A water-based coating for automobiles and its preparation process

Abstract

This invention belongs to the field of waterborne coating preparation, specifically relating to a waterborne automotive coating and its preparation process. The waterborne automotive coating is prepared through the following steps: preparation of a waterborne dispersion, synthesis of a polyurethane prepolymer waterborne dispersion, synthesis of a waterborne polyurethane dispersion, pre-emulsification, initiation and seed emulsion activation, and mixing. This coating possesses the protective, decorative, and weather-resistant properties of traditional high-end waterborne automotive coatings. It allows the coating to achieve micro-repair after minor scratches by heating or leaving it at room temperature. It exhibits high compatibility with existing automotive painting lines and can dynamically adjust the absorption and reflection of sunlight (especially near-infrared light) according to ambient temperature and sunlight intensity.

Description

Technical Field

[0001] This invention belongs to the field of water-based coating preparation technology, specifically relating to a water-based coating for automobiles and its preparation process. Background Technology

[0002] Traditional automotive painting primarily uses solvent-based coatings, which not only contain a significant amount of harmful heavy metals but also have high VOC (volatile organic compound) emissions. With the increasing emphasis on environmental protection, green production in the automotive industry has gained widespread attention. Consequently, water-based coatings with low VOC emissions have emerged. Water-based coatings are typically non-toxic or low-toxic, posing minimal impact on human health and aligning with modern environmental principles, gradually becoming the mainstream in the automotive painting industry.

[0003] However, water-based coatings for automobiles still suffer from drawbacks in process adaptability and performance. Regarding performance adaptability, some water-based coatings may achieve excellent results in short-term xenon lamp tests, but under long-term exposure in complex industrial environments, they are prone to peeling, fading, flaking, and cracking, failing to meet long-term durability requirements. Furthermore, they also exhibit deficiencies in abrasion resistance and impact resistance, leading to paint damage and shortening the vehicle's lifespan. Regarding process adaptability, traditional coating formulation methods often result in uneven pigment distribution, leading to agglomeration of pigment particles, increasing the frequency of color differences and color deviations, and causing bubble formation, thus reducing coating quality. Therefore, actively exploring water-based coatings for automobiles and their preparation processes is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a water-based automotive coating and its preparation process. This coating not only possesses the protective, decorative, and weather-resistant properties of traditional high-end water-based automotive coatings, but also dynamically adjusts the absorption and reflection capabilities of the paint film to sunlight (especially near-infrared light) according to ambient temperature and sunlight intensity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A process for preparing a water-based coating for automobiles includes the following steps:

[0007] Step (a): Preparation of aqueous dispersion: Weigh ammonium metavanadate (NH4VO3) and sodium tungstate (Na2WO4) in a mass ratio of 20:1 and dissolve them in deionized water. Add oxalic acid while stirring to form a blue transparent solution. React at 200°C for 20-24 hours. After cooling, centrifuge and wash to obtain a dark blue precipitate. Then disperse it in water, add silane coupling agent, and react at 80°C for 6-8 hours to obtain an aqueous dispersion.

[0008] Step (b): Synthesis of polyurethane prepolymer aqueous dispersion: Weigh polycarbonate diol (PCDL) and dimethylolpropionic acid (DMPA) in a mass ratio of 100:7, remove trace amounts of water, then cool to 65°C, add 34 parts of isophorone diisocyanate and 1-3 drops of DBTDL under nitrogen protection, react at 75-80°C for 2-3 hours, cool to 60°C, add 3-4 parts of bis(2-hydroxyethyl) disulfide (HEDS), react for 1-2 hours, add 7 parts of DMPA, continue reacting at 70°C for 4-5 hours, cool to below 40°C, add 4 parts of triethylamine, react for 30 minutes, add 200 parts of ice-water mixture to the system under high-speed stirring at 1000 rpm, emulsify, and obtain polyurethane prepolymer aqueous dispersion;

[0009] Step (c): Synthesis of aqueous polyurethane dispersion: A small amount of ethylenediamine is added dropwise to the aqueous dispersion of polyurethane prepolymer, and the mixture is reacted for 1-2 hours under stirring. The aqueous polyurethane dispersion is obtained by vacuum distillation.

[0010] Step (d): Pre-emulsification: MMA (methyl methacrylate), BA (butyl acrylate), and HEA (hydroxyethyl acrylate) are mixed in proportion, a small amount of sodium dodecyl sulfate and deionized water are added, and emulsification is carried out at high speed for 15 minutes to obtain a monomer pre-emulsion. Then, the 1 / 3 monomer pre-emulsion prepared is mixed evenly with the aqueous dispersion obtained in step (a) and set aside.

[0011] Step (e): Initiation and seed emulsion activation: The aqueous polyurethane dispersion obtained in step (c) was adjusted to pH 7.5-8.0 with sodium bicarbonate solution, heated to 80°C, and then ammonium persulfate solution was added. The reaction was carried out for 15 minutes to obtain an activated emulsion.

[0012] Step (f): The remaining monomer preemulsion, the monomer preemulsion mixed with the aqueous dispersion, and the activated solution obtained in step (e) are added dropwise simultaneously. After the addition is complete, the temperature is raised to 85°C and kept at that temperature for 1 to 2 hours. Then, the temperature is slowly lowered to below 45°C, the pH of the emulsion is adjusted, and the final product is obtained by filtration.

[0013] Preferably, the silane coupling agent is one or more of vinyltrimethoxysilane and KH-570 silane coupling agent.

[0014] Preferably, the dehydration conditions in step (b) are vacuum dehydration at 80°C for 2 hours.

[0015] Preferably, in step (d), the ratio of MMA (methyl methacrylate), BA (butyl acrylate), and HEA (hydroxyethyl acrylate) is 6:3:1.

[0016] Preferably, the dropping conditions in step (f) are as follows: the total dropping time is approximately 3-4 hours, and the dropping is done slowly and at a uniform rate. During this process, the temperature of the reaction system is maintained at 78-80°C using a water bath.

[0017] Preferably, the pH of the emulsion is adjusted to 8.0-8.5 using triethylamine.

[0018] Preferably, the sieving is performed through a 200-mesh sieve.

[0019] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0020] The phase transition temperature of pure VO2 is approximately 68°C, which is too high for automotive coatings (in summer sunlight, the paint surface temperature of a car is typically between 50 and 70°C; when internal cooling is required, the phase transition should be triggered earlier). This invention introduces tungsten (W) as a dopant. After tungsten atoms enter the VO2 lattice, they stabilize its metallic phase at high temperatures, thereby systematically lowering the phase transition temperature and dramatically increasing near-infrared reflectivity. This allows for precise control of the temperature range (Tc) from 68°C to around 35°C, achieving wide-range, smooth, and continuous photothermal regulation.

[0021] The particles are surface-treated using a silane coupling agent containing double bonds (such as VTMS). The hydrolyzed group at one end of the silane reacts chemically with the hydroxyl groups (-OH) on the particle surface to form a strong covalent bond. This "grafts" an organic molecular layer containing vinyl groups (C=C) onto the surface of the inorganic particles. This molecular layer changes the surface properties of the particles from hydrophilic to hydrophobic, significantly improving compatibility with resins and enabling long-term stable dispersion in aqueous emulsions. It imparts hardness and weather resistance to the coating. In-situ copolymerization achieves covalent bonding between inorganic nanoparticles and organic resins, allowing stress to be effectively transferred through chemical bonds, greatly enhancing the coating's mechanical strength, toughness, and wear resistance. The coating can self-heal from minor scratches by heating or leaving it at room temperature, and it exhibits high compatibility with existing automotive painting lines. Detailed Implementation

[0022] The embodiments of the technical solution of the present invention will be described in detail below with reference to the examples. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, and are therefore only examples, and should not be used to limit the scope of protection of the present invention.

[0023] It should be noted that, unless otherwise specified, the experimental methods used in the implementation examples are all conventional methods; and the materials and reagents used are all commercially available unless otherwise specified.

[0024] In this invention, unless otherwise stated, all “parts” and percentages (%) refer to weight percentages.

[0025] In this invention, unless otherwise stated, the sum of all percentages in all compositions is 100%.

[0026] In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" have been listed in this document, and "0~5" is simply a shortened representation of these numerical combinations.

[0027] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0028] In this invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially; for example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially; for example, the method may also include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0029] In this invention, unless otherwise specified, the specific values ​​and substances in the embodiments of this invention can be combined with other features in the description of this invention; for example, if the specification mentions that the reaction temperature is 10~100℃, while the embodiment mentions that the reaction temperature is 20℃, then it can be considered that this invention has specifically disclosed the range of 10~20℃ or the range of 20~100℃, and this range can be combined with other features in the description to form a new technical solution.

[0030] Example 1;

[0031] In a 250 mL beaker, 0.909 g (7.8 mmol) of NH₄VO₃ and 0.026 g (0.08 mmol) of Na₂WO₄·2H₂O were added sequentially, followed by 60 mL of deionized water. The mixture was magnetically stirred in an 80°C water bath for 10 minutes. At this point, the solid did not completely dissolve, and the solution was a pale yellow turbidity. 1.8 g of oxalic acid was added while stirring, forming a clear blue solution. Stirring was continued for another 20 minutes. The mixture was reacted at 200°C for 20 hours, cooled, and centrifuged for 10 minutes. The supernatant was discarded, and the precipitate was washed three times alternately with anhydrous ethanol and deionized water to obtain a deep blue precipitate. The dried, dark blue-black precipitate was then gently ground using an agate mortar and pestle.

[0032] Then add 100 mL of deionized water and 50 mL of anhydrous ethanol, ultrasonically disperse in an ultrasonic cleaner for 30 minutes, disperse in water, slowly add 1.5 mL of vinyltrimethoxysilane in a constant pressure dropping funnel, react at 80 °C for 8 hours, and cool to obtain an aqueous dispersion.

[0033] Synthesizing polyurethane prepolymer aqueous dispersion: Weigh 100.0g polycarbonate diol (PCDL) and 7g dimethylolpropionic acid (DMPA) and dehydrate under vacuum at 80℃ for 2 hours to remove trace amounts of water. Then, cool to 65℃ and add 34g isophorone diisocyanate and 3 drops DBTDL under nitrogen protection. After reacting at 80℃ for 3 hours, cool to 60℃ and slowly add 3.5 parts of bis(2-hydroxyethyl) disulfide (HEDS) pre-dissolved in 15g acetone over 15 minutes. After reacting for 2 hours, add 7g DMPA and continue reacting at 70℃ for 4 hours. Cool to below 40℃ and add 4g triethylamine. React for 30 minutes. Add 200g ice-water mixture to the system under high-speed stirring at 1000rpm for emulsification to obtain polyurethane prepolymer aqueous dispersion.

[0034] Synthesis of aqueous polyurethane dispersion: 1.2 g of ethylenediamine was added dropwise to the aqueous dispersion of polyurethane prepolymer, and the reaction was carried out under stirring for 2 hours. The aqueous polyurethane dispersion was obtained by vacuum distillation.

[0035] Pre-emulsification: Mix 48g MMA (methyl methacrylate), 24g BA (butyl acrylate), and 8g HEA (hydroxyethyl acrylate), add a small amount of sodium dodecyl sulfate and deionized water, and emulsify at high speed for 15 minutes to obtain a monomer pre-emulsion. Then mix the 1 / 3 monomer pre-emulsion obtained in the preparation with the aqueous dispersion obtained in step (a) evenly for later use.

[0036] Initiation and seed emulsion activation: The aqueous polyurethane dispersion obtained in step (c) was adjusted to pH 7.5-8.0 with sodium bicarbonate solution, heated to 80°C, and then ammonium persulfate solution was added. The reaction was carried out for 15 minutes to obtain the activated emulsion.

[0037] The remaining monomer preemulsion, the monomer preemulsion mixed with the aqueous dispersion, and the activated solution obtained in step (e) were added dropwise simultaneously over a total time of approximately 3-4 hours, at a slow and uniform rate. During this process, the reaction system temperature was maintained at 78°C using a water bath. After the addition was complete, the temperature was raised to 85°C and held for 2 hours, then slowly lowered to below 45°C. The pH of the emulsion was adjusted to 8.0-8.5 with triethylamine, and the mixture was filtered through a 200-mesh sieve to obtain the final product 1.

[0038] Example 2;

[0039] In a 250 mL beaker, 0.909 g (7.8 mmol) of NH₄VO₃ and 0.026 g (0.08 mmol) of Na₂WO₄·2H₂O were added sequentially, followed by 60 mL of deionized water. The mixture was magnetically stirred in an 80°C water bath for 10 minutes. At this point, the solid did not completely dissolve, and the solution was a pale yellow turbidity. 1.8 g of oxalic acid was added while stirring, forming a clear blue solution. Stirring was continued for another 20 minutes. The mixture was reacted at 200°C for 24 hours, cooled, and centrifuged for 10 minutes. The supernatant was discarded, and the precipitate was washed three times alternately with anhydrous ethanol and deionized water to obtain a deep blue precipitate. The dried, dark blue-black precipitate was then gently ground using an agate mortar and pestle.

[0040] Then add 100 mL of deionized water and 50 mL of anhydrous ethanol, ultrasonically disperse in an ultrasonic cleaner for 30 minutes, disperse in water, slowly add 1.5 mL of vinyltrimethoxysilane in a constant pressure dropping funnel, react at 80 °C for 8 hours, and cool to obtain an aqueous dispersion.

[0041] Synthesizing polyurethane prepolymer aqueous dispersion: Weigh 100.0g polycarbonate diol (PCDL) and 7g dimethylolpropionic acid (DMPA) and dehydrate under vacuum at 80℃ for 2 hours to remove trace amounts of water. Then, lower the temperature to 65℃ and add 34g isophorone diisocyanate and 1-3 drops of DBTDL under nitrogen protection. After reacting at 80℃ for 3 hours, cool down to 60℃ and slowly add 3.5 parts of bis(2-hydroxyethyl) disulfide (HEDS) pre-dissolved in 15g acetone over 15 minutes. After reacting for 2 hours, add 7g DMPA and continue reacting at 70℃ for 4-5 hours. Cool down to below 40℃ and add 4g triethylamine. React for 30 minutes and add 200g ice-water mixture to the system under high-speed stirring at 1000rpm for emulsification to obtain polyurethane prepolymer aqueous dispersion.

[0042] Synthesis of aqueous polyurethane dispersion: 1.2 g of ethylenediamine was added dropwise to the aqueous dispersion of polyurethane prepolymer, and the reaction was carried out under stirring for 2 hours. The aqueous polyurethane dispersion was obtained by vacuum distillation.

[0043] Pre-emulsification: Mix 48g MMA (methyl methacrylate), 24g BA (butyl acrylate), and 8g HEA (hydroxyethyl acrylate), add a small amount of sodium dodecyl sulfate and deionized water, and emulsify at high speed for 15 minutes to obtain a monomer pre-emulsion. Then mix the 1 / 3 monomer pre-emulsion obtained in the preparation with the aqueous dispersion obtained in step (a) evenly for later use.

[0044] Initiation and seed emulsion activation: The aqueous polyurethane dispersion obtained in step (c) was adjusted to pH 7.5-8.0 with sodium bicarbonate solution, heated to 80°C, and then ammonium persulfate solution was added. The reaction was carried out for 15 minutes to obtain the activated emulsion.

[0045] The remaining monomer preemulsion, the monomer preemulsion mixed with the aqueous dispersion, and the activated solution obtained in step (e) were added dropwise simultaneously over a total time of approximately 4 hours, at a slow and uniform rate. During this process, the reaction system temperature was maintained at 78–80°C using a water bath. After the addition was complete, the temperature was raised to 85°C and held for 2 hours, then slowly lowered to below 45°C. The pH of the emulsion was adjusted to 8.0–8.5 with triethylamine, and the mixture was filtered through a 200-mesh sieve to obtain the final product 2.

[0046] Example 3;

[0047] In a 250 mL beaker, 0.909 g (7.8 mmol) of NH₄VO₃ and 0.026 g (0.08 mmol) of Na₂WO₄·2H₂O were added sequentially, followed by 60 mL of deionized water. The mixture was magnetically stirred in an 80°C water bath for 10 minutes. At this point, the solid did not completely dissolve, and the solution was a pale yellow turbidity. 1.8 g of oxalic acid was added while stirring, forming a clear blue solution. Stirring was continued for another 20 minutes. The mixture was reacted at 200°C for 20 hours, cooled, and centrifuged for 10 minutes. The supernatant was discarded, and the precipitate was washed three times alternately with anhydrous ethanol and deionized water to obtain a deep blue precipitate. The dried, dark blue-black precipitate was then gently ground using an agate mortar and pestle.

[0048] Then add 100 mL of deionized water and 50 mL of anhydrous ethanol, ultrasonically disperse in an ultrasonic cleaner for 30 minutes, disperse in water, slowly add 2.0 mL of KH-570 silane coupling agent in a constant pressure dropping funnel, react at 80°C for 8 hours, and cool to obtain an aqueous dispersion.

[0049] Synthesizing polyurethane prepolymer aqueous dispersion: Weigh 100.0g polycarbonate diol (PCDL) and 7g dimethylolpropionic acid (DMPA) and dehydrate under vacuum at 80℃ for 2 hours to remove trace amounts of water. Then, cool to 65℃ and add 34g isophorone diisocyanate and 3 drops DBTDL under nitrogen protection. After reacting at 80℃ for 3 hours, cool to 60℃ and slowly add 3.5 parts of bis(2-hydroxyethyl) disulfide (HEDS) pre-dissolved in 15g acetone over 15 minutes. After reacting for 2 hours, add 7g DMPA and continue reacting at 70℃ for 4 hours. Cool to below 40℃ and add 4g triethylamine. React for 30 minutes. Add 200g ice-water mixture to the system under high-speed stirring at 1000rpm for emulsification to obtain polyurethane prepolymer aqueous dispersion.

[0050] Synthesis of aqueous polyurethane dispersion: 1.2 g of ethylenediamine was added dropwise to the aqueous dispersion of polyurethane prepolymer, and the reaction was carried out under stirring for 2 hours. The aqueous polyurethane dispersion was obtained by vacuum distillation.

[0051] Pre-emulsification: Mix 48g MMA (methyl methacrylate), 24g BA (butyl acrylate), and 8g HEA (hydroxyethyl acrylate), add a small amount of sodium dodecyl sulfate and deionized water, and emulsify at high speed for 15 minutes to obtain a monomer pre-emulsion. Then mix the 1 / 3 monomer pre-emulsion obtained in the preparation with the aqueous dispersion obtained in step (a) evenly for later use.

[0052] Initiation and seed emulsion activation: The aqueous polyurethane dispersion obtained in step (c) was adjusted to pH 7.5-8.0 with sodium bicarbonate solution, heated to 80°C, and then ammonium persulfate solution was added. The reaction was carried out for 15 minutes to obtain the activated emulsion.

[0053] The remaining monomer preemulsion, the monomer preemulsion mixed with the aqueous dispersion, and the activated solution obtained in step (e) were added dropwise simultaneously over a total time of approximately 3-4 hours, at a slow and uniform rate. During this process, the reaction system temperature was maintained at 78°C using a water bath. After the addition was complete, the temperature was raised to 85°C and held for 2 hours, then slowly lowered to below 45°C. The pH of the emulsion was adjusted to 8.0-8.5 with triethylamine, and the mixture was filtered through a 200-mesh sieve to obtain the final product 3.

[0054] Performance testing

[0055] The waterborne automotive coating prepared by this invention meets the requirements of HG / T 4570–2013 "Waterborne Automotive Coatings", and the specific test results are shown in Table 1.

[0056] Table 1

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A preparation process for a water-based coating for automobiles, characterized in that, The preparation process includes the following steps: Step (a): Preparation of aqueous dispersion: Weigh 0.909 g of ammonium metavanadate and 0.026 g of sodium tungstate, dissolve them in deionized water, add oxalic acid under stirring to form a blue transparent solution, react at 200℃ for 20-24 hours, cool, centrifuge and wash to obtain a dark blue precipitate, then disperse it in water, add one or more of vinyltrimethoxysilane and KH-570 silane coupling agent, react at 80℃ for 6-8 hours to obtain an aqueous dispersion; Step (b): Synthesis of polyurethane prepolymer aqueous dispersion: Weigh 100 parts of polycarbonate diol and 7 parts of dimethylolpropionic acid by mass, remove trace amounts of water, then cool to 65°C, add 34 parts of isophorone diisocyanate and 1-3 drops of DBTDL under nitrogen protection, react at 75-80°C for 2-3 hours, cool to 60°C, add 3-4 parts of bis(2-hydroxyethyl) disulfide, react for 1-2 hours, add 7 parts of dimethylolpropionic acid, continue to react at 70°C for 4-5 hours, cool to below 40°C, add 4 parts of triethylamine, react for 30 minutes, add 200 parts of ice-water mixture to the system under high-speed stirring at 1000 rpm, emulsify, and obtain polyurethane prepolymer aqueous dispersion; Step (c): Synthesis of aqueous polyurethane dispersion: A small amount of ethylenediamine is added dropwise to the aqueous dispersion of polyurethane prepolymer, and the reaction is carried out under stirring for 1 to 2 hours. The aqueous polyurethane dispersion is obtained by vacuum distillation. Step (d): Pre-emulsification: Methyl methacrylate, butyl acrylate, and hydroxyethyl acrylate are mixed in proportion, a small amount of sodium dodecyl sulfate and deionized water are added, and emulsification is carried out at high speed for 15 minutes to obtain a monomer pre-emulsion. Then, 1 / 3 of the monomer pre-emulsion prepared is mixed evenly with the aqueous dispersion obtained in step (a) to obtain a monomer pre-emulsion mixed with the aqueous dispersion for later use. Step (e): Initiation and seed emulsion activation: The aqueous polyurethane dispersion obtained in step (c) was adjusted to pH 7.5-8.0 with sodium bicarbonate solution, heated to 80°C, and then ammonium persulfate solution was added. The reaction was carried out for 15 minutes to obtain an activated emulsion. Step (f): Mixing: The remaining monomer preemulsion, the monomer preemulsion mixed with the aqueous dispersion, and the activated emulsion obtained in step (e) are added dropwise simultaneously. After the addition is complete, the temperature is raised to 85°C and kept at that temperature for 1 to 2 hours. Then the temperature is slowly lowered to below 45°C, the pH of the emulsion is adjusted, and the final product is obtained by filtration.

2. The preparation process of a water-based automotive coating according to claim 1, characterized in that, The dehydration conditions in step (b) are vacuum dehydration at 80°C for 2 hours.

3. The preparation process of a water-based automotive coating according to claim 1, characterized in that, In step (d), the mass ratio of methyl methacrylate, butyl acrylate, and hydroxyethyl acrylate is 6:3:

1.

4. The preparation process of a water-based automotive coating according to claim 1, characterized in that, The dropping conditions in step (f) are as follows: the total dropping time is 3 to 4 hours, the dropping is slow and uniform, and the temperature of the reaction system is maintained at 78 to 80°C by a water bath during this process.

5. The preparation process of a water-based automotive coating according to claim 1, characterized in that, The pH of the emulsion is adjusted to 8.0-8.5 using triethylamine.

6. The preparation process of a water-based automotive coating according to claim 1, characterized in that, The filtration process involves passing the material through a 200-mesh sieve.

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