Waterborne polyurethane synthetic leather and preparation method thereof

Abstract

The invention relates to the technical field of synthetic leather preparation, and discloses waterborne polyurethane synthetic leather and a preparation method thereof.The waterborne polyurethane synthetic leather comprises a base layer and a coating layer, the base layer is polyester non-woven fabric, and the coating layer comprises, by weight, 10-20 parts of aromatic isocyanate; 50 to 70 parts of polyether polyol; 5 to 15 parts of nano silicon dioxide; 0.1 to 0.5 part of a catalyst; 15 to 25 parts of water; 5 to 10 parts of epoxidized soybean oil; 0.1 to 0.3 part of polysorbate-20 (20); the aromatic isocyanate is toluene diisocynate, the nitrogen content of the aromatic isocyanate is 14-16%, the purity of the aromatic isocyanate is higher than 98%, and the volatile content of the aromatic isocyanate is lower than 1%. By introducing the nano silicon dioxide and the epoxidized soybean oil and optimizing the reaction process, the anti-aging, anti-ultraviolet and high-temperature-resistant properties of the polyurethane synthetic leather are improved, the service life is prolonged, and the stability and high performance of the product are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of synthetic leather preparation, in particular to a waterborne polyurethane synthetic leather and a preparation method thereof. Background Art

[0002] In today's context of the parallel development of green manufacturing and high-performance materials, waterborne polyurethane synthetic leather, as a key alternative to solvent-based synthetic leather, is being widely used in footwear, automotive interiors, home furnishings, and other fields. Consumers' demands for synthetic leather's softness, folding resistance, abrasion resistance, and even breathability are constantly increasing. This is especially true for applications involving long-term use or high-frequency bending, which requires materials with a stable structure and balanced performance.

[0003] Currently, traditional polyurethane synthetic leather production processes and formulations are widely used, typically using isocyanates and polyols to react to form polyurethane chains. These products typically exhibit good mechanical properties and can meet certain durability requirements in the short term. Furthermore, some existing methods incorporate plasticizers and modifiers to enhance the flexibility and ductility of polyurethane, making it suitable for a wider range of applications. Overall, existing polyurethane synthetic leather can provide basic wear resistance and a certain degree of aging resistance under some common usage conditions.

[0004] However, the existing technology still has some shortcomings. First, the polyurethane materials in traditional formulas usually lack sufficient UV resistance and aging resistance, which makes polyurethane synthetic leather prone to performance degradation or even brittleness when exposed to sunlight, humidity or high temperature for a long time. Second, the existing polyurethane synthetic leather fails to effectively control the uniformity of the molecular chain during the reaction process, resulting in unstable mechanical properties and susceptibility to moisture and oxygen, resulting in inconsistent quality. Third, many existing synthetic leather production processes do not fully introduce effective reinforcing materials during the reaction process, resulting in the durability and comprehensive performance of the final product failing to meet higher standards. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention provides a waterborne polyurethane synthetic leather and a preparation method thereof, which solves the problems of emulsion instability, uneven filler dispersion, incomplete chain extension reaction and difficulty in achieving multi-performance balance in the existing technology.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a waterborne polyurethane synthetic leather, the synthetic leather comprising a base layer and a coating layer, the base layer being a polyester non-woven fabric, the coating layer comprising the following components in parts by weight: 10-20 parts of an aromatic isocyanate, the aromatic isocyanate being toluene diisocyanate, having a nitrogen content of 14-16%, a purity greater than 98%, and a volatile matter content less than 1%, the isocyanate groups (-NCO) in toluene diisocyanate (TDI-80) reacting with hydroxyl groups (-OH) in a polyether polyol (such as PEG-1000) to generate the hard segment portion of the polyurethane chain, the 14-16% nitrogen content ensuring an effective concentration of the isocyanate functional groups, making the crosslinking density controllable, and providing a reaction basis for the subsequent formation of a dense, continuous film-forming network. High purity (≥98%) helps reduce the introduction of by-products, improves reaction stability and polymer structural integrity; and controlling the volatile matter below 1% can significantly reduce the irritating odor, bubble defects, or toxic release caused by the volatilization of residual TDI during the drying process, helping to improve the environmental friendliness and safety of the final synthetic leather product. Polyether polyol: 50-70 parts. The polyether polyol is polyethylene glycol with a molecular weight of 400-1000, a hydroxyl value of 110-280 mgKOH / g, and a purity of ≥99%. The polyether structure contains hydroxyl groups at the end, which react with toluene diisocyanate to form a polyurethane backbone. Multiple hydroxyl groups (-OH) react with isocyanate groups (-NCO) to form the soft segment of the polyurethane. The molecular structure of polyethylene glycol features long chain segments, which impart greater flexibility, elasticity, and ductility to the final polyurethane synthetic leather. The molecular weight is controlled within the range of 400-1000, ensuring the chain segments are sufficiently flexible to impart appropriate flexibility to the polymer while remaining moderately long enough to compromise dispersibility and mechanical strength, thereby achieving a balance between flexibility and mechanical properties. The hydroxyl value range is set between 110-280 mgKOH / g, representing the number density of effective hydroxyl groups in the polyether. A higher hydroxyl value indicates greater reactivity with isocyanates, favoring the formation of a more cross-linked polyurethane network structure and enhancing the strength and durability of the film. Furthermore, the polyethylene glycol purity exceeds 99%, effectively preventing impurities from affecting the uniformity of the prepolymerization reaction and the stability of the subsequent emulsion particle size distribution, thereby ensuring uniformity and safety during the actual film-forming process of the synthetic leather. Nanosilica: 5-15 parts. Nanosilica is a reinforcing agent with an extremely high specific surface area and active surface area. It can interact with the molecular chains in the polyurethane matrix, forming physical crosslinks or enhancing interfacial contact, thereby enhancing the overall strength and stability of the polyurethane. By being evenly dispersed in the polyurethane matrix, nanosilica not only improves the material's tensile strength but also enhances its aging resistance, especially its resistance to ultraviolet rays and high temperatures. Catalyst: 0.1-0.5 parts, the catalyst is 1,4-diazabicyclo[2.2.2]octane, its molecular weight is 89-91, density is 1.0154-1.0171g / cm 3 The 1,4-diazabicyclo[2.2.2]octane (DABCO) is a highly efficient tertiary amine catalyst, which is widely used in the polycondensation reaction between isocyanates and active hydrogen compounds in polyurethane systems. Its molecular weight is 89–91, indicating that it is a low molecular weight homogeneous body with high participation in the reaction. It can exert a significant catalytic effect at a low dosage, which is beneficial to controlling the stability and uniformity of the reaction process. Its density is 1.0154–1.0171 g / cm 3 If the concentration is between 10 and 20, it means that it is easy to disperse in the liquid phase reaction system, mixes evenly with the reactants, and the catalytic reaction conditions are mild, avoiding the risk of local overheating or uneven reaction; Water: 15-25 parts. Water reacts with isocyanate groups to extend the length of the polyurethane chain and adjust the crosslinking degree of the material. The addition of water not only enhances the flexibility of the polyurethane, but also improves the water resistance and plasticity of the final synthetic leather. Epoxidized soybean oil: 5-10 parts. The epoxy groups in epoxidized soybean oil react with the amino or hydroxyl groups in polyurethane to form a cross-linked structure, enhancing the polyurethane's thermal stability, wear resistance, and aging resistance. Furthermore, as a plasticizer, epoxidized soybean oil can reduce the hardness of polyurethane while increasing its flexibility and ductility. The reaction of epoxy groups with water and other ingredients also improves the processing and surface properties of polyurethane synthetic leather. Polysorbate 20: 0.1-0.3 parts. Through the interaction between its hydrophilic and lipophilic groups, polysorbate 20 reduces the surface tension between the aqueous phase and the polyurethane particles, promoting emulsion formation. This helps improve the dispersion of the polyurethane particles and prevents aggregation or precipitation between particles, thereby ensuring the uniformity and stability of the emulsion. Polysorbate 20 also contributes to improved surface smoothness and stain resistance of the final synthetic leather.

[0007] The present invention also provides a method for preparing waterborne polyurethane synthetic leather, comprising the following steps: S1, mixing aromatic isocyanate and polyether polyol, performing a prepolymerization reaction, and obtaining a prepolymer; S2, adding nano-silica to the prepolymer, adding a catalyst, and continuing the reaction until the desired viscosity is reached; S3, slowly adding water and epoxidized soybean oil to carry out chain extension reaction to obtain a waterborne polyurethane emulsion; S4, adding polysorbate 20 to adjust the surface tension of the emulsion to obtain an aqueous polyurethane synthetic leather emulsion; S5. Select polyester non-woven fabric and preheat it to 30-40℃ after cutting to make it have good coating adaptability and adhesion; S6, applying the prepared aqueous polyurethane emulsion evenly to the surface of the polyester non-woven fabric by roller coating, and controlling the coating thickness to be 0.2-0.5 mm; S7. Place the coated polyester nonwoven fabric in a hot air circulation oven for drying and film formation.

[0008] Preferably, said S1 comprises the following steps: Add aromatic isocyanate and polyether polyol into a reaction vessel and stir and mix under nitrogen protection; The stirring time is 3-5 hours, the stirring rate is 300-500 rpm, and the prepolymer is obtained. The temperature is maintained at 55°C-65°C during the reaction to ensure complete reaction. At a reaction temperature of 55-65°C, the isocyanate group reacts with the hydroxyl group in the polyether polyol to form an addition reaction. This reaction is a basic reaction in polyurethane synthesis. The generated amide bond (-NH-CO-NH-) constitutes the hard segment of the polyurethane chain. Too low a temperature will lead to a slow reaction rate, while too high a temperature will trigger side reactions or overreactions. At a stirring rate of 300-500 rpm, the isocyanate groups and polyol molecules in the reaction system can fully contact and react. This not only ensures uniform mixing of the reactants, but also helps maintain uniform heat distribution during the reaction, thereby ensuring the uniformity of the reaction and the quality of the prepolymer.

[0009] Preferably, said S2 comprises the following steps: Adding nanosilica and catalyst 1,4-diazabicyclo[2.2.2]octane into the prepolymer; The reaction is continued at 85-95°C and a stirring rate of 400-600 rpm for 1-1.5 hours to fully disperse the nano-silica and embed it into the polyurethane network structure, and the reaction reaches the desired viscosity. 1,4-diazabicyclo[2.2.2]octane (DABCO) acts as a catalyst to accelerate the reaction between the isocyanate group and the other components. In this reaction, DABCO can promote the reaction by adsorbing the isocyanate group (-NCO) and reducing its activation energy. The catalytic effect of DABCO helps increase the reaction rate, ensuring that the reaction reaches the desired viscosity in a relatively short period of time, and ensuring the physical properties and stability of the final synthetic leather. Preferably, said S3 comprises the following steps: While maintaining the temperature of the reaction system at 90℃-100℃, water and epoxidized soybean oil are slowly added dropwise. In this step, it reacts with the isocyanate group (-NCO) in the polyurethane to generate a urea group (-NH-CO-NH-). This reaction not only extends the length of the polyurethane chain, but also adjusts the degree of cross-linking of the polyurethane. Water triggers the growth of the polyurethane chain by reacting with the isocyanate group, thereby affecting the hardness and flexibility of the final material; the epoxy group in the epoxidized soybean oil molecule can react with the amino or hydroxyl group in the polyurethane chain to generate a cross-linked structure. This reaction helps to improve the thermal stability, weather resistance and aging resistance of the polyurethane. At the same time, epoxidized soybean oil can also act as a plasticizer to enhance the flexibility and ductility of polyurethane and improve the touch of polyurethane synthetic leather. The epoxy groups in the epoxidized soybean oil work together with water and other components to further improve the physical properties and chemical stability of the final product. The reaction is stirred at 90-100° C. and a stirring rate of 200-400 rpm for 1-3 hours to form an emulsion, allowing water molecules to undergo a chain extension reaction with the -NCO groups in the prepolymer, while the epoxidized soybean oil is cross-linked with the functional groups. Stirring within this temperature range can promote the full fusion of water and epoxidized soybean oil to form a uniform emulsion. Too low a temperature will lead to a slow reaction, while too high a temperature will cause side reactions or degradation of the polyurethane chain. During the reaction, the stirring rate within this range helps to evenly disperse the water and epoxidized soybean oil, prevent stratification and uneven reaction, and ensure the stability of the emulsion. The reaction is carried out for 1 to 3 hours, ensuring that the reaction between water and epoxidized soybean oil is fully carried out, while avoiding polymer degradation caused by excessively long reaction times.

[0010] Preferably, said S4 comprises the following steps: After the emulsion temperature drops to 20-25°C, polysorbate 20 is added and stirred continuously at a stirring rate of 300-500 rpm for 1-1.5 hours to adjust the surface tension of the system and improve the stability of the emulsion. Upon completion of this operation, a water-based polyurethane synthetic leather emulsion is obtained. Polysorbate 20 reduces the surface tension between the aqueous phase and the polyurethane particles, allowing the polyurethane particles to be better dispersed in the aqueous phase, forming a uniform emulsion. The addition of polysorbate 20 not only prevents the aggregation or precipitation of polyurethane particles but also ensures the stability of the water-based polyurethane emulsion, preventing stratification during storage and application. Preferably, S7 includes the following steps: Initial drying stage: Constant temperature drying is performed at 55-65°C for 5-8 minutes to prevent internal water vapor accumulation that could cause bubbling, film collapse, or cracking. At 55-65°C, the water in the emulsion begins to evaporate through heat conduction, and the vapor is discharged quickly. This rapid evaporation ensures the dispersion of the polyurethane in the aqueous solution, preventing particle aggregation or uneven agglomeration of the material. Initial film formation: After the water is removed, the polyurethane molecules in the emulsion begin to gradually aggregate and form the initial structure of the film. Curing stage: Continue drying at 80-90°C for 10-15 minutes to allow directional migration, heat-induced fusion, and micro-crosslinking reactions between the polyurethane particles in the emulsion to occur, gradually forming a continuous film structure. Under heating conditions of 80-90°C, the chemical bonds between the waterborne polyurethane molecules gradually strengthen, especially in areas containing isocyanate groups, which react with waterborne polyether polyols and other reactive groups to form a crosslinked structure. This crosslinking process gives the film strength and stability; Hot Pressing: The cured material is fed into the hot pressing zone and pressurized at 90-100°C for 8-12 seconds. This applies pressure to the film, helping to remove internal dispersion unevenness, smoothing the film surface while also improving the material's density. This step helps reduce defects like bubbles and cracks, ensuring the visual quality and performance of the final product. At high temperatures of 90-100°C, polyurethane molecules exhibit excellent fluidity in their thermoplastic state. The applied pressure causes the molecular chains to rearrange, binding them more tightly together and further enhancing the film's density and uniformity.

[0011] The present invention provides a waterborne polyurethane synthetic leather and a preparation method thereof. It has the following beneficial effects: 1. This invention utilizes a combination of toluene diisocyanate and polyethylene glycol to achieve an optimal balance between hard and soft segments in polyurethane synthesis. Compared to the prior art methods that use only isocyanates or polyols, the polyurethane structure formed by the synergistic reaction of the two is more stable. This structural design not only enhances the mechanical properties of the polyurethane, but also improves its flexibility and aging resistance, resolving the difficulty in balancing mechanical strength and ductility in traditional polyurethane materials.

[0012] 2. The present invention further optimizes the weather resistance and aging resistance of polyurethane by introducing nanosilica. The high specific surface area and active surface of nanosilica physically crosslink with the molecular chains in the polyurethane matrix, significantly enhancing the overall strength of the material. Compared with polyurethanes without reinforcing materials in the prior art, the nanosilica modification of the present invention significantly improves their UV resistance, tensile strength, and aging resistance, solving the problem of existing polyurethane materials being susceptible to degradation due to UV rays and temperature changes during long-term use.

[0013] 3. This invention utilizes epoxidized soybean oil as a plasticizer and crosslinker, significantly improving the thermal stability and wear resistance of polyurethane. The epoxy groups in epoxidized soybean oil react with amino or hydroxyl groups in the polyurethane to form a more stable crosslinked structure, enhancing the aging resistance and durability of the final product. Compared to conventional plasticizers used in the prior art, this invention utilizes this environmentally friendly material modification, not only improving performance but also avoiding the environmental pollution associated with the use of hazardous solvents.

[0014] 4. This invention also ensures uniform mixing of reactants during polyurethane synthesis by utilizing a nitrogen-protected reaction technique, preventing unwanted reactions between airborne moisture or oxygen and isocyanate groups. Compared to traditional open-environment reaction methods, this technical solution significantly improves reaction stability and product quality, addressing the issue of unstable product performance caused by hydrolysis or oxidation reactions, thereby further enhancing the uniformity and performance consistency of polyurethane synthetic leather. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the specification of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0018] The sources of the raw materials used in the following examples and comparative examples are as follows: Toluene diisocyanate was purchased from Wanhua Chemical Group, model TDI-80; Polyethylene glycol was purchased from Dow Chemical, model PEG-1000; 1,4-Diazabicyclo[2.2.2]octane was purchased from Evonik Industries AG with the model number 280-57-9.

[0019] Please see the attached Figure 1 : Example 1: Component ratio: aromatic isocyanate (toluene diisocyanate, TDI-80): 15 parts, polyethylene glycol (PEG-600): 60 parts, nano-silica: 10 parts, 1,4-diazabicyclo[2.2.2]octane (DABCO): 0.3 parts, water: 20 parts, epoxidized soybean oil: 7 parts, polysorbate-20: 0.2 parts, polyester non-woven fabric.

[0020] Preparation steps: S1: Prepolymerization: Under nitrogen protection, aromatic isocyanate (TDI) and polyethylene glycol (PEG-600) were added to a reaction vessel with a stirring rate of 300 rpm, a reaction time of 4 hours, and a reaction temperature of 60° C. to obtain a prepolymer.

[0021] S2: Nano-silica addition: 10 parts of nano-silica and 0.3 parts of DABCO were added to the prepolymer at a temperature of 85° C. and a stirring rate of 450 rpm, and the reaction was carried out for 1 hour until the desired viscosity was reached.

[0022] S3: Chain extension reaction: 20 parts of water and 7 parts of epoxidized soybean oil were slowly added, the reaction temperature was 95° C., the stirring rate was 300 rpm, and the reaction time was 2 hours to form an aqueous polyurethane emulsion.

[0023] S4: Stable emulsion: The emulsion temperature was lowered to 25° C., 0.2 parts of polysorbate 20 was added, the stirring rate was 350 rpm, and the mixture was stirred for 1 hour to obtain a stable aqueous polyurethane synthetic leather emulsion.

[0024] S5-S7: coating and drying: The polyester non-woven fabric was cut and preheated to 35°C, and the emulsion was evenly coated using a roller coating method with a coating thickness of 0.3 mm.

[0025] The preparation was completed by drying at 55°C for 5 minutes, curing at 80°C for 12 minutes, and hot pressing at 90°C for 9 seconds.

[0026] Example 2: Component ratio: aromatic isocyanate (toluene diisocyanate, TDI-80): 12 parts, polyethylene glycol (PEG-800): 65 parts, nano-silica: 7 parts, 1,4-diazabicyclo[2.2.2]octane (DABCO): 0.2 parts, water: 18 parts, epoxidized soybean oil: 6 parts, polysorbate-20: 0.15 parts, polyester non-woven fabric.

[0027] Preparation steps: S1: Prepolymerization: Under nitrogen protection, aromatic isocyanate (TDI) and polyethylene glycol (PEG-800) were added to a reaction vessel with a stirring rate of 320 rpm, a reaction time of 5 hours, and a reaction temperature of 63° C. to obtain a prepolymer.

[0028] S2: Nano-silica addition: 7 parts of nano-silica and 0.2 parts of DABCO were added to the prepolymer at 90° C. and a stirring rate of 500 rpm. The mixture was reacted for 1.5 hours to reach the desired viscosity.

[0029] S3: Chain extension reaction: 18 parts of water and 6 parts of epoxidized soybean oil were slowly added, the reaction temperature was 100° C., the stirring rate was 350 rpm, and the reaction time was 3 hours to form an emulsion.

[0030] S4: Stable emulsion: The emulsion temperature was lowered to 23° C., 0.15 parts of polysorbate 20 were added, and the mixture was stirred at a rate of 400 rpm for 1 hour to obtain a stable aqueous polyurethane synthetic leather emulsion.

[0031] S5-S7: coating and drying: The polyester non-woven fabric was cut and preheated to 32°C, and the emulsion was evenly coated using a roller coating method with a coating thickness of 0.25 mm.

[0032] The preparation was completed by drying at 60°C for 6 minutes, curing at 85°C for 10 minutes, and hot pressing at 95°C for 10 seconds.

[0033] Example 3: Component ratio: aromatic isocyanate (toluene diisocyanate, TDI-80): 18 parts, polyethylene glycol (PEG-1000): 55 parts, nano-silica: 12 parts, 1,4-diazabicyclo[2.2.2]octane (DABCO): 0.4 parts, water: 22 parts, epoxidized soybean oil: 8 parts, polysorbate-20: 0.1 parts, polyester non-woven fabric.

[0034] Preparation steps: S1: Prepolymerization: Under nitrogen protection, aromatic isocyanate (TDI) and polyethylene glycol (PEG-1000) were added to a reaction vessel with a stirring rate of 350 rpm, a reaction time of 3.5 hours, and a reaction temperature of 58° C. to obtain a prepolymer.

[0035] S2: Nano-silica addition: 12 parts of nano-silica and 0.4 parts of DABCO were added to the prepolymer at a temperature of 87° C. and a stirring rate of 600 rpm. The mixture was reacted for 1.2 hours to reach the desired viscosity.

[0036] S3: Chain extension reaction: 22 parts of water and 8 parts of epoxidized soybean oil were slowly added, the reaction temperature was 95° C., the stirring rate was 250 rpm, and the reaction time was 2 hours to form an emulsion.

[0037] S4: Stable emulsion: The emulsion temperature was lowered to 22° C., 0.1 parts of polysorbate 20 was added, and the stirring rate was 450 rpm. The mixture was stirred for 1 hour to obtain a stable aqueous polyurethane synthetic leather emulsion.

[0038] S5-S7: coating and drying: The polyester non-woven fabric was cut and preheated to 36°C, and the emulsion was evenly coated using a roller coating method with a coating thickness of 0.35 mm.

[0039] The preparation was completed by drying at 65°C for 7 minutes, curing at 90°C for 13 minutes, and hot pressing at 100°C for 11 seconds.

[0040] Comparative Example 1: Compared with Example 1, the difference is that the nano-silicon dioxide is removed, and the other components and conditions remain the same; Comparative Example 2: Compared with Example 2, the difference is that the epoxidized soybean oil is removed, and the other components remain the same as the conditions; Comparative Example 3: Compared with Example 3, the difference is that the stirring condition under nitrogen protection is cancelled, and the reaction is directly exposed to air for stirring during the reaction, and the other components remain the same as the conditions.

[0041] Experiment 1: Experimental purpose: to test the mechanical properties (tensile strength, flexibility, ductility) and aging resistance of Examples 1-3 and Comparative Examples 1-3, and to analyze the effects of different formulations on waterborne polyurethane synthetic leather through the test results.

[0042] Experimental steps: Sample preparation: Waterborne polyurethane synthetic leather was prepared according to the formulations of Examples 1-3 and Comparative Examples 1-3, ensuring that each sample had the same thickness and used the same coating method and curing process.

[0043] Mechanical properties test: Use a tensile tester (such as an Instron device) to perform tensile testing. The sample needs to be cut into a standard rectangular sample with a test width of 20 mm and a length of 100 mm.

[0044] The test parameters were set as follows: the tensile rate was 50 mm / min, and the test was conducted until the sample broke. The maximum tensile strength (MPa), elongation at break (%), and tensile modulus (MPa) were recorded.

[0045] Aging resistance test: Use an accelerated aging test chamber with the temperature set at 80°C and the humidity at 50% for 500 hours of UV aging testing.

[0046] The changes in tensile strength, elongation and hardness were recorded before and after the test, and the surface hardness (Shore A) of the sample was tested using a hardness tester.

[0047] Data Records: The changes in tensile strength, elongation and hardness of each sample before and after aging were recorded (see Table 1 for experimental results).

[0048] Table 1: Mechanical properties and aging resistance test data From Table 1, we can get: Examples 1-3 are significantly superior to Comparative Examples 1-3 in terms of mechanical properties and aging resistance. This phenomenon is closely related to the material combination and reaction mechanism used. In particular, the addition reaction between toluene diisocyanate (TDI) and polyethylene glycol (PEG) forms an optimized structure of hard and soft segments of polyurethane. The combination of TDI and PEG, through the mutual reaction of their respective functional groups, not only enhances the mechanical properties of polyurethane, but also improves its flexibility. In particular, in the examples, the high nitrogen content of TDI (14-16%) ensures the concentration and cross-linking degree of isocyanate groups, forming a strong hard segment part, thereby enhancing the strength and aging resistance of the final material.

[0049] In addition, the introduction of nano-silica plays a key role in improving the mechanical properties of polyurethane. Nano-silica has an extremely high specific surface area and active surface, and can undergo physical cross-linking with the molecular chains in the polyurethane matrix, further enhancing the overall strength and stability of the material. In the experiment, the samples of Examples 1-3 contained nano-silica, which was able to significantly improve their tensile strength and aging resistance by enhancing interfacial contact and promoting physical cross-linking. This enhancement effect is not only manifested in the unaged samples, but the aged samples can still maintain a high tensile strength and ductility, especially the performance of Example 3 is particularly outstanding.

[0050] In contrast, comparative examples 1 and 2, which remove nano silicon dioxide and epoxidized soybean oil, show poor performance in mechanical properties and aging resistance. The absence of nano silicon dioxide has led to a decrease in the tensile strength and UV resistance of the material, and the degradation in performance during aging is more obvious. Similarly, the removal of epoxidized soybean oil has also weakened the flexibility and ductility of polyurethane, because epoxidized soybean oil not only reduces hardness as a plasticizer, but also crosslinks with the polyurethane chain through its epoxy group, thus enhancing the heat resistance and wear resistance of polyurethane. The stirring process not using nitrogen protection has also caused uneven reaction, thereby affecting the formation of the polyurethane network, making the sample of comparative example 3 further decline in mechanical properties and durability after aging.

[0051] Experiment 2: Experimental Purpose: To test the weather resistance (UV resistance, weather resistance) of Examples 1-3 and Comparative Examples 1-3 after UV irradiation, as well as their water resistance (water absorption, water permeability) under humid conditions. By comparing the UV resistance and water resistance of these samples, we evaluated the effects of different formulations on waterborne polyurethane synthetic leather.

[0052] Experimental steps: Sample preparation: Waterborne polyurethane synthetic leather samples were prepared according to the formulations of Examples 1-3 and Comparative Examples 1-3, ensuring that the thickness of each sample was consistent and the coating was even.

[0053] The samples were cut into rectangles of the same size (length 100 mm, width 50 mm).

[0054] UV resistance test: The samples were placed in a UV aging tester (Q-SUNUV tester) and irradiated with UV rays for 200 hours.

[0055] UV irradiation conditions: UV intensity 400W / m 2 , temperature 40℃, humidity 60%.

[0056] The color change and intensity change of the samples were measured using a gloss meter and a tensile tester before and after UV irradiation.

[0057] Measurement items: tensile strength, elongation at break, and surface color change (ΔE) before and after UV irradiation.

[0058] Water resistance test: The water absorption of each sample was measured within 24 hours using the standard ASTM D570 method.

[0059] Each sample was first weighed in a dry environment, and then soaked in water at room temperature for 24 hours before weighing again.

[0060] Calculate the water absorption rate: Water absorption rate (%) = (mass after immersion in water - dry mass) / dry mass × 100%.

[0061] Data Records: The tensile strength, elongation, color change (ΔE), and water absorption of each sample were recorded before and after UV aging.

[0062] The experimental data were collated and compared and analyzed (the experimental results are shown in Table 2).

[0063] Table 2: Weather resistance and water resistance test data From Table 2, we can get: Examples 1-3 exhibit excellent UV resistance and low water absorption after ultraviolet irradiation, which is significantly better than Comparative Examples 1-3. This phenomenon is closely related to the polyurethane synthesis mechanism used. The polyurethane chain generated by the reaction of toluene diisocyanate (TDI) and polyethylene glycol (PEG) has a hard segment supported by isocyanate groups with a high nitrogen content, while the soft segment is provided with sufficient flexibility by polyether polyols. This balance of soft and hard segments and the highly cross-linked network structure effectively improve the stability of polyurethane under ultraviolet irradiation. The high nitrogen content of TDI ensures the cross-linking density and structural strength of the polyurethane network, which plays a key role in the face of aging and decomposition caused by ultraviolet rays.

[0064] In addition, the introduction of nano-silica in the embodiment further improves the weather resistance of polyurethane. The extremely high specific surface area and active surface of nano-silica are physically cross-linked with the molecular chains in the polyurethane matrix, making the polyurethane matrix not prone to chain breakage or degradation under ultraviolet irradiation. This physical cross-linking process not only improves the overall structural strength of polyurethane, but also enhances its ultraviolet resistance. In the experiment, the intensity attenuation of the samples of Examples 1-3 after ultraviolet irradiation was less, indicating that the addition of nano-silica enhances the ultraviolet shielding performance of the material and effectively delays the loss of gloss on the polyurethane surface and the rupture of the molecular chains.

[0065] In comparison, Comparative Examples 1 and 2, which do not use nano-silica or epoxidized soybean oil, have poor UV resistance and water resistance, showing a significant performance degradation. The absence of nano-silica causes the polyurethane chains to break easily after ultraviolet irradiation, and the aging caused by ultraviolet rays exacerbates the embrittlement of the material. The removal of epoxidized soybean oil reduces the flexibility of the polyurethane, resulting in a significant decrease in its anti-aging and water penetration capabilities when facing ultraviolet irradiation and a humid environment. In particular, in Comparative Example 3, the stirring process without nitrogen protection results in an uneven distribution of the reactants, further exacerbating the UV degradation and moisture permeability of the material. These factors together lead to its poor performance in the test.

[0066] Experiment 3: Experimental Purpose: To test the stability of Examples 1-3 and Comparative Examples 1-3 during the production process, specifically the homogeneity during the reaction and the stability of the emulsion. This experiment was used to evaluate the effects of different formulations and process conditions on the production process and final product quality of polyurethane synthetic leather.

[0067] Experimental steps: Sample preparation: Waterborne polyurethane synthetic leather samples were prepared according to the formulations of Examples 1-3 and Comparative Examples 1-3, ensuring that the thickness of each sample was consistent and using the same coating method and curing process.

[0068] The samples were cut into rectangular samples with a size of 100 mm x 50 mm.

[0069] Reaction uniformity test: During the preparation process, the reactants were stirred in the reaction vessel. The stirring conditions (stirring rate, stirring time, temperature, etc.) were kept consistent across all experimental groups. Tests were performed to determine if there was uneven distribution of the material.

[0070] Observe the sample surface for uneven areas or air bubble defects.

[0071] Emulsion stability test: After the reaction is complete, check the stability of the polyurethane emulsion. Record the surface tension, particle size (measured using a particle size analyzer), and storage stability (observe whether the emulsion has stratification or precipitation).

[0072] Under storage conditions, regularly check the emulsion stability and test its particle size distribution and uniformity.

[0073] Data recording and analysis: Record the reaction uniformity and emulsion stability of each sample, including surface tension, particle size distribution, bubble defects, etc. Compare the reaction and emulsion stability of different formulations (see Table 3 for experimental results).

[0074] Table 3: Production process stability test data From Table 3 we can get: Examples 1-3 performed better than Comparative Examples 1-3 in terms of reaction uniformity and emulsion stability. This difference is closely related to the material ratios used and their reaction mechanisms. The addition reaction between toluene diisocyanate (TDI) and polyethylene glycol (PEG) forms hard and soft segments of the polyurethane, providing a highly cross-linked and uniformly distributed polyurethane network. In Examples 1-3, the nitrogen content of TDI ensures the full reaction of the isocyanate groups, promotes strong cross-linking between polyurethane chains, and ensures uniform reaction of the molecular chains. The stability of this structure makes the mixing during the reaction process and the stability of the emulsion more excellent, the emulsion particle size distribution is uniform, and no stratification occurs during storage, further demonstrating the good compatibility between the materials.

[0075] In addition, the introduction of nano-silica plays a crucial role in Examples 1-3. Nano-silica has an extremely high specific surface area and surface activity, and can interact with the molecular chains in the polyurethane matrix to promote physical crosslinking and enhance interfacial contact. This enhanced interfacial contact not only helps to improve the overall strength and stability of the polyurethane, but also effectively reduces the aggregation and precipitation of particles in the emulsion, maintaining the uniformity and stability of the emulsion. In the experiment, the samples of Examples 1-3 showed fewer bubble defects and better emulsion stability, while the samples of Comparative Examples 1-3 were prone to uneven material distribution during the reaction process due to the lack of nano-silica, resulting in poor emulsion stability and obvious stratification.

[0076] In contrast, the lack of effective material cross-linking and reinforcement in Comparative Examples 1-3 led to uneven distribution of polymer chains during the reaction, which in turn affected the stability and surface quality of the emulsion. In particular, since Comparative Example 3 did not utilize nitrogen-protected stirring, the interference of oxygen and moisture during the reaction led to partial hydrolysis or oxidation of the polyurethane chains, reducing product uniformity and reaction efficiency. These factors led to bubble defects and poor emulsion stability, further highlighting the importance of material selection and reaction conditions in the production of polyurethane synthetic leather.

[0077] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A waterborne polyurethane synthetic leather, characterized in that: The synthetic leather comprises a base layer and a coating layer, wherein the base layer is a polyester non-woven fabric, and the coating layer comprises the following components in parts by weight: Aromatic isocyanate: 10-20 parts; Polyether polyol: 50-70 parts; Nano silicon dioxide: 5-15 parts; Catalyst: 0.1-0.5 parts; Water: 15-25 parts; Epoxidized soybean oil: 5-10 parts; Polysorbate 20: 0.1-0.3 parts.

2. A waterborne polyurethane synthetic leather according to claim 1, characterized in that: The aromatic isocyanate is toluene diisocyanate, which has a nitrogen content of 14-16%, a purity higher than 98%, and a volatile matter lower than 1%.

3. The waterborne polyurethane synthetic leather according to claim 1, characterized in that: The polyether polyol is polyethylene glycol, with a molecular weight of 400-1000, a hydroxyl value of 110-280 mgKOH / g, and a purity of ≥99%. The polyether structure contains hydroxyl groups at the end, and reacts with toluene diisocyanate to form a polyurethane main chain.

4. The waterborne polyurethane synthetic leather according to claim 1, characterized in that: The catalyst is 1,4-diazabicyclo[2.2.2]octane, which has a molecular weight of 89-91 and a density of 1.0154-1.0171 g / cm 3 .

5. A method for preparing waterborne polyurethane synthetic leather, characterized in that: The method for preparing the waterborne polyurethane synthetic leather according to any one of claims 1 to 4 comprises the following steps: S1, mixing aromatic isocyanate and polyether polyol, performing a prepolymerization reaction, and obtaining a prepolymer; S2, adding nano-silica to the prepolymer, adding a catalyst, and continuing the reaction until the desired viscosity is reached; S3, slowly adding water and epoxidized soybean oil to carry out chain extension reaction to obtain a waterborne polyurethane emulsion; S4, adding polysorbate 20 to adjust the surface tension of the emulsion to obtain an aqueous polyurethane synthetic leather emulsion; S5. Preheat the polyester non-woven fabric to 30-40°C after cutting to make it have good coating adaptability and adhesion; S6, applying the prepared aqueous polyurethane emulsion evenly to the surface of the polyester non-woven fabric by roller coating, and controlling the coating thickness to be 0.2-0.5 mm; S7. Place the coated polyester nonwoven fabric in a hot air circulation oven for drying and film formation.

6. The method for preparing a waterborne polyurethane synthetic leather according to claim 5, characterized in that: Said S1 comprises the following steps: Add aromatic isocyanate and polyether polyol into a reaction vessel and stir and mix under nitrogen protection; The stirring time is 3-5 hours, the stirring rate is 300-500 rpm, and the prepolymer is obtained. The temperature is maintained at 55° C.-65° C. during the reaction to ensure complete reaction.

7. The method for preparing a waterborne polyurethane synthetic leather according to claim 5, characterized in that: The S2 comprises the following steps: Adding nanosilica and catalyst 1,4-diazabicyclo[2.2.2]octane into the prepolymer; The reaction is continued at 85-95° C. and a stirring rate of 400-600 rpm for 1-1.5 hours to fully disperse the nano-silica and embed it into the polyurethane network structure, and the reaction reaches the desired viscosity.

8. The method for preparing a waterborne polyurethane synthetic leather according to claim 5, characterized in that: The S3 includes the following steps: While maintaining the reaction system temperature at 90°C-100°C, slowly add water and epoxidized soybean oil dropwise; The mixture is stirred at 90-100°C and 200-400 rpm for 1-3 hours to form an emulsion, so that the water molecules react with the -NCO groups in the prepolymer to extend the chain, and the epoxidized soybean oil is cross-linked with the functional groups.

9. The method for preparing a waterborne polyurethane synthetic leather according to claim 5, characterized in that: The S4 comprises the following steps: After the emulsion temperature is reduced to 20°C-25°C, polysorbate 20 is added and stirring is continued for 1-1.5 hours at a stirring rate of 300-500 rpm to adjust the surface tension of the system and improve the stability of the emulsion. After the operation is completed, an aqueous polyurethane synthetic leather emulsion is obtained.

10. The method for preparing waterborne polyurethane synthetic leather according to claim 5, characterized in that: The S7 comprises the following steps: Initial drying stage: Dry at a constant temperature of 55-65°C for 5-8 minutes to prevent internal water vapor accumulation from causing bubbling, film collapse or cracking; Curing stage: Continue drying at 80-90°C for 10-15 minutes to allow directional migration, heat-induced fusion and micro-crosslinking reactions to occur between the polyurethane particles in the emulsion, gradually forming a continuous film structure; Hot pressing: The cured material is sent into the hot pressing area and pressurized at 90℃-100℃ for 8-12 seconds.

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