A polyester polyol and its preparation method and application

Abstract

The present invention belongs to the technical field of polyols. The present invention provides a polyester polyol and a preparation method and application thereof. The preparation method comprises mixing a diol, hydroxypivalic acid neopentyl glycol monoester, and trimethylolpropane, subjecting the mixture to an esterification reaction with a dibasic acid; subjecting the esterification product to a polycondensation reaction, and then adding castor oil and a catalyst to an ester exchange reaction. The polyester polyol prepared by the present invention contains both saturated polyester segments and long side-group segments of castor oil fatty acids, and has a low molecular weight and high functionality. When used in a two-component solvent-free metal anticorrosion coating, the coating can be endowed with high weather resistance and durability, enabling it to adapt to changes in outdoor ambient temperature, having good UV resistance and adhesion, and enabling the cured metal anticorrosion coating to form a complete network structure, giving the paint film excellent weather resistance, wear resistance, impact resistance, corrosion resistance, and stability, and meeting various performance requirements of the metal anticorrosion coating.

Description

Technical Field

[0001] The present invention relates to the technical field of polyol preparation, in particular to a polyester polyol and a preparation method and application thereof. Background Art

[0002] Metal corrosion can lead to a decline in metal performance and shortened lifespan, and is the biggest cause of metal material loss. The application of anti-corrosion coatings is the most effective protective method to reduce or delay metal corrosion, and is currently the most widely used metal anti-corrosion technology. Anti-corrosion coatings have the advantages of easy construction, strong adaptability, no restrictions on equipment area, structure and shape, easy recoating and repair, and low cost. According to the corrosion resistance of the coating film layer and the requirements of use, anti-corrosion coatings can be divided into general-purpose and heavy-duty anti-corrosion types. Under the corrosive conditions of general atmospheric environments, such as machine tools, automobiles, railway vehicles, home appliances and other industries, general-purpose anti-corrosion coatings are usually used; under the environmental conditions of industrial or marine atmospheric corrosion, such as chemical, metallurgical, marine engineering and other industries, heavy-duty anti-corrosion coatings are mostly used. In addition to the basic physical and mechanical properties of general coatings, anti-corrosion coatings should also have the following characteristics: (1) High corrosion resistance: not easily swollen, dissolved, destroyed, or decomposed by corrosive media, and in a stable state; (2) High weather resistance: adapting to changes in outdoor ambient temperature and having good UV resistance; (3) High durability: the coating has a long service life; (4) The coating film is thick, and the air permeability and water permeability of the coating are low; (5) Good construction and supporting performance.

[0003] In recent years, many new, high-performance anti-corrosion coatings have been developed, including high-solids coatings, long-lasting, heavy-duty anti-corrosion coatings, powder coatings, water-based coatings, and fluorine-containing coatings. There are also specialized anti-corrosion coatings, such as heat exchanger coatings, antistatic coatings, highly elastic coatings, anti-cracking coatings, and non-toxic coatings. Despite the current abundance of anti-corrosion coatings, their production volume is enormous, and their applications are widespread, they are essentially solvent-based, resulting in significant annual emissions of volatile organic compounds (VOCs). These VOCs are difficult to recycle, significantly polluting the environment and wasting resources, while also posing serious safety risks to coating workers. Consequently, with the increasingly severe environmental challenges, countries around the world have begun to phase out or restrict the use of high-solvent-based anti-corrosion coatings, shifting towards environmentally friendly alternatives.

[0004] Two-component solvent-free metal anti-corrosion coatings contain no organic solvents, completely overcoming the drawbacks of conventional solvent-based anti-corrosion coatings, such as environmental pollution and health hazards to coating workers. They also address the problems of low adhesion, slow curing, and poor anti-corrosion effectiveness of water-based anti-corrosion coatings, making them a new type of anti-corrosion coating with the greatest development potential. The polyester polyol series used as the main agent in two-component solvent-free metal anti-corrosion coatings is a key raw material that determines the performance of two-component solvent-free metal anti-corrosion coatings and is also a fine chemical with high added value. Currently, there is no production and supply of high-functionality, branched polyester polyols suitable for two-component solvent-free metal anti-corrosion coatings. Therefore, the development of polyester polyols for two-component solvent-free metal anti-corrosion coatings is a key step in improving the overall technical level of two-component solvent-free metal anti-corrosion coatings and enhancing their core competitiveness. Summary of the Invention

[0005] The purpose of the present invention is to provide a polyester polyol and a preparation method and application thereof in view of the deficiencies in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing polyester polyol, comprising the following steps:

[0008] 1) mixing a diol, hydroxypivalic acid neopentyl glycol monoester and trimethylolpropane, and subjecting the mixture to an esterification reaction with a dibasic acid to obtain an esterified product;

[0009] 2) After the esterification product is subjected to polycondensation reaction, castor oil and a catalyst are added to carry out ester exchange reaction to obtain polyester polyol.

[0010] Preferably, in step 1), the diol is one or more of ethylene glycol, propylene glycol, 1,6-hexanediol and 2,4-diethyl-1,5-pentanediol; the dibasic acid is one or more of adipic acid, hexahydrophthalic anhydride, sebacic acid and 1,12-lauric acid; and the mass ratio of the diol, hydroxypivalic acid neopentyl glycol monoester, trimethylolpropane and dibasic acid is 10-30:5-15:8-15:20-35.

[0011] Preferably, the mixing temperature in step 1) is 110-130° C., and the mixing is carried out in a nitrogen atmosphere.

[0012] Preferably, the temperature of the esterification reaction in step 1) is 210-230° C., the rate of heating to the esterification reaction temperature is 10-15° C. / h, and the esterification reaction time is based on the amount of water produced by the esterification reaction reaching the theoretical water output; the hydroxyl value of the esterified product is 370-400 mg KOH / g, and the acid value is ≤25 mg KOH / g.

[0013] Preferably, the temperature of the polycondensation reaction in step 2) is 210 to 230° C., the time of the polycondensation reaction is 4 to 8 hours, and the polycondensation reaction is carried out in a vacuum atmosphere with a vacuum degree of -0.1 to -0.06 MPa.

[0014] Preferably, after the polycondensation reaction in step 2) is completed, the hydroxyl value of the polycondensation product is 385-400 mg KOH / g, and the acid value is ≤2 mg KOH / g.

[0015] Preferably, in step 2), the catalyst is dibutyltin dilaurate; the mass ratio of castor oil to catalyst is 45-55:0.03-0.08; and the mass ratio of castor oil to esterification product is 45-55:50-60.

[0016] Preferably, the temperature of the transesterification reaction in step 2) is 150-170° C., the time of the transesterification reaction is 2-4 hours, and the transesterification reaction is carried out in a vacuum atmosphere with a vacuum degree of -0.095 to -0.085 MPa.

[0017] The present invention also provides a polyester polyol prepared by the preparation method.

[0018] The present invention also provides application of the polyester polyol in a two-component solvent-free metal anticorrosive coating.

[0019] The beneficial effects of the present invention include the following:

[0020] 1) The present invention synthesizes a series of branched esterification products by esterification reaction using multiple saturated dibasic acids and diols, then adds a catalyst and castor oil to carry out an ester exchange reaction, introducing castor oil fatty acid segments into the esterification product molecules, and synthesizing a composite low-molecular-weight, high-functionality branched polyester polyol containing both saturated polyester segments and long side-group segments of castor oil fatty acids. The composite low-molecular-weight, high-functionality branched polyester polyol can be used to produce two-component solvent-free metal anti-corrosion coatings with various properties.

[0021] 2) The polyester polyol prepared by the present invention uses a large number of saturated polyester segments, which gives the two-component solvent-free metal anti-corrosion coating high weather resistance and durability, enabling it to adapt to changes in outdoor ambient temperature, has good ultraviolet resistance, and greatly extends the service life of the coating. At the same time, the polyester segments can improve its adhesion to the metal substrate.

[0022] 3) The invention imparts lower air permeability and water permeability to the paint film by introducing castor oil fatty acid side chains, so that the paint film has good water repellency and better construction performance and supporting performance.

[0023] 4) The polyester polyol prepared by the present invention has a low molecular weight and high functionality, so when used in a two-component solvent-free metal anti-corrosion coating, the cured metal anti-corrosion coating can form a complete network structure, giving the paint film excellent weather resistance, wear resistance, impact resistance and corrosion resistance, and is not swollen, dissolved, destroyed or decomposed by corrosive media. It remains in a stable state for a long time and can fully meet the various performance requirements of the two-component solvent-free metal anti-corrosion coating.

[0024] 5) The preparation method of the polyester polyol of the present invention is simple, environmentally friendly, highly safe, and has broad application prospects. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing polyester polyol, comprising the following steps:

[0026] 1) mixing a diol, hydroxypivalic acid neopentyl glycol monoester and trimethylolpropane, and subjecting the mixture to an esterification reaction with a dibasic acid to obtain an esterified product;

[0027] 2) After the esterification product is subjected to polycondensation reaction, castor oil and a catalyst are added to carry out ester exchange reaction to obtain polyester polyol.

[0028] In the present invention, the diol in step 1) is preferably one or more of ethylene glycol, propylene glycol, 1,6-hexanediol and 2,4-diethyl-1,5-pentanediol; the dibasic acid is preferably one or more of adipic acid, hexahydrophthalic anhydride, sebacic acid and 1,12-lauric acid; the mass ratio of the diol, hydroxypivalic acid neopentyl glycol monoester, trimethylolpropane and dibasic acid is preferably 10-30:5-15:8-15:20-35, more preferably 15-25:7-13:10-13:25-30, and more preferably 18-22:9-11:11-12:26-28.

[0029] In the present invention, the mixing temperature in step 1) is preferably 110-130° C., more preferably 115-125° C., and even more preferably 120° C.; the mixing is preferably carried out in a nitrogen atmosphere.

[0030] In the present invention, the temperature of the esterification reaction in step 1) is preferably 210-230°C, more preferably 215-225°C, and more preferably 220°C; the rate of heating to the esterification reaction temperature is preferably 10-15°C / h, more preferably 15°C / h; the time of the esterification reaction is preferably based on the amount of water produced by the esterification reaction reaching the theoretical water output; the hydroxyl value of the esterified product is preferably 370-400 mg KOH / g, more preferably 375-395 mg KOH / g, and more preferably 380-390 mg KOH / g; the acid value is preferably ≤25 mg KOH / g, more preferably ≤20 mg KOH / g, and more preferably ≤15 mg KOH / g.

[0031] In the present invention, the temperature of the polycondensation reaction in step 2) is preferably 210 to 230°C, more preferably 215 to 225°C, and more preferably 220°C; the time of the polycondensation reaction is preferably 4 to 8 hours, more preferably 5 to 7 hours, and more preferably 6 hours; the polycondensation reaction is preferably carried out in a vacuum atmosphere, and the vacuum degree of the vacuum atmosphere is preferably -0.1 to -0.06 MPa, more preferably -0.09 to -0.07 MPa, and more preferably -0.08 MPa.

[0032] In the present invention, the polycondensation reaction in step 2) is preferably carried out in sequence at a vacuum degree of -0.07 to -0.06 MPa, -0.09 to -0.075 MPa, and -0.1 to -0.095 MPa. The polycondensation reaction time at a vacuum degree of -0.07 to -0.06 MPa is preferably 0.5 to 1.5 h, more preferably 1 h. The polycondensation reaction time at a vacuum degree of -0.09 to -0.075 MPa is preferably 0.5 to 1.5 h, more preferably 1 h. The polycondensation reaction time at a vacuum degree of -0.1 to -0.095 MPa is preferably 3 to 5 h, more preferably 4 h.

[0033] In the present invention, after the polycondensation reaction in step 2) is completed, the hydroxyl value of the polycondensation product is preferably 385 to 400 mg KOH / g, more preferably 390 to 395 mg KOH / g, and more preferably 392 to 394 mg KOH / g; the acid value is preferably ≤2 mg KOH / g, more preferably ≤1.5 mg KOH / g, and more preferably ≤1 mg KOH / g.

[0034] In the present invention, the catalyst in step 2) is preferably dibutyltin dilaurate; the mass ratio of the castor oil to the catalyst is preferably 45-55:0.03-0.08, more preferably 48-52:0.04-0.06, and more preferably 50:0.05; the mass ratio of the castor oil to the esterification product is preferably 45-55:50-60, more preferably 48-52:52-58, and more preferably 50:55.

[0035] In the present invention, the temperature of the transesterification reaction in step 2) is preferably 150-170°C, more preferably 155-165°C, and more preferably 160°C; the time of the transesterification reaction is preferably 2-4h, more preferably 2.5-3.5h, and more preferably 3h; the transesterification reaction is preferably carried out in a vacuum atmosphere, and the vacuum degree of the vacuum atmosphere is preferably -0.095 to -0.085MPa, and more preferably -0.09MPa.

[0036] The present invention also provides polyester polyol prepared by the preparation method.

[0037] The present invention also provides application of the polyester polyol in a two-component solvent-free metal anticorrosive coating.

[0038] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0039] Example 1

[0040] 5 kg of propylene glycol, 10 kg of 2,4-diethyl-1,5-pentanediol, 8 kg of hydroxypivalic acid neopentyl glycol monoester and 10 kg of trimethylolpropane were mixed uniformly in an esterification reaction kettle filled with nitrogen at a temperature of 120° C., and then 12 kg of adipic acid and 15 kg of sebacic acid were added to the mixture. The esterification reaction kettle was heated to 220° C. at a rate of 15° C. / h. The esterification reaction began when water was distilled out of the esterification reaction kettle. The esterification reaction was completed when the water output of the esterification reaction reached a theoretical water output of 5.6 kg. The hydroxyl value of the esterified product was measured to be 380 mg KOH / g, and the acid value was 15 mg KOH / g.

[0041] The temperature of the esterification reaction kettle was maintained at 220°C, and it was vacuumed for polycondensation reaction, wherein the vacuum degree was maintained at -0.06 MPa for 1 hour, the vacuum degree was maintained at -0.08 MPa for 1 hour, and the vacuum degree was maintained at -0.095 MPa for 4 hours. After the polycondensation reaction was completed, sampling and measuring the hydroxyl value of the polycondensation product were 391 mg KOH / g, and the acid value was 1.1 mg KOH / g.

[0042] After the temperature of the esterification reactor was lowered to 160° C., 48 kg of castor oil and 0.05 kg of dibutyltin dilaurate were added, and then vacuum was applied. The transesterification reaction was carried out at a vacuum degree of -0.09 MPa for 2 h to obtain polyester polyol.

[0043] The polyester polyol prepared in this example has a hydroxyl value of 288 mg KOH / g, a viscosity (25° C.) of 550 mPa·s, an acid value of 0.5 mg KOH / g, and a molecular weight of 682.

[0044] Example 2

[0045] 6 kg of ethylene glycol, 8 kg of 2,4-diethyl-1,5-pentanediol, 8 kg of hydroxypivalic acid neopentyl glycol monoester and 11 kg of trimethylolpropane were uniformly mixed in an esterification reaction kettle filled with nitrogen at a temperature of 110° C., and then 10 kg of adipic acid and 16 kg of hexahydrophthalic anhydride were added to the mixture. The esterification reaction kettle was heated to 210° C. at a rate of 15° C. / h. The esterification reaction began when water was distilled out of the esterification reaction kettle. The esterification reaction was completed when the water output of the esterification reaction reached a theoretical water output of 6.0 kg. The hydroxyl value of the esterified product was 389 mg KOH / g and the acid value was 19 mg KOH / g.

[0046] The temperature of the esterification reaction kettle was maintained at 210°C, and it was vacuumed for polycondensation reaction, wherein the vacuum degree was maintained at -0.07 MPa for 1.5 hours, the vacuum degree was maintained at -0.09 MPa for 0.5 hours, and the vacuum degree was maintained at -0.1 MPa for 5 hours. After the polycondensation reaction was completed, sampling and measuring the hydroxyl value of the polycondensation product were 395 mg KOH / g, and the acid value was 1.0 mg KOH / g.

[0047] After the temperature of the esterification reactor was lowered to 150° C., 48 kg of castor oil and 0.05 kg of dibutyltin dilaurate were added, and then vacuum was applied. The transesterification reaction was carried out at a vacuum degree of -0.095 MPa for 3 h to obtain polyester polyol.

[0048] The polyester polyol prepared in this example has a hydroxyl value of 282 mg KOH / g, a viscosity (25° C.) of 620 mPa·s, an acid value of 0.8 mg KOH / g, and a molecular weight of 696.

[0049] Example 3

[0050] 8 kg of 1,6-hexanediol, 12 kg of 2,4-diethyl-1,5-pentanediol, 6 kg of hydroxypivalic acid neopentyl glycol monoester and 13 kg of trimethylolpropane were mixed uniformly in an esterification reaction kettle filled with nitrogen at a temperature of 130° C., and then 12 kg of sebacic acid and 15 kg of hexahydrophthalic anhydride were added to the mixture. The esterification reaction kettle was heated to 230° C. at a rate of 15° C. / h. The esterification reaction began when water was distilled out of the esterification reaction kettle. The esterification reaction was completed when the water output of the esterification reaction reached a theoretical water output of 5.6 kg. The hydroxyl value of the esterified product was 392 mg KOH / g and the acid value was 11 mg KOH / g.

[0051] The temperature of the esterification reaction kettle was maintained at 230°C, and it was vacuumed for polycondensation reaction, wherein the vacuum degree was maintained at -0.065 MPa for 0.5 h, the vacuum degree was maintained at -0.08 MPa for 0.5 h, and the vacuum degree was maintained at -0.095 MPa for 3 h. After the polycondensation reaction was completed, sampling and measuring the hydroxyl value of the polycondensation product was 385 mg KOH / g, and the acid value was 1.0 mg KOH / g.

[0052] After the temperature of the esterification reaction kettle was lowered to 170° C., 49 kg of castor oil and 0.05 kg of dibutyltin dilaurate were added, and then vacuum was applied. The transesterification reaction was carried out at a vacuum degree of -0.085 MPa for 4 hours to obtain polyester polyol.

[0053] The polyester polyol prepared in this example has a hydroxyl value of 287 mg KOH / g, a viscosity (25° C.) of 540 mPa·s, an acid value of 0.8 mg KOH / g, and a molecular weight of 665.

[0054] Example 4

[0055] 5 kg of propylene glycol, 10 kg of 1,6-hexanediol, 9 kg of hydroxypivalic acid neopentyl glycol monoester and 13 kg of trimethylolpropane were mixed uniformly in an esterification reaction kettle filled with nitrogen at a temperature of 125° C., and then 15 kg of 1,12-lauric acid and 13 kg of hexahydrophthalic anhydride were added to the mixture. The esterification reaction kettle was heated to 220° C. at a rate of 15° C. / h. The esterification reaction began when water was distilled out of the esterification reaction kettle. The esterification reaction was completed when the water output of the esterification reaction reached a theoretical water output of 5.4 kg. The hydroxyl value of the esterified product was 379 mg KOH / g and the acid value was 12 mg KOH / g.

[0056] The temperature of the esterification reaction kettle was maintained at 220°C, and it was vacuumed for polycondensation reaction, wherein the vacuum degree was maintained at -0.06 MPa for 1 hour, the vacuum degree was maintained at -0.08 MPa for 1 hour, and the vacuum degree was maintained at -0.095 MPa for 4 hours. After the polycondensation reaction was completed, sampling and measuring the hydroxyl value of the polycondensation product was 391 mg KOH / g, and the acid value was 1.2 mg KOH / g.

[0057] After the temperature of the esterification reaction kettle was lowered to 160° C., 52 kg of castor oil and 0.08 kg of dibutyltin dilaurate were added, and then vacuum was applied. The transesterification reaction was carried out at a vacuum degree of -0.09 MPa for 2.5 hours to obtain polyester polyol.

[0058] The polyester polyol prepared in this example has a hydroxyl value of 286 mg KOH / g, a viscosity (25° C.) of 610 mPa·s, an acid value of 0.4 mg KOH / g, and a molecular weight of 687.

[0059] Comparative Example 1

[0060] 9 kg of propylene glycol, 10 kg of 2,4-diethyl-1,5-pentanediol, 8 kg of hydroxypivalic acid neopentyl glycol monoester and 5 kg of trimethylolpropane were mixed uniformly in an esterification reaction kettle filled with nitrogen at a temperature of 120° C., and then 12 kg of adipic acid and 15 kg of hexahydrophthalic anhydride were added to the mixture. The esterification reaction kettle was heated to 220° C. at a rate of 15° C. / h. The esterification reaction began when water was distilled out of the esterification reaction kettle. The esterification reaction was completed when the water output of the esterification reaction reached a theoretical water output of 6.5 kg. The hydroxyl value of the esterified product was measured to be 384 mg KOH / g, and the acid value was 19 mg KOH / g.

[0061] The temperature of the esterification reaction kettle was maintained at 220°C, and it was vacuumed for polycondensation reaction, wherein the vacuum degree was maintained at -0.06 MPa for 1 hour, the vacuum degree was maintained at -0.08 MPa for 1 hour, and the vacuum degree was maintained at -0.095 MPa for 4 hours. After the polycondensation reaction was completed, the hydroxyl value of the polycondensation product was measured by sampling and the acid value was 390 mg KOH / g, and 1.0 mg KOH / g.

[0062] After the temperature of the esterification reactor was lowered to 160° C., 48 kg of castor oil and 0.05 kg of dibutyltin dilaurate were added, and then vacuum was applied. The transesterification reaction was carried out at a vacuum degree of -0.09 MPa for 2 h to obtain polyester polyol.

[0063] The polyester polyol prepared in this comparative example had a hydroxyl value of 280 mg KOH / g, a viscosity (25° C.) of 560 mPa·s, an acid value of 0.3 mg KOH / g, and a molecular weight of 600.

[0064] Comparative Example 2

[0065] The amount of trimethylolpropane in Example 1 was modified to 3 kg, the temperature of the esterification reaction was modified to 180° C., the time of the transesterification reaction was modified to 0.5 h, and other conditions were the same as in Example 1 to obtain polyester polyol.

[0066] The polyester polyol prepared in this comparative example had a hydroxyl value of 270 mg KOH / g, a viscosity (25° C.) of 510 mPa.s, an acid value of 0.2 mg KOH / g, and a molecular weight of 519.

[0067] 100 g of the polyester polyols prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were respectively mixed with 75 g of PM-200 curing agent to prepare a two-component solvent-free metal anticorrosion coating, which was then evenly coated on a carbon steel surface (coating thickness of 0.1 mm). The performance of the carbon steel surface coating was tested, and the test results are shown in Table 1.

[0068] Table 1 Performance test results of two-component solvent-free metal anticorrosion coatings made from different polyester polyols

[0069]

[0070]

[0071] As can be seen from Table 1, the polyester polyols prepared in Examples 1 to 4 are esterified products with good temperature resistance and hydrolysis resistance by introducing a highly hydrophobic diol, a long carbon chain dibasic acid and trifunctional trimethylolpropane, and the trifunctional natural oil castor oil and a catalyst are added to the esterified product to carry out an ester exchange reaction, thereby further improving the air permeability and water permeability of the cured two-component solvent-free metal anti-corrosion coating.

[0072] The polyester polyol prepared by the present invention is a composite low-molecular-weight, high-functionality, branched polyester polyol containing both saturated polyester segments and long side-group segments of castor oil fatty acids. The use of a large number of saturated polyester segments imparts high weather resistance and durability to the two-component solvent-free metal anti-corrosion coating, enabling it to adapt to changes in outdoor ambient temperature, exhibiting good UV resistance and improving its adhesion to metal substrates. Furthermore, its use in the two-component solvent-free metal anti-corrosion coating enables the cured metal anti-corrosion coating to form a complete network structure, imparting excellent weather resistance, wear resistance, impact resistance, and corrosion resistance to the paint film. The coating resists swelling, dissolution, destruction, and decomposition by corrosive media, maintaining a stable state over a long period of time, and fully meeting the various performance requirements of the two-component solvent-free metal anti-corrosion coating.

[0073] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing polyester polyol, characterized in that: The following steps are included: 1) mixing diol, hydroxypivalic acid neopentyl glycol monoester and trimethylolpropane, and subjecting the mixture to an esterification reaction with a dibasic acid to obtain an esterified product; 2) After the esterification product is subjected to polycondensation reaction, castor oil and a catalyst are added to carry out transesterification reaction to obtain polyester polyol; The mass ratio of the diol, neopentyl glycol monohydroxypivalate, trimethylolpropane and dibasic acid is 10-30:5-15:8-15:20-35; Step 1) The diol is a combination of propylene glycol and 2,4-diethyl-1,5-pentanediol, a combination of ethylene glycol and 2,4-diethyl-1,5-pentanediol, a combination of 1,6-hexanediol and 2,4-diethyl-1,5-pentanediol, or a combination of propylene glycol and 1,6-hexanediol; the dibasic acid is a combination of adipic acid and sebacic acid, a combination of adipic acid and hexahydrophthalic anhydride, a combination of sebacic acid and hexahydrophthalic anhydride, or a combination of 1,12-lauric acid and hexahydrophthalic anhydride; Step 1) The esterification reaction temperature is 210-230°C, and the rate of heating to the esterification reaction temperature is 10-15°C / h. The esterification reaction time is based on the esterification reaction water output reaching the theoretical water output. The esterification product has a hydroxyl value of 370-400 mg KOH / g and an acid value of ≤25 mg KOH / g. Step 2) the polycondensation reaction is carried out at a temperature of 210-230° C. for 4-8 hours in a vacuum atmosphere at a vacuum degree of -0.1-0.06 MPa; Step 2) After the polycondensation reaction is completed, the hydroxyl value of the polycondensation product is 385-400 mg KOH / g and the acid value is ≤2 mg KOH / g; Step 2) The temperature of the transesterification reaction is 150-170° C., and the time of the transesterification reaction is 2-4 hours. The transesterification reaction is carried out in a vacuum atmosphere, and the vacuum degree of the vacuum atmosphere is -0.095-0.085 MPa.

2. The preparation method according to claim 1, characterized in that The mixing temperature in step 1) is 110-130° C. and the mixing is performed in a nitrogen atmosphere.

3. The preparation method according to claim 2, characterized in that Step 2) The catalyst is dibutyltin dilaurate; the mass ratio of castor oil to catalyst is 45-55:0.03-0.08; the mass ratio of castor oil to esterification product is 45-55:50-60.

4. The polyester polyol prepared by the preparation method according to any one of claims 1 to 3.

5. Use of the polyester polyol according to claim 4 in a two-component solvent-free metal anti-corrosion coating.

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