Self-crosslinking fluorocarbon modified waterborne polyurethane wood coating and preparation method thereof

Abstract

The invention discloses a self-crosslinking type fluorocarbon modified waterborne polyurethane wood coating. The self-crosslinking type fluorocarbon modified waterborne polyurethane wood coating comprises a fluorocarbon modified waterborne polyurethane emulsion, a self-crosslinking system, a nano reinforcing agent and auxiliary components. The preparation method of the self-crosslinking fluorocarbon modified waterborne polyurethane wood coating comprises the following steps: mixing nano dispersion liquid with deionized water; adding a fluorocarbon modified waterborne polyurethane emulsion and a self-crosslinking monomer, and mixing; and finally, adding the auxiliary components, uniformly mixing, and filtering to obtain the wood coating. The fluorocarbon modified waterborne polyurethane emulsion comprises a fluorine-containing waterborne polyurethane core layer and a styrene-acrylic polymer shell layer, wherein the fluorine-containing waterborne polyurethane core layer is composed of a fluorine-containing acrylate monomer capable of spontaneously migrating, and the surface of the core layer is coated with the styrene-acrylic polymer shell layer. The self-enrichment effect of a fluorine-containing chain segment is utilized to improve the weather resistance and hydrophobicity, and the matching and graft copolymerization reaction between a fluorine-containing waterborne polyurethane core layer and a styrene-acrylic resin shell layer is utilized to improve the weather resistance, wear resistance, the binding force between the core-shell layers and the overall flexibility, so that the performance of the wood coating containing the core-shell emulsion is improved.

Description

Technical Field

[0001] This invention relates to the field of wood coating technology, specifically to a self-crosslinking fluorocarbon modified waterborne polyurethane wood coating and its preparation method. Background Technology

[0002] With increasingly stringent environmental regulations and growing consumer awareness of environmental protection, water-based coatings have become a development trend in the wood coating industry. However, traditional water-based polyurethane coatings suffer from poor weather resistance, susceptibility to cracking, and insufficient temperature resistance when used outdoors. While fluorocarbon resin coatings offer excellent weather resistance and chemical resistance, they are expensive, and the flexibility and abrasion resistance of pure fluorocarbon coatings are insufficient to meet the requirements of wood coating.

[0003] In the prior art, Chinese patent CN120059536A discloses a flexible, wear-resistant fluorocarbon coating modified with nano-two-dimensional sheets. This improves the flexibility and wear resistance of the fluorocarbon coating by adding castor oil polyol and nano-two-dimensional sheets, but it still requires isocyanate curing agents, resulting in problems such as a short activation period and high VOC emissions. Another Chinese patent, CN116656161A, discloses a high-strength, thermally insulating, environmentally friendly, and fire-retardant coating and its preparation method, introducing self-crosslinking monomers to achieve room-temperature crosslinking; however, its weather resistance is insufficient for outdoor use.

[0004] Furthermore, the "Preparation and Application Technology of Fast-Drying Waterborne UV-Curing Wood Coatings" developed by the Chinese Academy of Forestry addresses the problems of slow curing speed and long drying time of waterborne UV coatings. It optimizes waterborne polyurethane acrylate UV-curing resins with a solid content of 75-90%, and based on the film formation reaction mechanism, selects and blends relevant additives to prepare high-performance fast-drying waterborne UV wood coatings (Energy Saving and Consumption Reduction and Production Safety Control Technology in the Wood Industry, Preparation and Application Technology of Fast-Drying Waterborne UV-Curing Wood Coatings, National Forestry and Grassland Science Data Center, 2020-12-22, CSTR:17575.11.0220230411022.0001.V1). However, although it has a fast drying speed and high film hardness, it requires significant investment in curing equipment and is limited in its application to complex-shaped workpieces.

[0005] To address the shortcomings of existing technologies, this invention provides a self-crosslinking fluorocarbon-modified waterborne polyurethane wood coating. By combining core-shell structure design, fluorocarbon segment introduction, and self-crosslinking technology, it significantly improves the weather resistance, abrasion resistance, and flexibility of the coating while maintaining the environmental advantages of waterborne coatings. It is particularly suitable for protective coating of outdoor wood products. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a self-crosslinking fluorocarbon-modified waterborne polyurethane wood coating. The core-shell structure fluorocarbon-modified waterborne polyurethane proposed in this invention has a core layer of fluorinated segments / groups and a shell layer of acrylate structure. The low surface energy fluorinated segments / groups slowly migrate to the core surface and shell layer due to their self-enrichment effect, which brings good hydrophobic properties to the fluorocarbon-modified waterborne polyurethane. In addition, this invention adopts self-crosslinking technology, utilizing the ketone carbonyl group (C=O) of diacetone ammonium acrylate (DAAM) and the acylhydrazide group (-NH-NH2-) of adipic acid dihydrazide (ADH) to generate hydrazone bonds (C=NN-), without the need to add additional crosslinking agents.

[0007] To solve this technical problem, the technical solution of the present invention is: a method for preparing a self-crosslinking fluorocarbon modified waterborne polyurethane wood coating, comprising the following steps: S1. Mix the nano-SiO2 dispersion, wetting and dispersing agent, and deionized water, and stir to disperse evenly to obtain a dispersion; S2. Add a fluorocarbon-modified aqueous polyurethane emulsion with a core-shell structure, a self-crosslinking monomer obtained by mixing diacetone acrylamide and adipate dihydrazide, and the remaining deionized water to the dispersion obtained in step S1, and stir to mix evenly to obtain a mixture. Fluorocarbon-modified waterborne polyurethane emulsion with a core-shell structure includes a fluorinated waterborne polyurethane core composed of spontaneously migrating fluorinated acrylate monomers and a styrene-acrylic polymer shell coating the surface of the fluorinated waterborne polyurethane core. S3. Add photoinitiator, defoamer, leveling agent and film-forming aid to the mixture obtained in step S2, stir and filter to obtain the finished coating.

[0008] Preferably, the method for preparing the fluorocarbon-modified waterborne polyurethane emulsion with a core-shell structure includes the following steps: S11. Under nitrogen protection, isophorone diisocyanate, polyether polyol, dimethylolpropionic acid and fluorinated acrylate monomer are added to the reactor and stirred to react. After the reaction is completed, acetone is added to dilute, followed by triethylamine to neutralize. The mixture is then stirred and emulsified in deionized water to obtain the core-layer fluorinated polyurethane prepolymer emulsion. S12. Add styrene, butyl acrylate and methyl methacrylate to deionized water, and disperse the emulsified monomers at high speed to obtain a monomer pre-emulsion for shell polymerization. S13. Add ammonium persulfate to the core-layer fluorinated polyurethane prepolymer emulsion obtained in step S11, and slowly heat it to 80 °C while stirring. Then slowly add the monomer pre-emulsion obtained in S12. Free radical copolymerization reaction occurs during the drop addition. Then, remove impurities by vacuum distillation to obtain a fluorocarbon modified waterborne polyurethane emulsion with a core-shell structure.

[0009] This invention incorporates fluorinated acrylate monomers into the core. Due to the low surface energy of the fluorinated segments / groups, they exhibit a spontaneous self-accumulation effect, migrating towards the surface. Simultaneously, the fluorinated segments / groups possess high bond energy, making them resistant to degradation under ultraviolet light. The outer shell, made from methyl methacrylate, benefits from the enhanced chemical stability of the methyl groups and the increased molecular chain rigidity through the conjugation of the ester groups. This combined effect results in excellent weather resistance and durability. Furthermore, after preparation, the fluorinated segments / groups continue to migrate slowly, eventually distributing across the core surface and shell. The combined effect of the fluorinated segments in the core and the methyl methacrylate in the shell contributes to the coating's superior weather resistance and durability. The core-shell structure of the fluorocarbon-modified waterborne polyurethane proposed in this invention is a fluorinated waterborne polyurethane core layer. Its flexible-rigid-flexible segment combination provides excellent flexibility, while the shell layer is a styrene-acrylic polymer shell with good wear resistance and scratch resistance. The double-layer structure of the core-shell layer enables the fluorocarbon-modified waterborne polyurethane to possess good flexibility while also exhibiting good wear resistance, scratch resistance, and workability thanks to the shell layer. Furthermore, during the synthesis process, the free radical copolymerization of the shell layer is initiated under the action of ammonium persulfate, and the acrylic segments of butyl acrylate and methyl methacrylate in the shell layer undergo graft copolymerization with the double bonds and active hydrogens of the fluorinated acrylate monomers in the core layer, further improving the tightness of the bonding between the core and shell layers and enhancing the overall integrity of the final core-shell material. This results in a core-shell structure fluorocarbon-modified waterborne polyurethane coating matrix that combines flexibility, wear resistance, scratch resistance, and workability.

[0010] In preferred step S11, the mass ratio of polyisocyanate, polyether polyol, dimethylolpropionic acid, and fluorinated acrylate monomer is 1:(0.8-1.2):(0.2-0.4):(0.4-0.8). In step S11, the emulsified and dispersed reaction solution in deionized water has a mass ratio of 1:(0.3-0.8) to deionized water.

[0011] In preferred step S12, the mass ratio of deionized water, styrene, butyl acrylate, and methyl methacrylate is 1:(0.16-0.24):(0.2-0.28):(0.06-0.2). In step S13, the mass ratio of ammonium persulfate to polyether polyol is 1:(0.01-0.03).

[0012] Preferred cross-linked fluorocarbon-modified waterborne polyurethane wood coatings include the following components: 40-60 parts of fluorocarbon modified waterborne polyurethane emulsion; 3-8 parts of self-crosslinking monomer; 2-5 parts of nano-SiO2 dispersion; Photoinitiator 0.5-2 parts; 0.5-1.5 parts of wetting and dispersing agent; 0.1-0.5 parts of defoamer; Leveling agent 0.2-1 part; 2-5 parts of film-forming aid; 20-30 parts deionized water.

[0013] In this invention, the wetting and dispersing agent is a commercially available product of polyether modified styrene-maleic anhydride copolymer, acrylic block copolymer, or anionic wetting and dispersing agent. Suitable choices include BYK-190 from BYK Chemical, EFKA-4575 from BASF, TEGO Dispers 752W from Evonik, and EFKA-4452 from BASF. Defoamers are commercially available products of silicone type, mineral oil type, and silicone-free type. Suitable choices include BYK-024, BYK-1660, BYK-045, and BYK-019 from BYK Chemical. The leveling agents are commercially available products such as polydimethylsiloxane, polyether-modified organosiloxane, and acrylic leveling agents. Suitable choices include BYK-333, BYK-381, Evonik TEGO Glide 450, and Levelol 495.

[0014] Preferably, the molar ratio of diacetone acrylamide to adipate dihydrazide in the self-crosslinking monomer is 1:(0.8-1.2).

[0015] The preferred solid content of the nano-SiO2 dispersion is 20-30%, and the particle size of the nano-SiO2 is 20-50 nm.

[0016] The preferred photoinitiator is a mixture of 2-hydroxy-2-methyl-1-phenyl-1-propanone with high initiation efficiency and 1-hydroxycyclohexylphenyl ketone with good resistance to yellowing, with a mass ratio of 1:(1-2).

[0017] The preferred film-forming aid is a mixture of dipropylene glycol methyl ether, which evaporates relatively quickly, and dipropylene glycol butyl ether, which evaporates relatively slowly, with a mass ratio of 1:(1-3).

[0018] Preferably, the mass ratio of the fluorinated waterborne polyurethane core to the styrene-acrylic polymer shell is 1:(0.3-0.6) to avoid poor wear resistance and hardness of the coating or cracking during the curing process due to an excessively low or high shell ratio. The fluorinated waterborne polyurethane core contains 15-25 wt. of fluorinated acrylate monomers.

[0019] By adopting the above technical solution, the beneficial effects of the present invention are: This invention utilizes a fluorocarbon-modified waterborne polyurethane with a bilayer structure comprising a fluorinated waterborne polyurethane core layer composed of spontaneously migrating fluorinated acrylate monomers and a styrene-acrylic polymer shell layer covering the core layer surface. The core layer contains fluorinated acrylate monomers, which, due to the low surface energy of the fluorinated segments / groups, exhibit a spontaneous self-accumulation effect by migrating to the surface. Simultaneously, the fluorinated segments / groups possess high bond energy, making them resistant to degradation under ultraviolet light. The outer shell layer uses methyl methacrylate as a raw material, benefiting from the enhanced chemical stability of the methyl groups and the enhanced molecular chain rigidity through the conjugation of the ester groups. This combined effect results in excellent weather resistance and durability for the shell layer. Furthermore, after preparation, the fluorinated segments / groups continue to migrate slowly, eventually distributing on the core layer surface and within the shell layer. The combined effect of the fluorinated segments in the core and the methyl methacrylate in the shell layer contributes to the coating's excellent weather resistance and durability.

[0020] The core layer of the proposed core-shell structure fluorocarbon-modified waterborne polyurethane is a fluorinated waterborne polyurethane. Its flexible polyether polyol segments can connect multiple rigid isocyanate segments to form a flexible-rigid-flexible segment combination, creating a physical cross-linking network that provides excellent flexibility. Simultaneously, the shell layer is a styrene-acrylic polymer shell with good wear resistance and scratch resistance. This bilayer structure, combining a flexible core layer with a certain proportion of hard, wear-resistant shell, allows the fluorocarbon-modified waterborne polyurethane to inherit the excellent flexibility of the core layer while also possessing good wear resistance, scratch resistance, and workability thanks to the shell layer. Furthermore, during the synthesis process, ammonium persulfate initiates free radical copolymerization of the shell layer, and the acrylic segments of butyl acrylate and methyl methacrylate in the shell layer undergo graft copolymerization with the double bonds and active hydrogens of the fluorinated acrylate monomers in the core layer. This further enhances the tightness of the bonding between the core and shell layers, improving the overall integrity of the final core-shell material, resulting in a core-shell structure fluorocarbon-modified waterborne polyurethane coating matrix that combines flexibility, wear resistance, scratch resistance, and workability.

[0021] This invention employs self-crosslinking technology. First, the rapid initiation effect of 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator 1173) and the initiation effect of 1-hydroxycyclohexylphenyl methyl ketone (photoinitiator 184) will first undergo a crosslinking reaction, providing a basic polymer network for the subsequent self-crosslinking process. Subsequently, the ketone carbonyl group (C=O) of diacetone ammonium acrylate (DAAM) and the acylhydrazide group (-NH-NH2-) of adipic acid dihydrazide (ADH) in the self-crosslinking monomer undergo self-crosslinking to generate hydrazone bonds (C=NN-), achieving the crosslinking effect without the need to add additional crosslinking agents, effectively reducing VOC content and improving environmental performance. Furthermore, this invention uses a mixture of dipropylene glycol methyl ether (DME), which evaporates relatively quickly, and dipropylene glycol butyl ether (DME), which evaporates relatively slowly, as a film-forming aid. DME rapidly initiates polymerization and film formation, while DME provides sustained polymerization. This fast-slow mixing method forms a uniform, dense, and high-strength coating. In addition, this invention controls the amount of fluorocarbon monomer used in the preparation process to 15-25%, which reduces the cost by 30-40% compared to pure fluorocarbon coatings, demonstrating a significant cost advantage. Attached Figure Description

[0022] Figure 1 The image shows the FT-IR spectrum of the fluorocarbon-modified waterborne polyurethane emulsion prepared in Example 1.

[0023] Figure 2 TEM images of the fluorocarbon-modified waterborne polyurethane emulsions prepared in Examples 1-3.

[0024] Figure 3 Microscopic images of the coatings prepared in Example 1 and the coatings prepared in Comparative Examples 1-3 after QUV accelerated aging test; Figure 1 In Figure a, is the FT-IR spectrum of isophorone diisocyanate; in Figure b, is the FT-IR spectrum of fluorinated polyurethane prepolymer emulsion; and in Figure c, is the FT-IR spectrum of fluorocarbon modified waterborne polyurethane emulsion.

[0025] Figure 2 a, b, and c represent the fluorocarbon-modified waterborne polyurethane emulsions of Examples 1-3, respectively.

[0026] Figure 3 Image a is the image of the coating prepared in Example 1 after aging; image b is the image of the coating prepared in Comparative Example 1 after aging; image c is the image of the coating prepared in Comparative Example 2 after aging; and image d is the image of the coating prepared in Comparative Example 3 after aging. Detailed Implementation

[0027] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0028] Example 1 This embodiment discloses a method for preparing a fluorocarbon-modified waterborne polyurethane emulsion, comprising the following steps: S11. Core layer synthesis: Under nitrogen protection, 25 parts of isophorone diisocyanate (IPDI), 20 parts of polyether polyol (N220), 6 parts of dimethylolpropionic acid (DMPA) and 15 parts of fluorinated acrylate monomer (DFHMA) were added to the reactor and stirred at 75 °C for 2.5 h. After the reaction was completed, 20 parts of acetone were added for dilution, followed by 4.5 parts of triethylamine for neutralization. Then, the mixture was stirred at 1400 rpm for 20 min to emulsify and disperse in 40 parts of deionized water to obtain the fluorinated polyurethane prepolymer emulsion. S12. Add 10 parts styrene (St), 12 parts butyl acrylate (BA), and 8 parts methyl methacrylate (MMA) to 100 parts deionized water, and then disperse at high speed for 15-30 min at 2500-3500 rpm to emulsify and disperse the monomers, to obtain a pre-emulsion for shell polymerization monomers. S13. Add 0.4 parts of ammonium persulfate (APS) to the fluorinated polyurethane prepolymer emulsion obtained in step S11, and slowly heat it to 80 ℃ at a heating rate of 3 ℃ / min while stirring. Then slowly add S12 to obtain a shell polymerization monomer preemulsion, controlling the addition time to 3 h. After the addition is completed, continue stirring for 1 h. Free radical copolymerization reaction occurs during the addition process. Then, remove impurities by vacuum distillation to obtain the fluorocarbon modified waterborne polyurethane emulsion.

[0029] This embodiment uses the above-mentioned fluorocarbon-modified waterborne polyurethane emulsion to create a self-crosslinking fluorocarbon-modified waterborne polyurethane wood coating, which comprises the following components by weight: Fluorocarbon modified waterborne polyurethane emulsion: 50 parts; Self-crosslinking monomer: 7.2 parts; Nano-SiO2 dispersion: 3 parts; Photoinitiator: 1.5 parts; Wetting and dispersing agent: 1 part; Defoamer: 0.3 parts; Leveling agent: 0.5 parts; Film-forming aid: 3.5 parts; Deionized water: 25 parts; The method for preparing self-crosslinking fluorocarbon modified waterborne polyurethane wood coatings in this embodiment includes the following steps: S1. Mix nano-SiO2 dispersion (solid content 25%), wetting and dispersing agent (BYK-190), and 10 parts of deionized water, and stir at 1200 rpm for 30 min to disperse evenly to obtain a dispersion. S2. Add fluorocarbon modified waterborne polyurethane emulsion, self-crosslinking monomer (obtained by mixing diacetone acrylamide and adipate dihydrazide at a mass ratio of 1:0.8) and the remaining 15 parts of deionized water to the dispersion obtained in step S1, and stir at 1000 rpm for 15 min to mix evenly to obtain a mixture. S3. Add photoinitiator (obtained by mixing photoinitiator 1173 and photoinitiator 184 at a mass ratio of 1:1.5), defoamer (BYK-024), leveling agent (BYK-381), and film-forming aid (obtained by mixing dipropylene glycol methyl ether and dipropylene glycol butyl ether at a mass ratio of 1:1.33) to the mixture obtained in step S2. Stir at 1200 rpm for 40 min, and then filter to obtain the finished coating.

[0030] Example 2 This embodiment discloses a method for preparing a fluorocarbon-modified waterborne polyurethane emulsion, comprising the following steps: S11. Core layer synthesis: Under nitrogen protection, 25 parts of isophorone diisocyanate (IPDI), 20 parts of polyether polyol (N220), 6 parts of dimethylolpropionic acid (DMPA) and 15 parts of fluorinated acrylate monomer (DFHMA) were added to the reactor and stirred at 75 °C for 2.5 h. After the reaction was completed, 20 parts of acetone were added for dilution, followed by 4.5 parts of triethylamine for neutralization. Then, the mixture was stirred at 1400 rpm for 20 min to emulsify and disperse in 40 parts of deionized water to obtain the fluorinated polyurethane prepolymer emulsion. S12. Add 8 parts styrene (St), 9.6 parts butyl acrylate (BA), and 6.4 parts methyl methacrylate (MMA) to 100 parts deionized water, and then disperse at high speed for 15-30 min at 2500-3500 rpm to emulsify and disperse the monomers, to obtain a shell polymerization monomer pre-emulsion. S13. Add 0.4 parts of ammonium persulfate (APS) to the prepolymer emulsion obtained in step S11, and slowly heat it to 80 °C at a heating rate of 3 °C / min while stirring. Then slowly add the shell polymerization monomer preemulsion obtained in S12, controlling the addition time to 3 h. After the addition is completed, continue stirring for 1 h. Free radical copolymerization reaction occurs during the addition process. Then, remove impurities by vacuum distillation to obtain fluorocarbon modified waterborne polyurethane emulsion.

[0031] The self-crosslinking fluorocarbon modified waterborne polyurethane wood coating and its preparation method in this embodiment are the same as in Example 1.

[0032] Example 3 This embodiment discloses a method for preparing a fluorocarbon-modified waterborne polyurethane emulsion, comprising the following steps: S11. Under nitrogen protection, 25 parts of isophorone diisocyanate (IPDI), 20 parts of polyether polyol (N220), 6 parts of dimethylolpropionic acid (DMPA) and 18 parts of fluorinated acrylate monomer (DFHMA) were added to a reactor and stirred at 75 °C for 2.5 h. After the reaction was completed, 20 parts of acetone were added for dilution, followed by 4.5 parts of triethylamine for neutralization. Then, the mixture was stirred at 1400 rpm for 20 min to emulsify and disperse in 40 parts of deionized water to obtain a fluorinated polyurethane prepolymer emulsion for nucleation. S12. Add 10 parts styrene (St), 12 parts butyl acrylate (BA), and 8 parts methyl methacrylate (MMA) to 100 parts deionized water, and then disperse at high speed for 15-30 min at 2500-3500 rpm to emulsify and disperse the monomers, to obtain a shell polymerization monomer pre-emulsion. S13. Add 0.4 parts of ammonium persulfate (APS) to the prepolymer emulsion obtained in step S11, and slowly heat it to 80 °C at a heating rate of 3 °C / min while stirring. Then slowly add the pre-emulsion obtained in S12, controlling the adding time to 3 h. After the adding is completed, continue stirring for 1 h. Free radical copolymerization reaction occurs during the adding process. Then, remove impurities by vacuum distillation to obtain fluorocarbon modified waterborne polyurethane emulsion.

[0033] The self-crosslinking fluorocarbon modified waterborne polyurethane wood coating and its preparation method in this embodiment are the same as in Example 1.

[0034] Comparative Example 1 This comparative example discloses a method for preparing a fluorinated waterborne polyurethane emulsion, comprising the following steps: Under a nitrogen atmosphere, 25 parts of isophorone diisocyanate (IPDI), 20 parts of polyether polyol (N220), 6 parts of dimethylolpropionic acid (DMPA), and 15 parts of fluorinated acrylate monomer (DFHMA) were added to a reactor and stirred at 75 °C for 2.5 h. After the reaction was completed, 20 parts of acetone were added for dilution, followed by 4.5 parts of triethylamine for neutralization. The mixture was then emulsified and dispersed in 40 parts of deionized water by stirring at 1400 rpm for 20 min to obtain a fluorinated polyurethane emulsion. This comparative example uses the above-mentioned fluorinated polyurethane emulsion in a self-crosslinking waterborne polyurethane wood coating, which comprises the following components by weight: Fluorinated waterborne polyurethane emulsion: 50 parts; Self-crosslinking monomer: 7.2 parts; Nano-SiO2 dispersion: 3 parts; Photoinitiator: 1.5 parts; Wetting and dispersing agent: 1 part; Defoamer: 0.3 parts; Leveling agent: 0.5 parts; Film-forming aid: 3.5 parts; Deionized water: 25 parts; The above-mentioned method for preparing self-crosslinking waterborne polyurethane wood coatings includes the following steps: S1. Mix nano-SiO2 dispersion (solid content 25%), wetting and dispersing agent (BYK-190), and 10 parts of deionized water, and stir at 1200 rpm for 30 min to disperse evenly to obtain a dispersion. S2. Add fluorinated aqueous polyurethane emulsion, self-crosslinking monomer (obtained by mixing diacetone acrylamide and adipate dihydrazide at a mass ratio of 1:0.8) and 15 parts of deionized water to the dispersion in step S1, and stir at 1000 rpm for 15 min to obtain a mixture; S3. Add photoinitiator (obtained by mixing photoinitiator 1173 and photoinitiator 184 at a mass ratio of 1:1.5), defoamer (BYK-024), leveling agent (BYK-381), and film-forming aid (obtained by mixing dipropylene glycol methyl ether and dipropylene glycol butyl ether at a mass ratio of 1:1.33) to the mixture obtained in step S2. Stir at 1200 rpm for 40 min, and then filter to obtain the finished coating.

[0035] Comparative Example 2 Ordinary water-based polyurethane coating, commercially available product, with a solid content of 35% and a VOC content of 180g / L.

[0036] Comparative Example 3 This comparative example discloses a pure fluorocarbon resin coating, which comprises the following components by weight: Water-soluble fluorocarbon resin: 50 parts; Self-crosslinking monomer: 7.2 parts; Nano-SiO2 dispersion: 3 parts; Photoinitiator: 1.5 parts; Wetting and dispersing agent: 1 part; Defoamer: 0.3 parts; Leveling agent: 0.5 parts; Film-forming aid: 3.5 parts; Deionized water: 25 parts.

[0037] This comparative example describes a method for preparing the above-mentioned pure fluorocarbon resin coating, comprising the following steps: S1. Mix nano-SiO2 dispersion (solid content 25%), wetting and dispersing agent (BYK-190), and 10 parts of deionized water, and stir at 1200 rpm for 30 min to obtain a dispersion; S2. Add water-soluble fluorocarbon resin (DF-S07), self-crosslinking monomer (a mixture of diacetone acrylamide and adipate dihydrazide at a mass ratio of 1:0.8), and 15 parts of deionized water to the dispersion obtained in step S1, and stir at 1000 rpm for 15 min to obtain a mixture; S3. Add photoinitiator (obtained by mixing photoinitiator 1173 and photoinitiator 184 at a mass ratio of 1:1.5), defoamer (BYK-024), leveling agent (BYK-381), and film-forming aid (obtained by mixing dipropylene glycol methyl ether and dipropylene glycol butyl ether at a mass ratio of 1:1.33) to the mixture obtained in step S2. Stir at 1200 rpm for 40 min, and then filter to obtain the finished coating.

[0038] Performance testing The fluorocarbon-modified waterborne polyurethane coatings prepared in Examples 1-3 of this invention and the different types of coatings provided in Comparative Examples 1-3 were respectively coated onto sanded ash wood boards, with the coating amount controlled at (1.0±0.1) g / dm². 2 The coating was dried at room temperature for 7 days before performance testing. The referenced testing standards and specific performance test results are shown in Table 1.

[0039] Table 1. Coating performance test results obtained in Examples 1 to 3 and Comparative Examples 1 to 3

[0040] As can be seen from the coating performance tests in Table 1, the coatings of Examples 1-3 of this invention are superior to Comparative Examples 1 and 3 in terms of hardness, wear resistance, and weather resistance, and superior to Comparative Example 2 in terms of flexibility and cost. Example 2 shows improved flexibility but a slight decrease in hardness due to a reduced shell ratio, demonstrating the regulatory effect of core-shell structure parameters on performance.

[0041] Figure 1 The image shown is the FT-IR spectrum of the fluorocarbon-modified waterborne polyurethane emulsion of this invention. It can be seen that 2263 cm⁻¹ in region a... -1 isocyanate group and 2951 cm -1 The characteristic peak of the methyl group disappeared after polyurethane synthesis, indicating that the polyurethane reaction was complete. Furthermore, the peak at 1089 cm⁻¹... -1 and 1233 cm -1 The presence of a CF characteristic peak at 3255-3400 cm⁻¹ indicates that the fluorinated acrylate monomer has entered the polyurethane chain segment. -1 The characteristic peak of NH at 1688 cm⁻¹ -1 The characteristic peak of C=O at 1534 cm⁻¹ -1 The characteristic peaks at all locations indicate the successful preparation of the fluorinated polyurethane prepolymer. Additionally, the presence of the 1688 cm⁻¹ peak in c further confirms this. -1The C=O characteristic peak at the location showed a significant change, which is due to the C=O bond of the shell ester group being covered, affecting the peak shape. This indicates that the preparation process of fluorocarbon modified waterborne polyurethane is feasible.

[0042] Figure 2 The TEM image shows the fluorocarbon-modified waterborne polyurethane emulsion of this invention. It clearly shows that the emulsion particles are regularly spherical or nearly spherical, and possess a distinct core-shell bilayer structure. In the image, the gray-white core region is the core layer, mainly composed of fluorinated polyurethane, while the gray-black surrounding region is the styrene-acrylic polymer shell. The clear boundary between the two demonstrates the feasibility of the preparation process of the core-shell structure fluorocarbon-modified waterborne polyurethane emulsion of this invention.

[0043] Combining performance testing and Figure 3 As can be seen, the coating of Example 1 of the present invention exhibits an extremely high gloss retention rate (>85%) during the test period, significantly better than the comparative example. Comparative Example 1, lacking an effective UV shielding structure, experienced a sharp decrease in gloss; Comparative Example 2, while initially performing well, suffered from insufficient flexibility, leading to microcracks and subsequent gloss degradation; Comparative Example 3, lacking the protection of fluorocarbon segments, showed significant powdering in its coating, resulting in the lowest gloss retention rate. Based on the above performance data, it can be concluded that the present invention significantly improves the weather resistance of the coating through the synergistic effect of the core-shell structure and fluorocarbon modification.

Claims

1. A method for preparing a self-crosslinking fluorocarbon-modified waterborne polyurethane wood coating, characterized in that: Includes the following steps: S1. Mix the nano-SiO2 dispersion, wetting and dispersing agent, and deionized water, and stir to disperse evenly to obtain a dispersion; S2. Add a fluorocarbon-modified aqueous polyurethane emulsion with a core-shell structure, a self-crosslinking monomer obtained by mixing diacetone acrylamide and adipate dihydrazide, and the remaining deionized water to the dispersion obtained in step S1, and stir to mix evenly to obtain a mixture. Fluorocarbon-modified waterborne polyurethane emulsion with a core-shell structure includes a fluorinated waterborne polyurethane core composed of spontaneously migrating fluorinated acrylate monomers and a styrene-acrylic polymer shell coating the surface of the fluorinated waterborne polyurethane core. S3. Add photoinitiator, defoamer, leveling agent and film-forming aid to the mixture obtained in step S2, stir and filter to obtain the finished coating.

2. The preparation method according to claim 1, characterized in that: The method for preparing the core-shell structured fluorocarbon-modified waterborne polyurethane emulsion includes the following steps: S11. Under nitrogen protection, isophorone diisocyanate, polyether polyol, dimethylolpropionic acid and fluorinated acrylate monomer are added to the reactor and stirred to react. After the reaction is completed, acetone is added to dilute, followed by triethylamine to neutralize. The mixture is then stirred and emulsified in deionized water to obtain the core-layer fluorinated polyurethane prepolymer emulsion. S12. Add styrene, butyl acrylate and methyl methacrylate to deionized water, and disperse the emulsified monomers at high speed to obtain a monomer pre-emulsion for shell polymerization. S13. Add ammonium persulfate to the core-layer fluorinated polyurethane prepolymer emulsion obtained in step S11, and slowly heat it to 80 °C while stirring. Then slowly add the monomer pre-emulsion obtained in S12. Free radical copolymerization reaction occurs during the drop addition. Then, remove impurities by vacuum distillation to obtain a fluorocarbon modified waterborne polyurethane emulsion with a core-shell structure.

3. The preparation method according to claim 2, characterized in that: In step S11, the mass ratio of polyisocyanate, polyether polyol, dimethylolpropionic acid, and fluorinated acrylate monomer is 1:(0.8-1.2):(0.2-0.4):(0.4-0.8). In step S11, the emulsified and dispersed reaction solution in deionized water has a mass ratio of 1:(0.3-0.8) to deionized water.

4. The preparation method according to claim 2, characterized in that: In step S12, the mass ratio of deionized water, styrene, butyl acrylate, and methyl methacrylate added is 1:(0.16-0.24):(0.2-0.28):(0.06-0.2). In step S13, the mass ratio of ammonium persulfate to polyether polyol is 1:(0.01-0.03).

5. The preparation method according to claim 1, characterized in that: Crosslinked fluorocarbon modified waterborne polyurethane wood coatings, comprising the following components: 40-60 parts of fluorocarbon modified waterborne polyurethane emulsion; 3-8 parts of self-crosslinking monomer; 2-5 parts of nano-SiO2 dispersion; Photoinitiator 0.5-2 parts; 0.5-1.5 parts of wetting and dispersing agent; 0.1-0.5 parts of defoamer; Leveling agent 0.2-1 part; 2-5 parts of film-forming aid; 20-30 parts deionized water.

6. The preparation method according to claim 1, characterized in that: The molar ratio of diacetone acrylamide to adipate dihydrazide in the self-crosslinking monomer is 1:(0.8-1.2).

7. The preparation method according to claim 1, characterized in that: The solid content of the nano-SiO2 dispersion is 20-30%, and the particle size of the nano-SiO2 is 20-50 nm.

8. The preparation method according to claim 1, characterized in that: The photoinitiator is a mixture of 2-hydroxy-2-methyl-1-phenyl-1-propanone and 1-hydroxycyclohexylphenyl ketone, with a mass ratio of 1:(1-2).

9. The preparation method according to claim 1, characterized in that: The film-forming aid is a mixture of dipropylene glycol methyl ether and dipropylene glycol butyl ether, with a mass ratio of 1:(1-3).

10. The preparation method according to any one of claims 1 to 9, characterized in that: The mass ratio of the fluorinated waterborne polyurethane core to the styrene-acrylic polymer shell is 1:(0.3-0.6), and the content of fluorinated acrylate monomer in the fluorinated waterborne polyurethane core is 15-25 wt.%.

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