Automotive leather with high bio-based content and preparation method

Abstract

The invention relates to the technical field of synthetic leather, in particular to automotive leather with high bio-based content and a preparation method thereof.The preparation method comprises the steps that ammonium polyphosphate modified chitosan and nano-montmorillonite are mixed, a hydrogen bond inhibitor is added to obtain flame-retardant composite filler, the flame-retardant composite filler, a hydrophilic copolymer, a dispersion system and a part of a polar organic solvent system are mixed, and the automotive leather with the high bio-based content is obtained. Carrying out rotating speed dispersion treatment to prepare flame-retardant pre-dispersed master batch; mixing the flame-retardant pre-dispersed master batch, the balance of polar organic solvent system and polyether type polyurethane resin to form wet-process slurry, coating the wet-process slurry on the velveteen-like base cloth layer, and feeding the wet-process slurry into a coagulating bath for phase separation to form a wet-process microporous layer; coating the release base material with the surface layer slurry, drying to form a dry surface layer, coating the bonding layer slurry, and carrying out semi-drying to form a dry bonding layer; the wet-process microporous layer and the dry-process bonding layer are subjected to hot-pressing lamination, curing treatment is performed after the release base material is separated, and the synthetic leather is obtained.According to the synthetic leather, excellent flame retardance, moisture permeability, durability and environmental protection performance of the leather for the automotive trim are achieved.

Description

Technical Field

[0001] This invention relates to the technical field of synthetic leather, specifically to a high-bio-based automotive leather and its preparation method. Background Technology

[0002] In existing technologies, polyurethane (PU) synthetic leather has been widely used in automotive interiors and other fields due to its excellent abrasion resistance, elasticity, and tunable chemical structure. However, with the depletion of petroleum resources and the advancement of the "carbon peak" and "carbon neutrality" goals, the development of flame-retardant PU synthetic leather with high bio-based content has become a focus of attention in the automotive industry. However, existing bio-based PUs still have shortcomings in terms of high mechanical properties (such as peel strength and abrasion resistance) and flame-retardant efficiency, which limits their application in automotive interiors (such as seats and dashboards).

[0003] Publication No. EP2860309A1 discloses a flame-retardant synthetic leather, comprising a fiber substrate, an adhesive layer, and a surface resin layer. It primarily uses organophosphorus compounds (such as pentaerythritol diphosphonate derivatives) as flame retardants, with an addition amount of 1-300 parts / 100 parts resin. The preparation process employs a dry process: coating with a surface resin containing the flame retardant, drying, laminating the substrate, and aging. This technology achieves halogen-free flame retardancy through phosphorus-promoted carbonization, meeting FMVSS-302 standards, and addressing the water resistance issue of the flame retardant (water solubility ≤0.5%). However, this method relies on petroleum-based raw materials, has a low bio-based content, and uneven dispersion of the flame retardant easily leads to poor interlayer bonding, affecting the heat resistance, grease resistance, and peel performance of automotive interior materials. Furthermore, the filler synergy in the wet coating process is not optimized, and the flame retardant efficiency depends on a high addition amount, increasing cost and environmental burden.

[0004] Patent publication number CN110483663B discloses a modified chitosan flame retardant, which is formed by phosphorylation of CS followed by reaction with thionyl chloride, and then linkage with melamine to create a C / P / N intumescent flame retardant. The preparation steps include phosphorylation of CS, acylation, and reaction with melamine. When applied to epoxy composites, a loading of 18% with organoclay achieves a LOI of 30.6%, UL-94V-0 rating, and no dripping. The advantage of this technology lies in utilizing the bio-based properties of CS to improve durability and uniform dispersion, avoiding small molecule migration. However, this method is mainly for epoxy resins rather than PU synthetic leather, and does not involve the synergistic effect of ammonium polyphosphate-modified CS and nano-montmorillonite. The problem is that modified CS is prone to agglomeration in wet slurries, affecting the balance of microporous structure and bio-based content, resulting in insufficient mechanical properties (such as peel strength) of the finished product, failing to meet the high-temperature grease resistance requirements of automotive interiors.

[0005] Chinese Patent Publication No. CN101343346A discloses a chitosan polyurethane material, which is produced by reacting isocyanate prepolymer with polyoxypropylene oxide to form a PU prepolymer, adding CS powder under high-speed stirring to dissolve, crosslinking and curing into an elastomer, and then expanding into a hydrogel. This material exhibits biocompatibility and oil and water resistance, making it suitable for the automotive industry. However, the bio-based content of this technology relies on the addition of CS, and it does not undergo ammonium polyphosphate modification to improve flame retardancy. Problems include a lack of optimization for wet coating processes, poor adhesion between dry and wet layers, and low peel strength and insufficient abrasion resistance, limiting its application in automotive interiors.

[0006] In summary, while existing technologies have made progress in the bio-based modification and basic preparation processes of flame-retardant PU synthetic leather, they generally suffer from problems such as low bio-based content, insufficient filler-flame retardant synergy, unstable wet-process microporous structure, poor dry-wet layer bonding, and weak high-temperature oil resistance. These issues result in the finished leather's mechanical properties (such as peel strength and abrasion resistance) and flame retardant efficiency failing to meet the high requirements of automotive interior materials. These problems limit the application of synthetic leather in sustainable automotive materials. Summary of the Invention

[0007] Therefore, the present invention provides a high bio-based content automotive leather and its preparation method, aiming to solve the problems of low bio-based content, insufficient flame retardant efficiency, and poor balance between mechanical properties and practicality in the prior art. It provides a method for preparing high bio-based content, high physical property flame retardant polyurethane synthetic leather, which achieves excellent flame retardant, moisture permeable, durable and environmentally friendly properties of automotive interior leather through synergistic technology of ammonium polyphosphate modified chitosan as filler, wet PU coating optimization and dry semi-dry bonding process.

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

[0009] A method for preparing high-bio-based synthetic leather for automobiles includes the following steps:

[0010] S1. Material pretreatment: Ammonium polyphosphate modified chitosan and surface-modified nano-montmorillonite are mixed at a mass ratio of 3:1-5:1. Hydrogen bond inhibitors are added to weaken the hydrogen bond interaction between chitosan and nano-montmorillonite surfaces, and hydrogen bond removal treatment is carried out to obtain flame-retardant composite filler.

[0011] Meanwhile, the polar organic solvent system and polyurethane resin used for wet pulping are dehydrated to ensure that the water content of both the polar organic solvent system and polyurethane resin is not higher than 0.3 wt%. The polar organic solvent system is selected from N,N-dimethylformamide and / or butanone.

[0012] S2. Preparation of flame-retardant pre-dispersed masterbatch: The flame-retardant composite filler, hydrophilic copolymer, dispersion system and a portion of the dehydrated polar organic solvent system are mixed and dispersed under controlled temperature conditions by gradient speed to obtain flame-retardant pre-dispersed masterbatch.

[0013] S3. Wet slurry preparation: The flame-retardant pre-dispersed masterbatch, the remaining dehydrated polar organic solvent system, and the polyether polyurethane resin are mixed to form a wet slurry, wherein the hydrophilic copolymer and the polyether polyurethane resin constitute a thermodynamically incompatible system, and the water content of the wet slurry is not higher than 0.3 wt%.

[0014] S4. Preparation of wet-process semi-finished product: The wet-process slurry is coated on the imitation cotton fleece base fabric layer and sent into the coagulation bath to undergo phase separation, forming a wet-process microporous layer with a double-pore moisture-permeable structure.

[0015] S5. Preparation of dry layer semi-finished product: A surface layer slurry is coated on the release substrate and dried to form a dry skin layer. Then, an adhesive layer slurry is coated on the side facing away from the release substrate and semi-dried to form a dry adhesive layer.

[0016] S6. Composite and Molding: The wet microporous layer and the dry adhesive layer are hot-pressed together. After separating the release substrate, a curing treatment is performed to allow the residual isocyanate groups in the adhesive layer to chemically graft with the hydroxyl and / or amino groups on the surface of chitosan in the wet microporous layer, forming urethane bonds and / or urea bonds. This results in a synthetic leather consisting of a dry outer skin layer, a dry adhesive layer, a wet microporous layer, and a cotton-like velvet base layer, from the outside in.

[0017] The present invention is further configured such that: the ammonium polyphosphate modified chitosan and the surface-modified nano-montmorillonite constitute a synergistic flame-retardant filler system; the particle size distribution D90 of the flame-retardant composite filler after drying is not greater than 50 μm; the nano-montmorillonite is surface-modified with γ-aminopropyltriethoxysilane, and its single-particle size is not greater than 50 nm; the hydrogen bond inhibitor is selected from one or more of N,N-dimethylurea, urea, and tetramethylurea, and its addition amount is 1.5% to 2.5% of the total mass of the flame-retardant composite filler.

[0018] The present invention is further configured such that: the dehydration treatment in step S1 is carried out by molecular distillation, and the dehydration conditions are a temperature of 110-130℃ and a vacuum of 0.0008-0.002MPa, so that the water content of the polar organic solvent system and the polyurethane resin after dehydration treatment is not higher than 0.3wt%; the material after dehydration treatment is transferred in a closed pipeline under nitrogen protection, and the relative humidity of the wet slurry preparation environment is controlled not higher than 40%.

[0019] The present invention is further configured such that: the hydrophilic copolymer is a PEG-modified block polyurethane, wherein the mass fraction of the PEG segment is 25% to 35%, and its addition amount is 3% to 5% of the mass of the polyether polyurethane resin; the dispersion system includes a polymeric carboxylate dispersant, the addition amount of which is 1.2% to 2.0% of the mass of the flame-retardant composite filler.

[0020] The present invention is further configured such that the gradient rotation speed dispersion in step S2 includes the following stages: the first stage, the rotation speed is 800-1200 rpm, and the dispersion time is 8-12 min; the second stage, the rotation speed is 1300-1700 rpm, and the dispersion time is 12-18 min; the third stage, the rotation speed is 1800-2200 rpm, and the dispersion time is 8-12 min; during the dispersion process, the temperature of the dispersion system is kept below 38°C by means of jacket cooling and internal cooling pipe cooling.

[0021] The present invention is further configured such that: the flame-retardant pre-dispersed masterbatch obtained in step S2 is introduced into the slurry preparation process in step S3 within 0.5 to 1.0 h after dispersion is completed; the polar organic solvent system in step S3 is a mixed solvent of N,N-dimethylformamide and butanone, with a mass ratio of 6:4 to 8:2; the viscosity of the wet slurry at 25°C is 4500 to 5500 cps, the water content is not higher than 0.3 wt%, and the particle size of the particles in the slurry is not greater than 10 μm.

[0022] The present invention is further configured such that: the mass concentration of N,N-dimethylformamide in the coagulation bath in step S4 is 17% to 19%, the coagulation bath temperature is 27 to 29°C, and the residence time of the wet slurry in the coagulation bath is 5 to 7 minutes; the formed dual-pore permeable structure includes primary microchannels with a pore size of 5 to 15 μm and secondary honeycomb micropores with a pore size of 10 to 50 μm.

[0023] The present invention is further configured such that: in step S5, the surface layer slurry contains a surface-active phosphorus- and / or silicon-containing flame retardant modifier, the amount of which is added is 0.8% to 1.2% of the mass of the surface layer resin; the adhesive layer slurry contains a phosphorus-nitrogen reactive flame retardant with terminal isocyanate groups, the amount of which is added is 2% to 4% of the mass of the adhesive layer resin.

[0024] The present invention is further configured such that: in step S6, the wet microporous layer and the dry adhesive layer are preheated before composite bonding, the preheating temperature is 120-130℃, and the preheating time is 4-6 min; the composite bonding pressure is 0.3-0.5 MPa; after bonding, the layers are cured for 20-28 h at a temperature of 45-55℃ and a relative humidity of 45%-55%; the crosslinking exothermic peak monitored by differential scanning calorimetry is located at 55-60℃, and the grafting rate of the flame retardant after curing is not less than 85%.

[0025] A type of automotive leather with high bio-based content, comprising, from top to bottom:

[0026] Dry surface coating;

[0027] Dry bonding layer;

[0028] The wet-process microporous layer comprises polyether-type polyurethane resin, flame-retardant composite filler and hydrophilic copolymer, and has a dual-pore moisture-permeable structure.

[0029] Imitation cotton fleece base layer.

[0030] Compared with the shortcomings of the prior art, the beneficial effects of the present invention are as follows:

[0031] Using bio-based chitosan as the core component, and modified with ammonium polyphosphate, it retains its high bio-based properties and releases no formaldehyde. This meets the current stringent requirements of the automotive industry for low VOC and recyclable materials, and solves the pain points of low bio-based content and poor environmental performance of traditional automotive synthetic leather.

[0032] The surface-active phosphorus-containing flame retardant in the outer layer enhances the surface flame retardant effect. The next layer uses a phosphorus-nitrogen reactive flame retardant with terminal isocyanate groups, which is chemically grafted and fixed. The wet-process layer combines ammonium polyphosphate-modified chitosan with modified nano-montmorillonite to form a synergistic flame-retardant filler. The final product has a limiting oxygen index (LOI) ≥31%, solving the problems of easy precipitation and poor durability associated with traditional synthetic leather flame retardants.

[0033] By utilizing the thermodynamic incompatibility between hydrophilic copolymers and polyether polyurethane, and with precisely controlled coagulation bath conditions, a dual-pore moisture-permeable structure is formed in the wet microporous layer. This structure has a moisture permeability exceeding that of traditional automotive synthetic leather, effectively improving the breathability of car seats and interior materials and alleviating stuffiness. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the present invention;

[0035] Figure 2 This is a structural diagram of the product obtained by the present invention; Detailed Implementation

[0036] Reference Figures 1 to 2 The embodiments of the present invention will be further described below.

[0037] Preparation of flame-retardant composite fillers:

[0038] First, ammonium polyphosphate-modified chitosan was prepared: chitosan was dissolved in a 1 wt% aqueous acetic acid solution to prepare a 5% chitosan solution. Ammonium polyphosphate powder was added at a chitosan mass ratio of 1:0.8. The mixture was stirred and reacted at 60℃ and 500 rpm for 2 hours. After vacuum freeze-drying (temperature -50℃, vacuum degree 0.008 MPa), the mixture was pulverized and passed through a 100-mesh sieve to obtain ammonium polyphosphate-modified chitosan with a bio-based component retention rate of ≥92%. This modification method allows ammonium polyphosphate to form a stable bond with chitosan, preserving the bio-based properties of chitosan while leveraging the flame-retardant activity of ammonium polyphosphate, laying the foundation for subsequent synergistic flame retardancy.

[0039] Surface modification of nano-montmorillonite: Sodium-based montmorillonite with a single particle size ≤50nm was taken and added to anhydrous ethanol to form a suspension with a mass concentration of 8%. γ-aminopropyltriethoxysilane was added at a ratio of 3% by mass of montmorillonite. The mixture was refluxed at 75℃ and 800rpm for 3h. After the reaction, the mixture was centrifuged, washed three times with anhydrous ethanol, and dried at 105℃ to constant weight to obtain surface-modified nano-montmorillonite, whose interlayer spacing was increased to 2.5-3.0nm compared to unmodified montmorillonite. Silane modification can reduce the hydrophilicity of montmorillonite, improve its compatibility with organic systems, and avoid aggregation.

[0040] According to the mass ratio of the corresponding embodiment, the above-mentioned ammonium polyphosphate modified chitosan and surface-modified nano-montmorillonite were mixed, and a hydrogen bond inhibitor (N,N-dimethylurea and urea mixed at a ratio of 1:1) corresponding to the total mass of the flame-retardant composite filler was added. The mixture was placed in a high-speed mixer and stirred for 30 minutes at 30°C and 800 rpm to remove hydrogen bonds. Subsequently, it was dried at 110°C for 2 hours, and after air-jet milling, it was screened to control the particle size distribution of the flame-retardant composite filler to D90≤50μm, and then set aside for later use. Adding a hydrogen bond inhibitor can effectively weaken the hydrogen bond interaction between chitosan and the surface of montmorillonite, prevent filler agglomeration, improve subsequent dispersion uniformity, and thus ensure the performance stability of synthetic leather.

[0041] Dehydration treatment of polar organic solvent systems and polyurethane resins:

[0042] N,N-dimethylformamide (DMF) and butanone (MEK) were mixed according to the proportions specified in the corresponding examples to form a polar organic solvent system. This system, along with the polyether-type polyurethane resin, was separately fed into a molecular distillation apparatus for dehydration. The dehydration conditions were controlled at 120°C, a vacuum of 0.001 MPa, and a treatment time of 2 hours. After dehydration, the moisture content of both materials was measured using a Karl Fischer moisture analyzer to ensure it was ≤0.3 wt%. The dehydrated materials were then transferred to the batching area via a nitrogen-protected, sealed pipeline to prevent moisture absorption from air throughout the process. The relative humidity of the batching environment was strictly controlled to ≤40%. Molecular distillation offers high precision in dehydration, effectively removing trace amounts of moisture and preventing hydrolysis of the polyurethane resin. The low-humidity environment also prevents secondary moisture absorption, ensuring the stability of the slurry.

[0043] The following examples only change four parameters: the mass ratio of ammonium polyphosphate-modified chitosan to surface-modified nano-montmorillonite, the amount of hydrogen bond inhibitor added, the mixing ratio of DMF and MEK, and the maturation time. The remaining process steps, material types, and basic proportions are completely consistent, and the total mass percentage of materials in each system is 100% to ensure the rationality of the proportions.

[0044] Example 1: The mass ratio of ammonium polyphosphate modified chitosan to surface-modified nano-montmorillonite was 4:1, the amount of hydrogen bond inhibitor added was 2.0% (relative to the total mass of flame-retardant composite filler), the mass ratio of DMF to MEK was 7:3, and the curing time was 24h.

[0045] Take 10 kg of flame-retardant composite filler (accounting for 23.8% of the total mass of the pre-dispersed masterbatch), add 0.4 kg of hydrophilic copolymer (PEG-modified block polyurethane, PEG segment mass fraction 30%, which is 4% of the mass of polyether polyurethane resin, accounting for 0.95% of the total mass of the pre-dispersed masterbatch), add 0.16 kg of high molecular weight carboxylate dispersant (sodium polyacrylate) (accounting for 1.6% of the mass of the flame-retardant composite filler, accounting for 0.38% of the total mass of the pre-dispersed masterbatch), and then add 30 kg of dehydrated polar organic solvent system (accounting for 74.87% of the total mass of the pre-dispersed masterbatch), bringing the total mass of the mixture to 40.56 kg. Put the mixture into a high-speed disperser with jacketed cooling and internal cooling pipes, and use gradient speed dispersion treatment: the first stage speed is 1000 rpm, and the dispersion time is 10 min; the second stage speed is 1500 rpm, and the dispersion time is 15 min; the third stage speed is 2000 rpm, and the dispersion time is 10 min. The gradient speed design gradually refines the particle size of the filler dispersion, avoiding localized overheating caused by high-speed dispersion in a single step. Simultaneously, the dual cooling system (jacket + internal cooling pipe) strictly controls the temperature to ≤38℃, preventing degradation of the hydrophilic copolymer and ensuring its ability to form a biporous structure. The dispersed material is fed into the next process within 0.8 hours to produce flame-retardant pre-dispersed masterbatch. Timely transfer prevents masterbatch agglomeration and sedimentation.

[0046] 40.56 kg of the above-mentioned flame-retardant pre-dispersed masterbatch (31.2% of the total mass of the wet slurry) was added to 70 kg of the remaining dehydrated polar organic solvent system (53.8% of the total mass of the wet slurry), followed by 10 kg of polyether polyurethane resin (7.7% of the total mass of the wet slurry). The mixture was stirred at 25°C and 600 rpm for 60 min to form a homogeneous wet slurry (total mass 120.56 kg, closed-loop formulation). The slurry properties were tested: viscosity at 25°C was 5000 cps, water content was 0.22 wt%, particle size was ≤10 μm, and the hydrophilic copolymer and polyether polyurethane resin formed a stable thermodynamically incompatible system. This incompatible system is key to the subsequent formation of the biporous structure, while the appropriate viscosity ensures coating uniformity, and the low water content avoids bubble defects during solidification.

[0047] A 0.8mm thick imitation cotton fleece base fabric layer was selected. The aforementioned wet slurry was uniformly coated onto the base fabric surface using a doctor blade coating machine, with the coating thickness controlled at 0.5mm. The coated base fabric was then placed in a coagulation bath to undergo phase separation. The coagulation bath was prepared as an 18% DMF aqueous solution, with the temperature controlled at 28℃, and the base fabric remained in the coagulation bath for 6 minutes. After phase separation, the fabric was removed, washed, and dried to obtain a wet microporous layer with a dual-pore breathable structure. The primary microchannel pore size is 8-12μm, and the secondary honeycomb micropore pore size is 20-40μm. This dual-pore structure balances breathability and mechanical support; the primary microchannels facilitate air and moisture wicking, while the secondary honeycomb micropores enhance structural toughness, meeting the comfort and durability requirements of automotive applications.

[0048] Using polycarbonate-based polyurethane resin as the base resin (30% of the total mass of the topcoat slurry), 1.0% of a surfactant-based phosphorus-containing flame retardant modifier (phosphate ester surfactant, 0.3% of the total mass of the topcoat slurry) was added, followed by dehydrated DMF solvent (69.7% of the total mass of the topcoat slurry). After thorough mixing, the viscosity was adjusted to 3500 cps. The mixture was then coated onto the surface of release paper (release substrate) using a comma-shaped doctor blade to a thickness of 0.15 mm. The coating was then dried at 80°C for 5 minutes to form a dry-process skin layer (0.1 mm thick). The surfactant-based flame retardant migrates to the surface of the skin layer, enhancing its flame retardant effect. Simultaneously, the polycarbonate-based polyurethane enhances the scratch resistance and weather resistance of the skin layer.

[0049] Using hydroxyl-terminated polyurethane resin as the matrix (25% of the total mass of the adhesive layer slurry), 3% (0.75% of the total mass of the adhesive layer slurry) of a phosphorus-nitrogen reactive flame retardant with terminal isocyanate groups was added. A dehydrated mixed solvent (74.25% of the total mass of the adhesive layer slurry) was added to adjust the viscosity to 4000 cps. This mixture was coated onto the side of the dry-laid skin layer facing away from the release paper, with a coating thickness of 0.2 mm. It was then semi-dried at 70°C for 3 minutes to form a dry-laid adhesive layer, ensuring that the residual isocyanate group content in the adhesive layer was 2.5 wt%. The reactive flame retardant can bond with the wet-laid layer through chemical bonds, preventing flame retardant migration. Simultaneously, the isocyanate groups provide active sites for subsequent chemical grafting.

[0050] The wet-process microporous layer and the dry-process adhesive layer were separately fed into a preheating furnace and preheated at 125°C for 5 minutes. They were then fed into a hot press and hot-pressed together for 30 seconds at a pressure of 0.4 MPa and a temperature of 125°C. After lamination, the release paper was peeled off, and the composite semi-finished product was sent to a curing chamber and cured for 24 hours at a temperature of 50°C and a relative humidity of 50%. Preheating improves the compatibility of the two layers, while the hot-pressing pressure and temperature ensure a tight bond. Suitable curing conditions promote the full reaction between the isocyanate groups and the hydroxyl and amino groups on the chitosan surface (DSC monitoring showed the crosslinking exothermic peak at 57°C), resulting in a flame retardant grafting rate of 88%, forming stable urethane and urea bonds, significantly improving the bonding strength between the two layers. The final product is a high-bio-based synthetic leather for automobiles, consisting of a dry-process outer skin layer, a dry-process adhesive layer, a wet-process microporous layer, and a cotton-like fleece base layer, with an overall bio-based content ≥35%.

[0051] Example 2: The mass ratio of ammonium polyphosphate modified chitosan to surface-modified nano-montmorillonite was 3:1, the amount of hydrogen bond inhibitor added was 1.5% (relative to the total mass of flame-retardant composite filler), the mass ratio of DMF to MEK was 8:2, and the curing time was 20h.

[0052] The remaining process steps, material types, and basic proportions are completely consistent with Example 1, with only the aforementioned core parameters adjusted. The prepared flame-retardant pre-dispersed masterbatch exhibits slightly lower dispersion uniformity than that of Example 1, with a wet slurry viscosity of 4800 cps at 25°C and a moisture content of 0.25 wt%. The final synthetic leather flame retardant has a grafting rate of 85% and a complete dual-pore structure (primary microchannel pore size 5-10 μm, secondary honeycomb micropore pore size 15-35 μm).

[0053] Example 3: The mass ratio of ammonium polyphosphate modified chitosan to surface-modified nano-montmorillonite was 5:1, the amount of hydrogen bond inhibitor added was 2.5% (relative to the total mass of flame-retardant composite filler), the mass ratio of DMF to MEK was 6:4, and the curing time was 28h.

[0054] The remaining process steps, material types, and basic proportions are completely consistent with Example 1, with only the aforementioned core parameters adjusted. The prepared flame-retardant pre-dispersed masterbatch exhibits excellent dispersion uniformity, with a wet slurry viscosity of 5200 cps at 25°C and a moisture content of 0.20 wt%. The final synthetic leather flame retardant has a grafting rate of 90% and a regular dual-pore structure (primary microchannel pore size 10-15 μm, secondary honeycomb micropore pore size 30-50 μm).

[0055] The following comparative examples only change one core process or parameter, while the rest are the same as in Example 1, in order to verify the necessity of the key technical features of the present invention.

[0056] The difference between Comparative Example 1 and Example 1: No hydrogen bond inhibitor was added, but all other processes and parameters were completely identical. Due to the lack of weakened hydrogen bonding, the flame-retardant composite filler exhibited significant agglomeration, with particle sizes reaching 15-20 μm in the slurry, resulting in uneven porosity in the wet-laid layer after solidification.

[0057] The difference between Comparative Example 2 and Example 1: Comparative Example 2 used a constant speed of 1500 rpm for 25 minutes (total dispersion time was the same as in Example 1), while all other processes and parameters were identical. The constant speed failed to gradually refine the particle size, resulting in insufficient uniformity of filler dispersion, incomplete dual-pore structure of the wet microporous layer, and blockage of the primary microchannels.

[0058] The difference between Comparative Example 3 and Example 1: No phosphorus-nitrogen reactive flame retardant with terminal isocyanate groups was added to the adhesive layer slurry; all other processes and parameters were identical. The adhesive layer and wet-process layer were bonded solely through physical bonding, without any chemical grafting.

[0059] The synthetic leathers prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing. The testing standards were based on industry standards for automotive synthetic leather, including GB / T 2790-1995 (peel strength), GB / T 5454-1997 (oxygen index), and GB / T 12704.1-2009 (moisture permeability). The results are shown in the table below:

[0060]

[0061] The test results show that the synthetic leather prepared in Examples 1-3 all meet the requirements for automotive applications. Among them, Example 3 has the best performance due to parameter optimization and extended curing time; while the comparative example has a significant decrease in performance due to the lack of key technical features.

[0062] The high bio-based content automotive synthetic leather prepared by this invention comprises, from top to bottom (i.e., from surface to substrate), layers with each layer having a mass percentage adapted to overall performance requirements:

[0063] Dry surface layer: 0.08-0.12mm thick, accounting for 8-10% of the total product weight, with polycarbonate-type polyurethane as the matrix, containing surface-active flame retardant modifiers, with excellent scratch resistance, weather resistance and surface flame retardant properties, smooth surface, color and gloss can be adjusted according to automotive needs, directly undertaking the functions of appearance and surface protection.

[0064] Dry adhesive layer: 0.15-0.25mm thick, accounting for 12-15% of the total product weight, containing phosphorus-nitrogen reactive flame retardant, which is tightly bonded to the wet microporous layer through chemical grafting, while also having an auxiliary flame retardant effect, ensuring the stability of the composite structure and avoiding interlayer delamination;

[0065] Wet microporous layer: 0.4-0.6mm thick, accounting for 45-50% of the total product weight, the core functional layer, containing polyether polyurethane resin, flame retardant composite filler and hydrophilic copolymer, the dual-pore breathable structure takes into account both breathability and comfort and mechanical support, the flame retardant composite filler achieves the main flame retardant effect, and the bio-based chitosan component improves the environmental friendliness of the material, and is the core performance bearing layer.

[0066] Imitation cotton fleece base layer: 0.6-1.0mm thick, accounting for 25-30% of the total product weight, providing a soft touch and structural support, enhancing the overall flexibility of synthetic leather, adapting to car seats, interiors and other fitting scenarios, and improving user comfort.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-bio-based synthetic leather for automobiles, characterized in that, Includes the following steps: S1. Material pretreatment: Ammonium polyphosphate-modified chitosan and surface-modified nano-montmorillonite were mixed at a mass ratio of 3:1-5:

1. Hydrogen bond inhibitors were added to weaken the hydrogen bond interaction between chitosan and nano-montmorillonite, and hydrogen bond removal treatment was carried out to obtain flame-retardant composite filler. Meanwhile, the polar organic solvent system and polyurethane resin used for wet pulping are dehydrated to ensure that the water content of both the polar organic solvent system and polyurethane resin is not higher than 0.3 wt%. The polar organic solvent system is selected from N,N-dimethylformamide and / or butanone. S2. Preparation of flame-retardant pre-dispersed masterbatch: The flame-retardant composite filler, hydrophilic copolymer, dispersion system and a portion of the dehydrated polar organic solvent system are mixed and dispersed under controlled temperature conditions by gradient speed to obtain flame-retardant pre-dispersion masterbatch. S3. Wet slurry preparation: The flame-retardant pre-dispersed masterbatch, the remaining dehydrated polar organic solvent system, and the polyether polyurethane resin are mixed to form a wet slurry, wherein the hydrophilic copolymer and the polyether polyurethane resin constitute a thermodynamically incompatible system, and the water content of the wet slurry is not higher than 0.3 wt%. S4. Preparation of wet-process semi-finished products: The wet slurry is coated onto the imitation cotton fleece base layer and fed into a coagulation bath to undergo phase separation, forming a wet microporous layer with a dual-pore moisture-permeable structure. S5. Preparation of dry-process semi-finished products: A surface layer paste is applied to the release substrate and dried to form a dry skin layer. Then, an adhesive layer paste is applied to the side of the skin layer facing away from the release substrate and semi-dried to form a dry adhesive layer. S6. Composite and Molding: The wet microporous layer and the dry adhesive layer are hot-pressed together. After separating the release substrate, a curing treatment is performed to allow the residual isocyanate groups in the adhesive layer to chemically graft with the hydroxyl and / or amino groups on the surface of chitosan in the wet microporous layer, forming urethane bonds and / or urea bonds. This results in a synthetic leather consisting of a dry outer skin layer, a dry adhesive layer, a wet microporous layer, and a cotton-like velvet base layer, from the outside in.

2. The method for preparing high bio-based synthetic leather for automobiles according to claim 1, characterized in that: The ammonium polyphosphate-modified chitosan and the surface-modified nano-montmorillonite constitute a synergistic flame-retardant filler system. The particle size distribution D90 of the flame-retardant composite filler after drying is not greater than 50 μm. The nano-montmorillonite is surface-modified with γ-aminopropyltriethoxysilane, and its single particle size is not greater than 50 nm. The hydrogen bond inhibitor is selected from one or more of N,N-dimethylurea, urea, and tetramethylurea, and its addition amount is 1.5% to 2.5% of the total mass of the flame-retardant composite filler.

3. The method for preparing high-bio-based synthetic leather for automobiles according to claim 1, characterized in that: The dehydration treatment in step S1 is carried out by molecular distillation under the following conditions: temperature 110-130℃ and vacuum degree 0.0008-0.002MPa, so that the water content of the polar organic solvent system and polyurethane resin after dehydration treatment is not higher than 0.3wt%. The dehydrated material is transferred in a closed pipeline under nitrogen protection, and the relative humidity of the wet slurry preparation environment is controlled not higher than 40%.

4. The method for preparing high bio-based synthetic leather for automobiles according to claim 3, characterized in that: The hydrophilic copolymer is a PEG-modified block polyurethane, wherein the mass fraction of the PEG segment is 25% to 35%, and its addition amount is 3% to 5% of the mass of the polyether polyurethane resin; the dispersion system includes a polymeric carboxylate dispersant, and its addition amount is 1.2% to 2.0% of the mass of the flame-retardant composite filler.

5. The method for preparing high-bio-based synthetic leather for automobiles according to claim 1, characterized in that, The gradient rotation speed dispersion in step S2 includes the following stages: the first stage, with a rotation speed of 800-1200 rpm and a dispersion time of 8-12 min; the second stage, with a rotation speed of 1300-1700 rpm and a dispersion time of 12-18 min; and the third stage, with a rotation speed of 1800-2200 rpm and a dispersion time of 8-12 min. During the dispersion process, the temperature of the dispersion system is kept below 38°C by using jacket cooling and internal cooling pipe cooling.

6. The method for preparing high-bio-based synthetic leather for automobiles according to claim 5, characterized in that: The flame-retardant pre-dispersed masterbatch obtained in step S2 is introduced into the slurry preparation process in step S3 within 0.5 to 1.0 h after dispersion. The polar organic solvent system in step S3 is a mixed solvent of N,N-dimethylformamide and butanone, with a mass ratio of 6:4 to 8:

2. The viscosity of the wet slurry at 25°C is 4500 to 5500 cps, the water content is not higher than 0.3 wt%, and the particle size of the particles in the slurry is not greater than 10 μm.

7. The method for preparing high-bio-based synthetic leather for automobiles according to claim 1, characterized in that, In step S4, the mass concentration of N,N-dimethylformamide in the coagulation bath is 17%–19%, the coagulation bath temperature is 27–29°C, and the residence time of the wet slurry in the coagulation bath is 5–7 min. The formed dual-pore permeable structure includes primary microchannels with a pore size of 5–15 μm and secondary honeycomb micropores with a pore size of 10–50 μm.

8. The method for preparing high-bio-based synthetic leather for automobiles according to claim 2, characterized in that, In step S5, the topcoat slurry contains a surface-active phosphorus- and / or silicon-containing flame retardant modifier, the amount of which is added is 0.8% to 1.2% of the mass of the topcoat resin; the adhesive layer slurry contains a phosphorus-nitrogen reactive flame retardant with terminal isocyanate groups, the amount of which is added is 2% to 4% of the mass of the adhesive layer resin.

9. The method for preparing high-bio-based synthetic leather for automobiles according to claim 8, characterized in that, In step S6, the wet microporous layer and the dry adhesive layer are preheated before composite bonding at a temperature of 120–130°C for 4–6 min. The composite bonding pressure is 0.3–0.5 MPa. After bonding, the layers are cured for 20–28 h at a temperature of 45–55°C and a relative humidity of 45%–55%. The crosslinking exothermic peak detected by differential scanning calorimetry is located at 55–60°C, and the grafting rate of the flame retardant after curing is not less than 85%.

10. A type of automotive leather with high bio-based content, characterized in that, From top to bottom, they include: Dry surface coating; Dry bonding layer; The wet-process microporous layer comprises polyether-type polyurethane resin, flame-retardant composite filler and hydrophilic copolymer, and has a dual-pore moisture-permeable structure. Imitation cotton fleece base layer.

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