Bio-based waterborne polyurethane coating and preparation method thereof

Abstract

The invention discloses a bio-based waterborne polyurethane coating and a preparation method thereof, and belongs to the technical field of coatings. The bio-based waterborne polyurethane coating prepared by the invention is prepared from the following raw material components in parts by weight: 70 to 80 parts by mass of bio-based polyurethane dispersion liquid, 40 to 60 parts by mass of polysiloxane dispersion liquid, 2 to 5 parts by mass of a cosolvent, 0.1 to 0.5 part by mass of a defoaming agent, 0.5 to 1 part by mass of a photoinitiator and 0.1 to 3 parts by mass of an antioxidant, wherein the bio-based polyurethane dispersion liquid is obtained by dispersing bio-based polyurethane in deionized water, and the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, castor oil and a chain extender; the polysiloxane dispersion liquid is obtained by performing polycondensation on siloxane monomers and then dispersing the siloxane monomers in deionized water.

Description

Technical Field

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

[0002] With the improvement of global environmental awareness and the advancement of sustainable development strategies, the development of environmentally friendly materials has become an important topic in scientific research and industrial production. Although traditional solvent-based polyurethane coatings have good adhesion, flexibility and chemical resistance, they release a large amount of volatile organic compounds (VOCs) during production and use, which not only pollutes the environment but also threatens human health, so they are gradually being eliminated from the market.

[0003] In recent years, waterborne polyurethane coatings have attracted widespread attention due to their low VOC emissions, non-toxicity, safety and reliability. However, existing waterborne polyurethane coatings still have some shortcomings, such as poor antifouling performance, low mechanical strength, weak wear resistance and corrosion resistance, which limit their application in high-performance applications. Especially under long-term outdoor exposure conditions, such as marine environments, chemical plants and other special fields, the requirements for coating materials are more stringent, and they need to have better comprehensive performance to meet actual needs.

[0004] In order to overcome the above problems, the present invention provides a bio-based waterborne polyurethane coating and a preparation method thereof. Summary of the invention

[0005] The purpose of the present invention is to provide a bio-based waterborne polyurethane coating and a preparation method thereof, so as to solve the technical problems mentioned in the above background technology.

[0006] The technical solution for achieving the purpose of the present invention is:

[0007] A bio-based waterborne polyurethane coating comprises, by weight, raw material components: 70-80 parts by weight of bio-based polyurethane dispersion, 40-60 parts by weight of polysiloxane dispersion, 2-5 parts by weight of cosolvent, 0.1-0.5 parts by weight of defoamer, 0.5-1 parts by weight of photoinitiator, and 0.1-3 parts by weight of antioxidant.

[0008] Furthermore, the bio-based polyurethane dispersion is obtained by dispersing the bio-based polyurethane in deionized water, wherein the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, castor oil, and a chain extender.

[0009] Furthermore, the polyisocyanate monomer includes any one or more combinations of HDI trimer, TDI trimer, IPDI trimer and MDI trimer.

[0010] Furthermore, the chain extender is glyceraldehyde and 2,2-dihydroxymethylbutyric acid.

[0011] Furthermore, the polysiloxane dispersion is obtained by polycondensing 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane and dispersing them in deionized water.

[0012] Furthermore, the cosolvent is diethylene glycol butyl ether; the defoamer is BYK-066N; the photoinitiator is photoinitiator 1173; and the antioxidant is antioxidant 1010.

[0013] The present invention also provides a method for preparing a bio-based waterborne polyurethane coating, comprising the following preparation steps: 70 to 80 parts by mass of a bio-based polyurethane dispersion, 40 to 60 parts by mass of a polysiloxane dispersion, 2 to 5 parts by mass of a cosolvent, 0.1 to 0.5 parts by mass of a defoamer, 0.5 to 1 parts by mass of a photoinitiator, and 0.1 to 3 parts by mass of an antioxidant are sequentially placed into a reactor, and dispersed and stirred at 1000 to 2000 rpm for 1 to 3 hours to obtain a bio-based waterborne polyurethane coating.

[0014] Furthermore, the preparation method of the bio-based polyurethane dispersion is as follows: under nitrogen protection, castor oil is placed in a reactor, the temperature is raised to 76-80°C and stirred, then a polyisocyanate monomer and a catalyst are added, the reaction is continued with stirring for 2.5-3.5 hours, and then a chain extender is added to continue the reaction for 1.8-2.2 hours, during which butanone is added to reduce the viscosity of the reaction system, and after the reaction is completed, the temperature is lowered to 40°C, triethylamine is added for neutralization and stirring is continued for 25-35 minutes, and finally cooled to room temperature to obtain a bio-based polyurethane, and then deionized water is added to the bio-based polyurethane for high-speed emulsification for 50-70 minutes, and the butanone is removed by rotary evaporation to obtain a biomass bio-based polyurethane dispersion.

[0015] Furthermore, the molar ratio of isocyanate group in the polyisocyanate monomer, hydroxyl group in castor oil, and hydroxyl group in the chain extender is 1.4:0.6-0.62:0.38-0.4; the molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender is 1:1-1.4; the molar ratio of triethylamine to 2,2-dihydroxymethylbutyric acid is 1:0.9-1.1, and the amount of catalyst added is 0.05%-0.1% of the mass of bio-based polyurethane; the mass of deionized water and the mass of butanone are both 8-10 times the mass of the polyisocyanate monomer.

[0016] Furthermore, the preparation method of the polysiloxane dispersion is as follows: take 20 to 22 parts by mass of 3-aminopropyltriethoxysilane and 15 to 17 parts by mass of 3-mercaptopropyltrimethoxysilane, dissolve them in 30 to 34 parts by mass of ethanol and place them in a reactor, introduce nitrogen into the reaction system, add 4.2 to 4.4 parts by mass of deionized water after excluding oxygen, heat to 59 to 61° C., reflux reaction under nitrogen protection for 3.5 to 4.5 hours, after the reaction is completed, remove small molecular substances such as ethanol and water by rotary evaporation, add 48 to 52 parts by mass of deionized water, and emulsify at a high speed of 3000 rpm for 50 to 70 minutes to obtain a polysiloxane dispersion.

[0017] The present invention also provides a method for using the bio-based waterborne polyurethane coating, wherein the bio-based waterborne polyurethane coating is uniformly sprayed on a base material to be sprayed, and then the power density is 30 to 50 mW / cm 2 , 365nm UV lamp irradiation for 55-65min, then dried at 29-31℃ for 2h to evaporate the surface moisture, then heated to 58-62℃ and continued curing for 7-9h.

[0018] By adopting the above technical solution, the present invention has the following beneficial effects:

[0019] The bio-based waterborne polyurethane coating prepared by the present invention comprises raw material components: 70-80 parts by weight of bio-based polyurethane dispersion, 40-60 parts by weight of polysiloxane dispersion, 2-5 parts by weight of cosolvent, 0.1-0.5 parts by weight of defoamer, 0.5-1 parts by weight of photoinitiator, and 0.1-3 parts by weight of antioxidant; wherein the bio-based polyurethane dispersion is obtained by dispersing the bio-based polyurethane in deionized water, the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, castor oil, and a chain extender, the polyisocyanate monomer comprises any one or more combinations of HDI trimer, TDI trimer, IPDI trimer, and MDI trimer, and the chain extender adopts glyceraldehyde and 2,2-dihydroxymethylbutyric acid; the polysiloxane dispersion is obtained by dispersing the siloxane monomer in deionized water after polycondensation, and the siloxane monomer adopts 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane.

[0020] Firstly, the bio-based polyurethane dispersion is obtained by dispersing the bio-based polyurethane in deionized water. The bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, castor oil and a chain extender. The polyisocyanate monomer adopts any one or more combinations of HDI trimer, TDI trimer, IPDI trimer and MDI trimer. The chain extender adopts glyceraldehyde and 2,2-dihydroxymethylbutyric acid to form a hyperbranched bio-based polyurethane. The chain extenders glyceraldehyde and 2,2-dihydroxymethylbutyric acid have certain hydrophilicity, which can effectively improve the dispersibility of the bio-based polyurethane in water, make the formed dispersion more stable, and improve the storage stability of the bio-based polyurethane dispersion.

[0021] Secondly, the polysiloxane dispersion is obtained by polycondensing siloxane monomers and dispersing them in deionized water. The siloxane monomers used are 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane. The introduction of hydrophilic groups such as amino groups and mercapto groups into the polysiloxane molecular chain can significantly improve the dispersibility and stability of the polysiloxane in water, prevent particle aggregation, and ensure that the dispersion remains uniform for a long time.

[0022] Finally, when the raw material components are mixed and sprayed for use, a large number of cavities are formed inside the hyperbranched structure of the bio-based polyurethane, which provide space for the polysiloxane molecular chains to penetrate; the polysiloxane molecular chains can pass through these cavities and form a mutually cross-linked polymer network with the bio-based polyurethane, thereby significantly improving the mechanical properties, wear resistance and corrosion resistance of the coating; the thiol groups on the polysiloxane molecular chains react with the olefin bonds on the bio-based polyurethane to undergo a thiol-ene click reaction, and the amino groups on the polysiloxane molecular chains react with the aldehyde groups on the bio-based polyurethane to form a Schiff base, which increases the antibacterial properties of the bio-based waterborne polyurethane coating. At the same time, the polysiloxane molecular chains react with the bio-based polyurethane to cross-link, further increasing the cross-linking density of the bio-based waterborne polyurethane coating, improving the incompatibility problem between the polysiloxane molecular chains and the bio-based polyurethane, ensuring a low degree of microphase separation, and giving the coating a continuous anti-fouling ability through the migration of low surface energy silicon long-chain molecules to the surface and the nano-pools formed inside. DETAILED DESCRIPTION

[0023] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with specific implementation methods.

[0024] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0025] The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the protection scope of the present invention.

[0026] Some of the raw materials of the embodiments and comparative examples are as follows:

[0027] The cosolvent is diethylene glycol butyl ether;

[0028] The defoamer is BYK-066N;

[0029] The photoinitiator used was photoinitiator 1173;

[0030] The antioxidant used is antioxidant 1010;

[0031] The polyisocyanate monomer uses TDI trimer;

[0032] The catalyst is dibutyltin dilaurate;

[0033] Example 1

[0034] A method for using a bio-based waterborne polyurethane coating comprises spraying the bio-based waterborne polyurethane coating evenly on a base material to be sprayed, and then spraying the base material with a power density of 30 mW / cm 2 , 365nm UV lamp irradiation for 55min, followed by drying at 29℃ for 2h to evaporate the surface moisture, then heating to 58℃ and continuing curing for 7h.

[0035] A method for preparing a bio-based waterborne polyurethane coating comprises the following preparation steps: 70 parts by mass of a bio-based polyurethane dispersion, 40 parts by mass of a polysiloxane dispersion, 2 parts by mass of a cosolvent, 0.1 parts by mass of a defoamer, 0.5 parts by mass of a photoinitiator, and 0.1 parts by mass of an antioxidant are sequentially put into a reaction kettle, and dispersed and stirred at 1000 rpm for 1 hour to obtain a bio-based waterborne polyurethane coating.

[0036] The preparation steps of the bio-based polyurethane dispersion are as follows: under nitrogen protection, castor oil is placed in a reactor, the temperature is raised to 76° C. and stirred at 200 rpm, then polyisocyanate monomer and catalyst are added, stirring and reacting are continued for 2.5 hours, then chain extender glyceraldehyde and 2,2-dihydroxymethylbutyric acid are added, the reaction is continued for 1.8 hours, butanone is added during the reaction to reduce the viscosity of the reaction system, the temperature is lowered to 40° C. after the reaction is completed, triethylamine is added for neutralization and stirring is continued for 25 minutes, and finally cooled to room temperature to obtain bio-based polyurethane, and then deionized water is added to the biomass polyurethane to The high-speed emulsification was carried out at 3000 rpm for 50 min, and butanone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion; wherein the molar ratio of isocyanate group in the polyisocyanate monomer, hydroxyl group in castor oil, and hydroxyl group in the chain extender was 1.4:0.6:0.38; the molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender was 1:1; the molar ratio of triethylamine to 2,2-dihydroxymethylbutyric acid was 1:0.9, and the amount of catalyst added was 0.05% of the mass of the bio-based polyurethane; the mass of deionized water and the mass of butanone were both 8 times the mass of the polyisocyanate monomer.

[0037] The preparation method of the polysiloxane dispersion is as follows: 20 parts by mass of 3-aminopropyltriethoxysilane and 15 parts by mass of 3-mercaptopropyltrimethoxysilane are dissolved in 30 parts by mass of ethanol and placed in a reaction kettle, nitrogen is introduced into the reaction system, 4.2 parts by mass of deionized water is added after oxygen is excluded, the temperature is raised to 59° C., and reflux reaction is carried out under nitrogen protection for 3.5 hours. After the reaction is completed, small molecular substances such as ethanol and water are removed by rotary evaporation, 48 parts by mass of deionized water are added, and high-speed emulsification is carried out at 3000 rpm for 50 minutes to obtain a polysiloxane dispersion.

[0038] Example 2

[0039] A method for using a bio-based waterborne polyurethane coating comprises spraying the bio-based waterborne polyurethane coating evenly on a base material to be sprayed, and then spraying the base material with a power density of 40 mW / cm 2 , 365nm UV lamp irradiation for 60min, then dried at 30℃ for 2h to evaporate the surface moisture, then heated to 60℃ and continued curing for 8h.

[0040] A method for preparing a bio-based waterborne polyurethane coating comprises the following preparation steps: 75 parts by mass of a bio-based polyurethane dispersion, 50 parts by mass of a polysiloxane dispersion, 3 parts by mass of a cosolvent, 0.3 parts by mass of a defoamer, 0.8 parts by mass of a photoinitiator, and 0.4 parts by mass of an antioxidant are sequentially put into a reaction kettle, and dispersed and stirred at 1500 rpm for 2 hours to obtain a bio-based waterborne polyurethane coating.

[0041] The preparation steps of the bio-based polyurethane dispersion are as follows: under nitrogen protection, castor oil is placed in a reactor, the temperature is raised to 78° C. and stirred at 250 rpm, then polyisocyanate monomer and catalyst are added, stirring and reacting are continued for 3 hours, then chain extender glyceraldehyde and 2,2-dihydroxymethylbutyric acid are added, the reaction is continued for 2 hours, butanone is added during the reaction to reduce the viscosity of the reaction system, the temperature is lowered to 40° C. after the reaction is completed, triethylamine is added for neutralization and stirring is continued for 30 minutes, and finally cooled to room temperature to obtain bio-based polyurethane, and then deionized water is added to the biomass polyurethane at 300° C. The mixture was emulsified at 0 rpm for 60 min, and butanone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion; wherein the molar ratio of isocyanate group in the polyisocyanate monomer, hydroxyl group in castor oil, and hydroxyl group in the chain extender was 1.4:0.61:0.39; the molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender was 1:1.2; the molar ratio of triethylamine to 2,2-dihydroxymethylbutyric acid was 1:1, and the amount of catalyst added was 0.08% of the mass of the bio-based polyurethane; the mass of deionized water and the mass of butanone were both 9 times the mass of the polyisocyanate monomer.

[0042] The preparation method of the polysiloxane dispersion is as follows: 21 parts by mass of 3-aminopropyltriethoxysilane and 16 parts by mass of 3-mercaptopropyltrimethoxysilane are dissolved in 32 parts by mass of ethanol and placed in a reaction kettle, nitrogen is introduced into the reaction system, 4.3 parts by mass of deionized water is added after oxygen is excluded, the temperature is raised to 60° C., and reflux reaction is carried out under nitrogen protection for 4 hours; after the reaction is completed, small molecular substances such as ethanol and water are removed by rotary evaporation, 50 parts by mass of deionized water are added, and high-speed emulsification is carried out at 3000 rpm for 60 minutes to obtain a polysiloxane dispersion.

[0043] Example 3

[0044] A method for using a bio-based waterborne polyurethane coating comprises spraying the bio-based waterborne polyurethane coating evenly on a base material to be sprayed, and then spraying the base material with a power density of 50 mW / cm 2 , 365nm UV lamp irradiation for 65min, then dried at 31℃ for 2h to evaporate the surface moisture, then heated to 62℃ and continued curing for 9h.

[0045] A method for preparing a bio-based waterborne polyurethane coating comprises the following preparation steps: 80 parts by mass of a bio-based polyurethane dispersion, 60 parts by mass of a polysiloxane dispersion, 5 parts by mass of a cosolvent, 0.5 parts by mass of a defoamer, 1 part by mass of a photoinitiator, and 3 parts by mass of an antioxidant are sequentially put into a reaction kettle, and dispersed and stirred at 2000 rpm for 3 hours to obtain a bio-based waterborne polyurethane coating.

[0046] The preparation steps of the bio-based polyurethane dispersion are as follows: under nitrogen protection, castor oil is placed in a reactor, the temperature is raised to 80° C. and stirred at 300 rpm, then polyisocyanate monomer and catalyst are added, stirring and reacting are continued for 3.5 hours, then chain extender glyceraldehyde and 2,2-dihydroxymethylbutyric acid are added, the reaction is continued for 2.2 hours, butanone is added during the reaction to reduce the viscosity of the reaction system, the temperature is lowered to 40° C. after the reaction is completed, triethylamine is added for neutralization and stirring is continued for 35 minutes, and finally cooled to room temperature to obtain bio-based polyurethane, and then deionized water is added to the biomass polyurethane to react with 3 The product was emulsified at a high speed of 000 rpm for 70 min, and butanone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion; wherein the molar ratio of isocyanate group in the polyisocyanate monomer, hydroxyl group in castor oil, and hydroxyl group in the chain extender was 1.4:0.62:0.4; the molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender was 1:1.4; the molar ratio of triethylamine to 2,2-dihydroxymethylbutyric acid was 1:1.1, and the amount of catalyst added was 0.1% of the mass of the bio-based polyurethane; the mass of deionized water and the mass of butanone were both 10 times the mass of the polyisocyanate monomer.

[0047] The preparation method of the polysiloxane dispersion is as follows: 22 parts by mass of 3-aminopropyltriethoxysilane and 17 parts by mass of 3-mercaptopropyltrimethoxysilane are dissolved in 34 parts by mass of ethanol and placed in a reaction kettle, nitrogen is introduced into the reaction system, 4.4 parts by mass of deionized water is added after oxygen is excluded, the temperature is raised to 61° C., and reflux reaction is carried out under nitrogen protection for 4.5 hours; after the reaction is completed, small molecular substances such as ethanol and water are removed by rotary evaporation, 52 parts by mass of deionized water are added, and high-speed emulsification is carried out at 3000 rpm for 70 minutes to obtain a polysiloxane dispersion.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 2 is that TDI is used as the polyisocyanate monomer; the other components and steps are the same as those of Example 2.

[0050] Comparative Example 2

[0051] The only difference between Comparative Example 2 and Example 2 is that the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, hydroxymethyl cellulose, and a chain extender; the remaining components and steps are the same as those of Example 2.

[0052] Comparative Example 3

[0053] The difference between Comparative Example 3 and Example 2 is that only 2,2-dihydroxymethylbutyric acid is used as the chain extender; the remaining components and steps are the same as those of Example 2.

[0054] Comparative Example 4

[0055] The difference between Comparative Example 4 and Example 2 is that the siloxane monomer uses only 3-aminopropyltriethoxysilane; the other components and steps are the same as those in Example 2.

[0056] Comparative Example 5

[0057] The difference between Comparative Example 5 and Example 2 is that the siloxane monomer uses only 3-mercaptopropyltrimethoxysilane; the other components and steps are the same as those in Example 2.

[0058] Comparative Example 6

[0059] The difference between Comparative Example 6 and Example 2 is that the siloxane monomer only uses γ-glycidyloxypropyltrimethoxysilane; the other components and steps are the same as those in Example 2.

[0060] Comparative Example 7

[0061] The only difference between Comparative Example 7 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating only use bio-based polyurethane dispersion, cosolvent, defoamer, photoinitiator, and antioxidant; the remaining components and steps are the same as Example 2.

[0062] Comparative Example 8

[0063] The difference between Comparative Example 8 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating only use bio-based polyurethane dispersion, polysiloxane dispersion, cosolvent, defoamer, and antioxidant;

[0064] The method of using a bio-based waterborne polyurethane coating in this comparative example is: spray the bio-based waterborne polyurethane coating evenly on the base material to be sprayed, then dry it at 30°C for 2 hours to volatilize the surface moisture, then heat it to 60°C and continue curing for 8 hours; the remaining components and steps are the same as those in Example 2.

[0065] Effect example

[0066] Tensile properties: The tensile test was performed using a universal testing machine of model XWW, produced by Chengde Jinjian Testing Equipment Co., Ltd., and the tensile properties were tested according to ASTM-D882-02 (2002) standard; the bio-based waterborne polyurethane coating prepared in the embodiment and the comparative example was used to prepare a test sample with a size of 45×12×2 mm using a PTFE mold, and the test conditions were set to a tensile rate of 1 mm / s.

[0067] Flexibility: A QTX flexibility tester produced by Tianjin Kexin Experimental Plant was used for testing according to ASTM D522. The bio-based waterborne polyurethane coating prepared in the examples and comparative examples was applied to tinplate sheets to obtain coating samples for testing. The samples were wound around shafts with different curvature radii, and their flexibility grades (F1-F7) were determined based on whether cracking, shedding, and the like occurred on the surface of the samples. The smaller the curvature radius of the shaft, the larger the number after "F", indicating that the flexibility of the coating is better. The shaft grade without obvious phenomena after bending is its flexibility grade.

[0068] Antifouling property: The bio-based waterborne polyurethane coating prepared in the examples and comparative examples was applied to a coating sample obtained on a tinplate sheet. A rubber stamp with four concentric rings and a radius of 2 cm was completely wetted with an artificial fingerprint liquid, and the stamp was firmly pressed on the tested surface with a weight of 500 g. After half a minute, the seal was removed and the presence of fingerprints after shrinkage was recorded for comparison between the tinplate sheets coated with the coating and the tinplate sheets not coated with the coating.

[0069] Table 1 below shows the performance data of the bio-based waterborne polyurethane coatings prepared in Examples and Comparative Examples:

[0070] Table 1

[0071]

[0072]

[0073] Comparison of the data in Table 1 shows that the bio-based waterborne polyurethane coating prepared in the embodiment has good mechanical properties, antifouling properties and flexibility. The main difference between Comparative Example 1 and Example 2 is that the polyisocyanate monomer uses only TDI, and the degree of branching of the formed bio-based waterborne polyurethane coating is lower than that of Example 2. The bio-based waterborne polyurethane coating prepared in Example 2 has good mechanical properties and flexibility.

[0074] The main difference between Comparative Example 2 and Example 2 is that the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, hydroxymethyl cellulose, and a chain extender; the introduction of hydroxymethyl cellulose changes the molecular structure of the bio-based polyurethane, which may reduce the mechanical strength and flexibility of the coating; at the same time, hydroxymethyl cellulose has a strong hydrophilicity, which may affect the antifouling performance of the coating, making it easy to absorb water and adsorb pollutants;

[0075] The main difference between Comparative Example 3 and Example 2 is that only 2,2-dihydroxymethylbutyric acid is used as the chain extender, and the lack of the introduction of glyceraldehyde will lead to a decrease in the crosslinking degree of the bio-based polyurethane, thereby affecting the mechanical properties and flexibility of the coating;

[0076] The main difference between Comparative Example 4 and Example 2 is that only 3-aminopropyltriethoxysilane is used as the siloxane monomer; the lack of the introduction of 3-mercaptopropyltrimethoxysilane will affect the multifunctionality of the polysiloxane molecular chain, especially the thiol-ene click reaction between the thiol group and the olefin bond on the bio-based polyurethane, thereby reducing the crosslinking density and mechanical properties of the coating.

[0077] The main difference between Comparative Example 5 and Example 2 is that the siloxane monomer only uses 3-mercaptopropyltrimethoxysilane. The lack of introduction of 3-aminopropyltriethoxysilane will affect the multifunctionality of the polysiloxane molecular chain, especially the Schiff base formed by the amino group and the aldehyde group on the bio-based polyurethane, thereby reducing the crosslinking density and mechanical properties of the coating.

[0078] The main difference between Comparative Example 6 and Example 2 is that the siloxane monomer only uses γ-glycidyloxypropyltrimethoxysilane; although this monomer has high reactivity, it lacks the multiple functions of amino and thiol groups and cannot effectively improve the compatibility and crosslinking density of polysiloxane with bio-based polyurethane, thereby affecting the mechanical properties, antifouling properties and flexibility of the coating.

[0079] The main difference between Comparative Example 7 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating only use bio-based polyurethane dispersion, cosolvent, defoamer, photoinitiator, and antioxidant; the lack of the introduction of polysiloxane dispersion leads to a significant decrease in the crosslinking density and mechanical properties of the coating; in addition, without the low surface energy material provided by polysiloxane, the anti-fouling performance of the coating will also be affected.

[0080] The main difference between Comparative Example 8 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating only use bio-based polyurethane dispersion, polysiloxane dispersion, co-solvent, defoaming agent, and antioxidant; lack of the introduction of photoinitiator, the thiol-ene click reaction cannot be triggered, which makes the crosslinking density and mechanical properties of the coating of the bio-based waterborne polyurethane coating significantly reduced, and the anti-fouling performance of the coating will also be affected.

[0081] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bio-based waterborne polyurethane coating, characterized in that: The raw material components include, by weight: 70 to 80 parts by weight of bio-based polyurethane dispersion, 40 to 60 parts by weight of polysiloxane dispersion, 2 to 5 parts by weight of cosolvent, 0.1 to 0.5 parts by weight of defoamer, 0.5 to 1 parts by weight of photoinitiator, and 0.1 to 3 parts by weight of antioxidant.

2. The bio-based waterborne polyurethane coating according to claim 1, characterized in that: The bio-based polyurethane dispersion is obtained by dispersing the bio-based polyurethane in deionized water, wherein the bio-based polyurethane is obtained by reacting a polyisocyanate monomer, a catalyst, castor oil, and a chain extender.

3. The bio-based waterborne polyurethane coating according to claim 2, characterized in that: The polyisocyanate monomer includes any one or more combinations of HDI trimer, TDI trimer, IPDI trimer and MDI trimer.

4. The bio-based waterborne polyurethane coating according to claim 2, characterized in that: The chain extender is glyceraldehyde and 2,2-dihydroxymethylbutyric acid.

5. The bio-based waterborne polyurethane coating according to claim 1, characterized in that: The polysiloxane dispersion is obtained by polycondensing 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane and dispersing them in deionized water.

6. A method for preparing a bio-based waterborne polyurethane coating, characterized in that: The method comprises the following preparation steps: 70 to 80 parts by weight of a bio-based polyurethane dispersion, 40 to 60 parts by weight of a polysiloxane dispersion, 2 to 5 parts by weight of a cosolvent, 0.1 to 0.5 parts by weight of a defoamer, 0.5 to 1 parts by weight of a photoinitiator, and 0.1 to 3 parts by weight of an antioxidant are sequentially put into a reaction kettle, and dispersed and stirred at 1000 to 2000 rpm for 1 to 3 hours to obtain a bio-based waterborne polyurethane coating.

7. The method for preparing the bio-based waterborne polyurethane coating according to claim 6, characterized in that: The preparation method of the bio-based polyurethane dispersion is as follows: under nitrogen protection, castor oil is placed in a reactor, the temperature is raised to 76-80° C. and stirred, then a polyisocyanate monomer and a catalyst are added, the reaction is continued with stirring for 2.5-3.5 hours, then a chain extender is added and the reaction is continued for 1.8-2.2 hours, during which butanone is added to reduce the viscosity of the reaction system, the temperature is lowered to 40° C. after the reaction is completed, triethylamine is added for neutralization and the stirring is continued for 25-35 minutes, and finally the reaction is cooled to room temperature to obtain bio-based polyurethane, and then deionized water is added to the bio-based polyurethane for high-speed emulsification for 50-70 minutes, and the butanone is removed by rotary evaporation to obtain a biomass bio-based polyurethane dispersion.

8. The method for preparing the bio-based waterborne polyurethane coating according to claim 6, characterized in that: The molar ratio of isocyanate group in the polyisocyanate monomer, hydroxyl group in castor oil and hydroxyl group in the chain extender is 1.4:0.6-0.62:0.38-0.4; the molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender is 1:1-1.4; the molar ratio of triethylamine to 2,2-dihydroxymethylbutyric acid is 1:0.9-1.1, the added amount of the catalyst is 0.05%-0.1% of the mass of the bio-based polyurethane; the mass of deionized water and the mass of butanone are both 8-10 times the mass of the polyisocyanate monomer.

9. The method for preparing the bio-based waterborne polyurethane coating according to claim 6, characterized in that: The preparation method of the polysiloxane dispersion is as follows: 20 to 22 parts by weight of 3-aminopropyltriethoxysilane and 15 to 17 parts by weight of 3-mercaptopropyltrimethoxysilane are dissolved in 30 to 34 parts by weight of ethanol and placed in a reaction kettle, nitrogen is introduced into the reaction system, 4.2 to 4.4 parts by weight of deionized water is added after oxygen is excluded, the temperature is raised to 59 to 61° C., reflux reaction is carried out under nitrogen protection for 3.5 to 4.5 hours, and after the reaction is completed, small molecular substances such as ethanol and water are removed by rotary evaporation, 48 to 52 parts by weight of deionized water are added, and high-speed emulsification is carried out at 3000 rpm for 50 to 70 minutes to obtain a polysiloxane dispersion.

10. A method for using a bio-based waterborne polyurethane coating, characterized in that: The bio-based waterborne polyurethane coating according to any one of claims 1 to 5 is uniformly sprayed on the base material to be sprayed, and then the power density is 30 to 50 mW / cm 2 , 365nm UV lamp irradiation for 55-65min, then dried at 29-31℃ for 2h to evaporate the surface moisture, then heated to 58-62℃ and continued curing for 7-9h.

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