Preparation method of superfine fiber synthetic leather suitable for manufacturing sports shoe leather

Abstract

The invention discloses a preparation method of superfine fiber synthetic leather suitable for manufacturing sports shoe leather. The preparation method comprises the following steps: step 1, preparing superfine fiber base cloth with a bionic fascia net-shaped structure; step 2, preparing organic silicon modified waterborne polyurethane functional slurry; and step 3, applying the functional slurry to the superfine fiber base cloth through a gradient curing process of three times of coating and two times of drying, and completing bonding, film forming and surface functionalization in one step. Through the synergistic effect of the bionic fascia net-shaped structure and the skin-core structure composite fibers, efficient one-way moisture conduction is achieved, sweat can be rapidly discharged out of a shoe, and the interior of the shoe is kept dry and comfortable in the movement process.

Description

Technical Field

[0001] This invention belongs to the field of synthetic leather technology, and specifically relates to a method for preparing microfiber synthetic leather suitable for manufacturing sports shoe leather. Background Technology

[0002] Microfiber synthetic leather is widely used in the footwear industry due to its properties being close to genuine leather and even superior in some physical properties. However, traditional synthetic leather for athletic shoes faces three core challenges:

[0003] 1. Significant environmental problems: Traditional synthetic leather uses a large amount of organic solvents such as DMF in the production process, causing environmental pollution; the products are difficult to degrade or recycle after disposal, forming "white pollution", which does not meet the requirements of sustainable development.

[0004] 2. Insufficient comfort: During high-intensity exercise, feet tend to produce a lot of sweat. Traditional synthetic leather has poor moisture management and insufficient moisture-wicking properties, resulting in a damp and stuffy environment inside the shoe, affecting wearing comfort and even causing health problems.

[0005] 3. Limited Functionality and Process Pollution: To achieve the function of waterproofing specific areas (such as the toe of shoes), additional post-processing steps (such as film application or coating) are usually required. This increases process complexity and cost, and may involve the use of more solvent-based chemicals. Traditional solvent-based polyurethane processes also have VOC emissions issues.

[0006] Therefore, developing a high-performance athletic shoe leather that is environmentally friendly throughout its entire life cycle, provides excellent dynamic comfort, and can achieve functional integration through cleaning processes has become an urgent need for the industry. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a method for preparing microfiber synthetic leather suitable for the manufacture of sports shoe leather, and the prepared synthetic leather has the advantages of being environmentally friendly, high-performance and having specific functionalities.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing microfiber synthetic leather suitable for manufacturing athletic shoe leather, comprising the following steps:

[0010] Step 1: Prepare an ultrafine fiber substrate with a biomimetic fascia mesh structure, specifically including the following steps:

[0011] Step 11, Fiber Preparation:

[0012] (1) Functional fiber preparation: core-sheath composite fiber, the sheath of which is hydrophilic polyacrylonitrile (PAN) and the core is hydrophobic polyethylene terephthalate (PET).

[0013] (2) Preparation of skeleton fiber: PET is used as the "island" component and water-soluble polyvinyl alcohol (PVA) is used as the "sea" component to form island-type ultrafine fiber;

[0014] (3) Mix the core-sheath composite fiber and the island-type microfiber in a certain proportion and disperse the two fibers evenly;

[0015] Step 12, Web Formation and Preprocessing:

[0016] (1) Web formation: The uniformly mixed fibers are combed by a carding machine so that the fibers are basically arranged in the same direction, and then cross-laid by a web laying machine to form a fiber web with uniform weight and improved anisotropy;

[0017] (2) Preliminary reinforcement: The laid-up fiber web is needle-punched pre-treatment. The surface fibers are pierced into the web with barbed needles to make them entangled with each other to obtain nonwoven fabric.

[0018] (3) Fiber opening treatment: The pre-reinforced nonwoven fabric is subjected to alkali dissolution treatment to remove the "sea" component in the island-type microfiber, leaving bundles of extremely fine PET "island" components;

[0019] Step 13, hot pressing to construct the biomimetic structure:

[0020] The nonwoven fabric after fiber opening is placed in a flat hot press. The hot pressing temperature is set to 180℃±5℃, the pressure is 5-15MPa, and the hot pressing time is 30-90 seconds. A stable three-dimensional skeleton network with a large number of interconnected channels similar to the fascia tissue in the body is formed, and an ultrafine fiber base fabric with a biomimetic fascia mesh structure is prepared.

[0021] Step 2: Prepare silicone-modified waterborne polyurethane functional slurry;

[0022] Step 3: The functional slurry is applied to the microfiber base fabric through a gradient curing process of "three coatings and two bakings" to complete bonding, film formation and surface functionalization in one step.

[0023] In the above technical solution, the specific configuration steps of step 2 include:

[0024] Step 21: Synthesize functional resins using a prepolymer dispersion method;

[0025] Step 22: Add additives to the functional resin, stir evenly, and adjust the viscosity to a suitable range for coating to obtain the functional slurry.

[0026] In the above technical solution, in step 1, the core-sheath composite fiber accounts for 10%-30% of the total mixed fiber mass, and the island-type microfiber accounts for 70%-90% of the total mixed fiber mass.

[0027] In the above technical solution, step 21, the specific synthesis steps of the functional resin include:

[0028] (1) Raw material dehydration pretreatment: In a flask equipped with a stirrer, thermometer, condenser and nitrogen inlet, add metered polycaprolactone polyol (PCL) and dihydroxybutyl polydimethylsiloxane (PDMS-OH) according to the designed molar ratio, and at the same time add a precisely metered small molecule chain extender 1,4-butanediol (BDO). Stir and dehydrate for 1-2 hours under vacuum degree ≥ -0.095MPa and temperature 110-120℃ until the moisture content in the system is less than 0.05%;

[0029] (2) Synthesis of prepolymer: The above dehydrated mixture is cooled to 75-85℃, and under nitrogen protection, a measured amount of diisocyanate is slowly added dropwise, and a small amount of catalyst dibutyltin dilaurate (DBTDL) is added. The reaction is kept at this temperature for 2-3 hours. The content of -NCO groups in the system is monitored by di-n-butylamine titration until the theoretical value is reached. At this time, the -OH of PCL, the -OH of PDMS-OH, and the -OH of BDO have all reacted with the -NCO of IPDI to generate a polyurethane prepolymer with -NCO at the end.

[0030] (3) Cool the system to 40-50℃, add a small amount of hydrophilic chain extender dimethylolpropionic acid (DMPA) dissolved in acetone. The carboxyl group of DMPA reacts with the -NCO at the end of the prepolymer to introduce the hydrophilic group into the polymer chain. After the reaction is complete, add a measured amount of neutralizing agent triethylamine (TEA). TEA reacts with the carboxyl group on DMPA to generate ammonium salt (-COO). - N + (C2H5)3), continue stirring to ensure complete neutralization;

[0031] (4) High-speed emulsification and dispersion: Under high-speed stirring, a measured amount of deionized water is slowly added to the above-neutralized prepolymer mixture to emulsify and form a prepolymer emulsion;

[0032] (5) Post-chain extension in water: A measured amount of aqueous solution of ethylenediamine (EDA), a water-soluble diamine chain extender, is added to the prepolymer emulsion. The amino group (-NH2) of EDA reacts with the -NCO of the prepolymer in the emulsion to form an aqueous polyurethane (WPU) dispersion. Stirring is continued to ensure that the chain extension reaction is complete, and the residual acetone is allowed to evaporate and be removed. Finally, an organosilicon-modified aqueous polyurethane dispersion with a solid content of about 30-40% and stable storage is obtained, which is the functional resin.

[0033] In the above technical solution, in step 22, the additives include leveling agents, defoamers, wetting agents, and color pastes.

[0034] In the above technical solution, step 3, the pasting step specifically involves applying a coating amount of 50-80 g / m². 2 The first coating is applied by coating the functional slurry onto the microfiber base fabric, followed by a first drying at a temperature of 60-70°C. After drying, the slurry is cured on the fiber surface and at the intersections, forming a microscopic "mechanical interlock" that firmly anchors the coating to the fiber.

[0035] In the above technical solution, step 3, the film-forming step specifically involves: a coating amount of 80-120 g / m². 2 The second coating is applied, followed by a second baking at 70-80℃. The polyurethane molecular chains are fully cross-linked to form a dense leather layer, giving the synthetic leather the mechanical properties required, thus completing the "film formation".

[0036] In the above technical solution, step 3, the surface functionalization step specifically involves: applying a coating of 30-50 g / m² to the functional area on the cured coating. 2 Apply the slurry, and then perform a third drying at 70-75°C.

[0037] The above technical solution also includes step 4, chemical recycling: when the synthetic leather product reaches the end of its service life, it is recycled.

[0038] The beneficial effects of this invention are as follows:

[0039] 1. It achieves efficient chemical recycling of synthetic leather products (recovery rate ≥90%), fundamentally solving the problem of waste shoe leather disposal, turning waste into treasure, and conforming to the concept of circular economy.

[0040] 2. Through the synergistic effect of the "bionic fascia mesh structure" and the "skin core composite fiber", efficient one-way moisture wicking is achieved, which can quickly wick away sweat from the inside of the shoe and keep the inside of the shoe dry and comfortable during exercise.

[0041] 3. The "one-step water-based gradient bonding and surface functionalization" process combines multiple processing steps into one, simplifying the production process, reducing costs, and enabling precise customization of product functions (such as hydrophobic toe caps). This integrated molding technology represents a significant breakthrough in manufacturing processes. Detailed Implementation

[0042] To better illustrate the objectives, technical solutions, and advantages of this invention, the invention will be further described below in conjunction with specific embodiments. This invention can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. This invention will be defined only by the claims.

[0043] This invention discloses a method for preparing microfiber synthetic leather suitable for sports shoe manufacturing. This method is a complete and coherent process, from base fabric preparation and integrated functional coating processing to imparting recyclable properties to the product. Its core lies in transforming material design, structural innovation, and environmental protection concepts into a mass-producible product through a series of precisely controlled steps. Specifically, it includes the following steps:

[0044] Step 1: Prepare an ultrafine fiber substrate with a biomimetic fascia mesh structure, which includes three parts: fiber preparation, web formation and pretreatment, and hot pressing to construct the biomimetic structure.

[0045] Step 11, Fiber Preparation: This step aims to prepare a blend of two complementary fibers to provide a raw material basis for constructing a base fabric with high specific surface area, good mechanical strength, and unidirectional moisture wicking function.

[0046] (1) Functional fiber preparation: core-sheath composite fiber, the sheath of which is hydrophilic polyacrylonitrile (PAN) and the core is hydrophobic polyethylene terephthalate (PET). This structural design utilizes the different affinities of the two polymers for water to achieve directional water transport.

[0047] (2) Preparation of skeleton fiber: used to form the island-type ultrafine fiber with high porosity, with PET as the "island" component and water-soluble polyvinyl alcohol (PVA) as the "sea" component.

[0048] (3) Weigh (1) and (2) precisely according to the proportion and mix them. Use an opening machine to fully open and mix them to ensure that the two fibers are evenly dispersed.

[0049] According to the technical solution and implementation requirements of the present invention, the specific range of fiber mixing ratios is as follows:

[0050] Core-sheath structure PAN-PET composite fiber (functional fiber): accounts for 10% - 30% of the total mass of the blended fiber.

[0051] Island-type microfiber (skeleton fiber): accounts for 70% - 90% of the total mass of blended fibers.

[0052] In practice, adjustments can be made within this range based on the performance priorities of the final product. For a focus on dryness and comfort: a ratio close to 30% can be selected to enhance moisture wicking. For a focus on high strength, abrasion resistance, and morphological stability: a ratio close to 10% can be selected to ensure a dense and robust framework.

[0053] Step 12, Web Formation and Pretreatment: This step aims to transform the mixed fibers into a fabric with a certain strength, and to "open" the island fibers through treatment, exposing the microfiber structure, thus creating conditions for subsequent hot pressing to build a stable three-dimensional network.

[0054] (1) Web formation: The uniformly mixed fibers are combed by a carding machine so that the fibers are basically arranged in the same direction, and then cross-laid by a web laying machine to form a fiber web with uniform weight and improved anisotropy.

[0055] (2) Preliminary reinforcement: The laid-up fiber web is pre-treated by needle punching. The surface fibers are pierced into the web with barbed needles to make them entangled and give the fiber web a certain initial strength, which facilitates subsequent processing and transportation. The uniform pre-reinforcement effect is obtained by controlling the needle punching density.

[0056] (3) Fiber opening treatment: The pre-reinforced nonwoven fabric is subjected to alkali dissolution treatment to remove the "sea" component in the island fibers. For example, the prefabricated fabric is placed in a sodium hydroxide aqueous solution of a certain concentration (5-10%) and temperature (80-95℃) for a certain period of time. The "sea" component is dissolved, leaving bundles of extremely fine PET "island" components. This process greatly increases the specific surface area of ​​the fibers, forming a porous and highly fluffy microfibrillated network structure, which is an important prerequisite for the subsequent formation of complex "biomimetic fascia network structure".

[0057] Step 13, Hot Pressing to Construct a Biomimetic Structure: This step is the core of the entire base fabric molding process. Through precise thermodynamic conditions, the loose ultrafine fiber network is solidified into a stable whole with a specific three-dimensional topology and porosity. The nonwoven fabric after fiber opening is placed in a flatbed hot press. The hot pressing temperature is set to 180℃±5℃, the pressure to 5-15MPa, and the hot pressing time to 30-90 seconds. Under this precisely controlled temperature and pressure: the PET component in the fiber network begins to soften at the fiber cross-contact points, but does not reach a completely melted and flowing state. Under pressure, the molecular chain segments at these softened points diffuse and entangle with each other, forming strong "weld points" after cooling. These "weld points" connect the originally loose fibers in three-dimensional space, forming a stable three-dimensional skeletal network with numerous interconnected channels, similar to fascia tissue in a biological organism.

[0058] Through this step, the base fabric acquires a stable biomimetic fascia mesh structure. Simultaneously, the hydrophilic sheath and hydrophobic core of the internally oriented PAN-PET core-sheath structure work synergistically with the continuous capillary channels provided by this mesh structure, collectively endowing the base fabric with highly efficient unidirectional moisture wicking capability from one side (in contact with the skin) to the other side (outer side). These three interconnected steps, from molecular-level material design (core-sheath fibers) to the precise construction of the macroscopic structure (hot pressing), systematically and creatively achieve the preparation of ultrafine fiber base fabrics with unique functions and structures.

[0059] In this step, the key process for structural forming is hot pressing under precisely controlled temperature (180℃±5℃) and pressure (5-15MPa). Under this temperature and pressure, some fiber surfaces and intersections of the microfiber soften and melt, but do not reach a state of complete melt flow; the softened points form strong weld points or bonding points at the intersections of the fibers, thereby constructing a stable, three-dimensional internet-like skeleton similar to biological fascia tissue. By controlling the hot pressing time, pressure, and temperature, the size and distribution of weld points, as well as the size and shape of pores between the skeletons, can be precisely controlled, thereby controlling the porosity of the final base fabric within the ideal range of 40%-60%, forming directional channels that facilitate the passage of airflow and moisture.

[0060] Achieving unidirectional moisture wicking: The outer layer uses a hydrophilic material, polyacrylonitrile (PAN). PAN molecules contain highly polar cyano groups, enabling rapid adsorption and conduction of moisture through hydrogen bonding. The core layer uses a hydrophobic material, polyethylene terephthalate (PET). PET itself has poor hygroscopicity, providing the driving force and directionality for moisture conduction. The core and outer fibers are blended or woven with the main microfiber network, forming a gradient distribution or orientation from the inner to the outer side of the fabric that contacts the skin. When sweat comes into contact with the inner side of the fabric, the hydrophilic PAN outer layer quickly adsorbs the liquid water and diffuses it along the fiber surface. Due to the hydrophobic nature of the PET core layer, moisture has difficulty diffusing to the fiber core and is mainly confined to conduction within the hydrophilic outer layer. Moisture is directionally driven and transported from the high-humidity inner side to the low-humidity outer side, ultimately evaporating on the outer side, achieving a unidirectional moisture wicking cycle of "rapid moisture absorption on the inner side → directional moisture wicking inside → efficient moisture dissipation on the outer side."

[0061] The core-sheath fiber is prepared using mature composite spinning technology, and the specific method is as follows:

[0062] (1) Raw material preparation: dried PET powder and PAN powder for making spinning solution.

[0063] (2) Spinning equipment and process: Composite spinning components are used to transport PET melt and PAN spinning solution respectively. At the spinneret, the two polymers are arranged in concentric circles (the skin layer wraps the core layer) and extruded from the same spinneret hole to form nascent fibers.

[0064] (3) Post-treatment: For melt-spun PET core and wet-spun PAN sheath, the extruded nascent fibers first enter the coagulation bath (PAN) and cooling air duct (PET) to solidify them. Subsequently, they undergo multi-stage hot drawing to orient the molecular chains and improve fiber strength. The drawn fibers are then relaxed and heat-set in hot rollers or hot air boxes to eliminate internal stress, stabilize the structure, and finally wind into a cylinder. Continuous filaments or cut short fibers are obtained. In the cross-section of the fiber, the hydrophilic PAN completely encapsulates the hydrophobic PET core, forming a stable core-sheath interface.

[0065] "Main microfiber network" refers to the microfiber network formed by opening up island-type microfibers, which constitute the main three-dimensional skeleton of the base fabric. The specific method is as follows:

[0066] (1) Composite spinning: PET and PVA polymers are used to make island-type composite fibers.

[0067] (2) Stretching and cutting: stretching and heat-setting the nascent fibers and cutting them into short fibers of the required length.

[0068] (3) Nonwoven fabric processing: The island fiber and the above-mentioned core fiber are mixed in proportion, opened, combed, and laid into a web, and then physically entangled and reinforced by needle punching process to form a nonwoven fabric with a certain strength.

[0069] (4) Fiber splitting: The fabric is immersed in hot water for treatment. At this time, the "sea" component in the fiber is dissolved and removed, while the "island" component is retained. The original island fiber splits into dozens to hundreds of independent, extremely fine PET microfibers.

[0070] (5) Network formation: The ultrafine fibers generated after fiber opening intertwine and entangle with each other, forming a three-dimensional fiber network with high porosity and huge specific surface area. This network structure is fluffy and soft, and serves as the physical framework and precursor for the subsequent construction of the "biomimetic fascia network structure".

[0071] The key to the "biomimetic fascia mesh structure" lies in utilizing the microfiber clusters formed after the opening of island-type ultrafine fibers as the structural basis. Meanwhile, the selection and structural design of the "shell-core structure PAN-PET composite fiber" are the material basis for achieving the "one-way moisture wicking" function.

[0072] Step 2: Prepare silicone-modified waterborne polyurethane functional slurry.

[0073] A prepolymer method was employed to chemically integrate dihydroxybutylated polydimethylsiloxane (DMPS) as a functional soft segment into the polyurethane backbone at a molar ratio of 12%-18% with polycaprolactone polyol. This design utilizes the low surface energy of the silicone segments, allowing them to spontaneously migrate and accumulate on the surface during coating curing, achieving a gradient structure of strong internal adhesion and superhydrophobic external adhesion in a single step. This slurry forms the material basis for achieving a "one-step method of waterborne gradient adhesion and surface functionalization," ultimately enabling specific areas of the product to achieve a superhydrophobic performance with a water contact angle ≥130°.

[0074] Among them, "incorporating 12%-18% of dihydroxybutyl polydimethylsiloxane as soft segments" into the waterborne polyurethane molecular chain is the key to the molecular design for achieving the integration of internal gradient bonding and surface superhydrophobicity. Specifically, this includes the following steps:

[0075] Step 21: Synthesize functional resins using a prepolymer dispersion method.

[0076] This step aims to covalently bond hydrophobic organosilicon segments to the waterborne polyurethane backbone through a chemical reaction, thereby preparing a core resin with excellent adhesion, film-forming properties, and surface functionalization potential. The specific synthetic route is as follows:

[0077] Raw material dehydration pretreatment: In a four-necked flask equipped with a stirrer, thermometer, condenser, and nitrogen inlet, add metered amounts of polycaprolactone polyol (PCL) and dihydroxybutyl polydimethylsiloxane (PDMS-OH) according to the designed molar ratio, along with a precisely metered amount of the small molecule chain extender 1,4-butanediol (BDO). Stir and dehydrate for 1-2 hours under vacuum ≥ -0.095 MPa and temperature 110-120℃ until the moisture content of the system is below 0.05%.

[0078] The molar number of dihydroxybutyl polydimethylsiloxane (PDMS-OH) is controlled to be 12%-18% of the total molar number of polycaprolactone polyol (PCL) and PDMS-OH.

[0079] The ratio (called R value) of the total molar number of isocyanate groups (-NCO) in the diisocyanate to be added in subsequent steps to the total molar number of hydroxyl groups in all hydroxyl-containing raw materials in this step is controlled to be between 1.5 and 2.2.

[0080] The molar amount of small molecule chain extender (BDO) is determined by the two core control points mentioned above, as well as the hardness and modulus of the resin. Typically, the molar amount of BDO accounts for a relatively small proportion (10%-30%) of the total polyol molar amount, and the specific value can be obtained using the R value mentioned above.

[0081] "Precise metering molar ratio" is a precise numerical system that ensures that PDMS-OH is introduced at a ratio of 12%-18%, and that the -NCO / -OH molar ratio of the entire system is between 1.5 and 2.2. This ensures that resins with the same chemical structure and properties can be obtained repeatedly in each synthesis.

[0082] (2) Prepolymer synthesis: The dehydrated mixture was cooled to 75-85℃. Under nitrogen protection, a measured amount of diisocyanate was slowly added dropwise. A small amount of catalyst, dibutyltin dilaurate (DBTDL), was added. The reaction was maintained at this temperature for 2-3 hours, and the content of -NCO groups in the system was monitored by di-n-butylamine titration until the theoretical value was reached. At this point, the -OH of PCL, the -OH of PDMS-OH, and the -OH of BDO had all reacted with the -NCO of IPDI to generate a polyurethane prepolymer with -NCO at the end.

[0083] (3) Cool the system to 40-50℃. Add a small amount of dimethylolpropionic acid (DMPA), a hydrophilic chain extender dissolved in acetone. The carboxyl group of DMPA reacts with the -NCO group at the end of the prepolymer, introducing a hydrophilic group into the polymer chain. After the reaction is complete, add a measured amount of triethylamine (TEA), a neutralizing agent. TEA reacts with the carboxyl group on DMPA to generate an ammonium salt (-COO). - N + (C2H5)3), continue stirring for 0.5 hours to ensure complete neutralization.

[0084] (4) High-speed emulsification dispersion: Under high-speed stirring, a measured amount of deionized water is slowly added to the above-neutralized prepolymer mixture to emulsify and form a prepolymer emulsion.

[0085] (5) Post-chain extension in water: A measured amount of aqueous solution of ethylenediamine (EDA), a water-soluble diamine chain extender, is added to the prepolymer emulsion. The amino group (-NH2) of EDA reacts with the -NCO group of the prepolymer in the emulsion, achieving chain extension in the aqueous phase, significantly increasing the molecular weight of the polymer, and forming an aqueous polyurethane (WPU) dispersion. Stirring is continued for 1-2 hours to ensure complete chain extension reaction and to allow residual acetone to evaporate and be removed. Finally, a silicone-modified aqueous polyurethane dispersion with a solid content of approximately 30-40% and stable storage is obtained.

[0086] Step 22, Slurry compounding: Add the above dispersion to the mixture and stir until homogeneous. Adjust the viscosity to a suitable range for coating to obtain the functional slurry.

[0087] The additives include leveling agents, defoamers, wetting agents, and color pastes.

[0088] As one embodiment, the leveling agent is: silicone leveling agent BYK-L-9565, BYK-346, BYK-348;

[0089] Defoamers: Organosilicon polyether copolymer defoamers JN3-095, BYK-024, BYK-054;

[0090] Pigment paste: halogen-free pigment paste for coatings, SEIKABEAM BC series;

[0091] Other additives: isocyanates, carbodiimide-modified waterborne crosslinking additives, organosilicon feel additive JN3-018, metal or amine catalysts, and Hexin Technology's HX-304 and HX-513.

[0092] The term "dispersion" here specifically refers to the "organosilicon-modified waterborne polyurethane dispersion" prepared by the aforementioned synthesis method. It is a stable colloidal system of water-in-water polymer microparticles. The dispersed phase microparticles are copolymers composed of polycaprolactone soft segments, polyurethane hard segments consisting of isocyanate and chain extenders, and chemically grafted polydimethylsiloxane segments. The microparticle surface is rich in hydrophilic ammonium carboxylate groups formed by the neutralization of dimethylolpropionic acid with triethylamine. These ionic groups maintain the stability of the dispersion through electrostatic repulsion.

[0093] Step 3: The functional slurry is applied to the microfiber base fabric through a gradient curing process of "three coatings and two bakings" to complete bonding, film formation and surface functionalization in one step.

[0094] "One-step completion" refers to achieving this in a single, uninterrupted processing flow through a pre-designed, precisely-parameterized "three-coating, two-baking" process on a continuous production line. Its core lies in utilizing specific materials (silicone-modified waterborne polyurethane) under specific process conditions. The specific process is as follows:

[0095] (1) Completion of bonding: The first coating is applied with a low coating amount (50-80 g / m). 2 The functional paste is applied to the "bionic fascia mesh structure" base fabric, followed by a first drying at a relatively low temperature of 60-70℃. This low-temperature, slow drying allows the low-viscosity paste to fully penetrate the ultrafine fiber pores on the surface of the base fabric. After drying, the paste solidifies on the fiber surface and at the intersections, forming microscopic "mechanical interlocks" that firmly bond the coating to the fibers.

[0096] (2) Completion of film formation: Based on the first layer, apply a medium coating amount (80-120 g / m²). 2 A second coating is applied, followed by a second baking at 70-80°C. The increased coating amount provides the necessary film thickness. At the higher curing temperature, the polyurethane molecular chains fully cross-link, forming a dense leather layer that imparts the required mechanical properties to the synthetic leather, completing the "film formation."

[0097] (3) Completion of surface functionalization: On the cured coating, a third thin layer (30-50 g / m²) is applied to the functional area. 2 The slurry is then baked a third time at 70-75°C. During the curing process, the silicone molecules in this thin slurry migrate to the new surface. The silicone molecules that have migrated to the subsurface during the second baking process are "captured" and fixed to the outermost layer, so that the silicone concentration on the surface of this region reaches its peak, thereby reducing the surface energy of this region to an extremely low level and achieving a superhydrophobic effect with a water contact angle ≥130°.

[0098] These three processes are interconnected, with the former providing the foundation for the latter and the latter embodying the function of the former. Coordinated under the same material system and temperature control program, they achieve complete structure and function from the base fabric to the final product. This realizes "integrated molding," offering significant advantages in efficiency, cost, and performance consistency.

[0099] Step 4, Chemical Recycling: When the synthetic leather product reaches the end of its service life, it can be recycled through dismantling and pretreatment, catalytic depolymerization, separation and recycling. The total material recovery rate of this process is not less than 90%.

[0100] Among them, the set of depolymerization process parameters of "120℃-140℃, 2-4 hours, and specific catalyst" is the core to achieving efficient and low-cost chemical recovery.

[0101] Step 41, Dismantling and Pretreatment: This step transforms waste synthetic leather products into a state suitable for efficient chemical depolymerization and removes major impurities. It mainly includes the following parts:

[0102] (1) Mechanical dismantling: Special tools are used to separate the synthetic leather upper material from other components in the discarded sports shoes. This yields relatively pure synthetic leather waste and reduces the interference of impurities in subsequent processing.

[0103] (2) Cleaning and drying: The separated synthetic leather waste is initially cleaned to remove obvious dirt adhering to the surface. Then it is dried to avoid unnecessary side reactions of moisture during the subsequent high-temperature depolymerization process.

[0104] (3) Crushing and refining: The dried synthetic leather waste is put into a crusher for mechanical crushing, and it is cut into uniformly sized fragments. The purpose of crushing is to increase the contact area between the reactants and the catalyst, and accelerate the depolymerization reaction rate.

[0105] Step 42, Catalytic Depolymerization: Under the influence of a catalyst, the chemical bonds in the polyurethane coating are selectively broken, achieving separation of the coating from the base fabric. This mainly includes the following parts:

[0106] (1) Feeding and Catalyst Addition: The pretreated synthetic leather fragments are fed into a pressure-resistant reactor equipped with a stirring and reflux condenser. Sufficient amounts of low-carbon alcohol solvents, such as ethylene glycol, are added as depolymerization media. These alcohols act as both reaction media and nucleophiles in the depolymerization reaction.

[0107] (2) Catalyst system: Specific catalysts are added to significantly reduce the activation energy of the depolymerization reaction and achieve degradation under mild conditions, such as dibutyltin dilaurate, which is used at 0.5% to 2.0% of the dry weight of synthetic leather fragments. This catalyst has high selective catalytic cleavage activity for urethane bonds and ester bonds.

[0108] (3) Reaction condition control: Under nitrogen protection, the reaction system is heated to 120℃~140℃ and stirred at this temperature for 2~4 hours. Selective depolymerization is achieved under the action of the catalyst, while avoiding thermal degradation or melting of PET base fabric fibers, thus ensuring the integrity of the fiber structure.

[0109] (4) Judgment of reaction endpoint: When the solid fragments in the reaction system are completely separated and dispersed, and the liquid phase becomes homogeneous and viscous, it indicates that the polyurethane coating has been fully depolymerized. This can be further judged by sampling and detecting characteristic functional groups in the solution (such as -NCO has completely disappeared and the hydroxyl value tends to be stable).

[0110] Step 43, Separation and Recovery: The depolymerization products are subjected to solid-liquid separation and purified separately to obtain high-purity reusable raw materials. This mainly includes the following parts:

[0111] (1) Primary solid-liquid separation: The depolymerized reaction mixture is cooled to below 80°C, and then the solid microfiber base fabric is separated from the liquid phase containing polycaprolactone polyol, catalyst and excess alcohol by pressure filtration or centrifugation. The collected microfiber base fabric is washed several times with hot water to remove residual oligomers and catalysts on the surface, and then dried to obtain recycled PET fiber material.

[0112] (2) Purification of liquid phase products: The separated liquid phase is subjected to vacuum distillation. First, excess alcohol solvent (ethylene glycol) is recovered and separated under low vacuum and temperature. This solvent can be recycled after purification. Adjust the distillation conditions to separate oligomers or monomer mixtures of polycaprolactone polyol.

[0113] This invention's preparation method achieves highly efficient chemical recycling of synthetic leather products (recovery rate ≥90%), fundamentally solving the disposal problem of waste shoe leather, turning waste into treasure, and conforming to the concept of a circular economy. Through the synergistic effect of the "biomimetic fascia mesh structure" and the "skin-core composite fiber structure," highly efficient one-way moisture wicking is achieved, quickly expelling sweat from the shoe and keeping the inside dry and comfortable during exercise. The "one-step water-based gradient bonding and surface functionalization" process combines multiple processing steps into one, simplifying the production process, reducing costs, and achieving precise regional customization of product functions (such as hydrophobic toe cap). This integrated molding technology represents a significant breakthrough in manufacturing processes.

[0114] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing microfiber synthetic leather suitable for manufacturing athletic shoe leather, characterized in that: Includes the following steps: Step 1: Prepare an ultrafine fiber substrate with a biomimetic fascia mesh structure, specifically including the following steps: Step 11, Fiber Preparation: (1) Functional fiber preparation: core-sheath composite fiber, the sheath of which is hydrophilic PAN and the core is hydrophobic PET; (2) Preparation of skeleton fiber: PET is used as the "island" component and PVA is used as the "sea" component to form island-type ultrafine fiber; (3) Mix the core-sheath composite fiber and the island-type microfiber in a certain proportion and disperse the two fibers evenly; Step 12, Web Formation and Preprocessing: (1) Web formation: The uniformly mixed fibers are combed by a carding machine so that the fibers are basically arranged in the same direction, and then cross-laid by a web laying machine to form a fiber web with uniform weight and improved anisotropy; (2) Preliminary reinforcement: The laid-up fiber web is needle-punched pre-treatment. The surface fibers are pierced into the web with barbed needles to make them entangled with each other to obtain nonwoven fabric. (3) Fiber opening treatment: The pre-reinforced nonwoven fabric is subjected to alkali dissolution treatment to remove the "sea" component in the island-type microfiber, leaving bundles of extremely fine PET "island" components; Step 13, hot pressing to construct the biomimetic structure: The nonwoven fabric after fiber opening is placed in a flat hot press. The hot pressing temperature is set to 180℃±5℃, the pressure is 5-15MPa, and the hot pressing time is 30-90 seconds. A stable three-dimensional skeleton network with a large number of interconnected channels similar to the fascia tissue in the body is formed, and an ultrafine fiber base fabric with a biomimetic fascia mesh structure is prepared. Step 2: Prepare silicone-modified waterborne polyurethane functional slurry; Step 3: The functional slurry is applied to the microfiber base fabric through a gradient curing process of "three coatings and two bakings" to complete bonding, film formation and surface functionalization in one step.

2. The preparation method according to claim 1, characterized in that: In step 1, the core-sheath composite fiber accounts for 10%-30% of the total mixed fiber mass, and the island-type microfiber accounts for 70%-90% of the total mixed fiber mass.

3. The preparation method according to claim 1, characterized in that: The specific configuration steps in step 2 include: Step 21: Synthesize functional resins using a prepolymer dispersion method; Step 22: Add additives to the functional resin, stir evenly, and adjust the viscosity to a suitable range for coating to obtain the functional slurry.

4. The preparation method according to claim 3, characterized in that: In step 21, the specific synthesis steps of the functional resin include: (1) Raw material dehydration pretreatment: In a flask equipped with a stirrer, thermometer, condenser and nitrogen inlet, add measured amounts of PCL and PDMS-OH according to the designed molar ratio, and at the same time add a precisely measured amount of small molecule chain extender BDO. Stir and dehydrate for 1-2 hours under vacuum degree ≥ -0.095MPa and temperature 110-120℃ until the moisture content in the system is less than 0.05%; (2) Synthesis of prepolymer: The above dehydrated mixture is cooled to 75-85℃, and under nitrogen protection, a measured amount of diisocyanate is slowly added dropwise, along with a small amount of catalyst DBTDL. The reaction is kept at this temperature for 2-3 hours. The content of -NCO groups in the system is monitored by di-n-butylamine titration until the theoretical value is reached. At this point, the -OH of PCL, the -OH of PDMS-OH, and the -OH of BDO have all reacted with the -NCO of IPDI to generate a polyurethane prepolymer with -NCO at the end. (3) Cool the system to 40-50℃, add a small amount of hydrophilic chain extender DMPA dissolved in acetone. The carboxyl group of DMPA reacts with the -NCO at the end of the prepolymer to introduce the hydrophilic group into the polymer chain. After the reaction is complete, add a measured amount of neutralizing agent TEA. TEA reacts with the carboxyl group on DMPA to generate -COO. - N + (C2H5)3, continue stirring to ensure complete neutralization; (4) High-speed emulsification and dispersion: Under high-speed stirring, a measured amount of deionized water is slowly added to the above-neutralized prepolymer mixture to emulsify and form a prepolymer emulsion; (5) Post-chain extension in water: A measured amount of water-soluble diamine chain extender EDA is added to the prepolymer emulsion. The -NH2 of EDA reacts with the -NCO of the prepolymer in the emulsion to form an aqueous polyurethane dispersion. Stirring is continued to ensure that the chain extension reaction is complete, and the residual acetone is allowed to evaporate and be removed. Finally, an organosilicon modified aqueous polyurethane dispersion with a solid content of about 30-40% and stable storage is obtained, which is the functional resin.

5. The preparation method according to claim 3, characterized in that: In step 22, the additives include leveling agents, defoamers, wetting agents, and color pastes.

6. The preparation method according to claim 1, characterized in that: In step 3, the specific steps for applying the coating are as follows: Apply 50-80 g / m² of coating material. 2 The first coating is performed by applying the functional slurry onto the microfiber base fabric, followed by a first drying at a temperature of 60-70°C. After drying, the slurry is cured on the fiber surface and at the intersections, forming a microscopic "mechanical interlock" that firmly anchors the coating to the fiber.

7. The preparation method according to claim 1, characterized in that: In step 3, the film-forming step specifically involves coating at an amount of 80-120 g / m². 2 The second coating is applied, followed by a second baking at 70-80℃. The polyurethane molecular chains are fully cross-linked to form a dense leather layer, giving the synthetic leather the mechanical properties required, thus completing the "film formation".

8. The preparation method according to claim 1, characterized in that: In step 3, the surface functionalization process specifically involves applying a coating of 30-50 g / m² to the functional areas on the cured coating. 2 Apply the slurry, and then perform a third drying at 70-75°C.

9. The preparation method according to claim 1, characterized in that: It also includes step 4, chemical recycling: recycling when the synthetic leather product reaches the end of its service life.