Environment-friendly impact-resistant water-based automobile coating and preparation method thereof

Abstract

The invention relates to the technical field of automobile coatings, and discloses an environment-friendly impact-resistant water-based automobile coating and a preparation method thereof.The environment-friendly impact-resistant water-based automobile coating is prepared by taking 4-carboxyphenylboronic acid, diethanol amine and isosorbide as raw materials to initiate polymerization with itaconic acid-based unsaturated polyester, acrylic acid and the like; dispersing with light calcium carbonate and auxiliaries to obtain the environment-friendly impact-resistant water-based automobile coating. The isosorbide is used as an ideal bio-based monomer, has a rigid spiral ring structure of a V-shaped bridge ring, and can better disperse and absorb energy when being impacted, reduce stress concentration during impact and improve the impact resistance of a coating film; a cyclic borate structure in the environment-friendly alkenyl borate monomer can form a layer of compact protective film on the metal surface, so that the metal is effectively prevented from reacting with substances such as acid and alkali in the external environment; the prepared water-based paint is low in VOC content, free of organic solvent residues and good in industrial application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of automobile coatings, in particular to an environmentally friendly impact-resistant water-based automobile coating and a preparation method thereof. Background Art

[0002] With the rapid development of society and the leap forward of science and technology, the relationship between cars and humans has become increasingly closely related. However, when a car is driving, its wheel arches, floor panels, lower longitudinal beams, fenders and other parts are easily impacted by sand and gravel, which can easily damage these parts and cause corrosion, thus bringing hidden dangers to driving. Paint, as the outer coat of a car, plays a vital role in the use of the car. At present, domestic and foreign automotive special coatings are generally based on solvent-based resins. These systems contain a large amount of volatile organic compounds (VOCs), which not only pollute the environment, but also are a serious waste of resources. Water-based coatings use water as a solvent and have the advantages of low VOC emissions, environmental protection, and easy construction, which meet the requirements of modern automobile manufacturing industry for environmental protection and sustainable development. However, water-based coatings still face some challenges in terms of impact performance, weather resistance, and corrosion resistance.

[0003] The car body is coated with a layer of paint film, which plays a protective and decorative role. However, during use, the car body often contacts and collides with hard objects. The car is exposed to various harsh environments for a long time, and the car surface is easily corroded, resulting in reduced glossiness. Patent No. CN100554352C discloses a method for preparing scratch-resistant nano water-based car coatings, which uses polyurethane as the main film-forming resin, introduces nano powders, including silicon dioxide, titanium dioxide, etc., and uses a mechanical and physical dispersion method to prepare nano water-based car coatings under the action of a crosslinking agent. However, the nano powders are easy to agglomerate and are difficult to disperse stably for a long time. , which ultimately affects the apparent quality of the car, and the impact resistance of the car coating is not strong; Patent No. CN105368294B discloses a high-gloss impact-resistant environmentally friendly water-based car coating and a preparation method thereof, which is prepared by mechanically blending modified water-based polyurethane, nano-amino POSS, polytetrafluoroethylene micropowder wax, deionized water, pigments and fillers, additives, and cross-linking agents in certain weight portions. However, when the water-based coating prepared by this method is sprayed on the surface of a car, the leveling property is poor, which easily causes a poor appearance, the mechanical properties need to be improved, and the problem of easy corrosion of the car surface is not solved.

[0004] After being cured, the unsaturated polyester resin has high hardness and good wear resistance, while the acrylic resin has good flexibility and impact resistance. In the prior art, the two resins have not been combined for use in the field of automotive coatings. The present invention aims to use renewable isosorbide as a raw material and introduce a borate structure to synthesize an environmentally friendly olefin borate monomer, which is grafted and polymerized with an environmentally friendly itaconic acid-based unsaturated polyester, and the advantages of the unsaturated polyester and the acrylic resin are combined to make the prepared water-based coating have good impact resistance and corrosion resistance, be green and environmentally friendly, and have no VOC emissions. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide an environmentally friendly impact-resistant water-based automotive coating and a preparation method thereof. The water-based coating has strong impact resistance and corrosion resistance, is green and environmentally friendly, and is suitable for industrial production.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing an environmentally friendly impact-resistant water-based automotive coating comprises the following steps:

[0008] Step (1), under a nitrogen atmosphere, add itaconic acid-based unsaturated polyester and deionized water into a four-necked flask, stir evenly, heat to 75-90° C., dropwise add acrylic acid, methyl methacrylate, environmentally friendly alkenyl borate monomer and dibenzoyl peroxide, continue to react for 3-8 hours, cool to 45-60° C., add triethylamine for neutralization reaction, and obtain acrylic acid-grafted unsaturated polyester.

[0009] Step (2), adding acrylic acid grafted unsaturated polyester and light calcium carbonate into a reaction flask, mixing evenly, adding dispersant, leveling agent and defoaming agent, and dispersing evenly with a high-speed disperser to obtain an environmentally friendly impact-resistant water-based automotive coating.

[0010] Preferably, in step (1), the mass ratio of itaconic acid-based unsaturated polyester, acrylic acid, methyl methacrylate, environmentally friendly alkenyl borate monomer, and dibenzoyl peroxide is 100:5-8:15-25:2-10:1.5-3.

[0011] Preferably, in step (2), the mass ratio of acrylic acid grafted unsaturated polyester to light calcium carbonate is 100:25-40.

[0012] Preferably, the method for preparing the environmentally friendly alkenyl borate monomer in step (1) comprises the following steps:

[0013] Step S1, under a nitrogen atmosphere, add 4-carboxyphenylboric acid and N,N-dimethylformamide to a reaction flask, stir evenly, add diethanolamine, stir to react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, to obtain borate benzoic acid monomer.

[0014] Step S2, under a nitrogen atmosphere, add isosorbide and xylene to a reaction flask, stir evenly, add borate benzoic acid monomer and p-toluenesulfonic acid, react at 120-135° C. for 8-16 hours, cool, extract with ethyl acetate and deionized water, and recrystallize with methanol to obtain an isosorbide borate monomer.

[0015] Step S3: under nitrogen atmosphere, add isosorbide borate monomer and N-methylpyrrolidone to the reaction flask, stir evenly, add allyl isocyanate, stir to react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, and obtain environmentally friendly alkenyl borate monomer. The preparation reaction process is as follows:

[0016]

[0017] Preferably, in step S1, the molar ratio of 4-carboxyphenylboronic acid to diethanolamine is 1:1.05-1.2.

[0018] Preferably, in step S1, the reaction temperature is 40-60° C. and the reaction time is 1-3 h.

[0019] Preferably, in step S2, the molar ratio of isosorbide, borate benzoic acid monomer, and p-toluenesulfonic acid is 1:2.1-2.4:0.3-0.5.

[0020] Preferably, in step S3, the molar ratio of the isosorbide borate monomer to the allyl isocyanate is 1:2.2-2.5.

[0021] Preferably, in step S3, the reaction temperature is 50-70° C. and the reaction time is 2-5 h.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The invention firstly reacts 4-carboxyphenylboronic acid with diethanolamine, then dehydrates and esterifies with degradable isosorbide, then reacts with allyl isocyanate to obtain an environmentally friendly alkenyl borate monomer, then initiates polymerization with itaconic acid-based unsaturated polyester and acrylic monomer to obtain acrylic acid-grafted unsaturated polyester, and finally disperses evenly with light calcium carbonate and an additive to obtain an environmentally friendly impact-resistant water-based automotive coating.

[0024] Isosorbide is a biomass material made from plant resources such as corn. The raw material source is abundant and renewable, which helps to reduce dependence on fossil energy, reduce carbon emissions, and is in line with the concepts of environmental protection and sustainable development. As an ideal bio-based monomer, isosorbide has a rigid spirocyclic structure with a V-shaped bridge ring and large steric hindrance. Its twisted and non-planar structure can prevent the close stacking of polymer macromolecular chains and increase the free volume of the coating. The olefin group in its structure can initiate polymerization with monomers such as acrylic acid to form a dense three-dimensional cross-linked network structure, improve compatibility with unsaturated polyesters, increase the elasticity and toughness of the coating, and better disperse and absorb energy when impacted, reduce stress concentration during impact, and effectively improve the impact resistance of the coating.

[0025] The cyclic borate structure in the environmentally friendly alkenyl borate monomer can increase the steric hindrance around the boron atom, making it difficult for water molecules or other corrosive substances to approach the empty orbital of the boron atom hybridization, and can form a dense protective film on the metal surface, which can seal the tiny holes and cracks on the metal surface of the car, thereby preventing oxygen and moisture from entering the metal, effectively preventing the metal from reacting with acids, alkalis and other substances in the external environment, not only reducing the corrosion rate of the metal, but also improving the surface quality of the metal; even in a high temperature, humid and corrosive environment, the cyclic borate can maintain a long service life, and is not prone to hydrolysis reaction leading to performance degradation. The water-based paint prepared by the present invention has a low VOC content and no organic solvent residue, meets the environmental protection requirements of automotive coatings, and has a good industrial application prospect. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the raw materials and reagents used in this application are commercially available or can be prepared by known methods.

[0028] The preparation of itaconic acid-based unsaturated polyester is carried out with reference to "Synthesis and Performance Study of Unsaturated Polyester Based on Itaconic Acid": add itaconic acid and 1,4-butanediol in a molar mass ratio of 1:2, 1% of the total mass of the catalyst p-toluenesulfonic acid, and 0.5% of the total mass of the inhibitor p-hydroxyanisole into a reaction flask equipped with a water separator, a reflux condenser and a thermometer, raise the temperature to 150°C while stirring under nitrogen protection, and react at a constant temperature with stirring until the acid value remains basically unchanged (about 2h), then add 5% of the total mass of dibutyltin dilaurate into a round-bottom flask, perform vacuum decompression, control the vacuum degree to 0.09-0.1MPa, and react at a constant temperature of 150°C until the acid value remains basically unchanged (about 4h), cool, and obtain itaconic acid-based unsaturated polyester.

[0029] 4-Carboxyphenylboronic acid, CAS number is 14047-29-1.

[0030] Diethanolamine, CAS number is 111-42-2.

[0031] Isosorbide, CAS number is 652-67-5.

[0032] Allyl isocyanate, CAS number is 1476-23-9.

[0033] Example 1

[0034] (1) Under a nitrogen atmosphere, 35 mmol of 4-carboxyphenylboronic acid and 420 mL of N,N-dimethylformamide were added to a reaction flask, stirred evenly, and then 40.6 mmol of diethanolamine was added. The mixture was reacted at 50° C. for 2 h, and the mixture was recrystallized from petroleum ether, filtered and washed to obtain a borate benzoic acid monomer.

[0035] (2) Under a nitrogen atmosphere, 42 mmol of isosorbide and 630 mL of xylene were added to a reaction flask. After stirring, 94.5 mmol of borate benzoic acid monomer and 16.8 mmol of p-toluenesulfonic acid were added. The mixture was reacted at 125° C. for 12 h. The mixture was cooled, extracted with ethyl acetate and deionized water, and recrystallized with methanol to obtain an isosorbide borate monomer.

[0036] (3) Under nitrogen atmosphere, 28 mmol of isosorbide borate monomer and 700 mL of N-methylpyrrolidone were added to a reaction flask, and after stirring, 65.8 mmol of allyl isocyanate was added, and the mixture was reacted at 60 °C for 4 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an environmentally friendly alkenyl borate monomer.

[0037] (4) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask, stirred evenly, and then heated to 85° C., 6 g of acrylic acid, 20 g of methyl methacrylate, 2 g of environmentally friendly alkenyl borate monomer and 2 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 5 h. The temperature was lowered to 50° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0038] (5) Add 100 g of acrylic acid grafted unsaturated polyester and 25 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoaming agent BYK-066N. After being dispersed well by a high-speed disperser, an environmentally friendly impact-resistant water-based automotive coating is obtained.

[0039] Example 2

[0040] (1) Under a nitrogen atmosphere, 150 mmol of 4-carboxyphenylboronic acid and 1200 mL of N,N-dimethylformamide were added to a reaction flask, stirred evenly, and then 157.5 mmol of diethanolamine was added. The mixture was reacted at 60° C. for 1 h, recrystallized from petroleum ether, filtered and washed to obtain a borate benzoic acid monomer.

[0041] (2) Under a nitrogen atmosphere, 135 mmol of isosorbide and 1620 mL of xylene were added to a reaction flask. After stirring, 283.5 mmol of borate benzoic acid monomer and 40.5 mmol of p-toluenesulfonic acid were added. The mixture was reacted at 135° C. for 8 h. The mixture was cooled, extracted with ethyl acetate and deionized water, and recrystallized with methanol to obtain an isosorbide borate monomer.

[0042] (3) Under nitrogen atmosphere, 120 mmol of isosorbide borate monomer and 2400 mL of N-methylpyrrolidone were added to a reaction flask, and after stirring, 264 mmol of allyl isocyanate was added, and the mixture was reacted at 70 °C for 2 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an environmentally friendly alkenyl borate monomer.

[0043] (4) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask, stirred evenly, and then heated to 90° C., 5 g of acrylic acid, 15 g of methyl methacrylate, 4 g of environmentally friendly alkenyl borate monomer and 1.5 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 3 h. The temperature was lowered to 60° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0044] (5) Add 100 g of acrylic acid grafted unsaturated polyester and 28 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoaming agent BYK-066N. After being dispersed well by a high-speed disperser, an environmentally friendly impact-resistant water-based automotive coating is obtained.

[0045] Example 3

[0046] (1) Under a nitrogen atmosphere, 60 mmol of 4-carboxyphenylboronic acid and 900 mL of N,N-dimethylformamide were added to a reaction flask, and after stirring, 72 mmol of diethanolamine was added, and the mixture was reacted at 40° C. for 3 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain a borate benzoic acid monomer.

[0047] (2) Under a nitrogen atmosphere, 55 mmol of isosorbide and 1100 mL of xylene were added to a reaction flask. After stirring, 132 mmol of borate benzoic acid monomer and 27.5 mmol of p-toluenesulfonic acid were added. The mixture was reacted at 120° C. for 16 h. The mixture was cooled, extracted with ethyl acetate and deionized water, and recrystallized with methanol to obtain an isosorbide borate monomer.

[0048] (3) Under a nitrogen atmosphere, 45 mmol of isosorbide borate monomer and 1350 mL of N-methylpyrrolidone were added to a reaction flask. After stirring, 112.5 mmol of allyl isocyanate was added and the mixture was reacted at 50 °C for 5 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an environmentally friendly alkenyl borate monomer.

[0049] (4) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask, stirred evenly, and then heated to 75° C., 8 g of acrylic acid, 25 g of methyl methacrylate, 6 g of environmentally friendly alkenyl borate monomer and 3 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 8 h. The temperature was lowered to 45° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0050] (5) Add 100 g of acrylic acid grafted unsaturated polyester and 32 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoaming agent BYK-066N. After being dispersed well by a high-speed disperser, an environmentally friendly impact-resistant water-based automotive coating is obtained.

[0051] Example 4

[0052] (1) Under a nitrogen atmosphere, 20 mmol of 4-carboxyphenylboronic acid and 250 mL of N,N-dimethylformamide were added to a reaction flask, stirred evenly, and then 23.6 mmol of diethanolamine was added. The mixture was reacted at 55° C. for 3 h, and then recrystallized from petroleum ether, filtered and washed to obtain a borate benzoic acid monomer.

[0053] (2) Under a nitrogen atmosphere, 18 mmol of isosorbide and 280 mL of xylene were added to a reaction flask. After stirring, 40.5 mmol of borate benzoic acid monomer and 6.3 mmol of p-toluenesulfonic acid were added. The mixture was reacted at 130° C. for 15 h. The mixture was cooled, extracted with ethyl acetate and deionized water, and recrystallized with methanol to obtain an isosorbide borate monomer.

[0054] (3) Under nitrogen atmosphere, 15 mmol of isosorbide borate monomer and 360 mL of N-methylpyrrolidone were added to a reaction flask. After stirring, 36 mmol of allyl isocyanate was added and the mixture was reacted at 65 °C for 4 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an environmentally friendly alkenyl borate monomer.

[0055] (4) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask. After stirring evenly, the temperature was raised to 80° C., 6 g of acrylic acid, 22 g of methyl methacrylate, 8 g of environmentally friendly alkenyl borate monomer and 2.5 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 7 h. The temperature was lowered to 55° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0056] (5) Add 100 g of acrylic acid grafted unsaturated polyester and 36 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoaming agent BYK-066N. After being dispersed well by a high-speed disperser, an environmentally friendly impact-resistant water-based automotive coating is obtained.

[0057] Example 5

[0058] (1) Under a nitrogen atmosphere, 50 mmol of 4-carboxyphenylboronic acid and 650 mL of N,N-dimethylformamide were added to a reaction flask, and after stirring, 59 mmol of diethanolamine was added, and the mixture was reacted at 45° C. for 3 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain a borate benzoic acid monomer.

[0059] (2) Under a nitrogen atmosphere, 42 mmol of isosorbide and 695 mL of xylene were added to a reaction flask. After stirring, 98.7 mmol of borate benzoic acid monomer and 14.7 mmol of p-toluenesulfonic acid were added. The mixture was reacted at 130° C. for 16 h. The mixture was cooled, extracted with ethyl acetate and deionized water, and recrystallized with methanol to obtain an isosorbide borate monomer.

[0060] (3) Under a nitrogen atmosphere, 35 mmol of isosorbide borate monomer and 980 mL of N-methylpyrrolidone were added to a reaction flask. After stirring, 84 mmol of allyl isocyanate was added and the mixture was reacted at 70 °C for 5 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an environmentally friendly alkenyl borate monomer.

[0061] (4) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask. After stirring evenly, the temperature was raised to 90° C., 7 g of acrylic acid, 18 g of methyl methacrylate, 10 g of environmentally friendly alkenyl borate monomer and 2.2 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 8 h. The temperature was lowered to 60° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0062] (5) Add 100 g of acrylic acid grafted unsaturated polyester and 40 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoaming agent BYK-066N. After being dispersed well by a high-speed disperser, an environmentally friendly impact-resistant water-based automotive coating is obtained.

[0063] Comparative Example 1

[0064] (1) Under nitrogen atmosphere, 42 mmol of isosorbide and 630 mL of xylene were added to a reaction flask. After stirring, 94.5 mmol of 4-vinylbenzoic acid (structural formula: CAS No. 1075-49-6) and 16.8 mmol p-toluenesulfonic acid, react at 125°C for 12 hours, cool, extract with ethyl acetate and deionized water, and recrystallize with methanol to obtain isosorbide olefin monomer.

[0065] (2) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask. After stirring, the temperature was raised to 85° C., 6 g of acrylic acid, 20 g of methyl methacrylate, 2 g of isosorbide olefin monomer and 2 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 5 h. The temperature was lowered to 50° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0066] (3) Add 100 g of acrylic acid grafted unsaturated polyester and 25 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoamer BYK-066N, and disperse well with a high-speed disperser to obtain a water-based automotive coating.

[0067] Comparative Example 2

[0068] (1) Under a nitrogen atmosphere, 28 mmol of borate benzoic acid monomer (prepared in Example 1) and 700 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 65.8 mmol of allyl isocyanate was added, and the mixture was reacted at 60° C. for 4 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain an alkenyl borate monomer.

[0069] (2) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask. After stirring, the temperature was raised to 85° C., 6 g of acrylic acid, 20 g of methyl methacrylate, 2 g of olefin borate monomer and 2 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 5 h. The temperature was lowered to 50° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0070] (3) Add 100 g of acrylic acid grafted unsaturated polyester and 25 g of light calcium carbonate to a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoamer BYK-066N, and disperse well with a high-speed disperser to obtain a water-based automotive coating.

[0071] Comparative Example 3

[0072] (1) Under a nitrogen atmosphere, 100 g of itaconic acid-based unsaturated polyester and 800 mL of deionized water were added to a four-necked flask, stirred evenly, and then heated to 85° C., 6 g of acrylic acid, 20 g of methyl methacrylate, and 2 g of dibenzoyl peroxide were added dropwise, and the reaction was continued for 5 h. The temperature was then lowered to 50° C., and triethylamine was added for neutralization reaction to obtain an acrylic acid-grafted unsaturated polyester.

[0073] (2) Add 100 g of acrylic acid grafted unsaturated polyester and 25 g of light calcium carbonate into a reaction flask, mix well, then add 2.4 g of dispersant BYK-163, 1.5 g of leveling agent BYK-388, and 1.2 g of defoamer BYK-066N. After being dispersed well by a high-speed disperser, a water-based automotive coating is obtained.

[0074] Preparation of coating film: The water-based automotive coatings prepared in the examples and comparative examples were sprayed on the front cover of the car, with a coating thickness of 25 μm, and baked at 140° C. for 20 min to obtain a water-based automotive coating film for testing its performance.

[0075] Pencil hardness test: Tested in accordance with GB / T 6739-2006 standard.

[0076] Adhesion test: Tested in accordance with GB / T 9286-2021 standard.

[0077] VOC content test: Tested in accordance with GB / T 23986-2009 standard.

[0078] Impact resistance test: According to GB / T 1732-1993 standard, the coating prepared in the above embodiments and comparative examples is placed in the spherical groove of the instrument, and an iron ball is allowed to fall freely at a certain height to hit the coating. The coating at the collision point is carefully observed to see if there is any damage. If not, the position is changed and the height is increased from 40 cm, increasing by 2 cm each time until cracks and damage appear on the paint film. The height (cm) at this time is recorded.

[0079] Table 1 Coating performance test

[0080]

[0081] It can be seen from the test results in the above table that with the increase of the content of environmentally friendly alkenyl borate monomers, the comprehensive performance of water-based automotive coatings is gradually enhanced. Isosorbide is a biomass material made from plant resources such as corn, with abundant raw material sources and renewable, and has the advantage of green environmental protection; Isosorbide has a rigid spirocyclic structure of a V-shaped bridge ring, with large steric hindrance, and its distortion and non-planar structure can prevent the close stacking between polymer macromolecular chains and increase the free volume of the coating; the alkenyl group in its structure can initiate polymerization with monomers such as acrylic acid to form a dense three-dimensional cross-linked network structure, improve the compatibility with unsaturated polyesters, increase the elasticity and toughness of the coating, and can better disperse and absorb energy when impacted, reduce stress concentration during impact, and effectively improve the impact resistance of the coating; At the same time, the water-based automotive coating prepared by the present invention has suitable hardness, excellent adhesion and low VOC emissions. Comparative Examples 2 and 3 do not contain isosorbide, and the impact resistance of the coating is poor.

[0082] Moisture and heat resistance test: Tested in accordance with GB / T 1740-2007 standard.

[0083] Neutral salt spray resistance test: Tested in accordance with GB / T 1771-2007 standard.

[0084] Table 2 Corrosion resistance test of coating

[0085] High temperature and humidity resistance (h) Salt spray resistance(h) Example 1 168 240 Example 2 204 360 Example 3 240 480 Example 4 288 576 Example 5 290 600 Comparative Example 1 96 108 Comparative Example 2 168 240 Comparative Example 3 96 108

[0086] It can be seen from the test results in the above table that with the increase of the content of environmentally friendly alkenyl borate monomers, the corrosion resistance of water-based automotive coatings gradually increases. This is because the cyclic borate structure in the environmentally friendly alkenyl borate monomers can increase the steric hindrance around the boron atom, making it difficult for water molecules or other corrosive substances to approach the empty hybrid orbits of the boron atom, and can form a dense protective film on the metal surface, which can seal the tiny holes and cracks on the metal surface of the car, thereby preventing oxygen and moisture from entering the metal, and effectively preventing the metal from reacting with acids, alkalis and other substances in the external environment, which can not only reduce the corrosion rate of the metal, but also improve the surface quality of the metal; even in high temperature, humid and corrosive environments, cyclic borate can maintain a long service life and is not prone to hydrolysis reactions that lead to performance degradation.

[0087] Those skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention (including the claims) is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes in different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly impact-resistant water-based automotive coating, characterized in that: The preparation method comprises the following steps: Step (1), under a nitrogen atmosphere, add itaconic acid-based unsaturated polyester and deionized water into a four-necked flask, stir evenly, heat to 75-90° C., dropwise add acrylic acid, methyl methacrylate, environmentally friendly alkenyl borate monomer and dibenzoyl peroxide, continue to react for 3-8 hours, cool to 45-60° C., add triethylamine for neutralization reaction, and obtain acrylic acid-grafted unsaturated polyester; Step (2), adding acrylic acid grafted unsaturated polyester and light calcium carbonate into a reaction flask, mixing evenly, adding dispersant, leveling agent and defoaming agent, and dispersing evenly with a high-speed disperser to obtain an environmentally friendly impact-resistant water-based automotive coating.

2. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 1, characterized in that: In the step (1), the mass ratio of itaconic acid-based unsaturated polyester, acrylic acid, methyl methacrylate, environmentally friendly alkenyl borate monomer, and dibenzoyl peroxide is 100:5-8:15-25:2-10:1.5-3.

3. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 1, characterized in that: In the step (2), the mass ratio of acrylic acid grafted unsaturated polyester to light calcium carbonate is 100:25-40.

4. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 1, characterized in that: The method for preparing the environmentally friendly alkenyl borate monomer in step (1) comprises the following steps: Step S1, under a nitrogen atmosphere, add 4-carboxyphenylboric acid and N,N-dimethylformamide to a reaction flask, stir evenly, add diethanolamine, stir to react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, to obtain a borate benzoic acid monomer; Step S2, under a nitrogen atmosphere, adding isosorbide and xylene to a reaction flask, stirring evenly, adding borate benzoic acid monomer and p-toluenesulfonic acid, reacting at 120-135° C. for 8-16 hours, cooling, extracting with ethyl acetate and deionized water, and recrystallizing with methanol to obtain an isosorbide borate monomer; Step S3, under a nitrogen atmosphere, add isosorbide borate monomer and N-methylpyrrolidone to a reaction flask, stir evenly, add allyl isocyanate, stir to react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, to obtain an environmentally friendly alkenyl borate monomer.

5. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 4, characterized in that: In step S1, the molar ratio of 4-carboxyphenylboric acid to diethanolamine is 1:1.05-1.

2.

6. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 4, characterized in that: In step S1, the reaction temperature is 40-60° C. and the reaction time is 1-3 h.

7. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 4, characterized in that: In step S2, the molar ratio of isosorbide, borate benzoic acid monomer, and p-toluenesulfonic acid is 1:2.1-2.4:0.3-0.

5.

8. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 4, characterized in that: In step S3, the molar ratio of the isosorbide borate monomer to the allyl isocyanate is 1:2.2-2.

5.

9. The method for preparing the environmentally friendly impact-resistant water-based automotive coating according to claim 4, characterized in that: In step S3, the reaction temperature is 50-70° C. and the reaction time is 2-5 h.

10. An environmentally friendly impact-resistant water-based automotive coating, characterized in that: Obtained by the preparation method according to any one of claims 1 to 9.

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