Wear-resistant coating and its use on leather surfaces

Abstract

The application discloses a wear-resistant coating and application thereof to a leather surface, and belongs to the technical field of leather finishing. The coating comprises a functional polyurethane-acrylate composite emulsion, a photoinitiator, an additive and deionized water. The composite emulsion is prepared through pre-polymerization, fluorine-containing grafting and in-situ sol-gel reaction of hyperbranched polyester polyol, dynamic bond chain extender and the like. The hyperbranched skeleton provides mechanical support, the double dynamic bonds endow the coating with self-repairing function, in-situ nano-composite enhances wear resistance, the double urea hydrogen bonds strengthen the bonding force, and the fluorine-containing side chains endow the coating with hydrophobic and stain-resistant properties. The coating is prepared by matching a gradient curing process. The coating prepared by the application has high wear resistance, efficient self-repairing property, firm adhesion, excellent stain resistance and leather-adaptive flexibility, and meets the actual needs of medium and high-end leather finishing.

Description

Technical Field

[0001] This invention relates to the field of leather finishing technology, and more particularly to an abrasion-resistant coating and its application on leather surfaces. Background Technology

[0002] Leather finishing is a crucial process for enhancing the appearance, texture, durability, and protective properties of leather. The performance of the finishing agent directly determines the quality and lifespan of leather products. Currently, the mainstream finishing agents in the leather industry are mainly concentrated in two categories: acrylic resin and polyurethane. Among them, acrylic resin is widely used due to its advantages such as low raw material cost and convenient application. However, its inherent "hot-adhesive, cold-brittle" property results in poor balance between abrasion resistance and flexibility of the leather after coating, making it difficult to meet the needs of mid-to-high-end leather. Polyurethane finishing agents, on the other hand, have excellent elasticity, adhesion, and abrasion resistance. However, their raw material cost is relatively high, and traditional solvent-based polyurethane finishing agents have volatile organic compound (VOC) emission problems, facing increasingly stringent environmental policy pressures.

[0003] To balance the performance advantages of acrylic resins and polyurethanes while mitigating their respective shortcomings, polyurethane-acrylate (PUA) hybrid systems have become an important research and development direction for leather finishing agents and have been widely applied. However, existing PUA finishing coatings mostly employ linear or slightly branched molecular structure designs, resulting in insufficient control over the crosslinking density of the system. This makes it difficult for the coatings to achieve excellent abrasion resistance while maintaining the high flexibility required by leather, thus failing to meet the needs of high-frequency use scenarios.

[0004] To further improve the abrasion resistance of PUA coatings, existing technologies often reinforce them by introducing inorganic fillers such as nano-silica and graphene oxide. However, most of these are added through simple physical blending, resulting in poor compatibility between inorganic particles and the organic matrix, which easily leads to agglomeration. This not only reduces the transparency of the coating but also damages the soft feel of the leather surface, affecting the product's appearance and user experience. Furthermore, ultraviolet (UV) curing technology is used for coating preparation due to its high curing efficiency and low VOC emissions. However, this technology is mostly used for hard substrates such as metals and glass. For flexible substrates like leather, the development of UV-cured coating solutions that combine low-temperature flexibility, high abrasion resistance, and a good appearance and feel remains relatively scarce.

[0005] In summary, developing a novel coating that combines high abrasion resistance, a soft feel, and compatibility with flexible leather substrates can effectively address the performance bottlenecks of existing leather finishing agents, aligns with the industry's development trends towards environmental protection and high-end products, and has significant practical value and market prospects. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a wear-resistant coating and its application on leather surfaces.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A wear-resistant coating is prepared from the following components in parts by weight: 60-80 parts of functionalized polyurethane-acrylate composite emulsion; 0.5-1.2 parts of photoinitiator; 0.3-0.8 parts of additives; and 20-40 parts of deionized water.

[0009] The preparation method of the functionalized polyurethane-acrylate composite emulsion includes the following steps:

[0010] S1: Preparation of hyperbranched polyurethane-acrylate prepolymer containing dual dynamic bonds and diurea hydrogen bonds

[0011] Hyperbranched polyester polyol and polytetramethylene ether glycol were added to a reaction vessel and dehydrated at 105-115℃ and a vacuum of -0.09 to -0.098 MPa for 1-2 hours. The temperature was then lowered to 70-80℃ and nitrogen gas was introduced for protection. Dibutyltin dilaurate catalyst was added, followed by dropwise addition of isocyanate. The reaction was maintained at this temperature for 0.8-1.2 hours until the isocyanate group content reached more than 95% of the theoretical value calculated based on the molar ratio of the feed. The temperature was then lowered to 60-70℃. Add a dynamic bond chain extender and N,N'-bis(2-hydroxyethyl)-urea, and stir for 1.5-2.5 h; then add dimethylolpropionic acid and 8-12% of acetone by weight of the total system mass to reduce viscosity, and continue the reaction for 1-2 h until the isocyanate group content fluctuates within ±0.2% of the theoretical value; finally, add a portion of 3-(methacryloyloxy)propyltrimethoxysilane, and react at 60-65℃ for 0.8-1.2 h to obtain the intermediate prepolymer;

[0012] S2: Fluorinated acrylate end-grafted modification

[0013] The intermediate prepolymer obtained in step S1 is cooled to 45-55℃, trifluoroethyl methacrylate is added, and the mixture is stirred for 1.2-1.8h. Then, the polymerization inhibitor 4-methoxyphenol is added and stirred evenly to obtain a hyperbranched polyurethane-acrylate prepolymer grafted with fluorinated segments.

[0014] S3: Water-dispersible and in-situ double-bond functionalized nano-silica composite

[0015] The prepolymer obtained in step S2 is cooled to 35-45℃, neutralized with a neutralizing agent to a degree of neutralization of 85-95%, and deionized water is slowly added dropwise under high-speed shear conditions of 2800-3200 r / min. The mixture is stirred for 25-35 min to form an aqueous hyperbranched polyurethane-acrylate emulsion. Acetone is removed under reduced pressure. 0.1-0.2 mol / L hydrochloric acid is added dropwise to the emulsion to adjust the pH to 2.5-3.0. A mixture of tetraethyl orthosilicate and the remaining 3-(methacryloyloxy)propyltrimethoxysilane with a mass ratio of (1.5-2.5):1 is slowly added. The mixture is stirred at 20-30℃ for 6-10 h. The pH is then adjusted to 6.5-7.0 with triethylamine. Large particles are removed by filtration to obtain a functionalized polyurethane-acrylate composite emulsion.

[0016] Preferably, the functionalized polyurethane-acrylate composite emulsion is prepared from the following components in parts by weight: 180-220 parts of hyperbranched polyester polyol, 280-320 parts of polytetramethylene ether glycol, 260-300 parts of isocyanate, 70-90 parts of dynamic bond chain extender, 12-18 parts of N,N'-bis(2-hydroxyethyl)-urea, 18-22 parts of dimethylolpropionic acid, and 2 parts of 3-(methacryloyloxy)propyltrimethoxysilane. 0-30 parts, trifluoroethyl methacrylate 5-25 parts, catalyst 0.06-0.10 parts, neutralizer 14-18 parts, polymerization inhibitor 0.04-0.06 parts, deionized water 800-1200 parts; the 3-(methacryloyloxy)propyltrimethoxysilane is used in two parts, one part is used for grafting and modifying polyurethane-acrylate chains, and the other part is used for in-situ modification of nano-silica, with a mass ratio of (3-5):1.

[0017] Preferably, the hydroxyl value of the hyperbranched polyester polyol is 180-240 mgKOH / g; the number average molecular weight of the polytetramethylene ether diol is 1800-2200; and the isocyanate is a mixture of isophorone diisocyanate and 4,4'-diphenylmethane diisocyanate, with a mass ratio of (3-5):1.

[0018] Preferably, the dynamic bond chain extender is composed of 30-35 parts of bis(4-hydroxyphenyl) disulfide and 40-55 parts of oxime ester-modified isophorone diisocyanate; the oxime ester-modified isophorone diisocyanate is prepared by reacting methyl ethyl ketoxime with isophorone diisocyanate at a mass ratio of (0.3-0.5):1, and its oxime ester group grafting rate is ≥85%; the total molar content of aromatic disulfide bonds and oxime ester bonds in the dynamic bond chain extender is 8-12% of the total molar number of hydroxyl groups in the polyols, including hyperbranched polyester polyol, polytetramethylene ether glycol and chain extender prepolymer; the molar proportion of N,N'-di(2-hydroxyethyl)-urea is 3-4%, which is based on the total molar number of hyperbranched polyester polyol, polytetramethylene ether glycol, isocyanate, N,N'-di(2-hydroxyethyl)-urea and dimethylolpropionic acid participating in the prepolymer reaction.

[0019] Preferably, the functionalized polyurethane-acrylate composite emulsion contains in-situ double-bond functionalized nano-silica, which is prepared by sol-gel reaction of tetraethyl orthosilicate and the remaining 3-(methacryloyloxy)propyltrimethoxysilane at a mass ratio of (1.5-2.5):1, and has a particle size of 10-50 nm.

[0020] Preferably, the photoinitiator is 1-hydroxycyclohexylphenyl ketone, or a mixture of 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methylphenylacetone; the additives include wetting and leveling agent BYK-333 and defoamer BYK-024, with a ratio of (1.2-1.7):1.

[0021] Preferably, the neutralizing agent is triethylamine with a neutralization degree of 85-95%, which is calculated based on the total carboxyl groups of dimethylolpropionic acid.

[0022] Through the above technical solution, the preparation of the functionalized polyurethane-acrylate composite emulsion of the present invention, with stepwise polymerization, self-emulsification and sol-gel reaction as the core, constructs an organic-inorganic hybrid system integrating "rigid reinforcement" and "dynamic repair", the specific principle of which is as follows:

[0023] In step S1, hyperbranched polyester polyol and polytetramethylene ether glycol are dehydrated under high temperature and vacuum, and then subjected to urethane esterification reaction with isocyanate under the protection of catalyst and nitrogen to construct a highly branched three-dimensional framework. Subsequently, bis(4-hydroxyphenyl) disulfide, oxime-modified isophorone diisocyanate, and N,N'-bis(2-hydroxyethyl)-urea are introduced sequentially at a lower temperature. Through grafting reactions of hydroxyl groups with isocyanate groups (-NCO), disulfide bonds, oxime ester bonds, and strongly polar urea groups are embedded into the prepolymer backbone. The urea groups form physical crosslinking points through intermolecular hydrogen bonds, enhancing intersegmental forces and modulus; while the dynamic bonds lie dormant in the network, providing channels for rearrangement of damaged molecular chains. Dimethylolpropionic acid is then added to introduce hydrophilic carboxyl groups, and some polymerizable double bonds are grafted with 3-(methacryloyloxy)propyltrimethoxysilane to obtain an intermediate prepolymer. Acetone is used to reduce viscosity and ensure the uniformity of the reaction.

[0024] In step S2, the intermediate prepolymer is cooled and then reacted with trifluoroethyl methacrylate to graft fluorinated segments onto the ends of the prepolymer. Utilizing the extremely low surface energy of fluorine atoms, they migrate to the surface during film formation, constructing a low surface energy protective layer that imparts water and stain resistance to the coating. Simultaneously, the high bond energy of the CF bonds enhances the surface abrasion resistance. The addition of 4-methoxyphenol effectively inhibits the self-polymerization of fluorinated monomers, ensuring the directional grafting of fluorinated segments and the stability of the emulsion during storage.

[0025] In step S3, triethylamine neutralizes the carboxyl groups and imparts charge to the particles. Deionized water is added dropwise under high-speed shear to achieve self-emulsification of the prepolymer. After depressurization to remove acetone, a stable emulsion is formed. Subsequently, the system is adjusted to an acidic environment, and tetraethyl orthosilicate is added to react with the remaining 3-(methacryloyloxy)propyltrimethoxysilane in a sol-gel reaction, generating in situ double-bonded functionalized nano-silica with a particle size of 10-50 nm. These nanoparticles form a strong chemical bond with the polymer matrix through 3-(methacryloyloxy)propyltrimethoxysilane, uniformly filling the micropores after film formation, forming an organic-inorganic interpenetrating network. This structure not only significantly improves the coating's hardness and scratch resistance, but the rigid support of the nanoparticles also allows them to bear the main load during friction, protecting the polymer matrix from excessive wear.

[0026] The application of an abrasion-resistant coating to a leather surface includes the following steps:

[0027] Step 1: Emulsion compounding

[0028] Take the functionalized polyurethane-acrylate composite emulsion, add photoinitiator and additives, stir at low speed for 25-35 minutes, adjust the construction viscosity with deionized water, and use the Forecast-4 cup to test the viscosity at 25℃, which is 25-30s, to obtain the wear-resistant coating liquid.

[0029] Step 2: Substrate Pretreatment and Coating

[0030] The leather substrate is sanded and dusted, and a layer of polyester-type waterborne polyurethane dispersion with a solid content of 30-40% is roller-coated and dried at 50-60℃ for 4-6 minutes to complete the pretreatment. The coating liquid is then applied to the pretreated leather surface by roller coating, and the wet film thickness is controlled to be 90-130μm.

[0031] Step 3: Gradient Curing

[0032] First, it is pre-cured with a 365nm ultraviolet light-emitting diode light source at an energy of 600-1000mJ / cm², and then cured by hot air baking at 55-65℃ for 6-10 minutes to form a wear-resistant coating with a dry film thickness of 10-15μm.

[0033] Through the above technical solution, this invention cleverly solves the technical problem of simultaneously achieving high wear resistance and self-healing performance of coatings by using component design and gradient curing process:

[0034] In the first step, photoinitiator, wetting and leveling agent BYK-333, and defoamer BYK-024 are added in proportion and dispersed evenly by low-speed stirring. This avoids uneven local concentrations that could affect film formation and prevents damage to the emulsion particle structure. The viscosity is adjusted with deionized water to match the roller coating process, ensuring coating uniformity and laying the foundation for the formation of a dense film layer.

[0035] In the second step, the leather substrate is polished and dusted to reduce film defects and strengthen interfacial adhesion; the pre-treated roller-coated polyester-based waterborne polyurethane dispersion is used to construct a compatible system of "substrate-transition layer-functional coating" to prevent coating peeling; and the appropriate wet film thickness is controlled to balance the dry film abrasion resistance and substrate flexibility.

[0036] In the third step, during UV pre-curing, the photoinitiator generates active free radicals, initiating double bond polymerization to form a cross-linked network and fix the film shape. Subsequent low-temperature hot air baking promotes complete cross-linking of residual double bonds and activates latent dynamic disulfide and oxime ester bonds in the polymer network. At this temperature, reversible exchange of dynamic bonds occurs, providing localized flowability to the molecular chains and facilitating the healing of microcracks through molecular diffusion, achieving a self-healing effect.

[0037] In this invention, in-situ generated nano-silica and a bisurea hydrogen-bonded physical cross-linking network jointly construct the rigid reinforcing phase of the coating, endowing the system with high modulus and excellent abrasion resistance. Meanwhile, the hyperbranched framework topology and dynamic reversible bond network ensure that the molecular chains possess sufficient mobility and an efficient energy dissipation mechanism. This rigid-flexible synergistic microstructure allows the rigid nanoparticles to bear the main frictional load when the coating is worn, while the hydrogen-bonded network simultaneously dissipates energy. When the coating is damaged and needs repair, the dynamic bonds undergo network recombination under thermal stimulation. Thus, without sacrificing abrasion resistance, the leather coating acquires a certain degree of self-healing ability, ultimately forming a high-performance leather coating that is firmly bonded to the substrate, has a dense surface, and combines high abrasion resistance with self-healing properties.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] 1. This invention utilizes hyperbranched polyester polyols to construct a highly branched three-dimensional crosslinked framework, significantly improving crosslinking density and mechanical strength compared to traditional linear polyurethanes. Simultaneously, it introduces bisurea hydrogen bonds as strong physical crosslinking points, forming a high-density hydrogen bond network in the hard segment micro-regions. This significantly enhances the coating's modulus and hardness to resist wear, while also enabling reversible dissociation to dissipate impact energy under external forces. This synergy between the hyperbranched framework and the hydrogen bond network effectively solves the core contradiction of traditional coatings—"increasing hardness leads to brittleness, increasing toughness leads to softness"—allowing the coating to maintain sufficient rigidity while also possessing good flexibility suitable for leather substrates.

[0040] 2. This invention integrates a dual dynamic network of aromatic disulfide bonds and oxime ester bonds in the system, combined with a gradient curing process of UV pre-curing and thermal post-curing. The UV curing stage rapidly constructs a surface cross-linking network to lock in the coating morphology and ensures efficient construction. The subsequent thermal post-curing not only promotes full cross-linking of deep double bonds in the coating and improves the film density, but also provides the activation energy required for dynamic bond exchange, enabling the dynamic bonds to achieve reversible rearrangement of molecular chains without destroying the main chain structure. This allows the coating to quickly initiate the repair process through thermal stimulation after being scratched, achieving efficient healing and overcoming the shortcomings of traditional self-healing coatings, such as low repair efficiency or significant decrease in mechanical properties after repair.

[0041] 3. This invention generates double-bonded functionalized nano-silica through an in-situ sol-gel reaction. Under the action of 3-(methacryloyloxy)propyltrimethoxysilane, it forms a stable chemical bond with the polymer matrix, fundamentally overcoming the industry pain points of easy agglomeration of nanoparticles and weak interfacial bonding in physical blending. The rigid nanoparticles uniformly fill the pores of the polymer network, forming a dense organic-inorganic interpenetrating network with the polymer skeleton. During friction, they work synergistically with the polymer to bear the load, significantly improving the coating's scratch resistance and wear resistance, while preserving the original soft feel of the leather.

[0042] 4. This invention utilizes fluorinated acrylate end-graft modification, enabling the fluorinated side chains to spontaneously accumulate on the surface during film formation. The extremely low surface energy of fluorine atoms forms a dense, low-surface-energy protective layer, endowing the coating with excellent hydrophobic, oleophobic, and stain-resistant properties, making it easy to clean and maintain in daily use. Simultaneously, the high bond energy of the CF bonds further enhances the surface structural stability and improves wear resistance. Furthermore, the composite emulsion used in the coating is a water-based system, with no harmful solvent volatilization, meeting environmental coating requirements. The coating process is simple and easy to operate, adaptable to industrial roller coating and spray coating production lines, requiring no special equipment investment, facilitating large-scale application and perfectly meeting the actual needs of mid-to-high-end leather finishing. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0044] Example 1: I. Preparation of Functionalized Polyurethane-Acrylic Composite Emulsion

[0045] (1) Components of the composite emulsion formulation (parts by weight): 180 parts of hyperbranched polyester polyol (hydroxyl value 180 mg KOH / g), 280 parts of polytetramethylene ether diol (number average molecular weight 1800), 260 parts of isocyanate mixture (isophorone diisocyanate: 4,4'-diphenylmethane diisocyanate = 3:1), 70 parts of dynamic bond chain extender (30 parts of bis(4-hydroxyphenyl) disulfide and 40 parts of oxime ester modified isophorone diisocyanate), 12 parts of N,N'-di(2-hydroxyethyl)-urea, 18 parts of dimethylolpropionic acid, 20 parts of 3-(methacryloyloxy)propyltrimethoxysilane, 5 parts of trifluoroethyl methacrylate, 0.06 parts of dibutyltin dilaurate, 14 parts of neutralizing agent triethylamine, 0.04 parts of 4-methoxyphenol, and 800 parts of deionized water.

[0046] Among them: oxime ester modified isophorone diisocyanate is prepared by reacting isophorone diisocyanate with methyl ethyl ketoxime at a mass ratio of 1:0.3, with an oxime ester group grafting rate of 85%, and the total molar content of aromatic disulfide bonds and oxime ester bonds is 8% of the total molar number of hydroxyl groups in the prepolymer polyol; the molar proportion of N,N'-di(2-hydroxyethyl)-urea is 3% of the total molar number of prepolymer monomers; the silane coupling agent 3-(methacryloyloxy)propyltrimethoxysilane is used in two parts, 15 parts for graft modification and 5 parts for in-situ modified nano silica (mass ratio 3:1); the nano silica is prepared by reacting tetraethyl orthosilicate with the remaining 3-(methacryloyloxy)propyltrimethoxysilane at a mass ratio of 1.5:1 via sol-gel reaction, with a particle size of 10 nm.

[0047] (2) Preparation steps of composite emulsion:

[0048] S1: Hyperbranched polyester polyol and polytetramethylene ether glycol were added to a reaction vessel and dehydrated at 105°C and a vacuum of -0.09 MPa for 1 hour. The temperature was then lowered to 70°C and protected with nitrogen. Dibutyltin dilaurate catalyst was added, and an isocyanate mixture was added dropwise. The reaction was maintained at this temperature for 0.8 hours until the isocyanate group content reached more than 95% of the theoretical value. The temperature was lowered to 60°C, and a dynamic bond chain extender and N,N'-di(2-hydroxyethyl)-urea were added. The mixture was stirred and reacted for 1.5 hours. Dimethylolpropionic acid and 8% (by weight) of acetone were added to reduce viscosity. The reaction was continued for 1.5 hours until the isocyanate group content fluctuated within ±0.2% of the theoretical value. Finally, 15 parts of 3-(methacryloyloxy)propyltrimethoxysilane were added, and the reaction was carried out at 60°C for 0.8 hours to obtain an intermediate prepolymer.

[0049] S2: Cool the intermediate prepolymer to 45°C, add trifluoroethyl methacrylate, stir and react for 1.2 h, then add the polymerization inhibitor 4-methoxyphenol and stir evenly to obtain the fluorinated segment grafted prepolymer.

[0050] S3: Cool the prepolymer to 35℃, add triethylamine to neutralize to a degree of neutralization of 85%, which is calculated based on the total carboxyl groups of dimethylolpropionic acid. Slowly add deionized water under high-speed shear at 2800 r / min and stir for 25 min to form an aqueous emulsion. Remove acetone under reduced pressure of -0.085 MPa. Adjust the pH to 2.5 by adding 0.1 mol / L hydrochloric acid. Add a mixture of tetraethyl orthosilicate and 5 parts of 3-(methacryloyloxy)propyltrimethoxysilane (mass ratio of 1.5:1). Stir at 20℃ for 6 h. Adjust the pH to 6.5 with triethylamine. Filter to remove large particles to obtain a functionalized composite emulsion.

[0051] The hyperbranched polyester polyol was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., product model H402; the polytetramethylene ether diol was purchased from Beijing Biolab Technology Co., Ltd.

[0052] II. Preparation of Wear-Resistant Coatings

[0053] Formula: 60 parts functionalized polyurethane-acrylate composite emulsion; 0.5 parts photoinitiator (1-hydroxycyclohexylphenyl ketone); 0.3 parts additives (wetting and leveling agent BYK-333: defoamer BYK-024 = 1.2:1); 20 parts deionized water.

[0054] Step 1: Take the functionalized polyurethane-acrylate composite emulsion, add the photoinitiator and additives, stir at low speed for 25 minutes, and adjust the application viscosity to 25s (Ford Cup 4, 25℃) with deionized water to obtain the coating solution.

[0055] Step 2: Sand and remove dust from the leather substrate, roll coat a layer of polyester-based waterborne polyurethane dispersion with a solid content of 30%, and dry at 50℃ for 4 minutes to complete the pretreatment; roll coat the coating liquid and control the wet film thickness to 90μm.

[0056] Step 3: Pre-curing with 365nm ultraviolet LED light source at 600mJ / cm² energy, followed by baking with hot air at 55℃ for 6 minutes to form a wear-resistant coating with a dry film thickness of 10μm.

[0057] The polyester-type waterborne polyurethane dispersion was purchased from Huashi (Guangdong) New Material Technology Co., Ltd., and its model number is PUR-S5718.

[0058] Example 2: I. Preparation of Functionalized Polyurethane-Acrylic Composite Emulsion

[0059] (1) Components of the composite emulsion formulation (parts by weight): 200 parts of hyperbranched polyester polyol (hydroxyl value 230 mg KOH / g), 300 parts of polytetramethylene ether glycol (number average molecular weight 2000), 280 parts of isocyanate mixture (isophorone diisocyanate: 4,4'-diphenylmethane diisocyanate = 4:1), 80 parts of dynamic bond chain extender (32.5 parts of bis(4-hydroxyphenyl) disulfide and 47.5 parts of oxime ester modified isophorone diisocyanate), 15 parts of N,N'-di(2-hydroxyethyl)-urea, 19 parts of dimethylolpropionic acid, 25 parts of 3-(methacryloyloxy)propyltrimethoxysilane, 15 parts of trifluoroethyl methacrylate, 0.08 parts of dibutyltin dilaurate, 16 parts of neutralizing agent triethylamine, 0.05 parts of 4-methoxyphenol, and 1000 parts of deionized water.

[0060] Among them: oxime ester modified isophorone diisocyanate is prepared by reacting isophorone diisocyanate with methyl ethyl ketoxime at a mass ratio of 1:0.4, with a grafting rate of 90% for the oxime ester group; the total molar content of aromatic disulfide bonds and oxime ester bonds is 10% of the total molar number of hydroxyl groups in the prepolymer polyol; the molar proportion of N,N'-di(2-hydroxyethyl)-urea is 3.5% of the total molar number of prepolymer monomers; 3-(methacryloyloxy)propyltrimethoxysilane is used in two parts, 20 parts for graft modification and 5 parts for in-situ modified nano silica (mass ratio 4:1); nano silica is prepared by reacting tetraethyl orthosilicate with the remaining 3-(methacryloyloxy)propyltrimethoxysilane at a mass ratio of 2:1 via sol-gel reaction, with a particle size of 30 nm.

[0061] (2) Preparation steps of composite emulsion:

[0062] S1: Hyperbranched polyester polyol and polytetramethylene ether glycol were added to a reaction vessel and dehydrated at 110°C and a vacuum of -0.094 MPa for 1.5 h. The temperature was then lowered to 75°C and protected with nitrogen. Dibutyltin dilaurate catalyst was added, and an isocyanate mixture was added dropwise. The reaction was maintained at this temperature for 1 h until the isocyanate group content reached more than 95% of the theoretical value. The temperature was lowered to 65°C, and a dynamic bond chain extender and N,N'-di(2-hydroxyethyl)-urea were added. The reaction was stirred for 2 h. Dimethylolpropionic acid and 10% of the system mass of acetone were added to reduce viscosity. The reaction was continued for 1.5 h until the isocyanate group content fluctuated within ±0.2% of the theoretical value. Finally, 20 parts of 3-(methacryloyloxy)propyltrimethoxysilane were added, and the reaction was carried out at 62°C for 1.0 h to obtain an intermediate prepolymer.

[0063] S2: Cool the intermediate prepolymer to 50°C, add trifluoroethyl methacrylate, stir and react for 1.5 h, then add the polymerization inhibitor 4-methoxyphenol and stir evenly to obtain the fluorinated segment grafted prepolymer.

[0064] S3: Cool the prepolymer to 40℃, add triethylamine to neutralize to a degree of neutralization of 90%, which is calculated based on the total carboxyl groups of dimethylolpropionic acid. Slowly add deionized water under high-speed shear at 3000 r / min and stir for 30 min to form an aqueous emulsion. Remove acetone under reduced pressure of -0.085 MPa. Adjust the pH to 2.7 by adding 0.15 mol / L hydrochloric acid. Add a mixture of tetraethyl orthosilicate and 5 parts of 3-(methacryloyloxy)propyltrimethoxysilane (mass ratio of 2.0:1). Stir at 25℃ for 8 h. Adjust the pH to 6.8 with triethylamine. Filter to remove large particles to obtain a functionalized composite emulsion.

[0065] The hyperbranched polyester polyol was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., product model H304; the polytetramethylene ether glycol was purchased from Beijing Biolab Technology Co., Ltd.

[0066] II. Preparation of Wear-Resistant Coatings

[0067] Formula: 75 parts of functionalized polyurethane-acrylate composite emulsion; 0.85 parts of photoinitiator (1-hydroxycyclohexylphenyl ketone: 2-hydroxy-2-methylphenylacetone = 1:1); 0.5 parts of additives (wetting and leveling agent BYK-333: defoamer BYK-024 = 1.45:1); 30 parts of deionized water.

[0068] Step 1: Take the functionalized polyurethane-acrylate composite emulsion, add photoinitiator and additives, stir at low speed for 30 minutes, and adjust the application viscosity to 27.5s (Ford-4 cup, 25℃) with deionized water to obtain the coating solution.

[0069] Step 2: Sand and remove dust from the leather substrate; roll-coat a layer of polyester-based waterborne polyurethane dispersion with a solid content of 35%, and dry at 55°C for 5 minutes to complete the pretreatment; roll-coat the coating liquid, controlling the wet film thickness to 110μm.

[0070] Step 3: Pre-curing with 365nm ultraviolet LED light source at 800mJ / cm² energy, followed by baking with hot air at 60℃ for 8 minutes to form a wear-resistant coating with a dry film thickness of 12.5μm.

[0071] The polyester-type waterborne polyurethane dispersion was purchased from Huashi (Guangdong) New Material Technology Co., Ltd., and its model number is PUR-S5718.

[0072] Example 3: I. Preparation of Functionalized Polyurethane-Acrylic Composite Emulsion

[0073] (1) Components of the composite emulsion formulation (parts by weight): 220 parts of hyperbranched polyester polyol (hydroxyl value 240 mg KOH / g), 320 parts of polytetramethylene ether diol (number average molecular weight 2200), 300 parts of isocyanate mixture (isophorone diisocyanate: 4,4'-diphenylmethane diisocyanate = 5:1), 90 parts of dynamic bond chain extender (35 parts of bis(4-hydroxyphenyl) disulfide and 55 parts of oxime ester modified isophorone diisocyanate), 18 parts of N,N'-di(2-hydroxyethyl)-urea, 22 parts of dimethylolpropionic acid, 30 parts of 3-(methacryloyloxy)propyltrimethoxysilane, 25 parts of trifluoroethyl methacrylate, 0.1 parts of dibutyltin dilaurate, 18 parts of neutralizing agent triethylamine, 0.06 parts of 4-methoxyphenol, and 1200 parts of deionized water.

[0074] Among them: oxime ester modified isophorone diisocyanate is prepared by reacting isophorone diisocyanate with methyl ethyl ketoxime at a mass ratio of 1:0.5, with an oxime ester group grafting rate of 95%; the total molar content of aromatic disulfide bonds and oxime ester bonds is 12% of the total molar number of hydroxyl groups in the prepolymer polyol; the molar proportion of N,N'-di(2-hydroxyethyl)-urea is 4% of the total molar number of prepolymer monomers; 3-(methacryloyloxy)propyltrimethoxysilane is used in two parts, 25 parts for graft modification and 5 parts for in-situ modified nano silica (mass ratio 5:1); nano silica is prepared by reacting tetraethyl orthosilicate with the remaining 3-(methacryloyloxy)propyltrimethoxysilane at a mass ratio of 2.5:1 via sol-gel reaction, with a particle size of 50 nm.

[0075] (2) Preparation steps of composite emulsion:

[0076] S1: Hyperbranched polyester polyol and polytetramethylene ether glycol were added to a reaction vessel and dehydrated at 115°C and a vacuum of -0.098 MPa for 2 hours. The temperature was then lowered to 80°C and protected with nitrogen. Dibutyltin dilaurate catalyst was added, and an isocyanate mixture was added dropwise. The reaction was maintained at this temperature for 1.2 hours until the isocyanate group content reached more than 95% of the theoretical value. The temperature was lowered to 70°C, and a dynamic bond chain extender and N,N'-di(2-hydroxyethyl)-urea were added. The mixture was stirred for 2.5 hours. Dimethylolpropionic acid and 12% (by weight) of acetone were added to reduce viscosity. The reaction was continued for 2 hours until the isocyanate group content fluctuated within ±0.2% of the theoretical value. Finally, 25 parts of 3-(methacryloyloxy)propyltrimethoxysilane were added, and the reaction was carried out at 65°C for 1.2 hours to obtain an intermediate prepolymer.

[0077] S2: Cool the intermediate prepolymer to 55°C, add trifluoroethyl methacrylate, stir and react for 1.8 h, then add the polymerization inhibitor 4-methoxyphenol and stir evenly to obtain the fluorinated segment grafted prepolymer.

[0078] S3: Cool the prepolymer to 45℃, add triethylamine to neutralize to a degree of neutralization of 95%, which is calculated based on the total carboxyl groups of dimethylolpropionic acid. Slowly add deionized water under high-speed shear at 3200 r / min and stir for 35 min to form a hyperbranched polyurethane-acrylate emulsion. Remove acetone under reduced pressure of -0.085 MPa. Adjust the pH to 3.0 by adding 0.2 mol / L hydrochloric acid. Add a mixture of tetraethyl orthosilicate and 5 parts of 3-(methacryloyloxy)propyltrimethoxysilane (mass ratio of 2.5:1). Stir at 30℃ for 10 h. Adjust the pH to 7.0 with triethylamine. Filter to remove large particles to obtain a functionalized composite emulsion.

[0079] The hyperbranched polyester polyol was purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd., product model H401; the polytetramethylene ether diol was purchased from Beijing Biolab Technology Co., Ltd.

[0080] II. Preparation of Wear-Resistant Coatings

[0081] Formula: 80 parts of functionalized polyurethane-acrylate composite emulsion; 1.2 parts of photoinitiator (1-hydroxycyclohexylphenyl ketone: 2-hydroxy-2-methylphenylacetone = 3:2); 0.8 parts of additives (wetting and leveling agent BYK-333: defoamer BYK-024 = 1.7:1); 40 parts of deionized water.

[0082] Step 1: Take the functionalized polyurethane-acrylate composite emulsion, add photoinitiator and additives, stir at low speed for 35 minutes, and adjust the application viscosity to 30s (Ford Cup 4, 25℃) with deionized water to obtain the coating solution.

[0083] Step 2: Sand and remove dust from the leather substrate; roll-coat a layer of polyester-based waterborne polyurethane dispersion with a solid content of 40%, and dry at 60℃ for 6 minutes to complete the pretreatment; roll-coat the coating liquid and control the wet film thickness to 130μm.

[0084] Step 3: Pre-curing with 1000mJ / cm² energy using a 365nm ultraviolet LED light source, followed by baking with hot air at 65℃ for 10 minutes to form a wear-resistant coating with a dry film thickness of 15μm.

[0085] The polyester-type waterborne polyurethane dispersion was purchased from Huashi (Guangdong) New Material Technology Co., Ltd., and its model number is PUR-S5718.

[0086] Comparative Example 1: Based on Example 2, the difference is that in the preparation of the functionalized polyurethane-acrylate composite emulsion, the hyperbranched polyester polyol was replaced with an equimolar mass of ordinary linear polyester polyol (with equivalent hydroxyl value), and the rest was the same as in Example 2.

[0087] Comparative Example 2: Based on Example 2, the difference is that N,N'-bis(2-hydroxyethyl)-urea was removed during the preparation of the functionalized polyurethane-acrylate composite emulsion, and no other substances were added. The rest was the same as in Example 2.

[0088] Comparative Example 3: Based on Example 2, the difference is that in the preparation of the functionalized polyurethane-acrylate composite emulsion, the dynamic bond chain extender bis(4-hydroxyphenyl) disulfide and oxime ester modified isophorone diisocyanate were removed, and the common chain extender 1,4-butanediol was used instead. The amount of additives was adjusted based on the molar ratio to make the NCO value of the system consistent. The rest is the same as in Example 2.

[0089] Comparative Example 4: Based on Example 2, the difference is that in the preparation of the functionalized polyurethane-acrylate composite emulsion, the in-situ sol-gel reaction in step S3 is omitted, and tetraethyl orthosilicate and 3-(methacryloyloxy)propyltrimethoxysilane are not added to prepare a pure polyurethane-acrylate emulsion. Only the neutralization, water dispersion, and acetone removal steps are retained, and the rest is the same as in Example 2.

[0090] Comparative Example 5: Based on Example 2, the difference is that in the preparation of the functionalized polyurethane-acrylate composite emulsion, the in-situ sol-gel composite was changed to physical blending. Aqueous methacryloyloxy modified nano silica dispersion (particle size 30nm, double bond grafting rate ≥80%, solid content 30%) was directly added to the prepolymer obtained in S2 and ultrasonically dispersed for 20min. The rest was the same as in Example 2.

[0091] Comparative Example 6: Based on Example 2, the difference is that in the preparation process of the wear-resistant coating, UV pre-curing and heat post-curing are replaced with simple UV curing (extending the UV time to complete curing), and the heat baking step is omitted. The rest is the same as Example 2.

[0092] Comparative Example 7: Based on Example 2, the difference is that trifluoroethyl methacrylate is not added in step S2, and no other components are added. The rest is the same as in Example 2.

[0093] Performance Testing: The wear-resistant coatings prepared in Examples 1-3 and Comparative Examples 1-7 (all prepared on the same batch of leather substrates) were tested for performance. The test items and standards are as follows: ① Abrasion Resistance: A Taber 5135 abrasion testing machine was used. Reference standard: GB / T 1768-2006. Conditions: CS-10 grinding wheel, load 1000g, rotation speed 60rpm, ambient temperature (23±2)℃, relative humidity (50±5)%. Procedure: Weighing was performed after 50 revolutions of pre-grinding, followed by 1000 revolutions of formal grinding, and the mass loss (mg) was calculated. ② Self-Healing Efficiency: A laser confocal microscope (Zeiss LSM 800) was used. Procedure: A scratch with a depth of approximately 1 / 2 the coating thickness was made on the coating surface using a scalpel blade. The surface was then placed in an oven and treated at 60℃ for 20 minutes. Before and after treatment, the depth and width of the scratch were measured at the same location using a microscope and photographed. Calculation: Self-healing efficiency η = (h0 - h1) / h0 × 100%, where h0 is the scratch depth before repair and h1 is the scratch depth after repair; ③ Adhesion: Cross-cut test, referring to GB / T 9286-1998 rating, with a cross-cut spacing of 1mm, scratching through the coating to the substrate, applying tape and quickly peeling it off, observing the coating peeling, rating 1-5 (1st grade is the best, 5th grade is the worst); ④ Hardness: Pencil hardness test, referring to GB / T 6739-2022 test, with a pencil at a 45° angle to the coating, applying a 1kg load to scratch, no obvious scratches indicate the corresponding hardness level; ⑤ Flexural strength test: Bally Flexometer. Reference standard: GB / T 20991-2007. Conditions: The coated leather strip (100mm × 25mm) is mounted on a fixture and repeatedly bent at room temperature at a frequency of (100±5) times / min and a bending angle of 22.5°. Endpoint: The machine is stopped every 20,000 cycles, and the coating is examined under a microscope for cracks, peeling, or flaking. The number of times the first crack appears is recorded. ⑥ Contact angle and stain resistance test: Static water contact angle: Using a contact angle meter, 5μL of deionized water is dropped onto the coating surface, and the reading is taken after standing for 5 seconds. Five points are measured for each sample, and the average value is taken. The larger the contact angle, the better the hydrophobicity. Stain resistance (ink test): A line is drawn on the coating surface with a black water-based marker, and wiped with a dry cloth after standing for 10 seconds. Observe whether a mark is left or whether it can be easily wiped off; Grade 1 (no mark, easily wiped off), Grade 2 (slight mark, wiped off), Grade 3 (more obvious mark, still has residue after repeated wiping, cannot be completely wiped off), Grade 4 (obvious mark, difficult to wipe off).

[0094] The test results are as follows:

[0095] Table 1. Performance test results of the examples and comparative examples.

[0096]

[0097] Data Analysis:

[0098] The wear-resistant coatings prepared in Examples 1-3 all exhibit excellent comprehensive performance, possessing high wear resistance, efficient self-healing ability, strong substrate adhesion, excellent stain resistance, and adaptability to leather flexibility. Moreover, the pencil hardness reaches the corresponding level, which can balance protective performance and leather feel.

[0099] Compared with Example 2, Comparative Example 1 showed a significant decrease in wear resistance, a marked reduction in self-healing efficiency, and a substantial weakening in flexural resistance. This is because after the hyperbranched polyester polyol was replaced with a linear polyester polyol, it was impossible to construct a highly branched three-dimensional crosslinked framework. The crosslinking density of the coating decreased, and the chain segment distribution was uneven. This not only weakened the mechanical strength and wear resistance but also hindered the synergistic effect of dynamic bonds and hydrogen bonds, resulting in a simultaneous decline in self-healing efficiency and flexibility. This confirms the supporting role of the hyperbranched structure in the overall performance of the coating.

[0100] Compared with Example 2, Comparative Example 2 showed a significant decline in wear resistance, a substantial reduction in self-healing efficiency, a decrease in adhesion level, and a deterioration in flexural resistance. This is because after removing N,N'-bis(2-hydroxyethyl)-urea, the physical cross-linking points of hydrogen bonds formed by urea groups were lost, the intermolecular forces of the coating were significantly weakened, the modulus and surface hardness decreased, and the load could not be effectively dispersed during friction. At the same time, the absence of hydrogen bond network destroyed the synergistic effect with dynamic bonds, highlighting the key role of bisurea hydrogen bonds in the synergistic effect of coating strength and function.

[0101] Compared with Example 2, Comparative Example 3 has extremely low self-healing efficiency and almost loses its self-healing ability. This is because after the dynamic bond chain extender is replaced by the ordinary chain extender, there is no dual dynamic network of aromatic disulfide bonds and oxime ester bonds in the coating. Under thermal stimulation, the reversible rearrangement of molecular chains and crack healing cannot be achieved, which verifies that the dual dynamic bond network is the core carrier of the coating's self-healing function. At the same time, the ordinary chain extender cannot give the coating excellent toughness, resulting in a lower bending resistance than Example 2.

[0102] Compared with Example 2, Comparative Example 4 showed significantly worse wear resistance, a lower pencil hardness rating, and weakened flexural strength. This is because, after omitting the in-situ sol-gel reaction, the coating lacked in-situ double-bonded functionalized nano-silica reinforcement, making it impossible to form an organic-inorganic interpenetrating network. Consequently, the film layer was not dense enough and could not withstand the load during friction, resulting in a significant weakening of hardness and scratch resistance. This demonstrates the enhancing effect of in-situ nanocomposite on the rigidity and wear resistance of the coating.

[0103] Compared with Example 2, Comparative Example 5 showed decreased wear resistance, reduced adhesion grade, and inferior flexural strength compared to Example 2. This is because the nanoparticles were physically blended instead of in-situ composites, and there was no chemical bonding mediated by 3-(methacryloyloxy)propyltrimethoxysilane. The nanoparticles had poor compatibility with the polymer matrix, were prone to agglomeration and formation of microscopic defects, and the interfacial bonding was weakened, thus failing to exert a highly efficient synergistic reinforcement effect. This confirms the necessity of in-situ composites for the synergistic effect of organic-inorganic composites.

[0104] Compared with Example 2, Comparative Example 6 showed reduced self-healing efficiency, decreased adhesion level, and worsened flexural resistance. This was because the single UV curing process omitted the thermal baking step, which not only resulted in insufficient cross-linking of deep double bonds and stress concentration within the film layer, but also failed to activate latent double dynamic bonds. The dynamic network could not play its role, and the molecular chains could not rearrange to repair scratches. This confirmed the importance of gradient curing process for coating density, dynamic bond activity, and performance balance.

[0105] Compared to Example 2, Comparative Example 7 showed a significantly reduced water contact angle and a marked deterioration in stain resistance. This is because the removal of trifluoroethyl methacrylate resulted in a lack of a low-surface-energy fluorinated side-chain enrichment layer on the coating surface, making it impossible to construct an effective hydrophobic protective barrier. Although the removal of fluorinated segments had a relatively small impact on the coating's bulk strength, such as abrasion resistance, the loss of its stain- and water-resistant functions directly affected the cleanliness and aesthetics of the leather coating in actual use, confirming the crucial role of fluorinated segments in enhancing the surface functionality of the coating.

[0106] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A wear-resistant coating, characterized in that, It is prepared from the following components in parts by weight: 60-80 parts of functionalized polyurethane-acrylate composite emulsion; 0.5-1.2 parts of photoinitiator; 0.3-0.8 parts of additives; and 20-40 parts of deionized water; The preparation method of the functionalized polyurethane-acrylate composite emulsion includes the following steps: S1: Preparation of hyperbranched polyurethane-acrylate prepolymer containing dual dynamic bonds and diurea hydrogen bonds Hyperbranched polyester polyol and polytetramethylene ether glycol were added to a reaction vessel and dehydrated at 105-115℃ and a vacuum of -0.09 to -0.098 MPa for 1-2 hours. The temperature was then lowered to 70-80℃ and nitrogen gas was introduced for protection. Dibutyltin dilaurate catalyst was added, followed by dropwise addition of isocyanate. The reaction was maintained at this temperature for 0.8-1.2 hours until the isocyanate group content reached more than 95% of the theoretical value calculated based on the molar ratio of the feed. The temperature was then lowered to 60-70℃. Add a dynamic bond chain extender and N,N'-bis(2-hydroxyethyl)-urea, and stir for 1.5-2.5 h; then add dimethylolpropionic acid and 8-12% of acetone by mass of the total system to reduce viscosity, and continue the reaction for 1-2 h until the isocyanate group content fluctuates within ±0.2% of the theoretical value; finally add a portion of 3-(methacryloyloxy)propyltrimethoxysilane, and react at 60-65℃ for 0.8-1.2 h to obtain the intermediate prepolymer; S2: Fluorinated acrylate end-grafted modification The intermediate prepolymer obtained in step S1 is cooled to 45-55℃, trifluoroethyl methacrylate is added, and the mixture is stirred for 1.2-1.8 hours. Then, the polymerization inhibitor 4-methoxyphenol is added and stirred evenly to obtain a hyperbranched polyurethane-acrylate prepolymer grafted with fluorinated segments. S3: Water-dispersible and in-situ double-bond functionalized nano-silica composite The prepolymer obtained in step S2 is cooled to 35-45℃, neutralized with a neutralizing agent to a degree of neutralization of 85-95%, and deionized water is slowly added dropwise under high-speed shear conditions of 2800-3200 r / min. The mixture is stirred for 25-35 min to form an aqueous hyperbranched polyurethane-acrylate emulsion. Acetone is removed under reduced pressure. 0.1-0.2 mol / L hydrochloric acid is added dropwise to the emulsion to adjust the pH to 2.5-3.

0. A mixture of tetraethyl orthosilicate and the remaining 3-(methacryloyloxy)propyltrimethoxysilane with a mass ratio of (1.5-2.5):1 is slowly added. The mixture is stirred at 20-30℃ for 6-10 h. The pH is then adjusted to 6.5-7.0 with triethylamine. Large particles are removed by filtration to obtain a functionalized polyurethane-acrylate composite emulsion.

2. The wear-resistant coating according to claim 1, characterized in that, The functionalized polyurethane-acrylate composite emulsion is prepared from the following components in parts by weight: 180-220 parts of hyperbranched polyester polyol, 280-320 parts of polytetramethylene ether glycol, 260-300 parts of isocyanate, 70-90 parts of dynamic bond chain extender, 12-18 parts of N,N'-bis(2-hydroxyethyl)-urea, 18-22 parts of dimethylolpropionic acid, and 20-... 30 parts, trifluoroethyl methacrylate 5-25 parts, catalyst 0.06-0.10 parts, neutralizer 14-18 parts, polymerization inhibitor 0.04-0.06 parts, deionized water 800-1200 parts; the 3-(methacryloyloxy)propyltrimethoxysilane is used in two parts, one part is used for grafting and modifying polyurethane-acrylate chains, and the other part is used for in-situ modification of nano-silica, with a mass ratio of (3-5):

1.

3. The wear-resistant coating according to claim 1, characterized in that, The hyperbranched polyester polyol has a hydroxyl value of 180-240 mg KOH / g; the polytetramethylene ether diol has a number average molecular weight of 1800-2200; the isocyanate is a mixture of isophorone diisocyanate and 4,4'-diphenylmethane diisocyanate, and the mass ratio of the two in the mixture is (3-5):

1.

4. The wear-resistant coating according to claim 1, characterized in that, The dynamic bond chain extender is composed of 30-35 parts of bis(4-hydroxyphenyl) disulfide and 40-55 parts of oxime ester-modified isophorone diisocyanate; the oxime ester-modified isophorone diisocyanate is prepared by reacting methyl ethyl ketoxime with isophorone diisocyanate at a mass ratio of (0.3-0.5):1, and its oxime ester group grafting rate is ≥85%; the total molar content of aromatic disulfide bonds and oxime ester bonds in the dynamic bond chain extender is 8-12% of the total molar number of hydroxyl groups in the polyols, including hyperbranched polyester polyol, polytetramethylene ether glycol and chain extender prepolymer; the molar proportion of N,N'-di(2-hydroxyethyl)-urea is 3-4%, which is based on the total molar number of hyperbranched polyester polyol, polytetramethylene ether glycol, isocyanate, N,N'-di(2-hydroxyethyl)-urea and dimethylolpropionic acid participating in the prepolymer reaction.

5. The wear-resistant coating according to claim 1, characterized in that, The functionalized polyurethane-acrylate composite emulsion contains in-situ double-bond functionalized nano-silica, which is prepared by sol-gel reaction of tetraethyl orthosilicate and the remaining 3-(methacryloyloxy)propyltrimethoxysilane at a mass ratio of (1.5-2.5):1, and has a particle size of 10-50 nm.

6. The wear-resistant coating according to claim 1, characterized in that, The photoinitiator is 1-hydroxycyclohexylphenyl ketone, or a mixture of 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methylphenylacetone; the additives include wetting and leveling agent BYK-333 and defoamer BYK-024, with a ratio of (1.2-1.7):

1.

7. The wear-resistant coating according to claim 1, characterized in that, The neutralizing agent is triethylamine, with a neutralization degree of 85-95%, which is calculated based on the total carboxyl groups of dimethylolpropionic acid.

8. The application of the wear-resistant coating as described in any one of claims 1-7 on a leather surface, characterized in that, Includes the following steps: Step 1: Emulsion compounding Take the functionalized polyurethane-acrylate composite emulsion, add photoinitiator and additives, stir at low speed for 25-35 minutes, adjust the construction viscosity with deionized water, and use the Forecast-4 cup to test the viscosity at 25℃, which is 25-30s, to obtain the wear-resistant coating liquid. Step 2: Substrate Pretreatment and Coating The leather substrate is sanded and dusted, and a layer of polyester-type waterborne polyurethane dispersion with a solid content of 30-40% is roller coated. The pretreatment is completed by drying at 50-60℃ for 4-6 minutes. The coating liquid is then applied to the pretreated leather surface by roller coating, and the wet film thickness is controlled to be 90-130μm. Step 3: Gradient Curing First, it is pre-cured with a 365nm ultraviolet light-emitting diode light source at an energy of 600-1000mJ / cm², and then cured by hot air baking at 55-65℃ for 6-10 minutes to form a wear-resistant coating with a dry film thickness of 10-15μm.

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