Modified acrylic polyester resin for water-based paint and preparation process of modified acrylic polyester resin

Abstract

The invention relates to resin, in particular to modified acrylic polyester resin for water paint and a preparation process of the modified acrylic polyester resin. The invention relates to a modified acrylic polyester resin which is prepared from the following raw materials through chemical reaction: neopentyl glycol, 2-methyl-1, 3, 4-trimethyl-1, 3-pentanediol and a catalyst. The invention relates to a high-temperature-resistant adhesive which is prepared from 1, 3-propylene glycol, trimethylolpropane, glycidyl tertiary carboxylic ester subjected to surface modification by a silane coupling agent, dibasic acid, maleic anhydride, tetrabutyl titanate, xylene, propylene glycol butyl ether, n-butyl acrylate, hydroxyethyl methylacrylate, an initiator, a cross-linking enhancing monomer and the like. The silane coupling agent is used for modifying the surface of the glycidyl tertiary carboxylic ester, and an epoxy group in the silane coupling agent reacts with a hydroxyl group on the surface of the glycidyl tertiary carboxylic ester to form a stable chemical bond, so that the compatibility of the glycidyl tertiary carboxylic ester and a polyester main chain is improved; glycidyl tertiary carboxylic ester is more evenly distributed in a polyester side chain, the situation that the overall performance is affected due to the fact that the main chain is too long is avoided, and the leveling property and stone impact resistance of a final coating film can be improved.

Description

Technical Field

[0001] The invention relates to a resin, in particular to a modified acrylic polyester resin for water-based paint and a preparation process thereof. Background Art

[0002] In the field of automotive coatings, the main function of automotive mid-coat is to cover substrate defects and ensure the smoothness of the surface after topcoat application. At the same time, it is necessary to give the coating film strong resistance to stone impact. In view of current environmental protection requirements and the current market status of various countries, water-based systems are mostly used. For water-based systems, they must have higher pinhole limits and sag limits to obtain mid-coat with high hiding power, strong resistance to stone impact and excellent surface leveling. The mid-coat must also consider the interlayer adhesion between the electrophoretic substrate and the base paint or metallic paint.

[0003] Commonly used water-based mid-coat paints are water-based polyester resins and water-based acrylic resins, of which water-based polyester resins are suitable for 3C2B systems, and water-based acrylic resins are suitable for 3C1B systems. Water-based polyester resins have good mechanical properties and chemical resistance, as well as good flexibility and impact resistance, while water-based acrylic resins are known for their excellent leveling and gloss retention, and provide higher cross-linking density and hardness. By combining the two, that is, modified acrylic polyester resins, the advantages of both can be obtained at the same time, improving the hiding power and flatness of the mid-coat paint, while enhancing the stone chip resistance of the coating film without sacrificing hardness, meeting the key requirements of automotive mid-coat paint.

[0004] Patent CN112390916B discloses an acrylic modified polyester resin and a preparation method thereof. In its background technology, it is mentioned that one problem faced by polyester system coatings is that they are not resistant to boiling water and steaming. The ester bonds on the polymer main chain are easily broken by hydrolysis reaction at high temperature, which causes the coating to deteriorate in performance due to the disintegration of the chemical structure. It is also mentioned that tert-butyl glycidyl carbonate is introduced to synthesize acrylic modified polyester to enhance the water resistance, alkali resistance and acid resistance of the coating. The steric barrier of the tert-butyl carbonate group protects the ester bonds on the main chain, thereby improving its hydrolysis stability.

[0005] However, tert-butyl glycidyl carbonate is easily enriched in certain areas during the synthesis process, resulting in excessive or insufficient local cross-linking, affecting the overall performance of the coating film, and tert-butyl glycidyl carbonate may migrate during the curing process, resulting in uneven coating surface performance, reducing chemical resistance and mechanical properties. In addition, tert-butyl glycidyl carbonate will preferentially react with other sites in the main chain, resulting in poor cross-linking density, and the introduction of monomers needs to have good compatibility with other components to avoid phase separation or uneven dispersion. Therefore, the present invention provides a modified acrylic polyester resin for water-based paint and a preparation process thereof to solve the above problems. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a modified acrylic polyester resin for water-based paint and a preparation process thereof.

[0007] A modified acrylic polyester resin for water-based paint is prepared by chemical reaction from the following raw materials in percentage by mass: 5-20% neopentyl glycol, 5-20% 2-methyl-1,3-propanediol, 2-5% trimethylolpropane, 5-15% tert-butyl carbonate, 10-30% dibasic acid I, 5-15% dibasic acid II, 1-3% maleic anhydride, 0.01-0.05% tetrabutyl titanate, 1-3% xylene, wherein the tert-butyl carbonate is surface-modified by a silane coupling agent before being added; 15-30% propylene glycol butyl ether, 5-10% n-butyl acrylate, 2-5% hydroxyethyl methacrylate, 3-10% styrene, 2-5% acrylic acid, 0.3-1.0% initiator I, 0.2-0.5% initiator II, 2-5% N,N-dimethylethanolamine, and 1-5% cross-linking reinforcing monomer.

[0008] Specifically, the dibasic acid I includes phthalic acid and / or isophthalic acid, and the dibasic acid II includes one or more of adipic acid, azelaic acid and sebacic acid.

[0009] Specifically, the initiator I is benzoyl peroxide or azobisisobutyronitrile, and the initiator II is tert-butyl hydroperoxide or dicyclohexyl peroxydicarbonate.

[0010] Furthermore, the cross-linking enhancing monomer is trimethylolpropane triacrylate and / or hexanediol diacrylate.

[0011] Furthermore, the silane coupling agent is γ-glycidyloxypropyltrimethoxysilane.

[0012] Furthermore, the solid content of the modified acrylic polyester resin for water-based paint is 74%.

[0013] A preparation process of a modified acrylic polyester resin for water-based paint comprises the following steps: (1) Esterification reaction stage: neopentyl glycol, 2-methyl-1,3-propanediol, trimethylolpropane, maleic anhydride, dibasic acid I, dibasic acid II, tetrabutyl titanate and xylene are added into a reactor, heated to 150-170°C for reaction for 2-3 hours, surface-modified tert-butyl carbonate is added, heated to 210-240°C for esterification until the acid value is reduced to below 5 mgKOH / g, and then cooled to 140-160°C; (2) Polymerization reaction stage: add 1 / 3 propylene glycol butyl ether to fully dissolve, cool to 100-130°C, add dropwise a mixture of n-butyl acrylate, hydroxyethyl methacrylate, styrene, acrylic acid, 1 / 3 propylene glycol butyl ether and initiator I within 2-5 hours, add a cross-linking enhancing monomer, raise the temperature to 125-145°C, continue to add dropwise a mixture of 1 / 3 propylene glycol butyl ether and initiator II within 0.5-2 hours, and keep warm for 2-3 hours to complete the reaction; (3) Neutralization and dispersion stage: cool to 80-90°C, add N,N-dimethylethanolamine for neutralization, cool to 50-60°C, filter the material, and obtain modified acrylic polyester resin.

[0014] Specifically, in the (1) esterification reaction stage, the surface-modified tert-butyl glycidyl carbonate is gradually added in 3-5 portions, and stirred for 5-10 minutes after each addition.

[0015] Specifically, in the (2) polymerization reaction stage, the monomer mixture is added dropwise in 1-2 times, the first addition time is 2-5 hours, and the second addition time is 0.5-2 hours.

[0016] Furthermore, in the (1) esterification reaction stage, xylene is removed by vacuum before adding propylene glycol butyl ether.

[0017] The beneficial effects achieved by the present invention are as follows: 1. The present invention uses a silane coupling agent to modify the surface of tert-butyl glycidyl carbonate. The epoxy groups in the silane coupling agent can react with the hydroxyl groups on the surface of tert-butyl glycidyl carbonate to form a stable chemical bond, thereby improving the compatibility of tert-butyl glycidyl carbonate with the polyester main chain. The modified tert-butyl glycidyl carbonate is more evenly distributed in the polyester side chain, avoiding the main chain being too long to affect the overall performance, while giving the coating film better leveling and flexibility, and improving the coating film's anti-stone impact performance.

[0018] 2. The present invention uses tetrabutyl titanate as an esterification catalyst, which can promote the esterification reaction at a lower temperature and ensure that tert-butyl carbonate reacts preferentially with the terminal hydroxyl group of the main chain rather than other sites in the main chain. This selective reaction helps to optimize the cross-linking structure and improve the mechanical properties and chemical resistance of the coating. Tetrabutyl titanate can effectively catalyze the esterification reaction at a lower temperature, shorten the reaction time, and improve production efficiency. The optimized cross-linking structure can also give the coating a higher hardness and wear resistance, while maintaining good flexibility and stone impact resistance.

[0019] 3. The present invention introduces multifunctional monomers, including trimethylolpropane triacrylate (TMPTA) or hexanediol diacrylate, which can introduce multiple active groups into the polyester molecular chain to enhance the crosslinking density and mechanical properties of the coating. These monomers can not only improve the hardness and wear resistance of the coating, but also improve its stone resistance and chemical resistance. Multiple active groups in the multifunctional monomers can react with different sites in the polyester molecular chain to form a highly crosslinked network structure, thereby improving the hardness and wear resistance of the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a schematic flow chart of the preparation process of the modified acrylic polyester resin for water-based paint. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0022] It should be understood that the following examples are only for illustrative purposes and explanation of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope of protection intended by the present invention.

[0023] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art.

[0024] Embodiment 1: A modified acrylic polyester resin for water-based paint is prepared by chemical reaction of the following raw materials in percentage by mass: 10% neopentyl glycol, 15% 2-methyl-1,3-propanediol, 3% trimethylolpropane, 10% tert-butyl carbonate (surface modified by a silane coupling agent), 20% dibasic acid I (phthalic acid), 10% dibasic acid II (adipic acid), 2% maleic anhydride, 0.03% tetrabutyl titanate, 2% xylene; 20% propylene glycol butyl ether, 8% n-butyl acrylate, 4% hydroxyethyl methacrylate, 6% styrene, 4% acrylic acid, 0.7% initiator I (benzoyl peroxide), 0.3% initiator II (tert-butyl hydroperoxide), 3% N,N-dimethylethanolamine and 3% cross-linking reinforcing monomer (trimethylolpropane triacrylate).

[0025] A preparation process of modified acrylic polyester resin for water-based paint, such as Figure 1 As shown, the following steps are included: (1) Esterification reaction stage: neopentyl glycol, 2-methyl-1,3-propanediol, trimethylolpropane, maleic anhydride, dibasic acid I, dibasic acid II, tetrabutyl titanate and xylene are added into a reactor, heated to 150°C for reaction for 2 h, and surface-modified tert-butyl carbonate is added in four portions. After each addition, the mixture is stirred for 10 minutes. The temperature is raised to 220°C to continue the esterification reaction until the acid value is reduced to below 5 mgKOH / g, and the temperature is lowered to 150°C. The xylene is removed by vacuum. (2) Polymerization reaction stage: add 1 / 3 propylene glycol butyl ether to fully dissolve, cool to 120°C, drop n-butyl acrylate, hydroxyethyl methacrylate, styrene, acrylic acid, 1 / 3 propylene glycol butyl ether and a monomer mixture of initiator I, and complete the addition within 3 hours, add a cross-linking enhancing monomer, raise the temperature to 130°C, continue to drop 1 / 3 propylene glycol butyl ether and a mixture of initiator II, and complete the addition within 1 hour, and continue to keep warm for 2 hours to complete the reaction; (3) Neutralization and dispersion stage: cool to 85°C, add N,N-dimethylethanolamine for neutralization, cool to 55°C, filter the material, and obtain a modified acrylic polyester resin with a solid content of 74%.

[0026] Example 2: A modified acrylic polyester resin for water-based paint is prepared by chemical reaction of the following raw materials in percentage by mass: 15% neopentyl glycol, 10% 2-methyl-1,3-propanediol, 4% trimethylolpropane, 12% tert-butyl carbonate (surface modified by a silane coupling agent), 15% dibasic acid I (isophthalic acid), 12% dibasic acid II (nonacid), 2% maleic anhydride, 0.04% tetrabutyl titanate, 2% xylene; 25% propylene glycol butyl ether, 7% n-butyl acrylate, 3% hydroxyethyl methacrylate, 8% styrene, 3% acrylic acid, 0.5% initiator I (azobisisobutyronitrile), 0.4% initiator II (dicyclohexyl peroxydicarbonate), 3% N,N-dimethylethanolamine and 4% cross-linking enhancing monomer (hexanediol diacrylate).

[0027] A preparation process of modified acrylic polyester resin for water-based paint, such as Figure 1 As shown, the following steps are included: (1) Esterification reaction stage: neopentyl glycol, 2-methyl-1,3-propanediol, trimethylolpropane, maleic anhydride, dibasic acid I, dibasic acid II, tetrabutyl titanate and xylene are added into a reactor, heated to 160°C for reaction for 2.5 hours, and surface-modified tert-butyl carbonate is added in 5 portions. After each addition, the mixture is stirred for 8 minutes. The temperature is raised to 230°C to continue the esterification reaction until the acid value drops below 5 mgKOH / g, and the temperature is lowered to 150°C. The xylene is removed by vacuum. (2) Polymerization reaction stage: add 1 / 3 propylene glycol butyl ether to fully dissolve, cool to 110°C, add dropwise a mixture of n-butyl acrylate, hydroxyethyl methacrylate, styrene, acrylic acid, 1 / 3 propylene glycol butyl ether and initiator I within 4 hours, add a cross-linking enhancing monomer, raise the temperature to 135°C, continue to add dropwise a mixture of 1 / 3 propylene glycol butyl ether and initiator II within 1.5 hours, and keep warm for 2.5 hours to complete the reaction; (3) Neutralization and dispersion stage: cool to 85°C, add N,N-dimethylethanolamine for neutralization, cool to 55°C, filter the material, and obtain a modified acrylic polyester resin with a solid content of 74%.

[0028] Example 3: A modified acrylic polyester resin for water-based paint is prepared by chemical reaction of the following raw materials in percentage by mass: 18% neopentyl glycol, 12% 2-methyl-1,3-propanediol, 5% trimethylolpropane, 15% tert-butyl carbonate (surface modified by a silane coupling agent), 25% dibasic acid I (phthalic acid), 10% dibasic acid II (sebacic acid), 2% maleic anhydride, 0.05% tetrabutyl titanate, 3% xylene; 28% propylene glycol butyl ether, 9% n-butyl acrylate, 5% hydroxyethyl methacrylate, 9% styrene, 4% acrylic acid, 0.8% initiator I (benzoyl peroxide), 0.4% initiator II (tert-butyl hydroperoxide), 4% N,N-dimethylethanolamine and 5% cross-linking reinforcing monomer (1:1 trimethylolpropane triacrylate and hexanediol diacrylate).

[0029] A preparation process of modified acrylic polyester resin for water-based paint, such as Figure 1 As shown, the following steps are included: (1) Esterification reaction stage: neopentyl glycol, 2-methyl-1,3-propanediol, trimethylolpropane, maleic anhydride, dibasic acid I, dibasic acid II, tetrabutyl titanate and xylene are added into a reactor, heated to 170°C for reaction for 3 h, and surface-modified tert-butyl carbonate is added in three portions. After each addition, the mixture is stirred for 10 minutes. The temperature is raised to 240°C to continue the esterification reaction until the acid value drops below 5 mgKOH / g, and the temperature is lowered to 160°C. The xylene is removed by vacuum removal; (2) Polymerization reaction stage: add 1 / 3 propylene glycol butyl ether to fully dissolve, cool to 125°C, add dropwise a mixture of n-butyl acrylate, hydroxyethyl methacrylate, styrene, acrylic acid, 1 / 3 propylene glycol butyl ether and initiator I within 2 hours, add a cross-linking enhancing monomer, raise the temperature to 140°C, continue to add dropwise a mixture of 1 / 3 propylene glycol butyl ether and initiator II within 1 hour, and keep warm for 3 hours to complete the reaction; (3) Neutralization and dispersion stage: cool to 85°C, add N,N-dimethylethanolamine for neutralization, cool to 55°C, filter the material, and obtain a modified acrylic polyester resin with a solid content of 74%.

[0030] Comparative Example 1: Compared with Example 1, this comparative example uses tert-butyl glycidyl carbonate that has not been surface-modified with a silane coupling agent.

[0031] Comparative Example 2: Compared with Example 1, this comparative example does not use a cross-linking enhancing monomer.

[0032] The modified acrylic polyester resins of Examples 1-3 and Comparative Examples 1-2 were used to prepare water-based mid-coat paints, and relevant performance tests were performed. The water-based mid-coat paints included the following components, by mass percentage: 30% modified acrylic polyester resin, 4% propylene glycol butyl ether, 4% diethylene glycol butyl ether, 7% water-based amino resin, 35% deionized water, 1.2% N,N-dimethylethanolamine, 18% resin-free mortar, 0.5% water-based defoamer, and 0.3% water-based thickener.

[0033] Add modified acrylic polyester resin, propylene glycol butyl ether, diethylene glycol butyl ether, water-based amino resin and part of deionized water into the paint mixing tank in turn for uniform dispersion and mixing, add N, N-dimethylethanolamine to adjust the pH value of the system to 8.5, then add resin-free mortar, water-based defoamer and water-based thickener in turn for full dispersion and mixing, and filter the material to obtain the water-based mid-coat paint.

[0034] In the following performance tests, the test substrate is an electrophoresis plate, and the baking process of the water-based mid-coat paint is flash drying at 80°C for 10 minutes and baking at 140°C for 20 minutes.

[0035] 1. Storage stability: In accordance with GB / T 6753.3-2007 (Determination of storage stability of paints and varnishes), seal the samples in the original packaging container and store them at the specified temperature (40°C) for a certain period of time (15 days). Take samples to observe whether there is stratification, precipitation, agglomeration, etc., and record any changes.

[0036] 2. Coating appearance: Prepare standard samples in accordance with GB / T 9761-2008 (General requirements for the appearance of paint and varnish coatings) to ensure uniform coating thickness. Observe the flatness, glossiness, color uniformity, etc. of the coating surface and use a gloss meter to measure the glossiness of the coating.

[0037] 3. Impact resistance: According to GB / T 1732-1993 (Determination of impact resistance of paint film), prepare standard samples to ensure uniform coating thickness, use an impact tester to perform impact tests on the coating, set different impact heights, observe and record whether the coating has cracks, peeling and other damage. Verify the impact resistance of the coating to ensure that it can maintain integrity when subjected to external impact.

[0038] 4. Chemical resistance: Prepare the coating test panel in accordance with ISO 2812-1:2019 (Resistance of paints and varnishes to the effects of liquid media - Part 1: Single liquid immersion method), ensure uniform coating thickness, immerse the test panel in sodium hydroxide, set the immersion time (24 hours), take out the test panel after immersion, rinse it with clean water, dry it naturally, observe and record the changes on the coating surface (such as blistering, shedding, discoloration, etc.).

[0039] 5. Adhesion: According to GB / T 9286-1998 (cross-cut test for paint and varnish film), prepare the coating test plate on the standard steel plate to ensure the uniform coating thickness. Use a cross-cutting tool to cut grid-like scratches on the coating surface with a grid spacing of 2mm. Use tape to stick on the scratches and quickly tear off the tape. Observe and record the coating peeling situation and assess the adhesion level from 0 to 5.

[0040] 6. Pencil hardness: According to GB / T 6739-2006 (Determination of pencil hardness of paints and varnishes), prepare a coating test plate on a standard steel plate to ensure uniform coating thickness. Use a pencil hardness tester to vertically press pencils of different hardness on the coating surface with a test pressure of 750 g. Push and pull the pencils at a constant speed of 1 cm / s to observe whether the coating is scratched. Record the hardest pencil hardness that does not scratch the coating.

[0041] 7. Stone impact resistance: According to GB / T 9753-2014 (Determination of stone impact resistance of paint and varnish coatings), prepare a standard steel plate with a size of 150mm×70mm×(0.8mm-1.5mm), ensure that the coating thickness is uniform and reaches the specified dry film thickness (30µm-60µm), and stick masking tape on one end of the sample, leaving about 1 / 3 of the area as a control area without stone impact test. Set the distance between the nozzle of the stone impact tester and the sample to 25mm±2mm, adjust the pressure of the compressed air source to 0.6MPa to 0.8MPa, and ensure that the spray angle is 90°±5°. Fix the sample on the bracket of the testing machine with the uncovered part facing the nozzle, and start spraying the abrasive for 2 minutes. After the spraying is completed, take down the sample and remove the masking tape. Use a magnifying glass (10x magnification) to observe the surface of the coating and record the damage, including scratches, peeling, exposure of the substrate, etc. Score the sample according to the degree of damage, using a 0-5 rating system, where 0 means no damage and 5 means severe damage.

[0042] 8. Salt spray resistance: According to GB / T 1771-2009 (Determination of neutral salt spray resistance of paint and varnish coatings), prepare a standard steel plate (70mm×150mm), ensure that the coating thickness is uniform and reaches the specified dry film thickness (30µm~60µm), and mark the position at one end of the sample for subsequent observation and recording of damage. Set the temperature of the salt spray test chamber to 35℃±2℃, prepare 5%±0.1% sodium chloride solution, and adjust the pH value to 6.5~7.2. Fix the sample on the support frame, ensure that its inclination angle is 15°~30°, so that the salt spray can evenly cover the entire surface, start spraying, and last for the predetermined time (168 hours). After the test, remove the sample and rinse it with distilled water or deionized water to remove residual salt on the surface. Use a magnifying glass (10x magnification) to observe the coating surface and record the damage (such as rust, blistering, peeling, discoloration). Score the sample according to the degree of damage (0~5 rating system, 0 means no damage and 5 means severe damage).

[0043] 9. Weather resistance: Prepare standard samples in accordance with GB / T 1865-2009 (artificial weathering and artificial radiation exposure of paints and varnishes) to ensure uniform coating thickness. Place the samples in a xenon lamp aging test chamber and set parameters such as light, humidity, and temperature. After a certain period of time (500 hours), take out the samples and observe and record the aging phenomena of the coating, such as loss of gloss, chalking, and cracking.

[0044] The performance test results are shown in Table 1 and Table 2.

[0045] Table 1 Test results of storage stability, film appearance and impact strength of water-based mid-coat

[0046] Table 2 Test results of chemical resistance, adhesion and pencil hardness of water-based mid-coat

[0047] Table 3 Test results of stone impact resistance, salt spray resistance and weather resistance of water-based mid-coat

[0048] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A modified acrylic polyester resin for water-based paint, characterized in that: The invention is prepared by chemical reaction of the following raw materials in mass percentage: 5-20% neopentyl glycol, 5-20% 2-methyl-1,3-propanediol, 2-5% trimethylolpropane, 5-15% tert-butyl carbonate, 10-30% dibasic acid I, 5-15% dibasic acid II, 1-3% maleic anhydride, 0.01-0.05% tetrabutyl titanate, 1-3% xylene, wherein the tert-butyl carbonate is surface-modified by a silane coupling agent before being added; 15-30% propylene glycol butyl ether, 5-10% n-butyl acrylate, 2-5% hydroxyethyl methacrylate, 3-10% styrene, 2-5% acrylic acid, 0.3-1.0% initiator I, 0.2-0.5% initiator II, 2-5% N,N-dimethylethanolamine and 1-5% cross-linking reinforcing monomer.

2. The modified acrylic polyester resin for water-based paint according to claim 1, characterized in that: The dibasic acid I includes phthalic acid and / or isophthalic acid, and the dibasic acid II includes one or more of adipic acid, azelaic acid and sebacic acid.

3. The modified acrylic polyester resin for water-based paint according to claim 1, characterized in that: The initiator I is benzoyl peroxide or azobisisobutyronitrile, and the initiator II is tert-butyl hydroperoxide or dicyclohexyl peroxydicarbonate.

4. The modified acrylic polyester resin for water-based paint according to claim 1, characterized in that: The cross-linking enhancing monomer is trimethylolpropane triacrylate and / or hexanediol diacrylate.

5. The modified acrylic polyester resin for water-based paint according to claim 1, characterized in that: The silane coupling agent is γ-glycidyloxypropyltrimethoxysilane.

6. The modified acrylic polyester resin for water-based paint according to claim 1, characterized in that: The solid content of the modified acrylic polyester resin for water-based paint is 74%.

7. The process for preparing a modified acrylic polyester resin for water-based paint according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) Esterification reaction stage: neopentyl glycol, 2-methyl-1,3-propanediol, trimethylolpropane, maleic anhydride, dibasic acid I, dibasic acid II, tetrabutyl titanate and xylene are added into a reactor, heated to 150-170°C for reaction for 2-3 hours, surface-modified tert-butyl carbonate is added, heated to 210-240°C for esterification until the acid value is reduced to below 5 mgKOH / g, and then cooled to 140-160°C; (2) Polymerization reaction stage: add 1 / 3 propylene glycol butyl ether to fully dissolve, cool to 100-130°C, add dropwise a mixture of n-butyl acrylate, hydroxyethyl methacrylate, styrene, acrylic acid, 1 / 3 propylene glycol butyl ether and initiator I within 2-5 hours, add a cross-linking enhancing monomer, raise the temperature to 125-145°C, continue to add dropwise a mixture of 1 / 3 propylene glycol butyl ether and initiator II within 0.5-2 hours, and keep warm for 2-3 hours to complete the reaction; (3) Neutralization and dispersion stage: cool to 80-90°C, add N,N-dimethylethanolamine for neutralization, cool to 50-60°C, filter the material, and obtain modified acrylic polyester resin.

8. The process for preparing a modified acrylic polyester resin for water-based paint according to claim 7, characterized in that: In the (1) esterification reaction stage, the surface-modified tert-butyl glycidyl carbonate is gradually added in 3-5 portions, and stirred for 5-10 minutes after each addition.

9. The process for preparing a modified acrylic polyester resin for water-based paint according to claim 7, characterized in that: In the (2) polymerization reaction stage, the monomer mixture is added dropwise in 1-2 times, the first addition time is 2-5 hours, and the second addition time is 0.5-2 hours.

10. The process for preparing a modified acrylic polyester resin for water-based paint according to claim 7, characterized in that: In the (1) esterification reaction stage, xylene is removed by vacuum before adding propylene glycol butyl ether.

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