Finishing-free water-based plain finishing paint and preparation method thereof

Abstract

The invention belongs to the technical field of automotive coatings, and particularly relates to finishing-free water-based plain finish paint and a preparation method thereof. The water-based blocked isocyanate and the water-based hydroxyl acrylate are crosslinked to form a carbamate bond and construct a three-dimensional hydrogen bond network, so that the mechanical strength, the sagging resistance and the chemical resistance of the finish paint are remarkably improved; amino resin is modified through dialdehyde lignin, hydrophilic groups in the amino resin are eliminated, reversible imine bonds are generated, and the acid-base hydrolysis resistance of the finish paint is enhanced; the polyether-polysiloxane is grafted with the water-based blocked isocyanate, so that the storage stability of the finish paint is ensured, the sagging phenomenon of a vertical surface is inhibited, the surface tension of the finish paint is reduced, orange peel is eliminated, and the integrated performance improvement of high weather resistance, sagging resistance and low orange peel of the finish paint is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive coatings, and particularly relates to a waterborne solid-color topcoat without clearcoat and a preparation method thereof. Background Art

[0002] With the rapid development of the automotive industry, consumers' requirements for the appearance of automobiles are increasing day by day, especially for the gloss, color saturation, weather resistance and environmental protection performance of the paint film. The traditional automotive painting process usually includes three layers: primer, color paint and clearcoat. The main function of the clearcoat is to improve the gloss and weather resistance of the paint film. However, this multi-layer painting process has the following technical problems: The traditional painting process requires multiple spraying and baking, with a complex process, increased production time and energy consumption, resulting in an increase in production costs; The solvents and volatile organic compounds (VOCs) used in the multi-layer painting process have a large emissions, causing environmental pollution, poor environmental protection performance, and not meeting the requirements of increasingly strict environmental protection regulations. In addition, during local repair of traditional multi-layer painting, it is difficult to achieve the same effect as the original paint film, increasing the repair difficulty and cost.

[0003] Waterborne single-coat solid-color paint materials are mainly composed of acrylic resin and melamine, which can significantly improve the hardness, wear resistance, solvent resistance and other properties of the paint film, have good anti-foaming and sagging properties, a wide construction window, and extremely low VOC emissions. More importantly, automotive single-coat solid-color paint materials eliminate the painting processes such as clearcoat spraying, color paint flash drying, and clearcoat leveling on the basis of the traditional process. After processes such as flash drying, pre-baking, and drying are completed, the entire painting process is completed, greatly improving the production rhythm, reducing energy consumption, having low equipment investment, low production costs, fast rhythm and high efficiency. However, affected by factors such as formulation design and construction process, the single-coat topcoat is prone to poor appearance such as sagging and orange peel, and there is still a certain gap compared with solvent-based topcoats in terms of acid and alkali hydrolysis resistance.

[0004] Patent CN114213916B provides a preparation method of a waterborne solid-color topcoat without clearcoat for automobiles, which shows good performance in terms of gloss, water resistance and weather resistance. However, in the color paste grinding part, the main resin acrylic dispersion 9160 is added for grinding, further restricting the universality of the color paste; Slight color change and loss of gloss occur in both acidic and alkaline environments, which is greatly affected by the addition of the drier CYCAT 4045; At the same time, the addition of CYCAT 4045 will affect the storage of the original paint, resulting in a shortened shelf life of the original paint. Summary of the Invention

[0005] The purpose of the present invention is to provide a non-topcoat solid color paint for automobiles. By optimizing the formula and process, while simplifying the painting process, reducing costs and environmental pollution, improving weather resistance and appearance performance, and improving the gloss loss rate, the above technical problems can be solved.

[0006] To achieve the above technical purpose, the technical solution of the present invention is as follows: A non-topcoat waterborne solid color topcoat, calculated by weight, includes the following components: Waterborne hydroxyacrylate dispersion: 40 - 50 parts; modified amino resin: 8 - 10 parts; waterborne blocked isocyanate: 2 - 4 parts; solvent A: 3 - 4 parts; solvent B: 0.5 - 1 part; solvent C: 1 - 3 parts; substrate wetting agent: 0.5 - 1 part; polyurethane thickener: 0.5 - 2 parts; waterborne color paste: 25 - 28 parts; pH regulator: 0.2 - 0.8 part; deionized water: 6 - 10 parts.

[0007] As a further improvement, the preparation method of the waterborne hydroxyacrylate dispersion is as follows: Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate with perfluorononyloxybenzenesulfonate sodium, add deionized water as a dispersion medium, and obtain an emulsion after high-speed shearing; add ammonium persulfate as a thermal initiator to the emulsion. After the reaction is completed, add dimethylethanolamine to adjust the pH value of the system to neutral, filter and then evaporate and dry to obtain the waterborne hydroxyacrylate dispersion.

[0008] As a further improvement, the mass ratio of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate is 1:3:2; the addition amount of perfluorononyloxybenzenesulfonate sodium is 0.5 - 0.8 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0009] As a further improvement, the preparation method of the modified amino resin is as follows: Using anhydrous ethanol as a medium, mix dialdehyde lignin and amino resin according to a mass ratio of 1:4, add triethylenediamine as a catalyst, adjust the pH to 2 - 5 with acetic acid, and heat from 60 °C to 80 °C at a heating rate of 5 °C / min, and keep warm for 2 h. After centrifugal drying, obtain the modified amino resin; among them, the addition amount of triethylenediamine is 0.6 - 1.2 wt% of the amino resin.

[0010] As a further improvement, the amino resin is CYMEL 325:CYMEL 303 = 5 to 7:1; the preparation method of the dialdehyde lignin is as follows: 1-ethyl-3-methylimidazolium acetate and sulfate lignin are mixed at a molar ratio of 2:1, and depolymerized at a constant temperature of 90 °C and 200 W ultrasonic in absolute ethanol. After the depolymerization is completed, centrifugation, washing and drying are carried out to obtain depolymerized sulfate lignin; the depolymerized sulfate lignin, aldehyde dehydrogenase and formate dehydrogenase are mixed at a molar ratio of 1:0.05:1.2, and under a phosphate buffer system with a pH of 6.8, a constant temperature water bath at 45 °C and 40 kHz ultrasonic treatment are carried out for 3 h. After filtration, washing and drying are carried out to obtain dialdehyde lignin.

[0011] As a further improvement, the preparation method of the waterborne blocked isocyanate is as follows: methyl ethyl ketoxime is added to the star-shaped isocyanate prepolymer, and the reaction is carried out at 60 °C for 1.5 h, and kept warm for 30 min. Then amino-terminated polyether-polysiloxane is added, and the reaction is carried out at 65 °C for 1 h. According to the mass ratio of 1:30, the obtained product is slowly added to a 0.5 wt% sodium dodecylbenzenesulfonate solution, and high-speed shear emulsification is carried out for 20 min. Then nano-cellulose crystals are added, and ultrasonic dispersion is carried out for 30 min. After rotary evaporation, the waterborne blocked isocyanate is obtained; among them, the addition amounts of methyl ethyl ketoxime and nano-cellulose crystals are 1 wt% and 0.5 wt% of the star-shaped isocyanate prepolymer respectively.

[0012] As a further improvement, the preparation method of the star-shaped isocyanate prepolymer is as follows: trimethylolpropane and isophorone diisocyanate are added to a dry reaction kettle at a molar ratio of 1:6 to 10. Under a nitrogen atmosphere, dibutyltin dilaurate is added, and low-speed stirring is carried out at 75 °C for 3 to 5 h to obtain the star-shaped isocyanate prepolymer; among them, the addition amount of dibutyltin dilaurate is 0.05 wt% of isophorone diisocyanate; the viscosity of the star-shaped isocyanate prepolymer is 2000 to 2500 mPa·s.

[0013] As a further improvement, the solvent A is any one or more of diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, dipropylene glycol monobutyl ether; the solvent B is n-butanol; the solvent C is any one or more of ethanol or isopropanol solution; the substrate wetting agent is TEGO Twin 4100; the polyurethane thickener is XS-83; the color paste is a waterborne general resin-free color paste; the pH regulator is DMEA.

[0014] As a further improvement, the preparation method of the amino-terminated polyether-polysiloxane is as follows: epoxy-terminated polysiloxane and amino-terminated polyetheramine are mixed at a molar ratio of 1:1, and according to the mass ratio of 1:60, a 30 wt% isopropanol solution is added as a solvent. After stirring evenly, the reaction is carried out at 80 °C for 5 h. After removing the isopropanol solution by vacuum distillation, the amino-terminated polyether-polysiloxane is obtained.

[0015] The present invention also provides a preparation method for a waterborne solid-color topcoat without clear coating, comprising the following steps: Sequentially add a waterborne hydroxyl acrylate dispersion, a modified amino resin, a waterborne blocked isocyanate, Solvent A, Solvent B, Solvent C, a substrate wetting agent, a polyurethane thickener, a waterborne color paste, a pH regulator, and deionized water into a reaction vessel, stir at 600 - 800 rpm for 30 min, and after mixing evenly, filter to obtain the waterborne solid-color topcoat without clear coating.

[0016] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: 1. The waterborne blocked isocyanate and the hydroxyl-type waterborne acrylic resin can crosslink to form urethane bonds under high-temperature baking conditions. Through the hydrogen bond network enhancement effect, the N-H and C=O groups in the urethane bonds form a three-dimensional hydrogen bond network, improving the crosslinking bond energy between polymer molecules, strengthening the mechanical properties and chemical resistance of the polymer material, reducing the occurrence of sagging phenomenon, and significantly improving the physical and chemical properties of the paint film.

[0017] 2. By modifying the amino resin with dialdehyde lignin, on the one hand, the hydroxymethyl groups after alcoholization of the -CH3OCH3 groups in the amino resin can undergo a crosslinking reaction with the aldehyde groups on the polymerization chain of dialdehyde lignin, thereby eliminating the residual hydrophilic hydroxymethyl groups in the amino resin and improving the water resistance of the waterborne solid-color topcoat without clear coating; on the other hand, the aldehyde groups (-CHO) in lignin can react with the primary amines (-NH2) and secondary amines (-NH-) in the amino resin to form reversible imine bonds (C=N), enhancing the dissociation bond energy of the amino resin and further improving the acid and alkali hydrolysis resistance of the waterborne solid-color topcoat without clear coating.

[0018] 3. The star-shaped topological structure of the waterborne blocked isocyanate can improve the branching degree of the blocked isocyanate, increase the low-shear viscosity, resist the flow on the vertical surface, and improve the sagging problem of the paint surface; introducing amino-terminated polyether-polysiloxane, the polysiloxane chain segments are grafted onto the prepolymer through the reaction of amino groups with residual -NCO, and the hydrophilic polyether chain segments endow the polymer molecules with water dispersibility, avoiding delamination during the storage period of the topcoat; the hydrophobic chain segments of polysiloxane can migrate to the surface of the topcoat during the curing of the coating film, reducing the surface tension of the topcoat and reducing the orange peel phenomenon.

[0019] 4. Sodium perfluorononyloxybenzenesulfonate has both emulsifying and surface modification functions, can reduce the surface tension of the hydroxyl-type waterborne acrylic resin, improve the leveling property of the topcoat, and enhance the smoothness and appearance quality of the coating film. Specific embodiments

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the following described embodiments are part of the embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained by purchasing in the market. Example 1

[0021] 1. Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate according to a mass ratio of 1:3:2. According to the mass ratio of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate to deionized water being 1:80, add deionized water as a dispersion medium. After high-speed shearing at 8000 rpm for 20 min, an emulsion is obtained. Add ammonium persulfate as a thermal initiator to the emulsion, stir at a low speed of 200 rpm for 30 min. After the reaction is completed, add dimethylethanolamine to adjust the pH of the system to 7.0. After filtration, place it in a vacuum drying oven at 60 °C for drying for 12 h to obtain an aqueous hydroxyacrylate dispersion; wherein, the addition amount of sodium perfluorononenyloxybenzenesulfonate is 0.5 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0022] 2. Mix 1-ethyl-3-methylimidazolium acetate and kraft lignin according to a molar ratio of 2:1. According to the mass ratio of the total mass of 1-ethyl-3-methylimidazolium acetate and kraft lignin to absolute ethanol being 1:90, use absolute ethanol as a solvent and carry out depolymerization under the conditions of constant temperature at 90 °C and ultrasonic treatment at 200 W. After the depolymerization is completed, centrifuge at 800 rpm for 15 min. Wash the centrifuged precipitate with absolute ethanol and dry it at 55 °C for 2 h to obtain depolymerized kraft lignin. Mix the depolymerized kraft lignin, aldehyde dehydrogenase and formate dehydrogenase according to a molar ratio of 1:0.05:1.2. According to a solid-liquid ratio of 1:180, add a phosphate buffer solution with a pH of 6.8, and carry out 40 kHz ultrasonic treatment in a constant temperature water bath at 45 °C for 3 h. After filtration, wash and dry to obtain dialdehyde lignin.

[0023] 3. Using absolute ethanol as the medium, dialdehyde lignin and amino resin (CYMEL 325:CYMEL 303 = 5:1) were mixed at a mass ratio of 1:4. Triethylenediamine was added as a catalyst, and the pH was adjusted to 2 with acetic acid. The temperature was raised from 60 °C to 80 °C at a heating rate of 5 °C / min, and the mixture was kept warm for 2 h. After centrifugation at 600 rpm, it was dried at 45 °C for 2.5 h to obtain the modified amino resin. Among them, the addition amount of triethylenediamine was 0.6 wt% of the amino resin.

[0024] 4. Epoxy-terminated polysiloxane and amino-terminated polyetheramine were mixed at a molar ratio of 1:1. According to a mass ratio of 1:60, a 30 wt% isopropanol solution was added as a solvent. After stirring evenly, the reaction was carried out at 80 °C for 5 h. After removing the isopropanol solution by vacuum distillation at 50 mmHg and 50 °C, amino-terminated polyether-polysiloxane was obtained.

[0025] 5. Trimethylolpropane and isophorone diisocyanate were added to a dry reaction kettle at a molar ratio of 1:6. Under a nitrogen atmosphere, dibutyltin dilaurate was added, and the mixture was stirred at a low speed at 75 °C for 3 h to obtain a star-shaped isocyanate prepolymer. Among them, the addition amount of dibutyltin dilaurate was 0.05 wt% of isophorone diisocyanate; the viscosity of the star-shaped isocyanate prepolymer was 2000 mPa·s.

[0026] 6. Methyl ethyl ketoxime was added to the star-shaped isocyanate prepolymer, and the reaction was carried out at 60 °C for 1.5 h and kept warm for 30 min. Amino-terminated polyether-polysiloxane was added, and the reaction was carried out at 65 °C for 1 h. According to a mass ratio of 1:30, the obtained product was slowly added to a 0.5 wt% sodium dodecylbenzenesulfonate solution, and high-speed shear emulsification was carried out for 20 min. Then, nanocellulose crystals were added, and after ultrasonic dispersion for 30 min, rotary evaporation was carried out at 30 mmHg, 45 °C, and 150 rpm to obtain a waterborne blocked isocyanate. Among them, the addition amounts of methyl ethyl ketoxime and nanocellulose crystals were 1 wt% and 0.5 wt% of the star-shaped isocyanate prepolymer, respectively.

[0027] 7. By mass parts, take waterborne hydroxyl acrylate dispersion: 40 parts; modified amino resin: 8 parts; waterborne blocked isocyanate: 2 parts; solvent A (diethylene glycol butyl ether): 3 parts; solvent B (n-butanol): 0.5 part; solvent C (ethanol): 1 part; substrate wetting agent (TEGO Twin 4100): 0.5 part; polyurethane thickener (XS-83): 0.5 part; waterborne general resin-free color paste: 25 parts; pH regulator (DMEA): 0.2 part; deionized water: 6 parts.

[0028] 8. Add aqueous hydroxyacrylate dispersion, modified amino resin, aqueous blocked isocyanate, solvent A, solvent B, solvent C, substrate wetting agent, polyurethane thickener, aqueous color paste, pH regulator and deionized water into the reaction vessel in sequence, stir at 600 rpm for 30 min, filter after mixing evenly to obtain the waterborne solid-color topcoat without clear coat. Example 2

[0029] 1. Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate in a mass ratio of 1:3:2. According to the mass ratio of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate to deionized water being 1:80, add deionized water as the dispersion medium, and perform high-speed shearing at 8000 rpm for 20 min to obtain an emulsion. Add ammonium persulfate as a thermal initiator to the emulsion, stir at a low speed of 200 rpm for 30 min. After the reaction is completed, add dimethylethanolamine to adjust the pH of the system to 7.0, filter, and place it in a vacuum drying oven at 60 °C for drying for 12 h to obtain the aqueous hydroxyacrylate dispersion. Among them, the addition amount of sodium perfluorononenyloxybenzenesulfonate is 0.6 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0030] 2. Mix 1-ethyl-3-methylimidazolium acetate and kraft lignin in a molar ratio of 2:1. According to the mass ratio of the total mass of 1-ethyl-3-methylimidazolium acetate and kraft lignin to absolute ethanol being 1:90, use absolute ethanol as the solvent, carry out depolymerization under the conditions of constant temperature at 90 °C and ultrasonic wave of 200 W. After the depolymerization is completed, centrifuge at 800 rpm for 15 min, wash the centrifuged precipitate with absolute ethanol, and dry it at 55 °C for 2 h to obtain the depolymerized kraft lignin. Mix the depolymerized kraft lignin, aldehyde dehydrogenase, and formate dehydrogenase in a molar ratio of 1:0.05:1.2. According to the solid-liquid ratio of 1:180, add phosphate buffer solution with a pH of 6.8, and carry out 40 kHz ultrasonic treatment in a constant temperature water bath at 45 °C for 3 h. After filtration, wash and dry to obtain dialdehyde lignin.

[0031] 3. Use absolute ethanol as the medium, mix dialdehyde lignin and amino resin (CYMEL 325:CYMEL303 = 6:1) in a mass ratio of 1:4, add triethylenediamine as a catalyst, adjust the pH to 3 with acetic acid, and increase the temperature from 60 °C to 80 °C at a heating rate of 5 °C / min, keep warm for 2 h, centrifuge at 600 rpm, and dry at 45 °C for 2.5 h to obtain the modified amino resin. Among them, the addition amount of triethylenediamine is 1.0 wt% of the amino resin.

[0032] 4. Mix epoxy-terminated polysiloxane and amino-terminated polyetheramine in a molar ratio of 1:1, add 30 wt% isopropanol solution as a solvent in a mass ratio of 1:60, stir evenly, react at 80°C for 5h, and remove the solvent by reduced pressure distillation at 50 mmHg and 50°C to obtain amino-terminated polyether-polysiloxane.

[0033] 5. Trimethylolpropane and isophorone diisocyanate were added to a dry reactor in a molar ratio of 1:8. Dibutyltin dilaurate was added under a nitrogen atmosphere. The mixture was stirred at a low speed for 4 hours at 75°C to obtain a star-shaped isocyanate prepolymer. The amount of dibutyltin dilaurate added was 0.05wt% of isophorone diisocyanate. The viscosity of the star-shaped isocyanate prepolymer was 2200 mPa·s.

[0034] 6. Add methyl ethyl ketone oxime to the star-shaped isocyanate prepolymer, react at 60°C for 1.5 hours, keep warm for 30 minutes, add amino-terminated polyether-polysiloxane, react at 65°C for 1 hour, and slowly add the resulting product to 0.5wt% sodium dodecylbenzene sulfonate solution at a mass ratio of 1:30. After high-speed shear emulsification for 20 minutes, add nanocellulose crystals, ultrasonically disperse for 30 minutes, and rotary evaporate at 30 mmHg, 45°C, and 150 rpm to obtain an aqueous blocked isocyanate; wherein, the addition amounts of methyl ethyl ketone oxime and nanocellulose crystals are 1wt% and 0.5wt% of the star-shaped isocyanate prepolymer, respectively.

[0035] 7. In parts by mass, take 45 parts of aqueous hydroxy acrylate dispersion; 9 parts of modified amino resin; 3 parts of aqueous blocked isocyanate; 4 parts of solvent A (ethylene glycol hexyl ether); 0.8 parts of solvent B (n-butanol); 2 parts of solvent C (isopropanol solution); 0.8 parts of substrate wetting agent (TEGO Twin 4100); 1.6 parts of polyurethane thickener (XS-83); 26 parts of aqueous general resin-free color paste; 0.5 parts of pH adjuster (DMEA); and 8 parts of deionized water.

[0036] 8. Add water-based hydroxy acrylate dispersion, modified amino resin, water-based blocked isocyanate, solvent A, solvent B, solvent C, substrate wetting agent, polyurethane thickener, water-based color paste, pH adjuster and deionized water to the reaction container in sequence, stir at 700 rpm for 30 min, mix well and filter to obtain a non-glazing water-based solid color topcoat. Example 3

[0037] 1. Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate according to a mass ratio of 1:3:2. Add deionized water as a dispersion medium according to a mass ratio of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate to deionized water of 1:80. After high-speed shearing at 8000 rpm for 20 min, an emulsion is obtained. Add ammonium persulfate as a thermal initiator to the emulsion, stir at a low speed of 200 rpm for 30 min. After the reaction is completed, add dimethylethanolamine to adjust the pH of the system to 7.0. After filtration, place it in a vacuum drying oven at 60 °C for drying for 12 h to obtain an aqueous hydroxyacrylate dispersion; among them, the addition amount of sodium perfluorononenyloxybenzenesulfonate is 0.8 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0038] 2. Mix 1-ethyl-3-methylimidazolium acetate and kraft lignin according to a molar ratio of 2:1. Use absolute ethanol as a solvent according to a mass ratio of the total mass of 1-ethyl-3-methylimidazolium acetate and kraft lignin to absolute ethanol of 1:90. Carry out depolymerization under the conditions of constant temperature at 90 °C and ultrasonic wave of 200 W. After the depolymerization is completed, centrifuge at 800 rpm for 15 min. Wash the precipitate obtained by centrifugation with absolute ethanol and dry it at 55 °C for 2 h to obtain depolymerized kraft lignin. Mix depolymerized kraft lignin, aldehyde dehydrogenase and formate dehydrogenase according to a molar ratio of 1:0.05:1.2. Add a phosphate buffer solution with a pH of 6.8 according to a solid-liquid ratio of 1:180. Carry out 40 kHz ultrasonic treatment in a constant temperature water bath at 45 °C for 3 h. After filtration, wash and dry to obtain dialdehyde lignin.

[0039] 3. Use absolute ethanol as a medium. Mix dialdehyde lignin and amino resin (CYMEL 325:CYMEL303 = 7:1) according to a mass ratio of 1:4. Add triethylenediamine as a catalyst. Adjust the pH to 5 with acetic acid. Heat from 60 °C to 80 °C at a heating rate of 5 °C / min and keep warm for 2 h. After centrifugation at 600 rpm, dry at 45 °C for 2.5 h to obtain a modified amino resin; among them, the addition amount of triethylenediamine is 1.2 wt% of the amino resin.

[0040] 4. Mix epoxy-terminated polysiloxane and amino-terminated polyetheramine according to a molar ratio of 1:1. Add a 30 wt% isopropanol solution as a solvent according to a mass ratio of 1:60. After stirring evenly, react at 80 °C for 5 h. After removing the solvent by vacuum distillation at 50 mmHg and 50 °C, obtain amino-terminated polyether-polysiloxane.

[0041] 5. Add trimethylolpropane and isophorone diisocyanate to a dry reaction kettle at a molar ratio of 1:10. Under a nitrogen atmosphere, add dibutyltin dilaurate, and stir at a low speed at 75 °C for 5 h to obtain a star-shaped isocyanate prepolymer. Among them, the addition amount of dibutyltin dilaurate is 0.05 wt% of isophorone diisocyanate; the viscosity of the star-shaped isocyanate prepolymer is 2500 mPa·s.

[0042] 6. Add methyl ethyl ketoxime to the star-shaped isocyanate prepolymer, react at 60 °C for 1.5 h, keep the temperature for 30 min, add amino-terminated polyether-polysiloxane, react at 65 °C for 1 h, and slowly add the obtained product to a 0.5 wt% sodium dodecylbenzenesulfonate solution at a mass ratio of 1:30. After high-speed shear emulsification for 20 min, add nanocrystalline cellulose, and after ultrasonic dispersion for 30 min, perform rotary evaporation at 30 mmHg, 45 °C, and 150 rpm to obtain a waterborne blocked isocyanate. Among them, the addition amounts of methyl ethyl ketoxime and nanocrystalline cellulose are 1 wt% and 0.5 wt% of the star-shaped isocyanate prepolymer, respectively.

[0043] 7. By mass, take waterborne hydroxyacrylate dispersion: 50 parts; modified amino resin: 10 parts; waterborne blocked isocyanate: 4 parts; solvent A (dipropylene glycol butyl ether): 4 parts; solvent B (n-butanol): 1 part; solvent C: ethanol: 2 parts, isopropanol solution: 1 part; substrate wetting agent (TEGO Twin 4100): 1 part; polyurethane thickener (XS-83): 2 parts; waterborne general resin-free color paste: 28 parts; pH regulator (DMEA): 0.8 part; deionized water: 10 parts.

[0044] 8. Add waterborne hydroxyacrylate dispersion, modified amino resin, waterborne blocked isocyanate, solvent A, solvent B, solvent C, substrate wetting agent, polyurethane thickener, waterborne color paste, pH regulator, and deionized water to the reaction vessel in sequence, stir at 800 rpm for 30 min, and filter after mixing evenly to obtain a waterborne solid-color topcoat without clear coat.

[0045] The difference between Comparative Example 1 and Example 1 is that the amino resin is not modified, and the specific steps are as follows: 1. Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate in a mass ratio of 1:3:2. Add deionized water as a dispersion medium according to the mass ratio of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate to deionized water being 1:80. After high-speed shearing at 8000 rpm for 20 min, an emulsion is obtained. Add ammonium persulfate as a thermal initiator to the emulsion, stir at a low speed of 200 rpm for 30 min. After the reaction is completed, add dimethylethanolamine to adjust the pH of the system to 7.0. After filtration, place it in a vacuum drying oven at 60 °C for drying for 12 h to obtain an aqueous hydroxyacrylate dispersion; wherein, the addition amount of sodium perfluorononenyloxybenzenesulfonate is 0.5 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0046] 2. Mix epoxy-terminated polysiloxane and amino-terminated polyetheramine in a molar ratio of 1:1. Add a 30 wt% isopropanol solution as a solvent according to a mass ratio of 1:60. After stirring evenly, react at 80 °C for 5 h. After removing the solvent by vacuum distillation at 50 mmHg and 50 °C, an amino-terminated polyether-polysiloxane is obtained.

[0047] 3. Add trimethylolpropane and isophorone diisocyanate to a dry reaction kettle in a molar ratio of 1:6. Under a nitrogen atmosphere, add dibutyltin dilaurate and stir at a low speed at 75 °C for 3 h to obtain a star-shaped isocyanate prepolymer; wherein, the addition amount of dibutyltin dilaurate is 0.05 wt% of isophorone diisocyanate; the viscosity of the star-shaped isocyanate prepolymer is 2000 mPa·s.

[0048] 4. Add methyl ethyl ketoxime to the star-shaped isocyanate prepolymer, react at 60 °C for 1.5 h, keep warm for 30 min, add amino-terminated polyether-polysiloxane, and react at 65 °C for 1 h. Slowly add the obtained product to a 0.5 wt% sodium dodecylbenzenesulfonate solution according to a mass ratio of 1:30. After high-speed shearing and emulsifying for 20 min, add nanocrystalline cellulose, and after ultrasonic dispersion for 30 min, perform rotary evaporation at 30 mmHg, 45 °C, and 150 rpm to obtain an aqueous blocked isocyanate; wherein, the addition amounts of methyl ethyl ketoxime and nanocrystalline cellulose are 1 wt% and 0.5 wt% of the star-shaped isocyanate prepolymer, respectively.

[0049] 5. By mass fraction, take the aqueous hydroxyacrylate dispersion: 40 parts; amino resin (CYMEL 325:CYMEL 303 = 5:1): 8 parts; aqueous blocked isocyanate: 2 parts; solvent A (diethylene glycol butyl ether): 3 parts; solvent B (n-butanol): 0.5 part; solvent C (ethanol): 1 part; substrate wetting agent (TEGO Twin 4100): 0.5 part; polyurethane thickener (XS-83): 0.5 part; aqueous general resin-free color paste: 25 parts; pH regulator (DMEA): 0.2 part; deionized water: 6 parts.

[0050] 6. Sequentially add the aqueous hydroxyacrylate dispersion, amino resin, aqueous blocked isocyanate, solvent A, solvent B, solvent C, substrate wetting agent, polyurethane thickener, aqueous color paste, pH regulator and deionized water into the reaction vessel, stir at 600 rpm for 30 min, filter after mixing evenly, and thus obtain the waterborne solid-color topcoat without clear coat.

[0051] The difference between Comparative Example 2 and Example 1 is that the aqueous blocked isocyanate is not grafted, and the specific steps are as follows: 1. Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and perfluorononenyloxybenzenesulfonate according to a mass ratio of 1:3:2. According to the mass ratio of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and perfluorononenyloxybenzenesulfonate to deionized water being 1:80, add deionized water as the dispersion medium, and perform high-speed shearing at 8000 rpm for 20 min to obtain an emulsion; add ammonium persulfate as a thermal initiator to the emulsion, stir at a low speed of 200 rpm for 30 min. After the reaction is completed, add dimethylethanolamine to adjust the pH of the system to 7.0, filter, and place it in a vacuum drying oven at 60 °C for drying for 12 h to obtain the aqueous hydroxyacrylate dispersion; among them, the addition amount of perfluorononenyloxybenzenesulfonate is 0.5 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate, and butyl acrylate; the addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

[0052] 2. Mix 1-ethyl-3-methylimidazolium acetate and sulfate lignin in a molar ratio of 2:1. Using absolute ethanol as the solvent, carry out depolymerization at a constant temperature of 90 °C and under ultrasonic conditions of 200 W according to the mass ratio of the total mass of 1-ethyl-3-methylimidazolium acetate and sulfate lignin to absolute ethanol being 1:90. After the depolymerization is completed, centrifuge at 800 rpm for 15 min, wash the centrifuged precipitate with absolute ethanol, and dry it at 55 °C for 2 h to obtain depolymerized sulfate lignin. Mix the depolymerized sulfate lignin, aldehyde dehydrogenase, and formate dehydrogenase in a molar ratio of 1:0.05:1.2, add phosphate buffer solution with a pH of 6.8 according to a solid-liquid ratio of 1:180, and carry out 40 kHz ultrasonic treatment in a 45 °C constant temperature water bath for 3 h. After filtration, wash and dry to obtain dialdehyde lignin.

[0053] 3. Using absolute ethanol as the medium, mix dialdehyde lignin and amino resin (CYMEL 325:CYMEL303 = 5:1) in a mass ratio of 1:4, add triethylenediamine as a catalyst, adjust the pH to 2 with acetic acid, heat from 60 °C to 80 °C at a heating rate of 5 °C / min, keep warm for 2 h, centrifuge at 600 rpm, and dry at 45 °C for 2.5 h to obtain modified amino resin; among them, the addition amount of triethylenediamine is 0.6 wt% of the amino resin.

[0054] 4. Mix epoxy group-terminated polysiloxane and amino group-terminated polyetheramine in a molar ratio of 1:1, add 30 wt% isopropanol solution as the solvent according to a mass ratio of 1:60, stir evenly, react at 80 °C for 5 h, and remove the solvent by vacuum distillation at 50 mmHg and 50 °C to obtain amino group-terminated polyether-polysiloxane.

[0055] 5. Add trimethylolpropane and isophorone diisocyanate to a dry reaction kettle in a molar ratio of 1:6. Under a nitrogen atmosphere, add dibutyltin dilaurate and stir at a low speed at 75 °C for 3 h to obtain a star-shaped isocyanate prepolymer; among them, the addition amount of dibutyltin dilaurate is 0.05 wt% of isophorone diisocyanate; the viscosity of the star-shaped isocyanate prepolymer is 2000 mPa·s.

[0056] 6. Add methyl ethyl ketoxime to the star-shaped isocyanate prepolymer, react at 60 °C for 1.5 h, and keep warm for 30 min. Slowly add the obtained product to a 0.5 wt% sodium dodecylbenzenesulfonate solution according to a mass ratio of 1:30, carry out high-speed shear emulsification for 20 min, add nanocrystalline cellulose, disperse by ultrasonic for 30 min, and then carry out rotary evaporation at 30 mmHg, 45 °C, and 150 rpm to obtain a waterborne blocked isocyanate; among them, the addition amounts of methyl ethyl ketoxime and nanocrystalline cellulose are 1 wt% and 0.5 wt% of the star-shaped isocyanate prepolymer, respectively.

[0057] 7. By mass, take the aqueous hydroxyacrylate dispersion: 40 parts; modified amino resin: 8 parts; aqueous blocked isocyanate: 2 parts; solvent A (diethylene glycol butyl ether): 3 parts; solvent B (n-butanol): 0.5 part; solvent C (ethanol): 1 part; substrate wetting agent (TEGO Twin 4100): 0.5 part; polyurethane thickener (XS-83): 0.5 part; aqueous universal resin-free color paste: 25 parts; pH regulator (DMEA): 0.2 part; deionized water: 6 parts.

[0058] 8. Add the aqueous hydroxyacrylate dispersion, modified amino resin, aqueous blocked isocyanate, solvent A, solvent B, solvent C, substrate wetting agent, polyurethane thickener, aqueous color paste, pH regulator and deionized water to the reaction vessel in sequence, stir at 600 rpm for 30 min, and filter after mixing evenly to obtain the waterborne solid-color topcoat without clear coat.

[0059] Technical tests were carried out on the waterborne solid-color topcoats without clear coat obtained in each example and comparative example, and the measurement results are shown in Table 1:

[0060] As can be seen from Table 1, the appearance quality of Examples 1-3 is better than that of Comparative Examples 1-2, and the acid and alkali hydrolysis resistance and water resistance are also much higher than those of Comparative Examples 1-2. The modification of amino resin by dialdehyde lignin plays an important role in the water resistance of the waterborne solid-color topcoat without clear coat, while the amino-terminated polyether-polysiloxane grafted aqueous blocked isocyanate significantly improves the anti-sagging and anti-orange peel properties of the paint film. The waterborne solid-color topcoat without clear coat provided by the present invention successfully solves the key problems in the prior art through innovative formulation design and process optimization, provides an efficient, environmentally friendly and high-performance solution for the automotive coating industry, and has broad market application prospects.

[0061] The specific embodiments of the present invention described above do not constitute a limitation to the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A waterborne solid-color topcoat without clear coating, by weight, comprises the following components: Waterborne hydroxyacrylate dispersion: 40 - 50 parts; Modified amino resin: 8 - 10 parts; Waterborne blocked isocyanate: 2 - 4 parts; Solvent A: 3 - 4 parts; Solvent B: 0.5 - 1 part; Solvent C: 1 - 3 parts; Substrate wetting agent: 0.5 - 1 part; Polyurethane thickener: 0.5 - 2 parts; Waterborne color paste: 25 - 28 parts; pH regulator: 0.2 - 0.8 part; Deionized water: 6 - 10 parts.

2. The waterborne solid color topcoat without overcoating according to claim 1, wherein, The preparation method of the waterborne hydroxyacrylate dispersion is as follows: Mix trimethoxysilylpropyl methacrylate, methyl methacrylate, butyl acrylate and sodium perfluorononenyloxybenzenesulfonate, add deionized water as the dispersion medium, and obtain an emulsion after high-speed shearing; Add ammonium persulfate as a thermal initiator to the emulsion. After the reaction is completed, add dimethylethanolamine to adjust the pH value of the system to neutral, filter and then evaporate and dry to obtain the waterborne hydroxyacrylate dispersion.

3. A water-based solid color topcoat without clear coating according to claim 2, characterized in that, The mass ratio of trimethoxysilylpropyl methacrylate, methyl methacrylate and butyl acrylate is 1:3:2; The addition amount of sodium perfluorononenyloxybenzenesulfonate is 0.5 - 0.8 wt% of the total mass of trimethoxysilylpropyl methacrylate, methyl methacrylate and butyl acrylate; The addition amount of ammonium persulfate is 0.2 wt% of the emulsion.

4. A water-based solid-color topcoat without clear coating according to claim 1, characterized in that, The preparation method of the modified amino resin is as follows: Using absolute ethanol as the medium, mix dialdehyde lignin and amino resin according to a mass ratio of 1:4, add triethylenediamine as a catalyst, adjust the pH to 2 - 5 with acetic acid, and heat from 60 °C to 80 °C at a heating rate of 5 °C / min, keep warm for 2 h, and obtain the modified amino resin after centrifugal drying; Among them, the addition amount of triethylenediamine is 0.6 - 1.2 wt% of the amino resin.

5. An aqueous solid-color topcoat without clearcoat according to claim 4, characterized in that, The amino resin is CYMEL 325:CYMEL 303 = 5 - 7:1; The preparation method of the dialdehyde lignin is as follows: Mix 1-ethyl-3-methylimidazolium acetate and kraft lignin according to a molar ratio of 2:1, keep the temperature at 90 °C and carry out ultrasonic depolymerization at 200 W in absolute ethanol. After the depolymerization is completed, carry out centrifugal washing and drying to obtain the depolymerized kraft lignin; According to a molar ratio of 1: 0.05:1.2, mix the depolymerized kraft lignin with aldehyde dehydrogenase and formate dehydrogenase, and carry out 40 kHz ultrasonic treatment for 3 h in a phosphate buffer system with a pH of 6.8 at a constant temperature of 45 °C. After filtration, carry out washing and drying to obtain the dialdehyde lignin.

6. The waterborne solid-color topcoat without clear coating according to claim 1, characterized in that The preparation method of the aqueous blocked isocyanate is as follows: Methyl ethyl ketoxime is added to the star isocyanate prepolymer, and the reaction is carried out at 60 °C for 1.5 h, and then kept at a constant temperature for 30 min. Then, amino-terminated polyether-polysiloxane is added, and the reaction is carried out at 65 °C for 1 h. According to the mass ratio of 1:30, the obtained product is slowly added to a 0.5 wt% sodium dodecylbenzenesulfonate solution, and high-speed shear emulsification is carried out for 20 min. Then, nanocrystalline cellulose is added, and after ultrasonic dispersion for 30 min, the aqueous blocked isocyanate is obtained by rotary evaporation; wherein, the addition amounts of methyl ethyl ketoxime and nanocrystalline cellulose are 1 wt% and 0.5 wt% of the star isocyanate prepolymer, respectively.

7. A waterborne solid color topcoat without clear coat according to claim 6, characterized in that The preparation method of the star isocyanate prepolymer is as follows: Trimethylolpropane and isophorone diisocyanate are added to a dry reaction kettle according to the molar ratio of 1:6 - 10. Under a nitrogen atmosphere, dibutyltin dilaurate is added, and low-speed stirring is carried out at 75 °C for 3 - 5 h to obtain the star isocyanate prepolymer; wherein, the addition amount of dibutyltin dilaurate is 0.05 wt% of isophorone diisocyanate; the viscosity of the star isocyanate prepolymer is 2000 - 2500 mPa·s.

8. A waterborne solid-color topcoat without clearcoat according to claim 1, characterized in that The solvent A is any one or more of diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, and dipropylene glycol monobutyl ether; the solvent B is n-butanol; the solvent C is any one or more of ethanol or isopropanol solution; the substrate wetting agent is TEGO Twin 4100; the polyurethane thickener is XS-83; the color paste is an aqueous general-purpose resin-free color paste; the pH regulator is DMEA.

9. A waterborne solid-color topcoat without clear coating according to claim 6, characterized in that, The preparation method of the amino-terminated polyether-polysiloxane is as follows: Epoxy-terminated polysiloxane and amino-terminated polyetheramine are mixed according to the molar ratio of 1:1, and according to the mass ratio of 1:60, a 30 wt% isopropanol solution is added as a solvent. After stirring evenly, the reaction is carried out at 80 °C for 5 h. After removing the isopropanol solution by vacuum distillation, the amino-terminated polyether-polysiloxane is obtained.

10. The preparation method of a water-based solid color topcoat without clear coating according to claim 1, characterized in that It includes the following steps: An aqueous hydroxyl acrylate dispersion, a modified amino resin, an aqueous blocked isocyanate, a solvent A, a solvent B, a solvent C, a substrate wetting agent, a polyurethane thickener, an aqueous color paste, a pH regulator, and deionized water are sequentially added to a reaction vessel, and stirred at 600 - 800 rpm for 30 min. After mixing evenly, filtration is carried out to obtain the waterborne solid-color topcoat without clear coat.

Images