Bio-based polyurethane coating and preparation method thereof

Abstract

The invention discloses a bio-based polyurethane coating, which is prepared from the following raw materials in parts by weight: 53.5 to 78.3 parts of diphenylmethane diisocyanate, 64.8 to 127.6 parts of polypropylene glycol, 14.6 to 17.4 parts of castor oil, 18.4 to 22.4 parts of dimethylolpropionic acid, 51.7 to 82.1 parts of 1, 4-butanediol, 9.5 to 12.1 parts of acetone, 3.5 to 9.5 parts of triethylamine, 13.5 to 15.1 parts of modified antibacterial agents and 21.9 to 45.8 parts of dispersing agents. The invention also discloses a preparation method of the coating. By adding the organic modified antibacterial agent, the antibacterial requirement of the polyurethane coating is met, high dispersity is achieved, the preparation method of the coating is simple and easy to implement, the raw materials are rich in source, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings and relates to a bio-based polyurethane coating and a preparation method thereof. Background Art

[0002] Polyurethane waterproof coatings were first developed and used in the United States. Japan introduced American technology for production in 1964. my country began industrial production of polyurethane in the early 1960s, and applied polyurethane materials to waterproof coatings in the early 1980s. Polyurethane waterproof coatings have good environmental adaptability. When it comes into contact with moisture in the air, it solidifies, forming a seamless overall waterproof film on the surface of the base layer. The coating has high tensile strength and strong flexibility. Even if the base layer is cracked or stretched, it will not be affected, so it has strong adaptability.

[0003] The demand for waterproof coatings is growing and the quantity is huge, but the raw materials are mostly common petroleum products. In order to adapt to the concept of green and sustainable development, bio-based polyurethane coating technology has been studied and developed. However, since polyurethane coatings are easily contaminated by bacteria during synthesis, storage, transportation and downstream use, resulting in deterioration, bactericides are usually required to be added for antibacterial effect. Such products are mostly achieved by adding external antibacterial agents such as nanosilver particles to achieve antibacterial requirements. However, most external antibacterial agents are difficult to achieve uniform dispersion with polyurethane materials. Therefore, the present invention achieves the antibacterial requirements of polyurethane coatings and achieves high dispersibility by adding organic modified antibacterial agents. Summary of the invention

[0004] The object of the present invention is to provide a bio-based polyurethane coating and a preparation method thereof, so as to solve the problem of poor antibacterial property of the polyurethane coating mentioned in the background technology.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A bio-based polyurethane coating comprises the following raw materials in parts by weight:

[0007] 53.5-78.3 parts of diphenylmethane diisocyanate, 64.8-127.6 parts of polypropylene glycol, 14.6-17.4 parts of castor oil, 18.4-22.4 parts of dimethylolpropionic acid, 51.7-82.1 parts of 1,4-butanediol, 9.5-12.1 parts of acetone, 3.5-9.5 parts of triethylamine, 13.5-15.1 parts of modified antibacterial agent, 1.9-45.8 parts of dispersant BYK-1632;

[0008] The bio-based polyurethane coating is made by the following steps:

[0009] Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 95-110° C. for reaction for 3-4 hours, castor oil, dimethylolpropionic acid and 1,4-butanediol are added thereto for 4-6 hours, the mixture is cooled to 45-50° C., the mixture is reacted for 2-3 hours, acetone and triethylamine are added thereto, the mixture is reacted for 1-2 hours, a dispersant BYK-163 is added thereto, the mixture is cooled to 25-28° C., and a prepolymer is obtained;

[0010] Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

[0011] The modified antibacterial agent is prepared by the following steps:

[0012] Step S1, add quinazolinone, 1,2-dichloroethane, SOC l2 and DMF into a three-necked flask, heat to 60-80°C for reaction for 7-8h, wash with water and recrystallize to obtain intermediate 1;

[0013] The reaction process is as follows:

[0014]

[0015] Step S2, add intermediate 1 and 1,4-dioxane into a three-necked flask, add methyl pipecolate dropwise under stirring, heat to 130-135° C., react for 9-10 hours, and filter to obtain intermediate 2;

[0016] The reaction process is as follows:

[0017]

[0018] Step S3, add intermediate 2, water and sodium hydroxide to a three-necked flask, stir for 10-12 hours, add 10% by mass HCl solution to adjust the pH until no solid precipitates, and filter to obtain intermediate 3;

[0019] The reaction process is as follows:

[0020]

[0021] Step S4, add 2,5-diaminobenzenethiol, 4-pyridinecarboxaldehyde, anhydrous ethanol and NH4Cl into a three-necked flask, heat to 65-70°C and react for 20-23h to obtain intermediate 4;

[0022] The reaction process is as follows:

[0023]

[0024] Step S5, adding intermediate 4, iodomethane and acetonitrile into a three-necked flask, reacting at 72-75° C. for 4-5 hours to obtain intermediate 5;

[0025] The reaction process is as follows:

[0026]

[0027] Step S6, add intermediate 3, triethylamine and tetrahydrofuran to a three-necked flask, add intermediate 5 and 4-dimethylaminopyridine at 0°C, add N,N'-dicyclohexylcarbodiimide after the reaction solution is clarified, heat to 25-30°C, react for 4-5 hours, and concentrate under reduced pressure. Add ethyl acetate and place in a -1°C refrigerator for 13-15 hours. Take the organic phase and wash it with 5% sodium bicarbonate solution and 1 mmol / L hydrochloric acid solution for 2-3 times, then dry it with anhydrous sodium sulfate and concentrate under reduced pressure to obtain a modified antibacterial agent.

[0028] The reaction process is as follows:

[0029]

[0030] Furthermore, in step S1, the usage ratio of quinazolinone, 1,2-dichloroethane, SOC l2, and DMF is 3.4-5.1 g: 40-50 mL: 25-28 mL: 1.2-1.5 mL.

[0031] Furthermore, in step S2, the usage ratio of the intermediate 1, 1,4-dioxane, and methyl pipecolate is 5.3-6.2 g: 60-70 mL: 5-6 mL.

[0032] Furthermore, in step S3, the usage ratio of the intermediate 2, water and sodium hydroxide is 3.7-4.5 g:70-80 mL:1.2-1.4 g.

[0033] Furthermore, in step S4, the usage ratio of 2,5-diaminobenzenethiol, 4-pyridinecarboxaldehyde, anhydrous ethanol and NH4Cl is 2.2-2.5g:1.8-2g:40-50mL:0.3-0.35g.

[0034] Furthermore, in step S5, the usage ratio of the intermediate 4, iodomethane and acetonitrile is 1.4-1.5 g: 0.8-0.9 g: 50-55 mL.

[0035] Furthermore, in step S6, the usage ratio of intermediate 3, triethylamine, tetrahydrofuran, intermediate 5, 4-dimethylaminopyridine and N,N'-dicyclohexylcarbodiimide is 0.5-0.6 mol: 6.7-7.6 g: 50-55 mL: 0.5-0.55 mol: 0.8-1.2 g: 0.9-1.5 g.

[0036] Beneficial effects of the present invention: The present invention provides a bio-based polyurethane coating and a preparation method thereof. The preparation method of the coating is simple and easy, the raw material source is abundant, and the cost is low. Since the polyurethane coating is very susceptible to bacterial contamination and deterioration during synthesis, storage, transportation and downstream use, in addition, it also has high requirements for antibacterial properties in some special application fields, and usually requires the addition of bactericides for antibacterial. Such products are mostly achieved by adding external antibacterial agents such as nanosilver particles to achieve antibacterial requirements. However, most external antibacterial agents are difficult to achieve uniform dispersion with polyurethane materials. Therefore, the present invention achieves the antibacterial requirements of polyurethane coatings and achieves high dispersibility by adding organic modified antibacterial agents. The structure of the modified antibacterial agent contains a quinazoline heterocyclic structure and a pyridinium salt structure, which play a synergistic role, has a good inhibitory effect on Escherichia coli and Staphylococcus aureus, can cause the leakage of genetic factors and proteins in bacteria, and show the ability to destroy the integrity of microbial cells, thereby inhibiting bacterial division, thereby exerting an antibacterial effect. In addition, the synthesized modified antimicrobial agent is an organic compound. According to the principle of like-for-like, the modified antimicrobial agent can be well mixed with the substrate, making the antibacterial performance of the polyurethane coating more stable and durable. Castor oil is used as a bio-based plasticizer. Compared with existing waterproof coating plasticizers, castor oil has better compatibility with polyurethane, which is beneficial to increase the mechanical properties of the product. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Example 1

[0039] The modified antibacterial agent is prepared by the following steps:

[0040] Step S1, add 3.4 g of quinazolinone, 40 mL of 1,2-dichloroethane, 25 mL of SOC l2 and 1.2 mL of DMF into a three-necked flask, heat to 60° C. and react for 7 h, wash with water and recrystallize to obtain intermediate 1;

[0041] Step S2, add 5.3 g of intermediate 1 and 60 mL of 1,4-dioxane into a three-necked flask, add 5 mL of methyl pipecolate dropwise under stirring, heat to 130° C., react for 9 h, and filter to obtain intermediate 2;

[0042] Step S3, add 3.7 g of intermediate 2, 70 mL of water, and 1.2 g of sodium hydroxide into a three-necked flask, stir for 10 h, add 10% by mass HCl solution to adjust the pH until no solid precipitates, and filter to obtain intermediate 3;

[0043] Step S4, add 2.2 g 2,5-diaminobenzenethiol, 1.8 g 4-pyridinecarboxaldehyde, 40 mL anhydrous ethanol, and 0.3 g NH4C l into a three-necked flask, heat to 65° C. and react for 20 h to obtain intermediate 4;

[0044] Step S5, add 1.4 g of intermediate 4, 0.8 g of iodomethane, and 50 mL of acetonitrile into a three-necked flask, and react at 72° C. for 4 h to obtain intermediate 5;

[0045] Step S6, add 0.5 mol intermediate 3, 6.7 g triethylamine and 50 mL tetrahydrofuran to a three-necked flask, add 0.5 mol intermediate 5 and 0.8 g 4-dimethylaminopyridine at 0°C, add 0.9 g N,N'-dicyclohexylcarbodiimide after the reaction solution is clarified, heat to 25°C, react for 4 hours, and concentrate under reduced pressure. Add ethyl acetate and put it in a -1°C refrigerator for 13 hours. Take the organic phase, wash it twice with 5% sodium bicarbonate solution and 1 mmol / L hydrochloric acid solution, respectively, and then dry it with anhydrous sodium sulfate and concentrate under reduced pressure to obtain a modified antibacterial agent.

[0046] Example 2

[0047] The modified antibacterial agent is prepared by the following steps:

[0048] Step S1, add 4.5 g of quinazolinone, 45 mL of 1,2-dichloroethane, 26 mL of SOC l2 and 1.3 mL of DMF into a three-necked flask, heat to 70° C. and react for 7 h, wash with water and recrystallize to obtain intermediate 1;

[0049] Step S2, add 5.8 g of intermediate 1 and 65 mL of 1,4-dioxane into a three-necked flask, add 5 mL of methyl pipecolate dropwise under stirring, heat to 132° C., react for 9 h, and filter to obtain intermediate 2;

[0050] Step S3, add 3.9 g of intermediate 2, 75 mL of water, and 1.3 g of sodium hydroxide into a three-necked flask, stir for 11 h, add 10% by mass HCl solution to adjust the pH until no solid precipitates, and filter to obtain intermediate 3;

[0051] Step S4, add 2.3 g 2,5-diaminobenzenethiol, 1.9 g 4-pyridinecarboxaldehyde, 44 mL anhydrous ethanol, and 0.33 g NH4C l into a three-necked flask, heat to 65-70° C. and react for 21 h to obtain intermediate 4;

[0052] Step S5, add 1.4 g of intermediate 4, 0.8 g of iodomethane, and 52 mL of acetonitrile into a three-necked flask, and react at 74° C. for 4 h to obtain intermediate 5;

[0053] Step S6, add 0.55 mol intermediate 3, 7.3 g triethylamine and 52 mL tetrahydrofuran to a three-necked flask, add 0.52 mol intermediate 5 and 1 g 4-dimethylaminopyridine at 0°C, add 1.2 g N,N'-dicyclohexylcarbodiimide after the reaction solution is clarified, heat to 27°C, react for 4 hours, and concentrate under reduced pressure. Add ethyl acetate and put it in a -1°C refrigerator for 14 hours. Take the organic phase, wash it twice with 5% sodium bicarbonate solution and 1 mmol / L hydrochloric acid solution, respectively, and then dry it with anhydrous sodium sulfate and concentrate under reduced pressure to obtain a modified antibacterial agent.

[0054] Example 3

[0055] The modified antibacterial agent is prepared by the following steps:

[0056] Step S1, add 5.1 g of quinazolinone, 50 mL of 1,2-dichloroethane, 28 mL of SOC l2 and 1.5 mL of DMF into a three-necked flask, heat to 80°C and react for 8 hours, wash with water and recrystallize to obtain intermediate 1;

[0057] Step S2, add 6.2 g of intermediate 1 and 70 mL of 1,4-dioxane into a three-necked flask, add 6 mL of methyl pipecolate dropwise under stirring, heat to 135° C., react for 10 h, and filter to obtain intermediate 2;

[0058] Step S3, add 4.5 g of intermediate 2, 80 mL of water, and 1.4 g of sodium hydroxide into a three-necked flask, stir for 12 h, add 10% by mass HCl solution to adjust the pH until no solid precipitates, and filter to obtain intermediate 3;

[0059] Step S4, add 2.5 g of 2,5-diaminobenzenethiol, 2 g of 4-pyridinecarboxaldehyde, 50 mL of anhydrous ethanol, and 0.35 g of NH4C1 into a three-necked flask, heat to 70°C and react for 23 h to obtain intermediate 4;

[0060] Step S5, add 1.5 g of intermediate 4, 0.9 g of iodomethane, and 55 mL of acetonitrile into a three-necked flask, and react at 75° C. for 5 h to obtain intermediate 5;

[0061] Step S6, add 0.6 mol intermediate 3, 7.6 g triethylamine and 55 mL tetrahydrofuran to a three-necked flask, add 0.55 mol intermediate 5 and 1.2 g 4-dimethylaminopyridine at 0°C, add 1.5 g N,N'-dicyclohexylcarbodiimide after the reaction solution is clarified, heat to 30°C, react for 5 hours, and concentrate under reduced pressure. Add ethyl acetate and put it in a -1°C refrigerator for 15 hours. Take the organic phase, wash it three times with 5% sodium bicarbonate solution and 1 mmol / L hydrochloric acid solution, respectively, and then dry it with anhydrous sodium sulfate and concentrate under reduced pressure to obtain a modified antibacterial agent.

[0062] Example 4

[0063] A bio-based polyurethane coating comprises the following raw materials in parts by weight:

[0064] 53.5 parts of diphenylmethane diisocyanate, 64.8 parts of polypropylene glycol, 14.6 parts of castor oil, 18.4 parts of dimethylol propionic acid, 51.7 parts of 1,4-butanediol, 9.5 parts of acetone, 3.5 parts of triethylamine, 13.5 parts of modified antibacterial agent, 1.9 parts of dispersant BYK-1632;

[0065] The bio-based polyurethane coating is made by the following steps:

[0066] Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 95° C. for reaction for 3 hours, castor oil, dihydroxymethylpropionic acid and 1,4-butanediol are added thereto for 4 hours, the temperature is lowered to 45° C., and the mixture is reacted for another 2 hours, acetone and triethylamine are added, and the mixture is reacted for another 1 hour, and then a dispersant BYK-163 is added, and the mixture is cooled to 25° C. to obtain a prepolymer;

[0067] Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

[0068] Example 5

[0069] A bio-based polyurethane coating comprises the following raw materials in parts by weight:

[0070] 66.8 parts of diphenylmethane diisocyanate, 83.6 parts of polypropylene glycol, 15.2 parts of castor oil, 19.9 parts of dimethylolpropionic acid, 71.6 parts of 1,4-butanediol, 10.8 parts of acetone, 6.2 parts of triethylamine, 14.1 parts of modified antibacterial agent, 33.3 parts of dispersant BYK-163;

[0071] The bio-based polyurethane coating is made by the following steps:

[0072] Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 100° C. for reaction for 3 hours, castor oil, dimethylolpropionic acid and 1,4-butanediol are added thereto for 5 hours, the temperature is lowered to 48° C., and the reaction is continued for 2 hours, acetone and triethylamine are added, and the reaction is continued for 1 hour, and then a dispersant BYK-163 is added, and the temperature is lowered to 27° C. to obtain a prepolymer;

[0073] Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

[0074] Example 6

[0075] A bio-based polyurethane coating comprises the following raw materials in parts by weight:

[0076] 78.3 parts of diphenylmethane diisocyanate, 127.6 parts of polypropylene glycol, 17.4 parts of castor oil, 22.4 parts of dimethylol propionic acid, 82.1 parts of 1,4-butanediol, 12.1 parts of acetone, 9.5 parts of triethylamine, 15.1 parts of modified antibacterial agent, and 45.8 parts of dispersant BYK-163;

[0077] The bio-based polyurethane coating is made by the following steps:

[0078] Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 110° C. for reaction for 4 hours, castor oil, dimethylolpropionic acid and 1,4-butanediol are added thereto for 6 hours, the temperature is lowered to 50° C., and the mixture is reacted for another 3 hours, acetone and triethylamine are added, and the mixture is reacted for another 2 hours, and then a dispersant BYK-163 is added, and the mixture is cooled to 28° C. to obtain a prepolymer;

[0079] Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

[0080] Comparative Example 1

[0081] Bio-based polyurethane coating produced by Senyang Insulation Materials Co., Ltd.

[0082] Comparative Example 2

[0083] The preparation method of the polyurethane coating of Comparative Example 2 refers to that of Example 4, except that no modified antibacterial agent is added.

[0084] The polyurethane coatings obtained in Examples 4-6 and Comparative Examples 1-2 were subjected to the following performance tests: (1) spraying the polyurethane coatings on a smooth metal plate, drying and curing (baking at 82°C for 1.5 h) to form a coating, testing the adhesion of the coating (according to GB / T9286-1988), and visually observing the appearance; (2) antibacterial performance test: the antibacterial performance of the samples was tested according to GB / T21510-2008. The test results are shown in Table 1:

[0085] Table 1

[0086]

[0087] It can be seen from Table 1 that compared with Comparative Examples 1-2, the polyurethane coatings prepared in Examples 4-6 have better antibacterial ability.

[0088] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0089] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A bio-based polyurethane coating, characterized in that: The invention comprises the following raw materials in parts by weight: 53.5-78.3 parts of diphenylmethane diisocyanate, 64.8-127.6 parts of polypropylene glycol, 14.6-17.4 parts of castor oil, 18.4-22.4 parts of dihydroxymethyl propionic acid, 51.7-82.1 parts of 1,4-butanediol, 9.5-12.1 parts of acetone, 3.5-9.5 parts of triethylamine, 13.5-15.1 parts of modified antibacterial agent, and 21.9-45.8 parts of dispersant; The bio-based polyurethane coating is made by the following steps: Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 95-110° C. for reaction for 3-4 hours, castor oil, dihydroxymethylpropionic acid and 1,4-butanediol are added thereto for 4-6 hours, the temperature is lowered to 45-50° C., and the reaction is continued for 2-3 hours, acetone and triethylamine are added, and the reaction is continued for 1-2 hours, and then a dispersant is added, and the temperature is lowered to 25-28° C. to obtain a prepolymer; Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

2. A bio-based polyurethane coating according to claim 1, characterized in that: The modified antibacterial agent is prepared by the following steps: Step S1, add quinazolinone, 1,2-dichloroethane, SOCl2 and DMF into a three-necked flask, heat to 60-80°C for reaction for 7-8h, wash with water and recrystallize to obtain intermediate 1; Step S2, add intermediate 1 and 1,4-dioxane into a three-necked flask, add methyl pipecolate dropwise under stirring, heat to 130-135° C., react for 9-10 hours, and filter to obtain intermediate 2; Step S3, add intermediate 2, water and sodium hydroxide to a three-necked flask, stir for 10-12 hours, add 10% by mass HCl solution to adjust the pH until no solid precipitates, and filter to obtain intermediate 3; Step S4, add 2,5-diaminobenzenethiol, 4-pyridinecarboxaldehyde, anhydrous ethanol and NH4Cl into a three-necked flask, heat to 65-70°C and react for 20-23h to obtain intermediate 4; Step S5, adding intermediate 4, iodomethane and acetonitrile into a three-necked flask, reacting at 72-75° C. for 4-5 hours to obtain intermediate 5; Step S6, add intermediate 3, triethylamine and tetrahydrofuran to a three-necked flask, add intermediate 5 and 4-dimethylaminopyridine at 0°C, add N,N'-dicyclohexylcarbodiimide after the reaction solution is clarified, heat to 25-30°C, react for 4-5 hours, and concentrate under reduced pressure. Add ethyl acetate and place in a -1°C refrigerator for 13-15 hours. Take the organic phase and wash it with 5% sodium bicarbonate solution and 1 mmol / L hydrochloric acid solution for 2-3 times, then dry it with anhydrous sodium sulfate and concentrate under reduced pressure to obtain a modified antibacterial agent.

3. A bio-based polyurethane coating according to claim 1, characterized in that: The dispersant is dispersant BYK-163.

4. A bio-based polyurethane coating according to claim 2, characterized in that: The usage ratio of quinazolinone, 1,2-dichloroethane, SOCl2 and DMF in step S1 is 3.4-5.1 g: 40-50 mL: 25-28 mL: 1.2-1.5 mL.

5. The bio-based polyurethane coating according to claim 2, characterized in that: The usage ratio of the intermediate 1, 1,4-dioxane and methyl pipecolate in step S2 is 5.3-6.2 g: 60-70 mL: 5-6 mL.

6. A bio-based polyurethane coating according to claim 2, characterized in that: The usage ratio of the intermediate 2, water and sodium hydroxide in step S3 is 3.7-4.5 g:70-80 mL:1.2-1.4 g.

7. A bio-based polyurethane coating according to claim 2, characterized in that: The usage ratio of 2,5-diaminobenzenethiol, 4-pyridinecarboxaldehyde, anhydrous ethanol and NH4Cl in step S4 is 2.2-2.5 g: 1.8-2 g: 40-50 mL: 0.3-0.35 g.

8. The bio-based polyurethane coating according to claim 2, characterized in that: The usage ratio of the intermediate 4, iodomethane and acetonitrile in step S5 is 1.4-1.5 g: 0.8-0.9 g: 50-55 mL.

9. The bio-based polyurethane coating according to claim 2, characterized in that: In step S6, the usage ratio of intermediate 3, triethylamine, tetrahydrofuran, intermediate 5, 4-dimethylaminopyridine and N,N'-dicyclohexylcarbodiimide is 0.5-0.6 mol: 6.7-7.6 g: 50-55 mL: 0.5-0.55 mol: 0.8-1.2 g: 0.9-1.5 g.

10. The method for preparing a bio-based polyurethane coating according to claim 1, characterized in that: The method comprises the following preparation steps: Step A1, diphenylmethane diisocyanate and polypropylene glycol are mixed and heated to 95-110° C. for reaction for 3-4 hours, castor oil, dihydroxymethylpropionic acid and 1,4-butanediol are added thereto for 4-6 hours, the temperature is lowered to 45-50° C., and the reaction is continued for 2-3 hours, acetone and triethylamine are added, and the reaction is continued for 1-2 hours, and then a dispersant is added, and the temperature is lowered to 25-28° C. to obtain a prepolymer; Step A2, emulsifying the prepolymer and the modified antibacterial agent in a supergravity emulsification device, and then rotary distilling the residual acetone to obtain a bio-based polyurethane coating.

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