-aminobenzenesulfonate, and dry tetrahydrofuran are added sequentially. The apparatus is placed in an ice-water bath (0-5℃), and stirring is turned on to allow the raw materials to cool and disperse fully. Then, 4-dimethylaminopyridine is slowly added while maintaining the ice bath. Dicyclohexylcarbodiimide is added slowly in batches. After the addition is complete, the ice-water bath is removed, and the reaction mixture is allowed to slowly return to room temperature. The reaction is carried out at room temperature for 6-8 hours. After the reaction is completed, the product A is obtained through post-processing.

[0013] A2. In a dry round-bottom flask, add reaction product A and dry dichloromethane in sequence and stir to dissolve. Then add N-hydroxysuccinimide and 4-dimethylaminopyridine in sequence. Then cool the reaction mixture in an ice-water bath for 10-20 minutes while stirring. During the stirring process, add dicyclohexylcarbodiimide. Then remove the ice bath and heat the apparatus to 50-55°C. Keep the temperature for 4-6 hours. After the reaction is completed, perform post-processing to obtain reaction product B.

[0014] A3. In a dry round-bottom flask, add chitosan and lactic acid aqueous solution (5% by volume) in sequence, and stir until the chitosan is completely dissolved. Dissolve the reaction product B in N,N-dimethylformamide in a beaker and transfer it to a constant pressure dropping funnel. Add it dropwise to the flask at room temperature. After the addition is complete, continue the reaction for 10-12 hours. After the reaction is completed, perform post-processing to obtain antibacterial chitosan.

[0015] As a further technical solution, in step A1, the ratio of the amounts of 5-hydroxyisophthalic acid, sodium p-aminobenzenesulfonate, dried tetrahydrofuran, 4-dimethylaminopyridine and dicyclohexylcarbodiimide is 20.1-21.7g:19.5g:150mL:0.5g:20.6g.

[0016] As a further technical solution, in step A2, the ratio of reaction product A, dried dichloromethane, N-hydroxysuccinimide, 4-dimethylaminopyridine and dicyclohexylcarbodiimide is 35.9g:150mL:11.5g:0.5g:20.6g.

[0017] As a further technical solution, in step A3, the ratio of chitosan, lactic acid aqueous solution, reaction product B, and N,N-dimethylformamide is 1g:100mL:2.7g:50mL.

[0018] The reaction formula for the preparation of the above antibacterial chitosan is as follows:

[0019]

[0020] In order to successfully carry out the above reaction formula, the amount of raw materials in step A1 needs to be limited, and the molar ratio of 5-hydroxyisophthalic acid to sodium p-aminobenzenesulfonate should be controlled to be close to 1:1, with the former in excess, and one carboxyl group reserved for the reaction in step A2.

[0021] Chitosan, a natural high-molecular-weight antibacterial component derived from biomass such as shrimp and crab shells, is biodegradable and leaves no environmental residue. This invention modifies chitosan by breaking its original hydrogen bond network, making the molecular chains easier to contact with water molecules, thus improving its hydrophilicity and making it easier to disperse in water-based paints, thereby better exerting its antibacterial properties. Furthermore, sodium sulfonate groups are introduced in step A1, further enhancing its hydrophilicity and thus strengthening the paint's antibacterial properties. In addition, phenolic hydroxyl groups are introduced onto the chitosan, which can denature proteins and disrupt cell membranes, further improving its antibacterial performance. Finally, nano-zinc oxide, as an inorganic antibacterial component, is environmentally friendly and non-toxic, exhibiting high antibacterial rates against pathogenic bacteria such as Escherichia coli and Staphylococcus aureus. The chitosan molecular chains can encapsulate the nano-zinc oxide, preventing aggregation, reducing the amount of nano-zinc oxide added, avoiding coating discoloration or decreased film-forming performance, and improving stability. Finally, by grafting chitosan, the loss of small organic molecules during use can be prevented, extending the antibacterial durability.

[0022] This invention also provides a method for preparing an environmentally friendly antibacterial paint, comprising the following steps:

[0023] B1. Add nano zinc oxide, antibacterial chitosan and deionized water to a high-speed disperser in sequence and stir for 20-30 minutes to form a uniform composite antibacterial dispersion.

[0024] B2. Place rutile titanium dioxide and ultrafine talc powder in a drying oven to dry them, remove moisture, and prevent the formation of bubbles and agglomeration during the preparation process to obtain dry filler.

[0025] B3. Add the remaining deionized water to the reactor, turn on the stirring device, and slowly add the dispersant. After the dispersant is added, continue stirring for 5-10 minutes. Then add the dry filler and defoamer in sequence and continue stirring for 30-40 minutes to form a uniform slurry.

[0026] B4. Transfer the slurry to a sand mill for grinding (particle size ≤ 50μm). After grinding, transfer it back to the reactor and slowly add water-based acrylic emulsion while stirring for 20-30 minutes until it is evenly mixed. Then add film-forming aid and thickener in sequence. Finally, filter with a filter screen to obtain environmentally friendly antibacterial paint.

[0027] As a further technical solution, the amount of deionized water used in step B1 accounts for 1 / 5 of the total mass of deionized water.

[0028] As a further technical solution, the rotational speed of the high-speed disperser is 1000-1500 r / min.

[0029] As a further technical solution, the drying temperature is 60-70℃ and the time is 2-4 hours.

[0030] As a further technical solution, the stirring device has a rotation speed of 800-1000 r / min.

[0031] As a further technical solution, the rotation speed of the sand mill is 2000-2500 r / min, and the grinding is performed 2-3 times, each time for 30 minutes.

[0032] As a further technical solution, the mesh size of the filter is 200 mesh or more.

[0033] The beneficial effects of this invention are:

[0034] 1. This invention uses water-based acrylic emulsion as the main film-forming substance, which significantly reduces VOC emissions and minimizes harm to the environment and human body;

[0035] 2. By introducing antibacterial chitosan and nano zinc oxide, a composite antibacterial system was constructed, which extended the antibacterial durability, prevented the loss of organic antibacterial components, and significantly improved the antibacterial properties of the paint; moreover, antibacterial chitosan has stronger hydrophilicity and antibacterial activity compared with ordinary chitosan.

[0036] 3. Rutile titanium dioxide and ultrafine talc are used as fillers to improve the wear resistance and durability of the paint;

[0037] In summary, this invention provides a paint that is both environmentally friendly and highly effective in antibacterial properties, effectively solving the problem of balancing environmental friendliness, antibacterial durability, and coating performance in traditional paints and existing antibacterial paints. It is suitable for places with high hygiene requirements, such as medical and food industries. Detailed Implementation

[0038] 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.

[0039] Example 1

[0040] Preparation of antibacterial chitosan:

[0041] A1. In a dry round-bottom flask, add 20.1 g of 5-hydroxyisophthalic acid, 19.5 g of sodium p-aminobenzenesulfonate, and 150 mL of dry tetrahydrofuran in sequence. Place the apparatus in an ice-water bath (0°C), turn on the stirrer, and allow the raw materials to cool and disperse fully. Then slowly add 0.5 g of 4-dimethylaminopyridine while maintaining the ice bath. Add 20.6 g of dicyclohexylcarbodiimide in batches. After the addition is complete, remove the ice-water bath and allow the reaction mixture to slowly return to room temperature. React at room temperature for 6 hours. After the reaction is complete, filter the reaction solution, wash the residue with dichloromethane, combine the filtrates, wash successively with HCl solution and saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure to obtain reaction product A.

[0042] A2. In a dry round-bottom flask, 35.9 g of reaction product A and 150 mL of dry dichloromethane were added sequentially and stirred until dissolved. Then, 11.5 g of N-hydroxysuccinimide and 0.5 g of 4-dimethylaminopyridine were added sequentially. The reaction mixture was then cooled and stirred in an ice-water bath for 10 min. During stirring, 20.6 g of dicyclohexylcarbodiimide was added. The ice bath was then removed, and the apparatus was heated to 50 °C and kept at this temperature for 4 h. The reaction solution was filtered, and the residue was washed with dichloromethane. The filtrates were combined and concentrated to dryness under reduced pressure using a rotary evaporator. The solution was then rapidly purified by silica gel column chromatography (using a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 5:1) and dried under vacuum to obtain reaction product B.

[0043] A3. In a dry round-bottom flask, add 1g of chitosan and 100mL of lactic acid aqueous solution (5% by volume) in sequence, and stir until the chitosan is completely dissolved. In a beaker, dissolve 2.7g of reaction product B in 50mL of N,N-dimethylformamide and transfer it to a constant pressure dropping funnel. Add the solution dropwise to the flask at room temperature. After the addition is complete, continue the reaction for 10h. After the reaction is complete, adjust the pH of the reaction system to 7.0 with hydrochloric acid solution. At this time, a precipitate appears and is filtered. Wash the obtained solid product with acetone and ethanol three times each. Dissolve the filter cake in deionized water and dialyze it in a dialysis bag (Mw=3500) for 2 days. Change the external dialysate deionized water three times a day. Freeze-dry the dialysis solution at -35℃ for 48h to obtain antibacterial chitosan.

[0044] A method for preparing an environmentally friendly antibacterial paint includes the following steps:

[0045] B1. Add 2 parts of nano zinc oxide, 3 parts of antibacterial chitosan and 4 parts of deionized water to a high-speed disperser (speed 1000 r / min) and stir for 20 min to form a uniform composite antibacterial dispersion.

[0046] B2. Place 15-20 parts of rutile titanium dioxide (particle size 0.2μm) and 10-15 parts of ultrafine talc powder (5μm) in a drying oven and dry at 60℃ for 2 hours to remove moisture and prevent the generation of bubbles and agglomeration during the preparation process, and obtain dry filler.

[0047] B3. Add 16 parts of deionized water to the reactor, turn on the stirring device (speed 800r / min), and slowly add 1 part of dispersant (BYK-190). After the addition is complete, continue stirring for 5 minutes, then add the dry filler and 0.5 parts of defoamer (BYK-024) in sequence, and continue stirring for 30 minutes to form a uniform slurry.

[0048] B4. Transfer the slurry to a sand mill (speed 2000 r / min) and grind it twice, 30 min each time, until the particle size is ≤50μm. After grinding, transfer it back to the reactor and slowly add 40 parts of water-based acrylic emulsion (SEACRYL11W18) while stirring continuously for 20 min until it is evenly mixed. Then add 2 parts of propylene glycol methyl ether acetate and 0.6 parts of hydroxyethyl cellulose in sequence. Finally, filter it through a 300 mesh filter to obtain environmentally friendly antibacterial paint.

[0049] Example 2

[0050] Preparation of antibacterial chitosan:

[0051] A1. In a dry round-bottom flask, add 21.7 g of 5-hydroxyisophthalic acid, 19.5 g of sodium p-aminobenzenesulfonate, and 150 mL of dry tetrahydrofuran in sequence. Place the apparatus in an ice-water bath (°C), turn on the stirrer to allow the raw materials to cool and disperse fully, and then slowly add 0.5 g of 4-dimethylaminopyridine. While maintaining the ice bath, slowly add 20.6 g of dicyclohexylcarbodiimide in batches. After the addition is complete, remove the ice-water bath and allow the reaction mixture to slowly return to room temperature. React at room temperature for 8 hours. After the reaction is complete, filter the reaction solution, wash the filter residue with dichloromethane, combine the filtrates, wash them successively with HCl solution and saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate the filtrate under reduced pressure to obtain reaction product A.

[0052] A2. In a dry round-bottom flask, 35.9 g of reaction product A and 150 mL of dry dichloromethane were added sequentially and stirred until dissolved. Then, 11.5 g of N-hydroxysuccinimide and 0.5 g of 4-dimethylaminopyridine were added sequentially. The reaction mixture was then stirred and cooled in an ice-water bath for 20 min. During stirring, 20.6 g of dicyclohexylcarbodiimide was added. The ice bath was then removed, and the apparatus was heated to 55 °C and kept at this temperature for 6 h. The reaction solution was filtered, and the residue was washed with dichloromethane. The filtrates were combined and concentrated to dryness under reduced pressure using a rotary evaporator. The solution was then rapidly purified by silica gel column chromatography (using a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 5:1) and dried under vacuum to obtain reaction product B.

[0053] A3. In a dry round-bottom flask, add 1g of chitosan and 100mL of lactic acid aqueous solution (5% by volume) in sequence, and stir until the chitosan is completely dissolved. In a beaker, dissolve 2.7g of reaction product B in 50mL of N,N-dimethylformamide and transfer it to a constant pressure dropping funnel. Add the solution dropwise to the flask at room temperature. After the addition is complete, continue the reaction for 12h. When the reaction is complete, adjust the pH of the reaction system to 7.0 with hydrochloric acid solution. At this time, a precipitate appears and is filtered. Wash the obtained solid product with acetone and ethanol three times each. Dissolve the filter cake in deionized water and dialyze it in a dialysis bag (Mw=3500) for 2 days, changing the external dialysate deionized water three times a day. Freeze-dry the dialysis solution at -35℃ for 48h to obtain antibacterial chitosan.

[0054] A method for preparing an environmentally friendly antibacterial paint includes the following steps:

[0055] B1. Add 3 parts of nano zinc oxide, 4.5 parts of antibacterial chitosan and 5 parts of deionized water to a high-speed disperser (speed 1500 r / min) and stir for 30 min to form a uniform composite antibacterial dispersion.

[0056] B2. Place 15-20 parts of rutile titanium dioxide (particle size 0.3μm) and 15 parts of ultrafine talc powder (10μm) in a drying oven and dry at 70℃ for 4 hours to remove moisture and prevent bubbles and agglomeration during the preparation process, and obtain dry filler.

[0057] B3. Add 20 parts of deionized water to the reactor, turn on the stirring device (speed is 1000 r / min), and slowly add 1.5 parts of dispersant (BYK-190). After the addition is complete, continue stirring for 10 min. Then add the dry filler and 0.75 parts of defoamer (BYK-024) in sequence, and continue stirring for 35 min to form a uniform slurry.

[0058] B4. Transfer the slurry to a sand mill (speed 2500 r / min) and grind it three times for 30 minutes each time until the particle size is ≤50μm. After grinding, transfer it back to the reactor and slowly add 45 parts of water-based acrylic emulsion (SEACRYL11W18) while stirring continuously for 25 minutes until it is evenly mixed. Then add 1.5 parts of propylene glycol methyl ether acetate and 0.9 parts of hydroxyethyl cellulose in sequence. Finally, filter it through a 300-mesh filter to obtain environmentally friendly antibacterial paint.

[0059] Example 3

[0060] The only difference between this embodiment and Embodiment 2 is that, in this embodiment, a method for preparing an environmentally friendly antibacterial paint includes the following steps:

[0061] B1. Add 4 parts of nano zinc oxide, 6 parts of antibacterial chitosan and 6 parts of deionized water to a high-speed disperser (speed 1500 r / min) and stir for 30 min to form a uniform composite antibacterial dispersion.

[0062] B2. Place 20 parts of rutile titanium dioxide (particle size 0.3 μm) and 15 parts of ultrafine talc powder (10 μm) in a drying oven and dry at 70°C for 4 hours to remove moisture and prevent the generation of bubbles and agglomeration during the preparation process, and obtain dry filler.

[0063] B3. Add 24 parts of deionized water to the reactor, turn on the stirring device (speed 1000r / min), and slowly add 2 parts of dispersant (BYK-190). After the addition is complete, continue stirring for 10 minutes, then add the dry filler and 1 part of defoamer (BYK-024) in sequence, and continue stirring for 40 minutes to form a uniform slurry.

[0064] B4. Transfer the slurry to a sand mill (speed 2500r / min) and grind it three times for 30min each time until the particle size is ≤50μm. After grinding, transfer it back to the reactor and slowly add 50 parts of water-based acrylic emulsion (SEACRYL11W18) while stirring continuously for 30min until it is evenly mixed. Then add 3 parts of propylene glycol methyl ether acetate and 1.2 parts of hydroxyethyl cellulose in sequence. Finally, filter it through a 300-mesh filter to obtain environmentally friendly antibacterial paint.

[0065] Comparative Example 1

[0066] The only difference between this comparative example and Example 3 is that in this comparative example, an equal amount of chitosan (unmodified) was used to replace the antibacterial chitosan to prepare the paint.

[0067] Comparative Example 2

[0068] Use commercially available water-based acrylic paint (product number: JBL-4166, Guangzhou Jiabaili Waterproofing Engineering Co., Ltd.).

[0069] The following performance tests were conducted on Examples 1, 2, and 3, and Comparative Examples 1 and 2:

[0070] Environmental friendliness was assessed using the GB / T 23986-2009 standard.

[0071] The antibacterial properties (Escherichia coli) were determined according to the national standard GB / T 21866-2008 "Determination of Antibacterial Properties and Antibacterial Effects of Antibacterial Coatings (Films)"; and the antibacterial durability of the examples was tested.

[0072] The performance test results are shown in Table 1:

[0073] Table 1

[0074]

[0075] As shown in Table 1, the paint prepared in the embodiments of the present invention has higher antibacterial properties than the comparative example, and its antibacterial durability and environmental friendliness are excellent. Therefore, the paint of the present invention has both environmental friendliness and high antibacterial efficiency, effectively solving the problem of balancing environmental friendliness, antibacterial durability and coating performance in traditional paints and existing antibacterial paints. It is suitable for places with high hygiene requirements such as medical and food industries.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. An environmentally friendly antibacterial paint, characterized in that, The raw materials include the following parts by weight: 40-50 parts water-based acrylic emulsion, 2-4 parts nano zinc oxide, 3-6 parts antibacterial chitosan, 15-20 parts rutile titanium dioxide, 10-15 parts ultrafine talc, 1-2 parts dispersant, 0.5-1 part defoamer, 2-3 parts film-forming aid, 0.6-1.2 parts thickener, and 20-30 parts deionized water; The antibacterial chitosan is prepared through the following steps: A1. In a flask, add 5-hydroxyisophthalic acid, sodium p-aminobenzenesulfonate and dry tetrahydrofuran in sequence. Place the apparatus in an ice-water bath, turn on the stirrer, and then add 4-dimethylaminopyridine and dicyclohexylcarbodiimide. After the addition is complete, remove the ice-water bath and react at room temperature for 6-8 hours. When the reaction is complete, the reaction product A is obtained. A2. In a flask, add reaction product A and dry dichloromethane in sequence, stir to dissolve, then add N-hydroxysuccinimide and 4-dimethylaminopyridine in sequence, stir and cool in an ice-water bath for 10-20 min, and add dicyclohexylcarbodiimide during stirring. Then remove the ice bath and keep the reaction at 50-55℃ for 4-6 h. After the reaction is completed, reaction product B is obtained. A3. In a flask, add chitosan and lactic acid aqueous solution in sequence and stir until the chitosan is completely dissolved. Dissolve reaction product B in N,N-dimethylformamide and add it dropwise to the flask at room temperature. After the addition is complete, continue the reaction for 10-12 hours. When the reaction is complete, antibacterial chitosan is obtained. In step A1, the ratio of the amounts of 5-hydroxyisophthalic acid, sodium p-aminobenzenesulfonate, dried tetrahydrofuran, 4-dimethylaminopyridine, and dicyclohexylcarbodiimide is 20.1-21.7g:19.5g:150mL:0.5g:20.6g.

2. The environmentally friendly antibacterial paint according to claim 1, characterized in that, In step A2, the ratio of reaction product A, dried dichloromethane, N-hydroxysuccinimide, 4-dimethylaminopyridine, and dicyclohexylcarbodiimide is 35.9 g: 150 mL: 11.5 g: 0.5 g: 20.6 g.

3. The environmentally friendly antibacterial paint according to claim 1, characterized in that, In step A3, the ratio of chitosan, lactic acid aqueous solution, reaction product B, and N,N-dimethylformamide is 1g:100mL:2.7g:50mL.

4. The environmentally friendly antibacterial paint according to claim 1, characterized in that, The dispersant is a polycarboxylate dispersant.

5. The environmentally friendly antibacterial paint according to claim 1, characterized in that, The defoamer is an organosilicone defoamer.

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