High-strength and anti-yellowing leather top layer finishing agent and preparation method thereof

Abstract

The invention relates to a high-strength and yellowing-resistant leather top layer finishing agent and a preparation method thereof. The coating agent comprises a modified waterborne polyurethane emulsion, a nano filler dispersion liquid, an anti-ultraviolet absorbent, a thermal oxidation stabilizer, a cross-linking agent and other assistants. The preparation method comprises the following steps: firstly, preparing a modified waterborne polyurethane emulsion, then uniformly mixing the modified waterborne polyurethane emulsion with a nano filler dispersion liquid, an anti-ultraviolet absorbent, a thermal oxidation stabilizer, a cross-linking agent and other raw materials, and defoaming to finally obtain the leather top layer finishing agent with excellent performance. A polyurethane soft and hard segment structure, a chain extension system, hydrophilic group content, crosslinking components and the like are optimally designed, a polymer skeleton structure with high crosslinking density, good compatibility and light stability is formed by introducing functional groups, and a specific coalescing agent, a light stabilizer and an auxiliary synergistic system are supplemented. It is ensured that the prepared leather top layer coating agent has excellent film-forming property, mechanical strength and yellowing resistance, and an effective way is provided for development of high-end leather coating materials.

Description

Technical Field

[0001] This invention relates to the fields of leather processing and new materials technology, specifically to a high-strength, yellowing-resistant leather top coating agent and its preparation method. Background Technology

[0002] With the increasing demands for green environmental protection, appearance quality, and service life in high-end leather products such as shoe uppers, bag leather, and automotive interior leather, coating materials are rapidly developing towards higher strength, higher weather resistance, and environmental friendliness. Among various coating materials, the top coating agent, as the outermost functional protective film on the leather surface, directly determines the surface strength, yellowing resistance, and overall durability of the finished leather.

[0003] Currently, the most widely used leather topcoat agents in industry mainly include polyurethane resins or acrylic resins and their composite systems. The abrasion resistance, scratch resistance, and other physical properties of conventional resin coatings formed by these materials are no longer sufficient to meet the high strength requirements of shoe uppers, bag leathers, and automotive interior leathers. Especially under repeated bending, stretching, or external friction conditions, the coating is prone to damage, peeling, or loss of gloss. Furthermore, as the automotive interior and home furnishing industries increasingly demand better lightfastness and color stability, traditional resin systems are prone to yellowing or loss of gloss under ultraviolet light and heat-oxygen environments, severely affecting the product's appearance. This poses even greater technical challenges to light-colored, white, or high-end fashion shoe leathers, particularly in terms of yellowing resistance.

[0004] Therefore, how to develop a leather topcoat agent that combines high strength, excellent yellowing resistance, good film-forming properties, and environmental friendliness has become a key research issue in the field of leather chemical materials. Summary of the Invention

[0005] This invention addresses the aforementioned problems and shortcomings of existing technologies by providing a high-strength, yellowing-resistant topcoat agent for leather. Through multiple measures, including rationally designing the structure of the waterborne resin system, introducing specific functional groups, and combining it with a specific compounded additive system, the resulting coating not only exhibits significantly enhanced mechanical properties but also substantially improved light stability and long-term anti-yellowing performance, effectively enhancing the appearance quality and durability of leather products.

[0006] Therefore, the high-strength, yellowing-resistant leather topcoat provided by this invention comprises a modified waterborne polyurethane emulsion, nanofillers, and additives. In the above scheme, the mass ratio of the modified waterborne polyurethane emulsion, nanofillers, and additives in the leather topcoat is controlled between 85-98:1-5:1-8.

[0007] In the above scheme, the nanofiller is selected from at least one of nano-SiO2 and TiO2. Adding nanofillers can effectively enhance the surface strength of the coating film and improve its wear resistance.

[0008] In the above scheme, the nanofiller is introduced in the form of an aqueous dispersion, and its mass percentage concentration does not exceed 15%, preferably 6%-12%.

[0009] In the above schemes, the additives are selected from one or more of the following: UV absorbers, thermal oxidative stabilizers, crosslinking agents, defoamers, antistatic agents, thickeners, leveling agents, and dispersants. Some schemes include at least UV absorbers, thermal oxidative stabilizers, and crosslinking agents, and may also include defoamers, antistatic agents, thickeners, leveling agents, and dispersants.

[0010] In the above scheme, the UV absorber is selected from at least one of benzophenone, benzotriazole, and triazine, and its addition amount accounts for no more than 40% of the mass of the additive, preferably 25%-40%. The UV absorber is mainly used to improve the yellowing resistance of the coating film.

[0011] In the above scheme, the thermal oxidative stabilizer is specifically a peroxide decomposition agent, including thioester decomposition agents and phosphite decomposition agents, and its addition amount accounts for no more than 35% of the mass of the additive, preferably 12.5%-35%. The thermal oxidative stabilizer is mainly used to improve the thermal stability of the coating film.

[0012] In the above scheme, the crosslinking agent includes aziridine crosslinking agents and isocyanate crosslinking agents, and the amount added accounts for no more than 15% of the mass of the additives, preferably 6%-13%. The crosslinking agent is mainly used to enhance the strength of waterborne polyurethane emulsions and improve the physical properties of leather finishing agents.

[0013] In the above scheme, the defoamer is selected from at least one of silicone-based, mineral oil-based, and polymer-based defoamers, and its addition amount accounts for no more than 15% of the mass of the additive, preferably 4%-13%. The defoamer is mainly used to eliminate or inhibit the formation of microbubbles inside the system during the transportation and use of the coating agent.

[0014] In the above scheme, the antistatic agent is selected from at least one of alkyl sulfonates, sulfates, and phosphates, and its addition amount accounts for no more than 15% of the mass of the additive, preferably 4%-13%. The antistatic agent is mainly used to prevent electrostatic discharge, adsorb dust or oil, and keep the coating surface clean, especially suitable for transparent coatings.

[0015] In the above scheme, the thickener is selected from at least one of acrylic and polyacrylamide thickeners, and its addition amount accounts for no more than 15% of the mass of the additive, preferably 0%-14%. The thickener is mainly used to precisely control the viscosity of the coating agent, facilitate production and construction processes and worker operation, reduce coating agent sedimentation and stratification, and extend storage time.

[0016] In the above scheme, the leveling agent is selected from at least one of silicone, polyether, and acrylic leveling agents, and its addition amount accounts for no more than 10% of the mass of the additive, preferably 4%-8%. The leveling agent is mainly used to reduce the surface tension of the coating agent, improve the leveling efficiency, improve the coating uniformity, and improve compatibility.

[0017] In the above scheme, the dispersant is selected from at least one of ethylene polyoxypropylene ether, polycarboxylate, and fatty acid polyethylene glycol ester, and its addition amount accounts for no more than 10% of the mass of the additive, preferably 4%-7%. The dispersant is mainly used to improve the dispersion stability and uniformity of the coating agent system.

[0018] The second objective of this invention is to provide a method for preparing the above-mentioned high-strength, yellowing-resistant leather top coating agent, comprising: firstly preparing a modified waterborne polyurethane emulsion, then mixing it with nanofillers and additives, and then stirring it evenly at a speed of 100-400 r / min in an environment of 20-40℃, and obtaining the high-strength, yellowing-resistant leather top coating agent after degassing.

[0019] The preparation method of the modified waterborne polyurethane emulsion in the above scheme includes: (a) adding 60-80 parts by weight of polyether polyol and 20-40 parts by weight of isocyanate into a reactor and heating to 75℃-85℃ for reaction; (b) adding 10-20 parts by weight of solvent to dilute the mixture, and then adding 15-30 parts by weight of chain extender and continuing the reaction at 75℃-85℃; (c) adding 20-30 parts by weight of solvent to dilute the reaction mixture, cooling to 50-65℃ and then adding 5-10 parts by weight of triethylamine for neutralization to obtain a prepolymer; (d) mixing the prepolymer with 400-600 parts by weight of deionized water evenly, and then distilling and aging the resulting mixture to obtain the modified waterborne polyurethane emulsion.

[0020] In the above scheme, the raw materials (polyether polyol, isocyanate, etc.) used to prepare the modified waterborne polyurethane emulsion need to be dehydrated before use. The specific method is as follows: place the raw materials in the reactor, evacuate the vacuum, heat to 80-100℃, and then cool naturally.

[0021] In the above scheme, the polyether-type polyol in step (a) is selected from at least one of polypropylene glycol and polytetrahydrofuran glycol, and the isocyanate is selected from at least one of hexamethylene diisocyanate and isophorone diisocyanate. The solvents used in steps (b) and (c) may be the same or different, and are both selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, and acetone.

[0022] In the above scheme, the chain extender mentioned in step (a) includes conventional chain extenders and functional chain extenders, with a mass ratio of 10-20:5-10. The reason for using two different types of chain extenders in combination is as follows: conventional chain extenders provide certain hydrophilic groups, making the waterborne polyurethane emulsion more stable, while also increasing the molecular chain length, thus laying the foundation for the material's basic properties; while functional chain extenders provide functional groups, improving the basic yellowing resistance of the waterborne polyurethane emulsion.

[0023] Furthermore, the conventional chain extender is selected from at least one of 2,2-dimethylolpropionic acid, 1,4-butanediol, ethylene glycol, and diethylene glycol, and the functional chain extender is selected from at least one of hydroxyl / amino silicone oil and 2-hydroxyethyl disulfide.

[0024] In the above scheme, in step (d), the prepolymer is slowly poured into deionized water, and then thoroughly mixed by eccentric stirring at a speed of 800-1200 r / min.

[0025] In the above scheme, the distillation temperature in step (d) is 50-60℃, and the product is aged at room temperature for 24-48 hours.

[0026] This invention uses waterborne polyurethane as the film-forming matrix. Through optimized design of the polyurethane's soft and hard segment structure, chain extender system, hydrophilic group content, and crosslinking components, a polymer skeleton structure with high crosslinking density, good compatibility, and light stability is constructed at the molecular level. In this process, polyether polyols with excellent light and hydrolysis resistance are selected as soft segments, and aliphatic isocyanates as hard segments, ensuring both the flexibility of the coating film and significantly improving its mechanical strength and resistance to yellowing. The introduction of chain extenders and crosslinking components facilitates the formation of a multi-point crosslinked network structure, improving the coating's abrasion resistance and durability. By rationally controlling the content of hydrophilic groups, the prepared modified waterborne polyurethane emulsion is ensured to have good dispersibility and stability. Based on the above, specific film-forming aids, light stabilizers, and synergistic additive systems are added, enabling the leather topcoat to possess excellent film-forming properties, mechanical strength, stability, and resistance to yellowing.

[0027] Compared with existing leather finishing agents, the advantages of this invention are mainly reflected in the following aspects: (1) The film layer formed by coating the leather top coating agent described in this invention has the advantages of high transparency, strong adhesion and green environmental protection. It can significantly enhance the tensile properties, elongation at break and yellowing resistance of natural leather and synthetic leather after top coating. It can maintain good stability even under ultraviolet light irradiation, high temperature aging and other environments. It is especially suitable for products such as shoe upper leather, automotive interior leather and bag leather with high weather resistance requirements.

[0028] (2) The present invention achieves synergistic improvement in terms of green environmental protection, light stability and comprehensive physical properties. Test results show that the tensile strength of the film formed by coating with the leather top coating agent described in the present invention is ≥40Mpa, the elongation at break is ≥800%, and the yellowing resistance grade is ≥4, which provides an effective way for the development of high-end leather coating materials.

[0029] (3) The preparation process of the leather top coating agent described in this invention is relatively simple and can be industrialized for large-scale mass production. It is widely used in leather (especially high-end leather). Attached Figure Description

[0030] Figure 1 The images show a comparison of the leather topcoat prepared in Example 1 and Comparative Example 1 before and after the yellowing resistance test. Detailed Implementation

[0031] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, further detailed description is provided below in conjunction with specific embodiments. It should be emphasized that the embodiments listed below are merely preferred embodiments of the present invention and do not constitute a limitation thereof. Any simple improvements made based on these embodiments will fall within the protection scope of the present invention.

[0032] It should be noted that, to avoid obscuring the invention with unnecessary details, the embodiments only show the raw materials, methods, and steps closely related to the technical solutions of the invention, while omitting other details. The term "comprising / including" herein indicates the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components. Unless otherwise specified, all raw materials mentioned in this invention are commercially available, and all units of measurement are SI units.

[0033] To fully understand the performance of the leather top coating agent prepared by the present invention, it was coated into a film and then tested for yellowing resistance, tensile strength, and elongation at break.

[0034] The yellowing resistance test was conducted in accordance with the standard "HG / T 3689-2014 Test Method for Yellowing Resistance of Footwear". The specific test method is as follows: the sample is placed 250mm away from the test sample in the test chamber and irradiated with a 300W sun lamp for 6 hours. The sample is then removed and the yellowing level is visually evaluated using a gray scale in a standard light source box.

[0035] The tensile strength and elongation at break test methods are carried out in accordance with GB / T 1040.1-2018 standard. The specific process is as follows: cut three samples to be tested using a cutter, place the cut samples in a constant temperature and humidity chamber at 20℃ and 65% humidity for 24-48 hours, and then take them out to perform tensile tests using a tensile testing machine.

[0036] Example 1 30 parts of isophorone diisocyanate and 70 parts of polytetrahydrofuran glycol were added to a reactor and stirred until homogeneous. The mixture was heated to 80°C and reacted for 2 hours under nitrogen protection. While maintaining the temperature and atmosphere, 10 parts of N-methylpyrrolidone, 5 parts of 2,2-dimethylolpropionic acid, 5 parts of 1,4-butanediol, 3 parts of hydroxyl silicone oil, and 2 parts of 2-hydroxyethyl disulfide were added sequentially. After stirring until homogeneous, the reaction continued for 4 hours. After the reaction was complete, 20 parts of acetone were added and stirred until homogeneous. The mixture was cooled to 50°C, and then 7 parts of triethylamine were added for neutralization for 20 minutes to obtain the prepolymer.

[0037] The prepolymer was slowly added to 500 parts of deionized water and stirred at 1000 r / min for 20 minutes to disperse it evenly, thus obtaining an emulsion. The emulsion was slowly heated to 60℃ and distilled for 3 hours. After cooling to room temperature, it was filtered, and the filtrate was allowed to stand at room temperature for 48 hours to mature, thus obtaining a stable modified waterborne polyurethane emulsion A.

[0038] 95 parts of modified waterborne polyurethane emulsion A, nano-SiO2 dispersion (2 parts nano-SiO2 dispersed in 20 parts water), 0.8 parts of UV absorber (benzophenone), 1 part of thermal oxidative stabilizer (phosphite decomposition agent), 0.2 parts of crosslinking agent (aziridine crosslinking agent), 0.3 parts of defoamer (organosilicone defoamer), 0.2 parts of antistatic agent (alkyl sulfonate), 0.1 parts of thickener (acrylic thickener), 0.2 parts of leveling agent (organosilicone leveling agent), and 0.2 parts of dispersant (polycarboxylate) were added to a reactor. The resulting mixture was stirred at 300 rpm for 2 hours at 30°C. After stirring, the mixture was transferred to a vacuum device for degassing treatment, finally obtaining a high-strength, yellowing-resistant leather topcoat.

[0039] Test results show that the yellowing resistance of the leather top coating agent prepared in Example 1 after film formation is not lower than level 4, the tensile strength is not lower than 40 MPa, and the elongation at break is not lower than 800%.

[0040] Comparative Example 1 30 parts of isophorone diisocyanate and 70 parts of polytetrahydrofuran diol were added to a reactor and stirred until homogeneous. The mixture was heated to 80°C and reacted for 2 hours under nitrogen protection. While maintaining the temperature and atmosphere, 10 parts of N-methylpyrrolidone, 5 parts of 2,2-dimethylolpropionic acid, and 5 parts of 1,4-butanediol were added sequentially, stirred until homogeneous, and the reaction continued for another 4 hours. After the reaction was complete, 20 parts of acetone were added and stirred until homogeneous. The mixture was then cooled to 50°C, and 7 parts of triethylamine were added for neutralization for 20 minutes to obtain the prepolymer.

[0041] The prepolymer was slowly added to 500 parts of deionized water and stirred at 1000 r / min for 20 minutes to disperse it evenly, thus obtaining an emulsion. The emulsion was slowly heated to 60℃ and distilled for 3 hours. After cooling to room temperature, it was filtered, and the filtrate was allowed to stand at room temperature for 48 hours to mature, thus obtaining modified waterborne polyurethane emulsion a.

[0042] Referring to the method in Example 1, the original modified waterborne polyurethane emulsion A was replaced with an equal amount of modified waterborne polyurethane emulsion a to prepare a leather topcoat.

[0043] Test results show that the yellowing resistance level of the leather top coat coating prepared in Comparative Example 1 is ≤3 after film formation, specifically as follows: Figure 1 As shown. The left side shows actual photos of the sample of Example 1 before and after coating, and the right side shows actual photos of the sample of Comparative Example 2 before and after coating. The actual effect is quite obvious, but the effect seen in the photos is not prominent enough due to the influence of lighting and camera.

[0044] Furthermore, the mechanical properties of the leather topcoat obtained in Comparative Example 1 decreased slightly after film formation, with tensile strength dropping to 37 MPa and elongation at break dropping to 740%. This significant difference in performance is mainly because Comparative Example 1 only added one chain extender in the preparation of the modified waterborne polyurethane emulsion, lacking a functional chain extender that can improve properties such as resistance to yellowing.

[0045] Comparative Example 2 Modified waterborne polyurethane emulsion a was prepared according to the method in Comparative Example 1. Then, 50 parts of modified waterborne polyurethane emulsion a and 50 parts of water were added to a reactor, and the resulting mixture was stirred at 30°C and 300 r / min for 2 hours. After stirring, the mixture was transferred to a vacuum device for degassing treatment to finally obtain the leather topcoat.

[0046] Test results show that the leather topcoat prepared in Comparative Example 2 has poor yellowing resistance after film formation (yellowing resistance level is approximately 1-2). This difference in performance is mainly due to the lack of chain extenders to improve yellowing resistance during the preparation of the waterborne polyurethane emulsion, and the absence of functional materials such as UV absorbers and thermal oxidation stabilizers in the subsequent compounding process. Therefore, leather coated with this topcoat is essentially indistinguishable from leather without the coating treatment.

[0047] Example 2 20 parts of isophorone diisocyanate and 80 parts of polypropylene glycol were added to a reactor and stirred until homogeneous. The mixture was heated to 82°C and reacted for 2 hours under nitrogen protection. While maintaining the temperature and atmosphere, 20 parts of N-methylpyrrolidone, 5 parts of 2,2-dimethylolpropionic acid, 2 parts of 1,4-butanediol, 5 parts of diethylene glycol, 4 parts of hydroxyl silicone oil, and 4 parts of 2-hydroxyethyl disulfide were added sequentially. After stirring until homogeneous, the reaction continued for 3 hours. After the reaction was complete, 20 parts of acetone were added and stirred until homogeneous. The mixture was cooled to 50°C, and then 6 parts of triethylamine were added for neutralization for 30 minutes to obtain the prepolymer.

[0048] The prepolymer was slowly added to 500 parts of deionized water and stirred at 1000 r / min for 20 minutes to disperse it evenly, thus obtaining an emulsion. The emulsion was slowly heated to 60℃ and distilled for 3 hours. After cooling to room temperature, it was filtered, and the filtrate was allowed to stand at room temperature for 48 hours to mature, thus obtaining a stable modified waterborne polyurethane emulsion B.

[0049] 92 parts of modified waterborne polyurethane emulsion B, nano-SiO2 dispersion (3 parts nano-SiO2 dispersed in 30 parts water), 2 parts of UV absorber (benzotriazole), 1 part of thermal oxidative stabilizer (thioester decomposition agent), 0.5 parts of crosslinking agent (isocyanate crosslinking agent), 0.5 parts of defoamer (mineral oil defoamer), 0.5 parts of antistatic agent (sulfate), 0.2 parts of leveling agent (polyether leveling agent), and 0.3 parts of dispersant (ethylene polyoxypropylene ether) were added to a reactor. The resulting mixture was stirred at 300 rpm for 2 hours at 30°C. After stirring, the mixture was transferred to a vacuum device for degassing treatment, finally obtaining a high-strength, yellowing-resistant leather topcoat.

[0050] Test results show that the yellowing resistance of the leather top coating agent prepared in Example 2 after film formation is not lower than level 4, the tensile strength is not lower than 35 MPa, and the elongation at break is not lower than 700%.

[0051] Example 3 Ten parts of hexamethylene diisocyanate, 20 parts of isophorone diisocyanate, 40 parts of polypropylene glycol, and 30 parts of polytetrahydrofuran glycol were added to a reactor and stirred until homogeneous. The mixture was heated to 75°C and reacted for 2 hours under nitrogen protection. While maintaining the temperature and atmosphere, 15 parts of acetone, 6 parts of 2,2-dimethylolpropionic acid, 6 parts of 1,4-butanediol, 5 parts of hydroxyl silicone oil, and 3 parts of 2-hydroxyethyl disulfide were added sequentially. After stirring until homogeneous, the reaction continued for another 3 hours. After the reaction was complete, 25 parts of acetone were added and stirred until homogeneous. The mixture was cooled to 50°C, and then 8 parts of triethylamine were added for neutralization for 30 minutes to obtain the prepolymer.

[0052] The prepolymer was slowly added to 600 parts of deionized water and stirred at 800 r / min for 30 minutes to disperse it evenly, thus obtaining an emulsion. The emulsion was slowly heated to 60℃ and distilled for 3 hours. After cooling to room temperature, it was filtered, and the filtrate was allowed to stand at room temperature for 48 hours to mature, thus obtaining a stable modified waterborne polyurethane emulsion C.

[0053] 93 parts of modified waterborne polyurethane emulsion C, nano-SiO2 dispersion (3 parts nano-SiO2 dispersed in 40 parts water), 1 part of anti-UV absorber (benzotriazole), 0.5 parts of thermal oxidative stabilizer (phosphite decomposition agent), 0.5 parts of crosslinking agent (aziridine crosslinking agent), 0.5 parts of defoamer (organosilicon defoamer), 0.5 parts of antistatic agent (sulfate), 0.3 parts of leveling agent (polyether leveling agent), 0.5 parts of thickener (acrylic thickener), and 0.2 parts of dispersant (ethylene polyoxypropylene ether) were added to a reactor. The resulting mixture was stirred at 300 rpm for 2 hours at 30°C. After stirring, the mixture was transferred to a vacuum device for degassing treatment, finally obtaining a high-strength, yellowing-resistant leather topcoat.

[0054] Test results show that the yellowing resistance of the leather top coating agent prepared in Example 3 after film formation is not lower than level 4, the tensile strength is not lower than 38 MPa, and the elongation at break is not lower than 650%.

[0055] Example 4 20 parts hexamethylene diisocyanate, 30 parts polypropylene glycol, and 50 parts polytetrahydrofuran glycol were added to a reactor and stirred until homogeneous. The mixture was heated to 78°C and maintained at this temperature for 2 hours under nitrogen protection. While keeping the temperature and atmosphere constant, 10 parts acetone, 8 parts 2,2-dimethylolpropionic acid, 4 parts 1,4-butanediol, 5 parts hydroxyl silicone oil, and 3 parts 2-hydroxyethyl disulfide were added sequentially. After stirring until homogeneous, the reaction continued for another 3 hours. After the reaction was complete, 20 parts acetone were added and stirred until homogeneous. The mixture was then cooled to 50°C, and 9 parts triethylamine were added for neutralization for 30 minutes to obtain the prepolymer.

[0056] The prepolymer was slowly added to 700 parts of deionized water and stirred at 1200 r / min for 25 minutes to disperse it evenly, thus obtaining an emulsion. The emulsion was slowly heated to 60℃ and distilled for 3 hours. After cooling to room temperature, it was filtered, and the filtrate was allowed to stand at room temperature for 24 hours to mature, thus obtaining a stable modified waterborne polyurethane emulsion D.

[0057] 90 parts of modified waterborne polyurethane emulsion D, nano-SiO2 dispersion (5 parts nano-SiO2 dispersed in 40 parts water), 2 parts of UV absorber (benzotriazole), 1 part of thermal oxidative stabilizer (phosphite decomposition agent), 0.5 parts of crosslinking agent (aziridine crosslinking agent), 0.2 parts of defoamer (organosilicon defoamer), 0.2 parts of antistatic agent (sulfate), 0.2 parts of leveling agent (polyether leveling agent), 0.7 parts of thickener (acrylic thickener), and 0.2 parts of dispersant (ethylene polyoxypropylene ether) were added to a reactor. The resulting mixture was stirred at 30°C and 200 rpm for 2 hours. After stirring, the mixture was transferred to a vacuum device for degassing treatment, finally obtaining a high-strength, yellowing-resistant leather topcoat.

[0058] Test results show that the yellowing resistance of the leather top coating agent prepared in Example 4 after film formation is not lower than level 4, the tensile strength is not lower than 35 MPa, and the elongation at break is not lower than 550%.

Claims

1. A high-strength, yellowing-resistant leather topcoat, characterized in that: The top coating agent comprises a modified waterborne polyurethane emulsion, nanofillers, and additives, wherein the nanofillers are selected from at least one of nano-SiO2 and TiO2, and the additives are selected from at least one of UV absorbers, thermal oxidation stabilizers, crosslinking agents, defoamers, antistatic agents, thickeners, leveling agents, and dispersants.

2. The high-strength, yellowing-resistant leather topcoat as described in claim 1, characterized in that: The mass ratio of modified waterborne polyurethane emulsion, nanofiller, and additives is 85-98:1-5:1-8.

3. The high-strength, yellowing-resistant leather topcoat as described in claim 1, characterized in that: The UV absorber is selected from at least one of benzophenone, benzotriazole, and triazine, and its mass percentage in the additive does not exceed 40%; the thermal oxidizing stabilizer is specifically a peroxide decomposing agent, and its mass percentage in the additive does not exceed 35%; the crosslinking agent is specifically an aziridine crosslinking agent or an isocyanate crosslinking agent, and its mass percentage in the additive does not exceed 15%; the defoamer is selected from at least one of silicone defoamers, mineral oil defoamers, and polymer defoamers, and its mass percentage in the additive does not exceed 15%; the antistatic agent is selected from alkane... The additive contains at least one of sulfonates, sulfates, and phosphates, with a mass percentage not exceeding 15% of the additive; the thickener is selected from at least one of acrylic thickeners and polyacrylamide thickeners, with a mass percentage not exceeding 15% of the additive; the leveling agent is selected from at least one of silicone leveling agents, polyether leveling agents, and acrylic leveling agents, with a mass percentage not exceeding 10% of the additive; and the dispersant is selected from at least one of ethylene polyoxypropylene ether, polycarboxylates, and fatty acid polyethylene glycol esters, with a mass percentage not exceeding 10% of the additive.

4. The high-strength, yellowing-resistant leather topcoat as described in claim 1, characterized in that: The nanofiller is introduced in the form of an aqueous dispersion, and the mass percentage concentration of the nanofiller in the dispersion does not exceed 15%.

5. The method for preparing the high-strength, yellowing-resistant leather topcoat according to any one of claims 1-4, characterized in that... The method includes: preparing a modified waterborne polyurethane emulsion and mixing it evenly with nanofillers and additives.

6. The method as described in claim 5, characterized in that... The method for preparing the modified waterborne polyurethane emulsion includes: mixing 60-80 parts of polyether polyol and 20-40 parts of isocyanate and heating to 75℃-85℃ for reaction; adding 10-20 parts of solvent to the mixture for dilution, then adding 15-30 parts of chain extender and continuing the reaction at 75℃-85℃; adding another 20-30 parts of solvent for dilution, cooling the resulting mixture to 50-65℃, and then adding 5-10 parts of triethylamine for neutralization to obtain a prepolymer; mixing the prepolymer with 400-600 parts of deionized water until homogeneous, and then distilling and aging the resulting mixture to obtain the modified waterborne polyurethane emulsion.

7. The method as described in claim 6, characterized in that: The polyether-type polyol is selected from at least one of polypropylene glycol and polytetrahydrofuran glycol, and the isocyanate is selected from at least one of hexamethylene diisocyanate and isophorone diisocyanate. The solvents added in the two additions may be the same or different, and both are selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, and acetone.

8. The method as described in claim 6, characterized in that: The chain extender is a mixture of conventional chain extenders and functional chain extenders, with a mass ratio of 10-20:5-10.

9. The method as described in claim 8, characterized in that: The conventional chain extender is selected from at least one of 2,2-dimethylolpropionic acid, 1,4-butanediol, ethylene glycol, and diethylene glycol, and the functional chain extender is selected from at least one of hydroxyl / amino silicone oil and 2-hydroxyethyl disulfide.

10. The method as described in claim 6, characterized in that: Slowly pour the prepolymer into deionized water, then stir thoroughly to mix it evenly. Control the distillation temperature at 50-60℃ and the aging temperature at room temperature.

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