CN114350248A

CN114350248A - Polyurethane coating and preparation method thereof

Info

Publication number: CN114350248A
Application number: CN202210002915.0A
Authority: CN
Inventors: 刘佐基
Original assignee: Shenzhen Inktop Ink Technology Co ltd
Current assignee: Shenzhen Inktop Ink Technology Co ltd
Priority date: 2022-01-04
Filing date: 2022-01-04
Publication date: 2022-04-15

Abstract

The invention relates to the technical field of coatings, and provides a polyurethane coating and a preparation method thereof. The polyurethane coating comprises the following components in parts by weight: 35-39% of component A, 39-45.6% of component B, 19-22% of solvent, 0.175-0.6% of wetting dispersant, 0.035-0.2% of flatting agent and 0.035-0.2% of defoaming agent; the component A comprises the following raw materials in parts by weight: 30% -50% of fatty acid; 20% -35% of dibasic acid; 25% -40% of polyol; 0.1 to 0.5 percent of antioxidant; 8% -13% of a solvent; the component B comprises the following raw materials in parts by weight: 9% -12% of fatty acid; 6 to 9 percent of dibasic acid; 9% -13% of polyol; 0.02% -0.1% of antioxidant; 28% -35% of diisocyanate; 35% -43% of a solvent; 0.01 to 0.05 percent of catalyst; wherein the number of carbon atoms of the fatty acid for synthesizing the A component and the B component is more than or equal to 8. According to the invention, the fatty acid with the carbon atom number of more than or equal to 8 is introduced into the component A and the component B in the polyurethane coating, so that the use amount of the solvent is reduced, and the VOC content of the polyurethane coating is reduced and reaches the national standard. The invention also provides a preparation method of the polyurethane coating.

Description

Polyurethane coating and preparation method thereof

Technical Field

The invention relates to the technical field of coatings, in particular to a polyurethane coating and a preparation method thereof.

Background

With the development of modern industry and society and the increasing awareness of environmental protection, environment-friendly coatings are more and more favored by people under the great trend. The so-called environment-friendly coating is a coating which does not cause harm to the ecological environment and does not have negative influence on human health, and is also called as a 'green coating'. The polyurethane coating is a novel material developed only in the latter half of the 20 th century, the Polyurethane (PU) coating occupies a large proportion in the field of coating chemical industry, and the polyurethane coating has the advantages of renewable raw materials, high fullness of a paint film, good transparency and the like.

In general, conventional alkyd polyurethane coatings are two-component products, i.e. the coating product is obtained by mixing and reacting two components. However, since the molecular weight distribution of the resin in the two-component is broad and the distribution of the functional groups is not uniform, when the resin reacts with the curing agent, the reaction of-OH in the resin and-NCO in the curing agent cannot proceed according to the theoretical conditions, and the compounding ratio needs to be excessive. Therefore, the coating product obtained by the reaction has the characteristics of wide molecular weight distribution and high viscosity. A large amount of solvent is required to be added for dilution in the spraying process, so that the spraying construction requirement can be met. This often results in spray-applied products containing high levels of Volatile Organic Compounds (VOC), resulting in high post-application VOC emissions, significantly exceeding national regulatory standards: VOC is less than or equal to 420 g/L. Not only causes damage to the environment, causes greenhouse effect, acid rain and the like, and is not beneficial to the sustainable development of ecology; it also has serious influence on human health.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a polyurethane coating and a preparation method thereof, and aims to reduce the component viscosity of the polyurethane coating, thereby reducing the using amount of a solvent in the spraying process, reducing the VOC content of a product and achieving the national standard.

In order to achieve the purpose, the invention provides a polyurethane coating which comprises the following components in parts by weight: 35-39% of component A, 39-45.6% of component B, 19-22% of solvent, 0.175-0.6% of wetting dispersant, 0.035-0.2% of flatting agent and 0.035-0.2% of defoaming agent;

the component A comprises the following raw materials in parts by weight: 30% -50% of fatty acid; 20% -35% of dibasic acid; 25% -40% of polyol; 0.1 to 0.5 percent of antioxidant; 8% -13% of a solvent;

the component B comprises the following raw materials in parts by weight: 9% -12% of fatty acid; 6 to 9 percent of dibasic acid; 9% -13% of polyol; 0.02% -0.1% of antioxidant; 28% -35% of diisocyanate; 35% -43% of a solvent; 0.01 to 0.05 percent of catalyst;

wherein,

the number of carbon atoms of the fatty acid for synthesizing the component A and the component B is 8-24;

the polyhydric alcohol for synthesizing the A component and the B component includes trihydric or higher alcohols.

In one embodiment, the fatty acids from which the a component is synthesized are selected from one or more of soybean oil fatty acids, epoxidized soybean oil, oleic acid, linoleic acid, ricinoleic acid, linoleic acid, dehydrated ricinoleic acid, lauric acid, isooctanoic acid, stearic acid, palmitic acid;

and/or the fatty acid for synthesizing the component B is selected from one or more of soybean oil fatty acid, epoxidized soybean oil, oleic acid, linoleic acid, ricinoleic acid, linoleic acid, dehydrated ricinoleic acid, lauric acid, isooctanoic acid, stearic acid and palmitic acid.

In one embodiment, the polybasic acid from which the a component is synthesized is selected from one or more of phthalic anhydride, phthalic acid, terephthalic anhydride, terephthalic acid, isophthalic anhydride, isophthalic acid, adipic acid, maleic anhydride, maleic acid;

and/or the polybasic acid for synthesizing the component B is selected from one or more of phthalic anhydride, phthalic acid, terephthalic anhydride, terephthalic acid, isophthalic anhydride, isophthalic acid, adipic acid, maleic anhydride and maleic acid.

In one embodiment, the polyol from which the a component is synthesized is selected from one or more of ethylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, glycerol, pentaerythritol;

and/or the polyhydric alcohol for synthesizing the component B is selected from one or more of ethylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, glycerol and pentaerythritol.

In one embodiment, the polyisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate.

In one embodiment, the antioxidant for synthesizing the component A is selected from one or more of hypophosphorous acid, triphenyl phosphite and B900;

and/or the antioxidant for synthesizing the component B is selected from one or more of hypophosphorous acid, triphenyl phosphite and B900.

In one embodiment, the catalyst is selected from one or more of stannous octoate, polyammonia, dibutyltin dilaurate, cobalt octoate, lead octoate, zinc naphthenate, and tetraisobutyl titanate.

The invention also provides a preparation method of the polyurethane coating, which comprises the following specific steps:

(a) and (3) synthesis of a component A: adding fatty acid, polybasic acid and polyalcohol into a reactor, mixing and reacting, heating and refluxing, and reacting at 120-160 ℃ for more than 1 hour; gradually heating to 200-240 ℃, separating water by a water separator, reacting for a sufficient time to obtain a product I1, and adding a solvent into I1 for dilution to obtain a component A;

(b) and (3) synthesis of a component B: adding fatty acid, polybasic acid and polyalcohol into another reactor, mixing and reacting, adding and refluxing, and reacting at 120-160 ℃ for more than 1 hour; gradually heating to 200-240 ℃, separating water by a water separator, reacting for a sufficient time to obtain a product I2, adding a solvent into I2 for dilution to obtain an intermediate product, and reacting the intermediate product with polyisocyanate to obtain a component B;

(c) in another reactor, adding the component A, the component B, the wetting dispersant, the flatting agent and the defoaming agent, and uniformly stirring; then adding the component B and the solvent, and mixing and stirring.

Advantageous effects

Firstly, fatty acid (with 8-24 carbon atoms), dibasic acid and polyalcohol are subjected to polycondensation reaction under the heating condition to obtain the fatty acid resin. Because a water separator is not adopted for water separation in the early stage of heating, ester groups in the fatty acid resin can be fully hydrolyzed under the acidic condition. And then controlling the depth of the polymerization reaction through a water diversion operation, so that the hydrolyzed polymer is copolymerized with dibasic acid and polyol to obtain a polymer A component with high functionality, and the A component has the characteristics of low molecular weight and uniform distribution of functional groups and has a regular arrangement structure. On the premise of not influencing the drying performance of the component A, the viscosity of the component A is greatly reduced, and the component A has lower viscosity.

Secondly, under the condition of heating and refluxing by adopting fatty acid (the number of carbon atoms is 8-24), dibasic acid and polyalcohol, the fatty acid resin is hydrolyzed under an acidic condition and then copolymerized with the dibasic acid and the polyalcohol to obtain an intermediate product with high functional group degree, uniform functional group distribution and low molecular weight; the intermediate product reacts with diisocyanate under the action of a catalyst. On one hand, the NCO content in the component B is controlled through the reaction of-OH and-NCO in the intermediate, so that the NCO content in the component B is consistent with a theoretical value, the ratio of the NCO functional group content in the component B to the functional group content in the component A is consistent with theoretical calculation, and unbalanced reaction caused by large difference of the functional groups is avoided. On the other hand, because the functional groups of the intermediate are uniformly distributed and have low molecular weight, the functional groups of the B component obtained by the reaction are uniformly distributed and have narrow molecular weight distribution, so that the B component also has low viscosity. More importantly, the aliphatic hydrocarbon polymer chain in the fatty acid resin is introduced into the component B, so that the polymer molecular weight of the component B is increased and the solid content is high.

By reacting the component A with the component B, the functional groups of the component A are high in functionality degree and uniform in distribution, the functional groups in the component B are uniform in distribution, and the molecular weight distribution is narrow, so that the functional groups of the component A and the component B can fully react under theoretical conditions to obtain a product with uniform molecular weight distribution and narrow molecular weight distribution. And because the solid content of the component A and the component B is high and the viscosity is low, the viscosity required by the spraying requirement can be met without adding extra solvent during the reaction, so that the organic solvent in the paint product is greatly reduced, the VOC discharge amount after use is greatly reduced and is less than the VOC discharge standard specified by the state, the environmental friendliness of the product is obviously improved, and the sustainable development of environment, ecology and human life is facilitated. And the high solid content provides powerful guarantee for the excellent performance of the product and meets the use requirement.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to specific embodiments, and it is obvious that the embodiments described below are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The raw materials and the purchasing manufacturers thereof are as follows: soybean oil fatty acid, made in China; lauric acid, domestic; phthalic anhydride, domestic; adipic acid, made in China; trimethylolpropane, domestic; pentaerythritol, made in China; glycerol, made in China; hypophosphorous acid, made in China; xylene, domestic; n-butyl acetate, made in China; ethyl acetate, made in China; TDI, wanhua; stannous octoate, made in China; BYK110, bike; EFKA4010, basf; TEG0610, winning; BYK323, bike; BYK333, bike; TEG0410, winning wound; BYK141, bike; EFKA2020, basf; g5400, gold ball.

Example 1:

the component A comprises: 30% of soybean oil fatty acid, 35% of phthalic anhydride, 20% of trimethylolpropane and 5% of pentaerythritol, 0.1% of hypophosphorous acid, 3% of xylene and 6.9% of n-butyl acetate;

and B component: 9.81 percent of soybean oil fatty acid, 7.85 percent of adipic acid, 3.927 percent of glycerin, 7.85 percent of trimethylolpropane, 0.038 percent of hypophosphorous acid, 30.66 percent of TDI, 0.02 percent of stannous octoate, 1.19 percent of xylene and 38.64 percent of ethyl acetate;

the wetting dispersant is BYK110, the flatting agent is BYK323, the defoaming agent is BYK141,

(a) taking a dry and clean reaction bottle, sequentially adding 60g of soybean oil fatty acid, 70g of phthalic anhydride, 40g of trimethylolpropane, 10g of pentaerythritol and 0.2g of hypophosphorous acid, and heating to 150 ℃ for refluxing; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and then adding 6g of dimethylbenzene and 13.8g of n-butyl acetate for dilution to obtain a component A;

(b) in another reactor, 98.1g of soybean oil fatty acid, 78.5g of adipic acid, 39.27g of glycerol, 78.5g of trimethylolpropane and 0.38g of hypophosphorous acid are sequentially added, and the mixture is heated to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and adding 11.9g of dimethylbenzene for dilution to obtain an intermediate product; adding 306.6g of TDI, 386.4g of ethyl acetate and 0.2g of stannous octoate into a reaction kettle in sequence, heating to 30-55 ℃, adding 281.9g of all intermediate products, heating to 55-75 ℃, preserving heat, and measuring an NCO value to obtain a component B;

(c) in another reactor, 70g of the component A, BYK1100.35g of wetting dispersant, BYK3230.07g of flatting agent and BYK1410.07g of defoaming agent are added in sequence and stirred for 5min to 10 min; then 86g of the component B and 40g of solvent xylene are added, and the mixture is mixed and stirred.

Example 2:

the component A comprises: 36% of soybean oil fatty acid, 25.3% of phthalic anhydride, 14.48% of trimethylolpropane, 14.48% of pentaerythritol, 0.1% of hypophosphorous acid, 2.9% of xylene and 6.52% of n-butyl acetate;

and B component: 11.63% of lauric acid, 6.15% of phthalic anhydride, 9.85% of trimethylolpropane, 0.1% of hypophosphorous acid, 29.5% of di-TDI, 0.04% of stannous octoate, 3.62% of xylene and 39.11% of ethyl acetate;

the wetting dispersant is EFKA4010, the flatting agent is BYK333, the antifoaming agent is EFKA2020,

(a) taking a dry and clean reaction bottle, sequentially adding 72g of soybean oil fatty acid, 50.6g of phthalic anhydride, 28.96g of trimethylolpropane, 28.96g of pentaerythritol and 0.2g of hypophosphorous acid, and heating to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and then adding 5.8g of dimethylbenzene and 13.04g of n-butyl acetate for dilution to obtain a component A;

(b) in another reactor, 23.26g of lauric acid, 12.3g of phthalic anhydride, 19.7 g of trimethylolpropane and 0.2g of hypophosphorous acid are sequentially added, and the mixture is heated to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 2mg KOH/g; cooling to below 150 ℃, and then adding 7.24g of dimethylbenzene for dilution to obtain an intermediate product; adding 59g of TDI, 78.22g of ethyl acetate and 0.08g of stannous octoate into a reaction kettle in sequence, heating to 30-55 ℃, adding 59.1g of all intermediate products, heating to 55-75 ℃, keeping the temperature, and measuring the NCO value to obtain a component B;

(c) in another reactor, 78g of the component A, EFKA40100.8g of wetting dispersant, 30.2g of flatting agent BYK3330.2g and EFKA20200.2g of defoaming agent are added in sequence and stirred for 5min to 10 min; then 82.8g of the component B and 38g of solvent toluene are added, and the mixture is mixed and stirred.

Example 3:

the component A comprises: 50% of soybean oil fatty acid, 20% of phthalic anhydride, 15% of trimethylolpropane and 10% of pentaerythritol, 0.5% of hypophosphorous acid, 4% of xylene and 9% of n-butyl acetate;

and B component: 10.8% of lauric acid, 8.95% of phthalic anhydride, 12.73% of trimethylolpropane, 0.1% of hypophosphorous acid, TDI 27.92%, 0.05% of stannous octoate, 1.64% of xylene and 37.9% of ethyl acetate;

the wetting dispersant is TEG0610, the flatting agent is TEG0410, the defoaming agent is G5400,

(a) taking a dry and clean reaction bottle, sequentially adding 100g of soybean oil fatty acid, 40g of phthalic anhydride, 30g of trimethylolpropane, 20g of pentaerythritol and 1g of hypophosphorous acid, and heating to 150 ℃ for refluxing; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and then adding 8g of dimethylbenzene and 18g of n-butyl acetate for dilution to obtain a component A;

(b) in another reactor, 21.6g of lauric acid, 17.9g of phthalic anhydride, 25.46g of trimethylolpropane and 0.2g of hypophosphorous acid are sequentially added, and the mixture is heated to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 2mg KOH/g; cooling to below 150 ℃, and then adding 3.28g of dimethylbenzene for dilution to obtain an intermediate product; adding 55.84g of TDI, 75.8g of ethyl acetate and 0.1g of stannous octoate into a reaction kettle in sequence, heating to 30-55 ℃, adding 64.3g of all intermediate products, heating to 55-75 ℃, keeping the temperature, and measuring the NCO value to obtain a component B;

(c) in another reactor, 74.16g of the component A, 1.2g of wetting dispersant, 0.4g of flatting agent and 0.4g of defoaming agent are added in turn, and the mixture is stirred for 5min to 10 min; then 84g of the component B and 40g of the solvent are added, mixed and stirred.

Example four:

the component A comprises: 35% of soybean oil fatty acid, 25% of phthalic anhydride, 23.8% of trimethylolpropane, 8% of pentaerythritol, 0.1% of hypophosphorous acid, 3% of xylene and 5% of n-butyl acetate;

the wetting dispersant is BYK110, the flatting agent is BYK323, and the defoaming agent is BYK 141;

(a) taking a dry and clean reaction bottle, sequentially adding 70g of soybean oil fatty acid, 50g of phthalic anhydride, 47.6g of trimethylolpropane, 16g of pentaerythritol and 0.2g of hypophosphorous acid, and heating to 150 ℃ for refluxing; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and then adding 6g of dimethylbenzene and 10g of n-butyl acetate for dilution to obtain a component A;

(b) in another reactor, 98.1g of soybean oil fatty acid, 78.5g of adipic acid, 39.27g of glycerol, 78.5g of trimethylolpropane and 0.38g of hypophosphorous acid are sequentially added, and the mixture is heated to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and adding 11.9g of dimethylbenzene for dilution to obtain an intermediate product; adding 306.6g of TDI, 386.4g of ethyl acetate and 0.2g of stannous octoate into a reaction kettle in sequence, heating to 30-55 ℃, adding 280.6g of all intermediate products, heating to 55-75 ℃, preserving heat, and measuring an NCO value to obtain a component B;

(c) in another reactor, 70g of the component A, BYK1100.35g of wetting dispersant, BYK3230.07g of flatting agent and BYK1410.07g of defoaming agent are added in sequence and stirred for 5min to 10 min; then 86g of the component B and 39g of solvent xylene are added, and the mixture is mixed and stirred.

Example five:

the component A comprises: 40% of soybean oil fatty acid, 25% of phthalic anhydride, 15% of trimethylolpropane and 15% of pentaerythritol, 0.1% of hypophosphorous acid, 4% of xylene and 9% of n-butyl acetate;

and B component: 11.13 percent of lauric acid, 7.95 percent of phthalic anhydride, 12.73 percent of trimethylolpropane, 0.1 percent of hypophosphorous acid, TDI 27.92 percent, 0.03 percent of stannous octoate, 1.59 percent of xylene and 38.53 percent of ethyl acetate;

(a) taking a dry and clean reaction bottle, sequentially adding 80g of soybean oil fatty acid, 50g of phthalic anhydride, 30g of trimethylolpropane, 30g of pentaerythritol and 0.2g of hypophosphorous acid, and heating to 150 ℃ for refluxing; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 5mg KOH/g; cooling to below 150 ℃, and then adding 8g of dimethylbenzene and 18g of n-butyl acetate for dilution to obtain a component A;

(b) in another reactor, 22.26g of lauric acid, 15.9g of phthalic anhydride, 25.46g of trimethylolpropane and 0.2g of hypophosphorous acid are added in sequence and heated to 150 ℃ for reflux; refluxing and preserving heat for 2 h; then installing a water separator on the reactor for water separation, gradually heating to 200-240 ℃ within 3h, and keeping the temperature to ensure that the acid value of the product is less than 8mg KOH/g; then the reactor is vacuumized to ensure that the acid value of the product is less than 2mg KOH/g; cooling to below 150 ℃, and then adding 3.18g of dimethylbenzene for dilution to obtain an intermediate product; sequentially adding 55.84g of TDI55, 77.06g of ethyl acetate and 0.06g of stannous octoate into a reaction kettle, heating to 30-55 ℃, adding 63g of all intermediate products, heating to 55-75 ℃, keeping the temperature, and measuring the NCO value to obtain a component B;

(c) in another reactor, 39g of the component A, 0.6g of wetting dispersant, 0.2g of flatting agent and 0.2g of defoaming agent are added in turn, and the mixture is stirred for 5min to 10 min; then adding 45.6g of B45 and 19g of n-butyl acetate serving as a solvent, and stirring.

Performance testing

The test was carried out according to the test methods prescribed by the national standards, and the test results are shown in the following table

According to the test data in the table above, the viscosity obtained after the reaction is between 12 seconds and 15 seconds by stirring and mixing the component A and the component B, and the direct spraying construction requirement is met. The VOC content after spraying is measured to be lower than the national specified standard. And the paint film of the sprayed product is plump and flat, the drying speed is high, the hardness can reach more than HB, and the use requirement is met.

The foregoing examples are merely illustrative and serve to explain some of the features of the method of the present invention. The appended claims are intended to claim as broad a scope as is contemplated, and the examples presented herein are merely illustrative of selected implementations in accordance with all possible combinations of examples. Accordingly, it is applicants' intention that the appended claims are not to be limited by the choice of examples illustrating features of the invention. Also, where numerical ranges are used in the claims, subranges therein are included, and variations in these ranges are also to be construed as possible being covered by the appended claims.

Claims

1. The polyurethane coating is characterized by comprising the following components in parts by weight: 35-39% of component A, 39-45.6% of component B, 19-22% of solvent, 0.175-0.6% of wetting dispersant, 0.035-0.2% of flatting agent and 0.035-0.2% of defoaming agent;

wherein,

the polyhydric alcohols for synthesizing the A component and the B component both comprise trihydric or higher alcohols.

2. The polyurethane coating of claim 1, wherein the fatty acids from which the a component is synthesized are selected from one or more of soybean oil fatty acids, epoxidized soybean oil, oleic acid, linoleic acid, ricinoleic acid, linoleic acid, dehydrated ricinoleic acid, lauric acid, isooctanoic acid, stearic acid, palmitic acid;

3. The polyurethane coating of claim 1, wherein the polyacid used in the synthesis of the a component is selected from one or more of phthalic anhydride, phthalic acid, terephthalic anhydride, terephthalic acid, isophthalic anhydride, isophthalic acid, adipic acid, maleic anhydride, maleic acid;

4. The polyurethane coating of claim 1, wherein the polyol from which the a component is synthesized is selected from one or more of ethylene glycol, diethylene glycol, neopentyl glycol, trimethylolpropane, glycerol, pentaerythritol;

5. The polyurethane coating of claim 1, wherein the polyisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate.

6. The polyurethane coating according to claim 1, wherein the antioxidant for synthesizing the a component is selected from one or more of hypophosphorous acid, triphenyl phosphite, and B900;

7. The polyurethane coating of claim 1, wherein the catalyst is selected from one or more of stannous octoate, polyammonia, dibutyltin dilaurate, cobalt octoate, lead octoate, zinc naphthenate, tetraisobutyl titanate.

8. A method for preparing the polyurethane coating as claimed in any one of claims 1 to 7, characterized by comprising the following steps:

(a) and (3) synthesis of a component A: adding fatty acid, polybasic acid and polyalcohol into a reactor, mixing and reacting, heating and refluxing, and reacting at 120-160 ℃ for more than 1 hour; then gradually heating to 200-240 ℃, separating water by a water separator, and reacting for sufficient time to obtain a product I₁In I₁Adding a solvent to dilute to obtain a component A;

(b) and (3) synthesis of a component B: adding fatty acid, polybasic acid and polyalcohol into another reactor, mixing and reacting, heating and refluxing, and reacting at 120-160 ℃ for more than 1 hour; then gradually heating to 200-240 ℃, separating water by a water separator, and reacting for sufficient time to obtain a product I₂In I₂Adding a solvent to dilute to obtain an intermediate product, and reacting the intermediate product with polyisocyanate to obtain a component B;