A yellowing-resistant polyurethane acrylate uv-cured coating and a preparation method thereof

Abstract

The application provides an anti-yellowing polyurethane acrylate UV curing paint, which comprises the following components in parts by weight: 60-70 parts of water-based polyurethane acrylate, 5-10 parts of composite short-cut fiber, 0.8-2.5 parts of antioxidant, 0.8-2.5 parts of leveling agent, 0.4-1.2 parts of dispersing agent, 1.5-3.5 parts of UV photoinitiator, 2-4 parts of matte powder, 5-10 parts of film-forming aid, and 90-130 parts of water. The water-based polyurethane acrylate UV curing paint prepared by the application has good anti-yellowing and adhesion due to reasonable formula design and introduction of anti-ultraviolet absorbing materials.

Description

Technical Field

[0001] This invention relates to the field of UV-curable coating technology, specifically to an anti-yellowing polyurethane acrylate UV-curable coating and its preparation method. Background Technology

[0002] Ultraviolet (UV) curable coatings are coatings that undergo physical or chemical changes in a short time after being irradiated by ultraviolet light or electron beams. In the past thirty years, with the gradual enhancement of people's environmental awareness, UV curable resins have been widely used due to their characteristics such as no volatile solvents, low pollution, low energy consumption, rapid curing and excellent film performance. With the development and maturity of UV curing technology, unsaturated polyester, UV-curable inks, epoxy acrylates and polyurethane acrylates (PUA) have been developed. The molecular structure of polyurethane acrylates contains two functional groups, acrylate and urethane, and the paint film has good physical properties such as toughness, hardness and strength, excellent adhesion and relatively ideal comprehensive performance. PUA has the following excellent properties: (1) Heat resistance: The heat distortion temperature of most polyurethane acrylates is between 50 and 60℃; (2) Good mechanical properties: Polyurethane acrylate resins have high elasticity, bending, flexibility and elongation; (3) Chemical resistance: Polyurethane acrylates have good resistance to dilute acids, dilute alkalis and water, and excellent resistance to organic solvents.

[0003] After prolonged exposure to ultraviolet light, most coating surfaces exhibit a significant tendency to discolor and a decline in mechanical properties. Even indoors, they are susceptible to damage from diffuse scattering or fluorescent radiation, leading to yellowing or aging degradation. The main cause of coating aging is that the unsaturated bonds and benzene rings in the coating are easily exposed to UV radiation, reacting with oxygen to form peroxides and pyroxene structures, thus affecting the coating's resistance to yellowing. Because TDI is much cheaper than IPDI, most PUA water-based coatings on the market currently use TDI as a raw material. These coatings yellow severely under light and cannot meet the needs of varnishes, white paints, and outdoor decoration. For home decoration coatings, people prefer varnishes, white paints, and light-colored paints, making excellent resistance to yellowing a key requirement for high-end coatings. Summary of the Invention

[0004] Technical problem to be solved: The purpose of this invention is to provide an anti-yellowing polyurethane acrylate UV-curable coating. Through reasonable formulation design and the introduction of anti-UV absorption materials, a water-based polyurethane acrylate UV-curable coating with good adhesion and resistance to yellowing is prepared.

[0005] Technical solution: A UV-curable polyurethane acrylate coating for resisting yellowing, comprising the following components in parts by weight:

[0006] The composition includes 60-70 parts waterborne polyurethane acrylate, 5-10 parts composite chopped fibers, 0.8-2.5 parts antioxidant, 0.8-2.5 parts leveling agent, 0.4-1.2 parts dispersant, 1.5-3.5 parts UV photoinitiator, 2-4 parts matting powder, 5-10 parts film-forming aid, and 90-130 parts water.

[0007] The antioxidant is a phosphite, or any one or more of antioxidant 1010 or antioxidant 168.

[0008] The leveling agent is any one or more of polydimethylsiloxane, polydimethylphenylsiloxane, or polyether-modified polydimethylsiloxane.

[0009] The dispersant is any one or more of dispersant BYK190, dispersant BYK167, dispersant BYK2050 or dispersant BYK-W966;

[0010] The film-forming aid is a medium film-forming aid containing any one or more of dipropylene glycol methyl ether, dipropylene glycol butyl ether, alcohol ester dodecyl, and diethylene glycol butyl ether;

[0011] The photoinitiator is any one or more of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0012] Preferably, the composite chopped fiber is a mixture of triangular cross-section fibers and circular cross-section fibers, the length of the triangular cross-section fibers and the circular cross-section fibers is 1-5 mm, and the mass ratio of the triangular cross-section fibers to the circular cross-section fibers is 10:3-8.

[0013] Preferably, the method for preparing the composite chopped fiber includes the following steps:

[0014] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, disperse them in DMF solution, add a dispersant, and ultrasonically disperse for 30-60 min to obtain a mixed dispersion.

[0015] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 10-15%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0016] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0017] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 10-15%, add ultraviolet light absorber solution, stir evenly, and then degas under vacuum to obtain polyacrylonitrile core spinning solution.

[0018] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0019] S6. The two types of fibers prepared in step S5 are immersed in an inorganic acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0020] S7. Shorten the porous fibers separately, mix them in a certain mass ratio to obtain composite short-cut fibers.

[0021] Preferably, the method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0022] S11. Add zinc nitrate hexahydrate to an ethanol-water solution and stir until dissolved. Then add urea, with a molar ratio of zinc nitrate hexahydrate to urea of ​​1:1.5-2. Stir and mix evenly, and react at 180-190℃ for 15-24h to obtain a precipitate. Dry the precipitate and calcine it at 500-550℃ for 3-5h to obtain flake-shaped nano zinc oxide.

[0023] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0024] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0025] S14. Add the lignin solution dropwise to the zinc oxide suspension and heat the reaction. The mass ratio of lignin to nano-sheet zinc oxide is 1-2:10. After the addition is complete, adjust the pH of the solution to neutral and filter to obtain lignin-coated sheet zinc oxide.

[0026] Preferably, in step S1, the mass ratio of lignin-coated flaky zinc oxide to calcium carbonate is 2-4:1, and the concentration of calcium carbonate in DMF is 1-3 wt%.

[0027] Preferably, in step S4, the content of the ultraviolet absorber in the polyacrylonitrile core spinning solution is 0.1-0.4 wt%.

[0028] Preferably, the inorganic acid in step S6 is any one of nitric acid, hydrochloric acid, or sulfuric acid.

[0029] The preparation method of the above-mentioned anti-yellowing polyurethane acrylate UV-curable coating includes the following steps: first, the water-based polyurethane acrylate is added to a container, and then composite short-cut fibers, antioxidants, leveling agents, dispersants, UV photoinitiators, matting powders, film-forming aids and water are added in sequence. After each reaction material is added, the next material is added after stirring evenly, until all materials are added and mixed evenly to obtain the anti-yellowing polyurethane acrylate UV-curable coating.

[0030] Beneficial effects: The anti-yellowing polyurethane acrylate UV-cured coating of the present invention has the following advantages:

[0031] 1. This invention incorporates composite chopped fibers into a UV-curable coating. These composite chopped fibers are composed of two fibers with different cross-sectional structures: one with a circular cross-section and the other with a triangular cross-section. The triangular cross-section fiber has a larger surface area than the ordinary circular cross-section fiber, resulting in higher UV reflectivity. At the same time, the triangular cross-section fiber can form more reflective surfaces on the fiber surface, thereby reducing UV transmittance. Furthermore, by changing the propagation path of light, it increases the number of reflections of UV rays within the fiber, thereby improving UV absorption efficiency.

[0032] 2. The composite chopped fiber in this invention has a core-sheath structure. An organic UV stabilizer is added to the core layer, while an inorganic composite UV stabilizer is added to the sheath layer. When the coating is irradiated with UV light, the composite chopped fiber first reflects some of the UV light through its surface, and then absorbs and reflects some of the UV light through the lignin-coated nano-sheet zinc oxide in the sheath layer. Some of the UV light also enters the interior of the fiber and is absorbed by the organic UV stabilizer contained in the core layer. This combination from the inside out achieves a better UV absorption effect, thereby improving the coating's resistance to yellowing.

[0033] 3. In this invention, the combination of nano zinc oxide and lignin further improves the UV absorption effect of the coating. The appropriate content and length of composite short-cut fibers also have a certain impact on the final yellowing resistance and flexibility. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0035] Example 1

[0036] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0037] Weigh the following components by weight: 60 parts waterborne polyurethane acrylate, 5 parts composite chopped fiber, 0.8 parts phosphite, 0.8 parts polydimethylsiloxane, 0.4 parts dispersant BYK167, 1.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2 parts matte powder, 5 parts dipropylene glycol methyl ether, and 90 parts water.

[0038] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0039] The preparation method of composite chopped fibers includes the following steps:

[0040] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 2:1, the mixture is dispersed in DMF solution, and a dispersant is added. The mixture is ultrasonically dispersed for 30 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF is 1 wt%.

[0041] S2. Dissolve 10% polyacrylonitrile in DMF by mass, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0042] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0043] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 10%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 7wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.1wt%.

[0044] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0045] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0046] S7. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 10:3, to obtain composite short-cut fibers;

[0047] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0048] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.5. After stirring and mixing evenly, react at 190℃ for 15h to obtain a precipitate. After drying the precipitate, calcine it at 500℃ for 5h to obtain sheet-like nano zinc oxide.

[0049] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0050] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0051] S14. Add the lignin solution dropwise to the zinc oxide suspension and heat to react. The mass ratio of lignin to nano-sheet zinc oxide is 1:5. After the addition is complete, adjust the pH of the solution to neutral and filter to obtain lignin-coated sheet zinc oxide.

[0052] Example 2

[0053] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0054] Weigh the following components by weight: 70 parts waterborne polyurethane acrylate, 10 parts composite chopped fiber, 2.5 parts phosphite, 2.5 parts polydimethylsiloxane, 1.2 parts dispersant BYK167, 3.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 4 parts matte powder, 10 parts dipropylene glycol methyl ether, and 130 parts water.

[0055] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0056] The preparation method of composite chopped fibers includes the following steps:

[0057] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 4:1, the mixture was dispersed in DMF solution, and a dispersant was added. The mixture was ultrasonically dispersed for 60 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF was 3 wt%.

[0058] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 15%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0059] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0060] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 15%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 7wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.4wt%.

[0061] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0062] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0063] S7. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 5:4, to obtain composite short-cut fibers;

[0064] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0065] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:2. After stirring and mixing evenly, react at 180℃ for 24h to obtain a precipitate. After drying the precipitate, calcine it at 550℃ for 3h to obtain sheet-like nano zinc oxide.

[0066] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0067] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0068] S14. Add the lignin solution dropwise to the zinc oxide suspension and heat to react. The mass ratio of lignin to nano-sheet zinc oxide is 1:10. After the addition is complete, adjust the pH of the solution to neutral and filter to obtain lignin-coated sheet zinc oxide.

[0069] Example 3

[0070] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0071] Weigh the following components by weight: 62 parts waterborne polyurethane acrylate, 6 parts composite chopped fiber, 1.2 parts phosphite, 1.5 parts polydimethylsiloxane, 0.6 parts dispersant BYK167, 2 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2.5 parts matte powder, 6 parts dipropylene glycol methyl ether, and 100 parts water.

[0072] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0073] The preparation method of composite chopped fibers includes the following steps:

[0074] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 2.5:1, the mixture was dispersed in DMF solution, and a dispersant was added. The mixture was ultrasonically dispersed for 45 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF was 1.5 wt%.

[0075] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0076] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0077] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 5wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.2wt%.

[0078] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0079] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0080] S7. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 10:4, to obtain composite short-cut fibers;

[0081] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0082] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution and stir until dissolved. Then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.8. After stirring and mixing evenly, react at 180℃ for 20h to obtain a precipitate. After drying the precipitate, calcine it at 540℃ for 4.5h to obtain sheet-like nano zinc oxide.

[0083] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0084] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0085] S14. The lignin solution was added dropwise to the zinc oxide suspension, and the reaction was heated. The mass ratio of lignin to nano-sheet zinc oxide was 1.2:10. After the addition was complete, the pH of the solution was adjusted to neutral, and the solution was filtered to obtain lignin-coated sheet zinc oxide.

[0086] Example 4

[0087] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0088] Weigh the following components by weight: 67 parts waterborne polyurethane acrylate, 9 parts composite chopped fiber, 2 parts phosphite, 2 parts polydimethylsiloxane, 1 part dispersant BYK167, 3 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3.5 parts matte powder, 9 parts dipropylene glycol methyl ether, and 120 parts water.

[0089] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0090] The preparation method of composite chopped fibers includes the following steps:

[0091] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 3.5:1, the mixture was dispersed in DMF solution, and a dispersant was added. The mixture was ultrasonically dispersed for 45 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF was 2.5 wt%.

[0092] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 14%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0093] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0094] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 14%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 7wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.3wt%.

[0095] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0096] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0097] S7. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 10:6, to obtain composite short-cut fibers;

[0098] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0099] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.6. After stirring and mixing evenly, react at 190℃ for 18h to obtain a precipitate. After drying the precipitate, calcine it at 520℃ for 3.5h to obtain sheet-like nano zinc oxide.

[0100] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0101] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0102] S14. The lignin solution was added dropwise to the zinc oxide suspension and heated to react. The mass ratio of lignin to nano-sheet zinc oxide was 1.8:10. After the addition was complete, the pH of the solution was adjusted to neutral and filtered to obtain lignin-coated sheet zinc oxide.

[0103] Example 5

[0104] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0105] Weigh the following components by weight: 65 parts waterborne polyurethane acrylate, 8 parts composite chopped fiber, 1.6 parts phosphite, 1.8 parts polydimethylsiloxane, 0.8 parts dispersant BYK167, 2.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts matte powder, 8 parts dipropylene glycol methyl ether, and 110 parts water.

[0106] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0107] The preparation method of composite chopped fibers includes the following steps:

[0108] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 3:1, the mixture is dispersed in DMF solution, and a dispersant is added. The mixture is ultrasonically dispersed for 50 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF is 2 wt%.

[0109] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0110] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0111] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 5wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.25wt%.

[0112] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0113] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0114] S7. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 2:1, to obtain composite short-cut fibers;

[0115] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0116] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.7. After stirring and mixing evenly, react at 180℃ for 20h to obtain a precipitate. After drying the precipitate, calcine it at 530℃ for 4h to obtain sheet-like nano zinc oxide.

[0117] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0118] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0119] S14. The lignin solution was added dropwise to the zinc oxide suspension and heated to react. The mass ratio of lignin to nano-sheet zinc oxide was 1.5:10. After the addition was complete, the pH of the solution was adjusted to neutral and filtered to obtain lignin-coated sheet zinc oxide.

[0120] Comparative Example 1

[0121] The difference between Comparative Example 1 and Example 5 is that the mass ratio of triangular cross-section fibers to circular cross-section fibers in the composite chopped fibers is 1:1.

[0122] Comparative Example 2

[0123] The difference between Comparative Example 2 and Example 5 is that only circular cross-section fibers are used.

[0124] Comparative Example 3

[0125] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0126] Weigh the following components by weight: 65 parts waterborne polyurethane acrylate, 8 parts composite chopped fiber, 1.6 parts phosphite, 1.8 parts polydimethylsiloxane, 0.8 parts dispersant BYK167, 2.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts matte powder, 8 parts dipropylene glycol methyl ether, and 110 parts water.

[0127] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0128] The preparation method of composite chopped fibers includes the following steps:

[0129] S1. Disperse lignin-coated flaky zinc oxide in DMF solution, add dispersant, and ultrasonically disperse for 50 min to obtain dispersion. The concentration of lignin-coated flaky zinc oxide in DMF is 5 wt%.

[0130] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0131] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0132] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 5wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.25wt%.

[0133] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0134] S6. Cut the two types of fibers to 1-5mm respectively, mix them by mass ratio, with the mass ratio of triangular cross-section fiber to circular cross-section fiber being 2:1, to obtain composite chopped fiber;

[0135] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0136] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.7. After stirring and mixing evenly, react at 180℃ for 20h to obtain a precipitate. After drying the precipitate, calcine it at 530℃ for 4h to obtain sheet-like nano zinc oxide.

[0137] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0138] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0139] S14. The lignin solution was added dropwise to the zinc oxide suspension and heated to react. The mass ratio of lignin to nano-sheet zinc oxide was 1.5:10. After the addition was complete, the pH of the solution was adjusted to neutral and filtered to obtain lignin-coated sheet zinc oxide.

[0140] Comparative Example 4

[0141] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0142] Weigh the following components by weight: 65 parts waterborne polyurethane acrylate, 8 parts composite chopped fiber, 1.6 parts phosphite, 1.8 parts polydimethylsiloxane, 0.8 parts dispersant BYK167, 2.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts matte powder, 8 parts dipropylene glycol methyl ether, and 110 parts water.

[0143] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0144] The preparation method of composite chopped fibers includes the following steps:

[0145] S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, with a mass ratio of 3:1, the mixture was dispersed in DMF solution, and a dispersant was added. The mixture was ultrasonically dispersed for 45 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF was 2 wt%.

[0146] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile spinning solution;

[0147] S3. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solution prepared in step S2 to obtain circular cross-section fibers and triangular cross-section fibers;

[0148] S4. The two types of fibers prepared in step S3 are immersed in 0.1 mol / L hydrochloric acid solution to remove nano-calcium carbonate and obtain fibers with porous surfaces.

[0149] S5. Shorten the porous fibers to 1-5mm, mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 2:1, to obtain composite short-cut fibers;

[0150] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0151] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.7. After stirring and mixing evenly, react at 180℃ for 20h to obtain a precipitate. After drying the precipitate, calcine it at 530℃ for 4h to obtain sheet-like nano zinc oxide.

[0152] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0153] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0154] S14. The lignin solution was added dropwise to the zinc oxide suspension and heated to react. The mass ratio of lignin to nano-sheet zinc oxide was 1.5:10. After the addition was complete, the pH of the solution was adjusted to neutral and filtered to obtain lignin-coated sheet zinc oxide.

[0155] Comparative Example 5

[0156] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0157] Weigh the following components by weight: 65 parts waterborne polyurethane acrylate, 8 parts composite chopped fiber, 1.6 parts phosphite, 1.8 parts polydimethylsiloxane, 0.8 parts dispersant BYK167, 2.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts matte powder, 8 parts dipropylene glycol methyl ether, and 110 parts water.

[0158] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0159] The preparation method of composite chopped fibers includes the following steps:

[0160] S1. After mixing flake zinc oxide and nano calcium carbonate at a mass ratio of 3:1, disperse them in DMF solution, add a dispersant, and ultrasonically disperse for 40 min to obtain a mixed dispersion. The concentration of calcium carbonate in DMF is 2 wt%.

[0161] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution.

[0162] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0163] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile core spinning solution with a concentration of 5wt%, and the content of ultraviolet light absorber in the polyacrylonitrile core spinning solution is 0.25wt%.

[0164] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0165] S6. The two types of fibers prepared in step S5 are immersed in a 0.1 mol / L hydrochloric acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface.

[0166] S7. Shorten the porous fibers to 1-5mm and mix them by mass ratio, with the mass ratio of triangular cross-section fibers to circular cross-section fibers being 2:1, to obtain composite short-cut fibers.

[0167] Comparative Example 6

[0168] A method for preparing anti-yellowing polyurethane acrylate UV-curable coatings includes the following steps:

[0169] Weigh the following components by weight: 65 parts waterborne polyurethane acrylate, 8 parts composite chopped fiber, 1.6 parts phosphite, 1.8 parts polydimethylsiloxane, 0.8 parts dispersant BYK167, 2.5 parts 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts matte powder, 8 parts dipropylene glycol methyl ether, and 110 parts water.

[0170] Add waterborne polyurethane acrylate to a container, then add composite chopped fibers, phosphite, polydimethylsiloxane, dispersant BYK167, 2-hydroxy-2-methyl-1-phenyl-1-propanone, matte powder, dipropylene glycol methyl ether and water in sequence. After each addition of a reactant, stir until homogeneous before adding the next reactant, until all reactants are added and the mixture is homogeneous to obtain an anti-yellowing polyurethane acrylate UV-curable coating.

[0171] The preparation method of composite chopped fibers includes the following steps:

[0172] S1. Disperse lignin-coated flaky zinc oxide in DMF solution, add dispersant, and ultrasonically disperse for 45 min to obtain a dispersion with a concentration of 4 wt%.

[0173] S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 14%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile core spinning solution.

[0174] S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution;

[0175] S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 12%, add ultraviolet light absorber solution, stir evenly and then degas under vacuum to obtain a polyacrylonitrile skin spinning solution with a concentration of 6wt%, and the content of ultraviolet light absorber in the polyacrylonitrile skin spinning solution is 0.25wt%.

[0176] S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers;

[0177] S6. Cut the two types of fibers to 1-5mm respectively, mix them by mass ratio, with the mass ratio of triangular cross-section fiber to circular cross-section fiber being 2:1, to obtain composite chopped fiber;

[0178] The method for preparing the lignin-coated flaky zinc oxide includes the following steps:

[0179] S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution, stir until dissolved, then add urea. The molar ratio of zinc nitrate hexahydrate to urea is 1:1.7. After stirring and mixing evenly, react at 180℃ for 20h to obtain a precipitate. After drying the precipitate, calcine it at 530℃ for 4h to obtain sheet-like nano zinc oxide.

[0180] S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension;

[0181] S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution;

[0182] S14. The lignin solution was added dropwise to the zinc oxide suspension and heated to react. The mass ratio of lignin to nano-sheet zinc oxide was 1.5:10. After the addition was complete, the pH of the solution was adjusted to neutral and filtered to obtain lignin-coated sheet zinc oxide.

[0183] Comparative Example 7

[0184] The difference between Comparative Example 7 and Example 5 is that the content of composite chopped fibers in the coating is different. The components are weighed according to the following parts by weight: 65 parts of waterborne polyurethane acrylate, 3 parts of composite chopped fibers, 1.6 parts of phosphite, 1.8 parts of polydimethylsiloxane, 0.8 parts of dispersant BYK167, 2.5 parts of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 3 parts of matte powder, 8 parts of dipropylene glycol methyl ether, and 110 parts of water.

[0185] Comparative Example 8

[0186] The difference between Comparative Example 1 and Example 5 is that the length of the composite chopped fiber is 5-8 mm.

[0187] The UV-curable coatings prepared in the above examples and comparative examples were applied to the substrate, with a coating amount of 8-20 g / m². 2 The number of coating layers is unlimited; finally, the coating composition is cured by ultraviolet irradiation, and the adhesion, yellowing after 1000h ultraviolet irradiation and other test properties are tested respectively, as shown in Table 1 below. Among them, the coating adhesion is determined according to ASTM D3359-09; the yellowing test is determined according to GB / T 23983-2009; and the flexibility test is determined according to GB / T 1731-2020.

[0188] Adhesion Yellowing after 1000 hours of ultraviolet radiation / ΔE Flexibility / mm Example 1 5B 0.89 0.5 Example 2 5B 0.85 1 Example 3 5B 0.92 1 Example 4 5B 0.88 0.5 Example 5 5B 0.82 0.5 Comparative Example 1 5B 1.23 1 Comparative Example 2 5B 3.69 1 Comparative Example 3 5B 4.56 1.5 Comparative Example 4 5B 2.89 0.5 Comparative Example 5 5B 1.44 1 Comparative Example 6 5B 2.16 0.5 Comparative Example 7 3B 2.54 1.5 Comparative Example 8 3B 0.91 1.5

[0189] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A UV-curable polyurethane acrylate coating with anti-yellowing properties, characterized in that, It contains the following components by weight: The composition includes 60-70 parts waterborne polyurethane acrylate, 5-10 parts composite chopped fibers, 0.8-2.5 parts antioxidant, 0.8-2.5 parts leveling agent, 0.4-1.2 parts dispersant, 1.5-3.5 parts UV photoinitiator, 2-4 parts matting powder, 5-10 parts film-forming aid, and 90-130 parts water. The antioxidant is any one or more of phosphites or antioxidant 1010; The leveling agent is any one or more of polydimethylsiloxane, polydimethylphenylsiloxane, or polyether-modified polydimethylsiloxane. The dispersant is any one or more of dispersant BYK190, dispersant BYK167, dispersant BYK2050 or dispersant BYK-W966; The film-forming aid is any one or more of dipropylene glycol methyl ether, dipropylene glycol butyl ether, alcohol ester dodecyl, and diethylene glycol butyl ether. The photoinitiator is any one or more of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; The composite chopped fiber is a mixture of triangular cross-section fibers and circular cross-section fibers, the length of which is 1-5 mm and the mass ratio of which is 10:3-8. The method for preparing the composite chopped fiber includes the following steps: S1. After mixing lignin-coated flaky zinc oxide and nano-calcium carbonate, disperse them in DMF solution, add a dispersant, and ultrasonically disperse for 30-60 min to obtain a mixed dispersion. S2. Dissolve polyacrylonitrile in DMF at a mass fraction of 10-15%, add it to the mixed dispersion at a volume ratio of 1:1, stir evenly, and then degas under vacuum to obtain polyacrylonitrile skin spinning solution. S3. Add the ultraviolet light absorber to the DMF solution, and after ultrasonic dispersion, obtain the ultraviolet light absorber solution; S4. Dissolve polyacrylonitrile in DMF at a mass fraction of 10-15%, add ultraviolet light absorber solution, stir evenly, and then degas under vacuum to obtain polyacrylonitrile core spinning solution. S5. Select circular and triangular cross-section spinnerets respectively, and perform coaxial spinning on the spinning solutions prepared in steps S2 and S4 to obtain circular cross-section fibers and triangular cross-section fibers; S6. The two types of fibers prepared in step S5 are immersed in an inorganic acid solution to remove the nano-calcium carbonate in the skin layer, resulting in fibers with a porous surface. S7. Shorten the porous fibers separately, mix them in a certain mass ratio to obtain composite short-cut fibers.

2. The anti-yellowing polyurethane acrylate UV-curable coating according to claim 1, characterized in that: The method for preparing the lignin-coated flaky zinc oxide includes the following steps: S11. Add zinc nitrate hexahydrate to an ethanol aqueous solution and stir until dissolved. Then add urea, with a molar ratio of zinc nitrate hexahydrate to urea of ​​1:1.5-2. Stir and mix evenly, and react at 180-190℃ for 15-24h to obtain a precipitate. Dry the precipitate and calcine it at 500-550℃ for 3-5h to obtain flake-shaped nano zinc oxide. S12. Add the sheet-like nano zinc oxide prepared in step S11 to water and disperse it evenly by ultrasonication to obtain a zinc oxide suspension; S13. Add lignin to an alkaline aqueous solution and stir until completely dissolved to obtain a lignin solution; S14. Add the lignin solution dropwise to the zinc oxide suspension and heat to react. The mass ratio of lignin to nano-flaky zinc oxide is 1-2:

10. After the addition is complete, adjust the pH of the solution to neutral and filter to obtain lignin-coated flaky zinc oxide.

3. The anti-yellowing polyurethane acrylate UV-curable coating according to claim 1, characterized in that: In step S1, the mass ratio of lignin-coated flaky zinc oxide to calcium carbonate is 2-4:1, and the concentration of calcium carbonate in DMF is 1-3 wt%.

4. The anti-yellowing polyurethane acrylate UV-curable coating according to claim 1, characterized in that: In step S4, the content of ultraviolet absorber in the polyacrylonitrile core spinning solution is 0.1-0.4 wt%.

5. The anti-yellowing polyurethane acrylate UV-curable coating according to claim 1, characterized in that: In step S6, the inorganic acid is any one of nitric acid, hydrochloric acid, or sulfuric acid.

6. The method for preparing the anti-yellowing polyurethane acrylate UV-curable coating according to claims 1-5, characterized in that, Includes the following steps: First, add the waterborne polyurethane acrylate to a container, then add composite chopped fibers, antioxidant, leveling agent, dispersant, UV photoinitiator, matting powder, film-forming aid and water in sequence. After each reactant is added, stir until homogeneous before adding the next reactant, until all reactants are added and mixed evenly to obtain the anti-yellowing polyurethane acrylate UV-curable coating.