A water-based wood coating suitable for high-pressure mechanical spraying and its preparation method

Abstract

This invention provides a water-based wood coating suitable for high-pressure mechanical spraying and its preparation method, belonging to the field of wood coating technology. The method includes the following steps: mixing betaine polyol, hexamethylene diisocyanate, and additives, then adding perfluoropolyether alcohol for further reaction; maintaining the temperature while cooling; distilling under reduced pressure; adding epoxidized soybean oil acrylate and mixing thoroughly to obtain a composite polyurethane emulsion; dispersing nano-titanium dioxide powder in toluene, adding lactic acid, ultrasonicating, stirring, centrifuging and discarding the supernatant; adding chloroform, ultrasonicating, centrifuging and discarding the supernatant to obtain a polylactic acid-titanium dioxide photoinitiator; mixing the composite polyurethane emulsion and the polylactic acid-titanium dioxide photoinitiator, and stirring at high speed to obtain the water-based wood coating. The water-based wood coating prepared by this invention can improve water resistance and heat resistance while achieving environmental protection, high efficiency, and energy saving.

Description

Technical Field

[0001] This invention relates to the field of wood coating technology, specifically to a water-based wood coating suitable for high-pressure mechanical spraying and its preparation method. Background Technology

[0002] Water-based wood coatings, which use water as a dispersion medium, are favored for their non-toxic, environmentally friendly, and harmless properties. However, water-based resins still lag behind oil-based resins in terms of durability and workability. Therefore, developing high-performance resin emulsions for use in water-based wood coatings is a research hotspot.

[0003] Polyurethane resin is a material with excellent chemical and mechanical properties, and it is used in the chemical field. Polyurethane coatings are widely used in wood coatings due to their excellent abrasion resistance, flexibility, and low-wet film-forming properties. With the increasing emphasis on environmental protection in wood coatings, waterborne polyurethane wood coatings are being developed and applied due to their low VOC and environmentally friendly characteristics. However, the drawbacks of waterborne polyurethane wood coatings are gradually becoming apparent. The introduction of hydrophilic groups leads to poor water resistance and heat resistance. As a wood coating, given the flammability and water-induced corrosion of wood materials, improving the water resistance and thermal stability of waterborne polyurethane wood coatings is essential. Current technology uses hydroxypropyl polydimethylsiloxane as a modifier to prepare polysiloxane-modified polyurethane emulsions to improve their hydrophobicity and thermal stability. However, embedding hydroxypropyl polydimethylsiloxane into the polyurethane molecular chain results in lower room temperature tensile strength, toughness, and brittleness. Furthermore, in waterborne polyurethane, the aqueous phase itself and water vapor in the air generate carbon dioxide during film formation, leading to bubble formation during curing, which requires further research and solutions.

[0004] When water-based wood coatings are applied using high-pressure spraying equipment, they can be sprayed evenly onto the wood surface, resulting in a smooth and even finish with good adhesion.

[0005] Therefore, there is a need to provide a water-based wood coating suitable for high-pressure mechanical spraying and its preparation method to solve the problems existing in the prior art. Summary of the Invention

[0006] In view of this, the present invention provides a water-based wood coating suitable for high-pressure mechanical spraying and its preparation method, which can improve water resistance and heat resistance while reducing air bubbles.

[0007] To achieve the above objectives, the present invention provides a method for preparing a water-based wood coating suitable for high-pressure mechanical spraying, comprising the following steps:

[0008] S1. After mixing beet polyol, hexamethylene diisocyanate and additives and reacting them, perfluoropolyether alcohol is added and reacted. The mixture is cooled and kept at a constant temperature, then distilled under reduced pressure. Epoxidized soybean oil acrylate is added and mixed to obtain a composite polyurethane emulsion.

[0009] S2. Disperse nano-titanium dioxide powder in toluene, slowly add lactic acid while stirring, sonicate, stir to react, centrifuge and discard the supernatant, add chloroform, sonicate, centrifuge and discard the supernatant to obtain polylactic acid-titanium dioxide photoinitiator.

[0010] S3. After mixing the composite polyurethane emulsion and polylactic acid-titanium dioxide photoinitiator, stir at high speed to obtain water-based wood coating.

[0011] This invention differs from traditional methods that use trace amounts of betaine as a surfactant. Instead, it prepares betaine polyols as raw materials for producing polyurethane prepolymers. The multi-branched structure of the betaine polyol and the incompletely converted residual lignin aromatic ring fragments promote the formation of a three-dimensional cross-linked network in the polyurethane upon reaction with hexamethylene diisocyanate, reducing water penetration and improving water resistance. Furthermore, during high-pressure spraying, the wide molecular weight distribution of the betaine polyol and the reverse emulsification process give the emulsion excellent shear-thinning properties, maintaining good atomization uniformity under spraying pressures of 10-20 MPa, and rapidly recovering viscosity after spraying, avoiding sagging. This makes the waterborne wood coating prepared by this method more suitable for high-pressure mechanical spraying and less prone to clogging the spray nozzle. In addition, the hydroxyl groups in the perfluoropolyether alcohol encapsulate the remaining isocyanate groups in the system, forming a hydrophobic layer on the coating surface, significantly improving water resistance. Moreover, the rigid aromatic ring structure in lignin and the double-bond cross-linking of epoxidized soybean oil acrylate impart heat resistance to the wood coating.

[0012] This invention prepares polylactic acid-titanium dioxide as a photoinitiator. Titanium dioxide is an excellent photoactive compound that is non-toxic, inert, and inexpensive. Using titanium dioxide as a photoinitiator for UV-curable composite polyurethane emulsions, the photoreaction under aerobic conditions can generate hydroxyl radicals, which initiate polymerization by opening the double bonds of the acrylic acid groups in epoxidized soybean oil acrylate. In addition, the isocyanate groups in the polyurethane will also react with the generated free radicals and participate in crosslinking to form a cured network. The introduction of the photoinitiator enables the composite polyurethane emulsion to polymerize and crosslink rapidly, and also limits the formation and enlargement of bubbles during the curing process, thus avoiding their retention in the paint film. However, nano-titanium dioxide is prone to agglomeration and has poor dispersibility. To solve this problem, polylactic acid (PLA) is introduced to graft nano-titanium dioxide. The carboxyl and hydroxyl groups in PLA form hydrogen bonds and non-covalent forces with the TiO2 surface. Due to the bidentate coordination between the titanium atoms and the carboxyl groups of lactic acid (a ligand forms a coordinate bond with the metal center through two atoms), the PLA molecules are grafted onto TiO2, providing hydroxyl groups for the whole, increasing its compatibility with composite polyurethane emulsions, and improving its dispersibility in water-based wood coatings.

[0013] Optionally, the beet-based polyol is prepared by mixing polyethylene glycol 400 and glycerol, adding beet pulp powder and stirring for 3-5 minutes, heating to 150-200°C, adding concentrated sulfuric acid, continuing the reaction at 200 rpm for 70-150 minutes, cooling, adding an aqueous solution of 1,4-dioxane and stirring for 2 hours, and then drying in an oven at 105°C for 24 hours.

[0014] This invention prepares beet-based polyols by first decomposing cellulose / hemicellulose in beet pulp into monosaccharides through acid hydrolysis, and then carrying out a condensation reaction in a composite solvent system of glycerol and polyethylene glycol to form a multi-branched polyol. Through sulfuric acid catalysis, the monosaccharides react with the functional groups of glycerol and polyethylene glycol to generate a bio-based polyol with rigidity and flexibility.

[0015] Optionally, the volume ratio of 1,4-dioxane to water in the aqueous solution of 1,4-dioxane is 4:1; and the volume concentration of the concentrated sulfuric acid is 95%.

[0016] Optionally, the beet pulp powder is prepared by drying beet pulp at 70°C for 48 hours, grinding it, and then sieving it to obtain beet pulp powder with a particle size of less than 60 μm.

[0017] Optionally, in step S1, vanillin is added along with betaine polyol.

[0018] In the process of preparing composite polyurethane emulsion, this invention adds a small amount of vanillin to improve the odor of the raw materials of polyurethane materials. Furthermore, the phenolic hydroxyl groups can react with free radicals to capture free radicals, thereby slowing down the oxidation reaction and improving the overall antioxidant properties.

[0019] Optionally, in step S1, after mixing betaine polyol and vanillin, hexamethylene diisocyanate is added and reacted at 70°C for 3 hours. After adding an auxiliary agent and reacting for 4 hours, perfluoropolyether alcohol is added and reacted at 80°C for 2-3 hours. The temperature is then lowered to 60°C and maintained for 2 hours. Butanone is added, and the temperature is lowered to 40°C. Glacial acetic acid is added to adjust the pH to 7.0-7.2. Then, vacuum distillation is carried out at -0.1 kPa and 40°C for 0.5-1 hours. Epoxidized soybean oil acrylate is added and mixed evenly. The temperature is then raised to 60-80°C and maintained for 0.5-1 hours. Ammonium persulfate is added dropwise over 4 hours and the temperature is maintained for 1-2 hours to obtain a composite polyurethane emulsion.

[0020] In the preparation of the composite polyurethane emulsion, the present invention adds methyl ethyl ketone (MEK) diluent to adjust the viscosity of the system and avoid excessive viscosity. Ammonium persulfate can promote a tighter bond between epoxidized soybean oil acrylate and polyurethane.

[0021] Optionally, the adjuvant is 1,4-butanediol, trimethylolpropane, and triethylamine.

[0022] In the preparation of the composite polyurethane emulsion, 1,4-butanediol is used as a chain extender to react with isocyanate to extend the polymer chain, and trimethylolpropane is used as a crosslinking agent to increase the compactness of the polymer, thereby making the internal structure more stable and improving the overall stability and durability.

[0023] Optionally, in step S2, nano-titanium dioxide powder is dispersed in toluene, lactic acid is slowly added under stirring, and the mixture is ultrasonically treated at 90°C for 40-60 min. The mixture is then stirred and reacted at 150°C under a nitrogen atmosphere for 24-36 h. After centrifugation at 5000 rpm for 0.5-1 h, the supernatant is discarded, chloroform is added, and the mixture is ultrasonically treated for 20-30 min. After centrifugation at 5000 rpm for 0.5-1 h, the supernatant is discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0024] Optionally, in step S3, after mixing the composite polyurethane emulsion and polylactic acid-titanium dioxide photoinitiator, the mixture is stirred at a high speed of 3000-5000 rpm for 10-15 min, then the ground pigments and fillers are added, and the mixture is stirred at a speed of 200-500 rpm for 20-30 min, then deionized water is added, and the mixture is subjected to high-speed reverse emulsification for 30-50 min to obtain a water-based wood coating.

[0025] The present invention also provides a water-based wood coating prepared by the above-mentioned method for preparing a water-based wood coating suitable for high-pressure mechanical spraying, comprising the following raw materials in parts by weight: 40-60 parts of composite polyurethane emulsion, 0.4-1 parts of polylactic acid-titanium dioxide photoinitiator, 1-5 parts of pigments and fillers, and 40-50 parts of deionized water.

[0026] The present invention uses this mass fraction of raw material to obtain the best overall performance, which can meet the requirements of high-pressure mechanical spraying.

[0027] The above-described technical solution of the present invention has at least the following beneficial effects:

[0028] 1. This invention innovatively utilizes beet pulp to prepare beet-based polyols as raw materials for polyurethane prepolymers. The multi-branched structure and residual lignin aromatic ring fragments react with hexamethylene diisocyanate to form a dense three-dimensional cross-linked network, significantly improving water resistance. The wide molecular weight distribution of beet-based polyols endows the emulsion with excellent shear-thinning properties, ensuring uniform atomization and rapid viscosity recovery under 10-20 MPa high-pressure spraying, preventing sagging, making it particularly suitable for mechanical spraying. Perfluoropolyether alcohol encapsulates isocyanate groups to form a hydrophobic surface layer, synergistically enhancing water and heat resistance through the rigidity of lignin aromatic rings and the cross-linking of epoxidized soybean oil acrylate. Compared to traditional beet-based surfactant applications, this invention achieves a balance between spray applicability and functionality through raw material improvement.

[0029] 2. This invention prepares polylactic acid-titanium dioxide as a photoinitiator. The photoreaction of titanium dioxide under aerobic conditions can generate hydroxyl radicals, which can initiate polymerization by opening the double bonds of acrylic acid groups in epoxidized soybean oil acrylate. In addition, the isocyanate groups in polyurethane will also react with the generated free radicals and participate in crosslinking to form a cured network. The introduction of the photoinitiator enables the composite polyurethane emulsion to polymerize and crosslink rapidly, and also limits the formation and enlargement of bubbles during the curing process, thus avoiding their retention in the paint film. By grafting TiO2 onto polylactic acid, its compatibility with the composite polyurethane emulsion is increased, and its dispersibility in wood coatings is improved. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0031] Example 1

[0032] 100 parts of beet pulp were dried at 70℃ for 48 hours, ground for 10 minutes, and then sieved to a particle size of less than 60 μm to obtain beet pulp powder. 80 parts of polyethylene glycol 400 and 40 parts of glycerol were mixed evenly, and 80 parts of beet pulp powder were added and stirred for 5 minutes. After heating to 200℃, 15 parts of sulfuric acid with a volume concentration of 95% were added. The reaction was continued at 200 rpm for 150 minutes, and then cooled to terminate the reaction. 100 parts of an aqueous solution of 1,4-dioxane (1,4-dioxane:water volume ratio of 4:1) were added and stirred for 2 hours. Then, the mixture was dried in an oven at 105℃ for 24 hours to obtain beet-based polyol.

[0033] After mixing 50 parts beetroot polyol and 0.12 parts vanillin evenly, 20 parts hexamethylene diisocyanate were added and reacted at 70℃ for 3 hours. Then, 3 parts 1,4-butanediol, 1 part trimethylolpropane, and 2 parts triethylamine were added and reacted for 4 hours. Then, 5 parts perfluoropolyether alcohol were added and reacted at 80℃ for 2 hours. After cooling to 60℃ and holding for 2 hours, 10 parts butanone were added and the temperature was lowered to 40℃. After adjusting the pH to 7.0 with glacial acetic acid, vacuum distillation was carried out at -0.1 kPa and 40℃ for 0.5 hours. After mixing evenly with 30 parts epoxidized soybean oil acrylate, the temperature was raised to 60℃ and held for 0.5 hours. Then, 2 parts ammonium persulfate were added dropwise over 4 hours and held for 1 hour to obtain a composite polyurethane emulsion.

[0034] Two parts of nano-titanium dioxide powder were dispersed in 16 parts of toluene, and four parts of lactic acid were slowly added under stirring. The mixture was then sonicated at 90°C for 40 min, and stirred at 150°C for 24 h under a nitrogen atmosphere. After centrifugation at 5000 rpm for 0.5 h, the supernatant was discarded. Ten parts of chloroform were added, and the mixture was sonicated for 20 min. After centrifugation at 5000 rpm for 0.5 h, the supernatant was discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0035] After mixing 40 parts of composite polyurethane emulsion and 0.4 parts of polylactic acid-titanium dioxide photoinitiator, the mixture was stirred at 3000 rpm for 10 min, then 1 part of ground pigments and fillers was added, and the mixture was stirred at 200 rpm for 20 min. Finally, 40 parts of deionized water were added, and the mixture was subjected to high-speed reverse emulsification for 30 min to obtain water-based wood coating.

[0036] Example 2

[0037] 100 parts of beet pulp were dried at 70℃ for 48 hours, ground for 6 minutes, and then sieved to a particle size of less than 60 μm to obtain beet pulp powder. 80 parts of polyethylene glycol 400 and 40 parts of glycerol were mixed evenly, and 60 parts of beet pulp powder were added and stirred for 3 minutes. After heating to 150℃, 10 parts of sulfuric acid with a volume concentration of 95% were added. The reaction was continued at 200 rpm for 70 minutes and then cooled to terminate the reaction. 80 parts of an aqueous solution of 1,4-dioxane (1,4-dioxane:water volume ratio of 4:1) were added and stirred for 2 hours. Then, the mixture was dried in an oven at 105℃ for 24 hours to obtain beet-based polyol.

[0038] After mixing 35 parts beetroot polyol and 0.15 parts vanillin evenly, 30 parts hexamethylene diisocyanate were added and reacted at 70℃ for 3 hours. Then, 5 parts 1,4-butanediol, 3 parts trimethylolpropane, and 4 parts triethylamine were added and reacted for 4 hours. Then, 5 parts perfluoropolyether alcohol were added and reacted at 80℃ for 3 hours. After cooling to 60℃ and maintaining for 4 hours, 10 parts butanone were added and the temperature was lowered to 40℃. After adjusting the pH to 7.2 with glacial acetic acid, vacuum distillation was carried out at -0.1 kPa and 40℃ for 1 hour. Then, 50 parts epoxidized soybean oil acrylate were added and mixed evenly. After heating to 80℃ and maintaining for 1 hour, 5 parts ammonium persulfate were added dropwise over 4 hours and maintained for 2 hours to obtain a composite polyurethane emulsion.

[0039] Five parts of nano-titanium dioxide powder were dispersed in 20 parts of toluene, and eight parts of lactic acid were slowly added under stirring. The mixture was then sonicated at 90°C for 60 min, and stirred at 150°C under a nitrogen atmosphere for 36 h. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded. Ten parts of chloroform were added, and the mixture was sonicated for 30 min. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0040] After mixing 60 parts of composite polyurethane emulsion and 1 part of polylactic acid-titanium dioxide photoinitiator, the mixture was stirred at 5000 rpm for 15 min, then 5 parts of ground pigments and fillers were added, and the mixture was stirred at 500 rpm for 30 min. Finally, 50 parts of deionized water were added, and the mixture was subjected to high-speed reverse emulsification for 50 min to obtain water-based wood coating.

[0041] Example 3

[0042] 100 parts of beet pulp were dried at 70℃ for 48 hours, ground for 7 minutes, and then sieved to a particle size of less than 60 μm to obtain beet pulp powder. 80 parts of polyethylene glycol 400 and 40 parts of glycerol were mixed evenly, and 70 parts of beet pulp powder were added and stirred for 3 minutes. After heating to 180℃, 12 parts of sulfuric acid with a volume concentration of 95% were added. The reaction was continued at 200 rpm for 120 minutes and then cooled to terminate the reaction. 90 parts of an aqueous solution of 1,4-dioxane (1,4-dioxane:water volume ratio of 4:1) were added and stirred for 2 hours. Then, the mixture was dried in an oven at 105℃ for 24 hours to obtain beet-based polyol.

[0043] After mixing 45 parts beetroot polyol and 0.2 parts vanillin evenly, 40 parts hexamethylene diisocyanate were added and reacted at 70℃ for 3 hours. Then, 5 parts 1,4-butanediol, 2 parts trimethylolpropane, and 3 parts triethylamine were added and reacted for 4 hours. Then, 5 parts perfluoropolyether alcohol were added and reacted at 80℃ for 2.5 hours. After cooling to 60℃ and maintaining for 5 hours, 10 parts butanone were added and the temperature was lowered to 40℃. After adjusting the pH to 7.1 with glacial acetic acid, vacuum distillation was carried out at -0.1 kPa and 40℃ for 1 hour. Then, 60 parts epoxidized soybean oil acrylate were added and mixed evenly. After heating to 70℃ and maintaining for 1 hour, 4 parts ammonium persulfate were added dropwise over 4 hours and maintained for 1.5 hours to obtain a composite polyurethane emulsion.

[0044] Three parts of nano-titanium dioxide powder were dispersed in 15 parts of toluene, and 6 parts of lactic acid were slowly added under stirring. The mixture was then sonicated at 90°C for 50 min, and stirred at 150°C under a nitrogen atmosphere for 30 h. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded. Ten parts of chloroform were added, and the mixture was sonicated for 25 min. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0045] After mixing 50 parts of composite polyurethane emulsion and 0.6 parts of polylactic acid-titanium dioxide photoinitiator, the mixture was stirred at 4000 rpm for 12 min, then 2 parts of ground pigments and fillers were added, and the mixture was stirred at 300 rpm for 25 min. Finally, 45 parts of deionized water were added, and the mixture was subjected to high-speed reverse emulsification for 40 min to obtain water-based wood coating.

[0046] Example 4

[0047] 100 parts of beet pulp were dried at 70℃ for 48 hours, ground for 8 minutes, and then sieved to a particle size of less than 60 μm to obtain beet pulp powder. 80 parts of polyethylene glycol 400 and 40 parts of glycerol were mixed evenly, and 75 parts of beet pulp powder were added and stirred for 4 minutes. After heating to 160℃, 14 parts of sulfuric acid with a volume concentration of 95% were added. The reaction was continued at 200 rpm for 90 minutes and then cooled to terminate the reaction. 85 parts of an aqueous solution of 1,4-dioxane (1,4-dioxane:water volume ratio of 4:1) were added and stirred for 2 hours. Then, the mixture was dried in an oven at 105℃ for 24 hours to obtain beet-based polyol.

[0048] After mixing 40 parts beetroot polyol and 0.12 parts vanillin evenly, 35 parts hexamethylene diisocyanate were added and reacted at 70℃ for 3 hours. Then, 4 parts 1,4-butanediol, 3 parts trimethylolpropane, and 4 parts triethylamine were added and reacted for 4 hours. Then, 5 parts perfluoropolyether alcohol were added and reacted at 80℃ for 3 hours. After cooling to 60℃ and maintaining for 5 hours, 10 parts butanone were added and the temperature was lowered to 40℃. After adjusting the pH to 7.2 with glacial acetic acid, vacuum distillation was carried out at -0.1 kPa and 40℃ for 1 hour. Then, 45 parts epoxidized soybean oil acrylate were added and mixed evenly. After heating to 75℃ and maintaining for 1 hour, 3 parts ammonium persulfate were added dropwise over 4 hours and maintained for 2 hours to obtain a composite polyurethane emulsion.

[0049] Three parts of nano-titanium dioxide powder were dispersed in 18 parts of toluene, and 6 parts of lactic acid were slowly added under stirring. After ultrasonic treatment at 90℃ for 60 min, the mixture was stirred and reacted at 150℃ under nitrogen atmosphere for 30 h. The supernatant was discarded after centrifugation at 5000 rpm for 1 h. Ten parts of chloroform were added, and the mixture was ultrasonically treated for 30 min. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0050] After mixing 55 parts of composite polyurethane emulsion and 0.6 parts of polylactic acid-titanium dioxide photoinitiator, the mixture was stirred at 4000 rpm for 15 min, then 2 parts of ground pigments and fillers were added, and the mixture was stirred at 500 rpm for 30 min. Finally, 45 parts of deionized water were added, and the mixture was subjected to high-speed reverse emulsification for 40 min to obtain water-based wood coating.

[0051] Example 5

[0052] 100 parts of beet pulp were dried at 70℃ for 48 hours, ground for 6 minutes, and then sieved to a particle size of less than 60 μm to obtain beet pulp powder. 80 parts of polyethylene glycol 400 and 40 parts of glycerol were mixed evenly, and 65 parts of beet pulp powder were added and stirred for 3 minutes. After heating to 170℃, 11 parts of sulfuric acid with a volume concentration of 95% were added. The reaction was continued at 200 rpm for 100 minutes and then cooled to terminate the reaction. 85 parts of an aqueous solution of 1,4-dioxane (1,4-dioxane:water volume ratio of 4:1) were added and stirred for 2 hours. Then, the mixture was dried in an oven at 105℃ for 24 hours to obtain beet-based polyol.

[0053] After mixing 45 parts beet-based polyol and 0.15 parts vanillin evenly, 30 parts hexamethylene diisocyanate were added and reacted at 70℃ for 3 hours. Then, 3 parts 1,4-butanediol, 2 parts trimethylolpropane, and 3 parts triethylamine were added and reacted for 4 hours. Then, 5 parts perfluorinated polyether alcohol were added and reacted at 80℃ for 2.5 hours. After cooling to 60℃ and maintaining for 3 hours, 10 parts butanone were added and the temperature was lowered to 40℃. After adjusting the pH to 7.0 with glacial acetic acid, vacuum distillation was carried out at -0.1 kPa and 40℃ for 0.5 hours. Then, 40 parts epoxidized soybean oil acrylate were added and mixed evenly. After heating to 70℃ and maintaining for 1 hour, 3 parts ammonium persulfate were added dropwise over 4 hours and maintained for 1.5 hours to obtain a composite polyurethane emulsion.

[0054] Two parts of nano-titanium dioxide powder were dispersed in 16 parts of toluene, and four parts of lactic acid were slowly added under stirring. The mixture was then sonicated at 90°C for 50 min, and stirred at 150°C for 28 h under a nitrogen atmosphere. After centrifugation at 5000 rpm for 1 h, the supernatant was discarded. Ten parts of chloroform were added, and the mixture was sonicated for 20 min. After centrifugation at 5000 rpm for 0.5 h, the supernatant was discarded to obtain polylactic acid-titanium dioxide photoinitiator.

[0055] After mixing 45 parts of composite polyurethane emulsion and 0.7 parts of polylactic acid-titanium dioxide photoinitiator, the mixture was stirred at 4000 rpm for 13 min, then 2 parts of ground pigments and fillers were added, and the mixture was stirred at 400 rpm for 25 min. Finally, 50 parts of deionized water were added, and the mixture was subjected to high-speed reverse emulsification for 35 min to obtain water-based wood coating.

[0056] The present invention also includes comparative examples and related experiments.

[0057] Comparative Example 1

[0058] Compared with Example 1, the difference is that methoxy polyethylene glycol was used directly as the raw material for the composite polyurethane emulsion instead of beet-based polyol. The other components and preparation steps were completely the same, and the water-based wood coating was finally obtained.

[0059] Comparative Example 2

[0060] Compared with Example 1, the difference is that perfluoropolyether alcohol was not added for reaction during the preparation of the composite polyurethane emulsion. The other components and preparation steps are completely the same, and water-based wood coating is prepared.

[0061] Comparative Example 3

[0062] Compared with Example 1, the difference is that nano-titanium dioxide was used directly as a photoinitiator, and polylactic acid-titanium dioxide photoinitiator was not prepared. The other components and preparation steps were completely the same, and water-based wood coating was prepared.

[0063] Comparative Example 4

[0064] Compared with Example 1, the difference is that commercially available photoinitiator 1173 was used directly, and polylactic acid-titanium dioxide photoinitiator was not prepared. The other components and preparation steps were completely the same, and water-based wood coating was prepared.

[0065] Performance testing

[0066] The water-based wood coatings obtained in Examples 1-5 and Comparative Examples 1-4 were subjected to basic performance tests on fineness, non-volatile matter, storage stability, gloss, abrasion resistance, and adhesion in accordance with the national standard GB / T23999-2009 for water-based wood coatings for interior decoration and finishing. The test results are shown in Table 1.

[0067] Table 1

[0068]

[0069] As shown in Table 1, the water-based wood coatings prepared in Examples 1-5 all meet the national standards specified in GB / T23999-2009 for water-based wood coatings used in interior decoration and renovation, with a fineness of ≤25μm, abrasion resistance of ≤0.02g, non-volatile matter of ≥40%, and adhesion of ≤1 grade.

[0070] As shown in Table 1, Example 1 exhibits superior adhesion, abrasion resistance, and gloss compared to Comparative Example 1 (using methoxy polyethylene glycol), indicating that beet-based polyols can enhance the crosslinking density and film-forming properties of polyurethane emulsions. Comparative Examples 3 and 4, lacking a polylactic acid-titanium dioxide photoinitiator, showed poor dispersion of individual nano-titanium dioxide powder or photoinitiator 1173 in the emulsion, resulting in lumps that affected fineness and gloss. This is because the polylactic acid-titanium dioxide photoinitiator improved dispersibility through chemical bonding, while also enhancing photocuring efficiency and coating uniformity. Comparative Example 2 showed a significant decrease in abrasion resistance due to the absence of perfluoropolyether alcohol, demonstrating that perfluoropolyether alcohol improves the abrasion resistance and hydrophobicity of the coating by introducing fluorine. In conclusion, the waterborne wood coating prepared by this invention exhibits significantly improved basic properties.

[0071] Examples 1-5 and Comparative Examples 1-4 were tested for drying time, water resistance, dry heat resistance and film appearance according to the execution standard of HG / T3655-1999 Ultraviolet (UV) Curing Wood Coatings. The test results are shown in Table 2.

[0072] Table 2

[0073]

[0074] As shown in Table 2, Comparative Example 1, without the use of beet-based polyol, resulted in low crosslinking density, slow curing, and blistering at the edges of the paint film. Compared to Comparative Example 2, the addition of perfluoropolyether alcohol in Example 1 significantly improved water resistance and dry heat resistance. Compared to Comparative Examples 3 and 4, the addition of polylactic acid-titanium dioxide photoinitiator in Example 1 resulted in high UV curing efficiency, significantly shortened curing time, and further prevented bubble formation. In contrast, the direct addition of nano-titanium dioxide in Comparative Example 3 led to agglomeration due to poor dispersibility, delayed curing, and large-area blistering due to paint film defects. Furthermore, the curing speed and dry heat resistance both met the standards of HG / T3655-1999 for ultraviolet (UV) curing wood coatings.

[0075] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a water-based wood coating suitable for high-pressure mechanical spraying, characterized in that, Includes the following steps: S1. After mixing betaine polyol, hexamethylene diisocyanate and additives and reacting, perfluoropolyether alcohol is added and reacted. The mixture is cooled and maintained, then distilled under reduced pressure. Epoxidized soybean oil acrylate is added and mixed evenly to obtain a composite polyurethane emulsion. Alternatively, after mixing betaine polyol and vanillin, hexamethylene diisocyanate is added and reacted at 70℃ for 3 hours. Adding additives and reacting for 4 hours, perfluoropolyether alcohol is added and reacted at 80℃ for 2-3 hours. The mixture is then cooled to 60℃ and maintained for 2 hours. Butanone is added, and the temperature is lowered to 40℃. Glacial acetic acid is added to adjust the pH to 7.0-7.

2. Then, under negative pressure of -0.1 kPa and a temperature of 40℃, reduced pressure distillation is carried out for 0.5-1 hours. Epoxidized soybean oil acrylate is added and mixed evenly. The temperature is then raised to 60-80℃ and maintained for 0.5-1 hours. Ammonium persulfate is added dropwise over 4 hours, and the mixture is maintained for 1-2 hours to obtain a composite polyurethane emulsion. S2. Disperse nano-titanium dioxide powder in toluene, slowly add lactic acid while stirring, sonicate, stir and react, centrifuge and discard the supernatant, add chloroform, sonicate, centrifuge and discard the supernatant to obtain polylactic acid-titanium dioxide photoinitiator; Disperse nano-titanium dioxide powder in toluene, slowly add lactic acid while stirring, sonicate at 90℃ for 40-60 min, stir and react at 150℃ under nitrogen atmosphere for 24-36 h, centrifuge at 5000 rpm for 0.5-1 h, discard the supernatant, add chloroform, sonicate for 20-30 min, centrifuge at 5000 rpm for 0.5-1 h, discard the supernatant to obtain polylactic acid-titanium dioxide photoinitiator; S3. After mixing the composite polyurethane emulsion and polylactic acid-titanium dioxide photoinitiator, stir at high speed to obtain water-based wood coating.

2. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 1, characterized in that, The beet-based polyol is prepared by mixing polyethylene glycol 400 and glycerol, adding beet pulp powder and stirring for 3-5 minutes, heating to 150-200°C, adding concentrated sulfuric acid, continuing the reaction at 200 rpm for 70-150 minutes, cooling, adding an aqueous solution of 1,4-dioxane and stirring for 2 hours, and then drying in an oven at 105°C for 24 hours.

3. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 2, characterized in that, The volume ratio of 1,4-dioxane to water in the aqueous solution of 1,4-dioxane is 4:1; the volume concentration of the concentrated sulfuric acid is 95%.

4. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 2, characterized in that, The beet pulp powder is prepared by drying beet pulp at 70°C for 48 hours, grinding it, and then sieving it to obtain beet pulp powder with a particle size of less than 60 μm.

5. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 2, characterized in that, In step S1, vanillin is added along with beetroot polyol.

6. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 1, characterized in that, The adjuvants are 1,4-butanediol, trimethylolpropane, and triethylamine.

7. The method for preparing a water-based wood coating suitable for high-pressure mechanical spraying according to claim 1, characterized in that, In step S3, the composite polyurethane emulsion and polylactic acid-titanium dioxide photoinitiator are mixed and stirred at a high speed of 3000-5000 rpm for 10-15 min. Then, the ground pigments and fillers are added and stirred at a speed of 200-500 rpm for 20-30 min. Finally, deionized water is added and the mixture is subjected to high-speed reverse emulsification for 30-50 min to obtain water-based wood coating.

8. A water-based wood coating suitable for high-pressure mechanical spraying, characterized in that, The water-based wood coating suitable for high-pressure mechanical spraying is prepared by any one of claims 1 to 7, comprising the following raw materials in parts by weight: 40 to 60 parts of composite polyurethane emulsion, 0.4 to 1 part of polylactic acid-titanium dioxide photoinitiator, 1 to 5 parts of pigments and fillers, and 40 to 50 parts of deionized water.

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