Super-hydrophobic modified polyurethane leather and preparation method thereof

Abstract

The invention relates to the technical field of polyurethane leather surface treatment, in particular to super-hydrophobic modified polyurethane leather and a preparation method thereof. The super-hydrophobic modified polyurethane leather comprises a soft polyurethane inner layer and a hard functional outer layer, and the hard functional outer layer contains polyion liquid brush grafted SiO2 to form a gradient structure with the SiO2 content decreasing gradually from outside to inside. According to the invention, the defect that SiO2 is easy to settle in a polyurethane gel layer is changed by grafting SiO2 with a polyion liquid brush, a reasonable process window is provided through competition between a steric hindrance-chemical anchoring synergistic slow sinking mechanism and polyurethane gelation kinetics and in combination with the selection of a chain extender BDO with moderate reaction activity, and the preparation method has the advantages of simple process, low cost and high efficiency. And the viscosity and the NCO value of a gel point are conveniently and accurately controlled, so that a novel leather surface modification process is realized, and a novel leather structure with a soft inner layer, gradient hardness distribution of an outer layer and a hydrophobic surface is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polyurethane leather surface treatment, and particularly relates to a super-hydrophobic modified polyurethane leather and a preparation method thereof. BACKGROUND

[0002] Polyurethane leather is widely used in furniture, automotive interiors, shoe materials and electronic product packaging fields due to its excellent wear resistance, flexibility and designability. However, the traditional polyurethane leather faces many challenges in long-term use: firstly, its surface is easily infiltrated and attached by water, oil stains and dirt, and it is difficult to clean and maintain; secondly, the surface hardness is insufficient, easy to scratch, and lacks the gradient hand feeling of "hard outside and soft inside" similar to natural leather; thirdly, the humid environment easily becomes a breeding ground for microorganisms (such as bacteria and mold), causing health and safety hazards.

[0003] To improve the surface performance, some technologies often use the addition of nano-particles (such as SiO2) to construct a rough surface to achieve super-hydrophobicity, or blend antibacterial agents to give antibacterial function. However, these methods have inherent defects:

[0004] (1) Conflict between function and bulk performance: simple blending of nano-SiO2 is easy to cause uneven distribution due to agglomeration and rapid sedimentation, not only difficult to effectively enrich on the surface to construct a stable super-hydrophobic layer, but also to destroy the internal elastic network of the polyurethane matrix, leading to material embrittlement or hard spots in the inner layer, losing flexibility.

[0005] (2) Difficulty in achieving gradient structure: achieving continuous gradient transition from high surface hardness to high internal elasticity is the key to simulating the hand feeling of natural leather, and balancing durability and comfort. Conventional coating or blending technology cannot accurately control the spatial distribution of fillers during the curing process, and cannot form a stable gradient structure.

[0006] (3) Difficulty in multi-functional synergy: super-hydrophobicity, high hardness and antibacterial properties are derived from different mechanisms, often requiring the addition of multiple functional additives, which easily leads to poor compatibility between components, complex interfaces, affecting the comprehensive performance and long-term stability of the material.

[0007] Therefore, developing a new type of material that can internally synergize to achieve super-hydrophobicity, significant hardness gradient and high-efficiency antibacterial properties without sacrificing the excellent mechanical properties of the polyurethane matrix has become a technical problem that needs to be broken through in this field. The key is to design a new type of functional filler that can be well compatible with the polyurethane matrix and can spontaneously form a gradient structure through controllable migration / anchoring behavior. SUMMARY

[0008] The present application aims to solve the problems in the prior art and provides a super-hydrophobic modified polyurethane leather and a preparation method thereof.

[0009] In order to achieve the above object, the present application adopts the following technical solutions:

[0010] The super-hydrophobic modified polyurethane leather comprises a soft polyurethane inner layer and a hard functional outer layer, and the hard functional outer layer contains poly ionic liquid brush grafted SiO2 (PIL-g-SiO2), forming a gradient structure with a decreasing SiO2 content from outside to inside.

[0011] The surface water contact angle of the hard functional outer layer is >150°, the Shore A hardness gradient difference is ΔShoreA≥30, and the antibacterial rate is >99%.

[0012] The soft polyurethane inner layer comprises the following components by weight:

[0013] 100 parts of high NCO polyurethane, 5-8 parts of chain extender;

[0014] The hard functional outer layer comprises the following components by weight:

[0015] 100 parts of poly ionic liquid brush grafted SiO2, 20-30 parts of low NCO polyurethane, and 1.5-2 parts of chain extender.

[0016] Preferably, the high NCO polyurethane is an NCO content of 15-20% NCO-terminated polyurethane prepolymer [colorless transparent viscous liquid, Wuhan Kemik Biomedical Technology Co., Ltd., both ends of which are NCO; it is prepared by reacting polytetrahydrofuran ether glycol (PTMEG, Mn=1000±100) and 4,4'-diphenyl methane diisocyanate (MDI) at a molar ratio of 1:1.3, catalyzed by dibutyltin dilaurate (DBTDL), at 80±2℃ for 2-2.5h, with a viscosity of 3000-4000mPa·s (80℃), and needs to be stored under sealed, light-proof, and low-temperature (<40℃) conditions].

[0017] Preferably, the low NCO polyurethane is an NCO content of 3-5% NCO-terminated polyurethane prepolymer [colorless transparent viscous liquid, Wuhan Kemik Biomedical Technology Co., Ltd., both ends of which are NCO; it is prepared by reacting polytetrahydrofuran ether glycol (PTMEG, Mn=1000±100) and 4,4'-diphenyl methane diisocyanate (MDI) at a molar ratio of 1:1.05, catalyzed by dibutyltin dilaurate (DBTDL), at 80±2℃ for 1.8-2.2h, with a viscosity of 2700-3800mPa·s (80℃), and needs to be stored under sealed, light-proof, and low-temperature (<40℃) conditions];

[0018] Preferably, the chain extender is 1,4-butanediol (BDO);

[0019] Other chain extenders are not suitable for the present application due to their low reactivity:

[0020] Amine chain extender (such as diethyltoluene diamine DETDA, Moca MOCA) forms urea bond with polyurethane prepolymer, high strength, high modulus, good heat resistance, but may lead to too rigid gel layer; its reaction activity is extremely high, the reaction speed is too fast (seconds), the viscosity increases instantaneously, the process window is very narrow, which is not suitable for the present scheme which needs to accurately control the coating time;

[0021] Low molecular weight polyether diol (such as PPG with a molecular weight of 200-400) has lower reaction activity, although it has better flexibility, but the initial strength is established slowly, and the obtained gel layer is softer.

[0022] Small molecule diol (such as 1,4-butanediol BDO, ethylene glycol EG) has moderate reaction activity, forms urethane bond with polyurethane prepolymer, has moderate strength and good flexibility. BDO is the most commonly used chain extender, which can form regular hard segment microdomains to provide good comprehensive performance; the reaction speed is controllable (several minutes to tens of minutes), which can provide a suitable process window to monitor NCO% and viscosity.

[0023] Preferably, the polyionic liquid brush grafted SiO2 comprises the following raw materials by weight:

[0024] 5-20 parts of nano-SiO2 particles with a particle size of 20-50 nm, 1-5 parts of γ-methacryloxypropyltrimethoxysilane, 10-50 parts of 1-vinylimidazole, 10-70 parts of 2-bromoethanol and 0.05-0.1 parts of azobis isobutyronitrile.

[0025] Further, the synthesis steps of the polyionic liquid brush grafted SiO2 are as follows:

[0026] (1) Preparation of silane modified SiO2

[0027] SiO2 particles and γ-methacryloxypropyltrimethoxysilane are added to a mixed solution of ethanol and water, the pH of the mixed solution is adjusted to 3-5 by hydrochloric acid, then heated to 50-70℃ and stirred for 6-12h, centrifuged and washed several times with ethanol, and dried to obtain silane modified SiO2, which is ready for use;

[0028] Mechanism reference Figure 1 Through acid catalytic hydrolysis-condensation (pH 3-5), the hydrolysis of silane coupling agent (MPS) is accelerated in an acidic environment to generate highly active silanol (Si-OH), and the condensation reaction of silanol with the surface hydroxyl group of SiO2 is promoted to form a firm Si-O-Si covalent bond, thereby grafting γ-methacryloxypropyltrimethoxysilane on the surface of SiO2, which has the following characteristics:

[0029] ①The generated methoxysilicon hydrolysis generates Si-OH, which can react with the condensation reaction of SiO2 surface hydroxyl to form a firm Si-O-Si covalent bond;

[0030] ②With double bond, copolymerization with subsequent 1-vinylimidazole ionic liquid monomer to generate polymer grafted SiO2;

[0031] ③γ-methacryloyloxypropyltrimethoxysilane has a propyl chain: -(CH2)3-, according to previous research, the propyl chain realizes the dynamic "elastic" nature through C-C bond rotation, which can increase the impact resistance of the hard functional outer layer.

[0032] (2) Preparation of ionic liquid monomer:

[0033] Stir 1-vinylimidazole and 2-bromoethanol at 80℃ for 12-36h to obtain an ionic liquid monomer solution;

[0034] Mechanism reference Figure 2 , through the quaternary ammonium reaction of 1-vinylimidazole (containing tertiary amine nitrogen atom and vinyl group) and 2-bromoethanol (containing halogenated alkyl and hydroxyl group) under heating (80℃); the tertiary amine nitrogen atom (usually N-3) with strong nucleophilicity in 1-vinylimidazole molecule attacks the carbon atom (connected with Br) of 2-bromoethanol, Br - leaves as a leaving group to generate 1-(2-hydroxyethyl)-3-vinylimidazolium bromide ion (abbreviated as [VHEIm]Br), which is an ionic liquid monomer (monomer synthesis), this reaction generates a new monomer [VHEIm]Br with vinyl group (CH2=CH-) and quaternary ammonium cation (-N + -), and hydroxyl group (-OH), which has the following characteristics:

[0035] ①The vinyl group retains the polymerization ability: the generated ionic liquid monomer contains vinyl group, which copolymerizes with SiO2 grafted with γ-methacryloyloxypropyltrimethoxysilane to obtain olefin copolymer, realizing in-situ polymerization reaction on SiO2;

[0036] ②The quaternary ammonium cation (-N + -) has the general characteristics of ionic liquid, which can promote the solubility of SiO2 in the polyurethane system, and also provides excellent antibacterial properties of the surface layer;

[0037] ③The hydroxyl group (-OH) can provide certain hydrophilicity, and also can react with the excess -NCO in the polyurethane system, realizing the anchoring effect of SiO2 in the polyurethane system during the reaction process;

[0038] (3) Synthesis of polyionic liquid brush grafted SiO2:

[0039] In the ionic liquid monomer solution, silane modified SiO2, azobisisobutyronitrile and acetone are added, the amount of acetone accounts for 30% of the total weight of the system, heated to 70-80℃ backflow reaction for 8-12h, finally dried at 80℃ under vacuum to white powder, get poly ionic liquid brush grafted SiO2, mechanism reference Figure 3 .

[0040] The final purpose of the application is to use SiO2 in the contradiction of polyurethane system gravity settlement and dissolution dispersion and chemical anchoring reaction, reduce the settlement rate of SiO2, so as to form the process that the content of SiO2 gradually decreases from the surface to the inside of polyurethane, that is, the hardness of the hard functional outer layer gradually decreases from the surface to the inside, therefore, the introduction of ionic liquid and hydroxyl group is very important to the application, the ionic liquid can promote the uniformity of SiO2 dispersion, the hydroxyl group can improve the reaction rate, that is, the anchoring reaction makes SiO2 suspended, under the action of gravity in the opposite direction, the settlement of SiO2 is slow, otherwise, according to the existing unmodified SiO2, it is impossible to form high hardness on the surface, instead, a large amount of SiO2 penetrates into the main body of the gel and destroys the elasticity of the main body, which is the fundamental reason why the application is designed in this way.

[0041] In addition, according to previous research, introducing polymer brush structure (poly ionic liquid brush) with specific function (ionicity, hydrophilicity / hydrophobicity, reactive hydroxyl group, etc.) on the surface of modified SiO2 may cause the settlement speed of SiO2 to be slower, which is not studied in depth here.

[0042] The application also provides a preparation method of the super-hydrophobic modified polyurethane leather.

[0043] S1, preparing a gel layer

[0044] The high NCO polyurethane is heated to 80℃, and the chain extender is uniformly and slowly added under high speed stirring of 500-800 rpm within 30-60 s, and the process needs to be kept good stirring to prevent local crosslinking too fast;

[0045] The temperature and stirring are kept, and the sample is taken every 1-2 min for titration until the NCO% is reduced to 7±1%, and the NCO% is determined by chemical titration method of di-n-butylamine;

[0046] When the NCO% is reduced to 7±1%, the viscosity is monitored by using a rotary viscometer, and when the viscosity reaches 20,000-40,000 mPa·s (80℃), it is the best coating point, at this time, the material should be in "stringing" state, and the reaction is immediately stopped, and the material is quickly injected into a mold preheated to 100-105℃, and the injection process should be completed within 1-2 min, and this step requires rapidness to prevent the material from gelling in the kettle;

[0047] S2, preparation of coating slurry

[0048] Mixing the polyionic liquid brush grafted SiO2, low NCO polyurethane and chain extender at room temperature under high speed stirring at 500-800 rpm to obtain a coating slurry;

[0049] S3, coating gradient layer

[0050] After the gel layer is injected into the mold, continue to heat the mold at 100-105°C for 1-2 min, at this time the surface of the material should lose fluidity, but it still feels sticky and can leave marks with a fine needle, at this time the reaction will continue at high temperature, the viscosity will further increase, and there are a large number of high activity -NCO groups on the surface, but the whole can support the second layer of material;

[0051] Continue to inject the coating slurry on the surface of the gel layer, and heat at 100-105°C for 4-5 min to allow the coating slurry system to have a short pre-reaction and SiO2 preliminary settlement / anchoring process to prevent the material from being excessively squeezed and damaged during the cover pressing;

[0052] S4, pressurized vulcanization

[0053] Cover film, pressurized to 1-5 MPa, heat at 110°C for 0.5-1 h;

[0054] The purpose of pressurization is to inhibit foaming (due to the possible generation of CO2), increase the density of the product, and promote the fusion between the two layers, and the pressure size needs to be balanced: if the pressure is too small, the product will have bubbles and be not dense; if the pressure is too large, the SiO2 gradient distribution formed may be damaged.

[0055] S5, secondary vulcanization

[0056] Release pressure, adjust the temperature to 100-105°C, and heat for 5-10 h to obtain the super-hydrophobic modified polyurethane leather product;

[0057] Secondary vulcanization is a very critical post-curing step in the polyurethane process, which aims to allow the unreacted -NCO groups to continue to react, so that the crosslinked network is perfected, thereby stabilizing the final size of the product, eliminating internal stress, and maximizing the mechanical properties, and the time and temperature need to be adjusted according to the thickness of the product.

[0058] In this process, the gel layer is cured as a soft polyurethane inner layer with a hardness of Shore A 65-75; and during the curing process, the polyionic liquid brush grafted SiO2 in the gradient layer slowly settles into the gel layer, and the gradient layer gradually diffuses and extends to the gel layer, with a diffusion thickness of 0.5-2 mm (related to the SiO2 particle size and the viscosity of the gel layer), and after curing, a hard functional outer layer with a thickness of about 1-3 mm is formed, with a surface hardness of Shore D 50-65.

[0059] The polyionic liquid brush improves the dispersibility of SiO2 in the polyurethane system through its quaternary ammonium cation, and the anchoring chemical reaction of its terminal hydroxyl group with the excess isocyanate group (-NCO) in the gel layer, the mechanism is referred to Figure 4 , and the synergistic effect of the two significantly slows down the settling rate of SiO2 particles.

[0060] The competition between the slow settling rate of SiO2 and the gelation process of polyurethane makes the SiO2 particles form a gradient distribution in the outer polyurethane system, with the content gradually decreasing from the surface to the inside, and then realize the gradient transition of the leather hardness from the surface to the inside, and the structure is shown as Figure 5 .

[0061] Preferably, the injection amount of the coating slurry in S3 is 400-450g / m 2 , and the thickness of the gradient layer (i.e. the coating thickness) is 0.5-1mm.

[0062] Compared with the prior art, the beneficial effects of the present application are:

[0063] 1. The present application adopts polyionic liquid brush grafted SiO2 to change the defect that SiO2 is easy to settle in the polyurethane gel layer, and through the synergistic slow settling mechanism of steric hindrance-chemical anchoring and the competition with the gelation kinetics of polyurethane, and by selecting a chain extender BDO with moderate reactivity, a reasonable process window is provided to accurately control the viscosity and NCO value at the gel point, thereby realizing a new type of leather surface modification process, and realizing a new type of leather structure with soft inner layer, gradient hardness distribution of outer layer, and surface hydrophobicity.

[0064] 2. The present application realizes the following product performance by the ingenious synergy of polyionic liquid brush grafted SiO2 (PIL-g-SiO2) and step-by-step reaction forming process:

[0065] (1) Excellent superhydrophobic performance (water contact angle > 150°)

[0066] The present application successfully constructs a stable micro-nano composite rough structure through the preferential enrichment of PIL-g-SiO2 in the outermost layer of leather. Among them, the nano-SiO2 particles provide primary nano-scale roughness, and the grafted polyionic liquid brush can contribute secondary micro-roughness due to the stacking and swinging of its molecular chain. At the same time, the polyionic liquid itself has a relatively low surface energy. The organic combination of "micro-nano rough structure" and "low surface energy chemical components" together realizes a static water contact angle of more than 150°, which endows the leather with excellent stain resistance and self-cleaning properties.

[0067] (2) Significant hardness gradient (ΔShoreA≥30)

[0068] The gradient hardness outer layer is realized by the synergistic slow-sedimentation mechanism of steric hindrance-chemical anchoring of PIL-g-SiO2:

[0069] Steric hindrance effect: The polyionic liquid brushes grafted on the surface of SiO2 fully stretch in the polyurethane system, generating a huge steric hindrance, effectively preventing the agglomeration and rapid sedimentation of SiO2 particles.

[0070] Chemical anchoring effect: The hydroxyl groups (-OH) at the end of the PIL brush can covalently bond with the excess isocyanate groups (-NCO) during the gelation process of the soft polyurethane inner layer, like throwing down a "chemical anchor", anchoring the SiO2 particles in the forming polymer network.

[0071] Gradient formation: The above dual effects significantly slow down the sedimentation rate of SiO2 particles under gravity. During the holding period after coating, the slow-sedimentation PIL-g-SiO2 particles compete with the rapidly gelling polyurethane system, ultimately resulting in a continuous gradient distribution of SiO2 particles with decreasing concentration from the outside to the inside. SiO2, as a rigid particle, its concentration gradient directly translates into a gradient transition of hardness, thus achieving a perfect combination of high surface hardness (Shore D 50-65) and high elasticity of the inner layer (Shore A 65-75), with a hand feel similar to natural leather.

[0072] (3) High and durable antibacterial property (antibacterial rate > 99%)

[0073] The antibacterial property comes from the quaternary ammonium cations in the polyionic liquid brush. These positively charged cations can adsorb negatively charged bacterial cell membranes through electrostatic interactions, thereby destroying the membrane structure and causing cell content leakage, thus achieving efficient physical sterilization. This mechanism is less likely to induce microbial resistance, and since the polyionic liquid is covalently grafted on SiO2 and solidified into a film, it is less likely to migrate and lose, ensuring the durability of the antibacterial effect.

[0074] (4) Excellent comprehensive mechanical properties and structural stability

[0075] Since the gradient distribution of PIL-g-SiO2 is controllable and natural, it avoids the chaotic distribution of rigid fillers in the matrix, maximizing the softness and flexibility of the underlying polyurethane. At the same time, the step vulcanization process of pressurized vulcanization + secondary vulcanization ensures the full and perfect crosslinking network, eliminates internal stress, and makes the product structure dense and dimensionally stable, with optimal mechanical properties.

[0076] (5) Good process controllability and reproducibility

[0077] The chain extender BDO with moderate reactivity provides a reasonable process window, which is convenient for precisely controlling the viscosity and NCO value of the gel point. The heat preservation step after coating provides a key time for the gradient self-assembly of SiO2, and the subsequent pressurization and two-stage vulcanization ensure the macro quality of the product and the final stability of the network, respectively. The whole process design is scientific, and each step is linked together, which ensures the stability and reproducibility of the performance of the final product.

[0078] 3. In summary, the present application ingeniously solves the contradiction between multi-functional integration and material intrinsic performance through molecular structure design and process innovation, successfully prepares a high-value-added polyurethane leather material with super-hydrophobicity, significant hardness gradient, high-efficiency antibacterial property and good mechanical property, and has broad industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 The preparation reaction formula of the silane-modified SiO2 proposed in the present application is as follows:

[0080] Figure 2 The preparation reaction formula of the ionic liquid monomer proposed in the present application is as follows:

[0081] Figure 3 The synthesis reaction formula of the poly ionic liquid brush grafted SiO2 proposed in the present application is as follows:

[0082] Figure 4 The anchoring chemical reaction principle diagram of the poly ionic liquid brush grafted SiO2 in the gel layer in the present application is as follows:

[0083] Figure 5 The gradient structure schematic diagram of the SiO2 content in the hard functional outer layer in the present application is as follows. DETAILED DESCRIPTION

[0084] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the prior known technologies. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0085] I. Synthesis of poly ionic liquid brush grafted SiO2

[0086] Preparation Example 1

[0087] SiO2 particles and γ-methacryloyloxypropyltrimethoxysilane were added to an ethanol and water mixed solution, the pH of the mixed solution was adjusted to 3-5 by using hydrochloric acid, then heated to 50℃ and stirred for 12h, centrifuged and washed several times with ethanol, and dried to obtain silane-modified SiO2, which was ready for use;

[0088] The 1-vinylimidazole and 2-bromoethanol were stirred at 80°C for 36h, then the silane-modified SiO2, azobisisobutyronitrile and acetone were added, the amount of acetone was 30% of the total weight of the system, heated to 70°C reflux reaction for 12h, and finally dried at 80°C under vacuum to white powder to obtain the poly-ionic liquid brush grafted SiO2.

[0089] The poly-ionic liquid brush grafted SiO2 included SiO2 particles (particle size of 500nm) 5kg, γ-methacryloyloxypropyltrimethoxysilane 1kg, 1-vinylimidazole 10kg, 2-bromoethanol 10kg and azobisisobutyronitrile 0.05kg.

[0090] Preparation Example 2

[0091] The SiO2 particles and γ-methacryloyloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water, the pH of the mixed solution was adjusted to 3-5 using hydrochloric acid, then heated to 60°C and stirred for 9h, centrifuged and washed several times with ethanol, and dried to obtain the silane-modified SiO2, which was used as prepared;

[0092] The 1-vinylimidazole and 2-bromoethanol were stirred at 80°C for 24h, then the silane-modified SiO2, azobisisobutyronitrile and acetone were added, the amount of acetone was 30% of the total weight of the system, heated to 75°C reflux reaction for 10h, and finally dried at 80°C under vacuum to white powder to obtain the poly-ionic liquid brush grafted SiO2.

[0093] The poly-ionic liquid brush grafted SiO2 included SiO2 particles (particle size of 500nm) 12kg, γ-methacryloyloxypropyltrimethoxysilane 3kg, 1-vinylimidazole 30kg, 2-bromoethanol 40kg and azobisisobutyronitrile 0.08kg.

[0094] Preparation Example 3

[0095] The SiO2 particles and γ-methacryloyloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water, the pH of the mixed solution was adjusted to 3-5 using hydrochloric acid, then heated to 70°C and stirred for 6h, centrifuged and washed several times with ethanol, and dried to obtain the silane-modified SiO2, which was used as prepared;

[0096] The 1-vinylimidazole and 2-bromoethanol were stirred at 80°C for 12h, then the silane-modified SiO2, azobisisobutyronitrile and acetone were added, the amount of acetone was 30% of the total weight of the system, heated to 80°C reflux reaction for 8h, and finally dried at 80°C under vacuum to white powder to obtain the poly-ionic liquid brush grafted SiO2.

[0097] The polyionic liquid brush-grafted SiO2 comprises 20 kg of SiO2 particles (500 nm in diameter), 5 kg of γ-methacryloyloxypropyltrimethoxysilane, 50 kg of 1-vinylimidazolium, 70 kg of 2-bromoethanol, and 0.1 kg of azobisisobutyronitrile.

[0098] Comparative Preparation Example 1

[0099] The formulation and steps were the same as those in Preparation Example 2, except that hydrochloric acid was not added to adjust the pH, and the pH of the mixed solution was tested to be 7.1.

[0100] Comparative Preparation Example 2

[0101] The formulation and steps are basically the same as those in Preparation Example 2, except that 2-bromoethanol is not added, and the steps are as follows:

[0102] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixed solution of ethanol and water. The pH of the mixed solution was adjusted to 3-5 using hydrochloric acid. The solution was then heated to 60°C and stirred for 9 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2 for later use.

[0103] 1-Vinylimidazole was added to silane-modified SiO2, azobisisobutyronitrile, and acetone, with acetone accounting for 30% of the total weight of the system. The mixture was heated to 75°C and refluxed for 10 hours. Finally, it was vacuum dried at 80°C to obtain a white powder, thus obtaining polyionic liquid brush-grafted SiO2.

[0104] Comparative preparation example 3

[0105] The formulation and steps are basically the same as those in Preparation Example 2, except that 1-vinylimidazole and 2-bromoethanol are not added. The steps are as follows:

[0106] SiO2 particles and γ-methacryloxypropyltrimethoxysilane were added to a mixture of ethanol and water. The pH of the mixture was adjusted to 3-5 using hydrochloric acid. The mixture was then heated to 60°C and stirred for 9 hours. After centrifugation, the mixture was washed several times with ethanol and dried to obtain silane-modified SiO2, which directly replaced the polyionic liquid-grafted SiO2 in the coating slurry in equal amounts.

[0107] Comparative preparation example 4

[0108] The polyionic liquid grafted with SiO2 in the coating slurry was directly replaced with an equal amount of SiO2 particles.

[0109] II. Preparation of Superhydrophobic Modified Polyurethane Leather

[0110] Example 1

[0111] formula:

[0112] The flexible polyurethane inner layer comprises the following components in parts by weight:

[0113] High NCO polyurethane 100 parts, chain extender 5 parts; high NCO polyurethane is NCO content of 15% end NCO polyurethane prepolymer, chain extender is BDO;

[0114] The hard functional outer layer comprises the following components by weight:

[0115] Polyionic liquid brush grafted SiO2 (preparation example 1) 100 parts, low NCO polyurethane 30 parts, chain extender 2 parts, low NCO polyurethane is NCO content of 3% end NCO polyurethane prepolymer.

[0116] Preparation method:

[0117] S1, preparation of gel layer

[0118] The high NCO polyurethane is heated to 80℃, and the chain extender is added uniformly and slowly under high speed stirring of 500-800 rpm within 30-60 s, and good stirring should be maintained during the process to prevent local crosslinking from being too fast.

[0119] The temperature and stirring are maintained, and the sample is titrated every 1-2 min until the NCO% is reduced to 7±1%, and the NCO% is determined by chemical titration method with di-n-butylamine;

[0120] When the NCO% is reduced to 7±1%, the viscosity is monitored using a rotary viscometer, and when the viscosity reaches 20,000-40,000 mPa·s (80℃), the reaction is immediately stopped, and the material is quickly injected into a mold preheated to 100-105℃, and the injection process should be completed within 1-2 min;

[0121] S2, preparation of coating slurry

[0122] The polyionic liquid brush grafted SiO2, low NCO polyurethane and chain extender are mixed at room temperature under high speed stirring of 500-800 rpm to obtain the coating slurry;

[0123] S3, coating gradient layer

[0124] After the gel layer is injected into the mold, continue to heat at 100℃ for 2 min, and then inject the coating slurry onto the surface of the gel layer, and the injection amount of the coating slurry is 400 g / m 2 , and heat at 100℃ for 5 min;

[0125] S4, pressurized vulcanization

[0126] Cover film, pressurized to 1 MPa, and heat at 110℃ for 1 h;

[0127] S5, secondary vulcanization

[0128] The pressure was released, the temperature was adjusted to 100℃, and the temperature was kept for 10 h to obtain the super-hydrophobic modified polyurethane leather product.

[0129] Example 2

[0130] Formulation:

[0131] The soft polyurethane inner layer comprises the following components by weight:

[0132] 100 parts of high NCO polyurethane, 6 parts of chain extender; the high NCO polyurethane is an NCO content of 18% NCO-terminated polyurethane prepolymer, and the chain extender is BDO;

[0133] The hard functional outer layer comprises the following components by weight:

[0134] 100 parts of poly ionic liquid brush grafted SiO2 (Preparation Example 2), 25 parts of low NCO polyurethane, and 1.8 parts of chain extender; the low NCO polyurethane is an NCO content of 4% NCO-terminated polyurethane prepolymer.

[0135] Preparation method:

[0136] S1, preparation of the gel layer

[0137] The high NCO polyurethane is heated to 80℃, and the chain extender is uniformly and slowly added within 30-60 s under high-speed stirring of 500-800 rpm; good stirring is required during the process to prevent local rapid crosslinking;

[0138] The temperature and stirring are kept, and the sample is titrated every 1-2 min until the NCO% is reduced to 7±1%; the NCO% is determined by chemical titration of di-n-butylamine;

[0139] When the NCO% is reduced to 7±1%, the viscosity is monitored using a rotary viscometer, and the reaction is stopped immediately when the viscosity reaches 20,000-40,000 mPa·s (80℃); the material is quickly injected into a mold preheated to 100-105℃, and the injection process should be completed within 1-2 min;

[0140] S2, preparation of the coating slurry

[0141] The poly ionic liquid brush grafted SiO2, low NCO polyurethane, and chain extender are mixed at room temperature under high-speed stirring of 500-800 rpm to obtain the coating slurry;

[0142] S3, coating of the gradient layer

[0143] After the gel layer is injected into the mold, the mold is kept at 102℃ for 1.5 min, and the coating slurry is continuously injected onto the surface of the gel layer; the injection amount of the coating slurry is 420 g / m 2 , and the temperature is kept at 102℃ for 4.5 min;

[0144] S4, pressurized vulcanization

[0145] Cover film, pressurized to 3 MPa, keep pressure at 110℃ for 0.7h;

[0146] S5, two-stage vulcanization

[0147] Release pressure, adjust temperature to 102℃, keep temperature for 7h, to obtain super-hydrophobic modified polyurethane leather product.

[0148] Example 3

[0149] Formulation:

[0150] The soft polyurethane inner layer comprises the following components by weight:

[0151] 100 parts of high NCO polyurethane, 8 parts of chain extender; the high NCO polyurethane is an NCO content of 20% NCO-terminated polyurethane prepolymer, and the chain extender is BDO;

[0152] The hard functional outer layer comprises the following components by weight:

[0153] 100 parts of poly ionic liquid brush grafted SiO2 (Preparation Example 3), 20 parts of low NCO polyurethane, and 1.5 parts of chain extender, and the low NCO polyurethane is an NCO content of 5% NCO-terminated polyurethane prepolymer.

[0154] Preparation method:

[0155] S1, preparation of gel layer

[0156] The high NCO polyurethane is heated to 80℃, and the chain extender is uniformly and slowly added within 30-60s under high-speed stirring of 500-800rpm, and good stirring should be maintained during the process to prevent local crosslinking from being too fast;

[0157] The temperature and stirring are maintained, and the sample is titrated every 1-2min until the NCO% is reduced to 7±1%, and the NCO% is determined by chemical titration with di-n-butylamine;

[0158] When the NCO% is reduced to 7±1%, the viscosity is monitored using a rotary viscometer, and when the viscosity reaches 20,000-40,000 mPa·s (80℃), the reaction is immediately stopped, and the material is quickly injected into a mold preheated to 100-105℃, and the injection process should be completed within 1-2min;

[0159] S2, preparation of coating slurry

[0160] The poly ionic liquid brush grafted SiO2, low NCO polyurethane, and chain extender are mixed at room temperature under high-speed stirring of 500-800rpm to obtain the coating slurry;

[0161] S3, coating gradient layer

[0162] After the gel layer was injected into the mold, the mold was continuously kept at 105℃ for 1 min, and the coating slurry was continuously injected onto the surface of the gel layer. The injection amount of the coating slurry was 450 g / m 2 , and kept at 105℃ for 4 min;

[0163] S4, pressurized vulcanization

[0164] The cover film was pressurized to 5 MPa, and kept at 110℃ for 0.5 h.

[0165] S5, two-stage vulcanization

[0166] The pressure was released, the temperature was adjusted to 105℃, and kept for 5 h to obtain the super-hydrophobic modified polyurethane leather product.

[0167] Comparative Example 1

[0168] The polyionic liquid brush grafted SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 1, and the rest was the same as Example 2.

[0169] Comparative Example 2

[0170] The polyionic liquid brush grafted SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 2, and the rest was the same as Example 2.

[0171] Comparative Example 3

[0172] The polyionic liquid brush grafted SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 3, and the rest was the same as Example 2.

[0173] Comparative Example 4

[0174] The polyionic liquid brush grafted SiO2 in Example 2 was replaced with the product of Comparative Preparation Example 4, and the rest was the same as Example 2.

[0175] Comparative Example 5

[0176] The chain extender in Example 2 was replaced with diethyl toluene diamine, and the rest was the same as Example 2.

[0177] Comparative Example 6

[0178] The chain extender in Example 2 was replaced with PPG-400, and the rest was the same as Example 2.

[0179] Comparative Example 7

[0180] The raw material SiO2 of the polyionic liquid brush grafted SiO2 in Example 2 was replaced with SiO2 with a particle size of 100-150 nm, and the rest was the same as Example 2.

[0181] Comparative Example 8

[0182] The raw material 2-bromoethanol for grafting SiO2 with polyionic liquid brush in Example 2 was replaced by bromoethane to obtain a hydroxyl-free ionic liquid monomer, and the rest was the same as Example 2.

[0183] Comparative Example 9

[0184] The injection amount of the coating slurry in Example 2 was replaced by 800 g / m 2 , and the rest was the same as Example 2.

[0185] Comparative Example 10

[0186] The S4, pressurized vulcanization process in Example 2 was cancelled, and the rest was the same as Example 2.

[0187] Comparative Example 11

[0188] The S5, two-stage vulcanization process in Example 2 was cancelled, and the rest was the same as Example 2.

[0189] Comparative Example 12

[0190] The high NCO polyurethane in the soft polyurethane inner layer in Example 2 was replaced by the same low NCO polyurethane as the hard functional outer layer, and the rest was the same as Example 2.

[0191] III. Performance Test

[0192] The leathers of Examples 1-3 and Comparative Examples 1-12 were subjected to the following performance tests:

[0193] 1. Static water contact angle

[0194] Referring to ASTM D7334 “Standard Practice for Evaluating Surface Wettability by Contact Angle Measurements”, a flat, clean, defect-free sample (2 cm x 5 cm) was cut from the finished leather product, and was balanced in a standard laboratory environment (usually temperature 23±2℃, relative humidity 50±10%) for testing with a contact angle measuring instrument.

[0195] 2. Hardness

[0196] Outer layer (hard): ASTM D2240, using a D-type durometer. The D-type durometer was perpendicular to the outer surface of the leather, and enough force was applied to make the foot fully contact the sample, and the hardness value was read after 1 second.

[0197] Inner layer (soft): ASTM D2240, using an A-type durometer. Inner layer hardness (Shore A): The hard functional outer layer was carefully peeled off or cut off with a sharp blade, and the exposed soft inner layer surface was measured with an A-type durometer perpendicular to the inner layer surface.

[0198] Each hardness was measured at least 5 times at different locations of the sample and averaged. The difference in Shore A hardness gradient, ASlioreA, was calculated by converting the surface hardness (Shore D) to an approximate Shore A value and subtracting the measured Shore A value of the inner layer.

[0199] 3. Antibacterial rate

[0200] Reference test standard: ISO 22196 "Measurement of antibacterial activity of plastics and other non-porous surfaces", which is the most commonly used and recognized standard for surface antibacterial properties.

[0201] Sterile test samples (5 cm x 5 cm) were prepared. The test bacteria were Escherichia coli and Staphylococcus aureus to verify broad-spectrum antibacterial properties.

[0202] Inoculation: A certain concentration of bacterial solution (100 μL) was dropped on the surface of the sample, covered with a sterile cover film, and ensured that the bacterial solution uniformly contacted the sample.

[0203] Incubation: The inoculated sample was incubated in a constant temperature and humidity chamber (35°C, >90% RH) for 24 hours.

[0204] Elution and counting: After incubation, the bacteria on the surface of the sample were eluted with a neutralizing solution, diluted and plated on agar plates. At the same time, untreated control samples (such as ordinary polyurethane leather) were set.

[0205] Calculation: Count the number of colonies (CFU) formed by the eluate of the control and experimental samples, and the antibacterial rate calculation formula is:

[0206] (1 - average number of colonies in experimental group / average number of colonies in control group) x 100%

[0207] An antibacterial rate > 99% (i.e. a reduction in logarithmic value of more than 2) indicates strong antibacterial properties. The experiment should be repeated more than 3 times to ensure reproducibility.

[0208] The test results are shown in Table 1 below:

[0209] Table 1. Effect of different formulations and process parameters on leather properties

[0210]

[0211] Data analysis:

[0212] 1. Effect of leather base formula:

[0213] From Table 1, the parameters of Example 2 are in the middle, representing the best overall performance. The PIL-g-SiO2 prepared in Preparation Example 2 has moderate grafting rate and high reactive hydroxyl groups, achieving the best dispersion, anchoring and gradient forming effect. The process parameters (such as holding time, pressure) are also the most balanced, so the highest WCA, ideal hardness gradient (ΔShoreA>30) and perfect interface are obtained.

[0214] The performance of Example 1 and Example 3 is still excellent, proving the rationality of the formula range. Example 1 uses a low NCO outer layer and a low SiO2 / PIL dosage of Preparation Example 1, resulting in slightly lower surface hardness and WCA than the benchmark, as there are fewer crosslinking points and roughness building units on the surface. Example 3 uses a high NCO outer layer and a high SiO2 / PIL dosage of Preparation Example 3, with the highest surface hardness, but the inner layer is also hard due to the high NCO, making the overall leather feel harder and less flexible than Example 2.

[0215] The NCO content of the outer layer and the amount of PIL-g-SiO2 together determine the surface hardening density and micro-nano roughness. The NCO content of the inner layer determines the crosslinking density and hardness of the inner layer. Fine-tuning is needed according to the final application (such as flexible shoe material or stiff table mat). Example 2 is the best balance between flexibility and stiffness.

[0216] 2. Effect of PIL-g-SiO2 synthesis parameters

[0217] Comparative Example 1 does not use pH adjustment, and the WCA and surface hardness decrease significantly, and the gradient becomes poor. Under neutral conditions (pH about 7), the hydrolysis rate of silane coupling agent (MPS) is extremely slow, and the hydrolysis product is prone to self-condensation to form dimers or polymers, rather than reacting with the SiO2 surface hydroxyl groups. This results in extremely low grafting efficiency of MPS on the SiO2 surface. The subsequent polyionic liquid brush grafting amount is insufficient, greatly reducing its dispersibility and anchoring ability, and the performance is between complete modification and no modification.

[0218] Comparative Example 2 has no 2-bromoethanol, and the WCA, hardness, and antibacterial rate decrease significantly. The absence of 2-bromoethanol means that the ionic liquid monomer cannot be synthesized. In the process, the 1-vinylimidazole monomer is directly polymerized onto the SiO2 surface. 1-vinylimidazole is a neutral molecule, and its polymer product does not contain quaternary ammonium salt cations, so the antibacterial property is lost. At the same time, the polymer brush lacks hydroxyl groups (-OH), which cannot perform anchoring reactions, leading to accelerated sedimentation and poor gradient structure. In addition, the hydrophobicity of neutral poly(1-vinylimidazole) brushes is not as good as that of quaternary ammonium salt type polyionic liquids, which also leads to a decrease in WCA.

[0219] Comparative Example 3 without 1-vinylimidazole and 2-bromoethanol, the product completely lost superhydrophobic and antibacterial function, hardness gradient disappeared. This comparative example actually only used SiO2 modified by MPS silanization. MPS only provides a double bond and a flexible chain, without introducing a polyionic liquid brush. Therefore, the material does not have the antibacterial property of quaternary ammonium salt, and the roughness of the surface is only from the original SiO2 particles, which cannot build an effective micro-nano composite structure, and the WCA is only 108°, showing hydrophilicity. At the same time, due to the lack of steric hindrance and anchoring effect of the PIL brush, the dispersion of SiO2 in PU is poor and the sedimentation is fast, which cannot form a gradient.

[0220] Comparative Example 4 without unmodified SiO2, the performance is the worst, compared with Comparative Example 3, due to the absence of MPS, the SiO2 agglomeration is more serious. Unmodified SiO2 is easily agglomerated in the polyurethane system due to van der Waals force, and quickly settles. The results are consistent with the previous analysis: ① The agglomerates cannot form a uniform micro-nano rough structure, and the WCA is low; ② The rapid sedimentation leads to the lack of surface SiO2 (low hardness), and a large amount of SiO2 sinks into the inner layer to form "hard points" (abnormally high inner layer hardness), completely destroying the gradient structure and the inner layer elasticity. This comparison most strongly proves the irreplaceability of PIL-g-SiO2 modification.

[0221] 3. Effect of chain extender and inner layer design

[0222] Comparative Example 5 uses amine chain extender DETDA, the process fails, and the inner layer is too hard. The reaction speed of DETDA with NCO is extremely fast (seconds), much faster than BDO (minutes). After adding, the viscosity of the system rises sharply, and it is impossible to realize controllable stirring, titration and injection molding operation, and the material quickly gels in the kettle, leading to processing failure. Even if forced injection molding, the generated urea bond has high strength and large modulus, resulting in a hard inner layer like plastic (> Shore A 85), completely losing the soft lining function required by leather.

[0223] Comparative Example 6 uses PPG-400 chain extender, the hardness of the inner and outer layers is low, and the overall product is soft. PPG with a molecular weight of 400 is a flexible long-chain molecule, and its reactivity is lower than that of BDO. After participating in chain extension, it is equivalent to introducing a longer flexible soft segment into the molecular chain, which destroys the ability to form regular hard segment microzones by BDO. The crosslinked network strength is slow to build, and the modulus and hardness of the final product are generally low, which cannot meet the hardness requirements of the leather surface.

[0224] The inner layer of Comparative Example 12 uses low NCO polyurethane, which is too soft, and the whole product collapses without support. The core role of the inner layer is to provide support and elasticity. Low NCO polyurethane means that its molecular chain is short, the functionality is low, and the crosslinking density is very low after curing, forming a soft and weak gel network. Such an inner layer cannot support the outer layer, resulting in the whole leather product like a soft and collapsed dough, without shape and no use value. It proves that "soft inner layer" is not the softer the better, but needs to match the support strength of "hard outer layer".

[0225] 4. Effect of leather preparation process parameters

[0226] Comparative Example 7 uses large particle size SiO2 of 100-150 nm, and the WCA and surface hardness decrease significantly. The micro-nano secondary rough structure required for superhydrophobicity requires small-sized nanoparticles (original scheme 20-50 nm) to construct. When the particle size increases to 100-150 nm, the number of particles decreases sharply at the same volume fraction, making it difficult to form a fine enough nanostructure, resulting in a decrease in surface roughness and thus WCA. At the same time, large particles have a stronger tendency to settle under gravity, which is not conducive to the formation of a gradient and surface enrichment, so the surface hardness is also lower.

[0227] Comparative Example 8 uses bromoethane, which has no hydroxyl group, and the surface hardness and gradient effect decrease. This comparison directly verifies the key role of the hydroxyl anchoring mechanism. Using bromoethane instead of 2-bromoethanol, the ionic liquid monomer obtained does not contain a hydroxyl group. Although its polymer brush can still provide steric hindrance to improve dispersion, it lacks the key "grip" of covalent bond anchoring with the gel layer-NCO. This results in the "anchor" not being able to hold the SiO2 particles during the settling process, the settling rate increases, and the transition zone of the gradient formed is shorter and steeper, the amount of SiO2 enriched on the surface decreases, and therefore the surface hardness is insufficient.

[0228] The coating amount of Comparative Example 9 is 800 g / m², which is too high, the surface performance is too high, but the product has increased brittleness. A too thick functional outer layer (thickness > 2 mm) brings extremely high surface hardness and WCA, but causes two problems: (1) the flexibility of the whole leather decreases significantly, and cracks are easily generated in the outer layer when bending; (2) the modulus difference between the outer layer and the inner layer is too large, and the interface is prone to peeling under stress. This shows that the coating amount needs to be within an optimal range to balance the surface performance and overall mechanical properties.

[0229] Comparative Example 10 cancels the pressurized vulcanization, the product has many bubbles and is not dense, and the performance decreases. Pressurized vulcanization has three purposes: ① to suppress bubbles (CO2 may be generated during the reaction or residual solvent volatilization); ② to increase the density; ③ to promote the fusion of the two layers. After canceling the pressurization, there will be a large number of bubbles in the product, and the strength will deteriorate. At the same time, the SiO2 gradient formed during the heat preservation stage after coating will be destroyed due to the slight flow of the material under the pressure-free state.

[0230] Comparative Example 11 cancels the second stage vulcanization, the initial performance is acceptable, but after storage, it deteriorates. The second stage vulcanization is a post-curing process to allow the residual -NCO groups to fully react. Without this step, the crosslinking network is imperfect, and there are unreacted monomers or oligomers inside the product. This leads to the product during storage: ① dimensional shrinkage; ② surface tackiness (small molecule migration); ③ long-term mechanical property degradation. This shows that the second stage vulcanization is essential to obtain stable and final properties.

[0231] 5. Summary

[0232] This series of experiments, through careful design of comparison, from raw material synthesis (PIL-g-SiO2), formula design (chain extender, NCO content) to process flow (coating amount, pressurization, vulcanization) and other multiple dimensions, comprehensively and profoundly verifies the scientificity and necessity of each link in the technical solution of the super-hydrophobic gradient polyurethane leather described in the invention. The core conclusion is that the "steric hindrance + chemical anchoring" synergistic slow sinking mechanism of polyionic liquid brush, combined with the carefully matched polyurethane chemical reaction kinetics and step-by-step processing technology, is the key to realizing the integration of hardness gradient from outside to inside, super-hydrophobicity, and antibacterial and other multifunctional. Deviation in any link will lead to significant decline in the performance of the final product or even failure.

[0233] The above describes only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art, according to the technical solution and inventive concept of the present application, within the technical range disclosed by the present application, makes equivalent replacement or change, should be covered within the protection scope of the present application.

Claims

1. A superhydrophobic modified polyurethane leather, characterized in that, The gradient structure is formed by a soft polyurethane inner layer and a hard functional outer layer containing poly ionic liquid brush grafted SiO2, and the content of SiO2 decreases from outside to inside. The surface water contact angle of the hard functional outer layer is greater than 150°, the Shore A hardness gradient difference is greater than or equal to 30, and the antibacterial rate is greater than 99%. The soft polyurethane inner layer comprises the following components by weight: 100 parts of high NCO polyurethane, 5-8 parts of chain extender; The hard functional outer layer comprises the following components by weight: 100 parts of poly ionic liquid brush grafted SiO2, 20-30 parts of low NCO polyurethane, and 1.5-2 parts of chain extender.

2. The superhydrophobic modified polyurethane leather according to claim 1, characterized in that, The high NCO polyurethane is an NCO content of 15-20% NCO-terminated polyurethane prepolymer.

3. The superhydrophobic modified polyurethane leather according to claim 1, characterized in that, The low NCO polyurethane is an NCO content of 3-5% NCO-terminated polyurethane prepolymer.

4. The superhydrophobic modified polyurethane leather according to claim 1, characterized in that, The chain extender is 1,4-butanediol.

5. The superhydrophobic modified polyurethane leather according to claim 1, characterized in that, The poly ionic liquid brush grafted SiO2 comprises the following raw materials by weight: 5-20 parts of nano SiO2 particles with a particle size of 20-50 nm, 1-5 parts of γ-methacryloyloxypropyltrimethoxysilane, 10-50 parts of 1-vinylimidazole, 10-70 parts of 2-bromoethanol, and 0.05-0.1 parts of azobisisobutyronitrile.

6. The superhydrophobic modified polyurethane leather according to claim 5, characterized in that, The synthesis steps of the poly ionic liquid brush grafted SiO2 are as follows: (1) Preparation of silane modified SiO2 SiO2 particles and γ-methacryloyloxypropyltrimethoxysilane are added to a mixed solution of ethanol and water, the pH of the mixed solution is adjusted to 3-5 with hydrochloric acid, and then heated to 50-70°C and stirred for 6-12h, centrifuged and washed several times with ethanol, and dried to obtain silane modified SiO2; (2) Preparation of ionic liquid monomer: 1-vinylimidazole and 2-bromoethanol are stirred at 80°C for 12-36h to obtain an ionic liquid monomer solution; (3) Synthesis of poly ionic liquid brush grafted SiO2: In the ionic liquid monomer solution, add silane modified SiO2, azobisisobutyronitrile and acetone, the amount of acetone is 30% of the total weight of the system, heat to 70-80°C and reflux for 8-12h, and finally vacuum dried at 80°C to white powder to obtain poly ionic liquid brush grafted SiO2.

7. A process for the preparation of a superhydrophobic modified polyurethane leather according to any one of claims 1-6, characterized in that, The following steps are included: S1, preparation of gel layer The high NCO polyurethane is heated to 80°C, and the chain extender is added uniformly and slowly under high-speed stirring at 500-800 rpm within 30-60s; Maintain temperature and stirring, take sample titration every 1-2 min until NCO% drops to 7±1%; When NCO% drops to 7±1% and viscosity reaches 20,000-40,000 mPa·s, stop the reaction immediately, and quickly inject the material into a mold preheated to 100-105°C, the injection process should be completed within 1-2 min; S2, preparation of coating slurry Poly ionic liquid brush grafted SiO2, low NCO polyurethane and chain extender are mixed at room temperature under high-speed stirring at 500-800 rpm to obtain a coating slurry; S3, coating gradient layer After the gel layer is injected into the mold, continue to heat at 100-105°C for 1-2 min. The coating slurry is continuously injected on the surface of the gel layer, and kept at 100-105℃ for 4-5 min; S4, pressurized vulcanization The cover film is pressurized to 1-5 MPa, and kept at 110℃ for 0.5-1 h; S5, two-stage vulcanization The pressure is released, the temperature is adjusted to 100-105℃, and kept for 5-10 h to obtain the super-hydrophobic modified polyurethane leather product.

8. The method of claim 7, wherein the method is characterized by, The injection amount of the coating slurry in S3 is 400-450 g / m 2 The thickness of the gradient layer is 0.5-1 mm.

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