A uvioresistant polyurethane coating and a method for its production

Abstract

The application belongs to the technical field of surface treatment agent production, and discloses a kind of ultraviolet resistant polyurethane coating, including polyurethane emulsion and inorganic matter dispersed in polyurethane emulsion, the inorganic matter is inorganic matter modified by silane coupling agent;The inorganic matter is at least one selected from zinc oxide, titanium dioxide, silicon dioxide;The mass ratio of the inorganic matter modified by silane coupling agent and polyurethane emulsion is 1:6~8, the application adjusts the mass ratio between inorganic filler and coupling agent, polyurethane emulsion, improves the overall ultraviolet reflection ability of polyurethane emulsion, and then reduces the absorption of polyurethane to ultraviolet, and then reduces the occurrence of ultraviolet aging of polyurethane, in addition, the application also discloses a kind of preparation method of ultraviolet resistant polyurethane coating.

Description

Technical Field

[0001] This application relates to the field of surface treatment agent production technology, and in particular to a UV-resistant polyurethane coating and its preparation method. Background Technology

[0002] Waterborne polyurethane (WPU), as an environmentally friendly coating and adhesive material, has attracted widespread attention due to its excellent performance and environmental friendliness. However, ultraviolet (UV) radiation can cause degradation of polyurethane materials, thereby affecting their service life and performance. Therefore, the development of UV-resistant waterborne polyurethane is of great significance.

[0003] First, UV-resistant waterborne polyurethanes can significantly improve material durability. Ultraviolet radiation causes the polyurethane chains to break and cross-link, leading to a decline in the material's physical properties, such as discoloration, cracking, and loss of elasticity. By introducing UV-resistant components, such as UV absorbers and light stabilizers, these degradation processes can be effectively slowed down, thereby extending the material's lifespan. This is particularly important for outdoor applications, such as architectural coatings, automotive coatings, and outdoor furniture.

[0004] Secondly, UV-resistant waterborne polyurethane helps maintain the aesthetic appeal of materials. UV-induced degradation not only affects the structural integrity of materials but also leads to color changes and loss of surface gloss. For applications requiring maintained appearance quality, such as decorative coatings and high-end furniture coatings, UV resistance is particularly crucial. By optimizing formulations and processes, the color stability and surface gloss of materials can be maintained, thereby meeting consumer demands for aesthetics.

[0005] Furthermore, waterborne polyurethane with UV aging resistance aligns with sustainable development requirements. Traditional solvent-based polyurethane coatings release large amounts of volatile organic compounds (VOCs) during production and use, posing harm to the environment and human health. Waterborne polyurethane, using water as the dispersion medium, significantly reduces VOC emissions, making it a more environmentally friendly option. By improving its UV aging resistance, the frequency of material replacement and resource consumption can be further reduced, minimizing environmental impact.

[0006] Finally, the development of waterborne polyurethanes with UV resistance has significant economic value. As people's requirements for environmental protection and durability increase, the market demand for high-performance waterborne polyurethanes continues to grow. By improving the UV resistance of materials, the market competitiveness of products can be enhanced, meeting the application needs of different industries and promoting the development of related industries.

[0007] In their paper "Research Progress on UV-resistant Polyurethane" published in July 2022 in the journal *Engineering Plastics Application*, Vol. 50, No. 7, Tian Yu, Huang Gaoshang, Huang Miaoming, Liu Hao, Liu Wentao, He Suqin, and others from the School of Materials Science and Engineering at Zhengzhou University, four directions for improving the UV resistance of polyurethane were described.

[0008] The first approach involves adjusting the structure and ratio of hard and soft segments. The principle is that ultraviolet (UV) irradiation damages the molecular structure of PUR, causing it to degrade and produce quinone imide structures, deepening the color of PUR products. Simultaneously, it leads to the breakage of C-N and C-O bonds, resulting in noticeable surface cracking and severely impacting the product's mechanical and physicochemical properties. However, there are many types of PUR with complex structures, and their UV aging resistance varies. Therefore, studying the influence of different hard and soft segment structures and ratios on the UV aging resistance of PUR and revealing its influencing mechanism can lay the foundation for the engineering applications of PUR.

[0009] The second approach involves modification with organic additives. The principle is that organic additives such as UV absorbers, free radical chain blockers, and hindered amine light stabilizers (HALS) can significantly improve the UV aging resistance of PUR. Free radical chain blockers and hindered amine light stabilizers are both antioxidants. UV absorbers absorb UV energy and dissipate it as heat, thus significantly reducing the rate of photo-oxidative degradation of PUR.

[0010] The third direction is the modification of nanofunctional fillers. The principle is that nanofunctional fillers, due to their chemical structure, possess excellent weather resistance and lightfastness, and are non-toxic, odorless, and exhibit good UV resistance and stability, making them promising candidates for application in the field of UV absorption resistance in polymer materials. Nanofunctional fillers mainly include organic nanofillers, metal oxide nanofillers, and inorganic non-metallic oxide nanofillers. Currently, excellent UV resistance is generally imparted to polymers by adding nanofillers with UV-resistant properties.

[0011] The fourth direction is the modification of natural polymers. The principle is that natural polymers have a variety of functional groups and have important application value in the field of polymers, especially in improving the UV resistance of PUR.

[0012] In summary, existing technologies for improving the UV aging resistance of polyurethane can be achieved through the four approaches mentioned above.

[0013] Chinese patent application 201510860355.2 discloses a weather-resistant polyester powder coating and its preparation method, comprising: a linear hydroxyl-terminated polyester prepolymer, 4,4-hexafluoroisopropylphthalic anhydride, hexafluorobutyl methacrylate, glycidyl methacrylate, an anti-UV coating additive, a silicone adhesive, nano-zirconia, nano-alumina, pigments and fillers, a curing agent, a leveling agent, and a multifunctional additive. The linear hydroxyl-terminated polyester prepolymer is formed by polycondensation polymerization of fluorinated glycol and terephthalic acid, directly introducing fluorocarbon chains into the polyester backbone, ensuring that the prepared weather-resistant polyester powder coating has water-resistant and heat-resistant properties. Secondly, the anti-UV coating additive imparts excellent UV resistance to the coating, improving its weather resistance. Thirdly, the silicone adhesive enhances the adhesion between the substrate and the coating.

[0014] Further observation of the scheme reveals that the UV-resistant coating additive in the scheme is prepared by mixing 3-5 parts by weight of nano-silica, 5-6 parts by weight of nano-zinc dioxide, 4-6 parts by weight of nano-cerium dioxide, 15-25 parts by weight of deionized water, 25-35 parts by weight of n-octanol, 8-10 parts by weight of KH550 silane coupling agent, 200-300 parts by weight of waterborne polyurethane, and 10-15 parts by weight of waterborne epoxy resin.

[0015] It can also be seen that this solution improves the UV resistance of polyurethane by modifying it with nano-functional fillers.

[0016] Chinese patent application 202211105941.2 discloses a yellowing-resistant masterbatch, a thermoplastic polyurethane film, its preparation method, and its application. The yellowing-resistant masterbatch comprises the following components in parts by weight: isocyanate: 20-40 parts; polytetrahydrofuran glycol: 0-120 parts, but not 0 parts; small molecule diol: 0-20 parts, but not 0 parts; catalyst: 0.001-0.1 parts; ultraviolet absorber: 3-6 parts; antioxidant: 2-5 parts; light stabilizer: 2-5 parts; the molecular weight of polytetrahydrofuran glycol is 800-5000 g / mol.

[0017] The preparation method of the yellowing-resistant masterbatch in this scheme is simple and low in cost. It can be used to prepare thermoplastic polyurethane films with good mechanical properties, good resistance to precipitation and yellowing. Moreover, the mechanical properties of the thermoplastic polyurethane film are relatively low after long-term ultraviolet irradiation.

[0018] Further observation of the scheme reveals that the UV absorber described in the scheme is a benzotriazole compound or a triazine compound. Simultaneously, the scheme also indicates that the components of the anti-yellowing masterbatch include one or more of a lubricant, dispersant, hydrolysis resistant agent, and light shielding agent. The light shielding agent is preferably nano-titanium dioxide, zinc oxide, carbon black, or talc, such as nano-titanium dioxide. The weight percentage of the light shielding agent is preferably 0.5-2 parts, more preferably 1-1.8 parts, for example, 1.5 parts. However, it should be noted that although the scheme describes the UV-resistant effects of nano-oxides, benzotriazole compounds, and triazine compounds, the matrix material of this scheme is thermoplastic polyurethane, not waterborne polyurethane. Furthermore, since waterborne polyurethane needs to be prepared as a water-based emulsion during the preparation process, the hydrophilicity of the additives must also be considered. Therefore, there is a significant difference between the two.

[0019] The problem this solution aims to solve is: how to develop a flame-retardant waterborne polyurethane coating agent that differs from existing technologies and possesses excellent flame-retardant capabilities. Summary of the Invention

[0020] The purpose of this application is to provide a UV-resistant polyurethane coating. This coating improves the overall UV reflectivity of the polyurethane emulsion by adjusting the mass ratio of inorganic fillers, coupling agents, and polyurethane emulsion, thereby reducing the absorption of ultraviolet light by the polyurethane and mitigating the occurrence of UV aging of the polyurethane.

[0021] To achieve the above objectives, this application discloses a UV-resistant polyurethane coating, comprising a polyurethane emulsion and an inorganic substance dispersed in the polyurethane emulsion, wherein the inorganic substance is an inorganic substance modified by a silane coupling agent.

[0022] The inorganic material is selected from at least one of zinc oxide, titanium dioxide, and silicon dioxide.

[0023] Preferably, the silane coupling agent is selected from at least one of KH540 and KH550.

[0024] Preferably, the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 0.8-1.2:0.8-1.2.

[0025] Preferably, the polyurethane emulsion comprises the following components by weight:

[0026]

[0027]

[0028] The ultraviolet absorber is selected from at least one of benzophenone compounds, benzotriazole compounds, and triazine compounds;

[0029] The free radical scavenger is selected from ethylenediaminetetraacetic acid and its derivatives.

[0030] Preferably, the diol is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol;

[0031] The diisocyanate is selected from at least one of dicyclohexylmethane diisocyanate, isoflurone diisocyanate, and phenyl dimethyl diisocyanate.

[0032] Preferably, the benzophenone compound is selected from at least one of 2-hydroxybenzophenone, 4-hydroxybenzophenone, and thiobenzophenone;

[0033] The benzotriazole compound is selected from at least one of 2-(2-hydroxy-5-methylphenyl)benzotriazole and 2-(2-hydroxy-3,5-ditert-phenyl)-5-chlorobenzotriazole;

[0034] The triazine compound is selected from at least one of 2,4-di(2-hydroxy-4-butylphenyl)-6-phenyl-1,3,5-triazine, 2-(2-hydroxy-4-hexoxyphenyl)-4,6-diphenyl-1,3,5-triazine, 2-(2-hydroxy-4-octoxyphenyl)-4,6-di(2,4-dimethylphenyl)-1,3,5-triazine, and 2-(2-hydroxy-4-octoxyphenyl)-4,6-di(4-methylphenyl)-1,3,5-triazine;

[0035] The ethylenediaminetetraacetic acid and its derivatives are selected from at least one of ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetic acid, and tetrasodium ethylenediaminetetraacetic acid.

[0036] Preferably, the polyester polyol is selected from at least one of polyethylene adipate diol, polybutylene adipate diol, and polycaprolactone diol.

[0037] Preferably, the free radical scavenger is a mixture of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA, and the mass ratio of EDTA to disodium EDTA is 2 to 4:1.

[0038] In addition, this application also discloses a method for preparing the above-mentioned UV-resistant polyurethane coating, which involves modifying an inorganic material with a silane coupling agent, and then dispersing the silane coupling agent-modified inorganic material into a polyurethane emulsion to obtain a UV-resistant polyurethane coating.

[0039] Preferably, the procedure specifically includes the following steps:

[0040] Step 1: Mix zinc oxide and silane coupling agent at a mass ratio of 1:1.5-2 and place them in ethanol solvent. React at 100-115℃ for 1-3 hours, then dry to obtain silane coupling agent modified inorganic material;

[0041] Step 2: Mix polyester polyol, diisocyanate and solvent and react at 70-80°C for 2-5 hours to obtain prepolymer;

[0042] Step 3: Mix the diol with the prepolymer and react at a temperature of 60-105℃ for 1-3 hours to obtain the chain-extended prepolymer;

[0043] Step 4: Add 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1-2 hours. Then add ultraviolet absorber and free radical scavenger and stir to mix. After mixing, add triethylamine for neutralization reaction for 30-50 minutes. Then add deionized water to emulsify and obtain polyurethane emulsion.

[0044] Step 5: Disperse the silane coupling agent-modified inorganic material into the polyurethane emulsion to obtain a UV-resistant polyurethane coating.

[0045] The beneficial effects of this application are:

[0046] The UV-resistant polyurethane coating disclosed in this application improves the overall UV reflectivity of the polyurethane emulsion by adjusting the mass ratio between inorganic fillers, coupling agents, and polyurethane emulsion, thereby reducing the absorption of ultraviolet light by the polyurethane and mitigating the occurrence of UV aging of the polyurethane. Detailed Implementation

[0047] The present application will be clearly and completely described below with reference to its embodiments. It should be noted that, unless specific conditions are specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0048] Before demonstrating the embodiments, the following necessary explanations are provided regarding the raw materials and preparation methods involved in the embodiments:

[0049] Information on the raw materials for each example is shown in Table 1:

[0050] Table 1

[0051]

[0052]

[0053] The preparation method of the polyurethane coating agent in the examples and comparative examples is as follows:

[0054] Step 1: Zinc oxide and silane coupling agent are mixed at a mass ratio of 1:2 and placed in ethanol solvent and reacted at 110±2℃ for 2h. Then the mixture is dried to obtain silane coupling agent modified inorganic material.

[0055] Step 2: Mix polyester polyol, diisocyanate and solvent and react at 75±5℃ for 3 hours to obtain prepolymer;

[0056] Step 3: Mix the diol with the prepolymer and react at 90±5℃ for 2 hours to obtain the chain-extended prepolymer;

[0057] Step 4: Add 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1.5 h. Then add ultraviolet absorber and free radical scavenger and stir to mix. After mixing, add triethylamine for neutralization reaction for 40 min. Then add deionized water to emulsify and obtain polyurethane emulsion.

[0058] Step 5: Disperse the silane coupling agent-modified inorganic material into the polyurethane emulsion to obtain a UV-resistant polyurethane coating.

[0059] Examples 1-4

[0060] A polyurethane emulsion, the formulation of which is shown in Table 2:

[0061] Table 2

[0062]

[0063]

[0064] It should be noted that in Examples 1-4, the polyester polyol is specifically polycaprolactone diol;

[0065] The diisocyanate is specifically dicyclohexylmethane diisocyanate;

[0066] The diol is specifically ethylene glycol;

[0067] The solvent is specifically acetone;

[0068] Furthermore, the inorganic material in Examples 1-4 is zinc oxide modified with a silane coupling agent, and the silane coupling agent is KH540;

[0069] Furthermore, in the preparation process of polyurethane coatings, the mass ratio of silane coupling agent-modified zinc oxide to polyurethane emulsion is 1:7.

[0070] Example 5

[0071] It is basically the same as Example 1, except that the silane coupling agent is KH550.

[0072] Example 6

[0073] The method is basically the same as in Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 0.8:1.2.

[0074] Example 7

[0075] The method is basically the same as in Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 1.2:0.8.

[0076] Example 8

[0077] The method is basically the same as in Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 1:1.

[0078] Example 9

[0079] It is basically the same as Example 1, except that 4-hydroxybenzophenone is used instead of 2-hydroxybenzophenone.

[0080] Example 10

[0081] The example is essentially the same as in Example 1, except that 2-(2-hydroxy-3,5-di-tert-phenyl)-5-chlorobenzotriazole is used instead of 2-hydroxybenzophenone.

[0082] Example 11

[0083] It is basically the same as Example 1, except that 2-(2-hydroxy-4-hexoxyphenyl)-4,6-diphenyl-1,3,5-triazine is used instead of 2-hydroxybenzophenone.

[0084] Example 12

[0085] It is basically the same as Example 1, except that disodium ethylenediaminetetraacetate is used instead of ethylenediaminetetraacetic acid.

[0086] Example 13

[0087] The method is basically the same as in Example 1, except that a mixture of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA is used instead of EDTA, and the mass ratio of EDTA to disodium EDTA is 1:1.

[0088] Example 14

[0089] It is basically the same as Example 1, except that titanium dioxide is used instead of zinc oxide.

[0090] Example 15

[0091] It is basically the same as Example 1, except that silicon dioxide is used instead of zinc oxide.

[0092] Example 16

[0093] The method is basically the same as in Example 1, except that commercially available zinc oxide (zinc oxide with a mass of 45µm mesh sieve residue not exceeding 0.2% of the total mass) is used instead of the zinc oxide in Example 1.

[0094] Example 17

[0095] The method is basically the same as in Example 1, except that commercially available zinc oxide (zinc oxide with a mass of 45µm mesh residue not exceeding 2±0.2% of the total mass) is used instead of the zinc oxide in Example 1.

[0096] Example 18

[0097] The preparation method is basically the same as in Example 1, except that no ultraviolet absorber and free radical scavenger are added to the polyurethane emulsion.

[0098] Step 1: Zinc oxide and silane coupling agent are mixed at a mass ratio of 1:2 and placed in ethanol solvent and reacted at 110±2℃ for 2h. Then the mixture is dried to obtain silane coupling agent modified inorganic material.

[0099] Step 2: Mix 50 parts of polyester polyol, 15 parts of diisocyanate and solvent and react at 75±5℃ for 3 hours to obtain the prepolymer;

[0100] Step 3: Mix 4 parts of diol with the prepolymer and react at 90±5℃ for 2 hours to obtain the chain-extended prepolymer;

[0101] Step 4: Add 3 parts of 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1.5 h. Then add triethylamine for neutralization reaction for 40 min. Finally, add deionized water for emulsification to obtain polyurethane emulsion.

[0102] Step 5: Disperse the silane coupling agent-modified inorganic material into the polyurethane emulsion at a mass ratio of 1:7 between the silane coupling agent-modified zinc oxide and the polyurethane emulsion to obtain a UV-resistant polyurethane coating.

[0103] Comparative Example 1

[0104] It is basically the same as Example 1, except that KH570 is used instead of KH540.

[0105] Comparative Example 2

[0106] It is basically the same as Example 1, except that the mass ratio of the silane coupling agent modified inorganic material to the polyurethane emulsion is 1:5.

[0107] Comparative Example 3

[0108] The process is basically the same as in Example 1, except that the mass ratio of the silane coupling agent-modified inorganic material to the polyurethane emulsion is 1:9.

[0109] Comparative Example 4

[0110] The preparation method is basically the same as in Example 1, except that no inorganic material modified with a silane coupling agent is added to the polyurethane coating.

[0111] Step 1: Mix 50 parts of polyester polyol, 15 parts of diisocyanate and solvent and react at 75±5℃ for 3 hours to obtain the prepolymer;

[0112] Step 2: Mix 4 parts of diol with the prepolymer and react at 90±5℃ for 2 hours to obtain the chain-extended prepolymer;

[0113] Step 3: Add 3 parts of 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1.5 h. Then add 2 parts of 2-hydroxybenzophenone and 2 parts of ethylenediaminetetraacetic acid and stir to mix. After mixing, add triethylamine for neutralization reaction for 40 min. Then add deionized water for emulsification to obtain polyurethane emulsion.

[0114] Comparative Example 5

[0115] The preparation method is basically the same as Comparative Example 4, except that no ultraviolet absorbers and free radical scavengers are added to the polyurethane coating.

[0116] Step 1: Mix 50 parts of polyester polyol, 15 parts of diisocyanate and solvent and react at 75±5℃ for 3 hours to obtain the prepolymer;

[0117] Step 2: Mix 4 parts of diol with the prepolymer and react at 90±5℃ for 2 hours to obtain the chain-extended prepolymer;

[0118] Step 3: Add 3 parts of 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1.5 h. Then add triethylamine for neutralization reaction for 40 min. Finally, add deionized water for emulsification to obtain polyurethane emulsion.

[0119] Performance testing:

[0120] 1. Yellowing resistance test:

[0121] Referring to QB / T4672-2014, the polyurethane coatings prepared in each example and comparative example were applied to the surface of white leather purchased from the same batch, and after drying, the yellowing resistance of artificial leather and synthetic leather was tested.

[0122] The method for determining the yellowing resistance of artificial and synthetic leather is as follows:

[0123] Ultraviolet lamp method

[0124] 1. Cover both ends of the sample radially with a light-shielding sheet for 20 mm. Place the sample on the sample tray with the irradiated surface of the sample facing the light source and the radial direction of the sample perpendicular to the radial direction of the lamp tube. The surface of the sample is parallel to the bottom surface of the lamp tube, with a vertical distance of (250±2) mm.

[0125] 2. Turn on the switch, and the sample will be continuously irradiated under ultraviolet light for a period of time that is an integer multiple of 6 hours. Immediately after the specified time (300 hours), remove the sample from the test chamber and remove the light-shielding sheet.

[0126] 3. Experimental Results and Evaluation

[0127] According to GB / T 2918-1998, under the standard environment of temperature (23±2)℃ and relative humidity (50±10)%, the color change grade of the covered and uncovered parts of the sample was tested in a quasi-multi-light source color matching box using a gray colorimetric card. The result with the largest difference in color change grade was selected as the final result.

[0128] Tensile strength aging rate after 300 hours of UV irradiation = (Tensile strength after 300 hours of UV irradiation - Initial tensile strength)

[0129] The test results of the examples and comparative examples are shown in Table 4:

[0130] Table 4

[0131]

[0132]

[0133] Results analysis:

[0134] 1. As can be seen from Examples 1-4, when the formulation of each raw material in the polyurethane emulsion is slightly adjusted, the tensile strength aging rate after UV irradiation in Examples 1-4 shows a certain fluctuation trend, but the fluctuation range is relatively small.

[0135] 2. As can be seen from Examples 1 and 5, when KH540 is replaced with KH550, the tensile strength aging rate after UV irradiation in Example 5 shows a certain degree of fluctuation compared to Example 1, but the fluctuation range is relatively small.

[0136] Further observation of Examples 1 and 6-8 reveals that when Examples 6-8 used a mixture of KH550 and KH540, the aging rate of Examples 6-8 showed a relatively significant decreasing trend compared to Example 1. It is speculated that the reason for this phenomenon may be that, on the one hand, the inorganic material itself has good ultraviolet absorption capacity, and on the other hand, after modification with silane coupling agent, its distribution in polyurethane is more uniform, which can more effectively absorb and scatter ultraviolet rays, reducing the damage of ultraviolet rays to the polyurethane matrix.

[0137] When the two silane coupling agents are used together, the synergistic effect of KH540 and KH550 may form a more stable chemical bond on the surface of inorganic materials, thereby reducing interface defects. This stable interface bond helps to improve the durability of materials under ultraviolet irradiation and reduce degradation.

[0138] 3. As can be seen from Examples 1 and 9-12, when the UV absorber and free radical scavenger in Example 1 were replaced with other UV absorbers or free radical scavengers, the aging rate of the polyurethane coating showed a certain upward trend. It can be seen that 2-hydroxybenzophenone and ethylenediaminetetraacetic acid produced a more significant anti-UV effect in this scheme.

[0139] Further observation of Example 13 shows that when a mixture of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA is used to replace EDTA, the aging rate of Example 13 shows a significant decreasing trend compared to Examples 1 and 12. This indicates that EDTA and disodium EDTA have a synergistic effect in UV protection, enabling the mixture of the two to achieve UV protection capabilities exceeding those of either of them when used alone.

[0140] 4. As can be seen from Examples 14-16, when other inorganic materials are used to replace the zinc oxide in Example 1, the aging rate of Examples 14-15 shows a certain upward trend compared to Example 1. This indicates that the coating prepared using zinc oxide as an inorganic material in this scheme has stronger UV resistance. Furthermore, when Example 16 uses zinc oxide with a mass of 45µm mesh sieve residue not exceeding 0.2% of the total mass to replace the zinc oxide in Example 1 (the mass of 45µm mesh sieve residue is 1.2±0.2% of the total mass of zinc oxide), the aging rate of Example 16 shows a certain upward trend compared to Example 1. It is speculated that the reason for this phenomenon may be that the zinc oxide in Example 1, due to its relatively high content of zinc oxide with a micron-sized particle size, may provide more UV scattering and shielding effects, thus leading to a more significant downward trend in the aging rate of Example 1.

[0141] The reason why the aging rate of Example 17 increased compared to Example 1 after using nano zinc oxide with an excessive amount of micron-sized zinc oxide may be because although micron-sized particles can effectively scatter ultraviolet rays, too many micron-sized particles will reduce the light scattering efficiency, because the mutual blocking between particles will reduce the effective scattering area, thereby reducing the overall UV resistance of the coating.

[0142] 5. As can be seen from Example 1 and Comparative Ratio 1, when KH570 was used to replace KH540, the aging rate of Comparative Ratio 1 showed a significant upward trend. The reason is that during the experiment, it was found that when KH570 was used, the inorganic matter in the coating exhibited a certain degree of agglomeration. This agglomeration may have led to a decrease in the reflectivity of the inorganic matter to ultraviolet rays, which in turn led to a decrease in the coating's UV resistance.

[0143] 6. Further observation of Example 1 and Comparative Examples 2-3 shows that when the proportion of inorganic matter in the coating is further increased or decreased, the aging rate of the coating increases to varying degrees. It is speculated that the reason for this phenomenon is that increasing the amount of inorganic matter added is not conducive to the dispersion of inorganic matter in the coating, which leads to a decrease in the ability to reflect ultraviolet rays. When there is too little inorganic matter, the density of the barrier that can resist ultraviolet rays is not enough, which leads to a decline in the coating's ability to resist ultraviolet rays.

[0144] 7. Further observation of Examples 1, 18, 4, and 5 shows that when UV absorbers and free radical scavengers were added to Comparative Example 4 compared to Comparative Example 5, the aging rate of Comparative Example 4 decreased by approximately 2.71% compared to Comparative Example 5.

[0145] When inorganic matter was added to Example 18 compared to Comparative Example 5, the aging rate of Example 18 decreased by approximately 5.70% compared to Comparative Example 5.

[0146] Further observation revealed that when UV absorbers, free radical scavengers, and silane coupling agents were added simultaneously to Example 1 compared to Comparative Example 5, the aging rate of Example 1 decreased by approximately 9.69% compared to Comparative Example 5.

[0147] As can be seen, Example 1 achieved results far exceeding those of a simple superposition of Example 18 and Comparative Example 4.

Claims

1. A UV-resistant polyurethane coating, characterized in that, It includes a polyurethane emulsion and inorganic substances dispersed in the polyurethane emulsion, wherein the inorganic substances are inorganic substances modified by a silane coupling agent; The inorganic substance is zinc oxide, and the zinc oxide is zinc oxide with a mass of 1.2 ± 0.2% of the total mass of the residue on a 45µm mesh sieve; The mass ratio of the inorganic material modified with silane coupling agent to the polyurethane emulsion is 1:6-8; The silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 0.8-1.2:0.8-1.

2.

2. The UV-resistant polyurethane coating according to claim 1, characterized in that, The polyurethane emulsion comprises the following components by mass parts: 40-60 parts of polyester polyol; 10-30 parts of diisocyanate; 1 to 5 parts of 2,2-dimethylolpropionic acid; 2-8 parts of diol; 1-3 parts of ultraviolet absorber; Free radical scavenger 1-3 parts; solvent 50-90 parts; The ultraviolet absorber is selected from at least one of benzophenone compounds, benzotriazole compounds, and triazine compounds; The free radical scavenger is a mixture of ethylenediaminetetraacetic acid (EDTA) and disodium EDTA, with a mass ratio of EDTA to disodium EDTA of 2–4:

1.

3. The UV-resistant polyurethane coating according to claim 2, characterized in that, The diol is selected from at least one of ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol; The diisocyanate is selected from at least one of dicyclohexylmethane diisocyanate, isoflurone diisocyanate, and phenyl dimethyl diisocyanate.

4. The UV-resistant polyurethane coating according to claim 2, characterized in that, The benzophenone compounds are selected from at least one of 2-hydroxybenzophenone, 4-hydroxybenzophenone, and thiobenzophenone. The benzotriazole compound is selected from at least one of 2-(2-hydroxy-5-methylphenyl)benzotriazole and 2-(2-hydroxy-3,5-di-tert-phenyl)-5-chlorobenzotriazole; The triazine compound is selected from at least one of 2,4-bis(2-hydroxy-4-butylphenyl)-6-phenyl-1,3,5-triazine, 2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, and 2-(2-hydroxy-4-octoxyphenyl)-4,6-bis(4-methylphenyl)-1,3,5-triazine.

5. The UV-resistant polyurethane coating according to claim 2, characterized in that, The polyester polyol is selected from at least one of polyethylene adipate diol, polybutylene adipate diol, and polycaprolactone diol.

6. A UV-resistant polyurethane coating according to any one of claims 1-5, characterized in that, Inorganic materials are modified using silane coupling agents, and then the silane-modified inorganic materials are dispersed into a polyurethane emulsion to obtain a UV-resistant polyurethane coating.

7. The UV-resistant polyurethane coating according to claim 6, characterized in that, Specifically, the following steps are included: Step 1: Mix zinc oxide and silane coupling agent at a mass ratio of 1:1.5-2 and place them in ethanol solvent. React at 100-115℃ for 1-3 hours, then dry to obtain silane coupling agent modified inorganic material; Step 2: Mix polyester polyol, diisocyanate and solvent and react at 70-80°C for 2-5 hours to obtain prepolymer; Step 3: Mix the diol with the prepolymer and react at a temperature of 60-105℃ for 1-3 hours to obtain the chain-extended prepolymer; Step 4: Add 2,2-dimethylolpropionic acid to the chain-extended prepolymer and react for 1-2 hours. Then add ultraviolet absorber and free radical scavenger and stir to mix. After mixing, add triethylamine for neutralization reaction for 30-50 minutes. Then add deionized water to emulsify and obtain polyurethane emulsion. Step 5: Disperse the silane coupling agent-modified inorganic material into the polyurethane emulsion to obtain a UV-resistant polyurethane coating.

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