A bio-based waterborne polyurethane coating and its preparation method

Abstract

This invention discloses a bio-based waterborne polyurethane coating and its preparation method, belonging to the field of coating technology. The bio-based waterborne polyurethane coating prepared by this invention comprises, by weight, the following 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 co-solvent, 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. The bio-based polyurethane dispersion is obtained by dispersing bio-based polyurethane in deionized water, wherein the bio-based polyurethane is obtained by reacting polyisocyanate monomers, a catalyst, castor oil, and a chain extender. The polysiloxane dispersion is obtained by dispersing siloxane monomers in deionized water after polycondensation.

Description

Technical Field

[0001] This invention relates to the field of coatings, specifically to a bio-based waterborne polyurethane coating and its preparation method. Background Technology

[0002] Traditional solvent-based polyurethane coatings, while possessing good adhesion, flexibility, and chemical resistance, are gradually being phased out of the market because they release large amounts of volatile organic compounds (VOCs) during production and use. This not only pollutes the environment but may also pose a threat to human health.

[0003] In recent years, waterborne polyurethane coatings have received widespread attention due to their advantages such as low VOC emissions, non-toxicity, and safety. However, existing waterborne polyurethane coatings still have some shortcomings, such as poor antifouling performance, low mechanical strength, and weak abrasion resistance and corrosion resistance. These defects limit their application range in high-performance applications. Especially under long-term outdoor exposure conditions, such as marine environments and chemical plants, the requirements for coating materials are more stringent, necessitating superior comprehensive performance to meet actual needs.

[0004] To overcome the above problems, this invention proposes a bio-based waterborne polyurethane coating and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a bio-based waterborne polyurethane coating and its preparation method to solve the technical problems mentioned in the background section.

[0006] The technical solution to achieve the objective of this invention is:

[0007] A bio-based waterborne polyurethane coating, by weight, comprises the following 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 bio-based polyurethane in deionized water, wherein the bio-based polyurethane is obtained by reacting polyisocyanate monomers, catalysts, castor oil, and chain extenders.

[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 dispersing 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane in deionized water after polycondensation.

[0012] Furthermore, the cosolvent is diethylene glycol butyl ether; the defoamer is BYK-066 N; 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: 70-80 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 are sequentially placed into a reaction vessel and dispersed and stirred at 1000-2000 rpm for 1-3 hours to obtain a bio-based waterborne polyurethane coating.

[0014] Further, the preparation method of the bio-based polyurethane dispersion is as follows: Under nitrogen protection, castor oil is placed in a reaction vessel, heated to 76-80℃ and stirred, then polyisocyanate monomer and catalyst are added, and the reaction is continued to be stirred for 2.5-3.5h. Then, chain extender is added and the reaction is continued for 1.8-2.2h. During this period, butanone is added to reduce the viscosity of the reaction system. After the reaction is completed, the temperature is lowered to 40℃, triethylamine is added for neutralization and stirring is continued for 25-35min. Finally, the temperature is cooled to room temperature to obtain bio-based polyurethane. Then, deionized water is added to the bio-based polyurethane for high-speed emulsification for 50-70min, and butanone is removed by rotary evaporation to obtain biomass bio-based polyurethane dispersion.

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

[0016] Further, the preparation method of the polysiloxane dispersion is as follows: Take 20-22 parts by mass of 3-aminopropyltriethoxysilane and 15-17 parts by mass of 3-mercaptopropyltrimethoxysilane, dissolve them in 30-34 parts by mass of ethanol and place them in a reaction vessel. Purge nitrogen into the reaction system to remove oxygen, then add 4.2-4.4 parts by mass of deionized water, heat to 59-61°C, and reflux under nitrogen protection for 3.5-4.5 h. After the reaction is completed, remove small molecules such as ethanol and water by rotary evaporation, add 48-52 parts by mass of deionized water and emulsify at 3000 rpm for 50-70 min to obtain the polysiloxane dispersion.

[0017] The present invention also provides a method for using a bio-based waterborne polyurethane coating, wherein the bio-based waterborne polyurethane coating is uniformly sprayed onto the substrate to be sprayed, and then irradiated with a UV lamp with a power density of 30~50 mW / cm² and 365 nm for 55~65 min, followed by drying at 29~31℃ for 2 h to evaporate the surface moisture, and then the temperature is raised to 58~62℃ and cured for 7~9 h.

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

[0019] The bio-based waterborne polyurethane coating prepared by this invention comprises the following 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. The bio-based polyurethane dispersion is obtained by dispersing bio-based polyurethane in deionized water. The bio-based polyurethane is obtained by reacting polyisocyanate monomers, a catalyst, castor oil, and a chain extender. The polyisocyanate monomers include any one or more combinations of HDI trimer, TDI trimer, IPDI trimer, and MDI trimer. The chain extender is glyceraldehyde and 2,2-dimethylolbutyric acid. The polysiloxane dispersion is obtained by dispersing siloxane monomers after polycondensation in deionized water. The siloxane monomers are 3-aminopropyltriethoxysilane and 3-mercaptopropyltrimethoxysilane.

[0020] First, the bio-based polyurethane dispersion is obtained by dispersing bio-based polyurethane in deionized water. The bio-based polyurethane is obtained by reacting polyisocyanate monomers, catalysts, castor oil, and chain extenders. The polyisocyanate monomers are any one or more combinations of HDI trimer, TDI trimer, IPDI trimer, and MDI trimer. The chain extender is glyceraldehyde and 2,2-dimethylolbutyric acid. This forms a hyperbranched bio-based polyurethane structure. Among them, the chain extenders glyceraldehyde and 2,2-dimethylolbutyric acid have certain hydrophilicity, which can effectively improve the dispersibility of bio-based polyurethane in water, making the resulting dispersion more stable and improving the storage stability of the bio-based polyurethane dispersion.

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

[0022] Finally, when the various raw material components are mixed and sprayed, the hyperbranched structure of the bio-based polyurethane forms a large number of cavities within it. These cavities provide space for the polysiloxane molecular chains to penetrate. The polysiloxane molecular chains can pass through these cavities and form a 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 undergo a thiol-olefin click reaction with the olefin bonds on the bio-based polyurethane, and the amino groups on the polysiloxane molecular chains react with the aldehyde groups on the bio-based polyurethane to form Schiff bases, increasing the antibacterial properties of the bio-based waterborne polyurethane coating. At the same time, the cross-linking reaction between the polysiloxane molecular chains and the bio-based polyurethane further increases the cross-linking density of the bio-based waterborne polyurethane coating, improving the incompatibility between the polysiloxane molecular chains and the bio-based polyurethane, ensuring a low degree of microphase separation, and endowing the coating with continuous antifouling ability through the migration of low surface energy silicon long-chain molecules to the surface and the formation of nanopools inside. Detailed Implementation

[0023] To better understand the above technical solution, the following will provide a detailed explanation of the technical solution in conjunction with specific implementation methods.

[0024] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

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

[0026] The following are some of the raw materials used in the examples and comparative examples:

[0027] The co-solvent used is diethylene glycol butyl ether;

[0028] The defoamer used is BYK-066 N;

[0029] The photoinitiator used is photoinitiator 1173;

[0030] The antioxidant used is antioxidant 1010;

[0031] The polyisocyanate monomer is TDI trimer;

[0032] The catalyst used is dibutyltin dilaurate; Example 1

[0033] A method for using a bio-based waterborne polyurethane coating involves uniformly spraying the bio-based waterborne polyurethane coating onto the substrate to be coated, then irradiating it with a UV lamp with a power density of 30 mW / cm² and 365 nm for 55 minutes, followed by drying at 29°C for 2 hours to allow surface moisture to evaporate, and then raising the temperature to 58°C and continuing to cure for 7 hours.

[0034] A method for preparing a bio-based waterborne polyurethane coating includes the following preparation steps: 70 parts by weight of bio-based polyurethane dispersion, 40 parts by weight of polysiloxane dispersion, 2 parts by weight of cosolvent, 0.1 parts by weight of defoamer, 0.5 parts by weight of photoinitiator, and 0.1 parts by weight of antioxidant are sequentially placed into a reaction vessel and dispersed and stirred at 1000 rpm for 1 hour to obtain the bio-based waterborne polyurethane coating.

[0035] The preparation steps of the bio-based polyurethane dispersion are as follows: Under nitrogen protection, castor oil is placed in a reaction vessel, heated to 76°C and stirred at 200 rpm. Then, polyisocyanate monomers and catalysts are added, and the reaction is continued for 2.5 h. Next, chain extender glyceraldehyde and 2,2-dimethylolbutyric acid are added, and the reaction continues for 1.8 h. During this period, butanone is added to reduce the viscosity of the reaction system. After the reaction is complete, the temperature is lowered to 40°C, triethylamine is added for neutralization, and stirring continues for 25 min. Finally, the mixture is cooled to room temperature to obtain bio-based polyurethane. Then, deionized water is added to the biomass polyurethane... The mixture was emulsified at 3000 rpm for 50 min, and methyl ethyl ketone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion. The molar ratio of isocyanate groups in the polyisocyanate monomer, hydroxyl groups in castor oil, and hydroxyl groups in the chain extender was 1.4:0.6:0.38. The molar ratio of glyceraldehyde to 2,2-dimethylolbutyric acid in the chain extender was 1:1. The molar ratio of triethylamine to 2,2-dimethylolbutyric acid was 1:0.9. The amount of catalyst added was 0.05% of the mass of the bio-based polyurethane. The mass of deionized water and methyl ethyl ketone were both 8 times the mass of the polyisocyanate monomer.

[0036] 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 vessel. Nitrogen gas is introduced into the reaction system to remove oxygen. Then, 4.2 parts by mass of deionized water are added. The temperature is raised to 59°C and refluxed under nitrogen protection for 3.5 h. After the reaction is completed, small molecules such as ethanol and water are removed by rotary evaporation. 48 parts by mass of deionized water are added and emulsified at 3000 rpm for 50 min to obtain the polysiloxane dispersion. Example 2

[0037] A method for using a bio-based waterborne polyurethane coating involves uniformly spraying the bio-based waterborne polyurethane coating onto the substrate to be coated, then irradiating it with a UV lamp with a power density of 40 mW / cm² and a wavelength of 365 nm for 60 minutes, followed by drying at 30°C for 2 hours to allow surface moisture to evaporate, and then raising the temperature to 60°C and continuing to cure for 8 hours.

[0038] A method for preparing a bio-based waterborne polyurethane coating includes the following preparation steps: 75 parts by weight of bio-based polyurethane dispersion, 50 parts by weight of polysiloxane dispersion, 3 parts by weight of cosolvent, 0.3 parts by weight of defoamer, 0.8 parts by weight of photoinitiator, and 0.4 parts by weight of antioxidant are sequentially placed into a reaction vessel and dispersed and stirred at 1500 rpm for 2 hours to obtain the bio-based waterborne polyurethane coating.

[0039] The preparation steps of the bio-based polyurethane dispersion are as follows: Under nitrogen protection, castor oil is placed in a reaction vessel, heated to 78°C and stirred at 250 rpm. Then, polyisocyanate monomer and catalyst are added, and the reaction is continued for 3 hours. Next, chain extender glyceraldehyde and 2,2-dimethylolbutyric acid are added, and the reaction continues for 2 hours. During this period, butanone is added to reduce the viscosity of the reaction system. After the reaction is complete, the temperature is lowered to 40°C, triethylamine is added for neutralization, and stirring continues for 30 minutes. Finally, the mixture is cooled to room temperature to obtain bio-based polyurethane. Then, deionized water is added to the biomass polyurethane at 300 rpm. The mixture was emulsified at 0 rpm for 60 min, and methyl ethyl ketone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion. The molar ratio of isocyanate groups in the polyisocyanate monomer, hydroxyl groups in castor oil, and hydroxyl groups in the chain extender was 1.4:0.61:0.39. The molar ratio of glyceraldehyde to 2,2-dimethylolbutyric acid in the chain extender was 1:1.2. The molar ratio of triethylamine to 2,2-dimethylolbutyric acid was 1:1. The amount of catalyst added was 0.08% of the mass of the bio-based polyurethane. The mass of deionized water and methyl ethyl ketone were both 9 times the mass of the polyisocyanate monomer.

[0040] 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 vessel. Nitrogen gas is introduced into the reaction system to remove oxygen. Then, 4.3 parts by mass of deionized water is added, the temperature is raised to 60°C, and the reaction is refluxed for 4 hours under nitrogen protection. After the reaction is completed, small molecules such as ethanol and water are removed by rotary evaporation. 50 parts by mass of deionized water are added and emulsified at 3000 rpm for 60 minutes to obtain the polysiloxane dispersion. Example 3

[0041] A method for using a bio-based waterborne polyurethane coating involves uniformly spraying the bio-based waterborne polyurethane coating onto the substrate to be coated, then irradiating it with a UV lamp with a power density of 50 mW / cm² and a wavelength of 365 nm for 65 minutes, followed by drying at 31°C for 2 hours to allow surface moisture to evaporate, and then raising the temperature to 62°C and continuing to cure for 9 hours.

[0042] A method for preparing a bio-based waterborne polyurethane coating includes the following preparation steps: 80 parts by mass of bio-based polyurethane dispersion, 60 parts by mass of polysiloxane dispersion, 5 parts by mass of cosolvent, 0.5 parts by mass of defoamer, 1 part by mass of photoinitiator, and 3 parts by mass of antioxidant are sequentially placed into a reaction vessel and dispersed and stirred at 2000 rpm for 3 hours to obtain the bio-based waterborne polyurethane coating.

[0043] The preparation steps of the bio-based polyurethane dispersion are as follows: Under nitrogen protection, castor oil is placed in a reaction vessel, heated to 80°C and stirred at 300 rpm. Then, polyisocyanate monomer and catalyst are added, and the reaction is continued for 3.5 h. Then, chain extender glyceraldehyde and 2,2-dimethylolbutyric acid are added, and the reaction is continued for 2.2 h. During this period, butanone is added to reduce the viscosity of the reaction system. After the reaction is completed, the temperature is lowered to 40°C, triethylamine is added for neutralization, and the mixture is stirred for 35 min. Finally, the mixture is cooled to room temperature to obtain bio-based polyurethane. Then, deionized water is added to the biomass polyurethane at 3... The mixture was emulsified at 000 rpm for 70 min, and methyl ethyl ketone was removed by rotary evaporation to obtain a bio-based polyurethane dispersion. The molar ratio of isocyanate groups in the polyisocyanate monomer, hydroxyl groups in castor oil, and hydroxyl groups in the chain extender was 1.4:0.62:0.4. The molar ratio of glyceraldehyde to 2,2-dimethylolbutyric acid in the chain extender was 1:1.4. The molar ratio of triethylamine to 2,2-dimethylolbutyric acid was 1:1.1. The amount of catalyst added was 0.1% of the mass of the bio-based polyurethane. The mass of deionized water and methyl ethyl ketone were both 10 times the mass of the polyisocyanate monomer.

[0044] 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 vessel. Nitrogen gas is introduced into the reaction system to remove oxygen. Then, 4.4 parts by mass of deionized water is added, the temperature is raised to 61°C, and the reaction is refluxed under nitrogen protection for 4.5 h. After the reaction is completed, small molecules such as ethanol and water are removed by rotary evaporation. 52 parts by mass of deionized water are added and emulsified at 3000 rpm for 70 min to obtain the polysiloxane dispersion.

[0045] Comparative Example 1

[0046] The only difference between Comparative Example 1 and Example 2 is that the polyisocyanate monomer used is TDI; the other components and steps are the same as in Example 2.

[0047] Comparative Example 2

[0048] The only difference between Comparative Example 2 and Example 2 is that the bio-based polyurethane is obtained by reacting polyisocyanate monomers, catalysts, hydroxymethyl cellulose, and chain extenders; the remaining components and steps are the same as in Example 2.

[0049] Comparative Example 3

[0050] The only difference between Comparative Example 3 and Example 2 is that the chain extender used is only 2,2-dihydroxymethylbutyric acid; the other components and steps are the same as in Example 2.

[0051] Comparative Example 4

[0052] The only difference between Comparative Example 4 and Example 2 is that the siloxane monomer used is only 3-aminopropyltriethoxysilane; the other components and steps are the same as in Example 2.

[0053] Comparative Example 5

[0054] The only difference between Comparative Example 5 and Example 2 is that the siloxane monomer used is only 3-mercaptopropyltrimethoxysilane; the other components and steps are the same as in Example 2.

[0055] Comparative Example 6

[0056] The only difference between Comparative Example 6 and Example 2 is that the siloxane monomer used is only γ-glycidoxypropyltrimethoxysilane; the other components and steps are the same as in Example 2.

[0057] Comparative Example 7

[0058] The only difference between Comparative Example 7 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating are only bio-based polyurethane dispersion, cosolvent, defoamer, photoinitiator and antioxidant; the remaining components and steps are the same as in Example 2.

[0059] Comparative Example 8

[0060] The difference between Comparative Example 8 and Example 2 is that the raw material components of the bio-based waterborne polyurethane coating only include bio-based polyurethane dispersion, polysiloxane dispersion, cosolvent, defoamer, and antioxidant.

[0061] Furthermore, the method of using a bio-based waterborne polyurethane coating in this comparative example is as follows: the bio-based waterborne polyurethane coating is evenly sprayed onto the base material to be sprayed, then dried at 30°C for 2 hours to allow surface moisture to evaporate, and then the temperature is raised to 60°C and cured for another 8 hours; the remaining components and steps are the same as in Example 2.

[0062] Example of effect

[0063] Tensile properties: Tensile tests were conducted using a universal testing machine of model XWW, manufactured by Chengde Jinjian Testing Equipment Co., Ltd., according to the ASTM-D882-02(2002) standard. Test samples of bio-based waterborne polyurethane coatings prepared in the examples and comparative examples were made using PTFE molds to obtain test samples with dimensions of 45 × 12 × 2 mm. The test conditions were set to a tensile rate of 1 mm / s.

[0064] Flexibility: A QTX-type flexibility tester manufactured by Tianjin Kexin Experimental Factory was used for testing according to ASTM D522 standard. Coated samples obtained by applying bio-based waterborne polyurethane coatings prepared in the examples and comparative examples to tinplate sheets were used for testing. The samples were wound around shafts with different radii of curvature. The flexibility grade (F1-F7) was determined based on whether cracking or peeling occurred on the sample surface. The smaller the radius of curvature of the shaft, the larger the number after "F", indicating better coating flexibility. The flexibility grade of the shaft that did not show obvious phenomena after bending was the flexibility grade.

[0065] Anti-fouling properties: The coating samples obtained by coating tinplate sheets with the bio-based waterborne polyurethane coating prepared in the examples and comparative examples were used to completely wet a rubber stamp with a radius of 2 cm and four concentric rings using artificial fingerprint liquid. The stamp was then firmly pressed onto the test surface with a weight of 500 g. After half a minute, the seal was removed and the presence of the fingerprint after shrinkage was recorded for comparison with coated tinplate sheets and uncoated tinplate sheets.

[0066] Table 1 below shows the performance data of the bio-based waterborne polyurethane coatings prepared in the examples and comparative examples:

[0067] Table 1

[0068]

[0069] As can be seen from the data comparison in Table 1, the bio-based waterborne polyurethane coatings prepared in the examples have better mechanical properties, antifouling properties, and flexibility. The main difference between Comparative Example 1 and Example 2 is that only TDI is used as the polyisocyanate monomer, resulting in a lower degree of branching in the bio-based waterborne polyurethane coating compared to Example 2. The bio-based waterborne polyurethane coating prepared in Example 2 has better mechanical properties and flexibility.

[0070] The main difference between Comparative Example 2 and Example 2 is that the bio-based polyurethane is obtained by reacting polyisocyanate monomers, catalysts, hydroxymethyl cellulose, and chain extenders. 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, the strong hydrophilicity of hydroxymethyl cellulose may affect the antifouling performance of the coating, making it easy to absorb water and adsorb pollutants.

[0071] The main difference between Comparative Example 3 and Example 2 is that only 2,2-dihydroxymethylbutyric acid is used as the chain extender. The lack 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.

[0072] The main difference between Comparative Example 4 and Example 2 is that the siloxane monomer used is only 3-aminopropyltriethoxysilane; the lack of 3-mercaptopropyltrimethoxysilane will affect the multifunctionality of the polysiloxane molecular chain, especially the mercapto-olefin click reaction between the mercapto group and the olefin bond on the bio-based polyurethane, thereby reducing the crosslinking density and mechanical properties of the coating.

[0073] The main difference between Comparative Example 5 and Example 2 is that the siloxane monomer used is only 3-mercaptopropyltrimethoxysilane. The lack 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.

[0074] The main difference between Comparative Example 6 and Example 2 is that the siloxane monomer used is only γ-glycidoxypropyltrimethoxysilane. 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 and bio-based polyurethane, thereby affecting the mechanical properties, antifouling properties and flexibility of the coating.

[0075] 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 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 antifouling performance of the coating will also be affected.

[0076] 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, cosolvent, defoamer, and antioxidant; the lack of photoinitiator makes it impossible to trigger the mercapto-alkene click reaction, which in turn significantly reduces the crosslinking density and mechanical properties of the bio-based waterborne polyurethane coating, and also affects the antifouling performance of the coating.

[0077] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 within the protection scope of the present invention.

Claims

1. A bio-based waterborne polyurethane coating, characterized in that, By weight, the raw material components include: 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; The preparation method of the bio-based polyurethane dispersion is as follows: Under nitrogen protection, castor oil is placed in a reaction vessel, heated to 76~80℃ and stirred, then polyisocyanate monomer and catalyst are added, and the reaction is continued to be stirred for 2.5~3.5h. Then chain extender is added and the reaction is continued for 1.8~2.2h. During this period, butanone is added to reduce the viscosity of the reaction system. After the reaction is completed, the temperature is lowered to 40℃, triethylamine is added for neutralization and the reaction is continued to be stirred for 25~35min. Finally, the temperature is cooled to room temperature to obtain bio-based polyurethane. Then deionized water is added to the bio-based polyurethane for high-speed emulsification for 50~70min, and butanone is removed by rotary evaporation to obtain bio-based polyurethane dispersion. The polyisocyanate monomer includes any one or more combinations of HDI trimer, TDI trimer, IPDI trimer, and MDI trimer; The molar ratio of glyceraldehyde to 2,2-dihydroxymethylbutyric acid in the chain extender is 1:1 to 1.

4. The preparation method of the polysiloxane dispersion is as follows: Take 20-22 parts by mass of 3-aminopropyltriethoxysilane and 15-17 parts by mass of 3-mercaptopropyltrimethoxysilane, dissolve them in 30-34 parts by mass of ethanol and place them in a reaction vessel. Purge nitrogen into the reaction system to remove oxygen, then add 4.2-4.4 parts by mass of deionized water, heat to 59-61℃, and reflux under nitrogen protection for 3.5-4.5 h. After the reaction is completed, remove ethanol and water by rotary evaporation, add 48-52 parts by mass of deionized water and emulsify at 3000 rpm for 50-70 min to obtain the polysiloxane dispersion.

2. The method for preparing the bio-based waterborne polyurethane coating according to claim 1, characterized in that, The preparation process includes the following steps: 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 are sequentially placed into a reaction vessel and dispersed and stirred at 1000-2000 rpm for 1-3 hours to obtain a bio-based waterborne polyurethane coating.

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

4. A method for using a bio-based waterborne polyurethane coating, characterized in that, The bio-based waterborne polyurethane coating of claim 1 is uniformly sprayed onto the substrate to be coated, and then irradiated with a UV lamp with a power density of 30~50 mW / cm² and 365 nm for 55~65 min. After that, it is dried at 29~31℃ for 2 h to allow the surface moisture to evaporate, and then the temperature is raised to 58~62℃ and cured for 7~9 h.

Images