Water-based single-component base coat for automobile exterior trimming parts and preparation method of water-based single-component base coat

Abstract

The invention belongs to the technical field of coatings for automobiles, and particularly relates to a water-based single-component base coat for automobile exterior trimming parts and a preparation method of the water-based single-component base coat. Aiming at the problems of poor adhesive force, low storage stability, insufficient weather resistance-flexibility balance and the like of the existing water-based colored paint for the automobile exterior trimming parts, aminated silicon dioxide and activated nanocellulose are adopted to synergistically modify the raw materials of the water-based single-component base paint; a synchronous dropwise adding process is adopted, the electrostatic shielding effect of lauryl sodium sulfate is utilized, the esterification efficiency of nano cellulose is improved, excellent weather resistance, good appearance and mechanical performance of the water-based single-component base coat are achieved, and the water-based single-component base coat has certain social and economic benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of automotive coatings, and particularly relates to an aqueous one-component primer paint for automotive exterior parts and a preparation method thereof. Background Art

[0002] With the strengthening of automotive lightweight and environmental protection regulations, automotive exterior parts (such as bumpers, spoilers, door handles, etc.) gradually use plastic substrates such as polypropylene (PP) and polycarbonate (PC / ABS) to replace metal materials. Plastic substrates have characteristics such as low surface energy and weak polarity compared to metal materials. Although traditional solvent-based coatings can wet the substrates through strong solvents, their VOC content is too high (>420 g / L), which can no longer meet environmental protection standards such as EU REACH and China's GB 24409-2020. Aqueous coatings have good flexibility, abrasion resistance, and tear resistance, can effectively improve the service life and performance of products, and have good controllability. They can be combined with various coatings and additives to effectively improve the overall performance of materials.

[0003] In recent years, due to the improvement of national environmental protection policy requirements and people's urgent need for a healthy life, the use of aqueous coatings has become more and more widespread, especially in the construction and home decoration industries, where solvent-based coatings have basically been replaced by aqueous coatings. In industries with higher performance and appearance requirements such as rail transit, construction machinery, passenger cars, and commercial vehicles, the use of aqueous coatings has also accelerated. Although certain progress has been made in the research of aqueous one-component primer paints for current automotive exterior plastic parts, there are still significant shortcomings in terms of adhesion universality, storage stability, weathering-flexibility balance, and low cost, and the following problems are likely to occur: (1) Poor pigment orientation: Due to the high surface tension of the aqueous system, metal pigments are difficult to arrange evenly, resulting in color difference (ΔE>1.5) and insufficient flash effect; (2) Weak interlayer compatibility: Poor compatibility with primer or varnish, and defects such as biting the bottom and loss of gloss are likely to occur during construction; (3) Insufficient chemical resistance: Corrosive media such as acid rain and snow melting salts are easy to penetrate the coating, causing blistering or peeling; (4) Failure in water resistance test: Blistering or poor adhesion usually occurs after long-term immersion in water. Summary of the Invention

[0004] The purpose of the present invention is to provide an aqueous one-component primer paint for automotive exterior parts and a preparation method thereof to solve the above technical problems.

[0005] To achieve the above technical purpose, the technical solution of the present invention is as follows: An aqueous one-component primer paint for automotive exterior parts, by mass, includes the following components: Modified aqueous polyurethane dispersion: 30 - 50 parts, self-crosslinking hydroxypropionate-nanocellulose complex: 20 - 40 parts, solvent: 3 - 5 parts, effect pigment: 2 - 4 parts, aqueous color paste: 15 - 30 parts, wetting and leveling agent: 0.05 - 0.5 parts, defoaming agent: 0.5 - 1.0 parts, thickening agent: 0.2 - 1.0 parts, anti-aging additive: 0.2 - 1.0 parts, pH regulator: 0.5 - 2.5 parts, deionized water: 15 - 32 parts.

[0006] As a further improvement, the preparation method of the modified aqueous polyurethane dispersion is as follows: Add polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate into a reaction kettle, add water for emulsification, stir and react at 80 °C for 3 h, add dimethylolpropionic acid, and continue to stir and react at 60 °C for 2 h to obtain a prepolymer containing -Si-O- structure; Cool the prepolymer to 40 °C, add triethylamine and amino-functionalized silica, adjust the pH of the system to 7.5 - 8.0, carry out vacuum desolvation after the stirring reaction is completed to obtain the modified aqueous polyurethane dispersion.

[0007] As a further improvement, the preparation method of the amino-functionalized silica is as follows: Disperse silica in a 5 wt% ethanol solution, after ultrasonic treatment for 30 min, adjust the pH to 4.3 - 4.7, under a nitrogen atmosphere, dropwise add a silane coupling agent, stir and react in a water bath at 80 °C for 45 min, obtain a precipitate after centrifugal separation, wash it successively with absolute ethanol and deionized water, and then vacuum dry at 60 °C for 3 h to obtain the amino-functionalized silica.

[0008] As a further improvement, the mass ratio of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate is 10 - 30:2:3, and the addition amounts of dimethylolpropionic acid, triethylamine, and amino-functionalized silica are 3 wt%, 8 wt%, and 3 wt% - 5 wt% of the total mass of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate, respectively.

[0009] As a further improvement, the preparation method of the self-crosslinking hydroxypropionate-nanocellulose complex is as follows: Shear and mix hydroxypropionate with a 12 wt% sodium dodecyl sulfate solution to form a hydroxypropionate monomer emulsion; Under a nitrogen atmosphere, add 1 / 3 of the hydroxypropionate monomer emulsion and an 8 wt% ammonium persulfate solution to the reaction kettle, stir in a water bath at 75 °C for 30 min, then synchronously dropwise add the remaining hydroxypropionate monomer emulsion and the activated nanocellulose dispersion liquid into the reaction kettle. After the dropping is completed, cool to 40 °C, adjust the pH to 7.5 - 8.0, and filter to obtain the self-crosslinking hydroxypropionate-nanocellulose complex.

[0010] As a further improvement, the preparation method of the activated nanocellulose dispersion is as follows: Disperse the oxidized nanocellulose into a phosphate buffer solution, perform ultrasonic treatment at a power of 800 W for 30 min, add carbodiimide and hydroxysuccinimide, and stir and react in a water bath at 50 °C for 2 h to obtain the activated nanocellulose dispersion.

[0011] As a further improvement, the preparation method of the oxidized nanocellulose is as follows: Mix choline chloride and citric acid and dissolve them in deionized water to obtain a DES solvent; after hot-pressing nanocellulose at 1.5 MPa and 60 °C for 15 min, immerse it in the DES solvent, add 0.5 wt% of nitrogen-doped titanium dioxide, irradiate with visible light with a wavelength of 420 nm, and simultaneously introduce oxygen at a flow rate of 0.1 L / min, react at 60 °C for 4 h, after the reaction is completed, centrifuge and separate the precipitate, wash the precipitate with anhydrous ethanol and acetone in sequence, and obtain oxidized nanocellulose after ultrasonic peeling.

[0012] As a further improvement, the hydroxy propionate is any one or more of MACRYNAL VSM 6299W / 42WA of Allnex, Setaqua® 9803, or Wantipro 0678 of Wanhua Chemical.

[0013] As a further improvement, the solvent is any one or more of ethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol methyl ether, diethylene glycol monobutyl ether, dipropylene glycol butyl ether, butanol, isopropanol, or isooctanol; the effect pigment is any one or more of NH97724B pearlescent powder of Okchem or ZW-7111A aluminum powder of Shandong Silver Arrow; the aqueous color paste is a WB aqueous color paste; the wetting and leveling agent is any one or more of Surfynol 440, BYK-381, BYK-347, BYK-345, PW-336, or TEGO 4100; the defoaming agent is any one or more of BYK-024, Tego airex 902W, Tego foamex810, Foamster 2400, or Surfynol 104E; the thickening agent is any one or more of RheovisAS1130, BYK-8421, THIXATROL 5020W, RHEOLATE299; the anti-aging aid is any one or more of Tinuvin 400 or Tinuvin 123; the pH regulator is AMP-95 or DMEA.

[0014] The present invention also provides a preparation method of an aqueous one-component primer for automotive exterior parts, comprising the following steps: S11. Add the modified aqueous polyurethane dispersion and the self-crosslinking hydroxy propionate-nanocellulose complex to the main cylinder and mix evenly. Stir and react in a 45°C water bath for 2 h. Use ultraviolet-induced grafting to trigger the crosslinking of acrylate double bonds, and finally let it stand for 24 h in an environment with a relative humidity of 50%. S12. Take another auxiliary cylinder, add 90% of the solvent and the effect pigment, stir evenly with a disperser, pour it into the main cylinder, then take the remaining 10% of the solvent to clean the auxiliary cylinder, pour the cleaning liquid into the main cylinder, and stir for 30 min until evenly dispersed. S13. Stir and add a wetting and leveling agent, an antifoaming agent, an anti-aging aid, and a thickener into the main cylinder. After 10 - 15 min, add an aqueous color paste, stir for 30 min, let it stand for 16 h, use a pH regulator to adjust the pH of the system to 8.0 - 8.8, use deionized water to adjust the construction viscosity to 80 - 120 s, and finally filter and package with a 200-mesh silk cloth to obtain the aqueous basecoat.

[0015] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: (1) Using the modified aqueous polyurethane as the main raw material endows the aqueous basecoat with high hardness and high stone impact resistance. The aqueous polyurethane is modified with amino-functionalized silica. Part of the amino groups are protonated to -NH 3 + in the polyurethane system, which improves the zeta potential of the aqueous polyurethane and enhances the electrostatic repulsion between particles, thereby improving the material stability of the aqueous polyurethane; the amino-functionalized silica forms a through-network structure in the aqueous polyurethane, further increasing the tensile strength of the polyurethane and further enhancing the storage stability and weather resistance of the aqueous basecoat.

[0016] (2) Using the self-crosslinking acrylate-nanocellulose composite dispersion as the auxiliary raw material improves the low-temperature film-forming property of the aqueous basecoat. The nanocellulose (CNF) is activated by carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The carboxyl groups on the surface of the nanocellulose react with carbodiimide to form an O-acylisourea intermediate, which reacts with N-hydroxysuccinimide to form a more stable N-hydroxysuccinimide ester. After being compounded with acrylate, it can reduce the hydrolysis side reaction of acrylate, lower the activation energy of the resin chain segment movement and the glass transition temperature, so that the aqueous resin can maintain sufficient molecular chain mobility at low temperature, improve the esterification efficiency, and improve the low-temperature film-forming property of the aqueous basecoat.

[0017] The specific reaction mechanism is as follows: CNF-COOH + EDC → CNF-COO- intermediate + NHS → CNF-COO-NHS.

[0018] (3) During the preparation of the self-crosslinking acrylate-nanocellulose composite dispersion, a process of synchronously dropping the activated nanocellulose dispersion and the self-crosslinking acrylate monomer emulsion is adopted, and the electrostatic shielding effect of sodium dodecyl sulfate is utilized to maintain nanodispersion, so that hydroxy succinimide ester forms a uniform three-dimensional network structure on the resin surface, reducing the decline of material performance caused by nanoaggregation. Detailed implementation mode

[0019] The technical solutions of the present invention will be clearly and completely described below in conjunction with the detailed implementation modes. 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 regarded 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 work fall within the scope of protection of the present invention. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0020] Example 1 A preparation method of an aqueous one-component primer for automotive exterior parts, comprising the following steps: 1. Disperse silicon dioxide in a 5wt% ethanol solution at a mass ratio of 1:200, perform ultrasonic treatment at 300W for 30 min, dropwise add acetic acid to adjust the pH to 4.3, under a nitrogen atmosphere, dropwise add a silane coupling agent, react at 80°C in a water bath with stirring at 300 r / min for 45 min, after the stirring ends, centrifuge at 600 r / min for 15 min, wash the obtained precipitate successively with absolute ethanol and deionized water, and vacuum dry at 60°C for 3 h to obtain amino-functionalized silicon dioxide; wherein, the addition amount of the silane coupling agent is 3wt% of the silicon dioxide.

[0021] 2. Add polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate to the reaction kettle at a mass ratio of 10:2:3 and a water-to-material ratio of 100:35, add water for emulsification, and react with stirring at 80°C for 3 h; add dimethylolpropionic acid, and continue to react with stirring at 60°C for 2 h to obtain a prepolymer containing a -Si-O- structure; cool the prepolymer to 40°C, add triethylamine and amino-functionalized silicon dioxide, adjust the pH of the system to 7.5 with ammonia water, and react with stirring at a shear rate of 40 m / s for 30 min; after the reaction is completed, carry out vacuum desolvation at 80°C for 1 h to obtain a modified aqueous polyurethane dispersion; wherein, the addition amounts of dimethylolpropionic acid, triethylamine, and amino-functionalized silicon dioxide are 3wt%, 8wt%, and 3wt% of the total mass of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate, respectively.

[0022] 3. Mix choline chloride and citric acid and dissolve them in deionized water to obtain a DES solvent; place nanocellulose in a vacuum drying oven, hot press it at 1.5 MPa and 60 °C for 15 min, then immerse it in the DES solvent, add 0.5 wt% of nitrogen-doped titanium dioxide, irradiate it with visible light with a wavelength of 420 nm, and simultaneously introduce oxygen at a flow rate of 0.1 L / min, and react at 60 °C for 4 h; after the reaction is completed, centrifuge the system at a rotation speed of 1000 r / min for 10 min to separate the precipitate, wash the precipitate with absolute ethanol and acetone in turn, and finally use ultrasonic stripping at 40 kHz for 30 min to obtain oxidized nanocellulose; among them, the mass ratio of choline chloride to citric acid is 1:2, the concentration of the DES solvent is 30 wt%, and the mass ratio of nanocellulose to the DES solvent is 1:80.

[0023] 4. Disperse the oxidized nanocellulose in a phosphate buffer solution with a pH of 9, ultrasonically treat it at a power of 800 W for 30 min, add carbodiimide and N-hydroxysuccinimide, and react with stirring in a water bath at 50 °C for 2 h to obtain an activated nanocellulose dispersion; among them, the mass ratio of oxidized nanocellulose to the phosphate buffer solution is 1:200; the total addition amount of carbodiimide and N-hydroxysuccinimide is 15 wt% of the oxidized nanocellulose, and the molar ratio of the two is 1:1.

[0024] 5. Mix hydroxypropionate (MACRYNAL VSM 6299W / 42WA) and a 12 wt% sodium dodecyl sulfate solution according to a mass ratio of 1:100, shear it at 2000 r / min for 15 min to form a hydroxypropionate monomer emulsion; under a nitrogen atmosphere, add 1 / 3 of the hydroxypropionate monomer emulsion and an 8 wt% ammonium persulfate solution to the reaction kettle, stir in a water bath at 75 °C for 30 min, and then synchronously drop the remaining hydroxypropionate monomer emulsion and the activated nanocellulose dispersion into the reaction kettle, and finish dropping within 2 h; after dropping, cool down to 40 °C, adjust the pH to 7.5 with ammonia water, and filter to obtain a self-crosslinking hydroxypropionate-nanocellulose complex; among them, the mass ratio of the hydroxypropionate monomer emulsion, the ammonium persulfate solution and the activated nanocellulose dispersion is 3:1:2.

[0025] 6. By mass, take 50 parts of modified aqueous polyurethane dispersion; 20 parts of self-crosslinking hydroxypropionate-nanocellulose complex; solvent: ethylene glycol monobutyl ether: 3 parts; effect pigment: NH97724B pearlescent powder: 2 parts; WB aqueous color paste: 15 parts; wetting and leveling agent: Surfynol 440: 0.05 part; defoaming agent: BYK-024: 0.5 part; thickener: Rheovis AS1130: 0.2 part; anti-aging aid: Tinuvin 400: 0.2 part; pH regulator: AMP-95: 0.5 part; deionized water: 15 parts.

[0026] 7. Add the modified aqueous polyurethane dispersion and the self-crosslinking hydroxy propionate-nanocellulose complex to the main cylinder and mix evenly. Stir and react in a 45°C water bath for 2 hours. Use ultraviolet-induced grafting to trigger the crosslinking of acrylate double bonds. The crosslinking time is 5 minutes. The UV-LED is 395 nm and the irradiance is 80 mW / cm². Finally, let it stand for 24 hours in an environment with a relative humidity of 50%.

[0027] 8. Take another auxiliary cylinder, add 90% of the solvent and the effect pigment, stir evenly with a disperser, pour it into the main cylinder, then take the remaining 10% of the solvent to clean the auxiliary cylinder, pour the cleaning liquid into the main cylinder, and stir for 30 minutes until evenly dispersed.

[0028] 9. Stir and add a wetting and leveling agent, an antifoaming agent, an anti-aging aid, and a thickening agent into the main cylinder. After 10 minutes, add the WB aqueous color paste, stir for 30 minutes, let it stand for 16 hours, use a pH regulator to adjust the pH of the system to 8.0, use deionized water to adjust the construction viscosity to 80 s, and finally filter and package with a 200-mesh silk cloth to obtain the aqueous base paint.

[0029] 10. Apply the obtained aqueous base paint to automotive exterior parts.

[0030] Example 2 A preparation method of an aqueous one-component base paint for automotive exterior parts, comprising the following steps: 1. Disperse silicon dioxide in a 5 wt% ethanol solution at a mass ratio of 1:200, perform ultrasonic treatment at 300 W for 30 minutes, add acetic acid dropwise to adjust the pH to 4.5. Under a nitrogen atmosphere, add a silane coupling agent dropwise, stir and react in an 80°C water bath at 300 r / min for 45 minutes. After the stirring is completed, centrifuge and separate at 600 r / min for 15 minutes. Wash the obtained precipitate successively with absolute ethanol and deionized water, and vacuum dry at 60°C for 3 hours to obtain amino-functionalized silicon dioxide; wherein, the addition amount of the silane coupling agent is 3 wt% of silicon dioxide.

[0031] 2. Add polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate to the reaction kettle at a mass ratio of 20:2:3 and a water-to-material ratio of 100:35, add water for emulsification, and stir and react at 80°C for 3 hours; add dimethylolpropionic acid and continue to stir and react at 60°C for 2 hours to obtain a prepolymer containing -Si-O- structure; cool the prepolymer to 40°C, add triethylamine and amino-functionalized silicon dioxide, adjust the pH of the system to 7.7 with ammonia water, and stir and react at a shear rate of 40 m / s for 30 minutes; after the reaction is completed, vacuum desolventize at 80°C for 1 hour to obtain the modified aqueous polyurethane dispersion; wherein, the addition amounts of dimethylolpropionic acid, triethylamine, and amino-functionalized silicon dioxide are 3 wt%, 8 wt%, and 4 wt% of the total mass of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate, respectively.

[0032] 3. Mix choline chloride and citric acid and dissolve them in deionized water to obtain a DES solvent; place nanocellulose in a vacuum drying oven, hot press it at 1.5 MPa and 60 °C for 15 min, then immerse it in the DES solvent, add 0.5 wt% of nitrogen-doped titanium dioxide, irradiate it with visible light with a wavelength of 420 nm, and simultaneously introduce oxygen at a flow rate of 0.1 L / min, and react at 60 °C for 4 h; after the reaction is completed, centrifuge the system at a rotation speed of 1000 r / min for 10 min, separate the precipitate, wash it successively with absolute ethanol and acetone, and finally use ultrasonic peeling at 40 kHz for 30 min to obtain oxidized nanocellulose; among them, the mass ratio of choline chloride to citric acid is 1:2, the concentration of the DES solvent is 30 wt%, and the mass ratio of nanocellulose to the DES solvent is 1:80.

[0033] 4. Disperse the oxidized nanocellulose in a phosphate buffer solution with a pH of 9, ultrasonically treat it at a power of 800 W for 30 min, add carbodiimide and N-hydroxysuccinimide, and stir and react in a water bath at 50 °C for 2 h to obtain an activated nanocellulose dispersion; among them, the mass ratio of oxidized nanocellulose to the phosphate buffer solution is 1:200; the total addition amount of carbodiimide and N-hydroxysuccinimide is 16 wt% of the oxidized nanocellulose, and the molar ratio of the two is 1:1.

[0034] 5. Mix hydroxypropionate (Setaqua® 9803) and a 12 wt% sodium dodecyl sulfate solution according to a mass ratio of 1:100, shear it at 2000 r / min for 15 min to form a hydroxypropionate monomer emulsion; under a nitrogen atmosphere, add 1 / 3 of the hydroxypropionate monomer emulsion and an 8 wt% ammonium persulfate solution to the reaction kettle, stir in a water bath at 75 °C for 30 min, and then simultaneously drop the remaining hydroxypropionate monomer emulsion and the activated nanocellulose dispersion into the reaction kettle, and finish dropping within 2 h; after dropping, cool down to 40 °C, adjust the pH to 7.7 with ammonia water, and filter to obtain a self-crosslinking hydroxypropionate-nanocellulose complex; among them, the mass ratio of the hydroxypropionate monomer emulsion, the ammonium persulfate solution and the activated nanocellulose dispersion is 3:1:2.

[0035] 6. By mass, take 35 parts of modified aqueous polyurethane dispersion; 35 parts of self-crosslinking hydroxypropionate-nanocellulose complex; solvent: propylene glycol monomethyl ether: 4 parts; effect pigment: ZW-7111A aluminum powder: 3 parts; WB aqueous color paste: 20 parts; wetting and leveling agent: BYK-381: 0.2 part; defoaming agent: Tego airex 902W: 0.8 part; thickening agent: BYK-8421: 0.6 part; anti-aging aid: Tinuvin 123: 0.8 part; pH regulator: DMEA: 1.5 parts; deionized water: 25 parts.

[0036] 7. Add the modified aqueous polyurethane dispersion and the self-crosslinking hydroxy propionate-nanocellulose composite into the main cylinder and mix evenly. Stir and react in a 45°C water bath for 2 h. Use ultraviolet-induced grafting to trigger the crosslinking of acrylate double bonds. The crosslinking time is 6 min, with a UV-LED of 395 nm and an irradiance of 80 mW / cm². Finally, let it stand for 24 h in an environment with a relative humidity of 50%.

[0037] 8. Take another auxiliary cylinder, add 90% of the solvent and the effect pigment, stir evenly with a disperser, pour it into the main cylinder, then take the remaining 10% of the solvent to wash the auxiliary cylinder, and pour the cleaning solution into the main cylinder, and stir for 30 min until evenly dispersed.

[0038] 9. Stir and add a wetting and leveling agent, an antifoaming agent, an anti-aging aid, and a thickener into the main cylinder. After 13 min, add the WB aqueous color paste, stir for 30 min, let it stand for 16 h, use a pH regulator to adjust the pH of the system to 8.5, use deionized water to adjust the construction viscosity to 100 s, and finally filter and package with a 200-mesh silk cloth to obtain the aqueous basecoat paint.

[0039] 10. Apply the obtained aqueous basecoat paint to automotive exterior parts.

[0040] Example 3 A preparation method of an aqueous one-component basecoat paint for automotive exterior parts, comprising the following steps: 1. Disperse silicon dioxide in a 5 wt% ethanol solution at a mass ratio of 1:200, perform ultrasonic treatment at 300 W for 30 min, add acetic acid dropwise to adjust the pH to 4.7. Under a nitrogen atmosphere, add a silane coupling agent dropwise, stir and react in an 80°C water bath at 300 r / min for 45 min. After stirring, centrifuge at 600 r / min for 15 min. Wash the obtained precipitate successively with absolute ethanol and deionized water, and vacuum dry at 60°C for 3 h to obtain amino-functionalized silicon dioxide; wherein, the addition amount of the silane coupling agent is 3 wt% of silicon dioxide.

[0041] 2. Add polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate into a reaction kettle at a mass ratio of 30:2:3 and a water-to-material ratio of 100:35, add water for emulsification, and stir and react at 80°C for 3 h; add dimethylolpropionic acid, and continue to stir and react at 60°C for 2 h to obtain a prepolymer containing a -Si-O- structure; cool the prepolymer to 40°C, add triethylamine and amino-functionalized silicon dioxide, adjust the pH of the system to 8.0 with ammonia water, and stir and react at a shear rate of 40 m / s for 30 min; after the reaction is completed, perform vacuum desolvation at 80°C for 1 h to obtain the modified aqueous polyurethane dispersion; wherein, the addition amounts of dimethylolpropionic acid, triethylamine, and amino-functionalized silicon dioxide are 3 wt%, 8 wt%, and 5 wt% of the total mass of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate, respectively.

[0042] 3. Mix choline chloride and citric acid and dissolve them in deionized water to obtain a DES solvent; place nanocellulose in a vacuum drying oven, hot press it at 1.5 MPa and 60 °C for 15 min, immerse it in the DES solvent, add 0.5 wt% of nitrogen-doped titanium dioxide, irradiate it with visible light with a wavelength of 420 nm, and simultaneously introduce oxygen at a flow rate of 0.1 L / min, and react at 60 °C for 4 h; after the reaction, centrifuge the system at a speed of 1000 r / min for 10 min, separate the precipitate, wash it successively with absolute ethanol and acetone, and finally use ultrasonic peeling at 40 kHz for 30 min to obtain oxidized nanocellulose; among them, the mass ratio of choline chloride to citric acid is 1:2, the concentration of the DES solvent is 30 wt%, and the mass ratio of nanocellulose to the DES solvent is 1:80.

[0043] 4. Disperse oxidized nanocellulose into a phosphate buffer solution with a pH of 9, ultrasonically treat it at a power of 800 W for 30 min, add carbodiimide and N-hydroxysuccinimide, and stir and react in a water bath at 50 °C for 2 h to obtain an activated nanocellulose dispersion; among them, the mass ratio of oxidized nanocellulose to the phosphate buffer solution is 1:200; the total addition amount of carbodiimide and N-hydroxysuccinimide is 18 wt% of oxidized nanocellulose, and the molar ratio of the two is 1:1.

[0044] 5. Mix hydroxypropionate (Wantipro 0678) and a 12 wt% sodium dodecyl sulfate solution according to a mass ratio of 1:100, shear it at 2000 r / min for 15 min to form a hydroxypropionate monomer emulsion; under a nitrogen atmosphere, add 1 / 3 of the hydroxypropionate monomer emulsion and an 8 wt% ammonium persulfate solution to the reaction kettle, stir in a water bath at 75 °C for 30 min, and then synchronously drop the remaining hydroxypropionate monomer emulsion and the activated nanocellulose dispersion into the reaction kettle, and finish dropping within 2 h; after dropping, cool down to 40 °C, adjust the pH to 8.0 with ammonia water, and filter to obtain a self-crosslinking hydroxypropionate-nanocellulose complex; among them, the mass ratio of the hydroxypropionate monomer emulsion, the ammonium persulfate solution and the activated nanocellulose dispersion is 3:1:2.

[0045] 6. By mass, take 30 parts of modified aqueous polyurethane dispersion; 40 parts of self-crosslinking hydroxypropionate-nanocellulose complex; solvent: dipropylene glycol methyl ether: 5 parts; effect pigment: NH97724B pearlescent powder: 4 parts; WB aqueous color paste: 30 parts; wetting and leveling agent: BYK-347: 0.5 part; defoaming agent: Tego foamex 810: 1 part; thickening agent: THIXATROL 5020W: 1 part; anti-aging aid: Tinuvin 400: 1 part; pH regulator: AMP-95: 2.5 parts; deionized water: 32 parts.

[0046] 7. Add the modified aqueous polyurethane dispersion and the self-crosslinking hydroxy propionate-nanocellulose complex to the main cylinder and mix evenly. Stir and react in a 45 °C water bath for 2 h. Use ultraviolet-induced grafting to trigger the crosslinking of acrylate double bonds. The crosslinking time is 8 min, with a UV-LED of 395 nm and an irradiance of 80 mW / cm². Finally, let it stand for 24 h in an environment with a relative humidity of 50%.

[0047] 8. Take another auxiliary cylinder, add 90% of the solvent and the effect pigment, stir evenly with a disperser, pour it into the main cylinder, then take the remaining 10% of the solvent to clean the auxiliary cylinder, and pour the cleaning solution into the main cylinder and stir for 30 min until evenly dispersed.

[0048] 9. Stir and add a wetting and leveling agent, an antifoaming agent, an anti-aging aid, and a thickener into the main cylinder. After 15 min, add the WB aqueous color paste and stir for 30 min. Let it stand for 16 h. Use a pH regulator to adjust the pH of the system to 8.8. Use deionized water to adjust the construction viscosity to 120 s. Finally, filter and package with a 200-mesh silk cloth to obtain the aqueous basecoat.

[0049] 10. Apply the obtained aqueous basecoat to automotive exterior parts.

[0050] Example 4 An aqueous one-component basecoat for automotive exterior parts, which is different from Example 1 in that some of the raw materials used in step 6 are different, specifically as follows: 6. By mass, take 50 parts of the modified aqueous polyurethane dispersion; 20 parts of the self-crosslinking hydroxy propionate-nanocellulose complex; Solvent: Diethylene glycol monobutyl ether: 3 parts; Effect pigment: NH97724B pearlescent powder: 2 parts; WB aqueous color paste: 15 parts; Wetting and leveling agent: PW-336: 0.05 part; Antifoaming agent: Foamster2400: 0.5 part; Thickener: RHEOLATE 299: 0.2 part; Anti-aging aid: Tinuvin 400: 0.2 part; pH regulator: AMP-95: 0.5 part; Deionized water: 15 parts.

[0051] Example 5 An aqueous one-component basecoat for automotive exterior parts, which is different from Example 1 in that some of the raw materials used in step 6 are different, specifically as follows: 6. By mass fraction, take 50 parts of modified aqueous polyurethane dispersion; 20 parts of self-crosslinking hydroxypropionate-nanocellulose complex; Solvent: dipropylene glycol butyl ether: 3 parts; Effect pigment: NH97724B pearlescent powder: 2 parts; WB aqueous color paste: 15 parts; Wetting and leveling agent: BYK345: 0.05 part; Defoaming agent: Surfynol 104E: 0.5 part; Thickening agent: THIXATROL 5020W: 0.1 part, RHEOLATE 299: 0.1 part; Anti-aging aid: Tinuvin 400: 0.2 part; pH regulator: AMP-95: 0.5 part; Deionized water: 15 parts.

[0052] Example 6. A one-component aqueous basecoat for automotive exterior parts, which is different from Example 1 in that some raw materials used in Step 6 are different, specifically as follows: 6. By mass fraction, take 50 parts of modified aqueous polyurethane dispersion; 20 parts of self-crosslinking hydroxypropionate-nanocellulose complex; Solvent: butanol: 1 part, isopropanol: 1 part, isooctanol: 1 part; Effect pigment: NH97724B pearlescent powder: 1 part, ZW-7111A aluminum powder: 1 part; WB aqueous color paste: 15 parts; Wetting and leveling agent: Surfynol 440: 0.02 part, TEGO Twin 4100: 0.03 part; Defoaming agent: Tego airex 902W: 0.2 part, Surfynol 104E: 0.3 part; Thickening agent: THIXATROL5020W: 0.1 part, RHEOLATE 299: 0.1 part; Anti-aging aid: Tinuvin 400: 0.2 part; pH regulator: AMP-95: 0.5 part; Deionized water: 15 parts.

[0053] Comparative Example 1. A one-component aqueous basecoat for automotive exterior parts, which is different from Example 1 in that the activation step of oxidized nanocellulose is removed, specifically as follows: 1. Disperse silicon dioxide in a 5wt% ethanol solution at a mass ratio of 1:200, perform ultrasonic treatment at 300W for 30 min, dropwise add acetic acid to adjust the pH to 4.3, under a nitrogen atmosphere, dropwise add a silane coupling agent, react at 80°C in a water bath with stirring at 300 r / min for 45 min, after the stirring ends, centrifuge at 600 r / min for 15 min, wash the obtained precipitate successively with absolute ethanol and deionized water, and dry it in vacuum at 60°C for 3 h to obtain amino-functionalized silicon dioxide; wherein, the addition amount of the silane coupling agent is 3wt% of the silicon dioxide.

[0054] 2. Add polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate to a reaction kettle according to a mass ratio of 10:2:3 and a water-to-material ratio of 100:35, add water for emulsification, and stir and react at 80 °C for 3 h; add dimethylolpropionic acid and continue to stir and react at 60 °C for 2 h to obtain a prepolymer containing -Si-O- structure; cool the prepolymer to 40 °C, add triethylamine and aminated silica, adjust the pH of the system to 7.5 with ammonia water, and stir and react at a shear rate of 40 m / s for 30 min; after the reaction is completed, carry out vacuum desolvation at 80 °C for 1 h to obtain a modified aqueous polyurethane dispersion; among them, the addition amounts of dimethylolpropionic acid, triethylamine, and aminated silica are 3 wt%, 8 wt%, and 3 wt% of the total mass of polycarbonate diol, polydimethylsiloxane, and isophorone diisocyanate, respectively.

[0055] 3. Mix choline chloride and citric acid and dissolve them in deionized water to obtain a DES solvent; place nanocellulose in a vacuum drying oven, hot press at 1.5 MPa and 60 °C for 15 min, immerse it in the DES solvent, add 0.5 wt% of nitrogen-doped titanium dioxide, irradiate with visible light with a wavelength of 420 nm, and simultaneously introduce oxygen at a flow rate of 0.1 L / min and react at 60 °C for 4 h; after the reaction is completed, centrifuge the system at a rotation speed of 1000 r / min for 10 min to separate the precipitate, wash the precipitate with anhydrous ethanol and acetone in sequence, and finally use ultrasonic peeling at 40 kHz for 30 min to obtain oxidized nanocellulose; disperse the oxidized nanocellulose in a phosphate buffer solution with a pH of 9 and perform ultrasonic treatment at a power of 800 W for 30 min to obtain an oxidized nanocellulose dispersion; among them, the mass ratio of choline chloride to citric acid is 1:2, the concentration of the DES solvent is 30 wt%, the mass ratio of nanocellulose to the DES solvent is 1:80, and the mass ratio of oxidized nanocellulose to the phosphate buffer solution is 1:200.

[0056] 4. Mix hydroxypropionate (MACRYNAL VSM 6299W / 42WA) and a 12 wt% sodium dodecyl sulfate solution according to a mass ratio of 1:100, shear at 2000 r / min for 15 min to form a hydroxypropionate monomer emulsion; under a nitrogen atmosphere, add 1 / 3 of the hydroxypropionate monomer emulsion and an 8 wt% ammonium persulfate solution to a reaction kettle, stir in a water bath at 75 °C for 30 min, and then synchronously drop the remaining hydroxypropionate monomer emulsion and the oxidized nanocellulose dispersion into the reaction kettle and complete the dropping within 2 h; after the dropping is completed, cool to 40 °C, adjust the pH to 7.5 with ammonia water, and filter to remove gelled particles to obtain a self-crosslinking hydroxypropionate-nanocellulose complex; among them, the mass ratio of the hydroxypropionate monomer emulsion, the ammonium persulfate solution, and the oxidized nanocellulose dispersion is 3:1:2.

[0057] 5. By mass, take 50 parts of modified aqueous polyurethane dispersion; self-crosslinking hydroxypropionate-nanocellulose complex: 20 parts; solvent: ethylene glycol monobutyl ether: 3 parts; effect pigment: NH97724B pearlescent powder: 2 parts; WB aqueous color paste: 15 parts; wetting and leveling agent: Surfynol 440: 0.05 part; defoaming agent: BYK-024: 0.5 part; thickening agent: Rheovis AS1130: 0.2 part; anti-aging aid: Tinuvin 400: 0.2 part; pH regulator: AMP-95: 0.5 part; deionized water: 15 parts.

[0058] 6. Add the modified aqueous polyurethane dispersion and the self-crosslinking hydroxypropionate-nanocellulose complex to the main cylinder and mix evenly. Stir and react in a 45°C water bath for 2 h. Use ultraviolet-induced grafting to trigger the crosslinking of acrylate double bonds. The crosslinking time is 5 min, UV-LED 395 nm, irradiance 80 mW / cm². Finally, let it stand for 24 h in an environment with a relative humidity of 50%.

[0059] 7. Take another auxiliary cylinder, add 90% of the solvent and the effect pigment, stir evenly with a disperser, pour it into the main cylinder, then take the remaining 10% of the solvent to clean the auxiliary cylinder, and pour the cleaning liquid into the main cylinder and stir for 30 min until evenly dispersed.

[0060] 8. Stir and add the wetting and leveling agent, defoaming agent, anti-aging aid and thickening agent into the main cylinder. After 10 min, add the aqueous color paste, stir for 30 min, let it stand for 16 h, use the pH regulator to adjust the pH of the system to 8.0, use deionized water to adjust the construction viscosity to 80 s, and finally filter and package with a 200-mesh silk cloth to obtain the aqueous primer paint.

[0061] 9. Apply the obtained aqueous primer paint to automotive exterior parts.

[0062] Comparative Example 2 An aqueous one-component primer paint for automotive exterior parts, which is different from Example 1 in that: purchase any brand of aqueous primer paint product on the market and apply it to automotive exterior parts.

[0063] The film composite performance indicators need to meet the technical requirements of the painting line, as shown in Table 1:

[0064] The test results after applying the aqueous one-component primer paints obtained in each example and comparative example to automotive exterior parts are shown in Table 2: Table 2. The test results of each example compared with the comparative example are as follows:

[0065] The construction process parameters are as follows: flash drying for 15 - 20 minutes, baking at 70 - 90 °C for 20 minutes, and the film thickness is 15 - 20 μm. The exterior trim parts are plastics sold on the market, including: polypropylene (PP), ABS (acrylonitrile - butadiene - styrene copolymer), polycarbonate (PC), PC / ABS alloy, and glass fiber reinforced plastic (GFRP).

[0066] The results show that the modified waterborne polyurethane and the self - crosslinking hydroxypropionate - nanocellulose complex play a crucial role in the stone - chip resistance and drainage performance of the waterborne basecoat system, and both have a strong self - crosslinking tendency. The self - crosslinking hydroxypropionate has a relatively large molecular weight, which can enable the effect pigments to be strongly and directionally attached, so as to meet the requirements for solid - color paints not only in each painting production line, but also provide important support for metallic paints with richer colors.

[0067] The products produced by the present invention are universal and can be used in all exterior trim parts with primer. They have excellent water resistance, good appearance, good mechanical properties, excellent comprehensive physical and chemical properties, and low cost.

[0068] The specific embodiments of the present invention described above do not constitute a limitation on 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 within the protection scope of the claims of the present invention.

Claims

1. A water-based one-component basecoat for automotive exterior parts, characterized in that: The invention comprises the following components by weight: 30 to 50 parts of modified waterborne polyurethane dispersion; 20 to 40 parts of self-crosslinked hydroxypropionate-nanocellulose composite; Solvent: 3~5 parts; Effect pigment: 2~4 parts; Water-based color paste: 15~30 parts; Wetting and leveling agent: 0.05~0.5 parts; Defoaming agent: 0.5~1.0 part; Thickener: 0.2~1.0 parts; anti-aging agent: 0.2~1.0 parts; pH adjuster: 0.5~2.5 parts; deionized water: 15~32 parts.

2. The water-based one-component basecoat for automobile exterior parts according to claim 1, characterized in that: The preparation method of the modified waterborne polyurethane dispersion comprises the following steps: adding polycarbonate diol, polydimethylsiloxane and isophorone diisocyanate into a reaction kettle, adding water for emulsification, stirring and reacting at 80° C. for 3 hours, adding dimethylol propionic acid, stirring and reacting at 60° C. for 2 hours, and obtaining a prepolymer containing an -Si-O- structure; cooling the prepolymer to 40° C., adding triethylamine and amino silicon dioxide, adjusting the pH of the system to 7.5-8.0, and performing vacuum desolventizing after the stirring reaction is completed, and obtaining the modified waterborne polyurethane dispersion.

3. The water-based one-component basecoat for automobile exterior parts according to claim 2, characterized in that: The preparation method of the amino silica is as follows: dispersing silica in a 5wt% ethanol solution, ultrasonically treating for 30 minutes, adjusting the pH of the system to 4.3-4.7, adding a silane coupling agent dropwise under a nitrogen atmosphere, stirring in a water bath at 80°C for 45 minutes, obtaining a precipitate after centrifugation, washing with anhydrous ethanol and deionized water in sequence, and vacuum drying at 60°C for 3 hours to obtain the amino silica.

4. The water-based one-component basecoat for automobile exterior parts according to claim 2, characterized in that: The mass ratio of the polycarbonate diol, polydimethylsiloxane and isophorone diisocyanate is 10-30:2:3, and the added amounts of dimethylol propionic acid, triethylamine and amino silica are 3wt%, 8wt% and 3wt%-5wt% of the total mass of the polycarbonate diol, polydimethylsiloxane and isophorone diisocyanate, respectively.

5. The water-based one-component basecoat for automobile exterior parts according to claim 1, characterized in that: The preparation method of the self-crosslinked hydroxypropionate-nanocellulose complex is as follows: hydroxypropionate and 12wt% sodium dodecyl sulfate solution are shear-mixed to form a hydroxypropionate monomer emulsion; under a nitrogen atmosphere, 1 / 3 of the hydroxypropionate monomer emulsion and 8wt% ammonium persulfate solution are added to a reactor, and after stirring in a 75°C water bath for 30 minutes, the remaining hydroxypropionate monomer emulsion and the activated nanocellulose dispersion are simultaneously dripped into the reactor, and after the dripping is completed, the temperature is lowered to 40°C, the pH is adjusted to 7.5-8.0, and the self-crosslinked hydroxypropionate-nanocellulose complex is obtained by filtering.

6. The water-based one-component basecoat for automobile exterior parts according to claim 5, characterized in that: The preparation method of the activated nanocellulose dispersion is as follows: dispersing oxidized nanocellulose in phosphate buffer, ultrasonically treating at 800W power for 30 minutes, adding carbodiimide and hydroxysuccinimide, stirring in a 50°C water bath for 2 hours, and obtaining the activated nanocellulose dispersion.

7. The water-based one-component basecoat for automobile exterior parts according to claim 6, characterized in that: The preparation method of the oxidized nanocellulose is as follows: choline chloride and citric acid are mixed and dissolved in deionized water to obtain a DES solvent; the nanocellulose is hot-pressed at 1.5 MPa and 60° C. for 15 minutes, then immersed in the DES solvent, 0.5 wt % of nitrogen-doped titanium dioxide is added, visible light with a wavelength of 420 nm is used for irradiation, oxygen is introduced at a flow rate of 0.1 L / min, and the reaction is carried out at 60° C. for 4 hours. After the reaction is completed, the precipitate is separated by centrifugation, and the precipitate is washed with anhydrous ethanol and acetone in sequence, and the oxidized nanocellulose is obtained after ultrasonic stripping.

8. The water-based one-component basecoat for automobile exterior parts according to claim 5, characterized in that: The hydroxypropionate is any one or more of MACRYNAL VSM 6299W / 42WA of Allnex, Setaqua® 9803 or Wantipro0678 of Wanhua Chemical.

9. The water-based one-component basecoat for automobile exterior parts according to claim 1, characterized in that: The solvent is any one or more of ethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol methyl ether, diethylene glycol monobutyl ether, dipropylene glycol butyl ether, butanol, isopropanol or isooctyl alcohol; the effect pigment is any one or more of NH97724B pearlescent powder of Ouke Chemical or ZW-7111A aluminum powder of Shandong Yinjian; the water-based color paste is WB water-based color paste; the wetting and leveling agent is any one or more of Surfynol 440, BYK-381, BYK-347, BYK-345, PW-336 or TEGO 4100; the defoamer is any one or more of BYK-024, Tego airex 902W, Tego foamex 810, Foamster 2400 or Surfynol 104E; the thickener is Rheovis Any one or more of AS1130, BYK-8421, THIXATROL 5020W, and RHEOLATE299; the anti-aging agent is any one or more of Tinuvin 400 or Tinuvin 123; and the pH regulator is AMP-95 or DMEA.

10. The method for preparing a water-based one-component basecoat for automobile exterior parts according to claim 1, characterized in that: The following steps are involved: S11, adding the modified waterborne polyurethane dispersion and the self-crosslinked hydroxypropionate-nanocellulose composite into the main tank and mixing them evenly, stirring and reacting in a water bath at 45°C for 2 hours, using UV-induced grafting to trigger the crosslinking of the double bonds of the acrylate, and finally standing for 24 hours in an environment with a relative humidity of 50%; S12, take another auxiliary tank, add 90% of the solvent and effect pigment, use a disperser to stir evenly, pour into the main tank, then take the remaining 10% of the solvent to clean the auxiliary tank, pour the cleaning liquid into the main tank, and stir for 30 minutes until it is evenly dispersed; S13. Stir and add wetting and leveling agent, defoaming agent, anti-aging additive and thickener into the main cylinder. After 10-15 minutes, add water-based color paste, stir for 30 minutes, let stand for 16 hours, use pH regulator to adjust the pH of the system to 8.0-8.8, use deionized water to adjust the construction viscosity to 80-120s, and finally filter and package with 200-mesh silk cloth to obtain water-based base paint.

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