Polyurethane coating as well as preparation method and application thereof

Abstract

The invention relates to the technical field of coatings, in particular to a polyurethane coating as well as a preparation method and application thereof. According to the polyurethane coating provided by the invention, the modified polyester type polyol is used as a raw material, so that the problems that the existing polyurethane coating is easy to crystallize and low in transparency are solved, and development of a wear-resistant and high-transmittance polyurethane protective coating is realized; modified polyester polyol is synthesized by using a monomer with a cyclic structure to reduce the symmetry of the polyester polyol, the polyurethane coating prepared from the modified polyester polyol serving as a raw material not only has high light transmittance after being prepared into a coating, but also improves the hard segment content and crosslinking density of a system as the polyurethane coating is crosslinked with isocyanate with three degrees of functionality in the system, so that the hardness of the coating is improved, and the service life of the coating is prolonged. According to the present invention, the mechanical property of the material is improved, the protective coating has good wear resistance, and the coating formed after the surface of the organic glass is coated with the protective coating can achieve high light transmittance, has good wear resistance and high adhesion, and can be used in the positions such as the canopy, the windshield and the like of the aircraft.

Description

Technical Field

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

[0002] Microscopically, polyurethane can be considered a block copolymer consisting of soft and hard segments. Within the polyurethane structure, the chemical structure and polarity of the soft and hard segments differ significantly. The structure formed by the reaction of chain extenders and isocyanates exhibits a rod-like structure at room temperature, exhibiting a stable conformation and a high glass transition temperature. This structure is therefore referred to as a "rigid hard segment structure." In contrast, macromolecular segments such as polyethers and polyesters exhibit a curled morphology at room temperature, exhibiting strong mobility and excellent compliance. These are therefore referred to as "flexible soft segments." Improvements in the crystallization behavior of polyurethane soft segments are primarily related to molecular chain mobility. Increasing the proportion of non-crystalline polyester polyols in the polyurethane soft segment weakens the interactions between the soft segments, enhancing their mobility and intensifying relative motion, making it more difficult for the soft segments to aggregate into crystalline domains. Synthesizing polyurethane coatings using cyclic polyester polyols as raw materials to achieve coatings with both high light transmittance and high wear resistance holds significant research value.

[0003] Traditional polyester polyol molecules have high symmetry. For example, polyester polyols synthesized from adipic acid and different diols such as ethylene glycol, butanediol, and hexanediol are commonly used polyester polyols in polyurethane production. Due to the symmetry of the diol structure in the polyester structure, the synthesized polyester polyol has a regular structure. The soft segment formed after reaction with isocyanate is easy to crystallize under the action of hydrogen bonds. Although this can increase the mechanical properties of the material, for optical protective coatings, the crystalline area will scatter light, resulting in a decrease in the material's transmittance and an increase in haze.

[0004] As can be seen from the polymer structure, crystalline copolymers exist in crystalline and amorphous regions. Due to the different refractive indices of light for these two phases, crystalline polymers are often opaque, and only random amorphous polymers can be transparent. In polyester polyurethane, due to the high polarity of the ester group, crystallization is easy to occur, affecting its transparency. However, the interaction between polyether molecular chains is weaker than that of polyester, and it is easy to arrange randomly and has low crystallinity, so it has good transparency. Currently, transparent polyurethane is mostly prepared using polyether polyols. However, due to the small intermolecular forces and low cohesive strength of polyether-type transparent polyurethane, its mechanical strength is poor and its UV resistance and solvent resistance are not ideal. Traditional polyester polyurethane has better mechanical properties and wear resistance than polyether polyurethane, making it the first choice for preparing wear-resistant polyurethane coating polyols. Wear-resistant transparent polyurethane coatings are usually used in harsh environments and need to withstand the impact of sand, gravel, raindrops and other small particles. They must have high adhesion and high wear resistance. Existing protective coatings are difficult to combine high transmittance, wear resistance, high adhesion and high mechanical strength. Therefore, in order to meet the increasingly stringent requirements of engineering applications, it is urgent to develop a transparent polyurethane coating with strong comprehensive performance. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is a polyurethane coating and its preparation method and application. The coating obtained by the polyurethane coating provided by the present invention not only has high light transmittance, but also has good wear resistance and high adhesion.

[0006] The present invention provides a polyurethane coating, which is prepared from the following components:

[0007] 10-20 parts by weight of modified polyester polyol; the modified polyester polyol is prepared from dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate;

[0008] 8-16 parts by weight of polycarbonate diol;

[0009] 10-25 parts by weight of aliphatic isocyanate;

[0010] 0.1-0.2 parts by weight of leveling agent;

[0011] 0.5-3 parts by weight of light stabilizer;

[0012] 0-3 parts by weight of antioxidant;

[0013] 0-3 parts by weight of ultraviolet absorber;

[0014] 0.03-0.08 parts by weight of catalyst;

[0015] and 45 to 72 parts by weight of solvent.

[0016] Preferably, the modified polyester polyol of the present invention is prepared from dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol, and tetrabutyl titanate in a mass ratio of (25-30):(13-18):(12-16):(0.050-0.100); wherein the ratio of the molar amount of dimethyl carbonate to the total molar amount of hydroxyl groups in the 1,4-butanediol, tricyclodecane dimethanol, and tetrabutyl titanate is 1-1.5. More specifically, the average molecular weight of the modified polyester polyol is 1000 g / mol to 1500 g / mol, preferably 1375 g / mol.

[0017] Preferably, the average molecular weight of the polycarbonate diol of the present invention is 1000 g / mol to 2000 g / mol. Preferably, the aliphatic isocyanate of the present invention is selected from one or more of 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate trimer, and hexamethylene diisocyanate trimer. Preferably, the leveling agent of the present invention is selected from one or more of silicone leveling agents and fluorine-containing leveling agents. Preferably, the light stabilizer of the present invention is selected from one or more of Light Stabilizer 770, Light Stabilizer 944, and Light Stabilizer 292. Preferably, the antioxidant of the present invention is selected from one or more of Antioxidant 264, Antioxidant 1010, Antioxidant 1076, and Antioxidant 1098. Preferably, the UV absorber of the present invention is selected from one or more of UV absorber 531, UV absorber 326, UV absorber 234, and UV absorber 329. Preferably, the catalyst of the present invention is selected from one or more of dibutyltin dilaurate and stannous zincate. Preferably, the solvent of the present invention is selected from one or more of butyl acetate, propylene glycol methyl ether propionate, cyclohexanone, and 2-heptanone.

[0018] Preferably, the polyurethane of the present invention is prepared from the following components: 10-15 parts by weight of modified polyester polyol; 10-15 parts by weight of polycarbonate diol; 10-20 parts by weight of aliphatic isocyanate; 0.1-0.2 parts by weight of leveling agent; 0.5-1 parts by weight of light stabilizer; 0.5-1 parts by weight of antioxidant; 0.5-1 parts by weight of ultraviolet absorber; 0.03-0.05 parts by weight of catalyst; and 50-60 parts by weight of solvent.

[0019] In one embodiment of the present invention, the polyurethane of the present invention is prepared from the following components: 13.75 parts by weight of modified polyester polyol; 10 parts by weight of polycarbonate diol; 18.76 parts by weight of aliphatic isocyanate; 0.16 parts by weight of leveling agent; 0.5 parts by weight of light stabilizer; 0.5 parts by weight of antioxidant; 0.5 parts by weight of ultraviolet absorber; 0.037 parts by weight of catalyst; and 55.8 parts by weight of solvent.

[0020] In another embodiment of the present invention, the polyurethane of the present invention is prepared from the following components: 13.75 parts by weight of modified polyester polyol; 15 parts by weight of polycarbonate diol; 12.08 parts by weight of aliphatic isocyanate; 0.14 parts by weight of leveling agent; 0.5 parts by weight of light stabilizer; 0.5 parts by weight of antioxidant; 0.5 parts by weight of UV absorber; 0.037 parts by weight of catalyst; and 57.5 parts by weight of solvent.

[0021] In another embodiment of the present invention, the polyurethane of the present invention is prepared from the following components: 13.75 parts by weight of modified polyester polyol; 12.8 parts by weight of polycarbonate diol; 13.21 parts by weight of aliphatic isocyanate; 0.11 parts by weight of leveling agent; 0.5 parts by weight of light stabilizer; 0.5 parts by weight of antioxidant; 0.5 parts by weight of UV absorber; 0.037 parts by weight of catalyst; and 58.6 parts by weight of solvent.

[0022] The present invention uses dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate as raw materials to prepare a modified polyester polyol product with a low symmetrical structure and low crystallinity. The modified polyester polyol is used to prepare a coating based on an overall formula to prepare a wear-resistant transparent polyurethane coating, effectively improving the high light transmittance of the polyurethane coating. At the same time, due to the addition of multifunctional isocyanate in the overall formula, the cross-linking degree of the system is increased, the coating has good mechanical properties, the protective coating has good wear resistance and environmental aging resistance, and can effectively extend the service life of the coating.

[0023] The present invention also provides a method for preparing the polyurethane coating according to any of the above technical solutions, comprising the following steps:

[0024] A polyurethane coating is prepared by mixing 10-20 parts by weight of a modified polyester polyol, 8-16 parts by weight of a polycarbonate diol, 10-25 parts by weight of an aliphatic isocyanate, 0.1-0.2 parts by weight of a leveling agent, 0.5-3 parts by weight of a light stabilizer, 0-3 parts by weight of an antioxidant, 0-3 parts by weight of a UV absorber, 0.03-0.08 parts by weight of a catalyst, and 45-72 parts by weight of a solvent. Specifically, the mixture is stirred at 20°C to 23°C for 1.5 to 2.5 hours, and allowed to stand for defoaming to obtain the polyurethane coating.

[0025] The materials described in the present invention are the same as those described above and will not be described in detail. The modified polyester polyol described in the present invention is the same as those described above, and its preparation method comprises the following steps: reacting dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate at 80°C to 100°C for 1.5 h to 2.5 h, heating to 180°C to 200°C and conducting a vacuum reaction for 2 h to 4 h to obtain a modified polyester polyol. Preferably, reacting dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate at 85°C to 95°C for 1.8 h to 2.2 h, heating to 180°C to 190°C and conducting a vacuum reaction for 2.5 h to 3.5 h to obtain a modified polyester polyol.

[0026] The present invention also provides a polyurethane coating, which is obtained by coating the polyurethane coating described in any of the above technical solutions and then curing it. The curing temperature of the present invention is 60°C to 80°C, and the curing time is 10 hours to 15 hours. Preferably, the curing temperature of the present invention is 65°C to 75°C, and the curing time is 11 hours to 13 hours.

[0027] The present invention also provides a product containing a polyurethane coating, comprising a substrate and a polyurethane coating disposed on the substrate. The polyurethane coating is obtained by coating the polyurethane coating described in any of the above technical solutions and then curing it. The curing process described in the present invention is the same as described above and will not be further described. The substrate described in the present invention is selected from organic glass, a PC substrate, or a metal substrate. The products containing the polyurethane coating described in the present invention include, but are not limited to, aircraft canopies, windshields, aircraft window glass, automotive exterior coatings, automotive glass, and the like.

[0028] The present invention provides a polyurethane coating, a preparation method and application thereof. The polyurethane coating provided by the present invention uses a modified polyester polyol as a raw material, which solves the problems of easy crystallization and low transparency of existing polyurethane coatings, and realizes the development of a polyurethane protective coating with both wear resistance and high transmittance. Specifically, the polyurethane coating provided by the present invention reduces the symmetry of the polyester polyol by synthesizing a modified polyester polyol using a monomer with a cyclic structure. The polyurethane coating prepared with it as a raw material not only has high light transmittance after being made into a coating, but also increases the hard segment content and crosslinking density of the system due to crosslinking with the trifunctional isocyanate in the system, thereby improving the mechanical properties of the material and making the protective coating have good wear resistance. The coating formed after the polyurethane coating provided by the present invention is applied to the surface of organic glass can achieve high light transmittance, good wear resistance and high adhesion, and can be applied to aircraft cockpit covers, windshields and other parts. DETAILED DESCRIPTION

[0029] The present invention discloses a polyurethane coating, a preparation method thereof, and an application thereof. Those skilled in the art may refer to the contents of this invention and appropriately improve the process parameters to achieve the desired effect. It should be noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0030] The modified polyester polyols used in Examples 1 to 3 of the present invention are all prepared by the following steps:

[0031] Weigh 27.03 g of dimethyl carbonate (DMC), 15.77 g of 1,4-butanediol (BDO), 14.72 g of tricyclodecane dimethanol (TCD), and 58 mg of tetrabutyl titanate (TBT). React at 90°C for 2 hours, then slowly raise the temperature to 180°C to ensure distillation. Vacuum the reaction for 3 hours. The DMC:OH ratio is 1.2. The resulting product is a white solid with an average molecular weight of approximately 1375 g / mol, which is the modified polyester polyol.

[0032] The present invention will be further described below with reference to the embodiments:

[0033] Example 1

[0034] A wear-resistant transparent polyurethane coating prepared by modified polyester polyol, the specific preparation method is as follows, the parts involved are all parts by weight: weigh 13.75 parts of modified polyester polyol, polycarbonate diol (molecular weight 1000 g / mol), 10.0 parts of isophorone diisocyanate, 5.6 parts of isophorone diisocyanate, 13.16 parts of isophorone diisocyanate trimer, 0.16 parts of fluorine-containing leveling agent, 0.5 parts of 770 light stabilizer, 0.5 parts of 264 antioxidant, 0.5 parts of 531 UV absorber, 0.037 parts of dibutyltin dilaurate, 30.9 parts of butyl acetate, 11.4 parts of propylene glycol methyl ether propionate, 9.7 parts of cyclohexanone, and 3.8 parts of 2-heptanone, the mixture was stirred at controlled temperature at 22°C for 2 hours, and allowed to stand for 2 hours to defoam, thereby obtaining a high-transmittance polyurethane coating. The coating was applied to the surface of organic glass and dried, and then cured at 70°C for 12 hours to obtain a high-transmittance polyurethane coating through a multifunctional polyester cross-linking system.

[0035] Example 2

[0036] A wear-resistant transparent polyurethane coating prepared by modified polyester polyol is prepared by the following specific preparation method, where all parts are by weight: 13.75 parts of modified polyester polyol, polycarbonate diol (molecular weight 2000) and g / mol), 15.0 parts of hexamethylene diisocyanate trimer, 3.5 parts of isophorone diisocyanate trimer, 8.58 parts of fluorine-containing leveling agent, 0.14 part of fluorine-containing leveling agent, 0.5 part of 770 light stabilizer, 0.5 part of 264 antioxidant, 0.5 part of 531 ultraviolet absorber, 0.037 part of dibutyltin dilaurate, 25.9 parts of butyl acetate, 11.4 parts of propylene glycol methyl ether propionate, 9.7 parts of cyclohexanone, and 10.5 parts of 2-heptanone, the mixture was stirred at controlled temperature at 22°C for 2 hours, and allowed to stand for 2 hours to defoam, thereby obtaining a high-transmittance polyurethane coating. The coating was applied to the surface of organic glass and dried, and then cured at 70°C for 12 hours to obtain a high-transmittance polyurethane coating through a multifunctional polyester cross-linking system.

[0037] Example 3

[0038] A wear-resistant transparent polyurethane coating prepared by modified polyester polyol, the specific preparation method is as follows, the parts involved are all parts by weight: weigh 13.75 parts of modified polyester polyol, polycarbonate diol (molecular weight 1000 g / mol), 12.8 parts of hexamethylene diisocyanate trimer, 5.8 parts of isophorone diisocyanate trimer, 7.41 parts of isophorone diisocyanate trimer, 0.11 parts of fluorine-containing leveling agent, 0.5 parts of 770 light stabilizer, 0.5 parts of 264 antioxidant, 0.5 parts of 531 UV absorber, 0.037 parts of dibutyltin dilaurate, 26.8 parts of butyl acetate, 11.4 parts of propylene glycol methyl ether propionate, 9.9 parts of cyclohexanone, and 10.5 parts of 2-heptanone, the mixture was stirred at controlled temperature at 22°C for 2 hours, and allowed to stand for 2 hours to defoam, thereby obtaining a high-transmittance polyurethane coating. The coating was applied to the surface of organic glass and dried, and then cured at 70°C for 12 hours to obtain a high-transmittance polyurethane coating through a multifunctional polyester cross-linking system.

[0039] Comparative Example 1

[0040] This comparative example provides a transparent polyurethane coating prepared by polyester polyol and a preparation method thereof. The difference between it and Example 1 is that Example 1 uses modified polyester polyol to prepare the high-transmittance polyurethane coating, and the polyester polyol used in this comparative example is commercially available polycaprolactone diol with a molecular weight of 1000 and polycarbonate polydiol with a molecular weight of 2000.

[0041] The following parts are all parts by weight. 12.5 parts of polycaprolactone diol, 12.8 parts of polycarbonate diol, 3.8 parts of isophorone diisocyanate, 2.58 parts of isophorone diisocyanate trimer, 0.11 parts of fluorine-containing leveling agent, 0.5 parts of 770 light stabilizer, 0.5 parts of 264 antioxidant, 0.5 parts of 531 UV absorber, 0.041 parts of dibutyltin dilaurate, 33.3 parts of butyl acetate, 10.9 parts of propylene glycol methyl ether propionate, 9.9 parts of cyclohexanone, and 12.6 parts of 2-heptanone were weighed, and the mixture was stirred at 22°C for 2 hours, allowed to stand for 2 hours to defoam, and a high-transmittance polyurethane coating was obtained. The coating was applied to the surface of the organic glass and dried, and then cured at 70°C for 12 hours to obtain a high-transmittance polyurethane coating prepared by polyester polyol.

[0042] Comparative Example 2

[0043] This comparative example provides a transparent polyurethane coating prepared by polyester polyol and a preparation method thereof. The difference between it and Example 1 is that Example 1 uses a modified polyester polyol prepared from dimethyl carbonate, 1,4-butanediol and tricyclodecane dimethanol, while the modified polyester polyol used in this comparative example is prepared from dimethyl carbonate, 1,4-butanediol and spirodiol.

[0044] Weigh 27.03 g of dimethyl carbonate (DMC), 20.28 g of 1,4-butanediol (BDO), 7.61 g of spirocyclic glycol (SPG), and 58 mg of tetrabutyl titanate (TBT). React at 90°C for 2 hours, then slowly raise the temperature to 180°C to ensure distillation. Vacuum the reaction for 3 hours, with a DMC:OH ratio of 1.2. The resulting product is a light yellow liquid with an average molecular weight of approximately 1258 g / mol, which is the modified polyester polyol. The following parts are all parts by weight. 12.58 parts of modified polyester polyol, 12.8 parts of polycarbonate diol (molecular weight 1000 g / mol), 5.8 parts of hexamethylene diisocyanate trimer, 7.41 parts of isophorone diisocyanate trimer, 0.11 parts of fluorine-containing leveling agent, 0.5 parts of 770 light stabilizer, 0.5 parts of 264 antioxidant, 0.5 parts of 531 UV absorber, 0.037 parts of dibutyltin dilaurate, 26.8 parts of butyl acetate, 11.4 parts of propylene glycol methyl ether propionate, 9.9 parts of cyclohexanone, and 10.5 parts of 2-heptanone were weighed, and the mixture was stirred at controlled temperature at 22°C for 2 hours, allowed to stand for 2 hours to defoam, and a high-transmittance polyurethane coating was obtained. The coating was applied to the surface of organic glass and dried, and then cured at 70°C for 12 hours to obtain a high-transmittance polyurethane coating through a multifunctional polyester cross-linking system.

[0045] The performance test is as follows:

[0046] The wear-resistant transparent polyurethane coatings obtained in Examples 1 to 3 and Comparative Examples 1 to 2 were subjected to the following tests:

[0047] Coating adhesion test: The coating adhesion was tested according to ASTM D3359-02.

[0048] Light transmittance and haze test: in accordance with GB / T 2410-2008 “Transparent plastics - Determination of light transmittance and haze”.

[0049] Abrasion resistance: Testing was conducted in accordance with ASTM F735-11 using a reciprocating sand abrasion tester (Taber 6160) at a cycle rate of 150 cycles per minute and 100 strokes. The degree of wear was measured by the change in light transmittance and haze before and after the test. This is expressed in Table 1 below as ΔTransmittance / ΔHaze after Taber.

[0050] Sand blasting test: According to the method specified in "GJB 150A 2009 Military Equipment Laboratory Environmental Test Method Part 12: Sand and Dust Test", after 30 minutes of sand blasting test, the transmittance and haze of the sample were tested. The following Table 1 uses Δ transmittance after sand blasting / Δ haze to express it.

[0051] Mechanical properties: According to the ASTM D638-14 standard test method, the tensile strength, elongation and modulus of the coating were measured.

[0052] The test results are shown in Table 1:

[0053] Table 1

[0054]

[0055] From the test results in Table 1, it can be seen that the wear-resistant transparent polyurethane coatings prepared in Examples 1 to 3 all have an adhesion grade of 5B; the light transmittance is about 91%, and the haze is less than 0.2; after the Taber 100 stroke friction test, the increase in light transmittance of the coating is basically within 0.7%, and the increase in haze is less than 1.0; after the sand blasting test for 30 minutes, the increase in light transmittance of the coating is basically within 1.5%, and the increase in haze is less than; among them, the tensile strength of the coating obtained in Example 1 is 31.4 MPa, the modulus is 327 MPa, and the elongation at break is 109%.

[0056] Compared with Example 1, the polyurethane coatings prepared in Comparative Examples 1-2 were subjected to the Taber 100 stroke friction test, and the increase in light transmittance of the coatings was basically within 1.1%, and the increase in haze was less than 1.5; after the sand blasting test for 30 minutes, the increase in light transmittance of the coatings was basically around 3.0%, and the increase in haze was greater than 5; the wear resistance was poor.

[0057] Compared with Example 1, the wear-resistant transparent polyurethane coating prepared in Comparative Example 1 meets the requirements of high transmittance and low haze, but the modulus of the mechanical properties is low. After 30 days of field environmental testing, the coating surface becomes sticky, the haze increases significantly, and the durability is poor.

[0058] Compared with Example 1, although the wear-resistant transparent polyurethane coating prepared in Comparative Example 2 meets the requirements of high transmittance and low haze, its overall mechanical properties are reduced. After 15 days of field environmental testing, the coating surface becomes sticky, the haze increases significantly, and the durability is poor.

[0059] In summary, in addition to having a high transmittance, the polyurethane coating of the present invention also has adhesion, wear resistance and mechanical properties that are at a relatively high level within the test standards, and is a polyurethane coating with relatively strong comprehensive performance.

[0060] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A polyurethane coating, characterized in that: It is made from the following components; 10-20 parts by weight of modified polyester polyol, 8-16 parts by weight of polycarbonate diol, 10-25 parts by weight of aliphatic isocyanate, 0.1-0.2 parts by weight of leveling agent, 0.5-3 parts by weight of light stabilizer, 0-3 parts by weight of antioxidant, 0-3 parts by weight of ultraviolet absorber, 0.03-0.08 parts by weight of catalyst and 45-72 parts by weight of solvent; The modified polyester polyol is prepared from dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate.

2. The polyurethane coating according to claim 1, characterized in that The mass ratio of dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate is (25-30): (13-18): (12-16): (0.050-0.100); The ratio of the molar amount of the dimethyl carbonate to the total molar amount of the hydroxyl groups in the 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate is 1 to 1.

5.

3. The polyurethane coating according to claim 1, characterized in that The average molecular weight of the modified polyester polyol is 1000 g / mol to 1500 g / mol.

4. The polyurethane coating according to claim 1, characterized in that The average molecular weight of the polycarbonate diol is 1000 g / mol to 2000 g / mol.

5. The polyurethane coating according to claim 1, characterized in that The aliphatic isocyanate is selected from one or more of 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate trimer, and hexamethylene diisocyanate trimer; The leveling agent is selected from one or more of silicone leveling agents and fluorine-containing leveling agents; The light stabilizer is selected from one or more of 770 light stabilizer, 944 light stabilizer, and 292 light stabilizer; The antioxidant is selected from one or more of antioxidant 264, antioxidant 1010, antioxidant 1076, and antioxidant 1098; The ultraviolet absorber is selected from one or more of 531 ultraviolet absorber, 326 ultraviolet absorber, 234 ultraviolet absorber, and 329 ultraviolet absorber; The catalyst is selected from one or more of dibutyltin dilaurate and stannous zincate; The solvent is selected from one or more of butyl acetate, propylene glycol methyl ether propionate, cyclohexanone, and 2-heptanone.

6. The polyurethane coating according to claim 1, characterized in that It is made from the following components; 10-15 parts by weight of modified polyester polyol, 10-15 parts by weight of polycarbonate diol, 10-20 parts by weight of aliphatic isocyanate, 0.1-0.2 parts by weight of leveling agent, 0.5-1 parts by weight of light stabilizer, 0.5-1 parts by weight of antioxidant, 0.5-1 parts by weight of ultraviolet absorber, 0.03-0.05 parts by weight of catalyst and 50-60 parts by weight of solvent.

7. The method for preparing the polyurethane coating according to any one of claims 1 to 6, characterized in that: The following steps are involved: A polyurethane coating is obtained by mixing 10-20 parts by weight of modified polyester polyol, 8-16 parts by weight of polycarbonate diol, 10-25 parts by weight of aliphatic isocyanate, 0.1-0.2 parts by weight of a leveling agent, 0.5-3 parts by weight of a light stabilizer, 0-3 parts by weight of an antioxidant, 0-3 parts by weight of an ultraviolet absorber, 0.03-0.08 parts by weight of a catalyst, and 45-72 parts by weight of a solvent.

8. The preparation method according to claim 7, characterized in that The preparation method of the modified polyester polyol comprises the following steps: Dimethyl carbonate, 1,4-butanediol, tricyclodecane dimethanol and tetrabutyl titanate are reacted at 80°C to 100°C for 1.5 h to 2.5 h, and then the temperature is raised to 180°C to 200°C for vacuum reaction for 2 h to 4 h to obtain a modified polyester polyol.

9. A polyurethane coating, characterized in that The polyurethane coating according to any one of claims 1 to 6 is obtained by coating to form a film and then curing it.

10. A product containing a polyurethane coating, characterized in that: The invention comprises a substrate and a polyurethane coating arranged on the substrate, wherein the polyurethane coating is obtained by coating the polyurethane coating according to any one of claims 1 to 6 and then curing the coating.

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