A low-VOC alkyd resin coating and preparation method thereof

Abstract

The invention discloses a low-VOC alkyd resin coating and a preparation method thereof, belonging to the technical field of alkyd resin coatings. The low-VOC alkyd resin coating comprises the following raw materials in parts by weight: 55-75 parts of a branched alkyd resin, 2-4 parts of an amine neutralizer, 0.05-0.1 parts of a defoamer, 0.3-0.5 parts of a dispersant, 8-15 parts of precipitated barium sulfate, 50-70 parts of deionized water, 0.3-1 parts of a leveling agent, and 0.3-0.5 parts of a drier; the branched alkyd resin, the deionized water, and the amine neutralizer are stirred and mixed for 40-45 minutes to obtain a water-dispersible resin body; and the water-dispersible resin body is uniformly mixed with the defoamer, the dispersant, the precipitated barium sulfate, and the remaining deionized water to obtain a low-VOC alkyd resin body. The preparation method is simple, the low-VOC alkyd resin body is water-based, and only a small amount of safe and environmentally friendly cosolvent is used. The final coating has a VOC content of less than 80 g / L, has high content and low viscosity, does not require the use of an organic diluent, and has the characteristics of fast drying, strong water resistance, and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of alkyd resin coatings, and particularly relates to a low-VOC alkyd resin coating and a preparation method thereof. Background Art

[0002] Alkyd resin is an oil-modified polyester, a type of artificial synthetic resin material obtained by condensation polymerization of polyols, polyacids and fatty acids or oils. Alkyd resin is air-drying and can be oxidatively cross-linked to form a film. It occupies an important position in coatings due to its high gloss, low surface tension, strong wetting ability, good leveling, and excellent adhesion to a variety of substrates.

[0003] With growing environmental awareness, effectively reducing VOC (volatile organic compound) emissions during coating production and application has become a pressing issue for coatings companies. The development of water-based and high-solids coatings has become a major trend in coatings development. Water-based alkyd resins, which have lower VOC levels than solvent-based alkyds, have become widely used. However, existing water-based alkyds have high viscosities, requiring the addition of solvents or modification of solvent properties to reduce viscosity for ease of use. However, the introduction of non-aqueous solvents increases VOC levels in coatings. Furthermore, existing water-based alkyds have slow drying times and poor water resistance, impacting their effectiveness. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-VOC alkyd resin coating and a preparation method thereof, so as to solve the problem of high viscosity of existing water-based alkyd resin coatings.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A low-VOC alkyd resin coating comprises the following raw materials in parts by weight:

[0007] 55-75 parts of branched alkyd resin, 2-4 parts of amine neutralizer, 0.05-0.1 parts of defoamer, 0.3-0.5 parts of dispersant, 8-15 parts of precipitated barium sulfate, 50-70 parts of deionized water, 0.3-1 parts of leveling agent, and 0.3-0.5 parts of drying agent;

[0008] The preparation method of the low-VOC alkyd resin coating comprises the following steps:

[0009] S1, stirring and mixing a branched alkyd resin, deionized water (1 / 3 of the mass of the branched alkyd resin), and an amine neutralizer for 40-45 minutes to obtain a water-dispersible resin;

[0010] S2. Add defoamer, dispersant, precipitated barium sulfate and remaining deionized water to the water-dispersible resin, disperse at a speed of 500-700 r / min for 20-30 min, grind to make the coating particle size ≤35 μm, then add leveling agent and drying agent, and stir at a speed of 300-500 r / min for 20-40 min to obtain low VOC alkyd resin coating.

[0011] As a preferred technical solution of the present invention, the preparation steps of branched alkyd resin are as follows:

[0012] Add vegetable oil fatty acid, phthalic anhydride, hydroxyl-terminated hyperbranched polyester, polyethylene glycol, phthalic anhydride and xylene into a reactor, and under nitrogen protection, heat the reactor to 210°C at a heating rate of 5°C / h, keep the temperature for 2 hours, then heat the reactor to 220-225°C, and keep the temperature within this range to react until the acid value reaches 8-12 mgKOH / g. Vacuum the reactor to remove the xylene, cool the reactor to 180°C, add maleic anhydride and adipic acid, keep the temperature at 180-185°C for 1-2 hours, cool the reactor to 130°C, add propylene glycol, stir the reactor and cool the reactor to 50°C to obtain a branched alkyd resin.

[0013] The mass ratio of vegetable oil fatty acid, phthalic anhydride, terminal hydroxyl hyperbranched polyester, polyethylene glycol, phthalic anhydride, xylene, maleic anhydride, adipic acid and propylene glycol is 26-30:15-20:15-20:10-15:18-20:3-5:3-5:4-8:15-25. Phthalic anhydride contains a rigid group benzene ring, which can increase the hardness of the product coating film. Maleic anhydride contains an active double bond, which increases the cross-linking degree of the coating film and improves the hardness. The present invention uses oxalic acid to replace part of the phthalic anhydride. The linear structure of oxalic acid gives the chain segments good free movement ability, reduces the entanglement probability between the molecular chains of the polymer, effectively reduces the viscosity of the polymer, and simultaneously improves the flexibility of the resin.

[0014] As a preferred technical solution of the present invention, the steps for preparing the hydroxyl-terminated hyperbranched polyester are as follows:

[0015] Cardanol triol and 2,2-dimethylolpropionic acid are placed in a flask, DMF is added, and ultrasonic treatment is carried out for 10-20 minutes. A DMF solution of N,N'-dicyclohexylcarbodiimide is added dropwise to the flask, and the mixture is stirred in an ice bath for 4-6 hours. After the reaction is completed, the reaction product is centrifuged to remove the white precipitate dicyclohexylurea, and deionized water is added to the supernatant to dissolve the residual dicyclohexylurea. This is repeated 3-5 times, and the supernatant is placed in a 4°C refrigerator for 12 hours, and the residual dicyclohexylurea is removed by centrifugation. Finally, N,N-dimethylformamide is removed by rotary evaporation, and the mixture is dried in a vacuum drying oven at 80°C for 12 hours to obtain a hydroxyl-terminated hyperbranched polyester.

[0016] Among them, the dosage ratio of cardanol triol, 2,2-dihydroxymethylpropionic acid, DMF, and DMF solution of N,N'-dicyclohexylcarbodiimide is 2g:6.04g:5-10mL:5mL, and the DMF solution of N,N'-dicyclohexylcarbodiimide is composed of N,N'-dicyclohexylcarbodiimide and DMF in a dosage ratio of 1.4-1.8g:5mL.

[0017] A hydroxyl-terminated hyperbranched polyester was synthesized in a one-step method using cardanol triol as the core molecule, 2,2-dihydroxymethylpropionic acid as the polymerization monomer, N,N'-dicyclohexylcarbodiimide as the dehydrating agent, and DMF as the solvent. It was used to prepare water-based alkyd resin, which is beneficial for obtaining resin coatings with high solid content and low viscosity, and is beneficial for improving the surface drying speed and water resistance of the coating.

[0018] As a preferred technical solution of the present invention, the steps for preparing cardanol-based triol are as follows:

[0019] Place cardanol glycidyl ether and diethanolamine in a flask, control the temperature at 60-70°C, stir and react for 8-10 hours, and cool to room temperature. The molar ratio of cardanol glycidyl ether and diethanolamine is 1:1. Cardanol glycidyl ether is obtained by substitution reaction of cardanol and epichlorohydrin. The epoxy group of cardanol glycidyl ether and the secondary amino group of diethanolamine undergo a ring-opening reaction to obtain cardanol triol.

[0020] As a preferred technical solution of the present invention, the vegetable oil fatty acid is one or more of linoleic acid, dehydrated ricinoleic acid, soybean oil acid, copper linoleic acid, eleostearic acid, linoleic acid, coconut oil acid and tall oil acid.

[0021] As a preferred technical solution of the present invention, the amine neutralizer is one or both of triethylamine and dimethylethanolamine.

[0022] As a preferred technical solution of the present invention, the defoaming agent is one or more of BYK-020, BYK-022, and BYK-024.

[0023] As a preferred technical solution of the present invention, the dispersant is one or more of BYK-190, BYK-180, and BYK-192.

[0024] As a preferred technical solution of the present invention, the leveling agent is one or more of BYK-300, BYK-333, BYK-345 and RM-2020.

[0025] As a preferred technical solution of the present invention, the drying agent is one or more of Octa-Soligen Zirconium 10aqua, Octa-Soligen Zinc 10aqua, Octa-Soligen Cobalt 7aqua, VXW4940 and VXW6206.

[0026] Beneficial effects of the present invention:

[0027] (1) The present invention provides a low-VOC alkyd resin coating with a simple preparation method. It is a water-based coating that uses only a small amount of safe and environmentally friendly cosolvent. The VOC content of the final coating is controlled below 80 g / L. It has high content and low viscosity characteristics, does not require the use of organic diluents, and has the characteristics of fast drying and strong water resistance.

[0028] (2) In the process of synthesizing alkyd resin, the present invention uses terminal hydroxyl hyperbranched polyester instead of polyol to react with monomers such as vegetable oil fatty acids and phthalic anhydride to obtain branched alkyd resin. Compared with linear alkyd resin, the branched alkyd resin has the advantages of high branching degree, good film-forming property, low intermolecular entanglement and low viscosity. The free radical volume within and between molecules is beneficial to improving the toughness of the coating. In addition, the end of its molecular chain is composed of a large number of reactive hydroxyl groups, which have high activity and are easy to fully cross-link during film formation to form a macromolecular network structure, which is beneficial to improving the drying speed. There is less residual solvent in the paint film, and the odor-free effect of the paint film is improved. Furthermore, the branched alkyd resin also contains long-chain hydrocarbon groups with unsaturated double bonds. The long-chain hydrocarbon groups have excellent flexibility and water resistance, which is beneficial to improving the water resistance of the coating. The unsaturated double bonds can be cross-linked with the double bonds of vegetable oil fatty acids, which can improve the dryness and cross-linking density of the resin and further improve the water resistance of the coating. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] Example 1

[0031] The preparation steps of cardanol glycidyl ether are as follows:

[0032] Add 0.1 mol cardanol, 0.8 mol epichlorohydrin and 0.91 g benzyltriethoxyammonium chloride to a four-necked flask, stir at 60 ° C for 1 hour, heat to 80 ° C and stir for 4 hours, cool to 60 ° C, add 22.8 g of 35% sodium hydroxide solution by mass, stir at 60 ° C for 3 hours after the addition is complete, cool to room temperature, wash with 40 ° C hot water until neutral, separate the organic phase in a separatory funnel, maintain reduced pressure rotary evaporation at 90 ° C under -0.097 MPa vacuum conditions, evaporate the water and epichlorohydrin in the organic phase, and finally obtain cardanol glycidyl ether.

[0033] Example 2

[0034] The preparation steps of hydroxyl-terminated hyperbranched polyester are as follows:

[0035] 20 g of cardanol triol and 60.4 g of 2,2-dimethylolpropionic acid were placed in a flask, 50 mL of DMF was added, and the mixture was ultrasonically treated for 10 min. 50 mL of N,N'-dicyclohexylcarbodiimide DMF solution was added dropwise to the flask, and the mixture was stirred in an ice bath for 4 h. After the reaction, the reaction product was centrifuged to remove the white precipitate dicyclohexylurea. Deionized water was added to the supernatant to dissolve the residual dicyclohexylurea. This was repeated 3 times. The supernatant was placed in a 4 ° C refrigerator and allowed to stand for 12 h. The residual dicyclohexylurea was removed by centrifugation. Finally, N,N-dimethylformamide was removed by rotary evaporation, and the mixture was dried in a vacuum drying oven at 80 ° C for 12 h to obtain a hydroxyl-terminated hyperbranched polyester. The DMF solution of N,N'-dicyclohexylcarbodiimide consisted of N,N'-dicyclohexylcarbodiimide and DMF in a dosage ratio of 14 g:50 mL.

[0036] The steps for preparing cardanol triol are as follows:

[0037] 0.1 mol of cardanol glycidyl ether from Example 1 and 0.1 mol of diethanolamine were placed in a flask, the temperature was controlled at 60° C., the reaction was stirred for 10 h, and the mixture was cooled to room temperature.

[0038] Example 3

[0039] The preparation steps of hydroxyl-terminated hyperbranched polyester are as follows:

[0040] 20 g of cardanol triol and 60.4 g of 2,2-dimethylolpropionic acid were placed in a flask, 100 mL of DMF was added, and ultrasonic treatment was carried out for 20 min. 50 mL of DMF solution of N, N'-dicyclohexylcarbodiimide was added dropwise to the flask. After the addition was complete, the mixture was stirred in an ice bath for 6 h. After the reaction was completed, the reaction product was centrifuged to remove the white precipitate of dicyclohexylurea. Deionized water was added to the supernatant to dissolve the residual dicyclohexylurea. This was repeated 5 times. The supernatant was placed in a 4 ° C refrigerator and allowed to stand for 12 h. The residual dicyclohexylurea was removed by centrifugation. Finally, N, N-dimethylformamide was removed by rotary evaporation and the mixture was dried in a vacuum drying oven at 80 ° C for 12 h to obtain a hydroxyl-terminated hyperbranched polyester. The DMF solution of N, N'-dicyclohexylcarbodiimide consisted of N, N'-dicyclohexylcarbodiimide and DMF in a dosage ratio of 18 g: 50 mL.

[0041] The steps for preparing cardanol triol are as follows:

[0042] 0.1 mol of cardanol glycidyl ether from Example 1 and 0.1 mol of diethanolamine were placed in a flask, the temperature was controlled at 70° C., the reaction was stirred for 8 h, and the mixture was cooled to room temperature.

[0043] Comparative Example 1

[0044] Preparation of terminal hydroxyl hyperbranched polyester: Compared with Example 2, 20 g of cardanol triol in Example 2 was replaced with 0.05 mol of trimethylolpropane, and the remaining raw materials and preparation process were the same as in Example 2.

[0045] Example 4

[0046] A low-VOC alkyd resin coating comprises the following raw materials in parts by weight:

[0047] 55 parts of branched alkyd resin, 2 parts of triethylamine, 0.05 parts of defoamer, 0.3 parts of dispersant, 8 parts of precipitated barium sulfate, 50 parts of deionized water, 0.3 parts of leveling agent, and 0.3 parts of drying agent;

[0048] The preparation method of the low-VOC alkyd resin coating comprises the following steps:

[0049] S1, stirring and mixing a branched alkyd resin, deionized water (1 / 3 of the mass of the branched alkyd resin), and triethylamine for 40 minutes to obtain a water-dispersible resin;

[0050] S2. Add defoamer, dispersant, precipitated barium sulfate and remaining deionized water to the water-dispersible resin, disperse at a speed of 500 r / min for 20 minutes, grind until the particle size of the coating is ≤35 μm, then add leveling agent and drying agent, and stir at a speed of 300 r / min for 20 minutes to obtain a low-VOC alkyd resin coating.

[0051] The preparation steps of branched alkyd resin are as follows:

[0052] 26 kg of linoleic acid, 15 kg of phthalic anhydride, 15 kg of the hydroxyl-terminated hyperbranched polyester of Example 2, 10 kg of polyethylene glycol, 18 kg of phthalic anhydride and 3 kg of xylene were added to a reactor. Under nitrogen protection, the temperature was raised to 210° C. at a heating rate of 5° C. / h. After being kept warm for 2 hours, the temperature was raised to 220° C. and maintained within this temperature range for reaction until the acid value reached 8 mgKOH / g. The xylene was removed by vacuumization, and the temperature was lowered to 180° C. 3 kg of maleic anhydride and 4 kg of adipic acid were added. The temperature was kept at 180° C. for 2 hours, then lowered to 130° C. 15 kg of propylene glycol was added, and the temperature was lowered to 50° C. with stirring to obtain a branched alkyd resin.

[0053] Among them, the defoamer is BYK-020, the dispersant is BYK-190, the leveling agent is BYK-300, and the drying agent is Octa-Soligen Zirconium 10aqua.

[0054] Example 5

[0055] A low-VOC alkyd resin coating comprises the following raw materials in parts by weight:

[0056] 65 parts of branched alkyd resin, 3 parts of dimethylethanolamine, 0.08 parts of defoamer, 0.4 parts of dispersant, 11 parts of precipitated barium sulfate, 60 parts of deionized water, 0.5 parts of leveling agent, and 0.4 parts of drying agent;

[0057] The preparation method of the low-VOC alkyd resin coating comprises the following steps:

[0058] S1, stirring and mixing a branched alkyd resin, deionized water (1 / 3 the mass of the branched alkyd resin), and dimethylethanolamine for 42 minutes to obtain a water-dispersible resin;

[0059] S2. Add defoamer, dispersant, precipitated barium sulfate and remaining deionized water to the water-dispersible resin, disperse at a speed of 600 r / min for 25 minutes, grind until the particle size of the coating is ≤35 μm, then add leveling agent and drying agent, and stir at a speed of 400 r / min for 30 minutes to obtain a low-VOC alkyd resin coating.

[0060] The preparation steps of branched alkyd resin are as follows:

[0061] 28 kg of soy acid, 18 kg of phthalic anhydride, 18 kg of the hydroxy-terminated hyperbranched polyester of Example 3, 12 kg of polyethylene glycol, 19 kg of phthalic anhydride and 4 kg of xylene were added to a reactor. Under nitrogen protection, the temperature was raised to 210° C. at a heating rate of 5° C. / h. After insulation treatment for 2 hours, the temperature was raised to 223° C. and maintained within this temperature range to react until the acid value reached 10 mgKOH / g. The xylene was removed by vacuumization, and the temperature was lowered to 180° C., 4 kg of maleic anhydride and 6 kg of adipic acid were added, and the temperature was kept at 182° C. for 1.5 hours. The temperature was lowered to 130° C., 20 kg of propylene glycol was added, and the temperature was lowered to 50° C. with stirring to obtain a branched alkyd resin.

[0062] Among them, the defoamer is BYK-022, the dispersant is BYK-180, the leveling agent is BYK-300, and the drying agent is Octa-Soligen Zinc 10aqua.

[0063] Example 6

[0064] A low-VOC alkyd resin coating comprises the following raw materials in parts by weight:

[0065] 75 parts of branched alkyd resin, 4 parts of triethylamine, 0.1 parts of defoamer, 0.5 parts of dispersant, 15 parts of precipitated barium sulfate, 70 parts of deionized water, 1 part of leveling agent, and 0.5 parts of drying agent;

[0066] The preparation method of the low-VOC alkyd resin coating comprises the following steps:

[0067] S1, stirring and mixing a branched alkyd resin, deionized water (1 / 3 the mass of the branched alkyd resin), and triethylamine for 45 minutes to obtain a water-dispersible resin;

[0068] S2. Add defoamer, dispersant, precipitated barium sulfate and remaining deionized water to the water-dispersible resin, disperse at a speed of 700 r / min for 30 minutes, grind until the coating particles have a particle size of ≤35 μm, add leveling agent and drying agent, and stir at a speed of 500 r / min for 40 minutes to obtain a low-VOC alkyd resin coating.

[0069] The preparation steps of branched alkyd resin are as follows:

[0070] 30 kg of linoleic acid, 20 kg of phthalic anhydride, 20 kg of the hydroxy-terminated hyperbranched polyester of Example 3, 15 kg of polyethylene glycol, 20 kg of phthalic anhydride and 5 kg of xylene were added to a reactor. Under nitrogen protection, the temperature was raised to 210° C. at a heating rate of 5° C. / h. After insulation treatment for 2 hours, the temperature was raised to 225° C. and maintained within this temperature range to react until the acid value reached 12 mgKOH / g. The xylene was removed by vacuumization, and the temperature was lowered to 180° C. 5 kg of maleic anhydride and 8 kg of adipic acid were added. The temperature was kept at 185° C. for 2 hours, then lowered to 130° C. 25 kg of propylene glycol was added, and the temperature was lowered to 50° C. with stirring to obtain a branched alkyd resin.

[0071] Among them, the defoamer is BYK-020, the dispersant is BYK-190, the leveling agent is BYK-300, and the drying agent is Octa-Soligen Zirconium 10aqua.

[0072] Comparative Example 2

[0073] A low-VOC alkyd resin coating is disclosed. Compared with Example 4, the terminal hydroxyl hyperbranched polyester in Example 4 is replaced with the product prepared in Comparative Example 1. The raw materials and preparation process are the same as those in Example 4.

[0074] Comparative Example 3

[0075] A low-VOC alkyd resin coating is disclosed. Compared with Example 4, the terminal hydroxyl hyperbranched polyester in Example 4 is replaced by pentaerythritol. The raw materials and preparation process are the same as those in Example 4.

[0076] The alkyd resins obtained in Examples 4 to 6 and Comparative Examples 2 to 3 were tested, and the viscosity was measured using a viscometer;

[0077] Refer to standard HG / T4847-2015 to test the volatile organic compound (VOC) content;

[0078] Refer to HG / T25251-2010 to test surface drying time and actual drying time;

[0079] The impact resistance was tested using an impact tester in accordance with the standard GB / T1732-1993.

[0080] Carry out water resistance test in accordance with the provisions of GB / T1733-1993;

[0081] The test results are shown in Table 1:

[0082] Table 1

[0083] project Example 4 Example 5 Example 6 Comparative Example 2 Comparative Example 3 Viscosity (mPa·s) 654 577 632 692 705 VOC content (g / L) 75 71 74 76 82 Surface drying time / h 0.8 0.5 0.7 0.9 1 Drying time / h 13 11 12 14 15 Impact resistance (kg·cm) 50 50 50 45 40 Water resistance / 480h Paint film is normal Paint film is normal Paint film is normal Paint film turns white Paint film turns white

[0084] It can be seen from the data recorded in Table 1 that, compared with Comparative Examples 2 and 3, the alkyd resin coatings obtained in Examples 4, 5 and 6 not only have lower VOC content, but also have better drying speed, mechanical properties and water resistance.

[0085] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0086] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low VOC alkyd resin coating, characterized in that: The invention comprises the following raw materials in parts by weight: 55-75 parts of branched alkyd resin, 2-4 parts of amine neutralizer, 0.05-0.1 parts of defoamer, 0.3-0.5 parts of dispersant, 8-15 parts of precipitated barium sulfate, 50-70 parts of deionized water, 0.3-1 parts of leveling agent, and 0.3-0.5 parts of drying agent; The preparation steps of branched alkyd resin are as follows: Add vegetable oil fatty acid, phthalic anhydride, hydroxyl-terminated hyperbranched polyester, polyethylene glycol, phthalic anhydride and xylene into a reactor, and under nitrogen protection, heat the reactor to 210°C at a heating rate of 5°C / h, keep the temperature for 2 hours, then heat the reactor to 220-225°C, and keep the temperature within this range to react until the acid value reaches 8-12 mgKOH / g. Vacuum the reactor to remove the xylene, cool the reactor to 180°C, add maleic anhydride and adipic acid, keep the temperature at 180-185°C for 1-2 hours, cool the reactor to 130°C, add propylene glycol, stir the reactor and cool the reactor to 50°C to obtain a branched alkyd resin. The mass ratio of vegetable oil fatty acid, phthalic anhydride, hydroxyl-terminated hyperbranched polyester, polyethylene glycol, phthalic anhydride, xylene, maleic anhydride, adipic acid and propylene glycol is 26-30:15-20:15-20:10-15:18-20:3-5:3-5:4-8:15-25; The preparation steps of hydroxyl-terminated hyperbranched polyester are as follows: Cardanol triol and 2,2-dimethylol propionic acid are placed in a flask, DMF is added, and ultrasonic treatment is performed for 10-20 minutes. A DMF solution of N,N'-dicyclohexylcarbodiimide is added dropwise to the flask, and the mixture is stirred in an ice bath for 4-6 hours to obtain a hydroxyl-terminated hyperbranched polyester.

2. A low VOC alkyd resin coating according to claim 1, characterized in that: The amount ratio of cardanol triol, 2,2-dihydroxymethylpropionic acid, DMF, and DMF solution of N,N'-dicyclohexylcarbodiimide is 2g:6.04g:5-10mL:5mL, and the DMF solution of N,N'-dicyclohexylcarbodiimide is composed of N,N'-dicyclohexylcarbodiimide and DMF in the amount ratio of 1.4-1.8g:5mL.

3. A low VOC alkyd resin coating according to claim 1, characterized in that: The steps for preparing cardanol triol are as follows: Place cardanol glycidyl ether and diethanolamine in a flask, control the temperature at 60-70°C, stir and react for 8-10 hours, and cool to room temperature. The molar ratio of cardanol glycidyl ether to diethanolamine is 1:

1.

4. The method for preparing a low-VOC alkyd resin coating according to claim 1, wherein: The following steps are involved: S1, stirring and mixing a branched alkyd resin, deionized water (1 / 3 of the mass of the branched alkyd resin), and an amine neutralizer for 40-45 minutes to obtain a water-dispersible resin; S2. Add defoamer, dispersant, precipitated barium sulfate and remaining deionized water to the water-dispersible resin, disperse at a speed of 500-700 r / min for 20-30 min, grind to a particle size of ≤35 μm, add leveling agent and drying agent, and stir at a speed of 300-500 r / min for 20-40 min to obtain a low-VOC alkyd resin coating.