Formula and preparation method of hydrolysis-resistant polyurethane synthetic leather
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-21
- Publication Date
- 2026-04-03
Smart Images
Figure CN121781435A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polyurethane materials technology, specifically to a formulation and preparation method for hydrolysis-resistant polyurethane synthetic leather. Background Technology
[0002] Polyurethane synthetic leather mainly consists of a base fabric and a polyurethane resin layer coated on its surface. Due to its resemblance to natural leather in appearance and excellent physical properties, it is widely used in clothing, footwear, and automotive interiors. The hydrolytic stability of the polyurethane resin layer is a key factor determining the service life of synthetic leather in humid and hot environments.
[0003] Currently, polyester-based polyurethane is widely used in industrial production for high-performance polyurethane synthetic leather. Due to its high intermolecular cohesive energy, polyester-based polyurethane exhibits excellent wear resistance, solvent resistance, and mechanical strength. However, the polyester chain contains a large number of ester groups, making it highly susceptible to hydrolysis and breakage under high temperature and humidity conditions. This leads to a sharp decrease in the resin's molecular weight, macroscopically manifesting as powdering, cracking, or peeling from the base fabric. While polyether-based polyurethane has good hydrolysis resistance, its tear strength, peel strength, and surface scratch resistance are generally lower than those of polyester-based polyurethane, making it difficult to meet the performance requirements of high-load applications.
[0004] To improve the hydrolysis resistance of polyester-based polyurethanes, existing technologies often employ the addition of carbodiimide-based anti-hydrolysis agents or physical blending of hydrophobic polymers. However, small-molecule anti-hydrolysis agents tend to migrate to the material surface, leading to a decline in long-term hydrolysis resistance and potentially affecting the surface feel of the product. On the other hand, purely physically blended hydrophobic materials often suffer from poor compatibility due to the significant polarity difference between the hydrophobic components and the polyurethane matrix, easily triggering microphase separation and ultimately resulting in a loss of the material's original mechanical strength.
[0005] Therefore, this invention proposes a formulation and preparation method for hydrolysis-resistant polyurethane synthetic leather to overcome the shortcomings of the prior art. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a formulation and preparation method for hydrolysis-resistant polyurethane synthetic leather, which solves the problems of poor hydrolysis resistance of existing polyester-type polyurethane synthetic leather and the difficulty of balancing mechanical strength and long-term stability by conventional physical modification methods.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] In a first aspect, the present invention provides a formulation for hydrolysis-resistant polyurethane synthetic leather, employing the following technical solution:
[0009] A formulation for hydrolysis-resistant polyurethane synthetic leather, wherein the polyurethane resin layer of the synthetic leather is made from raw materials comprising the following parts by weight:
[0010] Poly(1,4-butene adipate): 85.0-90.0 parts; dimer acid polyester polyol: 12.0-15.0 parts; epoxidized linseed oil: 3.0-4.0 parts; castor oil: 1.0-1.5 parts; diphenylmethane diisocyanate: 41.0-46.0 parts; chain extender solution: 13.3-20.0 parts; wherein the chain extender solution is prepared by dissolving 4.0-6.0 parts of 2-butyl-2-ethyl-1,3-propanediol in 9.3-14.0 parts of N,N-dimethylformamide.
[0011] By employing the above technical solution, this invention improves the poor hydrolysis resistance of polyester-type polyurethanes by combining long-chain hydrophobic structure modification with steric hindrance effect. The specific principle is as follows:
[0012] Dimeric acid polyester polyol contains a C36 dimeric acid backbone with long-chain nonpolar alkyl side chains. Introducing this component into polyurethane soft segments utilizes the volume effect and nonpolar characteristics of the side chains to create a hydrophobic microenvironment around easily hydrolyzed ester bonds. This increases the resistance to water molecule diffusion and penetration into the ester bonds, thereby inhibiting the hydrolytic breakage of the ester bonds.
[0013] 2-Butyl-2-ethyl-1,3-propanediol was selected as the chain extender, and its side groups contain ethyl and butyl groups. Compared with straight-chain chain extenders, the larger volume of this side group generates significant steric hindrance in the hard segment microregion. This steric hindrance effect effectively shields the urethane bonds, reducing the probability of water molecules contacting and reacting with the urethane bonds.
[0014] Epoxy linseed oil and castor oil participate in the reaction as hydrophobic modifiers. The epoxy groups in epoxy linseed oil and the hydroxyl groups in castor oil participate in the construction of the polyurethane network. This long carbon chain structure derived from vegetable oils further improves the hydrophobicity of the resin matrix. At the same time, the multifunctional vegetable oil components promote the formation of a moderately cross-linked network, increase the density of the resin layer, and reduce the transport channels of water molecules from a physical structure perspective.
[0015] By adding the chain extender in a pre-dissolved manner, the phenomenon of excessively high local concentration or uneven reaction that may be caused by directly adding solid chain extenders is avoided. This ensures the uniform distribution of hard segments in the polymer chain and makes the above-mentioned steric hindrance protection effect consistent throughout the material.
[0016] Preferably, the raw material further includes the following components in parts by weight:
[0017] N,N-Dimethylformamide: 340-360 parts; Organic bismuth catalyst: 0.04-0.06 parts; Methanol: 0.15-0.25 parts.
[0018] By employing the above technical solution, the amount of diluent used is limited to ensure a suitable viscosity of the reaction system. Using an organobismuth catalyst instead of a traditional organotin catalyst, organobismuth exhibits higher catalytic selectivity for the reaction of isocyanates with hydroxyl groups, while its catalytic activity for the reaction of isocyanates with water is relatively lower, which helps reduce side reactions and improve the hydrolytic stability of the material. Methanol is used as a capping agent to precisely control the endpoint of the polymerization reaction and prevent excessively large molecular weights from causing a decline in processing performance.
[0019] Preferably, the preparation method of the dimer acid polyester polyol includes:
[0020] The product is prepared by first esterification of dimer fatty acids and 1,6-hexanediol under the catalysis of tetrabutyl titanate at 160-235℃, followed by polycondensation under vacuum ≥-0.095MPa and temperature 230-235℃. The dimer fatty acid polyester polyol has a hydroxyl value of 35.1-37.4mgKOH / g and a number-average molecular weight Mn of 2995-3190g / mol.
[0021] By employing the above technical solution, the acid value of the dimer acid polyester polyol is controlled to be low, reducing the autocatalytic effect of residual carboxyl groups on ester bond hydrolysis. The specific molecular weight range ensures good compatibility with the main soft segment poly(1,4-butene adipate), avoiding the decrease in mechanical properties caused by phase separation, while also ensuring the uniformity of the hydrophobic modification effect.
[0022] Preferably, the formulation further includes an additive for preparing the impregnation or coating slurry, the additive comprising, based on 100 parts by weight of polyurethane resin slurry:
[0023] Lignin powder: 4.5-5.5 parts; black paste: 2.8-3.2 parts; silicone leveling agent: 0.4-0.6 parts.
[0024] By adopting the above technical solution, the biomass hydrophobic structure and filling effect of lignin powder are utilized to further block water vapor penetration; the organosilicon leveling agent improves the surface condition of the coating and reduces water erosion caused by surface defects.
[0025] Preferably, the purity of the 2-butyl-2-ethyl-1,3-propanediol is ≥99.0%; and the epoxy value of the epoxidized linseed oil is ≥9.0%.
[0026] By adopting the above technical solutions, high-purity raw materials reduce the interference of impurities on the polymerization reaction, and high epoxy value ensures the number of active sites for cross-linking reaction, thereby ensuring the stability of material performance.
[0027] Secondly, the present invention provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, employing the following technical solution:
[0028] A method for preparing hydrolysis-resistant polyurethane synthetic leather includes the following steps:
[0029] S1. Mix dimer polyester polyol, epoxy linseed oil, and castor oil, and heat and stir until a homogeneous, transparent, hydrophobic mixture is formed; S2. Add poly(1,4-butene adipate) to the hydrophobic mixture, mix evenly, and then perform vacuum dehydration to obtain a dehydrated polyol mixture; S3. Lower the temperature of the polyol mixture, add diphenylmethane diisocyanate to react, and obtain a polyurethane prepolymer; S4. Cool the polyurethane prepolymer and add N,N-dimethylformamide to dissolve it, add chain extender solution and organic bismuth catalyst to carry out chain extension reaction, and terminate the reaction when the predetermined viscosity is reached to obtain a hydrolysis-resistant polyurethane resin slurry; S5. Add lignin powder, black paste, and organic silicone leveling agent to the hydrolysis-resistant polyurethane resin slurry, disperse evenly, and use it as an impregnation slurry and coating slurry. Combine with a base fabric and perform wet coagulation, washing, and drying to obtain the hydrolysis-resistant polyurethane synthetic leather.
[0030] By adopting the above technical solution, the present invention establishes a corresponding polymerization process for special formulation systems containing hydrophobic side chains, and its mechanism of action is as follows:
[0031] Premixing process of hydrophobic components (steps S1-S2): Dimeric acid polyester polyol and vegetable oil components have long-chain alkyl structures and low polarity, while conventional poly(1,4-butene adipate) has relatively high polarity. If they are directly mixed and dehydrated, microphase separation is likely to occur due to the difference in polarity. This method first heats and mixes the hydrophobic components to make them mutually soluble, and then introduces them into the main soft segment. The thermal motion is used to overcome the polarity difference and form a stable homogeneous system, ensuring the uniform dispersion of each component before the polymerization reaction.
[0032] Solution chain extension control strategy (step S4): The chain extender 2-butyl-2-ethyl-1,3-propanediol used in this formulation contains large-volume side groups, resulting in significant steric hindrance. Diffusion and migration are difficult in the molten state, limiting its reactivity. This invention employs a method of first dissolving and diluting the prepolymer before adding the chain extender solution. This significantly reduces the system viscosity, decreases the resistance to diffusion of chain extender molecules to the NCO end groups of the prepolymer, and ensures the smooth progress of the chain extension reaction and effective molecular weight increase.
[0033] Preferably, in step S1, the heating and stirring temperature is 65-70℃ and the time is 40-50 minutes; in step S2, the vacuum dehydration treatment temperature is 105-110℃, the vacuum degree is controlled between -0.095MPa and -0.098MPa, and the dehydration is carried out until the moisture content of the polyol mixture is ≤0.025%.
[0034] By adopting the above technical solution, a temperature range of 65-70℃ ensures the fluidity of high-viscosity raw materials while preventing thermal oxidation of vegetable oils. Strictly controlling the moisture content after dehydration to between 0.015% and 0.025% serves two purposes: firstly, to maximize moisture removal and prevent the side reaction between water and isocyanate to generate carbon dioxide bubbles, which would affect resin density; secondly, retaining trace amounts of moisture allows it to act as an auxiliary foaming agent, facilitating the formation of a microporous structure in subsequent wet coagulation processes.
[0035] Preferably, in step S3, diphenylmethane diisocyanate is added after cooling to 60-65°C, and the reaction temperature is controlled at 80-85°C until the isocyanate group content reaches 6.5%-7.3%.
[0036] By adopting the above technical solution, cooling before adding materials is to control the exothermic rate in the initial stage of the reaction and prevent local overheating that could lead to gelation. Controlling the NCO content at 6.5%-7.3% ensures that the prepolymer has a suitable molecular weight and crosslinking point spacing, giving the final product both the flexibility of the soft segments and the strength of the hard segments.
[0037] Preferably, in step S4, N,N-dimethylformamide is added to dissolve the product at a temperature of 45-50°C, and the chain extension reaction temperature is controlled at 70-75°C; the predetermined viscosity is 45,000-58,000 mPa·s (25°C); methanol is added to terminate the reaction.
[0038] By employing the above technical solution, low-temperature dissolution reduces solvent evaporation. 70-75℃ is the equilibrium temperature for the reaction between this sterically hindered chain extender and the NCO group, ensuring both the reaction rate and suppressing side reactions. Controlling the final viscosity at 45,000-58,000 mPa·s ensures the leveling properties of the slurry on the base fabric, avoiding sagging due to excessively low viscosity or uneven coating due to excessively high viscosity.
[0039] Preferably, in step S5, the coagulation bath for wet coagulation is an 18%-22% N,N-dimethylformamide aqueous solution, and the coagulation temperature is 25-30℃; the coating amount of the coating slurry is 140-160 g / m³. 2
[0040] By employing the above technical solution, an aqueous solution of N,N-dimethylformamide is used as a coagulation bath to regulate the bidirectional diffusion rate between the solvent and non-solvent. A concentration range of 18%-22% allows for a moderate rate of phase separation in the polyurethane resin, promoting the formation of a uniform island-like microporous structure and imparting excellent breathability and a full hand feel to the synthetic leather.
[0041] This invention provides a formulation and preparation method for hydrolysis-resistant polyurethane synthetic leather. It possesses the following beneficial effects:
[0042] 1. This invention introduces dimer acid polyester polyol and epoxy linseed oil into the polyester soft segment. By utilizing the long carbon chain side group characteristics of the dimer acid backbone, the permeation resistance of water molecules is increased, and the easily hydrolyzed ester groups in the main chain are protected. At the same time, the chemical cross-linking network constructed by the vegetable oil component improves the resin density and further blocks the water vapor channel at the physical level, thus solving the problem of short service life of polyester polyurethane due to the easy hydrolysis and breakage of ester bonds.
[0043] 2. This invention uses 2-butyl-2-ethyl-1,3-propanediol, which has a large side group volume, as a chain extender to generate a steric hindrance effect in the hard segment region, which hinders the attack of water molecules on the urethane bond and reduces the probability of hydrolysis reaction. This structural design improves hydrolysis resistance while reducing the crystal regularity of the hard segment, improving the flexibility of synthetic leather, and overcoming the defect that traditional hydrolysis resistance modification often leads to a hardening of the material's feel.
[0044] 3. This invention solves the problem of uneven dispersion of high-stress chain extenders and hydrophobic raw materials by pre-dissolving chain extenders and pre-mixing hydrophobic components, ensuring the uniform distribution of hydrolysis-resistant structural units in the resin. Combined with the filling effect of lignin powder, it further fills the micropores in the resin matrix, slows down the diffusion path of water molecules, and the resulting synthetic leather significantly improves its hydrolysis resistance stability in humid and hot environments while maintaining high peel strength. Attached Figure Description
[0045] Figure 1 The following is a comparison chart of the surface anti-precipitation and contact angle stability test data of each group of samples in Test Example 1 of the present invention; wherein, (a) shows the oil absorption weight gain rate of each group of samples after thermal aging, and (b) shows the contact angle change of each group of samples before and after wiping with ethanol.
[0046] Figure 2 This is a schematic diagram showing the comparison of the acid value growth rate of each group of samples in Test Example 2 of the present invention after 28 days of wet heat aging treatment. Detailed Implementation
[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0048] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.
[0049] Poly(1,4-butene adipate): CAS No. 25103-87-1, number average molecular weight Mn is approximately 2000 g / mol, hydroxyl value is 54-58 mgKOH / g, acid value is ≤0.3 mgKOH / g.
[0050] Dimeric fatty acids: CAS No. 61788-89-4; 1,6-hexanediol: CAS No. 629-11-8.
[0051] Epoxy linseed oil: CAS No. 8016-11-3, epoxy value ≥9.0%, iodine value ≤5.0gI2 / 100g.
[0052] Castor oil: CAS No. 8001-79-4, hydroxyl value 160-165mgKOH / g, moisture ≤0.05%, acid value ≤2.0mgKOH / g.
[0053] Diphenylmethane diisocyanate: CAS No. 101-68-8, NCO group mass fraction is 33.4%-33.6%.
[0054] 2-Butyl-2-ethyl-1,3-propanediol: CAS No. 115-84-4, purity ≥99.0%.
[0055] N,N-Dimethylformamide: CAS No. 68-12-2, industrial grade, dehydrated by molecular sieve with moisture content ≤0.02%.
[0056] Organic bismuth catalyst: bismuth isooctanoate, CAS No. 67874-71-9, bismuth metal content 20%.
[0057] Methanol: It is anhydrous methanol, analytical grade.
[0058] Lignin powder, CAS No. 8068-05-1.
[0059] Black pigment: It is a commercially available black pigment specifically for polyurethane synthetic leather. The main coloring component is carbon black, CAS number 1333-86-4.
[0060] The silicone leveling agent is polydimethylsiloxane, CAS number 9016-00-6.
[0061] Preparation Example 1:
[0062] This preparation example provides a method for preparing a dimerized polyester polyol, including the following steps:
[0063] (1) In a four-necked flask equipped with a stirrer, thermometer, condenser with fractionating column and vacuum interface, add 100 parts by weight of dimer fatty acid and 26.2 parts by weight of 1,6-hexanediol, purge the air in the vessel with nitrogen, and start stirring and heat up under nitrogen protection.
[0064] (2) When the temperature rises to 160-165℃, esterified water begins to distill out. Control the heating rate and slowly raise the temperature to 230℃ within 3 hours. Keep the reaction at the temperature until the amount of water distilled reaches more than 95% of the theoretical value, and the top temperature of the fractionation column does not exceed 100℃.
[0065] (3) Add 0.01% of tetrabutyl titanate as a catalyst, turn on the vacuum pump, and gradually reduce the absolute pressure of the system to below 5 kPa (i.e., vacuum degree ≥ -0.095 MPa), and maintain the vacuum polycondensation reaction at 230°C for 3 hours.
[0066] (4) Take a sample to test the acid value. When the acid value drops to below 0.5 mg KOH / g, stop heating and release the vacuum. Cool down to 80°C and discharge the material to obtain dimer acid polyester polyol product A.
[0067] The test results showed that the hydroxyl value of the dimer acid polyester polyol A was 37.4 mg KOH / g, the number average molecular weight Mn was 2995 g / mol, and the appearance was a yellow transparent viscous liquid.
[0068] Preparation Example 2:
[0069] This preparation example provides a method for preparing a dimerized polyester polyol, including the following steps:
[0070] (1) In a four-necked flask equipped with a stirrer, thermometer, condenser with fractionating column and vacuum interface, add 100 parts by weight of dimer fatty acid and 25.5 parts by weight of 1,6-hexanediol, purge the air in the vessel with nitrogen, and start stirring and heat up under nitrogen protection.
[0071] (2) When the temperature rises to 165℃, esterified water begins to distill out. Control the heating rate and slowly raise the temperature to 235℃ within 3.5 hours. Keep the reaction at the temperature until the amount of water distilled reaches more than 95% of the theoretical value. During this period, control the fractionation reflux ratio to reduce the loss of diol.
[0072] (3) Add 0.015% of tetrabutyl titanate as a catalyst, turn on the vacuum pump, and gradually reduce the absolute pressure of the system to below 2 kPa (i.e., vacuum degree ≥ -0.098 MPa), and maintain the vacuum polycondensation reaction at 235℃ for 4 hours.
[0073] (4) Take a sample to test the acid value. When the acid value drops below 0.4 mg KOH / g, stop heating and release the vacuum. Cool down to 80°C and discharge the material to obtain dimer acid polyester polyol product B.
[0074] The test results showed that the hydroxyl value of the dimer acid polyester polyol B was 35.1 mgKOH / g, the number average molecular weight Mn was 3190 g / mol, and the appearance was a yellow transparent viscous liquid.
[0075] Example 1:
[0076] This embodiment provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, including the following steps:
[0077] Step S1: In a reactor equipped with a stirrer, thermometer, and reflux condenser, mix 13.5 parts by weight of the dimer polyester polyol product A obtained in Preparation Example 1, 3.5 parts by weight of epoxy linseed oil, and 1.2 parts by weight of castor oil. Start stirring, control the speed at 450 rpm, raise the temperature to 68°C, and stir at a constant temperature for 45 minutes for pre-swelling treatment until the mixture becomes homogeneous and transparent, thus obtaining a hydrophobic mixture.
[0078] Step S2: Add 88.0 parts of poly(1,4-butenyl adipate) to the hydrophobic mixture obtained in step S1, mix thoroughly, and then heat to 108°C. Turn on the vacuum pump and perform vacuum dehydration treatment for 2 hours under a vacuum degree of -0.096MPa to -0.098MPa until the moisture content of the mixture is detected to be 0.02%. Release the vacuum to obtain the dehydrated polyol mixture.
[0079] Step S3: Cool the polyol mixture obtained in step S2 to 62°C and add 43.5 parts of diphenylmethane diisocyanate. Utilize the exothermic reaction to naturally raise the temperature, and control the jacket temperature of the reactor to maintain the reaction solution temperature at 82-85°C. React for 2 hours, and sample testing shows that the isocyanate group content reaches the theoretical value of 6.9%, thus obtaining the polyurethane prepolymer.
[0080] Step S4: Cool the polyurethane prepolymer obtained in Step S3 to 48°C and dilute and disperse it with 350 parts of N,N-dimethylformamide. Then, add dropwise a chain extender solution prepared by dissolving 5.0 parts of 2-butyl-2-ethyl-1,3-propanediol in 11.7 parts of N,N-dimethylformamide (2-butyl-2-ethyl-1,3-propanediol is pre-dissolved in N,N-dimethylformamide), and add 0.05 parts of organic bismuth catalyst. Heat to 72°C to carry out the chain extension reaction. Monitor the viscosity of the reaction solution. When the viscosity reaches 52,000 mPa·s (25°C), add 0.2 parts of methanol to terminate the reaction. Filter the solution to obtain a hydrolysis-resistant polyurethane resin slurry with a solid content of approximately 30%.
[0081] Step S5: Take 100 parts of the hydrolysis-resistant polyurethane resin slurry obtained in Step S4, add 5 parts of lignin powder, 3 parts of black paste, and 0.5 parts of organosilicon leveling agent, and disperse at high speed to prepare a homogeneous mixed slurry. This mixed slurry serves as both the impregnation slurry and the coating slurry. Using existing conventional wet-process synthetic leather preparation technology, the impregnation slurry is impregnated into the nonwoven fabric base, and the coating slurry is coated onto the surface of the base fabric (coating amount is 150g / m²). 2 The mixture was introduced into a coagulation bath containing 20% N,N-dimethylformamide aqueous solution and subjected to phase separation and coagulation at 28°C. After multiple water washes to remove residual solvent and drying, the hydrolysis-resistant polyurethane synthetic leather described in Example 1 was obtained.
[0082] Example 2:
[0083] This embodiment provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, including the following steps:
[0084] Step S1: In a reactor equipped with a stirrer, thermometer, and reflux condenser, mix 15.0 parts by weight of the dimer acid polyester polyol product B obtained in Preparation Example 2, 4.0 parts by weight of epoxy linseed oil, and 1.5 parts by weight of castor oil. Start stirring, control the speed at 500 rpm, raise the temperature to 70°C, and stir at a constant temperature for 50 minutes for pre-swelling treatment until the mixture becomes homogeneous and transparent, thus obtaining a hydrophobic mixture.
[0085] Step S2: Add 85.0 parts of poly(1,4-butenyl adipate) to the hydrophobic mixture obtained in step S1, mix thoroughly, and then heat to 110°C. Turn on the vacuum pump and perform vacuum dehydration treatment for 1.5 hours under a vacuum of -0.098 MPa until the moisture content of the mixture is detected to be 0.015%. Release the vacuum to obtain the dehydrated polyol mixture.
[0086] Step S3: Cool the polyol mixture obtained in step S2 to 65°C and add 45.0 parts of diphenylmethane diisocyanate. Utilize the exothermic reaction to naturally raise the temperature, and control the jacket temperature of the reactor to maintain the reaction liquid temperature at 85°C. React for 2 hours, and sample testing shows that the isocyanate group content reaches the theoretical value of 7.1%, thus obtaining the polyurethane prepolymer.
[0087] Step S4: Cool the polyurethane prepolymer obtained in Step S3 to 50°C and dilute and disperse it by adding 360 parts of N,N-dimethylformamide. Then, add dropwise a chain extender solution prepared by dissolving 5.5 parts of 2-butyl-2-ethyl-1,3-propanediol in 12.8 parts of N,N-dimethylformamide, and add 0.06 parts of organic bismuth catalyst. Heat to 75°C to carry out the chain extension reaction. Monitor the viscosity of the reaction solution; when the viscosity reaches 48,000 mPa·s (25°C), add 0.25 parts of methanol to terminate the reaction. Filter the solution to obtain a hydrolysis-resistant polyurethane resin slurry with a solid content of approximately 30%.
[0088] Step S5: Take 100 parts of the hydrolysis-resistant polyurethane resin slurry obtained in Step S4, add 5.5 parts of lignin powder, 2.8 parts of black paste, and 0.6 parts of silicone leveling agent, and disperse at high speed to prepare a homogeneous mixed slurry. This mixed slurry serves as both the impregnation slurry and the coating slurry. Impregnate the nonwoven fabric base with the impregnation slurry, and then coat the surface of the base fabric with the coating slurry (coating amount: 140 g / m²). 2 The mixture was introduced into a coagulation bath containing 22% N,N-dimethylformamide aqueous solution and subjected to phase separation and coagulation at 30°C. After multiple water washes to remove residual solvent and drying, the hydrolysis-resistant polyurethane synthetic leather described in Example 2 was obtained.
[0089] Example 3:
[0090] This embodiment provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, including the following steps:
[0091] Step S1: In a reactor equipped with a stirrer, thermometer, and reflux condenser, mix 12.0 parts by weight of the dimer polyester polyol product A obtained in Preparation Example 1, 3.0 parts by weight of epoxy linseed oil, and 1.0 part by weight of castor oil. Start stirring, control the speed at 400 rpm, raise the temperature to 65°C, and stir at a constant temperature for 40 minutes for pre-swelling treatment until the mixture becomes homogeneous and transparent, thus obtaining a hydrophobic mixture.
[0092] Step S2: Add 90.0 parts of poly(1,4-butenyl adipate) to the hydrophobic mixture obtained in step S1, mix thoroughly, and then heat to 105°C. Turn on the vacuum pump and perform vacuum dehydration treatment for 2.5 hours under a vacuum degree of -0.095 MPa until the moisture content of the mixture is detected to be 0.025%. Release the vacuum to obtain the dehydrated polyol mixture.
[0093] Step S3: Cool the polyol mixture obtained in step S2 to 60°C and add 42.0 parts of diphenylmethane diisocyanate. Utilize the exothermic reaction to naturally raise the temperature, and control the jacket temperature of the reactor to maintain the reaction solution temperature at 80°C. React for 2.5 hours, and sample testing shows that the isocyanate group content reaches the theoretical value of 6.7%, thus obtaining the polyurethane prepolymer.
[0094] Step S4: Cool the polyurethane prepolymer obtained in Step S3 to 45°C and dilute and disperse it by adding 340 parts of N,N-dimethylformamide. Then, add dropwise a chain extender solution prepared by dissolving 4.5 parts of 2-butyl-2-ethyl-1,3-propanediol in 10.5 parts of N,N-dimethylformamide, and add 0.04 parts of organic bismuth catalyst. Heat to 70°C to carry out the chain extension reaction. Monitor the viscosity of the reaction solution; when the viscosity reaches 58,000 mPa·s (25°C), add 0.15 parts of methanol to terminate the reaction. Filter the solution to obtain a hydrolysis-resistant polyurethane resin slurry with a solid content of approximately 30%.
[0095] Step S5: Take 100 parts of the hydrolysis-resistant polyurethane resin slurry obtained in Step S4, add 4.5 parts of lignin powder, 3.2 parts of black paste, and 0.4 parts of silicone leveling agent, and disperse at high speed to prepare a homogeneous mixed slurry. This mixed slurry serves as both the impregnation slurry and the coating slurry. Impregnate the nonwoven fabric base with the impregnation slurry, and then coat the surface of the base fabric with the coating slurry (coating amount: 160 g / m²). 2 The mixture was introduced into a coagulation bath containing 18% N,N-dimethylformamide aqueous solution, and phase separation and coagulation were carried out at 25°C. The residual solvent was then removed by multiple water washes and dried to obtain the hydrolysis-resistant polyurethane synthetic leather described in Example 3.
[0096] Example 4:
[0097] This embodiment provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, including the following steps:
[0098] Steps S1-S3: The operation steps and raw material types are exactly the same as in Example 1. In step S1, the amount of each hydrophobic raw material remains unchanged. In step S2, the amount of poly(1,4-butene adipate) is 88.0 parts. However, in step S3, the amount of diphenylmethane diisocyanate added is adjusted to 46.0 parts. The reaction temperature is controlled at 85°C. The reaction is carried out until the isocyanate group content reaches the theoretical value of 7.3%, and a polyurethane prepolymer is obtained.
[0099] Step S4: Cool the polyurethane prepolymer obtained in Step S3 to 50°C and dissolve it in 355 parts of N,N-dimethylformamide. Then, add dropwise a chain extender solution prepared by dissolving 6.0 parts of 2-butyl-2-ethyl-1,3-propanediol in 14.0 parts of N,N-dimethylformamide, and add 0.05 parts of organic bismuth catalyst. Heat to 75°C to carry out the chain extension reaction. The final viscosity of the reaction is controlled at 45,000 mPa·s (25°C). After terminating the reaction, a hydrolysis-resistant polyurethane resin slurry is obtained.
[0100] Step S5: Using the hydrolysis-resistant polyurethane resin slurry obtained in step S4, prepare the hydrolysis-resistant polyurethane synthetic leather as described in step S5 of Example 1 to obtain the hydrolysis-resistant polyurethane synthetic leather described in Example 4.
[0101] Example 5:
[0102] This embodiment provides a method for preparing hydrolysis-resistant polyurethane synthetic leather, including the following steps:
[0103] Steps S1-S3: The operation steps and raw material types are exactly the same as in Example 1. In step S1, the amount of each hydrophobic raw material remains unchanged. In step S2, the amount of poly(1,4-butene adipate) is 88.0 parts. However, in step S3, the amount of diphenylmethane diisocyanate added is adjusted to 41.0 parts. The reaction temperature is controlled at 80°C. The reaction is carried out until the isocyanate group content reaches the theoretical value of 6.5%, and a polyurethane prepolymer is obtained.
[0104] Step S4: Cool the polyurethane prepolymer obtained in Step S3 to 45°C and dissolve it in 345 parts of N,N-dimethylformamide. Then, add dropwise a chain extender solution prepared by dissolving 4.0 parts of 2-butyl-2-ethyl-1,3-propanediol in 9.3 parts of N,N-dimethylformamide, and add 0.05 parts of organic bismuth catalyst. Heat to 70°C to carry out the chain extension reaction. The final viscosity of the reaction is controlled at 55,000 mPa·s (25°C). After terminating the reaction, a hydrolysis-resistant polyurethane resin slurry is obtained.
[0105] Step S5: Using the hydrolysis-resistant polyurethane resin slurry obtained in step S4, prepare the hydrolysis-resistant polyurethane synthetic leather as described in step S5 of Example 1 using the same process.
[0106] Comparative Example 1: Compared with Example 1, the difference lies in the change of the feeding sequence and process: the pre-swelling process in step S1 is cancelled, and in step S2, the dimer acid polyester polyol product A, epoxy linseed oil, castor oil and poly(1,4-butene adipate) are directly added to the reactor at the same time for mixing and dehydration, and then the subsequent reaction is carried out. The amount of other raw materials and the steps are the same.
[0107] Comparative Example 2: Compared with Example 1, the difference is that castor oil was removed from the raw materials, and the amount of dimer polyester polyol product A obtained in Preparation Example 1 was adjusted to 17.0 parts (an increase of 3.5 parts to maintain hydroxyl equivalent balance), and all other aspects were the same.
[0108] Comparative Example 3: Compared with Example 1, the difference is that the epoxidized linseed oil was replaced with an equal weight of ordinary linseed oil (CAS No.: 8001-26-1), and all other aspects were the same.
[0109] Comparative Example 4: Compared with Example 1, the difference is that the chain extender 2-butyl-2-ethyl-1,3-propanediol was replaced with an equimolar amount of 1,4-butanediol (CAS No.: 110-63-4, amount: 2.8 parts), and all other aspects are the same.
[0110] Test Example 1:
[0111] 1. Experiment Description
[0112] (1) Select polyurethane synthetic leather samples prepared in Examples 1-5 and Comparative Examples 1-2 and cut them into test pieces with a specification of 100mm×100mm. Place the samples in a constant temperature and humidity chamber (temperature 23±2℃, relative humidity 50±5%) for 24 hours to adjust the state, so as to eliminate the thermal history and internal stress during the sample preparation process and to make the moisture content reach equilibrium.
[0113] (2) The precipitation after thermal aging was determined by the oil-absorbing paper adsorption method. The initial mass of the quantitative filter paper was weighed ( It was then placed over the surface of the test sample and a pressure of 200 g / cm was applied. 2 The heavy object was placed in an 80℃ forced-air drying oven and heated continuously for 168 hours (7 days).
[0114] (3) Remove the sample and cool it to room temperature, then remove the weight. First, conduct a sensory evaluation of the surface condition. Three laboratory personnel (professional technicians with over 3 years of experience in synthetic leather testing, normal vision, and sensitive touch) will judge the surface condition through touch and visual observation. The evaluation criteria are divided into three levels:
[0115] Dry: The surface shows no visible change in gloss, and feels dry to the touch with no residue;
[0116] Slightly oily: The surface has a slight sheen and feels slightly sticky to the touch, but there is no droplet aggregation;
[0117] Severe precipitation: There is a noticeable oil film or droplets on the surface, and it feels greasy to the touch.
[0118] (4) Immediately afterwards, weigh the filter paper. The formula for calculating the oil absorption weight gain rate of filter paper is: .
[0119] (5) Take another sample from the same batch that has not undergone heat aging treatment and test it using an optical contact angle meter. The test liquid is deionized water, and the droplet volume is set to 3 μL. The sessile drop method is used to randomly select 5 points on the sample surface for measurement. The stable value within 3 seconds after the droplet contacts the sample surface is read, and the average value is recorded as the initial contact angle. ).
[0120] (6) Use a lint-free cloth soaked in anhydrous ethanol to apply the above-mentioned test results. The sample surface was wiped 10 times in both longitudinal and transverse directions, with the applied force controlled at approximately 5N. After drying at room temperature for 30 minutes, the water contact angle of the same area was measured again and recorded as the contact angle after wiping. ).
[0121] (7) Calculate the change in contact angle. This value reflects the adhesion stability of hydrophobic components on the substrate surface.
[0122] 2. Experimental data (see Table 1)
[0123] Table 1: Test results of surface anti-precipitation and contact angle stability of each group of samples
[0124] Group Oil absorption weight gain rate of filter paper (%) Initial contact angle (°) Contact angle after wiping (°) Contact angle change value (°) Sensory evaluation of surface condition Example 1 0.12 104.5 102.8 1.7 dry Example 2 0.15 103.2 101.1 2.1 dry Example 3 0.09 105.1 103.9 1.2 dry Example 4 0.13 104.0 102.4 1.6 dry Example 5 0.11 104.8 103.5 1.3 dry Comparative Example 1 1.84 107.5 93.2 14.3 Micro oil Comparative Example 2 3.56 108.2 84.6 23.6 Severe precipitation
[0125] 3. Conclusion Analysis
[0126] Table 1 and Figure 1 Data shows that after 168 hours of heat aging, the oil absorption weight gain rate of the filter paper in Examples 1 to 5 was controlled between 0.09% and 0.15%, and the change in water contact angle before and after ethanol wiping was ( The temperature was maintained within the range of 1.2°–2.1°, and the sensory evaluation showed a dry feel. This result indicates that, through the preparation process of this invention, the hydrophobic additive epoxy linseed oil maintained a stable dispersion in the polyurethane matrix and did not undergo significant migration due to heat or solvent wiping.
[0127] Although Comparative Example 1 used the same raw materials as the examples, the direct mixing reaction without a pre-swelling process resulted in a 1.84% increase in the oil absorption weight gain of its filter paper, and a 14.3° decrease in the contact angle after wiping, with a slightly oily feel on the surface. These differences indicate that without prior compatibility penetration between the dimer polyester and epoxy linseed oil, the cross-linked network generated in the subsequent reaction cannot effectively encapsulate the hydrophobic agent. Free epoxy linseed oil gradually diffuses from the polymer interior to the surface under thermodynamic drive, leading to a decrease in anti-exudation properties.
[0128] Comparative Example 2, which removed castor oil from the raw materials, further increased the oil absorption weight gain to 3.56%. Expanding to 23.6°, the surface exhibits severe precipitation. Castor oil, as a multifunctional crosslinking agent, plays a role in constructing a local three-dimensional network during the reaction. Without this component, the system cannot form physical barriers that restrict the movement of macromolecules. Even if the epoxy linseed oil molecular chains have a certain degree of physical compatibility with the matrix, they are unable to resist long-term thermal migration, resulting in the failure of hydrophobic function and surface stickiness.
[0129] A comprehensive comparison shows that neither simple physical mixing of raw material components (Comparative Example 1) nor single chemical modification (Comparative Example 2) can solve the problem of hydrophobic agent precipitation. The pre-swelling combined with in-situ micro-crosslinking technology used in this invention effectively inhibits the migration of small molecule hydrophobic additives by utilizing physical entanglement and steric hindrance effects.
[0130] Test Example 2:
[0131] 1. Experiment Description
[0132] (1) Select polyurethane synthetic leather samples prepared in Examples 1-5 and Comparative Example 3 and cut them into pieces of about 10g each. Place all samples in a constant temperature and humidity test chamber with a set temperature of 70℃ and a relative humidity of 95% for accelerated damp heat aging treatment.
[0133] (2) The sampling time points were set as 0 days (before aging), 7 days, 14 days and 28 days. At each time point, a portion of the sample was taken out and placed in a vacuum drying oven at 40°C for 24 hours to remove the adsorbed moisture, and then cooled to room temperature for later use.
[0134] (3) Accurately weigh 1.00 g of the dried sample (accurate to 0.001 g), place it in an Erlenmeyer flask, and add 50 mL of N,N-dimethylformamide solvent that has been pre-neutralized with 0.05 mol / L potassium hydroxide-ethanol standard solution (which is prepared by dissolving 2.8 g of potassium hydroxide in 1000 mL of anhydrous ethanol and then standardizing it) until the phenolphthalein indicator turns slightly red.
[0135] (4) The sample is fully dissolved or swollen by gentle heating under magnetic stirring, and then titrated with 0.05 mol / L potassium hydroxide-ethanol standard solution until the solution turns pink and does not fade within 30 seconds. Record the volume of titrant consumed.
[0136] (5) According to the formula Calculate the acid value (AV, unit: mgKOH / g) of the sample. To determine the volume consumed in the titration, 56.1 represents the concentration of the standard solution and the molar mass of potassium hydroxide (g / mol). This represents the sample mass. This value reflects the accumulation of free carboxyl groups generated during the aging process of the material due to the hydrolytic breakage of ester bonds.
[0137] (6) Based on the acid value data obtained above, calculate the acid value growth rate after 28 days of aging relative to the initial state to assess the retention of the material's hydrolysis resistance. The calculation formula is:
[0138] ;
[0139] in, The acid value of the sample after 28 days of aging; The initial acid value before aging (day 0).
[0140] 2. Experimental data (see Table 2)
[0141] Table 2: Acid value evolution data of each group of samples during wet heat aging (unit: mgKOH / g)
[0142] Group Day 0 (Initial value) 7 days 14 days 28 days Acid value growth rate (0-28 days) Example 1 0.18 0.22 0.29 0.41 127.8% Example 2 0.16 0.19 0.24 0.33 106.3% Example 3 0.21 0.26 0.35 0.54 157.1% Example 4 0.19 0.23 0.31 0.45 136.8% Example 5 0.17 0.21 0.27 0.38 123.5% Comparative Example 3 0.19 0.84 2.15 4.67 2357.9%
[0143] 3. Conclusion Analysis
[0144] Table 2 and Figure 2 Data shows the changes in acid value of each group of samples under conditions of 70℃ and 95%RH. In the initial stage (day 0), the acid value of each group of samples was between 0.16-0.21 mgKOH / g, indicating that the initial chemical structure of each group of polyurethane synthetic leather was relatively complete and the residual carboxyl content was similar.
[0145] After 28 days of wet heat aging, the acid value of Comparative Example 3 increased from an initial 0.19 mg KOH / g to 4.67 mg KOH / g, representing a growth rate of 2357.9%. Comparative Example 3 used ordinary linseed oil without epoxy groups, which could not chemically consume the carboxylic acids generated by polyester hydrolysis. As aging progressed, carboxyl groups generated from polyester chain breakage accumulated continuously, leading to an increase in the internal acidity of the material. The high concentration of carboxyl groups catalyzed further hydrolysis of the remaining ester bonds, causing a rapid, non-linear increase in the acid value.
[0146] Examples 1 to 5 showed relatively small increases in acid value under the same aging conditions. For example, in Example 2, the acid value after 28 days was only 0.33 mg KOH / g. This is because epoxidized linseed oil was introduced into the formulation of these examples, and the epoxy groups in its molecular structure can undergo ring-opening esterification with the carboxyl groups generated by hydrolysis. This reaction consumes catalytically active protons, inhibiting the acidic autocatalytic effect and thus reducing the degradation rate of the polyurethane backbone.
[0147] Furthermore, comparing the data from Example 2 (4.0 parts of epoxidized linseed oil, final acid value 0.33 mg KOH / g) and Example 3 (3.0 parts of epoxidized linseed oil, final acid value 0.54 mg KOH / g), the increase in acid value was negatively correlated with the amount of epoxidized linseed oil added. This indicates that the molar content of epoxy groups directly affects the removal efficiency of hydrolysis products. Increasing the amount of epoxidized linseed oil within a certain range helps to more effectively control the acid value level inside the material and delay the hydrolysis aging process.
[0148] Test Example 3:
[0149] 1. Experiment Description
[0150] (1) The polyurethane synthetic leather samples prepared in Examples 1-5 and Comparative Examples 1-4 were cut into dumbbell-shaped tensile specimens conforming to GB / T 1040.2. For each example or comparative example (hereinafter referred to as "each group"), 30 specimens were prepared.
[0151] (2) The 30 specimens in each group were left to stand for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±5% to eliminate internal stress. Then they were randomly divided into 6 groups, each containing 5 specimens.
[0152] (3) Take the first group as the "initial group" and use a universal testing machine to measure its breaking strength (N) at a tensile speed of 200 mm / min. Take the arithmetic mean of the 5 values as the initial breaking strength. .
[0153] (4) The second to fifth groups (a total of 20 samples) were suspended in a constant temperature and humidity test chamber for jungle experiment. The jungle experiment is an accelerated aging test method that simulates the high temperature and high humidity environment of tropical rainforest. The environmental conditions were set as 70±1℃ temperature and 95±2% relative humidity.
[0154] (5) The sixth group (5 samples) is kept in the standard environment as a backup group for supplementary testing when the test data at a certain time point is abnormally discrete or there is an operational error. If there is no abnormality, it will not be included in the final data.
[0155] (6) At aging times of 3, 5, 8, and 10 weeks, one group (i.e., groups 2, 3, 4, and 5) was sequentially removed from the test chamber. After removal, the groups were placed in a standard environment (23℃, 50%RH) for 24 hours for conditioning, and then the breaking strength was measured. The average value was recorded as follows. .
[0156] (7) According to the formula Calculate the strength retention rate at each time point.
[0157] 2. Experimental data (see Table 3)
[0158] Table 3: Strength retention rate (%) of each sample group under accelerated aging conditions at 70℃ / 95%RH
[0159] Group Initial strength (N) 3-week retention rate (%) 5-week retention rate (%) 8-week retention rate (%) 10-week retention rate (%) Remark Example 1 485.2 96.4 91.2 83.5 76.8 No change in appearance Example 2 492.1 97.8 93.4 86.1 79.2 No change in appearance Example 3 476.5 95.1 89.6 80.4 72.5 No change in appearance Example 4 504.3 96.0 90.8 82.7 75.4 No change in appearance Example 5 468.9 95.5 89.9 81.3 73.1 No change in appearance Comparative Example 1 481.5 92.3 78.4 55.6 32.7 The surface becomes sticky Comparative Example 2 474.8 89.1 71.2 43.8 18.4 Severe surface precipitation Comparative Example 3 483.6 85.2 42.6 12.5 - The sample pulverized after 5 weeks. Comparative Example 4 512.4 64.8 21.3 - - Surface cracks after 3 weeks
[0160] 3. Conclusion Analysis
[0161] Table 3 shows the changes in mechanical properties of different formulation systems under high temperature and high humidity conditions. After 10 weeks of jungle testing, the strength retention rate of Examples 1 to 5 remained in the range of 72.5%-79.2%, indicating that the materials have excellent hydrolytic stability.
[0162] The experimental results of Comparative Example 4 show that the side chain structure has a significant impact on hydrolysis resistance. Comparative Example 4 used linear 1,4-butanediol instead of the side-chain-containing 2-butyl-2-ethyl-1,3-propanediol. Although its initial strength was higher, the retention rate decreased to 64.8% after 3 weeks of aging and to 21.3% after 5 weeks. The hard segments formed by 1,4-butanediol were tightly packed but lacked steric hindrance protection, allowing water molecules to easily penetrate and attack the urethane bonds, leading to rapid polymer chain breakage. The 2-butyl-2-ethyl-1,3-propanediol used in the examples contained ethyl and butyl side chains, increasing the steric hindrance between molecular chains, hindering the nucleophilic attack of water molecules, and reducing the hydrolysis reaction rate.
[0163] Comparative Example 3 data confirmed the scavenging effect of epoxy groups on acidic products. This group of samples retained only 42.6% of their composition after 5 weeks of aging and pulverized after 8 weeks. Due to the lack of epoxy groups, the system was unable to consume the carboxylic acids produced by hydrolysis, leading to the accumulation of acidic substances and catalyzing the self-accelerated decomposition of ester bonds.
[0164] The data from Comparative Examples 1 and 2 reflect the impact of the stability of the hydrophobic component on long-term performance. Both groups of samples showed an accelerated rate of performance degradation in the later stages of aging (5-10 weeks). Comparative Example 1 did not employ a pre-swelling process, and Comparative Example 2 lacked castor oil crosslinking agent, resulting in weaker bonding between the hydrophobic component and the matrix. With prolonged aging, the hydrophobic component migrated and was lost to the surface, the material interior lost its hydrophobic protection, and moisture intrusion increased, thus accelerating the hydrolysis process.
[0165] Based on the above data, the embodiments, by introducing side-chain steric hindrance chain extenders, epoxy components with acid-scavenging functions, and in-situ micro-crosslinking locking processes, achieved the synergistic effect of multiple hydrolysis resistance mechanisms, ensuring the stability of the material's mechanical properties under long-term humid and hot environments.
[0166] Test Example 4:
[0167] 1. Experiment Description
[0168] (1) Sample preparation and grouping: Polyurethane synthetic leather prepared in Examples 1-5 and Comparative Example 4 was selected as the test objects. For each example or comparative example (hereinafter collectively referred to as each group), the following three types of samples were independently cut and prepared, totaling 11 samples:
[0169] Tensile test specimens: 5 specimens, dumbbell-shaped according to GB / T1040.2 standard. Flexural endurance test specimens: 3 specimens, rectangular with dimensions of 70mm × 45mm. Hand feel evaluation specimens: 3 specimens, cubes with dimensions of 200mm × 200mm. All specimens were conditioned for 24 hours in a standard environment at 23±2℃ and 50±5% relative humidity before testing.
[0170] (2) Double-blind touch evaluation: The three touch evaluation samples in each group were shuffled and randomly coded (e.g., Group A, Group B, etc.), and the specific formula information was hidden. Three professionals with more than five years of experience in synthetic leather were organized to independently evaluate one group (3 samples) by touch. The evaluation indicators included softness and fullness, and the comprehensive judgment result was recorded as: soft and full, moderate, or hard and stiff. The final result was the mode of the evaluation results of the three people.
[0171] (3) Room temperature mechanical property testing and data calculation: Five tensile specimens in each group were tested sequentially using a universal testing machine. The tensile speed was set to 200 mm / min, and the equipment was started to allow the clamps to continuously elongate the specimens until they broke. The equipment automatically recorded the load-displacement curve of each specimen during the tensile process and calculated the following two indicators for each specimen:
[0172] 100% elongation modulus ( ): Extract load data at the moment when the distance between the markings on the specimen is stretched to twice the initial distance (i.e., the strain reaches 100%). If the specimen breaks before the elongation reaches 100%, this index is not recorded (in the range of soft synthetic leather involved in this experiment, the elongation usually far exceeds 100%). The calculation formula is:
[0173] ;
[0174] In the formula, 100% elongation modulus (MPa); Load (N) at 100% deformation; The width of the sample is (mm). The thickness of the sample is (mm).
[0175] Elongation at break ( ): Extract displacement data at the instant the specimen fractures. The calculation formula is:
[0176] ;
[0177] In the formula, Elongation at break (%) The distance between the marks when the specimen breaks (mm); The initial distance between the markings on the specimen (mm) is used. After the test, the arithmetic mean of the 100% tensile modulus and elongation at break values of the five specimens is calculated as the final test result for each group.
[0178] (4) Low temperature flexural endurance test: Using a Bally flexural tester (compliant with GB / T 8948 standard), the test environment temperature was lowered to -20℃ and kept constant for 30 minutes. The three flexural endurance specimens of each group were installed in the test fixture, and one end of the specimen was folded (to simulate the wrinkles in actual use), and repeated flexural movements were performed under pressure.
[0179] (5) Evaluation of flexural endurance: The flexural cycles were set at 100,000. After the test, all samples were removed and allowed to return to room temperature. The folded area of each sample was observed under a 10x magnifying glass to check for cracks, whitening, or coating peeling. If none of the three samples had the above defects, it was recorded as "no cracks"; if any sample had a defect, the specific defect was recorded.
[0180] 2. Experimental data (see Table 4)
[0181] Table 4: Evaluation results of room temperature mechanical properties, low temperature folding resistance, and hand feel of each group of samples
[0182] Group 100% elongation modulus (MPa) Elongation at break (%) -20℃ flexural strength (100,000 cycles) Feel evaluation results Example 1 4.2 485 The surface is intact and there are no cracks. Soft and plump Example 2 3.9 512 The surface is intact and there are no cracks. Soft and plump Example 3 4.5 468 The surface is intact and there are no cracks. Moderate Example 4 4.1 496 The surface is intact and there are no cracks. Soft and plump Example 5 4.3 474 The surface is intact and there are no cracks. Moderate Comparative Example 4 9.8 315 Fine cracks appeared hardened and compacted
[0183] 3. Conclusion Analysis
[0184] According to the data in Table 4, different chain extender structures significantly affected the mechanical behavior and feel of the materials. The 100% tensile modulus values of Examples 1 to 5 were relatively low, ranging from 3.9 to 4.5 MPa; the elongation at break was relatively high, remaining between 468% and 512%. After undergoing 100,000 flexural cycles at -20°C, no cracks appeared on the surface of the example samples. The sensory evaluation results were consistent with the objective test data, and the example samples exhibited a soft and full feel. This indicates that the formulation of the present invention improves hydrolysis resistance without sacrificing the material's flexibility and the feel of the finished leather.
[0185] Comparative Example 4 achieved a 100% tensile modulus of 9.8 MPa, significantly higher than the Example group, but its elongation at break was only 315%. It felt stiff and rigid to the touch and cracked during low-temperature flexural endurance testing. Comparative Example 4 used 1,4-butanediol as a chain extender. The 1,4-butanediol molecule has a short, straight-chain structure with high symmetry. This structure facilitates the tight packing of polyurethane hard segments, leading to a high degree of physical crystallization. The crystalline regions, acting as physical crosslinking points, increase the material's rigidity (increased modulus) but also restrict the mobility of the polymer chains. Under low-temperature conditions, the highly crystalline hard segments further hinder the movement of the soft segments, causing the material to exhibit brittleness and be unable to withstand repeated deformation.
[0186] The 2-butyl-2-ethyl-1,3-propanediol used in the examples contains large ethyl and butyl side chains. These side chain groups introduce steric hindrance into the molecular chain, disrupting the regular stacking of hard segments, reducing intermolecular forces and the density of physical cross-linking points, thereby lowering the material's tensile modulus and making it feel softer. Simultaneously, the presence of side chains increases the free volume between polymer chains. This structural feature allows the material to maintain a certain degree of chain mobility at low temperatures, thus exhibiting excellent flexural strength under testing conditions of -20°C.
[0187] Furthermore, the dimer acid polyester polyol selected in this invention contains a long side-chain aliphatic hydrocarbon structure, which works in conjunction with the side-chain structure of 2-butyl-2-ethyl-1,3-propanediol and the long-chain structure of epoxy linseed oil to jointly construct a polymer network with high free volume, thus solving the problems of low-temperature hardening and hardening of the hand feel that are easy to occur in traditional high hydrolysis resistant polyurethane.
[0188] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A formulation for hydrolysis-resistant polyurethane synthetic leather, characterized in that, The polyurethane resin layer of the synthetic leather is made from raw materials comprising the following parts by weight: Poly(1,4-butene adipate): 85.0-90.0 parts; Dimer acid polyester polyol: 12.0-15.0 parts; Epoxy linseed oil: 3.0-4.0 parts; Castor oil: 1.0-1.5 parts; Diphenylmethane diisocyanate: 41.0-46.0 parts; Chain extender solution: 13.3-20.0 parts; wherein the chain extender solution is prepared by dissolving 4.0-6.0 parts of 2-butyl-2-ethyl-1,3-propanediol in 9.3-14.0 parts of N,N-dimethylformamide.
2. The formulation for a hydrolysis-resistant polyurethane synthetic leather according to claim 1, characterized in that, The raw materials also include the following components in parts by weight: N,N-Dimethylformamide: 340-360 parts; Organic bismuth catalyst: 0.04-0.06 parts; Methanol: 0.15-0.25 parts.
3. The formulation for a hydrolysis-resistant polyurethane synthetic leather according to claim 1, characterized in that, The preparation method of the dimer acid polyester polyol includes: The product is prepared by first esterification of dimer fatty acids and 1,6-hexanediol under the catalysis of tetrabutyl titanate at 160-235℃, followed by polycondensation under vacuum ≥-0.095MPa and temperature 230-235℃. The dimer fatty acid polyester polyol has a hydroxyl value of 35.1-37.4mgKOH / g and a number-average molecular weight Mn of 2995-3190g / mol.
4. The formulation for a hydrolysis-resistant polyurethane synthetic leather according to claim 1, characterized in that, The formulation also includes additives for preparing impregnation or coating slurries, said additives comprising, based on 100 parts by weight of polyurethane resin slurry: Lignin powder: 4.5-5.5 parts; Black paste: 2.8-3.2 parts; Organosilicon leveling agent: 0.4-0.6 parts.
5. The formulation for a hydrolysis-resistant polyurethane synthetic leather according to claim 1, characterized in that, The purity of the 2-butyl-2-ethyl-1,3-propanediol is ≥99.0%; the epoxy value of the epoxidized linseed oil is ≥9.0%.
6. A method for preparing hydrolysis-resistant polyurethane synthetic leather as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix dimer polyester polyol, epoxy linseed oil and castor oil, and heat and stir until a homogeneous, transparent hydrophobic mixture is formed. S2. Add poly(1,4-butene adipate) to the hydrophobic mixture, mix evenly, and then perform vacuum dehydration to obtain a dehydrated polyol mixture. S3. Lower the temperature of the polyol mixture, add diphenylmethane diisocyanate to react, and obtain a polyurethane prepolymer. S4. Cool the polyurethane prepolymer and add N,N-dimethylformamide to dissolve it. Add chain extender solution and organic bismuth catalyst to carry out chain extension reaction. Terminate the reaction when the predetermined viscosity is reached to obtain hydrolysis resistant polyurethane resin slurry. S5. Add lignin powder, black paste and organosilicon leveling agent to the hydrolysis-resistant polyurethane resin slurry, disperse evenly and use it as impregnation slurry and coating slurry. Combine with base fabric and perform wet coagulation, water washing and drying to obtain the hydrolysis-resistant polyurethane synthetic leather.
7. The method for preparing hydrolysis-resistant polyurethane synthetic leather according to claim 6, characterized in that, In step S1, the heating and stirring temperature is 65-70℃, and the time is 40-50 minutes; In step S2, the temperature of the vacuum dehydration treatment is 105-110℃, the vacuum degree is controlled between -0.095MPa and -0.098MPa, and the dehydration is carried out until the moisture content of the polyol mixture is ≤0.025%.
8. The method for preparing hydrolysis-resistant polyurethane synthetic leather according to claim 6, characterized in that, In step S3, diphenylmethane diisocyanate is added after cooling to 60-65℃, and the reaction temperature is controlled at 80-85℃ until the isocyanate group content reaches 6.5%-7.3%.
9. The method for preparing hydrolysis-resistant polyurethane synthetic leather according to claim 6, characterized in that, In step S4, N,N-dimethylformamide is added to dissolve the product at a temperature of 45-50°C, and the chain extension reaction temperature is controlled at 70-75°C; the predetermined viscosity is 45,000-58,000 mPa·s; methanol is added to terminate the reaction.
10. The method for preparing hydrolysis-resistant polyurethane synthetic leather according to claim 6, characterized in that, In step S5, the coagulation bath for wet coagulation is an aqueous solution of N,N-dimethylformamide with a concentration of 18%-22%, and the coagulation temperature is 25-30℃. The coating amount of the coating slurry is 140-160 g / m³. 2 .