Preparation method of polyurethane composite material based on protein modification

Abstract

The invention discloses a preparation method of a polyurethane composite material based on protein modification. The preparation method comprises the following steps: S10, providing a high-elastic superfine fiber base material layer; carrying out mechanical foaming treatment on the first polyurethane resin to obtain micro-foaming polyurethane slurry; coating the micro-foaming polyurethane slurry on the high-elastic superfine fiber base material layer, and drying to form a composite base material containing a micro-foaming polyurethane micropore middle layer; s20, a solution containing protein and an emulsion containing a waterborne polyurethane prepolymer are provided; the protein solution and the waterborne polyurethane prepolymer emulsion are mixed and subjected to a reaction, and protein modified polyurethane slurry is formed; coating release paper with the protein modified polyurethane slurry, and curing to form a protein modified polyurethane surface layer on the release paper; and S30, compounding the release paper with the surface layer in the step S20 with the composite base material in the step S10, and then stripping the release paper from a composite body. The polyurethane composite material prepared by the technical scheme can provide lasting and stable skin-friendly experience.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane materials, and in particular to a method for preparing a polyurethane composite material based on protein modification. Background Art

[0002] Polyurethane (PU) synthetic leather, as an important industrial material, has been widely used in footwear and apparel fabrics. However, the surface of current PU synthetic leather feels cold and stiff, lacking the warmth and delicate feel of natural leather. To address this issue, the industry has adopted methods such as physical blending of substances such as collagen powder. However, this simple physical filling method has poor compatibility between the protein and the resin matrix, making it prone to migration and shedding due to friction and washing during subsequent use, resulting in performance degradation and failing to provide a long-lasting, stable skin-friendly experience. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects or problems existing in the background technology and provide a method for preparing a protein-modified polyurethane composite material, which can provide a long-lasting and stable skin-friendly experience.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] Technical solution 1: A method for preparing a protein-modified polyurethane composite material, which includes the following steps: S10: Preparation of a composite substrate, which includes: providing a high-elastic microfiber substrate layer; mechanically foaming a first polyurethane resin to obtain a micro-foamed polyurethane slurry; coating the micro-foamed polyurethane slurry on the high-elastic microfiber substrate layer, and forming a composite substrate containing a micro-foamed polyurethane microporous intermediate layer after drying; S20: Preparation of a protein-modified surface layer, which includes: providing a solution containing protein and an emulsion containing an aqueous polyurethane prepolymer; mixing the protein solution with the aqueous polyurethane prepolymer emulsion and reacting them to form a protein-modified polyurethane slurry; coating the protein-modified polyurethane slurry on a release paper and curing it to form a protein-modified polyurethane surface layer on the release paper; S30: Overall compounding, which includes: compounding the release paper with the surface layer in step S20 with the composite substrate in step S10, and then peeling the release paper from the composite.

[0006] Technical solution 2 based on technical solution 1: the protein used in step S20 is silk fibroin.

[0007] Technical solution three based on technical solution one: in step S20, before the protein solution is mixed with the aqueous polyurethane prepolymer emulsion, it also includes a pretreatment step: adjusting the pH value of the protein solution to 8.0-9.0 by adding an alkaline regulator.

[0008] Technical solution four based on technical solution three: In the mixing reaction of step S20, by controlling the feed ratio of the protein solution and the aqueous polyurethane prepolymer emulsion, the molar ratio of the free amino functional groups on the protein molecules to the isocyanate functional groups on the polyurethane prepolymer is 0.8:1 to 1.0:1.

[0009] Technical Solution 5 based on Technical Solution 1: The mechanical foaming treatment in step S10 is secondary mechanical foaming, including: foaming the first polyurethane resin for the first time at a first rotational speed, and then immediately foaming it for the second time at a second rotational speed, wherein the second rotational speed is higher than the first rotational speed.

[0010] Technical Solution 6 based on Technical Solution 1: The curing step in step S20 adopts a step-by-step temperature rise curing, including a low-temperature section in the temperature range of 70°C to 90°C, and a high-temperature section in the temperature range of 120°C to 130°C.

[0011] Technical Solution 7 based on Technical Solution 1: In the overall composite of step S30, composite is achieved by applying a polyurethane adhesive layer on the surface of the surface layer or the composite substrate.

[0012] Technical Solution 8 based on Technical Solution 1: The polyurethane in the aqueous polyurethane prepolymer emulsion in step S20 is selected from one or more of polyether type, polyester type or copolymer type thereof.

[0013] Technical solution nine based on technical solution one: the first polyurethane resin used in step S10 is a water-based polyurethane resin.

[0014] Technical solution 10 based on technical solution 1: The mixing reaction in step S20 further includes the step of adding a tertiary amine catalyst.

[0015] From the above description of the present invention, it can be seen that compared with the prior art, the present invention has the following beneficial effects:

[0016] Technical Solution 1 provides a method for preparing a protein-modified polyurethane composite material, which improves the problem in the prior art that polyurethane synthetic leather cannot provide a long-lasting and stable skin-friendly experience.

[0017] First, this solution successfully overcomes the compatibility and stability challenges of processing sensitive biomacromolecules in complex multiphase colloidal systems through its unique reaction mechanism defined in step S20. As a biomacromolecule, silk fibroin's high-order structure is highly sensitive to external environmental factors such as mechanical shear, temperature, and pH, making it prone to irreversible denaturation and loss of performance. Furthermore, the aqueous polyurethane prepolymer emulsion itself is an unstable colloidal system, its stability relying on the weak surface charge of the emulsion particles or the protection of nonionic surfactants. Simply physically mixing these two inherently sensitive substances is highly likely to cause protein aggregation and precipitation or polyurethane emulsion demulsification due to charge neutralization or interfacial tension disruption, rendering the entire system ineffective. Step S20 explicitly defines the mixing and reaction of a protein-containing solution with an aqueous polyurethane prepolymer emulsion. In this system, protein molecules are dissolved in a continuous aqueous phase, while the polyurethane prepolymer is dispersed in the aqueous phase as tiny, water-insoluble, oil-droplet-like particles. Therefore, the chemical bonding reaction between the two phases inevitably occurs preferentially at the interface between the aqueous phase and the polyurethane particle phase. This chemical reaction at the interface creates a crucial intrinsic stabilization mechanism that is independent of subsequent qualification. When the protein molecule is covalently anchored to the surface of the polyurethane particle, it naturally forms a hydrophilic protein shell on the surface of each polyurethane particle. This newly formed shell itself becomes a powerful steric stabilizer. The protein molecular chains extend into the surrounding aqueous phase, covering the surface of each particle with a protective layer. When two particles approach each other, these protein shells will produce physical obstruction and repulsion, thereby effectively preventing the aggregation and precipitation of polyurethane particles. In other words, this solution uses the chemical reaction itself to create a new, more powerful stabilization system for unstable emulsion particles. This is fundamentally different from the simple physical addition in existing technologies that may destabilize the system.

[0018] Secondly, this solution achieves dynamic, long-lasting wearing comfort through the synergistic effect of preparing the protein-modified surface layer (step S20) and the micro-foamed intermediate layer (step S10). The core of step S20 is to construct a stable, protein-rich interface on the outermost layer of the material through chemical bonding. Protein molecules, particularly their polar groups, impart a certain hydrophilicity and unique surface energy to this surface. This, when in static contact with human skin, avoids the cold, harsh touch associated with traditional polyurethane materials due to their hydrophobic nature, thereby providing a warm, delicate initial skin feel. However, this excellent static skin feel is fragile in actual use. Human skin continuously evaporates hot and humid sweat. If this sweat is not effectively removed, it accumulates in the microenvironment between the material and the skin. When the water vapor concentration reaches saturation, it condenses into liquid water on the cooler surface of the material, causing the surface to become clammy, cold, and sticky, completely destroying the comfortable experience provided by the protein layer. This is where the role of the micro-foamed intermediate layer prepared in step S10 becomes apparent. This layer boasts a large number of interconnected micropores, providing a macroscopically continuous channel for gas molecules. Based on the principle of natural diffusion caused by gas partial pressure differences, water vapor molecules at high concentrations near the skin spontaneously diffuse through this low-resistance channel into the lower-concentration environment outside the material. This continuous process effectively maintains the water vapor concentration near the surface layer below the saturation point, thereby preventing condensation of liquid water on the surface. Therefore, the presence of the micro-foamed interlayer serves more than just breathability. Through continuous mass transfer, it creates and maintains an ideal working environment for the main protein-modified surface layer. It is this consistently dry microenvironment that ensures the excellent static tactile feel of the protein surface is fully and durably maintained even under dynamic conditions.

[0019] Again, this solution solves the core contradiction between material softness and structural durability by combining the preparation step S10 of the micro-foamed intermediate layer with the selection of a highly elastic microfiber substrate layer. The micro-foamed intermediate layer prepared in step S10 is essentially a porous foam structure. In order to achieve excellent softness and cushioning properties, it needs to contain a large number of bubbles inside, which inevitably leads to a reduction in the cross-sectional area of ​​its skeleton material and low overall mechanical strength and fatigue resistance. If this material is repeatedly bent and compressed without effective support, stress will be highly concentrated at the fragile pore wall connections, which can easily lead to pore wall fracture or permanent plastic deformation, that is, the collapse of the pore structure, causing the material to lose its softness and breathability. This solution composites this soft microporous layer onto a highly elastic microfiber substrate. The substrate is composed of high-strength microfibers interwoven in a three-dimensional network, and itself has high tensile strength, tear resistance and excellent elastic recovery rate. When the composite material as a whole is subjected to external forces such as bending, the highly elastic substrate layer, as a mechanical skeleton, will bear most of the stress. It disperses external concentrated stress throughout the entire substrate network, significantly reducing the actual stress value transmitted to the fragile structure of the upper micro-foam interlayer. When the external force is removed, the strong elastic recovery force of the substrate layer drives the entire composite structure, including the weaker micro-foam interlayer, to return to its original shape. This structural design effectively protects the integrity of the microporous structure, preventing it from being crushed or torn during long-term use. Therefore, the presence of the substrate layer makes it possible to use a softer and more functional interlayer without sacrificing the mechanical durability and fatigue life of the entire material.

[0020] Finally, the overall composite step S30 of this scheme, that is, the use of a dry transfer process, is an enabling technical means to achieve all the synergistic effects mentioned above. An ideal surface layer needs to be uniform, dense, and defect-free. And an ideal breathable layer must have a porous and uneven surface. If you try to apply the liquid surface layer slurry on the porous middle layer by conventional direct coating, the slurry will inevitably penetrate into the micropores in large quantities due to the capillary action and gravity of the liquid in the porous medium. This will cause the surface to be unable to level, forming an uneven appearance; the thickness of the surface layer cannot be controlled, resulting in huge material waste; more seriously, the infiltrated slurry will clog the micropores, greatly reducing or even completely losing the breathability of the middle layer. This scheme circumvents this manufacturing problem through step S30, that is, first preparing the protein-modified surface layer on a temporary carrier, that is, release paper, and then transferring it as a whole to the composite substrate. This process synergistically resolves the manufacturing conflict between the required integrity of the surface film and the porosity of the intermediate layer structure, ensuring that the final product possesses both a high-performance biomimetic surface and a functional porous internal structure. Therefore, this process step is more than a simple bonding operation; it is the key bridge connecting all the innovative concepts of this invention and transforming them from theoretical to high-quality industrial products.

[0021] Technical Solution 2, by explicitly selecting silk fibroin as the modified protein, achieves a superior sensory experience compared to using other proteins like collagen. Silk fibroin's unique amino acid composition and molecular chains easily form a regular β-pleated sheet structure, which manifests itself macroscopically as a unique, inimitable luster and smooth feel. Therefore, the use of silk fibroin imparts a more refined texture to the surface of the final product, creating a biomimetic effect closer to that of high-quality silk, significantly enhancing the product's sensory quality and market value.

[0022] In technical solution three, through the pretreatment step of adjusting the pH value of the protein solution, the amino groups on the protein molecules are converted into free amino groups with higher reaction activity, thereby significantly accelerating the rate of chemical bonding, shortening the production cycle, and making the final covalent bonds more numerous and more evenly distributed, thereby making the performance of the surface layer better and its water washability and friction resistance further enhanced.

[0023] In Technical Solution 4, the molar ratio of free amino groups to isocyanate groups directly determines the molecular weight and crosslink density of the final polymer. Controlling this ratio within the range of 0.8:1 to 1.0:1 ensures a fully crosslinked yet not overly brittle network. This allows for precise adjustment of the material's final physical properties, such as hardness, elasticity, and solvent resistance, based on specific application requirements, by fine-tuning this ratio. This provides a reliable technical foundation for customized product production and performance optimization.

[0024] In Technical Solution 5, the larger cells formed by the first low-shear foaming process form the bulk of the middle layer, contributing primarily to the material's softness, compression resilience, and overall breathability. The fine-cell skin layer formed by the second high-shear foaming process plays two key roles: first, its finer structure enhances the material's feel when compressed, making it more dense; second, it provides a smoother, more robust bonding interface for subsequent lamination, increasing the contact area with the adhesive layer and thus improving the interlayer peel strength of the final product.

[0025] In Technical Solution 6, after coating, the slurry contains a large amount of water. If directly exposed to a high-temperature environment, this water would boil over, forming numerous surface defects such as bubbles and pinholes in the film. The low-temperature section ensures gentle and controlled evaporation of the water. The high-temperature section, on the other hand, provides sufficient activation energy for the chemical cross-linking reaction, ensuring the complete reaction and ultimately achieving stable physical and mechanical properties.

[0026] In Technical Solution 7, compared to simple hot-press lamination, a specialized adhesive layer can better fill microscopic interfacial gaps, forming a strong mechanical lock and chemical adhesion. This significantly improves the interlayer peel strength of the composite material, preventing delamination and shedding under harsh operating conditions such as long-term bending, stretching, and washing, thus ensuring the overall structural integrity and long-term durability of the product.

[0027] In Technical Solution 8, the polyether polyurethane's backbone is composed of flexible ether bonds, resulting in high molecular chain mobility. This results in the final product exhibiting enhanced flexibility and hydrolysis resistance, making it suitable for high-end footwear and apparel requiring exceptional softness. The polyester polyurethane's backbone contains ester groups, resulting in strong intermolecular forces. This results in the final product exhibiting enhanced wear resistance and mechanical strength, making it suitable for applications requiring even greater durability, such as luggage and automotive interiors.

[0028] In Technical Solution 9, by limiting the first polyurethane resin used in the intermediate layer to a water-based system, the entire core manufacturing process of the composite material can be completed in a water-based system. This eliminates the use of large amounts of toxic and harmful organic solvents at the source, significantly reducing emissions of volatile organic compounds (VOCs), making the production process less impactful on the environment and less harmful to the health of operators, making the entire technical solution consistent with the current requirements for green and sustainable development in the manufacturing industry.

[0029] In Technical Solution 10, the addition of a tertiary amine catalyst to the reaction system significantly accelerates the reaction rate between isocyanate groups, free amino groups, and water. This significantly increases the production line's operating speed and significantly reduces energy consumption per unit of product, making the entire process more economical for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 Schematic cross-sectional view of a protein-modified polyurethane composite material according to an embodiment of the present invention.

[0032] Description of main reference numerals:

[0033] Protein-modified polyurethane surface layer 1; polyurethane adhesive layer 2; micro-foamed polyurethane microporous middle layer 3; high-elastic microfiber base material layer 4. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be regarded as excluding other embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0035] In the claims, description and drawings of the present invention, unless otherwise clearly defined, the use of terms such as "first", "second" or "third" is for the purpose of distinguishing different objects rather than for describing a specific order.

[0036] In the claims, description and above-mentioned drawings of the present invention, unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" should be understood in a broad sense, that is, any connection method without displacement relationship and relative rotation relationship between the two parties, that is, including non-detachable fixed connection, detachable fixed connection, integral connection and fixed connection through other devices or elements.

[0037] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0038] An embodiment of the present invention relates to a method for preparing a protein-modified polyurethane composite material, which comprises the following steps:

[0039] S10: preparing a composite substrate, which includes: providing a high-elastic ultrafine fiber substrate layer; mechanically foaming a first polyurethane resin to obtain a micro-foamed polyurethane slurry; coating the micro-foamed polyurethane slurry on the high-elastic ultrafine fiber substrate layer, and drying to form a composite substrate comprising a micro-foamed polyurethane microporous intermediate layer;

[0040] S20: preparing a protein-modified surface layer, which comprises: providing a solution containing protein and an emulsion containing an aqueous polyurethane prepolymer; mixing the protein solution and the aqueous polyurethane prepolymer emulsion and reacting them to form a protein-modified polyurethane slurry; coating the protein-modified polyurethane slurry on a release paper and curing the slurry to form a protein-modified polyurethane surface layer on the release paper;

[0041] S30: Overall lamination, which includes laminating the release paper with the surface layer in step S20 with the composite substrate in step S10, and then peeling the release paper from the composite.

[0042] The structure of the polyurethane composite material prepared by the above steps is shown in FIG. Figure 1 From top to bottom, they are protein-modified polyurethane surface layer, polyurethane adhesive layer 2, micro-foamed polyurethane microporous middle layer 3, and high-elastic microfiber base material layer 4.

[0043] The preparation method is described in detail below.

[0044] Regarding step S10: preparation of a composite substrate.

[0045] First, a highly elastic microfiber substrate layer is provided. This substrate layer serves as the backbone of the entire composite material and is typically constructed from a microfiber nonwoven fabric with a thickness of 0.8 to 1.5 mm and a mass per unit area of ​​400 to 600 g / m2. This nonwoven fabric is made from microfibers of polyester, nylon, or a composite thereof, three-dimensionally interwoven through processes such as needlepunching and hydroentanglement. It is then impregnated and shaped with a polyurethane resin, resulting in excellent tensile strength, tear resistance, and dimensional stability. The so-called high elasticity refers to the substrate's high elastic recovery rate after deformation under stress, providing excellent rebound performance for the entire composite material.

[0046] Next, the micro-foamed polyurethane slurry for forming the microporous interlayer needs to be prepared. This slurry consists of a first polyurethane resin, fillers, and additives. The first polyurethane resin is a water-based polyurethane resin, specifically an anionic, aliphatic polyether-based aqueous polyurethane dispersion. It should exhibit excellent mechanical stability to withstand the high shear forces during foaming without demulsification, as well as good filler compatibility, allowing stable coexistence with large amounts of inorganic fillers such as calcium carbonate. Its solids content is typically between 50-60%, and its viscosity is moderate to facilitate control of the foaming process. The use of an aliphatic system ensures excellent yellowing resistance in the final interlayer. The slurry also includes inorganic powders as functional fillers, such as 1250 mesh or finer light calcium carbonate, to adjust the slurry viscosity and the physical properties of the final foamed layer. Furthermore, additives are required, including silicone foam stabilizers to stabilize bubbles during foaming and wetting and leveling agents to improve the slurry's fluidity and coating properties. Specific parts by mass of each component, for example, 100 parts of the first polyurethane resin, 60 parts of calcium carbonate, and 3 parts of the foam stabilizer, are mixed uniformly in a high-speed disperser.

[0047] Next, the prepared slurry is subjected to a mechanical foaming treatment. This treatment is carried out in a dedicated mechanical foaming machine, preferably using a secondary mechanical foaming process. The process includes: first, the slurry is foamed for the first time at a lower first speed, such as 800 rpm, and compressed air is introduced to form relatively large and evenly distributed bubbles inside the slurry, forming the main buffer structure of the middle layer; then, the initially foamed slurry is immediately fed into a high shear foaming head running at a higher second speed, such as 1500 rpm, for a second refined foaming. The purpose of the second foaming is to break the large bubbles into smaller microbubbles and form a cortex with extremely fine bubbles on the surface of the slurry. The final foaming ratio is controlled between 1.0 and 1.5 times.

[0048] Finally, the foamed slurry is evenly applied to the surface of the highly elastic microfiber substrate layer using a doctor blade. The coating thickness is controlled by adjusting the gap between the doctor blade and the substrate to achieve a desired dry coating weight, for example, 150 g / m2. After coating, the composite is dried in a tunnel oven at 110°C to 120°C for approximately 3 minutes to evaporate the moisture and solidify the microporous structure. After cooling, the composite substrate containing the microporous intermediate layer of micro-foamed polyurethane is obtained. This semi-finished product can be rolled for future use.

[0049] Regarding step S20: preparation of protein-modified surface layer.

[0050] The purpose of this step is to prepare a surface film with bionic skin-friendly properties attached to a temporary carrier.

[0051] First, a solution containing a protein is provided, preferably silk fibroin. The silk fibroin is derived from mulberry silk and is prepared by boiling high-grade mulberry silk in a 0.5% sodium carbonate aqueous solution at high temperature to remove sericin. This process can be repeated until pure silk fibroin fibers are obtained. Then, the purified silk fibroin fibers are dissolved in a high-concentration lithium bromide solution. Finally, the resulting silk fibroin solution is dialyzed to remove salt, resulting in a clear, transparent silk fibroin aqueous solution having a specific solids content, for example, 10% by weight.

[0052] Before use, the silk fibroin aqueous solution is pretreated. The pretreatment step is carried out at a constant temperature of 25°C. In the continuously stirred solution, a 0.1M sodium hydroxide solution or other suitable alkaline regulator is slowly added dropwise. During this process, a calibrated precision pH meter is used to monitor the pH value of the solution in real time until it stabilizes in the range of 8.0 to 9.0, preferably 8.5±0.2. After reaching the target pH value, continue to stir at this temperature for 30 minutes to fully stretch the silk fibroin molecular chain and ensure that the amino functional groups on the molecules are converted from the protonated inactive state (-NH3 + ) is fully converted into a free amino form (-NH2) with high nucleophilic reactivity. After the aging is completed, the solution is filtered through a 200 mesh or higher mesh filter to remove any possible micro-aggregates.

[0053] At the same time, an emulsion containing a waterborne polyurethane prepolymer is provided. The polyurethane in the emulsion can be selected based on the performance requirements of the final product, for example, one or more of polyether, polyester, or copolymer thereof can be selected. When the product is required to have an extremely soft feel, excellent hydrolysis resistance, and low-temperature folding resistance, an aliphatic polyether-type waterborne polyurethane prepolymer emulsion can be used. When the product is required to have higher wear resistance and strength, an aliphatic polyester-type waterborne polyurethane prepolymer emulsion can be used. These prepolymers are all anionic self-emulsifying systems to ensure their dispersion stability in water. Their solids content is generally in the range of 30-45%, and they have a specific content of active isocyanate groups.

[0054] Next, a mixing reaction is performed to prepare a protein-modified polyurethane slurry. In this step, a tertiary amine catalyst, such as triethylenediamine (TEDA), can be added to the aqueous polyurethane prepolymer emulsion. It is usually used in the form of a solution soluble in dipropylene glycol and other solvents. The catalyst is added before the protein solution is mixed and stirred evenly. Its addition amount is usually 0.1% to 0.5% of the total weight of the polyurethane solids. Its function is to significantly accelerate the subsequent chemical reaction rate and shorten the curing time. Then, under continuous medium-speed stirring, the pretreated protein solution is slowly added to the polyurethane emulsion containing the catalyst. By accurately controlling the solid content and feed quality of the two liquid raw materials, the molar ratio of the free amino functional groups on the protein molecules in the system to the isocyanate functional groups on the polyurethane prepolymer falls within the target range of 0.8:1 to 1.0:1. This ratio ensures that the chemical bonding reaction is fully carried out, and can be fine-tuned as needed to control the cross-linking density and physical properties of the final product. After mixing evenly, a protein-modified polyurethane slurry is obtained.

[0055] The prepared protein-modified polyurethane slurry is then coated onto a release liner. Release liner is a type of paper coated with a release agent such as silicone oil, which serves as a temporary support. Coating is performed using a precision scraper, typically with a dry weight of 60 to 100 g / m².

[0056] Finally, the release paper coated with the slurry is cured. This curing process is carried out in a multi-temperature tunnel oven using a stepped temperature ramp. The material first enters a low-temperature section of 70°C to 90°C for approximately 3 minutes. The main purpose of this step is to gently evaporate most of the water in the slurry, avoiding the formation of defects such as bubbles or pinholes on the film surface due to excessively high temperatures causing water boiling. The material then enters a high-temperature section of 120°C to 130°C for approximately 3 minutes. This step is intended to provide sufficient activation energy for the chemical cross-linking reaction, ensuring complete covalent bonding between the protein and the polyurethane, forming a stable network structure, and achieving the final physical and mechanical properties. After cooling, the protein-modified polyurethane surface layer formed on the release paper is obtained.

[0057] Regarding step S30: overall compounding.

[0058] The purpose of this step is to combine the two prepared components mentioned above into the final composite material.

[0059] First, a polyurethane adhesive layer is evenly applied to the surface of the release paper film with the top layer, prepared in step S20. This adhesive is typically a two-component water-based polyurethane adhesive. Before use, the base and curing agent are mixed in a specified ratio. The mixed adhesive is evenly applied to the top layer using gravure roller coating or doctor blade coating, maintaining a wet weight coating range of 40-60 g / m2.

[0060] Then, the composite substrate prepared in step S10 (with its microporous polyurethane foam middle layer) is immediately pressed against the adhesive-coated surface layer. This process is performed on a continuous laminating machine, where the pressure of precision pressing rollers ensures a tight fit between the two parts, ensuring no bubbles or wrinkles.

[0061] After the composite is completed, the entire composite is passed through a short oven again for heat treatment to promote the complete curing of the adhesive layer and form a strong interlayer bond.

[0062] Finally, after the composite has fully cooled, the release paper is smoothly peeled from its surface. At this point, the protein-modified surface layer has been completely transferred from the release paper to the composite substrate. The peeled material is then trimmed, inspected, and rolled to yield the final high-performance biomimetic microfiber polyurethane composite.

[0063] In order to better illustrate the present invention, the technical solution provided by the present invention will be described in detail below with reference to the embodiments. It should be noted that this embodiment is preferred and is not intended to limit the scope of protection of the present invention. Any non-substantial changes and adjustments made by those skilled in the art based on the core idea of ​​the present invention still fall within the scope of protection of the present invention.

[0064] Raw materials used in the examples

[0065] High elastic microfiber substrate layer: thickness 1.0mm, weight 500g / m 2 Polyester / nylon composite microfiber non-woven fabric is provided by Zhejiang Huafeng Microfiber Materials Co., Ltd.

[0066] The first polyurethane resin (for the middle layer): a water-based aliphatic polyether polyurethane dispersion, brand WPU-6050, solid content 50%, provided by Wanhua Chemical Group Co., Ltd.

[0067] Aqueous polyurethane prepolymer emulsion (for the surface layer): used in Example 1 and Comparative Example 2 (polyether type): Covestro WPU-8301.

[0068] Example 2 (polyester type): Covestro WPU-8501 (solid content 40%, -NCO% 2.8%).

[0069] Protein: Examples 1, 2, and Comparative Example 2 used: 5A grade mulberry silk. Comparative Examples 1 and 3 used: industrial grade hydrolyzed collagen powder.

[0070] Filler: 1250 mesh light calcium carbonate.

[0071] Additives: TEGOST-8820 (foam stabilizer), DABCO33-LV (catalyst), analytical grade sodium hydroxide.

[0072] Adhesive: Bayer 810A / B.

[0073] Release paper: 100g / m 2 Silicone-coated release paper with a high-gloss matte finish.

[0074] Example 1

[0075] This embodiment is carried out in full accordance with the technical solution of the present invention, and is intended to prepare a flexible product. The preparation process first prepares a composite substrate (step S10): 100 parts by mass of a first polyurethane resin (WPU-6050), 60 parts by mass of calcium carbonate, and 3 parts by mass of a foam stabilizer (TEGOST-8820) are mixed uniformly in a high-speed disperser, and the slurry is treated by a secondary mechanical foaming process, that is, first foaming is performed at a speed of 800 rpm, and then a second fine foaming is performed immediately at a speed of 1500 rpm, with a final foaming ratio of 1.15 times. The foamed slurry is evenly coated on a high-elastic microfiber substrate layer, the dry weight is controlled to be 150 g / m2, and after drying at 110°C for 3 minutes, a composite substrate comprising a micro-foamed polyurethane microporous intermediate layer is obtained. Then, the protein-modified surface layer is prepared (step S20): mulberry silk is prepared into a silk fibroin aqueous solution with a solid content of 10%, and its pH value is accurately adjusted to 8.5 with sodium hydroxide solution, 100 parts by mass of aqueous polyurethane prepolymer emulsion (WPU-8301, polyether type) is taken, 0.2 parts by mass of tertiary amine catalyst (DABCO33-LV) is added, and stirred evenly. Under stirring, 50 parts by mass of pretreated silk fibroin aqueous solution are slowly added to the polyurethane emulsion, and mixed evenly to obtain a protein-modified polyurethane slurry, which is evenly coated on the release paper, the dry weight is controlled to 80 g / m2, and a step-by-step temperature rise curing is adopted, that is, first running at 80°C for 3 minutes, and then running at 130°C for 3 minutes. Finally, the entire surface is composited (step S30): a two-component water-based polyurethane adhesive (810A / B) is applied to the surface of the cured surface layer, and the composite substrate prepared in step S10 is immediately composited and pressed with the surface layer with the adhesive. After aging at 120°C for 2 minutes, the composite substrate is cooled and the release paper is peeled off to obtain the final product.

[0076] Example 2

[0077] This example is intended to prepare a wear-resistant product and illustrate the flexibility of the solution. The preparation process is exactly the same as in Example 1, with the only difference being that the aqueous polyurethane prepolymer emulsion used in step S20 is replaced with WPU-8501 (polyester).

[0078] Comparative Example 1

[0079] This comparative example simulates the conventional physical blending + direct coating of the existing technology. The preparation process includes: first preparing a slurry, that is, taking 100 parts by mass of water-based polyurethane resin (WPU-6050), adding 20 parts by mass of industrial-grade hydrolyzed collagen powder, and performing physical high-speed dispersion mixing in a high-speed disperser for 30 minutes to obtain a physical blending slurry; then coating, directly coating the above slurry on the high-elastic microfiber substrate layer, controlling the dry weight to 230 grams / square meter, and drying at 120 ° C for 5 minutes to obtain the final product. This solution does not involve chemical bonding reaction, does not prepare a special microporous intermediate layer, and does not use a dry transfer process.

[0080] Comparative Example 2

[0081] This comparative example highlights the importance of the microporous intermediate layer. Its preparation process includes: first, preparing the surface layer, which is identical to step S20 in Example 1, using a chemical bonding method to prepare a protein-modified polyurethane slurry (using WPU-8301 polyether type); then coating, directly coating the chemically modified surface layer slurry onto the high-elastic microfiber substrate layer, controlling the dry weight to 80 grams per square meter, and using the same step-by-step temperature curing method as in Example 1. This solution has a chemically bonded surface layer, but does not prepare a dedicated microporous intermediate layer, using a direct coating method.

[0082] Comparative Example 3

[0083] This comparative example is intended to highlight the importance of chemically bonded surface layers. The preparation process includes: first, preparing a composite substrate, which is exactly the same as step S10 of Example 1, that is, preparing a composite substrate comprising a micro-foamed polyurethane microporous intermediate layer; then preparing a surface layer, which is exactly the same as Comparative Example 1, that is, using a physical blending method to mix 100 parts by mass of WPU-6050 resin with 20 parts by mass of hydrolyzed collagen powder; finally, compounding, using a dry transfer process, coating the above-mentioned physically blended surface layer slurry on release paper, drying, and then compounding with the composite substrate prepared in step 1 through an adhesive. This solution has a dedicated microporous intermediate layer, but the surface layer is physically blended, not chemically bonded.

[0084] Performance testing

[0085] The samples prepared in all the above examples and comparative examples were tested for performance. After a simulated home wash (using the 4N procedure in GB / T8629-2017, washing at 40°C for 30 minutes), all samples were tested for hand feel and peel strength. The test results are shown in the table below.

[0086]

[0087]

[0088] Comparison of Example 1 and Comparative Example 1 demonstrates the significant advantages of the present invention's overall technical solution. Example 1 outperforms Comparative Example 1, which simulates conventional prior art, in all key performance indicators, including hand feel, moisture permeability, air permeability, interlayer peel strength, and performance retention after washing. This demonstrates that the present invention's overall system design achieves comprehensive performance improvements over prior art approaches.

[0089] The test results of Comparative Example 2 illustrate the role of the microporous interlayer. Comparative Example 2 utilizes the chemically bonded surface layer of the present invention, resulting in a warm initial feel. However, due to the lack of a dedicated microporous interlayer, its moisture permeability and air permeability are at the same low level as Comparative Example 1, significantly lower than Example 1. This results in a subjective feel of warm but stuffy, failing to achieve dynamic comfort. This result demonstrates that a biomimetic surface layer alone is insufficient; the microporous interlayer specifically incorporated in the present invention is a necessary technical means for achieving both air permeability and dynamic comfort.

[0090] The test results of Comparative Example 3 illustrate the effect of the chemically bonded surface layer. Comparative Example 3 uses the microporous intermediate layer of the present invention, so its moisture permeability and air permeability are at the same high level as Example 1. However, since its surface layer adopts physical blending, its initial feel is soft but rough, lacking bionic skin-friendly feel. After washing with water, its feel becomes rough and hard, and the interlayer peeling strength drops from 38N / cm to 20N / cm. This is because the physically blended collagen is washed out by water, destroying the surface texture and the bonding interface between the layers. This result shows that air permeability alone is not enough. The protein-modified surface layer prepared by chemical bonding in the present invention is a key technical means to achieve lasting bionic skin-friendly feel and a stable interlayer structure, and its effect cannot be achieved by physical blending.

[0091] Comparison between Example 1 and Example 2 demonstrates the adaptability of the present invention. By replacing the PUD type, Example 2 improves peel strength while maintaining a high level of comfort, demonstrating that the present invention's performance can be customized to meet different application requirements.

[0092] A comparative analysis of the above examples and comparative examples demonstrates that the inventiveness of this invention stems not from the application of any single technical feature, but rather from the synergistic effect of several key technical approaches: the chemically bonded surface layer, the microporous intermediate layer, the highly elastic substrate, and the dry transfer process. The results of Comparative Examples 2 and 3 demonstrate that the overall technical effect of this invention cannot be achieved without any of these key elements.

[0093] The above description and embodiments are intended to explain the scope of protection of the present invention, but do not constitute a limitation thereto. Modifications, equivalent substitutions, or other improvements to the embodiments of the present invention or portions thereof that can be obtained by a person of ordinary skill in the art through logical analysis, reasoning, or limited experimentation based on the teachings of the present invention or the above embodiments, combined with common knowledge, ordinary technical knowledge in the field, and / or prior art, should all be included within the scope of protection of the present invention.

Claims

1. A method for preparing a protein-modified polyurethane composite material, characterized in that: The following steps are involved: S10: preparing a composite substrate, which includes: providing a high-elastic ultrafine fiber substrate layer; mechanically foaming a first polyurethane resin to obtain a micro-foamed polyurethane slurry; coating the micro-foamed polyurethane slurry on the high-elastic ultrafine fiber substrate layer, and drying to form a composite substrate comprising a micro-foamed polyurethane microporous intermediate layer; S20: preparing a protein-modified surface layer, which comprises: providing a solution containing protein and an emulsion containing an aqueous polyurethane prepolymer; mixing the protein solution and the aqueous polyurethane prepolymer emulsion and reacting them to form a protein-modified polyurethane slurry; coating the protein-modified polyurethane slurry on a release paper and curing the slurry to form a protein-modified polyurethane surface layer on the release paper; S30: Overall lamination, which includes laminating the release paper with the surface layer in step S20 with the composite substrate in step S10, and then peeling the release paper from the composite.

2. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The protein used in step S20 is silk fibroin.

3. The method for preparing a protein-modified polyurethane composite material according to claim 1, wherein: In step S20, before the protein solution is mixed with the aqueous polyurethane prepolymer emulsion, a pretreatment step is further included: the pH value of the protein solution is adjusted to 8.0-9.0 by adding an alkaline regulator.

4. The method for preparing a protein-modified polyurethane composite material according to claim 3, characterized in that: In the mixing reaction of step S20, the feed ratio of the protein solution to the aqueous polyurethane prepolymer emulsion is controlled so that the molar ratio of the free amino functional groups on the protein molecules to the isocyanate functional groups on the polyurethane prepolymer is 0.8:1 to 1.0:

1.

5. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The mechanical foaming process in step S10 is a secondary mechanical foaming process, which includes: foaming the first polyurethane resin for the first time at a first rotation speed, and then immediately foaming the resin for the second time at a second rotation speed, wherein the second rotation speed is higher than the first rotation speed.

6. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The curing step in step S20 adopts a step-by-step temperature-raising curing process, including a low-temperature section within a temperature range of 70° C. to 90° C., and a high-temperature section within a temperature range of 120° C. to 130° C.

7. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: In the overall compounding of step S30 , compounding is achieved by applying a polyurethane adhesive layer on the surface of the surface layer or the surface of the composite substrate.

8. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The polyurethane in the aqueous polyurethane prepolymer emulsion in step S20 is one or more selected from polyether type, polyester type or copolymer type thereof.

9. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The first polyurethane resin used in step S10 is a water-based polyurethane resin.

10. The method for preparing a protein-modified polyurethane composite material according to claim 1, characterized in that: The mixing reaction in step S20 further includes the step of adding a tertiary amine catalyst.

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